Voltage and frequency control of offshore DFIG-based wind farms with line commutated HVDC connection

The paper considers a previously unreported control approach for the control of off-shore DFIG-based wind farm grid with line commutated HVDC connection. The method is applicable for wind farms based-on doubly fed induction generators (DFIGs) or generators interfaced with full-rated power electronic converters. The paper focused on DFIG- based generation. The proposed control scheme allows each wind turbine to share in the voltage and frequency control of the offshore grid. The classical approach of using droop characteristics for adjusting the voltage and frequency according to the power flow of each turbine is employed. In result, the offshore grid is controlled by each turbine using only the electrical variables of its local connection point. The proposed control approach is validated via PSCAD simulations of normal operation regime and of ride-through operation under loss of the main onshore AC grid. The results confirm very good active and reactive power sharing between wind-farm DFIGs while frequency and voltage deviations in the off-shore grid are very small.