A mechanical flux weakening method via split rotor in permanent magnet aerospace alternators

Kulan, MC; Baker, NJ; Turvey, S

doi:10.1049/icp.2022.1026

A mechanical flux weakening method via split rotor in permanent magnet aerospace alternators

Lookup NU author(s): Dr Mehmet Kulan ORCiD, Professor Nick Baker ORCiD

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Abstract

Whilst permanent magnet (PM) electrical machines often offer very high power density, they suffer from the issue that the voltage output from the machine is a function of speed due to the fixed nature of the flux delivered by the PM poles within the machine. The best performance of PM machines achieved at lower speeds might not be achieved at higher speeds due to the fact that the voltage of the machine at high speeds is greater than the rating. In order to overcome this issue in PM machines, this paper proposes a mechanical flux weakening method via a split rotor. The key feature of the proposed scheme is that the fixed nature of rotor magnet flux can be altered by means of a simple mechanism that helps reduce the magnet flux by realigning part of the rotor at higher speeds. The rotor is axially split into two sections to achieve two states of field excitations: maximum and the least output depending upon the alignment between the rotor sections. A number of key 3-dimensional (3D) finite element (FE) simulations have been used to demonstrate the effectiveness of the proposed mechanical flux weakening approach. The results indicate that the split rotor method can be an alternative to more complicated mechanical flux weakening approaches in safety critical applications such as aerospace. Thus, a PM machine with split rotor could be used over a wide speed range without applying excessive voltages to the load at higher speeds in fault tolerant aerospace applications.