【文章內(nèi)容簡介】 t tolerance is best achieved by having redundant drive ponents. This may either be achieved by duplicating or triplicating the whole drive or otherwise have independent redundant systems the number of duplicates depending on the reliability of the particular ponent. It is however important in any choice of fault tolerant topology to have each system isolated from the others so as to minimize the possibility of mon failure. This is finally a cost and size optimization exercise depending heavily on the actuator function. From an electrical drive point of view it is often argued that the electrical machine itself can be made fault tolerant up to a certain degree not needing a duplicate one. This is usually achived by designing machines to operate with short circuit and open circuit faults. This is done by using multi phase machines and ensuring that the phase windings and the power electronics supplying them are magically, electrically and physically decoupled. The main disadvantage of using multiphase machines is the duplication of the power and control electronics, which have a low reliability. Another promise to make is on the type of machine to use. Sinusoidally excited machines are generally preferred if the machine is to be fed from an AC bus, this being mainly due to the patibility with matrix converters which give distinct advantages in case of an AC distribution system, mainly due to the elimination of the DC link and the unreliable electrolytic capacitors [1,2]. Sinusoidally supplied machines are however seen as not being fault tolerant in their more traditional form due to the high magic and physical coupling of their phase windings. Nonsinusoidally fed machines are potentially more fault tolerant but are not practical to be used with a matrix converter due to the resulting supply current distortion. Machines which are sinusoidally supplied but have concentrated coils giving the required levels of phase isolation are seen as a good solution for such applications [3,4]. A) Geared vs. Direct Drive Systems There are a number of advantages in using a direct drive system. The elimination of the intermediate gearbox gives the following advantages : 1) Reduced Component Count 2) Reduced jamming probability thus increasing reliability 3) Increased System Efficiency 4) Reduced Inertia This may potentially lead as well to a reduced actuator weight and volume. Increased system efficiency due to the elimination of the intermediate gearbox will reflect in a lower power rating of the machine. As regards to the inertia, this may be of a major advantage depending on the actuator acceleration requirements and on the duty cycle characteristics. In the developed system there was a fivefold improvement in the inertia of the motor and gear train in going to a direct drive system rather than using a gearbox. III. MID SPOILER ACTUATION SYSTEM The actuator considered in this study is that for a mid spoiler flight surface for a large civil aircraft. An EMA using a highspeed motor coupled to the roller screw through a 6:1 speed reduction gearbox has already been developed. The design of a machine able of the same performance at the roller screw end without the gearbox is considered and pared with the existing actuator. The Spoiler surface serves a dual purpose in flight. It can, as its name suggests, spoil the flow of air over the surface of the wing thereby reducing lift and it can also be used in conjunction with the ailerons to assist the roll function. In the spoiler function large movements of the actuator are seen in order to fully extend the surface and ‘spoil’ the lift. In its use for roll assist, smaller movements are seen with a high dynamic response to match the aileron movements. This dual role of the spoiler surface makes the actuator performance requirements quite demanding. The duty cycle of the spoiler varies during the flight with higher duty during the landing periods and a lower one during the cruise. Full movement of the spoiler is only required at landing for descent and post touch down. During cruise there are only occasional small movements of the surface for roll assistance. The actuator itself is normally acting to hold the surface down as the aerodynamic forces over the wing attempt to lift the surface. By incorporating the roll assist requirement to the spoiler surface, the duty on the actuator bees more onerous. The dynamic requirements for the actuator bee highly demanding such that a hold down brake is unfeasible when the actuator is stowed, then a steady state background load has also to be dealt with. These two elements result in the spoiler case being very similar as to that for the primaries where efficiency bees key to the actuator performance. Other demanding requirements on the actuator occur in emergency scenarios. One is when there is the case of an aborted take off and the other is an emergency descent in the event of cabin depressurisation. This last case is the most demanding requirement for a spoiler as it requires full deployment for a period of minutes. IV. MACHINE DESIGN The machine has to meet all the transient and steady state specifications keeping the machine size to a minimum. The size of the machine is mainly limited by physical dimension constraints, the loading characteristics and the temperature range the actuator should be able to operate in. The internal rotor diameter is constrained by the roller screw nut whilst the outside stator diameter is constrained by the maximum package size. A surface mount mag machine was opted for due to high torque requirement throughout the operating speed range and due to the relatively low centrifugal forces experienced by the mags. A) Number of Poles As the number of poles goes up the copper packing factor is reduced if the number of slots per pole per