Internal Model Control: Pid Controller Design

For a large number of single input-single output (SISO) models typically used In the process industries, the Internal Model Control (IMC) design procedure Is shown to lead to PID controllers, occasionally augmented with a first-order lag. These PID controllers have as their only tuning parameter the closed-loop time constant or, equivalently, the closed-loop bandwidth. On-line adjustments are therefore much simpler than for general PID controllers. As a special case, PI- and PID-tuning rules for systems modeled by a first-order lag with dead time are derived analytically. The superiority of these rules In terms of both closed-loop performance and robustness is demonstrated.