PATENT DOCUMENT

Publication Number: US-10804748-B2
Application Number: US-201715817036-A
Country: US
Kind Code: B2

Title: Wireless power system with foreign object detection

Abstract:
Wireless power transmitting equipment may transmit wireless power signals to wireless power receiving equipment. The wireless power transmitting equipment may have a wireless power transmitter coupled to a wireless power transmitting coil. The wireless power receiving equipment may have a wireless power receiving coil coupled to wireless power receiving circuitry such as a rectifier. Foreign object detection coil arrays may be formed from arrays of metal traces on printed circuit substrates that overlap the wireless power transfer coils. Control circuitry in the transmitting equipment and the receiving equipment may monitor signals from foreign object detection circuitry that is coupled to the coil arrays. The foreign object detection circuitry may produce in-phase and quadrature signals that are indicative of whether a foreign object is overlapping a foreign object detection coil array.

Claims:
What is claimed is: 
     
       1. A wireless power transfer system comprising:
 a wireless power transfer coil; 
 a foreign object detection coil array overlapping the wireless power transfer coil; 
 foreign object detection circuitry that is coupled to the foreign object detection coil array and that is configured to produce in-phase and quadrature signals indicative of whether a foreign object is overlapping the foreign object detection coil array, wherein the foreign object detection circuitry comprises:
 an oscillator configured to supply an oscillator output to a transmitting coil in the foreign object detection coil array, wherein the foreign object detection coil array comprises a receiving coil that at least partially overlaps the transmitting coil; and 
 
 control circuitry configured to receive the in-phase and quadrature signals from the foreign object detection circuitry. 
 
     
     
       2. The wireless power transfer system defined in  claim 1  wherein the oscillator is configured to supply the oscillator output at a frequency less than 1 MHz to the transmitting coil in the foreign object detection coil array, wherein the receiving coil in the foreign object detection coil array is configured to receive signals corresponding to the oscillator output supplied to the transmitting coil and wherein the wireless power transfer system further comprises:
 filter circuitry configured to filter the signals received by the receiving coil to produce filtered signals. 
 
     
     
       3. The wireless power transfer system defined in  claim 2  wherein the foreign object detection circuitry comprises:
 a phase shifter configured to receive the oscillator output and provide a corresponding phase-shifted oscillator output; 
 a first multiplier configured to multiply the oscillator output and the filtered signals to produce the in-phase signal; and 
 a second multiplier configured to multiply the phase-shifted oscillator output and the filtered signals to produce the quadrature signal. 
 
     
     
       4. The wireless power transfer system defined in  claim 3  further comprising:
 circuitry configured to remove direct-current offsets from the in-phase and quadrature signals. 
 
     
     
       5. The wireless power transfer system defined in  claim 3  further comprising:
 low pass filter circuitry configured to filter the in-phase and quadrature signals. 
 
     
     
       6. The wireless power transfer system defined in  claim 2  wherein the filter circuitry comprises a passive filter and an active filter. 
     
     
       7. The wireless power transfer system defined in  claim 1  further comprising:
 a ferromagnetic layer, wherein the wireless power transfer coil overlaps the ferromagnetic layer. 
 
     
     
       8. The wireless power transfer system defined in  claim 7  wherein the wireless power transfer coil is a wireless power transmitting coil, the wireless power transfer system further comprising a wireless power transmitter coupled to the wireless power transmitting coil that is configured to transmit power wirelessly to wireless power receiving equipment. 
     
     
       9. The wireless power transfer system defined in  claim 8  further comprising a mains power source configured to supply power to the wireless power transmitter. 
     
     
       10. The wireless power transfer system defined in  claim 7  wherein the wireless power transfer coil is a wireless power receiving coil, the wireless power transfer system further comprising a rectifier coupled to the wireless power receiving coil to receive power wirelessly from wireless power transmitting equipment. 
     
     
       11. The wireless power transfer system defined in  claim 10  further comprising a battery that is configured to receive power from the rectifier. 
     
     
       12. The wireless power transfer system defined in  claim 1  wherein the foreign object detection coil array comprises cross-shaped coils. 
     
     
       13. The wireless power transfer system defined in  claim 12  wherein each cross-shaped coil has a metal trace on a printed circuit board. 
     
     
       14. The wireless power transfer system defined in  claim 1  wherein the control circuitry is configured to process signals from the foreign object detection circuitry to identify a signal peak associated with a location on the foreign object detection coil array at which foreign object is located. 
     
