Feedforward control: a full-information approach

The Youla parametrization of two-degree-of-freedom controllers reveals that the design of the prefilter and the design of the regulator can be done in dependently. In this paper, a unified framework is proposed to address the design of the feedforward part of a two-degree-of-freedom controller. The a pproach deals both with tracking of a causal reference signal and with reje ction of a causal measurable disturbance. It is shown that the determinatio n of a feedforward filter, with a constraint on the nominal control effort, reduces to the solution of a particular full-information problem. The appr oach is attractive because it leads to a significant reduction in the numbe r of decision variables in the design process. The method also extends natu rally to plants in a polytope. Its effectiveness is demonstrated on two num erical examples. In the first example, the design of a linear time-invarian t feedforward controller is carried out to reject a measurable disturbance and to follow a reference signal; while in the second example, we address t he design of a robust gain scheduled two-degree-of-freedom controller. (C) 2000 Elsevier Science Ltd. All rights reserved.