Patent Description:
Different kinds of current sensors are known in the art, for example (<NUM>) current sensors using a shunt resistor, (<NUM>) using a current transformer, (<NUM>) or using a magnetic sensor.

In current sensors using a shunt resistor, a voltage is measured over the shunt resistor, and the current value can be determined by dividing the measured voltage value and the resistor value. A disadvantage of this type is that the measurement circuit is not electrically isolated from the load. A current transformer includes primary and secondary coils. While this type of current sensor provides galvanic separation, it is usually very bulky. Current sensors based on magnetic sensors provide both galvanic separation and can be very compact.

Known current sensors are typically designed to measure DC currents or low frequency currents, for example currents having a frequency of about <NUM> or about <NUM>.

Various electrical motor types exist, for example: so called DC brushed motors, DC brushless motors, AC brushless motors, linear motors, stepper motors, etc. In electrical vehicles, the following motor types are typically used: DC Series Motor, Brushless DC Motor, Permanent Magnet Synchronous Motor (PMSM), Three Phase AC Induction Motors, Switched Reluctance Motors (SRM).

Various electrical circuits for driving and/or controlling and/or monitoring electrical motors exist. In some of these circuits the actual currents provided to the motor need to be measured. These currents may have a magnitude of several tens or even hundreds of Ampères, and may have a frequency or frequency components up to several kHz. These currents are typically provided to the motor via so called "busbars". Busbars often come in the form of a metallic strip or bar, for example a copper bar.

It is known that, when AC currents flow through an electrical conductor, a phenomenon known as "skin effect" will occur. This causes the effective electrical resistance of the electrical conductor to increase. The higher the frequency of the electrical current, the higher the effective resistance of the electrical conductor.

<CIT>) describes a magnetic field-based current sensor for frequency-compensated measurement of alternating currents using a sensor element which is sensitive to magnetic fields. The sensor element is arranged spatially adjacent to a conductor for detecting a magnetic field caused by the alternating current flowing through the conductor. At least one conductive compensating element is arranged disconnected from the conductor and spatially adjacent to the sensor element and to the conductor for compensating for frequency-dependent distortions of the magnetic field by means of a compensation magnetic field which can be generated by induction.

It is a challenge to measure an AC current with high accuracy.

It is an object of embodiments of the present invention to provide a current sensor system for measuring an AC current, for example an AC current flowing through a busbar.

It is an object of embodiments of the present invention to provide a current sensor system for measuring an AC current with improved accuracy, and/or which is less sensitive to mounting tolerances, and/or which is less sensitive to temperature variations, and preferably two of these, or all of these.

It is an object of embodiments of the present invention to provide a current sensor system for measuring an AC current having frequencies up to about <NUM> or up to about <NUM> with improved accuracy.

It is an object of embodiments of the present invention to provide a current sensor system for measuring the instantaneous or momentary amplitude of an AC current having frequencies up to about <NUM> or up to about <NUM> with improved accuracy.

It is an object of embodiments of the present invention to provide a current sensor system for measuring an AC current with improved accuracy in a simple manner, e.g. without having to perform spectral analysis (e.g. Fourier analysis), and/or without having to analyse the current waveform in the time domain (e.g. sinusoidal, square, triangular).

It is an object of embodiments of the present invention to provide a current sensor system for measuring an AC current having an amplitude of up to <NUM> Amps or up to <NUM> Amps or up to <NUM> Amps or up to <NUM> Amps or up to <NUM> Amps, and having frequencies up to about <NUM> or up to about <NUM>, which is more accurate, and which is preferably also less sensitive to mounting tolerances and/or to temperature variations, and preferably both.

It is an object of embodiments of the present invention to provide a current sensor system capable of measuring an AC current with an absolute accuracy within ± <NUM>% (or better) for AC currents having amplitudes up to <NUM> Amps (or more, e.g. up to <NUM> A), and having frequencies up to <NUM> (or more, e.g. up to <NUM>), in an ambient temperature in the range from <NUM> to <NUM> (or a larger range, e.g. from -<NUM> to +<NUM>, or from -<NUM> to +<NUM>), and for mounting tolerances of a magnetic sensor device up to ± <NUM> (or up to ± <NUM>, or up to ± <NUM>).

It is also an object of embodiments of the present invention to provide a three-phase current sensor system comprising three busbars for measuring three AC currents, each having an amplitude of up to <NUM> Amps or up to <NUM> Amps or up to <NUM> Amps or up to <NUM> Amps, and frequencies up to about <NUM> or up to about <NUM>, with an improved accuracy, and/or which is less sensitive to mounting tolerances, and/or which is less sensitive to temperature variations.

These and other objects are accomplished by a current sensor according to embodiments of the present invention.

According to a first aspect, the present invention provides a current sensor system having the features of independent claim <NUM>.

