Measuring shunts

Abstract

The invention relates to a measuring shunt (1). The measuring shunt (1) comprises a resistance element (3) and a magnetic core (5). The resistance element (3) has two main contacts (7, 9) and a middle section (11) extending between the main contacts (7, 9) and is used to conduct current (I1, I2) between the two main contacts (7, 9) through the middle section (11). The magnetic core (5) extends in a ring shape around the middle section (11) of the resistance element (3).

Description

Technical Field

[0001] The invention relates to a measuring shunt, in particular to a circuit arrangement for a half-bridge having electronic switches connected in parallel, and to a current transformer having such a circuit arrangement. Background Art

[0002] In order to achieve sufficient converter power, parallel circuits of half-bridges of electronic switches are used in converters in particular. In such parallel circuits, the electronic switches are arranged in close spatial proximity, whereby the electronic switches are coupled. In order to decouple the electronic switches, inductors can be used, but are often abandoned for cost reasons. Measuring shunts are also used to measure phase currents in converters, for example, for speed control of motors that are driven by converters.

[0003] US 2008 / 074225 A1 discloses an inductor having an inductor body. A cavity passes through the inductor body and extends between two opposite end surfaces of the inductor body. A thermally stable resistor element extends through the cavity, the resistor element faces the upper surface of the inductor body and has a surface-mountable interface.

[0004] US 2014 / 292458 A1 discloses a magnetic device having a magnetic core and a conductive coil inductively coupled to the magnetic core. The conductive coil comprises a first interface portion, a second interface portion and an inductive portion connected in series between the interface portions. The first interface portion comprises a current detection element. Summary of the invention

[0005] The object of the invention is to specify an improved measuring shunt, in particular for a circuit arrangement having half-bridges connected in parallel of electronic switches and a converter having such a circuit arrangement.

[0006] The object according to the invention is achieved by a measuring shunt having the features of the invention, a circuit arrangement having the features of the invention and a current transformer having the features of the invention.

[0007] Advantageous embodiments of the invention are the subject of the individual exemplary embodiments.

[0008] The measuring shunt according to the invention comprises a resistance element having two main contacts and a middle section extending between the main contacts, and is used to conduct current between the two main contacts through the middle section. In addition, the measuring shunt has a magnetic core that extends in an annular manner around the middle section of the resistance element.

[0009] The magnetic core extending around the resistor element imparts an inductance to the measuring shunt, which can be used to decouple the electronic switches in the half-bridges connected in parallel. The measuring shunt according to the invention thus makes it possible, in addition to measuring the current, to decouple the electronic switches in the half-bridges connected in parallel. Furthermore, the measuring shunt according to the invention makes it possible, by means of the filtering effect of its inductance, to limit the asymmetries and voltage gradients at the outputs of the half-bridges connected in parallel. This can advantageously increase the functionality of the measuring shunt.

[0010] Furthermore, the measuring shunt has two auxiliary contacts for tapping a measuring voltage which drops between measuring locations of the resistance element on different sides of the magnetic core. This aspect of the invention enables an improved measuring accuracy of the measuring shunt by means of a four-wire measurement in which the current flowing through the resistance element is measured via a measuring voltage which is tapped at the auxiliary contacts.

[0011] One of the auxiliary contacts extends from one of the measuring positions through the magnetic core. This prevents the measuring voltage tapped at the auxiliary contact from containing voltages induced by the magnetic core and avoids distorting the measuring signal.

[0012] The central section of the resistor element is designed in the shape of a U. As a result, the measuring shunt can be arranged in a simple manner with the main contacts on a flat circuit carrier.

[0013] The design of the present invention proposes that the magnetic core is composed of two core parts that are joined to each other. The design of the present invention can realize a simple assembly of the magnetic core around the resistor element by splicing the two core parts.

[0014] Another embodiment of the invention provides that the magnetic cores of the resistor elements are separated by an air gap. The inductance of the measuring shunt can be advantageously influenced by the air gap.

[0015] An alternative to the above two embodiments of the present invention provides that the magnetic core surrounding the middle section of the resistor element is injection molded. This embodiment of the present invention enables simple mass production of the measuring shunt by injection molding of the magnetic core.

[0016] The magnetic core is preferably made of a material with high magnetic permeability, high saturation magnetic induction and / or with small frequency-dependent magnetic losses. For example, the magnetic core is made of ferrous or ferrimagnetic material. When the magnetic core is injection molded, the magnetic core is made of, for example, a mixture of a carrier material, for example a synthetic material, and a magnetic material, for example a magnetic powder such as iron powder or ferrimagnetic powder.

