Optimal Control Method and Design for Modular Battery Energy Storage System Based on Partial Power Conversion

This article addresses a bidirectional low power loss series-parallel partial-power modular converter (SPPC) suitable for series-connected high voltage large power battery energy storage system (BESS). A specific capacitor is placed on the top of the series battery packs, which voltage can be adjusted by the SPPC to compensate for the voltage fluctuation of the battery packs and the DC power line. The power loss and cost of the SPPC are relatively low since its rated power is reduced to about 22%–48% of the full-power converter. A 3 level distributed control method is proposed to achieve the fast transient response of the DC power line current and deal with the series inconsistency of battery packs during discharging and charging, further improving the total energy utilization efficiency (EUE) of the BESS. The critical design considerations for SPPC-BESS are analyzed. A bidirectional 800W phase-shift full-bridge (PSFB) converter hardware prototype along with the Gallium Nitride (GaN) devices is provided to verify the high efficiency of DC-DC sub-module. Then a simulation model of a 6.6kW SPPC-BESS with 3 sub-modules to verify the feasibility of the control method. Theoretical analysis proves that the total power loss of the SPPC is lower than the existing types of modular converters. The EUE of the SPPC-BESS is 1.7% higher than the conventional BESS when the average maximum available capacities of batteries attenuate to 80% of the initial maximum available capacity.