Pid controller design for process with time delay

The IMC structure, a control structure incorporating the internal model of plant control, has been widely utilized in the design of PID-type controllers, usually denoted IMC-PID controllers, because of its simplicity, flexibility, and apprehensibility. The most important advantage of IMC-PID tuning rules is that the tradeoff between closedloop performance and robustness can be directly obtained using a single parameter related to the closed-loop time constant. IMC-PID tuning rules can provide good set-point tracking, but have been lacking regarding disturbance rejection, which can become severe for processes with a small time-delay/time constant ratio. Disturbance rejection is more important than set-point tracking in many process control applications, and thus is an important research topic.