Magnetic field based current sensor for frequency compensated measurement of alternating current

Abstract

The invention relates to a current sensor (10, 20, 30, 40, 50, 60, 70) for magnetic field-based current determination of an alternating current I through a current conductor (38, 56) based on a magnetic field-sensitive sensor element (12, 108). The sensor element (12, 108) is arranged spatially adjacent to the current conductor (38, 56) to detect a magnetic field generated by the alternating current I in the current conductor (38, 56). At least one electrically conductive compensation element (80, 90) is provided, separated from the current flow I through the current conductor (38, 56) and spatially adjacent to the sensor element (12, 108) and the current conductor (38, 56), to compensate for frequency-dependent distortions of the magnetic field by means of an inductively generated compensation magnetic field.

Description

Technical Field

[0001] The invention relates to an AC sensor with a frequency-compensated measuring characteristic for accurately measuring the intensity of a current through a current conductor over a large frequency range based on a magnetic field. Furthermore, the invention relates to the use of such an AC sensor. Background Art

[0002] Current sensors based on magnetic fields are used for the electrically isolated, contactless measurement of electric currents.

[0003] For the purposes of the present invention, a magnetic field-based current sensor is considered for measuring the intensity of a current having at least a component affected by an alternating current through one or more conductors based on a magnetic field around the conductor. The current can be a pure (usually sinusoidal) alternating current (AC current), an alternating current affected by a direct current (DC current), a current affected by harmonics having one or more frequency components, or indeed a DC current with a high switching frequency - in any case, a current that results in an alternating magnetic field capable of inducing eddy currents in the metallic conductor.

[0004] Current sensors of the type in question are used, for example, in powertrain and charging applications for electric vehicles, as well as in automotive applications for electrically driven private and commercial vehicles, large-scale industrial drives and for renewable energy technologies (such as photovoltaic or wind power). Currently, these sectors use conventional current sensors in closed-loop / open-loop Hall or fluxgate technology with decoupled measuring shunt isolation transformers. Such current sensors are cheap and have a lower frequency bandwidth. However, they also require a relatively large installation space and have an increased EMC sensitivity (electromagnetic compatibility) or require additional cooling.

[0005] Contactless current sensors for measuring the intensity of the current through one or more current conductors based on a magnetic field H along a closed curve S and surrounding the current conductors are sufficiently well known in the art. According to Ampere's law, they are based on the conclusion drawn from the total current I through the area A defined by the curve S:

[0006]

[0007] This allows contactless current detection without interference with the operation of the circuit, in particular without interrupting or intervening in the circuit.

[0008] Such arrangements are known in the prior art, which use magnetic field-sensitive gradient sensors to measure the difference in magnetic field strength in the measurement plane between the conduction currents of adjacent current conductors. Magnetoresistive sensor elements are usually used as magnetic field-sensitive sensor elements, which operate, for example, according to the planar Hall effect, the AMR effect, the GMR effect or the TMR effect, or are configured as magnetoresistors (MDR-magnetic sensitive resistors). However, these also include sensors that provide a magnetic field-dependent voltage (e.g. Hall sensors) or otherwise provide a sensor signal as a function of the strength of the magnetic field. As an example and not exhaustive, reference is further made to SQUID-based sensors (superconducting quantum interference devices) or fluxgate magnetometers.

[0009] In the field of magnetoresistive sensor elements, the AMR effect is based on the change in resistance in a ferromagnetic layer with internal polarization due to a magnetic field, wherein an external magnetic field causes a change in the angle of the resultant magnetic vector of the ferromagnetic layer relative to the direction of the current. TMR and GMR sensors are based on the TMR or GMR effect and consist of a few nanometers thick multilayer, where at least one reference layer has a magnetization with a fixed orientation and the magnetization of the free layer follows the external magnetic field. The angle of the magnetization between the reference layer and the free layer affects the resistance value, which changes with the change in the angle of the external magnetic field.

[0010] If two sensor elements are arranged at a distance from one another, the sensor can be made robust to external interference fields by differential evaluation of the sensor signal. The difference quotient is understood to be the gradient of the magnetic field. These gradient sensors are particularly suitable for use in current sensors. Such a magnetic field-sensitive sensor element can therefore take the form of a gradient sensor based on two magnetic field sensors, wherein the respective magnetic field sensor detects the magnetic field caused by each current portion and the magnetic field sensor determines the gradient value therefrom internally or externally.

[0011] In a magnetic-field-sensitive current sensor, the sensor element is arranged in the region of a conductor portion active with respect to current measurement, so that due to the spatial orientation of the sensor element relative to the conductor portion having a parasitic effect with respect to current measurement and / or due to field compensation effects of further current-carrying elements, the magnetic field of the conductor portion active with respect to current measurement leads to a major change in the sensor value, in particular a major change in the resistance, and the magnetic field of the conductor portion having a parasitic effect with respect to current measurement leads to a slight change or essentially no change in the sensor value.

[0012] Previous solutions for current measurement in gradiometer arrangements are usually based on a U-shaped current conductor for generating a primary current-dependent field gradient, as described, for example, in DE 43 00 605 A1. For this purpose, a current flowing in two branches of the U-shaped current conductor is considered, wherein the current flowing into one branch and out in the adjacent branch forms a superimposed total magnetic field between the branches, the field gradient of which is detected in the measurement plane. Naturally, the same amount of current flows in both branches but in opposite directions. With the increasing miniaturization of sensors, interfering field components appear in such current sensors (for example due to currents in the connecting piece between the branches of the U-shaped conductor) and present amplitudes that lead to changes in the magnetization intensity of the magnetic field-sensitive layer of the xMR sensor.

[0013] WO 2014 / 001473A1 discloses a further development of this previously known U-shaped geometry, wherein the U-shaped current conductor comprises at least one conductor portion effective in current measurement and at least one conductor portion having a parasitic effect in current measurement. The sensor element has at least one sensitivity direction in which a magnetic field component causes a major change in the sensor value. For this purpose, the sensor element is oriented in the region of the conductor portion effective in current measurement, in particular rotated, tilted and / or offset in height relative to the conductor portion having a parasitic effect in current measurement, in such a way that the magnetic field of the conductor portion effective in current measurement of the U-shaped conductor element is substantially oriented in the sensitivity direction, and the magnetic field of the conductor portion having a parasitic effect in current measurement of the U-shaped conductor element is substantially not oriented in the sensitivity direction, in particular at right angles to the sensitivity direction. In order to support the sensitivity of the sensor element, the sides of the parallel branches can be permanent magnets, which provide auxiliary magnetic fields for supporting the internal magnetization of the sensor element.

[0014] The inductance formed by the U-shaped current branch leads to voltage peaks, which must be compensated by the switched-on power semiconductor electronics unit, which is designed, for example, for converter operation. This must therefore be designed for relatively high voltage peaks.

[0015] Recently, a further development of the current sensor was described in WO 2019 / 072421 A1, which instead of the U-shaped current branch comprises two parallel conductor sections that are highly offset relative to the measuring plane of the gradient sensor element, and a portion of the current to be measured flows in the same direction through each of these conductor sections. By means of current distribution, the current load of the conductor sections can be reduced and parasitic interference fields of transverse branches or connecting lines can be prevented.

[0016] In the field of alternating current measurement, the skin effect is caused by the self-inductance of the alternating magnetic field generated by the current in the current conductor. Due to the high-frequency alternating current in the current conductor, a lower current density is established in the inner area than in the outer area through the current displacement effect. This means that in the case of alternating currents, eddy currents and electromagnetic fields are generated as a function of the frequency, which displace the charge carriers to the surface of the conductor. However, in such a way that when the frequency increases, the magnetic field around the current conductor changes, so that for the same amount of current, the sensor element sees a different magnetic field than in the case of direct current. In order to improve the measuring accuracy of the current sensor, it is known, for example from DE 101 10 254 A1, to shape the cross section of the current conductor in such a way that no eddy currents occur in the current conductor itself.

[0017] Furthermore, the proximity effect acts between two closely adjacent conductors. The proximity effect is a current displacement phenomenon, wherein this frequency-dependent phenomenon is limited to eddy currents between closely adjacent conductors, wherein the alternating currents flow in the same or opposite directions, as in the case of highly offset conductor sections or U-shaped conductor sections. Depending on the current intensity, the proximity effect can act on conductor spacings of a few millimeters to a few centimeters. According to the proximity effect, which is particularly pronounced at higher frequencies, high-frequency currents in opposite directions (as in U-shaped current conductors) tend to flow as close to each other as possible, and high-frequency currents of the same orientation (as in highly offset parallel current conductors) tend to be displaced from each other. The current flow is concentrated on an area where two conductors are located in close proximity to each other or are separated by a great distance.

[0018] The skin effect and the proximity effect are caused by the Lorentz force which repels opposite currents or identically oriented partial currents in two conductor sections and is reinforced by eddy currents inside the conductor sections. In contrast to U-shaped current conductors, where the proximity effect leads to a current concentration close to the sensor and the accompanying rise in amplitude in the frequency response of the sensor arrangement can be compensated with RC elements, in highly offset conductor sections an increase in the amplitude of the higher frequency components is hardly possible without a loss of DC measuring capability or considerable measuring signal effort. In view of the lower current carrying capacity per wire diameter of HF litz wires compared to solid materials, the suppression of these HF current density effects by using, for example, intrinsically insulated HF litz wires fails in terms of economic feasibility and the possibility of generating sufficiently large fields at the sensor location.

[0019] In the case of a U-shaped current conductor, the superposition of the two above-mentioned effects leads to higher current densities in the inner region of the branch, in particular in the edges. In the case of a highly offset current conductor flowing in parallel, high current densities are generated in the outer region, in particular in the edges, due to the above-mentioned distortion effects. As a result, the high-frequency current is carried significantly more or less intensively with respect to a pure direct current measurement, and the field gradient increases or decreases in the sensor region. In this regard, previously known current sensors depend on the current frequency in terms of their measurement quality, wherein different signal values ​​of the current sensor are generated at the same current intensity and at different frequencies.

[0020] Starting from the above-mentioned prior art, the problem arises therefore that measurement errors occur as a function of the current frequency or the transient current behavior.

[0021] In pure DC or pure AC measurements with a limited frequency range, the geometry can be designed exactly for this case, but if the limits are exceeded, the errors increase significantly. For current sensors with U-shaped current conductors, relatively complex geometries can be realized for the selected application and the skin effect and proximity effect can be compensated within the previously known narrow frequency range.

[0022] Furthermore, subsequent correction within certain frequency ranges can be provided by complex signal processing by determining the frequency components.

[0023] Based on the above-mentioned prior art, the object of the present invention is to reduce the disadvantages of the known arrangements. In particular, it is intended to measure high current intensities of several hundred amperes over a large frequency range with a simple, inexpensive structure. Small spatial dimensions and good measurement accuracy at DC operating frequencies of up to 50 to 150 kHz are desired.

[0024] The above-mentioned disadvantages are solved by the current sensor according to the invention. Advantageous further developments of the invention form the subject matter of the present invention. Summary of the invention

[0025] The object of the invention is achieved by a current sensor for magnetic field-based current determination of an alternating current I through a current conductor based on a magnetic field-sensitive sensor element, wherein the sensor element is arranged spatially adjacent to the current conductor for detecting a magnetic field generated by the alternating current I in the current conductor.

