U.S. patent application number 12/390616 was filed with the patent office on 2009-10-29 for method and apparatus for receiving a universal input voltage in a welding power source.
This patent application is currently assigned to Illinois Tool Works Inc.. Invention is credited to James M. Thommes.
Application Number | 20090266805 12/390616 |
Document ID | / |
Family ID | 23341583 |
Filed Date | 2009-10-29 |
United States Patent
Application |
20090266805 |
Kind Code |
A1 |
Thommes; James M. |
October 29, 2009 |
Method And Apparatus For Receiving A Universal Input Voltage In A
Welding Power Source
Abstract
A method and apparatus for providing a welding current is
disclosed. The power source is capable of receiving any input
voltage over a wide range of input voltages and includes an input
rectifier that rectifies the ac input into a dc signal. A dc
voltage stage converts the dc signal to a desired dc voltage and an
inverter inverts the dc signal into a second ac signal. An output
transformer receives the second ac signal and provides a third ac
signal that has a current magnitude suitable for welding. The
welding current may be rectified and smoothed by an output inductor
and an output rectifier. A controller provides control signals to
the inverter and an auxiliary power controller that can receive a
range of input voltages and provide a control power signal to the
controller.
Inventors: |
Thommes; James M.;
(Escondido, CA) |
Correspondence
Address: |
CORRIGAN LAW OFFICE
5 BRIARCLIFF CT
APPLETON
WI
54915
US
|
Assignee: |
Illinois Tool Works Inc.
Glenview
IL
|
Family ID: |
23341583 |
Appl. No.: |
12/390616 |
Filed: |
February 23, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11839702 |
Aug 16, 2007 |
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12390616 |
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11086842 |
Mar 21, 2005 |
7319206 |
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11839702 |
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10774128 |
Feb 5, 2004 |
7049546 |
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11086842 |
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09827440 |
Apr 6, 2001 |
6849827 |
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10774128 |
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09200058 |
Nov 25, 1998 |
6239407 |
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09827440 |
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08779044 |
Jan 6, 1997 |
6002103 |
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09200058 |
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08342378 |
Nov 18, 1994 |
5601741 |
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08779044 |
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Current U.S.
Class: |
219/130.21 |
Current CPC
Class: |
H02M 2001/007 20130101;
H02M 5/458 20130101; B23K 9/0953 20130101; B23H 7/08 20130101 |
Class at
Publication: |
219/130.21 |
International
Class: |
B23K 9/10 20060101
B23K009/10 |
Claims
1. A welding power source capable of receiving a range of input
voltages, comprising: an input rectifier configured to receive an
ac input and providing a first dc signal; a dc voltage stage
configured to receive the first dc signal and providing a second dc
signal; an inverter configured to receive the second dc signal and
providing a second ac signal and configured to receive at least one
control input; an output transformer configured to receive the
second ac signal and providing a third ac signal having a current
suitable for welding; an output circuit configured to receive the
third ac signal and providing a welding signal; a controller
configured to provide at least one control signal to the inverter;
and an auxiliary power controller configured to receive a range of
input voltages and providing a control power signal to the
controller.
2. The apparatus of claim 1, wherein the auxiliary power controller
is capable of providing the control power signal at a preselected
control signal voltage, regardless of the magnitude of the ac input
signal.
3. The apparatus of claim 2, further including an auxiliary
transformer with a plurality of primary taps, wherein the auxiliary
power controller is in electrical communication with the plurality
of primary taps.
4. The apparatus of claim 1, wherein the dc voltage stage includes
a boost circuit.
5. The apparatus of claim 1, wherein the inverter includes a pulse
width modulator.
6. The apparatus of claim 1, wherein the range of input voltages is
230 volts to 575 volts.
7. The apparatus of claim 1 wherein the output circuit includes a
rectifier.
8. The apparatus of claim 1 wherein the output circuit includes a
cycloconverter.
9. A method of providing a welding current from a range of input
voltages, comprising: rectifying an ac input and providing a first
dc signal; converting the dc signal to a second ac signal;
transforming the second ac signal into a third ac signal having a
current suitable for welding; and receiving the ac input and
providing an auxiliary power signal source at a preselected control
power signal voltage, regardless of the magnitude of the ac input
signal.
10. The method of claim 9, wherein the step of converting the dc
signal includes the steps of converting the dc signal to a second
dc signal and inverting the second dc signal to provide the second
ac signal.
11. The method of claim 9 further including the step of providing
control signals to an inverter.
12. The method of claim 9, wherein the step of providing the
auxiliary power signal includes the step of transforming the ac
input signal.
13. The method of claim 10, wherein the step of converting the
first dc signal to a second dc signal includes boosting the voltage
of the first dc signal.
14. The method of claim 10, wherein the step of inverting includes
the step of pulse width modulating.
15. The method of claim 10 further including the step of rectifying
the third ac signal.
16. The method of claim 10 further includes the step of
cycloconverting the third ac signal.
