Current sensor and measuring system comprising such a current sensor

Description

[0001] The present invention relates to a current sensor and a measurement system comprising such a current sensor.

[0002] Rogowski coils are current sensors capable of measuring the intensity of an alternating current flowing in an electrical conductor.

[0003] Such a sensor generally comprises a wound coil which defines a closed contour around a central opening in which the electrical conductor is received. The current flowing in the electrical conductor induces an electrical voltage across the coil.

[0004] Rogowski coils can be fabricated on a printed circuit board (PCB). For example, an insulating substrate is perforated with a plurality of plated-through holes arranged on its faces in a predefined pattern and positioned to define a closed loop around a central opening. The succession of plated-through holes and electrically conductive traces formed on layers of the substrate together define an electrically conductive path that forms a coil winding.

[0005] Examples of known current sensors are described in US documents 2003 / 011458 A1 and US 2014 / 198463 A1.

[0006] Rogowski coils on printed circuit boards ( PCB Rogowski coils (in English) have the advantage of being relatively simple and inexpensive to manufacture on an industrial scale. They are also easy to miniaturize.

[0007] One drawback of these sensors is their low gain (for example, on the order of 10 µV per Ampere), which makes it difficult to detect small current variations in the electrical conductor. This limitation is a major drawback in certain applications, for example, when such a sensor is used as a current sensor in an electrical protection device within a power distribution system.

[0008] There is therefore a need for current sensors, particularly Rogowski coils on printed circuit boards, which overcome these drawbacks.

[0009] A first aspect of the invention relates to a current sensor, according to claim 1.

[0010] According to advantageous but not mandatory aspects, such a current sensor may incorporate one or more of the following characteristics, taken in isolation or in any technically admissible combination: The coil comprises a plurality of coil portions electrically connected in series, the coil portions being rectilinear in shape and arranged to form a closed contour in the shape of a quadrilateral around the central opening. The ferromagnetic layer is common to all the coil portions. The ferromagnetic layer is divided into several parts each associated with one of the coil portions. The ferromagnetic layer comprises a sub-layer of an iron and nickel alloy and two sub-layers of copper stacked on either side of the sub-layer of iron and nickel alloy. The iron and nickel alloy is a Fe-Ni36% alloy. The thickness of the ferromagnetic layer is greater than or equal to 150 µm. The substrate comprises a through-via perpendicular to the plane of the substrate, and in which the ferromagnetic layer is separated from said through-via by a buffer zone devoid of ferromagnetic material.The substrate and a printed circuit board having one or more stacked layers of a cured polymer material.

[0011] According to another aspect of the invention, a measurement system comprises a current sensor as described previously and an electronic processing circuit configured to process the signal measured by the current sensor.

[0012] The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of an embodiment of a current sensor given solely by way of example and with reference to the appended drawings, in which: [ Fig 1 ] there figure 1 is a schematic representation of a measurement system comprising a current sensor according to embodiments of the invention; [ Fig 2 ] there figure 2 is a schematic representation of a current sensor of a first embodiment of the invention; [ Fig 3 ] there figure 3 is a schematic representation in cross-section of the current sensor of the figure 2 ; [ Fig 4 ] there figure 4 is a schematic representation of a current sensor of a second embodiment of the invention;

[0013] On the figure 1 is represented a measurement system 2 for measuring the intensity of an electric current flowing in an electrical conductor 4, such as a cable or wire or connecting bar.

[0014] The system 2 here comprises a current sensor 6 and an electronic processing circuit 8 connected to the current sensor 6 and configured to process the signal measured by the current sensor 6.

[0015] According to embodiments, the current sensor 6 is a Rogowski winding comprising a coil which delimits a closed contour around a central opening 7 in which the conductor 4 is received. End terminals of the winding are connected to an input of the processing circuit 8.

[0016] For example, the closed contour has a polygon shape, especially a quadrilateral, such as a square. Alternatively, other shapes can be considered, such as a circle or an ellipse.

[0017] According to examples, the current flowing in the electrical conductor induces an electrical voltage across the coil. This voltage is proportional to the time derivative of the intensity of the current flowing in the conductor 4.

[0018] The processing circuit 8 is, for example, configured to calculate the value of the current from the voltage signal supplied at the output of the current sensor 6.

