A non-singular sliding mode controller for quadrotor attitude with predefined time disturbance observer

In this paper, a quadrotor attitude controller based on a predefined time disturbance observer and non-singular predefined time sliding mode is proposed to reject unknown disturbances. Based on the predefined time stability theory, a novel predefined time disturbance observer (PTDO) is designed by constructing an auxiliary equation. The designed observer can ensure the estimation of disturbances within the predefined time. By adjusting the predefined time parameters, the estimation rate of the disturbances can be changed. A non-singular predefined time sliding mode surface is designed by constraining the exponent coefficient of the exponential function in the sliding mode surface. The designed sliding mode surface can avoid the singular problem that occurs in the non-singular predefined time sliding mode (NPTSM) controller. The Lyapunov function is used to prove that the designed observer and controller can converge within the predefined time. The simulation results verify that the proposed controllers and observers can converge within the predefined time, and also show that the proposed NPTSM has a convergence time that is approximately 20% less than the predefined time sliding mode (PTSM), approximately 80% less than the fixed time sliding mode (FTSM) and approximately 60% less than the PID.