[0026] For the current sensor according to the invention, it is proposed that at least one electrically conductive compensation element is arranged separately from the flow of the alternating current I through the current conductor and spatially adjacent to the sensor element and the current conductor in order to compensate for frequency-dependent distortions of the magnetic field by means of an inductively generateable compensation magnetic field.

[0027] In the case of alternating current (AC current), eddy currents are generated in the compensating element, which is usually formed as a metal block, by induction of the alternating magnetic field, which eddy currents can compensate or significantly suppress undesirable current distributions caused by skin effect and proximity effect in the current conductor in the case of a suitable arrangement of the compensating element. In the best case, the magnetic field generated is completely independent of the current frequency.

[0028] The invention considerably expands the usable frequency range, so that the useful range is no longer limited. As mentioned above, the geometry of the current conductor can be relatively simple. The complexity of the filter circuits of the downstream electronic equipment can be simplified or optionally completely omitted. Finally, a significant cost reduction can be achieved in the production and integration of the current sensor into the electrical system.

[0029] The current sensor according to the invention is based on the principle of keeping the magnetic field gradient constant for current measurement in the frequency range to be measured. By means of the compensation element, opposing eddy currents are induced at high frequencies, an effect which can be referred to as "eddy current trapping". The compensation can be used regardless of the current sensor technology used and thus for xMR sensor element technology, Hall sensor element technology or any other sensor element technology for measuring magnetic field gradients, since only the frequency dependence of the magnetic field at the sensor location is manipulated.

[0030] A significant advantage of the arrangement with the compensation element consists in compensating the disturbing influence of the frequency-dependent current density effect directly at the magnetic field gradient as input variable of the measuring system using simple means. Compared with previously known current sensors, this enables compensation at the measurement output of the sensor element, so that subsequent processing of the measurement signal, for example by means of RC elements which usually reduce the frequency range, can be omitted or simplified. This bandwidth advantage opens up the use of current sensors in modern power electronics at higher energy efficiency and power density through increased operating frequencies.

[0031] For the purposes of the present invention, an alternating current I is considered to be a current having a component affected by an alternating current capable of generating such an alternating magnetic field around the current conductor that these alternating magnetic fields can in turn induce eddy currents in the compensation element. These eddy currents thus generate a compensation magnetic field that can compensate for the original magnetic field distorted in a manner determined by the frequency due to the skin effect and the proximity effect. In addition to pure alternating currents (AC currents), these currents also include alternating currents affected by a direct current component and direct currents (DC currents) affected by harmonics, as well as currents generally affected by harmonics or DC currents that actually exhibit a series of fast switching operations (which may appear, for example, in PWM modeling or on the transmission of digital information). For example, when a dual inverter structure is used, for example, to feed an electric motor, an inverter with a nominal frequency and a second inverter with a higher frequency can also be used to smooth the harmonics. In this case, the phase current to be measured includes a plurality of frequency components that can be accurately measured relative to the current sensors known from the prior art (which appear to have significant inaccuracies).

[0032] In an advantageous embodiment, it is proposed that the electrical conductivity of the compensation element can be greater than or equal to the electrical conductivity of the current conductor. The compensation element can preferably consist of copper, aluminum or silver. Thus, even in the case of a weak alternating field, a current can be induced into the compensation element and a compensation magnetic field can be performed. In this way, for example, the compensation element can consist of copper and the current conductor of aluminum.

[0033] In an advantageous embodiment, it is proposed that the current conductor can comprise two conductor sections, wherein the sensor element can be arranged between the two conductor sections and is preferably configured as a gradient sensor. In this case, at least one and preferably two compensation elements can essentially follow the course of the two conductor sections along a sensor active subsection. Thus, a simple structure of a current conductor is proposed, wherein two separated conductor sections are flowed by a current. The conductor sections can be oriented parallel to one another and can be flowed through by a current I or in each case by a portion of the current I in the same or opposite direction. The compensation element can essentially follow the course of the conductor sections and be spatially arranged close to the conductor sections and the sensor element in order to influence the alternating magnetic field according to a DC behavior, wherein an inexpensive compensation of frequency-determined magnetic field distortions is enabled, which is easy to produce in terms of manufacturing technology.

[0034] In an advantageous embodiment, it is proposed that the alternating current I of the current conductor flowing through the conductor portion is subdivided relative to the cross-sectional plane through the conductor portion and flows in the same direction. For this purpose, it can be provided in particular that the current conductor is divided into two parallel conductor portions, wherein the total current is conducted as two partial currents through two conductor portions that are generally guided in parallel. The sensor element is arranged between the two conductor portions, and the compensation element corrects the alternating magnetic field oriented in the same direction by the two conductor portions in each case according to the DC behavior. For this purpose, the compensation element can be formed as a conductive solid (in particular as a metal block), which is arranged between the conductor portion and the sensor element or at an angle to the conductor portion and the sensor element with a radius comparable to or smaller than the conductor portion when viewed from the sensor element. Alternatively, the conductor portion can also be guided so that the total current I is carried in the same direction relative to the sensor element through one conductor portion and through the second conductor portion, so as to achieve an increase in the magnetic field and thus an increase in sensitivity at low currents.

