Magnetic field sensor

Abstract

The invention relates to a magnetic field sensor for measuring an electric current, the magnetic field sensor comprising: - a transducer (1) comprising at least one coil made of superparamagnetic material (LN1, LN2); - an excitation voltage generator (VEXC) configured to inject an excitation current into the at least one coil made of superparamagnetic material (LN1, LN2); - means for measuring the voltage across the terminals of the coil made of superparamagnetic material (LN1, LN2) vSPM(t) in order to estimate the value of the circulation of the external magnetic field C(t). This sensor is particular in that it further comprises a means for measuring the excitation current iexc(t) in order to estimate the value of the circulation of the external magnetic field C(t). The invention also relates to a method for estimating the value of the circulation of a magnetic field in order to measure an electric current by means of a magnetic field sensor according to the invention.

Description

Magnetic field sensor

[0001] The present invention relates to a non-contact device for measuring an electric current flowing in a conductor by measuring the magnetic field induced by that current. More particularly, the invention relates to a magnetic field sensor incorporating a transducer based on a super-paramagnetic material, suitable for current measurement.

[0002] To measure a current I, different physical principles can be exploited to generate a physical quantity representative of this current I. For example, magnetic sensors implement transducers that are sensitive to magnetic quantities, such as the magnetic field, induced by the current to be measured.

[0003] Document FR3133677, from the applicant, proposes such a magnetic sensor, incorporating a transducer with superparamagnetic core coils. This transducer consists of at least one superparamagnetic core coil (SPM hereafter) coupled to an excitation module and a conditioning or analysis module. The transducer is intended to be subjected to an external magnetic field to be measured. In practice, the external magnetic field to be measured includes frequencies ranging from DC to a frequency significantly lower than the excitation frequency, preferably at least ten times lower. The excitation module is configured to generate and inject an excitation signal into the transducer, for example, in the form of an "excitation" current with a frequency corresponding to a predefined excitation frequency Fe.

[0004] The analysis module is configured to retrieve and analyze a raw SPM measurement signal, such as the electromotive force across the transducer, which represents the time variation of the magnetic induction in the SPM coils. The analysis of this raw SPM signal involves generating a readily usable signal containing the relevant information about the magnetic field or current to be measured. This analysis includes, for example, removing unwanted frequency components from the SPM signal to retain only the useful frequency component. The estimated value of the magnetic field circulation C is then deduced from the SPM signal. est , and thus, taking into account the length of the contour considered, the value of the magnetic field H.

[0005] This solution, which is effective for some applications, is not effective for applications in which the magnetic fields involved are too large, and in particular when these magnetic fields undergo rapid variations over time.

[0006] The present invention aims to overcome these drawbacks by providing a magnetic field sensor for measuring an electric current, comprising: - at least one transducer, including at least one coil made of super-paramagnetic material (LN1, LN2) intended to be subjected to an external magnetic field to be measured, - a capacitor (C s), one terminal of which is connected to a terminal of said coil of superparamagnetic material, and a second terminal is connected to a reference potential, the capacitance of said capacitor being independent of the intensity of the external magnetic field; - an excitation voltage generator (VEXC), configured to inject an excitation current into at least one coil of superparamagnetic material, said excitation current comprising at least one substantially sinusoidal component at an excitation frequency f exc - a means for measuring the voltage across at least one coil made of super-paramagnetic material v SPM (t), and an analysis module configured to take into account the data from said voltage measurement means in order to estimate the value of the circulation of the external magnetic field C(t).

[0007] This sensor is special in that it also includes a means for measuring the excitation current flowing through at least one coil made of super-paramagnetic material i exc (t), said analysis module being configured to take as input the measured excitation current i exc (t) in order to estimate the value of the circulation of the external magnetic field C(t).

[0008] Thanks to these arrangements, it is possible to measure the current under conditions of strong fields and / or rapid changes and significant amplitude of the field level, knowledge of the phase of the excitation current making it possible to compensate for the problems encountered in these cases due to the variation of the impedance of the SPM coils with the variation of the magnetic field.

