PATENT DOCUMENT

Publication Number: US-10734847-B2
Application Number: US-201815880214-A
Country: US
Kind Code: B2

Title: Wireless power system with coupling-coefficient-based coil selection

Abstract:
A wireless power system may have a wireless power transmitting device and a wireless power receiving device. The wireless power receiving device may have a receive coil that receives wireless power signals from the wireless power transmitting device and may have a rectifier that produces direct-current power from the received wireless power signals. The wireless power transmitting device may have an array of transmit coils. Each transmit coil has a respective magnetic coupling coefficient characterizing its magnetic coupling with the receive coil. The wireless power transmitting device may have control circuitry that uses the magnetic coupling coefficient values in selecting transmit coils to use in transmitting wireless power to the wireless power receiving device.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device configured to wirelessly transmit power to a wireless power receiving device having a receive coil, comprising:
 wireless power transmitting circuitry including transmit coils characterized by coupling coefficients associated with electromagnetic coupling between the transmit coils and the receive coil; and 
 control circuitry configured to:
 transmit wireless power to the wireless power receiving device using the wireless power transmitting circuitry while receiving non-zero rectifier output voltage measurements from the wireless power receiving device; 
 determine a magnetic coupling coefficient value for each of the transmit coils as a function proportional to the non-zero rectifier output voltage measurements and a transmit-coil-inductance-to-receive-coil-inductance-ratio; and 
 use the wireless power transmitting circuitry to transmit wireless power to the wireless power receiving device with a subset of the transmit coils selected based on the magnetic coupling coefficient values. 
 
 
     
     
       2. The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to obtain device type information from the wireless power receiving device and is configured to determine the transmit-coil-inductance-to-receive-coil-inductance-ratio based on the device type information. 
     
     
       3. The wireless power transmitting device of  claim 2  further comprising a capacitor coupled to each of the transmit coils that is characterized by a capacitor voltage, wherein the control circuitry is configured to:
 measure the capacitor voltages; and 
 use the measured capacitor voltages in determining the magnetic coupling coefficient values. 
 
     
     
       4. The wireless power transmitting device of  claim 3  wherein:
 the wireless power transmitting circuitry includes inverter circuitry controlled by the control circuitry to provide alternating-current signals to the transmit coils; 
 the control circuitry is configured to measure a direct-current input voltage to the inverter circuitry; and 
 the control circuitry is configured to use the measured direct-current input voltage in determining the magnetic coupling coefficient values. 
 
     
     
       5. The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to compare the magnetic coupling coefficient values to a minimum coupling coefficient threshold. 
     
     
       6. The wireless power transmitting device of  claim 5  wherein the subset of transmit coils includes a pair of transmit coils with respective magnetic coupling coefficient values that exceed the minimum coupling coefficient value, wherein a first of the pair of transmit coils has a first coupling coefficient value, wherein the second of the pair of the transmit coils has a second coupling coefficient value that is higher than the first coupling coefficient value, and wherein a ratio of the first coupling coefficient value to the second coupling coefficient value exceeds a predetermine ratio threshold. 
     
     
       7. The wireless power transmitting device of  claim 5  wherein the control circuitry is configured to transmit wireless power using each of the transmit coils having a magnetic coupling coefficient value that exceeds the minimum coupling coefficient value. 
     
     
       8. The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to obtain receive coil inductance information from the wireless power receiving device and is configured to determine the transmit-coil-inductance-to-receive-coil-inductance-ratio based on the receive coil inductance information. 
     
     
       9. The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to measure a transmit coil inductance for each of the transmit coils and is configured to determine ratios of each of the transmit coil inductances to the receive coil inductance to use in determining the magnetic coupling coefficient values. 
     
     
       10. The wireless power transmitting device of  claim 9  wherein the control circuitry is configured to transmit wireless power to the wireless power receiving device using the wireless power transmitting circuitry while receiving the rectifier output voltage measurements from the wireless power receiving device. 
     
