Abstract: In a current type GTO inverter, commutation surge voltage is inevitably generated from an inductive load whenever each GTO is turned off. The commutation surge voltage thus generated is once stored in a capacitor through a diode surge voltage rectifier and then restored or regenerated to the DC source terminals of the GTO bridge-connected inverter through a pair of other GOTS turned on only when the capacitor voltage exceeds a predetermined value beyond the DC source voltage. After energy restoration, magnetic energy stored in a reactor is recharged in the same capacitor. The necessary elements are a capacitor, two GTOs, two diodes and a DC reactor, thus simplifying the circuit configuration and reducing the cost. Additionally, since no vibration circuits to turn off thyristors for restoring the energy charged in the capacitor to the GTO bridge-connected inverter are required, the circuit operation is stable at higher frequency range, in particular.

Abstract: In a current type GTO inverter, commutation surge voltage is inevitably generated from an inductive load whenever each GTO is turned off. The commutation surge voltage thus generated is once stored in a capacitor (C.sub.1) through a diode surge voltage rectifier (5) and then restored to the DC source terminals (3A, 3B) of the GTO bridge-connected inverter (3) through a pair of other GTOs (G.sub.7, G.sub.8) turned on during steady state intervals of inverter commutation. Magnetic energy stored in a reactor (Lr.sub.1, Lr.sub.2) in motor-driving operation is recharged to the capacitor (C.sub.1) through the diode surge voltage rectifier (5) after the GTOs (G.sub.7, G.sub.8) have been turned off; the motor kinetic energy stored in the capacitor (C.sub.1) through diodes (D.sub.8, D.sub.9) in motor-braking operation is regenerated to the AC source side of the inverter (3) through a pair of other GTOs (G.sub.9, G.sub.10) when the voltage across the capacitor (C.sub.