Time-dependent Demagnetization of NdFeB Magnets under DC and Pulsed Magnetic Fields

This article investigates the time-dependent demagnetization behavior of NdFeB permanent magnets used for electrified vehicles. A mathematical model of magnetic viscosity was derived using maximum-likelihood estimation based on the test data. This magnetic viscosity model was then used to predict the magnet demagnetization behavior over time. A demagnetization test fixture and a programmable dc power supply were used to apply a constant demagnetizing field to N48H magnet samples. A hall-effect sensor was used for online measurement of the magnetic field under a constant demagnetizing field over a wide time range. A buck converter was used to generate a pulsed demagnetizing field in the timescale of milliseconds. The results of this article will help understand the demagnetization behavior of NdFeB magnets caused by overcurrent faults in permanent-magnet synchronous machines.