Analyzing Extrapolation-based Co-simulation Methods with Control Systems: A Linearized Two-Area Power System with Automatic Generation Control

In recent years, co-simulation has gained importance for simulating multidisciplinary systems with increasing levels of complexity. These systems comprise the interaction of physical and technological systems, also known as Cyber-Physical systems. Furthermore, many of them include highly automated control systems and different modeling and simulation techniques, as well as different time dynamics. Co-simulation consists of coupling available simulators and exchanging their coupling outputs, using a communications interval known as macro-step size, which contrasts with the micro-step size used by the solver of each individual simulator. Coupling techniques and the macro-step size selection determine an important trade off between accuracy and performance. Although these tradeoffs have been analyzed in unforced systems, an approach for systems with forcing functions is still missing. This is particularly important for the incorporation of control systems into existing co-simulation scenarios. This article presents an initial step in this direction. We propose a framework for incorporating control systems and external inputs, and illustrate this approach in a two area power system with an Automatic Generation Control (AGC). Simulation results show the effect of the control system on the dynamics of the co-simulation and on its resulting accuracy, considering fixed macro-step sizes.