Cogging Torque Reduction of Integer Gear Ratio Axial-flux Magnetic Gear for Wind-Power Generation Application by Using Two New Types of Pole-Pieces

Abstract

Listen

Translate article

Introduction - Flux-modulated type magnetic gears are expected to be applied as step-up gears for wind-power generation because of their advantages, including high torque density and maintenance-free operation [1]. Among them, an axial-flux magnetic gear (AFMG) has attracted great attention recently since it has a smaller axial length and is easy to assemble. In some cases, magnetic gears are required to have an integer gear ratio based on design requirements of the entire system, which results in larger cogging torque in the high-speed rotor that causes vibration and startup error. In addition, the conventional skew rotor structure is complicated and poor in assembling [2]. To solve the problems described above, this paper proposes two new types of pole-pieces, one is an unequal-width-type, another is an unequal-spacing-type.Two new types of pole-pieces – Fig. 1(a) shows the AFMG [3] investigated in this paper, while the (b) and (c) are the proposed unequal-width-type and unequal-spacing-type pole-pieces, respectively. The gear ratio of this AFMG is an integer of 10 given by the number of pole pairs of the high-speed and the low-speed rotors of 3 and 30, respectively. As shown in Fig. 1(b), pole-pieces with three different circumferential width ratios, which are 0.3, 0.8, and 0.7, are combined in the unequal-width-type, while as shown in Fig. 1(c), the relative position of the pole-pieces is adjusted which leads to an unequal interval structure. Both types are aimed at canceling the cogging torque. The cogging torque is calculated by the three-dimensional finite element method (3D-FEM).Fig. 2 shows the results of the high-speed rotor cogging torque of the two proposed new types, where (a) is of the unequal-width-type and (b) is of the unequal-spacing-type, respectively. As shown in the figure, it is clear that both proposed types can reduce the cogging torque significantly.This work was supported in part by the WISE Program for AI Electronics, Tohoku University.  Fig. 1 The investigated AFMG and the proposed two types of pole-pieces; (b) unequal width, (c) unequal spacing.  Fig. 2 The calculated high-speed rotor cogging torque of the two types of pole-pieces; (a) unequal width, (b) unequal spacing.