Optimal design of multilevel modular switched-capacitor dc-dc converter

Abstract

Magnetic-less multilevel dc-dc converter attracts much attention in automotive application due to its small size and high temperature operation features. Multilevel modular switched-capacitor dc-dc converter (MMSCC) is one of the most promising topologies among them with simple control and reduced switch current stress. This paper presents an optimal design method for MMSCC to achieve the highest efficiency with smallest size. In order to design the converter with the highest efficiency, the analytical power loss equation of MMSCC should be derived. By considering the stray inductance existing in the circuit, the optimal design point should be considered in two cases, over-damped and under-damped. The converter can be designed to achieve the highest efficiency in both cases. However, in under-damped case, small size multilayer ceramic capacitor can be utilized due to the low capacitance requirement. Although higher switching frequency is required in under-damped case due to practical considerations, zero current switching (ZCS) can be achieved for all the devices. Therefore, the optimal design point of MMSCC with the smallest size and the highest efficiency should be chosen at under-damped case with ZCS. Experimental results of designing MMSCC at under-damped case with ZCS are provided to demonstrate the validity of the proposed method.