In order to obtain the design capacity boundaries and optimal design results of the battery energy storage system（BESS） based on cascaded H-bridge converter（CHBC-BESS） integrated into a 35 kV grid

we firstly analyze the capacity boundaries within the restraints of capacity of power devices

battery system technology and safety design of BESS separately. The suppression of common-mode current is realized by changing the layout scheme of CHBC-BESS. Then

the optimization design method of the CHBC-BESS is proposed. The reliability of the system is calculated by the Markov chain reliability model. The efficiency and reliability of the system with different modules are comprehensively evaluated. The research results show that the maximum design capacity of CHBC-BESS is 32 MW under the existing technology. Changing the layout scheme of CHBC-BESS can reduce the loss and current stress caused by the common-mode current

protect the power devices

and reduce the influence of common-mode current on the optimal design of the number of modules. By the proposed optimization design method

the optimal number of modules can be obtained according to the design requirements of system in different applications. The research results can provide references for the design of ultra-large capacity CHBC-BESS and serve as a theoretical guidance to the compilation of planned maintenance.