Current sensor system

Abstract

A current sensor system is disclosed. A current sensor system (100; 300) for measuring an AC current, the system comprising: an electrical conductor part (101) for conducting the AC current and generating a first magnetic field; a U-shaped magnetic shield (140) partially surrounding the electrical conductor part and having a central shield part and two shield leg parts; a metal plate or layer (103) arranged at a distance (g) from the shield leg parts for allowing eddy current flow and for generating a second magnetic field; a magnetic sensor device (102) arranged between the conductor part and the metal plate or layer and between the shield leg parts, configured for measuring a magnetic field component (Bx). A three-phase current sensor system (450; 550).

Description

TECHNICAL FIELD

[0001] The present invention relates generally to the field of magnetic current sensor systems, and more specifically to a current sensor system capable of accurately measuring AC currents having a frequency of up to about 1500 Hz or up to about 2 kHz. BACKGROUND

[0002] Different kinds of current sensors are known in the art, for example (1) current sensors using shunt resistors, (2) current sensors using current transformers, or (3) current sensors using magnetic sensors.

[0003] In current sensors using shunt resistors, the voltage is measured across the shunt resistor, and the current value can be determined by dividing the measured voltage value by the resistance value. A disadvantage of this type is that the measurement circuit is not galvanically separated from the load. Current transformers comprise a primary coil and a secondary coil. Although this type of current sensor provides galvanic separation, it is usually bulky. Magnetic sensor based current sensors provide both galvanic separation and can be very compact.

[0004] Known current sensors are usually designed for measuring DC currents or low frequency currents, for example currents having a frequency of about 50 Hz or about 60 Hz.

[0005] There are various types of electric motors, for example: so-called DC brush motors, DC brushless motors, AC brushless motors, linear motors, stepper motors, etc. In electric vehicles, the following motor types are usually used: DC series motors, brushless DC motors, Permanent Magnet Synchronous Motors (PMSM), three-phase AC induction motors, Switched Reluctance Motors (SRM).

[0006] There are various circuits for driving and / or controlling and / or monitoring electric motors. In some of these circuits, the actual current provided to the motor needs to be measured. These currents can have an amplitude of tens of amperes or even hundreds of amperes, and can have a frequency or frequency component of up to several kHz. These currents are usually provided to the motor via so-called "busbars". Busbars usually occur in the form of metal strips or metal bars, for example copper bars.

[0007] It is known that when an AC current flows through an electrical conductor, a phenomenon called "skin effect" will occur. This results in an increase of the effective resistance of the electrical conductor. The higher the frequency of the current, the higher the effective resistance of the electrical conductor.

[0008] It is a challenge to measure AC current with high accuracy. SUMMARY

[0009] It is an object of embodiments of the invention to provide a current sensor system for measuring AC current, e.g. AC current flowing through a busbar.

[0010] It is an object of embodiments of the invention to provide a current sensor system that measures AC current with improved accuracy, and / or that is less sensitive to installation tolerances, and / or that is less sensitive to temperature variations, and preferably two of these, or all of these.

[0011] It is an object of embodiments of the invention to provide a current sensor system for measuring AC current with a frequency of at most about 1500 Hz, or at most about 2000 Hz, with improved accuracy.

[0012] It is an object of embodiments of the invention to provide a current sensor system for measuring the instantaneous or momentary amplitude of AC current with a frequency of at most about 1500 Hz, or at most about 2000 Hz, with improved accuracy.

[0013] It is an object of embodiments of the invention to provide a current sensor system for measuring AC current with improved accuracy in a simple way, e.g. without the need to perform spectral analysis, e.g. Fourier analysis, and / or without the need to analyze the current waveform in the time domain, e.g. sinusoidal, square, triangular.

[0014] It is an object of embodiments of the invention to provide a current sensor system for measuring AC current with an amplitude of at most 500 Ampere, or at most 750 Ampere, or at most 1000 Ampere, or at most 1250 Ampere, or at most 1500 Ampere, and with a frequency of at most about 1500 Hz, or at most about 2000 Hz, that is more accurate, and preferably also less sensitive to installation tolerances and / or temperature variations, and preferably both.

[0015] It is an object of embodiments of the invention to provide a current sensor system that is able to measure an AC current with an absolute accuracy within ±3% (or better) of the AC current, which has an amplitude of at most 750 Ampere (or more, e.g. at most 1500 A) and has a frequency of at most 1500 Hz (or more, e.g. at most 2000 Hz), in a range of ambient temperatures from 25°C to 105°C (or a larger range, e.g. a range from -20°C to +125°C, or a range from -40°C to +160°C), and with a mounting tolerance of the magnetic sensor device of at most ±0.3 mm (or at most ±0.5 mm, or at most ±1 mm).

[0016] It is a further object of embodiments of the invention to provide a three-phase current sensor system that comprises three busbars for measuring three AC currents with improved accuracy, each AC current having an amplitude of at most 500 Ampere or at most 750 Ampere or at most 1000 Ampere or at most 1500 Ampere and having a frequency of at most about 1500 Hz or at most about 2000 Hz, and / or that is less sensitive to mounting tolerances, and / or that is less sensitive to temperature variations.

[0017] These and other objects are achieved by a current sensor according to embodiments of the invention.

[0018] According to a first aspect, the invention provides a current sensor system for measuring an AC current having a frequency in a predefined frequency range, the current sensor system comprising: an electrical conductor part extending in a first direction (e.g. Y) and configured for conducting the AC current, thereby creating a first magnetic field; a U-shaped magnetic shield partially surrounding the electrical conductor part and having a central shield part extending in a second direction (e.g. X) perpendicular to the first direction (e.g. Y) and having two shield leg parts extending in a third direction (e.g. Z) perpendicular to the first and second direction; a metal plate or metal layer arranged at a predefined distance (e.g. g) from the shield leg parts for allowing eddy currents to flow in the metal plate or metal layer, thereby creating a second magnetic field superimposed with the first magnetic field; a magnetic sensor device arranged between the conductor part and the metal plate or metal layer and arranged between the two shield leg parts and configured for measuring a magnetic field component (e.g. Bx) oriented in the second direction (e.g. X); wherein the metal plate or metal layer has a length (e.g. Lp) larger than a length (e.g. Lsh) of the shield measured in the first direction (e.g. Y) and has a width (e.g. Wp) larger than 90% of a distance (e.g. Wsi) between inner sides of the shield leg parts and has a thickness (e.g. Tp); or wherein the metal plate or metal layer is a part of a metal housing with a cavity in the vicinity of the magnetic sensor, the metal plate or metal layer having a residual thickness (e.g. Tres).

[0019] The inventors found that by adding an electrically conductive surface (e.g. a metal plate made of Al or Cu) the AC current can be measured with improved accuracy. They surprisingly found that if the magnetic field induced by the eddy currents is located at a suitable distance from the shield and has a suitable plate thickness, the error can be reduced, thereby improving the accuracy of the current measurement. This is completely unexpected and highly counter-intuitive, as it is commonly known and generally accepted / believed that eddy currents negatively affect the measurements rather than improving them.

[0020] The invention has the advantage that the AC current is determined by multiplication of the measured magnetic field components, in contrast to systems that measure the peak current and then multiply this peak current e.g. by the square root of 2 (approximately 1.4142), as this system is only accurate if the waveform of the AC current is a perfect sinusoidal signal.

[0021] The advantage of the present invention is that the measurement is accurate for any AC waveform (e.g. sinusoidal, square, triangular, etc.). Although preferred, embodiments of the present invention are not necessarily limited to solutions wherein the accuracy is ±1.5% for frequencies in the range from 50 Hz to 1500 Hz.

[0022] In embodiments, the thickness or residual thickness (e.g. Tp or Tres) and the distance (e.g. g) between the metal plate or metal layer and the shield leg are such that the amplitude variation of the magnetic field component (e.g. Bx) of the combined first and second magnetic fields oriented at the sensor location and in the second direction (e.g. X) is less than ±1.5% for frequencies in the range from 50 Hz to 1500 Hz.

