Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 CONTROLLED RELUCTANCE AC INDUCTION MOTOR
2 The invention relates generally to the field of
3 electric motors and specifically to an AC motor with
4 improved performance characteristics.
' PRIOR ART
6 Many types of electric motors are known to the
7 industry. Typically, these known motors have certain
desirable characteristics such as high starting torque,
9 variable speed and/or high power density. Often,
however, a motor with desirable characteristics for a
11 given application has certain disadvantages or
12 deficiencies. These undesirable characteristics often
13 include relatively high cost, electrical circuit
14 complexity, radio frequency or electromagnetic
interference; energy inefficiency, limited reliability
16 and/or comparatively short service life.
17 SUMMARY OF THE INVENTION
1~ The invention provides an AC power operated
19 electric motor that exhibits desirable torque/speed
characteristics when operated in an open loop condition
21 and is effectively speed and/or torque controlled with
22 relatively simple and economical electrical circuitry.
23 The motor has a stator with field windings that are
24 energized with alternating current and that, in one
embodiment, are arranged to induce an AC current in a
26 conductive loop on a rotor or armature. In various
27 configurations of the motor, the field windings
2~ comprise at least two coils angularly displaced from
29 one another around the rotor axis. The positions of
the windings in some configurations represent
31 physically or mechanically distinct phases.
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1 The AC stator field is caused to move about the
2 axis of the rotor and, in the aforementioned
3 embodiment,~the induced AC field in the conductive loop
4 produces a torque on the rotor causing it to rotate in
synchronization with the field rotation. The rotation
6 of the stator field is produced by switching or
7 appropriately modulating AC power to successive
8 angularly displaced field coils.
9 The motor can be arranged with 2, 4, 6 or even a
greater number of even poles and with as many field
11 winding phases as suitable for a particular
12 application. Motor torque, and therefore power, is
13 multiplied in proportion to the number of poles
14 provided in the motor. The motor has open loop
speed/torque characteristics approaching the desirable
16 ideal of constant horsepower. These characteristics
17 include high starting torque and high speed at low
18 load.
19 In another embodiment of the invention, the rotor
comprises a cylindrical body formed of magnetic
21 material such as a stack of magnetic silicon steel
22 laminations having a diametral air gap running the
23 axial length of the laminations. The reluctance of the
24 air gap causes the rotor to synchronize its rotation
with the rotation of the magnetic field produced by the
26 stator in a manner analogous to that described with the
27 first embodiment. The air gap rotor has the potential
28 of high operating efficiency since there are no
29 substantial I2R losses associated with currents induced
in the rotor. In still another embodiment, the
31 diametral air gap in the rotor can be filled with an
32 electrically conductive non-magnetic plate or body to
33 increase the torque developed in the rotor.
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1 Importantly, the motor lends itself to relatively
2 simple and energy efficient speed, control and/or torque
3 control. A standard speed control over a 10:1 ratio is
4 readily achieved. Rated torque can be achieved at zero
speed with proper circuitry and therefore the speed
6 r-ange can be from zero to the maximum rated speed.
7 Some of the additional advantages of the motor include
8 low stall current, operation on simple square wave
9 power.without difficulty with harmonics, anal increased
power and/or torque for a given physical size motor as
11 compared to conventional induction motors, fo.r example.
12 BRIEF DESCRIPTION OF THE DRAWINGS
13 FIG. 1 is a schematic perspective view of a motor
14 illustrating principles of the invention;
FIG. 2 is a generalized graph illustrating the
16 relationship of torque versus rotor deflection angle
I7 for motors onstructed in accordance with the
c
18 invention; '
I9 FIG. 3 is a schematic perspective view of a motor
constructed in accordance with the invention;
21 FIG. 4 is an electrical circuit diagram of a
22 controller or the motor of FIG. 3;
f
23 FIG. 5 is a generalized graph illustrating the
24 relationship of speed versus torque of a motor
constructed in accordance with the invention;
26 FIG. 6A is a diagram of square wave power
27 available om an inverter illustrated in FIG. 7;
fr
28 FIG. 6B is a diagram of a modified square wave
29 power signal produced by the Circuit of FIG. 7; '
FIG. 7 is a circuit diagram for controlling the
31 speed of the motor of FIG. 3;
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1 FIGS. 8A through
SD are diagrammatic
2 representations of signals developed in the circuit
of
3 FIG. 7;
4 FIG. 9 is a diagrammatic
illustration
of a system
for controlling the speed of a motor constructed in
6 accordance with the invention;
7 FIG. 10 is a schematic illustration of a motor
arranged for speed
control by the
control system
of
9 FIG. 9;
FIG. 11 is an alternative circuit for driving the
11 motor of FIG.
