Integrated Electronic Capacitors-Based Split BES-Assisted Modular Multiport Power Electronic Transformer for Fast EV Charging Station

A multiport power electronic transformer based on cascaded H-bridge (CHB) converter with split battery energy storage (BES) units is a viable solution for fast electric vehicle (EV) charging station, eliminating the need for line-frequency transformers and reducing the influence of charging station on distribution grid. In the absence of bulky CHB module capacitors or
LC
secondary resonant filters in CHB converter, second-order frequency power ripple impacts the controllability of the overall system, and the lifetime of BES units as well as EV batteries. In state-of-the-art, electronic capacitor (EC) is employed in single-phase PFC converters to deal with 2
${\text{nd}}$
ripple issue, however, its implementation in CHB converters leads to increased switch requirements and losses. Therefore, this work introduces an integrated EC (IEC)-based isolated dc–dc converter for each conversion-chain, to reduce the CHB module capacitance requirement without using extra switches. Derived from a buck-based EC and isolated dc–dc converter, IEC diverts second-order frequency power ripple into decoupling storage capacitance, while maintaining the desired output power. In addition, in off-grid mode, where split BES's supply power to EV batteries, the IEC functions as a bidirectional isolated dc–dc converter. Moreover, the principle of operation of all modes, zero-voltage switching conditions in grid-connected mode, and associated functions are also discussed in this article. Proof-of-concept of IEC-based fast EV charging station is verified with simulation results. Finally, hardware results are provided using a developed downscaled single-conversion chain prototype of IEC.