Push–Pull Forward Three-Level Converter With Reduced Rectifier Voltage Stress

This paper proposes a push-pull forward three-level (TL) converter, which is suitable for low and wide-range input-voltage applications, such as fuel cell and solar cell. Half of the switches sustain half of the input voltage, and the others sustain one and one-half input voltage. The input ripple current and output filter inductor ripple current can be reduced with TL waveform of the secondary rectified voltage. However, the voltage stress of a rectifier diode is high with the conventional TL control strategy in a high output-voltage situation, considering voltage spike across the rectifier diode caused by the leakage inductance. When 1/2 level of the secondary rectified voltage shows first and one level of that appears later, the voltage stress of the rectifier diode can be reduced by paralleling with a small external capacitor. The operating principle, control strategy, and design guidelines and example are analyzed. Finally, experimental results verify the theoretical analysis.