GB2257312A - Ac motor control system - Google Patents
Ac motor control system Download PDFInfo
- Publication number
- GB2257312A GB2257312A GB9111326A GB9111326A GB2257312A GB 2257312 A GB2257312 A GB 2257312A GB 9111326 A GB9111326 A GB 9111326A GB 9111326 A GB9111326 A GB 9111326A GB 2257312 A GB2257312 A GB 2257312A
- Authority
- GB
- United Kingdom
- Prior art keywords
- phase
- motor
- motor shaft
- angular position
- thyristors
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M5/25—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M5/27—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means for conversion of frequency
- H02M5/271—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means for conversion of frequency from a three phase input voltage
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/08—Arrangements for controlling the speed or torque of a single motor
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/14—Electronic commutators
- H02P6/16—Circuit arrangements for detecting position
- H02P6/18—Circuit arrangements for detecting position without separate position detecting elements
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Ac Motors In General (AREA)
Abstract
The angular position of the shaft of a three-phase induction motor 11 is controlled by energising the induction motor from a cycloconverter 1 and suitably changing the polarity of the phase-sequence of the output 8, 9 and 10 of the cycloconverter so as to tend to reduce to zero with time an error signal 19 obtained from a comparison between a required angular shaft position 18 and the actual shaft position 13, via a position transducer 14, processing algorithm 16 and a microcomputer 15. The error signal is processed in an algorithm 21 to produce an actuating signal 22 which modulates at a frequency OMEGA the firing angles of the switch means 2, 3 and 4, such as thyristors or transistors, of the cycloconverter 1 via a firing unit 23 and changes the polarity of the phase-sequence of the modulated output of the cycloconverter in accordance with direction and change of shaft angular position required. In an alternative no motor shaft position measuring device is used and the motor shaft positioning is performed by applying to the motor the cycloconverter output of frequency OMEGA which exists for a time interval DELTA t related to the magnitude of angular rotation required. <IMAGE>
Description
PATENT SPECIFICATION
MOTOR CONTROL SYSTEM
The motor control system according to the invention by way of example is shown in block diagram form in Figure 1 in which the angular position of the shaft of a three-phase induction motor 11 is controlled by energising the induction motor from a single-pulse cycloconverter 1 and suitably changing the polarity of the phase-sequence of the output 8,9 and 10 of the cycloconverter so as to tend to reduce to zero with time an error signal 19 obtained from a comparison between a required angular shaft position 18 and the actual shaft position 13, via a position transducer 14, processing algorithm 16 and a microcomputer 15.
The error signal is processed in an algorithm 21 to produce an actuating signal 22 which modulates at a frequency the firing angles of the switch means 2,3 and 4, of the single-pulse cycloconverter 1 via a firing unit 23 and changes the polarity of the phase-sequence of the modulated output of the cycloconverter in accordance with direction and change of shaft angular position required.
I, SYDNEY LLOYD, 5 Lloyd Road, Hove, Sussex, British, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is periormed, to be particularly described in and by the following statement
The invention relates to electrical alternating current servo systems and more particularly to alternating current servo systems in which the angular position oj an induction motor shaft is controlled by means of a single-pulse cycloconverter.
Background to the invention.
It is well known that a 3-phase induction motor energised from a 3-phase alternating current supply of frequency G) has a forward or positive direction of shaft rotation when the 3-phase supply voltage vectors have a positive phase-sequence in real-time vector space and that if two supply phases to the motor are interchanged then the phase-sequence of the 3-phase voltage applied to the induction motor changes polarity and becomes negative in real-time vector space and causes the induction motor rotor to rotate in a reverse direction.
A switching device such as an inverter of known form can, by means of the technique known as Pulse-Width-Xodulation (fix), produce an output of variable frequency ~SL and of either polarity of phase-sequence enabling an induction motor to which it is connected to be run in either direction and thus operate as part of a servo system.
Another switch device known as a cycloconverter, by phase angle controlling the a.c. supply directly, can also produce an output of variable frequency a SL < (;L < W) and o either polarity of pbase-sequence, but the device generally requires 6m switches, or thyristors, in its implementation, where m is the pulse number, defined as the number of different sources of the supply voltage half- cycles that appear in any one half-cycle of the cycloconverter low frequency output.
Typical applications of the cycloconverter have m=3, or m=6 (m=2 requires a transformer), making the device uneconomic for servo applications except for very large systems. If m=l the device becomes a single-pulse cycloconverter and only employs six switches, or thyristors.
The present invention described herein relates to alternating current servo systems in which the angular position of an induction motor shaft is controlled by means of a single-pulse cycloconverter, and closed loop control of shaft position is enabled by feedback from an angular position measuring device attached to the motor sbaft and where the phase-angle modulation algorithms for the cycloconverter and the feedback control algorithms are implemented by means of a microcomputer and thus the invention in this preferred form can be described as a single-pulse cycloconverter controlled induction motor servo system, and as such is a simpler and more economic alternative to the inverter controlled induction motor servo system.
