Research On Modeling Of Doubly-Fed Induction Generators And Reactive Power And Voltage Control Of Wind Farm

With the continuous improvement of the grid-connected capacity of wind power,the influence of the dynamic characteristics of wind farm on large power grids becomes more apparent.From the local perspective,the dynamic characteristics of wind farm can be studied and analyzed by establishing suitable model of wind turbines.However,the detailed electromagnetic transient simulation model is not suitable for practical engineering applications because of the slow simulation speed.Therefore,in this paper,the electromagnetic transient time scale model and electromechanical transient time scale model of doubly-fed induction generators(DFIG)are established by using the coupling relationship between variables.Without affecting the overall trend of the DFIG system,the 26-order detailed model is decomposed into 14-order electromagnetic transient model and 12 or 10-order electromechanical transient model.The rationality and effectiveness of the reduced-order model are verified by two large disturbance conditions: abrupt change of wind speed and voltage drop.From the whole perspective,the reactive power and voltage control of the wind farm is closely related to the voltage stability of the wind farm at point of common coupling(PCC),which can directly affect the grid-connected performance of wind farm.The existing reactive power and voltage control mostly starts from the whole wind farm to make the reactive power distribution of the reactive power source in the wind farm unreasonable,which leads to the increase of the active power loss of the wind farm or the over-limit of the turbine terminal voltage at the end of power collection lines.Therefore,on the basis of deducing the reactive power output limit,this paper proposes a reactive power coordination distribution method between wind turbines in the wind farm and selects the constant voltage control as the reactive power control strategy of the DFIG.On the premise of only considering the reactive power output of wind turbines,the proposed distribution method is compared with the common reactive power distribution method under different scheduling instructions to verify the effectiveness of the proposed method in reducing the network loss of wind farm.The constant voltage control and constant reactive power control of DFIG are modeled and simulated when gust disturbance occurs in the wind farm,which verifies that the constant voltage control of DFIG is beneficial to suppress the fluctuation of the voltage at PCC and the terminal voltage of DFIG.