Simulation of Variable Structure Models Using Rand Model Designer

Abstract

Rand Model Designer (RMD) is a modeling environment that supports Model Vision Language, an object-oriented modeling language for hybrid-DAE systems. Model Vision Language allows describing the continuous-time part of the model combining the use of equations (i.e., a causal modeling) and sequences of assignment statements. The hybrid behavior is described using behavior charts (B-chart). A B-chart is a diagram consisting of modes, transitions internal to the modes and transitions between modes. The activity of the mode is specified by a local class (the so-called activity class of the mode) that describes the system structure and behavior while in this mode. The system of equations that describes the complete model at certain time is automatically built by RMD at run time. Every time a transition takes place (i.e., the model structure changes), RMD constructs the mathematical description of the actual model, eliminates the redundant variables and trivial equations resulting from component connections, analyzes the model solvability and structure, selects the best-suited numerical method and generates the input to this numerical method. This approach provides high flexibility in the description of variable structure models. This feature is demonstrated using variable structure models arisen in two different applications. The first application is the run-time change in the selection of the model state variables. Support for several selections of the state variables is typically required in interactive simulations. The second application is the description of systems with variable behavior. The model of an industrial boiler is used to illustrate the description of this type of variable structure models.