WO2018108876A1

WO2018108876A1 - Protection arrangement for protecting a transformer, and method for protecting transformer

Info

Publication number: WO2018108876A1
Application number: PCT/EP2017/082367
Authority: WO
Inventors: Ansgar Schuler
Original assignee: TRUMPF Hüttinger GmbH + Co. KG
Priority date: 2016-12-13
Filing date: 2017-12-12
Publication date: 2018-06-21
Also published as: DE102016124233A1

Abstract

In a protection arrangement (1) for protecting a transformer (2), an AC source (6) and/or AC sink (6), comprising a transformer (2), of which one winding (3) is connected to an AC source (6) or to an AC sink via a first and a second line (4, 5), a DC measuring arrangement (7) is connected electrically in parallel with one of the lines (4, 5), the inductance value of said DC measuring arrangement being greater than the inductance value of the first or of the second line (4, 5) and said DC measuring arrangement having a DC current measuring device (12).

Description

Protective device for protecting a transformer and method for the

Protection of a transformer

The invention relates to a protective arrangement for protecting a transformer, an AC source and / or an AC sink, comprising a transformer whose one winding is connected via a first and second line to an AC source or an AC sink.

Furthermore, the invention relates to an AC power source or AC sink with a transformer and such a protection arrangement.

Furthermore, the invention relates to a method for protecting a transformer connected via a first and a second line to an alternating current source or alternating current sink, and / or for protecting the alternating current source or alternating current sink. Such or similar arrangements and / or methods are for. B. known from the following publications: GB 1 513 038, US 7,852,647 B2, US 2015/0204918 AI, JP S59-174 277A, FR 2 868 844 Bl, DE 10 2007 013 634 AI, DE 196 48 696 AI, DE 693 09 168 T2. When a transformer is operated on an AC power source or an AC sink, often a DC component also occurs. This DC component can cause the transformer to saturate. Losses also increase due to the DC component in the transformer before it reaches saturation. This must be prevented. The DC component and the saturated transformer can also damage the AC source or AC sink.

Control methods have been developed with which the DC component can be set by a controllable AC source or sink. However, the DC component often varies with difficulty, predictably, by external influences, e.g. Load change, temperature, etc. It would be advantageous to control the DC component, that is to say a control as a function of a measured value of the DC component. The higher the requirements for reducing the leakage line, the more precise such a regulation should be.

It is therefore necessary to be able to measure the DC component with sufficient accuracy. For this purpose, e.g. in a transformer for 500 A AC at 50 to 100 KHz, an all-current measurement (measurement of AC and DC share together) only sufficient if this is able to detect with high accuracy and small DC currents, since such a transformer already at very low direct currents (1 to 5 amperes) can reach saturation.

In conventional current transformers (current measuring devices), which are suitable for measuring the total current, however, the offset is already in the range of a few amperes. They are therefore not sufficiently accurate for a DC measurement in the range 1 to 5 amperes.

Object of the present invention is therefore an arrangement for protecting a transformer, an AC power source and / or a To provide AC sink, with the DC components can be measured with sufficient accuracy in order to then be able to compensate.

This object is achieved by an arrangement having the features of claim 1 and by methods or arrangements with the features of the independent claims. Advantageous developments can be found in the features of the subclaims, the following description and the drawings.

