State Observation-Based AC Voltage Measurement Fault Detection for Modular Multilevel Converters

The ac voltage measurement plays a crucial role in modular multilevel converter (MMC) systems. When a measurement fault occurs, it significantly impacts the system’s normal operation. However, a simple and reliable detection method for ac voltage measurement faults in MMC systems is still missing. To fill this gap, this article begins by analyzing the impact of measurement faults on the MMC control system. Then, a detection method based on the Kalman filter (KF) state observation is proposed. The ac voltage measurement serves as the KF input, and the MMC output current is chosen as the KF output. The MMC output current is accurately observed, and fault detection can be achieved by comparing the observed current with the actual current. The proposed method allows for independent monitoring of ac voltage measurements in each phase. Moreover, the fault detection time is investigated in detail, verifying the rapidity of the proposed method. With the proposed method and corresponding voltage correction, MMC can maintain uninterrupted operation until the measurement returns to normal, or facilitates a smooth shutdown, minimizing the impact on the power system. Finally, the effectiveness of the proposed method is validated through simulations in MATLAB/Simulink and experiments in a three-phase MMC platform.