Multivariable robust controller design for a boiler system

In an industrial boiler system, multiloop (decentralized) proportional-integral (PI) control is used because of its implementational advantages. We show that such control schemes sacrifice robustness and performance of the overall system. In particular, under normal boiler operating conditions, we design a robust multivariable controller using loop-shaping techniques; for consideration in implementation, we then reduce this controller to a multivariable PI controller. Both the controller and its PI approximation are tested extensively in the frequency domain as well as in the time domain, using a complex nonlinear simulation software; the results show that the designed controllers are superior in robustness and performance to the existing multiloop controller.