Study On Reactive Power And Voltage Control Technology Of Wind Power Integrated To The Grid

In recent years, with the shortage of global energy and aggravated pollution of environment, the development and utilization of new energy become imperative. Wind energy, as an important part of new energy, is used widely. However, the grid-connected node voltage becomes fluctuation because of the characteristic of wind power, such as randomness, intermittent and volatility. Power quality and the stability of the grid are influenced by the voltage fluctuation. The doubly-fed induction generator(DFIG) and Static Var Compensator(SVC) are researched in this thesis to solve the problem of controlling reactive power and voltage of the power integrated to the grid.In order to solve the problem of the instability of fan grid-connected node voltage, the working principle and strategy of DFIG are studied deeply. And the mathematical model based on three-phase static coordinate system and two phase synchronous coordinates system is established. Then the features of the active and reactive power control of the dq axis component are analyzed under two-phase synchronous rotating coordinates. On the basis of the network measurement converter stator voltage oriented vector control and stator flux rotor side converter control, an improved control method of PWM inverter based on Internal Model Control is proposed. Through controlling d and q axis current component in the two-phase synchronous rotating coordinate system, the active power and the reactive power are ajusted. Through the active and reactive decoupling control of the double fed induction generator, the grid-connected voltage is controlled steadily. Finally, the simulation result on Matlab shows the effectiveness of the improved control method.Aimming at the problem of the grid-connected voltage instability which is caused by the electric field internal fault, the coordination control between DFIG and SVC is discussed on the basis of the modified Internal Model Control method of PWM inverter. Then the mathematical model of the TCR+FC mixed SVC is established. And the coordination control strategy of DFIG and SVC is applied. Finally, the improved coordination control of DFIG and SVC is simulated on Matlab. The results show that the reactive power adjusting ability of DFIG is enhanced effectively, and the fluctuation of the stator and rotor transient current and over-voltage of DC bus are inhibited.