Note: Descriptions are shown in the official language in which they were submitted.
3D-LO-4835
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The present invention relates generally to dynamo-
electric machines and more particularly to control circuitry
for such machines for energizing those machines from a direct
current or rectified alternatiny current source.
Conventional direct current dynamoelectric machines
employ brushes and segmented commutators for supplying
current to rotor windings and have historically been plague~ ,
by arcing and wear problems associated wi-th those brushes and
commutators. More recently, motors for example, as disclosed
in U. S. Patent No. 4,005,347 dated January 25, 1977, have
been devised for direct current energization employing
permanent magnet rotors without brushes or segmented com-
mutators and their attendant problems. Typically, such
brushless direct current motors may employ optical or magnetic
sensing arrangements to determine the rotor position and
therefore also the control required for energizing their
stator supported armature windings. Additional motor
leads are typically required for such position sensors and
the added cost in providing such position sensors is not
insignificant. The afore-mentioned contemporaneously U.S.
patent No. 4,005,347 dated January 25, 1977 provides inter
alia at least one scheme for eliminating such position
sensors by deriving a signal indicative of rotor speed
from a determination of the current drawn through the
, stator windings, e.g., total line current.
i' Among the several objects of the present invention may
be noted the provision of an improved commutation circuit
~ for a brushless direct current motor; the provision of
-, method and apparatus for dispensing with mechanical rotor
position sensing devices while still providing commutating
signals to a brushless direct current motor; the provision
of a scheme for detecting the rest position of a permanent
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magnet rotor of a direct current motor having armature windings
on the stator -thereof; the provision of a circuit for de-
termining rotor position of a brushless direct current motor
rotor and providing commutated enabling signals to the
armature of that motor without directly sensing the relative
angular position of the rotor; the provision o~ commutation
circuitry for a brushless direct current motor which cir-
cuitry senses wave forms which reflect rotor positlon re-
lative to motor enabling signals; and the provision of a
circuit for producing an approximation to a sinusoidal
wave form for energizing an induction motor rather than a
direct current motor.
In general and in one form of the invention, commutating
signals for a brushless direct current motor are achieved
by energizing at least one armature winding and sampling
the voltage induced across an unenergized winding whereafter
that voltage sample is integrated and compared to a re
ference voltage and when the integral exceeds the reference ?~
voltage, another winding is energized and the integral
returned to its initial value. A counter may be employed -
to identify a particular currently energized winding and
that counter may further be used for sampling, for example,
the voltage across the next winding in the sequence to be
energized.
Also in general the rest position of the permanent
magnet rotor of a direct current motor may be detected by
applying a voltage pulse to one of the stator supported `
armature windings and sensing the voltage induced by that
voltage pulse and any associated rotor motion in another
stator supported armaturr winding of that motor. A second
similar pulse may be applied to a different winding and the
induced voltage sim larly sensed to resolve any ambiguities
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or lack of indication resulting from the first sensing pulse.
Still further and also in general an induction motor
can be energized with an inverted wave form of lowered third
and fifth harmonic content as compared to a more typical
winding energizing wave form produced by known types of
inverters.
The forgoing as well as numerous other objects, features
and advantages of the present invention will become more
readily apparent from the following detailed description
taken in conjunction with the accompanying drawings in
which:
Fig. 1 is an exploded, perspective view of the main
elements of a brushless direc-t current motor;
Fig. 2 is a schematic diagram of circuitry for se-
quentially enabling the stator supported armature windings
of a brushless direct current motor of the type illustrated
in Fig. l;
Fig. 3 is a schematic diagram of a wave form responsive
circuit embodying features of my invention in one form
thereof, and which may be substituted for the conventional
position sensOrs to supply A and B signals to the circuit
of Fig. 2;
Fig. 4a is an idealized depiction of a single armature
coil in relation to the rotor flux field;
~ Fig. 4b illustrates current wave forms in the coil of
,, :
Fig. 4a for early, preferred, and late, commutation, re-
; spectively;
Fig. 5 depicts several voltage wave forms associated
with the circuit of FigO 3, illustrating proper (preferred)
and improper (not-preferred~ commutation timing;
Fig. 6 illustrates in schematic form a four-phase sensor-
less commutating circuit;
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Fig. 8 illustrates in schematic form a more sophisticated
and more efficient three-phase sensorless commutating circuit;
Fig. 9 is a schematic diagram of a circuit for in-
verting a DC voltage to produce a nearly approximate
sinusoidal wave form which can be used to energize an in-
duction motor;
Fig. 9a illustrates the winding current associated
with the commutating circuit of Fig. 9; and
Fig. 10 is a simplified end view of a permanent magnet
rotor and system for determining by a test pulse the position
of that rotor.
