SU1738521A1 - Arc welding power source - Google Patents

Abstract

The invention relates to a welding technique, in particular to power sources for electric arc welding with an increased conversion frequency, and can be used in various fields of engineering. The purpose of the invention is to increase the source efficiency by transferring the reactive energy of the inverter switching circuit to the load and reducing the noise level by allowing the arc current to change during the welding process without adjusting the inverting operating frequency. For this purpose, a power source for arc welding, comprising a rectifier, a high-frequency power transformer, charge, discharge and reverse thyristors, a working capacitor, a mid-point diode full-wave rectifier, current sensors and arc voltage, a device for forming the external source characteristic, charge and discharge thyristor control units, two adjustable delay lines, charge, discharge and reverse thyristor control pulse shapers, a comparator and a voltage control unit are introduced on the working capacitor. This source provides jet transfer of the electrode metal without splashing during welding on modes from 80 to 160 A, allows welding in various spatial positions, it is easy to hold the bath on the ceiling and vertical planes, provides good weld formation, does not require cleaning of the weld and heat affected zone after welding. The noise level during welding is lower than the allowable values specified by the State Standard. 2 hp f-ly, 5 ill. CO С vi with 00 ate N3

Description

The invention relates to welding engineering, in particular to power sources for electric arc welding with an increased conversion frequency.

The aim of the invention is to increase the efficiency of the source by transferring the reactive energy of the inverter switching circuit to the load and reducing the noise level by providing the possibility of changing

arc current in the welding process without adjusting the inverting operating frequency, as well as improving the dynamic and mass-dimensional characteristics of the source and reducing the noise level by increasing the maximum inverting operating frequency.

FIG. 1 shows a basic electrical power supply circuit.

and a block diagram of an inverter control unit; in fig. 2 - electrical circuit diagram of the inverter; in fig. 3- inverter using a high-frequency power transformer with an additional winding; in fig. 4 shows voltage plots on various elements of the inverter and currents in some of its circuits; in fig. 5 is a simplified circuit diagram of one of the possible variants of the inverter control unit.

The power source (Fig. 1) consists of the rectifier 1 of the industrial mains voltage with the output voltage E, a serial unbalanced resonant inverter, which includes a charge, discharge 3 and inverse 4 thyristors, a working capacitor 5, a high-power power transformer 6 and two-half diode rectifier 7 with a midpoint. The latter is connected through a filter capacitor 8, an output choke 9 and a dropping diode 10 to an arc gap. The arc circuit includes current sensors 11 and voltage 12,

The inverter control unit contains devices 13 and 14 for monitoring the state of charge 2 and discharge 3 thyristor, respectively, voltage control device 15 at working capacitor 5 and comparator 16, first 17 and second 18 adjustable signal delay lines, control pulse drivers 19-21 charge 2, discharge 3 and inverse 4 thyristors, respectively, the device 22 forming an external characteristic.

The power source works as follows.

At the beginning of the next cycle of operation of the inverter (moment to, Fig. 4), the control electrode of the charging thyristor 2 receives the signal Uy from the former 19. Charging thyristor 2 turns on (diagrams U2 and 12) and the resonant charge of the working capacitor 5 to the voltage I Ucmi I E (plot Uc). The amplitude Demi and the duration of the current flow through the thyristor 2 depend on the magnitude of E and the load resistance, as well as on the voltage K o on the working capacitor 5 at the beginning of the cycle.

At the moment ti of the end of the charge on the charge of the thyristor 2, the reverse voltage U06pi I Ucmi I - Е appears, which is fixed by the device 13 of the control of the state of the charge thyristor 2. After the delay (pause) specified by the adjustable line 17 has expired TB, where rs is the nominal charge off time

thyristor 2, at time t2, control driver 20 includes discharge thyristor 3 (plot Us and 3). The resonant discharge of the working capacitor 5 (through the load) occurs. The capacitor 5 is recharged to the voltage Ucm2 (the voltage on the capacitor 5 changes sign at the time ta). The amplitude value Ucm2, as well as the duration Gy of the resonant discharge of the capacitor 5 depends on the magnitude of Ucmi and the load during this process. With a nominal load of Ucm2 “I Ucmi 1-E.

