Co-simulation errors due to step size changes

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.