Coupling coefficient in a wireless power system

Abstract

This disclosure provides systems, methods and apparatuses that enable a Power Transmitter of a wireless power system to determine a coupling coefficient k (k-factor). The k-factor represents an amount of a magnetic field coupling between a primary coil of the Power Transmitter and a secondary coil of a Power Receiver. The k-factor impacts the effectiveness of power transfer at various operating frequencies. In some aspects, a Power Transmitter can determine the k-factor prior to a power negotiation such that the Power Transmitter can negotiate a negotiated power level limit based, in part, on considerations of potential operating frequencies and the k-factor. In some aspects, a k-factor measurement protocol enables the Power Transmitter and the Power Transmitter to coordinate k-factor evaluations prior to or during the power state.

Description

COUPLING COEFFICIENT IN A WIRELESS POWER SYSTEMTECHNICAL FIELD

[0001] This disclosure relates generally to wireless power and some aspects relate to a managing wireless power transfer based on coupling of an electromagnetic field in a wireless power system.DESCRIPTION OF RELATED TECHNOLOGY

[0002] A wireless power system includes a Power Transmitter (PTx, sometimes also referred to as a wireless power transmission apparatus) and a Power Receiver (PRx, sometimes also referred to as a wireless power reception apparatus). The Power Transmitter includes a primary coil that produces an electromagnetic field during a power state to induce a voltage in a secondary coil of the Power Receiver when the secondary coil is placed in an electromagnetic field of the primary coil. The induced voltage can generate power for a load or for use by a rectifier that powers the load. Thus, the Power Transmitter can wirelessly transfer power to the Power Receiver using inductive coupling between the primary coil and the secondary coil. An appliance can use the power from the Power Receiver to operate a load (such as a motor, a heating element, electronics, or a power storage device, among other examples). The Power Transmitter can control an operating frequency, an operating voltage, or other parameters at the Power Transmitter to control how much wireless power is delivered to the Power Receiver. Power negotiation and power control messages between the Power Receiver and the Power Transmitter can control some aspects of a wireless power system.

[0003] As described, the primary coil of the Power Transmitter produces an electromagnetic field and the secondary coil of the Power Receiver captures the magnetic field. The primary coil and the secondary coil form a loosely coupled transformer. The amount of magnetic flux linkage between the Power Transmitter and the Power Receiver depends on the magnetic coupling between the primary coil and the secondary coil. A coupling coefficient k (also referred to as k-factor) is a value indicating how much of the electromagnetic field is being induced from the primary coil to the secondary coil. The coupling coefficient k can depend on the electrical properties of the coils, their relativesizes, the distance between the coils, the alignment of the coils, and the presence of other metals in the electromagnetic field.BRIEF SUMMARY

[0004] The systems, methods, and apparatuses of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0005] In one aspect, a method performed by a Power Transmitter, includes determining a first coupling coefficient k (k-factor) based on a first instance of a k-factor evaluation prior to a power state of the wireless power system, where the first k-factor represents an amount of a magnetic field coupling between a primary coil of the Power Transmitter and a secondary coil of a Power Receiver. The method includes negotiating, prior to the power state, a negotiated power level limit based, at least in part, on the first k-factor. The method includes controlling transmission of the wireless power from the Power Transmitter to the Power Receiver based on the negotiated power level limit during the power state.

[0006] In one aspect, a method performed by a Power Receiver, includes receiving one or more pulses via a secondary coil of the Power Receiver as part of a coupling coefficient k (k-factor) evaluation prior to a power state of the wireless power system, where a k-factor represents an amount of a magnetic field coupling between a primary coil of a Power Transmitter and the secondary coil of the Power Receiver. The method includes communicating a measurement report message to the Power Transmitter, the measurement report message including one or more measurements of the one or more pulses at the secondary coil of the Power Receiver.

[0007] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Like reference numbers and designations in the various drawings indicate like elements. Note that the relative dimensions of the figures may not be drawn to scale.

[0009] FIG. 1 illustrates an example wireless power system that includes a Power Transmitter and a Power Receiver.

[0010] FIG. 2 illustrates electromagnetic coupling between a primary coil and a secondary coil.

[0011] FIG. 3 illustrates how coupling coefficient k (k-factor) impacts wireless power transmission at various operating frequencies.

[0012] FIG. 4 illustrates a state diagram of a wireless power system and possible instances of coupling coefficient k (k-factor) evaluations in accordance with aspects of this disclosure.

[0013] FIG. 5 illustrates example operations of a Power Transmitter in accordance with some aspects of this disclosure.

[0014] FIG. 6 illustrates example operations of a Power Receiver in accordance with some aspects of this disclosure.

[0015] FIG. 7 illustrates a timing diagram and associated operations in various states of a wireless power system.

[0016] FIG. 8 A illustrates an example k-factor evaluation prior to a power negotiation operation in accordance with some aspects of this disclosure.

[0017] FIG. 8B illustrates an example k-factor evaluation prior to a power state in accordance with some aspects of this disclosure.

[0018] FIG. 8C illustrates another example k-factor evaluation during a power state in accordance with some aspects of this disclosure.

[0019] FIG. 9 illustrates an example k-factor evaluation using Power Receiver measurements in accordance with some aspects of this disclosure.

[0020] FIG. 10 illustrates timing considerations for a k-factor evaluation in accordance with some aspects of this disclosure.

[0021] FIG. 11 illustrates example operations for a k-factor evaluation using Power Transmitter estimation in accordance with some aspects of this disclosure.

[0022] FIG. 12 illustrates operations in a power state of the wireless power system.

[0023] FIG. 13 illustrates a communication timing protocol for a k-factor evaluation using measurements during a power state of the wireless power system.

[0024] FIG. 14 illustrates an example Power Transmitter.

[0025] FIG. 15 illustrates an example Power Receiver.

[0026] FIG. 16 illustrates a block diagram of an example apparatus for use in a wireless power system.DETAILED DESCRIPTION

[0027] The following description is directed to certain implementations for the purpose of describing innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. The described implementations can be implemented in any means, apparatus, system, or method for transmitting or receiving wireless power.

[0028] A wireless power system includes a Power Transmitter (PTx, sometimes also referred to as a wireless power transmission apparatus) and a Power Receiver (PRx, sometimes also referred to as a wireless power reception apparatus). The Power Transmitter includes a primary coil that produces an electromagnetic field to induce a voltage in a secondary coil of the Power Receiver in an electromagnetic field of the primary coil. The amount of magnetic flux linkage between the Power Transmitter and the Power Receiver depends on the magnetic coupling between the primary coil and the secondary coil. A coupling coefficient k (also referred to as k-factor) is a value indicating the amount of a magnetic field coupling between the primary coil and the secondary coil. The k-factor indicates how much of the electromagnetic field can be induced from the primary coil to the secondary coil at various operating frequencies during power transfer. The k-factor can depend on the electrical properties of the coils, their relative sizes, the distance between the coils, the alignment of the coils, and the presence of other metals in the electromagnetic field. A quality factor (Q-factor) is another value in wireless power systems. Q-factor may depend on thermal or electrical properties (such as capacitance, inductance, resistance, etc.) of the coils. The k-factor and the Q-factor can both impact the effectiveness of wireless power transfer. While this disclosure relates to a protocol for determining k-factor, some concepts also may apply to Q-factor evaluations.

[0029] This disclosure provides systems, methods and apparatuses that enable a Power Transmitter to determine the k-factor and use the k-factor during power negotiation and power control operations. In some aspects, a Power Transmitter can determine the k-factor prior to a power negotiation such that the Power Transmitter can negotiate a negotiated power level limit based, in part, on considerations of potential operating frequencies and the k-factor. For example, a low k-factor can result in a lossy or less efficient system. Conversely, a high k-factor can indicate an over-coupled system in which a Power Transmitter cannot satisfy a rated power of the Power Receiver. By determining the k- factor prior to power negotiation, the Power Transmitter can decide whether it can satisfy the requested power. In some implementations, the negotiated power level limit can belimited based on the k-factor. In some implementations, the Power Transmitter might decide whether to proceed with power transfer or refrain from entering a power state based on the k-factor.

[0030] In some aspects, the Power Transmitter and the Power Receiver can participate in a k-factor evaluation in accordance with a protocol. This disclosure includes several example protocols for managing a k-factor evaluation. For example, the k-factor evaluation can include test signals (such as one or more pulses) during a k-factor measurement period to enable the Power Receiver to measure the test signals. The Power Receiver can communicate one or more measurements to the Power Transmitter to aid the Power Transmitter in calculating the k-factor.

[0031] In some aspects, a first k-factor evaluation can occur during a discovery state or a connected state prior to a power negotiation. Additionally, or alternatively, a second k- factor evaluation can occur during the connected state prior to a transition to the power state. Furthermore, in some implementations, the k-factor protocol can initiate occasional k-factor evaluations during the power state. When the k-factor changes, the Power Transmitter can determine whether it can still satisfy the negotiated power level limit. In some implementations, the Power Transmitter might end the power state when the k-factor changes such that the Power Transmitter cannot satisfy the negotiated power level limit or when a change in the k-factor indicates a foreign object detection or fault of the Power Receiver.

[0032] Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. A k-factor protocol enables the Power Transmitter and the Power Receiver to coordinate k-factor evaluations during various states of the wireless power system. The k-factor protocol can include predetermined times for k-factor evaluations based on state transitions or protocol messages. Alternatively, or additionally, a Power Transmitter can manage when and how the k-factor evaluations are performed based on communication messages. Thus, this disclosure provides some flexibility to manage k-factor evaluation while also improving the ability to negotiate negotiated power level limit. Furthermore, the k-factor can improve operation and efficiency of the Power Transmitter by enabling power control based on measured k-factor.

[0033] FIG. 1 illustrates an example wireless power system 100 that includes a Power Transmitter 102 and a Power Receiver 118. In FIG. 1, dashed lines represent communications to distinguish from solid lines that represent electrical circuit lines.

[0034] The Power Transmitter 102 includes a primary coil 104 and a Power Transmitter (PTx) controller 108. The primary coil 104 may be associated with a power transmitter circuit 106 (sometimes also referred to as a power signal generator or a driver circuit). The primary coil 104 may be a wire coil which transmits wireless power (which also may be referred to as wireless energy). The primary coil 104 may transmit wireless energy using inductive or magnetic resonant field. The power transmitter circuit 106 may include components (not shown) to prepare the wireless power. For example, the power transmitter circuit 106 may include one or more switches, drivers, series capacitors, rectifiers, inverters, or other components. In some implementations, the power transmitter circuit 106, PTx controller 108 and other components (not shown) may be collectively referred to as a power transmitter unit 110. Some or all of the power transmitter unit 110 may be embodied as an integrated circuit (IC) that implements features of this disclosure for controlling and transmitting wireless power to one or more wireless power reception apparatuses. The PTx controller 108 may be implemented as a microcontroller, dedicated processor, integrated circuit, application specific integrated circuit (ASIC) or any other suitable electronic device.

[0035] A power source 112 provides power to the power transmitter unit 110. In some implementations, the power source 112 may convert alternating current (AC) power to direct current (DC) power. For example, the power source 112 may include a converter that receives an AC power from an external power supply and converts the AC power to a DC power used by the power transmitter circuit 106. Alternatively, or additionally, a component (such as an inverter) of the power transmitter circuit 106 may convert the DC power to the AC power. The power source 112 may be integrated as part of the Power Transmitter 102 or may be external to the Power Transmitter 102.

[0036] In some implementations, the Power Transmitter 102 causes the power source 112 to regulate the DC output voltage of the power source 112. For example, the PTx controller 108 can set DC voltage of the power source 112 based on information (such as a value indicating a requested power) received from the Power Receiver 118. The Power Transmitter 102 can receive power configuration information from the Power Receiver 118 and use the information to set a parameter (such as the DC output voltage of the power source 112). The Power Transmitter 102 can receive the power configuration informationduring various operating states, such as the discovery state or power state. In some implementations, the Power Transmitter 102 includes a DC-DC converter (not shown) between the power source 112 and the Power Transmitter circuit 106 to control the variable DC output voltage.

[0037] The PTx controller 108 is connected to a first communication interface 114. The first communication interface 114 is connected to a first communication coil 116. In some implementations, the first communication interface 114 and the first communication coil 116 may be collectively referred to as the first communication unit 122. In some implementations, the first communication unit 122 may support Near-Field Communication (NFC). NFC is a technology by which data transfer occurs on a carrier frequency of 13.56 Megahertz (MHz). In some implementations, the first communication unit 122 may support Bluetooth (BT) communications. The first communication unit 122 also may support any suitable communication protocol. The first communication unit 122 may contain modulation and demodulation circuits to wirelessly communicate via the first communication coil 116. Alternatively, or additionally, the TX controller 108 may use frequency modulation to communicate via an in-band communication link (not shown) that includes the primary coil 104.

[0038] The Power Receiver 118 may include a secondary coil 120, a rectifier 124, a Power Receiver (PRx) controller 126, a second communication interface 130, a load controller 134, a load 128, and a memory (not shown). In some implementations, the load 128 can include a drive (not shown) for controlling at least one parameter such as charging current, speed, or torque of the load. In some implementations, the rectifier 124 may be omitted such as when the voltage induced in the secondary coil 120 can directly power the load 128. In some implementations, a series switch (not shown) may be included in series with the secondary coil 120 or in series between the rectifier 124 and the load 128. Although not shown, a load capacitance can be used after the rectifier 124 to reduce the rate of rise of load voltage that would otherwise occur when the load 128 suddenly reduces power consumption. Although shown as different components, some components may be packaged or implemented in the same hardware. For example, in some implementations, the PRx controller 126 and the load controller 134 may be implemented as a single controller. The PRx controller 126, the load controller 134, or any combination thereof, may be implemented as a microcontroller, dedicated processor, integrated circuit, application specific integrated circuit (ASIC) or any other suitable electronic device.

[0039] The PTx controller 108 may detect the presence or proximity of a Power Receiver 118. This detection may happen during a periodic pinging process of the first communication interface 114. During the pinging process, the first communication interface 114 also may supply power to the second communication interface 130 when the Power Receiver 118 is in proximity to the Power Transmitter 102. The second communication interface 130 may “wake up” and power-up the PRx controller 126 and may send a reply signal back to the first communication interface 114. Prior to power transfer, a handshaking process may take place during which the PTx controller 108 may receive configuration data related to the power rating of the receiver, among other information. The PTx controller 108 may control characteristics of wireless power it provides to the Power Receiver 118 based on the configuration data.

[0040] A PRx controller 126 may be operationally coupled to the rectifier 124 and the second communication interface 130. The second communication interface 130 may contain modulation and demodulation circuits to wirelessly communicate via the second communication coil 132. Thus, the PRx controller 126 may wirelessly communicate feedback information to the PTx controller 108 via the second communication interface 130 to the first communication interface 114 using NFC communications. Alternatively, or additionally, the PRx controller 126 may use load modulation to communicate via an in- band communication link (not shown) that includes the secondary coil 120.

[0041] A load controller 134 may be operationally coupled to the load 128 and the second communication interface 130. The load controller 134 may detect changes to load states such as change in charging currents in a battery charging application. The load controller 134 also may determine a load voltage reference. The load controller 134 also may load voltage references, load current, and any other suitable information to the PRx controller 126 or the second communication interface 130 for communication to the Power Transmitter 102. The PRx controller 126 may additionally determine and provide feedback information indicating a measured load voltage available to the load 128. In some feedback messages, the feedback information may include a reference voltage indicating a required voltage for the load 128. In some feedback messages, the feedback information may indicate an error in the output voltage of the load 128. In some feedback messages, the feedback information may include the required power for the load. Although the PRx controller 126 and load controller 134 are shown separately, they may be included in the same component of the Power Receiver 118.

[0042] The Power Transmitter 102 controls an operating point of the Power Transmitter circuit 106 using a control loop and a control algorithm. For example, when the PTx controller 108 receives a control error value from the Power Receiver 118, the PTx controller 108 can calculate a reference current (preference) using the control error value. The PTx controller 108 also obtains a measured current (Imeasured) using sensors (not shown), where the Imeasured is a current at the Power Transmitter circuit 106. The PTx controller 108 uses the Ireference, the Imeasured, and the control algorithm to calculate an operating point for the Power Transmitter circuit 106. The operating point can be a voltage (also referred to as operating voltage), a current (also referred to as an operating current), a duty cycle, a phase shift, or other parameter which controls the how the Power Transmitter circuit 106 drives the wireless power signal to the primary coil 104.

[0043] FIG. 2 illustrates electromagnetic coupling 200 between a primary coil 104 and a secondary coil 120. A Power Transmitter creates a time-varying magnetic field by driving an alternating current through its primary coil 104. A Power Receiver captures this magnetic field using its secondary coil 120. The primary coil 104 and the secondary coil 120 form a loosely coupled transformer. The amount of magnetic flux linkage between the Power Transmitter and the Power Receiver depends on the magnetic coupling coefficient k between the two coils, defined as (Formula 1):, M k — _Lpt x LsiFormula 1. where M represents the mutual inductance between the two coils, Lp' represents the self-inductance of the primary coil 104 in a coupled condition, and Ls' represents the selfinductance of the secondary coil 120 in a coupled condition.

[0044] The coupling coefficient k in a wireless power system is appreciably lower than in conventional core-based transformers, which typically have values of k close to 1 (meaning that both coils capture almost all of the magnetic field lines). The best magnetic coupling typically results when the two coils are similar in size, are properly aligned, and are close together (such as at a distance that is well below their diameter). The coupling coefficient decreases the more the coils are misaligned and the more the coils differ in size. It also decreases as the distance and / or angle between the coils increases. The presence ofmetals, ferrites, or other magnetically active materials near the coils also impacts the coupling coefficient.