[0019] According to embodiments, the current sensor 6 and the processing circuit 8 can be mounted on the same printed circuit support.

[0020] A first embodiment of the current sensor 6 is shown in the figures 2 And 3 .

[0021] The current sensor 6 comprises a substrate 10, preferably having a planar shape.

[0022] On the figure 2 , the current sensor 6 is shown in an elevation view in a geometric plane parallel to the substrate 10, thus showing the appearance of the sensor 6 on the upper face of the substrate 10. However, the substrate 10 itself is not illustrated in order to facilitate reading of the figure. On the figure 3 , a part of the current sensor 6 is shown in a section plane perpendicular to the plane of the substrate 10.

[0023] Preferably, the substrate 10 is electrically insulating.

[0024] In examples, the substrate 10 is a printed circuit board having one or more stacked layers of a cured polymer material, such as an "FR-4" type epoxy resin.

[0025] The substrate 10 may, for example, be manufactured by laminating several layers of fibrous fabrics pre-impregnated with resin, or by deposition of material, or by additive manufacturing, or by any other suitable method.

[0026] According to embodiments, the Rogowski winding comprises at least one coil 12 wound around a portion of the substrate 10.

[0027] For example, an electrical conductor is wound in turns around one or more of the layers of the substrate 10.

[0028] According to examples, the coil 12 passes at least partially through the substrate 10, for example by means of metallized holes (also called "vias") drilled in the substrate 10, passing through the substrate 10 at least through part of its thickness and in a direction perpendicular to the plane of the substrate 10. The coil 12 also has electrically conductive tracks, for example formed of metal, such as copper, which extend over one or more of the layers of the substrate 10, for example in a direction parallel to the plane of the substrate 10.

[0029] In other words, the coil 12 is formed by the association of the metallized holes which extend perpendicular to the plane of the substrate 10 and the electrically conductive tracks which extend over layers of the substrate 10.

[0030] Generally speaking, the term "Rogowski coil" does not prejudge a particular shape of a coil, which may have a circular, ovoid, polygonal or any other shape. In the embodiment described by way of example, the coils have a polygonal shape, for example rectangular or square.

[0031] Preferably, a portion of the coil 12 emerges on an outer face of the substrate 10, as will be described in more detail below.

[0032] According to one or more embodiments, the coil 12 comprises a plurality of coil portions 16, 18, 20, 22 electrically connected in series.

[0033] In the illustrated example, the coil portions 16, 18, 20, 22, also called coil segments, are rectilinear in shape and are arranged to form a closed contour in the shape of a quadrilateral around the central opening. For example, the closed contour is centered on the central opening.

[0034] For example, four coil portions 16, 18, 20, 22 are arranged end to end at right angles around the central opening, parallel to the plane of the substrate, being connected only by a portion of the wire forming the winding.

[0035] In the illustrated embodiments, the Rogowski winding advantageously comprises the association of two coils: a second coil 14 is electrically connected in series with the first coil 12.

[0036] It is nevertheless specified that, according to alternative embodiments, the Rogowski winding may comprise only one coil. Thus, one or the other of the coils 12 and 14 may be omitted.

[0037] According to yet other variants, other additional coils can be associated in a similar way to form the Rogowski coil.

[0038] In the illustrated example, coils 12 and 14 are wound around different portions of substrate 10 and are interlaced with each other.

[0039] For example, by "interlaced" is meant that, over at least part of the length of the closed contour, the respective turns of the coils 12 and 14 are arranged alternately.

[0040] Preferably, said portions of the substrate 10 are offset in a direction perpendicular to the plane of the substrate 10.

[0041] In the example shown on the figure 3 , the turns of the first coil 12 surround a first portion of the substrate 10 formed between the upper face of the substrate 10 and an interface 26 between sublayers of the substrate, by means of holes or orifices, such as blind vias or through vias, extending deep into the substrate 10 perpendicular to the plane of the substrate 10. The coil 12 emerges on an upper face of the substrate 10.

[0042] For example, the interface 26 extends in a geometric plane parallel to the plane of the substrate 10. On the figure 3 , interface 26 is shown with exaggerated spacing to facilitate understanding of the drawing. However, in practice, the substrate sub-layers are in direct contact at these interfaces.

