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Top1. Introduction
Axial flux ironless permanent magnetic synchronous motor (AFIPMSM) is a new type of high performance servo motor developing in recent years. The AFIPMSM with outer rotor introduced in this paper is shown in Figure 1 (a), which has two disc rotors and a winding with ironless stator. The two disc shaped rotors carry the axially magnetized NdFeB magnets which are mounted axially on the inner surfaces of the two rotor discs. Halbach array were used in the rotor, and the flux density in circumferential direction is approximate sinusoidal distribution, which makes the back-EMF is sine. The waveforms of no-load back EMF is shown in Figure 1 (b).
Figure 1. Basic structure and the wave of Back EMF
Because of the ironless structure, there is no tooth or slot in the stator of the motor. The stator structure can not only eliminate cogging torque and reluctance torque, but also the quality of the motor has been reduced. And the motor’s efficiency is increased, because there have no iron losses in it. The parameters are linear for the magnet medium of AFIPMSM is almost air. The armature reaction is so small that the effect to no-load magnetic field may be neglected. Compared with the conventional motors with iron core, AFIPMSM have the advantages of high power density, small size, high overload capability, efficiency, no cogging torque and so on. Since it has the characteristics of the flat structure, particularly suitable for the workplace where have special requirements of the volume of motor (Wang Xiaoyuan, Chen Jing, Wang Pingxin, 2010; Xiaoyuan Wang, & Jingjuan Du, 2006). Based on the AFIPMSM has the advantages of the above, most studies for Axial flux ironless permanent magnetic synchronous machines focus on the electromagnetic aspects of analysis, optimization, design and the characterization of axial flux generator (A. Mahmoudi, S. Kahourzade, N. A. Rahim, and7 H. W. Ping, 2012; T. F. Chan, and L. L. Lai, 2007; S. Javadi and7 M. Mirsalim, 2008; W. Fei, P. C. K. Luk, and7 T. S. El-Hasan, 2011; S. M. Hosseini, M. Agha-Mirsalim, and7 M. Mirzaei, 2008; R. J. Wang, M. J. Kamper, K. V. Westhuizen, and7 J. F. Gieras, 2005; F. Sahin, A. M. Tuckey, and7 A. J. A. Vandeput, 2001; R. J. Hill-Cottingham, P. C. Coles, J. F. Eastham, F. Profumo, A. Tenconi, and7 G. Gianolio, 2002).