T18.2 - 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 with switching duty ratio-based estimated grid current. In general, the current is estimated depending on sampled values in the fault diagnosis techniques using the current estimation. Therefore, the switching state of each switch used to estimate the current is 0 (off) or 1 (on). However, when PWM control method is applied, the switching state may change within the control period. As a result, estimating the current using 0 or 1 for the switching state can lead to inaccurate estimated current. To solve this problem, the paper proposes an OCS fault diagnosis based on estimated grid current that considers the changing switching state of each switch within the control period. The proposed technique estimates the grid current by deriving the switching duty ratio of each switch within the control period. In addition, the fault switch location is distinguished by comparing the measured grid current with the estimated grid current by using switching duty ratio and dc-link voltage. The validity of the proposed technique is verified by simulation and experimental results.