Split Complementary Modulation for Switching Loss Balancing of Phase-Shifted Full-Bridge Converter

In a phase-shifted full-bridge (PSFB) converter, the switches on each leg are driven by complementary pulse-width-modulation (PWM) signals and achieve zero-voltage-switching (ZVS). However, the PSFB converter inevitably experiences the unbalanced switching losses on its leading and lagging legs. In this article, we propose a split complementary modulation for balancing the switching losses on leading and lagging legs of PSFB converter. The split complementary modulation enables each leg operate in leading leg and lagging leg alternatively every switching period. The extra dead-time is usually required for ZVS turn-on of the lagging leg switches at the light load. Under the split complementary modulation, since the role of leading and lagging legs are shifted every switching period, the corresponding extra-dead time is also applied before the turn-on of the lagging-leg switches. Thus, the resulting dead-time sequence applied for the primary-side switches at the light load becomes different during the odd switching period and even switching period. This split complementary modulation can be easily implemented by using combination of “AND gates” and “OR gates”. The feasibility and effectiveness of the proposed switching modulation were verified by the experimental results from 1-kW prototype. The temperatures for the primary-side switches were well balanced even at 7% load condition.