State-of-charge balancing control strategy for battery energy storage systems based on a modern cascaded multilevel PWM converter

According to the development of the electric energy storage systems, found that the battery energy storage systems have become a very important factor in the process of system stability and optimal operation. Modern multilevel converters, namely cascaded H-bridge multilevel pulse width modulation (CHBM-PWM) converters have been attracting the attention of researchers in the world, in addition to the development for the industry in the modern decade for medium voltage/high power applications. A 14.14kV, 1MW, 1000Ah system combine a three-phase CHBM-PWM converter with forty-five Li (Lithium)-ion battery units is designed in this paper. The designed system can directly connect to medium/high voltage bus without transformer and realize better output harmonics performance under lower switching frequency. The whole control system is composed of state-of-charge (SOC) balancing control and active power control. First one is necessary for efficient utilization of battery energy to manage the percentage of SOC to avoid the excessive charging and discharging while the second is required for producing a balanced three phase voltage. Controller efficiency is verified by using MATLAB/SIMULINK to present results.