Wireless power transfer device and wireless power transfer system

A wireless power transfer system according to an embodiment of the present invention is a wireless power transfer system having a receiving part for receiving power from a transmitting part, wherein the transmitting part comprises: a power conversion part comprising a full bridge inverter; and a control part for controlling the power conversion part using a pulse width modulation (PWM) control signal, the duty ratio of the PWM control signal being determined by a duty ratio in which the ratio of the magnitude of harmonics to the magnitude of a fundamental frequency among frequency components of the output signal of the power conversion part is a minimum.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International Application No. PCT/KR2015/000163, filed on Jan. 7, 2015, which claims priority under 35 U.S.C. 119(a) to Patent Application No 10-2014-0002327, filed in the Republic of Korea on Jan. 8, 2014 and Patent Application No. 10-2014-0009243, filed in the Republic of Korea on Jan. 24, 2014, all of which are hereby expressly incorporated by reference into the present application.

TECHNICAL FIELD

Embodiments relate to a wireless power transfer technology.

BACKGROUND ART

Wireless power transfer (WPT) system is a technology of transferring power through a space without any wire, which maximizes ease of providing mobile equipment and digital appliances with power.

The wireless power transfer system has advantages of saving energy by a power usage control in real time, overcoming a restriction of space needed for providing power and reducing waste batteries by recharging batteries.

The wireless power transfer system is typically embodied in a magnetic induction scheme or a magnetic resonance scheme.

The magnetic induction scheme is a non-contact energy transfer technique where current is applied to one of two coils disposed closely each other and by means of the magnetic flux generated accordingly electromotive force is also applied to the other coil, which may use frequencies of hundreds of kHz.

The magnetic resonance scheme is a magnetic resonance technique where electric field or magnetic field only is used without using electromagnetic waves or current so that the distance of power transfer is more than several meters, which has a characteristic that band having tens of MHz is used.

However, there is a problem that power loss occurs due to the current loss at a receiving side.

Additionally, in the wireless power transfer system, there occurs a spurious wave, that is, a harmonic coming from a power transmitter, and such a harmonic component may cause an electromagnetic interference effect, thereby having a harmful effect on a body.

The harmonic refers to a frequency higher than a commercial frequency in terms of power, hundreds of Hz or higher, for example, which has integer multiple frequency of a fundamental.

The wireless power transfer system generates the harmonic component near the multiple frequency of the receiving frequency due to a non-linear characteristic of the receiver load, basically. That is, the AC signal provided from the receiver does not remain as its waveform but is distorted due to the non-linear load, forming a harmonic.

The harmonic component disturbs normal operations of surrounding equipment or causes undesired power reception, noise and various obstacles.

In more detail, changes of magnetic field emitting from the power transmitter generate current caused by electromagnetic induction phenomenon in a conductor of a stationary surrounding equipment, capable of causing abnormal operations. Also, magnetic field generated in the power transmitter causes current in a mobile equipment when the mobile equipment moves around the magnetic field, capable of causing obstacles. Also, when the power transmitter has a resonance condition similar to that of the surrounding equipment that does not want to receive power, there may occur a magnetic resonance coupling, capable of causing erroneous operations in the surrounding equipment.

Since the harmonic component may cause harmful effect on an electronic equipment and a body as described above, it is important to meet regulations for an electromagnetic compatibility (EMC), an electromagnetic interference (EMI) and an electromagnetic susceptibility (EMS).

FIG. 1is a block diagram of a transmitter for transmitting power in a conventional wireless power transfer system.

Referring toFIG. 1, the transmitter1may include a gate driver2, a power converter3of a half bridge type, a matching circuit4, and a transmission coil5.

A half bridge circuit of the power converter3in the art has two switches that are complementarily turned on and turned off when proper voltage waveforms are applied to gage driving inputs, respectively.

At this time, a square wave voltage generates which is used to switch between a common node of the two switches and the ground.

Since the output not of a sine wave but of the square wave has a problem that it has many of harmonic components that are integer multiple frequency of a fundamental wave, it is limited to reduce the harmonic using the power converter3in the art.

INVENTION

Technical Problem

An embodiment of the present disclosure provides a wireless power transfer device that is capable of minimizing current wasted or consumed and enhancing a wireless power transfer efficiency.

Another embodiment of the present disclosure provides a wireless power transfer system that includes the wireless power transfer device.

Yet another embodiment of the present disclosure provides a wireless power transfer device and a wireless power transfer system including the same that solve obstacles such as power reception and noise due to harmonic components included in an output signal of a power conversion part of a transmitter for transmitting power.

Still yet another embodiment of the present disclosure provides a wireless power transfer device and a wireless power transfer system including the same that approximates an output waveform of the power conversion part to a sign wave using the power conversion part including a full bridge inverter, improving a harmonic distortion ratio.

Still yet another embodiment of the present disclosure provides a wireless power transfer device and a wireless power transfer system including the same that feedback an output signal outputted from a power conversion part to measure a distribution of harmonic elements of the output signal and to provide a duty ratio that is capable of minimizing the harmonic components.

Technical Solution

In accordance with an embodiment of the present disclosure, there is provided a transmitter for generating a wireless power to be transmitted to a receiver, the transmitter comprising a power conversion part comprising a full bridge inverter; and a control part for controlling the power conversion part using a pulse width modulation (PWM) control signal, wherein a duty ratio of the PWM control signal is determined by a duty ratio in which a ratio of the magnitude of an harmonic to the magnitude of a fundamental frequency among frequency components of an output signal of the power conversion part is a minimum.

In the transmitter according to another embodiment of the present disclosure, the harmonic may have the maximum magnitude of a plurality of harmonic components that have frequencies of the output signal different with one another.

In the transmitter according to another embodiment of the present disclosure, the duty ratio may be 26% to 44%.

In the transmitter according to another embodiment of the present disclosure, the duty ratio may be 41% or 32%.

In the transmitter according to another embodiment of the present disclosure, the transmitter may further include a rectifying and filtering part configured to receive an input AC power and to generate a DC voltage; a DC/DC converter for regulating a level of the DC voltage outputted from the rectifying and filtering part to be outputted to the power conversion part; and a matching part for performing an impedance matching between the transmitter and the receiver, wherein the control part controls a DC voltage level of the DC/DC converter.