[0035] Based on the above-described embodiments, the conductor sections of the current conductor can also advantageously be offset in height relative to the measuring plane of the magnetic field-sensitive gradient sensor. In particular, one conductor section can be guided below the measuring plane and one conductor section can be guided above the measuring plane, wherein, relative to the sensor element, at least two compensation elements and the sensor element can be arranged in a plane, which does not have to be the measuring plane and which extends at an angle, in particular at a right angle, relative to the plane running through the conductor sections and the sensor element. In addition, the radial distance between the compensation element and the sensor element can preferably be less than or equal to the radial distance between the conductor section and the sensor element. After the nominal current to be measured and the desired frequency range have been preset, the exact geometric spacing and design of the compensation elements can be specified, for example based on electromagnetic simulation methods and empirical values.

[0036] As an alternative to the above-described embodiment, the alternating current flowing through the conductor portion of the current conductor may flow through the conductor portion in opposite directions relative to the cross-sectional plane. In this case, a U-shaped course of the current conductor can be provided in particular, in which the total current moves in one conductor portion and is fed back in a parallel second conductor portion. The sensor element is arranged between the two conductor portions with a high offset, so that the magnetic field has a tangential component in the direction of the conductor portion, and the compensation element corrects the alternating magnetic field directed in opposite directions by the two conductor portions in each case according to the DC behavior. To this end, the compensation element can be formed as a conductive solid (in particular a metal block) which is on the side of the conductor portion when viewed from the sensor element. Alternatively, the conductor portions can also be guided so that in each case, a portion of the total current I is conveyed through one conductor portion, and a portion of the total current I is conveyed through the second portion of the conductor portion but in the opposite direction relative to the position of the sensor element, so as to allow the magnetic field to be reduced in the case of high currents and thus allow the measuring range to be extended.

[0037] Based on the above-described embodiment, the conductor portion of the current conductor and at least two compensation elements are located in a highly offset plane arranged parallel to the measuring plane of the sensor element, wherein the radial distance between the compensation elements is greater than the radial distance between the conductor portion and the sensor element. In particular, the compensation elements in the effective sub-portion of the sensor can be symmetrically arranged around the conductor portion. In this regard, the conductor portion is arranged along the measuring plane of the sensor element symmetrically on both sides, and the compensation elements are radially arranged farther from the outside. As previously described, as the frequency increases, current concentration and field overshoot occur in the area of ​​the sensor element. In order to overcome this, the peripheral compensation element generates a compensation field due to the increase in inductivity, which offsets the field overshoot between the conductor portions and thus achieves a field distribution comparable to the DC case. In this way, frequency-dependent signal value distortions can be effectively compensated over a wide frequency range.

[0038] In an advantageous further development of the above-described embodiment, the current conductor can be substantially U-shaped with two parallel branches and a transverse branch, wherein the two parallel branches of the current conductor form the conductor part and wherein the further compensation element can preferably be arranged spatially adjacent to the transverse branch. Thus, a metal block can be arranged, for example, as a compensation element around the U-shaped branch. It is important that the metal is not in contact with the actual conductor or cannot be flowed through by the current I. The same effect can also be used in the case of a transverse branch of the U-shaped current conductor, which means that there is no risk that the support field of the sensor element is too influenced by the AC current.

[0039] In an advantageous embodiment, the cross-sectional area of ​​the compensating element is 100% or less, preferably 80% or less, in particular 50% or less, of the cross-sectional area of ​​the conductor portion in the direction of the alternating current I. In this regard, the cross-sectional area of ​​the compensating element(s) may be smaller than or equal to the cross-sectional area of ​​the conductor portion or conductor portions, such that the compensating element is relatively not larger than the structure of the current conductor and is integrated in the component without significantly increasing the size of the component. Since the compensation field to be generated is relatively small compared to the measurement field to be generated by the conductor portion, the size of the compensating element may accordingly be the same size as the conductor portion or smaller than the conductor portion.

[0040] In an advantageous embodiment, the compensation element and the current conductor are arranged in a galvanically isolated manner. This allows maximum freedom in the choice of materials and in the arrangement of the geometry and the distance of the current conductor and the sensor element. In order to generate an effective compensation field, an optimized compensation element length is required, in particular in the direction of the path of the current through the current conductor, which is easily achieved with an electrically isolated configuration. For this purpose, the compensation element and the current conductor are advantageously coupled together mechanically non-conductively and in a positionally fixed manner via a support structure (such as a printed circuit board, a plastic holder), or are integrated in a common housing, for example encapsulated by injection molding or casting using a casting resin or plastic.

[0041] Alternatively, the compensating element can be formed as a branch of the current conductor, which follows the course of the current conductor in parallel. For this purpose, in the case of preferably two conductor parts, the branch assigned to the conductor part is oriented alternately relative to the direction of the alternating current I. Although this configuration forms a structural constraint for defining the design and spatial arrangement of the compensating element, it is simple from a manufacturing point of view to produce it in a single piece with the current conductor, with a connecting bridge as a mechanical connection to the compensating element. It has been found that the alternating orientation of the branch, i.e. the alternating orientation of the position of the connecting bridge relative to the direction of the current through the conductor part, provides an enhanced compensation effect. In the case of highly offset conductor parts flowing in the same direction, the compensating element can be oriented antiparallel to each other starting from one conductor part in each case. In the case of a U-shaped current conductor, the two compensating elements can be oriented in the same branch direction as the two parallel branches, because the two branches are flowed through by the current I in antiparallel. It is important that the compensating element, which is usually configured as a metal block, is not electrically connected or is only connected to the current conductor in the case of a branch, and does not participate in the current conduction. Depending on the geometry of the current conductor and the nominal current, the compensation element can be designed with respect to the cross section, length and distance relative to the current conductor.

