Bidirectional Series Resonant DC/AC Converter for Energy Storage Systems

This paper presents a novel bidirectional series resonant converter for energy storage systems (ESS). Conversion between a dc energy storage device and an ac grid has grown in importance because of the renewable energy generators and ESS used in microgrids, which usually use batteries or supercapacitors as storage devices in order to provide different services and improve the quality and reliability of the grid. This novel converter avoids the need to have two converting stages: one for converting the energy from the storage device to a regulated dc value, and the other for converting the regulated dc to the ac output. Conversion occurs via a modified dc/dc dual-bridge series resonant converter. The output bridge of the converter is attached to the input bridge through a resonant branch and a high frequency (HF) transformer, and it is also attached to the ac link through an output filter. Therefore, two ac power signals are mixed in the output bridge: a HF signal, which maintains the dc link capacitor voltage, and a low frequency power signal, which transfers energy to the grid. This paper details the different working modes of the converter and presents a 3000 W prototype that validates the design.