Control of nonlinear steam generation process with time lags usings an H_∞ design

In [15], the first application of the H_∞ design methodology to a gas-or oil-fired boiler was presented. The initial model, however, did not contain time delays. Recent experiments conducted by the authors on the actual plant indicated that time delays play a noticeable role in the system dynamics, and motivated the improvement of the model through the inclusion of time delays. The corresponding redesign of an H_∞ controller that takes into account lags is carried out in this paper, with the order of the controller having fourteen states less prior to model reduction, and three states less in the final controller, in comparison to that of [15] while preserving similar performance and robustness of the design. In addition, the paper demonstrates a trade-off between the reduction of controller order and the loss of controller performance and investigates the necessity for more than a single controller to satisfy performance and robustness criteria for a full range of operating regimes.