Power transmitter, system and method thereof

Abstract

A power transmitter (101) provides wireless power transmission to a power receiver (105) via a wirelessly inductive power transmission signal. The power transmitter (101) includes a transmitter coil (203) for generating the power transmission signal and a driver (201) for generating a drive signal for this purpose. A communicator (207) communicates with the power receiver (105) via a communication channel that does not use the power transmission signal as a communication carrier. A power loop controller (205) implements a power control loop by adjusting the power level of the power transmission signal in response to a power control error message received from the power receiver (105). A generator (209) introduces a power level change sequence into the power transmission signal, and a validity detector (211) detects data received by the communicator (207) as invalid data for power transmission in response to a comparison of the power level change sequence and the power change request of the power control error message.

Description

Technical Field

[0001] This invention relates to wireless power transmitters, systems, and methods thereof, and particularly, but not exclusively, to wireless power transmitters for higher power transmission applications. Background Technology

[0002] Most electrical products today require dedicated electrical contacts to be powered from an external power source. However, this is often impractical and requires the user to physically insert connectors or otherwise establish physical electrical contact. Power requirements also typically vary significantly, and most devices are currently supplied with their own dedicated power supplies, resulting in a typical user having a large number of different power supplies, each dedicated to a specific device. While the use of an internal battery can eliminate the need for a wired connection to a power source during use, this only provides a partial solution, as the battery will require recharging (or replacement). The use of a battery can also significantly increase the weight of the device, as well as potential cost and size.

[0003] To provide a significantly improved user experience, the use of wireless power has been proposed, in which power is inductively transmitted from a transmitter sensor in a power transmitter device to a receiver coil in an individual device.

[0004] Power transfer via magnetic induction is a well-known concept, primarily used in transformers where there is tight coupling between the primary transmitter coil / coil and the secondary receiver coil. Wireless power transfer between these devices becomes possible by separating the primary transmitter coil and the secondary receiver coil, based on the principle of loosely coupled transformers.

[0005] This arrangement allows for wireless power transfer to the device without requiring any wired or physical electrical connections. In practice, it can simply allow the device to be placed near or on top of the transmitter coil for external recharging or power supply. For example, the power transmitter device can be arranged on a horizontal surface, allowing the device to be easily placed on the surface for power supply.

[0006] Furthermore, such a wireless power transmission arrangement can be advantageously designed to allow power transmitter devices to be used with a range of power receiver devices. Specifically, a wireless power transmission method known as the Qi specification has been defined and is currently under further development. This method allows power transmitter devices that comply with the Qi specification to be used with power receiver devices that also comply with the Qi specification, without requiring these devices to come from the same manufacturer or to be proprietary to each other. The Qi standard also includes a feature to allow operation adapted to a specific power receiver device (e.g., depending on specific power consumption).

[0007] The Qi specification was developed by the Wireless Power Consortium.

[0008] Other developments are attempting to introduce a range of new applications and features. For example, the Wireless Power Consortium is developing a standard based on the Extended Qi principle for application in a range of kitchen applications and appliances, including heaters, kettles, blenders, and pans. This development specifically supports much higher power levels for power delivery and is being called the Cordless Kitchen Standard. Other developments include medium-power level applications, targeting applications such as charging laptops and power tools.

[0009] The Qi standard supports communication from a power receiver to a power transmitter, enabling the power receiver to provide information that allows the power transmitter to adapt to a specific power receiver. The current standard defines a unidirectional communication link from the power receiver to the power transmitter, where the power receiver communicates by performing load modulation on the power transmission signal. Specifically, the load applied to the power transmission signal by the power receiver is changed to provide modulation of the power signal. Changes in the electrical characteristics of the power transmitter pair (e.g., changes in the drawn current) can be detected and decoded (demodulated).

[0010] Therefore, at the physical layer, the communication channel from the power receiver to the power transmitter uses a power transmission signal as the data carrier. The power receiver modulates the load detected by changes in the amplitude and / or phase of the transmitter coil current or voltage. Data is formatted in bytes and packets.

[0011] More information can be found in Chapter 6 of Part 1 of the Qi Wireless Charging Specification (Version 1.0).

[0012] Initially, Qi utilized only a unidirectional communication link, but bidirectional communication links have also been introduced to allow for more advanced control and flexibility in power transmission operations. For example, communication from the power transmitter to the power receiver can be achieved by modulating the power transmission signal, for example, using amplitude, frequency, or phase modulation.

[0013] However, it has been found that communication using power-transmitted signals is not always optimal. Specifically, the communication capabilities and possible data rates of communication using power-transmitted signals as a carrier tend to be quite limited, often confined to a few hundred bits per second. With increasing power levels, the suitability of power-transmitted signals for communication tends to decrease significantly.

[0014] In many high-power-level power transmission systems, it has been proposed to use a separate communication system that is independent of the power transmission signal and therefore specifically does not use the power transmission signal as a carrier for the communication link.

[0015] Such a standalone communication system typically offers substantially higher data rates and often provides more reliable communication. This allows for improved and more reliable power delivery in most practical applications.

[0016] However, while the use of a standalone communication system can provide many advantages, the inventors have recognized that it can also lead to suboptimal operation in some situations, and specifically, it can lead to potential erroneous situations, such as when the power receiver is moved, removed, or replaced.

[0017] Therefore, improved power delivery methods will be advantageous, and specifically, methods that allow for increased flexibility, reduced costs, reduced complexity, enhanced user experience, additional or improved functionality or services, more reliable operation, improved error detection, and / or improved performance will be advantageous. Summary of the Invention

[0018] Therefore, the present invention seeks to mitigate, alleviate or eliminate one or more of the above-mentioned disadvantages, either alone or in any combination.

[0019] According to one aspect of the present invention, a power transmitter for a wireless power transmission system is provided, the wireless power transmission system including at least one power receiver for receiving power transmission from the power transmitter via a wirelessly induced power transmission signal; the power transmitter includes: an output circuit including a transmitter coil for generating the power transmission signal in response to a drive signal being applied to the output circuit; a driver for generating the drive signal; a communicator for communicating with the power receiver, the communicator being arranged to receive data from the power receiver via a communication channel not using the power transmission signal as a communication carrier, the data including a power control error message; a power loop controller for implementing a power control loop, the power loop controller being arranged to adjust the power level of the power transmission signal in response to a power change request of the power control error message; a generator for introducing a power level change sequence into the power transmission signal; and an validity detector for detecting data received by the communicator as invalid data for the power transmission in response to a comparison of the power level change sequence with the power change request of the power control error message.

[0020] This invention can provide improved performance and / or operation in many wireless power transfer systems. It can provide improved operation, including effective control over power transfer operations and mitigation or reduction of the risk of unwanted or undetected errors, such as in the event of power receiver removal.

