Patent Publication Number: US-10333359-B2

Title: Method and apparatus for controlling wireless power of a receiver in a wireless power transmission/reception system

Description:
PRIORITY 
     This application is a Continuation of U.S. Ser. No. 14/704,467, which was filed in the U.S. Patent and Trademark Office (USPTO) on May 5, 2015, which is a Continuation of U.S. Ser. No. 13/490,963, which was filed in the USPTO on Jun. 7, 2012, issued as U.S. Pat. No. 9,024,484 on May 5, 2015, and claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application Ser. No. 61/494,175, which was filed in the USPTO on Jun. 7, 2011, and Korean Patent Application Serial No. 10-2012-0060595, which was filed in the Korean Intellectual Property Office on Jun. 5, 2012, the entire disclosure of each of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a wireless power transmission and reception system, and more particularly, to a method and apparatus for controlling power of a receiver in a wireless power transmission and reception system, wherein a wireless power quantity supplied to receivers from a transmitter is controlled through communication between the receivers. 
     2. Description of the Related Art 
     Wireless charging (or non-contact) technology uses wireless power transmission and reception, for example, to charge a battery of an electronic device by placing the electronic device on a charging pad, without having to connect a separate charging connector to the electronic device. 
     Wireless charging technology may be roughly divided into an electromagnetic induction type using a coil, a resonance type using resonance, and a Radio Frequency (RF)/micro wave radiation type for transforming electrical energy into a microwave. 
     In the resonance type of the wireless charging technology, a resonance type power transmission principle is used to wirelessly transmit electricity a distance of several meters from a charging device. Basically, resonance type power transmission uses a similar concept of physics in which vibration of a tuning fork causes a wine glass beside the tuning fork to vibrate at the same frequency. However, instead of resonating sound, resonance type power transmission resonates an electromagnetic wave containing electrical energy. 
     The resonated electrical energy is directly delivered to a device having a same resonance frequency, and the non-used portion of the resonated electrical energy is absorbed again into an electromagnetic field, instead of being spread through the air, such that unlike other electromagnetic waves, the resonated electrical energy does not to have an influence upon a peripheral machine or human body. 
     When charging using the resonance type of the wireless charging technology, each of a plurality of receivers that wants charging requests transmission of wireless power from a transmitter for transmitting the wireless power. The transmitter then supplies wireless power to each of the receivers. Basically, the receiver requests the transmitter to transmit wireless power, and is supplied with wireless power from the transmitter in response to the request. 
     Additionally, a single transmitter may charge a plurality of receivers at the same time. Further, when a receiver is being charged, i.e., supplied with wireless power from the transmitter, the transmitter may receive a request to transmit wireless power from another receiver. 
     However, when a plurality of receivers are supplied with wireless power from a transmitter at the same time, an over-powered state of over-voltage or over-current may occur in the transmitter or the receivers. Thereafter, the transmitter or receivers stop the charging, for example, by short-circuiting a circuit or the like, to protect against over powering. However, when the transmitter or the receivers stop the charging in this way, inconveniently, a user cannot charge the receiver using the transmitter or cannot use the receiver. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is designed to address at least the problems and/or disadvantages described above and to provide at least the advantages described below. 
     An aspect of the present invention is to provide a method and apparatus for controlling power of a receiver in a wireless power transmission and reception system, wherein a wireless power quantity supplied to receivers from a transmitter is controlled through communication between the receivers. 
     According to an aspect of the present invention, a method is provided for controlling wireless power at an electronic device. The method includes receiving power information from a receiver within a charging area; determining whether power is available for the receiver based on the power information; if the power is available for the receiver, transmitting, to the receiver, a first response requesting the receiver to perform charging; and if the power is not available for the receiver, transmitting, to the receiver, a second response requesting the receiver to maintain a standby state. 
     According to another aspect of the present invention, an electronic device is provided for controlling wireless power. The electronic device includes a communication unit; and a processor configured to receive, through the communication unit, power information from a receiver within a charging area, determine whether power is available for the receiver based on the power information, control the communication unit to transmit, to the receiver, a first response requesting the receiver to perform charging, if the power is available for the receiver, and control the communication unit to transmit, to the receiver, a second response requesting the receiver to maintain a standby state, if the power is not available for the receiver. 
