Patent Publication Number: US-9843196-B2

Title: Wireless power transmitter, wireless power receiver and wireless charging system in home appliances

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to U.S. Provisional Application No. 61/833,762, filed on Jun. 11, 2013 and Korean Application No. 10-2014-0069604, filed on Jun. 9, 2014, the contents of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     This specification relates to a wireless power transmitter, a wireless power receiver and a wireless charging system in a wireless power transfer field. 
     2. Background of the Disclosure 
     In recent years, the method of contactlessly supplying electrical energy to wireless power receivers in a wireless manner has been used instead of the traditional method of supplying electrical energy in a wired manner. The wireless power receiver receiving energy in a wireless manner may be directly driven by the received wireless power, or a battery may be charged by using the received wireless power, then allowing the wireless power receiver to be driven by the charged power. 
     The Wireless Power Consortium (WPC) which manages technologies for a magnetic inductive wireless power transfer has published a standard document “System description Wireless Power Transfer, Volume 1, Low Power, Part 1: Interface Definition, Version 1.00 Release Candidate 1 (RC1)” for interoperability in the wireless power transfer on Apr. 12, 2010. The standard document of the WPC has described a method of transferring power from one wireless power transmitter to one wireless power receiver by a magnetic induction. 
     The version 1.00 is involved with low power of 5 W power transmission and reception. In recent years, an application of a wireless power transfer technology to home appliances, which require for power over several tens of watts (W), as well as low-power products, are researched. In such a medium-power condition, several problems may be caused due to a voltage induced in the range of several tens to several hundreds of volts (V), and a solution of those problems may be taken into account. 
     SUMMARY OF THE DISCLOSURE 
     Therefore, an aspect of the detailed description is to provide a wireless power transmitter, a wireless power receiver and a wireless charging system for medium power. 
     Another aspect of the detailed description is to provide a wireless power transmitter, a wireless power receiver and a wireless charging system, which can be utilized in home appliances which are used in household electronics. 
     Another aspect of the detailed description is to provide a wireless power transmitter, a wireless power receiver and a wireless charging system, which are capable of enhancing operation efficiency of a control circuit. 
     To achieve these and other advantages and in accordance with the purpose of this specification, as embodied and broadly described herein, there is provided a wireless power receiver including a first coil configured to transmit and receive a wireless power signal to and from a wireless power transmitter, a second coil having a wire wound to receive power from the wireless power transmitter in a wireless manner, and a controller configured to control the transmission and reception of the wireless power signal and the reception of the wireless power, wherein the first coil and the second coil may be disposed neighboring to each other. 
     In one exemplary embodiment disclosed herein, the first coil may be provided with a wire wound along an edge of a shape of the second coil. 
     In one exemplary embodiment disclosed herein, the wire of the first coil may be wound along one of an inner edge or an outer edge of the second coil. 
     In one exemplary embodiment disclosed herein, the wire of the first coil may be surrounded by the inner edge of the second coil or surround the outer edge of the second coil. 
     In one exemplary embodiment disclosed herein, the shape of the first coil may correspond to the shape of the second coil. 
     In one exemplary embodiment disclosed herein, the wire of the second coil may be formed on a single layer, and the wire of the first coil may be disposed on the single layer. 
     In one exemplary embodiment disclosed herein, the second coil may be provided with a wire which is turned 20 times on the single layer and has a thickness of 1.15 mm±0.3. 
     In one exemplary embodiment disclosed herein, the first coil and the second coil may be configured to receive the wireless power signal and the wireless power, respectively, through a transmitting coil provided at the wireless power transmitter. The transmitting coil may have an inner diameter of 72 mm (±10%), and an outer diameter of 120 mm. 
     In one exemplary embodiment disclosed herein, the second coil may have an inner diameter of 52 mm (±10%), and an outer diameter of 100 mm. 
     In one exemplary embodiment disclosed herein, the wireless power receiver may further include a shielding member configured to overlap the first and second coils. The shielding member may have a shape of a rectangular plate of 105 mm long sides and a thickness of at least 2.5 mm. 
     In one exemplary embodiment disclosed herein, the number of turns of the wire of the first coil may be smaller than the number of turns of the wire of the second coil. 
     In one exemplary embodiment disclosed herein, a low voltage induced in the first coil may be lower than a medium voltage induced in the second coil. 
     In one exemplary embodiment disclosed herein, the wireless power signal received through the first coil may be a wireless power signal of low power, and the wireless power received through the second coil may correspond to medium power. 
     To achieve these and other advantages and in accordance with the purpose of this specification, as embodied and broadly described herein, there is provided a wireless charging system including a wireless power transmitter and a wireless power receiver, wherein the wireless power receiver may include a first coil configured to transmit and receive a wireless power signal to and from a single coil of the wireless power transmitter, and a second coil having a wire that is wound to receive power from the single coil of the wireless power transmitter in a wireless manner, wherein the wire may have a shape corresponding to a shape of the first coil. 
     In one exemplary embodiment disclosed herein, the wireless power transmitter may include a single transmitting coil. 
     In one exemplary embodiment disclosed herein, the wire of the first coil may be wound along one of an inner edge or an outer edge of the second coil. 
     In one exemplary embodiment disclosed herein, the wire of the first coil may be surrounded by the inner edge of the second coil, or surround the outer edge of the second coil. 
     In one exemplary embodiment disclosed herein, the shape of the first coil may correspond to the shape of the second coil. 
     In one exemplary embodiment disclosed herein, the wire of the second coil may be formed on a single layer, and the wire of the first coil may be disposed on the single layer. 
     In one exemplary embodiment disclosed herein, the second coil may be provided with a wire that is turned 20 times on the single layer and has a thickness of 1.15 mm±0.3. 
     In one exemplary embodiment disclosed herein, the wireless power transmitter may include a first transmitting coil configured to transfer a wireless power signal to the wireless power receiver, a second transmitting coil having a wire wound to transfer power to the wireless power receiver in a wireless manner, and a controller configured to control operations of the first and second transmitting coils. Here, the first transmitting coil may be provided with a wire wound along an edge of a shape of the second transmitting coil. 
     In one exemplary embodiment disclosed herein, the second transmitting coil may have an inner diameter of 72 mm (±10%) and an outer diameter of 120 mm. 
     In one exemplary embodiment disclosed herein, the wireless charging system may further include a shielding member configured to overlap the first and second transmitting coils. The shielding member may have a shape of a rectangular plate of 125 mm long sides and a thickness of at least 2.5 mm. 
     Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from the detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the disclosure. 
       In the drawings: 
         FIG. 1  is an exemplary view conceptually illustrating a wireless power transmitter and a wireless power receiver according to the embodiments of the present invention; 
         FIGS. 2A and 2B  are exemplary block diagrams illustrating the configuration of a wireless power transmitter and a wireless power receiver that can be employed in the embodiments disclosed herein, respectively; 
         FIG. 3  is a view illustrating a concept in which power is transferred from a wireless power transmitter to a wireless power receiver in a wireless manner according to an inductive coupling method; 
         FIGS. 4A and 4B  are a block diagram illustrating part of the wireless power transmitter and wireless power receiver in a magnetic induction method that can be employed in the embodiments disclosed herein; 
         FIG. 5  is a block diagram illustrating a wireless power transmitter configured to have one or more transmitting coils receiving power according to an inductive coupling method that can be employed in the embodiments disclosed herein; 
         FIG. 6  is a view illustrating a concept in which power is transferred to a wireless power receiver from a wireless power transmitter in a wireless manner according to a resonance coupling method; 
         FIGS. 7A and 7B  are a block diagram illustrating part of the wireless power transmitter and wireless power receiver in a resonance method that can be employed in the embodiments disclosed herein; 
         FIG. 8  is a block diagram illustrating a wireless power transmitter configured to have one or more transmitting coils receiving power according to a resonance coupling method that can be employed in the embodiments disclosed herein; 
         FIG. 9  a view illustrating a concept of transmitting and receiving a packet between a wireless power transmitter and an electronic device through the modulation and demodulation of a wireless power signal in transferring power in a wireless manner disclosed herein; 
         FIG. 10  is a view illustrating a configuration of transmitting and receiving a power control message in transferring power in a wireless manner disclosed herein&#39; 
         FIG. 11  is a view illustrating forms of signals upon modulation and demodulation executed in a wireless power transfer disclosed herein; 
         FIG. 12  is a view illustrating a packet including a power control message used in a contactless (wireless) power transfer method according to the embodiments disclosed herein; 
         FIG. 13  is a view illustrating operation phases of the wireless power transmitter and wireless power receiver according to the embodiments disclosed herein; 
         FIGS. 14 to 18  are views illustrating the structure of packets including a power control message between the wireless power transmitter  100  and the wireless power receiver; 
         FIG. 19  is a conceptual view illustrating a method of transferring power to at least one wireless power receiver from a wireless power transmitter; 
         FIG. 20  is a block diagram exemplarily illustrating partial configurations of a wireless power transmitter and a wireless power receiver disclosed herein; 
         FIG. 21  is a detailed circuit view of the block diagram illustrated in  FIG. 20 ; 
         FIG. 22  is a conceptual view of a transmitting coil; 
         FIGS. 23A and 23B  are conceptual views of a receiving coil; 
         FIG. 24  is a conceptual view illustrating exemplary variations of transmitting and receiving coils and a related shielding member; 
         FIGS. 25A and 25B  are conceptual views illustrating exemplary variations of a receiving coil; 
         FIG. 26  is a block diagram illustrating varied configurations of a wireless power transmitter and a wireless power receiver in accordance with the present disclosure; 
         FIG. 27  is a detailed circuit view of the block diagram illustrated in  FIG. 26 ; 
         FIGS. 28A, 28B and 28C  are conceptual views illustrating a transmitting coil; 
         FIG. 29  is a conceptual view illustrating exemplary variations of transmitting coils and a related shielding member; 
         FIG. 30  is a flowchart illustrating one exemplary embodiment of a wireless power transfer method for reducing standby power; and 
         FIG. 31  is a flowchart illustrating another exemplary embodiment of a wireless power transfer method for reducing standby power. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The technologies disclosed herein may be applicable to wireless power transfer (contactless power transfer). However, the technologies disclosed herein are not limited to this, and may be also applicable to all kinds of power transmission systems and methods, wireless charging circuits and methods to which the technological spirit of the technology can be applicable, in addition to the methods and apparatuses using power transmitted in a wireless manner. 
     It should be noted that technological terms used herein are merely used to describe a specific embodiment, but not to limit the present invention. Also, unless particularly defined otherwise, technological terms used herein should be construed as a meaning that is generally understood by those having ordinary skill in the art to which the invention pertains, and should not be construed too broadly or too narrowly. Furthermore, if technological terms used herein are wrong terms unable to correctly express the spirit of the invention, then they should be replaced by technological terms that are properly understood by those skilled in the art. In addition, general terms used in this invention should be construed based on the definition of dictionary, or the context, and should not be construed too broadly or too narrowly. 
     Incidentally, unless clearly used otherwise, expressions in the singular number include a plural meaning. In this application, the terms “comprising” and “including” should not be construed to necessarily include all of the elements or steps disclosed herein, and should be construed not to include some of the elements or steps thereof, or should be construed to further include additional elements or steps. 
     In addition, a suffix “module” or “unit” used for constituent elements disclosed in the following description is merely intended for easy description of the specification, and the suffix itself does not give any special meaning or function. 
     Furthermore, the terms including an ordinal number such as first, second, etc. can be used to describe various elements, but the elements should not be limited by those terms. The terms are used merely for the purpose to distinguish an element from the other element. For example, a first element may be named to a second element, and similarly, a second element may be named to a first element without departing from the scope of right of the invention. 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, and the same or similar elements are designated with the same numeral references regardless of the numerals in the drawings and their redundant description will be omitted. 
     In describing the present invention, moreover, the detailed description will be omitted when a specific description for publicly known technologies to which the invention pertains is judged to obscure the gist of the present invention. Also, it should be noted that the accompanying drawings are merely illustrated to easily explain the spirit of the invention, and therefore, they should not be construed to limit the spirit of the invention by the accompanying drawings. 
     DEFINITION 
     Many-to-one communication: communicating between one transmitter (Tx) and many receivers (Rx) 
     Unidirectional communication: transmitting a required message only from a receiver to a transmitter 
     Here, the transmitter and the receiver indicate the same as a transmitting unit (device) and a receiving unit (device), respectively. Hereinafter, those terms may be used together. 
     Conceptual View of Wireless Power Transmitter and Wireless Power Receiver 
       FIG. 1  is an exemplary view conceptually illustrating a wireless power transmitter and a wireless power receiver according to the embodiments of the present invention. 
     Referring to  FIG. 1 , the wireless power transmitter  100  may be a power transfer apparatus configured to transfer power required for the wireless power receiver  200  in a wireless manner. 
     Furthermore, the wireless power transmitter  100  may be a wireless charging apparatus configured to charge a battery of the wireless power receiver  200  by transferring power in a wireless manner. A case where the wireless power transmitter  100  is a wireless charging apparatus will be described later with reference to  FIG. 9 . 
     Additionally, the wireless power transmitter  100  may be implemented with various forms of apparatuses transferring power to the wireless power receiver  200  requiring power in a contactless state. 
     The wireless power receiver  200  is a device that is operable by receiving power from the wireless power transmitter  100  in a wireless manner. Furthermore, the wireless power receiver  200  may charge a battery using the received wireless power. 
     On the other hand, an electronic device for receiving power in a wireless manner as described herein should be construed broadly to include a portable phone, a cellular phone, a smart phone, a personal digital assistant (PDA), a portable multimedia player (PMP), a tablet, a multimedia device, or the like, in addition to an input/output device such as a keyboard, a mouse, an audio-visual auxiliary device, and the like. 
     The wireless power receiver  200 , as described later, may be a mobile communication terminal (for example, a portable phone, a cellular phone, and a tablet and the like) or a multimedia device. 
     On the other hand, the wireless power transmitter  100  may transfer power in a wireless manner without mutual contact to the wireless power receiver  200  using one or more wireless power transfer methods. In other words, the wireless power transmitter  100  may transfer power using at least one of an inductive coupling method based on magnetic induction phenomenon by the wireless power signal and a magnetic resonance coupling method based on electromagnetic resonance phenomenon by a wireless power signal at a specific frequency. 
     Wireless power transfer in the inductive coupling method is a technology transferring power in a wireless manner using a primary coil and a secondary coil, and refers to the transmission of power by inducing a current from a coil to another coil through a changing magnetic field by a magnetic induction phenomenon. 
     Wireless power transfer in the inductive coupling method refers to a technology in which the wireless power receiver  200  generates resonance by a wireless power signal transmitted from the wireless power transmitter  100  to transfer power from the wireless power transmitter  100  to the wireless power receiver  200  by the resonance phenomenon. 
     Hereinafter, the wireless power transmitter  100  and wireless power receiver  200  according to the embodiments disclosed herein will be described in detail. In assigning reference numerals to the constituent elements in each of the following drawings, the same reference numerals will be used for the same constituent elements even though they are shown in a different drawing. 
       FIGS. 2A and 2B  are exemplary block diagrams illustrating the configuration of a wireless power transmitter  100  and a wireless power receiver  200  that can be employed in the embodiments disclosed herein. 
     Wireless Power Transmitter 
     Referring to  FIG. 2A , the wireless power transmitter  100  may include a power transmission unit  110 . The power transmission unit  110  may include a power conversion unit  111  and a power transmission control unit  112 . 
     The power conversion unit  111  transfers power supplied from a transmission side power supply unit  190  to the wireless power receiver  200  by converting it into a wireless power signal. The wireless power signal transferred by the power conversion unit  111  is generated in the form of a magnetic field or electro-magnetic field having an oscillation characteristic. For this purpose, the power conversion unit  111  may be configured to include a coil for generating the wireless power signal. 
     The power conversion unit  111  may include a constituent element for generating a different type of wireless power signal according to each power transfer method. For example, the power conversion unit  111  may include a primary coil for forming a changing magnetic field to induce a current to a secondary coil of the wireless power receiver  200 . Furthermore, the power conversion unit  111  may include a coil (or antenna) for forming a magnetic field having a specific resonant frequency to generate a resonant frequency in the wireless power receiver  200  according to the resonance coupling method. 
     Furthermore, the power conversion unit  111  may transfer power using at least one of the foregoing inductive coupling method and the resonance coupling method. 
     Among the constituent elements included in the power conversion unit  111 , those for the inductive coupling method will be described later with reference to  FIGS. 4A and 4B and 5 , and those for the resonance coupling method will be described with reference to  FIGS. 7A and 7B and 8 . 
     On the other hand, the power conversion unit  111  may further include a circuit for controlling the characteristics of a used frequency, an applied voltage, an applied current or the like to form the wireless power signal. 
     The power transmission control unit  112  controls each of the constituent elements included in the power transmission unit  110  The power transmission control unit  112  may be implemented to be integrated into another control unit (not shown) for controlling the wireless power transmitter  100 . 
     On the other hand, a region to which the wireless power signal can be approached may be divided into two types. First, an active area denotes a region through which a wireless power signal transferring power to the wireless power receiver  200  is passed. Next, a semi-active area denotes an interest region in which the wireless power transmitter  100  can detect the existence of the wireless power receiver  200 . Here, the power transmission control unit  112  may detect whether the wireless power receiver  200  is placed in the active area or detection area or removed from the area. Specifically, the power transmission control unit  112  may detect whether or not the wireless power receiver  200  is placed in the active area or detection area using a wireless power signal formed from the power conversion unit  111  or a sensor separately provided therein. For instance, the power transmission control unit  112  may detect the presence of the wireless power receiver  200  by monitoring whether or not the characteristic of power for forming the wireless power signal is changed by the wireless power signal, which is affected by the wireless power receiver  200  existing in the detection area. However, the active area and detection area may vary according to the wireless power transfer method such as an inductive coupling method, a resonance coupling method, and the like. 
     The power transmission control unit  112  may perform the process of identifying the wireless power receiver  200  or determine whether to start wireless power transfer according to a result of detecting the existence of the wireless power receiver  200 . 
     Furthermore, the power transmission control unit  112  may determine at least one characteristic of a frequency, a voltage, and a current of the power conversion unit  111  for forming the wireless power signal. The determination of the characteristic may be carried out by a condition at the side of the wireless power transmitter  100  or a condition at the side of the wireless power receiver  200 . 
     The power transmission control unit  112  may receive a power control message from the wireless power receiver  200 . The power transmission control unit  112  may determine at least one characteristic of a frequency, a voltage and a current of the power conversion unit  111  based on the received power control message, and additionally perform other control operations based on the power control message. 
     For example, the power transmission control unit  112  may determine at least one characteristic of a frequency, a voltage and a current used to form the wireless power signal according to the power control message including at least one of rectified power amount information, charging state information and identification information in the wireless power receiver  200 . 
     Furthermore, as another control operation using the power control message, the wireless power transmitter  100  may perform a typical control operation associated with wireless power transfer based on the power control message. For example, the wireless power transmitter  100  may receive information associated with the wireless power receiver  200  to be auditorily or visually outputted through the power control message, or receive information required for authentication between devices. 
     In exemplary embodiments, the power transmission control unit  112  may receive the power control message through the wireless power signal. In other exemplary embodiment, the power transmission control unit  112  may receive the power control message through a method for receiving user data. 
     In order to receive the foregoing power control message, the wireless power transmitter  100  may further include a modulation/demodulation unit  113  electrically connected to the power conversion unit  111 . The modulation/demodulation unit  113  may modulate a wireless power signal that has been modulated by the wireless power receiver  200  and use it to receive the power control message. 
     In addition, the power transmission control unit  112  may acquire a power control message by receiving user data including a power control message by a communication means (not shown) included in the wireless power transmitter  100 . 
     [For Supporting in-Band Two-Way Communication] 
     Under a wireless power transfer environment allowing for bi-directional communications according to the exemplary embodiments disclosed herein, the power transmission control unit  112  may transmit data to the wireless power receiver  200 . The data transmitted by the power transmission control unit  112  may be transmitted to request the wireless power receiver  200  to send the power control message. 
     Wireless Power Receiver 
     Referring to  FIG. 2B , the wireless power receiver  200  may include a power supply unit  290 . The power supply unit  290  supplies power required for the operation of the wireless power receiver  200 . The power supply unit  290  may include a power receiving unit  291  and a power reception control unit  292 . 
     The power receiving unit  291  receives power transferred from the wireless power transmitter  100  in a wireless manner. 
     The power receiving unit  291  may include constituent elements required to receive the wireless power signal according to a wireless power transfer method. Furthermore, the power receiving unit  291  may receive power according to at least one wireless power transfer method, and in this case, the power receiving unit  291  may include constituent elements required for each method. 
     First, the power receiving unit  291  may include a coil for receiving a wireless power signal transferred in the form of a magnetic field or electromagnetic field having a vibration characteristic. 
     For instance, as a constituent element according to the inductive coupling method, the power receiving unit  291  may include a secondary coil to which a current is induced by a changing magnetic field. In exemplary embodiments, the power receiving unit  291 , as a constituent element according to the resonance coupling method, may include a coil and a resonant circuit in which resonance phenomenon is generated by a magnetic field having a specific resonant frequency. 
     In another exemplary embodiments, when the power receiving unit  291  receives power according to at least one wireless power transfer method, the power receiving unit  291  may be implemented to receive power by using a coil, or implemented to receive power by using a coil formed differently according to each power transfer method. 
     Among the constituent elements included in the power receiving unit  291 , those for the inductive coupling method will be described later with reference to  FIGS. 4A and 4B , and those for the resonance coupling method with reference to  FIGS. 7A and 7B . 
     On the other hand, the power receiving unit  291  may further include a rectifier and a regulator to convert the wireless power signal into a direct current. Furthermore, the power receiving unit  291  may further include a circuit for protecting an overvoltage or overcurrent from being generated by the received power signal. 
     The power reception control unit  292  may control each constituent element included in the power supply unit  290 . 
     Specifically, the power reception control unit  292  may transfer a power control message to the wireless power transmitter  100 . The power control message may instruct the wireless power transmitter  100  to initiate or terminate a transfer of the wireless power signal. Furthermore, the power control message may instruct the wireless power transmitter  100  to control a characteristic of the wireless power signal. 
     In exemplary embodiments, the power reception control unit  292  may transmit the power control message through at least one of the wireless power signal and user data. 
     In order to transmit the foregoing power control message, the wireless power receiver  200  may further include a modulation/demodulation unit  293  electrically connected to the power receiving unit  291 . The modulation/demodulation unit  293 , similarly to the case of the wireless power transmitter  100 , may be used to transmit the power control message through the wireless power signal. The power communications modulation/demodulation unit  293  may be used as a means for controlling a current and/or voltage flowing through the power conversion unit  111  of the wireless power transmitter  100 . Hereinafter, a method for allowing the power communications modulation/demodulation unit  113  or  293  at the side of the wireless power transmitter  100  and at the side of the wireless power receiver  200 , respectively, to be used to transmit and receive a power control message through a wireless power signal will be described. 
     A wireless power signal formed by the power conversion unit  111  is received by the power receiving unit  291 . At this time, the power reception control unit  292  controls the power communications modulation/demodulation unit  293  at the side of the wireless power receiver  200  to modulate the wireless power signal. For instance, the power reception control unit  292  may perform a modulation process such that a power amount received from the wireless power signal is varied by changing a reactance of the power communications modulation/demodulation unit  293  connected to the power receiving unit  291 . The change of a power amount received from the wireless power signal results in the change of a current and/or voltage of the power conversion unit  111  for forming the wireless power signal. At this time, the modulation/demodulation unit  113  at the side of the wireless power transmitter  100  may detect a change of the current and/or voltage to perform a demodulation process. 
     In other words, the power reception control unit  292  may generate a packet including a power control message intended to be transferred to the wireless power transmitter  100  and modulate the wireless power signal to allow the packet to be included therein, and the power transmission control unit  112  may decode the packet based on a result of performing the demodulation process of the power communications modulation/demodulation unit  113  to acquire the power control message included in the packet. 
     In addition, the power reception control unit  292  may transmit a power control message to the wireless power transmitter  100  by transmitting user data including the power control message by a communication means (not shown) included in the wireless power receiver  200 . 
     [For Supporting In-Band Two-Way Communication] 
     Under a wireless power transfer environment allowing for bi-directional communications according to the exemplary embodiments disclosed herein, the power reception control unit  292  may receive data to the wireless power transmitter  100 . The data transmitted by the wireless power transmitter  100  may be transmitted to request the wireless power receiver  200  to send the power control message. 
     In addition, the power supply unit  290  may further include a charger  298  and a battery  299 . 
     The wireless power receiver  200  receiving power for operation from the power supply unit  290  may be operated by power transferred from the wireless power transmitter  100 , or operated by charging the battery  299  using the transferred power and then receiving the charged power. At this time, the power reception control unit  292  may control the charger  298  to perform charging using the transferred power. 
     Hereinafter, description will be given of a wireless power transmitter and a wireless power receiver applicable to the exemplary embodiments disclosed herein. First, a method of allowing the wireless power transmitter to transfer power to the electronic device according to the inductive coupling method will be described with reference to  FIGS. 3 through 5 . 
     Inductive Coupling Method 
       FIG. 3  is a view illustrating a concept in which power is transferred from a wireless power transmitter to an electronic device in a wireless manner according to an inductive coupling method. 
