Design and control of a modular two-stage SST- based bidirectional EV charger

• A new topological architecture incorporating isolated SEPIC converter for SST-based two-stage EV charger is proposed. • The charger features uncomplicated and independent controllers for both the input and output stages, which enhances its modularity and reliability. • The state space and averaged small signal models of the converters are established, and the controllers are designed based on these models to bolster stability. • The average power factor of the source and the total harmonic distortion of the source current are recorded at 0.9995 and 2.84 %, respectively, with an overall efficiency of 92.75 %, demonstrating the effectiveness of the adopted control mechanisms. • Power loss analysis is carried out with Simscape model and the power dissipation of individual components is presented. Currently, modular Solid-State Transformer (SST)-based electric vehicle (EV) charging stations are becoming increasingly popular, primarily because they operate without line frequency transformers (LFTs) for the conversion of grid voltage to low voltage AC output. The advanced controllability associated with SST technology enhances the flexibility of EV charging systems in relation to the power grid, enabling efficient synchronization between EV batteries and renewable energy sources to facilitate quicker charging. This paper discusses the design and control strategy of a modular two-stage SST-based bidirectional EV charging system intended for medium power EV charging applications. For the front-end rectification, the Totem-pole PFC (TPLPFC) topology has been adopted, followed by an isolated SEPIC (iSEPIC) converter in the output stage. The rationale behind the selection of these topologies for the Solid-State Transformer (SST) lies in their ability to minimize device count, provide a simple structural design, and allow for straightforward control, all without sacrificing performance. Small signal transfer functions are derived, and controllers are designed accordingly. The performance of the proposed charger is confirmed through simulation, and a subsequent power loss analysis is performed, with the findings presented. A relative comparison of the proposed charger with those suggested in literature is also presented to highlight the benefits of the proposed configuration.