Study of PID controller design for systems with Time delay

PID controllers are being widely used in industry due to their well-grounded established theory, simplicity, maintenance requirements, and ease of retuning online. In the past four decades, there are numerous papers dealing with tuning of PID controller. Designing a PID controller to meet gain and phase margin specification is a well-known design technique. If the gain and phase margin are not specified carefully then the design may not be optimum in the sense that could be large phase margin (more robust) that could give better performance. This paper studies the relationship between ISE performance index, gain margin, phase margin and compares two tuning technique, based on these three parameters. These tuning techniques are particularly useful in the context of adaptive control and auto-tuning, where the control parameters have to be calculated on-line. In the first part, basics of various controllers, their working and importance of PID controller in reference to a practical system (thermal control system) is discussed. In the latter part of the work, exhaustive study has been done on two different PID controller tuning techniques. A compromise between robustness and tracking performance of the system in presence of time delay is tried to achieve. Results of simulation, graph, plots, indicate the validity of the study