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Compensation of Control
valve stiction
Supervised by
Dr. Dr. M.A.A. Shoukat Choudhury
Professor
Department of Chemical Engineering
BUET
Prepared by
Md. Habibur Rahman
Std. ID- 0902016
Outline of presentation
Background Of Study
Objective Of Study
Available Compensation methods
Development of a new stiction compensation model
Comparison of Different Models
Experimental evaluation
Conclusions And Recommendations
Background of Study
Automation of modern plants
Control loop performance
Stiction as a process nonlinearity
Stiction in
Control valve
Stiction in Control valve(cont’d)
Objectives
The overall objectives of our study are:
Study different Compensation techniques
Development of a new technique
Evaluation of the performance of new method
Available Compensation Methods
Knocker method
CR method
Two move method
Adaptive control method
Proposed Model
Controlle
rValve
inputProcess
Simulation Diagram
Proposed Model Mechanism
1800 1900 2000 2100 2200 2300 2400-4
-3
-2
-1
0
1
2
3
4
Time(s)
Co
mp
ensa
tor
Ou
tpu
tC
on
tro
ller
Ou
tpu
tS
tem
Po
siti
on
Set
po
int
Compensator Output
Set Point
Stem Position
Controller Output
A B
Comparison of different models
Models
Knocker model
CR model
Adaptive model
Proposed model
Parameters
Process variable
Stem Position
Impact on valve reversals
0 200 400 600 800 1000 1200 1400 1600-8
-6
-4
-2
0
2
4
6
8
PV Vs. Time
Time(s)
PV
Comparison(cont’d)
Knocker Model
Comparison(cont’d)
CR Model
0 200 400 600 800 1000 1200 1400 1600-8
-6
-4
-2
0
2
4
6
8
PV Vs. Time
Time(s)
PV
0 200 400 600 800 1000 1200 1400 1600-8
-6
-4
-2
0
2
4
6
8
PV Vs. Time
Time(s)
PV
Comparison(cont’d)
Adaptive Model
Comparison(cont’d)
0 200 400 600 800 1000 1200 1400 1600-8
-6
-4
-2
0
2
4
6
8PV Vs. Time
Time(s)
PV
Proposed Model
Parameter Knocker CR Adaptive Proposed
Initial
variance(PV)
6.00 6.00 6.00 6.00
Final
Variance(PV)
1.148 1.074 0.32 0.27
Variance Ratio 0.1913 0.1790 0.0533 0.045
%Reduction in
Variance
80.86 82.1 94.66 95.5
Analysis of Process variable varianceComparison(cont’d)
Comparison(cont’d)
Analysis of Valve reversals
11 11
18
6
0
2
4
6
8
10
12
14
16
18
20
Knocker CR Adaptive Proposed
No
of
Val
ve
rev
ersa
ls
Model
No of Valve reversals vs. Process model
Comparison(cont’d)
Analysis of Stem Position of valve
0.571
0.535
0.321
0.214
0
0.1
0.2
0.3
0.4
0.5
0.6
Knocker CR Adaptive Proposed
Stem
po
siti
on
Am
plit
ud
e R
atio
Model
Stem position Amplitude Ratio vs.Model
Comparison(cont’d)
Summary of comparison Analysis
The Proposed model is beneficial over other models in
the following manners:
Reduction of oscillations in process
Reduction of valve movement
Good set point tracking and disturbance rejection.
Avoidance of excessive control action.
Experimental Evaluation
0 1000 2000 3000 4000 5000 6000-5
0
5
10
15
20
25
30
35
40
45
Time(s)
Pro
cess
Vari
ab
le(P
V)
Process Variable(PV) vs. Time
Experimental Evaluation(cont’d)
Experimental Evaluation(cont’d)
143
23
0
20
40
60
80
100
120
140
160
PV variance(Initial) PV variance(Final)
Pro
cess
Var
iable
var
iance
Condition
Process Variable varance
Conclusions
A new model for stiction compensation is developed
Comparison of different models are done
Performance test of the proposed model is evaluated
experimentally
Experimental work to compare with other models
Correlation of model parameter with different
processes
Recommendations
Any Question?