Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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INDUCTION MOTOR CONTROL
APPARATUS AND METHOD
CROSS REFERENCE TO RELATED APPLiCATIONS
_
The present application is related to the follow-
ing concurrently filed patent applications Serial No.
500,751 , by D. J. Shero et al. and entitled "Induction
Motor Synthesis Control Apparatus And Method", (l~.E. Case
50,932), Serial No. 500,753, by H. Dadpey et al. and
entitled "Torque Determination for Control of An Induction
Motor Apparatus" (W.E. Case 51,489) and Serial No.500,752,
by H. Dadpey et al. and entitled "Induction Motor Regenera-
tive Brake Control Apparatus And Method" (W.E. Case
51,700), which are assigned to the same assignee.
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BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates in general to the control
of an induction motor apparatus driven from a DC power
source through an inverter.
Description of the Prior Art:
It is known to provide a closed loop control of
an AC motor drive apparatus, including a three phase AC
motor which is powered using a GTO based voltage fed
inverter that is powered directly from a DC power source.
The GTO switches in the inverter are to have a predeter-
mined connection time between each phase of the motor and
either one of the two power rails, i.e. high and low
voltage. The relationship of each phase with respect to
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the other phases generates the needed AC waveforms in order
to properly excite the motor.
For a transit vehicle, it is known that the
torque output from the one or more propulsion motors is to
be maintained at a particular level to accelerate or
decelerate the vehicle at a predetermined rate. Due to
various disturbances and unknown variables, it is known to
provlde a closed loop control apparatus that determines the
torque output of the motor and controls the AC waveforms to
that motor so as to maintain the desired torgue output from
that motor.
The toraue output from an AC motor can be con-
trolled by varying the slip frequency and/or the motor
voltage. In a motor drive system where the input voltage
source is DC, a variable voltage and variable freguency
voltage source inverter can be used to vary these motor
parameters.
It is known in the prior art to provide an AC
motor drive controller including a microprocessor control
three-phase inverter coupled with a three-phase induction
motor, as described in an article entitled "Microprocessor
Based Control of an AC Motor Drive" that appeared at pages
452-456 in the conference record of the IEEE Industry
Application Society Meeting ~or October 1982.
25It is known in the prior art to provide pulse
`~ width modulated inverter pulse switching control signals
with a microprocessor based modulator in response to input
voltage and frequency commands to determine the conduction
time periods for an inverter driving a three-phase induc-
~0 tion motor, as described in an article entitled "A High
Performance Pulse Width Modulator for an Inverter Fed Drive
System Using a Microprocessor" that appeared at pages
847-853 of the above-reference conference record of the
IEEE Industry Application Society Meeting for October 1982.
35It is known in the prior art to provide an
induction motor control system including a regenerative
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braking mode operative with an inverter supplying the motor vol-
tage for determining the provided brake torque.
S UMMARY OF THE I NVENT I ON
A variable voltage and variable frequency inverter ener-
gized induction motor control apparatus and method are provided
for an AC induction motor drive system using a programmed micro-
processor for operation with gate turn-off thyristors in the
inverter apparatus to determine the required switching of the
motor currents on and off.
In accordance with the present invention, there is pro-
vided in apparatus for controlling the torque of an induction
motor in response to an operation request signal and operative
with an inverter coupled to a DC power source having a voltage,
the combination of first means coupled with the motor to provide a
motor speed signal, said motor having a base speed, interactive
slip~ and brake controller means responsive to the operation
request signal for providing through said slip controller means a
~: desired slip frequency, said slip controller means also being
adapted to hold the slip Erequency constant at a predetermined
~ rated elip frequency during braking in an extended speed voltage
control interim of motor operation above base speed, second means
:~ comparlng the desired slip frequency with the motor speed signal
for providing a requested inverter frequency signal, third means
responsive to the requested inverter frequency signal and the slip
frequency for providing a desired inverter voltage, and fourth
means responsive to the desired inverter voltage and the power
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source voltage for providing a requested inverter voltage across
said motor and a requested inverter vol-tage percent signal, with
the inverter being coupled between the DC power source and the
motor and responsive to the requested inverter frequency signal
and the requested inverter voltage percent signal for providing a
first energizing voltage across said motor which depends on the
requested inverter voltage for controlling the motoring and said
brake controller means providing a variable voltage for air gap
flux control of braking in the extended speed, voltage control
interim with the predetermined rated slip held constant by said
slip controller means having a variable gain that is thereafter
increased in the speed interim above the extended voltage control
interim and in proportion to the square of the ratio of desired
inverter voltage to the requested inverter voltage across said
motor for motor speeds above base speed so that the system torque
is substantially constant for operating motor speeds.
In accordance with the present invention, there is
further provided the method of controlling an induction motor in
response to an operation reques-t signal and operative with a DC
:~ 20 power s~ource having a voltage, the steps of energizing the motor
: with an inverter coupled with the DC power source, determining a
motor speed signal in accordance with the speed of the motor,
providing a desired slip frequency signal from an interactive slip
and brake controller operating in response to the operation
request signal, said slip controller portion holding the slip
frequency at a predetermined rated slip ireguency during ùraking
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in an extended speed vol-tage control interim of motor operation
above base speed, providing a requested inverter frequency signal
in response to the slip frequency signal and the motor speed sig-
nal, providing a requested inverter voltage percent signal in
response to the desired slip frequency signal and the power source
voltage, controlling the energization of the motor by the inverter
in response to the requested inverter frequency signal and the
requested inverter voltage percen-t signal, and controlling the
gain of the interactive controller so as to increase it non-
linearly in the speed interim above the extended speed, voltagecontrol interim from a motor base speed gain of unity, for
increasing motor speeds when the operating speed of the motor is
above base speed so that the composite control gain of said motor
and interactive controller is substantially constant in order to
maximize the speed torque range for a broad range of operating
~speeds.
In accordance with the present invention, there is
further provided in apparatus for controlling the torque of an
induction motor in a transit vehicle in response to an operation
request signal and operative with an inverter coupled to a DC
power source having a voltage, the combination of means coupled
with the motor to provide a motor speed signal, said motor having
a base speed, slip controller means responsive to the operation
request signal for providing a desired slip frequency, said slip
controlIer means having a non-linear gain characteristic for motor
speeds above base speed and being clamped below base speed to a
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gain of unity, means comparing the desired slip frequency with
the motor speed signal for providing a requested inverter
frequency signal, means responsive to the requested inverter
frequency signal and the slip frequency for providing a desired
inverter voltage, and means responsive to the desired inverter
voltage and the power source voltage for providing a requested
inverter voltage across said motor, said requested inverter
voltage below base speed equals said desired inverter voltage and
above base speed is voltage limited by the power source, means
responsive to the requested inverter voltage and the power source
voltage for providing a requested inverter voltage percent signal,
said requested inverter voltage percent signal below base speed is
within the range of zero to one hundred percent and above base
speed is clamped at one hundred percent, said non-linear gain
characteristic of said slip controller means being proportional to
the square of the ratio determined by desired inverter voltage
divided by the requested inverter voltage across said motor, said
inverter being coupled between the DC power source and the motor
and responsive to the requested inverter frequency signal and the
requested inverter voltage percent signal for providing a first
energizing voltage across said motor which depends on the request-
ed inverter voltage for controlling the motoring and braking tor-
que of the motor, so that the available:composite torque gain for
controlling said motor is substantially constant for a useful
range of operating speeds.
In accordance with the present invention, there is
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further provided the method of controlling an induction motor for
a transit vehicle in response to an operation request signal and
operative with a DC power source having a voltage, the steps of,
energizing the motor with an inverter coupled with the DC power
source, determining a motor speed signal in accordance with the
speed of the motor, providing a desired slip frequency signal from
a slip controller operating in response to the operation request
signal, clamping a predetermined slip frequency signal for the
motor when operating above base speed during an extended speed,
variable voltage braking torque interim of operation, providing a
requested inverter frequency signal in response to the slip fre-
quency signal and the motor speed signal, providing a requested
inverter voltage across said motor in response to the desired slip
frequency signal and the power source voltage, providing a re-
quested inverter voltage percent signal in response to the re-
quested inverter voltage and the power source voltage, controlling
the energization of the motor by the inverter in response to the
requested inverter frequency signal and the requested inverter
voltage percent signal, and increasing the gain of the slip con-
troller non-linearly, from a motor base speed gain of unity, for
increasing motor speed according to a voltage ratio relationship
with the inverse squared of requested inverter voltage when the
operating speed of the motor is above base speed and above the
: extended speed variable voltage braking torque interim so that the
: avallable composite torque gain for controlling said motor is
maximized for a useful range of operating speeds.
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BRIEF DESCRIPTION OF TFIE DRAWINGS
Figure 1 shows a prior art AC induction motor control
apparatus;
Figure 2 shows a -typical prior art transit vehicle
operative with a roadway track and an AC propulsion motor appara-
tus;
Figure 3 shows the well known torque and voltage versus
speed relationship curves for a transit vehicle AC induction pro-
pulsion motor;
Figure 4 shows a well known equivalent circuit model of
one line-to-neutral phase of a three phase AC induction motor;
Figure 5 shows the well known torque change of an AC
induction motor when the air gap flux is kept constant while vary-
ing the slip frequency;
Figure 6 shows a prior art family of torque versus slip
frequency curves, with each curve being at a different air gap
flux value;
~ : Figure 7 shows a block diagram of the present AC induc-
: tion motor control apparatus;
Figure 8 shows functionally the motor controller of the
~ ~ present AC induction motor control apparatus;
:~ Figure 9 shows the control states of the present AC
: ~motor control apparatus;
: Flgure 10 shows the brake T~ control substrates of the
present AC motor control apparatus;
Figure 11 shows a flow chart of the main start-up loop
: program and the start-up after a fault condition;
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Figures 12A and 12B show a flow chart of the main
interrupt program;
Figure 13 shows a flow chart of the check invert-
er routine called by the interrupt program of Figure 12A;
Figure 14 shows a flow chart of the negative tach
test routine called by Figure 13;
Figure lS shows a flow chart of the positive tach
recovery routine called by Figure 13;
Figure 16 shows a flow chart of the emergency off
state routine called by Figure 13;
Figure 17 shows a flow chart of the inverter
disabled routine called by Figure 13;
Figure 18 shows a flow chart of the inverter test
routine called by, Figure 13;
Figure 19 shows a flow chart of the rail gap
recovery routine called by F1gures 14 and 15;
Figure 20 shows a flow chart of the control loop
routine called by Figure 12B;
Figure 21 shows a flow chart of the determine
mode routine called by Figure 20;
Figure 22 shows a flow chart of the brake TX
: routine called by Figure 21;
Figure 23 shows a f low chart of the TX no TX
routine called by Figure 22 of the emergency off routine
called by Eigure 21 and of the normal off routine called by
Figure 21;
~ Figure 24 shows a flow chart of the recovery
:: ~ routine called by Figure 21;
Figure 25 shows a flow chart of the brake open
loop routine cal:led by Figure 21;
: Figure 26 shows a flow chart of the brake below
six-step routine called by Figure 21;
Figure 27 shows a flow chart of the brake
six-step routine called by Figure 21;
: Figure 28 shows a flow chart of the TX below
six-step transition routine called by Figure 22;
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Figure 29 shows a flow chart of the TX six-step
transition routine called by Figure 22;
Figure 30 shows a flow chart of the TX below
six-step routi~e called by Figure 22;
Figure 31 shows a flow chart for the TX six-step
routine called by Figure 22;
; Figure 32 shows a flow chart for the TX angle
control routine called by Figure 22;
Figure 33 shows a flow chart for the TX high slip
control routine called by Figure 22;
Figure 34 shows a flow chart for the power
six-step routine called by Figure 21; r
Figure 35 shows a flow chart or the power open
loop routine called by Figure 21;
Figure 36 shows a flow chart for the power below
six-step routine called by Figure 21;
Figure 37 shows a flow chart for the TER jerk
limit routine called by Figure 20;
Figure 38 shows a flow chart for the control
state control routine c~lled by Figure 20;
Figure 39 shows a flow chart or the CSC brake TX
routine called by Figure 33;
: Figure 40 shows a flow chart for the CSC TX no TX
routine called by Figure 39 and the CSC emergency off
routine and CSC normal off routine called by Figure 38;
Figure 41 shows a flow chart for the CSC TX below
six-step transltion routine, the CSC TX six-step transition
: routine and the CSC TX below six-step routine called by
: Figure 39;
Figure 42 shows a flow chart for the CSC TX
six-step routine called by Figure 39;
Eigure 43 shows a flow chart:for the CSC TX angle
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control routine called by Figure 39;
Figures 44A and 44B show a flow:chart for the CSC
~ TX high slip control routine called by Figure 39;
~:: Figure 45 shows a flow chart for the CSC racovery
~: ~ routine called by Figure 33;
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Figure 46 shows a flow chart for the CSC brake
open loop routine and the CSC power open loop routine
called by Figure 38;
Figure 47 shows a flow chart for the CSC brake
below six-step routine and the CSC brake six-step routine
called by Figure 38;
Figure 48 shows a flow chart for the CSC power
below six-step routine and the CSC power six-step routine
called by Figure 38;
10Figure 49 shows a flow chart for the slip PI
control routine called by Figure 41;
Figure 50 shows a flow chart or the caiculate
variable slip gain routine called by Figures 32, 35, 41, 47
and 48;
15Figure 51 shows a flow chart for the adjust
clamped controller routine called by Figures 32, 35, 41,
42, 44, 47 and 48;
Figure 52 shows a flow chart for the 'orake PI
; control rputine called by Figure 43;
20Figure 53 shows a flow chart for the rework brake
PI routine called by Figures 31 and 43;
Figure 54 shows a flow chart for the brake adjust
clamped controller routine called by Figures 33 and 53;
Figure 55 shows a flow chart for the brake angle
: 25 calculation routine called by Figures 43 and 44;
:. Figure 56 shows a flow chart for the voltage and
: frequency control routine called by Figure 20;
Flgure 57 shows a flow chart for the calculate
voltage routine called by Fig~res 19 and 56;
: Figure 58 shows a flow chart for the boost exit
:routine jumped to from Figure 57;
Figure 59 shows a flow chart for the frequency
check routine called by Figure 58;
Figure 60 shows a flow chart for the calculate
3 5min~mum angle routine called by Figures 42, 43 and 44;
Figure 61 shows a flow chart for the normal PWM
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start routine called by Figures 13 and 14;
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Figure 62 shows a flow chart for the start quasi
six-step routine called by Figure 19;
Figure 63 shows a flow chart for the shutdown
procedure routine called by Figures 12B, 18, 19, 23, 40 and
48;
Figure 64 shows a flow chart for the restart
routine called by Figure 63; and
Figure 65 shows a flow chart for the recovery
: control routine called by Fi~gure 45.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In Figure 1 there is shown a prior art AC induc-
tion motor control apparatus irlcluding a DC power source 10
coupled with an inverter 11 for determining the operation
of a three-phase. AC induction motor 14 connected with a
load 12 which represents a transit vehicle. A torque
sensor 13 is coupled with the motor 14 to provide a torque
feedback 15 to a motor controller 16. A power controller
17 receives as inputs an acceleration request 18 from the
transit vehicle operator, the transit vehicle weight 19,
and the transit vehicle wheel diameters 20. The power
controller 17 produces a torque effort request 21, which
represents the torque to be achieved by the AC motor 14 in
order to accelerate the transit vehicle, load 12, at the
rate defined by acceleration request 18. A jerk limiter 22
takes the torque effort request 21 and jerk limi~s it to
providé a jerk limited torque effort request 23 to the
motor controller 16. The motor controller 16 produces GTO
firing pulses 24 for the inverter 11, in order to match the
torque feedback 15 to the torque effort request 23.
