Some New Aspects in the Design of PWM Inverters

Two methods are described for decreasing switching losses and voltage stresses in the modified McMurray inverter operating with a PWM control. The first method consists of adjusting the firing of the complementary main thyristor during a commutation cycle, according to the actual load current. As a result, one reduces the trapped energy losses and the dv/dt stresses. With the second method, a freewheeling diode is connected across the inverter dv/dt inductor, thus decreasing the effect of the diode reverse recovery current, the voltage overcharge on the commutation capacitor, and the circuit clearing time. Experimental verification of both methods was performed on a 50-kVA inverter.