Download A novel energyretaining inverter for AC arc welding machines

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS
Int. J. Circ. Theor. Appl. 2012; 40:107–126
Published online 1 July 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cta.708
A novel energy-retaining inverter for AC arc welding machines
Jian-Min Wang1, ∗, † , Sen-Tung Wu2 and Huang-Jen Chiu2
1 Department
2 Department
of Vehicle Engineering, National Formosa University, Yunlin, Taiwan
of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
SUMMARY
A novel energy-retaining power supply for AC arc welding machines is proposed in this paper. In this
kind of power supply, current-steering diodes connected across the output chokes keep the inductor current
continuous and retain the energy during the commutation period, hence reducing the commutation time
to ensure a better welding performance. In addition, the stored energy can be released in the next energy
transfer cycle to raise the conversion efficiency. The circuit operations and design procedures are likewise
examined thoroughly. Experimental results on a prototype inverter for driving a 100-A AC arc welding
machine are recorded to validate the effectiveness of the presented scheme. Copyright 䉷 2010 John Wiley
& Sons, Ltd.
Received 9 December 2008; Revised 1 March 2010; Accepted 2 May 2010
KEY WORDS:
inverter; voltage spike; current commutation; power supply
1. INTRODUCTION
Arcs are used in many industrial applications, such as arc lamps for lighting [1–3], joining metals
for constructions, and arc furnace equipment for steel melting. The arc phenomenon starts from two
electrodes conducted through an invisible path with high voltage in air. The characteristic curve
of an arc is shown in Figure 1 (distance between two electrodes; d = 0.00762 mm). Arc behavior
can be described in three states. The first state is ‘Townsend discharge’ named by its discoverer.
It happens in the beginning of the arc with a high voltage (about 320 V) for breakdown voltage.
The second state is the ‘glow discharge’, in which the voltage VG is typically about 280 V. In this
state, however, the electrodes are conducted with a spark. The last state is the ‘arc discharge’, in
which VA is typically 12 V and the current starts to flow. Basically, the current can be very large
in the last state because the path is yet established [4]. Given this reason, the operating principle
of arc welding is described as follows: first, the path of conduction has to be established by an
arc inducing device. After the path is established, the constant current starts to flow through the
path. Finally, the current that passes through the path with an arc will generate a considerably high
temperature for welding [5].
Inert gas welding technology with wolfram electrodes requires AC currents for welding
aluminum. To control the welding characteristics, the output current, instead of the voltage, is
regulated [5–16]. Therefore, if we want to obtain more stable characteristics of arc welding
and good arc welding beads, we need to reduce the output ripple current [17, 18]. Compared to
∗ Correspondence
to: Jian-Min Wang, Department of Vehicle Engineering, National Formosa University, Yunlin,
Taiwan
† E-mail: [email protected]
Copyright 䉷 2010 John Wiley & Sons, Ltd.
108
J.-M. WANG, S.-T. WU AND H.-J. CHIU
d
i
+
v
1000V
VB
v Arc
Glow
Townsend
VG
100V
VA
10V
10-12 10-10 10-8 10-6 10-4
1
10
i
Figure 1. The characteristic curve of arc.
D1
Q1
D2
T
Q2
Q5
ns
Vi
np
ns
Q3
Q4
D3
L
D4
Q6
iO
RO
Figure 2. Conventional AC arc welding driver.
their DC counterparts, AC arc welding machines provide smoother welding processes and better
performances. Conventionally, a current-regulated inverter is adopted to serve as the driving power
supply for an AC arc welding machine [19–23]. Earlier studies focused on the dynamic response
of arc welding drivers. For this reason, a brand new digital control method is thus proposed
[20–23]. In order to reduce the input current harmonics phenomenon [24–29], PFC is added in
the pre-stage of the inverter [20]. ZVS and ZCS [30–41] are also utilized to improve the efficiency
of the inverter [30].
Figure 2 shows one popular inverter topology mainly composed of a high-frequency (usually
above 20 kHz) full-bridge DC/AC inverter and a low-frequency (usually from DC to several
hundreds of hertz) half-bridge inverter. In the AC arc welding applications, the amplitude of the
load current i O can reach up to several hundreds of amperes. Thus, IGBTs are often used as the
switching devices because of their high current capability. In most cases, the load current is a
squarewave. A high rate of step change for the load current during the commutation period is a
fundamental requirement to produce a standard squarewave and avoid arc extinction.
