Dahlin Control of a Wood Flake Conveyor Dryer Robert Spring, P. Eng., CAP

Presenter Robert Spring, P.Eng, CAP A specialist in heat energy and wood drying. Interests include optimization, sensors and advanced controls. Work experience in the mineral processing, pulping, paper-making and wood products industries.

Why Dry?

Conveyor Dryers – Transportation Delay Transport Delay = 15 minutes Energy Usage = 10,000 Households

Dryer Schematic

PID versus Dahlin - Simulations

“Not-dumb” Use of Information   Error Past Move Dead-time Fixed Parameters

Design the Trajectory

Synthesis Steps – Model Identification Process Gain Process Time Constant   Dead-time Control Time Interval

Synthesis Steps – Controller Implementation  

Adaptive Dead-time    

Bumpless Transfer and Anti-windup  

Bumpless Transfer and Anti-windup  

Feed-forward

Feed-forward  

Disturbance Model Time Constant Gain   Dead-time

Feed-forward  

Benefit of Feed forward - Simulations

Before and After Dahlin Control σ=1.8% σ=0.7%

PLC Implementation

Ladder Logic Sample  

Structured Text Sample // b*x(t) NewSpeed := Lambda *OldSpeed; // DelayAdj changes with the speed Index := DelayAdj; // Reference into stored vector of past speeds SpeedDelayedN := Speed_Time_Series[Index]; // (1-b)*x(t-n) NewSpeed := NewSpeed+(1.0-Lambda)*SpeedDelayedN;  

Packaging as a Subroutine or Add-on

Conclusions – Dahlin Control Suited for: long dead-time variable dead-time feed-forward compensation Simple to program (ladder logic or structured text) Single tuning parameter

Result: Make Every Board the Same