Capacitive-Link Universal Converters with Low Voltage Stress and High Switching Frequency

Abstract

Capacitive-link universal converters are a relatively new class of single-stage power converters that can transfer power from any type of source (dc, single-phase ac, or three-phase ac) to any type of load. These converters offer numerous advantages including high reliability, due to using small film capacitors instead of electrolytic capacitors, high power density, due to possibility of using integrated high frequency transformers instead of bulky low frequency transformers when isolation is needed, and high efficiency, due to possibility of having zero current turn-on and turn-off for all switches. The main drawbacks of the capacitive-link universal converters are high voltage stress across the switches as well as limited range of switching frequency at low power levels. In this paper, a novel technique is proposed for addressing these two limitations. The proposed method allows the link voltage, which varies between 0 and a peak value in conventional control approach of these converters, to have a flexible non-zero minimum voltage. This flexible minimum voltage acts as an additional degree of freedom for design and control of this converter, and allows minimizing the voltage stress of the switches and increasing the switching frequency at low power levels. The effectiveness of the proposed method is verified through simulation and experiments in this paper.