Pär Samuelsson

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.

A JAVA based simulator of activated sludge processes

A simulator of activated sludge processes in wastewater treatment plants has been implemented in the programming language JAVA. The simulator can be reached over Internet and operated from a web browser. A novel graphical user interface is used to operate the simulator and to present the simulation results in real time. Different automatic control strategies are implemented in order to illustrate the importance of automatic control in wastewater treatment plants. The simulator has been used for educational purposes both for university students and personnel from wastewater treatment plants. A demo version of the simulator is located at the URL address: www.syscon.uu.se/JASS/.

Technical communique: An integrating linearization method for Hammerstein models

This paper considers a method for linearization of models containing static input nonlinearities in series with a linear model, so called Hammerstein models. The method linearizes the system exactly, and is performed by differentiating the nonlinearity with respect to the input signal. Using this approach, an integration is added in the loop gain of the linearized system via the internal feedback. The method presented here is in essential senses an equivalent alternative to the standard method that utilizes the inverse of the static nonlinearity complemented with an integration. Particularly, in cases when analytic inversion is difficult, the presented method provides an attractive alternative.

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.