Coupling Dynamics Research Of A Doubly-Fed Wind Turbine Drivetrain

With the increasing installed capacity of onshore wind turbines being gradually saturated,the wind power exploitation in the deep sea is becoming a research focus,the fixed base supporting structure is changing to be a floating type,and the power capacity of a wind turbine is developing toward a large scale.These tendencies require wind turbine drivetrain to have a higher reliable design.The high-speed drivetrain,which is usually applied in a doubly-fed wind turbine,has the obvious advantages that include higher quality stability,reliability,and lower maintenance cost,compared with other transmission systems.Currently,the wind power exploitation market is mainly dominated by high-speed drivetrains even if fewer years later.The high-speed drivetrain is a typical electromechanical coupling system that is driven by a multistage gear transmission system,where not only the driven side will suffer the time-varying aerodynamic torque,but also the loaded side will be affected by the electromagnetic torque impact induced by the grid disturbance.Obviously,this system will be influenced by the remarkable multi-source excitations.Besides,owing to the base supporting structure of the wind turbine being designed to be a floating type,the drivetrain vibrations are also subjected to the base motion.All the above-mentioned factors will cause the dynamic performance of the wind turbine to be affected by the operating surrounding,transmission structure,and control system,however,its detailed mechanism of action lacks in-depth study.This thesis takes a megawatt level doubly-fed wind turbine drivetrain as the research object by combining structural features with multi-source excitation features,in which structural features include the multi-component installation positions,multistage transmissions,multi-mesh points,multi-support points,and multi-flexibility components,and multi-source excitation features include the base motion,aerodynamic torque,electromagnetic torque,and internal excitations.With the consideration of the above-mentioned critical factors,the dynamics research method is applied to study the influence of the structural and electrical parameters on the modal and dynamic characteristics.On this basis,the effects of the base motion on the electromechanical characteristics of the drivetrain are discussed.The research results are of great significance to the dynamics design and dynamic performance optimization of the doubly-fed wind turbine drivetrain.The main contents of the thesis are classified as follows:(1)Combing the Euler's rotation theorem with the Timoshenko beam theory,the dynamic equations of a high-power wind turbine drivetrain are derived based on the base motions with the orthogonal decomposition in the inertial coordinate system.The control system of the aerodynamic torque is established by considering the pitch angle and wind energy utilization coefficient.The control system of the generator's electromagnetic torque is constructed by combining the equivalent circuit model of the generator with the rotor side control model.Finally,an electromechanical coupling dynamic model of a doubly-fed wind turbine drivetrain is proposed by integrating the drivetrain's transmission structure system and the control systems of the aerodynamic torque and the generator's electromagnetic torque,realizing the dynamic correlations among environmental parameters,structural parameters,electrical parameters,and control parameters.(2)From the perspective of the structural and electrical parameters of the system,the analysis method of the modal characteristic for the coupling system with the multistage transmission structures is proposed based on the modal shape,modal energy,and amplitude-frequency response analysis.On this basis,the vibration modes of the drivetrain are analyzed and summarized,and then the potential resonance points of the system are identified.Furthermore,the influences of the flexible main shaft and its suspension configuration on the potential resonance points of the system are studied.Based on the wind field test data of the generator rotor torque for a doubly-fed wind turbine and an equivalent two-mass model,the electromagnetic stiffness of the generator is found and calculated,and then the influences of the electromagnetic stiffness on the modal shape,modal energy,and amplitude-frequency response characteristics of the drivetrain are investigated.Finally,the load transfer paths and vibration forms of the system are obtained when the wind turbine is started.(3)The sensitivity analysis method of structural parameters in the system is proposed based on the couplings between the multi-structure parameters and multi-source excitations.Under the steady operating conditions,the influences of the flexible main shaft and its suspension configuration on the dynamic mesh forces of the gear pair,bearing loads and the load-sharing performance of the planetary gear stage are studied.Besides,the differences due to the influences of the flexible main shaft and its suspension configuration on loads of key components are compared.Considering the nonlinear factors such as the grid fault of the low voltage ride through,bearing clearance and gear backlash,the dynamic response characteristics of the drivetrain during grid voltage drop are analyzed.The action law of transmission structure parameters on the transfer paths of dynamic loads in the system is discussed.(4)Aiming at the dynamic performance analysis of the drivetrain with the coupling of base motions,the research method for analyzing the electromechanical dynamic characteristics of the wind turbine drivetrain under the excitation of base motions is proposed.The additional excitation matrix expressions for the components in the drivetrain induced by base motions are derived,and then the spectral characteristics of the system vibration responses are analyzed under the different base motions.Furthermore,the sensitivity for the vibration information of key components in the drivetrain to the base motion is analyzed,and the influences of operating conditions and base motions on the electromagnetic torque and stator current of the generator are compared.Finally,the feasibility of using the generator's stator current signal as the monitoring base motion condition is explored.(5)The dynamic characteristics test of a 2MW doubly-fed wind turbine drivetrain was carried out,and then an on-line vibration detection system for a wind turbine drivetrain was built.The vibration response characteristics of key measurement points are analyzed.The simulation results and test data are compared to verify the theoretical analysis.