At the time t4 of the end of the flow of current through the discharge thyristor 3, a reverse voltage U06p2 Ucm2 occurs on it, detected by the device 14 of the control of the state of the discharge thyristor 3. After a certain period of time (pause tn TV) specified by the adjustable delay line 18, namely, at the time ts, the former 21 includes a reverse thyristor 4 (plot C). The resonant overcharge of the capacitor 5 begins through the primary winding of the transformer 6 (load) and the inverse thyristor 4. Simultaneously (at a signal from the output of the adjustable delay line 18), the comparator 16 begins to compare the voltage Uc on the capacitor 5 with the reference voltage 1) 0 set by the device 22 forming an external characteristic (or an operator). When the voltage Uc as a result of the resonant recharge of the capacitor 5 through the reverse thyristor 4 falls to Uo (i.e. after

time interval Tz). the comparator 16 outputs a signal to the driver 19 of the thyristor control pulses 2. The latter is turned on (the moment te, similar to the moment to). On the reverse thyristor

4, a reverse voltage appears, equal to the output voltage E of the supplying rectifier 1, and the thyristor 4 is turned off. This is where the inverter cycle ends. As a result of periodic repetition of the cycles, a alternating voltage is induced on the secondary winding of the transformer, which, after rectification with the help of the full-wave rectifier 7, is fed through a filter 8 and a reset diode 10

on the welding arc, creating a current in its circuit that pulses with a frequency f of cycles (inversion frequency).

The amplitude of the voltage Ucmi, to which capacitor 5 is charged in each

the next cycle, depends on the voltage level Uo, from which this next cycle begins; By adjusting this initial level Uo, it is possible to vary the range (Ucmi + Ucm2) of the voltage within considerable limits

on the windings of the transformer 6 and, accordingly, the load current (arc). Maintaining the same level of voltage Do on capacitor 5 at the initial moment of its charge reduces the effect of the load on the amplitudes Ucm1 and Ucm2.

The control of the arc current, and hence the formation of the required external characteristic, is possible in the traditional way - by adjusting the inversion frequency f by changing the pause etc. The frequency f (Fig. 4) is determined by the expression

f

one

T3 + Gr + 2 tn

where T3 is T3 + Gz and is limited by the limiting value f1

 before Te + Tr + 2tv

Current and voltage feedback, carried out with the help of sensors 11 and 12, allows the device 22 for forming an external characteristic to maintain a given arc burning mode by changing Do. For the case of a short-circuit arc gap, in which the depth of welding current adjustment by this method may not suffice, as well as in case of small reverse voltages on the thyristor discharge 3, when this method of current regulation becomes ineffective, the device may provide functional communication 22 with adjustable delay lines 17 and 18 (Fig. 1, not shown) for implementing said traditional method of adjusting the arc current by the inversion frequency by varying the pause duration tn.

The power source based on the inverter (Fig. 2) works in the same way as described, except that the recharging of the working capacitor 5 through the reverse thyristor 4 occurs through part of the primary winding of the high-frequency transformer 6. Such a construction of the circuit reduces the duration of current flow through the reverse thyristor 4 (decrease T3) and because of this, increase the limiting frequency f of the inversion.

The same applies to the possible variant of the power source, shown in FIG. 3, containing a high-frequency transformer 6 without a tap, but with an additional winding having a smaller number of turns than the primary one.

One of the possible implementation variants of the inverter control unit (Fig. 5), in the upper part of which is repeated for

readability diagram of the power section of the inverter (the external characteristic formation device 22 is not shown).

To shorten the description, the circuit diagram of the GI pulse generator is not disclosed, the adjustable delay lines are conventionally depicted as adjustable RC chains. With the same purpose, the operation of the control unit is described without

0 influences Zener diode VD9 and diodes VD10, VD11 (Fig. 5, dashed line). The function of these elements is that they allow the inverter to go into the well-known alternating-mode operation.

5 charge and discharge thyristors without switching on the reverse thyristor at small values of the reverse voltage on the discharge thyristor (or amplitude UCm2). The transition from one mode to another is determined by the parameters of the Zener diodes VD9 and VD5.

