Tuning of digital pid controllers based on ziegler-nichols method

摘要

A unified algorithm for auto-tuning of digital PID controllers for n-order process model have bene derived in this paper. Tuning procerdure uses the identification of ARX process model parameters uisng recursive least squares method (RLSM) with adaptive directional forgetting. The parameter estimates serve for computing of the ultimate (critical) proportional gain and period of oscillations on the basis of modified Ziegler-Nichols method for digital control loops. The relations for setting procedures in case of the 2nd and the 3rd order model are derived in the form of analytical formulas. In case of the higher order ARX models the MATLAB Symoblic Math Toolbox was used. These algorithms are suitable for automatic tuning of digital PID controllers or of the adaptive control of technological processes. The digital PID controller with weghting factor and noise filtering constant in the derivative componet has been applied for temperature control of a laboratory fermentor. There has been developed the MATLAB-Toolbox ATC PID for designing, testing simualting and real time of auto-tuning digital PID controllers.