JP2012531176A - Method and apparatus for detecting a device in a wireless power transfer system - Google Patents

Abstract

  A method for detecting receiver 214 by a transmitter and a transmitter for detecting the receiver are provided. The transmitter is intended to inductively transmit power to the receiver 214. The transmitter includes a first transmission coil as the first electrode 204 and a second electrode 206. The first electrode 204 and the second electrode 206 form a capacitor 202. The method includes applying a voltage 216 to one of the electrodes 204, 206 and detecting a change in capacitance of the capacitor 202.

Description

  The present invention relates to a power transmission technique.

  Enables wireless power transfer to charge batteries of battery powered devices such as mobile phones, PDAs, remote controls, laptops etc. or directly power devices such as lamps or kitchen appliances directly An inductive power system can be used. Inductive power systems for transmitting power or charging mobile devices are known, for example, from WO 2008/050260. Such a system generally includes a power transmission device, hereinafter referred to as a transmitter, having a plurality of transmitter coils that can be individually energized and thereby generate an alternating magnetic field. Have. The inductive power system includes a power receiving device having a load that requires power. To receive power, the power receiver is provided with a receiver coil in which the alternating magnetic field provided by the transmitter coil applied with voltage induces a current. This current can drive the load of the receiver, for example, charge a battery or turn on a lamp. Hereinafter, the power receiving device is referred to as a receiver, and includes a receiver coil and a load.

  It is very important to enable low, preferably (virtually) zero standby power. For example, if there is no device on the wireless power transmitter, the power loss should be almost zero.

  United States Patent Application US2008 / 0157909 provides a system for detecting coupling between a transmitter coil of a power transmitter device and a transmitter coil of a power receiver device. While applying a voltage to the transmitter coil, a current sensor monitors the current through the transmitter coil to determine whether the receiver coil of the power receiver is coupled to the transmitter coil. The system periodically requires voltage application of the transmitter coil, resulting in too much power consumption by the power transmitter device, especially when no power receiver device is present.

  When the US patent application system is used in a power transmitter device having multiple transmitter coils, each of the transmitter coils must be periodically energized, further power usage. Bring about an increase. In addition, periodic voltage application of the transmitter coil periodically introduces an electromagnetic field, which can cause, for example, electromagnetic interference or, for example, a bank card is accidentally placed on the power transmitter device. Information on the magnetic strip of the bank card can be erased.

  It would be advantageous to provide a method and transmitter that has low power consumption in standby mode.

  A first aspect of the invention provides a method for detecting a receiver with a transmitter according to claim 1. A second aspect of the invention provides a transmitter for detecting a receiver as claimed in claim 8. A third aspect of the present invention provides a method for detecting a receiver by a transmitter according to claim 12. A fourth aspect of the present invention provides a transmitter for detecting a receiver according to claim 13. Advantageous embodiments are defined in the dependent claims.

  According to a first aspect of the invention, a method for detecting a receiver by a transmitter is provided. The transmitter is intended to transmit power inductively to the receiver. The transmitter has a first transmission coil as a first electrode and a second electrode. The first electrode and the second electrode form a capacitor. The method includes applying a voltage to any one of the electrodes and detecting a change in capacitance of the capacitor.

  The present invention proposes a method and apparatus for detecting whether the receiver is located on the surface of the transmitter by capacitance detection, which is fast and does not interfere with inductive power transfer. Thus, detection of devices on the wireless charging pad is not interfered with by other devices that are already charged on the same pad. Furthermore, the proposed detection method operates with little (or virtually no) power loss.

  The method is such that a device arranged on the display of the transmitter is between two electrodes arranged below the surface of the transmitter, or between one electrode and ground, or between one electrode and the receiver. Based on the fact that the capacitance between the two is changed. The arrangement of such a device on the surface of the transmitter changes the capacitance of the capacitor that exists between the different electrodes. This is due to an induced change in the dielectric constant of the space between the two electrodes, or a dielectric distance between the two electrodes, or a combination of changes in dielectric constant and dielectric distance. In the context of the present invention, this method is also referred to as “capacitance detection method”.

  Capacitance change detection can be performed relatively power-efficiently compared to inductive detection. As long as the capacitance does not change and if a DC voltage is used, no current flows from or to the capacitor, and only if the capacitance changes, a small amount of current goes to or from the capacitor. Flowing. Also, if an AC voltage is applied to the capacitor and the AC voltage can be appropriately sized, a relatively small amount of current flows through the capacitor. Thus, the current through the capacitor can be relatively small or substantially equal to zero, so the power consumption of the capacitance detection method is relatively small. The detection can be performed efficiently using, for example, a low power consumption integrated circuit. Therefore, the method of detecting the receiver is relatively power efficient.

  Furthermore, capacitance detection does not require inductive action of the transmitter coil, and therefore no electromagnetic field is generated and no electromagnetic interference is created.

  Furthermore, the use of the first transmitter coil as one of the electrodes reduces the number of components required to build a transmitter that uses capacitance detection to detect the receiver. Instead of introducing additional first and second electrodes, the method of the present invention only requires the introduction of a second electrode, so the transmitter has a low complexity design and costs To save money.

  In one embodiment, the transmitter includes a second transmission coil that functions as the second electrode. That is, two neighboring transmit coils are used as the two electrodes of the capacitor. The presence and location of the receiver coil can be detected by measuring the change in capacitance of the capacitor formed by the two transmitter coils.

  The first transmission coil operates as a first capacitor electrode connected to the first terminal. A nearby transmitter coil operates as a second capacitor electrode and is connected to the second terminal. Another nearby coil operates as, for example, a third capacitor electrode and is connected to the third terminal. The location of the receiver coil relative to the location of the transmitter coil is the capacitance between the first terminal and the second terminal or, for example, between the first terminal and the third terminal. decide.

  In other words, the transmitter can have more than one transmitter coil. Each pair of transmitter coils of the transmitter can form a capacitor. By using a first transmitter coil as the first electrode and a third transmitter coil as the second electrode, efficient use of the transmitter components is realized. No additional electrodes need be introduced on the surface of the transmitter, which prevents possible interactions between the transmitter coil of the transmitter and the additional electrode.

  A receiver is on the first transmitter coil, on the second transmitter coil, or partially on the first transmitter coil and / or partially on the second transmitter coil. , The capacitance of the capacitor formed by the two transmitter coils changes, which is detected by a detection circuit. Thus, for the detection, a receiver is arranged on or near the first transmitter coil and / or on or near the second transmitter coil. This information can initiate a further process of receiver identification by the transmitter, or power transfer to the receiver is initiated by the first transmission coil and / or the second transmission coil. be able to.

