Large Power Hybrid Soft Switching Mode PWM Full Bridge DC–DC Converter With Minimized Turn-on and Turn-off Switching Loss

A novel PWM full bridge (FB) dc-dc converter for large power industrial applications is proposed in this paper. The soft switching mode of the primary switches can be varied under different input and output conditions to achieve optimum system efficiency. In the zero-voltage and zero-current switching (ZVZCS) mode, the turn-on and turn-off switching loss can be optimized because the soft switching conditions of the turn-on and turn-off instants are well decoupled. In the zero-voltage switching (ZVS) mode, the turn-off switching loss can also be optimized because there is no requirement for light load operation in this mode. Four mosfets with ultra-low on-state resistance are used, thus, the added conduction loss is small. The auxiliary MOSFETs with high switching frequency are turned on with zero-current and off with zero-voltage, hence, the added switching loss can also be neglected. Furthermore, some drawbacks of the conventional ZVS and ZVZCS converters, e.g., narrow ZVS load range, high primary circulating current, incomplete reset of the primary current, and unreasonable VA rating of the added components, have been well solved. The operation principles and soft switching characteristics are discussed. Experimental results from an 18-kW prototype are provided to verify the proposed converter.