This current sensor system is configured for measuring an AC electrical current having frequencies in 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 said AC electrical current, thereby creating a first magnetic field; a U-shaped magnetic shielding partially surrounding said electrical conductor portion, and having a central shielding portion extending in a second direction (e.g. X) perpendicular to the first direction (e.g. Y), and having two shielding leg portions 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 shielding legs portions for allowing eddy currents to flow in said metal plate or metal layer, thereby creating a second magnetic field which is 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 shielding 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 length (e.g. Lp) larger than a length (e.g. Lsh) of the shielding measured in the first direction (e.g. Y), and has a width (e.g. Wp) larger than <NUM>% of a distance (e.g. Wsi) measured in the second direction (X) between inner sides of the shielding leg portions, and has a thickness (e.g. Tp); or wherein the metal plate or metal layer is a portion 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) in the vicinity of the magnetic sensor.

The inventors discovered that the AC current can be measured with improved accuracy by addition of an electrically conductive surface, e.g. a metal plate made from Al or Cu. They surprisingly found that the magnetic field induced by the eddy currents can reduce the error, thus improve the accuracy of the current measurement, if located at a suitable distance from the shield, and if having a suitable plate thickness. This is totally unexpected, and highly counter-intuitive because it is well known and commonly accepted/believed that eddy currents negatively influence measurements rather than improving them.

It is an advantage of the present invention that the AC current is determined by multiplication of a measured magnetic field component, in contrast to systems measuring a peak current, which is then for example multiplied by the square root of <NUM> (approximately <NUM>), because this is only accurate if the waveform of the AC current is a perfect sinusoidal signal.

It is an advantage of the present invention that the measurement is accurate for any AC waveform, e.g. sinusoidal, square, triangular, etc..

While preferred, embodiments of the present invention are not necessarily limited to solutions wherein the accuracy is ±<NUM>% for frequencies in the range from <NUM> to <NUM>.

In an embodiment, the thickness (e.g. Tp or Tres) and the distance (e.g. g) between the metal plate or metal layer and the shielding legs are such that the amplitude of the magnetic field component (e.g. Bx) of the combined first and the second magnetic field at the sensor location and oriented in the second direction (e.g. X) varies less than ±<NUM>% for frequencies in the range from <NUM> to <NUM>.

Or stated in other words: wherein the distance (g) and a thickness (Tp, Tres) of the metal plate or metal layer are such that an attenuation of the magnetic field component (Bx) varies less than ±<NUM>% for frequencies up to <NUM>.

For example, if the plate thickness or layer thickness is fixed or predefined, suitable values for the distance "g" can be found, or an optimal value of "g" can be found. Alternatively, if the distance "g" is fixed or predetermined, suitable values for the plate thickness "Tp or Tres" can be found, or an optimal value of the plate thickness can be found. In other words, in practice one parameter may be chosen, and a suitable range for the other parameter, or an optimum value for the other parameters can be found.

It is explicitly pointed out that the claim does not only cover the most optimal solution, but also covers other "good working solutions", because these are also a considerable improvement over the prior art, e.g. in terms of a reduced amplitude variation error.

It is an advantage of this current sensor system that it allows accurate measurement of the AC electrical current, which may have frequencies up to about <NUM> or about <NUM>, in a fast and simple manner, without requiring heavy processing, without having to perform spectral analysis techniques (e.g. Fourier analysis).

In an embodiment, the thickness of the metal plate or metal layer (e. Tp, Tres) is at least <NUM> or at least <NUM> or at least <NUM>.

In an embodiment, the thickness of the metal plate or metal layer (e. Tp) is a value in the range from <NUM> to <NUM>.

In an embodiment, the distance (e.g. g) between the metal plate or metal layer and the shielding legs is at most <NUM> or at most <NUM>, or at most <NUM>, or at most <NUM>.

The plate thickness Tp or Tres may be a value in the range from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, e.g. equal to <NUM>, or equal to <NUM>, or equal to <NUM>.

In an embodiment, the distance (e.g. g) between the metal plate or metal layer and the shielding legs is at least <NUM>, or at least <NUM>, or at least <NUM>.

The magnetic sensor device may be configured for determining the AC electrical current as a value proportional to the magnetic field component value.

In an embodiment, amplitude of the magnetic field component varies less than ±<NUM>% for frequencies in the range from <NUM> to <NUM>.

In an embodiment, the thickness (e.g. Tp, Tres) of the metal plate or metal layer and the distance (e.g. g) are such that amplitude of the magnetic field component (Bx) varies less than ±<NUM>% or less than ±<NUM>% for frequencies in the range from <NUM> to <NUM>.

In an embodiment, the metal plate or metal layer comprises or consists of an electrically conductive but non-magnetic material.

In an embodiment, the metal plate is made from aluminum or an aluminum alloy, or from copper or a copper alloy, or from a non-magnetic stainless steel.

In an embodiment, the metal plate or metal layer is a portion of a metal plate having said thickness (e.g. Tp) and having a length (e.g. Lp) larger than a length (e.g. Lsh) of the shielding measured in the first direction (e.g. Y).

In an embodiment, the metal plate or metal layer is a portion of a metal plate having said thickness (e.g. Tp) and having a width (e.g. Wp) larger than <NUM>% of a distance (Wsi) between inner sides of the shielding legs (or a width (Wp) larger than a distance Wso between outer surfaces of the shielding legs, or larger than <NUM>% * Wso).

In an embodiment the metal plate or metal layer is a portion 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) larger than <NUM>% of a length (e.g. Lsh) of the shielding measured in the first direction (e.g. Y).

