Shunt resistor for current measuring device of busbar, current measuring device and busbar

Abstract

The invention relates to a shunt resistor for a current measuring device of a busbar, the resistor comprising a planar resistor body and two connection terminals for measuring a voltage across the planar resistor body, wherein each of the two connection terminals is connected to one of two conductive tracks provided on opposite sides of the resistor body, and wherein each conductive track comprises a measurement portion and a connection portion for connecting the measurement portion to one of the connection terminals. The invention further relates to a current measuring device comprising said shunt resistor and a current path provided in parallel to the shunt resistor. The invention further relates to a busbar having a corresponding current measuring device, wherein the shunt resistor and the current path are provided to connect the busbar to an electronic component.

Description

TECHNICAL FIELD

[0001] The invention relates to a shunt resistor for a current measuring device of a busbar, the resistor comprising a planar resistor body and two connection terminals for measuring a voltage across the planar resistor body, wherein each of the two connection terminals is connected to one of two conductive tracks provided on opposite sides of the resistor body, and wherein each conductive track comprises a measurement portion and a connection portion for connecting the measurement portion to one of the connection terminals. The invention further relates to a current measuring device comprising said shunt resistor and a current path provided in parallel to the shunt resistor. The invention further relates to a busbar having a corresponding current measuring device, wherein the shunt resistor and the current path are provided to connect the busbar to an electronic component. BACKGROUND

[0002] Known solutions for measuring current in a busbar, in particular short circuit current, comprise large and expensive closed loop current transducers. Known solutions rely on desaturation protection. Typically, this means that short circuit protection is delayed to occur and it cannot be guaranteed that the short circuit current remains low enough to avoid damaging components connected to the busbar.

[0003] Furthermore, known solutions can be based on indirect current measurement by magnetic field sensing. Therefore, they can not be suitable for measuring low frequency current, i.e. normal 50 / 60 Hz current, because magnetic fields from adjacent busbars can distort the measurement. This is shown in Figures 6a-6b Although this can be mathematically compensated, short circuit and similar abnormal events are still difficult to measure even assuming a symmetrical three-phase current waveform. SUMMARY

[0004] It is an object of the invention to provide an improved device for measuring current in a busbar, wherein the device is compact and capable of accurately measuring low frequency current and short circuits.

[0005] This object is achieved by the shunt resistor according to claim 1, the current measuring device according to claim 9 and the busbar according to claim 10.

[0006] According to claim 1, a shunt resistor for a current measuring device of a busbar is provided. The resistor comprises a planar resistor body and two connection terminals for measuring a voltage across the planar resistor body, wherein each of the two connection terminals is connected to one of two conductive tracks provided on opposite sides of the resistor body, and wherein each conductive track comprises a measurement portion and a connection portion for connecting the measurement portion to one of the connection terminals. The presently described shunt resistor provides a compact and universally applicable solution for measuring current in a busbar.

[0007] In a preferred embodiment of the application, the measuring portions are linear and / or horizontal portions of the electrically conductive tracks, and / or are arranged at a bottom portion or an upper portion of the resistor body. In general, the measuring portion of each electrically conductive track can be positioned such that it is located at a position where the maximum current can be expected during operation of the resistor. This increases the sensitivity of the measurement made using the shunt resistor.

[0008] In another preferred embodiment of the application, the connecting portions are connected to the middle of the measuring portions. Each electrically conductive track can comprise a measuring portion which is connected to its connecting terminal via a respective connecting portion. The connecting portions make it possible to space the connecting terminals apart from the measuring portions. Thus, the measuring portions can be arranged in a region where the measurement sensitivity is optimized, while the connecting portions can be arranged in a region which facilitates connecting the shunt resistor to other components.

[0009] In another preferred embodiment of the application, the connecting portions and / or the measuring portions of the two electrically conductive tracks are arranged symmetrically to each other. The symmetry between the corresponding portions of the two electrically conductive tracks can be mirror-symmetrical with respect to a center plane of the resistor body. The measuring portions can be oriented horizontally, and / or at least a portion of the connecting portions can be oriented vertically and / or horizontally and / or perpendicular to the measuring portions and / or at an angle of less than 90° with respect to the measuring portions.

[0010] In another preferred embodiment of the application, the connecting terminals are arranged at an upper portion or a bottom portion of the resistor body, and / or are arranged opposite the measuring portions. The measuring portions can be spaced apart from the connecting terminals and arranged at the resistor body at a maximum possible distance or close to a maximum possible distance. This ensures that no interference occurs between the electrical connections attached to the connecting terminals and the measuring portions. Furthermore, it ensures that the surface area of the resistor body is used as efficiently as possible.