Disclosed is a protection arrangement for protecting a transformer, an AC power source and / or sink, comprising a transformer whose one winding is connected to an AC source or AC sink via first and second lines, one DC line electrically connected to one of the lines is connected in parallel whose inductance value is greater than the inductance value of the first or the second line and having a DC current measuring device. Accordingly, a high-inductance DC current measuring device is connected in parallel with the low-inductance main current flow via the first and second line. Depending on how their direct current conductance relates to the direct current value of the main current flow, proportionally a proportion of the total DC current will move through this DC current measuring device. It is therefore possible to decouple only a portion of the direct current. It can be a share of approx. 10% of the total DC current is passed through the DC current measuring device. For a very good measurement of the DC component is possible and thus a very good control of the DC component. However, since there is hardly any AC current flowing through this current measuring device due to the very high AC conductance, a DC current measuring device having a high resolution with a small measuring range can now be used. The offset value and the accuracy of such a DC current measuring device depend on the measuring range. Since the measuring range is significantly reduced by the measuring arrangement, the circumstances for the DC current measurement are much cheaper than in known solutions. In particular, the current direction of the DC component can thus be determined reliably. That's up for an accurate and reliable scheme minimal power very helpful. As a further advantage, it has been found that it is no longer necessary with the arrangement according to the invention to break open the low-inductance main current flow in the first or second line in order to provide a current measuring device in one of these lines. Until now, this was necessary for the measurement of the total current and had led to some negative effects, such as stray inductances, stray fields, losses, heat generation, asymmetries, etc. These disadvantages have therefore also been overcome. Additional DC blocking capacitors can be dispensed with.

A DC line of the DC measuring arrangement may have an inductance value which is greater than the inductance value of the first or the second line. By providing a corresponding DC line, the inductance value of the DC measuring arrangement can be increased.

An AC power source or sink may be a bridge circuit of transistors, in particular IGBTs or MOSFETs, which are suitably driven by a controller. Thus, such a bridge circuit can be operated both as an AC source and as an AC sink.

The inductance value of the DC measuring arrangement can be at least a factor of 10, in particular at least a factor of 100, greater than the inductance value of the first or the second line. The greater the inductance value, the safer it can be avoided that an alternating current component flows via the DC measuring arrangement.

To increase the inductance value of the DC measuring arrangement, it can be provided that the DC measuring arrangement has a throttle. The throttle may have an electrical conductor, for example made of copper, with a large cross-section. The cross section may in particular be greater than 0.5 mm ² , in particular greater than 1 mm ² , in particular greater than ² mm ² . In particular, the electrical conductor can have a very low ohmic resistance. The ohmic resistance may in particular be less than 0.1 ohm, in particular less than 0.05 ohm, in particular less than 25 ohm. This ladder can be from be surrounded by an inductance-increasing device, in particular iron or ferrite.

The DC measuring arrangement, in particular its DC line, can have a conductance which is greater than 1% of the conductance of the first or the second line. This can ensure that a sufficiently large proportion of the DC current flows through the DC measuring arrangement, so that the entire DC component can be determined with sufficient certainty, in particular the current flow direction. The conductance of the DC measuring arrangement can be greater than the conductance of the first or the second line by a factor of 0, 1, preferably by a factor of 10.

Furthermore, a control device can be provided which is connected to the DC measuring arrangement and is set up to control a direct current detected by the DC current measuring device, in particular to values of less than 1 A, in particular less than 0.5 A, in particular less than 0.2 A. Thus, the transformer can be prevented from saturating due to undesired direct current.

In this context, it is particularly advantageous if the control device is connected to an AC power source or sink. In this case, the control device may be connected to the AC power source or sink, which is connected via the first and second line to a winding of the transformer. However, it is also conceivable that the control arrangement is connected to an AC power source or sink, which is connected to the other winding of the transformer. The control device may be connected to the AC power source or sink such that it can drive them. It can regulate the DC so. This can be done in particular by pulse width modulation.

The DC measuring arrangement can be connected to the first or the second line at two connection points. In this case, the inductance value of the DC measuring arrangement is preferably greater than the inductance value of Line section of the first or the second line between the connection points. Also, the conductance of the DC measuring arrangement is preferably greater than 1% of the conductance of the first or the second line between the two connection points. The connection points can basically lie anywhere along the first or second line. Preferably, however, the connection points are in the region of the terminals of the first or the second line to the winding of the transformer and the AC power source or the AC sink.

The scope of the invention also includes the AC source and / or the AC sink with the transformer and one of the protection arrangements previously described for protecting the transformer.

