Almost global trajectory tracking control of quadrotors with constrained control inputs

Control system design of small unmanned aerial vehicles with constrained inputs is an important design problem in practice which is usually not taken into account in many autopilot systems. This paper addresses a new control algorithm for trajectory tracking control of quadrotor aircrafts in the presence of control input constraint. To convert tracking-control problem to regulator one, the modified Rodrigues parameters (MRPs) based relative position and attitude kinematic and dynamic equations of a quadrotor are developed. The proposed algorithm employs the cascaded control scheme that is connected by a MRPs attitude extraction algorithm. The almost global closed-loop stability is guaranteed via the use of Lyapunov analysis tools, and an implicit manipulation for input constraint is obtained by employing the properties of the MRPs representation and hyperbolic tangent function. Finally, simulations are performed to demonstrate the validity and effectiveness of the proposed algorithm.