In the transmitter according to an embodiment of the present disclosure, there is provided a method for driving a wireless power transfer system that includes a transmitter having a power conversion part to convert power applied from an external power supply and a receiver to receive power from the transmitter, the method comprising

allowing, when the receiver approaches a charging region of the transmitter, one of the transmitter and the receiver to sense the other one; allowing the receiver to request the transmitter to transfer power allowing a control part of the transmitter to regulate a DC voltage level of the DC/DC converter depending on the amount of power requested by the receiver; and allowing the control part to control the power conversion part depending on a duty ratio of a predetermined PWM control signal, wherein the duty ratio of the PWM control signal is determined by a duty ratio in which a ratio of the magnitude of an harmonic to the magnitude of a fundamental frequency among frequency components of an output signal of the power conversion part is a minimum.

In the transmitter according to another embodiment of the present disclosure, the harmonic may have the maximum magnitude of a plurality of harmonic components that have frequencies of the output signal different with one another.

In the transmitter according to another embodiment of the present disclosure, the power conversion part may include a full bridge inverter that receives a DC voltage from a DC/DC converter to output an AC signal.

In the transmitter according to another embodiment of the present disclosure, the duty ratio may be 26% to 44%.

In the transmitter according to another embodiment of the present disclosure, the duty ratio may be 41% or 32%.

In the transmitter according to another embodiment of the present disclosure, the control part may be fed back with an output signal outputted from the power conversion part and provides the power conversion part with a PWM control signal having a duty ratio in which a ratio of the magnitude of an harmonic to the magnitude of a fundamental frequency of the output signal is a minimum.

In the transmitter according to an embodiment of the present disclosure, there is provided a transmitter for generating a wireless power to be transmitted to a receiver, the transmitter comprising a control part for generating first to fourth AC power control signals; and a power conversion part for generating an AC power including a positive polarity electrode voltage and a negative polarity electrode voltage in response to the first to fourth AC power control signals, wherein the power conversion part generates the positive polarity electrode voltage in response to the first and fourth AC power control signals, and the negative polarity electrode voltage in response to the second and third AC power control signals.

In the transmitter according to another embodiment of the present disclosure, a duty ratio of the positive polarity electrode voltage may be determined by a falling time of the fourth AC power control signal,

wherein a duty ratio of the negative polarity electrode voltage may be determined by a falling time of the third AC power control signal.

In the transmitter according to another embodiment of the present disclosure, the duty ratio may be regulated depending on a power receiving status of the receiver.

In the transmitter according to another embodiment of the present disclosure, the falling time of the fourth AC power control signal may be ahead of the falling time of the first AC power control signal.

In the transmitter according to another embodiment of the present disclosure, the falling time of the third AC power control signal may be ahead of the falling time of the second AC power control signal.

In the transmitter according to another embodiment of the present disclosure, the maximum AC power is generated when the duty ratio may be 50%, the magnitude of the AC power may be reduced when the duty ratio is decreased.

In the transmitter according to another embodiment of the present disclosure, the power conversion part may include first to fourth switching elements, the second and third switching elements may be turned off in a time interval when the first and fourth switching elements are turned on, and the first and fourth switching elements may be turned off in a time interval when the second and third switching elements are turned on.

Advantageous Effects

An embodiment of the present disclosure may change an AC power control signal to control an AC power generator depending on a receiving status of a receiver, and control a duty ratio of an AC voltage of an AC power outputted from an AC power generator in response to the change of the AC power control signal to control the magnitude of the AC power, thereby blocking an occurrence of current loss to prevent power from being wasted.

An embodiment of the present disclosure may solve obstacles such as power reception and noise due to harmonic components included in an output signal of a power conversion part of a transmission part for transmitting power, improve a harmonic distortion ratio by approximating an output waveform of the power conversion part to a sign wave using the power conversion part including a full bridge inverter as the embodiment, and provide a duty ratio that may measure a distribution of harmonic components of the output signal and minimize the harmonic components by feedbacking an output signal outputted from a power conversion part.

Meanwhile, a variety of other effects will be directly or suggestively disclosed in the detailed description according to embodiments described below.

BEST MODE

Hereinafter, a wireless power transfer device and a wireless power transfer system according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. Following embodiments are provided as examples to make those skilled in the art understand ideas of the present disclosure. Accordingly, the present disclosure may not be restricted to the following embodiments but concretely realized in other forms. In the drawings, further, the size and thickness of devices may be exaggeratedly expressed for the convenience of description. The same reference numerals are used to indicate the same or similar components throughout the specification.

Embodiments selectively use various kinds of frequency bands from a low frequency of 50 kHz to a high frequency of 15 MHz to transfer a wireless power, and it is needed to support a communication system in which data and control signals may be exchanged to control a system.

Embodiments may be applied to a variety of industrial fields that use electronic equipment which uses and needs batteries, such as mobile terminal industry, home appliance industry, electric automobile industry, medical device industry and robot industry.

Embodiments may consider a system that is capable of transferring power to a number of equipment using one transmission coil that provides an equipment.

Terms and abbreviations used in the embodiments are as follows.

Wireless Power Transfer System: a system providing a wireless power transfer in a magnetic field region

Wireless Power Transfer System-Charger: a device providing a wireless power transfer in a magnetic field region

Wireless Power Transfer System-Device: a device to which a wireless power transfer is provided from a power transmitter in a magnetic field area

Charging Area: a region where a practical wireless power transfer is performed in a magnetic field area, which may be changed depending on size, required power and operating frequency of an application product

FIG. 2is a view illustrating a wireless power transfer system according to an embodiment.

Referring toFIG. 1, a wireless power transfer system10according to an embodiment may include a power source300, a transmitting part100which is a wireless power transfer device, a receiving part200which is a wireless power receiving device, and a load240.

In the embodiment, the power source300may be included in the transmitter100, which is not limited thereto. The transmitting part100may include a transmitting induction coil102aand a transmitting resonance coil102b.