     
       11. The wireless power transmitting device of  claim 8  further comprising a capacitor coupled to each of the transmit coils that is characterized by a capacitor voltage, wherein the control circuitry is configured to:
 measure the capacitor voltages; and 
 use the measured capacitor voltages in determining the magnetic coupling coefficient values. 
 
     
     
       12. The wireless power transmitting device of  claim 8  wherein:
 the wireless power transmitting circuitry includes inverter circuitry controlled by the control circuitry to provide alternating-current signals to the transmit coils; 
 the control circuitry is configured to measure a direct-current input voltage to the inverter circuitry; and 
 the control circuitry is configured to use the measured direct-current input voltage in determining the magnetic coupling coefficient values. 
 
     
     
       13. The wireless power transmitting device of  claim 1 , wherein the function is proportional to a square root of the transmit-coil-inductance-to-receive-coil-inductance-ratio. 
     
     
       14. The wireless power transmitting device of  claim 13 , wherein the function is proportional to the rectifier output voltage measurements multiplied by the square root of the transmit-coil-inductance-to-receive-coil-inductance-ratio. 
     
     
       15. The wireless power transmitting device of  claim 1 , wherein the transmit-coil-inductance-to-receive-coil-inductance-ratio is directly proportional to an inductance of the transmit coils and wherein the transmit-coil-inductance-to-receive-coil-inductance-ratio is inversely proportional to an inductance of the receive coil. 
     
     
       16. The wireless power transmitting device of  claim 15 , wherein the function is directly proportional to a square root of the inductance of the transmit coils and is inversely proportional to a square root of the inductance of the receive coil. 
     
     
       17. A wireless power transmitting device configured to wirelessly transmit power to a wireless power receiving device having a receive coil, comprising:
 wireless power transmitting circuitry including transmit coils each of which is characterized by a coupling coefficient value associated with magnetic coupling between that transmit coil and the receive coil; and 
 control circuitry configured to:
 store a plurality of transmit-coil-inductance-to-receive-coil-inductance ratio values corresponding to different device identifiers; 
 receive a device identifier from the wireless power receiving device that identifies a device type of the wireless power receiving device; 
 identify a transmit-coil-inductance-to-receive-coil-inductance ratio value from the stored plurality of transmit-coil-inductance-to-receive-coil-inductance ratio values that corresponds to the device identifier received from the wireless power receiving device; 
 determine the coupling coefficient values as a function of the identified transmit-coil-inductance-to-receive-coil-inductance ratio; and 
 select which of the transmit coils to use in transmitting wireless power to the wireless power receiving device based on the coupling coefficient values. 
 
 
     
     
       18. The wireless power transmitting device of  claim 17  wherein the control circuitry is configured to identify a subset of the transmit coils for which the coupling coefficient values are larger than the coupling coefficient values of all other of the transmit coils. 
     
     
       19. The wireless power transmitting device of  claim 18  wherein the control circuitry is configured to transmit the wireless power using the subset of the transmit coils. 
     
     
       20. The wireless power transmitting device of  claim 19  wherein the subset of the transmit coils is a pair of the transmit coils. 
     
     
       21. The wireless power transmitting device of  claim 17 , wherein the function is proportional to a rectifier output voltage of the wireless power receiving device multiplied by a square root of the identified transmit-coil-inductance-to-receive-coil-inductance ratio. 
     
