Design of an enhanced nonlinear PID controller

An enhanced nonlinear PID (EN-PID) controller that exhibits the improved performance than the conventional linear fixed-gain PID controller is proposed in this paper, by incorporating a sector-bounded nonlinear gain in cascade with a conventional PID control architecture. To achieve the high robustness against noise, two nonlinear tracking differentiators are used to select high-quality differential signal in the presence of measurement noise. The criterion to determine the nonlinear gain to retain the stability of the proposed EN-PID control system is addressed, by using the Popov stability criterion. The main advantages of the proposed EN-PID controller lie in its high robustness against noise and easy of implementation. Simulation results performed on a robot manipulator are presented to demonstrate the better performance of the developed EN-PID controller than the conventional fixed-gain PID controller.