KR102128487B1 - Apparatus for transmitting wireless power and method for controlling power thereof - Google Patents

Abstract

In an embodiment of the present invention, a wireless power transmission device that transmits power to a load through a wireless power reception device includes a power supply device that generates AC power and a receiving coil provided in the wireless power reception device using resonance of the AC power. It includes a transmitting coil and a detection unit for detecting a coupling state of the transmitting coil and the receiving coil, wherein the wireless power transmission apparatus is characterized in that for controlling the transmission power transmitted to the load based on the detected coupling state do.

Description

Wireless power transmitter and its power control method{APPARATUS FOR TRANSMITTING WIRELESS POWER AND METHOD FOR CONTROLLING POWER THEREOF}

The present invention relates to a wireless power transmission technology. More specifically, the present invention relates to a method of maximizing power transmission efficiency by controlling transmit power according to a combined state between a wireless power transmitter and a wireless power receiver.

In the 1800s, electric motors or transformers using electromagnetic induction principles began to be used in wireless power transmission or wireless energy transfer technology that wirelessly transmits electric energy to a desired device. A method of transmitting electric energy by emitting the same electromagnetic wave has also been attempted. Electric toothbrushes and some wireless shavers that we commonly use are actually charged with electromagnetic induction. Electromagnetic induction refers to a phenomenon in which voltage is induced and current flows when the magnetic field is changed around the conductor. In the electromagnetic induction method, commercialization is rapidly progressing around small devices, but there is a problem in that the transmission distance of power is short.

To date, the energy transmission method using the wireless method includes magnetic resonance and long-distance transmission technology using a short-wavelength radio frequency in addition to electromagnetic induction.

Recently, an energy transmission method using resonance has been widely used among such wireless power transmission technologies.

However, in the conventional energy transfer method using resonance, power transmission efficiency may be changed according to a combined state of the wireless power transmitter and the wireless power receiver.

Therefore, there is a need for a method to maximize power transmission efficiency by reflecting the combined state of the wireless power transmitter and the wireless power receiver.

An object of the present invention is to provide a method for maximizing power transmission efficiency according to a combined state of a wireless power transmitter and a wireless power receiver.

An object of the present invention is to provide a method for detecting transmission coefficients of a wireless power transmitter and a wireless power receiver and controlling transmission power according to the detected coupling coefficient.

In an embodiment of the present invention, a wireless power transmission device that transmits power to a load through a wireless power reception device includes a power supply device that generates AC power and a receiving coil provided in the wireless power reception device using resonance of the AC power. It includes a transmitting coil and a detection unit for detecting a coupling state of the transmitting coil and the receiving coil, wherein the wireless power transmission apparatus is characterized in that for controlling the transmission power transmitted to the load based on the detected coupling state do.

The wireless power transmission apparatus is characterized in that it determines the first received power of the load corresponding to the detected combined state, and controls the transmitted power according to the determined first received power.

The wireless power transmission apparatus checks the second reception power currently being received by the load, and when the second reception power is different from the first reception power, controlling the transmission power according to the first reception power It is characterized by.

The wireless power transmission device is characterized in that it checks the second received power through in-band or out-of-band communication with the wireless power receiving device.

The wireless power transmission device is characterized in that to check the second received power by measuring the intensity of the current flowing therein.

The wireless power transmission apparatus further includes a detection unit that detects a coupling state according to a coupling factor between the transmitting coil and the receiving coil, and the wireless power transmitting apparatus increases transmission power as the coupling coefficient increases. .

The detection unit is characterized in that it detects the coupling coefficient based on the measured input impedance by measuring the input impedance looking at the wireless power transmitter in the power supply.

The power supply device receives DC power from a power supply device to generate AC power, and the wireless power transmission device controls the transmission power by adjusting the power output from the power supply device.

The power supply device is characterized in that it transmits a power control signal for controlling the DC power output from the power supply using power line communication.

The power supply device further includes an AC power generation unit that receives DC power from the power supply and generates AC power, and the wireless power transmission device is input to the AC power generation unit or output from the AC power generation unit. It characterized in that to control the transmission power based on the intensity of the current.

The wireless power transmission apparatus is characterized in that it further comprises a storage unit for storing the combined state and the transmission power.

The transmitting coil includes a transmitting induction coil generating a magnetic field through the power supplied from the power supply device and a transmitting resonance coil coupled to the transmitting induction coil and transmitting the received power to the receiving coil using resonance. Should be

According to another embodiment of the present invention, a power control method of a wireless power transmission device that transmits power to a load through a wireless power reception device includes detecting a coupling state between the wireless power transmission device and the wireless power reception device and And determining a transmission power based on the detected coupling state and transmitting the determined transmission power to the load using resonance.

Determining the transmit power includes determining a first receive power that the load should receive in response to the detected combined state and determining the transmit power according to the determined first receive power.

Determining the transmission power according to the determined first received power includes: checking the second received power currently being received by the load and comparing the first received power with the second received power; and comparing the second received power. As a result, when the first received power and the second received power are different, determining the transmission power according to the first received power.

The step of checking the second received power that the load is currently receiving includes checking the second received power through in-band or out-of-band communication with the wireless power receiver.

The step of checking the second received power that the load is currently receiving includes checking the second received power by measuring the intensity of a current flowing inside the wireless power transmitter.

The detecting of the coupling state includes detecting the coupling coefficient for determining the coupling state, and the determining of the transmission power includes increasing the transmission power as the coupling coefficient increases. It is characterized by.

Determining the transmit power includes determining the transmit power based on a lookup table including the combined state and corresponding transmit power.

The detecting of the coupled state includes detecting the intensity of the current flowing inside the wireless power transmitter or using the input impedance of the wireless power transmitter.

According to an embodiment of the present invention, an object of the present invention is to provide a method for maximizing power transmission efficiency by controlling transmit power according to a combined state of a wireless power transmitter and a wireless power receiver.

The present invention can determine the optimal reception power based on the detected coupling coefficient by detecting the coupling coefficient of the wireless power transmitter and the wireless power receiver, and maximize the power transmission efficiency by controlling the transmission power according to the determined received power have.

Meanwhile, various other effects will be disclosed directly or implicitly in a detailed description according to an embodiment of the present invention to be described below.

1 is a block diagram of a wireless power transmission system according to an embodiment of the present invention.
2 is an equivalent circuit diagram of a wireless power transmission system according to an embodiment of the present invention.
3 is a flowchart illustrating a power control method according to an embodiment of the present invention.
4 is a view showing the relationship between the coupling coefficient and load impedance to satisfy the maximum power transmission efficiency.
5 is a view showing an example of the relationship between the coupling coefficient and the load impedance to satisfy the maximum power transmission efficiency when the load is a battery.
6 is a view showing a relationship between a current applied to a voltage applied to a battery when the load is a battery.
7 is a view showing a relationship between a load impedance and an amount of power applied to a battery when the load is a battery.
FIG. 8 is a diagram illustrating a relationship between a coupling coefficient and a received power of a load for satisfying maximum power transmission efficiency when the load is a battery.
9 is a block diagram of a wireless power transmission system according to another embodiment of the present invention.
10 is a ladder diagram for explaining a power control method according to another embodiment of the present invention.
11 is a flowchart illustrating a power control method according to another embodiment of the present invention.
12 is a view for explaining a look-up table that corresponds to a current value measured when the first output voltage is applied to the AC power generating unit, a coupling coefficient, a second output voltage, and an appropriate current range.
13 is a flowchart illustrating a method of detecting a coupling coefficient according to another embodiment of the present invention.
14 is a view for explaining a case in which the switch is opened to change the output impedance.
15 is a view for explaining a case in which a switch is shorted to change the output impedance.
16 is a flowchart illustrating a power control method according to another embodiment of the present invention.
17 is a view for explaining a lookup table used in the power control method according to the embodiment of FIG. 16.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily practice.

1 is a configuration diagram of a wireless power transmission system 10 according to an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of a wireless power transmission system 10 according to an embodiment of the present invention.

Referring to FIG. 1, the wireless power transmission system 10 may include a power supply device 100, a wireless power transmission device 200, a wireless power reception device 300 and a load 400.

In one embodiment, the power supply device 100 may be provided separately from the wireless power transmission device 200 as shown in FIG. 1, or may be included in the wireless power transmission device 200.

Referring to FIG. 1, the power supply device 100 includes a power supply unit 110, a switch 120, a direct current DC converter 130, a current sensor unit 140, an oscillator 150, and an AC power generation unit 160. , A control unit 170 and a storage unit 180.

The power supply unit 110 may supply DC power to each component of the power supply device 100. The power supply unit 110 may be provided separately from the power supply device 100.

In one embodiment, if the wireless power transmitter 200 transmits power to the wireless power receiver 300 using resonance, the wireless power transmitter 200 transmits and transmits the induction coil unit 211 to be described later. The resonant coil unit 212 is included, but when transmitting power to the wireless power receiver 300 using electromagnetic induction, the wireless power transmitter 200 may not include the transmitting resonant coil unit 212. have.

The switch 120 may connect or disconnect the power supply unit 110 and the DC-DC converter 130. The switch 120 may be opened or shorted by an open signal or a short signal from the controller 180. In one embodiment, the switch 120 may be opened or shorted by an operation of the controller 180 according to a power transmission state between the wireless power transmitter 200 and the wireless power receiver 300.

The DC-DC converter 130 may convert and output a DC voltage having a predetermined voltage value using the DC voltage supplied from the power supply unit 110.

