Apparatus, system, and method for detecting a foreign object in an inductive wireless power transfer system via coupling coefficient measurement

• US 9,551,805 B2
• Filed: 03/30/2012
• Issued: 01/24/2017
• Est. Priority Date: 10/13/2011
• Status: Active Grant

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Inventors: Singh, Manjit
• Primary Examiner(s): Fureman, Jared
• Assistant Examiner(s): Perez Borroto, Alfonso
• Application Number:
  US13/435,996
• Publication Number:
  US 20130257165A1
• Time in Patent Office: 1,761 Days
• Field of Search: 307/104, 320/108
• US Class Current: 1/1
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/60 responsive to the presence of foreign objects, e.g. detection of living beings
• CPC Class Codes: H02J 50/80 involving the exchange of data, concerning supply or distribution of electric power, between transmitting devices and receiving devices
• CPC Class Codes: H02J 50/90 involving detection or optimisation of position, e.g. alignment

Abstract

An inductive wireless power device comprises a transmitter configured to generate an electromagnetic field to a coupling region for wireless power transfer to a receiver, and control logic configured to determine a coupling coefficient of the wireless power transfer when the receiver is within the coupling region. The control logic also determines a presence of a foreign object within the coupling region responsive to a comparison of the determined coupling coefficient and an expected coupling coefficient for the wireless power transfer. An inductive wireless power device comprises a receiver configured to couple with an electromagnetic field in a coupling region for inductive wireless power transfer from a transmitter. The receiver is configured to alter a wireless power transfer characteristic of the transmitter for a determination of a presence of a foreign object within the coupling region responsive to a determination of a coupling coefficient of the wireless power transfer.

Claims

1. An inductive wireless power device, comprising:

a transmitter configured to generate an electromagnetic field to a coupling region for wireless power transfer to a receiver;

a predefined coupling coefficient for the wireless power transfer; and

a control logic configured to determine a coupling coefficient of the wireless power transfer when the receiver is within the coupling region by detecting a change in a wireless power transfer characteristic caused by the receiver at a first time and a second time, and to determine a presence of a foreign object within the coupling region responsive to a comparison of the determined coupling coefficient and the predefined coupling coefficient for the wireless power transfer.

2. The inductive wireless power device of claim 1, wherein the control logic is configured to determine that the foreign object is present within the coupling region when the determined coupling coefficient is by a predetermined threshold below the predefined coupling coefficient.

3. The inductive wireless power device of claim 2, wherein the predetermined threshold is determined as a percentage of the predefined coupling coefficient.

4. The inductive wireless power device of claim 2, wherein the predetermined threshold is determined as a difference of the predefined coupling coefficient and the determined coupling coefficient.

5. The inductive wireless power device of claim 1, further comprising a power sense element coupled to a transmit coil of the transmitter and to the control logic, the power sense element configured to measure power components of the transmit coil of the transmitter, and to send the measured power components to the control logic, wherein the coupling coefficient is based, at least in part, on the power components.

6. The inductive wireless power device of claim 5, wherein the measured power components includes a voltage across the transmit coil and a current flowing through the transmit coil.

7. The inductive wireless power device of claim 5, wherein the coupling coefficient is determined as approximately √

(1-R_S1CLOSED/R_S1OPEN)), wherein R_S1CLOSED is a resistance of the transmit coil during the first time, and R_S1OPEN is a resistance of the transmit coil during the second time.

8. The inductive wireless power device of claim 5, wherein the control logic is configured to compare the power components of the transmit coil at the first time when a receiver coil of the receiver is in a shorted state through a path parallel to the receiver coil, and at the second time when the receiver coil of the receiver is not in the shorted state.

9. An inductive wireless power device, comprising a receiver configured to couple with an electromagnetic field in a coupling region for inductive wireless power transfer from a transmitter, wherein the receiver includes a receive coil configured to generate an AC signal responsive to coupling with the electromagnetic field, wherein the receiver is configured to alter a wireless power transfer characteristic of the transmitter by shorting the receive coil through a path parallel to the receiver coil at a first time, and to not short the receive coil at a second time, wherein shorting the receive coil through the path parallel to the receiver coil includes directly connecting across the receive coil.

10. The inductive wireless power device of claim 9, wherein the receiver further comprises a switch coupled in parallel with the receive coil, such that enablement of the switch shorts the receive coil through the path, wherein the receiver is configured to enable the switch at the first time and disable the switch at the second time.

11. The inductive wireless power device of claim 10, wherein the receiver further comprises a rectifier configured to convert the AC signal from the receive coil to a DC signal to be output to a load.

