Coupling coefficients in wireless power systems

Abstract

This disclosure provides systems, methods, and apparatus 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 magnetic field coupling between a primary coil of the power transmitter and a secondary coil of a power receiver. The k factor affects the effectiveness of power transfer at various operating frequencies. In some aspects, a power transmitter may determine the k-factor prior to power negotiation, such that the power transmitter may negotiate a negotiated power level limit based in part on a potential operating frequency and a consideration of the k-factor. In some aspects, a k-factor measurement protocol enables the power transmitters and the power transmitters to coordinate k-factor evaluation before or during a power supply state.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to wireless power, and some aspects relate to managing wireless power transmission based on coupling of electromagnetic fields in a wireless power system. BACKGROUND

[0002] A wireless power system includes a power transmitter (PTx, sometimes also referred to as a wireless power transmitting device) and a power receiver (PRx, sometimes also referred to as a wireless power receiving device). The power transmitter includes a primary coil that generates 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 the electromagnetic field of the primary coil. The induced voltage can generate power for a load or be used by a rectifier to power a load. Thus, the power transmitter can use inductive coupling between the primary coil and the secondary coil to wirelessly transmit power to the power receiver. 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 the wireless power system.

[0003] As described, the primary coil of the power transmitter generates 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. The coupling coefficient k (also referred to as the k-factor) is a value that indicates 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 relative sizes, the distance between the coils, the alignment of the coils, and the presence of other metals in the electromagnetic field. SUMMARY

[0004] The systems, methods, and devices of the present 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 a wireless power system, where the first k-factor represents an amount of magnetic field coupling between a primary coil of the power transmitter and a secondary coil of a power receiver. The method includes negotiating a negotiated power level limit prior to the power state based at least in part on the first k-factor. The method includes controlling a transmission of wireless power from the power transmitter to the power receiver during the power state based on the negotiated power level limit.

[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-on state of a wireless power system, where the k-factor represents an amount of 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 DRAWINGS

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

[0009] Figure 1 An example wireless power system including a power transmitter and a power receiver is illustrated.

[0010] Figure 2 Electromagnetic coupling between a primary coil and a secondary coil is illustrated.

[0011] Figure 3 How a coupling coefficient k (k-factor) affects wireless power transfer at various operating frequencies is illustrated.

[0012] Figure 4 State diagrams and possible instances of k-factor evaluation for a wireless power system in accordance with aspects of the disclosure are illustrated.

[0013] Figure 5 Example operations of a power transmitter in accordance with some aspects of the disclosure are illustrated.

[0014] Figure 6 Example operations of a power receiver in accordance with some aspects of the disclosure are illustrated.

[0015] Figure 7 Timing diagrams and associated operations in various states of a wireless power system are illustrated.

[0016] Figure 8A Example k-factor evaluation prior to power negotiation operations in accordance with some aspects of the disclosure are illustrated.

[0017] Figure 8B Example k-factor evaluation prior to a power-on state in accordance with some aspects of the disclosure is illustrated.

[0018] Figure 8C Another example k-factor evaluation during a power-up state is illustrated in accordance with some aspects of the present disclosure.

[0019] Figure 9 An example k-factor evaluation using power receiver measurements is illustrated in accordance with some aspects of the present disclosure.

[0020] Figure 10 Timing considerations for k-factor evaluation are illustrated in accordance with some aspects of the present disclosure.

[0021] Figure 11 An example operation for k-factor evaluation using power transmitter estimates is illustrated in accordance with some aspects of the present disclosure.

[0022] Figure 12 Operation in a power-up state for a wireless power system is illustrated.

[0023] Figure 13 A communication timing protocol for k-factor evaluation using measurements during a power-up state for a wireless power system is illustrated.

[0024] Figure 14 An example power transmitter is illustrated.

[0025] Figure 15 An example power receiver is illustrated.

[0026] Figure 16 A block diagram of an example apparatus for use in a wireless power system is illustrated. DETAILED DESCRIPTION

[0027] For purposes of describing the innovative aspects of the present disclosure, the following description is directed to certain implementations. A person with ordinary skill in the art, however, will readily recognize that the teachings herein can be applied in a multitude of different ways. The described implementations can be implemented in any component, 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 device) and a power receiver (PRx, sometimes also referred to as a wireless power reception device). The power transmitter includes a primary coil that generates an electromagnetic field to induce a voltage in a secondary coil of the power receiver in the 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. The coupling coefficient k (also referred to as the k-factor) is a value that indicates the amount of 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 transmission. 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. The quality factor (Q-factor) is another value in a wireless power system. The Q-factor can depend on the thermal or electrical properties of the coils, such as capacitance, inductance, resistance, and so on. Both the k-factor and the Q-factor can affect the effectiveness of wireless power transmission. While the present disclosure relates to protocols for determining the k-factor, some concepts can also apply to Q-factor evaluation.

[0029] The present 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, the power transmitter can determine the k-factor prior to 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 system that is lossy or less efficient. In turn, a high k-factor can indicate an over-coupled system in which the power transmitter cannot meet the power receiver's rated power. By determining the k-factor prior to power negotiation, the power transmitter can decide whether it can meet the requested power. In some implementations, the negotiated power level limit can be limited based on the k-factor. In some implementations, the power transmitter can decide whether to proceed with power transmission or to inhibit entry into a powered state based on the k-factor.

[0030] In some aspects, the power transmitter and the power receiver can engage in k-factor evaluation according to a protocol. The present disclosure includes several example protocols for managing k-factor evaluation. For example, the k-factor evaluation can include a test signal, such as one or more pulses, during a k-factor measurement period to enable the power receiver to measure the test signal. The power receiver can communicate one or more measurements to the power transmitter to help the power transmitter calculate the k-factor.

[0031] In some aspects, the first k-factor evaluation can occur during a discovery state or a connected state prior to power negotiation. Additionally, or alternatively, the second k-factor evaluation can occur during the connected state prior to transitioning to a power state. Further, 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 can end the power state when the change in k-factor causes the power transmitter to be unable to satisfy the negotiated power level limit or when the change in k-factor indicates a foreign object detection or a failure 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. The 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, the power transmitter can manage when and how to perform k-factor evaluations based on communication messages. Thus, the present disclosure provides some flexibility in managing k-factor evaluations while also improving the ability to negotiate a negotiated power level limit. Further, by enabling power control based on a measured k-factor, the k-factor can improve the operation and efficiency of the power transmitter.

[0033] Figure 1 An example wireless power system 100 is illustrated that includes a power transmitter 102 and a power receiver 118. In Figure 1 In the figures, dashed lines represent communications to distinguish from solid lines that represent circuitry.