[0045] FIG. 3 illustrates how k-factor impacts wireless power transmission at various operating frequencies. Both the Power Transmitter and the Power Receiver exhibit resonant behavior. In isolation and thus without interaction between the two (k=0), these resonances occur at the frequencies fp and fs. When the Power Receiver is placed above the Power Transmitter, both elements are coupling and the resonance frequencies fp and fs repel each other. The resulting system transfer function may have one or two peaks depending on coupling and Power Receiver quality (Q-factor). The resonances may be affected by the coupling and by the Q-factor, with a system transfer function with a single peak occurring with a low coupling. Regardless of the number of peaks, the resonances can be shifted from fp and fs. FIG. 3 shows a graph 300 of an example of different k-factors. The horizontal axis (relative operating frequency 304) indicates the operating frequency divided by the primary resonance fp. The vertical axis indicates the transfer function 302, in which the voltage across the load is divided by the voltage of the Power Transmitter's power source.

[0046] Examining the graph 300, a first curve 306 shows the transfer function for a coupling coefficient k of k=0.5. A second curve 308 shows the transfer function for a coupling coefficient k of k=0.4. For the first curve 306, it is clear that two distinct peaks appear in the transfer function. The separation between the two peaks might increase as the coupling coefficient k increases. The appearance of two peaks in the transfer function and the complex behavior of their position with respect to frequency indicate that the coupling coefficient k and load impedance typically have a substantial impact on the system's power transfer efficiency.

[0047] Empirical tests results indicate that low and high k-factors can impact system performance in different ways. In some instances, a high k-factor can result in the Power Transmitter being unable to meet the load demand. For example, the flattened peaks in the power transfer curve can mean that no operating frequency can be selected to meet the required power. Conversely, a low k-factor (such as illustrated with curve 308) can result in a single large peak that could exceed the power capability of the Power Transmitter. Thus, some aspects of this disclosure enable the Power Transmitter to determine the k- factor prior to a power negotiation so that the Power Transmitter can determine whether it can meet the power requirements of the Power Receiver and has enough available power to operate within the power transfer function of the k-factor.

[0048] FIG. 4 illustrates a state diagram 400 of a wireless power system and possible instances of coupling coefficient k (k-factor) evaluations in accordance with aspects of this disclosure. The state diagram 400 illustrates the operating states in which the wireless power system may operate. When a Power Receiver is placed within an interface surface of a Power Transmitter, the two start to communicate with the aim to configure and control the power transfer. There can be four operating states associated with the wireless power system: a standby state 402 (sometimes also referred to as a ping state), a discovery state 404 (sometimes referred to as a configuration state), a connected state 406, and a power state 408 (sometimes referred to as a power transfer state). A technical specification may define how the Power Transmitter and Power Receiver can transition between the operating states. For example, the wireless power system typically begins in the standby state 402 until the Power Transmitter detects a Power Receiver, then continues to the discovery state 404. In the discovery state 404 the Power Transmitter establishes communication and receives the identification of the Power Receiver and its static configuration data. In the connected state 406 and the power state 408, the Power Transmitter and Power Receiver exchange information to agree and adjust parameters related to wireless power transfer. The system can move to a reinitialization state (not shown) as needed to reinitialize or return to the standby state when communication, powering, or other activities are no longer taking place. Each of the operating states are briefly described herein for reference.

[0049] In the standby state 402, the Power Transmitter tries to establish communications with a Power Receiver. The Power Receiver may be just placed on the interface surface or may not be present during this operating state. The Power Transmitter may attempt to communicate or detect the presence of the Power Receiver. For example, the Power Transmitter may use an analog ping, out-of-band communication (such as NFC), a digital ping, or any combination thereof, to determine that a compatible Power Receiver is present. Once the wireless power system determines that a Power Receiver is present (such as by confirming NFC communication), the wireless power system may transition to the discovery state 404.

[0050] In the discovery state 404, the Power Receiver may send basic identification and configuration data to the Power Transmitter. For example, the Power Transmitter may retrieve static configuration information from the Power Receiver via the NFC communication. The Power Transmitter and the Power Receiver may use this information to verify that they both use compatible versions of a technical specification or protocol for wireless power transfer. The Power Transmitter and Power Receiver may communicatebasic settings or communicate regarding their respective capabilities. From the discovery state 404, the wireless power system may transition to the connected state 406.

[0051] In the connected state 406, the Power Transmitter and the Power Receiver may exchange further communications to negotiate the parameters that govern the power state. For example, a power negotiation 410 can occur during the connected state 406. After negotiating the parameters, the Power Transmitter may be prepared to transfer wireless power and the Power Receiver may be prepared to receive the wireless power. However, the Power Transmitter may wait for a request or command from the Power Receiver before transitioning to the power state 408. This may be useful, for example, when a cordless appliance (such as a blender, toaster, mixer, or microwave, among other examples) is configured for use pending a user interaction. The user may initiate the power state 408 by a user interface (such as an activation switch) of the Power Receiver, which in turn communicates to the Power Transmitter to transition to the power state 408.

[0052] In the power state 408, the Power Transmitter may transfer wireless power to the Power Receiver. Typically, the Power Transmitter will periodically perform a foreign object detection (FOD) assessment during the power state 408. In some, the Power Transmitter may perform an FOD assessment to ensure that no foreign objects are present before transitioning from the connected state 406 to the power state 408. The Power Transmitter also may perform periodic FOD assessments during the power state 408. The standby state 402, the discovery state 404, and the connected state 406 may be collectively referred to as pre-power states, while the power state 408 may be referred to as a during- power state.

[0053] In accordance with aspects of this disclosure, a Power Transmitter might perform one or more k-factor evaluations. For example, the Power Transmitter might perform a first k-factor evaluation 412 as part of a state transition from the discovery state 404 to the connected state 406. The first k-factor evaluation 412 might be included at the end of the discovery state 404 or the beginning of the connected state 406. The Power Transmitter might perform a second k-factor evaluation 414 as part of the transition from the connected state 406 to the power state 408 (such as at the end of the connected state 406 or beginning of the power state 408). Additionally, or alternatively, the Power Transmitter might perform one or more further k-factor evaluation(s) 416 during the power state 408.

[0054] This disclosure includes several examples of k-factor evaluations. For example, a k-factor evaluation can be based on measurements obtained by the Power Receiver during a k-factor measurement period and communicated to the Power Transmitter. The Power Transmitter can calculate the k-factor based on the measurements. Alternatively, or additionally, the k-factor evaluation can include an estimation of the electromagnetic coupling based on configuration data or other communications from the Power Receiver without explicit measurements for the k-factor evaluation.

[0055] FIG. 5 illustrates example operations 500 of a Power Transmitter in accordance with some aspects of this disclosure. For example, the operations 500 might be performed by the Power Transmitter 102 or the Power Transmitter 1400 described with reference to other Figures of this disclosure. In block 502, Power Transmitter determines a first coupling coefficient k (k-factor) based on a first instance of a k-factor evaluation prior to a power state of the wireless power system, where the first k-factor represents an amount of a magnetic field coupling between a primary coil of the Power Transmitter and a secondary coil of a Power Receiver. In block 504, Power Receiver negotiates, prior to the power state, a negotiated power level limit based, at least in part, on the first k-factor. In block 506, Power Receiver controls transmission of the wireless power from the Power Transmitter to the Power Receiver based on the negotiated power level limit during the power state.

[0056] FIG. 6 illustrates example operations 600 of a Power Receiver in accordance with some aspects of this disclosure. For example, the operations 600 might be performed by the Power Receiver 118 or the Power Receiver 1500 described with reference to other Figures of this disclosure. In block 602, Power Receiver receives one or more pulses via a secondary coil of the Power Receiver as part of a coupling coefficient k (k-factor) evaluation prior to a power state of the wireless power system, where a k-factor represents an amount of a magnetic field coupling between a primary coil of a Power Transmitter and the secondary coil of the Power Receiver. In block 604, Power Receiver communicates a measurement report message to the Power Transmitter, the measurement report message including one or more measurements of the one or more pulses at a secondary coil of the Power Receiver.

[0057] FIG. 7 illustrates a timing diagram 700 and associated operations in various states of a wireless power system. The timing diagram 700 is used to describe the operations of a Power Receiver (PRx) 118 and a Power Transmitter (PTx) 102. Although described as operations of the Power Receiver 118 and the Power Transmitter 102, it should be apparentthat the operations might be performed by the PTx controller 108 and the PRx controller 126, respectively. The Power Receiver 118 and the Power Transmitter 102 may follow the state diagram of various operating states, as described with reference to FIG. 4. In FIG. 7, the standby state and some operations in the discovery state 404 are omitted for brevity. During the standby state, a user may place an appliance having the Power Receiver in an interface space of the Power Transmitter. The Power Transmitter detects the Power Receiver and communicates with the Power Receiver to obtain identification and configuration information (not shown).

[0058] When the Power Receiver 118 has completed the identification and configuration phase, the Power Receiver 118 communicates a state transition request (NEXT / con) 702. The “NEXT” message is a type of communication message that indicates a request to transition to another state. The “NEXT” message also indicates the requested state: such as NEXT / con for a request to transition to the connected state or a NEXT / pow for a request to transition to the power state. The Power Transmitter 102 may respond to the state transition request (NEXT / con) 702 with a response message ("RESP / ok") 704. The “RESP” message might indicate okay (“ok”), not okay ("nok"), not defined ("nd"), or busy ("bsy"). In some implementations, the “RESP” message is a response that can indicate acknowledgement ("ack"), non-acknowledgement ("nak") or not defined ("nd"). In the example of FIG. 7, the response (RESP / ok) 704 is an “ok” or “ack” to indicate an agreement to transition to the connected state 406.

[0059] At time 706, the Power Receiver 118 detects that an activation switch associated with the load has been turned on. For example, the activation switch may include user input indicating a desire to activate the load. Examples of the activation switch may include a button, a flip switch, a knob, or a touchscreen (and associated processor), among other examples. Some appliances may not include an activation switch and the Power Receiver 118 may assume that the load is always ready to receive wireless power. The Power Receiver 118 may participate in a power negotiation 708 with the Power Transmitter 102 based on a power requirement of the load. The power negotiation 708 might include one or more power negotiation messages, such as a first power negotiation message 710 from the Power Receiver 118 to the Power Transmitter 102 and a second power negotiation message 712 from the Power Transmitter 102 to the Power Receiver 118.

[0060] After the power negotiation 708, the Power Receiver 118 transmits a state transition request (NEXT / pow) 714 to request a state transition to the power state 408. In some implementations, the Power Transmitter 102 might perform one or more operationsfor a FOD assessment 716 before agreeing to transition to the power state 408. In some implementations, the FOD assessment 716 may be required to be performed before transitioning from the connected state 406 to the power state 408. For an FOD assessment, the Power Transmitter 102 may scan for foreign objects using a variety of techniques, such as active excitation or passive excitation of foreign object detection coils to observe differences in impedance that indicate the presence of a foreign object. Assuming no foreign object is detected during the FOD assessment 716, the Power Transmitter 102 responds with a response (RESP / ok) 718.

[0061] After receiving the response (RESP / ok) 718 in response to the state transition request (NEXT / pow) 714, the Power Receiver 118 may activate an enablement switch 720 to cause a switch in the Power Receiver couple the secondary coil to power reception circuit (such as a rectifier or load). In the first position (which may be a default or “normal” position), the switch may disable a secondary coil of the Power Receiver from conducting energy. For example, the first position may disconnect or decouple the secondary coil from a power reception circuit. The first position may open a circuit that includes the secondary coil. In the second position, the switch may enable the secondary coil to conduct energy - such as an induced voltage from a magnetic field. After the switch has changed to the second position, the Power Receiver 118 may communicate a power request message 722 (such as a control message ("CTRL") indicated a requested power, or "CTRL / rqp") to the Power Transmitter 102.

[0062] The Power Transmitter 102 may receive the power request message 722 and enable a power signal generator (such as an inverter) of the Power Transmitter to begin the transmission of a wireless power signal 726. In some implementations, the power signal generator is enabled at or after the first natural zero cross (shown at time 724) of the AC main power or AC cycle following the power request message 722. For systems that are operated off the grid (such as a DC operated PRx), the power signal generator may be enabled after a small delay after the power request message 722 is received.

[0063] FIG. 7 also illustrates the activity of a communication channel 730 in relation to the timing of the operations of a Power Receiver 118 and a Power Transmitter 102. The communication channel 730 might be an out-of-band communication (such as NFC) that uses separate antennas and signals. Although the communication channel 730 is separate from the primary coil and the secondary coil, communications via the 730 can impact some operations, such as the FOD assessment 716. In some implementations, communication signals may cease during the FOD assessment 716 to prevent interference. Furthermore,the communication channel 730 timeline illustrates communications 736, 738, and 740 that occur during communication time slots in the power state 408. The communication time slots may occur in relation to a zero-cross event associated with an AC cycle of a wireless power signal 726.

[0064] Having described the operations 700 of FIG. 7 as background, several examples of k-factor evaluations can be described with reference to FIG. 8 A through FIG. 11. There are three example times (locations in the various operating states) when k-factor evaluations might be performed. For example, the k-factor evaluation can be performed as part of a state transition or during the connected state 406 prior to the power negotiation 708. The k-factor evaluation can be performed in relation to the FOD assessment 716 before a state transition to the power state 408. One or more k-factor evaluations can be performed during the 408. FIG. 8A through FIG. 11 provide more details about these various k-factor evaluations, their potential uses, and associated protocols. For example, a k-factor evaluation before the power negotiation 708 can enable the Power Transmitter to more accurately calculate power capability and a negotiated power level limit. A k- factor evaluation before the power state 408 can enable the Power Transmitter to more accurately calculate an operating point for the wireless power signal. A k-factor evaluation during the power state 408 can enable the Power Transmitter to detect changes in the power transfer function, potentially requiring an end of the power state 408 to renegotiate the negotiated power level limit.

[0065] FIG. 8A illustrates an example k-factor evaluation 800a prior to a power negotiation operation in accordance with some aspects of this disclosure. The messages and operations in FIG. 8A include similar messages and operations (having the same reference numbers) as described with reference to FIG. 7. In FIG. 8 A, a first K-factor evaluation 806 occurs as part of a state transition from the discovery state 404 to the connected state 406 (such as at the end of the discovery state 404 or the beginning of the connected state 406).

[0066] In some implementations, the first K-factor evaluation 806 is initiated by the Power Transmitter 102 following the state transition request (NEXT / con) 702. For example, in the response (RESP / ok) 804, the Power Transmitter 102 might include an indicator to inform the Power Receiver 118 that the Power Transmitter 102 is initiating the first K-factor evaluation 806 as part of the state transition. The procedure for the first K- factor evaluation 806 might include one or more operations and messages, as further described with reference to FIG. 9.

[0067] The Power Transmitter 102 can determine the first K-factor evaluation 806 to determine the k-factor and use the k-factor in its process for the power negotiation 808. For example, the Power Transmitter 102 might calculate an available power of the Power Transmitter (available for the Power Transmitter to transfer to the Power Receiver) based on a power transfer function that accounts for the k-factor. The power negotiation 808 might result in a negotiated power level limit that can be met based on the power transfer function associated with the k-factor.

[0068] In some instances, the Power Transmitter 102 might determine a maximum power transfer capability under existing k-factor conditions and set the negotiated power level limit accordingly. In some instances, if the k-factor is too high (above a first threshold), the Power Transmitter 102 may determine that it cannot set an operating frequency that would deliver the requested negotiated power to the Power Receiver 118. An over-coupled system (high k-factor) might experience a reduction in voltage gain at rated PRx load condition. Therefore, although the Power Transmitter might be rated for higher power, due to low voltage gain, the Power Receiver cannot receive the necessary voltage to satisfy the rated power of the load. In such cases, the Power Transmitter 102 might reject the requested negotiated power and suggest a different negotiated power level limit or inform the 118 that the Power Transmitter 102 cannot satisfy the rated power for the Power Receiver 118.

[0069] In some instances, if the k-factor is too low (below a second threshold), the Power Transmitter 102 may determine that the operating frequency needed to deliver the requested power would cause the Power Transmitter 102 to exceed its available power or PTx rated power and reject the requested negotiated power. In some implementations, the Power Transmitter 102 might inform the Power Receiver 118 that the k-factor is low (indicating a low alignment of the primary coil and the secondary coil) and the Power Receiver 118 might prompt a user to correct the alignment by repositioning the Power Receiver 118.

[0070] FIG. 8B illustrates an example k-factor evaluation 800b prior to a power state in accordance with some aspects of this disclosure. The messages and operations in FIG. 8A include similar messages and operations (having the same reference numbers) as described with reference to FIG. 7 and FIG. 8A. FIG. 8B describes a second k-factor evaluation 820 that occurs prior to a state transition to the power state 408. In some implementations, the second k-factor evaluation 820 can be in addition to the first K-factor evaluation 806. Alternatively, the first K-factor evaluation 806 might be omitted in some implementations.The second k-factor evaluation 820 might be useful to the Power Transmitter 102 to determine a power transfer function (such as curve 306 or 308 described with reference to FIG. 3) that aids the Power Transmitter 102 in setting an operating frequency to satisfy a requested power. The procedure for the second k-factor evaluation 820 might include one or more operations and messages, as further described with reference to FIG. 9. In some implementations, the response (RESP / ok) 816 (as a response to the state transition request (NEXT / pow) 714) might include an indicator to inform the Power Receiver 118 that the Power Transmitter 102 will initiate the second k-factor evaluation 820 before transitioning to the power state 408. Although FIG. 8B shows the second k-factor evaluation 820 occurring after the FOD assessment 716, the timing of the second k-factor evaluation 820 can be elsewhere in the connected state 406, such as before the FOD assessment 716 or after the power request message 722. For example, the second k-factor evaluation (shown as second k-factor evaluation 824) can be performed before the FOD assessment 716 as shown in FIG. 8C.