In an embodiment the metal plate or metal layer is a portion 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) larger than <NUM>% of a distance (e.g. Wsi) between inner sides of the shielding legs; or has a width (e.g. Wp) larger than a distance (e.g. Wso) between outer surfaces of the shielding legs, or larger than <NUM>% * said distance (e.g. Wso).

In an embodiment, the thickness (e.g. Tp) or the residual thickness (e.g. Tres) of the metal plate or metal layer is a value in the range from <NUM> to <NUM>.

The metal plate or metal layer is galvanically separate from the electrical conductor. The metal plate or metal layer may be part of a metal housing. The metal plate or metal layer may be grounded.

The shielding is galvanically separate from the electrical conductor. The shielding may be grounded.

The magnetic sensor device may comprise a semiconductor substrate, e.g. a silicon substrate. The magnetic sensor device may be a packaged semiconductor device (also known as "chip").

The electrical conductor is arranged outside of said integrated semiconductor device.

The electrically conductive surface may be galvanically separate from said electrical conductor and from said magnetic sensor device.

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

In an embodiment, at least <NUM>%, or at least <NUM>% or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>% of the power of the AC current is situated below <NUM> or below <NUM>.

In an embodiment the magnetic sensor device is an integrated semiconductor device (also referred to as "chip").

The magnetic sensor device may be mounted on a printed circuit board.

In an embodiment, the magnetic sensor device is configured for determining said magnitude of the AC electrical current in accordance with the formula: I=K*Bx, where I is the magnitude of the AC electrical current to be measured, K is a predefined constant independent of frequency, and Bx is the measured magnetic field component.

In this embodiment, the magnetic sensor device is configured for determining the AC electrical current as a value proportional to the magnetic field component value.

In an embodiment, the electrical conductor portion has a central conductor portion situated between the shielding legs, which central conductor portion is a solid beam shaped portion with a substantially constant cross-section.

With "solid beam shaped portion" is meant that the central conductor portion is not perforated, or stated in other words, does not have a slit or a hole or a through-opening causing the current flowing through the central conductor portion to be split in two discrete conductive paths, e.g. as illustrated in <FIG>.

The cross section may be a rectangular cross section having a predefined width Wc and a height Tc.

In an embodiment, the electrical conductor portion has a central conductor portion situated between the shielding legs, and the central conductor portion has a through opening (e.g. a slit).

The sensor device is preferably located in the vicinity of said through-opening, e.g. at a distance of at most <NUM> from said through-opening.

In an embodiment, the magnetic sensor device comprises a vertical Hall element, configured for measuring said magnetic field component (e.g. Bx) oriented in the second direction (e.g. X).

In an embodiment, the magnetic sensor device comprises at least one magneto-resistive (MR) element, configured for measuring said magnetic field component (e.g. Bx) oriented in the second direction (e.g. X).

In an embodiment, the magnetic sensor comprises two vertical Hall elements, each configured for measuring said magnetic field component (e.g. Bx) oriented in the second direction (e.g. X).

In an embodiment, the outputs of the two vertical Hall elements may be combined (e.g. be added) to increase the signal-to-noise ratio of the measured signal.

In an embodiment, the magnetic sensor device comprises circuitry for allowing each of the vertical Hall elements to be read-out separately, e.g. for diagnostic purposes.

In an embodiment, 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).

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

In an embodiment, 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 and the second side being <NUM>° angularly spaced. The values obtained from H1 and H2 may be combined, e.g. summed or averaged to yield a first value h12, and the values obtained from H3 and H4 may be combined, e.g. summed or averaged to yield a second value h34, and the magnetic field component Bx is proportional to (h12-h34).

According to a second aspect, the present invention also provides a three-phase current sensor system having the features of claim <NUM>.

This three-phase current sensor system is configured for measuring three AC electrical current 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 <FIG>.

In an embodiment (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 stated in other words, this three-phase current sensor system comprises a single metal plate, or a single metal housing. According to a third aspect, the present invention also provides a current sensor system according to the first aspect, wherein the metal plate or metal layer is arranged outside of the U-shaped magnetic shielding.

The present invention relates in general to the field of magnetic current sensor systems, and more in particular to a current sensor system capable of accurately measuring an AC current.

The AC current may have an amplitude up to about <NUM> or up to about <NUM> Amps or up to about <NUM> or up to about <NUM> Amps, and may have frequencies up to about <NUM> or up to about <NUM>. Such current sensor system may be used in industrial, robotic and automotive applications, e.g. for measuring one or more currents provided to an electrical motor, e.g. in electrical or hybrid vehicles. Such electrical motors may be driven using relatively large AC currents, for example substantially sinusoidal currents having amplitudes of tens or even hundreds of amperes. The present invention is particularly concerned with accurately measuring such AC currents.

As already mentioned in the background section, a specific problem that occurs when trying to measure AC currents having a relatively high frequency (e.g. higher than <NUM> or <NUM>) is that a phenomenon known as the "skin effect" occurs, which causes the current density to increase near the outer periphery of the electrical conductor, and causes the current density 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. As far as is known to the inventors, 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 a determination of the AC current as a value proportional to a measured magnetic field component or proportional to a measured magnetic field gradient, without any correction, will result in an error, which may typically amount to about <NUM>%.

