Co-Simulation Errors Due to Step Size Changes

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 changing the step size during simulation can cause such discrepancies to increase even when the change is towards smaller steps. We derive a leading-order analytic expression for the errors, showing that, under broadly applicable assumptions about the smoothness of q , they are proportional to the differences between consecutive step sizes.