Performance measure for obstacle avoidance of a 4-dimensional aircraft autopilot with anti-windup feature

Lots of algorithms that calculate an obstacle avoidance route for fixed-wing aircraft can be found in the literature. In this work, a controller was designed that can track the route given by these algorithms in the 3 spatial dimensions and the time dimension. The controller was designed with two negative feedback loops. A robust and multi-input multi-output state-space controller was used in the inner loop to control the attitude of the aircraft whereas PID controllers were used in the outer loop to navigate the aircraft in 4-dimensional space. Since the aircraft is maneuvered aggressively during obstacle avoidance procedures, the actuators can saturate, which leads to a deterioration of the state variables of the controller due to a phenomenon called windup. This problem is specifically observed at the thrust channel of aircraft controllers since the dynamics between the thrust and the airspeed of the aircraft are slower relative to the dynamics related to the other actuators. Unfortunately, anti-windup solutions for state-space controllers, which our controller in the inner loop also belongs to, are complicated and lack performance since such solutions are corrective. In this work, an anti-windup scheme is realized in the form of a state machine, which embraces the saturated form of the controller. Since the saturated form is directly integrated into the anti-windup scheme, the resulting system has high performance. Furthermore, the design of the scheme is relatively basic and easily understandable, easily applicable. It is shown through sample tests, that the whole controller system assisted by the anti-windup scheme can track the 4-dimensional waypoints successfully. The devised system is particularly well suited for obstacle avoidance algorithms given its high performance and its ability to correctly track time of arrival requirements. The contributions of this theses do not only include a control system that successfully tracks routes created by avoidance algorithms found in the literature, but they also include the design of a test system that determines a performance measure to quantify whether those routes are trackable. In this system, an aggressivity parameter is initially designed based on the position of targets. Next, Monte-Carlo tests are performed to determine the accuracy of the controller, which are used to quantify a performance measure for the controller, given an application with a certain accuracy requirement. This way, for applications that require obstacle avoidance maneuvers, constraints in the 4-dimensional space can be determined for the position of the final targets. The writing style of this thesis is application-oriented. All designs and tests, including the control system designs, the anti-windup scheme designs and verifications, and the Monte-Carlo tests for finding the performance measures are studied on the Cessna 172 airplane as an example.