Analytical Model And Suppression Method Of Rotor Eddy Current Loss For High Speed Permanent Magnet Synchronous Motors

High-speed permanent magnet synchronous motors（HSPMSMs）have become a research hotspot in the field of motors due to their high efficiency and high power density.For HSPMSMs,the magnetic field of the motor contains a large number of high-frequency harmonics,which will cause more eddy current losses in the rotor.At the same time,the poor heat dissipation conditions of the rotor can easily cause the temperature of the permanent magnet to be too high,and there is a risk of irreversible demagnetization.The rotor eddy current loss of HSPMSMs is difficult to accurately calculate and effectively suppress.Therefore,it is necessary to study the accurate calculation model of rotor eddy current loss of high-speed permanent magnet motor and its suppression technology.In this paper,the subdomain method is used to establish the analytical model of rotor eddy current loss of HSPMSMs,and the influencing factors of rotor eddy current loss are analyzed by the established model.The specific research contents are as follows:Firstly,according to the source of rotor eddy current loss of high-speed permanent magnet motor,the analytical models of rotor eddy current loss under the combined action of armature magnetic field,ideal no-load magnetic field and armature winding and permanent magnet are established based on the accurate subdomain method.In order to meet the highspeed calculation accuracy,a diffusion equation is established to reflect the effect of eddy currents on the magnetic field.At the same time,for the problem that the dimension of the coefficient matrix of the accurate subdomain method is too large,periodic boundary conditions are used to improve the computational efficiency of the analytical model.In order to verify the accuracy of the analysis model,the loss separation method is used to separate the stator iron loss,copper loss and mechanical loss from the total loss of the motor,and obtain the rotor eddy current loss.The analytical model is validated by experiments and finite element simulations.Secondly,for the HSPMSMs with circumferentially segmented permanent magnets,an analytical model of rotor eddy current loss is established by using the subdomain method.The armature winding is equivalent to a current sheet model,and the effect of stator slotting is considered in combination with the permeability model.The permanent magnet segmentation effect is achieved by analytically forcing the eddy current on the cross section of each permanent magnet to be zero.In order to consider the influence of eddy current reaction,an attenuation coefficient including the penetration depth of harmonics is introduced to improve the analytical calculation accuracy.Through the C-type core loss measurement method,the segmented permanent magnets are tested to verify the correctness of the analytical model.Finally,using the established analytical model,the factors affecting the rotor eddy current loss of the HSPMSMs are discussed,including the number of stator slots,PWM switching frequency,slot width,air gap length and permanent magnet segment.From the overall trend,the rotor eddy current loss decreases with the increase of the number of stator slots,PWM switching frequency and air gap length,and increases with the increase of the slot width.Affected by high-order current harmonics,the rotor eddy current loss of high-speed permanent magnet motor will first increase and then decrease with the increase of the number of permanent magnet segments.When the circumferential width of the permanent magnet is two to three times the penetration depth of a certain current harmonic,the loss caused by the harmonic will reach its maximum value.