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

A wireless power transmitter for transmitting power to a wireless power receiver in a wireless scheme includes 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 detect a coupling state between the transmitting coil and the receiving coil using an input impedance of the wireless power transmitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application Nos. 10-2012-0016237, filed Feb. 17, 2012 and 10-2012-0023329, filed Mar. 7, 2012, which are hereby incorporated by reference in their entirety.

BACKGROUND

The embodiment relates to a wireless power transmitter, a wireless power receiver, and a power transmission method of a wireless power transmission system.

A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800's, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been suggested. Actually, electrical toothbrushes or electrical razors, which are frequently used in daily life, are charged based on the principle of electromagnetic induction. Until now, the long-distance transmission using the magnetic induction, the resonance and the short-wavelength radio frequency has been used as the wireless energy transfer scheme.

Recently, among wireless power transmitting technologies, an energy transmitting scheme employing resonance has been widely used.

Since an electric signal generated between the wireless power transmitter and the wireless power receiver is wirelessly transferred through coils in a wireless power transmitting system using resonance, a user may easily charge electronic appliances such as a portable device.

An example of the wireless power transmitting technology is described in Korean Unexamined Patent Publication No. 10-2006-0031526, entitled “Bidirectional chargeable wireless charging pad and battery pack”, which implements a separating type transformer having a simple structure and a high coupling coefficient to detect a portable device or the battery pack mounted on a top surface of the wireless charging pad, and to monitor and control a charged state based on the detection result.

However, since impedance of a load side connected to a receiver side or inductance of a coil of the receiver side is fixed, a coupling state between a transmitter side and the receiver side varies so that power transmission efficiency is degraded.

BRIEF SUMMARY

The embodiment provides a wireless power transmitter capable of actively controlling impedance of a load side by efficiently detecting a coupling state between the wireless power transmitter and a wireless power receiver, the wireless power receiver, and a power transmitting method of a wireless power transmitting system.

The embodiment provides a wireless power transmitter capable of varying inductance of a coil included in a wireless power receiver by efficiently detecting a coupling efficient state between the wireless power transmitter and the wireless power receiver, the wireless power receiver, and a power transmitting method of a wireless power transmitting system.

According to the embodiment, there is provided a wireless power transmitter for transmitting power to a wireless power receiver in a wireless scheme, the wireless power transmitter including: a transmitting coil configured to transmit, which is supplied by a power source, to a receiving coil of the wireless power receiver using resonance; and a detecting unit configured to detect a coupling state between the transmitting coil and the receiving coil using an input impedance of the wireless power transmitter.

The detecting unit may detect the coupling state by measuring the input impedance of the wireless power transmitter after fixing output impedance of the wireless power receiver.

The wireless power transmitter may further including a transmission induction coil coupled with the transmitting coil to transfer the power, which is supplied by a power source, to the transmitting coil using electromagnetic induction, wherein the detecting unit may detect a coupling coefficient between the transmitting coil and the receiving coil using the measured input impedance of the wireless power transmitter and an inductance of the transmission induction coil after the output impedance of the wireless power receiver is removed.

The detecting unit may detects the coupling state after fixing output impedance of the wireless power receiver, and transmit 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.

The detecting unit may detect the coupling state after fixing output impedance of the wireless power receiver, and determine impedance variation information of the wireless power receiver based on the coupling state between the transmitting coil and the receiving coil and transmit the determined impedance variation information to the wireless power receiver.

The impedance variation information of the wireless power receiver may include 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.

According to the embodiment, there is provided a wireless power receiver for receiving power from a wireless power transmitter in a wireless scheme, the wireless power receiver including: a receiving coil receiving power from a transmitting coil of the wireless power transmitter using resonance; and an impedance varying unit varying an output impedance of the wireless power receiver in order to detect a coupling state between the transmitting coil and the receiving coil.

The impedance varying unit may include a switch for removing the output impedance of the wireless power receiver.

The wireless power receiver may further include a variable reception induction coil varying an inductance based on the coupling state between the transmitting coil and the receiving coil.

The variable reception induction coil may include a plurality of inductors connected to each other in series and a plurality of switches connected to the inductors in parallel, respectively.

The wireless power receiver may further include a load impedance varying unit varying an impedance of a load side based on the coupling state between the transmitting coil and the receiving coil.

The load impedance varying unit may include one of a Battery Management IC (BMIC) and a DC-DC converter.

According to the embodiment, there is provided a wireless power transmission method of a wireless power transmitting system for transferring power to a load side, the wireless power transmitting method including: varying an output impedance of a wireless power receiver; measuring an input impedance of a wireless power transmitter according to the varied output impedance of the wireless power receiver; and detecting a coupling state between a transmitting coil of the wireless power transmitter and a receiving coil of the wireless power receiver using the measured input impedance of the wireless power transmitter.

The varying of the output impedance of the wireless power receiver may include fixing the output impedance.