A preferred alternative form of the invention is one where the servo system operates under open loop conditions with no motor shaft position measuring device employed and where the motor shaft positioning is performed by applying to the motor a time pulse of the single-pulse cycloconverter output of frequency ~rL which exists for a time interval A t related to the magnitude of angular rotation Ae required, by the equeation :: dead = laotsr p, neglecting the slip of the motor at frequency JL ,and the direction of rotation through angle A e is determined by the polarity of the phase. sequence of the cycloconverter three-phase output at frequency A According to the invention there is provided a power control circuit of the known single-pulse cycloconverter form , comprising a bidirectional electrical power switch means connectedin series between each alternating current supply phrase and the corresDondinz motor shase, oreferablv the bidirectional electrical power switch means is a baWck-to-baack paif of thyristors, or triac, in which the firing or conduction angles of the said switch means are varied or modulated in time in the known manner by means of a microcomputer at a frequency il where R is less than the supply frequency CO so that for for each phase of the a.c.
supply a dominant harmonic phase voltage of frequency ,n! is applied to each phase of the motor and the polarity of the phase sequence of the said firing angle modulation is set, either positive to give a clockwise or forward rotation in time of the dominant harmonic voltage phase vectors applied to the motor, or set negative to give an anticlockwise or reverse rotation in time of the dominant harmonic voltage phase vectors applied to the motor so that the direction of rotation of the rotor of the motor is clockwise for the said positive phase-sequence modulation and anticlockwise for the said negative phase-sequence modulation and an angular position measuring device, preferably an encoder, attached to the motor shaft has a pulse train output which is applied to the said microcomputer and therein processed to produce a signal e0 proportional to the angular position of the motor shaft, and % is compared by means of the said microcomputer, with a demanded or reference position signal so so as to produce an error signal e = ## ce - 80 ) the polarity of which determines the polarity of the said phase-sequence of the said firing angle modulation and hence determines the direction of rotation of the motor shaft in a manner such that the said direction of rotation is always varied so as to progessively, or rapidly, reduce the said error signal e to zero and hence place the motor shaft in an angular position e0 equal to the demanded or required angular position 0g .
The present invention will be further described by way of example, with reference to the accompanying drawings in which
Figure 1 is a block diagram of the invention,
Figure 2 is a flow chart depicting the motor shaft positioning algorithm according to the invention and
Figure 3 is a number of graphs of voltage waveforms and pulse trains plotted against time which together from a descriptive examination of same illustrate by way of example the principle of the method of production of the output voltage waveform of the single-pulse cycloconverter for the R phase only.
The block diagram of the present invention shown in Figure 1 consists of a single-pulse cycloconverter 1 of known form conprising three bidirectional switch means 2, 3 and 4 said switch means preferably in the form of pairs of thyristors, or transistors, each pair arranged in a back-to-back configuration between associated 3-phase a.c. supply terminals 5, 6 and 7 corresponding to the a.c. supply R, Y and B phases respectively and the corresponding input terminals 8, 9 and 10 of the 3-phase a.c. motor 11, preferably an induction motor. A load 12 mechanically coupled to the motor shaft has a servo output signal 13 representing the the load shaft angular position 0 and this angular position is monitored or measured by an angular position measuring device 14 preferably an encoder or similar transducer.The output of the angular position measuring device is applied as an input to a microcomputer 15 and therein processed in accordance with a signal processing algorithm 16 to produce a signal 17 proportional to O the servo angular position output signal 13.
The signal 17 is compared with a required output angular position signal #R# 18 and an error signal 19 given by the equation e = (#R - #o) is produced by the comparator 20. This error signal 19 is processed in accordance with an algorithm 21 resulting a signal 22 which (a) Sets the polarity of the phase-sequence of the phase angle modulation at frequency JQ of the single-pulse cycloconverter 1 in accordance with the polarity of the error signal 19 and in a manner specified by the flow chart shown in Figure 2 and the equations El, E2 and E3 given below.
(b) Modulates the firing angles of each of the three bidirectional switch means 5, 6 and 7 in a manner which generates a series of said switch means conduction time instants 'Pj-R ,CTjr and 1rjB , j=1 ,2,3 in each half cycle up to and including the jth half cycle of each of the corresponding said supply phases R, Y and B expressed in mathematical form by the equations
j=1,2.3 ......
where f= 2X > c is the supply frequency in Hz,
F= 21tJL is the modulation frequency in Hz, X is a modulation index, 0 < k < i, and is a measure of the depth of modulation and thus a measure of the amplitude of the dominant harmonic output at frequency ~ÇL of the single-pulse cycloconverter, and Y=2, B=4, P=1 for a positive phase sequence of the single-pulse cycloconverter modulated output. Y=4, B=2, P= -1 for a negative phase sequence of the output of the single-pulse cycloconverter.