[0009] The means for measuring the excitation current may include a means for measuring the voltage across the capacitor C swhich is a reliable and easy-to-implement method.

[0010] The said analysis module may include: - a first synchronous demodulator with angular frequency ω exc = 2πf exc , configured to take as input the excitation current i exc (t) measured by the current measuring means, and provide at output a complex excitation signal I exc (t), and a second synchronous demodulator with angular frequency ω SPM , ω SPM being an even multiple of ω exc configured to take an SPM signal as input SPM (t), said SPM signal s SPM (t) corresponding to the voltage v SPM (t), or to the voltage v SPM (t) converted into a current, and outputting a complex SPM signal S SPM (t); which is a simple and reliable way to obtain the phase of the excitation signal, and to analyze the SPM signal to estimate the circulation of the magnetic field.

[0011] The analysis module may include: - a phase determination unit, configured to calculate a correction angle θ(t) taking into account the complex current signal I exc (t), - a magnetic field circulation estimation unit, configured to perform the following operations: application of a phase rotation of the correction angle θ(t) to the complex SPM signal S SPM (t), to obtain a corrected SPM signal S' SPM (t), estimation of the value of the circulation of the external magnetic field C(t) as being equal to the value of the projection of the corrected SPM signal S' SPM (t) on a reference axis of the complex plane; which is a simple and quick way to compensate for phase variations of the useful SPM signal, and thus to obtain an accurate estimate of the circulation of the external magnetic field.

[0012] The magnetic field circulation estimation unit can be configured so that: - after phase rotation, a rectification step takes place in which a rectified SPM signal S" is calculated SPM (t) as being dependent on the corrected SPM signal S' SPM (t) and the argument of the complex current signal I exc (t), and during the estimation step, the value of the circulation of the external magnetic field C(t) is estimated to be equal to the value of the projection of the rectified SPM signal S" SPM (t) on said reference axis of the complex plane; which makes it possible to obtain a one-to-one relationship between the useful SPM signal projected onto a reference axis of the complex plane and the circulation level of the external magnetic field to be measured, whatever the level of this field, which makes it possible to use the sensor without a feedback system.

[0013] The rectified SPM signal S" SPM(t) can be equal to the sum of the corrected SPM signal S' SPM (t) and the corrected SPM signal S' SPM (t) multiplied by a correction factor l θ and an integer power of the argument of the complex current signal I exc (t).

[0014] The phase determination unit can be configured to calculate the correction angle θ(t) as an affine function of the argument of the complex current signal I exc (t), said affine function being defined by a slope k θ and an ordinate at the origin θ0, which is an approximation that greatly simplifies calculations while still obtaining sufficiently accurate results.

[0015] The phase determination unit can be configured to calculate the argument of the complex current signal using a coordinate rotation numerical calculation algorithm and / or the magnetic field circulation estimation unit can be configured to apply the phase rotation of the correction angle θ(t) using a coordinate rotation numerical calculation algorithm, thus optimizing the computing power required for these calculations and making them compatible with the constraints of a small and inexpensive sensor.

[0016] The said analysis module may include a means for measuring temperature, and a unit configured to determine the values ​​of the slope coefficient k θ and / or of said ordinate at the origin θ0 taking into account the temperature measured by said means of temperature measurement, which allows the sensor to be efficient under different temperatures.

[0017] The present invention also relates to a method for estimating the value of the circulation of a magnetic field for measuring an electric current, using a magnetic field sensor according to the invention, comprising the following steps: - measuring the voltage across at least one coil made of super-paramagnetic material v SPM (t),- measurement of the excitation current flowing through at least one coil of super-paramagnetic material i exc (t),- taking into account the data from the means of measuring the voltage and the data from the means of measuring the excitation current in the analysis module in order to estimate the value of the circulation of the external magnetic field C(t).

[0018] Thanks to these arrangements, it is possible to measure the current under conditions of strong fields and / or rapid changes and significant amplitude of the field level, knowledge of the phase of the excitation current making it possible to compensate for the problems encountered in these cases due to the variation of the impedance of the SPM coils with the variation of the magnetic field.