The fixing of the output impedance may include removing the output impedance of the wireless power receiver by shorting a switch connected to the load side in parallel.

The detecting of the coupling state may include detecting a coupling coefficient between the transmitting coil and the receiving coil using the measured input impedance of the wireless power transmitter and inductance of a reception induction coil coupled with the receiving coil after removing the output impedance.

The wireless power transmission method may further include varying an impedance of the load side based on the detected coupling state between the transmitting coil and the receiving coil.

The wireless power transmission method may further include 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.

The wireless power transmission method may further include 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.

A recording medium is recorded with a program for executing the wireless power transmission method.

According to the embodiment, power transmitting efficiency of the wireless power transmitting system can be improved by adjusting impedance of a load side through efficient detection of a coupling state between the wireless power transmitter and the wireless power receiver.

According to the embodiment, power transmitting efficiency of the wireless power transmitting system can be improved by changing impedance of a coil included in the wireless power receiver through detection of a coupling state between the wireless power transmitter and the wireless power receiver.

Meanwhile, other various effects may be directly or indirectly disclosed in the following description of the embodiment of the disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described in detail with reference to accompanying drawings so that those skilled in the art can easily work with the embodiments.

FIG. 1is a diagram showing a configuration of a resonant wireless power transmitting system100according to the embodiment.

Referring toFIG. 1, the wireless power transmitting system1000may include a power source100, a wireless power transmitter200, a wireless power receiver300, and a load side400.

The wireless power transmitter200may include a transmitting unit210and a detecting unit220.

The transmitting unit210may include a transmission induction coil unit211and a transmission resonance coil unit212.

The wireless power receiver300may include a receiving unit310, an output impedance varying unit320, and a load impedence adjusting unit330.

The receiving unit310may include a reception resonance coil unit311and a reception induction coil unit312.

The power source100may supply power to the wireless power transmitter200. The power source100may supply AC power to the wireless power transmitter200.

The power generated from the power source100is transmitted to the wireless power transmitter200. The power received in the wireless power transmitter200is transmitted to the wireless power receiver300that makes resonance with the wireless power transmitter200due to a resonance phenomenon. The power from the wireless power transmitter20to the wireless power receiver300is transmitted to the load side400through a rectifier circuit (not show). The load side400may include a rechargeable battery or other devices requiring power. An impedance of the load side400is denoted as ‘ZLO’ in the embodiment. In the embodiment, the load side400may refer to a battery which supplies power to an electronic device.

In the embodiment, the load side400may be included in the wireless power receiver300.

In more detail, the power source100may supply AC power having a predetermined frequency to the wireless power transmitter200.

The transmitting unit210of the wireless power transmitter200may include the transmission induction coil unit211and the transmission resonance coil unit212.

The transmission induction coil unit211is connected to the power source100, and AC current flows through the transmission induction coil unit211by the AC current from the power source100. When the AC current flows through the transmission induction coil unit211, the AC current may be induced to the transmission resonance coil unit212physically spaced apart from the transmission coil21due to electromagnetic induction.

The transmission resonance coil212may transmit the power from the transmission resonance coil unit212to the reception resonance coil unit311of the wireless power receiver300using resonance.

Power may be transferred using resonance between two LC circuits which are impedance-matched with each other. The power transfer using resonance is able to transfer power at higher efficiency to a longer distance than those by electromagnetic induction.

The transmission induction coil unit211may include a transmission induction coil L1and a capacitor C1. A capacitance of the capacitor C1may have a fixed value.

One terminal of the capacitor C1may be connected to one terminal of the power source100, and the other terminal of the capacitor C1may be connected to one terminal of the transmission induction coil L1. The other terminal of the transmission induction coil L1may be connected to the other terminal of the power source100.

The transmission resonance coil unit212may include a transmission resonance coil L2, a capacitor C2, and a resistor R2. The transmission resonance coil L2may include one terminal connected to one terminal of the capacitor C2and the other terminal connected to one terminal of the resistor R2. The other terminal of the resistor R2may be connected to the other terminal of the capacitor C2. A resistance of the resistor R denotes an amount of power loss of the transmission resonance coil L2.

The detecting unit220may detect a first input impedance Z1which is an impedance measured when viewing the wireless power transmitter200at the power source100toward. The first input impedance Z1may be detected using a voltage across the power source100and a current flowing through a circuit of the power source100.

The detecting unit220may detect a coupling state between the wireless power transmitter200and the wireless power receiver300using the first input impedance Z1. In the embodiment, the coupling state may be obtained based on the coupling coefficient between the transmission resonance coil L2and the reception resonance coil L3. The coupling coefficient represents a degree of the electromagnetic coupling between the transmission resonance coil L2and the reception resonance coil L3, and may be varied by at least one of a position, a direction and a distance between the transmission resonance coil L2and the reception resonance coil L3.

The detecting unit220may detect the coupling coefficient k2between the transmission resonance coil L2and the reception resonance coil L3using the first input impedance Z1.

