Robust Geometric Trajectory Tracking Control of a Variable-Pitch Quadrotor

Abstract

In this paper, a robust trajectory tracking control design of a variable-pitch quadrotor (VPQ) under the adverse conditions of external disturbance and parametric uncertainties is presented. The rotors of the VPQ are assumed to be operating at the same nominal speed, and the thrust variation is achieved by means of variable-pitch actuation. Blade element theory along with momentum theory is used to calculate the thrust and torque as a function of thrust coefficients. The control is designed using a traditional outer and inner loop structure. The effect of unknown disturbances and parametric uncertainties are treated as external bounded disturbances, and this is handled using a robust control design known as a super twisting algorithm. The control design demands knowledge of the disturbance bounds. This work considers five different static control allocation methods, namely, a fixed point iteration, static optimization without yaw dynamics, static optimization with yaw dynamics, nonlinear least squares, and Newton–Raphson, that address the problem of the nonlinear relationship between forces and moments. The five control allocation methods are compared through numerical simulation. The robustness of the control design is also shown through numerical simulation. Furthermore, the inverted flight capability of the VPQ is demonstrated.