Research On Harmonics Adaptability Of Offshore Wind Turbine To Power Grid

With the increasing penetration of wind energy technology for the last three decades,the use of the offshore wind power has also been massively increased with the improvement of technology.No doubt wind power system is clean source of generating electricity however it does impose adverse effects on the distribution grid as well.Considering the application of grid connected offshore wind farm the most primary issue of power quality based on harmonic distortion is put forward in this thesis for three cases which include a large scale offshore wind farm consisted of individual strings of wind turbines,harmonic grid adaptability testing and low voltage ride through(LVRT)testing.As offshore wind farm comprises of numbers of wind turbines,harmonics analysis and especially harmonic resonance has become very compulsory.The resonance in offshore wind farm is caused due to the extensive combination of inductive and capacitive elements including undersea cables,shunt capacitors,converters,transformers etc,the emergence of resonance in turn will cause amplification of voltage distortion due to parallel resonance or it may also result in the harmonic current due to series resonance at the resonance frequency.A detailed approach of DFIG based offshore wind farm is considered to primarily focus on the harmonic penetration and mitigating those potential order of harmonics by using passive filters.For the purpose of reliability of grid connected offshore wind farm,a method is proposed to help perform harmonic grid adaptability testing easily.The harmonics generated by the testing equipment based on the testing standard may get intervened with undersea cable causing amplification and thus exceeding the actual testing standard or even resulting in resonance to occur.In order to deal with such adverse impacts while performing the harmonic grid adaptability testing,the resonance with particular testing frequency should be avoided,which is achieved with the help of resonance frequency(RFS)shift method.The proposed procedure highlighting modification equation helps in generating accurate level of harmonics according to the testing standard provided length of cable and its parameters are given.Further,in the case of low voltage ride through testing of offshore wind farm from harmonic distortion point of view,effects of passive filters are evaluated to measure the level of harmonic compensation and its effectiveness for transient as well steady state condition.Based on the testing standard the voltage sag of 0.5p.u is considered in the proposed approach of filter implementation.For more precision and understanding the effectiveness of the filters,the incurring orders of potential harmonics are compared with and without implementation of passive filter for both transient and steady state.For practicality of the aforementioned research MATLAB/Simulink is utilized for each of the three cases with supporting results to validate the proposed research.