Heterogeneous Modeling and Design of Control Systems

Xiaojun Liu, Jie Liu, Johan Eker, and Edward A. Lee

in Software-Enabled Control: Information Technology for Dynamical Systems
Tariq Samad and Gary Balas (eds.), Wiley-IEEE Press, April 2003

Prepublished version
Published version


Complex control systems are heterogeneous both in their physical composition and from a modeling and design perspective. They consist of subsystems with very different characteristics that need to be modeled in various formalisms, such as differential equations and discrete events. Their software employs multiple computational mechanisms, such as finite state machines, dataflow models, and real-time scheduling. Design tools for such systems need to support multiple models of computation. Ptolemy II is a system-level design environment with a component-based architecture. Its model structure is designed such that a variety of models of computation can be implemented, many of which are useful for control systems. The disciplined composition of different models of computation in a hierarchical model ensures that their properties are preserved. With modal models, Ptolemy II provides a clean structure for studying modal systems that are common in control engineering. An inverted pendulum controller is used to demonstrate how Ptolemy II can be used in the design process of control systems.