| Large horizontal axis doubly-fed wind turbine is one of the most important clean energy equipment at present.However,with the rapid development of wind power,the blades of the turbines are getting longer and the tower are getting taller,which result in more complex dynamic characteristics of the turbines and seriously affect the safety of the turbines.Among them,incoming turbulence,aerodynamic imbalance and vortex-induced vibration of wind turbines have critical effects on drive train,column load and dynamic characteristics.Therefore,this paper takes two large horizontal axis doubly-fed wind turbines(WT3300D146,WT2000D121)as the research object,mainly through the method of field test,combined with numerical simulation,to carry out the dynamic characteristics analysis and load identification of key components of large doubly-fed wind turbines.The main results are as follows:(1)Influence of turbulence intensity on dynamic characteristics of wind turbine drive train and towerThrough the field tests on WT3300D146 doubly-fed wind turbine for 18 months,the load and dynamic characteristics of the turbine affected by turbulence intensity were studied and the mechanism was analyzed.Based on the tests to summarize the laws of the turbulence intensity influence on the load and dynamic characteristics of wind turbine drive train and tower cylinder.The turbulence intensity increases by 0.02,the load torque of drive train,the bending moment of tower cylinder load and the front and rear vibration acceleration of tower all increase by about 10%.The power spectrum analysis was carried out on test loads of drive train and tower to explore the correlation mechanism between turbulence intensity and dynamic characteristics.The power spectrum of blades,transmission chain and tower top Mx and My showed obvious spikes,which mainly came from the unit frequency and natural frequency of component.(2)Influence of wind turbine rotor aerodynamic imbalance on dynamic characteristics of drive train and towerThe field experiments of aerodynamic imbalance of wind turbine was carried out with WT2000D121 doubly-fed wind turbine,and the mechanism of load rise of drive train and tower caused by aerodynamic unbalance was discussed.When the aerodynamic imbalance of wind turbine was 3.91°,the blade root swing load of one blade was seriously separated.The imbalance of blade root load brings the fluctuation in the tested drive train bending moment My and yaw Mz,which seriously affected the fatigue life of drive train and tower.The spectral kurtosis theory was introduced to analyze the measured load and vibration acceleration data of the tower,and a method for identifying aerodynamic unbalance features was obtained..Combined with the blade elements momentum theory,a set of simulation analysis method was proposed under the condition of aerodynamic unbalance of wind turbine.(3)The influence of vortex-induced coupling between turbine blade and tower on the dynamic characteristics of towerAccording to the vortex excitation theory,the test method of vortex excitation was developed,and the test was carried out on the WT3300D146 wind turbine.The mechanism of coupled vortex excitation between blade and tower was discussed based on the experimental data of vortex excitation in the field,indicating that the obvious shaking of non-operating wind turbine was caused by the coupling of vortex excitation between blade and tower.Through the laser displacement verification scheme,the VIV recognition model based on the acceleration signal was established.In addition,the vortex-induced vibration of the wind turbine will not bring obvious load to the drive train.Therefore,the key influence was the fatigue life of wind turbine tower.According to the analysis of the frequency spectrum of the column acceleration,there were obvious first-order blade oscillation frequency(0.808Hz)and second-order blade oscillation frequency(1.945Hz).Thus,it can be determined that the vortex induced force of the wind turbine blade is transmitted to the tower,and the vortex induced coupling characteristics of the wind turbine blade and the tower are further verified;The CFD flow field simulation of blade and tower coupling is carried out based on the strip principle.The characteristics of unit dynamics and flow field structure are analyzed by using the one-way fluid structure coupling method.(4)Tests and analysis of dynamic characteristics of wind turbine drive trainThe drive train vibration test was carried out in the field and on the test bench,and a set of drive train sweep frequency test system was built and a set of vibration sweep frequency test method was formed.Based on WT3300D146 wind turbine,vibration sweep test of drive train in outfield and test-bed was carried out,and the consistency of the results was verified.The Overall Level Burt diagram showed that the second and third levels of the drive train gearbox of the wind turbine had resonance points at 1720 RPM,and the resonance frequencies of the drive train gearbox of the wind turbine were screened out at 750 Hz and 1500 Hz by using the Colormap analysis method.A rigid-flexible coupling multi-body dynamics simulation model was constructed to study the dynamic characteristics and mechanism of the drive train system,and guide the experiment to identify the gearbox and resonance parts.The vibration characteristics of the drive train system are analyzed by loading turbulent wave load.The results show that the meshing force of the first,second and third gears is affected by turbulent wave load,but the vibration frequency and acceleration amplitude of the drive train do not change significantly.(5)Wind turbine drive train dynamic load identification algorithm and verificationThe dynamic load characteristic model of transmission chain was established,and a low speed shaft torsion load identification algorithm combining torsional vibration of drive train and torque characteristic of generator was proposed.The multi-body dynamic rigid-flexible coupling model simulation calculation was carried out,and the experimental verification of WT3300D146 doubly-fed wind turbine was carried out.Load identification algorithm was independently written by Matlab,and load identification method was applied to calculate the torsional load of low-speed shaft without adding load measurement sensors,and dynamic identification load model was verified by field test.In the low wind speed section,the deviation of equivalent fatigue value of identified load was slightly larger,but the deviation of average value was small.Above the rated wind speed,the dynamic identification load was in good agreement with the average value and equivalent fatigue load measured,and the deviation was more than 5%,which met the engineering requirements.(6)Research and verification of wind turbine tower dynamic load identificationA dynamic simulation model was established for WT2000D121 doubly-fed wind turbine.The sensitivity analysis of the aerodynamic and dynamic characteristics of the unit was carried out,and the correlation between the tower cylinder load and the aerodynamic and dynamic characteristics of the wind turbine was given from the variation trend of load and operation state.According to the aerodynamic and dynamic characteristics of the wind turbine,a tower dynamic load identification model was built,and the constructed model was embedded into the test wind turbine to carry out field experiments.The tests results showed that the overall deviation between the dynamic identification load and the measured average value should be less than 10%,which had a high degree of coincidence and could meet the requirements of engineering application.However,the simulation results were more consistent with the measured results near the rated wind speed.Experimental results showed that the dynamic load model identification results were relatively stable,and this method could provide support for the application of wind turbine tower,and provide a convenient method for the safety monitoring of wind turbine. |
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