Isolated 4- Level DC- DC Converter with Enhanced Soft-Switching Adaptability and Output Voltage Flexibility for High-Power Charger Applications

An isolated 4-level DC-DC converter is proposed to achieve complete zero-voltage-switching (ZVS) adaptability of all active switches while remaining output voltage flexibility of the phase-shifted converters for the high-power universal fast charger applications. A dedicated four-level modulation scheme ensures that the peaks of magnetizing currents of the two H - bridges at primary side are independent of load current and voltage, and phase variations. The magnetizing to leakage inductance ratios of the leading and lagging transformers are improved to be 100 and 25 respectively and the additional series inductors are eliminated. As a result, the circulating current, duty cycle loss and stress on snubber circuit are reduced significantly. The sizing of the output inductor is also decreased because of the 4-level operation. A 30kW isolated DC-DC converter with 7.2kW/L power density (cooling inclusive), 98.5 % peak efficiency, flexible 165V-680V output voltage verifies the features and feasibility of the proposed H8 tonology and four-level modulation scheme.