Modeling Physical Systems as Physical Networks with the Simscape Language

Engineers are relying more and more on simulation to accelerate development processes. Combining computer simulation with Model-Based Design techniques enables engineers to not only complete tasks in a shorter period of time, it makes it possible to find design errors before building hardware, making the errors easier and less expensive to fix.[1] As the systems they develop require integrating control systems with physical systems spanning multiple physical domains (mechanical, electrical, etc.), a useful model of the physical system (plant) is critical for developing an optimized system. Traditional methods (C, FORTRAN, etc.) and signal-based or input-output (causal) methods in graphical software tools (Simulink, etc.) were useful for control engineers because they were written in a language they could easily understand and integrate with their control system models. However, these models can be difficult to reuse, leading to redundant work. A technique which has been applied to electrical systems for quite some time is now being used on multidomain physical systems. The physical network approach, often referred to as acausal modeling, enables engineers to create reusable models of physical components that can span multiple physical domains. Simulation tools that support this method (Simscape, etc.) then build up the equations for the system and solve the differential algebraic equations directly, resulting in accurate simulations of the entire system. This paper focuses on the physical network technique for modeling physical systems and its use in Simscape within the Simulink environment.