Quaternion Based Nonlinear Trajectory Control of Quadrotors with Guaranteed Stability

This paper investigates a dual loop quaternion-based nonlinear control scheme for a quadrotor: the inner feedback loop controls the attitude of the quadrotor while the outer control loop aims to control the linear velocity, and/or position, of the quadrotor. The paper shows that global exponential stability of a quadrotor can be achieved with the proposed control scheme. The presented controller includes feedback and feedforward compensation of the nonlinear dynamics of the quadrotor and gyroscopic torques to guarantee global stability of the attitude controller. The outer velocity control loop uses a PI feedback structure, where the proportional action is primarily used to control linear velocity, and the integral action can either be used for linear position and/or eliminating velocity steady-state error. The inner attitude control includes a PD feedback loop, where the proportional action is in terms of the vector part of the quaternion and the derivative action is in terms of the aircraft angular velocity. The proposed controller has been both simulated and tested experimentally with a commercial quadrotor.