Efficiency Improvement and Transient Characteristics of the 750-V, 100-kW, 20-kHz Bidirectional Isolated DC-DC Converter

This paper describes the 750-V, 100-kW, 20-kHz bidirectional isolated dual-active-bridge (DAB) dc-dc converter using the latest 1.2-kV, 400-A SiC-MOSFET 4-in-1 modules integrated with SBDs. It focuses on power conversion efficiency and transient characteristics. This dc-dc converter is characterized by being capable of an appropriate switchover between continuous operation and intermittent operation for the purpose of efficiency improvement. The intermittent operation achieves more efficient power conversion for partial loads than does the continuous operation. However, the intermittent operation may cause different upper and lower peak currents in the converter, thus resulting in an increase in the amount of switching loss. This paper introduces an advanced control method for the intermittent operation, which improves the efficiency. Experimental results reveal that the advanced method improves the efficiency from 98.4% in the previous method to 98.6% at 22kW. The efficiency in continuous operation at 100kW is 98.3% in the case of using the previous four 2-in-1 modules without SBD, while it is improved to 98.9% in the case of using the two 4-in-1 modules. Experimental transient characteristics show that no dc magnetic-flux bias occurs even during switchover between continuous and intermittent operation when power reversal from -100kW to 100kW occurs within a time interval of 1ms. Finally, it is verified that the dc-dc converter is capable of providing fast power-reversing performance from -100kW to 100kW within a time interval as short as 25µs.