[0042] The mechanical connection and mechanical fastening of the compensation element (which can, for example, take the form of a metal block) should advantageously be carried out using non-conductive components. In an advantageous embodiment, the compensation element and the current conductor can be arranged on a PCB (printed circuit board - electronic board). To this end, the sensor element is preferably arranged on the same side or on opposite sides of the PCB, and / or the compensation element and the current conductor are arranged in a housing. In this case, the current conductor and the compensation element can be connected together, for example, screwed, clamped or otherwise fixed together, and / or fixed relative to each other in a housing, for example cast in plastic. For example, the current conductor (for example, as a U-shaped conductor in one embodiment) is typically fixed to the back side of the PCB, and the sensor element is positioned on the front side of the PCB. The compensation element can also be fixed on the back side of the printed circuit board and / or the current conductor, the compensation element and the PCB being included in one and the same housing and advantageously cast in the housing.

[0043] Embodiments of the compensation element offer different control and influencing variables which have a decisive influence on whether the frequency dependence is overcompensated, undercompensated or fully compensated. Therefore, the parameters of the materials used (resistivity, skin effect penetration depth and additional height and width dimensions and also length) are optimization variables for compensation. These dimensions include a considerable proportion of the effective area for incoupling of the alternating magnetic field, the impedance and therefore the current amplitude of the circulating current path of the eddy currents. The position of the compensation element relative to the sensor element and the distance from the current conductor are likewise optimizable as important control variables which can vary according to the field of application depending on the manufacturing technology.

[0044] The invention likewise relates to the use of the above-described current sensor for magnetic field-based measurement of a current through a current conductor. To this end, it is proposed that frequency-dependent distortions of the magnetic field can be compensated by means of an inductively generated compensation magnetic field in at least one electrically conductive compensation element. This results in an inexpensive, directly implementable option for accurately measuring both DC and AC currents even in the case of superimposed currents and transient switching operations.

[0045] Based on the embodiments shown in the figures, a preferred configuration of the current sensor is described in more detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings and the associated description of the drawings reveal further advantages. The drawings show exemplary embodiments of the present invention. The drawings, description and claims contain many features in combination. Those skilled in the art will also readily consider these features individually and combine them into meaningful additional combinations.

[0047] In the figure:

[0048] FIG1 is a perspective view of a prior art current sensor having a U-shaped current conductor;

[0049] FIG2 is a plan view of a U-shaped current conductor of the prior art;

[0050] FIG3 is a perspective view of a prior art current sensor having a highly offset conductor portion;

[0051] FIG4 is a perspective view of a shielded prior art current sensor having highly offset conductor portions;

[0052] Figure 5a to Figure 5d shows plan views of first, second and third exemplary embodiments of a current sensor with a U-shaped current conductor according to the invention;

[0053] Figures 6a to 6c shows the current density and magnetic field distribution of the current sensor shown in FIG. 5 in different embodiments;

[0054] Figure 7 shows simulated gradient fields with different spacings of current conductors in different embodiments of FIG. 6 ;

[0055] Figure 8 is a plan view of a fourth exemplary embodiment of a current sensor having a highly offset conductor portion according to the present invention;

[0056] Fig. 9 is a plan view of a fifth exemplary embodiment of a current sensor having a highly offset conductor portion and a magnetic shield according to the present invention;

[0057] Fig.10 Shows Fig. 9 Current density and magnetic field distribution of the exemplary embodiment shown in;

[0058] Fig.11 Shows Fig. 9 The signal curve of the switching operation of the current sensor shown in FIG.

[0059] Fig.12 is a perspective view of a sixth exemplary embodiment of a current sensor according to the present invention;

[0060] Fig.13 is a perspective view of a seventh exemplary embodiment of a current sensor according to the present invention;

[0061] Fig.14 is a schematic diagram of an eighth exemplary embodiment of a current sensor according to the present invention.

[0062] In the drawings, like elements are indicated with like reference numerals. The drawings show examples only and are not to be construed as limiting. DETAILED DESCRIPTION

[0063] 1 shows a first prior art current sensor 1000 known from WO 2014 / 001473 A1. The current sensor 1000 has a sensor element 108 and a U-shaped current conductor 38, wherein a branch 104 active in current measurement is arranged in the z direction at the rear relative to a transverse branch 102 and a connecting line 106 having a parasitic effect in current measurement, so that the parasitic magnetic field components penetrate the magnetic field-neutral orientation plane of the sensor structure of the sensor element 108 essentially at right angles. The arrangement of the branch 104 offset in the z direction relative to the connecting line 106 and the transverse branch 102 ensures that the parasitic magnetic field components are suppressed or only pass through the magnetic field-neutral orientation plane, while the magnetic field components active in current measurement and to be detected pass through the magnetic field-sensitive orientation plane of the sensor element 108. The measurement of higher frequency currents above 100 Hz, preferably above 500 Hz, in particular above 1 kHz and especially above 10 kHz is affected by the fact that due to the skin effect and the proximity effect the alternating magnetic field is concentrated between the two conductor parts 104, resulting in a significant non-linear deviation of the signal value from the current amplitude, which can only be compensated by means of complex filter circuits.

[0064] For this purpose, FIG. 2 shows an improved layout of a U-shaped current conductor 38 optimized for AC measurements. For this purpose, the current conductor 38 has an AC matching structure 1012 in the transverse branch 102 and a matching structure 1014 in the conductor section 104. In addition, the corners and edges 1016 are rounded, primarily for thermal optimization of the operating behavior. In this case, the current sensor 1000 with a U-shaped current conductor 38 can have a relatively complex geometry for the selected application and allows compensation of skin effects and proximity effects in a narrow, previously known frequency range.

