Zero Voltage Vector Based Open Fault Detection Method for a Grid-Connected Single Phase CHMI with Phase-Shifted PWM

This paper proposes an open fault detection method using zero voltage vectors (ZVs) in the single-phase cascaded H-bridge multilevel inverter (CHMI) with phase-shifted (PS) PWM. When the open fault occurs on switches in CHMI, the freewheeling diodes of faulty switches provide current paths, and the distortion is induced in the output current. In CHMI based on level-shifted (LS) PWM, faulty switches can be diagnosed by the level of distorted output current. However, with this method, it is not able to locate faulty switches in the CHMI with PS PWM. Therefore, in this paper, the zero voltage vector (ZV) based open fault (ZVOF) detection method is proposed for the CHMI with PS PWM. In this method, ZV states are applied to cells in turn. As the output current characteristic differs according to cells where ZV is applied, it is easily capable of detecting the faulty switch without additional sensors. The effectiveness of the ZVOF detection method is verified by PSIM simulations.