17. A welding power source for providing a welding current from a
range of input voltages, comprising: rectifier means for receiving
an ac input and providing a first dc signal; converting means for
converting the dc signal to a second ac signal; transforming means
for transforming the second ac signal into a third ac signal having
a current suitable for welding; output means for providing a
welding current; and auxiliary power means for receiving the ac
input and providing an auxiliary power signal at a preselected
control power signal voltage, regardless of the magnitude of the ac
input signal.
18. The apparatus of claim 17, wherein the means for converting
includes means for converting the dc signal to a second dc signal
and means for inverting the second dc signal to provide the second
ac signal.
19. The apparatus of claim 17 further including means for providing
control signals to an inverter.
20. The apparatus of claim 17, wherein the means for providing the
auxiliary power signal includes means for transforming the ac input
signal into the auxiliary power signal.
21. The apparatus of claim 17, wherein the means for converting the
dc signal to a second dc signal includes means for boosting the
voltage.
22. The apparatus of claim 17, wherein the means for inverting
includes means for pulse width modulating.
23. The apparatus of claim 17, wherein the output means includes
means for rectifying the third ac signal.
24. The apparatus of claim 17, wherein the output means includes
means for cycloconverting the third ac signal.
Description
FIELD OF THE INVENTION
[0001] This invention generally relates to power sources. More
particularly, this invention relates to inverter power sources
employed in welding, cutting and heating applications.
[0002] Power sources typically convert a power input to a necessary
or desirable power output tailored for a specific application. In
welding applications, power sources typically receive a high
voltage alternating current (VAC) signal and provide a high current
output welding signal. Around the world, utility power supplies
(sinusoidal line voltages) may be 200/208V, 230/240V, 380/415V,
460/480V, 500V and 575V. These supplies may be either single-phase
or three-phase and either 50 or 60 Hz. Welding power sources
receive such inputs and produce an approximately 10-40 volt dc high
current welding output.
[0003] Welding is an art wherein large amounts of power are
delivered to a welding arc which generates heat sufficient to melt
metal and to create a weld. There are many types of welding power
sources that provide power suitable for welding. Some prior art
welding sources are resonant converter power sources that deliver a
sinusoidal output. Other welding power sources provide a squarewave
output. Yet another type of welding power source is an
inverter-type power source.
[0004] Inverter-type power sources are particularly well suited for
welding applications. An inverter power source can provide an ac
square wave or a dc output. Inverter power sources also provide for
a relatively high frequency stage, which provides a fast response
in the welding output to changes in the control signals.
[0005] Generally speaking, an inverter-type power source receives a
sinusoidal line input, rectifies the sinusoidal line input to
provide a dc bus, and inverts the dc bus and may rectify the
inverted signal to provide a dc welding output. It is desirable to
provide a generally flat, i.e. very little ripple, dc bus.
Accordingly, it is not sufficient to simply rectify the sinusoidal
input; rather, it is necessary to also smooth, and in many cases
alter the voltage of, the input power. This is called preprocessing
of the input power.
[0006] There are several types of inverter power sources that are
suitable for welding. These include boost power sources, buck power
sources, and boost-buck power sources, which are well known in the
art.
[0007] Generally, a welding power source is designed for a specific
power input. In other words, the power source cannot provide
essentially the same output over the various input voltages.
Further, components which operate safely at a particular input
power level are often damaged when operating at an alternative
input power level. Therefore, power sources in the prior art have
provided for these various inputs by employing circuits which can
be manually adjusted to accommodate a variety of inputs. These
circuits generally may be adjusted by changing the transformer
turns ratio, changing the impedance of particular circuits in the
power source or arranging tank circuits to be in series or in
parallel. In these prior art devices, the operator was required to
identify the voltage of the input and then manually adjust the
circuit for the particular input.
[0008] Generally, adapting to the various voltage inputs in the
prior art requires that the power source be opened and cables be
adjusted to accommodate the particular voltage input. Thus, the
operator was required to manually link the power source so that the
appropriate output voltage was generated. Operating an improperly
linked power source could result in personal injury, power source
failure or insufficient power.
[0009] Prior art devices accommodated this problem by configuring
the power source to operate at two different VAC input levels. For
example, U.S. Pat. No. 4,845,607, issued to Nakao, et al. on Jul.
4, 1989, discloses a power source which is equipped with voltage
doubling circuits that are automatically activated when the input
is on the order of 115 VAC, and which is deactivated when the input
is on the order of 230 VAC. Such sources are designed to operate at
the higher voltage level, with the voltage doubling circuit
providing the required voltage when the input voltage is at the
lower level. This type of source, which uses a voltage doubling
circuit, must use transistors or switching devices as well as other
components capable of withstanding impractical high power levels to
implement the voltage doubling circuit. Further, the circuitry
associated with the voltage doubling circuit inherently involves
heat dissipation problems. Also, the voltage doubling circuit type
of power source is not fully effective for use in welding
applications. Thus, there exists a long felt need for a power
source for use in welding applications which can automatically be
configured for various VAC input levels.
