Three-port bi-directional converter for electric vehicles: focus on high-frequency coaxial transformer

A bi-directional multi-port converter can accommodate various energy storages and sources. Therefore, a multiport converter will be a good candidate for application as a future universal converter for (hybrid) electrical vehicles or local distribution systems. The main design challenge of the multiport converter analyzed in this paper is the design of its three-phase symmetrical transformer. In this converter symmetry of the leakage inductances is essential to ensure balanced three-phase currents (transferred power). These currents are interconnected by three-phase bridges which are linked together by a three-phase, three-port, transformer. To realize the equality of the leakage inductances a specific transformer design is necessary. Since conventionally wound three-phase transformer core shapes suitable for high-frequency are expensive and difficult to build, a coaxial wound transformer will be designed in this paper.