RU2777986C2 - System of wireless power transmission - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: power transmitter (101) for a system of wireless power transmission is proposed, containing transmitter coil (103) and exciter (201) generating an excitement signal for coil (103), using a repeating time frame with a time interval of power transmission and a time interval of lowered power, during which a power level of a power transmission signal is reduced. Exciter (201) generates an excitement signal for transmitter coil (103) in order to generate a power transmission signal. Communication device (205) receives messages from power receiver (105), and adapter (213) adapts synchronization characteristics of the time interval of lowered power in response to at least the reception of the first message from power receiver (105). Synchronizer (206) is made with the possibility of synchronization of foreign object detection and generation of a verification signal, which should occur during the time interval of lowered power.

EFFECT: increase in synchronization characteristics, for example the duration of a time interval of lowered power, as well as reduction in interference for additional operations, for example foreign object detection or communication.

14 cl, 6 dwg

Description

FIELD OF TECHNOLOGY

The present invention relates to the operation of a system for wireless power transmission and, in particular, to the detection of a foreign object in a system for wireless power transmission.

BACKGROUND OF THE INVENTION

To power most modern electrical products from an external power source, it is necessary to provide a specially designed electrical contact. However, this is generally impractical and involves the user physically connecting connectors or otherwise providing physical electrical contact. As a rule, power requirements also vary greatly, and nowadays most devices have their own specially designed power supply, leaving the average user with a large number of different power supplies, each designed for a specific device. While the use of internal batteries may avoid the need for a wired connection to power during use, this is only a partial solution as the batteries need to be recharged (or replaced). The use of batteries can also lead to a significant increase in weight and a potential increase in the cost and size of devices.

In order to provide the user with a much better user experience, it has been proposed to use a wireless power supply in which power is inductively transferred from the transmitter inductance in the power transmitter device to the receiver coil in separate devices.

Power transfer by magnetic induction is a well-known concept, mainly applied in transformers having full flux inductive coupling between the transmitter's primary inductor/coil and the receiver's secondary coil. By separating the primary transmitter coil and the secondary receiver coil between the two devices, it becomes possible to wirelessly transfer power between them based on the loosely coupled transformer principle.

This design allows wireless power to be transferred to the device without the need for any wired or physical electrical connections. In fact, this may allow the device to be placed next to or on top of the transmitter coil for external charging or power supply. For example, power transmitter devices may be placed near a horizontal surface on which the device may simply be placed to provide power.

In addition, such wireless power transmission structures can preferably be designed such that a power transmitter device can be used with a plurality of power receiver devices. In particular, an approach to wireless power transmission, known as Qi Specifications, has been proposed and is currently under development. This approach allows power transmitter devices that meet Qi specifications to be used with power receiver devices that also meet Qi specifications, without having to be made by the same manufacturer or specifically made for each other. The Qi standard additionally includes some functionality to tailor the operation to a particular power receiver device (eg, depending on a particular power consumption).

The Qi specification was developed by the Wireless Power Consortium and further information is available, for example, on its website: http://www.wirelesspowerconsortium.com/index.html, where, in particular, you can find the defining documents of this specification .

In power transmission systems such as Qi, the electromagnetic field created to transmit the required power levels to the power receiver is often very significant. The presence of such a strong field in many situations can affect the environment.

For example, a potential problem with wireless power transmission is that unintentional power transmission can occur, for example, to metallic objects that are in the vicinity of the power transmitter. For example, if a foreign object such as a coin, key, ring, etc., is placed on a power transmitter platform configured to receive power by the receiver, the magnetic flux generated by the transmitter coil will create eddy currents in the metal objects. leading to heating of these objects. The rise in temperature can be very significant and highly undesirable.

To reduce the risk of such situations, it has been proposed to introduce foreign object detection, in which the power transmitter is able to detect the presence of a foreign object and reduce the transmission power and/or generate an alert to the user when a positive detection occurs. For example, the Qi system includes functionality to detect a foreign object and reduce power when a foreign object is detected. In particular, section 11 of the Qi specification version 1.2.1 describes various methods for detecting a foreign object.

One method for detecting such foreign objects is disclosed in WO2015018868A1. In another example, presented in WO 2012127335, an approach based on the determination of unknown power losses is disclosed. In this approach, both the power receiver and the power transmitter measure their power, with the receiver reporting the measured received power to the power transmitter. When a power transmitter detects a significant difference between the power transmitted by the transmitter and the power received by the receiver, an undesirable foreign object may potentially be present and, for security reasons, the power transmission may be reduced or terminated. This method of determining power loss requires synchronized, accurate power measurements by transmitter and receiver.

For example, according to the Qi power transmission standard, a power receiver estimates the power it has received, for example, by measuring the rectified voltage and current, multiplying them, and adding an estimate of the internal power losses in the power receiver (for example, losses of the rectifier, receiver coil, metal parts that are part of the receiver, and etc.). The power receiver transmits the determined received power to the power transmitter at a certain minimum frequency, eg every four seconds.

The power transmitter estimates the power it has delivered, for example, by measuring the DC input voltage and inverter current, multiplying them, and correcting the result by subtracting an estimate of the internal power losses in the transmitter, such as the estimated power losses in the inverter, primary coil, and metal parts that are part of the power transmitter.

The power transmitter may estimate the power loss by subtracting the reported received power from the transmitted power. If the difference exceeds the threshold, the transmitter will assume that a large amount of power is being dissipated by a foreign object, after which it may stop transmitting power.

As an alternative, it has been proposed to measure the quality or quality factor of the resonant circuit formed by the primary and secondary coils together with their respective capacitances and resistances. A decrease in the measured quality factor may indicate the presence of a foreign object.

In practice, as a rule, it is difficult to achieve sufficient accuracy of determination using the methods described in the Qi specification. This complexity is exacerbated by many uncertainties regarding specific current operating conditions.

For example, the potential presence of native metals (i.e., the metal parts of the device that house the power receiver or power transmitter) is a particular concern, as their magnetic and electrical properties may be unknown (and differ from device to device) and thus can be be hard to compensate.

In addition, unwanted heating may be the result of even a relatively small amount of power being dissipated by a metallic foreign object. Thus, even a small power discrepancy between transmitted and received power needs to be detected, and this can be particularly difficult when transmit power levels increase.

The Q-factor degradation approach can in many cases be characterized by better sensitivity for detecting the presence of metallic objects. However, it may still not provide sufficient accuracy and, for example, may also be affected by its own metal.

The effectiveness of foreign object detection depends on the specific operating conditions when the test is actually performed. For example, if, as described in the Qi specification, a foreign object detection measurement is performed in the selection step of the power transmission initialization process, the signal that the power transmitter provides for the measurement must be weak enough to prevent activation of the power receiver. However, for such a weak signal, the signal-to-noise ratio is usually low, resulting in poor measurement accuracy.

Requiring a weak measuring signal can lead to other undesirable effects. A power receiver exposed to a weak measurement signal may experience leakage current, which depends on the level of the measurement signal, the coupling between the primary and secondary coils, and the state of charge of the capacitor at the output of the rectifier. Thus, this leakage current may be different depending on the actual conditions. Since the leakage current affects the impedance introduced into the power transmitter coil, the measurement of the Q factor will also depend on the specific current conditions.

Another problem is that foreign object detection is usually a very sensitive test, in which it is desirable that relatively small changes caused by the presence of a foreign object be detected in an environment with as wide a range of operating conditions and cases as possible for which the test is performed.

Accordingly, existing workflows are generally sub-optimal and may, in some instances and instances, provide sub-optimal performance. In particular, this may result in the presence of foreign objects not being detected, or may result in false detection of foreign objects when they are absent.

Accurate detection of foreign objects is particularly difficult in cases where the power level of the power transmission signal is high and/or when it changes. Thus, the detection of foreign objects is particularly difficult in the power transmission phase, in particular for power receivers which present a large and fluctuating load.

In addition, other operations of the power transmission system may be susceptible to such effects. For example, in many cases communication between a power transmitter and a power receiver can be adversely affected by large loads, and in particular by large load changes.

In many systems, when communicating from a power receiver to a power transmitter, load modulation can be used in which the load on the power transmission signal varies depending on the data to be transmitted. However, such load modulation can be difficult to determine while changing the power transfer load for the power transfer signal. Similarly, communication from a power transmitter to a power receiver can be achieved by modulating the power transmit signal (eg, amplitude or frequency modulation), but interference with such modulation may be caused by changes in the parameters of the power transmit signal due to varying load.

In fact, even if a completely separate carrier is used for communication, such as a Near Field Communication (NFC) channel, the very large and varying electromagnetic field created by the power transmission signal can cause significant interference despite being in a completely different frequency range. .

Thus, the presence of a power transmission signal and its load may have a negative impact on other operations such as foreign object detection and communication operations.

Therefore, it would be preferable to improve the performance of the power transmission system, in particular, it would be preferable to apply an approach that can increase flexibility, reduce cost, reduce complexity, improve foreign object detection, improve communication, improve support for various loads, improve adaptability, backward compatibility and/ or improve performance.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is preferably directed to the reduction, mitigation or elimination of one or more of the above disadvantages alone or in any combination.

According to an aspect of the present invention, there is provided a power transmitter for wirelessly supplying power to a power receiver via an electromagnetic power transmission signal; comprising: a transmitter coil for generating a power transmission signal, wherein a repeating time frame is used for the power transmission signal at the power transmission stage, comprising at least a power transmission time interval and a reduced power time interval during which the power level of the power transmission signal is reduced; a driver for generating a drive signal for the transmitter coil to generate a power transmission signal; a first communication device for receiving messages from the power receiver; an adapter for adapting a low power slot timing characteristic in response to at least a first message received from the power receiver; and a synchronizer for synchronizing the power transmitter operation to occur during the low power time interval; a test coil for generating an electromagnetic test signal; a test generator configured to generate a test drive signal for the test coil; and a foreign object detector configured to conduct a foreign object detection test in response to receiving a measured parameter for the drive test signal during the low power time interval; wherein the synchronizer is configured to synchronize the test oscillator to provide an electromagnetic test signal during the reduced power time interval.

