A Quad-Active-Bridge Series Resonant-Based Converter with Automatic Voltage-Balancing for Bipolar DC Grids

The conventional isolated bipolar DC-DC converters based on dual-active-bridge (DAB) and triple-active-bridge (TAB) structures required extra balancing inductor(s) or complex control algorithms to keep the output port voltages balanced. In addition, their transformer windings experience DC-offset current whenever they are fed with an unbalanced load or mismatch in the centre-tap transformer winding used for bipolar DAB. In this paper, a novel structure of quad-active-bridge (QAB) series-resonant-based converter (SRC) on input-parallel output-series (IPOS) configuration is proposed for bipolar DC grids with inherent voltage balancing features. The proposed structure eliminates the need for extra balancing inductors or complex control algorithms and addresses the problem of DC-offset current, which can be extended to modular IPOS DAB applications. The performance of the proposed converter is verified experimentally up to 2-kW.