Multiport converters for fast chargers of electrical vehicles - Focus on high-frequency coaxial transformers

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. For the multiport converter proposed in this paper, the main design challenge 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 single-phase high-frequency link transformers. 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 coaxially wound transformer will be designed in this paper.