Voltage-source Control Of Doubly-fed Induction Generator Wind Turbines

With the large-scale integration of distributed power generation systems with wind turbines as the dominant capacity in the grid,the uncertainty of wind energy has caused fluctuations in the output of wind turbines,which has an impact on the reliability of the system,which is mainly reflected in the output voltage of the stator and system frequency stability.This kind of distributed power generation system is integrated into the power grid on a large scale,resulting in a reduction in the number of conventional synchronous generators,a reduction in system voltage control capability,a high risk of cascading failures,and a threat to the stable operation of the system.Wind turbines are generally connected to the power grid through power electronic equipment,leading to power electronic power systems,which weaken the inertia and damping of the system,and reduce the anti-disturbance of the power grid.Because traditional large-scale wind turbines are attached to the large power grid through phase-locked loop technology,doubly-fed wind turbines exist in the form of current sources.When the doubly-fed wind turbine exists in the form of a current source,the wind turbine cannot provide inertia support to the system,which is unfriendly to the grid operation in the current high-permeability mode of wind power,and aggravates the disturbance of the grid,especially the short circuit ratio is relatively small in remote areas,systems with relatively poor anti-disturbance become worse due to the connection stability of the wind turbines.Therefore,it is of far-reaching significance to explore new methods of wind turbine control in high-proportion new energy power systems.The specific work arrangements for this paper are as follows:(1)First of all,this article comprehensively considers the dynamic characteristics of the rotor side and grid side of the DFIG.The mechanical dynamic performance of the wind turbine is considered as well.The principle of wind energy capture of the wind turbine and the establishment of the transmission mechanism model are described,and the operation area of the wind turbine is analyzed in detail;the voltage source output control strategy of the doubly-fed wind turbine is established,and the Bode diagram obtained by the closed-loop transfer function Analyze the stability of the control structure of the doubly-fed fan;(2)Secondly,considering the unbalanced load condition under the output characteristics of the voltage source of the doubly-fed wind turbine,the inner loop PIR controller is designed for the double frequency oscillation of the stator flux caused by unbalanced load switching,instead of the traditional PI controller.A double frequency notch filter is designed to suppress the double frequency oscillation caused by the negative sequence component.The MATLAB/Simulink simulation results verify that the improved voltage source control strategy is used in unbalanced load power.The adaptability of the system under typical working conditions;(3)Then,the energy storage system is modeled,and the design of the LCL filter of the interface inverter is analyzed in detail;the dynamic droop mechanism is added on the basis of the DFIG voltage source output control strategy,and the DFIG and the energy storage system are designed to pass the droop The coordinated island microgrid operation program simulates and verifies the ability of wind turbines to actively participate in system frequency modulation.(4)Finally,based on the above-mentioned control of the DFIG voltage source and droop control,a DFIG-BESS microgrid simulation model based on the output of the voltage source is built in RT-LAB to further verify the effectiveness of the proposed control strategy.