  If the transmitter has a plurality of transmitter coils and the capacitance is monitored to detect a change in the capacitance between each pair of neighboring transmitter coils, the receiver relative to the position of the transmitter coil A reasonably accurate estimate of the location of can be obtained. The detected position may be used to activate a further process of receiver identification or to initiate power transfer to the receiver by a transmit coil that is near or closest to the detected position of the receiver. it can.

  As an example of this embodiment, a detection circuit is connected to the second coil, a voltage is applied to the first transmission coil, and the detection circuit is connected to the first coil and the second coil. Used to monitor capacitance changes between formed capacitors.

  In another embodiment, the second electrode of the capacitance is located in the center of the first transmitter coil.

  Said embodiment proposes to locate the receiver by using capacitance detection. This method involves little power consumption, is fast, and does not interfere with inductive power transfer. The detection capacitor is realized between a primary coil as a first electrode and a second electrode located at the center of the primary coil. The detection of the receiver thus directly corresponds to the position of the electrode transmitter coil and requires a low complexity localization algorithm.

  In other words, the provision of an electrode at the center of the first transmitter coil allows for a more accurate detection of the position of the receiver relative to the position of the first transmitter coil. In particular, the transmitter is more accurate in situations where the receiver is accurately placed over the first transmitter coil and other situations where the receiver partially covers the first transmitter coil. Can be distinguished. If the receiver is accurately placed over the first transmitter coil, the capacitance change is greater than if the receiver is partially placed over the first transmitter coil.

  Further, when the transmitter has a plurality of transmission coils, each transmission coil includes an electrode at the center of the transmission coil, and each of the transmission coils forms a capacitor together with the center electrode. When a receiver is placed on the surface of the transmitter, one of the capacitors exhibits the maximum change in capacitance. The capacitor is a capacitor formed by a corresponding center electrode closest to the transmitter coil and the receiver. Thus, determining which transmitter coil is closest to the receiver is relatively simple.

  The second electrode may have various shapes such as round, oval, rectangular metal plates, coils, a set of thin conductors connected together on one side, etc., optionally with slits to reduce eddy currents. Can have. The second electrode can be accurately placed in the center of the first transmission coil, however, so as to form a capacitor between the first transmission coil and the second transmission coil. The second electrode may be disposed so as to deviate from the center. It is only necessary that the second electrode is arranged in the first transmission coil.

  As an example of this embodiment, a detection circuit is connected to any one of the electrodes of the capacitor, a voltage is applied to the first transmission coil, and the detection circuit includes the first transmission coil and the first transmission coil. A capacitance change between the capacitors formed by the second electrode in the center of the first transmission coil is detected.

A wireless power transmitter for detecting a receiving device has a first transmission coil as a first electrode of a capacitor, and a second electrode of a capacitor located at the center of the first transmission coil, and the transmitter Further comprises a detection circuit connected to any one of the electrodes of the capacitor, the transmitter comprising:
A first unit for applying a voltage to the first transmitter coil;
A detection circuit for detecting a capacitance change of a capacitor formed by the first electrode and the second electrode;
Have

  In one embodiment, the winding of the first transmission coil has an inner portion of the winding and an outer portion of the winding. The inner part of the winding is the first electrode, and the outer part of the winding is the second electrode.

  If the inner and outer windings are disconnected from each other, for example in the standby mode of the transmitter device, this configuration is a capacitance configuration and the inner and outer portions are used as electrodes. The capacitance between these electrodes increases when a device with capacitance properties is placed over the configuration. A device can be detected by measuring the capacitance using one of the above methods. When a device is detected, the inner winding and the outer winding can be connected to operate the transmitter coil as an inductive power transmitter. There is no need for additional electrodes to be provided on the surface of the transmitter. Using the inner winding and the outer winding allows accurate detection of the position of the receiver relative to the position of the first transmitter coil.

  In another embodiment, the detected capacitance change indicates that the receiver is near the transmitter. The method further comprises activating the transmitter such that the transmitter begins to communicate with the receiver or begins to transmit power to the receiver.

  The embodiment allows the transmitter to enter a low power sleep state and upon detecting an event related to a wireless power receiver, the transmitter is awakened from the low power sleep state. Such an event can be the detection of a capacitance change.

  In other words, if no receiver is detected, the transmitter is in standby mode, which means that the transmit coil is not activated to transmit or communicate power to the receiver. If a capacitance change is detected, perhaps the receiver is placed on top of the transmitter. Thus, the transmitter is woken up, which means that the standby mode is terminated and the transmitter enters the operating mode. In the mode of operation, the transmitter can inductively provide power to the receiver or can first initiate an additional communication process to further identify the receiver. In the mode of operation, one or more transmit coils of the transmitter are used to inductively transmit power to or inductively communicate with the receiver.

  In one embodiment, the applied voltage is an AC voltage, a DC voltage, a voltage pulse, or a step function.

  When the voltage applied to one of the electrodes of the capacitor is an AC voltage, current flows through the capacitor in proportion to the capacitance of the capacitor. By making the value and frequency of the AC voltage the correct magnitude, the current can be made relatively small so that a small amount of power is lost. The change in current relates to a possible arrangement of receivers on the transmitter. Detecting a change in the current, for example, by detecting whether the current exceeds a predetermined value and / or by detecting whether the current decreases below a predetermined value is a comparison Is simple and can be implemented power-efficiently.

  If the applied voltage is a voltage pulse or step function, the response of the capacitor in the time domain can be analyzed by the detection circuit. Depending on the capacitance of the capacitor, a specific response can be detected. If the receiver is located on the transmitter, the response is different from the situation where the receiver is not located on the wireless power device.

  Measuring the response characteristic can be done by coupling a resistor in series with the capacitor and applying the voltage pulse or step function to the series configuration. The voltage across the capacitance rises when the voltage change forms a neutral for a given value, and specific information is measured depending on the capacitance of the capacitor and the given value of the voltage. be able to. The capacitance increases when the device is deployed, so the rise time is long when the device is deployed. When a voltage pulse of a predetermined length is applied to the series configuration, the voltage across the capacitor gradually decreases as the applied voltage decreases from a predetermined voltage to a neutral voltage. The decay time is a measurement of the capacitance of the capacitor.