: In Figure 2 there is shown a transit vehicle 25
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operative with a roadway track 26 and including the invert-
er 11, the induction motor 14, the motor controller 16 and
the torque sensor 13 coupled with the motor 14. The power
source 10 energizes the inverter 11 through a power line
: 35 27-
~: In Figure 3 there are shown the well-known torque
and volt ge versus speed curves for an induction m~tor 14.
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The power torque of the motor as shown by curve 28 is
constant from zero speed up to base speed and then falls
off for speeds above base speed which is shown to be 50 Hz
and approximately 20 mph of vehicle operation. The motor
voltage increases linearly as shown by curve 31 up to base
speed and then stays constant for motor speeds above that
base speed of the motor.
Figure 4 shows the well known equivalent circuit
model of one line-to-neutral phase of a three phase AC
motor. R2 and L2 are the resistance and inductance of the
rotor, with the indicated resistor value being R2 divided
by S where S is the slip. Slip is defined as the ratio of
the inverter frequency minus the rotation of the rotor
frequency and divided by the inverter frequency. The
voltage indicated by Vg is the air gap voltage and results
in a corresponding air gap flux. If the air gap flux is
kept constant while varying the slip frequency, the torque
of the motor will change as shown in Figure 5. Varying the
slip of the motor while holding the air gap flux constant
results in a change in rotor current. Since torque is
proportional to air gap flux multiplied by rotor current
Ir, this change in ro~or current will result in a change in
motor torque.
A~ can be seen in Figure 4, the air gap voltage
Vg sees an inductive impedance, so that as the inverter
frequency ns changes, the air gap voltage Vg must change
also in order to maintain the same current through Lm which
will in turn keep the air gap flux constant. To vary Vg,
~he control must vary the inverter voltage. The other
components in the equivalent circuit model of Figure 4 also
affect Vg under different operàting conditions. The slip
of the motor is determined by the relationship
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where s is the slip, ns is the inverter frequency and n is
the rotor frequency, and where rotor frequency is deter-
mined by the relationship
n = mechanical frequencY x 120 (2)
number of motor poles
where rotor frequency is in hertz and the mechanical
frequency is in RPM. As the slip of the motor increases to
increase the motor torque, the rotor current Ir and stator
current Is will increase. Since the stator and rotor have
resistance associated with them, the voltage Vg and the air
gap flux will drop unless something is done to increase the
inverter output voltage. The compensation done to avoid
this drop in air gap flux is known as IR drop compensation
since it compensates for the resistive loss in the motor.
Assuming that the inverter voltage is maintained to compen-
sate for IR drop and the inverter frequency changes, theair gap flux of the motor can be maintained at a constant
value over all operating conditions. This type of control
is known as constant V/F or volts per hertz control.
Constan~: V/F control is maintained up until the
inverter frequency is increased to the point where the
inverter voltage can no longer be increased to maintain
constant air gap flux. This limitation is set by the DC
line voltage input to the inverter. At this point where
the inverter voltage can no longer be increased to keep the
air gap voltage constant, begins the reduced flux mode of
motor operation, and from this point on the air gap flux
will decrease as the motor speed is increased such that the
amount of torque produced by the motor will decrease if the
same slip frequency is maintained. As can be seen from
Eigure 4, as the air gap flux decreases, the rotor current
will also decrease; therefore, since torque is proportional
to air gap ~lux multiplied by the rotor current, the torque
will drop off rapidly. Knowing this, the motor torque can
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be shown to be proportional to the square of the inverter
voltage if slip frequency and inverter frequency are held
constant.
By varying either the slip frequency or the air
gap flux, the torque of an AC induction motor can be
controlled. Slip frequency is controlled by changing the
fundamental output frequency of the inverter. Air gap flux
is controlled by making changes to the fundamental output
voltage of the inverter in addition to the changes needed
to maintain constant V/F operation.
Figure 6 S}lOWS a family of torque versus slip
frequency curves, with each curve being at a different air
gap flux value to show the relationship between torque and
the two control parameters, slip frequency and air gap
flux.
In Fi~ure 7 there is shown a suitable motor
control apparatùs for operation in accordance with the
present invention to control a three phase AC motor, such
as the propulsion motor of a mass transit passenger vehi-
cle. The vehicle operator can provide a power controller17 with a vehicle acceleration request which by taking into
account the vehicle wei~ht and vehicle wheel diameters, the
power controller 17 translates into a torque effort request
signal 21 which is input to a signal limiter 32 for pre-
venting unreasonable torque effort requests. A jerklimiter 2Z is provided in relation to a desired jerk rate
36 for establishing a jerk limited torque request 23 for
the comfort of the vehicle passengers. A torque feedback
determination apparatus 38 determines the torque feedback
40 by measuring the system input power in relation to the
DC volta~e 43 and DC current 44 provided by a power supply
` 10 and in relation to the inverter frequency 48 and the
. synthesis mode 50 and the tachometer speed 52 provided by a
tachometer 54 coupled with the propulsion motor 14 to
estimate the output torque of the motor 14. The torque
feedback signal 40 is supplied to the negative input of a
summing junction 58 for comparison with the jerk limited
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torque request signal 23 supplied to the positive input of
the summing junction 58. The resultlng torque error signal
60 is supplied to a motor controller 62. A car control
enable signal 64 from the operator permits the propulsion
motor 14 to run or not. Other needed inputs by the motor
controller 62 consist of the DC line voltage 43 and the
synthesis mode of the inverter 50. The motor controller 62
outputs the braking thyristors enable 68, the requested
braking angle 70, the requested inverter frequency 48, and
the requested inverter voltage percent 74 to the inverter
and braking synthesis apparatus 76, which in addition has
as an input and output the control state signal 78 and
provides the synthesis mode signal 50 to the motor control-
ler 62 and to the torque feedback determination apparatus
38. When the motor 14 is in brake operation, with addi-
tional voltage supplied by the transformer braking circuit
80, the control state signal 78 operates to keep the
synthesis mode in six-step and prevents a change to the
quasi six-step or PWM modes. The inverter and braking
synthesis apparatus 76 outpu~s the inverter GTO firing
pulses 82 to the inverter 11 and the brake GTO firing
pulses 86 to the braking circuit 80. The inverter 11
drives the motor 14 in power and in brake operation and the
braXing circuit 80 operates with the motor 14 when addi-
tional braking torque is desired above base speedoperation.
In Figure 8 there is functionally shown the motor
controller 62, including the control state determination
apparatus 90, which has as an input and output the present
control state 78 for determining the next control state.
The inputs are the inverter frequency 4~, the car control
; enable 64 to indicate if the inverter is enabled to run,
the tach frequency 52, and the jerk limited torque request
; 23 ~TERJ) which determines whether in power or brake. If
the TERJ is positive, then the control operation is goinq
to be a power state, if the TERJ is negative, the control
is going to be in brake. The synthesis mode SO prevents a
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change to transformer brake apparatus operation if the
control operation is not in six-step. The apparatus
includes a brake PI controller 102 and the slip controller
104. The control state determination apparatus 90 control
provides a slip enable 105 to the switch 106 which routes
the torque error signal 60 into the slip controller 104.
If the operation excludes the transformer braking apparatus
80, for example, where it is desired to vary the motor slip
in order to control the motor torque, the switch 106 will
be closed permitting the torque error signal 60 to go into
the slip P + I controller 104 and output a desired slip
frequency 108 into the limiter 110 which prevents too much
slip and avoids going over the knee of the torque versus
slip curve. The limiter 110 provides a slip limit feedback
15 112 into the slip P + I controller 104 to limit the slip to
a desired maximum level and to preset the slip P + I
controller 104 to clamp the controller 104 so the inte-
; gral portion does not continue rising. The output 114 of
the limiter 110 is the slip frequency 114 which is also fed
back into the control state determination apparatus 90 to
control a couple of different state determinations. The
slip frequency 114 is added to the tach frequency 52 in an
adder 116 and the output is the inverter frequency 48. The
function generator 120 uses the inverter frequency 48 and
another input, the slip frequency 114 to generate a desired
inverter voltage 122 that will result in the ~C motor 14
being operated below base speed at constant rated air gap
flux. This desired inverter voltage 122 is not obtainable
above base speed from the inverter due to limits imposed by
the DC line voltage. Therefore, voltage limiter 124
monitors the DC line voltage 43 to determine if its other
input, desired inverter voltage 122 can be obtained. If
the voltage 122 cannot be obtained, the voltage limiter 124
; will clamp to a voltage that can be obtained. If the
35 voltage 122 can be obtained, the voltage limiter 124 will
not modify the voltage 122. The output of the limiter 124
is the re~uested inverter voltage 126 and that goes into
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another function generator 128 which has as another input
the DC voltage 43, and the output is the requested inverter
voltage percent 74. The DC line voltage 43 multiplied by
.78 represents the maximum obtainable inverter output
voltage. The inverter voltage 126 is divided by this
maximum obtainable inverter output voltage resulting in a
requested inverter voltage percent 74. The inverter
frequency 48 is an output from the adder 116. The brake
voltage P + I controller 102 has an input switch 130. If
the control state determination apparatus 90 wants to
activate the brake controller 102, the braking enable 129
closes the switch 130 to enable the error signal 60 to be
fed into the brake P + I controller 102 that is function-
ally an integral controller. The output of the brake P + I
controller 102 is the desired motor voltage 132, which goes
into adder 134, which has another input called six-step
inverter voltage 136. The DC line voltage 43 goes through
a multiplier 138 to be multiplied times a constant K of .78
and the output of the multiplier 138 is the six-step
inverter voltage 136 which is the maximum amount of voltage
that the inverter 11 can put out in six-step operation.
The adder 134 takes the desired motor voltage 132 and
subtracts the six-step inverter voltage 136 and the result
is the desired transformer output voltage 140, which is
then fed into function generator 142 in relation to the DC
line voltage 43 to produce the desired braking angle 144.
This is the angle that the GT0 switches in the brake
circuit 80 must be turned off during every 180 cycle in
order to produce the desired transformer output voltage
140. The function generator 142 calculates the desired
braking angle 144 using the following equation: -
ANGLE = 3n0 ARCSIN ( 4 ~ V
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where VTx is the desired transformer output voltage 140 and
VTDc is the instantaneous voltage appearing across the
secondary of the braking transformer, such as 550V for a
turns ratio of 9 and a power supply 10 voltage of 600V.
This braking angle 144 must be between zero and 80 out of
that 180 during which the GTO switches in the braking
circuit 80 will be turned off and thus be providing the
brake circuit voltage across the motor for that angle. The
desired braking angle 144 goes into the limiter 146 to
limit the desired braking angle to no less than zero
degrees and to no more than 80. The zero degree limit is
provided because a negative amount of time is not available
out of the GTO switch, and the 80 limit is provided
because at that point the GTO switch is getting close to
being off when the current has the wrong polarity such that
this would induce a negative voltage to subtract from the
provided inverter motor voltage. One output of the limiter
146 is the requested braking angle 70 and another output is
the angle limit 148, which is fed back to preset the brake
P + I controller 102 to clamp the integral portion of the P
+ I controller 102. The angle limit 148 also feeds back
into the control state determination apparatus 90 to
determine if a change to a different control state is
needed. For example, once the transformer brake operation
runs out of voltage, which happens when the braking angle
reaches 80, the control state determination ap~aratus 90
may want to go to the high slip next control state which
results in holding the maximum braking angle and then
increasing the slip to get a little bit of additional
braking torque. For another example, once the GTO switch
operation reaches a zero degree angle, the control state
determination apparatus 90 can get out of transformer
braking since there is no longer a need for it. The
control state determination apparatus 90 outputs a braking
thyristor enable 68 to either turn on the thyristors or
turn them off. Within a state of transformer braking, the
braking ~hyristor en~ble 66 ~eeps the thyris~ors of, and
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when not in a state of transformer braking, the thyristors
are kept on.
The slip controller preset 107 operates when
needed to provide a desired slip frequency 108 having a
predetermined or clamped value. The brake controller
preset 109 operates when needed to provide a desi'red motor
voltage 132 having a predetermined or clamped value.
The inverter and braking synthesis apparatus 76
provides a synthesis mode determination 50. The re~uested
inverter frequency 48, the requested inverter voltage
percent 74 and the present control state 78 are input to
the synthesis apparatus 76, and the synthesis mode output
50 will determine the type of synthesis operation that is
wanted, such as one of PWM, quasi six-step or six-step.
In Figure 9 there is shown the control states of
the present AC motor control apparatus.
The operation of the present control apparatus
can be divided into the three basic states: off, power, or
brake. The off state can be further divided into normal or
emergency off states, which both indicate that the system
is not operational. A normal off condition results from a
command by the vehicle control input, such as from the
operator's master controller. An emergèncy off condition
results fro~ a system shutdown as a result of an unaccept-
able condition such as overcurrent or low line voltage.
The power state is divided into the two regionsof below or above base speed. The distinctlon is made
because below base speed the motor is essentially operated
under constant volts per hertz condition resulting in
maintaining a desired air gap flux density, whereas in the
above base speed range the inverter is operated in the
six-step mode to give the maximum obtainable output torque
from the motor and the air gap flux density is decreased as
a result of increased speed. Above base speed operation is
similar to the field weakening region in DC propulsion
equipment.
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16 52,282
The brake state comprises the same two basic
divisions as the power state of below and above base speed.
The below base speed region is also similar to the po~Jer
case since the inverter is capable of providing the demand-
ed torque by itself. The brake above base speed is morecomplicated since the inverter cannot generate the required
torque alone and the regeneration braking circuit must be
used. The brake above base speed region is further divided
into three separate sections:
A~ brake above base speed and below rated slip;
B) brake above base speed at rated slip with
regeneration circuit not at max capability;
C) brake above base speed with regeneration
circuit at max capability and slip at more
than rated slip.
The transitions between these control states are
; made through special transition routines which define the
possible control states that can be entered based on the
present control state and the existing conditions such that
a transition can be made from power above base speed to
brake above base speed and below rated slip A, but not to
the other two brake above base speed conditions B or C.
The basic control philosophy is one of slip
control, that is, the slip of the motor is adjusted by
varying the operating frequency of the inverter in order to
achie~e the desired torque output. During the operation in
the below base speed region, the motor is kept in the rated
volts per hertz operation, resulting in rated air gap flux
density. Whereas above base speed, the inverter is at
maximum voltage output. In this mode of operation inverter
voltage cannot be manipulated to obtain rated air gap flux
density.
; If a motor is in a braking state above base
speed, it is desirable to obtain more braking torque than
can be achieved by adjusting slip at the maximum voltage
output. It is not possible to get the required braking
rate without ~omehow increasing the motor voltage. A
17 52,282
special transformer circuit is used to provide the extra
voltage needed by the motor. ~hen braking the motor above
base speed, the slip of the motor is manipulated to arrive
at the desired torque. If by the time slip reaches the
rated value and the desired torque is not reached, then the
slip is held at that value and the transformer voltage
controller is released to increase the voltage on the motor
for increasing the torque output in brake until the maximum
angle is reached at about 80. Then the transformer
controller is locked at this position and the slip control-
ler is released allowing the slip to increase above its
rated value up to an absolute maximum slip in order to
satisfy the torque request. This strategy is provided to
keep the currents in the GTOs under a preset limit of 350
amps RMS in order to avoid shutdowns due to overcurrent
conditions while providing the torque needed to satisfy the
torque request.~
The control operation is initialized at the
I control state of emergency off, such that the start-up or
power-up operation is emergency off. From emergency off,
the only other next state is normal off, and the operator
car controller allows that transition. Once in normal off
and the car controller requests go, a jump can be made to
either the recovery state, to the power open loop state, or
to the power below six-step state. While in the emergency
off state, a check is made to see if the recovery timer is
timed out, which is a timer provided to keep the control
state in emergenc~ off for a predetermined time period.
Then a change of the control state to normal off and then
; 30 to either power below six-step, power open loop, or recov-
ery is made depending upon operating conditions. Once the
inverter is running then the determine mode routine is
executed to see if it is desired to change to another
state. For example, if the control was in power below
; 35 six-step and a brake request is received, a change would be
made to brake below six-step, and the operation is going to
change from power to brake. Most of the paths indicated in
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18 52,282
Figure 9 are determined in the determine mode routine with
the exception of the changes between six-step and below
six-step which are in the synthesis transition. The other
paths are done under the determine mode routine. For
example, i the present control state is power below
six-step, the determine mode routine will check the condi-
tions to go either to power open loop, or to go to brake
below six-step and those are the only choices available.
The synthesis will check the conditions to go to po~er
six-step.
In Figure 10 there are shown the brake TX
substates, which are control states within brake TX as
shown in Figure 9. In Figure 9 there are shown the ten
different contro~ states, and the brake TX as shown in
Eigure 10 includes six substates. Every time the operation
cycles through the determine mode routine a check is made
to see if theré is a desire to go to a different control
state or control substate. The determine mode routine
checks predetermined criteria to see if there is a desire
to change to another control state.
In Figure 11, there is shown the power-up or
start routine. ~lhen the processor powers up, a jump is
made to this location. In block 200, the stack pointer is
~; initialized for all of the stack functions. The synthesis
timers and the brake timers are set in the OFF state. The
RAM memory is initialized as well as the car control
communications for communication with the car control. A
real time clock timer is initialized to the right frequency
of 720 Hz. Block 202 clears all of the interrupts. The
program then enables all interrupts at block 204. The only
; interrupts that should be present are from the real time
clock since the motor operation is not started yet. Block
~ 206 initializes all variables associated with the synthesis
; operation. Every time the control pulse synthesis opera-
tion starts or restarts, it is necessary to initialize the
associated variables.
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19 52,282
A check is made at block 208 to see if the
transformer brake reset timer is timed out. When the
transformer braking operation is shut down for a fault
condition, it is shut down to one state and after a certain
while it is changed to another state, and there is a timer
provided between those two states to control the change to
the ~inal state. If this timer is not timed out, the
program waits at block 208 for the timer to time out. At
block 210, the brake control hardware is disabled as the
second state of the brake control shutdown, and this
involves turning the thyristors ON and the GTO switches are
turned OFF in the braking circuit. At block 212, the
inverter ready flag is set equal to true to tell the main
control loop that the processor is ready to do the synthe~
sis operation. The real time interrupts are looking at
this flag, ~nd until this flag is set equal to true the
program does not proceed to operate the motor. The back-
ground monitor is initialized at block 214 to operate with
; a video display to show what is going on. At block 216 the
background monitor is operated to provide desired testing
for develop~ent and related purposes to display diagnostic
type information. Real time interrupts occur while in this
background monitor loop. The actual motor controller 62
functions shown in Figure 8 are performed during these real
time interrupts. The inverter and braking synthesis 76 is
performed by the microprocessor during interrupts from the
synthesis timers which can occur whenever the microproces-
sor is either in the background monitor loop or the real
time interrupt calculations. After performing the instruc-
tions in an interrupt procedure, the microprocessor returns
to the routine it was performing when the interrupt oc-
curred. The flow chart in Figure 11 shows the main
start-up loop program and also the start-up after a fault
condition.
The flow chart in Figures 12A and 12B shows the
interrupt program to which the operation jumps upon receiv-
ing a real time interrupt. Once an interrupt is received,
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52,282
the first thing at block 250 is to disable the real time
interrupt. Block 252 clears the real time interrupt to
acknowledge receipt of the interrupt. At block 254 the
line voltage is read. A serial communications link can be
S provided with the power controller 17 so this serial
information is obtained at a 720 Hz rate, and at block 256
new pieces of information are obtained and they are stored
until the whole block of information is obtained.
There is an interrupt available for the real time
clock set at a 720 Hz rate, but it is not desired to do
everything at that high rate. The real time counter is
incremented every time at block 258 when an interrupt is
received, and once that real time counter is greater than
or equal to three at block 260, the slower type of control
is performed at a 240 Hz rate.
At block 262 a check is made to see if the real
time flag equa~s true. If this flag equals true, the
program was already in the process of performing the 240 Hz
calculations when the 720 Hz real time interrupt occurred.
It is not desirable for the 240 Hz calculations to be
started again until the last set of calculations is com-
plete. This flag is set at the beginning of the 240 Hz
calculations and reset at the end in order to prevent a
second set of 240 Hz calculations being started prior to
the completion of the current 240 Hz calculations. If this
real time flag is set to true, no new 240 Hz calculations
will be started, and a jump to E~IT INT0 at the end of this
routine is performed. If this flag is not equal to true, a
240 Hz calculation set can be started. At block 264, the
real time flag is set to true to disable the starting of a
~ new 240 Hz calculation set until this set is complete and
; the real time flag is reset back to false. At block 266
three is subtracted from the real time counter. The blocks
258, 260, 262, 264 and 266 permit operation at a 240 Hz
efective interrupt rate. At block 268 the real time
interrupt is again enabled such that during the 240 Hz set
of calculations additional 720 Hz real time interrupts can
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:1 ~8560~3
21 52,282
be processed. At block 270 there is an update of the
timers ~sed in all routines of the program to add 1/240 of
a second to each of the timers. For a 1 second timer this
routine would run 240 times for that timer to finally
expire. ~t block 272 the tachometer frequency is read. If
the communication at block 256 with the car control logic
has provided a whole block of information, then at block
274, the commands from the power controller 17 are pro-
cessed, such as the desired tractive effort w~nted from the
motors and the desired direction o forward or reverse. At
block 276, a branch is made to a subroutine called Check
Inverter, which checks to see whether the inverter wants to
be run or is running. In block 276 as well as throughout
the flowcharts, the abbreviation BSR is used to indicate a
branch to subroutine. The name of the subroutine to be
branched follows the BSR initials. When a branch to
subroutine, also referred to as a subroutine call, is
encountered, the program execution jumps to that subroutine
and the instructions of that subroutine are executed. At
the end of the subroutine is a return statement that causes
the program execution to be transferred back to the routine
that contains the subroutine call; and execution resumes
with the first instruction after that call instruction. At
block 278, the inverter run flag is checked to see if it
equals true, and if not a real time exit is made to a later
part of the program. If this flag is true, at block 280,
shown in Figure 12B, a branch is made to a control loop
routine which is the actual control program. At block 282,
a check is made to see if the inverter frequency is less
than .5 Hz and at block 284 a check is made to see if the
power controller 17 is requesting a tractive effort less
than or equal to zero. If the answer is yes, the motor is
almost stopped and there i,s no request to go into power, so
a software stop shutdown is provided by a shutdown routine
;~ 35 that actually shuts down the inverter, the braking circuit,
and reinitializes all the variables, and then returns back
to the power up routine in Figure 11 at the car control G0
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2~ 52,282
label. In block 286, a check is made to see if the car
control or power controller 17 is requesting a coast mode.
When the car control requests a coast mode, the inverter is
shut down and the car coasts and the program goes to a
coast shutdown routine. The exit real time label from
block 278 is provided here. At block 288, this is close to
tha end of the real time interrupt, so the real time
interrupt is now disabled to permit a check of the real
time counter at block 290, without the 720 Hz routine
providing an interrupt at the same time. If that real time
counter is still greater than or equal to 3, indicating
that it got incremented before the program couId get
through this routine, the program goes back to block 266 to
repeat the 240 Hz calculation portion of the routine until
the real time counter is less than 3. Eventually, it will
get to be less than 3. At block 292, the real time flag is
set equal to false so future 240 Hz calculation sets can be
performed. Block 294 re-enables the real time interrupts
and a return is made to the perform background monitor
block 216 of Figure 11.
In block 276 a branch is made to a check inverter
subroutine shown in Figure 13. Block 300 makes a check to
see if the inverter ready flag is equal to true. During
the power up routine, when the processor is ready to go,
this flag is set equal to true. If this flag is not equal
to true, then a jump is made to a label called INV DISABLED
which prevents the inverter start up. If this flag is
true, a check is made at block 302 to see if the car
control wants the inverter to run, and if not a jump is
made to the INV DISABLED label. I~ it does, at block 304 a
check is made to see if the inverter is presently running.
If it is presently running, the program goes to block 306
to an inverter test subroutine shown in Figure 18 to make a
desired test, and then it branches to CHKXIT to exit from
the routine. If the inverter is not presently running, a
check is made at block 308 to see if the car control is
reguesting COAST MODE. If the car control is requesting
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23 52,282
COAST MODE, then there is no need to restart the inverter
until that COAST MODE request disappears and the routine
exits. If it is not requesting COAST MODE, at block 310 a
check is made to see if the current control state is
EMERGENCY OFF. If so, a fault condition such as a current
overload caused the last shutdown and the car control must
okay a restart before the inverter can be started again.
If the control state is EMERGENCY OFF, a jump to the
emergency off state routine of Figure 16 is performed. If
the control state is not set to EMERGENCY OFF, it must be
set to NORMAL OFF and block 312 will be executed. At block
312 the direction is set equal to the requested direction
which comes from the car control. At block 314 a check is
made to see if a direction change has occurred. If a
direction change is made from forward to reverse, or from
reverse to forward, at block 316 the tach frequency is set
equal to the minus tach frequency, since for a change of
direction the tach reading is actually the negative tach
because it is desired to go in the opposite direction.
20At block 318 a check is made to see if the tach
frequency is less than zero. If the tach frequency is less
than zero, that means the train is rolling backwards, and
the program goes to the negative tach test routine. If
not, at block 320 a check is made to see if the absolute
value of the tach is greater than 4 Hz. If it is greater
than 4 Hz, then a recovery procedure is needed to avoid
; voltage transients. If the tach is less than 4 Hz, at
block 322, a branch is made to an inv~rter test subroutine
which basically checks whether the line voltage is within
desired limits for the inverter to run. At block 324, the
control state is set equal to power below six-step. At
block 326, a branch is made to a subroutine shown in Figure
61 providing a normal PWM start of the synthesis operation
and then a jump is made to checX exit which is the end of
this routine.
In Figure 1~, there is shown the negative tach
test subroutine jumped to from bloc~ 318 of Figure 13. At
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24 52,282
block 350 a check is made to see if the trac~ive effort
request is greater than zero. If the car is rolling back
and the tractive effort request is not greater than zero,
the program goes to check exit and lets the friction brake
stop the vehicle. If the tractive effort re~uest is
greater than zero, then at block 352 a check is made to see
if the tach is less than minus 10 Hz, and if it is, this is
going to result in an error shutdown. This would indicate
that the car is rolling back faster than about 4
miles/hour, which is an unlikely condition and is actually
probably due to a fault in the tachometer and it is not
desirable to start up under such conditions. If the car is
not rolling back faster than 10 Hz, at block 354 a check is
made to see if the absolute value of the tach, which in
this case is negative, is greater than 4 Hz. If the car is
not rolling back at more than 4 Hz, at block 356 a branch
is made to the inverter test subroutine, where a check is
made to see if the line voltage is within desired limits.
At block 358 the control state is set equal to power open
loop. Since the vehicle is rolling backwards, the car must
first be slowed to a stop and then accelerated in the
desired direction. The process of slowing the vehicle is
actually a braking operation, and the torque feedback
calculation is not reliable at extremely low frequencies
below 10 Hz; ~therefore, the vehicle must be slowed down
under an open loop control method. With open loop control,
an amount of slip frequency proportional to the car control
175 torque request is applied to the motor and the calcu-
lated feedback torque is ignored. The applied slip fre-
quency will result in a motor torgue which crudelyapproximates the desired motor torque. At block 360 a
` branch is made to a subroutine called normal PWM start
shown in Figure 61 which will start the inverter using PWM
synthesis. If there was a tach frequency ~reater than 4 Hz
at block 354 a recovery procedure is required and at block
362 a branch is made to the subroutine called inverter test
to make sure the line voltage is within desired limits. If
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52,282
it is, then at block ~64 the control state is set equal to
recovery. At block 366 a subroutine branch is made to the
rail gap recovery routine shown in Figure 19 which will
start the inverter using a special recovery procedure that
will increase the motor voltage slowly enough so as not to
result in large transient currents which would immediately
cause the inverter to shut down again.
In Figure 15, there is shown the flow chart for
the positive tach recovery routine jumped to from block 320
of Figure 13. This routine is jumped to ~rom block 320 if
the tach frequency is positive and greater than 4 Hz. If
the inverter is to be started, a recovery procedure will
have to be performed. At block 370 a check is made to see
if the tach is greater than 5 Hz, and if it is greater than
5 Hz, it doesn't matter what the tractive effort is. If at
block 370, the tach is not greater than 5 Hz and at block
372 the tractive effort request is not greater than zero,
then a branch is made to check exit, and the inverter is
not started. If either one of those conditions is true,
then at block 374 a branch is made to inverter test, which
checks the line voltage. At block 376 the control state is
set equal to recovery and at block 378 a branch is made to
the rail gap recovery subroutine to start the inverter.
In Figure 16, there is shown the flow chart for
the emergency off state routine, which was jumped to from
310 of Figure 13. This path will be executed if the
current control state is EMERGENCY OFF. At block 380 a
check is made to see if the recovery timer has timed out.
After the inverter is shut down, a certain amount of time
is required for all the currents and flux to die in the
motor before an effort to start is made to avoid getting a
transient and another current overload and shut down again.
If this timer is not timed out, the program goes to check
exit. If it is timed out, a check is made at block 382 to
see if the car controller has approved a recovery. If it
is okay to recover, then at block 384, the control state is
set to NORMAL OFF thus allowing the inverter to start up in
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26 52,282
the future if so desired. The inverter cannot be s~arted
from the EMERGENCY OFF control state. The control state
must be NORMAL OF~ for the inverter to be started as shown
in Fi~ure 9.
In Figure 17 there is shown a flow chart for the
inverter disabled routine jumped to from blocks 300 and 302
of Figure 13. This routine is executed if the inverter is
desired to be off. At block 386 a check is performed to
see if the inverter is presently running. If yes, a jump
is performed to the shutdown procedure shown in Figure 63
to shut down the inverter. If the inverter is not present-
ly running at block 386, CH~XIT is jumped to and the
inverter remains off.
In Figure 18, there is shown the inverter test
subroutine. At block 390, a check is made to see if the
line voltage is between the desired limits of 400 and 800
volts. If it ls, then a return is made. If not within
these limits, then a bad line voltage shutdown will be
performed by the shutdown procedure shown in Figure 63
which will shut down the inverter if it is running.
The rail gap recovery routine shown in Figure 19
is called from block 366 of Figure 14. This subroutine
starts the inverter if the motor is rotating at`a speed
greater than the equivalent of 4 Hz which is 120 rpm. It
; 25 initiates the use of a special recovery procedure which
conslsts of increasing the motor voltage slow enough so
that large transient currents do not occur which would
immediately result in the inverter shutting back down again
due to an overcurrent condition. In block 400, a check is
made to see if the absolute value of the tach frequency is
between 3/64 Hz and 200 Hz, and if not, a start up of the
inverter is not desired and a bad recovery error shutdown
is performed by Figure 63. If those tests pass, at block
402, the requested inverter frequency is set equal to the
tach frequency to provide zero slip. In block 404, the
frequency is set equal to the requested inverter frequency.
At block 406, the calc voltage subroutine is called and
27 52,282
this routine takes that frequency that FREQ variable is set
to in block 404, and calculates what voltage is desired to
keep a constant volts per hert~ motor operation, and
provides a requested inverter voltage. Since this is a
recovery operation, that whole voltage is not applied
across the motor. At block 408 a percentage of 10% is
selected. At block 410 the requested inverter voltage is
set equal to the requested inverter voltage times the
recovery percent to determine the volts that are desired.
At block 412, the new voltage flag is set equal to true
because a new voltage has been determined, so the synthesis
operation has to calculate a few extra steps. At block 414
a check is made of the requested inverter frequency. If
the requested in~erter frequency is less than zero hertz,
at block 416 the recovery control state is set equal to the
recovery mode minus state since there is a negative fre-
quency and at block 418 a branch is made to the START PWM
subroutine or starting the inverter using PWM synthesis.
If the frequency is between zero and 70 Hz, at block 420
the recovery control state is set equal to the recovery
mode low state, and at block 422 a branch is made to the
START PWM subroutine for a start-up using PWM synthesis.
If the frequency is between 70 and 100 Hz, at blQck 424 the
; recovery control state is set equal to the recovery mode
mid state, and a branch is made to the subroutine START PWM
at block 426. If the frequency is greater than 100 Hz, at
block 428 the recovery control state is set equal to
recovery mode high state. In block 430 a branch is made to
the START QSIX subroutine to start the inverter using Quasi
six-step synthesis.
Another subroutine called by the main real time
interrupt routine shown in Figure 12B is the control loop
routine shown in Figure 20, which is the basic control loop
- : program. In block 440 a subroutine called Determine Mode
~' 35 is calledl There are only two places where control state
changes are permitted, with one bein~ in this determine
mode subroutine, and the other being in the synthesis
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~L2~i56;~)B
- 28 - 67880-45
operation for controlling changes between Quasi six-step and six-
step. The control loop subroutine performs all other control
state changes. In block 442 the TER or torque effort request
coming from the car control is checked to be within reasonable
limits of the motor, and it is clamped if not within reasonable
limits. At block 444 a check is made to see if the control state
equals recovery and if it does not equal recovery at block 446 a
branch is made to the TER jerk limit subroutine, which calculates
the jerk limited torque effort request to provide a comfortable
change in acceleration. If the control state does equal recovery,
it is desired to hold the torque effort request at zero because
the motor is held at zero slip until the voltage is brought up.
Then TERJ will increase from the zero value set in the recovery
state. At block 448, a branch is made to the TE feedback routine,
disclosed in the above cross referenced patent application
500,751, to ealculate the feedback torque of the motor. In block
450, delta TE is set equal to TERJ - TEF, which is the difference
between the desired jerk limited torque effort and the calculated
feedback torque effort. Delta TE is an error signal for the motor
controller. In block 452 a branch is made to the control state
; ~ control subroutine, and this establishes the PI controller for the
slip and the integral controller for the transformer voltage. At
block 454 a check is made to see if the control state equals
recovery, and if it does not at block 456, a branch is made to the
~/F control subroutine that checks -to see if the inverter
frequency is within desired limits and calculates the voltage that
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corresponds with the inverter frequency. If the control state is
equal to recovery, it is not desired to calculate the inverter
voltage at this time because for the recovery case the inverter
voltage is calculated in the control state control subroutine
called by block 452.
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29 52,282
In Figure 21, there is shown the flow chart for
the determine mode subroutine which determines if a control
state change is desirable. If so, the control state is
changed to the new desired state. Figures 9 and 10 show
all of the allowable control states and all of the allow-
able control state change paths. The Quasi six-step to
six-step transitions are not included since they are
controlled by the synthesis routine and not controlled by
the determine mode routine. In block 460, the synthesis
timers and the real time interrupts are disabled. Since a
change of the control state is provided, it is not desired
to be in the middle of changing the control state and then
get a synthesis interrupt which can also change the control
state. During the control state change, it is desired to
disable those interrupts. In block 462 a check is made to
see what is the present control state and this determines
the branch made to a desired routine, such as Emergency
Off, Normal Of, Recovery, Brake Open Loop, Brake Below
Six-Step, ~rake Six-S~ep, Brake TX, Power Open Loop, Power
~0 Below Six-Step and Power Six-Step as shown in Figure 9.
In Figure 22, there is shown the flow chart for the
~rake TX branch routine. In block 464, a check is made to
see what is the current brake control state. The brake TX
state is operative when the braking transformer circuit is
included in the circuit to provide additional braking
voltage to the motor. There are seven possible branches
within the brake TX branch. They are TX No ~X branch which
is provided when leaving brake TX, TX Below Six-Step
Transition, TX Six-Step Transition, TX Below Six-Step, TX
Six-Step, TX Angle Control and TX High Slip Control as
shown in Figure I0.
In Figure 23, there is shown the flow chart for
any of the TX No TX branch, Emergency Off branch or the
Normal Of branch. Such control states are not possible at
this part of the program and should not occur. If they do,
a software error e~ists and the in~erter will be shut down
by the shutdown procedure in Figure 63.
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In Figure 24, there is shown a flow chart for the
recovery branch. ~hen the control state is equal to
recovery, this branch is taken. The recovery ~tate con-
sists of substates ~efined by the recovery control state
variable. Recovery control state is equal to one of five
values: none, minus, low, mid, and high. Recovery control
state is set equal to one of these last four states by the
railgap recovery subroutine shown in Figure 19 when the
recovery procedure is initialized. Upon completion of the
recovery procedure, the recovery control state is set equal
to none which indicates that the control state can be
switched from Recovery to another more desirable state. If
the recovery control state is not equal to none at block
470, a jump is made to exit and the operation will remain
in recovery. If the recovery state is equal to none, that
means the voltage has been ramped up and the control
operation is ready to do some torque control again. If it
is none, then at block 472 a check is made to see if the
tach frequency is less than zero hertz. If it is less than
zero hertz, at block 474 the control state is set to power
open loop, because when the tach frequency is less than
zero hertz, the control has to do open loop power control.
If the tach frequency is not below zero hertz, at block 476
a check is ~ade to see if the synthesis mode after recovery
is equal to six-step. If it is equal to six-step, then at
block 478 the control state is set equal to power six-step.
If it is not equal to six-step at block 476, then at block
480 the control state is set equal to power below six-step.
In Figure 25, there is shown the flow chart for
the brake open loop branch. At block 484, a check is made
to see if the jerk limited torque effort request or TERJ is
greater than or equal to zero for selecting between power
or brake. If the controller is asking for a positive
torque effort request! then the control should be in power,
if it is negative, then the operation should be in brake.
i ~ If the control state is in brake the TERJ becomes greater
than or equal to zero, at block 486 the control state is
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31 52,282
set equal to power open loop. If the TERJ is not greater
than or equal to zero, then the operation remains in brake.
At block 488 a check is made to see if the tach frequency
is greater than or equal to 10 Hz. Since the torque
feedback calculation, as described in the above cross-ref-
erenced patent application, is not considered satisfactory
below 10 Hz, which is a motor speed of 300 rpm, closed loop
torque control cannot be performed. If motor braking is
desired at such low operating speeds, open loop torque
control must be used. With open loop torque control a slip
frequency proportional to TERJ is used to achieve the
approximate desired motor torque. No feedback torque value
is used when open loop control is being performed. Normal-
ly in transit applications, motor braking is not attempted
at such low operating speeds. Instead, friction brakes are
called upon to bring the transit vehicle to a complete
stop. At block 488, if the tach frequency is less than 10
Hz, the control state remains in brake open loop and if it
is greater than or equal to 10 Hz, then a change is made to
closed loop control. At block 490, a branch is made to th
subroutine to calculate variable slip gain. The slip PI
controller has a variable gain associated with it that
compensates for variations in the gain of the system being
controlled. For instance if the AC motor is being operated
below base speed where rated air gap flux is maintained in
the motor a certain slip frequency will result in a certain
amount of motor torque. However, if the motor is being
operated at high speed where rated air gap flux cannot be
maintained, a much lower motor tor~ue will result from that
same slip ~requency. The system is said to have a lower
gain at the high speed than it does at below base speed.
To compensate for this drop in gain, the controller's gain
is raised at high speeds. After the variable slip gain is
calculated, a branch is made to the subroutine adjust
clamped controller, which sets up the PI controller to be
at the right initial conditions to make a smooth transition
from open loop to closed loop control. At block 492 the
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control state is set equal to brake below six-step and an
exit is made. This completes the brake open loop case.
In Figure 26, there is shown the flow chart for
the brake below six-step branch. At block 500 a check is
made to see if the TERJ is greater than or equal to zero.
If it is, at block 502 a change is made to the correspond-
ing power below six-step state. If not, at block 504, a
check is made to see if the tach frequency is less than 10
Hz, and if the tach frequency has fallen below 10 Hz, then
at block 506 the control state is set to brake open loop.
If the tach frequency is not below 10 Hz, the controller
remains in the brake below six-step control state.
In Figure 27 there is shown the flow chart for
the brake six-step branch. The brake transformer circuit
can only provide brake voltage in six~step, so this routine
has to consider that event. At block 510, a check is made
of the TERJ to see if we're greater than or equal to zero
to establish if we should go to power, and if it is greater
than or equal to zero, then at block 512 the control state
is set to power six-step and an exit is made. If not, at
block 514 a check is made to see if transformer braking is
enabled to determine that there is no problem with the use
of the braking transformer. If the transformer braking is
not enabled, an exit is made. A change of state to below
six-step cannot be made here, since this has to be done by
the synthesis program. At block 516 if transformer braking
it is enabled, a check is made to see if the desired slip
frequency is less than or equal to minus 2.2 Hz. A minus
2.3 Hz would be less than minus 2.2 Hz. So, if not, then
transformer braking will not be done. If it is, then
additional braking voltage is desired, and the operation
can go to transformer braking. At block 518, the control
state is set equal to Brake TX. At block 520, the brake
control state is set equal to TX six-step, where TX stands
for transformer. At block 522 all interrupts are enabled
because the control state change is finished and the
lnterrupts that were disabled in olock 460 of Figure 21
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should be re-enabled as ~oon as possible. The TX angle
wait timer is set equal to 1/40 of a second, since the
change of braking control from brake six-step requires
remaining in TX six-step control state for a certa.in amount
of time to allow for all of the thyristors to turn off.
The TX abort timer is set equal to .5 seconds, which timer
is used to take the transformer out.
The normal transformer brake operation is for a
period of about 15 seconds. The TX six-step state brings
the transformer into the circuit, but does not start
modulating the GTOs even though they are turned ON. To
prevent staying in that state too long, the half-second
abort timer operates if after half a second some angle
control is not started, the transformer is removed since it
is not needed. The brake slip boundary flag is set equal
to false, which flag is used by the TX six-step to proceed
onto the next state, so that flag is initialized. At block
524, a request is made to turn on the brake GTOs and to
stop gating the thyristors which are shorting the trans-
former to bring the transformer into the circuit. The GTOsin the braking circuit are turned on because there is no
need for angle control yet.
In Figure 28, there is shown the flow chart for
the TX below six-step transition branch. While the br~king
transformer is in the motor circuit, it is possible for the
DC line voltage to increase rapidly to a much higher
voltage (for example from 500 volts to 700 volts). Such a
rise in DC line voltage would result in an equally rapid
rise in motor voltage unless the voltage from the braking
çircuit is reduced. R~pid rises in motor voltage cause
large transient motor currents and should be avoided. The
DC line voltage rise may come at a time when the trans-
former braking circuit is providing only a small amount of
the motor voltage. In such a case, the transformer voltage
would have to be reduced to zero by turning on the braking
GTO's 100% of the time. Also, the inverter output voltage
might have to be decreased to a value below the six-step
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34 52,282
output in order to maintain the same motor voltage.
However, the braking transformer cannot be remo~ed immedi-
ately from the motor circuit; therefore, it is necessary to
allow quasi six-step inverter synthesis when the trans-
former is in the motor circuit but providing no voltage tothe motor. However, as mentioned earlier, it is not
desirable to remain in transformer braking without provid-
ing motor voltage for long periods of time. If such a
condition lasts for more than .5 seconds the transformer
will be removed from the motor circuit. At the time that
it is removed, the inverter could be in either six-step or
quasi six-step synthesis; therefore, TX braking exit paths
must be provided for both cases. In order to exit trans-
former braking, the thyristors must be allowed to turn on
so as to short out the transformer windings. The thyris
tors should be on for a shor~ period, such as approximately
1/80 second, before the braking GTOs can be turned off,
thus completing the transition to no transformer braking.
The temporary states used for this transition are TX below
six-step trans if the synthesis mode is quasi six-step and
TX six-step trans if the synthesis mode is six-step at the
time of the transition.
At blocX 530, if the 1/80 second transition timer
~ is not timed out then the control remains in the TX Below
; 25 Six-Step transition state a little bit longer to allow
things to stabilize and to allow the thyristors to be
turned on long enough before the GTOs can be turned off.
~; In block 530, if the timer does time out, then at block 532
the control state is set equal to ~rake Below Six-Step. At
block 534 the brake control state is set equal to TX NO TX.
In block 536, all of the interrupts are enabled because the
`control state change is completed. In block 538, a re~uest
is made to turn off the GTOs and keep the thyristors gated,
and that will finalize the transition out of Brake TX Below
; 35 Six-Step. When the control state goes to TX Below Six-Step
Transition, the thyristors are turned on and the GTOs are
kept on too. At block 538 the GTOs are turned off.
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In Figure 29, there is shown the flow chart for
the TX Six-Step Transition branch. At block 540 a check is
made to see if the transition has timed out. If so, at
block 542, the control state is set equal to Brake
Six-Step. At block 544, the brake control state is set to
TX NO TX. At block 546, all interrupts are enabled and at
block 5~8, a request is made to turn off the GTOs and keep
the thyristors gated.
In Figure 30, there is shown the flow chart for
the TX Below Six-Step branch. At block 560, a check is
made to see if the .5 second TX abort timer is timed out.
If it is, that indicates the transformer will be removed
from the brake circuit. Assume it is not timed out, and at
block 562 a check is made to see if the desired slip
frequency is greater than minus 1.8 Hz. If either the TX
abort timer is timed out or the slip frequency is greater
than minus 1.8 kz, which is less negative than minus 1.8
Hz, the braking transformer will be removed from the motor
circuit and the brake control state will be changed to TX
below six-step trans. This set of events begins with block
564. If neither o these conditions is met, the controller
remains in the TX below six-step state. At block S~4, the
brake control state is set equal to the TX Below Six-Step
Transition state. At block 566, all interrupts are en-
abled. At block 568, the TX transition timer is set equalto an eightieth of a second and the TX break reset timer is
set equal to .05 seconds. The TX transition timer deter-
mines how long the operation has to stay in the TX Below
Six-Step Transition routine before the brake GTOs can be
turned off. In block 570, a request is made to gate the
thyristors to turn them on and Xeep the GTOs on, so both
the secondary and the primary of the transformer are
shorted for this short period of time. At block 572 the
braking angle request is reset to zero degrees.
In Figure 31, there is shown the flow chart for
the TX Six-Step branch. At block 576 a check is made of
the brahe slip boun~ary flag, which is set by the slip
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36 52,282
controller when doin~ slip control. When the slip becomes
less than or equal to minus 2.4 Hz, less than would be mors
negative, this flag will get set to true and that will mean
that it is okay to change to the TX angle control. If it
is true, at block 578 a check is made to see if the forti-
eth of a second TX angle wait timer is timed out. This is
a timer that requires being in TX six-step for at least a
fortieth of a second to allow the thyristors to totally
turn of~. If yes, then at block 580 a check is made to see
if the voltage percent is greater than or egual to 100%.
For a voltage percent of 100%, the inverter should be in
six-step, and the synthesis has not yet made the change to
quasi-six-step. If not 100%, the control is going to
remain in this state unless there are conditions to drop
lS out of the transformer braking. If the voltage percent is
greater than or equal to 100%, and the TX angle wait timer
is timed out, at block 5~32 the brake control state is set
equal to TX angle control to start modulating the brake
GTOs. At block 584 all interrupts are enabled, and at
block 586 a branch is made to the subroutine Rework Brake
PI, which could be a proportional plus integral brake
controller, but at present is just an integral controller,
to initialize all of the intermediate values of the PI
controller for a smooth transition. It calculates back-
wards for the PI and comes up with all of the correctintermediate values for a smooth transition. At block 588
a request is made to allow the GTOs to be modulated based
on what the brake angle request is and to keep the thyris-
tors off. At block 590, a couple of flags are set initial-
ized to false, which flags are used by the TX angle controlroutine. If the brake slip boundary flag at block 576 is
not set to true, that means it is not desired to go to TX
angle control. At block 592 a check is made to see if the
.5 second TX abort timer is timed out and at block 592 a
check is made to see if the desired slip frequency is
greater than minus 1.8 Hz, and if yes to either check, then
~ the program is going to take the transformer out. If not,
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37 52,282
a jump is made to exit to stay in this state. If yes, at
block 594 the brake control state is set equal to TX
Six-Step Transition because the transformer is to be taken
out. At block 596 all the interrupts are enab'ed, the TX
transition timer is set equal to an eightieth of a second
to determine how long the program will remain in the
transition state and the TX brake reset timer is set e~ual
the .05 seconds in case there is a shut down in the near
future. At block 598, a request is made to gate the
thyristors on and keep the GTOs on to short both sides of
the transformer. At block 600, the braking angle request
is reset to zero and then an exit is made.
In Figure 32, there is shown a flow chart for the
TX Angle Control substate branch. While in the TX angle
control state, the controller holds the slip frequency
constant and controls the brake GTO firing angle, thus
controlling thè transformer voltage, to maintain the
desired motor torque. As shown in Figure 10, the synthesis
cannot chan~e state to quasi six-step while in this control
state, so at block 602 the interrupts can be immediately
enabled. At block 604, a check is made of the TX max-angle
flag, which flag is set again by the control and if set
true means that the control is at 80 and the controller
should go to TX High slip control. If it is true, at block
606, the brake slip boundary flag is initialized to false.
.
This flag is used in the TX High Slip control to indicate
when it is time to switch back to TX angle control. At
block 608, a branch is made to the calculate Variable Slip
Gain subroutine and the Adjust Clamped Controllers subrou-
tine. The slip controller is readjusted to bring that backinto play. At block 610, the brake control state is set
equal to TX High Slip Control and this is the maximum brake
control state as shown in Figure 10. If the TX max-angle
flag was not set to true at block 604, then there is no
need to go any higher in the braking operation, and at
block 612, a check is made to see if the TX zero angle flag
is set to true. thir i~ another ~la~ set to true by the
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38 52,282
controller when the angle of the brake GTOs is zero degrees
which means the transformer braking is no longer needed.
If it is false, then a jump is made to exit. If it is
true, then the control is going to proceed to TX Six-Step
as shown in Figure lO. At block 614, the TX abort timer is
set to .5 second. It is not desired to stay with the
shorted GTOs for more than half a second. At block 616, a
branch is made to the calculate variable slip gain subrou-
tine and the adjust clamped controller subroutine to set up
the slip controller for the correct intermediate conditions
and then at block 618 a request is made to turn on the GTOs
and keep the thyristors off. In the TX angle control
substate the GTOs are modulated so block 618 now turns them
on all the time and keeps the thyristors off. Then in
block 620 the brake slip boundary flag, which is used in
the TX Six-Step Control to get back to the TX angle con-
trol, is initialized to false. In addition, the desired TX
voltage, which is the output of the brake controller, is
reset to zero, the brake request and the desired motor
voltage, which are outputs of the brake voltage controller,
are also reset to zero.
In Figure 33, there is shown the flow chart for
the TX High Slip Control substrate branch. This is the
maximum brake control state. During this control state the
transformer braking circuit output voltage is held at its
maximum value and the slip controller is operated to
provide a small amount of additional braking torque from
the motor. At block 622, all interrupts are immediately
enabled because the synthesis cannot make a change in this
control state. At block 624 a check is made to see if the
brake slip ~oundary flag is equal to true. The brake slip
boundary flag is equal to true if the motor slip has
fallen, less negative than minus 2.3 Hz slip, in which case
it is necessary to start adjusting the transformer output
voltage again. If it is false, a jump is made to exit to
remain in the TX high slip control state until the slip
reaches minus 2.3 Hz slip. If it is true, then block 626
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39 52,282
initializes two flags used by the TX angle control, the TX
zero angle flag and the TX max angle flag. In block 628 a
variable called max obtainable motor voltage is calculated,
which is the maximum motor voltage that can be obtained
from the DC line voltage with 80 on the braking GTOs, and
it is determined as 1.7 times the DC link voltage. This is
the line to line motor voltage across the motor.
At block 630, a check is made to see if the
desired motor voltage, which is the motor voltage presently
across the motor, is greater than the maximum obtainable
voltage minus 10 volts for hysteresis. If it is, then
block 632 sets the desired motor voltage eq~al to this
maximum value minus 10. At block 634, a branch is made to
the brake adjus~ clamped controller subroutine. At block
636 the brake control state is set equal to TX angle
control and this completes the transition.
In Fi~ure 34 there is shown a flow chart for the
Power Six-Step state branch. At block 640 a check is made
to see if TERJ is less than zero. If it is less than zero,
at block 642 the control state is set equal to Brake
Six-Step. Otherwise, the control state stays at Power
Six-Step.
In Figure 35 there is shown a flow chart for the
Power Open Loop control state branch. At block 646 a check
is made to see if TERJ is less than zero. If it is less
than zero, at block 648 the control state is set equal to
Brake Open Loop and an exit is made. If it is not, at
block 650 a check is made to see if the tach frequency is
greater than or equal to zero hertz. If it is not greater
than or equal to zero hertz, then the control state remains
in power open loop and an exit is made. If yes, then at
block 652 a branch is made to the subroutine to calculate
the variable slip gain and also to adjust the clamped
controller for setting up the PI controller correctly. At
block 65~ the control state is set equal to Power Below
Six-Step and the operation is in closed loop contro1. If
the tach fFequency is n-g~tive, the vehicle i- rol1ing
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40 52,282
backwards from the desired direction of travel. Until the
vehicle has been brou~ht to zero speed, the torque control
must be performed open loop. Then closed loop control can
be used to accelerate the vehicle in the desired direction.
In Figure 36 there is shown a flow chart for the
Power Below Six-Step control state branch. At block 656, a
check is made to see if TERJ is less than zero. If it is,
at block 658 the control state is set to Brake Below
Six-Step. If the TERJ is greater than or equal to zero, at
block 660 a check is made to see if the tach frequency is
less than zero hertz. If it is less than zero hertz, at
block 662 the control state is set equal to Power Open Loop
because it is necessary to do open loop control and an exit
is made. If not, at block 660 the control state stays in
the same Power Open Loop branch and a jump is made to exit.
This exit is for all of the control branches shown in
Figures 24 to 36 that will eventually jump here. At block
664 all interrupts are disabled because there will be a
change in the brake configuration. At block 668 a new
brake configuration request is output to the hardware, and
at block 670 all interrupts are enabled and then a return
is made.
In Figure 37 there is shown the flow chart for
the torque request jerk }imit routine, which is called by
25 the main control at block 446 of Figure 20 to jerk limit
the torque request. The torque request is jerk limited to
provide a smooth ride to the car passengers. The jerk
limit routine prevents rapid acceleration changes, which
would cause the ride to be jerky, by limiting how fast the
motor torque request can be varied. At block 680 a vari-
able DIFF is set equal to the tor~ue effort request TER
minus the current jerk limited torque effort reques~ TERJ.
In block 682 a check is made to see whether DIFF is greater
than or equal to zero or is less than zero. If it is less
than zero this TERJ is greater than TER and it is desired
to ramp down the TERJ to meet TER. For a maximum slip
condition the max TEF ilag is set equal to tr~le b~! the slip
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41 52,282
controller to indicate that the maximum torque possible is
bein~ provided by the motor. This maximum torque is either
less than or equal to the desired jerk limited torque
request but it is the most that can be obtained. The
reason for this maximum torque being less-than the desired
torque may be due to a lower DC line voltage. If the DC
line voltage is to suddenly rise significantly, the torque
output of the motor would suddenly rise significantly, too.
