High frequency AC microgrid based on a highly reliable single-stage converter

In this paper, a highly reliable microgrid formed by a single-stage high frequency ac (HFAC) link converter is proposed. This single-stage hybrid converter introduces several advantages over conventional hybrid converters that are commonly used in microgrids. The proposed converter is capable of interfacing any number of sources and loads with any forms/number of phases/ frequencies/voltage levels. Galvanic isolation in the proposed microgrid can be provided by adding a single-phase high frequency ac transformer. In this converter, soft-switching can be realized by a small modification in the configuration. Accordingly, the zero-voltage turn-on and soft turn-off of the switches result in negligible switching losses and minimum voltage stress on the switches. The proposed microgrid has a fast response due to the high frequency of the operation. The other major advantage of the proposed hybrid system is that no bulky electrolytic capacitor is needed at the link to decouple different converters. In a dc microgrid or even in a low frequency ac (LFAC) microgrid, several converters are cascaded, and large electrolytic capacitors are required for decoupling different power converters. Electrolytic capacitors are the most unreliable components in a power converter and are responsible for most of the failures, particularly at high temperature. Thus, eliminating the dc electrolytic capacitors will significantly increase the reliability of the microgrid. One limiting factor in adopting the HFAC microgrid is that the voltage drop and losses are increased by increasing the frequency; thus, this system is more suitable when sources and loads are relatively close. This paper evaluates the performance of the proposed microgrid.