Abstract: High-speed permanent magnet (PM) electric machines are widely used. However, their extreme operating conditions, e.g., high temperature and high mechanical stress, lead to variations of the PM characteristics and affect the machine performance. In the present study, an experimental device is designed to test the PM characteristics by simulating the stress and temperature conditions of high-speed machines. The experimental results indicate that the PM remanence not only varies at high temperatures, which is well known, but also changes under high mechanical stress. It is shown that the PM remanence increases with the mechanical stress but decreases with the temperature rise. Accordingly, a new demagnetization-curve model of the magnets under multiple stresses is refined to better express the PM characteristics. The performance of a high-speed PM machine is then analyzed as an example to indicate the necessity of the model refinement. The effects of the temperature and mechanical stress on the conductivity of the PMs are also examined. The experimental results indicate that the conductivity of the PM increases with the temperature and pressure.

Key words: High-speed machine, permanent magnet, mechanical stress, remanence variation, demagnetization-curve model