A Stability-Oriented Current Scheme for a Wind Farm Connected to a MMC-HVDC Under Severe Faults

The offshore wind farm connected modular multilevel converter (MMC)-based high-voltage direct-current (HVDC) transmission system is prone to lose transient synchronization stability under AC faults. The multi-wind turbine (WT) interaction can cause a great deal WTs to lose stability in quick succession. Moreover, the multiple WTs further interact with the control of MMC, making the system stability analysis complicated. In order to guarantee a reliable operation of the system, based on equal area criterion (EAC), this paper exhaustively analyzes the stability problem of such offshore wind farm. The investigated wind farm is made up of full-scale type-4 wind turbines (WTs). It is found that the injected current distribution of MMC and WT are especially predominant in such two interactions. Based on above analysis, a stability-oriented current scheme is proposed to minimize the adverse effect of interactions, enhancing the synchronization stability. Finally, above theoretical analysis and effectiveness of the proposed current scheme are verified by MATLAB/Simulink simulation results.