Highly Efficient Single Power-Conversion Resonant DC/AC Converter Without Output Filter

This article introduces the single power-conversion resonant dc/ac converter, which eliminates the requirement for an output filter. Use of a resonant neutral-point-clamped cell allows nearly zero-voltage-switching turn-off of the primary-side outer switches at high instantaneous power, and close to half of the input voltage at low instantaneous power. Through the use of split transformer and semibridgeless structure with the secondary-side duty-ratio fixed at 0.5, the converter ensures a ripple-free output current, negating the need for an additional output filter. Notably, this topology also circumvents magnetizing current flow through the external resonant inductor, thereby, reducing the core size of the resonant inductor. In addition, the design facilitates zero current switching turn-off at the primary-side inner switches and effectively prevents any reverse recovery problem with the primary-side diodes. To validate the proposed concept, a 1-kW rated prototype capable of converting 400-V input to a 220-V_rms grid voltage was constructed and experimentally tested.