A permanent magnet assisted switched reluctance machine for more electric aircraft

Actuators for more electric aircraft are predominantly based on permanent magnet machines for the best power to weight ratio. However, permanent magnet machines can give rise to drag torque under short circuit conditions. This paper explains the concept of permanent magnet assistance in switched reluctance machines and sets out a topology which maximizes the benefits of permanent magnet assistance without compromising fault tolerance. The problem of demagnetization in this topology is explored and a revised design proposed. The increased torque from permanent magnet assistance is demonstrated, and laboratory tests on a prototype machine evidence the fault tolerant nature of the proposed machine by comparison with a baseline permanent magnet machine design. It is suggested that the permanent magnet assisted segmental rotor switched reluctance machine could achieve similar torque to a permanent magnet machine in this application with much improved fault tolerance and with much reduced magnet mass.