The DC-DC converter 130 converts the DC voltage output from the power supply unit 110 into an AC voltage, and then boosts or step-downs the rectified AC voltage and rectifies the DC voltage to have a predetermined voltage value. Can output

As a DC-DC converter 130, a switching regulator or a linear regulator may be used.

A linear regulator is a converter that receives an input voltage and sends out the output voltage as needed, and discharges the remaining voltage as heat.

A switching regulator is a converter that can regulate the output voltage using Pulse Width Modulation (PWM).

The current sensor unit 140 may measure the intensity of the sensed current by sensing the current flowing inside the power supply device 100.

In one embodiment, the current sensor unit 140 may measure the intensity of current flowing when the DC voltage output from the DC-DC converter 130 is applied to the AC power generator 160, but is not limited thereto. No, it is also possible to measure the intensity of the current output from the AC power generating unit 160.

In one embodiment, the current sensor unit 140 may be a current transformer (CT). In one embodiment, the intensity of the current applied to the AC power generating unit 160 may be used to find the close proximity distance between the wireless power transmitter 200 and the wireless power receiver 300. In one embodiment, the intensity of the current applied to the AC power generating unit 160 may be a measure indicating a combined state between the wireless power transmitter 200 and the wireless power receiver 300. The coupling state may be used to find a coupling coefficient between the wireless power transmitter 200 and the wireless power receiver 300.

The current sensor unit 140 may transmit a signal for the detected intensity of the current to the controller 180.

In FIG. 1, the current sensor unit 140 is illustrated as a separate component from the controller 180, but may be included in the controller 180.

The oscillator 150 may generate an AC signal having a predetermined frequency and apply it to the AC power generator 160.

The AC power generating unit 160 may generate AC power using the DC voltage received from the DC DC converter 130 and the AC signal.

The AC power generator 160 may amplify the AC signal generated by the oscillator 150. The amplification amount of the AC signal may be varied according to the magnitude of the DC voltage applied through the DC-DC converter 130.

In one embodiment, the AC power generation unit 160 may be a push-pull type dual MOSFET.

The controller 180 can control the overall operation of the power supply device 100.

The controller 180 may control the DC-DC converter 130 so that a predetermined DC voltage is applied to the AC power generator 160.

When the DC voltage output from the DC sensor 130 is applied to the AC power generating unit 160 from the current sensor unit 140, the controller 180 receives a signal about the strength of the current flowing, and the received current Using the signal for the intensity of the DC voltage output from the DC-DC converter 130 and the frequency of the AC signal output from the oscillator 150 can be adjusted.

The controller 180 may receive a signal for the intensity of the current applied to the AC power generating unit 160 from the current sensor unit 140 to determine whether the wireless power receiving device 300 is present. That is, the controller 180 may check whether there is a wireless power receiving device 300 capable of receiving power from the wireless power transmitting device 200 using the intensity of the current applied to the AC power generating unit 160. .

The controller 180 may control the oscillator 150 to generate an AC signal having a predetermined frequency. The predetermined frequency may mean the resonance frequency of the wireless power transmitter 200 and the wireless power receiver 300 when power transmission is performed using resonance.

The storage unit 170 is the strength of the current applied to the AC power generation unit 160, the coupling coefficient of the wireless power transmitter 200 and the wireless power receiver 300 and the DC voltage output from the DC DC converter 130. It may be stored in correspondence. That is, the storage unit 170 may store the three values in the form of a look-up table.

The controller 180 searches the storage unit 170 for a DC coefficient output from the DC-DC converter 130 and a coupling coefficient corresponding to the strength of the current applied to the AC power generating unit 160, and outputs the searched DC voltage. The DC-DC converter 130 can be controlled to do so.

The wireless power transmitter 200 receives AC power from the AC power generator 160.

When the wireless power transmitter 200 transmits power to the wireless power receiver 300 using resonance, the wireless power transmitter 200 is a transmission induction nose which is a configuration of the transmitter 210 shown in FIG. 2 to be described later. A part 211 and a transmission resonance coil part 212 may be included.

When the wireless power transmitter 200 transmits power to the wireless power receiver 300 using electromagnetic induction, the wireless power transmitter 200 induces transmission among the components of the transmitter 210 shown in FIG. 2 to be described later. Only the coil portion 211 may be included.

The transmission resonance coil unit 212 transmits the AC power received from the transmission induction coil unit 211 to the wireless power receiver 300 using resonance. At this time, the wireless power receiver 300 may include a receiving resonant coil 310 and a receiving induction coil 320 shown in FIG. 2.

Next, referring to FIG. 2, the wireless power transmission system 10 may include a power supply device 100, a wireless power transmission device 200, a wireless power reception device 300, and a load 400.

The power supply device 100 includes all the components described in FIG. 1, and the function of the components also essentially includes the contents described in FIG. 1.

The wireless power transmitter 200 may include a transmitter 210 and a detector 220.

The transmission unit 210 may include a transmission induction coil unit 211 and a transmission resonance coil unit 212.

The AC power generated by the power supply device 100 is transmitted to the wireless power transmission device 200 and transmitted to the wireless power reception device 300 that makes resonance with the wireless power transmission device 200. The power delivered to the wireless power receiver 300 is transmitted to the load 400 through the rectifier 320.

The load 400 may mean a rechargeable battery or any device requiring power, and in the embodiment of the present invention, the load resistance of the load 400 is represented by RL. In one embodiment, the load 400 may be included in the wireless power receiver 300.

The power supply device 100 may supply AC power having a predetermined frequency to the wireless power transmission device 200. The power supply device 100 may provide AC power having a resonance frequency during resonance between the wireless power transmitter 200 and the wireless power receiver 300.

* The transmission unit 210 may be composed of a transmission induction coil unit 211 and a transmission resonance coil unit 212.

The transmission induction coil unit 211 is connected to the power supply device 100, and an alternating current flows by the power supplied from the power supply device 100. When an AC current flows through the transmission induction coil unit 211, an AC current is induced and flows into the transmission resonance coil unit 212 that is physically separated by electromagnetic induction. The power transmitted to the transmission resonance coil unit 212 is transmitted to the wireless power receiving apparatus 300 constituting a resonance circuit with the wireless power transmitting apparatus 200 by resonance.

Power may be transmitted by resonance between two LC circuits having impedance matching. Such power transmission by resonance enables power transmission at a higher efficiency over a longer distance than power transmission by electromagnetic induction.

The transmission resonance coil unit 212 of the wireless power transmission device 200 may transmit power to the reception resonance coil unit 311 of the wireless power reception device 300 through a magnetic field.

Specifically, the transmission resonance coil unit 212 and the reception resonance coil unit 311 are magnetically resonantly coupled to operate at a resonance frequency.

Due to the resonant coupling of the transmission resonance coil unit 212 and the reception resonance coil unit 311, the efficiency of power transmission between the wireless power transmitter 200 and the wireless power receiver 300 may be greatly improved.

The transmission induction coil unit 211 may include a transmission induction coil L1 and a capacitor C1. Here, the capacitance of the capacitor C1 is a value adjusted to operate at the resonance frequency.

One end of the capacitor C1 is connected to one end of the power supply device 100, and the other end of the capacitor C1 is connected to one end of the transmission induction coil L1. The other end of the transmission induction coil L1 is connected to the other end of the power supply device 100.

The transmission resonance coil unit 212 includes a transmission resonance coil L2, a capacitor C2, and a resistor R2. The transmission resonant coil L2 includes one end connected to one end of the capacitor C2 and the other end connected to one end of the resistor R2. The other end of the resistor R2 is connected to the other end of the capacitor C2. R2 represents the amount generated by power loss in the transmission resonant coil (L2) as a resistance. The capacitance of the capacitor C2 is a value adjusted to operate at a resonance frequency.

The detector 220 may detect a coupling state between the wireless power transmitter 200 and the wireless power receiver 300. In one embodiment, the coupling state may be determined through a coupling coefficient between the transmitting resonance coil unit 212 and the receiving resonance coil unit 311. Here, the detection unit 220 may detect the coupling coefficient by measuring the input impedance. This will be described later.

The wireless power receiver 300 may include a receiver 310 and a rectifier 320.

The wireless power receiver 300 may be embedded in electronic devices such as a mobile phone, mouse, laptop, MP3 player, and the like.

The receiving unit 310 may include a receiving resonance coil unit 311 and a receiving induction coil unit 312.

The reception resonance coil unit 311 includes a reception resonance coil L3, a capacitor C3, and a resistor R3. The receiving resonant coil L3 includes one end connected to one end of the capacitor C3 and the other end connected to one end of the resistor R3. The other end of the resistor R3 is connected to the other end of the capacitor C2. The resistor R3 represents the amount generated by power loss in the receiving resonance coil L3 as a resistor. The capacitance of the capacitor C3 is a value adjusted to operate at a resonance frequency.

The receiving induction coil unit 312 may include a receiving induction coil L4 and a capacitor C4. One end of the receiving induction coil L4 is connected to one end of the capacitor C4, and the other end of the receiving induction coil L4 is connected to the other end of the rectifier 320. The other end of the capacitor C4 is connected to one end of the rectifying view 320.

The receiving resonance coil unit 311 maintains a resonance state at the resonance frequency with the transmitting resonance coil unit 212. That is, the receiving resonant coil unit 311 is resonantly coupled to the transmitting resonant coil unit 212 so that an AC current flows, thereby receiving power from the wireless power transmitter 200 in a non-radiative manner. Can.

The receiving induction coil unit 312 receives power by electromagnetic induction from the receiving resonant coil unit 311, and the power received by the receiving induction coil unit 312 is rectified through the rectifying unit 320 to the load 400. Is delivered.

