Life extending control of boiler–turbine systems via model predictive methods

Boiler–turbine units constitute a critical component of a co-generation system. During operation, especially the start-up operation, these units are subject to high-temperature variations that aggravate the stress of the material used in their construction and thus a negative effect in their life spans. This paper is about designing a life extending controller (LEC) to obtain a good tradeoff between the life of a boiler–turbine system and control system performance. Because the boiler system is multivariate and there exist some constraints on the inputs to plant, model predictive control theory is used. For practical consideration, the original controller of the boiler system designed for dynamic performance is taken as a pre-compensator. For ease in LEC design, the pre-compensated closed-loop system is reduced in order using the system identification method. Finally, the resulting system is extensively simulated and tested on a computer, using a sophisticated nonlinear model of the boiler system.