Transmitter and receiver tuning in a wireless charging system
A wireless charging system includes a transmitter with tunable reactive components (such as capacitance or inductance). A metric related to power transfer from the transmitter through a coil is used to determine an amount to modify a Parameter. One metric is equal to |Vs|·|Is|·cos(φ)·(Vcoil_ref/Vcoil), where |Vs| is magnitude of the power source voltage, |Is| is magnitude of the power source current, φ is phase difference between the power source voltage and power source current, Vcoil_ref is a normalization value, and Vcoil is voltage across the coil. The transmitter can further include a phase tracking and adjustment loop (such as a phase-locked loop).
1. A transmitter circuit suitable for use in wireless power transfer to a power receiving device, the transmitter circuit operable with an alternating current power source; the transmitter circuit comprising:
a transmitter coil;
Power transfer circuitry coupled between the power source and the transmitter coil, and including at least one tunable reactive component;
tuning heuristic circuitry configured to control power transfer from the power source to the power receiving device by tuning the at least one tunable reactive component based on a metric equal to:
| Vs|·|Is |·cos(φ)·( V coil_ref/ V coil),
where, |Vs| is the magnitude of the power source voltage, |Is| is the magnitude of the power source current, φ is the phase difference between the power source voltage and power source current, Vcoil_ref is a normalization value, and Vcoil is the voltage across the transmitter coil.
2. The circuit of claim 1 , wherein the at least one tunable reactive component comprises a tunable capacitance.
3. The circuit of claim 1 , wherein the at least one tunable reactive component comprises a tunable inductance.
4. The circuit of claim 1 , further comprising:
an oscillator providing a periodic signal;
a pulse width modulator controlling the frequency of the power source based on the periodic signal provided by the oscillator;
a phase detector detecting the difference between the phase of the power source voltage and the phase of the power source current; and
frequency tuning heuristic circuitry configured to adjust the oscillator based on the phase of the power source.
5. The circuit of claim 4 , the oscillator, the pulse width modulator, the phase detector, and the frequency tuning heuristic circuitry being implemented as a phase-locked loop (PLL).
6. The circuit of claim 1 , wherein the power source is configured with a tunable duty cycle, the duty cycle being adjusted to control transmitter magnetic field intensity and thereby adjust the amount of power being transferred.
7. A method suitable for use in wireless power transfer from a transmitter including a transmitter coil, to a power receiving device, the transmitter operable with an alternating current power source, comprising:
controlling power transfer from the power source to the transmitter coil with power transfer circuitry that includes at least one tunable reactive component;
tuning the at least one tunable reactive component based on a metric equal to:
| Vs|·|Is |·cos(φ)·( V coil_ref/ V coil),
where, |Vs| is the magnitude of the power source voltage, |Is| is the magnitude of the power source current, φ is the phase difference between the Power source voltage and power source current, Vcoil_ref is a normalization value, and Vcoil is the voltage across the transmitter coil.
8. The method of claim 7 , wherein the at least one tunable reactive component comprises a tunable capacitance.
9. The method of claim 7 , wherein the at least one tunable reactive component comprises a tunable inductance.
10. The method of claim 7 , further comprising adjusting the frequency of the power source based on the difference between the phase of the power source voltage and the phase of the power source current.
11. The method of claim 10 , adjusting the frequency of the power source using a phase-locked loop (PLL).
12. The method of claim 7 , further comprising adjusting a duty cycle of the power source to control transmitter magnetic field intensity and thereby adjusting the amount of power being transferred.