International Journal of Current Engineering and Technology ISSN 2277 - 4106 © 2013 INPRESSCO. All Rights Reserved. Available at http://inpressco.com/category/ijcet

Research Article

Design of Gas Tungsten Arc using Power Electronic for Steel and AluminiumWelding

R.Shiju Kumara and T.Ruban Deva Prakashb*

aSathyabama University, Chennai ,Tamilnadu India b Sree Narayana Gurukulam College of Engineering, Kollenchery, Kerala

Accepted 10 October 2013, Available online 19 October 2013, Vol.3, No.4 (October 2013)

Abstract

Welding power supply is a device that supplies high current at low voltages in the range of 50V. Gas tungsten draws low current in the range of 5A. machine operates with dc supply for steel welding and operates with 150Hz rectangular wave ac supply for aluminium welding to avoid oxidation and better welding quality. Welding power supply has constant current or constant voltage operation. This paper deals with constant voltage welding power supply. Conventional welding power supplies are transformer style or IC engine/motor driven generator style or inverter style devices. Harmonics, low power factor and transient disturbance are the major problems with conventional welding power supply. Recently, power electronic transformer gains importance due to reduced size and weight in many applications. Traditional power electronic transformer with its power quality analysis is presented in this paper. This paper also proposes a novel modular power electronic transformer based dc welding power supply for gas tungsten arc welding of steel. Modular topology based on dc-dc buck converter is used for the design. Also matrix converter power electronic transformer based ac welding power supply for gas tungsten arc welding of aluminium is proposed in this paper. DC link in input side is eliminated using 3-phase to 1-phase matrix converter. A simple control method for the matrix converter is explained in this paper. Performance is validated by simulation studies. It if found that the input voltage and current has some harmonics, but much less than that of traditional power electronic transformer topologies.

Keywords: Power quality, welding power supply, power electronic transformer, high frequency transformer, gas tungsten arc welding, steel and aluminium welding.

1. Introduction constant voltage sources but constant current is also possible with a voltage sensing wire feeder. 1A welding power supply is a device that provides an The nature of the CV machine is required by gas metal arc electric current to perform welding. Welding usually welding and flux-cored arc welding because the is requires high current (over 80 amperes) and it can need not able to control the arc length manually. If a welder above 12,000 amperes in . Low current can attempted to use a CV machine to weld with shielded also be used; welding two razor blades together at 5 amps metal arc welding the small fluctuations in the arc distance with gas tungsten arc welding is a good example. A would cause wide fluctuations in the machine's output. welding power supply can be as simple as a car battery With a CC machine the welder can count on a fixed and as sophisticated as a modern machine based on silicon number of amps reaching the material to be welded controlled technology with additional logic to regardless of the arc distance but too much distance will assist in the welding process. Welding machines are cause poor welding. A transformer style welding power usually classified as constant current (CC) or constant supply converts the high voltage and low current voltage (CV); a constant current machine varies its output electricity from the utility mains into a high current and voltage to maintain a steady current while a constant low voltage, typically between 17 to 45 volts and 55 to voltage machine will vary its output current to maintain a 590 amps. A rectifier converts the AC into DC on more set voltage. Shielded metal arc welding and gas tungsten expensive machines. Welding power supplies may also arc welding will use a constant current source and gas use generators or alternators to convert mechanical energy metal arc welding and flux-cored arc welding typically use into electrical energy. Modern designs are usually driven by an internal combustion engine but older machines may use an electric motor to drive an alternator or generator. In this configuration the utility power is converted first into *Corresponding author: T.Ruban Deva Prakash

