Robust H-Infinity Control of Industrial Boiler Drum Level with Structured and Unstructured Uncertainty Model

The water level control in boiler drums is a crucial process in many process industries. In industries, water spillage or overheated tubes of the water boiler are the serious consequences of extremely high or low-level drum water level maintenance. The boiler drum is a MIMO system, consists of dead time nonlinearity and thereby there exists a transportation lag between the input and the system. Also, they possess high dynamic variations. Hence, the control of the boiler drum level is of great importance. Though, conventional PID controllers are employed in industries, due to the presence of nonlinearity, boiler drum performance can be affected when it is controlled by a PID controller. Moreover, the PID controller produces a larger settling time. Here, a robust controller for the boiler drum level control based on the H-infinity technique is designed. The first-principle mathematical model of the boiler drum is formulated. The uncertainties namely: structured uncertainty, unstructured uncertainty, and nonlinear uncertainty are modeled by incorporating the boiler drum dynamics including its inherent nonlinearity. The boiler drum level control is carried out using the H-infinity controller scheme with the uncertainties accounted for and the performance is compared with that of a conventional PID controller. The qualitative and quantitative comparison of performances of the above control schemes reveals that the H-infinity controller has a quick rise time and faster settling time.