[0021] Specifically, the present invention can allow for an additional layer of security by providing a method for detecting invalid data received from out-of-band communication (which does not use a power transmission signal as a communication carrier) (which specifically may reflect that it may not be received from a power receiver that is receiving / extracting power from a power transmission signal).

[0022] Specifically, this invention provides means for determining that a power transmitter is receiving data from the correct power receiver, and specifically, that it is receiving data from a power receiver that is extracting power from a self-powered transmission signal. This can reduce the risk of undesirable situations, such as power transmission to a power receiver being controlled by data from a nearby power receiver that may be receiving power from another power transmitter (e.g., after a rapid switchover of two power receivers). This method can be combined with other operations such as power receiver authentication and power receiver removal detection to provide a more reliable power transmission system.

[0023] This method can (at least partially) utilize existing functionality, and specifically, the power control loop function can be reused to determine the validity of data received via out-of-band communication channels. This method requires no modification to the power receiver and can be used with conventional power receivers, thus providing improved backward compatibility.

[0024] This operation can also be performed during normal power transfer and is compatible with ongoing power transfer operations.

[0025] A power level change sequence can be a type or feature applied to a power level change sequence.

[0026] A validity detector can be configured to determine that data received by a communicator is invalid in response to a detected criterion that a comparison between a power level change sequence and a power change request meets a certain standard. The criteria may include the requirement that the power change request (appropriately) matches a power level change introduced into the power transmission signal by the power level change sequence to compensate for / counteract / cancel / reduce the power level change. The validity detector can generate a match indication indicating the degree of match between the received power change request and the expected power change request, which compensate for the power level change sequence. If the match indication is below a threshold, the validity detector can determine that no match has occurred and the data received by the communicator is invalid.

[0027] An effectiveness detector can be configured to detect power level changes caused by a power level change sequence, resulting in an appropriate power change request being received in a power control message to compensate for the power level changes.

[0028] A validity detector can be configured to modify or terminate the power transmitter in response to the detection of invalid data.

[0029] A comparison of the power level change pattern and the power change request of the power control error message can be a comparison of the power control error messages received within the time interval during which the power control loop reacts to changes introduced by the power level change sequence through the generator.

[0030] In some embodiments, the validity detector may continuously compare received power change requests with a sequence of power level changes, and if no match is found within a given time interval, the data may be determined as invalid data.

[0031] Power change requests in power control error messages can originate from a subset of power control error messages. These power change requests can be power change requests received within a time interval. In some embodiments, the timing of the time interval can be set relative to the time it takes to introduce a sequence of power level changes into the power transmission signal.

[0032] According to an optional feature of the invention, the validity detector is arranged to determine a compensation metric indicating the degree to which the power change request matches the compensation for the power level change sequence; and to detect data as invalid data for the power transfer in response to the compensation metric.

[0033] In many embodiments, this can provide improved detection and operation.

[0034] If the compensation measure exceeds a threshold, the validity detector can determine the data as valid. Compensation for power level changes in a power level change sequence can correspond to offsetting / denying / counteracting a power change request that introduces a power level change by the power level change sequence.

[0035] According to an optional feature of the invention, the validity detector is arranged to extract the requested power change sequence from the power control error message; and to detect data received by the communicator as invalid data for the power transmission in response to a comparison of the power level change sequence with the requested power change sequence.

[0036] In many embodiments, this can provide improved detection, performance, and operation.

[0037] In some embodiments, the validity detector may be arranged to determine a similarity measure indicating a match between the change in the power level change sequence and the change in the requested power change sequence.

[0038] In some embodiments, the validity detector is configured to designate data as valid in response to the correlation between the power level change sequence and the requested power change sequence exceeding a threshold.

[0039] According to an optional feature of the invention, the validity detector is arranged to designate data as invalid in response to the correlation between the power level change sequence and the requested power change sequence.

[0040] According to an optional feature of the invention, the validity detector is arranged to designate data as invalid in response to the correlation between the power level change sequence and the requested power change sequence not exceeding a threshold.

[0041] According to an optional feature of the invention, the power level variation sequence includes at least three different power level offsets for the power transmission signal.

[0042] In many embodiments, this can provide improved detection, performance, and operation. One of at least three different power level offsets can be zero offset.

[0043] According to an optional feature of the invention, the power level variation sequence includes at least one power level offset for the power transmission signal, the at least one power level offset being constant for a duration of not less than three time intervals between power control error messages.

[0044] In many embodiments, this can provide improved detection, performance, and operation.

[0045] According to an optional feature of the invention, the power level change sequence includes only a power level offset of the power transmission signal that is no greater than 10% of the current power level of the power transmission signal.

[0046] In many embodiments, this can reduce the impact of introducing a power level variation sequence to an acceptable level while allowing for sufficiently accurate detection.

[0047] According to an optional feature of the invention, the validity detector is arranged to determine the data received by the communicator as invalid data in response to detecting a power level change exceeding a power change threshold, the power change threshold exceeding the maximum power level offset of the power level change sequence.

[0048] According to an optional feature of the invention, the generator is arranged to introduce the power level variation sequence by applying a frequency offset variation sequence to the frequency of the power transmission signal.

[0049] In many embodiments, this can provide improved detection, performance, and operation.

[0050] According to an optional feature of the invention, the generator is arranged to adjust the power level change sequence in response to the timing of the power control error message.

[0051] In many embodiments, this can provide improved detection, performance, and operation.

[0052] According to an optional feature of the invention, the generator is arranged to adjust the power level change sequence in response to a power level change requested by the power control error message.

[0053] In many embodiments, this can provide improved detection, performance, and operation.

[0054] According to an optional feature of the invention, the validity detector is arranged to adjust the detection criteria used for the comparison in response to a power level change requested by the power control error message.

[0055] In many embodiments, this can provide improved detection, performance, and operation.

[0056] According to another aspect of the present invention, a method of operating a power transmitter for a wireless power transmission system is provided, the wireless power transmission system including at least one power receiver for receiving power transmission from the power transmitter via a wirelessly induced power transmission signal; the power transmitter including: an output circuit including a transmitter coil for generating the power transmission signal in response to a drive signal being applied to the output circuit; and the method including: generating the drive signal; communicating with the power receiver, the communication including receiving data from the power receiver via a communication channel not using the power transmission signal as a communication carrier, the data including a power control error message; implementing a power control loop that adjusts the power level of the power transmission signal in response to a power change request of the power control error message; introducing a power level change sequence into the power transmission signal; and detecting data received by a communicator as invalid data for the power transmission in response to a comparison of the power level change sequence with the power change request of the power control error message.