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

<FIG> illustrates a current sensor system <NUM> in cross-section, and <FIG> illustrates the current sensor system <NUM> in perspective view.

The current sensor system <NUM> comprises an electrical conductor portion <NUM> for conducting the AC current to be measured. The electrical conductor portion <NUM> extends in the Y direction. The electrical conductor portion <NUM> may be part of a busbar <NUM>, and may have a rectangular cross section, optionally with rounded or truncated edges. The electrical conductor portion <NUM> may be solid, or may have a through-hole in the Z-direction, e.g. as illustrated in <FIG>. The electrical conductor portion <NUM> may have a thickness Tc from <NUM> to <NUM> or from <NUM> to <NUM>, and may have a width Wc from <NUM> to <NUM> or from <NUM> to <NUM> or from <NUM> to <NUM>, but these values are not critical.

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

The current sensor system <NUM> further comprises: a U-shaped magnetic shielding <NUM> partially surrounding the electrical conductor portion <NUM>. The magnetic shielding <NUM> has a U-shape comprising a central shielding portion <NUM> situated below the electrical conductor portion <NUM> of <FIG>, and two shielding leg portions <NUM>, <NUM> oriented substantially perpendicular to the central shielding portion <NUM>. The U-shaped shielding <NUM> is open at the top. The central conductor portion <NUM> is situated between the legs <NUM>, <NUM> of the U-shaped magnetic shielding <NUM>, or stated in other words, the magnetic shielding <NUM> partially surrounds the central conductor portion <NUM>. Preferably, the electrical conductor portion <NUM> is situated substantially in the middle between the legs <NUM>, <NUM> of the shielding <NUM> in the direction X. The shielding <NUM> shown in <FIG> has sharp edges, but alternatively may have rounded edges.

The shielding may define a distance Wsi between inner surfaces of the shielding legs <NUM>, <NUM>, and may define an outer width Wso in the X direction. Typical values of Wsi are <NUM> to <NUM>, or <NUM> to <NUM>, e.g. <NUM> to <NUM>, e.g. equal to about <NUM>. The shielding <NUM> may have a thickness Tsh in the range from <NUM> to <NUM> (e.g. equal to about <NUM>, or equal to about <NUM>, or equal to about <NUM>). The distance Wso between outer surfaces of the shielding legs <NUM>, <NUM> is equal to Wsi + <NUM>* Tsh, and may have a value in the range from (<NUM>+<NUM>*<NUM>)=<NUM> to (<NUM>+<NUM>*<NUM>)=<NUM>. But the present invention is not limited to these values, and other values may also be used.

The current sensor system <NUM> further comprises: a magnetic sensor or a magnetic sensor device <NUM>. While not shown in <FIG>, the magnetic sensor device may be a packaged semiconductor device. The magnetic sensor device <NUM> is arranged in the vicinity of the electrical conductor portion <NUM>, e.g. at a distance h in the range from <NUM> to <NUM> above the central conductor portion <NUM>. The magnetic sensor <NUM> is preferably arranged centrally above the electrical conductor portion <NUM>, halfway between the shielding legs <NUM>, <NUM>. The magnetic sensor device <NUM> may be configured for measuring a magnetic field component Bx oriented in the X-direction, transverse to the direction Y in which the AC current flows. The magnet sensor device <NUM> may be mounted on a printed circuit board (not shown) in known manners.

According to an underlying principle of the present invention, the current sensor system <NUM> further comprises an electrically conductive surface, e.g. an electrically conductive plate <NUM> or metallic plate, further referred to herein as a "metal plate" for ease of the description. The metal plate <NUM> is arranged at a distance "g" from the shielding legs <NUM>, <NUM> in the range from about <NUM> to about <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, equal to about <NUM> or equal to about <NUM>. In some embodiments, the metal plate or metal layer is in contact with the shielding legs. In other embodiments, the metal plate or metal layer <NUM> is not in contact with the shielding legs. The distance "dsp" between the magnetic sensor (device) <NUM> and the metal plate <NUM> may be a value in the range from <NUM> to <NUM>, or from <NUM> to <NUM>, e.g. equal to about <NUM>.

The metal plate <NUM> has a width Wp extending in the X-direction, which is preferably equal to or larger than <NUM>% of the inner distance Wsi between the legs <NUM>, <NUM> of the shield <NUM>. This can be written mathematically as follows: Wp ≥ <NUM>% * Wsi. In some embodiments Wp ≥ <NUM>% * Wsi, or Wp ≥ Wsi, or Wp ≥ <NUM>%*Wsi, or Wp ≥ Wso, or Wp ≥ <NUM>% * Wso, or Wp ≥ <NUM>% * Wso.

The inventors surprisingly discovered that by adding a metal plate, the frequency characteristic of the current sensor system can be influenced. More specifically, they discovered that by arranging a metal plate <NUM> of a particular thickness "Tp" at a particular distance "g", the amplitude variation and phase versus frequency characteristic can be improved. 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 <NUM>% at <NUM> in <FIG> to about <NUM>% at <NUM> in <FIG>, excluding mounting tolerances.

