Research On Phenomenological Modeling And Fault Characteristics Of Vibration Signals Of The Wind Turbine Gearbox

With the increasing problems of global energy shortage and deterioration of the ecological environment,as a green and renewable energy source,wind energy has developed rapidly in various countries worldwide.As a key component of wind turbines,the gearbox is prone to gear faults such as cracks,wear,and broken teeth under harsh service conditions such as long-term speed changes,heavy loads,and frequent impacts.Once a fault occurs,the cascading effect between components is likely to lead to the loss of function of the entire transmission system,resulting in huge economic losses.The vibration signal of the wind turbine gearbox contains a wealth of key information on the health status.How to accurately reveal the generation mechanism and clarify the fault characteristics of the vibration signal is of great significance to realizing the fault diagnosis of key components,ensuring the safe operation of equipment,and avoiding major safety accidents.However,for the actual engineering application requirements of fault diagnosis for wind turbine gearbox,there are still two difficulties that have not been effectively solved:(1)There is a lack of an efficient and universal phenomenological vibration signal model.Most vibration signal models of wind turbine gearboxes are proposed based on dynamic methods and for specific parameter systems,which are heavily dependent on the certainty and accuracy of system parameters,resulting in low efficiency and poor universality of the modelling methods.(2)The law of fault characteristics of complex vibration signals is unclear.The industrial wind turbine gearbox is a multi-stage gear transmission system consisting of fixed-axis and planetary gear trains.Most vibration signal models do not consider the coupling between the vibrations of all stages and the influence of the time-varying transmission path effect in the multi-stage gear system,resulting in the "abnormal" features in the vibration signal that cannot be traced to the source,which further leads to misdiagnosis.Faced with the above difficult problems,this paper takes the typical structure of "one-stage planetary stage and two parallel stages" of the wind turbine gearbox as the research object and aims to realize the efficient diagnosis of typical faults based on fault feature characterization,the phenomenological modelling and fault feature analysis of vibration signal of wind turbine gearbox is systematically studied;the phenomenological vibration model established according to the operation characteristics of the wind turbine gearbox,the vibration information transmission mode,the fault evolution law and the experimental observation only need the basic parameters of the system to reveal the characteristic law of the vibration signal from the macroscopic level,and the modelling efficiency is high and universal.At the same time,it can provide answers to questions such as "why the fault features occur" and "what are the fault features",providing a theoretical basis and method for fault diagnosis.(1)Modulation mechanism and improvement of the phenomenological model of vibration signal of the fixed-axis gear train.The vibration signal model of a gear pair in a fixed-axis gear train is the basis for studying other complex gear systems.However,the traditional AM-FM vibration signal model has the limitation that it cannot effectively diagnose and distinguish between a local fault and distributed fault.Therefore,based on the established dynamics model of gear pair considering displacement error excitation and time-varying mesh stiffness excitation,the system kinematic differential equation is transformed into a linear system with different excitation forces.Using the frequency holding characteristic of the linear system the characteristic variation law of vibration signal is deduced under normal operating conditions,a distributed fault,a local fault,and compound faults,the modulation mechanism of vibration signal and the generation mechanism of vibration characteristics is revealed,the source of each frequency component is analyzed.Based on these,an improved AM-FM phenomenological vibration model of gear pair is proposed,which provides a basis for the research on the generation mechanism of vibration signal and phenomenological modelling of other complex systems.(2)Phenomenological vibration signal modeling and vibration characteristic analysis of planetary gear train under normal condition.Firstly,the two factors that affect the complex vibration response of the planetary gear train even under normal condition are analyzed and modelled.Based on the gear meshing mechanism,the meshing pair phase model with the initial meshing point as the reference point is established,and the phase relationship of each meshing pair is obtained;through the detailed analysis of the time-varying transmission path in the planetary gear train,the vibration attenuation theory is introduced,and two transmission path effect models based on the properties of the gearbox and the modulation phenomenon are proposed.Based on these,a phenomenological vibration model of the planetary gear train under normal condition is established considering the phase difference of gear pairs,the time-varying transmission path effect,and the position and bearing characteristics of the planet gears.Based on the phenomenological model,the frequency characteristic distribution law of modulation sidebands around meshing frequency harmonics is deduced,and the frequency characteristic generation mechanism of the planetary gear train under normal condition is revealed.(3)Phenomenological vibration signal modeling and vibration characteristic analysis of planetary gear train under faulty conditions.Based on the phenomenological modelling of the typical fault vibration signal of the fixed-axis gear train and the research results of the gear pair phase model and the time-varying transmission path effect under normal condition of the planetary gear train,Considering factors such as the phase difference of gear pairs,timevarying transmission path effect,position and bearing characteristics of planet gears,a phenomenological vibration model of the planetary gear train with distributed and local faults of a sun gear,ring gear and planet gear are established.Based on the phenomenological model,the change law of fault characteristics of each component under different fault modes is deduced,the generation mechanism of each frequency component is analyzed,and the typical fault identification and characterization mechanism based on vibration signal characteristics are clarified.(4)Research on phenomenological vibration signal modeling and fault diagnosis strategy of multi-stage gear transmission system of wind turbine gearbox.The vibration signal modulation mechanism and phenomenological modelling research results of fixed-axis gear train and planetary gear train are applied to the multi-stage gear transmission system of wind turbine gearbox,and the equivalent transmission path effect function model of the multistage gear transmission system is proposed.The phenomenon of inter-stage meshing frequency modulation in the muti-stage gear transmission system is presented,and the ISMFM model of vibration at the meshing point is proposed to explain the reason for the generation of inter-stage meshing frequency modulation sidebands.Based on these,a phenomenological vibration model of multi-stage gear transmission system considering the influence of inter-stage vibration coupling and time-varying transmission path is established,and the characteristic change law of vibration signal corresponding to different sensor measuring points in different health states is deduced,the generation mechanism of interstage meshing frequency modulation sidebands and transmission path effect modulation sidebands is revealed,which avoids the problem of misdiagnosis caused by unclear frequency components.In this paper,the measured vibration signals of the experimental bench and the industrial wind turbine gearboxes under different gear fault conditions are used to verify the correctness of the proposed series of phenomenological vibration models,and to diagnose the gear fault based on the vibration fault characteristics.Studying the above-mentioned theories and methods of phenomenological modelling of the vibration signal of wind turbine gearboxes,clarifying the change law of the fault characteristics of the vibration signal,and realizing the fault diagnosis of key components,it is of great significance to ensure the safe operation of wind turbine equipment,improve the power generation efficiency,alleviate the energy dilemma,and help green sustainable development.At the same time,the phenomenological modelling ideas and strategies of vibration signals proposed in this paper are not only applicable to the wind turbine gearboxes studied in this paper,but also to other multi-stage gear systems with similar structures,providing a theoretical reference for the research on vibration signal modelling.