[0057] According to another aspect of the present invention, a wireless power transmission system is provided, comprising at least one power transmitter and at least one power receiver, the at least one power receiver being configured to receive power transmission from the power transmitter via a wirelessly inductive power transmission signal; the power transmitter comprising: an output circuit including a transmitter coil configured to generate the power transmission signal in response to a drive signal being applied to the output circuit; a driver configured to generate the drive signal; a communicator configured to communicate with the power receiver, the communicator being configured to receive data from the power receiver via a communication channel not using the power transmission signal as a communication carrier, the data including a power control error message; a power loop controller configured to implement a power control loop, the power loop controller being configured to adjust the power level of the power transmission signal in response to a power change request of the power control error message; a generator configured to introduce a power level change sequence into the power transmission signal; and a validity detector configured to detect data received by the communicator as invalid data for the power transmission in response to a comparison of the power level change sequence with the power change request of the power control error message.

[0058] These and other aspects, features, and advantages of the invention will become apparent and will be set forth with reference to one or more embodiments described below. Attached Figure Description

[0059] Embodiments of the invention will be described by way of example only with reference to the accompanying drawings, wherein:

[0060] Figure 1 Examples of elements of a wireless power transmission system according to some embodiments of the present invention are illustrated;

[0061] Figure 2 Examples of elements of a power transmitter according to some embodiments of the present invention are illustrated;

[0062] Figure 3 The illustration shows an example of elements of a power receiver for a wireless power transmission system according to some embodiments of the present invention;

[0063] Figure 4 Examples of elements for a driver for a power transmitter according to some embodiments of the present invention are illustrated; and

[0064] Figure 5 Examples of elements for a driver for a power transmitter according to some embodiments of the present invention are illustrated. Detailed Implementation

[0065] The following description focuses on embodiments of the invention applicable to wireless power transmission systems utilizing power transmission methods known from the Qi specification. However, it will be appreciated that the invention is not limited to this application, but can be applied to many other wireless power transmission systems.

[0066] Figure 1 An example of a power transmission system according to some embodiments of the present invention is illustrated. The power transmission system includes a power transmitter 101, which includes (or is coupled to) a transmitter coil / inductor 103. The system also includes a power receiver 105, which includes (or is coupled to) a receiver coil / inductor 107.

[0067] This system provides wireless inductive power transfer from a power transmitter 101 to a power receiver 105. Specifically, the power transmitter 101 generates a wireless inductive power transfer signal (also referred to as a power transfer signal or inductive power transfer signal), which propagates as a magnetic flux through a transmitter coil or sensor 103. The power transfer signal can typically have a frequency between about 20 kHz and about 500 kHz, and is often in the range of 95 kHz to 205 kHz for Qi-compatible systems (or, for example, for high-power kitchen applications, the frequency can typically be in the range of 20 kHz to 80 kHz). The transmitter coil 103 and the receiver coil 107 are loosely coupled, and thus the receiver coil 107 picks up (at least a portion) of the power transfer signal from the power transmitter 101. Therefore, power is transferred from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the receiver coil 107. The term power transmission signal is primarily used to refer to the induced signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the receiver coil 107, but it will be appreciated that, equivalently, it can also be considered and used as a reference to the electrical signal provided to the transmitter coil 103 or picked up by the receiver coil 107.

[0068] In this example, power receiver 105 is specifically a power receiver that receives power via receiver coil 107. However, in other embodiments, power receiver 105 may include a metallic element, such as a metallic heating element, in which case the power transmission signal induces eddy currents, thereby causing direct heating of the element.

[0069] The system is configured to transmit substantial power levels, and specifically, the power transmitter in many embodiments can support power levels exceeding 500mW, 1W, 5W, 50W, 100W, or 500W. For example, for Qi-compliant applications, power transmission is typically within the 1-5W range for low-power applications; while for high-power applications supported by the Cordless Kitchen standard developed by the Wireless Power Consortium, power transmission exceeds 100W and reaches over 1000W.

[0070] In the following description, the operation of the power transmitter 101 and the power receiver 105 will be described with specific reference to embodiments of the Qi specification (other than the modifications and enhancements described herein or applicable to higher power cordless kitchen specifications).

[0071] Figure 1 The system utilizes bidirectional communication to support power transfer operations. Bidirectional communication is used to configure, establish, and control power transfer and can include the exchange of a range of control data. Specifically, a communication channel between the wireless power transmitter and the wireless power receiver is considered necessary to establish a feedback loop from the wireless power receiver to the wireless power transmitter, which is crucial for the stability of the power system.

[0072] As an example, the current Qi specification limits the amount of power transmitted wirelessly to 15 watts. This power level can be considered a low-power wireless system. Such a system uses modulation of the transmitted power signal as a means of communication between the power transmitter and the power receiver. This is also known as an in-band communication channel.

[0073] However, such communication is not ideal for all systems, and tends to be suboptimal, especially for higher power levels. Specifically, for applications with higher transmission power levels, modulation of the power transmission signal creates additional sources of loss, and the absolute value of the loss increases with the power level. These losses lead to heat dissipation, for example, in the power electronics of the wireless power system, or in the materials within the operating range of the wireless power system. Moreover, electromagnetic interference can increase and is often a limiting factor.

[0074] Furthermore, to provide effective control over power transmission, a high communication data rate between the power transmitter and the power receiver is desired. However, this is often very difficult to achieve using the power transmission signal as the carrier signal, and especially for higher-power applications (e.g., kitchen applications), the achievable data rate is often too low to support the desired functionality. Specifically, when the operating frequency of the power transmission signal is on the order of 20 to 300 kHz, the channel bandwidth is often insufficient for more complex operations, such as, for example, authorization of the power receiver. Communication from the power transmitter to the power receiver may be required for error control, authentication (which typically requires high data rates), and possibly other applications (e.g., even providing Internet connectivity).

[0075] Therefore, higher-power-level systems (e.g., those compatible with cordless kitchen specifications) tend to replace in-band communication using power-transmitted signals with out-of-band communication channels implemented by a separate, often dedicated, short-range communication system. This separate communication system is independent of the power-transmitted signal and does not use the power-transmitted signal as a carrier for communication. It is often a short-range communication system, such as Bluetooth or NFC communication systems.

[0076] Reference Figure 2 To describe in more detail Figure 1 The system Figure 2 The components of the power transmitter 101 are illustrated, and Figure 3 A more detailed illustration is provided. Figure 1 The power receiver 105 is a component.

[0077] The power transmitter 101 includes a driver 201 that generates a drive signal that is fed to an output circuit, in this example, a resonant circuit formed by a transmitter coil 103 and a transmitter capacitor 203. In response to being driven by the drive signal, the transmitter coil 103 generates an electromagnetic field and thus provides an electromagnetic power transfer signal to the power receiver 105. The power transfer signal is provided (at least) during the power transfer phase.

