Frequency Domain Design of a Series Structure of Robust Controllers for Multi-Input Single-Output Systems

Abstract EN

The regulation of a disturbed output can be improved when several manipulated inputs are available.

A popular choice in these cases is the series control scheme, characterized by (1) a sequential intervention of loops and (2) faster loops being reset by slower loops, to keep their control action around convenient values.

This paper tackles the problem from the frequency-domain perspective.

First, the working frequencies for each loop are determined and closed-loop specifications are defined.

Then, Quantitative Feedback Theory (QFT) bounds are computed for each loop, and a sequential loop-shaping of controllers takes place.

The obtained controllers are placed in a new series architecture, which unlike the classical series architecture only requires one controller with integral action.

The benefits of the method are greater as the number of control inputs grow.

A continuous stirred tank reactor (CSTR) is presented as an application example.