12. The inductive wireless power device of claim 11, wherein the rectifier is a synchronous rectifier including a plurality of switches for converting the AC signal to the DC signal to be output to the load.

13. The inductive wireless power device of claim 12, wherein the switch coupled parallel with the receive coil for altering the wireless power transfer characteristic of the transmitter is one plurality of switches of the rectifier used for converting the AC signal to the DC signal to be output to the load.

14. The inductive wireless power device of claim 11, wherein the switch coupled parallel with the receive coil for altering the wireless power transfer characteristic of the transmitter is separate from the rectifier used for converting the AC signal to the DC signal to be output to the load.

15. An inductive wireless power transfer system, comprising:

a wireless power transmitting apparatus configured to generate an electromagnetic field in a coupling region for wireless power transfer;

a predefined coupling coefficient for the wireless power transfer; and

a wireless power receiving apparatus configured to couple with the electromagnetic field and generate an output signal in response thereto and to alter a wireless power transfer characteristic of the wireless power transmitting apparatus at a first time and a second time by shorting across a receive coil of the wireless power receiving apparatus at the first time and not shorting across the receive coil at the second time, wherein at least one of the wireless power transmitting apparatus and the wireless power receiving apparatus is configured to determine a coupling coefficient by a first comparison of the wireless power transfer characteristic at the first time and the second time, and determining the presence of a foreign object within the coupling region based, at least in part, on a second comparison of the coupling coefficient for the wireless power transfer between the wireless power transmitting apparatus and the wireless power receiving apparatus, and the predefined coupling coefficient for the wireless power transfer, wherein shorting across the receive coil includes directly connecting across the receive coil.

16. The inductive wireless power transfer system of claim 15, wherein the wireless power receiving apparatus includes a mobile electronic device.

17. The inductive wireless power transfer system of claim 15, wherein the wireless power transmitting apparatus includes control logic configured to compare the determined coupling coefficient to a predetermined threshold to determine the presence of the foreign object.

18. The inductive wireless power transfer system of claim 17, wherein the predetermined threshold is relative to an expected coupling coefficient for a fixed distance between the wireless power transmitting apparatus and the wireless power receiving apparatus.

24. The inductive wireless power transfer system of claim 15, wherein the coupling coefficient is determined as approximately √

(1-R_S1CLOSED/R_S1OPEN)), wherein R_S1CLOSED is a resistance of the transmit coil of the wireless power transmitting apparatus during the first time, and R_S1OPEN is a resistance of the transmit coil of the wireless power transmitting apparatus during the second time.

19. A method for detecting a foreign object in a coupling region of an inductive wireless power transfer system, the method comprising:

determining a predefined coupling coefficient for the inductive wireless power transfer system;

detecting a change in an inductive wireless power transfer characteristic of a transmitter caused by a receiver at a first time and a second time, wherein the receiver shorts across a receiver coil at the first time and provides no short across the receiver coil at the second time;

determining a coupling coefficient for wireless power transfer between the transmitter and the receiver based on the change; and

determining a presence of a foreign object based, at least in part, on a comparison of the determined coupling coefficient and the predefined coupling coefficient.

20. The method of claim 19, further comprising taking an action on the inductive wireless power transfer system in response to determining the presence of the foreign object.

21. The method of claim 20, wherein the action is at least one of reducing the wireless power transfer, disabling wireless power transfer, and notifying a user that the foreign object is present within the coupling region.

22. A method for altering a wireless power transfer characteristic of a wireless power transmitter for a determination of a presence of a foreign object within a coupling region of a wireless power transfer system based on a first state of a wireless power transfer characteristic and a second state of the wireless power transfer characteristic, the method comprising:

determining a predefined coupling coefficient for the inductive wireless power transfer system;

shorting a receive coil of a receiver by directly connecting across the receive coil in a path parallel with the receive coil at a first time for a wireless power transmitter to determine a wireless power transfer characteristic in the first state; and

operating the receive coil of the receiver in a non-shorted state for the wireless power transmitter to determine the wireless power transfer characteristic in the second state;

determining a coupling coefficient for wireless power transfer between the transmitter and the receiver based at least on the first state of the wireless power transfer characteristic and the second state of the wireless power transfer characteristic;

determining the presence of a foreign object based, at least in part, on a comparison of the determined coupling coefficient and the predefined coupling coefficient.

23. The method of claim 22, wherein shorting the receive coil includes closing a switch coupled in parallel with the receive coil, and wherein operating the receive coil in the non-shorted state includes opening the switch.