[0023] Or in other words: wherein the distance (g) and the thickness (Tp, Tres) of the metal plate or metal layer are such that the decay variation of the magnetic field component (Bx) is less than ±1.5% for frequencies up to 1500 Hz.

[0024] For example, if the plate thickness or layer thickness is fixed or predefined, a suitable value for the distance “g” can be found, or an optimal value for “g” can be found. Alternatively, if the distance “g” is fixed or predetermined, a suitable value for the plate thickness “Tp or Tres” can be found, or an optimal value for the plate thickness can be found. In other words, in practice, one parameter can be chosen, and for a suitable range of the other parameter, or an optimal value of the other parameter can be found.

[0025] It is explicitly stated that the claims encompass not only the optimal solution, but also other “good working solutions”, as these are also a considerable improvement over the prior art (e.g. in terms of reduced amplitude variation error).

[0026] The advantage of this current sensor system is that it allows for an accurate measurement of an AC current, which can have a frequency up to about 1500 Hz, in a fast and simple manner, without requiring heavy processing, without having to perform spectral analysis techniques (e.g. Fourier analysis).

[0027] In embodiments, the thickness (e.g. Tp, Tres) of the metal plate or metal layer is at least 0.3 mm or at least 0.5 mm or at least 1.0 mm.

[0028] In embodiments, the thickness (e.g. Tp) of the metal plate or metal layer is a value in the range from 0.5 mm to 1.5 mm.

[0029] In embodiments, the distance (e.g., g) between the metal plate or metal layer and the shield leg is at most 10.0 mm or at most 5.0 mm, or at most 4.0 mm, or at most 3.0 mm.

[0030] The plate thickness Tp or Tres can be a value in the range from 0.3 mm to 5.0 mm, or from 0.5 mm to 4.0 mm, or from 0.8 mm to 3.0 mm, e.g., equal to 1.0 mm, or equal to 1.5 mm, or equal to 2.0 mm.

[0031] In embodiments, the distance (e.g., g) between the metal plate or metal layer and the shield leg is at least 0.1 mm, or at least 0.2 mm, or at least 0.3 mm.

[0032] The magnetic sensor device is configured to determine the AC current as a value proportional to the magnetic field component value.

[0033] In embodiments, the amplitude variation of the magnetic field component is less than ±1.25% for frequencies in the range from 50 Hz to 1500 Hz.

[0034] In embodiments, the thickness (e.g., Tp, Tres) and the distance (e.g., g) of the metal plate or metal layer are such that the amplitude variation of the magnetic field component (Bx) is less than ±1.0% or less than ±0.75% for frequencies in the range from 50 Hz to 1500 Hz.

[0035] In embodiments, the metal plate or metal layer comprises or consists of an electrically conductive but non-magnetic material.

[0036] In embodiments, the metal plate is made of aluminum or an aluminum alloy, or of copper or a copper alloy, or of non-magnetic stainless steel.

[0037] In embodiments, the metal plate or metal layer is a portion of the metal plate having said thickness (e.g., Tp) and having a length (e.g., Lp) greater than the length (e.g., Lsh) of the shield measured in the first direction (e.g., Y).

[0038] In embodiments, the metal plate or metal layer is a portion of the metal plate having said thickness (e.g., Tp) and having a width (e.g., Wp) greater than 90% of the distance (Wsi) between the inner sides of the shield legs (or greater than the distance Wso between the outer surfaces of the shield legs, or greater than 110% x Wso).

[0039] In embodiments, the metal plate or metal layer is a part of a metal housing with a cavity (or blind opening) in the vicinity of the magnetic sensor, the metal plate or metal layer having a residual thickness (e.g. Tres) and a length (e.g. Lcav) greater than 90% of a length (e.g. Lsh) of the shield measured in a first direction (e.g. Y).

[0040] In embodiments, the metal plate or metal layer is a part of a metal housing with a cavity (or blind opening) in the vicinity of the magnetic sensor, the metal plate or metal layer having a width (e.g. Wcav) greater than 90% of a distance (e.g. Wsi) between inner sides of the shield legs, or having a width (e.g. Wp) greater than a distance (e.g. Wso) between outer surfaces of the shield legs, or having a width greater than 110%* said distance (e.g. Wso).

[0041] In embodiments, the thickness (e.g. Tp) or residual thickness (e.g. Tres) of the metal plate or metal layer is a value in the range from 0.5 to 1.5 mm.

[0042] The metal plate or metal layer is galvanically separated from the electrical conductor. The metal plate or metal layer can be a part of a metal housing. The metal plate or metal layer can be grounded.

[0043] The shield is galvanically separated from the electrical conductor. The shield can be grounded.

[0044] The magnetic sensor device can comprise a semiconductor substrate (e.g. a silicon substrate). The magnetic sensor device can be a packaged semiconductor device (also referred to as a “chip”).

[0045] The electrical conductor is arranged outside of the integrated semiconductor device.

[0046] The electrically conductive surface can be galvanically separated from the electrical conductor and the magnetic sensor device.

[0047] The metal plate or metal layer can be made of, for example, copper or a copper alloy, or aluminum or an aluminum alloy.

[0048] In embodiments, at least 90%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99% of the power of the AC current is below 1500 Hz or below 2000 Hz.

[0049] In embodiments, the magnetic sensor device is an integrated semiconductor device (also referred to as a “chip”).

[0050] The sensor device can be mounted on a printed circuit board.

[0051] In embodiments, the magnetic sensor device is configured to determine the amplitude of the AC current according to the formula: I = K * Bx, where I is the amplitude of the AC current to be measured, K is a predefined constant independent of the frequency, and Bx is the measured magnetic field component.

[0052] In this embodiment, the magnetic sensor device is configured to determine the AC current as a value proportional to the magnetic field component value.

[0053] In embodiments, the electrical conductor portion has a central conductor portion between the shield legs, which central conductor portion is a solid bundle shaped portion having a substantially constant cross section.

[0054] By "solid bundle shaped portion" it is meant that the central conductor portion is not perforated, or in other words, does not have slits or holes or through-openings causing the current flowing through the central conductor portion to be shunted to two separate conductive paths, for example as illustrated in Fig. 1 (a).

[0055] The cross section can be a rectangular cross section having a predefined width Wc and height Tc.

[0056] In embodiments, the electrical conductor portion has a central conductor portion between the shield legs, and the central conductor portion has a through-opening (e.g. a slit).

[0057] The sensor device is preferably located in the vicinity of said through-opening, for example at a distance of at most 10.0 mm from said through-opening.

[0058] In embodiments, the magnetic sensor device comprises a vertical Hall element configured to measure said magnetic field component (e.g. Bx) oriented in a second direction (e.g. X).

[0059] In embodiments, the magnetic sensor device comprises at least one magneto-resistive (MR) element configured to measure said magnetic field component (e.g. Bx) oriented in a second direction (e.g. X).

[0060] In embodiments, the magnetic sensor device comprises two vertical Hall elements, each configured to measure said magnetic field component (e.g. Bx) oriented in a second direction (e.g. X).

[0061] In embodiments, the outputs of the two vertical Hall elements can be combined (e.g. added) to increase the signal-to-noise ratio of the measured signal.

[0062] In embodiments, the magnetic sensor device comprises circuitry for allowing each of the vertical Hall elements to be read out individually, e.g. for diagnostic purposes.

[0063] In embodiments, the magnetic sensor device comprises an integrated magnetic concentrator (IMC) and two horizontal Hall elements arranged on opposite sides of the IMC, spaced apart in a second direction (e.g. X).

[0064] If the first Hall element H1 provides a signal h1 and the second Hall element provides a signal h2, then the magnetic field component Bx is proportional to (h1 - h2).

[0065] In embodiments, the magnetic sensor device comprises two horizontal Hall elements (e.g. H1 and H2) on a first side of the IMC, and two horizontal Hall elements (e.g. H3 and H4) arranged on a second side of the IMC, the first side being angularly spaced apart from the second side by 180°. Values obtained from H1 and H2 can be combined, e.g. summed or averaged, to produce a first value h12, and values obtained from H3 and H4 can be combined, e.g. summed or averaged, to produce a second value h34, and the magnetic field component Bx is proportional to (h12 - h34).

[0066] According to a second aspect, the application also provides a three-phase current sensor system for measuring three AC currents having frequencies in a predefined frequency range, the system comprising: a first current sensor system according to the first aspect, comprising a first electrical conductor, and a first magnetic sensor device, and a first metal plate or metal layer; a second current sensor system according to the first aspect, comprising a second electrical conductor, and a second magnetic sensor device, and a second metal plate or metal layer; and a third current sensor system according to the first aspect, comprising a third electrical conductor, and a third magnetic sensor device, and a third metal plate or metal layer. Examples of such three-phase systems are illustrated in Figure 4 and Figure 5

[0067] In embodiments (of the second aspect), the first metal plate or metal layer and the second metal plate or metal layer and the third metal plate or metal layer are integrally formed. Or in other words, the three-phase current sensor system comprises a single metal plate, or a single metal housing.

[0068] ​According to a third aspect, the invention provides a current sensor system for measuring an AC current having a frequency within a predefined frequency range, the current sensor system comprising: an electrical conductor portion extending in a first direction (e.g. Y) and configured for conducting the AC current, thereby creating a first magnetic field; a U-shaped magnetic shield partially surrounding the electrical conductor portion and having a central shield portion extending in a second direction (e.g. X) perpendicular to the first direction (e.g. Y) and having two shield leg portions extending in a third direction (e.g. Z) perpendicular to the first and second directions; a metal plate or metal layer arranged at a predefined distance (e.g. g) from the shield leg portions for allowing eddy currents to flow in the metal plate or metal layer, thereby creating a second magnetic field superimposed with the first magnetic field; a magnetic sensor device arranged between the conductor portion and the metal plate or metal layer and arranged between the two shield leg portions and configured for measuring a magnetic field component (e.g. Bx) oriented in the second direction (e.g. X); wherein the metal plate or metal layer has a thickness (e.g. Tp or Tres) of at least 0.3 mm or at least 0.5 mm or at least 1.0 mm; and wherein the distance (e.g. g) is at most 10.0 mm or at most 5.0 mm, or at most 4.0 mm, or at most 3.0 mm.

[0069] In embodiments (of the third aspect), the distance (g) is at least 0.1 mm or at least 0.2 mm or at least 0.3 mm.

[0070] According to a fourth aspect, the invention also provides a three-phase current sensor system for measuring three AC currents having a frequency within a predefined frequency range, the system comprising: a first current sensor system according to the third aspect comprising a first electrical conductor and a first magnetic sensor device and a first metal plate or metal layer; a second current sensor system according to the third aspect comprising a second electrical conductor and a second magnetic sensor device and a second metal plate or metal layer; and a third current sensor system according to the third aspect comprising a third electrical conductor and a third magnetic sensor device and a third metal plate or metal layer.

[0071] According to a fifth aspect, the present application also provides a current sensor system for measuring an AC current having a frequency in a predefined frequency range (e.g. a range from 50 Hz to 2000 Hz), the current sensor system comprising: an electrical conductor portion extending in a first direction (e.g. Y) and configured for conducting the AC current, thereby creating a first magnetic field; a U-shaped magnetic shield partially surrounding the electrical conductor portion and having a central shield portion extending in a second direction (e.g. X) perpendicular to the first direction (e.g. Y) and having two shield leg portions extending in a third direction (e.g. Z) perpendicular to the first and second directions (e.g. X, Y); a metal plate or metal layer arranged at a predefined distance (e.g. g) from the shield leg portions for allowing an eddy current to flow in the metal plate or metal layer, thereby creating a second magnetic field superimposed with the first magnetic field; a magnetic sensor device arranged between the conductor portion and the metal plate or metal layer and also arranged between the two shield leg portions and configured for measuring a magnetic field component (e.g. Bx) oriented in the second direction (e.g. X); wherein the metal plate or metal layer is arranged outside the U-shaped magnetic shield.

[0072] In embodiments, the thickness (e.g. Tp, Tres) and the distance (e.g. g) between the metal plate or metal layer and the shield leg portions are such that for frequencies in a range from 50 Hz to 1500 Hz, the amplitude variation of the magnetic field component (e.g. Bx) of the combined first and second magnetic fields oriented in the second direction (e.g. X) at the sensor position is less than ±1.5%.

[0073] In embodiments, the thickness (e.g. Tp) or residual thickness (e.g. Tres) is at least 0.3 mm; and / or the distance (e.g. g) is at most 10.0 mm; and optionally, the distance (e.g. g) is at least 0.1 mm.

[0074] In embodiments, for frequencies in a range from 50 Hz to 1500 Hz, the thickness (e.g. Tp) or residual thickness (e.g. Tres) of the metal plate or metal layer and the distance (e.g. g) are such that the amplitude variation of the magnetic field component (Bx) is less than ±1.0% or less than ±0.75%.

[0075] In embodiments, the metal plate or metal layer comprises or consists of an electrically conductive but non-magnetic material.

[0076] In embodiments, the residual thickness (e.g. Tres) of the metal plate or metal layer is a value in a range from 0.5 to 1.5 mm.

[0077] In embodiments, the metal plate or metal layer is a portion of the metal housing with the cavity near the magnetic sensor and has at least one of the following features: (i) the metal plate or metal layer has a length (Lcav) that is greater than 90% of a length (Lsh) of the shield measured in the first direction (Y); (ii) the metal plate or metal layer has a width (Wcav) that is greater than 90% of a distance (Wsi) between inner sides of the shield leg.

[0078] In embodiments, the magnetic sensor device comprises at least one vertical Hall element configured to measure the magnetic field component (e.g., Bx) oriented in the second direction (e.g., X).

[0079] In embodiments, the magnetic sensor device comprises at least one magnetoresistive element configured to measure the magnetic field component (e.g., Bx) oriented in the second direction (e.g., X).

[0080] In embodiments, the magnetic sensor device comprises two vertical Hall elements each configured to measure the magnetic field component (e.g., Bx) oriented in the second direction (e.g., X).

[0081] In embodiments, the magnetic sensor device comprises an integrated magnetic concentrator (IMC) and two horizontal Hall elements arranged on opposite sides of the IMC spaced apart in the second direction (e.g., X).

[0082] Particular and preferred aspects of the present application are set out in the attached independent and dependent claims. Features from the dependent claims can be combined with features of the independent claims and the features of other dependent claims as appropriate and non- solely as the claims depend on them.

[0083] These and other aspects of the present application will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating the principles of the application. BRIEF DESCRIPTION OF DRAWINGS

[0084] Figures 1(a) and 1(b) illustrate a current sensor system according to embodiments of the application in cross-sectional and perspective views, respectively.

[0085] Figures 2(a) to 2(d) Examples of arrangements of electrical conductor portions and U-shaped magnetic shields that can be used in embodiments of the application (e.g., in the current sensor system of Figure 1(a)) are shown.

[0086] Figures 3(a) to 3(c)Figures illustrate current sensor systems according to further embodiments of the application, the current sensor systems having a metal plate or metal layer (e.g. a metal plate) with a blind hole or cavity.

[0087] Figure 4 A three-phase current sensor system according to an embodiment of the application is shown. The three-phase current sensor system comprises three current sensor subsystems as illustrated in Figure 1 (b) in combination with Figure 2 (a) or Figure 2 (c). This system is also referred to herein as "current sensor system with full metal plate".

[0088] Figure 5 A three-phase current sensor system according to an embodiment of the application is shown. The three-phase current sensor system comprises three current sensor subsystems as illustrated in Figure 3 (c) in combination with Figure 2 (a) or Figure 2 (c). This system is also referred to herein as "current sensor system with metal plate with cavity".