  In another embodiment, the transmitter has a plurality of capacitances formed by the first and second electrode pairs. The method further comprises detecting a capacitance change of each of the plurality of capacitors, and determining a position of the receiver depending on which capacitance change of the plurality of capacitors is detected. .

  By providing a plurality of electrodes, each neighboring pair of electrodes forms a capacitor. By detecting the capacitance change between each of the electrode pairs, the transmitter can detect where the receiver is located on the transmitter relatively accurately. The capacitance with the largest change in capacitance is close to the receiver.

  According to a second aspect of the present invention, a transmitter for detecting a receiver is provided. The transmitter is intended to inductively transmit to the receiver. The transmitter has a first transmission coil and a second electrode as a first electrode. The first electrode and the second electrode form a capacitor. The transmitter further includes a first unit that applies a voltage to any one of the electrodes, and a detection circuit connected to any one of the electrodes of the capacitance that detects a change in capacitance of the capacitor.

  In one embodiment, the transmitter further includes a second transmission coil that is the second electrode.

  In another embodiment, the second electrode is located at the center of the first transmission coil.

  In another embodiment, detection of the capacitance change indicates that the receiver is near the transmitter, and the transmitter begins to communicate with the receiver or powers the receiver. A second unit that activates the transmitter so that it can begin transmitting.

  The transmitter and the transmitter embodiment provide the same benefits as the method according to the first aspect of the invention and the corresponding embodiment of the method according to the first aspect of the invention. The transmitter has a similar embodiment with similar effects as the corresponding embodiment of the method.

  According to a third aspect of the invention, another method for detecting a receiver by a transmitter is provided. The transmitter is intended to inductively transmit power to the receiver. The transmitter has a first transmission coil as an electrode. The method comprises applying a voltage to the electrode and detecting a capacitance change of a capacitor formed by the first electrode and ground or formed by the first electrode and the receiver. .

  The first electrode forms a capacitance with ground or with a receiver. When the receiver is near the first electrode, the capacitance changes and the charge flows towards or away from the first electrode. By detecting the current to or from the first electrode, an effective and efficient solution to detect the receiver is obtained, which is not a complex design and thus saves costs.

  According to a fourth aspect of the invention, another transmitter for detecting a receiver is provided. The transmitter is intended to inductively transmit power to the receiver. The transmitter is formed by a first transmission coil as a first electrode, a first unit for applying a voltage to the electrode, and the electrode, and the electrode and ground or the electrode and receiver. And a detection circuit for detecting a change in capacitance of the capacitor.

  It should be noted with respect to this document that the use of word capacitors does not indicate a lumped capacitor. Further, transmitter, power transmitter and wireless power transmitter are interchangeable terms with respect to the present invention. The characteristic of the transmitter is that the transmitter is intended to inductively transmit power to the receiver. Receiver, receiver device and power receiver device are interchangeable terms with respect to the present invention. The characteristic of the receiver is that the receiver is intended to receive power inductively. Furthermore, the first unit for applying a voltage to one of the electrodes or one of the transmission coils may be a voltage source.

  These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

  It will be appreciated by those skilled in the art that two or more of the above-described embodiments, implementations and / or aspects of the present invention can be combined in any way deemed useful.

  Modifications and variations of the system and / or method corresponding to the described modifications and variations of the system can be performed by those skilled in the art based on this description.

1 depicts the principle of capacitance detection according to the present invention. 1 depicts the basic structure of capacitance detection according to the present invention. Draw several different circuit topologies for capacitance detection. 1 depicts a block schematic representation system of a freely arranged transmitter according to the present invention. 4 depicts a schematic representation circuit of the system of FIG. 1 depicts a circuit according to a first embodiment of the present invention. The equivalent circuit of FIG. 5 is drawn. Draw a transmitter surface covered by multiple coils. 1 depicts a capacitance detection system according to one embodiment. 1 depicts a capacitance detection system according to one embodiment. Fig. 6 depicts a capacitance detection system using localization according to another embodiment. A first example of a detection circuit when a DC voltage is applied will be described. A second example of a detection circuit when a DC voltage is applied is depicted. A third example of a detection circuit when a DC voltage is applied will be described. A fourth example of a detection circuit when an AC voltage is applied is drawn. Draw an example with a star electrode in the center of the primary coil. Depict a transmitter with a single coil represented by L1 and a sensing capacitor. Figure 3 depicts an embodiment in which a detection unit measures voltage instead of current. An outline of a capacitance measurement circuit between two coils is depicted. Describes a basic overview of the capacitance measurement circuit between the coil and the center electrode. Draw a mechanical overview with the implemented capacitance. 1 depicts an equivalent electrical circuit for the described measurement method. The equivalent electric circuit of the 2nd Example in which the measuring method was described is drawn. Draw a plot of the dielectric constant spectrum over a wide range of frequencies. The real and imaginary parts of the dielectric constant are shown, depicting various processes: ion and dipole relaxation, and atomic and electronic resonances at higher energies. Draw a low standby power architecture. 1 schematically shows a flow diagram of the method of the invention.

  It should be noted that items denoted by the same reference numbers in different figures have the same structural features and functions, or are the same signal. Where the function and / or structure of such an item has been described, there is no need for these repeated descriptions in the detailed description.

  The figure is purely schematic and is not drawn to scale. Some dimensions are strongly exaggerated, especially for clarity.

  FIG. 1 depicts the principle of a method for detecting a device 106 placed on a surface 102 of a transmitter according to the invention. The electrodes 108, 110, 112, 114 under the transmitter surface are used to detect the device 106 to be charged that is placed on the transmitter surface 102. The method is based on the fact that the device 106 disposed above the transmitter surface 102 changes the capacitance between the two electrodes 108, 110, 112, 114 disposed below the transmitter top surface 102. Based. The placement of such a device 106 on the transmitter surface 102 changes the value of the capacitance that exists between the different electrodes 108, 110, 112, 114. This is due to the dielectric constant of the portion of the space between the two capacitor plates formed by the electrodes 108, 110, 112, 114, the dielectric distance of the two electrodes, or a combination thereof. The change in capacitance is represented in FIG. 1 by the difference in the pattern of electric field lines 104 between the covered and uncovered surfaces.

For a parallel plate capacitor, the capacitance between the two electrodes is
C = εA / d
Where ε is the dielectric constant of the medium between the plates, A is the area of the plates, and d is the distance between the plates. Therefore, the capacitance is linearly dependent on the dielectric constant of the medium between the plates. A more complex relationship exists for two plates in the same plane. However, the dependence on the dielectric constant remains the same. For the capacitor formed between the two electrodes 108, 110, 112, 114 under the transmitter surface 102, the dielectric constant changes when the device 106 is placed over the transmitter top surface 102 ( To increase. The resulting change in capacitance can be detected in a number of ways.