[0071] FIG. 8C illustrates another example k-factor evaluation 800c during a power state in accordance with some aspects of this disclosure. The messages and operations in FIG. 8A include similar messages and operations (having the same reference numbers) as described with reference to FIG. 7, FIG. 8 A, and FIG. 8B. In FIG. 8C, one or more k- factor evaluation(s) 822 can occur during the power state 408. The procedure for the one or more k-factor evaluation(s) 822 might include one or more operations and messages, as further described with reference to FIG. 12 and FIG. 13. The one or more k-factor evaluation(s) 822 might result in an updated k-factor due to changes in the alignment or electromagnetic coupling of the primary coil and the secondary coil.

[0072] In some implementations, one or more k-factor evaluation(s) 822 can be in addition to the first K-factor evaluation 806, the second k-factor evaluation 824, or both. Alternatively, the first K-factor evaluation 806, the second k-factor evaluation 824, or both, might be omitted in some implementations. The one or more k-factor evaluation(s) 822 might be useful to the Power Transmitter 102 to determine a power transfer function (such as curve 306 or 308 described with reference to FIG. 3) that aids the Power Transmitter 102 in setting an operating frequency to satisfy a requested power.

[0073] In some implementations, if the k-factor changes (such as an updated k-factor during the power state 408 being different from the first k-factor used for the power negotiation 808), the Power Transmitter might determine whether it can still satisfy the negotiated power level limit based on the updated k-factor. The Power Transmitter 102might end the power state 408 and return to the discovery state 404 or the connected state 406 if the Power Transmitter 102 cannot satisfy the negotiated power level limit as a result of a change between the first k-factor and the updated k-factor.

[0074] FIG. 9 illustrates an example k-factor evaluation 910 using Power Receiver measurements in accordance with some aspects of this disclosure. A timing diagram 900 shows operations of the Power Receiver 118, the Power Transmitter 102, and the activity on the communication channel 730. The example k-factor evaluation 910 might be an example of the first K-factor evaluation 806, the second k-factor evaluation 820, or the second k-factor evaluation 824 as described with reference to FIG. 8A, FIG. 8B, and FIG. 8C. For context and brevity, the example k-factor evaluation 910 is shown in a position of the second k-factor evaluation 820 of FIG. 8B.

[0075] In response to a state transition request message 912 (such as a "NEXT" message) from the Power Receiver 118, the Power Transmitter 102 may communicate a RESP / ok message 914. The state transition request message 912 might be a “NEXT / con” (such as state transition request (NEXT / con) 702) or a “NEXT / pow” (such as state transition request (NEXT / pow) 714). For brevity, the state transition request message 912 is referred to as a “NEXT / x” message. In the scenario where the state transition request message 912 is a “NEXT / pow” message, the Power Transmitter 102 might perform a FOD assessment 716 before (or after) the k-factor evaluation 910.

[0076] The RESP / ok message 914 might include an indication that the k-factor evaluation 910 will be performed before the state transition. For example, the RESP / ok message 914 might include a hold indicator, flag, or other value to cause the Power Receiver 118 to refrain from immediately taking a next step for the state transition. For example, the hold indicator might prevent the Power Receiver 118 from activating an enablement switch at the secondary coil. In some implementations, the hold indicator might be included in a PTx status field of the RESP / ok message 914.

[0077] The k-factor evaluation 910 may begin with a k-factor measurement request message 916 from the Power Transmitter 102 to the Power Receiver 118. For example, the k-factor measurement request message 916 might be a “MEAS” and may optionally include an indication to measure one or more parameters. The Power Receiver 118 may respond with an acknowledgment 918 (such as a “RESP / ok”) to acknowledge receipt of the k-factor measurement request message 916.

[0078] During a k-factor measurement period 932, the Power Transmitter 102 transmits one or more one or more pulses 920 for the k-factor measurement. At block 922, the Power Receiver 118 measures parameters (such as voltage, current, frequency, among other examples) at the secondary coil. For example, the parameters might indicate an amount of induced voltage or some reference metric indicating the amount of electromagnetic coupling between the secondary coil and the primary coil based on the one or more pulses 920.

[0079] After the k-factor measurement period 932, the Power Receiver 118 communicates a measurement report 924 to the Power Transmitter 102 to indicate the measurement values. The Power Transmitter 102 might respond with a RESP / ok message 926 to acknowledge receipt of the measurement report 924. At block 928, the Power Transmitter 102 can calculate the k-factor based on the measurements in the measurement report 924 and corresponding measurements taken by the Power Transmitter 102 during the k-factor measurement period 932.

[0080] Following the k-factor evaluation 910, the Power Receiver 118 might proceed with a next action 930, such as a state transition to the requested next state. In the example where the k-factor evaluation 910 occurs after the FOD assessment 716 and prior to the state transition to the power state, the next action 930 might include activation of a switch and communication of a CTRL / rqp message.

[0081] FIG. 9 also shows activity of the communication channel 730 in relation to the k- factor evaluation 910. In some implementations, the Power Receiver 118 and the Power Transmitter 102 might pause communication during the k-factor measurement period 932 to prevent interference or inaccurate measurements that might otherwise occur as a result of a communication.

[0082] FIG. 10 illustrates timing considerations 1000 for a k-factor evaluation in accordance with some aspects of this disclosure. The example k-factor evaluation includes the same operations and messages as the k-factor evaluation 910 described with reference to FIG. 9. However, a technical specification may define time limits (such a maximum time period) for particular operations. For example, a first time period (Tl) 1010 might be a maximum time permitted between a state transition request message 912 ("NEXT / x") and the next action 930 (such as activating a switch or a “CTRL / rqp” message). For example, the Tl 1010 might be a maximum of 100 milliseconds (ms). The Power Transmitter 102 might communicate the k-factor measurement request message 916 to initiate an instanceof the k-factor evaluation during the T1 1010 following the state transition request message 912.

[0083] The Power Transmitter 102 and the Power Receiver 118 might be required to complete the k-factor evaluation within a maximum time period (T2) 1012 during the first time period (Tl). For example, the T2 1012 might be a maximum of 50 ms between the k- factor measurement request message 916 and the RESP / ok message 926 that concludes the k-factor evaluation. In some implementations, the k-factor measurement period might have a maximum time period (T3) such as 10 ms.

[0084] FIG. 11 illustrates example operations 1100 for a k-factor evaluation 1110 using Power Transmitter estimation in accordance with some aspects of this disclosure. The k- factor evaluation 1110 might not include measurements or protocol messages. Instead, the Power Transmitter 102 might estimate k-factor based on data available to Power Transmitter (shown as block 1112). For example, the Power Transmitter 102 might estimate the k-factor using calculations based on NFC data exchange format (NDEF) parameters and initial ("starting") load resistance or power value of the Power Receiver 118. In some implementations, the Power Transmitter 102 can obtain this data during communications in the discovery state or connected state. Although shown as following the FOD assessment 716, the k-factor evaluation 1110 could occur at any time during the discovery state or connected state, including concurrently with other operations such as the FOD assessment 716.

[0085] FIG. 12 illustrates operations 1200 in a power state 408 of the wireless power system. During the power state 408, the Power Transmitter applies the power signal 1204 for a duration of Tp0Wer followed by a slot of Tsiot, then turns on the power signal 1204 for another duration of Tp0Wer. This is repeated for as long as the Power Transmitter remains in the power state 408. During the slots, the Power Transmitter or the Power Receiver might perform communication 1206 or an FOD assessment 1202. In accordance with some aspects of this disclosure, one or more slots might be used for k-factor measurement 1208 and communication related to a k-factor evaluation. There is no specific order or sequence for which slots might include an FOD assessment 1202, a communication 1206, or a k- factor measurement 1208. However, as described with reference to FIG. 13, a communication protocol can enable scheduling of the k-factor measurement 1208 in a particular slot.

[0086] FIG. 13 illustrates a communication timing protocol 1318 for a k-factor evaluation using measurements during a power state of the wireless power system. The top portion of FIG. 13 shows the power signal 1204 occurring for repeated instances of Tp0Wer within the power state 408. The slots are indicated by dashed lines (such as slot 1302) and typically occur in relation to a zero cross event of an AC signal that corresponds to the power signal 1204. FIG. 13 provides an example of how the slots might be used for communication, FOD assessment or k-factor measurement.

