Three-Level SOC Equalization Control Strategy for MMC-BESS Based on Feedforward Sliding Window Integral Method

The modular multilevel converter of the battery energy storage system (MMC-BESS) not only is suitable for large-scale and dispatching AC DC grids, but also has a strong ability to suppress power fluctuations caused by new output or grid failures. When an asymmetric voltage sudden change in load occurs grid, order compensate difference between sides, submodule MMC-BESS will have large unbalanced charging discharging current, destroying equalization state SOC seriously affecting capacity utilization service life. In deal with above problems, this paper, characteristics phase unit upper lower bridge arms are analyzed. It found that when considering fluctuation capacitor voltage, fundamental frequency circulating current component, component. Therefore, three-level correction control strategy proposed based on interphase, arms, submodules, feedforward sliding window integral method introduced into layer so as achieve purpose more balanced accurate distribution among phases each phase. simulation results show effective compensation there grid. Under working conditions three-phase can quickly reach equalization, total harmonic content 1.38%, unbalance degree 2.4%. same operating conditions, compared traditional optimal one-third average method, paper smaller rate, distortion current. And faster convergence speed.