Global trajectory tracking for quadrotors: An MRP-based hybrid strategy with input saturation
Luís Martins, Carlos Cardeira, Paulo Oliveira
Abstract
This paper proposes a novel inner–outer loop control methodology to tackle the trajectory tracking problem for input-saturated quadrotors. The outer-loop, encapsulating the position tracking dynamics, is rendered input-to-state stable by designing a nested saturated control law with integrative action and applying small-gain arguments. The control strategy comprises an inner-loop that relies on a hybrid controller with integral action, designed based on the modified Rodrigues parameters attitude description, to solve the attitude tracking problem. The hybrid formulation of the controller benefits from the unique properties of the mentioned attitude description. Furthermore, it also provides a favorable framework to overcome the global stabilizing continuous feedback topological obstruction. For any given initial state, the resulting double-loop control architecture asymptotically tracks a position trajectory that satisfies some assumptions, while minimizing the distance to the desired attitude and satisfying the saturation limits of the thrust and torque inputs. The simulation results demonstrate the potential of the strategy. The experimental test carried out with a commercially available quadcopter and a motion capture system highlighted the proposed solution tracking capabilities, validating thereby the global saturated trajectory tracking controller. The proposed strategy is the first saturated MRP-based hybrid solution for quadrotor trajectory tracking.