A magnet assisted segmental rotor switched reluctance machine suitable for fault tolerant aerospace applications

Abstract

The aerospace industry is moving towards more-electric aircraft. These electrical systems are lighter, more efficient and smaller compared to present hydraulic system. The permanent magnet electrical machine is an obvious choice to replace these hydraulic systems because of its high torque density. However for low speed applications, there are significant drag torque issues which negate some of the machine’s advantages. This thesis introduces a new permanent magnet assisted segmental rotor switched reluctance machine. This machine was first designed by using finite element software and then compared with a conventional segmental rotor switched reluctance machine, showing an increase in torque by increasing non saturation region of the stator lamination. On this basis, a fault-tolerant permanent magnet assisted segmental rotor switched reluctance machine was designed to replace the permanent magnet machine used in the nose wheel of the aeroplane. Both two-dimensional and three-dimensional finite element analyses were conducted to analyse the dominant end winding effect. Fault-tolerant segmental rotor switched reluctance machine was then built and tested. Static analysis was conducted to determine current-flux linkage and torque values at different rotor angles. The machine was analysed both with and without magnets to assess the effect of reverse magnetization with magnets at the stator tooth tip. Mutual inductance was also found using the same test rig. Dynamic testing of the machine was done to determine open circuit voltage and short-circuit current. A novel pot core permanent magnet assisted inductor was also designed and compared with the conventional E-E core inductor. The magnet was used to hold the inductance of the inductor constant for high current values and the inductor was then tested to determine magnet’s effect. A dominant inner loop effect was found which was proved by doing several tests. Various recommendations were made to further improve overall performance of the machine and the inductor.