Usually, a nonlinear plant needs to be linearized before using some design method for control law synthesis. Is there any design method, which does not require a linearization?
I am not sure about the system you are trying to model. But if you have enough data on you system you can use balck box modeling tools such as ANN ( Artificial Neural Network) model. But you have to be very careful
Thanks for answering. But i dont' try to model some system. The question is about control law synthesis methods (for example, classical methods in frequency domain, modern methods such as LQ, LQR, H2, H_inf etc.)