     According to another aspect of the present invention, a method is provided for receiving wireless power at a receiver. The method includes transmitting power information to an electronic device; performing charging, if a first response is received indicating that the wireless power is available from the electronic device; and maintaining a standby state, if a second response is received indicating that the wireless power is not available from the electronic device. 
     According to another aspect of the present invention, a receiver is provided for receiving wireless power. The receiver includes a communication unit; and a controller configured to control the communication unit to transmit power information to an electronic device, perform charging, if a first response is received through the communication unit indicating that the wireless power is available from the electronic device, and maintain a standby state, if a second response is received through the communication unit indicating that the wireless power is not available from the electronic device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a wireless power transmission and reception system according to an embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a transmitter and a receiver in a wireless power transmission and reception system according to an embodiment of the present invention; 
         FIG. 3  is a signal flow diagram illustrating a method for controlling power of receivers in a wireless power transmission and reception system according to an embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating a method for controlling power of a receiver in a wireless power transmission and reception system according to an embodiment of the present invention; 
         FIG. 5  is a flowchart illustrating a method for controlling power of a receiver in a wireless power transmission and reception system according to an embodiment of the present invention; 
         FIGS. 6A and 6B  are graphs showing a wireless power quantity transmitted to a receiver in a wireless power transmission and reception system according to prior art; 
         FIGS. 7A and 7B  are graphs showing a wireless power quantity transmitted to a receiver in a wireless power transmission and reception system according to an embodiment of the present invention; and 
         FIGS. 8A and 8B  are graphs showing a wireless power quantity transmitted to a receiver in a wireless power transmission and reception system according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, specific items such as detailed components are described, and it is apparent to those of ordinary skill in the art that those specific items are provided only for overall understanding of the present invention and predetermined changes or modifications can be made without departing from the scope of the present invention. 
       FIG. 1  is a block diagram illustrating a wireless power transmission and reception system according to an embodiment of the present invention. 
     Referring to  FIG. 1 , a wireless power transmission and reception system includes a transmitter  100  and N receivers  200 , i.e., a first receiver  200 - 1  and a second receiver  200 - 2  through an Nth receivers  200 -N. 
     The transmitter  100  transmits wireless power to the receivers  200 . The transmitter  100  includes a resonator (hereinafter, a ‘Tx resonator’), and transmits wireless power to the receivers  200  by resonating carrier frequencies including electrical energy using the Tx resonator. 
     The receivers  200  transmit control signals, via communication interfaces, requesting the transmitter  100  to supply wireless power, and receive the wireless power from the transmitter  100 . The receivers  200  include resonators (hereinafter, ‘Rx resonators’) for receiving the wireless power from the transmitter  100 . 
     Additionally, the resonators also generate a signal in a particular frequency band, such that the receivers  200  may request supply of the wireless power from the transmitter  100  by resonating carrier frequencies in a frequency band for supply of the wireless power through the Rx resonators. The transmitter  100  also receives wireless power transmission requests from the receivers  200  through the Tx resonator. 
     In accordance with an embodiment of the present invention, each of the receivers  200  communicates with each other, when in a range in which the transmitter  100  can transmit wireless power. Herein, an area in which the transmitter  100  can transmit wireless power will be referred to as a “charging area.” For example, assuming that the first receiver  200 - 1  and the second receiver  200 - 2  are located in the charging area, the first receiver  200 - 1  and the second receiver  200 - 2  communicate with each other using their respective wired or wireless communication interfaces. 
     When a new receiver  200  joins the charging area, the new receiver  200  requests the transmitter  100  to transmit required power thereto. Herein, receivers previously included in the charging area will be referred to as “registered receivers” and a receiver newly joining the charging area will be referred to as a “joining receiver.” The registered receivers receive a power transmission request transmitted from the joining receiver to the transmitter  100  and analyze the desired-power transmission request in order to calculate the required power with which the joining receiver desires to be supplied from the transmitter  100 . The registered receivers then determine if the transmitter  100  can supply the required power of the joining receiver. 
