RU2168825C1 - Bridge-type single-phase transistor inverter - Google Patents

Abstract

FIELD: off-line bridge-type inverters for various secondary power supplies. SUBSTANCE: inverter has transistors, power supply with ripple capacitor at its output, load, mainly of transformer type, connected across diagonally opposite ac terminals of inverter through capacitor, load current sensor, and control system depending for its operation on negative feedback. Novelty is that through-current sensor in the form of saturable transformer is introduced in inverter circuit. Transformer has three similar primary windings and one secondary winding. One primary winding is inserted between like-polarity poles of power supply and diagonally opposite dc terminal leads of inverter. Two remaining primary windings differentially connected to first one are inserted in bridge-type transistor inverter arms having common point with one of diagonally opposite ac terminal leads of this inverter. One of mentioned windings is connected between plus of diagonally opposite dc terminals of inverter and collector of respective transistor; other winding is inserted between minus of diagonally opposite dc terminals of inverter and emitter of respectivetransistor. EFFECT: improved reliability of inverter. 2 dwg

Description

 The present invention relates to the field of electrical engineering, namely to autonomous single-phase inverters, and can be used in various secondary power sources, for example, in electric welding machines, single-phase plasmatrons, etc.

 Known single-phase bridge transistor inverters containing a transistor bridge in the power section, shunted by a reverse diode bridge and connected by a diagonal of direct current to a power source, and by a diagonal of alternating current to a load (see "Transpoket" - Austria, Catalog 1995-96, "Castolin" GmbH "- Germany," Kraftzwerg "1994-96," DS200 A1-Technotron "- Russia," Invertec "V-130-S-Lincoln-USA.) To reduce the slew rate in emergency situations between the power source and the transistor inverter, a choke shunted by a reverse diode is usually connected in series, and a smoothing capacitor is connected in parallel with the power source. Inverters in the above installations also contain load current sensors and sensors of current consumed by the inverter. The listed sensors provide protection operation at load currents and through currents exceeding the permissible value.

 A network unit is known (see certificate for utility model N 3514, 1995), where a Hall sensor is used as the current sensor consumed by the inverter, the output signal of which leads to the unit shutdown if the sum of the load current and the through current exceeds the permissible value .

 In welding machines of the inverter type of the Veriverter company (Finland), the control of through currents is carried out by parametric sensors of the inductive type installed in the monitored arms of the single-cycle inverter. The outputs of these sensors through the control and protection system act to shut down the installation.

The reasons that impede the achievement of the following technical result include the following:
- Hall sensors are difficult to calibrate and require signal amplification, which complicates the device;
- known parametric inductive sensors require autonomous sources of high frequency, also complicating the device;
- both generator and parametric known sensors do not in themselves limit the current, but only act on the control and protection system, which has its own response time, which, especially with the high steepness of the current rise characteristic of through short circuits, does not provide sufficiently reliable protection .

 The closest device of the same purpose to the claimed invention in terms of features is a "Secondary power source" (see patent N 2131640 of the authors G.G. Storekina, V.P. Shingarova, L.T. BI store No. 16, 1999), which a single-phase bridge transistor inverter with a transformer load is connected to a DC source. To eliminate the DC component in the load, a capacitor is connected in series with it. Mentioned secondary power source is taken as a prototype.

 The reasons that impede the achievement of the technical result indicated below when using both the above analogues and the prototype include the fact that the known device has insufficient protection against the through currents of a single-phase bridge transistor inverter. A simplified prototype diagram is shown in FIG. 1 and contains in the power part a single-phase bridge transistor inverter including transistors 1, 2, 3, 4, shunted by a reverse diode bridge with diodes 5, 6, 7, 8 and connected by a direct current diagonal to a power source with a smoothing capacitor 9 at the output, and a diagonal alternating current to the transformer load 10 through the capacitor 11. The current sensor 12 included in the load circuit is connected to the control system 13 according to the principle of negative feedback. The total current sensor of the inverter 14 provides inverter shutdown both during unacceptable overloads and through short circuits.

 The advantage of the prototype in comparison with analogues is the lack of a constant component in the primary load circuit at any frequency of the inverter, which allows the efficient use of a single-phase bridge circuit of the inverter with transformer load.

 EFFECT: increased reliability of a single-phase bridge transistor inverter.