[0089] Figure 6 A three-phase current sensor system comprising three arrangements as illustrated in Figure 2 (c) with no metal plate on top is shown. This system is also referred to herein as "current sensor system without metal plate". This system is provided for comparison.

[0090] Figures 7 (a) and 7 (b) show computer simulation results for the "current sensor system without metal plate" (e.g. for the three mounting positions of the sensor device as illustrated in Figure 6 Figures 6 (a) and 6 (b).

[0091] Figures 8 (a) and 8 (b) show computer simulation results for the "current sensor system with full metal plate" (e.g. as illustrated in Figures 1 (b), or as illustrated in Figure 1 (a)). Figure 4

[0092] Figure 8 (a) shows the amplitude variation for the three mounting positions of the sensor device, and Figure 8 (b) shows the phase as a function of frequency for the three mounting positions of the sensor device.

[0093] Figure 8 (c) shows the amplitude variation as a function of frequency for a fixed sensor position, for two different temperatures, and Figure 8 (d) shows the amplitude variation as a function of frequency for a fixed sensor position, for three positions of the metal plate.

[0094] Figures 9(a) to 9(d) Figures 9 (a) and 9 (b) show computer simulation results for the "current sensor system with metal plate with cavity" (e.g. as illustrated in Figures 3 (c), or as illustrated in Figure 3 (a)). Figure 5

[0095] ​​Figure 9(a) shows amplitude variation as a function of frequency for two different temperatures.

[0096] Figure 9(b) shows amplitude variation as a function of frequency for three positions of the metal plate.

[0097] Figure 9(c) shows amplitude variation for three mounting positions of the sensor device, and Figure 9(d) shows phase shift as a function of frequency for three mounting positions of the sensor device.

[0098] Figure 10(a) shows amplitude variation at 1500 Hz as a function of plate thickness (Tp) for a "full metal plate" or residual plate thickness (Tres) for a "metal plate with cavity" for a fixed distance "g" between the metal plate and the leg of the U-shaped shield of 1.0 mm.

[0099] Figure 10(b) shows amplitude variation at 1500 Hz as a function of distance "g" between the metal plate and the leg of the U-shaped shield of plate thickness (Tp) for a "full metal plate" or residual plate thickness (Tres) for a "metal plate with cavity" fixed at 1.5 mm.

[0100] Figure 11 An illustrative block diagram of a sensor device that can be used in embodiments of the present application (e.g., in any of the current sensor systems of Figures 1(a) to 5 Figures 1 to 10.

[0101] The drawings are merely schematic and are non-limiting. In the drawings, the size of some of the elements can be exaggerated and not drawn on scale for illustrative purposes. Any reference signs in the claims should not be construed as limiting the scope. The same reference signs in different drawings denote the same or similar elements. DETAILED DESCRIPTION

[0102] The application will be described with respect to the particular embodiments and with reference to specific drawings but the application is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements can be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to the actual reduction to practice of the application.

[0103] Furthermore, the terms first, second, etc. are used herein, are also used merely as identifiers that distinguish one element from another, and are not necessarily used to describe a sequence or order of, or chronology with respect to, the described implementation. It will be appreciated that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the application described herein are capable of operating in other sequences than the one described or otherwise illustrated herein.

[0104] Furthermore, the terms top, under and the like in the description and in the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the application described herein are capable of operation in other orientations than the one described or illustrated herein.

[0105] It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted that the term "comprising" means "consisting at least of the stated features", but it does not exclude the presence of one or more additional features, steps, or components, or groups thereof. It is thus to be interpreted in accordance with the purposes for which the feature or features is / are introduced, in particular the purposes of supplementing, replacing or modifying the indicated function or technique, to provide heuristics to solve or alleviate the problem addressed by the application, to provide alternatives to the stated features, and the like.

[0106] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but can refer to different embodiments. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0107] Similarly, it is to be appreciated that, in the description of exemplary embodiments of the application, various features of the application can be grouped together or described in a single embodiment for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the aspects of the application. This method of disclosure, however, is not to be interpreted as reflecting an intention that the application requires more features than are explicitly recited in each claim. Rather, inventive aspects lie in fewer than all features of the exemplary embodiments described. Accordingly, the claims and their equivalents are intended to cover all treatment alternatives of the application irrespective of a particular claimed category. Thus, by way of example, in the event the claim term "comprising" is used in the claims and one of ordinary skill in the art is able to adopt available alternatives, this disclosure assumes any result thus achieved is within the scope of the application. The claims are thus to be understood in the broadest sense as encompassing only the claimed subject matter.

[0108] Furthermore, although some embodiments described herein include some features of other embodiments but not others, combinations of features of different embodiments are meant to be within the scope of the application, and form different embodiments, as will be understood by those skilled in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination.

[0109] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the application can be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0110] The present application relates generally to the field of magnetic current sensors, and more particularly to a current sensor system capable of accurately measuring AC currents.

[0111] The AC current can have an amplitude of up to about 500 or up to about 750 or up to about 1000 or up to about 1500 amperes, and can have a frequency of up to about 1500 Hz or up to about 2 kHz. Such current sensor systems can be used in industrial, robotic, and automotive applications, for example, for measuring one or more currents provided to an electric motor (e.g., in an electric or hybrid vehicle). Such electric motors can be driven using relatively large AC currents (e.g., substantially sinusoidal currents having tens or even hundreds of amperes of amplitude). The present application is particularly concerned with accurately measuring such AC currents.

[0112] As already mentioned in the background section, a particular problem that occurs when trying to measure an AC current having a relatively high frequency (e.g., above 50 or 60 Hz) is that a phenomenon known as the "skin effect" occurs, which causes the current density to increase near the periphery of the electrical conductor, and to decrease near the center of the electrical conductor. The inventors have found that this not only changes the effective resistance of the busbar, but also changes the magnetic field around the electrical conductor. To the inventors' knowledge, the way in which the skin effect changes the magnetic field around the conductor cannot be easily described mathematically. As the frequency of the AC current increases, this effect becomes more and more pronounced, and determining the AC current as a value proportional to the measured magnetic field component or to the measured magnetic field gradient without any correction will result in an error that is typically in the order of about 10%.

[0113] Since the error - and thus also the correction - is frequency dependent, the logical approach would be to analyze the frequency content of the AC signal to be measured and correct the measured value accordingly. But performing a frequency analysis, e.g. by means of a Fourier transform, has several drawbacks, such as requiring considerable processing power, having to use a sampling window which typically has at least 16 or 32 samples, thereby causing a delay, etc., which is disadvantageous, especially in motor control. The inventors wanted to find another solution.

[0114] Fig. 1 (a) illustrates a current sensor system 100 in a cross-sectional view, and Fig. 1 (b) illustrates the current sensor system 100 in a perspective view.

[0115] The current sensor system 100 comprises an electrical conductor portion 101 for conducting an AC current to be measured. The electrical conductor portion 101 extends in the Y direction. The electrical conductor portion 101 can be a portion of a busbar 106 and can have a rectangular cross-section, optionally with rounded or truncated edges. The electrical conductor portion 101 can be solid or can have a through-hole in the Z direction, e.g. as illustrated in Figs. 2(a) and 2(b). The electrical conductor portion 101 can have a thickness Tc from 1.0 mm to 20.0 mm or from 1.0 mm to 5.0 mm and can have a width Wc from 2.0 mm to 50.0 mm or from 5.0 mm to 40 mm or from 10 mm to 40 mm, but these values are not critical.

[0116] When an electrical current flows through the electrical conductor portion, a "first magnetic field" is generated. A rough sketch of some of the field lines of the first magnetic field is shown for illustrative purposes, and while the orientation and density of these field lines can not be correct, they can help to better understand the invention.

