A Power Decoupling Control Method for an Isolated Single-Phase AC-to-DC Converter Based on a Hign-Frequency Cycloconverter

Abstract

This paper proposes a new power decoupling method for a high-frequency cycloconverter which converts the single-phase line-frequency ac input to the high-frequency ac output directly. The cycloconverter consists of two half-bridge inverters, two input filter capacitors, and a series-resonant circuit. 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 ac input and a constant current 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 power decoupling method, and the viability is confirmed by using an experimental isolated ac-to-dc converter based on the high-frequency cycloconverter. As a result, the proposed power decoupling method effectively improved the displacement power factor in the line current to more than 0.99 and reduced the output voltage ripple to 4% without any electrolytic capacitor.