     
       22. The wireless power transmitting device of  claim 21 , wherein the rectifier output voltage is non-zero.

Description:
This patent application claims the benefit of provisional patent application No. 62/549,258, filed on Aug. 23, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to power systems, and, more particularly, to wireless power systems for charging electronic devices. 
     BACKGROUND 
     In a wireless charging system, a wireless charging mat wirelessly transmits power to a portable electronic device that is placed on the mat. The portable electronic device has a coil and rectifier circuitry. The coil receives alternating-current wireless power signals from a coil in the wireless charging mat that is overlapped by the coil in the portable electronic device. The rectifier circuitry converts the received signals into direct-current power. 
     SUMMARY 
     A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power receiving device has a receive coil that receives wireless power signals from the wireless power transmitting device and has a rectifier that produces direct-current power from the received wireless power signals. 
     The wireless power transmitting device has an array of transmit coils. Each transmit coil has a respective magnetic coupling coefficient characterizing its magnetic coupling to the receive coil. The wireless power transmitting device has control circuitry that uses the magnetic coupling coefficient values in selecting which transmit coils to use in transmitting the wireless power signals to the wireless power receiving device. 
     The coupling coefficient values may be determined by the control circuitry based on rectifier output voltages in the power receiving device, information on a voltage input value to inverter circuitry in the wireless power transmitting device, information on voltages across capacitors coupled to the transmit coils, and, if desired, other information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless charging system that includes a wireless power transmitting device and a wireless power receiving device in accordance with an embodiment. 
         FIG. 2  is a top view of an illustrative wireless power transmitting device having a charging surface on which a wireless power receiving device has been placed in accordance with an embodiment. 
         FIG. 3  is a circuit diagram of illustrative wireless power transmitting circuitry and illustrative wireless power receiving circuitry in accordance with an embodiment. 
         FIG. 4  is a circuit diagram of an equivalent circuit for the circuity of  FIG. 3  in accordance with an embodiment. 
         FIG. 5  is a flow chart of illustrative operations involved in calibrating and using wireless power transmitting and receiving devices in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system includes a wireless power transmitting device such as a wireless charging mat. The wireless power transmitting device wirelessly transmits power to a wireless power receiving device such as a wristwatch, cellular telephone, tablet computer, laptop computer, or other electronic equipment. The wireless power receiving device uses power from the wireless power transmitting device for powering the device and for charging an internal battery. 
     The wireless power transmitting device communicates with the wireless power receiving device and obtains information on the characteristics of the wireless power receiving device. The wireless power transmitting device uses information from the wireless power receiving device and measurements made in the wireless power transmitting device to determine a value of the magnetic coupling coefficient between each of multiple transmit coils in the wireless power transmitting device and a receive coil in the wireless power receiving device. Coil selection is then performed in the wireless power transmitting device based on the coupling coefficient measurements. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  includes a wireless power transmitting device such as wireless power transmitting device  12  and includes a wireless power receiving device such as wireless power receiving device  24 . Wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Control circuitry in system  8  such as control circuitry  16  and control circuitry  30  is used in controlling the operation of system  8 . This control circuitry may include processing circuitry associated with microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. The processing circuitry implements desired control and communications features in devices  12  and  24 . For example, the processing circuitry may be used in selecting coils, determining power transmission levels, processing sensor data and other data, processing user input, handling negotiations between devices  12  and  24 , sending and receiving in-band and out-of-band data, making measurements, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be configured to perform operations in system  8  using hardware (e.g., dedicated hardware or circuitry), firmware and/or software. Software code for performing operations in system  8  is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) in control circuitry  8 . The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, or the like. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  16  and/or  30 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, a central processing unit (CPU) or other processing circuitry. 
