Research Of The Voltage Stability Of Wind Power System Based On Sensitivity Analysis

As one form of renewable power, wind power has the most mature technology and developed rapidly in recent years. Because wind farm is of randomness, intermittency and instability, its power output dynamic changes, which restricts grid-connected wind farm, which is the main reason to hinder the wind field expansion. Also,wind farms will absorb considerable amount of reactive power from system while sending outactive power, and due to the close revalence of voltage stability and reactive power, large-scale wind farms have certain influence on voltage stability.This thesis focuses on voltage stability of wind power system based on sensitivity analysis, the main work is as following:Margin sensitivity analysis based on Continuation Power Flow (CPF) is performed, and the voltage stability index is derived using the combination of the tangent vector around the critical point and the right eigenvector and the right singular vector. This index can be used to describe the critical factors affecting the stability of the system. The calculation of the loading margin sensitivity with respect to excitation system parameters, network parameters and load parameters is obtained by estimating the transfer margin, and this calculation is applied to judge the sensitive nodes of the system, to choose the most appropriate position of reactive power compensation and to study the effect of load growth on the voltage stability of the system. The presented method is validated by simulation on the IEEE-39bus system.The effect of integrating doubly-fed induction wind turbine generators access to different buses through different transmission line configurations is analyzed. The IEEE39-bus test system is used to compare results with previous works. Results show that the wind generators connect to different buses through transmission lines lead to the dynamic responses speed delays of existing synchronous generators, and these delays would in turn affect the voltage oscillations of the buses. Results also show that there is no significant effect on the base cases when the wind generators connect into the system using different interconnection voltages.The wind turbine generator with stochastic and intermittent is modeled, and the modeling is used to measure the associated stability margin in terms of system load margin. To model the variation nature of stochastic and intermittent wind power injection as the load increases, the thesis proposes to use the Weibull distribution of wind speed to model the intermittent factor. The slip of asynchronous wind generators is introduced as a new state variable, and thus new power balance equations including the slip as a state variable are formulated. The balance between the average electromechanical power conversion and mechanical power of wind turbines is utilized to incorporate the uncertainty of wind power stochastic and intermittent. In the nonlinear control terminology, this thesis investigats the stochastic nature of the equilibrium points associated with the uncertainty of the wind generation. Accordingly, a new sensitivity index based on the wind farm terminal bus voltage and a novel sensitivity index of voltage stability considering the stochastic and intermittent nature of wind speed through the slip effect are presented, which use the Jacobian matrix of the newly formulated power flow equations. In addition, the probabilistic stability margins in terms of load for various wind speed distribution and penetration are investigated by using of the proposed CPF and Monte Carlo method.