 The specified technical result in the implementation of the invention is achieved by the fact that the known device contains transistors, a power source with a smoothing capacitor at the output, a load, mainly of a transformer type, connected through a capacitor to the AC diagonal of the aforementioned single-phase bridge transistor inverter, and also contains a load current sensor connected output with a control and protection system based on the principle of negative feedback. The peculiarity is that the single-phase bridge transistor inverter is equipped with a through-current sensor made in the form of a four-winding saturable transformer with three identical primary and one secondary windings, the first primary winding of a four-winding saturable transformer connected in series between one of the poles of the power source and the same output of the DC diagonal single-phase bridge transistor inverter, two other primary windings, counterclockwise connected from Solutions to the first one are included in two arms of a single-phase bridge transistor inverter, having a common point with one of the terminals of the diagonal of the alternating current of this single-phase bridge transistor inverter, one of the two primary windings being connected between the positive terminal of the diagonal of the direct current of the single-phase bridge transistor inverter and the collector of the corresponding a transistor, another primary winding is connected between the negative terminal of the DC diagonal of this bridge transistor inverter and the emitter of the corresponding transistor, and the secondary winding of the four-winding saturable transformer is connected to the corresponding input of the control and protection system.

 This allowed the preventive protection of a single-phase bridge transistor inverter from through currents and, thereby, significantly improve the reliability of the device as a whole.

 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 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 derive explicitly from the prior art for the specialist, since the influence of the transformations provided for by the essential features of the claimed invention on the achievement of the technical result is not revealed from the prior art determined by the applicant, 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 same exception due to its function and the achievement of the usual result for such an exception (simplification, reduction of mass, 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;
- creating a tool consisting of known parts, the choice of which and the connection 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 connections 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 in FIG. 2, which shows a diagram of a single-phase bridge transistor inverter.

 Information confirming the possibility of carrying out the invention to obtain the above technical result are as follows.

 The device (Fig. 2) contains in the power part a single-phase bridge transistor inverter, including transistors 1, 2, 3, 4, shunted by reverse diodes 5, 6, 7, 8, a constant voltage source with a smoothing capacitor 9 at the output. In the diagonal of the alternating current of a single-phase bridge transistor inverter, a load of 10, mainly a transformer type, is included. Moreover, a capacitor 11 and a current sensor 12 are connected in series with the load in this diagonal. The circuit also contains a through-current sensor made in the form of a saturable four-winding transformer 13 with the same primary windings 14, 15, 16 and the secondary winding 17. The first primary winding 14 is connected between one from the poles of the power source and the same-name output of the DC diagonal of a single-phase bridge transistor inverter, and the primary windings 15 and 16 are turned on counter to the winding 14. In this case, the primary A current 15 is connected between the positive terminal of the DC diagonal of a single-phase bridge transistor inverter and the collector of transistor 1 combined with the cathode of the inverse diode 5. The primary winding 16 is connected between the negative terminal of the power diagonal of a single-phase bridge transistor inverter and the emitter of transistor 3, combined with the anode of the shunt reverse diode 7 The output of the current sensor 12 and the secondary winding 17 of the four-winding saturable transformer 13 are connected to the corresponding inputs of the protection system and control Ia 18.

 The operation of the device is as follows.

 In normal operation, i.e. in the absence of through currents, the inverter operation is no different from the operation of the known single-phase bridge transistor inverters. Let, for example, diagonal transistors 1 and 2 are included in the first cycle of the inverter operation. Then the current from the plus of the power source flows along the circuit: windings 14 and 15 of the four-winding saturable transformer 13, transistor 1, capacitor 11, current sensor 12 of load 10, transistor 2, minus the power source. Since the primary windings 14 and 15 are turned on in the opposite direction and have the same number of turns, they form a bifillary, i.e., their total flux is zero.

 Thus, the inductance of the four-winding saturable transformer 13 in the current circuit of a single-phase bridge transistor inverter is zero, and the resistive resistance of its windings is negligible. In the next cycle of the inverter, transistors 4 and 3 are turned on and the current from the plus of the power source passes through the first primary winding 14, transistor 4, load 10, current sensor 12, capacitor 11, transistor 3, primary winding 16, minus the power source. Again, in the inverter current circuit, there are two bifillarily switched on primary windings 14 and 16 of a four-winding saturable transformer 13 with a common zero impedance. Note that in transient conditions, for example, when the current in load 10 drops, the reactive energy stored in the load is discharged into the smoothing capacitor 9 also always through two windings of the four-winding saturable transformer 13: either through 14 and 15, or through 14 and 16, forming bifillary. It is obvious that in the cases considered, the EMF of the secondary winding 17 is zero.

