Actuator Saturation Handling using Weighted Optimal Control Allocation Applied to an INDI Controlled Quadcopter

Abstract

Incremental Nonlinear Dynamic Inversion provides a high performance attitude controller for multi-rotor Micro Aerial Vehicles by providing very good disturbance rejection capabilities. Flights conducted with a quadcopter revealed undesired pitch and rolling motions which occurred simultaneously with actuator saturation for instantaneous yaw angle reference tracking commands. Constrained control allocation methods can increase the system's performance by providing an effective strategy to prioritize control objectives, and redistribute control effort accordingly. Weighted Least Squares control allocation makes the constrained control allocation problem a quadratic optimization problem. An iterative solver based on the computationally efficient active-set algorithm finds the optimal control distribution for a weighted control objective. In this paper the Weighted Least Squares control allocator is used to overcome two challenges 1) increase performance by applying prioritization between control objectives and redistribute control effort accordingly, accounting for the actuator limits 2) enable flight when flying with severely compromised actuator(s). Real-world flight experiments are performed and show a significant increase in performance for high load yaw maneuvers, and enabled a quadcopter to perform controlled flight with a severely compromised actuator