Overcoming the challenges of “drag torque” in a dual-lane actuator for an aircraft

Actuators for the more electric aircraft are predominantly based on permanent magnet machines to achieve the optimum power to weight ratio. High reliability of these actuators is important and typically this results in the adoption of a dual-lane multiphase topology. This is to provide redundancy in both the power electronics and the machine so as to achieve the desired reliability. However, in fault conditions, it is possible for the drag torque caused by a short-circuited phase of a permanent magnet machine to be sufficiently large that the rating of the healthy lane needs to be significantly overrated to ensure it can meet the operational specification. This effectively negates the advantages of the machine to some degree. Segmental Rotor Switched Reluctance machines have been demonstrated to provide enhanced performance compared with conventional Switched Reluctance machines and have the potential to overcome this problem of drag torque in a faulted lane whilst maintaining the necessary power to weight requirements. This paper explores some of the challenges involved in the design and realization of a novel motor and drive solution suitable for a fault tolerant aerospace nose-wheel actuator. For example, the actuator under investigation has a very short stack length resulting in significant end-winding effects. By introducing small sections of permanent magnet material between the stator teeth the performance of the machine can be improved even further, thus mitigating these end-winding effects. Design considerations and simulation results are presented with a narrative of our development program to date.