Note: Descriptions are shown in the official language in which they were submitted.
--1--
Description
Elevator Polyphase Motor Control
Technical Field
This invention pertains to elevators, in
particular, polyphase motor control in elevators.
Background Art
It is well known that the speed and torque of a
polyphase induction motor is a function of the
frequency of the alternating power that is supplied to
the motor and the voltage that is applied to the
windings
It is also well known that the motor can operate
at either a synchronous speed, the same frequency as
the power to it, and an asynchronous speed, higher or
lower than that frequency. It operates at the
synchronous speed when the motor is under no load and
at the asynchronous speed when the motor is under load
or being driven. The speed difference is known as
slip, the magnitude of which dramatically impacts the
motor's efficiency and performance.
Therefore, manufacturers of polyphase motors often
specify maximum slip requirements, typically about Ho.,
depending on the motor design and whether it is motoring
or regenerating, or harking. To develop maximum torque
and maximize motor efficiency, the slip under load
conditions should be held at that figure. For instance,
if a two-pole motor is powered from a 60 Ho. source
-2-
during motoring, the speed at rated torque would be
about 3540 rum that being a positive slip of
1 Ho.
Following a converse concept, but using the same
criteria, if the motor is operating at a speed winch
is greater than the frequency, power can be supplied from
it or regenerated back to the source. The slip also
should be maintained within those limits in this case,
but, for regeneration or braking, the speed of the
motor may be, for instance, 3660 at rated torque. In
this case, the slip is negative, -1 Ho.
So, it is not surprising that many techniques
have been tried to control slip precisely; however,
most have met with less than desirable results because
they are too costly, too complicated or do not provide
good performance.
In an elevator slip control it is particularly
important and demanding because motor performance
there must be superior to that in most other
applications. For instance, for a comfortable ride
the motor must be accelerated and decelerated
smoothly, without vibration and noise; yet, for system
speed it must be fast. It should also be efficient,
which means it should regenerate power, and,
naturally, it must be operated in such a way as to
provide precise car positioning at the floors. Most
important, the motor often must be operated at near
zero speed, a condition in which precise frequency control
is critically important for smooth performance.
Jo
I'
~2~42~
. -3-
Disclosure of Invention
on object of the present invention is to provide
a polyphase motor-powered elevator with speed and
torque control.
According to one aspect of the present invention,
a polyphase motor is powered by an inventor that is
powered by a DC power supply such as a battery that is
charged by a battery charger. The inventor is controlled
in such a way that the motor slip is controlled to achieve
maximum torque and also maximum regeneration to charge the
battery. The inserters output frequency and magnitude
are also controlled to control the motor's speed and
torque.
According to another aspect, this inventor is
controlled by a device thaw provides signals that represent
a computed motor speed and slip. Using these signals,
the inventor is driven so as to follow a sine curve
pattern that is at the desired frequency for the computed
slip and at a desired magnitude to achieve desired motor
operation with that slip. These signals are digitally
produced by sensing the motor shaft position and constantly
accumulating count and augmenting that count in proportion
to the desired slip. The accumulated count occurs in some
particular period of time that corresponds to one-quarter
of the period of that sine curve. Taking into account the
characteristic interrelationship between the various
phases of the signals that are to be supplied to the
motor, the relative instantaneous Y-value on the sine
curve signal at each phase is produced from that
I
-4-
count. The Y-value is adjusted up and down to reflect
the instantaneous levels for each phase that drives
the inventor. This yields a signal which is supplied
to each phase input on the inventor by a switching
arrangement. The magnitude of that signal is scaled
up or down to control motor current or voltage.
Hence, starting with a simple count that represents
motor speed and shaft position and adding some numbers
to that, a multi phase drive is provided to the
inventor to control motor speed, slip and torque.
A feature of the invention is that the slip
control that is achieved is very precise, because the
shaft is encoded at a very high rate, far higher than
the motor's speed, in other words, many times during
each revolution.