[0078] Driver 301 is typically a drive circuit in the form of an inverter, which generates an AC signal based on a DC voltage. The output of driver 201 is typically a switching bridge, which generates a drive signal by appropriately switching the switches of the switching bridge. Figure 4 A half-bridge switching inverter is shown. Control switches S1 and S2 are configured such that they never close simultaneously. Alternatingly, S1 is closed while S2 is open, and S2 is closed while S1 is open. The switches open and close at a desired frequency, thereby generating an AC signal at the output. Typically, the inverter output is connected to a transmitter inductor via a resonant capacitor. Figure 5A full-bridge switched bridge / inverter is illustrated. Control switches S1 and S2 are closed such that they never close simultaneously. Control switches S3 and S4 are closed such that they never close simultaneously. Alternatingly, switches S1 and S4 close while S2 and S3 open, and then S2 and S3 close while S1 and S4 open, thereby creating a square wave signal at the output. The switches open and close at the desired frequency.

[0079] The driver 201 thus generates a drive signal for the output resonant circuit and therefore for the transmitter coil 103.

[0080] The driver 201 is coupled to a power transmitter controller 205, which is arranged to control the operation of the power transmitter 101. The power transmitter controller 205 may be arranged to control the operation of the power transmitter 101 to perform required and desired functions associated with the power transfer protocol of the system, and in this example, may be specifically arranged to control the power transmitter 101 to operate according to the cordless kitchen specification. For example, the power transmitter controller 205 may include functions for: detecting the power receiver, initiating power transfer, supporting power transfer, terminating power transfer, etc.

[0081] The power transmitter 101 also includes a transmitter communicator 207, which is arranged to communicate with the power receiver 105 independently of the power transmission signal, and therefore does not use the power transmission signal as a communication carrier. The transmitter communicator 207 is arranged to communicate with the power receiver 105 using a communication link that uses a different communication carrier than the power transmission signal. Therefore, the transmitter communicator 207 establishes an out-of-band communication link independent of the power transmission signal, and data transmitted via this link is not modulated onto the power transmission signal.

[0082] Therefore, the power transmitter communicates with the power receiver using a communication system and channel that is not limited or constrained by using the power transmission signal as a communication carrier.

[0083] The exact communication method and communication carrier used can vary in different embodiments and can depend on the preferences and requirements of a particular application. Out-of-band communication links are typically implemented by short-range communication systems, however, these short-range systems have a range substantially greater than the power transmission range and substantially exceeding the operational volume of wireless power transmission.

[0084] In many embodiments, the in-band communication link can be implemented by a standardized short-range communication system such as Bluetooth or NFC. Such a communication system can provide an efficient out-of-band communication link, offering high data rates, reliable communication, and generally low-cost implementation. Specifically, it can enable efficient control data exchange for power transmission. In many embodiments, the transmitter communicator 207 can support bidirectional communication; however, it will be appreciated that in some embodiments, communication may be unidirectional.

[0085] like Figure 3 As illustrated, the receiver coil 107 of the power receiver 105 is coupled to a power receiver controller 301, which in turn couples the receiver coil 107 to a load 303. The power receiver controller 301 includes a power control path that converts the power extracted by the receiver coil 107 into a power supply suitable for supplying the load 303. Furthermore, the power receiver controller 301 may include various power receiver controller functions required to perform power transfer, and particularly those required to perform power transfer according to cordless kitchen specifications.

[0086] The power receiver 105 also includes a receiver communicator 305, which establishes an out-of-band communication link with the transmitter communicator 207. The receiver communicator 305 can therefore complement the first transmitter communicator 205.

[0087] Therefore, the system uses out-of-band communication to exchange data between the power transmitter 101 and the power receiver 105. The exchanged data specifically consists of various control and configuration data required, desired, or specified by a particular wireless transmission system, such as specific Qi control data or cordless kitchen power control data.

[0088] Specifically, the system utilizes an out-of-band communication channel to implement a power control loop. The power receiver controller 301 can specifically monitor whether the power level of the power transmission signal is too high or too low and generate a power error indication / power change request, which is then sent by the receiver communicator 305 as a power control error message to the power transmitter. The transmitter communicator 207 of the power transmitter 101 receives the power control error message and can forward it to the power transmitter controller 205, which can implement the power control loop function.

[0089] The power transmitter controller 205 is configured to adjust the power level of the power transmission signal in response to a received power control error message. If a power error indicator indicating that the current power transmission signal power level is too low is received, the power transmitter controller 205 increases the power level by, for example, a predetermined amount. If a power error indicator indicating that the current power transmission signal power level is too high is received, the power transmitter controller 205 decreases the power level by, for example, a predetermined amount. In some embodiments, the received power control error message may include a power change request that indicates not only the direction of change but also the magnitude or amount of the requested change.

[0090] The power receiver 105 can send power control error messages at relatively short intervals. In Qi, power control error messages need to be sent at least once every 250 ms, but in many embodiments, the interval can be substantially shorter. For example, for motor regulation, power control error messages can be sent at intervals of approximately, for example, 10 ms.

[0091] The power receiver 105 can therefore continuously control the power level of the power transmission signal to the desired level by transmitting power control error messages. The power transmitter and power receiver accordingly implement a power control loop to maintain the desired power level.

[0092] Using out-of-band communication channels and systems to exchange control data (such as power control error messages) offers several advantages, including allowing high data rates and providing more reliable communication than when the power transmission signal is used as a communication carrier, such as FM, AM, or PM modulation (from power transmitter to power receiver) or load modulation (from power receiver to power transmitter). However, the inventors have recognized that associated disadvantages may also exist in this approach. Specifically, the inventors have recognized that the use of out-of-band communication systems can increase the risk of interference between adjacent power transmission operations and / or increase the risk that power transmission operations can be controlled by a power receiver other than the intended power receiver (i.e., other than the power receiver to which power is being transmitted).

[0093] The inventors have recognized that while conventional in-band communication provides a tight link between communication and power transfer, this may not be the case to the same degree when using out-of-band communication channels. Specifically, the inventors have recognized that the range of out-of-band communication is generally substantially greater than the range of the power transfer signal and the distance between the power transmitter and the power receiver during power transfer, and this may increase the risk that communication received by the power transmitter may not necessarily be received from the powered power receiver, but may instead be received, for example, from another power receiver near the power transmitter. Similar problems may arise if there is a positional misalignment between the power transfer coil and the communication coil, even if the range of out-of-band communication is smaller than the power transfer range, as can be seen in the case of NFC communication.