The receiving part200may include a receiving resonance coil202b, a receiving induction coil202aand a rectifying part220. Both ends of the power source300may be connected to both ends of the transmitting induction coil102a, respectively. The transmitting resonance coil102bmay be disposed apart from the transmitting induction coil102ain a predetermined distance. The receiving resonance coil202bmay be disposed apart from the receiving induction coil202ain a predetermined distance. Both ends of the receiving induction coil202amay be connected to both ends of the rectifying part220, respectively. The load240may be connected to both ends of the rectifying part220. In the embodiment, the load240may be included in the receiving unit200.

The power generated in the power source300may be transferred to the transmitting part100, and the power transferred to the transmitting part100may be transferred to the receiving part200that is resonated with the transmitting part100by a resonance phenomenon, that is, has the same resonance frequency as the transmitting part100.

Hereinafter, a power transmission procedure may be described in more detail.

The power source300may generate an AC power having a predetermined frequency to transfer it to the transmitting part100. The transmitting induction coil102aand the transmitting resonance coil102bmay be inductively coupled each other. That is, an AC current is generated in the transmitting induction coil102aby the AC power supplied from the power source300, and an AC current may also be induced in the transmitting resonance coil102bseparated physically, by an electromagnetic induction caused by such an AC current. Then, the power transferred to the transmitting resonance coil102bmay be transmitted to the receiving part200having the same resonance frequency as that of the transmitting part100using a frequency resonance scheme.

Power may be transferred between two impedance-matched LC circuits by resonance. The power transfer by resonance makes it possible to transfer power farther and at a higher transfer efficiency, compared with a power transfer by an electromagnetic induction scheme.

The receiving resonance coil202bmay receive the power that is transferred from the transmitting resonance coil102busing a frequency resonance scheme. An AC current may flow in the receiving resonance coil200bdue to the received power, and the power transferred to the receiving resonance coil202bmay be transferred to the receiving inductance coil202athat is inductively coupled with the receiving resonance coil202bby an electromagnetic induction. The power transferred to the receiving induction coil202amay be rectified by the rectifying part220to be transferred to the load240.

In the embodiment, the transmitting induction coil102a, the transmitting resonance coil102b, the receiving resonance coil202band the receiving induction coil202amay have a spiral or helical structure, which are not limited thereto.

The transmitting resonance coil102band the receiving resonance coil202bmay be resonantly coupled each other so as to transfer power in a resonance frequency. Due to the resonance coupling between the transmitting resonance coil102band the receiving resonance coil202b, a power transfer efficiency between the transmitting resonance coil102band the receiving resonance coil202bmay be considerably enhanced.

The wireless power transfer system has described a power transfer in the resonance frequency scheme.

The embodiment may also be applied to the power transfer in the electromagnetic induction scheme other than in the resonance frequency. That is, when the wireless power transfer system performs the power transfer based on an electromagnetic induction according to the embodiment, the transmitting resonance coil102bincluded in the transmitting part100and the receiving resonance coil202bincluded in the receiving part200may be omitted.

A quality factor and a coupling coefficient may have a significant meaning in the wireless power transfer. That is, a power transfer efficiency may have a proportional relationship with each of the quality factor and the coupling coefficient. Accordingly, as a value of at least one of the quality factor and the coupling coefficient becomes great, a power transfer efficiency may be enhanced. The quality factor may mean an index of energy accumulated near the transmitting part100or the receiving part200. The quality factor may be changed depending on an operating frequency (w) and a shape, dimension and material of coil. The quality factor may be expressed in the following equation 1.
Q=w*L/R[Equation 1]

L is an inductance of a coil, and R means a resistance corresponding to a power loss amount occurring in the coil itself. The quality factor may have a value from zero (0) to infinity, and the higher the quality factor is, the more the power transfer efficiency between the transmitting part100and the receiving part200is enhanced. The coupling coefficient means a degree of coupling between a coil of a transmitting side and a coil of a receiving side, having a range from zero (0) to one (1). The coupling coefficient may be changed depending on a relative position or distance between the coil of the transmitting side and the coil of the receiving side.

FIG. 3is an equivalent circuit diagram of a transfer induction coil according to an embodiment.

As illustrated inFIG. 3, the transmitting induction coil102amay be configured of an inductor L1and a capacitor C1, which may configure a circuit having a suitable inductance value and a suitable resistance value. The transmitting induction coil102amay be configured with an equivalent circuit in which both ends of the inductor L1are connected to both ends of the capacitor C1, respectively. That is, the transmitting induction coil102amay be configured with an equivalent circuit in which the inductor L1and the capacitor C1are connected in parallel. The capacitor C1may be a variable capacitor, so that an impedance matching is performed by controlling a capacitance of the capacitor C1. An equivalent circuit of the transmitting resonance coil102b, the receiving resonance coil202band the receiving induction coil202amay also be the same as or similar to that illustrated inFIG. 2, which is not limited thereto.

FIG. 4is an equivalent circuit diagram of a power source and a wireless transfer device according to an embodiment.

As illustrated inFIG. 4, the transmitting induction coil102aand the transmitting resonance coil102bmay be configured with the inductors L1and L2and the capacitors C1and C2, respectively, the inductors and capacitors having their inductance values and capacitance values, respectively.

FIG. 5is an equivalent circuit diagram of a receiver according to an embodiment.

As illustrated inFIG. 5, the receiving resonance coil202band the receiving resonance coil202amay be configured with inductors L3and L4and capacitors C3and C4, respectively, the inductors and capacitors having their inductance values and capacitance values, respectively. The rectifying part220may convert an AC power transferred from the receiving inductance coil202ainto a DC power to transfer the converted DC power to the load240. In more detail, the rectifying part220may include a rectifier and a smoothing circuit, which are not illustrated. In the embodiment, the rectifier may be a silicon rectifier that may be equalized with a diode D1as illustrated inFIG. 5, which is not limited thereto. The rectifier may convert an AC power transferred from the receiving induction coil202ainto a DC power.

The smoothing circuit may remove an AC component included in the DC power converted in the rectifier and output a smooth DC power. In the embodiment, the smoothing circuit may employ a rectifying capacitor C5as illustrated inFIG. 5, which is not limited thereto.