3;
12 FIG. 12 is a schematic representation of a motor
13 of the invention having field windings arranged in
14 qu.adrature;
FIG. 13 is a circuit for driving the motor of FIG.
16 12;
17 FIG. 14 is a schematic perspective view of a four
18 pole three-phase motor constructed in accordance with
19 the invention;
FIG. 15 is a diagrammatic illustration of the
21 field vectors one of the windings of the motor of
of
22 FIG. 14;
23 FIG. 16 is a diagrammatic representation of a
24 rotor for use the motor of the invention in
in
accordance with a second embodiment; and
26 FIG. l7 is a diagrammatic representation of a
27 rotor for use the motor of the invention in
in
2~ accordance with
a third embodiment.
29 DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, a motor 10 has a stator
31 11 with a field winding 12 and a rotor or armature 14
32 supported~by suitable bearing structure for rotation
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1 about an axis 16. The winding 12 is arranged in two
2 sections or portions 12a, 12b on diametrally opposite
3 sides of the rotor 14'. The rotor 14 has a conductive
4 loop 17 that has two diametrically opposite portions 18
5 near the periphery of the rotor that extend parallel to
6 the rotor axis 16 and two end portions 19. A main body
7 21 of the rotor 14 can be constructed of suitable
8 magnetic silicon steel laminations in a manner known in
9 the art. The two loop portions 18 that extend
10- longitudinally of the rotor lie in a common plane that
11 passes through the rotor axis 16. For purposes of this
12 disclosure, the plane of the conductive loop 17 is
13 taken as the plane of the conductor portions 18. The
14 conductive loop 17, which can be made of copper or
aluminum, for example, is electrically continuous; the
16 end portions 19 shunt the longitudinal portions 18.
17 The stator 11 has its fief. windings 12a, 12b wound
18 about suitable magnetic material such as a stack of
19 magnetic silicon steel laminations 22a and b.
When the field coil or winding 12 is energized
21 with an AC voltage, a magnetic.field is created with a
22 vector that is parallel to an axis 23 extending between
23 the windings 12a, b. With the field coil 12 thus
24 energized with an AC voltage, when the rotor 14 is
displaced from the. illustrated solid line position
26 through an angle ~r magnetic field conditions urge the
27 rotor 14 to return to the solid line position where the
28 plane of the conductive loop 17 is aligned with the
29 field axis~23. That is, the magnetic field conditions
urge the rotor 14 to the position where the angle tar is
31 0.
32 FIG. 2 is a generalized diagram of the
33 relationship betweeiz. torque and angular displacement ~r .
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1 The diagram shows that the torque tending to move the
2 rotor Z4 towards the position of alignment with the
3 axis 23 increases proportionately with the displacement
4 or angle fir. Torque reaches a maximum value at about
S 70°; at displacements beyond this, the torque
6 diminishes . At ~r equal to 90°, i . a . when the plane of
7 the conductive loop 17 is transverse to the direction
8 of the field vector of the winding 12, the torque
9 reduces to 0. This ~r = 90° position can be called a
hard neutral while the position at ~r equal to 0 can be
11 called a soft neutral.
12 When the plane of the conductive loop 17 is turned.
13 from alignment with the field vector of the stator 11,
14 i.e. tar not equal to 0, the AC magnetic field produced
by the winding 12 induces an AC current in the
16 conductive loop 17. This rotor current produces its
17 own magnetic field which opposes the stator field. The
18 opposing field produced by the conductive loop 17
19 increases the reluctance of the flux path of the stator
field. It can be shown that in an electromechanical
21 system, such as the motor 10 illustrated in FIG. 1,
22 physical laws,work to reduce the reluctance in the
23 system. Consequently, the motor 10 behaves as
24 discussed with the rotor 14 being urged to a position
2S where the plane of the conductive loop 17 is aligned
26 with the axes 23 and the reluctance of the motor system
27 being reduced.
