http://www.ifac-papersonline.net/ en Copyright 06:12 PM Tuesday 07, 2012 IFAC-PapersOnline http://www.ifacpapersonline.com 06:12 PM Tuesday 07, 2012 06:12 PM Tuesday 07, 2012 ET webmaster@ifac-papersonline.net webmaster@ifac-papersonline.net http://www.ifac-papersonline.net/Detailed/42029.html 04:00 PM Wednesday 31, 1969 The study of protein folding and its ramifications in biological contexts is at the heart of computational biology. In this paper, we discuss a number of tools in systems engineering that would provide an analysis framework to help explain the observed dynamic behavior of the protein, ultimately making the connection between protein structure and functionality. A case study of villin headpiece folding using principal components analysis as well as clustering demonstrates the potential of these tools in responding to this challenge. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42066.html 04:00 PM Wednesday 31, 1969 The dynamic behaviour of a coal slurry gasifier in an Integrated Gasification Combined Cycle is modelled by means of mass, energy and momentum conservation equations as well as reaction kinetics descriptions. The main phenomena taken into consideration are (i) slurry drying and devolatilisation, (ii) char and volatile gas combustion, char gasification and water-gas shift reaction, and (iii) syngas cooling. The proposed 0-dimensional description is sufficient to capture process dynamics and it is a useful starting point for control design and verification. In particular, basic control strategies are discussed. Both model and control implementation is carried out in the Matlab-Simulink environment. Simulation results are shown to support model reliability and control effectiveness. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42074.html 04:00 PM Wednesday 31, 1969 High purity distillation control of a binary mixture in a tray column is considered in the paper at hand. The approach is based on an inferential control idea: dynamics within the column may be described as movements of concentration waves; the position of the wave front on the one hand side can be inferred from few temperature measurements, on the other hand the position implies the product concentrations. Dynamics of wave propagation is derived by simplification of a first principles model of the column. The resulting descriptor model is the basis for a recent LMI based controller design scheme that provides general quadratic performance for descriptor systems. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42057.html 04:00 PM Wednesday 31, 1969 In this paper we consider a hierarchical approach to solve an optimal control problem for a hybrid chromatographic batch process. The plant consists of several chromatographic columns which can be connected in an arbitrary way. The plant configuration can therefore be considered as a discrete-valued control input. The dynamics of each chromatographic column is described by two coupled nonlinear partial differential equations. Hence, we have a hybrid optimisation problem with highly nonlinear dynamics. To handle complexity, we propose a hierarchical two-level optimisation scheme: first, we solve a number of continuous optimisation problems that correspond to fixed configurations. In a subsequent step, on the basis of these solutions, we solve a discrete optimisation problem to generate the optimal configuration or configuration signal. Because of the imposed structure, we can of course not expect the overall solution to be optimal. However, we demonstrate that, by using the plant configuration as an an additional control input, performance may be considerably improved when compared to the constant configuration scenario. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42090.html 04:00 PM Wednesday 31, 1969 The new methodology presented provides a way to optimize the operation of a variety of batch processes (chemical, pharmaceutical, food processing, etc.) especially when at least one time-varying operating decision function needs to be selected. This methodology calculates the optimal operation without the use of an a priori model that describes in some accuracy the internal process characteristics. The approach generalizes the classical and widely used Design of Experiments (DoE), which is limited in its consideration of decision variables that are constant with time. The new approach, called the Design of Dynamic Experiments (DoDE), systematically designs experiments that explore a considerable number of dynamic signatures in the time variation of the unknown decision function(s). Constrained optimization of the interpolated response surface model, calculated from the performance of the experiments, leads to the selection of the optimal operating conditions. Two examples demonstrate the powerful utility of the method. The first examines a simple reversible reaction in a batch reactor, where the time-dependant reactor temperature is the decision function. The second example examines the optimization of a penicillin fermentation process, where the feeding profile of the substrate is the decision variable. In both cases, a finite number of experiments (4 or 16, respectively) lead to the very quick and efficient optimization of the process. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42013.html 04:00 PM Wednesday 31, 1969 For obvious industrial and theoretical reasons the problem of accounting for the effect of impurities in the population balance modelling of solution crystallization processes is a very important issue, and yet it has never been reported until today. Meanwhile, several kinetic models are proposed in the literature that relate the effect of impurities on the crystal growth and could be used for PBE modelling. The goal of the present paper is to address this issue and to present a new method, based on characteristics, which is shown to efficiently solve the difficulties raised by the specificity of the mathematical formulation of the Population Balance Equation (PBE) in the presence of impurities. Indeed, as far as hindering effects of the impurities on the crystal growth are concerned, it turns out that the "age" of the particles (i.e. the time they spent in the presence of impurities) might plays a key-role in the overall dynamic crystallization process. Accounting for such a new internal variable required a specific PBE resolution algorithm to be developed and evaluated. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42096.html 04:00 PM Wednesday 31, 1969 A suitable design of state estimators requires a representative model for capturing the plant behavior and knowledge about the noise statistics, which are generally not known in practical applications. While the measurement noise covariance can be directly derived from the measurement device reproducibility, the choice of the process noise covariance is much less straightforward. Further, processes such as continuous process with grade transitions and batch or semi-batch process are characterized by time-varying structural uncertainties which are, in many cases, partially and indirectly reflected in the uncertainty of the model parameters. It has been shown that the robust performance of state estimators significantly enhances with a time-varying and non-diagonal process noise covariance matrix, which explicitly takes parameter uncertainty into account. For this case, the parameter uncertainty is quantified through the parameter covariance matrix. This paper presents a direct and a sensitivity method for the parameter covariance matrix computation. In the direct method, the parameter covariance matrix is found during the parameter estimation step of the SELEST algorithm, while in the sensitivity method, the parameter covariance matrix is obtained through a time-varying sensitivity matrix. The results have shown the efficacy of these methods in improving the performance of an extended Kalman filter (EKF) for a semi-batch reactor process. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42122.html 04:00 PM Wednesday 31, 1969 A nonlinear control strategy based on Interconnection Damping Assignment Passivity Based Control (IDA-PBC) is proposed for a process with bidirectional flow. The bidirectional flow condition introduces singularities in the control action under certain operation conditions. A solution to this problem is proposed such that operation through the singular points is possible and the stability conditions around the desired operation point are exactly preserved. In addition, a passivity based integral action is included in order to take into account the effects of model uncertainties and unknown step like disturbances. A description of the process and the controller design methodology is presented along with some numerical simulations illustrating the closed-loop behavior of the proposed controller. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42044.html 04:00 PM Wednesday 31, 1969 Controlling the interface between Bitumen-froth and Middlings in separation cells in the oil sands industry is important for economical and environmental reasons. Traditional sensors do not provide reliable measurements of this interface level and image based sensors are being used to alleviate this problem. Previous work in this area has focussed on separation cells with a single side-view glass. The current work describes a new image based algorithm for interface level detection and confidence estimation based on the concept of image differencing. The algorithm can be extended in a straight-forward manner to separation cells with arbitrary number of side-view glasses. Off-line and on-line results show that the algorithm accurately detects the interface level in normal process conditions and outputs correct confidence values in other situations with very low false positive and negative rates. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42128.html 04:00 PM Wednesday 31, 1969 In this paper we present an automatic tuning methodology for PID controllers for distributed-lag processes. The technique is based on the evaluation of a closed-loop set-point or load disturbance step response and it can be therefore employed with process routine operating data. Further, a performance assessment index is also proposed in order to establish when the performance of a PID controller can be improved by retuning it according to the proposed method. Simulation results show the effectiveness of the approach. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42141.html 04:00 PM Wednesday 31, 1969 We address the problem of linear parameter estimation in discrete time state space models in the presence of serially correlated error in variables. The common way to solve parameter estimation problem is least squares (LS) methods. LS method is not considered to be effective when both dependent and independent variables are contaminated by noise. Total Least Squares (TLS) has been introduced as the method for parameter estimation in the case of noisy response and predictor variables. However, TLS solution is not optimal when number of data is limited and noise is correlated. Constrained TLS is a variant of TLS that considers correlation of noise in the data as additional constraints. We introduced a novel method based on a stochastic sampling method to solve estimation problem from correlated noisy measurements, and we compared it with the existing methods through in silico examples. Our method demonstrates significant improvement over other common estimation algorithms, LS, TLS and Constrained TLS under the different amount of correlated noise and data points. It has the potential to be the valuable tool for the difficult real life problems, such as, biological systems where data is limited and noisy. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42032.html 04:00 PM Wednesday 31, 1969 This work aims a stochastic approach for the calculation of robust anti-solvent addition policies for controlling the mean crystal size (MCS) in fed-batch crystallization operations. The proposed strategy is based-on a non-structured population balance where uncertainties associated with the start-up condition and random fluctuations along the fed-batch operation can be taken into account in a very natural fashion. We include and quantify the effect of the uncertainties by embedding a deterministic crystal growth model into a Fokker-Planck equation (FPE) resulting in a stochastic model for the MCS dynamics. This approach uses the Generalized Logistic equation (GLE) that has an adequate mathematical structure that suits the dynamic characteristic of the crystal growth. Thus, the numerical solution of the FPE provides the most likely MCS evolution for a given anti-solvent flow-rate. The effect of the anti-solvent is incorporated into the parameters of the FPE. The parameters of the FPE are computed as linear piece-wise interpolating functions of the anti-solvent flow-rate. The strategy uses a PID-like regulator in closed-loop fashion with the FPE to compute the anti-solvent addition flow-rates for different set-point targets in the MCS. In order to validate the stochastic model and assess the merits of the proposed strategy, the crystallization of sodium chloride in water using ethanol as anti-solvent is performed in a bench-scale fed-batch crystallizer. The implementation of the calculated anti-solvent policies resulted in a good control of the MCS despite modelling mismatch and uncertainties present during the crystallization operation. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42156.html 04:00 PM Wednesday 31, 1969 This work presents a strategy for controlling acetaldehyde content in Brazilian bioethanol, based in simulation results of a typical industrial distillation plant. The major problem of acetaldehyde in bioethanol is that, during the storage period, it can oxidize to acetic acid, increasing fuel acidity above the legislation limit. This work tested, by dynamic simulation, simple loops to control acetaldehyde in bioethanol. The dynamic simulation generated a disturbance in the wine to be distilled by increasing acetaldehyde content, and verified how those loops were able to control the acetaldehyde level in bioethanol. Two different column system configurations were investigated. The first one includes a degassing system and a second one that produces pasteurized alcohol without or with a degassing system. Suggestions for the best control system of acetaldehyde contamination in bioethanol were formulated according to the acetaldehyde level in the wine. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42028.html 04:00 PM Wednesday 31, 1969 Overflow metabolism characterizes cells strains that are likely to produce inhibiting metabolites resulting from an excess of substrate feeding and a saturated respiratory capacity. The critical substrate level separating the two different metabolic pathways is generally not well defined. This paper proposes two non-model based extremum-seeking strategies preventing a too important accumulation of inhibiting metabolites in fed-batch cultures, by estimating the critical substrate level on the basis of 3 simple measurements related to the feeding, oxygen and carbon dioxide. A simple substrate controller based on Lyapunov stability arguments is then designed and tested in combination with the two extremum-seeking schemes. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42146.html 04:00 PM Wednesday 31, 1969 Fuel cell systems can produce clean energy and have attracted the interest of both industrial and basic research in the recent years. They are part of a promising benign and environmentally friendly technology and they can be used both in mobile and stationary applications. A dynamic model was constructed and validated using experimental data based on a specific application, consisting of a high temperature PEM Fuel Cell (FC) working at a constant pressure and a Power Conversion Device that controls the current drawn from the FC. An integrated framework that consists of an online maximum power point prediction algorithm and a non-linear model based control scheme is presented. The proposed framework aims to maintain the fuel cell close to the optimum power point and the corresponding oxygen excess ratio level. Simulation studies show that the proposed control framework results in improved performance regarding the efficient and safe fuel cell operation under varying operating conditions. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42021.html 04:00 PM Wednesday 31, 1969 The purpose of this paper is to stress the importance of selecting the right plantwide control structure and the need for a formalized approach that can encompass the many issues that arise in plantwide control design. Since the concept of process control design based on a holistic view of the process came about, the variety of procedures and approaches to the design problem have illustrated the difficulty of a unified approach. Using examples, a formal design approach is presented to help put in context the need and advantages of using such an approach. The examples deal with disturbance rejection, throughput maximization and economic optimization of plants consisting of parallel units. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42091.html 04:00 PM Wednesday 31, 1969 Existing tuning rules for mid-ranging control can be improved. In this paper a novel strategy for midranging control based on Internal Model Control (IMC) principles is presented. The design reformulates mid-ranging control specifications in terms of classical bandwidth and sensitivity requirements. The performance of this design is demonstrated through simulation studies. The overall benefits of the IMC design are that it provides transparent and flexible tuning, and that it offers a natural framework for anti-windup. Both classical IMC and modified IMC structures are considered for anti-windup. Their performance during saturation is demonstrated through simulation studies, where minimal degradation is observed. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42131.html 04:00 PM Wednesday 31, 1969 Distributed Model Predictive Control (DMPC) has received significant attention in the literature. However, the robustness of DMPC with respect to model errors has not been explicitly addressed. In this paper, an online algorithm that deals explicitly with model errors for DMPC is proposed. The algorithm requires decomposing the entire system into N subsystems and solving N convex optimization problems to minimize an upper bound on a robust performance objective by using a time-varying state-feedback controller for each subsystem. Simulations on two typical examples were considered to illustrate the application of the proposed method. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42027.html 04:00 PM Wednesday 31, 1969 For a successful application of any industrial Z. mobilis facility, it is necessary to have an efficient and simple control strategy. This paper analyzes the control and optimization problem of a continuous ZM bioreactor modeled by Jöbses et al. (1986). This system has steady state multiplicity in part of the operating range. The idea is to maintain the process close to the manifold border where is achievable the highest ethanol production. Based on a systematically analysis of the operational controllability using the nonlinear RPN indices it is identified that the process can be controlled using a linear controller. Finally the paper proposes a variable transformation that makes easy to maintain the bioreactor close to the optimum. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42153.html 04:00 PM Wednesday 31, 1969 In this paper, a new scheme for adaptive unfalsified control with non-ideal measurements is presented and demonstrated for a well-known example of a nonlinear plant, the continuous stirred tank reactor (CSTR) with the van-der-Vusse reaction scheme. In our adaptive control algorithm, there are two adaptation mechanisms: 1. Switching of the active controller in a fixed set of candidate controllers by the ε-hysteresis switching algorithm. 2. Adaptation of the set of controllers performed by a population-based evolutionary algorithm. In this paper, the effect of measurement errors on the adaptive control scheme is investigated. The total least squares method is used to perform the deconvolution of noisy signals. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42126.html 04:00 PM Wednesday 31, 1969 While batch processes are gaining ever increasing importance in the manufacturing industries, control of the product quality remains to be a serious challenge. To improve overall process understanding and control, new analytical techniques, such as Near-Infrared (NIR) Spectroscopy, are starting to be employed in industry. Currently, these techniques are primarily used for process monitoring purposes and have not yet been explicitly included in feedback control systems. This paper investigates the ability of three different control systems to adequately control a simulated batch reactor using the NIR spectra as feedback information such that the product meets quality specifications. The particular problem considered in this paper is adequate representation of the NIR spectrum using a single variable that is then controlled by employing Model Predictive Controller (MPC). It is shown that the resulting controller performances are highly variable if the controlled variable is chosen by selecting a single peak in the NIR spectrum to represent that variable. On the other hand, by using Principal Component Analysis (PCA) to extract information from all of the wavenumbers and represent it using a single composite variable, which is then controlled, it is shown that the process can be adequately regulated. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42143.html 04:00 PM Wednesday 31, 1969 This paper addresses the application of a new MPC to a distillation system where isobutane and light butenes are separated from butane and heavier compounds. This system is located in the alkylation unit of an oil refinery. The MPC considered here is based on the infinite horizon MPC extended to the case where the system has stable and integrating modes. The controller is developed based on a particular state space model in the incremental form, which considers the existence of time delays. The proposed controller provides nominal stability to the closed loop system. Practical tests in a distillation system show that the performance of the new controller, which can be extended to consider robustness to model uncertainty is similar to the performance of the conventional MPC with finite prediction horizon. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42030.html 04:00 PM Wednesday 31, 1969 Biopharmaceutical manufacturing processes are inherently complex due to their nonlinear bioprocess dynamics, variability in batch operations and manufacturing schedule, raw materials involved, and automatic process control. A typical processed lot generates large amounts of data that need to be analyzed and interpreted for process troubleshooting and continuous improvement purposes in addition to product release. Multivariate Batch Process Modeling, Monitoring and Control approaches in real-time are elaborated by providing industrial examples from the commercial manufacturing processes. Examples and opportunities in cell culture (e.g., bioreactor applications) and purification (e.g., large-scale chromatography) operations are summarized. Impact of Process Analytical Technologies (PAT), softsensor development, first principles modeling applications and commercial-scale examples are presented. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42010.html 04:00 PM Wednesday 31, 1969 In this talk, we assess the potentials of the approximate dynamic programming (ADP) approach for process control, especially as a method to complement the model predictive control (MPC) approach. In the Artificial Intelligence (AI) and Operations Research (OR) research communities, ADP has recently seen significant activities as an effective method for solving Markov Decision Process (MDP), which represents a type of multi-stage decision problems under uncertainty. Process control problems are similar to MDPs with the key difference being the continuous state and action spaces as opposed to discrete ones. In addition, unlike in other popular ADP application areas like robotics or games, in process control applications first and foremost concern should be on the safety and economics of the on-going operation rather than on efficient learning. We explore different options within ADP design, such as the pre-decision state vs. post-decision state value function, parametric vs. nonparametric value function approximator, batch-mode vs. continuous-mode learning, exploration vs. robustness, etc. We argue that ADP possesses great potentials, especially for obtaining effective control policies for stochastic constrained nonlinear or linear systems and continually improving them towards optimality. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/42093.html 04:00 PM Wednesday 31, 1969 This paper makes two key contributions. First there is a definition and implementation of a novel auto-tuned predictive controller. The key novelty is that the modelling is based on relatively crude but pragmatic plant information. Secondly, the paper tackles the issue of availability of predictive control for low level control loops. Hence the paper describes how the controller is embedded in an industrial Programmable Logic Controller (PLC) using the IEC 1131.1 programming standard. Laboratory experiment tests were carried out in two bench-scale laboratory systems to prove the effectiveness of the combined algorithm and hardware solution. For completeness, the results are compared with a commercial PID controller (also embedded in the PLC) using the most up to date auto-tuning rules. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif