Medium-Voltage Power Conversion Systems in the Next Generation

This paper describes the next-generation medium-voltage power conversion systems characterized by using bidirectional isolated dc/dc converters. A 350-V, 10-kW and 20-kHz dc/dc converter is designed, constructed and tested as a core circuit of the medium-voltage power conversion systems. It consists of two single-phase full-bridge converters with the latest trench-gate Si-IGBTs and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive circuit and control circuit losses from the whole loss. Moreover, loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc/dc converter. As a result, the overall efficiency may reach 99% or higher