Active Fault Current Limitation for VSC-MTDC Integrated Offshore Wind Farms Participating in Frequency Regulation

The onshore local grid is facing the challenge to avoid continuously increasing fault current caused by frequency regulation (FR) of broad-scale offshore wind farms (OWFs) integrated by voltage source converter based multi-terminal high voltage direct current (VSC-MTDC) system. To tackle this challenge, an active fault current limitation (AFCL) method is proposed in four aspects: 1) a fault current contribution factor (FCCF) is introduced for grid side VSC (GSVSC) to quantify the incremental degree of fault current caused by FR of GSVSC under different fault types; 2) a current phase angle control (CPAC) strategy based on vector analysis is conducted for GSVSC to actively mitigate the fault current increment; 3) according to FCCF and CPAC, an active and reactive current quantification (ARCQ) strategy is developed for GSVSC to satisfy bilateral demands of AFCL and FR; 4) an adaptive frequency regulation (AFR) strategy, which considers FCCF and the operating conditions of the offshore system (e.g., rotor speed and DC voltage), is formulated for OWFs to quantify and generate the active power required for FR and AFCL. Numerous test results are analyzed to verify the effectiveness and performance of the proposed AFCL method in satisfying system fault current limitation during FR of OWFs.