As depicted in Figure 3, three cases may occur at the end of the commutation period, tc . The
first case is that i o exactly decreases or increases to zero. Therefore, no abrupt change of i o occurs.
However, the time interval required for L to be fully discharged varies with the magnitude of
the load current. The controller would be more complex if tc needs to be adjusted according
to the load current. The second case is that the commutation time is long enough for L to be
completely discharged. The only disadvantage is that there is a dead zone where i o remains zero.
This will seriously affect the welding performance. The third case is that tc is too short, causing
L to maintain a residue energy at the end of the commutation period. Then i o decreases to zero
immediately. Therefore, during the commutation, the energy stored in L is wasted; furthermore,
the fast changing rates of i o may result in high voltage spikes that are often destructive [19].
RC snubbers can be connected across L to clamp the overshoot spikes. Nevertheless, the stored
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
ENERGY-RETAINING INVERTER FOR AC ARC WELDING MACHINES
109
Q5
tc
t
tc
Q6
t
case 1
io
t
case 2
io
t
case 3
io
t
Figure 3. Timing graphs of a conventional AC arc welding inverter.
energy is still completely dissipated at the end of each half-cycle. It can be seen in Figure 3 that
the conventional inverter topology suffers from the following three drawbacks:
• A non-ideal square waveform for the load current i o .
• Lower conversion efficiency.
• High voltage spikes on the output choke during the commutation periods.
This paper describes the operation principles of the conventional and the proposed energyretaining inverter for the AC arc welding. A second output inductor is added. An anti-parallel
diode connected across the output choke keeps the inductor current continuous and retains the
energy during the commutation period in order to produce a qualified squarewave output current.
Moreover, the stored energy can be released in the next half-cycle to reduce the commutation time.
Experimental results on a 100-A AC arc welding inverter are recorded to validate the effectiveness
of the presented scheme.
2. DESCRIPTIONS OF THE CONVENTIONAL AC ARC WELDING INVERTER
Figure 4 shows the block diagram of the AC arc welding inverter controller. The PWM controller
compares the sensed rectified output current and the current reference Io,ref , and produces a pair
of complementary gating signals, Q PWM1 and Q PWM2 . A microprocessor-based controller sends
out the gating signals for Q 5 and Q 6 according to the commands of frequency, duty ratio, and the
required commutation time. During the commutation period, both Q 5 and Q 6 are turned on and
all four switches on the primary side are turned off. Thus, the gating signals for Q 1 to Q 4 can be
expressed as:
Q 1 /Q 4 = Q PWM1 ·(Q 5 ⊕ Q 6 ),
(1)
Q 2 /Q 3 = Q PWM2 ·(Q 5 ⊕ Q 6 ).
(2)
Figures 5 and 6 show the respective conduction paths of the five operating states and the key
waveforms during the positive half-cycle for the conventional AC arc welding inverter. States 1–4
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
frequency
Q5
Microprocessor
duty ratio
Q1 /Q 4
Q6
comm. time
Q PWM1
|i o |
Push-pull
PWM
controller
I o,ref
Q2 /Q 3
Q PWM2
Figure 4. Block diagram of the AC arc welding inverter controller.
D1
Q1
Q2
Q5
T
ns
np
Vi
D2
ns
L
iO
Q3
D4
D3
Q4
VD
VCE
iO
RO
Q6
L
VL
(V i-2VCE )n
RO
(a)
D1
Q1
D2
Q5
T
Q2
ns
np
Vi
ns
L
iO
Q3
D4
D3
Q4
VD
iO
VCE
L
VL
RO
Q6
RO
(b)
D1
Q1
Q2
D2
Q5
T
ns
np
Vi
ns
L
iO
Q3
Q4
D3
(c)
D4
Q6
VD
RO
iO
VCE
L
VL
(V i-2VCE )n
RO
Figure 5. Operation modes of the conventional AC arc welding inverter during a positive half-cycle:
(a) State 1; (b) State 2, State 4, and State 5; and (c) State 3.
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
ENERGY-RETAINING INVERTER FOR AC ARC WELDING MACHINES
111
Figure 6. Waveforms of gate signals and i O for the conventional AC arc welding inverter.
repeatedly circulate in the steady state, whereas State 5 only operates during the commutation
from the positive half-cycle to the negative half-cycle. These five states of the circuit operations
for the conventional topology are described below with two assumptions.
