METHODS AND SYSTEMS FOR MEASURING POWER IN WIRELESS POWER SYSTEMS

• US 20160084894A1
• Filed: 09/24/2014
• Published: 03/24/2016
• Est. Priority Date: 09/24/2014
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Maalouf, Joseph Najib, Govindaraj, Arvind
• Granted Patent: US 9,784,777 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 25/00 Arrangements for measuring phase angle between a voltage and a current or between voltages or currents
• CPC Class Codes: G01R 25/005 Circuits for comparing several input signals and for indicating the result of this comparison, e.g. equal, different, greater, smaller, or for passing one of the input signals as output signal
• CPC Class Codes: G01R 25/04 involving adjustment of a phase shifter to produce a predetermined phase difference, e.g. zero difference
• 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: H03K 2005/00286 Phase shifter, i.e. the delay between the output and input pulse is dependent on the frequency, and such that a phase difference is obtained independent of the frequency
• CPC Class Codes: H04B 5/73 for taking measurements, e.g. using sensing coils
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer

Abstract

The invention provides a method and system for precisely measuring AC power and detecting load impedance using a precise analog front-end, zero-crossing detectors, and a phase detection system capable of extracting precise phase information from the sensed voltage and current measurements. More particularly, the invention provides an apparatus, comprising a transmit circuit configured to generate a wireless field via an antenna for transferring charging power to a receiver device, for determining a phase difference between a first signal and a second signal. The apparatus further comprises a phase detection circuit to output a phase signal indicating a duration of a phase offset between a time-varying voltage and a time-varying current of the transmit circuit. The apparatus further comprises a capacitor configured to receive a variable current from a current source for the duration of the phase offset between the time-varying voltage and a time-varying current.

Claims

1. An apparatus for determining a phase difference between a time-varying voltage and a time-varying current, comprising:

a transmit circuit comprising an antenna, the transmit circuit configured to generate a wireless field via the antenna for transferring charging power to a receiver device, the wireless field based on the time-varying voltage and the time-varying current;

a phase detection circuit configured to output a phase signal indicating a duration of a phase offset between the time-varying voltage and the time-varying current;

a capacitor configured to receive a current from a current source for the duration of the phase offset between the time-varying voltage and the time-varying current; and

at least one switch operably coupled to the capacitor and configured to selectively couple the current from the current source to the capacitor in response to the phase signal, the phase signal allowing activation of the at least one switch.

2. The apparatus of claim 1, wherein the current source comprises a dynamically variable current source, and wherein the current comprises a dynamically variable current from the dynamically variable current source based on an input signal indicating a request to increase or decrease the current based on a voltage of the capacitor compared to a working voltage of the capacitor.

3. The apparatus of claim 1, further comprising a controller configured to determine the phase difference based on a voltage across the capacitor, a capacitance of the capacitor, and the current from the current source.

4. The apparatus of claim 3, wherein the controller is further configured to determine a power of the time-varying voltage and the time-varying current based at least in part on at least one of a peak voltage of the time-varying voltage, or a peak current of the time-varying current, or the phase difference, or any combination thereof.

5. The apparatus of claim 4, wherein the controller is further configured to correct the determined power by a sum of powers of the time-varying voltage and the time-varying current at various harmonic frequencies of the time-varying voltage and the time-varying current.

6. The apparatus of claim 3, wherein the controller is further configured to control a discharge of the capacitor.

7. The apparatus of claim 1, further comprising a controller configured to determine a number of phase cycles over which the phase difference is determined, wherein increasing the number of phase cycles over which the phase difference is determined increases an accuracy of the determined phase difference.

8. The apparatus of claim 1, further comprising a voltage sensor coupled to a transmitter and configured to sense a voltage signal from the transmitter, wherein the time-varying voltage represents the voltage signal sensed by the voltage sensor.

9. The apparatus of claim 8, further comprising a phase compensation circuit configured to limit an effect of the voltage sensor on relative phase shifts between the time-varying voltage and the time-varying current.

10. The apparatus of claim 1, further comprising a current sensor coupled to a transmitter and configured to sense a current signal from the transmitter, wherein the time-varying current represents the current signal sensed by the current sensor.

11. The apparatus of claim 10, further comprising a phase compensation circuit configured to limit an effect of the current sensor on phase shifts between the time-varying voltage and the time-varying current.

12. The apparatus of claim 1, wherein the phase detection circuit is configured to determine a magnitude of the phase offset between the time-varying voltage and the time-varying current, the phase offset indicating a duration between a zero-crossing of the time-varying voltage and a zero-crossing of the time-varying current.

13. The apparatus of claim 1, further comprising a controller configured to calibrate the phase detection circuit using a reference waveform, wherein the reference waveform includes a controlled phase offset between the time-varying voltage and the time-varying current, and configured to characterize and compensate the determined phase difference for a phase measurement error between the time-varying voltage and the time-varying current.

14. The apparatus of claim 1, further comprising amplitude scaling circuits configured to limit amplitudes of the time-varying voltage and the time-varying current to be within 10% of each other.

15. A method for determining a phase difference between a first signal and a second signal, comprising:

generating a phase signal indicating a duration of a phase offset between the first and second signals;

selectively coupling a current source to a capacitor in response to the phase signal, the phase signal allowing activation of at least one switch; and

receiving a current from the current source for the duration of the phase offset between the first and second signals.

16. The method of claim 15, further comprising generating a wireless field for transferring charging power to a receiver device via an antenna coupled to a transmit circuit, the wireless field based on a time-varying voltage and a time-varying current, wherein the first signal comprises the time-varying voltage and the second signal comprises the time-varying current.

17. The method of claim 15, wherein the current source comprises a dynamically variable current source, and wherein the current from the current source comprises a dynamically variable current from the dynamically variable current source based on an input signal indicating a request to increase or decrease the current based on a voltage of the capacitor compared to a voltage capacity or rating of the capacitor.

18. The method of claim 15, further comprising determining the phase difference based on a voltage across the capacitor, a capacitance of the capacitor, and the current from the current source.

19. An apparatus for determining a phase difference between a first signal and a second signal, comprising:

means for generating a phase signal indicating a duration of a phase offset between the first and second signals;

means for receiving a current from a current source for the duration of the phase offset between the first and second signals; and

at least one means for selectively coupling the current from the current source to the means for receiving a current in response to a phase signal, the phase signal allowing activation of the at least one means for selectively coupling.

20. The apparatus of claim 19, further comprising a means for transmitting wireless power to a receiver device, wherein the means for transmitting comprises a means for generating a wireless field based on a time-varying voltage and a time-varying current, wherein the first signal comprises the time-varying voltage and the second signal comprises the time-varying current.