Utility AC interfaced soft-switching sinewave PWM power conditioner with two-switch flyback high-frequency transformer

High-frequency switching pulse modulation utility-interfaced power conditioners (HF-UPC) with a high-frequency transformer link have attracted special interest for renewable and sustainable energy utilisation. These conditioners are small and cost-effective for meeting the requirements of small-scale residential power applications. However, switching power losses due to high-frequency switching operations are unavoidable. Efforts to reduce the power losses by implementing additional snubber components can complicate the controlling methods of the system. To solve these problems, a flyback transformer linked HF-UPC is proposed. The high-frequency flyback transformer is introduced into the power conditioner system instead of the typical forward transformer to simplify the circuit configuration and related controlling methods. With the aid of the resonant snubber circuits, the high-frequency switching devices in the primary side of the proposed DC-to-AC power conditioner can be turned off with zero-voltage soft-switching (ZVS). In addition, the proposed power conditioner system takes advantage of operating the currents by the discontinuous conduction mode (DCM) to realise turn-on commutation of zero-current soft-switching schemes. The output ports of the HF-UPC treated here are directly connected to the utility grid single-phase AC power source. A prototype of the proposed soft-commutation HF-UPC has been built and tested in experiments. Its power conversion processing is verified and its output current is qualified in accordance with the guidelines of the power utility companies.