Lateral-directional autopilot design of Unmanned Aerial Vehicles using quaternion feedback sliding mode approach

Small Unmanned Aerial Vehicle(UAV) is well suited for missions that are dangerous to perform with human pilots. Control effort in the form of Automatic Flight Control System(AFCS) for achieving the desired flight profile against any unexpected disturbance or parameter variations is needed in such UAV´s. Most of the UAV dynamics uses Euler rate method for axis transformation. Alternate computational methods have been evolved to compute and derive parameters from the available sensors. This paper attempts to employ quaternion based closed loop attitude control. The major problem encountered with the axis transformation with Euler rates is the singularity at 900 theta which can be directly removed when quaternion based control is employed. One of the major advantages in employing quaternion based closed loop control is that, it is independent of the error due to sensors. Hence this paper attempts to employ quaternion based control in a low speed subsonic UAV platform. The main aim of this paper is to introduce quaternion based feedback approach into the nonlinear UAV simulation model with Proportional Integral(PI) controller, and Sliding Mode Controller(SMC). Unexpected disturbance and parameter variation can be tolerated by using robust fuzzy SMC. Simulation results shows the effectiveness of the proposed method.