[0010] Welding power sources are generally known which receive a
high VAC signal and generate a high current dc signal. A
particularly effective type of the power source for welding
applications which avoids certain disadvantages of the voltage
doubling circuit type of power source generally relies on a high
frequency power inverter. Inverter power sources convert high
voltage dc power into high voltage AC power. The AC power is
provided to a transformer which produces a high current output.
[0011] Power inverters for use over input voltage ranges are
generally known in the art. For example, a power inverter which is
capable of using two input voltage levels is disclosed in U.S. Pat.
No. 3,815,009, issued to Berger on Jun. 4, 1974. The power inverter
of that patent utilizes two switching circuits; the two switching
circuits are connected serially when connected to the higher input
voltage, but are connected in parallel to account for the lower
input voltage. The switching circuits are coupled to each other by
means of lead wires. This inverter is susceptible to operator
errors in configuring the switching circuits for the appropriate
voltage level, which can result in power source malfunction or
human injury.
[0012] Other prior art welding sources that improved upon manual
linking provided an automatic linkage. For example, the Miller
Electric AutoLink is one such power source and is described in U.S.
Pat. No. 5,319,533 incorporated herein by reference. Such power
sources test the input voltage when they are first connected and
automatically set the proper linkage for the input voltage sensed.
Such welding power sources, if portable, are generally
inverter-type power sources, and the method by which linking is
accomplished is by operating the welding power source as two
inverters. The inverters may be connected in parallel (for 230V,
for example) or in series (e.g., for 460V). Such arrangements
generally allow for two voltage connection possibilities. However,
the higher voltage must be twice the lower voltage. Thus, such a
power source cannot be connected to supplies ranging from 230V-460V
to 380V-415V or 575V.
[0013] A 50/60 Hz transformer could be used to provide multiple
paths for various input voltages. It would, however, have the
disadvantage of being heavy and bulky compared to an inverter-type
welding power source of the same capacity. In addition, if it was
automatically linked as in the Miller AutoLink example given above,
it would have to have link apparatus for each voltage. Such an
automatic linkage would be complicated and probably uneconomical
for the range of voltages contemplated by this invention. Thus, it
is unlikely that prior art power sources that automatically select
the proper of two input voltage settings will accommodate the full
range of worldwide electrical input power. This shortcoming may be
significant in that many welding power sources are purchased to be
transportable from site to site. The ability to automatically adapt
to a number of input power voltage magnitudes is thus
advantageous.
[0014] It is, therefore, one object of this invention to provide a
welding power source that receives any of the above-mentioned input
voltages, or any other input voltage, without the need of any
linkages, whether manual or automatic. Additionally, it is
desirable to have such a welding power source that incorporates
inverter technology and without using high power 50/60 Hz
transformers.
SUMMARY OF THE INVENTION
[0015] The present invention is a power source that is capable of
receiving any input voltage over a wide range of input voltages.
The power source includes an input rectifier that rectifies the ac
input into a dc signal. A dc voltage stage converts the dc signal
to a desired dc voltage and an inverter inverts the dc signal into
a second ac signal. An output transformer receives the second ac
signal and provides a third ac signal that has a desired current
magnitude. Although not necessary, the output current may be
rectified and smoothed by an output inductor and an output
rectifier. A controller provides control signals to the inverter
and an auxiliary power controller is capable of receiving a range
of input voltages and provides a control power signal to the
controller.
[0016] A method for providing a welding current includes rectifying
an ac input and providing a first dc signal. The first dc signal is
then converted into a second ac signal. Then the second ac signal
is converted into a third ac signal that has a current magnitude
suitable for welding. The welding current may then be rectified and
smoothed to provide a dc welding current and an auxiliary power
signal is supplied at a preselected control power signal voltage,
regardless of the magnitude of the ac input signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a block diagram of the preferred embodiment of the
present invention;
[0018] FIG. 2 is a detailed diagram of the input rectifier of FIG.
1;
[0019] FIG. 3 is a detailed diagram of the boost circuit of FIG.
1;
[0020] FIG. 4 is a detailed diagram of the pulse width modulator of
FIG. 1; and
[0021] FIG. 5 is a control circuit for the auxiliary power
controller of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Referring now to FIG. 1, the welding power source 100
includes an input rectifier 101, a boost circuit 102, a pulse-width
modulator 103, a controller 104, an auxiliary power controller 105,
a pair of storage capacitors C3 and C7, and their associated
protective resistors R4 and R10, an output transformer T3, an
output inductor L4, feedback current transformers T4 and T6,
feedback capacitors and resistors C13, C14, R12 and R13, and output
diodes D12 and D13 to provide a welding output current on welding
output terminals 108. A cooling fan 110, a front panel 111, and a
remote connector 112 are also shown schematically.
[0023] In operation, power source 100 receives a three-phase line
voltage on input lines 107. The three-phase input is provided to
input rectifier 101. Input rectifier 101 rectifies the three-phase
input to provide a generally dc signal. A 10 microfarad capacitor
C4 is provided for high frequency decoupling of the boost circuit.
