A Review of the State of the Art in Control of Variable-Speed Wind Turbines

The wind turbines constituting large wind power plants are challenged to satisfy the revised grid codes, which require them to withstand grid faults, support grid during faults, and provide ancillary services such as frequency control, and voltage control. In order to meet the grid code requirements, control strategies for variable-speed wind turbines are developed and reported by academy and wind industry, where these strategies are reviewed and discussed in this paper. The strategies for active and reactive power control at the wind turbine level, fault ride-through capability with contribution to grid voltage regulation by reactive current injection, and local voltage control at the wind turbine level are introduced. The support of wind turbines to grid frequency regulation is discussed for main three functions; primary frequency control, inertia emulation, and power oscillation damping. Also, coordinated control solutions between wind turbine controller and wind power plant controller are investigated.