Wireless Power Transfer

Abstract

The power transmitter 101 provides power to the power receiver 105 via an electromagnetic signal generated by an output resonant circuit, which comprises a transmitting coil 103 and at least one capacitor 303. A measuring device 307 measures a load parameter indicative of a load on the transmitting coil 103 during a time interval in which power transmission is inactive. A determiner 309 determines a maximum electromagnetic signal level of the electromagnetic signal during power transmission according to the load parameter. A driver 301 generates a drive signal for the output resonant circuit 103 to generate the electromagnetic signal. The driver 301 is configured to limit the drive signal such that the electromagnetic field signal does not exceed the maximum electromagnetic signal level during power transmission.

Description

[Technical field]

[0001] The present invention relates to wireless power transfer systems, particularly but not exclusively to the operation of a power transmitter to provide inductive power transfer to high power devices such as kitchen appliances. [Background technology]

[0002] Most electronic products today require a dedicated electrical contact to receive power from an external power source. However, this tends to be impractical, requiring the user to physically insert a connector or otherwise establish physical electrical contact. Power requirements also typically vary widely, and since most devices now have their own dedicated power source, a typical user will have many different power sources, each dedicated to a specific device. Using an internal battery eliminates the need for a wired connection to a power source during use, but this is only a partial solution, as the battery must be charged (or replaced). Using a battery can significantly increase the weight, and potentially the cost and size, of the device.

[0003] To provide a significantly improved user experience, it has been proposed to use wireless power sources in which power is inductively transferred from a transmitting inductor in a transmitting device to a receiving coil in an individual device.

[0004] Power transmission by magnetic induction is a well-known concept and is mainly applied to transformers with tight coupling between the primary transmitting inductor / coil and the secondary receiving coil. By splitting the primary transmitting coil and the secondary receiving coil between the two devices, wireless power transfer between them becomes possible based on the principle of loosely coupled transformers.

[0005] Such a configuration allows for wireless power transfer to the device without the need for establishing wires or physical electrical connections. In fact, this allows a device to be charged or powered externally by simply placing the device next to or on the transmitting coil. For example, the transmitting device may be configured with a horizontal surface on which the device is powered by simply placing it.

[0006] Moreover, such wireless power transfer configurations are advantageously designed to allow the power transmitting device to be used with a variety of power receiving devices. In particular, a wireless power transfer approach known as the Qi specification has been defined and is currently being further developed. This approach allows a power transmitting device that meets the Qi specification to be used with a power receiving device that also meets the Qi specification, without both devices having to be made by the same manufacturer or proprietary to each other. The Qi standard also includes features for adapting operation to a particular power receiving device (e.g., depending on a particular power drain).

[0007] The Qi specification has been developed by the Wireless Power Consortium, further details of which can be found, for example, on their website at http: / / www.wirelesspowerconsortium.com / index.html, where, inter alia, the defined specification documents can be found.

[0008] The Wireless Power Consortium is developing the Ki specification (also known as the Cordless Kitchen Specification) which is based on the Qi specification and aims to provide safe, reliable and efficient wireless power transfer to kitchen appliances. Ki will support much higher power levels up to 2.2KW.

[0009] A potential problem with wireless power transfer is the unintentional transfer of power to, for example, a metal object that happens to be in the vicinity of the transmitter. For example, if a foreign object, such as a coin, key, or ring, is placed on the platform of the transmitter that is configured to receive the receiver, the magnetic flux generated by the transmitting coil will induce eddy currents in the metal object, causing the object to heat up. The heat increase can be very noticeable and very inconvenient.

[0010] To reduce the risk of such situations occurring, it has been proposed to introduce foreign object detection, where the transmitter can detect the presence of a foreign object and reduce the transmitted power and / or generate a user alert when a foreign object is detected. For example, the Qi system includes functionality for detecting foreign objects and for reducing power when a foreign object is detected. Specifically, Section 11 of the Qi specification version 1.2.1 describes various methods for detecting foreign objects.

[0011] One method for detecting such foreign objects is disclosed in WO2015018868A1. Another example is provided in WO2012127335, which discloses an approach based on determining unknown power loss. In this approach, both the receiver and the transmitter measure the power, and the receiver transfers the measured received power to the transmitter. If the transmitter detects a large difference between the power sent by the transmitter and the power received by the receiver, an undesired foreign object may be present, and power transmission is discontinued for safety reasons. This power loss based approach requires synchronized and accurate power measurements to be performed by the transmitter and the receiver.

[0012] For example, in the Qi power transfer standard, the receiver estimates the received power, e.g., by measuring the rectified voltage and current, multiplying them, and adding an estimate of the receiver's internal power losses (e.g., losses in the rectifier, the receiver coil, metal parts that are part of the receiver, etc.) The receiver reports the determined received power to the transmitter at a minimum frequency, e.g., every 4 seconds.

[0013] The transmitter estimates the transmitted power by measuring the DC input voltage and current of the inverter, multiplying them, and correcting the result by subtracting an estimate of the transmitter's internal power losses, such as the estimated power losses in the inverter, the primary coil, and metal components that are part of the transmitter.

[0014] The transmitter can estimate the power loss by subtracting the reported received power from the transmitted power, and if this difference exceeds a threshold, the transmitter assumes that too much power is being dissipated in the foreign object and subsequently terminates power transmission.

[0015] Alternatively, it has been proposed to measure the quality or Q-factor of the resonant circuit formed by the primary coil and the corresponding capacitance and resistance: a decrease in the measured Q-factor indicates the presence of a foreign object.

[0016] In some systems, the initialization of power transfer is contingent on foreign object detection being performed successfully, such that foreign object detection is deemed not present. However, if the test indicates that a foreign object is present, the transmitter will not initialize power transfer. For such operation, a Q-factor based test is often advantageous.

[0017] The performance of foreign object detection depends on the particular operating conditions present when the test is actually performed. Furthermore, foreign object detection is typically a very sensitive test, where it is desirable to detect relatively small changes caused by the presence of a foreign object in an environment where the operating conditions and circumstances under which the test is performed may vary widely.

[0018] Thus, foreign object detection tends to be suboptimal and the test is prone to false positives (detecting a foreign object when one is not present) or false negatives (not detecting a foreign object when one is present), which can lead to undesirable situations, particularly where no power transfer occurs even when no foreign object is present.

[0019] Accordingly, improvements in power transfer operation would be advantageous, particularly techniques that allow for increased flexibility, reduced cost, reduced complexity, improved operation, more accurate power transfer operation, more flexible power transfer, improved suitability for the transfer of higher power levels, and / or improved performance. Summary of the Invention [Problem to be solved by the invention]

[0020] SUMMARY OF THE DISCLOSURE Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination. [Means for solving the problem]

[0021] According to one aspect of the present invention, there is provided a power transmitter for wirelessly providing power to a power receiver via an electromagnetic signal, the power transmitter comprising: an output resonant circuit having a transmitting coil and at least one capacitor; a driver configured to generate a drive signal for the output resonant circuit to generate the electromagnetic signal; a meter configured to measure a load parameter, the load parameter indicative of a load on the transmitting coil during a time interval in which power transmission is inactive; and a determiner configured to determine a maximum electromagnetic signal level of the electromagnetic signal during power transmission in response to the load parameter, wherein the driver is configured to limit the drive signal such that the electromagnetic field signal does not exceed the maximum electromagnetic signal level during power transmission.

[0022] The present invention provides improved and / or easier performance, operation, and / or implementation of wireless power transfer systems. This approach provides an improved approach to accommodate foreign objects that may be present. This approach allows for a way in which power transfer may continue even in the presence of a possible foreign object while ensuring safe operation and simultaneously preventing unacceptable heating of the foreign object in some scenarios.

[0023] In many embodiments, the determiner is configured to determine at least two different non-zero values ​​of the maximum electromagnetic signal level for different values ​​of the load parameter, hi many embodiments, the maximum electromagnetic signal level is a monotonic function of the load parameter value.

[0024] The load parameter indicates the total loading of the transmitting coil. The load parameter indicates the loading of the transmitting coil by any object. The load parameter indicates the loading of the transmitting coil by any foreign object. A foreign object is an object other than a receiver or transmitter. The load parameter indicates the total load / impedance presented to the drive signal by the output resonant circuit / transmitting coil. The load / impedance reflects the total magnetic coupling / load of the electromagnetic signal.

[0025] The loading parameter is a measure of the (total) loading of the transmitting coil. The loading parameter is an indicator / measure of the equivalent series resistance of the transmitting coil. The loading parameter is an indicator / measure of the contribution to the equivalent series resistance of the transmitting coil by external materials such as receivers and foreign objects. The loading parameter is an indicator / measure of the (total) power extracted from the electromagnetic signal generated by the transmitting coil.