     When the power of the wireless power transmitter  100  is transferred in an inductive coupling method, if the strength of a current flowing through a primary coil within the power transmission unit  110  is changed, then a magnetic field passing through the primary coil will be changed by the current. The changed magnetic field generates an induced electromotive force at a secondary coil in the wireless power receiver  200 . 
     According to the foregoing method, the power conversion unit  111  of the wireless power transmitter  100  may include a transmitting (Tx) coil  1111   a  being operated as a primary coil in magnetic induction. Furthermore, the power receiving unit  291  of the wireless power receiver  200  may include a receiving (Rx) coil  2911   a  being operated as a secondary coil in magnetic induction. 
     First, the wireless power transmitter  100  and wireless power receiver  200  are disposed in such a manner that the transmitting coil  1111   a  at the side of the wireless power transmitter  100  and the receiving coil at the side of the wireless power receiver  200  are located neighboring (or adjacent) to each other. Then, if the power transmission control unit  112  controls a current of the transmitting coil (Tx coil)  1111   a  to be changed, then the power receiving unit  291  controls power to be supplied to the wireless power receiver  200  using an electromotive force induced to the receiving coil (Rx coil)  2911   a.    
     The efficiency of wireless power transfer by the inductive coupling method may be little affected by a frequency characteristic, but affected by an alignment and distance between the wireless power transmitter  100  and the wireless power receiver  200  including each coil. 
     On the other hand, in order to perform wireless power transfer in the inductive coupling method, the wireless power transmitter  100  may be configured to include an interface surface (not shown) in the form of a flat surface. One or more electronic devices may be placed at an upper portion of the interface surface, and the transmitting coil  1111   a  may be mounted at a lower portion of the interface surface. In this case, a vertical spacing is formed in a small-scale between the transmitting coil  1111   a  mounted at a lower portion of the interface surface and the receiving coil  2911   a  of the wireless power receiver  200  placed at an upper portion of the interface surface, and thus a distance between the coils becomes sufficiently small to efficiently implement contactless power transfer by the inductive coupling method. 
     Furthermore, an alignment indicator (not shown) indicating a location where the wireless power receiver  200  is to be placed at an upper portion of the interface surface. The alignment indicator indicates a location of the wireless power receiver  200  where an alignment between the transmitting coil  1111   a  mounted at a lower portion of the interface surface and the receiving coil  2911   a  can be suitably implemented. The alignment indicator may alternatively be simple marks, or may be formed in the form of a protrusion structure for guiding the location of the wireless power receiver  200 . Otherwise, the alignment indicator may be formed in the form of a magnetic body such as a magnet mounted at a lower portion of the interface surface, thereby guiding the coils to be suitably arranged by mutual magnetism to a magnetic body having an opposite polarity mounted within the wireless power receiver  200 . 
     On the other hand, the wireless power transmitter  100  may be formed to include one or more transmitting coils. The wireless power transmitter  100  may selectively use some of coils suitably arranged with the receiving coil  2911   a  of the wireless power receiver  200  among the one or more transmitting coils to enhance the power transmission efficiency. The wireless power transmitter  100  including the one or more transmitting coils will be described later with reference to  FIG. 5 . 
     Hereinafter, configurations of the wireless power transmitter and electronic device using an inductive coupling method applicable to the embodiments disclosed herein will be described in detail. 
     Wireless Power Transmitter and Electronic Device in Inductive Coupling Method 
       FIGS. 4A and 4B  are a block diagram illustrating part of the wireless power transmitter  100  and wireless power receiver  200  in a magnetic induction method that can be employed in the embodiments disclosed herein. A configuration of the power transmission unit  110  included in the wireless power transmitter  100  will be described with reference to  FIG. 4A , and a configuration of the power supply unit  290  included in the wireless power receiver  200  will be described with reference to  FIG. 4B . 
     Referring to  FIG. 4A , the power conversion unit  111  of the wireless power transmitter  100  may include a transmitting (Tx) coil  1111   a  and an inverter  1112 . 
     The transmitting coil  1111   a  may form a magnetic field corresponding to the wireless power signal according to a change of current as described above. The transmitting coil  1111   a  may alternatively be implemented with a planar spiral type or cylindrical solenoid type. 
     The inverter  1112  transforms a DC input obtained from the power supply unit  190  into an AC waveform. The AC current transformed by the inverter  1112  drives a resonant circuit including the transmitting coil  1111   a  and a capacitor (not shown) to form a magnetic field in the transmitting coil  1111   a.    
     In addition, the power conversion unit  111  may further include a positioning unit  1114 . 
     The positioning unit  1114  may move or rotate the transmitting coil  1111   a  to enhance the effectiveness of contactless power transfer using the inductive coupling method. As described above, it is because an alignment and distance between the wireless power transmitter  100  and the wireless power receiver  200  including a primary coil and a secondary coil may affect power transfer using the inductive coupling method. In particular, the positioning unit  1114  may be used when the wireless power receiver  200  does not exist within an active area of the wireless power transmitter  100 . 
     Accordingly, the positioning unit  1114  may include a drive unit (not shown) for moving the transmitting coil  1111   a  such that a center-to-center distance of the transmitting coil  1111   a  of the wireless power transmitter  100  and the receiving coil  2911   a  of the wireless power receiver  200  is within a predetermined range, or rotating the transmitting coil  1111   a  such that the centers of the transmitting coil  1111   a  and the receiving coil  2911   a  are overlapped with each other. 
     For this purpose, the wireless power transmitter  100  may further include a detection unit (not shown) made of a sensor for detecting the location of the wireless power receiver  200 , and the power transmission control unit  112  may control the positioning unit  1114  based on the location information of the wireless power receiver  200  received from the location detection sensor. 
     Furthermore, to this end, the power transmission control unit  112  may receive control information on an alignment or distance to the wireless power receiver  200  through the power communications modulation/demodulation unit  113 , and control the positioning unit  1114  based on the received control information on the alignment or distance. 
     If the power conversion unit  111  is configured to include a plurality of transmitting coils, then the positioning unit  1114  may determine which one of the plurality of transmitting coils is to be used for power transmission. The configuration of the wireless power transmitter  100  including the plurality of transmitting coils will be described later with reference to  FIG. 5 . 
     On the other hand, the power conversion unit  111  may further include a power sensing unit  1115 . The power sensing unit  1115  at the side of the wireless power transmitter  100  monitors a current or voltage flowing into the transmitting coil  1111   a . The power sensing unit  1115  is provided to check whether or not the wireless power transmitter  100  is normally operated, and thus the power sensing unit  1115  may detect a voltage or current of the power supplied from the outside, and check whether the detected voltage or current exceeds a threshold value. The power sensing unit  1115 , although not shown, may include a resistor for detecting a voltage or current of the power supplied from the outside and a comparator for comparing a voltage value or current value of the detected power with a threshold value to output the comparison result. Based on the check result of the power sensing unit  1115 , the power transmission control unit  112  may control a switching unit (not shown) to cut off power applied to the transmitting coil  1111   a.    
     Referring to  FIG. 4B , the power supply unit  290  of the wireless power receiver  200  may include a receiving (Rx) coil  2911   a  and a rectifier  2913 . 
     A current is induced into the receiving coil  2911   a  by a change of the magnetic field formed in the transmitting coil  1111   a . The implementation type of the receiving coil  2911   a  may be a planar spiral type or cylindrical solenoid type similarly to the transmitting coil  1111   a.    
     Furthermore, series and parallel capacitors may be configured to be connected to the receiving coil  2911   a  to enhance the effectiveness of wireless power reception or perform resonant detection. 
     The receiving coil  2911   a  may be in the form of a single coil or a plurality of coils. 
     The rectifier  2913  performs a full-wave rectification to a current to convert alternating current into direct current. The rectifier  2913 , for instance, may be implemented with a full-bridge rectifier made of four diodes or a circuit using active components. 
     In addition, the rectifier  2913  may further include a regulator for converting a rectified current into a more flat and stable direct current. Furthermore, the output power of the rectifier  2913  is supplied to each constituent element of the power supply unit  290 . Furthermore, the rectifier  2913  may further include a DC-DC converter for converting output DC power into a suitable voltage to adjust it to the power required for each constituent element (for instance, a circuit such as a charger  298 ). 
     The power communications modulation/demodulation unit  293  may be connected to the power receiving unit  291 , and may be configured with a resistive element in which resistance varies with respect to direct current, and may be configured with a capacitive element in which reactance varies with respect to alternating current. The power reception control unit  292  may change the resistance or reactance of the power communications modulation/demodulation unit  293  to modulate a wireless power signal received to the power receiving unit  291 . 
     On the other hand, the power supply unit  290  may further include a power sensing unit  2914 . The power sensing unit  2914  at the side of the wireless power receiver  200  monitors a voltage and/or current of the power rectified by the rectifier  2913 , and if the voltage and/or current of the rectified power exceeds a threshold value as a result of monitoring, then the power reception control unit  292  transmits a power control message to the wireless power transmitter  100  to transfer suitable power. 
     Wireless Power Transmitter Configured to Include One or More Transmitting Coils 
       FIG. 5  is a block diagram illustrating a wireless power transmitter configured to have one or more transmission coils receiving power according to an inductive coupling method that can be employed in the embodiments disclosed herein. 
     Referring to  FIG. 5 , the power conversion unit  111  of the wireless power transmitter  100  according to the embodiments disclosed herein may include one or more transmitting coils  1111   a - 1  to  1111   a - n . The one or more transmitting coils  1111   a - 1  to  1111   a - n  may be an array of partly overlapping primary coils. An active area may be determined by some of the one or more transmitting coils. 
     The one or more transmitting coils  1111   a - 1  to  1111   a - n  may be mounted at a lower portion of the interface surface. Furthermore, the power conversion unit  111  may further include a multiplexer  1113  for establishing and releasing the connection of some of the one or more transmitting coils  1111   a - 1  to  1111   a - n.    
     Upon detecting the location of the wireless power receiver  200  placed at an upper portion of the interface surface, the power transmission control unit  112  may take the detected location of the wireless power receiver  200  into consideration to control the multiplexer  1113 , thereby allowing coils that can be placed in an inductive coupling relation to the receiving coil  2911   a  of the wireless power receiver  200  among the one or more transmitting coils  1111   a - 1  to  1111   a - n  to be connected to one another. 
     For this purpose, the power transmission control unit  112  may acquire the location information of the wireless power receiver  200 . For example, the power transmission control unit  112  may acquire the location of the wireless power receiver  200  on the interface surface by the location detection unit (not shown) provided in the wireless power transmitter  100 . For another example, the power transmission control unit  112  may alternatively receive a power control message indicating a strength of the wireless power signal from an object on the interface surface or a power control message indicating the identification information of the object using the one or more transmitting coils  1111   a - 1  to  1111   a - n , respectively, and determines whether it is located neighboring to which one of the one or more transmitting coils based on the received result, thereby acquiring the location information of the wireless power receiver  200 . 
     On the other hand, the active area as part of the interface surface may denote a portion through which a magnetic field with a high efficiency can pass when the wireless power transmitter  100  transfers power to the wireless power receiver  200  in a wireless manner. At this time, a single transmitting coil or one or a combination of more transmitting coils forming a magnetic field passing through the active area may be designated as a primary cell. Accordingly, the power transmission control unit  112  may determine an active area based on the detected location of the wireless power receiver  200 , and establish the connection of a primary cell corresponding to the active area to control the multiplexer  1113 , thereby allowing the receiving coil  2911   a  of the wireless power receiver  200  and the coils belonging to the primary cell to be placed in an inductive coupling relation. 
     Furthermore, the power conversion unit  111  may further include an impedance matching unit (not shown) for controlling an impedance to form a resonant circuit with the coils connected thereto. 
     Hereinafter, a method for allowing a wireless power transmitter to transfer power according to a resonance coupling method will be disclosed with reference to  FIGS. 6 through 8 . 
     Resonance Coupling Method 
       FIG. 6  is a view illustrating a concept in which power is transferred to an electronic device from a wireless power transmitter in a wireless manner according to a resonance coupling method. 
     First, resonance will be described in brief as follows. Resonance refers to a phenomenon in which amplitude of vibration is remarkably increased when periodically receiving an external force having the same frequency as the natural frequency of a vibration system. Resonance is a phenomenon occurring at all kinds of vibrations such as mechanical vibration, electric vibration, and the like. Generally, when exerting a vibratory force to a vibration system from the outside, if the natural frequency thereof is the same as a frequency of the externally applied force, then the vibration becomes strong, thus increasing the width. 
     With the same principle, when a plurality of vibrating bodies separated from one another within a predetermined distance vibrate at the same frequency, the plurality of vibrating bodies resonate with one another, and in this case, resulting in a reduced resistance between the plurality of vibrating bodies. In an electrical circuit, a resonant circuit can be made by using an inductor and a capacitor. 
     When the wireless power transmitter  100  transfers power according to the inductive coupling method, a magnetic field having a specific vibration frequency is formed by alternating current power in the power transmission unit  110 . If a resonance phenomenon occurs in the wireless power receiver  200  by the formed magnetic field, then power is generated by the resonance phenomenon in the wireless power receiver  200 . 
     The resonant frequency may be determined by the following formula in Equation 1. 
     