The present invention may provide improved performance in many embodiments, and may provide overall improved performance of the power transfer operation in many systems and embodiments. For example, in many embodiments, improved foreign object detection and possibly communication can be achieved by performing these operations during time intervals with particularly favorable conditions for performing such operations.

This approach may allow complexity to be reduced in many embodiments and may allow a high degree of backward compatibility to be achieved in many systems. In particular, this approach may be particularly useful for improving foreign object detection and possibly communication in Qi wireless power transmission systems, such as operating in accordance with Qi specifications version 1.2 or earlier.

In many embodiments, the duration of the low power slot is no more than 5%, 10%, or 20% of the duration of the time frame. In many embodiments, the duration of the low power slot(s) is at least 70%, 80%, or 90% of a time frame.

In some embodiments, the power transmitter may be configured to perform foreign object detection and possibly communication operations during a reduced power transmission time interval. In some embodiments, the power transmitter may be configured to adjust the timing of either foreign object detection or possibly a communication operation to occur during the reduced power transmission time interval.

During the reduced power time interval, the power level of the power transmission signal decreases in accordance with the decreasing power level transmitted from the power transmitter to the power receiver. During the low power time interval, the power level transmitted from the power transmitter to the power receiver is reduced relative to the power level transmitted from the power transmitter to the power receiver during the power transmission time interval (the same low power time interval). Power level and references to power and power level can in particular be considered as referring to real power (I⋅U⋅Cos ϕ).

According to an optional feature of the present invention, the timing characteristic is the length of the low power time interval.

The system may be configured to adapt the duration of the low power slot in response to communication from the power receiver to the power transmitter. This may allow improved performance in many embodiments and may allow operations such as communication or foreign object detection to be performed at times when conditions are particularly suitable for doing so. Adapting the low power slot length allows for a better compromise between different conflicting requirements, such as between the requirements and preferences for transmitting power from a power transmitter to a power receiver, and the requirements and preferences for detecting foreign objects and communicating.

The power transmitter may be configured to adapt the duration of the low power time interval to the minimum duration.

According to an optional feature of the present invention, the timing characteristic is the duration between low power slots of successive repeated time frames.

In some embodiments, the timing characteristic is the duration between successive repeated time frames. In some embodiments, the timing characteristic is the duration of repeated time frames.

The system may be configured to adapt the duration between the reduced power slots of successive repeated time frames in response to communication from the power receiver to the power transmitter. This may allow for improved performance in many embodiments and may allow operations such as communication or foreign object detection to be performed at times when conditions are particularly suitable for doing so. Duration adaptation between the reduced power slots of successive repeated time frames allows for a better compromise between different conflicting requirements, for example between the requirements and preferences for transmitting power from a power transmitter to a power receiver, and the requirements and preferences for detecting foreign objects and communicating.

The power transmitter may be configured to adapt the duration between low power transmission instants of successive repeated time frames to accommodate the maximum duration.

In accordance with an optional feature of the present invention, the first communication device is configured to transmit messages to the power receiver; and the power transmitter is configured to transmit a message indicating at least one of the duration of the low power slot and the duration between the low power slots of successive repeated time frames to the power receiver prior to receiving the first message.

This, in particular, may allow for the preferred operation in many embodiments. The message may specifically indicate acceptable, acceptable, limited and/or preferred values.

The message may in particular be transmitted in response to a request for such information transmitted from the power receiver to the power transmitter.

According to an optional feature of the present invention, the first message is a request message indicating the requested value for the timing characteristic; and the power transmitter is configured to approve or reject the requested value.

This, in particular, may allow for the preferred operation in many embodiments. This may in particular allow the power receiver to maintain initiative and provide operational control, which may be very advantageous in many situations.

In accordance with an optional feature of the present invention, the adapter is configured to determine the timing characteristic in an initialization step prior to the power transfer step.

This, in particular, may allow to provide the preferred operation in many embodiments, and may, in particular, allow to reduce the complexity of operation in many embodiments.

In accordance with an optional feature of the present invention, the adapter is configured to dynamically adapt the timing characteristic during the power transmission step in response to receiving a plurality of messages received from the power receiver during the power transmission step.

This, in particular, may allow for the preferred operation in many embodiments, and may, in particular, allow for optimization for current conditions.

In accordance with an optional feature of the present invention, the first communication device is configured to synchronize communication with the power receiver that occurs during low power time slots.

The present invention may improve communication in many embodiments. This approach may improve the accuracy and/or reliability of communication between the power receiver and the power transmitter during the power transmission step.

Communication timing may be applied only to certain communications, eg, only to communications for power control, only to communications from a power transmitter to a power receiver, or only from a power receiver to a power transmitter, etc.

The power transmitter also includes: a test coil for generating an electromagnetic test signal; a test generator configured to generate a test drive signal for the test coil; and a foreign object detector configured to conduct a foreign object detection test in response to receiving a measured parameter for the drive test signal during the low power time interval; wherein the synchronizer is configured to synchronize the test oscillator to provide an electromagnetic test signal during the reduced power time interval.

The present invention may allow for improved foreign object detection in many embodiments. This approach may improve the accuracy and/or reliability of the foreign object detection checks during the power transfer phase. In many embodiments, this approach can reduce the uncertainty and variability of foreign object detection checks and thus improve performance. Such an approach may, in particular, make it possible to reduce the impact of changes in power transmission and operating conditions when foreign objects are detected. Such an approach may, for example, tend to operate the system in accordance with a specific, eg, predetermined, reference scenario and operating mode when foreign objects are detected. This may improve the consistency and predictability of the foreign object detection test. In particular, this may allow more accurate and more reliable evaluation of the influence of the power receiver on the electromagnetic test signal, and thus may allow improved compensation by the foreign object detector.

This approach may, for example, involve the introduction of a foreign object detection time interval during which the power receiver can operate with a high induced voltage and still with a small load corresponding to a high magnetic field strength and still with a small load for the electromagnetic signal. In such cases, the influence of a foreign object may be more noticeable, since the power induced in such an object will have a higher share in the total received power. In fact, a larger magnetic field may result in a stronger induced signal at any foreign object present, and a reduced loading may allow the effect of the presence of the power receiver to be reduced when the presence of a foreign object is detected.

The foreign object detector may be configured to determine that a foreign object has been detected if the difference between the power level of the electromagnetic test signal and the power indicated by the load indication received from the power receiver and indicating the expected load of the electromagnetic test signal is above a threshold value. If this difference is below a threshold, the foreign object detector may determine that no foreign object has been detected.

The foreign object detector may be configured to determine that a foreign object has been detected if a quality factor (determined based on measurements of the drive signal) for the resonant circuit comprising the test coil is below a threshold value. The threshold value, as a rule, may depend on the message received from the power receiver.

In many embodiments, the test coil and the transmitter coil may be the same coil. In many embodiments, the exciter and test oscillator may be the same component, thus the same circuit may generate both a drive signal and a test drive signal. In many embodiments, the power transfer signal and the excitation test signal may share many parameters, for example, they may have the same frequency.

In accordance with an aspect of the present invention, a wireless power transmission system is provided, comprising a power transmitter as described above, and also comprising a power receiver, comprising: a second communication device for communicating with the power transmitter; a request controller for transmitting a first message to the power transmitter, the first message containing a request for a requested timing characteristic value; a response controller for receiving a response to the request from the power transmitter and for determining a timing characteristic in response to receiving the response to the request, the response to the request indicating whether the requested value was approved by the power transmitter; and a load controller for adapting the load for the power transmission signal such that the load is reduced during the reduced power time slots.

The present invention allows improved performance of a wireless power transmission system.

In accordance with an optional feature of the present invention, the request controller is configured to request a limitation of the synchronization characteristic from the power transmitter; the response controller is configured to receive an indication of the synchronization response limitation from the power transmitter, and the request controller is configured to determine the requested synchronization response value in response to the synchronization response limitation.

This may improve and/or facilitate operation in many embodiments.

In accordance with an optional feature of the present invention, the timing characteristic is a low power slot duration and the request controller is configured to determine the requested timing characteristic value given the maximum duration, and the adapter is configured to determine the timing characteristic value in response to receiving the minimum duration.

This may improve and/or facilitate operation in many embodiments.

In some embodiments, the power receiver is configured to set a maximum value and the power transmitter is configured to set a minimum value for the duration of the low power time interval.

In accordance with an optional feature of the present invention, the timing characteristic is the duration between the transmission of reduced power of successive repeated time frames and the request controller is configured to determine the requested value of the synchronization characteristic given the minimum duration, and the adapter is configured to determine the value of the synchronization characteristic in response to receiving maximum duration.

This may improve and/or facilitate operation in many embodiments.

In some embodiments, the power receiver may set a minimum value, and the power transmitter may set a maximum value, for the duration between times of reduced power transmission of successive repeated time frames.

According to an aspect of the present invention, there is provided a method for operating a power transmitter to wirelessly supply power to a power receiver via a power transmission electromagnetic signal; wherein the method includes performing by the power transmitter the following steps: generating a power transmission signal, wherein for the power transmission signal, the power transmission step uses a repeating time frame comprising at least a power transmission time interval and a reduced power time interval during which the power level of the power transmission signal lowered; generating a drive signal for the transmitter coil to generate a power transmission signal; receiving messages from the power receiver; adapting a low power slot timing characteristic in response to at least the first message received from the power receiver; and synchronization of the operation of the power transmitter, which should occur during the time interval of reduced power; generating a test drive signal for the test coil to generate an electromagnetic test signal; and performing a foreign object detection test in response to receiving a measured parameter for the drive test signal during the low power time interval; wherein the timing includes timing the drive test signal to provide an electromagnetic test signal during the reduced power time interval.

