Wireless power transmitter, wireless power receiver, and power transmission method of wireless power transmitting system

1. A wireless power transmitter for transmitting power to a wireless power receiver in a wireless scheme, the wireless power transmitter comprising:

a transmitting coil configured to transmit power, which is supplied by a power source, to a receiving coil of the wireless power receiver using resonance; and

a detecting unit configured to measure an input impedance of the wireless power transmitter according to a varied output impedance of the wireless power receiver and detect a coupling coefficient between the transmitting coil and the receiving coil using the measured input impedance of the wireless power transmitter; and

an output impedance varying unit, configured to vary the output impedance viewed from the receiving coil to a load side, comprising a switch and a capacitor,

wherein a switch of wireless power receiver is connected to the receiving coil in parallel such that current does not flow to a load of the wireless power receiver when the switch of wireless power receiver is shorted,

wherein the switch of wireless power receiver has a first terminal connected to the capacitor and a second terminal connected to a terminal of the load side,

wherein the input impedance is measured as seen by the power source, wherein the output impedance signifies an impedance viewed from the receiving coil to the load side,

wherein the measured input impedance for detecting the coupling coefficient is measured when the switch of wireless power receive is shorted such that the output impedance is zero.

2. The wireless power transmitter of claim 1 , wherein the detecting unit detects the coupling state after fixing output impedance of the wireless power receiver, and

transmits information about the coupling state for adjusting impedance of the wireless power receiver to the wireless power receiver through in-band communication or out-of-band communication.

3. The wireless power transmitter of claim 1 , wherein the detecting unit detects the coupling state after fixing output impedance of the wireless power receiver, and determines impedance variation information of the wireless power receiver based on the coupling coefficient between the transmitting coil and the receiving coil and transmits the determined impedance variation information to the wireless power receiver.

4. The wireless power transmitter of claim 3 , wherein the impedance variation information of the wireless power receiver comprises one of impedance variation information of a reception induction coil coupled with the receiving coil to receive power and impedance variation information of a load side.

5. A wireless power receiver for receiving power from a wireless power transmitter in a wireless scheme, the wireless power receiver comprising:

a receiving coil configured to receive power from a transmitting coil of the wireless power transmitter using resonance;

an impedance varying unit configured to vary an output impedance of the wireless power receiver in order to detect a coupling coefficient between the transmitting coil and the receiving coil; and

a load impedance adjusting unit configured to vary an impedance of a load side according to the detected coupling coefficient based on the varied output impedance from the wireless power transmitter,

wherein the output impedance signifies an impedance viewed from a receiving unit to a load side,

wherein the impedance varying unit includes a switch that is configured to change the output impedance to zero for detecting the coupling coefficient.

6. The wireless power receiver of claim 5 , further comprising a variable reception induction coil configured to vary an inductance based on the coupling state between the transmitting coil and the receiving coil.

7. The wireless power receiver of claim 6 , wherein the variable reception induction coil comprises a plurality of inductors connected to each other in series and a plurality of switches connected to the inductors in parallel, respectively.

8. A wireless power transmission method of a wireless power transmitting system for transferring power to a bad side, the wireless power transmitting method comprising:

varying an output impedance of a wireless power receiver to zero by shorting a switch connected to a load of the wireless power receiver in parallel;

measuring an input impedance of a wireless power transmitter when the varied output impedance of the wireless power receiver is zero; and

detecting a coupling coefficient between a transmitting coil of the wireless power transmitter and a receiving coil of the wireless power receiver by using the measured input impedance of the wireless power transmitter,

wherein the input impedance is measured as seen by a power source, wherein the output impedance signifies an impedance viewed from a receiving coil to a the bad side, and

wherein the coupling coefficient is periodically measured between a transmission resonance coil unit and a reception resonance coil unit.

9. The wireless power transmission method of claim 8 , wherein the varying of the output impedance of the wireless power receiver comprises fixing the output impedance.

10. The wireless power transmission method of claim 8 , further comprising varying an inductance of a reception induction coil transferring the power to the load side based on the detected coupling state between the transmitting coil and the receiving coil.

11. The wireless power transmission method of claim 8 , further comprising transmitting information about the detected coupling state to the wireless power receiver through in-band communication or out-of-band communication by the wireless power transmitter.