RU2242835C1 - Secondary power supply - Google Patents

Abstract

FIELD: electrical engineering; electric welders.

SUBSTANCE: secondary power supply has controllable power rectifier, transistor inverter whose input is connected to dc current leads of mentioned rectifier, matching transformer connected through primary winding to transistor inverter output and through secondary winding, to diode rectifier. Diode rectifier has its dc leads connected to load through series-connected smoothing reactor to organize main power supply to load. It also has standard control circuit. Novelty is that mentioned matching transformer has one more secondary winding connected through series-connected capacitor across two opposite ac terminals of diode bridge whose opposite dc terminals are connected through L-shaped filter to load in parallel with main power supply. L-shaped filter has reactor connected in series between one of leads of mentioned diode bridge and respective lead of load; filter capacitor incorporated in this filter is connected in parallel with load.

EFFECT: reduced current amplitude of inverter transistors.

1 cl, 2 dwg

Description

The present invention relates to the field of electrical engineering and is intended primarily for electric welding machines.

Widely known are secondary inverter-type power supplies intended for electric welding machines and containing in the power part a network-driven rectifier, usually in the form of a diode-thyristor bridge, a transistor inverter connected to the DC terminals of the said rectifier, a matching transformer, connected by a primary winding to the inverter output and a secondary winding connected to a diode rectifier. The DC terminals of said diode rectifier are connected to the load through a series-connected smoothing inductor. In addition, the known secondary power sources contain a control system for the network rectifier and inverter [1-6].

· ≈ 300 В напряжение на входе инвертора обеспечивает коэффициент трансформации 300:100=3.The reasons that impede the achievement of the technical result indicated below include the fact that the current amplitude in the power transistors of the inverter of known secondary power sources intended for electric welding machines is large and amounts to about one third of the current in the load, i.e. in an electric arc. This drawback is due to the fact that in order to stabilize the “burning” mode of the electric arc and its easy “ignition”, the developers of the known devices are forced to make the voltage of the secondary winding of the matching transformer very high compared to the voltage in the arc and approximately equal to 100 V. Accordingly, with the primary voltage 220 V network, rectified and smoothed to U _m ≈ 220

· ≈ 300 V, the voltage at the inverter input provides a transformation ratio of 300: 100 = 3.

With such a transformation coefficient, the aforementioned current amplitude in the power transistors of the inverter is equal to one third of the arc current. At the same time, it is known that, in fact, the voltage in the arc does not exceed 25 V when welding in air, and when welding in CO ₂ and argon, the arc voltage is much less. The disadvantage described, i.e. overstating the voltage leads, firstly, to an increase in the power and cost of the inverter transistors, and secondly, to an increase in losses in them.

The closest device of the same purpose to the claimed invention in terms of features is a welding machine Castolin GmbH. - Germany, Catalog 1994-96 [4], “Kraftzwerg”, containing in the power part a network controlled rectifier in the form of a di-single-thyristor bridge, a transistor inverter connected to its output, loaded onto a matching transformer with an output voltage of about 100 V, a diode rectifier connected to the secondary voltage input winding matching transformer, and DC output through a series-connected smoothing inductor connected to the load. The network controlled rectifier and inverter are controlled from a conventional closed-loop control system. Mentioned Castolin GmbH is taken as a prototype. The reasons that impede the achievement of the technical result indicated below are listed above and relate to both well-known analogues and the prototype.

The technical result is a decrease in the amplitude of the current in the transistors of the inverter and, as a consequence, a decrease in the power of the transistors, cost and losses.

The specified technical result during the implementation of the invention is achieved by the fact that in a known device containing a network controlled rectifier, a transistor inverter connected to the DC terminals of the said controlled rectifier, a matching transformer, connected by a primary winding to the inverter output, and connected to a diode rectifier by a secondary winding, DC outputs of which through a series-connected smoothing inductor are connected to the load and form the main source its power supply infrared, as well as containing a typical control system, the said matching transformer is equipped with an additional secondary winding connected through a series-connected capacitor with an diagonal of the alternating current of the diode bridge, the direct current diagonal of which is connected through the L-shaped filter to the load in parallel with the main power source, and -shaped filter contains a choke connected in series between one of the terminals of the aforementioned diode bridge and the corresponding terminal of the load, and a filter A capacitor connected in parallel with the load.

This allowed the function of “ignition” and stabilization of the electric arc in the zone of small currents to be assigned to an additional power source, to reduce the voltage of the main secondary winding of the matching transformer to 35 V and, thus, to reduce the current amplitude of the inverter transistors by almost three times, i.e. solve the problem.