While the inventors do not wish to be bound by any theory, a possible explanation may be the following: the AC current flowing through the electrical conductor <NUM> causes a first magnetic field, but the first magnetic field does not have a flat frequency characteristic due to the "skin effect". The metal plate allows "eddy currents" to flow in the metal plate <NUM> induced by the varying first magnetic field, and these eddy currents induce a second magnetic field which is superimposed with the first magnetic field, and a superposition of the first and second magnetic field is measured by the magnetic sensor <NUM>.

After many experiments, the inventors found that:.

The inventors are of the opinion that this could not have been predicted based on what is known in the prior art. On the contrary, eddy currents are usually considered a parasitic effect that needs to be avoided, but in this invention, the eddy currents can be used in a positive way, namely to reduce or at least partially compensate the negative effect of the skin effect.

<FIG> shows a perspective view of the sensor system <NUM> of <FIG>. As can be seen, the length Lp of the metal plate <NUM> (measured in the Y-direction) is preferably equal to or larger than the length Lsh of the shielding (measured in the Y-direction).

The sensor device <NUM> is not shown in <FIG>, but the position of the magnetic sensor is indicated by means of a black circle inside the space between the two shielding legs <NUM>, <NUM> and between the electrical conductor portion <NUM> and the metal plate <NUM>. As can be seen, the central electrical conductor portion <NUM> may be part of a U-shaped busbar <NUM>, but that is not absolutely required for the invention to work.

<FIG> show examples of arrangements of an electrical conductor portion <NUM> and a U-shaped magnetic shielding <NUM> which may be used in embodiments of the present invention, e.g. in the current sensor system of <FIG>, but also in the current sensor system <NUM> of <FIG> which will be described further.

The arrangement 200a of <FIG> shows an electrical conductor portion and a U-shaped magnetic shielding (only the shielding legs <NUM>, <NUM> are visible). The electrical conductor portion has a U-shape comprising a central conductor portion 201a extending in the Y-direction, and two conductor leg portions oriented in the Z-direction, substantially perpendicular to the central conductor portion 201a. The central conductor portion 201a of <FIG> has a through-opening <NUM>. The central conductor portion 201a may be narrowed between the shielding legs <NUM>, <NUM>, or stated in other words: the width of the electrical conductor portion 201a may be locally reduced between the shielding legs <NUM>, <NUM>, e.g. in order to increase the current density, and thus the magnitude of the magnetic field component Bx to be measured.

The arrangement of <FIG> shows another example of an electrical conductor portion 201b and a U-shaped magnetic shielding portion (only the shielding legs <NUM>, <NUM> are visible). The electrical conductor portion 201b is a substantially planar portion. The magnetic shielding has a U-shape comprising a central shielding portion, not visible in <FIG>, but located under the central conductor portion 201b, oriented parallel to the electrical conductor portion 201b, and has two leg portions <NUM>, <NUM> oriented perpendicular to the central conductor portion 201b. The electrical conductor portion 201b is situated between the legs <NUM>, <NUM> of the U-shaped magnetic shield, or stated in other words, the magnetic shielding at least partially surrounds the electrical conductor portion 201b. The central electrical conductor portion 201b has a through-opening <NUM>. The width of the electrical conductor portion (in the X-direction) is locally reduced to increase the current density, but this is not absolutely required for the invention to work.

The arrangement of <FIG> is a variant of the arrangement of <FIG>, wherein the electrical conductor portion 201c does not have a through-opening, but is solid.

The arrangement of <FIG> is a variant of the arrangement of <FIG>, wherein the electrical conductor portion 201d does not have a through-opening, but is solid.

These are only a few examples of arrangements, but the present invention is not limited hereto. For example, in variants (not shown) of the arrangements shown in <FIG> the electrical conductor portion is not locally narrowed between the legs of the U-shaped shielding, but has a constant width. The main purpose of <FIG> is to show that the electrical conductor portion may have a U-shape, and/or may have a through opening <NUM>, and/or may be locally narrowed, but none of these is required.

It is noted that the magnetic sensor device <NUM> is only shown in <FIG>, and is omitted from <FIG> for illustrative purposes. It is important, however, that the magnetic sensor device <NUM> is situated in the space above the central electrical conductor portion and between the shielding legs. The main purpose of the shielding legs is to prevent the magnetic sensor device <NUM> from measuring a disturbance field oriented in the X-direction. The latter is especially true for a three-phase system, e.g. as shown in <FIG>, where the magnetic shieldings are configured to reduce cross-talk between the different phases.

<FIG> illustrate a current sensor system <NUM> according to another embodiment of the present invention, which can be seen as a variant of the current sensor system <NUM> of <FIG>, the main difference being that the current sensor system <NUM> has a metal or metallic surface <NUM> with a blind opening or cavity or recess, situated in the vicinity of the sensor device <NUM>.

The metal plate or metal layer (e.g. metal plate) <NUM> has a residual thickness "Tres" which is located at a distance "g" from the legs of the U-shaped shielding <NUM>. In other words, the metallic surface <NUM> may be part of a metallic housing with non-constant thickness, but the thickness "Tres" in the vicinity of the sensor device <NUM>, and the distance "g" have the same role or meaning as the parameters "Tp" and "g" discussed above. The metal plate or metal layer may be part of a metal housing. In fact, the housing (if present) does not need to be completely metallic, but could also be made from a plastic or ceramic material, as long as it has "metallic surface portions" with a thickness "Tp" or "Tres" in the vicinity of the sensor device, e.g. above the space defined by the U-shaped shielding. In the embodiment of <FIG>, the electrical conductor portion <NUM> is shown with a through-opening <NUM>, but as explained above, that is not absolutely required.