[0034] The power transmitter 102 includes a primary coil 104 and a power transmitter (PTx) controller 108. The primary coil 104 can be associated with a power transmitter circuit 106 (sometimes also referred to as a power signal generator or driver circuit). The primary coil 104 can be a wound coil that transmits wireless power (which can also be referred to as wireless energy). The primary coil 104 can transmit wireless energy using an inductive or magnetic resonant field. The power transmitter circuit 106 can include components (not shown) that prepare the wireless power. For example, the power transmitter circuit 106 can include one or more switches, drivers, series capacitors, rectifiers, inverters, or other components. In some implementations, the power transmitter circuit 106, the PTx controller 108, and other components (not shown) can be collectively referred to as a power transmitter unit 110. Some or all of the power transmitter unit 110 can be implemented as an integrated circuit (IC) that implements features of the present disclosure for controlling and transmitting wireless power to one or more wireless power receiving devices. The PTx controller 108 can be implemented as a microcontroller, a special purpose processor, an integrated circuit, an 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 can convert alternating current (AC) power to direct current (DC) power. For example, the power source 112 can include a converter that receives AC power from an external power supply and converts the AC power to DC power used by the power transmitter circuit 106. Alternatively, or additionally, components of the power transmitter circuit 106, such as an inverter, can convert DC power to AC power. The power source 112 can be integrated as part of the power transmitter 102, or can be external to the power transmitter 102.

[0036] In some implementations, the power transmitter 102 causes the power source 112 to adjust a DC output voltage of the power source 112. For example, the PTx controller 108 can set the DC voltage of the power source 112 based on information received from the power receiver 118, such as a value indicating a requested power. The power transmitter 102 can receive power configuration information from the power receiver 118 and use the information to set parameters, such as the DC output voltage of the power source 112. The power transmitter 102 can receive the power configuration information during various operating states, such as a discovery state or a power supply 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 a 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 embodiments, the first communication interface 114 and the first communication coil 116 can be collectively referred to as a first communication unit 122. In some implementations, the first communication unit 122 can support near field communication (NFC). NFC is a technology where data transfer occurs over a carrier frequency of 13.56 megahertz (MHz). In some implementations, the first communication unit 122 can support Bluetooth (BT) communication. The first communication unit 122 can also support any suitable communication protocol. The first communication unit 122 can include modulation and demodulation circuitry to wirelessly communicate via the first communication coil 116. Alternatively, or additionally, the TX controller 108 can use frequency modulation to communicate via an in-band communication link (not shown) that includes the primary coil 104.

[0038] The power receiver 118 can 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 driver (not shown) to control at least one parameter of the load, such as a charging current, a speed, or a torque. In some implementations, the rectifier 124 can be omitted, such as when a voltage induced in the secondary coil 120 can directly power the load 128. In some implementations, a series switch (not shown) can 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 a rate of rise of a load voltage that would otherwise occur when the load 128 suddenly reduces power consumption. Although shown as distinct components, some components can be packaged or implemented in the same hardware. For example, in some implementations, the PRx controller 126 and the load controller 134 can be implemented as a single controller. The PRx controller 126, the load controller 134, or any combination thereof can be implemented as a microcontroller, a special purpose processor, an integrated circuit, an application specific integrated circuit (ASIC), or any other suitable electronic device.

[0039] The PTx controller 108 can detect the presence or proximity of the power receiver 118. This detection can occur during a periodic ping process of the first communication interface 114. During the ping process, the first communication interface 114 can also 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 can "wake up" the PRx controller 126 and power up the PRx controller 126, and can send a reply signal to the first communication interface 114. Prior to power transfer, a handshake process can occur during which the PTx controller 108 can receive configuration data related to the power rating of the receiver, as well as other information. The PTx controller 108 can control the characteristics of the wireless power it provides to the power receiver 118 based on the configuration data.

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

[0041] The load controller 134 can be operatively coupled to the load 128 and the second communication interface 130. The load controller 134 can detect changes in load conditions, such as changes in charging current in a battery charging application. The load controller 134 can also determine a load voltage reference. The load controller 134 can also load the PRx controller 126 or the second communication interface 130 with the load voltage reference, load current, and any other suitable information for communication to the power transmitter 102. The PRx controller 126 can additionally determine and provide feedback information indicative of a measured load voltage available to the load 128. In some feedback messages, the feedback information can include a reference voltage indicative of a voltage required by the load 128. In some feedback messages, the feedback information can indicate an error in the output voltage of the load 128. In some feedback messages, the feedback information can include the power required by the load. Although the PRx controller 126 and the load controller 134 are shown separately, they can be included in the same component of the power receiver 118.

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

[0043] Figure 2 Figure 1 illustrates the electromagnetic coupling 200 between the primary coil 104 and the secondary coil 120. The power transmitter creates a time-varying magnetic field by driving an alternating current through its primary coil 104. The power receiver uses its secondary coil 120 to capture this magnetic field. 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, which is defined as (Equation 1):

[0044]

[0045] Equation 1.

[0046] where M represents the mutual inductance between the two coils, Lp' represents the self-inductance of the primary coil 104 under coupling conditions, and Ls' represents the self-inductance of the secondary coil 120 under coupling conditions.

[0047] The coupling coefficient k in a wireless power system is significantly lower than in traditional core-based transformers, which typically have a k value close to 1 (meaning that both coils capture almost all of the magnetic field lines). The best magnetic coupling is typically produced when the two coils are similar in size, properly aligned, and close together, such as at a distance much less than their diameters. 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 of metal, ferrite, or other magnetically active materials near the coils also affects the coupling coefficient.

[0048] Figure 3The k-factor is shown to affect wireless power transfer at various operating frequencies. Both the power transmitter and the power receiver exhibit resonant behavior. When isolated from each other and thus no interaction (k = 0), these resonances occur at the resonant frequencies fpand fs. When the power receiver is placed over the power transmitter, the two elements couple and the resonant frequencies fpand fsrepel each other. The resulting system transfer function can have one or two peaks, depending on the coupling and power receiver quality (Q-factor). The resonances can be affected by the coupling and Q-factor, with the system transfer function having a single peak due to low coupling. Regardless of the number of peaks, the resonances can be shifted from fpand fs. Figure 3 A plot 300 showing examples of different k-factors is shown. 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, where the voltage across the load is divided by the voltage of the power source of the power transmitter.

[0049] Observing the plot 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. As the coupling coefficient k increases, the separation between the two peaks can increase. The appearance of two peaks in the transfer function and their location relative to frequency indicates that the coupling coefficient k and the load impedance generally have a significant effect on the power transfer efficiency of the system.

[0050] Empirical test results indicate that low and high k-factors can affect 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, a flat peak 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 can exceed the power capabilities of the power transmitter. Accordingly, some aspects of the present disclosure enable the power transmitter to determine the k-factor prior to power negotiation, so that the power transmitter can determine whether it can meet the power requirements of the power receiver and have sufficient available power to operate within the power transfer function of the k-factor.