     
       15. The wireless power transfer system defined in  claim 1  wherein the oscillator is configured to supply the oscillator output at a frequency less than 1 MHz to the transmitting coil in the foreign object detection coil array. 
     
     
       16. Wireless power transmitting equipment, comprising:
 a wireless power transmitting coil; 
 a wireless power transmitter coupled to the wireless power transmitting coil and configured to wirelessly transmit power to wireless power receiving equipment through the wireless power transmitting coil; 
 a foreign object detection coil array overlapping the wireless power transmitting coil; and 
 foreign object detection circuitry coupled to the foreign object detection coil array, wherein the foreign object detection circuitry is configured to produce in-phase and quadrature output signals based on a signal received from a coil in the foreign object detection coil array and wherein the foreign object detection circuitry comprises:
 an oscillator configured to supply an oscillator output corresponding to the signal to an additional coil in the foreign object detection coil array, wherein the coil and the additional coil in the foreign object detection coil array are at least partially overlapping. 
 
 
     
     
       17. The wireless power transmitting equipment defined in  claim 16  wherein the foreign object detection coil array is formed from metal traces on a printed circuit, the wireless power transmitting equipment further comprising control circuitry configured to stop wireless power transmission with the wireless power transmitter in response to determining that a foreign object is present on the foreign object detection coil array based on the in-phase and quadrature output signals. 
     
     
       18. The wireless power transmitting equipment defined in  claim 17  wherein the oscillator is configured to produce the oscillator output at a frequency between 100 kHz and 1 MHz, wherein the oscillator is configured to provide the oscillator output to the additional coil in the foreign object detection coil array, wherein the wireless power transmitter is configured to transmit the wireless power at an additional frequency of less than 100 kHz, and wherein the oscillator is configured to produce the oscillator output at a first power when the wireless power transmitter is inactive and a second power that is greater than the first power when the wireless power transmitter is wirelessly transmitting power to the wireless power receiving equipment. 
     
     
       19. Wireless power receiving equipment, comprising:
 a wireless power receiving coil; 
 a rectifier coupled to the wireless power receiving coil and configured to wirelessly receive power from wireless power transmitting equipment through the wireless power transmitting coil; 
 a foreign object detection coil array overlapping the wireless power receiving coil; and 
 foreign object detection circuitry coupled to the foreign object detection coil array, wherein the foreign object detection circuitry is configured to produce in-phase and quadrature output signals based on a signal received from a coil in the foreign object detection coil array and wherein the foreign object detection circuitry comprises:
 an oscillator configured to supply an alternating current drive signal corresponding to the signal to an additional coil in the foreign object detection coil array, wherein the coil and the additional coil in the foreign object detection coil array are at least partially overlapping. 
 
 
     
     
       20. The wireless power receiving equipment defined in  claim 19  further comprising control circuitry configured to determine when a foreign object is present based on the in-phase and quadrature output signals, wherein the alternating current drive signal is supplied at a frequency that is at least 100 kHz and less than 1 MHz and wherein the foreign object detection coil array is formed from an array of copper traces on a printed circuit.

