A family of multilevel passive clamp circuits with coupled inductor suitable for single-phase isolated full-bridge boost PFC converter

A family of multilevel passive clamp circuits is proposed and investigated in a single-phase isolated full-bridge boost power factor correction (PFC) converter, by which the voltage spike across primary side of the power transformer can be suppressed effectively, and the absorbed energy can be transferred to the output side automatically. These clamp circuits are composed of several capacitors, diodes and one coupled inductor. With the help of the coupled inductor, synchronous resonances of the different resonant circuits can be achieved, which will avoid the unbalance of the voltage and current in these circuits. For the N-level passive clamp circuit, as N increases, the maximum duty cycle of the PFC converter will increase, the current stress of the switches will decrease, and the volume of the coupled inductor will decrease. Take a three-level clamp circuit for example, the operational principle of multilevel clamp circuits are discussed. Furthermore, some related analysis and comparison are given. Finally, experimental study has been done on a laboratory-made single-phase PFC prototype in which a four-level and a five-level clamp circuits are adopted, respectively. The feasibility of the proposed method and the validity of the theoretical analysis are verified by the experimental results.