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R.Shiju Kumar et al International Journal of Current Engineering and Technology, Vol.3, No.4 (October 2013) mechanical energy then back into electrical energy to reduced size and weight. The principle of power electronic achieve the step-down effect similar to a transformer. transformer is converting 50Hz ac to high frequency ac Since the advent of high-power semiconductors such as and given as input to a high frequency transformer and its the insulated gate bipolar transistor (IGBT), it is now output is converted back to 50Hz ac. It gains the advantage possible to build a switched-mode power supply capable of reduction in size and weight due to high frequency of coping with the high loads of arc welding (Huang. N et transformer which also gives galvanic isolation and al., 2005). These designs are known as inverter welding voltage transformation. Power flow control, bidirectional units. They generally first rectify the utility AC power to power flow and power quality mitigation are added DC; then they switch (invert) the DC power into a step- features of modern power electronic . down transformer to produce the desired welding voltage Different topologies of power electronic transformers or current. The switching frequency is typically 10 kHz or are under research. In one approach 50Hz ac is converted higher. Although the high switching frequency requires into dc using diode bridge rectifier. The next stage consists sophisticated components and circuits, it drastically of IGBT 3-leg, 6- pulse inverter which converts dc into 50 reduces the bulk of the step down transformer, as the mass KHz ac. In between the two stages there is a dc link of magnetic components (transformers and inductors) that capacitor. A high frequency transformer is used for is required for achieving a given power level goes down galvanic isolation and changing voltage levels. The 50 rapidly as the operating (switching) frequency is KHz ac output is converted to dc using diode bridge increased. The inverter circuitry can also provide features rectifier. such as power control and overload protection (Khairy This is followed by dc link capacitor and inverter Sayed et al., 2011). The high frequency inverter-based stage. The IGBT based voltage source inverter converts welding machines are typically more efficient and provide the dc to 50 Hz ac. The conventional welding transformer better control of variable functional parameters than non- can be replaced by such power electronic transformer inverter welding machines (Jinhong Zhu et al., 2008). The which reduces size and weight. Also it eliminates the IGBTs in an inverter based machine are controlled by a current unbalance problem. The simulink model of this microcontroller, so the electrical characteristics of the power electronic transformer is shown in Fig.1. welding power can be changed by software in real time, even on a cycle by cycle basis, rather than making changes slowly over hundreds if not thousands of cycles. N.R. Mandal explained the distortion created by welding power supply (Mandal.N.R, 2009). Harmonics, low power factor and transient disturbance are the major problems with conventional welding power supply (ZHANG E.F. de Silva et al., 2011). Power factor corrected converter based welding power supply is also proposed in literature (Huang. N et al., 2005 and Khairy Fig. 1. Simulink model of power electronic transformer Sayed et al., 2011). Power quality improvement using three phase modular converter for welding power supply is 3. Power Quality Analysis Of Power Electronic proposed by Singh (Singh.B et.al., 2012). Recently power Transformer electronic transformer gains importance due to reduced size and weight (Hosseini.S.H et al., 2008). It is applied The voltage and current waveform at the input side of the for electric traction, smart grid, wind electric generation, power electronic transformer explained in section-II is ship power supplies, welding power supplies etc (Wrede.H shown in Fig. 2. et al., 2002). Some topologies of power electronic 4 x 10 transformer themselves act as source of power pollution 1.5 (Sabahi.M et al., 2009). Power flow control, bidirectional 1 power flow and power quality mitigation are added 0.5 features of power electronic transformers. In this paper we 0 -0.5 propose a novel power electronic transformer based -1 welding power supply for gas tungsten arc welding of steel -1.5 0.5 and aluminium. Gas tungsten arc welding machine 0.4 0.3 operates with dc supply for steel welding and operates 0.2 0.1 with 150Hz rectangular wave ac supply for aluminium 0 -0.1 welding to avoid oxidation and better welding quality. -0.2 -0.3 Welding power supply has constant current or constant -0.4 -0.5 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 voltage operation. This paper deals with constant voltage welding power supply. Fig. 2. Input voltage and current of power electronic 2. Power Electronic Transformer transformer

Power electronic transformer gains importance due to its From the figure, it is evident that the transient disturbances

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R.Shiju Kumar et al International Journal of Current Engineering and Technology, Vol.3, No.4 (October 2013) due to high frequency switching are very high especially of power electronic transformer produces input current in current waveform. The FFT analysis of the waveforms harmonics. The voltage and current at the output side is is shown in Fig. 3. shown in Fig. 4. Both voltage and current are non sinusoidal with very high distortion index (DIN).