[0087] Every other slot might normally alternate between a read ("R") slot and a write ("W") slot. In the read slots (such as read slot 1304) the Power Transmitter 102 receives data from the Power Receiver 118. For example, the Power Transmitter 102 might read an NFC tag or other communication that includes data from the Power Receiver 118. The read slots can be used by the Power Receiver 118 to communicate power control messages to the Power Transmitter 102. In the write slots, the Power Transmitter 102 might communicate data to the Power Receiver 118, such as writing data to the NFC tag.

[0088] Some of the read slots might be repurposed for an FOD assessment or a k-factor measurement. For example, in write slot 1306, the Power Transmitter 102 might indicate that the next write slot 1308 will be used for an FOD assessment. To avoid communication from interfering with the FOD assessment, the write slot 1308 might not have a communication during that Tsiot. Similarly, a k-factor measurement can be requested in a write slot to enable accurate measurement without communication interference. In write slot 1310, the Power Transmitter 102 might communicate a k-factor measurement request message to the Power Receiver 118 to indicate that the next write slot 1312 will be a k- factor measurement period. During the Tsiot for slot 1312, the Power Receiver 118 and the Power Transmitter 102 may refrain from communication. In some implementations, the Power Transmitter 102 might transmit at least one pulse during the write slot 1312 and the Power Receiver 118 might measure a parameter (such as induced voltage) associated with the at least one pulse. During the subsequent read slot 1314, the Power Receiver 118 communicates a measurement report 1316 to indicate the measurement of the parameter.

[0089] FIG. 14 illustrates an example Power Transmitter 1400. The Power Transmitter 1400 might be an example of the Power Transmitter 102 described herein. The Power Transmitter 1400 may include a power source 112, a power signal generator 106, and a primary coil 104. The power signal generator 106 is illustrated with a half-bridge circuit to convert a DC power from the power source 112 to an AC signal applied to the primary coil 104. Although not illustrated in FIG. 14, the power source 112 may include aconversion unit that converts an AC mains power to the DC power of the power source 112. Furthermore, the power signal generator 106 may be any type of power conversion circuit capable of providing an AC signal to the primary coil 104. For example, the power signal generator 106 may include the half-bridge circuit with parallel capacitors. Alternatively, the power signal generator 106 may include a full-bridge circuit. The power signal generator 106 also may be referred to as an inverter.

[0090] The Power Transmitter 1400 also may include a wireless communication interface 114 and a communication coil 116. The wireless communication interface 114 may be configured to send or receive communication signals via the communication coil 116 (which may be a coil or a loop antenna, among other examples). The wireless communication interface 114 may implement short range radio frequency communication (such as Bluetooth™ or Near-Field Communication (NFC), among other examples). The wireless communication interface 114 may include logic for controlling one or more switches and other components that cause transmission and reception of wireless communication signals via the communication coil 116. The wireless communication interface 114 may be configured to communicate with the Power Receiver (not shown) using a wireless communication signal.

[0091] In some implementations, the wireless communication interface 114 may communicate with a Power Receiver by transmitting a wireless communication signal and detecting changes in the wireless communication signal that represent communication of information. The wireless communication interface 114 may support NFC Type 2 Tag specifications or NFC Type 4A Tag specifications, as specified by an NFC specification. During a power state besides the communications carrier the power signal is additionally active. Due to the frequency range used for the power signal, the inter-modulation products of the two signals result in interferences disturbing the reliable NFC communication. In order to avoid this unwanted effect, the power signal may be periodically switched-off for short time intervals. The time intervals may be referred to as communication time slots. Typically, the communication time slots may occur in relation to a zero-cross event associated with an AC cycle of an AC mains power or wall plug.

[0092] The Power Transmitter 1400 also includes a PTx controller 108. The PTx controller 108 may be configured to implement any of the k-factor evaluations described herein, including processing messages and controlling operations for a k-factor measurement, a power negotiation, and power control based on the k-factor. The PTx controller 108 may control the operation of the power signal generator 105. Furthermore,the PTx controller 108 may manage the state of the Power Transmitter 1400 as the transitions between various operating states. The PTx controller 108 may communicate (such as transmit or receive communications) with the Power Receiver using the wireless communication interface 114. In some implementations, the PTx controller 108 may be implemented in an integrated circuit (IC). The PTx controller 108 may be implemented as a microcontroller, dedicated processor, integrated circuit, application specific integrated circuit (ASIC) or any other suitable electronic device. In some implementations, the wireless communication interface 114 and the PTx controller 108 may be implemented in a common unit.

[0093] The PTx controller 108 may detect the presence or proximity of a Power Receiver. In some implementations, the presence or proximity of the Power Receiver may be detected based on a load change in response to a periodic low power signal generated by the power signal generator 106 and the primary coil 104. In some implementations, the presence or proximity of the Power Receiver may happen during a periodic pinging process of the wireless communication interface 114 in the Power Transmitter 1400. Alternatively, or additionally, the Power Transmitter 1400 may detect the presence or proximity of the Power Receiver 118 based on a communication via a wireless communication signal associated with the wireless communication interface 114. For example, the Power Transmitter 1400 may cause the wireless communication interface 114 to periodically or continually transmit a communication or polling signal. In some implementations, a wireless communication signal (transmitted by the wireless communication interface 114) may include a small amount of power (which may be referred to as a communication bias power or bias power) to power a one or more components of a Power Receiver.

[0094] The PTx controller 108 may control characteristics of wireless power that the Power Transmitter 1400 provides to the Power Receiver. After detecting the Power Receiver 118, the PTx controller 108 may receive information from a Power Receiver (via the wireless communication interface 114). For example, the PTx controller 108 may receive the information as part of a handshake communication with the Power Receiver. A handshake communication (sometimes referred to as a digital handshake) refers to a one- to-one communication between the Power Receiver and the Power Transmitter 1400. During the handshake communication, the Power Transmitter 1400 may transmit a first communication signal and the Power Receiver may respond to the first communication signal by transmitting information (such as a power rating, the manufacturer, the model, or parameters of the receiver when operating on a standard transmitter, among otherexamples). The PTx controller 108 may use the information it receives from the Power Receiver to determine at least one operating control parameter (such as frequency, duty cycle, voltage, etc.) for wireless power it provides to the Power Receiver. To configure the wireless power, the PTx controller 108 may modify (shown as “A” and “B”) the frequency, duty cycle, voltage or any other suitable characteristic of the power signal generator 106 during the power state.

[0095] FIG. 15 illustrates an example Power Receiver 1500. The example Power Receiver 1500 may be an example of the Power Receiver 118 described with reference to any of the figures herein. The Power Receiver 1500 may include a load 128 or the load 128 may be an external component connected to the Power Receiver 1500. The example rectifier 124 illustrated in FIG. 15 is a full bridge rectifier configured to convert a received power from an AC signal to a DC power used by the load 128. In some implementations, the Power Receiver 1400 may not include a rectifier 126. Other types of rectifiers or power conversion units may be used in various implementations. Furthermore, the Power Receiver 1400 illustrates an optional capacitor 1504 coupled between the two legs of the rectifier 124. In some implementations, the Power Receiver 1500 may not include the optional capacitor 1504. FIG. 15 also shows a capacitor 1502 that may be coupled to one or more legs of the secondary coil 120. The example Power Receiver 1500 includes a switch 1506. In FIG. 15, the switch 1506 is shown connected in series between one leg of the secondary coil 120 and the rectifier 124. The switch 1406 may be connected before or after the capacitor 1502 when the capacitor 1502 is present on that leg. Although the 1506 is shown as being connected in series, other configurations are possible. For example, instead of a single series switch (such as the switch 1506 shown in FIG. 15), the Power Receiver 1500 may include first and second switches (not shown) connected in series between both legs of the secondary coil 120 and the rectifier 124. A first switch (not shown) may be connected in series to a first leg of the secondary coil 120. A second switch (not shown) may be connected in series to a second leg of the secondary coil 120. The first and second switches may be collective referred to as a switch. Other types of switches may be used with the techniques of this disclosure. For example, a switch may include a shunt switch may be connected in parallel with the legs of the secondary coil 120 such that the shunt switch short circuits the ends of a secondary coil 120 during k-factor measurement periods.

[0096] The Power Receiver 1500 includes a second communication coil 132, a second communication interface 130, and a PRx controller 126 as described with reference to FIG.1. The second communication coil 132 may be configured to receive a communication signal from a Power Transmitter. The second communication interface 130 may contain modulation and demodulation circuits to wirelessly communicate via the second communication coil 132 (which may be a coil or a loop antenna, among other examples). Thus, the PRx controller 126 may wirelessly communicate with the Power Transmitter via the second communication interface 130. In some implementations, the second communication coil 132 may be configured to communicate using NFC or Bluetooth technology.

