| With the rapid development of global industry,the atmospheric greenhouse effect is intensifying,and the impact on global climate,environment and economy is becoming more and more serious.Therefore,the concepts of energy saving and emission reduction,sustainable development are gradually being brought to an unprecedented strategic level.As a highly efficient energy conversion medium,permanent magnet motors are widely used in wind power generation,new energy vehicles and other fields with high market potential.In conventional pre-magnetization technology,the magnets are fully magnetized before mounted on the rotor to form the magnetic poles.Strong magnetic forces will be generated during installation due to the strong magnetism of saturated magnets,making this technology has the shortcomings of high installation difficulty,low efficiency,and the consistency of the magnetic poles cannot be guaranteed.Post-assembly magnetization(PAM)is a technology in which unmagnetized magnets are mounted on the rotor before the motor or pole is magnetized by a specially designed magnetizing coil.This technology can realize the non-magnetic installation of magnets,which can greatly improve the production efficiency and is beneficial to ensure the consistency of the magnetic poles and improve the motor performance,making this technology of great significance to the design and manufacture of permanent magnet motors,especially large-power permanent magnet motors.As the power and volume of motor increase,the action range of magnetizing field increase,which significantly increase the design difficulty of PAM system.The existing research results cannot comprehensively guide the PAM system design of medium and large power permanent magnet motor.Therefore,the key technologies of PAM system of permanent magnet motor,such as target magnetizing field acquisition method,magnetization scheme design,and collaborative optimization of power supply and magnetizing coil,are studied in depth through theoretical analysis and experimental verification in this paper.The main research contents and results are summarized as follows.In terms of investigation of saturation magnetization characteristics of permanent magnets in post-assembly magnetization application,the influence of magnetization history on the magnetization characteristics of permanent magnets is analyzed and revealed taking sintered neodymium iron boron(Nd Fe B)magnet as the object.It is pointed out that both the remanence and intrinsic coercivity of permanent magnets should be taken as the assessment indicator of saturated magnetization,which can avoid the problem that taking only the remanence as indicator may lead to poor anti-demagnetization ability.The calculation formulas of the saturated magnetizing field along the easy axis and deviate from the easy axis are proposed based on the principle of demagnetization field and the starting field theory.Theoretical basis for the PAM system to obtain target magnetizing field is provided based on the above results.The magnetization experiment platform is designed,based on which the correctness of the formulas for calculating the saturated magnetizing field are verified experimentally.In terms of investigation of demagnetization characteristics of permanent magnets,according to the overall demagnetization demand of permanent magnet motor,the effect of field demagnetization and thermal demagnetization on sintered Nd Fe B magnets are studied in comparison at first,and it is pointed out that the former method is more suitable for the application of demagnetization of motor or magnetic pole.Then,the demagnetization pattern of permanent magnets in pulsed magnetic fields of different amplitudes and directions in PAM applications is revealed by experiments.On this basis,the fitting formula of field for demagnetization in the sense of nonlinear least square are proposed.In addition,the criterion of demagnetization is proposed,which provide theoretical guidance and design basis for the optimization of PAM system.In terms of investigation of PAM scheme,an optimal design scheme of PAM system of interior permanent magnet motor based on auxiliary stator type magnetizing yoke,which considers both the shape of the magnetizing poles and the turn number of the magnetizing coil is proposed.The rotor is saturated and the required energy is reduced by 23.1%.Based on additional integrated magnetizing coil method,an optimal design scheme of PAM system of surface-mounted permanent magnet motor considering the thermal demagnetization effect of permanent magnets and an improved PAM scheme combining stator winding and integrated magnetizing coil are proposed,which can saturate the surface-mounted permanent magnet motor while avoiding thermal demagnetization of permanent magnets and reduce the cost of copper wire of the integrated magnetizing coil by 14.3% and the required energy by 64%.For the application of PAM technology in a 2.5 MW permanent magnet wind generator,a multi-objective optimization method for the PAM system considering the eddy effect and the demagnetization of adjacent pole is proposed.The current pole can be saturated while avoiding demagnetization of adjacent pole using the optimized PAM system designed by this method.The coil temperature rise and the consumed energy are reduced by 50.9% and14.7% compared with the method of increasing discharge voltage.According to the requirements of continuous discharge in practical application,a scheme of water-cooled magnetizing coil using hollow conductor is designed.When the cooling water flow rate reaches 1 m/s,the continuous discharge at an interval of 4 minutes can be realized.A prototype of pulse magnetizing device whose capacity is 2 MJ is developed,and the magnetizing experiment is carried out with three rotor poles of the 2.5 MW permanent magnet wind generator.The saturated magnetization of a 1.5 m-long pole is realized without demagnetizing the adjacent saturated pole.The feasibility of the design scheme is verified. |
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