A Full Load Range ZVS Isolated Three-Level DC/DC Converter with Active Commutation Auxiliary Circuit Suitable for Electric Vehicle Charging Application

Abstract

The isolated three-level DC/DC converter (ITLDC) can be used to charge electric vehicles. During the constant current charging stage, the ITLDC can be designed to realize nature zero voltage switching (ZVS). However, during the constant voltage charging stage, the charging current is small; thus, nature ZVS cannot be realized. This paper presents an active commutation auxiliary circuit (ACAC) for the ITLDC to realize the full load range ZVS. With the proposed ACACs, all the main switches achieve zero-voltage turn-on and quasi zero-voltage turn-off, and the auxiliary switches realize zero current turn-on and zero-voltage turn-off; thus, the efficiency will be high. The auxiliary currents generated by the ACACs are controllable. During the constant current charging stage, the ITLDC realizes nature ZVS and the auxiliary currents are controlled to zero; thus, the ACACs do not result in high current stress or bring in additional losses, and the efficiency will be high. During the constant voltage charging stage, the charging current decreases with charging time and the charging current is too small to realize nature ZVS. Thus, the ITLDC can work with the proposed ACACs and the auxiliary currents can be controlled within a suitable value to realize ZVS. With the proposed ACACs, the ITLDC can realize ZVS during the whole charging process; thus, the efficiency will be high. The structure and operating principle of the ITLDC with ACACs are introduced and the performance of the proposed TLDC is experimentally verified on a 1.5 kW prototype converter.