[0051] Figure 4A state diagram 400 of a wireless power system and possible instances of coupling coefficient k (k-factor) evaluation are illustrated in accordance with aspects of the present disclosure. The state diagram 400 illustrates the operational states in which a wireless power system can operate. When a power receiver is placed within the interface surface of a power transmitter, the two begin to communicate with the goal of configuring and controlling power transfer. There can be four operational states associated with a 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 supply state 408 (sometimes referred to as a power transfer state). Technical specifications can define how a power transmitter and power receiver can transition between operational states. For example, a wireless power system typically begins in the standby state 402 until the power transmitter detects a power receiver, then proceeds to the discovery state 404. In the discovery state 404, the power transmitter establishes communication and receives the identity of the power receiver and its static configuration data. In the connected state 406 and the supply state 408, the power transmitter and power receiver exchange information to agree on and adjust parameters related to wireless power transfer. The system can move to a re-initialization state (not shown) as needed to re-initialize or return to the standby state when communication, power supply, or other activities no longer occur. Each of the operational states is briefly described herein for reference.

[0052] In the standby state 402, the power transmitter attempts to establish communication with a power receiver. The power receiver can or can not be present on the interface surface during this operational state. The power transmitter can attempt to communicate or detect the presence of a power receiver. For example, the power transmitter can use analog ping, out-of-band communication such as NFC, 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 can transition to the discovery state 404.

[0053] In the discovery state 404, the power receiver can send basic identification and configuration data to the power transmitter. For example, the power transmitter can retrieve static configuration information from the power receiver via NFC communication. The power transmitter and power receiver can use this information to verify that they are both using compatible versions of the technical specification or protocol for wireless power transfer. The power transmitter and power receiver can communicate basic settings or about their respective capabilities. From the discovery state 404, the wireless power system can transition to the connected state 406.

[0054] In the connected state 406, the power transmitter and the power receiver can exchange additional communications to negotiate parameters governing the powered state. For example, a power negotiation 410 can occur during the connected state 406. After negotiating the parameters, the power transmitter can be ready to transmit wireless power, and the power receiver can be ready to receive wireless power. However, the power transmitter can wait for a request or command from the power receiver before transitioning to the powered state 408. This can be useful, for example, when a cordless appliance, such as a blender, toaster, mixer, or microwave, is configured to await user interaction to use. The user can initiate the powered state 408 through a user interface of the power receiver, such as activating a switch, which in turn communicates with the power transmitter to transition to the powered state 408.

[0055] In the powered state 408, the power transmitter can transmit wireless power to the power receiver. Typically, the power transmitter will perform a foreign object detection (FOD) evaluation periodically during the powered state 408. In some implementations, the power transmitter can perform an FOD evaluation before transitioning from the connected state 406 to the powered state 408 to ensure that no foreign objects are present. The power transmitter can also perform periodic FOD evaluations during the powered state 408. The standby state 402, the discovery state 404, and the connected state 406 can be collectively referred to as pre-power states, while the powered state 408 can be referred to as an in-power state.

[0056] According to aspects of the present disclosure, the power transmitter can perform one or more k-factor evaluations. For example, the power transmitter can 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 can be included at the end of the discovery state 404 or the beginning of the connected state 406. The power transmitter can perform a second k-factor evaluation 414 as part of a transition from the connected state 406 to the powered state 408, such as at the end of the connected state 406 or the beginning of the powered state 408. Additionally, or alternatively, the power transmitter can perform one or more additional k-factor evaluations 416 during the powered state 408.

[0057] The present 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 a k-factor based on the measurements. Alternatively, or additionally, a k-factor evaluation can include estimating electromagnetic coupling based on configuration data or other communications from the power receiver, without requiring explicit measurements for the k-factor evaluation.

[0058] Figure 5Example operations 500 of a power transmitter are illustrated in accordance with some aspects of the present disclosure. For example, operations 500 can be performed by power transmitter 102 or power transmitter 1400 described with reference to other figures of the present disclosure. In block 502, the power transmitter determines a first coupling coefficient k (k-factor) based on a first instance of k-factor evaluation prior to a power-on state of a wireless power system, where the first k-factor represents an amount of magnetic field coupling between a primary coil of the power transmitter and a secondary coil of a power receiver. In block 504, the power receiver negotiates a negotiated power level limit based at least in part on the first k-factor prior to the power-on state. In block 506, the power receiver controls the transfer of wireless power from the power transmitter to the power receiver during the power-on state based on the negotiated power level limit.

[0059] Figure 6 Example operations 600 of a power receiver are illustrated in accordance with some aspects of the present disclosure. For example, operations 600 can be performed by power receiver 118 or power receiver 1500 described with reference to other figures of the present disclosure. In block 602, the power receiver receives one or more pulses via a secondary coil of the power receiver as part of coupling coefficient k (k-factor) evaluation prior to a power-on state of a wireless power system, where the k-factor represents an amount of magnetic field coupling between a primary coil of a power transmitter and the secondary coil of the power receiver. In block 604, the 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 the secondary coil of the power receiver.

[0060] Figure 7 A timing diagram 700 and associated operations in various states of a wireless power system are illustrated. Timing diagram 700 is used to describe operations of a power receiver (PRx) 118 and a power transmitter (PTx) 102. Although described as operations of power receiver 118 and power transmitter 102, it should be clear that the operations can be performed by PTx controller 108 and PRx controller 126, respectively. As described with reference to other figures of the present disclosure, power receiver 118 and power transmitter 102 can follow a state diagram of various operational states. In the following description, for brevity, some operations in the standby state and discovery state 404 are omitted. During the standby state, a user can place an appliance with a power receiver in an interface space of a power transmitter. The power transmitter detects the power receiver and communicates with the power receiver to obtain identification and configuration information (not shown). Figure 4 Figure 7 In the discovery state 404, the power transmitter and power receiver exchange identification and configuration information. The power transmitter and power receiver can also exchange a k-factor. The k-factor represents an amount of magnetic field coupling between a primary coil of the power transmitter and a secondary coil of the power receiver. The k-factor can be used to determine a power level limit for the power receiver. The power transmitter and power receiver can also exchange a power level limit. The power level limit can be used to determine a power level for the power receiver. The power level limit can be based on the k-factor. The power level limit can be based on a power level limit negotiated by the power transmitter and the power receiver. The power level limit can be based on a power level limit determined by the power transmitter and the power receiver.

[0061] ​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 NEXT / pow for a request to transition to the powered state. The power transmitter 102 can respond to the state transition request (NEXT / con) 702 with a response message ("RESP / ok") 704. The "RESP" message can indicate allowed ("ok"), not allowed ("nok"), undefined ("nd"), or busy ("bsy"). In some implementations, the "RESP" message is a response that can indicate acknowledged ("ack"), not acknowledged ("nak"), or undefined ("nd"). In Figure 7 In the example of FIG. 6, the response (RESP / ok) 704 is "ok" or "ack" to indicate agreement to transition to the connected state 406.

[0062] 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 can include a user input that indicates a desire to activate the load. Examples of activation switches can include a button, a toggle switch, a knob, or a touchscreen (and associated processor), among others. Some appliances can not include an activation switch and the power receiver 118 can assume that the load is always ready to receive wireless power. The power receiver 118 can engage in a power negotiation 708 with the power transmitter 102 based on the power requirements of the load. The power negotiation 708 can 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.

