Wireless power system with coupling-coefficient-based coil selection
A wireless power system may have a wireless power transmitting device and a wireless power receiving device. The wireless power receiving device may have a receive coil that receives wireless power signals from the wireless power transmitting device and may have a rectifier that produces direct-current power from the received wireless power signals. The wireless power transmitting device may have an array of transmit coils. Each transmit coil has a respective magnetic coupling coefficient characterizing its magnetic coupling with the receive coil. The wireless power transmitting device may have control circuitry that uses the magnetic coupling coefficient values in selecting transmit coils to use in transmitting wireless power to the wireless power receiving device.
1. A wireless power transmitting device configured to wirelessly transmit power to a wireless power receiving device having a receive coil, comprising:
wireless power transmitting circuitry including transmit coils characterized by coupling coefficients associated with electromagnetic coupling between the transmit coils and the receive coil; and
control circuitry configured to:
transmit wireless power to the wireless power receiving device using the wireless power transmitting circuitry while receiving non-zero rectifier output voltage measurements from the wireless power receiving device;
determine a magnetic coupling coefficient value for each of the transmit coils as a function proportional to the non-zero rectifier output voltage measurements and a transmit-coil-inductance-to-receive-coil-inductance-ratio; and
use the wireless power transmitting circuitry to transmit wireless power to the wireless power receiving device with a subset of the transmit coils selected based on the magnetic coupling coefficient values.
2. The wireless power transmitting device of claim 1 wherein the control circuitry is configured to obtain device type information from the wireless power receiving device and is configured to determine the transmit-coil-inductance-to-receive-coil-inductance-ratio based on the device type information.
3. The wireless power transmitting device of claim 2 further comprising a capacitor coupled to each of the transmit coils that is characterized by a capacitor voltage, wherein the control circuitry is configured to:
measure the capacitor voltages; and
use the measured capacitor voltages in determining the magnetic coupling coefficient values.
4. The wireless power transmitting device of claim 3 wherein:
the wireless power transmitting circuitry includes inverter circuitry controlled by the control circuitry to provide alternating-current signals to the transmit coils;
the control circuitry is configured to measure a direct-current input voltage to the inverter circuitry; and
the control circuitry is configured to use the measured direct-current input voltage in determining the magnetic coupling coefficient values.
5. The wireless power transmitting device of claim 1 wherein the control circuitry is configured to compare the magnetic coupling coefficient values to a minimum coupling coefficient threshold.
6. The wireless power transmitting device of claim 5 wherein the subset of transmit coils includes a pair of transmit coils with respective magnetic coupling coefficient values that exceed the minimum coupling coefficient value, wherein a first of the pair of transmit coils has a first coupling coefficient value, wherein the second of the pair of the transmit coils has a second coupling coefficient value that is higher than the first coupling coefficient value, and wherein a ratio of the first coupling coefficient value to the second coupling coefficient value exceeds a predetermine ratio threshold.
7. The wireless power transmitting device of claim 5 wherein the control circuitry is configured to transmit wireless power using each of the transmit coils having a magnetic coupling coefficient value that exceeds the minimum coupling coefficient value.
8. The wireless power transmitting device of claim 1 wherein the control circuitry is configured to obtain receive coil inductance information from the wireless power receiving device and is configured to determine the transmit-coil-inductance-to-receive-coil-inductance-ratio based on the receive coil inductance information.
9. The wireless power transmitting device of claim 1 wherein the control circuitry is configured to measure a transmit coil inductance for each of the transmit coils and is configured to determine ratios of each of the transmit coil inductances to the receive coil inductance to use in determining the magnetic coupling coefficient values.
10. The wireless power transmitting device of claim 9 wherein the control circuitry is configured to transmit wireless power to the wireless power receiving device using the wireless power transmitting circuitry while receiving the rectifier output voltage measurements from the wireless power receiving device.
11. The wireless power transmitting device of claim 8 further comprising a capacitor coupled to each of the transmit coils that is characterized by a capacitor voltage, wherein the control circuitry is configured to:
measure the capacitor voltages; and
use the measured capacitor voltages in determining the magnetic coupling coefficient values.
12. The wireless power transmitting device of claim 8 wherein:
the wireless power transmitting circuitry includes inverter circuitry controlled by the control circuitry to provide alternating-current signals to the transmit coils;
the control circuitry is configured to measure a direct-current input voltage to the inverter circuitry; and
the control circuitry is configured to use the measured direct-current input voltage in determining the magnetic coupling coefficient values.
13. The wireless power transmitting device of claim 1 , wherein the function is proportional to a square root of the transmit-coil-inductance-to-receive-coil-inductance-ratio.
14. The wireless power transmitting device of claim 13 , wherein the function is proportional to the rectifier output voltage measurements multiplied by the square root of the transmit-coil-inductance-to-receive-coil-inductance-ratio.
15. The wireless power transmitting device of claim 1 , wherein the transmit-coil-inductance-to-receive-coil-inductance-ratio is directly proportional to an inductance of the transmit coils and wherein the transmit-coil-inductance-to-receive-coil-inductance-ratio is inversely proportional to an inductance of the receive coil.
16. The wireless power transmitting device of claim 15 , wherein the function is directly proportional to a square root of the inductance of the transmit coils and is inversely proportional to a square root of the inductance of the receive coil.
17. A wireless power transmitting device configured to wirelessly transmit power to a wireless power receiving device having a receive coil, comprising:
wireless power transmitting circuitry including transmit coils each of which is characterized by a coupling coefficient value associated with magnetic coupling between that transmit coil and the receive coil; and
control circuitry configured to:
store a plurality of transmit-coil-inductance-to-receive-coil-inductance ratio values corresponding to different device identifiers;
receive a device identifier from the wireless power receiving device that identifies a device type of the wireless power receiving device;
identify a transmit-coil-inductance-to-receive-coil-inductance ratio value from the stored plurality of transmit-coil-inductance-to-receive-coil-inductance ratio values that corresponds to the device identifier received from the wireless power receiving device;
determine the coupling coefficient values as a function of the identified transmit-coil-inductance-to-receive-coil-inductance ratio; and
select which of the transmit coils to use in transmitting wireless power to the wireless power receiving device based on the coupling coefficient values.
18. The wireless power transmitting device of claim 17 wherein the control circuitry is configured to identify a subset of the transmit coils for which the coupling coefficient values are larger than the coupling coefficient values of all other of the transmit coils.
19. The wireless power transmitting device of claim 18 wherein the control circuitry is configured to transmit the wireless power using the subset of the transmit coils.
20. The wireless power transmitting device of claim 19 wherein the subset of the transmit coils is a pair of the transmit coils.
21. The wireless power transmitting device of claim 17 , wherein the function is proportional to a rectifier output voltage of the wireless power receiving device multiplied by a square root of the identified transmit-coil-inductance-to-receive-coil-inductance ratio.
22. The wireless power transmitting device of claim 21 , wherein the rectifier output voltage is non-zero.