Power circuit for variable frequency, variable magnitude power

Abstract

A power circuit arrangement for a power conditioning system adapted to supply variable frequency, variable magnitude voltage to an electromagnetic device such as an electric motor having a center-tapped winding includes first and second inverting thyristors connected to the respective winding ends and connected in series with a transistor chopper across a unidirectional source so that the inverting thyristors may be gated on alternately at a relatively low modulation frequency while the chopper is time ratio controlled at a higher carrier frequency to selectively vary the voltage applied to the winding; a capacitor in shunt to the chopper which is overcharged due to winding leakage reactance when the chopper is turned off to reverse bias and 'soft' commutate the thyristors when they are not conducting load current; a free-wheeling thyristor connected between the winding center tap and the chopper and poled to form a low-impedance free-wheeling path for winding current in series with the inverting thyristors when the chopper is turned off; and first and second energy recovery diodes connected across the serial arrangement of the chopper with the respective inverting thyristors to provide paths for out-of-phase currents and for current when the free-wheeling thyristor is turned off during commutation of the inverting thyristors.