Description:
This application claims the benefit of provisional patent application No. 62/434,251, filed on Dec. 14, 2016, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to wireless systems, and, more particularly, to systems in which power is transferred wirelessly. 
     BACKGROUND 
     In a wireless power transfer system, a wireless power transmitting device such as charging mat may wirelessly transmit power to wireless power receiving equipment. The wireless power receiving equipment may use this power to charge a battery. In some situations, unwanted foreign objects may be present in the vicinity of wireless power transfer equipment. Foreign object detection circuitry may be used to detect these objects. 
     SUMMARY 
     Wireless power transmitting equipment may transmit wireless power signals to wireless power receiving equipment. The wireless power transmitting equipment may have a wireless power transmitter coupled to a wireless power transmitting coil. A power source such as a mains power source may provide the wireless power transmitter with power. 
     The wireless power receiving equipment may have a wireless power receiving coil coupled to wireless power receiving circuitry such as a rectifier. The rectifier may supply wirelessly received power to a battery in the wireless power receiving equipment to charge the battery. 
     Foreign object detection coil arrays may be formed from arrays of metal traces on printed circuit substrates that overlap the wireless power transfer coils. The foreign object detection coil arrays may overlap the wireless power transmitting coil and the wireless power receiving coil. Foreign object detection circuitry may be coupled to the coil arrays. The foreign object detection circuitry may include an oscillator that serves as a transmitter to transmit signals from a coil in a foreign object detection coil array and may include mixing circuitry such as multipliers, phase-shifting circuitry, filtering circuitry, and other circuitry for producing in-phase and quadrature signals from corresponding signals received with a coil in the foreign object detection coil array. The in-phase and quadrature signals may be indicative of whether a foreign object is overlapping a foreign object detection coil array. 
     Control circuitry in the transmitting equipment and the receiving equipment may monitor signals from the foreign object detection circuitry. If a foreign object is detected, appropriate actions may be taken such as issuing alerts and stopping power transfer operations until the foreign object is cleared. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless charging system in accordance with some embodiments. 
         FIG. 2  is a schematic diagram of an illustrative foreign object detection system in accordance with an embodiment. 
         FIG. 3  is a diagram of an illustrative foreign object detection coil for a foreign object detection coil array in accordance with an embodiment. 
         FIG. 4  is a top view of an illustrative foreign object detection coil array in accordance with an embodiment. 
         FIG. 5  is a diagram showing how adjacent foreign object detection coils may be oriented relative to each other in accordance with an embodiment. 
         FIG. 6  is a diagram of illustrative detection circuitry for a foreign object detection system in accordance with an embodiment. 
         FIG. 7  shows equations associated with processing foreign object detection system signals with the circuitry of  FIG. 6  in accordance with an embodiment. 
         FIG. 8  is a flow chart of illustrative operations associated with monitoring for foreign objects in a wireless power transfer system in accordance with an embodiment. 
         FIG. 9  is a circuit diagram of illustrative foreign object detection circuitry in a system in which magnetic fields from a charging coil are monitored to detect the presence of foreign objects in accordance with an embodiment. 
         FIG. 10  is a graph showing how a signal peak may be identified in a signal received from foreign object detection circuitry (e.g., an in-phase or quadrature signal) when a foreign object is present on a foreign object detection coil array in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power transfer system may have wireless power transfer equipment such as wireless power transmitting equipment that transmits power and corresponding wireless power receiving equipment that receives wirelessly transmitted power. 
     The wireless power transmitting equipment may be equipment such as a wireless charging mat, wireless charging station, wireless charging puck, wireless charging stand, wireless charging table, or other wireless power transmitting equipment. The wireless power transmitting equipment may have one or more coils that are used in transmitting wireless power to wireless power receiving equipment. The wireless power receiving equipment may be an electronic device such as a portable electronic device, a vehicle, or other electronic equipment that receives wirelessly transmitted power. 
     During operation, the wireless power transmitting equipment may supply alternating-current signals to one or more wireless power transmitting coils. This causes the coils to transmit alternating-current electromagnetic signals (sometimes referred to as wireless power signals) to the wireless power receiving equipment. The wireless power receiving equipment may have one or more coils for receiving the transmitted wireless power signals. 
