This paper presents a high efficiency 5-kW bidirectional DC-DC converter for use in electric vehicle super-capacitor systems. Super-junction MOSFETs are deployed in the power stage to minimize losses. This is achieved using a snubber inductor and by arranging the gate signal underlap delays in order to control charging current caused by the devices' highly non-linear output capacitance and to deactivate the intrinsic body drain diode respectively. The result is a 5-kW power converter with an estimated efficiency exceeding 99% in the power semiconductor stage and requiring no forced cooling. I.

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Silicon super-junction MOSFETs have very low onstate resistances and fast switching characteristics. However, their use in voltage-source converters is hindered by the poor reverse recovery performance of their body drain diode and an adverse output capacitance characteristic. These both act to increase the overall switching loss. The on-state resistance and output capacitance characteristics of super junction devices are both related to the area of the silicon die. As this increases, the on-state resistance decreases but the output capacitance increases. A figure of merit is evaluated with both predicted and experimental results using a 400-V, DC-DC synchronous buck-converter operating over a range of output currents and switching frequencies. I.

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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.