Non‐Contact Turn‐Off Time Measurement Method for IGBTs in the Half‐Bridge Submodule Configuration of MMC

Modular multilevel converters (MMCs) are widely employed in power applications due to their modular scalability, excellent harmonic suppression capability, and low‐loss characteristics. However, their reliability is constrained by the insulated‐gate bipolar transistor (IGBT) devices within the submodules. Consequently, improving the reliability of IGBT devices is crucial for enhancing the overall performance of MMCs. In recent years, state monitoring techniques based on dynamic electrical parameters have emerged as an effective means to improve IGBT reliability. Among these parameters, turn‐off time is a key health indicator and is widely used for junction temperature monitoring and failure mode detection. This study presents a non‐contact turn‐off time measurement method based on the load common‐mode current decay during the turn‐off process, aiming to overcome the limitations of existing electrical measurement methods. By leveraging existing load current monitoring, real‐time monitoring of IGBT turn‐off time can be achieved without disrupting normal equipment operation. Experimental results demonstrate that this method can accurately monitor turn‐off time and evaluate its impact on variations in load current, capacitor voltage, and junction temperature. The feasibility of this method for practical engineering applications is validated through MMC power‐equivalent experimental results.