28 The motor 10 of FIG. 1, as so far described, is
29 not practical as a general purpose rotating motor since
it cannot sustain continuous rotation of the rotor. '
31 However, the motor s characteristics, as described, are
32 helpful in understanding the operation of other motors,
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1 constructed in accordance with the invention, such as
2 those described hereinbelow.
3 FIG. 3 diagrammatically shows a motor 26 that
4 applies the foregoing principles in a two pole rotor
14, like that described with reference to FIG. 1, but
6 with a three phase stator 28. (The "two pole"
7 designation pertains to the rotor or armature and
8 derives from north and south magnetic poles produced by
9 the conductive loop 17 when the loop is in an AC
magnetic field.) The stator 28 typically includes a
11 body formed by a stack of laminations of suitable
12 magnetic silicon steel with internal axially oriented
13 slots 30 distributed about the periphery of the rotor
14 14 as is generally conventional in motor construction.
A winding A has turns wrapped axially around the rotor.
16 The turns include longitudinal or axially oriented
17 portions disposed,in the lamination slots 30 on
18 diametrically opposite sides of the rotor 14 and end
19 portions circumferentially looped around the axial
projection of the rotor in a manner known in the motor
21 art. The longitudinal portions of the turns of the.
22 winding A are~geometrically centered on a plane
23 represented at 31 that passes through the rotor axis
24 16. For clarity, only the winding A is illustrated. in
FIG. 3 and it will be understood that the other
26 windings B and C are similar in construction. The
27 planes o~ the windings A, B and C are oriented at 120°
28 relative to one another with reference to the axis 14
29 of rotation of the rotor 14 and pass through this axis
so that adjacent portions o~ the windings A, B and C
31 are centered at 60° intervals. The winding A, when
32 energized with AC power develops an AC magnetic ~ield
33 vector 32 in a plane 33 perpendicular to the plane 31
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1 of the winding A. The other windings B, C, similarly,
2 produce AC magnetic field vectors perpendicular to
3 'their respective planes. The windings A, B and C are
4 thus in a physical or mechanical phase relationship to
one another and are electrically isolated from one
6 another. By switching or modulating AC power
7 sequentially to the mechanically phased windings A, B
8 and C, the rotor 14 will be driven in rotation. As
9 explained hereinabove, the rotor 14 will tend to align
itself with the field vector of an energized winding
11 (or as discussed later the resultant field vector of
12 simultaneously energized field windings). When the
13 plane of the rotor conductive loop 17 approaches the.
14 vector of the field from one energized winding, that
winding is de-energized while the adjacent winding in
16 the direction of rotor rotation is energized. By
17 continuing this field switching process, the rotor 14
18 is caused to rotate continuously.
19 FIG. 4 illustrates an example of a circuit or
controller 36 suitable for driving the two pole, three
21 winding phase motor 26 of FIG. 3. The motor windings
22 are represented as A, B and C in the circuit of FIG. 4.
23 In the circuit, commercial power, e.g. 60 Hz, 110 volt,
24 single phase power is connected to lines 37, 38. This
power is converted to DC in a rectifier and voltage
26 doubler circuit comprising a pair of diodes 39, 41 and
27 capacitors 42, 43. Positive and negative voltages are
28 developed on respective lines or busses 46, 47.
29 Square wave AC power is supplied independently to
each winding A, B or C from paired power mosfet
32 switches 51, 52 associated with each winding. One of
32 the mosfet switches 51 supplies positive voltage while
33 the other 52 supplies negative voltage. thereby
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1 producing an AC power signal. The mosfet switches 51,
2 52 are driven by an associated integrated circuit 53
3 (such as an IR 2104). These drivers 53 are powered by
4 a suitable 12 volt DC source. Each driver 53
alternately operates the associated mosfets 51, 52 at a
6 frequency imposed by a frequency generator 54 (such as
7 an MCI 4046) signaling from its output (pin 4) to an
8 input (pin 2) of each driver 53. The frequency can be
9 any suitable frequency, preferably higher than
commercial power of 60 or 50 Hz. A typical frequency
11 can be between 100 to 250 Hz but can be higher if
12 design parameters require such and appropriate
13 materials are used.
