Control allocation as part of a fault-tolerant control architecture for UAVs

[摘要] ENGLISH ABSTRACT: The development of a control allocation system for use as part of a fault-tolerant control(FTC) system in unmanned aerial vehicles (UAVs) is presented. This system plays avital role in minimising the possibility that a fault will necessitate the reconfiguration ofthe control, guidance or navigation systems of the aircraft by minimising the differencebetween the desired and achievable aircraft performance parameters. This is achievedby optimising the allocation of control effort commanded by the virtual actuators to thephysical actuators present on the aircraft.A simple general six degree of freedom aircraft model is presented that contains all ofthe relevant terms needed to find the trim biases of the aircraft actuators and evaluatethe performance of the virtual actuators. This model was used to develop a controlallocation formulation that optimises the performance of the virtual actuators of theaircraft while minimising adverse effects and avoiding actuator saturation. The resultingproblem formulation was formulated as a multi-objective optimisation problem which wassolved using the sequential quadratic programming method.The control allocation system was practically implemented and tested. A number offailure categories of varying severity were defined and two aircraft with different levelsof actuator redundancy were used to test the system. The control allocation algorithmwas evaluated for each failure category, aircraft test case and for a number of differingcontrol allocation system configurations. A number of enhancements were then madeto the control allocation system which included adding frequency-based allocation andadapting the algorithm for an unconventional ducted-fan UAV.The control allocation system is shown to be applicable to a number of different conventionalaircraft configurations with no alterations as well as being applicable to unconventionalaircraft with minor alterations. The control allocation system is shown tobe capable of handling both single and multiple actuator failures and the importance ofactuator redundancy is highlighted as a factor that influences the effectiveness of controlallocation. The control allocation system can be effectively used as part of a FTC systemor as a tool that can be used to investigate control allocation and aircraft redundancy.

[发布机构] Stellenbosch University