Patent Publication Number: US-10320236-B2

Title: Wireless power transmission apparatus and method of controlling the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2015-0150053, filed on Oct. 28, 2015 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     BACKGROUND 
     1. Field 
     The following description relates to a wireless power transmission apparatus and a method of controlling the same. 
     2. Description of Related Art 
     In accordance with the development of wireless technology, non-contact type wireless charging techniques capable of charging electronic apparatuses even in a non-contact state are being developed. 
     In wireless charging techniques according to the related art, settings for wireless charging are fixed. For example, to implement efficient wireless charging, an object for wireless charging needs to be set, or a position or the like, of a wireless power reception apparatus should be fixed. 
     Therefore, in the related art technologies, when the object for wireless charging is changed, or variations in wireless charging environments such as changes in position occur, wireless charging is not available, or wireless charging efficiency may be significantly lowered. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     According to a general aspect, a wireless power transmission apparatus includes a resonator configured to be magnetically coupleable to a wireless power reception apparatus; an inverter configured to operate the resonator; and a resonant frequency controller configured to control a resonant frequency of the resonator in response to a change in operating frequency of the inverter. 
     The resonant frequency controller may be further configured to decrease the resonant frequency in response to the operating frequency increasing to a predetermined level or more. 
     The resonant frequency controller may be further configured to increase the resonant frequency in response to the operating frequency decreasing to a predetermined level or less. 
     The resonant frequency controller may be further configured to vary capacitance of the resonator, thereby varying the resonant frequency. 
     The wireless power transmission apparatus may further include a controller configured to identify a required power of the wireless power reception apparatus and adaptively adjust the operating frequency of the inverter in response to the required power. 
     The controller may be further configured to decrease the operating frequency in response to the required power increasing. 
     The resonant frequency controller may include a variable capacitor configured to vary capacitance of the resonator; and a capacitance controller configured to detect the operating frequency of the inverter and compare the operating frequency with a predetermined range to change capacitance of the variable capacitor responsive to the comparison. 
     The capacitance controller may be further configured to increase the capacitance of the variable capacitor in response to the operating frequency reaching a predetermined upper limit. 
     The capacitance controller may be further configured to decrease the capacitance of the variable capacitor in response to the operating frequency reaching a predetermined lower limit. 
     According to another general aspect, a method of controlling a wireless power transmission apparatus includes identifying a required power of a wireless power reception apparatus; changing an operating frequency of an inverter connected to a resonator in response to a change in the required power, the resonator being magnetically coupled to the wireless power reception apparatus; and changing a resonant frequency of the resonator when the operating frequency is outside of a predetermined range. 
     The changing of the operating frequency of the inverter may include decreasing the operating frequency in response to the required power increasing; and increasing the operating frequency in response to the required power decreasing. 
     The changing of the resonant frequency of the resonator may include decreasing the resonant frequency in response to the operating frequency increasing to a predetermined level or more. 
     The changing of the resonant frequency of the resonator may include increasing the resonant frequency in response to the operating frequency decreasing to a predetermined level or less. 
     The changing of the resonant frequency of the resonator may include increasing capacitance of the resonator in response to the operating frequency increasing to a predetermined level or more. 
     The changing of the resonant frequency of the resonator may include decreasing capacitance of the resonator in response to the operating frequency decreasing to a predetermined level or less. 
     According to another general aspect, a wireless power transmission apparatus, includes a wireless power resonator; a power supply operably coupled to the wireless power resonator and configured to supply power thereto; and a resonant frequency controller configured to control a resonant frequency of the wireless power resonator in response to a detected operational characteristic of the power supply. 
     The resonant frequency controller may be further configured to detect a load on the power supply and adaptively adjust the resonant frequency of the wireless power resonator in response to the detection. 
     The power supply may include an inverter, and the resonant frequency controller may be further configured to detect an operational frequency of the inverter and adaptively adjust the resonant frequency of the wireless power resonator in response to the detection. 
