A Passive Flyback Auxiliary Circuit With Integrated Transformer Suitable for Three-Phase Isolated Full-Bridge Boost PFC Converter

A passive flyback auxiliary circuit with integrated transformer is proposed and investigated in a three-phase isolated full-bridge boost power factor correction (PFC) converter, by which the voltage across primary side of the power transformer can be clamped to a fixed value and the absorbed energy can be transferred to the load by itself automatically. The auxiliary circuit is composed of two capacitors, four diodes, and one flyback integrated transformer. With the help of the flyback integrated transformer, synchronous resonances in the auxiliary circuit can be achieved, which will avoid the unbalance of the voltage and current in the auxiliary circuit. Compared with the passive snubbers, voltage spike of the three-phase PFC converter is suppressed more effectively with the adoption of the auxiliary circuit, and current stress of the switches is much lower. The operational principle of the auxiliary circuit is discussed in the three-phase isolated full-bridge boost PFC converter. Furthermore, the design considerations of the auxiliary circuit are analyzed. Finally, experimental study of the auxiliary circuit has been done on a laboratory-made three-phase PFC prototype, and the feasibility of the proposed method and the validity of the theoretical analysis are verified by the experimental results.