     Foreign object detection equipment may be used to monitor for the intrusion of coins, paper clips, soda cans, and other undesired conductive objects in the vicinity of the wireless power system. If these foreign objects are detected, power transfer operations can be suspended and a may be issued an alert such as an alert instructing the user to clear the objects away from the wireless power system. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  may include wireless power transfer equipment such as wireless power transmitting equipment  12  and wireless power receiving equipment  10 . 
     Power transmitting equipment  12  may be a mat, equipment built into a parking space, circuitry built into furniture or part of a vehicle, a charging stand, an electronic device such as a portable electronic device or desktop equipment, or may be other power transmitting equipment. For example, power transmitting equipment  12  may be a wireless charging mat or other wireless charger that rests under a vehicle during wireless charging, may be a wireless charging mat that rests on a table or other surface and that receives a portable electronic device on its surface, may be a wireless charger embedded into furniture, or other wires power transmitting equipment. Equipment  10  may be a vehicle, an electronic device, or other wireless power receiving equipment. 
     As shown in  FIG. 1 , wireless power transmitting equipment  12  may have one or more power transmitting coils such as wireless power transmitting (wireless power transfer) coil(s)  30 . Wireless power transmitter  32  may provide alternating current signals to coil(s)  30  that cause coil(s)  30  to emit electromagnetic fields  26  that are near-field coupled to corresponding wireless power receiving coil(s)  20  in wireless power receiving equipment  10 . Rectifier  18  may rectify received signals from coil(s)  20  and may produce corresponding direct-current (DC) power for equipment  10 . Coil(s)  30  and coil(s)  20  may have ferromagnetic and conductive shield layers or other shields (e.g., ferrite tiles, a layer of metal such as an aluminum layer, etc.), as illustrated by shielding layers  30 ′ and  20 ′ to shield internal circuitry from electromagnetic fields  26  during operation. 
     Power transmitting equipment  12  may have a power source such as power source  38 . Power source  38  may be a source of alternating current voltage such as a wall outlet that supplies line power or other source of mains electricity or a source of direct-current voltage such as a battery. Power transmitting equipment  12  may have a power converter such as an AC-DC power converter for converting power from a mains power source or other power source into DC power. Power source  38  may be used to power control circuitry  34  and components  36  in equipment  12  and may be used to provide transmitter  32  with power to transmit to equipment  10 . In equipment  10 , power from rectifier  18  may be used to charge battery  22  and to power control circuitry  14  and components  16 . Components  36  and  16  may include light-emitting components, displays, buttons, sensors, wireless communications circuitry, audio equipment and/or other input-output devices and components for supporting the operation of equipment  12  and/or  10 . In some configurations, equipment  10  and/or  12  may include motors, transmissions, steering systems, seating, body panels, doors and windows, and other vehicle components. 
     Equipment  12  may include an array of foreign object detection coils such as array  28 . Equipment  10  may include an array of foreign object detection coils such as array  24 . Array  28  may overlap coil(s)  30  and may be used to monitor for the presence of foreign objects that overlap coil(s)  30 . Array  24  may overlap wireless power receiving (wireless power transfer) coil(s)  20  and may be used to monitor for the presence of foreign objects that overlap coils  20 ( s ). During operation, control circuitry  34  can use array  28  to detect whether foreign objects are in the vicinity of array  28  and control circuitry  14  can use array  24  to detect whether foreign objects are in the vicinity of array  24 . Configurations in which circuitry  34  and/or circuitry  14  uses array  28  and/or array  24  or other foreign object detection components to monitor for the presence of foreign objects at other locations between arrays  24  and  28  (e.g., at locations within an air gap separating arrays  24  and  28  that are not immediately adjacent to arrays  24  and  28 ) may also be used, if desired. 
     Control circuitry  34  and  14  may include storage and may include processing circuitry such as microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. Control circuitry  34  and  14  may be configured to execute instructions for implementing desired control and communications features in system  8 . For example, control circuitry  34  and/or  14  may be used in determining power transmission levels, processing sensor data, processing user input, processing other information such as information on wireless coupling efficiency from transmitting circuitry  32 , processing information from wireless power receiving circuitry in equipment  10  such as rectifier  18 , using information from arrays  28  and  24  and sensors in components  16  and/or  36  to determine when to start and stop wireless charging operations, adjusting charging parameters such as charging frequencies, coil assignments in a multi-coil array, and wireless power transmission levels, and performing other control functions. Control circuitry  34  and/or  14  may be configured to perform these operations using hardware (e.g., dedicated hardware or circuitry) and/or software (e.g., code that runs on the hardware of system  8 ). Software code for performing these operations may be stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media). 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, other computer readable media, or combinations of these computer readable media. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  34  and/or  14 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, or other processing circuitry. 