  FIG. 2a depicts a method of detection according to one embodiment. A voltage source 216 is employed to apply a voltage, which can be an AC or DC voltage of zero or greater amplitude, to one electrode 204 (representing one capacitor plate). A detection circuit 212 connected to the other electrode 206 (representing the second capacitor plate) is used to monitor the capacitance between the two electrodes 204 and 206 forming the capacitor 202. The change in capacitance indicates the placement of the device 214 and this event is signaled using the detection signal 208. Line 210 represents a line of electric force between electrodes 204 and 206 of capacitor 202.

  When a DC voltage is applied to capacitor 202 and device 214 is subsequently placed on the transmitter, charge redistribution produces a small current that can be detected as a voltage across a sensing resistor.

The change in charge accumulated in the capacitor plate is
ΔQ = U · ΔC
Where U is the DC voltage applied to the capacitor and ΔC is the change in capacitance due to the placement of the device.

The resulting current is
i = ∂Q / ∂t
Where ∂Q / ∂t is the charge per unit time flowing towards the capacitor plate. It should be noted that charge redistribution also occurs when a device having an electrostatic charge is deployed. Thus, the detection signal may have a component as a result of a change in capacitance and / or a component as a result of placing a statically charged device.

When an AC voltage is applied to the capacitor 202, a current flows through the capacitor and the current can be monitored. As the capacitance increases relative to the arrangement of the device 214, the current amplitude also increases, indicating the presence of the device 214. The current amplitude is
i = u · ωC
Where u is the AC voltage applied to capacitor 202, ω is the frequency of the applied AC voltage, and C is the capacitance between electrodes 204 and 206. Thus, the current is linearly dependent on the charged capacitance with respect to the arrangement of the device 214. Note that the current can be kept arbitrarily small to limit power loss.

  The method of detecting the receiver by capacitance change is the so-called analog pin method, which is based on the change in capacitance of electrodes on or near the interface surface due to the placement of objects on the interface surface.

  The method is particularly suitable for power transmitters that use free positioning because it allows implementations with very low standby power and still exhibits acceptable response times for the user. The reason is that it is a relatively expensive operation to (continuously) scan the interface surface for changes in the target and the placement of power receivers on the target. In contrast, changes in electrode capacitance can be very inexpensive (in terms of power requirements). Note that capacitance sensing can proceed with most of the base stations turned off.

  A power transmitter design based on an array of primary (transmitting) coils uses the array of primary coils as the electrode in question. For this purpose, the multiplexer should connect all (or related subsets) of the primary coils in the array to a capacitance sensing unit and at the same time disconnect the primary coil from the drive circuit. A power transmitter design based on a moving primary coil can use a sensing coil on the interface surface as an electrode.

  It is recommended that the capacitance sensing circuit be able to detect changes with a resolution of 100 fF or higher. If the sensed capacitance change exceeds some implementation-defined threshold, the power transmitter can infer that an object is placed on or removed from the interface surface. In this case, the power transmitter should proceed with locating the object and attempt to identify the power receiver on the interface.

  FIG. 2b depicts several alternative circuit topologies for the capacitance detection. In example (i), two electrodes form a capacitor. In embodiment (ii), two transmitter coils 218 form the capacitor. Embodiments (i)-(iv) respectively match embodiments (viii)-(xi), which differ with respect to the position of the detection circuit 212. In the embodiments (i) to (iv), the detection circuit is connected to the electrodes 204 and 206 to which the voltage of the voltage source 216 is applied. In the embodiments (viii)-(xi), the voltage source 216 is connected not to the detection circuit 212 but to the other electrode of the capacitor. In embodiments (v) and (xii), it is illustrated that multiple transmitter coils 218 or multiple electrodes 204, 206 can be configured to form multiple capacitors in a parallel arrangement. It should be noted that the embodiments (iii), (iv), (viii) to (xi) may have their respective equivalents in which a plurality of capacitors are arranged in parallel.

  Examples (vi), (vii), (xiii) and (xiv) of FIG. 2b illustrate other aspects of the present invention. The detection circuit 212 and the voltage source 216 are connected to the same electrode 220. The electrode can be a dedicated electrode or can be formed by one or more transmitter coils. The capacitor formed by this electrode and ground 222 is monitored by detection circuit 212. The detection circuit 212 measures the current flowing toward the electrode 220 at a predetermined applied voltage, which can be an AC voltage, a DC voltage or a pulse pattern, which indicates the capacitance. After device placement, the capacitance changes and thus the current flowing towards the electrodes changes. Thus, a sudden change in current flowing toward the electrode indicates device placement. In embodiment (xiii), the transmitter coil is used as a single electrode, and in embodiments (vii) and (xiv), multiple electrodes and / or multiple transmitter coils are connected to earth or the receiver. The capacitors are connected in parallel to form capacitors.

  FIG. 3 depicts a block schematic representation of an exemplary free placement reference transmitter. In this figure, hexagonal coils L1, L2 are used for power transfer and are arranged next to each other in the same plane. Although only two coils L1, L2 are shown, there are more coils (in fact that the entire surface is filled with coils) to allow free placement of the receiver on the transmitter. That is, multiplexers MUX1, MUX2 are used to select a coil located directly below the receiver for power transfer. Multiplexers MUX1 and MUX2 include capacitors C1 and L2 connected in series so that the combination of coils L1 and L2 and capacitors C1 and C2 form a resonant tank circuit required for efficient power transfer. Connect to C2. The resonant tank is driven from half-bridge circuits HB1 and HB2. Finally, a sense resistor Rsense is used to monitor the coil current for control purposes.

  FIG. 4 depicts a schematic representation of the system of FIG. The half bridges HB1 and HB2 are composed of two FETs M1, M2, M3, and M4 that are driven from a microcontroller (not shown). The supply voltage applied to the half bridge is typically 12V to 16V. Multiplexers MUX1, MUX2 consist of switches used to connect the appropriate coils L1, L2 to the half bridge driver.

