A Novel Construction Method and Control Strategy of Modular Battery Energy Storage Systems Based on Improved Droop Control

The battery balancing technology based on modular converters needs to solve the problem of how to make many modular converters in series and parallel work together stably. In this article, according to the characteristics of modular battery energy storage systems, the application form of droop control is improved, and a battery unit with converter (BUC) is designed by combining battery, modular converter, and droop control. The properties of parallel BUCs and series BUCs are analyzed and redesigned to make them suitable for series–parallel expansion and the output current sharing control of the batteries. On this basis, a construction method of energy storage systems based on BUCs is proposed. In addition, a two-layer composite control strategy based on improved droop control is proposed, including the lower control strategy and the upper control strategy. Both simulation and physical experiments show that the proposed scheme can realize the constant voltage or constant current control of the total output of the energy storage system, and it can make the output current of each battery shared according to a given ratio with high control accuracy, and it can tolerate the communication failure of up to 2.5 s.