A novel topology of zero-current switching voltage-source PWM inverter for high-power applications

A new scheme of soft-switched VSI three-phase inverter, capable of true PWM, is presented. It utilizes inductors in series with the main switches to limit di/dt during turn on, while the inductor energy is recovered by a resonant turn off process, which is allowed by the presence of two auxiliary switches. As inductive di/dt snubbers are usually needed in high-power GTO power converters, the proposed topology offers a solution to the problem of snubber energy recovery. The control strategy explained in the paper allows both full-range PWM and minimization of stresses during the resonant commutation process. Results of a theoretical analysis and design criteria are reported in the paper. Examples of PWM control schemes are also described, both for analog (ramp-comparison based) and digital (space-vector based) implementations. Experimental results obtained from a small-size laboratory prototype are given