I have my block diagram with transfer function, PID and two saturation. When I simulate the program, it work very good. The problem occur when I put some noise to the system and that noise is a second order transfer function with an input of random numbers, I simulate the systems and the simulation time goes crazy. In the beginning starts well but then stop, begin again, goes slower and 45 seconds later the simulation goes very very very slow. I don't know why is the reason.