Wireless power supply system

Abstract

This wireless power supply system includes: a transmission device provided with a transmission resonance circuit including a transmission coil and a transmission resonance capacitor; and a reception device that is electrically connected to a load and includes a reception resonance circuit including a reception coil and a reception resonance capacitor. Electromagnetic field resonance coupling is formed by the transmission coil and the reception coil to supply power from the transmission device to the reception device. The transmission device includes a transmission power conversion circuit and a transmission control circuit. The transmission power conversion circuit is electrically connected to an input DC power supply and the transmission coil, converts DC power supplied from the input DC power supply into AC power by switching operation by a semiconductor switching element, and causes the AC current to flow to the transmission coil. The transmission control circuit controls the switching operation of the transmission power conversion circuit. The reception device includes a reception power rectification circuit, a smoothing circuit, and a rectification control circuit. The reception power rectification circuit is electrically connected to the reception resonance circuit, and rectifies the power of the high frequency AC received by the reception coil. The smoothing circuit is electrically connected to the reception power rectification circuit, and smooths the power rectified by the reception power rectification circuit to the reception DC voltage. The rectification control circuit is electrically connected to the reception resonance circuit, and controls execution and stop of the rectification operation of the reception power rectification circuit. The capacitance of the transmission resonance capacitor is equal to or less than the capacitance at which an input impedance seen from the transmission coil to the load side becomes a minimum at the switching frequency, and the capacitance is set so that when the rectification control circuit stops the rectification operation of the reception power rectification circuit and performs power reception cutoff control, the DC current input from the input DC power supply to the transmission device decreases as the coupling coefficient between the transmission coil and the reception coil increases.

Description

Wireless Power Supply System

[0001] The present invention relates to a wireless power supply system that wirelessly supplies power from a power transmitting device to a power receiving device using electromagnetic resonance coupling.

[0002] Patent Documents 1 to 3 describe wireless power supply systems, each of which describes a circuit configuration for cutting off power reception.

[0003] International Publication No. 2017-213032 Patent No. 6677306 Patent No. 6379660

[0004] In conventional wireless power transfer systems such as those disclosed in Patent Documents 1 to 3, resonance parameters are set to improve power supply efficiency when power reception is not interrupted (steady state). On the other hand, when power reception is interrupted or when there is no load or a light load, a large resonant current flows due to changes in the resonance conditions of the power transmission resonant circuit. As a result, in the power transmission device, when power reception is interrupted, the input current increases, power loss increases, and heat generation increases.

[0005] Furthermore, when power reception is interrupted, the resonant current in the power transmitting device increases, generating a strong magnetic field. As a result, the power receiving coil in the power receiving device is subjected to this strong magnetic field, resulting in problems such as increased power loss and heat generation in the power receiving resonant circuit and power reception interruption circuit. These problems become more pronounced as the coupling coefficient between the power transmitting coil and the power receiving coil increases.

[0006] Therefore, the present invention aims to suppress an increase in power loss and suppress heat generation in the power transmitting device and the power receiving device in a wireless power supply system in which the coupling coefficient varies from large to small values ​​and there is a high degree of freedom in the placement of the power transmitting device and the power receiving device, even when power reception is interrupted.

[0007] A wireless power supply system according to one embodiment of the present invention comprises a power transmitting device having a power transmitting resonant circuit including a power transmitting coil and a power transmitting resonant capacitor, and a power receiving device having a power receiving resonant circuit including a power receiving coil and a power receiving resonant capacitor and electrically connected to a load, and an electromagnetic field resonant coupling is formed by the power transmitting coil and the power receiving coil to supply power from the power transmitting device to the power receiving device.

[0008] The power transmitting device includes a transmission power conversion circuit and a transmission control circuit. The transmission power conversion circuit is electrically connected to an input DC power source and a transmission coil, and converts DC power supplied from the input DC power source into AC power through switching operations of semiconductor switching elements, and passes the AC current through the transmission coil. The transmission control circuit controls the switching operations of the transmission power conversion circuit.

[0009] The power receiving device includes a power receiving rectifier circuit, a smoothing circuit, and a rectification control circuit. The power receiving rectifier circuit is electrically connected to the power receiving resonant circuit and rectifies the high-frequency AC power received by the power receiving coil. The smoothing circuit is electrically connected to the power receiving rectifier circuit and smoothes the power rectified by the power receiving rectifier circuit into a received DC voltage. The rectification control circuit is electrically connected to the power receiving resonant circuit and controls the start and stop of the rectification operation of the power receiving rectifier circuit.

[0010] The capacitance of the transmitting resonant capacitor is set to be equal to or less than the capacitance at which the input impedance seen from the transmitting coil to the load side is minimized at the switching frequency, and when the rectification control circuit stops the rectification operation of the receiving rectification circuit and performs power reception cut-off control, the capacitance is set so that the DC current input from the input DC power source to the transmitting device decreases as the coupling coefficient between the transmitting coil and receiving coil increases.

[0011] In this configuration, as the coupling coefficient between the power transmitting coil and the power receiving coil increases, the DC current input from the input DC power source to the power transmitting device decreases. This reduces the increase in power consumption of the power transmitting device and the heat generation of the power transmitting device when the power transmitting coil can supply a large amount of power to the power receiving coil and the rectification operation of the power receiving device is stopped (power receiving cut-off state). Furthermore, the power receiving resonant circuit is prevented from being exposed to a strong magnetic field, reducing the current flowing through the power receiving resonant circuit and the heat generation of the power receiving device. On the other hand, when the coupling coefficient between the power transmitting coil and the power receiving coil is small, the power supplied from the power transmitting device to the power receiving device is small and the heat generation of the power transmitting device and the power receiving device is reduced.