     Power transmitting device  12  may be a stand-alone power adapter (e.g., a wireless charging mat that includes power adapter circuitry), may be a wireless charging mat that is coupled to a power adapter or other equipment by a cable, may be a portable device, may be equipment that has been incorporated into furniture, a vehicle, or other system, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging mat are sometimes described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wristwatch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. Power transmitting device  12  may be coupled to a wall outlet (e.g., an alternating current power source), may have a battery for supplying power, and/or may have another source of power. Power transmitting device  12  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  14  for converting AC power from a wall outlet or other power source into DC power. DC power may be used to power control circuitry  16 . During operation, a controller in control circuitry  16  may use power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  60  formed from transistors) that is turned on and off based on control signals provided by control circuitry  16  to create AC current signals through one or more transmit coils  42 . Coils  42  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat). 
     As the AC currents pass through one or more coils  42 , alternating-current electromagnetic (e.g., magnetic) fields (signals  44 ) are produced that are received by one or more corresponding receiver coils such as coil  48  in power receiving device  24 . When the alternating-current electromagnetic fields are received by coil  48 , corresponding alternating-current currents are induced in coil  48 . Rectifier circuitry such as rectifier  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from coil  48  into DC voltage signals for powering device  24 . 
     The DC voltages produced by rectifier  50  can be used in powering a battery such as battery  58  and can be used in powering other components in device  24 . For example, device  24  may include input-output devices  56  such as a display, touch sensor, communications circuits, audio components, sensors, and other components and these components may be powered by the DC voltages produced by rectifier  50  (and/or DC voltages produced by battery  58 ). 
     Device  12  and/or device  24  may communicate wirelessly using in-band or out-of-band communications. Device  12  may, for example, have wireless transceiver circuitry  40  that wirelessly transmits out-of-band signals to device  24  using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals to device  12 . Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals from device  12 . 
     Wireless transceiver circuitry  40  can use one or more coils  42  to transmit in-band signals to wireless transceiver circuitry  46  that are received by wireless transceiver circuitry  46  using coil  48 . Any suitable modulation scheme may be used to support in-band communications between device  12  and device  24 . With one illustrative configuration, frequency-shift keying (FSK) is used to convey in-band data from device  12  to device  24  and amplitude-shift keying (ASK) is used to convey in-band data from device  24  to device  12 . Power may be conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions. Other types of in-band communications may be used, if desired. 
     During wireless power transmission operations, circuitry  52  supplies AC drive signals to one or more coils  42  at a given power transmission frequency. The power transmission frequency may be, for example, a predetermined frequency of about 125 kHz, at least 80 kHz, at least 100 kHz, less than 500 kHz, less than 300 kHz, or other suitable wireless power frequency. In some configurations, the power transmission frequency may be negotiated in communications between devices  12  and  24 . In other configurations, the power transmission frequency may be fixed. 