A DC power transferred from the rectifying part220may be a DC voltage or a DC current, which is not limited thereto.

The load240may be an arbitrary charger or device that needs a DC power. For example, the load240may mean a battery.

The receiving part200may be mounted on an electronic equipment that needs a power, such as a mobile phone, a laptop computer, a mouse, etc. Accordingly, the receiving resonance coil202band the receiving inductance coil202amay have a shape adapted to that of the electronic equipment.

The transmitting part100may exchange information using an in-band or out-of-band communication with the receiving part200.

The in-band communication may mean a communication scheme to exchange information between the transmitting part100and the receiving part200using signals having a frequency used for a wireless power transfer. For this, the receiving part200may further include a switch, and may or may not receive the power transmitted from the wireless power transfer device200through a switching operation of the switch. Accordingly, the transmitting part100may detect the amount of power consumed in the transmitting part100to recognize an on or off signal of the switch included in the receiving part200.

In more detail, the receiving part200may change the amount of power absorbed in a resistor element using the resistor element and a switch, capable of changing the amount of power consumed in the receiving part200. The transmitting part100may sense changes of power consumed and obtain status information of the load240. The switch and resistor element may be serially connected. In the embodiment, the status information of the load240may include a current charging amount and a charging amount development of the load240. The load240may be included in the receiving part200.

In more detail, when the switch is opened, the power absorbed by the resistor element becomes zero (0), and the power consumed in the receiving part200is also reduced.

When the switch is shorted, the power absorbed by the resistor element becomes more than zero (0), and the power consumed in the transmitting part100is increased. When such operations repeat in the receiving part200, the transmitting part100may detect the power consumed in the transmitting part100and perform a digital communication with the receiving part200.

The transmitting part100may receive status information of the load240by the operations described above, and transmit a suitable power.

On the contrary, with a resistor element and a switch included in the transmitting part100, it may be possible to transfer the status information of the transmitting part100to the receiving part200. In the embodiment, the status information of the transmitting part100may include the maximum providing the amount of power that is transferred by the transmitting part100, the number of the receiving parts200to which the transmitting part100provides the power, and available amount of power of the transmitting part100.

Next, the out-of-band communication will be describe.

The out-of-band communication refers to a communication scheme in which information needed when transferring power is exchanged using a separate frequency band other than a resonance frequency band. An out-of-band communication module is mounted on both the transmitting part100and the receiving part200, so that they may exchange information needed to transfer power. The out-of-band communication module may be mounted on the power source300, which is not limited thereto. In the embodiment, the out-of-band communication module may use a local area communication scheme such as blueTooth, Zigbee, wireless LAN and NFC, which is not limited thereto.

Hereinafter, a subsystem of the transmitting part100and the receiving part200of a wireless power transfer system10will be described in detail.

FIG. 6is a block diagram illustrating a transmitter of a wireless power transfer system according to an embodiment of the present disclosure, andFIG. 7is a block diagram illustrating a receiver of a wireless power transfer system according to an embodiment of the present disclosure.

Referring toFIGS. 6 and 7, the wireless power transfer system10according to an embodiment of the present disclosure may include a transmitting part100transmitting power in a wireless manner and a receiving part200receiving power from the transmitting part100.

On reviewing a block diagram of a subsystem of the transmitting part100illustrated inFIG. 6, the subsystem of the transmitting part100may include a transmitting power converter system101and a transfer antenna system102.

The transmitting power converter system101may include a number of subsystems, including a rectifying and filtering part110, a converter120, a power converting part130, a control part140and a matching part150.

The rectifying and filtering part110generates a DC voltage to be used in the next stage, and the generated DC voltage is supplied to the converter120and then to the transmitting antenna system120.

The converter120together with the rectifying and filtering part110is configured of an AC/DC converter, which may rectify an AC voltage having a band of tens of Hz to generate a DC voltage.

Further, the converter120is configured independently from the rectifying and filtering part110to be a DC/DC converter that generates a DC voltage suitable to a power transfer. Also, the converter120may be a step-down converter to provide an output DC voltage that is lower than an input voltage, which is not limited thereto.

The converter120may output a DC voltage whose voltage level is controlled by the control part140.

The power conversion part130may convert a DC voltage of a certain level into an AC voltage by a switching pulse signal of tens of KHz to tens of MHz, generating power. That is, the power conversion part130may convert a DC voltage into an AC voltage, generating a target, that is, “a wake-up voltage’ or “a charging power” that is used in eh receiving part200which is brought into a charging region.

Here, the wake-up power means a small power of 0.1 to 1 mWatt, and the charging power is a power that is needed to charge a battery of the receiving part200or consumed when operating the receiving part200, indicating a large power of 1 mWatt to 200 Watt consumed in a load of the target receiving part200.

Meanwhile, the power conversion part130may include a power amplifier that amplifies a DC voltage according to a switching pulse signal.

The power conversion part130may be configured of a full bridge inverter.

The control part140may generate a frequency and a switching waveforms to drive the power conversion part130in consideration of the maximum power transfer efficiency, controlling the power to be transferred.

The matching part150performs an impedance matching between the transmitting part100and the receiving part200.

The transmitting antenna system102may include at least one of the inductance coil102aand the resonance coil102b.

When the wireless power transfer system10transfers power only in a magnetic induction scheme, the transmitting antenna system102may include the induction coil102aonly. When the wireless power transfer system10transfers power only in a magnetic resonance scheme, the transmitting antenna system102may include the resonance coil102bonly. Also, when the wireless power transfer system10transfers power in mixed schemes of the magnetic induction scheme and the magnetic resonance scheme, the transmitting antenna system102may include both the induction coil102aand the resonance coil102b.

Further, the induction coil102aor the resonance coil102bmay be included in a single or in plural. When the induction coil102aor the resonance coil102bare included in plural, they may be disposed in an overlapping manner and an overlapping area may be determined in consideration of a deviation of magnetic flux.

The receiving part200illustrated inFIG. 7may include a receiving power converter system201and a receiving antenna system202.

The receiving antenna system202of the receiving part200may be the same as the transmitting antenna system102, and dimensions of the receiving antenna may be changed depending on electrical characteristics of the receiving part200.

