Comparing Incremental Nonlinear Dynamic Inversion and Total Energy Control for Morphing Wing UAVs

Abstract

This paper explores the performance of a control system using incremental nonlinear dynamic inversion (INDI) for the longitudinal control of the morphing wing drone Proteus and compares it to a total energy control system (TECS). The main factors investigated are the decoupling of vertical flight path and horizontal speed, the tracking performance of a landing profile, and the robustness against changes in flight dynamics, caused by the morphing wing. Both systems showed similar and satisfying decoupling of speed and vertical flight path. The INDI system slightly outperformed the TECS in its path-tracking ability and was slightly more robust against perturbations of the eigendynamics. Both systems are considered suitable for the longitudinal control of the drone, with the INDI having slightly superior performance and robustness. When also accounting for the high disturbance rejection capabilities for INDI control systems outlined in the literature, the system is considered a capable candidate for the control of the drone. A difficulty when investigating the stability of the INDI controller was the nonlinearity of the control system, as the computation of margins is not directly possible. The Monte-Carlo parameter sampling approach was useful for gaining a general impression of the robustness. The INDI required additional computation performance compared to the TECS. Optimization of the control allocation algorithm by adding an analytical solution to the weighted least squares problem did not improve the computation time required.