Control of a battery-energy-storage system based on a cascaded H-Bridge converter under fault condition

Failure of power cells of cascaded H-Bridge power conversion system (PCS) often occurs. In order to maintain the normal operation of the system, failed H-Bridge power cells must be bypassed and certain control technique also should be adjusted accordingly. This paper applies the neutral shift technology to the control strategy for cascaded H-Bridge cell failure and deduces the zero-sequence voltage formula which is suitable for any number of failed H-Bridge cells conditions. The paper also proposes a solution to the problem that H-Bridge cells fail when state-of-charge (SOC) values of the battery units are not balance. The solution can balance output line-to-line voltage of the convertor as well as SOC values of the batteries. Then the paper builds the model of cascaded H-Bridge power conversion system in MATLAB/SIMULIK environment. Simulation results which verify the validity of the control scheme are presented in this paper.