[0094] To address this issue, a power transmission system may include functionality to detect whether a power receiver has been removed from the power transmitter and to terminate power transmission if this occurs. For example, if the power transmitter detects a rapid and substantial decrease in power extracted from the power transmission signal, it can determine that this is likely because the power receiver has been removed and can therefore proceed to terminating power transmission. This would ensure, for example, that if a wirelessly powered kettle or blender is removed from a designated power area, such as a kitchen countertop, power transmission is terminated and the power transmission signal is removed.

[0095] However, the inventors have recognized that even such functionality could potentially still allow undesirable situations to occur. For example, if a workbench has two adjacent power zones and a pan is positioned on each of them, a user could potentially move the pan quickly (e.g., to facilitate stirring the contents of one pan). This could cause both pans to move their power transmitters and thus be powered by a different power transmitter than before the switch (i.e., the power transmitters would also switch). However, out-of-band communication could have a range that still allows previous communication to continue regardless of the new position, and therefore each power transmitter could receive power control error messages from the pan powered by the other power transmitter. In other words, the power supply to the pans could switch between the two power transmitters without a corresponding switch in communication. Such a situation could lead to undesirable operation because both power control loops are effectively interrupted.

[0096] Figure 1-3 The system includes specific features that allow for close communication between the power transmission signal and the power transmitter and power transmitter pairs in out-of-band. This can provide improved reliability and operation, and can reduce the risk of situations as described above occurring in many applications.

[0097] In the exemplary system, the power transmitter 101 includes a generator function, which will be referred to below as a sequence adapter 209. The sequence adapter 209 is arranged to introduce a sequence of power level changes into the power transmission signal.

[0098] The power transmitter 101 also includes a validity detector 211, which is arranged to detect that the data received by the communicator is invalid data for the current power transmission in response to a comparison of a power level change sequence with a power change request received in a power control error message.

[0099] The generator and validity detector can be implemented in any suitable form, such as in discrete electronic circuits. However, in most embodiments, the generator and validity detector will be implemented, at least in part, as executable code executed by one or more suitable processing units, such as firmware or software running on a central processing unit, signal processing unit, microcontroller or microprocessor or any other suitable processing device.

[0100] The validity detector 211 is specifically fed information about the power level change sequence introduced by the sequence adapter 209. It then monitors power change requests to detect whether these requests match the power level changes introduced by the sequence adapter 209. For example, if the power extracted by the power receiver for the load 303 is constant over the duration of the power level change sequence, power requests are expected to counteract the introduced changes. For example, if the power level change sequence includes an increase in the power level, this will be detected by the power receiver as the power level being too high for the load, and it will therefore proceed to generate one or more power reduction requests and send such requests in one or more power control error messages. If the power level change sequence then reverses back to a zero power level offset, this will now cause the power level to be detected by the power receiver as too low, and this can accordingly generate power increase requests and send these requests to the power transmitter in power control error messages. The power level change sequence can then introduce a negative offset, thereby reducing the power level, which also results in further power increase requests. Finally, the power level change sequence can return to a zero offset, resulting in a power control error message that includes a power reduction request. In this way, the power requests in power control error messages can reflect a sequence of power level changes.

[0101] The validity detector 211 is thus provided with information about the power level change sequence, and thereby it can generate an estimate of the expected power request included in the power control error message, i.e., determine the estimated sequence of power change requests. This estimated sequence can then be compared with the received sequence, and if these match closely enough according to appropriate criteria, the data received by the transmitter communicator 207 is considered valid and transmitted from the power receiver that is actually currently powered by the power transmission signal.

[0102] However, if the estimated sequence and the received sequence do not match sufficiently closely, the received power control error message indicates that it was not actually received from the power receiver being powered by the power transfer signal; that is, it indicates that the received data is not tightly linked to the generated power transfer signal. In this case, the received data can be considered invalid.

[0103] The power transmitter may take different actions in response to the detection of invalid data, depending on the individual embodiment and application preferences and requirements. In many embodiments, it may proceed to modifying or terminating power transmission in response to the detection of invalid data. In many embodiments, the detection of invalid data may cause the power transmission operation to be completely terminated. In other embodiments, it may, for example, proceed to limiting the power level of the power transmission signal, such as applying a maximum power level.

[0104] Therefore, the sequence adapter 209 can introduce power level changes into the power transfer signal. This power level change can be complementary to other power level changes, and specifically, to power level changes caused by power control operations. Thus, in addition to power level changes that may occur due to power transfer operations, the sequence adapter 209 can introduce changes that are independent of power transfer operations and, in most cases, independent of power control error messages, and in fact, generally independent of all data received from the power receiver. The power level change sequence can therefore be a type or characteristic of power level changes that can be superimposed on the power transfer signal.

[0105] This sequence will cause the power control loop to attempt to compensate for, counteract, and negate power level changes. This is done by seeking to elicit the opposite power level change in the power change request received in the power control error message. The effect of the power level change sequence is reflected accordingly by the power change request received from the power receiver and by comparing the power change request with those expected for a given sequence.

[0106] The validity detector 211 can determine a compensation metric reflecting the degree to which the compensation for the power level change in the power change request matches the power level change sequence. This compensation metric can then be used to determine whether out-of-band communication is providing valid data from a power receiver currently exposed to the power transmission signal. For example, if the compensation metric is above a given threshold, the received data can be determined to be valid, and otherwise invalid.

[0107] Compensation for a power level change sequence can be a request to counteract the change introduced by the power level change sequence, i.e., it can be a power change request by requesting a power level change opposite to the change introduced by the power level change sequence.

[0108] In some embodiments, validity detector 211 is arranged to extract a requested power change sequence from a power control error message. The requested power change sequence may indicate the power change requested in the power control error message, and the validity detector may specifically generate a sequence or pattern of power changes requested by the power control error message. The requested power change sequence may reflect a power level change resulting from adjusting the power transmission signal, as requested by the power control error message. Therefore, the requested power change sequence may specifically be a requested power level change sequence. For example, if a power control error message requesting an increase in power level, say, by 1W, is received, the requested power level change sequence can be increased by adding another power level data point that is 1W higher than the previous value.

[0109] The validity detector 211 can then determine the similarity between the power level change sequence and the requested power change sequence (and specifically the requested power level change sequence). The validity detector 211 can generate an appropriate similarity or matching metric using an appropriate similarity or matching metric.

[0110] For example, in many embodiments, the correlation between the power level change sequence applied by the sequence adapter 209 and the requested power level change sequence generated by the validity detector 211 can be determined and used as a similarity measure.

[0111] If the similarity metric indicates a sufficiently similar sequence, the validity detector 211 can determine that the received power control error messages are linked to the power transmission signal, and therefore they are received from the power receiver currently receiving the power transmission signal. Thus, in this case, the power transmission signal and communication are tightly linked, and the received data actually comes from the power receiver to which power is being transmitted. Therefore, the validity detector 211 can determine that the received data and out-of-band communication are generally valid, and power transmission can proceed without any intervention.

