For modular multilevel converter-based battery energy storage systems (MMC-BESS)

uneven power among batteries of SMs will be deduced by battery aging

battery fault

etc.

which will degrade performance and even lead to system failure. For maintaining the balance of capacitor voltage

this paper analyzes the limits of the uneven power of batteries

which are presented as the current limits in this paper. According to analysis

an analytical method is proposed that only the dc and fundamental frequency components of the arm current are used to calculate current limits. With the current limits it is able to evaluate the reasonability of power distribution among batteries. Meanwhile

increase of fundamental frequency component will enhance the current limits

and the dc component determines the size relationship between the absolute values of the upper and lower current limits. Finally

simulation model and experiment prototype are built for verifying the theoretical analysis and current limits calculation method

and satisfactory results are provided.