Two-Degree-of-Freedom Control System Design in Consideration of Actuator Saturation

In this paper, we propose a design method of a reference-filtering-type two-degree-of-freedom control system with a structure of antiwindup feedback control in order to overcome actuator saturation problem. By using a hyperbolic tangential function as the saturation function, the time derivative of the controller output is introduced in order to construct a servo system. Thus, a linear parameter-varying system is formulated to design a gain-scheduled feedback controller by using linear matrix inequalities. In order to manage the reference signal taking account of actuator saturation, the feedforward reference signal is obtained offline by applying final-state control with error learning for the closed-loop system including the gain-scheduled feedback controller that may continuously vary before the actuator saturates. The effectiveness of our proposed method is verified by carrying out both simulations and experiments for stabilizing and positioning control of a cart and inverted pendulum system.