A DC-Link Capacitor Voltage Balancer Integrated into LLC-based Auxiliary Power Supply

Capacitor voltage balancing circuits are required for applications using series capacitor to provide high dc-link voltage. This paper propose a new dc-link capacitor voltage balancer integrated into the LLC auxiliary power supply. Only small balancing inductors are added which are connected between the middle points of adjacent capacitors and half-bridge legs in the LLC auxiliary converter. Taking advantages of the 50 % duty cycle operation, the capacitor voltage can be automatically balanced without extra control, thus reducing the system complexity and cost and improving the overall system efficiency.

I. Introduction

In power converters, low voltage rating electrolytic capacitors are usually put in series to withstand high dc-link voltage. With up to ±20% capacitance tolerance and different leakage currents, the capacitor voltages can be significantly unbalanced if no balancing method is applied.