The rectifying unit 320 may receive AC power from the receiving induction coil unit 312 and convert the received AC power into DC power.

The rectifying unit 320 may include a rectifying circuit (not shown) and a smoothing circuit (not shown).

The rectifying circuit may be composed of a diode and a capacitor, and convert AC power received from the receiving induction coil unit 312 into DC power, and transmit the AC power to the load 400.

The smoothing circuit serves to smooth the rectifying output. The smoothing circuit may be composed of a capacitor.

The load 400 may receive rectified DC power from the rectifier 320.

The load 400 can be any rechargeable battery or device that requires direct current power. For example, the load 400 may be a battery of a portable terminal, but need not be limited thereto.

In one embodiment, the load 400 may be included in the wireless power receiver 300.

In wireless power transmission, quality factor and coupling coefficient have important meanings.

The quality factor may mean an index of energy that can be accumulated in the vicinity of a wireless power transmitter or wireless power receiver.

The quality factor may vary depending on the operating frequency w, coil shape, dimensions, and materials. In the formula, Q=w*L/R can be expressed. L is the inductance of the coil, and R is the resistance corresponding to the amount of power loss occurring in the coil itself.

The quality factor may have a value from 0 to infinity.

Coupling Coefficient refers to the degree of magnetic coupling between the transmitting side coil and the receiving side coil, and has a range of 0 to 1.

The coupling coefficient may vary depending on the relative position or distance of the transmitting side coil and the receiving side coil.

The wireless power transmitter 200 and the wireless power receiver 300 may exchange information with the wireless power receiver 300 through in-band or out-of-band communication.

**In-band communication may refer to a communication that exchanges information between the wireless power transmitter 200 and the wireless power receiver 300 by using a signal having a frequency used for wireless power transmission. The wireless power receiver 300 may or may not receive power transmitted from the wireless power transmitter 200 through a switching operation. Accordingly, the wireless power transmitter 200 may detect the amount of power consumed by the wireless power transmitter 200 to recognize the on or off signal of the wireless power receiver 300.

Specifically, the wireless power receiver 300 may change power consumed by the wireless power transmitter 200 by changing the amount of power absorbed by the resistor using a resistor and a switch. The wireless power transmitter 200 may detect changes in the consumed power and obtain status information of the wireless power receiver 300. The switch and resistor can be connected in series. In one embodiment, the status information of the wireless power receiving device 300 may include information about the current charging amount and the charging amount trend of the wireless power receiving device 300.

More specifically, when the switch is opened, the power absorbed by the resistor becomes 0, and power consumed by the wireless power transmitter 200 is also reduced.

When the switch is short-circuited, the power absorbed by the resistor becomes greater than 0, and the power consumed by the wireless power transmitter 200 increases. When the wireless power receiving device repeats the above operation, the wireless power transmitting device 200 may detect power consumed by the wireless power transmitting device 200 and perform digital communication with the wireless power receiving device 300.

The wireless power transmitter 200 may receive status information of the wireless power receiver 300 according to the above-described operation, and transmit power suitable for it.

On the contrary, it is also possible to transmit the status information of the wireless power transmitter 200 to the wireless power receiver 300 by providing a resistor and a switch on the wireless power transmitter 200 side. In one embodiment, the status information of the wireless power transmitter 200 is the maximum amount of power that the wireless power transmitter 200 can transmit, and the wireless power receiver 300 that the wireless power transmitter 200 provides power. It may include information about the number of and the amount of available power of the wireless power transmitter 200.

Out of band communication refers to communication that exchanges information necessary for power transmission by using a separate frequency band rather than the resonant frequency band. The wireless power transmitter 200 and the wireless power receiver 300 may be equipped with an out-of-band communication module to exchange information necessary for power transmission. The out-of-band communication module may be mounted in a power supply device. In one embodiment, the out-of-band communication module may use a short-range communication method such as Bluetooth, ZigBee, wireless LAN, NFC, but need not be limited thereto.

Next, a power control method according to an embodiment of the present invention will be described in detail with reference to FIGS. 3 to 8.

3 is a flowchart for explaining a power control method according to an embodiment of the present invention, FIG. 4 is a view showing a relationship between a coupling coefficient and a load impedance for satisfying the maximum power transmission efficiency, and FIG. 5 is a load battery In the case of, it is a diagram showing an example of the relationship between the coupling coefficient and the load impedance to satisfy the maximum power transmission efficiency, and FIG. 6 is a diagram showing the relationship of the current to the voltage applied to the battery when the load is a battery, FIG. 7 is a diagram showing the relationship between the amount of power applied to the battery and the load impedance when the load is a battery, and FIG. 8 shows the relationship between the coupling coefficient and the received power of the load to satisfy the maximum power transmission efficiency when the load is a battery It is a drawing to show.

First, in FIG. 3, a power control method according to an embodiment of the present invention will be described with reference to FIGS. 1 and 12.

The wireless power transmitter 200 measures the input impedance (S101). The input impedance may be the first input impedance Z1. As shown in FIG. 2, the first input impedance Z1 may be an impedance measured when the wireless power transmitter 200 is viewed from the power supply device 100. In one embodiment, the detector 220 may measure the first input impedance Z1 using the current and voltage input from the power supply device 100 to the wireless power transmission device 200.

Referring to FIG. 3 again, the detector 220 detects a coupling coefficient using the measured input impedance (S103). Here, the coupling coefficient (K2) indicates the degree of electromagnetic coupling between the transmitting resonant coil (L2) and the receiving resonant coil (L3), the distance between the wireless power transmitter 200 and the wireless power receiver 300, It is a value that can be changed by at least one of direction and position.

The measured coupling coefficient may be used to control the transmit power that the wireless power transmitter 200 transmits to the wireless power receiver 300. In one embodiment, the wireless power transmission apparatus 200 may increase the transmission power as the detected coupling coefficient increases, and may decrease the transmission power as the detected coupling coefficient decreases.

A method of detecting the binding coefficient will be described.

Referring to FIG. 2, the third input impedance Z3 may mean an impedance when the reception induction coil unit 312 is viewed from the reception resonance coil unit 311, and may be expressed as [Equation 1]. Can.

[Equation 1]

Here, w is a resonance frequency when the transmission resonance coil L2 and the reception resonance coil L3 resonate, and M3 represents mutual inductance between the reception resonance coil L3 and the reception induction coil L4. In addition, ZL means output impedance. The output impedance ZL may be equal to RL, which is the impedance of the load 400.

The mutual inductance (M3) can be calculated through the following [Equation 2].

[Equation 2]

Here, K3 is a coupling coefficient between the receiving resonance coil L3 and the receiving induction coil L4, and is a fixed value. Since the inductance of the receiving resonant coil L3 and the inductance of the receiving induction coil L4 are also fixed values, the mutual inductance M3 is also a fixed value.

In [Equation 1], since the resonance frequency (w), mutual inductance (M3), load impedance (ZL), inductance of the receiving induction coil (L4), and the capacitance of the capacitor (C4) are fixed values, the third input impedance ( Z3) has a fixed value.

[Equation 1] is a formula based on the frequency domain, and the following formulas are also expressed based on the frequency domain.

The second input impedance Z2 refers to an impedance measured when the wireless power transmitter 200 looks at the wireless power receiver 300, and may be expressed as Equation (3).

[Equation 3]

Here, M2 denotes mutual inductance between the transmit resonant coil L2 and the receive resonant coil L3, and C3 denotes a capacitor expressed when the receive resonant coil unit 311 is converted into an equivalent circuit. In addition, R3 represents the amount of loss generated by power loss in the receiving resonance coil L3 as a resistance.

The capacitance of the capacitor C3, the inductance of the receiving resonance coil L3, the third input impedance Z3, and the resistance R3 are fixed values.

The mutual inductance M2 may be calculated through Equation 4 below.

[Equation 4]

Here, since the inductance of the transmitting resonant coil L2 and the inductance of the receiving resonant coil L3 are fixed values, the mutual inductance M2 is the coupling coefficient K2 between the transmitting resonant coil L2 and the receiving resonant coil L3. It can be changed according to.

Therefore, when substituting the third input impedance Z3 of [Equation 1] into [Equation 3], the second input impedance Z2 can be expressed by the expression of the mutual inductance M2, and the mutual inductance ( M2).

The first input impedance Z1 refers to the impedance measured when the wireless power transmitter 200 is viewed from the power supply device 100 and may be expressed as Equation 5.

[Equation 5]

Here, M1 is a mutual inductance between the transmission induction coil L1 and the transmission resonant coil L2.

The mutual inductance M1 can be calculated through Equation 6 below.

[Equation 6]

Here, since the inductance of the transmission resonant coil L1, the inductance of the transmission induction coil L2, and the coupling coefficient K1 of the transmission resonant coil L1 and the transmission induction coil L2 are fixed values, the mutual inductance M1 Also has a fixed value.

The inductance of the transmission induction coil L1, the capacitance of the capacitor C1, the mutual inductance M1, the inductance of the transmission resonance coil L2, the capacitor C2, and the resistance R2 are all fixed values, but the second input Impedance Z2 is a value that can be varied by mutual inductance M2.

Substituting [Equation 2] into [Equation 3], the first input impedance Z1 may be expressed by an equation relating to the mutual inductance M2.

The detector 220 may calculate the mutual inductance M2 using the first input impedance Z1 measured in step S101 and the first input impedance Z1 related to the mutual inductance M2, and calculate The coupling coefficient (K2) can be detected through the mutual inductance (M2) and [Equation 4].

Another method of detecting the binding coefficient K2 is described in FIG. 13.

