Patent Publication Number: US-2016226312-A1

Title: Wireless power reception system, wireless power transmission system, control method, computer program, and recording medium

Description:
TECHNICAL FIELD 
     The present invention relates to a wireless power reception system and a wireless power transmission system in which electric power can be transmitted in a wireless or noncontact manner, a control method in the wireless power reception system, a computer program, and a recording medium on which the computer program is recorded. 
     BACKGROUND ART 
     In this type of system, impedance changes due to a variation in distance (i.e. a gap) between a power transmission side antenna and a power reception side antenna, a change in charging state of a battery when a load electrically connected to a power reception side is the battery, and a circuit load variation. 
     Thus, for example, Patent Literature 1 describes a technology in which an electric power conversion unit provided with a DC-DC converter is provided between a secondary side (or power reception side) antenna and a battery, and in which duty of the DC-DC converter is controlled to perform impedance matching. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid Open No. 2011-120443 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the technology described in the Patent Literature 1, however, if the duty of the DC-DC converter changes, output voltage of the DC-DC converter also changes. Then, there is such a technical problem that constant voltage output characteristics cannot be obtained, which is required for a power supply to which the load such as, for example, the battery, is electrically connected. 
     In view of the aforementioned problem, it is therefore an object of the present invention to provide a wireless power reception system, a wireless power transmission system, a control method, a computer program, and a recording medium, in which the constant voltage output characteristics can be maintained even if the power reception side load changes in the wireless power transmission system. 
     Solution to Problem 
     The above object of the present invention can be achieved by a wireless power reception system is provided with: a power reception antenna configured to receive, in a wireless manner, electric power outputted from a power transmission antenna of a power transmitting apparatus, which comprises a power supply and the power transmission antenna electrically connected to the power supply; a rectifier electrically connected between the power reception antenna and a load, the load being supplied with the electric power received by the power reception antenna; a constant voltage circuit electrically connected between the rectifier and the load; an obtaining device configured to obtain input impedance associated with the constant voltage circuit; and a controlling device configured to calculate an output adjustment value associated with the power supply on the basis of the obtained input impedance and to transmit the calculated output adjustment value to the power transmitting apparatus. 
     The above object of the present invention can be achieved by a wireless power transmission system comprising a power transmitting apparatus and a power receiving apparatus electrically connected to a load, wherein the power transmitting apparatus is provided with: a power supply; a power transmission antenna electrically connected to the power supply; and a power supply controlling device configured to control the power supply, the power receiving apparatus is provided with: a power reception antenna configured to receive, in a wireless manner, electric power outputted from the power transmission antenna; a rectifier electrically connected between the power reception antenna and the load; a constant voltage circuit electrically connected between the rectifier and the load; an obtaining device configured to obtain input impedance associated with the constant voltage circuit; and a controlling device configured to calculate an output adjustment value associated with the power supply on the basis of the obtained input impedance and to transmit the calculated output adjustment value to the power transmitting apparatus, and the power supply controlling device controls the power supply on the basis of the transmitted output adjustment value. 
     The above object of the present invention can be achieved by a control method in a wireless power reception system is provided with: (i) a power reception antenna configured to receive, in a wireless manner, electric power outputted from a power transmission antenna of a power transmitting apparatus, which comprises a power supply and the power transmission antenna electrically connected to the power supply; (ii) a rectifier electrically connected between the power reception antenna and a load, the load being supplied with the electric power received by the power reception antenna; and (iii) a constant voltage circuit electrically connected between the rectifier and the load, the control method is provided with: an obtaining process of obtaining input impedance associated with the constant voltage circuit; and a controlling process of calculating an output adjustment value associated with the power supply on the basis of the obtained input impedance and of transmitting the calculated output adjustment value to the power transmitting apparatus. 
