The Control Strategy Study Of Doubly-Fed Induction Wind Generator Participation In System Frequency Regulation

With the development of wind power technology,the capacity of wind farms connected to grid is increasing rapidly.Due to the role of the converter,the rotor speed of wind turbine rotor and system frequency decoupled,which leads to the wind farm can not provide inertia support for the system as the traditional synchronous generator.Besides,because of wind speed fluctuations,the wind farm will have a great impact on the frequency stability of power system.Therefore,it is of great sense and practical significance to explore the new strategy of frequency control of wind farm in power system.In this paper,the influence of grid connection of doubly-fed induction generator(DFIG)is analyzed,and the control strategy of frequency regulation of power system is designed.First of all,the basic model and control method of DFIG are introduced,and the advantages and disadvantages of DFIG traditional frequency control method and power control method are analyzed.The virtual inertia control and over-speed deloading control are described in detail.The contradiction between virtual inertia control and maximum power tracking control is expounded,and the influence of virtual inertia parameters on frequency control is analyzed.Then,an integrated virtual inertia control method is proposed to combine the improved over-speed deloading control with the drop control in the virtual inertia control.According to the different frequency of the system,by inputting the variable deloading factor,the over-speed deloading control module can quickly output the power reference value and transfer the power tracking curve,so that the wind turbine has the power-frequency response characteristic,and through analyzing the influence of control parameters on power system,the specific control model is designed.The simulation results show that the integrated inertial control method proposed in this paper can make the wind farms composed of DFIGs more responsive to the changes of the system frequency and provide the active power to the system,provide active power support to the system.Finally,in order to further improve the ability of DFIG to participate in the frequency control of the power system,which could participate in the primary frequency regulation and the secondary frequency regulation at the same time.By analyzing the process of synchronous generator participation in the second frequency modulation,the additional pitch angle controller of DFIG is designed to simulate the process of synchronous power generator's driven power-frequency characteristic curve.It can take the initiative to respond to automatic power generation control(AGC)Control signals to participate in the secondary frequency regulation.And in coordination with the synchronous generator in the system,the power control coefficient is automatically assigned according to the state of the wind farm.The simulation results show that the proposed control strategy can make the wind farm more effective in the primary and secondary frequency regulation of the power system,and the frequency regulation ability of the whole system is improved.