WO2009126963A2 - Power control duty cycle throttling scheme for planar wireless power transmission system - Google Patents

Abstract

Embodiments of a power transmission system and power control scheme are provided. The power control scheme utilizes the power requirements for each receiver of a device on a charging pad for highly efficient charging of multiple devices. According to an embodiment, each receiver transmits its power requirement to the transmitter, and based on this power requirement, the most power hungry device is used to set the duty cycle of the transmitter. Each individual receiver can continue to monitor its power requirement and make necessary adjustments to ensure efficient power transfer. Once all the devices are fully charged, the transmitter can be powered off or have its duty cycle reduced to performance trickle charging. The transmitter can continue to access the load conditions while in standby to detect any new device being placed on the charging pad.

Description

DESCRIPTION

POWER CONTROL DUTY CYCLE THROTTLING SCHEME FOR PLANAR WIRELESS POWER TRANSMISSION SYSTEM

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional Application Serial No. 61/044,327, filed April 11, 2008, which is hereby incorporated by reference herein in its entirety, including any figures, tables, or drawings.

BACKGROUND OF INVENTION

Wireless power transmission is an emerging technology as trends move toward completely wireless devices. Currently, power control can be achieved via changing the operating frequency of a transmitter, tuning the transmitter's matching network, and changing the transmitter's supply voltage. However, limited dynamic range can be attained by changing the operating frequency. It can be difficult and costly to find tunable components to operate at such high power level. In addition, system performance tends to degrade when the supply voltage deviates too far from it nominal operating voltage.

BRIEF SUMMARY

Embodiments of the present invention relate to a method and apparatus for power control in wireless power transmission. According to an embodiment, multiple receivers can be used with a single transmitter. In an embodiment, a low cost microprocessor can be used to perform timing control for the transmitter output. Embodiments of the present invention have a significantly wider power dynamic range than other competing solutions. In addition, it is possible to scale the timing control technique to charge a large number of devices concurrently, thus becoming more flexible.

In an embodiment, an intelligent power control technique is implemented that attends to the power requirement for the receiver of each device on a charging pad. According to an embodiment, each receiver transmits the power requirement of the receiver to the transmitter, and based on this power requirement, the most power hungry device is used to set the duty cycle of the transmitter. Each individual receiver can continue to monitor its power requirement and make necessary adjustments to ensure efficient power transfer. Once all the devices are fully charged, the transmitter can be powered off or have its duty cycle reduced to perform trickle charging. The transmitter can continue to access the load conditions while in standby to detect any new device being placed on the charging pad.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 shows a system overview according to an embodiment of the present invention.

Figure 2 shows a duty cycling throttling scheme according to an embodiment of the present invention.

Figure 3 shows a timing scheme according to an embodiment of the present invention for three receivers of significantly different per-unit area power requirement (75 W, 25W, 5W) placed on a IOOW transmitting pad.

Figure 4 shows an optimum duty cycling throttling scheme according to an embodiment of the present invention.

DETAILED DISCLOSURE

Embodiments of the present invention provide a method and apparatus for power control in wireless power transmission. Embodiments of the subject invention can be utilized in a planar power transmission system that is capable of charging multiple portable devices as well as powering them at close proximity. Since different devices have different power requirements that can span across a large dynamic range, embodiments of the present invention provide an intelligent power control scheme that allows contemporaneous charging of multiple devices that may span across a large dynamic range. According to an embodiment, multiple receivers can be used with a single transmitter. Certain embodiments of the present invention can attain 81% efficiency while delivering 68W of power to an ideal load. A peak power of 132W has been achieved using a specific embodiment of the present invention. In a further embodiment, a peak power of 300W has been achieved.

Figure 1 illustrates a power transmission system according to an embodiment of the present invention that can utilize one or more power control schemes. The power-related systems of this example are shown, following a power path. Power control techniques according to embodiments of the present invention can be applied to the power-related systems. In the transmitter portion of the system, the amplifier supply voltage 10 and the duty cycle can be tuned. In a specific embodiment, a duty cycle of driving square pulses can be tuned. In addition, in a system where the class E transmitter portion 20 includes two transistors, one of the two transmitting transistors can be shut down to reduce power output. In one embodiment, two independent clocks can be used to separately drive the two transistors, such that a power control scheme is capable of shutting down one transistor when the power requirement is low. Synchronization between the independent clocks can be provided. In an embodiment of the power control scheme, the system duty cycle for the transmitter can be controlled. On the receiver end, the system duty cycle can also be controlled as part of a power scheme according to an embodiment of the present invention. In an embodiment, receivers from different devices can have different duty cycles. Receivers from different devices can communicate with each other and coordinate such that the receivers reduce the amount of the duty cycle where no receiver is receiving power and/or the more than one, or more than two, receivers are receiving power, so as to enhance the charging of the two or more devices.

In one embodiment, the system duty cycle of a receiver can be controlled using, for example, discrete rectifying diodes 30 with a voltage regulator 40. For example, the voltage regulator part LM5574 for 50OmA output current and part LM5576 for 3 A output current can be used. In another example, voltage regulation can be performed by a microprocessor having an RF receiver such as the Chipcon CC2510F8.

Figure 2 shows a power control scheme according to an embodiment of the present invention. As shown in Figure 2, the transmitter (e.g., reference 20 of Figure 1) excites the coil (e.g., reference 50 of Figure 1 ) for a short period of time (X/Y seconds) to access a pad's load condition so as to determine if any device (e.g., reference 60 of Figure 1) is on or near the pad and to power down for X seconds if no load is detected. Values of X and Y are determined by the settling time of the system and the response time requirement once the receiver(s) is/are placed on the pad. In a specific embodiment, X can be about one second and X/Y can be from about 500 μsec to about 1 msec, so as to promptly start charging a device placed in appropriate position and avoid wasting power.

The load condition can be monitored, in order to determine when a device to be charged is put in an appropriate position by, for example, comparing one or more of the following with values that occur when no load is present: transmitter supply current, transmitter coil voltage, and transmitter coil current. The transmitter is also able to detect a device on the pad via a near field wireless communication link (e.g., reference 70 of Figure 1) if there is still charge left in the receiver's battery. However, if there is not sufficient charge left in the battery, the transmitter can power up at full 100% duty cycle to transmit power to the power depleted receiver(s). In another embodiment, the transmitter is powered up to at least 50% duty cycle. Upon receiving sufficient power to power the near field communication module, the receiver can then transmit its power requirement to the transmitter. Based on the power requirement of the receiver(s), the transmitter can then determine a duty cycle that is, for example, sufficient to power the most power hungry device without wasting extra energy. In specific embodiments, the selected duty cycle can optimize the efficiency of charging.

When there is a single device to be charged the transmitter can detect the presence of the device to be charged by detecting load conditions, and can then adjust the duty cycle of the transmitter appropriately. In embodiments having two or more devices to be charged the transmitter can detect the devices to be charged by detecting load conditions and then receiving communications from the receiver(s) of the device(s) to be charged as to the charging requirements. In a specific embodiment, the devices to be charged can communicate with each other as to what portions of the transmitters duty cycle to receive power. The receiver can determine the transmitter duty cycle. In a specific embodiment, the receiver can determine the transmitter duty cycle via the envelope detect technique. In addition, clock synchronization can also be performed during the process of determining the transmitter duty cycle. Depending on the power requirement of the receiver, the receiver can transmit its requirement if insufficient power is being transmitted or perform further duty cycling on the transmitter duty cycled power transmission to obtain the required power level. In a specific embodiment, a device placed on charging pad is recognized by the transmitter as a change in load. If a battery is drained, then the near field communication module is powered-up using power from the transmitter.

Figure 3 shows a duty cycle scheme according to an embodiment of the present invention. In a specific embodiment, a duty cycle scheme for a 100 W per unit area transmitter is provided with examples of three receivers' per unit area power requirement of 75 W, 25 W and 5 W respectively. The shaded portions show when the transmitter is transmitting or when the receivers are receiving, while the dark line shows when the receivers are on. The transmitter is shown as having a 75% duty cycle, as turning the transmitter off for a portion of the cycle can be helpful. Other percentage duty cycles can also be used. Each receiver can determine its duty cycle and turn on charging in accordance with its power requirement. Other than the most power hungry device, which is reflected in the scheme shown by receiver 1 in Figure 3, all other receivers (receiver 2 and receiver 3 of Figure 3) can stop receiving power by disengaging the coil during the beginning of the next cycle of power transmission from the transmitter. Each individual receiver can continue to monitor its power requirement and make necessary adjustments to ensure efficient power transfer. The scheme is capable of seamlessly letting any device receive power even if there are other devices under charge. In another specific embodiment, the duty cycling scheme can be optimized as shown in Figure 4. The difference between the scheme illustrated by Figure 4 and the scheme illustrated by Figure 3 is the change in the window position of receiver 2. This change in window position can provide improved distribution of power transmission between lower power devices by reducing overlapping of receivers being on. However, synchronization between receivers can be important. If desired, the receivers can be turned off while the transmitter is off. In addition, the window of when the receivers are turned on can be moved to reduce the amount of overlapping of receiver charging in order to further improve charging efficiency.

Then, once all the devices are fully charged, which can be determined via feedback from the receiver(s), the transmitter can be powered off or its duty cycle can be reduced to performance trickle charging. The transmitter can continue to access the load conditions while in standby to detect any new device being placed on the transmitting pad.

Through using a duty cycle scheme according to embodiments of the present invention, it is possible to provide a high efficiency and low cost wireless power charging platform that is capable of concurrent charging/powering of one or more portable devices such as mobile phones, mp3 players, and laptop computers. Embodiments of the present invention can be implemented, for example, at home, at airports, hotel rooms, or any public location. Accordingly, this would bring great convenience to general consumers, especially frequent travelers, as it would provide a universally charging interface and eliminate the need to carry multiple chargers. In addition, the user is able to charge all of his portable devices at the same time without significant impact on charge time.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.