     The above object of the present invention can be achieved by a computer program for making a computer function as an obtaining device and a controlling device, the computer being mounted on a wireless power reception system is provided with: (i) a power reception antenna configured to receive, in a wireless manner, electric power outputted from a power transmission antenna of a power transmitting apparatus, which comprises a power supply and the power transmission antenna electrically connected to the power supply; (ii) a rectifier electrically connected between the power reception antenna and a load, the load being supplied with the electric power received by the power reception antenna; and (iii) a constant voltage circuit electrically connected between the rectifier and the load, the obtaining device being configured to obtain input impedance associated with the constant voltage circuit; and the controlling device being configured to calculate an output adjustment value associated with the power supply on the basis of the obtained input impedance and to transmit the calculated output adjustment value to the power transmitting apparatus. 
     The above object of the present invention can be achieved by a recording medium on which the computer program according to the present invention is recorded. 
     The operation and other advantages of the present invention will become more apparent from embodiments and examples explained below. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration of a wireless power transmission system according to an example. 
         FIG. 2  is a characteristic diagram illustrating one example of transmission efficiency characteristics. 
         FIG. 3  is a circuit diagram illustrating a DC-DC converter using a step-down chopper. 
         FIG. 4  is a characteristic diagram illustrating one example of a relation between input voltage and input impedance associated with the DC-DC converter, for each varying load. 
         FIG. 5  is a flowchart illustrating a transmitted power control process performed in the wireless power transmission system according to the example. 
         FIG. 6  is a block diagram illustrating a configuration of a wireless power transmission system according to a first modified example of the example. 
         FIG. 7  is a block diagram illustrating a configuration of a wireless power transmission system according to a second modified example of the example. 
         FIG. 8  is a block diagram illustrating a configuration of a wireless power transmission system according to a third modified example of the example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The wireless power reception system, the wireless power transmission system, the control method, the computer program, and the recording medium according to embodiments of the present invention will be explained. 
     (Wireless Power Reception System) 
     A wireless power reception system according to an embodiment is provided with a power reception antenna, a rectifier, a constant voltage circuit, an obtaining device, and a controlling device. 
     The power reception antenna is configured to receive, in a wireless or noncontact manner, electric power outputted from a power transmission antenna of a power transmitting apparatus, which is provided with a power supply and the power transmission antenna electrically connected to the power supply. 
     The rectifier is electrically connected between the power reception antenna and a load, the load being supplied with the electric power received by the power reception antenna (e.g. a battery, etc.). The constant voltage circuit, such as, for example, a DC-DC converter and a three-terminal regulator, is electrically connected between the rectifier and the load. 
     The obtaining device obtains input impedance associated with the constant voltage circuit. As a method of obtaining the input impedance, for example, an input current value and an input voltage value associated with the constant voltage circuit may be measured and the measured input voltage value may be divided by the measured input current value to obtain the input impedance. 
     The controlling device, such as, for example, a memory and a processor, calculates an output adjustment value associated with the power supply of the power transmitting apparatus on the basis of the obtained input impedance, and transmits the calculated output adjustment value to the power transmitting apparatus. 
     According to the study of the present inventors, it has been found that even if the load electrically connected to a later stage of the rectifier changes, the input impedance associated with the constant voltage circuit can be kept constant by changing the input voltage value associated with the constant voltage circuit according to the change in the load (refer to an example described later for the details). 
     Therefore, as described above, if the output adjustment value calculated by the controlling device is transmitted to the power transmitting apparatus, and as a result, if the power supply is controlled according to the transmitted output adjustment value (i.e. if feedback control is performed according to the input impedance), the input voltage value associated with the constant voltage value changes, and the input impedance can be kept constant. 
     As a result, according to the wireless power reception system in the embodiment, the constant voltage output characteristics can be maintained even if the load changes. 
     In one aspect of the wireless power reception system according to the embodiment, the controlling device calculates the output adjustment value that allows the input impedance to approach a predetermined value, on the basis of the obtained input impedance. 
     According to this aspect, the input impedance can be kept constant (at the predetermined value), relatively easily. Here, the “predetermined value” may be set, on the basis of a variable range of circuit resistance on an output side of the constant voltage circuit caused by the change in the load during power transmission, as a value that allows the constant voltage output characteristics to be maintained in the variable range. 
     In this aspect, the controlling device may calculate a difference between the obtained input impedance and an input impedance target value, which is the predetermined value, and may calculate the output adjustment value that approaches the calculated difference to approach zero. 
     (Wireless Power Transmission System) 