The invention also includes a method for protecting a transformer connected to an AC or AC sink via first and second leads, and for protecting the AC source or AC sink, wherein a DC current flowing between the transformer and AC source or AC sink is at least partially protected is coupled by a DC line to the first or the second line is electrically connected in parallel and the DC current is measured in the DC line. This makes it possible to obtain very accurate information about the DC current and to be able to intervene when needed in order to prevent saturation of the transformer.

Saturation of the transformer can be avoided, in particular, by at least partially correcting the DC current flowing between the transformer and the alternating current source or alternating current sink by changing the control of the alternating current source or sink as a function of the DC current measured in the DC line. This can be done in particular by pulse width modulation. To ensure that a sufficiently small portion of the AC current flows through the DC line, the inductance of the DC line can be increased by inserting a choke into the DC line.

Further features and advantages of the invention will become apparent from the following description of an embodiment of the invention with reference to the figures of the drawing, the invention essential details and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

A preferred embodiment of the invention is illustrated in the schematic drawing and is explained below with reference to the figures of the drawing. Show it :

Fig. 1 is a highly schematic representation of a protective arrangement for

Protection of a transformer;

Fig. FIG. 2 is an overview diagram, such as a protective device as

Sub-component of the protection device can be realized on a printed circuit board;

Fig. 3 a position of a printed circuit board on which the protective device is realized.

FIG. 1 shows a protective arrangement 1 with a transformer 2, the winding 3 of which is connected via a first line 4 and a second line 5, which are arranged to transmit an alternating current signal, to an alternating current source 6 or an alternating current sink 6. An AC power source 6 in the sense of this invention is a device for generating AC power or for converting any power into an AC power. The AC power can, for example, from DC power by means of this AC power source. 6 be generated. For this purpose, different electromechanical and electronic arrangements are suitable. A typical arrangement is a bridge circuit, in particular a full bridge circuit, as shown in Fig. 2 as a switching bridge with four switching elements 6a to 6d. An AC sink 6 in the sense of this invention is a device for consuming, converting or subtracting AC power. The AC power can be converted, for example by means of this AC sink 6 in DC power. For this purpose, different electromechanical and electronic arrangements are suitable. A typical arrangement is a bridge circuit, in particular a full bridge circuit, as shown in Fig. 2 as a switching bridge with four switching elements 6a to 6d. Parallel to the first line 4, a DC measuring arrangement 7 is connected. The DC measuring arrangement 7 in this case comprises a DC line 8, which is connected to connection points 9, 10 with the first line 4.

The lines 4 and 5 can be performed as bifilar as possible in order to generate the lowest possible stray fields and to realize the lowest possible inductance. Inductors smaller than 10 μΗ have been found to be required. In particular, they can be guided on a printed circuit board (PCB) in parallel planes largely congruent. This makes it possible to achieve inductances of less than 2 μΗ, which is even more advantageous. You should also have the lowest possible ohmic resistance to minimize losses. Therefore, they can have the largest possible cross-section. This can be realized in a printed circuit board, inter alia, by a conductor track which is as wide as possible in terms of area, in particular as far as possible the entire width of the printed circuit board filling conductor track. For the DC measuring device 7 then only limited space remains on the circuit board. Nevertheless, the conductance should not be too low for the DC measuring arrangement 7, because the DC current is distributed according to the conductance values on the line 4 and DC measuring arrangement 7. If a share of about 10% of the total DC current is passed through the DC measuring device 7, a very good measurement of the DC component is possible and thus a very good control of DC component. For this purpose, the conductance of the DC measuring arrangement 7 should be about 10% of the conductance of the line 4.

The DC measuring arrangement 7 furthermore comprises a throttle 11, by means of which the inductance value of the DC measuring arrangement 7 is increased. In addition, the DC measuring device 7 includes a DC current measuring device 12. A DC current measuring device is a device that can measure DC current. It determines the DC current to be measured with the aid of a sensor and generates a measurement signal, which is dependent on the measured current and is usually proportional, which can be used by a control system. The measurement signal can be analog or digital. The person skilled in various embodiments of sensors for detecting DC are known. You can work according to different principles, eg. Determining a voltage drop across a shunt, detecting a magnetic field generated by the current, or detecting heat generated by the current or others. The current through the DC measuring device 7 is equal to the current through the inductor 11 and the DC current measuring device 12. This is connected to a control arrangement 13, which can control the AC source or sink 6 based on the measured DC current value, so that the DC current flowing through the DC measuring device 7 can be regulated (reduced).

