High-robustness detection method for AC voltage measurement fault in MMC-HVDC systems

Accurate grid AC voltage information is crucial for the stable control of Modular Multilevel Converter (MMC) systems. Due to limitations in design and manufacturing, AC voltage measurement is susceptible to failure, causing measured value to deviate from the actual one. Moreover, when grid faults, particularly voltage sag or swell, occur, the actual grid AC voltage may deviate from its nominal value. However, the MMC cannot distinguish between measurement faults and grid faults, which may lead to inappropriate countermeasures. To solve this problem, the MMC mathematical model is first modified to compensate for zero-sequence voltage components and three-phase voltage coupling effects. Then, based on the modified model, a Kalman Filter (KF)-based observer is established, using the measured AC voltages as inputs and the observed output currents as outputs. The proposed observer is sensitive only to AC voltage measurement fault while immune to voltage sags and swells, thereby achieving robust measurement fault detection. The method is simple yet effective, allowing the MMC system to adopt appropriate measures corresponding to the actual fault type, thus minimizing the impact on system operation. Finally, the effectiveness of the proposed method is validated through both simulations and experimental results. © 2017 Elsevier Inc. All rights reserved.