Large electromechanical actuation systems for flight control surfaces

The paper outlines the aims and achievements to date of the LEMAS (Large Electromechanical Actuation Systems) Research Project. It is concerned with electromechanical actuation systems for flight control surfaces, specifically a spoiler surface, for which permanent magnet brushless DC machines and power electronic converters have been developed to drive a gearbox and ballscrew mechanism. In order to meet the requirements for spoiler actuation, which does not necessitate fault-tolerance, but is fault-critical, a conventional three-phase drive has been developed, incorporating appropriate diagnostic features so as to ensure fail-safe operation. However, in view of future electromechanical actuation of more critical flight surfaces, which may necessitate fault-tolerance, a second drive has been developed incorporating phase redundancy in both the machine and drive electronics. A modular topology for the power electronic converter enables potentially catastrophic faults to be isolated, and their propagation to be contained, whilst the machine essentially has electrically, magnetically and thermally isolated phases with a 1 p.u. phase reactance, which limits the maximum fault current in the event of a short-circuited phase to the rated full-load value. Speed and position control of the spoiler surface, motor phase current control and diagnostic and safety features have been implemented on both analogue and TMS320C31 floating-point DSP hardware platforms, communication with the on-board flight control computer being via a fault-tolerant serial link.