[0097] The PRx controller 126 may sense the status of the load 128 using a sense signal 1410. In some implementations, the sense signal 1410 may be directly related to the load 128. Alternatively, or additionally, the sense signal 1410 may indicate status of optional components, such as an activation switch (not shown) or a load switch (not shown). An activation switch may be based on a user interface such as a button, touchscreen, or any component that can indicate a user request to activate the load 128. The load switch (not shown) may include a temperature switch, overvoltage / overcurrent protection switch, motor lock, or any type of load-sensitive switch that controls whether the load 128 is active. The PRx controller 126 may control the switch 1406 using a switch signal (SI). In accordance with aspects of this disclosure, the PRx controller 126 may operate the switch signal SI based on a protocol for obtaining k-factor measurements at various states of the wireless power system. For example, the PRx controller 126 may cause the switch 1406 to disconnect the secondary coil 120 from the rectifier 126 (or the load 128) during k-factor measurement periods.

[0098] The second communication interface 130 may support NFC Type 2 Tag specifications or NFC Type 4A Tag specifications, as specified by an NFC specification. In some implementations, the wireless communication unit is configured to communicate with the Power Transmitter by storing information in a passive tag (such as an NFC Type 2 Tag) that can be read by a wireless communication interface of a Power Transmitter. Alternatively, wireless communication unit may be configured to communicate with the Power Transmitter by transmitting information (such as using an NFC Type 4A Tag) in a wireless communication signal to the wireless communication interface of the Power Transmitter.

[0099] The Power Receiver 1400 shown in FIG. 15 may be an example of one type of Power Receiver 1400. For example, the Power Receiver 1400 includes a rectifier 126 and may be suitable for an appliance in which the load 128 includes one or more motors or anyload operated with DC power. Because the Power Receiver 1400 includes the rectifier 126, the Power Receiver 1400 may implement a type 0 control architecture. Other types of Power Receivers may not have motors and may not require the rectifier 126. For example, the load 128 may be a resistive load (such as a heating element) or any load which can be operated with AC power.

[0100] FIG. 16 illustrates a block diagram of an example apparatus for use in a wireless power system. In some implementations, the apparatus 1500 may be a wireless power transmission apparatus (such as the Power Transmitter 102) described herein. The apparatus 1500 can include a processor 1502 (possibly including multiple processors, multiple cores, multiple nodes, or implementing multi -threading, etc.). The apparatus 1500 also can include a memory 1504. The memory 1504 may be system memory or any one or more of the possible realizations of computer-readable media described herein. The apparatus 1500 also can include a bus 1506 (such as PCI, ISA, PCI-Express, HyperTransport®, InfiniBand®, NuBus,® AHB, AXI, etc.).

[0101] The apparatus 1500 may include one or more controllers 1508 (such as a TX controller) configured to manage a Power Transmitter circuit 106. In some implementations, the controller 1508 can be distributed within the processor 1502, the memory 1504, and the bus 1506. The controller 1508 may perform some or all of the operations described herein. For example, the controller 1508 may implement the processes described with reference to any one of FIG. 4 through FIG. 13, or any combination thereof.

[0102] The memory 1504 can include computer instructions executable by the processor 1502 to implement the functionality of the implementations described herein. Any one of these functionalities may be partially (or entirely) implemented in hardware or on the processor 1502. For example, the functionality may be implemented with an application specific integrated circuit, in logic implemented in the processor 1502, in a co-processor on a peripheral device or card, etc. Further, realizations may include fewer or additional components not illustrated in FIG. 15. The processor 1502, the memory 1504, and the controller 1508 may be coupled to the bus 1506. Although illustrated as being coupled to the bus 1506, the memory 1504 may be coupled to the processor 1502.

[0103] FIG. 1 through FIG. 16 and the operations described herein are examples meant to aid in understanding example implementations and should not be used to limit the potential implementations or limit the scope of the claims. Some implementations mayperform additional operations, fewer operations, operations in parallel or in a different order, and some operations differently.

[0104] The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects. While the aspects of the disclosure have been described in terms of various examples, any combination of aspects from any of the examples is also within the scope of the disclosure. The examples in this disclosure are provided for pedagogical purposes. Alternatively, or in addition to the other examples described herein, examples include any combination of the following implementation options (identified as clauses for reference).

[0105] Clauses

[0106] Clause 1. A method performed by a Power Transmitter of a wireless power system, including: determining a first coupling coefficient k (k-factor) based on a first instance of a k-factor evaluation prior to a power state of the wireless power system, where the first k-factor represents an amount of a magnetic field coupling between a primary coil of the Power Transmitter and a secondary coil of a Power Receiver; negotiating, prior to the power state, a negotiated power level limit based, at least in part, on the first k-factor; and controlling transmission of the wireless power from the Power Transmitter to the Power Receiver based on the negotiated power level limit during the power state.

[0107] Clause 2. The method of clause 1, where determining the first k-factor includes: performing the first instance of the k-factor evaluation prior to the power negotiation during a discovery state or a connected state of the wireless power system.

[0108] Clause 3. The method of clause 1 or 2, where negotiating the negotiated power level limit includes: calculating an available power of the Power Transmitter based, at least in part, on the first k-factor; receiving a message from the Power Receiver indicating a requested power; and determining the negotiated power level limit based, at least in part, on the available power and the requested power.

[0109] Clause 4. The method of any one of clauses 1 to 3, where the first instance of the k-factor evaluation includes: obtaining configuration data from the Power Receiver during a discovery state or a connected state of the wireless power system; and estimating the first k-factor based, at least in part, on the configuration data.

[0110] Clause 5. The method of any one of clauses 1 to 3, where the first instance of the k-factor evaluation includes: transmitting one or more pulses via the primary coil during a k-factor measurement period; receiving a measurement report message from the Power Receiver, the measurement report message including one or more measurements of the one or more pulses at the secondary coil; and calculating the first k-factor based, at least in part, on the one or more measurements.[OHl] Clause 6. The method of any one of clauses 1 to 5, further including: determining a second k-factor after negotiating the negotiated power level limit and before a state transition to the power state.

[0112] Clause 7. The method of clause 6, where determining the second k-factor includes: performing a second instance of the k-factor evaluation to measure the second k-factor before or after a foreign object detection (FOD) assessment that occurs as a precursor of the state transition to the power state.

[0113] Clause 8. The method of clause 6 or 7, further including: refraining from transitioning to the power state if the second k-factor differs from the first k-factor such that the magnetic field coupling has changed after negotiating the negotiated power level limit.

[0114] Clause 9. The method of any one of clauses 1 to 8, further including, for each instance of the k-factor evaluation: communicating a k-factor measurement request message from the Power Transmitter to the Power Receiver, the k-factor measurement request message associated with initiating an instance of the k-factor evaluation; receiving an acknowledgement from the Power Receiver acknowledging the k-factor measurement request message; transmitting one or more pulses via the primary coil during a k-factor measurement period of the k-factor evaluation; receiving a measurement report message from the Power Receiver, the measurement report message including one or more measurements of the one or more pulses at the secondary coil; and calculating a k-factor based, at least in part, on the one or more measurements.

[0115] Clause 10. The method of clause 9, further including: refraining from communication during the k-factor measurement period.

[0116] Clause 11. The method of clause 9 or 10, further including: receiving a state transition request message (NEXT / x) from the Power Receiver; communicating the k- factor measurement request message to initiate an instance of the k-factor evaluation during a first time period (Tl) following the state transition request message; andcompleting the k-factor evaluation within a maximum time period (T2) during the first time period (Tl).

[0117] Clause 12. The method of clause 11, where the k-factor measurement period has a maximum time period (T3) during the maximum time period (T2).

[0118] Clause 13. The method of any one of clauses 1 to 12, further including: occasionally determining an updated k-factor during the power state; and verifying whether the Power Transmitter can continue to satisfy the negotiated power level limit based on the updated k-factor.

[0119] Clause 14. The method of clause 15, where occasionally determining the updated k-factor includes, during the power state: communicating, during a first Power Transmitter communication time slot, an indication that a second Power Transmitter communication time slot will be a k-factor measurement period; transmitting at least one pulse via the primary coil during the second Power Transmitter communication time slot; receiving, during a Power Receiver communication time slot that follows the second Power Transmitter communication time slot, a measurement report message indicating a measurement of the at least one pulse of the second Power Transmitter communication time slot; and calculating the updated k-factor based, at least in part, on the measurement of the at least one pulse.

[0120] Clause 15. The method of clause 13 or 14, further including: determining whether the Power Transmitter can satisfy the negotiated power level limit based on the updated k-factor; and ending the power state based on a determination that the Power Transmitter cannot satisfy the negotiated power level limit as a result of a change between the first k-factor and the updated k-factor, where ending the power state includes transitioning to the discovery state or the connected state.

[0121] Clause 16. A Power Transmitter, including: a primary coil configured to transmit wireless power to a Power Receiver; and a controller configured to implement the method of any one of clauses 1 to 15.

[0122] Clause 17. A method performed by a Power Receiver of a wireless power system, including: receiving one or more pulses via a secondary coil of the Power Receiver as part of a coupling coefficient k (k-factor) evaluation prior to a power state of the wireless power system, where a k-factor represents an amount of a magnetic field coupling between a primary coil of a Power Transmitter and the secondary coil of the Power Receiver; and communicating a measurement report message to the PowerTransmitter, the measurement report message including one or more measurements of the one or more pulses at the secondary coil of the Power Receiver.