In a variant of <FIG>, the sensor device has a semiconductor substrate oriented parallel with the Z direction and parallel with the Y-direction. This sensor device may comprise a single horizontal Hall element for measuring the Bx-component (oriented perpendicular to the semiconductor substrate.

<FIG> shows a perspective view of a metal plate <NUM> with a cavity <NUM> for reducing the thickness of the plate "above the sensor device", as may be used in the current sensor system <NUM> of <FIG>. The cavity <NUM> shown has a rectangular shape having a width "Wcav" and a length "Lcav", but this shape is not critical for the invention to work, and another shape, e.g. an elliptical shape or a circular shape or a polygonal shape may also be used.

<FIG> shows a perspective view of the current sensor system <NUM> of <FIG>. As can be seen, the main difference between <FIG> and <FIG> is that the metal plate of <FIG> has a cavity <NUM>. In case of a rectangular cavity, the width of the cavity Wcav is preferably at least <NUM>% or at least <NUM>% or at least <NUM>% or at least <NUM>% of the distance Wsi between the shielding legs, or at least equal to the outer distance Wso of the shielding legs; and the length of the cavity Lcav is preferably equal to or larger than the length Lsh of the shielding. As explained above, important parameters are the remaining thickness "Tres" of the metallic surface, and the distance "g" between the legs of the shielding and the metallic surface. In the specific example of <FIG>, Wso = <NUM>, and the width Wcav of the cavity is <NUM>, the length Lcav is <NUM>, the residual thickness of the plate Tres is <NUM>, and the distance "g" between the shielding legs and the plate is <NUM>, but of course the present invention is not limited to these specific values. In other embodiments, the value of "g" may be a value in the range from <NUM> to <NUM>.

<FIG> shows a three-phase current sensor system <NUM> according to an embodiment of the present invention. The three-phase current sensor system <NUM> comprises three current sensor subsystems 400a, 400b, 400c as illustrated in <FIG>, arranged side by side, such that the three electrical conductor portions extend in the Y-direction, and the central shielding portions are aligned and extend in the X-direction. The system <NUM> is also referred to herein as a "current sensor system with a full metal plate", where "full" means "not having a cavity". This system can be used to measure three AC currents, typically denoted as lu, Iv, Iw, flowing through the respective busbars.

The current sensor system <NUM> contains three magnetic sensors, one for each subsystem, the locations of which are indicated by a black dot. Each magnetic sensor is configured for measuring a respective magnetic field component Bx oriented in the X-direction. The respective current can then be calculated as I = Bx * K, where K is a predefined constant, which may be determined for example by simulation, by measurement, or by calibration, and may be hardcoded, or may be stored in a non-volatile memory of the respective sensor device. Suitable magnetic sensor devices may be capable of measuring a magnetic field component generated by currents up to about <NUM> Amps or up to <NUM> Amps with a non-linearity error smaller than <NUM>%.

It was found that the cross-talk between the different phases of this current sensor system <NUM> was smaller than <NUM>%, thanks to the presence of the magnetic shields.

In the example of <FIG>, the system <NUM> contains a single metal plate <NUM> extending over the three subsystems, and having a constant thickness Tp. In practice, the metal plate <NUM> may be part of a metal housing (not shown) shaped to protect the magnetic sensor devices mechanically and/or for EMC (electro-magnetic interference). The three sensor devices may be mounted on a single printed circuit board (not shown). Simulation results of the current sensor system <NUM> of <FIG> will be provided in <FIG>.

The distance between the magnetic shields of two adjacent subsystems (in the X-direction) may be a value in the range from <NUM> to <NUM>, e.g. from <NUM> to <NUM>, e.g. from <NUM> to <NUM>, e.g. <NUM>, but the present invention is not limited hereto, and other values may also be used.

<FIG> shows a three-phase current sensor system <NUM> according to an embodiment of the present invention. The three-phase current sensor system <NUM> of <FIG> comprises three current sensor subsystems 500a, 500b, 500c as illustrated in <FIG> arranged side by side, such that the three electrical conductor portions extend in the Y-direction, and the central shielding portions are aligned and extend in the X-direction. The system <NUM> is also referred to herein as a "current sensor system with a metal plate with cavities". The current sensor system <NUM> of <FIG> is a variant of the current sensor system <NUM>, the main difference being that the metal plate <NUM> has three cavities 505a, 505b, 505c having a residual thickness "Tres" as explained above in <FIG>. Simulation results of the current sensor system <NUM> of <FIG> will be provided in <FIG>.

In a variant of <FIG>, the metal plate <NUM> may have a single cavity extending over the three subsystems. Such a system would provide substantially the same accuracy, but may have a reduced mechanical robustness.