14 A shaft encoder 56 (FIG. 3) of any suitable type
1.5 and preferably a non-contact type monitors the angular
16 position of the rotor 27 and, therefore, the plane of
17 the conductive loop 17. In the illustrated example of
18 ~ FIG. 3, the shaft encoder 56 senses when a 60° arc on a
19 drum rotating with the rotor 14 associated with each
winding A, B or C passes the reference point of a non-
21 rotating part 59 of the encoder fixed relative to the
22 stator 28. The drum 57 of the encoder 5-6 is divided
23 into three channels, each channel corresponding to one
24 of the field windings A, B or C. The encoder 56
signals the driver 53 of a particular field winding A,
26 B or C when an angular sector on the drum 57 associated
27 with that particular winding is in proximity to the
28 non-rotating part 59 of the~encoder. The encoder 56
29 maintains the signal to the appropriate driver 53 for a
time in which a field winding A,. B or C develops a
31 relatively large torque on the rotor. This period will
32 be, roughly when the plane of the conductive loop 17 is
33 between. 75 and 15° out of alignment with the magnetic
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I field vector of a particular winding (i.e. 75°_> ~r >_
2 15°) .
3 The time period or, more properly, the angular
4~ duration of energization of a particular field A, B or
5 C can be set by the geometry of the codes on the drum
6 57 of the encoder 56. The drum 57 may be encoded with
7 arcs of detectable material that have a dwell of 60°.
8 This geometry allows each winding, where there are
9 three windings, to be energized twice for each
10 revolution of the rotor 14. While a driver 53 is
11' enabled (i.e. turned on) from a channel of the encoder
12 56, the driver cycles the associated mosfet switches
13 51, 52 on and off at the frequency produced by the
14 frequency generator 54. The mosfet switches 51, 52
thereby apply a square wave AC power signal, at the
16 frequency of the generator 54, to the associated field
17 winding A, B or C. With the circuit of FIG. 4 when one
18 of the windings A, B or C is energized the other two
19 windings are inactive.
The motor 26 of FIG. 3, driven by the open loop
21 circuit 36 of FIG. 4 has a desirable speed torque curve
22 schematically illustrated in FIG. 5. It will be seen
23 that the motor 26 approaches a constant horsepower
24 device. Additionally, the motor 26 is characterized by
relatively high starting torque and is capable of
26 relatively high speed operation. A motor operating
27 with the principles of the motor 26 discussed in
28 connection with FIGS. 3 and 4 can be constructed with
29 more field windings or field phases. The windings,
typically, can be evenly spaced around the stator and
31 suitable corresponding additional driver circuits and a
32 modified shaft encoder can be employed. Such a motor
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1 has the advantage of less torque ripple than that of
2 the illustrated three phase motor 26.
3 ~ The speed of the motor 26 and like motors can be
4 controlled by either controlling the power delivered to
.the motor or by controlling the position of the shaft
6 encoder signals relative to the stator. Each method
7 can have many variations. Controlling the power to the
8 motor may be implemented very simply, but such control
9 may not necessarily produce the best efficiency over a
wide speed range. Controlling the relative positions
11 of the encoder signals may produce better efficiency,
12 but may be more complex in circuit implementation for
13 certain applications. In some applications, a
14 combination of both methods may be useful.
One way of controlling power for speed control is
16 to control the width of each i~ cycle of a voltage
17 square wave delivered to the motor. Full power of the
18 square wave is applied when each half cycle occupies
19 the total time of one half period as depicted in FIG.
6A. If the beginning of each half cycle is delayed by
21 some fraction of the half period, as depicted in FIG.
