Comparative Analysis of a Coaxial Magnetic Gear With a Flux Concentration Rotor and Consequent Pole Rotor Typology

Abstract

By utilizing magnetic field space modulation magnetic gearboxes (MGs) are able to create speed amplification without any physical contact [1–3]. An example of a flux-focusing coaxial MG is illustrated in Fig. 1. This coaxial MG consists of an inner rotor 1 that contains $p_{1} = 4$ pole-pairs an outer rotor 3 with $p_{3} = 13$ pole-pairs and a central ferromagnetic segment central rotor 2 that consists of $n_{2} = 17$ pieces. The $n_{2}$ ferromagnetic segments serve to modulate the inner and outer rotor magnetic fields. In order to create the highest level of field coupling between the inner and outer rotors the number of ferromagnetic segments must be chosen to satisfy $n_{2} = p_{1}+p_{3}$. With this condition satisfied the rotor angular velocity relationship between each rotor is $\mathrm{w}_{2} \mathrm{p}_{2} = \mathrm{w}_{3} \mathrm{p}_{3}+ \mathrm{w}_{1} \mathrm{p}_{1}$ where the subscript denotes rotor number. If the outer rotor is fixed $( \omega _{3} = 0)$ the torque will be maximized and the gearing ratio will be $\mathrm{w}1 = $ Gw 2 where $\mathrm{G} = n_{2}/ p_{1}$. For the example MG shown in Fig. 1 the gear ratio is $\mathrm{G} = 4.25$. In order to try to increase the torque density of a MG a range of different coaxial type rotor typologies have recently been investigated [4–14]. Along with the flux focusing MG design two other coaxial radial type MG rotor typologies that have been shown to create high torque density are the flux concentration Halbach rotor typology [15] and the consequent pole triple-PM rotor MG typology [16]. In this paper, these two design typologies are compared for the first time. The objective is to provide an idealized comparative analysis of the two competing typologies and then present the experimental design and testing of the best design.