[0065] FIG3 shows a second prior art current sensor 1020 known from WO 2019 / 072421A1. The current conductor 56 is subdivided into two conductor parts 14a, 14b, wherein corresponding current components 16a and current components 16b flow in the same current flow direction in the conductor parts 14a, 14b. The sensor element 12 on the PCB film 18 is placed between the two conductor parts 14a, 14b, wherein the sensor element 12 takes the form of a gradient sensor that measures the magnetic field intensity difference of a tangential component of the magnetic field in the measurement plane 24. In this case, the measurement plane 24 is defined so that the magnetic field sensitive resistors of the sensor element 12 are located therein, which are sensitive to the vector components (tangential components) of the magnetic field that are located parallel in the measurement plane 24. In addition, the two conductor parts 14a, 14b are highly offset antiparallel to the measurement plane 24. When measuring high-frequency currents, the skin effect and proximity effect cause nonlinear distortion of the measured magnetic field at the location of the sensor element 12, resulting in significant deviations of the sensor signal with the same current strength relative to the DC case, and therefore the current sensor 1020 can only be used for accurate current measurement within a narrow, limited frequency range.

[0066] The configuration of the current sensor 1020 shown in FIG. 3 is depicted in FIG. 4 as a further further developed fourth current sensor 1030 known from WO 2019 / 072421A1. This current sensor arrangement comprises two conductor portions 14a, 14b and a sensor element 11. Arranged between the two conductor portions 14a, 14b is the sensor element 11, in which a magnetic field-sensitive sensor element 12 detects the gradient field and which is arranged on a PCB film 18. The two conductor portions 14a, 14b are highly offset symmetrically and antiparallel relative to a measuring plane 24 in which the difference in magnetic field strength is measured. The current component 16a and the current component 16b flow in the same direction in the conductor portions 14a, 14b. According to Fig. 9 , outside the current sensor arrangement, two rectangular shielding parts 54 are formed as magnetic shields 34, which have two slots 32 and provide shielding against interfering influences. In this regard, the current sensor 1030 is protected from external stray fields and the EMC robustness is increased. However, the problem associated with the current sensor 1020 of FIG. 3 still exists, namely, the frequency-dependent sensor signal makes broadband measurement of currents at different frequency locations more difficult.

[0067] Figure 5a and Figure 5b A first embodiment 10 of a current sensor according to the invention is shown in plan view and in cross-section. Figure 5a A plan view of the current conductor 38 is shown, and Figure 5b Shown along Figure 5a . The current conductor 38 is U-shaped and comprises two connecting wires 106 for coupling and dissipating the current I to be measured. In the DC case, the arrow represents the current direction. The current conductor 38 comprises a transverse branch 102 and two longitudinal branches as conductor parts 104, which generate a measurement magnetic field, the gradient of which can be detected by the sensor element 108 symmetrically arranged between them. In order to compensate for the skin effect and the proximity effect, two metal blocks are arranged as compensation elements 80 in the section AA radially spaced from the branch parts 104. In these compensation elements 80, eddy currents are generated by induction, which lead to a compensation field, which in the region of the sensor element 108 that is highly offset relative to the plane of the conductor parts 104 and the compensation elements 80, in its measurement plane 24, cancels the frequency-dependent nonlinear field distortion and thus generates a similar measurement signal at the same current intensity as in the DC case. Therefore, at the same nominal current, the signal behavior can be presented as uniform over a wide frequency range, and the influence of the skin effect and the proximity effect is compensated.

[0068] The arrangement of the additional metal of the compensation element 80 uses the actual interference effects (skin effect and proximity effect) to make the resulting alternating magnetic field or transient magnetic field independent of the frequency of the current. In this case, the current distribution (and especially the magnetic field) should ideally correspond to those of the DC case (direct current measurement).

[0069] Compared with the first embodiment 10, Figure 5c The second embodiment 20 shown in FIG. 1 likewise has a compensation element 80 arranged along the transverse branch 102. This serves to compensate the interfering magnetic field generated by the transverse branch 102 to the same extent as the measured magnetic field of the conductor section 104, in order to compensate for secondary frequency-dependent influences of the parasitic interfering field of the transverse branch 102. However, it is also possible to provide a further compensation element in the region of the connecting line 106.

[0070] and, Figure 5d A plan view of a third embodiment 30 is shown, which differs from the second embodiment 20 in that the compensating element 80 is connected to the current conductor 38 in one piece via a connecting bridge 94. The connecting bridge 94 is formed, for example, together with the compensating element 80 and the current conductor 38 as a stamped part. Alternatively, the connecting bridge 94 can also be subsequently welded or soldered, for example, to a metal connection and form a metal connection without current flowing between the current conductor 38 and the compensating element 94. Alternatively, the connecting bridge 94 can consist of a non-conductive material, such as plastic. The connecting elements 94 can advantageously be arranged in the direction of the current travel at alternating ends of the compensating element 80, such as Figure 5dThe case in which the compensating element 80 is assigned to the conductor section 104. It is also conceivable that the connecting bridge 94 is arranged in the center of the compensating element 80, as shown on the transverse branch 102.

[0071] Based on electromagnetic simulation, Figures 6a to 6c The flow of a U-shaped current conductor having parallel conductor sections 104 is shown. Figure 5b , and the magnetic flux lines of the alternating magnetic field in the section AA of FIG. 1 , wherein the parallel conductor sections are arranged in parallel planes below the measuring plane 24 at a height offset relative to the gradient sensor element 108 . Figure 6a Here, direct current operation (DC case) is shown. Figure 6b The currents affected by an alternating current (AC case) without compensation are shown, schematically indicating potential locations of the compensating element 80. Relative to the DC case, changes in the current density distribution and magnetic field of the two conductor parts 104 are evident, both moving closer together. Figure 6c The measurement of an alternating current with an optimized position and shape of the compensation element 80 (AC case with compensation) is shown. In this case, the compensation element 80 is made of copper and the conductor part 104 is made of aluminum. In the case without compensation, Figure 6b The concentration of the current in the middle is clearly shown, which results in a greater increase in the gradient field compared to DC current. Figure 6c In the case of compensation in , it is clear that part of the current is drawn outward to the copper block of the compensation element 80. This results in the establishment of a current at the sensor element 108 in accordance with Figure 6a The magnetic field is almost the same in the DC case, and thus the nonlinear distortions of the skin effect and the proximity effect are compensated.

