Partitioned stator flux reversal machines having Halbach array PMs

Partitioned stator (PS) flux reversal (FR) (PS-FRPM) machine in which PMs are surface-mounted in one stator whilst the armature windings are wound in the other stator can produce higher torque density than the conventional FRPM machine with single stator, due to the higher utilization of inner space. As shown in Fig.1(a) for 12/10-pole PS-FRPM machine, the surface-mounted PM (SPM) inner stator is similar to the rotor in SPM machine. SPM with Halbach array PMs have the benefits of lower back-EMF harmonics and smaller cogging torque due to sinusoidal PM MMF, as pointed out in [2][3]. In this paper, PS-FRPM machine having Halbach array PMs is proposed and comparatively analyzed. The cross-sections of the proposed PS-FRPM machine having Halbach array PMs are illustrated in Fig. 1(b)-(e) for ideal, 2, 3 and 4 segments/pole Halbach ones. All these 4 Halbach array machines have the same dimension parameters as that with parallel magnetized PMs, Fig.1(a), except the PM arc. In Halbach array machines, PM arc is obtained from the optimization for the largest average electromagnetic torque. As shown in Fig.1(f)-(g), higher phase back-EMF peak value and the fundamental component can be achieved with more segments/pole. More importantly, in Halbach array machines they are higher than the parallel magnetized machine, Fig.1(a). This is also applicable for cogging torque, as shown in Fig.1(h) . Consequently, the proposed PS-FRPM machine having Halbach array PMs can deliver higher electromagnetic torque but lower torque ripple as illustrated in Fig.1(i). Moreover, this trend is stronger when the segment number per pole is higher. However, the phase back-EMF harmonics are low in all the machines. Fig.2 shows the photos and experimental results for the 12/10-pole PS-FRPM prototype machine with parallel magnetized PMs. As shown in Fig.2(d)-(g), good agreements can be achieved between the measured and 2D finite element (FE) predicted phase back-EMFs and static torques. The prototype Halbach array machine with 2 segments/pole is under assembling, of which the experiment results will be report in the full paper.