Resonance tuning

• US 9,203,380 B2
• Filed: 05/27/2011
• Issued: 12/01/2015
• Est. Priority Date: 12/29/2010
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Choudhary, Vijay N., Loke, Robert
• Primary Examiner(s): Barnie, Rexford
• Assistant Examiner(s): Kessie, Daniel
• Application Number:
  US13/117,186
• Publication Number:
  US 20120169132A1
• Time in Patent Office: 1,649 Days
• Field of Search: 307/104
• US Class Current: 1/1
• CPC Class Codes: H03J 1/0091 provided with means for scanning over a band of frequencies H03J1/0058 takes precedence

Abstract

One heuristic for tuning a wireless power transfer device includes monitoring a circuit parameter while sweeping a power source frequency; identifying two frequencies related to local maxima of the circuit parameter values; estimating self-resonant frequency of an electromagnetically coupled device based on the two frequencies; determining a value for a tuning component of the wireless power transfer device such that the device self-resonant frequency equals the estimated coupled device self-resonant frequency; and adjusting the tuning component to the determined value.

Another tuning heuristic includes monitoring a circuit parameter while sweeping the power source frequency; identifying two frequencies related to two local maximum for the values of the circuit parameter; determining a desired resonance frequency for the wireless power transfer device based on stored information; and adjusting the tuning component to a value that causes the wireless power transfer device when uncoupled to operate at or near the desired resonance frequency.

Claims

1. A method suitable for wireless power transfer between a wireless power transfer device coupled to an alternating current (AC) power source, and a wireless power receiver device, each device including a series resonator with a resonator capacitor in series with a resonator power transfer coil that establish a self-resonant frequency, the wireless power transfer device including a series resonator in which the resonator capacitor is an adjustable tuning capacitor with an adjustable tuning capacitance C_A, comprising:

establishing an initial self-resonant frequency fA for the power transfer device based on an initial capacitance value C_A for the adjustable tuning capacitor;

coupling the power transfer device and the power receiver device;

iteratively adjusting self-resonant frequency fA for the power transfer device by iteratively adjusting capacitance C_A for the tuning capacitor based on iteratively estimating a self-resonant frequency fB of the power receiver device by;

sweeping the frequency of the AC power source in discrete frequency steps, and in each frequency step, monitoring a circuit parameter of the power transfer device;

identifying a first local maximum and a second local maximum for the values of the circuit parameter corresponding to two resonant modes of the coupled devices;

ascertaining a first frequency and a second frequency corresponding to the first and second local maxima, respectively;

estimating a self-resonant frequency fB_est of the power receiver device based on the first and second frequencies;

determining whether (fA−

fB_est) is different than a threshold value, and if yes, then

adjusting the tuning capacitance C_A so that fA is substantially equal to fB_est; and

iteratively performing a next estimation for a next estimated self-resonant frequency fB_est;

if (fA−

fB_est) is not different than the threshold, then transferring power between Dower transfer device and the power receiver device.

2. The method of claim 1, the circuit parameter being current provided by the power source.

3. The method of claim 1, the circuit parameter being voltage across the terminals of the power source.

4. The method of claim 1, the circuit parameter being voltage across the power transfer coil on the wireless power transfer device resonator.

5. The method of claim 1, the circuit parameter being voltage across a capacitor in a resonance circuit of the wireless power transfer device.

6. The method of claim 1, wherein estimating the self-resonant frequency fB of the wireless power receiver device is based on fB=m*f1+n*f2, wherein fB_est is the estimated self-resonant frequency of the power receiver device, f1 is the first frequency, f2 is the second frequency, and m and n are variables.

7. The method of claim 1, wherein adjusting the tuning capacitance C_A so that fA is substantially equal to fB_est is accomplished by calculating a value of the tuning capacitance C_A such that the power transfer device is self-resonant at fA=fB_est, and adjusting C_A to the calculated value.

8. The method of claim 1, wherein adjusting the tuning capacitance C_A so that fA is substantially equal to fB_est is accomplished by:

determining a value of the tuning capacitance C_A by;

uncoupling the power transfer device from the power receiver device;

setting the frequency of the AC power source to fB_est;

sweeping the frequency of the AC power source in discrete steps, and, for each discrete frequency step, monitoring a circuit parameter; and

determining a maximum value for the monitored parameter;

adjusting C_A to the value corresponding to the maximum value of the monitored parameter; and

coupling the power transfer device to the power receiver device.

9. The method of claim 1, wherein establishing an initial self-resonant frequency fA for the power transfer device based on an initial capacitance value C_A for the adjustable tuning capacitor comprises:

uncoupling the power transfer device from the power receiver device;

sweeping the frequency of the AC power source in discrete frequency steps, and for each discrete frequency step, monitoring a circuit parameter;

determining a maximum value for the monitored parameter; and

establishing an initial self-resonant frequency fA for the power transfer device as a frequency corresponding to the maximum value for the monitored parameter.