22 6B, then the total amount of power delivered to the
23 motor is reduced. The motor is not sensitive to
24 waveform (does not need sine waves) so that only the
total energy per half cycle is significant. There are
26 many ways to implement this kind of control; a simple
27 version is shown in FIG. 7. This circuit is used in
28 conjunction with the circuit of FIG. 4. The frequency
29 generator 54 is redrawn here. As will be understood
from the following discussion, the circuit of FIG. 7 is
31 interposed in the lines from the encoder 56 to the
32 drives,53 for the field windings A, B and C. The
33 frequency signal output of the frequency generator 54
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I is 'fed into pin 2 of IC 12 which is a four stage binary
2 counter. Each stage divides the frequency by 2. At
3 pin 6 of IC 12 (the output of the 4th stage), the
4 frequency is 1/16 of the input at pin 2. The output
frequency at pin 6 is fed into the driver stages 53 (at
6 pin 2) of each power mosfet switch 51, 52 (FIG. 4) that
7 delivers power to a particular stator winding phase or
8 coil A, B or C. In this arrangement, the freq-U.ency
9 generator 54 is typically set,to.a frequency that is 16
times greater than what is used in the original circuit
11 in FTG. 4.' The binary outputs from the other three
12 stages are connected to a summing resistor network 61
13 at the input of an operational amplifier~designated as
I4 IC 13 at pin 2. The output signal at pin 1 of IC 13
will appear as a sawtooth waveform and will be related
I6 to the square wave output on pin 6 of TC 12 as shown in
17 FIGS. 8A and 8B, respectively.
18 A speed command signal and a speed feedback signal
19 (e. g. derived from the shaft encoder) are summed
algebraically at pin 9 of IC 13 and the difference
21 (speed error signal) is produced at pin 8 of IC 13. At
22 pin.rl4 of IC 13 the polarity inversion of the error
is
23 signal. The error signal is then compared with the
24 sawtooth waveform by the comparator circuit composed
of
pins 6, 5 and 7 of IC 13. With reference to FIG. SC,
26 when the magnitude of the error signal is below the
27 sawtooth level, th e output of pin 7 is 0; when the
28 magnitude of the rror signal is above the sawtooth
e
29 level, the output of pin 7 is positive (a logic 1").
This output signal modulates the encoder signals that
31 feed into the power mosfet drivers 53. In essence, the
32 signal controls the turn on of each driver 53 at its
33 pin 3. This is accomplished by dual input "and" gates
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l shown as IC 14 (MC 14081B). Signals from the encoder
2 56 feed into one gate input and the signal from pin 7
3 of IC 13 feeds into the second gate input. The output
4 of each gate IC 14 then feeds into the pin 3 of a
respective driver 53. The result is a power signal
6 applied to the motor field windings A, B or C as shown
7 in FIG. 6D. As the speed error signal varies in
8 magnitude, the width of each half cycle will vary in
9 accordance. Where the power is supplied as a sine
wave, such as from commercial power, a speed control
11 circuit can be arranged to eliminate the beginning of
12 each half cycle, typically in the manner an SCR is
13 regularly used in like. service.
14 The second method that can be used for speed
control is to shift the encoder signals to different
16 phase or winding drivers in accordance to the magnitude
17 of the speed error signal. FIG. 9 illustrates
18 circuitry to accomplish this. The select signal is
19 derived from the speed control error signal.
A motor 62 schematically shown in FIG. 10 has
21 eight field windings (a - h) and, accordingly, eight
22 driver circuits (corresponding to elements 53, 51 and
23 52 in FIG. 4). The field windings a - h are like the
24 windings A, B and C in FIG. 3, If a shaft position.
encoder or sensor 63 has its signals directed to turn
26 on the field coils which produce the maximum torque,
27 then the motor speed will increase to the point where
28 the load torque is equal to the produced or developed
29 motor torque. To reduce the torque and lower the
speed, it is necessary to direct the signals of the
31 position encoder 63 to different field coils. Speed
32 control can thus be obtained by switching the encoder,
33 signals to different coils, in response to the speed
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1 control error signal. The plane of the armature
2 conductive loop 17 is shown in relationship to the
3 field coil position labeled a - h. If coil a is
4 energized, maximum torque is generated in the counter-
s clockwise direction. A magnetic field vector 64 of
6 winding a is perpendicular to the plane of winding a.