     During wireless power transfer operations, while power transmitting circuitry  52  is driving AC signals into one or more of coils  42  to produce signals  44  at the power transmission frequency, wireless transceiver circuitry  40  uses FSK modulation to modulate the power transmission frequency of the driving AC signals and thereby modulate the frequency of signals  44 . In device  24 , coil  48  is used to receive signals  44 . Power receiving circuitry  54  uses the received signals on coil  48  and rectifier  50  to produce DC power. At the same time, wireless transceiver circuitry  46  uses FSK demodulation to extract the transmitted in-band data from signals  44 . This approach allows FSK data (e.g., FSK data packets) to be transmitted in-band from device  12  to device  24  with coils  42  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     In-band communications between device  24  and device  12  uses ASK modulation and demodulation techniques. Wireless transceiver circuitry  46  transmits in-band data to device  12  by using a switch (e.g., one or more transistors in transceiver  46  that are coupled coil  48 ) to modulate the impedance of power receiving circuitry  54  (e.g., coil  48 ). This, in turn, modulates the amplitude of signal  44  and the amplitude of the AC signal passing through coil(s)  42 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  42  and, using ASK demodulation, extracts the transmitted in-band data from these signals that was transmitted by wireless transceiver circuitry  46 . The use of ASK communications allows ASK data bits (e.g., ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  42  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     Control circuitry  16  has external object measurement circuitry  41  (sometimes referred to as foreign object detection circuitry or external object detection circuitry) that detects external objects on a charging surface associated with device  12 . Circuitry  41  can detect foreign objects such as coils, paper clips, and other metallic objects and can detect the presence of wireless power receiving devices  24 . During object detection and characterization operations, external object measurement circuitry  41  can be used to make measurements on coils  42  to determine whether any devices  24  are present on device  12 . 
     In an illustrative arrangement, measurement circuitry  41  of control circuitry  16  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator, etc.) and signal detection circuitry (e.g., filters, analog-to-digital converters, impulse response measurement circuits, etc.). During measurement operations, switching circuitry in device  12  may be adjusted by control circuitry  16  to switch each of coils  42  into use. As each coil  42  is selectively switched into use, control circuitry  16  uses the signal generator circuitry of signal measurement circuitry  41  to apply a probe signal to that coil while using the signal detection circuitry of signal measurement circuitry  41  to measure a corresponding response. Measurement circuitry  43  in control circuitry  30  and/or in control circuitry  16  may also be used in making current and voltage measurements. 
     The characteristics of each coil  42  depend on whether any foreign objects overlap that coil (e.g., coins, wireless power receiving devices, etc.) and also depend on whether a wireless power receiving device with a coil such as coil  48  of  FIG. 1  is present, which could increase the measured inductance of any overlapped coil  42 . Signal measurement circuitry  41  is configured to apply signals to the coil and measure corresponding signal responses. For example, signal measurement circuitry  41  may apply an alternating-current probe signal while monitoring a resulting signal at a node coupled to the coil. As another example, signal measurement circuitry  41  may apply a pulse to the coil and measure a resulting impulse response (e.g., to measure coil inductance). Using measurements from measurement circuitry  41 , the wireless power transmitting device can determine whether an external object is present on the coils. If, for example, all of coils  42  exhibit their expected nominal response to the applied signals, control circuitry  16  can conclude that no external devices are present. If one of coils  42  exhibits a different response (e.g., a response varying from a normal no-objects-present baseline), control circuitry  16  can conclude that an external object (potentially a compatible wireless power receiving device) is present. 