[0019] The said method for estimating the value of the circulation of a magnetic field may further include a step of calibrating the values ​​of the slope coefficient k θ and the y-intercept θ 0, in which these values ​​are deduced from tests carried out on said magnetic sensor, during which the values ​​of the circulation of the external magnetic field C(t) are known, which is a simple and effective embodiment, said calibration being able to be integrated for each sensor into an industrial manufacturing process.

[0020] The calibration step may include a plurality of sub-steps carried out at different temperatures, which allows the sensor to perform well under different temperatures.

[0021] The present invention and its advantages will become more apparent from the following description of several embodiments given by way of non-limiting examples, with reference to the accompanying drawings, in which:

[0022] This is a schematic view of a transducer for a sensor according to a preferred embodiment of the invention.

[0023] This is a schematic view of a sensor according to a preferred embodiment of the invention.

[0024] Lamontre, for example, shows the variation of a useful SPM signal according to the magnetic field H, in a sensor according to the prior art.

[0025] Lamontre, for example, shows the phase variation of the excitation signal as a function of the field to which the sensor is subjected.

[0026] Lamontre, for example, provides the relationship between the phase variation of the signal and the correction angle to be applied to the SPM signal, and an estimate of this relationship in the form of an affine function.

[0027] Lamontre, for example, shows the variation of an SPM signal corrected according to the magnetic field H, after the phase rotation operation,

[0028] lamontre as an example the variation of a rectified SPM signal according to the magnetic field H, after the rectification operation.

[0029] The magnetic field sensor according to the invention, illustrated by way of example in Figure 1, is used to measure an electric current IP flowing through a primary conductor. The current to be measured can be a direct current, or a current comprising at least one alternating current component. The magnetic field sensor comprises an SPM transducer 1, illustrated by way of example in Figure 2, comprising at least one coil of SPM material intended to be subjected to an external magnetic field to be measured, and disposed between two extreme terminals of the transducer 31, 32. In a preferred embodiment of the invention, the SPM transducer comprises at least one pair of two identical SPM coils LN1, LN2 disposed between the two extreme terminals 31, 32. The SPM transducer may further comprise two or more pairs of SPM coils.

[0030] The core of the SPM LN1, LN2 coil(s) may have a cross-section less than or equal to 5 mm 2, and / or a volume concentration of SPM material of less than 10%. These provisions allow for a reduced use of SPM materials, which are particularly expensive.

[0031] The sensor according to the invention also includes a capacitor Cs, that is to say, a substantially capacitive impedance at the excitation frequency. excThe capacitor Cs comprises a first terminal, connected to one terminal of the SPM coil, and a second terminal, connected to a reference potential. If the SPM transducer has one pair of SPM coils, the first terminal of the capacitor Cs is preferably connected to the common connection point 33 of the two SPM coils. If the SPM transducer has two pairs of SPM coils, the first terminal of the capacitor Cs is preferably connected to the common connection point of one of the pairs of SPM coils. The capacitor Cs is independent of the magnetic field being measured; that is, its capacitance does not depend on the strength of the magnetic field.

[0032] The sensor according to the invention further comprises an excitation voltage generator VEXC, configured to inject an excitation current into the SPM coil(s), said excitation current comprising at least one substantially sinusoidal component at an excitation frequency excThe excitation voltage generator VEXC is, for example, connected between the reference potential and the midpoint 34 of a center-tapped coil P11-P12, which is part of the transducer 1. The center-tapped coil consists of two substantially identical windings wound on the same magnetic core. The outer terminals of the center-tapped coil P11-P12 can be connected to the outer terminals of the transducer 31, 32.

[0033] The sensor according to the invention further includes a means for measuring the voltage across the terminals of the SPM coil(s) LN1, LN2, that is to say, the voltage between the extreme terminals 31, 32. This voltage is hereafter denoted v SPM(t). The measuring means includes, for example, a coil S1, integrated into the transducer 1 and forming with the center-tapped coil P11-P12 a transformer, a capacitor C1 and a resistor R1. The coil S1 and the capacitor C1 can be connected in series between the reference potential and a first terminal of the resistor R1, the second terminal of the resistor R1 being able to be connected to the reference potential.

