Wireless power supply system

Abstract

This wireless power supply system comprises: a power transmission device including a power transmission coil; and a power reception device including a power reception coil. The power transmission device comprises: a power conversion circuit that converts an input DC voltage into an AC current by a switching operation and causes the AC current to flow through the power transmission coil; and a power transmission resonance circuit including the power transmission coil and a power transmission resonance capacitor. The power reception device comprises: a power reception resonance circuit that includes the power reception coil and a power reception resonance capacitor; a power reception rectification circuit that rectifies the AC current received by the power reception coil; and a smoothing capacitor that smoothes the rectified current and outputs a DC voltage. The power transmission coil is configured from an air-core planar spiral loop coil with no magnetic core. The power reception coil is configured from a cored helical solenoid coil with a magnetic core having a relative magnetic permeability of 100 or more, and has a greater number of turns than the number of turns of the power transmission coil. The power transmission resonance capacitor is set to a capacitance value at which the impedance looking into the power reception device at the switching frequency at which the switching operation is performed is close to the minimum. The capacitance value of the power reception resonance capacitor is set so that the power reception resonance frequency of the power reception resonance circuit is substantially the same as the switching frequency.

Description

Wireless power supply system ,

[0010]

[0001] The present disclosure relates to a wireless power supply system that wirelessly supplies power from a power transmission device including a power transmission coil to a power reception device including a power reception coil.

[0002] Conventionally, as shown in Patent Documents 1, 2, and 3, wireless power supply systems having various structures have been devised.

[0003] Such a wireless power supply system includes a power transmission device and a power reception device. The power reception device is mounted on, for example, an electronic device and is used for charging a secondary battery of the electronic device. The power transmission device includes a power transmission coil. The power reception device includes a power reception coil. The wireless power supply system supplies power from the power transmission device to the power reception device by bringing the power transmission coil close to the power reception coil.

[0004] Japanese Patent No. 7422554, Japanese Patent No. 7378084, Japanese Patent No. 6632435

[0005] Due to the miniaturization of electronic devices, it is necessary to configure the power reception coil mounted inside to be small.

[0006] However, when the power reception coil is made small, problems such as a decrease in the inductance of the power reception coil occur, which has an adverse effect on the power reception characteristics and causes a problem that the power required by the electronic device cannot be received.

[0007] In addition, in order to efficiently supply power from the power transmission device to the power reception device (electronic device), it is necessary to maintain the electromagnetic field coupling between the power transmission coil and the power reception coil at a predetermined level or higher.

[0008] However, for example, due to the structure of the electronic device or the like, it is difficult to stably arrange the power reception coil in a predetermined positional relationship with respect to the power transmission coil, and there is a problem that efficient power transmission cannot be performed. In particular, when the power reception coil is miniaturized, such problems become prominent.

[0009] Therefore, an object of the present disclosure is to realize a wireless power supply system that stably and efficiently transmits power from a power transmission coil to a power reception coil while miniaturizing the power reception coil.

[0010] A wireless power supply system according to one embodiment of this invention comprises a power transmission device including a power transmission coil and a power receiving device including a power receiving coil.

[0011] The power transmission device comprises a power conversion circuit that converts an input DC voltage into AC current by switching operation and supplies it to a power transmission coil, and a power transmission resonant circuit that includes a power transmission coil and a power transmission resonant capacitor. The power receiving device comprises a power receiving resonant circuit that includes a power receiving coil and a power receiving resonant capacitor, a power receiving rectifier circuit that rectifies the AC current received by the power receiving coil, and a power receiving smoothing circuit that smooths the rectified current and outputs a DC voltage.

[0012] The transmission coil consists of a planar spiral loop coil with an air core that does not have a magnetic core. The receiving coil consists of a cored helical solenoid coil with a magnetic core that has a relative permeability of 100 or more, and has more turns than the transmission coil.

[0013] The transmitting resonant capacitor is set to a capacitance value such that the impedance seen on the receiving device side is near minimum at the switching frequency during switching operation. The receiving resonant capacitor is set to a capacitance value such that the receiving resonant frequency of the receiving resonant circuit is approximately the same as the switching frequency. The transmitting coil and receiving coil each constitute a transmitting resonant circuit and a receiving resonant circuit, forming an electromagnetic field resonant coupling to transmit electromagnetic field energy as power. The transmitting resonant circuit uses the electromagnetic field resonance phenomenon to increase the resonant current flowing through the transmitting coil and transmit power. The receiving resonant circuit uses the electromagnetic field resonance phenomenon to increase the resonant current flowing through the receiving coil and receive power. Furthermore, the receiving coil uses the electromagnetic induction phenomenon due to the difference in turns ratio between the transmitting coil and the receiving coil to increase the resonant voltage generated in the receiving coil with respect to the electromagnetic field created by the resonant current flowing through the transmitting coil and receive power.