1. The conducting voltages of the active switches and the diodes are represented by VCE and
VD , respectively.
2. The turn ratio of the transformer is n, which is equal to the ratio of n s to n p .
State 1 (t0 –t1 )
Figure 5(a) shows the conduction paths in State 1. Q 1 , Q 4 , and Q 5 are turned on and D1
conducts. L is charged and i o increases to track a constant reference level. The power transfer
from the input voltage source to the load occurs.
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
The induct current i L can be determined by the following equation:
(Vi −2VCE )n − VD − VCE
di L (t) RO
+
i L (t) =
dt
L
L
where i O equals i L . Hence, Equation (3) can be rewritten as follows:
(Vi −2VCE )n
(Vi −2VCE )n
iO =
(e−(RO /L)(t−t0) )
+ IL (t0 )−
RO
RO
(3)
(4)
This state ends when Q 1 and Q 4 are turned off at t1 . IL (t0 ) is the initial value of the inductor
current from the previous state.
State 2 (t1 –t2 )
State 2 begins when Q 1 , Q 2 , Q 3 , and Q 4 are turned off (see Figure 5(b)). Q 5 remains
turned on. In this state, the transformer stops transferring power and the output rectifiers D1 and
D2 conduct. The output current shares equally in the two secondary windings. L discharges via
the load resistor and the switch devices. In State 2, i o decreases until the next power transferring
state.
The equation of i L is determined by
di L (t) RO
−VD − VCE
+
i L (t) =
dt
L
L
(5)
i O = IL (t1 )e−(RO /L)(t−t1 )
(6)
where i O equals i L .
IL (t1 ) is the final value of the inductor current for State 1.
State 3 (t2 –t3 )
Q 2 and Q 3 are turned on to charge L during State 3, as seen in Figure 5(c). At the secondary
side, D2 and Q 5 are conducting. The power is transferred through the transformer and i O
increases.
The equation of i O is determined by:
(Vi −2VCE )n − VD − VCE
di L (t) RO
+
i L (t) =
dt
L
L
where i O equals i L .
iO =
(Vi −2VCE )n
(Vi −2VCE )n
(e−(RO /L)(t−t2) )
+ IL (t2 )−
RO
RO
(7)
(8)
IL (t2 ) is the final value of the inductor current for State 2.
State 4 (t3 –t4 )
This stage begins when Q 1 , Q 2 , Q 3 , and Q 4 are again turned off (see Figure 5(b)). Therefore,
L discharges and i O decreases. The equation for i O is determined in Equation (6). The initial value
of inductor current is the final value for State 3.
State 5 (t5 –t6 )
Commutation time tc is defined as (t6 −t5 ). During the commutation, Q 1 , Q 2 , Q 3 , and Q 4
are turned off, whereas Q 5 and Q 6 are turned on simultaneously. Nevertheless, i O flows through
Q 5 because of current continuity. Figure 5(b) shows the resulting equivalent circuit, wherein i O
likewise decreases. The equation of i O is determined in Equation (4).
Referring to Figure 6, one clearly understands that in the positive half-cycles, i O increases when
Q 1 and Q 4 or Q 2 and Q 3 are turned on. In contrast, i O decreases when these four switches
are turned off. To balance the magnetic flux in the transformer primary, Q 1 /Q 4 and Q 2 /Q 3
combinations alternately conduct. At the start of each positive half-cycle, i O increases from zero.
To speed up the commutation process, the duty cycles of the switches at the primary side are set
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
ENERGY-RETAINING INVERTER FOR AC ARC WELDING MACHINES
113
as large as possible during T . On the other hand, the average value of the output current when
only Q 5 remains turned on is a constant level, IO . Thus, the duty cycle D of the switches of the
front-stage full-bridge inverter in the steady state can be determined from the flux balance of the
transformer.
D=
VD + VCE + IO RO
2n(Vi −2VCE )
(9)
When Q 5 turns off at t6 , the conducting path for the inductor current is disconnected. The energy
previously stored in the inductor is completely dissipated instantaneously. Sharp and high voltage
spikes appear across the inductor. These voltage spikes may not only destroy the insulation of the
inductor winding but also break through the switches. The operating modes described for the positive half-cycle are equally applicable for the negative half-cycle, which starts right after Q 5 is turned
off. It should be noted that although the duration between t5 and t6 can be made longer to lessen
the level of the current step change, the fall time of i O is increased. Consequently, the arc welding
performance will deteriorate because of the non-ideal square waveform of the output current.
3. DESCRIPTIONS OF THE PROPOSED AC ARC WELDING INVERTER
In this paper, we present an energy-retaining inverter to prevent the stored energy from being
wasted. As shown in Figure 7, there are two output inductors, L 1 for the positive load current
and L 2 for the negative load current. In addition, two reversely conducting diodes are parallelconnected for conduction path 1 and conduction path 2, respectively (path 1: L 1 , L 2 , and Q5 are
a series; path 2: L 1 , L 2 , and Q6 are a series). The main drawback of the conventional inverter
topology with a single output inductor filter is that all the energy stored in the output inductor
must be dumped at the end of a half-cycle to shorten the commutation time. Therefore, the output
current has to increase from zero at the start of the next half-cycle. As a result, the commutation
process lasts longer. In the proposed inverter topology, inductors L 1 and L 2 on the positive and
negative output current paths, respectively, is adopted. There is only one inductor with an output
current at any time.
Figure 8 shows the conduction paths of the six operating states in one positive half-cycle for
the proposed AC arc welding inverter. The circuit operations of the first five states are the same
as those of the conventional inverter, except that the output inductor L is replaced by the inductor
L 1 . Next, we will have a discussion about the State 6.
State 6 (t6 –t7 )
Figure 8(d) depicts the conduction paths in State 6. In this state, Q 2 , Q 3 , and Q 6 are turned on
and Q 5 is turned off, such that L 1 is discharged. The energy is delivered from L 1 to L 2 , then the
output current i o will increase to track the constant reference level.
iL
D1
Q1
D2
T
Q2
Q5
L1
D5
ns
np
Vi
iL
ns
L2
Q6 D6
Q3
Q4
D3
RO
iO
D4
Figure 7. Proposed AC arc welding inverter.
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
(a)
(b)
(V
(c)
(d)
Figure 8. Operation modes of the proposed AC arc welding inverter in a positive half-cycle: (a) State 1;
(b) State 2, State 4, and State 5; (c) State 3; and (d) State 6.
The equation of i L2 = i O is determined by the following equation:
L1
(VD + VCE )
(Vi −2VCE )n −
L1 + L2
(1−e−(RO /(L 1 //L 2))(t−t6 ) )
iO =
RO
(10)
This state ends when Q 2 and Q 3 are turned off at t7 .
Figure 9 shows the related key waveforms. Specifically, both Figures 6 and 9 show that the
major difference between these two inverter topologies is the output current waveform during the
commutation period. In Figure 9, when Q 5 is turned off at t6 , the energy stored in L 1 is changed
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
ENERGY-RETAINING INVERTER FOR AC ARC WELDING MACHINES
115
Figure 9. Key waveforms of the proposed AC arc welding inverter topology.
from L 1 to L 2 , forcing the L 1 inductor current to flow through the Q 6 and D6 . Consequently,
Q 6 carries the inductor current and i L2 jumps from 0 to −IC1 instantaneously and i L1 jumps from
IC to IC1 instantaneously. States 1–4 are then sequentially applied for i O to track −IO . Observing
Equation (10), we can find that i L2 is charged whereas i L1 is discharged in this continuous state.
When compared with Equation (4), the output current IO will reach −IO much quicker in half
rise time. Two advantageous features can be observed in the proposed inverter topology. The first
is that the overlapping of the turn-on signals of Q 5 and Q 6 can be shortened, hence resulting in
the speedup of the commutation process. In addition, more energy can be conserved in another
inductor so that its conversion efficiency is improved. The second one is that the output current has
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
a faster response time from the transient state to a steady state during each half-cycle. Therefore,
the time required for i O to track its reference value is much shorter than T (see Figure 6).
4. EFFICIENCY ANALYSIS
Figure 10 shows the inductor current i L and the output current i O , not considering the highfrequency switching ripples, for the conventional and the presented AC arc welding inverters.
As shown in Figure 10(a), the inductor current i L for the conventional inverter topology is not
continuous during the whole commutation period. The output current first jumps to zero and then
returns to its steady-state level with a finite time T . Consequently, the energy stored in the
inductor in the steady state is totally wasted during the commutation. Then the inductor is refilled
at the start of the next half-cycle. The inductor current in the steady state can be expressed as
follows:
1
W = L Io2
2
(11)
As this charging–discharging process happens twice in a complete output cycle, the average power
loss of the conventional inverter can be calculated as
Pconventional
loss =
2W L Io2
=
T
T
(12)
Figure 10(b) shows the inductor current i L1 , i L2 , and the output current i O for the proposed AC arc
welding driver inverter. The losses in diodes, IGBT, cores of inductor, and copper wires will be
ignored. When the direction of output current from the positive half-cycle changes to the negative
one, i L1 will change from IO to IC1 and i L2 will change from 0 to −IC1 instantaneously. Hence,
the energy stored in the previous inductor will be transferred to another conductor. Assuming
that L 1 = L 2 = L during the commutation period, the initial value IC1 of inductor current can be
determined by the following equation:
IC1 = 12 Io
(13)
The loss caused by energy transferring of inductors is shown below:
2
Wloss = 12 L 1 Io2 − 12 (L 1 + L 2 )IC1
= 14 L Io2
(14)
According to Equation (12), the average power loss of the proposed inverter can be recalculated as:
Pproposed
loss =
L Io2
2T
(15)
Equations (12) and (15) compare the differences in the average power loss between the conventional and the proposed AC arc welding inverters. The average power loss for the proposed type is
half the time of the conventional one. Consequently, the average power loss of the AC arc welding
inverter is proposed to be smaller than that of the conventional AC arc welding inverter, in which
few power dissipations occur during the commutation period. Next, when the pre-stage full-bridge
switches start to operate at high frequency, the energy will be delivered to the output load through
the transformer. At the same time, L 2 will receive the previous energy and continue reserving
it, and L 1 will release the energy to zero. As the energy stored in the inductor can be retained
for the next energy transfer stage, the conversion efficiency especially at a heavy load can be
improved.
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
ENERGY-RETAINING INVERTER FOR AC ARC WELDING MACHINES
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Figure 10. Waveforms of the output current for (a) the conventional and
(b) the presented AC arc welding inverters.
5. SIMULATION AND EXPERIMENT RESULTS
The differences between the conventional and the proposed AC arc welding inverters are compared
by simulations and experiments. The simulations and experiments are performed with the following
circuit parameters:
Input voltage Vi = 155 VDC
Load resistance Ro = 0.05
Switching frequency = 22 kHz
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
Figure 11. Simulated waveforms of Q 5 , Q 6 , and i O for (a) the conventional and (b) the proposed inverters.
Inductance L = L 1 = L 2 = 60 H
Transformer turns ratio n = 5
Commutation time tc = 10 s
Primary-side full-bridge converter (Q1–Q4) = Mitsubishi CM50DY-12H IGBTs
Secondary-side half-bridge inverter (Q5–Q6) = Mitsubishi CM150DY-12H IGBTs
Output rectifier diodes (D1–D4) = Mitsubishi RM200DA-20F
The output current is a symmetrical squarewave with a frequency of 100 Hz and an amplitude
up to 100 A. Figure 11 shows the simulation results of the driving signals for Q 5 , Q 6 , and the
output current i O . One can clearly see that the quality of the squarewave current produced by the
proposed inverter is much better. Figure 12 shows the simulation results in the vicinity of current
commutation. In Figure 12(a), i O first changes abruptly from −100 A to 0, then increases from 0
to 100 A within a 1200-s transient for the conventional AC arc welding inverter. On the other
hand, in Figure 12(b), i O increases speed from 0 to a positive value of 100 A. The transient lasts
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
ENERGY-RETAINING INVERTER FOR AC ARC WELDING MACHINES
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Figure 12. Simulated waveforms of Q 5 , Q 6 , and i O for (a) the conventional and (b) the proposed inverters
in the vicinity of the current commutation.
less than 500 s. Figure 13 shows the inductor current and the output current waveforms of the
presented AC arc welding inverter.
Prototype inverters with the same specifications as stated in the simulations are constructed to
conduct the experiments. The experimental results corresponding to the simulations in Figure 11
are depicted in Figure 14. It is noted that the experimental results agree well with the theoretical
analysis. Figures 15(a),(b) show the transient behaviors at the current commutation. Figure 16
shows that the proposed topology for two output inductors can inherit 0.11 joule for each inductor
during the commutation state. Figure 17 shows the voltage spikes, vp , on the inductors for the
conventional and the proposed inverters, respectively, at the current commutation. In Figure 17(a),
the maximum voltage spike is about 600 V, whereas in Figure 17(b) it is recorded at about 300 V.
