Wireless electric power transmission apparatus
View Patent ↗A wireless electric power transmission apparatus as an embodiment of the present disclosure includes: two antennas having the ability to transmit electric power by a non-contact method via resonant magnetic coupling, one of the two antennas being a series resonant circuit, of which the resonant frequency is fs, the other antenna being a parallel resonant circuit, of which the resonant frequency is fp; an oscillator which is connected to one of the two antennas that transmits RF power; and a control section which controls a transmission frequency according to the magnitude of the electric power to be transmitted from one of the two antennas to the other. If a coupling coefficient between the two antennas is k, then fs and fp are set so as to satisfy the inequality fs/fp<−0.6074×k 2 +0.0466×k+0.9955.
1. A wireless electric power transmission apparatus comprising:
two antennas having the ability to transmit electric power by a non-contact method via resonant magnetic coupling, one of the two antennas being a series resonant circuit, of which the resonant frequency is fs, the other antenna being a parallel resonant circuit, of which the resonant frequency is fp;
an oscillator which is connected to one of the two antennas that transmits RF power; and
a control section which controls a transmission frequency according to the magnitude of the electric power to be transmitted from one of the two antennas to the other,
wherein if a coupling coefficient between the two antennas is k, then fs and fp are set so as to satisfy the inequality fs/fp<−0.6074×k 2 +0.0466×k+0.9955.
2. The wireless electric power transmission apparatus of claim 1 , wherein the control section sets the transmission frequency to be a value that falls within a first frequency range if the electric power is greater than a reference value P 1 but sets the transmission frequency to be a value that falls within a second frequency range, which is higher than the first frequency range, if the electric power is smaller than the reference value P 1 .
3. The wireless electric power transmission apparatus of claim 1 , wherein if the electric power has changed from a value that is greater than the reference value P 1 into a value that is smaller than the reference value P 1 or if the electric power has changed from a value that is smaller than the reference value P 1 into a value that is greater than the reference value P 1 , then the control section makes the transmission frequency hop between a value falling within the first frequency range and a value falling within the second frequency range.
4. The wireless electric power transmission apparatus of claim 3 , wherein in making the transmission frequency hop, the control section changes the modes of a resonant magnetic field, which couples the two antennas together, from an even mode into an odd mode, and vice versa.
5. The wireless electric power transmission apparatus of claim 1 , wherein the coupling coefficient k between the two antennas is kept constant while the electric power is being transmitted.
6. The wireless electric power transmission apparatus of claim 1 , wherein the reference value P 1 is set to be within the range of 60% to 80% of a maximum electric power to transmit Pmax.
7. The wireless electric power transmission apparatus of claim 1 , wherein when one of the two antennas that is located on a receiving end has its output terminal connected to a load that follows the antenna, the output impedance Zoc of the oscillator that supplies RF energy to the other antenna on a transmitting end is equal to the input impedance Zin of the power transmitting antenna.
8. The wireless electric power transmission apparatus of claim 1 , wherein when one of the two antennas that is located on the transmitting end has its input terminal connected to an output terminal of the oscillator, the output impedance Zout of the other antenna on the receiving end is equal to the input impedance of a load that is connected to the output of the antenna on the receiving end.
9. The wireless electric power transmission apparatus of claim 1 , wherein the control section estimates whether transmission efficiency increases or decreases as the transmission frequency rises or falls with respect to at least one value of the electric power to transmit and determines a control pattern for the transmission frequency based on the result of the estimation.
10. The wireless electric power transmission apparatus of claim 1 , wherein the two antennas have a resonant frequency adjustment function to change at least one of fs and fp, and
wherein the control section changes the fs/fp value after the wireless electric power transmission apparatus has been installed.
11. The wireless electric power transmission apparatus of claim 10 , wherein after the wireless electric power transmission apparatus has been installed, the control section transmits electric power wirelessly with fs/fp set to be multiple different values, measures transmission efficiency, and then determines an fs/fp value for a normal operation based on the transmission efficiency.
12. A power transmitting device for use in the wireless electric power transmission apparatus of claim 1 , comprising:
one of the two antennas configured to transmit RF power; and
an oscillator that is connected to the antenna.
13. A power receiving device for use in the wireless electric power transmission apparatus of claim 1 , comprising one of the two antennas configured to receive RF power.
14. A controller for use in the wireless electric power transmission apparatus of claim 1 , configured to control the resonant frequency according to the magnitude of the electric power to be transmitted from one of the two antennas to the other.