The exemplifications set out herein illustrate the
present invention in preferred forms thereof and such ex-
emplifications are not to be construed as limiting the scope
of the invention in any manner.
Referring to Fig. 1, there is illustrated the relevant
components of a brushless direct current motor of one type
suitable for the practice of the present invention. A
permanent magnet rotor 10 is mounted on a shaft 11 which
in turn is rotatably supported by conventional bearings in
a conventional housing, neither of which are illustrated in
Fig. 1. The rotor 10 is magnetized across its diameter and'
comprises a macJnetic steel core 12 and a pair of arcuate
magnets 13 and 14 dispose~on the periphery of the core in
diametrically opposed relationshlp. The stationary armature
assembly 15 includes a relatively low reluctance magnetic
member 16 which is formed of a plurality of like stator
laminations 17 assembled in juxtaposed relationship in the
manner conventional in alternating current dynamoelectric ';
machine construction. The windings 22 may be, as ill-
ustrated in Fig. 2, four separate windings 18, 19, 20 and 21
bifilarly wound in pairs to provide a distributed winding ~.
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four pole configuration.
In Fig. 2, position sensor signals are received at ter-
minals 23 and 25 which signals may for example, be optically
or magnetically derived according to the teachings of the
U.S. Patent No. 4,005,347 dated January 25, 1977, or those
signals may for example, be generated by the circuitry ill-
ustrated in Fig. 3 to be discussed subsequently. The A and
B signals at terminals 23 and 25 are inverted by NOR gates
27 and 29 and those two signals along with their complements
are supplied to a decoder 31 comprising four NOR gates, the
output of exactly one of which is high at any given time.
Transistors, such as 33, are enabled by the NOR gate high
; output and in turn conduction by the transistors, such as
33, enables a pair of transistors 35 and 37, connected
together in a modified Darlington configuration, to supply
the direct current voltage to a motor winding, such as 18.
As more fully discussed in the afore-mentioned U.S. Pat.,
No. 4,005,347 dated January 25, 1977, diodes, such as 39,
bleed the trapped inductive energy from the motor winding
when it is disabled to be either returned to the source
or stored, for example, on a capacitor such as 41. The
operation of Figs. 1 and 2 is more completely described in
the afore-mentioned U.S. Patent No. 4,005,347 dated January
25, 1977 wherein the signals to terminals 23 and 25 are
erived from position sensors, however, those sensors may be
eliminated by following the teachings of the present in-
vention, one form of which is illustrated, for example, in
~ig. 3.
Sensor substitute signals are provided as the outputs
of NAND gates 43 and 45 and the two-phase orthogonally
positioned motor windings provide voltage input signals to
terminals 47 and 49. A shift register 51 which is connected
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as a ~our bit ring counter identifies which of the four windings
18, l9, 20 or 21 is the currently energized winding and the
volta~e induced in a winding not currently energized is sampled
by enabling one of the two switches 53 and 55. Fre~uently the
winding which is sample is the winding next in sequence to be
energized. The induced ~oltage sample is integrated by an
integrator 57 and compared to a predetermined reference
; voltage 59 in the comparator 61. When the level of the integral
exceeds the reference voltage thereb~ indicating the rotor has
reached a predetermined position, the comparator output goes
high and a differentiating circuit 63, which constitutes a
means responsive to the comparator ou~put, increments the
shift register 51 to its ne~t indication. Any change in the
high bit position of the shift register 51 is sensed by
- NAND gates 65 and 67 which by way of inverters 69 and 71
and a further NAND gate 73 triggers the one-shot timer
75 to reset the integrator 57 to its initial condi.-tion - ,
for the next integrating cycle. An initial condition
interval is also established by the one-shot timer 75 which
interval is not only sufficiently long to reset the
integrator 57 but further eliminates switching transients
from the calculation and insures that the induced voltage
due to a collapsing magnetic field from a winding being
disable is not included in the computation. Only two voltage
sensing terminals 47 and 49 are employed and the voltage `
across only two of the four windings illustrated in Fig.