<FIG> shows a three-phase current sensor system <NUM> comprising three arrangements 600a, 600b, 600c as illustrated in FIG. <NUM>(c) without a metal plate. The system <NUM> is also referred to herein as a "current sensor system without a metal plate". This system is provided as a point of reference (or baseline) for comparison. Simulation results of the current sensor system <NUM> of <FIG> will be provided in <FIG>.

<FIG> show simulation results. Unless explicitly mentioned otherwise, the simulations assume an environmental temperature of <NUM>.

<FIG> show computer simulations results for a "current sensor system without a metal plate", e.g. as illustrated in <FIG>. These curves may be considered as "reference curves" that had to be improved. <FIG> shows the amplitude variation as a function of frequency. <FIG> shows the phase shift as a function of frequency. In fact, three curves are shown, each associated with a different mounting position (in the Z-direction) of the magnetic sensor device, to show the impact of mounting tolerances of this system. As can be seen, the simulated curves are substantially overlapping, which illustrates the negligible influence of mounting tolerances of the sensor device of this system. As can also be seen, the magnetic field (and thus the value of the current) at <NUM> is attenuated by approximately -<NUM>% (for the central curve corresponding to the envisioned mounting position without offset in the Z-direction), and is phase shifted by approximately -<NUM>° at <NUM>.

<FIG> show computer simulations results for a "current sensor system with full metal plate", e.g. as illustrated in <FIG> or <FIG>, using a distance (or air gap) "g" between the metal plate and the legs of the shielding of <NUM>, and using a plate thickness "Tp" of <NUM>. It is noted that these values are not the optimal values, as will be further explained in <FIG>, but nevertheless, they provide a significant reduction of the amplitude variation error and phase error (for a correct mounting of the sensor device).

<FIG> shows the amplitude variation as a function of frequency. The central curve, corresponding to a correct mounting position of the sensor device, has a maximum amplitude variation error of about <NUM>% (in absolute value). As can be seen, however, the performance of this current sensor system with g=<NUM> and Tp=<NUM> is quite sensitive to mounting tolerances.

<FIG> shows the phase shift as a function of frequency. The central curve, corresponding to a correct mounting position of the sensor device, has a maximum phase shift error of about <NUM>° (in absolute value), which is not perfect, but an improvement with respect to the simulations of <FIG>.

<FIG> 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 is dependent on temperature.

<FIG> shows the amplitude variation as a function of frequency for a fixed sensor position, but for three positions of the metal plate.

It can be concluded from <FIG> that, even though the metal plate of this current sensor system was not optimized, it still provides a considerable improvement over the system without a metal plate, in terms of flattening the amplitude variation and phase curves, or in terms of reducing the maximum amplitude variation error or phase error, from DC to about <NUM>, if the mounting tolerances are sufficiently low.

<FIG> show computer simulations results for a "current sensor system with a metal plate with cavities", e.g. as illustrated in <FIG> and <FIG>, using a distance (or air gap) "g" between the metal plate and the legs of the shielding of <NUM>, and using a residual plate thickness "Tres" of <NUM>. The position and residual thickness of the metal plate of this current sensor system is optimized, as will be explained further in <FIG>.

<FIG> shows the amplitude variation as a function of frequency for a fixed mounting position of the sensor device, and for two different temperatures. As can be seen, the amplitude variation curves are substantially flat, and the maximum amplitude variation error is less than <NUM>% (in absolute value) from DC to about <NUM>, and for temperatures ranging from <NUM> to <NUM>, which is a major improvement as compared to <FIG>, where the maximum error was about <NUM>%.

<FIG> shows the amplitude variation as a function of frequency for a fixed mounting position of the sensor device, but for three distances between the metal plate and the shielding. As can be seen, the maximum error is about <NUM>% in <FIG>, which is a major improvement as compared to <FIG>, where the maximum error was about <NUM>%.

<FIG> shows the amplitude variation, and <FIG> shows the phase shift as a function of frequency for three different positions of the sensor device. As can be seen, the maximum amplitude variation error of the central curve (corresponding to correct mounting position of the sensor device) is only about <NUM>% in <FIG>, which is a considerable improvement compared to the <NUM>% error of <FIG>. And the maximum phase error of the central curve is about <NUM>° in <FIG>, which is comparable to the <NUM>° of <FIG>.

It can be concluded from <FIG> that the system with a "metal plates with cavities", wherein "g" and "Tres" are optimized, has a reduced amplitude variation error and phase error (for correct mounting of the sensor device and the metal plate), but also that the amplitude variation error and phase error remain very small (smaller than <NUM>% and smaller than <NUM>° in absolute value) for mounting tolerances of the sensor device of ±<NUM>.

<FIG> show, by way of two examples, how the plate distance (g) and the plate thickness (Tp) or the residual plate thickness (Tres) may be optimized. While 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), thus only one parameter needs to be optimized.

<FIG> shows the amplitude variation error of a "current sensor system with a metal plate with cavity", at <NUM> for a given distance "g" between the metal plate and the shielding legs. This graph allows to optimize the value of the plate thickness for the given value of "g". As can be seen, the amplitude variation error is smaller than <NUM>% (in absolute value) for values of Tres from about <NUM> to <NUM> (and probably also larger, but not simulated). When considering solutions with an amplitude variation error smaller than <NUM>% (in absolute value) as satisfactory, it can be seen that all values of Tres in the range from about <NUM> to <NUM> are good values.