[0123] Clause 18. The method of clause 17, further including: receiving a k-factor measurement request message from the Power Transmitter, the k-factor measurement request message associated with initiating the k-factor evaluation; communicating an acknowledgement to the Power Transmitter acknowledging the k-factor measurement request message; measuring the one or more pulses during a k-factor measurement period after the acknowledgement.

[0124] Clause 19. The method of clause 18, further including: refraining from communication during the k-factor measurement period.

[0125] Clause 20. The method of any one of clauses 17 to 19, further including, during the power state: receiving, during a first Power Transmitter communication time slot, an indication that a second Power Transmitter communication time slot will be a k-factor measurement period; measuring at least one pulse received at the secondary coil during the second Power Transmitter communication time slot; and communicating, during a Power Receiver communication time slot that follows the second Power Transmitter communication time slot, a measurement report message indicating a measurement of the at least one pulse.

[0126] Clause 21. A Power Receiver, including: a second coil configured to receive wireless power from a Power Transmitter; and a controller configured to implement the method of any one of clauses 17 to 20.

[0127] Another innovative aspect of the subject matter described in this disclosure can be implemented as a computer-readable medium having stored therein instructions which, when executed by a processor, causes the processor to perform any one of the above- mentioned functionalities.

[0128] Another innovative aspect of the subject matter described in this disclosure can be implemented as a system having means for implementing any one of the above-mentioned functionalities.

[0129] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus having one or more processors configured to perform one or more operations from any one of the above-mentioned methods.

[0130] As used herein, a phrase referring to “at least one of’ or “one or more of’ a list of items refers to any combination of those items, including single members. For example,“at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c.

[0131] The various illustrative components, logic, logical blocks, modules, circuits, operations and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware or software, including the structures disclosed in this specification and the structural equivalents thereof. The interchangeability of hardware, firmware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware, firmware or software depends upon the particular application and design constraints imposed on the overall system.

[0132] The hardware and data processing apparatus used to implement the various illustrative components, logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general -purpose processor may be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor also may be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes, operations and methods may be performed by circuitry that is specific to a given function.

[0133] As described above, some aspects of the subject matter described in this specification can be implemented as software. For example, various functions of components disclosed herein, or various blocks or steps of a method, operation, process or algorithm disclosed herein can be implemented as one or more modules of one or more computer programs. Such computer programs can include non-transitory processorexecutable or computer-executable instructions encoded on one or more tangible processor-readable or computer-readable storage media for execution by, or to control theoperation of, a data processing apparatus including the components of the devices described herein. By way of example, and not limitation, such storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store program code in the form of instructions or data structures. Combinations of the above should also be included within the scope of storage media.

[0134] Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.

[0135] Additionally, various features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described above as acting in particular combinations, and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0136] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one or more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Claims

CLAIMSWhat is claimed is:

1. A method performed by a Power Transmitter of a wireless power system, comprising: determining a first coupling coefficient k (k-factor) based on a first instance of a k- factor evaluation prior to a power state of the wireless power system, wherein the first k- factor represents an amount of a magnetic field coupling between a primary coil of the Power Transmitter and a secondary coil of a Power Receiver; negotiating, prior to the power state, a negotiated power level limit based, at least in part, on the first k-factor; and controlling transmission of the wireless power from the Power Transmitter to the Power Receiver based on the negotiated power level limit during the power state.

2. The method of claim 1, wherein determining the first k-factor includes: performing the first instance of the k-factor evaluation prior to the power negotiation during a discovery state or a connected state of the wireless power system.

3. The method of claim 1 or 2, wherein negotiating the negotiated power level limit includes: calculating an available power of the Power Transmitter based, at least in part, on the first k-factor; receiving a message from the Power Receiver indicating a requested power; and determining the negotiated power level limit based, at least in part, on the available power and the requested power.

4. The method of any one of claims 1 to 3, wherein the first instance of the k-factor evaluation includes: obtaining configuration data from the Power Receiver during a discovery state or a connected state of the wireless power system; and estimating the first k-factor based, at least in part, on the configuration data.

5. The method of any one of claims 1 to 3, wherein the first instance of the k-factor evaluation includes: transmitting one or more pulses via the primary coil during a k-factor measurement period;receiving a measurement report message from the Power Receiver, the measurement report message including one or more measurements of the one or more pulses at the secondary coil; and calculating the first k-factor based, at least in part, on the one or more measurements.

6. The method of any one of claims 1 to 5, further comprising: determining a second k-factor after negotiating the negotiated power level limit and before a state transition to the power state.

7. The method of claim 6, wherein determining the second k-factor includes: performing a second instance of the k-factor evaluation to measure the second k- factor before or after a foreign obj ect detection (FOD) assessment that occurs as a precursor of the state transition to the power state.

8. The method of claim 6 or 7, further comprising: refraining from transitioning to the power state if the second k-factor differs from the first k-factor such that the magnetic field coupling has changed after negotiating the negotiated power level limit.

9. The method of any one of claims 1 to 8, further comprising, for each instance of the k- factor evaluation: communicating a k-factor measurement request message from the Power Transmitter to the Power Receiver, the k-factor measurement request message associated with initiating an instance of the k-factor evaluation; receiving an acknowledgement from the Power Receiver acknowledging the k- factor measurement request message; transmitting one or more pulses via the primary coil during a k-factor measurement period of the k-factor evaluation; receiving a measurement report message from the Power Receiver, the measurement report message including one or more measurements of the one or more pulses at the secondary coil; and calculating a k-factor based, at least in part, on the one or more measurements.

10. The method of claim 9, further comprising: refraining from communication during the k-factor measurement period.

11. The method of claim 9 or 10, further comprising: receiving a state transition request message (NEXT / x) from the Power Receiver; communicating the k-factor measurement request message to initiate an instance of the k-factor evaluation during a first time period (Tl) following the state transition request message; and completing the k-factor evaluation within a maximum time period (T2) during the first time period (Tl).

12. The method of claim 11, wherein the k-factor measurement period has a maximum time period (T3) during the maximum time period (T2).

13. The method of any one of claims 1 to 12, further comprising: occasionally determining an updated k-factor during the power state; and verifying whether the Power Transmitter can continue to satisfy the negotiated power level limit based on the updated k-factor.

14. The method of claim 15, wherein occasionally determining the updated k-factor includes, during the power state: communicating, during a first Power Transmitter communication time slot, an indication that a second Power Transmitter communication time slot will be a k-factor measurement period; transmitting at least one pulse via the primary coil during the second Power Transmitter communication time slot; receiving, during a Power Receiver communication time slot that follows the second Power Transmitter communication time slot, a measurement report message indicating a measurement of the at least one pulse of the second Power Transmitter communication time slot; and calculating the updated k-factor based, at least in part, on the measurement of the at least one pulse.

15. The method of claim 13 or 14, further comprising: determining whether the Power Transmitter can satisfy the negotiated power level limit based on the updated k-factor; and ending the power state based on a determination that the Power Transmitter cannot satisfy the negotiated power level limit as a result of a change between the first k-factorand the updated k-factor, wherein ending the power state includes transitioning to the discovery state or the connected state.

16. A Power Transmitter, comprising: a primary coil configured to transmit wireless power to a Power Receiver; and a controller configured to implement the method of any one of claims 1 to 15.

17. A method performed by a Power Receiver of a wireless power system, comprising: receiving one or more pulses via a secondary coil of the Power Receiver as part of a coupling coefficient k (k-factor) evaluation prior to a power state of the wireless power system, wherein a k-factor represents an amount of a magnetic field coupling between a primary coil of a Power Transmitter and the secondary coil of the Power Receiver; and communicating a measurement report message to the Power Transmitter, the measurement report message including one or more measurements of the one or more pulses at the secondary coil of the Power Receiver.

18. The method of claim 17, further comprising: receiving a k-factor measurement request message from the Power Transmitter, the k-factor measurement request message associated with initiating the k-factor evaluation; communicating an acknowledgement to the Power Transmitter acknowledging the k-factor measurement request message; measuring the one or more pulses during a k-factor measurement period after the acknowledgement.

19. The method of claim 18, further comprising: refraining from communication during the k-factor measurement period.

20. The method of any one of claims 17 to 19, further comprising, during the power state: receiving, during a first Power Transmitter communication time slot, an indication that a second Power Transmitter communication time slot will be a k-factor measurement period; measuring at least one pulse received at the secondary coil during the second Power Transmitter communication time slot; and communicating, during a Power Receiver communication time slot that follows the second Power Transmitter communication time slot, a measurement report message indicating a measurement of the at least one pulse.

1. A Power Receiver, comprising: a second coil configured to receive wireless power from a Power Transmitter; and a controller configured to implement the method of any one of claims 17 to 20.

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