Current transformer with shunt and magnetic field detector

Abstract

Current transformer (1) comprising a primary conductor rail (2), a first current measuring device (5) and a second current measuring device (6), wherein the primary conductor rail comprises a first measuring section (12) comprising a shunt resistor (9) and a second measuring section (14) comprising notches (16), wherein the first current measuring device (5) comprises - the shunt resistance (9), - a first circuit board (11) and - Shunt terminals (15) connecting the circuit board to the primary busbar to measure a voltage across the shunt resistor (9), the first current measuring device (6) comprising - a magnetic field transducer comprising a magnetic field detector (8) for measuring a primary current flowing through the core segment (18), characterized in that the second current measuring device (6) comprises a U-shaped magnetic core (7) having an end leg (7a) and lateral legs (7b) extending from the end leg to free ends and defining a central slot (26) between them, wherein the core segment (18) of the primary conductor rail is mounted within the central slot (26) and the magnetic field detector (8) is mounted on a second circuit board (13) independent of the first circuit board (11) and is inserted into an air gap formed between the lateral legs (7b).

Description

[0001] The present invention relates to a current transformer comprising a magnetic field detector and a primary conductor rail with a shunt resistor.

[0002] One of the known shunt converter designs, particularly for high-current applications, comprises a busbar, typically in the form of a rectangular-profile rail, designed to be clamped or otherwise connected to a primary conductor carrying the current to be measured. The busbar typically has a section of a shunt material such as manganin—a copper-manganese-nickel alloy—formed in one piece and connected at both ends to the copper busbar, thereby measuring the resistance across the shunt material section.

[0003] In many applications, such as automotive, it is important to have a redundant measurement signal for safety and reliability reasons, which generally requires a second current transducer. It is known to provide a magnetic field sensor in the form of a Hall cell on an integrated circuit mounted on a printed circuit board positioned near the primary conductor rail, with the circuit board also processing the shunt resistance signal. Although such arrangements are compact, reliability and safety are not optimal, since a faulty printed circuit board common to both the shunt sensor and the magnetic field sensor could cause both current sensors to fail.In addition, the accuracy of the magnetic field detector depends on the accuracy of the distance and positioning of the Hall cell with respect to the primary conductor rail, and at low currents the magnetic field strength is low and leads to a high noise-to-signal ratio, which can be problematic in demanding applications such as electric motors in automotive drive applications.

[0004] In view of the above, it is an object of the present invention to provide a current transformer having a primary conductor bar and two current measuring systems that is durable, reliable and accurate over a wide range of operating conditions.

[0005] It is advantageous to provide a current transformer that is economical to manufacture.

[0006] It is advantageous to provide a shunt current transformer that is compact and can be easily integrated into an external system.

[0007] For certain applications, it is advantageous to provide a current transformer suitable for measuring high currents and in the form of a busbar that can be coupled to standard circuits provided with busbar terminal connections.

[0008] Objects of the present invention have been achieved by providing a system according to claim 1. The dependent claims describe various advantageous features of embodiments of the invention.

[0009] Disclosed herein is a current transformer comprising a primary conductor bar, a first current measuring device, and a second current measuring device. The primary conductor bar comprises a first measuring section comprising a shunt resistor and a second measuring section comprising notches.

[0010] The first current measuring device includes: - the shunt resistance, - a first circuit board, and - Shunt terminals that connect the circuit board to the primary conductor rail to measure a voltage across the shunt resistor.

[0011] The second current measuring device includes: - a magnetic field converter comprising a magnetic field detector for measuring a primary current flowing through the core segment, and - a U-shaped magnetic core comprising an end leg and lateral legs extending from the end leg to free ends and forming a central slot therebetween.

[0012] The core segment of the primary conductor rail is mounted in the central slot and the magnetic field detector is mounted on a second circuit board independent of the first circuit board and inserted into an air gap formed between the side legs.

[0013] In an advantageous embodiment, the end leg of the U-shaped magnetic core is mounted against one side of the core segment of the primary conductor rail.

[0014] In an advantageous embodiment, the second circuit board is arranged parallel to the lateral legs, and the magnetic field detector comprises an integrated circuit chip in an insulating overmolding, which is surface-mounted on the second circuit board.

[0015] In an advantageous embodiment, an insulating housing is overmolded or mounted around the U-shaped magnetic core and the core segment, the housing comprising a cavity within the central slot of the U-shaped magnetic core into which the magnetic field detector and a portion of the second circuit board are inserted.

