Three-phase soft-switched pwm inverter for motor drive application

A novel soft-switched inverter topology in which three mutually coupled inductors at a time are involved in the resonance process is proposed. By the introduction of magnetic coupling between three resonant inductors, the zero-voltage instants for the inverter can be generated by one auxiliary switch. Also, the resonant energy can be recycled, and the maximum voltage stress on the auxiliary circuit diode components is confined to the DC-link clamp voltage level. The DC link can be clamped to 1.1-1.3 times the DC-source value. This is unlike the soft-switched inverter in which two mutually coupled inductors are at a time are involved in a resonance process, wherein the clamping diode experiences voltage stress of the order of 11 per unit when clamping the DC-link voltage at 1.1 per unit. The proposed inverter also provides pulse-width modulated operation. An analysis of this novel quasi-resonant DC-link inverter topology is presented to reveal its soft-switching characteristics. Simulation and laboratory experiments are performed to validate the analysis.