     For example, when the transmitter  100  can supply wireless power of 50W in total to the receivers  200  and the transmitter  100  is already supplying 45W of wireless power to the registered receivers included in the charging area, when the joining receiver requests 7W of wireless power from the transmitter  100 , the transmitter  100  cannot supply the power to the joining receiver because the remaining power of the transmitter  100  is only 5W. In accordance with an embodiment of the present invention, the transmitter  100  supplies only wireless power at the request of the receivers  200 , such that the registered receivers, in place of the transmitter  100 , may inform the joining receiver that the required power of 7W cannot be supplied by the transmitter  100 . 
     In accordance with another embodiment of the present invention, the joining receiver may calculate the remaining power of the transmitter  100 . The joining receiver receives control signals from the registered receivers in the charging area, for example, charging power information, and determines whether the transmitter  100  can transmit the required power to the joining receiver based on the charging power information. 
     In accordance with an embodiment of the present invention, the charging power information broadcast from the registered receivers includes a wireless power quantity supplied to the respective registered receivers, and a total wireless power quantity that the transmitter  100  can supply. Therefore, based on the charging power information, the joining receiver calculates the remaining power of the transmitter  100  and determines whether the calculated remaining power is larger than the power desired by the joining receiver. If the remaining power of the transmitter  100  is smaller than the power desired by the joining receiver, the transmitter  100  cannot supply the desired power to the joining receiver. Therefore, the joining receiver requests the transmitter  100  to transmit the desired power only when the remaining power of the transmitter  100  is larger than the desired power of the joining receiver. 
     In accordance with another embodiment of the present invention, the receivers  200  included in the charging area broadcast the charging power information at preset broadcasting intervals. For example, when the first receiver  200 - 1  is being supplied with 5W of wireless power from the transmitter  100 , the first receiver  200 - 1 , the second receiver  200 - 2 , and a third receiver  200 - 3  are included in the charging area, and a broadcasting interval of the first receiver  200 - 1  is 5 minutes, the first receiver  200 - 1  broadcasts a signal to the charging area indicating that it is supplied with 5W of wireless power from the transmitter  100  every 5 minutes,. 
       FIG. 2  is a block diagram illustrating structures of a transmitter and a receiver in the wireless power transmission and reception system according to an embodiment of the present invention. 
     Referring to  FIG. 2 , the transmitter  100  includes a Tx resonator  102 , a Tx matching inductance (L)/capacitance (C) circuit), a Tx power converter  106 , and a Tx Micro Control Unit (MCU)  110 . The Tx resonator  102  is coupled with an Rx resonator  202  of the receiver  200  to resonate an Alternating Current (AC) voltage into a resonance wave, thereby supplying wireless power to the receiver  200 . Additionally, the Tx resonator  102  receives various control signals, e.g., the charging power information, the requested power information, etc., transmitted from the receiver  200 . 
     The Tx matching L/C  104  includes an impedance that is matched for the Tx resonator  102  and the Rx resonator  202  to be coupled and the Rx resonator  202  to smoothly receive the resonance wave resonated from the Tx resonator  102 . The Tx matching L/C  104  controls the impedance under control of the Tx MCU  110 . 
     The Tx power converter  106  converts a Direct Current (DC) voltage input from a DC adaptor (not shown) connected with the transmitter  100  into an AC voltage. For voltage conversion, the Tx power converter  106  includes, for example, a Class-E amplifier (not shown) and a driver amplifier (not shown). The Driver Amp converts a DC voltage input from the DC adaptor into an AC voltage. The Class-E Amp amplifies the AC voltage amplified by the Driver Amp under control of the Tx MCU  110 . 