Equations E1,E2 and E3 are derived from an inspection of Figure 3 which depicts, for the R phase only,the principle of phase angle modulation for the singlepulse cycloconverter.
Figure 2 shows a flow chart for the determining of the phase-sequence of the single-pulse cycloconverter output. If in 24 the magnitude of the error signal 19 is less than or equal to a dead zone angle fl e then the power to the motor 11 is switch off by blocking off the firing unit 23. The dead zone angle e is created by the discretised measurement of the motor shaft angular position 13 by transducer 14. If the magnitude of the error is greater thande th n the modulation phase sequence is set either positive for the condition
-180 > error 4 180 in 26 and 27, or is set negative in 28 for the condition
0 > error > -180 in 26 and 27.The motor is then turned on and rotates in a forward direction for a positive phase-sequence and rotates in the reverse direction for a negative phase-sequence.
Figure 3 depicts the principle of the method of producing the modulated waveform at the output of the single-pulse cycloconverter for the R phase only.
A reference sine wave 29 is sampled in the regular manner by the sampling pulses 30 at the zero voltage crossover points of the said R phase supply voltage 31 and each of the sampled values of the reference sine wave is held constant for half of one period of the supply of frequency f Hz.
The firing time instants teR , 1iR , AiR 1rjR at 32 in the 1st, 2nd, 3rd..
....jth half cycles of the R phase voltage 31 are established at the instants when the held value of each sample of the reference sinewave is equal to the instantaneous magnitude of a cosinusoidal waveform 33 in each corresponding half cycle of 31. The shaded portions of waveform 31 represent the conduction time intervals of the switch means 2 illustrating the modulation of conduction at frequency JL A further alternative form of the invention is one where the microcomputer processes the encoder 14 output to produce an additional signal proportional to motor shaft speed which is then used to provide velocity control of the angular position of the motor shaft by means of an algorithm implemented by the microcomputer which changes the modulation freqency F and adjusts the value of the modulation index k in accordance with the load torque required so as to optimise the dynamic response of the motor shaft positioning utilising known optimal control techniques.
It is evident from the description of the invention that it can also be applied to alternating current servo systems with numbers of phases other than three.
Claims (8)
- WHAT I CLAIM IS :1. A three-phase induction motor control system which operates from an alternating current supply of frequency o) having at least two phases, comprising a bidirectional electrical power semiconductor switch means connected between the said alternating current supply and the said motor and a control means for varying or modulating at a frequency -D ( Q < c) the commencement and duration of the conduction time intervals of the said switch means so that a dominant harmonic phase voltage of frequency SL and amplitude determined by a modulation index k is applied to each phase of the said motor and the phase- sequence or direction of rotation in vector space of the resulting dominant harmonic phase voltages of frequency JI applied to the said motor is set by the said control means to be either, positive phasesequence clockwise so that the direction of rotation of the rotor of the said motor is clockwise or, the said phase-sequence or direction of rotation in vector space of the said dominant harmonic phase voltages of frequency A applied to the said motor is set by the said control means to be negative phase-sequence anti-clockwise so that the direction of rotation of the rotor of the said motor is anti-clockwise, and a motor shaft angular position determining means attached to the said motor shaft has an output signal which is proportional to the said angular position of the said motor shaft and the said angular position signal is processed and compared in a processing means with a motor shaft reference angular position signal to produce an error signal which is the difference between the said motor shaft angular position reference signal and the motor shaft angular position signal obtained from the said processing means ; and the polarity of the said error signal determines the said direction of rotation in vector space of the said dominant harmonic phase voltages applied to the said motor and so determines the direction of rotation of the said motor shaft in a manner such that the said direction of motor shaft is always varied so as to progressively, or rapidly, reduce the said error signal to zero and hence position the said motor shaft in an angular position equal to the said motor shaft reference angular position, where the rate of reduction of the said error signal is determined by processing the said error signal in a suitable manner in the said processing means.
- 2. A three-phase induction motor control system as claimed in Claim 1, in which the said alternating current supply has two phases and the said switch means comprises two pairs of thyristors, or two triacs, where each pair of thyristors is connected in the known back-to-back configuration and in which a said pair of thyristors, or a triac, is connected between phase 1 of the said alternating current supply and phase 1 of the said motor and the second pair of thyristors, or a triac, is connected between phase 2 of the said alternating current supply and phase 2 of the said motor.
