Hi stepa,
The provided model is stiff and has both fast and slow-changing components. The “Solver” used in the “Configuration Parameters” is not able to solve the model quickly, as “ode45” is a non-stiff solver. When the “Solver” is changed to “auto” mode, Simulink automatically takes up “ode23tb”- a stiff solver and the speed of the simulation picks up. You can refer to the following documentation to learn more about the various stiff solvers available in Simulink:
Stiff models work with less computation cost and more speed using stiff solvers. You can refer to the following documentation to determine the stiffness of a model:
