RU2131640C1 - Secondary power supply - Google Patents

Abstract

FIELD: electrical engineering, in particular, inverting power supplies for manual electric welding in argon and carbon dioxide mix. SUBSTANCE: device has single- phase bridge transistor inverter, which is connected to power rectifier and loaded to primary winding of power transformer in series of capacitor. Secondary winding supplies load through rectifier with zero terminal. Load and soothing choke are by-passed by reverse diode. Control system has current detector and setter, comparator and inverter control unit. Said unit is designed as active generator of alternating current of rectangular shape, high frequency and is supplied from power rectifier and is loaded by switching transformer, which four secondary windings are connected in series opposing to windings of pulse saturating transformer and is connected to bases of transistors of inverter. EFFECT: simplified design, increased reliability, decreased switching losses. 4 dwg

Description

 The invention relates to the field of electrical engineering, and in particular to inverter-type power supplies intended primarily for manual electric welding, welding in an argon and carbon dioxide environment. Inverter-type electric welding machines are widely known that contain a network diode rectifier with a smoothing capacitor at the output and a transistor inverter (modulator) with reverse diodes connected to this rectifier and loaded on a power transformer (see "Transpocket-1400" - Austrian production, catalog 1995-96, "Castolin GmbH" - Germany, Krafzwerq, 1994-96, "DS 200 A1" - Technotron, Russia; InvertecV 130-S "- Lincoln, USA).

 The secondary winding of the power transformer through a diode rectifier is connected to the load and? together with a smoothing inductor connected in series in its circuit, it is shunted by a reverse diode. The control system includes a sensor and a current setter, as well as a closed-loop control system using a pulse-width (PWM) method. The reasons that impede the achievement of the technical result indicated below when using known devices include the fact that it is impossible to use an economical push-pull bridge circuit of the inverter due to the inevitable asymmetry of the voltage on the power transformer at high frequencies, as well as the need to use transistor modules with optocoupler isolation and individual bias sources for each module, which complicates and increases the cost of installation. It should also be noted that the losses in the module (composite transistor) are slightly greater than in a single transistor.

 The closest device of the same purpose to the claimed invention in terms of features is a secondary power source based on resonant bridge inverters, in which a capacitor is connected in series with the primary winding of the power transformer at the output of the inverter (see O. G. Bulatov and other Thyristor-capacitor sources power supply for electrical technology, Chapter 2. - M .: Energoatomizdat, 1989) and adopted as a prototype.

For reasons that impede the achievement of the following technical result when using the known device adopted for the prototype, is that in the known device
1. Impulse transformers are practically not applicable for galvanic isolation; optocoupled transistor modules are required.

 2. Individual transistor bias sources are required. This complicates the installation as a whole and increases switching losses.

 To expand the load range in the direction of decreasing and to increase the operating frequency of the inverter, thyristors (in low power installations) are usually replaced by transistor modules, and to reduce the number of diodes and losses in them, the output bridge rectifier is replaced by a zero-rectifier rectifier. A simplified prototype diagram with the above-mentioned non-fundamental changes is shown in FIG. 1 and contains in the power part a network diode rectifier (not shown for simplicity), a smoothing capacitor 1 at the output of the rectifier, a bridge transistor inverter 2, 3, 4, 5 connected to it with a reverse diode bridge 6, 7, 8, 9, loaded on the primary winding 10 of the power transformer 11 with a capacitor 12 connected in series to the circuit of this winding or a group of capacitors switched to change the capacitance. The secondary winding 13 of the power transformer 11 is connected to the diode rectifier 14, 15 according to the circuit with a zero output. The rectifier output is connected to a load 16, shunted, together with a series-connected smoothing inductor 17, a reverse diode 18. The power part of the prototype circuit is given in the aforementioned book of OG Bulatov, in Fig. 3.3, a, p. 70 (thyristor version). The control system comprises a comparator 19 connected by an inverse input to a current sensor 20, a direct input to a current master 21, and an output to an input of a control unit inverter 22, the outputs of which are connected to the corresponding control inputs of transistor modules 2, 3, 4, 5, and the input is with one of the outputs of the power supply 23. A control system with an identical structure is shown in Fig. 5.4 of the mentioned book of Bulatov. Instead of the generally accepted term “comparator”, the term “comparison scheme” is adopted in the book. The remaining elements relate to the inverter control unit. The principle of operation of the system is the classic principle of "systems with negative feedback in an adjustable coordinate." Its description is given on page 118 of the mentioned book.

