Comparative study of classical and robust control techniques for process control

The authors use three different linear control system design methods to obtain three-level-control systems for a simple process called a deaerator. The three linear control system design methods are proportional plus integral (PI), linear quadratic Gaussian (LQG), and linear quadratic Gaussian with loop transfer recovery (LQG/LTR). Control system performance and stability robustness are evaluated for a given set of system design specifications. The tools for analysis are the return ratio, return difference, and inverse return difference singular-value plots for a loop break at the plant output