Wireless Power Transfer

Abstract

A power transmitter 101 for wirelessly providing power to a power receiver 105 comprises an output circuit 303, 103 comprising a transmit coil 103 generating a power transmission signal when a drive signal is applied to the output circuit 303, 103. A load function circuit 307 determines a load function expressing a dependency of the loading of the drive signal by the output circuit 303, 103 on the frequency of the drive signal for a combined configuration of the power transmitter and the power receiver. An interval circuit 309 determines two operating frequency ranges separated by a non-operating frequency range in response to the load function. A power controller 305 controls the power level of the power transmission signal by adjusting the frequency of the drive signal over at least frequencies within the operating frequency range while excluding frequencies within the non-operating frequency range.

Description

[Technical field]

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

[0002] Modern electronic products require dedicated electrical contacts to receive power from an external power source. Even then, this tends to be impractical, requiring the user to physically insert a connector or otherwise establish physical electrical contact. Typically, power requirements also vary significantly, and most devices are now provided with their own dedicated power source, resulting in a typical user having a number of different power sources, each dedicated to a particular device. Using an internal battery eliminates the need for a wired connection to a power source during use, but the battery needs to be recharged (or replaced), so this is only a partial solution. Using a battery also significantly adds weight and potentially cost and size to the device.

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

[0004] Power transmission via magnetic induction is a well-known concept and is mostly applied in transformers with strong coupling between a primary transmitting inductor / coil and a secondary receiving coil. Based on the principle of weakly coupled transformers, by separating the primary transmitting coil and the secondary receiving coil into two devices, wireless power transfer between them becomes possible.

[0005] Such a configuration allows wireless power transfer to the device without the need for any wires or physical electrical connections. In practice, this configuration allows the device to simply be placed adjacent to or on top of the transmitting coil for external recharging or powering. For example, the power transmitting device is provided with a horizontal surface on which the device can simply be placed to receive power.

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

[0007] The Qi standard was developed by the Wireless Power Consortium and you can find more information, and in particular the defined standard documents, for example on its website: http: / / www.wirelesspowerconsortium.com / index.html.

[0008] Based on the Qi standard, the Wireless Power Consortium has moved to develop the Ki standard (also known as the Cordless Kitchen standard), which aims to provide safe, reliable and efficient wireless power transfer to kitchen appliances. Ki will support higher power levels up to 2.2KW. Summary of the Invention [Problem to be solved by the invention]

[0009] A potential problem with wireless power transfer is that power transfer performance is highly dependent on specific conditions. In particular, power transfer performance in terms of efficiency, achievable power levels, matching response time, etc., tends to depend heavily on the properties of the power transmitter and receiver, such as size, induction, and load, which vary quite significantly between different devices. Power transfer operation also depends heavily on how the transmitting and receiving coils are positioned relative to each other. In general, more efficient and reliable power transfer tends to be achieved when the coils are aligned and close to each other. Typically, power transfer performance depends on a coupling factor or coefficient, and the higher the coupling factor, the more efficient the power transfer.

[0010] Therefore, power transfer operation is highly dependent on the specific transmitter and receiver combination configuration, including both parameters, for a particular operating scenario, such as the transmitter and receiver, and the relative placement of the transmitter and receiver.

[0011] Typically, wireless power transfer systems employ a power control loop to steer the system towards a suitable operating point. This power control loop varies the amount of power transmitted from the transmitter to the receiver. The received power (or voltage or current) can be measured and, together with a set point power value, an error signal can be generated. The receiver sends this error signal to the power control function of the transmitter to reduce the static error, ideally to zero. In many systems, the transmitter controls the power level by varying the frequency, amplitude level, and / or duty cycle of the power transmission signal. Examples of wireless power transfer systems that use frequency variation to control the power level are disclosed in U.S. Patent Application Publication No. 2019 / 089197(A1) and CN103299512A.

[0012] Yet, efficient operation of such power control loops is very challenging and difficult when the power transfer nature of the system varies widely. In particular, efficient power control operation is difficult to achieve when frequency control is used to adapt power transfer levels. Many approaches tend to result in less than optimal and / or more complex operation and control for some scenarios and power transfer configurations.

[0013] Accordingly, improved operation for power transmission systems would be advantageous, and in particular, approaches that enable increased flexibility, reduced cost, reduced complexity, improved power control operation, improved adaptation to load changes and / or variations in operating conditions, backward compatibility, improved suitability for transmitting higher power levels, improved power transfer, improved adaptation to specific operating conditions, and / or improved performance. [Means for solving the problem]

[0014] SUMMARY OF THE DISCLOSURE Accordingly, the invention preferably seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0015] According to one aspect of the invention, there is provided a power transmitter for wirelessly providing power to a power receiver via an inductive power transmission signal, the power transmitter comprising: an output circuit including a transmit coil configured to generate an inductive power transmission signal in response to a drive signal applied to the output circuit; a driver configured to generate the drive signal; a load function circuit configured to determine a load function for a combined configuration of the transmitter and receiver, the load function representing a dependence of a load provided by the output circuit to the drive signal on a frequency of the drive signal for the transmitter and receiver configuration; a power controller for controlling a power level of the inductive power transmission signal by adjusting the frequency of the drive signal; and an interval circuit for determining first and second operating frequency ranges separated by a non-operating frequency range in response to the load function, the power controller configured to adapt the power level of the inductive power transmission signal by varying the frequency of the drive signal across at least frequencies in the first and second operating frequency ranges excluding frequencies in the operating frequency range.

[0016] The present invention provides, in many embodiments, improved performance, and in particular, in many embodiments, improved power control for wireless power transfer. The approach, in many embodiments, facilitates power control and allows for lower complexity operation. The approach, in many embodiments, allows for improved power control, e.g., in many embodiments, an improved power level range, smoother power control, improved drive of the output circuitry (e.g., using zero voltage switching), reduced transients, reduced overpower, and / or reduced overvoltage.

[0017] The present approach allows for improved power control for systems, especially when the parameters of the power transfer vary significantly. In particular, the inventors have found that, for example, in the case of power transfer systems using resonant coupling (with a transmit coil and / or a receive coil that are part of a resonant circuit), the dependence of the power transfer on frequency often involves different behavior in different frequency ranges, and by selectively constraining the power control to a subset of the frequency range, significantly improved performance can often be obtained.

[0018] In some embodiments, the load function is or includes a power transfer function (indicating the level of power transferred to the receiver as a function of the frequency of the drive signal), a transfer power load (indicating the loading of the driver / drive signal caused by the power transfer as a function of the frequency of the drive signal), a power loading (indicating the loading of the driver / drive signal by the output circuit as a function of the frequency of the drive signal), and / or a load impedance of the output circuit (indicating the impedance of the output circuit as a function of the frequency of the drive signal). In some embodiments, the load function is or includes a load phase function (indicating the phase offset between the current and voltage of the output circuit and / or the drive signal as a function of frequency).

[0019] The load function may indicate the load of the driver. The load function may represent the load of an output of a driver that generates / provides a drive signal to an output circuit. The load is the impedance of the output circuit presented to the output of the driver that generates the drive signal.

[0020] The power level ranges of the power transmission signal for the first and second operating frequency ranges are different, in many embodiments, a maximum power level of the power transmission signal for the first operating frequency range is higher than a maximum power level of the power transmission signal for the second operating frequency range and a minimum power level of the power transmission signal for the second operating frequency range is lower than a minimum power level of the power transmission signal for the first operating frequency range (or vice versa).

[0021] The power controller is configured to reduce a power level of the power transmission signal by changing a frequency of the drive signal from a frequency in a first operating frequency range to a frequency in a second operating frequency range where the frequency of the drive signal is not a frequency in the non-operating frequency range.The power controller is configured to increase a power level of the power transmission signal by changing a frequency of the drive signal from a frequency in the first operating frequency range to a frequency in a second operating frequency range where the frequency of the drive signal is not a frequency in the non-operating frequency range.

[0022] According to an optional feature of the invention, the interval circuit is configured to determine the first operating frequency range and the second operating frequency range in response to a reactive component of the impedance of the output circuit in response to a frequency of the drive signal.