[0011] In another preferred embodiment of the application, the resistor body is encapsulated in a non-conductive material / insulator. The term "non-conductive material" is to be understood as a broad term and can refer to a material which has a lower electrical conductivity than the electrical conductors connected to the resistor body or the entire shunt resistor. The electrical conductivity of the non-conductive material can be, for example, ten or several tens of percent or one or more orders of magnitude less than the electrical conductivity of the conductors. The resistor body can be encapsulated such that at least three of its sides are at least partially covered and / or in contact with the non-conductive material.

[0012] In a particularly preferred embodiment of the application, the non-conductive material encapsulating the resistor body covers both major faces and the bottom edge of the resistor body, and the non-conductive material encapsulating the resistor body exposes the connection terminals. The bottom edge of the resistor can be defined as the edge close to the edge from which the measurement section is provided. The two major faces of the resistor body can be the two opposite faces of the resistor body having the largest surface area among all faces of the resistor body.

[0013] In another preferred embodiment of the application, the resistor body has a rectangular shape. This shape can not be limited to a square, but can be any shape, for example a circle, an ellipse, a rectangle with or without rounded edges.

[0014] The application is also directed to a current measurement device according to claim 9. The current measurement device comprises the shunt resistor presently described, and a current path arranged in parallel with the shunt resistor. The shunt resistor can be connected to any other means required to provide a current measurement.

[0015] The application is also directed to a busbar with a corresponding current measurement device, wherein the shunt resistor and the current path are provided to connect the busbar to an electronic component. BRIEF DESCRIPTION OF DRAWINGS

[0016] Further details and advantages of the application are described with reference to the accompanying drawings. The drawings show:

[0017] Figure 1 : Wireframe view of a shunt resistor according to the application;

[0018] Figure 2 : Perspective view of a shunt resistor according to the application;

[0019] Figure 3 : Graph of the voltage of a simulated shunt resistor;

[0020] Figures 4a-4b : Perspective view of a known shunt resistor;

[0021] Figures 5a-5b : Electric field in a known shunt resistor;

[0022] Figures 6a-6b : Busbar in a compact three-phase inverter and its corresponding graph; and

[0023] Figure 7 : Shunt resistor R according to the prior art DC . DETAILED DESCRIPTION

[0024] Figure 1 is a wireframe view of a shunt resistor 1 according to the application. The shunt resistor 1 is arranged in a current measurement device for a busbar.Figure 1 The busbars and other components of the measuring device are not shown in the figures. The resistor 1 comprises a planar resistor body 2, at Figure 1 which is shown to be oriented vertically. The resistor body 2 can be made of any suitable material that is sufficiently electrically conductive.

[0025] The resistor 1 comprises two connection terminals 3, 4 for measuring the voltage across the planar resistor body 2. The two connection terminals are provided on opposite sides of the resistor body 2.

[0026] Each of the two connection terminals 3, 4 is connected to one of two electrically conductive tracks 5, 6, which are also provided on opposite sides of the resistor body 2. Each of the electrically conductive tracks 5, 6 comprises a measurement portion 51, 61 and a connection portion 52, 62 for connecting the measurement portion 51, 61 to one of the connection terminals 3, 4. The two electrically conductive tracks 5, 6 are electrically separated from each other by the resistor body 2.

[0027] The measurement portions 51, 61 are shown to be linear and horizontal portions of the electrically conductive tracks 5, 6 and / or are provided at a bottom portion of the resistor body 2. The measurement portions 51, 61 can extend over the entire width of the resistor body 2. The measurement portions 51, 61 can extend over a smaller portion of the resistor body 2. However, it is advantageous that the measurement portions 51, 61 cover a substantial portion of the width of the resistor body 2.

[0028] To improve the accuracy of the current measurement, the connection portions 52, 62 can advantageously be connected to the middle of the measurement portions 51, 61. The connection portions 52, 62 can comprise a bend and two linear sub-portions connected by the bend. The sub-portions of the connection portions 52, 62 can be at a perpendicular angle with respect to each other.

[0029] In the shown embodiment, the connection portions 52, 62 and the measurement portions 51, 61 of the two electrically conductive tracks 5, 6 are arranged symmetrically to each other. Thus, the electrically conductive tracks 5, 6 can be at least partially arranged opposite to each other at or inside the resistor body 2 at opposite sides.

[0030] The connection terminals 3, 4 are provided at an upper portion of the resistor body 2 and opposite to the measurement portions 51, 61. The two connection terminals 3, 4 can be arranged asymmetrically with respect to each other in order to facilitate the attachment of some electrical components to the connection terminals 3, 4. However, the connection terminals 3, 4 can be arranged such that they at least partially overlap when viewed in a direction perpendicular to the resistor body 2.

[0031] The resistor body 2 can be encased by a non-conductive material 7. The non-conductive material 7 can be arranged between the two conductors 9, 9’. The two conductors 9, 9’ electrically connect the resistor 1 to, for example, bus bars and some electronic components that require a bus bar connection. The resistor body 2 can have a rectangular shape.