The control is universal; it can be used on all
multi phase motors, and by augmenting the motor speed
count with different pole configurations, and, being
that it is not inherently frequency limited, it can
control a motor over very wide speed ranges,
especially at near zero and low speed, hence making it
very attractive for elevators. At the same time, by
providing for very precise slip control, the invention
optimizes regeneration of power back into the battery,
and that is a feature which is particularly useful in
an elevator system where regeneration occurs about 30%
of the time because the load is counterweighted.
Other objects, benefits and features of the
invention will become apparent to one skilled in the
art from the description that follows.
~Z~42~
-5-
Brief Description of Drawings
Fig. 1 is a block diagram of an elevator system
utilizing an inventor to drive a 3-phase motor, and
that inventor being powered by a battery and
controlled in accordance with the present invention;
Fig. 2 is a block diagram of an amplitude and
frequency control (AFCL) that is used in the system in
Fig. l to drive the inventor to obtain slip, torque
and speed control; and
Fig. 3 consists of several waveforms that are in
a common time basso
Best Mode for Carrying Out the Invention
Fig. l shows an elevator control system which
includes a number of functional components that are
well known and whose design is not critical to the
invention. Hence, those components are not described
in detail, except to the extent that is needed to
describe the invention. These components include a
motion controller, profile generator and speed and
torque controller, and others identified in what
follows.
In Fig. l an elevator car 10 is connected by a
cable 11 to a counterweight 12. The car is connected
to the phase induction motor 13 which receives 3-phase
power from an inventor I The motor drives a
tachometer 15 (shaft encoder) which produces a
tachometer output, TECH 1 signal, on the line aye,
that signal reflecting the instantaneous speed of the
--I--
motor. The inventor receives DC power from a batter
16, and the battery is charged by a charger 17 josh
is connected to a power source. The DC power may flow
to and from the battery through the inventor. Power
may flow to the battery by regeneration from the motor
as a result of the motion of the car in one direction
(e.g. down), and that, in addition to the charger,
charges the battery. The battery provides most of the
surge or peak power to the inventor, meaning that the
system is virtually isolated from the power source,
which eliminates one source of RFI and other
electrical noises that can build up in the power
system and disturb other equipment connected to it.
A system controller 18 receives car controls and
calls, and in response communicates with a motion
controller 19 over a plurality of lines lea. The
motion controller sends signals from lines lob to a
profile generator 20, which, in a predetermined or
programmed manner, establishes a particular motion or
velocity profile for the elevator car to move in
response to the motion control, this concept being
shown in numerous patents. The profile generator
provides an output, PRO 1 signal, on line aye which
is supplied to a speed and torque control 21. This
speed and torque control unit provides, in response to
the PRO 1 signal, a first DC signal, SLIP 1 signal,
on line aye, the SLIP 1 signal reflecting a desired
slip for the particular PRO 1 signal generated by the
profile generator. The profile generator also
provides, on line 21b, a second DC output, AMPLITUDE 1
Z I
signal, which represents the desired amplitude of
current (or voltage) to the motor winding to move the
car as desired.
The interrelationship between the SLIP 1 and
AMPLITUDE 1 signals determine the torque and speed of
the motor, and the interrelationship is established
through feedback control, that control centering on
sensing the TECH 1 signal, supplied from the
tachometer, and supplying it to the motion controller,
the profile generator, the speed and torque
controller, which use it to generate their respective
signals, and the SLIP 1 and AMPLITUDE 1 signals to
obtain a desired motor performance characteristic at
any instant to control the car motion as required.
The TECH 1 signal is also supplied to an
amplitude and frequency control circuit ~AFCL) 22
which also receives the SLIP 1 and AMPLITUDE 1 signal.
The AFCL circuit uses those signals to generate PHASE
1, 2, 3 signals over the three output lines aye, each
of those signals comprising a staircase sine wave of
high resolution, whose magnitude is varied in a
selected relation to the AMPLITUDE 1 signal in order
to control the car motion in a certain manner.
