Capacitor voltage change rate based fault localization strategy for modular multilevel converters

With the widespread application of the modular multilevel converter (MMC) in the fields of electronic and electrical engineering, the open-circuit failure problem of the power devices in submodules (SMs) has become the main factor restricting its stable operation. Therefore, power device open-circuit fault diagnosis is widely studied as the main means to ensure the ongoing and stable operation of MMCs. The existing fault diagnosis approaches on the basis of voltage of capacitor change are only applicable to fault diagnosis under active power conditions. However, in reactive power scenarios, MMC systems have very important applications, such as power grid steady-state reactive power regulation and transient reactive power support. Therefore, an effective fault diagnosis method based on the capacitance voltage change rate is put forward for the diagnosis of faults under reactive conditions. This method differentiates the capacitor voltage and compares it with the threshold to diagnose faults under reactive power operation. The proposed method is simulated using PSCAD simulation software. Simulation results verify the practicability of the presented approach.