Control Method of Quad-Active-Bridge Converter for Unipolar-to-Bipolar DC/DC Conversion Systems

This paper proposes a control method for a Quad-Active-Bridge (QAB) converter applied in Unipolar-to-Bipolar DC/DC conversion systems. This converter facilitates isolated and bidirectional power transfer through a single-core four-winding transformer. Aiming to address voltage imbalance and load asymmetry, an energy-based PI control method is used to regulate each port voltage. Power references are mapped to phase shifts using a derived power transfer matrix. Simulations and experiments are conducted on an 80 kW QAB converter prototype under steady and dynamic load conditions to verify the accuracy of the proposed method. Results confirm stable voltage control, proper power distribution, and robustness to mismatches in inductance and capacitance between designed and measured values.