Fault Tolerant Electromechanical Actuators for Aircraft

This thesis reviews the developments in commercial aviation resulting from More Electric Aircraft initiatives. The present level of electromechanical actuation is considered with discussion of the factors affecting more widespread use. Two rather different electromechanical actuators are presented for commercial aircraft; DEAWS electrical flap actuation and ELGEAR nose wheel steering. Both projects are industrially driven with specifications based on existing medium-sized commercial aircraft. Methods comparing fault tolerant electric drive topologies for electrical actuators are presented, showing two different categories of electric drive and comparing each category in a variety of operating conditions to assess size and component count. The safety-driven design process for electromechanical actuators is discussed with reliability calculations presented for both proposed actuators, showing where fault tolerant design is required to meet safety requirements. The selection of an optimum fault tolerant electric drive for each actuator is discussed and fault tolerant control schemes are presented. The development of the electric flap and nose wheel steering systems is described, with the focus on the work performed by the author, primarily on the power electronic converters and control software. A comprehensive range of laboratory and industrial results are given for both actuators, showing demonstrations of fault tolerance at power converter and actuator levels. Following testing, further analysis is given on various issues arising prior and during testing of both converters, with design considerations for future electromechanical actuators. From design testing and analysis, the two projects can be compared to attempt to determine the optimal electromechanical actuator topology and to consider the challenges in evolving the two actuators to aerospace products.