Multilevel Switched Capacitor LLC-DCX Converter With Embedded Filter

Abstract

A multilevel switched capacitor LLC-DC transformer (LLC-DCX) converter with an embedded filter is presented for a power module of solid-state transformers. The proposed converter is a hybrid converter composed of resonant switched capacitor converters (RSCCs) and a previously reported ripple-cancel converter. In contrast to the conventional SCC, which faces the issue of an inrush hard-charging current during switching transition, the proposed converter can be implemented using a soft-charging operation without additional inductors. Further, it inherits the advantages of the two converters, including load-independent soft switching, automatic voltage sharing, automatic current sharing, reduction of the current ripple, an embedded filter function, constant voltage gain, and flexible extensibility. This paper comprehensively analyzes these characteristics and the conditions for soft-charging operation. The design theory based on the analysis is also presented. We fabricated a prototype of the proposed converter with input and output voltages of 900 V and 150 V, respectively and the rated output power of 2 kW to demonstrate the validity of the analysis and design.