[0023] This results in improved performance and / or operation in many embodiments. In particular, it allows for improved drive, such as when using zero voltage switching. The load function describes the reactive component of the impedance of the output circuit as a function of the frequency of the drive signal.

[0024] According to an optional feature of the invention, the interval circuit is configured to determine the first operating frequency range and the second operating frequency range such that the non-operating operating frequency range includes frequencies over which the impedance of the output circuit has an inductive reactance and frequencies over which the output circuit has a non-inductive impedance.

[0025] This results in improved performance and / or operation in many embodiments. In particular, it allows for improved drive, such as when using zero voltage switching. The load function describes the reactive component of the impedance of the output circuit as a function of the frequency of the drive signal.

[0026] According to an optional feature of the invention, the interval circuitry is configured to determine the first operating frequency range and the second operating frequency range such that a transmit power loading for an upper frequency limit of the first operating frequency range matches a transmit power loading for a lower frequency limit of the second operating frequency range.

[0027] This in many embodiments results in improved performance and / or operation. In particular, this reduces transition effects when switching between operating frequency ranges. In many embodiments, this reduces electromagnetic interference, especially when significantly changing the drive frequency.

[0028] The interval circuit is configured to determine that the transmit power loads match if the transmit power loads for the frequencies satisfy a match or similarity measure. For example, the transmit power loads are considered to match if they differ by only 1%, 2%, 5%, or 10%. In some embodiments, the match measure is that the transmit power loads are as close to each other as possible, provided certain other constraints are met.

[0029] The interval circuit, in some embodiments, is configured to determine the operating frequency range such that the transition frequency corresponds to a maximum power level at which a match occurs. The interval circuit, in some embodiments, is configured to determine the operating frequency range such that the transition frequency corresponds to a minimum power level at which a match occurs.

[0030] The transmit power load indicates the power level of the loading of the drive signal by the output circuit and / or the receiver.

[0031] According to an optional feature of the invention, the interval circuit is further configured to determine the first operating frequency range and the second operating frequency range in response to a slope of the load function for an upper frequency limit of the first operating frequency range and a slope of the load function for a lower frequency limit of the second operating frequency range.

[0032] This in many embodiments results in improved performance and / or operation. In particular, this reduces transition effects when switching between operating frequency ranges. In many embodiments, this reduces electromagnetic interference, especially when significantly changing the drive frequency.

[0033] According to an optional feature of the invention, the interval circuit is configured to determine the first operating frequency range and the second operating frequency range in response to a slope of a load function as a function of the frequency of the drive signal.

[0034] This in many embodiments results in improved performance and / or operation. In particular, this reduces transition effects when switching between operating frequency ranges. In many embodiments, this reduces electromagnetic interference, especially when significantly changing the drive frequency.

[0035] According to an optional feature of the invention, the interval circuit is configured to determine the first operating frequency range and the second operating frequency range such that the load function is monotonic with frequency in the first operating frequency range and the second operating frequency range.

[0036] This may result in improved performance and / or operation in many embodiments, and in particular in smoother and / or easier power control in many embodiments.

[0037] In many embodiments, the load function is not monotonic for at least some frequencies in the non-operating frequency range.

[0038] In accordance with an optional feature of the invention, the load function is monotonically decreasing for increasing frequencies in the first and second operating frequency ranges.

[0039] This, in many embodiments, results in improved performance and / or operation.

[0040] In accordance with an optional feature of the invention, the interval circuit is configured to determine the load function in response to measurements of a property of the drive signal while varying the frequency of the drive signal.

[0041] This, in many embodiments, results in improved performance and / or operation.

[0042] According to an optional feature of the invention, the driver is configured to generate a drive signal for applying a repeating time frame to the power transmission signal including at least one power transmission interval during which the power transmission signal is configured to transmit power to the receiver and at least one reduced power interval during which the power transmission signal is reduced in power compared to the power transmission interval, and the power controller is configured to only change the frequency of the drive signal outside the power transmission interval.

[0043] This results in improved performance in many scenarios, and in particular in many embodiments reduces electromagnetic interference.

[0044] The repetitive time frame is a periodic time frame. The repetitive time frame has a fixed or variable repetition frequency / period. The power transfer signal is active / on during the power transfer time intervals and inactive / off during the reduced power time intervals.

[0045] In some embodiments, during the reduced power time intervals, no power transfer signal is generated.

[0046] According to an optional feature of the invention, the driver is configured to generate a drive signal for applying a repeating time frame to the power transmission signal including at least one power transfer interval during which the power transmission signal is configured to transfer power to the receiver and at least one reduced power interval during which the power transmission signal is reduced in power compared to the power transfer interval, and the power controller is configured to only change the frequency of the drive signal within the first operating frequency range or the second operating frequency range during one power transfer time interval.

[0047] This results in improved performance in many scenarios, and in particular reduces electromagnetic interference while allowing improved power control in many embodiments.

[0048] The power controller is configured to only vary the frequency of the drive signal between the first and second operating frequency ranges when the drive signal is not within a power transfer time interval. The power controller is configured to vary the frequency of the drive signal between the first and second operating frequency ranges only when the drive signal is not within a power transfer time interval.

[0049] A repetitive time frame is a periodic time frame. A repetitive time frame has a fixed or variable repetition frequency / period. A power transfer signal is active / on during power transfer time intervals and inactive / off during communication time intervals.

[0050] In some embodiments, during the reduced power time intervals, no power transfer signal is generated.

[0051] According to an optional feature of the invention, the power controller is configured to adapt the power level by reducing a duty cycle of the drive signal during at least one of a power-on interval at the beginning of the power transfer time interval and a power-off interval at the end of the power transfer time interval.

[0052] This, in many embodiments, results in improved performance and / or operation.

[0053] According to one aspect of the invention, there is provided a method of operation of a power transmitter to wirelessly provide power to a power receiver via an inductive power transmission signal, the power transmitter comprising an output circuit comprising a transmit coil configured to generate an inductive power transmission signal in response to a drive signal being applied to the output circuit, the method comprising: generating a drive signal; determining a load function for a combined configuration of the power transmitter and power receiver, the load function representing a dependence of a load provided to the drive signal by the output circuit on a frequency of the drive signal for the combined configuration of the power transmitter and power receiver; controlling a power level of the inductive power transmission signal by adjusting the frequency of the drive signal; and determining first and second operating frequency ranges separated by a non-operating frequency range in response to the load function, the controlling the power level comprising adapting the power level of the inductive power transmission signal by varying the frequency of the drive signal across at least frequencies in the first and second operating frequency ranges, excluding frequencies in the operating frequency range.

[0054] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0055] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which: [Brief description of the drawings]

[0056] [Figure 1] 1 is a diagram of an example of elements of a power transfer system according to some embodiments of the present invention. [Diagram 2] FIG. 2 is an example of an electrical equivalent diagram of power transfer in the power transfer system of FIG. 1. [Diagram 3] 2 is a diagram of example elements of a transmitter according to some embodiments of the present invention. [Figure 4] FIG. 1 is a diagram of an example of a half-bridge inverter for a transmitter. [Diagram 5] FIG. 1 shows an example of a full-bridge inverter for a transmitter. [Figure 6] 1A-1C are diagrams of example elements of a receiver according to some embodiments of the present invention. [Figure 7] FIG. 2 is a diagram of an example of a load function for the power transfer system of FIG. [Figure 8] FIG. 2 is a diagram of an example of a load function for the power transfer system of FIG. [Figure 9] FIG. 2 is a diagram of an example of a load function for the power transfer system of FIG. [Figure 10] FIG. 2 is a diagram of an example of a load function for the power transfer system of FIG. [Figure 11] FIG. 2 is a diagram of an example of a load function for the power transfer system of FIG. [Figure 12] FIG. 2 is a diagram of an example of a load function for the power transfer system of FIG. [Figure 13] 1 is a diagram of an example of a repeating time frame for a power transmission signal. [Figure 14] 1 is a diagram of an example of a repeating time frame for a power transmission signal. [Figure 15] 5 is a diagram showing an example of a change in frequency of a drive signal of the power transmitter of FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] The following description focuses on embodiments of the invention that are applicable to wireless power transfer systems that utilize power transfer approaches as seen in the Qi or Ki standards, nevertheless, it will be understood that the invention is not limited to this application and applies to many other wireless power transfer systems.

