Research On The Small Signal Stability Of Power System Integrated Large-scale Wind Farms

With the deterioration of environment and energy problem become more and more severer, to reduce the number of traditional energy consumption, wind power as one of the most development potential of renewable energy in the world is developing rapidly. In order to guarantee the safe and stable operation of power grid, the traditional power grid analysis of small signal stability issues should be considered. However, because of the properties of randomness and volatility, wind power can be regarded as a kind of disturbance injectted into power grid. Therefore, on this background, studying the influence of wind power grid to power system small signal stability is very meaningful.Firstly, this thesis embarks from the simple power system model, studies the small signal stability of systems which have the single typhoon electrical units connected to the infinite system.Eigenvalue analysis method is used to study system oscillation mode, the participation levels of state variables to system oscillation modes are researched through the calculation of the numerical value of participation factors, so that the mechanism of simple wind power generation system to produce low frequency oscillation are revealed. Analysis results show that the simple constant speed asynchronous wind power system exists oscillation modes and nonoscillatory decay modes, low frequency oscillation modes are included in the oscillation modes, but all models have higher damping ratio, so system can keep small signal stability. System models are mainly related to wind turbine state variables and wind speed. Simple doubly-fed asynchronous wind power system and permanent magnet direct-drive wind power system are only exist nonoscillatory decay modes, systems can keep small signal stability too. The two systems have three modes mainly related to the fan rotor angular velocity, the fan speed and pitch angle respectively and have the same eigenvalues.Other modes are mainly associated with the fan characteristic state variables.Then, the influences to oscillation modes and damping characteristics considered different factors, such as the fan type, grid position and the way to adopt wind, are studied systematic. Through the analysis of system eigenvalues and damping characteristics, the results show that under the same conditions, the influence of doubly-fed induction wind farm and permanent magnet wind farm to small signal stability of the system are relatively serious when connected to the grid. On this basis, on the one hand, the influence is smaller when the wind farm connected to the grid at the power sending end; on the other hand, compared with the ways of new and replace to adopt wind, the way of spinning reserve to adopt wind has less impact,and the conclusion is contrary to constant speed asynchronous wind farm access system.Finally, the influences of large-scale wind farms connected to the grid to the small signal stability of the system are studied on the basis of the key characteristic way. The analysis results show that the wind power output has significant effects on the small signal stability of the system, reduced wind power output properly can make the system small signal stability. On the premise of keeping system small signal stability, the spinning reserve way has a higher acceptance of wind power capacity than new wind way. And the system damping characteristics changes slowly when wind farm grid distance changes, but with the increase of space grid can make negative damped oscillation mode damping ratio becomes worse because of the increase of grid space, so that it will be bad for the small signal stability.