The important advantages of the prototype compared with the above analogues include:
1. The absence of a constant component in the output voltage of the inverter, which allows the use of a small-sized transformer with a core without a gap as a power one.

 2. Doubling the amplitude of the voltage at the load at a constant average straightened value, which facilitates the ignition of the arc and allows you to almost halve the amplitude of the current in power transistors.

 3. Switching current is carried out in the range of workloads not by transistors of the inverter, but by a capacitor, which reduces overvoltage and loss.

 4. Constant power in the load.

 The invention consists in the following.

 The technical result is the simplification of the power source, increasing its reliability, reducing switching losses. The specified technical result in the implementation of the invention is achieved by the fact that in the known device including an inverter connected to a network rectifier with a smoothing capacitor at the output and made in the form of a single-phase transistor bridge with a reverse diode bridge, loaded on the primary winding of the power transformer, in series with which the capacitance is connected from one or more capacitors connected by a switch to different groups of different total capacitance, and the secondary winding of the mentioned forces of the transformer is connected to the diode rectifier in a single-phase circuit with a zero output, the output of which is connected in series to a load and a smoothing inductor, shunted by a reverse diode, and a control system as part of a comparator connected by an inverse input to the output of a current sensor connected to one of the arms of the diode rectifier, direct input with current setter, and output with inverter control unit.

 The peculiarity lies in the fact that the inverter control unit is made in the form of a rectangular high-frequency alternating current generator with a frequency-setting R - C chain of two series-connected resistors and a capacitor, and a diode bridge with a constant diagonal is connected in parallel to one of the mentioned resistors current, shunted in the conducting direction by a transistor, the control input of which is shunted by a negative bias resistor and is connected to ode to the aforementioned comparator, the collector-base junction is shunted by a positive bias resistor, the power input of the said oscillator is connected directly to the said smoothing capacitor, two identical half-windings of a switching transformer are connected to the output of the oscillator, its four identical secondary windings are connected counter-in-series each to one of four identical secondary saturating pulse transformer windings and through current-limiting resistors are connected to bases with corresponding transistors of said inverter, and the primary winding of a saturable pulse transformer is connected through a current-limiting resistor and a diode to the fifth secondary winding of a switching transformer and is shunted by a reverse diode. This allowed us to simplify the circuit by excluding the power supply with bias sources from it, and to provide direct control of the inverter power transistors without modules with optocoupler isolation, i.e. increase reliability, reduce losses in power transistors.

 The analysis of the prior art by the applicant, including a search by patent and scientific and technical sources of information and identification of sources containing information about analogues of the claimed invention, allowed to establish that the applicant did not find an analogue characterized by features identical to all the essential features of the claimed invention. The definition from the list of identified analogues of the prototype, as the closest in the set of essential features of the analogue, allowed us to identify the set of essential distinctive features perceived by the applicant in the claimed device set forth in the form of the invention.

Therefore, the claimed invention meets the condition of "novelty." To verify compliance of the claimed invention with the condition "inventive step", the applicant conducted an additional search for known solutions in order to identify signs that match the distinctive features of the claimed device from the prototype. The search results showed that the claimed invention does not follow explicitly from the prior art for the specialist, since the prior art determined by the applicant did not reveal the effect of the transformations provided for by the essential features of the claimed invention on the achievement of the technical result, in particular, the following transformations are not provided for by the claimed invention:
- addition of a known product by any known part (s) attached to it according to known rules to achieve a technical result in respect of which the effect of such additions is established;
- replacement of any part (s) of a known product with another known part to achieve a technical result, in respect of which the effect of such a replacement is established;
- the exclusion of any part (element) of the product with the simultaneous exclusion of its function and the achievement of the usual result for such exclusion (simplification, reduction of mass, dimensions, material consumption, increased reliability and more durable);
- an increase in the number of elements of the same type to enhance the technical result due to the presence in the tool of just such elements;
- the implementation of a known tool or part (s) of a known material to achieve a technical result due to the known properties of this material;
- the creation of a tool consisting of known parts, the choice of which and the relationship between them are based on known rules, recommendations and the technical result achieved in this case is due only to the known properties of the parts of this tool and the relationships between them.

