Abstract：This paper presents a push-pull forward (PPF) three-level (TL) converter, which is suitable for low and wide-range input voltage applications, such as renewable energy resources. Half of the switches sustain half of the input voltage, and the others sustain one and one-half input voltage. However, voltage stress of the rectifier diode is high with the conventional TL control strategy, especially in high output-voltage condition, considering voltage spike across the rectifier diode caused by leakage inductance. When 1/2 level of the secondary rectified voltage shows first and 1 level of that appears later, the voltage stress across the rectifier diode can be reduced by paralleling with external capacitor. The operating principle and selection of the external capacitor are analyzed. Finally, experimental results of a 500 W PPF TL converter verify the theoretical analysis.
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2012, Vol. 27 
