Abstract:
Due to the increasing availability of microprocessor hardware, control algorithms are now
usually implemented in digital controllers. In this thesis, sampled-data sliding mode control
(SMC) of the fixed wing unmanned aerial vehicle (UAV) is presented. Three Sliding mode
controllers have been effectively applied to fixed wing UAV. First, the sampled-data SMC is
designed using continuous time system. In this technique the control law is design for the
continuous time system and then this control law is discretized. The second technique is by
finding the approximate discrete equivalent system of continuous time system and then designing
a discrete control law for the discrete equivalent model. To avoid chattering issues with the
classical sliding mode control a second order sliding mode controller is also designed.
Due to the robustness of the SMC to matched uncertainties and disturbances, sliding mode
technique is a well-known technique that is used to avoid performance degradation. In order to
analyse the robustness of the controllers, simulations are performed with the wind gust as
external disturbance. Which showed that the sliding mode controller based on continuous time
system is more robust than the sliding mode controller based on approximate discrete equivalent
system. With the application of sliding mode, the system shows robustness properties to matched
uncertainties and external disturbances. However, the realization of the ideal sliding mode is not
possible because it requires switching with infinite frequency. Due to the limitations of the
hardware it is not practically possible so the sliding mode shows chattering in control input. To
avoid chattering issues with the classical sliding mode control a second order sliding mode
controller is also designed using super twisting algorithm. The second order SMC is not only
shows robustness to the external disturbances but also tackles the chattering issue.