     The transmitter  100  receives, for example, a DC voltage of 7-15V from a DC adaptor (not shown). Upon input of the DC voltage, the Tx MCU  110  controls the Tx power converter  106  to convert the DC voltage into an AC voltage and to amplify the converted AC voltage. The Tx MCU  110  regulates an amplification rate of the AC voltage in the Tx power converter  106 . The amplified AC voltage is delivered to the Rx resonator  202  of the receiver  200  by the Tx resonator  102 . 
     The Tx MCU  110  controls overall operation of the transmitter  100 . Specifically, the Tx MCU  110  controls the transmitter  100  to receive the DC voltage from the DC adaptor, and controls the Tx power converter  106  to regulate the power of the amplified AC voltage. Once the charging of the receiver  200  is completed, the transmitter  100  may be controlled not to transmit power to the receiver  200  anymore. The Tx MCU  110  regulates the impedance of the Tx matching L/C  104  to facilitate power transmission of the transmitter  100 . The Tx MCU  110  compares the power transmitted from the transmitter  100  with the power delivered to the receiver  200  to calculate a power efficiency. Based on the calculated power efficiency, the Tx MCU  110  regulates the impedance of the Tx matching L/C  104  in order to maximize the power efficiency. 
     The receiver  200  includes the Rx resonator  202 , an Rx matching L/C  204 , an Rx power converter  206 , a communication interface  208 , and an Rx MCU  210 . The Rx resonator  202  is coupled with the Tx resonator  102  to receive a resonated resonance wave from the Tx resonator  102 , thus being supplied with wireless power from the transmitter  100 . 
     The Rx matching L/C  204  regulates an impedance to be matched for the Tx resonator  102  and the Rx resonator  202  to be coupled and a resonated resonance wave to be smoothly received from the Tx resonator  102 . A total impedance of the Tx matching L/C  104  and a total impedance of the Rx matching L/C  204  are preferably matched to have the same value. 
     The Rx power converter  206  converts the AC voltage received through the Rx resonator  202  into the DC voltage. For voltage conversion, the Rx power converter  206  includes, for example, an AC/DC rectifier (not shown) and a DC/DC converter (not shown). The AC/DC rectifier converts the AC voltage received through the Rx resonator  202  into the DC voltage, and the DC/DC converter amplifies the DC voltage converted through the AC/DC rectifier. The Rx power converter  206  delivers the DC voltage output through the DC/DC converter to a device connected with the receiver  200 , e.g., a portable terminal, such that the portable terminal can be driven by the DC voltage. 
     The communication interface  208  performs wired or wireless communication of the receiver  200 . The communication interface  208  transmits a control signal requesting power supply or stopping of the power supply from the transmitter  100  to the transmitter  100 . The communication interface  208  broadcasts the control signal to the charging area. 
     The communication interface  208  also communicates with another receiver in the charging area, and receives a control signal broadcast from the another receiver. For example, the control signal includes a wireless power request signal for requesting wireless power from the transmitter  100 , a status signal indicating the current status of the receiver  200 , etc. 
     The Rx MCU  210  controls the overall operation of the receiver  200 . The Rx MCU  210  controls the receiver  200  to deliver a DC voltage for driving a portable terminal connected with the receiver  200 . 
     The Rx MCU  210  controls the Rx power converter  206  to regulate an amplification rate of an amplified DC voltage. The Rx MCU  210  also regulates the impedance of the Rx matching L/C  204  to smoothly receive wireless power delivered through the Tx resonator  102  of the transmitter  100 . 
     The Rx MCU  210  generates a control signal broadcast through the communication interface  208  to the transmitter  100  and registered receivers included in the charging area or a joining receiver. The Rx MCU  210  controls the communication interface  208  to receive control signals broadcast from the registered receives included in the charging area or the joining receiver. The Rx MCU  210  identifies a wireless power quantity (charging power) supplied to the respective registered receives included in the charging area or a wireless power quantity (required power) requested by the joining receiver from the control signals. The Rx MCU  210  calculates a total wireless power quantity of the wireless power supplied to the respective registered receivers, and calculates a remaining power quantity of the transmitter  100  using the total wireless power quantity. The Rx MCU  210  also determines whether the remaining power quantity is larger than the required power quantity of the joining receiver. If the remaining power quantity is smaller than the required power quantity of the joining receiver, then the Rx MCU  210  controls the communication interface  208  to generate a standby request control signal and to transmit the generated standby request control signal to the joining receiver. 
