LQG-Optimal Feedforward Regulators
and T Söderström
Automatica, vol 24, pp 557-561, July 1988.
Disturbances which act on a process can sometimes be
measured and used by a controller.
The use of such disturbance measurement feedforward
can lead to large performance improvements, as compared to the use
of feedback only. The paper presents the optimal structure
and design of
scalar LQG control laws which utilize feedforward based on
ARMA models of the measurable disturbances.
A polynomial LQG approach to the design of feedforward
regulators is presented.
Given a linear system and possibly a prespecified feedback,
optimal feedforward filters for non-minimum phase systems can be
calculated in a simple way.
An infinite horizon criterion including a filtered input
signal is minimized.
This makes it possible to include frequency-dependent
trade-offs between input energy and disturbance rejection
in the design.
The achievable feedforward control performance
turns out to be unaffected by the choice of feedback,
if the optimal regulator structure is used.
This suggests a simple way of optimizing combined feedback and
a main output feedback is first optimized with respect to
The feedforward link is then optimized with respect
to the measurable disturbance.
- Related publications:
Paper in IJC 1991,
on adaptive scalar LQG combined feedback and
on multivariable LQG feedforward
and adaptive LQG control.
Paper in IJC 1993,
on the duality between feedforward control and deconvolution.
Paper in Automatica 1993
which includes the robust design of
scalar feedforward filters.
by Kenth Öhrn 1996, with robust design of
multivariable feedforward filters.