Because the inductance value of the DC measuring arrangement 7 is much greater than the inductance value of the first line 4, the alternating current component can be reduced compared to the DC component in the DC measuring arrangement 7. With an inductance value of the DC measuring arrangement 7, which is greater by at least a factor of 100 than the inductance value of the first line 4, very good results can already be achieved. In a preferred embodiment, the inductance value of the DC measuring arrangement 7 is larger than the inductance value of the first line 4 by a factor of 1000. The inductance value is decisively influenced by the throttle 11.

The AC power source or AC sink 6 typically operates at frequencies greater than 10 kHz, outside of the audible range for humans. A frequency of approx. 50 kHz. The transformer is designed for currents greater than 200 A AC. Preferably, the transformer is designed for currents greater than 500 A AC. At such frequencies and currents, low-cost, low-weight, low-loss components can be used.

With appropriate adjustment of the inductance value of the DC measuring arrangement 7, an alternating current which is less than 500 mA flows via the DC measuring arrangement 7.

Furthermore, the conductance of the DC measuring arrangement is greater than at least 1% of the conductance of the first line 4, in particular between the connection points 9, 10, so that it is ensured that a significant DC component via the DC measuring arrangement 7 and not via the first line. 4 flows. In this way, a portion of the DC current flowing between the AC power source 6 and the transformer 2 can be coupled out.

FIG. 2 shows a protective device Γ realized as part of the protective arrangement 1 according to FIG. 1 on a printed circuit board 20. For the AC power source or sink 6 as a switching bridge with four switching elements 6a to 6d suitable connection points are provided. The connection points of the switching bridge and thus of the alternating current source or sink 6 are connected via a line 21 to a positive DC connection 22 and via a line 23 to a negative DC connection 24.

The first line 4 and the second line 5 are connected to the connection point 9, wherein the connection point 9 also represents the connection of the transformer 2, which is not shown and can be connected as inductively as possible with the circuit board 20 at the connection point 9.

Parallel to the first line 4, the DC measuring arrangement 7 is arranged, which includes the DC line 8, which at the connection point 10, which in this case still within the AC power source or sink 6 is connected to the first line 4.

Of course, instead of arranging the DC measuring arrangement 7 parallel to the first line 4, it is likewise possible to arrange the DC measuring arrangement 7 parallel to the second line 5. In the present example, this might even be preferable, since the second line 5 has an already somewhat longer path from the four switching elements 6a to 6d to the terminal 9.

The inductor 11 comprises a bridge I Ia, which is designed in particular as a copper conductor with a large cross-section, and a ferrite I Ib surrounding this. The ferrite I Ib is preferably annular. The inductance value of the inductor 11 is significantly influenced by the properties of the ferrite I Ib. A ferrite may be used which raises the inductance value at the typical switching frequency of the alternating current source or sink 6 from 50 kHz to values greater than 0.1 μΗ, in particular greater than ΙμΗ. Furthermore, it can be seen that a DC current measuring device 12 is provided.

FIG. 3 shows a position of the printed circuit board 20 of the protective device Γ. In particular, it can be seen here that the first line 4 is formed very wide. The parallel thereto extending DC line 8 is narrower. Schematically, the elements DC connection 22 and DC connection 24, AC source or sink 6, inductor 11, DC current measuring device 12 and connection point 9 are also shown. The second terminal of the transformer is provided congruent to the connection point 9 in another position. The DC terminals 22, 24 are located in an inner layer of the printed circuit board 20 and are formed as full as possible. The second line 5 may also be provided in a further, not shown, inner layer of the printed circuit board 20 and be formed substantially congruent to the first line 4. Furthermore, 20 control lines may be provided in other inner layers of the printed circuit board, not shown. Through-contacts of the layer shown in Figure 3, which represents an inner layer of the printed circuit board 20, the first line 4 with further inner layers or an outer layer of the printed circuit board 20, z. B. a component side, connect. The plated-through holes of another inner layer, on which the second line 5 is located, can connect the second line 5 with further inner layers or the other outer layer of the printed circuit board, for example the underside. The vias can be designed so that they do not go through all the layers. There are then used so-called blind holes. This results in a particularly low-induction construction and a bifilar design of the lines 4, 5.