     If the receiver  200  is a joining receiver, the Rx MCU  210  determines whether the remaining power quantity is larger than a desired power quantity. If the remaining power quantity is smaller than the desired power quantity, the joining receiver maintains a standby state without requesting the transmitter  100  to supply the desired power. The Rx MCU  210  generates a control signal indicating maintenance of the standby state and broadcasts the control signal to the transmitter  100  and the registered receivers included in the charging area through the communication interface  208 . 
       FIG. 3  is a signal flow diagram illustrating a method for controlling power of receivers in a wireless power transmission and reception system according to an embodiment of the present invention. 
     Referring to  FIG. 3 , in step S 302 , i.e., a charging state, the first receiver  200 - 1  receives wireless power from the transmitter  100 . 
     In step S 304 , the second receiver  200 - 2 , which is a joining receiver, enters the charging area. 
     In step S 306 , the second receiver  200 - 2  requests joining from the transmitter  100 . Specifically, the Rx MCU  210  of the second receiver  200 - 2  generates a joining request control signal for requesting joining from the transmitter  100 , and transmits the joining request control signal to the transmitter  100  through the communication interface  208 . 
     In step S 306 , the second receiver  200 - 2  transmits a control signal including required power information to the transmitter  100 . Specifically, the second receiver  200 - 1  transmits the required power information to the transmitter  100  by broadcasting the control signal including the required power information to the charging area. The required power information indicates a wireless power quantity the joining receiver, i.e., the second receiver  200 - 2 , requires from the transmitter  100 . The first receiver  200 - 1  receives the control signal broadcast by the second receiver  200 - 2 . As described above, the first receiver  200 - 1  receives the control signals transmitted to the transmitter  100  in order to acquire the required power information of the second receiver  200 - 2 . 
     In step S 308 , the first receiver  200 - 1  calculates a remaining power of the transmitter  100 . The first receiver  200 - 1 , together with respective registered receivers included in the charging area, knows a total wireless power quantity that is being supplied or is to be supplied from the transmitter  100 . The first receiver  200 - 1  also knows the total wireless power quantity that can be output from the transmitter  100 . Using this information, the first receiver  200 - 1  calculates the remaining power of the transmitter  100 . 
     In step S 310 , the first receiver  200 - 1  determines whether the transmitter  100  can supply the required power to the second receiver  200 - 2 , based on the remaining power of the transmitter  100 . 
     If the transmitter  100  can supply the required power to the second receiver  200 - 2  (YES in step S 310 ), the first receiver  200 - 1  does not perform any subsequent operation. However, if the transmitter  100  cannot supply the required power to the second receiver  200 - 2  (NO in step S 310 ), the first receiver  200 - 1  requests the second receiver  200 - 2  to maintain a standby state in step S 312 . Specifically, the Rx MCU  210  of the first receiver  200 - 1  generates a standby state request signal and transmits the standby state request signal to the second receiver  200 - 2  through the communication interface  208 . 
     In step S 314 , the second receiver  200 - 2  maintains the standby state. 
     In accordance with an embodiment of the present invention, the first receiver  200 - 1  determines in step S 310  that the transmitter  100  cannot supply the required power to the second receiver  200 - 2  if the remaining power of the transmitter  100 , after transmitting the required power the second receiver  200 - 2  would be smaller than a preset reference value, although the total remaining power, prior to transmitting the required power the second receiver  200 - 2 , is larger than the power the second receiver  200 - 2  requires from the transmitter  100 . For example, when the required power of the second receiver  200 - 2  is 7W, the remaining power of the transmitter  100  is 9W, and the reference value is 3W, the first receiver  200 - 1  determines that the remaining power of the transmitter  100 , i.e., 2W, would be smaller than the reference value, i.e., 3W, when the transmitter  100  supplies wireless power to the second receiver  200 - 2 . Therefore, in this case, the first receiver  200 - 1  determines that the transmitter  100  cannot supply the required power to the second receiver  200 - 2 . 
