Normal-mode-inaction adaptive PID controller

Abstract

This paper presents a new adaptive PID controller that we call the normal-mode-inaction (NMI) adaptive PID controller. Unlike the conventional adaptive PID controller, its control parameters are normally fixed, and adaptation only occurs when there is a significant change in the magnitude or phase of certain point on the Nyquist plot that is being tracked continuously. In the proposed NMI adaptive PID controller, a relay tuning procedure is used to initialize the adaptive controller. The adjustment of the PID controller parameters is based on the refined Ziegler-Nichols tuning formula. Simulation results and analysis have confirmed that the NMI adaptive PID controller has improved robustness properties.