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?