Open-Circuit Switch Fault Diagnosis in Single-Phase CHMC with Switching Duty Ratio-Based Estimated Grid Current

This paper proposes an open-circuit switch (OCS) fault diagnosis of single-phase cascaded H-bridge multilevel converter (CHMC) with switching duty ratio-based estimated grid current. Generally, the current is estimated depending on sampled values. However, when pulse width modulation (PWM) is used, the switching state may change within the control period, resulting in inaccuracies in both the estimated current and fault diagnosis. In the proposed technique, for considering switching state variations, the grid current is estimated by deriving the switching duty ratio of each switch within the control period. Subsequently, the fault switch pair is determined through the sign and magnitude of the residual between the estimated grid current and the sampled grid current. Finally, the fault switch location is distinguished by comparing the magnitude of the residual with the reversely calculated residual. The validity of the proposed technique is verified by simulation results.