Method and system for performing foreign object detection in an inductive wireless power transfer system

• US 9,474,031 B1
• Filed: 04/16/2015
• Issued: 10/18/2016
• Est. Priority Date: 04/16/2015
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Niessen, Patrick, Sedzin, Aliaksei Vladimirovich, Brink, Klaas, Geraets, Rene, Moonen, Oswald
• Primary Examiner(s): Sorowar, Golam
• Application Number:
  US14/688,886
• Publication Number:
  US 20160309418A1
• Time in Patent Office: 551 Days
• US Class Current: 1/1
• 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: H04B 5/263 Multiple coils at either side
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer
• CPC Class Codes: H04W 52/243 taking into account interferences

Abstract

A method for performing foreign object detection in an inductive wireless power transfer system is disclosed. In the embodiment, the method involves obtaining measurements from a base station of a wireless power transfer system during charging and determining transmitter energy loss in a power transmitter, P_txloss, using the obtained measurements, wherein the transmitter energy loss, P_txloss, is a function of at least V_cap and P_Tx, wherein V_cap is proportional to the voltage amplitude across the capacitor of an LC tank circuit in a power transmitter and P_Tx is the total power supplied to the power transmitter. The method also involves detecting the presence of a foreign object in response to the estimated transmitter energy loss.

Claims

1. A method for performing foreign object detection in an inductive wireless power transfer system, the method comprising:

obtaining measurements from a base station of a wireless power transfer system during charging;

determining transmitter energy loss in a power transmitter, P_txloss, using the obtained measurements, wherein the transmitter energy loss, P_txloss, is a function of at least V_cap and P_Tx,

wherein V_cap is proportional to the voltage amplitude across the capacitor of an LC tank circuit in a power transmitter and P_Tx is a total power supplied to the power transmitter, and wherein P_txloss is determined using a two variable model defined by an equation a*V_cap²+b*P_Tx+c, wherein V_cap and P_Tx are the measurements obtained from the base station of the wireless power transfer system; and

detecting the presence of a foreign object in response to the transmitter energy loss.

2. The method of claim 1, wherein the two-variable model is generated by:

obtaining measurements of the wireless power transfer system in various operating conditions;

generating data points based on the measurements; and

performing curve fitting on the generated data points to generate the predetermined coefficients of the two-variable model.

3. The method of claim 1, further comprising performing a curve fitting by deriving values for the coefficients of the two-variable model such that the resulting curve has a root mean square error value equal to sixty mW or less.

4. The method of claim 1, wherein the presence of a foreign object is detected if P_fo exceeds a certain threshold when using the value of P_txloss to solve for P_fo using the equation:

P_Tx=P_txloss+P_fo+(P_rxloss+P_rxload)

where P_Tx represents the total power supplied to the power transmitter, P_txloss represents the losses in the power transmitter itself, P_fo represents a power dissipation in a foreign object, P_rxloss represents power losses in the power receiver, and P_rxload represents a net power delivered to a load.

5. The method of claim 4, wherein the threshold is within 10% of 300 mW.

6. The method of claim 1, wherein at least one of the coefficients of the two-variable model is adjusted based on the type of a coil within of the transmitter.

7. The method of claim 1, wherein the inductive wireless power transfer system is comprised of a Qi transmitter.

8. The method of claim 1, wherein the coefficients b and c are fixed in firmware of the wireless power transfer system.

9. The method of claim 1, wherein V_cap is a peak voltage over a capacitor within the power transmitter.

10. An inductive wireless power transfer system, the inductive wireless power transfer system comprising:

a base station comprising;

a system unit;

at least one power transmitter coupled to the system unit, the at least one power transmitter having a power conversion unit and a communications and a control unit;

wherein the inductive wireless power transfer system is configured to perform foreign object detection, foreign object detection comprising;

obtaining measurements from a base station of a wireless power transfer system during charging;

determining transmitter energy loss in a power transmitter, P_txloss, using the obtained measurements, wherein the transmitter energy loss, P_txloss, is a function of at least V_cap and P_Tx,

wherein V_cap is proportional to the voltage amplitude across the capacitor of an LC tank circuit in a power transmitter and P_Tx is a total power supplied to the power transmitter, and wherein P_txloss is determined using a two variable model defined by an equation a*V_cap²+b*P_Tx+c wherein V_cap and P_Tx are the measurements obtained from the base station of the wireless power transfer system; and

detecting the presence of a foreign object in response to the transmitter energy loss.

11. The system of claim 10, wherein the two-variable model is generated by:

obtaining measurements of the wireless power transfer system in various operating conditions;

generating data points based on the measurements; and

performing curve fitting on the generated data points to generate the two-variable model.

12. The system of claim 10, wherein foreign object detection further comprises performing a curve fitting by deriving values for the coefficients of the two-variable model such that the resulting curve has a root mean square error value equal to sixty mW or less.

13. The system of claim 10, wherein the presence of a foreign object is detected if P_fo exceeds a certain threshold when using the value of P_txloss to solve for P_fo using the equation:

P_Tx=P_txloss+P_fo+(P_rxloss+P_rxload)

where P_Tx represents the total power supplied to the power transmitter, P_txloss represents the losses in the power transmitter itself, P_fo represents the power dissipation in a foreign object, P_rxloss represents the power losses in the power receiver, and P_rxload represents the net power delivered to the load.

14. The system of claim 13, wherein the threshold is within 10% of 300 mW.

15. The system of claim 10, wherein the inductive wireless power transfer system is comprised of a Qi transmitter.

16. The system of claim 10, wherein the coefficients b and c are fixed in firmware of the wireless power transfer system.

17. A non-transitory computer-readable storage medium storing instructions to be executed by a computerized system for:

obtaining measurements from a base station of a wireless power transfer system during charging;

determining transmitter energy loss in a power transmitter, P_txloss, using the obtained measurements, wherein the transmitter energy loss, P_txloss, is a function of at least V_cap and P_Tx,

wherein V_cap is proportional to the voltage amplitude across the capacitor of an LC tank circuit in a power transmitter and P_Tx is a total power supplied to the power transmitter, and wherein P_txloss is determined using a two variable model defined by an equation a*V_cap²+b*P_Tx+c wherein V_cap and P_Tx are the measurements obtained from the base station of the wireless power transfer system; and

detecting the presence of a foreign object in response to the transmitter energy loss.