The detecting unit220may detect the coupling coefficient k2between the transmission resonance coil L2and the reception resonance coil L3by changing an output impedance. In detail, when the output impedance is changed to zero, the detecting unit220may detect the coupling coefficient based on the output impedance changed to the zero. In the embodiment, the output impedance may signify an impedance viewed from the receiving unit310to the load side400.

The detector220may measure the first input impedance based on the output impedance changed to the zero, and then detect the coupling coefficient k2using the first input impedance Z1.

The coupling coefficient k2represents a degree of the electromagnetic couple between the transmission resonance coil L2and the reception resonance coil L3, and may be varied by at least one of a distance, a direction and a position between the wireless power transmitter200and the wireless power receiver300in the wireless power transmitting system1000. The power transfer efficiency in the resonant wireless power transmitting system1000may be varied due to the variation in the coupling coefficient k2. The wireless power transmitting system1000actively controls the impedance of the load side400so that the power transfer efficiency may be improved according to the variation in the coupling coefficient k2.

In order to actively control the impedance of the load side400, the coupling coefficient K2between the transmission resonance coil L2and the reception resonance coil L3is required. A detailed procedure of detecting the coupling coefficient k2between the transmission resonance coil L2and the reception resonance coil L3will be described below.

The wireless power receiver300includes a receiving unit310, an output impedance varying unit320, and a load impedance adjusting unit330. The wireless power receiver300may further include a controlling unit (not shown).

The receiving unit310may include a reception resonance coil unit311and a reception induction coil unit312.

The reception resonance coil unit311may include a reception resonance coil L3, a capacitor C3, and a resistor R3. The reception resonance coil L3may include one terminal connected to one terminal of the capacitor C3and the other terminal connected to one terminal of the resistor R3. The other terminal of the resistor R3may be connected to the other terminal of the capacitor C2. A resistance of the resistor R3denotes an amount of lost power caused due to a power loss of the reception resonance coil L3.

The reception induction coil unit312includes a reception induction coil L4which has both terminals connected to both terminals of the impedance varying unit320and a capacitor (not shown). The reception induction coil unit312may form a circuit having suitable inductance and capacitance values.

The reception resonance coil unit311may maintain the resonance state with the transmission resonance coil unit212at the resonance frequency. That is, the reception resonance coil unit311is loosely-coupled with the transmission resonance coil unit212such that an AC current flows therethrough. Accordingly, the wireless power transmitter200may transmit power to the wireless power receiver300side in a non-radiative scheme.

The reception induction coil unit312may receive power from the reception resonance coil unit311by electromagnetic induction, and the power received at the reception induction coil unit312may transferred to the load side400after the power is rectified by a rectifier circuit (not shown).

The output impedance varying unit320may include a switch SW and a capacitor C4. The switch SW may include one terminal connected to one terminal of the capacitor C4and the other terminal connected to one terminal of the load side400. The other terminal of the load side400is connected to the other terminal of the capacitor C4.

The impedance varying unit320may vary an output impedance ZLviewed from the reception induction coil L4to the load side400. The impedance varying unit320may vary the output impedance through the switch SW such that the first input impedance Z1may be varied.

The switch SW may be shorted for a predetermined time at a predetermined period. The predetermined time may be one second and the predetermined period may be 100 us, but the embodiment is not limited thereto.

The controlling unit (not shown) applies a control signal to the switch SW such that the switch SW is allowed to be open or shorted.

The load impedance adjusting unit330may vary the impedance of the load side400based on the coupling coefficient k2between the transmission resonance coil L2and the reception resonance coil L3.

The load impedance adjusting unit330may vary a impedance across the load side400through two methods. The two methods will be described with reference toFIGS. 4 and 5.

Hereinafter, a method for detecting the coupling coefficient k2between the transmission resonance coil L2and the reception resonance coil L3by measuring the first input impedance Z1varied by the output impedance varying unit320will be described with reference toFIGS. 2 and 3.

The third input impedance Z3signifies a measured impedance seen to the load side400at the reception resonance coil L3and may expressed as Equation 1:

wherein ‘w’ denotes a resonance frequency between the transmission resonance coil L2and the reception resonance coil L3, and ‘M3’ may be a mutual inductance between the reception resonance coil L3and the reception induction coil L4. Further, ‘ZL’ may denote an output impedance. Equation 1 is based on the frequency domain and equations which will be described below are also based on the frequency domain.

The second input impedance Z2signifies a measured impedance viewed to the wireless power receiver300at the wireless power transmitter200and may be expressed as Equation 2:

wherein ‘M2’ may denote a mutual inductance between the transmission resonance coil L3and the reception induction coil L4, and ‘C3’ may denote a capacitor which is an equivalent circuit corresponding to the reception resonance coil unit311. Further, ‘R3’ denotes a resistance corresponding to an amount of power loss caused by power loss of the reception resonance coil L3.