[0034] The sensor also includes an analysis module 2, configured to take the voltage v as input SPM (t), and determine from this input the value of the circulation of the external magnetic field C est .

[0035] The sensor architecture shown is one example of a possible implementation. Many other ways to implement this sensor are possible, as illustrated by the possibilities described in document FR3133677.

[0036] The applicant has developed an analysis module in which the SPM signalSPM (t) is sent to a synchronous demodulator, the effect of which is to generate an in-phase component and a quadrature component in phase with the demodulation carrier. These components can be represented as a complex quantity:

[0037]

[0038] The circulation of the magnetic field C est is then estimated by projecting this complex quantity onto an axis θ = θ0, which amounts to taking the real part of the complex obtained by applying a rotation of angle -θ0 to S SPM :

[0039]

[0040] When θ0 is correctly adjusted, and the magnetic field to be measured H is close to 0, the imaginary part of S' SPM is close to 0 and the real part of S' SPM is roughly proportional to C est Conversely, when the magnetic field increases, non-linearities appear, and the function C est= f(H) has a maximum for a value that we denote by H max For a magnetic field greater than H max Therefore, it is not possible to directly deduce the value of H from the value of V SPM To avoid this situation, a feedback field is applied, which is superimposed on the excitation field, in order to obtain a circulation of the magnetic field estimated at C est = 0. Fields much greater than H max can thus be measured.

[0041] In order to control the feedback field, the real part of the SPMS signal SPM,r is analyzed: - siS SPM,r > 0, we seek to increase the feedback field, to decrease the overall field H under which the transducer is located, and thus approach C est = 0, and- ifS SPM,r < 0, we seek to decrease the feedback field, to increase the overall field H under which the transducer is located, and thus approach C est = 0.

[0042] To implement this, we generally use a compensator of the proportional, integral, proportional / integral or proportional / integral / derivative type.

[0043] The applicant observed that this feedback-based solution works satisfactorily for certain applications. However, in some cases, particularly when the magnetic field is subject to rapid variations of large amplitudes, or when the excitation field is significantly greater than the maximum field allowed by the feedback, this solution does not work.

[0044] The problem encountered is illustrated by the diagram, which shows as an example the evolution of the real parts (solid line, S). SPM,r ) and imaginary (dotted line, S SPM,i ) of the signalS SPMdepending on the magnetic field H. This change is due to the fact that the transducer's impedance depends on the applied magnetic field H. We observe on which the signal S SPM,r The sign changes around 5000 A / m. In the operation described above, this causes the feedback system to act in the wrong direction, resulting in feedback divergence and rendering the sensor inoperative. This situation occurs particularly when the transducer is activated in the presence of a pre-existing high field or during rapid changes in high-amplitude fields: in these cases, the response time of the controller leads to the temporary appearance of strong fields in the transducer.

[0045] Therefore, the applicant has developed the sensor according to the invention, which further includes a means for measuring the excitation current of the SPM coil(s) LN1, LN2i exc(t). The current measurement means includes, for example, a means for measuring the voltage across the capacitor C s , which makes it easy to deduce the current exc (t).

[0046] Thanks to this method of measuring the excitation current, the analysis module 2, in addition to the voltage v SPM (t), also takes as input the currenti exc (t) in order to determine the value of the circulation of the external magnetic field C est Indeed, the signal exc (t) Contains information relating to variations in the transducer impedance according to the applied external magnetic field H. Thus, by analyzing this signal, the analysis module 2 can be configured to compensate for these variations in its estimation of the circulation of the external magnetic field C est .

[0047] In a preferred embodiment, the analysis module 2 comprises two synchronous demodulators: a first synchronous demodulator 3 and a second synchronous demodulator 5.