4 x 10 Selected signal: 5 cycles. FFT window (in red): 1 cycles The FFT analysis (Fig.5) shows that THD of voltage and 1 current are 53.65% and 155.59% respectively which are

0 very high.

-1 0 0.02 0.04 0.06 0.08 0.1 Time (s) Selected signal: 5 cycles. FFT window (in red): 1 cycles 500

Fundamental (50Hz) = 8981 , THD= 2.51% 0.015 0

-500 0.01 0 0.02 0.04 0.06 0.08 0.1 Time (s)

0.005 Fundamental (50Hz) = 347.4 , THD= 53.65% Mag Mag (% of Fundamental) 30 0 0 5 10 15 20 25 Harmonic order 20

15

10

Mag Mag (% of Fundamental) 5

FFT window: 1 of 5 cycles of selected signal 0 0.5 0 5 10 15 20 Harmonic order 0 -0.5

-1 0.04 0.042 0.044 0.046 0.048 0.05 0.052 0.054 0.056 0.058 Time (s) Selected signal: 5 cycles. FFT window (in red): 1 cycles

10

Fundamental (50Hz) = 0.2153 , THD= 66.24% 0

-10 15 0 0.02 0.04 0.06 0.08 0.1 Time (s) 10

Fundamental (50Hz) = 2.029 , THD= 158.89%

5 Mag Mag (% of Fundamental) 30 0 0 5 10 15 20 25 Harmonic order 20 15 10

Fig. 3. FFT analysis of input voltage and current Mag (% of Fundamental) 5

0 0 5 10 15 20

600 Harmonic order

400

200 Fig. 5. FFT analysis of output voltage and current 0

-200

-400 Thus the traditional topology of power electronic

-600 transformer produces output voltage and current 20 harmonics. The above topology of traditional power 15

10 electronic transformer can replace the conventional 50Hz 5 welding transformer but it suffers from power quality 0

-5 problems. Also this topology requires three phase high -10 frequency transformer which is costly. -15 -20 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 4. Proposed Power Electronic DC Welding Power Supply Fig. 4. Output voltage and current of power electronic transformer The Gas tungsten arc welding machine operates with dc supply for steel welding. Welding power supply has The FFT analysis shows that THD of voltage is 2.51% constant current or constant voltage operation. Simulink which is within the limits, but the THD of current is model of power Electronic transformer based constant 66.24% which is very high. Thus the traditional topology voltage welding power supply is shown in Fig. 6.

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Fig. 6. Simulink model of proposed dc welding power supply

Three phase 50Hz ac supply is the input of the modular transient disturbances prevails due to switching. The power electronic transformer which is fed from a 3-phase voltage and current are balanced and the unbalance factor generator. The power electronic transformer consists of is zero. three single phase diode bridge rectifier. Phase voltages are fed as input to the and the output side of 250 200 rectifiers has dc link capacitors. The dc is converted to 150 100 high frequency ac using three, 2-leg IGBT inverter. Output 50 0 voltage is kept constant at 50V by a closed loop controller -50 -100 which produces gating pulses for the 2-leg IGBT inverters. -150 -200 The high frequency outputs from the three inverters are -250 200 fed to single phase three winding high frequency 150 100 transformers. All the upper secondary windings are 50 connected in series. One end of the series connected 0 -50 windings is grounded and the other end has rectifier diodes -100 -150 which gives rectified output during positive half cycle. All -200 -250 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 the lower secondary windings are connected in series. One end of the series connected windings is grounded and the other end has rectifier diodes which gives rectified output Fig. 7. Input voltage and current of proposed dc welding during negative half cycle. This dc output is fed to welding power supply through series inductor and parallel capacitor. The topology is similar to dc-dc buck converter if we Selected signal: 5 cycles. FFT window (in red): 1 cycles exclude the input rectifiers. The output voltage is kept 200 constant at 50V using a closed loop controller. The 100 0 difference between the desired voltage (50V) and the -100

