PROPORTIONAL-INTEGRAL-DERIVATIVE (PID) CONTROLLER DESIGN FOR ROBUST STABILITY OF ARBITRARY ORDER PLANTS WITH TIME-DELAY AND ADDITIVE UNCERTAINTY A Thesis By

In the process control industry, majority of control loops are based on ProportionalIntegral-Derivative (PID) controllers. The basic structure of the PID controllers makes it easy to regulate the process output. Design methods leading to an optimal and effective operation of the PID controllers are economically vital for process industries. Robust control has been a recent addition to the field of control engineering that primarily deals with obtaining system robustness in presences of uncertainties. In this thesis, a graphical design method for obtaining the entire range of PID controller gains that robustly stabilize a system in the presence of time delays and additive uncertainty is introduced. This design method primarily depends on the frequency response of the system, which can serve to reduce the complexities involved in plant modeling. The fact that time-delays and parametric uncertainties are almost always present in real time processes makes our controller design method very vital for process control. We have applied our design method to a DC motor model with a communication delay and a single area nonreheat steam generation unit. The results were satisfactory and robust stability was achieved for the perturbed plants.