Small Signal Stabilty Analysis Of Power System Connected Wind Farm

With the growth of interconnected power systems, problem related to small signal stability of power system have been concerned with people more and more. Wind power is increasing in power system, owning to its advantages of no pollution, reproducibility, and the most mature technology. However, small signal stability analysis of power system connected to wind farm have become a new subject today. In this paper,the modle of a simple wind farm with wind turbine genetators are established,oscillation modes and damping characteristic of a simple system with wind farm are analyzed,On the basis of which the impact of small signal stability of power system connected wind farm is studied.The main contents of this paper are as follows:(1) The mechanical system models of wind turbine generator are established in Matlab/simulink, including the aerodynamic model, shaft control system model and pitch control system model. The paper derives the status equations of asynchronous generator and doubly-fed induction generator(DFIG) and permanent magnet synchronous generator(PMSG) with dq rotation axis(synchronous rotation axis) as the reference.The model of the converter and its controlling systems in wind turbines based on DFIG and PMSG are established.(2) A simple wind power system is established in Matlab/simulink, its composed of a single machine and an infinite bus, including wind turbines based on a synchronous generator, DFIG and PMSG. The oscillation modes and damping characteristics of a simple wind power system are analyzed with eigenvalue analysis, and the principle of the oscillation modes is analyzed with participation factor. The analysis results demonstrate that there are oscillation modes and attenuation modes in the simple wind power system, and that these oscillation modes have good damping characteristics. For the simple system based on asynchronous generator, wind turbine speed and shaft distortion angle decided to oscillation modes, transient potential and pitch angle decided to attenuation modes. For the simple system based on DFIG, generator slip and transient potential and wind turbine speed and shaft distortion angle decided to oscillation modes, pitch angle and parameters of converter control system decided to attenuation modes. For the simple system based on PMSG, q-component of stator current and parameters of converter control system decided to oscillation modes, wind turbine speed and parameters of converter control system and d-component of stator current decided to attenuation modes. The simulation analysis of the wind generator to improve small signal stability has certain practical value.(3) Frist, IEEE three-genarator-seven-bus power system is established in PSASP(power system comprehensive analysis software), wind farm connected to the system bus. Considering wind farm before and after connected to power system and output of wind farm, analysis small signal stability influence of asynchronous machine wind farm, DFIG wind farm, PMSG wind farm connected to power system. Through the simulation analysis, Asynchronous machine wind farm connected to power system, increased the damping ratio of system oscillation, beneficial to small signal stability of power system. DFIG wind farm and PMSG wind farm connected to power system, reduced the system damping ratio of oscillation, deteriorated to small signal stability of power system. With the output of asynchronous machine wind farm increasing, the more beneficial to small signal stability of power system, and influence to inter-area oscillation more than local oscillation. With the output of DFIG wind farm and PMSG wind farm increasing, the more detrimental to small signal stability of power system, influence to inter-area oscillation more than local oscillation. Finally, through time domain simulation observed power angle curve of generator verify the correctness of anlysis.