       
         
           
             
               
                 
                   f 
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       π 
                       ⁢ 
                       
                         LC 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, the resonant frequency (f) is determined by an inductance (L) and a capacitance (C) in a circuit. In a circuit forming a magnetic field using a coil, the inductance can be determined by a number of turns of the coil, and the like, and the capacitance can be determined by a gap between the coils, an area, and the like. In addition to the coil, a capacitive resonant circuit may be configured to be connected thereto to determine the resonant frequency. 
     Referring to  FIG. 6 , when power is transmitted in a wireless manner according to the resonance coupling method, the power conversion unit  111  of the wireless power transmitter  100  may include a transmitting (Tx) coil  1111   b  in which a magnetic field is formed and a resonant circuit  1116  connected to the transmitting coil  1111   b  to determine a specific vibration frequency. The resonant circuit  1116  may be implemented by using a capacitive circuit (capacitors), and the specific vibration frequency may be determined based on an inductance of the transmitting coil  1111   b  and a capacitance of the resonant circuit  1116 . 
     The configuration of a circuit element of the resonant circuit  1116  may be implemented in various forms such that the power conversion unit  111  forms a magnetic field, and is not limited to a form of being connected in parallel to the transmitting coil  1111   b  as illustrated in  FIG. 6 . 
     Furthermore, the power receiving unit  291  of the wireless power receiver  200  may include a resonant circuit  2912  and a receiving (Rx) coil  2911   b  to generate a resonance phenomenon by a magnetic field formed in the wireless power transmitter  100 . In other words, the resonant circuit  2912  may be also implemented by using a capacitive circuit, and the resonant circuit  2912  is configured such that a resonant frequency determined based on an inductance of the receiving coil  2911   b  and a capacitance of the resonant circuit  2912  has the same frequency as a resonant frequency of the formed magnetic field. 
     The configuration of a circuit element of the resonant circuit  2912  may be implemented in various forms such that the power receiving unit  291  generates resonance by a magnetic field, and is not limited to a form of being connected in series to the receiving coil  2911   b  as illustrated in  FIG. 6 . 
     The specific vibration frequency in the wireless power transmitter  100  may have L TX , C TX , and may be acquired by using the Equation 1. Here, the wireless power receiver  200  generates resonance when a result of substituting the L RX  and C RX  of the wireless power receiver  200  to the Equation 1 is same as the specific vibration frequency. 
     According to a contactless power transfer method by resonance coupling, when the wireless power transmitter  100  and wireless power receiver  200  resonate at the same frequency, respectively, an electromagnetic wave is propagated through a short-range magnetic field, and thus there exists no energy transfer between the devices if they have different frequencies. 
     As a result, an efficiency of contactless power transfer by the resonance coupling method is greatly affected by a frequency characteristic, whereas the effect of an alignment and distance between the wireless power transmitter  100  and the wireless power receiver  200  including each coil is relatively smaller than the inductive coupling method. 
     Hereinafter, the configuration of a wireless power transmitter and an electronic device in the resonance coupling method applicable to the embodiments disclosed herein will be described in detail. 
     Wireless Power Transmitter in Resonance Coupling Method 
       FIGS. 7A and 7B  are a block diagram illustrating part of the wireless power transmitter  100  and wireless power receiver  200  in a resonance method that can be employed in the embodiments disclosed herein. 
     A configuration of the power transmission unit  110  included in the wireless power transmitter  100  will be described with reference to  FIG. 7A . 
     The power conversion unit  111  of the wireless power transmitter  100  may include a transmitting (Tx) coil  1111   b , an inverter  1112 , and a resonant circuit  1116 . The inverter  1112  may be configured to be connected to the transmitting coil  1111   b  and the resonant circuit  1116 . 
     The transmitting coil  1111   b  may be mounted separately from the transmitting coil  1111   a  for transferring power according to the inductive coupling method, but may transfer power in the inductive coupling method and resonance coupling method using one single coil. 
     The transmitting coil  1111   b , as described above, forms a magnetic field for transferring power. The transmitting coil  1111   b  and the resonant circuit  1116  generate resonance when alternating current power is applied thereto, and at this time, a vibration frequency may be determined based on an inductance of the transmitting coil  1111   b  and a capacitance of the resonant circuit  1116 . 
     For this purpose, the inverter  1112  transforms a DC input obtained from the power supply unit  190  into an AC waveform, and the transformed AC current is applied to the transmitting coil  1111   b  and the resonant circuit  1116 . 
     In addition, the power conversion unit  111  may further include a frequency adjustment unit  1117  for changing a resonant frequency of the power conversion unit  111 . The resonant frequency of the power conversion unit  111  is determined based on an inductance and/or capacitance within a circuit constituting the power conversion unit  111  by Equation 1, and thus the power transmission control unit  112  may determine the resonant frequency of the power conversion unit  111  by controlling the frequency adjustment unit  1117  to change the inductance and/or capacitance. 
     The frequency adjustment unit  1117 , for example, may be configured to include a motor for adjusting a distance between capacitors included in the resonant circuit  1116  to change a capacitance, or include a motor for adjusting a number of turns or diameter of the transmitting coil  1111  to change an inductance, or include active elements for determining the capacitance and/or inductance 
     On the other hand, the power conversion unit  111  may further include a power sensing unit  1115 . The operation of the power sensing unit  1115  is the same as the foregoing description. 
     Referring to  FIG. 7B , a configuration of the power supply unit  290  included in the wireless power receiver  200  will be described. The power supply unit  290 , as described above, may include the receiving (Rx) coil  2911   b  and resonant circuit  2912 . 
     In addition, the power receiving unit  291  of the power supply unit  290  may further include a rectifier  2913  for converting an AC current generated by resonance phenomenon into DC. The rectifier  2913  may be configured similarly to the foregoing description. 
     Furthermore, the power receiving unit  291  may further include a power sensing unit  2914  for monitoring a voltage and/or current of the rectified power. The power sensing unit  2914  may be configured similarly to the foregoing description. 
     Wireless Power Transmitter Configured to Include One or More Transmitting Coils 
       FIG. 8  is a block diagram illustrating a wireless power transmitter configured to have one or more transmission coils receiving power according to a resonance coupling method that can be employed in the embodiments disclosed herein. 
     Referring to  FIG. 8 , the power conversion unit  111  of the wireless power transmitter  100  according to the embodiments disclosed herein may include one or more transmitting coils  1111   b - 1  to  1111   b - n  and resonant circuits ( 1116 - 1  to  1116 - n ) connected to each transmitting coils. Furthermore, the power conversion unit  111  may further include a multiplexer  1113  for establishing and releasing the connection of some of the one or more transmitting coils  1111   b - 1  to  1111   b - n.    
     The one or more transmitting coils  1111   b - 1  to  1111   b - n  may be configured to have the same vibration frequency, or some of them may be configured to have different vibration frequencies. It is determined by an inductance and/or capacitance of the resonant circuits ( 1116 - 1  to  1116 - n ) connected to the one or more transmitting coils  1111   b - 1  to  1111   b - n , respectively. 
     For this purpose, the frequency adjustment unit  1117  may be configured to change an inductance and/or capacitance of the resonant circuits ( 1116 - 1  to  1116 - n ) connected to the one or more transmitting coils  1111   b - 1  to  1111   b - n , respectively. 
     In-Band Communication 
       FIG. 9  a view illustrating the concept of transmitting and receiving a packet between a wireless power transmitter and a wireless power receiver through the modulation and demodulation of a wireless power signal in transferring power in a wireless manner disclosed herein. 
     As illustrated in  FIG. 9 , the power conversion unit  111  included in the wireless power transmitter  100  may generate a wireless power signal. The wireless power signal may be generated through the transmitting coil  1111  included in the power conversion unit  111 . 
     The wireless power signal  10   a  generated by the power conversion unit  111  may arrive at the wireless power receiver  200  so as to be received through the power receiving unit  291  of the wireless power receiver  200 . The generated wireless power signal may be received through the receiving coil  2911  included in the power receiving unit  291 . 
     The power reception control unit  292  may control the modulation/demodulation unit  293  connected to the power receiving unit  291  to modulate the wireless power signal while the wireless power receiver  200  receives the wireless power signal. When the received wireless power signal is modulated, the wireless power signal may form a closed-loop within a magnetic field or an electro-magnetic field. This may allow the wireless power transmitter  100  to sense a modulated wireless power signal  10   b . The modulation/demodulation unit  113  may demodulate the sensed wireless power signal and decode the packet from the demodulated wireless power signal. 
     The modulation method employed for the communication between the wireless power transmitter  100  and the wireless power receiver  200  may be an amplitude modulation. As aforementioned, the amplitude modulation is a backscatter modulation may be a backscatter modulation method in which the power communications modulation/demodulation unit  293  at the side of the wireless power receiver  200  changes an amplitude of the wireless power signal  10   a  formed by the power conversion unit  111  and the power reception control unit  292  at the side of the wireless power transmitter  100  detects an amplitude of the modulated wireless power signal  10   b.    
     Modulation and Demodulation of Wireless Power Signal 
     Hereinafter, description will be given of modulation and demodulation of a packet, which is transmitted or received between the wireless power transmitter  100  and the wireless power receiver  200  with reference to  FIGS. 10 and 11 . 
       FIG. 10  is a view illustrating a configuration of transmitting or receiving a power control message in transferring power in a wireless manner disclosed herein, and  FIG. 11  is a view illustrating forms of signals upon modulation and demodulation executed in the wireless power transfer disclosed herein. 
     Referring to  FIG. 10 , the wireless power signal received through the power receiving unit  291  of the wireless power receiver  200 , as illustrated in  FIG. 11A , may be a non-modulated wireless power signal  51 . The wireless power receiver  200  and the wireless power transmitter  100  may establish a resonance coupling according to a resonant frequency, which is set by the resonant circuit  2912  within the power receiving unit  291 , and the wireless power signal  51  may be received through the receiving coil  2911   b.    
     The power reception control unit  292  may modulate the wireless power signal  51  received through the power receiving unit  291  by changing a load impedance within the modulation/demodulation unit  293 . The modulation/demodulation unit  293  may include a passive element  2931  and an active element  2932  for modulating the wireless power signal  51 . The modulation/demodulation unit  293  may modulate the wireless power signal  51  to include a packet, which is desired to be transmitted to the wireless power transmitter  100 . Here, the packet may be input into the active element  2932  within the modulation/demodulation unit  293 . 
     Afterwards, the power transmission control unit  112  of the wireless power transmitter  100  may demodulate a modulated wireless power signal  52  through an envelop detection, and decode the detected signal  53  into digital data  54 . The demodulation may detect a current or voltage flowing into the power conversion unit  111  to be classified into two states, a HI phase and a LO phase, and acquire a packet to be transmitted by the wireless power receiver  200  based on digital data classified according to the states. 
