The battery energy storage system based on cascaded H-bridge converter is widely used in medium-voltage grid to solve the power quality problems caused by the connection between the renewable energy and power grid. The issues of converter reliability are critical due to the large number of power switching devices used in cascaded H-bridge converter. Therefore

we put forward a fault-tolerant control method for common single switch open-circuit fault. This method can be adopted to prevent the faulty H-bridge module from quitting operation

and the full-bridge mode can be seamlessly switched to the fault-tolerant mode and half output of the rated AC voltage is realized. In addition

in order to achieve the state-of-charge balance of the battery units in all H-bridge modules after the fault

a four-layer system control method based on proposed fault-tolerant control method which consists of total power control

fault-tolerant control

inter-phase power balance control and inner-phase power balance control is proposed. A simulation model is built on MATLAB/Simulink software and the feasibility and effectiveness of the proposed control method are verified.