Switched Capacitor Energy Buffer Architecture

Problem: Power conversion systems that interface between dc and single-phase ac need energy storage to provide buffering between the constant power desired by a dc source or load and the continuously varying power desired for a single-phase ac system. While electrolytic capacitors are generally used to provide high-density energy storage for buffering, their limited-life and reliability are a concern. Film capacitors have much longer life and higher reliability, but an order of magnitude lower peak energy density. Therefore, for long-life and compact grid-interface systems there is a strong interest in developing energy buffers based on film capacitors that provide effective energy density comparable to electrolytic capacitors. Technology: This patent describes the Stacked Switched Capacitor (SSC) energy buffer, which is composed of two series connected blocks of switches and capacitors. It works on the principle that while the voltages of individual capacitors can vary over a wide range, the voltage at the buffer port remains constrained to a desired narrow range. By using long-life capacitors that can be efficiently charged and discharged over a wide voltage range (e.g., film capacitors) it achieves effective energy densities comparable to electrolytic capacitors and much longer life. Christopher Noble crn@mit.edu