Naturally Adaptive, Low-Loss Zero-Voltage-Transition Circuit for High-Frequency Full-Bridge Inverters with Hybrid PWM

This paper proposes a low-loss, auxiliary zero-voltage-transition (ZVT) circuit to realize zero-voltage-switching (ZVS) for all the main switches of a full-bridge inverter, and inherent zero-current-switching (ZCS) turn-on and ZCS turn-off for the auxiliary switches. Two configurations consisting of discrete inductor and coupled inductor structures are proposed. The advantages of the proposed strategy include the provision to implement zero-state modulation schemes such as unipolar and hybrid pulse width modulation schemes in the full-bridge inverter to achieve low THD, naturally adaptive auxiliary inductor current and the elimination of capacitor voltage balancing issues seen in other similar ZVT approaches. The modulation scheme and the commutation stages are analyzed in detail. The complete inverter including the auxiliary ZVT branch is modeled in detail. Finally, a 1 kW, 400 kHz switching frequency inverter of the proposed topology using SiC MOSFETs has been built to validate the theoretical analysis. The ZVT with hybrid modulation technique is implemented in DSP TMS320F28335 resulting in full ZVS for the main switches in the full-bridge inverter. Compared to conventional hard switching full-bridge inverter, the proposed scheme improves the California Energy Commission efficiency from 95.58% to 97.63% and the peak efficiency from 96.29% to 97.91%.