2 is sensed. To insure that the same sense or polarity
of winding voltage is sensed each time, an inverter 77
along with alternately enabled switches 79 and 81 are provided.
These last mentioned switches are alternately enabled by
the output of ~AND gate 43 and inverter 83. It should be
noted that a change inrotor speed changes the time of
integration but has no effect on the overall result and
accordingly the integrator output is representative of rotor
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position or total flux change rather than rotor speed or the
flux rate of change.
Wave forms associated with the circuit of Fig. 3 are
illustrated in Fig. 5 with the short ini-tial condition
(IC) pulse 85 being the initial condition signal to the in-
tegrator as supplied by way of inverter 87. The output of
integrator 57 is illustrated for a proper preferred "brush
position" in the second wave form whereas switching too
late and switching too early respectively lead to the third
and fourth integrator wave forms as illustrated. Considering
the "too late" wave form, it will be noted that the in-
tegrator output will achieve its reference voltage value
sooner in time than for the optimuM situation in which case,
of course, shift register 51 is incremented earlier, com-
pensating for the 'Itoo late" situation. Bias input 89 to
the integrator 57 is provided to sequence the swit~hing
when no counter emf is present on terminal 47 or 49, i.e.,
when the motor is at standstill. This bias 89 functions to
make the circuit act as though the motor were running at a
slow speed in the desired direction and materially aids
the starting of the motor. It should also be noted that
rather than creating the A and B signals as were employed
in sensor type brushless motors, the outputs from shift
register 51 could be employed directly for enabling winding
energizing circuitry, such as the Darlington pair 35, 37
and the input transistor 33 for each winding as illustrated
in Figure 2, thereby eliminating the need for the decoder
31.
While the wave forms of Fig. 5 represented the integral
of the voltage across a winding not at the time energized,
but for example next in the sequence to be energized, the
~ave forms in Fig. 4b represent the current flow through an
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~08Z3~2 3D--LO--4 8 3 5
energized winding with the upper wave form thereof illustrating
a heavy }oad or earl~ commutation situation while the lowermost
wave form illustrates a light load or late commutation situation
with the intermediate wave form being the optimum "brush
position" or commutation time wave form. The proper commutation
time wave form corresponds to the relative positioning of an
exemplary coil 91 and the rotor flux pattern 93 which is relatively
uniform throughout its duration as illustrated in Fig. 4a. If
: the coil of Fig. 4a were located to the right of the position :~
shown in Fig. 4a, the situation of a heavy rotor load or early
energization of the coil 91, a peak in current would develop
on the front edge of the conduction interval as illustrated in
the upper wave form of Fig. 4b and would correspond to the
integrator output illustrated in the lowermost wave form oE
Fig. 5.
As noted earlier, the ring counter, which as input
signals are counted, has one specified "1" state which moves ~
. in an ordered sequence about a loop, may be used directly for ~. .
energizing winding enabling circuitry and this is done in the
: ~0 circuit of Fig. 6 which illustrates a four phase or four winding : ~.
motor where ~hose windings are energiæed in a sequence four, .. ~
. three, two, one, four, three, etc. The ring counter 95 directly ~:
provides those winding enabling signals identified as (1), (2~
(3) and (4) and also those signals are coupled to switches 97,
99, 101, which constitute~a sampling means, and 103 in a
'! sequence (2), (3), (4), (1) such that the next to be enabled :
winding voltage is sensed during a sampling interval established ~.
by the appropriately enabled switch. For example switch 101
couples winding numher 3 to amplifier 105 when the
fourth stage of ring counter 95 is providing the output signal .
