Study On Effect And Control Of DFIG Connection To System Frequency

With the development of new energy power generation technology,more and more new generators are connected to the grid.Among them,wind power is the fastest growing and one of the most widely used new energy power generations.Doubly-Fed Induction Generator(DFIG)is the most widely used among various types of wind turbines.Due to the decoupling characteristics of its speed and grid frequency,it does not have the ability to participate in the system frequency regulation.This reduces the stability of the power system after large-scale wind power is connected to the grid.After analyzing the operating characteristics of the DFIG,this paper aims to improve the primary frequency regulation capability of the DFIG and does the following:First,the structure and operating characteristics of DFIG are analyzed.Based on this,from the aspects of wind power penetration rate,wind turbine frequency regulation control parameters,wind power grid connection points,etc.,the influence of wind power grid connection on the frequency characteristics of the power system is studied,which provides a reference for wind power grid connection.Secondly,the equivalent inertial time constant of the wind turbine with frequency modulation capability is calculated by analogy to the inertial time constant of the synchronous generator.Based on this,the maximum constraint of the inertial control coefficient during the frequency regulation of the DFIG is obtained.At the same time,analogous to the adjustment characteristics of the synchronous generator,the maximum constraint of the droop control coefficient is obtained.Both guarantee the stability of the controller designed later.Thirdly,due to the non-linear operating characteristics of wind turbines,traditional control methods cannot fully utilize their ability to adjust the system frequency,resulting in poor frequency characteristics of the system after wind power is connected to the grid.Designed the FM control parameter adjustment controller based on fuzzy control,which dynamically adjusts the control coefficient according to the frequency change in different stages of FM,which improves the frequency adjustment capability of the system after the wind turbine is connected to the grid.Finally,for the problem of active standby distribution,a method for grouping control of wind turbines under different wind speeds is proposed.According to the operating characteristics of doubly-fed wind turbines under different wind speeds,different load deloaded coefficients are used to improve the maximum power output.The simulation model of the proposed control strategy was built on the Matlab/Simulink simulation platform to simulate different frequency disturbances.The results show that the frequency response is significantly improved,proving the effectiveness and robustness of the proposed method.