[0117] The current sensor system 100 further comprises a U-shaped magnetic shield 140 which partially surrounds the electrical conductor portion 101. The U-shaped magnetic shield 140 has a U-shape, comprising a central shield portion 143 which is located below the electrical conductor portion 101 of Fig. 1 (a), and two shield leg portions 141, 142 which are oriented substantially perpendicular to the central shield portion 143. The U-shaped magnetic shield 140 is open at the top. The electrical conductor portion 101 is located between the shield leg portions 141, 142 of the U-shaped magnetic shield 140, or in other words, the U-shaped magnetic shield 140 partially surrounds the electrical conductor portion 101. Preferably, the electrical conductor portion 101 is located substantially in the middle between the shield leg portions 141, 142 of the U-shaped magnetic shield 140 in the direction X. The U-shaped magnetic shield 140 shown in Fig. 1 (a) has sharp edges, but can alternatively have rounded edges.

[0118] The shield can define a distance Wsi between inner surfaces of the shield leg portions 141, 142, and can define an outer width Wso in the X-direction. Typical values for Wsi are 10 to 50 mm, or 10 to 30 mm (e.g. 12 to 25 mm, e.g. equal to about 15 mm). The U-shaped magnetic shield 140 can have a thickness Tsh in the range from 1.0 mm to 3.0 mm (e.g. equal to about 1.5 mm, or equal to about 2.0 mm, or equal to about 2.5 mm). The distance Wso between outer surfaces of the shield leg portions 141, 142 is equal to Wsi + 2*Tsh, and can have a value in the range from (10+2*1)=12 mm to (50+2*3)=56 mm. But the invention is not limited to these values, and other values can also be used.

[0119] The current sensor system 100 further comprises a magnetic sensor or magnetic sensor device 102. Although not shown in Fig. 1(a), the magnetic sensor device can be a packaged semiconductor device. The magnetic sensor device 102 is arranged in the vicinity of the electrical conductor portion 101, e.g. at a distance h in the range from 0.1 mm to 5.0 mm above the electrical conductor portion 101. The magnetic sensor 102 is preferably arranged centrally above the electrical conductor portion 101, in the middle between the shield leg portions 141, 142. The magnetic sensor device 102 can be configured to measure a magnetic field component Bx oriented in the X-direction, which is transverse to the direction Y of the AC current flow. The magnetic sensor device 102 can be mounted on a printed circuit board (not shown) in a known manner.

[0120] According to the basic principle of the invention, the current sensor system 100 further comprises an electrically conductive surface (e.g. an electrically conductive plate 103 or metal plate), which is further referred to herein as “metal plate” for ease of description. The metal plate 103 is arranged at a distance “g” from the shield leg portions 141, 142, which distance “g” is in the range from about 0.0 mm to about 10.0 mm, or from 0.0 mm to 5.0 mm, or from 0.2 mm to 5.0 mm (equal to about 2.0 mm or equal to about 3.0 mm). In some embodiments, the metal plate or metal layer is in contact with the shield legs. In other embodiments, the metal plate or metal layer 103 is not in contact with the shield legs. The distance “dsp” between the magnetic sensor (device) 102 and the metal plate 103 can be a value in the range from 2.0 mm to 10.0 mm or from 4.0 mm to 8.0 mm (e.g. equal to about 6.0 mm).

[0121] The metal plate 103 has a width Wp extending in the X-direction, which is preferably equal to or larger than 80% of the inner distance Wsi between the shield leg portions 141, 142 of the U-shaped magnetic shield 140. This can be written mathematically as follows: Wp≥ 80%*Wsi. In some embodiments, Wp≥ 90%*Wsi, or Wp≥ Wsi, or Wp≥ 120%*Wsi, or Wp≥ Wso, or Wp≥ 110%*Wso, or Wp≥ 120%*Wso.

[0122] The inventors have surprisingly found that by adding a metal plate, the frequency characteristic of a current sensor system can be influenced. More specifically, they have found that by arranging a metal plate 103 of a certain thickness "Tp" at a certain distance "g", the amplitude variation and the phase can be improved with respect to the frequency characteristic. For example, by adding a "full metal plate" with appropriate values "g" and "Tp", the absolute value of the amplitude variation error can be reduced from about 2.3% at 1500 Hz in Fig. 7(a) to about 1.3% at 1000 Hz in Fig. 8(a), excluding mounting tolerances.

[0123] Although the inventors do not wish to be bound by any theory, one possible explanation can be as follows: the AC current flowing through the electrical conductor portion 101 induces a first magnetic field, but due to the "skin effect", the first magnetic field does not have a flat frequency characteristic. The metal plate allows "eddy currents" induced by the varying first magnetic field to flow in the metal plate 103, and these eddy currents induce a second magnetic field, which superimposes with the first magnetic field, and the superposition of the first magnetic field with the second magnetic field is measured by the magnetic sensor 102.

[0124] After many experiments, the inventors have found that:

[0125] i) if the metal plate or metal layer 103 is too far away (e.g. g > 10 mm) and / or the metal plate is too thin (e.g. Tp < 0.3 mm), the second magnetic field (related to the eddy currents) undercompensates the skin effect;

[0126] ii) but very surprisingly, by choosing appropriate values for the plate thickness "Tp" and the plate distance "g", the overall frequency characteristic of the current sensor system 100 can be substantially improved in such a way that the second magnetic field can substantially reduce or even largely compensate the skin effect.

[0127] The inventors believe that this cannot be predicted based on what is known in the prior art. On the contrary, eddy currents are generally considered to be parasitic effects that need to be avoided, but in the present invention, the eddy currents can be used in a positive way, i.e. to reduce or at least partly compensate the negative effects of the skin effect.

[0128] Fig. 1 (b) shows a perspective view of the sensor system 100 of Fig. 1 (a). As can be seen, the length Lp (measured in the Y-direction) of the metal plate 103 is preferably equal to or larger than the length Lsh (measured in the Y-direction) of the shield.

[0129] The sensor device 102 is not shown in Fig. 1 (b), but the position of the magnetic sensor is indicated by means of a black circle within the space between the two shield leg portions 141, 142 and between the electrical conductor portion 101 and the metal plate 103. As can be seen, the electrical conductor portion 101 can be a portion of the U-shaped busbar 106, but this is not absolutely necessary for the invention to work.

[0130] Figures 2(a) to 2(d) An example of an arrangement of an electrical conductor portion 101 and a U-shaped magnetic shield 140 that can be used in embodiments of the invention (e.g. in the current sensor system of Figs. 1 (a) and 1 (b), but also in the current sensor system 300 of Figs. 3(a) and 3(b), Figures 3(a) to 3(c) An example of an arrangement of an electrical conductor portion 101 and a U-shaped magnetic shield 140 that can be used in embodiments of the invention (e.g. in the current sensor system of Figs. 1 (a) and 1 (b), but also in the current sensor system 300 of Figs. 3(a) and 3(b), Figures 3(a) to 3(c) The current sensor system 300 of Figs. 3(a) and 3(b) will be further described.

[0131] The arrangement 200a of Fig. 2(a) shows an electrical conductor portion and a U-shaped magnetic shield (only the shield leg portions 241, 242 are visible). The electrical conductor portion has a U-shape that comprises a central conductor portion 201a that extends in the Y-direction and two conductor leg portions that are oriented in the Z-direction, which two conductor leg portions are substantially perpendicular to the central conductor portion 201a. The central conductor portion 201a of Fig. 2(a) has a through opening 207. The central conductor portion 201a can narrow between the shield leg portions 241, 242, or in other words: the width of the central conductor portion 201a can be locally reduced between the shield leg portions 241, 242 (e.g. in order to increase the current density, and thereby the amplitude of the magnetic field component Bx to be measured).

[0132] The arrangement of Fig. 2(b) shows another example of a central conductor portion 201b and a U-shaped magnetic shield portion (only shield leg portions 241, 242 are visible). The central conductor portion 201b is a substantially planar portion. The magnetic shield has a U-shape comprising a central shield portion which is not visible in Fig. 2(b) but is located below the central conductor portion 201b, is oriented parallel to the central conductor portion 201b and has two shield leg portions 241, 242 which are oriented perpendicular to the central conductor portion 201b. The central conductor portion 201b is located between the shield leg portions 241, 242 of the U-shaped magnetic shield, or in other words, the magnetic shield partially surrounds the central conductor portion 201b. The central conductor portion 201b has a through opening 207. The width (in X-direction) of the electrical conductor portion is locally reduced to increase the current density, but this is not absolutely necessary for the present invention to work.

[0133] The arrangement of Fig. 2(c) is a variant of the arrangement of Fig. 2(a) wherein the central conductor portion 201c does not have a through opening but is solid.

[0134] The arrangement of Fig. 2(d) is a variant of the arrangement of Fig. 2(b) wherein the central conductor portion 201d does not have a through opening but is solid.

[0135] These are only a few examples of arrangements, but the present invention is not limited thereto. For example, in a variant of the shown arrangements (not shown) the electrical conductor portion is not locally narrowed between the legs of the U-shaped shield but has a constant width. Figures 2(a) to 2(d) Figures 2(a) to 2(d) The main purpose is to show that the electrical conductor portion can have a U-shape and / or can have a through opening 207 and / or can be locally narrowed, but these are not necessary.

[0136] It should be noted that the magnetic sensor device 202 is only shown in Fig. 2(a) and for illustrative purposes, from above. Figures 2(b) to 2(d) It is omitted in the other figures. However, it is important that the magnetic sensor device 202 is located in the space above the central electrical conductor portion and between the shield legs. The main purpose of the shield legs is to prevent the magnetic sensor device 202 from measuring disturbance fields which are oriented in the X-direction. The latter is especially true for three-phase systems, for example as shown in Figures 4 to 6 wherein the magnetic shield is configured to reduce cross-talk between different phases.

[0137] Figures 3(a) to 3(c) ​The figure illustrates a current sensor system 300 according to another embodiment of the present invention. The current sensor system 300 can be regarded as a variant of the current sensor system 100 of FIG1(a) and FIG1(b), the main difference being that the current sensor system 300 has a metal or metal surface 303 with a blind opening or cavity or recess located near the magnetic sensor device 302.

[0138] The metal plate or layer (e.g., metal plate) 303 has a residual thickness “Tres” located at a distance “g” from the shielding leg portions 341, 342 of the U-shaped magnetic shield 340, which includes a central shielding portion 343 below the electrical conductor portion 301. In other words, the metal surface 303 can be part of a metal housing with a non-constant thickness, but the thickness “Tres” and distance “g” near the magnetic sensor device 302 have the same role or meaning as the parameters “Tp” and “g” discussed above. The metal plate or layer can be part of a metal housing. In practice, the housing (if present) does not need to be entirely metallic, but can also be made of plastic or ceramic materials, as long as it has a “metallic surface portion” of thickness “Tp” or “Tres” near the sensor device (e.g., above the space defined by the U-shaped shield). In the embodiment of FIG. 3(a), the electrical conductor portion 301 is shown as having a port 307, but as explained above, that is not absolutely necessary.

[0139] In a variant of Figure 3(a), the sensor device has a semiconductor substrate oriented parallel to both the Z and Y directions. The sensor device may include a single horizontal Hall element for measuring the Bx component (oriented perpendicular to the semiconductor substrate).

[0140] Figure 3(b) shows a perspective view of a metal plate 303 with a cavity 305, which is used to reduce the thickness of the plate "above the sensor device," as can be used in the current sensor system 300 of Figure 3(a). The cavity 305 shown has a rectangular shape with a width "Wcav" and a length "Lcav," but this shape is not critical to the function of the invention, and other shapes (e.g., elliptical, circular, or polygonal) can also be used.

[0141] Fig. 3(c) shows a perspective view of the sensor system 300 of Fig. 3(a). As can be seen, the main difference between Fig. 3(c) and Fig. 1(b) is that the metal plate of Fig. 3(c) has a cavity 305. In case of a rectangular cavity, the width Wcavof the cavity is preferably at least 70% or at least 80% or at least 90% or at least 100% of the distance Wsi between the shield legs, or at least equal to the outer distance Wso of the shield legs; and the length Lcavof the cavity is preferably equal to or larger than the length Lsh of the shield. As explained above, important parameters are the remaining thickness "Tres" of the metal surface, and the distance "g" between the shield legs and the metal surface. In the specific example of Fig. 3(c), Wso = 21 mm, and the width Wcavof the cavity is 25.2 mm, the length Lcavis 16.6 mm, the remaining thickness Tres of the plate is 1.0 mm, and the distance "g" between the shield legs and the plate is 2.3 mm, but the application is of course not limited to these particular values. In other embodiments, the value of "g" can be a value in the range from 1.0 mm to 3.0 mm.

[0142] Figure 4 A three-phase current sensor system 450 according to an embodiment of the application is shown. The three-phase current sensor system 450 comprises three current sensor subsystems 400a, 400b, 400c arranged side-by-side as illustrated in Fig. 1(b), such that the three electrical conductor portions extend in the Y direction, and the central shield portion is aligned and extends in the X direction. The system 450 is also referred to herein as a "current sensor system with full metal plate", where "full" means "without cavity". This system can be used to measure three AC currents flowing through the respective bus bars, typically denoted Iu, Iv, Iw.

[0143] The current sensor system 450 contains three magnetic sensors, one for each subsystem, the positions of which are indicated by the black dots. Each magnetic sensor is configured to measure a respective magnetic field component Bx that is oriented in the X direction. The respective current can then be calculated as I = Bx * K, where K is a pre-defined constant that can be determined, e.g., by simulation, by measurement, or by calibration, and can be hard-coded, or can be stored in a non-volatile memory of the respective sensor device. A suitable magnetic sensor device is able to measure the magnetic field component generated by a current of up to about 750 amperes or up to 1500 amperes with a non-linear error of less than 0.2%.

[0144] It was found that the cross-talk between the different phases of this current sensor system 450 is less than 1% due to the presence of the magnetic shield.

[0145] In Figure 4In the example of system 450, a single metal plate or metal layer 403 extends over the three subsystems and has a constant thickness Tp. In practice, the metal plate or metal layer 403 can be part of a metal housing (not shown) that is shaped for mechanically protecting the magnetic sensor devices and / or for EMC (electromagnetic compatibility). The three sensor devices can be mounted on a single printed circuit board (not shown). Figure 4 The simulation results for the current sensor system of Figures 8(a) to 8(d) will be provided in

[0146] The distance between the magnetic shields of two adjacent subsystems (in the X-direction) can be a value in the range from 1 mm to 100 mm (e.g. from 2 mm to 50 mm, e.g. from 5 mm to 25 mm, e.g. 10 mm), but the application is not limited thereto, and other values can also be used.

[0147] Figure 5 A three-phase current sensor system 550 according to an embodiment of the application is shown. Figure 5 The three-phase current sensor system 550 comprises three current sensor subsystems 500a, 500b, 500c arranged side-by-side as illustrated in Fig. 3(c) such that the three electrical conductor portions extend in the Y-direction and the central shield portions are aligned and extend in the X-direction. The system 550 is also referred to herein as “current sensor system with metal plate with cavities”. Figure 5 The current sensor system 550 is a variant of the current sensor system 450, the main difference being that the metal plate or metal layer 503 has three cavities 505a, 505b, 505c, the metal plate or metal layer 503 having a residual thickness “Tres” as explained above in Figures 3(a) to 3(c) Figure 5 The simulation results for the current sensor system 550 will be provided in Figures 9(a) to 9(d)

[0148] In a variant of Figure 5 , the metal plate or metal layer 503 can have a single cavity extending over the three subsystems. Such a system would provide essentially the same accuracy but can have reduced mechanical robustness.

[0149] Figure 6 A three-phase current sensor system 650 is shown that comprises three arrangements 600a, 600b, 600c without a metal plate as illustrated in Fig. 2(c). The system 650 is also referred to herein as “current sensor system without metal plate”. This system is provided as a reference point (or baseline) for comparison. Figure 6 The simulation results for the current sensor system 650 will be provided in Fig. 7(a) and Fig. 7(b). ​​

[0150] Figures 7(a) to 10(b) The simulation results are shown. The simulation assumes an ambient temperature of 25°C, unless explicitly mentioned otherwise.

[0151] Figures 7(a) and 7(b) show computer simulation results for a "current sensor system without metal plate" (e.g. as illustrated in Fig. 1 (a) or Fig. 1 (b)). These curves can be considered as "reference curves" that have to be improved. Figure 7(a) shows the amplitude variation as a function of frequency. Figure 7(b) shows the phase shift as a function of frequency. In fact, three curves are shown, each curve being associated with a different mounting position (in the Z direction) of the magnetic sensor device, to illustrate the effect of the system mounting tolerance. As can be seen, the simulation curves are substantially overlaid, which illustrates that the mounting tolerance of the sensor device of this system can be neglected. Also as can be seen, the magnetic field (and thus the value of the current) at 1500 Hz is attenuated to about -2.3% (for the central curve corresponding to the envisaged mounting position without offset in the Z direction), and is shifted at 1500 Hz to about -1.4°. Figure 6 Figures 8(a) and 8(b) show computer simulation results for a "current sensor system with full metal plate", using a distance (or air gap) "g" of 2.3 mm between the metal plate and the shield leg, and using a plate thickness "Tp" of 2.5 mm, e.g. as illustrated in Fig. 1 (b) or Fig. 1 (c). It should be noted that these values are not optimal values, as will be further explained in Figures 10(a) and 10(b), but nevertheless they provide a significant reduction of the amplitude variation error and the phase error (for a correct mounting of the sensor device).

[0152] Figure 4 Figure 8(a) shows the amplitude variation as a function of frequency. The central curve, corresponding to the correct mounting position of the sensor device, has a maximum amplitude variation error of about 1.3% (absolute value). However, as can be seen, the performance of this current sensor system with g = 2.3 mm and Tp = 2.5 mm is quite sensitive to the mounting tolerance.

[0153] Figure 8(b) shows the phase shift as a function of frequency. The central curve, corresponding to the correct mounting position of the sensor device, has a maximum phase shift error of about 0.5° (absolute value), which is not perfect but an improvement with respect to the simulation of Figures 7(a) and 7(b).

[0154] Figure 8(c) shows the amplitude variation as a function of frequency for a fixed sensor position but for two different temperatures, showing that the amplitude variation error depends on the temperature.

[0155] Figure 8(d) shows the phase shift as a function of frequency for a fixed sensor position but for two different temperatures, showing that the phase shift error depends on the temperature.

[0156] ​Figure 8(d) shows the amplitude variation as a function of frequency for a fixed sensor position but for three positions of the metal plate.

[0157] From Figures 8(a) to 8(d) It can be concluded that even if the metal plate of this current sensor system is not optimized, it still provides a considerable improvement in flattening the amplitude variation and phase curve or in reducing the maximum amplitude variation error or phase error from DC to about 1500 Hz compared to a system without a metal plate if the installation tolerances are low enough.

[0158] Figures 9(a) to 9(d) Computer simulation results for the "current sensor system with metal plate with cavity" using a distance (or air gap) "g" of 2.3 mm between the metal plate and the shield leg and using a residual plate thickness "Tres" of 1.0 mm are shown, for example, as illustrated in Figures 3(c) and Figure 5 The position and residual thickness of the metal plate of this current sensor system are optimized as will be further explained in Figures 10(a) and 10(b).

[0159] Figure 9(a) shows the amplitude variation as a function of frequency for a fixed sensor position of the sensor device and for two temperatures. As can be seen, the amplitude variation curve is essentially flat from DC to about 1500 Hz and for temperatures ranging from 25 °C to 105 °C and the maximum amplitude variation error is less than 0.3% (absolute), which is a major improvement compared to Figure 8(c) where the maximum error is about 1.3%.

[0160] Figure 9(b) shows the amplitude variation as a function of frequency for a fixed sensor position of the sensor device but for three distances between the metal plate and the shield. As can be seen, the maximum error in Figure 9(b) is about 0.4%, which is a major improvement compared to Figure 8(d) where the maximum error is about 1.5%.

[0161] Figure 9(c) shows the amplitude variation as a function of frequency for three different positions of the sensor device and Figure 9(d) shows the phase shift as a function of frequency for three different positions of the sensor device. As can be seen, in Figure 9(c) the maximum amplitude variation error of the central curve (corresponding to the correct installation position of the sensor device) is only about 0.3%, which is a considerable improvement compared to the 1.3% error of Figure 8(a). And the maximum phase error of the central curve in Figure 9(d) is about 0.5°, which is comparable to the 0.5° of Figure 8(b).

[0162] From Figures 9(a) to 9(d)It can be concluded that the system with "metallic plate with cavity" (where "g" and "Tres" are optimized) has reduced amplitude variation error and phase error (for correct mounting of the sensor device and the metallic plate) and that for a mounting tolerance of the sensor device of ±0.5 mm, the amplitude variation error and the phase error are still very small (less than 0.8% in absolute value and less than 0.8°).

[0163] Figures 10(a) and 10(b) show, by two examples, how the plate distance (g) and the plate thickness (Tp) or residual plate thickness (Tres) are optimized. Although at first sight two parameters are involved, in practice one parameter is predefined or chosen based on other criteria (e.g. weight or sufficient mechanical stiffness), whereby only one parameter needs to be optimized.

[0164] Figure 10(a) shows the amplitude variation error of the "current sensor system with metallic plate with cavity" at 1500 Hz for a given distance "g" between the metallic plate and the shield leg. This figure allows to optimize the value of the plate thickness for a given value of "g". As can be seen, for Tres values from about 0.3 mm to 1.5 mm (and possibly larger, but not simulated), the amplitude variation error is less than 1.6% (in absolute value). When considering a solution with amplitude variation error less than 1.5% (in absolute value) as satisfactory, it can be seen that all values of Tres in the range from about 0.33 mm to 1.5 mm are good values.

[0165] It can also be seen that for a (given) value g = 1.0 mm, the optimal value of Tres is approximately Tres = 0.8 mm.

[0166] The skilled person, having the benefit of the present disclosure, can easily find the optimal value of Tp or Tres for another (given) value of "g" in a similar way. This figure also confirms the above statement that if the plate thickness is "too small" (e.g. less than 0.3 mm), the metallic plate cannot sufficiently compensate for the skin effect.

[0167] Figure 10(b) shows the amplitude variation error of the "current sensor system with metallic plate with cavity" at 1500 Hz for a given residual thickness Tres equal to 1.5 mm. This figure allows to optimize the distance "g" between the plate and the magnetic shield for a given value of this Tres.

[0168] As can be seen, the optimal value of "g" is approximately equal to 1.9 mm, but other values of g less than about 5.0 mm also provide good results, in particular: amplitude variation error in absolute value less than 1.5%.

[0169] A person skilled in the art, having the benefit of the present disclosure, can easily find the optimal value of "g" for another (given) value of Tp or Tres in a similar manner. The graph also confirms the statement made above, that the distance "g" should not be too large (e.g. less than 5.0 mm in the present example).

[0170] For the sake of completeness, it should be noted that the curves of Fig. 10(a) and Fig. 10(b) are simulated only at 1500 Hz, which can not provide the worst case, but this can easily be solved, e.g. by performing simulations at 500 Hz and 1000 Hz. Then, the three resulting curves can be combined, yielding a range of amplitude variations instead of a single value. Then, the optimal value of Tres can be chosen, e.g. as the smallest range of amplitude variations centered at 0%.

[0171] It should also be noted that the curves of Fig. 10(a) and Fig. 10(b) are performed for aluminum as the material of the metal plate, but the present invention is not limited to this, and the metal plate can also be made of an aluminum alloy, or of copper, or of a copper alloy, or of stainless steel 316L. A person skilled in the art, having the benefit of the present invention, can easily find suitable values for the distance "g" and the plate thickness, in particular after being told that the frequency response of the current sensor system can be influenced by installing a "full metal plate" or a "metal plate with a cavity" in the vicinity of the sensor device, while leaving a gap "g" between the metal plate and the shield leg. In fact, the parameter "g" can be optimized for a given or chosen plate thickness, or a given or chosen plate thickness can be optimized for the parameter "g", and the parameter "Tp" or "Tres" can be optimized for a given or chosen distance "g".

[0172] Figure 11 A high-level block diagram of a magnetic sensor device 1110 that can be used in the current sensor device described above is shown. The circuit 1110 can comprise a silicon substrate. The circuit 1110 comprises at least one magnetic sensor element 1111 (e.g. at least one horizontal Hall element, or at least one vertical Hall element, or at least one magnetoresistive (MR) element). The sensor device is configured to measure a magnetic field component Bx that is oriented in the X direction (e.g. parallel to the silicon substrate).

[0173] In a particular embodiment, the sensor device comprises an integrated magnetic concentrator (IMC) and two horizontal Hall elements arranged on opposite sides of the IMC, providing signals h1 and h2, respectively. In this case, the magnetic field component Bx can be calculated as a value proportional to (h1 - h2).

[0174] In another embodiment, the sensor device comprises a single vertical Hall element providing a signal v1. In this case, the magnetic field component Bx can be calculated as a value proportional to v1.

[0175] The processing unit 1130 can be adapted to determine the current to be measured according to the formula I = K * v1, or according to the formula I = K. (h1 - h2), where K is a pre-defined constant, which can be determined during design, by simulation or during an evaluation or calibration phase. The subtraction can be done in hardware, before amplification or after amplification, or can be performed in the digital domain. The processing unit 1130 can comprise a digital processor comprising or being connected to a non-volatile memory 1131 storing said at least one constant value K.

[0176] The circuit 1110 can further comprise one or more of the following components: a biasing circuit, a read-out circuit, an amplifier or differential amplifier, an analog-to-digital converter (ADC), etc. The ADC can be part of the digital processor circuit.

[0177] The current to be measured can be provided as an analog output signal proportional to the current, or can be provided as a digital signal indicative of the current to be measured, e.g. via a digital data interface, e.g. via a serial data bus (e.g. using the I2C protocol, or using the RS232 protocol, or any other suitable protocol).

Claims

1. A current sensor system (100; 300) for measuring an AC current having a frequency in a predefined frequency range, the current sensor system comprising: - an electrical conductor portion (101; 301) extending in a first direction (Y) and configured for conducting the AC current, thereby creating a first magnetic field; - a U-shaped magnetic shield (140; 340) partially surrounding the electrical conductor portion and having a central shield portion (143; 343) extending in a second direction (X) perpendicular to the first direction (Y) and having two shield leg portions (141, 142; 241, 242; 341, 342) extending in a third direction (Z) perpendicular to the first and second directions (X, Y); - a metal plate or layer (103; 303) arranged at a predefined distance (g) from the shield leg portions for allowing eddy currents to flow in the metal plate or layer, thereby creating a second magnetic field superimposed with the first magnetic field; - a magnetic sensor device (102; 202; 302) arranged between the electrical conductor portion (101; 301) and the metal plate or layer and between the two shield leg portions (141, 142; 241, 242; 341, 342) and configured for measuring a magnetic field component (Bx) oriented in the second direction (X); characterized in that the metal plate or layer has a length (Lp) greater than a length (Lsh) of the shield measured in the first direction (Y) and has a width (Wp) greater than 90% of a distance (Wsi) between inner sides of the shield leg portions measured in the second direction (X) and has a thickness (Tp); or the metal plate or layer is a portion of a metal housing having a cavity in the vicinity of the magnetic sensor, the metal plate or layer having a residual thickness (Tres) in the vicinity of the magnetic sensor.

2. The current sensor system (100; 300) of claim 1, the thickness (Tp, Tres) and the distance (g) between the metal plate or layer and the shield leg portions being such that for frequencies in the range from 50 Hz to 1500 Hz the amplitude variation of the magnetic field component (Bx) of the combined first and second magnetic fields oriented in the second direction (X) at the sensor location is less than ±1.5%.

3. The current sensor system (100; 300) of any of the preceding claims, wherein, the thickness (Tp, Tres) being at least 0.3 mm; and / or wherein the distance (g) is at most 10.0 mm; wherein ​ ​ and optionally wherein said distance (g) is at least 0.1 mm.

4. The current sensor system (100; 300) of claim 1, wherein said thickness (Tp, Tres) of said metal plate or metal layer and said distance (g) are such that the amplitude variation of said magnetic field component (Bx) is less than ±1.0% or less than ±0.75% for frequencies in the range from 50 Hz to 1500 Hz.

5. The current sensor system (100; 300) of claim 1, wherein said metal plate or metal layer (103; 303) comprises or consists of an electrically conductive but non-magnetic material.

6. The current sensor system (100; 300) of claim 1, wherein said metal plate or metal layer is a portion of said metal casing with said cavity in the vicinity of said magnetic sensor and has at least one of the following features: (i) wherein said metal plate or metal layer has a length (Lcav) greater than 90% of the length (Lsh) of said shield measured in said first direction (Y); (ii) wherein said metal plate or metal layer has a width (Wcav) greater than 90% of the distance (Wsi) between the inner sides of said shield leg portions.

7. The current sensor system (100; 300) of claim 1, wherein said residual thickness (Tres) of said metal plate or metal layer is a value in the range from 0.5 mm to 1.5 mm.

8. The current sensor system (100; 300) of claim 1, wherein, said magnetic sensor device is configured to determine the amplitude of said AC current according to the formula: I = K * Bx, wherein I is the amplitude of the AC current to be measured, K is a predefined constant independent of frequency, and Bx is the measured magnetic field component.

9. The current sensor system (100; 300) of claim 1, wherein said electrical conductor portion has a central conductor portion (201c, 201d) between said shield leg portions, said central conductor portion being a solid strand shaped portion with a substantially constant cross section; or wherein said electrical conductor portion has a central conductor portion (201a, 201b) between said shield leg portions, said central conductor portion (201a, 201b) having a through opening.

10. The current sensor system (100; 300) of claim 1, wherein, said magnetic sensor device (102; 302) comprises at least one vertical Hall element configured to measure said magnetic field component (Bx) oriented in said second direction (X); or wherein said magnetic sensor device (102; 302) comprises at least one magnetoresistive element configured to measure said magnetic field component (Bx) oriented in said second direction (X).

11. The current sensor system (100; 300) of claim 1, wherein The magnetic sensor comprises two vertical Hall elements, each configured for measuring the magnetic field component (Bx) oriented in the second direction (X).

12. The current sensor system (100; 300) of claim 1, wherein The magnetic sensor device comprises an integrated magnetic concentrator (IMC) and two horizontal Hall elements arranged on opposite sides of the IMC, spaced apart in the second direction (X).

13. The current sensor system of claim 1, wherein The metal plate or metal layer is arranged outside the U-shaped magnetic shield.

14. A three-phase current sensor system (450; 550) for measuring three AC currents having frequencies in a predefined frequency range, the system comprising three current sensor systems (400a, 400b, 400c; 500a, 500b, 500c) according to any one of the preceding claims, each comprising an electrical conductor, and a magnetic sensor device, and a metal plate or metal layer.

15. The three-phase current sensor system (450; 550) of claim 14, wherein The metal plates or metal layers of the three current sensor systems (400a, 400b, 400c; 500a, 500b, 500c) are integrally formed.

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