Coreless current transducer

Abstract

A coreless current transducer (2) comprising: - a primary conductor (3) having a central section with a substantially rectangular cross- section having a width to height ratio greater than 5, the primary conductor (3) comprising a reduced width centre measurement portion (10) of the primary conductor, - a circuit board (4) having a first side (12) and an opposed second side (13), and - a magnetic field sensor (5) mounted on said second side (13) of the circuit board, the magnetic field sensor (5) comprising one, or two, or more than two sensing portions (20). The circuit board (4) comprises primary conductor solder fixing pads (14) positioned on the first side (12), the primary conductor mounted directly against the first side of the circuit board and being soldered to the primary conductor solder fixing pad or pads (14) at the centre measurement portion (10).

Description

[0001] CORELESS CURRENT TRANSDUCER

[0002] The present invention relates to a coreless current transducer, in particular for measuring high current densities, for instance for electrical vehicle or battery management systems.

[0003] Electrical vehicles typically have three phase motors and electrical systems, each phase having a dedicated current transducer that may be positioned in different parts of the electrical system between power supplies, motors, and controllers. Typical electrical parameters in such applications may include currents in a range of 10 to 10k amperes, frequencies from DC to 50kHz, and voltages from 12 volt to 1.2 kvolts.

[0004] It is known to provide current transducers comprising a section of primary conductor that is connected (clamped, welded, bolted or soldered) to the phase of the electrical system to be measured, for instance at the output of an inverter or integrated within other electrical systems.

[0005] The primary conductor may typically have a substantially rectangular cross section busbar made of copper, aluminum or alloys thereof, around which a ferromagnetic core is mounted having an airgap within which a magnetic field detector is positioned to measure the electrical current flowing in the primary conductor.

[0006] It is also known to provide coreless transducers, which have a magnetic field detector positioned in proximity to the primary conductor busbar. The magnetic field sensor may have a pair of magnetic field sensing elements that are separated apart and positioned around a portion of the primary conductor to measure a differential magnetic field, or a magnetic field gradient, that represents the primary current to be measured. The accuracy of the measurement output is however dependent on the precise relative positioning of the magnetic field sensing elements and the primary conductor portion, whereby the positioning is affected by relative displacements caused by mechanical or thermal effects. For instance, the primary conductor will have a different thermal dilatation coefficient than the support on which the magnetic field sensing device is connected. Also, there may be slight manufacturing tolerances in the coupling between the magnetic field sensing device and the primary conductor, or there may be slight displacements in mechanical couplings between the magnetic field sensor and the primary conductor due to vibrations and shocks.

[0007] Current transducers with magnetic cores are less sensitive to a relative position between magnetic core and the primary conductor, however such transducers are bulkier and generally more costly than coreless transducers. Smaller transducers are easier to integrate in the footprints of electronic components, and there is a continuing need to further reduce the size of coreless transducers, since the more compact they are, the easier it is to also reduce the size of the components in which they are integrated.

[0008] In view of the foregoing, it is an object of this invention to provide a coreless current transducer for high current applications that is accurate yet compact and economical to produce.

[0009] It is advantageous to provide a coreless current transducer that is robust and reliable in harsh environments subject to mechanical and thermal effects such as found in the automotive applications.

[0010] It is advantageous to provide a current transducer that may be easily integrated into electrical systems, in particular of electric vehicles.

[0011] Objects of the invention have been achieved by providing a system according to claim 1.

[0012] Dependent claims set out various advantageous features of embodiments of the invention.

[0013] Disclosed herein is a coreless current transducer comprising:

[0014] - a primary conductor having a central section with a substantially rectangular cross-section having a width to height ratio greater than 5, the primary conductor comprising a reduced width centre measurement portion of the primary conductor,

[0015] - a circuit board having a first side and an opposed second side, and

[0016] - a magnetic field sensor mounted on said second side of the circuit board, the magnetic field sensor comprising one, or two, or more than two sensing portions.

[0017] The circuit board comprises primary conductor solder fixing pads positioned on the first side, the primary conductor mounted directly against the first side of the circuit board and being soldered to the primary conductor solder fixing pad or pads at the centre measurement portion.

