Adaptive current injecting strategy for VSC-HVDC connected offshore wind farms during symmetrical faults.

• The transient stability model is established for VSC-HVDC connected offshore wind farms with different fault positions. • The initial and subsequent fault characteristics are analyzed, the requirements for optimal voltage profile are revealed. • An adaptive current injecting strategy is proposed, both the voltage profile and synchronization stability are enhanced. For the voltage source converter based high voltage direct current transmission (VSC-HVDC) connected offshore windfarm, loss of synchronization (LOS) during the AC collection and transmission system faults can lead to frequency shift and low-voltage ride-through (LVRT) failure. Moreover, the fault characteristics, such as voltage profile and phase angle difference between currents at both ends of transmission lines, are significantly affected by the frequency shift. In this paper, the mechanism of synchronization is theoretically explained. Specifically, the parametric impact of the ratio between the active current and reactive current of wind turbines (WTs) is revealed analytically. Then, the fault characteristics including the AC system voltage profile with the frequency deviation and equilibrium points considered and the initial states during the faults are derived. Based on the fault characteristics and demands for optimal voltage profile, an adaptive current injecting strategy for full-scale type-4 WTs is proposed to enhance synchronization capability and optimize voltage profile during the high voltage transmission line faults. Simulations in EMTP demonstrated the analysis and effectiveness in improvement of transient stability and voltage profile of the proposed scheme. [ABSTRACT FROM AUTHOR]