Enhancement of Power Conversion Efficiency in a Low-Power Range of a Bidirectional Isolated DC-DC Converter by Intermittent Operation

This paper describes a 750-Vdc, 100-kW, 20-kHz bidirectional isolated dual-active-bridge (DAB) dc-dc converter using SiC-MOSFET modules without free-wheeling diodes, focusing on the output voltage ripple and power conversion efficiency. Intermittent operation brings higher conversion efficiencies in a low-power range to the dc-dc converter than does continuous operation because it makes a significant contribution to reducing switching (snubber) and iron losses. Experimental results reveal that the efficiency at 10kW (10% of the rated power) is 95.1% in continuous operation, whereas it is improved to 98.2% in intermittent operation. The combination of intermittent operation with continuous operation makes the efficiencies in a power range from 3 to 100kW higher than 98%, excluding power losses produced by the control and gate-drive circuits. However, the intermittent operation may bring additional voltage ripples to the dc output terminals. Theoretical analysis confirms that the voltage ripples in a power range from 1 to 18kW are lower than 7V in peak-to-peak, which is only 0.9% of 750Vdc. Theoretical results are confirmed by comparison to simulated and experimental ones.