[0018] In an embodiment, the primary conductor comprises lateral slots including at least a first lateral slot extending from a first side edge of the primary conductor and a second lateral slot extending from a second side edge of the primary conductor forming the centre measurement portion of the primary conductor. In an advantageous embodiment, the first and second lateral slots overlap each other and are spaced apart from each other forming the centre measurement portion of the primary conductor such that the primary current flows through in a meandering path.

[0019] In an embodiment, the primary conductor is soldered to the primary conductor solder fixing pads at outer sides of the first and second lateral slots.

[0020] In an embodiment, the primary conductor solder fixing pads comprise a plurality of rows including a centre row and first and second outer edge rows, each row being formed of a plurality of spaced apart solder fixing pads.

[0021] In an embodiment, the plurality of solder fixing pads forming said rows extend substantially a whole width between the first and second sides of the primary conductor.

[0022] In an embodiment, the sensing portions of the magnetic field sensor are positioned overhead the centre measurement portion or the lateral slots of the primary conductor.

[0023] In an embodiment, the magnetic field sensor comprises at least first and second magnetic field sensing portions, the first magnetic field sensing portion being positioned overhead the first lateral slot and the second magnetic field sensing portion being positioned overhead the second lateral slot.

[0024] In an embodiment, the sensing portions are positioned substantially centrally between outer side edges of the centre section of the primary conductor.

[0025] In an embodiment, the magnetic field sensor comprises an integrated circuit chip, having therein Hall effect sensing portions or TMR magnetic field sensing portions.

[0026] In an embodiment, the primary conductor extends between connection terminals at opposed ends of the primary conductor, the circuit board being positioned substantially centrally between the connection terminals.

[0027] In an embodiment, the primary conductor extends between connection terminals each connection terminal being configured for a weld, solder, bolt or mechanical clamping connection in series to a conductor carrying the current to be measured.

[0028] In an embodiment, the circuit board comprises a secondary connection arrangement for connecting the magnetic field sensor to power supply and measurement signal processing circuitry, the secondary connection arrangement comprising contact pins upstanding from the second side of the circuit board or by contact pads formed on the surface of the second side of the circuit board.

[0029] In an embodiment, the transducer further comprises a housing overmolded over a centre measurement portion of primary conductor except for a portion of a surface of the primary conductor against which the first side of the circuit board is rigidly attached.

[0030] In an embodiment, the housing has side walls upstanding from a base wall such that a recess is formed receiving fully the circuit board therein and allowing space for a potting resin to cover the second side of the circuit board and magnetic field sensor position thereon.

[0031] Also disclosed herein is a multiphase current transducer arrangement comprising a plurality of current transducers according to any of the preceding embodiments.

[0032] In an embodiment, the multiphase current transducer is a three-phase current transducer arrangement, including a housing securing three said current transducers and a circuit board connected to the secondary connection arrangement (7) of the three current transducers.

[0033] Further advantageous features of the invention will be apparent from the following detailed description of embodiments of the invention and the accompanying illustrations.

[0034] Brief description of the figures

[0035] Figure 1a is a perspective view of a current transducer according to an embodiment of this invention;

[0036] Figure 1 b is a perspective view from a bottom side of embodiment of figure 1 a;

[0037] Figure 2 is a perspective view similar of a current transducer according to another embodiment of this invention;

[0038] Figure 3a is a schematic perspective view of a circuit board of a current transducer according to an embodiment of the invention;

[0039] Figure 3b is a perspective view of an underside of the circuit board of figure 3a;

[0040] Figure 3c is a perspective view of a primary conductor of a current transducer according to an embodiment of the invention;

[0041] Figure 3d is a view of the circuit board of figure 3b showing in dotted outline the position of the primary conductor and of magnetic sensing elements, according to an embodiment of the invention;

[0042] Figure 4a is a perspective view of a current transducer according to another embodiment of the invention;

[0043] Figure 4b is an exploded view of the transducer of figure 4a;

[0044] Figure 5a is a perspective view of a multiphase current transducer arrangement with current transducers according an embodiment of the invention;

[0045] Figure 5b is a view of the multiphase current transducer arrangement of figure 1 with a housing and circuit board removed;

[0046] Figure 5c is view similar to figure 5b of a variant.