[0048] The first synchronous demodulator 3 is located downstream of the excitation current measurement device, and takes the excitation current signal as its input. exc (t). The first synchronous demodulator 3 operates at the angular frequency ω exc = 2πf exc The first synchronous demodulator 3 provides a complex excitation signal at its output. exc (t), which includes the signals in phase and in quadrature phase with the angular frequency ω exc :

[0049]

[0050] with T exc = 1 / f exc

[0051] The second synchronous demodulator 5 is located downstream of the voltage measurement device v SPM It takes an SPM signal as input. SPM(t), which preferably corresponds to the SPMv voltage signal SPM (t), but can also be a current signal directly derived from the SPMv voltage signal SPM (t). The second synchronous demodulator 5 operates at the angular frequency ω SPM ,ω SPM being an even multiple of ω exc, par exempleωSPM= 2ωexc. En effet, comme expliqué dans la publication FR3133677 du demandeur, l’information utile se trouve dans les harmoniques de rang pair du signal SPMsSPM(t), particulièrement dans l’harmonique de rang 2. Le deuxième démodulateur synchrone 5 fournit en sortie un signal d’excitation complexeSSPM(t), qui comporte les signaux en phase et en quadrature de phase avec la pulsationωSPM :

[0052]

[0053] with T SPM = 2π / ω SPM

[0054] The first synchronous demodulator 3 makes it possible, in particular, to obtain the phase of the excitation signal exc (t). Indeed, the information needed to compensate for variations in transducer impedance is found in this phase. Thus, by calculating the phase of the excitation signal exc (t), the analysis module 2 can be configured to estimate the circulation of the external magnetic fieldC est more specifically.

[0055] The first synchronous demodulator 3 could be replaced by a comparator, in which the zero crossing of the excitation current is detected and compared to a reference signal that caused this excitation current. In such an embodiment, the phase information of the excitation current, which is the information needed for subsequent steps, could be recovered from the time difference between the zero crossings of these two signals.

[0056] Thus, the phase of the excitation signal exc (t) depends on the value of the transducer inductance, and also on the value of the capacitor Cs inserted in series with the SPM coils LN1, LN2 to form a resonant circuit. This resonant circuit is excited by the voltage generator VEXC, which has a relatively low output impedance, so the phase of the excitation current exc(t) varies almost exclusively with the phase of the resonant circuit's impedance. At resonance, the phase of the resonant circuit's impedance is zero, but since the inductance of the SPM transducer depends on the applied external magnetic field, the resonant frequency also varies. This behavior is illustrated by the figure, which shows, as an example, at a constant excitation frequency, the value that the phase variation of the excitation current Δθ can take as a function of the applied external magnetic field.

[0057] To solve this problem, it is possible to control the excitation frequency. exc at the system's resonant frequency, in order to obtain zero phase. This solution can be implemented within the scope of the present invention. However, it is not suitable for all applications, as it is complex to implement and generates a significant response time. Furthermore, the SPM signal processing SPMintroduces a phase shift dependent on the excitation frequency and therefore the excitation frequency control does not allow to compensate for this phase shift.

[0058] The preferred solution is then to try to compensate for this phase variation, and to use an excitation frequency exc constant.

[0059] To do this, analysis module 2 includes a phase determination unit 6. Phase determination unit 6 calculates, from the complex current signal I exc (t), a correction angle θ(t).

[0060] Analysis module 2 then includes a magnetic field circulation estimation unit 7, in communication with the phase determination unit 6. The magnetic field circulation estimation unit 7 takes as input the complex SPM signal S SPM(t) at the output of the demodulator, the value of the correction angle θ(t), and performs two successive operations: - application of a phase rotation to the complex SPM signal S SPM (t), of the value of the correction angle θ(t), to obtain a corrected signal S' SPM (t)then- estimation of the value of the magnetic field circulation C(t) by projecting the signal thus obtained onto a reference axis of the complex plane. This axis is preferably the real axis or the purely imaginary axis. For example, if the projection is made onto the real axis, an estimate of the magnetic field circulation can be obtained using the following equation:

[0061]

[0062] The correction angle θ(t) must therefore be calculated to implement this estimation.

[0063] The excitation field is of the form:

[0064]

[0065] When subjected to this field, the non-linearities of the SPM material produce a useful SPM magnetization signal of the form:

[0066] Where the useful component is the component in cos(2ωt+2φ).

