Improvements in or relating to Slip Frequency Control of an Asynchronous Electrical Machine

摘要

1,187,709. Control of A.C. motors. ROBERT BOSCH G.m.b.H. 19 Dec., 1968 [20 Dec., 1967], No. 60500/68. Heading H2J. [Also in Division G3] In a system for controlling the slip frequency of an asynchronous machine 20 which is supplied at controlled frequency from a source 27 adapted to receive regenerated power, the stator 21 is connected to inverter 22 associated with generator 28 whereby the motor voltage increases with frequency to maintain constant flux. The control generator 28 is connected to oscillator 31 producing a wave whose frequency is proportional to the voltage derived from an integrator 32 associated with a digital-analogue converter 33. The latter is connected with a bidirectional counter 34 whose input r receives pulses from the oscillator 31, whilst input v is fed from summer 35. The output slip frequency signal from oscillator 38 is applied to the input 36 of the summer 35, this signal being determined by the setting of an accelerator pedal 39 or the output of a comparator 42 forming part of a speed-regulating system. A signal from tachometer generator 24 is fed to the input 37 of adder 35. If the motor speed exceeds a predetermined value, an increased rate of pulses is fed to input v of the counter 34, exceeding the rate fed to the input r, whereby the frequency of the oscillator 31 is increased until a new steady state is obtained and the counter 34 returns to zero output. When the machine 20 operates as a generator, the inputs to the summer 35 are changed over. The bi-directional counter comprises counting stage 46 (Fig. 2) receiving signals V, R, from stage 49 to decide the direction of counting in dependence upon the state of flip-flop 47. When stage 46 reaches its maximum count, this information is fed to stage 49 whereby the counter is influenced only by pulses which reduce its number. A coincidence gate 50 eliminates simultaneous pulses tending to move the counter in opposite directions. An adder stage 56 receives a constant frequency signal from oscillator, 64 which determines the transition from motor to generator operation, as well as the signal from generator 24. Adder stage 55 receives a feedback signal from oscillator 31 and the slip reference signal from oscillator 61.