Hello Paul
It's possible that the two models working together are producing numerical problems that don't exist when they run separately. Since both models work individually, it's possible that the issue is with how they are being connected together.
Here are few suggestions that you could try to resolve the error -
- Try reducing the maximum time step to see if a smaller time step helps the simulation converge.
- Try using different solver, such as "ode15s" or "ode23tb" for the combined model.
- Check that the physical units of the inputs and outputs between the two models are consistent.
If the issue still persists, then please share some more information about your model. It will allow me to better understand the issue so that I can assist you in resolving it.