     Hereinafter, a process of allowing the wireless power transmitter  100  to acquire a power control message to be transmitted by the wireless power receiver  200  from the demodulated digital data will be described. 
     Referring to  FIG. 11B , the power transmission control unit  112  detects an encoded bit using a clock signal (CLK) from an envelope detected signal. The detected encoded bit is encoded according to a bit encoding method used in the modulation process at the side of the wireless power receiver  200 . The bit encoding method may correspond to any one of non-return to zero (NRZ) and bi-phase encoding. 
     For instance, the detected bit may be a differential bi-phase (DBP) encoded bit. According to the DBP encoding, the power reception control unit  292  at the side of the wireless power receiver  200  is allowed to have two state transitions to encode data bit 1, and to have one state transition to encode data bit 0. In other words, data bit 1 may be encoded in such a manner that a transition between the HI state and LO state is generated at a rising edge and falling edge of the clock signal, and data bit 0 may be encoded in such a manner that a transition between the HI state and LO state is generated at a rising edge of the clock signal. 
     On the other hand, the power transmission control unit  112  may acquire data in a byte unit using a byte format constituting a packet from a bit string detected according to the bit encoding method. For instance, the detected bit string may be transferred by using an 11-bit asynchronous serial format as illustrated in  FIG. 12C . In other words, the detected bit may include a start bit indicating the beginning of a byte and a stop bit indicating the end of a byte, and also include data bits (b 0  to b 7 ) between the start bit and the stop bit. Furthermore, it may further include a parity bit for checking an error of data. The data in a byte unit constitutes a packet including a power control message. 
     [For Supporting In-Band Two-Way Communication] 
     As aforementioned,  FIG. 9  has illustrated that the wireless power receiver  200  transmits a packet using a carrier signal  10   a  formed by the wireless power transmitter  100 . However, the wireless power transmitter  100  may also transmit data to the wireless power receiver  200  by a similar method. 
     That is, the power transmission control unit  112  may control the modulation/demodulation unit  113  to modulate data, which is to be transmitted to the wireless power receiver  200 , such that the data can be included in the carrier signal  10   a . Here, the power reception control unit  292  of the wireless power receiver  200  may control the modulation/demodulation unit  293  to execute demodulation so as to acquire data from the modulated carrier signal  10   a.    
     Packet Format 
     Hereinafter, description will be given of a structure of a packet used in communication using a wireless power signal according to the exemplary embodiments disclosed herein. 
       FIG. 12  is a view illustrating a packet including a power control message used in a contactless (wireless) power transfer method according to the embodiments disclosed herein. 
     As illustrated in  FIG. 12A , the wireless power transmitter  100  and the wireless power receiver  200  may transmit and receive data desired to transmit in a form of a command packet (command_packet)  510 . The command packet  510  may include a header  511  and a message  512 . 
     The header  511  may include a field indicating a type of data included in the message  512 . Size and type of the message may be decided based on a value of the field which indicates the type of data. 
     The header  511  may include an address field for identifying a transmitter (originator) of the packet. For example, the address field may indicate an identifier of the wireless power receiver  200  or an identifier of a group to which the wireless power receiver  200  belongs. When the wireless power receiver  200  transmits the packet  510 , the wireless power receiver  200  may generate the packet  510  such that the address field can indicate identification information related to the receiver  200  itself. 
     The message  512  may include data that the originator of the packet  510  desires to transmit. The data included in the message  512  may be a report, a request or a response for the other party. 
     According to one exemplary embodiment, the command packet  510  may be configured as illustrated in  FIG. 12B . The header  511  included in the command packet  510  may be represented with a predetermined size. For example, the header  511  may have a 2-byte size. 
     The header  511  may include a reception address field. For example, the reception address field may have a 6-bit size. 
     The header  511  may include an operation command field (OCF) or an operation group field (OGF). The OGF is a value given for each group of commands for the wireless power receiver  200 , and the OCF is a value given for each command existing in each group in which the wireless power receiver  200  is included. 
     The message  512  may be divided into a length field  5121  of a parameter and a value field  5122  of the parameter. That is, the originator of the packet  510  may generate the message by a length-value pair ( 5121   a - 5122   a , etc.) of at least one parameter, which is required to represent data desired to transmit. 
     Referring to  FIG. 12C , the wireless power transmitter  100  and the wireless power receiver  200  may transmit and receive the data in a form of a packet which further has a preamble  520  and a checksum  530  added to the command packet  510 . 
     The preamble  520  may be used to perform synchronization with data received by the wireless power transmitter  100  and detect the start bit of the header  520 . The preamble  520  may be configured to repeat the same bit. For instance, the preamble  520  may be configured such that data bit  1  according to the DBP encoding is repeated eleven to twenty five times. 
     The checksum  530  may be used to detect an error that can be occurred in the command packet  510  while transmitting a power control message. 
     Operation Phases 
     Hereinafter, description will be given of operation phases of the wireless power transmitter  100  and the wireless power receiver  200 . 
       FIG. 13  illustrates the operation phases of the wireless power transmitter  100  and the wireless power receiver  200  according to the embodiments disclosed herein. Furthermore,  FIGS. 14 to 18  illustrate the structures of packets including a power control message between the wireless power transmitter  100  and the wireless power receiver  200 . 
     Referring to  FIG. 13 , the operation phases of the wireless power transmitter  100  and the wireless power receiver  200  for wireless power transfer may be divided into a selection phase (state)  610 , a ping phase  620 , an identification and configuration phase  630 , and a power transfer phase  640 . 
     The wireless power transmitter  100  detects whether or not objects exist within a range that the wireless power transmitter  100  can transmit power in a wireless manner in the selection state  610 , and the wireless power transmitter  100  sends a detection signal to the detected object and the wireless power receiver  200  sends a response to the detection signal in the ping state  620 . 
     Furthermore, the wireless power transmitter  100  identifies the wireless power receiver  200  selected through the previous states and acquires configuration information for power transmission in the identification and configuration state  630 . The wireless power transmitter  100  transmits power to the wireless power receiver  200  while controlling power transmitted in response to a control message received from the wireless power receiver  200  in the power transfer state  640 . 
     Hereinafter, each of the operation phases will be described in detail. 
     1) Selection State 
     The wireless power transmitter  100  in the selection state  610  performs a detection process to select the wireless power receiver  200  existing within a detection area. The detection area, as described above, refers to a region in which an object within the relevant area can affect on the characteristic of the power of the power conversion unit  111 . Compared to the ping state  620 , the detection process for selecting the wireless power receiver  200  in the selection state  610  is a process of detecting a change of the power amount for forming a wireless power signal in the power conversion unit at the side of the wireless power transmitter  100  to check whether any object exists within a predetermined range, instead of the scheme of receiving a response from the wireless power receiver  200  using a power control message. The detection process in the selection state  610  may be referred to as an analog ping process in the aspect of detecting an object using a wireless power signal without using a packet in a digital format in the ping state  620  which will be described later. 
     The wireless power transmitter  100  in the selection state  610  can detect that an object comes in or out within the detection area. Furthermore, the wireless power transmitter  100  can distinguish the wireless power receiver  200  capable of transferring power in a wireless manner from other objects (for example, a key, a coin, etc.) among objects located within the detection area. 
     As described above, a distance that can transmit power in a wireless manner may be different according to the inductive coupling method and resonance coupling method, and thus the detection area for detecting an object in the selection state  610  may be different from one another. 
     First, in case where power is transmitted according to the inductive coupling method, the wireless power transmitter  100  in the selection state  610  can monitor an interface surface (not shown) to detect the alignment and removal of objects. 
     Furthermore, the wireless power transmitter  100  may detect the location of the wireless power receiver  200  placed on an upper portion of the interface surface. As described above, the wireless power transmitter  100  formed to include one or more transmitting coils may perform the process of entering the ping state  620  in the selection state  610 , and checking whether or not a response to the detection signal is transmitted from the object using each coil in the ping state  620  or subsequently entering the identification state  630  to check whether identification information is transmitted from the object. The wireless power transmitter  100  may determine a coil to be used for contactless power transfer based on the detected location of the wireless power receiver  200  acquired through the foregoing process. 
     Furthermore, when power is transmitted according to the resonance coupling method, the wireless power transmitter  100  in the selection state  610  can detect an object by detecting that any one of a frequency, a current and a voltage of the power conversion unit is changed due to an object located within the detection area. 
     On the other hand, the wireless power transmitter  100  in the selection state  610  may detect an object by at least any one of the detection methods using the inductive coupling method and resonance coupling method. The wireless power transmitter  100  may perform an object detection process according to each power transmission method, and subsequently select a method of detecting the object from the coupling methods for contactless power transfer to advance to other states  620 ,  630 ,  640 . 
     On the other hand, for the wireless power transmitter  100 , a wireless power signal formed to detect an object in the selection state  610  and a wireless power signal formed to perform digital detection, identification, configuration and power transmission in the subsequent states  620 ,  630 ,  640  may have a different characteristic in the frequency, strength, and the like. It is because the selection state  610  of the wireless power transmitter  100  corresponds to an idle state for detecting an object, thereby allowing the wireless power transmitter  100  to reduce consumption power in the idle state or generate a specialized signal for effectively detecting an object. 
     2) Ping State 
     The wireless power transmitter  100  in the ping state  620  performs a process of detecting the wireless power receiver  200  existing within the detection area through a power control message. Compared to the detection process of the wireless power receiver  200  using a characteristic of the wireless power signal and the like in the selection state  610 , the detection process in the ping state  620  may be referred to as a digital ping process. 
     The wireless power transmitter  100  in the ping state  620  forms a wireless power signal to detect the wireless power receiver  200 , modulates the wireless power signal modulated by the wireless power receiver  200 , and acquires a power control message in a digital data format corresponding to a response to the detection signal from the modulated wireless power signal. The wireless power transmitter  100  may receive a power control message corresponding to the response to the detection signal to recognize the wireless power receiver  200  which is a subject of power transmission. 