[0047] Figure 6a is a perspective view of a primary conductor of a current transducer according to another embodiment of the invention;

[0048] Figure 6b is a view of a circuit board of a current transducer according to the embodiment of figure 6a;

[0049] Figure 7a is a perspective view of a primary conductor of a current transducer according to yet another embodiment of the invention;

[0050] Figure 7b is a view of a circuit board of a current transducer according to the embodiment of figure 7a.

[0051] Referring to the figures, a current transducer 2 according to embodiments of the invention comprises a primary conductor 3, a circuit board 4, and a magnetic field sensor 5.

[0052] The primary conductor 3 is in the form of what is commonly known as a busbar that has a generally rectangular cross section with a width to height ratio that is typically greater than 5 and having a generally planar central section extending between connection terminals 11a, 11b at ends of the busbar. The connection terminals may have various shapes and dimensions that are adapted for connection to complimentary terminals of a conductor carrying the current to be measured. The connection terminals may comprise a hole for a bolt, or a bent foot for a solder or weld connection, or various other forms per se known for mechanical, weld, or solder connections. The connection terminals at opposed ends of the primary conductor 3 may also be different, for instance as illustrated in the example embodiment of figure 2, or may be the same, for instance as illustrated in the example embodiment of figure 1a. For instance, one end of the transducer may be clamped, welded or bolted to an output of an inverter, and the other end to a cable or other form of conductor connected to an electrical component supplied with power from the inverter. The current transducers are thus connected in line with the conductor carrying the current to be measured.

[0053] The current transducer 2 may be part of a multiphase current transducer arrangement 1 as illustrated in figures 5a to 5c, for instance a three-phase arrangement. Each electrical phase may comprise its own current transducer. Typical maximum currents that flow through the transducer in applications such as in electrical vehicles may be in a range of 100 to 1500 amperes. In such applications, the cross-sectional area of the primary conductor busbar, which is often made of copper or aluminum alloy, will be typically in a range of 10 to 70 mm2.

[0054] The primary conductor 3 has substantially parallel side edges 8 that define the width of the busbar. In embodiments, the primary conductor 3 comprises at least two lateral slots 9, a first lateral slot 9a extending from one of the side edges 8a and a second lateral slot 9b extending from the opposed second side edge 8b such that a reduced cross-section centre measurement portion 10 is formed.

[0055] In a preferred embodiment, the second lateral slot 9b is spaced apart from the first lateral slot in the general direction of current flow between connection terminals 11a, 11b, such that the current flowing through the primary conductor from one connection terminal 11a to the other connection terminal 11 b goes through a meandering path. The lateral slots overlap each other such that a transversely oriented centre measurement portion 10 is formed between the pair of lateral slots 9a, 9b. In this advantageous embodiment, the primary current flowing through the centre measurement portion 10 has a transverse flow direction to the general direction of current flow between the connection terminals 11a, 11b.

[0056] In variants, it is possible to have other shapes of measurement portions that concentrate the current to be measured, that are not based on a transverse current flow direction as illustrated in figures 6a and 7a. For instance indents 9a, 9b that are not offset but aligned and simply create a narrow section of the primary conductor centre measurement portion 10 may also be provided. Also, a centre slot 9c may be provided as illustrated in figure 7a.

[0057] The smaller section centre measurement portion 10 has a higher current density than the adjoining sections of the primary conductor, to increase the magnetic field intensity in the proximity of the centre measurement section ,as per se known in coreless current transducers.

[0058] The magnetic field sensor 5 comprises one or more magnetic field sensing portions 20 that are positioned overhead the lateral slots 9 and centre measurement portion 10. If there is a single sensing portion on the magnetic field sensor, it is preferably positioned overhead the centre measurement portion 10. If the magnetic field sensor comprises two or at least two sensing portions 20, they may be positioned over edges of the centre measurement portion. In the illustrated embodiment with a transversely oriented centre measurement portion (figures 3c to 3d), at least one of the two sensing portions may be positioned overhead the first lateral slot 9a and a second of the least two sensing portions may be positioned overhead the second lateral slot 9b for instance as schematically illustrated in figure 3d.