Normally, the controller would do nothing to halt this
sudden rise in torque until the motor torgue exceeded the
torque request. At this point the controller would finally
attempt to slow the torque rise. Such a sudden rise in
torque would cause the transit car to jerk which is not
desirable. Therefore, to prevent this sudden jerk, the
jerk limited torque request (TERJ) is not allowed to exceed
the actual motor feedback torque (TEF) by more than + 25
lb-ft when the~motor is producing its maximum possible
torque. Using this approach, if the voltage were to rise
rapidly, the controller would respond almost immediately,
as soon as the 25 lb-ft margin is reached, by limiting the
torgue increase. The jer~ limit routine would then ramp
the TERJ up at an acceptable rate until the TER value is
reached.
At block 6~4 a check is made to see if the max
TEF flag is set equal to true. If yes, TERJ must be kept
within 25 lb-ft of TEF. AT block 686, a check is made to
see if TERJ is less than TEF minus 25. I~ yes, then TERJ
is more than 25 lb-ft less than TEF and must be increased.
In block 688, TERJ is increased by an amount of torque, TER
jerk rate, which is small enough to remain within the jerk
limits required. If either max TEF flag is false or TERJ
is not more than 25 lb-ft less than TEF, TERJ will be
adjusted so as to approach the torque request TER. At
block 690 DIFF is set equal to the absolute value of DIFF,
which will make it positive. If DIFF is less than TER jerk
rate, the maximum allowed change in TERJ in one cycle's
calculation, then TERJ is set to TERJ minus DIFF by block
~L285~013
42 52,282
696 which results in TERJ being equal to TER. If DIFF is
not less than TER jerX rate, then block 694 will limit DIFF
to the TER jerk rate value and after block 696 modifies
TERJ, TERJ will be closer to TER but not equal to TER. If
TER changes abruptly, the TER jerk rate will limit how fast
TERJ is allowed to change in an effort to meet TER.
If at block 682, DIFF is greater than or equal to
zero, TERJ is less than or equal to TER. AT block 683 max
TEF flag is tested to see if the motor is in a maximum
torque condition. If yes, block 685 tests to see if TERJ
is greater than or equal to TEF plus 25 lb-ft. If yes,
then TERJ is more than 25 lb-ft greater than TEF and must
be decreased. In block 687, TERJ is dacreased by the TER
jerk rate. If either max TEF flag is false or TERJ is not
more than 25 lb-ft greater than TEF, TERJ will be adjusted
so as to approach the torque request TER. AT block 689
; DIFF is compared against TER jerk rate. If DIFF is not
less than TER jerk rate, DIFF is limited by being set equal
to TER jerk rate. At block 693, TERJ is modified by adding
DIFF to the previous TERJ value. Block 693 will result in
TERJ becoming closer to the torque request TER.
In Figure 38 there is shown the flow chart for
the control state control subroutine. At block 700 the max
TEF flag is set equal to false and then if the operation
goes to a condition where the slip is limited to its
maximum extremes, thereby getting the most torque avail-
able, this flag is set equal to true. At block 702 a checX
is made to see what is the current control state and a
branch is made to a routine corresponding to that control
state. Each branch will perform the type of control
necessary for that control state. Figure 9 shows all of
the possible control states.
In Figure 39 there is shown the flow chart for
the CSC brake TX control substate branch. At block 703 a
check is made to see what the current brake control
substate is, and a branch is made to a routine correspond-
ing to that brake control state. Figure 10 shows all o~
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43 52,282
the possible brake control substates. The CSC branches
referred to in Figures 38 and 39 are found in Figures 39
through 48. The CSC initials are used to abbreviate
control state control.
I~ Figure 40 there is shown the flow chart for
an~ one of the CSC TX no TX branch, the CSC emergency off
branch or the CSC normal off branch. If any one of these
branches did occur, it would involve an error in the
software, so a software error shutdown would result.
In Figure 41 there is shown a 1OW chart for the
CSC TX Bel~w Six-Step Transition, the CSC TX Six-Step
Transition and the CSC TX Below Six-Step control substate
branches. In any one of the TX Below Six-Step Transition,
TX Six-Step Transition or TX ~elow Six-Step states occurs,
; 15 a control operation is provided for controlling slip.
These are brake control substates with the transformer in
the brake circùit but providing no voltage to the motor.
At block 704, the variable slip gain is calculated. At
block 706 a branch is made to the slip PI control routine
and then the controller will come up with a desired slip
requency as an output. At block 70~ a check is made to
see if this desired slip frequency is more negative than
minus 2.4 Hz. If it is, at block 710 the desired slip
frequency is clamped at minus 2.4 Hz. At block 712 the
clamped controller is adjusted to set up all the interme-
diate values so that minus 2.4 Hz is reflected throughout
; all the intermediate values of the controller. A branch is
made at block 714 to the calculate inverter frequency
routine.
In Figure 42 there is shown the flow chart for
the CSC TX Six-Step control routine, which is similar to
the control routine shown in Figure 41. In the TX six-step
control state, the braking transformer is in the motor
circuit but is providing no voltage to the motor. Slip
control using the slip PI controller is active and is used
to maintain the desired torque TERJ from the motor. At
block 716 a branch is made to calculate the min-angle
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44 52,282
routine. It is necessary to start the brake hardware
timers, and this requires outputting to the counters the
minimum braking angle because of the synthesis operation.
The braking timers start although the GTOs are not modulat-
ed, but the timers will be working. A branch is made tothe calculate variable slip gain subroutine to calculate
the variable slip gain for the slip PI control. A branch
is made to the slip PI control subroutine to provide the
desired slip ~requency. In block 718 a check is made to
see if the desired slip frequency is less than or equal to
minus 2.4 Hz. If no, block 720 sets the brake slip bounda-
ry flag equal to false which means it is not desired to gointo TX angle control because there is not enough brake
slip. If if is more negative than minus 2.4 Hz, at block
722 the brake slip boundary flag is set equal to true. At
block 722 the desired slip frequency is set equal to minus
2.4 Hz. Block 724 adjusts the clamped controller.
In Figure 43 there is shown the flow chart for
the CSC TX Angle Control substate branch, which has the
transformer in the brake circuit and is actually modulating
the brake GTO switches. While modulating the brake GTOs,
`~ this control state holds the slip at minus 2.4 Hz. At
block 728 a branch is made to the Brake PI Control subrou-
tine to get the desired transformer voltage. Then a branch
is made to the Brake Angle Calculate subroutine to change
that desired transformer voltage into an angle. At block
730 a check is made to see if the angle called Brake
Request is greater than 80. If it is greater than 80, at
block 732 it is clamped equal to 80 because it should not
go higher. At block 734 the Braking Angle Request is set
equal to 80, which is the actual angle that the synthesis
looks at to calculate the actual times for the braking
timers. In block 736 a branch is made to Rework Brake PI
routine to clamp the controller and all the desired inter-
mediate values. In block 738, two flags are set; one isthe TX max angle flag set equal to true because the control
operation is at maximum angle and this will tell the
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Determine Mode subroutine to change to the TX High Slip
control and the second is the zero angle flag set equal to
false because it is not desired to go back to the TX
Six-Step substate. Then a jump is made to calculate
inverter frequency at block 740. If the Braking Request at
block 730 is not greater than 8~, at block 742 the TX max
angle flag is set equal to false because the operation is
not at the maximum angle. In block 744 a branch is made to
calculate minimum angle subroutine to establish the minimum
angle to fire the GT~s, which below around 100 Hz is an
angle of 2~2 and above 100 Hz is an angle of 5. The
reason for the higher angle at a higher frequency is that
5 at 200 Hz is substantially the same time duration as 2l,2
at 100 Hz, and o~e angle is not enough to cover the entire
range.- At block 746 a check is made to see if the Brake
Request is equal to zero degrees. The brake PI controller
will set it equàl to zero, if it goes below zero. If it is
e~ual to zero degrees, in block 748 the zero angle flag is
set equal to true to tell the determine mode subroutine to
change back to the TX Six-Step substate. In block 750 the
Brake Request is set equal to the minimum angle calculated
in block 744 and the Braking Angle Request is also set
equal to the minimum angle. Then at block 714 a jump is
made to calculate inverter frequency routine. In block
746, if the Brake Request does not equal zero, then block
752 sets the TX zero angle flag equal to false. In block
754 a check is made to see if the Brake Request is greater
than or equal to minimum angle. If it is greater than the
minimum angle, then bloc~ 756 will set the Braking Angle
Request equal to Brake Request. I~ not, block 750 sets the
Brake Request e~ual to minimum angle and also sets the
Braking Angle Request equal to the minimum angle.
In Figure 44 there is shown the flow chart for
the CSC TX High Slip Control substate branch. The TX high
slip control state maintains the braking angle at 80,
unl~ss the DC line voltage~experiences a sudden increase,
and controls the slip fre~uency of the motor ~o control the
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12~5~)8
46 52,282
motor tor~ue. If the DC line voltage experiences a sudden
increase in voltage, this control state will decrease the
braking angle to hold the motor voltage constant. Then the
motor voltage will be allowed to increase at a fixed,
controllable rate up until the braking angle. again reaches
80. During this voltage control, the slip of the motor is
still controlled to control the motor torque. At block 750
a calculation is made of the maximum obtainable motor
voltage, which is equal to the DC line voltage times 1.7.
This is done using the 80 brake angle request. At block
752 a check is made to see if the desired motor voltage is
less than the maxi~um obtainable. If it is, that means a
line voltage transient has occurred and a drop in the brake
angle is perfor~ed in an effort to keep the same motor
voltage. Then it is desired to ramp the brake angle back
up to 80, and this is done slow enough so the slip con-
troller, which is slower than the voltage controller, has
time to respond. In effect a jerk limit of 480 volts per
second is provided to raise the motor voltage. If the
desired motor voltage is less than maximum obtainable at
block 752, it is raised up to the maximum obtainable at the
240 Hz rate that this routine is executed. This is done by
adding at block 754 ~wo volts to the desired motor voltage
every time through the program to provide essentially a 480
volt per second rise. If not less than the maximum obtain-
able at block 752, then at block 756 each time through the
program subtracts 2 volts. This operation results in
hovering around the maximum obtainable voltage. At block
758, the maximum obtainable inverter voltage, which is the
inverter voltage in six-step operation, is calculated as
equal to the DC line voltage times .78. At block 760 the
desired TX transformer voltage is calculated as the desired
motor voltage minus the maximum obtainable inverter volt-
age. At block 762 a check is made to see if the desired TX
voltage is less than zero. If it is, then an extremely
large line voltage transient has been received, since the
brake angle was at 80 and a transient must have brought
~28560~il
47 52,282
the angle down to belo~ zero degrees. Such a condition is
extremely rare and is not compensated for; however, if it
does occur, a shutdown of the inverter and braking circuit
would result. If the desired TX voltage at block 762 is
not less than zero, at block 764 the corresponding brake
request is calculated in relation to the desired TX volt-
age. At block 766 a check is made to see if the calculated
brake request is greater than 80. If it is, at block 768
the brake request is set equal to 80 and the braking angle
request is set equal to 80. If not greater than at block
766 then at block 770 a branch is made to the subroutine to
caiculate the minimum brake GT0 angle. At block 772 a
check is made to be sure the brake request is not below the
minimum angle and it probably will not be unless there was
an extremely large line voltage transient and then a brake
voltage transient error shutdown is provided. If the brake
request is grea~er than or equal to minimum angle, at block
774 the braking angle request is set equal to the brake
re~uest. At block 776 a branch is made to the slip PI
control subroutine, because this operation is controlling
slip, and open loop voltage control is trying to maintain
constant or slower changing voltage. In block 778 a check
~ is made of the desired slip frequency to see if it is
; greater than minus 2.3 Hz. If it is, then at block 780
desired slip frequency is clamped at minus 2.3 Hz and the
brake slip boundary flag is set true to tell the determine
mode subroutine to go back to TX angle control. If not
greater than minus 2.3 Hz at block 778, that means it is
still more negative than minus 2.3 Hz, the operation can
stay in the same control state. The brake slip boundary
flag is set equal. to false at block 782. In block 784 a
check is made to see if the desired slip fre~uency is less
than or equal to minus 5.2 Hz, which is the most slip
allowed for the motor in the braking transformer operation.
If it is less than minus 5.2 Hz, at block 786 it is clamped
at that value, and the max TEF flag is set equal to true
sin~e additioral torque cannot be obtained from the motor.
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48 52,282
At block 788 a branch is made to the adjust clamped con-
troller routine to adjust the clamped slip controller.
Then a jump is made to the calculate inverter frequency
routine.
5In Figure 45 there is shown the flow chart for
the CSC recovery branch, which makes a branch at block 790
to the recovery control subroutine shown in Figure 65.
While in the recovery control state, the slip frequency is
; held at zero Hz and neither the slip PI controller or
braking transformer voltage PI controller is active. The
function of this recovery control state is to ramp up the
motor voltage slow enough such that large transient cur-
rents do not occur that would shut the inverter down again.
The recovery control is used to restart an inverter follow-
ing a shutdown where~the motor is rotating faster than 120
rpm or 4 ~æ.
In Fi`gure 46 there is shown the flow chart for
the CSC brake open loop and CSC power open loop control
state branches. These control states perform open loop
torque control by declaring a slip frequency that is
proportional to the jerk limited torque effect request
TERJ. ~hese two control states are used at very low motor
operating speeds where the calculated torque feedback
signal is too unreliable to use thus necessitating the use
of open loop control. In block 792 the desired slip
frequency is set equal to the TERJ times the rate of slip
over the rated torque effort. If the TERJ is equal to the
rated torque effort of the motor, then rated slip is
applied to the motor. A jump is then made to calculate
; 30 inverter frequency.