     An array of coils may be used to perform foreign object detection. An illustrative coil array (e.g., coil array  28  or coil array  24  of  FIG. 1 ) is shown in  FIG. 2 . As shown in  FIG. 2 , coil array  50  may include coils (loops of wire that form inductors) such as coils  52 . Coil array  50  may include 2-100 coils, 5-20 coils, 10-500 coils, 40-150 coils, fewer than 500 coils, fewer than 300 coils, fewer than 100 coils, at least 10 coils, at least 20 coils, at least 40 coils, at least 80 coils, at least 160 coils, at least 400 coils, or other suitable number of coils  52 . Coils  52  may be arranged in a two-dimensional planar array (e.g., to form an upper layer of a charging mat, etc.). 
     Switching circuitry  54  may include an array of transistors and/or other switching circuitry that can be configured by control signals produced by control circuitry  34  and/or  14 . The control signals may, for example, switch a desired one of coils  52  into use as a transmitting coil and may switch a desired one of coils  52  into use as a receiving coil by selectively coupling the transmitting and receiving coils to detection circuitry  56 . 
     Detection circuitry  56  may include circuitry such as signal generator circuitry (transmitter circuitry) and signal detection circuitry (receiver circuitry). Control circuitry  34  and/or  14  may use detection circuitry  56  to supply alternating current signals to one or more coils  52  in array  50  that have been selected by switching circuitry  54 . These selected transmitting coil(s)  52  in array  50  may then produce corresponding electromagnetic signals (e.g., time-varying magnetic fields). The electromagnetic signals may be detected by one or more selected receiving coils  52  in array  50 . Control circuitry  34  and/or  14  may configure switching circuitry  54  so that current signals from the selected electromagnetic signal receiving coils are routed to the signal detection circuitry. In presence of foreign objects, the electromagnetic signals that are conveyed between the signal transmitting coil(s) and the signal receiving coil(s) will be altered. Detection circuitry  56  can detect the presence of foreign objects by processing the received signals (e.g., by comparing the transmitted and received signals and processing associated phase and magnitude information from this comparison). 
     Coils  52  may have any suitable shapes. An illustrative cross-shaped coil is shown in  FIG. 3 . As shown in  FIG. 3 , coil  52  may be formed from a metal trace such as metal trace  58  (e.g., a copper line or a conductive signal path formed from one or more other metals). Traces such as trace  58  may be arranged to form an array of coils  52  on substrate  60 . Substrate  60  may be a printed circuit such as a flexible printed circuit formed from a sheet of polyimide or other flexible polymer layer or a rigid printed circuit board formed from a rigid printed circuit board substrate material such as fiberglass-filled epoxy (e.g., FR4). Terminals  62  of each trace  58  may be coupled to detection circuitry  56  through switching circuitry  54 . 
     Trace  58  may have a width W. The value of width W may be, for example, 0.9 mm, 0.1 to 3 mm, at least 0.5 mm, at least 0.8 mm, less than 1.4 mm, less than 2 mm, 0.3-1.5 mm, or other suitable width. The thickness of trace  58  may be 200 microns, at least 50 microns, at least 100 microns, less than 200 microns, less than 250 microns, less than 300 microns, less than 400 microns, or other suitable thickness (e.g., less than 250 microns, which is the skin depth of copper at 50-400 kHz, to help minimize eddy currents in trace  58 , etc.). The lateral dimensions (dimensions along axes X and Y in the X-Y plane of substrate  60 ) of coil  52  may be at least 5 mm, at least 1 cm, at least 2 cm, at least 4 cm, at least 6 cm, less than 10 cm, less than 8 cm, less than 5 cm, 1-6 cm, 2-5 cm, or other suitable size. Relatively small coils  52  may be provided to help enhance foreign object detection accuracy while minimizing the amount of magnetic field that is received by each coil  52  during operation of power transmitting coil(s)  30  and power receiving coil(s)  20  to transfer wireless power. The use of a layout such as the cross-shaped outline of  FIG. 3  for coils  52  may also help minimize magnetic field reception from coil(s)  30  without compromising sensitivity when detecting small coins and other small foreign objects. 
       FIG. 4  is a top view of an illustrative array  50  of coils  52 . As shown in  FIG. 4 , cross-shaped coils  52  may be arranged in a two-dimensional array in the X-Y plane on substrate  60 . Adjacent coils  52  may overlap to minimize coverage gaps.  FIG. 5  shows how coils  52  (e.g., square coils in the  FIG. 5  example) can be overlapped so that the amount of magnetic field flux B that is generated by transmitting coil  52 T is equally divided between upwardly oriented flux (B 1 ) and downwardly oriented flux (B 2 ) within receiving coil  52 R. As a result, the net magnetic flux through coil  52 R and therefore the received signals at coil  52 R are minimized the absence of foreign objects such as foreign object  62  that overlaps coil  52 T and/or  52 R. This type of balanced flux arrangement may help minimize noise and enhance detection sensitivity. 
