Abstract
This paper deals with the trajectory tracking problem for a quadrotor unmanned aerial vehicle (UAV). For this purpose, two control strategies are proposed. First, a flight controller with a hierarchical structure is designed, whereby the complete closed-loop system is divided into two blocks. The system has an inner block for attitude control and an outer block for position stabilization, for a total of six proportional-derivative/proportional-integral-derivative (PD/PID) controllers. The second new trajectory tracking strategy is based on attitude stabilization. In addition to a direct stabilization of yaw and altitude, the x and y positions are stabilized by choosing an appropriate control of roll and pitch angles. The relations between positions (x, y) and rotations (roll, pitch) are derived from the natural flight of the quadcopter. In this second approach, with only four controllers, the quadrotor UAV is able to follow any trajectory. In both approaches, the PD/PID controllers are synthesized using the genetic algorithm method, and compared with those obtained by the reference model method. Furthermore, a comparison between PD and PID controller performance is performed. Thereafter, the robustness of the proposed controllers is tested for trajectory tracking in a disturbed environment. Simulation results demonstrate that for the two approaches, PD controllers show a better behavior with respect to quadcopter stabilization than in trajectory tracking under different conditions.
Highlights
In recent years, the control scheme design of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs) has become a significant research topic
The results show that the Reference Model-Based Hierarchical Controller (RMHC) and Genetic Algorithm-Based Hierarchical Controller (GAHC) controllers can stabilize the quadcopter, and achieve the desired path in a disturbed environment
These results show that the Tracking Using the Reference Model Method (TTRM)-PID and Trajectory Tracking Using Genetic Algorithms Method (TTGA)-PID controllers give the best responses, when compared to TTRM-PD and TTGA-PD in the presence of disturbances
Summary
The control scheme design of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs) has become a significant research topic. Quadcopters are most well known for being small aircrafts with multiple rotors, with under-actuated, nonlinear, and coupled systems. These characteristics lead to great control challenges. The under-actuated property of quadcopters leads to strong coupling between translational and rotary motions. It is an arduous task to control the position or the trajectory tracking of the quadcopter. To deal with this dilemma, the hierarchical control strategy has demonstrated positive performances and it has been widely used to solve trajectory-tracking problems. Since the introduction of quadcopters to the robotic community, numerous projects have been devoted to model and control these platforms, Appl.
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