Characteristics Regulation for Manufacture of Permanent-Magnet Motors Using Post-Assembly Magnetization

This paper proposes a technique for manufacturing permanent-magnet (PM) motors by means of post-assembly magnetization (PAM) rather than assembling with the rotor premagnetized. This can be used to vary the operating characteristics of the motor. PAM utilizes the stator windings of the PM motor to magnetize the magnets after complete assembly, where large current pulses are applied to magnetize the machine. However, in this paper, it is shown that PAM can be used in a manner where a degree of unsaturated magnetization is allowed, so that the motor back EMF constant can be regulated without modifying windings or geometry. Various magnetizing current pulses are applied which result in a range of back EMFs. These are measured for verification. From the experimental results, the feasibility of this magnetizing technique is demonstrated for a rare-earth magnet motor. It is also suggested that the magnetizing efficiency can be improved and the copper ratings reduced since it is found that large magnetizing currents may not contribute to magnetization beyond a certain current level