     Illustrative detection circuitry  56  is shown in  FIG. 6 . Detection circuitry such as circuitry  56  of  FIG. 6  may be used with the coils of array  28  to detect foreign objects in the vicinity of array  28  and detection circuitry such as circuitry  56  of  FIG. 6  may be used with the coils of array  24  to detect foreign objects in the vicinity of array  24 . 
     In the example of  FIG. 6 , detection circuitry  56  has a signal generator such as oscillator (signal transmitter)  70 . Oscillator  70  may produce an alternating-current (AC) signal (current) that is driven through a transmitting coil  52 T in foreign object coil array  50  (e.g., array  28  or array  24 ). Switching circuitry  54  ( FIG. 2 ) may be used to route signals from oscillator  70  to a selected transmitting coil  52 T. Coil  52 T may have a cross-shape, a rectangular shape, or other suitable shape. 
     The frequency of oscillator  70  may be 350-360 kHz, at least 100 kHz, at least 200 kHz, at least 300 kHz, less than 1 MHz, less than 500 kHz, 355 kHz, or other suitable frequency. Frequency hopping and/or frequency shifting techniques may be used to help reduce interference between the foreign object detection circuitry  56  and other circuitry in system  8  (e.g., power transmitting coil(s)  30  and power receiving coil(s)  20 , which may operate at a frequency of 85 kHz, at least 20 kHz, less than 100 kHz, less than 125 kHz, less than 150 kHz, or other suitable frequency. The frequency of oscillator  70  may be selected to avoid overlap with fundamental and harmonic frequencies of the power transmitting and receiving circuitry of system  8  to minimize interference. Detection circuitry  56  may also exhibit a relatively high impedance (e.g., at least 10 k-ohm) at the wireless charging frequency so that eddy currents are not induced in array  24 . 
     The AC signal driven into coil  52 T by oscillator  70  produces a corresponding electromagnetic signal (magnetic field) that is received by a selected receiving coil in the foreign object coil array (e.g., coil  52 R, which is near-field coupled to coil  52 T and which may be coupled to filter  72  by switching circuitry  54  of  FIG. 2 ). In the presence of a foreign object, eddy currents are induced in the foreign object that produce detectible perturbations in the signals received by coil  52 R. 
     When power is not actively being transmitted between equipment  12  and equipment  10 , foreign object detection signals from oscillator  70  may be maintained at a relatively low power. During active wireless power transfer operations, the power of the foreign object detection signals produced by oscillator  70  may be increased to help maintain a desired signal-to-noise ratio for foreign object detection operations. When power is not being wirelessly transferred, oscillator  70  may produce a first output power (e.g., foreign object detection circuitry  56  may operate in a low-signal or low-power foreign object detection mode). When power is being wirelessly transferred, oscillator  70  may produce a second output power that is greater than the first output power (e.g., foreign object detection circuitry  56  may operate in a high-signal or high power foreign object detection mode). 
     As shown in  FIG. 6 , the detected signals from coil  52 R may be filtered using filter  72  (e.g., to remove signals such as signals associated with wireless power transfer that do not correspond to foreign object detection signals). Filter  72  may be a passive filter to help ensure that filter  72  can withstand high voltages (e.g., 50 V peak-to-peak) that may be induced on coil  52 R during wireless power transfer operations. Filter  72  may be a notch filter, bandpass filter, or other suitable frequency-dependent filter that helps remove signals at the wireless power transfer frequency of system  8  (e.g., signals at 85 kHz as an example) or other noise signals and allows foreign object detection signals from coil  52 R to pass. Filter  74 , which may be, for example, an active filter that is characterized by a high Q factor, may be a bandpass filter that is aligned with the frequency of oscillator  70  (e.g., 355 kHz, etc.). Gain block  76  may strengthen the signal at the output of filter  74  and may provide this signal to mixing circuitry such as multipliers  78 I and  78 Q. 
     Multiplier  78 I may multiply the received signal from coil  52 R by the output of oscillator  70  to produce an in-phase signal I_signal on path  80 I. Multiplier  78 Q may multiply the received signal from coil  52 R by the output of oscillator  70  that has been shifted in phase by 90° using phase shifter  82  to produce a quadrature signal Q_signal on path  80 Q. Direct-current (DC) offset circuits  841  and  84 Q and summers  861  and  86 Q may be used to remove a DC offset from the signals on respective paths  80 I and  80 Q. The offset that is removed may be computed based on data gathered during precharacterization measurements, information on temperature drift, etc. 
