Slip torque investigation and magnetic redesign of motor integrated permanent magnet gear

Abstract

This paper presents an investigation of 20% difference between the measured and calculated slip torque of a Motor Integrated Permanent Magnet Gear (MIPMG) prototype. The High Speed (HS) side of the Magnetic Gear (MG) was fixed by loading the motor when conducting the slip torque measurement. Suspicion of the motor saturating before the MG reached peek torque and thus measuring the maximum torque of the motor instead, made the method questionable. The MIPMG has been modified to lock the HS side of the MG mechanically and new measurements have been conducted but with the same low slip torque as result. It was realized that some magnets most likely are partly demagnetized due to an inappropriate magnetic design which can explain the measured slip torque to be lower than the results from static 2 and 3D FEA. With the discovered demagnetization and several years of experience with the technology, the MIPMG is theoretical redesigned and semi optimized regarding the use of magnet material while maintaining a reasonable torque density and high efficiency.