  For power transmission, the coils L1, L2 are used as inductors, but the present invention aims to use two adjacent coils L1, L2 as two plates of a capacitor. The value of this capacitor changes when the device is placed on the transmitter surface. This value can be monitored using the same hardware used for power transfer. This is shown in FIG. When the multiplexer switch is set and the FETs are connected by FIG. 5, the resulting equivalent circuit is shown in FIG. The applied 12V DC voltage produces a DC voltage for the capacitor Ceq formed by the two coils L1, L2. No current flows during quiescent operation, ie no power is lost. When a device is placed on the transmitter surface, a small current flows towards the Ceq, which can be detected as a voltage relative to Rsense.

  A complete transmitter pad 700 consisting of multiple coils can be monitored simultaneously in a convenient manner. The coil on the transmitter surface is shown in FIG. A DC voltage is applied to the gray coil 704 and current is sensed with the white coil 702 (when the device is in place). In this way, all coils of pad 700 can be sensed simultaneously, and static location information is obtained when the receiver device is sensed.

  FIG. 8 shows an embodiment according to the present invention. In this embodiment, two adjacent coils 810, 812 of system 800, otherwise used for inductive power, form capacitor 802. Using this embodiment, no dedicated sensing electrode is required. Contrary to the previously discussed embodiment, a dedicated voltage source 808 may be used, and a dedicated detection circuit 804 is used. The voltage source 808 is used to apply a voltage that can be an AC or DC voltage with an amplitude greater than or equal to zero. Depending on the applied voltage, an appropriate detection circuit 804 is used to generate the detection signal 806. Some of these detection circuits 804 can be used in parallel to obtain simultaneous detection and localization. The coils 810 and 812 to which the voltage is applied can be, for example, the gray coil of FIG. 7, and the coil connected to the detection circuit 804 can be a white coil.

  FIG. 9 shows another third embodiment according to the present invention. This embodiment uses dedicated sensing electrodes 904, 906 and circuitry. Many configurations of electrodes 904, 906 are possible and all fall within the scope of the present invention. FIG. 10 depicts another example of an electrode configuration. In the example of FIG. 9, two interdigitated electrodes 904, 906 are used on the surface 902 of the transmitter device. The voltage source 808 is used to apply a voltage that can be an AC or DC voltage with an amplitude greater than or equal to zero, and depending on the applied voltage, an appropriate detection circuit 804 is used. The location of the device on the transmitter surface 902 is performed using other (known) methods if necessary, for example by attempting to communicate with the device via a local magnetic field or electric field. Can.

  FIG. 10 shows another embodiment according to the present invention. In this embodiment, the electrodes are present in two layers 1002, 1004 below the transmitter surface. Dedicated detection circuits 1006, 1008 exist for each possible horizontal and vertical position (layers 1002, 1004). A control system 1010 controls the applied voltage, processes the output signals of the detection circuits 1006, 1008, and generates a detection signal 1012 that carries information regarding the location of the detected device. This electrode configuration has the advantage that the number of detection circuits 1006, 1008 corresponds to the square root of the transmitter area. However, other electrode configurations that allow combined detection and localization are possible. All of these configurations fall within the scope of the present invention.

  Combined detection and localization can alternatively be obtained by using a single detection circuit combined with multiple voltage sources applying a voltage having a location dependent frequency. The amplitudes of the different spectral components of the detection signal carry detection and location information.

  In the following, examples of detection circuits are presented. However, other embodiments can be used. These alternative circuits are also within the scope of the present invention.

  FIG. 11 depicts an embodiment of the detection circuit 1102 when a DC voltage greater than or equal to zero volts is applied to one of the electrodes of the capacitor C. When the device is placed, the value of C changes and the amount of charge on the capacitor plate changes as a result of the constant voltage across C. This charge flow or current is supplied by an operational amplifier. In the configuration shown in FIG. 11, the current flowing toward C flows through the feedback resistor of the operational amplifier, resulting in a voltage change at the output of the operational amplifier. Accordingly, the charge current is converted into a voltage. This voltage is first amplified in the (NPN) transistor circuit so that the detection signal 1104 is equal to the transistor supply voltage and, after device placement, the detection signal decreases below 0.5V. A microprocessor μP connected to the detection circuit 1102 can be configured to register this voltage change indicative of device placement.

  The circuit 1202 of FIG. 12 differs from FIG. 11 in that a diode and a capacitor are inserted into the base of the transistor. This capacitor is charged during the device arrangement and slowly discharged through the base of the transistor, thereby increasing the time that the detection signal 1104 is low, making easier detection of this condition by the μP. to enable.

  The circuit 1302 of FIG. 13 differs from FIG. 11 to the extent that the transistor circuit is replaced by a comparator 1304 having a specific threshold voltage Vref. The output of the comparator 1304 is zero when the output voltage of the operational amplifier is less than Vref, and is equal to the supply voltage when the operational amplifier 1306 output voltage exceeds Vref. The output of the comparator 1304 is monitored by the microprocessor μP. Optionally, a diode and a capacitor may be added between the output of the comparator 1304 and the input of the microprocessor μP in order to increase the duration of the detection signal.

  FIG. 14 depicts a detection circuit 1402 that is appropriate when an AC voltage Vref is applied. The change in capacitance induced by the arrangement of the device results in a change in the amplitude of the output signal of the operational amplifier 1404. This amplitude is obtained by performing demodulation in the demodulator 1406 and filtering in the low-pass filter 1408 on the output signal of the operational amplifier 1404.

  For example, the detection capacitor 1502 shown in FIG. 15 is realized between the primary coil as the first electrode and the second electrode 1506 positioned at the center of the primary coil 1504. The second electrode may have a plurality of shapes including circular, elliptical, possibly a rectangular metal plate with a slit to reduce eddy current, a coil, a set of thin film conductors connected to each other on one side, etc. .

  FIG. 15 shows an example with a star electrode 1506 in the center of the primary coil 1504. This figure also shows on the right side a symbolic representation of the sensing capacitor formed between the primary coil 1504 and the second electrode 1506.

  When the device is placed on or removed from the primary coil 1504, the value of capacitor C changes. The value increases significantly if the device covers at least a portion of the C second electrode 1506 and the primary coil 1504 (located in the center of the primary coil 1504). The capacitance does not increase much if the device does not cover the C second electrode 1506. Capacitor C is therefore suitable for detecting whether the device is located on primary coil 1504.