Although the capacitor C3and the leakage resistor R3may have fixed values, the mutual inductance M2may vary according to a coupling coefficient k2between the transmission resonance coil L2and the reception resonance coil L3.

The first input impedance Z1is an impedance measured when viewing the wireless power transmitter200at the power source100and may be expressed as Equation 3:

wherein ‘M1’ may denote a mutual inductance between the transmission induction coil L1and the transmission resonance coil L2.

If it is assumed that R1and R2have very small values, the R1and R2may become ‘0’ (zero). In addition, if the first input impedance Z1is selected such that resonances between the transmission induction coil L1and the capacitor C1, between the transmission resonance coil L2and the capacitor C2, and between the reception resonance coil L3and the capacitor C3occur at the same resonance frequency w, the first input impedance Z1may be expressed as Equation 4:

Further, if following Equation 5 and Equation 7 are applied to Equation 4, Equation 4 may be expressed as Equation 8:
M1=k1√{square root over (L1L2)}  [Equation 5]

wherein ‘M1’ may denote a mutual inductance between the transmission induction coil L1and the transmission resonance coil L2. The ‘k1’ may denote a coupling coefficient between the transmission induction coil L1and the transmission resonance coil L2.
M2=k2√{square root over (L2L3)}  [Equation 6]

wherein ‘M2’ may denote a mutual inductance between the transmission resonance coil L3and the reception induction coil L4. The ‘k2’ may denote a coupling coefficient between the transmission resonance coil L3and the reception induction coil L4.
M3=k3√{square root over (LeL4)}  [Equation 7]

wherein ‘M3’ may be a mutual inductance between the reception resonance coil L3and the reception induction coil L4. The ‘k3’ may denote a coupling coefficient between the reception resonance coil L3and the reception induction coil L4.

If following Equations 5 to 7 are applied to Equation 4, Equation 4 may be expressed as Equation 8:

Referring to Equation 8, as the output impedance ZLvaries, the first input impedance Z1may vary. This procedure will be described in detail with reference toFIGS. 2 and 3.

The controlling unit (not shown) applies a control signal to the impedance varying unit320such that the impedance varying unit320is controlled. The control signal may include a driving signal for allowing the switch SW to be open or shorted.

Hereinafter, the variations of the output impedance ZLand the first input impedance Z1according to whether the switch SW is open or shorted will be described with reference toFIGS. 2 and 3.

FIG. 2is a circuit diagram showing a state that the switch SW of the impedance varying unit320is open according to the embodiment.

When the switch SW is open, the output impedance varying unit320may be expressed as a circuit diagram depicted inFIG. 2.

In this case, the output impedance ZLmay be expressed as Equation 9:

If the values of the reception induction coil L4and the capacitor C4are selected to allow the reception induction coil L4and the capacitor C4to resonate with each other at the resonance frequency w, the first input impedance ZLof Equation 8 is expressed as Equation 10:

In the Equation 10, the ‘k1’ may denote a coupling coefficient between the transmission induction coil L1and the transmission resonance coil L2, and the ‘k3’ may denote a coupling coefficient between the reception resonance coil L3and the reception induction coil L4. The ‘k1’ and ‘k3’ may be fixed and known.

The resonance frequency w, the inductance of the transmission induction coil L1and the inductance of the reception induction coil L4may be fixe and known. However, the coupling coefficient k2may be varied by a position, a direction and a distance between the wireless power transmitter200and the wireless power receiver300. When a load having a variable impedance is used, the impedance ZLO of the load side400may be changed, it is difficult to detect the coupling coefficient k2.

Hereinafter, a procedure of detecting the coupling coefficient k2will be described with reference toFIG. 3.

FIG. 3is a circuit diagram illustrating a state that the switch SW of the impedance varying unit320is shorted.

When the switch SW is shorted, the output impedance varying unit320may be expressed as a circuit diagram depicted inFIG. 3.

In this case, the output impedance ZLmay be expressed as Equation 11:
ZL=0   [Equation 11]

If the reception induction coil L4and the capacitor C4are selected to resonate with each other at the resonance frequency w, the first input impedance Z1of Equation 8 may be expressed as Equation 12:

The ‘k1’ may denote a coupling coefficient between the transmission induction coil L1and the transmission resonance coil L2, and the ‘k3’ may denote a coupling coefficient between the reception resonance coil L3and the reception induction coil L4. The ‘k1’ and ‘k3’ may be fixed and known.

The resonance frequency w and the inductance of the transmission induction coil L1may be fixed and known.

Accordingly, if the first input impedance Z1is measured by the detecting unit220, the coupling coefficient k2may be obtained. In the embodiment, when a voltage input to the wireless power transmitter200is constant, the detecting unit200detects a current input to the wireless power transmitter200so that the first input impedance Z1may be measured.

