Isae 2011 A HYBRID CONTROLLER DESIGN FOR KEEPING CONSTANT VOLTAGE AND CURRENT OF A GAS METAL ARC WELDING SYSTEM
Pandu Sandi Pratama, Tan-Tung Phan, Hak Kyeong Kim, and Sang Bong Kim Presented by : Pandu Sandi PratamaNovember 11, 2011, Pukyong National University, KoreaInternational Symposium on Advanced Engineering 2011
IntroductionDynamic 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 WFUSimulation ResultConclusion
GMAW are the most popular welding machine in various industries.The welding current and voltage are the most decisive factors on the qualityof welding product.Type of controller : PID controller, Fuzzy logic control Not Robust Sliding mode control Chattering A new controller is needed.
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 resultBy fuzzifying the sliding surface, the feedback control gain from the fuzzyinference rule base can be obtained to avoid chattering phenomenon.
Basic GMAW equipment 4 3 2 9 1 9 6 + 9 7 Is Us 5 81 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
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 circuitConsist of : (1) Supply 220VAC /60Hz (5) Halfbridge Rectifier; (2) Fullbridge Rectifier; (6) Inductor; (3) Inverter; (7) DC motor ; (4) Transformer; (8) DSP/Microcontroller;
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
Relationship between melting rate and welding current is usually describe byThe electrode feed-rate must be equal to the electrode melting-rateto maintain a stable arc lengthWelding current can be expressed asThe dynamic relationship between the electrode feed-rate and the voltage ofa DC servomotorIf is considered as disturbance of the system, the transfer functionBecomes G Vm (s ) b0 W f (s ) 1 Iw s2 a1s a0 Ki
When the welding arc is ON and stable, the welding voltage can beestimated as follows: output voltage of transformer is 86Vrelationship between the controller and D 256 100 256 100 Ua Uu D 2 86 U a where H= 129/400. 48 48 H where
The state-equation with zero initial values of system can be expressed as followsThe 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 2The sliding mode controller can be drawn from the Lyapunov’s condition:
. 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 Mamdanis mini- operation fuzzy implication and adopt the center of area as defuzzification method to construct the rule set shown as surface.
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.