Potential Failure Risk of Fault Location for Modular Multilevel Converters under Light Loads and A Current Reshaping-based Solution

In the state-of-the-art fault location of modular multilevel converters, capacitor voltage deviations between the faulty and healthy submodules are extensively utilized to identify open-circuit faults. However, there is a potential risk of overlooking the ineffectiveness of the fault location under light load conditions. This article presents an analytical model that reveals the fault phenomena and mechanisms specific to light load scenarios. A crucial finding is the strong coupling among faulty arm current, voltage deviations between faulty and healthy submodules, and load conditions. Ignoring this effect can result in underperformance of the fault location, such as seriously delayed detection or missing detection. To address this issue, a current-reshaping-based solution is proposed to ensure optimal fault location performance across the full power range. The effectiveness of the proposed analysis and method is validated through simulations and a downscale experimental platform.