Study Of Coordination Control Of Reactive Power And Voltage Of Large-scale Wind Farms

Wind power is taken seriously as a kind of environment friendly plant style. And wind resources are developed and utilized on a large scale. However, many challenges are brought to the grid because of the integration of large-scale wind power. Reactive power and voltage control is one of the challenges. The fluctuation of the wind power is the fundamental cause, which brings about the voltage fluctuation. Randomness and fluctuation of the wind, response feature of different time scale regulation devices in the wind farms combined increase the difficulty of the reactive power and voltage control. The thesis makes a study of reactive power and voltage control of large scale wind farms in the above background.Firstly, three common kinds of wind turbines are studied, including fixed speed induction generator (FSIG), doubly fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG). Equivalent circuit of FSIG is established, according to which the relation of reactive power, terminal voltage and active power is deduced; vector control of DFIG is studied and reactive power limit is deduced. Besides, the features of several reactive power and voltage regulation devices are studied:including shunting capacitors, on load tap changer (OLTC), SVC and STATCOM.Secondly, influence to the grid voltage of wind power integration is studied. First of all, the principle of the influence of wind farms to the feature of reactive power and voltage is given; next, the influence to the grid voltage of three cases is studied, including FSIG as the wind turbine type, DFIG as the wind turbine type of constant terminal voltage and constant power factor; and then, the influence to the grid voltage when wind power integrates to the grid from different buses.Finally, on the above basis, the reactive power and voltage control mode of large scale wind farms integrating into the grid is constructed, including system level control, wind farm level control and devices level control. For the wind farm level control, a control strategy of two-tier and multi-stage of wind farm cluster is proposed. The model considers the uncertainty of the wind power and the response features of different time scale devices. NSGA-Ⅱ (non-dominated sorting genetic algorithm Ⅱ) is selected to solve the model, because the model is a multi-objective problem. After the solution, analytic hierarchy process is used to select a best solution for the operator. At last, a typical topology of multiple wind farms integrating to the grid is used to testify the proposed model, which can control the voltage fluctuation caused by the wind speed fluctuation and decrease the switching times of discrete devices, obtaining the economic objective.