(4). These sensed winding voltages are amplified by an amplifier :
`~ 105 and pass through a half wave rectifier 107 which is included
, :,
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to prevent integrator saturation during possible large
negative values of the integral. Those half were rectified
signals then pass through integrator 109, amplifier 111 and arc
compared in a comparator 113 to a reference voltage 115 and,
when the integral exceeds the level of the reference voltage,
one-shot timer 117, which constitutes a means reponsive to the
comparator output functions by way of inverter 119 to reset the
integrator and, by way of differentiating circuit 121, to
incxement the ring counter 95.
Fig. 7 illustrates the application of these same
principles to a three-phase (grounded neutral) circuit with
corresponding parenthetical numbers indicating outpu-ts from
ring counter 137 and enabling inputs to sensing switches
such as 142 and winding enabling or power switches such
as 140. As illustrated in Fig. 7, amplifier 123, half
wave rectifier 125, integrator 127, comparator 129,
comparator bias 131 and integrator bias 132 for motor
starting purposes, one-shot timer 133, differentiating
circuit 135 and ring counter 137 perform substantially as
described previously in discussing Figs. 3 and 6. With
three windings only three power switches such as 140 are
; required and no logic circuitry is necessary to control
those windings, however, each phase is filtered by resistors,
such as 139, and capacitors, such as 141, which for example
have a o l millisecond time constant and function to reduce
the transients present during the switching interval. In
the circuit of Fig. 7, each winding is energized about one-
third of the time, and in the circuit of Fig. 6, each winding ~
is energized about one-fourth of the time, however, more ~ ;
sophisticated circuitry, such as illustrated in Fig. 8, may
be employed to energize each winding of a three phase motor
arrangement two-thirds of the time. A system such as illus-
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~0~323(~2
trated in Fig. 8 has the advantage that each winding in the
motor is used or energized two--thirds of the time, thus pro-
viding a motor of more efficiency for a given size as compared
to the system of Figure 7.
In the system of Fig. 8, six power switches or trans-
istors such as 143, 145 and 147 are used since with no
grounding of the neutral connection, the Y connected three
windings will have two of those windings carrying current
at any given time. Thus, for example, when current is
flowing into the alpha winding and out of the beta winding,
transistors 143 and 147 will be simultaneously energi~ed.
The circuit of Fig. 8 again employs a ring counter 149,
this time of six stages, which is incremented by a dif-
ferentiating circuit 151. The alpha, beta and gamma windings ~ ~
are sequentially sampled (the winding not then carrying -
current) by sequential enablement of switches such as 153
.
which sampled voltage is amplified by amplifier 155 and
since as in the case of the Fig. 3 circuit, two polarities
of sensed voltage may be encountered, this sensed voltage
is passed by one of the switches 157 or 159, optionally
by way of inverter 161 to a further amplifier 163. ~m-
plifier 163 may function like the previously discussed
half wave rectifier and provides an output signal to
integrating circuit 165 which has a bias or starting voltage
applied thereto at 167 and that integrator output is
supplied by way of amplifier 169 to the comparator 171
which, when the integrating circuit voltage exceeds the
reference voltage supplied by source 173, causes one-shot
timer 175 to reset the integrator 165 and also the ring
counter by way of differentiating circuit 151. Noting
that an asterisk before a winding indentifying symbol
indicates current flow through that same winding in an
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Z3~Z
opposite direction to the un-asterisked indication, the six
bit positions of the ring counter are coupled inverted in
the manner indicated to the inputs of the several NAND gates
such as 177 and those N~ND gate outputs 1, 2, 3, ~, 5 and 6
enable correspondingly identified -transistors such as 143.
The outputs of NAND gates such as 177 are also coupled to
the correspondingly numbered inputs of NAND gates such as
179, the outputs of which are decoded and, for example
NAND gate 181 controls switch 159, whereas NAND gate 183
controls switch 153. The other similarly positioned NAND
gates control correspondingly identified switches. Thus,
in the circuits of Fig. 8, higher utilization of the wind-
ings is achieved at the cost of additional logic circuitry.
