Push-Pull Forward Three-Level Converter for High-Voltage Fuel Cell Applications

This paper proposes a push-pull forward three-level converter (PPF TL converter) for high-voltage fuel cell applications. It integrates the advantages of the TL converter and the PPF converter. It can operate at both three-level (M) mode and two-level (2L) mode, so it is suitable for wide input voltage application, such as fuel cell power system. Half of the switches sustain half of the input voltage. The others sustain one and one-half input voltage in the M mode and sustain the input voltage in the 2L mode, which can realize zero-voltage switching (ZVS) by the leakage inductance. Voltage spikes across the switches caused by leakage inductance can be clamped by the clamping capacitor. The input current ripple and the output filter inductor current can be reduced with the built-in input filter of PPF and TL waveform of the secondary rectified voltage. In order to reduce the voltage spikes across the rectifier diodes caused by the leakage inductance in a high output voltage situation, 1/2 level of the secondary rectified voltage appears first, and 1 level of that appears later. The operating principle of the proposed converter is analyzed and verified by the simulation.