Study on the Optimization and Improvement of Control Strategies for Modular Multilevel Converter High Voltage Direct Current Connected to Weak Alternative Current Systems

Wankai Yang (), Guoliang Zhao and Dongming Han
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Wankai Yang: Department of Power Electronics Technology, China Electric Power Research Institute, Beijing 100192, China
Guoliang Zhao: Department of Power Electronics Technology, China Electric Power Research Institute, Beijing 100192, China
Dongming Han: State Grid Electric Power Engineering Research Institute Co., Ltd., Beijing 100069, China

Energies, 2025, vol. 18, issue 11, 1-13

Abstract: To address the stability problem related to grid-connected modular multilevel converter high voltage direct current (MMC HVDC) connected to weak alternative current (AC) systems, the short-circuit ratio (SCR) that affects the stability of the system was analyzed first. Short-circuit ratios with SCR values greater than 1.3 were obtained, and the system could still operate stably. By applying the theoretical equations of classical circuits, it has been theoretically proven that for the constant active power and constant AC voltage control modes on the weak system side, after the flexible direct current enters the weak system mode, the power must be reduced to ensure the stable operation of the system. Combined with the actual situation of the north channel of the Chongqing–Hubei back-to-back MMC HVDC project, which is connected to the weak system mode, measures such as the optimization of the control mode and the improvement of control functions in the weak system mode were proposed, and simulation calculations and real time digital simulator (RTDS) simulation verifications were carried out. These control strategies have been applied to the Chongqing–Hubei MMC HVDC project, and on-site verification tests have been conducted to ensure stable operation in the weak system mode.

Keywords: MMC-HVDC system; weak AC power grid; control strategy improvement; control mode optimization; theoretical proof (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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