A Novel Solid-State Transformers Structure With a Single Galvanic Isolation Stage for Multi-Outlet EV Fast Charging Stations

Solid-state transformers (SSTs) have emerged as a promising alternative to bulky line-frequency transformers, providing electrical isolation between medium-voltage grids and low-voltage systems with enhanced controllability and compactness. However, efficiency and cost limitations hinder their large-scale adoption. SSTs are particularly advantageous for DC load applications such as electric vehicle (EV) fast charging stations (FCS). According to the standard IEC-61851, multi-outlet charging stations are required to ensure galvanic isolation between each EV. Consequently, existing SST-based FCS architectures typically adopt a two-stage conversion system, where additional isolated DC-DC converters are installed after the common DC bus, resulting in increased system cost and power losses. This paper proposes a novel SST topology that eliminates the need for these extra DC/DC converters, enabling a more compact and cost-effective architecture for multi-outlet EV FCS. Furthermore, the proposed topology can also address the power imbalance issue inherent in single-stage multi-outlet SSTs, which achieves a balancing capability far beyond the limit of control methods alone. The proposed topology is thoroughly analyzed in terms of its modulation schemes and operational strategies, and its voltage balancing capability is mathematically validated. An experimental 150 V / 1.5 kW prototype is developed to validate the feasibility and performance of the proposed system, including its power balancing capability and total efficiency.