An IGBT open-circuit fault detection method for modular multilevel converters

Recently, the modular multilevel converter (MMC) has attracted increasing attentions due to its distinctive features, especially in the application of HVDC power transmission. One of the most significant characteristic of MMC is that it is composed of identical low-voltage submodules (SMs). As a result, the low-voltage IGBTs can be employed in each SM as the main power switch. However, since an MMC station usually contains hundreds of SMs, the IGBT becomes the most fragile component. In this paper, the failure characteristics of the IGBT open-circuit fault in a SM are firstly analyzed. Then, an observer-based IGBT open-circuit detection method is proposed, which can accurately detect the fault by comparing the estimated values with the actual sampled values. Finally, the validity and effectiveness of the proposed fault detection method are demonstrated by experimental results based on a single-phase MMC prototype in the laboratory.