According to an aspect of the present invention, there is provided a method for operating a wireless power transmission system, comprising: a power transmitter for wirelessly supplying power to a power receiver via a power transmission electromagnetic signal; wherein the method includes performing by the power transmitter the following steps: generating a power transmission signal, wherein for the power transmission signal, the power transmission step uses a repeating time frame comprising at least a power transmission time interval and a reduced power time interval during which the power level of the power transmission signal lowered; generating a drive signal for the transmitter coil to generate a power transmission signal; receiving messages from the power receiver; adapting a low power slot timing characteristic in response to at least the first message received from the power receiver; and synchronization of the operation of the power transmitter, which should occur during the time interval of reduced power; generating a test drive signal for the test coil to generate an electromagnetic test signal; performing a foreign object detection test in response to receiving a measured parameter for the drive test signal during the low power time interval; wherein the timing includes timing the drive test signal to provide an electromagnetic test signal during the reduced power time interval; in addition, the method includes performing by the power receiver the following steps: communicating with the power transmitter; transmitting a first message to the power transmitter, the first message comprising a request for a requested timing characteristic value; receiving a response to the request from the power transmitter; determining a timing characteristic in response to receiving a response to the request, the response to the request indicating whether the requested value has been approved by the power transmitter; and adapting the load for the power transmission signal such that the load is reduced during the reduced power time intervals.

These and other aspects, features and advantages of the present invention will become apparent and will be explained with reference to the embodiment(s) described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described solely by way of example with reference to the drawings, in which

FIG. 1 shows an example of elements of a power transmission system in accordance with some embodiments of the present invention.

in FIG. 2 shows an example of elements of a power transmitter in accordance with some embodiments of the present invention;

in FIG. 3 shows an example of elements of a power receiver in accordance with some embodiments of the present invention;

in FIG. 4 shows an example of elements of a power receiver in accordance with some embodiments of the present invention;

in FIG. 5 shows an example time frame for the wireless power transmission system of FIG. one; and

in FIG. 6 shows an example time frame for a wireless power transmission system in accordance with some embodiments of the present invention.

IMPLEMENTATION OF THE INVENTION

The following description focuses on embodiments of the present invention that can be applied to a wireless power transmission system and which involve the use of a power transmission approach such as that known from the Qi specification. However, it should be understood that the present invention is not limited to this application, but can be applied to many other wireless power transmission systems.

FIG. 1 shows an example of a power transmission system in accordance with some embodiments of the present invention. The power transmission system comprises a power transmitter 101 which contains (or is connected to) a transmitter coil/inductance 103. The system also includes a power receiver 105 which contains (or is connected to) a receiver coil/inductance 107.

The system provides an electromagnetic power transfer signal that allows power to be inductively transferred 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 the coil or inductance 103 of the transmitter. The power transmission signal may correspond to an electromagnetic power transmission component that transmits power from the power transmitter to the power receiver, and may be considered to correspond to a component of the generated electromagnetic field that transmits power from the power transmitter to the power receiver. For example, if the pickup coil 107 is not loaded, the power receiver will not receive power from the generated electromagnetic field (not including losses). In such a case, when the transmitter coil 103 is energized, an electromagnetic field with a potentially high field strength can be generated, but the power level of the power transmission signal will be zero (excluding losses). In some situations, if a foreign object is present, the power transmission signal can be considered as including a component corresponding to the power transmission of the foreign object, and thus the power transmission signal can be considered as corresponding to the power received from the electromagnetic field generated by the power transmitter.

The power transmit signal can typically range from about 20 kHz to about 500 kHz, and often for Qi-compatible systems, typically in the range of 95 kHz to 205 kHz (or, for example, for high power kitchen applications). the frequency may, for example, typically be in the range of 20 kHz to 80 kHz). The transmitter coil 103 and the power reception coil 107 are loosely coupled, and thus the power reception coil 107 receives a power transmission signal (at least a portion of the signal) from the power transmitter 101. Thus, power is transmitted from the power transmitter 101 to the power receiver 105 by wireless inductive coupling from the transmitter coil 103 to the power receive coil 107. The term "power transmission signal" is mainly used to refer to the inductive signal/magnetic field between the transmitter coil 103 and the power (flux signal) receiving coil 107, but it should be understood that, equivalently, it can also be considered and used to refer to the electrical signal provided by on the transmitter coil 103 or received by the power reception coil 107 .

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

The system is capable of transmitting significant power levels, and in particular, the power transmitter can deliver power levels in excess of 500 mW, 1 W, 5 W, 50 W, 100 W, or 500 W in many embodiments. For example, for Qi compliant applications, power transfer can typically occur in the power range of 1-5 W for low power applications (basic power profile), up to 15 W for Qi specification version 1.2, in the range up to 100 W for higher power applications such as power tools, laptops, drones, robots, etc. and 100 to 1000 W for very high power applications such as kitchen applications.

In the following, the operation of the power transmitter 101 and the power receiver 105 will be described with direct reference to an embodiment generally conforming to the Qi specification (except as described (or subsequent) changes and improvements) or suitable to the Consortium's high power kitchen specification. wireless power transmission. In particular, power transmitter 101 and power receiver 105 may support or be substantially compliant with elements of the Qi specification version 1.0, 1.1, or 1.2 (except as described herein (or subsequent) changes and improvements).

Further operation of the system according to FIG. 1 will be described with particular reference to foreign object detection.

In wireless power transmission systems, the presence of an object (typically a conductive element that receives power from a power transmission signal and is not part of the power transmitter 101 or power receiver 105, i.e., being an unintended, unwanted and/or interfering element with respect to the power transmission ) can be very undesirable in power transmission. Such an unwanted object is also known as a foreign object.

The foreign object may not only reduce efficiency by adding power losses to the operation, but may also degrade the power transfer operation itself (eg, by influencing the efficiency of power transfer or receiving power not directly controlled, for example, by a power transfer loop). In addition, the induction of currents in the foreign object (in particular, eddy currents in the metal part of the foreign object) can often lead to highly undesirable heating of the foreign object.

To solve this problem, wireless power transmission systems such as Qi include a foreign object detection function. In particular, the power transmitter has the functionality to detect the presence of a foreign object. If it is detected, the power transmitter may, for example, stop transmitting power or reduce the maximum amount of power that can be transmitted.

Existing approaches proposed in the Qi specifications are based on power loss detection (by comparing transmitted and reported received power) or Q factor degradation detection of the output resonant circuit. However, in current use, these approaches have been found to provide sub-optimal performance in many cases, and their use may, in particular, lead to inaccurate detection, resulting in missed detections and/or false positives when a foreign object is detected despite the absence of such an object.

The foreign object detection may be performed before the power transfer step is initiated at the power receiver (eg, during power transfer initialization) or during the power transfer step. Detection during the power transfer step is often based on a comparison of measured transmitted power and received power, while detection that occurs prior to the power transfer step is often based on insertion impedance measurements, such as by measuring the Q factor of the transmitter coil with a small measurement signal.

The authors found that conventional foreign object detection does not perform optimally and that this is due in part to variations and uncertainties in the specific operating conditions and situations in which foreign object detection is performed, including changes and uncertainties in power transmitter properties, power receiver properties, applied test conditions, etc. d.

An example of the difficulty in foreign object detection tests is the requirement to make sufficiently precise measurements to achieve sufficiently reliable foreign object detection. For example, if a foreign object detection measurement occurs in the selection step of power transmission initialization Qi, the signal that the power transmitter provides for this measurement must be weak enough to not activate the power receiver. However, this generally results in a poor signal-to-noise ratio, which reduces detection accuracy. Thus, the detection performance may depend on the particular signal level applied and there are usually conflicting requirements.

In a power receiver exposed to a weak electromagnetic signal, leakage current may occur, which depends on the level of the electromagnetic signal, the coupling between the primary and secondary coils, and the state of charge of the capacitor at the output of the rectifier. Thus, this leakage current may vary depending on the actual current conditions and depending on the specific parameters (eg capacitor properties) of the individual power receiver. Because the leakage current affects the impedance introduced into the primary coil, the measurement of the Q factor is also dependent on the actual conditions and this tends to prevent optimal detection.

Another foreign object detection problem is based, for example, on the fact that the reported received power data at different loads or signal levels may be less reliable than required due to the fact that the ratios between transmitted and received power are different for different loads and signal levels. .

In the system of FIG. 1 uses a foreign object detection approach to reduce uncertainty and sensitivity to change, and thus to provide better foreign object detection. This approach in many embodiments allows for better detection of foreign objects and, in particular, in many embodiments, the implementation allows for more accurate and/or reliable detection of foreign objects. This approach can also provide low complexity and low resource requirements. The advantage of this approach is that it may be suitable for use in many existing systems, for example, in particular in a Qi wireless power transmission system, and in fact this can often be achieved by making minor changes.

Another operation that can be affected by the properties (and in particular changes in properties) of the power transmission signal is communication between a power receiver and a power transmitter (in either direction). As will be described later, for communication from a power receiver to a power transmitter, load modulation is often used, in which the load for the power transmission signal is changed by the power receiver in accordance with the data to be transmitted. The power transmitter can then detect the resulting changes in the excitation signal that generates the power transmission signal and decode the transmitted data based on them. However, the effect of load modulation is difficult to determine when the effective load on the power transmission signal at the power receiver is very high, and the determination becomes even more difficult when this load changes.

In the system of FIG. 1 uses a communication approach that aims to reduce uncertainty and sensitivity, and thus to provide improved communication performance, in particular for communication with load modulation from a power receiver to a power transmitter. This approach in many embodiments allows for improved communication and, in particular, in many embodiments, allows for more accurate and/or reliable communication from the power receiver to the power transmitter. This approach can also provide low complexity and low resource requirements. The advantage of this approach is that it may be suitable for use in many existing systems, for example, in particular in a Qi wireless power transmission system, and in fact this can often be achieved by making minor changes.

As will be described in more detail below, this approach is a time division approach in the power transfer stage, whereby operations such as foreign object detection and communication, and power transfer can, for example, be performed in different time intervals, which can significantly reduce mutual interference between them (in particular, the effect of power transmission on the detection of foreign objects / communication).

In particular, for a wireless power transmission system, the power transmission signal must correspond to a repeating time frame that contains at least one power transmission time slot and one reduced power time slot.

The power level of the power transmission signal is reduced during the low power time interval compared to the power transmission time interval, and typically the maximum allowable power during the low power time interval is at least 5, 10, or 50 times lower than the power level. during the power transfer time interval. The reduction in power level may result from effects on the power transmitter and/or the power receiver. For example, in some embodiments, the power transmitter may be configured to turn off the power transmission signal during the low power time interval and/or the power receiver may be configured to turn off the load during the low power time interval.

