Modulation Strategies for Fault-Tolerant Operation of H-Bridge Multilevel Inverters

The operation of the H-bridge multilevel inverter under fault conditions is examined in this paper. In the event of a fault, the cell with problems can be bypassed to enable the operation of the inverter with fewer cells. This approach could result in an unbalanced inverter configuration which can be corrected by modifying the modulation scheme. Two different approaches based on the phase shift-PWM (PS-PWM) and the space phasor modulation (SPM) are considered to compensate the voltage unbalance. Aspects such as the firing pulses generation and the use of optimal sequences are also discussed. The feasibility of the method is demonstrated using simulated as well as experimental results in a 5-level H-bridge multilevel inverter