Further, the receiving antenna system202may receive power in the magnetic induction scheme or magnetic resonance scheme. As such, the receiving antenna system202may include at least one of the induction coil202aand the resonance coil202bdepending on the power receiving scheme. Also, the receiving antenna system202may further include a near field communication antenna.

The receiving power converter system201may include a matching part210, a rectifying part220, a receiving side converter230, a load240and a receiving side controller250.

The matching part210performs an impedance matching between the transmitter100and the receiver200.

The rectifying part220rectifies an AC voltage outputted from the receiving antenna system202to generate a DC voltage.

The receiving side converter230may be configured of a DC/DC converter to control a level of the DC voltage outputted from the rectifying part220according to a load capacity.

The load240may include a battery, a display device, a sound output circuit, a main processor and kinds of sensors.

The receiving side control part250may be activated by a wake-up power from the transmitting part100, perform a communication with the transmitting part100, and control an operation of the subsystem of the receiving part200.

The receiving part200may be configured in a single or in plural, to simultaneously receive energy from the transmitting part100in a wireless manner. That is, in the wireless power transfer system employing the resonance scheme, a plurality of target receiving parts200may be supplied with power from one transmitting part100.

Here, the matching part150of the transmitting part100may adaptively perform an impedance matching among a plurality of receiving parts200.

Meanwhile, when the receiving part200is configured in plural, they may become the same kind of system or different kinds of system.

Meanwhile, the control part140of the transmitting part100may generally control the transmitting part100. The control part140may control the power conversion part130.

The control part140may control the power conversion part130depending on statuses of the receiving part200, that is, a charging status or a receiving status. For example, when the receiving part200requires a higher wireless power, the control part140may control the power conversion part130to generate a higher wireless power to be transmitted to the receiving part200. For example, when the receiving part200requires a lower wireless power, the control part140controls the power conversion part130to generate a lower wireless power to be transmitted to the receiving part200.

The status of the receiving part200may be provided from the receiving part200in response to a request of the transmitting part100. On the other hand, information on the status of the receiving part200may be provided to the transmitting part100arbitrarily or in a predetermined interval.

The control part140may supply the power conversion part130with a PWM control signal whose duty ratio is controlled according to statuses of the receiving part200based on status information provided from the receiving part200. Accordingly, the embodiment may regulate a control signal used to generate an AC power instead of regulating the magnitude of the power of the power source300or the output of the converter120in order to regulate an AC power to be transmitted to the receiving part200so as to change the magnitude of the AC power, preventing current from being lost and power from being wasted, thereby enhancing power transfer efficiency.

<Power Conversion Part of Wireless Power Transfer System According to an Embodiment of the Present Disclosure>

FIG. 8is a view illustrating a light device according to an embodiment.

A connection relationship and an operation method of the power conversion part130will be described with reference toFIG. 8.

The power conversion part130may convert power provided from the converter120into an AC power based on an AC power control signal provided from the control part140and amplify it. Also, the power conversion part130may include a full bridge inverter.

The power conversion part130may include a first to a fourth switching elements S1, S2, S3and S4.

The first to fourth switching elements S1, S2, S3and S4each may conduct when a first to a fourth AC power control signals C11, C12, C21and C22provided from the control part140are in a high level, and open when in a low level.

The first switching element S1may be connected between a first node N1and the converter120, and controlled by a first AC power control signal C11of the control part140. Also, the second switching element S2may be connected between the first node N1and a ground and controlled by a second AC power control signal C12of the control part140.

The third switching element S3may be connected between the second node N2and the converter120, and controlled by a third AC power control signal C21of the control part140. Also, the fourth switching element S4may be connected between the second node N2and a ground, and controlled by a fourth AC power control signal C22of the control part140.

The first to fourth switching elements S1, S2, S3and S4may be N-type MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor), which is not limited thereto. Rather, elements that perform a switching operation by the AC power control signal of the control part140may be available.

Meanwhile, when the first to fourth switching element S1, S2, S3and S4are a transistor that is a device having three terminals, each gate terminal of the first to fourth switching elements S1, S2, S3and S4is applied an AC power control signal. Remaining two terminals of the first to fourth switching elements S1, S2, S3and S4may be source and drain terminals and current may flow from the drain terminal to the source terminal in the first to fourth switching elements S1, S2, S3and S4.

<Operation Scheme of Power Conversion Part According to an Embodiment of the Present Disclosure>

FIGS. 9 and 10are views illustrating operations of a power conversion part, andFIG. 11is a waveform view of an output signal of a power conversion part according to an AC power control signal.

An operation scheme of the power conversion part130will be described with reference toFIGS. 9 to 11.

As illustrated inFIG. 9, when the first and fourth switching elements S1and S4are turned on by the first and fourth AC power control signals C11and C22that are PWM control signals provided from the control part140and the second and third switching elements S2and S3are turned off by the second and third AC power control signals C12and C21, a positive polarity output voltage Vo may be applied to the matching part150. As illustrated inFIG. 10, when the first and fourth switching elements S1and S4are turned off by the first and fourth AC power control signals C11and C22provided from the control part140and the second and third switching elements S2and S3are turned on by the second and third AC power control signals C12and C21, a negative polarity output voltage Vo may be applied to the matching part150.

FIG. 11shows the first to fourth AC power control signals C11, C12, C21and C22applied to the first to fourth switching elements S1, S2, S3and S4and a resultant output voltage Vo when a duty ratio is 50%, for example. Here, there may exist a blank interval where the first and second AC power control signals C11and C12to control the first and second switching elements S1and S2and the third and fourth AC power control signals C21and C22to control the third and fourth switching elements S3and S4are not overlapped each other. It is for the purpose of preventing an output voltage Vo of the converter120from not appearing due to the fact that when the first and second switching elements S1and S2are simultaneously turned on so that they are conductively connected, or the third and fourth switching elements S3and S4are simultaneously turned on so that they are conductively connected, the output voltage of the converter120is grounded.

<Duty Ratio Regulation Using a Blank Interval Regulation>

FIGS. 12 and 13are views illustrating waveform diagrams to control a duty ratio of an AC voltage by controlling a blank interval.