Referring to FIG. 3 again, the wireless power transmitter 200 determines the received power corresponding to the detected coupling coefficient K2 (S105). Here, the determined received power may mean power that should be received at the load 400 in order to maximize the power transmission efficiency between the wireless power transmitter 200 and the load 400.

Hereinafter, a method of detecting the coupling coefficient K2 and determining the received power to be received by the load 400 according to the detected coupling coefficient K2 will be described.

Referring to FIG. 2, power transmission efficiency may be calculated through Equation 7 below.

[Equation 7]

Here, Pin is the transmission power that the power supply device 100 transmits to the wireless power transmission device 200, and Pout is the power consumed by the load 400 and the received power received by the load 400 at the same time. can do. IL is a current flowing through the load 400.

The current I1 is a current input to the wireless power transmission apparatus 200, and at the same time is a current flowing through the transmission induction coil unit 211.

The current I1 can be calculated through the following process.

First, if the current flowing through the receiving resonance coil unit 311 is I3, I3 may be expressed as in Equation 8 below.

[Equation 8]

If the current flowing through the transmission resonant coil unit 212 is I2, I2 may be expressed as in Equation 9 below.

[Equation 9]

If the current flowing through the transmission induction coil unit 211 is I1, I1 may be expressed as in Equation 10 below.

[Equation 10]

Substituting [Equation 8] into [Equation 9], substituting the equation into [Equation 10] and the first input impedance (Z1) expressed by the mutual inductance (M2) calculated above Substituting in [Equation 7], the following [Equation 11] for the power transmission efficiency is obtained.

[Equation 11]

[Equation 11] is summarized as [Equation 12] below.

[Equation 12]

The quality index (Q2) of the transmission resonant coil unit 212 is expressed by Equation 13 below, and the quality index (Q3) of the reception resonant coil unit 311 is expressed by Equation 14 below do.

[Equation 13]

[Equation 14]

When [Equation 13] and [Equation 14] are substituted into [Equation 12], the following [Equation 15] is summarized.

[Equation 15]

For convenience of calculation, x is replaced with the following [Equation 16] and m with the following [Equation 17].

[Equation 16]

[Equation 17]

When [Equation 16] and [Equation 17] are substituted for [Equation 15], which is an equation for power transmission efficiency, the power transmission efficiency can be summarized as [Equation 18] below.

[Equation 18]

When [Equation 18] is differentiated with respect to x in order to obtain a condition in which the power transmission efficiency is maximized, it can be arranged as [Equation 19] below.

[Equation 19]

In [Equation 19], the condition that the power transmission efficiency is maximized is when x is equal to [Equation 20] below.

[Equation 20]

Substituting x in [Equation 16] and m in [Equation 17] in [Equation 20], the following [Equation 21] is obtained.

[Equation 21]

When [Equation 21] is summarized for RL, the following [Equation 22] is obtained.

[Equation 22]

That is, when the impedance RL of the load 400 has a value equal to [Equation 22], the power transmission efficiency becomes maximum. At this time, the power transmission efficiency can be calculated as in [Equation 23].

[Equation 23]

That is, when the impedance RL of the load 400 is equal to [Equation 22], the maximum power transmission efficiency can be obtained as [Equation 23].

Referring to [Equation 22], it is shown that the impedance RL of the load 400 that satisfies the condition that the power transmission efficiency is maximized may vary according to the coupling coefficient K.

Specifically, the relationship between the coupling coefficient (K) of [Equation 22] and the impedance of the load 400 is illustrated in a graph, as shown in FIG. 4.

In FIG. 4, the x-axis represents the coupling coefficient (K), and the y-axis represents the load impedance.

Referring to FIG. 4, it can be seen that the load impedance decreases as the coupling coefficient K increases, and the load impedance increases as the coupling coefficient K decreases. That is, the power transmission efficiency can be maximized only when the load impedance is variable according to the coupling coefficient K.

Coupling coefficient (K) may vary depending on any one or more of the distance between the wireless power transmitting device 200 and the wireless power receiving device 300, the mutually positioned, accordingly, in order to obtain the maximum power transmission efficiency, load ( The impedance of 400) needs to be changed.

5 is a graph showing the relationship between the coupling coefficient (K) and the load impedance through specific values.

When the coupling factor (K) is 0.05, the load impedance is 13.3 ohms, when the coupling factor (K) is 0.10, the load impedance is 8 ohms, and when the coupling factor (K) is 0.25, the load impedance is 5 ohms. , When the load impedance decreases as the coupling coefficient (K) increases, the power transmission efficiency becomes maximum.

Generally, there is a battery of a portable terminal used for the load 400. The impedance of the battery tends to vary depending on the amount of power applied to the battery. Here, the battery of the portable terminal is mentioned as an example of the load 400, but it is not necessary to be limited thereto, and it does not matter as long as the impedance of the load 400 varies according to the amount of power applied to the load 400.

Referring to FIG. 6, the relationship of the current to the voltage applied to the battery is illustrated graphically.

The impedance RL of the battery may be expressed as in Equation 24 below.

[Equation 24]

Here, V is a voltage applied to the battery, and I is a current flowing through the battery.

If 4V is applied to the battery, the amount of power applied to the battery is 1.2W (4V X 0.3A), and the impedance of the battery is 13.3 ohms (4V/0.3A).

If 4.583V is applied to the battery, the amount of power applied to the battery is 2.0W (4.583V X 0.437A), and the impedance of the battery is about 10.5 ohms (4.458V/0.437A).

If 5V is applied to the battery, the amount of power applied to the battery is 5.0W (5V X 1.0A), and the impedance of the battery is 5.0 ohm (5V/1A).

That is, the impedance of the battery may vary according to the amount of power applied to the battery.

In addition, using this result, a graph showing a relationship between load impedance according to the amount of power applied to the battery to satisfy the maximum power transmission efficiency is shown in FIG. 7.

In FIG. 7, the x-axis is the amount of power applied to the battery, and the y-axis is the impedance of the battery (load).

As shown in FIG. 7, it can be seen that the impedance of the battery varies depending on the amount of power applied to the battery.

Here, when comparing FIGS. 5 and 7, it can be confirmed that the shapes of the graphs are similar. Specifically, referring to FIG. 5, it can be seen that the load impedance decreases as the coupling coefficient K increases, and the load impedance increases as the coupling coefficient K decreases. Referring to FIG. 7, the battery It can be seen that the impedance of the battery decreases as the amount of power applied to the battery decreases, and the impedance of the battery increases as the amount of power applied to the battery decreases, and the shapes of the graphs shown in FIGS. 5 and 7 are very similar. can confirm.

That is, if the load 400 of the wireless power transmission system 10 is employed such as a battery, the impedance of which can vary depending on the amount of power applied, a specific correspondence between the coupling coefficient K and the received power of the load 400 It can be confirmed that is established. In this case, if the transmission power of the load 400 is adjusted so that the corresponding relationship is established according to the coupling coefficient K, the condition for obtaining the maximum power transmission efficiency shown in FIG. 5 can be satisfied.

* That is, it is necessary to adjust the load impedance to obtain the maximum power transmission efficiency according to the coupling coefficient (K), which is possible by controlling the amount of power, as shown in FIG. In other words, if the reception power of the battery can be determined according to the coupling coefficient K, and if the transmission power is adjusted so that the battery receives the determined reception power, the condition that the power transmission efficiency of FIG. 5 is maximized is satisfied to transmit the maximum power. Efficiency can be obtained.

The correspondence can be represented as the graph of FIG. 8.

Referring to FIG. 8, a relationship between received powers received from the battery according to the coupling coefficient K is illustrated in a graph. When the coupling coefficient (K) is 0.05, when the power received from the battery is 1.2 W, when the coupling coefficient (K) is 0.10, when the power received from the battery is 2.0 W, and when the coupling coefficient (K) is 0.25, If the amount of power received by the battery is 5W, the condition for obtaining the maximum power transmission efficiency shown in FIG. 5 is satisfied.

*After all, in order to obtain the maximum power transmission efficiency, it is necessary to determine the received power that the load 400 should receive according to the coupling coefficient (K).

In one embodiment, the wireless power transmission apparatus 200 may further include a storage unit (not shown) that stores received power corresponding to the coupling coefficient K2. The wireless power transmitter 200 may search the storage unit and find the received power corresponding to the coupling coefficient K2 to determine the received power.

Referring to FIG. 3 again, the wireless power transmitter 200 checks the received power currently received by the load 400 (S107). Since the wireless power receiver 300 directly transmits the power received from the wireless power transmitter 200 to the load 400, the power received by the wireless power receiver 300 and the power received by the load 400 are Assume the same.

Various methods may be used for the wireless power transmitter 200 to check the power currently being received by the load 400.

In one embodiment, the wireless power transmitter 200 may check the received power currently received by the load 400 through the out-of-band communication described in FIG. 2. Specifically, the wireless power transmitter 200 requests information on the received power currently received by the wireless power receiver 300 through out of band communication, and receives a response to the request to check the current received power Can.

In one embodiment, the wireless power transmitter 200 may measure the intensity of current flowing inside the wireless power transmitter 200 to check the received power that the load 400 is currently receiving. In this case, the wireless power transmission device 200 may include the power supply device 100 described in FIG. 1. For example, the intensity of the current flowing inside the wireless power transmitter 200 may be related to the received power that the load 400 is currently receiving. Specifically, when the distance between the wireless power transmitter 200 and the wireless power receiver 300 is constant, the more power the load 400 is receiving, the greater the strength of the current flowing inside the wireless power transmitter 200. May increase, and the smaller the power received by the load 400, the smaller the intensity of the current flowing inside the wireless power transmitter 200 may be.

