Modeling Of Doubly Fed Induction Generator Type Wind Turbine On Current Control-time Scale When Considering The Dynamic Of Phase Locked Loop

The renewable energy power generation represented by wind power has developed rapidly in recent years.Among them,the doubly-fed wind power generation technology has become the mainstream of wind power generation because of its lower converter capacity and strong controllability.However,the large-scale wind power connecting to the grid also brings hidden dangers to the power system.Some of the oscillation phenomena related to the fast-time-scale of the doubly-fed wind turbines occur at different times and in different regions.The dynamics of the doubly-fed generator is the key factor determining the dynamics of the system,and modeling of the doubly-fed generator is the basis for analyzing and studying its dynamic characteristics.The modeling of the doubly-fed wind turbine should base on the understanding of the equipment characteristics,and has an intuitive understanding of the dynamic process of the equipment,through the abstraction of certain physical concepts.The existing model can't describe its behavior well on these issues.To analyze the mechanism of oscillation and analyze the role of the doubly-fed generator equipment in the dynamic process of the system,a model with faster time scale of the equipment,and also a deeper understanding are needed.By applying the idea of the internal voltage's amplitude and frequency motion equation,and based on the knowledge of the doubly-fed wind turbine dynamic in current control time scale,the equipment model with the unbalanced current as the input and the internal potential amplitude and frequency as the output is established.In this process,the variation of slip in the dynamic process of doubly-fed induction machine is revealed.Based on this model,the dynamic characteristics and influencing factors of the current control of the doubly-fed wind turbine are studied.The specific content can be divided into the following aspects:(1)Based on the typical control framework of the doubly-fed wind turbine,the sequential action characteristics of the doubly-fed wind turbine controller and the multitime-scale dynamic characteristics are analyzed.This paper expounds the modeling problem of the doubly-fed wind turbine in the current control time scale under the small disturbance.On this basis,the research focus of this paper is defined.(2)According to the current control time scale problem studied in this paper,the dynamic behavior and influencing factors of the doubly-fed wind turbine at this time scale are analyzed.The amplitude/frequency of the internal voltage in the rotor side converter is analyzed under the dynamic of Phase-locked loop.The formation mechanism reveals the characteristics of the time-varying amplitude-frequency of the internal potential during dynamic process.The analysis of the simple circuit under the time-varying amplitudefrequency signal,demonstrates the necessity of the equivalent of the complex doubly-fed generator circuit,under the time-varying amplitude-frequency internal potential excitation.And the dynamic equivalent circuit diagram of the doubly-fed generator is given.In the dynamic process,the expression of the variation slip of the doubly-fed generator is given,which provides the basis for subsequent modeling and analysis.(3)From the perspective of knowing and understanding of the equipment,this paper introduces the amplitude-frequency motion equation idea of modeling with intuitive meaning.In the common synchronous rotating coordinate system,the unbalanced active reactive current as the excitation input,and the amplitude frequency response of internal voltage as the output,the motion equation model is established.In the modeling process,the state quantity and the output internal voltage of the equipment are used to replace the terminal voltage information that needs to be obtained from the external network.So a model that only reflects the characteristics of the equipment is obtained.On this basis,the branch of the terminal voltage information from the internal voltage and the feedback current is further simplified,and linearized near the steady-state operating point,a small perturbation model for analyzing the current control time scale dynamic is derived.(4)By comparing the time domain simulation of the detailed model with the amplitudefrequency motion equation model in a single-machine infinite system,the accuracy of the amplitude-frequency equation model of the doubly-fed wind turbine in the current time control is verified.The correctness of the derived small perturbation model is also verified from time domain simulation and eigenvalue analysis.At the same time,based on the small perturbation model,the dynamic characteristics of the doubly-fed wind turbine in the current control time scale under small disturbances are analyzed.The time domain simulation is performed from the spectrum characteristics of the transfer function which the unbalanced current excitation as input–the amplitude frequency response of internal voltage as output.The above analysis results were verified and explained.In the dynamic process,the influence of the variation of the slip on the equipment characteristics is studied,and some phenomena appearing in the previous analysis are analyzed and explained.