PATH TRACKING CONTROL OF A QUADROTOR UAV WITH BACKSTEPPING METHOD
Quadrotor is a very popular unmanned air vehicle(UAV) which has been worked by many researchers in recent years. Quadrotor is advantageous to classical UAVs since it can perform vertical take-off and landing(VTOL) with high maneuverability. Thanks to VTOL ability, it can be used in rough and limited environments without the need of long runways for take-off and landing. In addition, quadrotor has a more simpler mechanical structure compared to other VTOL UAVs. Although it has many advantageous features, quadrotor has a highly nonlinear and unstable dynamics. Therefore, designing autonomous control systems for quadrotor is a challenging task and it draws attention of many researchers.
In this work, path tracking control of a quadrotor UAV is obtained by using a nonlinear control method called backstepping. While designing the control system, attitude control is built as an inner loop and position control is built as an outer loop to track the desired trajectory with high accuracy. First, nonlinear dynamic model of quadrotor is obtained by using Newton's equations of motion. This nonlinear model is used in simulations as dynamic model (plant). Then, to use in the formulation of backstepping controller, nonlinear dynamic model is simplified by making some assumptions. By using simplified nonlinear dynamic model, backstepping controller is obtained in three steps. The controller is tested by simulations which are performed in MATLAB/Simulink environment. Disturbance rejection properties of the controller are also tested by simulations. Simulation results show that, desired path is tracked with high accuracy thanks to backstepping controller. Moreover, it is seen that, backstepping controller can reject various types of strong disturbances efficiently.
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