Adaptive Control for a Hypersonic Glider using Parameter Feedback from System Identification

Abstract

The design and simulation of an adaptive longitudinal control system for a Mach 8 hypersonic glider is detailed. The vehicle is equipped with two elevons for control surfaces. It is required to perform a flight-path angle pull-up manoeuvre during the reentry phase of a parabolic trajectory. This is achieved with a normal acceleration longitudinal controller. The controller uses the pole-placement technique to calculate gains in real time. The gain calculations are based on a set of error-minimised model parameters, which are a fusion of real-time measured parameters, found using recursive least squares and stored look-up table parameters. In addition, a first order filter is used to update the look-up table parameters so that future control system gain calculations are not dependent on the presence of system excitation. It is shown that such a system can provide a small performance improvement in overshoot. One fundamental problem with implementation of the system in real time is the lag between the fused parameter estimates and when such parameters are required by the autopilot. Typically the autopilot operates at a higher frequency than the fused parameter estimates and thus corrects a disturbance due to real parameter change before suitable update information is received for gain calculation. The system is suggested as a useful diagnostic tool for experimental flights of this nature, or for real-time use on a more suitable dynamic system.