It can also be seen that the optimum value of Tres for a (given) value g = <NUM> is approximately Tres=<NUM>.

The skilled person, having the benefit of the present disclosure, can easily find an optimum value of Tp or Tres for another (given) value of "g", in a similar manner. This graph also confirms the statement above, that the metal plate cannot sufficiently compensate the skin effect if the plate thickness is "too small" (e.g. smaller than <NUM>).

<FIG> shows the amplitude variation error of a "current sensor system with a metal plate with cavity", at <NUM> for a given residual plate thickness Tres equal to <NUM>. This graph allows to optimize the distance "g" between the plate and the magnetic shielding for this given value of Tres.

As can be seen, the optimum value of "g" is approximately equal to <NUM>, but other values of g smaller than about <NUM> also offer very good results, in particular: an amplitude variation error smaller than <NUM>% in absolute value.

The skilled person, having the benefit of the present disclosure, can easily find an optimum value of "g" for another (given) value of Tp or Tres, in a similar manner. This graph also confirms the statement above, that the distance "g" should not be too large (e.g. smaller than <NUM> in this example).

For completeness, it is noted that the curves of <FIG> are simulated only at <NUM>, which may not provide the worst case situation, but this can easily be addressed for example, by performing simulations at <NUM> and at <NUM>. The three resulting curves may then be combined, yielding an amplitude variation range instead of a single value. The optimum value of Tres may then for example be chosen as the smallest amplitude variation range centred at <NUM>%.

It is also noted that the curves of <FIG> are performed for Aluminum as the material of the metal plate, but the present invention is not limited thereto, and the metal plate can also be made from Aluminum alloy, or Copper, or a Copper alloy, or from stainless steel <NUM>. The skilled person having the benefit of the present invention, in particular, after being told that the frequency response of the current sensor system can be influenced by mounting 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 legs of the shielding, can easily find suitable values for the distance "g" and the plate thickness. Indeed, the parameter "g" can be optimized for a given or chosen plate thickness, or vice versa, the parameter "Tp" or "Tres" can be optimized for a given or chosen distance "g".

<FIG> shows a high-level block-diagram of a magnetic sensor device <NUM> that may be used in current sensor devices described above. The circuit <NUM> may comprise a silicon substrate. The circuit <NUM> comprises at least one magnetic sensor element <NUM>, e.g. at least one horizontal Hall element, or at least one vertical Hall element, or at least one magneto-resistive (MR) element. The sensor device is configured for measuring a magnetic field component Bx oriented in the X-direction, e.g. parallel to the silicon substrate.

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 may be calculated as a value proportional to (h1-h2).

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

The processing unit <NUM> may be adapted for determining the current to be measured in accordance with the formula: I=K*v1, or in accordance with the formula I=K. (h1-h2), where K is a predefined constant, which may be determined during design, by simulation, or during an evaluation or calibration phase). The subtraction may be done in hardware before amplification or after amplification, or can be performed in the digital domain. The processing unit <NUM> may comprise a digital processor comprising or connected to a non-volatile memory <NUM> storing said at least one constant value K.

The circuit <NUM> may further comprise one or more of the following components: a biasing circuit, a readout circuit, an amplifier or differential amplifier, an analog-to-digital convertor (ADC), etc. The ADC may be part of a digital processor circuit.

Claim 1:
A current sensor system (<NUM>; <NUM>; <NUM>; <NUM>) for measuring an AC electrical current having frequencies in a predefined frequency range, the current sensor system comprising:
- an electrical conductor portion (<NUM>; <NUM>) extending in a first direction (Y) and configured for conducting said AC electrical current, thereby creating a first magnetic field;
- a U-shaped magnetic shielding (<NUM>; <NUM>) partially surrounding said electrical conductor portion, and having a central shielding portion (<NUM>; <NUM>) extending in a second direction (X) perpendicular to the first direction (Y), and having two shielding leg portions (<NUM>, <NUM>; <NUM>, <NUM>; <NUM>; <NUM>) extending in a third direction (Z) perpendicular to the first and second direction (X, Y);
- a metal plate or a metal layer (<NUM>; <NUM>; <NUM>; <NUM>) arranged at a predefined distance (g) from the shielding legs portions for allowing eddy currents to flow in said metal plate or metal layer, thereby creating a second magnetic field which is superimposed with the first magnetic field;
- a magnetic sensor device (<NUM>; <NUM>; <NUM>) arranged between the conductor portion (<NUM>; <NUM>) and the metal plate or metal layer, and arranged between the two shielding leg portions (<NUM>, <NUM>; <NUM>, <NUM>; <NUM>; <NUM>), and configured for measuring a magnetic field component (Bx) oriented in the second direction (X);
characterised in that
the metal plate or metal layer has a length (Lp) larger than a length (Lsh) of the shielding measured in the first direction (Y), and has a width (Wp) larger than <NUM>% of a distance (Wsi) measured in the second direction (X) between the inner sides of the shielding leg portions, and has a thickness (Tp); or
the metal plate or metal layer is a portion of a metal housing with a cavity in the vicinity of the magnetic sensor, the metal plate or metal layer having a residual thickness (Tres) in the vicinity of the magnetic sensor.