H∞ control design for an industrial boiler

In the control of an industrial boiler system, multi-loop (decentralized) PI control is used because of its simplicity and the existence of simple online tuning rules. We show that such control schemes sacrifices robustness and performance of the overall system. In particular, under normal boiler operating conditions, we design a robust multivariable controller using the H_∞ loop-shaping technique. For reason of implementation, we then reduce this controller to a multivariable PI structure. Both the H_∞ 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 obtained show that the designed controllers are superior in robustness and performance compared to the existing multi-loop controller