0 0.02 0.04 0.06 0.08 0.1 actual output voltage is compared with a saw tooth Time (s) waveform of high frequency to generate the gating pulses Fundamental (50Hz) = 110 , THD= 48.40% to IGBT inverter. 14 12 10

5. Power Quality Analysis of Power Electronic 8 Transformer Based DC Welding Power Supply 6 4

Mag (% of Fundamental) 2

0 The input voltage and current of proposed welding power 0 5 10 15 20 Harmonic order supply is shown in Fig. 7. During the first few cycles

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the work surface, and the positively charged argon gas Selected signal: 5 cycles. FFT window (in red): 1 cycles ions flow from the work surface to the tungsten. DCEN 100 works well for steel and other common ferrous metals, but 0 the oxide layer that forms on nonferrous metals such as -100

0 0.02 0.04 0.06 0.08 0.1 aluminum and magnesium melts at a higher temperature Time (s) than the base metal. Trying to weld with this process

Fundamental (50Hz) = 174.2 , THD= 2.09% causes the base metal underneath the oxide layer to liquefy 2.5 while the surface remains hard and impenetrable. Direct 2 current positive (DCEP) solves the oxide 1.5 problem because the current flows from the work-piece to 1 the tungsten, lifting the oxide off the material in the arc

0.5 Mag Mag (% of Fundamental) zone. DCEP alone provides the oxide cleaning action and

0 0 5 10 15 20 very little penetration. Because the heat is concentrated on Harmonic order the tungsten instead of the work-piece, DCEP also causes the tungsten to ball up at the end. Fig. 8. FFT analysis of input voltage and current AC power supply combines DCEN and DCEP to provide good heat penetration with cleaning action. The FFT analysis of input voltage and current are shown Historically, though, AC has posed an obstacle to GTAW in Fig. 8. The THD of voltage and current are 48% and 2% because the arc frequently extinguishes itself as the current respectively which are much less than the THD level in reaches a zero point before reversing directions. Without traditional power electronic transformer. THD of current is any current passing between the tungsten and the base well below the limits specified in IEEE standards. metal, the arc simply goes out. Improvements in The output voltage and current of proposed welding transformer-based GTAW machines created the power supply is shown in Fig. 9. The output voltage is wave, which increased the amount of time the arc spends kept constant at 50V by the closed loop controller. at full-current flow in both DCEN and DCEP. Square- wave technology eliminated the tendency for the arc to 70 extinguish when the current came to a halt as it reversed 60 directions by making the transition very quickly. This 50 40 greatly improved the stability of the arc and made square- 30

20 wave technology the preferred method for GTAW of 10 aluminum and other materials that form an oxide layer, 0 14 such as magnesium. The second major revolution in 12 frequency technology came with the invention of the 10

8 inverter, which created the ability to increase or decrease 6 output frequency beyond the standard 60 Hz, which is the 4

2 standard frequency delivered to every outlet in the U.S.

0 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 (other countries, such as Germany, England, and France, deliver AC power at 50 Hz). The inverter also allowed for Fig. 9. Output voltage and current of proposed dc welding the development of the advanced square wave, which power supply decreases the time it takes for the current to reverse directions, increasing arc stability even more and 6. Proposed Power Electronic AC Welding Power eliminating the need for continuous high frequency (Tae- Supply Jin Kim et al., 2006). The proposed power electronic ac welding power supply produces square wave output with Before the advent of inverter-based gas tungsten arc 150Hz frequency for better welding quality. The simulink welding (GTAW) machines, frequency control was rarely model of the proposed power electronic ac welding power thought of as a way to improve aluminum welding. The supply and its control strategy are shown in Fig. 10. Three current that came from the wall—50 hertz—was the same phase 50Hz supply is first converted to 50KHz single current that went into the weld. Since then countless phase ac using 3-phase to 1-phase matrix converter. The manufacturers have sworn off this mentality after seeing next in the link is the single phase high frequency three firsthand the benefits of adjustable output frequency. In winding transformer. There are two output windings with alternating current (AC) GTAW, frequency refers to the same voltage rating. The second terminal of the first number of times that the direction of the electrical current output winding and the first terminal of the second output completes a full cycle every second, expressed in hertz. winding are connected to the ground. The first terminal of Frequency is represented by a sine wave, which depicts the first output winding and the second terminal of the the current flow rising and falling as it reverses direction. second output winding are connected together through two Direct current (DC) cannot be used with nonferrous metals rectifier diodes. One diode will be conducting during because of the oxide layer that forms on the surface of the positive half cycle and the other diode during negative half base material. In direct current electrode negative (DCEN) cycle. This is followed by a dc link capacitor and two leg GTAW, the current flows from the tungsten electrode to IGBT inverter which converts the dc to 50Hz ac output.