If the coupling coefficient k2is obtained, the power transfer efficiency may be increased by varying the impedance of the load side400based on the coupling coefficient k2. The impedance of the load side400may be varied through active control. A method of adjusting the impedance of the load side400will be described with reference toFIG. 4below.

Particularly, when it is necessary to periodically detect the coupling coefficient k2 between the transmission resonance coil L2and the reception resonance coil L3prior to transmitting power to a load of the wireless power receiver300or while transmitting power to the wireless power receiver300, as shown inFIG. 3, the switch SW is shorted so that the coupling coefficient k2 may be obtained.

When the switch SW is shorted, power is not transmitted from the wireless power transmitter200to the load side400. Accordingly, when the coupling coefficient is detected while the power is transmitted, it is necessary to reduce a time of a state that the switch SW is shorted. In the embodiment, the switch SW may be shorted for 100 us at a time period of one second. In this case, a failure ratio of power transmission is 1/10000 which does not cause a serious influence on the power transmission.

FIG. 4is a diagram illustrating a method of adjusting impedance of a load side according to the embodiment.

The load impedance adjusting unit330of the wireless power receiver300may adjust the impedance of the load side400according to the detected coupling coefficient k2. The method of adjusting the impedance of the load side400may be implemented by using the following two methods.

One method is to adjust the impedance of the load side400by using a Battery Management IC (BMIC)331after the BMIC is connected to one terminal and the other terminal of the load side400.

The BMIC331is a device which adjusts an amount of current flowing through a battery. Referring toFIG. 4(a), the impedance of the load side140may be expressed by following equation 13:

wherein, ICdenotes a current adjusted through the BMIC, and VCdenotes a voltage applied to the load side400. In this case, the load side400may signify a battery for providing power necessary to operate an electronic device.

When a value of VCis known, the current IC input to the load side400may be adjusted through the BMIC331such that the impedance ZLO of the load side400may be adjusted through equation 13.

The other method is to adjust the impedance of the load side400by using a DC-DC converter332which is located at the one terminal and the other terminal of the load side400.

The DC-DC converter332performs a function of converting a direct voltage into another direct voltage and is classified into a switching type and a linear type. Preferably, a switching type of DC-DC converter may be used. The switch type is to allow an output side to obtain a suitable current by converting an unstable direct current generated by rectifying AC current into a pulse current by a switch circuit.

Referring toFIG. 4(b), the impedance of the load side400may be expressed as following equation 14. In this case, the impedance ZLO of the load side400may be replaced with Rin, and the existing load impedance ZLO may be fixed.

wherein, Eddenotes an efficiency of the DC-DC converter332, Voutdenotes a voltage applied to an load impedance ZLO, Vin denotes a voltage applied to the load side140, and Rinmay denote an impedance measured when viewing the DC-DC converter332.

Generally, since the efficiency Edof the DC-DC converter332, the voltage Vinapplied to the load side400, and the existing load impedance have fixed values, the wireless power receiver300may change the voltage applied to the load impedance ZLO, thereby adjusting the substituted load impedance Rinof the load side400.

FIG. 5is a flowchart illustrating a wireless power transmission method of a wireless power transmitting system according to the embodiment.

Hereinafter, the wireless power transmission method according to the embodiment will be described in cooperation with description ofFIGS. 1 to 4.

First, in step S101, an output impedance varying unit320of the wireless power receiver300varies an output impedance. As shown inFIG. 1, the output impedance ZL signifies the impedance measured from the receiving unit310to the load side400. In the embodiment, the impedance varying unit320may include the switch SW, and may vary the output impedance by using the switch SW.

The output impedance varying unit320applies a short signal to the switch SW so that the switch SW may be shorted for a predetermined time at a predetermined period. The predetermined time may be one second and the predetermined period may be 100 us, but the embodiment is not limited thereto. A procedure of varying the output impedance is the same as that illustrated inFIGS. 2 and 3, and thus the detailed description thereof is appropriately omitted.

Next, the detecting unit220of the wireless power transmitter200measures an input impedance viewed from a power source100to the wireless power transmitter200based on the varied output impedance (S103). In the embodiment, when a voltage input to the wireless power transmitter200is known, the detecting unit220may detect a current input to the wireless power transmitter200to measure a first input impedance Z1based on the detected input current.

After that, the detecting unit200of the wireless power transmitter200may detect a coupling coefficient between the transmission resonance coil L2of the transmitting unit210and a reception resonance coil L3of the receiving unit310using the measured input impedance (S105). A procedure of detecting the coupling coefficient by the detecting unit220is the same as that illustrated inFIG. 3.

Thereafter, the wireless power receiver300receives the detected coupling coefficient from the wireless power transmitter200(S107). The wireless power receiver300may receive the coupling coefficient from the wireless power transmitter200through in-band communication or out-of-band communication. The embodiment has illustrated that the information transmitted from the wireless power transmitter200to the wireless power receiver300is information regarding the coupling coefficient, but the transmitted information is not limited thereto. That is, the transmitted information may include information signifying a coupling state between the transmission resonance coil and the reception resonance coil, and information regarding the impedance of the load side400to be varied by the wireless power receiver300based on the coupling state.