[0012] According to this invention, in a wireless power supply system in which the coupling coefficient varies from large to small values ​​and there is a high degree of freedom in the placement of the power transmitting device and the power receiving device, even when power reception is interrupted, it is possible to suppress an increase in power loss and suppress heat generation in the power transmitting device and the power receiving device.

[0013] FIG. 1 is a functional block diagram showing an example of a wireless power supply system according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing an example of a power transmitting device according to an embodiment of the present invention. FIG. 3 is a functional block diagram showing an example of a power receiving device according to an embodiment of the present invention. FIG. 4 is a graph showing an example of the relationship between the distance between the power transmitting coil and the power receiving coil and the power transmission current. FIG. 5 is a graph showing a simulation of the relationship between the frequency and the power transmission current for each coupling coefficient k when the resonant frequency frp of the power transmitting resonant circuit is set higher than the switching frequency ftyp in a power receiving cutoff state. FIG. 6 is a graph showing a simulation of the relationship between the frequency and the power transmission current for each coupling coefficient k when the resonant frequency frp of the power transmitting resonant circuit is set lower than the switching frequency ftyp in a power receiving cutoff state (reference condition). FIG. 7 is a graph showing the relationship between the power transmitting capacitance and the input DC current value at a predetermined coupling coefficient k when power receiving is cut off. FIG. 8 is a graph showing a simulation of the relationship between the power transmitting resonant capacitance and the power receiving circuit output power. Fig. 9 is a graph showing a simulation result of the relationship between the frequency and the power transmission current for each coupling coefficient k when the resonant frequency frp of the power transmission resonant circuit is set higher than the switching frequency ftyp in the power reception interruption stopped state. Fig. 10 is a functional block diagram showing an example of a derived example of a power transmission device according to an embodiment of the present invention. Figs. 11(A), 11(B), and 11(C) are circuit diagrams showing example patterns of the power transmission resonant circuit and the power receiving resonant circuit.

[0014] A wireless power supply system according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a functional block diagram showing an example of a wireless power supply system according to an embodiment of the present invention. Fig. 2 is a functional block diagram showing an example of a power transmitting device according to an embodiment of the present invention. Fig. 3 is a functional block diagram showing an example of a power receiving device according to an embodiment of the present invention.

[0015] (Configuration of Wireless Power Supply System 10) As shown in FIGS. 1, 2, and 3, the wireless power supply system 10 includes a power transmitting device 20 and a power receiving device 30.

[0016] (Configuration of power transmission device 20) The power transmission device 20 includes a DC power supply 21, an input capacitor 22, a power transmission control circuit 23, a power transmission power conversion circuit 24, and a power transmission resonance circuit 25. The power transmission power conversion circuit 24 includes a switching element QH and a switching element QL. The switching element QH and the switching element QL are configured by semiconductor switching elements for power conversion.

[0017] The input capacitor 22 is connected in parallel to the DC power supply 21. A drain terminal of a switching element QH of the transmission power conversion circuit 24 is connected to a node (electrical connection point) between the positive electrode of the DC power supply 21 and the input capacitor 22.

[0018] The source terminal of the switching element QH is connected to the drain terminal of the switching element QL. The source terminal of the switching element QL is connected to the negative electrode of the DC power supply 21 and the node of the input capacitor 22. The node of the negative electrode of the DC power supply 21 and the input capacitor 22 is connected to a reference potential.

[0019] The power transmission control circuit 23 is configured by an MCU etc. The power transmission control circuit 23 is connected to the gate terminal of the switching element QH and the gate terminal of the switching element QL.

[0020] The power transmitting resonant circuit 25 includes a power transmitting coil 251 and a power transmitting resonant capacitor 252. The power transmitting resonant capacitor 252 is connected in series to the power transmitting coil 251. As a result, the power transmitting resonant circuit 25 forms a series resonant circuit of the power transmitting coil 251 and the power transmitting resonant capacitor 252.

[0021] One input terminal of the power transmitting resonant circuit 25 is connected to the node between the switching element QH and the switching element QL, and the other input terminal of the power transmitting resonant circuit 25 is connected to the source terminal of the switching element QL.

[0022] (Configuration of power receiving device 30) The power receiving device 30 includes a power receiving resonant circuit 31, a power receiving rectifier circuit 32, a smoothing circuit 33, and a rectifier control circuit 34. The power receiving device 30 also includes a charging circuit 351, a battery BAT, a HI-side output terminal POH, and a LOW-side output terminal POL.

[0023] The power receiving resonant circuit 31 includes a power receiving coil 311 and a power receiving resonant capacitor 312. The power receiving resonant capacitor 312 is connected in parallel to the power receiving coil 311. As a result, the power receiving resonant circuit 31 forms a parallel resonant circuit of the power receiving coil 311 and the power receiving resonant capacitor 312.

[0024] The power receiving rectifier circuit 32 includes a diode D11, a diode D12, a diode D21, and a diode D22, and forms a full-wave rectifier circuit. The diodes D11 and D12 are connected in series, and the diode D12 is connected to a reference potential. The diodes D21 and D22 are connected in series, and the diode D22 is connected to the reference potential.

[0025] A node between the anode of the diode D11 and the cathode of the diode D12 is connected to one output terminal of the power receiving resonant circuit 31, and a node between the anode of the diode D21 and the cathode of the diode D22 is connected to the other output terminal of the power receiving resonant circuit 31. A node between the cathode of the diode D11 and the cathode of the diode D21 is connected to a HI side output terminal of the power receiving rectifier circuit 32, and a node between the anode of the diode D12 and the anode of the diode D22 is connected to a LOW side output terminal of the power receiving rectifier circuit 32.

[0026] A switching element Q1 is connected in parallel to the diode D12. A switching element Q2 is connected in parallel to the diode D22. The switching elements Q1 and Q2 are switching elements using power semiconductors, and are configured by, for example, FETs. The switching elements Q1 and Q2 are elements used for power receiving control.

[0027] A smoothing circuit 33 is connected to the HI-side output terminal and the LOW-side output terminal of the power receiving rectifier circuit 32. More specifically, a smoothing capacitor is connected between the HI-side output terminal and the LOW-side output terminal of the power receiving rectifier circuit 32, and this smoothing capacitor constitutes the smoothing circuit 33.

[0028] The output voltage of the smoothing circuit 33, that is, the voltage across the smoothing capacitor, is the receiving voltage (receiving DC voltage) Vrec in the power receiving device 30.

[0029] An input terminal of a charging circuit 351 is connected to the output terminals (Hi-side output terminal and Low-side output terminal) of the smoothing circuit 33. The Hi-side terminal of the battery BAT is connected to the Hi-side output terminal of the charging circuit 351, and the Low-side terminal of the battery BAT is connected to the Low-side output terminal of the charging circuit 351. The Hi-side terminal of the battery BAT is connected to the Hi-side output terminal POH of the power receiving device 30, and the Low-side terminal of the battery BAT is connected to the Low-side output terminal POL of the power receiving device 30. The charging circuit 351 and the battery BAT form a load 35 of the power receiving device 30. Note that if there are electronic devices or electronic circuits connected to the Hi-side output terminal POH and the Low-side output terminal POL of the power receiving device 30, these electronic devices and electronic circuits are also included in the load 35.

[0030] The rectification control circuit 34 includes a comparator and a reference voltage generating unit. The reference voltage generating unit generates a reference voltage Vref, which is a predetermined DC voltage. The reference voltage Vref corresponds to the "control value." The comparator is composed of an operational amplifier. The non-inverting input terminal of the operational amplifier is connected to the high-side output terminal of the smoothing circuit 33. The inverting input terminal of the operational amplifier is connected to the positive electrode of the reference voltage generating unit. The negative electrode of the reference voltage generating unit is connected to the reference potential.

[0031] The output terminal of the rectification control circuit 34 (the output terminal of the comparator) is connected to the gate terminal of the switching element Q1 and the gate terminal of the switching element Q2 of the power receiving rectification circuit 32 .

[0032] (Power Supply Operation) The power transmission control circuit 23 is driven by receiving power supply from the DC power supply 21. The power transmission control circuit 23 may receive power supply via an LDO or the like.

[0033] The power transmission control circuit 23 generates a switching drive signal of a predetermined frequency and outputs it to the switching elements QH and QL. As a result, the power transmission control circuit 23 controls the switching of the switching elements QH and QL at a predetermined frequency (switching frequency). The switching frequency is set to, for example, 6.78 MHz.

[0034] The transmission power conversion circuit 24 converts the DC power supplied from the DC power supply 21 into AC power of a frequency corresponding to the switching frequency by the switching operation (on / off switching operation) of the switching element QH and the switching element QL, and outputs the AC current to the transmission resonant circuit 25.

[0035] The power transmitting resonant circuit 25 is set to have a predetermined resonant frequency. In this case, the inductance of the power transmitting coil 251 is predetermined based on the shape of the power transmitting device 20, the switching frequency (e.g., 6.78 MHz) used for electromagnetic field resonance coupling between the power transmitting coil 251 and the power receiving coil 311, and the like. Therefore, the power transmitting resonant circuit 25 realizes the predetermined resonant frequency by appropriately setting the capacitance of the power transmitting resonant capacitor 252. Note that a detailed method for setting the power transmitting resonant capacitance Crp of the power transmitting resonant capacitor 252 will be described later.

[0036] The power transmitting coil 251 generates an alternating magnetic field by the AC current input from the power transmitting power conversion circuit 24. The frequency of this alternating magnetic field is determined by the switching frequency of the power transmitting power conversion circuit 24. The operating state of the power receiving device 30 is based on the state of the load 35 of the power receiving device 30 and the power receiving cut-off state described below.

[0037] The power receiving coil 311 generates an AC power receiving current by electromagnetic resonance coupling with the power transmitting coil 251 and outputs the AC power receiving current to the power receiving rectifier circuit 32 .

[0038] In the power reception cutoff state, the power reception rectifier circuit 32 rectifies the AC power reception current and outputs the rectified current. In the power reception cutoff state, the power reception rectifier circuit 32 stops rectifying the power reception current.

[0039] The smoothing circuit 33 smoothes the rectified current and rectified voltage and outputs a DC receiving voltage Vrec. The charging circuit 351 converts the DC receiving voltage Vrec into a charging voltage. The battery BAT is charged by the applied charging voltage (charging current). Note that the charging circuit 351 can be omitted by using the rectification control circuit 34 (described later) to adjust the receiving voltage. The battery BAT can also be omitted.

[0040] The rectification control circuit 34 compares the receiving voltage Vrec with the reference voltage Vref and outputs a control signal corresponding to the comparison result between the receiving voltage Vrec and the reference voltage Vref to the switching elements Q1 and Q2 of the receiving rectification circuit 32.

[0041] Specifically, if the receiving voltage Vrec is higher than the reference voltage Vref, the rectification control circuit 34 outputs an ON control signal to the switching elements Q1 and Q2 of the receiving rectifier circuit 32. This causes the switching elements Q1 and Q2 to be turned on (conductive), and the receiving rectifier circuit 32 stops rectifying. In other words, if the receiving voltage Vrec is higher than the reference voltage Vref, the rectification control circuit 34 controls the power receiving cutoff so that the power receiving cutoff is active. The power receiving cutoff state (power receiving cutoff active state) corresponds to a no-load state (or a low-load state) when viewed from the power transmitting coil 251 toward the load 35.

[0042] On the other hand, if the receiving voltage Vrec is lower than the reference voltage Vref, the rectification control circuit 34 outputs an OFF control signal to the switching elements Q1 and Q2 of the receiving rectifier circuit 32. This causes the switching elements Q1 and Q2 to be turned off (open), and the receiving rectifier circuit 32 performs rectification. In other words, if the receiving voltage Vrec is lower than the reference voltage Vref, the rectification control circuit 34 controls the receiving rectifier circuit 32 to enter a power receiving operating state.

[0043] By performing such control, the power receiving device 30 achieves power reception interruption and power reception voltage adjustment. That is, by intermittently interrupting power reception, the power receiving device 30 adjusts the voltage supplied to the circuit (load 35) subsequent to the charging circuit 351 to a desired voltage value. This allows the wireless power transfer system 10 to suppress undesirable high voltage states during steady power supply and stabilize the voltage at a predetermined value. This allows for lower voltage resistance of circuit components constituting the charging circuit 351 and the like of the power receiving device 30. Furthermore, the wireless power transfer system 10 can eliminate the need for a voltage stabilization circuit (LDO, buck converter) in the power receiving device 30.

[0044] Furthermore, when the charging voltage suddenly increases (overvoltage state), the power receiving device 30 cuts off the power reception, thereby protecting the circuits (load 35) subsequent to the charging circuit 351 from the overvoltage.

[0045] In the wireless power supply system 10 having the above-described configuration and operation, the capacitance of the power transmission resonant capacitor 252 (power transmission resonant capacitance Crp) is set as follows.

[0046] First, when setting the power transmission resonant capacitance Crp, the setting of the resonant frequency frp that is uniquely determined by the power transmission resonant capacitance Crp will be described.

[0047] Fig. 4 is a graph showing an example of the relationship between the distance between the power transmitting coil and the power receiving coil and the power transmitting current. In Fig. 4, ftyp is a frequency that matches the switching frequency. frp is the resonant frequency of the power transmitting resonant circuit 25 (power transmitting resonant frequency). The solid line shows the characteristic of frp > ftyp, and the dashed line shows the characteristic of frp < ftyp. Fig. 4 shows the case when the power receiving is cut off (no load state: the receiving DC current is 0 mA).

[0048] First, the reference configuration for the present invention is frp<ftyp. As shown by the dashed line in Fig. 4, when frp<ftyp, that is, when the resonant frequency frp of the power transmitting resonant circuit 25 is lower than the switching frequency ftyp, the shorter the distance between the power transmitting coil 251 and the power receiving coil 311, the larger the power transmitting current (current (input DC current) flowing through the power transmitting power conversion circuit 24). In other words, when the resonant frequency frp of the power transmitting resonant circuit 25 is lower than the switching frequency ftyp, the larger the coupling coefficient k of the power transmitting coil 251 and the power receiving coil 311, the larger the power transmitting current.

[0049] Therefore, when the power receiving device 30 is in a power interruption state, in other words, when power supply to the power receiving device 30 is unnecessary, the larger the coupling coefficient k, the larger the unnecessary current flowing through the power transmitting device 20. This makes it easier for the power transmitting device 20 to generate heat.

[0050] 4, when frp>ftyp, that is, when the resonant frequency frp of the power transmitting resonant circuit 25 is higher than the switching frequency ftyp, the shorter the distance between the power transmitting coil 251 and the power receiving coil 311, the smaller the power transmitting current (current flowing through the power transmitting power conversion circuit 24). In other words, when the resonant frequency frp of the power transmitting resonant circuit 25 is higher than the switching frequency ftyp, the larger the coupling coefficient k of the power transmitting coil 251 and the power receiving coil 311, the smaller the power transmitting current.

[0051] Fig. 5 is a graph showing a simulation result of the relationship between the frequency and the power transmission current for each coupling coefficient k when the resonant frequency frp of the power transmission resonant circuit is set higher than the switching frequency ftyp in the power reception cutoff state. Fig. 6 is a graph showing a simulation result of the relationship between the frequency and the power transmission current for each coupling coefficient k when the resonant frequency frp of the power transmission resonant circuit is set lower than the switching frequency ftyp in the power reception cutoff state (reference condition).

[0052] 5 and 6, when the coupling coefficient k changes, the frequency of the resonant peak of the electromagnetic resonance coupling changes, and the frequency characteristics (transition of the transmission current with frequency) also change. More specifically, the frequency of the resonant peak shifts to the higher frequency side as the coupling coefficient k increases.

[0053] 5, the resonant frequency frp of the power transmitting resonant circuit 25 when the coupling coefficient k = 0 is set higher than the switching frequency ftyp. By setting it in this manner, the power transmitting current at the switching frequency ftyp is kept small as the coupling coefficient k increases.

[0054] 6, the resonant frequency frp of the power transmitting resonant circuit is set lower than the switching frequency ftyp when the coupling coefficient k = 0. By setting it in this way, the power transmitting current at the switching frequency ftyp increases as the coupling coefficient k increases.

[0055] Therefore, when the power receiving device 30 is in a power reception interruption state, the resonant frequency frp of the power transmitting resonant circuit is set higher than the switching frequency ftyp. By setting it in this manner, it is possible to suppress an increase in the power transmission current at the switching frequency due to an increase in the coupling coefficient k, and to keep the power transmission current low.

[0056] As a result, when the power receiving device 30 is in a power interruption state, in other words, when power supply to the power receiving device 30 is unnecessary, unnecessary current flowing through the power transmitting device 20 is suppressed even if the coupling coefficient k increases. As a result, heat generation in the power transmitting device 20 can be suppressed.

[0057] Furthermore, as the current flowing through the power transmitting coil 251 increases, the magnetic field strength generated by the power transmitting coil 251 increases. When the magnetic field strength increases, the magnetic field strength acting on the power receiving coil 311 also increases, resulting in increased heat generation in the power receiving resonant circuit 31 and the power receiving rectifier circuit 32 that is performing the power receiving cutoff operation. This adverse effect is particularly likely to occur when the coupling coefficient k is large.

[0058] However, by setting the resonant frequency frp of the power transmitting resonant circuit 25 higher than the switching frequency ftyp, the current flowing through the power transmitting coil 251 when the coupling coefficient k is large can be kept small. That is, the magnetic field strength acting on the power receiving coil 311 can be kept low. This makes it possible to suppress heat generation in the power receiving resonant circuit 31 and the power receiving rectifier circuit 32 that is performing the power receiving cutoff operation. In particular, a large coupling coefficient k is prone to adverse effects, but by keeping the magnetic field strength low, this adverse effect can be suppressed.

[0059] On the other hand, when the coupling coefficient is small, the transmission current is larger than when the coupling coefficient is large. This prevents the strength of the electromagnetic resonance field formed by the power transmitting resonant circuit 25 and the power receiving resonant circuit 31 from becoming undesirably small. Therefore, even when the coupling coefficient is small, the desired amount of power can be supplied from the power transmitting device 20 to the power receiving device 30. In this case, the transmission current does not become excessively large, so heat generation in the power transmitting device 20 and the power receiving device 30 can be suppressed.

[0060] In this way, by having the above-mentioned configuration, the wireless power supply system 10 can suppress an increase in power consumption and suppress heat generation in the power transmission device 20 and the power receiving device 30 even when power reception is interrupted in a system with a high degree of freedom in the placement of the power transmission device 20 and the power receiving device 30, in which the coupling coefficient k changes from large to small values.

[0061] In order to set the resonant frequency frp of the power transmitting resonant circuit 25 higher than the switching frequency ftyp, the power transmitting device 20 sets the magnitude of the power transmitting resonant capacitance Crp of the power transmitting resonant capacitor 252 of the power transmitting resonant circuit 25 to be smaller than the magnitude of the capacitance Ctyp for setting the switching frequency ftyp. In a broader sense, the magnitude of the power transmitting resonant capacitance Crp can also be equal to or smaller than the magnitude of the capacitance Ctyp.

[0062] In this way, by setting the magnitude of the transmission resonance capacitance Crp to be smaller than the magnitude of the capacitance Ctyp, the power transmission device 20 can suppress an undesirable increase in power consumption in the power transmission device 20 due to an increase in the coupling coefficient k, and can suppress heat generation in the power transmission device 20 and the power receiving device 30.

[0063] In other words, the power transmission device 20 sets the magnitude of the power transmission resonant capacitance Crp to be smaller than the magnitude of the capacitance (capacitance Ctyp) at which the input impedance viewed from the power transmission coil 251 to the load 35 is minimized at the switching frequency, and when the rectification control circuit 34 stops the rectification operation of the power receiving rectification circuit 32 and performs power receiving cut-off control, the capacitance is set so that the DC current input to the power transmission device 20 from the DC power source 21 decreases as the coupling coefficient k between the power transmission coil 251 and the power receiving coil 311 increases, thereby suppressing heat generation in the power transmission device 20 and the power receiving device 30.

[0064] Furthermore, the power transmitting device 20 can appropriately set the transmission current so that it does not become too large, by making the magnitude of the power transmitting resonant capacitance Crp smaller than the magnitude of the capacitance Ctyp, as shown in FIG.

[0065] Fig. 7 is a graph showing the relationship between the power transmitting capacitance and the input DC current value at a predetermined coupling coefficient k when power reception is interrupted. In Fig. 7, Ctyp is the magnitude of the capacitance for setting the switching frequency ftyp, which coincides with the switching frequency of the power transmitting power conversion circuit 24. Crp is the magnitude of the capacitance (power transmitting resonant capacitance) set in the power transmitting resonant capacitor 252. IinMAX is the power transmitting current value when set to capacitance Ctyp, and IinA is the power transmitting current value when set to power transmitting resonant capacitance Crp.

[0066] As shown in FIG. 7, by setting the power transmission resonant capacitance Crp, it is possible to prevent the power transmission current from becoming excessively large, and to set it to an appropriate value for power transmission.

[0067] In this case, it is preferable that the magnitude of the power transmitting resonant capacitance Crp is smaller than the magnitude of the capacitance Ctyp and larger than about 0.5 times (0.5Ctyp) the capacitance Ctyp, thereby enabling the power transmitting device 20 to suppress undesired reductions in the transmitted power and maintain an appropriate power transmission capacity.

[0068] Furthermore, the power transmitting device 20 can appropriately set the output power of the power receiving circuit as shown in FIG. 8 by setting the magnitude of the power transmitting resonant capacitance Crp to be within a predetermined range smaller than the magnitude of the capacitance Ctyp.

[0069] 8 is a graph showing a simulation of the relationship between the power transmitting resonant capacitance and the power receiving circuit output power. The power receiving circuit output power is the power at the output terminal of the smoothing circuit 33, and is the power when power receiving is not interrupted. Fig. 8 shows a simulation performed based on a predetermined coupling coefficient.

[0070] As shown in FIG. 8, the power receiving circuit output power can be adjusted by appropriately setting the magnitude of the power transmitting resonant capacitance Crp.

[0071] As a result, the wireless power supply system 10 can suppress heat generation in the power transmitting device 20 and the power receiving device 30, and can also suppress the supplied power from becoming undesirably low when power supply to the power receiving device 30 is required. The wireless power supply system 10 can also suppress the supplied power from becoming unnecessarily high. Therefore, the wireless power supply system 10 can supply appropriate power according to the received power required by the load.

[0072] Although the above configuration does not specify a specific range for the coupling coefficient k, the above configuration actually works effectively when the coupling coefficient is, for example, approximately 0<k<0.6. Furthermore, the above configuration actually works even more effectively when the coupling coefficient is approximately 0.01<k<0.6.

[0073] The above-described configuration is effective in the power reception cut-off state, but has almost no adverse effect even in the power reception cut-off stop state (power reception state).

[0074] FIG. 9 is a graph showing a simulation result of the relationship between the frequency and the power transmission current for each coupling coefficient k when the resonant frequency frp of the power transmission resonant circuit is set higher than the switching frequency ftyp in the power reception interruption stopped state.

[0075] As shown in FIG. 9 , even in the power reception interruption stopped state, the power transmission current does not increase as the coupling coefficient k increases at the switching frequency ftyp. Furthermore, once the coupling coefficient reaches a predetermined value or greater, the power transmission current converges to a substantially constant value. Therefore, the power transmission device 20 can suppress an undesired increase in the power transmission current and suppress heat generation even in the power reception interruption stopped state. Furthermore, by suppressing the power transmission current, the wireless power transfer system 10 can suppress an undesired increase in the magnetic field strength coupled to the power receiving coil 311, and suppress heat generation in the power receiving device 30. In this state, the wireless power transfer system 10 can supply appropriate power to the load 35 of the power receiving device 30.

[0076] (Power transmission device 20A as a derivative example) Fig. 10 is a functional block diagram showing an example of a derivative example of a power transmission device according to an embodiment of the present invention. As shown in Fig. 10, the power transmission device 20A as a derivative example differs from the above-described power transmission device 20 in that it includes a resistive element 261 and a differential amplifier circuit 262. The circuit configured from the resistive element 261 and the differential amplifier circuit 262 corresponds to the "electrical variable detection unit."

[0077] The resistive element 261 is connected between the node between the positive electrode of the DC power supply 21 and the input capacitor 22 and the transmission power conversion circuit 24 .

[0078] A terminal of the resistor element 261 on the DC power supply 21 side is connected to a non-inverting input terminal of a differential amplifier circuit 262. A terminal of the resistor element 261 on the transmission power conversion circuit 24 side is connected to an inverting input terminal of the differential amplifier circuit 262. An output terminal of the differential amplifier circuit 262 is connected to the power transmission control circuit 23.

[0079] The power transmitting device 20A having such a configuration is used when the power receiving device 30 performs power transmission control using resonance modulation.

[0080] In the power receiving device 30 that performs resonance modulation, the rectification control circuit 34 controls the resonance modulation using the power receiving rectifier circuit 32. For example, although not shown, the rectification control circuit 34 obtains the charge state of the battery BAT from the charging circuit 351. When the rectification control circuit 34 detects that the battery BAT is fully charged and no supply of received power (charging power) is required, it outputs an ON control signal to the switching elements Q1 and Q2 of the power receiving rectifier circuit 32. This causes the switching elements Q1 and Q2 to be turned on (conductive), changing the input impedance seen from the power transmitting coil 251 toward the power receiving device 30, and causing resonance modulation. At this time, the switching elements Q1 and Q2 being turned on (conductive), causes the power receiving device 30 to be in a power reception cut-off state.

[0081] When resonance modulation occurs, the current value of the AC current flowing through the power transmitting resonance circuit 25 changes, and the input DC current value changes. The change in the input DC current value causes the voltage across the resistor element 261 to change.

[0082] The differential amplifier circuit 262 outputs an output signal based on a change in the voltage across the resistor element 261 to the power transmission control circuit 23. The power transmission control circuit 23, for example, intermittently stops switching control of the power transmission power conversion circuit 24 based on this output current. This allows the power transmission device 20A to detect information from the power receiving device 30 that power supply is unnecessary and suppress undesired switching control without using any other communication means. This allows the power transmission device 20A to suppress power consumption.

[0083] Even in such resonance modulation, power reception is interrupted in the power receiving device 30. However, even in such a case, by setting the power transmitting resonance capacitance Crp as described above, it is possible to suppress an undesired increase in the power transmission current that occurs during indirect switching control. Therefore, the wireless power transfer system can suppress heat generation in the power transmitting device 20A and the power receiving device 30.

[0084] (Examples of patterns of power transmitting resonant circuit and power receiving resonant circuit) FIGS. 11A, 11B, and 11C are circuit diagrams showing examples of patterns of a power transmitting resonant circuit and a power receiving resonant circuit.

[0085] The power transmitting resonant circuit 25 in Fig. 11A has the same configuration as the power transmitting resonant circuit 25 in Fig. 2. The power receiving resonant circuit 31X1 in Fig. 11A has a configuration in which a power receiving resonant capacitor 313 is added to the power receiving resonant circuit 31 in Fig. 2. The power receiving resonant capacitor 313 is connected in series to a parallel circuit of the power receiving coil 311 and the power receiving resonant capacitor 312. In other words, one terminal of the power receiving resonant capacitor 313 is connected to the node between the power receiving coil 311 and the power receiving resonant capacitor 312, and the other terminal of the power receiving resonant capacitor 313 is connected to the output terminal of the power receiving resonant circuit 31X1.

[0086] The power transmitting resonant circuit 25 in Fig. 11(B) has the same configuration as the power transmitting resonant circuit 25 in Fig. 2. The power receiving resonant circuit 31X2 in Fig. 11(B) has a configuration in which a power receiving resonant capacitor 314 is added to the power receiving resonant circuit 31 in Fig. 2. The power receiving resonant capacitor 314 is connected in series to the power receiving coil 311, and the series circuit of the power receiving coil 311 and the power receiving resonant capacitor 314 is connected in parallel to the power receiving resonant capacitor 312. In other words, one terminal of the power receiving resonant capacitor 314 is connected to one output terminal of the power receiving coil 311, and the other terminal of the power receiving resonant capacitor 314 is connected to one terminal of the power receiving resonant capacitor 312. The other terminal of the power receiving resonant capacitor 312 is connected to the other output terminal of the power receiving coil 311.

[0087] 2. The power transmitting resonant circuit 25X3 in FIG. 11C has a configuration in which a power transmitting resonant capacitor 253 and a power transmitting resonant inductor 254 are added. The power transmitting resonant capacitor 253 is connected in parallel to the series circuit of the power transmitting coil 251 and the power transmitting resonant capacitor 252. One terminal of the power transmitting resonant inductor 254 is connected to the node of the power transmitting resonant capacitor 252 and the power transmitting resonant capacitor 253. The other terminal of the power transmitting resonant inductor 254 is connected to the node of the switching elements QH and QL of the power transmitting power conversion circuit 24. The power receiving resonant circuit 31 in FIG. 11C has a configuration similar to that of the power receiving resonant circuit 31 in FIG. 2.

[0088] As shown in these figures, the power transmitting resonant circuit only needs to include at least a series resonant circuit of the power transmitting coil 251 and the power transmitting resonant capacitor 252. The power receiving resonant circuit only needs to include at least a parallel resonant circuit of the power receiving coil 311 and the power receiving resonant capacitor 312.

[0089] In the above description, 6.78 MHz was used as an example of the switching frequency, but the present invention is not limited to this frequency. However, the switching frequency is preferably a frequency in the ISM band, for example, 6.78 MHz or 13.56 MHz. In other words, the frequency band of the electromagnetic field resonance is preferably the 6.78 MHz band or the 13.56 MHz band.

[0090] <1> A wireless power transfer system comprising: a power transmitting device having a power transmitting resonant circuit including a power transmitting coil and a power transmitting resonant capacitor; and a power receiving device having a power receiving resonant circuit including a power receiving coil and a power receiving resonant capacitor, and electrically connected to a load, wherein electromagnetic resonance coupling is formed between the power transmitting coil and the power receiving coil to supply power from the power transmitting device to the power receiving device, wherein the power transmitting device comprises: a power transmitting power conversion circuit electrically connected to an input DC power source and the power transmitting coil, and converting DC power supplied from the input DC power source into AC power by switching operation of a semiconductor switching element, and passing the AC current to the power transmitting coil; and a power transmitting control circuit controlling the switching operation of the power transmitting power conversion circuit, wherein the power receiving device comprises: a power receiving rectifier circuit electrically connected to the power receiving resonant circuit and rectifying high frequency AC power received by the power receiving coil; and a smoothing circuit electrically connected to the power receiving rectifier circuit and smoothing the power rectified by the power receiving rectifier circuit into a received DC voltage. a rectification control circuit electrically connected to the receiving resonant circuit and controlling start and stop of the rectification operation of the receiving rectifier circuit, wherein the capacitance of the transmitting resonant capacitor is equal to or less than the capacitance at which the input impedance seen from the transmitting coil to the load side is minimized at a switching frequency, and when the rectification control circuit stops the rectification operation of the receiving rectifier circuit to perform power reception cut-off control, the capacitance is set so that the DC current input to the power transmitting device from the input DC power source becomes smaller as the coupling coefficient between the transmitting coil and the receiving coil becomes larger.

[0091] <2> The wireless power supply system according to <1>, wherein the capacitance of the power transmitting resonant capacitor is set such that, when the load is unloaded, the DC current input to the power transmitting device decreases as the coupling coefficient increases.

[0092] <3> The wireless power supply system according to <1> or <2>, wherein the power transmitting resonant circuit includes a series circuit of the power transmitting coil and the power transmitting resonant capacitor.

[0093] <4> The wireless power supply system according to any one of <1> to <3>, wherein the rectification control circuit controls execution and stop of the rectification operation of the power receiving rectifier circuit to perform resonance modulation.

[0094] <5> The wireless power supply system according to <4>, wherein the power transmitting device includes an electric variable detection unit that detects a change in DC current flowing through the power transmitting device due to a change between execution and stop of the power receiving rectifier circuit during the resonance modulation.

[0095] <6> The wireless power supply system according to any one of <1> to <5>, wherein the rectification control circuit adjusts the receiving voltage by controlling execution and stop of the rectification operation of the receiving rectifier circuit based on a control value for adjusting the receiving voltage that is set for the receiving DC voltage.

[0096] <7> The wireless power supply system according to any one of <1> to <6>, wherein the rectification control circuit performs resonance modulation by varying the execution and stop of the receiving rectification circuit, and adjusts the receiving voltage by controlling the execution and stop of the rectification operation of the receiving rectification circuit based on a control value for adjusting the receiving voltage that is set for the receiving DC voltage.

[0097] <8> The wireless power supply system according to any one of <1> to <7>, wherein the frequency band of the electromagnetic resonance coupling is a 6.78 MHz band or a 13.56 MHz band.

[0098] 10: Wireless power transfer system 20, 20A: Power transmitting device 21: DC power supply 22: Input capacitor 23: Power transmitting control circuit 24: Power transmitting power conversion circuit 25, 25X3: Power transmitting resonant circuit 30: Power receiving device 31, 31X1, 31X2: Power receiving resonant circuit 32: Power receiving rectifier circuit 33: Smoothing circuit 34: Rectification control circuit 35: Load 251: Power transmitting coil 252, 253: Power transmitting resonant capacitor 254: Power transmitting resonant inductor 261: Resistance element 262: Differential amplifier circuit 311: Power receiving coil 312, 313, 314: Power receiving resonant capacitor 351: Charging circuit BAT: Battery D11, D12, D21, D22: Diodes POH: Hi-side output terminal POL: LOW-side output terminal Q1, Q2, QH, QL: switching elements

Claims

1. A wireless power transfer system comprising: a power transmitting device having a power transmitting resonant circuit including a power transmitting coil and a power transmitting resonant capacitor; and a power receiving device having a power receiving resonant circuit including a power receiving coil and a power receiving resonant capacitor, and electrically connected to a load, wherein electromagnetic resonance coupling is formed between the power transmitting coil and the power receiving coil to supply power from the power transmitting device to the power receiving device, wherein the power transmitting device comprises: a power transmitting power conversion circuit electrically connected to an input DC power source and the power transmitting coil, and converts DC power supplied from the input DC power source into AC power by switching operation of a semiconductor switching element, and flows the AC current to the power transmitting coil; and a power transmitting control circuit controlling the switching operation of the power transmitting power conversion circuit, wherein the power receiving device comprises: a power receiving rectifier circuit electrically connected to the power receiving resonant circuit and rectifying high frequency AC power received by the power receiving coil; and a smoothing circuit electrically connected to the power receiving rectifier circuit and smoothing the power rectified by the power receiving rectifier circuit into a received DC voltage. a rectification control circuit electrically connected to the power receiving resonant circuit and controlling start and stop of the rectification operation of the power receiving rectifier circuit, wherein the capacitance of the power transmitting resonant capacitor is equal to or less than the capacitance at which the input impedance seen from the power transmitting coil to the load side is minimized at a switching frequency, and when the rectification control circuit stops the rectification operation of the power receiving rectifier circuit to perform power receiving cutoff control, the capacitance is set so that the DC current input to the power transmitting device from the input DC power source becomes smaller as the coupling coefficient between the power transmitting coil and the power receiving coil becomes larger.

2. The wireless power supply system according to claim 1, wherein the capacitance of the power transmitting resonant capacitor is set so that when the load is unloaded, the DC current input to the power transmitting device decreases as the coupling coefficient increases.

3. The wireless power supply system according to claim 1 or 2, wherein the power transmission resonant circuit includes a series circuit of the power transmission coil and the power transmission resonant capacitor.

4. The wireless power supply system according to any one of claims 1 to 3, wherein the rectification control circuit controls the execution and suspension of the rectification operation of the power receiving rectifier circuit to perform resonance modulation.

5. The wireless power supply system according to claim 4, wherein the power transmitting device includes an electric variable detection unit that detects a change in the DC current flowing through the power transmitting device due to a change between operation and stop of the power receiving rectifier circuit during the resonant modulation.

6. The wireless power supply system according to any one of claims 1 to 5, wherein the rectification control circuit adjusts the receiving voltage by controlling the execution and stop of the rectification operation of the receiving rectifier circuit based on a control value for adjusting the receiving voltage that is set for the receiving DC voltage.

7. A wireless power supply system according to any one of claims 1 to 6, wherein the rectification control circuit performs resonance modulation by varying the execution and suspension of the receiving rectification circuit, and adjusts the receiving voltage by controlling the execution and suspension of the rectification operation of the receiving rectification circuit based on a control value for adjusting the receiving voltage set for the receiving DC voltage.

8. The wireless power supply system according to any one of claims 1 to 7, wherein the frequency band of the electromagnetic resonance coupling is the 6.78 MHz band or the 13.56 MHz band.

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