  FIG. 16 shows a transmitter circuit 1602 having a single coil represented by L1 and a sensing capacitor C2. A series resonant circuit is formed by L1 and C1. The resonant circuit is driven by a half bridge inverter represented by switches S1 and S2. The detection unit 1604 is connected via a switch S3 so as to detect a change in current with respect to C2. During detection, switches S1 and S2 are both open, or at least one is open and the other is closed, while S3 is closed. During power transmission, S3 is open and S1 and S2 are alternately closed. When the device is placed on or removed from the primary cell, a change in the value of C2 results in a small current to / from C2 to be measured by detection unit 1604.

  Detection of the current caused by the change in capacitance of C2 can be used to determine the direction of movement of the device relative to the primary cell. When the device is moved towards the transmitter cell, the capacitance increases, resulting in a positive current. When a device is removed from the cell, the capacitance decreases, resulting in a negative current.

  The transmitter may comprise a matrix of primary cells, each primary cell including at least a primary coil, a detection capacitor, and a detection unit. Alternatively, all detection capacitors are connected in parallel to one detection circuit. In this case, position specifying information cannot be obtained. The transmitter can determine the position and shape of the device placed on the surface of the transmitter by examining which detection unit measured the increase in capacitance C2. Such localization resolution is determined by the physical size of the transmitter coil and the sensitivity of the detection unit.

  FIG. 17 shows an embodiment of a circuit 1702 in which the detection unit 1704 measures voltage instead of current. Switches S4 and S5 are added in order to be able to use a central detection unit 1704 and a central power signal generator that handle multiple primary cells. This allows the transmitter to have a more sophisticated and expensive implementation of both the signal generator and detection unit 1704, so that the cost per primary cell only increases moderately.

  S4 can be part of a multiplexer that allows selective connection of the primary cell to the central oscillator. S5 can be part of a multiplexer that allows selective connection of the primary cell to the detection unit.

  During power transfer, S4 is closed and S3 and S5 are open. During device location, at the transmitter, switch S4 is open for each primary cell involved in the location. In order to examine device location changes, the following is repeated cyclically for each participating primary cell using a predetermined cycle time.

  At the start of the cycle, the capacitor C2 of the primary cell is charged with a DC voltage by closing the switch S3 for a short period of time.

  During the cycle, the capacitor discharges through a known high value (parasitic) resistor R.

  At the end of the cycle, the voltage change is measured by the detection unit. Switch S5 is closed for this purpose.

The following situations should be distinguished:
-If no device is present on the primary cell and no device is placed on the primary cell, the capacitance of C2 does not change and the voltage measured is that of the capacitor on the resistor within the cycle time. Within a predetermined range due to discharge.
-If no device is present on the primary cell and the device is placed on the primary cell, the capacitance of C2 is increased and the voltage measured is that of the capacitor on the resistor within the cycle time. It is under a predetermined range due to discharge.
-If a device is present on the primary cell and the device is removed from the primary cell, the capacitance of C2 is reduced and the measured voltage is determined by the discharge of the capacitor on the resistor within a cycle time. Above the range.
-If a device is present on the primary cell and the device is not removed from the primary cell, the capacitance of C2 does not change and the voltage measured is that of the capacitor on the resistor within the cycle time. Within a predetermined range due to discharge.

  Another method of detecting and locating the device measures the capacitance of C2 by using AC instead of a DC source.

  The above method can be used to detect and locate a device on a transmitter to select one or more transmitter coils for power transfer to the receiver.

  The above-described method requires existing detection and reception that requires a power signal in the transmitter coil that lasts relatively long to wait for the receiver's response to the power signal (eg, by providing data using load modulation). Can be used in conjunction with vessel location methods. In this case, the above method may limit the number of transmitter coils that need to be tested by the existing method, and the time to test the transmitter coil after the response of the receiver and Causes total power limit.

  In FIG. 18, an overview of a transmitter circuit 1100 that detects the capacitance between coils Lx1 and Lx2 is shown. This circuit illustratively consists of two half bridges 1811, 1812. Each of the half bridges illustratively comprises two MOSFET switches. Each switch consists of an active controllable path 1101 that includes a capacitance Cds 1802 and a freewheeling diode 1803. The center tap of the half bridge is connected to transmitter coils Lx1 1806, Lx2 via a resonant circuit Cr1804 and optionally a series inductance Lr1805. The resonant frequency of the circuit is determined by the capacitance, the series inductance and the transformer leakage inductance.

  In FIG. 18, by way of example, two half bridges 1811, 1812 that supply an AC voltage to the resonant circuit during power transmission are depicted for illustrative purposes. More transmitter coils and supply circuits can be used in the configuration shown in FIG.

  In FIG. 18, transmitter coils Lx1 and Lx2 are supplied using half bridges 1811 and 1812. This configuration is used for illustrative purposes. Other configurations for the AC voltage supply are conceivable (eg full bridge configuration or class A / B analog amplifier).

  In FIG. 19, an overview of a second transmitter circuit 1900 that detects the capacitance between transmitter coil 1806 and electrode 1909 located in the center of transmitter coil 1806 is shown.

  In another embodiment, the self-capacitance of the transmitter coil is measured. Since this is a planar coil, the self-capacitance increases when a device with capacitive characteristics is placed on the transmitter coil. The self-capacitance can be measured, for example, by measuring the self-resonance of the transmitter coil. A device is detected when the self-resonance decreases below a predetermined reference frequency. Several methods are known in the art for measuring the self-resonance.

  In another embodiment, the transmitter winding is divided into an inner portion and an outer portion of the winding. Both parts are arranged concentrically in the same horizontal layer. These are connected by a switch (for example, a transistor). When the switch is open, this configuration is a capacitive configuration, and the inner and outer portions are used as electrodes. The capacitance between these electrodes increases when a device with capacitive characteristics is placed on the configuration. The device can be detected by measuring the volume using one of the above methods. When a device is detected, the switch is closed to operate the transmitter coil as an inductive power transmitter.

  In one embodiment, the capacitance is measured in the frequency domain. This described embodiment implies two capacitances Ck 1807 at the end of each participating transmitter coil 1806. In order to measure the capacitance between the two coils shown exemplarily as shown in FIG. 18, the ends of both coils are connected in the same manner. The capacitance measuring unit 1813 is arranged at the junction point of the coupling capacitor Ck1807. In order to measure the capacitance of the coil and its central electrode 1909 as shown in FIG. 19, a capacitance measurement unit 1813 is placed between the junction of the coupling capacitor Ck 1807 and its central electrode 1909. Preferably, the measurement frequency is different from the operating frequency of the transmitter coil. The method described here uses a low cost dedicated capacitance measurement unit 1813.