[0112] However, if the similarity metric indicates insufficient similarity, it can be determined that there is an unacceptably high risk that the data was indeed received from a power receiver that is not currently exposed to the power transmission signal and is extracting power from it. Therefore, the received data, and indeed the typical out-of-band communication channel, can be considered invalid. This can lead to the termination of power transmission.

[0113] In many embodiments, the validity detector 211 may be specifically arranged to correlate the power level change sequence with the requested power change sequence, and to consider the data valid if the correlation between these sequences is high enough.

[0114] It will be recognized that when a power change request attempts to counteract a power level change introduced by a power level change sequence, the requested power change sequence can be generated as the inverse of the requested power change. For example, a request to increase the power level by a given amount can be reflected by a decrease in the power level in the requested power change sequence. Alternatively, the similarity measure can be modified, for example, by changing the sign of the correlation value, or the decision criterion can be adjusted to take this into account (e.g., by requiring a high negative value for the correlation measure).

[0115] Therefore, a comparison between the power level change sequence and the requested power change sequence can reflect that the increase in the power level of the requested power change sequence is compensated by the request to reduce the power level (and vice versa).

[0116] Therefore, the validity detector 211 can be arranged to determine a similarity measure of the match between the change in the power level change sequence and the change in the requested power change sequence. It can also be arranged to designate data as valid in response to a correlation exceeding a threshold between the power level change sequence and the requested power change sequence.

[0117] The specific power level variation sequence used can be selected based on the specific nature, requirements, and preferences of the individual implementation.

[0118] In many embodiments, the power level change sequence can be a predetermined sequence or pattern, and this sequence can be known in advance by the validity detector 211. In other embodiments, the power level change sequence may not be predetermined, but may be randomly generated, for example, by the sequence adapter 209. In this case, the sequence adapter 209 can provide the validity detector 211 with information about the specific power level change sequence being used.

[0119] In many embodiments, the power level change sequence can be a sequence of power level offsets applied to the power transmission signal. Therefore, the power level of the power transmission signal can be determined based on the operation of the power control loop, and in addition to this setting, the sequence adapter 209 can add sequences that do not depend on the power level offset of the power control loop. In other embodiments, the power level change sequence can be, for example, a relative power level change, such as scaling of the power level by a varying gain factor (which will typically be close to one).

[0120] In some embodiments, the power level change sequence can be a single binary sequence, wherein the power level offset or scaling factor simply switches between two different levels according to an appropriate form. For example, the sequence adapter 209 can periodically switch between applying a positive power level offset (increasing the power level by a small predetermined amount) and applying a negative power level offset (decreasing the power level by a small predetermined amount). This will be expected to result in a bias toward a power reduction request shortly after a switch applying a small positive offset and a bias toward a power increase request shortly after a switch applying a small negative offset. The validity detector 211 can accordingly evaluate power control error messages to detect the presence of such a bias. If not, out-of-band communication can be designated as invalid.

[0121] In many embodiments, the power level change sequence may include a power level offset of the power transmission signal that is constant for a duration of not less than three, and sometimes not less than five or ten, time intervals between power control error messages. Therefore, the offset can be constant for at least some of the received power control error messages. In many embodiments, this can provide improved reliability in detecting the response of the power control loop to the power level change sequence. Specifically, in many cases, it can provide the loop with increased time to adapt to changes in the power level offset and can reduce uncertainty and noise when detecting whether a received power control error message matches the power level change sequence.

[0122] In some embodiments, the power level change sequence may be binary and involves only two possible power level changes. However, in many embodiments, the power level change sequence may include more than two power level changes. Specifically, in many embodiments, the power level change sequence may include at least three distinct power level offsets for the power transmission signal.

[0123] For example, in many embodiments, the power level change sequence may apply varying power level offsets, which include offsets of different magnitudes. Thus, some offsets can be larger than others, resulting in a power change request that demands a larger change. In many embodiments, the power change request may indicate the magnitude of the requested power level change. For example, a power control error message may include bytes as a signed integer, where the integer indicates the magnitude of the required step change. In such embodiments, the validity detector 211 may also consider the magnitude of the offset and the magnitude of the requested power level change in the power control error message.

[0124] For example, validity detector 211 can generate a sequence of requested power level changes that reflects not only the direction of the requested power level changes but also the magnitude of these changes. This can be compared with an introduced sequence of power level changes, for example, by determining a correlation value that reflects the magnitude changes in the sequence.

[0125] In many embodiments, this approach can provide improved reliability in detecting whether power control error messages reflect a sequence of introduced power level changes, and thus provide more reliable detection of whether out-of-band communication is effective.

[0126] In most embodiments, the power level change sequence consists of relatively small power level variations that do not significantly affect power transmission or require large compensation through the power control loop. This minimizes the impact on power transmission operation. Meanwhile, the power level change sequence preferably includes sufficiently large variations so that the response of the power control loop can be detected reliably enough. Preferably, the average power level change introduced by the power level change sequence is substantially zero.

[0127] In many embodiments, the power level change sequence includes only a power level offset of the power transmission signal that does not exceed 10% (or 5%) of the current power level of the power transmission signal.

[0128] In many embodiments, the power level change sequence includes only a power level offset of the power transmission signal that does not exceed 10% (or 5%, or 1%) of the maximum power level of the power transmission signal used for power transmission.

[0129] This allows the effects of power level variation sequences to be small enough not to have an unacceptable impact on ongoing power transfer operations, while still allowing for reliable detection.

[0130] It will be appreciated that, in many embodiments, there may be timing correlation or synchronization between the operation of sequence adapter 209 and validity detector 211.

[0131] For example, in some embodiments, a power level change sequence can be introduced within a relatively short time interval having a relatively long intermediate interval in which no power level change sequence is introduced. In this case, the effectiveness detector 211 can be arranged to evaluate the response of the power control loop within a detection time interval synchronized with the sequence interval. The timing and duration of this detection time interval can depend on the response time and temporal nature of the power control loop.

[0132] For example, the validity detector 211 can begin monitoring for power control error messages at the start of the sequence interval and end within a detection time interval of a predetermined amount of time after the sequence interval. The end time can be selected to ensure that the power control loop has time to react to the final offset of the power level change sequence.

[0133] The validity detector 211 can then search for power level change sequences within that time interval. For example, the requested power level change sequences can be generated for the entire interval, and for different time offsets between sequences, correlation values ​​between the requested power level change sequences and the introduced power level change sequences can be generated. The maximum correlation value can then be considered to correspond to a similarity value, and if this is above a given threshold, the out-of-band communication can be considered valid.