[0059] The sensing portion(s) 20 may be configured to measure a magnetic field that is orthogonal to the surface of the circuit board 4 on which the magnetic field sensor is mounted, for instance Hall effect sensors measuring a current flowing through the centre measurement portion 10. In a variant, the sensing portions may comprise tunnel magnetoresistance (TMR) sensors that measure an in-plane magnetic field gradient, representative of the current flowing through the centre measurement portion 10 of the primary conductor 3.

[0060] The circuit board 4 comprises a first side 12 corresponding to a primary conductor mounting side, and a second opposed side 13 corresponding to a magnetic field sensor mounting side.

[0061] The magnetic field sensor 5 is mounted on the second side 13 and may in particular comprise an integrated circuit chip 18 that includes the one or more sensing portions 20 as perse well known in the art, the integrated circuit chip 18 being connected to circuit traces on the second side of the circuit board, for instance in a surface mount connection, as perse well known in the art.

[0062] Further electronic components may be mounted on the second side of the circuit board 4.

[0063] The transducer includes a secondary connection arrangement 7 for transmission of power and measurement signals between the magnetic field sensor 5 and an external system. The secondary connection arrangement 7 may comprise pin contacts such as illustrated in the embodiments of figures 1a and 5b, or metallized pads such as illustrated in the embodiments of figures 2, or other perse known connection elements for connection to an external system.

[0064] According to an aspect of the invention, on the first side 12 of the circuit board 4, primary conductor solder fixing pads 14 are provided for direct solder attachment of the primary conductor 3 against the second side 13 of the circuit board 4 at least in the vicinity of the centre measurement portion 10. The primary conductor solder fixing pads 14 are arranged such that there is at least one or more centre pads 15 that attaches to the centre measurement portion 10 of the primary conductor.

[0065] In the illustrated embodiment of figures 3c to 3d with lateral offset slots forming the transversely oriented centre measurement portion 10, there are provided at least first and second outer edge rows 16, 17 of solder fixing pads that attach to the primary conductor adjacent outer edges of the first lateral slot 9a and second lateral slot 9b respectively. The primary conductor 3 is thus securely attached to the circuit board along edges of each lateral slot, whereby there may be additional rows 16b, 17b adjacent the outer edge rows 16, 17 for a more secure attachment of the primary conductor to the circuit board.

[0066] In the other embodiments as illustrated in figures 6a to 7b, there may also be provided at least first and second outer edge rows 16, 17 of solder fixing pads that attach to the primary conductor adjacent ends of the centre measurement portion 10.

[0067] The primary conductor solder fixing pads 14 may comprise metallized pads formed on the first side of the circuit board similar to connection circuit pads that are commonly formed on circuit boards for interconnecting to electrical components. The solder fixing pads serve to fix the primary conductor securely to the circuit board in a direct solder attachment for instance via a solder reflow connection, that is well known in circuit board connection technology, or by welding, for instance spot welding the primary conductor to the corresponding solder fixing pads. In addition to the solder or weld connection, adhesive bonding material may be provided between the circuit board and the primary conductor.

[0068] The solder fixing pads 14 are preferably configured as individual pads that are spaced apart from each other such that the primary conductor is fixed to the circuit board in a plurality of discrete positions. This allows solder to flow more evenly for an accurate control of the spacing between the primary conductor and the first side 12 of the circuit board, in particular to have a minimal spacing therebetween.

[0069] In the illustrated embodiment, the primary conductor solder fixing pads 14 may be arranged in rows that extend across from one side edge 8a of the primary conductor to the other side edge 8b.