     A wireless power transmission system according to an embodiment is provided with a power transmitting apparatus and a power receiving apparatus electrically connected to a load, such as, for example, a battery. 
     The power transmitting apparatus is provided with: a power supply; a power transmission antenna electrically connected to the power supply; and a power supply controlling device configured to control the power supply. 
     The power receiving apparatus is provided with: a power reception antenna; a rectifier; a constant voltage circuit; an obtaining device configured to obtain input impedance associated with the constant voltage circuit; and a controlling device configured to calculate an output adjustment value associated with the power supply on the basis of the obtained input impedance and to transmit the calculated output adjustment value to the power transmitting apparatus. 
     Particularly, here, the power supply controlling device of the power transmitting apparatus controls the power supply on the basis of the output adjustment value transmitted from the power receiving apparatus. 
     According to the wireless power transmission system in the embodiment, as in the wireless power reception system in the embodiment described above, the constant voltage output characteristics can be maintained even if the load changes. 
     The wireless power transmission system according to the embodiment can also adopt the same various aspects as those of the wireless power reception system in the embodiment described above. 
     (Control Method) 
     A control method according to an embodiment is a control method in a wireless power reception system comprising: (i) a power reception antenna configured to receive, in a wireless manner, electric power outputted from a power transmission antenna of a power transmitting apparatus, which comprises a power supply and the power transmission antenna electrically connected to the power supply; (ii) a rectifier electrically connected between the power reception antenna and a load, the load being supplied with the electric power received by the power reception antenna; and (iii) a constant voltage circuit electrically connected between the rectifier and the load. 
     The control method is provided with: an obtaining process of obtaining input impedance associated with the constant voltage circuit; and a controlling process of calculating an output adjustment value associated with the power supply on the basis of the obtained input impedance and of transmitting the calculated output adjustment value to the power transmitting apparatus. 
     According to the control method in the embodiment, as in the wireless power reception system in the embodiment described above, the constant voltage output characteristics can be maintained even if the load changes. 
     The control method according to the embodiment can also adopt the same various aspects as those of the wireless power reception system in the embodiment described above. 
     (Computer Program) 
     A computer program according to an embodiment makes a computer function as an obtaining device and a controlling device, the computer being mounted on a wireless power reception system comprising: (i) a power reception antenna configured to receive, in a wireless manner, electric power outputted from a power transmission antenna of a power transmitting apparatus, which comprises a power supply and the power transmission antenna electrically connected to the power supply; (ii) a rectifier electrically connected between the power reception antenna and a load, the load being supplied with the electric power received by the power reception antenna; and (iii) a constant voltage circuit electrically connected between the rectifier and the load, the obtaining device being configured to obtain input impedance associated with the constant voltage circuit; and the controlling device being configured to calculate an output adjustment value associated with the power supply on the basis of the obtained input impedance and to transmit the calculated output adjustment value to the power transmitting apparatus. 
     According to the computer program in the embodiment, the wireless power reception system according to the embodiment described above can be relatively easily realized as the computer provided in the wireless power reception system reads and executes the computer program from a recording medium for storing the computer program, such as a random access memory (RAM), a compact disc read only memory (CD-ROM) and a DVD read only memory (DVD-ROM), or as it executes the computer program after downloading the program through a communication device. By this, as in the wireless power reception system according to the embodiment described above, the constant voltage output characteristics can be maintained even if the load changes. 
     Example 
     A wireless power transmission system according to an example of the present invention will be explained on the basis of the drawings. 
     A configuration of the wireless power transmission system according to the example will be explained with reference to  FIG. 1 .  FIG. 1  is a block diagram illustrating the configuration of the wireless power transmission system according to the example. 
     In  FIG. 1 , a wireless power transmission system  1  is provided with a power transmitting apparatus  100  and a power receiving apparatus  200 . In the example, wireless power transmission by magnetic resonant coupling is performed between the power transmitting apparatus  100  and the power receiving apparatus  200 . 
     The power transmitting apparatus  100  is provided with a power transmission side control unit  110 , a wireless interface  120 , a power transmission antenna  130 , a matching circuit  140 , and a high-frequency power supply apparatus  150 . “Z 0 ” in  FIG. 1  indicates characteristic impedance of the high-frequency power supply apparatus  150 . 
