Control of parallel connected Dual Active Bridge converters under unbalanced input voltages in an MV compliant Solid State Transformer

The modular solid-state transformer, based on a cascaded front end and an isolated back end, has become a popular choice for EV charging stations. The simplicity, scalability, and direct interconnection with medium voltage grids enable power engineers to adopt it based on the existing technology. A robust, grid-connected SST system must be able to ride-through abnormal grid conditions. During this scenario, the back-end, comprised of parallel connected Dual Active Bridge converters, may experience imbalances induced due to disturbance from the grid. This paper explores the operation of parallel connected DAB converters under unbalanced input conditions, emphasizing maintaining desired power sharing through all parallel connected DABs. Further, a feed-forward-based method is proposed to improve the transient response during the unbalanced input scenario.