Hervé Guéguen

Safety verification and reachability analysis for hybrid systems

Safety verification and reachability analysis for hybrid systems is a very active research domain. Many approaches that seem quite different, have been proposed to solve this complex problem. This paper presents an overview of various approaches for autonomous, continuous-time hybrid systems and presents them with respect to basic problems related to verification.

MODEL PREDICTIVE CONTROL FOR HYBRID SYSTEMS UNDER A STATE PARTITION BASED MLD APPROACH (SPMLD)

This paper presents the State Partition based Mixed Logical Dynamical (SPMLD) formalism as a new modeling technique for a class of discrete-time hybrid systems, where the system is defined by different modes with continuous and logical control inputs and state variables, each model subject to linear constraints. The reformulation of the predictive strategy for hybrid systems under the SPMLD approach is then developed. This technique enables to considerably reduce the computation time (with respect to the classical MPC approaches for PWA and MLD models), as a positive feature for real time implementation. This strategy is applied in simulation to the control of a three tanks benchmark.

An Optimization Procedure of the Start-Up of Combined Cycle Power Plants

Abstract This paper presents an optimization procedure for the definition of the gas turbine load profile during the hot start-up of Combined Cycle Power Plants (CCPP). First a dynamic model of CCPP is briefly described, together with its implementation in the Modelica language. Then, an identification procedure is developed to determine a simplified model to be implemented in Matlab/Simulink and to be used for the solution of the optimization problem. This simplified model is built by interpolating a number of linear estimated models with local validity. The load profile is assumed to be described by a suitable function, whose parameters are optimized by solving a minimum time problem subject to the plant (simulator) dynamics and to a number of constraints to be imposed on the main plant variables, such as temperatures, pressures, thermal and mechanical stresses. A number of simulation experiments is reported to witness the performance of the proposed approach.

Formal approach to compute hybrid automata models for linear physical systems with switches

This paper considers the computation of a hybrid automaton that models the behaviour of a switching linear physical system using energy considerations. The system is represented in a compositional way with bond graphs that include switches. In a first step the switches are considered from a functional point of view. This allows to determine the locations that are associated to consistent configuration of switches, the continuous activities and the jumps. In a second step elementary models of switches are introduced and allow to determine the invariants and the guards of transitions. The approach is exemplified with a simple electronics circuit

Using timed automata for the verification of IEC 61499 applications

Abstract This paper presents a methodology for the modelling of IEC 61499 function blocks behaviour using timed automata. The aim is to be able to associate basic timed automata with each functional block and to compose them in order to verify the execution of a network of functional blocks. The method and the verification that can be made are exemplified on a distributed control application.

Extensions of Grafcet to structure behavioural specifications

Abstract Grafcet is a powerful tool to specify sequential behaviours. However some limits of this formalism may be reached when dealing with complex systems. The aim of this paper is to present new mechanisms that have been proposed in order to extend specification capabilities of Grafcet and that have been taken up by the revision process of the IEC 61848 standard: enclosed step and stored actions. The consistency of these extensions with basic formalism is shown and their usefulness is illustrated by an example. Theoretical definitions of Grafcet and its extensions are given in Appendix A.

A Robust Receding Horizon Control Approach to Artificial Glucose Control for Type 1 Diabetes

The problem of controlling the blood glucose value of a patient suffering from type 1 diabetes is considered. The proposed strategy consists in designing a robust nonlinear model predictive controller based on a minimal nonlinear model. The various uncertainties and disturbances are introduced through the use of a variational model. The control problem is then expressed as a constrained game type minimax optimization problem. The choice of a final cost which ensures good stability properties are detailed. The performances of the controller are exemplified on a virtual testing platform showing its good properties.

Hierarchical Model Predictive Control Approach for Start-up Optimization of a Combined Cycle Power Plant

Due to their numerous advantages, Combined Cycle Power Plants (CCPPs) have become an important technology for power generation. The participation of the CCPPs on the power production market involves frequent start-up/shutdown operations. In this context, optimizing their start-up procedure is of high interest. The optimization objective corresponds to problems that must be solved in real time while fulfilling operating constraints and in the mean time minimizing costs. In this paper a hierarchical model predictive control (H-MPC) structure is proposed to improve the start-up performances and to reduce the computation time. The structure includes two layers, each having a different time scale. The control problem at each level is formulated and based on a model developed in the modeling language Modelica and it aims at determination of an optimal profile of the gas turbine (GT) load. The CCPP model is adapted for optimization purposes and the load profile is assumed to be describable by parameterized functions, whose parameters are computed by solving a constrained optimal control problem. Numerical results prove the potential advantages of the proposed approach.

A double resonance generator simulation using a hybrid approach

By using a hybrid approach the authors present the modelling of a double resonant DC/DC converter. This kind of generator is used for medical imagery applications, requiring high tensions, typically 40 kV to 200 kV, associated with high powers (about 100 kW). The proposed methodology can constitute an effective method allowing a structured and systematic approach of the dynamic systems modelling

HYBRID ABSTRACTIONS OF AFFINE SYSTEMS

Abstract This paper considers the problem of building a set of hybrid abstractions for affine systems in order to compute over approximations of the reachable space. Each abstraction is based on a partition of the continuous state space that is defined by hyperplanes generated by near combinations of two vectors. The choice of these vectors is based on considerations on the dynamics of the system and uses, for example, the left eigen vectors of the matrix that defines this dynamics. It is shown how the reachability calculus can then be performed on a composition of such abstractions and how its accuracy depends on the choice of hyperplanes that defines the abstraction but also on the number of abstractions that are composed.