Foreign Object Detection in Inductive Coupled Devices

• US 20110128015A1
• Filed: 10/29/2010
• Published: 06/02/2011
• Est. Priority Date: 11/03/2009
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Kumar, Rajeev, Ganguly, Surabhi, Dorairaj, Hariharakumaran
• Granted Patent: US 8,575,944 B2
• Time in Patent Office: Days
• US Class Current: 324/629
• CPC Class Codes: G01V 3/101 by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil measuring impedance or characteristics derived therefrom G01R27/00, e.g. quality factor G01R27/26
• CPC Class Codes: H02J 50/10 using inductive coupling
• 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 7/00712 the cycle being controlled or terminated in response to electric parameters

Abstract

A primary device for inductive power transfer to a secondary device is disclosed. The primary device includes a primary coil, the primary device being configured to (i) operate in a first mode during which the primary coil transfers power through inductive coupling to the secondary device, and (ii) operate in a second mode during which a foreign object is detected. The primary device further includes a primary controller configured to operate the primary coil (i) using a first frequency during the first mode, and (ii) using a second frequency during the second mode. A method to detect a foreign object which is in proximity of an inductively coupled environment of a primary device is also disclosed.

Claims

1. A primary device for inductive power transfer to a secondary device, the primary device comprising:

a primary coil, the primary device being configured to (i) operate in a first mode during which the primary coil transfers power through inductive coupling to the secondary device, and (ii) operate in a second mode during which a foreign object is detected; and

a primary controller configured to operate the primary coil (i) using a first frequency during the first mode, and (ii) using a second frequency during the second mode.

2. A primary device according to claim 1 wherein the primary controller is configured to select the first frequency based upon feedback from the secondary device.

3. A primary device according to claim 1 wherein the primary device is configured to transfer power during the first mode from the primary device to the secondary device to charge the load.

4. A primary device according to claim 1 wherein the primary device is configured to measure a primary current in the primary device during the second mode to detect presence or absence of a foreign object.

5. A primary device according to claim 1 wherein the second frequency corresponds to a point where a first current curve corresponding to a minimum air gap between the primary device and the secondary device meets a second current curve corresponding to a maximum air gap between the primary device and the secondary device.

6. A primary device according to claim 5 wherein the current corresponding to the point is used as a threshold to compare with the input current in the primary device to determine whether the foreign object is within the proximity of the primary device.

7. A method to detect a foreign object which is in proximity of an inductively coupled environment of a primary device, comprising:

connecting a load to a secondary device and operating a primary coil of the primary device using a first frequency during a power transfer mode;

disconnecting the load from the secondary device and operating the primary coil using a second frequency during a measurement mode, the second frequency being the point where a first current curve corresponding to a minimum air gap between the primary device and the secondary device meets a second current curve corresponding to a maximum air gap between the primary device and the secondary device;

measuring the primary current during the measurement mode so as to sense a measured current; and

detecting whether a foreign object is present by comparing the measured current with a set threshold.

8. A method to detect a foreign object according to claim 7 wherein the first frequency is selected based on feedback from the secondary device.