[0058] 1 illustrates an example of a power transfer system according to some embodiments of the present invention. The power transfer system comprises a power transmitter 101 including (or coupled to) a transmit coil / inductor 103. The system further comprises a power receiver 105 including (or coupled to) a receive coil / inductor 107.

[0059] The system provides an electromagnetic inductive power transmission signal that inductively transmits power from the power transmitter 101 to the power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal that propagates as a magnetic flux by a transmitting coil or inductor 103. The power transmission signal typically has a frequency of about 20 kHz to about 500 kHz, and often typically ranges from 95 kHz to 205 kHz for Qi-compatible systems, or typically ranges from 20 kHz to 80 kHz for Ki-compatible systems. The transmitting coil 103 and the receiving coil 107 are loosely coupled, and thus the receiving coil 107 picks up (at least a portion of) the power transmission signal from the power transmitter 101. Thus, power is transmitted from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitting coil 103 to the receiving coil 107. The term power transmission signal is primarily used to refer to the induced signal / magnetic field (magnetic flux signal) between the transmitting coil 103 and the receiving coil 107, but by equivalence it will be understood that this is also considered and used to refer to the electrical signal provided to the transmitting coil 103 or picked up by the receiving coil 107.

[0060] In the example, the power receiver 105 is specifically a power receiver that receives power via a receiving coil 107. Yet, in other embodiments, the power receiver 105 comprises a metallic element, such as a metallic heating element, in which case the power transmission signal directly induces eddy currents and thus directly heats the element.

[0061] The system is configured to transmit significant power levels, and in particular the transmitter in many embodiments supports power levels of 500 mW, 1 W, 5 W, 50 W, 100 W, or greater than 500 W. For example, for Qi-enabled applications, power transmission typically ranges from 1-5 W power for low power applications (baseline power profile), up to 15 W for Qi standard version 1.2, up to 100 W for higher power applications such as power tools, laptops, drones, robots, and beyond 100 W up to 2000 W for very high power applications, such as for Qi kitchen applications.

[0062] In the following, the operation of the transmitter 101 and receiver 105 is described generally with specific reference to embodiments that are in accordance with the Qi or Ki standard (except for (or significant) modifications and enhancements described herein) or that are suitable for higher power kitchen standards being developed by the Wireless Power Consortium. In particular, the transmitter 101 and receiver 105 conform to or are substantially compatible with elements of the Qi standard version 1.0, 1.1, 1.2, or 1.3 (except for (or significant) modifications and enhancements described herein).

[0063] Many wireless power transfer systems, and particularly high power systems such as Ki, utilize resonant power transfer, where the transmit coil 103 is part of a resonant circuit, and typically the receive coil 107 is also part of the resonant circuit. In many embodiments, the resonant circuit is a series resonant circuit, such that the transmit coil 103 and the receive coil 107 are coupled in series with corresponding resonant capacitors. The use of a resonant circuit tends to provide more efficient power transfer.

[0064] In most power transfer systems, before power transfer begins, a communication channel between the power transmitter 101 and the power receiver 105 is established. Once communication is set up and the identities of the two devices are obtained, the power transmitter 101 starts transmitting power to the power receiver 105.

[0065] Typically, wireless power transfer systems employ a power control loop to steer the system towards a suitable operating point. This power control loop varies the amount of power transmitted from the transmitter to the receiver. The received power (or voltage or current) can be measured and, together with the set point power value, an error signal can be generated. The instrument sends this error signal to the transmitter's power control function to reduce the static error, ideally to zero.

[0066] An example of an electrical equivalent diagram for the power transfer function of the transmitter 101 and the receiver 105 is illustrated in FIG. 2. A wide range of transmitters and receivers exist in a given system, with significantly different properties and parameters. For example, coil size, induction, and load vary significantly. Thus, the system parameters as embodied in FIG. 2 will in fact vary significantly with different devices, mechanical structures, configurations, etc. In particular, the configuration of the receiver, and thus the relative position of the receiving coil 107 and the transmitting coil 103, significantly affects the coupling between the coils, i.e., the coupling between the primary (transmitter side) inductor Lp and the secondary (transmitter side) inductor Ls, and thus significantly changes the system behavior.

[0067] Furthermore, the powered device may have several different modes in which it operates in different modes, e.g., some loads may be switched on or off. For example, if the powered device is an air fryer appliance, the heating element may be switched on and off. This may result in very large load steps, e.g., from approximately 50 to 1200 W, or vice versa. Furthermore, such load switching may be repeated during operation of the device to keep the temperature constant.

[0068] The system can also include a nonlinear load rather than a resistive component, for example the receiver drives a motor, such as the motor in a food processor, which can result in a completely different response of the system, which has a large impact on control system design in particular.

[0069] Wireless power transfer systems employ a power control loop to steer the system towards a suitable operating point. This power control loop varies the amount of power transmitted from the transmitter to the receiver. The received power (or voltage or current) can be measured and, together with a set point power value, an error signal can be generated. The instrument sends this error signal, or possibly the desired power set point, to the transmitter's power control function to reduce the static error, ideally to zero.

[0070] Yet, because system performance and operation vary greatly depending on the combination and placement of existing transmitters and receivers, the appropriate operating point also varies greatly.

[0071] FIG. 3 illustrates elements of the transmitter 101 of FIG. 1 in more detail.

[0072] The power transmitter 101 includes a driver 301 capable of generating a drive signal that is provided to the transmitting coil 103, which in return generates an electromagnetic power transfer signal for power transfer to the power receiver 105. The transmitting coil 103 is part of an output resonant circuit that includes the transmitting coil 103 and a capacitor 303. In the example, the output resonant circuit is a series resonant circuit, but it will be appreciated that in other embodiments the output resonant circuit is a parallel resonant circuit. It will be appreciated that any suitable resonant circuit may be used, including those that include multiple inductors and / or capacitors. It will be appreciated that the output circuit 103, 303 may in some embodiments also include additional components (such as, for example, current or voltage sensor components).

[0073] The driver 301 generates a current and voltage that is supplied to the output resonant circuit and thus to the transmit coil 103. The drive signal induces a current through the transmit coil 103, resulting in the generation of an electromagnetic power transfer signal.

[0074] The driver 301 is typically an inverter type drive circuit that generates an AC signal from a DC voltage. The output of the driver 301 is typically a switch bridge, which generates the drive signal by appropriate switching of the switches of the switch bridge. FIG. 4 shows a half-bridge switch bridge / inverter. Switches S1 and S2 are controlled to never close at the same time. Alternately, S1 is closed while S2 is open, and S2 is closed while S1 is open. The switches are opened and closed at a desired frequency, thereby generating an AC signal at the output. Typically, the output of the inverter is connected to a transmitting inductor via a resonant capacitor. FIG. 5 shows a full-bridge switch bridge / inverter. Switches S1 and S2 are controlled to never close at the same time. Switches S3 and S4 are controlled to never close at the same time. Alternately, switches S1 and S4 are closed while S2 and S3 are open, and then S2 and S3 are closed while S1 and S4 are open, thereby creating a square wave signal at the output. The switches are opened and closed at a desired frequency.

[0075] The power transmitter 101 further comprises a power transmission controller 305 configured to control the operation of the power transmitter 101 according to a desired operating principle. In particular, the power transmitter 101 includes many of the functions necessary to implement power control according to the Qi or Ki standards.

[0076] The power transmission controller 305 is configured, inter alia, to control the generation of the drive signal by the driver 301, and in particular the power level of the drive signal and thus the level of the generated power transmission signal. The power transmission controller 305 comprises a power loop controller that controls the power level of the power transmission signal in response to a power control message being received from the power receiver 105 during a power transfer phase.

[0077] The power transmission controller 305 further comprises functionality for communicating with the power receiver 105. For example, the power transmission controller 305 is configured to transmit data to the power receiver 105 by modulating the power transmission signal and receive data from the power receiver 105 by detecting load modulation of the power transmission signal. It will be understood that in other embodiments, other communication means are used, for example, a separate communication function is performed, such as NFC communication.

[0078] It is well known that the use of a resonant circuit including the transmitting coil 103 can provide more efficient power transfer in many scenarios. Furthermore, when there is a receiver that further employs a resonant circuit, i.e., when the receiving coil 107 is part of the resonant circuit, it becomes a resonant power transfer that provides several advantages, including very efficient power transfer and easy control of the power transfer, for example, by controlling the frequency of the driving signal.

[0079] FIG. 6 illustrates some example elements of the power receiver 105.

[0080] The receiving coil 107 is coupled to the power receiving controller 601 via a capacitor 603 which forms an input resonant circuit together with the receiving coil 107. The power transfer is therefore a resonant power transfer between the resonant circuits.

[0081] The power receiving controller 601 couples the receiving coil 107 to the load 605 via a switch 607 that can specifically short the load 605. The power receiving controller 601 includes a power control path that converts the power extracted by the receiving coil 107 to a suitable supply to the load 605. In some embodiments, the power receiving controller 601 provides a direct power path that simply connects the input resonant circuit to the switch 607 or the load 605, i.e., the power path of the power receiving controller 601 is simply constructed with two wires. In other embodiments, the power path includes, for example, a rectifier to provide a DC voltage, and possibly a smoothing capacitor. In still other embodiments, the power path includes more complex functions, such as, for example, a voltage control circuit device, an impedance matching circuit device, a current control circuit device, etc. Similarly, it will be understood that the switch 607 is only present in some embodiments, and in some embodiments the load 605 is permanently coupled to the input resonant circuit.

[0082] Additionally, the power receiving controller 601 includes various power receiving controller functions necessary to implement power transfer, and in particular, functions necessary to implement power transfer according to the Qi or Ki standards.

[0083] The power receiver controller 601 further comprises functionality for communicating with the power transmitter 101. For example, the power receiver controller 601 is configured to decode and demodulate data modulated onto the power transmission signal by the load modulating the power transmission signal, and to transmit the data to the power transmitter 101. In some embodiments, a separate communication functionality is employed, such as an NFC communication functionality.

[0084] In operation, the system is configured to control the drive signal such that the power transmission signal has appropriate operating parameters / characteristics and such that the power transmission operates at an appropriate operating point. To do so, the power transmitter is configured to control the parameters of the drive signal using a power control loop in which the power characteristics of the power transmission signal / drive signal are controlled in response to power control error messages received from the power receiver.

[0085] At regular and typically frequent intervals, the receiver transmits a power control error message to the transmitter. In some embodiments, a direct power setpoint change message is transmitted (rather than a relative error message) indicating the absolute power level desired. The receiver 105 includes functionality to support such a power control loop; for example, the receiver controller 601 constantly monitors the power or voltage of the load signal provided to the load and detects whether the power or voltage is above or below a desired value. The receiver 105 generates a power control error message at regular intervals requesting that the power level of the power transmission signal be increased or decreased, and transmits this power control error message to the transmitter.

[0086] Upon receiving the power control error message from the receiver, the transmit controller 305 determines how the drive signal parameters should be modified to increase or decrease the power level of the power transmission signal as requested. The transmit controller 305 then controls and adapts the drive signal parameters accordingly.

[0087] A power control loop is suitably employed to control the power characteristics of the power transfer signal to achieve a desired operating point at the receiver. The operation of the power transfer is therefore controlled by the power control loop, and effective operation of the power control loop is critical to the performance of the system. Initializing the power control loop, or adapting it to operating conditions, is therefore important for optimal performance.

[0088] In many systems, power adaptation is achieved fully or partially by adapting the frequency of the drive signal and the power transmission signal. Particularly when using resonantly coupled transmit output and receive input circuits, i.e., when the transmit coil 103 and receive coil 107 are part of the respective resonant circuits, varying the frequency of the drive signal provides a very efficient and easy to implement approach to adapt the transmitted power level.

[0089] Nevertheless, while such an approach to adjusting frequencies has some advantages, the inventors have found that such an approach also has disadvantages, and that effective and accurate control is difficult to achieve in some scenarios. The inventors have further found that improved performance can be obtained in many systems and scenarios by adapting frequencies within a suitable disjoint operating frequency range, separated by an excluded non-operating frequency range, such that frequencies within this detail are not allocated to the drive signal.

[0090] It has been found that a highly irregular, non-monotonic, and / or non-linear relationship between power transfer and drive signal frequency often occurs, especially when there are two or more resonant frequencies in the system and highly varying characteristics exist between the resonant frequencies. Figure 7 illustrates an example of a possible power transfer function that may be encountered. The form of the function is one that is frequently encountered in practical wireless power transfer systems.

[0091] Yet such power transfer functions are difficult to control, and in particular, it is challenging to operate the power control loop accurately so that smooth, efficient, and reliable power adaptation is achieved. Such problems are typically exacerbated when the transfer function is not monotonic, and in some cases, nonlinear.

[0092] For example, in an example such as FIG. 7 where the system has two distinct resonant peaks, it is sometimes necessary to control the frequency closer to the lower frequency peak to achieve the desired power level (e.g., to reach 2.2 kW, the frequency needs to be controlled closer to the lower frequency peak). Nevertheless, it is usually desirable or even necessary to control the frequency higher than the second (higher frequency) peak to reduce the power level to a sufficiently low value and with sufficient accuracy. Nevertheless, the control is less than optimal due to a non-monotonic relationship that is further dependent on the specific operating conditions and varies widely. For example, increasing the frequency from near the first resonant peak to being higher than the second resonant peak will cause the system to sweep the second peak itself, which may cause undesirable performance, such as over-voltage or over-current at the receiver, as the power increases as part of this sweep to the second peak.

[0093] The transmitter of FIG. 3 is configured to provide improved operation and / or performance in many scenarios, often avoiding, ameliorating, reducing, and / or mitigating shortcomings such as those described in the previous paragraph.

[0094] The transmitter of claim 3 comprises a load function circuit 307 configured to determine a load function for a current transmitter and receiver configuration, the load function reflecting how the loading of the drive signal by the output circuit depends on the frequency of the drive signal for the current transmitter and receiver configuration.

[0095] Load is the load of the driver. Load is the load of the output of the driver that generates / provides the drive signal to the output circuit. Load is the load of the output circuit experienced by the output of the driver that provides the drive signal to the output circuit. Load of the signal is the load of the output that generates / provides the signal. Load is an impedance. Load is the impedance of the output circuit. The loading and / or loading of the drive signal by the output circuit is the nature / characteristics of the power provided to the output circuit. Power is a composite power that includes both active and reactive power components. Load is an indication of the active, reactive, and / or apparent power provided / transmitted by the drive signal to the output circuit.

[0096] The transmitter and receiver configuration includes the parameters and characteristics of the transmitter and receiver individually, such as component values. Such parameters and characteristics are static. The combined configuration of the transmitter and receiver further includes the parameters and characteristics of the interaction between the transmitter and receiver for the current scenario / situation / configuration. Such parameters and characteristics include the relative position and, for example, the coupling between the transmitter and receiver. Such parameters and characteristics are typically dynamic and vary with the power transfer between the same transmitter and receiver. The load provided by the output circuit to the driver and the drive signal depends on the receiver and how the receiver is coupled to the transmit coil 103 (including the relative position, coupling parameters, etc.). Thus, the load is determined by the transmitter and is an internal transmitter parameter (coupling between the driver and the output circuit), but the load depends on and reflects the combined configuration of the transmitter and receiver.

[0097] The load function thus reflects the changes in loading that occur when the frequency of the drive signal, and therefore the power transfer signal, changes. In many embodiments, the load function is a load power function that indicates the power extracted by the output circuit 103, 303 from the drive signal, and therefore from the driver 301. In many embodiments, the load power function is specifically a power transfer function that indicates the power level transferred by the power transfer signal to the receiver, and specifically a load power level function that indicates the power level provided to the receiver's load 605.

[0098] In a resonant system employing a resonant circuit at the output of the transmitter for generating a power transmission signal and / or a resonant circuit for extracting power from the power transmission signal by the receiver, the transmitted power level depends on the frequency of the drive signal and the power transmission signal. Thus, the power level provided to the load 605 depends on the drive signal frequency, and thus also the power extracted from the receiver input circuit, the power transmission signal, the transmitter output circuit, the drive signal, and the drive, respectively. Thus, each of these varies with frequency, and the load function represents one or more, or indeed all, of these power levels and loads.

[0099] Nevertheless, the dependence on the drive signal frequency and the power transmission signal frequency is not limited to the power signal, but extends to other parameters, such as the drive signal current (i.e., the load current extracted by the output circuit 103, 303). Similarly, the current or voltage at the receiver depends on the frequency and thus reflects the load of the drive signal. In some embodiments, a load function represents such other parameters of the load of the drive signal. In particular, the load function indicates the variation of the current and / or voltage parameters of the drive signal as a function of frequency for a particular transmitter and receiver configuration. The power level of the drive signal as a function of frequency is an example of a load function that reflects the variation of the current and voltage parameters as a function of frequency (given that power is determined by voltage and current).

[0100] In many embodiments, the load function indicates the phase difference between the voltage and current of the drive signal, or possibly the induced signal at the receiver, as a function of frequency. The phase difference of the drive signal indicates, for example, whether the load by the output circuit 103, 303 has an inductive or capacitive reactance.

[0101] In some embodiments, the load function is a multi-dimensional function that provides multiple values, for example, the load function in some embodiments reflects both the power transfer level of the power transfer signal and the phase difference of the drive signal.

[0102] The load function circuit 307 is configured to determine a load function for the current receiver and transmitter configuration, and specifically, for the current power transfer operation.

[0103] In some embodiments, the load function circuit 307 is configured to determine the load function based on calculations or determinations from known properties of the transmitter and receiver. For example, the load function circuit 307 stores information providing parameters of the transmitter for the components of the equivalent diagram of FIG. 2. For example, the load function circuit 307 has information about the inductance of the transmitting coil 103 and the capacitance of the resonant capacitor, etc. Furthermore, the receiver transmits information about the parameters of the receiver, such as the inductance of the receiving coil 107, the resonant capacitor, and the load. The load function circuit 307 further estimates or calculates the coupling coefficient. The load function circuit 307 then proceeds to analyze the behavior of the equivalent circuit and determine the load function. For example, the load function circuit 307 determines the load of the output circuit 103, 303 for the driver 201 and the drive signal as a function of frequency.

[0104] Thus, in some embodiments, the load function is extracted from already known system information, i.e. electrical parameters including resonant frequency, inductance, load value, coupling coefficient, etc. Some of these parameters are possibly extracted by measurement or compliance testing. These parameters can then be used together with the already known load function equation to determine the load function.

[0105] In some embodiments, the load function circuit 307 is configured to determine the load function in response to measurements of the properties of the drive signal while varying the frequency of the drive signal. The load function circuit 307 performs a frequency sweep over a frequency range and directly measures the parameters of the drive signal. For example, the drive signal frequency is varied from 20 kHz to 100 kHz and the current and voltage of the drive signal are measured. The load function circuit 307 then determines, for example, the phase offset / difference between the voltage and the current (and thus the phase of the impedance of the output circuit 103, 303 loading the drive signal) and / or determines the level of the (resistance) power of the drive signal.

[0106] In some embodiments, the interval circuit 309 is configured to directly evaluate the load function as it is being generated (and thus the load function does not necessarily need to be stored). For example, the interval circuit 309 directly evaluates the current and voltage of the drive signal during a frequency sweep and directly detects the frequency intervals during which the impedance of the output circuit 103, 303 is an inductive impedance.

[0107] The load function circuit 307 is specifically configured to detect the extremes of the load function, such as the lower and upper frequency peaks of the power loading / transfer function, and possibly the minimum therebetween.

[0108] The load function circuit 307 is coupled to an interval circuit 309 to which the load function is provided. The interval circuit 309 is configured to determine (at least) two operating frequency ranges separated by a non-operating frequency range. The interval circuit 309 is configured to control the power transmission controller 205 and the driver such that the drive frequency (of the drive signal / power transmission signal) is restricted so as not to fall into the non-operating frequency range. Thus, in this approach, the power transmission controller 205 is configured to employ frequency-based power control such that the frequency is limited to the operating frequency range and excluded from one or possibly several non-operating frequency ranges. Thus, the transmit coil 103 varies the drive frequency over an operating range that includes at least a lower frequency range and a higher frequency range, but excluding a non-operating frequency range that separates the lower and higher frequency ranges.

[0109] In some embodiments, the interval circuit 309 is configured to determine first and second operating frequency ranges, and therefore a non-operating frequency range, depending on the phase difference between the current and voltage of the drive signal, and specifically, whether the phase is positive or negative (and thus, for example, whether the current leads or lags the voltage).

[0110] The interval circuit 309 is configured in some embodiments to determine the first and second operating frequency ranges, and therefore the non-operating frequency range, depending on the phase of the impedance of the output circuit 103, 303 for different frequencies. The interval circuit 309 is configured in some embodiments to determine the first and second operating frequency ranges, and therefore the non-operating frequency range, depending on the reactive component of the impedance of the output circuit 103, 303 for different frequencies, and specifically depending on the imaginary component of the impedance.

[0111] For example, in some embodiments, the impedance of the output circuit 103, 303 is measured during a frequency sweep and the relative phase difference between the current and voltage of the drive signal is evaluated to determine the phase of the impedance of the output circuit 103, 303. The interval circuit 309 then proceeds to determine the first and second operating frequency ranges as those frequency ranges within which the phase of the impedance falls within a predetermined interval.

[0112] In some embodiments, the interval circuit 309 is specifically configured to determine the first and second operating frequency ranges depending on whether the impedance has an inductive reactive component, a non-inductive reactive component, or a capacitive reactive component. The interval circuit 309 determines the impedance as indicated above and then determines whether the impedance has a phase greater than zero or less than zero, and therefore whether the impedance is a capacitive reactance or an inductive reactance. The interval circuit 309 specifically ignores any resistive components of the impedance in some embodiments.

[0113] Zero phase offset between the voltage and current of the drive signal, and therefore purely resistive loading by the output circuit 103, 303, will tend to coincide with local minima and maxima of the load function, which represents the power loading of the drive signal or the power transfer level of the power provided to the receiver.

[0114] The interval circuit 309 then determines the first and second operating frequency ranges to be intervals in which the impedance of the output circuit has an inductive reactance and for at least some frequencies in the non-operating operating frequency range the impedance has a non-inductive impedance. This approach thus ensures that the frequency of the drive signal is such that the load presented by the output circuit 103, 303 is inductive.

[0115] 8 illustrates an example of a load function formed by two separate (partial) load functions, each providing one output value of the load function. In particular, the first load function provides the phase of the impedance of the output circuit 103, 303 as a function of the frequency of the drive signal, and the second function provides the power transfer level / load power level as a function of the drive signal. It will be understood that in a similar sense each of the functions can be considered to be a separate and complete load function.

[0116] For example, in some embodiments, the interval circuit 309 considers only the impedance phase function and determines the frequency range based on the phase of the impedance.

[0117] For example, as illustrated in FIG. 8, the interval circuit 309 determines the frequency at which the phase is zero, i.e. the impedance is completely resistive and the phase difference between the current and the voltage is zero. In the example of FIG. 8, this occurs at approximately 23 kHz, 32 kHz, and 46 kHz. The system is designed to regulate the power by controlling the drive signal to have a frequency higher than the first resonant frequency (which coincides with the impedance being purely resistive, i.e. having zero phase), in the specific example, 23 kHz. The system then determines the first frequency range to be the range from the first resonant frequency of 23 kHz until the impedance becomes capacitive at 32 kHz. The system then determines the second frequency range to be the frequency range beyond the frequency at which the impedance becomes inductive again, i.e. the frequency higher than 46 kHz. Typically, there should also be an upper limit range, for example given by practical considerations. Thus, the two frequency ranges illustrated in FIG. 9 are determined to be the operating frequency ranges, and the range in between (in the example, from 32 kHz to 46 kHz) is determined to be the non-operating frequency range.

[0118] The interval circuit 309 is configured to provide information of the determined operating frequency range to the power transmission controller 205, which is configured to control the power of the power transmission signal by varying the frequency of the drive signal within the operating frequency range while avoiding / excluding the non-operating frequency range. For example, the frequency is initially set to approximately 64 kHz. The power receiver moves to request a higher power level, and in response, the power transmission controller 205 reduces the frequency, resulting in a higher power level. As the power receiver continues to request higher power, the drive signal frequency reaches a peak of 46 kHz, but the request to increase the power level is still received. In response, rather than moving to the non-operating frequency range, the power transmission controller 205 will move to reduce the frequency, and the power transmission controller 205 will move to reduce the frequency to 32 kHz, and as the request to increase power continues, the frequency is reduced step by step until the desired power level is reached. In this way, by continually lowering the frequency while skipping over non-operating frequency ranges, the power level can be increased from the original 500 W to, say, 2.0 kW. Similarly, by continually increasing the frequency and skipping over non-operating frequency ranges, the power can be reduced.

[0119] In this approach, power level control is implemented by varying the drive signal frequency over discrete ranges such that the frequency is changed gradually within the frequency range, but by jumping over / skippling non-operating frequency ranges, e.g., a predetermined percentage frequency change is used except when crossing non-operating frequency ranges, in which case an abrupt change from the end of one operating frequency range to the beginning of the next operating frequency range is implemented.

[0120] The present approach results in improved operation and performance in many situations, and especially for scenarios with complex power transfer / load functions such as the one illustrated.

[0121] A particular advantage of the described example is that it makes the impedance of the output circuit 103, 303, and therefore the load driven by the driver 201, inductive (or possibly resistive, i.e. non-capacitive) load for all frequencies. This is a significant advantage in many embodiments, as it facilitates or enables the output circuit of the driver 201 to operate using a technique known as Zero Voltage Switching (ZVS). With ZVS, the switching of the output transistors is performed when the voltage of the individual transistors becomes zero. This significantly lowers the system losses and improves efficiency. Nevertheless, ZVS requires that the phase angle between the main current and voltage is negative, i.e. the impedance has an inductive reactance. The described approach, and indeed the operating frequency range selection example of FIG. 9, specifically ensures that the impedance driven by the driver 201 is always inductive, even in the case of complex loads and power transfer functions, thereby enabling efficient ZVS operation.

[0122] To operate in inductive mode to achieve efficient ZVS operation, a standard phase detector that measures the phase between the inverter voltage and the inverter output current can be applied as in the example implementation.

[0123] In some embodiments, the interval circuit 309 is configured to determine the operating frequency ranges such that the power transfer loads of the output circuits 103, 303 match each other for the transition frequencies of the two operating frequency ranges. Specifically, the frequency ranges are selected such that the loading of the drive signal caused by the power transfer (possibly including losses) is approximately the same for the upper frequency limit of the lower operating frequency range and the lower frequency limit of the upper operating frequency range.

[0124] A match of transmit power loading is deemed to occur when the transmit power loading at the two frequencies meet a match or similarity measure. The exact measure depends on the specific requirements and settings of each individual embodiment. In many embodiments, a match is deemed to exist when the power transmit loading at the two frequencies differ by no more than 10%, 5%, 2%, or perhaps 1% by the interval circuit 309.

[0125] The matching measure is not important, especially if the load is a resistive element. Under- or over-power will be controlled back to the original power by the power control.

[0126] The power transfer load matching measure is combined with other requirements, specifically, a requirement for the load to be inductive. For example, the interval circuit 309 first determines the frequency range where the output circuit load for the drive signal is inductive. For example, the range indicated in FIG. 9 is identified. The interval circuit 309 then moves on to determining frequencies within the frequency range where the power transfer load is the same, specifically, where the power transfer is the same.

[0127] This is accomplished, for example, by determining a frequency within the lower frequency range where the power transfer load is the same as the lowest frequency of the higher frequency range. The lower frequency range is then set to cover the range from the load becoming inductive, i.e. typically from the first peak frequency, to the frequency where the power transfer load is the same as the lowest frequency of the higher frequency range. In this example, the lower frequency range is reduced to match the upper frequency range. Example of resulting frequency ranges for the example of FIG. 10.

[0128] As another example, the interval circuit 309 is configured to determine the frequency within the upper frequency range at which the power transfer load is the same as the power transfer load of the highest frequency of the lower frequency range. The upper frequency range is then set to cover the range from this frequency. In this example, the upper frequency range is therefore reduced to match the lower frequency range. Example of resulting frequency ranges for the example of FIG.

[0129] In some embodiments, the interval circuit 309 is configured to determine the operating and non-operating frequency ranges depending on the slope of the load function.

[0130] For example, the slope of the phase of the impedance of the output circuit 103, 303 is determined and the frequency at which the impedance changes from capacitive to inductive (or vice versa) is determined as the frequency at which the magnitude of the slope is maximum, i.e., as the extreme value of the slope of the phase offset of the impedance of the output circuit 103, 303. This approach is based on the idea that the phase zero crossings are typically aligned with the maximum phase change, i.e., the frequency at which the slope is at a maximum value.

[0131] In some embodiments, the rate of change of phase with respect to frequency (dfase / df rate of change) is monitored and a frequency jump to another frequency slot / time interval is decided based thereon, e.g., when a given threshold is exceeded.

[0132] In some embodiments, the interval circuit 309 is configured to determine the operating frequency range in response to a slope of the load function for an upper frequency limit of a lower operating frequency range and a slope of the load function for a lower frequency limit of an upper operating frequency range. The interval circuit 309 is configured to determine the operating frequency range based on a slope at a transition / termination frequency for the operating frequency range and for a frequency at which a jump or transition between the operating frequency ranges occurs.

[0133] In some embodiments, the interval circuit 309 is configured to determine the operating frequency range such that the slopes at the transition frequencies match as closely as possible, and such that the slopes meet a match metric, such as, for example, the slopes differing by no more than 10%, 5%, 3%, 2%, or 1%. Such an approach, for example, may result in improved power control and regulation in many embodiments. For example, such an approach may result in smoother power regulation and stabilize the power increase rate across drive frequency gaps, making the jumps between them less noticeable.

[0134] In many embodiments, the determination of the operating frequency range takes into account several parameters, one of which is the slope of the load function. For example, as described previously, the interval circuit 309 determines the frequency at which the load of the output circuits 103, 303 is inductive and the power transfer load is the same. Nevertheless, as can be seen from Figs. 9 to 11, these requirements are met for a frequency range that includes the ranges of the lower and upper operating frequency ranges, respectively, where the gain is less than the maximum of the second peak and greater than the minimum gain between the peaks. The interval circuit 309 then moves on to selecting the transition frequency as the frequency at which the power transfer load is the same, is within this interval, and where the slope is the same or the difference between them is as small as possible. An example of the resulting frequency range is illustrated in Fig. 12. Such an approach results in a particularly efficient and smooth power control in many embodiments.

[0135] This approach allows the power level to vary smoothly and continuously between maximum and minimum levels, for example, as the drive frequency is swept from a lower frequency range to a higher frequency range (or vice versa) as part of the power control.

[0136] The interval circuit 309 is configured to determine the operating frequency range such that the load function, and in particular when the load function is or includes a power transfer or load power function, is monotonic with respect to frequencies in the operating frequency range. In particular, for all frequencies in the operating frequency range, the load power and / or the power transferred decreases for increasing frequencies (or is constant for some frequencies, as the case may be). This monotonic nature extends throughout the operating frequency range. In contrast, for frequencies in the non-operating frequency range, the function is not monotonic, e.g., the power level increases for some frequencies in the non-operating frequency range, as in the examples of Figs. 9 to 12. In many embodiments, the interval circuit 309 determines the operating frequency range such that the load function dictates a monotonically decreasing load power level for increasing frequencies in any of the operating frequency range.

[0137] In the example of Figures 1 and 3, the driver 201 is configured to generate a drive signal that will employ a repeating time frame for the drive signal and the power transfer signal during the power transfer phase.

[0138] The recurring time frame includes at least one power transfer time interval and one communication time interval. An example of such a recurring time frame is illustrated in FIG. 13, where the power transfer time interval is designated PT and the communication time interval is designated C. In the example, each time frame FRM includes only one communication time interval C and one power transfer time interval PT, which (and the time frame itself) have substantially the same duration from frame to frame. Nevertheless, it will be understood that in other embodiments, other time intervals (such as, for example, foreign object detection intervals) are also included in the recurring time frame, or multiple communication time intervals and / or power transfer time intervals are included per time frame. Furthermore, the durations of the different time intervals (and indeed the time frame itself) vary dynamically in some embodiments, as will be explained later.

[0139] In the example, power transfer is performed within the power transfer time interval. The driver is configured to generate a drive signal, such that a power transfer signal during the power transfer time interval, and specifically a drive signal having a non-zero amplitude / power, is generated during the power transfer time interval. Nevertheless, during the communication time interval, no (significant) power transfer signal is generated. Typically, this is achieved by the driver 201 not generating a drive signal (i.e., the drive signal is controlled to have zero or near-zero amplitude / power (e.g., specifically below an amplitude threshold of 0, 1, 2, 3, or 5, or 10V, and / or below a power threshold of less than 1, 2, 3, 5, 10W, or, for example, below 1, 2, 3, 5, or 10% of the maximum power of the power transfer).

[0140] Using such a repetitive time frame allows communication and power transfer to be separated in the time domain, which greatly reduces (and in some cases eliminates) the mutual interference from power transfer to communication operations. Thus, the interference caused by the power transfer signal to communication is greatly reduced, in fact reduced to essentially zero. This very significantly improves communication performance and reliability, thereby making power transfer operations improved and more reliable.

[0141] In the power transfer phase, the power transmitter is therefore configured to perform power transfer during the power transfer time intervals of the time frame. Specifically, during these time intervals, the power transmitter 101 and the power receiver 105 operate a power control loop. The power control loop is based on communication within the power transfer time interval or based on communication outside the power transfer time interval, e.g., within a dedicated communication time interval. For example, each foreign object time interval is separated by a number of alternating power transfer time intervals and communication time intervals. Thus, the transmitted power level varies dynamically. In the communication time intervals, the power transfer signal is effectively switched off, but a power control error message is communicated to control the power loop operation during the power transfer time interval.

[0142] In many embodiments, the drive signals and power transmission signals are thus driven to employ a repeating time frame that includes power transmission time intervals (where power is transmitted and the power control loop is typically operated) and reduced power time intervals (where power is reduced compared to the power transmission time intervals). These reduced power time intervals are typically used as communication time intervals where at least some communication (with no or reduced interference from power transmission) is performed. Alternatively or additionally, the reduced power time intervals are used for foreign object detection, and indeed in many embodiments the reduced power time intervals are used to perform simultaneous communication and foreign object detection.

[0143] In many embodiments, the driver 201 is supplied by a fluctuating power supply signal, and typically by a fluctuating supply voltage. The drive signal is typically generated to have an amplitude according to the fluctuating power supply signal, and in particular according to the fluctuating supply voltage. For example, in the case of an output inverter of the driver 201 corresponding to, for example, FIG. 4 or FIG. 5, the drive signal will have an amplitude equal to the supply voltage, except for a small voltage drop across the switch elements.

[0144] For example, in many embodiments, the supply voltage for the driver 201 and the output inverter is generated from a rectified (and possibly partially smoothed) AC mains voltage. In the case of an unsmoothed rectified voltage, the input supply voltage, and therefore the drive signal voltage, will reach a minimum value of zero volts at a time corresponding to a zero crossing of the mains voltage. In the case of a partially smoothed rectified supply voltage, the minimum voltage occurs with a delay relative to the zero crossing and may be higher than zero volts.

[0145] In such an embodiment, the reduced power / foreign object detection / communication time interval is synchronized to the minimum of the (absolute) supply signal / voltage. Synchronizer 209 synchronizes the communication time interval such that the time of the minimum of the fluctuating power supply signal is within the reduced power time interval, typically configured to be centered on the minimum of the fluctuating power supply signal.

[0146] In many embodiments, the timing of the reduced power time interval is such that the reduced power time interval is centered around a time of a minimum value of the varying power supply signal, and thus is typically also centered around a minimum value of the power transmission signal. In many embodiments, synchronizer 209 is configured to control the timing of the communication time interval such that the communication time interval is substantially centered around a zero level of the input supply voltage (often a zero crossing of the input power supply voltage).

[0147] For example, if the driver 201 is supplied with a 50 Hz rectified mains voltage, the power supply zero crossings and the rectified supply voltage minimums occur at 10 msec intervals, and each repeating time frame is set to have a 10 msec duration. An example of the resulting drive signal / power transfer signal is illustrated in Figure 14, which shows the drive signal / power transfer signal during power transfer time interval PT and during communication / foreign object detection time interval C.

[0148] In some embodiments, using such a recurring time frame, the power transmission controller 205 is configured to only change the frequency of the drive signal between power transfer intervals. Thus, in some embodiments, the drive frequency, and therefore the power level, is changed based on the control error message received from the power receiver, but only between power transfer intervals and remains constant within each time interval. A change from one frequency range to another occurs during a reduced power time interval in such a case, and this approach reduces the transient effects that would otherwise occur for large frequency steps. FIG. 15 illustrates an example of how the frequency is changed to reduce power in such an embodiment (in an example where the upper frequency limit of the lower frequency range is 28 kHz and the lower frequency limit of the upper frequency range is 56 kHz).

[0149] The present approach achieves a gradual change without any significant power discontinuities or transient effects associated with frequency changes occurring at reduced power levels. In an example, during a reduced power time interval, a new frequency for the power signal is determined, and this frequency then remains stable for the entire power transfer time interval. During the subsequent reduced power time interval, a new frequency is determined and applied. This ensures that the frequency does not suddenly jump during a power transfer slot, which could cause significant transient effects, such as increased electromagnetic interference.

[0150] In some embodiments, the power transmission controller 205 is configured to change the frequency within the power transfer time interval but only within the frequency range and not between the frequency ranges. Thus, in some embodiments, the power transmission controller 205 is configured to only change the frequency of the drive signal either within the lower operating frequency range or within the higher operating frequency range during the power transfer time interval but not between the different operating frequency ranges. Thus, in such an embodiment, the power control loop dynamically updates the drive signal frequency and power level during each power transfer time interval. Nevertheless, even if the power control loop attempts to change the frequency to raise it above the upper frequency limit of the lower frequency range or to lower it below the lower frequency range, such a change will not be made until the next reduced power time interval. Thus, while smaller frequency variations within each operating frequency range are allowed, large frequency steps between operating frequency ranges are prevented during the power transfer time interval and are limited to reduced power time intervals where the power level is low (or, in fact, substantially zero).

[0151] In some embodiments, the transition between the power transfer time interval and the reduced power time interval is more gradual by gradually reducing the power level during the power-up interval during the beginning of the power transfer time interval and / or during the power-down interval during the end of the power transfer time interval, which reduces power transients and electromagnetic interference, resulting in more efficient operation.

[0152] For example, rather than having a constant frequency for the entire reduced power time interval, the beginning and end of the reduced power slot includes a change in the drive signal to smooth the on-off switching of power for the power transfer time interval. This achieves an improved spectrum for electromagnetic compatibility.

[0153] In many embodiments, the power level is reduced by reducing the duty cycle of the drive signal during a power-up interval at the beginning of the power transfer time interval and / or by increasing the duty cycle during a power-down interval at the end of the power transfer time interval. Thus, by controlling the duty cycle of the drive signal, smoother power transients can be achieved at the beginning and end of the power transfer time interval without affecting power control operation based on the drive frequency of the drive signal.

[0154] In some embodiments, the transmitter includes a hysteresis effect in switching between operating frequency ranges. For example, in some embodiments, when changing from a lower operating frequency range to a higher operating frequency range, the new frequency after the jump is set to be higher than the lowest frequency of the operating frequency range by a certain appropriate value (e.g., 3 kHz higher than the lowest frequency of the higher operating frequency range for some embodiments). Similarly, when changing from a higher operating frequency range to a lower operating frequency range, the new frequency after the jump is set to be lower than the maximum frequency of the operating frequency range by a certain appropriate value (e.g., 3 kHz lower than the maximum frequency of the lower operating frequency range). Equivalently, the operating frequency ranges are considered to have different end frequencies depending on which operating frequency range the drive frequency is currently within.