Accordingly, the above-described object can also be achieved by a protective device Γ for protecting a transformer 2 and an alternating current source 6 or sink 6, having a first and a second line 4, 5, from a connection point 9 for connecting a winding 3 of the transformer 2 with an alternating current source 6 or an alternating current sink 6, to one of the lines 4, 5 a DC measuring arrangement 7 is electrically connected in parallel whose inductance value is greater than the inductance value of the first or the second line 4, 5 and the one DC - Current measuring device 12 has. The protection arrangement 1 described above additionally has the transformer 2 and the AC power source 6 or sink 6. All embodiments described above for the protective arrangement 1 also apply individually or in combination for the protective device Γ.

Claims

claims

1. Protection arrangement (1) for protecting a transformer (2), a

AC source (6) and / or AC sink (6), comprising a transformer (2) having one winding (3) via a first and a second line (4, 5) with an AC source (6) or a

AC sink (6) is connected, wherein to one of the lines (4, 5) is a DC measuring arrangement (7) is electrically connected in parallel whose inductance value is greater than the inductance value of the first or the second line (4, 5) and the one DC current measuring device (12).

2. Protection arrangement according to claim 1, characterized in that a DC line of the DC measuring arrangement (7) has an inductance value which is greater than the inductance value of the first or the second line (4, 5).

3. Protection arrangement according to one of the preceding claims, characterized in that the inductance value of the DC measuring arrangement (7) is at least a factor of 10, in particular at least a factor of 100, greater than the inductance value of the first or the second line (4, 5 ).

4. Protection arrangement according to one of the preceding claims, characterized in that the DC measuring arrangement (7) has a throttle (11).

5. Protection arrangement according to one of the preceding claims, characterized in that the DC measuring arrangement (7), in particular its DC line (8), has a conductance which is greater than 1% of the conductance the first or the second line (4, 5).

6. Protection arrangement according to one of the preceding claims, characterized in that a control device (13) is provided, which is connected to the DC measuring arrangement (7) and is adapted to correct a detected by the DC current measuring device (12) direct current.

7. Protection arrangement according to claim 6, characterized in that the control device (13) with an AC power source or sink (6) is connected.

8. Protection arrangement according to one of the preceding claims, characterized in that the DC measuring arrangement (7) at two

Connection points (9, 10) with the first or the second line (4, 5) is connected.

9. A method for protecting a via a first and a second line (4, 5) to an AC power source (6) or AC sink connected transformer (2), and for the protection of the AC power source (6) or AC sink (6), in which a between Transformer (2) and AC power source (6) or AC sink (6) is at least partially decoupled by a DC line (8) to the first or the second line (4, 5) is electrically connected in parallel and the DC Current in the DC line (8) is measured.

10. The method according to claim 9, characterized in that between the transformer (2) and AC power source (6) or AC sink (6) flowing DC current is at least partially compensated by the control of the AC power source or sink (6) in dependence of in the DC line measured DC current is changed.

11. Protection device (Γ) for protecting a transformer (2), a

AC source (6) and / or AC sink (6), having a first and a second line (4, 5), wherein to one of the lines (4, 5) a DC measuring arrangement (7) is electrically connected in parallel, the

Inductance value is greater than the inductance value of the first or the second line (4, 5) and having a DC current measuring device (12).

12. AC power source (6) with a transformer (2) and a

Protection arrangement (1) for protecting the transformer (2) according to one of the preceding claims 1 to 8 or 11.

13. AC sink (6) with a transformer (2) and a