Wireless power transfer system for wirelessly transferring electric power in noncontact manner by utilizing resonant magnetic field coupling

1. A frequency controller apparatus for use in a wireless power transmitter apparatus configured to wirelessly transmit an inputted power from a power transmitting antenna including a first resonant circuit, toward a power receiving antenna that includes a second resonant circuit and is electromagnetically coupled to the power transmitting antenna at a predetermined transmission frequency, the frequency controller apparatus comprising:

a controller configured to change the transmission frequency during a power transfer,

wherein the controller increases the transmission frequency upon sweeping the transmission frequency without decreasing the transmission frequency,

wherein every time when the transmission frequency is increased in steps from a predetermined minimum frequency to a predetermined maximum frequency upon sweeping the transmission frequency, the controller (i) measures, as a predetermined power transfer characteristic, an output voltage and an output current outputted to a load and (ii) stores the measured output voltage and the measured output current into a storage unit,

wherein the controller controls the power transfer to stop the power transfer after sweeping the transmission frequency, the controller retrieves a transmission frequency corresponding to the measured output voltage and the measured output current when the output voltage and the output current become a predetermined voltage and current from among the measured output voltages and the measured output currents stored in the storage unit, and

wherein the controller starts the power transfer at the retrieved transmission frequency.

2. The frequency controller apparatus as claimed in claim 1 ,

wherein the controller controls the power transfer to inhibit increasing the transmission frequency and continue the power transfer when the measured power transfer characteristic satisfies a predetermined condition.

3. The frequency controller apparatus as claimed in claim 2 ,

wherein the power transfer characteristic is at least one of a voltage and a current inputted to the wireless power transmitter apparatus and a voltage and a current outputted from the power receiving antenna.

4. The frequency controller apparatus as claimed in claim 1 ,

wherein the controller measures, as the predetermined power transfer characteristic, the voltage and the current after a predetermined time has elapsed from when the transmission frequency is increased.

5. The frequency controller apparatus as claimed in claim 1 ,

wherein the predetermined voltage and current are the measured output voltage and the measured output current when a maximum electric power is achieved.

6. The frequency controller apparatus as claimed in claim 1 ,

wherein the predetermine voltage and current are the measured output voltage and the measured output current when a transmission efficiency of the power transfer becomes maximized.

7. The frequency controller apparatus as claimed in claim 1 ,

wherein the controller increases the transmission frequency upon sweeping the transmission frequency without decreasing the transmission frequency so as to reduce an electrical stress to the components or elements of a wireless power transfer system including the wireless power transmitter apparatus and a wireless power receiver apparatus transmitted the power from the wireless power transmitter apparatus during the power transfer.

8. The frequency controller apparatus as claimed in claim 1 ,

wherein a magnitude of the power changes in accordance with a change in a power necessary for the load.

9. A power transfer method for use in a wireless power transmitter apparatus configured to wirelessly transmit an inputted power from a power transmitting antenna including a first resonant circuit, toward a power receiving antenna that includes a second resonant circuit and is electromagnetically coupled to the power transmitting antenna at a predetermined transmission frequency, the power transfer method comprising:

a control step of changing the transmission frequency during a power transfer,

wherein the control step includes a step of increasing the transmission frequency upon sweeping the transmission frequency without decreasing the transmission frequency,

wherein in the control step, every time when the transmission frequency is increased in steps from a predetermined minimum frequency to a predetermined maximum frequency upon sweeping the transmission frequency, the control step includes (i) a step of measuring, as a predetermined power transfer characteristic, an output voltage and an output current outputted to a load and (ii) a step of storing the measured output voltage and the measured output current into a storage unit,

wherein the control step includes a step of controlling the power transfer to stop the power transfer after sweeping the transmission frequency, the control step includes a step of retrieving a transmission frequency corresponding to the measured output voltage and the measured output current when the output voltage and the output current become a predetermined voltage and current from among the measured output voltages and the measured output currents stored in the storage unit, and

wherein the control step includes a step of starting the power transfer at the retrieved transmission frequency.

10. A power transfer method as claimed in claim 9 ,

wherein the control step includes (i) a step of controlling the power transfer to stop the power transfer after sweeping the transmission frequency and (ii) a step of retrieving a transmission frequency corresponding to the measured output voltage and the measured output current when a maximum electric power is achieved.