[0070] The direct solder attachment of the centre measurement portion 10 of the primary conductor, as well as the direct solder attachment of the primary conductor on outer edges of the lateral slots 9, very securely and rigidly fixes and adjusts the position of the centre measurement portion 10 with respect to the position of the magnetic field sensor 5 and the associated sensing portions 20 on the second side of the circuit board. Contrary to conventional devices, the localized attachment of the centre measurement portion in a solder connection ensures a very accurate dimensional positioning of the centre measurement portion relative to the magnetic field sensor, which is not affected by thermal dilatation of the components, nor by mechanical stresses. Moreover the positioning of the magnetic field sensor and primary conductor on opposite sides of the circuit board allows to benefit from the surface area of the insulating material of the circuit board to easily provide a large electrical creepage distance. In addition, soldering the primary conductor to fix the centre portion accurately with respect to the magnetic field sensor can be performed with per se conventional solder reflow techniques used simultaneously for the connection of other SMD components on the circuit board.

[0071] The circuit board material, which may be of per se known materials for circuit boards, has a lower thermal expansion coefficient than metals such as copper or aluminum used for the primary conductor. Such circuit board materials may for instance include glass fibre reinforced epoxy resin, woven glass reinforced hydrocarbon / ceramics, ceramic-filled reinforced material with very low fiberglass content, and woven Glass Reinforced PTFE.

[0072] In the preferred illustrated embodiment, the rigid attachment of the primary conductor along the slot edges further assists the very accurate positioning of the sensing portions 20 with respect to the primary conductor with a low variability over a large temperature range. Also, mechanical stresses and vibration do not shift the position of the sensing portions 20 with respect to the primary conductor portion 10 and lateral slots 9. Moreover, the direct attachment of the primary conductor via the solder fixing pads on the surface of the circuit board first side 12 ensures that the primary conductor is as close as possible to the magnetic field sensor positioned directly against the second side 13 of the circuit board.

[0073] An additional advantage of the described arrangement is that the circuit board substrate, which is an insulating material, and the central position of the magnetic field sensor thereon acts to provide a large electrical creepage distance between the magnetic field sensor 5 and the primary conductor 3. The primary conductor 3 is spaced from the magnetic field sensor 5 on the other side of the circuit board by a large creepage distance that is defined by the central position of the magnetic field sensor 5 on the circuit board to the edges of the circuit board, whereby the circuit board may be dimensioned in width and length to adjust the creepage distance and thus form a ledge that extends over the side edges 8 of the primary conductor as best illustrated in figure 1b.

[0074] In an embodiment, an insulating housing 6, for instance of a thermosetting or thermoplastic polymer, may be molded over a central section of the primary conductor, for instance as illustrated in figures 4a and 4b while leaving an exposed surface of the primary conductor for direct mounting and attachment of the circuit board 4 thereagainst. Side walls of the overmolded housing may extend beyond the thickness of the circuit board 4, in other words forming a recess within which the circuit board 4 is received, the recess then being filled with an insulating material, for instance a potting resin that covers the circuit board 4 and magnetic field sensor 5. Potting resins for covering electronic and electrical components are per se well known and do not need to be further described herein.

[0075] The current transducer 2 may be interconnected to external electronics for power supply and measurement signal processing by way of a circuit board 100 connected to the secondary connection arrangement 7 of the current transducer 2, whereby a plurality of current transducers may be connected to a single circuit board for instance as illustrated in the multiphase current transducer arrangement 1 of figure 5a. The circuit board 100 of the multiphase current transducer arrangement 1 illustrated in figure 5a may comprise further electronic components of an external system for instance of a multiphase current inverter. The current transducer connection terminals that are outside of the multiphase current transducer arrangement 1 may be for plugging, clamping or bolt connection to conductor cables or other conductor systems supplied with the phase currents.

