VP12-05: Investigation of the Over-Load Unintentional Remagnetization Effect in Series Hybrid Magnet Variable Flux Memory Machine

I. Introduction Variable flux memory machines (VFMMs) [1]-[4] using low coercive force (LCF) permanent magnets (PMs) have been extensively investigated. A series hybrid magnet VFMM (SHM-VFMM) with high coercive force (HCF) and LCF PMs is proposed in [2], featuring large flux regulation range and high efficiency. It is widely acknowledged that over-load currents may cause unintentional demagnetization. However, over-load unintentional remagnetization (UR) is also found in the SHM-VFMM. In this paper, the over-load UR effect and its mechanism are investigated. II. Investigation of Over-Load Unintentional Remagnetization Effect The machine topology is shown in Fig. 1 (a). To analyze the UR effect, the machine is initially set under the flux-weakened state, and then three periods including no-load, over-load and no-load operations are successively conducted. The back-EMF and LCF PM flux density are shown in Fig. 1 (b). The back-EMF has a 16% increase, and partial remagnetization happens in the LCF PMs, indicating that UR effect exists during over-load operation. The frozen permeability (FP) analysis [5] is applied to study the mechanism of this effect. Fig. 2 (a) shows the magnetic field with only over-load current. Due to the absence of HCF PMs, parts of the LCF PMs are demagnetized. Figs. 2 (b) shows the magnetic field of both over-load current and HCF PMs. The magnetic fields of the over-load current are pushed by the HCF PMs to the other parts of the LCF PMs, leading to UR effect. As shown in Figs. 2 (c), both PM flux linkages and LCF PM magnetization ratios increase with q-axis currents, indicating that magnetic cross-coupling [6] happens. III. Experimental Validation Fig. 2 (d) shows the SHM-VFMM prototype. The open-circuit back-EMFs under the flux-enhanced and -weakened states are shown in Fig. 2 (e). The test results agree well with the finite element (FE) results. The detailed UR mechanism, analyses and test results will be given in the full paper.References: [1] V. Ostovic, "Memory motors," IEEE Ind. Appl. Mag., vol. 9, no. 1, pp. 52-61, Jan./Feb. 2003. [2] H. Yang, H. Zheng, H. Lin, Z. Q. Zhu and S. Lyu, "A novel variable flux dual-layer hybrid magnet memory machine with bypass airspace barriers," in 2019 IEEE Int. Electric Machines & Drives Conf. (IEMDC), pp. 2259-2264. 2019. [3] Hui Yang, Xiaomin Chen, Heyun Lin, Z. Q. Zhu, and Shukang Lyu, “On-load demagnetization effect of high-coercive-force PMs in switched flux hybrid magnet memory machine”, AIP Advances, vol. 9, no. 12, Article No. 125152, 2019. [4] R. Tsunata, M. Takemoto, S. Ogasawara and K. Orikawa, "Variable flux memory motor employing double-layer delta-type PM arrangement and large flux barrier for traction applications," IEEE Trans. Ind. Appl., vol. 57, no. 4, pp. 3545-3561, July-Aug. 2021. [5] W. Q. Chu and Z. Q. Zhu, "Average torque separation in permanent magnet synchronous machines using frozen permeability," IEEE Trans. Magn., vol. 49, no. 3, pp. 1202-1210, March 2013. [6] G. Qi, J. T. Chen, Z. Q. Zhu, D. Howe, L. B. Zhou and C. L. Gu, "Influence of skew and cross-coupling on d- and q-axis inductances and flux-weakening performance of PM brushless AC machines," in 2008 Int. Conf. Electric. Machines & Syst. (ICEMS), Wuhan, China, 2008, pp. 2854-2859.