Energy density enhancement of unipolar SSC energy buffers through capacitance ratio optimization

The recently proposed Stacked Switched Capacitor (SSC) energy buffer architecture with film or ceramic capacitors can increase the life of single-phase ac-dc converters by eliminating electrolytic capacitors needed for twice-line-frequency energy storage, while maintaining comparable energy density. This paper presents a methodology for further increasing the energy density of enhanced unipolar SSC energy buffers by optimizing the capacitance ratio of the capacitors used in the energy buffer. It is shown that the relative enhancement in energy density depends on the required ripple ratio and the number of supporting capacitors in the energy buffer. The presented methodology is validated using a 1-2 enhanced unipolar SSC energy buffer designed for an 8-W offline LED driver.