[0043] Similarly, the turns of the second coil 14 surround a second portion of the substrate 10 formed between the lower face of the substrate 10 and an interface 24 between sub-layers similar to the interface 26, passing through holes extending between the interface 24 and the lower face of the substrate 10.

[0044] In this example, interface 24 is located above interface 26. Coil 14 emerges on a lower face of substrate 10.

[0045] According to embodiments, the additional coil 14 comprises coil portions similar to the coil portions 16, 18, 20, 22 of the coil 12.

[0046] Preferably, the portions of the coil 14 are aligned or superimposed with the corresponding coil portions 16, 18, 20, 22 of the coil 12, in a direction perpendicular to the plane of the substrate 10, as illustrated in the figure 2 .

[0047] According to optional embodiments, through vias 28 may be formed in the substrate 10, for example by drilling through the entire thickness of the substrate 10 in a direction perpendicular to the plane of the substrate 10.

[0048] Optionally, metal pads 30, 36 are deposited in contact with the through vias at the upper and lower faces of the coils when said through via is in the vicinity of a coil. For example, the pads are arranged at the interfaces 24 or 26.

[0049] Preferably, the metal pads are made of copper. According to an exemplary manufacturing method, the metal pads 30, 36 are manufactured before the assembly of the substrate 10 by depositing a metal layer on a base stack of the substrate. This metal layer is then etched in a predetermined pattern to form the pads 30 and 36, and is then covered by other layers of the substrate 10. When the substrate 10 is then pressed by rolling to finalize the manufacture of the sensor 6, the layers come into contact at the interfaces 24 and 26, respectively, and fill the void left by the metal removed by the etching.

[0050] In the example illustrated, the through via 28 is arranged in the vicinity of the coil 12. Metal pads 30 are arranged in the interface 26, where the lower face of the coil 12 is arranged.

[0051] For example, the metal pads have a circular or square shape and are arranged around the section of the through via 28 in this interface 26.

[0052] Preferably, metal pads 32 are arranged at the upper and lower ends of the through via 28 on the upper and lower faces, respectively, of the substrate 10.

[0053] In the illustrated example, a second through via 34, similar to the through via 28, is arranged in the vicinity of the second coil 14. Metal pads 36 similar to the metal pads 30 are arranged in the interface 24.

[0054] These examples are not limiting and other through vias may be configured differently. Alternatively, through vias 28, 34 may be omitted.

[0055] According to particularly advantageous embodiments, the current sensor 6 comprises at least one ferromagnetic layer 40, 42 integrated into the or each portion of the insulating substrate 10 surrounded by the or each coil, so that said coil surrounds said ferromagnetic layer.

[0056] In the illustrated example, a first ferromagnetic layer 40 is integrated into the first portion of the substrate 10 which is surrounded by the first coil 12, between the upper face of the substrate 10 and the interface 24.

[0057] A second ferromagnetic layer 42 is integrated into the second portion of substrate 10 which is surrounded by the second coil 14, between the lower face of substrate 10 and the interface 26.

[0058] Thanks to the addition of such a ferromagnetic layer, the gain of the current sensor 6 is improved. This ultimately improves the accuracy of the current measurement by both the measuring sensor 6 and the measuring system 2.

[0059] In a non-limiting example given by way of illustration, the inventors have found that, thanks to the embodiments of the invention, the measurement gain of the current sensor 6 can be improved by a factor greater than or equal to five compared to known Rogowski windings on printed circuits, for example to obtain a gain greater than or equal to 80 µV per Ampere.

[0060] This increase in gain is particularly advantageous when the sensor 6 is used as a current sensor in an electrical protection device within an electricity distribution installation. Indeed, an electrical protection device must be able to be triggered quickly as soon as an electrical fault is measured. However, certain signal processing means, such as passive integrators, introduce an attenuation of the signal which, with current sensors having a low gain, can degrade the signal to the point of compromising the ability of the processing circuit 8 to detect the electrical fault. The use of a digital integrator would make it possible to attenuate the measured signal only slightly, but would have the disadvantage of introducing a high latency time to the point that the protection device could not react sufficiently quickly in the event of detection of an electrical fault.On the contrary, thanks to the sensor 6, the processing circuit 8 can include a simple passive integrator, which is simpler to manufacture and avoids the aforementioned problems.

[0061] Alternatively, the number of ferromagnetic layers may be different. For example, it is chosen according to the number of coils 12 or 14. It is therefore understood that, in the variants where the coil 14 is omitted, the layer 42 may also be omitted.