     The wireless power transmission apparatus may further include a power controller configured to adaptively adjust an operational characteristic of the power supply in response to a detected operational characteristic of a wireless power reception apparatus. 
     The wireless power transmission apparatus may further include a power controller configured to adaptively adjust an operational frequency of the inverter in response to a power requirement of a wireless power reception apparatus. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a wireless power transmission apparatus according to an embodiment. 
         FIG. 2  is a view illustrating a wireless power transmission apparatus according to an embodiment. 
         FIG. 3  is a block diagram illustrating the wireless power transmission apparatus according to an embodiment. 
         FIG. 4  is a graph illustrating an example of a relationship between a voltage gain and an operating frequency of a wireless power transmission apparatus. 
         FIG. 5  is a graph illustrating an example of a relationship between a voltage gain and a resonant frequency of the wireless power transmission apparatus. 
         FIG. 6  is a circuit diagram illustrating a wireless power transmission apparatus according to an embodiment. 
         FIG. 7  is a flow chart illustrating a method of varying capacitance performed in a wireless power transmission apparatus according to an embodiment. 
         FIG. 8  is a graph illustrating a method of varying capacitance according to an embodiment. 
         FIG. 9  is a flow chart illustrating a method of controlling a wireless power transmission apparatus according to an embodiment. 
     
    
    
     Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
     The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art. 
     Throughout the specification, it will be understood that when an element, such as a layer, region or wafer (substrate), is referred to as being “on,” “connected to,” or “coupled to” another element, it can be directly “on,” “connected to,” or “coupled to” the other element or other elements intervening therebetween may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element, there are no elements or layers intervening therebetween. Like numerals refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be apparent that though the terms first, second, third, etc. may be used herein to describe various members, components, regions, layers and/or sections, these members, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one member, component, region, layer or section from another region, layer or section. Thus, a first member, component, region, layer or section discussed below could be termed a second member, component, region, layer or section without departing from the teachings of the embodiments. 
     Spatially relative terms, such as “above,” “upper,” “below,” and “lower” and the like, may be used herein for ease of description to describe one element&#39;s relationship to another element(s) as shown in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “above,” or “upper” relative to other elements would then be oriented “below,” or “lower” than the other elements or features. Thus, the term “above” can encompass both the above and below orientations depending on a particular direction of the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly. 
     The terminology used herein is for describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, members, elements, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, elements, and/or groups thereof. 
     Hereinafter, embodiments will be described with reference to schematic views. In the drawings, for example, due to manufacturing techniques and/or tolerances, modifications of the shape shown may be encountered. Thus, embodiments should not be construed as being limited to the particular shapes of regions shown herein, but should be understood to include, for example, a change in shape resulting from manufacturing. The following embodiments may also be constituted by one or a combination thereof. 
       FIG. 1  is a view illustrating an example of applying a wireless power transmission apparatus according to an embodiment.  FIG. 2  is a view illustrating another example of applying the wireless power transmission apparatus according to an embodiment. 
       FIG. 1  illustrates an example in which the wireless power transmission apparatus  100  performs charging on a mobile terminal  301 , and  FIG. 2  illustrates an example in which the wireless power transmission apparatus  100  performs charging on a wearable device  302 . 
     The mobile terminal  301  is internally or externally connected to a wireless power reception apparatus. The wireless power reception apparatus wirelessly receives power from the wireless power transmission apparatus  100  and provides power to the mobile terminal  301 . 
     Similarly, the wearable device  302  includes a wireless power reception apparatus. The wireless power reception apparatus wirelessly receives power from the wireless power transmission apparatus  100  and provides power to the wearable device  302 . 
     In this manner, the wireless power reception apparatus may be applied to various electronic apparatuses, and depending on the electronic apparatus type and required power levels, the wireless power reception apparatus may have different charging characteristics, for example, variations in resonant frequency, a required level of power, and the like. 
