Multivariable robust control of a rotary dryer: Analysis and design

This paper describes the analysis and control of an industrial process usually controlled in manual mode: a continuous rotary dryer. Two process variables are controlled simultaneously: the outlet moisture of the dried material and the output temperature of the exhaust air. To do this, the flow of wet material and the flow of fuel are used as control variables. Thus, this constitutes a MIMO system, with two inputs and two outputs. The system is identified at several operating points, and a controllability analysis is performed in order to find any constraints in its performance. A multivariable robust control based on the H∞H∞ mixed sensitivity problem is proposed. Simulation and experimental results are included, using different adjustments of the weighting matrices based on the performed experiments. Results attained agree with the controllability analysis conclusions.