A single-phase high-frequency transformer isolated buck converter with both in-phase and out-of-phase operations

Traditional non-isolated ac-ac converters require an external bulky line frequency transformer for electrical isolation and safety, for applications such as dynamic voltage restorers (DVRs) etc. This line frequency transformer has some demerits such as; high cost, large size, relatively high losses, saturation and start up inrush current. To overcome this drawback, an isolated buck type ac-ac converter is proposed with high frequency transformer isolation. The high frequency transformer incorporated in proposed converter provides the necessary isolation and safety with high power density, as it eliminates the need for external bulky line frequency transformer. In addition, the proposed converter can produce both in-phase and out-of-phase ac output voltage, and therefore, it can compensate both voltage sags and swells when used as DVR. Moreover, the proposed converter can also be used to rectify the input ac voltage and can also provide output voltage with step-changed frequency similar to single-phase matrix converter. The PWM switching strategies for in-phase and out-of-phase operations and circuit analysis are also given, followed by the experimental results.