Control unit null of magnetic flux control forma PWM invar -

摘要

PURPOSE:To prevent overcurrent on starting by setting a frequency of a flux control type PWM inverter at a value directly before its momentary stop when stopping momentarily and restarting said PWM inverter. CONSTITUTION:A control circuit for a flux control type PWM inverter 10 driving an induction motor 12 is composed of a frequency setter 1, a flux amplitude arithmetic circuit 2, a sine wave generator circuit 3, a multiplier circuit 4, a flux regulator 5, a comparison circuit 6, a carrier signal generator circuit 7, a flux detector 8 and a pulse distributor circuit 9 to turn ON-OFF a switching element for said in verter 10. In this case, said control circuit is also provided with a momentary stop detection circuit 20, a sequence circuit 21, slow-reset circuits 22 to 23 and limiting circuits 24 to 25. Thus, an undervoltage signal of supply voltage stops operation of the inverter 10 and, after said signal has disappeared, both an amplitude of flux command signal of the flux regulator 5 and a limiting value of output signal thereof are reduced to zero. Moreover, after the frequency has been fixed to a value at the time of generation of said undervoltage signal, said stop of operation is released and a voltage on restarting is made to start from zero.