     Therefore, the wireless power transmission apparatus according to an embodiment wirelessly transmits power in response to variable charging characteristics so as to correspond to various wireless power reception apparatuses as described above. 
     The following description provides various embodiments of a wireless power transmission apparatus capable of effectively transmitting power even when charging characteristics are changed, and a method of controlling the wireless power transmission apparatus. 
     Hereinafter, various embodiments will be described in further detail with reference to  FIG. 3  through  FIG. 9 . 
       FIG. 3  is a block diagram illustrating the wireless power transmission apparatus according to an embodiment. 
     Referring to  FIG. 3 , the wireless power transmission apparatus  100  includes an inverter  120 , a resonator  130 , and a resonant frequency controller  140 . According to embodiments, the wireless power transmission apparatus  100  further includes a power supply  110  and/or a controller  150 . 
     The power supply  110  provides a power source for power transmission. For example, the power supply  110  includes a direct current (DC)-DC conversion circuit varying a magnitude of an input voltage and outputting power. 
     The inverter  120  performs a switching operation and operates the resonator  130 . 
     The resonator  130  is magnetically coupleable to a resonator of a wireless power reception apparatus to wirelessly provide power to the wireless power reception apparatus. 
     The resonant frequency controller  140  controls a resonant frequency of the resonator  130  in response to a change in operating frequency of the inverter  120 . 
     For example, when the operating frequency of the inverter  120  increases to a predetermined level or more, the resonant frequency controller  140  decreases the resonant frequency of the resonator  130 . Alternatively, when the operating frequency of the inverter  120  decreases to a predetermined level or less, the resonant frequency controller  140  increases the resonant frequency of the resonator  130 . 
     In an embodiment, the resonant frequency controller  140  controls capacitance or inductance of the resonator  130  to control the resonant frequency of the resonator  130 . 
     The resonant frequency controller  140  is further described with reference to  FIG. 5  through  FIG. 8 . 
     The controller  150  controls an operation of the inverter  120 . 
     The controller  150  includes a processor. According to one or more embodiments, the controller  150  further includes a memory. Here, the processor includes, for example, a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) and the like, and may have a plurality of cores. The memory may be a volatile memory (for example, a RAM or the like), a non-volatile memory (for example, a ROM, a flash memory, or the like), or combinations of these memories. 
     The controller  150  identifies power requirements of the wireless power reception apparatus. 
     By way of example, the above-described required power is received from the wireless power reception apparatus in an in-band communication scheme performing communications by modulating or demodulating a wireless power signal. That is, since the wireless power signal formed between the wireless power reception apparatus and the wireless power transmission apparatus forms a magnetic field or a closed loop within the magnetic field, in a case in which the wireless power reception apparatus modulates the wireless power signal while receiving the wireless power signal, the wireless power transmission apparatus  100  senses the modulated wireless signal. The wireless power transmission apparatus  100  demodulates the modulated wireless signal and identifies the required power of the wireless power reception apparatus. 
     Alternatively, the wireless power reception apparatus provides an indication of required power to the wireless power transmission apparatus  100  using a near field communication (NFC) or short range wireless method such as Bluetooth, Zigbee, Wifi, or other suitable short range wireless scheme. 
     The controller  150  controls the operating frequency of the inverter  120  according to the identified required power. 
       FIG. 4  is a graph illustrating an example relationship between a voltage gain and an operating frequency of the wireless power transmission apparatus. With reference to  FIG. 3  and  FIG. 4 , control of the operating frequency of the inverter  120  by the controller  150  is further described. 
       FIG. 4  is a graph illustrating a resonant frequency of the wireless power transmission apparatus, according to an embodiment. 
     It is seen, in  FIG. 4 , that when the operating frequency decreases from an operating frequency f 1  to an operating frequency f 2 , the voltage gain increases from G 1  to G 2 . In a similar manner, it is seen that when the operating frequency increases from the operating frequency f 1  to the operating frequency f 3 , the voltage gain decreases from G 1  to G 3 . That is, it is seen that variations in operating frequency and variations in voltage gain are in inverse proportion to each other within the relevant illustrative operational window. 
