Highly-Efficient Quasi-Resonant DC/AC Converter Using T-Type Half-Bridge

This article introduces a T-type half-bridge quasi-resonant dc/ac converter that reduces switching loss significantly over the entire range of grid voltage. The voltage fluctuation in the quasi-resonant T-type half-bridge cell is exploited to turn off the hard-switched components with nearly zero-voltage switching (ZVS) at high instantaneous power and with less than half of the input voltage at low instantaneous power. Little instantaneous reactive current flows through the circuit regardless of the grid voltage variation; this phenomenon facilitates ZVS for all switches in a T-type half-bridge cell. Turn-off of output diodes does not cause the reverse recovery problem. As a result, all active power components are softly switched. A prototype with 1-kW output power verified the superior characteristics of the proposed dc/ac converter.