[0067] A phase shift Δφ of the excitation current therefore produces a phase shift of 2Δφ in the SPM magnetization, and thus in the SPM voltage induced in the transducer. However, as explained above, the sensor according to the invention includes a resonant circuit around the angular frequency 2ω due to the presence of the capacitor Cs, an impedance that is substantially capacitive at the angular frequency 2ω. Since the output impedance of the transducer is essentially an inductance dependent on the applied field, this second resonant circuit introduces an additional phase shift, leading to a total phase shift of the demodulator output signal that differs from 2φ. It is this total phase shift that we seek to estimate in order to compensate for it using the correction angle θ(t).

[0068] Within the framework of the present invention, the value of the correction angle θ(t) can be obtained by theoretical calculations taking into account the precise values ​​of the impedances involved. However, this calculation is difficult to perform in practice, requires complex calculations, and is therefore not compatible with a simple and low-cost sensor.

[0069] We can then preferably obtain the function of the variation of the correction angle θ, as a function of the variation of the phase of the excitation signal, θ = f(Δφ), experimentally.

[0070] To do this, Δφ is first measured, for example by measuring the voltage across the series capacitor Cs of the excitation circuit. Demodulation at angular frequency ω, synchronized with the demodulation of the SPM signal, for example at 2ω, provides the phase of the excitation current, up to a phase shift. This phase shift arises from the phase of the impedance formed by the excitation capacitor and parasitic impedances and is approximately 90°, to which must be added any assumed fixed delays between the different demodulations and means of generating the excitation voltage. Knowing this phase shift is not important; only the phase shift Δφ is useful.

[0071] The function f can advantageously be obtained by calibrating the open-loop transfer function of the system, either by varying the field to be measured while disabling the feedback system, or preferably by varying the feedback field in the absence of a primary field. This calibration can be performed for each sensor individually, or for a reference sensor.

[0072] The rigorous analytical expression defest complex. However, tests carried out by the applicant showed that an affine function could be used:

[0073]

[0074] Therefore, the estimation of the correction angle θ is made by approximating such an affine function in the preferred embodiment of the invention.

[0075] Laillustre en en example :- in solid line, the relation between θ and Δφ as measured,- in dotted line, the approximation of the relation between θ and Δφ by an affine function.

[0076] In certain embodiments, other types of functions, in particular polynomials of degree 2, 3 or higher, may be used, without departing from the scope of the present invention.

[0077] In some applications, the correction angle θ may depend on the sensor temperature. To improve the accuracy of sensor measurements, the phase determination unit 6 can then be designed to take temperature into account. For example, if the affine function approximation is used, several values ​​of θ0 and k θ can be used, corresponding to different temperature ranges. The calibration step to determine these values ​​is then carried out under several temperatures.

[0078] During the mass production of sensors according to the invention, this temperature calibration operation can be performed only once for a series of identically manufactured sensors. Alternatively, and to ensure greater accuracy, this calibration operation can be performed for each sensor individually.

[0079] After the phase rotation operation, and using an estimate of the correction angle θ using an affine relationship to the argument of the excitation signal, the corrected signal S' SPM no longer presents a sign inversion, as illustrated as an example on the, which can be compared to the.

[0080] As seen as an example on the image, after the detailed processing described above, the corrected signal S' SPMmay not have a one-to-one relationship with the applied field H: two real field values ​​correspond to the same measured field value. In an open-loop measurement, the range of use is thus limited to fields between the two extremes of S' SPM around -2000 and 2000 A / m. In a closed-loop application, the desired zero-field state can be achieved thanks to the feedback system and the unambiguous sign of this quantity. However, the feedback system introduces a delay dependent on the applied field level: for strong fields, the response time will be longer than for weak fields.

[0081] However, the applicant observed that the absolute value of strong fields can be determined by the variation in the phase of the excitation signal Δφ. Since the sign and absolute value of weak fields are better determined by the corrected signal S' SPMIt is possible to make a correction by calculating a rectified SPM signal of the type:

[0082]

[0083] To simplify the notation and express the preferred mode of realization, we write here S' SPM,r the real part of the corrected SPM signal SPM , but we could just as easily use instead a projection onto another reference axis of the complex plane.

