Foreign object detection in wireless energy transfer systems

• US 10,063,110 B2
• Filed: 10/19/2016
• Issued: 08/28/2018
• Est. Priority Date: 10/19/2015
• Status: Active Grant

Abstract

The disclosure features wireless energy transfer systems that include a plurality of sensors coupled to a controller, wherein the controller is configured to: obtain a system calibration state including a set of basis vectors derived from a first set of electrical signals generated by the plurality of sensors with no foreign object debris in proximity to the system; measure a second set of electrical signals from the sensors; calculate a projection of the second set of electrical signals onto the set of basis vectors; calculate a detection signal based on the projection; determine whether foreign object debris is present in proximity to the system by comparing the calculated detection signal to a detection threshold value; and adjust the system calibration state based on the presence or absence of foreign object debris in proximity to the system to generate an updated system calibration state.

Claims

1. A wireless energy transfer system, comprising:

a source resonator configured to generate an oscillating magnetic field to transfer energy to a receiver resonator;

a plurality of sensors, wherein each of the sensors is configured to generate an electrical signal in response to a magnetic field; and

a controller coupled to each of the sensors,

wherein during operation of the system, the controller is configured to;

obtain a system calibration state comprising a set of basis vectors derived from a first set of electrical signals generated by the plurality of sensors with no foreign object debris in proximity to the system;

measure a second set of electrical signals generated by the plurality of sensors;

calculate a projection of the second set of electrical signals onto the set of basis vectors;

calculate a detection signal based on the projection of the second set of electrical signals;

determine whether foreign object debris is present in proximity to the system by comparing the calculated detection signal to a detection threshold value; and

adjust the system calibration state based on the presence or absence of foreign object debris in proximity to the system to generate an updated system calibration state.

2. The system of claim 1, wherein the controller is configured to obtain the system calibration state by:

determining an inverse covariance matrix for the first set of electrical signals; and

determining the set of basis vectors by determining a set of eigenvectors of the inverse covariance matrix.

3. The system of claim 2, wherein the controller is configured to determine the inverse covariance matrix based on mean-subtracted values derived from the first set of electrical signals.

4. The system of claim 3, wherein values comprise at least one of amplitudes of the first set of electrical signals and phases of the first set of electrical signals.

5. The system of claim 1, wherein the plurality of sensors comprises n sensors, and wherein each of the basis vectors comprises n elements.

6. The system of claim 5, wherein for each basis vector, each of the n elements corresponds to a contribution from a different one of the n sensors.

7. The system of claim 5, wherein the projection comprises a vector of length p<

n, and wherein each element of the projection corresponds to a contribution of a different one of the basis vectors to a representation of the second set of electrical signals.

8. The system of claim 7, wherein the controller is configured to calculate the detection signal as a norm of the projection.

9. The system of claim 7, wherein the controller is configured to calculate the detection signal as a scaled norm of the projection in which each element of the projection is scaled according an eigenvalue associated with a corresponding one of the basis vectors.

10. The system of claim 2, wherein the controller is configured to adjust the system calibration state when foreign object debris is not in proximity to the system.

11. The system of claim 10, wherein the controller is configured to adjust the system calibration state by generating an updated inverse covariance matrix based on the second set of electrical signals.

12. The system of claim 11, wherein the controller is configured to generate the updated inverse covariance matrix using an infinite impulse response filter.

13. The system of claim 1, wherein prior to obtaining the system calibration state, the controller is configured to determine whether foreign object debris is present in proximity to the system.

14. The system of claim 13, wherein the controller is configured to determine whether foreign object debris is present in proximity to the system prior to obtaining the system calibration state by:

measuring a plurality of sets of electrical signals generated by the plurality of sensors, wherein each set of electrical signals corresponds to a different relative position of the source and receiver resonators;

generating a position covariance matrix based on the plurality of sets of electrical signals;

determining a set of position basis vectors corresponding to eigenvectors of an inverse of the position covariance matrix;

measuring a third set of electrical signals generated by the plurality of sensors;

calculating a projection of the third set of electrical signals onto the set of position basis vectors; and

determining whether foreign object debris is present in proximity to the system based on a magnitude of the projection of the third set of electrical signals.

15. The system of claim 14, wherein the set of position basis vectors corresponds to a set of m eigenvectors of the inverse of the position covariance matrix that correspond to m largest eigenvalues of the inverse of the position covariance matrix.

16. The system of claim 1, wherein obtaining the system calibration state comprises retrieving the system calibration state from an electronic storage medium.

17. The system of claim 1, wherein obtaining the system calibration state comprises:

determining an inverse covariance matrix for the first set of electrical signals;

determining a set of eigenvectors of the inverse covariance matrix; and

determining the set of basis vectors from the eigenvectors of the inverse covariance matrix.

18. A method, comprising:

determining a system calibration state comprising an inverse covariance matrix for a first set of electrical signals generated by a plurality of sensors in proximity to a wireless energy transfer system when no foreign object debris is in proximity to the wireless energy transfer system;

determining a set of basis vectors from eigenvectors of the inverse covariance matrix;

measuring a second set of electrical signals generated by the plurality of sensors;

calculating a detection signal based on a projection of the second set of electrical signals onto the set of basis vectors;

determining whether foreign object debris is present in proximity to the wireless energy transfer system by comparing the calculated detection signal to a detection threshold value; and

adjusting the system calibration state based on the presence or absence of foreign object debris in proximity to the system to generate an updated system calibration state.

19. The method of claim 18, further comprising determining the inverse covariance matrix based on values derived from the first set of electrical signals, wherein the values comprise at least one of amplitudes of the first set of electrical signals and phases of the first set of electrical signals.

20. The method of claim 18, wherein:

the plurality of sensors comprises n sensors;

each of the basis vectors comprises n elements each corresponding to a contribution from a different one of the n sensors;

the projection comprises a vector of length p<

n;

each element of the projection corresponds to a contribution of a different one of the basis vectors to a representation of the second set of electrical signals.