Research On Strategy Of Active Participation In Grid Frequency Regulation For De-loaded Wind Turbines In The Whole Wind Speed Section

With the gradual increase of wind power penetration in modern power generation systems,in order to ensure the stability of power system operation,wind plants are required to provide frequency support similar to conventional plants.However,when the wind turbine realizes the maximum power tracking through the converter,because of the wind turbine is usually completely decoupled from the system frequency,the inertia of the power system is reduced and the frequency regulation capability is weakened,the safe and stable operation of the power grid is difficult to be guaranteed.Based on the above background,this paper further studies the strategy of actively participating in grid frequency regulation in the whole wind speed range of de-loaded wind turbines for doubly-fed wind turbines and permanent magnet wind turbines.The main work is as follows:Firstly,considering the extensive application of variable speed wind turbines in engineering,in order to simulate the dynamic response of wind turbines after system disturbance,a dynamic mathematical model of variable speed wind power generation system is built for common control structures,including: a doubly-fed asynchronous generator model based on the active power,which controls rotor side converter,a permanent magnet synchronous generator model based on the rotor,which controls machine side converter,wind turbine and pitch angle control system model.The Matlab/Simulink model is built to compare and analyze the differences in the structure of the two variable speed wind turbines.Combined with the power output characteristics of different operating stages under the maximum power tracking control strategy under the control of rotor speed and pitch angle,a structural foundation is laid for the wind turbine to provide active power support to the system after it is connected to the grid.Secondly,by analyzing the traditional wind turbine superimposed auxiliary frequency controller to participate in the control method of frequency regulation,based on the doubly-fed wind turbine model,by controlling the active power reference value of the rotor-side converter,the inertial control method is improved,and a control strategy of parameterized power curve is proposed.Additional active power support is provided by modifying parameterized power versus rotor speed curve,including virtual inertial power versus rotor speed curve and droop power versus rotor speed curve.Under different wind speeds,according to the operating state of the wind turbine and system frequency,the active power output reference value is adaptively changed,at the same time,it avoids the careful selection of the control gain coefficient and prevents the rotor speed over-decelerating.In addition,considering the action of the pitch angle during the actual operation,the relationship between the pitch angle and the active power is fitted,in order to achieve de-loaded control and frequency regulation in the whole wind speed section without additional wind speed measurement information.The effectiveness of the proposed control strategy is verified by building simulation models under different wind speeds.Finally,based on the permanent magnet synchronous wind turbine,a frequency regulation control strategy for equivalent rotor speed compensation is designed.A new variable that combining the pitch angle and the rotor speed information is defined as the equivalent rotor speed.On this basis,through data fitting,the equivalent rotor speed versus de-loaded power curve is defined,and the electromagnetic power is used to find the curve to preserve a part of active power among the whole wind speed section.At the same time,in order to in directly couple the rotor speed and pitch angle with the system frequency,a virtual compensation equivalent speed variable is added to the equivalent rotor speed.The inertial control method is optimized,and the reference value of the rotational speed of the rotor control loop of the machine-side converter and the reference value of the pitch angle of the wind turbine are obtained.By analyzing the dynamic process of the frequency regulation of the control strategy,the affect of the equivalent rotor speed compensation control strategy is verified in the comparative simulation model.