     The power receiving apparatus  200  is provided with a power reception side control unit  210 , a wireless interface  220 , a power reception antenna  230 , a matching circuit  240 , a rectifier  250 , a DC-DC converter  260 , and a voltage/current monitoring unit  270 . The DC-DC converter  260  is electrically connected to a varying load  300  in which a load varies depending on a charging state, such as, for example, a battery. 
     Here, the wireless power transmission system  1  using the magnetic resonance coupling has such characteristics that electric power transmission efficiency varies depending on the value of a load electrically connected to a later stage of the power reception antenna  230  of the power receiving apparatus  200  (which will be hereinafter referred to as a “circuit load” as occasion demands, to prevent confusion with the “varying load  300 ”). 
     The transmission efficiency characteristics will be specifically explained with reference to  FIG. 2 .  FIG. 2  is a characteristic diagram illustrating one example of the transmission efficiency characteristics. The characteristics illustrated in  FIG. 2  are characteristics when Q values and loss resistance r associated with the power transmission antenna  130  and the power reception antenna  230  are respectively 700 and 1.0Ω, and a coupling coefficient between the power transmission antenna  130  and the power reception antenna  230  is 0.0423. 
     As is seen from  FIG. 2 , there is a circuit load having maximum transmission efficiency (refer to a horizontal axis in  FIG. 2 ). The circuit load having the maximum transmission efficiency is referred to as an “optimal load”. The optimal load varies depending on the Q value and the loss resistance r associated with the antenna to be used (i.e. the power transmission antenna and the power reception antenna), and the coupling coefficient k. In other words, if the Q value and the loss resistance r associated with the antenna and the coupling coefficient k are known, the optimal load can be obtained in advance. Therefore, in order to perform power transmission with relatively high efficiency, the circuit load is set to be the optimal load. 
     Moreover, if the magnetic resonance coupling is used, as in the wireless power transmission system  1 , the matching circuit is provided for each of the power transmitting apparatus  100  and the power receiving apparatus  200  (or is provided for one of the power transmitting apparatus and the power receiving apparatus) to perform impedance conversion or impedance matching, in many cases. 
     By the way, an electronic circuit electrically connected to the power receiving apparatus  200  as the varying load  300  (e.g. various processing circuits that operate at a power supply voltage of 12V or 5V or the like) stably operates by being supplied with predetermined voltage of electric power. Thus, a constant voltage output function is required for the wireless power transmission system  1 . Therefore, the power receiving apparatus  200  is provided with the DC-DC converter  260  having the constant voltage output function. 
     As a circuit having the constant voltage output function, except the DC-DC converter, for example, a three-terminal regulator or the like is known; however, the DC-DC converter is used in many cases from the viewpoint of power consumption. 
     It is guaranteed that the voltage on an output side of the DC-DC converter  260  (i.e. on a side on which the varying load  300  is electrically connected) is constant even if the value of the varying load  300  changes. 
     On the other hand, at least one of the voltage and current on an input side of the DC-DC converter  260  (i.e. on a side on which the rectifier  250  is electrically connected) changes due to the change in the value of the varying load  300 . As a result, the change in the value of the varying load  300  changes a load located after the rectifier  250 , by which the power transmission with the aforementioned optimal load (i.e. with the maximum efficiency) cannot be performed. 
     Moreover, as in the power transmitting apparatus  100 , if the matching circuit  140  is provided between the high-frequency power supply apparatus  150  and the power transmission antenna  130 , and if the power transmission is performed after the impedance matching, when the value of the load on the power reception side changes, the input impedance associated with the power transmission antenna  130  also changes. Then, the high-frequency power supply apparatus  150  and the power transmission antenna  130  become in an impedance mismatching state to cause a power loss (i.e. a reflection loss). 
     In order to solve the impedance mismatching state, for example, changing a circuit constant associated with the matching circuit  140  can be considered. However, as the matching circuit  140 , a variable impedance matching circuit having a variable inductor and a variable capacitor needs to be used, which cause such technical problems as an increase in apparatus size and complicated control. 
     With respect to the technical problems described above, for example, in the technology described in the Patent Literature 1, the duty of the DC-DC converter  260  is controlled so that the input impedance associated with the DC-DC converter  260  is constant. As a result, even if the value of the varying load  300  changes, the load located after the rectifier  250  is constant, and it is possible to prevent the impedance mismatching state of the power transmitting apparatus  100 . 
     Here, the technical problems caused by changing the duty of the DC-DC converter  260  will be explained with reference to  FIG. 3 .  FIG. 3  is a circuit diagram illustrating a DC-DC converter using a step-down chopper. 
     The operation of the DC-DC converter  260  illustrated in  FIG. 3  is described by the following three equations if there is no internal loss. “D” means “On Duty”. “R L ” is a value of the varying load  300 . 
       V out =DV in   [Equation 1]
 