The in-band communication may refer to the communication for exchanging information between the wireless power transmitter200and the wireless power receiver300through a signal having a frequency used in the wireless power transmission.

The out-of-band communication refers to the communication performed through a specific frequency band other than the resonance frequency band in order to exchange information necessary for the power transmission. The wireless power transmitter200and the wireless power receiver300can be equipped with out-of-band communication modules to exchange information necessary for the power transmission. The out-of-band communication module may be installed in the power supply apparatus. In one embodiment, the out-of-band communication module may use a short-distance communication technology, such as Bluetooth, Zigbee, WLAN or NFC, but the embodiment is not limited thereto.

Subsequently, the wireless power receiver300may determine the impedance of the load side400based on the received coupling coefficient (S109). The wireless power receiver may further include a storage unit (not show) in which the coupling coefficient and the impedance of the load side400are stored corresponding to each other. The wireless power receiver300may receive the detected coupling coefficient from the wireless power transmitter200, and may determine the impedance of the load side400using the received coupling coefficient. This will be described with reference toFIG. 6in detail.

FIG. 6is an example of a lookup table in which the coupling coefficient and the impedance of the load side400are stored corresponding to each other according to the embodiment.

Referring toFIG. 6, the coupling coefficient and the impedance of the load side400correspond to each other. That is, the storage unit (not shown) of the wireless power receiver300stores a lookup table in which the coupling coefficient and the impedance of the load side400are stored corresponding to each other so that the power transmission efficiency between the wireless power transmitter200and the wireless power receiver300is maximized.

The wireless power receiver300may receive the detected coupling coefficient from the wireless power transmitter200to search the impedance of the load side400corresponding to the received coupling coefficient. The wireless power receiver300may determine the impedance of the load side400through the search.

In the embodiment, the storage unit (not shown) may be included in the wireless power transmitter200. That is, the wireless power transmitter200may store a lookup table in which the coupling coefficient and the impedance of the load side400are stored corresponding to each other. The wireless power transmitter200may determine the impedance corresponding to the detected coupling coefficient, and may transmit information about the determined load impedance to the wireless power receiver300through in-band communication or out-of-band communication. Since the information about the determined load impedance is information about the load impedance varied according to the detected coupling coefficient, the information about the determined load impedance may be referred to impedance variation information of the wireless power receiver300.

The load impedance adjusting unit330of the wireless power receiver300may vary the impedance of the load side400using the information about the load impedance received from the wireless power transmitter200.

Referring back toFIG. 5, the wireless power receiver300adjusts the impedance of the load side400according to the determined impedance (S111).

The wireless power receiver300receives power according to the adjusted impedance of the load side400from the wireless power transmitter200(S113).

As described above, the embodiment can improve the power transmission efficiency by varying the impedance of the load side400based on the coupling coefficient detected between the transmission resonance coil L2and the reception resonance coil L3of the receiving unit310.

Hereinafter, an embodiment for varying inductance of the reception induction coil unit312according to the coupling coefficient according to the coupling coefficient between the wireless power transmitter200and the wireless power receiver300is described.

Hereinafter, a wireless power transmitting system and a wireless power transmission method thereof according to another embodiment will be described in cooperation with description ofFIGS. 1 to 3.

FIG. 7is a diagram illustrating a configuration of a wireless power transmitting system according to another embodiment.

Referring toFIG. 7, the wireless power transmitting system1000according to another embodiment may include a power source100, a wireless power transmitter200, a wireless power receiver300, and a load side400.

The power source100and the wireless power transmitter200have substantially the same functions as those of the power source100and the wireless power transmitted200shown inFIG. 1, and thus the detailed description thereof is appropriately omitted.

The wireless power receiver300may include a receiving unit310, an inductance varying unit313, an output impedance varying unit320, a storage unit340, and a controlling unit350.

The receiving unit310may include a reception resonance coil unit311and a reception induction coil unit312.

The reception resonance coil unit311may receive power from the transmission resonance coil unit213through resonance coupling with the transmission resonance coil unit212. The reception resonance coil unit311and the reception induction coil unit312have the same configurations as those illustrated inFIG. 1.

The output impedance varying unit320may vary an output impedance ZL viewed from an inductance varying unit313to be described below to the load side400.

The inductance varying unit313may receive power from the reception resonance coil unit311by electromagnetic induction, and may transfer the received power to the load side400.

The inductance varying unit313may basically correspond to the reception induction coil unit illustrated inFIG. 1.

When receiving the coupling coefficient k2from the wireless power receiver200, the inductance varying unit313may vary the impedance of the reception induction coil unit312according to the received coupling coefficient k2. The inductance varying unit313may be a variable reception induction coil for varying the inductance of the reception induction coil unit312. The inductance is varied according to the coupling coefficient k2in order to maximize the power transmission efficiency between the wireless power transmitter200and the wireless power receiver300. This will be described with reference toFIGS. 8 to 15.