     Therefore, when the required power increases (as reported by the wireless power receiver), the controller  150  reduces the operating frequency of the inverter  120  to increase the voltage gain. When the required power decreases, the controller  150  increases the operating frequency of the inverter  120  to decrease the voltage gain. 
     As illustrated in  FIG. 4 , even in a case in which the operating frequency of the inverter  120  is controlled, it may be controlled within a predetermined range. For example, the operating frequency may have a predetermined range according to wireless power charging standards. 
     Therefore, in an embodiment, the resonant frequency is controlled in response to variations in the operating frequency. Hereinafter, with reference to  FIG. 5  through  FIG. 7 , the wireless power transmission apparatus capable of controlling the resonant frequency and a method of controlling the wireless power transmission apparatus according to an embodiment will be described in further detail. 
       FIG. 5  is a graph illustrating an example relationship between a voltage gain and a resonant frequency of the wireless power transmission apparatus. 
     Reference numeral  51  indicates a voltage gain curve of the wireless power transmission apparatus in a reference resonant frequency, reference numeral  52  indicates a voltage gain curve of the wireless power transmission apparatus in a resonant frequency higher than the reference resonant frequency, and reference numeral  53  indicates a voltage gain curve of the wireless power transmission apparatus in a resonant frequency lower than the reference resonant frequency. 
     In the illustrated graph, the operating frequency of the inverter  120  (illustrated in  FIG. 2 ) is in a state of being fixed to the operating frequency f 1 . 
     As illustrated in the graph, in a case in which the operating frequency f 1  of the inverter  120  is fixed, it can be seen that when the resonant frequency increases from the resonant frequency  51  to the resonant frequency  52 , the voltage gain increases from G 1  to G 2 . It can also be seen that when the resonant frequency increases from the resonant frequency  51  to the resonant frequency  53 , the voltage gain decreases from G 1  to G 3 . 
     The reason for this is that the resonant frequency according to the current wireless power transmission standards has voltage gain characteristics as illustrated in  FIG. 3 . 
     Consequently, in an embodiment, when required power of the wireless power reception apparatus increases, the resonant frequency is increased to increase the voltage gain. In addition, when the required power of the wireless power reception apparatus decreases, the resonant frequency is reduced to lower the voltage gain. 
     Therefore, as described in  FIG. 3  and  FIG. 4 , the wireless power transmission apparatus according to an embodiment controls the operating frequency of the inverter  120  within a predetermined range, and controls the resonant frequency of the resonator  130  when the operating frequency of the inverter  120  is outside of a predetermined range. 
     Thus, the wireless power transmission apparatus according to an embodiment, covers a range of various required power levels for different wireless power reception apparatuses as compared to a wireless power transmission apparatus according to the related art. The resonant frequency of the wireless power transmission apparatus, according to an embodiment, may be changed according to identified changes in required power of the wireless power reception apparatus even in various circumstances regardless of a kind of a wireless power reception apparatus, distance limitation, etc., thereby leading to an increase in voltage gain and efficient provision of power. The wireless power transmission apparatus according to an embodiment may also be applied to cases in which a kind of a wireless power reception apparatus is altered or a position thereof is changed. 
     A resonant frequency f r  may be represented by the following mathematical formula 1, where f r  is a resonant frequency, L r  is inductance of a resonator of the wireless power transmission apparatus, and C r  is capacitance of the resonator. 
     
       
         
           
             
               
                 
                   
                     f 
                     r 
                   
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                     1 
                     
                       2 
                       ⁢ 
                       π 
                       ⁢ 
                       
                         
                           
                             L 
                             r 
                           
                           ⁢ 
                           
                             C 
                             r 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
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                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     In other words, a resonant frequency f r  is equal to 1 over 2πtimes the square root of inductance of the resonator wireless power transmission apparatus L r  times the capacitance of the resonator C r . 