[0063] After the power negotiation 708, the power receiver 118 communicates a state transition request (NEXT / pow) 714 that requests a state transition to the powered state 408. In some implementations, the power transmitter 102 can perform one or more operations for a FOD evaluation 716 before agreeing to transition to the powered state 408. In some implementations, the FOD evaluation 716 can be required to be performed before transitioning from the connected state 406 to the powered state 408. For the FOD evaluation, the power transmitter 102 can use various techniques to scan for foreign objects, such as active excitation or passive excitation of a foreign object detection coil to observe differences in impedance that indicate the presence of a foreign object. Assuming that no foreign object is detected during the FOD evaluation 716, then the power transmitter 102 responds with a response (RESP / ok) 718.

[0064] After receiving the response (RESP / ok) 718 in response to the state transition request (NEXT / pow) 714, the power receiver 118 can activate an enable switch 720 to cause a switch in the power receiver to couple the secondary coil to a power receiving circuit (such as a rectifier or a load). In a first position (which can be a default or "normal" position), the switch can disable the secondary coil of the power receiver from conducting energy. For example, the first position can disconnect or decouple the secondary coil from the power receiving circuit. The first position can open a circuit that includes the secondary coil. In a second position, the switch can 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 can communicate a power request message 722 (such as a control message ("CTRL") indicating a requested power, or "CTRL / rqp") to the power transmitter 102.

[0065] The power transmitter 102 can receive the power request message 722 and cause the power signal generator (such as an inverter) of the power transmitter to begin transmission of a wireless power signal 726. In some implementations, the power signal generator is enabled at or after an AC cycle following the power request message 722 or a first natural zero crossing of the AC mains power (shown at time 724). For systems operating off-grid (such as DC operated PRx), the power signal generator can be enabled after a small delay after receiving the power request message 722.

[0066] Figure 7 Activity of a communication channel 730 is also illustrated in relation to the timing of the operation of the power receiver 118 and the power transmitter 102. The communication channel 730 can be an out-of-band communication (such as NFC) using a separate antenna and signal. Although the communication channel 730 is separate from the primary and secondary coils, communication via 730 can affect some operations, such as the FOD assessment 716. In some implementations, the communication signal can be stopped during the FOD assessment 716 to prevent interference. Further, the communication channel 730 timeline illustrates communications 736, 738, and 740 that occur during a communication time slot in the powered state 408. The communication time slot can occur in relation to a zero crossing event associated with the AC cycle of the wireless power signal 726.

[0067] The operation 700 has been described as background Figure 7 After the operation 700, reference can be made to Figure 8A through Figure 11Several examples of k-factor evaluation are described. There are three example times (locations in various operational states) where k-factor evaluation can be performed. For example, k-factor evaluation can be performed prior to power negotiation 708 during the connected state 406 or as part of a state transition. K-factor evaluation can be performed in relation to FOD assessment 716 prior to state transition to the powered state 408. One or more k-factor evaluations can be performed during 408. Figure 8A through Figure 11 More details are provided regarding these various k-factor evaluations, their potential uses, and associated protocols. For example, k-factor evaluation prior to power negotiation 708 can enable the power transmitter to more accurately calculate power capability and negotiated power level limits. K-factor evaluation prior to the powered state 408 can enable the power transmitter to more accurately calculate operating points for the wireless power signal. K-factor evaluation during the powered state 408 can enable the power transmitter to detect changes in the power transfer function that potentially require the end of the powered state 408 to renegotiate the negotiated power level limits.

[0068] Figure 8A An example k-factor evaluation 800a prior to power negotiation operations in accordance with some aspects of the present disclosure is illustrated. Figure 8A The messages and operations in include similar messages and operations (with the same reference numbers) to those described with reference to Figure 7 The messages and operations described are similar to those described with reference to Figure 8A In, the 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.

[0069] 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 can include an indicator informing the power receiver 118 that the power transmitter 102 is initiating the first K-factor evaluation 806 as part of the state transition. As described further with reference to Figure 9 The process of the first K-factor evaluation 806 can include one or more operations and messages, as described further.

[0070] The power transmitter 102 can determine the first K-factor evaluation 806 to determine a k-factor and use the k-factor in the processing of its power negotiation 808. For example, the power transmitter 102 can calculate the available power of the power transmitter (available for the power transmitter to transfer to the power receiver) based on the power transfer function taking into account the k-factor. The power negotiation 808 can result in a negotiated power level limit that can be satisfied based on the power transfer function associated with the k-factor.

[0071] In some examples, the power transmitter 102 can determine the maximum power transfer capability under the existing k-factor condition and set the negotiated power level limit accordingly. In some examples, if the k-factor is too high (above a first threshold), the power transmitter 102 can determine that it cannot set the operating frequency that would deliver the requested negotiated power to the power receiver 118. An over-coupled system (high k-factor) can experience a reduction in voltage gain under rated PRx load conditions. Thus, although the power transmitter can be rated for higher power, the power receiver cannot receive the necessary voltage to meet the rated power of the load due to the low voltage gain. In such a case, the power transmitter 102 can reject the requested negotiated power and suggest a different negotiated power level limit or inform the 118 power transmitter 102 that it cannot meet the rated power of the power receiver 118.

[0072] In some examples, if the k-factor is too low (below a second threshold), the power transmitter 102 can 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 can inform the power receiver 118 that the k-factor is low (indicating a low alignment of the primary and secondary coils) and the power receiver 118 can prompt the user to correct the alignment by repositioning the power receiver 118.

[0073] Figure 8B FIG. 8B illustrates an example k-factor evaluation 800b prior to a power state, in accordance with some aspects of the present disclosure. Figure 8A The messages and operations in FIG. 8B include similar messages and operations (with the same reference numbers) as described with reference to Figure 7 and Figure 8A The messages and operations in FIG. 8B include similar messages and operations (with the same reference numbers) as described with reference to Figure 8B A second k-factor evaluation 820 is described that occurs prior to the state transition to the power state 408. In some implementations, the second k-factor evaluation 820 can be performed in addition to the first K-factor evaluation 806. Alternatively, the first K-factor evaluation 806 can be omitted in some implementations. The second k-factor evaluation 820 can be useful for the power transmitter 102 to determine a power transfer function (such as the curves 306 or 308 described with reference to FIG. 3) that helps the power transmitter 102 set the operating frequency that meets the requested power. As described with reference to Figure 3 Figure 9 ​Further described, the process of the second k-factor evaluation 820 can include one or more operations and messages. In some implementations, the response (RESP / ok) 816 (as a response to the state transition request (NEXT / pow) 714) can include an indicator informing the power receiver 118 that the power transmitter 102 will initiate the second k-factor evaluation 820 before transitioning to the powered state 408. Although Figure 8B The second k-factor evaluation 820 is shown as occurring after the FOD evaluation 716, but the timing of the second k-factor evaluation 820 can be elsewhere under the connected state 406, such as before the FOD evaluation 716 or after the power request message 722. For example, as shown in FIG. 8B, a second k-factor evaluation (shown as second k-factor evaluation 824) can be performed before the FOD evaluation 716. Figure 8C The second k-factor evaluation 820 is shown as occurring after the FOD evaluation 716, but the timing of the second k-factor evaluation 820 can be elsewhere under the connected state 406, such as before the FOD evaluation 716 or after the power request message 722. For example, as shown in FIG. 8B, a second k-factor evaluation (shown as second k-factor evaluation 824) can be performed before the FOD evaluation 716.