The storage unit340may store the coupling coefficient k2and the impedance of the reception induction coil unit312corresponding to each other. That is, the storage unit340of the wireless power receiver300stores a lookup table in which the coupling coefficient k2and the impedance of the reception induction coil unit312are stored corresponding to each other so that the power transmission efficiency between the wireless power transmitter200and the wireless power receiver300is maximized.

The wireless power receiver300may receive the detected coupling coefficient from the wireless power transmitter200to search the inductance of the reception induction coil unit312corresponding to the received coupling coefficient from the storage unit340, and may determine the inductance of the reception induction coil unit312through the search.

In the embodiment, the storage unit340may be included in the wireless power transmitter200. That is, the wireless power transmitter200may store a lookup table in which the coupling coefficient k2and the impedance of the reception induction coil unit312are stored corresponding to each other. The wireless power transmitter200may determine the inductance of the reception induction coil unit312corresponding to the detected coupling coefficient, and may transmit information about the determined inductance through in-band communication or out-of-band communication. Since the information about the determined inductance of the reception induction coil unit312is information about the load impedance varied according to the detected coupling coefficient, the information about the determined inductance of the reception induction coil unit312may be referred to impedance variation information of the wireless power receiver300.

The inductance varying unit313of the wireless power receiver300may vary the impedance of the reception induction coil unit312using the information about the determined inductance from the wireless power transmitter200.

Hereinafter, the variation of the power transmission efficiency according to the inductance of the reception induction coil unit312will be described with reference toFIGS. 8 to 15.

FIGS. 8 to 11are graphs illustrating power transmission efficiency according to a resonant frequency when inductance of a reception induction coil unit312is fixed as illustrated inFIG. 1.FIGS. 12 to 15are graphs illustrating power transmission efficiency according to a resonant frequency when an inductance varying unit313varies inductance of a reception induction coil according to a coupling coefficient k2.

It is assumed that impedance of the reception induction coil is 5 uH inFIGS. 8 to 11, and a resonant frequency is 308 KHz inFIGS. 8 to 11. However, the embodiment is not limited to 308 KHz.

In the embodiment, when the wireless power transmitter200transmits power to the receiving unit310in a wireless scheme, power transmitted to the receiving unit310from the wireless power transmitter200may have various frequency bands. The various frequency bands may three types of frequency bands in the embodiment.

A first frequency band may be in the range of 110 KHz to 205 KHz, and may have a frequency band used in Wireless Power Consortium (WPC) which is a technical specification transmitting power through electromagnetic induction in a wireless scheme.

A second frequency band may be 6.78 MHz, or may have a frequency band used in Alliance for Wireless Power (A4WP) which is a technical specification transmitting power through resonance in a wireless scheme.

A third frequency band may be in the range of 206 KHz to 300 KHz, and may have a frequency band used in Power Matters Alliance (PMA) which is a technical specification transmitting power through electromagnetic induction in a wireless scheme.

However, the above frequency bands are illustrative purpose only.

InFIGS. 8 to 15, a horizontal axis indicates a frequency (unit: MHz), and a vertical axis indicates power transmission efficiency (unit: %) between the wireless power transmitter200and the wireless power receiver300.

Referring toFIG. 8, when inductance of the reception induction coil L4is fixed to 5 uH, power transmission efficiency at a resonant frequency (308 KHz) is about 58%. In a case ofFIG. 12, when the inductance of the reception induction coil L4is varied to 20 uH, the power transmission efficiency at a resonant frequency (308 KHz) is increased to about 85%. The power transmission efficiency in a frequency band similar to the resonant frequency (308 KHz) is substantially maintained constant.

That is, if the inductance of the reception induction coil L4is varied corresponding to the coupling coefficient k2, it may be confirmed that the power transmission efficiency is improved.

Referring toFIG. 9, when inductance of the reception induction coil L4is fixed to 5 uH, power transmission efficiency at a resonant frequency (308 KHz) is about 75%. In a case ofFIG. 13, when the inductance of the reception induction coil L4is varied to 5 uH, the power transmission efficiency at a resonant frequency (308 KHz) is increased to about 75%, which is the same as that ofFIG. 9.

That is, in a case where the coupling coefficient k2is 0.05, if the inductance of the reception induction coil L4is 5 uH, the power transmission efficiency is optimized at a resonant frequency band.

Referring toFIG. 10, when inductance of the reception induction coil L4is fixed to5uH, power transmission efficiency at a resonant frequency (308 KHz) is about 68%. In a case ofFIG. 14, when the inductance of the reception induction coil L4is varied to 4 uH, the power transmission efficiency at a resonant frequency (308 KHz) is increased to about 68%, which is similar to that ofFIG. 10, but the power transmission efficiency in a frequency band greater than the resonant frequency (308 KHz) may be improved.