[0014] This configuration allows for efficient and stable power transmission from the transmitting coil to the receiving coil, even if there are variations in the placement of the receiving coil relative to the transmitting coil, by utilizing the electromagnetic field resonance phenomenon in the receiving coil, which has a magnetic core.

[0015] According to this invention, power can be transmitted stably and efficiently from the transmitting coil to the receiving coil while miniaturizing the receiving coil.

[0016] Figure 1 is an equivalent circuit diagram of a wireless power supply system according to an embodiment of the present disclosure. Figure 2(A) is a plan view of a power transmission coil according to an embodiment of the present disclosure, and Figure 2(B) is a cross-sectional view of the power transmission coil. Figure 3(A) is a perspective view of a power receiving coil according to an embodiment of the present disclosure, Figure 3(B) is a plan view of the power receiving coil, and Figure 3(C) is a side view of the power receiving coil. Figure 4 is a perspective view showing an example of the positional relationship between the power transmission coil and the power receiving coil during wireless power supply.

[0017] A wireless power supply system according to an embodiment of this disclosure will be described with reference to the figures. Figure 1 is an equivalent circuit diagram of the wireless power supply system according to an embodiment of this disclosure.

[0018] (Circuit configuration of wireless power supply system 10) As shown in Figure 1, the wireless power supply system 10 comprises a power transmission device 20 and a power receiving device 30. The power transmission device 20 and the power receiving device 30 are physically separate. One example to which the power receiving device 30 is applied is a small electronic device (for example, a wearable electronic device), and the power transmission device 20 is a charging device for the electronic device.

[0019] (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 conversion circuit 24, and a power transmission resonant circuit 25.

[0020] The input capacitor 22 is connected in parallel to the DC power supply 21.

[0021] The power transmission control circuit 23 receives power from the DC power supply 21 and outputs a switching control signal to the power conversion circuit 24.

[0022] The power conversion circuit 24 includes a switching element QH and a switching element QL. The switching elements QH and QL are made of power semiconductors.

[0023] The drain terminal of switching element QH is connected to the positive terminal of the DC power supply 21. The drain terminal of switching element QL is connected to the source terminal of switching element QH. The source terminal of switching element QL is connected to the negative terminal of the DC power supply 21.

[0024] The source terminal of switching element QH and the drain terminal of switching element QL are connected to the power transmission resonant circuit 25.

[0025] The switching control signal output from the power transmission control circuit 23 is input to the gate terminal of switching element QH and the gate terminal of switching element QL.

[0026] The power transmission resonant circuit 25 comprises a power transmission coil 26 and a power transmission resonant capacitor 27. The power transmission coil 26 and the power transmission resonant capacitor 27 are connected in series to form a power transmission series resonant circuit.

[0027] The resonant frequency of the power transmission resonant circuit 25 is set to be approximately the same as the switching frequency of the power conversion circuit 24 (the frequency of the switching control signal output from the power transmission control circuit 23).

[0028] The switching frequency is preferably in the 6.78 MHz or 13.56 MHz band of the ISM band.

[0029] (Power receiving device 30) The power receiving device 30 comprises a power receiving resonant circuit 31, a power receiving rectifier circuit 34, and a smoothing capacitor 35. The smoothing capacitor 35 corresponds to the power receiving smoothing circuit. The power receiving resonant circuit 31 comprises a power receiving coil 32 and a power receiving resonant capacitor 33. The resonant frequency (power receiving resonant frequency) of the power receiving resonant circuit 31 is set to approximately match the switching frequency of the power transmitting device 20.

[0030] The power receiving coil 32 and the power receiving resonant capacitor 33 are connected in parallel to form a power receiving parallel resonant circuit. The output terminal of the power receiving resonant circuit 31 is connected to the input terminal of the power receiving rectifier circuit 34.

[0031] A smoothing capacitor 35 is connected in parallel to the output terminal of the power receiving rectifier circuit 34. Both ends of the smoothing capacitor 35 are connected to the output terminal of the power receiving device 30, and the output terminal is connected to the load.

[0032] (Wireless power supply) The power transmission control circuit 23 sets a switching control signal to supply a desired DC current to the load. The power transmission control circuit 23 outputs the switching control signal to the switching elements QH and QL of the power conversion circuit 24.

[0033] When a switching control signal is input, switching elements QH and QL alternately turn on (conduct) and off (open) at a predetermined switching frequency based on the switching control signal.

[0034] As a result, the power conversion circuit 24 converts the input DC voltage into AC current through switching operation and sends it to the power transmission coil 26 of the power transmission resonant circuit 25. The power transmission coil 26 generates an alternating magnetic field in response to the input AC current.

[0035] When the power receiving device 30 is positioned in a predetermined location relative to the power transmitting device 20, the power transmitting coil 26 and the power receiving coil 32 are positioned in a way that allows for electromagnetic field coupling.