As illustrated inFIGS. 12 and 13, duty ratios of the first to fourth AC power control signals C11, C12, C21and C22that are PWM signals provided from the control part140may be changed. For example, rising times Tr11Tr12, Tr21and Tr22and falling times Tf11, Tf12Tf21and Tf22of high levels of the first to fourth AC power control signals C11, C12, C21and C22that are PWM signals provided from the control part140may be changed. In response to the first to fourth AC power control signals C11, C12, C21and C22that are changed, conduction times of the first to fourth switching elements S1, S2, S3and S4are changed and resultantly a duty ratio Ton of the AC voltage Vo of the AC power supplied to the transmitting antenna system102may be changed.

The embodiment may enable the receiving part200to receive a constant power by differing a duty ratio Ton of the AC voltage Vo of the AC power depending on a status of the receiving part200, for example, a charging status and/or a receiving status.

In addition, the embodiment may interrupt the current that may be lost when an AC power is generated in the transmitting part100, minimizing power consumption.

FIG. 12illustrates waveform diagrams of the first to fourth AC power control signals that are PWM signals to generate an AC power having an AC voltage of 50% duty ratio.

As illustrated inFIG. 12, the first to fourth AC power control signals C11, C12, C21and C22may be generated based on clock signals.

The clock signal (Clock) may be generated based on ban AC signal of an oscillator (not illustrated) or by a separate means, which is not limited thereto.

The clock signal (Clock) may be repeatedly generated in a cycle having a high level pulse and a low level pulse.

For example, the first AC power control signal C11defines a rising time Tr11for a high level at a time delayed for a predetermined time from a rising time of a first high level pulse in the clock signal (Clock) and a falling time Tf11for a low level at a rising time of a second high level pulse.

For example, a high level section of the second AC power control signal C12is not overlapped with a high level section of the first AC power control signal C11. If the high level section of the first AC power control signal C11is overlapped with the high level section of the second AC power control signal C12, the first and second switching elements S1and S2are simultaneously conducted, an output voltage of the converter120is discharged to a ground, the output voltage of the converter120is not applied to the first node N1. As a result, power is not transferred to the transfer antenna system102. Accordingly, a blank interval TPAmay be defined where high level intervals of the first and second AC power control signals C11and C12do not exist between the falling time Tf11of the first AC power control signal C11and the rising time Tr12of the second AC power control signal C12or between the rising time Tr11of the first AC power control signal C11and the falling time Tf12of the second AC power control signal C12.

The second AC power control signal C12may define a rising time Tr12for a high level at a time delayed for a predetermined time from a rising time of a second high level in the clock signal (Clock) and a falling time Tf12for a low level at a rising time of a third high level pulse.

For example, a high level interval of the third AC power control signal C21may be partially overlapped with a high level interval of the first AC power control signal C11and a high level interval of the second AC power control signal C12. That is, the rising time Tr21of the third AC power control signal C21is ahead of a falling time Tf11of the first AC power control signal C11, and the falling time Tf21of the third AC power control signal C21follows the rising time Tr12of the second AC power voltage signal C12.

For example, a high level interval of the fourth AC power control signal C22is not overlapped with a high level interval of the third AC power control signal C21. Likewise, when the high level interval of the third AC power voltage signal C21is overlapped with the high level interval of the fourth AC power control signal C22, the third and fourth switching elements S3and S4are simultaneously conducted, an output voltage of the converter102is discharged to a ground and the output voltage of the converter120is not applied to the second node N2. As a result, power is not transferred to the transfer antenna system102. Accordingly, a blank interval TAPmay be defined where high level intervals of the third and fourth AC power control signals C21and C22do not exist between a falling time Tf21of the third AC power control signal C21and a rising time Tr22of the fourth AC power control signal C22or between a rising time Tr21of the third AC power control signal C21and a falling time Tf22of the fourth AC power control signal C22.

In addition, the high level interval of the fourth AC power control signal C22may be partially overlapped with the high level interval of the first AC power control signal C11and a high level interval of the second AC power control signal C12. That is, the rising time Tr22of the fourth AC power control signal C22is ahead of a falling time Tf12of the second AC power control signal C12, and follows the rising time Tr11of the first AC power voltage signal C11.

Respective high level intervals of the first to fourth AC power control signals C11, C12, C21and C22may be defined in a cycle of the clock signal (Clock).

Meanwhile, an high level overlapping interval of the first and fourth AC power control signals C11and C22is a power transfer interval, which may be defined as a duty ratio (Ton). The duty ratio (Ton) is an interval where a power may be transferred for a cycle, the maximum being set 50%, which is not limited thereto. For example, when a duty ratio is 50%, power can be transferred in a half cycle and cannot be transferred in the reaming half cycle. Further, an overlapped high level interval of the second and third AC power control signals C12and C21is a power transfer available interval, which may be defined as a duty ratio (Ton).

InFIG. 12, it may be understood that the duty ratio (Ton) is determined the falling time Tf21of the third AC power control signal C21and the falling time Tf22of the fourth AC power control signal C22. When the falling time Tf22is delayed, the duty ratio Ton may be increased, and when the falling time is quickened, the duty ratio Ton may be decreased.

When the duty ratio Ton is increased, since an AC power transferred to the transmitting antenna system102is increased, a wireless power received by the receiving part200may also be decreased. When the duty ratio Ton is decreased, since the AC power transferred to the transmitting antenna system102is decreased, a wireless power received by the receiving part200may also be decreased.

The embodiment may reflect an increase or decrease of the AC power to be transferred to the receiving part200so that the control part140generates the first to fourth AC power control signals C11, C112, C21and C22, a duty ratio (Ton) of an AC voltage (Vo) output from the power conversion part130may be regulated by the first to fourth AC power control signals C11, C12, C21and C22, and the wireless power having an AC voltage (Vo) of the regulated duty ratio (Ton) may be transmitted to the receiving part200by the transmitting antenna system102.

FIG. 13illustrates a waveform diagram of the first to fourth AC power control signals to generate an AC power having an AC voltage of 30% duty ratio.

