Isae 2011 A HYBRID CONTROLLER DESIGN FOR KEEPING CONSTANT VOLTAGE AND CURRENT OF A GAS METAL ARC WELDING SYSTEM

November 11, 2011, Pukyong National University, Korea

International Symposium on Advanced Engineering 2011

Pandu Sandi Pratama, Tan-Tung Phan, Hak Kyeong Kim, and Sang Bong Kim

Presented by :

Pandu Sandi Pratama

Introduction

Dynamic System Modeling

Dynamics Model of GMAW Power Supply

Dynamics Model of Wire Feeding Unit (WFU)

Control Method

Voltage Controller design for GMAW power supply

Current Controller design for WFU

Simulation Result

Conclusion

GMAW are the most popular welding machine in various industries.

The welding current and voltage are the most decisive factors on the quality

of welding product.

PID controller, Fuzzy logic control

Sliding mode control Chattering

Not Robust

A new controller is needed.

Type of controller :

Based on modeling of GMAW

power supply (PS-GMAW)

Proportional controller is

proposed

to keep the output

welding voltage

Based on dynamics modeling

of wire feeding unit (WFU)

Fuzzy-sliding mode controller

(FSMC) is proposed

to change the electrode feed rate

to keep the output welding current

By fuzzifying the sliding surface, the feedback control gain from the fuzzy

inference rule base can be obtained to avoid chattering phenomenon.

Good welding result

+

Is Us

2

34

5

7

6

1

9

9

9

8

Shielding gas; DC motor & gear box; electrode wire roll; WFU; PS-GMAW;

Control box; Welding gun or welding torch; workpiece; control cable

51

6

2

7

3

8 9

4

Basic GMAW equipment

AC

220-

60Hz

20kHz

- Earth

+ Torch

50V DC

Isolated PWM for

IGBT1 and IGBT2

Control duty of PWM

CT

Setting Value

IGBT1 IGBT2

+

-

DC

Ind

ucto

r

High frequency

transformer

Fe

ed

ba

ck c

urre

nt

Control

circuit

DSP

TMS320F2812

Generate and

control PWM

Fe

ed

ba

ck lo

op

vo

ltag

e

Temperature

sensor

M

Wire

fee

d s

pe

ed

co

ntro

l

Schematic circuit of GMAW

Consist of :

(1) Supply 220VAC /60Hz

(2) Fullbridge Rectifier;

(3) Inverter;

(4) Transformer;

(5) Halfbridge Rectifier;

(6) Inductor;

(7) DC motor ;

(8) DSP/Microcontroller;

Welding

electrodeWFU

nR

PR

L

aU

aRArc Work pice

Contact tip

The main purpose of GMAW power supply is to keep the welding voltage

( ) constant.

= average output voltage of GMAW power supply (V),

= resistance of PS (Ω),

= parasitic resistance in the circuit (Ω),

= resistance between contact tip and wire (Ω),

= welding current (A)

= inductance of the GMAW power supply (H)

= constant value 14.5 V

The Kirchhoff’s voltage law for welding circuit can be expressed as follows :

)(sVm

01

2

0

asas

b

iK

1

G

wI)(sW f

Relationship between melting rate and welding current is usually describe by

The electrode feed-rate must be equal to the electrode melting-rate

to maintain a stable arc length

Welding current can be expressed as

The dynamic relationship between the electrode feed-rate and the voltage of

a DC servomotor

If is considered as disturbance of the system, the transfer function

Becomes

When the welding arc is ON and stable, the welding voltage can be

estimated as follows:

output voltage of transformer is 86V

where H= 129/400.

where

relationship between the controller and D

H

aU

aUDuU 86248

100256

48

100256

The state-equation with zero initial values of system can be expressed as follows

The current error is defined as follows:ie

In order to obtain a sliding mode controller, a sliding surface is defined as follows:

The Lyapunov’s function is chosen as 22/1 sV

The sliding mode controller can be drawn from the Lyapunov’s condition:

0 3-3

N PZ1

S

μs

0 3-3

N PZ1

S

μs

0-1

NB PBZE1

μu

-2-3-4-5-6 1 2 3 4 5 6

NM NS PS PM

u

if < 0, then decreasing will result in decreasing of

if > 0, then increasing will result in decreasing of

.

The resulting fuzzy control rule base

P Z N

S

P PB PM PS

Z PS ZE NS

N NS NM NB

Then, apply the Mamdani's mini-

operation fuzzy implication and adopt

the center of area as defuzzification

method to construct the rule set shownas surface.

Membership function

comparison of the conventional PID controller and the FSMC

Output current Sliding surface

Output voltage

Based on the dynamics models of GMAW, the hybrid controller wasproposed by combining proportional controller and fuzzy sliding modecontroller.

The proposed hybrid controller tracks its setting value and keepsconstant voltage and current of a Gas Metal Arc Welding (GMAW).

Simulation result shows that the performance of rising time, settlingtime and steady state error of the output current of GMAW is betterusing proposed controller than using conventional PID controller.