Four Quadrant Operation Control for Cascade H-Bridge Converter-Based Battery Energy Storage System

Exposure to battery microcycles under low power factor for cascaded H-bridge (CHB) converter-based battery energy storage system (BESS) increases additional charge throughput and may accelerate lithium-ion battery cycle-aging. Aiming to eliminating battery microcycles current and further extend operating range, this paper proposes a complete four-quadrant operation control strategy for CHB-based BESS to avoid detrimental effects on cells. First, the battery current components with LC filter are decomposed quantitatively and feasible range of avoiding microcycles under four-quadrant operation are obtained theoretically. By vector decomposition of closed-loop generated modulation phase voltage, the grid-side power factor is not unaffected and all submodules power factor are compensated without exceeding the microcycles boundary. Besides, unified modulation strategy considering eliminating microcycles and inner-phase state of charge (SOC) equalization is analyzed and the system control diagram is given. At last, a 35kV/12MW/24MWh BESS simulation model and a downscaled prototype system with four cascaded 25.6V-rated Lithium-battery modules are built for principal validation. The experimental results at two different low power factor cases verify the feasibility of the proposed control strategy.