[0074] Figure 8C FIG. 8C illustrates another example k-factor evaluation 800c during the powered state, according to some aspects of the present disclosure. Figure 8A The messages and operations in FIG. 8C include similar messages and operations (with the same reference numbers) as described with reference to Figure 7 , Figure 8A and Figure 8B The messages and operations in FIG. 8C include similar messages and operations (with the same reference numbers) as described with reference to Figure 8C In FIG. 8C, one or more k-factor evaluations 822 can occur during the powered state 408. As further described with reference to Figure 12 and Figure 13 Further described, the process of the one or more k-factor evaluations 822 can include one or more operations and messages. The one or more k-factor evaluations 822 can result in an updated k-factor due to changes in the alignment or electromagnetic coupling of the primary and secondary coils.

[0075] In some implementations, the one or more k-factor evaluations 822 can be performed 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 can be omitted in some implementations. The one or more k-factor evaluations 822 can be useful for the power transmitter 102 to determine a power transfer function (such as the curve 306 or 308 described with reference to Figure 3 FIG. 8B) that helps the power transmitter 102 set an operating frequency that meets the requested power.

[0076] In some implementations, if the k-factor changes (such as an updated k-factor during the power supply state 408 is different than the first k-factor used for the power negotiation 808), the power transmitter can determine whether it can still satisfy the negotiated power level limit based on the updated k-factor. If the power transmitter 102 cannot satisfy the negotiated power level limit as a result of the change between the first k-factor and the updated k-factor, the power transmitter 102 can end the power supply state 408 and return to the discovery state 404 or the connected state 406.

[0077] Figure 9 FIG. illustrates an example k-factor evaluation 910 using power receiver measurements, in accordance with some aspects of the present disclosure. The timing diagram 900 shows the operation of the power receiver 118, the power transmitter 102, and activity on the communication channel 730. The example k-factor evaluation 910 can 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 FIGS. 7-9. Figure 8A , Figure 8B and Figure 8C For context and brevity, the example k-factor evaluation 910 is shown in place of the second k-factor evaluation 820 of FIG. 8. Figure 8B

[0078] In response to a state transition request message 912 (such as a "NEXT" message) from the power receiver 118, the power transmitter 102 can deliver a RESP / ok message 914. The state transition request message 912 can be a "NEXT / con" (such as the state transition request (NEXT / con) 702) or a "NEXT / pow" (such as the state transition request (NEXT / pow) 714). For brevity, the state transition request message 912 is referred to as a "NEXT / x" message. In scenarios where the state transition request message 912 is a "NEXT / pow" message, the power transmitter 102 can perform the FOD assessment 716 prior to (or after) the k-factor evaluation 910.

[0079] The RESP / ok message 914 can include an indication that the k-factor evaluation 910 is to be performed prior to the state transition. For example, the RESP / ok message 914 can include a hold indicator, flag, or other value to cause the power receiver 118 to refrain from taking the next step immediately for the state transition. For example, the hold indicator can prevent the power receiver 118 from activating an enable switch at the secondary coil. In some implementations, the hold indicator can be included in the PTx status field of the RESP / ok message 914.

[0080] ​The k-factor evaluation 910 can 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 can be "MEAS," and can optionally include an indication to measure one or more parameters. The power receiver 118 can respond with an acknowledgement 918, such as "RESP / ok," to acknowledge receipt of the k-factor measurement request message 916.

[0081] During the k-factor measurement period 932, the power transmitter 102 transmits one or more pulses 920 for k-factor measurement. At block 922, the power receiver 118 measures a parameter at the secondary coil, such as voltage, current, frequency, etc. For example, the parameter can indicate an amount of induced voltage, or some reference metric based on the one or more pulses 920 that indicates an amount of electromagnetic coupling between the secondary coil and the primary coil.

[0082] After the k-factor measurement period 932, the power receiver 118 communicates a measurement report 924 to the power transmitter 102 to indicate the measured value. The power transmitter 102 can 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 measurement in the measurement report 924 and corresponding measurements taken by the power transmitter 102 during the k-factor measurement period 932.

[0083] Following the k-factor evaluation 910, the power receiver 118 can perform a next action 930, such as a state transition to a next state requested. In examples where the k-factor evaluation 910 occurs after the FOD evaluation 716 and before a state transition to the powered state, the next action 930 can include activation of the switch and communication of a CTRL / rqp message.

[0084] Figure 9 Activity of the communication channel 730 is also shown in relation to the k-factor evaluation 910. In some implementations, the power receiver 118 and the power transmitter 102 can suspend communication during the k-factor measurement period 932 to prevent interference or inaccurate measurements that can otherwise occur as a result of communication.

[0085] Figure 10 Timing considerations 1000 for k-factor evaluation are illustrated in accordance with some aspects of the present disclosure. The example k-factor evaluation includes a reference Figure 9The described k-factor evaluation 910 is the same operation and messages. However, the technical specification can define a time limit for certain operations (such as a maximum time period). For example, a first time period (Tl) 1010 can be a maximum time allowed 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, Tl 1010 can be a maximum of 100 milliseconds (ms). The power transmitter 102 can follow the state transition request message 912 with a k-factor measurement request message 916 to initiate an instance of k-factor evaluation during Tl 1010.

[0086] The power transmitter 102 and the power receiver 118 can be required to complete the k-factor evaluation within a maximum time period (T2) 1012 during the first time period (Tl). For example, T2 1012 can be a maximum of 50 ms between the k-factor measurement request message 916 and a RESP / ok message 926 that terminates the k-factor evaluation. In some implementations, the k-factor measurement period can have a maximum time period (T3), such as 10 ms.

[0087] Figure 11 Figure illustrates example operations 1100 of a k-factor evaluation 1110 using power transmitter estimates according to some aspects of the present disclosure. The k-factor evaluation 1110 can not include measurements or protocol messages. Instead, the power transmitter 102 can estimate the k-factor based on data available to the power transmitter (shown as block 1112). For example, the power transmitter 102 can estimate the k-factor using a calculation based on NFC Data Exchange Format (NDEF) parameters and an initial ("start-up") load resistance or power value of the power receiver 118. In some implementations, the power transmitter 102 can obtain this data during communication in the discovery state or the connected state. Although shown as following the FOD evaluation 716, the k-factor evaluation 1110 can occur at any time during the discovery state or the connected state, including concurrently with other operations such as the FOD evaluation 716.

[0088] Figure 12 Figure illustrates operations 1200 in the power supply state 408 of a wireless power system. During the power supply state 408, the power transmitter applies a power signal 1204 for a time period of T Slot Power Power ​​another period of time. This repeats as long as the power transmitter remains in the power on state 408. During the time slots, the power transmitter or the power receiver can perform communication 1206 or FOD evaluation 1202. According to some aspects of the disclosure, one or more of the time slots can be used for k-factor measurement 1208 and communication related to k-factor evaluation. There is no specific order or sequence for which time slots can include FOD evaluation 1202, communication 1206, or k-factor measurement 1208. However, as described with reference to Figure 13 the communication protocol can enable scheduling of k-factor measurement 1208 in particular time slots.

