Abstract-We propose a computational-oriented perspective within the study of discontinuous chaotic systems, and provide insights into the modelling, control and simulation of chaotic systems with switching dynamics. In particular, the Lorenz system in its piecewise-linear version is studied. This system is reinterpreted within the hybrid-automaton framework, and what is referred to as the Lorenz hybrid automaton is established. Furthermore, a discontinuous control which eliminates the chaotic behaviour and steers the trajectories to a desired equilibrium is proposed. An integral characteristic of the modelling framework is that the controlled system, exhibiting three discontinuity surfaces, is reduced to the composition of several Lorenz hybrid automata. The approach proposed here is especially useful in order to specify the transitions between the different system operation modes, which becomes a crucial problem due to the existence of multiple switching surfaces.
I. MOTIVATIONWhat is the best model to describe variable structure systems with multiple switching elements and exhibiting several types of complex behaviours? How to specify all their transitions in a deterministic way to facilitate the simulation? Every mathematical model is an approximation of the real world, and is full of limitations. However, some models are better than others at describing the evolution of certain physical and engineering systems. The hybrid systems framework, in particular, the computational hybridautomaton one is very adequate for modelling and controlling complex systemsThis paper is devoted to the specification and the computational abstraction of a particular discontinuous system with chaotic behaviour: the piecewise-linear (PWL) Lorenz system. The computational framework used is that of hybrid automata [2] faced when the trajectories either cross or slide on the discontinuity surfaces. Furthermore, due to the coexistence of several discontinuity surfaces, the problem of specification of the transitions between the system operation modes is critical, and special care has to be taken in the numerical integration [13], [14], [15]. The use of a hybrid automaton to describe the system is presented here as a solution to this problem. This paper is inspired by Navarro's previous results related to the modelling and discrete abstraction of discontinuous dynamical systems (DDSs) under the hybrid-automaton framework [4], [5], [6].The Lorenz hybrid automaton with 6 discrete locations is given. To prove the efficacy of the hybrid-automaton framework, a second hybrid automaton with 18 locations is proposed. This second automaton corresponds to the controlled PWL Lorenz system with three discontinuity surfaces, which is obtained by considering a sliding-modebased control. The control strategy is based on inserting a discontinuity surface on which the system presents the desired behaviour and forces the system trajectories to slide on this surface. The controlled Lorenz hybrid automaton, by following the computer science divide-and-conq...