The signals (PHASE 1-3) are phased apart as required
by the phase of the motor (e.g. 0, 120, 240, for a 3-
phase motor, the example shows), and their frequency
reflects the desired motor speed and slip for a
selected SLIP 1 signal. Their magnitude reflects
desired motor current, that being controlled by the
AMPLITUDE 1 signal.
I
These PHASE 1-3 signals that comprise the AFCL
output are supplied to a current regulator (OR) 23,
which then produces output OR signals, also sine
waves, on its output lines aye, these signals being
provided to a pulse width modulator (PAM) 24. The PAM
supplies corresponding output signals, PAM signals,
each signal comprising a pulse whose duration varies
in proportion to the magnitude of its corresponding OR
signal. The PAM signals are supplied to the inventor
on line aye. The current regulator provides closed
loop control of the motor current to ensure that it
accurately tracks the PHASE 1-3 signals. This type of
control is well known in the field.
The PAM signals that are supplied from the PAM to
the inventor turn separate sections or portions of the
inventor on and off in direct proportion to the
duration of the pulses in the PAM signal. The
inventor turns the battery voltage on and off in
proportion to the duration of the pulses that comprise
the PAM signals, that voltage being applied on the
lines aye to the motor windings. Because the duration
of those pulses that drive the inventor are
interrelated in a sinusoidal fashion by the AFCL
circuit, the average values of the pulses on the
inventor output are sinusoidal also. But, even though
the output signal on each of the lines aye from the
inventor comprises voltage pulses, the inductive
characteristics of the motor result in a sinusoidal
current (I) through the motor over each of the lines
aye, the frequency of that current being the primary
--9--
frequency of the PHASE 1, 2, 3 signals. The harmonics
are dramatically suppressed due to the motors
inductance, and, hence, the inventor provides, in
effect, sinusoidal 3-phase current to the motor, that
current being in response to digital pulses that
reflect the current's frequency, magnitude and the
phase relationship among the motor's windings. This
current I is adjustable in its frequency and its
magnitude, through which the motor speed, torque and
slip are controlled. This adjustment is accomplished
through the AFCL circuit 22, the detailed description
of which follows.
Fig. 2 shows the AFCL circuit 22. The AFCL
circuit receives the SLIP 1 signal and also the
AMPLITUDE 1 signal. The SLIP 1 signal is applied to a
voltage controlled oscillator (VCO) 30 which produces
an output VCO signal, on line aye. The VCO signal,
which is supplied to a flip-flop 32, consists of a
string of pulses whose frequency (VCO frequency) F1
varies in proportion to the DC level of the SLIP 1
signal, which can be adjusted between predetermined
positive and negative values, whose levels defining a
motor speed range, over which the frequency of the VCO
may vary to control motor slip.
The flip-flop 32 also receives a ILK output
signal from a clock 33; that signal strobes the signal
from the VCO to the flip-flop output, producing a
flip-flop output signal, also a string of pulses at
F1, which are supplied over line aye to a SLIP counter
34; it counts those pulses. The SLIP counter
-ill-
continually counts up, and on reaching its maximum
count (ens. bits) starts over. So, its output is
actually a signal, COT 1, reflecting the count at
any instant.
Fig. 3 shows this type of recurring count over
time, the Y coordinate there representing the digital
output or COURT 1, the X-coordinate time.
The SLIP 1 signal is also supplied to a second
flip-flop 36. Also stroked by the ILK signal, this
lo flip-flop is responsive to the polarity of the SLIP l
signal, chasing state from high to low depending on
that polarity in order to provide a count direction
signal, CUD signal, that commands the SLIP counter
to count up or to covet down. COUNT 1, from the SLIP
counter, is supplied on lines aye to a motor speed (MS)
adder 38, which also receives the output from another
counter, speed (SWEDE counter 40, over the lines aye.
The SPEED counter receives the output from a
circuit 42 which includes a flip-flop aye . This
flip-flop aye provides on its output lines 42b a
train of square wave pulses. These are provided in
response to the output from a divider circuit eye
which receives the TECH signal that is supplied on
the line aye. That line actually comprises two lines,
each of which provide a square wave pulse relative
to each other, the pulses on these lines bins in
quadrature (90 apart).
The divider circuit eye receives the square
wave pulses an one of these lines and provides, as
its output, trigger pulses which are at a repetition
rate that is equal to or lower than the repetition
rate of the square wave pulses provided to its input.
-11
The output from the flip-flop 42B is provided to the
input of the SPEED counter 40.
Both of the signals that comprise the TECH signal
are also supplied to a comparator circuit 42c , and
this circuit produces, in response, an output signal,
which, depending upon the relationship between those
two pulses (i.e. which one leads, which one lags),
represents the direction in itch the motor is turn-
in. The output from the comparator 42c is then
supplied to a flip-flop 42d, which, in response,
produces an output signal which is either high or low.
This signal is supplied to the count control terminal
on the counter 40 to command it to count up or count
down the pulses from the flip-flop aye, depending on
whether the signal is high or low. Just like the SLIP
counter, the SPEED counter also continuously counts up,
resets, and then counts up again. It can also count
down depending on the output from the flip-flop 42d.
The result is an output signal, COUNT 2, from the counter
40. This signal is also shown in Fig. 2. The repetition
rate for COUNT 2 is F2, which is in proportion to the
motor speed, since they are generated from the motor's
rotation. The pulses that comprise the TECH 1 signal
are generated very rapidly during each rotation of the
motor, the effect of this being that the rotational
position is resolved very precisely The purpose for
the divider then becomes correlating that count to the
driving frequency of the motor, which is necessary in
order to take into account the number of poles in the
motor, since the number of poles determines the speed
OX the motor. This correlation is important because
-12-
the repetition rate F2 should correspond to the driving
frequency. For example, comparing a four-pole and
two-pole motor, the shaft position in the four-pole
motor must be resolved so that the COUNT 2 is pro-
duped more rapidly per revolution. Hence, the TAC~signal must be divided by two for a two-pole motor,
otherwise F2 would be too high - the motor would not be
synchronized within the slip range. (this assumes
that the same tachometer is used, further, the count/
revolution would be the same regardless of motor speed.)
The reason for this will become even more apparent
from the remaining portions of this description, which
will show that from the basic frequency F2, a higher
or lower frequency is established from the COUNT 1
signal in order to vary the driving frequency from
that of the actual motor speed, this being done in
order to control slip.
The MS adder adds COUNT 1 and COUNT 2, producing
at its output lines aye, an output COUNT 3 (waveform A)
which is the sum of the two. The effect of adding COUNT 1
and COUNT 2 is to shorten the time it takes to
obtain a particular COUNT 3, and thus shorten T in
Fig. 3. In other words, as the SLIP counter counts
up, the slope of waveform A will increase because T
becomes less. As it counts slower, the slope will be
less because T will increase. So, by changing the
VCO frequency, T can be increased and decreased in
proportion to COUNT 1, that range being the SLIP RANGE
or at, that defining a change in frequency between
Fly the frequency of COUNT 1, and F2, the frequency of
COUNT 2.
,;~,
I
-13-
As explained later in detail, to maintain a
certain slip, COUNT 1 is controlled to be higher
or lower than COUNT 2 by an amount that equals the
slip that is desired (e.g. specified for the motor).
The overall action of the AFCL circuit on the motor's
operation is represented by this equation I
F SYNCH = + MOTOR + FLIP (1)
Here, F SYNCH is also the frequency ~F3) of the PHASE
1-3 signals, which is the inventor driving frequency.
FM is the motor speed and COUNT 2 is a function of it,
but may be + depending on the direction of rotation,
because COUNT 2 can be a down count or up count. F
SLIP, the same as the VCO frequency, may be + depend-
in on the SLIP signal, which may be + to effect + slip.
Thus, a smooth transition between motor functions is
obtained, which is important for leveling at "close
speed" (near zero speed).
In addition to COUNT 3, the adder 35 also provides
a digital output, QC signal, which is a representation
of the number (0-4) of cycles made by the COUNT 2.
Each cycle is a quadrant, representing 90 in a full
cycle of 360. To do this, the MS adder output may
have N bits, but actually use NO bits for COUNT 3,
and the remainder of the N bits for indicating the
quadrant and the sign of the sine curve in that qua-
drank.
COUNT 3, from the MS adder, is supplied to a
second adder, the PHASE adder 44. The PHASE adder
44 also receives, on the lines aye, a phase identify-
-14-
cation (PC) signal, from a ring counter 46, that
signal being provided in response to the ILK signal.
The PC signal identifies, at any instant in time,
one of the desired phases, i.e. windings ego. 0,
5 120, 240). This PC is a number which, if added
to COUNT 3, would reflect what would be COUNT 3 at
that phase; that is, a phase shifted by some amount
reflected in the PC signal. In other words, the
ring counter continually provides a "circulating
digital" number which, when added to COUNT 3, reflects
a count for one of the phases. The PC signal is
also added with the QC signal in the PHASE adder,
producing a PI signal that represents the right
quadrant for the phase for the PC signal, since the
quadrant Jay be different for a different phase.
Thus, the output from the PHASE adder 44 includes
(l) an instantaneous digital representation, COUNT 4,
of the count for a particular point X or counts for
one phase, and (2) a digital representation of the
quadrant or the PI signal and its sign.
COUNT 4 represents the coordinate for any point
on the SINE curve in Fig. 3, but only between 0-~0.
From the two, the proper point on the SINE curve for
that coordinate is generated at any instant. This
is done in the AFCL circuit for each phase, each time
the PC signal changes, which occurs at the ILK rate.
COUNT 4 and the PI signal are supplied to a sub-
tractor unit 48, over the lines aye. In response to
the PI signal, the subtracter provides an output,
the IT signal, which is the proper coordinate value for
the quadrant indicated in the PI signal for COUNT 3.
The subtracter counts down from the COUNT 4 signal for
other quadrants during the presence of a PI signal
identifying that quadrant which, if not present,
in actuates the subtracter. Then, it can be seen that
the effect of the PC signal is to shift the IT signal
between 0, 120 and 240.
The IT signal from the subtracter is a coordinate
(e.g. X), and it is furnished on lines aye to a lockup
table, ROM 50. That IT signal addresses a particular
number in the lockup table, that number corresponding
to the sine value for a joint on the SINE curve
between 0-90. The ROM thus produces, on its output
lines aye, a digital output, SWIG 1, that is the sine
value for the coordinate identified by COUNT 3, but
still uncorrected for the polarity for its quadrant.
The SWIG 1 sisal is supplied to a digital to analog
(D/A) converter 52 which produces an analog output,
DRIVE 1 signal, on line aye. This DRIVE 1 signal is
supplied to a switch circuit 54, which also receives
I the PI signal and, depending on what quadrant that
identifier identifies, switches the DRIVE 1 signal
between a positive or negative value, which gives
the DRIVE 1 signal the right polarity for the quadrant.