7 If field coil b were energized, a lesser torque would
8 be created, and if field coil c were energized, an even
9 lesser torque would be developed. By shifting the
encoder connection to energize different coils, the
1I torque is controlled. By using the speed error signal
12 to~determine the switching, the motor speed can be
13 regulated. The speed error signal magnitude is
I4 compared to fixed signal voltage levels that are
stepped by fixed increments. When the speed error
16 exceeds each fixed level, a new connection arrangement
17 is made.between the encoder and the field coils. For
I8 example,~with eight field coils, suppose that at the
19 maximum level, encoder output A controls coil a and
encoder B controls coil b, etc. Then, when the error
21 signal drops to the next level, a logic switching
22 action, takes place in a multiplex gate 63 (FTG. 9) to
23 connect encoder output A to coil b, and encoder output
24 B to coil c, encoder C to coil d, etc. Then, when the
error signal drops to the next level down (third
26 level), the logic switching action connects encoder
27 output A to coil c, and encoder output B to coil d,
28 encoder output C to coil e, etc. Thus, the control
29 acts to shift the position of the encoder signals in
- proportion to the magnitude of the error signal. This
31 action will then increase or decrease torque and,
32 accordingly, increase or decrease speed.
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1 FTG. 11 shows an alternative controller or circuit
2 70, of simplified design, for operating the motor 26..
3 Single phase alternating current power such as 110 volt
4 60 Hz commercial power is supplied to the windings A, B
5 and C through corresponding triacs 71 or other
6 electrically controllable switches. A frequency
7 generator 73, (MCI 4046) produces a series of pulses
8 having a frequency~that is proportional to the voltage
9 set by a potentiometer 72. The pulses~are input to a
10 counter 74 such as a CMOS 4017. The three outputs of
11 the counter 74 are applied to sequentially fire the
12 , triacs 71 through a buffer 76 such as a CMOS 4049
13 inverting buffer that feeds the opto isolator trigger
14 to each triac. The counter 74 assures that the
15 windings or phases A, B and C are triggered
16 sequentially at a rate corresponding to the frequency
17 set by the voltage at the potentiometer 72. The motor
I8 26, when operated by the circuit of FIG. 11, will run
19 at a speed synchronous with the rate that the field
windings A, B and C are triggered. The circuit 70 with
21 the adjustable potentiometer 72 and variable frequency
22 of the generator 73 thus provides a simple method of
23 speed control for the motor 26.. As this circuit 70 of
24 FIG. 11 suggests, the motor 26 and others constructed
like it in accordance with the invention can be
26 operated directly off a commercial single phase power
27 supply such as, for example, 120 volt 60Hz-power where
28 high speed operation is not required. Conversely, this
29 motor 26 and the circuit 70 can be supplied with a
higher frequency power supply where it is desired to
31 operate the motor at higher speeds. Innumerable other
32 control systems and circuits are suitable for operating
33 a motor constructed in accordance with the invention as
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1 will be apparent from an understanding of the present
2 disclosure. .
3 A flux vector drive is also contemplated for the
4 motor of the invention. Referring to FIG. 12, a simple
field winding configuration for a two winding two pole
6 motor 80 is shown. Stator field or phase windings X, Y
7 are physically located in quadrature and labeled X and
8 Y to correspond with x and y axes. The windings X, Y
9 create magnetic flux vectors along the corresponding x
and y axes. Currents flowing through both sets of
11 windings X and Y create a magnetic field flux vector 81
12 which is the vector sum of the individual magnetic flux
13 vectors created by the currents in the separate
I4 windings X, Y. A vector angle O of the vector varies
with respect to the X axis depending on respective
16 magnitudes of the currents in windings X, Y.
17 The magnitudes of the AC currents in the windings
18 X, Y are
19 IX=cos0 sin2nf~t; and
IY=sin0 sin2nf~t;
21 where f~ is the frequency of the current supplied, such
22 as 60 Ha. The field flux vector 81 represents an
23 alternating magnetic field with the frequency f~. The
24 field flux vector 81 can be positioned at any angle O
by varying the currents in the field windings X, Y
26 according to the following relationship:
2~
_ r
. e=sin
. 1 ~ 'IX ~~Y
28
29 ~ . _. _.
The motor 80 has a rotor 14 like.that described in
31 connection with FIG. 1; the plane of the conductive
32 loop 17 is displaced from the'X axis by a rotor angle
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1 ~. The rotor 14 rotates synchronously at the speed
2 that the field vector 81 is rotated. As discussed
3 below, the.field windings can be supplied with
4 modulated AC currents from power amplifiers operated by
a signal processor to appropriately rotate the magnetic
6 field vector 81. -
7 By creating and controlling a difference between
8 the field flux vector angle O and the rotor angle ~,
9 the torque output of the motor 80 can be controlled.
