The influence of demagnetisation and temperature on the performance of PM machines.

Purpose ? The paper seeks to present finite element methods for modelling hard magnetic material magnetisation and degradation ?in service?. It aims to describe methods of representing the hysteretic behaviour of permanent magnets, and allowing for variations in the material characteristics caused by temperature and demagnetising fields. Design/methodology/approach ? A permanent magnet DC motor example is used to demonstrate the complete modelling cycle. The magnetisation of the ring-segments of the stator magnets was modelled using a transient, non-linear, eddy-current solver. The rings were transferred to the PMDC motor. The de-magnetisation of the magnets ?in service? was studied as a function of load, operating armature current and temperature. Findings ? The effect of hard magnetic material de-magnetization was accurately quantified. Its dependence on the reverse-field armature currents and operating temperature was demonstrated. The benefits of accurately representing the material characteristics in PMDC motors were clearly identified. Research limitations/implications ? The model for hard magnetic materials under magnetizing and demagnetising fields can only be perfected by using measured data. The measurements are hard to perform, in particular the effect of demagnetising fields at an angle to the easy magnetization axis is very difficult to measure. Originality/value ? The paper enhances the understanding of the process of hard magnetic material magnetisation and demagnetisation, fully examining the mechanisms and their dependence on parameters such as magnetising and demagnetising fields and temperature. The paper demonstrates how FEA methods can help to design electrical machine by accurately representing magnetic material properties and processes. [ABSTRACT FROM AUTHOR]