Seven-Level Cascaded H-Bridge Inverter and Fault-Tolerant Control Strategy

Due to modularity structure, voltage balancing, reliability and lower stresses on switching devices, cascaded H-bridge (CHB) multilevel topology is a good choice for high-power medium-voltage applications. Therefore, phase- and level-shifted PWM scheme based seven-level CHB inverter is presented in this paper. In-phase disposition (IPD) multicarrier technique is used for level-shifted PWM as it provides the best harmonic profile in compared to other techniques. In addition to that fundamental output voltage phase shift compensation based fault-tolerant control strategy is presented which maintains the balanced three-phase currents during faulty conditions. Simulation for seven-level CHB inverter and fault-tolerant control topology is carried out extensively in MATLAB/Simulink software. It is found that although having different device switching frequency, the total harmonic distortion (THD) of the inverter output line-to-line voltage is better with IPD level-shifted in compared to phase-shifted PWM schemes.