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 to identify the set of essential distinguishing features in relation to the applicant's technical result in the claimed device set forth in the claims.

Therefore, the claimed invention meets the condition of "novelty."

To verify the conformity of the claimed invention with the condition "inventive step", the applicant conducted an additional search for solutions 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 a specialist, since the influence of the transformations provided for by the essential features of the claimed invention on the achievement of a technical result is not revealed from the prior art as defined by the applicant, in particular, the following transformations are not provided for by the claimed invention:

- addition of a known product to any known part (s) attached to it according to known rules to achieve a technical result, in relation to which the influence 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 influence 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 weight, dimensions, material consumption, increased reliability, etc.);

- 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 a quantitative characteristic (s), the presentation of such signs in relationship, or a change in its appearance. 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 in figure 1, which presents a diagram of a secondary power source and figure 2 with explanatory diagrams. Information confirming the possibility of carrying out the invention with obtaining the above technical result are as follows.

The device (figure 1) contains a network control rectifier 1, a transistor inverter 2, connected by an input to the DC terminals of the network control rectifier 1, a matching transformer 3, the primary winding of which 4 is connected to the output of the transistor inverter 2. The secondary winding 5 of the matching transformer 3 is connected to diode rectifier 6, the DC terminals of which, through a series-connected smoothing inductor 7, are connected to a load 8, including an electrode and a welding arc, and form the main source IR power. The network control rectifier 1 and transistor inverter 2 are controlled from a typical control system 9, to the input of which a current command signal i ₃ is supplied. In addition, the matching transformer 3 is equipped with an additional secondary winding 10 connected through a series-connected capacitor 11 with an ac diagonal of the diode bridge 12, which is an additional power source. The diagonal of the direct current of the diode bridge 12 through the L-shaped filter is connected to the load 8 in parallel with the main power source. The L-shaped filter contains a choke 13 connected in series between one of the terminals of the diode bridge 12 and the corresponding terminal of the load 8, and a filter capacitor 14 connected in parallel with the load 8.

The operation of the device is as follows.

When connected to the supply network at the output of the network control rectifier 1 (Fig. 1), the rectified voltage appears and smoothly increases to the maximum. The rectifier output in known circuits of secondary power sources is shunted by a large capacitor. For simplicity, this capacitor is not shown in the diagram of FIG. 1, and the charge of the charge is ensured by the control system 9. With the growth of the rectified voltage U _d1 (see FIG. 1), the voltage U ₁ at the output of inverter 2, which is close to “ rectangular ”shape and frequency of about 100 kHz. Through a matching transformer 3, this voltage is transformed into a secondary winding 5 and an additional secondary winding 10. The transformation coefficients are such that the voltage of the secondary winding 5 is about 35 V, i.e. has a certain margin with respect to the voltage drop in the welding arc, which is equal to 20-25) V in air welding. The voltage of the secondary secondary winding 10 is about 100 V. In the idle mode of the installation, the voltage drop across the capacitor 11 is practically zero and the filter capacitor 14 charges up to charges up to the voltage amplitude of the secondary secondary winding 10, i.e. up to about 100 V.

Therefore, the voltage at the load 8 (electrode) in idle is about 100 V, and the diode rectifier 6 is locked with this voltage. At the moment of touching the electrode with the area to be welded, the filter capacitor 14 starts to discharge, which ensures the appearance of a “spark”, ionization of the arc gap and maintaining the arc when the electrode “breaks off”. The arc is already supported from the main power source. The process of parallel operation of both sources to the total load is illustrated by the diagrams of figure 2: U ₁ - voltage at the output of the transistor inverter 2 (neglecting inter-pulse pauses); U ₁₁ is the voltage across the capacitor 11, with a gradual increase in the load current 8; U ₁₄ - external characteristic of an additional power source; U ₆ - external characteristic of the main power source; I _slave - zone of working load currents.

The device is characterized by the following external characteristics:

1. The external characteristic of the main power source (U ₆ in Fig. 2) is typical for a system closed by current (Fig. 1 does not show a load current sensor and current feedback circuit). The characteristic is depicted perfectly stiff. In reality, it has a slight slope due to the impedance of the mains and the internal impedance of the device itself.

