Nonlinear modeling and control for electro hydraulic servo system in pipe expanding process

The dynamics of electro hydraulic servo system (EHSS) in pipe expanding process are highly nonlinear. The system may be subjected to large extent of model uncertainties, non-smooth and discontinuous nonlinearities of asymmetry proportional-servo valve, asymmetry cylinder, friction, etc. To address these challenging issues, the nonlinear character of asymmetry cylinder actuated by asymmetry valve was modeled, then a nonlinear control approach was put forward by employing two-step nonlinear PID predictive control technology. In this controller, system disturbance was estimated by a nonlinear observer, and its PID parameters are nonlinear convertible to fitting real complicated EHSS. Compared with classical model and conventional PID control of EHSS, the proposed nonlinear controller is easy to design, and is more suitable for implementation.