[0134] In other embodiments, the sequence adapter 209 may, for example, continuously apply a power level variation sequence, and may, for example, continuously repeat a predetermined finite-length power level variation sequence to provide a continuous sequence. The validity detector 211 may be synchronized with this (e.g., by finding the time offset that results in the highest correlation value) and continuously evaluate matches within a sufficiently large sliding window.

[0135] In many embodiments, the power level change sequence may be a predetermined power level change sequence. However, in other embodiments, the sequence adapter 209 may be arranged to dynamically adjust the power level change sequence in response to one or more operating parameters.

[0136] In some embodiments, the sequence adapter 209 may be configured to adjust the power level change sequence in response to the timing of power control error messages. For example, the power level change sequence may be adjusted in response to the frequency at which power control error messages are received.

[0137] As a specific example, a power transmitter might power a kitchen appliance such as a kettle, where the power supply function is heating of a heating element. This is typically a slowly varying operation, and therefore power control error messages are sent relatively infrequently, say at intervals of approximately 250 ms. Alternatively, if the power transmitter were powering a motor-driven appliance, such as a blender, faster power control might be needed to maintain the desired speed, and thus more frequent transmission of power control error messages would be necessary. For example, power control error messages might be sent at 10 ms intervals.

[0138] In such an example, the sequence adapter 209 can adjust the power level change sequence to have more frequent changes for the second case than for the first case; that is, it can introduce faster changes for the higher frequency of power control error messages being sent. This allows the detection process to adapt to a specific situation and provides improved and more reliable testing in most embodiments.

[0139] In some embodiments, the sequence adapter 209 may be arranged to adjust the power level change sequence in response to a power level change requested by a power control error message. For example, it may be arranged to adjust the magnitude of the change in the power level change sequence in response to a power level change requested by a power control error message. Specifically, the magnitude of the change may increase with an increase in the level of the power change requested by the power control error message.

[0140] As an example, some power receivers require substantially constant power with very small variations. For instance, a battery charger can extract substantially constant power. In this case, power control error messages typically do not request a change in power level or request only a very small change in power level. Therefore, even relatively small power level changes introduced by sequence adapter 209 can be detected in power control error messages requesting a power level change caused by power transfer operations. Thus, in this case, the power level change sequence can be set to have relatively small power level variations.

[0141] Alternatively, if the power receiver requires frequent and substantial power level changes and therefore sends many and large power level change requests (e.g., to control a motor experiencing a changing load), the validity detector 211 will find it much more difficult to detect small power level changes. In such a scenario, the sequence adapter 209 can be configured to have large power level changes in response to large and frequent power level change requests, resulting in a greater need for compensation by the power control loop. This can facilitate and / or improve detection.

[0142] In some embodiments, the validity detector 211 may alternatively or additionally be arranged to adjust the detection criteria used for comparison in response to power level changes requested by a power control error message. For example, if the power control error message includes requests for frequent and / or large changes (and specifically more frequent and larger than those required to compensate for a sequence of power level changes), the validity detector 211 may increase the detection interval over a longer duration.

[0143] Alternatively or additionally, in such cases, the validity detector 211 may modify the detection threshold so that, for example, even for lower values ​​of similarity measure or correlation, out-of-band communication is considered valid.

[0144] In practice, in many situations, the validity detector 211 can be configured to determine data as valid data in response to detecting a power level change exceeding a power change threshold caused by a power control error message. Specifically, the validity detector 211 can be configured to deny data as invalid data in response to detecting a power level change exceeding a power change threshold caused by a power control error message.

[0145] The power level change can be determined for a time interval, which may include, exclude, or include only the time interval in which a power change request for comparison is made (i.e., in some embodiments, a detection may be denied if the power level change within the comparison interval is too high; in other embodiments, a detection may be denied if the power level change outside the comparison interval (e.g., just before the comparison interval) is too high; and in some embodiments, a detection may be denied if the power level change within a time interval that includes both the non-comparison interval and the comparison interval is too high).

[0146] Therefore, in such a situation, validity detector 211 can proceed to detect that the requested power change is higher than a given threshold, and if this occurs, it can be considered that the detection of invalid data is prohibited because it may not be a sufficiently reliable detection operation.

[0147] The power change threshold for this purpose will exceed the maximum power level offset of the power level change sequence; that is, detection will be prohibited only when the requested power change is higher (and usually substantially higher) than the required and expected change in the compensating power level change sequence.

[0148] In some embodiments, the requested power level change may exclude power level changes caused by power change requests used in the comparison, while in other embodiments it may include power level changes caused by power change requests used in the comparison as well as other power level changes, and in fact in some embodiments it may be based solely on power level changes caused by power change requests used in the comparison.

[0149] As another specific example of adjusting the detection criteria, the system can, for example, generate a measure of the level of the requested power level change over the past N seconds. While a comparison is being made, the system can, for example, adjust the duration of the comparison based on this measure, such that the higher the level of the requested power level change, the longer the duration, thereby compensating for noise introduced into the comparison by power level changes not directly generated by the power level change sequence. If the N-second time interval is chosen to be N seconds before the introduction of the power level change sequence, a method can be implemented in which the adjustment is based on the requested power level change not included in the comparison. However, if the N-second time interval is chosen to be N seconds immediately before the comparison is performed (and therefore after the power change request used in the comparison has been received), a method can be implemented in which the adjustment is based on the requested power level change that is indeed included in the comparison. In practice, if the N-second time interval is less than the time interval after the power change request used in the comparison has been received, the adjustment of the detection criteria can be based solely on the requested power level change also considered in the comparison.

[0150] It will be appreciated that, in different embodiments, the sequence adapter 209 may use different methods to introduce a power level change sequence. In some embodiments, a power level change may be simply introduced by altering the voltage and / or current of the drive signal according to the power level change sequence. For example, the supply voltage of the output inverter of the driver 201 may be modified according to the change in the power level change sequence.

[0151] In some embodiments, the sequence adapter 209 may be arranged to introduce a power level variation sequence by applying a frequency offset variation sequence to the frequency of the power transmission signal.

[0152] In many wireless power transmission systems, power transmitters and / or power receivers can use resonant circuits for power transmission. In such cases, the power level can be adjusted by changing the frequency of the drive signal and thus tuning the frequency of the power transmission signal closer to or further away from the resonant frequency of the resonant circuit. In some embodiments, the power level can be adjusted by changing the phase or duty cycle of the drive signal.

[0153] In some embodiments, such frequency control can be used to introduce a sequence of power level changes. For example, a positive power level offset can be introduced by adjusting the frequency closer to the resonant frequency, and a negative power level offset can be introduced by adjusting the frequency further away from the resonant frequency. The power receiver will respond to such a power level change by sending an appropriate power change request, which can then be compared to the sequence of power level changes.