[0062] Preferably, each coil 12 or 14 surrounds only one ferromagnetic layer.

[0063] In practice, the first coil 12 passes through the first ferromagnetic layer 40. The second coil 14 passes through the second ferromagnetic layer 42. Preferably, the coils 12 and 14 are not in electrical contact with the ferromagnetic layers 40 and 42.

[0064] According to examples, the ferromagnetic layers 40 and 42 are identical.

[0065] Preferably, the ferromagnetic layers 40 and 42 have similar or identical dimensions and geometric arrangements, for example aligned or superimposed with respect to each other in a direction perpendicular to the plane of the substrate 10.

[0066] In the following, only the ferromagnetic layer 40 is described in detail, but this teaching can be transposed to the ferromagnetic layer 42.

[0067] According to embodiments, the ferromagnetic layer 40 comprises a sub-layer of an iron and nickel alloy 44 and two sub-layers of copper 46, 48 stacked on either side of the sub-layer 44.

[0068] For example, the iron and nickel alloy is a Fe-Ni36% alloy, also known under the registered trademark “Invar”. This alloy advantageously provides good magnetic properties, while having mechanical properties that facilitate the construction and maintenance of the substrate 10.

[0069] The ferromagnetic layer 40 may be formed by deposition of material, or be constructed in the form of a plate integrated into the substrate 10 during its manufacture.

[0070] Alternatively, other materials may be used to form the ferromagnetic layer 40, such as a ferromagnetic metal alloy.

[0071] According to embodiments, the ferromagnetic layer 40 is greater than or equal to 150 µm, or greater than or equal to 250 µm.

[0072] In the illustrated example, the ferromagnetic layer 40 is arranged between a first sub-layer 41 of the substrate 10 and a second sub-layer 43 of the substrate. The interface 24 is formed between the second sub-layer 43 and a layer of the core of the substrate 10. A similar arrangement is used for the ferromagnetic layer 42 with respect to the interface 26.

[0073] In a non-limiting example given by way of illustration, the total thickness of the substrate 10, measured along a direction perpendicular to the plane of the substrate 10, can be between 0.1 cm and 1 cm.

[0074] According to embodiments, when one or more through vias 28, 34 cross the substrate 10, the ferromagnetic layer 40 can be separated laterally from said through via 28, 34 by a buffer zone 50 devoid of ferromagnetic material.

[0075] It is understood that this buffer zone 50 is arranged in alignment with the ferromagnetic layer 40.

[0076] According to examples, the buffer zone 50 can be filled with an electrically insulating material, or be formed by a recess in the ferromagnetic layer 40. In other words, the ferromagnetic layer 40 is not in electrical contact with the through vias 28 and 34. The recess can be obtained by drilling the ferromagnetic layer or by etching the ferromagnetic layer.

[0077] For example, the buffer zone 50 is sized so that the distance between the lateral edge of the through via 28, 34 and the ferromagnetic material of the ferromagnetic layer 40 closest to said lateral edge, this distance being measured in a direction parallel to the plane of the substrate 10, is greater than or equal to 25% of the width of said through via.

[0078] In a non-limiting example given for illustrative purposes, the width of the through via 28 is equal to 650 µm. On each side of the through via 28, the buffer zone 50 has a width greater than or equal to 200 µm.

[0079] There figure 4 represents a current sensor 6' according to a second embodiment. Current sensor elements 6' which are analogous to the first embodiment bear the same references and are not described in detail, since the description given above with reference to the figures 2 And 3 can be transposed to them.

[0080] The current sensor 6' is essentially identical or similar to the current sensor 6, and notably comprises a plurality of coil portions 14, 18, 20 and 22.

[0081] The current sensor 6' differs in particular from the current sensor 6 in that each ferromagnetic layer 40, 42 is divided, in the plane of the ferromagnetic layer, into several parts preferably electrically insulated from one another, each of these parts being associated with one of the coil portions 14, 18, 20 and 22.

[0082] In the illustrated example, the plate 40 is divided into four parts 60, 62, 64 and 66 respectively associated with the coil portions 18, 20, 22 and 16.

