Integration of Minimum-Voltage Active-Clamping to Three-Phase Four-Wire Rectifiers with a Balancing Leg

Three-phase four-wire rectifiers with a balancing leg are often used as front-end converters in uninterruptible power supplies (UPS). The integration of minimum-voltage active-clamping (MVAC) to these rectifiers is proposed. With the proposed Zero-Voltage-Switching Sinusoidal PWM (ZVS-SPWM) scheme, ZVS operation for all power semiconductor devices of the rectifier are realized. The ZVS conditions under balanced and unbalanced load are derived. Then voltage and current stress of switching devices and auxiliary circuit are compared with the compound-active-clamping (CAC) three-phase four-wire rectifier. Finally, the proposed circuit and its control scheme are verified with a 10kW experiment prototype.