Practical-optimal control of a drum boiler power plant

Multivariable control of power plants has been studied by many researchers and also a number of practical applications have been presented in the last few years with the aim of improving the load following capabilities of thermal units. This paper summarizes the main results of an experimental application of optimal control to a drum boiler power plant at the Italian national electricity board. Referring to a previous work for the process model building, first a model reduction is performed with the main purpose of getting a simplified control structure. Then, an optimal regulator including feedforward and integral control is synthesized and some practical drawbacks of the synthesis are discussed with referrence to traditional control schemes leading to a reformulation of the optimal regulator which, while conserving optimality, exhibits a number of practical advantages and improved robustness against typical plant parameter variations. Since the motivation of the control structure reformulation is mostly derived from experimental results, field trials are reported where the performances of a well tuned coordinated control, of the classical optimal regulator and of the reformulated optimal control structure are compared. Perspectives of future industrial applications are briefly discussed in the conclusions.