In situ coil parameter measurements and foreign objects detection

• US 10,581,281 B2
• Filed: 10/19/2016
• Issued: 03/03/2020
• Est. Priority Date: 10/23/2015
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Muratov, Vladimir A.
• Primary Examiner(s): Fleming, Fritz M
• Application Number:
  US15/297,226
• Publication Number:
  US 20170117756A1
• Time in Patent Office: 1,231 Days
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• 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 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/00034 Charger exchanging data with an electronic device, i.e. telephone, whose internal battery is under charge

Abstract

A foreign object detection method and apparatus for performing same. A wireless power transmitter has a matching network and transmit coil. The method includes, stimulating the transmit coil with electrical signals at a plurality of frequencies, measuring a response of the transmit coil to the electrical signals, determining a quality factor and/or resonant frequency of the transmit coil based upon the measured response, and analyzing the quality factor and/or resonant frequency to determine whether a foreign object is coupled to an electromagnetic field generated by the transmit coil.

Claims

1. A foreign object detection method for a wireless power transmitter having a matching network and transmit coil, the method comprising:

(A) stimulating the transmit coil with electrical signals at a plurality of frequencies;

(B) measuring a response of the transmit coil to the electrical signals;

(C) determining a quality factor and/or resonant frequency of the transmit coil based upon the measured response; and

(D) analyzing the quality factor and/or resonant frequency to determine whether a foreign object is coupled to an electromagnetic field generated by the transmit coil,

wherein the wireless power transmitter energizes the transmit coil sufficiently to charge a capacitor of a rectifier of a wireless power receiver to reverse-bias diodes of the rectifier prior to measuring the response of the transmit coil.

2. The foreign object detection method of claim 1, wherein the plurality of frequencies comprises no more than ten frequencies.

3. The foreign object detection method of claim 2, wherein the plurality of frequencies comprises no more than five frequencies.

4. The foreign object detection method of claim 1, wherein the plurality of frequencies are between 0.5 and 1.5 times an anticipated resonant frequency of the transmit coil.

5. The foreign object detection method of claim 1, wherein the plurality of frequencies are between 0.9 and 1.1 times an anticipated resonant frequency of the transmit coil.

6. The foreign object detection method of claim 1, wherein at least one of the frequency of the plurality of frequencies is determined adaptively based upon a measured response at one or more other frequencies.

7. The foreign object detection method of claim 1, wherein at least one first frequency of the plurality of frequencies is below a resonant frequency of the transmit coil and at least one second frequency of the plurality of frequencies is above the resonant frequency of the transmit coil.

8. The foreign object detection method of claim 1, further comprising calculating a first estimate of a resonant frequency of the transmit coil based on a first plurality of measurements, calculating a second estimate of the resonant frequency of the transmit coil based on a second plurality of measurements, and comparing the first and second estimates.

9. The foreign object detection method of claim 1, wherein (B) comprises measuring a voltage of the transmit coil, a voltage of the matching network, a current of the transmit coil and/or a current of the matching network.

10. The foreign object detection method of claim 1, wherein (C) comprises fitting a quality factor curve to measurement values produced in (B) at different frequencies.

11. The foreign object detection method of claim 1, wherein (D) comprises comparing the quality factor and/or the resonant frequency to an acceptable quality factor and/or resonant frequency for wireless power transmission.

12. The foreign object detection method of claim 1, wherein the acceptable quality factor and/or resonant frequency is at least in part derived from a quality factor value and/or resonant frequency value provided to the wireless power transmitter by a wireless power receiver via in-band or out-of-band communication.

13. The foreign object detection method of claim 1, wherein in (A) the transmit coil is stimulated at a level below that which is necessary to transmit wireless power to a wireless power receiver.

14. At least one non-transitory computer readable storage medium having stored thereon instructions, which, when executed by a processor, perform a foreign object detection method for a wireless power transmitter having a matching network and transmit coil, the method comprising:

(A) stimulating the transmit coil with electrical signals at a plurality of frequencies;

(B) measuring a response of the transmit coil to the electrical signals;

(C) determining a quality factor and/or resonant frequency of the transmit coil based upon the measured response; and

(D) analyzing the quality factor and/or resonant frequency to determine whether a foreign object is coupled to an electromagnetic field generated by the transmit coil,

wherein the wireless power transmitter energizes the transmit coil sufficiently to charge a capacitor of a rectifier of a wireless power receiver to reverse-bias diodes of the rectifier prior to measuring the response of the transmit coil.

15. An apparatus that performs foreign object detection, the apparatus comprising:

a probing circuit configured to stimulate a transmit coil with electrical signals at a plurality of frequencies and measure the response of the transmit coil to the electrical signals; and

a controller configured to determine a quality factor and/or resonant frequency of the transmit coil based upon the measured response and analyze the quality factor and/or resonant frequency to determine whether a foreign object is coupled to an electromagnetic field generated by the transmit coil,

wherein the probing circuit is configured to energize the transmit coil sufficiently to charge a capacitor of a rectifier of a wireless power receiver to reverse-bias diodes of the rectifier prior to measuring the response of the transmit coil.

16. The apparatus of claim 15, wherein the probing circuit comprises a voltage sensor, a current sensor, or both a voltage sensor and a current sensor.

17. The apparatus of claim 15, wherein the probing circuit comprises a charge pump.

18. The apparatus of claim 15, wherein the plurality of frequencies comprises no more than ten frequencies.

19. The apparatus of claim 15, wherein the plurality of frequencies are between 0.5 and 1.5 times a resonant frequency of the transmit coil.

20. The apparatus of claim 15, wherein the controller is configured to adaptively determine at least one of the plurality of frequencies based upon a measured response at one or more other frequencies.

21. The apparatus of claim 15, wherein at least one first frequency of the plurality of frequencies is below a resonant frequency of the transmit coil and at least one second frequency of the plurality of frequencies is above the resonant frequency of the transmit coil.

22. The apparatus of claim 15, wherein the controller is configured to fit a quality factor curve to measurement values produced at different frequencies.