Research On The Mechanism Of Dynamic Reactive Power Compensation And Sub-synchronous Oscillation In Large-scale Wind Farms Integration Area

At present,as the representative of new energy power generation,the wind power technology develops rapidly,which is changing the operating characteristics of traditional power system.Especially in the northwest of China where wind energy resources are abundant,large-scale wind power intensive development has polymerization effect.The coupling effects between the dynamic characteristics of power electronic equipment and its interaction with the AC / DC power system lead to new oscillation stability problems.Firstly,an equivalent model of the system was established on the basis of reactive power and voltage control in typical large-scale wind power integration areas in DIgSILENT / PowerFactory.Focusing mainly on control modes of SVC,two control modes,namely constant voltage control and constant reactive power control,were compared and analyzed via adopting different stability analysis methods including eigenvalue analysis in small signal stability,time-domain simulation.The results demonstrate that: SVC with different control modes has different adaptability regarding to the system's change.In terms of the number of wind farms with SVC and the impedance of the system,the constant reactive power control mode performs better than the constant voltage control mode with respect to weak delivery systems in large-scale wind integration area.Secondly,this paper proposed an analysis method for multiple SVCs' interaction in wind power integration area based on frequency scanning-sensitivity transfer function.On the theoretical basis of small signal stability,the method for open loop transfer function's derivation in terms of particular variables was introduced combining modal analysis in DIgSILENT / PowerFactory and programming tools of MAYLAB.The problem of instability caused by multiple SVCs' interaction was analyzed from the perspective of a new controller at the theoretical level.This method plays a significant guiding role for system's planning and actual site's operation on the aspect of a new SVC's parameter tuning.Finally,the mechanism of the interaction between the dynamic reactive powercompensator and the network resonance in wind power integration system was discussed.The wind turbine controller of an actual wind farm was connected into the system established in RTDS thus setting up a hardware closed-loop simulation platform.Then,a frequency domain analysis method based on digital physical hybrid simulation was proposed.The results reveal that the system strength,single-fed power electronic capacity(the number of wind turbines)and multi-fed power electronic devices' coupling effect have an impact on the first resonant frequency of the AC system.With the continuous input of new SVCs in different wind farms and the increase of the number of wind turbines in the same wind farm,the first resonant frequency of the system decreases.