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Active Fault Current Limitation for VSC-MTDC System During Frequency Regulation

With the continuous development of offshore wind farms (OWFs), voltage source converter based multi-terminal high voltage direct current (VSC-MTDC) system has become an effective and economical way to connect onshore mainland grid. However, with massive integration of OWFs, the VSC-MTDC system faces the challenge to avoid increasing system fault currents during frequency regulation. To solve this challenge, an active fault current limitation (AFCL) method is proposed for the frequency regulation of VSC-MTDC system. In the AFCL method, 1) an adaptive coefficient is conducted to suppress the fault current according to the current injected by VSC stations; 2) a coordinated control method based on virtual synchronous generator is developed to support frequency, in order to provide inertial for AC system. The effectiveness and superiority of the proposed scheme for frequency support and AFCL are validated by case study.