The power transmitter (and typically the power receiver) can then perform one or more operations (functions, processes, procedures) during the reduced power time interval, i.e. it may synchronize the execution of one or more power transmitter operations during the low power time interval. For example, it can typically synchronize the execution of foreign object detection, and possibly communication, during the low power time interval. Thus, due to this, the influence of the power transmission and the power transmission signal on the desired operation, in particular, the detection of foreign objects and the implementation of communication, can be reduced and often minimized.

FIG. 2 shows the elements of the power transmitter 101 in more detail, and FIG. 3 shows the elements of the power receiver 105 of FIG. one.

The power transmitter 101 includes a driver 201 that is configured to generate a drive signal applied to the transmitter coil 103 which in turn generates a power transfer electromagnetic signal that can provide power to the power receiver 105. The power transmission signal is provided (at least) during the power transmission time intervals of the power transmission step.

Driver 201 may typically comprise an inverter output circuit, typically formed by full or half bridge driving, as is well known to those skilled in the art.

The power transmitter 101 also includes a power transmitter controller 203 that is configured to control the operation of the power transmitter 101 in accordance with desired operating principles. In particular, the power transmitter 101 may have many of the functionality needed to perform power control in accordance with the Qi specifications.

The power transmitter controller 203 is particularly configured to control the generation of the drive signal by the driver 201, and it is configured to specifically control the power level of the drive signal, and thus the level of the generated power transmission signal. The transmitter power controller 203 includes a power loop controller controlling the power level of the power transmission signal in response to the power control messages received from the power receiver 105 during the power control step.

To receive data and messages from the power receiver 105, the power transmitter 101 includes a first communication device 205 that is configured to receive data and messages from the power receiver 105 (as will be apparent to one skilled in the art, the data message may comprise one or more bits information). In this example, the power receiver 105 is configured to load modulate the power transmission signal generated by the transmitter coil 103, and the first communication device 205 is configured to detect voltage and/or current changes on the transmitter coil 103 and demodulate the load modulation based on them. Those skilled in the art are familiar with the principles of load modulation, such as those used in Qi wireless power transmission systems, so they will not be described in more detail.

In many embodiments, the first communication device 205 is also configured to transmit data to the power receiver 105 and may in particular be configured to modulate the power transmission signal using frequency, amplitude, or phase modulation.

In some embodiments, communication may be performed using a separate communication channel, which may be achieved using a separate communication coil or, in fact, using the transmitter coil 103. For example, in some embodiments, short range communication may be implemented, or a high frequency carrier (eg, carrier frequency of 13.56 MHz) may be superimposed on the power transmission signal.

In the system of FIG. 1-3, communication during the power transmission phase occurs in reduced power slots. In particular, some or substantially all of the low power time slots may be communication time slots during which communication occurs between power transmitter 101 and power receiver 105. In particular, the transmitter controller 203 may comprise/provide a synchronizer 206 configured to synchronize the first communication device 205 such that a communication operation (typically both receiving and transmitting data) is performed in (and typically only in) time slots. communication intervals of the power transmission stage, i. e. in the low power time slots that are intended for communication.

This can significantly improve the quality of communication.

The power transmitter 101 also includes a foreign object detector 207 that is configured to perform foreign object detection checks, i. a specific determination of how likely it is that any unwanted conductive elements are present within the generated electromagnetic field.

In this system, the foreign object detection checks are based on measurements performed during the foreign object detection time intervals, i.e. during low power time intervals, which are designed to detect foreign objects.

In this example, the electromagnetic power transmission signal and the electromagnetic test signal used to detect foreign objects are generated by two different coils (driven by different drivers). In addition, these signals will be referred to by different terms, namely, the electromagnetic signal generated during the power transmission time intervals will be referred to as the power transmission signal, and the electromagnetic signal generated during the foreign object detection time intervals will be referred to as the electromagnetic test signal, or simply test signal. However, it should be understood that in many embodiments, the electromagnetic signal can be generated by the same coil in both the power transfer time slot and the foreign object detection time slot, and, in fact, the same driver, etc. can be used both in the power transmission time slot and in the foreign object detection time slot. In fact, references to test signals in many embodiments can be considered equivalent to a power transmission signal during the foreign object detection time interval.

During the foreign object detection time intervals, the power level of the power transmit signal is reduced, for example, by turning off the load of the power receiver and reducing the overall load on the power transmit signal. In many embodiments, the power receiver 105 can be configured to minimize the load on the power transmit signal to match only the load from its own metal (the metal parts of the power receiver itself), and possibly a small amount of power used by the power receiver's functional control unit. The power receiver can often completely turn off the target load for the power transmit signal during the low power time slots. This can often, for example, result in a reduction in load on the power transfer signal, for example from 5-50 W during power transfer times to less than 500 mW during low power times.

It should be noted that the power level of the power transmission signal can be reduced without causing (or being caused by) a reduction in the strength of the generated electromagnetic field. For example, disconnecting the load by the power receiver will reduce the power available from the electromagnetic field and the power transmission signal, and thus from the drive signal to the transmitter coil 103. However, this need not necessarily lead to a decrease in the strength of the generated field, and in fact may provide a large field strength, since the opposite electromagnetic field created by the current in the coil 107 of the receiver is reduced.

Thus, in many embodiments, reduced power slots are characterized by the transmission of reduced power from the power transmitter to the power receiver compared to such power transmission during the power slots (or at least the transmission of reduced maximum possible/available power from the power transmitter to the receiver). power compared to transmitting the maximum possible/available power during power transmission time slots). However, the strength of the electromagnetic field generated by the transmitter coil 103 may remain the same or even increase.

In fact, in many embodiments in which foreign object detection is based on a measurement of the electromagnetic field load generated by the transmitter coil 103, it may be desirable to tailor the drive signal such that the generated electromagnetic field has a field strength suitable to perform the intended operation during the reduced interval. power. This may be even higher field strength than during the power transmission time interval, but the amount of transmitted power is reduced due to the fact that the power receiver tends to turn off the load.

Although in some embodiments it is possible to simply not change the parameters of the drive signal, the drive signal is typically adapted during the low power time interval when the load on the power receiver is reduced. Removing the load will result in less vibration damping in the transmitter coil 103 and, accordingly, since the drive parameters remain unchanged, there will be an increase in current in the transmitter coil 103/output resonant circuit. This will result in a higher induced voltage in receiver coil 107, and in some situations may lead to an overvoltage condition. Such a problem can, for example, be solved by changing the parameters of the drive signal to reduce the amplitude of the drive signal during the time interval of reduced power.

Reducing the load allows much more accurate detection of foreign objects in many situations. This will cause the power dissipated in the foreign object to be a much larger proportion of the total power dissipation, and in fact, as a rule, the power dissipated in the foreign object exceeds the power dissipated in the power receiver, thus facilitating detection of power dissipation by this foreign object.

In many embodiments, the transmitter controller 203 is configured to reduce the power level of the power transmission signal during foreign object detection time intervals, and in particular, it may turn off the power transmission signal completely (in particular, in the example of using different coils to generate the power transmission signal and electromagnetic test signal to detect foreign objects).

During the interval in which foreign object detection is performed, i.e. during the foreign object detection time interval, the foreign object detector 207 may evaluate the conditions to determine whether the foreign object can be considered to be present or not. During the foreign object detection time interval, the power transmitter 101 generates an electromagnetic test signal, and the foreign object detection is based on an evaluation of the characteristics and properties of this signal.

For example, the power level (power derived from) the generated test signal can be used as an indicator of the power received by potential foreign objects (generally by comparing it with the expected power data received from the power receiver 105). The power level of the electromagnetic test signal corresponds to the power received from the electromagnetic test signal by the conductive elements (including the receiver coil 107) in the electromagnetic field. Thus, it indicates the power received by the combination from the power receiver 105 as well as any foreign objects that may be present. The difference between the power level of the electromagnetic signal and the power received by the power receiver 105, respectively, reflects the power received by any foreign objects present. The foreign object detection may, for example, be a low complexity detection in which the foreign object detection is considered to have occurred if the difference between the electromagnetic signal power level (hereinafter referred to as the transmit power level) exceeds the reported power received by the power receiver 105 (hereinafter referred to as the received power level) .

According to this approach, foreign object detection is accordingly based on a comparison of power levels between the transmitted power level and the reported received power level. The response to the detection of a foreign object may be different in different embodiments. However, in many embodiments, the power transmitter 101 can be configured to stop transmitting power (at least temporarily) in response to the detection of a foreign object.

To generate a test signal, the power transmitter 101 includes a test coil 209 that is connected to a test oscillator 211. The test oscillator 211 is configured to generate a test drive signal for the test coil 209 to provide an electromagnetic test signal during the foreign object detection time interval. The drive test signal is an electrical signal applied to the test coil 209, resulting in the generation of an electromagnetic test signal, i. the test coil 209 generates a corresponding electromagnetic field with a field strength dependent on the test excitation signal.

Test oscillator 211 may have substantially the same functionality as driver 201, for example, the output of test oscillator 211 may be a half-bridge or full-bridge inverter. In fact, as previously mentioned, in many embodiments, test oscillator 211 may be implemented with driver 201 and test coil 209 may be implemented with transmitter coil 103. Accordingly, hereinafter, all references to test oscillator 211 and test coil 209 may, respectively, be considered as references to driver 201 and transmitter coil 103 for embodiments in which the same coil is used to generate both the power transmission signal and the electromagnetic test coil. signal. In such a situation, the power of the generated electromagnetic signal can be adapted to a generally fixed reference level during the foreign object detection time interval.

The power transmitter also includes an adapter 213 which, as will be described in more detail below, is configured to adapt the low power slot timing response in response to one or more messages received from the power receiver.

FIG. 3 shows some exemplary elements of power receiver 105.

Receiver coil 107 is connected to power receiver controller 301 which connects receiver coil 107 to load 303 via switch 305 (ie, switched load 305). The power receiver controller 301 includes a power control path that converts the power received by the receiver coil 107 into a signal suitable for supply to a load. In addition, the power receiver controller 301 may include various functional blocks of the power receiver controller necessary to perform power transmission, and in particular, functional blocks necessary to perform power transmission in accordance with Qi specifications.

