Evaluation of a modular system topology for large-scale wireless EV charging in a commercial parking facility

This paper evaluates the operation of a modular transformer-less grid interface topology for large-scale wireless charging of electric vehicles (EVs) under a loading scenario for a commercial parking facility. The studied configuration is based on a Modular Multilevel Converter (MMC) topology where each module is supplying the wireless EV charger installed in one parking spot of a largescale charging infrastructure. Thus, the load distribution within this MMC-based topology depends on the location and charging demand of each EV. Furthermore, unbalanced loading imposes the need for introducing circulating currents to maintain stable operation of the topology. The additional losses caused by the circulating currents needed for load balancing are assessed for a realistic loading scenario during one day in a commercial parking facility. The presented numerical analysis identifies the impact on the conduction losses from an algorithm used to optimize the circulating current references. The resulting conduction losses are compared to an idealized case without need for balancing and to the continuous operation with constant circulating current corresponding to the worst-case load unbalance. Furthermore, the presented results identify the effect of the rated charging power on the loading scenario. The results show how operation with very low and unbalanced loading is causing high relative conduction losses. Thus, the studied MMC-based topology can be most effectively utilized in locations with a high average occupancy of the charging units or if active scheduling of the EV charging is introduced.
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