Symmetric Cascaded H-Bridge Multilevel Inverter With Enhanced Multi-Phase Fault Tolerant Capability

In this article, a new method is introduced for operation of three-phase symmetric cascaded H-bridge (CHB) multilevel inverter after failure of power switches. When a switch fails, the faulty leg of the H-bridge is bypassed and the remaining leg is kept in use. Even with multiple faults in different H-bridge cells, the CHB is optimally reconfigured to continue its operation with its maximum healthy capacity. Based on the remaining operational part of the converter, a fault tolerant control scheme with zero-sequence voltage injection is proposed to synthesize a balanced line-to-line voltage. Using this method, the postfault line-to-line voltage of CHB is maximized with the minimum common mode voltage (CMV). Reduction of CMV is of importance in motor drive application. Also, fundamental component of CMV affects the real power of CHB phase legs. Through reducing the fundamental CMV, unidirectional power transfer from the dc side to the ac load is achieved in a wide operation region. The performance of the presented fault tolerant technique is verified in MATLAB/Simulink environment and validated on a three-phase five-level hardware prototype.