drehzahlgeleinrichtung for an alternating current or drehstromnetz on controllable valves connected in antiparallelschaltung universal or induction motor

摘要

1,102,316. Control of A.C. motors. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 1 Sept., 1966 [4 Sept., 1965], No. 39000/66. Heading H2J. [Also in Division G3] Thyristors 3, connected in the supply circuit of an A.C. commutator motor 2, are triggered by signals from a frequency comparator 5 which receives a reference signal from the mains. The motor drives an auxiliary machine 7, fed from control frequency generator 8, and acting as a frequency converter to provide an output at mains frequency to the comparator 5 when the motor is operative at a desired speed. If the speed of the motor decreases due to increased load, the output of the machine 7 increases in frequency momentarily and its waveform is advanced in phase with respect to the signal derived from the mains. This increases the duration of the conductive periods of the thyristors during subsequent half-cycles of the supply voltage and so restores the speed to its former value by increasing the driving torque The behaviour with a decreasing load is similar to that described. When the motor is adjusted to a lower speed by altering the control frequency, the supply current is interrupted by the absence of trigger signals, and enforced braking may be initiated by reverse-current or eddy currents until the prescribed speed is attained. In another arrangement, the motor under control is of the three-phase induction type with pairs of thyristors in each supplyline. Speed fluctuations are reduced by frequency or phase modulation of the control frequency, the modulating signals being obtained from a tachometer generator. Alternatively, a low-pass filter 23 is associated with the control frequency generator 8 or with a phaseshifter between the machine 7 and the comparator 5 for this purpose.