The dc signal has a magnitude of approximately 1.35 times the
magnitude of the three-phase input. The decoupled dc bus is
provided to boost circuit 102. As will be described in greater
detail below, boost circuit 102 processes the dc bus provided by
input rectifier 101 to provide a dc output voltage having a
controllable magnitude. In the preferred embodiment the output of
boost circuit 102 will be approximately 800 volts, regardless of
the input voltage.
[0024] The output of boost circuit 102 is provided to pulse-width
modulator 103, where the dc bus is inverted and pulse-width
modulated to provide a controllable signal suitable for
transforming into a welding output. Controller 104 is a main
control board such as that found in many inverter-type welding
power sources. The main control board provides the control signals
to pulse-width modulator 103, to control the frequency and
pulse-width of pulse-width modulator 103. Input rectifier 101,
pulse-width modulator 103, controller 104 and output transformer T3
are well known in the art.
[0025] The output of pulse-width modulator 103 is provided to an
output transformer T3, which, transforms the output of PWM 103 to
provide a voltage and current suitable for welding. Transformer T3
has a center tap secondary and is provided with a turns ratio of 32
turns on the primary to 5 turns on each half for the center tap
secondary. Of course, other transformers may be used. The
alternating output of transformer T3 is rectified and smoothed by
an output inductor L4 and output diodes D12 and D13. Inductor L4
has an inductance sufficient to provide desirable welding
characteristics, such as, for example, in a range of 50-150
microhenrys.
[0026] Auxiliary power controller 105 receives the input line
voltage and converts that voltage to a 18 volt dc control signal.
The 18 volt control signal is created regardless of the input
voltage, and is provided to boost circuit 102. Boost circuit 102
uses the 18 volt control signal to control its switching frequency
and the magnitude of its output. Auxiliary power controller 105
also provides a 48 volt center tap ac power signal to controller
104.
[0027] Front panel 104 is shown schematically and is used to convey
operating status to the user, as well as receive inputs as to
operating parameters. Similarly, remote connector 112 is shown
schematically and is used to receive inputs as to operating
parameters.
[0028] Generally speaking, at power-up a three phase input is
provided on input lines 107. A plurality of initially open
contactors 115 isolates the input power from input rectifier 101.
However, the input power is provided to auxiliary power controller
105. As will be described in greater detail below, auxiliary power
controller 105 determines the magnitude of the input power, and
opens or closes a number of cont acts to provide a 48 volt center
tap ac output to controller 104, regardless of the input. The
contacts are closed and opened in such a way as to provide
safeguards against underestimating the magnitude of the input
voltage, and thus protecting the circuit components. Also,
auxiliary power controller 105 provides an 18 volt dc control
signal to boost circuit 102, regardless of the magnitude of the
input.
[0029] After the voltage level has been properly determined by
closing the proper contacts controller 104 causes contacts 115 to
be closed, thus providing power to input rectifier 101. Input
rectifier 101 includes a precharge circuit to prevent a resonant
overcharge from harming capacitors C3 and C7 and to avoid
excessively loading of the input source. A signal received by input
rectifier 101 from a tap on transformer T3 turns on an SCR
(described in more detail below). The conducting SCR bypasses input
current around the precharge resistors.
[0030] The output of input rectifier 101 is provided to boost
circuit 102. Boost circuit 102 is well known in the art and
integrated circuit controllers for boost circuits may be purchased
commercially. In operation boost circuit 102 senses the voltage at
its inputs and its outputs. As will be described in more detail
later and IGBT (or other switching element) is switched on and off
at a frequency and duty cycle (or pulse width) to obtain a desired
output voltage. In the preferred embodiment the desired output
voltage is approximately 800 volts.
[0031] Boost circuit 102 thus provides an output of about 800 volts
to 800 microfarad electrolytic capacitors C3 and C7, which have 45K
ohm bleeder and balancing resistors R4 and R7 associated therewith.
Capacitors C3 and C7 thus acts as a dc link for PWM 103.
[0032] PWM 103 receives a generally constant 800 dc signal and
modulates it to provide, after transformation, rectification and
smoothing, a welding output at a user selected magnitude. PWM 103
modulates its input in accordance with control signals received
from controller 104. PWM 103 also receives a 25 volt dc power
signal from controller 104. Such a PWM is well known and PWM 103
may be purchased commercially as a single module.
[0033] The output of PWM 103 is provided to output transformer T3
and which transforms the relatively high voltage, low current
signal to a voltage suitable for use in welding. The output of
transformer T3 is rectified by diodes D12 and D13, and smoothed by
output inductor L4. Thus, a generally constant magnitude dc welding
output is provided on welding outputs 108.
[0034] Current transformers T4 and T5, provide feedback signals to
controller 104, snubber capacitors C13 (0.1 microfarads) and C14
(0.022 microfarads), and snubber resistors R12 (12 ohms) and R13
(47 ohms) suppress voltage transients associated with recovery of
D12 and D13. Controller 104 compares the feedback signals to the
desired welding current, and appropriately controls PWM 103 to
adjust its switching pulse width if necessary.
[0035] Referring now to FIG. 2, the preferred embodiment for input
rectifier 101 is shown in detail and includes a full wave bridge
comprised of diodes D4, D5, D6, D9, D10 and D11. The bridge
rectifies the three phase input to provide a signal having a
magnitude of about 1.35 times the input voltage magnitude. A pair
of 50 ohm resistors R1 and R2 are provided to precharge capacitors
C4, C3 and C7 (shown in FIG. 1) upon start up. This prevents a
sudden surge of current from being dumped into capacitors C4, C3
and C7.
[0036] After the precharge is completed an SCR Q1 is turned on via
a signal from a tap on output transformer T3 (also in FIG. 1). The
signal from transformer T3 is provided to the gate of SCR Q1 via a
current limiting resistor R6 and capacitor C6. A recovery diode D7
and snubber resistor R5 are provided across the gate of SCR Q1. SCR
Q1 shunts the resistors and allows the maximum current flow to
inductor L2 of boost circuit 102.
[0037] A plurality of varistors RV1-RV3 are provided to suppress
line spikes. Additional varistors (not shown) may be provided
between D9-D11 and ground to further suppress spikes.
[0038] As one skilled in the art will readily recognize, other
circuits and circuit elements will accomplish the function of input
rectifier 101.
[0039] Referring now to FIG. 3, the details of one embodiment of
boost circuit 102, which operates in a manner well known in the
art, is shown. Generally speaking, boost circuit 102 provides an
output voltage that is equal to the input voltage divided by one
minus the duty cycle of a switch IGBT1 in boost circuit 102.
[0040] Thus, if the switch IGBT1 is off 100% of the time the output
voltage (the dc link voltage) is equal to the input voltage (from
capacitor C4 and input rectifier 101). In one embodiment the lowest
input is about 200 volts, and the desired output (dc link voltage)
is 800 volts, thus the upper limit for the "boost" is about 400%,
and requires a duty cycle of about 75%.
[0041] The operation of a boost circuit should be well known in the
art and will be briefly described herein. When switch IGBT1 is
turned on, current flows through an inductor L2 to the negative
voltage bus, thus storing energy in inductor L2. When switch IGBT1
is subsequently turned off, the power is returned from inductor L2
through a diode D1 and a 14 microhenry saturable reactor L1 to the
dc link. The amount of energy stored versus returned is controlled
by controlling the duty cycle in accordance with the formula stated
above. In order for the boost circuit to operate properly inductor
L2 must have continuous current, therefore inductor L2 should be
chosen to have a large enough inductance to have a continuance
current over the range of duty cycles. In one embodiment inductor
L2 is a 3 millihenry inductor. The remaining elements of boost
circuit 102 include a 0.0033 microfarad capacitor C1, a diode D3, a
1 ohm resistor R3, a 50 ohm resistor R6, a diode D8, a 50 ohm
resistor R7 and a 0.1 microfarad capacitor C8 which are primarily
snubbers and help the diode recover when switch IGBT1 is turned
on.
[0042] Boost circuit 102 includes an IGBT driver 301 that controls
the duty cycle of switch IGBT1. Driver 301 receives feedback
signals indicative of the output voltage and the input current, and
utilizes this information to drive switch IGBT1 at a duty cycle
sufficient to produce the desired output voltage.
[0043] In one embodiment, boost circuit 102 includes a shunt S1
(shown on FIG. 1). Shunt S1 provides a feedback signal that is the
current flowing in the positive and negative buses. A Unitrode
power factor correction chip is used to implement boost circuit 102
in the preferred embodiment and requires average current flow as an
input. In response to this information and the dc link voltage,
driver 301 turns switch IGBT1 on and off.
[0044] As one skilled in the art will readily recognize, other
circuits and circuit elements will accomplish the function of boost
circuit 102.
[0045] As stated above, the output of boost circuit 102 is provided
to capacitors C3 and C7 (FIG. 1) and is the dc link voltage. In one
embodiment the dc link voltage is 800 volts, as determined by the
switching of switch IGBT1. In the preferred embodiment, using the
component values described herein the dynamic regulation of the dc
link voltage is 80 volts from full load to no load. Static
regulation is about a +/-2 volts, with a ripple of about +/-20
volts.
[0046] The dc link voltage is provided to pulse width modulator
103. PWM 103 is a standard pulse with modulator and provides a
quasi-square wave output having a magnitude equal to the magnitude
of the input, as would any other PWMs. Thus, the output of PWM 103
is about +400 volts to -400 volts for an 800 volt peak to peak
centered about zero.
[0047] PWM 103 includes a pair of switches Q3 and Q4 (preferably
IGBTs) and a pulse width driver 401. Driver 401 receives feedback
from current transformers T1 and T2, and receives control inputs
from controller 104. In response to these inputs driver 401
provides gate signals to switches Q3 and Q4, thereby modulating the
input signal. A capacitor C2 (4 microfarad) a capacitor C9 (4
microfarad) are provided between the dc link and the output
transformer T3. A capacitor C5 (0.0022 microfarad), resistor R11
(50K ohm) and resistor R9 (50K ohm) are snubber circuits.
[0048] As one skilled in the art will readily recognize, other
circuits and circuit elements will accomplish the function of PWM
103.
[0049] The output of PWM 103 is provided to transformer 103, and
the current in transformer 103 is determined by the modulation of
PWM 103. As stated above, the output of transformer T3 is rectified
by diodes D12 and D13 and is smoothed by inductor L4. The dc output
current is fairly flat; the ripple at full load (300 amps) is about
12 amps peak to peak. At full load the duty cycle of each switch Q3
and Q4 of PWM 103 would be about 20-35% (40-70% overall duty
cycle).
[0050] In an alternative embodiment the output of PWM 103 may be
rectified by other output rectifiers such as a synchronous
rectifier (cycloconverter) that provides an ac output signal at a
frequency less than or equal to the frequency of the output of PWM
103. Other output circuits, including inverters, that provide a
welding current may also be used.
[0051] Referring again to FIG. 1, controller 104 is connected to
current transformers T4 and T5, which provide feedback information.
Controller 104 receives power from auxiliary power controller 105
and provides as one of its output the driver control for the PWM
driver. It also includes an over voltage protection sense which
monitors the voltage coming out of input rectifier 101. If the
voltage from input rectifier 101 is dangerously high controller 104
causes contactors 115 to open, to protect circuit components.
According to one embodiment 930 volts dc is the cut off point for
what is considered to a dangerously high voltage.
[0052] As may be seen from the above description, welding power
source 100 receives an input voltage and provides a welding output.
Regardless of the magnitude of the input voltage boost circuit 102
boosts the input voltage to a desired (800 volts e.g.) level. Then
PWM 103 modulates the signal to provide an appropriate level of
power, at 800 volts, to transformer T3.
[0053] The above arrangement is satisfactory for any input voltage,
however, there must be some mechanism to provide control voltages
at the proper level. As will be described below, auxiliary power
controller 105 performs that function, and the embodiment thereof
is shown schematically in FIG. 5.
[0054] With reference now to FIG. 5, a plurality of connectors J1,
J2, J3 and J4 are shown. An 18 volt dc control voltage output is
provided on connector J1 to boost circuit 102 (shown on FIG. 1). As
will be described in greater detail below, the 18 volt dc control
signal is provided regardless of the magnitude of the input
voltage. Connector J2 feeds power back to auxiliary power
controller 105 for internal use. Connector J3 connects the input ac
voltage to appropriate taps on a transformer T7 (FIG. 1) to provide
a 30 volt ac signal to remote connector 112 (FIG. 1). Similarly, a
48 volt center tap ac signal is provided to controller 104.
Controller 104 uses the 48 volt center tap ac signal to generate dc
control signals and to power fan 110. Connector J4 of auxiliary
power controller 105 is connected via a user controlled on/off
switch S4 to the input power lines (FIG. 1).
[0055] Auxiliary power controller 105 controls the connections to
taps on the primary of an auxiliary power transformer T7.
Transformer T7 is a 200 VA transformer whose primaries are
connected to auxiliary power controller 105 as described above with
reference to connector J2 and J3. Several taps on its secondary are
connected to controller 104 and the remaining secondary taps are
connected to remote connector 112.
[0056] Referring again to FIG. 5, the taps on J3 are associated
with the following voltages: 575, 460, 380, 230 volts, and the
return, beginning at the uppermost tap and proceeding downward. As
will be described below, when auxiliary power controller 105
selects the appropriate tap for a given input voltage, transformer
T7 will provide a 48 volt center tap ac signal on its secondary for
use by controller 104.
[0057] As may be seen on FIG. 5, the ac input is received on
connector J4 and provided (via a fuse F1, and a pair of 4.7 ohm
resistors R18 and R19) to a series of relays K2B, K1B, K3C and K3B
that determine the tap on connector J3 selected for the output.
When 575 volts are present at the input relays K2B and K3C should
be to the right. Then the input is connected across the upper and
lower most taps on connector J3. These taps are connected to the
appropriate taps on transformer T7 such that the output of
transformer T7 that is provided to controller 104 is approximately
48 volts center tap when 575 volts are provided to the primary of
transformer T7.
[0058] When 460 volts are present at the input relay K2B should be
to the left, and relay K1B should be to the right. This connects
the ac input to the second uppermost and the lowest taps on
connector J3. The remaining voltages are similarly accommodated. A
pair 0.15 microfarad capacitors C13 and C14 are provided for
snubbing and spike suppression as the primaries of transformer T7
are switched.
[0059] In operation the circuitry on the left side of FIG. 5
determines the input voltage, and sets the relays for that voltage.
At start up the relays are as shown in FIG. 5 and are suitable for
an input voltage of 575 volts. Because this is the highest possible
input voltage, all components will be protected, i.e. either the
voltage is properly selected, or the input voltage is less than the
component design capabilities. If auxiliary power controller 105
determines that 575 volts are in fact present, the relays will
remain as shown. However, if auxiliary power controller 105
determines that less than 575 volts are present, the state of relay
K2B will be changed (to be to the left), so that the output is
appropriate for a 460 volt input.
[0060] This process is repeated, always stepping down to the next
highest voltage, until the appropriate input voltage is sensed. In
this manner the components in controller 104 will be protected from
a dangerously high voltage being applied to controller 104.
[0061] The voltage for sensing is provided to auxiliary power
controller 105 via connector J2, which is connected to secondary
taps on transformer T7. Thus, if the tap selected on connector J3
was not correct, then the voltage on connector J2 will be too low,
and auxiliary power controller 105 will select the appropriate
relay setting to step down to the next voltage level. As stated
above, the stepping down continues until the proper voltage is
sensed on connector J2.
[0062] The input from connector J2 is provided to a rectifier
comprised of diodes CR1, CR2, CR3 and CR4. These diodes rectify the
ac signal and provide it to a pair of 220 microfarad smoothing
capacitors C1 and C2. The rectified voltage is +/-18 volts dc if
the proper tap on connector J3 is selected. If the incorrect tap is
selected the voltage will be less than +/-18 volts, but will be
referred to as nominally +/-18 volts. The nominal +/-18 volt supply
is provided at other locations throughout the auxiliary power
controller 105 circuit, including to a 30 volt zener diode CR7,
used to determine if the proper tap on connector J3 has been
selected.
[0063] Auxiliary power controller 105 determines if 575 volts is
present on the input using the following components: zener diode
CR7, a 10 microfarad capacitor C9, a pair of gates U2B and U2C
configured as darlington drivers for a winding K2A of relay K2, a
10K ohm resistor RN2A, a 10K ohm resistor RN2B, a 820 ohm resistor
R9, and a diode U3B. Gates U2B and U2C are also used as sensing
devices and have a threshold of about 4 volts (relative to their
reference voltages) on the input (pin 1) of gate U2B pin 1.
[0064] Initially, gate U2B has a LOW output and is referenced to
nominal -18 volts. Gate U2B will not switch states so long as the
input is at least 4 volts greater than its reference voltage
(nominally -18 volts relative to ground). In operation the nominal
+18 volts will be provided to diode CR7 and the nominal -18 volt
signal is applied to a 10 microfarad capacitor C9. As a result of
the 30 volt zener drop, the input to gate U2B will be at -12 volts
(relative to ground) if the proper tap has been selected. If 575
volts are present at the input, there will be 6 volts relative to
the reference voltage (-18 volts) at the input to op amp U2B, and
the output state of gate U2B will remain low. So long as the output
of U2B remains low the current will not flow in the winding of
relay K2 and relay K2B will remain as shown in FIG. 5.
[0065] However, if only 460 volts are present on the input and the
relays are as shown in FIG. 5 (as they will be at power up), then
the nominal +/-18 volts will actually be +/-14.4 volts. Thus, 28.8
volts are applied across zener diode CR7 and capacitor C9. Given
the 30 volt zener drop, -14.4 volts will be applied to the input of
gate U2B. Because this is also the reference voltage for gate U2B,
the threshold is crossed, and the output of gate U2B will change
states. Current will then flow in the winding of relay K2 and relay
K2B will change states, configuring the J3 taps for 460 volts. If
less than 460 volts is present at the input the same result will
occur.
[0066] The sensing and stepping down to 380 volts and 230 volts
occur in a similar manner using similar components. Referring to
FIG. 5, the sense and step down circuit to 380 volts include a 100
ohm resistor R17, a pair of 10K ohm resistors RN2C and RN2D, an 820
ohm resistor R8, a diode U3C, a 10 microfarad capacitor C6, a pair
of gates U2D and U2E, and a winding K1A for relay K1. A relay K2C
is provided to prevent relay K1 from changing states before the
step down to 460 volts occurs. In the manner described above with
respect to the step down to 460 volts, the current will be provided
to winding K1A of relay K1 if less than 460 volts is provided at
the input. This will cause relay K1B to move to the left position
and connect the tap on J3 associated with a 380 volt input.
[0067] The circuitry associated with the step down to 230 volts
includes a 100 ohm resistor R16, a pair of 10K ohm resistors RN1A
and RN1B, an 820 ohm resistor R11, a diode U3E, a pair of gates U2F
and U2G, a winding K3A for relay K3, relay K1C, diode CR5 and zener
diode CR4. A relay K1C is provided to prevent relay K3 from
changing states before the step down to 380 volts occurs. The step
down to 230 volts operates in the same manner as the step down to
380 volts and 460 volts as described above. If less than 380 volts
is applied on the connector J4 inputs, gates U2F and U2G will cause
current to flow through winding K3A of relay K3. This will cause
relay K3B to move to the left and connect the tap on J3 for 230
volts to the ac input.
[0068] Thus, as may be seen from the above description, the
circuitry of auxiliary power controller 105 senses the ac input
voltage and connects the appropriate tap on the auxiliary power
transformer T7 to the ac input voltage. As may be seen from the
above discussion, this is done in a manner which protects
components by assuming the voltage is, upon start up, the highest
possible voltage. If the voltage is less than the highest possible
voltage, the next lowest voltage will then be assumed. This process
is repeated until the actual voltage is obtained.
[0069] In the event that the ac input is 230 volts, at start up
there will not be sufficient power from the nominal +/-18 volt
signal to drive the relays because the tap associated with 575
volts on connector J3 is selected at start up. To compensate for
this, circuitry that boosts the voltage supplied on connector J2 is
provided. This circuitry includes a 1 millihenry inductor L1, a
switch Q4, a timer U1, a switch Q2, a switch Q1, and a switch
TIP120. Also included are associated circuitry including a 22 ohm
shunt resistor R13, a 1K resistor R5, a 10K resistor R12, a 10K
resistor R14, a 2.2K resistor R4, a 1K resistor R6, a 1K resistor
R2, a 20K resistor R3, a 220 ohm resistor R7, a 10K resistor RN1D,
a 4.7K resistor R10, a 470 picofarad capacitor C4, a 0.001
microfarad capacitor C3, a 0.1 microfarad capacitor C5, a 220
microfarad capacitor C11, a 220 microfarad capacitor C12, a diode
CR12, a diode CR8, a zener diode CR10, a diode CR5, and a zener
diode CR11.
[0070] The boost power source circuitry operates as a typical boost
circuit. The boost is provided by inductor L1 and switch Q4. During
the time switch Q4 is ON, current flows through inductor L1, shunt
resistor R13 and switch Q4 to the negative voltage supply. During
this time, energy is stored in inductor L1. When switch Q4 is OFF,
the energy stored in inductor L1 is returned to the positive
voltage supply (+B) through diode CR12. By appropriate timing of
the turning ON and OFF of switch Q4, a desired voltage may be
obtained. Timer chip U1 is used to provide the ON/OFF gate signals
to switch Q4 and is an LM555 timer. When the voltage on resistor
R13 becomes sufficiently high, it will trip the input on U1, which
in turn will cause the output of timer U1 to turn switch Q4
OFF.
[0071] Initially, switch Q4 is in the ON position and current
increases and eventually reaches the point where the voltage on
resistor R13 is sufficiently high to trip the threshold on timer U1
through resistor R12. Thus, switch Q4 will remain ON for a length
of time sufficient to build up enough energy to, when it is turned
OFF, raise the nominal +/-18 volts to a level sufficient to drive
the relays.
[0072] Switches Q2 and Q1 enable or disable timer U1 when the taps
on connector J3 are such that the nominal +/-18 volt signal is
actually +/-18 volts. When switch Q2 is turned OFF, timer U1 is
disabled through its VCC input. Also, switch TIP120 is a linear
regulator. When the nominal +18 volt supply is insufficient to
drive the relay, switch TIP120 will provide the boost source to
drive the relays. When the nominal +18 voltage is sufficient to
drive the relay, switch Q2, timer U1 and switch Q4 are turned off.
The +18 volt supply is coupled through L1 and CR12 to regulator
TIP120; the +B boost supply is then fed directly by the
sufficiently high +18 volt supply. The TIP120 regulator regulates
relay supply at 24 volts relative to the -18 volt supply.
[0073] In addition to the circuitry above, circuitry is provided
that protects in the event of an overvoltage. This circuitry
includes a switch Q5, a gate U2A, a 100 ohm resistor R15, a 10K ohm
resistor RN3A, a 10K ohm resistor RN3B, a 10K ohm resistor RN3C, a
10 microfarad capacitor C10, diodes CR14 and U3H, and 10 volt zener
diode CR13. An overvoltage occurs when the tap selected on
connector J3 corresponds to a voltage less than the voltage at the
ac input. This may occur when either the incorrect tap has been
selected or when a temporarily high voltage is provided at the ac
input.
[0074] In the event an overvoltage occurs, the voltage at the node
common to diodes CR13 and CR7 will rise to a voltage greater than
14 volts with respect to the nominal -18 volt signal. This causes
the low side of diode CR13 to be greater than 4 volts with respect
to the nominal -18 volt signal, and the input of U2A will change
from an input low state to an input high state. When the input of
U2A changes from low to high, the output will change from an output
high state to an output low state. The output low state of U2A will
bring the relay supply voltage to a virtual 0 through diodes U3H
and CR14. This causes the relays to return to the state shown in
FIG. 2, which accommodates the highest voltage possible (575
volts). At that time the previously described tap selection process
stepping from the 575 to 460 to 380 to 230 taps begins again until
the correct tap is selected to match the input voltage received on
connector J4. Accordingly, the components of controller 104 will be
protected.
[0075] Other modifications may be made in the design and
arrangement of the elements discussed herein without departing from
the spirit and scope of the invention as expressed in the appended
claims.
* * * * *