Abstract

Safety, reliability and acceptable level of performance of dynamic control systems are the major keys in all control systems especially in safety-critical control systems. A controller should be capable of handling noises and uncertainties imposed to the controlled
process. A fault-tolerant controller should be able to control a system with guaranteed stability
and good or acceptable performance not only in normal operation conditions but also
in the presence of partial faults or total failures that can be occurred in the components
of the system. When a fault occurs in a system, it suddenly starts to behave in an unanticipated
manner. Thereby, a fault-tolerant controller should be designed for being able
to handle the fault and guarantee system stability and acceptable performance in the presence
of faults/damages. This shows the importance and necessity of Fault-Tolerant Control
(FTC) to safety-critical and even nowadays for some new and non-safety-critical systems.
During recent years, Unmanned Aerial Vehicles (UAVs) have proved to play a significant role in military and civil applications. The success of UAVs in different missions guarantees the growing number of UAVs to be considerable in future. Reliability of UAVs and their components against faults and failures is one of the most important objectives for safety-critical systems including manned airplanes and UAVs. The reliability importance
of UAVs is implied in the acknowledgement of the Office of the Secretary of Defense in the
UAV Roadmap 2005-2030 by stating that, ”Improving UA [unmanned aircraft] reliability is
the single most immediate and long-reaching need to ensure their success”. This statement gives a wide future scenery of safety, reliability and Fault-Tolerant Flight Control (FTFC) systems of UAVs.
The main objective of this thesis is to investigate and compare some aspects of fault tolerant flight control techniques such as performance, robustness and capability of handling the faults and failures during the flight of UAVs. Several control techniques have been developed and tested on two main platforms at Concordia University for fault-tolerant control techniques development, implementation and flight test purposes: quadrotor and fixedwing UAVs. The FTC techniques developed are: Gain-Scheduled Proportional-Integral-Derivative (GS-PID), Control Allocation and Re-allocation (CA/RA), Model Reference Adaptive Control (MRAC), and finally the Linear Parameter Varying (LPV) control as an
alternative and theoretically more comprehensive gain scheduling based control technique.
The LPV technique is used to control the quadrotor helicopter for fault-free conditions.
Also a GS-PID controller is used as a fault-tolerant controller and implemented on a fixedwing
UAV in the presence of a stuck rudder failure case.