     Control circuitry  30  has measurement circuitry  43 . In an illustrative arrangement, measurement circuitry  43  of control circuitry  30  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator, etc.) and signal detection circuitry (e.g., filters, analog-to-digital converters, impulse response measurement circuits, etc.). During measurement operations, device  24  may use measurement circuitry  43  to make measurements to characterize device  24  and the components of device  24 . For example, device  24  may use measurement circuitry  43  to measure the inductance of coil  48  (e.g., signal measurement circuitry  43  may be configured to measure signals at coil  48  while supplying coil  48  with signals at one or more frequencies (to measure coil inductances), signal pulses (e.g., so that impulse response measurement circuitry in the measurement circuitry can be used to make inductance and Q factor measurements), etc. Measurement circuitry  43  may also make measurements of the output voltage of rectifier  50 , the output current of rectifier  50 , etc. 
     A top view of an illustrative configuration for device  12  in which device  12  has an array of coils  42  is shown in  FIG. 2 . Device  12  may, in general, have any suitable number of coils  42  (e.g., 22 coils, at least 5 coils, at least 10 coils, at least 15 coils, fewer than 30 coils, fewer than 50 coils, etc.). Coils  42  may be arranged in rows and columns and may or may not partially overlap each other. System  8  may be configured to accommodate the simultaneous charging of multiple devices  24 . Illustrative operations involved in operating system  8  to provide power wirelessly to a single device  24  are described herein as an example. 
     A user of system  8  may place wireless power receiving devices such as device  24  of  FIG. 2  on device  12  for charging. Magnetic coupling coefficient k represents the amount of magnetic coupling between transmitting and receiving coils in system  8 . Wireless power transfer efficiency scales with k, so optimum charging (e.g., peak efficiency) may be obtained by evaluating the coupling coefficient k for each coil and choosing appropriate coil(s) to use in transmitting wireless power to device  24  based on the coupling coefficients. 
     Illustrative circuitry of the type that may be used for forming power transmitting circuitry  52  and power receiving circuitry  54  of  FIG. 1  is shown in  FIG. 3 . As shown in  FIG. 3 , power transmitting circuitry  52  may include drive circuitry (inverter circuitry) for supplying alternating-current drive signals to coils  42 . With one illustrative configuration, the inverter circuitry includes multiple inverter circuits such as inverter  60  of  FIG. 3  each of which is controlled by control circuitry  16  of device  12  and each of which is coupled to a respective one of coils  42 . After coupling coefficients k have been determined for each coil  42 , control circuitry  16  can switch appropriate coil(s)  42  into use by selecting corresponding inverters  60  to use in driving signals into the coils. 
     Each inverter  60  has metal-oxide-semiconductor transistors or other suitable transistors. These transistors are modulated by an AC control signal from control circuitry  16  ( FIG. 1 ) that is received on control signal input  62 . The AC control signal controls modulate the transistors so that direct-current power (input voltage Vindc across direct-current power supply input terminals  63 ) is converted into a corresponding AC drive signal applied to coil  42  (having a self-inductance of Ltx) via its associated capacitor Ctx. This produces electromagnetic signals  44  (magnetic fields), which are electromagnetically (magnetically) coupled into coil  48  in wireless power receiving device  54 . 
     The degree of electromagnetic (magnetic) coupling between coils  42  and  48  is represented by magnetic coupling coefficient k. Signals  44  are received by coil  48  (having a self-inductance of Lrx). Coil  48  and capacitor Crx are connected to rectifier  50 . During operation, the AC signals from coil  48  that are produced in response to received signals  44  are rectified by rectifier  50  to produce direct-current output power (e.g., direct-current rectifier output voltage Vo) across output terminals  65 . Terminals  65  are connected to and provide power to the load of power receiving device  24  (e.g., battery  58  and other components in device  24  that are being powered by the direct-current power supplied from rectifier  50 ). 
     An equivalent circuit for the circuitry of  FIG. 3  is shown in  FIG. 4 . Mutual inductance Lm results from the coupling between coils  42  and  48 . Transmit coil leakage inductance Ltx  1  is equal to Ltx−Lm. Receive coil leakage inductance Lrx 1  is equal to Lrx−Lm. During operation, a peak-to-peak voltage Vctx is produced across capacitor Ctx. Voltage Vrx is present at the node between inductance Lrx 1  and capacitor Crx. Capacitance Cp and resistance Rload represent the capacitance associated with rectifier  50  and the equivalent resistance of the load of the circuitry in device  24 . Voltage Vo is the output voltage of rectifier  50  that is being applied to resistance Rload. Current Io is the output current of coil  48 . 
     Coupling coefficient k can be calculated using equations 1 and 2.
 