     As described above, a registered receiver instructs a joining receiver to maintain a standby state in order to prevent a circuit included in the transmitter  100  or the receiver  200  from being damaged by over loading even when the remaining power of the transmitter  100  is larger than the required power of the joining receiver. 
       FIG. 4  is a flowchart illustrating a method for controlling power of a joining receiver by a registered receiver in a wireless power transmission and reception system according to an embodiment of the present invention. 
     Referring to  FIG. 4 , in step S 322 , the receiver  200 , i.e., the registered receiver, receives required power information broadcast from the joining receiver through the communication interface  208 . For example, the receiver  200  receives a control signal including the required power information. 
     In step S 324 , the receiver  200  calculates the remaining power of the transmitter  100 . In step S 326 , the receiver  200  determines whether the required power of the joining receiver is larger than the remaining power of the transmitter  100 . 
     If the required power of the joining receiver is larger than the remaining power of the transmitter  100  (YES in step S 326 ), the receiver  200  requests the joining receiver to maintain the standby state in step S 328 . Specifically, the Rx MCU  210  of the receiver  200  generates a standby state request signal and transmits the standby state request signal to the joining receiver through the communication interface  208 . 
     In step S 330 , the receiver  200  checks, e.g., at predetermined intervals, if its charging has been completed. When the charging has been completed (YES in step S 330 ), the receiver  200  requests the joining receiver to perform charging in step S 332 . The receiver  200  that has been completely charged maintains the standby state or leaves the charging area. 
     If the required power of the joining receiver is smaller than the remaining power of the transmitter  100  (NO in step S 326 ), the receiver  200  requests the joining receiver to perform charging in step S 332 . Alternatively, if the required power of the joining receiver is smaller than the remaining power of the transmitter  100  (NO in step S 326 ), the receiver  200  may take no further action. 
       FIG. 5  is a flowchart illustrating a method for controlling power of a joining receiver, by the joining receiver, in a wireless power transmission and reception system according to an embodiment of the present invention. 
     Referring to  FIG. 5 , the receiver  200 , i.e., the joining receiver, enters the charging area in step S 342 . 
     In step S 344 , the receiver  200  transmits required power information to the transmitter  100  through the communication interface  208 . Specifically, the receiver  200  generates a control signal including the required power information and transmits the control signal to the transmitter  100 . 
     In step S 346 , the receiver  200  receives charging power information from respective registered receives included in the charging area through the communication interface  208 . Alternatively, steps S 344  and S 346  may be performed at the same time, or the order of these steps may be interchanged. 
     As described above, the charging power information includes a wireless power quantity with which the registered receiver is being supplied from the transmitter  100 , and further includes a total wireless power quantity the transmitter  100  can supply to the receiver  200 . 
     The receiver  200  calculates the remaining power of the transmitter  100  based on the charging power information and determines whether the remaining power of the transmitter  100  is larger than a required power in step S 348 . 
     If the remaining power of the transmitter  100  is larger than the required power (YES in step S 348 ), the receiver  200  requests the transmitter  100  to supply the required power in step S 350 . In step S 352 , the receiver  200  performs a charging operation by receiving the wireless power from the transmitter  100 . 
     However, if the remaining power of the transmitter  100  is smaller than the required power in step S 348 , the receiver  200  maintains the standby state in step S 354 . 
       FIGS. 6A and 6B  are graphs showing a wireless power quantity transmitted to a receiver in a wireless power transmission and reception system according to prior art. Specifically,  FIG. 6A  shows a total load (Total RXs Load (W)) applied to receivers (RXs), and  FIG. 6B  shows a wireless power quantity, i.e., an input voltage (RX 1  Input Voltage (V)) with which the first receiver RX 1   200 - 1  among the registered receivers is supplied from the transmitter  100 . 
