isae 2011 a hybrid controller design for keeping constant voltage and current of a gas metal arc...
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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.
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