PERFORMANCE ANALYSIS OF SYSTEMS WITH PD, PI & PID CONTROLLERS

Abstract

This dissertation deals with the various methods for determination of the parameters or tuning of digital PD, PI & PID controllers.The method used are Pole-Zero cancellation, Ziegler Nichols, Cohen-Coon. The accuracy of Ziegler-Nichols tuning formula, Cohen-Coon tuning formula is analysed in context of tuning of PID and PI controllers. The performance is analysed in terms of over shoot, rise time, peak time, steady state error. For tuning of PID controllers, it is analysed that , for excessive overshoot in set point response, setpoint weighting can reduce the over shoot to specified value. It is observed that set point weighting is superior to the conventional solution of reducing large overshoot by setpoint filtering. For tuning of P1 controllers, it is analysed that the Ziegler-Nichols tuning formula is inadequate and has to be completely revised. The application of the set point weighting and the modifications are based on the knowledge of normalised gain.These heuristic refinements when incorporated, show appreciable improvement in the performance of auto tuners. The software has been developed to study the relative performance of PD, PI & PID controllers with different algorithms (position, velocity, forward word length).