 It is known that in case of malfunctions in the control system, an increase in the turn-off time of transistors due to, for example, heating, insufficient pause when switching diagonal bridge transistors, etc. reasons, an end-to-end short circuit through series-connected transistors in two or four shoulders at once can occur. This accident is the most severe, as the current closes, bypassing the load. To reduce the slew rate of the through current di / dt, a choke shunted by a reverse diode is connected in series to the power supply circuit. However, a significant decrease in di / dt negatively affects the dynamics of the device, the dimensions of the mentioned inductor also increase. At the same time, at large di / dt, the emergency shutdown current can reach an unacceptable value, since in known devices the protection comes into effect after the current reaches the maximum permissible value and is delayed by its own operating time.

 In the present invention, when a through current occurs, the circuit operates as follows.

 If, for example, transistors 1 and 3 are simultaneously turned on, the current passes through the primary windings 14, 15, 16. An uncompensated magnetic flux is created, and the secondary winding 17 gives a signal to the protection and control system 18. In this case, the through current cannot be higher than the magnetization current four-winding saturable transformer 13, i.e. negligible and safe for inverter transistors.

 The four-winding saturable transformer 13 is calculated based on a saturation time slightly larger than the recovery time of the locking properties of the inverter transistors. In this case, if the system failure and the appearance of the through current are random and the duration of the through current is less than the recovery time of the locking properties of the inverter transistors, the through current will be limited at the level of the magnetizing current of the four-winding saturable transformer 13. With an increase in the duration of the through current pulses, the signal from the secondary winding 17 four-winding saturable transformer 13, acting on the protection and control system 18, the installation is turned off.

 It is important to note that the shutdown command occurs at almost zero through current, i.e. preventively, and the trip signal, i.e. the voltage of the secondary winding 17 is determined only by the transformation coefficient and does not require amplification.

 With a through current through transistors 2, 4, the circuit works similarly to the above. Finally, with a simultaneous through current in both branches of a single-phase bridge transistor inverter, the appearance of an uncompensated flow in a four-winding saturable transformer 13 is also inevitable, since it is almost impossible to split the current in half in the branches of a single-phase bridge transistor inverter.

 The dimensions of the four-winding saturable transformer 13 in fractions of the dimensions of the load transformer 10 are approximately t / 0.5T, where t is the recovery time of the locking properties of the inverter transistors, and T is the inverter voltage period.

 For example, at t = 1 μs and a frequency of 50 kHz, t / 0.5T = 0.1. At lower t, the four-winding saturable transformer 13 will be even smaller. Thus, the above technical result is achieved by simple means. In this case, there is no need for a common current sensor of the inverter and other any sensors of through current.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed invention:
- a tool embodying the claimed invention in its implementation, is intended for use in industry, namely in electrical engineering, in various secondary power sources;
- for the claimed device in the form described in the independent clause of the claims, the possibility of its implementation using the means and methods described in the application or known prior to the priority date 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 single-phase bridge transistor inverter containing transistors, a power supply with a smoothing capacitor at the output, a load, mainly of a transformer type, connected via a capacitor to the alternating current diagonal of the aforementioned single-phase bridge transistor inverter, and also containing a load current sensor connected to the control and protection system via negative feedback principle, characterized in that the said single-phase bridge transistor inverter is equipped with a through-through sensor made in the form of a four-winding saturable transformer with three identical primary and one secondary windings, the first primary winding of the said transformer connected in series between one of the poles of the power source and the same-name output of the DC diagonal of a single-phase bridge transistor inverter, the other two primary windings, connected in opposite directions relative to the first, are included in two shoulders of a bridge transistor inverter having a common point with one of the conclusions of the diagonal n the alternating current of this bridge transistor inverter, one of the two primary windings being connected between the positive terminal of the DC diagonal of the bridge transistor inverter and the collector of the corresponding transistor, the other primary winding is connected between the negative terminal of the DC diagonal of the bridge transistor and the emitter of the corresponding transistor, and the secondary winding saturable transformer is connected to the corresponding input of the control and protection system.

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