 Vrx =( Io/ 2 fswCrx )+ V diode+ Vo   (1)
 
 k =2 Vrx ( Ltx/Lrx ) 1/2 /( Vctx+Vindc )  (2)
 
     In equation 1, fsw is the frequency of the signal applied to transmit coil  42  and Vdiode is the voltage drop associated with the transistors of rectifier  50 . The first two terms of equation 1 are small and can be ignored. As a result, Vrx can be taken to be equal to Vo in equation 2. During operation, measurement circuitry  43  (e.g., voltage and current measurement circuitry) in control circuitry  30  of device  24  measures Vo and Io. This allows the value of Io and Vo (and therefore Vrx) to be obtained by device  12  wirelessly over an in-band communications link or other wireless communications link between device  24  and device  12 . 
     In equation 2, Vrx is known from equation 1 and Vctx and Vindc are measured by measurement circuitry in control circuitry  16 . The values of Ltx and Lrx can be obtained using measurements made on system  8  (or a representative system) during manufacturing and/or measurements made by system  8  following manufacturing (e.g., when being used in the field by a user). During operation of system  8 , wireless power receiving device  24  may convey device type information, inductance measurements such as a measurement of Lrx, and/or other power receiving device characteristics such as rectifier output voltage Vo to device  12  using in-band communications. Using this information and/or information in device  12  (e.g., information stored during manufacturing, and/or measurements made using control circuitry  16 ), control circuitry  16  can determine k from equation 2. 
     With one illustrative configuration, system  8  is characterized during manufacturing to determine Ltx/Lrx. This inductance ratio, which may vary depending on the type of device  24  that is being characterized (e.g., the model of cellular telephone, wristwatch, etc.), is stored in device  12  (e.g., in memory in circuitry  16 ) and is associated with the device type (e.g., a device identifier, etc.) for device  24 . Subsequently, device  12  receives device type information (e.g., an ID or other information identifying device  24 ) wirelessly from device  24  and uses this information to retrieve the appropriate device-type-specific value of Ltx/Lrx from memory in circuitry  16 . 
     With another illustrative configuration, measurement circuitry in control circuitry  16  is used to measure Ltx and measurement circuitry  43  in device  24  is used to measure Lrx. During operation, device  12  wirelessly obtains Lrx from device  24  and uses this information in determine the value of Ltx/Lrx. 
     The use of the value of k to determine which coils  42  to switch into use during charging operations is more accurate than using other parameters (e.g., measured values of Vo). Consider, as an example, a scenario in which a first of coils  42  is coupled to coil  48  with a first coupling coefficient k1 and results in a voltage Vo 1  at the output of rectifier  50  whereas a second of coils  42  is coupled to coil  48  with a second coupling coefficient k2 and results in a voltage Vo 2  at the output of rectifier  50 . The first coil in this example might be located closer to a ferrite layer at the bottom of device  12  and might therefore have a higher inductance, whereas the second coil might be located farther from the ferrite layer and might therefore have a lower inductance. In this illustrative scenario, the value of Vo 1  might be less than Vo 2  (e.g., voltage Vo 1  may be low due to the larger inductance of the first coil which creates a larger “windings ratio” with coil  48  than the second coil of lower inductance), while k1 is greater than k2 (because the first coil is better coupled to coil  48  than the second coil). The greatest wireless power transfer efficiency in this example, is obtained when using the first coil (the coil with the larger coupling coefficient), rather than using the second coil (the coil producing the larger value of rectifier output voltage Vo 2 ). 
     The array of coils  42  in device  12  lie in a plane parallel to a charging surface on which device  24  rests. The value of Ltx/Lrx does not vary significantly as device  24  moves around a given one of coils  42  and has an applicable k for charging (e.g., when device  24  is placed at different lateral positions in lateral dimensions X and Y of  FIG. 2  such that coupling coefficient k is sufficiently high for charging). The value of Ltx/Lrx will also not vary significantly as a function of changes in the height of device  24  above the charging surface. In some situations, device  24  is not housed in a removable battery case and will rest directly on the charging surface (e.g., height Z=0). In other situations, a user may enclose device  24  in a removable case (e.g., a removable battery case or a removable protective case without a battery). When placed on the charging surface when device  24  is in a removable case, coil  48  may be at a nonzero height (e.g., Z=Z1 relative to its uncased height). As the height of coil  48  above devices  12  increases, Lrx will decrease (because the distance from coil  42  is increasing). The value of Ltx also drops as the height of coil  48  increases above coil  42  (because coil  42  is becoming more distant from coil  48 ). As a result, the ratio of Ltx/Lrx does not vary significantly with changes in the height of coil  48 . This makes the value of Ltx/Lrx independent of factors such as whether a user has placed a removable case on device  24 . It can therefore be beneficial to obtain Ltx/Lrx (e.g., measured at height Z=0) during characterizing measurements (e.g., during manufacturing) and to store the measured value of Ltx/Lrx in device  12  (for each type of supported device  24 ) for later use by device  12  in evaluating equation 2 and accurately determining k. If desired, however, Lrx can be measured by device  24  in the field and Ltx can be measured by device  12  in the field. 
