| Since the late twentieth Century,the energy problem had become a global problem to be solved,and the development of renewable energy is the key to solve the global energy shortage.Wind power is an important part of renewable energy.The current trend for the design of a wind turbine is to have larger and more power units,reaching higher into the atmosphere to obtain more wind energy.And with the development of wind turbines,more turbines are installed in seismically active regions and offshore regions with rich wind resources,which makes the wind turbines under normal operation loads,and may experience seismic and typhoon loads.The damage of collapse maybe occur under external loads,which causes great economic losses.For the large-scale wind turbines,the baseline control system(BCS)is used to control the output power by adjusting the rotor speed and the blade pitch angle.According to the blade element momentum(BEM)theory,the rotor speed and the blade pitch angle directly affectt the aerodynamic loads and then affect the dynamic response of wind turbine.Therefore,in order to ensure the security and stability of wind turbines in the whole life period,it is very meaningful to study the structure-pitch intelligent methods for controlling the dynamic responses of wind turbines under normal operation loads,earthquake and typhoon loads.In this thesis,for large-scale wind turbines,according to the structure-pitch interdisciplinary,the dynamic characteristics and intelligent control methods under normal operation loads,earthquake and typhoon loads were studied.The influence of BCS on the dynamic characteristics of wind turbines was studied.Based on the artificial bee colony(ABC)algorithm,the optimization method of pitch controller parameters,which the control targets are to reduce the structural responses and output power fluctuation of wind turbines,was studied.The fragility of wind turbines with the combined excitation of wind and earthquake was studied.Based on the fuzzy control theory,the developed pitch control method was studied to control the dynamic responses of wind turbines with the combined excitation of wind and earthquake.Based on magnetorheological(MR)damper and fuzzy control theory,the strategy and method of vibration control for wind turbine blades under extreme wind loads were studied.Through systematic analysis and research,some valuable scientific research achievements have been obtained.The main research contents and conclusions are as follows:(1)The influence of the BCS on the dynamic responses and fatigue loads of wind turbines was studied.According to FAST(Fatigue,Aerodynamics,Structures and Turbulence)nonlinear wind turbine model,the variable speed,variable pitch control were realized by the combined simulation in MATLAB/SIMULINK control system,which contains the structural dynamic equations and multibody dynamic equations.The damage equivalent load(DEL)was calculated through the rain flow counting method.The dynamic responses and fatigue loads of the wind turbine under two conditions of normal operation,fixed rotor speed and blade pitch angle are compared and analyzed in the whole wind speed ranges.The simulation results show that the dynamic responses of wind turbine will be overestimated and the fatigue loads of wind turbine will be underestimated if the BCS is not considered.(2)An ABC-PID control method based on the ABC algorithm was proposed.To reduce the structural responses and output power fluctuation of wind turbines were identified as the control objectives.The multiobjective control function was designed through the displacement of tower top and rotor speed error,and the related overshoot penalties.The variable pitch controller parameters were considered as nectar and the optimal parameters combination can be searched through ABC.Using the combined FAST and MATLAB/SIMULINK simulation model,the ABC-PID optimization algorithm was implemented and compared with the existing control methods.The simulation results show that the proposed method can effectively reduce the dynamic responses and the fluctuation of output power and at the same time reduce the fatigue loads of the key parts of wind turbines,which improve the service life of wind turbines.(3)The fragility of wind turbines subjected to the combination of seismic and aerodynamic loads was studied.According to pushover analysis and the International Electrotechnical Commission(IEC)61400-1,the critical moment and displacement for wind turbines were proposed.Sensitive analysis of number of earthquake records on fragility of large-scale wind turbines subjected to seismic and aerodynamic loads was studied and the reasonable reference number was also given.The comparison of fragility in the whole wind speed ranges between the operation condition and parked condition was studied.And the influence of BCS on the fragility of wind turbines subjected to seismic and aerodynamic loads was studied.The simulation results show that,in the combined action of wind and earthquake loads,the continuous adjustment of the rotor speed and the blade pitch angle increases the aerodynamic damping,which causes the less dynamic response and fragility of wind turbine when compared the parked condition.(4)A self-adaptive fuzzy pitch(SFP)control method was proposed to reduce the ground motion responses of wind turbines subjected to seismic and aerodynamic loads.The S function containing the ground motion model and simulation interface was generated through the Fortran program and MATLAB compiler.The control system model combined with the fuzzy control theory was established in MATLAB/SIMULINK,and the fuzzy adaptive scale factor adjusting function based on the index function was also added in the system model.The SFP control method was verified by comparing the dynamic responses and fragility curves with the normal pitch control method.The simulation results show that the proposed SFP method can effectively reduce the responses and failure probability of wind turbines subjected to seismic and aerodynamic loads.(5)A semi-active fuzzy control method of edgewise vibrations in wind turbine blades under extreme wind was proposed.According to the characteristics of blade structure,the MR damper is mounted on a frame supported by the blade.Then the fuzzy rules and triangle membership function were deterrmined.The fuzzy control system produces the required voltage to be input to the damper so that a desirable damper force can be produced.The finite element model was established in ANSYS,and the corresponding mass matrix and stiffness matrix were extracted.Finally,the simulation control system model was established in MATLAB/SIMULINK to achieve the mitigation of edgewise vibrations.The control effect of the scheme if verified by comparing the blade tip displacement and the blade root shear force in the respects of the number and the position of the controllers,and the wind direction rotation 90 degrees.The simulation results show that the control scheme can be effectively used for suppressing edgewise vibrations of wind turbine blade under extreme wind loads,and has the characteristics of failure safety(Fail-Safe). |
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