Voltage Control Method Of Wind Power System Based On Reactive Power Capacity Improvement Of Dfig Under Wind Speed Variations

When the wind energy resources and load centers are inversely distributed,the development mode of large-scale centralized development and long-distance high-voltage transmission is generally adopted by wind power to achieve the cross-regional optimal allocation of wind energy resources.Large-scale wind farms are generally located at the end of grid,the grid is insufficient to support the access point voltage of wind farm,then the access point voltage is vulnerable to the active and reactive power of wind farm.Doubly-fed induction generators(DFIGs)generally operate at unit power factor.Under wind speed variations,the active power of wind farm changes whereas the reactive power of wind farm usually remains unchanged,this difference will lead to the voltage fluctuation of wind farm access point,which could further affect the power quality,power transmission and equipment safety of wind farm,and even deteriorate the voltage stability of power system.At present,reactive power compensation devices are utilized to suppress the voltage changes of wind farm,but it cannot reconcile the requirements of response speed and compensation capacity.Using the fast power decoupling control capability of DFIG,the voltage stability of wind farms under wind speed variations can be improved.Therefore,in this paper,the characteristics of wind farm access point voltage change under wind speed variations is studied,the reactive power capacity of DFIG and its dynamic changes under wind speed variations is analyzed,the reactive power control method of DFIG-based wind farm under wind speed variations is proposed.This paper is organized as follows:(1)Based on the control model of DFIG,the circuit model of wind power transmission system and the wind speed model,the simulation model of DFIG-based wind power system is established.The relationship between the voltage variation of wind farm access point and wind speed fluctuation,grid strength and reactive power output of wind farm is verified.(2)When the analysis of reactive power capacity of DFIG is incomplete,the reactive power capacity could not be utilized adequately,or leads to over-limit control.Considering the constraints of rotor current and converter capacity,the reactive power capacity of DFIG is characterized.Considering the dynamic characteristics of reactive power capacity of wind farm and reactive power demand of system under wind speed variations,a reactive power control strategy of DFIG-based wind farms is proposed and verified by simulation.(3)In some emergencies of wind speed drastic variation,the reactive power demand of system could exceed the reactive power capacity of wind farm.Based on the co-constraints of the active power output and reactive power capacity of DFIG,the active voltage control idea of DFIG-based wind farm is proposed.Based on the power control characteristics of DFIGs and the interaction between source and network,the active voltage control methods for DFIG-based wind farms in different wind speed ranges are proposed and verified by simulation.