In Eigure 47 there is shown the flow chart for
the CSC brake below six-step and CSC brake six-step control
state branches. Under these two control states, closed
loop slip control is used and the braking transformer is
out of the motor circuit. At block 796 a branch is made to
the calculate variable slip gain subroutine and to the slip
PI control subroutine. At block 798 a check is made o the
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49 52,282
desired slip frequency. If the desired slip frequency is
more negative than minus 4 Hz, at block 800 it is clamped
at minus 4 ~Iz and the max TEF flag is set equal to true.
At block 802 a branch is made to the adjust clamped con-
troller routine to clamp the slip controller. If thedesired slip frequency is greater than .5 Hz at block 798,
at block 804 the desired slip frequency is clamped to .S
Hz, since in brake it is not desired to have positive slip.
If the slip is within the two limits of .5 Hz and minus 4
Hz, the slip is accepted and a jump is made to the calcu-
late inverter frequency routine.
In Figure 48 there is shown the flow chart for
the CSC power below six-step and the CSC power six-step
control state br,anches. Under these two control states,
closed loop slip control is used and the braking trans-
former is out of the motor circuit. In block 810 a branch
is made to the~variable slip gain calculation and to the
slip PI control routine. In block 812 a check is made of
the desired slip frequency, and similar to the brake
operation there is a limit on the maximum slip. It is not
; ~ desired to go above ~ Hz and to go Iess than minus .5 Hz,
and in either one of those cases it is clamped to those
values. In the case of the slip greater than 4 Hz, at
block 814 it i5 clamped to 4 Hz and the MAX TEF flag is set
to true. In block 816 it is clamped to minus .5 Hz. In
block 818 a subroutine branch is made to adjust the clamped
controller. If the slip is within limits, then a jump is
made around blocks 816 and 818. At label 714 is the
~ beginning of the calculate inverter frequency routine.
This is the same label 714 to which the routines shown in
Figures 41 to 47 go. In block 822 the desired inverter
~ frequency is set equal to the desired slip fr quency plus
; the tach frequency. In block 824 a check is made to see if
the desired inverter frequency is greater than 200 Hz,
~which is the maximum for the motor operation. If not
greater than 200 Hz at block 824, then the routine goes to
the control exit label 826. It if lS greater at block 824,
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52,282
at block 828 a check is ma~e to see if the control state is
brake TX when the motor is above 200 Hz. It is highly
unlikely that the motor could be at 200 Hz while the
controller is braking the motor, but if such a condition
did occur, the inverter and brake circuit would be shut
down. If that is not the case, at block 830 the desired
inverter frequency is set equal to 200 Hz and the desired
slip frequency is set equal to 200 minus the tach frequen-
cy. At block 832, a check is made to see if the desired
slip frequency is less than minus 4 Hz, and if it is, this
; would result in a shutdown. If not, at block 834 a branch
is made to the variable slip gain calculation and a branch
is made to the adjust clamped controller subroutine to
clamp the slip controller at the clamped slip amount. At
block 826 a branch is made to the control exit routine
which makes a return.
The vàriable PI gain subroutine is provided to
effectively increase the gain of the slip controller at the
higher frequencies of motor operation. When the motor is
operating in the rated volts per hert~ range below base
speed, a condition of 1.5 Hz slip might provide an output
torque of 740 lb-ft at a given motor temperature. Once the
motor frequency increases and the motor is no longer in the
constant volts per hertz range`but is in the reduced flux
range such as with motor operation at 200 Hz, a slip of 1.5
Hz might result in an output torque of only 40 lb-ft.
The slip controller with constant gain to be fast
enough, would have to have enough gain to provide reason-
able response for 200 H, However, such a high gain would
be too high for below base spéed operation. This very high
gain would result in a below base speed operation which
would be too fast and would, therefore, be susceptible to
uncontrollable oscillations resulting in instability. The
;
solution is to use a variable gain in the controller so
that at high speeds the variable gain is increased and
during below base speed operation the variable gain is
decreased. The controller would then have the same
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51 52,282
response speed over the entire operating range. In other
words, the overall system bandwidth is constant for all
motor speeds.
In Figure 49 there is shown the 1OW chart for
the slip PI control subroutine. In block 840 the variable
delta TEl is calculated as delta TE, which is the differ-
ence between the jerk limited torque effort request TERJ
and the feedback torque, times the variable PI gain. The
variable PI gain is set up in the calculate variable slip
gain routine shown in Figure 50. Delta TE1 provides the
desired gain increase for high speed operation such as 200
Hz. A PI controller has a proportional part and integral
part. In block 842, the proportional TE1 is equal to P
gain, which is set for the individual controller, times
delta TEl. The integral TE1 is equal to a previous inte-
gral value plus a gain constant times delta TE1. At block
844, the output TEl of the controller is equal to the
proportional TE1 plus the integral~TE1. At block 846 the
desired slip frequency is set equal to the bverall design
gain of the controller, which does not change, times this
output TE1 and then a return is made.
In Figure 50 there is shown a flow chart for the
calculate variable slip gain subroutine, which is performed
prior to the slip PI control routine shown in Figure 49.
At block 850 the actual voltage across the motor is calcu-
lated as equal to the requested inverter voltage plus the
desired transformer voltage, that is, the actual
line-to-line voltage across the motor. At block 852 the
variable PI gain is set equal to the ratio of the desired
inverter voltage, which is what constant volts per hertz
would provide, divided by the actual voltage, with that
` ratio squared. For example, in power at 50 Hz, the actual
voltage may be 468 volts and the desired inverter voltage
may be 468 volts, then the variable PI gain will be equal
to one, and anywhere below 50 H7 they approximate each
other. However, in power at 200 Hz, the desired inverter
voltage would ~e four tlme= the value at 50 Uz or 463 x 4,
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52 52,282
which is rou~hly 1800 volts, while the actual voltage is
equal to the inverter output in power or 468 volts.
Therefore, this variable PI gain would be the ratio of 4
times to 1 squared or 16. This results in an increase in
the variable PI gain increase at higher frequencies in
power. In brake there can be some extra actual voltage due
; to the voltage supplied by the transformer braking circuit.
At block 854 a check is made to see if the variable PI gain
is less than one or greater than ten. If it is less than
one at ~lock 856, it is set equal to one and a return is
made. If it is greater than ten, at block 858 it is
limited to ten.
In Figure 51 there is shown the flow chart for
the adjust clamped controller routine, for clamping the
integral portion of the slip controller when the output is
clamped. A~ block 860 the variable TEl is calculated as
equal to the desired slip frequency divided by the gain PI.
To figure out what the integral TE1 is, in block 862 delta
TE1 is set e~ual to delta TE times the variable PI gain.
To figure out what the proportional amount is, the propor-
tional TEl in block 864 is set equal to the P gain times
delta TEl. In block 866 the integral TE1 is determined by
subtracting the proportional TE1 from the TE1. By clamping
the integral portion, a smooth transition is provide~ when
coming back to use of the unclamped controller.
In Figure 52 there is shown the flow chart for
-~ the brake PI control routine, which is basically an inte-
gral controller. A~ block 870 a variable dèlta TE2 is set
equal to minus delta TE. In the slip controller routine
shown in Figure 49, the delta TE1 was multiplied by a
variable PI gain, but in this program delta TE1 is multi-
plied by negative one since there is no variable PI gain.
The multiplier is a negative one, since for increased
braking torque more negative torque is needed, and to get
more negative torgue requires a more positive braking
angle. At block 872 the integral TE2 part is set equal to
integral TE2 plus the brake integral gain times delta TE2.
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S3 52,282
In block 874, TE2 is equal to integral TE2. In block 876
the desired motor voltage is set equal to the brake gain PI
times TE~. In block 878 the inverter voltage is set equal
to the DC line voltage times .78. In block 880 the desired
TX voltage is determined by subtracting the inverter
voltage from the desired motor voltage from block 876. In
block 882 a check is made to see if the desired TX voltage
is less than zero, and if it is, at block 884 it is clamped
to zero. If not, that clamp is bypassed.
In Figure 53 there is shown a flow chart for the
rework brake PI subroutine, which is used when it is
desired to clamp the braking angle out of the brake PI; and
this routine sets up the integral portion correctly. At
block 890 a check is made of the braking angle request,
15 which is only clamped to one of 2.5, 5 or 80 angles.
~epending on what it is equal to, a multiplier is here
provided to determine how many volts is obtainable in
transformer brake operation in relation to the line voltag-
es available. For example, for a 500-volt link voltage and
20 a brake angle request of 80, there will result .92 x 500
volts line-to-line RMS across the motor out of the braking
circuit. For a braking angle request of 2.5 this multi-
plier is .0342, and for a braking angle request of 5 this
multiplier is .0676. At block 892 the desired TX voltage
is determined as the multiplier constant K times the DC
line voltage. The inverter portion is set equal to .78
times the DC line voltage, and the desired motor voltage is
set equal to the desired TX voltage plus the inverter
portion. The controller is clamped at this desired motor
voltage. At block 894 a branch is made to the brake adjust
clamped controller subroutine which will take that desired
` motor voltage and come up with the correct intermediate
~: controller results.
In Figure 5~ there is shown the flow chart for
~` 35 the brake adjust clamped controller subroutine. At block
896 TE2 is set e~uaI to the desired motor voltage divided
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54 52,282
by the gain of the brake PI. In block 898 the integral TE2
i5 set equal to TE2.
In Figure 55 there is shown the flow chart for
the brake angle calculation subroutine, which operates
after a desired TX voltage is determined, to calculate what
the brake angle corresponding to that TX voltage is. In
block 900 brake X is set equal to .7 times the ratio of the
desired TX voltage divided by the DC link voltage. The
brake request is set equal to 2 times the arc sine of the
brake X, so the brake request is the output brake angle.
In Figure 56 there is shown the flow chart for
the V/F control subroutine, which operates after the
desired inverter frequency is calculated to make sure it is
within correct cperational limits, and also calculates a
voltage that corresponds to that inverter frequency. In
block 902 a branch is made to the frequency check subrou-
tine. In next block 904 the frequency is set equal to the
requested inverter frequency which is returned by the
frequency check subroutine. At block 906 the calculate
voltage subroutine is called to take that frequency and
calculate a corresponding voltage. In block 908 a checX is
made to see if the requested voltage percent has changed
since the last time it was calculated. If it has changed,
at block 910 the new voltage flag is set equal to true to
indicate to the synthesis that a few extra calculations are
necessary. If not, the block 910 is bypassed. This flag
is set back to false by the synthesis once it is
acknowledged.
In Figure 57 there is shown a flow chart for the
; 30 calculate voltage subroutine. In block 912 a check is made
to see if the inverter frequency is greater than or equal
to zero to determine if the vehicle is rolling back. If
the frequency is negative, the vehicle is rolling back-
wards. To stop a rollback, the actual technique used here
is to first slow the car to a stop and then accelerate it
in the proper direction. Motor voltage waveforms hsving
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55 52,282
the following equations a~-e applied to the motor whenever
the inverter is operating:
Phase A = V ~ sin (2~ft)
Phase B = V * sin (2~ft + 120)
S Phase C = V * sin (2~ft + 240)
where V is the peak amplitude of the line to neutral motor
voltages, t is time, and f is the frequency of the applied
inverter waveforms. When the vehicle is rolling backwards
it may be necessary for f to be negative but not as nega-
tive as the tachometer frequency if it is desired to slow
down the vehicle. Once the vehicle reaches approximately
zero speed, f will become positive and will act to acceler-
ate the vehicle in the proper direction. During the
portion of the run where f is negative the control state is
power open loop even though the motor is actually braking
at this time. The reason for declaring a power state is
that the slip frequency appears to be positive since it is
equal to the inverter frequency minus the tach frequency
and the inverter frequency is the less negative of the two.
Actually negative frequencies do not exist and the motor's
mechanical tach frequency and the inverter frequency are
positive but rotating in the reverse direction. This means
that the 51ip frequency is actually negative during such
operation. It is, however, much easier to treat the
frequencies rotating in the reverse direction as negative
~ frequencies as far as the control is concerned. However,
;~ ~ when calculating the voltage needed to maintain constant
rated air gap flux, positive frequencies rotating in the
reverse direction are preferred to negative frequencies.
In block 914, if the freque~cy value is negative,
we convert it to a positive value. The slip frequency must
also be negated to obtain the actual slip frequency.
At block 916 a check is made to see if the slip is less
than zero, meaning that the motor is braking, or is greater
than or equal to zero, meaning that the motor is in power.
If the slip is less than zero, at block 918 a check is made
to see if the frequency is less than 3 Hz. If the
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56 52,2~2
frequency is less than 3 Hz in the brake operation, a
lookup table is used to figure out the voltage needed to
maintain the desired constant volts per hertz and to
account for IR losses so as to maintain rated air gap flux
in the motor especially down at the lo~ end where these
losses become nonlinear. At block 920 a lookup table,
which is a function of frequency and slip, is used to
determine the voltage. If the frequency is not less than 3
Hz at block 928, at block 922 an approximate boost value is
calculated as six times the ratio of slip over rated slip
plus one. Then at block 924 the voltage is set equal to
9.33 times the frequency plus the boost value just calcu-
lated to determine the voltage wanted across the motor. If
the slip is greater than or equal to zero at block 916,
this is power operation and a check is made at block 926 to
see if the frequency is less than 3/4 Hz. If the frequency
is greater than 3/4 Hz at block 926, then at block 928
boost is set equal to 9 times the ratio of slip over rated
slip plus 1, and then at block 924 the voltage is calculat-
ed as equal to 9.33 times frequency plus boost. If fre-
quency is less than 3/4 Hz at block 926, a jump is made to
block 930 where a different lookup table is used to deter-
mine the voltage wanted across the motor, as a function of
frequency and slip for the power mode.
In Figure 58 there is shown a flow chart for the
boost exit branched to from the end of the calculate
voltage subroutine shown in Figure 57 and which determines
the desired voltage across the motor. During operation
withc~ transformer braking, there are thyristors shorting
out: ~he transformer and the thyristors have voltage drops
associated with them. These voltage drops are only one or
two volts, but one or two volts is a good percentage of the
total output voltage at very low operating frequencies so
it must be considered. How these voltage drops affect the
motor voltage depends on the angle by which the motor
current lags the motor voltage. This angle is checked at
block 940. If the current angle is less thar or equal ~o
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57 52,282
75, then at block 942 two volts are added to the voltaye.
