Power Oscillation Analysis Of Doubly Fed Wind Farm Connected To Power System

With the rapid development of wind power generation,more and more wind farms are connected to the power system.The randomness and fluctuation of wind energy have a great impact on the stability of the power system,and have gradually attracted attention.The power oscillation caused by the doubly fed wind farm connected to the power system is a hot topic in the field of wind power research.The operation characteristics of DFIG are complex,which can be divided into no action area,start-up area,maximum power tracking area,constant speed area and constant power area under different wind speed ranges.In this paper,different small signal analysis models are built according to different operation characteristics and control modes of DFIG in different operating zones.The eigenvalue analysis method is used to study the variation of each oscillation mode with relevant influencing factors in different operatin zones.and a classification method of wind farm units based on operatin zones is proposed.And to establish the equivalent description model of wind farm accurately,a classification method of wind farm units based on operatin zones is proposed.The main work of this paper is as follows:(1)This paper analyzes the working principle of DFIG and its control system,and establishes the mathematical models of wind turbine drive chain,pitch angle control,induction generator,converter and its control system,line series compensation.The mathematical model is linearized,the state variable is selected,the state equation is constructed,and the small signal model of DFIG connected to the power system is established.(2)This paper analyzes the operation characteristics of DFIG in different operating zones,and establishes a small signal model of single machine equivalent DFIG connected to power system in different operating zones.Through the analysis of the eigenvalues of the system in different operating zones,six groups of oscillation modes are obtained.Through the participation factor analysis,the influencing factors such as wind speed,line series compensation and converter control parameters are obtained.(3)Taking wind speed,line series compensation and converter control parameters as influencing factors,the power oscillation analysis of DFIG connected to power system is carried out,and compare the influence of different operating zones on the power oscillation modes.The corresponding time-domain simulation model is established to verify the power oscillation mode.(4)This paper analyzes the distribution characteristics of the operating zone of wind farm units at the same time,puts forward that the distribution of the operating zone of wind farm units can be judged based on the wind speed of benchmark wind turbine,and establishes the principle of priority for the selection of the operation area.Based on the correlation between the wind speed and the wind speed of the current wind tower,a method is designed to divide the distribution of wind farm units according to the operating zone On this basis,the Markov state transition probability matrix describing the wind speed interval transition is established to further predict the wind farm unit division at the next time.This subject has conducted in-depth analysis of the power oscillations of a doubly-fed wind farm connected to the power system.The proposed method has certain engineering practical significance for accurately grasping the dynamic characteristics of large-scale wind power connected to the power system.