Realization of Adaptive Soft-switching in High-frequency Single-phase Inverter Based on Parallel Half Bridges

This paper proposes and develops a hybrid QCM/CCM soft-switching scheme for a single-phase PV inverter with two or multiple SiC MOSFETs in parallel. When implemented in a DC-AC converter, conventional soft-switching modulation like critical conduction mode (CRM) suffers from increased condition loss at high load conditions and variable switching frequency. In the proposed modulation technique, a phase-shift modulation scheme is applied to inductor-decoupled parallel half-bridge legs, generating a controllable circulating current flowing through these commutation inductors. Thus, the current of each half-bridge leg is reshaped as quadrilaterals, which enables all the parallel MOSFETs to achieve zero-voltage switching (ZVS). The proposed switched QCM/CCM soft-switching scheme is featured by partial soft-switching, constant switching frequency, seamless and load-dependent mode transition, and high full-power-range efficiency. A 4.4 kW single-phase PV inverter is developed and tested to verify the advantages of the hybrid QCM/CCM operation in power loss reduction and efficiency improvement.