battery energy storage system (bess), star structure, triangular structure, modular multilevel structure, Applications of electric power, TK4001-4102, Production of electric energy or power. Powerplants. Central stations, TK1001-1841, Science

With the increasing proportion of new energy in the total installed capacity, the capacity and scale of battery storage power stations are expanding. The improvement of unit capacity of battery energy storage system (BESS) has important engineering practical significance. To explore the BESS topology with more advantages in the face of the development trend of large capacity and large-scale battery storage power stations, the paper first analysed the problems of the traditional centralized BESS and the reasons why the voltage level and capacity of the single machine are limited. Then, the single unit capacity of three kinds of high voltage transformerless BESS was analysed through calculation, i.e. the star structure, triangle structure and modular multilevel structure. After that, the star structure was taken as an example to carry out a detailed study. The topological structure and mathematical model of star structure were introduced, and the basic control strategies of high voltage transformerless BESS were analysed, including the power control at the grid side and state of charge equalization control. The effectiveness of the control strategies was verified by 35 kV/10 MW simulation model. The research results show that the high voltage transformerless BESS has obvious advantages in single machine capacity and capacity expansion, and is more suitable for high-voltage, high-capacity applications.