RESONANT SYSTEM FOR WIRELESS POWER TRANSMISSION TO MULTIPLE RECEIVERS

• US 20120169137A1
• Filed: 12/20/2011
• Published: 07/05/2012
• 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: Lisi, Gianpaolo, Socci, Gerard G., Djabbari, Ali, Kiaei, Ali, Bahai, Ahmad R.S., Morroni, Jeffrey A.
• Granted Patent: US 9,231,412 B2
• Time in Patent Office: Days
• US Class Current: 307/104
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/40 using two or more transmitting or receiving devices H02J50/50 takes precedence
• 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 50/90 involving detection or optimisation of position, e.g. alignment
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current

Abstract

In a wireless power transfer system with multiple receivers, receiver management may be necessary to effectively provide power to the multiple receivers. In one implementation, receiver management includes sweeping or stepping the transmitter resonant and/or operating frequency. In another implementation, receiver management includes receiver self-management, in which the receiver load current duty cycle is controlled to maintain receiver voltage even in the presence of multiple receivers. In another implementation, receiver management includes receiver self-management, in which one or more receivers use a time-sharing heuristic to identify when other receivers are charging and wait to begin receiving a transfer of power until another receiver has stopped receiving a transfer of power.

Claims

1. A transmitter, comprising:

an alternating current (AC) power supply;

a resonant circuit receiving power from the AC power supply, including a power transfer coil configured for wireless power transfer;

an impedance-matching circuit; and

a power tracker configured, when the transmitter is magnetically coupled to at least one receiver, to determine a resonant frequency of the at least one receiver.

2. The transmitter of claim 1, the power tracker causing the frequency of the AC power supply to be adjusted to be substantially equivalent to the resonant frequency of the at least one receiver.

3. The transmitter of claim 1, the resonant circuit including at least one variable component.

4. The transmitter of claim 3, the power tracker further configured to cause the resonant frequency of the transmitter resonant circuit to be adjusted to be substantially equal to the resonant frequency of a first receiver of the at least one receiver, the power tracker causing the resonant frequency of the transmitter resonant circuit to be adjusted by causing the value of the at least one variable component in the transmitter resonant circuit to change.

5. The transmitter of claim 4, the power tracker causing the frequency of the AC power supply to be adjusted to be substantially equivalent to the adjusted frequency of the transmitter resonant circuit.

6. The transmitter of claim 5, the impedance-matching circuit including at least one variable component, the power tracker further configured to cause the at least one variable component of the impedance-matching circuit to be adjusted to compensate for the adjusted AC power supply frequency.

7. The transmitter of claim 4, the power tracker further configured to subsequently cause the resonant frequency of the transmitter resonant circuit to be adjusted to be substantially equal to the resonant frequency of a second one of the at least one receiver.

8. The transmitter of claim 3, the power tracker further configured to cause the resonant frequency of the transmitter resonant circuit to be adjusted in a sequence by causing the value of the at least one variable component in the transmitter resonant circuit to change in a sequence.

9. The transmitter of claim 3, the power tracker further configured to cause the resonant frequency of the resonant circuit to be swept from a starting frequency to an ending frequency by causing the value of the at least one variable component in the resonant circuit to be swept from a starting value to an ending value.

10. The transmitter of claim 1, the transmitter included in a wireless power transfer system, the wireless power transfer system further including the at least one receiver magnetically coupled to the transmitter, a first receiver of the at least one receiver including a power transfer self-management.

11. The transmitter of claim 10, the power transfer self-management including a controller that controls the duty cycle of a switch allowing current to the first receiver load, to control the effective load of the first receiver as seen by the transmitter.

12. The transmitter of claim 10, the power transfer self-management including a heuristic that recognizes when others of the at least one receiver start or stop receiving power transfer from the transmitter, the heuristic causing the first receiver to wait to begin receiving power transfer from the transmitter until no other receiver of the at least one receiver is receiving power.

13. A method, comprising:

receiving alternating current (AC) power at a power transfer coil in a wireless power transfer receiver;

converting the AC power to direct current (DC) power;

providing the DC power to a load as a controlled current through the load, the current controlled by varying the duty cycle of a switch to vary the magnitude of the current, thereby varying the effective load of the receiver.

14. The method of claim 13, the current through the load being controlled such that the receiver load current is maintained around a peak value, thereby maximizing the power to the load.

15. The method of claim 14, the receiver load current being adjusted to find the peak value as the peak value changes due to changing system conditions.

16. A method, comprising:

in a first receiver configured to receive a transfer of energy wirelessly from a source,

initializing a counter and starting an incremental count;

while the counter is incrementing,

if the first receiver determines that another receiver is starting to receive a transfer of energy from the source, reinitializing and restarting the counter;

if the first receiver determines that another receiver stops receiving a transfer of energy from the source, ending the incrementing of the count;

otherwise, when the counter reaches a predefined end value, ending the incrementing of the count;

waiting a random or pseudo-random period; and

if the first receiver determines that, during the wait period, no other receiver started to receive a transfer of energy from the source, the first receiver starting to receive a transfer of energy from the source.

17. The method of claim 16, the first receiver stopping the receiving of a transfer of energy from the source at the end of a predefined charge period.

18. The method of claim 17, including the first receiver in a wireless power transfer system with a transmitter and at least one receiver, the first receiver being one of the at least one receiver and further magnetically coupling the first receiver to the transmitter, configuring the transmitter for detecting when the first receiver starts and stops receiving a transfer of power.

19. The method of claim 18, the at least one receiver further including a second receiver, the transmitter detecting when one of the first receiver or the second receiver starts or stops receiving a transfer of power by detecting a decrease or increase, respectively, of the voltage on a power transfer coil in the transmitter.

20. The method of claim 19, the transmitter

determining, from the information from the detecting, an average idle voltage;

and

turning off at least part of the transmitter circuitry if the average idle voltage crosses an idle threshold.

21. The method of claim 20, the transmitter

determining, if the average idle voltage crosses an excess threshold, that a metal object is in proximity to the transmitter.

22. The method of claim 19, the transmitter

determining, from the information from the detecting, an idle voltage range;

and

turning off at least part of the transmitter circuitry if at least one limit of the idle voltage range crosses an idle threshold.

23. The method of claim 22, the transmitter

determining, if at least one limit of the idle voltage range crosses an excess threshold, that a metal object is in proximity to the transmitter.