Co-simulation errors due to step size changes

TL;DR

This paper investigates how changing step sizes in continuous-time co-simulation can unexpectedly increase errors, especially when internal states depend on extrapolated variables, challenging the assumption that smaller steps always reduce errors.

Contribution

It reveals that step size changes can sometimes worsen co-simulation errors, providing new insights into error behavior during step size adjustments.

Findings

Step size changes can increase errors under certain conditions.

Error reduction with smaller steps is not guaranteed when internal states depend on extrapolated variables.

The study highlights the need for careful step size management in co-simulation.

Abstract

When two simulation units in a continuous-time co-simulation are connected via some variable $q$, and both simulation units have an internal state which represents the time integral of $q$, there will generally be a discrepancy between those states due to extrapolation errors. Normally, such extrapolation errors diminish if the macro time step size is reduced. Here we show that, under certain circumstances, step size changes can cause such discrepancies to increase even when the change is towards smaller steps.