[0072] Figure 7 A study of the measured magnetic field depending on the basic width of the sensor element 108 is shown in the three cases DC, AC and AC with compensation (AC comp) and the same nominal current intensity I: the basic width SW of the sensor element 108 associated with the distance for determining the gradient field is plotted on the x-axis and the amplitude of the measured magnetic field intensity gradient is plotted on the y-axis. In the case of direct current measurement (DC case) and in the case of optimized compensation (AC comp case), the amplitude of the basic width of the sensor element 108 has practically no influence on the measured value of the gradient field. This shows that the compensation field provides the same field configuration in the compensated AC case as in the DC case. In the case without the compensation element 80 (AC case), the gradient field deviates significantly from the DC case with increasing basic sensor width SW.

[0073] Figure 83 is a schematic diagram of a fourth embodiment of a current sensor 40 with highly offset conductor sections 14a, 14b. In principle, the structure and function of the current sensor 40 correspond to the structure and function of the prior art current sensor 1020 shown in FIG. 3. In addition, two compensating elements 90 are provided, which are highly offset relative to the measuring plane 24 and are arranged complementary to the conductor sections 14a, 14b. The cross-sectional area of ​​the compensating elements 90 corresponds to approximately 35% of the cross-sectional area of ​​the conductor sections 14a, 14b, and the radial distance of the center of gravity of the compensating element 80 from the sensor element 12 is significantly smaller than the radial distance of the center of gravity of the conductor elements 14a, 14b.

[0074] based on Figure 8 The fourth embodiment 40, Fig. 9 A fifth embodiment 50 is shown, which likewise corresponds in principle to the prior art current sensor 1030 shown in FIG. 4 . The arrangement of the compensation element 90 substantially follows Figure 8 Regardless of the magnetic shield 54, the compensation element 90 produces a total alternating magnetic field that corresponds to the DC current measurement.

[0075] Fig.10 yes Fig. 9 Depiction of the current density distribution and magnetic field of the current sensor 50 in AC operation is shown in . Eddy currents and compensation fields are clearly visible in the compensation elements 90 which, independent of the magnetic shield 54 on the sensor element 12, produce a frequency-independent magnetic field distribution.

[0076] Fig.11 The diagram shows Fig. 9 4 . The output signal curve of the current sensor 50 is shown in FIG. 4 . In this case, the DC current is switched in a short time sequence and the output voltage signal curve of the sensor element 12 is plotted over time. In the compensated variant (ACcomp.), the output signal curve of the sensor element 12 completely follows the reference curve Ref, wherein in the uncompensated variant, as shown in the current sensor 1030 in FIG. 4 , a significant undershoot occurs due to the transient step changes with multiple frequencies and the corresponding distortion caused by the mutual inductance of the current conductor 56.

[0077] Fig.12A sixth embodiment 60 of a current sensor arrangement is shown. The current conductor 56 takes the form of a one-piece stamped curved section which is subdivided into two parts and has a slot 32, in which the sensor element 11 is arranged on the PCB film 18. The slotted sections are configured in this case as conductor sections 14a, 14b. A primary current I flows in the current conductor 56, which is subdivided by the conductor sections 14a, 14b into two current components 16a, 16b and is carried in the same direction relative to the magnetic field-sensitive sensor element 12. Due to the flexible PCB film 18, the magnetic field-sensitive sensor element 12 can be introduced into the slot 32 in the current conductor 56 in a spatially variable manner. Two compensation elements 90 are arranged in each case in a complementary manner to the conductor sections 14a, 14b and in a substantially parallel arrangement, so that this arranges a suitable compensation field for a wide frequency range. The compensation elements 90 can be temporarily fastened to the current conductor 38, for example by means of a plastic mounting, and cast firmly in the housing by means of a flowable plastic or casting resin.

[0078] Fig.13 A seventh embodiment of a current sensor arrangement 70 is shown. Fig.12 Instead, the current conductor takes the form of two stamped bends connected together. The stamped bend 72a and the stamped bend 72b are brazed, riveted or welded together so that the two stamped bends can be connected together and optionally separated by spacers that define a spatial distance from the measuring plane 24. In this way, the stamped bends 72a, 72b can be formed into two conductor parts 14a, 14b. Since the two stamped bends 72a, 72b are configured antiparallel to each other, the magnetic field-sensitive sensor element 12 can optionally (not shown) be arranged tilted relative to the two stamped bends, preferably tilted 45° relative to the two stamped bends, so as to adapt the measuring plane to the magnetic field profile. The primary current I can thus be measured. The compensation element 90 can be formed in a single piece with the stamped bends 72a, 72b as an elongated finger or branch 92 with an integrated connecting bridge 94. The compensating elements 94 are arranged alternately, in this case antiparallel to one another with respect to the direction of the current flow through the current conductor 38 , as a result of which an optimal compensation of the frequency-dependent distortion can be achieved.