That is, the torque is controlled by controlling the
11 relative positions of the field flux vector and the
12 plane of the conductive loop 17 on the rotor 14. As
13 discussed previously with reference to FIG. 2, torque
14 is developed when the rotor or armature 14 is located
where there is an angular deflection ~r between the
16 plane of the conductive loop 17 and the flux vector
17 between the winding portions 12a, b; this torque varies
18 with the magnitude of the angle fir. Similarly, in FIG.
19 12, the torque varies with the difference between the
flux vector angle O and-the rotor angle ~. Note the
21 relationship ~r = O - ~ . -
22 As previously discussed, the vector angle 0 is~
23 varied by varying the current amplitudes in the field
24 windings X, Y. Since the currents are AC, the field
currents will be suppressed carrier amplitude modulated
26 sine waves that can be represented as:
27 IX=cos (c~Rt~~r) sin2nf~t ; and
28 IY=sin (c~Rt~~r) sin2nf~t ;
29 where c~R is the rotational speed of the rotor 14. The
angular deflection ~r with respect to the field flux
31 vector is.determined by the respective field currents
32 Ix, IY and the angular velocity c~R,
33
~~r=s in-1
- ~-
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1
2
3 Referencing FIG. 2, the deflection angle 1[r is
4 varied to achieve the desired torque characteristics by
varying the currents IX, IY. The rotor position ~ is
6 sensed, for example, by a transducer or electrical
7 parameters. Rotor position information is used to
8 control the flux vector position O to maintain the
9 desired deflection ~r and, therefore, the motor torque.
A flux vector control circuit 85 that applies the
'l1 foregoing principles and relationships of field
12 current, field vector and rotor angle for torque
13 control is shown in FTG. 13. The control 85 includes a
14 signal processor 86 with two outputs for generating the
currents IX, Ix. The currents are fed through
16 respective power amplifiers 87 to the field windings X,
17 Y. Frequency F~ is set by a suitable frequency input.
18 A rotor position sensor 89, such as a numerical shaft
19 position sensor, provides rotor position information
data to the signal processor 86. A torque command
21 input, corresponding to a deflection angle ~r is
22 provided to the signal processor to control torque.
23 The signal processor 86 in accordance with the
24 foregoing formulas generates the currents TX, IYas
functions of the frequency F~, rotor position cp (which
26 indicates rotor speed wR), and torque command
27 deflection angle ~r to control the torque
28 characteristics of the motor 80. The speed of the
29 motor is controlled according to the rate c~ at which
the carrier signal is modulated, which can be selected
31 by a speed input. The rotor position sensor can be
32 connected to provide speed or position feedback,
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1 diagrammatically represented at 88, through a torque
2 control 84 to control the torque command angle setting
3 ~r .
4 A motor constructed in accordance with the
invention can be made with four poles as schematically
6 shown in FIG. 14. The motor 90 can develop twice the
7 torque of a similarly sized two pole motor such as the
8 motor 26 in FIG. 3. The illustrated motor 90 has three
9 field winding phases designated Phase A, Phase B and
Phase C. Each Phase A, B and C has f our coils 91,.92,
11 93, and 94. Each of these coils has a pair of spaced
12 axially extending portions 96 and a pair. of end turn
13 portions 97, one at each end of a stator typically of
14 suitable laminations represented by the circular line
98. The coils 91, 92, 93 and 94 are connected in
16 series with alternate coils wound in a clockwise
17 direction and intervening coils wound in counter-
18 clockwise direction. Alternatively, the coils 91 - 94
19 Can be connected i:n parallel. For clarity, the coils
91 - 94 of only one phase (A) is shown, it being
21 understood that the other phases B and C are identical.
22 A rotor 99 of the motor 90 has four conductive wires or
23 rods 100 equally spaced around the circumference of the
24 rotor 99 and extending longitudinally of the rotor.
The conductors 100 are interconnected or shunted by end
26 wires or conductors 101 at each end of each conductor
27 100. The longitudinal conductors 100, like the
28 conductors 17 of the rotor 14 of FIG. 3, are parallel
29 with the axis of rotation of the rotor 99 on a shaft
95. The rotor 99 and stator 98 typically include
31 bodies formed of silicon steel laminations as
32 previously described. The windings of Phases A, B and
33 C can be energized by a circuit like that shown in
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1 FIGS. 4 or 11.. Motors having a greater even number of
2 poles such as 6, 8 or more, can be constructed
3 similarly to the four pole motor of_FIG. 14 and such
4 motors will have a proportionately higher torque
S capacity. .
