Mieczyslaw Metzger

Filtering in adaptive control of distributed parameter bioreactors in the presence of noisy measurements

Abstract This paper deals with simulation experiments on the model-based adaptive control of the distributed parameter bioreactor in the presence of the measurement noise. Since in such cases the adaptive controller itself is not able to ensure good control performance, there is a need to propose more sophisticated application. It is based on the first-order digital low-pass filters and allows us to decrease the influence of the measurement noise on the control performance. In order to decrease this influence it is possible to adjust three parameters of the application: controller tuning parameter, forgetting factor for the estimation of the substrate consumption rate and time constant of the low-pass filters. Simulation results, presented in this paper, have been obtained for different values of these parameters and, based on these results, it is possible to propose a robust application for the adaptive control of the bioreactor with optimally chosen values of the adjustable parameters. This application can be suggested to be applied in the adaptive control of a real industrial distributed parameter bioreactor with noisy measurement data.

New boundary conditions and adaptive control of fixed-bed bioreactors

Modelling, simulation, state estimation and feedback control of a distributed parameter fixed-bed bioreactor are studied in reference to two different types of boundary conditions. The bioreactor is described by two nonlinear and coupled partial differential equations including a single space variable. Classical Danckwerts boundary conditions and so-called Salmi and Romanainen boundary conditions are the two alternatives applied. For process model simulation the method of orthogonal collocation is used in the spatial discretisation. The idea of linearising state-feedback control is applied in the controller design. For control law calculation, two estimation procedures are used: one for estimating the state variables and the specific growth rate, and the other for obtaining the substrate consumption rate of the micro-organisms in the reactor. The state estimator is based on asymptotic observer design. Estimation of the substrate consumption rate is based on temporal discretisation and on the recursive exponentially weighted least-squares procedure resulting in adaptive nature of the final control law.

Multi-Agent System for Hierarchical Control with Self-organising Database

The paper presents hierarchical and multi-agent control and information system with real-time update of self organising database as well as with negotiation capability for control events and decisions. A practical application is presented, that utilizes the OPC technology in the continuous-time part, and scripts using XML in the discrete-time part of the system for negotiation and cooperation in multi-agent environment. This feature is applied for the improvement of a non-conventional biotechnological process control in the pilot plant.

A comparative evaluation of DRE integration algorithms for real-time simulation of biologically activated sludge process

Abstract An activated sludge process is considered in this work for comparative tests of new integration algorithms. Based on the configuration of the process and on the process kinetics for heterotrophic bacterial growth, the mathematical model of the considered process has been derived in the form of a state ordinary differential equation system. The state ordinary differential equation system describing the considered process may be both stiff and non-stiff for operators control changes of the oxygen feeding flow rate. In the work, new discrete response equivalent (DRE) integration algorithms are proposed for simulation runs with a fixed integration step size, which is independent of the process dynamics (this possibility is due to self-adaptive features of the algorithms). The proposed algorithms have been compared with most other frequently used integration algorithms. The comparative tests show that, among the compared algorithms, only the DRE integration algorithms may be used with a fixed, arbitrarily chosen integration step size for simulation of the state ordinary differential equation system which may be both stiff and non-stiff during simulation.

Comparison of the RK4M4, RK4LIN and RK4M1 methods for systems with time-delays

The higher-order Runge-Kutta methods can be used in three different ways when the time- delays occur. The RK4M4, RK4LIN and RK4M1 methods are an application of the most popular fourth-order Runge- Kutta method for time-delays. The RK4M4 method requires a storage of four variables, so it is hardly ever used. Based on the discussion and experimental testing it has been shown that the RK4M4 method nevertheless provides the most significant economy of memory and shortest computing time.

Holonic Multiagent-Based System for Distributed Control of Semi-industrial Pilot Plants

Semi-industrial pilot plants are the best experimental domain for advanced control systems testing with the real-world instrumentation. At the same time, inexpensive flexible process real-time simulators and virtual soft controllers are indispensable in the research and education field. Integrating control instrumentation of varying manufacturers, plant simulators, and virtual controllers into uniform system capable of flexible research and educational experiments is a complex problem to solve. A tool is needed to describe and organise knowledge on such integrated structure involving many communication channels and using distributed processing power. In the presented case-study, holarchy paradigm is applied, resulting in an untypical holonic multiagent system. The concept, architecture and development of application framework for the system are presented thoroughly in the paper.

Cooperative validation in distributed control systems design

The team of engineers designing and implementing distributed control system software must communicate within a multidisciplinary environment. One of the main problems is the interaction between hardware and software solutions. Software project presumptions may not be based only on minimum hardware requirements and on technology rules. Modern distributed control systems embrace all aspects of a complex and widespread object. Hence, every modification within any discipline requires interference into the system and validation of its new features, which in turn constraints effectiveness of designing. This paper discusses how to increase effectiveness and speed up validation, in a standardised CAD environment, by using: Multi-Agent System in order to limit the number of interactions between particular subsystems, ontology for assisting topology description and properties of system entropy for assessment of introduced solutions. The proposed system was implemented and worked out in a biotechnological pilot plant.

Agent---Based Approach for LabVIEW Developed Distributed Control Systems

Idea of networked software agents is particularly popular in the field of information sciences dealing with distributed content, whereas in industrial automation its use is usually limited to manufacturing systems. This work presents a concept of multi---agent networked system for automation of continuous processes. Some properties of typical software agent (i.e. advanced high level languages and social skills) had to be dropped in exchange for determinism and satisfying time performance in negotiations between network---connected control components. The proposed environment is National Instruments LabVIEW, very popular solution for automation and measurement. LabVIEW is equipped with advanced data acquisition tools and is capable of artificial intelligence methods, although it lacks agentification mechanisms. A framework is presented, providing LabVIEW the required functionality.

Application of the Holonic Approach in Distributed Control Systems Designing

Design of a multidisciplinary project is a complicated process requiring cooperation of different designers specialized in particular branches of engineering. The paper proposes a holonic approach to testify that a solution of distributed control systems is compliant with dynamically changing technology rules with ontology-based decomposition. The proposed holarchy includes a multi-agent system considering also its hybrid control architecture connected with a self-organization database. The proposed approach was implemented for a biotechnological pilot-plant continuously working as a platform for several process investigations.

Performance evaluation of the parallel processing producer-distributor-consumer network architecture

The CSMA/CD access method is no longer invoked in switched, full-duplex Ethernet, but the industrial protocols still take the presence of the method into account. The parallel processing producer-distributor-consumer network architecture (ppPDC) was designed specifically to actively utilize the frame queuing. The network nodes process frames in parallel, which shortens the time needed to perform a cycle of communication, especially in cases when frame processing times within the nodes are not uniform. The experiments show that the achievable cycle times of the ppPDC architecture are an order of magnitude shorter than in the well-known sequential PDC protocol.