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The control strategy of matrix converter is comparing the 800 600 phase voltages with a rectangular wave. The rectangular 400 wave is generated with the desired output frequency of 200 0 matrix converter and magnitude equal to half of maximum -200 -400 value of nominal phase voltage of input supply. During the -600

-800 positive half cycle of rectangular wave, gating pulse for 2 IGBT based bipolar switch is produced when the 1.5 1 corresponding phase voltages are greater than rectangular 0.5 wave. During the negative half cycle of rectangular wave, 0 gating pulse for IGBT based bipolar switch is produced -0.5 -1

-1.5 when the corresponding phase voltages are lesser than 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 rectangular wave. The bipolar switches of the matrix converter are realized using one IGBT and four diodes Fig. 11. Input voltage and current of proposed dc welding with configuration shown in Fig.10. power supply

Selected signal: 5 cycles. FFT window (in red): 1 cycles

500

0

-500 0 0.02 0.04 0.06 0.08 0.1 Time (s)

Fundamental (50Hz) = 338.7 , THD= 56.88%

1.5

1

0.5 Mag Mag (% of Fundamental)

0 0 5 10 15 20 Harmonic order

Selected signal: 5 cycles. FFT window (in red): 1 cycles

1

0

-1 0 0.02 0.04 0.06 0.08 0.1 Time (s)

Fundamental (50Hz) = 0.6844 , THD= 75.68%

20

15

10

5 Mag (% of Fundamental) 0 Fig. 10. Simulink model of proposed ac welding power 0 5 10 15 20 Harmonic order supply

7. Power Quality Analysis of Power Electronic Fig. 12. FFT analysis of input voltage and current Transformer Based Ac Welding Power Supply

50

40

30 The input voltage and current of proposed ac welding 20 10 power supply is shown in Fig. 11. The distortion index 0 -10

-20 (DIN) which is the ratio between the rms value of -30 -40 harmonic component to rms value of current/voltage is -50 0.15 very high for both voltage and current, but the input power 0.1 factor is almost unity. 0.05

The FFT analysis of input voltage and current are 0 shown in Fig. 12. The THD of voltage and current are -0.05

-0.1 56% and 75% respectively which are far above the limits 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 specified in IEEE standards. Efforts can be taken in future designs for limiting the same. Fig. 13. Output voltage and current of proposed dc welding power supply