For example, the SWIG 1 signal (so also DRIVE 1) would
be negative in quadrants 3 and 4, as shown by the broken
sine curve containing SWIG 1' (SWIG 1' being SWIG 1 on
the true sine curve). Thus a full sine curve is
venerated through the four quadrants shown over time -
as different SWIG 1 signals are provided and given the
right polarity
-16-
From the switch circuit the DRIVE 1 signal is
supplied on line aye to an amplifier Go 56, whose
gain is controlled in response to the magnitude of
the AMPLITUDE 1 signal, in order to produce an output,
DRIVE 2, whose magnitude is proportional to the
AMPLITUDE l signal. This DRIVE 2 output signal is
simultaneously supplied to three switches 60, 62, 64,
each one corresponding to one phase drive of the
inventor, each providing one of the PHASE 1, 2, 3
signals. These three switches receive the PC signal
from the ring counter 46, that signal identifying
the phase for the DRIVE 2 signal, and, depending on
what that signal is, one of these switches is actuated,
which transfers the DRIVE 2 signal to correct one of
the sample and hold circuits 55, which produces a
staircase size signal over time - as the DRIVE 2
signal is generated. The SO outputs are the PHASE 1,
PHASE 2 and PHASE 3 signals.
The PHASE l, PHASE 2, PHASE 3 signals are thus
phased according to the PC signal and are at a common
frequency, F SYNCH (see equation l).
To demonstrate this slip control, this example is
provided. Assume a two-pole AC motor at 3600 rum
that is, driven by variable frequency drive using the
invention; what are the frequencies of the VCO output
(Fly) and TECH signals and slip characteristics required
for, (Case 1) zero torque; (Case 2) positive driving
torque; and (Case 3) negative regeneration or
braking using a constant AMPLITUDE 1 signal.
~%~
--1 7--
Case 1: FM = 60 Ho.
F SLY P = 0
F SYNCH = 60 Ho.
VCO frequency = 0
TOKYO frequency = 1024 pulses/second
Case 2: FM = 60 Ho.
F SLIP = Al Ho.
F SYNCH = 61 Ho.
VCO frequency = ~170
TECH frequency = 1024 pulses/second
Case 3: FM = 60 Ho.
F SLIP = -1 Ho.
F SYNCH = 5 9 Ho .
VCO frequency = -170
TECH frequency = 1024 pulses/second
Hence, with this system the car can be moved from
zero to full speed at a controlled rate and with a
controllable slip, by controlling the SLIP 1 and
AMPLY TUNE 1 s i gnats.
Obviously, various operations in this system
may be performed with computer based equipment.
Discreet portions have been used in this description
for illustrative purposes to demonstrate one way to
implement the invention. To one skilled in the art
there will be modifications and variations that can
be made to the embodiment that has been shown and
describe without departing from the true scope and
spirit of the invention. Some of those variations
may include the use of a computer to carry out a
number of functions performed in the discreet system
comprising the AFCL circuit.
I
lug
Needless to say, other applications for the
invention exist. For example, it can be used to drudge
a cycloconverter, rather than an inventor, in order to
power the motor. That is lo say, the AFCL circuit can
be used to provide sine related signals to operate the
cycloconverter in order to provide AC power to a
polyphase motor.
The use of the invention to control a 3-phase
motor has been shown and described because it
facilitates an understanding of the invention. Even
so, it should be apparent to one skilled in the art
that it could be used to control other motors, such as
a 2-phase motor, simply by using the right phase
signal relationship, in order to identify the phase
windings and in order to generate the correct
coordinate on the sine curve for the winding and
establish the correct polarity for it.
Although the invention has been shown for use for
controlling the current of the motor, it could be used
to control motor voltage. Further, by correlating the
amplitude and slip, different motor and slip controls
can be obtained, e.g. one signal can dictate motor
torque.
From the foregoing it will be seen that there are
many applications for the invention to control
induction motors and that the invention may be carried
out in many ways, perhaps through computer utilization
for carrying out various computational type functions
that are performed by the discreet circuits and units
that have been described. This may, in fact, be an
~Z~42~
lug
economically attractive alternative to using such
items as the adders, counters and flip-flops, which
simply provide a convenient, comparatively low cost
way to perform certain functions that could be done in
a computer, for example, one using a microprocessor.
Other modifications, variations and alterations
may be made to the embodiments of the invention that
have been described without departing from the true
scope and spirit of the invention as described in the
claims that follow.
