| In recent years,wind energy has become one of the most promising renewable energy sources.In China wind energy is abundant and has a wide distribution.Through a wind resource assessment in China,it estimates to provide wind power potential of 1 billion k W.In 2018,the number of newly installed wind turbines in China ranked first worldwide.A wind turbine gearbox is a core component of the double-fed induction generator,which is commonly used in the market.Of the entire wind turbine,the gearbox has the highest failure rate,due to the irregular loads applied by the wind force.The permanent magnetic gear provides a good solution to the issue mentioned above.The inherited features of the permanent magnetic gear has several advantages includes overload protection,isolation of vibration and shock;in addition,no need for lubrication.Therefore,the permanent magnetic gear is a popular research topic in the field of electromechanical transmission field.Although the permanent magnetic gear has the above-described advantages,the transmission structure and the properties of the magnetic material,limits its transmission power and ratio.The transmission power and ratio is insufficient,because it doesn't meet the need of a megawatt-level powered wind turbine gear transmission system.This dissertation proposed a Magnetic Increasing Speed Gearing System(MISGS),aiming to solve the key technical problems mentioned above.The MISGS cascaded together multiple Field Modulated Permanent Magnetic Gears(FMPMG),which enables to achieve large power and high transmission ratio.In this dissertation,in order to achieve the above technical objectives,the research focused mainly on the following aspects:(1)This dissertation categorized the existing permanent magnetic gears by the torque density.For permanent magnetic gears,only the torque density greater than 100k N·m/m~3 were taken into analysis.There were only a few types of permanent magnetic gear met above conditions:cycloid permanent magnetic gear,harmonic drive gear,2K-H type permanent magnetic gear and Field Modulated Permanent Magnetic Gear(FMPMG).The output mechanism of cycloid and harmonic drive magnetic gears were comparably complicated,and the dynamic characteristics of the 2K-H type permanent magnetic gear can not be adoptive widely.Therefore,in this dissertation,the analysis focused on the transmission characteristics of FMPMG.(2)Based on the mechanical structure and operating mechanism of FMPMG,there were three speed-shift operating modes:the pole pieces were in a fixed position,the outer rotor and the inner rotor rotated in the reverse direction,which resulted in negative acceleration and deceleration;the outer rotor was in a fixed position,and the inner rotor and pole pieces rotated in the same direction,which created positive acceleration and deceleration;the inner rotor was in a fixed position,the outer rotor and the pole pieces rotated in the same direction,which created positive acceleration and deceleration.For each operating mode,the mathematical expression of torque and angular velocity were analyzed,based on the wave theory.(3)A mathematical model of the dynamic torque of FMPMG was established using the Maxwell stress tensor,which revealed the formation of the torque and the wave mechanism.It could be seen from the model,that the FMPMG torque,consisted of infinite waves of different periods and different amplitudes.The torque varied periodically.The dynamic characteristics of the FMPMG depended on the superimposition of the dynamic torque from each harmonic wave.(4)Based on the three speed-shift operating modes of FMPMG,this dissertation listed four possible cascade modes.Detailed performance and comparison were analyzed on its structures.It determined the detailed composition structure of MISGS,which were suitable for the increased magnetic torque of wind power generator.Similarly to the transmission ratio derived for the mechanical epicyclic gears train,this dissertation established the total transmission ratio equation for the MISGS.It can be derived from the equation that the total transmission ratio of MISGS is greater than that of the multiple of the transmission ratio from each single stage.(5)This dissertation divided the MISGS into two relevant modules:input module and connection module.Within the connection module,all three rotors rotated and the rotational direction of the magnetic ring opposes to that of the outer rotor.It requires to overcome the magnetic resistance of the outer rotor in order to produce the desired motion.In addition,this results in a larger distribution of generated power.Therefore,the connection module is the most complex component of MISGS.In order to optimize the connection module,this dissertation also included the detailed analysis of the dynamic characteristics of the connection module.The characteristics of the input module is also substantially described in this dissertation.(6)The input module and the connection module have the same basic structure as the FMPMG and so is the electromagnetic relationship.There are two air gaps present in the FMPMG:the inner air gaps and outer air gaps.All the harmonic magnetic fields which are present in the air gaps,can cut the magnetic fields originate from pole pieces,inner and outer permanent magnet and corresponding yokes.This generates eddy current loss and core loss,in the form of heat energy.As a result,this lowers the operation efficiency of FMPMG.Therefore,it was necessary to study the loss formation mechanism of FMPMG.This dissertation included an analysis of loss formation of each component and its affecting factors of FMPMG.Then,the dissertation calculated the loss value of each component using the finite element simulation with different influencing factors.Finally,the optimization measures are taken into account to reduce core loss for each component level.(7)Based on the above analysis and theory,this dissertation proposed and established a complete scheme for the megawatt-level transmission MISGS,including the mechanical structure and the calculation of the magnetic transmission.As an example,this dissertation detailed out the calculation of all parameters of 1 MW connection module and input module.The scheme of the permanent magnetic gear structure was also shown.The dynamic simulation model using the finite element analysis,together with the power transmission of each component were also shown in this dissertation.(8)A MISGS principle machine was designed and developed,based on the theory of this dissertation,which simulated a megawatt-level wind turbines.The transmission loss and transmission efficiency were measured under different conditions,e.g.increasing loads under the same rotation speed etc.The measurements were compared with the finite element simulation results,which verified and validated the reliability of the theory and techniques described in this dissertation. |
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