An electronically commutated motor operating without ``
position sensors functions much like an induction motor and
induction motors function more efficiently with an applied
sinusoidal voltage wave form. An approximation to such a
sinusoidal wave form employing direct current switching
circuitry of the type so far discussed is illustrated in
~ig. 9a. To obtain the wave form of Fig. 9a, the energy
content of which is somewhat sinusoidal, the illustrated ~ ;
360 time priod is divided into eight subintervals of 45
each. During the first subinterval, no current is supplied
to a winding. During the second subinterval, current is
supplied to a winding. However, that current is periodi-
cally interrupted by a chopper 185 of Fig. 9, which has
a free running repetition rate several times that of the
repetition rate of the one 360 illustrated cycle. During
~- the third of the eight subintervals, the chopper is in-
effective and current flows to the windings during the
entire portion of this subinterval. The remaining 225 are
subdivided into five intervals which are respectively chopped,
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2302
full off, chopped but in the negative sense, full on in
the negative sense, and chopped in -the negative sense re-
spectively. The wave form illustrated in Fig. 9a has the
third and fifth harmonic content of the corresponding rec- ~
tangular wave form suppressed and energywise approximate ~ -
a sinusoidal wave form and the principles thereof may be
implemented in any of the foregoing sensorless control
circuits with one commutating circuit employing this
feature being illustrated in Fig. 9.
In Fig. 9, the chopper 185 behaves much like a free
running multivibrator and employs a pair of NAND gates
187 and 189 with a resistance-capacitance feedback network
having a time constant to give the chopper 135 a repetition
rate, for example, around 32 times the repetition rate of
the Fig. 9a wave form. This chopper signal is combined
with A, B and C signals in NAND gates such as with those
A, B and C signals functioning to subdivide the interval
of the illustrated wave form into its eight subintervals
; and to hold the winding current full off during the
appropriate subintervals. NAND gates, such as 193, enable
when on, for example, power switching transistors for the
respective windings, as previously illustrated. The A,B .`
and C signals are derived from a pair of concatenated
or series connected operational amplifiers 195 and 197,
which in turn drive a two stage counter 199 which may,
for example, be a CD4013AE. The input to the counter which
comprises the output of amplifier 197 also provides directly
the C signal and by way of inverter or NAND gate 201 provides
a not C signal. The output from amplifier 197 also enables '
. 30 a transistor 203 to charge and discharge capacitor 205 and
cycle the output of amplifier 195, driving amplifier 197
alternately to its high and low states.
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Representative component values or element identifi-
cation for the circuits of Figures 2 and 9:
Ref. No. Component
215 15V. zenerdiode
41 100 ufd
217 39 ohm 2W
223 10 K ohms
225 150 ohm
2N5988 Heat sink mounted ~ .
37 2N6258 Heat sink mounted
31 CD4001 AE
33 2N4401
39 A15
221 2000 ufd 300V.
195, 197 LM324
205 .01 ufd
231 lOOK ohm
233 10 K ohm ~:
235 100 K ohm - '
: 219,239 22K ohm :
241 lOK ohm
199 CD4013 AE :
243 220 pf
251 10 meg. ohms
The NAND gates in Figures 9 are of a C MOS variety and
~ include 4 type 4012 and 3 type 4011.
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In Fig. 10, there is illustrated in cross section, the
magnet rotor 10 of Fig. 1 having a permanent magnet north
pole 13 and a permanent magnet south pole 14. A voltage
pulse is applied to one armature winding 205 by briefly
closing switch 207 to couple the battery 209 or other
voltage source thereto. With the rotor in the position
illustrated and assuming winding 205 creates a north pole
in its vicinity~ the rotor will move a short distance ~ `
in the counterclockwise direction changing the flux in
winding due to the north pole created by magnet 13 moving
in its vicinity and inducing a voltage in that winding
211 which may be sensed, for example, by galvanometer 213.
Any pair of motor windings could be selected for test pulse `
~ application and induced voltage sensing and the polarity
i of that induced voltage will give an indication of rotor
. :~
position. In some cases, the results of the test pulse ~-
method may be ambiguous, for example, if the proper rotor
magnet is directly under the test pulse winding, no rotor
motion will occur. The proper selection of a different
winding and application of a second test pulse will re-
solve such ambiguities.
While the present invention has been described
with respect to the preferred embodiment, numerous modi-
fications will suggest themselves to those of ordinary
skill in the art and accordingly the scope of the present
invention is to be measured only by that of the appended
claims. ~ ~ `
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