6 As will be understood from the foregoing
7 disclosure, the motor of the invention can take various
8 forms and can be powered by innumerable electrical
9 circuit arrangements, both open and closed loop. .
10 Switches for the field windings can include triacs,
11 transistors, silicon controlled rectifiers (SCR's) and
12 magnetic amplifiers, for example. The rotor, rather
13 than having a conductive loop to present a variable
24 reluctance to the stator field, can be formed with a
1S diametrically disposed air gap (FIG. 16) or a
16 conductive plate (FIG. 17) in the plane otherwise
17 occupied by the conductive rotor loop.
28 In the embodiment of FIG. 16, a rotor is
19 diagrammatically illustrated at 120. The rotor 120
20 includes a stack of laminations 121 of magnetic silicon
21 steel. The laminations 121 can be "D" shaped elements
22 arranged on opposite sides of a diametral air gap 122.
23 Non-magnetic end plates 123 with integral co-axial stub
24 shafts 124 are held in the illustrated assembled
2S configuration with tension rods 126 that are preferably
26 non-magnetic. Various other arrangements for
27 supporting the magnetic rotor halves or portions on~~the
28 shaft elements or their equivalent are envisioned.
29 This rotor with a suitable shaft encoder can be used in
the general types of stators illustrated in FIGS. 3, 10
31 and 12. The reluctance of the air gap 122 enables the
32 rotor to follow the rotation of the field of the
33 stator. A motor employing the rotor 122 has the
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1 potential of high efficiency since there is no
2 substantial I~R loss developed by induced currents in
3 the rotor.
4 FIG. 17 illustrates an embodiment of a rotor 130
similar to that of FIG. 16 (using identical reference
6 numerals for like parts) except that the air gap is
7 filled with an electrically conductive plate or body
8 131. As before, a suitable shaft encoder can be
9 employed. The motor can be used with the stators of
FIGS. 3, 10 and 12. The rotor 130 has the potential of
11 producing a relatively high torque because of the high
12 magnetomotive .force that induced currents in the plate
13 131 can produce.
14 The rotor can be disposed around, rather than in,
the stator. The conductive loop or loops on the rotor
16 can be skewed in a helical or like sense to reduce
17 torque ripple. The number of field windings and
18 related electronic switches, also, can be increased to
19 decrease torque ripple. Some of the turns of a
particular winding can share the same stator lamination
21, slot or angular position as some of the winding turns
22 of an adj.,acent winding .
23 The motor can be supplied with a shaft encoder and
24 appropriate circuitry for operation as a stepping motor
and is especially suitable for large size stepping
26 motors. A desired angular resolution for a stepping
27 motor application can be achieved by providing a
2,8' suitable number of field windings. As previously
29 discussed herein, the rotor will seek to align the
plane of the conductive loop, or equivalent structure,
31 to the magnetic field vector. of a particular winding
32 that is energized. The motor is reversible simply by
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1 reversing the sequence that the field. windings are
2 energized by the related circuitry.
3 A circuit powering the field windings. of the motor
4 can energize more than one field winding at a time to
reduce torque ripple and/or the circuit can be arranged
6 to modulate power to the windings rather than simply
7 turning them on and off. Field windings on the stator
can have various configurations besides those
9 illustrated in FIGS. 1, 3 and 14, it being important
~10, that the winding arrangement be capable of producing an
11 AC magnetic field in the space of the rotor that moves
12 around the axis of the rotor.
13 While the invention has been shown and described
14 with respect to particular embodiments thereof, this is
for the purpose of illustration rather than limitation,
16 and other variations and modifications of the specific
17 embodiments herein shown and described will be apparent
18 to those skilled in the art all within the intended
19 spirit and scope of the invention. Accordingly, the
patent is not to be limited in scope and effect to the
-21 specific embodiments herein shown and described nor in
22 any other way that is inconsistent with the extent to
23 which the progress in the art has been advanced by the
24 invention.
