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 article 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 innerphase state of charge equalization is analyzed and the system control diagram is given. At last, a 35 kV/12 MW/24 MWh BESS simulation model and a downscaled prototype system with four cascaded 25.6 V-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.