       V in I in =V out I out   [Equation 2]
 
       V out =R L I out   [Equation 3]
 
     From the “Equation 1” and the “Equation 2”, a relation between input current I in , and output current I out  associated with the DC-DC converter  260  is obtained as in the following equation. 
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         out 
                       
                       D 
                     
                      
                     
                       I 
                       in 
                     
                   
                   = 
                   
                     
                       
                         
                           V 
                           out 
                         
                          
                         
                           I 
                           out 
                         
                       
                        
                       
                           
                       
                       ∴ 
                       
                         I 
                         in 
                       
                     
                     = 
                     
                       DI 
                       out 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     From the “Equation 1” to the “Equation 4”, input impedance Z in =(=V in /I in ) associated with the DC-DC converter  260  is as in the following equation. 
     
       
         
           
             
               
                 
                   
                     Z 
                     in 
                   
                   = 
                   
                     
                       
                         V 
                         in 
                       
                       
                         I 
                         in 
                       
                     
                     = 
                     
                       
                         
                           
                             V 
                             out 
                           
                           D 
                         
                         × 
                         
                           1 
                           
                             DI 
                             out 
                           
                         
                       
                       = 
                       
                         
                           
                             1 
                             
                               D 
                               2 
                             
                           
                           × 
                           
                             
                               V 
                               out 
                             
                             
                               I 
                               out 
                             
                           
                         
                         = 
                         
                           
                             1 
                             
                               D 
                               2 
                             
                           
                            
                           
                             R 
                             L 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     As is clear from the “Equation 5”, the input impedance Z in  associated with the DC-DC converter  260  can be changed by changing the duty of the DC-DC converter  260  (i.e. “D”) (whose characteristics are used by the technology described in the Patent Literature 1). 
     As is clear from the “Equation 1”, however, if the input voltage V in  associated with the DC-DC converter  260  is constant, when the duty changes, the output voltage V out  changes. In other words, the constant voltage output function of the DC-DC converter  260  is lost. 
     Thus, if the output voltage V out  is set to be a constant K vo  (i.e. V out =K vo ) and if that is applied to the “Equation 1” and the “Equation 3”, then, the following equation is obtained. 
     
       
         
           
             
               
                 
                   D 
                   = 
                   
                     
                       K 
                       VO 
                     
                     
                       V 
                       in 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     6 
                   
                   ] 
                 
               
             
             
               
                 
                   
                     I 
                     out 
                   
                   = 
                   
                     
                       K 
                       VO 
                     
                     
                       R 
                       L 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     7 
                   
                   ] 
                 
               
             
           
         
       
     
     If the “Equation 6” and the “Equation 7” are used to arrange the equation associated with the input impedance Z in  so that a duty item is deleted from the “Equation 5”, then, the following equation is obtained. 
     
