SAMPLED DATA SLIDING MODE CONTROL OF FIXED WING UNMANNED AERIAL VEHICLE

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.