The wireless power transmitter 200 may include a storage unit 170 that stores the strength of the current flowing inside the wireless power transmitter 200 and the power received by the load 400 in correspondence, and stores the above. The storage unit 170 may be searched to find the received power corresponding to the measured intensity of the current and check the received power currently received by the load 400.

Thereafter, the wireless power transmitter 200 checks whether the identified received power is the same as the determined received power (S109).

If it is determined that the received power is different from the determined received power, the wireless power transmitter 200 determines the transmit power to be transmitted to the wireless power receiver 300 (S111). That is, the wireless power transmitter 200 may determine the transmit power corresponding to the determined received power in order to obtain the maximum power transmission efficiency.

The wireless power transmitter 200 controls the transmission power transmitted to the wireless power receiver 300 to transmit the determined transmission power to the wireless power receiver 300 (S113). In one embodiment, the wireless power transmission apparatus 200 may be a method of controlling the transmission power by controlling the power supply unit 110 that supplies power to the power supply apparatus 100, which is illustrated in FIGS. 9 and 10. Explain in detail.

In another embodiment, the wireless power transmitter 200 may measure the current flowing inside the wireless power transmitter 200 to control the transmit power. This will be described later in detail in FIGS. 11 and 12.

The wireless power transmitter 200 receives the determined transmission power from the power supply device 100 and transmits it to the wireless power receiver 300. The load 400 may receive the received power that satisfies the maximum power transmission efficiency from the wireless power receiving device 300.

As described above, according to an embodiment of the present invention, the wireless power transmission apparatus 200 transmits transmission power for maximum power transmission efficiency, and the load 400 receives for maximum power transmission efficiency. Power can be received, and consequently, power transmission efficiency can be maximized.

Next, a power control method according to another embodiment of the present invention will be described with reference to FIGS. 9 to 10 in conjunction with the contents of FIGS. 1 to 8. 9 to 10 are contents of a method for controlling the transmission power in step S113 of FIG. 3.

9 is a configuration diagram of a wireless power transmission system 20 according to another embodiment of the present invention, and FIG. 10 is a flowchart for explaining a power control method according to another embodiment of the present invention.

First, the wireless power transmission system 20 may include a power supply device 500, a wireless power transmission device 900, and a wireless power reception device 300.

The wireless power receiver 300 is the same as that described with reference to FIGS. 1 to 2.

The wireless power transmitter 900 may receive DC power from the power supply 500. Specifically, the wireless power transmitter 900 may transmit a voltage control signal to the power supply 500 to receive the regulated DC voltage.

The wireless power transmitter 900 includes a transmitter 910, a current sensing unit 930, an oscillator 940, an AC power generating unit 950, a control unit 960, a storage unit 970, and a DC blocking unit 980. It may further include.

When the DC voltage received from the power supply 500 is applied to the AC power generating unit 950, the current sensing unit 930 may sense a current flowing in the circuit and measure the strength of the sensed current. However, the point measured by the current sensing unit 930 need not be limited to this, and a point output from the AC power generation unit 950, which will be described later, may also be included.

The intensity of the current flowing inside the wireless power transmitter 900 may be varied according to the power transmission state between the wireless power transmitter 900 and the wireless power receiver 300. The power transmission state will be described later.

In one embodiment, the current sensing unit 930 may be a current transformer (CT).

The oscillator 940 (Oscillator) may generate an AC signal having a predetermined frequency. When the transmitter 910, which will be described later, transmits power to the wireless power receiver 300 using resonance, the oscillator 940 has a resonance frequency so that the transmission resonance coil included in the transmitter 910 operates at a resonance frequency. The AC signal may be generated and transmitted to the AC power generator 950. The AC signal generated by the oscillator 940 is applied to the AC power generator 950.

The AC power generation unit 950 may generate AC power using the AC signal received from the oscillator 940 of the DC power received from the AC DC converter 510 of the power supply 500.

The AC power generator 950 may amplify the AC signal applied from the oscillator 940. In one embodiment, the degree of amplification may vary depending on the magnitude of the DC voltage applied to the AC power generator 950.

In one embodiment, the AC power generation unit 950 may be a push-pull type dual MOSFET.

The controller 960 may control the overall operation of the wireless power transmitter 900.

The control unit 960 may detect a change in the power transmission state between the wireless power transmitter 900 and the wireless power receiver 300. The control unit 960 may detect a change in the power transmission state and determine DC power to be received from the power supply 500, and transmit power control signals to the power supply 500 to receive the determined DC power. You can use it to transmit. In one embodiment, the power transmission state may be for a distance between the wireless power transmitter 900 and the wireless power receiver 300 and the direction in which both devices are placed.

In one embodiment, the power transmission state may be for the power reception state of the wireless power receiver 300. For example, when the charging amount of the wireless power receiver 300 is less than the reference amount, the wireless power receiver 300 transmits more power than currently transmitted power through out-of-band communication. The wireless power transmission device 200 may be requested. Then, the wireless power transmitter 900 may determine the transmit power to be transmitted to the wireless power receiver 300 in response to the request. The wireless power transmitter 900 may determine DC power to be received from the power supply 500 in response to the determined transmission power, and may control the power supply 500 to receive the determined DC power. Thereafter, the wireless power transmitter 900 may receive the determined DC power from the power supply 500, convert the received DC power into AC power, and transmit the converted DC power to the wireless power receiver 300.

The control unit 960 receives the strength of the current measured by the current sensing unit 930, and the proximity distance between the wireless power transmitter 900 and the wireless power receiver 300 based on the measured current strength. You can check

The controller 960 may determine the DC voltage to be received from the power supply 500 using the identified proximity distance. The control unit 960 may transmit the voltage control signal including the determined DC voltage information to the power supply 500. At this time, the voltage control signal may be transmitted between the wireless power transmitter 900 and the power supply 500 by using power line communication. Power line communication refers to a technology that transmits data on high-frequency signals of hundreds of kHz to tens of MHz or more using a power line that supplies power as a medium. That is, in the power line communication, a dedicated communication line is not separately installed, and communication is performed using the power line in which wiring is completed.

In one embodiment, the controller 960 may check the proximity distance, which is a distance between the wireless power transmitter 900 and the wireless power receiver 300, based on the measured current strength.

In one embodiment, the controller 960 may determine the DC voltage to be received from the power supply 500 based on the measured intensity of the current rather than the identified proximity distance.

The storage unit 970 may store the strength of the current measured by the current sensing unit 930 and the proximity distance between the wireless power transmitter 900 and the wireless power receiver 300 in the form of a look-up table.

The storage unit 970 may store the intensity of the current measured by the current sensing unit 930 and the DC voltage that the wireless power transmitter 900 receives from the power supply 500 in the form of a look-up table.

The storage unit 970 includes the strength of the current measured by the current sensing unit 930, the proximity distance between the wireless power transmitter 900 and the wireless power receiver 300, and the wireless power transmitter 900 power supply ( 500) may correspond to a DC voltage to be received from and stored in the form of a look-up table.

The DC blocking unit 980 may block the DC signal applied to the control unit 960. In one embodiment, the DC blocking unit 980 may be configured as a capacitor.

The transmitter 910 may wirelessly transmit AC power output from the AC power generator 950 to the wireless power receiver 300.

The power supply 500 may include an AC DC converter 510, a control unit 520, and a DC blocking unit 530. In one embodiment, the power supply 500 may be an adapter capable of converting AC power received from the outside into DC power.

The AC DC converter 510 may convert AC voltage received from the outside into DC voltage having a predetermined size. At this time, the AC voltage received from the outside may have a size of 220V and a frequency of 60 Hz, but need not be limited thereto. The controller 520 may control the AC DC converter 510 to receive the voltage control signal from the wireless power transmitter 900 and output the DC voltage determined by the wireless power transmitter 200. That is, the control unit 520 generates a voltage control signal to control the AC DC converter 510 to output a DC voltage corresponding to the strength of the current measured by the wireless power transmitter 900 to the AC DC converter 510 Can transmit. The AC/DC converter 510 may receive the voltage control signal and convert the AC voltage received from the outside into a DC voltage of a predetermined size and output the AC voltage.

The DC blocking unit 530 may block the DC signal applied to the control unit 520. In one embodiment, the DC blocking unit 530 may be configured as a capacitor.

10 is a ladder diagram for describing a power control method according to another embodiment of the present invention.

Hereinafter, a power control method according to an exemplary embodiment of the present invention will be described with reference to FIG. 9.

Referring to FIG. 10, first, the current sensing unit 930 may measure the intensity of a current flowing inside the wireless power transmitter 900 (S201 ). The current sensing unit 930 may sense the current flowing inside the wireless power transmitter 900 to measure the strength of the sensed current.

In one embodiment, the current sensing unit 930 may measure the intensity of the current input to the AC power generating unit 950 illustrated in FIG. 9. In another embodiment, the current sensing unit 930 may measure the intensity of the current output from the AC power generating unit 950, but is not limited thereto, and the current flowing inside the wireless power transmitter 900 You can measure the intensity.

In one embodiment, the current sensing unit 930 may be a current transformer (CT). The current transformer is a device that can measure by lowering the high current flowing in the circuit to a low current with a required value. That is, the current transformer may be deformed with a current proportional to any current flowing through the circuit to measure the current. More specifically, the current transformer is composed of a primary winding, a secondary winding, and an iron core. When an electromagnetic induction phenomenon occurs due to a magnetic flux passing through the iron core, the primary current can be transformed into a secondary current in proportion to the current ratio. , The modified secondary current can be measured.