That is, when the inductance of the reception induction coil L4is varied corresponding to the coupling coefficient k2, the power transmission efficiency may be improved.

Referring toFIG. 11, when inductance of the reception induction coil L4is fixed to 5 uH, power transmission efficiency at a resonant frequency (308 KHz) is about 27%. In a case ofFIG. 15, when the inductance of the reception induction coil L4is varied to 1.5 uH, the power transmission efficiency at a resonant frequency (308 KHz) is increased to about 34%, so that efficiency can be improved.

That is, when the inductance of the reception induction coil L4is varied corresponding to the coupling coefficient k2, the power transmission efficiency may be improved.

FIG. 16is a graph illustrating variation of power transmission efficiency E in a case of fixing inductance of the reception induction coil L4and in a case of varying the inductance according to the coupling coefficient k2.

Referring toFIG. 16, a graph A illustrates the variation of the power transmission efficiency E according to variation in the coupling coefficient k2when the inductance of the reception induction coil L4is fixed. A graph B illustrates the variation of the power transmission efficiency E according to the coupling coefficient k2when the inductance of the reception induction coil L4is varied according to the coupling coefficient k2 by the inductance varying unit313.

As illustrated inFIG. 16, the case of varying the inductance of the reception induction coil L4according to the coupling coefficient k2by the inductance varying unit313may be improved in the power transmission efficiency E as compared with the case of fixing the inductance of the reception induction coil L4.

The inductance varying unit313may be variously implemented in order to vary the inductance of the reception induction coil L4shown inFIG. 1. In the embodiment, the inductance varying unit313may vary the inductance of the reception induction coil L4through a plurality of inductors and a plurality of switches. The configuration of the inductance varying unit313will be described with reference toFIG. 17.

FIG. 17is a diagram illustrating an example of a configuration of the inductance varying unit313according to the embodiment.

Referring toFIG. 17, the inductance varying unit313according to the embodiment may include a plurality of inductors313aand a plurality of switches313b. The inductance varying unit313may include fourth inductors and four switches, but the embodiment is not limited to the fourth inductors and the four switches.

Inductances of the inductors313amay be the same as or different from each other.

One terminal of each inductor313ais connected to each switch313bin parallel. The inductors313aare connected to each other in series so that the inductance may be increased. The inductors313aare connected to each other in parallel so that the inductance may be reduced.

The controlling unit350of the wireless power receiver300may receive the coupling coefficient k2from the wireless power transmitter200, and may determine inductance corresponding to the received coupling coefficient k2.

The inductance varying unit313may vary the inductance of the inductance varying unit313by shorting or opening at least one of the switches313baccording to the determined inductance. When the four switches313bare all open, the four inductors313amay be connected to each other in series. The serially connected inductors may correspond to the reception inductor coil unit312ofFIG. 1.

The inductance varying unit313may acquire the inductance determined through a combination of the inductors313a. Accordingly, the power transmission efficiency between the wireless power transmitter200and the wireless power receiver300may be optimized.

Referring back toFIG. 7, the storage unit340may store the coupling coefficient k2and the inductance of the reception induction coil corresponding to each other. That is, the storage unit340may store the coupling coefficient k2and the inductance of the reception induction coil corresponding to each other in the form of a lookup table.

The controller350may control an overall operation of the wireless power receiver300. Particularly, the controlling unit350may apply a control signal to respective switches313bof the inductance varying unit313so that the inductance of the reception induction coil corresponds to the coupling coefficient k2detected by the detecting unit220. In the embodiment, the control signal may be an open or short signal to be transferred to at least one switch.

FIG. 18is a flowchart illustrating a wireless power transmission method of a wireless power transmitting system according to another embodiment.

Hereinafter, the wireless power transmission method of a wireless power transmitting system according to another embodiment will be described with reference toFIGS. 1 to 17.

First, steps S201to S207are the same as steps S101to S107illustrated inFIG. 5, and thus the detailed description thereof is appropriately omitted.

A wireless power receiver300determines inductance of a reception induction coil based on a coupling coefficient received from a wireless power transmitter200(S209). In the embodiment, the wireless power receiver300may receive the detected coupling coefficient from the wireless power transmitter200to search the inductance of the reception induction coil corresponding to the received coupling coefficient. The wireless power receiver300may determine the inductance of the reception induction coil through the search.

After that, an inductance varying unit313of the wireless power receiver300varies the inductance of the reception induction coil according to the determined inductance (S211). A method of varying the inductance is the same as that illustrated inFIG. 17.

The wireless power receiver300receives power from the wireless power transmitter200according to the variation in the inductance of the reception induction coil.

In the embodiment, the method of transmitting power through electromagnetic induction may signify tight coupling having a relatively low Q value. The method of transmitting power through resonance may signify loose coupling having a relatively high Q.