 The described invention is not based on a change in the quantitative characteristic (s), the presentation of such signs in relationship, or a change in its form. This refers to the case when the fact of the influence of each of these characteristics on the technical result is known and new values of these signs or their relationship could be obtained on the basis of known dependencies and patterns.

 Therefore, the claimed invention meets the condition of "inventive step".

 The invention is illustrated by drawings, in which: FIG. 2 is a diagram of a secondary power source, FIG. 3 is a timing diagram of stresses, in FIG. 4 - external characteristics at various levels of welding power.

 Information confirming the possibility of carrying out the invention to obtain the above technical result is as follows. The device (Fig. 2) contains in the power part a smoothing capacitor 1 connected to the output of a network rectifier, not shown in the diagram for simplicity, an inverter as part of a transistor brain 2, 3, 4, 5; a reverse diode bridge 6, 7, 8, 9 connected to a network rectifier of diagonally direct current, a power transformer 10, the primary winding of which 11 is connected in series with a capacitor 12 in a diagonally alternating current of the transistor bridge, and two secondary half-windings 13 and 14 are connected to a single-phase diode to the rectifier 15, 16 according to the circuit with a zero output, to the output of which a load 18 is connected in series with the smoothing reactor 17, shunted together with the inductor by a reverse diode 19. In one of the arms of a single-phase diode rectifier a current sensor 20. The control system contains an inverter control unit as part of a typical rectangular alternating voltage generator 21, connected to the rectifier by an input through the opening contact 22 of the protection relay (for simplicity, the relay coil is not shown), and the output to a switching transformer 23 with two identical primary windings 24 and 25. The secondary four identical windings of this transformer 26, 27, 28 and 29 are connected counter-in-series each with secondary windings 30, 31, 32 and 33 pulse saturating transformer 34, the primary winding of which 35 through a diode 36 and a current-limiting resistor 37 is connected to the fifth secondary winding 38 of the switching transformer 23 and is shunted by the reverse diode 39. The frequency-generating circuit of the oscillator 21 contains two resistors 40, 41 and connected in series to the control input of the oscillator capacitor 42. Resistor 41 is also connected to the diagonal of the alternating current of the diode bridge 43, 44, 45 and 46, the diagonal of the direct current of which is shunted in the conducting direction of the tra a resistor 47, the control input of which is shunted by the resistor 48 and connected to the output of the comparator 49, and the collector – base circuit is shunted by the resistor 50. In addition to the comparator 49, the control system includes a current switch 51 and the said current sensor 20. Moreover, the output of the current sensor 20 is connected to the inverse, and the output of the current master 51 to the direct inputs of the comparator 49. To limit the current in series in the circuit without transistors of the inverter, resistors 52, 53, 54 and 55 are included.

 The operation of the device is as follows.

When the unit is turned on, the capacitor 1 is charged and the oscillator 21 through the switching transformer 23 produces a rectangular voltage U ₁ (see diagram 1 in Fig. 3) with a maximum operating frequency, since the transistor 47 is unlocked by a positive bias signal through a resistor 50, and The frequency setting circuit 40-41-42 has a minimum time constant of RxC. At the same time, a pulse saturable transformer 34 generates pulses, the amplitudes of these pulses being approximately twice as large as the voltage amplitude U ₁ (curve 2 in Fig. 3), and the duration t _of these pulses is equal to the recovery time of the locking properties of the power transistors 2, 3, 4, 5 inverter. As a result of the algebraic summation of the voltages of the secondary windings of the transformers 23 and 34, a voltage with a large by t _{in the} negative half-cycle is obtained (curve 3 in Fig. 3), supplied to the base of the inverter power transistors. This form of voltage ensures maximum use of the inverter voltage and, at the same time, a clear negative bias of the transistors during the non-working half-cycle, which, in turn, guarantees high noise immunity without additional sources of negative bias. In the diagonal of the inverter’s alternating current, as a result of summing the voltages of different arms, voltage U _{2 is formed} (curve 4 in FIG. 3), supplied through a capacitor 12 to the winding 11 of the power transformer 10. The presence of a capacitor 12 provides a doubling of the voltage amplitude (curve 5 in FIG. 3) at operating load currents, i.e. during welding, and with increasing current, the voltage amplitude does not decrease (only the average and effective values decrease). Thus, favorable conditions are provided for ignition and stable burning of the arc. In addition, the capacitor eliminates the DC component of the voltage due to the inevitable asymmetry of the inverter and eliminates the saturation of the transformer with decreasing frequency. As the load current increases, the signal from the current sensor 20 increases and at a current equal to the specified one, this signal becomes larger than the signal with the current master 51, the transistor 47 goes out of saturation and starts to lock. The resistance of the frequency setting chain increases, since the resistor 41 is unblocked. As a result, the frequency and the external characteristic of the source with a natural hyperbolic decrease - section 1 switches to steeply falling section 2 (see Fig. 4). The intersection point of curve 2 with line 3, which is the voltage drop in the internal resistance of the source, network and welding wires, that is, the total voltage drop to the point of short circuit characterizes the maximum value of the short circuit current. Hyperbola 1 shows that at a given value of the capacitance of the capacitor 12, the welding power is constant before the start of current limitation. Moreover, even when the control system opens, for example, due to a malfunction, the power will remain constant and, therefore, constant, up to a short circuit, the current consumed from the network will be. During current limiting operation (curve 2 in Fig. 4), the power decreases as the current increases to a short circuit current (i $\genfrac{}{}{0ex}{}{\text{*}}{\text{short}}$ in FIG. 4). By changing the current setpoint of the setpoint 51, it is possible to change the current limiting setting (curve 2 'in Fig. 4) over a wide range, however, it is impractical to expand the frequency range of the oscillator 21 within more than 2.5: 1, since current pulsations in the circuit increase with decreasing frequency of the load and the dimensions of the transformer 23 are slightly increased. Note that the dimensions of the power transformer 10 do not affect the frequency regulation downward from the maximum value, since with an increase in the load current, the duration of the recharging of the capacitor 12 for any frequency decreases (see curve 6 in Fig. 3).

