Improved capacitance ratio optimization methodology for stacked switched capacitor energy buffers

The recently proposed stacked switched capacitor (SSC) energy buffers with film or ceramic capacitors can increase the lifetime of single-phase ac/dc converters by eliminating the relatively short lifetime electrolytic capacitors used for twice-line-frequency energy buffering. This paper presents an improved methodology to minimize the passive volume of SSC energy buffers by optimally selecting their capacitance ratios while taking into account the variation in capacitor energy density with voltage rating. The proposed methodology is compared with the state-of-the-art approach for both unipolar and bipolar SSC energy buffers. It is shown that for designs with 10% voltage ripple, it reduces the passive volume by up to 43% depending on the capacitor technology and type of SSC energy buffer. The effectiveness of the proposed optimization methodology is validated using a prototype SSC energy buffer designed for an 8-W offline LED driver.