To communicate the power receiver 105 with the power transmitter 101, the power receiver 105 has a second communication device 307 .

The second communication device 307 is configured to transmit data to the power transmitter when the load of the receiver coil 107 changes in response to the data to be transmitted to the power transmitter 101. Load changes are then detected and demodulated by power transmitter 101 in a manner known to those skilled in the art.

In this example, the second communication device 307 is also configured to demodulate the amplitude, frequency and/or phase modulation of the power transmission signal to obtain data transmitted from the power transmitter.

The power receiver controller 301 is also configured to control the second communication device 307 such that communication during the power transmission step takes place in communication intervals, i.e. during the time intervals in which the power level of the power transmission signal decreases.

Thus, just as the first communication device synchronizes communication with the power receiver so that it occurs during the low power time slots, the second communication device also synchronizes communication with the power transmitter so that it occurs during the low power time intervals.

FIG. 4 is a schematic diagram of the elements of an exemplary power path of power receiver 105. In this example, power receiver 105 includes a receiver coil 107, designated LRX. In this example, the receiver coil 107 is part of a resonant circuit, and the power receiver 105 accordingly also includes a resonant capacitor CRX. The receiver coil 107 is affected by an electromagnetic signal and, accordingly, an alternating voltage/current is induced in the coil. The resonant circuit is connected to a rectifier bridge with a smoothing capacitor C1 connected to the output of the bridge. Thus, a constant voltage is generated across the capacitor C1. The amount of DC voltage ripple will depend on the size of the smoothing capacitor as well as the load.

Bridge B1 and smoothing capacitor C1 are connected to a load 303, which is indicated by the reference numeral RL, through a switch 305, which is shown as switch S1. The switch 305, respectively, can be used to connect or disconnect the load from the power path and, thus, the load is a switched load 305. It should be understood that although the switch S1 is shown as a conventional switch, it can, of course, be implemented using any suitable means, including, as a rule, a metal-oxide-semiconductor field-effect transistor (MOSFET). Furthermore, it should be understood that the load 303 is depicted as a simple passive two-pole element, but of course it could be any suitable load. For example, load 303 may be a rechargeable battery, mobile phone, or other communication or computing device, may be a simple passive load, and so on. As such, the load 303 need not be an external or dedicated internal load, but may, for example, include elements of the power receiver 105 itself. Thus, the load 303 shown in FIG. 3 and 4 can be considered to be any receiver/electromagnetic signal coil 107 load that can be turned off by the switch 305/S1 and, accordingly, it is also referred to as switched load 305.

FIG. 4 also shows the load modulation capacitor C2, which can be disconnected or connected in parallel with the resonant circuit, depending on the position of the switch S2. The second communication device 307 may be configured to control the switch S2 so that the load of the modulating capacitor C2 can be connected and disconnected in response to data to be transmitted to the power transmitter 101, thus allowing the load to be modulated.

The power receiver 105 is configured to enter a low power mode during the low power time interval(s) of each time frame during the power transmission step. In this example, power receiver 105 includes a load controller 309 that controls a switch 305 (equivalently, switch 305 can be considered part of the load controller). During the reduced power time interval, the load controller 309 may disconnect the load 303 from the power receiver, i. e. turn off the load of the controller 301 of the power receiver and, thus, the load of the coil 107 of the receiver. Thus, in this case, the load controller 309 may reduce the load on the receiver coil 107 during the reduced power time interval. In addition, not only is the load on the power receiver 105 reduced, making it easier to detect other power losses or modulation, but more importantly, the power receiver 105 enters a more pronounced or defined state in which the effect of load changes on the electromagnetic test signal is reduced.

It should be understood that the loading of the receiver coil 107 cannot be completely turned off during the foreign object detection interval. For example, power receiver 105 may still receive power to operate some internal circuitry, for example. Thus, the load controller 309 may be configured to disconnect the load from the receiver coil 107 while the receiver coil 107 may be loaded with one or more other loads. In fact, the load of the receiver coil 107 can be considered as consisting of the load turned off by the load controller 309 during the foreign object detection interval and the load not turned off by the load controller 309. Thus, the load 303 can be considered as being the load turned off by the receiver coil 107 during the foreign object detection interval. This load may include both an external load and an internal load for which power transmission is set, but may also include, for example, an internal control function block temporarily disabled during the foreign object detection interval.

In some embodiments, the switched load may, for example, be turned off by reducing the induced voltage at the input of the rectifier B1 while maintaining a high voltage level at the output of the rectifier due to the stored power on the switched load (which may be a battery) and/or on the capacitor C1. This can stop the flow of current through the rectifier B1 and thus can reliably disconnect the switched load.

The power receiver 105 includes a power controller 311 configured to create a power control loop with the power transmitter 101 . In particular, the power controller 311 may transmit messages for power control to the power transmitter 101, and in response, the power transmitter 101 may change the power level of the power transmission signal during the power transmission time intervals. Typically, the power controller 311 is configured to generate power control error messages that indicate a request for the power transmitter 101 to increase or decrease the power level. The power controller 311 is configured to determine appropriate error messages by comparing the measured value with a reference value. During power transmission, the power controller 311 may compare the provided power level with the required power level and, based on this comparison, request an increase or decrease in the power level.

As previously mentioned, the system employs a repeating time frame in the power transmission step, wherein the time frame comprises at least one power transmission time slot and one reduced power time slot. An example of such a repeating time interval is shown in FIG. 5, in which the power transfer slots are denoted as PT and the low power slots are denoted as D. In this example, each FRM slot contains only one low power slot and one power transfer slot. However, it should be understood that in other embodiments, other time slots may also be included in a time frame, or multiple low power time slots and/or power transmission time slots may be included in each time frame. In particular, the repeated time frame may comprise various types of low power slots, such as one or more foreign object detection slots and one or more communication slots.

According to this approach, operations such as foreign object detection and/or communication can be performed in lower power time slots, and thus foreign object detection/communication and power transmission can be separated in the time domain, thereby reducing crosstalk from power transmission for foreign object detection/communication. Thus, the variability and uncertainty resulting from changes in operating conditions for power transmission can be eliminated in foreign object detection/communication, thus achieving more reliable and accurate foreign object detection/communication.

Thus, in the power transmission step, the power transmitter is configured to perform power transmission during the power transmission time interval of the time frames of the power transmission step. In particular, during these time slots, the power transmitter and the power receiver may control the power control loop (operation of the power control loop may be based on communication within communication time slots corresponding to repetitive time slots). Thus, the transmit power level can change dynamically.

In the low power time slots of the time frames of the power transmission stage, the power level of the power transmission signal (in particular, the power level transmitted to the power receiver) is reduced and often minimized. This can be achieved with a power transmitter, eg by limiting the drive signal (eg turning it off completely), and/or a power receiver, eg by turning off the target load.

In many embodiments, particularly when the same coil is used for both the power transmission signal and the electromagnetic test signal used to detect foreign objects, the power transmitter may be configured to reduce the level of the power transmission signal over a time interval. reduced power relative to its level during the power transmission time interval. In many situations, the power level of the power transmission signal can be increased to high levels, for example, to levels of 10-100 watts, or even significantly higher in many applications (eg, power transmission for kitchen appliances). However, during the reduced power time interval, the power level of the generated electromagnetic signal may be reduced to a predetermined level that is well below the current or maximum allowable power level during the power transmission time interval. For example, the power level may be set to a predetermined level not exceeding 1W. In other words, the power of the electromagnetic test signal during the foreign object detection time interval can be limited to a power level that is significantly (for example, not less than 2, 5, or 10 times) lower than the maximum allowable power level of the power transmission signal during the transmission time interval. power.

As mentioned earlier, a decrease in power level does not necessarily correspond to a decrease in the strength of the generated electromagnetic field. For example, the transmit power level can be significantly reduced by reducing the load on the field by the power receiver, such as by turning off the load 303. As shown in FIG. 4, this can be achieved, for example, by slightly reducing the field strength, so that the induced voltage (on the LRX) remains lower than the voltage on the capacitor (C1), causing the rectifier bridge (B1) to effectively isolate the capacitor (C1) from the coil. (LRX) of the receiver, allowing efficient internal load disconnection (RL).

It may be desirable to maintain a relatively high magnetic field strength in order to be able to measure sufficient power dissipation on a foreign object and thus facilitate and improve the detection of foreign objects.

Alternatively or additionally, power receiver 105 may be configured to reduce the load on the generated electromagnetic signal/field during the reduced power time interval relative to its level during the power transmission time interval, i.e. the power receiver 105 is configured to reduce the load on the power receiver 105 for the electromagnetic test signal during the reduced power time interval relative to the load for the power transmission signal during the power transmission time interval. In particular, in the example shown in FIG. 3, the load controller 309 and the switch 305 can be configured to turn off the switched load 303 during the foreign object detection time interval and connect it during the power transfer time interval. Thus, during the low power time interval, power receiver 105 can turn off (generally) the main/target load, and in fact, in many embodiments, can only provide the minimum load necessary for continuous operation of power receiver 105.

In the example shown in FIG. 4, switch S1 can be used to disconnect the load during the foreign object detection time interval. It should be understood that in embodiments in which the switched load 303 requires a more constant power supply, the switch S1 may be located before the capacitor C1 or another power storage device may be provided after the switch S1 to supply power to the switched load 303 for a temporary foreign object detection interval (or, for example, the previously described approach with reducing the induced voltage at the input of rectifier B1 while maintaining a high voltage level at the output of rectifier B1 due to the accumulated power on the switched load (for example, battery) and / or capacitor C1).

The power receiver 105 can appropriately reduce the load of the power receiver during the low power time interval. In particular, the load on the electromagnetic test signal provided by the power receiver during the foreign object detection time interval will be less than the load on the power transmission signal provided by the power receiver during the power transmission time interval (the load may, for example, be considered the effective impedance , respectively, the transmitter coil 103 and the test coil 209 during the power transmission time interval and the foreign object detection time interval, respectively). Typically, the power transmission signal and the electromagnetic test signal will have corresponding properties and thus both induce a signal in the receive coil 107. Thus, turning off the switched load 303 during the foreign object detection time interval will result in a decrease in the load of the electromagnetic test signal compared to with the load for the power transfer signal (and thus for the electromagnetic test signal) generated during the power transfer time interval with the load connected.