[0154] This invention can be implemented in any suitable form, including hardware, software, firmware, or any combination thereof. Optionally, the invention can be implemented, at least in part, as computer software running on one or more data processors and / or digital signal processors. The elements and components of embodiments of the invention can be implemented physically, functionally, and logically in any suitable manner. In practice, functionality can be implemented in a single unit, in multiple units, or as part of other functional units. Thus, the invention can be implemented in a single unit or physically and functionally distributed among different units, circuits, and processors.

[0155] Although the invention has been described in conjunction with some embodiments, it is not intended to limit the invention to the specific forms set forth herein. Rather, the scope of the invention is limited only by the appended claims. Furthermore, while features may appear to have been described in conjunction with specific embodiments, those skilled in the art will recognize that various features of the described embodiments can be combined according to the invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0156] Furthermore, although listed individually, multiple modules, elements, circuits, or method steps can be implemented, for example, by a single circuit, unit, or processor. Moreover, although individual features may be included in different claims, these can be advantageously combined, and inclusion in different claims does not imply that the combination of features is infeasible and / or disadvantageous. Including a feature in one class of claims does not imply a limitation on that class, but rather indicates that the feature is equally applicable to other classes of claims where appropriate. Furthermore, the order of features in a claim does not imply any particular order in which the features must operate, 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 can be performed in any suitable order. Additionally, singular references do not exclude plural. Therefore, references to “a,” “an,” “first,” “second,” etc., do not exclude plural. Reference numerals in the claims are provided merely for clarity of example and should not be construed as limiting the scope of the claims in any way.

Claims

1. A power transmitter (101) for a wireless power transmission system, the wireless power transmission system including at least one power receiver (105) for receiving power transmission from the power transmitter (101) via a wireless inductive power transmission signal; the power transmitter (101) comprising: Output circuits (103, 203) include a transmitter coil (103) for generating the power transmission signal in response to a drive signal being applied to the output circuits (103, 203); A driver (201) for generating the drive signal; A communicator (207) for communicating with the power receiver (105) is arranged to receive data from the power receiver (105) via a communication channel that does not use the power transmission signal as a communication carrier, the data including power control error messages; A power loop controller (205) for implementing a power control loop, the power loop controller (205) being arranged to adjust the power level of the power transmission signal in response to a power change request of the power control error message; A generator (209) is used to introduce a power level change sequence into the power transmission signal; A validity detector (211) is used to detect data received by the communicator (207) as invalid data for the power transmission in response to a comparison of the power level change sequence with the power change request of the power control error message.

2. The power transmitter according to claim 1, wherein, The validity detector (211) is configured to: determine a compensation metric indicating the degree to which the power change request matches the compensation for the power level change sequence; and detect data as invalid data for the power transmission in response to the compensation metric.

3. The power transmitter according to claim 1 or 2, wherein, The validity detector (211) is configured to extract the requested power change sequence from the power control error message; Furthermore, in response to a comparison between the power level change sequence and the requested power change sequence, the data received by the communicator is detected as invalid data for the power transmission.

4. The power transmitter according to claim 3, wherein, The validity detector (211) is configured to designate data as invalid in response to the correlation between the power level change sequence and the requested power change sequence.

5. The power transmitter according to claim 4, wherein, The validity detector (211) is configured to designate data as invalid in response to the correlation between the power level change sequence and the requested power change sequence not exceeding a threshold.

6. The power transmitter according to claim 1 or 2, wherein, The power level variation sequence includes at least three different power level offsets for the power transmission signal.

7. The power transmitter according to claim 1 or 2, wherein, The power level change sequence includes at least one power level offset for the power transmission signal, the at least one power level offset being constant for a duration of not less than three time intervals between power control error messages.

8. The power transmitter according to claim 1 or 2, wherein, The power level change sequence includes only power level offsets of the power transmission signal that are no greater than 10% of the current power level of the power transmission signal.

9. The power transmitter according to claim 1 or 2, wherein, The validity detector (211) is configured to determine the data received by the communicator (207) as invalid data in response to detecting a power level change exceeding a power change threshold, which is greater than the maximum power level offset of the power level change sequence.

10. The power transmitter according to claim 1 or 2, wherein, The generator (209) is arranged to introduce the power level change sequence by applying a frequency offset change sequence to the frequency of the power transmission signal.

11. The power transmitter according to claim 1 or 2, wherein, The generator (209) is configured to adjust the power level change sequence in response to the timing of the power control error message.

12. The power transmitter according to claim 1 or 2, wherein, The generator (209) is configured to adjust the power level change sequence in response to a power level change requested by the power control error message.

13. The power transmitter according to claim 1 or 2, wherein, The validity detector (211) is configured to adjust the detection criteria used for the comparison in response to a power level change requested by the power control error message.

14. A method of operating a power transmitter (101) for a wireless power transmission system, the wireless power transmission system comprising at least one power receiver (105) for receiving power transmission from the power transmitter (101) via a wireless inductive power transmission signal; the power transmitter (101) comprising: Output circuits (103, 203) include a transmitter coil (103) for generating the power transmission signal in response to a drive signal being applied to the output circuits (103, 203); And the method includes: Generate the drive signal; Communicating with the power receiver (105), the communication including receiving data from the power receiver (105) via a communication channel that does not use the power transmission signal as a communication carrier, the data including power control error messages; A power control loop is implemented, which adjusts the power level of the power transmission signal in response to a power change request from a power control error message; The power level change sequence is introduced into the power transmission signal; and The data received by the communicator (207) is detected as invalid data for the power transmission in response to a comparison between the power level change sequence and the power change request of the power control error message.

15. A wireless power transmission system comprising at least one power transmitter (101) and at least one power receiver (105), the at least one power receiver being configured to receive power transmission from the power transmitter (101) via a wireless inductive power transmission signal; the power transmitter (101) comprising: Output circuits (103, 203) include a transmitter coil (103) for generating the power transmission signal in response to a drive signal being applied to the output circuits (103, 203); A driver (201) for generating the drive signal; A communicator (207) for communicating with the power receiver (105) is arranged to receive data from the power receiver (105) via a communication channel that does not use the power transmission signal as a communication carrier, the data including power control error messages; A power loop controller (205) for implementing a power control loop, the power loop controller (205) being arranged to adjust the power level of the power transmission signal in response to a power change request of the power control error message; A generator (209) is used to introduce a power level change sequence into the power transmission signal; A validity detector (211) is used to detect data received by the communicator (207) as invalid data for the power transmission in response to a comparison of the power level change sequence with the power change request of the power control error message.

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