[0017] The resistance element is preferably made of a material having a small resistivity and a small temperature dependence of resistance, for example, a copper-nickel-manganese alloy.

[0018] The circuit arrangement according to the invention has at least two half-bridges connected in parallel with each other, in whose bridge arms at least one electronic switch is arranged, wherein a measuring shunt according to the invention is arranged on the bridge branch of each half-bridge. The measuring shunt makes it possible, on the one hand, to measure the current flowing in the bridge branch and, on the other hand, to decouple the half-bridges connected in parallel without having to use further components. Furthermore, the voltage gradient at the output of the circuit arrangement is limited by the filtering effect of the measuring shunt.

[0019] The converter according to the invention has a circuit arrangement according to the invention having at least one half-bridge connected in parallel with electronic switches. The advantages of such a converter are derived from the above-mentioned advantages of the circuit arrangement according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above-mentioned characteristics, features and advantages of the present invention and the ways and methods of achieving them are more clearly shown according to the following description of the embodiments in conjunction with the accompanying drawings. Here, it is shown:

[0021] Figure 1 First stereogram of the measuring shunt,

[0022] Figure 2 exist Figure 1 A second perspective view of the measuring shunt is shown in FIG.

[0023] Figure 3 A circuit arrangement having two half-bridges of electronic switches connected in parallel with one another,

[0024] Figure 4 Circuit diagram of the converter.

[0025] Corresponding parts are provided with the same reference numerals in the figures. DETAILED DESCRIPTION

[0026] Figure 1 and Figure 2 Two different perspective views of an embodiment of a measuring shunt 1 according to the invention are shown, wherein, in order to make the perspective views more clear, a Cartesian coordinate system is shown with coordinates x, y, z. The measuring shunt 1 has a resistor element 3 and a magnetic core 5 .

[0027] The resistor element 3 has two main contacts 7, 9, a middle section 11 and two auxiliary contacts 13, 15. The middle section 11 extends between the main contacts 7, 9. The middle section 11 is designed as a U-shaped central section 21 having two legs 17, 19 and extending between the legs 17, 19. Each main contact 7, 9 is bent by the legs 17, 19 so that the main contacts 7, 9 extend from the middle section 11 at opposite sides and facing away from each other.

[0028] The magnetic core 5 extends in an annular manner around the central section 21 of the resistor element 3 and is separated from the central section 21 by an air gap 23. The magnetic core 5 is composed of two core parts 25 and 27 that are engaged with each other, and the core parts are each designed to be U-shaped. The magnetic core 5 is in the shape of a rectangular parallelepiped with an opening, and the central section 21 of the resistor element 3 extends through the opening.

[0029] Each auxiliary contact 13, 15 extends from a measuring position 29, 31 in the central region 21 to an end in the region of the first main contact 7 of the resistor element 3. Here, the two measuring positions 29, 31 are arranged on mutually different sides of the magnetic core 5. The first auxiliary contact 13 extends from the first measuring position 29 completely on the side of the magnetic core 5 facing the first main contact 7. The second auxiliary contact 15 extends from a second measuring position 31 on the side of the magnetic core 5 facing the second main contact 9, through the magnetic core 5 to the side of the magnetic core 5 facing the first main contact 7.

[0030] Measure the current of shunt 1 at Figure 1 and 2 The auxiliary contacts 13, 15 of the exemplary embodiment shown in FIG. 1 are produced in the resistor element 3 by two slots 33, 35, which extend respectively through a partial region of the central section 21 and the first leg 17 of the middle section 11 to the end of the resistor element 3 in the region of the first main contact 7. The slots 33, 35 separate the two auxiliary contacts 13, 15 from one another and from the first main contact 7, wherein the first slot 33 separates the first auxiliary contact 13 from the first main contact 7 and the second slot 35 separates the two auxiliary contacts 13, 15 from one another.

[0031] The resistor element 3 is used to measure the current flowing through the intermediate section 3 between the main contacts 7, 9. The current is measured according to the four-wire measuring principle by applying an electrical measuring voltage between two measuring points 29, 31, which is tapped at the auxiliary contacts 13,15.

[0032] The core 5 is used to decouple the electronic switches 43 connected in parallel, such as in Figure 3 The case of a circuit arrangement 37 is shown.

[0033] In an alternative embodiment of the measuring shunt 1, the auxiliary contacts 13, 15 can be connected as in Figure 1 and 2 Here, however, one of the two auxiliary contacts 13 or 15 extends through the magnetic core 5 parallel to the flow direction of the current flowing through the resistor element 3. In addition, the magnetic core 5 can be arranged in the same manner as in the embodiment shown in FIG. Figure 1 and 2The exemplary embodiment shown in FIG. 5 can be implemented in different ways. For example, the magnetic core 5 can be injection molded around the central section 11 of the resistor element 3 , for example made of a mixture of a carrier material, for example a plastic, and an electromagnetic material, for example a magnet powder.