       
         
           
             
               
                 
                   
                     Z 
                     in 
                   
                   = 
                   
                     
                       
                         V 
                         in 
                       
                       
                         I 
                         in 
                       
                     
                     = 
                     
                       
                         
                           V 
                           in 
                         
                         
                           DI 
                           out 
                         
                       
                       = 
                       
                         
                           
                             V 
                             in 
                           
                           × 
                           
                             
                               V 
                               in 
                             
                             
                               K 
                               VO 
                             
                           
                           × 
                           
                             
                               R 
                               L 
                             
                             
                               K 
                               VO 
                             
                           
                         
                         = 
                         
                           
                             
                               ( 
                               
                                 
                                   V 
                                   in 
                                 
                                 
                                   K 
                                   VO 
                                 
                               
                               ) 
                             
                             2 
                           
                            
                           
                             R 
                             L 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     8 
                   
                   ] 
                 
               
             
           
         
       
     
     As is clear from this equation, the input impedance Z in  can be changed regardless of the duty by changing the input voltage V in . 
     Thus, in the wireless power transmission system  1 , firstly, on the power reception side control unit  210 , an estimated resistance value R in  of the input impedance Z in  associated with the DC-DC converter  260  is calculated on the basis of the input voltage V in  and the input current I in  measured by the voltage/current monitoring unit  270  (refer to a reference numeral  211  in  FIG. 1 ). 
     Then, an output adjustment value associated with the high-frequency power supply apparatus  150  is arithmetically operated on the basis of the calculated estimated resistance value R in  and a target resistance value R ref  of the input impedance Z in  (refer to a reference numeral  212  in  FIG. 1 ) by a controller arithmetic operation unit  213  of the power reception side control unit  210 . Specifically, for example, the controller operation unit  213  obtains a difference between the calculated estimated resistance value R in  and the target resistance value R ref  and arithmetically operates the output adjustment value that allows the obtained difference to approach zero. 
     Now, the target resistance value R ref  will be explained with reference to  FIG. 4 .  FIG. 4  is a characteristic diagram illustrating one example of a relation between the input voltage and the input impedance associated with the DC-DC converter, for each varying load. 
     As illustrated in  FIG. 4 , the input impedance Z in  of the DC-DC converter  260  that can be kept constant in a variation range of the varying load  300  (which is here  30 Q to  80 Q) is, for example, 50Ω. As described above, the input impedance Z in  that can be kept constant in the variation range of the varying load  300  may be set as the target resistance value R ref . 
     The output adjustment value arithmetically operated by the controller arithmetic operation unit  213  is transmitted to the power transmitting apparatus  100  via the wireless interface  220 . The power transmission side control unit  110  of the power transmitting apparatus  100  controls the high-frequency power supply apparatus  150  on the basis of the transmitted output adjustment value. As a result, the input voltage V in  associated with the DC-DC converter  260  changes so that the input impedance Z in  approaches a target value. 
     A transmission power control process performed in the wireless power transmission system  1  as configured above will be explained with reference to a flowchart in  FIG. 5 . 
     In  FIG. 5 , firstly, the voltage/current monitoring unit  270  of the power receiving apparatus  200  measures voltage V in  and current I in  on an output side of the rectifier  250  of the power receiving apparatus  200  (in other words, on an input side of the DC-DC converter  260 ) (step S 101 ). 
     Then, the power reception side control unit  210  of the power receiving apparatus  200  calculates the estimated resonance value R in  on the basis of the measured voltage V in  and current I in  (step S 102 ). Then, the power reception side control unit  210  calculates a difference e between the calculated estimated resonance value R in  and the target resonance value R ref  (step S 103 ). 
