The Application of Robust Control
to VSTOL Aircraft
R. A. Hyde
Abstract
This thesis looks at some of the implementation issues which
arise for multivariable and H-infinity
designed controllers.
The motivation for tackling these issues is provided by
an example control law development for a Generic VSTOL Aircraft Model
(GVAM). Linear designs are carried out for the GVAM using a
loop-shaping followed by an H-infinity
robust stabilisation
approach. The particular H-infinity
robustness optimisation used utilises
additive uncertainty to normalised coprime factor plant
descriptions. A weighting selection strategy is developed
for this design approach.
Controllers designed by the H-infinity
approach are not as easy
to schedule as classically
designed controllers.
Two approaches for gain scheduling
H-infinity
controllers are developed. The first makes use of a
switching strategy and bumpless transfer technique, and the
second gain schedules by utilising the observer structure
unique to the normalised coprime factor robust stabilisation
problem formulation.
Multivariable controllers
pose additional problems in the event of actuator
saturations, and various schemes are investigated.
An design study using fixed structure low order controllers
and parametric optimisation is also carried out for
comparison with the H-infinity
designs. Two
H-infinity
control
laws are developed, one based on switching and one based on
scheduling. These have been evaluated using the Royal Aerospace
Establishment piloted simulation facility at Bedford.