Figure 18 shows the output current waveforms whereas Figure 19 shows the resulted inductor
voltage spike for commutation times of 1370 s. From these results, and as illustrated in
Figures 14(a) and 17(a), it is verified that for the conventional AC arc welding inverter, a shorter
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
Figure 13. Simulated waveforms of i L1 , i L2 , and i O for the proposed inverters.
Figure 14. Waveforms of Q 5 , Q 6 , and i o for (a) the conventional and (b) the proposed inverters (Q 5 /Q 6 :
20 V/div., i O : 100 A/div., Time: 4 ms/div.).
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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Figure 15. Waveforms of Q 5 , Q 6 , and i O for (a) the conventional and (b) the proposed inverters in the
vicinity of the current commutation.
Figure 16. Waveforms of i L1 , i L2 and i O for the proposed inverters.
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
Figure 17. The resulted voltage spikes for (a) the conventional and (b) the proposed inverters.
Figure 18. Waveforms of i O for the conventional AC arc welding inverter with tc = 1370 s.
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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Figure 19. Waveforms of vp for the conventional AC arc welding inverter with tc = 1370 s.
Figure 20. The output voltage and output current waveforms during the ignition period.
commutation time may improve the quality of the output current waveform at the falling edge in
the positive half-cycle and the rising edge in the negative half-cycle. However, a higher voltage
spike and a lower conversion efficiency are resulted. Moreover, the output current increases or
decreases from the zero level at the start of each half-cycle with a limited slope, which further
impairs the welding performance. As for the proposed inverter and operations, the commutation
time can be set much shorter to maintain more energy and to achieve better welding performance.
The system efficiency can thus be raised and the commutation process shortened.
As shown in Figure 20, it shows the output voltage and output current of ignition before arc
welding behavior and identifies the previous description of arc. In order to create a loop easily
with high voltage by arcing device, the proper high voltage should be 5–7 kV in commercial
application. As long as the loop is established, the output high current starts to flow through the
path. Therefore, the arc welding process is going on. The igniter will generate high voltage when
ignition occurs. However, the initiate energy from the ignition device will by pass through the
snubber circuit, as shown in Figure 21. Base on the reasons above, they would not affect the design
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
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J.-M. WANG, S.-T. WU AND H.-J. CHIU
D1
Q1
D2
T
Q2
D5
L1
Q5
ns
Vi
Igniter
Circuit
np
ns
L2
Q6 D 6
Q3
D3
Q4
RO
R
iO
D4
C
Figure 21. The conduction path of ignition.
Table I. Comparisons of input power and efficiency.
Topology
Commutation time tc (s)
Input power Pi (W)
Efficiency (%)
10
1370
10
906
850
858
55.1
57.8
57.2
Conventional
Conventional
Proposed
60
Efficiency(%)
55
50
45
40
35
30
proposed topology
conventional topology
25
theoretical
20
20
30
40
50
60
70
80
90
100
io(A)
Figure 22. Measured and theoretical conversion efficiencies of the proposed inverter.
rules of components stress in power stage. Table I lists the input power and efficiency for the two
inverters under various commutation times. The output power is 500 W. It can be seen that the
proposed AC arc welding inverter features the shortest commutation period, the highest efficiency,
and the most qualified output current waveform. Figure 22 shows the conversion efficiencies of
the conventional and the proposed inverters with tc = 10 s. The theoretical data are obtained by
adding the calculation results of Equation (14) into the measured input powers of the conventional
topology.
Copyright 䉷 2010 John Wiley & Sons, Ltd.
Int. J. Circ. Theor. Appl. 2012; 40:107–126
DOI: 10.1002/cta
ENERGY-RETAINING INVERTER FOR AC ARC WELDING MACHINES
125
6. CONCLUSIONS
The proposed inverter for driving an AC arc welding machine can effectively improve the welding
performance in many aspects. In this study, for instance, a single output filter choke is replaced by
an inductor L 1 for positive load current and an inductor L 2 for negative load current. The energy
stored in the inductor can be saved during the commutation periods and released in the next energy
transfer cycle. The voltage spikes during the commutation times are thus reduced. For the AC arc
welding, the welding performance can thus be enhanced because of the shortened commutation
time and the less distorted output current. Accordingly, the proposed AC arc welding inverter is
especially suitable for high-output current AC arc welding applications.
ACKNOWLEDGEMENTS
This work was supported by the National Science Council of Taiwan under Grant NSC 97-2218-E-150-005.
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