       FIG. 5  is a flow chart of illustrative steps involved in operating system  8 . 
     During the operations of block  200 , test equipment may be used to measure Lrx and Ltx in system  8  (or only Lrx in some arrangements). The system in which Lrx and Ltx are measured may be a representative system with a representative (sample) device  12  and representative (sample) device  24 . The test equipment may be located in a manufacturing facility. Following measurement of Lrx and Ltx (and determination of Ltx/Lrx), this information and associated device type information that identifies the type of device  24  associated with the stored Ltx/Lrx measurement can be stored in memory in device  12  using the test equipment or associated programming equipment for subsequent retrieval and use by control circuitry  16 . 
     Later, in the field, devices  12  and  24  can operate in accordance with blocks  202 ,  204 , and  208 . In particular, during the operations of block  202 , device  12  can transmit power to device  24  with one of coils  42 . Device  24  can receive the transmitted wireless power signals with coil  48  and can use rectifier  50  to produce output power (voltage Vo) on output terminals  65  ( FIG. 3 ). While receiving power in this way, device  24  can communicate with device  12  using in-band communications (or, if desired, using out-of-band communications). 
     With one illustrative arrangement, device  24  provides device  12  with device type information (e.g., a device identifier that identifies the type of cellular telephone or other device to be charged) during block  202 . 
     With another illustrative arrangement device  24  measures Lrx and provides Lrx to device  12  during block  202 . 
     Device  24  can also use control circuitry  30  to measure the value of Vo at the output of rectifier  50  and to measure other desired power receiving device characteristics. These power receiving device characteristics (e.g., rectifier output voltage Vo) can also be provided wirelessly to device  12  during block  202 . 
     During the operations of block  204 , power transmitting device  12  may measure characteristics of device  12  such as the value of voltage Vctx across capacitor Ctx (e.g., a peak-to-peak voltage measurement), the value of direct-current input voltage Vindc across terminals  63 , and other wireless power transmitting device characteristics. The value of Lrx may be obtained from device  24  during block  202  and the value of Ltx may be measured by device  12  or the value of Ltx/Lrx can be retrieved from storage in circuitry  16  based on the device type information received from device  24  during block  202 . 
     Device  12  can then use equations 1 and 2 to determine k for the current coil  42 . As indicated by line  206 , if all coils  42  of interest have not been measured (e.g., all coils in the array of coils  42  in device  12 , all coils in the array of coils  42  in device  12  that are believed to be overlapped by an external object in accordance with results from external object measurement circuit  41 , etc.), a different coil  42  can be selected (e.g., by using a different inverter  60  to produce signals  44 ) and the operations of blocks  202  and  204  can be repeated. If, however, all coils of interest have been characterized, processing can proceed to block  208 . 
     During the operations of block  208 , control circuitry  16  of device  12  can analyze the values of k that have been measured and, based on this analysis, select which coil  42  or which set of multiple coils  42  (e.g., which pair of coils  42 ) to use in transmitting wireless power to device  12 . 
     With one illustrative configuration, the coils  42  that have the highest values of coupling coefficient k are selected and used to transmit power, unless the lower of the two coupling coefficient values is less than a predetermined minimum coupling coefficient threshold value or the ratio of the second highest k to the highest k is less than a predetermined threshold ratio. If either of the coils  42  in the pair of coils with the highest k values has a k value that is less than the threshold or the ratio of the second highest to the highest k value is less than the predetermined threshold ratio, device  12  will select the single coil  42  with the highest k value and will use this single selected coil to transmit wireless power. 
     Other coil selection criteria based on the measured values of coupling coefficient k can be used, if desired (e.g., selection criteria that result in selection of three or more active coils to transmit power to each wireless power receiving device  12 , etc.). As an example, all coils having a coupling coefficient greater than a predetermined threshold may be selected and used in transmitting wireless power, etc. Coils can be selected based on measured k values in scenarios in which there is a single wireless power receiving device on the charging surface of device  12  and when there are more than one wireless power receiving devices present. For example, if there are three devices  24  present on device  12 , device  12  can select three sets of coils  42  (each containing one or more coils) to supply wireless power. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20180125
Publication Date: 20200804
Grant Date: 20200804
Priority Date: 20170823
Inventors: LIU, NAN
BERDNIKOV, DMITRY
QIU, WEIHONG
MOUSSAOUI, ZAKI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/00034", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J7/00034", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 65436227