Fuzzy Control On A Fluff Pulp Machine To Reduce Consistency and Moisture Variability, 18PaperCon

On certain control loops manual intervention by operators distracts operators from other functions and can result in high variability. The use of fuzzy control to mimic favorable operator actions provides for less variability. This paper details real-world examples using fuzzy control in situations difficult to control using typical PID strategies such as bias, ratio, and mid-ranging. The general methodology of fuzzy control is to evaluate the truth of a condition based on a set of membership functions then change the output according to a set of rules based on operator experience. Fuzzy control was implemented on high-density (HD) stock chest dilution control due to dead time between the main valve and consistency measurement, the need to keep the trim valve in control, demand fluctuations, and uncertain dilution line pressure. Fuzzy control was also implemented on the main section steam control of a fluff pulp machine due to long dead time and the need to eliminate oscillation. The HD stock dilution benefitted from fuzzy control by eliminating roaming on the main dilution valve which resulted in more stable consistency control. The fuzzy control on the steam section resulted in reduced moisture variability and freed operators for other tasks. Fuzzy control strategies can be successfully implemented on loops that operators typically control in manual due to complexity and shortcomings of typical PID strategies. 

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