98.3% Efficient Multiport System with Multi-Directional Power Flow to Integrate Battery Storage/Renewables with the Grid for EV Charging

This article proposes an efficient and optimized 3-φ unfolding-based grid-tied ac-dc multiport system for integrating battery storage or renewable energy sources with the grid for electric vehicle (EV) charging applications. Compared to conventional approaches, the proposed architecture reduces the number of power conversion stages and magnetic components, thereby enhancing power density and system efficiency. An unfolding-based grid interface is introduced to reduce switching losses through low-frequency operation and improve overall performance. A current injection circuit is employed to simplify interfacing with the Unfolder, enabling the implementation of a triple active bridge (TAB)-based dc-dc converter. The TAB tank circuit is optimized to minimize conduction losses and ensure zero-voltage switching across various power flow conditions, with the required tank inductance embedded into the leakage of a three-winding transformer. To support a wide voltage range for interfacing EV batteries, an LCL resonant tank is used for power transfer to the EV port. The analysis of power flow between different ports is presented, a control architecture is developed to autonomously manage power flow among them, and small-signal modeling of the system is derived. The proposed system is validated using a 5 kW, 480 V grid-tied SiC-based hardware prototype, achieving a peak ac-dc efficiency of 98.3% and maintaining above 97% efficiency across various operating conditions, power flow directions, and a battery voltage range of 200–800 V. The prototype also maintains a low grid current total harmonic distortion of 2%. Furthermore, a modular approach is demonstrated for the scalability of the multiport topology, with parallel dc-dc converter modules interfacing with a single gridtied Unfolder. Scalability is demonstrated through simulations at 50 kW and further validated in hardware at the 10 kW level, achieving a peak efficiency of 98.1%