On-line adaptive tuning for PID controllers

Adaptive and robust designs are two major approaches to deal with possible modelling errors in a control system. This paper proposes an adaptive control system for on-line tuning of PID controllers for SISO systems. The proposed system comprises of two adaptive loops. The first loop monitors and tunes the controllers on-line to ensure the system is robustly stable. This first loop enables the system to achieve robust stability over a wide range of possible modelling errors without trading off performance against nominal design. When modelling errors occur, the second adaptive loop conducts recursive on-line identification and retunes the controller. Because the nominal model is corrected on-line, directly following the on-line identification the system can continue as a new nominal system which is designed to have tight control performance. Numerical examples are presented to illustrate this adaptive control with two loops