This current angle is calculated as disclosed in concur-
rently iled patent application Serial No. (W.E.
Case 50,932). If the current angle is between 75 and
110, then at block 944 there is added to the voltage one
volt. If this angle is between 110 and 130 no volts are
added. If the angle is between 130 and 165, at block 946
one volt is subtracted from the voltage. If the angle is
greater than 165 then at block 948 two volts are subtract-
ed from the voltage. At block 950 the desired inverter
voltage is set equal to the requested inverter voltage
which is equal to the calculated voltage plus 2 plus 2
times the absolute value of the ratio of slip over rated
slip. The 2 plus 2 times the absolute value of the ratio
of slip over rated slip is a fudge factor found experimen-
tally to correct for random losses. At block 952 a check
is made to see if the requested voltage is greater than the
maximum requested inverter voltage. The maximum requested
inverter voltage is a jerk limited value of the maximum
obtainable inverter output voltage using six-step synthe-
sis. It is used to limit how fast the motor voltage may
rise if operating the motor above base speed in the region
of reduced air gap flux. For instance, if the motor is
operating at 100 Hz, less voltage is being applied to the
motor than is needed to maintain rated air gap flux. If
the DC line voltage is 600 volts, 468 volts RMS
line-to-line would be being applied to the motor with
six-step synthesis. If the DC line voltage were to sudden-
ly increase t~ 700 volts and no attempts were made to leave
six-step synthesis, the motor voltage would suddenly
increase to about 5~6 volts. A rapid increase of voltage
will result in large transient currents and a rapid in-
crease in motor torque both of which are undesirable.
The value called maximum requested inverter
voltage hovers just above the current maximum obtainable
inverter voltage. If a sudden change should occur in the
DC line voltage, this maximum voltage would follow the new
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58 52,282
DC line voltage but at a more reasonable, controllable rate
of about ~80 volts/second. The requested inverter voltage
is never allowed to exceed this maximum voltage. There-
fore, in the previous example there the DC line voltage
went from 600 to 700 volts, the maximum requested inverter
frequenc~ would slowly, such as at 480 volts per second,
rise from just over 468 volts to just over 546 volts. The
requested inverter voltage will be limited to a voltage no
greater than this maximum. This will result in an inverter
voltage initially being requested which is less than the
546 volts that six-step would produce. The synthesis would
then switch to quasi six-step and the motor voltage would
slowly rise at a rate of 4~0 volts/second from 468 volts to
532 volts where six-step synthesis would again be employed.
The voltage rise is slow enough, however, to avoid large
transient motor currents and rapid increases in torque
output.
If the requested voltage is greater than the
maximum requested inverter voltage, at block 954 of Figure
58 the requested inverter voltage is clamped to the maximum
requested inverter voltage to provide a jerk limited jump
in the requested inverter voltage. If not, the same
requested inverter voltage is used. At block 956 a check
is made to see if the requested inverter voltage is greater
than the maximum obtainable inverter voltage. If yes, that
is not desired so at block 958 the requested inverter
voltage is clamped to be equal to the maximum obtainable
inverter voltage. The re~uested voltage percent that is
wanted is 100% since that is what is provided in six-step
and a jump is made to return. If the requested inverter
voltage is not greater than the maximum obtainable inverter
` voltage at block 956, at block 960 the requested voltage
~; percent is calculated as equal to 100% times the ratio of
the requested inverter voltage over the maximum obtainable
inverter voltage. This requested voltage percent is used
by the synthesis to get the right inverter output voltage.
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In Figure 59 there is shown a flow chart for the
frequency check subroutine, which checks to see if a
reasonable inverter frequency is requested. At block 970 a
check is made to see if the desired inverter frequency,
which is output from the controller, is greater than 200
Hz. If yes, at block 972 the desired inverter frequency is
clamped to a maximum operational frequency of 200 Hz. At
block 97~ a check is made to see if the desired inverter
frequency is less than zero. The problem here is that only
frequencies above 3/64 Hz and below minus 3/64 Hz can be
produced by the synthesis. Frequencies between ~inus 3/64
Hz and plus 3/64 Hz cannot be produced; therefore, if a
frequency in this narrow range is requested a frequency of
either 3/64 Hz or minus 3/64 Hz will be generated instead.
The vehicle is moving and may be recovering from a rollback
condition and the known unstable operation is between minus
3/64 Hz and positive 3/64 Hz. At block 974 if the desired
inverter frequenc~i is less than zero then at block 976 a
check is made to see if it is greater than minus 3/64 Hz.
If it is greater than minus 3/64 Hz, at block 978 the
desired inverter frequency is clamped to minus 3/64 Hz. If
the desired inverter frequency is not less than zero at
block 974 then at block 980 a check is made to see if the
desired inverter frequency is less than 3/64 Hz, and if
yes, then at block g82 it is clamped to 3/64 Hz. In block
984 a check is made to see if the desired inverter frequen-
cy is equal to the requested inverter frequency. If they
are equal, a jump is made to return. If they are not
equal, at block 986 the requested inverter frequency is set
equal to the desired inverter frequency. In block 988 the
new frequency flag is set to true to tell the synthesis
that there is a new frequency and it has to do a few extra
calculations. The requested inverter frequency and the
requested voltage percent is what the synthesis then uses
to output the right inverter voltage.
In Figure 60 there is shown a flow chart for the
calculate minimum angle subroutine, which i~ calculating
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the minimum braking angle that can be output to the braking
timers. In block 990 a check is made of the current
minimum angle to see if it is equal to 2.5 or is not equal
to 2.5. This minimum brake angle is usually going to be
2.5 or 5, but upon power-up it could be zero degrees. If
this angle is equal to 2.5, at block 992 a check is made
to see if the absolute value of the inverter frequency is
greater than or equal to 100 Hz. If it is, then at block
994 the minimum angle is set equal to 5, and if not, at
10 block 996 the minimum angle is set equal to 2.5. If the
minimum angle is not equal to 2.5 at block 990, then at
block 998 a check is made to see if the inverter frequency
is less than 90 Hz. If it is less than 90 Hz, at block 996
the minimum angle is set equal to 2.5~. If it is not less
15 than 90 Hz at block 994, the minimum angle is set equal to
5. The 90 Hz and lO0 Hz values are selected to provide
some hysteresis to keep the control operation from unstable
back and forth changes. A jump is made to return.
In Figure 61 there is shown the flow chart for
the nor;nal PWM start routine, which is called by the
interrupt routine shown in Figure 12 when it is desired to
start up the inverter using PWM synthesis operation. In
block 1000, the desired inverter frequency is set equal to
the tach frequency, since it is desired to start with zero
slip. A branch is made in block 1002 to the subroutine V/F
control shown in Figure 56 to set up the right frequency
and voltage. For example, if the frequency is zero here,
it is not desired to start with a zero frequency, so the
frequency is set to 3/64th of a hertz and the right voltage
signal is set to go along with that frequency to provide
the constant volts per hertz control. In block 1004, a
branch is made to the start PWM routine which is disclosed
in above-referenced patent application (50,932) of the
synthesis case, and this will start the synthesis timers.
In Figure 62 there is shown the flow chart for
the start Q six routine, which is used whenever starting up
the motor when already going at a higher frequency, so that
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the start should be with the quasi six-step synthesis since
the inverter frequency is too high for PWM synthesis
operation. At block 1006, a check is made to see if the
GT0 gate driver boards are okay. If they are not okay,
this is an error and a shutdown will result.. If they are
okay, then at block 1008 a branch is made to the subroutine
load Q Qsix six times. This subroutine calculates quasi
six-step GT0 firing times corresponding to one sixty degree
~; section of quasi siY~-step, which is disclosed in
above-referenced patent application Serial No. 5O0,~S
(W.E. Case 50,932). Since this subroutine is called six
times, 360 worth of quasi six-step GT0 firing times will
end up being calculated and placed in their respective
timer queues in memory. At block 1010 the first count is
moved from each of the six timer queues to the appropriate
GT0 timer. In block 1012, the synthesis mode is declared
as being quasi siY.-step. In block 1014, the timer and the
real time clock interrupts are disabled while starting up
the synthesis timers. In block 1016, a check is made to
see what direction is desired, whether forward or reverse.
The difference between forward and reverse is the switch
made of the B and the C motor phases. If the direction is
forward, block 1018 initializes the A, ~, and C plus
interrupt flags to indicate that the minus timers will
cause the first interrupts for the A and the C timers and
the plus timer will cause the first interrupt from the B
timers. Each phase has two timers, one being plus and one
being minus. At block 1020, the A-, C-, and B~ GT0 timers
are enabled. In blocX 1022, an indication is made that the
30 invert~r is running. At block 1024, the rest of the GT0
timers, the B-, A+, and C+ timers are enabled. All six
timers are now running, however, only the three that were
started and enabled first are currently counting. In block
1026, the GT0 timer counts are moved ~rom the A-, B+ and C-
queues to the A-, B+ and C- timers. These are the timers
that were started first and are ready to get new counts
into their holding bu~fers. ~a~h timer has one count that
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is stored besides the count it is co~nting. In addition,
decrementing is done of the queue counts and queue pointers
appropriately to indicate that three more counts have been
removed. Then at block 1028 the queue needs data flag is
reset to indicate no calculations are in progress. The
interrupt routines from the timers use this data flag to
figure out whether or not they need to calculate data, so
that is in the synthesis operation. The timer interrupts
are enabled in block 1030 and then a return is made. By
the time this return is made, the quasi six-step operation
is started and the timers are running and everything is
fine. If the direction is reverse in block 1016, then at
block 1032 the A, B and C plus interrupt flags are initial-
ized to indicate that the minus timers will cause the first
interrupts from the A and B timers and the plus timer will
cause the first interrupt from the C timers. This is
similar to the forward direction operation except the B and
the C phases are interchanged. At block 103~ the A-, B-,
and C+ GTO timers are enabled. At block 1036, an indica-
tion is made that the inverter is running. At block 1038,the rest of the GTO timers are enabled, which are the A+,
B+, and C- timers. Then in block 1040, the GT0 timer
counts are moved from the A-, B-, and C+ queues to the A-,
B- and C+ timers. These were the three timers that were
started up in block 1034, and the queue counts and queue
pointers are decremented appropriately.
In Figure 63 there is shown a flow chart for the
shutdown or error procedure routine. This routine is
called from the flow charts shown in Figures 12, 1~, 17,
30 18, 19, 23, 40, 44 and 48. At block 1050, all interrupts
are disabled. In block 1052 all of the inverter GT0 timers
are disabled and this is going to turn off all of the GTOs
in the inverter. In block 1054, a check is made to see if
` the thyristors are presently shorting the braking trans-
former. If they are not, then a couple of intermediate
steps are required, since it is desired to bring bac~ in
the thyristors to st~rt shorting the transformer but it is
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63 52,282
not done all at once. At block 1056, the braking GTOs are
turned off while the thyristors are still off. The objec-
tive is to eventually turn the thyristors on and turn the
braking GTOs of~. At block 1058, the TX brake reset timer
is started, which is a .05 second timer which is just a
delay. Once this timer times out, there is another routine
in Figure 11 in the start-up that will turn on the thyris-
tors and turn off the braking GTOs, to provide a normal
condition for starting up in power. Block 1060 initializes
the synthesis timers and the brake timers. When it is
desired to start again, the timers are ready. At block
1062, the inverter is indicated as not running and is not
ready to run because it is necessary to initialize the
values which is done in the restart routine. Block 1064
initializes the recovery timer, which is a .2 second timer
and this provides, after the inverter is shutdown during an
emergency situation, a wait of .2 seconds or a certain
amount of time for the currents to die out. Block 1066
sets the inverter frequency equal to zero and inverter
~requency magnitude equal to zero. The inverter frequency
is a signed number and the magnitude is the absolute value
of it. Block 1068 sets the control state equal to emergen-
cy off. Block 1070 checks to see if the shutdown is a
coast shutdown or a software stop shutdown. If it is
either one of those, then block 1072 sets the control state
equal to normal off and block 1074 enables the interrupts.
If not, one of the shutdowns is checked at block 1070, then
the control state is kept at emergency off, and block 1076
records the shutdown. Then a branch is made to the restart
routine shown in Figure 64.
In Figure 64 there is shown a flow chart for the
restart routine called by the shutdown routine shown in
Figure 63. In the restart routine at block 1080 the stack
pointer is initialized. At block 1082 the real time flag
is set equal to false in the event there was an interrupt
while doing the real time routines. At block 1084 the
variables associated with the synthesis operation are
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64 52,282
initialized. At block 1086 all interrupts are enabled. At
label lOgO, the program goes to block 208 of the start
routine shown in Eigure 11.
In Figure 65 there is shown a flow chart for the
recovery control routine called by the reco~ery branch
routine shown in Figure 45. At block 1092 the desired
inverter frequency is set equal to the measured tachometer
frequency to provide a slip frequency of zero for the motor
and to result in a no torque operation of the motor. At
block 1094 a branch is made to the frequency check subrou-
tine to make sure that a reasonable inverter frequency is
requested, as shown in relation to Figure 59. At block
1096 a branch is made to the calculate voltage routine
shown in Figure 57 to calculate the inverter voltage wanted
for the desired inverter frequency, and this establishes
; the requested inverter voltage and the requested inverter
percent for the latter frequency and the desired constant
V/F operational relationship. At block 1098 the recovery
percent is set equal to the last recovery percent plus
.75%, and since this ~s done every 1/240 second, this
operation will increase the recovery percent that was
initially set at 10% in block 408 of the rail gap recovery
routine shown in Figure 19 up to 100% and full voltage
corresponding to the requested inverter voltage in about ~2
second. At block 1100 a check is made to see if the
recovery percent is greater than 100%, and if so at block
1102 the recovery percent is clamped to 100%. At block
1104 the requested inverter voltage is set equal to the
recovery percent times the requested inverter voltage to
increase the actual requested inverter voltage up to the
calculated constant V/F requested inverter voltage in about
second. In block 1106 the requested voltage percent is
set equal to the recovery percent times the calculated
constant V/F requested voltaye percent which is determined
by the calculate voltage routine. At block 1108 the new
voltage flag is set equal to true, so the synthesis opera-
tion will know there is a new requested inverter voltage
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.that might require the calculation of the variables influ-
enced by this voltage.
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