Parallel connected triple-active-bridge converters with current and voltage balancing coupled inductor for bipolar DC distribution

Bipolar dc distribution system is an attractive alternative to replace the conventional ac distribution system; however, it suffers from voltage and current unbalances. In parallel-connected triple-active-bridge (TAB) converters that form a bipolar dc distribution system, the current unbalance between each TAB module and the voltage unbalance between each load are the main issues that make controlling the system difficult. These unbalances occur due to the inevitable mismatch of gate signals and circuit parameters, despite having the same circuit components. A four-winding coupled inductor is proposed in this paper to handle these issues. The coupled inductor is formed by the magnetic integration of the inductors, which are present in TAB converters. Inductors in the same TAB module are directly coupled and the two directly coupled inductors are integrated again in the inverse direction. The proposed coupled inductor automatically balances the currents in each module and the voltages of each load under unbalanced conditions. Moreover, the proposed balancing scheme does not require additional control method or balancer circuit. The performance of the proposed coupled inductor was verified with a 10-kW prototype.