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The output voltage and current of proposed ac welding References power supply is shown in Fig. 13. The output voltage is a square wave with 150Hz frequency. Thus the welding Hosseini.S.H, M. B. Sharifian, M. Sabahi, A. Yazdanpanah, and G. quality will be very good for welding aluminium using gas H. Gharehpetian (May 2008), Bidirectional power electronic transformer for induction heating systems, in Proc. Can. Conf. tungsten arc welding machine. Electr. Comput. Eng., May 4–7,pp. 347–350. Huang. N, D. Zhang, T. Song, M. Fan, Y. Liu and Y. Zhao (2005), A Conclusion 10 kW single-stage converter for welding with inherent power factor correction, in Proc. of IEEE APEC'05, vol. 1, pp. 254-259. Harmonics, low power factor and transient disturbance are Jinhong Zhu, Shuzhong Song, Hongxin Shi and Kang Yong Lee (2008), Investigation on control strategies for pulse gas metal arc the major problems with conventional welding power welding process, in Proc. of IEEE Industrial Electronics and supply. It is suggested to replace conventional welding Applications (ICIEA), pp. 1276-1281. transformer by power electronic transformer. The power Khairy Sayed, Keiki Morimoto, Soon-Kurl Kwon, Katsumi Nishida quality issues in traditional power electronic transformer and Mutsuo Nakaoka (2011), DC-DC converter with three-phase are analyzed in this paper by simulation. Traditional power factor correction for arc welder, in Proc. of IEEE ICPE- topology of power electronic transformer produces input ECCE Asia. Mandal.N.R (2009), Welding Techniques, Distortion Control and current harmonics, output voltage and output current Line Heating, Narosa Publication House Pvt. Ltd., India. harmonics. Also this topology requires three phase high Sabahi.M, S. H. Hosseini, M. B. Sharifian, A. Yazdanpanah, andG. frequency transformer which is costly. Hence this paper H. Gharehpetian (Mar. 2009), A three-phase dimmable lighting proposed a novel power electronic transformer based dc system using a bidirectional power electronic transformer, IEEE welding power supply for gas tungsten arc welding of Trans. Power Electron., vol. 24, no. 3, pp. 830–837, steel. Modular topology based on dc-dc buck converter is Singh.B, Narula.S, Bhuvaneswari.G (Dec 2012), Power quality improvement using three phase modular converter for welding used for the design. Also a novel power electronic power supply, Power India Conference, 2012 IEEE Fifth , pp. 1-6 transformer based ac welding power supply for gas Tae-Jin Kim, Jong-Pil Lee, Han-Woong, Park Kim and Cheul-U tungsten arc welding of aluminium is proposed. DC link in Kim (2006), Development of a power supply for the pulse MIG input side is eliminated using 3-phase to 1-phase matrix arc welding with a wire melting rate change, in Proc. of IEEE converter. A simple control method for the matrix PESC'06, pp. 1-4. Wrede.H, V. Staudt, and A. Steimel (2002) Design of an electronic converter is explained in this paper. Performance of the power transformer, in Proc. IEEE 28th Annu. Conf. Ind. Electron. proposed power electronic transformer based welding Soc., vol. 2, pp. 1380–1385. power is validated by simulation. However the input Zhang E.F. de Silva, R.M. Jose, A. Scotti and J.C. de Oliveira voltage and current are having some harmonics, but much (2011), Power quality analysis of process less than that of traditional power electronic transformer operating under different drop transfer modes, in Proc. of IEEE topology. Efforts can be taken in future designs for COBEP, pp. 129-135, limiting the same.

A welding power supply is a device that provides an

electric current to perform welding. Welding usually

requires high current (over 80 amperes) and it can need

above 12,000 amperes in spot welding. Low current can

also be used; welding two razor blades together at 5 amps

with gas tungsten arc welding is a good example. A

welding power supply can be as simple as a car battery

and as sophisticated as a modern machine based on silicon

controlled rectifier technology with additional logic to

assist in the welding process. Welding machines are

usually classified as constant current (CC) or constant

voltage (CV); a constant current machine varies its output

voltage to maintain a steady current while a constant

voltage machine will vary its output current to maintain a

set voltage. Shielded metal arc welding and gas tungsten

arc welding will use a constant current source and gas

metal arc welding and flux-cored arc welding typically use

constant voltage sources but constant current is also

possible with a voltage sensing wire feeder.

The nature of the CV machine is required by gas metal arc

welding and flux-cored arc welding because the welder is

not able to control the arc length manually. If a welder

attempted to use a CV machine to weld with shielded

metal arc welding the small fluctuations in the arc distance

would cause wide fluctuations in the machine's output.

With a CC machine the welder can count on a fixed

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