Capacitor voltage balancing control of a fully integrated three-level isolated AC-DC PFC converter for reliable operations

Three-level ac-dc converters are widely used in high-voltage input applications due to the reduced voltage stress on switches and extended range of dc link voltage. For three-level ac-dc converters, the asymmetry of the main circuit and drive circuit can result in voltage unbalance among the split dc link capacitors, which would cause higher voltage stress on the power switches and the output rectifying diodes. In addition, it can lead to asymmetrical transformer and output inductor current, which in-turn decreases the reliability of the components. To address this issue, this paper proposes a capacitor voltage control strategy for a fully integrated three-level isolated ac/dc power factor correction (PFC) converter, which adjusts the duty cycle to balance the dc link capacitor voltages. With three independent voltage controllers, the dc link capacitor voltages can be balanced, and the output voltage and the dc link voltages can be regulated at desired values. The effectiveness of the capacitor voltage balancing control strategy is verified with the simulation and experimental results on a 500W/48V prototype.