     For example, the wireless power transmission apparatus controls capacitance of the resonator, thereby changing the resonant frequency. That is, capacitance of the resonator may be reduced to increase the resonant frequency. Alternatively, capacitance of the resonator may be increased to reduce the resonant frequency. Still further, the inductance may be suitably increased or reduced to respectively reduce or increase the resonant frequency. 
     Hereinafter, with reference to  FIG. 6  through  FIG. 7 , the wireless power transmission apparatus capable of controlling the resonant frequency by varying capacitance, and a method of controlling the wireless power transmission apparatus according to an embodiment, will be further described. 
     However, unlike a description to be described later, the resonant frequency may also be controlled by varying inductance of the resonator, which will be understood with reference to the following description. 
       FIG. 6  is a circuit diagram illustrating a wireless power transmission apparatus according to an embodiment. The wireless power transmission apparatus illustrated in  FIG. 6  relates to an embodiment in which the resonant frequency controller  140  varies capacitance to control the resonant frequency. However, according to one or more embodiments, the wireless power transmission apparatus is modified in such a manner that the resonant frequency controller  140  varies inductance to control the resonant frequency. 
     Referring to  FIG. 6 , a wireless power transmission apparatus  200  includes the power supply  110 , the inverter  120 , the resonator  130 , and the resonant frequency controller  140 . 
     The inverter  120  converts a DC voltage output from the power supply  110  into an AC voltage appropriate for wireless power transmission. Inverter  120  is illustrated as a half-bridge inverter in which two switches Q 2  and Q 3  are connected in series. However, the inverter  120  is not limited thereto. Inverter  120 , may be implemented with another type of inverter such as a full-bridge inverter, or other suitable inverter, as would be known to one of skill in the art after gaining a thorough understanding of the subject application. A switching operation of switches included in the inverter  120  are controlled by a controller and thus, the controller controls a switching frequency of the switches to thereby control the operating frequency of the inverter  120 . 
     The resonator  130  is magnetically coupleable to a resonator of the wireless power reception apparatus, and wirelessly provides power to the wireless power reception apparatus. For example, the AC voltage output by the inverter  120  generates a magnetic field through the resonator  130 , and the generated magnetic field is induced to the resonator of the wireless power reception apparatus, whereby power is transmitted to a receiving side. 
     The resonator  130  is connected to the resonant frequency controller  140 . A resonant frequency of the resonator  130  is changed due to a capacitance variation in a variable capacitor  142  of the resonant frequency controller  140 . 
     In the illustrated embodiment, the resonator  130  and the variable capacitor  142  are described as separate components, but it is merely for clarity, conciseness, and convenience of explanation. Thus, the resonator  130  and the variable capacitor  142  may be implemented as a single component. 
     The resonant frequency controller  140  varies the resonant frequency of the resonator  130  in response to a change in operating frequency of the inverter  120 . The resonant frequency controller  140  detects the operating frequency of the inverter  120 , and in response to the operating frequency departing a predetermined range, the resonant frequency controller  140  varies the capacitance of the resonator  130  in response thereto to vary the resonant frequency of the resonator  130 . 
     The resonant frequency controller  140  includes the variable capacitor  142  and a capacitance controller  141 . 
     The variable capacitor  142  varies capacitance of the resonator  130 . 
     The variable capacitor  142  one end connected to the resonator  130 . By way of example, the capacitor controller  141  is connected to at least one capacitor of the resonator  130  in series, and has the other end connected to an output terminal of the inverter  120 . Capacitance of the variable capacitor  142  is varied according to an operation of the capacitance controller  141 , and accordingly, synthetic capacitance of the variable capacitor  142  and the resonator  130  are also variably set. 