In one embodiment, the current sensing unit 930 may be any one of a current transformer, a rod type, a through type, a third winding type, and a multi-core iron core type current transformer.

In one embodiment, the intensity of the current measured by the current sensing unit 930 may be varied according to a distance between the wireless power transmitter 900 and the wireless power receiver 300. That is, as the intensity of the current measured by the current sensing unit 930 increases, it means that the distance between the wireless power transmitting apparatus 900 and the wireless power receiving apparatus 300 approaches, and measured by the current sensing unit 930. As the intensity of the current decreases, it may mean that the distance between the wireless power transmitter 900 and the wireless power receiver 300 increases.

The proximity distance between the wireless power transmitter 900 and the wireless power receiver 300 may mean a distance between coils included in the device.

The controller 960 may check the proximity distance, which is a distance between the wireless power transmitter 900 and the wireless power receiver 300, based on the measured intensity of the current (S203). The wireless power transmitter 900 may check the proximity distance, which is a distance between the wireless power transmitter 900 and the wireless power receiver 300, based on the strength of the current measured through the controller 960. In one embodiment, the storage unit 970 may store the strength of the measured current and the proximity distance in the form of a look-up table, and the control unit 960 searches the storage unit 970 for the measured current. The proximity distance corresponding to the intensity can be checked.

The controller 960 determines a DC voltage to be received from the power supply 500 based on the identified proximity distance (S205).

In one embodiment, the controller 960 may determine the DC voltage to be received from the power supply 500 based on the measured intensity of the current rather than the identified proximity distance. At this time, step S203 may be omitted. That is, when the storage unit 970 stores the measured intensity of the current and the DC voltage to be received by the wireless power transmitter 900, the control unit 960 searches the storage unit 970 and measures the The wireless power transmitter 900 corresponding to the current strength may determine the DC voltage to be received.

In another embodiment, the storage unit 970 is the strength of the current measured by the current sensing unit 930, the proximity distance between the wireless power transmitter 900 and the wireless power receiver 300 and the power supply 500 It may be stored in correspondence with the DC voltage to be received.

The wireless power transmitter 900 transmits a voltage control signal based on the determined DC voltage to the power supply 500 (S207). In one embodiment, the voltage control signal may be a signal for the wireless power transmitter 900 to control the power supply 500 to receive the determined DC voltage from the power supply 500.

In one embodiment, the wireless power transmitter 900 and the power supply 500 may perform communication using a power line communication (PLC) method. The wireless power transmitter 900 may transmit the voltage control signal to the power supply 500 using power line communication. Power line communication refers to a technology that transmits data on high-frequency signals of hundreds of kHz to tens of MHz or more using a power line that supplies power as a medium. That is, in the power line communication, a dedicated communication line is not separately installed, and communication is performed using the power line in which wiring is completed.

As described above, when the voltage control signal is transmitted using the power line communication according to the embodiment of the present invention, there is no need for a power line to separately transmit the voltage control signal, so that an effect of cost reduction can be obtained. That is, according to an embodiment of the present invention, since the voltage control signal is transmitted and received using a power line that is a medium for transmitting power between the power supply 500 and the wireless power transmitter 900, a separate power line is not required. Does not.

In addition, according to an embodiment of the present invention, the DC voltage received from the power supply 500 can be adjusted using power line communication without a DC-DC converter that converts the DC voltage to a predetermined voltage. The manufacturing cost of the power transmission device 900 can be greatly reduced.

In the process of the wireless power transmitter 900 transmitting a voltage control signal to the power supply 500, the DC blocking unit 980 may block the DC signal applied to the control unit 960. The wireless power transmitter 900 receives the DC voltage from the power supply 500. When the DC voltage is applied to the controller 960, the controller 960 may be damaged. The DC voltage may be cut off to protect the controller 960.

In one embodiment, the DC blocking unit 980 may be configured as a capacitor. The impedance of the capacitor can be expressed as Xc=1/2ㅠfC. When a DC signal is applied to the capacitor (the frequency is f=0), the impedance becomes infinite, and the DC signal can be blocked.

Since the voltage control signal transmitted from the wireless power transmitter 900 to the power supply 500 is an AC signal, the control unit 960 sends the voltage control signal to the power supply 500 regardless of the DC blocking unit 980. Can transmit.

The power supply 500 receives a voltage control signal from the wireless power transmitter 900 and generates a voltage control signal for outputting a DC voltage to be transmitted to the wireless power transmitter 900 according to the received voltage control signal ( S209). The power supply device 500 may generate a voltage control signal for outputting a DC voltage to be transmitted to the wireless power transmitter 900 through the control unit 520. The control unit 520 may transmit the voltage control signal to the AC DC converter 510.

In the process of the power supply 500 receiving a voltage control signal from the wireless power transmitter 900, the DC blocking unit 530 of the power supply 500 may block the DC signal applied to the control unit 520. have. The AC DC converter 510 of the power supply 500 transmits a DC voltage to the wireless power transmitter 900. When the DC voltage is applied to the controller 520, the controller 520 may be damaged. The DC blocking unit 530 may block the DC voltage to protect the control unit 520.

In one embodiment, the DC blocking unit 530 may be configured as a capacitor. The impedance of the capacitor can be expressed as Xc=1/2ㅠfC. When a DC signal is applied to the capacitor (the frequency is f=0), the impedance becomes infinite, and the DC signal can be blocked.

The power supply device 500 receives the voltage control signal from the control unit 520 to adjust the DC voltage (S211). The power supply device 500 may receive a voltage adjustment signal through the AC DC converter 510 to adjust the DC voltage to be transmitted to the wireless power transmitter 200. The AC DC converter 510 may convert an AC voltage applied from the outside into a predetermined DC voltage based on the voltage adjustment signal and output the AC voltage.

The power supply 500 transmits the regulated DC voltage to the wireless power transmitter 200 (S113). The power supply 500 may transmit the regulated DC voltage to the wireless power transmitter 900 through the AC DC converter 510.

The AC power generator 950 converts the received DC power into AC power based on the AC signal having a constant frequency received from the oscillator 940 (S215).

The AC power generator 950 transmits the output AC power to the transmitter 910 (S217).

The AC power delivered to the transmitter 910 may be transmitted to the wireless power receiver 300 by resonance.

As described above, according to an embodiment of the present invention, power provided by the power supply device can be controlled according to a power transmission environment between the wireless power transmitter and the wireless power receiver, so that a separate DC-DC converter is not required. Accordingly, it is possible to obtain an effect of significantly reducing the manufacturing cost of the wireless power transmission device.

Next, referring to FIGS. 11 to 12, a power control method according to another embodiment of the present invention will be described in connection with the contents of FIGS. 1 to 8. 11 to 12 are contents of a method for controlling the transmission power in step S113 of FIG. 3.

11 is a flowchart for explaining a power control method according to another embodiment of the present invention, and FIG. 12 is a current value, a coupling coefficient, and a second output voltage measured when the first output voltage is applied to the AC power generating unit, It is a figure for demonstrating the lookup table which matched an appropriate current range.

The description of the wireless power transmission apparatus 200 is the same as described in FIG. 1, and in this case, it is assumed that the wireless power transmission apparatus 200 includes all of the components of the power supply apparatus 100.

First, the controller 180 controls the DC-DC converter 130 so that the voltage applied to the AC power generating unit 160 is adjusted to the first output voltage (S301). Here, the first output voltage may mean a predetermined DC voltage.

Thereafter, the current sensor unit 140 measures the intensity of the current applied to the AC power generating unit 160 when the DC voltage output from the DC DC converter 130 is applied to the AC power generating unit 160. It can be (S303). The intensity of the current applied to the AC power generating unit 160 may be varied according to the power transmission state between the wireless power transmitter 200 and the wireless power receiver 300. In one embodiment, the power transmission state may mean a distance and a direction between the wireless power transmitter 200 and the wireless power receiver 300. That is, the power transmission state may refer to a combined state between the wireless power transmitter 200 and the wireless power receiver 300.

In the present invention, the combined state may refer to an index related to a coupling coefficient between a transmitting coil and a receiving coil due to a distance and a positional relationship between the wireless power transmitting device 200 and the wireless power receiving device 300. That is, in the present invention, the combined state may collectively refer to all indicators associated with a coupling coefficient, such as the amount of current flowing through the wireless power transmitter 200 and the input impedance of the wireless power transmitter 200.

In one embodiment, the power transmission state may refer to information on the power reception state of the wireless power receiver 300.

In addition, the intensity of the current applied to the AC power generation unit 160 may be associated with a coupling coefficient between the transmission resonance coil unit 212 and the reception resonance coil unit 311 of the wireless power transmitter 200. Coupling coefficient refers to the degree of electromagnetic coupling between the transmitting resonant coil unit 212 and the receiving resonant coil unit 311 and has a range from 0 to 1.

Meanwhile, the controller 180 checks whether the measured intensity of the current is greater than or equal to a threshold (S305). In one embodiment, the threshold may be 100mA, but this is only an example. The threshold value may mean a minimum current value required for the wireless power receiver 300 to be detected. That is, when the intensity of the measured current is greater than or equal to a threshold, the wireless power receiver 300 may be detected, and when the intensity of the measured current is less than the threshold, the wireless power receiver 300 It can be considered that is not detected.

If the intensity of the measured current is greater than or equal to the threshold, the controller 180 determines a second output voltage corresponding to the measured intensity of the current (S307). The controller 180 may determine the second output voltage by searching the storage unit 170 for a DC voltage corresponding to the strength of the current applied to the AC power generator 160. In one embodiment, the second output voltage may refer to a voltage required to transmit power to the detected wireless power receiver 300.

Thereafter, the controller 180 controls the DC-DC converter 130 so that the determined second output voltage is applied to the AC power generator 160 (S309). DC DC converter 130 outputs the second output voltage under the control of the controller 180 and transmits it to the AC power generator 160.

Thereafter, the current sensor 270 measures the intensity of the current applied to the AC power generation unit 160 again (S111).

Thereafter, the controller 180 may check whether the measured intensity of the current corresponds to an appropriate current range (S313). Here, the appropriate current range may mean a current range corresponding to the second output voltage when the second output voltage is applied to the AC power generator 160. The proper current range may increase as the second output voltage increases, and the range of the value may decrease as the second output voltage decreases.

The controller 180 may search the storage unit 170 for an appropriate current range corresponding to the second output voltage, and check whether the measured current intensity corresponds to an appropriate current range.

If, when the measured current strength is within the appropriate current range, the controller 180 waits for a predetermined time (S315) and returns to step S311. That is, the controller 180 may periodically check whether the measured intensity of the current corresponds to the second output voltage applied to the AC power generating unit 160 by measuring the intensity of the current applied to the AC power generating unit 160. have.

On the other hand, when the intensity of the current measured in step S105 is less than the threshold, the controller 180 controls the DC-DC converter 130 to adjust the first output voltage to be 0V (S317).

That is, when the measured intensity of the current is less than the threshold, the controller 180 determines that the wireless power receiver 300 is not detected and adjusts the first output voltage to be 0V. When the voltage applied to the AC power generating unit 160 becomes 0V, the wireless power transmitter 200 does not transmit power to the wireless power receiver 300.

Accordingly, when the wireless power receiving apparatus 300 is not detected, the wireless power transmitting apparatus 200 may prevent insignificant power loss.

Meanwhile, when the first output voltage is adjusted to be 0 V, the controller 180 waits 0.1 seconds (S319). Here, 0.1 second is only an example.

When 0.1 second has elapsed, the controller 180 returns to step S301 and adjusts the DC voltage applied to the AC power generating unit 160 to be the first output voltage.

On the other hand, if the intensity of the current measured in step S313 does not fall within the appropriate current range, the process returns to step S307. That is, the controller 180 may control the DC-DC converter 130 so that the second output voltage corresponding to the strength of the current measured in step S113 is applied to the AC power generator 160. The intensity of the current measured in step S313 may refer to the power reception state of the wireless power receiver 300.

For example, when the intensity of the current measured in step S313 is measured to be lower than an appropriate current range, the distance between the wireless power transmitter 200 and the wireless power receiver 300 is considered closer, and the controller 180 In order to reduce the amount of transmission power transmitted to the wireless power receiver 300, the DC direct current converter 130 may be controlled such that a lower DC voltage is applied to the AC power generating unit 160.

As described above, according to the power control method according to an embodiment of the present invention, the power reception state of the wireless power receiving apparatus 300 is determined through the intensity of the current applied to the AC power generation unit 160 to determine the power corresponding thereto. The amount of transmission power can be adjusted to transmit. Due to this, the power transmission efficiency is maximized, there is an effect that can reduce the amount of power loss.

12 is a view for explaining a look-up table corresponding to a current value, a coupling coefficient, a second output voltage, and an appropriate current range measured when the first output voltage is applied to the AC power generating unit 160.

The lookup table of FIG. 12 is stored in the storage unit 170.

When the first output voltage is applied to the AC power generating unit 160 when the current measured by the current sensor unit 140 is 100 mA or more, the wireless power receiver 300 may be regarded as detected.

The first output voltage may be 12V, but this is only an example.

If, when the first output voltage is applied to the AC power generation unit 160, the current measured by the current sensor unit 140 is 120mA, the transmission resonance coil unit 212 and the wireless power of the wireless power transmission device 200 The coupling coefficient of the reception resonance coil unit 311 of the reception device 300 corresponds to 0.05. In this case, the controller 180 determines that the wireless power receiving device 300 is far from the wireless power transmitting device 200, and sets the DC voltage applied to the AC power generating unit 160 to 28V (second output voltage). ), the DC-DC converter 130 is controlled.

Thereafter, when the DC voltage applied to the AC power generating unit 160 is maintained at 28V, the controller 180 determines whether the current applied to the AC power generating unit 160 satisfies an appropriate current range (751 to 800mA). To confirm.

If the current applied to the AC power generating unit 160 is out of an appropriate current range, a current is measured by applying the first output voltage 12V to the AC power generating unit 160. When the measured current value is 180mA, the controller 180 determines that the distance between the wireless power transmitter 200 and the wireless power receiver 300 is closer than the 120mA case, and adjusts the second output voltage to 26V. do.

In the above example, the distance between the wireless power transmitter 200 and the wireless power receiver 300 has been described in relation to the current intensity, but in addition, the direction in which the wireless power transmitter 200 and the wireless power receiver 300 are placed Various power transmission states may be considered.

As described above, the wireless power transmitter 200 controls power transmitted to the wireless power receiver 300 in consideration of various power transmission conditions such as distance and direction from the wireless power receiver 300 to maximize power transmission efficiency. And can prevent power loss.

Next, with reference to FIGS. 13 to 15, a method for detecting a coupling coefficient according to another embodiment of the present invention will be described in conjunction with the contents of FIGS. 1 to 3.

13 is a flow chart for explaining a method of detecting a coupling coefficient according to another embodiment of the present invention, and FIG. 14 is a view for explaining a case in which the switch SW is opened to vary the output impedance ZL. , FIG. 15 is a view for explaining a case where the switch SW is shorted to change the output impedance ZL.

First, a method of detecting a coupling coefficient according to another embodiment of the present invention will be described with reference to FIG. 13.

First, the wireless power receiver 300 varies the output impedance (S401). The output impedance ZL may be the impedance measured when the load 400 is viewed by the receiver 310. The wireless power receiver 300 may include a switch SW, and the output impedance may be varied through the switch SW. One end of the switch SW is connected to the capacitor C4, and the other end is connected to one end of the load 400. The other end of the capacitor C4 is connected to one end of the load 400.

Referring to FIG. 14, the wireless power receiving device 300 may open the switch SW by transmitting an open signal to the switch SW. When the switch SW is opened, the output impedance ZL can be expressed as Equation 25 below.

[Equation 25]

In Equation 1, Equation 3, and Equation 5, R2 and R3 are assumed to have very small values and are set to 0 ohms, and the transmission induction coil L1, the capacitor C1, and the transmission resonance coil (L2) and the capacitor (C2), the receiving resonance coil (L3) and the capacitor (C3) and receiving induction coil (L4) and the capacitor (C4) both set the value to resonate at the resonance frequency (Equation 5) The first input impedance Z1 of may be arranged as shown in [Equation 26].

[Equation 26]

In addition, when [Equation 2], [Equation 4], and [Equation 6] are used, [Equation 26] may be summarized as [Equation 27] below.

[Equation 27]

When the receiving induction coil L4 and the capacitor C4 are set to resonate at the resonant frequency w, and substituting the output impedance ZL of Equation 25 into Equation 27, the first input impedance ( Z1) is summarized as [Equation 28] below.

[Equation 28]

Referring to FIG. 15, the wireless power receiver 300 may short-circuit the switch SW by transmitting a short-circuit signal to the switch SW. When the switch SW is short-circuited, the output impedance ZL becomes 0, and the first input impedance Z1 is summarized as in Equation 29 below.

[Equation 29]

The wireless power receiver 300 may apply the control signal to the switch SW to short the switch SW for a predetermined period of time. A certain period may be 1 second, and a certain time may be 100us, but this is only an example.

Then, the detection unit 220 measures the input impedance (S403). In one embodiment, the detector 220 may measure the first input impedance Z1 using the current and voltage input from the power supply device 100 to the wireless power transmission device 200.

Thereafter, the detection unit 220 may detect the coupling coefficient between the transmission resonance coil L2 of the transmission unit 210 and the reception resonance coil L3 of the reception unit 310 using the measured input impedance (S405 ). That is, referring to [Equation 29] and [Equation 30], since all other variables except the coupling coefficient K2 are fixed values, when measuring the first input impedance Z1, the coupling coefficient K2 is Can be detected.

Next, a power control method according to another embodiment of the present invention will be described with reference to FIGS. 16 to 17.

16 is a flowchart illustrating a power control method according to another embodiment of the present invention, and FIG. 17 is a view for explaining a lookup table used in the power control method according to the embodiment of FIG. 16.

First, referring to FIG. 16, the wireless power transmitter 200 measures an input impedance (S501).

The detection unit 220 detects a coupling coefficient between the transmission resonance coil unit 212 and the reception resonance coil unit 311 using the measured input impedance (S503). The method of detecting the coupling coefficient is the same as that described with reference to FIGS. 3 and 13, so detailed descriptions are omitted.

The wireless power transmitter 200 searches for transmit power corresponding to the detected coupling coefficient (S505). The storage unit 170 of the wireless power transmission device 200 stores a look-up table in which transmission power is correlated according to the coupling coefficient, and the wireless power transmission device 200 searches the storage unit 170 for detection. Find the transmission power corresponding to the coupling coefficient.

The lookup table will be described with reference to FIG. 17.

Referring to FIG. 17, a lookup table to which distance, input test current, coupling coefficient, load impedance, received power, power transmission efficiency, and transmission power correspond may be confirmed.

Here, the distance may mean a distance between the wireless power transmitter 200 and the wireless power receiver 300, specifically, the distance between the wireless power transmitter 200 and the wireless power receiver 300 is illustrated in FIG. 2. It may be a distance between one transmission resonance coil unit 212 and the reception resonance coil unit 311. Referring to FIG. 17, it can be confirmed that the coupling coefficient decreases as the distance increases.

The input test current is a current applied to the wireless power transmitter 200.

The power transmission efficiency refers to power transmission efficiency between the wireless power transmitter 200 and the wireless power receiver 300 or between the wireless power transmitter 200 and the load 400.

Load impedance refers to the impedance that the load 400 must have in order to obtain maximum power transmission efficiency. It can be confirmed that the relationship between the load impedance and the coupling coefficient is the same as the trend of the graph shown in FIG. 4.

The received power is the power received by the load 400 and represents the power that the load 400 should receive in order to obtain the maximum power transmission efficiency in correspondence with the coupling coefficient.

The transmit power is power that the wireless power transmitter 200 needs to transmit to the wireless power receiver 300 to obtain maximum power transmission efficiency.

The wireless power transmission apparatus 200 may search transmission power corresponding to the detected coupling coefficient through the look-up table.

The wireless power transmitter 200 determines the transmit power obtained by the search as the transmit power for transmitting to the load 400 (S507). That is, the wireless power transmission apparatus 200 may determine the transmission power corresponding to the detected coupling factor in order to obtain the maximum power transmission efficiency.

The wireless power transmission apparatus 200 controls the transmission power to transmit the determined transmission power to the load 400 (S509). In one embodiment, the wireless power transmission apparatus 200 may be a method of controlling the transmission power by controlling the power supply 500 that supplies power to the power supply 100, and for this, FIGS. 9 and 10 Same as described in

In another embodiment, the wireless power transmitter 200 may measure the current flowing inside the wireless power transmitter 200 to control the transmit power. This is the same as described in FIGS. 11 and 12.

In the power control method according to another embodiment of the present invention, since the transmission power can be determined through the detection of the coupling coefficient and the search process of the storage unit, the configuration of parts is simplified and the power control process is simplified.

The power control method according to the above-described exemplary embodiment of the present invention is manufactured as a program to be executed in a computer and stored in a computer-readable recording medium. Examples of the computer-readable recording medium include ROM, RAM, and CD -ROM, magnetic tape, floppy disk, optical data storage, and the like, and also includes those implemented in the form of a carrier wave (for example, transmission via the Internet).

The computer-readable recording medium can be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. And, functional programs, codes, and code segments for implementing the method can be easily inferred by programmers in the technical field to which the present invention pertains.

In addition, although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the technical field to which the present invention pertains without departing from the gist of the present invention claimed in the claims. In addition, various modifications can be implemented by those having ordinary knowledge in the course, and these modifications should not be individually understood from the technical idea or prospect of the present invention.

100: power supply
200: wireless power transmission device
210: transmitting unit
211: transmission induction coil unit
212: transmission resonance coil unit
220: detection unit
300: wireless power receiver
310: receiver
311: receiving resonance coil unit
312: receiving induction coil unit
320: rectifier
400: load
500: power supply

Claims (36)

A transmitting coil that wirelessly transmits power to the receiving coil of the wireless power receiving apparatus; And
It includes a control unit for limiting the transmission power according to the coupling state between the transmitting coil and the receiving coil,
The control unit,
When the combined state is the first coupled state, the transmission power is limited to the first power,
When the combined state is the second combined state, the transmission power is limited to the second power,
When the combined state is the third combined state, the transmission power is limited to the third power,
The coupling coefficient of the first coupling state is greater than the coupling coefficient of the second coupling state, and the coupling coefficient of the second coupling state is greater than the coupling coefficient of the third coupling state,
The first power is greater than the second power, the second power is greater than the third power,
The first power is the maximum power corresponding to the maximum power transmission efficiency of the first combined state,
The second power is the maximum power corresponding to the maximum power transmission efficiency of the second combined state,
The third power is a wireless power transmission device that is the maximum power corresponding to the maximum power transmission efficiency of the third combined state. According to claim 1,
A wireless power transmission device including a power supply device for supplying power to the transmission coil. The method according to claim 1 or 2,
A wireless power transmitter that exchanges information through the in-band communication with the wireless power receiver. The method according to claim 1 or 2,
A wireless power transmission device that receives status information of the wireless power reception device. According to claim 4,
The status information of the wireless power receiving device is a wireless power transmission device that includes information about the current charge amount or charge trend. The method according to claim 1 or 2,
A wireless power transmission device that receives status information of the wireless power reception device and transmits power suitable for it. The method according to claim 1 or 2,
A wireless power transmission device that transmits status information of the wireless power transmission device. The method of claim 7,
The status information of the wireless power transmission device is a wireless power transmission device that includes information about the maximum amount of power supplied or available power. delete delete A transmitting coil that wirelessly transmits power to the receiving coil of the wireless power receiving apparatus; And
It includes a control unit for limiting the current input to the transmitting coil according to the coupling state between the transmitting coil and the receiving coil,
The control unit,
When the coupled state is the first coupled state, the current is limited to the first current,
When the coupling state is the second coupling state, the current is limited to the second current,
When the coupling state is the third coupling state, the current is limited to the third current,
The coupling coefficient in the first coupling state is greater than the coupling coefficient in the second coupling state,
The first current is greater than the second current, and the second current is greater than the third current,
The first current is a maximum current corresponding to the maximum power transmission efficiency of the first combined state,
The second current is a maximum current corresponding to the maximum power transmission efficiency of the second combined state,
The third current is a wireless power transmission device that is the maximum current corresponding to the maximum power transmission efficiency of the third combined state. The method of claim 11,
A wireless power transmission device including a power supply device for supplying power to the transmission coil. The method of claim 11 or 12,
A wireless power transmitter that exchanges information through the in-band communication with the wireless power receiver. The method of claim 11 or 12,
A wireless power transmission device that receives status information of the wireless power reception device. The method of claim 14,
The status information of the wireless power receiving device is a wireless power transmission device that includes information about the current charge amount or charge trend. The method of claim 11 or 12,
A wireless power transmission device that receives status information of the wireless power reception device and transmits power suitable for it. The method of claim 11 or 12,
A wireless power transmission device that transmits status information of the wireless power transmission device. The method of claim 17,
The status information of the wireless power transmission device is a wireless power transmission device that includes information about the maximum amount of power supplied or available power. Transmitting power wirelessly to a receiving coil of the wireless power receiving device; And
And limiting the transmission power according to the coupling state between the transmission coil and the reception coil of the wireless power transmission device,
The step of limiting the transmission power,
When the combined state is the first coupled state, limiting the transmission power to the first power:
Limiting the transmission power to the second power when the combined state is the second coupled state; And
And when the combined state is the third combined state, limiting the transmission power to third power.
The coupling coefficient in the first coupling state is greater than the coupling coefficient in the second coupling state,
The first power is greater than the second power, the second power is greater than the third power,
The first power is the maximum power corresponding to the maximum power transmission efficiency of the first combined state,
The second power is the maximum power corresponding to the maximum power transmission efficiency of the second combined state,
The third power is a wireless power transmission method that is the maximum power corresponding to the maximum power transmission efficiency of the third combined state. The method of claim 19,
A wireless power transmission method comprising the step of supplying power to the transmission coil by a power supply device. The method of claim 19 or 20,
Wireless power transmission method comprising the step of exchanging information through the in-band communication with the wireless power receiver. The method of claim 19 or 20,
And receiving status information of the wireless power receiver. The method of claim 22,
The status information of the wireless power receiving device is a wireless power transmission method that includes information about the current charge amount or charge trend. The method of claim 19 or 20,
And receiving status information of the wireless power receiving device and transmitting power suitable for the wireless power receiving device. The method of claim 19 or 20,
And transmitting status information of the wireless power transmitter. The method of claim 25,
The wireless power transmission method of the wireless power transmission apparatus includes information about the maximum amount of power supplied or the amount of power available. delete delete Transmitting power wirelessly to a receiving coil of the wireless power receiving device; And
And limiting a current input to the transmitting coil according to a coupling state between the transmitting coil and the receiving coil of the wireless power transmitter,
The step of limiting the current,
When the combined state is the first coupled state, limiting the current to the first current;
Limiting the current to a second current when the coupled state is the second coupled state; And
When the coupling state is the third coupling state, the current is limited to the third current,
Including,
The coupling coefficient in the first coupling state is greater than the coupling coefficient in the second coupling state,
The first current is greater than the second current, and the second current is greater than the third current,
The first current is a maximum current corresponding to the maximum power transmission efficiency of the first combined state,
The second current is a maximum current corresponding to the maximum power transmission efficiency of the second combined state,
The third current is a wireless power transmission method that is the maximum current corresponding to the maximum power transmission efficiency of the third combined state. The method of claim 29,
A wireless power transmission method comprising the step of supplying power to the transmission coil by a power supply device. The method of claim 29 or 30,
Wireless power transmission method comprising the step of exchanging information through the in-band communication with the wireless power receiver. The method of claim 29 or 30,
And receiving status information of the wireless power receiver. The method of claim 32,
The status information of the wireless power receiving device is a wireless power transmission method that includes information about the current charge amount or charge trend. The method of claim 29 or 30,
And receiving status information of the wireless power receiving device and transmitting power suitable for the wireless power receiving device. The method of claim 29 or 30,
And transmitting status information of the wireless power transmitter. The method of claim 35,
The wireless power transmission method of the wireless power transmission apparatus includes information about the maximum amount of power supplied or the amount of power available.

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