Incremental nonlinear control applied to tiltrotor aircraft

Abstract

Incremental nonlinear control is a promising control method that can be applied in controlling tasks that involve systems with highly nonlinear dynamics. Incremental nonlinear control is a feedback linearization method that requires less model knowledge than conventional Nonlinear Dynamic Inversion and is robust against model mismatches. This thesis presents an incremental based control method to control a longitudinal model of the XV-15 tiltrotor aircraft. Firstly, an attitude controller is designed that solves the over actuated system of tiltrotor’s longitudinal cyclic and elevator pitch control by using a weighted least squares control allocation method. Secondly, an incremental based velocity controller is designed which integrates the use of the tiltrotor nacelles. The controllers have been tested against attitude and speed tracking tasks to evaluate their performance. The attitude controller showed to be able to follow the reference signal while adjusting to the changing aircraft dynamics. In combination with the velocity controller, the aircraft was able to follow a complete speed profile starting from the tiltrotor’s helicopter mode to the final fixed-wing mode and back. It was demonstrated that this transition manoeuvre could be performed in a fully coordinated way within the tiltrotor’s conversion corridor.