  Driver half bridges and additional resistors can be used to satisfy capacitance measurements. The individual coils that are addressed in one measurement cycle are decoupled using a multiplexer that can have a relay. AC measurements are made by providing an AC voltage to one capacitance terminal (provided by the first winding coil). The AC frequency is generated using a transmitter coil driver. However, high frequencies, preferably in the low MHz range, are suitable for capacitance measurements. Therefore, the transmitter coil driver or frequency limit must be enabled.

  The capacitance measurement is performed more accurately using the capacitance measurement circuit 1813. This measuring unit 1813 is connected to the transmitter coil via a capacity 1807.

  The series inductance Lr 1805 decouples the high frequency used for the capacitance measurement from the switch parasitic capacitance Cds 1802.

  The capacitance between the two coils Lx1 and Lx2 or between the coils Lx1, 1806 and the central electrode 1909 is implied by the object implicated in specific conductivity or exhibits a high dielectric constant on the transmitter coil. Changes when it is done or removed.

  Connecting the coils in the manner as shown in FIGS. 18 and 19 provides capacitive coupling to the winding and avoids interference caused by external influences.

  The capacitance measured by unit 1813 in FIG. 18 indicates whether the receiver coil covers (part of) two transmitter coils Lx1, Lx2. By measuring the capacitance between each neighboring pair of transmitter coils Lx1, Lx2, the transmitter can receive a receiver, for example by summing the measured capacitances for each transmitter cell for neighboring transmitter coils. The location of the coil can be calculated. This method works as long as the receiver coil covers a portion of at least two transmitter coils (eg, when the receiver coil is larger than each transmitter coil).

  The capacitance measured by unit 1813 in FIG. 19 indicates whether the receiver coil covers (part of) the transmitter coil and its central electrode. This method directly indicates whether the receiver coil is located above the transmitter coil, and may also be used when the receiver coil covers only one part of the transmitter coil. it can.

  In another exemplary embodiment, the capacitance between the electrodes is measured by using a pulse or step function on the capacitance configuration to measure capacitance in the time domain. The pulse generator is connected in series in a capacitive configuration with a predetermined resistance. The voltage between the electrodes is measured.

  In an exemplary embodiment, a step function is used for the circuit after the capacitive configuration is discharged. This can be approximated by a pulse long enough to be considered a step function for all possible cases. The rise time and decay time of this voltage depends on the capacitance of the capacitive configuration and can therefore be related to the presence of objects between the electrodes of the capacitive configuration. The rise time of the electrode voltage is measured by comparing the electrode voltage with a reference voltage using a comparator. The controller can measure the time from the start of the step function to the time at which the comparator changes its output. If this time exceeds a predetermined value, the device is detected. The reference value can be continuously adapted by the control algorithm.

  In another exemplary embodiment, pulses of predetermined length and amplitude are used after the capacitive configuration is discharged. Specifically, the pulse shape and length are selected so that the amount of charge delivered to the electrode is clearly defined. After the pulse is applied, the voltage at the electrode is measured and compared to a reference value. If the capacitive configuration has a low capacitance corresponding to “no device on”, the resulting voltage is high. If a device with capacitive characteristics is placed on top of the configuration, the configuration has a high capacitance. In this case, the resulting voltage is low. Thus, if the measured voltage is below the reference value, the device is detected.

  Another embodiment is shown in FIGS. 21a, 20b, 20c.

  If an object with a high dielectric constant (but not a receiver coil) is placed on the transmitter coil, the value of the measured capacitance will also change. For example, placing a key on the surface affects the capacitance between the coils or between the coil and its central electrode. In both cases mentioned, the transmitter coil does not start transmitting power because the unit placed on the surface is not a valid unit for receiving power.

  Two methods can be used to distinguish and identify receiver coils.

  One embodiment for identifying a valid receiver uses the dielectric material properties of the receiver. This embodiment consists of a dedicated material around or at least on the underside of the receiver, which has a predetermined frequency nature. This can be accomplished by providing a housing (eg, plastic) with a frequency dependent impedance. Frequency dependence can be achieved by using Debye relaxation, which is the dielectric relaxation response of an ideal non-interacting population of dipoles to an alternating external electric field. Knowing the housing material of the receiver coil, detection and spatial identification of the housing can be performed. In FIG. 21, a dielectric permittivity spectrum over a wide range of frequencies is illustrated. The real and imaginary parts of the dielectric constant are illustrated, and various processes are depicted: ion and dipole relaxation, and atomic and electronic resonances at higher energies. Knowing the special frequencies of electron, atom, dipole and ion relaxation frequencies, the material can be identified. Using a dedicated material, the material intrinsic relaxation frequency can be set to a desired frequency. Preferably, the identification is performed at a frequency different from the operating frequency of the coil / power transfer operation.

  Another embodiment for identifying an effective receiver uses a frequency dependent dielectric constant that varies with frequency without using the Debye relaxation effect. This can be achieved by adding a dedicated material between the receiver coil and the housing. This setup is illustrated in FIGS. 20a, 20b, 20c.

  This system consists of a transmitter coil array housing 2001 in which a transmitter coil 2002 is disposed. Each transmitter coil optionally comprises a magnetic core that improves the magnetic flux characteristics of the transmitter coil. The magnetic core can either be individual for each magnetic core or a common magnetic backplane can be implemented.

  In another example of identifying a valid receiver, the receiver winding 2005 is embedded in and electrically connected to a material 2006 having a predetermined dielectric constant. Thus, the receiver winding operates as an inductance / capacitance network. An equivalent electrical circuit is shown in FIG. 20b.

  For illustration purposes only, three transmitter coils and one receiver coil are shown in the figure. However, more than three transmitter coils and / or receiver coils are contemplated. The drawing is rotated counterclockwise.

  The transmitter coil 2002 and the capacitance measurement units 2013 and 2014 are arranged in the transmitter housing 2001. Receiver coil 2005 is disposed within receiver housing 2003. Each winding turn Lw has a predetermined capacitance Cw that determines a specific resonant frequency as a whole. For the receiver coil location, the measured capacitance between the first and second windings is the capacitance measured between the second and third windings. Is different. Only the capacitance measurement between the windings is part of this embodiment. Changing the measurement frequency indicates the frequency dependence of the measured capacitance. Since the impedance varies with frequency, the presence of the receiver can be distinguished from the presence of other items located on the transmitter array. Specific frequency dependence can be used as a key. If different types of receivers (eg different power demands / characteristics) are placed on the transmitter array, they can be individually identified and addressed with respect to power demand or charging demand. In this embodiment, the capacitance measurement frequency and the frequency at which the frequency dependency of the receiver coil changes are different from the operating frequency when power is supplied to the receiver coil.

  The capacitance added to the receiver coil can be less than the series capacitance that can be used in addition to the receiver coil. Therefore, the embedded capacitance does not affect the power transfer characteristics.

  In the above summary, the unit for measuring the capacitance / frequency dependence of the device is connected to the winding end of the transmitter coil. Alternatively, the measurement unit can be connected to each central tap of the transmitter coil. This summary is shown in FIG. 20c.

  FIG. 22 depicts a low standby power architecture 2200. In this architecture 2200, the bias power source 2204, which often affects standby power loss, is turned off using the AC switch 2202 when the transmitter is in a sleep state (ie, standby mode). During this state, only controller 2208 and detection circuit 2210 are powered from the energy stored in capacitor 2209. This subsystem is isolated from the rest of the transmitter electronics using switch 2205 to ensure that only these two components are powered from storage capacitor 2209. A small program running on the controller 2208 periodically checks to see if the supply voltage, eg, the voltage on the capacitor 2209 is still high enough. If this is not the case, both switches 2202, 2205 are closed for a short period of time so as to recharge the storage capacitor 2209. In this way, controller 2208 and detection circuit 2210 are always powered, while the rest of the system is in a low power sleep mode most of the time.

  Using normally closed switches 2202, 2205 alleviates the cold start problem, i.e., when the transmitter is first connected to the distribution line, this should cause the system to enter sleep mode. That is, it is fully powered until the controller 2208 determines that no device is present on the transmitter surface.

  System 200 is woken up when a stimulus 2212 detected by detection electronics 2210 that sends a signal to controller 2208 indicating that system 2200 should wake up is applied to the transmitter. The controller 2208 in this case closes both switches 2202, 2205 to power the complete transmitter electronics.

  The applied stimulus 2212 should indicate the placement of the receiver device on the transmitter surface in a wireless power transmitter. Stimulus detection based on volume detection has been described in previous examples.

  FIG. 23 schematically shows a flow diagram of a method according to one aspect of the invention. The method is performed by a wireless power transmitter that detects a receiver device. The wireless power transmitter includes a first electrode of a capacitor and a second electrode of the capacitor. The wireless power transmitter further includes a detection circuit connected to one of the electrodes. The method includes a step 2302 of applying a voltage to the other of the electrodes, and a step 2304 of detecting a capacitance change between the capacitors formed by the electrode by a detection circuit. The detected capacitance change can be regarded as an event related to the receiver device. The method may further comprise a step 2306 of waking up a transmitter device that is the wireless power transmitter so that the transmitter device powers or communicates with the receiver device. Activated to be able to. In other words, the transmitter is activated.

  FIG. 23 may also be used to illustrate a method 2300 according to the third aspect of the invention. Method 2300 is a method of detecting a receiver by a transmitter. The transmitter is intended to inductively transmit power to the receiver. The transmitter has a first transmission coil as an electrode. The electrode forms a capacitor with ground or the receiver. In a first step 2302 of the method 2300, a voltage is applied to the electrodes. In a second step 2304 of method 2300, a change in capacitance of the capacitor is detected.

  It should be noted that the embodiments described above are described rather than limiting the invention, and that many alternative embodiments can be designed by those skilled in the art without departing from the scope of the appended claims.

  In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” preceding an element does not exclude the presence of a plurality of such elements. The present invention can be implemented using hardware having a plurality of separate elements and using a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims (13)

In a method of detecting a receiver by a transmitter, the transmitter is intended to inductively transmit power to the receiver, the transmitter comprising: a first transmission coil as a first electrode; A second electrode, wherein the first electrode and the second electrode form a capacitor, and the method comprises:
Applying a voltage to any one of the electrodes;
Detecting a change in capacitance of the capacitor;
Having a method.   The method of claim 1, wherein the transmitter has a second transmitter coil, and the second transmitter coil is the second electrode.   The method of claim 1, wherein the second electrode of the capacitor is located in the center of the first transmitter coil.   The winding of the first transmission coil has an inner part of the winding and an outer part of the winding, the inner part of the winding is the second electrode, and the outer part of the winding The method of claim 1, wherein is the second electrode. The transmitter comprises a plurality of capacitors formed by a plurality of pairs of the first electrode and the second electrode, the method comprising:
Detecting a change in capacitance of each of the plurality of capacitors;
Determining the position of the receiver in dependence on detecting a capacitance change of one of the plurality of capacitors;
The method according to claim 1, comprising: The detected capacitance change indicates that the receiver is near the transmitter, the method comprising:
Activating the transmitter such that the transmitter begins to communicate with the receiver or begins to transmit power to the receiver;
The method according to claim 1, comprising: The detected capacitance change indicates that the receiver is near the transmitter, the method comprising:
Activating the transmitter such that the transmitter begins to communicate with the receiver or begins to transmit power to the receiver;
The method of claim 5, comprising: In a transmitter detecting a receiver, the transmitter is intended to inductively transmit power to the receiver, the transmitter comprising:
A first transmission coil and a second electrode as a first electrode forming a capacitor;
A first unit for applying a voltage to any one of the electrodes;
A detection circuit connected to any one of the electrodes of the capacitor and detecting a capacitance change of the capacitor;
Having a transmitter.   The transmitter according to claim 8, wherein the transmitter has a second transmission coil, and the second transmission coil is the second electrode.   The transmitter of claim 8, wherein the second electrode is located in the center of the first transmission coil.   The detected capacitance change indicates that the receiver is near the transmitter, and the transmitter begins to communicate with the receiver or transmit power to the receiver. 11. A transmitter as claimed in any one of claims 8 to 10, comprising a second unit for activating the transmitter. In a method for detecting a receiver by a transmitter, the transmitter is intended to inductively transmit power to the receiver, the transmitter having a first transmission coil as an electrode, The method is
Applying a voltage to the electrode;
Detecting a capacitance change of a capacitor formed by the electrode and ground or formed by the electrode and the receiver;
Having a method. In a transmitter detecting a receiver, the transmitter is intended to inductively transmit power to the receiver, the transmitter comprising:
A first transmission coil as a first electrode;
A first unit for applying a voltage to the electrode;
A detection circuit connected to the electrode and detecting a capacitance change of a capacitor formed by the electrode and ground or formed by the electrode and the receiver;
Having a transmitter.

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