[0155] It will be appreciated that the above description has, for clarity, described embodiments of the invention with reference to different functional circuits, units, and processors. Nevertheless, it will be apparent that any suitable distribution of functionality between different functional circuits, units, or processors may be used without detracting from the invention. For example, functionality illustrated as being performed by separate processors or controllers may be performed by the same processor or controller. Thus, references to specific functional units or circuits should not be considered as indicative of a strict logical or physical structure or organization, but merely as references to suitable means for providing the described functionality.

[0156] The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention is optionally implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of the embodiments of the invention may be physically, functionally and logically implemented in any suitable way. In practice, functionality may be performed in a single unit, in several units or as part of other functional units. Thus, the invention may be implemented in a single unit or may be physically and functionally distributed between different units, circuits and processors.

[0157] Although the present invention has been described with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the appended claims. Moreover, while features may appear to be described with specific embodiments, those skilled in the art will recognize that various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

[0158] Furthermore, although individually listed, a plurality of means, elements, circuits or method steps may be performed by, for example, a single circuit, unit or processor. Moreover, although individual features are included in different claims, they may, in some cases, be advantageously combined, and the inclusion in different claims does not imply that the combination of features is not feasible and / or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate. The inclusion of a feature in a dependent claim of an independent claim does not imply a limitation to this independent claim, but rather indicates that the feature is equally applicable to other independent claims, as appropriate. Moreover, the order of features in the claims does not imply any particular order in which the features must be performed, and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. Moreover, the singular reference does not exclude a plurality. Thus, references to "first," "second," etc. do not exclude a plurality. Reference signs in the claims are provided merely as an obvious example and are not to be taken as limiting the scope of the claims in any way.

[0159] The following is provided: A power transmitter (101) for wirelessly providing power to a power receiver (105) via an inductive power transmission signal, the power transmitter (101) comprising: an output circuit (303, 103) comprising a transmit coil (103) configured to generate a power transfer signal in response to a drive signal being applied to the output circuit (303, 103); a driver (301) configured to generate a drive signal; a load function circuit (307) configured to determine a load function for a combined configuration of a transmitter and a receiver, the load function representing a dependence of a load of a drive signal by the output circuit (303, 103) on a frequency of the drive signal for the transmitter and receiver configuration; a power controller (305) for controlling the power level of the power transmission signal by adjusting the frequency of the drive signal; an interval circuit (309) for determining a first operating frequency range and a second operating frequency range separated by a non-operating frequency range in response to a power transfer function; Equipped with A power transmitter (101), wherein the power controller (305) is configured to adapt the power level of the power transmission signal by varying the frequency of the drive signal across at least frequencies within a first operating frequency range and a second operating frequency range, except for frequencies within the operating frequency range. A method of operation of a power transmitter (101) for wirelessly providing power to a power receiver (105) via an inductive power transmission signal, the method comprising: The method includes an output circuit (303, 103) comprising a transmit coil (103) configured to generate a power transfer signal in response to a drive signal being applied to the output circuit (303, 103), the output circuit (303, 103) comprising: generating a drive signal; determining a load function for the transmitter and receiver configuration, the load function representing a dependence of a load of a drive signal by an output circuit (303, 103) on a frequency of the drive signal for the transmitter and receiver configuration; Controlling the power level of the power transmission signal by adjusting the frequency of the drive signal; determining a first operating frequency range and a second operating frequency range separated by a non-operating frequency range according to a power transfer function; having The method, wherein controlling the power level includes adapting the power level of the power transmission signal by varying the frequency of the drive signal across at least frequencies within the first operating frequency range and the second operating frequency range, except for frequencies within the operating frequency range.

Claims

1. 1. A power transmitter for wirelessly providing power to a power receiver via an inductive power transmission signal, comprising: an output circuit including a transmit coil that generates the inductive power transfer signal in response to a drive signal applied to the output circuit; A driver for generating the drive signal; a load function circuit for determining a load function for a combined configuration of the power transmitter and the power receiver, the load function representing a dependency of a load on a frequency of the drive signal for the combined configuration of the power transmitter and the power receiver, the load being a load of the drive signal by the output circuit; a power controller for controlling a power level of the inductive power transfer signal by adjusting the frequency of the drive signal; an interval circuit for determining a first operating frequency range and a second operating frequency range separated by a non-operating frequency range in response to the load function; Equipped with 11. A power transmitter, wherein the power controller adapts the power level of the inductive power transmission signal by varying the frequency of the drive signal across at least frequencies within the first operating frequency range and the second operating frequency range, excluding frequencies within the non-operating frequency range.

2. The transmitter of claim 1 , wherein the interval circuit determines the first operating frequency range and the second operating frequency range in response to a reactive component of an impedance of the output circuit in response to the frequency of the drive signal.

3. 3. The transmitter of claim 2, wherein the interval circuit determines the first operating frequency range and the second operating frequency range such that the interval circuit is a frequency range in which the impedance of the output circuit has an inductive reactance, and the non-operating frequency range includes frequencies in which the output circuit has a non-inductive impedance.

4. 4. The power transmitter of claim 1, wherein the interval circuit determines the first operating frequency range and the second operating frequency range such that a transmission power load for an upper limit frequency of the first operating frequency range matches a transmission power load for a lower limit frequency of the second operating frequency range.

5. 5. The transmitter of claim 4, wherein the interval circuit determines the first operating frequency range and the second operating frequency range in response to a slope of the load function for the upper frequency limit of the first operating frequency range and a slope of the load function for the lower frequency limit of the second operating frequency range.

6. 6. The power transmitter of claim 1, wherein the interval circuit determines the first operating frequency range and the second operating frequency range in response to a slope of the load function as a function of the frequency of the drive signal.

7. 7. The power transmitter of claim 1, wherein the interval circuit determines the first operating frequency range and the second operating frequency range such that the load function is monotonic with respect to frequencies in the first operating frequency range and the second operating frequency range.

8. 8. The transmitter of claim 7, wherein the load function is monotonically decreasing for increasing frequencies in the first and second operating frequency ranges.

9. 9. The transmitter of claim 1, wherein the interval circuit determines the load function in response to measurements of a property of the drive signal while varying the frequency of the drive signal.

10. the driver generates the drive signal to apply a repetitive time frame to the inductive power transmission signal including at least one power transfer interval during which the inductive power transmission signal transfers power to the power receiver and at least one reduced power time interval during which a power of the inductive power transmission signal is reduced relative to the power transfer interval; The transmitter of claim 1 , wherein the power controller only changes the frequency of the drive signal outside of a power transfer interval.

11. the driver generates the drive signal to apply a repetitive time frame to the inductive power transmission signal including at least one power transfer interval during which the inductive power transmission signal transfers power to the power receiver and at least one reduced power time interval during which a power of the inductive power transmission signal is reduced relative to the power transfer interval; 11. The power transmitter of claim 1, wherein the power controller only changes the frequency of the drive signal within the first operating frequency range or the second operating frequency range during one power transfer time interval.

12. 11. The transmitter of claim 9 or 10, wherein the power controller adapts the power level by reducing a duty cycle of the drive signal during at least one of a power-on interval at the beginning of a power transfer time interval and a power-off interval at the end of the power transfer time interval.

13. 1. A method of operation of a power transmitter for wirelessly providing power to a power receiver via an inductive power transfer signal, the power transmitter comprising an output circuit comprising a transmit coil that generates the inductive power transfer signal in response to a drive signal applied to the output circuit, the method comprising: generating the drive signal; determining a load function for a combined configuration of the power transmitter and the power receiver, the load function representing a dependency of a load on a frequency of the drive signal for the combined configuration of the power transmitter and the power receiver, the load being a load of the drive signal by the output circuit; controlling a power level of the inductive power transfer signal by adjusting the frequency of the drive signal; determining a first operating frequency range and a second operating frequency range separated by a non-operating frequency range in response to the load function; having The method, wherein controlling the power level comprises adapting the power level of the inductive power transfer signal by varying the frequency of the drive signal across at least frequencies within the first operating frequency range and the second operating frequency range, excluding frequencies within the non-operating frequency range.

14. A wireless power transmission system comprising: the power transmitter according to claim 1 ; and the power receiver.

Images