A simple DC-rail soft switched voltage source inverter

A simple DC-rail soft switched resonant circuit is proposed for a three-phase voltage source inverter. The proposed resonant circuit consists of a DC-rail switch with an antiparallel diode and two auxiliary switch. The DC-rail switch is turned on and off under zero voltage condition, and the auxiliary switches are turned on and off under zero current condition. Since the resonant inductor is disconnected at zero current instant, the proposed circuit requires no resonant inductor freewheeling diodes. Furthermore, the freewheeling diodes in the bridge are softly turned off. Also, the proposed circuit has another advantage that the required power ratings of the resonant inductor and capacitor are small. With the proposed scheme, it is possible to make zero DC-rail voltage with resonance in a PWM period whenever a switching transition is required. The rule of selecting the switching time instant is very simple and less dependent on the system. Furthermore, the proposed scheme can be applied with space vector modulation PWM for motor drives without any modifications. The authors analyze the proposed circuits, and demonstrate its performance through simulations, as well as through experiments.