Design of high-efficiency bidirectional DC-DC converter and high-precision efficiency measurement

This paper first introduces the design of an ultra high-efficiency 50 kW bidirectional DC-DC converter at ZVS operation and then a high-precision efficiency measurement method using regenerative approach. The ultra high-efficiency bidirectional DC-DC converter is achieved with (1) the use of CoolMOS as the main switch under zero-voltage soft switching condition (2) multiple phase legs for current sharing to reduce the conduction loss, and (3) coupling inductors between each two phase legs to reduce the core loss. Two identical hardware prototypes were designed, fabricated and tested for performance evaluation. In order to precisely measure the converter efficiency, the two identical bidirectional DC-DC converters are tested with one as the device under test (DUT) and the other as the regenerative unit. With the use of plusmn0.5% current shunt and regenerative measurement, the relative efficiency error stays below plusmn0.025%. Measured efficiency from 20% to 100% load consistently show above 97.50% and peaks at 99.05%.