[0016] In an advantageous embodiment, the second current measuring device comprises a second connector, wherein the second connector has an insulating housing portion comprising a sheath formed integrally with the housing and surrounding the U-shaped magnetic core and the core segment.

[0017] In an advantageous embodiment, the primary conductor rail comprises transformer terminals at opposite ends of the primary conductor rail for clamping or screwing connection to external conductors, wherein the first current measuring device and the second current measuring device are positioned between the transformer terminals and adjacent to each other in close proximity.

[0018] In an advantageous embodiment, the first circuit board of the first current measuring device is mounted directly on a surface of the primary conductor rail above the shunt resistor.

[0019] In an advantageous embodiment, the first current measuring device comprises a first connector mounted on a top side of the first circuit board opposite to a bottom side mounted against the primary conductor rail.

[0020] In an advantageous embodiment, the first circuit board comprises shunt terminals (15) in the form of solder reflow contacts that are directly connected to the primary conductor rail.

[0021] In an advantageous embodiment, the shunt resistor consists of manganin.

[0022] In an advantageous embodiment, the current converter is intended for use in a battery management system for electric vehicles.

[0023] In an advantageous embodiment, a width (W3) of the lateral legs of the U-shaped magnetic core is equal to or smaller than a width (W2) of the corresponding notch in which the lateral leg is positioned.

[0024] In an advantageous embodiment, a width (W1) of the core segment formed between the notches is equal to a width of the central slot between inner sides of the lateral legs, except for a manufacturing tolerance which allows the assembly of the core segment within the central slot.

[0025] Further advantageous features of the invention will become apparent from the following detailed description of embodiments of the invention and the accompanying illustrations. Short description of the characters Fig. 1 is a perspective view of a current transformer according to an embodiment of the invention; Fig. Figure 2 is an exploded view of the embodiment of Fig. 1; Fig. 3 is a side view of the embodiment of Fig. 1; Fig. 4 is a cross-sectional view through line EE of Fig. 1; Fig. 5 is a schematic diagram illustrating measurement channels of a current transformer according to an embodiment of the invention.

[0026] With reference to the figures, a current transformer 1 according to an embodiment of the invention comprises a primary conductor bar 2, a first current measuring device 5, and a second current measuring device 6. The first current measuring device forms part of a first measuring channel 3, which outputs a first measurement output signal. The second current measuring device forms part of a second measuring channel 4, which outputs a second measurement output signal. An external measurement processing unit connected to the current transformer 1 may comprise a control system that compares or cross-checks the first and second measurement output signals to detect a fault in the current transformer and ensure the safe operation of components monitored or controlled by the current transformer. Such components may include, for example, battery packs or electric motors of electric vehicles, which require a high level of safety.

[0027] The power converter according to an embodiment of the invention can be used, for example, in a battery management system for electric vehicles.

[0028] The primary conductor can be provided with transformer terminals 10, for example, in the form of holes, as is well known for clamping on a screw-and-nut connection. Other well-known connection methods, with or without the provision of holes, for example, by clamp welding or soldering, can be provided in variants.

[0029] The primary conductor may have a non-planar shape, for example, with a curved section, and where the transformer terminals are not necessarily aligned. Various busbar configurations can be provided to suit the devices and the primary conductor configuration of the device to which they are to be coupled.

[0030] One or a plurality of the current transformers 1 may be integrated directly into an electrical system of a device having one or more electrical phases, or they may be provided as a single component for mounting and connection to external devices.

[0031] The primary conductor bar 2 may, in particular, have a busbar shape with a generally rectangular cross-section. The primary conductor bar 2 extends between opposite ends where the terminals 10 are provided. Between the terminals 10, the primary conductor bar 2 comprises a first measuring section 12, which includes a shunt resistor 9, and a second measuring section 14, which includes notches 16 flanking a narrow core segment 18.

[0032] The first current measuring device 5 comprises the shunt resistor 9, a first circuit board 11, and a first connector 20 mounted on and connected to the first circuit board. The shunt resistor 9 is connected to the first circuit board via shunt terminals 15 positioned at the ends of the shunt resistor, such that a current flowing through the shunt section can be measured. The circuits for measuring a shunt resistor are well known per se.

[0033] In an advantageous embodiment, the shunt terminals comprise solder pads on the circuit board that are soldered to the primary conductor at corresponding discrete points, for example, by reflow soldering. Reflow soldering can be performed using a standard soldering process for SMD components. The solder pads are separated from each other, and the voltages applied to these pads are separate inputs for processing by the analog front-ends.