So, after the occurrence at ti time (Fig. 4) of the reverse voltage Uo6pi on the VS1 thyristor (which is detected by the device controlling its state, containing the diode VD1, resistor R1 and Zener diode VD4) on the base 2 of the single junction transistor VT1 occurs equal to the voltage U4 of the stabilization of the Zener diode VD4 / H30 example, 18 V), and the capacitor C1 of the adjustable RC-chain from the resistor R4 and the capacitor C1 begins to charge, which functions as the first adjustable delay line of the signal. Through given

5 time tn, equal to the constant time of this chain, the voltage on C1 reaches the pickup voltage of the single junction transistor VT1 and on the secondary winding of the output transformer T1

0 pulse generator, a thyristor control signal VS2 (moment ta) appears.

With the occurrence of reverse voltage Loop2 on the thyristor VS2 (the moment

5 t4), which is fixed by a thyristor state control device containing a VD2 diode, a resistor R2 and a Zener diode VD5, on the base of the 2 single junction transistor VT3, a voltage equal to the voltage Us stabilizing VD5 (and Us U) occurs and the charge starts A capacitor C3 of an adjustable RC-chain of resistor R6 and a capacitor C3, which performs the function of the second adjustable gapping line. After a predetermined time tn, determined by the time constant of this chain, the output pulse shaper, assembled on the transformer TK, produces a control pulse of the inverse thyristor VS3 (moment ts).

At the output of a parametric stabilizer consisting of a resistor R13 and a Zener diode VD6 and part of the voltage monitoring device on the working capacitor C of the inverter, there is a voltage from the time of the appearance of capacitor C on the capacitor C (as a result of its resonant discharge through the thyristor VS2) of a positive voltage (Fig. 4), By the time T4 the amplitude value of the voltage Ucm2 reaches (and the occurrence of the reverse voltage on the thyristor VS2), there is a voltage equal to the voltage of the uni-transistor VT2 on base 2 NIJ Ue stabilizing zener diode VD6 (wherein Ue Us and is, for example, 30 V), of course, provided that UCm2 Ue. Therefore, at time t4, the capacitor C2 of the chain R5C2 starts to charge. As a result of its charging, through the time t tn voltage Ua at the emitter VT2 set by the parameters of this chain, reaches the voltage Ue of the stabilization of the Zener diode VD8 (for example, 12 V), and Usy Us Uey, where y is the turn-on factor VT2 and, for example, 0 ,five. Since the stabilization voltage VD6 (VOV) is greater than the U3 / y value (24 V), VT2 is not included. The working capacitor C and the capacitor C4 connected to it through the diode VD3 during the pause tn are slowly discharged by the current of the stabilizer R13VD6. At the time t5 of turning on the inverse thyristor VS3, the working capacitor C begins to discharge quickly through the load, and the capacitor C4 discharges now not only with the stabilizer current R13VD6, but also with the adjustable collector current of transistor VT4.

When the voltage on the base 2 of the single junction transistor VT2 decreases to the value Ua / y (24B), i.e. After a period of time when the reverse thyristor VS3 is turned on, the single junction transistor VT2 is turned on and a control pulse appears on the output winding of the transformer T2 of the control thyristor of the charge thyristor VS1 (Fig. 4, moment t, similar to the moment to).

Obviously, the duration can be controlled by the discharge rate of the capacitor C4, i.e. current collector transistor VT4. So it is seen from the diagram that the amplitude of the collector current of transistor VT4 is determined by the pulse voltage at its base, which is fed through the isolation transformer T4 from the variable amplitude GI pulse generator and is set by the external control signal Uynp. The generator GI is synchronized by control pulses VS1 and reverse VS3 thyristors so that transistor VT4 is turned on at the instant ts of turning on the reverse thyristor VS3 and is turned off at the moment te is turned on of the charge thyristor VS1.

By changing the discharge rate of capacitor C4 by the collector current of transistor VT4, it is possible to change the duration of the time interval between turning on the reverse VS3 and charging VS1 thyristors, and this initial voltage level Uo at the working capacitor C, at which the latter is connected through the charge thyristor VS1 to the power supply inverter rectifier. Obviously, depending on the length of time provided by the circuit for the flow of current through the VS3 reverse thyristor, the value of Uo at the moment of switching on the charging thyristor VS1 can be either positive or negative (or equal to zero).

