PhD Thesis, July 1998.
Robust Control System Design: H-infinity Loop Shaping and Aerospace
Applications
G. Papageorgiou
Abstract
In this thesis, a control system design
procedure is developed that is particularly suited for designing
flight controllers. The design procedure is based on H-infinity loop
shaping and recent theoretical developments that enable the synthesis
of a robust gain scheduled controller. It is shown that this procedure
can systematically deal with multi-input multi-output plants,
plants with nonlinear and parameter-dependent dynamics, and
uncertainty in the mathematical model of the plant used for the
controller design. The designer can also build many of the closed loop
specifications into the cost function used for the controller
synthesis. To this end, H-infinity loop shaping is discussed in some
detail, a procedure for computing non-diagonal pre- and/or
post-compensators is developed, and the H-infinity loop shaping cost
function is modified to include specifications on the transfer matrix
from references to outputs. To be able to use the robust gain
scheduling synthesis results, a ``quasi-LPV'' model of the
longitudinal dynamics of an aircraft is developed. This model is
tested by designing a robust gain scheduled flight controller for the
High Incidence Research Model used in the GARTEUR design challenge. In
an effort to increase the designer's faith in the proposed procedure,
a wind tunnel model was designed and built. This wind tunnel model is
shown to be a challenging rig for active control experiments. A number
of flight controllers were designed for the model and subsequently
flight tested successfully.
Keywords: H-infinity loop shaping, Weight selection, Model
matching, Gain scheduling, LPV modelling, Flight control, Experimental
rigs.