Hybrid Sorting Strategy for Modular Multilevel Converters With Partially Integrated 2^nd Life Battery Energy Storage Systems for fast EV charging

Electric vehicles charging stations requires significant amounts of power from the utility grid leading to a continuous expansion and modernization of its power flow capacity. However this can be alleviated with battery energy storage systems by injecting power at the hours of peak consumption. This work proposes a control strategy for parallelized Modular Multilevel Converter (M2C) with partially rated storage system that allows dc fast charging with power sharing between batteries and the grid. The proposed control allows M2C to operate with any amount of Dummy-SMs, which are SMs with floating capacitors in their DC-link without battery energy storage unit. Consequently, the converter can operate under batteries faults, or different power references, facilitating the integration of 2nd life batteries to BESS-SMs with different degradation levels. The intra-power balance and the control of the capacitors voltage of Dummy-SMs, is achieved through an hybrid sorting of carriers made in the modulation stage, where LS-PMW is used. As a result, the proposed control strategy allows the flexible operation of the M2C regardless of the availability of battery energy storage and Dummy-SMs among the clusters.