Comparison of PID and nonlinear feedback linearization controls for longitudinal dynamics of hypersonic vehicle at subsonic speeds

A hypersonic aircraft vehicle is a highly complex nonlinear system, whose model possibly contains uncertainties in the dynamics. This paper presents the design of proportional-integral-derivative (PID), and nonlinear feedback linearization (FL) for a hypersonic vehicle at subsonic speeds. The complexity of the dynamic system is considered in the design structure in order to address robustness issues. The control system design should decouple the longitudinal and lateral dynamics to handle the flight of hypersonic vehicle under specific conditions. In this paper, we only consider longitudinal dynamics, which are divided into vehicle speed subsystem and flight-path angle subsystem. Different control design methodologies are implemented to provide asymptotic tracking regulation of vehicle speed and flight-path angle. The nonlinear FL control is employed in this study because of its potential robustness properties. Based on the stability analysis, the nonlinear FL control is derived for a Lyapunov function candidate of feedback closed-loop system. The simulation results for each control technique demonstrate the effectiveness of control inputs.