     Referring to  FIGS. 6A and 6B , when the first receiver RX 1   200 - 1  is supplied with the input voltage from the transmitter  100  and the second receiver RX 2   200 - 2  enters the charging area at time t 11  to be supplied with wireless power from the transmitter  100 , a load (RX 2  load) is applied. As the second receiver RX 2  enters the charging area, a load in the charging area changes. Because the wireless power is supplied to the second receiver RX 2 , a total load (Total RXs Load) applied to the receivers  200  sharply increases from the time t 11 , and exceeds a total power capacity (TX Power Capacity), which can be supplied from the transmitter  100  to the receivers  200 . 
     Further, the input voltage of the first receiver RX 1  sharply decreases, such that the input voltage supplied to the first receiver RX 1  may drop below a threshold voltage. In  FIG. 6B , the input voltage supplied to the first receiver RX 1  sharply drops below the threshold voltage from the time t 11 . The first receiver RX 1  is reset at time t 12  (RX 1  reset) to request the transmitter  100  to transmit the input voltage, a load change by the first receiver RX 1  occurs at t 13 , and the first receiver RX 1  is supplied with the input voltage larger than the threshold voltage from the transmitter  100 . However, due to the second receiver RX 2   200 - 2 , a total wireless power quantity supplied to the receivers  200  sharply increases from the time t 13  at which the first receiver RX 1  is supplied with the input voltage, such that the total wireless power quantity exceeds the total power capacity of the transmitter  100 . Thus, the first receiver RX 1  is turned off again and reset again at time t 14  (RX 1  reset again). 
       FIGS. 7A and 7B  are graphs showing a wireless power quantity transmitted to a receiver in the wireless power transmission and reception system according to an embodiment of the present invention. Specifically,  FIG. 7A  is a graph showing a total load (Total RXs Load (W)) applied to the receivers  200  RXs, and  FIG. 7B  is a graph showing a wireless power quantity, that is, an input voltage (RX 1  Input Voltage (V)) with which the first receiver RX 1   200 - 1  among the registered receivers is supplied from the transmitter  100 . 
     Referring to  FIGS. 7A and 7B , when the first receiver RX 1   200 - 1  is supplied with the input voltage from the transmitter  100  and the second receiver RX 2   200 - 2  enters the charging area at time t 21  to be supplied with the wireless power from the transmitter  100  (RX 2  load), the transmitter  100  senses a load change generated in the charging area, and receives required power information transmitted from the second receiver RX 2 . The first receiver RX 1  is temporarily turned off based on the required power information to reduce the input voltage supplied from the transmitter  100  to the threshold voltage. If the input voltage supplied to the first receiver RX 1  during t 22  is reduced to the threshold voltage or less, the total load amount (Total RXs Load) supplied to the receivers  200  does not exceed the total power capacity (Tx Power Capacity) of the transmitter  100 . 
       FIGS. 8A and 8B  are graphs showing a wireless power quantity transmitted to a receiver in a wireless power transmission and reception system according to an embodiment of the present invention. Specifically,  FIG. 8A  is a graph showing a total load (Total RXs Load (W)) applied to the receivers RXs, and  FIG. 8B  is a graph showing an estimated wireless power quantity (Estimated TX Power Budget (W)) supplied to the receivers  200  by the transmitter TX  100 . 
     Referring to  FIGS. 8A and 8B , at time t 31 , a load is applied to a client device including the receivers  200 . Thus at time t 32 , the receiver RX may be turned on to transmit required power information of the client device to the transmitter  100 . In  FIGS. 8A and 8B , it is assumed that a threshold value for a total wireless power quantity that can be supplied to the receivers  200  by the transmitter  100  is W 1  and a required power quantity of the client device is W 2 . 
     The transmitter  100  estimates a total wireless power quantity based on the required power information of the client device. 
     Referring to  FIGS. 8A and 8B , when a load is applied to both the client device and the receivers  200 , then an estimated wireless power quantity supplied to the client device and the receivers  200  exceeds the threshold value W 1 . Thus, the receiver RX maintains the standby state at time t 33  and only the client device may be supplied with wireless power from the transmitter  100 . 
     While the present invention has been particularly shown and described with reference to certain embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents.