Method of operating an electromagnetic induction charging system

Abstract

A method of operating a system (1) for charging a receiving object (2) by electromagnetic induction, the system comprising a charging surface (4), an insulating layer (6) arranged under the charging surface (4), a charging coil (8) arranged under the insulating layer (6), a capacitive sensor (10) comprising a first electrode (A) and a second electrode (B) arranged between the charging surface (4) and the charging coil (8), the capacitive sensor (10) being configured to carry out electrical capacitance measurements between the first electrode (A) and the second electrode (B), the method comprising: - comparing a value derived from at least one electrical capacitance measurement with a threshold value representative of a capacitance of a degraded insulating layer (6), and - when a result of the comparison indicates that the insulating layer (6) is degraded, preventing generation of the charging magnetic field. Figure for abstract: Figure 1

Description

Title of the invention: Method of operating an electromagnetic induction charging system Technical field

[0001] The present invention relates generally to the field of contactless charging, also known as induction charging, and more specifically relates to a method of operating a system for charging by electromagnetic induction a receiving object, in particular a vehicle. Technological background

[0002] Inductive charging offers a practical solution for charging electric vehicles, including autonomous vehicles. These vehicles require regular charging to maintain their battery levels, but the traditional approach with cables can be difficult and impractical. Inductive charging eliminates the need for physical connectors and offers an efficient way to charge autonomous vehicles without human intervention.

[0003] In addition, inductive charging allows for seamless integration with parking infrastructure. Inductive charging stations can be integrated into parking lots, garages, and public roads, allowing autonomous vehicles to recharge during their periods of inactivity, for example when they are parked overnight. This helps optimize the use of autonomous vehicles by allowing them to remain operational for longer periods, without the need for a driver to manually recharge them.

[0004] With the expected growth of autonomous vehicles in the coming years, inductive charging is becoming a key part of the infrastructure needed to support this transition. It offers a convenient, wireless, and automated solution for charging autonomous vehicles, contributing to their widespread adoption and efficient operation.

[0005] Furthermore, the safety dimension represents a crucial challenge in the development of induction charging systems. The safety of charging operations is of paramount importance to avoid any risk of accidents or potential damage.

[0006] Inductive charging uses charging coils present on both the object to be charged and the charging station. When the charging station is supplied with electricity, a coil generates a magnetic field. When the object to be charged is placed nearby, the magnetic field induces an electric current in its charging coil, which is then converted into direct current to recharge the object's battery.

[0007] Electrical intensities and voltages can take on high values, and in the Since a charging station must be accessible to the public and operate autonomously, it is essential to ensure user safety at all times. One of the main dangers is the presence of a conductive foreign object between the charging surface of the station and the receiving object, such as a piece of metal waste such as an empty can. Such a foreign object can be subject to induced currents, which can cause its temperature to increase. These high temperatures can pose a danger to the charging station or to users who might handle this object. For example, a can can reach 100 degrees Celsius in just 30 seconds. It is therefore essential to detect these conductive foreign objects and not to start charging if there is a safety risk.

[0008] Some approaches use a camera to detect the presence of such a foreign body on the charging surface. Unfortunately, such detection does not allow the detection of certain foreign bodies, particularly small ones, especially when the detection conditions are not optimal (low lighting, dirty charging surface, etc.). Other approaches use a thermal camera, which only allows the detection of the foreign object once it has started to heat up, and therefore already presents a danger. The use of cameras is also dependent on a clear field of vision of the charging surface, and detection is therefore no longer possible when an object such as a vehicle is above the charging surface, or even simply obstructs the field of vision. It is then necessary to multiply the cameras, which can significantly increase costs, without any guarantee of infallibility.

[0009] Other approaches use electrical sensors to detect the presence of foreign objects, for example by detecting an increase in temperature due to the heating of such a foreign object. This is for example the case of patent application EP3568718, and patent application EP2773012.

[0010] While these systems can improve the detection of foreign objects, they do not, however, completely ensure user safety. In fact, induction charging systems use charging coils that operate at several kilovolts. If the charging surface or the underlying insulating layer has been degraded, there is a risk of electrocution for the user. In addition, the monitored electrical characteristics can be affected by the condition of the charging surface, which can lead to the presence of a foreign object not being detected. Presentation of the invention

[0011] A method of operating a system for charging a receiving object by electromagnetic induction is proposed, the system comprising: - a load surface, - an insulating layer of electrically insulating material disposed beneath the surface of charge, - a charging coil arranged under the insulating layer and configured to generate a magnetic charging field intended for the receiving object to be charged through the insulating layer in an emission direction when the charging coil is traversed by an electric current, - a capacitive sensor comprising a first electrode and a second electrode arranged between the charging surface and the charging coil, the capacitive sensor being configured to perform electrical capacitance measurements between the first electrode and the second electrode, the system being configured to condition the generation of the magnetic charging field by the charging coil as a function of at least one value taken by an electrical capacitance measurement, characterized in that the method comprises: - the comparison between a value derived from at least one electrical capacitance measurement and a threshold value representative of a capacitance of a degraded insulating layer, and - when a result of the comparison indicates that the insulating layer is degraded, preventing generation of the charging magnetic field.

[0012] Thanks to the proposed method, it is possible to detect an operating anomaly of the charging station even before the induction charging starts, and therefore before the charging coils are energized. It is therefore possible to avoid any risk of electrical accident for the user. In addition, this method uses a technology compatible with foreign object detection, allowing easy implementation at a lower cost.

[0013] This invention is advantageously completed by the following characteristics, taken alone or in any technically possible combination thereof: - the threshold value is representative of a capacity of a degraded insulating layer which is lower than a reference value corresponding to the absence of degradation of the insulating layer, - the reference value has been previously determined by an electrical capacity measurement, - the electrically insulating material has a relative permittivity with a variation of less than + / -20% between 0 and 100°C, - the system further comprises a thermometer configured to measure a temperature representative of a temperature of the insulating layer, and the method comprises a correction, as a function of the measured temperature, of at least one value among the value derived from at least one electrical capacitance measurement and the threshold value representative of a capacitance of a degraded insulating layer, - the system comprises several first electrically distinguishable electrodes separated from each other by a second electrode or a part of the second electrode, and each defining a detection zone on the charging surface, - a capacity measurement is carried out for each detection zone, - the system also comprising: the comparison between a value derived from at least one measurement of electrical capacitance and a second threshold value representative of a capacitance indicating the presence of a foreign body on the charging surface, and-when a result of the comparison indicates a presence of a foreign body on the charging surface, preventing generation of the charging magnetic field

[0014] The invention relates to a system for charging a receiving object by electromagnetic induction, the system comprising: - a load surface, - an insulating layer of electrically insulating material arranged under the charging surface, - a charging coil arranged under the insulating layer and configured to generate a magnetic charging field intended for the receiving object to be charged through the insulating layer in an emission direction when the charging coil is traversed by an electric current, - a capacitive sensor comprising a first electrode and a second electrode arranged between the charging surface and the charging coil, the capacitive sensor being configured to perform electrical capacitance measurements between the first electrode and the second electrode, the system being configured to condition the generation of the charging magnetic field as a function of at least one value taken by an electrical capacitance measurement, and to implement the method according to any one of the preceding claims. Presentation of figures

[0015] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which: - [Fig.l] is a diagram illustrating a sectional view of an induction charging system according to a possible embodiment of the invention, - [Fig.2] is a diagram showing an example of arrangement of two electrodes of a capacitive sensor according to a possible embodiment of the invention, - [Fig.3] is a diagram showing an example of arrangement of two electrodes of a capacitive sensor according to a possible embodiment of the invention, - [Fig.4] is a diagram showing an example of arrangement of electrodes of a capacitive sensor according to a possible embodiment of the invention, - [Fig.5] is a diagram showing an example of arrangement of two electrodes of a capacitive sensor according to a possible embodiment of the invention. Detailed description

[0016] With reference to [Fig.l], a system 1 for charging by electromagnetic induction a receiving object 2 comprises a charging surface 4, an insulating layer 6 of electrically insulating material arranged under the charging surface 4. Typically, the charging surface 4 is part of the insulating layer 6, constituting the interface with the outside air. It is however possible for the charging surface 4 to be distinct from the insulating layer 6, and for example forms the interface between the air and an intermediate layer separating the air from the insulating layer. The material underlying the charging surface 4 may be concrete, bituminous coating, or even plastic, for example POM or Polyoxymethylene. These materials may be those of the insulating layer 6, or the latter may be formed from a different material, in particular in order to ensure better electrical insulation, for example POM or Polyoxymethylene.

[0017] The system 1 also comprises a charging coil 8 arranged under the insulating layer 6 and configured to generate a magnetic charging field for the receiving object 2 to be charged through the insulating layer 6 in an emission direction Z when the charging coil 8 is traversed by an electric current. The charging coil 8 can be subjected to very high voltages, from which the user is protected by the insulating layer 6. In fact, several charging coils 8 are generally provided.

[0018] The receiving object 2 to be charged comprises a receiving coil 20, which when subjected to the magnetic charging field generated by the charging coil 8, creates a charging current which recharges the battery 22 of the receiving object 2.

[0019] The charging surface 4 is exposed to the open air, and is therefore subject to a risk of degradation that is all the greater since it is located on the surface of the ground where vehicles or users circulate. The same applies to the insulating layer 6, which may also be degraded. However, a break in the physical continuity of the insulating layer 6 and the charging surface 4 may break the electrical insulation and therefore expose the receiving object 2 or the user to the high voltages of the charging coil 8.

[0020] In order to detect an anomaly likely to present a safety risk, the system 1 comprises a capacitive sensor 10 comprising a first electrode A and a second electrode B arranged between the charging surface 4 and the charging coil. 8, the capacitive sensor 10 being configured to carry out electrical capacitance measurements between the first electrode A and the second electrode B. The electrodes A, B extend under the insulating layer 6 in the sense that at least a portion of the insulating layer 6 is located between the electrodes A, B, and the charging surface 4, in the emission direction Z. The electrodes A, B may be arranged inside the insulating layer 6. It is however possible for the insulating layer 6 to be entirely above the electrodes A, B, the electrodes A, B then being arranged in another layer under the insulating layer 6, also electrically insulating. The electrodes A, B are of course electrically conductive, and are typically metallic. Preferably, the electrodes A, B are formed on a dedicated support, and in particular may be carried by a printed circuit on which these electrodes A, B are printed.

[0021] The capacitive sensor 10 performs electrical capacitance measurements at the terminals of the electrodes A, B. These measurements can be direct or indirect. Although it is possible to perform a quantification of the electrical capacitance, the measurement of the electrical capacitance may only account for the variation of the electrical capacitance. It is for example possible to form a low-pass filter at the terminals of the electrodes A, B. When the low-pass filter is powered by an excitation signal, for example a square-wave voltage, the rise time of the signal measured at the output of the low-pass filter is directly proportional to the value of the electrical capacitance, which can be deduced by knowing the value of the equivalent resistance of the circuit, typically between 500 kΩ and 5 MΩ.

[0022] The excitation signal feeding the low-pass filter can be directly the output of a microcontroller, thus reducing costs. Changing the frequency of the excitation signal makes it possible to obtain information on the conductivity of the object to be tested. A frequency sweep can be used to draw a Bode diagram of the electrodes A, B. For example, the range of excitation frequencies can be between 10 and 200 kHz, and several frequencies can be used, such as 20, 50 and 100 kHz. It is also possible to form a resonant system with an inductance and then measure the resonant frequency of the association of the resonant system with the electrodes A, B. Finally, it is possible to equip the system with a capacitance meter, for example based on the measurement of the phase shift of a known sinusoidal current.

[0023] The equivalent capacitance between electrodes A, B of a capacitive sensor 10 is altered by the materials present in the vicinity of the space between these electrodes A, B. By analyzing the equivalent capacitance, and particularly its variation, it becomes possible to detect a change in the environment of the electrodes A, B.

[0024] The electrodes A, B are arranged so as to generate an equivalent capacitance between them, and are therefore electrically isolated from each other. The electrodes A, B are shaped to limit their interaction with the magnetic field emitted by the charging coil 8, which could cause the induction of currents in the electrodes A, B, reducing the efficiency of the charge of the battery 22 of the receiving object 2, and above all leading to heating of the electrodes A, B. [Fig.2], [Fig.3], [Fig.4], and [Fig.5] show examples of the arrangement of the electrodes A, B.

[0025] Generally, the first electrode A and the second electrode B each form a circuit without a loop, in order to avoid magnetic loops in which currents could be induced. Similarly, in order to minimize the surface formed perpendicular to the magnetic field, that is to say perpendicular to the emission direction Z, each electrode A, B has a transverse conductive section in a plane containing the emission direction Z less than or equal to 2 mm, preferably less than or equal to 1 mm, and more preferably less than 0.5 mm.

[0026] Preferably, in order to better detect possible foreign objects present on the charging surface 4, the electrodes are formed of tracks or wires with a section preferably less than 1 mm. These tracks can be grouped together in order to improve detection as shown in [Fig.3] and [Fig.5]. The spacing between an electrode A and a second electrode B is preferably between 10 mm and 100 mm.

[0027] In the illustrated embodiments, the first electrode A and the second electrode B comprise several parts A;, B; each extending over a respective area, each part Ab A2, A3, A4, A5 of the first electrode A being separated from another part Ab A2, A3, A4, A5 of the first electrode A by a part Bb B2, B3, B4, B5 of the second electrode B. In the examples of [Fig.2] and [Fig.3], a first part Ai of a first electrode A is separated from a second part A2 of the first electrode A by a first part Bi of a second electrode B. Conversely, a first part Bi of the second electrode B is separated from a second part B2 of the second electrode B by a second part A2 of the first electrode A. There is thus, according to an alignment, an alternation of a part of an electrode A, B with a part of another electrode A, B.Each of the parts A i, B; of an electrode A, B can extend in a rectilinear manner and parallel to another part A;, B; of the other electrode A, B. Such a part A;, B; of electrode A, B can be made up of several rectilinear and parallel conductive lines.

[0028] It is possible for the capacitive sensor 10 to comprise more than two electrodes, and may in particular comprise several electrically distinguishable electrodes, separated from each other by a first electrode or a part of the first electrode, and each defining a detection zone on the charging surface 4. A capacitance measurement can then be carried out for each detection zone.

[0029] For example, the arrangement of [Fig.4] repeats that of [Fig.3], but here each part B; of the second electrode B now constitutes a separate second electrode B, C, D. Each second electrode B, C, D is separated from another second electrode B, C, D by a part A; of the first electrode A. For example, a first second electrode B is separated from a second second electrode C by a second part A2 of the first electrode A. It is then possible to make as many measurements as there are pairs of first and second electrodes, and for example a capacitance measurement between the first electrode A and the first second electrode B, a capacitance measurement between the first electrode A and the second second electrode C, a capacitance measurement between the first electrode A and the third second electrode D.We thus have several measurements, each corresponding to a spatial zone of the capacitive sensor 10, and therefore to a spatial zone of the charging surface 4. It is then possible to locate any anomaly detected by a measurement.

[0030] [Fig.5] shows yet another arrangement of electrodes of the capacitive sensor 10, where the first electrode A comprises a plurality of parts A; each connected to a common section Acom by a switch T;, i between 1 and 10, and each part A; being separated from the others by a section of the second electrode B in an alternating fashion in two dimensions. In this example, the parts A; of the first electrode A have a matrix arrangement. When only one part A; is connected to the common section Acom, by the switch T;, the capacitive sensor 10 measures the capacitance between the second electrode B and said connected part A;. The measurement thus recorded relates to the equivalent capacitance between the second electrode B and said connected part A;, and is therefore indicative of the environment of this connected part A;. Each measurement thus corresponds to a spatial zone of the capacitive sensor 10, and therefore to a spatial zone of the charging surface 4.It is then possible to locate any anomaly detected by a measurement.

[0031] The capacitive sensor 10 can transmit the measurement or measurements of electrical capacitance to a control unit 12 which can process it and control the charging system 1 as a function of these measurements, and in particular control the generation of the magnetic charging field by the charging coil 8. Such a control unit 12 typically comprises a processor and a memory, and may in particular be a microprocessor. The control unit 12 may comprise means for measuring the capacitive sensor 10. The charging system 1, and more precisely the control unit 12, is in particular configured to condition the generation of the magnetic charging field as a function of at least one value taken by a measurement of electrical capacitance. More precisely, the charging system 1 is configured to prevent the generation of the magnetic charging field by the charging coil 8 when a difference between a reference value and a value derived from at least one electrical capacitance measurement is greater than a margin.

[0032] Indeed, in the absence of disturbance, the capacitance measured by the capacitive sensor 10 is fairly constant, but it varies significantly in the event of disturbance such as the presence of a conductive object on the charging surface 4 or in the event of degradation of the insulating layer 6.

[0033] The method thus comprises, in order to detect a degradation of the insulating layer 6: - the comparison between a value derived from at least one measurement of electrical capacitance and a threshold value representative of a capacitance of a degraded insulating layer 6, and - when a result of the comparison indicates that the insulating layer is degraded, preventing generation of the charging magnetic field by the coil 8.

[0034] Since the dielectric permittivity of air is different from that of the insulating layer 6, the capacitance measured between the two electrodes will not be the same if the insulating layer 6 is degraded, and in particular has structural discontinuities, such as cracks or holes. The threshold value is therefore chosen so that the comparison makes it possible to detect such degradation. For example, the threshold value may correspond to an electrical capacitance which would be greater than the electrical capacitance measurement carried out by the capacitive sensor 10 with an insulating layer 6 and a charging surface 4 in good condition. In other words, the threshold value is representative of a capacitance of a degraded insulating layer 6 which is lower than a reference value representative of an electrical capacitance corresponding to the absence of degradation of the insulating layer.

[0035] The threshold value may have been previously entered, but is preferably derived from an electrical capacitance measurement by the capacitive sensor 10, acting as a reference value. For example, the reference value may correspond to an electrical capacitance measurement carried out on the charging system 1 in a controlled environment, typically after its installation at its location where the system will provide charging, with the assurance of the absence of a foreign body 16 or degradation of the insulating layer 6. It is also possible to construct the reference value from a set of capacitance measurements carried out by the capacitive sensor 10 in the absence of a receiving object, such as for example by taking an average or the median of these measurements. The two approaches can be combined.The use of an initial measurement makes it possible in particular to take into account a progressive aging of the insulating layer 6, which would not result in a significant variation in the capacitance measurement. The use of measurements spread over time makes it possible to take into account variations in capacitance due to external factors, such as temperature.

[0036] The threshold value can then be derived from this reference value, for example by lowering the corresponding electrical capacitance beyond a margin. Typically, a capacitance will be considered to be that of a degraded insulating layer if it is at least 20% lower, preferably 50% lower, than the reference value.

[0037] The method may also comprise, in order to detect the presence of a conductive foreign body 16 on the charging surface 4: - the comparison between a value derived from at least one electrical capacitance measurement and a second threshold value representative of a capacitance indicating the presence of a conductive foreign body 16 on the charging surface 4, and - when a result of the comparison indicates a presence of a conductive foreign body 16 on the charging surface 4, preventing generation of the charging magnetic field.

[0038] As previously, the second threshold value may have been entered beforehand, but is preferably derived from an electrical capacitance measurement by the capacitive sensor 10, acting as a reference value. For example, the reference value may correspond to an electrical capacitance measurement carried out on the charging system 1 in a controlled environment, typically after its installation at its location where the system will ensure charging, with the assurance of the absence of the foreign body 16 or of degradation of the insulating layer 6. It is also possible to construct the reference value from a set of capacitance measurements carried out by the capacitive sensor 10 in the absence of a receiving object, such as for example by taking an average or the median of these measurements. The two approaches can be combined.The use of an initial measurement makes it possible in particular to take into account a progressive aging of the insulating layer 6, which would not result in a significant variation in the capacitance measurement. The use of measurements spread over time makes it possible to take into account capacitance variations due to other factors, such as temperature or aging of the materials.

[0039] The second threshold value can then be derived from this reference value, for example by increasing the corresponding electrical capacitance beyond a margin. Typically, a capacitance will be considered as reflecting the presence of a conductive foreign body 16 on the charging surface 4 if it is at least 20% higher, preferably 50% higher, than the reference value. The reference value can be the same for the second threshold value representative of a capacitance indicating the presence of a foreign body 16 on the charging surface 4 and for the threshold value representative of a capacitance of a degraded insulating layer 6. Of course, the second threshold value representative of a capacitance indicating the presence of a foreign body 16 on the charging surface 4 is higher than the threshold value representative of a capacitance of a degraded insulating layer 6, and preferably at least 20% higher than this, and preferably at least 50% higher.

[0040] Thus, the detection of the degradation of the insulating layer 6 can be advantageously implemented within the framework of the detection of a conductive foreign body 16 on the charging surface 4, and then does not require additional resources concerning the capacitive sensor 10 or the processing unit 12.

[0041] The electrical capacitance may vary with the temperature. In order to take this parameter into account, the system 1 may further comprise a thermometer 14 configured to measure a temperature representative of a temperature of the insulating layer 6, and the method comprises a correction, as a function of the measured temperature, of at least one value among the value derived from at least one electrical capacitance measurement and the threshold value representative of a capacitance of a degraded insulating layer 6 or the second threshold value representative of a capacitance indicating the presence of a conductive foreign body 16 on the charging surface 4.

[0042] Preferably, in order to limit the variations in capacitance due to temperature, and possibly to do without a thermometer 14 or at least to improve the precision of the measurements, the electrically insulating material forming the bulk of the insulating layer 6 preferably has a relative permittivity with a variation of less than + / -20% between 0 and 100°C, and more preferably between -10°C and 200°C.

[0043] The system 1, and more particularly the processing unit 12, may comprise communication members, and the system 1 may be configured to transmit data which are functions of the values ​​of the electrical capacitance measurements. It is in particular possible to transmit an alert indicating that the insulating layer 6 is degraded or that a conductive foreign body 16 has been detected on the charging surface 4, and that the generation of the magnetic charging field by the coil 8 has been prevented. It is also possible to transmit information relating to the evolution over time of a value derived from at least one electrical capacitance measurement measured by the capacitive sensor 10, for example in order to provide information on the evolution of the state of the insulating layer 6, thus making it possible, for example, to plan and carry out preventive maintenance actions, such as the replacement of a system part 1 or the repair of a coating of the charging surface 4.

[0044] The proposed charging system 1, as well as its operating method, makes it possible to detect any degradation of the insulating layer 6 which would affect the electrical insulation provided by this insulating layer 6, and which could therefore endanger a user.

[0045] The invention is not limited to the embodiment described and shown in the attached figures. Modifications remain possible, in particular from the point of view of the constitution of the various technical characteristics or by substitution of equivalents. techniques, without departing from the scope of protection of the invention.

Claims

Claims

1. Method of operating a system (1) for charging by electromagnetic induction a receiving object (2), the system comprising: - a charging surface (4), - an insulating layer (6) of electrically insulating material arranged under the charging surface (4), - a charging coil (8) arranged under the insulating layer (6) and configured to generate a magnetic charging field intended for the receiving object (2) to be charged through the insulating layer (6) in an emission direction (Z) when the charging coil (8) is traversed by an electric current, - a capacitive sensor (10) comprising a first electrode (A) and a second electrode (B) arranged between the charging surface (4) and the charging coil (8), the capacitive sensor (10) being configured to carry out electrical capacitance measurements between the first electrode (A) and the second electrode (B),the system being configured to condition the generation of the charging magnetic field by the charging coil (8) as a function of at least one value taken by an electrical capacitance measurement, characterized in that the method comprises: - the comparison between a value derived from at least one electrical capacitance measurement and a threshold value representative of a capacity of a degraded insulating layer (6), and - when a result of the comparison indicates that the insulating layer (6) is degraded, preventing generation of the charging magnetic field.,

2. A method according to claim 1, wherein the threshold value is representative of a capacity of a degraded insulating layer (6) which is lower than a reference value corresponding to the absence of degradation of the insulating layer (6).

3. Method according to the preceding claim, in which the reference value has been previously determined by a measurement of electrical capacitance.

4. A method according to any preceding claim, wherein the electrically insulating material has a relative permittivity with a variation of less than + / -20% between 0 and 100°C.

5. Method according to any one of the preceding claims, in which the system further comprises a thermometer (14) configured to measure a temperature representative of a temperature of the insulating layer (6), and the method comprises a correction, as a function of the measured temperature, of at least one value among the value derived from at least one measurement of electrical capacitance and the threshold value representative of a capacitance of a degraded insulating layer.

6. A method according to any one of the preceding claims, comprising a plurality of electrically distinguishable first electrodes (Ai, A2, A3, A4, A5, Bb B2, B3, B4, B5) separated from each other by a second electrode or a portion of the second electrode (Ab A2, A3, A4, A5, Bb B2, B3, B4, B5), and each defining a detection zone on the charging surface (4).

7. Method according to the preceding claim, in which a capacitance measurement is carried out for each detection zone.

8. Method according to any one of the preceding claims, also comprising: - the comparison between a value derived from at least one measurement of electrical capacitance and a second threshold value representative of a capacitance indicating the presence of foreign body (16) on the charging surface (4), and - when a result of the comparison indicates a presence of a foreign body on the charging surface, preventing generation of the charging magnetic field.

9. system for charging by electromagnetic induction a receiving object, the system comprising: - a charging surface (4), - an insulating layer (6) of electrically insulating material arranged under the charging surface (4), - a charging coil (8) arranged under the insulating layer (6) and configured to generate a magnetic charging field intended for the receiving object (2) to be charged through the insulating layer (6) in an emission direction when the charging coil (8) is traversed by an electric current, - a capacitive sensor (10) comprising a first electrode and a second electrode (A, B) arranged between the charging surface (4) and the charging coil (8), the capacitive sensor (10) being configured to carry out electrical capacitance measurements between the first electrode and the second electrode (A, B), the system being configured to condition the generation of the magnetic charging field as a function of at least one value taken by an electrical capacitance measurement, and to implement the method according to any one of the preceding claims.

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