[0084] Since the sign and absolute value of weak fields are best determined by the corrected signal S' SPM The function management is advantageously of the following type:

[0085]

[0086] For weak fields, we thus have:

[0087]

[0088] This works well, because as we have seen the relationship between the field and the corrected signal S' SPM,r is unambiguous for weak fields up to a certain level.

[0089] And for strong fields, we have:

[0090]

[0091] The function g may take a mathematical form other than this advantageous example, without departing from the scope of the present invention, as long as it takes into account: - the corrected SPM signal S' SPM , predominantly for weak fields, and the phase variation of the excitation signal, which can be represented by the argument of the complex excitation signal I exc (t), which is predominant for strong fields, and which is preferably used while preserving the sign of the corrected SPM signal S' SPM Preserving this sign allows us to maintain the oddness of the corrected SPM signal. SPM relative to the magnetic field H, and therefore allows the one-to-one relationship between the rectified signal S" SPM and the applied field H.

[0092] An alternative function could, for example, be of the following form:

[0093]

[0094] Netl values θ can be obtained through calibration, as in the step of determining the correction angle θ(t). This calibration can also be performed for each sensor individually, and / or carried out for different temperatures.

[0095] As illustrated as an example, the rectified signal S" SPM ,r , in continuous line, now presents a one-to-one relationship to the field, unlike the corrected signal S' SPM ,,r , in dotted lines.

[0096] After this calculation, this is therefore the rectified signal. SPM which can be used to estimate the value of the circulation of the external magnetic field C(t) according to the following relationship:

[0097]

[0098] Once again, the rectified signal SPMcould be projected onto a different reference axis than the real axis for estimating the circulation of the external magnetic field, without departing from the scope of the present invention.

[0099] As detailed above, the sensor according to the invention performs a series of relatively complex calculations in real time. These calculations are typically performed at time intervals ranging from 1 μs to 10 μs. Phase determination and rotation operations are computationally expensive for a microcontroller. Therefore, advantageously, certain operations, and in particular the calculation of the argument of the complex current signal performed in the phase determination unit and / or the phase rotation calculation performed in the magnetic field circulation estimation unit 7, can be performed by a coordinate rotation numerical calculation algorithm implemented in CORDIC (Coordinate Rotation Digital Computer) type devices.When implemented in microcontrollers, for example STM32G4 series microcontrollers, such devices can perform the required operations with sufficient accuracy in a few system clock cycles.

[0100] The sensor according to the invention thus makes it possible to estimate the value of the circulation of a magnetic field for the measurement of a current, by a process comprising the following steps: - measurement of the voltage across at least one coil made of super-paramagnetic material v SPM (t),- measurement of the excitation current flowing through at least one coil of super-paramagnetic material i exc (t),- taking into account the data from the means of measuring the voltage and the data from the means of measuring the excitation current in order to estimate the value of the circulation of the external magnetic field C(t).

[0101] The present invention is not limited to the embodiments described but extends to any modification and variation obvious to a person skilled in the art. Furthermore, the technical features of the various embodiments and variations mentioned above may be combined, in whole or in part.