2. The external characteristic of the additional power source (U ₁₄ in Fig. 2) at load currents I _n ≤ I _{cr is} linear and rigid, since the capacitor 11 does not have time to charge in time τ (diagram 1 in Fig. 2) to an additional secondary voltage amplitude winding 10 and therefore (neglecting negligible losses in the capacitor) does not affect the value of the average rectified voltage U ₁₄ . When I _d > I _cr (chart 3 in figure 2), the capacitor 11 is charged to the amplitude in time t ₁ <τ (chart 4 in figure 2). The amplitude of the rectified voltage across the capacitor 11 at I _d = I _cr

since over time τ the load current can be considered unchanged (τ ≈ 10 ^-5 s). Similarly, the voltage amplitude in mode I> I _cr

Since the voltage amplitude U _m in the compared modes is the same, expressions (1) and (2) can be equated:

But in accordance with diagram 4 in figure 2 t ₁ / τ = U _{d (t1)} / d _(τ) , where U _d is the average rectified voltage. Therefore, I _cr / I _t = U _{d (t)} / d _(τ) , whence I _cr · U _{d (τ)} = I _t · U _{d (t)} = const for any t <τ.

Thus, in zone I _cr <I <I _{slave min, the} additional power source has an external characteristic of a hyperbolic type with constant power in the load: P _d = U _d · I _d = const, which is ideal for an electric arc in air.

At I> I, the _{slave min the} additional source is locked, since its voltage is less than the voltage of the main source, and finally, at I = I _{max the} voltage of both sources approaches zero already under the influence of current feedback in the inverter control system.

From the above diagrams it can be seen that in the area of the operating load (welding) currents, an additional source, i.e. diode bridge 12 is locked. At the same time, a relatively high voltage in idle mode and low currents provides easy “ignition” and arc maintenance at low currents.

In well-known secondary power sources, including the prototype, the voltage of the secondary winding of the matching transformer, as described above, is approximately 100 V. 3 and, accordingly, the amplitude of the current in the transistors of the inverter is equal to 1/3 of the load current. For example, at a load current of 200 A, the current (in amplitude) of the transistors of known devices will be 200 / 3≈ 67 A.

In the proposed device, the voltage is reduced to 35 V, which means that when the load current is the same as in the known devices, the current amplitude in the inverter transistors will be 100 / 35≈ 2.85 times less, which is very significant, since power transistors or transistor composite modules firstly, they constitute an essential part of the total cost of the device; secondly, a decrease in current reduces losses. Note that the losses in the additional power source are negligible, since it turns on only for a short time. It should be noted that to translate the proposed device in the welding mode in a CO ₂ or argon medium, it is sufficient to disconnect the additional secondary winding 10 of the matching transformer 3, since in these modes a rigid external characteristic is required and an increased voltage is not required for arc “ignition”. Thus, the proposed device is not inferior to the known in the sense of versatility and, at the same time, has significant advantages in the welding mode in air: the current of the transistors of the inverter 2 is almost three times lower than the current (amplitude) in the known devices, and the conditions for “igniting” the electric arc even somewhat improved, since the touch of the electrode to the welded part is accompanied by a forced discharge of energy stored in the filter capacitor 14.

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 claims, 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 perceived by the applicant technical result.

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

Sources of information

1. DS-200 AL - Technotron. - Russia, catalog, 1995

2. Transpoket. - Austria, catalog, 1995-96

3. Invertec V-130-S - Linkoln-USA (1997).

4. Castolin GmbH. - Germany, “Kraftzwerg” - 1994-96.

5. Secondary power source (US Pat. No. 2131640 dated 01/12/98, authors Magazin GG, Shingarov VP, Magazin L.T.).

6. Storekeeper A.G., Storekeeper L.T., Storekeeper G.G. Correction of power factor of secondary power sources // Electrical Engineering, No. 5, 2001, p. 40 ... 42.

Claims (1)

A secondary power source, mainly for electric welding machines, containing a network controlled rectifier, a transistor inverter connected to the DC terminals of the aforementioned network controlled rectifier, a matching transformer, connected by a primary winding to the output of a transistor inverter, and connected to a diode rectifier by a secondary winding, DC outputs which through a series-connected smoothing inductor are connected to the load and form its main source power supply, as well as containing a typical control system, characterized in that the matching transformer is equipped with an additional secondary winding connected through a series-connected capacitor with an diagonal of the alternating current of the diode bridge, the direct current diagonal of which is connected through the L-shaped filter to the load in parallel with the main power source, and The L-shaped filter contains a throttle connected in series between one of the terminals of the diode bridge and the corresponding terminal of the load, and a filter cond A sensor connected in parallel with the load.

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