     The variable capacitor  142  includes a plurality of switches SW 1  to SW 3  and a plurality of capacitors VC 1  to VC 3  connected in series to the plurality of switches SW 1  to SW 3 , respectively. The switches are controlled by capacitance controller  141 . 
     In an embodiment, the plurality of capacitors VC 1  to VC 3  have different levels of capacitance. For example, a first capacitor VC 1  has a reference capacitance, a second capacitor VC 2  has a capacitance two times greater than that of the first capacitor VC 1 , and a third capacitor VC 3  has a capacitance five times greater than that of the first capacitor VC 1 . In the embodiment as described above, since various combinations of synthetic capacitors with regard to the plurality of capacitors VC 1  to VC 3  are enabled, variously variable capacitance is provided even with a small number of capacitors. 
     The capacitance controller  141  detects the operating frequency of the inverter  120 , and compares the operating frequency with a predetermined range to change capacitance of the variable capacitor  142 . 
     The capacitance controller  141 , in an embodiment, is implemented as a processor. According to embodiments, the capacitance controller  141  further includes a memory. The processor includes, for example, a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and the like, and may have a plurality of cores. 
       FIG. 7  is an example flow chart illustrating a method of varying capacitance performed in the wireless power transmission apparatus illustrated in  FIG. 6 . With reference to  FIG. 6  through  FIG. 7 , operations of the capacitance controller  141  are further described. 
     The capacitance controller  141  detects an operating frequency Fop of the inverter  120  (S 710 ). 
     The capacitance controller  141  identifies whether the operating frequency Fop of the inverter  120  is within a predetermined range (S 720 ). Here, the predetermined range of the operating frequency includes a predetermined upper limit Fup_lim and a predetermined lower limit Flow_lim. 
     When the operating frequency Fop of the inverter  120  has a value between the predetermined upper limit Fup_lim and the predetermined lower limit Flow_lim (S 720 , YES), the capacitance controller  141  does not vary capacitance. 
     When the operating frequency Fop of the inverter  120  is less than the predetermined lower limit Flow_lim (S 730 , YES), the capacitance controller  141  controls the variable capacitor  142  to increase the resonant frequency. That is, the capacitance controller  141  controls the variable capacitor  142  to reduce capacitance of the variable capacitor  142  (S 740 ). 
     On the other hand, when the operating frequency Fop of the inverter  120  is greater than the predetermined upper limit Fup_lim (S 750 , YES), the capacitance controller  141  controls the variable capacitor  142  to reduce the resonant frequency. That is, the capacitance controller  141  controls the variable capacitor  142  to increase capacitance of the variable capacitor  142  (S 740 ) to thereby reduce the resonant frequency. 
       FIG. 7  explains the method of varying capacitance, on a one-time operation basis, but according to embodiments, the method of varying capacitance illustrated in  FIG. 7  is consecutively and repeatedly performed in a continuous calculation. 
       FIG. 8  is an example graph illustrating the method of varying capacitance illustrated in  FIG. 6 . With reference to  FIG. 6  through  FIG. 7 , a method of controlling capacitance is further described. The graph shows an operating frequency on a first axis and a time (delineated by periods e.g.  801 ,  802 ,  803 ) on a second axis. 
     Explaining the method with reference to  FIG. 6  and  FIG. 8 , a period  801  is in a state in which the operating frequency Fop of the inverter  120  is present between the predetermined upper limit Fup_lim and the predetermined lower limit Flow_lim. 
     In this state, since the operating frequency Fop of the inverter  120  is varied but within a predetermined range, the period  801  is a period in which capacitance is not varied, thereby resulting in no variation in the resonant frequency. 
     A period  802  is a period in which a charging distance or a charging angle is reduced, and thus, required power gradually decreases. That is, it is seen that the operating frequency of the inverter  120  increases, and when the operating frequency reaches the predetermined upper limit Fup_lim (points of time T 1 , T 2 , and T 3 ), capacitance is varied to reduce the resonant frequency. 
