Novel DC-rail soft-switched three-phase voltage-source inverters

A family of DC-rail soft-switched three-phase voltage-source inverters (VSIs) adopting the zero-voltage-transition (ZVT) or zero-current-transition (ZCT) techniques are proposed in this paper. Adding an active switch on the DC-rail makes the implementation of the ZVT and ZCT as easy as in a single-ended DC/DC power converter, while true pulse-width-modulation (PWM) operation is achieved by a modified space-vector modulation. As a result, these inverters can run at much higher switching frequencies than conventional hard-switched VSIs, and with higher power density and efficiency. The operation and control strategy are analyzed. Implementation and experimental results of a prototype DC-rail ZVT VSI, which is rated at 15 kVA and run at a switching frequency of 62.5 kHz, are presented. The measured efficiency with static loads reaches 93% under the input voltage of 400 V.