To expand the limits of current control with a downward frequency range, it is advisable to stepwise switch capacitance 12. For example, only two capacitors with a capacitance ratio of 1: 2 give four steps of welding power: 1 ^* , 0.66 ^* , 0.33 ^* , 0.22 ^* (see curves 4, 5, 6 in Fig. 4). Inside each stage, the current regulator 51 continuously regulates.

 When the load current exceeds the permissible value, the overcurrent relay, for example a reed relay, is activated. Its coil (not shown for simplicity) can be connected to the output of the current sensor 20. Contact 22 is opened in the power supply circuit of the oscillator. The control voltage generation stops and the inverter transistors are locked.

Thus, the above information indicates the following conditions are met when using the claimed device:
- a tool embodying the claimed device in its implementation, is intended for use in industry, namely in the field of electrical engineering;
- for the claimed device in the form as described in the independent clause of the stated form of the invention, the possibility of its implementation using the means and methods described in the application is confirmed;
- a tool embodying the claimed invention in its implementation, is able to ensure the achievement of the perceived by the applicant technical result.

 Therefore, the claimed invention meets the condition of "industrial applicability".

Claims (1)

 A secondary power source, including an inverter connected to a network rectifier with a smoothing capacitor at the output and made in the form of a single-phase transistor bridge with a reverse diode bridge, loaded onto the primary winding of the power transformer, in series with which a capacitance of one or more capacitors connected by a switch to various groups of different total capacitance, and the secondary winding of the said power transformer is connected to a diode rectifier in a single-phase circuit with a zero output, the output of which is connected in series to a load and a smoothing inductor, shunted by a reverse diode, and a control system consisting of a comparator connected by an inverse input to the output of a current sensor connected to one of the arms of the diode rectifier, a direct input to a current regulator, and output - with an inverter control unit, characterized in that the said inverter control unit is made in the form of a square-wave high-voltage alternator with a frequency input an RC chain of two series-connected resistors and a capacitor, and a diode bridge with a DC diagonal shunted in the conducting direction by a transistor connected to an output of the aforementioned negative bias resistor and connected to the output of the aforementioned comparator is connected in parallel to one of the aforementioned resistors, the transition collector - the base is shunted by a positive bias resistor, the power input of the mentioned oscillator is connected directly to the mentioned at the smoothing capacitor, two identical primary half-windings of a switching transformer are connected to the output of the oscillator, its four identical secondary windings are connected in opposite each other to one of four identical secondary windings of a saturable pulse transformer and are connected via current-limiting resistors to the bases of the corresponding transistors of the inverter mentioned, and the primary winding a saturable pulse transformer connected through a current limiting resistor and a diode to This secondary winding of a switching transformer and is shunted by a reverse diode.

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