Design of a Three-winding Transformer for Power Decoupling of a Three-port Series Resonant Converter for an Integrated On-board EV Charger

Integrated on-board charger (IOBC) provides simultaneous charging to the traction high-voltage battery and the auxiliary low-voltage battery of an electric vehicle. Owing to the advantages of electrical isolation and an efficient single-stage power conversion, three-port series resonant converter (TPSRC) has become a potential candidate for IOBC. However, due to the finite leakage inductance in the three-winding transformer used in TPSRC, the power flow in different ports are found closely coupled with each other, which affects both the charging current and the high-frequency link current. In the literature, power decoupling is achieved either by complex control system design or by using a capacitor. A transformer design is proposed in this article, which can decouple the power flow to the different ports without using any extra capacitor. It also simplifies the control system design for a TPSRC. In the proposed design, first the analytical expressions of the three terminal leakage inductances of the proposed three-winding transformer are derived. Then the suitable winding arrangements and the winding spacing are determined to achieve a zero terminal leakage inductance responsible for decoupled power flow. A hardware prototype of the proposed three-winding transformer is developed, and the power decoupling is verified in a 2.3kW TPSRC circuit.