InFIG. 13, a method for generating the first to fourth AC power control signals C11, C12, C21and C22is the same as that described with reference toFIG. 8.

An AC voltage (Vo) illustrate inFIG. 13has a duty ratio (Ton) of 30%, which is smaller than the duty ratio (To) of 50% illustrated inFIG. 12. In other word, a width of a positive polarity voltage or a negative polarity voltage having a duty ratio (To) of 30% may be smaller than that of a positive polarity voltage or a negative polarity voltage having a duty ratio (To) of 50%.

As such, the first to fourth AC power control signals C11, C12, C21and C22may be changed so that the duty ratio of the AC voltage (Vo) may be reduced to 30%. That is, the falling time Tf12of the second AC power control signal C12and the falling time Tf21of the third AC power control signal C21illustrated inFIG. 13may be ahead of the falling time Tf12of the second AC power control signal C12and the falling time Tf21of the third AC power control signal C21illustrated inFIG. 12. Accordingly, as the duty ratio (Ton) of the AC voltage Vo is reduced, the falling time Tf12of the second AC power control signal C12and the falling time Tf21of the third AC power control signal C21may be quickened more and more. For example, the falling time Tf12of the second AC power control signal C12and the falling time Tf21of the third AC power control signal C21may be more quickened in a duty ratio (Ton) of 20% rather than a duty ratio (Ton) of 30%.

Meanwhile, the control part140may include a first serve control part that generates the first to fourth AC power control signals C11to C22that are PWN signals, to be provided to the first to fourth switching elements S1to S4and a second serve control part that provides the first serve control part with a duty ratio regulation signal to regulate duty ratios of the first to fourth AC power control signals C11to C22.

The second serve control part may supply the first serve control part with a duty ratio regulation signal regulated depending on a status of the receiving part200based on status information provided from the receiving part200.

For example, the duty ratio regulation signal may be a binary data of 6 bits. For example, when the duty ratio regulation signal is 000001, the first serve control part may generate the first to fourth AC power control signals C11to C22to generate an AC power having an AC voltage of a duty ratio of 50% in response to the duty ratio regulation. The AC power having the AC voltage of a duty ratio of 50% may be the maximum AC power to be transmitted to the receiving part200, which is not limited thereto.

For example, when a duty ratio regulation signal is 000010, the first serve control part may generate the first to fourth AC power control signals C11to C22to generate an AC power having an AC voltage of a duty ratio of 40% in response to the control signal.

For example, when a duty ratio regulation signal is 000011, the first serve control part may generate the first to fourth AC power control signals C11to C22to generate an AC power having an AC voltage of a duty ratio of 30% in response to the control signal.

For example, when a duty ratio regulation signal is 000100, the first serve control part may generate the first to fourth AC power control signals C11to C22to generate an AC power having an AC voltage of a duty ratio of 20% in response to the control signal.

For example, when a duty ratio regulation signal is 000101, the first serve control part may generate the first to fourth AC power control signals C11to C22to generate an AC power having an AC voltage of a duty ratio of 10% in response to the control signal.

In addition, by setting the duty ratio regulation signal with a binary data of 6 bits, the first to fourth AC power control signals C11to C22to generate an AC power in a duty ratio unit of 5%, a duty ratio unit of 3%, or a duty ratio unit of 2%, which is not limited thereto.

FIGS. 14A, 14B, 15A, 15B, 16A and 16Bare views illustrating the magnitude of a fundamental wave of a signal outputted as a result of simulating an output waveform when changing a duty ratio of a full bridge of a power converter and the magnitude of a harmonic that is multiple components of a fundamental wave.

A simulation is performed using a Fourier analysis of an output signal, basically.

An exponential Fourier series may be expressed as

f⁡(t)=∑n=-∞∞⁢⁢Cn⁢ej⁢⁢n⁢⁢ωo⁢t
and a harmonic component may be searched through the magnitude of complex coefficient Gn.

Further, a total harmonics distortion THD is used in order to compare degrees of harmonic components depending on duty ratios.

The total harmonics distortion THD is defined as a ratio of an RMS of a harmonic component and an RMS of a fundamental wave, which indicates degrees of harmonic occurrence.

In the embodiment, the total harmonics distortion THD is defined as a maximum harmonics distortion that is a ratio of an RMS of a maximum magnitude harmonic component having the maximum magnitude of harmonic components and an RMS of a fundamental wave. That is, the maximum harmonic distortion is defined as a ratio of an RMS of a maximum magnitude harmonic component contrasted with an RMS of a fundamental wave.

A distribution and magnitude of a harmonic component according to a duty ratio will be described with reference to the drawing.

A simulation result is produced by changing a duty ratio to 50%, 40% and 30% based on an amplitude of an output waveform 1V and a cycle, 143 Hz.

InFIGS. 14A and 14B, when a duty ratio is 50%, a fundamental wave has a magnitude between 0.6V and 0.7V, and even number harmonics appear but odd number harmonics do not appear.

When a duty ratio is 50%, an approximate value of the maximum harmonics distortion is 0.22/0.65=24%.

InFIGS. 15A and 15B, when a duty ratio is 40%, it is noted that a fundamental wave has a value of about 0.6V, and even number and even number harmonics appear and the magnitude of a first harmonic component which is twice of a fundamental frequency among harmonic components is between 0.1V and 0.2V. As such, when a duty ratio is reduced from 50% to 40%, a maximum harmonics distortion becomes 0.15/0.6=25%, so that it may be confirmed that while even number and odd number harmonic components appear, the maximum harmonics distortion is improved.

FIGS. 16A and 16Billustrate a case that a duty ratio is 30%. Here, a fundamental wave has a magnitude between 0.5V and 0.6V, the magnitude of a harmonic component that is five times of a fundamental frequency among harmonic components is between 0.1V and 0.2V. So, when calculating the maximum harmonic distortion with approximate values, it is 1.25/5.1=24%, so that it is noted that the maximum harmonics distortion is reduced.

FIG. 17is a view illustrating a simulation result of the maximum harmonic distortion ratio when changing a duty ratio.