     That is, in the period  802 , since the required power gradually decreases, the capacitance controller  141  increases capacitance of the variable capacitor  142 , thereby decreasing the resonant frequency. Since the resonant frequency decreases in accordance with an increase in capacitance, a voltage gain may be lowered in response to a decrease in required power. 
     A period  803  is a period in which a charging distance or a charging angle increases away from a normal, coaxial alignment, and thus required power for charging gradually increases. That is, it is seen that the operating frequency of the inverter  120  decreases, and when the operating frequency reaches the predetermined lower limit Flow_lim (points of time T 4 , T 5 , and T 6 ), capacitance is varied to increase the resonant frequency. 
     That is, in the period  803 , since the required power gradually increases, the capacitance controller  141  decreases capacitance of the variable capacitor  142 , thereby increasing the resonant frequency. Since the resonant frequency increases in accordance with a decrease in capacitance, a voltage gain is increased in response to an increase in required power. 
     In the foregoing embodiments, descriptions are made on the basis of controlling the resonant frequency by changing capacitance of the resonator, using the variable capacitor  142  connected to the resonator  120 . However, according to one or more embodiments, modifications to the resonant frequency are made in such a manner that the resonant frequency is controlled by changing inductance in lieu, or in addition, to the changes in capacitance. 
       FIG. 9  is a flow chart illustrating a method of controlling a wireless power transmission apparatus according to an embodiment. 
     A method of controlling a wireless power transmission apparatus described hereinafter is a method of controlling the wireless power transmission apparatus described with reference to  FIG. 3  through  FIG. 8 , and thus may be further understood with reference to the contents described in  FIG. 3  through  FIG. 8 . 
     Referring to  FIG. 9 , the wireless power transmission apparatus identifies information regarding required power from a wireless power reception apparatus (S 910 ). 
     The wireless power transmission apparatus adaptively adjusts the operating frequency of the inverter in response to a change in required power (S 920 ). 
     When the operating frequency is outside of a predetermined range, the wireless power transmission apparatus changes the resonant frequency of the resonator thereof (S 930 ). 
     In an embodiment of the operation S 920 , the wireless power transmission apparatus decreases the operating frequency of the inverter when the required power increases and, on the other hand, increases the operating frequency when the required power decreases. 
     In an embodiment of the operation S 930 , the wireless power transmission apparatus reduces the resonant frequency when the operating frequency increases to a predetermined level or more. That is, as described above, since an increase in operating frequency corresponds to a case in which required power decreases, the wireless power transmission apparatus reduces the resonant frequency of the resonator and controls the voltage gain to be lowered. 
     In an embodiment of the operation S 930 , the wireless power transmission apparatus increases the resonant frequency when the operating frequency decreases to a predetermined level or less. That is, as described above, since a decrease in operating frequency corresponds to a case in which required power increases, the wireless power transmission apparatus increases the resonant frequency of the resonator to control the voltage gain to be increased. 
     In an embodiment of the operation S 930 , the wireless power transmission apparatus increases capacitance of the resonator when the operating frequency increases to a predetermined level or more. That is, as described above, since an increase in operating frequency corresponds to a case in which required power decreases, the wireless power transmission apparatus reduces the resonant frequency of the resonator to lower the voltage gain. To this end, the wireless power transmission apparatus increases capacitance of the resonator, thereby decreasing the resonant frequency. 
     In an embodiment of the operation S 930 , the wireless power transmission apparatus decreases capacitance of the resonator when the operating frequency decreases to a predetermined level or less. That is, as described above, since a decrease in operating frequency corresponds to a case in which required power increases, the wireless power transmission apparatus increases the resonant frequency of the resonator to increase the voltage gain. To this end, the wireless power transmission apparatus decreases capacitance of the resonator, thereby increasing the resonant frequency. 
