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Traducere Negulaev_2_engleza
Contents
From the author _ 3
1. A bit of theory and basic requirements for welding invertoru__ 4
2. Types of high-frequency transducers, the most frequently used for the construction of welding inverters.
(Review) _ 7
3. Asymmetrical bridge, or single-ended forward,
or simply "an oblique bridge. " _12
4. Half-bridge push-pull inverter with PWM, resonant, with throttle rasseyaniya._ 16
5. Bridged push-pull inverter with PWM, with throttle scattering, resonance,
resonance for current 10-350A in duge._ 24
6. Selecting the power tranzistorov_ 36
7. Design tweaks and nuances of making responsible uzlov._ 39
8. Useful devices and circuits: "hot start", "antiprigar", "mild ignition. _ 41
9. Options ferritov_ 45
10. Examples of PCB layout and komponovki_ 47
10. List literatury_ 50
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From the author
This book is a logical extension and complement to my first book - "welding inverter - it's easy." There
you will find answers to most questions faced by radio amateurs in konstruirova Institute of welding
power sources at home. And if the first book was almost entirely devoted to the resonant inverter welding,
then at this, I will try to capture and describe the full range of welding inverters, starting with the simplest
and ending with a powerful half-bridge resonant source! Over the past year, after my first book and
publication on the Internet circuits of resonant inverters welding my design, I have received hundreds of
emails with questions and suggestions. All the letters were me carefully analyzed the technical solutions
repeatedly tested in the hardware, and only after that, I hate them for yours, dear reader, the court. All
texts are provided with detailed wiring diagrams and drawings.
Shows the actual waveforms at key points, developed and tested in practice, technique setting apparatus
with PWM, PFM and phase-controlled output current and voltage. Maybe I'm missing something, or not
adequately provided a description of the processes, but as they say - there is no limit to perfection.
I think this book can be useful for both experienced developers of new schemes of power converters, and
those who are just going to plunge into the world of power electronics. Try, wrong, fix their own and
others' mistakes, learn on their own and foreign experience, and very soon you will notice that wins is
always greater than defeats and disappointments!
I thank all who sent letters with comments and suggestions, demands and curses, and just a sign of
attention. The very fact that these letters were written, shows that my work was not in vain. Thank you all!
Good luck!
The author, designer, engineer, electronics VY Negulyaev, Kiev, 2006
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1. A bit of theory and basic requirements for welding inverter.
I, like many of you do not like theory. But to understand the principles of welding power inverter is
required to slightly affect the processes of formation and combustion of the arc. I hope this chapter does
not discourage the desire to read to the end. Petomu will be brief and immediately start with the current-
voltage characteristics of the arc. (hereafter VCC)
Figure 1 shows the current-voltage characteristics of the arc in a general way. As can be seen at low
currents, up to about 80A of the arc has a type of incident, or if the fingers - in Britain rose-current arc
voltage drops. This is a very interesting property of the arc which can and should use it! Proceeding from
the above schedule may be inconclusive - the higher the voltage applied to the spark gap, the easier the
process of the arc, the arc lights at a current much smaller than if we try to light it on the straight section
IVC! It is to facilitate the ignition of the arc used oscillators and other devices increase the output voltage
welders. Standard open-circuit voltage (XX) for inverter welders range from 70V to 95V, and depends
only on the design voltodobavki. The main source typically has a gently dipping feature with steep tail
section that limits the maximum short-circuit (SC). Approximate schedule CVC welding inverter must
have the form shown in Figure 2. As we see high output voltage of the twentieth ensures stable ignition
and maintenance of sustainable arc on all modes of operation. With such a CVC welding inverter, easily
ignited and burns steadily all brands of electrodes, including electrodes for welding stainless steels,
nonferrous metals and iron.
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Welding current (A)
As I said earlier, Figure 2 shows the approximate timetable for the IVC, and the actual IVC may
differ significantly, but ideally it should strive to obtain a similar output characteristics of the welding
machine.
We have considered only the portion CVC arc for currents less than 100A, but that's how
characteristics of the source at this site will be similar to the arc, depends on the stability of the arc, and as
a consequence of the quality of the weld.
So we have formulated the first requirement for welding inverter - steep characteristic. This is
required unless it is satisfied, then we will hardly get a welder worthy options.
Consider the following part of VAC of the arc that begins after 80A, and to continue to
approximately 800A.
On this site I-V, the arc is a voltage stabilizer, it is this area is most suitable for transferring
molten metal from the electrode to the work piece.
Voltage in the arc in this region does not depend on the applied current, and depends only on the
length of the arc. The magnitude of this voltage can be calculated by the formula:
Ud = a bn.
where Ud - arc voltage, V; ^ ^ ^ 1
a - constant coefficient, which expresses the sum of voltage drops on
cathode and anode of the arc, which does not depend on the length of the arc in;

b - the average voltage drop per unit length of arc / mm; L - length of arc, mm. For steel
electrodes can take an average of a = b = 10V and 2V/MM. Then the arc voltage of length
L = 4mm is:
U = 10 2 * 4 = 18B.
At atmospheric pressure, the arc welding metal electrode burns steadily at a voltage 18 -
28V.
This will be the following requirements to our source.
Over the entire operating range, from I = 80A to Imax, the voltage
should be less than 18V, and for stability
Noah works at least 22-24V
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Now consider the third, the tail section of I-V welding inverter. This segment of the curve is very
important for a stable arc, current limiting circuit to limit the power inverter for the safe operation of
power switches!
Different designs of transducers it is formed in different ways, and as a consequence, has a different slope.
In PWM inverters, the restriction of the maximum-current power switches arranged through the operating
system as a sensor can be used current transformer. Upon reaching the boundary current, pulse current
trans-formators to the input current limit to the control unit, and interrupt control pulse fed to the power
switches. On the waveform it looks as how the restriction of the control pulse. And the greater the load,
the shorter becomes the momentum of governance. Output voltage starts to drop, although the current
increases. The steepness of the site depends on the time lag reaction controller lera to load changes.
For resonant inverters, this site CVC has flatter slope, its value depends only on Q resonant LC chain, and
the higher it is, the steeper the angle. As you can see if the unit is properly configured, you can do without
running current! Limitation of power will occur automatically. It is therefore considered that the resonant
converters are not afraid of the regime fault! And it's true!
That is formed, and the third main requirement - to restrict the maximum current of power switches! This
is the most important requirement!
These three conditions must be fulfilled without fail!
All other requirements for power sources are not so important. But I must tell you about them. They are:
a) safety, the welder must be sure not to fall
under stress is dangerous to life;
b) the presence of anti-regime long circuit;
c) the availability of protection against overheating of the apparatus of power;
d) protection from moisture and dust;
d) the presence of ignition and stabilization of the arc.
I think this is sufficient, although welders foreign firms have a variety of additional modes that make life
easier welder. But that is another story, we now consider only the very power the car, I mean high-
frequency transducer, because it is dependent on its design tactic - technical characteristics of the entire
system, ie its power, size and weight.
The next chapter will be given the types of converters most commonly used for the construction of
welding power sources.
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2. Types of high-frequency transducers, the most frequently used for the construction of welding inverters.
(Review)
Most often, the construction of welding inverters, used three main types of high-GOVERNMENTAL
converters: half-bridge, asymmetrical bridge (or "skew bridge") and full bridge. Subspecies gyulumosta
and full bridge, are resonant converters. Depending on the control system output parameters, converters
are PWM (pulse width), with PFM (frequency control), with phase adjustment, and combinations of these
three. All of these types of transducers have their own advantages and disadvantages.
I propose to begin with a half-bridge PWM. The block diagram of such a converter is shown in Figure 3.
This is the easiest converter of the family dvuhtaktnikov, but no less reliable. The disadvantage of this
scheme is that the "swinging" stresses on the primary winding of power transformer is equal to half the
supply voltage. But on the other hand, this fact is a plus, you can use a smaller core, without the fear of
entering the saturation regime. For inverter low-power (2-ZkVt), this converter is very promising.
However, PWM control requires special care when installing power circuits, for management of power
transistors is necessary to put the drivers. Transistors of the half-bridge operating in hard switching mode,
so to control signals increased demands. Necessarily the presence of "dead time" between the two
antiphase pulses, no breaks, or lack of its duration, always leads to a pass-through current through power
transistors. Consequences are predictable - the output transistors failed.
Very promising kind of half-bridge converter is a resonant half-bridge. The block diagram of a half-bridge
is shown in Figure 4.
