Energy Density Enhancement of Stacked Switched Capacitor Energy Buffers Through Capacitance Ratio Optimization

Abstract

The recently proposed stacked switched capacitor (SSC) energy buffer architecture can extend the lifetime of single-phase ac-dc converters by replacing the electrolytic capacitors needed for twice-line-frequency energy storage with film or ceramic capacitors, while maintaining comparable effective energy density. This paper presents a methodology for further increasing the effective energy density of SSC energy buffers by optimizing the capacitance ratios of the capacitors used in the energy buffer. It is systematically shown that the relative enhancement in effective energy density depends on the required ripple ratio and the number of backbone and supporting capacitors in the energy buffer. The proposed approach can substantially increase the effective energy density of the energy buffer. For example, the effective energy density of a 1-10 enhanced unipolar SSC energy buffer, designed for a 10% ripple ratio, can be increased by 100% as a result of this capacitance ratio optimization. The presented methodology is validated using a 1-2 enhanced unipolar SSC energy buffer designed for an 8-W offline LED driver.