Unregulated interface converter based on cascaded switched capacitor converters for supercapacitors in alternative battery applications

Although supercapacitors (SCs) offer many advantages over traditional secondary batteries, they have two major drawbacks-low specific energy and large voltage variations due to cycling. For SCs to be used as alternatives to batteries, a high efficiency power converter that can operate in a wide voltage range is required to maximize the use of the stored energies of SCs. In this paper, we propose an unregulated interface converter using cascaded switched capacitor converters (SCCs) with selectable intermediate taps for SCs in alternative battery applications. The interface converter realizes high efficiency power conversion using the cascaded SCCs, and its voltage conversion ratio is roughly regulated by selectable intermediate taps. Its operation principle and design guidelines are presented in detail. An SC module with a rated charge voltage of 60 V was cycled with a 150 W prototype whose measured peak power conversion efficiency was greater than 95%. The SC module was cycled deeply in the range of 24-60 V while the load/charger voltage was maintained between 24-33.6 V.