Resonance tuning

• US 10,141,749 B2
• Filed: 11/30/2015
• Issued: 11/27/2018
• 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): Kessie, Daniel
• Application Number:
  US14/954,501
• Publication Number:
  US 20160141889A1
• Time in Patent Office: 1,093 Days
• Field of Search: 307104
• 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 wireless power transfer device, comprising:

power transfer terminals for coupling to a power transfer resonator external to the device, the resonator including;

a resonator power transfer coil, and

a resonator tuning capacitor with an adjustable tuning capacitance C_A,

the power transfer resonator having a self-resonant frequency controllable based on adjusting C_A;

a variable converter circuit to generate a variable alternating current voltage Vac and adjustable tuning signals to adjust adjustable tuning capacitance C_A, output through the power transfer terminals, corresponding to the controllable self-resonant frequency of the power transfer resonator;

the variable converter circuit operable, when the power transfer device is magnetically coupled through the power transfer resonator to a power receiver device with a power receiver resonator, to;

output through the power transfer terminals an initial Vac corresponding to an initial self-resonant frequency fA for the power transfer resonator, based on an initial capacitance value C_A for the adjustable tuning capacitor;

iteratively adjust Vac to control the self-resonant frequency fA for the power transfer resonator, including iteratively adjusting capacitance C_A for the resonator tuning capacitor, based on iteratively estimating a self-resonant frequency fB of the power receiver device, by;

sweeping the frequency of Vac in discrete frequency steps, and in each frequency step, monitoring a circuit parameter of the variable converter circuit,

identifying a first local maximum and a second local maximum for the values of the circuit parameter corresponding to two resonant modes of the power transfer resonator and the power receiver resonator,

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

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

the variable converter circuit operable, when (fA−

fB_est) is different than a threshold value, to;

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

iteratively perform a next estimation for a next estimated self-resonant frequency fB_est.

2. The device of claim 1, wherein, if (fA−

fB_est) is not different than the threshold, the variable converter circuit is operable to transfer power between power transfer device and the power receiver device.

3. The device of claim 1, the circuit parameter being a current provided by the variable converter circuit.

4. The device of claim 1, the circuit parameter being a voltage across the power transfer terminals.

5. The device of claim 1, the circuit parameter being voltage across the power transfer coil.

6. The device 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 device 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 device 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 device 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.

10. The device of claim 1, wherein the power transfer resonator is a series resonator with a resonator capacitor in series with a resonator power transfer coil coupled between the power transfer terminals.