Autopilot design of tilt-rotor UAV using particle swarm optimization method

This paper describes an autopilot design of tilt-rotor UAV, which is being developed by KARI as a Smart UAV Development Program in Korea, using particle swarm optimization (PSO) method. The tilt-rotor UAV considered in this paper holds five control modes in the stability and control augmentation system (SCAS) depending on flight mode. Flight control systems designed via the classical approach have been performed in such a way that yields linear models about several trim flight conditions, designing linear controllers for each condition, and integrating these design points with a gain scheduling scheme. However, it is very tedious and time-consuming to design an autopilot of a tilt-rotor UAV which represents various dynamic characteristics, nonlinearity, and uncertainty via classical control technique, because there are many design points and operating conditions throughout the flight envelope. To solve this problem, an automatic tool for control system design using PSO method is developed and applied to autopilot design of tilt-rotor UAV. The desired output of control system is chosen to satisfy the control system requirement. Gain margin and phase margin of control system are additionally considered as a penalty term in the objective function. The designed control system guarantees the satisfaction of the control system requirement ensuring a sufficient stability margin of the control system. Also, the gain scheduling scenario and SCAS switching logic of each control mode are successfully designed. Fully nonlinear 6-DOF simulation for an automatic landing scenario is performed to verify the performance of autopilot system of tilt-rotor UAV. The results from the nonlinear simulation show good control performance of the tilt-rotor UAV.