It is confirmed that the maximum harmonic distortion has a relatively small value in a duty ration interval of 0.26 to 0.44 (26% to 44%). That is, the duty ratio interval is an interval where less harmonic components are distributed.

Further, the maximum harmonic distortion is smallest when a duty ratio is 0.41 (41%) and 0.32 (32%), and the value of the maximum harmonic distortion becomes 23.6%.

As such, when using a full bridge inverter as the power converter130and regulating a duty ratio, it may be possible to control an output waveform to be approximated to a sign wave.

As described above, while a perfect sine wave does not include harmonic components, a sine wave having a distorted waveform due to a non-linear characteristic of a load includes harmonic components. Accordingly, when controlling an output voltage Vo to be approximated to a sine wave, the harmonic components may be reduced and an electromagnetic compatibility EMC may be maximized.

While the above-described simulation reviews an EMC characteristic using a ratio of the magnitude of a fundamental wave and the magnitude of the maximum harmonic component, which is not limited thereto. Rather, the EMC characteristic may be considered using a ratio of the magnitude of a fundamental wave and the magnitude of total harmonic components.

Here, it is desirable to control the power converter using a duty ratio with which the total harmonic distortion calculated with a ratio of the magnitude of a fundamental wave and the magnitude of total harmonic components.

<Method for Driving a Wireless Power Transfer System According to an Embodiment of the Present Disclosure>

FIG. 18is a signal flow chart illustrating operations of a wireless power transfer system according to an embodiment of the present disclosure.

A first step is a sensing step (S100).

In case that the receiving part200approaches a charging region of the transmitting part100, a wireless power transfer may start when the transmitting part100senses the receiving part200or in reverse the receiving part200senses the transmitting part100.

The sensing step (S100) may be configured of sub-steps, a selection step to sense the receiving part200, a ping step to receive a packet, and an identification and configuration step to receive a unique ID, an extension ID, and information on control parameters.

A second step is a power requesting step (S200).

In case that the receiving part200requests the transmitting part100to transmit power, for example, the receiving part200may request the transmitting part100to transmit a certain amount of power depending on status of the receiving part200, that is, battery charging status of the receiving part200, temperature status of the receiving part200and battery, the amount and degree of battery power consumption and battery charging speed.

A third step is a step to control the control part140and the converter120(S300).

The power transmission amount may be changed depending on status of the receiving part200, and accordingly the control part140of the transmitting part100may control the converter120to regulate level of the DC power.

A fourth step is a step to control the power conversion part130of the control part140(S400) and a step to transmit power (S500).

The converter120may control first to fourth switching elements S1, S2, S3and S4of a full bridge inverter inside the power conversion part130using a PWM control signal.

A turning on or off ratio of the first to fourth switching elements S1, S2, S3and S4may be changed according to a duty ratio, and a degree of the harmonic components included in the power conversion part130may be changed according to a duty ratio. Accordingly, the control part may analyze the magnitude of the DC voltage transferred to the power conversion part130from the converter120and a frequency component of the output signal outputted from the power conversion part130to control a duty ratio of the PWM control signal.

As such, the control part140may determine a duty ratio to have a predetermined value among 26% to 44%, for example and provide the power conversion part130with a PWM control signal having the predetermined value as well. Also, the control part140may be fed back with signals outputted from the power conversion part130, analyze harmonic components of the output signal to provide the power conversion part130with PWM control signal having a duty ratio in which a ratio of the magnitude of a fundamental wave and the magnitude of a maximum harmonic is a minimum, so that the control part140may enable the transmitting part100to provide the power requested by the receiving part200.

When analyzing the harmonic components of the output signal fed back from the power conversion part130and analyzing, the output signal of the power conversion part130may be fed back and analyzed each predetermined period. Therefore, a real time control may be performed to determine a distortion degree of the power conversion part130depending on changes of the power transmission condition of the wireless power transfer system10or changes of system characteristic to output signals having optimized electromagnetic characteristic.

The transmitting part100of the wireless power transfer system10according to the embodiment of the present disclosure uses a full bridge inverter as the power converter130.

The full bridge inverter has an effect to approximate the output signal to a sine wave so that the harmonic components are minimized, as well as an effect to increase the maximum power provided to the transmitting antenna system102compared with an half bridge inverter in the art.

Further, the control part140may regulate a duty ratio of the DC voltage level outputted from the converter120and first to fourth AC power control signals C11, C12, C21and C22that are PWM control signals provided to the power conversion part130to reduce harmonic components of the output signals outputted from the power conversion part130. Also, the control part140may be fed back with the amount of power requested in the receiving part200and distortion status of the output signal of the power conversion part130depending on current status of the transmitting part and receiving part100and200to regulate a duty ratio of the first to fourth power control signals C11, C12, C21and C22, thereby improving electromagnetic wave characteristics.

The method according to the above-described embodiment may be manufactured with a computer executable program and stored in a computer readable recording medium. Examples of the computer-readable recording medium include a ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage device and so on. Also, it may be implemented in the form of a carrier wave (e.g., transmission over Internet).

The computer-readable recording medium may be distributed in the computer system connected through a computer communication network, and may be stored and executed as codes readable in a distributed manner. Furthermore, functional program, code and code segments, used to implement the present disclosure can be derived by a skilled computer programmer from the description of the disclosure contained herein.

The receiving part200according to the embodiment may be mounted on a mobile terminal such as a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistance PDA, a portable multimedia player PMP, a navigation, and so on.

However, it is well known by those skilled in the art that the configuration of the embodiment may also be applicable to stationary terminals such as digital TV, desktop computer and the like, except the case applicable to mobile terminal only.

In the embodiment, the power transmission scheme by electromagnetic induction may mean a relatively low Q value and a tight coupling, and the power transmission scheme by resonance may mean a relatively high Q value and a loose coupling.

Although the present disclosure were described with reference to preferred embodiments, these are just examples and do not limit the present disclosure. The present disclosure may be changed and modified in various ways, without departing from the ideas and technical regions described in claims, by those skilled in the art. Accordingly, technical scope of the present disclosure is not restricted to the detailed description but should be defined by claims only.

INDUSTRIAL APPLICATION

The wireless power transfer device may be used in the field of wireless charging system.