[0032] As shown in Figure 2 , the non-conductive material 7 does not cover all parts of the resistor body 2. The non-conductive material 7 covers most of the two major faces 21, 22 and some or most of the bottom edge 23 of the resistor body 2. The first major face 21 and the bottom edge 23 are not visible in Figure 2 , as they are oriented away from the observer. They are denoted by reference numerals 21 and 23, respectively.

[0033] The non-conductive material 7 can be in contact with the bottom edge 23 of the resistor body 2, or there can be a gap between the non-conductive material 7 and the bottom edge 23. The non-conductive material 7 can comprise a U-shaped portion, wherein the bottom edge 23 of the resistor body 2 or some other part of the resistor body 2 is at least partially contained. The non-conductive material 7 exposes the connection terminals 3, 4 and the respective parts of the resistor body 2. The non-conductive material 7 also exposes the upper edge 24 opposite the measurement portions 51, 61 and / or the left side edge 25 and the right side edge 26 of the resistor body 2. The measurement portions 51, 61 are shown in Figure 1 , located near the bottom U-shaped portion of the non-conductive material 7.

[0034] The sandwich structure of the resistor 1 is clearly visible in Figure 2 . The innermost part of the resistor 1 comprises the resistor body 2. The resistor body 2 is encased by the non-conductive material 7 at its two opposite major faces 21, 22 and the bottom edge 23. The two conductors 9, 9’ form the outermost layers of the sandwich structure.

[0035] The upper part 11 of the sandwich structure shows a total of five layers arranged next to each other and parallel. The outermost layers comprise the two conductors 9, 9’. These two conductors 9, 9’ are in contact with the non-conductive material 7, which in turn encases the resistor body 2. The upper part 11 of the sandwich structure of the resistor 1 can be planar, such that the upper edges of the five layers forming the sandwich structure are arranged coplanar to each other.

[0036] The resistor 1 can comprise two side parts 12, 13, a right side part 12 and a left side part 13. The left side part 13 can comprise the connection terminals 3, 4. The connection terminal 3 is positioned opposite the connection terminal 4 and away from the observer. The connection terminal 3 is therefore not visible in Figure 2 . The left and right sides of the resistor 1 can be oriented in the horizontal direction of the resistor 1.

[0037] The two side portions 12, 13 can comprise stepped sub-portions formed by the previously mentioned layers of the sandwich structure. The resistor body 2 can form the innermost layer of the sandwich structure and at the same time represent the outermost layer of the sandwich structure. In other words, the resistor body 2 can extend the furthest in the horizontal direction of the resistor 1 while being the innermost component of the sandwich structure.

[0038] The conductors 9, 9’ can extend the least in the horizontal direction among all components of the sandwich structure. The non-conductive material 7 can extend further in the horizontal direction than the conductors 9, 9’, but less than the resistor body.

[0039] Among the components of the sandwich structure, at least one of the conductors 9, 9’ can extend the furthest in its vertical direction. The resistor body 2 can extend the least in the vertical direction of the sandwich structure. The non-conductive material 7 can extend further in the vertical direction than the resistor body 2, but less than at least one of the conductors 9, 9’.

[0040] The current measurement device can comprise the shunt resistor 1 and a current path 8 arranged in parallel with the shunt resistor 1. Both the resistor 1 and the current path 8 can electrically connect the electronic component to the busbar. The measurement device can further comprise any additional means required for providing current measurement.

[0041] The current measurement device and thus the shunt resistor 1 can be integrated with the busbar, wherein the shunt resistor 1 and the current path 8 are provided for connecting the busbar to the electronic component.

[0042] The sandwiched conductors 9, 9’ between which the current can flow can force the electromagnetic field to be uniform and remain between the conductors 9, 9’. Figure 2 The electromagnetic field within the sandwich of the shunt resistor 1 can not affect any measurement of the current flowing between 9, 9’.

[0043] In the resistive portion of the measurement portion 51, 61, a voltage resulting from the current flowing through the measurement portion 51, 61 can be measured. The measurement portion 51, 61 can be manufactured using high-precision metallurgical techniques, as shown in Figure 1 The resulting static R resistance value can be used to estimate the current using Ohm’s law.

[0044] The connection terminal 3, the measurement portion 51, and the connection portion 52 can be manufactured using high-precision metallurgical techniques, as shown in Figure 1The connection terminals 4, the measuring portion 61 and / or the connection portion 62 shown are placed symmetrically adjacent. The symmetrical arrangement of the portions 3, 51, 52 adjacent to the portions 4, 61, 62 can ensure an accurate voltage measurement due to the symmetrical current distribution in the arrangement. The symmetrical arrangement can help an accurate voltage measurement even during a short circuit which leads to a high current flow through the arrangement and during the current flow through the conductors 9, 9’.