     The detection signal formed to allowing the wireless power transmitter  100  in the ping state  620  to perform a digital detection process may be a wireless power signal formed by applying a power signal at a specific operating point for a predetermined period of time. The operating point may denote a frequency, duty cycle, and amplitude of the voltage applied to the transmitting (Tx) coil. The wireless power transmitter  100  may generate the detection signal generated by applying the power signal at a specific operating point for a predetermined period of time, and attempt to receive a power control message from the wireless power receiver  200 . 
     On the other hand, the power control message corresponding to a response to the detection signal may be a message indicating strength of the wireless power signal received by the wireless power receiver  200 . For example, the wireless power receiver  200  may transmit a signal strength packet  5100  including a message indicating the received strength of the wireless power signal as a response to the detection signal as illustrated in  FIG. 15 . The packet  5100  may include a header  5120  for notifying a packet indicating the signal strength and a message  5130  indicating strength of the power signal received by the wireless power receiver  200 . The strength of the power signal within the message  5130  may be a value indicating a degree of inductive coupling or resonance coupling for power transmission between the wireless power transmitter  100  and the wireless power receiver  200 . 
     The wireless power transmitter  100  may receive a response message to the detection signal to find the wireless power receiver  200 , and then extend the digital detection process to enter the identification and configuration state  630 . In other words, the wireless power transmitter  100  maintains the power signal at a specific operating point subsequent to finding the wireless power receiver  200  to receive a power control message required in the identification and configuration state  630 . 
     However, if the wireless power transmitter  100  is not able to find the wireless power receiver  200  to which power can be transferred, then the operation phase of the wireless power transmitter  100  will be returned to the selection state  610 . 
     3) Identification and Configuration State 
     The wireless power transmitter  100  in the identification and configuration state  630  may receive identification information and/or configuration information transmitted by the wireless power receiver  200 , thereby controlling power transmission to be effectively carried out. 
     The wireless power receiver  200  in the identification and configuration state  630  may transmit a power control message including its own identification information. For this purpose, the wireless power receiver  200 , for instance, may transmit an identification packet  5200  including a message indicating the identification information of the wireless power receiver  200  as illustrated in  FIG. 16A . The packet  5200  may include a header  5220  for notifying a packet indicating identification information and a message  5230  including the identification information of the electronic device. The message  5230  may include information ( 2531  and  5232 ) indicating a version of the contract for contactless power transfer, information  5233  for identifying a manufacturer of the wireless power receiver  200 , information  5234  indicating the presence or absence of an extended device identifier, and a basic device identifier  5235 . Furthermore, if it is displayed that an extended device identifier exists in the information  5234  indicating the presence or absence of an extended device identifier, then an extended identification packet  5300  including the extended device identifier as illustrated in  FIG. 16B  will be transmitted in a separate manner. The packet  5300  may include a header  5320  for notifying a packet indicating an extended device identifier and a message  5330  including the extended device identifier. When the extended device identifier is used as described above, information based on the manufacturer&#39;s identification information  5233 , the basic device identifier  5235  and the extended device identifier  5330  will be used to identify the wireless power receiver  200 . 
     The wireless power receiver  200  may transmit a power control message including information on expected maximum power in the identification and configuration state  630 . To this end, the wireless power receiver  200 , for instance, may transmit a configuration packet  5400  as illustrated in  FIG. 17 . The packet may include a header  5420  for notifying that it is a configuration packet and a message  5430  including information on the expected maximum power. The message  5430  may include power class  5431 , information  5432  on expected maximum power, an indicator  5433  indicating a method of determining a current of a main cell at the side of the wireless power transmitter, and the number  5434  of optional configuration packets. The indicator  5433  may indicate whether or not a current of the main cell at the side of the wireless power transmitter is determined as specified in the contract for wireless power transfer. 
     On the other hand, the wireless power transmitter  100  may generate a power transfer contract which is used for power charging with the wireless power receiver  200  based on the identification information and/or configuration information. The power transfer contract may include the limits of parameters determining a power transfer characteristic in the power transfer state  640 . 
     The wireless power transmitter  100  may terminate the identification and configuration state  630  and return to the selection state  610  prior to entering the power transfer state  640 . For instance, the wireless power transmitter  100  may terminate the identification and configuration state  630  to find another electronic device that can receive power in a wireless manner. 
     4) Power Transfer State 
     The wireless power transmitter  100  in the power transfer state  640  transmits power to the wireless power receiver  200 . 
     The wireless power transmitter  100  may receive a power control message from the wireless power receiver  200  while transferring power, and control a characteristic of the power applied to the transmitting coil in response to the received power control message. For example, the power control message used to control a characteristic of the power applied to the transmitting coil may be included in a control error packet  5500  as illustrated in  FIG. 18 . The packet  5500  may include a header  5520  for notifying that it is a control error packet and a message  5530  including a control error value. The wireless power transmitter  100  may control the power applied to the transmitting coil according to the control error value. In other words, a current applied to the transmitting coil may be controlled so as to be maintained if the control error value is “0,” reduced if the control error value is a negative value, and increased if the control error value is a positive value. 
     The wireless power transmitter  100  may monitor parameters within a power transfer contract generated based on the identification information and/or configuration information in the power transfer state  640 . As a result of monitoring the parameters, if power transmission to the wireless power receiver  200  violates the limits included in the power transfer contract, then the wireless power transmitter  100  may cancel the power transmission and return to the selection state  610 . 
     The wireless power transmitter  100  may terminate the power transfer state  640  based on a power control message transferred from the wireless power receiver  200 . 
     For example, if the charging of a battery has been completed while charging the battery using power transferred by the wireless power receiver  200 , then a power control message for requesting the suspension of wireless power transfer will be transferred to the wireless power transmitter  100 . In this case, the wireless power transmitter  100  may receive a message for requesting the suspension of the power transmission, and then terminate wireless power transfer, and return to the selection state  610 . 
     For another example, the wireless power receiver  200  may transfer a power control message for requesting renegotiation or reconfiguration to update the previously generated power transfer contract. The wireless power receiver  200  may transfer a message for requesting the renegotiation of the power transfer contract when it is required a larger or smaller amount of power than the currently transmitted power amount. In this case, the wireless power transmitter  100  may receive a message for requesting the renegotiation of the power transfer contract, and then terminate contactless power transfer, and return to the identification and configuration state  630 . 
     To this end, a message transmitted by the wireless power receiver  200 , for instance, may be an end power transfer packet  5600  as illustrated in  FIG. 20 . The packet  5600  may include a header  5620  for notifying that it is an end power transfer packet and a message  5630  including an end power transfer code indicating the cause of the suspension. The end power transfer code may indicate any one of charge complete, internal fault, over temperature, over voltage, over current, battery failure, reconfigure, no response, and unknown error. 
     Communication Method of Plural Electronic Devices 
     Hereinafter, description will be given of a method by which at least one electronic device performs communication with one wireless power transmitter using wireless power signals. 
       FIG. 19  is a conceptual view illustrating a method of transferring power to at least one wireless power receiver from a wireless power transmitter. 
     The wireless power transmitter  100  may transmit power to one or more wireless power receivers  200  and  200 ′.  FIG. 19  illustrates two electronic devices  200  and  200 ′, but the methods according to the exemplary embodiments disclosed herein may not be limited to the number of electronic devices shown. 
     An active area and a detection area may be different according to the wireless power transfer method of the wireless power transmitter  100 . Therefore, the wireless power transmitter  100  may determine whether there is a wireless power receiver located on the active area or the detection area according to the resonance coupling method or a wireless power receiver located on the active area or the detection area according to the induction coupling method. According to the determination result, the wireless power transmitter  100  which supports each wireless power transfer method may change the power transfer method for each wireless power receiver. 
     In the wireless power transfer according to the exemplary embodiments disclosed herein, when the wireless power transmitter  100  transfers power to the one or more electronic devices  200  and  200 ′ according to the same wireless power transfer method, the electronic devices  200  and  200 ′ may perform communications through the wireless power signals without inter-collision. 
     Referring to  FIG. 19 , a wireless power signal  10   a  generated by the wireless power transmitter  100  may arrive at the first electronic device  200 ′ and the second electronic device  200 , respectively. The first and second electronic devices  200 ′ and  200  may transmit wireless power messages using the generated wireless power signal  10   a.    
     The first electronic device  200 ′ and the second electronic device  200  may operate as wireless power receivers for receiving a wireless power signal. The wireless power receiver in accordance with the exemplary embodiments disclosed herein may include a power receiving unit  291 ′,  291  to receive the generated wireless power signal, a modulation/demodulation unit  293 ′,  293  to modulate or demodulate the received wireless power signal, and a controller  292 ′,  292  to control each component of the wireless power receiver. 
     The foregoing description has been given of the WPC-based wireless power transmission and reception method. In addition, the present disclosure proposes a wireless power transmitter, a wireless power receiver, and a wireless charging system for medium power. Also, the present disclosure provides a new type of coil solution capable of enhancing power transfer efficiency in a wireless charging system using medium power. Hereinafter, description thereof will be given in more detail. 
     Here, a wireless power transmitter for medium power refers to a wireless power transmitter that transfers medium power to a wireless power receiver in a wireless manner. Also, a wireless power receiver for medium power refers to a wireless power receiver capable of receiving medium power transferred from the wireless power transmitter. 
     Here, medium power indicates power more than several tens of watts (W), and home appliances using such medium power may include, for example, a citrus press, a handblender, a blender, a juicer, a smart pan, a kettle, a rice cooker and the like. 
     Meanwhile, those home appliances may be classified into Class A, Class B and Class C, as shown in the following Table 1, according to guaranteed power. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Appliance Class 
                 Diameter 
                 Guaranteed Power 
               