[0026] In some embodiments, the driver includes functionality for setting a power level of the drive signal in response to a power error / control message received from the receiver, and the power level setting is limited such that the electromagnetic field signal does not exceed a maximum electromagnetic signal level during power transfer.

[0027] The electromagnetic signal is the electromagnetic field generated by the sending coil when a drive signal is applied to the output resonant circuit. The load of the sending coil is the load of the electromagnetic signal / field generated by the sending coil when a drive signal is applied to the output resonant circuit.

[0028] In many embodiments, the time interval during which power transfer is inactive is the time interval before power transfer / power transfer phase begins. The time interval is the time interval during the power transfer initialization phase. In some embodiments, the time interval during which power transfer is inactive is the time interval of the power transfer phase during which power transfer is suspended.

[0029] In many embodiments, the driver is configured to limit the drive signal during a power transfer time interval or power transfer phase that follows a time interval during which power transfer is inactive.

[0030] In some embodiments, the transmitting coil is one of multiple transmitting coils that generate an electromagnetic signal for power transmission to a receiver, in which case the loading parameter is a parameter indicative of the loading of the electromagnetic field generated by the combination of transmitting coils (and thus the loading of the transmitting coils as well).

[0031] According to an optional feature of the invention, the load parameters include a coupling coefficient parameter indicative of a coupling coefficient between the transmitting coil and a receiving coil of the receiver.

[0032] This allows for particularly advantageous operation and / or performance in many embodiments.

[0033] According to an optional feature of the invention, the load parameters include a quality factor parameter indicative of a quality factor of the output resonant circuit.

[0034] This allows for particularly advantageous operation and / or performance in many embodiments.

[0035] In some embodiments, the load parameters include an equivalent series resistance parameter indicative of an equivalent series resistance of the transmitting coil.

[0036] In some embodiments, the loading parameter includes an equivalent series resistance parameter indicative of a contribution to the equivalent series resistance of the sending coil caused by a material that loads the electromagnetic signal.

[0037] The term determined / processed equivalent series resistance includes contributions to the determined / processed equivalent series resistance, specifically contributions caused by external materials such as the receiver and foreign objects.

[0038] The equivalent series resistance includes contributions from loading of the electromagnetic signal by (any) material in which the electromagnetic signal induces a current, such as the conductive materials of the transmitter and receiver or indeed the conductive materials of a foreign object.

[0039] According to an optional feature of the invention, the load parameter is a self-inductance parameter indicative of a self-inductance of the sending coil.

[0040] This allows for particularly advantageous operation and / or performance in many embodiments.

[0041] According to an optional feature of the invention, the determiner is configured to determine the maximum electromagnetic signal level in response to a measured value of the load parameter relative to a value of the load parameter of a reference configuration of the receiver.

[0042] This allows for particularly advantageous operation and / or performance in many embodiments.

[0043] According to an optional feature of the invention, the driver is configured to determine a maximum sending coil current corresponding to a maximum electromagnetic signal level, and to control the drive signal such that the sending coil current is maintained below the maximum sending coil current.

[0044] This allows for particularly advantageous operation and / or performance in many embodiments: limiting the maximum sending coil current often provides improved control and limitation of the electromagnetic signal / field generated by the sending coil, and thus more direct control of the maximum power dissipated in foreign objects that may be present.

[0045] According to an optional feature of the invention, the load parameters include a measured equivalent series resistance of the transmitting coil, and the driver is configured to determine a maximum transmitting coil current as a function of the measured equivalent series resistance relative to a minimum expected equivalent series resistance of the receiver and transmitter configuration.

[0046] This provides particularly advantageous operation and / or performance in many embodiments.

[0047] According to an optional feature of the invention, the measured equivalent series resistance represents the total external loading of the electromagnetic signal, and the minimum predicted equivalent series resistance represents the loading of the electromagnetic signal due to materials of the receiver only.

[0048] In some embodiments, the load parameters include a contribution to the measured equivalent series resistance of the sending coil caused by materials of the receiver, and the driver is configured to determine a maximum sending coil current in response to the measured contribution to the equivalent series resistance caused by foreign materials, which is the contribution of the receiver and transmitter configuration to a minimum expected contribution equivalent series resistance caused only by the receiver materials and the foreign object.

[0049] According to an optional feature of the invention, the power transmitter further comprises a receiver configured to receive from the power receiver an indication of the minimum expected contribution to the equivalent series resistance.

[0050] According to an optional feature of the invention, the minimum expected equivalent series resistance depends on a coupling coefficient, and the determiner is configured to determine a coupling coefficient between the transmitting coil and a receiving coil of the receiver, and to determine the minimum expected equivalent series resistance as a function of the coupling coefficient.

[0051] This provides particularly advantageous operation and / or performance in many embodiments.

[0052] According to an optional feature of the invention, the minimum expected equivalent series resistance depends on the self-inductance, and the determiner is configured to determine a self-inductance parameter indicative of a self-inductance of the sending coil and to determine the minimum expected equivalent series resistance as a function of the self-inductance.

[0053] This provides particularly advantageous operation and / or performance in many embodiments.

[0054] In some embodiments, the minimum expected equivalent series resistance depends on the resonant frequency, and the determiner is configured to determine a resonant frequency of the output resonant circuit and to determine the minimum expected equivalent series resistance as a function of the resonant frequency.

[0055] According to an optional feature of the invention, the transmitter comprises a receiver configured to receive an indication of a reference minimum expected equivalent series resistance from the receiver, the reference minimum expected equivalent series resistance being a minimum equivalent series resistance of a transmitting coil of the reference transmitter coupled to a receiving coil of the receiver, and the determiner configured to determine the minimum expected equivalent series resistance in response to the reference minimum expected equivalent series resistance.

[0056] This allows for particularly advantageous operation and / or performance in many embodiments.

[0057] According to an optional feature of the invention, the determiner is configured to determine the minimum expected equivalent series resistance in response to compensating the reference minimum expected equivalent series resistance for a difference between the series resistance of the transmitting coil and a reference series resistance of a transmitting coil of a reference transmitter.

[0058] This allows for particularly advantageous operation and / or performance in many embodiments.

[0059] According to an optional feature of the invention, the determiner is configured to determine the minimum expected equivalent series resistance as a function of the reference minimum expected equivalent series resistance and a self-inductance of the sending coil relative to a self-inductance of the sending coil of a reference transmitter.

[0060] This allows for particularly advantageous operation and / or performance in many embodiments.

[0061] In some embodiments, the determiner is configured to determine the minimum expected equivalent series resistance as a function of a reference minimum expected equivalent series resistance and a resonant frequency of the output resonant circuit relative to a resonant frequency of the output resonant circuit of the reference transmitter, the resonant frequency being an angular resonant frequency.

[0062] In some embodiments, the determiner is configured to determine the minimum expected equivalent series resistance in dependence on temperature and / or the operating frequency of the drive signal. In particular, the determiner is configured to determine the minimum expected equivalent series resistance in dependence on the operating frequency of the drive signal relative to the resonant frequency of the output resonant frequency.

[0063] According to an optional feature of the invention, the determiner is configured to determine a contribution to the equivalent series resistance of the sending coil due to a material of the receiver as a function of the contribution to the equivalent series resistance of the reference sending coil due to a material of the receiver and a frequency of the drive signal relative to a reference frequency of the reference sending coil.

[0064] According to an optional feature of the invention, the determiner is configured to determine the measured equivalent series resistance as a function of a decay rate of self-oscillation of the output resonant circuit.

[0065] This allows for particularly advantageous operation and / or performance in many embodiments.

[0066] According to an optional feature of the invention, the determiner is configured to determine a contribution to the equivalent series resistance of the sending coil due to a material of the receiver as a function of the contribution to the equivalent series resistance of the reference sending coil due to a material of the receiver and a frequency of the drive signal relative to a reference frequency of the reference sending coil.

[0067] According to an optional feature of the invention, the determiner is configured to determine the measured equivalent series resistance in response to a measured resonant frequency of the resonant circuit.

[0068] This allows for particularly advantageous operation and / or performance in many embodiments.

[0069] According to an optional feature of the invention, the determiner is configured to determine the measured equivalent series resistance in response to the measured quality factor of the resonant circuit.

[0070] This allows for particularly advantageous operation and / or performance in many embodiments.

[0071] According to one aspect of the present invention, there is provided a method of operation for a power transmitter that wirelessly provides power to a power receiver via an electromagnetic signal, the power transmitter comprising an output resonant circuit comprising a transmitting coil and at least one capacitor, the method comprising the steps of generating a drive signal for the output resonant circuit to generate an electromagnetic signal, measuring a load parameter, the load parameter indicative of a load on the transmitting coil during a time interval in which power transmission is inactive, determining a maximum electromagnetic signal level of the electromagnetic signal during power transmission in response to the load parameter, and limiting the drive signal such that the electromagnetic field signal does not exceed the maximum electromagnetic signal level during power transmission.