[0079] Fig.14An eighth embodiment of a current sensor arrangement 100 is shown. The current conductor 56 is subdivided into two conductor parts 14a, 14b of different cross-sections and located in a common conductor plane 22. Different current components 16a and 16b are carried in the two conductor parts 14a, 14b corresponding to the cross-section, which components have the same direction but different magnitudes. The sensor element 11 arranged on the PCB film 18 is arranged at an angle β36 relative to the conductor plane 22, that is, the magnetic field-sensitive sensor element 12 is inclined relative to the conductor plane 22. The angle β36 is preferably selected in the range from 30° to 60°, preferably 45°. If the current component 16a is smaller than the current component 16b, the two conductor parts 14a, 14b are arranged asymmetrically relative to the measuring plane 24. In other words, the distance between the measuring plane 24 and the conductor part 14a can be smaller than the distance between the measuring plane 24 and the conductor part 14b, whereby the magnetic field strength difference can be accurately measured by the magnetic field-sensitive sensor element 12.

[0080] In this case, current measurement associated with an eighth embodiment of a current sensor arrangement 100 is shown. Two conductor portions 14a, 14b are arranged in a common conductor plane, wherein the conductor portions 14a, 14b have current components 16a and current components 16b, which have different current amplitudes and are carried in the same current flow direction. The measurement plane 24 is inclined at an angle β relative to the two conductor portions 14a, 14b, wherein due to the current asymmetry, the two conductor portions 14a, 14b are arranged asymmetrically relative to the measurement plane 24. In this embodiment, the distance d1 between the conductor portion 14a and the conductor plane 24 is smaller than the distance d2 between the conductor portion 14b and the conductor plane 22. The two generated magnetic fields 60a, 60b intersect at the measurement plane 24. The magnetic field-sensitive gradient sensor can thus measure the difference between the two magnetic fields. The optimal asymmetric orientation and various distances relative to the conductor portions can be pre-identified during the design process by means of computer-assisted field simulations or empirically by mechanical calibration of the desired current measurement range. The frequency-dependent measuring behavior can be compensated by compensating elements 90 , which are located in a plane at right angles to the plane defined by the conductor sections 14 a , 14 b .

[0081] Reference numerals list

[0082] 10 First Exemplary Embodiment of Current Sensor

[0083] 12 Sensor element

[0084] 14a Conductor part a

[0085] 14b Conductor part b

[0086] 16a Current component a

[0087] 16b Current component b

[0088] 18 PCB film 20 Second Exemplary Embodiment of Current Sensor 22 Conductor plane

[0089] 24 Measurement plane 30 Third Exemplary Embodiment of Current Sensor 32 Slots

[0090] 34 Magnetic Shielding 36 Angle β 38 Current Conductor Fourth Exemplary Embodiment of Current Sensor Fifth Exemplary Embodiment of Current Sensor 54 Shielding part

[0091] 56 Current Conductor Sixth Exemplary Embodiment of Current Sensor Seventh Exemplary Embodiment of Current Sensor 72a U-shaped stamping bending part a

[0092] 72b U-shaped stamping bending part b

[0093] 80 Compensation components

[0094] 90 Compensation element

[0095] 92 Branch Line

[0096] 94 branch line connecting bridge Eighth Exemplary Embodiment of Current Sensor 102 Horizontal branch

[0097] 104 Conductor part, branch

[0098] 106 Connection cable

[0099] 108 sensor element

[0100] 1000 First current sensor (prior art)

[0101] 1010 Current conductor for current sensor (prior art)

[0102] 1012 AC matching structure in the lateral branch

[0103] 1014 AC matching structure in the longitudinal branch

[0104] 1016 Rounding and beveling of current conductors

[0105] 1016 Rounding and bending of conductor guides

[0106] 1020 Second current sensor (existing technology)

[0107] 1030 Third current sensor (existing technology)

[0108] d1 Distance between conductor part a and the measuring plane

[0109] d2 Distance between conductor part b and the measuring plane

[0110] I Alternating current to be measured

Claims

1. A current sensor for magnetic field-based current determination of an alternating current I through a current conductor based on a magnetic field-sensitive sensor element, wherein: The sensor element is spatially arranged adjacent to the current conductor for detecting a magnetic field generated by the alternating current I in the current conductor, wherein at least two metal blocks in the form of conductive compensation elements are arranged separately from the alternating current I passing through the current conductor and spatially arranged adjacent to the sensor element and the current conductor, wherein the cross-sectional area of ​​the compensation element is at least 50% to 100% of the cross-sectional area of ​​the current conductor, so as to compensate for the frequency-dependent distortion of the magnetic field by the compensation magnetic field generated by eddy current induction, so that the disturbing influence of the frequency-dependent current density effect of the current conductor on the sensor element is compensated by the compensation magnetic field of the conductive compensation element, characterized in that the current conductor comprises two The invention relates to a magnetic field-sensitive gradient sensor and to a magnetic field-sensitive gradient sensor comprising: a first compensation element and a second compensation element; a second compensation element and a second compensation element; and a first compensation element and a second compensation element. The invention relates to a magnetic field-sensitive gradient sensor and ...

2. The current sensor according to claim 1, characterized in that: The electrical conductivity of the compensating element is greater than or equal to the electrical conductivity of the current conductor.

3. The current sensor according to claim 1, characterized in that: One conductor section is guided below the measuring plane and one conductor section is guided above the measuring plane.

4. The current sensor according to claim 1, characterized in that: A radial distance between the compensation element and the sensor element is smaller than or equal to a radial distance between the conductor portion and the sensor element.

5. The current sensor according to claim 1, characterized in that: The compensating element and the current conductor are arranged on a PCB, wherein the sensor element is arranged on the same side or on opposite sides of the PCB, and / or the compensating element and the current conductor are arranged in a housing.

6. Use of the current sensor according to claim 1 for measuring a current through a current conductor based on a magnetic field, characterized in that: The frequency-dependent distortion of the magnetic field is compensated by a compensating magnetic field induced by eddy currents in the at least two electrically conductive compensating elements.

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