Turning off the switched load 303 not only reduces the load on the electromagnetic test signal, but also allows for a more predictable load and less variation. Typically, the loading of a power transmitter by a power receiver can vary significantly not only across applications, but also over time for the same application and power transmission session. The power control loop is activated during the power transfer phase to adapt to such changes. However, by introducing a reduced power time interval in which the load can be turned off (or otherwise set, for example, to a given level), it is possible to put the power receiver into a reference mode in which the load of the electromagnetic field is more predictable. Thus, for example, foreign object detection tests can be performed based on the assumption that the power receiver is in a specified reference or test mode, and thus, for example, the predetermined load of the electromagnetic test signal can be assumed. Thus, this approach may not only allow the loading of the power receiver 105 to be reduced (thus improving accuracy with relatively greater interference from any foreign objects), but also make it more predictable, thus making it easier to compensate for the presence of the power receiver during a detection test. foreign objects.

Thus, the system shown in FIG. 1-4 provides a significantly improved approach to foreign object detection testing, in which foreign object detection tests are performed under much more controlled conditions, allowing for more accurate and reliable foreign object detection tests. Likewise, it provides an environment to improve communication with less interference caused by the power transmission operation.

In many embodiments, the low power time slot may include both a communication time slot and a foreign object detection time slot.

In the system shown in FIG. 1, a power transmitter and a power receiver are configured to change the timing characteristics of a low power slot of a repeating time frame based on a relationship between two entities.

In particular, the power transmitter includes an adapter 213 for adapting the low power slot timing response in response to at least receiving a first message from the power receiver.

In many embodiments, the power receiver may send one or more messages to the power transmitter requesting a particular low power slot timing characteristic. The power transmitter and power receiver can then apply these timing parameters for a subsequent operation.

In many embodiments, the power transmitter and power receiver may specifically be configured to communicate to establish the duration of low power slots and/or the period between low power slots, and typically the period between successive low power slots.

Such an approach may allow better compromises to be reached and may in particular allow operation to be tailored to the particular properties of the individual devices and, in many embodiments, to the particular characteristics of the individual power transfer operation. For example, the timing may be adapted according to the power level of the power transmission.

This approach makes it possible to ensure that the duration of the low power time interval influences the behavior of not only the power transmitter and power receiver, but also potentially the final load, such as, for example, a device that is powered by the power receiver.

Often, if the low power time interval is too long, the device can be supplied with a reduced effective supply voltage. This is particularly relevant when the power storage of the device is limited, for example, when the capacitor at the input of the device (at the output of the power receiver) has a capacitance less than required. The device must be capable of covering the time during which the power transmission is interrupted, and this typically requires a relatively large capacitor (it should be noted that in many embodiments, the power receiver may itself contain such a capacitor, as well as potentially a device for adjusting the voltage to provide a constant output voltage, however, this only means that the described problem will be relevant to the power receiver, and not to the external load device).

If the time slot is too short, the power transmitter may not be able to perform a certain operation in an acceptable manner. For example, the power transmitter may not be able to perform a measurement to detect foreign objects with sufficient accuracy, for example, because the measurement signal was not stabilized when the measurement was made, or because insufficient samples may have been taken. As another example, a low power time interval that is too short may not provide sufficient communication bandwidth, eg, it may not be possible to transmit enough data to provide power control messages and provide other measurements.

The optimal duration of the reduced power time interval, accordingly, may depend on a number of characteristics and properties, such as specific operating parameters and implementation of the power receiver. In some embodiments, the power receiver may accordingly transmit a message to the power transmitter, and the power transmitter may be configured to adapt the low power slot timing in response to receiving the message.

The message may in particular be an explicit request for a predetermined duration of the low power slot. In many embodiments, the power receiver can estimate operating conditions, such as the power being drawn by an external load, and can calculate the maximum duration that the power storage device/capacitor is able to maintain sufficient charge to prevent the supply voltage from dropping too much across the load. For example, the maximum duration can be twice as long for a 1A load as compared to a 2A load. Thus, the power receiver can transmit a request for a duration that is twice as long for a 2A load as it is for a 1A load.

As another example, suitable values for the duration of the time interval of reduced power can be set for the power receiver, for example, at the stage of manufacture. For example, the power receiver may be a battery charger with a maximum charging current. An appropriate period of time for which the built-in capacitor can retain sufficient charge to provide the maximum charging current can be determined at the design stage and stored permanently in the power receiver at the manufacturing stage. When power transmission is initiated by the power transmitter, the power receiver may obtain this value and send a request for the duration of the low power slot to the power transmitter. The power transmission step can then be performed using a repeating time frame in which the reduced power time slots correspond to the stored value. Since power receivers can vary greatly in requirements and functions, these capabilities may allow power transmitter operation and power transmission operations to be tailored to the specific characteristics of the power receiver.

In some embodiments, the system may be configured to set the duration between low power slots based on a message transmitted from the power receiver to the power transmitter. The system may in particular set the duration between the low power slots of successive repeated time frames, and may efficiently adapt the length of the low power slot in response to transmission of messages from the power receiver to the power transmitter.

In order to ensure the transmission of sufficient average power, provide the greater the level of peak power in the transmission of power during the time intervals of power transmission, the shorter their duration. In many embodiments, the power level during transmission may be limited (by a power transmitter or possibly a power receiver, which may be configured to only receive a predetermined maximum amount of power). In such cases, the power receiver may send a request for duration between low power slots sufficient to ensure that the capacitor is fully charged before the start of the next repeating slot (this is particularly applicable for embodiments in which the power transmitter turns off the power transmit signal during periods of reduced power).

In some embodiments, a single request may be transmitted for both the duration of the low power slot and the duration between such intervals. For example, in some embodiments, the implementation of the repeating time frame may have a constant duration and the power receiver may request the application of a certain duty cycle.

In many embodiments, the power transmitter is configured to impose a minimum duration requirement on the duration of the low power slot. This minimum duration can be used to ensure that the operation to be performed in the low power time slot is substantially given sufficient time to achieve the desired result. For example, this may allow foreign object detection to be performed with sufficient reliability (including sufficient time to set up and stabilize the measurement signal). As another example, the power transmitter may be configured to request a minimum duration so that sufficient bandwidth is provided during communication.

In many embodiments, the power transmitter is configured to impose a maximum duration requirement on duration between low power slots. This maximum duration can be used to ensure that the operation to be performed in the low power time interval is performed frequently enough. For example, this allows foreign object detection to be performed at a high enough frequency that the presence of the foreign object is detected before it can be heated to an unacceptable level. As another example, this allows for sufficiently frequent communication (eg enabling a sufficient update rate for the power control loop).

As another example, in some embodiments, foreign object detection measurements may be spread over multiple low power intervals to improve accuracy and/or add some redundancy. This provides greater accuracy in detecting foreign objects. If the duration of the low power time intervals is short and thus only a small number of samples/measurements are possible, the duration between the low power time intervals may be short to compensate and ensure that enough samples/measurements can be obtained within a given required time to allow detection of an intruder. object before it gets too hot.

Likewise, the power receiver may be configured to set limits on time values. For example, the power receiver may determine the required low power time interval value based on the maximum value to ensure that sufficient power can be supplied to an external load without discharging the power storage device (typically a capacitor) which could result in unacceptable drops. voltage.

Likewise, the power receiver may, as mentioned above, determine the required duration value between the low power time intervals, taking into account the minimum value that allows the power receiver capacitor to be fully charged.

In many embodiments, the timing characteristics of the repeating slot will depend on requirements set by both the power receiver and the power transmitter. As a general rule, the requirements for the power transmitter and power receiver must be met at the same time in order to validate the timing value. For example, setting the duration of a repeating time interval and/or the duration between successive repeating time intervals depends on values that satisfy the requirements of both the power transmitter and the power receiver.

In addition, in many embodiments, typically one of the devices (ie, power receiver or power transmitter) can set a limit on the maximum value, and the other device set a limit on the minimum value of the settable synchronization characteristic.

In particular, as explained previously, in many embodiments, the duration of the low power time interval may depend on the minimum duration specified by the power transmitter and the maximum duration specified by the power receiver.

Similarly, in many embodiments, the duration between low power slots may depend on the maximum duration specified by the power transmitter and the minimum duration specified by the power receiver.

Such implementations can effectively manage the appropriate timing for the low power slots in many embodiments, and can reduce complexity and simplify independent communication with both devices, ensuring that the low power slots have timing characteristics to achieve acceptable performance for both devices, and thus for the entire power transmission.

The particular approach and messaging used to set the timing characteristics of the low power slots depends on the preferences and requirements of the particular embodiment, and different approaches may be used in different systems.

However, in many systems, such as those typically used for Qi-type implementations, the approach is based on receiver power requests for appropriate timing values and the transmitter power accepting or rejecting said values.

Accordingly, the power receiver shown in FIG. 3 includes a request controller 311 that is configured to send a request message to the power transmitter, the request message comprising a request for a requested timing property value.

For example, the power receiver may determine an appropriate value for the duration of the low power slot. For example, it can estimate the external load and, based on it, calculate the total power consumption (of both the target load and the power receiver itself). It can then calculate the time it takes the voltage across the power storage device to drop to a given acceptable value for that total power input. The resulting time corresponds to the maximum possible duration of the reduced power time interval. Typically, the power receiver may then initially request a significantly shorter duration in order to provide sufficient headroom and safer operation. For example, it may send a message to the power transmitter requesting a low power slot length equal to half of the specified maximum value.

Upon receiving the message, the power transmitter may judge if the requested duration is acceptable. For example, it may compare the requested duration with a pre-stored minimum period of time needed to perform reasonably accurate foreign object detection. If the requested duration exceeds this minimum time period, the power transmitter approves the requested duration, otherwise it rejects it.

The power transmitter may then send back to the power receiver a response message that contains an indication of whether the requested value has been approved by the power transmitter. This response message is received by the response controller, which in response determines the timing characteristics for the low power slot.

For example, the response message may contain one bit indicating whether the requested duration is approved or denied. If the requested duration is approved, both devices then perform the power transfer step using the agreed duration of the low power time slot (after completion of the initialization process in case additional operations or negotiations need to be performed before starting the power transfer). If the requested duration is denied, the response controller 313 may instruct the request controller 311 to transmit a new request. For example, it may request a duration of 75% of the maximum allowable value. The process may then be repeated until a suitable value for the timing characteristic is agreed upon.

If no common value to be granted for approval has been agreed, in particular if the power transmitter has rejected a request for a low power slot length corresponding to the maximum allowable duration calculated by the power receiver, the power receiver and the power transmitter may terminate the power transmission process or, for example, the receiver power can change the parameters of its operation by increasing the time interval of reduced power (for example, the maximum power that can be provided on an external load can be reduced).

It should be understood that a similar approach can be used to set the duration between low power slots.

In many embodiments, the power transmitter may send a message indicating the preferred or acceptable timing characteristics to the power receiver. For example, the power transmitter may send one or more messages to the power receiver indicating the minimum allowed duration of the low power slot and/or the maximum allowed duration between the low power slots (or, of course, in some embodiments, only one of these parameters may be transmitted). synchronization). The power receiver can then take these values into account when determining appropriate requested values. Such an approach may allow for ease of operation in many embodiments, and may often allow for a reduction in the number of requests that a power receiver must transmit. In particular, instead of assuming a value valid for the power transmitter, the power receiver may directly determine the requested value, which is indicated as valid by the power transmitter. Typically, for example, if conditions at the power transmitter have not changed, then the first value requested will be accepted by the power transmitter.

In many such embodiments, the power transmitter may be configured to send a message indicating recommended/allowed/approved values to the power receiver in response to a request for such information from the power receiver. Thus, the power receiver can remain the initiator, retain the initiative, and provide control over the messaging and operation.

In particular, in many embodiments, the request controller 311 is configured to cause the second communication device to transmit a request to the power transmitter in order to provide synchronization performance limitation. This limitation of the timing characteristics involves limiting the values of the given characteristics of the synchronization, such as the duration of the time interval of low power or the duration between successive time intervals of low power. Limiting timing characteristics may, for example, involve specifying a maximum value, a minimum value, an acceptable range, a recommended and/or preferred range, and so on.

The power receiver may then proceed to determine the requested timing property value corresponding to the specified constraint, if possible. For example, it may change the behavior or interface with an external load if necessary to comply with a given constraint.

In many embodiments, determination of an appropriate timing characteristic may be performed in an initialization step prior to the power transfer step. Thus, before starting a new power transmission operation, the power transmission system may enter an initialization step during which the determination of suitable timing characteristics for the low power time slot, as described above, occurs. The power transmitter and power receiver can then proceed to apply certain characteristics in the power transmission step. In particular, determination of suitable timing characteristics of a repeated time frame may be performed in a negotiation step performed during the initialization of a new power transfer operation.

This may allow suitable parameters to be determined while maintaining low complexity and high operational reliability. The timing characteristic values determined in the initialization step may in particular be used throughout the power transfer step without change or modification.

However, in some embodiments, the synchronization characteristic (or characteristics) may change dynamically during the power transfer phase. In some embodiments, the power receiver may be configured to dynamically and repeatedly send messages to the power transmitter requesting the value of a given timing characteristic, such as the duration of the low power time interval. The adapter 213 in such embodiments may be configured to dynamically adapt timing characteristics during the power transmission phase in response to receiving these messages.

For example, during the power transfer step, the power receiver may continuously measure the power delivered to the target load. If it becomes less than expected for the load negotiated during the initialization step, the power receiver may proceed to request a new low power slot duration that is greater than the current value to reflect the fact that the power storage capacitor is discharging at a slower rate. Conversely, if it detects that the power is increasing at the target load, the power receiver may proceed to request a shorter duration of the reduced power slot than the current duration. The power receiver can continuously measure these values and continuously transmit request messages to the power transmitter.

In response to receiving these messages, the power transmitter may approve or reject the requested values. If they are approved, an acknowledgment message is sent to the power receiver and the new value is considered approved. In the event of a deviation, a deviation message is sent to the power receiver, while the previous value remains unchanged.

The power receiver and power transmitter in some embodiments are able to efficiently establish a control loop adapting the low power slot timing characteristic.

It should be understood that dynamically changing the timing characteristic in the power transfer step may be performed in addition to setting initial values in the initialization step. In other embodiments, the power transfer step may instead begin with the same timing characteristics setpoints that were determined for the worst case and without any initialization step. Then, thanks to the work of the dynamic control loop, they are adapted to more suitable values.

Next, a specific example of the approach and aspects for a Qi type power transmission system will be described. In this system, the low power time slot will include low power time slots corresponding to both foreign object detection time slots and communication time slots.

In a specific description, the following abbreviations and abbreviations will occur:

PTx is a power transmitter.

PRx - power receiver.

Device - a device containing a PRx, a (partially) switchable load, own metal.

Intrinsic Metal - The metal of the device that, when exposed to a PTx magnetic field, dissipates power.

FO - foreign object.

FOD - foreign object detection.

Com - communication.

PTx Coil - A single coil or set of coils in a PTx to which the PTx supplies AC voltage and current to create a magnetic field (power transfer signal) for the power receiver.

TS - time slot corresponding to the time interval.

FOD TS - Foreign Object Detection Time Slot, low power time slot used for foreign object detection.

Com TS - communication time slot, low power time slot used for communication.

In a specific example, a time division approach with a repeating time frame is used, as shown in FIG. 6. In this figure, NP stands for "no power", which corresponds to a time interval of reduced power, which usually corresponds to the loss of power to the target load by the receiver. PWR indicates a power transmission time interval.

Time Slot FOD

PRx has disconnected its load. This means that no power (or very little power) is being supplied to its load. PTx applies, for example, saves the setting of the measuring signal and measures the combined effect of own metal and FO. It compares this influence to the stored expected influence of own metal to determine the influence of any FOs. It can then use the determined FO influence to determine the maximum excitation signal amplitude relative to the frequency at which it considers the situation to be safe, i.e. at which it expects the FO temperature rise to be within safe limits (or in some embodiments, it may simply stop transmitting power if said influence has been determined to be too strong). The PTx will then limit its excitation signal to this maximum value and issue a warning if the PRx attempts to control the excitation signal above this maximum value.

If the PTx detects a change in the combined influence of home metal and FO, it can return to the initialization timeslot to re-set the measurement conditions for the FOD. To prevent early triggers back to the initialization timeslot, the PTx may combine the results for multiple FOD timeslots (eg, apply an averaging window) and/or adjust the excitation signal within certain limits.

Time slot COM

PRx has disconnected its load. This means that no power (or very little power) is being supplied to its load. The PRX can now communicate, for example, to:

• Obtaining information about power management

• Identification

• Obtaining measurement results for PRX, such as receiving power, battery status, case temperature

• Obtaining measurement results for PTX, such as coil current, power supply, component temperature

Initialization timeslot

Typically performed before the power transfer step, but may be performed during the power transfer step, for example as part of each repeating time frame.

PRx has disconnected its load. This means that no power (or very little power) is being supplied to its load.

The PTx controls its excitation signal applied to the PTx coil to create a situation where the following conditions are met:

• Influence of the device's own metal on the magnetic field

PRx is known or PRx can be precisely determined.

For example, power dissipation in intrinsic metal at a given amplitude and frequency of the magnetic field are known PRx

• PTx can accurately measure the cumulative impact

own metal and FO. For example, the transmitted power can be precisely determined by PTx.

As a result, the system can accurately determine the effect of FO on the magnetic field. This effect is preferably related to the expected temperature increase caused by power dissipation in the FO caused by its effect on the magnetic field of the PTx coil when PTx supplies power to the PRx.

To create the above situation, the PRx can provide information about the corresponding magnetic field, such as its type, allowed frequency range, and, if necessary, the required drive signal amplitude for the PTx coil. The last parameter, of course, depends on the design of the PTx coil. In addition, the PRx may have a pickup coil whose induced voltage gives a good indication of the field that is being exerted on the device's own metal. In this case, the PRx can provide control information on the PTx to provide a field level at which the influence of own metal can be accurately determined by the PRx.

When the above situation is created, PTx saves the excitation signal setting and expected native metal influence as determined by PRx.

Measurements and communication can be separated in time to avoid interference between them.

In this example, prior to power transmission, a negotiation/initialization step is performed in which PTx and PRx negotiate time limits for different time slots. These timings include two parameters: the duration of each slot (SLOT_duration) and the time interval between different slots (SLOT_interval).

The following will present some examples of power receiver and power transmitter aspects regarding individual timeslots:

FOD related aspects of PTx:

• PTx maintains a minimum FOD_duration (FOD_duration_min) at which it can take at least one FOD measurement for its FOD function; it does not support shorter FOD_duration values.

• To achieve sufficient FOD reliability, the PTx performs the minimum number of FOD measurements (FOD_count_min). In order to react to the presence of the FO before it gets too hot, the PTx must be able to make the necessary measurements for the FOD for some maximum time (FOD_detection_max).

• After PTx negotiates the FOD_duration value, it can calculate how many FOD measurements it can perform in the FOD slot (FOD_meas_nr) and can determine the maximum FOD interval time (FOD_interval_max).

• FOD_interval_max = FOD_detection_max * FOD_meas_nr / FOD_count_min

COM related aspects of PTx:

• PTx maintains a minimum COM_duration (COM_duration_min) that it can send/receive at least one message; it does not support shorter Com_duration values. To ensure a minimum number of messages, PTx uses a minimum number of messages to communicate (COM_count_min).

• After PTx negotiates the COM_duration value, it can calculate how many communication messages it can process in the COM slot (COM_mes_nr) or vice versa;

• After PTx agrees on the number of messages to communicate (COM_mes_nr), it can calculate the maximum duration for a communication slot (COM_duration_max).

Aspects of PRx

• PRx provides a maximum FOD slot duration (FOD_duration_max) or a maximum COM slot duration (COM_duration_max) to prevent the device from being discharged too much to store the power it uses during one of the specified time intervals.

• PRx requires a minimum timeslot interval (FOD_interval_min or COM_interval_min) to be set to ensure that the device is sufficiently charged to accumulate power at the beginning of any of the timeslots.

Some of the following specific examples describe communication via messages between a power receiver and a power transmitter to establish timing parameters:

FOD slot duration

• (PTx tells PRx the FOD_duration_min value (as requested by PRx)

• PRx requests FOD_duration value

(For optimal FOD, PRx preferably requests a FOD_duration close to FOD_duration_max)

• PTx responds if it approved/rejected the proposed FOD_duration value

FOD slot interval

• PTx calculates the FOD_interval_max value

• (PTx tells PRx the FOD_interval_max value (as requested by PRx)

PRx requests a FOD_interval value (For optimal FOD, PRx preferably requests a FOD_interval value close to FOD_interval_min)

• PTx responds if it approved/rejected the proposed FOD_interval value.

COM slot duration

• (PTx tells PRx the value of COM_duration_min (as requested by PRx)

• PRx requests:

- minimum value of COM_duration

- or the minimum number of messages to communicate (COM_count_min).

• PTx responds if it approved/rejected the proposed COM_duration value

COM slot interval

• PTx calculates the value of COM_interval_max

• PTx tells PRx the value of COM_interval_max (as requested by PRx)

• PRx requests the value of COM_interval

- For optimal communication, the PRx preferably requests a COM_interval time close to FOD_interval_time

• PTx responds if it approved/rejected the proposed COM_interval value.

It should be understood that in the foregoing description, for clarity, embodiments of the present invention are presented with reference to various functional circuits, blocks, and processors. However, it is clear that any suitable distribution of functionality between different functional circuits, blocks or processors can be used without prejudice to the present invention. For example, functionality shown as being performed by separate processors or controllers may be performed by the same processor or controllers. Therefore, references to specific functional blocks or diagrams should be considered only as references to suitable means for providing the described functionality, and not as an indication of a strict logical or physical structure or organization.

The present invention may be implemented in any suitable form, including hardware, software, firmware, or any combination thereof. The present invention may also 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 an embodiment of the present invention may be physically, functionally and logically implemented in any suitable manner. In fact, functionality may be implemented in a single block, in multiple blocks, or as part of other functional blocks. Thus, the present invention may be implemented as a single unit, or may be physically and functionally distributed among various blocks, circuits, and processors.

Although the present invention has been described in relation to some embodiments, it is not limited to the specific form set forth herein. On the contrary, the scope of the present invention is limited only by the appended claims. In addition, although one might think that the feature is described in relation to specific embodiments, it will be obvious to a person skilled in the art that various features of the described embodiments can be combined in accordance with the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

It should be understood that reference to a preferred value does not imply any restrictions, unless it is a value defined in the foreign object detection initialization mode, i. it is preferred due to the fact that it is determined in the adaptation process. References to the preferred value may be replaced by references to, for example, the first value.

Also, although listed individually, a plurality of means, elements, circuits, or method steps may be implemented with, for example, a single circuit, a single block, or a single processor. In addition, although individual features may be included in different claims, they may preferably be combined and their inclusion in different claims does not mean that a combination of features is not possible and/or not preferred. In addition, the inclusion of a feature in one category of claims is not intended to limit that category, but rather indicates that the feature is equally applicable to other categories of claims, as the case may be. Furthermore, the order of the features in the claims does not imply any particular order in which the features are to operate, and in particular, the order of the individual steps in the claims does not imply that the steps must be performed in that order. Rather, the steps may be performed in any suitable order. In addition, references in the singular do not exclude plurality. Thus, references to the grammatical means of expressing the singular form, as well as the terms "first", "second", etc. do not exclude the presence of a plurality. Reference numerals in the claims are provided solely as an illustrative example and should in no way be construed as limiting the scope of the claims.

Claims (51)

1. Power transmitter (101) for wirelessly supplying power to power receiver (105) by means of an electromagnetic power transmission signal, comprising: a transmitter coil (103) for generating a power transmission signal, the power transmission signal in the power transmission step using a repeating time frame comprising at least a power transmission time interval and a low power time interval during which the power level of the power transmission signal is reduced; an exciter (201) for generating a drive signal for the transmitter coil (103) to generate a power transmission signal; a first communication device (205) for receiving messages from a power receiver (105); an adapter (213) for adapting a low power slot synchronization characteristic in response to at least the first message received from the power receiver (105); a synchronizer (206) for synchronizing the operation of the power transmitter (101), which should occur during the low power time interval, and differing in that it also contains: a test coil (209) for generating an electromagnetic test signal; a test generator (211) configured to generate a test drive signal for the test coil (209); a foreign object detector (207) configured to conduct a foreign object detection test in response to receiving a measured parameter for the drive test signal during the low power time interval; moreover, the synchronizer (206) is configured to synchronize the test generator (211) to provide an electromagnetic test signal during the reduced power time interval. 2. The power transmitter (101) of claim 1, wherein the timing characteristic is the duration of the low power time interval. 3. The power transmitter (101) of claim 1, wherein the timing characteristic is the duration between low power slots of successive repeated time frames. 4. The power transmitter (101) according to any one of the preceding claims, wherein the first communication device (205) is configured to transmit messages to the power receiver (105) and the power transmitter (101) is configured to transmit a message indicating at least one of the duration of the low power slot and the duration between the low power slots of successive repeated time frames, to the power receiver until the first message is received. 5. The power transmitter (101) according to any one of the preceding claims, wherein the first message is a request message indicating a requested value for the timing characteristic, and the power transmitter (101) is configured to approve or reject the requested value. 6. The power transmitter (101) according to any one of the preceding claims, wherein the adapter (213) is configured to determine the timing characteristic in an initialization step prior to the power transmission step. 7. The power transmitter (101) as in any of the preceding claims, wherein the adapter (213) is configured to dynamically adapt the timing characteristic during the power transmission step in response to receiving a plurality of messages received from the power receiver (105) during the power transmission step. 8. The power transmitter (101) according to any one of the preceding claims, wherein the first communication device (205) is configured to synchronize communication with the power receiver (105) that occurs during the reduced power time slots. 9. A wireless power transmission system, comprising a power transmitter according to claim 1, and also comprising a power receiver (105), comprising: a second communication device (307) for communicating with a power transmitter (101); a request controller (311) for transmitting a first message to the power transmitter (101), the first message containing a request for the requested timing characteristic value; a response controller (313) for receiving a response to the request from the power transmitter (101) and for determining a timing characteristic in response to receiving the response to the request, the response to the request indicating whether the requested value was approved by the power transmitter (101); and a load controller (309) for adapting the load for the power transmission signal such that the load is reduced during the reduced power time intervals. 10. The wireless power transmission system of claim 9, wherein the request controller (311) is configured to request a synchronization response limitation from the power transmitter (101), the response controller (313) is configured to receive an indication of the synchronization performance limitation from the transmitter (101) power, and the request controller (311) is configured to determine the requested value of the timing characteristic in response to the limitation of the timing characteristic. 11. The wireless power transmission system according to claim 9 or 10, in which the synchronization characteristic is the duration of the low power time interval and the request controller (311) is configured to determine the requested value of the synchronization characteristic, taking into account the maximum duration, and the adapter (213) is made with the ability to determine the value of the synchronization characteristic in response to receiving the minimum duration. 12. The wireless power transmission system according to claim 9 or 10, in which the synchronization characteristic is the duration between the moments of transmission of reduced power of successive repeated time frames and the request controller (311) is configured to determine the requested value of the synchronization characteristic, taking into account the minimum duration, and the adapter (213) is configured to determine the value of the timing characteristic in response to receiving the maximum duration. 13. A method for operating a power transmitter (101) to wirelessly supply power to a power receiver (105) via an electromagnetic power transmission signal, the method comprising performing by the power transmitter (101) the following steps: generating a power transmission signal, wherein the power transmission signal in the power transmission step uses a repeating time frame comprising at least a power transmission time interval and a reduced power transmission time interval during which the power level of the power transmission signal is reduced; generating a drive signal for the transmitter coil (103) to generate a power transmission signal; receiving messages from the power receiver (105); adapting a low power slot synchronization characteristic in response to at least the first message received from the power receiver (105); synchronization of the operation of the transmitter (101) power, which should occur during the time interval of reduced power, and characterized in that it also includes: generating a test drive signal for the test coil (209) to generate an electromagnetic test signal, and performing a foreign object detection test in response to receiving a measured parameter for the drive test signal during the low power time interval; wherein the timing includes timing the drive test signal to provide an electromagnetic test signal during the reduced power time interval. 14. A method of operating a wireless power transmission system comprising a power transmitter (101) for wirelessly powering a power receiver (105) via a power transmission electromagnetic signal, the method comprising the power transmitter (101) performing the following steps: generating a power transmission signal, wherein the power transmission signal in the power transmission step uses a repeating time frame comprising at least a power transmission time interval and a reduced power transmission time interval during which the power level of the power transmission signal is reduced; generating a drive signal for the transmitter coil (103) to generate a power transmission signal; receiving messages from the power receiver (105); adapting a low power slot synchronization characteristic in response to at least the first message received from the power receiver (105); and synchronization of the operation of the transmitter (101) power, which should occur during the time interval of reduced power; generating a test drive signal for the test coil (209) to generate an electromagnetic test signal; performing a foreign object detection test in response to receiving a measured parameter for the drive test signal during the low power time interval; wherein the timing includes timing the drive test signal to provide an electromagnetic test signal during the reduced power time interval; and the method also includes performing by the power receiver (105) the following steps: communication with the transmitter (101) power; transmitting a first message to the power transmitter (101), the first message containing a request for the requested value of the timing characteristic; receiving a response to the request from the transmitter (101) power; determining a timing characteristic in response to receiving a response to the request, the response to the request indicating whether the requested value was approved by the power transmitter (101); and adapting the load for the power transmission signal such that the load is reduced during the low power time intervals.

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