http://www.ifac-papersonline.net/ en Copyright 02:30 PM Saturday 18, 2013 IFAC-PapersOnline http://www.ifacpapersonline.com 02:30 PM Saturday 18, 2013 02:30 PM Saturday 18, 2013 ET webmaster@ifac-papersonline.net webmaster@ifac-papersonline.net http://www.ifac-papersonline.net/Detailed/41935.html 04:00 PM Wednesday 31, 1969 http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41936.html 04:00 PM Wednesday 31, 1969 http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41937.html 04:00 PM Wednesday 31, 1969 This paper describes the main issues encountered when applying model predictive control to hybrid processes. Hybrid model predictive control (HMPC) is a research field non fully developed with many open challenges. The paper describes some of the techniques proposed by the research community to overcome the main problems encountered. Issues related to the stability and the solution of the optimization problem are also discussed. The paper ends by describing an application to a solar power plant, that illustrates how HMPC can be applied in real time. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41938.html 04:00 PM Wednesday 31, 1969 This paper proposes a hierachical hybrid MPC approach to design feedback control functions for stabilization and autonomous navigation of unmanned air vehicles. After formulating the nonlinear dynamical equations of a "quadcopter" air vehicle, a linear MPC controller is designed to stabilize the vehicle around commanded desired set-points. These are generated at a slower sampling rate by a hybrid MPC controller at the upper control layer, based on a hybrid dynamical model of the UAV and of its surrounding environment, with the overall goal of controlling the vehicle to a target set-point while avoiding obstacles. The performance of the complete hierarchical control scheme is assessed through simulations and visualization in a virtual 3D environment, showing the ability of linear MPC to handle the strong couplings among the dynamical variables of the quadcopter under various torque and angle/position constraints, and the flexibility of hybrid MPC in planning the desired trajectory on-line. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41939.html 04:00 PM Wednesday 31, 1969 The AQUASOL solar desalination plant at the Plataforma Solar de Almería (Spain) is based on a multi-effect desalination technology that combines gas and solar thermal energy to achieve a desired distillation flow. The process hybrid behavior involves interactions between continuous and discrete dynamics. This paper proposes a two-layer hierarchical scheme; the first layer decides the most suitable operating mode, and the second is for reaching local references. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41940.html 04:00 PM Wednesday 31, 1969 Solar systems are deeply affected by weather conditions and their main energy source, irradiation, cannot be manipulated. This paper describes a solar cooling system located at the University of Almería, Spain. The system is composed by a solar collector, a gas heather, and two serial connected tanks to storage hot water. They are used as energy sources for an absorption machine whose objective is to obtain chilled water for the fan-coil system. All these components are included or excluded from the cooling system by means of switching valves and activating or deactivating signals. The switching among different configuration modes in real time increases the system challenge to be modeled or controlled, due to the mix of both discrete signals and continuous dynamics. In this paper, a model for each energy source is developed and afterwards they are integrated into one state-space model used to obtain a hybrid model. This hybrid model is able to simulate the different configuration modes of the solar cooling system. Some real tests are presented. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41941.html 04:00 PM Wednesday 31, 1969 The problem of modeling and control of a three-stage steam reheating process in a steam power plant is considered in this paper. Mathematical model of this process is marked by considerable nonlinearity. Moreover, switching of dynamic behavior occurs because individual reheat stages are bypassed depending on the value of manipulated variable. For both of these reasons, there is a little chance that replacing the traditional control system based on cascade PID/PI loops with advanced control methods such as MPC based on single linearized model may bring any performance improvement. However, both of these features make the steam reheating process a suitable object of modeling with a hybrid model in the form of a switched piecewise affine (PWA) system. Hybrid MPC based on this model then becomes a promising candidate approach to control. This paper describes the results of PWA modeling of the steam reheating process. A good agreement of responses between PWA model and nonlinear first principles model is shown. Following the development of this model, the design of a hybrid MPC controller is outlined. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41942.html 04:00 PM Wednesday 31, 1969 An industrially applied LCC power converter is modelled as a hybrid system. It is found that the hybrid system given a parameter set up and different initial conditions has three different limit cycles, one unstable and two asymmetric stable limit cycles. Effects of the asymmetric limit cycles are considered. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41943.html 04:00 PM Wednesday 31, 1969 This paper considers the problem of controlling timed continuous Petri nets under infinite server semantics. The proposed control strategy assigns piecewise constant flows to transitions in order to reach the target state. First, by using linear programming, a method driving the system from the initial to the target state through a linear trajectory is developed. Then, in order to improve the time of the trajectory, intermediate states are added by means of bilinear programming. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41944.html 04:00 PM Wednesday 31, 1969 The efficient management of the Emergency Department (ED) has become an important issue in the past decade. Indeed, the increased demand for emergency services has saturated the capacity of EDs that require suitable tools for the efficient flow of work and people. The paper proposes a model to describe in a concise and effective way the structure and dynamics of a critical ED of the general hospital of Bari (Italy): the Emergency Cardiology Department (ECD). The model describes in a continuous Petri net framework the complete workflow and management of patients starting from their arrival to the ED until either their discharge from the hospital or their admission in a suitable hospital department. The fluid approximation allows defining suitable optimization problems to optimize the system performances and determine the optimal resource dimension guaranteeing the efficient management of the ECD. A simulation study shows that the optimized parameters lead to an effective workflow organization while maximizing the patient flow. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41945.html 04:00 PM Wednesday 31, 1969 A Markovian Petri net is a stochastic discrete event system (DES) frequently used for analysis and performance evaluation purposes. In the past, the fluidification has been proposed in different DES's as a relaxation technique for avoiding the "state explosion problem". Following the same approach, in this paper a hybrid Petri net model is defined as a partial relaxation of an original Markovian Petri net. It is shown through a simple example that such partial relaxation can be worse than a full relaxation (given by a fully continuous Petri net). Therefore, the rest of the paper is devoted to obtain sufficient conditions for guaranteeing the approximation of the hybrid Petri net model to the original discrete system. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41946.html 04:00 PM Wednesday 31, 1969 Reliability analysis is often based on stochastic discrete event models like Markov models or stochastic Petri nets. For complex dynamical systems with numerous components, analytical expressions of the steady state are tedious to work out because of the combinatory explosion with discrete models. The contribution of this paper is to approximate the steady state of mono T-semiflow stochastic nets by mean of continuous Petri nets according to a modification of the maximal firing speed vector definition. This result is then used to accelerate convergence of stochastic simulations. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41947.html 04:00 PM Wednesday 31, 1969 The dynamics of timed continuous Petri nets under infinite server semantics can be expressed by a piecewise linear system with polyhedral regions. In this paper we establish connections between the qualitative behavior of the dynamics of the continuous marking and the net structure. In particular, Petri nets with symmetries are addressed where symmetry is understood as a permutation symmetry of the nodes. It is shown that such a symmetry leads to a permutation of the regions and equivariant dynamics. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41948.html 04:00 PM Wednesday 31, 1969 We present a formal Modeling and Simulation (M&S) methodology for hybrid control of networking systems. The method is used for analysis, design and implementation of Quality of Service (QoS) control systems in Network Processor (NP)-based applications. We apply continuous Control Systems Theory to enforce Admission Control strategies into discrete-event network traffic. This represents a hybrid system modeling problem, that has to be treated formally to guarantee the applicability of the continuous control theoretical results into discrete-event systems. We show that using DEVS (Discrete Event System Specification), in combination with Quantized State Systems (QSS) numerical methods for the approximation of continuous systems, offers numerous advantages: these frameworks provide the means to accurately analyze and design hybrid models for Admission Control and they can be seamlessly integrated into a unified formal framework. It also enables the transition between the DEVS-based simulation and the deployment of the obtained hybrid models into the target networking platform. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41949.html 04:00 PM Wednesday 31, 1969 In the brewing process, a well-functioning temperature control in the mashing phase is of paramount importance for a good quality of the final product. Given the complexity of the underlying biochemical reactions, a reliable process model can be of great help. However, most of the models developed in the literature are not suited for that task, since the mash temperature is considered an exogenous input. In this work, literature models are complemented with suitable energy balance equations, implemented in the Modelica language, and verified against literature data. A temperature control system is then set up with one of those (first principle) models, to illustrate the usefulness of the idea, including the possibility of simulating the control code up to a quasi-replica setting--i.e., integrating continuous-time and event-based modelling. Future developments will include more extensive use of model-based control techniques, and also the integration of model forecasts and process measurements, to further improve the control results. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41950.html 04:00 PM Wednesday 31, 1969 DEVSLib is a free Modelica library, developed by the authors, that supports the Parallel DEVS formalism. The library is mainly designed to model discrete-event systems. It also includes interfaces to communicate the DEVSLib models with the rest of the Modelica libraries. Thus, the library can be used in the development of multi-domain and multi-formalism hybrid models. This manuscript discusses the modeling of the system "Crane and Embedded Controller," proposed by ARGESIM, using Modelica and DEVSLib. The crane system is composed of a car that moves along a rail and a load connected to the car by a cable. A discrete controller controls the position of the car and its movement. The crane system is implemented in Modelica as a continuous-time model and the discrete controller is constructed using DEVSLib. The communication between the continuous-time and the discrete-event parts is performed using the DEVSLib interfaces. DEVSLib is freely available for download at http://www.euclides.dia.uned.es. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41951.html 04:00 PM Wednesday 31, 1969 The final department of any sugar factory is in charge of producing commercial sugar grains out of an impure sucrose in water solution by means of crystallization. Quality requirements demand a fed-batch mode of operation from most of the process units of the section and in particular from the industrial crystallizers. A library of reusable simulation models of the Sugar House have been developed taking advantage of object oriented modeling concepts. The dynamic simulation of batch equipment usually demands the use of hybrid type models. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41952.html 04:00 PM Wednesday 31, 1969 A pursuit-evasion differential game with bounded controls and prescribed duration is considered. The evader has a finite number of possible dynamics, while the dynamics of the pursuer is fixed. The evader can change its dynamics several times during the game. The pursuer knows all possible evader dynamics, but not the actual one. The optimal pursuer feedback strategy in this game is obtained. This strategy is robust with respect to the order of the evader dynamics during the game, as well as instants of changing the dynamics. For this strategy, the capture zone is constructed. An illustrative example is presented. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41953.html 04:00 PM Wednesday 31, 1969 This paper presents a hybrid algorithm for solving complex optimal control problems based on decomposition. The general finite-time optimal control problem for a class of hybrid dynamical systems is considered, which has not been solved in a decomposed way by existing methods. The problem is first decomposed into a master problem and a subproblem, and then the two are linked via logic-based Benders decomposition. Computational experiments have been carried out for the considered problem. The results show that the proposed algorithm could substantially reduce the solving time, compared with directly solving by mixed integer solvers. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41954.html 04:00 PM Wednesday 31, 1969 This paper presents a novel optimal adaptive feedback control concept for nonlinear switched autonomous systems. Our proposed controller implements a closed-loop switching law, which is represented by a parametrized switching plane in the state space. During the plant operation, the plane parameters are incrementally adapted to state measurements in real time by iteratively solving an associated nonlinear optimization problem over a finite time horizon. The combination of this control approach with ideas from model predictive control yields the so-called crawling window optimal control scheme that achieves the optimal stabilization of periodically operated switched systems. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41955.html 04:00 PM Wednesday 31, 1969 We propose a numerical method to approximate the value function for the optimal stopping problem of a general class of hybrid processes, namely piecewise deterministic Markov processes (PDMP's). Our approach is based on quantization of the post jump location - inter-arrival time Markov chain naturally embedded in the PDMP, and path-adapted time discretization grids. It allows us to derive bounds for the convergence rate of the algorithm and to provide a computable ε-optimal stopping time. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41956.html 04:00 PM Wednesday 31, 1969 A generalization of a polynomial approach to solve the optimal control problem of nonlinear switched systems is presented. We present a technique to deal with the more general non-polynomial switched systems, using the polynomial approach previously presented, combined with a recasting process. It is shown that the representation of the original switched problem into a continuous polynomial system allows us to use the generalized Maximum Principle. With this method and from a theoretical point of view, we provide necessary and sufficient conditions for the existence of minimizer by using particular features of its relaxed, convex formulation using the theory of moments. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41957.html 04:00 PM Wednesday 31, 1969 This contribution presents an approach to synthesize logic feedback controllers for Discretely Controlled Continuous Systems such that given specifications are fulfilled. This class of systems consists of a continuous plant with nonlinear dynamics which is controlled by a logic controller that processes discrete measurements. The control problem is to optimally steer the system from a set of initial states to a set of target states without reaching unsafe states. For given thresholds, the algorithm first computes the optimal discrete inputs for each boundary section to obtain optimal trajectories from each boundary section to the target by a dynamic programming approach. The controller then has to be verified to guarantee that the unsafe states are not reached for arbitrary trajectories. The approach is demonstrated for a two-tank benchmark. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41958.html 04:00 PM Wednesday 31, 1969 In previous work we have shown how a max-plus algebraic model can be derived for cyclically operated high-throughput screening systems and how such a model can be used to design a controller to handle unexpected deviations from the predetermined cyclic operation during runtime. In this paper, we introduce an extension of this approach for high-throughput screening systems containing multi-capacity resources, i.e., resources that can handle more than one activity at the same time. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/41959.html 04:00 PM Wednesday 31, 1969 This paper deals with the stability analysis, as well the synthesis design for positive linear systems subject to random Markovian switching. The proposed stabilizing control laws are required to preserve the positivity of the system, that is the state variable take nonnegative values whenever the initial state is nonnegative. For this kind of systems, different notions of stochastic stability are defined and it is shown that they are all equivalent. Moreover, all the provided conditions are necessary and sufficient. Beside that, it is shown how the proposed approach can handle the case when the Markovian switching process is not exactly know. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif