JP6569799B2 - Power receiver and power transmission system - Google Patents

Description

  The present invention relates to a power receiver and a power transmission system.

  Conventionally, a resonant element that is contactlessly supplied with alternating-current power by resonance from a resonance element that is a power supply source, an excitation element that is supplied with alternating-current power by electromagnetic induction from the resonant element, and a direct current from the alternating-current power from the excitation element There is a non-contact power receiving apparatus including a rectifier circuit that generates and outputs electric power and a switching circuit that switches supply / non-supply of AC power to the rectifier circuit.

  Priority for receiving power of each non-contact power receiving apparatus, receiving means for receiving priority setting input from a user, communicating with other non-contact power receiving devices through the short-range wireless communication means, and the short-range wireless communication means In consideration of the above, a control means for controlling the switching circuit is provided so that the non-contact power receiving devices do not receive power simultaneously (see, for example, Patent Document 1).

JP 2011-019291 A

  By the way, when power is distributed by a plurality of power receivers, the priority of the non-contact power receiving device (power receiver) is taken into consideration, and thus there is a possibility that power cannot be supplied to the plurality of power receivers in a balanced manner.

  Then, it aims at providing the power receiver and power transmission system which can improve the supply balance of electric power.

  A power receiver according to an embodiment of the present invention includes a first secondary resonance coil that receives power from the primary resonance coil by magnetic field resonance or electric field resonance that occurs between the primary resonance coil and the first resonance coil. A rectifier circuit connected to the secondary side resonance coil and full-wave rectifying the AC power input from the first secondary side resonance coil, and a first on the high potential side connected to the output side of the rectifier circuit. A line, a second line on the low potential side connected to the output side of the rectifier circuit, a pair of output terminals respectively connected to the first line and the second line, the rectifier circuit and the pair of A first smoothing capacitor provided between the first line and the second line between the output terminal, and the first line and the pair of output terminals between the first smoothing capacitor and the pair of output terminals. A second smoothing capacitor provided between the second line and A switch inserted in series with the first line between the first smoothing capacitor and the second smoothing capacitor and switching a connection state of the first line; and between the first smoothing capacitor and the switch, or , An inductor inserted in series with the first line between the switch and the second smoothing capacitor, and a drive control unit that drives the switch with a first PWM drive pattern.

  A power receiver and a power transmission system that can improve the power supply balance can be provided.

1 is a diagram illustrating a power transmission system 50. FIG. It is a figure which shows the state which transmits electric power from the power transmission apparatus 10 to electronic device 40A, 40B by magnetic field resonance. It is a figure which shows the state which transmits electric power by the magnetic field resonance from the power transmission device 10 to electronic device 40B1, 40B2. It is a figure which shows the power receiving device 100 and power transmission apparatus 80 of embodiment. It is a figure which shows the power transmission apparatus 80 and electronic device 200A and 200B using the power transmission system 500 of embodiment. It is a figure showing the relationship between the duty ratio of power receiving device 100A and 100B, and power receiving efficiency. It is a figure which shows the simulation result using the power receivers A and B for a comparison. It is a figure which shows the simulation result using the power receivers A and B for a comparison. It is a figure which shows the simulation result using the power receivers A and B for a comparison. It is a figure which shows the simulation result using the power receivers A and B for a comparison. It is a figure which shows the simulation result using power receiving device 100A and 100B of embodiment. It is a figure which shows the simulation result using power receiving device 100A and 100B of embodiment. It is a figure which shows the relationship between the duty ratio of a PWM drive pattern, and the received electric energy of the receiving device 100A and 100B. It is a figure which shows the relationship between the duty ratio of the PWM drive pattern in the electric power receiver, and received electric power. It is a task figure showing processing which power transmitter 10 and power receivers 100A and 100B perform in order to set a duty ratio. It is a figure which shows the equivalent circuit of the power transmission apparatus 80 and the electronic devices 200A and 200B. It is a figure which shows the table data which linked _| related the duty ratio with respect to the relationship between a mutual inductance _MTA and a mutual inductance MTB. This is table data in which mutual inductance is associated with M _TA and M _TB and power reception efficiency. It is a flowchart which shows the method in which the power transmission device 10 of embodiment sets the duty ratio of the power receiving device 100A or 100B.

  Embodiments to which the power receiver and the power transmission system of the present invention are applied will be described below.

<Embodiment>
Prior to description of an embodiment to which the power receiver and the power transmission system of the present invention are applied, the prerequisite technology of the power receiver and power transmission system of the embodiment will be described with reference to FIGS. 1 to 3. .

  FIG. 1 is a diagram illustrating a power transmission system 50.

  As shown in FIG. 1, the power transmission system 50 includes an AC power source 1, a primary side (power transmission side) power transmitter 10, and a secondary side (power reception side) power receiver 20. The power transmission system 50 may include a plurality of power transmitters 10 and power receivers 20.

  The power transmitter 10 includes a primary side coil 11 and a primary side resonance coil 12. The power receiver 20 includes a secondary side resonance coil 21 and a secondary side coil 22. A load device 30 is connected to the secondary coil 22.

  As shown in FIG. 1, the power transmitter 10 and the power receiver 20 transmit power by magnetic field resonance (magnetic field resonance) between a primary side resonance coil (LC resonator) 12 and a secondary side resonance coil (LC resonator) 21. Energy (electric power) is transmitted from the electric device 10 to the electric power receiver 20. Here, the power transmission from the primary side resonance coil 12 to the secondary side resonance coil 21 can be performed not only by magnetic field resonance but also by electric field resonance (electric field resonance). However, in the following description, magnetic field resonance is mainly used as an example. explain.

  In the first embodiment, as an example, the frequency of the AC voltage output from the AC power supply 1 is 6.78 MHz, and the resonance frequency of the primary side resonance coil 12 and the secondary side resonance coil 21 is 6.78 MHz. Will be described.

  Note that power transmission from the primary side coil 11 to the primary side resonance coil 12 is performed using electromagnetic induction, and power transmission from the secondary side resonance coil 21 to the secondary side coil 22 also uses electromagnetic induction. Done.

  1 shows a form in which the power transmission system 50 includes the secondary side coil 22, the power transmission system 50 may not include the secondary side coil 22. In this case, the secondary side resonance What is necessary is just to connect the load apparatus 30 to the coil 21 directly.

  FIG. 2 is a diagram illustrating a state in which power is transmitted from the power transmitter 10 to the electronic devices 40A and 40B by magnetic field resonance.

  The electronic devices 40A and 40B are a tablet computer and a smartphone, respectively, and each include a power receiver 20A or 20B. The power receivers 20A and 20B have a configuration in which the secondary coil 22 is removed from the power receiver 20 (see FIG. 1) shown in FIG. That is, the power receivers 20 </ b> A and 20 </ b> B have the secondary side resonance coil 21. In addition, although the power transmission device 10 is simplified and shown in FIG. 2, the power transmission device 10 is connected to AC power supply 1 (refer FIG. 1).

  In FIG. 2, the electronic devices 40 </ b> A and 40 </ b> B are disposed at equal distances from the power transmitter 10, and each of the power receivers 20 </ b> A and 20 </ b> B incorporated therein receives power from the power transmitter 10 in a non-contact state due to magnetic resonance. Power is being received.

  As an example, in the state shown in FIG. 2, the power receiving efficiency of the power receiver 20A built in the electronic device 40A is 40%, and the power receiving efficiency of the power receiver 20B built in the electronic device 40B is 40%. .

  The power receiving efficiency of the power receivers 20A and 20B is represented by the ratio of the power received by the secondary coil 22 of the power receivers 20A and 20B to the power transmitted from the primary coil 11 connected to the AC power source 1. . In addition, when the power transmitter 10 does not include the primary side coil 11 and the primary side resonance coil 12 is directly connected to the AC power source 1, the primary side resonance is used instead of the power transmitted from the primary side coil 11. The received power may be obtained using the power transmitted from the coil 12. When the power receivers 20A and 20B do not include the secondary coil 22, the received power may be obtained using the power received by the secondary resonance coil 21 instead of the power received by the secondary coil 22. .

  The power receiving efficiency of the power receivers 20A and 20B is determined by the coil specifications of the power transmitter 10 and the power receivers 20A and 20B, and the distance and attitude between the power receivers 20A and 20B. In FIG. 2, the configurations of the power receivers 20A and 20B are the same, and are disposed at the same distance and posture from the power transmitter 10, so that the power receiving efficiencies of the power receivers 20A and 20B are equal to each other. %.

  The rated output of the electronic device 40A is 10 W, and the rated output of the electronic device 40B is 5 W.

  In such a case, the power transmitted from the primary side resonance coil 12 (see FIG. 1) of the power transmitter 10 is 18.75W. 18.75W is obtained by (10W + 5W) / (40% + 40%).

  By the way, when 18.75 W of power is transmitted from the power transmitter 10 toward the electronic devices 40A and 40B, the power receivers 20A and 20B receive a total of 15 W of power, and the power receivers 20A and 20B are equal. Therefore, each of them receives 7.5 W of power.

  As a result, the electronic device 40A has a power shortage of 2.5 W, and the electronic device 40B has a power surplus of 2.5 W.

  That is, even if 18.75 W of power is transmitted from the power transmitter 10 to the electronic devices 40A and 40B, the electronic devices 40A and 40B cannot be charged in a balanced manner. In other words, the power supply balance when charging the electronic devices 40A and 40B simultaneously is not good.

  FIG. 3 is a diagram illustrating a state in which power is transmitted from the power transmitter 10 to the electronic devices 40B1 and 40B2 by magnetic field resonance.

  The electronic devices 40B1 and 40B2 are smartphones of the same type, and include power receivers 20B1 and 20B2, respectively. The power receivers 20B1 and 20B2 are the same as the power receiver 20B shown in FIG. That is, the power receivers 20B1 and 20B2 include the secondary side resonance coil 21. In addition, in FIG. 3, although the power transmitter 10 is simplified and shown, the power transmitter 10 is connected to AC power supply 1 (refer FIG. 1).

  In FIG. 3, the angles (attitudes) of the electronic devices 40B1 and 40B2 with respect to the power transmitter 10 are the same, but the electronic device 40B1 is disposed farther from the power transmitter 10 than the electronic device 40B2. The power receivers 20B1 and 20B2 built in the electronic devices 40B1 and 40B2 respectively receive power from the power transmitter 10 in a non-contact state by magnetic field resonance.

  As an example, in the state shown in FIG. 3, the power receiving efficiency of the power receiver 20B1 built in the electronic device 40B1 is 35%, and the power receiving efficiency of the power receiver 20B2 built in the electronic device 40B2 is 45%. .

  Here, since the angles (attitudes) of the electronic devices 40B1 and 40B2 with respect to the power transmitter 10 are equal, the power receiving efficiency of the power receivers 20B1 and 20B2 is determined by the distance between each of the power receivers 20B1 and 20B2 and the power transmitter 10. For this reason, in FIG. 3, the power receiving efficiency of the power receiver 20B1 is lower than the power receiving efficiency of the power receiver 20B2. The rated outputs of the electronic devices 40B1 and 40B2 are both 5W.

  In such a case, the power transmitted from the primary resonance coil 12 (see FIG. 1) of the power transmitter 10 is 12.5W. 12.5W is obtained by (5W + 5W) / (35% + 45%).

  By the way, when 12.5 W of power is transmitted from the power transmitter 10 toward the electronic devices 40B1 and 40B2, the power receivers 20B1 and 20B2 receive a total of 10 W of power. In FIG. 3, since the power receiving efficiency of the power receiver 20B1 is 35% and the power receiving efficiency of the power receiver 20B2 is 45%, the power receiver 20B1 receives about 4.4 W of power, and the power receiver 20B2 , About 5.6% of power is received.

  As a result, the electronic device 40B1 has a power shortage of about 0.6 W, and the electronic device 40B2 has a power excess of 0.6 W.

  That is, even if 12.5 W of power is transmitted from the power transmitter 10 to the electronic devices 40B1 and 40B2, the electronic devices 40B1 and 40B2 cannot be charged in a balanced manner. In other words, the power supply balance when charging the electronic devices 40B1 and 40B2 at the same time is not good (there is room for improvement).

  Here, the power supply balance when the angles (attitudes) of the electronic devices 40B1 and 40B2 with respect to the power transmitter 10 are equal and the distances from the power transmitter 10 of the electronic devices 40B1 and 40B2 are different has been described.

  However, since the power reception efficiency is determined by the distance and angle (posture) between the power transmitter 10 and the power receivers 20B1 and 20B2, if the angle (posture) of the electronic devices 40B1 and 40B2 is different in the positional relationship shown in FIG. The power receiving efficiencies of the power receivers 20B1 and 20B2 are different from the 35% and 45% described above.

  Moreover, even if the distances from the power transmitter 10 of the electronic devices 40B1 and 40B2 are equal, the power receiving efficiencies of the power receivers 20B1 and 20B2 are different from each other if the angles (attitudes) of the electronic devices 40B1 and 40B2 with respect to the power transmitter 10 are different. .

  Next, the power receiver and the power transmission system according to the embodiment will be described with reference to FIGS. 4 and 5.

  FIG. 4 is a diagram illustrating the power receiver 100 and the power transmission device 80 according to the embodiment. The power transmission device 80 includes an AC power source 1 and a power transmitter 10. The AC power source 1 and the power transmitter 10 are the same as those shown in FIG. 1, but FIG. 4 shows a more specific configuration.

  The power transmission device 80 includes an AC power source 1 and a power transmitter 10.

  The power transmitter 10 includes a primary side coil 11, a primary side resonance coil 12, a matching circuit 13, a capacitor 14, and a control unit 15.

  The power receiver 100 includes a secondary resonance coil 110, a rectifier circuit 120, lines 125A and 125B, a switch 130, a smoothing capacitor 141, a smoothing capacitor 142, an inductor 145, a control unit 150, and output terminals 160A and 160B. A DC-DC converter 210 is connected to the output terminals 160 </ b> A and 160 </ b> B, and a battery 220 is connected to the output side of the DC-DC converter 210.

  First, the power transmitter 10 will be described. As shown in FIG. 4, the primary side coil 11 is a loop-shaped coil, and is connected to the AC power source 1 via a matching circuit 13 between both ends. The primary side coil 11 is disposed in close proximity to the primary side resonance coil 12 and is electromagnetically coupled to the primary side resonance coil 12. The primary coil 11 is disposed so that its central axis coincides with the central axis of the primary resonance coil 12. Matching the central axes improves the coupling strength between the primary side coil 11 and the primary side resonance coil 12 and suppresses leakage of magnetic flux, so that unnecessary electromagnetic fields are generated by the primary side coil 11 and the primary side resonance coil. This is to suppress the occurrence of the noise around 12.

  The primary coil 11 generates a magnetic field by AC power supplied from the AC power supply 1 through the matching circuit 13 and transmits the power to the primary resonance coil 12 by electromagnetic induction (mutual induction).

  As shown in FIG. 4, the primary side resonance coil 12 is disposed in close proximity to the primary side coil 11 and is electromagnetically coupled to the primary side coil 11. The primary side resonance coil 12 is designed to have a predetermined resonance frequency and a high Q value. The resonance frequency of the primary side resonance coil 12 is set to be equal to the resonance frequency of the secondary side resonance coil 110. A capacitor 14 for adjusting the resonance frequency is connected in series between both ends of the primary side resonance coil 12.

  The resonance frequency of the primary side resonance coil 12 is set to be the same frequency as the frequency of the AC power output from the AC power supply 1. The resonance frequency of the primary side resonance coil 12 is determined by the inductance of the primary side resonance coil 12 and the capacitance of the capacitor 14. For this reason, the inductance of the primary side resonance coil 12 and the capacitance of the capacitor 14 are set so that the resonance frequency of the primary side resonance coil 12 is the same as the frequency of the AC power output from the AC power supply 1. Has been.

  The matching circuit 13 is inserted for impedance matching between the primary side coil 11 and the AC power source 1 and includes an inductor L and a capacitor C.

  The AC power source 1 is a power source that outputs AC power having a frequency necessary for magnetic field resonance, and includes an amplifier that amplifies the output power. The AC power supply 1 outputs high-frequency AC power of about several hundred kHz to several tens of MHz, for example.

  The capacitor 14 is a variable capacitance type capacitor inserted in series between both ends of the primary side resonance coil 12. The capacitor 14 is provided to adjust the resonance frequency of the primary side resonance coil 12, and the capacitance is set by the control unit 15.

  The control unit 15 performs control of the output voltage and output frequency of the AC power supply 1, control of the capacitance of the capacitor 14, and the like.

  The power transmission device 80 as described above transmits AC power supplied from the AC power source 1 to the primary side coil 11 to the primary side resonance coil 12 by magnetic induction, and receives power from the primary side resonance coil 12 by magnetic field resonance. Power is transmitted to the secondary resonance coil 110.

  Next, the secondary side resonance coil 110 included in the power receiver 100 will be described.

  The secondary resonance coil 110 has the same resonance frequency as the primary resonance coil 12 and is designed to have a high Q value. A pair of terminals of the secondary side resonance coil 110 is connected to the rectifier circuit 120.

  The secondary resonance coil 110 outputs AC power transmitted from the primary resonance coil 12 of the power transmitter 10 by magnetic field resonance to the rectifier circuit 120.

  The rectifier circuit 120 includes four diodes 121A to 121D. The diodes 121 </ b> A to 121 </ b> D are connected in a bridge shape, and perform full-wave rectification and output of the power input from the secondary side resonance coil 110.

  The lines 125A and 125B are power supply paths that connect the rectifier circuit 120 and the output terminals 160A and 160B. The line 125A is a high-potential side line, and the line 125B is a low-potential side line. For example, the line 125B is grounded and held at the ground potential. The ground potential is an example of a reference potential.

  The switch 130 is inserted between the smoothing capacitor 141 and the inductor 145 in series with the line 125A on the high voltage side. The switch 130 may be a switch that can transmit and block a DC voltage at high speed, such as an FET.

  The switch 130 receives power that has been full-wave rectified by the rectifier circuit 120 and smoothed by the smoothing capacitor 141. Since the smoothed power is DC power, the switch 130 may be a DC switch. The DC switch 130 can be downsized because a switch having a simple structure such as an FET can be used.

  Here, AC switches include relays, triacs, and switches using FETs. Since the relay is a mechanical switch, the relay is large in size and may cause a durability problem when performing high-speed switching. Triac is not suitable for high-speed switching such as 6.78 MHz. In addition, since an AC switch using FETs includes a plurality of FETs, it is larger than a DC FET, and the parasitic capacitance has an effect on AC. For this reason, it is advantageous to use a DC FET as the switch 130 because it can be miniaturized and is not affected by parasitic capacitance.

  Although details of the drive pattern of the switch 130 will be described later, the switch 130 is PWM (Pulse Width Modulation) driven by the controller 150. The duty ratio of the PWM drive pattern of the switch 130 is determined based on the power reception efficiency of the secondary resonance coil 110 of the power receiver 100 and the rated output of the load circuit that receives power from the power receiver 100. In FIG. 4, the load circuit is a battery 220.

  The frequency of the PWM drive pattern is set to be equal to or lower than the frequency of the AC frequency received by the secondary resonance coil 110.

  The smoothing capacitor 141 is provided between the lines 125 </ b> A and 125 </ b> B on the output side of the rectifier circuit 120, and smoothes the power that has been full-wave rectified by the rectifier circuit 120. The power smoothed by the smoothing capacitor 141 is DC power.

  If the smoothing capacitor 141 is provided in front of the switch 130, the power rectified by the rectifier circuit 120 can be smoothed before being input to the switch 130. For example, it is included in the power rectified by the full wave. This is effective for suppressing the influence of ripple noise when the influence of ripple noise occurs. In order to suppress the influence of such ripple noise, in the embodiment, the capacitance of the smoothing capacitor 141 is set to a certain large value. A value that is somewhat large is a value that can absorb ripple noise.

  The inductor 145 is inserted in series with the line 125 </ b> A between the switch 130 and the smoothing capacitor 142. The inductor 145 generates a back electromotive force when the switch 130 is turned on (closed) and the charge is about to move from the smoothing capacitor 141 to the smoothing capacitor 142, and moves from the smoothing capacitor 141 to the smoothing capacitor 142. It is provided to suppress electric charges.

  The period during which the switch 130 is turned on is determined by the duty ratio of the PWM drive pattern that drives the switch 130. For example, when the power receiver 100 does not include the inductor 145, in an operating state in which the duty ratio is small and the switch 130 is on for a short period of time, the charge is instantaneously moved from the smoothing capacitor 141 to the smoothing capacitor 142, and the duty is Assume that adjustment of the received power by the ratio may not be easy. In such a case, the received power can be easily adjusted by connecting the inductor 145 in series with the switch 130 and slowing the movement of charges. The function of the inductor 145 will be described later.

  The smoothing capacitor 142 is inserted in series with the line 125A between the inductor 145 and the output terminal 160A, and further smoothes and outputs the power smoothed by the smoothing capacitor 141. Output terminals 160 </ b> A and 160 </ b> B are connected to the output side of the smoothing capacitor 142. In the embodiment, in order to suppress the influence of ripple noise, the capacitance of the smoothing capacitor 142 is set to a large value to some extent.

  The DC-DC converter 210 is connected to the output terminals 160 </ b> A and 160 </ b> B, and converts the DC power voltage output from the power receiver 100 into the rated voltage of the battery 220 and outputs the converted voltage. DC-DC converter 210 steps down the output voltage of rectifier circuit 120 to the rated voltage of battery 220 when the output voltage of rectifier circuit 120 is higher than the rated voltage of battery 220. Further, DC-DC converter 210 boosts the output voltage of rectifier circuit 120 to the rated voltage of battery 220 when the output voltage of rectifier circuit 120 is lower than the rated voltage of battery 220.

  The battery 220 may be a secondary battery that can be repeatedly charged. For example, a lithium ion battery may be used. For example, when the power receiver 100 is built in an electronic device such as a tablet computer or a smartphone, the battery 220 is a main battery of such an electronic device.

  In addition, the primary side coil 11, the primary side resonance coil 12, and the secondary side resonance coil 110 are produced by winding a copper wire, for example. However, the material of the primary side coil 11, the primary side resonance coil 12, and the secondary side resonance coil 110 may be a metal other than copper (for example, gold, aluminum, etc.). The materials of the primary side coil 11, the primary side resonance coil 12, and the secondary side resonance coil 110 may be different.

  In such a configuration, the primary side coil 11 and the primary side resonance coil 12 are the power transmission side, and the secondary side resonance coil 110 is the power reception side.

  In order to transmit electric power from the power transmission side to the power reception side using magnetic field resonance generated between the primary side resonance coil 12 and the secondary side resonance coil 110 by the magnetic field resonance method, electric power is transmitted from the power transmission side to the power reception side by electromagnetic induction. It is possible to transmit electric power over a longer distance than the electromagnetic induction method for transmitting.

  The magnetic field resonance method has a merit that it has a higher degree of freedom than the electromagnetic induction method with respect to the distance or displacement between the resonance coils and is position-free.

  FIG. 5 is a diagram illustrating a power transmission device 80 and the electronic devices 200A and 200B using the power transmission system 500 according to the embodiment.

  The power transmission device 80 is the same as the power transmission device 80 shown in FIG. 4, but in FIG. 5, components other than the primary side coil 11 and the control unit 15 in FIG. 4 are represented as a power supply unit 10 </ b> A. The power supply unit 10A collectively represents the primary side resonance coil 12, the matching circuit 13, and the capacitor 14. The AC power source 1, the primary side resonance coil 12, the matching circuit 13, and the capacitor 14 may be collectively regarded as a power source unit.

  The power transmission device 80 further includes an antenna 16. The antenna 16 may be any antenna that can perform wireless communication at a short distance, such as Bluetooth (registered trademark). The antenna 16 is provided to receive data representing power reception efficiency and rated output from the power receivers 100A and 100B included in the electronic devices 200A and 200B, and the received data is input to the control unit 15. The control unit 15 is an example of a control unit and an example of a third communication unit.

  The electronic devices 200A and 200B are terminals such as a tablet computer or a smartphone, respectively. Electronic devices 200A and 200B contain power receivers 100A and 100B, DC-DC converters 210A and 210B, and batteries 220A and 220B, respectively.

The power receivers 100A and 100B have a configuration in which antennas 170A and 170B are added to the power receiver 100 shown in FIG. The DC-DC converters 210A and 210B are
Each is the same as the DC-DC converter 210 shown in FIG. The batteries 220A and 220B are the same as the battery 220 shown in FIG.

  The power receiver 100A includes a secondary resonance coil 110A, a rectifier circuit 120A, a smoothing capacitor 141A, a switch 130A, an inductor 145A, a smoothing capacitor 142A, a control unit 150A, and an antenna 170A. The secondary side resonance coil 110A, the rectifier circuit 120A, the smoothing capacitor 141A, the switch 130A, the inductor 145A, the smoothing capacitor 142A, and the control unit 150A are respectively the secondary side resonance coil 110, the rectifier circuit 120, and the smoothing capacitor 141 shown in FIG. , Switch 130, inductor 145, smoothing capacitor 142, and control unit 150. In FIG. 5, the secondary side resonance coil 110A, the rectifier circuit 120A, the smoothing capacitor 141A, the switch 130A, the inductor 145A, and the smoothing capacitor 142A are shown in a simplified manner, and the output terminals 160A and 160B are omitted.

  The power receiver 100B includes a secondary side resonance coil 110B, a rectifier circuit 120B, a smoothing capacitor 141B, a switch 130B, an inductor 145B, a smoothing capacitor 142B, a control unit 150B, and an antenna 170B. The secondary side resonance coil 110B, the rectifier circuit 120B, the smoothing capacitor 141B, the switch 130B, the inductor 145B, the smoothing capacitor 142B, and the control unit 150B are respectively the secondary side resonance coil 110, the rectifier circuit 120, and the smoothing capacitor 141 shown in FIG. , Switch 130, inductor 145, smoothing capacitor 142, and control unit 150. In FIG. 5, the secondary side resonance coil 110B, the rectifier circuit 120B, the smoothing capacitor 141B, the switch 130B, the inductor 145B, and the smoothing capacitor 142B are shown in a simplified manner, and the output terminals 160A and 160B are omitted.

  The antennas 170A and 170B may be any antenna that can perform wireless communication at a short distance, such as Bluetooth (registered trademark). The antennas 170A and 170B are provided to perform data communication with the antenna 16 of the power transmitter 10, and are connected to the control units 150A and 150B of the power receivers 100A and 100B, respectively. Control units 150A and 150B are examples of drive control units, and are examples of a first communication unit and a second communication unit, respectively.

  The controller 150A of the power receiver 100A transmits data representing the power reception efficiency of the secondary resonance coil 110A and the rated output of the battery 220A to the power transmitter 10 via the antenna 170A. Similarly, the control unit 150B of the power receiver 100B transmits data representing the power reception efficiency of the secondary resonance coil 110B and the rated output of the battery 220B to the power transmitter 10 via the antenna 170B.

  The electronic devices 200 </ b> A and 200 </ b> B can charge the batteries 220 </ b> A and 220 </ b> B without being in contact with the power transmission device 80 in a state of being disposed near the power transmission device 80. The batteries 220A and 220B can be charged at the same time.

  The power transmission system 500 is constructed by the power transmitter 10 and the power receivers 100A and 100B among the components shown in FIG. That is, the power transmission device 80 and the electronic devices 200A and 200B employ a power transmission system 500 that enables power transmission in a non-contact state by magnetic field resonance.

  Here, if the batteries 220A and 220B are charged at the same time, as described with reference to FIGS. 2 and 3, a state in which the balance of power supply to the electronic devices 200A and 200B is not good may occur.

  Accordingly, in order to improve the balance of power supply, the power receivers 100A and 100B have the power reception efficiency of the secondary side resonance coil 110A, the rated output of the battery 220A, the power reception efficiency of the secondary side resonance coil 110B, and the rating of the battery 220B. Based on the output, the duty ratio of the PWM drive pattern for driving the switches 130A and 130B is set.

  Next, before explaining the power distribution by the power receivers 100A and 100B of the embodiment, the power distribution by the comparative power receivers A and B will be described. The comparative power receivers A and B have a configuration in which the inductors 145A and 145B are removed from the power receivers 100A and 100B, respectively.

  FIG. 6 is a diagram illustrating the relationship between the duty ratio of the PWM drive pattern and the amount of power received by the power receivers A and B for comparison. Here, when the capacitances of the smoothing capacitors 141A and 142A of the power receiver A and the smoothing capacitors 141B and 142B of the power receiver B are set to 1 μF, the received power amount is adjusted by changing the duty ratio. The case will be described.

  Further, here, in a state where the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver B is fixed to 100%, the duty ratio (duty A) of the PWM drive pattern for driving the switch 130A of the power receiver A is set to 100. The case of lowering from% will be described.

In FIG. 6, the horizontal axis represents the duty ratio of the PWM drive pattern that drives the switch 130 </ b> A of the power receiver A. The vertical axis indicates the power reception efficiency η _A , η _{B of} the power receivers A and B for comparison, the sum η (= η _A + η _B ) of the power reception efficiency, and the ratio η _A / η _B of the power reception efficiency, respectively. .

The power receiving efficiency η _A is a value obtained by dividing the power received by the power receiver A by the transmitted power. The power reception efficiency η _B is a value obtained by dividing the power received by the power receiver B by the transmission power.

When the duty ratios of the PWM drive patterns for driving the switches 130A and 130B of the power receivers A and B are both 100%, the power receiving efficiencies η _A and η _B of the power receivers A and _B are both about 30%. At this time, the sum η of the power reception efficiency is about 60%, and the ratio η _A / η _B of the power reception efficiency is 1 (100%).

When the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver A is reduced to 100% in a state where the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver B is fixed to 100%, FIG. As shown in FIG. 6, the power receiving efficiency η _A of the power receiver _A is lowered. As a result, the power receiving efficiency η _B of the power receiver _B increases.

  When the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver A is lowered in this way, the amount of power received by the power receiver A is decreased, and the current flowing through the power receiver A is also decreased. That is, the impedance of the power receiver A changes due to the change in the duty ratio.

  In power transmission using magnetic field resonance, the power transmitted from the power transmitter 10 to the comparative power receivers A and B by the magnetic field resonance is distributed between the power receivers A and B. For this reason, when the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver A is decreased from 100%, the amount of power received by the power receiver B is increased by the amount that the power received by the power receiver A is decreased. .

For this reason, as shown in FIG. 6, when the power receiving efficiency η _A of the power receiver _A decreases, the power receiving efficiency η _B of the power receiver _B increases accordingly.

When the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver A is reduced to 1%, the power reception efficiency η _A of the power receiver _A is reduced to about 0%, and the power reception efficiency η _B of the power receiver _B is about Increase to 40%.

At this time, the sum η of the power receiving efficiencies of the comparative power receivers A and B is about 40%, and the ratio η _A / η _B of the power receiving efficiencies is about 0 (about 0%).

In this way, with the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver B fixed at 100%, the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver A is reduced from 100%. When it goes, the power receiving efficiency η A of the power receiver _A decreases, and the power receiving efficiency η _B of the power receiver _B increases.

  This is a case where the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver B is lowered from 100% in a state where the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver A is fixed to 100%. Is the same.

Therefore, if the duty ratio of the PWM drive pattern for driving either the switch 130A or 130B of the power receiver A or B is adjusted, the power receiving efficiencies η _A and η _B of the power receivers A and B for comparison are adjusted. Can do. The ability to adjust the power receiving efficiencies η _A and η _B is that the received power can be adjusted.

As described above, when the duty ratio of the PWM drive pattern for driving the switch 130A or 130B is changed, the power reception efficiencies η _A and η _{B of the} secondary resonance coils 110A and 110B of the comparative power receivers A and _B are changed. .

  Therefore, if the duty ratio of one of the PWM drive patterns of the switches 130A and 130B of the power receivers A and B is changed from the reference duty ratio, the ratio at which the power receivers A and B distribute power Can be changed. The reference duty ratio is 100%, for example.

  By the way, in the comparative power receiver A or B as described above, if the capacitances of the smoothing capacitors 141A and 142A or 141B and 142B are not sufficient, ripple noise is caused by the switching of the switch 130A or 130B. It may occur and direct current power cannot be obtained. If DC power cannot be obtained by the power receiver A, the power supply balance between the power receivers A and B cannot be improved.

  FIG. 7 is a diagram illustrating a simulation result using the power receivers A and B for comparison.

  In the simulation, the capacitances of the smoothing capacitors 141A, 142A, 141B, and 142B of the power receivers A and B for comparison are all set to 1 μF, the duty ratio of the PWM drive pattern of the switch 130A is 50%, and the switch 130B The duty ratio of the PWM drive pattern was set to 100%. The switching frequency is 100 kHz as an example.

  In FIG. 7, the horizontal axis is a time axis, and indicates an elapsed time (0 milliseconds to 0.15 milliseconds) since the start of switching of the switches 130A and 130B. The vertical axis in FIG. 7 indicates transmitted power, received power A, and received power B. The transmitted power is the power transmitted by the power transmission device 80, and is, for example, high frequency power of 6.78 MHz. In FIG. 7, the envelope of the 6.78 MHz waveform is indicated by a one-dot chain line. In the envelope of the transmission power, even after the transition period, the transmission power fluctuates in the region surrounded by the broken line (1).

  The received power A and B are the received power of the power receivers A and B, the received power A is indicated by a solid line, and the received power B is indicated by a broken line. The received power A oscillates at 100 kHz even in the region indicated by the broken line in (2). A region indicated by a broken line in (2) is a region where the transition period immediately after the switching of the switches 130A and 130B is started. That is, it can be seen that the received power A does not stop oscillating even after the transition period, and ripple noise is generated.

  In addition, the amount of power received by electric power B has stabilized after the transition period has passed, but fluctuations have occurred as in the case of transmitted power.

  The fluctuation of the transmitted power and the received power B is considered to be caused by the ripple noise of the received power A propagating to the power transmitting device 80 and the power receiver B. The received power A shown in FIG. 7 is not DC power but AC power.

  When ripple noise occurs as in the received power A shown in FIG. 7, it is not direct current power, so that it is impossible to charge the battery with the power receiver A or supply power to the DC-DC converter.

  FIG. 8 is a diagram illustrating a simulation result using the power receivers A and B for comparison. FIG. 8 shows nine simulation results obtained by changing the capacitances of the smoothing capacitors 141A, 142A, 141B, and 142B. Each simulation result is obtained by the same simulation as that of FIG. 7 except for the capacitances of the smoothing capacitors 141A, 142A, 141B, and 142B. The range of the horizontal axis (time axis) is 0 milliseconds to 0.15 milliseconds.

  Here, the capacitances of the capacitors 141A and 141B of the power receivers A and B are denoted by C1, and the capacitances of the capacitors 142A and 142B of the power receivers A and B are denoted by C2. Nine types of simulation results were obtained using three values of 1 μF, 10 μF, and 100 μF as the capacitances C1 and C2.

  The simulation was performed by setting the duty ratio of the PWM drive pattern of the switch 130A of the power receiver A to 50% and the duty ratio of the PWM drive pattern of the switch 130B of the power receiver B to 100%. The switching frequency is 100 kHz as an example.

  As shown in FIG. 8, it was found that as the values of the capacitances C1 and C2 increase, the ripple noise of the received power A is reduced, and the fluctuations of the transmitted power and the received power B are also reduced. When both the capacitances C1 and C2 are set to 100 μF, the received power A is substantially DC power, and the transmission power and the received power B are in a good state with almost no fluctuations.

  From this result, it was found that the smoothing capacitors 141A, 142A, 141B, and 142B need to have a certain capacitance to absorb the ripple noise.

FIG. 9 is a diagram illustrating a simulation result using the power receivers A and B for comparison. FIG. 9 shows the result of the same simulation as in FIG. 8 with the duty ratio of the PWM drive pattern of the switch 130A of the power receiver A set to 1%. In FIG. 9, the power reception efficiency ratio η _A / η _B is shown in each of the nine results. The range of the horizontal axis (time axis) is 0 milliseconds to 0.15 milliseconds.

  The nine simulation results shown in FIG. 9 generally show a tendency that the ripple noise is slightly larger than the nine simulation results shown in FIG.

Further, the ratio η _A / η _B of power reception efficiency tends to increase when the capacitance C1 or C2 increases, and significantly increases when both the capacitances C1 and C2 increase. When both the capacitances C1 and C2 are 1 μF, the power reception efficiency ratio η _A / η _B is 0.04, whereas when both the capacitances C1 and C2 are 10 μF, the power reception The efficiency ratio η _A / η _B was 0.43.

When the capacitances C1 and C2 were 10 μF and 100 μF, respectively, the power reception efficiency ratio η _A / η _B was 0.40. When the capacitances C1 and C2 were 100 μF and 10 μF, respectively, the power reception efficiency ratio η _A / η _B was 0.49.

When the capacitances C1 and C2 were both 100 μF, the power reception efficiency ratio η _A / η _B was 0.61.

This is despite reducing the duty ratio of the PWM driving pattern of the switch 130A of the power receiver A 1%, the power receiving efficiency eta _A indicates that no decrease. That is, even if the duty ratio of the PWM drive pattern of the switch 130A is reduced to 1%, the received power of the power receiver A is not reduced, and the dynamic range of the received power that can be adjusted by the power receiver A is narrow. I understand.

In particular, when the capacitances C1 and C2 are both 100 μF and the power reception efficiency ratio η _A / η _B is 0.61, the received power A and the received power B cannot even be adjusted to 1: 2. become.

  In the simulation result shown in FIG. 9, the range of the horizontal axis (time axis) is set to 0 milliseconds to 0.15 milliseconds. However, as the values of the capacitances C1 and C2 increase, the range of 0.115 millimeters. Since the transmission power and the received power A and B did not converge in seconds, data was collected until they converged. This result will be described with reference to FIG.

  FIG. 10 is a diagram illustrating a simulation result using the power receivers A and B for comparison. The simulation result shown in FIG. 10 is calculated until 2 milliseconds elapse after the switching of the switches 130A and 130B is started.

The horizontal axis represents the duty ratio (duty A) of the PWM drive pattern for driving the switch 130A of the power receiver A. In addition, the vertical axis indicates the power reception efficiency η _A and η _{B of} the power receivers A and B for comparison, the sum η of the power reception efficiency, and the ratio η _A / η _B of the power reception efficiency, respectively.

When the capacitances C1 and C2 were both set to 100 μF and calculated, the ratio η _A / η _B of power reception efficiency when the duty ratio was 100% was 1 (100%). However, the power reception efficiency ratio η _A / η _B when the duty ratio was 1% was 0.92 (92%).

  That is, when both the capacitances C1 and C2 are set to 100 μF, the received power A and the received power B can hardly be adjusted even if the duty ratio of the PWM drive pattern of the switch 130A is reduced to 1%. .

  From the above, it was found that when both the capacitances C1 and C2 are set to relatively large values, the ripple noise is reduced, but the dynamic range of the received power that can be adjusted by the duty ratio is narrowed.

  Here, when both the capacitances C1 and C2 are set to relatively large values, one of the reasons why the received power does not decrease even when the duty ratio is lowered can be considered as follows.

  4 has a configuration in which the inductor 145 is removed from the power receiver 100 of the embodiment in FIG. 4, the duty ratio is small, and in an operation state in which the period during which the switch 130 is on is short. Charges instantaneously move from the smoothing capacitor 141 to the smoothing capacitor 142. This is because the capacitors can instantaneously transmit even a relatively large electric power.

  In such a case, even if the period during which the switch 130 is turned on is shortened, the charge instantaneously moves from the smoothing capacitor 141 to the smoothing capacitor 142 while the switch 130 is on. It becomes impossible to adjust.

  For the above reasons, in the power receiver 100 of the embodiment, the inductor 145 is inserted in series with the switch 130 in the high-potential line 125A between the smoothing capacitor 141 and the smoothing capacitor 142. This is because instantaneous movement of charges from the smoothing capacitor 141 to the smoothing capacitor 142 is suppressed by the back electromotive force of the inductor 145.

  FIG. 11 is a diagram illustrating a simulation result using the power receivers 100A and 100B according to the embodiment. FIG. 11 shows nine simulation results obtained by changing the capacitances of the smoothing capacitors 141A, 142A, 141B, and 142B. Each simulation result is the same as the simulation result (see FIGS. 8 and 9) using the power receivers A and B of the comparative example. The range of the horizontal axis (time axis) is 0 milliseconds to 0.5 milliseconds.

  Here, the capacitances of the capacitors 141A and 141B of the power receivers 100A and 100B are denoted by C1, and the capacitances of the capacitors 142A and 142B of the power receivers 100A and 100B are denoted by C2. Nine types of simulation results were obtained using three values of 1 μF, 10 μF, and 100 μF as the capacitances C1 and C2.

  The inductance of the inductor 145 was set to 0.47 μH.

  The simulation was performed by setting the duty ratio of the PWM drive pattern of the switch 130A of the power receiver 100A to 1% and the duty ratio of the PWM drive pattern of the switch 130B of the power receiver 100B to 100%. The switching frequency is 100 kHz as an example.

As shown in FIG. 11, when both the values of the capacitances C1 and C2 are 1 μF, no ripple noise occurs in the received power A, and no fluctuation occurs in the transmitted power and the received power B. This tendency was the same even when the values of the capacitances C1 and C2 were increased to 10 μF and 100 μF. In all nine simulation results, the power reception efficiency ratio η _A / η _B was substantially zero.

  From this, it was found that by inserting the inductor 145, the received power A can be made substantially zero when the duty ratio is reduced to 1%.

  FIG. 12 is a diagram illustrating a simulation result using the power receivers 100A and 100B according to the embodiment. FIG. 12 shows a simulation result when the duty ratio of the PWM drive pattern of the switch 130A of the power receiver 100A is set to 50%. The simulation result shown in FIG. 12 is the same as the simulation result shown in FIG. 11 except that the duty ratio of the PWM drive pattern of the switch 130A of the power receiver 100A is set to 50%.

  As shown in FIG. 12, ripple noise occurs in the received power A when the values of the capacitances C1 and C2 are both 100 μF and when the values of the capacitances C1 and C2 are 10 μF and 100 μF, respectively. In addition, good results were obtained in which there was no fluctuation between the transmitted power and the received power B.

  When the value of the capacitance C2 is 1 μF or 10 μF, significant ripple noise is generated in the received power A, and thus the power receiver 100A cannot receive DC power. Further, when the values of the capacitances C1 and C2 are 1 μF and 100 μF, respectively, the ripple noise of the received power A is suppressed, but noise is generated in the transmitted power and the received power B.

  The simulation result of FIG. 12 with the duty ratio set to 50% shows the effect of ripple noise when the values of the capacitances C1 and C2 are small compared to the simulation result of FIG. 11 with the duty ratio set to 1%. However, good results were obtained when both the values of the capacitances C1 and C2 were 100 μF and when the values of the capacitances C1 and C2 were 10 μF and 100 μF, respectively.

  As described above, the electrostatic capacity of the smoothing capacitors 141A, 142A, 141B, and 142B is set to a relatively large value of about 100 μF, and the inductor 145 is inserted, thereby suppressing the generation of ripple noise and the power receiver 100A. It was found that the received power can be adjusted according to the duty ratio at 100B. That is, it has been found that it is possible to achieve both suppression of ripple noise and securing of a dynamic range.

  FIG. 13 is a diagram illustrating the relationship between the duty ratio of the PWM drive pattern and the amount of power received by the power receivers 100A and 100B. Here, when the capacitances of the smoothing capacitors 141A and 142A of the power receiver 100A and the smoothing capacitors 141B and 142B of the power receiver 100B are set to 100 μF, the received power amount is adjusted by changing the duty ratio. The case will be described.

  Further, here, in a state where the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver 100B is fixed to 100%, the duty ratio (duty A) of the PWM drive pattern for driving the switch 130A of the power receiver 100A is set to 100. The case of lowering from% will be described.

In FIG. 13, the horizontal axis represents the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver 100A. The vertical axis indicates the power receiving efficiency η _A and η _{B of} the power receivers 100A and 100B, the sum η of the power receiving efficiency, and the ratio η _A / η _B of the power receiving efficiency in percentage.

  The simulation results shown in FIG. 13 are calculated until 2 milliseconds have elapsed since the start of switching of the switches 130A and 130B.

When the duty ratios of the PWM drive patterns that drive the switches 130A and 130B of the power receivers 100A and B are both 100%, the power receiving efficiencies η _A and η _B of the power receivers 100A and 100B are both about 30%. At this time, the sum η of the power reception efficiency is about 60%, and the ratio η _A / η _B of the power reception efficiency is 1 (100%).

If the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver 100A is decreased from 100% to 1% with the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver 100B fixed at 100%, The power receiving efficiency η _A of the electric device 100A is reduced to about 0%, and the power receiving efficiency η _B of the electric power receiver 100B is increased to about 45%.

At this time, the sum η of the power reception efficiency of the power receivers 100A and 100B is about 45%, and the ratio η _A / η _B of the power reception efficiency is about 0 (about 0%).

In this way, with the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver 100B fixed to 100%, the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver 100A is decreased from 100%. When it goes, the power receiving efficiency η _A of the power receiver 100A decreases, and the power receiving efficiency η _B of the power receiver 100B increases.

  This is a case where the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver 100B is lowered from 100% in a state where the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver 100A is fixed to 100%. Is the same.

Therefore, if the duty ratio of the PWM drive pattern for driving either one of the switches 130A or 130B of the power receiver 100A or B is adjusted, the power receiving efficiencies η _A and η _B of the power receivers 100A and 100B can be adjusted. The ability to adjust the power receiving efficiencies η _A and η _B is that the received power can be adjusted.

As described above, when the duty ratio of the PWM drive pattern for driving the switch 130A or 130B is changed, the power receiving efficiencies η _A and η _{B of the} secondary resonance coils 110A and 110B of the power receivers 100A and 100B are changed.

  Therefore, if the duty ratio of one of the PWM drive patterns of the switches 130A and 130B of the power receivers 100A and 100B is changed from the reference duty ratio, the ratio at which the power receivers 100A and 100B distribute power Can be changed. The reference duty ratio is 100%, for example.

  By setting the capacitances of the capacitors 141A, 142A, 141B, and 142B to a relatively large value of about 100 μF and inserting the inductor 145, the power receivers 100A and 100B are duty-controlled while suppressing the occurrence of ripple noise. It was found that the received power can be adjusted according to the ratio.

  For this reason, in the embodiment, the duty ratio of one of the PWM drive patterns of the switches 130A and 130B of the power receivers 100A and 100B is changed from the reference duty ratio. The reference duty ratio is, for example, 100%. In this case, one of the duty ratios is set to an appropriate value less than 100%.

  At this time, which of the PWM drive patterns of the switches 130A and 130B is to be changed from the reference duty ratio is determined as follows. The method for setting the duty ratio described here is an example, and the method for setting the duty ratio of the PWM drive pattern for driving the switches 130A and 130B may be a method other than the method described below.

  First, a first value obtained by dividing the rated output of the battery 220A by the power reception efficiency of the secondary side resonance coil 110A, and a second value obtained by dividing the rated output of the battery 220B by the power reception efficiency of the secondary side resonance coil 110B. Find the value of.

  The duty ratio of the PWM drive pattern corresponding to the smaller one of the first value and the second value (100A or 100B) is set to an appropriate value with a duty ratio of less than 100%. .

  The value obtained by dividing the rated output by the power receiving efficiency represents the amount of power (necessary power transmission) that the power transmitter 10 transmits to the power receiver (100A or 100B). The required power transmission amount is the amount of power transmitted from the power transmitter 10 so that the power receiver (100A or 100B) can receive power without generating surplus power or insufficient power.

  Therefore, if the power supply amount to the power receiver (100A or 100B) having the smaller required power transmission amount is reduced, the power supply amount to the power receiver (100A or 100B) having the larger necessary power transmission amount can be increased. As a result, the balance of the amount of power supplied to the power receivers 100A and 100B can be improved.

  As can be seen from FIG. 13, when the duty ratio of any one of the power receivers (100A or 100B) is reduced, the amount of power received by the power receiver (100A or 100B) decreases. Further, the power reception amount of the other power receiver (100A or 100B) is increased in a state where the duty ratio is fixed.

  For this reason, if the duty ratio of the PWM drive pattern corresponding to the power receiver (100A or 100B) having the smaller required power transmission amount is reduced, the power supply amount to the power receiver (100A or 100B) having the smaller required power transmission amount. The power supply amount to the power receiver (100A or 100B) having the larger required power transmission amount can be increased.

  In this way, the balance of the amount of power supplied to the power receivers 100A and 100B may be improved. A specific duty ratio setting method will be described later.

  At this time, the frequency of the PWM drive pattern is set to a frequency equal to or lower than the frequency of AC power transmitted by magnetic field resonance. More preferably, the frequency of the PWM drive pattern is set to a frequency lower than the frequency of AC power transmitted by magnetic field resonance. For example, the frequency of the PWM drive pattern may be set to a frequency that is one or two digits lower than the frequency of the AC power transmitted by magnetic field resonance.

  This is because if the frequency of the PWM drive pattern is higher than the frequency of AC power transmitted by magnetic resonance, the switch 130A or 130B is turned on / off in the middle of one cycle of the full-wave rectified power. This is because the electric energy may not be adjusted properly.

  Therefore, it is necessary to set the frequency of the PWM drive pattern to a frequency equal to or lower than the frequency of the AC power transmitted by magnetic field resonance. At this time, if the frequency of the PWM drive pattern is set to a frequency that is one or two digits lower than the frequency of the AC power transmitted by magnetic resonance, the amount of power can be adjusted more appropriately.

  For example, when the frequency of AC power transmitted by magnetic field resonance is 6.78 MHz, the frequency of the PWM drive pattern may be set to about 100 kHz to several hundred kHz.

  Here, the relationship between the duty ratio of the PWM drive pattern and the received power will be described with reference to FIG.

  FIG. 14 is a diagram illustrating the relationship between the duty ratio of the PWM drive pattern in the power receiver 100 and the received power.

  In FIG. 14, the secondary side resonance coil 110, the rectifier circuit 120, the smoothing capacitor 141, and the switch 130 of the power receiver 100 are shown in a simplified manner, and power waveforms (1), (2), and (3) are shown.

  A power waveform (1) indicates a waveform of power obtained between the secondary side resonance coil 110 and the rectifier circuit 120. The power waveform (2) shows a waveform of power that has been full-wave rectified by the rectifier circuit 120. A power waveform (3) indicates a waveform of power smoothed by the smoothing capacitor 141.

  Here, since the power waveforms on the input side and the output side of the switch 130 are substantially equal, the power waveform (3) is also a power waveform obtained on the output side of the switch 130 (the right side of the switch 130).

  Here, the frequency of the AC voltage output from the AC power supply 1 is 6.78 MHz, and the resonance frequency of the primary side resonance coil 12 and the secondary side resonance coil 21 is 6.78 MHz. The frequency of the PWM pulse of the PWM drive pattern is 300 kHz, and the duty ratio is 50%.

  The power receiver 100 actually has a circuit configuration that forms a loop between the secondary side resonance coil 110 and the battery 220, as shown in FIG.

  Therefore, a current flows through the loop circuit while the switch 130 is on, but no current flows through the loop circuit while the switch 130 is off.

  The power waveform (1) is a waveform in which AC power supplied from the secondary resonance coil 110 to the rectifier circuit 120 flows intermittently according to the on / off state of the switch 130.

  The power waveform (2) is a waveform in which the power that has been full-wave rectified by the rectifier circuit 120 flows intermittently according to the on / off state of the switch 130.

  The power waveform (3) is DC power obtained by smoothing the power supplied from the rectifier circuit 120 to the smoothing capacitor 141. The voltage value of the power waveform (3) increases as the duty ratio increases and decreases as the duty ratio decreases.

  As described above, the voltage value of the DC power output from the smoothing capacitor 141 can be adjusted by adjusting the duty ratio of the drive pattern.

  Next, the duty setting method will be described.

  If the duty ratio of the PWM drive pattern is changed when performing magnetic field resonance type power transmission, the degree of change in power reception efficiency does not change linearly with respect to the degree of change in duty ratio.

  For example, when the duty ratio of the PWM drive pattern corresponding to the power receivers 100A and 100B is 100%, the power receiving efficiency of the secondary side resonance coils 110A and 110B is 40%, respectively.

  In this case, when the duty ratio of the PWM drive pattern corresponding to the power receiver 100B is reduced to 71% in a state where the duty ratio of the PWM drive pattern corresponding to the power receiver 100A is held at 100%, the secondary side resonance coil 110A. And the power receiving efficiency of 110B are 50% and 25%, respectively.

  As described above, since the degree of change in the duty ratio of the PWM drive pattern and the degree of change in power reception efficiency are in a non-linear relationship, table data in which the duty ratio and power reception efficiency are associated with each other is created in advance. A duty ratio for obtaining power reception efficiency may be selected.

  Next, a method in which the power transmitter 10 obtains data representing the power reception efficiency and the rated output from the power receivers 100A and 100B will be described using FIG.

  FIG. 15 is a task diagram showing processing executed by the power transmitter 10 and the power receivers 100A and 100B to set the duty ratio. This task is executed by the control units 15, 150A, and 150B (see FIG. 5).

  First, the power receiver 100A transmits data representing the received power to the power transmitter 10 (step S1A). Similarly, the power receiver 100B transmits data representing the received power to the power transmitter 10 (step S1B). Thereby, the power transmitter 10 receives data representing the received power from the power receivers 100A and 100B (step S1).

  Transmission of data representing received power may be performed by the control units 150A and 150B via the antennas 170A and 170B in response to a request from the power transmitter 10, for example. The data representing the received power may include an identifier for identifying the power receivers 100A and 100B.

  What is necessary is just to acquire the data showing received electric power as follows. First, a signal for setting the duty ratio to 0% is transmitted from the power transmitter 10 to the power receiver 100B by wireless communication, and a signal for setting the duty ratio to 100% is transmitted from the power transmitter 10 to the power receiver 100A by wireless communication. .

  Then, predetermined power is transmitted from the power transmitter 10 to the power receiver 100A by magnetic field resonance, and the power is received by the power receiver 100A. At this time, if a signal representing the amount of power received by the power receiver 100A is transmitted to the power transmitter 10, the power reception efficiency of the power receiver 100A can be measured by the power transmitter 10. At this time, the power receiver 100A is turned off (non-operating state) when the duty ratio is 0%.

  In order to measure the power receiving efficiency of the power receiver 100B, a signal for setting the duty ratio to 0% is transmitted from the power transmitter 10 to the power receiver 100A by wireless communication, and the duty ratio is set from the power transmitter 10 to the power receiver 100B. A signal set to 100% is transmitted by wireless communication. If power is transmitted from the power transmitter 10 to the power receiver 100B by magnetic resonance and a signal representing the amount of power received by the power receiver 100B is transmitted to the power transmitter 10, the power receiving efficiency of the power receiver 100B is measured by the power transmitter 10. can do.

  Next, the power receiver 100A transmits data representing the rated output to the power transmitter 10 (step S2A). Similarly, the power receiver 100B transmits data representing the rated output to the power transmitter 10 (step S2B). Thereby, the power transmitter 10 receives data representing the rated output from the power receivers 100A and 100B (step S2).

  Data representing the rated output of the electronic devices 200A and 200B is stored in advance in the internal memory of the control units 150A and 150B, for example, and after the data representing the power reception efficiency is sent, the control units 150A and 150B perform the antennas 170A and 170B. It is sufficient to transmit to the power transmitter 10 via.

  Next, the power transmitter 10 transmits power to the power receivers 100A and 100B based on data representing the power receiving efficiency of the power receiver 100A, data representing the rated output, data representing the power receiving efficiency of the power receiver 100B, and data representing the rated output. The duty ratio of the corresponding PWM drive pattern is calculated (step S3). One of the duty ratios is a reference duty ratio (100%), and the other duty ratio is an optimized duty ratio of less than 100%. Details of step S3 will be described later with reference to FIG.

  Next, the power transmitter 10 transmits data representing the duty ratio to the power receivers 100A and 100B (step S4). Then, the power receivers 100A and 100B receive the duty ratio (steps S4A and S4B).

  Here, the control unit 15 of the power transmitter 10 is set to transmit data representing the duty ratio to the power receivers 100A and 100B via the antenna 16 after calculating the duty ratio.

  Control units 150A and 150B of power receivers 100A and 100B set the duty ratio to a PWM drive pattern (steps S5A and S5B).

  The power transmitter 10 starts power transmission (step S6). The process of step S6 may be executed when, for example, notification is sent to the power transmitter 10 indicating that the control units 150A and 150B have completed setting the duty ratio to the PWM drive pattern.

  Here, a method for acquiring data representing the power reception efficiency of the power receivers 100A and 100B will be described with reference to FIGS.

  FIG. 16 is a diagram illustrating an equivalent circuit of the power transmission device 80 and the electronic devices 200A and 200B. The equivalent circuit illustrated in FIG. 16 corresponds to the power transmission device 80 and the electronic devices 200A and 200B illustrated in FIG. However, here, the power transmission device 80 will be described assuming that the primary side coil 11 is not included and the primary side resonance coil 12 is directly connected to the AC power source 1.

In Figure 16, the secondary side resonance coil 110A is a coil _{L RA} and the resistor _{R RA,} smoothing capacitor 141A, 142A is a capacitor _{C SA1, C SA2,} inductor 145A is inductor _{L A,} DC-DC converter 210A and the battery 220A is a resistor _{R LA.}

Similarly, the secondary side resonance coil 110B is a coil _{L RB} and the resistor _{R RB,} smoothing capacitor 141B, 142B are capacitor _{C SB1, C SB2,} inductor 145B is inductor _{L B,} DC-DC converter 210B and the battery 220B is a resistor _{R LB.}

Further, the resonance coil 12 of the power transmission device 80 is a resistor _{R T} and the coil _{L T,} the AC power source 1 is a power supply _{V S} and resistor _{R S.}

The mutual inductance between the power transmission device 80 and the electronic device 200A is M _TA , the mutual inductance between the power transmission device 80 and the electronic device 200B is M _TB , and the mutual inductance between the electronic devices 200A and 200B is M _AB .

Here, when comparing the mutual inductance _{M TA} and mutual inductance _{M TB,} since the mutual inductance _{M AB} enough negligible small, here, a mutual inductance _{M TA} and mutual inductance discuss _{M TB.}

The mutual inductance _MTA is determined by the power reception efficiency between the power transmission device 80 and the power receiver 100A of the electronic device 200A. This is because the power reception efficiency is determined by the position (distance) and posture (angle) of the power receiver 100A with respect to the power transmission device 80. Similarly, the mutual inductance M _TB is determined by the power reception efficiency between the power transmission device 80 and the power receiver 100B of the electronic device 200B.

  The power receiving efficiency of the power receiver 100A can be obtained by transmitting power from the power transmitter 10 to the power receiver 100A with the power receiver 100B turned off and measuring the amount of power received by the power receiver 100A. Similarly, the power receiving efficiency of the power receiver 100B can be obtained by transmitting power from the power transmitter 10 to the power receiver 100B with the power receiver 100A turned off, and measuring the amount of power received by the power receiver 100B. it can.

Therefore, by obtaining alone power receiving efficiency of the power receiving device 100A and 100B, the mutual inductance and _{M TA,} mutual inductance can be calculated _{M TB.}

  In the embodiment, the duty ratio of the PWM drive pattern for driving the switch 130A or 130B is changed in order to change the ratio of the power reception efficiency of the secondary resonance coils 110A and 110B of the power receivers 100A and 100B.

For this reason, table data in which the duty ratio is associated with the relationship between the mutual inductance M _TA and the mutual inductance M _TB is prepared in advance, and the duty ratio of the PWM drive pattern is prepared using such table data. Adjust.

Figure 17 is a mutual inductance of M _TA and mutual inductance with respect to the relationship between the M _TB, is a diagram showing a table data associating the duty ratio.

  FIG. 17A shows table data for adjusting the duty ratio of the PWM drive pattern for driving the switch 130A in a state where the duty ratio of the PWM drive pattern for driving the switch 130B is fixed to 100%.

The mutual inductances M _TA 1, M _TA 2, M _TA 3... Actually take a specific value of the mutual inductance M _TA . Similarly, the mutual inductances M _TB 1, M _TB 2, M _TB 3... Actually take a specific value of the mutual inductance M _TB . The duty ratios duty1A, duty2A, duty3A,..., Duty11A, duty12A, duty13A,... Take values of specific duty ratios obtained experimentally.

  FIG. 17B is table data for adjusting the duty ratio of the PWM drive pattern for driving the switch 130B in a state where the duty ratio of the PWM drive pattern for driving the switch 130A is fixed to 100%.

The mutual inductances M _TA 1, M _TA 2, M _TA 3... And the mutual inductances M _TB 1, M _TB 2, M _TB 3... _{Are the same} as those in FIG. The duty ratios duty1B, duty2B, duty3B,..., Duty11B, duty12B, duty13B,... Take values of specific duty ratios obtained experimentally.

The table data shown in FIGS. 17A and 17B are obtained by measuring the mutual inductances M _TA and M _TB with various positions and postures of the power receivers 100A and 100B with respect to the power transmitter 10. It can be created by optimizing the duty ratio.

FIG. 18 is table data in which mutual inductances are associated with M _TA and M _TB and power reception efficiency. (A) of FIG. 18, the mutual inductance _{M TA,} a table data that associates a power receiving efficiency of the power receiving device 100A, (B) in FIG. 18, the mutual inductance and _{M TB,} receiving the power receiver 100B It is table data that associates efficiency.

The mutual inductances M _TA and M _TB are determined by power receiving efficiencies E _A and E _{B of} the power transmitting device 80 and the power receivers 100A and 100B, respectively.

In FIG. 18A, mutual inductances M _TA 1, M _TA 2,... Are associated with power receiving efficiencies E _A 1, E _A 2,. In FIG. 18B, the mutual inductances M _TB 1, M _TB 2,... Are associated with the power receiving efficiencies E _B 1, E _B 2,.

Measure the mutual inductance of the power receivers 100A and 100B in advance through experiments such as M _TA and M _TB and power reception efficiency, and create table data as shown in FIGS. 18A and 18B. For example, the mutual inductances M _TA and M _TB of the power receivers 100A and 100B can be obtained from the power reception efficiency of the power receivers 100A and 100B. Or you may obtain | require by Simulation.

  Next, a method for setting the duty ratio will be described with reference to FIG.

  FIG. 19 is a flowchart illustrating a method in which the power transmitter 10 according to the embodiment sets the duty ratio of the power receiver 100A or 100B. This flow represents processing executed by the control unit 15 of the power transmitter 10, and shows details of the processing content of step S3 in FIG.

  When the control unit 15 receives the signal representing the received power from the power receivers 100A and 100B to obtain the power reception efficiency, receives the signal representing the rated output from the power receivers 100A and 100B, and proceeds to step S3, it shows in FIG. Start processing.

  The control unit 15 divides the rated output of the battery 220A by the power receiving efficiency of the secondary side resonance coil 110A and the first value obtained by dividing the rated output of the battery 220A by the power reception efficiency of the secondary side resonance coil 110B. A second value to be obtained is obtained, and it is determined whether or not the first value is larger than the second value (step S31).

  When determining that the first value is larger than the second value (S31: YES), the controller 15 sets the duty ratio of the PWM drive pattern for driving the switch 130A of the power receiver 100A to 100% (step S32A). ).

Next, the control unit 15 sets the duty ratio of the PWM drive pattern that drives the switch 130B of the power receiver 100B (step S32A). Specifically, based on the table data shown in FIGS. 18A and 18B, the control unit 15 reciprocally receives the power receiving efficiencies E _A and E _B of the power receiving devices 100A and 100B from the power receiving devices 100A and 100B. The inductance is determined as M _TA and M _TB . Then, the control unit 15, the table data shown in (B) of FIG. 17, the power receiving device 100A, the mutual inductance of the 100B based on the _{M TA, M TB,} the PWM driving pattern for driving the switch 130B of the power receiver 100B Obtain the duty ratio.

  When the process of step S32A ends, the control unit 15 advances the flow to step S4 (see FIG. 15).

  Further, when determining that the first value is smaller than the second value (S31: NO), the control unit 15 sets the duty ratio of the PWM drive pattern for driving the switch 130B of the power receiver 100B to 100% ( Step S32B).

Next, the control unit 15 sets the duty ratio of the PWM drive pattern that drives the switch 130A of the power receiver 100A (step S32B). Specifically, based on the table data shown in FIGS. 18A and 18B, the control unit 15 reciprocally receives the power receiving efficiencies E _A and E _B of the power receiving devices 100A and 100B from the power receiving devices 100A and 100B. The inductance is determined as M _TA and M _TB . Then, the control unit 15, the table data shown in (A) of FIG. 17, the power receiving device 100A, the mutual inductance of the 100B based on the _{M TA, M TB,} the PWM driving pattern for driving the switch 130A of the power receiver 100A Obtain the duty ratio.

  When the process of step S32B ends, the control unit 15 advances the flow to step S4 (see FIG. 15).

  As described above, the control unit 15 sets the duty ratio of the PWM drive pattern that drives the switches 130A and 130B of the power receivers 100A and 100B.

  As described above, according to the embodiment, the capacitance of the smoothing capacitors 141A, 142A, 141B, and 142B is set to a relatively large value, and the inductor 145 is inserted, thereby suppressing the occurrence of ripple noise. It has been found that the received power can be adjusted according to the duty ratio by the power receivers 100A and 100B. That is, it has been found that it is possible to achieve both suppression of ripple noise and securing of a dynamic range.

  In determining the duty ratio, the required power transmission amount to the power receivers 100A and 100B is determined by the power reception efficiency of the secondary resonance coils 110A and 110B of the power receivers 100A and 100B and the rated output of the electronic devices 200A and 200B. Ask.

  Then, the duty ratio of the PWM drive pattern corresponding to the power receiver (100A or 100B) having the smaller required power transmission amount among the power receivers 100A and 100B is decreased.

  As a result, if the duty ratio of the PWM drive pattern corresponding to the power receiver (100A or 100B) having the smaller required power transmission amount is reduced, the power supply amount to the power receiver (100A or 100B) having the smaller required power transmission amount The power supply amount to the power receiver (100A or 100B) having the larger required power transmission amount can be increased.

  In this way, the balance of the amount of power supplied to the power receivers 100A and 100B is improved.

  Therefore, according to the embodiment, the power receiver 100A or 100B that can improve the balance of the power supply amount can be provided. Moreover, according to the embodiment, it is possible to provide the power transmission system 500 that can improve the balance of the power supply amount.

  In the above description, the mode in which the capacitance of the smoothing capacitors 141A, 142A, 141B, and 142B is set to a relatively large value of about 100 μF has been described. However, the optimum capacitances of the smoothing capacitors 141A, 142A, 141B, and 142B vary depending on the amount of power transmitted from the power transmission device 80 and the amount of power received by the power receivers 100A and 100B. For this reason, what is necessary is just to set it as big as the ripple noise does not generate | occur | produce according to the electric energy to transmit, and the electric energy to receive.

  In the above description, the inductor 145 is inserted between the switch 130 and the smoothing capacitor 142 in series with the line 125A. However, the positions of the inductor 145 and the switch 130 may be interchanged. That is, the line 125A between the smoothing capacitor 141 and the smoothing capacitor 142 may be inserted in series so that the inductor 145 is located on the smoothing capacitor 141 side and the switch 130 is located on the smoothing capacitor 142 side.

  Further, in the above, by reducing the duty ratio of the PWM drive pattern corresponding to the power receiver (100A or 100B) having the smaller required power transmission amount between the two power receivers 100A and 100B, the power to the power receivers 100A and 100B is reduced. The embodiment for improving the balance of the power supply amount has been described.

  However, more than two power receivers may be charged at the same time. In such a case, the duty ratio of the PWM drive pattern of the power receiver other than the power receiver having the maximum required power amount, that is, the power amount obtained by dividing each rated power by each power receiving efficiency should be reduced. Good.

  In the above description, the electronic devices 200A and 200B are described as an example of a terminal such as a tablet computer or a smartphone. However, the electronic devices 200A and 200B are, for example, a notebook PC (Personal Computer), a mobile phone, and the like. An electronic device incorporating a rechargeable battery such as a telephone terminal, a portable game machine, a digital camera, or a video camera may be used.

  Although the power receiver and the power transmission system according to the exemplary embodiment of the present invention have been described above, the present invention is not limited to the specifically disclosed embodiment, and is not limited to the claims. Various modifications and changes can be made without departing from the above.

DESCRIPTION OF SYMBOLS 10 Power transmitter 11 Primary side coil 12 Primary side resonant coil 13 Matching circuit 14 Capacitor 15 Control part 100, 100A, 100B Power receiver 110, 110A, 110B Secondary side resonant coil 120, 120A, 120B Rectifier circuit 125A, 125B Line 130, 130A, 130B Switch 141, 141A, 141B, 142, 142A, 142B Smoothing capacitor 145, 145A, 145B Inductor 150, 150A, 150B Control unit 160A, 160B Output terminal 170A, 170B Antenna 200A, 200B Electronic device 500 Power transmission system

Claims (12)

A first secondary side resonance coil that receives power from the primary side resonance coil by magnetic field resonance or electric field resonance generated between the primary side resonance coil and the primary side resonance coil;
A rectifier circuit connected to the first secondary resonance coil and full-wave rectifying AC power input from the first secondary resonance coil;
A first line on the high potential side connected to the output side of the rectifier circuit;
A second line on the low potential side connected to the output side of the rectifier circuit;
A pair of output terminals respectively connected to the first line and the second line;
A first smoothing capacitor provided between the first line and the second line between the rectifier circuit and the pair of output terminals;
A second smoothing capacitor provided between the first line and the second line between the first smoothing capacitor and the pair of output terminals;
A switch that is inserted in series with the first line between the first smoothing capacitor and the second smoothing capacitor, and switches a connection state of the first line;
An inductor inserted in series with the first line between the first smoothing capacitor and the switch or between the switch and the second smoothing capacitor;
And a drive control unit that drives the switch with a first PWM drive pattern.   The drive control unit is generated between a first power receiving efficiency of the first secondary resonance coil, a first rated output of a first load connected to the pair of output terminals, and the primary resonance coil. A second power receiving efficiency of a second secondary resonance coil of another power receiver that receives power from the primary resonance coil by magnetic field resonance, and a second load supplied with power from the other power receiver. The power receiver according to claim 1, wherein the first PWM drive pattern is determined by a first duty ratio set based on a second rated output and a first frequency equal to or lower than a frequency of the magnetic field resonance. The first duty ratio is a first value obtained by dividing the first rated output by the first power receiving efficiency, and a second value obtained by dividing the second rated output by the second power receiving efficiency. If the value is smaller than the value, the predetermined duty ratio is set to be smaller than the first initial value of the first duty ratio,
The predetermined duty ratio is a duty ratio that improves a balance of power received by the first load and the second load as compared with a case where the first duty ratio is the first initial value. 2. The power receiver according to 2.   The first duty ratio is a first value obtained by dividing the first rated output by the first power receiving efficiency, and a second value obtained by dividing the second rated output by the second power receiving efficiency. The power receiver according to claim 3, wherein the power receiver is set to the first initial value when larger than the value.   The power receiver according to claim 4, wherein the first initial value is 100%. A first secondary side resonance coil that receives power from the primary side resonance coil by magnetic field resonance or electric field resonance generated between the primary side resonance coil and the primary side resonance coil;
A rectifier circuit connected to the first secondary resonance coil and full-wave rectifying AC power input from the first secondary resonance coil;
A first line on the high potential side connected to the output side of the rectifier circuit;
A second line on the low potential side connected to the output side of the rectifier circuit;
A pair of output terminals respectively connected to the first line and the second line;
A first smoothing capacitor provided between the first line and the second line between the rectifier circuit and the pair of output terminals;
A second smoothing capacitor provided between the first line and the second line between the first smoothing capacitor and the pair of output terminals;
A switch that is inserted in series with the first line between the first smoothing capacitor and the second smoothing capacitor, and switches a connection state of the first line;
An inductor inserted in series with the first line between the first smoothing capacitor and the switch or between the switch and the second smoothing capacitor;
A power receiver having a drive control unit that drives the switch with a first PWM drive pattern;
With other power receivers,
A power transmission system comprising: a power transmitter having the primary side resonance coil.   The drive control unit is generated between a first power receiving efficiency of the first secondary resonance coil, a first rated output of a first load connected to the pair of output terminals, and the primary resonance coil. A second power receiving efficiency of a second secondary resonance coil of another power receiver that receives power from the primary resonance coil by magnetic field resonance, and a second load supplied with power from the other power receiver. The power transmission system according to claim 6, wherein the first PWM drive pattern is determined by a first duty ratio set based on a second rated output and a first frequency equal to or lower than the frequency of the magnetic field resonance.   The power transmission system according to claim 7, wherein the other power receiver has the same circuit configuration as the power receiver. In the other power receiver, the second power receiving efficiency, the second rated output, the first power receiving efficiency, the second duty ratio set based on the first rated output, and the magnetic field resonance The switch is driven with a second PWM drive pattern determined by a second frequency equal to or lower than the frequency,
The second duty ratio is a first value obtained by dividing the second rated output by the second power receiving efficiency, and obtained by dividing the first rated output by the first power receiving efficiency. A smaller value than the second initial value of the second duty ratio is set to a predetermined duty ratio,
The predetermined duty ratio is a duty ratio that improves a balance of power received by the first load and the second load as compared with a case where the second duty ratio is the second initial value. 8. The power transmission system according to 8.   The second duty ratio is a first value obtained by dividing the second rated output by the second power receiving efficiency, and obtained by dividing the first rated output by the first power receiving efficiency. The power transmission system according to claim 9, wherein the power transmission system is set to the second initial value when larger than the value.   The power transmission system according to claim 10, wherein the second initial value is 100%. The power receiver, the other power receiver, and the power transmitter each include a first communication unit, a second communication unit, and a third communication unit,
The third communication unit of the power transmitter receives first data representing the first power reception efficiency and the first rated output from the first communication unit of the power receiver, and the third power unit of the other power receiver Receiving second data representing the second power receiving efficiency and the second rated output from a second communication unit;
The power transmitter calculates the first value based on the first power reception efficiency and the first rated output represented by the first data received by the third communication unit, and the third communication unit receives the first value. Calculating the second value based on the second power receiving efficiency represented by the second data and the second rated output;
The third communication unit of the power transmitter transmits data representing the first value to the first communication unit of the power receiver, and the second communication unit of the other power receiver receives the second communication unit. The power transmission system according to claim 9, wherein data representing a value is transmitted.

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