The global shift towards sustainable energy sources, together with rapid technological advancements, has driven a significant increase in the demand for electric vehicles (EVs) over recent years. This surge in EV adoption highlights the critical need for robust supporting infrastructure, particularly in the deployment of efficient and accessible EV chargers. Gallium Nitride (GaN) is a wide bandgap semiconductor material that offers better performance characteristics compared to traditional silicon-based components in medium-power and high-frequency application. Its higher electron mobility, saturation electron velocity and breakdown electric field make GaN an ideal candidate for high-frequency power conversion applications in EV chargers. To explore the potential of GaN technology in EV charging applications, an 11kW GaN based isolated bidirectional multi-port EV charger with a two-stage architecture has been designed to interconnect bipolar DC grid and electric vehicles. The two stages of the charger consist of a three-level triple active bridge converter and a three-level interleaved buck converter. The TAB converter is an extension of conventional dual active bridge (DAB) converter, offering capability to direct power transmission among three ports. However, the addition of a third port introduces complexity in managing power flow. The TAB converter can operate under various modulation schemes, including three-level and five-level modulation. An analysis of the switching modes associated with each modulation scheme has been
erformed. In order or derive the soft switching range of the converter, the current expression
of series inductors of each port are derived based on generalized-harmonic approximation method and equivalent circuit models. A detailed analysis of the commutation process during critical switching transitions has been conducted, leading to the derivation of the soft
witching criteria for both three-level and five-level operations of the TAB converter. To validate the design and verify the soft switching range, simulations have been carried out. Moreover, the prototype of the 11 kW multi-port EV charger is designed based on calculation and simulation results. The prototype employs a top-side cooled GaN high-electron-mobility transistor (HEMT) to enhance thermal dissipation. Testing of the prototype indicates that the converter can transmit 1.2 kW from the primary to the secondary side at the rated voltage
of 700 V.