摘要
A battery energy storage system using modular multilevel converter(MMC)as the interfacing converter could have several inherent advantages when compared with battery energy storage systems based on two-level inverter or cascaded H-bridge converter.It can manage the state-of-charges(SOCs)of all batteries to be equal to avoid the overcharge or over discharge of single battery.The inherent power exchange characteristics using circulating currents could increase the control flexibility and consequently improve the output quality and the internal regulation capability.This paper investigates the operational principle and control strategy of MMC battery energy storage system under unbalanced grid voltage condition,where key issues of system model and corresponding control methods are very different from those under the normal grid voltage condition.The injected de current control,SOC balancing control and circulating current control methods are fully discussed in this paper.Finally,the theoretical findings were verified through Matlab simulation and a scaled down experimental prototype.
