Improved Modulation Technique in Cascaded H-Bridge Inverters for Fault-Tolerant With Full Bridge Single Phase Rectifier Structure

This paper presents a novel fault-tolerant approach for cascaded H-bridge inverters with a full-bridge single-phase rectifier cell structure. Upon a fault, the faulty cell is disconnected from the circuit, and the inverter switches from normal operation (symmetric mode) to faulted operation (asymmetric mode). In asymmetric mode, one of the full-bridge single-phase rectifier cells in the faulty phase transitions from a full-bridge to a half-bridge configuration. The level-shift pulse-width modulation (PWM) is employed during symmetric mode, while a modified level-shift PWM is utilized in asymmetric mode. The inverter's output power and voltage remain unchanged during faults in the modified PWM method. Additionally, the performance of the proposed fault-tolerant algorithm is evaluated and validated using results from simulations and an experimental prototype of a seven-level inverter.