- 3. A three-phase induction motor control system as claimed in Claim 1, in which the said alternating current supply has three phases and the switch means comprises three pairs of thyristors, or three triacs, arranged in the known three-phase configuration where each pair of thyristors is connected in the known back-to-back arrangement and in which a said pair of thyristors, or a triac, is connected between phase 1 of the said alternating current supply and phase 1 of the said motor, and a second said pair of thyristors, or a triac, is connected between phase 2 of the said alternating current supply and phase 2 of the said motor, and a third said pair of thyristors is connected between phase 3 of the said alternating current supply and phase 3 of the said motor.
- 4. A three-phase induction motor control system as claimed in Claims 2 and 3 in which each of the said pairs of thyristors is replaced by a pair of transistors connected in the known back-to-back configuration so as to conduct bidirectionally as aforesaid in response to the control signals produced by the said control means.
- 5. A three-phase induction motor control system as claimed in any one of the preceding Claims in which the control means and the processing means comprises either a microcomputer, or microcontroller, which is programmed to vary or modulate as aforesaid the commencement and duration of the conduction time intervals of the said switch means and to determine as aforesaid the polarity of the said phase-sequence of the said dominant harmonic phase voltages in vector space to position as aforesaid the said motor shaft in an angular position equal to the said motor shaft reference angular position.
- 6. A three-phase induction motor control system as claimed in Claim 1 in which there is no said motor shaft angular position determining means and where the said motor shaft angular positioning is performed by applying to the said motor for a predetermined interval of time At the said dominant harmonic phase voltages of frequency 1L obtained from the said switch means, where the desired angle of rotation A 9 of the said motor shaft, neglecting motor slip at the modulation frequency JQ, , is proportional to the product of the said frequency . and the magnitude of the predetermined interval of time At and inversely proportional to the number of pairs of poles of the said motor and where the direction of angular rotation t L?r is determined by the polarity of the said phase-sequence of the said dominant harmonic phase voltages applied to the said motor.
- 7. A three-phase induction motor control system as claimed in one of the previous Claims in which the output signal of the said motor shaft angular position determining means is processed in the said processing means to produce a signal proportional to the angular velocity of the said motor and the said processing means provides velocity control of the angular position of the said motor shaft by varying the magnitudes of the modulation frequency ji and the modulation index k in accordance with the load torque required and so optimise the dynamic response of the said motor shaft positioning utilising known optimal control techniques.
- 8. A three-phase induction motor control system substantially as hereinbefore described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9111326A GB2257312B (en) | 1991-05-24 | 1991-05-24 | Motor control system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9111326A GB2257312B (en) | 1991-05-24 | 1991-05-24 | Motor control system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9111326D0 GB9111326D0 (en) | 1991-07-17 |
| GB2257312A true GB2257312A (en) | 1993-01-06 |
| GB2257312B GB2257312B (en) | 1995-08-16 |
Family
ID=10695603
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9111326A Expired - Fee Related GB2257312B (en) | 1991-05-24 | 1991-05-24 | Motor control system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2257312B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6061391A (en) * | 1997-02-28 | 2000-05-09 | Fujitsu Limited | Error indicator, and data modulator-demodulator and indicating method of light emitter therein |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1150719A (en) * | 1965-05-29 | 1969-04-30 | Bbc Brown Boveri & Cie | Arrangements for Controlling the Speed of Asynchronous Electrical Machines |
| GB1382297A (en) * | 1971-06-29 | 1975-01-29 | Siemens Ag | Method of and apparatus for controlling a synchronous machine |
| EP0119583A1 (en) * | 1983-03-16 | 1984-09-26 | Kabushiki Kaisha Toshiba | AC current control system |
| EP0216373A2 (en) * | 1985-09-25 | 1987-04-01 | Hitachi, Ltd. | Induction generator/motor system |
-
1991
- 1991-05-24 GB GB9111326A patent/GB2257312B/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1150719A (en) * | 1965-05-29 | 1969-04-30 | Bbc Brown Boveri & Cie | Arrangements for Controlling the Speed of Asynchronous Electrical Machines |
| GB1382297A (en) * | 1971-06-29 | 1975-01-29 | Siemens Ag | Method of and apparatus for controlling a synchronous machine |
| EP0119583A1 (en) * | 1983-03-16 | 1984-09-26 | Kabushiki Kaisha Toshiba | AC current control system |
| EP0216373A2 (en) * | 1985-09-25 | 1987-04-01 | Hitachi, Ltd. | Induction generator/motor system |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6061391A (en) * | 1997-02-28 | 2000-05-09 | Fujitsu Limited | Error indicator, and data modulator-demodulator and indicating method of light emitter therein |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9111326D0 (en) | 1991-07-17 |
| GB2257312B (en) | 1995-08-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19951116 |