Research And Improvement Of Stability Of Grid-connected Double-fed Wind Farm

As a branch of renewable clean energy,wind energy plays a very important role.With the development of wind power technology,the manufacturing of wind turbines continues to improve.At present,the mainstream model on the market is a double-fed wind generator(DFIG).Its main feature is that it can perform PQ decoupling control.However,due to the increasing capacity of wind power grid connection and the randomness,intermittence and fluctuation of wind speed itself,it is easy to cause voltage fluctuation,power fluctuation and low-frequency oscillation and other stability problems after wind power grid connection,which affects the safe and stable operation of the system.Based on the above problems,this paper uses different control strategies and methods to improve the stability of the wind farm when it is connected to the grid from two aspects of static stability and transient stability.In this paper,according to the working principle of DFIG and the different influences of various parameters on its operating characteristics,a static model and a transient model were established,and reasonable simplifications were made while ensuring its accuracy.According to the requirements of this paper,the control model of DFIG was introduced,and the reactive power control model studied in this paper was emphatically analyzed.At the same time,an aerodynamic model was established to describe the process of wind energy capture by the wind turbine,emphasizing the importance of wind speed changes to the operation of the wind turbine.Then,the wind speed model was simulated and analyzed,and a wind speed model capable of accurately simulating the actual wind speed variation characteristics was obtained.The wind speed was applied to the grid-connected system of the wind farm,and it was verified that the wind speed fluctuation has an important influence on the system stability.In terms of static stability,aiming at the problem that the point-of-common coupling(PCC)voltage level and high power factor cannot be taken into account simultaneously during the operation of the wind farm,the constant voltage control with wind speed feedforward control was improved,and Based on the layered processing method of active prediction layer and reactive power control layer,a control strategy named Joint control that combines improved constant voltage control and constant power factor control was proposed.Based on the Power System Analysis Software Package(PSASP),a system model of a windfarm incorporated into a WSCC 3 machine and 9 nodes was established.Three control strategies were simulated and compared.The results show that the joint control strategy can effectively suppress PCC Node voltage fluctuations can also ensure that the generator runs at a higher power factor,thereby improving the static stability of the system.In terms of transient stability,aiming at the low-frequency oscillation caused by the wind farm connected to the interconnected system,the multi band power system stabilizer(MB PSS)and static var compensator(SVC)jointly operated were proposed to suppress low-frequency oscillations and stability issues such as voltage and power fluctuations during transient operation of the system.And setting the objective function for the joint operation of MB-PSS and SVC has achieved the purpose of optimizing it.The wind farm was connected to an IEEE 2 region and 4 machine interconnected system,and the four operating conditions were simulated on the MATALB simulation platform.The results show that the proposed joint operation strategy has superior performance in suppressing interval low-frequency oscillation and stabilizing system voltage and power fluctuation,Which effectively improves the transient stability of the system.