Parallel Capacitive-Link Universal Converters With Low Current Stress and High Efficiency

Series capacitive-link universal converters are a relatively new class of single-stage power converters that offer numerous advantages including high reliability, high power density, and high efficiency. However, one of the limitations of these converters is high current stress of the switches, which lowers their efficiency especially in high current applications. In this article, a new class of soft-/hard-switched parallel capacitive-link converters is introduced to address this limitation of the series capacitive-link universal converter while keeping its advantages. Apart from providing bidirectional power transfer, the proposed ac–ac converter can implement voltage stepping up/down as well as frequency transformation. A small film capacitor, which is placed in parallel with the input and output switch bridges, is responsible for transferring the power from input towards output. A small inductor can be placed in series with the link capacitor to realize zero-current-switching for all the switches under any load conditions, which lowers the switching losses and reduces electromagnetic interference (EMI). The proposed parallel capacitive-link converter is expected to offer an enhanced efficiency and reduced current stress compared to the series capacitive-link universal converters. In this article, principles of the operation of the proposed converter are presented, and its performance and advantages are verified by simulation and experiment.