[0089] Figure 13 FIG. 13 illustrates a communication timing protocol 1318 for k-factor evaluation using measurements during the power on state of a wireless power system. Figure 13 The top of FIG. 13 illustrates the power signal 1204 within the power on state 408 at T Power repeating instances of T Figure 13 Examples of how the time slots can be used for communication, FOD evaluation, or k-factor measurement are provided.

[0090] Every other time slot can generally alternate between a read ("R") time slot and a write ("W") time slot. In a read time slot, such as read time slot 1304, the power transmitter 102 receives data from the power receiver 118. For example, the power transmitter 102 can read an NFC tag or other communication that includes data from the power receiver 118. The read time slot can be used by the power receiver 118 to communicate power control messages to the power transmitter 102. In a write time slot, the power transmitter 102 can communicate data to the power receiver 118, such as writing data to an NFC tag.

[0091] Some of the read time slots can be repurposed for FOD evaluation or k-factor measurement. For example, in write time slot 1306, the power transmitter 102 can indicate that the next write time slot 1308 will be used for FOD evaluation. To avoid communication interfering with the FOD evaluation, the write time slot 1308 can not have communication during that T Slot Similarly, k-factor measurement can be requested in a write time slot to enable accurate measurement without communication interference. In write time slot 1310, the power transmitter 102 can communicate a k-factor measurement request message to the power receiver 118 to indicate that the next write time slot 1312 will be a k-factor measurement period. The write time slot 1312 can not have communication during that T SlotDuring this period, the power receiver 118 and the power transmitter 102 can refrain from communication. In some implementations, the power transmitter 102 can transmit at least one pulse during the write time slot 1312, and the power receiver 118 can measure a parameter (such as the induced voltage) associated with the at least one pulse. During a subsequent read time slot 1314, the power receiver 118 communicates a measurement report 1316 to indicate the measurement of the parameter.

[0092] Figure 14 An example power transmitter 1400 is illustrated. The power transmitter 1400 can be an example of the power transmitter 102 described herein. The power transmitter 1400 can include the power source 112, the power signal generator 106, and the primary coil 104. The power signal generator 106 is shown as having a half-bridge circuit to convert DC power from the power source 112 to an AC signal applied to the primary coil 104. Although not illustrated in Figure 14 the power source 112 can include a conversion unit to convert AC mains power to DC power for the power source 112. Further, the power signal generator 106 can 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 can include a half-bridge circuit with a parallel capacitor. Alternatively, the power signal generator 106 can include a full-bridge circuit. The power signal generator 106 can also be referred to as an inverter.

[0093] The power transmitter 1400 can also include the wireless communication interface 114 and the communication coil 116. The wireless communication interface 114 can be configured to transmit or receive communication signals via the communication coil 116 (which can be a coil or a loop antenna, etc.). The wireless communication interface 114 can implement short-range radio frequency communication, such as Bluetooth™ or near field communication (NFC), etc. The wireless communication interface 114 can include logic to control one or more switches and other components to cause transmission and reception of wireless communication signals via the communication coil 116. The wireless communication interface 114 can be configured to communicate with a power receiver (not shown) using the wireless communication signals.

[0094] In some implementations, the wireless communication interface 114 can communicate with the power receiver by transmitting wireless communication signals and detecting changes in the transfer of information represented by the wireless communication signals. The wireless communication interface 114 can support the NFC Type 2 Tag specification or the NFC Type 4A Tag specification as specified by the NFC specification. During the powered state, in addition to the communication carrier, the power signal is active. Due to the frequency range used for the power signal, the intermodulation products of the two signals cause interference that disrupts reliable NFC communication. To avoid this unwanted effect, the power signal can be periodically turned off for short time intervals. The time intervals can be referred to as communication slots. Typically, the communication slots can occur in relation to zero-crossing events associated with the AC cycle of the AC mains power or wall outlet.

[0095] The power transmitter 1400 also includes a PTx controller 108. The PTx controller 108 can be configured to implement any of the k-factor evaluations described herein, including processing messages and controlling operations for k-factor measurements, power negotiations, and k-factor based power control. The PTx controller 108 can control the operation of the power signal generator 105. In addition, the PTx controller 108 can manage the state of the power transmitter 1400 as it transitions between various operational states. The PTx controller 108 can communicate with the power receiver using the wireless communication interface 114, such as transmitting or receiving communications. In some implementations, the PTx controller 108 can be integrated in an integrated circuit (IC). The PTx controller 108 can be implemented as a microcontroller, a special purpose processor, an integrated circuit, an application specific integrated circuit (ASIC), or any other suitable electronic device. In some implementations, the wireless communication interface 114 and the PTx controller 108 can be implemented in a common unit.

[0096] The PTx controller 108 can detect the presence or proximity of a power receiver. In some implementations, the presence or proximity of a power receiver can be detected based on a change in load 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 a power receiver can occur during a periodic ping process of the wireless communication interface 114 in the power transmitter 1400. Alternatively, or additionally, the power transmitter 1400 can detect the presence or proximity of a power receiver 118 based on communications via a wireless communication signal associated with the wireless communication interface 114. For example, the power transmitter 1400 can cause the wireless communication interface 114 to periodically or continuously transmit a communication or polling signal. In some implementations, the wireless communication signal (transmitted by the wireless communication interface 114) can include a small amount of power, which can be referred to as a communication bias power or bias power, to power one or more components of the power receiver.

[0097] The PTx controller 108 can control characteristics of the wireless power provided by the power transmitter 1400 to the power receiver. After detecting the power receiver 118, the PTx controller 108 can receive information from the power receiver (via the wireless communication interface 114). For example, the PTx controller 108 can 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 can transmit a first communication signal and the power receiver can respond to the first communication signal by transmitting information such as a power rating, a manufacturer, a model, or parameters of the receiver when operating on a standard transmitter, etc. The PTx controller 108 can use the information it receives from the power receiver to determine at least one operational control parameter of the wireless power it provides to the power receiver such as a frequency, a duty cycle, a voltage, etc. To configure the wireless power, the PTx controller 108 can modify (shown as "A" and "B") the frequency, the duty cycle, the voltage, or any other suitable characteristic of the power signal generator 106 during the power-on state.