[0072] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0073] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which: [Brief description of the drawings]

[0074] [Figure 1] FIG. 2 illustrates an example of elements of a power transfer system according to some embodiments of the present invention. [Diagram 2] 2 is a diagram illustrating an example of an equivalent circuit of the power transmission system of FIG. 1. [Diagram 3] FIG. 2 illustrates an example of elements of a power transmitter according to some embodiments of the present invention. [Figure 4]FIG. 1 illustrates an example of a half-bridge inverter for a power transmitter. [Diagram 5] FIG. 1 illustrates an example of a full-bridge inverter for a power transmitter. [Figure 6] FIG. 2 illustrates an example of elements of a power receiver according to some embodiments of the present invention. [Figure 7] FIG. 2 is a diagram illustrating an example of a relative arrangement of a power transmitter and a power receiver. [Figure 8] FIG. 2 is a diagram illustrating an example of a relative arrangement of a power transmitter and a power receiver. [Figure 9] 1A and 1B are diagrams illustrating an example of the relationship between the quality factor and the coupling factor in different relative arrangements of a power transmitter and a power receiver. [Figure 10] 1A and 1B are diagrams illustrating an example of the relationship between the quality factor and the coupling factor in different relative arrangements of a power transmitter and a power receiver. [Figure 11] FIG. 2 is a diagram showing an example of an equivalent electric circuit of a power transmitter and a reference power transmitter. [Figure 12] FIG. 13 is a diagram illustrating an example of damping of self-oscillation of a resonant circuit of a power transmitter. [Figure 13] 1A and 1B are diagrams illustrating an example of the relationship between the equivalent series resistance and the coupling coefficient in different relative arrangements of a power transmitter and a power receiver. [Figure 14] 1A to 1C are diagrams illustrating an example of the relationship between equivalent series resistance and inductance in different relative arrangements of a power transmitter and a power receiver. [Figure 15] 1A to 1C are diagrams illustrating an example of the relationship between the equivalent series resistance and the inductance in different relative arrangements of a power transmitter and a power receiver. [Figure 16] 1A to 1C are diagrams illustrating an example of the relationship between equivalent series resistance and inductance in different relative arrangements of a power transmitter and a power receiver. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075] The following description focuses on embodiments of the invention applicable to wireless power transfer systems utilizing power transfer techniques as known from the Qi or Ki specifications, however, it will be understood that the invention is not limited to this application and applies to many other wireless power transfer systems.

[0076] 1 illustrates an example of a power transfer system according to some embodiments of the present invention. The power transfer system comprises a power transmitter 101 including (or coupled to) a transmitting coil / inductor 103. The system further comprises a power receiver 105 including (or coupled to) a receiving coil / inductor 107.

[0077] The system provides an inductive electromagnetic signal that inductively transfers power from the power transmitter 101 to the power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal that is propagated as a magnetic flux by a power transmitting coil or inductor 103. The electromagnetic signal is a signal generated by the power transmitting coil 103 in response to a drive signal being provided to the power transmitting coil 103. During power transfer, the electromagnetic signal transfers power to the power receiver 105 (specifically the power receiving coil 107). The electromagnetic signal is hereinafter referred to as a power transfer signal.

[0078] The power transmission signal typically has a frequency in the range of about 20 kHz to about 500 kHz, often typically in the range of 95 kHz to 205 kHz for Qi-compatible systems and typically in the range of 20 kHz to 80 kHz for Ki-compatible systems. The transmitting coil 103 and the receiving coil 107 are loosely coupled, and thus the receiving coil 107 picks up (at least a portion of) the power transmission signal from the transmitter 101. Thus, power is transmitted from the transmitter 101 to the receiver 105 via wireless inductive coupling from the transmitting coil 103 to the receiving coil 107. It will be understood that the term power transmission signal is used primarily to refer to the inductive signal / magnetic field (magnetic flux signal) between the transmitting coil 103 and the receiving coil 107, but is also considered to refer to and is used to refer to an electrical signal provided to the transmitting coil 103 or picked up by the receiving coil 107.

[0079] In this example, the power receiver 105 is specifically a power receiver that receives power via a power receiving coil 107. However, in other embodiments, the power receiver 105 includes a metallic element, such as a metal heating element, in which case the power transmission signal directly induces eddy currents that result in direct heating of the metallic element.

[0080] The system is configured to transmit significant power levels, and specifically, in many embodiments, the transmitter supports power levels of 500 mW, 1 W, 5 W, 50 W, 100 W, or greater than 500 W. For example, for Qi-enabled applications, power transmission is typically in the range of 1-5 W power for low power applications (basic power profile), up to 15 W for Qi specification version 1.2, up to 100 W for high power applications such as power tools, laptops, drones, and robots, and greater than 100 W, up to greater than 2000 W for very high power applications such as, for example, Ki kitchen applications.

[0081] The operation of the power transmitter 101 and the power receiver 105 is described below with particular reference to an embodiment that conforms generally to the Qi or Ki specifications (except for modifications and extensions described (or resulting from) herein) or is suitable for the high-power kitchen specification being developed by the Wireless Power Consortium. In particular, the power transmitter 101 and the power receiver 105 conform to or are substantially compatible with elements of the Qi specification version 1.0, 1.1, or 1.2 (except for modifications and extensions described (or resulting from) herein).

[0082] Many wireless power transfer systems, especially high power systems such as Ki, utilize resonant power transfer, where the transmit coil 103 is part of a resonant circuit and typically the receive coil 107 is also part of the resonant circuit. In many embodiments, the resonant circuit is a series resonant circuit, whereby the transmit coil 103 and the receive coil 107 are coupled in series with corresponding resonant capacitors. The use of a resonant circuit tends to provide more efficient power transfer.

[0083] In most power transfer systems, before power transfer begins, a communication channel between the power transmitter 101 and the power receiver 105 is established. Once communication is set up and identification of the two devices is achieved, the power transmitter 101 begins transmitting power to the power receiver 105.

[0084] FIG. 2 shows an example of an electrical equivalent diagram of the power transfer function of the transmitter 101 and the receiver 105. In a given system, there are a variety of transmitters and receivers, which have significantly different characteristics and parameters. For example, the coil sizes, induction values, and loads vary significantly. Thus, the system parameters specifically depicted in FIG. 2 will in fact vary significantly for various devices, mechanical structures, configurations, etc. In particular, the configuration of the receiver, and therefore the relative positions of the receiver coil 107 and the transmitter coil 103, greatly affect the coupling between the coils, i.e., the primary (transmitter side) inductor Lp and the secondary (transmitter side) inductor Ls, and thus greatly change the behavior of the system.

[0085] Furthermore, the powered device has several different operating modes, for example operating at different voltage levels (5V, 12V, 20V) to supply power to a load.

[0086] Typically, wireless power transfer systems employ a power control loop to steer the system to a suitable operating point. This power control loop modifies the amount of power sent from the transmitter to the receiver. The received power (or voltage, current) is measured and an error signal can be generated along with a set power value. The appliance sends this error signal to the transmitter's power control function to reduce, ideally to zero, the static error.

[0087] However, the performance and operation of the system is highly dependent on the combination and arrangement of existing transmitters and receivers, and therefore the appropriate operating point varies greatly, including the conditions during start-up / initialization of power transfer.

[0088] FIG. 3 shows elements of the transmitter 101 of FIG. 1 in greater detail.

[0089] The power transmitter 101 includes a driver 301 capable of generating a drive signal that is supplied to the power transmitting coil 103, which generates an electromagnetic power transmission signal, thereby realizing power transmission to the power receiver 105. The power transmitting coil 103 is part of an output resonant circuit comprising the power transmitting coil 103 and a capacitor 303. In this example, the output resonant circuit is a series resonant circuit, although it will be appreciated that in other embodiments, the output resonant circuit is a parallel resonant circuit. It will be appreciated that any suitable resonant circuit may be used, including a resonant circuit including multiple inductors and / or capacitors.

[0090] The driver 301 generates the current and voltage that are supplied to the output resonant circuit and thus the transmitting coil 103. The driver 301 is typically a drive circuit in the form of an inverter that generates an AC signal from a DC voltage. The output of the driver 301 is typically a switch bridge that generates the drive signal by appropriately switching the switches of the switch bridge. Figure 4 shows a half-bridge switched bridge / inverter. The switches S1 and S2 are controlled such that they are never closed at the same time. Alternately, S1 is closed while S2 is open and S2 is closed while S1 is open. The switches are opened and closed at a desired frequency, thereby generating an AC signal at the output. Typically, the output of the inverter is connected to the transmitting inductor via a resonant capacitor. Figure 5 shows a full-bridge switched bridge / inverter. The switches S1 and S2 are controlled such that they are never closed at the same time. The switches S3 and S4 are controlled such that they are never closed at the same time. Alternately, switches S1 and S4 are closed while switches S2 and S3 are open, then S2 and S3 are closed while switches S1 and S4 are open, thereby producing a square wave signal at the output. The switches are opened and closed at the desired frequency.