[0045] Figure 3 is a plot of the simulated shunt resistor voltage at a short circuit current equal to 1500 A in 4 ps. Due to the specific structure of the shunt resistor 1, the shunt resistor 1 is able to accurately measure dynamic short circuit events, where the linear voltage slope increases as a function of the current. The trace of the connection of the shunt resistor 1 to the electrical line or the conductor 9, 9’ shown previously is sandwiched in between to minimize stray inductance and noise sensitivity. The initial jump in voltage is due to the parasitic inductance L = V jump / di / dt = 0 mV / 1500 A / 4 ps = 80 pH, which is very low. This step voltage change causes an offset which can provide an early detection of a possible short circuit event and a subsequent observation of the linearly increasing voltage across the shunt resistor 1.

[0046] Figure 4a and Figure 4b is a perspective view of a known shunt resistor 1’. Figure 4a is a simulation model of a known shunt resistor 1’ for a DC+ to DC- short circuit, and Figure 4b is a simulation model of a known shunt resistor 1’ for a DC to ground short circuit. In Figure 4a and Figure 4b both cases, the known shunt resistor 1’ is arranged between a busbar and a device powered by the busbar. However, in the example of Figure 4a an additional current path 8 is provided between the device and the busbar.

[0047] In the known shunt resistor 1’, the short circuit current does not flow uniformly through the known shunt resistor 1’ due to the skin effect and the proximity effect. This is shown in Figure 5a and Figure 5b where the known plate-shaped shunt resistor 1’ is mounted to a DC link terminal between the conductors 9, 9’. The same principle holds if the resistor 1’ is placed on the AC side of an inverter module. Figure 5a shows the electric field in a known shunt resistor 1’ for a 1500 A DC+ to DC- short circuit at 1 MHz, Figure 5b shows the electric field in a known shunt resistor 1’ for a 1500 A DC+ to DC- short circuit at 1 kHz.

[0048] Figure 6a and Figure 6b The busbars in a compact three-phase inverter and the corresponding voltage diagram are shown. Current measurement in this case can typically be based on magnetic field sensing. In a compact three-phase inverter, the busbars and sensors are placed in close proximity and the magnetic fields of adjacent phases will influence the sensor measurements. The measured current depends on the sensor position and the currents of the adjacent phases. Thus, the u-phase and the v-phase should measure equal magnetic field amplitudes, but they do not, measuring for example Figure 6b point 4 in Fig. 4.

[0049] Figure 7 The prior art FI U20219, where the short circuit current does not flow uniformly through the shunt resistor R DC comprises Figure 1 The present invention, including the conductive traces 5, 6 shown in Fig. 5, overcomes the related measurement limitations of the prior art.

Claims

1. A shunt resistor (1) for a current measuring device of a busbar, the resistor (1) comprising a planar resistor body (2) and two connection terminals (3, 4) for measuring a voltage across the planar resistor body (2), the planar resistor body (2) having a bottom edge and two opposite main faces, wherein each of the two connection terminals (3, 4) being connected to one of two conductive tracks (5, 6) provided on the opposite main faces of the planar resistor body (2), wherein each of the conductive tracks (5, 6) comprises a measurement portion (51, 61) and a connection portion (52, 62) for connecting the measurement portion (51, 61) to one of the connection terminals (3, 4), and wherein the measurement portion (51, 61) is a linear portion provided at the bottom edge of the planar resistor body (2).

2. The shunt resistor (1) according to claim 1, characterized in that the connection portion (52, 62) is connected to the middle of the measurement portion (51, 61).

3. The shunt resistor (1) according to claim 1, characterized in that the connection portions (52, 62) and the measurement portions (51, 61) of the two conductive tracks (5, 6) are arranged symmetrically to each other with respect to a center plane of the planar resistor body (2).

4. The shunt resistor (1) according to claim 1, characterized in that the connection terminals (3, 4) are provided at an upper portion of the resistor body (2) and are arranged opposite to the measurement portions (51, 61).

5. The shunt resistor (1) according to claim 1, characterized in that the resistor body (2) is encapsulated in a non-conductive material (7).

6. The shunt resistor (1) according to claim 5, characterized in that the non-conductive material (7) encapsulating the resistor body (2) covers the main faces (21, 22) and the bottom edge (23) of the resistor body (2) and the non-conductive material (7) encapsulating the resistor body (2) exposes the connection terminals (3, 4).

7. The shunt resistor (1) according to claim 1, characterized in that the resistor body (2) has a rectangular shape.

8. A current measuring device comprising a shunt resistor (1) according to claim 1 and a current path (8) provided in parallel to the shunt resistor (1).

9. A busbar having a current measuring device according to claim 8, characterized in that the shunt resistor (1) and the current path (8) are provided for connecting the busbar to an electronic component.

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