Harmonic Resonance Assessment And Harmonic Instability With A Large Scale Wind Parks

With the fast development of wind power generation in all around the world,there are more than 40 countries in the world who owns the integration of large wind power skills.This master's thesis aims at the large scale wind farms that has a huge number of cable laying and submarine transmission.Distributed capacitance and inductance exists in wind parks interact with each other,it is likely to cause harmonic resonance.Moreover,because of the negative dampling of the VSC output impedance,sometimes there are the harmonice instability problem.This paper studies the resonance problem and harmonic instability phrnomenon in the wind farm in order to ensure the safe of the wind power and stable efficient operation.And the main work of this paper is as follows:Firstly,the harmonic model of wind farms is built in this paper.Based on the study of the back-to-back VSC harmonic model and the asynchronous motor harmonic model,the DFIG harmonic model with speed change is further established.At the same time,the harmonic model of important parts of the wind farm including cable,transformer,power gird side,reactive power compensation device is created.The research methods of harmonic resonance problem and instability problem,such as model analysis method,sensitivity method,Nyquist criterion and so forth are studied in this paper.Secondly,harmonic charateristics and resonance mechanism of the wind farm is studied.This paper investigates the law that grid side converter and rotor side converter inject the hamonics into the wind farm.Combined with the measured data,summarizing the harmonic law of the wind farm.Futhermore,the frequency scan method is used to analyze the different resonant conditions caused by the uncertain factors such as the change of the topology structure and the change of the working conditions.The general rule of the resonant frequency and amplitude is seek out.Thirdly,based on the model sensitivity analysis,the harmonic resonance and its suppression strategy is researched.Author utilizes the modal analysis method to find the resonant rule impact on the different system parameters and different opeating.The node sensitivity index is defined to quantify the influence of each node in the wind farm on the resonance.It reveals the penetration and propagation scale of resonance.Moreover,the sensitivity analysis is taken advantage to define the impedance sensitivity and the frequency sensitivity indexes,which are the foundation of the reasoant suppression.Meanwhile,using the frequency transfer method to cooperate with the filter to propose the resonance suppression scheme.Lastly,the VSC impedance model base on the control parameters is established to explore the output characteristics of the VSC in the wind turbine.In the meantime,exploring the transmission and amplication laws of the harmonics in VSC control loop.Furhermore,the Nyquist stability criterion is used to analyze the influencing factors of harmonic instability.Overall,this paper explore the harmonic resonance problem of the wind farm by using the harmonic resonance based on the measured data.At the same time,exploring the mechanism of harmonic instability problem.It is expected that this study can provide support to the related studies.