     The apparatuses, units, modules, devices, controllers, random number generators, and other components illustrated in  FIGS. 1-3 and 6  that perform the operations described herein with respect to  FIGS. 4-5 and 7-9  are implemented by hardware components. Examples of hardware components include controllers, sensors, generators, drivers, and any other electronic components known to one of ordinary skill in the art. In one example, the hardware components are implemented by one or more processors or computers. A processor or computer is implemented by one or more processing elements, such as an array of logic gates, a controller and an arithmetic logic unit, a digital signal processor, a microcomputer, a programmable logic controller, a field-programmable gate array, a programmable logic array, a microprocessor, or any other device or combination of devices known to one of ordinary skill in the art that is capable of responding to and executing instructions in a defined manner to achieve a desired result. In one example, a processor or computer includes, or is connected to, one or more memories storing instructions or software that are executed by the processor or computer. Hardware components implemented by a processor or computer execute instructions or software, such as an operating system (OS) and one or more software applications that run on the OS, to perform the operations described herein with respect to  FIGS. 4-5 and 7-9 . The hardware components also access, manipulate, process, create, and store data in response to execution of the instructions or software. For simplicity, the singular term “processor” or “computer” may be used in the description of the examples described herein, but in other examples multiple processors or computers are used, or a processor or computer includes multiple processing elements, or multiple types of processing elements, or both. In one example, a hardware component includes multiple processors, and in another example, a hardware component includes a processor and a controller. A hardware component has any one or more of different processing configurations, examples of which include a single processor, independent processors, parallel processors, single-instruction single-data (SISD) multiprocessing, single-instruction multiple-data (SIMD) multiprocessing, multiple-instruction single-data (MISD) multiprocessing, and multiple-instruction multiple-data (MIMD) multiprocessing. 
     The methods illustrated in  FIGS. 4-5 and 7-9  that perform the operations described herein may be performed by a processor or a computer as described above executing instructions or software to perform the operations described herein. 
     Instructions or software to control a processor or computer to implement the hardware components and perform the methods as described above are written as computer programs, code segments, instructions or any combination thereof, for individually or collectively instructing or configuring the processor or computer to operate as a machine or special-purpose computer to perform the operations performed by the hardware components and the methods as described above. In one example, the instructions or software include machine code that is directly executed by the processor or computer, such as machine code produced by a compiler. In another example, the instructions or software include higher-level code that is executed by the processor or computer using an interpreter. Programmers of ordinary skill in the art, after gaining a thorough understanding of the present disclosure, can readily write the instructions or software based on the block diagrams and the flow charts illustrated in the drawings and the corresponding descriptions in the specification, which disclose algorithms for performing the operations performed by the hardware components and the methods as described above. 
     The instructions or software to control a processor or computer to implement the hardware components and perform the methods as described above, and any associated data, data files, and data structures, are recorded, stored, or fixed in or on one or more non-transitory computer-readable storage media. Examples of a non-transitory computer-readable storage medium include read-only memory (ROM), random-access memory (RAM), flash memory, CD-ROMs, CD-Rs, CD+Rs, CD-RWs, CD+RWs, DVD-ROMs, DVD-Rs, DVD+Rs, DVD-RWs, DVD+RWs, DVD-RAMs, BD-ROMs, BD-Rs, BD-R LTHs, BD-REs, magnetic tapes, floppy disks, magneto-optical data storage devices, optical data storage devices, hard disks, solid-state disks, and any device known to one of ordinary skill in the art that is capable of storing the instructions or software and any associated data, data files, and data structures in a non-transitory manner and providing the instructions or software and any associated data, data files, and data structures to a processor or computer so that the processor or computer can execute the instructions. In one example, the instructions or software and any associated data, data files, and data structures are distributed over network-coupled computer systems so that the instructions and software and any associated data, data files, and data structures are stored, accessed, and executed in a distributed fashion by the processor or computer. 
     As set forth above, a wireless power transmission apparatus according to an embodiment effectively performs wireless charging even in circumstances in which required power of a wireless power reception apparatus is variously changed. 
     While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.