GB1353759A - Controlling of asynchronous motors - Google Patents

Abstract

1353759 Control of AC motors; automatic speed control CSEPELI SZERSZAMGEPGYAR 19 April 1971 [13 April 1970] 26803/71 Heading H2J [Also in Division G3] The invention relates to the control of an asynchronous A.C. motor 2 fed from a D.C. source 1. The motor has for each pole two conductors wound in antiphase and connected at a common point to one side of the D.C. supply. The other ends of the windings are connected in turn to the other side of the D.C. supply by pulse inverters 7, 8 controlled in accordance with an input signal at 26 and a current feedback by half-sine-wave pulses from a generator 22. As shown the input voltage at 26 controls the frequency of a generator 25 feeding a shift register 24 which through a decoder 23 causes the generator 22 to deliver half-sinewave signals at t, s, r separated 120 degrees in phase and further signals at 18, 27, 28 to cause the switching devices 7, 8 to be operated alternately in the correct sequence. The amplitude of the signals at t, s, r depends on the signal at 26 by means of a D/A converter 20 fed by the pulse generator 25. The individual signals at t, s, r are fed to devices 16 which also receive the current feedback signal from an integrator 12 fed from a resistor 11 in series with the windings. The output of device 16 is differentiated at 13 and applied to gated amplifiers 14, 15. These are alternately gated on by a trigger circuit 10 fed by the signal at 18 to supply gating pulses, of frequency dependent upon the signal at 26 and amplitude dependent on the signal at 26 and the feedback signal from 12, to the inverters 7, 8. Switching means may be provided (Fig. 2, not shown) to interchange the connections from t, s to 18, 27 to reverse the motor. For automatic speed control the signal at 26 is derived from a pulse generator 3 or a tachogenerator coupled to the motor. The output of this generator is applied through a buffer 50, shaper 49 to charge a capacitor 57 and through shaper 47 and inverter 53 to discharge a capacitor 56. Similarly a set speed pulse signal from a generator 43 charges capacitor 56 and discharges 57. The values in capacitors 56, 57 are applied by impedance transformers 58, 59 to a summing circuit 40 to produce the signal at 26. In a modification (Fig. 4, not shown) the trigger circuits 10 and connections 18, 27, 28 are omitted and the generator 22 directly produces six gating signals to the various amplifiers 14, 15.