     The presence of foreign objects may lead to differences in the signals on paths  80 I and  80 Q between different coils in the array. Overall changes in these signals may be a result of temperature drift or other signal drift. After removing offsets, low-pass filters  88 I and  88 Q may remove undesired AC signals on paths  861  and  86 Q (e.g., beat terms from the multiplication performed by multipliers  78 I and  78 Q) and gain blocks  90 I and  90 Q can strengthen these low-pass-filtered signals to produce corresponding in-phase and quadrature signals on outputs  92 I and  92 Q (signal I_out and signal Q_out, respectively). 
     The in-phase and quadrature output signals from foreign object detection circuitry  56  may be processed by control circuitry  34  and/or  14  and suitable action taken by control circuitry  34  and/or  14  based on these signals. For example, circuitry  34  and/or  14  may use components  36  and/or  16  to issue visual and/or audible alerts for a user or may produce other information that informs users of system  8  that foreign objects may be present and/or may take action such as shutting down wireless power transfer operations until the foreign object has been cleared from system  8 . 
     The operation of circuitry  56  of  FIG. 6  may be understood with reference to equations 1-6 of  FIG. 7 . Equations 1-3 show how in-phase signal I_signal on path  80 I and in-phase signal I′_signal at the output of low-pass filter  88 I may be produced using circuitry  56 . Equations 4-6 show how quadrature signal Q_signal on path  80 Q and quadrature signal Q′_signal at the output of low-pass filter  88 Q may be produced using circuitry  56 . 
     Term  94  in equation (1) represents the raw signal output from coil  52 R (coefficient A f  corresponds to deviations due to a foreign object present between coils  28 ′ and  24 ′) and term  96  (with coefficient A m ) is the output from oscillator  70  that is mixed with this raw signal output using multiplier  78 I. Term  98  of equation (2) corresponds to a DC signal produced by a foreign object on the foreign object detection coil array (e.g., array  28  or  24  of  FIG. 1 ). HF_noise represents a noise component (e.g., noise produced as a result of wireless power transmission operations, etc.). 
     Terms  96  of equation 2, which results from simplifying equation 1, may be removed using low-pass filter  88 I, thereby allowing term  98  of equation 2 to be extracted. The signal I′ signal at the output of low-pass filter  88 I is shown in equation 3. Term  100  of equation 3 corresponds to the contribution to I_signal from the foreign object. Term  102  of equation 3 corresponds to normal transmitter-receiver coupling through coils  52 T and  52 R. Terms  102  and  104  can be removed by adjustment of signal DC offset from circuit  841 . 
     Gain stage  90 I and analog-to-digital converter circuitry (e.g., an analog-to-digital converter with at least 10 bits of resolution or other suitable analog-to-digital converter circuitry) and processing circuitry (e.g., microprocessor circuitry) in control circuitry  14  and/or  34  can use the resulting in-phase signal I_out at output line  92 I and the corresponding quadrature signal Q_out that is produced at output line  92 Q in accordance with equations 4, 5, and 6. In particular, the control circuitry can use the I_out and Q_out signals to detect and analyze foreign objects. If desired, the I_out and Q_out signals may be analyzed by the control circuitry within a relatively short amount of time (e.g., less than 100 ms or other suitable time) to produce phase shift and magnitude information that provides insight into the metallurgy, shape, and size of the foreign object in real time, so that appropriate action can be taken (e.g., actions such as shutting off wireless power transmission to avoid undesirable eddy current heating in conductive foreign objects, alerting a user, etc.). 
     Detection circuitry  56  of  FIG. 6  may be systematically coupled to each of a number of different transmitting coils  52 T and each of a number of corresponding different receiving coils  52 R using switching circuitry such as switching circuitry  54  of  FIG. 2 . In this way, system  8  may step sequentially through each transmitting coil and each receiving coil in coil array  50  during foreign object detection operations, thereby avoiding the need to replicate circuitry  56  repeatedly to accommodate measurements with various different sets of coils. 
     Illustrative operations involved in using detection circuitry  56  of  FIG. 6  to monitor for foreign objects during use of system  8  are shown in  FIG. 8 . 
     During the operations of block  120 , wireless power transfer operations may be initiated. For example, a user command, a sensor output (e.g., the output of a proximity sensor), a signal from a wireless communications circuit, or other signal may indicate to control circuitry  14  and/or  34  that power receiving equipment  10  is in the vicinity of power transmitting equipment  12  and is ready to receive wireless power. 
