Power decoupling control method for an isolated single-phase ac-to-dc converter based on high-frequency cycloconverter topology

This paper proposes a new power decoupling method for a high-frequency cycloconverter. The cycloconverter consists of two half-bridge inverters, two input filter capacitors, and a series-resonant circuit, which enables to convert the single-phase line-frequency ac input to the high-frequency ac output directly. The proposed power decoupling method stores the input power ripple at double the line frequency in the filter capacitors. Therefore, the proposed method achieves a unity power factor in the ac input and a constant amplitude in the high-frequency output without any additional switching device or energy storage element. This paper theoretically discusses the principle and operating performance of the proposed method and confirms the effectiveness of the proposed method in experiments using an isolated ac-to-dc converter based on the high-frequency cycloconverter. As a result, the proposed power decoupling method effectively improved the displacement factor of the ac-input current to more than 0.99 and reduced the voltage ripple in the dc output to 7%.