Achieving Efficiencies Exceeding 99% in a Super-Junction 5-kW DC-DC Converter Power Stage Through the Use of an Energy Recovery Snubber and Dead Time Optimization

A highly efficient 5-kW bidirectional DC-DC converter power stage operating from a 400-V supply implementing Super-Junction (SJ) MOSFETs is presented. SJ MOSFETs have low on-state resistances and low switching losses. However, their application in voltage-source converters can be compromised by the reverse recovery behavior of their intrinsic diodes and their highly non-linear output capacitances. A series switching-aid circuit is used to control the output capacitance charging current. The dead times between switching transitions are assessed and optimized in order to deactivate the intrinsic diodes. The combination of these techniques enables very high efficiencies to be attained. Calorimetric measurements indicate a full-load efficiency of 99.1% for the prototype 5-kW DC-DC converter power stage. A loss reduction of approximately 50% is achieved with the prototype converter power stage when compared to an equivalent IGBT based power stage. Lastly, a loss vs. duty cycle function is experimentally determined which can be used to inform the design of a maximum efficiency point tracking system.