Research On Reactive Power And Voltage Regulation Of DFIG-based Wind Farms

Wind power is intermittent and random while providing clean energy,these features will produce negative effect on power system.Also,wind farms will absorb considerable amount of reactive power from system while sending out active power,and due to the close relevance of reactive power and voltage stability,large-scale wind farms have some influence on voltage stability.In this thesis, based on mathematic model of DFIG,the decoupled control principle of RSC and GSC are derived.The control model of DFIG is builded in DIgSILENT/PowerFactory,it is the base of further research on reactive power and voltage regulation of DFIG-based wind farms.The coordinated control strategy of wind farms based on reactive power optimization of distrbution is proposed.Its premise is wind power prediction,control target is minimization of network loss,constraints are nodes voltage and reactive power capacity,control mean is reactive power regulation.Through OPF the regulated amount of wind farms are established,and then distributed by equal power factor algorithm to single wind generator.The study case proves that the control strategy can minimise the network loss.The above mentioned control strategy is suitable for normal operation condition of wind farms,in order to enhance the ability of LVRT during voltage dip,the control strategy of subnormal voltage operation is adopted.It consists of three parts: voltage support control,Crowbar protection and reactive power boosting.The study case proves that the control strategy can enhance the the ability of LVRT.The online early-warning system on the basis of the software DIgSILENT/PowerFactory is developed. The system can predict nodes voltage and lines current trend in the region of wind power integration with security assessment. The results of practical application prove that the system realizes the online early-warning function of wind power integration, and is significant to the dispatching management of large-scale wind farm and safe operation of the power network.