[0034] In variations, the shunt terminals may comprise pin terminals that are welded or soldered to the surface of the primary conductor or that are press-fitted into corresponding terminal receiving cavities formed in the primary conductor.

[0035] The shunt terminals 15 are preferably connected to the main material of the primary conductor at the interface (boundary) of the shunt section rather than being directly connected to the material of the shunt resistor.

[0036] The material of the shunt resistor 9 is preferably a material with a low temperature coefficient of resistance, in particular a copper-manganese-nickel (Cu-Mn-Ni) alloy such as Manganin (Cu84 / Mn12 / Ni4 or Cu86 / Mn12 / Ni2) or the copper-nickel (Cu-Ni) alloy Constantan (Cu55 / Ni35), which are well known for use in shunt resistors due to their very low temperature coefficient of resistance properties. Other materials with low temperature coefficients of resistance, such as certain nickel-chromium alloys (NiCr), can also be advantageously used.

[0037] The second current measuring device comprises a magnetic field transducer. The magnetic field transducer comprises a U-shaped magnetic core 7, a magnetic field detector 8 mounted in an air gap of the magnetic core 7, and a second connector 24 connected to the magnetic field detector.

[0038] The U-shaped magnetic core 7 consists of an end leg 7a and two parallel, spaced-apart lateral legs 7b extending from the end leg 7a to respective free ends. The two parallel, spaced-apart lateral legs 7b define a central slot 26, which also forms the air gap formed at the free ends of the lateral legs.

[0039] The magnetic field detector 8 is mounted on a second circuit board 13, which is also at least partially positioned in the air gap. The magnetic field detector may, for example, comprise a Hall sensor in an integrated circuit chip (IC) 11, which is well known in the field of magnetic field detectors.

[0040] The magnetic field transducer also comprises an insulating housing 22 which surrounds the U-shaped magnetic core 7 and a portion 18 of the second measuring section 14 of the primary conductor rail 2.

[0041] The central slot 26 of the U-shaped magnetic core 7, which defines the distance between the inner parallel sides of the lateral legs 7b, has a width equal to the width W1 of the core segment 18, except for a slight tolerance that allows the mounting of the central slot 26 between the lateral legs 7b. The U-shaped magnetic core is inserted over the core segment 18 until the end leg 7a abuts the core segment 18. A width W3 of the lateral legs 7b is preferably smaller than a width W2 of the notches 16, such that the lateral legs 7a are fully positioned in the notches 16. In this way, the width of the magnetic field converter remains within the width of the primary conductor rail, resulting in a compact design.

[0042] The insulating housing 22 can be overmolded or, alternatively, assembled around the U-shaped magnetic core 7 and the core segment 18 of the primary conductor bar on a side opposite the side contacting the end leg 7a of the U-shaped magnetic core. The housing further comprises a housing portion forming a housing section of the second connector 24 and, in particular, forming a shell 27 surrounding the electrical terminals 25 of the second connector. In the illustrated embodiment, the electrical terminals are in the form of pin terminals 25 surrounded by the shell 27 of the second connector housing portion, with an opposite end of the pin contacts connected to the second circuit board 13 and supported by the overmolded housing.

[0043] The second circuit board 13 is arranged substantially parallel to the lateral legs 7b, and the magnetic field detector 8 can be surface-mounted on the second circuit board 13 and inserted with the circuit board into the central slot 26, in particular, housed in the central housing slot 29. The positioning of the magnetic field detector 8 and the second circuit board 13 can be defined by the housing 22, which is overmolded or mounted around the lateral legs 7b of the U-shaped magnetic core 7.

[0044] As in Fig.As best seen in Figure 4, the magnetic field transducer can have a width that lies within the width of the primary conductor rail 2 for a very compact design, yet still have a relatively low height, while benefiting from the good sensing of the magnetic field generated by the reduced-width core segment 18 of the primary conductor. Given the relatively short length of the magnetic field transducer 6, it can be positioned close to the first current measuring device 5 with a shunt resistor 9, while at the same time having completely separate circuit boards and connectors for safe and reliable operation.

[0045] The first circuit board 11 of the first current measuring device can be mounted directly against the surface of the primary conductor rail 2 and the first connector 20 can be mounted on top of the first circuit board 11, whereby the first connector 20 can either be formed separately and mounted on the circuit board or comprise a housing overmolded around the first circuit board 11 and optionally around a portion of the primary conductor rail.

[0046] It should be noted that in a variant, the insulating housings of the first connector 20 and the magnetic field transducer may be formed together as a single overmolding (not shown).