     Then, the power reception side control unit calculates the output adjustment value associated with the high-frequency power supply apparatus  150  such that the difference e approaches zero (step S 104 ). The calculated output adjustment value is transmitted to the power transmission side control unit  110  of the power transmitting apparatus  100  via the wireless interfaces  220  and  120 . 
     The power transmission side control unit  110  controls the high-frequency power supply apparatus  150  on the basis of the transmitted output adjustment value (step S 105 ). 
     In the wireless power transmission system  1  according to the example, as described above, the output of the high-frequency power supply apparatus  150  (i.e. the input voltage V in  associated with the DC-DC converter  260 ) is changed, by which the load at an output terminal of the rectifier  250  of the power receiving apparatus  200  becomes constant or substantially constant even if the value of the varying load  300  varies. Therefore, even if the value of the varying load  300  varies, the power transmission with the maximum efficiency can be performed without changing the constant of the matching circuit and with satisfying a condition for the optimal load associated with the power transmission antenna  130  and the power reception antenna  230 . 
     In particular, it is not necessary to use the variable impedance matching circuit as the matching circuit, and it is thus possible to miniaturize and lighten the power transmitting apparatus  100  and the power receiving apparatus  200  that constitute the wireless power transmission system  1 , which is extremely useful in practice. 
     The “power transmission side control unit  110 ”, the “power receiving apparatus  200 ”, and the “DC-DC converter  260 ” according to the example are respectively one example of the “power supply controlling device”, the “wireless power reception system”, and the “constant voltage circuit” according to the present invention. The “power reception side control unit  210 ” according to the example is one example of the “obtaining device” and the “controlling device” according to the present invention. 
     First Modified Example 
     A first modified example of the wireless power transmission system  1  according to the example will be explained with reference to  FIG. 6 .  FIG. 6  is a block diagram illustrating a configuration of the wireless power transmission system according to the first modified example of the example. 
     In  FIG. 6 , the wireless power transmission system  1  is provided with a power transmitting apparatus  100   a  and the power receiving apparatus  200 . Here, the power transmitting apparatus  100   a  is provided with a high-frequency power supply apparatus  151  having output impedance Z o  that is low enough to be ignored. 
     In this case, it is not necessary to provide the impedance matching circuit between the high-frequency power supply apparatus  151  and the power transmission antenna  130 . Therefore, as illustrated in  FIG. 6 , the power transmitting apparatus  100   a  can be configured not to be provided with the impedance matching circuit. 
     Second Modified Example 
     A second modified example of the wireless power transmission system  1  according to the example will be explained with reference to  FIG. 7 .  FIG. 7  is a block diagram illustrating a configuration of the wireless power transmission system according to the second modified example of the example. 
     In  FIG. 7 , the wireless power transmission system  1  is provided with the power transmitting apparatus  100  and a power receiving apparatus  200   a.    
     If it is not necessary to perform the impedance matching between the optima load associated with the power reception antenna  230  and the input impedance associated with the rectifier  250 , then, as illustrated in  FIG. 7 , the power receiving apparatus  200   a  can be configured not to be provided with the impedance matching circuit. 
     Third Modified Example 
     A third modified example of the wireless power transmission system  1  according to the example will be explained with reference to  FIG. 8 .  FIG. 8  is a block diagram illustrating a configuration of the wireless power transmission system according to the third modified example of the example. 
     In  FIG. 8 , the wireless power transmission system  1  is provided with the power transmitting apparatus  100   a  and the power receiving apparatus  200   a.    
     If the power transmitting apparatus  100   a  is provided with the high-frequency power supply apparatus  151  having the output impedance Z o  that is low enough to be ignored, and if it is not necessary to perform the impedance matching between the optima load associated with the power reception antenna  230  and the input impedance associated with the rectifier  250 , then, as illustrated in  FIG. 8 , both of the power transmitting apparatus  100   a  and the power receiving apparatus  200   a  can be configured not to be provided with the impedance matching circuit. 
     The present invention is not limited to the aforementioned embodiment and example, but various changes may be made, if desired, without departing from the essence or spirit of the invention which can be read from the claims and the entire specification. A wireless power reception system, a control method, a computer program, and a wireless power transmission system which involve such changes are also intended to be within the technical scope of the present invention. 
     DESCRIPTION OF REFERENCE NUMERALS AND LETTERS 
     
         
           1  wireless power transmission system 
           100 ,  100   a  power transmitting apparatus 
           110  power transmission side control unit 
           120 ,  220  wireless interface 
           130  power transmission antenna 
           140 ,  240  matching circuit 
           150 ,  151  high-frequency power supply apparatus 
           200 ,  200   a  power receiving apparatus 
           210  power reception side control unit 
           230  power reception antenna 
           250  rectifier 
           260  DC-DC converter 
           270  voltage/current monitoring unit 
           300  varying load