[0098] Figure 15 An example power receiver 1500 is illustrated. The example power receiver 1500 can be an example of the power receiver 118 described herein with reference to any of the Figures. The power receiver 1500 can include the load 128, or the load 128 can be an external component connected to the power receiver 1500. Figure 15 The example rectifier 124 shown in is a full-bridge rectifier configured to convert received power from an AC signal to DC power used by the load 128. In some implementations, the power receiver 1400 can not include the rectifier 126. In various implementations, other types of rectifiers or power conversion units can be used. In addition, the power receiver 1400 illustrates an optional capacitor 1504 coupled between two legs of the rectifier 124. In some implementations, the power receiver 1500 can not include the optional capacitor 1504. Figure 15 Also shown is a capacitor 1502 that can be coupled to one or more legs of the secondary coil 120. The example power receiver 1500 includes a switch 1506. In Figure 15 In, the switch 1506 is shown as connected in series between one leg of the secondary coil 120 and the rectifier 124. When the capacitor 1502 is present on that leg, the switch 1406 can be connected before or after the capacitor 1502. Although 1506 is shown as connected in series, other configurations are possible. For example, instead of a single series switch (such as 1506), a pair of switches can be used to connect the capacitor 1502 in parallel with the rectifier 124. Figure 15The power receiver 1500 can include first and second switches (not shown) connected in series between the two branches of the secondary coil 120 and the rectifier 124 (as shown in the switch 1506). The first switch (not shown) can be connected in series to the first branch of the secondary coil 120. The second switch (not shown) can be connected in series to the second branch of the secondary coil 120. The first and second switches can be collectively referred to as switches. Other types of switches can be used with the techniques of the present disclosure. For example, the switches can include shunt switches that can be connected in parallel to the branches of the secondary coil 120 such that the shunt switches short the ends of the secondary coil 120 during the k-factor measurement period.

[0099] 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 Figure 1 The second communication coil 132 can be configured to receive communication signals from a power transmitter. The second communication interface 130 can include modulation and demodulation circuitry to wirelessly communicate via the second communication coil 132, which can be a coil or loop antenna, etc. Thus, the PRx controller 126 can wirelessly communicate with a power transmitter via the second communication interface 130. In some implementations, the second communication coil 132 can be configured to communicate using NFC or Bluetooth technology.

[0100] The PRx controller 126 can sense a condition of the load 128 using a sense signal 1410. In some implementations, the sense signal 1410 can be directly related to the load 128. Alternatively, or additionally, the sense signal 1410 can be indicative of a condition of an optional component such as an activation switch (not shown) or a load switch (not shown). The activation switch can be based on a user interface such as a button, touch screen, or any component that can indicate a user request to activate the load 128. The load switch (not shown) can include a temperature switch, an over-voltage / over-current protection switch, a motor lock, or any type of load sensitive switch that controls whether the load 128 is active. The PRx controller 126 can control the switch 1406 using a switch signal (SI). According to aspects of the present disclosure, the PRx controller 126 can operate the switch signal SI based on a protocol for obtaining k-factor measurements in various states of the wireless power system. For example, during a k-factor measurement period, the PRx controller 126 can cause the switch 1406 to disconnect the secondary coil 120 from the rectifier 126 (or the load 128).

[0101] The second communication interface 130 can support the NFC Type 2 Tag specification or the NFC Type 4A Tag specification as specified by the NFC specification. In some implementations, the wireless communication unit is configured to communicate with a power transmitter by storing information in a passive tag, such as an NFC Type 2 Tag, that can be read by the wireless communication interface of the power transmitter. Alternatively, the wireless communication unit can be configured to communicate with a power transmitter by transmitting information in a wireless communication signal, such as using an NFC Type 4A Tag, to the wireless communication interface of the power transmitter.

[0102] Figure 15 The power receiver 1400 shown in FIG. 14A can be an example of one type of power receiver 1400. For example, the power receiver 1400 includes the rectifier 126 and can be suitable for an appliance in which the load 128 includes one or more motors or any load that operates with DC power. Because the power receiver 1400 includes the rectifier 126, the power receiver 1400 can implement a Type 0 control architecture. Other types of power receivers can not have a motor and can not require the rectifier 126. For example, the load 128 can be a resistive load, such as a heating element, or any load that can operate with AC power.

[0103] Figure 16 A block diagram of an example apparatus for use in a wireless power system is shown. In some implementations, the apparatus 1500 can be a wireless power transmitting apparatus, such as the power transmitter 102, described herein. The apparatus 1500 can include a processor 1502, which can include multiple processors, multiple cores, multiple nodes, or implement multi-threading, etc. The apparatus 1500 can also include a memory 1504. The memory 1504 can be system memory, or any one or more of the possible implementations of computer-readable media described herein. The apparatus 1500 can also include a bus 1506, such as a PCI, ISA, PCI-Express, HyperTransport®, InfiniBand®, NuBus®, AHB, AXI, etc.

[0104] The apparatus 1500 can include one or more controllers 1508 configured to manage the power transmitter circuit 106, such as a TX controller. In some implementations, the controller 1508 can be distributed within the processor 1502, the memory 1504, and the bus 1506. The controller 1508 can perform some or all of the operations described herein. For example, the controller 1508 can implement the processes described with reference to any one or any combination of the processes described herein. Figure 4 through Figure 13

[0105] ​Memory 1504 can include computer instructions executable by processor 1502 to implement the functionality described herein. Any of these functions can be implemented partially (or entirely) in hardware, or by a combination of hardware and software, within processor 1502. For example, the functionality can be implemented by an application specific integrated circuit, logic implemented in processor 1502, a co-processor on a peripheral device or card, etc. Further, implementation can include fewer components or additional components not expressly mentioned herein. Figure 15 Processor 1502, memory 1504, and controller 1508 can be coupled to bus 1506. Although illustrated as being coupled to bus 1506, memory 1504 can be coupled to processor 1502.

[0106] Figure 1 through Figure 16 The operations described herein are intended to be examples and are not intended to limit the potential implementations or limit the scope of the claims. Some implementations can perform additional operations, fewer operations, operations in parallel, or different order of operations, and some implementations can not perform some operations.

[0107] 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 can be made in light of the above disclosure or can be acquired from practice of the aspects. While aspects of the present disclosure have been described from the perspective of various examples, combinations of aspects from any of the examples are also within the scope of the present disclosure. The examples in the present disclosure are provided for purposes of teaching and illustration. Alternatively, or in addition, the examples can be used to provide any of the following implementations (identified as clauses for reference):

[0108] Clause

[0109] Clause 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-on state of the wireless power system, wherein the first k-factor represents an amount of magnetic field coupling between a primary coil of the power transmitter and a secondary coil of a power receiver; negotiating a negotiated power level limit based at least in part on the first k-factor prior to the power-on state; and controlling transfer of wireless power from the power transmitter to the power receiver during the power-on state based on the negotiated power level limit.

[0110] Clause 2. The method of clause 1, wherein determining the first k-factor comprises: performing the first instance of the k-factor evaluation prior to power negotiation during a discovery state or a connected state of the wireless power system.

[0111] Clause 3. The method of clause 1 or 2, wherein negotiating the negotiated power level limit comprises: calculating 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.

[0112] Clause 4. The method of any of clauses 1-3, wherein the first instance of the k- factor evaluation comprises: 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.

[0113] Clause 5. The method of any of clauses 1-3, wherein the first instance of the k- factor evaluation comprises: 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 comprising 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.

[0114] Clause 6. The method of any of clauses 1-5, further comprising: determining a second k-factor after negotiating the negotiated power level limit and before a state transition to the power supply state.

