Research On Nonlinear Dynamic Behavior Of Doubly Fed Wind Power System Based On Bifurcation Theory

In today’s world,people’s demand for electricity is increasing day by day.At the same time,China is also facing energy shortage and environmental protection problems.This has accelerated the development of renewable resources such as wind power and photovoltaic.However,wind energy,as a clean and sustainable development,has received extensive attention.Due to the excellent operation characteristics of doubly-fed wind turbines,doubly-fed wind turbines have become the most important wind power equipment at present.However,if a large number of doubly-fed wind turbines are used,it will have a great impact on the operation of the grid.Starting from the nonlinear dynamic equation of the system,this paper applies the bifurcation theory to analyze the nonlinear dynamics of the doubly-fed wind generator,inverter and the whole system,in order to improve the operation stability of the doubly-fed wind power generation system.The main contents of this article include:（1）The mathematical model of doubly-fed wind turbine is established in dq rotating coordinate system;The equilibrium solution of the system is studied by using MATCONT technology.On this basis,the bifurcation points are solved,and the bifurcation phenomenon of the system is verified by time domain and stereogram,and its stability is analyzed.The research results show that there is Hopf bifurcation phenomenon in the doubly fed wind generator,and the operation state will change with the change of bifurcation parameters,which has a certain impact on the safe and stable operation of the generator.（2）Taking SMVSC-H bridge inverter as the research object,the discrete iterative mathematical model of the system is constructed by stroboscopic mapping method;Using bifurcation diagram,folding diagram and fast changing stability theorem,the nonlinear dynamic behavior of the system sampling near wave crest and wave trough with the change of proportional coefficient k₁ SMVSC method is proposed to solve the problem of narrow stable working area of proportional coefficient k₁ and sliding mode control coefficient k₂.The effectiveness of the improved SMVSC method is verified by studying the nonlinear dynamic behavior of external parameters.The research results show that the system has a dynamic process from single period stable state to period doubling bifurcation state and then to chaos state,and the improved SMVSC method can effectively expand the stable working area of system parameters,which provides a theoretical basis for the parameter design of SMVSC-H bridge inverter.（3）Taking a 3-node system with doubly fed machine as an example,its nonlinear dynamic mathematical model is established.The equilibrium solution epidemic curve of the system is obtained by using MATCONT simulation software.The voltage stability of the system is analyzed according to the motion trajectory of the system Jacobian matrix eigenvalue,and the dynamic process of the system is studied by using time domain diagram and phase diagram;A Washout Hopf bifurcation controller is introduced to suppress the bifurcation phenomenon in the system.The results show that appear with the change of bifurcation parameters,and both of these bifurcation points will lead to the oscillation and voltage collapse of the system;The addition of Washout Hopf bifurcation controller can eliminate Hopf bifurcation,expand the stability margin of the system,and improve the anti-interference ability of the system.