Virtually Isolated Class E Converter with Coupled Capacitors

This paper proposes a notion of virtual isolation that uses capacitors instead of transformers. Unlikely in the magnetically isolated converter, capacitors create an electrical path connecting the primary and secondary sides. Consequentially, touch currents and electromagnetic interferences (EMIs) are generated by the common-mode current through the path. In this paper, virtual isolation is defined as satisfying touch current and EMI regulations, just as electrical isolation does, despite its electrical path. With the virtual isolation, high power density is achieved by replacing a transformer with a capacitor while ensuring human safety. Since the grid frequency component of the common-mode current is related to the touch current and the switching frequency component is responsible for the conducted EMI, the grid and switching frequency bands are analyzed separately. The maximum capacitance allowed in the grid frequency range is calculated to meet the touch current regulation. Also, a high-frequency balanced class E converter with an LC series network is proposed to reduce the common-mode current in the switching frequency band. The experimental results from a 40W converter prototype confirm the effectiveness of the proposed design.