Get operating point (trimming) with matlab simulink

Hello fellows,

I have a controlled plant modeled using simulink. I'm able to get operating point for this plant when I open the loop but I can't do the same with closed loop. This is a standard PID controller. I initially set the range of the states as the same for the open loop and used the same algorithm to get operating point, Gradient descent with elimination of the findop function. I guessed a priori that this was a problem of convergence of the algorithm so I got the open loop operating point to set each plant state of the closed loop with the its result. I also set the integrators of PID's in the closed loop with the values of input for the open loop.

Using this double search of operating point made the results to be better but doesn't resolved the problem and it didn't find the operating point for the closed loop. I guess it is a question of numerical error.

I would like to know if anyone knows a way to make it more precise and what could be the problem.

Regards, Leandro