A CHB grid⁃forming Energy Storage Control Strategy Considering SOC Balance in Unbalanced Grid

A cascaded H-bridge(CHB) grid⁃forming energy storage control strategy considering the state of charge (SOC) balance in unbalanced grid is presented. Utilizing voltage-type virtual synchronous generator (VSG) control enables grid-forming energy storage to address issues arising from the characteristics of renewable energy sources, such as low inertia and underdamping, which result in insufficient voltage support and lower power supply reliability. Establishing a mathematical model of the VSG, the synthesized three-phase voltage serves as the positive-sequence voltage command signal for the voltage-current loop. Addressing SOC issues present in VSG based on CHB in unbalanced grids, a SOC-balancing control method based on negative-sequence voltage closed-loop is proposed, with the injected negative-sequence voltage serving as the instruction signal. The stability of the VSG is assessed through root locus analysis, followed by the design of critical parameters. Finally, simulation analysis is conducted to validate the effectiveness of the proposed CHB grid⁃forming energy storage control strategy considering SOC-balancing in unbalanced grid.