[0115] Clause 7. The method of clause 6, wherein determining the second k-factor comprises: 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 to a state transition to the power supply state.

[0116] Clause 8. The method of clause 6 or 7, further comprising: inhibiting a transition to the power supply state if the second k-factor is different from the first k- factor such that the magnetic field coupling has changed after negotiating the negotiated power level limit.

[0117] Clause 9. The method of any of clauses 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 the instance of initiating 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.

[0118] Clause 10. The method of clause 9, further comprising: refraining from communication during the k-factor measurement period.

[0119] Clause 11. The method of clause 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 the instance of the k-factor evaluation following the state transition request message during a first time period (Tl); and completing the k-factor evaluation within a maximum time period (T2) of the first time period (Tl).

[0120] Clause 12. The method of clause 11, wherein the k-factor measurement period has a maximum time period (T3) during the maximum time period (T2).

[0121] Clause 13. The method of any of clauses 1 to 12, further comprising: occasionally determining an updated k-factor during the power supply state; and verifying whether the power transmitter can continue to meet the negotiated power level limit based on the updated k-factor.

[0122] Clause 14. The method of clause 15, wherein occasionally determining the updated k-factor comprises, during the power supply state: communicating an indication during a first power transmitter communication slot that a second power transmitter communication slot will be a k-factor measurement period; transmitting at least one pulse via the primary coil during the second power transmitter communication slot; receiving a measurement report message during a power receiver communication slot following the second power transmitter communication slot, the measurement report message indicating a measurement of the at least one pulse of the second power transmitter communication slot; and calculating the updated k-factor based at least in part on the measurement of the at least one pulse.

[0123] Clause 15. The method of clause 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 supply 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, wherein ending the power supply state comprises transitioning to the discovery state or the connected state.

[0124] Clause 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 of clauses 1-15.

[0125] Clause 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 supply state of the wireless power system, wherein the k-factor represents an amount of 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 comprising one or more measurements of the one or more pulses at the secondary coil of the power receiver.

[0126] Clause 18. The method of clause 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 following the acknowledgement.

[0127] Clause 19. The method of clause 18, further comprising: refraining from communication during the k-factor measurement period.

[0128] Clause 20. The method of any of clauses 17-19, further comprising during the power supply state: receiving an indication that a second power transmitter communication time slot will be a k-factor measurement period during a first power transmitter communication time slot; measuring at least one pulse received at the secondary coil during the second power transmitter communication time slot; and communicating a measurement report message during a power receiver communication time slot following the second power transmitter communication time slot, the measurement report message indicating a measurement of the at least one pulse.

[0129] Clause 21. 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 of clauses 17-20.

[0130] Another innovative aspect of the subject matter described in this disclosure can be implemented as a computer-readable medium having instructions stored thereon that, when executed by a processor, cause the processor to perform any of the above-mentioned functions.

[0131] Another innovative aspect of the subject matter described in this disclosure can be implemented as a system with means for implementing any of the above-mentioned functions.

[0132] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus with one or more processors configured to perform one or more operations from any of the above-mentioned methods.

[0133] 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 alone, b alone, c alone, 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.

[0134] The various illustrative components, logic, logical blocks, modules, circuits, operations and algorithm processes described in connection with the implementations disclosed herein can 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 generally been described in terms of overall functionality with the description of various illustrative components, blocks, modules, circuits and processes. Whether such functionality is implemented in hardware, firmware or software depends on the particular application and design constraints imposed on the overall system.

[0135] The hardware and data processing apparatus used to implement the various illustrative components, logic, logical blocks, modules and circuits described in connection with the aspects disclosed herein can 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 can be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes, operations and methods can be performed by an

[0136] As described above, some aspects of the subject matter described in this specification can be implemented as software. For example, various functions of the 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 processor- or computer- executable instructions encoded on one or more tangible processor- or computer-readable storage media for execution by, or to control the operation of, data processing apparatus including the components of the devices described herein. By way of example, and without limitation, such storage media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Combinations of the above should also be included within the scope of storage media.

[0137] Various modifications to implementations described in this disclosure can be readily apparent to those with ordinary skill in the art, and the general principles defined herein can 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 the principles and novel features disclosed herein.

[0138] Further, various features described in this specification in the context of separate implementations can also be implemented in combinations with one another. Conversely, various features described in the context of a single implementation can also be implemented on other implementations, alone or in any suitable sub-combination. Accordingly, although features can 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 can be directed to a sub-combination or a variation of a sub-combination.

[0139] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring such an order, or that all illustrated operations be performed, to implement and / or make use of the present disclosure. Further, the drawings can schematically depict one more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated into the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously with, or between any illustrated operations. In some cases, multitasking and parallel processing can 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

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-on state of the wireless power system, wherein the first k-factor represents an amount of magnetic field coupling between a primary coil of the power transmitter and a secondary coil of a power receiver; negotiating a negotiated power level limit based at least in part on the first k-factor prior to the power-on state; and controlling transfer of wireless power from the power transmitter to the power receiver during the power-on state based on the negotiated power level limit.

2. The method of claim 1, wherein determining the first k-factor comprises: performing the first instance of the k-factor evaluation prior to 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 comprises: 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 of claims 1-3, wherein the first instance of the k-factor evaluation comprises: 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 of claims 1-3, wherein the first instance of the k-factor evaluation comprises: transferring 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 of claims 1-5, further comprising: determining a second k-factor after negotiating the negotiated power level limit and prior to a state transition to the power-on state.

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

8. The method of claim 6 or 7, further comprising: inhibiting a transition to the power-on state if the second k-factor is different 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 of claims 1-8, 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 the instance of the k-factor evaluation; ​ ​ ​ ​ receive, from the power receiver, an acknowledgement of the k-factor measurement request message; transmit, via the primary coil, one or more pulses during a k-factor measurement period of the k-factor evaluation; receive, from the power receiver, a measurement report message including one or more measurements of the one or more pulses at the secondary coil; and calculate a k-factor based at least in part on the one or more measurements.

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

11. The method of claim 9 or 10, further comprising: receive, from the power receiver, a state transition request message (NEXT / x); follow the state transition request message with a delivery of the k-factor measurement request message during a first time period (Tl) to initiate an instance of the k-factor evaluation; and complete 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 of claims 1 to 12, further comprising: determine, occasionally during the power supply state, an updated k-factor; and verify 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 determining the updated k-factor occasionally includes, during the power supply state: deliver an indication that a second power transmitter communication time slot will be a k-factor measurement period during a first power transmitter communication time slot; transmit, via the primary coil, at least one pulse during the second power transmitter communication time slot; receive, during a power receiver communication time slot following 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 calculate 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: determine, based on the updated k-factor, whether the power transmitter can satisfy the negotiated power level limit; and end the power supply 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, wherein ending the power supply 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 of claims 1 to 15.

17. A method performed by a power receiver of a wireless power system, comprising: 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 powered state of the wireless power system, where the k-factor represents an amount of 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 following the acknowledgement.

19. The method of claim 18, further comprising: suppressing communications during the k-factor measurement period.

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

21. 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 of claims 17 to 20.

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