               
                   
               
             
            
               
                 A 
                 18-24 cm 
                     2.4 kW 
               
               
                 B 
                 13-17 cm 
                 800 W 
               
               
                 C 
                  8-12 cm 
                 200 W 
               
               
                   
               
            
           
         
       
     
     Table 1 shows a class-based SPEC that is proposed by Kitchen Working Group (KWG), established for discussing a SPEC for medium power in the Wireless Power Consortium (WPC). Here, a diameter refers to a diameter of a receiving coil of a wireless power receiver provided in a home appliance for medium power. 
     In the wireless power receiver for medium power, a voltage in the range of several tens to several hundreds of volts (V) is induced. A control circuit provided in a power reception control unit of the wireless power receiver for medium power is typically driven (or operated) by a voltage less than 5V. 
     That is, a wireless charging system for medium power uses a transmitting/receiving coil having high inductance for high efficiency. This causes a difficulty in an operation of a control circuit driven by a low voltage. Accordingly, a voltage induced into the several tens to several hundreds of volts (V) has to be converted (changed) for driving the control circuit. To convert the induction voltage of the several tens to several hundreds of volts (V) to be less than 5V, a large-sized voltage converter is required, and this causes problems related to price, heat generation and size. Therefore, the present disclosure proposes a new type of coil solution which solves those problems and generates a low voltage for driving a control circuit of a wireless power receiver for medium power. 
     Hereinafter, description will be given in detail of a wireless power receiver for medium power, proposing a new type of coil solution, with reference to the accompanying drawings.  FIG. 20  is a block diagram exemplarily illustrating partial configurations of a wireless power transmitter and a wireless power receiver disclosed herein,  FIG. 21  is a detailed circuit view of the block diagram illustrated in  FIG. 20 ,  FIG. 22  is a conceptual view of a transmitting coil, and  FIGS. 23A and 23B  are conceptual views of a receiving coil. 
     Hereinafter, the following description is given of magnetic induction type wireless power transmitter and wireless power receiver. However, it will be obvious to a person skilled in the art that a structure of a receiving coil disclosed herein can be applied to a receiving coil for resonance type wireless power transmitter and wireless power receiver. 
     First, a power conversion unit  111  of a wireless power transmitter  100  illustrated in (a) of  FIG. 20  may include a transmitting (Tx) coil  1111  operating as a primary coil in magnetic induction. In this specification, the transmitting coil  1111  may also be named as ‘second coil’ of the wireless power transmitter  100 . 
     The primary coil may be provided at the power conversion unit  111  (see  FIG. 2 ) included in a power transmission unit  110  (see  FIG. 2 ), illustrated in  FIG. 2 . At least some of components of the power conversion unit  111  are illustrated in (a) of  FIG. 20   
     The power conversion unit  111  may convert power supplied from a power supply unit  190  into a wireless power signal, and transfer the wireless power signal to a wireless power receiver  200  illustrated in (b) of  FIG. 20 . A voltage in the range of several tens to several hundreds of volts (V) is induced on the transmitting coil  1111  of the wireless power transmitter  100  for medium power. 
     Meanwhile, when the wireless power transmitter  100  transfers power in a wireless manner to an appliance corresponding to Class C shown in Table 1, a wire of the transmitting coil  1111 , as illustrated in  FIG. 22 , may be formed on a single layer (1-layer) and turned (or wound) 20 times on the single layer (20 turns per layer). Also, the wire of the transmitting coil  1111  may have a thickness of 1.15 mm+0.3. In addition, an inner diameter (ID) of the transmitting coil  1111  may be 72 mm (±10%), and an outer diameter (OD) thereof may be 120 mm. 
     Referring to  FIG. 22 , a shielding unit or a shielding member  310  may be provided on one surface of the transmitting coil  1111 . As illustrated, the shielding member  310  may be disposed beneath the transmitting coil  1111 . The shielding member  310  may prevent an electromagnetic affection to devices (for example, a microprocessor) mounted on a printed circuit board (PCB) due to an operation of the transmitting coil  111 , or an electromagnetic affection to the transmitting coil due to operations of the devices mounted on the PCB. 
     The shielding member  310  may overlap the transmitting coil. For example, the shielding member  310  may be formed between a case of a base station and the transmitting coil  111 . 
     The shielding member  310  may be formed in a manner that at least part thereof extends based on the outer diameter OD of the transmitting coil  1111 . For example, the shielding member  310  may extend from the outer diameter OD of the transmitting coil  1111  by about 5 mm so as to be arranged on one surface of the transmitting coil  1111 . The shielding member  310  may surround one surface of the transmitting coil  1111 . The shielding member  310  may have a shape of a rectangular plate of 125 mm long sides, and have a thickness of at least 2.5 mm. 
     Meanwhile, the wireless power receiver  200  which receives power from the wireless power transmitter  100  in the wireless manner, as illustrated in (b) of  FIG. 20 , may include receiving coils  2911  and  2911 ′ that operate as a secondary coil, in which a current is induced from the wireless power transmitter  100 . The secondary coil may be provided at a power reception unit  291  (see  FIG. 2 ) included in the power supply unit  290  (see  FIG. 2 ), illustrated in  FIG. 2 . Here, at least some of components of the power reception unit  291  are illustrated in (b) of  FIG. 20 . 
     The receiving coils  2911  and  2911 ′ of the wireless power receiver  200  disclosed herein may include at least two coils, for example, a first coil  2911  and a second coil  2911 ′. 
     That is, the wireless power receiver  200  proposes a new type of coil solution, having a wireless power signal receiving coil (or the first coil)  2911  and a wireless power receiving coil (or the second coil)  2911 ′. 
     Accordingly, a control circuit (or the power reception control unit  292 ) of the wireless power receiver  200  may be driven using a voltage induced in the wireless power signal receiving coil (or the first coil)  2911 . 
     The power reception control unit  292  may control the first and second coils  2911  and  2911 ′ in a manner that the power reception control unit  292  receives power in a wireless manner from the wireless power transmitter  100  through the second coil  2911 ′ when enabled to receive the power in the wireless manner after driven by the voltage induced in the first coil  2911 . 
     In such a manner, the wireless power receiver  200  disclosed herein may supply an operation voltage to the power reception control unit  292  using a low voltage induced through the first coil  2911  having low inductance, and wirelessly receive power corresponding to medium power from the wireless power transmitter  100  using the second coil  2911 ′ having higher inductance than the first coil  2911 . 
     In more detail, the wireless power receiver  200 , as aforementioned, may include a first coil  2911  that is formed to transmit and receive a wireless power signal to and from the wireless power transmitter  100 , and a second coil  2911 ′ having a wire which is wound (or turned) to wirelessly receive power from the wireless power transmitter  100 . 
     As illustrated in  FIGS. 23A and 23B , the first coil  2911  of the wireless power receiver  200  may include a wire wound along an edge of a shape of the second coil  2911 ′. The wire of the first coil  2911  may be wound along an inner edge of the second coil  2911 ′, as illustrated in  FIG. 23A , or wound along an outer edge of the second coil  2911 ′, as illustrated in  FIG. 23B . 
     That is, as illustrated in  FIGS. 23A and 23B , the wire of the first coil  2911  may be surrounded by the inner edge of the second coil  2911 ′, or surround the outer edge of the second coil  2911 ′. As such, the shape of the first coil  2911  may correspond to the shape of the second coil  2911 ′ because the first coil  2911  is wound along the edge of the second coil  2911 ′. 
     Meanwhile, when the wireless power receiver  200  is an appliance corresponding to Class C shown in Table 1, the wire of the second coil  2911 ′ may be formed on a single layer (1-layer), and turned (or wound) 20 times on the single layer (20 turns per layer). Also, the wire of the second coil  2911 ′ may have a thickness of 1.15 mm+0.3. In addition, an inner diameter (ID) of the second coil  2911 ′ may be 52 mm (±10%), and an outer diameter (OD) thereof may be 100 mm. 
     In correspondence to this, the number of turns of the wire of the first coil  2911  may be smaller than the number of turns of the wire of the second coil  2911 ′. That is, the first coil  2911  may have low inductance inducing a low voltage so as to transfer an operation voltage to the control circuit, and the second coil  2911 ′ may have high inductance so as to wirelessly transfer power to a medium-power appliance. 
     Meanwhile, referring to  FIG. 24 , a shielding unit or a shielding member  320  may be provided on one surface of the first and second coils  2911 ,  2911 ′. As illustrated, the shielding member  320  may be disposed beneath the first and second coils  2911  and  2911 ′. The shielding member  320  may prevent an electromagnetic affection to devices (for example, a microprocessor) mounted on a printed circuit board (PCB) due to operations of the first and second coils  2911  and  2911 ′, or an electromagnetic affection to the transmitting coil due to operations of the devices mounted on the PCB. 
     The shielding member  320  may overlap the first and second coils  2911  and  2911 ′. For example, the shielding member  320  may be formed between a case (not illustrated) of a base station and the first and second coils  2911 , and  2911 ′. 
     The shielding member  320  may surround one surface of the first and second coils  2911  and  2911 ′. The shielding member  320  may have a shape of a rectangular plate of 105 mm long sides, and have a thickness of at least 2.5 mm. 
     Although not illustrated, currents induced through the first and second coils  2911 ,  2911 ′ may be converted into direct currents through separate rectifiers, respectively. 
     In addition, the power reception control unit  292  of the wireless power receiver  200  may control each component of the wireless power receiver  200  using a current or voltage induced through the first coil  2911 . In this case, the second coil  2911 ′ may serve to wirelessly transfer power to a load, a charger, a battery and the like. 
     In such a manner, the wireless power receiver  200  disclosed herein may be separately provided with a first coil  2911  for transmitting and receiving a control message to and from the wireless power transmitter  100 , and a second coil  2911 ′ for wirelessly receiving power from the wireless power transmitter  100 , thereby implementing a wireless charging system for a medium-power appliance. 
     A control message transmission and reception method between the wireless power transmitter  100  and the wireless power receiver  200  is the same or similar to the control message transmission and reception method illustrated with reference to  FIGS. 1, 2A, 2B, 3, 4A, 4B, 5, 6, 7A, 7B, 8-14, 15A, 15B and 16-19 , excluding that the wireless power receiver  200  transmits and receives the control message to and from the wireless power transmitter  100  through separate coils for inducing a low voltage. Therefore, detailed description thereof will not be repeated. 
     Meanwhile, a wireless charging system disclosed herein may include the wireless power transmitter  100  and the wireless power transmitter  200 , as aforementioned. 
     In addition, the wireless power transmitter  100  and the wireless power receiver  200  may be implemented similar to a circuit illustrated in  FIG. 21 . In more detail, a voltage or current corresponding medium power induced in the transmitting coil (or Tx coil)  1111  may be induced to the second coil  2911 ′ of the receiving side. Here, the induced voltage may range from several tens to several hundreds of volts (V). The voltage induced in the second coil  2911 ′ may be converted into a direct current (DC) through a second rectifier  2913   b  and the converted DC may be transferred to a load. In addition, a voltage used in a control circuit of the receiving side may be induced through the first coil  2911  separately provided from the second coil  2911 ′. The voltage induced in the first coil  2911  may be converted into a direct current (DC) through a first rectifier  2913   a  and the converted DC may be transferred to the control circuit. The first rectifier  2913   a  may be provided with four diodes. The first coil  2911  may thusly be designed to have extremely low inductance rather than the second coil  2911 ′. Therefore, an induced voltage value may be converted by changing inductance of each coil, which may allow for generating a desired output voltage value while using small-sized components, without a large-sized converter. 
     The structure of the receiving coil disclosed herein may also be configured into various shapes, in addition to the circular shape as illustrated in  FIGS. 23A and 23B . 
     For example, a structure of a receiving coil may be configured into a rectangular shape, as illustrated in (A) and (B) of  FIG. 25A . 
     As illustrated, the first and second coils  2911  and  2911 ′ corresponding to the receiving coil may be provided with wires which are wound into a rectangular shape. In this case, the first coil  2911  may be arranged along an inner or outer edge of the second coil  2911 ′. 
     As another example, the structure of the receiving coil may be configured into a triangular shape, as illustrated in (a) and (b) of  FIG. 25B . 
     As illustrated, the first and second coils  2911  and  2911 ′ corresponding to the receiving coil may be provided with wires wound into a triangular shape. Here, the first coil  2911  may be arranged along an inner or outer edge of the second coil  2911 ′. 
     The foregoing description has been given of the wireless power receiver  200  having the first coil  2911  for driving the control circuit and the second coil  2911 ′ for receiving power in the wireless manner. However, the present disclosure may not be limited to this but proposes a wireless power transmitter  100  having at least two transmitting coils. Hereinafter, it will be described in more detail with reference to the accompanying drawings.  FIG. 26  is a block diagram illustrating varied configurations of a wireless power transmitter and a wireless power receiver in accordance with the present disclosure,  FIG. 27  is a detailed circuit view of the block diagram illustrated in  FIG. 26 ,  FIGS. 28A, 28B and 28C  are conceptual views illustrating a transmitting coil, and  FIG. 29  is a conceptual view illustrating exemplary variations of transmitting coils and a related shielding member. 