Claims

CLAIMS What is claimed is:

1. A method for wireless power transmission, comprising: (a) exciting a transmitter coil of a transmitter of a wireless power transmission system for X/Y seconds, wherein the transmitter coil transmits an RF magnetic field when the transmitter coil is excited;

(b) determining a load condition so as to determine if a device is positioned to be charged, wherein each device to be charged comprises a receiver coil inductively coupled to the transmitter coil when the device is positioned to be charged and a receiver for receiving a receiver current from the receiver coil, wherein if there is no device positioned to be charged, then after a delay of X seconds returning to (a);

(c) if there is a device positioned to be charged, then exciting the transmitter coil so as to transmit power to the device positioned to be charged.

2. The method according to claim 1 , further comprising receiving at the transmitter a power requirement for the device positioned to be charged provided by the receiver of the device positioned to be charged.

3. The method according to claim 2, wherein when there are two or more devices positioned to be charged, receiving at the transmitter the power requirement for each device positioned to be charged provided by the receiver of each device positioned to be charged.

4. The method according to claim 2, wherein the receiver comprises a near field communication module for providing the power requirement, wherein when a battery of the device positioned to be charged is not sufficiently charged to power the near field communication module of the receiver to provide the power requirement the receiver of the device positioned to be charged provides the power requirement to the transmitter upon receiving sufficient power from the transmitter to power the near field communication module of the receiver.

5. The method according to claim 3, further comprising: detecting at the receiver a transmitter duty cycle.

6. The method according to claim 5, wherein the transmitter duty cycle is detected by using an envelope detect technique.

7. The method according to claim 5, wherein each of the two or more devices positioned to be charged detects the transmitter duty cycle and charges according to the power requirement of the device.

8. The method according to claim 1, wherein X is less than or equal to 1 second.

9. The method according to claim 1, wherein X/Y is in the range of 500 μsec to 1 msec.

10. The method according to claim 1, further comprising adjusting a duty cycle of the transmitter based on the load condition.

11. The method according to claim 2, further comprising adjusting a duty cycle of the transmitter based on the power requirement provided by the receiver of the device positioned to be charged.

12. The method according to claim 1, wherein determining the load condition comprises determining a transmitter supply current.

13. The method according to claim 1, wherein determining the load condition comprises determining a transmitter coil voltage.

14. The method according to claim 1 , wherein determining the load condition comprises determining a transmitter coil current.

15. A system for wireless power transmission, comprising: a transmitter having a transmitter coil, wherein the transmitter coil transmits an RF magnetic field when the transmitter coil is excited; a device having a receiver and a receiver coil, wherein the receiver coil is inductively coupled to the transmitter coil when the device is positioned to be charged, wherein the receiver receives a receiver current from the receiver coil; a means for exciting the transmitter coil for X/Y seconds; and a means determining a load condition after exciting the transmitter coil for X/Y seconds so as to determine if the device is positioned to be charged, wherein if the device is not positioned to be charged, then after a delay of X seconds initiating the means for exciting the transmitter coil for X/Y seconds, wherein if the device is positioned to be charged, then exciting the transmitter coil so as to transmit power to the device positioned to be charged.

16. The system according to claim 15, wherein the receiver further comprises a means for transmitting to the transmitter a power requirement for the device.

17. The system according to claim 16, wherein the system comprises two or more devices.

18. The system according to claim 16, wherein the means for transmitting to the transmitter the power requirement comprises a near field communication module for providing the power requirement, wherein when a battery of the device is not sufficiently charged to power the near field communication module to provide the power requirement the receiver of the device positioned to be charged provides the power requirement to the transmitter upon receiving sufficient power from the transmitter to power the near field communication module of the receiver.

19. The system according to claim 17, wherein at least one device further comprises: a means for detecting a transmitter duty cycle.

20. The system according to claim 19, wherein the transmitter duty cycle is detected by using an envelope detect technique.

21. The system according to claim 19, wherein each of the two or more devices detect the transmitter duty cycle and charges according to the power requirement of the device.

22. The system according to claim 15, wherein X is less than or equal to 1 second.

23. The system according to claim 15, wherein X/Y is in the range of 500 μsec to 1 msec.

24. The system according to claim 15, wherein the transmitter further comprises a means for adjusting a duty cycle of the transmitter based on the load condition.

25. The system according to claim 16, wherein the transmitter further comprises a means for adjusting a duty cycle of the transmitter based on the power requirement provided by the receiver of the device.

26. The system according to claim 15, wherein the means for determining the load condition comprises a means for determining a transmitter supply current.

27. The system according to claim 15, wherein the means for determining the load condition comprises a means for determining a transmitter coil voltage.

28. The system according to claim 15, wherein the means for determining the load condition comprises a means for determining a transmitter coil current.