     During the operations of block  122 , before power is wirelessly transmitted, control circuitry  34  and  14  may use arrays  28  and  24  to monitor for foreign objects in a low-power foreign object detection mode. In particular, detection circuitry such as circuitry  56  of  FIG. 6  may be used with array  28  and with array  24  to monitor for the presence of foreign objects, as described in connection with  FIGS. 6 and 7  while oscillator  70  and the other circuits of  FIG. 6  are operated at low powers. Frequency hopping and/or shifting may be used to help reduced interference. In-phase and quadrature signals may be gathered and processed in real time to determine whether a foreign object is present and, if present, to characterize the foreign object. As an example, a magnitude M that is equal to the square root of the in-phase signal squared plus the quadrature signal squared may be computed and this magnitude may be plotted as a function of phase shift. If the value of magnitude M is zero, it can be concluded that no foreign object is present. Magnetic objects (e.g., ferromagnetic objects) such as steel washers may be characterized by negative phase shifts. Conductive nonmagnetic objects may be characterized by positive phase shifts. During the operations of block  122 , information on phase shift, magnitude M, and other information associated with the in-phase and quadrature signals may be analyzed and used in monitoring for the presence of foreign objects and used in characterizing any foreign objects that are present. 
     In response to detection of a foreign object, appropriate action may be taken during the operations of block  124 . For example, system  8  may shut down wireless power transfer operations until the foreign object is cleared, may issue an alert to a user, or may take other suitable actions. 
     In response to determining that no foreign objects are present during the operations of block  122 , system  8  may wirelessly transfer power from equipment  12  to equipment  10 . During power transmission operations, transmitter  32  may wirelessly transmit power using one or more power transmitting coils  30  while power receiving circuitry such as rectifier  18  may use one or more power receiving coils  20  to receive the wirelessly transmitted power. As power is being transmitted in this way, foreign object detection circuitry  56  associated with coil array  28  and foreign object detection circuitry  56  associated with coil array  24  may be operated in a high power foreign object detection mode to monitor for the presence of foreign objects. 
     If a foreign object is detected during the operations of block  126 , suitable action may be taken at block  124  (e.g., wireless power transmission may be stopped, etc.). If no foreign objects are detected, wireless power transfer operations may continue until wirelessly transmitted power is no longer desired. For example, in a system such as system  8  of  FIG. 1 , wireless power transfer operations may continue until equipment  10  has recharged battery  22  and no longer is using the wirelessly transmitted power. In this type of scenario, wireless power transmission operations may be halted during the operations of block  128 . 
     If desired, wireless signals for foreign object detection may be transmitted using one or more power transmitting coil(s)  30  while circuitry  56  monitors corresponding received signals in coil array  50  (e.g., array  28  and/or array  24 ). Illustrative circuitry for this type of arrangement is shown in  FIG. 9 . As shown in  FIG. 9 , control circuitry  14  and/or  34  (e.g., inductive charger controller  150 ) may receive oscillator output signals from oscillator  70  and may use these signals in creating corresponding wireless power transmission signals with charging coil(s)  30  (e.g., transmitter circuitry in controller  150  such as transmitter  32  of  FIG. 1  may supply signals from oscillator  70  or may supply signals that are synchronized to the output of oscillator  70  to coil  30  so that coil  30  can use these signals to transmit corresponding wireless electromagnetic signals that are detected by array  50 ). The output of oscillator  70  may also be provided to multiplier  78 I and (via phase shifter  82 ) to multiplier  78 Q. Low-pass filters  88 I and  88 Q may then produce in-phase and quadrature signals on respective outputs  152 I and  152 Q for real-time analysis by control circuitry  14  and/or  34  as described in connection with  FIG. 6 . 
     Regardless of whether oscillator  70  of the circuitry of  FIG. 9  uses coil  30  to transmit electromagnetic signals for detection by the foreign object detection coil array or whether oscillator  70  of the circuitry of  FIG. 6  uses transmitting coil  52 T in the foreign object detection coil array to transmit electromagnetic signals for detection by the foreign object detection coil array, control circuitry  14  and/or  34  may be configured to process the resulting in-phase and quadrature signals that are detected by circuitry  56  to identify signal characteristics that are indicative of the presence of foreign objects. The control circuitry of system  8  may, as an example, make measurements from a series of coils  52  at different lateral positions and can analyze these measurements to identify signal peak(s) indicative of the presence of foreign objects. As an example, the control circuitry may use the in-phase and/or quadrature signals to produce a graph of the type shown in  FIG. 10  in which signal strength (e.g., quadrature signal Q or other suitable measured signal) is plotted as a function of lateral position X across the foreign object detection coil array. Analyzing curve  200  of  FIG. 10 , the control circuitry can identify signal peaks such as signal peak  202  that is indicative of the presence of a foreign object at a corresponding X location within the foreign object detection coil array. 
     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: 20171117
Publication Date: 20201013
Grant Date: 20201013
Priority Date: 20161214
Inventors: WU, Hunter H.
LU, ANLANG
PIERQUET, BRANDON
JADIDIAN, Jouya
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2885", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2885", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 62490396