     As illustrated in  FIG. 26 , transmitting coils  1111  and  1111 ′ for a wireless power transmitter  100  disclosed herein may include a first transmitting coil (or a first coil)  1111  that transfers a wireless power signal to a wireless power receiver  200 , and a second transmitting coil (or a second coil)  1111 ′ which is provided with a wire wound to transfer power to the wireless power receiver  200  in a wireless manner. 
     In such a manner, the wireless power transmitter  100  disclosed herein may transfer the wireless power signal to the wireless power receiver  200  using a low voltage induced through the first transmitting coil  1111  having low inductance, and wirelessly supply power corresponding to medium power to the wireless power receiver  100  using the second transmitting coil  1111 ′ having higher inductance than the first transmitting coil  1111 . 
     In more detail, as illustrated in (a) and (b) of  FIG. 28A , the first transmitting coil  1111  of the wireless power transmitter  100  may be provided with a wire wound along an edge of a shape of the second transmitting coil  1111 ′. The wire of the first transmitting coil  1111  may be wound along an inner edge of the second transmitting coil  1111 ′ as illustrated in (a) of  FIG. 28A , or along an outer edge of the second transmitting coil  1111 ′ as illustrated in (b) of  FIG. 28A . 
     That is, as illustrated in  FIG. 28A , the wire of the transmitting coil  1111  may be surrounded by the inner edge of the second transmitting coil  1111 ′, or surround the outer edge of the second transmitting coil  1111 ′. In such a manner, the shape of the first transmitting coil  1111  may correspond to the shape of the second transmitting coil  1111 ′ because the first transmitting coil  1111  is wound along the edge of the second transmitting coil  1111 ′. As illustrated, the first and second transmitting coils  1111  and  1111 ′ may be circular. 
     Meanwhile, when the wireless power transmitter  100  transfers power to an appliance corresponding to Class C shown in Table 1 in a wireless manner, the wire of the second transmitting coil  1111 ′ may be formed on a single layer (1-layer), and turned 20 times on the single layer (20 turns per layer). Also, the wire of the second transmitting coil  1111 ′ may have a thickness of 1.15 mm+0.3. In addition, an inner diameter (ID) of the transmitting coil  1111  may be 72 mm (±10%), and an outer diameter (OD) thereof may be 120 mm. 
     Referring to  FIG. 29 , a shielding unit or a shielding member  310  may be provided on one surface of the first and second transmitting coils  1111  and  1111 ′. That is, the shielding member  310  may be disposed beneath the first and second transmitting coils  1111  and  1111 ′. The shielding member  310  may prevent an electromagnetic affection to devices (for example, a microprocessor) mounted on a printed circuit board (PCB) due to operations of the first and second transmitting coils  1111  and  1111 ′, or an electromagnetic affection to the transmitting coil due to operations of the devices mounted on the PCB. 
     The shielding member  310  may overlap the first and second transmitting coils  1111  and  1111 ′. For example, the shielding member  310  may be formed between a case (not illustrated) of a base station and the first and second transmitting coils  1111  and  1111 ′. 
     The shielding member  310  may be formed in a manner that at least part thereof extends based on an outer diameter of the second transmitting coil  1111 ′. For example, the shielding member  310  may extend from the outer diameter of the second transmitting coil  1111 ′ by about 5 mm so as to be arranged on one surface of the first and second transmitting coils  1111  and  1111 ′. The shielding member  310  may surround one surface of the first and second transmitting coils  1111  and  1111 ′. The shielding member  310  may have a shape of a rectangular plate of 125 mm long sides, and have a thickness of at least 2.5 mm. 
     Although not illustrated, alternating currents (ACs) induced in the first and second transmitting coils  1111  and  1111 ′ may be converted through separate bridge circuits, respectively. For example, the wireless power transmitter disclosed herein, as illustrated in the detailed circuit view of  FIG. 27 , may separately be provided with a bridge circuit on each of the first transmitting coil  1111  and the second transmitting coil  1111 ′. 
     Meanwhile, the wireless power transmitter disclosed herein, as illustrated in  FIGS. 28B and 28C , may be configured into various shapes in addition to the circular shape. 
     For example, a structure of a transmitting coil may be configured into a rectangular shape, as illustrated in (a) and (b) of  FIG. 28B . 
     The first and second transmitting coils  1111  and  1111 ′ corresponding to the transmitting coil may be provided with wires wound into a rectangular shape, respectively. In this case, the first transmitting coil  1111  may be arranged along an inner or outer edge of the second transmitting coil  1111 ′. 
     As another example, the structure of the transmitting coil may be configured into a triangular shape, as illustrated in (a) and (b) of  FIG. 28C . 
     The first and second transmitting coils  1111  and  1111 ′ corresponding to the transmitting coil may be provided with wires wound into a triangular shape, respectively. In this case, the first transmitting coil  1111  may be arranged along the inner or outer edge of the second transmitting coil  1111 ′. 
     Meanwhile, in a wireless charging system having a wireless power transmitter with a plurality of transmitting coils, a structure and a detailed description of a wireless power receiver will be understood by the description of the aforementioned wireless power receiver with the plurality of receiving coils. 
     The aforementioned wireless power receiver may be equipped in those appliances, and examples of the appliances may include a digital TV, an electric range, an electronic burner, and the like. 
     In addition, the present disclosure may provide a wireless power transmitter when an appliance to which a wireless power receiver is applied is in a power-off state, a wireless power transmitter which is capable of reducing standby power of the appliance, and a wireless power transfer method thereof. Hereinafter, the configurations of such method and apparatus will be described with reference to  FIGS. 30 and 31 . 
       FIG. 30  is a flowchart illustrating one exemplary embodiment of a wireless power transfer method for reducing standby power. 
     As illustrated in  FIG. 30 , a wireless power transmitter may transfer power to a wireless charging coil of an appliance having a wireless power receiver in a wireless manner after receiving a power-on signal when a remote controller generates the power-on signal. Accordingly, the appliance may be powered on, and this may result in preventing consumption of standby power in the appliance. 
     In more detail, a remote control signal receiver of a wireless power transmitter may receive a power-on signal or a power-off signal from a remote controller. When the remote control signal receiver receives the power-off signal, the power transmission control unit may be turned off, such that power wirelessly transmitted from the wireless power transmitter to the wireless power receiver can be cut off and simultaneously the wireless power transmitter except for the remote control signal receiver can be powered off (S 11 ). 
     The remote control signal receiver may receive power from an independent power supply source (for example, a battery, a DC supply terminal, etc.). For example, the remote control signal receiver may include a charging device that charges the wireless power output from the wireless power receiver, and supplies the charged power to the remote control signal receiver while the wireless power transmitter and/or the wireless power receiver are(is) turned off. The charging device may be a secondary cell or a super capacitor. 
     When the remote control signal receiver receives the power-on signal from the remote controller (S 12 ), the wireless power transmitter except for the remote control signal receiver may be turned on based on the power-on signal (S 13 ). For example, when the remote control signal receiver receives the power-on signal from the remote controller (S 12 ), the power transmission control unit of the wireless power transmitter may be turned on based on the power-on signal, thereby operating the wireless power transmitter. Here, the power supply unit may supply a DC input voltage to the power transmission control unit when the power transmission control unit is turned on. 
     When the remote control signal receiver receives the power-on signal, the power transmission control unit may generate a driving signal for supplying power for an operation of an appliance. 
     The power conversion unit may generate a wireless power signal based on a switching operation by the supplied DC input voltage and the driving signal (S 15 ), and transfer power to the wireless power receiver in a wireless manner (S 16 ). The appliance may be turned on when the wireless power is received. 
     In this case, prior to the wireless power transfer, the wireless power transmitter and the wireless power receiver may execute communication with each other, and a coil for receiving the communication may be the second coil of the aforementioned wireless power receiver. 
     According to the operation, when the appliance is not used, only the remote control signal receiver of the wireless power transmitter may be used, thereby reducing standby power of the wireless power transmitter and standby power of the appliance. 
       FIG. 31  is a flowchart illustrating another exemplary embodiment of a wireless power transfer method for reducing standby power. 
     A wireless power transmitter disclosed herein may transfer low power to a remote controller-related receiving circuit of an appliance. When a power-on signal is generated in the remote controller, the appliance may be powered on after the receiving circuit related to the remote controller receives the power-on signal. Therefore, the consumption of standby power in the appliance may be prevented. 
     In this case, the receiving circuit may operate with low power. Hence, the wireless power transmitter may be provided with a separate transmission block for operating the receiving circuit for transmitting the low power. The wireless power receiver may receive the low power to supply to the receiving circuit. When the appliance which is a load is in a power-off state, a main power transmission block may not operate but only the transmission block for operating the receiving circuit may operate. When a power-on signal is received from a remote controller or the like, the main power transmission block may start to operate by communication between the wireless power transmitter and the wireless power receiver and simultaneously the appliance may start to operate. 
     In more detail, a power supply unit of the wireless power transmitter may supply a DC input voltage. 
     A controller may generate a low power driving signal for supplying low power to operate a remote controller-related receiving circuit (receiver) of an appliance based on the DC input voltage (S 21 ). 
     A sub power supply unit (a transmission block for operating the receiving circuit) may be separately provided to convert the DC input voltage into a low voltage (S 22 ). The sub power supply unit may then form a wireless low power signal based on a switching operation by the converted low voltage and the low power driving signal, thereby generating wireless low power (S 23 ). The sub power supply unit may thus apply the wireless low power to the receiving circuit (S 24 ). For example, the controller may generate a low power driving signal for supplying the low power to operate the receiving circuit. The DC input voltage supplied from the power supply unit may be converted into low power by a low power conversion unit, and a wireless low power signal may be generated based on a switching operation by the converted low power and the low power driving signal. 
     The wireless power receiver may receive the wireless low power signal, and to this end, may be provided with the aforementioned second coil. Power may thusly be supplied to the receiving circuit by the wireless lower power signal. 
     The receiving circuit related to the remote controller may determine whether or not it has received a power-on signal or a power-off signal from the remote controller (S 25 ). When the power-off signal has been received in the receiving circuit, the appliance may execute communication with the wireless power transmitter. Accordingly, the power transmission control unit may be powered off, and power wirelessly transferred from the wireless power transmitter to the wireless power receiver may be cut off. 
     When the power-on signal is received from the remote controller, the receiving circuit may turn on the wireless power transmitter based on the power-on signal (S 26 ). For example, when the power-on signal is received from the remote controller, the appliance may communicate with the wireless power transmitter based on the power-on signal. Accordingly, the power transmission control unit may be powered on such that the wireless power transmitter can operate. Here, the power supply unit may supply the DC input voltage to the power transmission control unit when the power transmission control unit is powered on. 
     Afterwards, the power transmission control unit may generate a driving signal to supply power for operating the appliance (S 27 ). 
     The power conversion unit may form a wireless power signal based on a switching operation by the supplied DC input voltage and the driving signal (S 28 ), and transmit power to the wireless power receiver in a wireless manner (S 29 ). The wireless power receiver may be powered on when the power is received in the wireless manner. 
     In such a manner, when the appliance having the wireless power receiver is in the turn-off state, the employment of the sub power supply unit which uses less power than power supplied from the wireless power transmitter may result in reducing standby power of the wireless power transmitter and standby power of the appliance. 
     Although not illustrated, the present disclosure may also be varied into an embodiment in which a wireless power receiver is provided with a separate power supply unit for supplying power to a receiving circuit related to a remote controller. In this case, the power supply unit, for example, may be a battery, a secondary cell or the like, which may thus supply low power only to the receiving circuit. 
     In this case, when the power-on signal is generated in the remote controller, the communication between the wireless power transmitter and the appliance may start after the receiving circuit receives the power-on signal. That is, in response to the signal reception, the wireless power receiver may generate and transmit a request signal for requesting power transfer. In response to the request signal, the wireless power transfer may start. By the wireless power transfer, the appliance having the wireless power receiver may be powered on. Therefore, the consumption of standby power in the appliance can be prevented. 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present disclosure. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. 
     As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.