[0076] List of references

[0077] Multiphase current transducer arrangement 1

[0078] Current transducer 2

[0079] Primary conductor 3

[0080] Busbar

[0081] Side edges 8

[0082] Lateral slots 9

[0083] First lateral slot 9a

[0084] Second lateral slot 9b

[0085] Centre slot 9c

[0086] Centre measurement portion 10

[0087] Connection terminals 11a, 11 b

[0088] Circuit board 4

[0089] First side (primary conductor mounting side) 12

[0090] Primary conductor solder fixing pads 14

[0091] Centre measurement portion pads 15

[0092] First and second side pads 16, 17

[0093] Second side (magnetic field sensor mounting side) 13

[0094] Magnetic field sensor 5

[0095] IC chip 18

[0096] Sensing portions 20

[0097] Housing 6

[0098] Secondary connection arrangement 7

Claims

Claims1 . A coreless current transducer (2) comprising:- a primary conductor (3) having a central section with a substantially rectangular crosssection having a width to height ratio greater than 5, the primary conductor (3) comprising a reduced width centre measurement portion (10) of the primary conductor,- a circuit board (4) having a first side (12) and an opposed second side (13), and- a magnetic field sensor (5) mounted on said second side (13) of the circuit board, the magnetic field sensor (5) comprising one, or two, or more than two sensing portions (20), characterized in that the circuit board (4) comprises primary conductor solder fixing pads (14) positioned on the first side (12), the primary conductor mounted directly against the first side of the circuit board and being soldered to the primary conductor solder fixing pad or pads (14) at the centre measurement portion (10).

2. The current transducer according to claim 1 wherein the primary conductor (3) comprises lateral slots (9) including at least a first lateral slot extending from a first side edge (8) of the primary conductor and a second lateral slot extending from a second side edge (8) of the primary conductor.

3. The current transducer according to claim 2 wherein the first and second lateral slots overlapping each other and spaced apart from each other forming the centre measurement portion (10) of the primary conductor.

4. The current transducer according to claim 2 or 3 wherein the primary conductor is soldered to the primary conductor solder fixing pads (14) at outer sides of the first and second lateral slots.

5. The current transducer according to claim 2, 3 or 4 wherein the primary conductor solder fixing pads comprise a plurality of rows including a centre row (15) and first and second outer edge rows (16), each row being formed of a plurality of spaced apart solder fixing pads.

6. The current transducer according to the preceding claim wherein the plurality of solder fixing pads forming said rows extend substantially a whole width between the first and second sides (8) of the primary conductor.

7. The current transducer according to any preceding claim 2-6 wherein the sensing portions (20) of the magnetic field sensor are positioned overhead the centre measurement portion (10) or the lateral slots (9) of the primary conductor.

8. The current transducer according to any preceding claim 2-7 wherein the magnetic field sensor comprises at least first and second magnetic field sensing portions (20), the first magnetic field sensing portion being positioned overhead the first lateral slot (9a) and the second magnetic field sensing portion being positioned overhead the second lateral slot (9b).

9. The current transducer according to any preceding claim wherein the sensing portions (20) are positioned substantially centrally between outer side edges (8) of the centre section of the primary conductor.

10. The current transducer according to any preceding claim wherein the magnetic field sensor (5) comprises an integrated circuit chip (18), having therein Hall effect sensing portions or TMR magnetic field sensing portions.

11. The current transducer according to any preceding claim wherein the primary conductor (3) extends between connection terminals (11a, 11b) at opposed ends of the primary conductor, the circuit board being positioned substantially centrally between the connection terminals (11a, 11b).

12. The current transducer according to any preceding claim wherein the primary conductor (3) extends between connection terminals (11a, 11b) each connection terminal being configured for a weld, solder, bolt or mechanical clamping connection in series to a conductor carrying the current to be measured.

13. The current transducer according to any preceding claim wherein the circuit board (4) comprises a secondary connection arrangement for connecting the magnetic field sensor (5) to power supply and measurement signal processing circuitry, the secondary connection arrangement (7) comprising contact pins upstanding from the second side (13) of the circuit board (4) or by contact pads formed on the surface of the second side (13) of the circuit board.

14. The current transducer according to any preceding claim further comprising a housing (6) overmolded over a centre measurement portion of primary conductor (3) except for a portion of a surface of the primary conductor against which the first side (12) of the circuit board (4) is rigidly attached.

15. A multiphase current transducer arrangement comprising a plurality of current transducers according to any of the preceding claims.

16. The multiphase current transducer arrangement according to the preceding claim being a three-phase current transducer arrangement, including a housing securing three saidcurrent transducers and a circuit board connected to the secondary connection arrangement (7) of the three current transducers.

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