Design and analysis of a two-stage transmission magnetic-geared machine

The purpose of this paper is to realize a two-stage transmission magnetic-geared (2-STMG) machine with high gear ratio. The proposed machine contains a concentric magnetic gear (CMG) and a Vernier machine (VM). Both the components meet the magnetic gearing effect and share a common high-speed rotor (HSR). The VM is the first stage, and the CMG is the second stage. The designed gear ratio of the proposed 2-STMG is 34. The magnetic flux is partially coupled to the HSR yoke. The cogging torque on the HSR is slightly higher than that on the low-speed rotor (LSR). A method is presented to detect the gear ratio of magnetic geared machines with the back-electromotive force (back-EMF). And the evaluated gear ratio of the prototype is found to be close to the design value. The amplitude of the fundamental back-EMF is nearly linear with the LSR speed, and the slope of the fitting curve is similar to 0.16 V/rpm. The peak static torques on both rotors are positively correlated with the DC currents applied to windings but limited by saturation when current is larger than 4A. The 2-STMG machine is controllable, and the speed ratio of HSR to LSR is close to the gear ratio of the outer CMG. (c) 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.