The generator GI can be built according to one of the well-known schemes of pulse amplifiers of adjustable amplitude. Real adjustable delay lines can be built on the basis of known circuits using resistor or transistor optocouplers. As for the external characteristic formation device 22 (Fig. 1), it is implemented on the basis of traditional analog or digital controller circuits.

Compared to the known power source, the proposed offer has the following advantages:

has a higher efficiency due to the beneficial use of the excess energy stored in the inductive elements of the inverter and transferred to the working capacitor, due to reloading the working capacitor through a reverse thyristor to the load. At the same time, the time provided by the circuit for switching off the charge and discharge thyristors is provided not dependent on the load and not less than the nominal turn-off time of the thyristors by setting a constant pause tn 2: rB;

allows to improve the working conditions of the welder by reducing the noise level when current changes during welding and, in particular, when welding with amplitude-modulated current. This is achieved due to the possibility of adjusting the welding current at a constant inversion frequency by changing the magnitude of the reference voltage U0;

allows you to change the welding current at high speed (transition time

the process is on the order of several charge cycles; d) e) at a constant inversion frequency;

allows you to increase the limit frequency of inversion and thereby improve the dynamic and mass-dimensional characteristics, as well as reduce the noise level, since to turn off the reverse thyristor there is no need to monitor its state and to maintain a pause corresponding to the time of its deactivation (in the proposed source the thyristor is turned off simultaneously with the inclusion of a charge thyristor). The source improves these characteristics also by further increasing the limit frequency of the inversion;

It has a simpler electrical circuit of the power unit and due to this, smaller dimensions and weight.

The source is recommended to be used for welding by a melting electrode in shielding gases at a high frequency of current modulation to ensure atomized and jet transfer of the electrode metal, as well as other types of arc welding — argon-arc, plasma, manual, etc.

Claims (3)

1. A power source for arc welding, containing a rectifier whose negative output through a charge and discharge thyristors is connected to its positive output, the cathode of the discharge thyristor through the primary winding of the power high-frequency transformer and the working capacitor with the anode of the discharge thyristor, to the secondary A mid-point diode full-wave rectifier coil with a midpoint is connected to the high-frequency power transformer winding, the output of which includes current and arc voltage sensors, cat outputs oxi are connected to the inputs of the device forming the external characteristic of the source, parallel to the charge and discharge thyristors, respectively, the inputs of the charge and discharge thyristor state control units are connected, the outputs of which are connected via adjustable delay lines of the signal with the inputs of the control thyroidor and pulse inverters, respectively, the reverse thyristor and the pulse thyristor control pulse generator characterized in that, in order to increase the efficiency of the source due to the transfer to the load of the reactive energy of the switching circuit of the inverter and reduce the level mind by the ability to change the arc current during the welding process without adjusting the working frequency of the inversion, serially connected voltage control devices on the working the capacitor and comparator, the output of which is connected to the input of the thyristor control pulse generator, the second and third inputs of the comparator are connected respectively to the output of the second adjustable delay line and the output device forming the external source characteristic, the inputs of the voltage monitoring device on the working capacitor are connected to the plates working capacitor. 2. The power source according to claim 1, that is, that the reverse thyristor is connected in parallel in the opposite direction to the discharge thyristor. 3. The power source according to claim 1, that is, in order to improve the dynamic and mass-dimensional characteristics of the power source and reduce the noise level by increasing the maximum inverting operating frequency, the primary winding of the power high-frequency transformer performed with a tap, to which the anode of the reverse thyristor is connected, the cathode of which is connected to the anode of the discharge thyristor. Setting the mode and 5y6or External characteristics of the source  but F1L.1 2 and with 4 F1 - V-I I G-Ttf U, 2 physical FIG. Sh ft C1 URB .-, VD7r -С ± Ц) Н Wu A i:  C2 Sh 5 6 g f VD12 Unum. ff / 7 W CZ3I / D13 Unum. with in UU0 / 3 W / 7 CZJ-KM Unum.