Tunable reactance circuits for wireless power systems
Disclosed herein are tunable reactance circuits configured to present a tunable or variable capacitive reactance when energized. The circuits can include a switch configured to be controlled by a gate driver, the gate driver configured to receive a control signal indicating an on-time of the switch; a diode coupled antiparallel to a switch; and one or more capacitors coupled in parallel to the diode. The tunable capacitive reactance can be based on the on-time of the switch and a total capacitance value of the one or more capacitors. The exemplary tunable reactance circuits may be used in wireless power transmitters and/or receivers for efficient power transmission and/or to deliver a particular level of power to a load.
1. A system comprising:
at least one tunable reactance circuit configured to present a continuously or discretely tunable capacitive reactance between a first capacitive reactance and a second capacitive reactance when energized, each circuit comprising:
a switch configured to be controlled by a gate driver, the gate driver configured to receive a control signal indicating an on-time of the switch;
a diode coupled antiparallel to the switch; and
one or more capacitors coupled in parallel to the diode,
wherein the tunable capacitive reactance is based on the on-time of the switch and a total capacitance value of the one or more capacitors.
2. The system of claim 1 wherein a capacitance value C eq of the tunable reactance circuit is defined by:
C
eq
=
C
total
·
2
2
-
(
2
φ
-
sin
2
φ
)
/
π
wherein C total is the total capacitance value and φ is a phase angle (i) between 90° and 180° or (ii) between 0° and 180°, and wherein the on-time of the switch is based on the phase angle.
3. The system of claim 1 wherein the switch is a MOSFET and the diode is a body diode of the MOSFET.
4. The system of claim 1 further comprising:
a driving circuit configured to output a driving signal at an operating frequency, the driving circuit having a first output node coupled to an input of the tunable reactance circuit; and
a resonator configured to generate an electromagnetic field based on the driving signal, the resonator having a first input node coupled to an output of the tunable reactance circuit.
5. The system of claim 4 wherein the gate driver is coupled to a bootstrap power supply, the bootstrap power supply comprising a bootstrap capacitor configured to charge during conduction of at least a portion of the driving circuit.
6. The system of claim 4 wherein the driving circuit is an inverter, and the system further comprises:
an auxiliary power source configured to energize one or more gate drivers of the inverter and the gate driver of the tunable reactance circuit.
7. The system of claim 6 wherein the auxiliary power source is an isolated DC-DC converter.
8. The system of claim 4 wherein the tunable capacitive reactance is based on a reflected impedance in the system.
9. The system of claim 4 wherein the tunable capacitive reactance is based on a power characteristic of the system.
10. The system of claim 4 wherein the at least one tunable reactance circuit comprises a first tunable reactance circuit and a second tunable reactance circuit, and
wherein the driving circuit has a second output node coupled to an input of the second tunable reactance circuit and the resonator has a second input node coupled to an output of the second tunable reactance circuit.
11. The system of claim 10 wherein a capacitance value of the first tunable reactance circuit is equal to a capacitance value of the second tunable reactance circuit.
12. The system of claim 1 further comprising:
a resonator having a first output node coupled to an input of the tunable reactance circuit; and
a rectifier having a first input node coupled to an output of the tunable reactance circuit.
13. The system of claim 12 wherein the gate driver is coupled to a bootstrap power supply, the bootstrap power supply comprising a bootstrap capacitor configured to charge during conduction of at least a portion of the rectifier.
14. The system of claim 12 further comprising:
an auxiliary power source configured to energize the gate driver of the tunable reactance circuit.
15. The system of claim 14 wherein the auxiliary power source is an isolated DC-DC converter.
16. The system of claim 12 wherein the tunable capacitive reactance is based on a reflected impedance in the system.
17. The system of claim 12 wherein the tunable capacitive reactance is based on a power characteristic of the system.
18. The system of claim 12 wherein the at least one tunable reactance circuit comprises a first tunable reactance circuit and a second tunable reactance circuit, and
wherein the resonator has a second output node coupled to an input of the second tunable reactance circuit and the rectifier has a second input node coupled to an output of the second tunable reactance circuit.
19. The system of claim 12 wherein a capacitance value of the first tunable reactance circuit is equal to a capacitance value of the second tunable reactance circuit.
20. A system comprising:
at least one tunable reactance circuit configured to present a tunable capacitive reactance when energized, each circuit comprising:
a switch configured to be controlled by a gate driver, the gate driver configured to receive a control signal indicating an on-time of the switch;
a diode coupled antiparallel to the switch; and
one or more capacitors coupled in parallel to the diode,
wherein the tunable capacitive reactance is based on the on-time of the switch and a total capacitance value of the one or more capacitors, and
a capacitance value C eq of the tunable reactance circuit is defined by:
C
eq
=
C
total
·
2
2
-
(
2
φ
-
sin
2
φ
)
/
π
wherein C total is the total capacitance value and φ is a phase angle (i) between 90° and 180° or (ii) between 0° and 180°, the on-time of the switch being based on the phase angle.
21. A system comprising:
at least one tunable reactance circuit configured to present a tunable capacitive reactance when energized, each circuit comprising:
a switch configured to be controlled by a gate driver, the gate driver configured to receive a control signal indicating an on-time of the switch;
a diode coupled antiparallel to the switch;
one or more capacitors coupled in parallel to the diode;
a driving circuit configured to output a driving signal at an operating frequency, the driving circuit having a first output node coupled to an input of the tunable reactance circuit; and
a resonator configured to generate an electromagnetic field based on the driving signal, the resonator having a first input node coupled to an output of the tunable reactance circuit,
wherein the tunable capacitive reactance is based on the on-time of the switch and a total capacitance value of the one or more capacitors.
22. A system comprising:
at least one tunable reactance circuit configured to present a tunable capacitive reactance when energized, each circuit comprising:
a switch configured to be controlled by a gate driver, the gate driver configured to receive a control signal indicating an on-time of the switch;
a diode coupled antiparallel to the switch;
one or more capacitors coupled in parallel to the diode;
a resonator having a first output node coupled to an input of the tunable reactance circuit; and
a rectifier having a first input node coupled to an output of the tunable reactance circuit,
wherein the tunable capacitive reactance is based on the on-time of the switch and a total capacitance value of the one or more capacitors.