Fault-tolerant cascaded multi-level inverter with improved output quality

This paper presents an enhanced reconfiguration method for the cascaded H-bridge inverter (CHBI) that maintains high quality of the output voltage waveforms. This method is based on controlled shifting of the system neutral point together with the phase-shifted pulse-width modulation (PS-PWM) scheme. During fault conditions, if the carrier signals are not properly adjusted in the healthy working power cells, then the output line-to-line voltages get distorted with high harmonic content. With the proposed method, carrier signals' frequency and phases are modified according to the available operative cells within the faulty phases. The proposed implementation is modeled in the MATLAB/Simulink for a 7-level CHBI under various cell fault conditions. Simulation test results confirm the performance enhancement attained with the proposed method. This reconfiguration method can easily be realized since the changes of the PS-PWM strategy can be implemented in software, without additional hardware requirements.