[0047] The central slot 26, into which the magnetic field detector 8 and the second circuit board 13 are inserted, can be closed by a separately mounted cover element 28. List of reference symbols 1 current transformer 2 primary conductor rail 10 converter connections 12 First measuring section 9 Shunt resistance 14 Second measuring section 16 notches 18 core segment 3 First measuring channel 5 First current measuring device 9 Shunt resistance 15 shunt connections 11 First circuit board 20 First connector 4 Second measuring channel 6 Second current measuring device magnetic field converter 7 U-shaped magnetic core 7a End leg 7b Lateral limbs 26 Middle slot 8 Magnetic field detector 11 e.g. Hall sensor in an integrated circuit chip (IC) 13 Second circuit board 22 housings 27 Connector sheath 29 Middle housing slot 28 Cover element 24 Second connector 25 pin connectors W Width of the primary conductor W1 Width of the core segment W2 notch depth W3 Width of the lateral leg L Length of the core segment

Claims

[1] Current transformer (1) comprising a primary conductor rail (2), a first current measuring device (5) and a second current measuring device (6), wherein the primary conductor rail comprises a first measuring section (12) comprising a shunt resistor (9) and a second measuring section (14) comprising notches (16), wherein the first current measuring device (5) comprises - the shunt resistance (9), - a first circuit board (11) and - shunt terminals (15) connecting the circuit board to the primary conductor rail to measure a voltage across the shunt resistor (9), wherein the first current measuring device (6) comprises - a magnetic field converter comprising a magnetic field detector (8) for measuring a primary current flowing through the core segment (18), characterized byin that the second current measuring device (6) comprises a U-shaped magnetic core (7) having an end leg (7a) and lateral legs (7b) extending from the end leg to free ends and defining a central slot (26) therebetween, wherein the core segment (18) of the primary conductor rail is mounted within the central slot (26) and the magnetic field detector (8) is mounted on a second circuit board (13) which is independent of the first circuit board (11) and is inserted into an air gap formed between the lateral legs (7b). [2] Current transformer according to claim 1, wherein the end leg (7a) of the U-shaped magnetic core (7) is mounted against one side of the core segment (18) of the primary conductor bar (2). [3] Current transformer according to one of the preceding claims, wherein the second circuit board (13) is arranged parallel to the lateral legs (7b) and the magnetic field detector (8) comprises an integrated circuit chip (11) in an insulating overmolding, which is surface-mounted on the second circuit board (13). [4] Current transformer according to one of the preceding claims, wherein an insulating housing (22) is overmolded or mounted around the U-shaped magnetic core (7) and the core segment (18), the housing comprising a cavity (29) in the central slot (26) of the U-shaped magnetic core, into which the magnetic field detector and a portion of the second circuit board (13) are inserted. [5] Current transformer according to one of the preceding claims, wherein the second current measuring device (6) comprises a second connector (24), the second connector (24) having an insulating housing portion comprising a sheath (27) formed integrally with the housing (22) and surrounding the U-shaped magnetic core (7) and the core segment (18). [6] A current transformer according to any one of the preceding claims, comprising transformer terminals (10) at opposite ends of the primary conductor rail for clamping or screwing connection to external conductors, the first current measuring device (5) and the second current measuring device (6) being positioned between the transformer terminals and adjacent to each other in close proximity. [7] Current transformer according to one of the preceding claims, wherein the first circuit board (11) of the first current measuring device (5) is mounted directly on a surface of the primary conductor rail above the shunt resistor. [8] Current transformer according to the preceding claim, wherein the first current measuring device (5) comprises a first connector (20) mounted on an upper side of the first circuit board (11) opposite to a lower side mounted against the primary conductor rail. [9] Current transformer according to one of the two directly preceding claims, wherein the first printed circuit board (11) comprises shunt terminals (15) in the form of solder reflow contacts which are directly connected to the primary conductor rail (2). [10] Current transformer according to one of the preceding claims, wherein the shunt resistor (9) consists of manganin. [11] Current converter according to one of the preceding claims for use in a battery management system for electric vehicles. [12] Current transformer according to one of the preceding claims, wherein a width (W3) of the lateral legs (7b) of the U-shaped magnetic core (7) is equal to or smaller than a width (W2) of the corresponding notch (16) in which the lateral leg is positioned. [13] Current transformer according to one of the preceding claims, wherein a width (W1) of the core segment (18) formed between the notches (16) is equal to a width of the central slot (26) between inner sides of the lateral legs (7b), except for a manufacturing tolerance which enables the mounting of the core segment (18) within the central slot (26).

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