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As seen from block diagrams, resonant half-bridge is much easier than the half-bridge PWM. Easily build
a converter for such a scheme due to the fact that the commutation of keys occurs at zero current or zero
voltage. Parasitic inductance assembly automatically taken into account, the maximum current through the
transistor is limited to a serial resonant circuit Dr.rez .- Slice. Current flowing through the power circuit
has a sinusoidal shape, and it offloads the filtering capacitors. With this build power switches do not need
drivers! Enough of the ordinary pulse transformer to switch the power transistors. Quality control pulse is
not as significant as in the circuit with PWM, although the pause ("dead time") should be. Another plus,
this scheme eliminates the need for overcurrent protection and the form CVC (current-voltage
characteristic) has a direct view of the incident and does not require parametric formation. Output current
is limited only by the magnetization inductance of the transformer and can reach significant values at CP,
it is also necessary, can be considered when choosing the output diodes, but this property has a positive
effect on the ignition and burning of the arc! Typically, the output parameters are regulated by varying the
frequency, but the application of phase control offers far more advantages and is the most promising for
welding inverter, since it allows to circumvent such an unpleasant thing as coincidence resonance mode
circuit, and the range of adjustment of output parameters are much wider. The phase adjustment allows
you to change the output current is almost 0 to Imax.
The following scheme - an asymmetrical bridge, or "skew bridge." The block diagram of such a converter
is shown in Figure 5 ..
Asymmetrical bridge - single-cycle, pryamohodovoy converter. Transducer of this configuration is very
popular, as the manufacturers of welding inverter-ers, and among hobbyists. The first welding inverters
were built as "skew bridge." The simplicity and reliability, ample opportunities to adjust the output
current, noise - all this attracts developers welding inverters so far. And although the disadvantages of
such a converter rather substantially, this large currents through the transistors, high requirements for the
form of governance -
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that returns the pulses, which implies the use of powerful drivers for the governance power switches, high
requirements for installation of power circuits, high surge current high demands on the input filter
capacitors-ra, electrolytic capacitors do not like large pulse currents. To keep the transistors in the DHS
(feasible region) requires RCD chain (snubbers).
Block
Fig.5 PWM control, "P-p
PWM BU
But despite all these flaws and the small efficiency, "an oblique bridge" to the present day is used in
welding inverters. Transistors T1 and T2 operate in phase, together with open and closed. Energy is stored
not in the transformer and the output coil inductor. Work cycle not exceeding 50%, which is why for the
same power with a bridge inverter requires double the current through the transistors. More detailed work
of this converter will be considered by the example of the real welding inverter.
The next type of converter - full bridge PWM. The classic two-stroke converter! Block diagram of full
bridge is shown in Figure 6.
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Brug stroombaan maak dit moontlik om 'n krag van 2 keer meer as die helfte' n myl te kry, en 2 keer meer
as "'n skuins brug, met daardie waardes van strome en verliese in die skakel insluiting. Dit is omdat die
"swaai" om die spanning van die primere winding van krag transformator is gelyk aan die
toevoerspanning. Onderskeidelik, vir dieselfde kovoy krag, soos half-brug (waar die spanning swing is
gelyk aan 0,511 put) sal vereis dat die stroom deur die transistors in 2 keer minder!
Transistors volle brug werk op die diagonaal, wanneer T1 - TK oopgemaak het, T2 - T4 is gesluit, en
omgekeerd. 'N huidige transformator monitors die piek waarde van stroomvloei deur die inlywing van die
diagonaal. Reguleer die uitset stroom van die pre-makers op twee maniere: 1) verander die duur van die
beheer pols, verlaat gelaat die donker spanning, 2) die vlak van spanning afkomstig van die cut-off stroom
van die transformator verander, verlaat gelaat die duur van die beheer pulse. Beide hierdie metodes kan jy
die uitset stroom in 'n redelik wye verskeidenheid te verander.
Tekortkominge en eise van die volledige brug PWM, presies soos in die half-brug PWM (sien hierbo)..
Ten slotte, ons kyk na die mees belowende skema vir HF inverter vir die sweis van inverter - 'n resonante
brug. Die blokdiagram getoon in Figuur 7
Blok
PFM beheer of fase beheer
Soos dit mag lyk op die eerste oogopslag, die skema van die resonansie van die brug is nie veel verskil
van die brug met PWM, en dit werklik is. Byna addisioneel bekendgestel net LC resonante ketting is in
serie met die krag transformator. Maar die bekendstelling van die ketting draai die prosesse van die
oordrag van Cardinaliteit. Afname verliese, verhoog doeltreffendheid deur ordes verlaag die vlak van
elektromagnetiese interferensie, verminder die las op die insette elektroliete. As jy sien jy heeltemal kan
verwyder die beskerming van toku1, bestuurders, kan krag transistors nodig wees net in geval esg.i.
MOSFET transistors word toegepas op die hek kapasitansie groter as 5000pF. Vir IGBT transistors slegs
een pols transformator. 'N meer gedetailleerde beskrywing van die werking en opset, sal gegee word' n
bietjie verder, na die voorbeeld van die werklike sweis omkeerder. Beheer oor die uitvoer
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