Claims

A magnetic field sensor for measuring an electric current, comprising: - at least one transducer (1), including at least one coil of super-paramagnetic material (LN1, LN2) intended to be subjected to an external magnetic field to be measured, - a capacitor (C s ), one terminal of which is connected to a terminal of said superparamagnetic coil, and a second terminal is connected to a reference potential, the capacitance of said capacitor being independent of the intensity of the external magnetic field; - an excitation voltage generator (VEXC), configured to inject an excitation current into at least one superparamagnetic coil (LN1, LN2), said excitation current comprising at least one substantially sinusoidal component at an excitation frequency f exc - a means for measuring the voltage across at least one coil made of super-paramagnetic material (LN1, LN2) v SPM(t), and an analysis module (2) configured to take into account the data from said voltage measurement means in order to estimate the value of the circulation of the external magnetic field C(t), characterized in that it further comprises a means for measuring the excitation current flowing through at least one coil of super-paramagnetic material (LN1, LN2) i exc (t), said analysis module (2) being configured to take as input the measured excitation current i exc (t) in order to estimate the value of the circulation of the external magnetic field C(t). A magnetic field sensor according to claim 1, characterized in that the excitation current measurement means comprises a voltage measurement means across capacitor C s . Magnetic field sensor according to any one of claims 1 to 2, characterized in that said analysis module comprises: - a first synchronous demodulator (3) with angular frequency ω ex c= 2πf exc , configured to take as input the excitation current i exc (t) measured by the current measuring means, and provide at output a complex excitation signal I exc (t), and a second synchronous demodulator (5) with angular frequency ω SPM , ω SPM being an even multiple of ω exc configured to take an SPM signal as input SPM (t), said SPM signal s SPM (t) corresponding to the voltage v SPM (t), or to the voltage v SPM (t) converted into a current, and outputting a complex SPM signal S SPM (t). A magnetic field sensor according to claim 3, characterized in that the analysis module comprises: - a phase determination unit (6), configured to calculate a correction angle θ(t) taking into account the complex current signal I exc(t),- a magnetic field circulation estimation unit (7), configured to perform the following operations: application of a phase rotation of the correction angle θ(t) to the complex SPM signal S SPM (t), to obtain a corrected SPM signal S' SPM (t), estimation of the value of the circulation of the external magnetic field C(t) as being equal to the value of the projection of the corrected SPM signal S' SPM (t) on a reference axis of the complex plane. Magnetic field sensor according to claim 4, characterized in that the magnetic field circulation estimation unit (7) is configured such that: - after phase rotation, a rectification step takes place in which a rectified SPM signal S" is calculated SPM (t) as being dependent on the corrected SPM signal S' SPM (t) and the argument of the complex current signal I exc(t), and during the estimation step, the value of the circulation of the external magnetic field C(t) is estimated to be equal to the value of the projection of the rectified SPM signal S" SPM (t) on said reference axis of the complex plane. Magnetic field sensor according to claim 5, characterized in that the rectified SPM signal S" SPM (t) is equal to the sum of the corrected SPM signal S' SPM (t) and the corrected SPM signal S' SPM (t) multiplied by a correction factor l θ and an integer power of the argument of the complex current signal I exc (t). A magnetic field sensor according to any one of claims 4 to 6, characterized in that the phase determination unit (6) is configured to calculate the correction angle θ(t) as an affine function of the argument of the complex current signal I exc (t), said affine function being defined by a slope k θand an ordinate at the origin θ0. Magnetic field sensor according to claim 7, characterized in that: - the phase determination unit (6) is configured to calculate the argument of the complex current signal by means of a numerical calculation algorithm by coordinate rotation and / or, - the magnetic field circulation estimation unit (7) is configured to apply the phase rotation of the correction angle θ(t) by means of a numerical calculation algorithm by coordinate rotation. A magnetic field sensor according to any one of claims 7 to 8, characterized in that said analysis module comprises a means for measuring temperature, and a unit configured for determining the values ​​of the slope coefficient k θ and / or of said ordinate at the origin θ0 taking into account the temperature measured by said means of temperature measurement. A method for estimating the value of the circulation of a magnetic field for measuring an electric current, using a magnetic field sensor according to any one of claims 1 to 9, comprising the following steps: - measuring the voltage across at least one coil made of super-paramagnetic material (LN1, LN2) v SPM (t),- measurement of the excitation current flowing through at least one coil made of super-paramagnetic material (LN1, LN2) i exc (t),- taking into account the data from the means of measuring the voltage and the data from the means of measuring the excitation current in the analysis module (2) in order to estimate the value of the circulation of the external magnetic field C(t). A method for estimating the value of the circulation of a magnetic field according to claim 10, using a magnetic field sensor according to any one of claims 7 to 9, further comprising a step of calibrating the values ​​of the slope coefficient kθ and the y-intercept θ 0, in which these values ​​are deduced from tests carried out on said magnetic sensor, during which the values ​​of the circulation of the external magnetic field C(t) are known. Method for estimating the value of the circulation of a magnetic field according to claim 11, by means of a magnetic field sensor according to claim 9, wherein the calibration step comprises a plurality of substeps carried out at different temperatures.

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