Analysis and Experimental Verification of Segmented Rotor Structure on Rotor Eddy Current Loss of High-Speed Surface-Mounted Permanent Magnet Machine

Abstract

—The eddy current loss in the permanent magnet (PM) and the sleeve of high-speed surface-mounted permanent magnet synchronous motors (HS-SPMSMs) increases the temperature rise of the rotor, which increases the risk of irreversible demagnetization of the PM. In order to reduce the rotor eddy current loss (RECL) of HS-SPMSM, this paper analyzes the suppression effect of four different segmented rotor structures (axially segmented sleeve, circumferentially segmented PM, axially segmented PM, PM and sleeve are simultaneously segmented) on the RECL of HS-SPMSM. On this basis, the applicability of the rotor segmented structure to the RECL with different sleeve materials is further analyzed. Finally, the C-core experiment was used to verify the influence of different segmented rotor structures on the RECL.I. IntroductionHigh-speed permanent magnet synchronous motors (HS-PMSMs) have the characteristics of high-power density, but they also have the characteristics of high loss density and high temperature rise [1]. The high temperature of the rotor not only affects the performance of the motor, but also increases the risk of irreversible demagnetization of the PMs [2].In order to suppress the RECL of the PMSM, the PM is usually divided into pieces [3-4]. This method is usually applied to conventional speed motors without sleeves. For HS-SPMSM, which is widely used in HS-PMSM, the RECL is mainly concentrated in the PM and sleeve [5], and the segmentation of the PM will affect the eddy current loss in the sleeve. However, there is little research on the effect of permanent magnet segmentation on the RECL of HS-SPMSM with sleeve structure.In this paper, four segmented rotor structures are established, including axial segmented sleeve, circumferential segmented PM, axial segmented PM, PM and sleeve segmented simultaneously. This paper uses different segmented rotor structures with three commonly used sleeve materials (carbon fiber, titanium alloy, stainless steel), and analyzes the influence of different segmented rotor structures on the RECL of HS-SPMSM. Finally, the C-core experiment is used to verify the influence of different rotor structures on RECL.II. Segmented Rotor Structure and AnalysisA 15 kW, 30000 rpm HS-PMSM is taken as an example to analyze the RECL under different sleeve structures. When the motor is running at the rated speed, the four segmented rotor structures are analyzed for their suppression effect on RECL. The four segmented rotor structures are shown in Fig. 1.This paper analyzes the RECL of HS-PMSM with several commonly used sleeve materials (carbon fiber, titanium alloy, stainless steel), and studies the influence of segmented rotor structure on the RECL of HS-PMSM by using the four structures shown in Fig. 1. According to the calculation results, for the high conductivity sleeve material, when the number of axial segments reaches a certain degree, it is helpful to reduce the RECL, while for the carbon fiber sleeve, the axial segmentations have little effect on the RECL. When the PM is segmented axially or circumferentially, the RECL can be significantly reduced for the carbon fiber sleeve, and the effect of axial segmentation is better than that of circumferential segmentation. However, for the sleeve made of high conductivity material, the shielding effect on the eddy current magnetic field is weakened due to the segmentation of the permanent magnet, which makes the sleeve produce more eddy current loss and increases the total RECL. If the rotor structure shown in Fig. 1 (d) is used, the RECL can be reduced for all three sleeve materials, but the number of segments of PMs and sleeves needs to be reasonably configured.III.Experimental VerificationIn order to verify the influence of various sleeve materials on rotor eddy current loss and the suppression effect of sleeve axial segment structure on rotor eddy current loss. This paper verifies the influence of different sleeve structures on the eddy current loss of the rotor through the C-core experiment. The C-core experimental platform and different sleeve materials are shown in Fig. 2.IV.CONCLUSIONSThis paper compares and analyzes the RECL of HS-SPMSM with different rotor structures. The RECL generated by the high-conductivity material sleeve is relatively high, but it can shield the eddy current loss of the permanent magnet. For high-conductivity sleeves, the axial segmentation can reduce the eddy current loss of the sleeve by increasing the equivalent resistance of the sleeve and further suppress the RECL, when using PM segments, the sleeve will generate more eddy current loss, resulting in increased RECL. However, for carbon fiber sleeves, circumferentially or axially segmented PMs can help reduce the RECL, but the axial segmentation of the sleeve has almost no effect on the RECL. For the three sleeve materials, segmenting the sleeve and the PM at the same time will reduce the RECL, but the number of segmentations of the sleeve and the PM should be reasonably configured. **