Adaptive Control Allocation: A Human-In-The-Loop Stability Analysis

Abstract

This paper demonstrates the stability limits of a human-in-the-loop closed loop control system, where the plant to be controlled has redundant actuators with uncertain dynamics. Two different human operator models are considered: For tasks that require very accurate control commands, pilots are shown to produce control commands resembling the output of a pure gain controller. Therefore, we first analyze the stability of the uncertain nonlinear closed loop system with a pure gain pilot model. Another commonly employed model, to represent the inability of the human operator to respond to high frequency inputs, is the lag filter. In our second analysis, we show the stability properties of the human-in-the-loop control system where a lag filter operator model is utilized. A flight control task, where the pilot controls the pitch angle via a pitch rate stick input, and the controller receives separate roll and yaw rate references, is simulated to demonstrate the accuracy of the stability analysis.