Impacts Of Large-scale Wind Power Integration On Static Voltage Stability And Corresponding Solutions

With the increasing capacity of wind power connected to the grid,the impact of the uncertainty of wind power on power systems cannot be ignored.It may lead to some problems,such as,voltage stability,frequency stability,power angle stability and power quality of power systems with wind power.The voltage stability problem has become the bottleneck of badly influencing the capacity of wind power integration.Hence it is a great significance to research the impact of wind power integration on voltage stability and improve voltage stability of power systems with wind integration.The impact of wind volatility on voltage stability and the controls are studied in this paper.Scenario-based methods have been widely used to model the uncertainty of power systems.Copula method is employed to generate the wind scenarios with correlations in this paper.The impacts of wind generator uncertainty on static voltage stability is also studied which includes the impacts of wind power volatility,the access location,the wind power penetration rate,the correlations among wind farms and the fluctuation degree on static voltage stability of power systems.A lot of simulation results demonstrate the intensive nonlinearity between the power of wind farms and the load margins to static voltage stability.From mathematics,the problem of the analysis and control of static voltage stability has been converted from a deterministic problem to an uncertainty one.The computational burden from the large number of scenarios due to the wind integration leads to great difficulties and complexity for the problem of static voltage stability.A scenario reduction method toward for static voltage stability problem is proposed in this paper.The scenarios reduction method is proposed to employ the load margin of each scenario at saddle node bifurcation point and the distance among wind power scenarios as the clustering indexes,which can avoid the elimination of the extreme scenarios for the voltage stability problem.The scenarios obtained by the proposed method are more representative of the voltage stability problem.To reduce the influence of wind power integration on static voltage stability,the network topology optimization(including transmission line switching and bus-bar splitting)is proposed to improve the static voltage stability of wind power system in this thesis.The line switching model and the bus-bar splitting model are presented to increase the load margins of power systems,respectively.The objective function is to maximize the load margin of power system determined by the predicted wind power,as well as the load margins of all wind power scenarios are greater than a given threshold value,and the post-switching or bus-bar splitting power system meets the static security constraints of power systems,so as to ensure the safe operation of wind power system.In order to solve the proposed problem rapidly for online requirements,the proposed scenario reduction method is used to reduce the number of wind scenarios,and then the sensitivity method is used to screen out those noneffective switching lines and bus-bar splitting schemes.Then look-ahead margin estimation method is employed to estimate the load margins of switching and bus-bar splitting power systems for ranking purpose.Finally,continuation power flow method is used to calculate the load margins for those top-ranked controls.Numerical studies are carried out in IEEE 118-bus and IEEE 1648-bus power systems to verify the effectiveness of the proposed method.