[0091] The power transmitter 101 further comprises a power transmission controller 305 configured to control the operation of the power transmitter 101 according to a desired operating principle. In particular, the power transmitter 101 includes many of the functions necessary to perform power control in compliance with the Qi or Ki specifications.

[0092] The power transmission controller 305 is specifically configured to control the generation of the drive signal by the driver 301, and may in particular control the power level of the drive signal and the level of the generated power transmission signal accordingly. The power transmission controller 305 includes a power loop controller that controls the power level of the power transmission signal in response to receiving a power control message from the power receiver 105 during a power transfer phase.

[0093] The power transmission controller 305 further includes functionality for communicating with the power receiver 105. For example, the power transmission controller 305 is configured to transmit data to the power receiver 105 by modulating the power transmission signal and receive data from the power receiver 105 by detecting load modulation of the power transmission signal. It will be understood that in other embodiments, other communication means are used, for example, a separate communication function is implemented, such as NFC communication.

[0094] The use of a resonant circuit including the transmit coil 103 is well known to provide more efficient power transfer in many scenarios, allowing the power transfer to be controlled by the frequency of the drive signal. Furthermore, when having a receiver that also employs a resonant circuit, i.e., the receive coil 107 is part of the resonant circuit, the result is a resonant power transfer, allowing for very efficient power transfer.

[0095] FIG. 6 illustrates some example elements of the power receiver 105.

[0096] The receiving coil 107 is coupled to the receiving controller 601 via a capacitor 603 which forms an input resonant circuit with the receiving coil 107. The power transfer is therefore a resonant power transfer between the resonant circuits.

[0097] The power receiving controller 601 connects the power receiving coil 107 to the load 605, particularly via a switch 607 that can connect and disconnect (or even short) the load 605. The power receiving controller 601 includes a power control path that converts the power extracted by the power receiving coil 107 into a power source suitable for the load 605. In some embodiments, the power receiving controller 601 provides a direct power path that simply connects the input resonant circuit to the switch 607 or the load 605. That is, the power path of the power transmitting controller 303 is implemented simply by two wires. In other embodiments, the power path includes, for example, a rectifier and possibly a smoothing capacitor to provide a DC voltage. In still other embodiments, the power path includes more complex functions, such as, for example, a voltage control circuit, an impedance matching circuit, a current control circuit, etc. It will be appreciated that in some embodiments, the switch 607 is simply present, and that in some embodiments, the load 605 is permanently coupled to the input resonant circuit.

[0098] In addition, the power receiving controller 601 includes various power receiving controller functions necessary to perform a power transfer, particularly functions necessary to perform a power transfer in accordance with the Qi or Ki specifications.

[0099] The power receiving controller 601 further comprises functionality for communicating with the power transmitter 101. For example, the power receiving controller 601 is configured to decode and demodulate data modulated onto the power transmission signal, and to transmit the data to the power transmitter 101 by load modulating the power transmission signal. In some embodiments, a separate communication functionality, such as an NFC communication functionality, is employed.

[0100] In operation, the system is configured to control the drive signal such that the power transmission signal achieves preferred operating parameters / characteristics and the power transmission operates at a preferred operating point, where the power transmitter is configured to control parameters of the drive signal using a power control loop in which the power characteristics of the power transmission signal / drive signal are controlled in response to power control error messages received from the power receiver.

[0101] The receiver periodically, typically frequently, transmits a power control error message to the transmitter. The receiver 105 includes functionality to support such a power control loop, e.g., the receiver controller 601 continuously monitors the power or voltage of the load signal provided to the load and detects whether it is above or below a desired value. The receiver periodically generates a power control error message requesting an increase or decrease in the power level of the power transmission signal and transmits this power control error message to the transmitter.

[0102] When the power transmission controller 305 receives the power control error message from the power receiver, it determines how to modify the drive signal parameters to increase or decrease the power level of the power transmission signal as required. The power transmission controller 305 then controls and adapts the drive signal parameters accordingly.

[0103] Accordingly, a power control loop is employed that controls the power characteristics of the power transfer signal to produce a desired operating point at the receiver. The operation of the power transfer is therefore controlled by the power control loop, and effective operation of this loop is essential to the performance of the system. Initializing or adapting the power control loop to the operating conditions is essential for optimal performance.

[0104] The power transmitter of Figures 1 and 3 provides the capability to adapt the operation of the power transfer system more flexibly than many existing approaches. Specifically, the power transmitter is configured to control the power transfer to dynamically and flexibly adapt to current conditions, such as the possible presence of a foreign object. The power transmitter is configured to perform measurements / estimations of the power transfer signal during time intervals when no power transfer is occurring, such as during initialization of the power transfer, and flexibly limit the generated electromagnetic signal level / field strength based on those measurements.

[0105] The power transmitter 101 specifically includes a measuring device 307 configured to measure a load parameter indicative of the load of the transmitting coil during a time interval in which the power transfer is inactive. The power transfer is inactive in that the power extracted from the power receiver is below a threshold value (e.g., less than 1 mW, 5 mW, 20 mW, 100 mW, 200 mW, 0.5 W, or 1 W). Inactive power transfer means that no power is transferred to the load (605) of the power receiver. The load parameter is indicative of the load of the electromagnetic signal generated by the transmitting coil 103 when supplied by the drive signal. The load parameter is indicative of the load of the electromagnetic field generated (or generated) by the transmitting coil 103. The load parameter is indicative of the load caused by the supply of the drive signal to the transmitting coil 103.

[0106] The load parameter thus reflects the energy or power extracted from the electromagnetic field generated by the transmitting coil 103. This load includes contributions from the receiving coil 107, any foreign objects present, and intimate metals in both the receiver and transmitter, etc. However, in many embodiments, the load parameter is compensated for known effects such as the load provided by the transmitter itself (e.g., due to intimate metals in the transmitter).

[0107] The load parameters therefore indicate in particular the load occurring before the power transfer begins or when no power transfer is taking place, for example during time intervals of a power transfer phase when power is temporarily stopped.

[0108] The load parameter specifically indicates or is a measurement / estimate of the impedance of the transmitting coil / output circuit, specifically the impedance seen by the driver 301 / drive signal. The load is specifically determined as a measurement of the current and / or voltage provided to the output circuit / transmitting coil. The load parameter indicates the loading of the transmitting coil due to objects that impose a load on the electromagnetic signal. The load parameter indicates the loading of the transmitting coil due to objects in which the electromagnetic signal induces a current. The load parameter typically indicates the total / combined loading of the electromagnetic signal. The load parameter is an indication of the loading of the electromagnetic signal due to objects other than the receiving coil. The load parameter in many embodiments indicates the loading due to the presence of any foreign object. A foreign object is any other object other than the receiver.

[0109] The load parameter is a measurement / indication of the equivalent series resistance of the transmit coil.

[0110] The load parameter is a measurement / indication of the contribution of the transmitter to the equivalent series resistance.

[0111] The measuring device 307 is coupled to a determiner 309 that implements circuitry / functionality for determining a maximum electromagnetic signal level of the electromagnetic signal during power transfer as a function of the load parameter. The maximum level of the electromagnetic field during power transfer is determined as a function of the load parameter. It will be understood that the maximum electromagnetic signal level is the level of any parameter indicative of the electromagnetic signal level / field strength. For example, in many embodiments this is represented by a maximum level of a characteristic of the drive signal provided to the sending coil 103. In particular, the determiner 309 determines the maximum electromagnetic signal level as a maximum level or current level of the drive signal. In many embodiments, the determiner 309 determines the maximum electromagnetic signal level as a maximum value of the current flowing through the sending coil 103.

[0112] The determiner 309 is configured to determine the maximum electromagnetic signal level value as a function of the load parameter, typically having different possible values ​​for different values ​​of the load parameter, such that the maximum level has at least two different non-zero values ​​for different values ​​of the load parameter. In many embodiments, the maximum level is a continuous monotonic function of the load parameter. In many embodiments, the determiner 309 is configured to determine the maximum level to have, possibly, 3, 5, 10, or 25 or more different values ​​(for different values ​​of the load parameter). In many embodiments, the maximum level is a one-to-one continuous function of the load parameter, and the maximum level to have, possibly, an infinite number of possible values.

[0113] The determiner 309 is coupled to the driver 301, which is provided with the determined maximum level. The driver 301 is configured to limit the drive signal such that the electromagnetic field signal does not exceed a maximum electromagnetic signal level during power transfer. The driver 301 is configured to generate an electromagnetic signal, a power transfer signal, during power transfer, which varies, for example, depending on the power control loop operation as described above. However, the driver 301 generates and adapts the drive signal subject to not exceeding the maximum level. For example, the maximum level is a maximum current of the drive signal, and the driver 301 is configured to limit the drive signal to not exceed this current.

[0114] Thus, in some embodiments, the driver is configured to vary the electromagnetic signal / power transmission signal in response to a power control error message received from the receiver during a power transfer phase / operation, however, varying the electromagnetic signal / power transmission signal in response to the power control error message is limited by the requirement that a maximum level not be exceeded.

[0115] Thus, rather than using the conventional approach of performing a foreign object detection test and initiating power transfer only if no foreign object is present, the described approach employs a significantly more flexible approach in which electromagnetic levels are limited but tailored to specific scenarios.

[0116] This technique is particularly used to improve adaptation to the presence or absence of foreign objects prior to power transfer.

[0117] The accuracy of conventional foreign object detection methods depends on the alignment of the transmitting coil and the receiving coil. If the coils are not properly aligned, the coupling between the coils is not good and the magnetic field generated by the transmitting coil leaks into the metal parts of the receiving device (so-called affinity metals). The relative position of the transmitting coil with respect to the receiving device, including the metal parts, affects the pre-power foreign object detection measurements at the transmitting coil.

[0118] This may result in, for example, the information about the expected / reference measurements provided by the power receiving device not matching the actual measurements if the coil alignment is different from the alignment applied as a reference.

[0119] If the receiving coil is not properly aligned with the transmitting coil or is further away, it can lead to undesirable situations such as the transmitter not detecting the foreign object. In addition, the transmitter may provide a strong magnetic field to compensate for the weak coupling, which further increases the power loss in the foreign object. Another disadvantageous situation is that the transmitter may erroneously detect the compatible metal as a foreign object and therefore not initiate power transfer.

[0120] 7 and 8 illustrate these issues for several different alignments of the coil for pre-power foreign object detection based on Q-factor measurements. In the example, the receiver 105 includes some intrinsic metal 701 located next to the receiver coil 107. The intrinsic metal adds load to the electromagnetic field generated by the transmitting coil 103.

[0121] If the power transmitter performs foreign object detection by determining the Q-factor of the output resonant circuit with the power transmitter coil 103, the affinitive metal reduces the measured Q-factor. In Q-factor foreign object detection, the Q-factor is determined and a foreign object is considered to be present if it is below a reference threshold. The reference threshold is adapted to take into account that the affinitive metal 701 of the power receiver 105 reduces the Q-factor, for example based on information transmitted from the power receiver to the power transmitter. However, the magnitude of the reduction depends on the relative positioning of the power transmitter and the power receiver and is therefore usually unknown in the current scenario.

[0122] As an example, the situation in Figure 8 corresponds to that in Figure 7, except that the power receiving device is moved to reduce the exposure of the friendly metal 701 (FM) to the magnetic field of the power transmitting coil. This increases the measured Q-factor. Thus, the Q-factor in the absence of a foreign object changes significantly when the alignment between the power receiver and the power transmitter is changed.

[0123] Therefore, it is very difficult to select a suitable reference threshold for detecting foreign objects. If the receiver and transmitter are aligned so that the influence of the affinity metal is minimized, the influence of the foreign object will not cause the Q factor to fall below the threshold. Conversely, if the receiver and transmitter are aligned so that the influence of the affinity metal is maximized, the presence of the affinity metal alone may cause the Q factor to fall below the reference threshold even when no foreign object is present. Thus, the risk of false negatives or false positives is higher than expected.

[0124] However, in the described approach, a load parameter is determined that is used as an indication of the alignment position of the receiver relative to the transmitter and / or is considered an indication to help assess the presence or absence of a foreign object. However, rather than proceeding or preventing power transfer based on whether or not a foreign object is present, the transmitter of FIG 2 subsequently adaptively determines a maximum electromagnetic signal level for power transfer and then proceeds with power transfer provided that the drive signal is limited to not exceed the maximum level.

[0125] Thus, a significantly more flexible approach is achieved that allows power transfer to proceed while still ensuring safe operation.

[0126] In some embodiments, the load parameter is a quality factor parameter indicative of a quality factor of the output resonant circuit. In some embodiments, the load parameter is an equivalent series resistance (ESR) measure of the sending coil 103. The ESR measure is any measure of the equivalent series resistance of the sending coil 103 to the current load of the generated electromagnetic field.

[0127] The Q factor is measured, for example, by a frequency sweep to determine the 3 dB bandwidth and calculate the Q. The ESR is measured, for example, based on the decay rate of the self-oscillation, as will be explained in more detail below.

[0128] It will be appreciated that various techniques for determining the Q factor and / or ESR are known to those skilled in the art and any suitable such technique may be used.

[0129] In some embodiments, the load parameters include or consist of a coupling coefficient parameter. The coupling coefficient is indicative of the coupling between the transmitting coil 103 and the receiving coil 107. A high coupling coefficient indicates that the transmitting coil 103 and the receiving coil 107 are closely aligned, and a low coupling coefficient indicates that the transmitting coil 103 and the receiving coil 107 are not closely aligned. Thus, the coupling coefficient is a good indicator of the relative position / alignment of the transmitting coil 103 and the receiving coil 107, and thus the relative position / alignment of the transmitter 101 and the receiver 105.

[0130] Different embodiments use different approaches to determine the coupling coefficient K. In some embodiments, the transmitter subsequently measures / estimates the coupling coefficient by determining one or more resonant frequencies of the transmitter resonant circuit when loaded by the receiver. The receiver goes into a high-Q mode during such measurements, and the resonant frequency is determined by the transmitter by a frequency sweep of the signal driving the transmitting coil 103. Based on the resonant frequency, a coupling coefficient can be calculated based on the free-running resonant frequencies of the receiver resonant circuit and the transmitter resonant circuit.

[0131] In some embodiments, the coupling coefficient is the ratio between the voltage u2 on the receiving coil 107 and the voltage u1 on the transmitting coil 103 at no load, and the ratio between the self-inductance (L1) of the transmitting coil 103 and the self-inductance (L2) of the receiving coil 107,

number

[0132] The measurements are made by the power receiver 105 and communicated to the power transmitter 101 .

[0133] In some embodiments, measurements of the inductance of the transmitting coil 103 are taken when the receiving coil 107 is open (L1) and when the receiving coil 107 is shorted (L1′). In that case, the coupling coefficient is:

number

[0134] In some embodiments, the measurement of the effective resonant frequency of the output circuit is performed in the condition where the receiving coil 107 is open (f res ) and a state where the power receiving coil 107 is short-circuited (f res This is implemented, for example, by a receiver including a switch function in the receiver coil 107. In that case, the coupling coefficient is

number

[0135] It will be appreciated that other approaches for determining or estimating the coupling coefficient K are used in other embodiments.

[0136] In some embodiments, the load parameter includes or is a self-inductance parameter indicative of the self-inductance of the sending coil. The self-inductance may be, for example,

number

[0137] The capacitance C is known and the angular resonant frequency is measured. For example, a frequency sweep is performed and the frequency ω res =2πf res As another example, the cycle time T between zero crossings during self-excitation of the output resonant frequency is measured, and the angular resonant frequency is

number

[0138] In many embodiments, the self-inductance is a good indicator or estimate of the alignment / position of the receiver relative to the transmitter.

[0139] In some embodiments, the resonant frequency is used as an indication of the position of the receiver relative to the transmitting coil.

[0140] A receiver typically applies ferrite behind its receive coil to curve the magnetic field back towards the receive coil and reduce the magnetic field behind the ferrite, which has the advantages of increasing the self-inductance of the receive coil, increasing the mutual inductance with the transmit coil, and reducing the leakage of the magnetic field into metal parts and components within the receiver.

[0141] Depending on the location of the receiving product and the transmitting coil, the ferrite also affects the magnetic field near the transmitting coil and its self-inductance value. The closer the ferrite in the receiver is to the transmitting coil, the higher the self-inductance and the lower the resonant frequency due to the unchanged capacitance in the transmitter's resonant tank. In practice, this approach therefore provides a particularly efficient operation due to the presence of ferrite in many real receivers.

[0142] The particular parameters used to limit the electromagnetic signal levels and the particular techniques for determining the maximum electromagnetic signal levels will vary from embodiment to embodiment.

[0143] In many embodiments, the maximum electromagnetic signal level depends on the measured value of the load parameter relative to a reference or nominal value of the load parameter.

[0144] The reference or nominal value is received from the receiver and is specifically one or more of the following: Quality (Q) factor ESR Coupling coefficient K - Self-inductance L of the transmitting coil Resonant frequency of the output resonant circuit

[0145] The reference value or nominal value is a value corresponding to a maximum or optimal value of the load parameter. For example, for a coupling coefficient parameter, the reference value is set to 1. For a Q-factor parameter, the reference value is set to, for example, the Q-factor expected when the transmitting coil 103 is unloaded.

[0146] In some embodiments, the reference value is a value corresponding to a reference configuration of the receiver relative to the transmitter, in particular an optimal configuration of the receiver and / or a position that results in a maximum or minimum value of the load parameter.

[0147] For example, the reference value and / or the reference position is the position where: - The most efficient power transmission and lowest power loss are achieved. Coupling between the transmitting coil 103 and the receiving coil 107 is maximized - Stray magnetic fields are minimized · The power loss of the transmitter due to the generation of unused stray signals is minimized. - Minimize interference with other devices Lowest exposure to compatible metals

[0148] In many embodiments, the reference position is considered to be the position that provides the optimum value of the load parameter.

[0149] In some embodiments, the measured load parameter is compared to such a reference parameter indicative of a desired value of the load parameter. A maximum level is then determined as a monotonic function of the difference between the measured value and the reference value. In particular, the closer the measured load parameter value is to the reference value, the higher the maximum level will be. This therefore reflects that the closer the actual load parameter value is to the currently preferred optimal value, the lower the potential losses due to a foreign object. In other words, the closer the value of the load parameter is to the optimal value, the lower the value of the power that may be consumed at a potential foreign object in its presence.

[0150] In some embodiments, the maximum level is determined in response to the measured load parameter value relative to a reference value that represents a least favorable but acceptable value, for example a minimum acceptable Q factor or coupling factor is determined.

[0151] If the load parameter does not meet such minimum acceptable value, no power transfer is performed. However, if the threshold is exceeded, the maximum level depends on the difference between the load parameter and the minimum acceptable threshold. Usually, the maximum level is a monotonic (usually increasing) function of this difference. Thus, the further the actual load parameter value is from the minimum acceptable value, the higher the acceptable signal level will be. This is used, for example, to ensure that even in the presence of a foreign object, the total effect of the signal dissipated in the foreign object is still acceptable.

[0152] It will be appreciated that in many embodiments, both the most preferred and minimum acceptable criteria values ​​are used or indeed one is determined from the other, for example the minimum acceptable criteria value is provided as the most preferred criteria value offset by a predetermined amount.

[0153] The reference load parameter is related to the placement of the receiver device relative to the reference transmitting coil. This is the position of the receiver when the load parameter is at its most favorable value or at its minimum acceptable value. Alternatively, the reference load parameter is determined by taking an average of the load parameter values ​​of multiple receiver positions. The plus or minus deviation from the average then provides additional information to allow the transmitter to determine the most favorable and minimum acceptable load parameters for these positions.

[0154] Thus, rather than simply deciding whether or not to perform a power transfer, the power transmitter limits the signal level of the electromagnetic signal to provide acceptable performance in the presence of the foreign object. This approach provides a flexible approach to handle uncertainty in the causes of deviations from optimal conditions, allowing some power transfer while ensuring that this operation is acceptable in worst-case scenarios.

[0155] In some embodiments the maximum signal level is provided as a power level value.Furthermore, in many embodiments the load parameter is compared to a threshold value and the maximum level is set to a predetermined value for the interval the current value falls.

[0156] For example, in the case of the Q-factor load parameter, the determiner 309 implements, for example, the following rules:

[0157] [Table 1]

[0158] In the case of the K-factor load parameter, the determiner 309 implements, for example, the following rules:

[0159] [Table 2]

[0160] In some embodiments, the determiner 309 is configured to determine a maximum transmitting coil current and the driver 301 is configured to limit the drive signal such that the transmitting coil current does not exceed this value during power transfer. Furthermore, the determination is a continuous function of the load parameters. For example, the maximum transmitting coil current I max is based on the load parameters in the form of the measured coupling coefficient K,

number

[0161] In another example, the maximum transmit coil current I max is calculated based on the load parameters in the form of the measured inductance value L of the transmit coil,

number

[0162] Similar examples can be presented for other load parameters such as resonant frequency, mutual inductance, and equivalent series resistance.

[0163] The maximum level being the maximum sending coil current level / value provides particularly efficient operation in many scenarios and embodiments: the strength of the generated electromagnetic field is directly given by the sending coil current, and therefore the potential power level that can be induced in a foreign object is directly controlled by the sending coil current.

[0164] In some embodiments, the determination of the maximum level, in particular the maximum level of the transmitting coil current, relies on the determination of an equivalent series resistance measurement indicative of the ESR of the transmitting coil 103. The measured / actual ESR is then compared to the minimum expected equivalent series resistance of the receiver and transmitter configuration. This minimum expected ESR is the ESR determined for the transmitter and receiver configuration by measurement.

[0165] For example, during the manufacturing or development phase of the power receiving device and / or the power transmitting device, measurements are performed to determine how the power receiver affects the loading of the magnetic field generated by the transmitting coil of the power transmitter. Typically, such measurements are performed on a standardized / reference power transmitter, and the power receiver stores information based on the measurements that indicates how the power receiver, and in particular the compatible metal of the power receiver, loads the power transmitter. The power receiver then communicates this data during use to the power transmitter, which takes this data into account when performing foreign object detection. Such information is also used to determine the maximum transmitting coil current.

[0166] In some cases, the measurements aim to determine the minimum level of loading that the receiver presents to the (reference) transmitter, which reflects the minimum impact that compatible metals etc. have on the power transmission signal at various locations. The transmitter then uses this value as the best-case scenario and assumes that all other unexplained power losses are due to foreign objects. Thus, if the measured loading differs significantly from the receiver's minimum loading, the transmitter determines that a foreign object is (potentially) present.

[0167] In some embodiments, the transmitter of FIG. 2 determines an indication of the minimum expected ESR. This determination is based on a communication received from the receiver, for example a communication indicating the minimum load of the receiver relative to a nominal or reference transmitter. A determiner 309 compares the measured ESR to the minimum expected ESR and determines a maximum transmitting coil current based on the comparison. In many embodiments, the maximum transmitting coil current is a monotonically decreasing function of the difference between the measured ESR and the minimum expected ESR.

[0168] For example, in many embodiments, the maximum transmitting coil current is

number

[0169] This formula takes into account different positions of the receiver relative to the transmitter and assumes that the values ​​are accurate measurements of the current conditions. The measurement uncertainty is, for example, given the following formula for the maximum transmit coil current:

number

[0170] Such an approach allows for efficient operation where power transfer can be adapted to reflect the uncertainty of whether a foreign object is present. In many scenarios, such an approach allows for power transfer that would otherwise not be performed due to the possibility that a foreign object is present. This is achieved while ensuring safe operation even in the presence of a foreign object.

[0171] In many embodiments, a more refined approach is used to determine the tolerance, specifically based on a location indicator of the receiver relative to the transmitter. Thus, rather than considering the minimum possible ESR for all possible locations, the minimum possible ESR for that location is estimated and used. As mentioned above, different parameters are used as location indicators.

[0172] In some embodiments, a coupling coefficient K is determined and used as an indication of the position of the receiver relative to the transmitter. The coupling coefficient is used, for example, to estimate the maximum predicted quality factor of the coupling coefficients.

[0173] Figure 9 shows the maximum Q factor Q max and the minimum Q factor Q min This relationship is determined, for example, during the design or manufacturing phase, by varying the position of the receiver in the allowable space relative to a reference transmitter and measuring the coupling coefficient and Q factor at different positions. Based on this measurement, the maximum Q factor Q max The relationship is determined. This relationship is stored in the receiver, for example as a function or a look-up table. When the receiver starts operating with the transmitter, the maximum Q factor Q max Data can be transmitted from the receiver to the transmitter indicating how depends on the coupling coefficient K.

[0174] Once the K factor is measured, the maximum Q factor Q max is determined, and this maximum Q factor Q max The minimum expected ESR is determined.

[0175] For example, the transmitter has a real quality factor Q actual , coupling coefficient K, resonance frequency ω res is measured, and then the following formula is

number

[0176] Considering the measurement uncertainty, the formula for maximum transmit coil current is:

number

[0177] In some embodiments, the minimum expected ESR is considered to depend on the self-inductance of the transmitting coil 103. In such embodiments, the same approach as above is used to characterize the receiver, but the measurement captures the self-inductance L and the equivalent series resistance. In this case, the receiver is determined by the ESR of the transmitting coil and the self-inductance ESR of the transmitting coil. min (L) and memorize the relationship between them.

[0178] This information is communicated to the transmitter during operation and used to determine the maximum transmit coil current. Specifically, the transmitter determines the expected minimum ESR: ESR based on the information received from the receiver. expmin Determine (L) and the resonant frequency ω res and ESR, which is the actual ESR actual The maximum transmit coil current is then determined as follows:

number

[0179] Considering the measurement uncertainty, the formula for maximum transmit coil current is:

number

[0180] In some embodiments, the minimum expected equivalent series resistance is frequency dependent, and in particular resonant frequency dependent, and thus in some embodiments, the determiner 309 measures the resonant frequency of the output resonant circuit and then determines the minimum expected equivalent series resistance as a function of this resonant frequency.

[0181] The frequency dependence of the equivalent series resistance, or in particular the frequency dependence of the receiver's contribution to the equivalent series resistance, may be predetermined at a reference transmitter by measuring the receiver's contribution to the equivalent series resistance of the transmitting coil over a range of frequencies. This information may be stored (in the receiver) and communicated (from the receiver) to the transmitter.

[0182] As described above, the transmitter includes functionality for receiving data from the receiver that provides information regarding a reference minimum expected equivalent series resistance, which is the minimum equivalent series resistance of the transmitting coil of the reference transmitter coupled to the receiving coil of the receiver. The receiver transmits data indicating, for example, a single value of the minimum expected ESR, or transmits an indication of how this depends directly or indirectly on various parameters, such as, for example, the coupling coefficient K or the self-inductance L. The transmitter then subsequently determines the minimum expected ESR based on this data and the indicated reference minimum expected equivalent series resistance.

[0183] The information provided by the receiver may include, for example, an indication of how the ESR (or a related parameter) depends on one or more of the following parameters determined by the transmitter: Quality (Q) factor ESR Coupling coefficient K - Self-inductance L of the transmitting coil Resonant frequency of the output resonant circuit

[0184] In some scenarios and embodiments, the transmitter is deemed similar enough to the reference transmitter so that the received data can be used directly, however, in other embodiments, the determiner 309 is configured to compensate for differences between the ESR of the reference transmitter and the ESR of the actual transmitter.

[0185] Thus, in some embodiments, the determiner 309 is configured to determine the minimum expected equivalent series resistance in response to compensating the reference minimum expected equivalent series resistance for a difference between the series resistance of the transmitting coil and the reference series resistance of the transmitting coil of the reference transmitter.

[0186] FIG. 11 shows an equivalent electrical circuit of a transmitter 1101 and an equivalent electrical circuit of a reference transmitter 1103.

[0187] As an example, the minimum expected equivalent series resistance of a reference transmit coil is ESR ref_expmin =ESR ref_coil +ESR ref_friendly and ESR ref_coil ESR of the reference transmit coil ESR ref_friendly ESR of the receiver's compatible metal Assume that.

[0188] The minimum expected equivalent series resistance of the sending coil is then ESR PTx_expmin =ESR PTX_drive +ESR PTx_cap +ESR PTx_coil +ESR ref_friendly is expressed as ESR PTX_drive Driver ESR ESR PTx_cap Resonant Capacitor ESR ESR PTx_coil ESR of the transmission coil ESR ref_friendly ESR of the receiver's compatible metal It is. As a result, ESR PTx_expmin=ESR PTX_drive +ESR PTx_cap +ESR PTx_coil +ESR ref_expmin -ESR ref_coil It becomes.

[0189] In many embodiments, the determiner 309 determines, for example, the self-inductance L of the reference transmitting coil. ref The self-inductance L of the transmitter's transmitting coil PTx and determining the minimum expected ESR of the current transmitter from the received minimum expected ESR of the reference transmitter, taking into account:

[0190] In this case, the equivalent series resistance of the transmitter's compatible metal is transformed by considering the ratio between the inductance values ​​as follows:

number

number

[0191] Alternatively or additionally, in some embodiments, the determiner 309 determines the angular resonant frequency ω of the reference transmitter. ref_res The angular resonant frequency ω of the transmitter with respect to PTx_res Consider:

[0192] In this case, the equivalent series resistance of the transmitter's compatible metal is transformed by considering the ratio between the resonant frequencies as follows:

number

number

[0193] In summary, the transmitter uses the following calculation to determine the expected minimum ESR:

number

[0194] In the above description, the angular resonant frequency of the transmitter is considered to determine the equivalent series resistance of the transmitting coil.

[0195] However, the transmitter usually operates at a resonant frequency ω PTx_res Different angular operating frequency ω PTx It is powered by.

[0196] Furthermore, the equivalent series resistance in the reference transmitting coil is ref_res Instead of a fixed frequency ω ref It is measured in.

[0197] To account for these differences, the transmitter then makes the following decisions:

number

[0198] Finally, the transmitter:

number

[0199] For the actual equivalent series resistance, the transmitter considers the difference between the operating frequency and the resonant frequency as follows:

[0200] Actual equivalent series resistance (ESR) of the transmit coil actual is the angular resonance frequency ω PTx_res Assuming it was measured at ESR actual depends on the individual factors as follows: For the angular resonance frequency, ESR actual (ωPTx_res )=ESR Ptx_drive +ESR Ptx_cap +ESR PTx_coil (ω PTx_res )+ESR PTx_friendly (ω PTx_res ) and For the angular operating frequency, ESR actual (ω PTx )=ESR Ptx_drive +ESR Ptx_cap +ESR PTx_coil (ω PTx )+ESRP Tx_friendly (ω PTx ) and

number

[0201] The transmitter determines the actual equivalent series resistance of the transmitting coil at the angular operating frequency based on the equivalent series resistance measured at the resonant frequency:

number

[0202] As described above, the determiner 309 determines the maximum transmit coil current based on considerations of the measured ESR, i.e., based on the actual ESR. In many embodiments, it is difficult to measure this value directly, and the transmitter uses a different, more indirect approach to measure the current ESR.

[0203] In some embodiments, the ESR is measured by determining the decay rate of the self-oscillation of the output resonant circuit. The transmitter is configured to initialize the self-oscillation and then measure the time it takes for the oscillation to decrease to a given level. The ESR is then calculated from this decay time.

[0204] Figure 12 shows an example of self-oscillation of the output circuit of a power transmitter. The period of resonance is T = 2π / ω res and the ESR is given by, for example,

number

[0205] In some embodiments, the ESR is determined from measurements of the resonant frequency and / or Q-factor of the output resonant circuit. For example, the transmitter performs a frequency sweep to find the resonant frequency and Q-factor. For example, the Q-factor is determined from the 3 dB bandwidth for the resonant frequency. The current ESR is then calculated as:

number

[0206] In some embodiments, the ESR is determined from only one measurement of, for example, the resonant frequency and the Q-factor, by assuming nominal values ​​for the other parameters.

[0207] In some embodiments, the contributions of the receiver's materials and foreign object contributions to the equivalent series resistance of the transmitter's external load are applied. For example, the receiver may be configured to calculate the minimum expected contribution to the equivalent series resistance of the reference transmitter coil: ESR ref_friendly_min The transmitter transmits the actual contribution of the external material to its transmitting coil: ESR external In addition, the receiver measures the ESR vs. inductance of the reference transmitter coil for various positions of the reference transmitter. ref_friendly_min Dependence on, e.g. ESR ref_friendly_min (L ref_PRx ) Communicate.

[0208] The receiver measures the ESR as a function of relative frequency. ref_friendly The frequency dependence of

number

[0209] The transmitter has an inductance value LPTx For example, from the resonant frequency,

number

number

number

[0210] The transmitter uses a function provided by the receiver to calculate the frequency of the given ref L in ref_PRx Predicted minimum contribution to equivalent series resistance due to compatible metals in reference transmitters: ESR ref_friendly_min (L ref_PRx ) and define this minimum contribution to the inductance value of the transmitter itself as:

number

number

number

[0211] The transmitter should measure its actual equivalent series resistance (ESR) in the coil of the transmitter at the resonant frequency. PTx_actual (f res ) and measure the coil's equivalent series resistance: ESR PTx_coil (f res ) itself, i.e. ESR PTx_external (f res )=ESR PTx_actual (f res )-ESR PTx_coil (f res ) to estimate the actual contribution of the external material to the equivalent series resistance.

[0212] To estimate the expected minimum contribution to the ESR of the transmit coil due to the receiver material at the transmitter operating frequency, the transmitter is PTx_friendly_min of,

number

[0213] To estimate the actual contribution to the actual ESR of the transmit coil due to external materials (external materials of the receiver and foreign objects) at the operating frequency of the transmitter, the transmitter PTx_external However, this is composed of the contribution of the friendly metal of the receiver and the contribution of potential foreign objects, so ESR PTx_external (f res )=ESR PTx_friendly (f res )+ESRPTx_FO (f res ) and the transformation involves two dependencies: About the affinity metal of PRx

number

number

number

number

[0214] Assuming that the frequency dependence of the foreign object is somewhat higher than that of the compatible metal of the receiver, the difference is the excess margin.

number

number

number

number

number

[0215] Figure 13 shows the minimum equivalent series resistance (ESR) min and maximum equivalent series resistance ESR max This figure shows an example of how ESR varies as a function of the coupling coefficient (K). This relationship is determined, for example, during the design or manufacturing phase, by varying the position of the receiver in the allowable space relative to a reference transmitter and measuring the equivalent series resistance at different positions. Based on this measurement, the minimum equivalent series resistance ESR min This relationship is stored in the receiver, for example as a function or a look-up table. When the receiver starts to operate with the transmitter, the minimum equivalent series resistance ESR min Data showing how ESR depends on the coupling coefficient K: expmin (K) can be transmitted from the receiver to the transmitter.

[0216] Figure 14 shows the minimum equivalent series resistance (ESR) min and maximum equivalent series resistance ESR max This figure shows an example of how ESR varies as a function of the inductance value (L) of the coil of the power transmitter. This relationship is determined, for example, during the design or manufacturing phase, by changing the position of the power receiver in the allowable space relative to a reference power transmitter and measuring the equivalent series resistance at different positions. Based on this measurement, the minimum equivalent series resistance ESR min This relationship is stored in the receiver, for example as a function or a look-up table. When the receiver starts to operate with the transmitter, the minimum equivalent series resistance ESR min Data showing how ESR depends on the inductance value L: expmin (L) can be transmitted from the receiver to the transmitter.

[0217] The position of the power receiver relative to the power transmitter in Figures 13 and 14 is as follows. - Near zero distance in 0.5mm increments up to 10mm (21 distances) At the center and 8 different positions on the radius around the center, in 1mm increments up to a maximum of 10mm (1+8×10) A total of 21 x (1 + 8 x 10) = 1701 positions

[0218] FIG. 15 shows a corresponding example, but where measurements are performed for fewer positions. - Near zero distance in 1mm increments up to 5mm (6 distances) At the center and at four different positions on the radius around the center, in increments of 5 mm up to a maximum of 10 mm (1+4×2) Total of 6×(1+8)=54 positions

[0219] FIG. 16 shows a corresponding example, but where measurements are performed for even fewer positions. Near zero distance and 5mm distance (2 distances) - 4 different positions (1+4) on the center and a 10mm radius around the center Total of 2×(1+4)=10 positions

[0220] The maximum value is no longer valid, but the minimum value is still representable.

[0221] It will be appreciated that in the above description, for clarity, embodiments of the invention are described with reference to different functional circuits, units, and processors. However, it will be apparent that any suitable distribution of functionality between different functional circuits, units, or processors may be used without detracting from the invention. For example, functions shown to be performed by separate processors or controllers are performed by the same processor or controller. Thus, references to specific functional units or circuits should not be considered as indicative of a strict logical or physical structure or organization, but merely as references to suitable means for providing the described functionality.

[0222] The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. Optionally, the invention is implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of the embodiments of the invention may be physically, functionally and logically implemented in any suitable way. In practice, functionality may be implemented in a single unit, in multiple units or as part of other functional units. Thus, the invention may be implemented in a single unit or may be physically and functionally distributed between different units, circuits and processors.

[0223] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form described herein. Rather, the scope of the present invention is limited only by the appended claims. Moreover, even if a feature appears to be described in connection with a particular embodiment, a person skilled in the art will recognize that various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term "comprises" does not exclude the presence of other elements or steps.

[0224] Furthermore, a plurality of means, elements, circuits, or method steps, although individually recited, may be implemented by, for example, a single circuit, unit, or processor. Furthermore, although individual features may be included in different claims, they may in some cases be advantageously combined, and their inclusion in different claims does not imply that the combination of features is infeasible and / or not advantageous. Furthermore, the inclusion of a feature in one category of claims does not imply that it is limited to this category, but indicates that the feature is equally applicable to other claim categories, where appropriate. The inclusion of a feature in a dependent claim of an independent claim does not imply that it is limited to this independent claim, but indicates that the feature is equally applicable to other independent claims, where appropriate. Furthermore, the order of features in the claims does not imply a particular order in which the features should be acted upon, and in particular the order of individual steps in a method claim does not imply that the steps must be performed in that order. Rather, the steps may be performed in any suitable order. Furthermore, the singular reference does not exclude the plural. Thus, reference to "first", "second", etc. does not exclude the plural. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

Claims

1. A power transmitter for wirelessly supplying power to a power receiver via an electromagnetic signal, wherein the power transmitter is An output resonant circuit comprising a power transmission coil and at least one capacitor, The output resonant circuit includes a driver that generates a drive signal for generating the electromagnetic signal, A measuring instrument for measuring load parameters, wherein the load parameters indicate the load of the power transmission coil during a time interval in which power transmission is inactive; A determination device that determines the maximum electromagnetic signal level of the electromagnetic signal during power transmission according to the load parameters. A power transmitter comprising the driver limiting the drive signal so that the electromagnetic field signal does not exceed the maximum electromagnetic signal level during power transmission.

2. The power transmitter according to claim 1, wherein the load parameter includes a coupling coefficient parameter indicating the coupling coefficient between the power transmission coil and the power receiving coil of the power receiver.

3. The power transmitter according to claim 1, wherein the load parameter includes a quality coefficient parameter indicating the quality coefficient of the output resonant circuit.

4. The power transmitter according to claim 1, wherein the load parameter is a self-inductance parameter indicating the self-inductance of the power transmission coil.

5. The transmitter according to claim 1, wherein the decision-maker determines the maximum electromagnetic signal level according to the measured value of the load parameter relative to the value of the load parameter in the reference arrangement of the power receiver.

6. The transmitter according to claim 1, wherein the driver determines a maximum transmission coil current corresponding to the maximum electromagnetic signal level and controls the drive signal so that the transmission coil current is maintained below the maximum transmission coil current.

7. The transmitter according to claim 6, wherein the load parameter includes the measured equivalent series resistance of the transmission coil, and the driver determines the maximum transmission coil current in accordance with the measured equivalent series resistance relative to the minimum predicted equivalent series resistance of the receiver and the transmitter configuration.

8. The transmitter according to claim 7, wherein the measured equivalent series resistance represents the total external load of the electromagnetic signal, and the minimum predicted equivalent series resistance represents the load of the electromagnetic signal due to the materials of the receiver alone.

9. The transmitter according to claim 7, further comprising a receiver that receives the index of the minimum predicted equivalent series resistance from the power receiver.

10. The transmitter according to claim 7, wherein the minimum predicted equivalent series resistance depends on the coupling coefficient, and the decision-maker determines the coupling coefficient between the transmitting coil and the receiving coil of the receiver, and determines the minimum predicted equivalent series resistance as a function of the coupling coefficient.

11. The power transmitter according to claim 7, wherein the minimum predicted equivalent series resistance depends on the self-inductance, the decision-maker determines a self-inductance parameter that indicates the self-inductance of the power transmission coil, and determines the minimum predicted equivalent series resistance as a function of the self-inductance.

12. The transmitter according to claim 7, comprising a receiver that receives an index of a reference minimum predicted equivalent series resistance from the receiver, wherein the reference minimum predicted equivalent series resistance is the minimum equivalent series resistance of the transmission coil of a reference transmitter coupled to the receiving coil of the receiver, and the decision-maker determines the minimum predicted equivalent series resistance according to the reference minimum predicted equivalent series resistance.

13. The power transmitter according to claim 12, wherein the decision-maker determines the minimum predicted equivalent series resistance in accordance with the compensation of the reference minimum predicted equivalent series resistance for the difference between the series resistance of the power transmission coil and the reference series resistance of the power transmission coil of the reference power transmitter.

14. The transmitter according to claim 13, wherein the decision-maker determines the minimum predicted equivalent series resistance as a function of the reference minimum predicted equivalent series resistance and the self-inductance of the transmission coil with respect to the self-inductance of the transmission coil of the reference transmitter.

15. The transmitter according to claim 13, wherein the decision-maker determines the contribution of the material of the receiver to the equivalent series resistance of the reference transmission coil as a function of the contribution of the material of the receiver to the equivalent series resistance of the reference transmission coil and the frequency of the drive signal with respect to the reference frequency of the reference transmitter.

16. The transmitter according to claim 7, wherein the decision-maker determines the measured equivalent series resistance according to the attenuation rate of the self-oscillation of the output resonant circuit.

17. The power transmitter according to claim 7, wherein the decision-maker determines the measured equivalent series resistance according to the measured resonant frequency of the resonant circuit.

18. The power transmitter according to claim 7, wherein the decision-maker determines the measured equivalent series resistance according to the measured quality coefficient of the resonant circuit.

19. A method of operation for a transmitter that wirelessly provides power to a receiver via an electromagnetic signal, wherein the transmitter is Output resonant circuit comprising a power transmission coil and at least one capacitor The method comprises, The output resonant circuit generates a drive signal for generating the electromagnetic signal, A step of measuring a load parameter, wherein the load parameter indicates the load of the power transmission coil during a time interval in which power transmission is inactive; The steps include determining the maximum electromagnetic signal level of the electromagnetic signal during power transmission according to the load parameters, The steps include limiting the drive signal so that the electromagnetic field signal does not exceed the maximum electromagnetic signal level during power transmission, and A method having.

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