Analysis And Modeling Of Iron Loss For Magnetic Field Modulated Permanent Magnet Machines

As the core driving component of advanced manufacturing and defense equipment,electrical machine is developing towards high precision,high torque density and high efficiency.However,the power density of traditional electrical machine is close to the upper limit,and it is difficult to get further improvement.At present,with the development and improvement of magnetic field modulation theory,the new magnetic field modulation permanent magnet machine has attracted extensive attention of scholars due to its advantages of high torque density and high reliability.But at present,the research of new magnetic field modulated permanent magnet machine mainly focuses on the working mechanism,topological structure,pole-slot combination and so on,but the research on the losses is very little.There are abundant spatial harmonic magnetic fields in the airgap of magnetic field modulated permanent magnet machine,which not only produce multiple torque components,but also produce various harmonic losses.Therefore,in the design and analysis of the magnetic field modulated permanent magnet machine,it is necessary to calculate not only the electromagnetic field distribution to ensure that the output characteristics meet the requirements,but also to calculate the losses to ensure that the thermal load in a safe range,avoiding the permanent magnet demagnetization.In this paper,as one of typical magnetic field modulation electrical machines,the flux switched permanent magnet machine is taken as the research object,mainly focuses on the fine calculation model of iron loss,the influence of the bidirectional coupling between the electromagnetic field and thermal field on iron loss and the influence of PWM inverter power supply on iron loss.The main research contents and achievements of this paper mainly include the following aspects:1.Based on magnetic field modulation theory,the coupling relationship between air gap magnetic field spatial harmonics and iron loss is revealed,and the unity of iron loss analysis of magnetic field modulated permanent magnet motor with different topologies is verified.2.The refined iron loss model and 3D finite element calculation model of transient thermal field for the nine-phase flux switched permanent magnet machine are established.Firstly,an improved iron loss model is proposed,which considers the effects of end-flux leakage,DC bias and rotating magnetization on iron loss.Secondly,in the 3D transient thermal field finite element model,the calculation methods of boundary condition coefficients such as the convective between frame and the environment,the convective heat dissipation in the end space,the convective between stator and rotor through the airgap and the contact thermal resistance are given,and the corresponding boundary conditions of the stiffness matrixes are deduced.The experimental platform of nine-phase flux switched permanent magnet machine is built,and the total loss of the machine and the temperature rise curves of the winding and the outer frame are measured.The accuracy of the proposed calculation method is verified by the experiment.3.The calculation method for the iron loss based on the bidirectional coupling analysis between the electromagnetic field and thermal field is proposed.Firstly,the iron loss curves under different magnetic flux densities at different temperatures are measured by Epstein’s square frame experiment,and the influence of DC magnetic bias on iron loss is considered.It is found that the iron loss decreases when the temperature increases.Secondly,an analytical calculation model of eddy current loss of permanent magnet is established,in which the influence of temperature and segment on the loss can be considered.Finally,based on the finite element program of 2D transient electromagnetic field and 3D transient temperature field,a bidirectional coupling calculation program of electromagnetic field and temperature field is established,in which radial basis function neural network is used to transfer data between different physical fields.An experimental platform of flux switching permanent magnet motor is built to verify the accuracy of the proposed method.4.The iron loss calculation model under the pulsation width modulation(PWM)inverter supply is established based on the magnetic field modulation theory.Firstly,based on the magnetic field modulation theory,the spatial harmonic distribution of no-load and armature reaction airgap magnetic field of flux switched permanent magnet machine is calculated,and the main spatial harmonics of air gap magnetic field that contribute to the iron loss are found.Secondly,the equivalent current layer in the 2D finite element model is used to synthesize the space harmonics which contribute to the stator/rotor iron losses,and the iron losses are calculated by the post-processing iron loss model.Finally,the influence of different control strategies on iron loss is considered,and the accuracy of the proposed method is verified by experimental measurements.5.The multi-physical field coupling simulation platform of motor is built.Based on the finite element program generation(FEPG),the finite element calculation programs of 2D transient electromagnetic field and 3D transient thermal field are developed,and the bi-directional coupling calculation platform of electromagnetic field and thermal field can be built based on radial basis function neural network,and the accuracy of the calculation is verified by experimental measurements.