[0034] Figure 3 1 shows a circuit diagram of an exemplary embodiment of a circuit arrangement 37 according to the invention having two half-bridges 39, 41 connected in parallel to one another, in whose bridge arms an electronic switch 43 is arranged in each case. In each bridge branch of the half-bridge 39, 41 an electronic switch 43 is arranged, as in Figure 1 and 2 The measuring shunt 1 designed in the embodiment of the present invention measures the currents I1, I2 in the bridge branches and flowing through the resistor element 3 of the measuring shunt 1 by means of the measuring shunt, via electrical measuring voltages U1, U2, which are tapped at the auxiliary contacts 13, 15 of the measuring shunt 1. The first bridge arm of each half bridge 39, 41 is connected to the first DC voltage interface 45 of the circuit device 37. The second bridge arm of each half bridge 39, 41 is connected to the second DC voltage interface 47 of the circuit device 37. The measuring shunt 1 is connected to the AC voltage interface 49 of the circuit device 37 on the output side. Figure 3 In the embodiment of the circuit arrangement 37 according to the invention shown in FIG. 4 , the electronic switch 43 is an insulated gate bipolar transistor (IGBT), but in other embodiments it can also be another semiconductor switch, such as a metal oxide semiconductor field effect transistor (MOSFET).

[0035] Figure 4 1 shows a circuit diagram of an embodiment of a converter 51 according to the invention. The converter 51 has two converter DC voltage interfaces 53, 55, three converter AC voltage interfaces 57 to 59 and three converters, each of which is like a Figure 3 The first DC voltage interface 45 of each circuit device 37 is connected to the first converter DC voltage interface 53. The second DC voltage interface 47 of each circuit device 37 is connected to the second converter DC voltage interface 55. The AC voltage interface 49 of each circuit device 37 is connected to the converter AC voltage interfaces 57 to 59.

[0036] Although the present invention has been illustrated and described in detail by means of preferred embodiments, the present invention is not limited to the disclosed examples, and those skilled in the art can devise other variants without departing from the scope of protection of the present invention.

Claims

1. A measuring shunt (1), comprising: - a resistor element (3) having a first main contact (7), a second main contact (9) and an intermediate section (11) extending between the first main contact (7) and the second main contact (9), the resistor element (3) being used to conduct a current (I1, I2) between the first main contact (7) and the second main contact (9) through the intermediate section (11), - a magnetic core (5) extending annularly around the middle section (11) of the resistor element (3), and - a first auxiliary contact (13) and a second auxiliary contact (15) for tapping off a measurement voltage (U1, U2) dropping between a first measurement point (29) and a second measurement point (31) of the resistor element (3), wherein: - the first measuring position (29) and the second measuring position (31) are located on different sides of the magnetic core (5), - the intermediate section (11) is designed in the shape of a U having two legs (17, 19) and a central section (21) extending between the legs (17, 19), - the second auxiliary contact (15) extends from the second measuring position (31) on the side of the magnetic core (5) facing the second main contact (9) through the magnetic core (5) to the side of the magnetic core (5) facing the first main contact (7), and - The first auxiliary contact (13) and the second auxiliary contact (15) are produced in the resistor element (3) by means of two slots, which extend respectively through a partial area of ​​the central section (21) and a first leg of the middle section (11) to the end of the resistor element (3) in the region of the first main contact (7).

2. The measuring shunt (1) according to claim 1, wherein: The first auxiliary contact (13) extends from the first measuring position (29) completely on the side of the magnetic core (5) facing the first main contact (7).

3. The measuring shunt (1) according to claim 1 or 2, wherein: The magnetic core (5) consists of two core parts (25, 27) that are joined to each other.

4. The measuring shunt (1) according to claim 1 or 2, wherein: The magnetic core (5) is separated from the resistance element (3) by an air gap (23).

5. The measuring shunt (1) according to claim 1 or 2, wherein: The magnetic core (5) is injection molded around the middle section (11) of the resistor element (3).

6. A circuit arrangement (37) having at least two half-bridges (39, 41) connected in parallel with one another, at least one electronic switch (43) being arranged in each bridge arm of the circuit arrangement, wherein: A measuring shunt (1) according to any one of claims 1 to 5 is arranged in each bridge branch of the half-bridge (39, 41).

7. A converter (51) having at least one circuit arrangement (37) according to claim 6.

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