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

Electric vehicles charging stations requires huge amounts of power from the grid, what can be alleviated with battery energy storage systems. Two-Level converter is the preferred topology for commercial BESS, but this topology do not offer modularity for the energy storage stage. This work proposes a parallelized Modular Multilevel Converter with partially rated storage systems with an overall control scheme that governs independently the active power reference of each BESS-SMs. The proposed control allows the operation with any amount of Dummy-SMs, which are SMs with floating capacitors in their DC-link without battery energy storage unit. This feature allows the converter to keep operating under batteries faults or disconnection, 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. This hybrid control strategy, allows the converter to operate each of its SMs as BESS or Dummy, depending of the connection or disconnection of its BESS.