Multifault Tolerance Strategy for Three-Phase Multilevel Converters Based on a Half-Wave Symmetrical Selective Harmonic Elimination Technique

This paper presents a generalized fault-tolerant strategy to improve the performance of the three-phase cascaded H-bridge converters with faulty cells. The proposed fault-tolerant strategy combines the fundamental phase-shift compensation (FPSC) method with half-wave symmetrical selective harmonic elimination (SHE) to rebalance the inverter voltages and limit the total harmonic distortion (THD) of the waveforms. In this paper, first, the FPSC method is explained and the formulation for a new half-wave symmetric SHE technique is provided. Then, the main idea of the paper is presented as to adjust the phase angles of the fundamental harmonic of the line-ground voltages while equalizing the amplitudes and phase shifts of the third-order harmonics and eliminating some higher order harmonics. The proposed fault-tolerant strategy uses the increased degree of freedom provided by half-wave symmetrical SHE to adjust phase angles and eliminate a wide range of lower order harmonics for limiting the THD of the converter voltages under the faulty conditions. Finally, several experimental results are provided to validate the operation of the proposed strategy.