Björn Halvarsson

Comparison of some Gramian based interaction measures

In this paper different interaction measures are reviewed and compared. In particular, the two Gramian based interaction measures the Hankel interaction index array (HIIA) and the participation matrix (PM) are considered. Moreover, motivations for incorporating the concept of output controllability in an interaction measure are given and a H2 norm based interaction measure is investigated.

Interaction analysis and control structure selection in a wastewater treatment plant model

This paper considers the problem of channel interaction in multivariable systems. As an application, nitrate removal in the activated sludge process (ASP) in a wastewater treatment plant is studied. To evaluate the degree of channel interaction, two different tools are compared: the well-known relative gain array (RGA) and the more recently developed Hankel interaction index array (HIIA). The results of the analysis are discussed from a process knowledge point of view, and are also illustrated with some control experiments. The main conclusion is that the HIIA gives a deeper insight about the actual cross couplings in the system. This insight is also used in order to design a suitable structured multivariable controller.

Empirical approach to robust gramian-based analysis of process interactions in control structure selection

This paper deals with the estimation of a gramian-based interaction measure from logged process data, and thereby removing the need of creating parametric models prior to the selection of the significant input-output interconnections. Moreover, the resulting confidence regions of the estimates can be used to perform a robust control structure selection.

APPLICATIONS OF COUPLING ANALYSIS ON BIOREACTOR MODELS

Abstract In this paper the well-known Relative Gain Array (RGA) and the recently proposed Hankel Interaction Index Array (HIIA) are utilized for quantifying the degree of channel interaction in a multivariable bioreactor model, an activated sludge process configured for nitrogen removal. The HIIA can deal with plant structures where the RGA fails and can furthermore also be used to evaluate multivariable controller structures. It was found that the RGA method was unable to give reasonable input-output pairing suggestions in some cases while the HIIA method provided useful information in all of the considered cases.

A new input/output pairing strategy based on linear quadratic Gaussian control

In this paper a new input/output pairing strategy based on linear quadratic Gaussian control (LQG) is suggested. The strategy is used to compare the expected performance of decentralized control structures in some illustrative examples. The pairing suggestions are compared with the recommendations previously obtained using other interaction measures such as the relative gain array (RGA). The new strategy gives suitable pairing recommendations and is easy to interpret.