[0083] It is understood that the parts 60, 62, 64 and 66 are electrically isolated from each other, for example by being separated, in the plane of the ferromagnetic layer 40, by a zone devoid of magnetic material or by an electrically insulating material, for example like the buffer zones 50 previously described.

[0084] By "associated with a coil portion" is meant here that the corresponding coil portion surrounds said ferromagnetic layer portion and that it is aligned with said ferromagnetic layer portion in a direction perpendicular to the plane of the substrate 10.

[0085] In practice, each part of the ferromagnetic layer 40, 42 is associated with only one of the coil portions 16, 18, 20 and 22.

[0086] Such a division of the ferromagnetic layer advantageously makes it possible to avoid premature magnetic saturation of the ferromagnetic layer when the current flowing in the conductor 4 reaches high values. The advantages provided by the presence of the ferromagnetic layer in terms of gain are nevertheless preserved.

[0087] Here again, this embodiment is not limited by the number of coil portions 16, 18, 20 and 22 or by the number of ferromagnetic layer parts 40, 42.

[0088] Although not illustrated in detail, it is understood that the same applies to layer 42, which is also divided in a similar way.

[0089] Advantageously, the magnetic layer portions 60, 62, 64 and 66 can be formed by depositing magnetic layers similar to layers 40 and 42 during substrate fabrication and then cutting these layers by drilling the substrate using a drilling tool. For example, several holes are drilled perpendicular to the plane of the substrate in the corners of the layers to form air gaps that delimit the portions 60, 62, 64 and 66. This method makes it possible to simultaneously cut the two ferromagnetic layers of the stack in the same way and thus to obtain portions 60, 62, 64 and 66 of the same dimensions for the two ferromagnetic layers. In addition, the width of the air gap can be easily adjusted by choosing a larger or smaller drilling tool, which makes it possible to easily adjust the gain value of the sensor.

[0090] The invention is defined by the attached claims.

Claims

1. Current sensor (6; 6'), comprising: - an insulating substrate (10) provided with a central opening, the central opening (7) being configured to receive an electrical conductor (4); - a winding surrounding the central aperture and including a coil (12, 14) wound around a portion of the insulating substrate; in which the current sensor comprises at least one ferromagnetic layer (40, 42) integrated in the portion of the insulating substrate, the coil (12, 14) surrounding the ferromagnetic layer characterised in that the winding further comprises an additional coil (14) wound around a further portion of the substrate offset in a direction perpendicular to the plane of the substrate (10), the two coils (12, 14) being interleaved and electrically connected in series, and wherein an additional ferromagnetic layer (42) is embedded in said further portion of the insulating substrate, the additional coil (14) surrounding the additional ferromagnetic layer.

2. Current sensor (6; 6') as claimed in claim 1, wherein the coil (12) comprises a plurality of coil portions (16, 18, 20, 22) electrically connected in series, the coil portions being rectilinear in shape and arranged to form a closed quadrilateral contour around the central opening.

3. Current sensor (6) according to claim 2, in which the ferromagnetic layer (40, 42) is common to all the coil portions.

4. Current sensor (6') according to claim 2, in which the ferromagnetic layer is divided into several parts (60, 62, 64, 66) each associated with one of the coil portions (16, 18, 20, 22).

5. Current sensor (6; 6') according to any one of the preceding claims, in which the ferromagnetic layer (40, 42) comprises an under layer of an iron-nickel alloy (44) and two copper under layers (46, 48) stacked on either side of the iron-nickel alloy under layer.

6. Current sensor (6; 6') according to claim 5, wherein the iron-nickel alloy is an Fe-Ni36% alloy.

7. Current sensor (6; 6') according to any of the preceding claims, in which the thickness of the ferromagnetic layer (40, 42) is greater than or equal to 150 µm.

8. Current sensor (6; 6') according to any one of the preceding claims, in which the substrate (10) comprises a through via (28, 34) perpendicular to the plane of the substrate, and in which the ferromagnetic layer (40, 42) is separated from said through via (28, 34) by a buffer zone (50) devoid of ferromagnetic material.

9. urrent sensor (6; 6') according to any one of the preceding claims, wherein the substrate (10) is a printed circuit substrate comprising one or more stacked layers of a cured polymer material.

10. Measurement system (2), characterised in that it comprises a current sensor (6; 6') according to any one of the preceding claims and an electronic processing circuit (8) configured to process the signal measured by the current sensor (6; 6').