1. Pandu Sandi Pratama, Tan-Tung Phan,
Hak Kyeong Kim, and Sang Bong Kim
Presented by :
Pandu Sandi Pratama
November 11, 2011, Pukyong National University, Korea
International Symposium on Advanced Engineering 2011

2. 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

3. 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.
Type of controller :
PID controller, Fuzzy logic control Not Robust
Sliding mode control Chattering
A new controller is needed.

4. Based on modeling of GMAW Based on dynamics modeling
power supply (PS-GMAW) of wire feeding unit (WFU)
Proportional controller is Fuzzy-sliding mode controller
proposed (FSMC) is proposed
to keep the output to change the electrode feed rate
welding voltage to keep the output welding current
Good welding result
By fuzzifying the sliding surface, the feedback control gain from the fuzzy
inference rule base can be obtained to avoid chattering phenomenon.

5. Basic GMAW equipment
4 3
2
9 1
9 6
+ 9
7
Is Us
5
8
1 Shielding gas; 2 DC motor & gear box; 3 electrode wire roll; 4 WFU; 5 PS-GMAW;
6 Control box; 7 Welding gun or welding torch; 8 workpiece; 9 control cable

6. Schematic circuit of GMAW
+
High frequency
transformer
AC
220-
60Hz
Inductor
DC
20kHz
M
CT
Wire feed speed control
+ Torch
Feedback loop voltage
Feedback current
50V DC
Temperature
sensor
- Earth
-
IGBT1 IGBT2
DSP Setting Value
Isolated PWM for TMS320F2812
IGBT1 and IGBT2
Generate and
Control Control duty of PWM control PWM
circuit
Consist of :
(1) Supply 220VAC /60Hz (5) Halfbridge Rectifier;
(2) Fullbridge Rectifier; (6) Inductor;
(3) Inverter; (7) DC motor ;
(4) Transformer; (8) DSP/Microcontroller;

7. The main purpose of GMAW power supply is to keep the welding voltage
( ) constant.
The Kirchhoff’s voltage law for welding circuit can be expressed as follows :
= average output voltage of GMAW power supply (V),
= resistance of PS (Ω),
= parasitic resistance in the circuit (Ω), Welding
electrode
= resistance between contact tip and wire (Ω), WFU
= welding current (A)
Rn
= inductance of the GMAW power supply (H) Contact tip
= constant value 14.5 V R P
L
Ua
Ra
Arc Work pice

8. 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
G
Vm (s ) b0 W f (s ) 1 Iw
s2 a1s a0 Ki

9. When the welding arc is ON and stable, the welding voltage can be
estimated as follows:
output voltage of transformer is 86V
relationship between the controller and D
256 100 256 100 Ua
Uu D 2 86 U a where H= 129/400.
48 48 H
where

10. The state-equation with zero initial values of system can be expressed as follows
The current error ei is defined as follows:
In order to obtain a sliding mode controller, a sliding surface is defined as follows:
The Lyapunov’s function is chosen as V 1 / 2s 2
The sliding mode controller can be drawn from the Lyapunov’s condition:

11. .
if < 0, then decreasing will result in decreasing of
if > 0, then increasing will result in decreasing of
Membership function The resulting fuzzy control rule base
μs μs
N Z P N Z P
1 1
P Z N
S S P PB PM PS
-3 0 3 -3 0 3
S Z PS ZE NS
μu
N NS NM NB
NB NM NS ZE PS PM PB
1
u
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6
Then, apply the Mamdani's mini-
operation fuzzy implication and adopt
the center of area as defuzzification
method to construct the rule set shown
as surface.

13. comparison of the conventional PID controller and the FSMC
Output current Sliding surface
Output voltage

14. Based on the dynamics models of GMAW, the hybrid controller was
proposed by combining proportional controller and fuzzy sliding mode
controller.
The proposed hybrid controller tracks its setting value and keeps
constant voltage and current of a Gas Metal Arc Welding (GMAW).
Simulation result shows that the performance of rising time, settling
time and steady state error of the output current of GMAW is better
using proposed controller than using conventional PID controller.