[0036] The receiving coil 32 couples with the alternating magnetic field generated by the transmitting coil 26, generating an alternating current. The receiving rectifier circuit 34 rectifies the alternating current output from the receiving coil 32 (receiving resonant circuit 31). The smoothing capacitor 35 smooths the rectified current (rectified voltage) and outputs a direct current (direct current voltage) to the load.

[0037] This ensures that the load receives the desired DC power.

[0038] In this configuration, the power transmission resonant capacitor 27 is set to a capacitance value such that the impedance seen on the power receiving device 30 side is near minimum at the switching frequency. Furthermore, the power receiving resonant capacitor 33 is set to a capacitance value such that the power receiving resonant frequency of the power receiving resonant circuit 31 is approximately the same as the switching frequency.

[0039] As a result, the power transmission resonance circuit 25 and the power reception resonance circuit 31 form an electromagnetic field resonance coupling. By using the electromagnetic field resonance phenomenon, the power transmission resonance circuit 25 can increase the resonance current flowing through the power transmission coil 26 and perform power transmission. The power reception resonance circuit 31 can increase the resonance current flowing through the power reception coil 32 and perform power reception by utilizing the electromagnetic field resonance phenomenon. As a result, the power transmission device 20 can transmit power by increasing the electromagnetic field energy related to power transmission with respect to the power reception device 30 and the load.

[0040] Furthermore, the wireless power supply system 10 realizes the power transmission coil 26 and the power reception coil 32 with the following configurations.

[0041] (Shape of the power transmission coil 26) FIG. 2(A) is a plan view of the power transmission coil according to the embodiment of the present disclosure, and FIG. 2(B) is a cross-sectional view of the power transmission coil. FIG. 2(B) shows the A-A cross-section shown in FIG. 2(A).

[0042] The power transmission coil 26 is constituted by a loop-shaped coil conductor 261. More specifically, the power transmission coil 26 includes a dielectric substrate 260 and a coil conductor 261.

[0043] The dielectric substrate 260 is a flat plate.

[0044] The coil conductor 261 is formed on the dielectric substrate 260. The coil conductor 261 has a substantially closed shape with an opening 262, and is formed in a plurality of layers in the thickness direction of the dielectric substrate 260. The coil conductors 261 of each layer are connected to each other to form a spiral shape.

[0045] As a result, the power transmission coil 26 constitutes an air-core planar spiral loop coil without a magnetic core.

[0046] (Shape of the power reception coil 32) FIG. 3(A) is a perspective view of the power reception coil according to the embodiment of the present disclosure, FIG. 3(B) is a plan view of the power reception coil, and FIG. 3(C) is a side view of the power reception coil.

[0047] The power receiving coil 32 includes a coil conductor 321 and a magnetic core 329. The magnetic core 329 is formed of a cylindrical magnetic material. The coil conductor 321 is disposed along the circumferential surface of the magnetic core 329. Thereby, the power receiving coil 32 constitutes a cored helical solenoid coil having the magnetic core 329 at its center.

[0048] The number of turns of the coil conductor 321 of the power receiving coil 32 is larger than the number of turns of the coil conductor 261 of the power transmitting coil 26.

[0049] The area of the central opening of the winding shape of the coil conductor 321 of the power receiving coil 32 is smaller than the area of the opening 262 of the coil conductor 261 of the power transmitting coil 26.

[0050] The magnetic core 329 is formed of, for example, ferrite or a metallic magnetic material. Thereby, a magnetic core 329 having a relative permeability of 100 or more can be formed.

[0051] Thus, by providing the magnetic core 329, the power receiving coil 32 can be miniaturized.

[0052] (An example of the arrangement of the power receiving coil 32 with respect to the power transmitting coil 26) FIG. 4 is a perspective view showing an example of the positional relationship between the power transmitting coil and the power receiving coil during wireless power supply.

[0053] As shown in FIG. 4, the power receiving coil 32 is arranged with respect to the power transmitting coil 26 such that the axial direction of the magnetic core 329 is substantially orthogonal to the winding plane of the coil conductor 261 of the power transmitting coil 26. The power receiving coil 32 is arranged within the opening 262 of the power transmitting coil 26 when viewed in plan (viewed in a direction orthogonal to the winding plane).

[0054] The power transmitting coil 26 is a planar spiral loop coil, and the area of the opening 262 is larger than the area in the axial direction of the winding of the coil conductor 321 of the power receiving coil 32 (the axial direction of the magnetic core 329). In other words, the shape of the winding of the power transmitting coil 26 when viewed in the axial direction is larger than the shape of the winding of the power receiving coil 32 when viewed in the axial direction, and is sized such that the power receiving coil 32 can be arranged in the air-core portion of the power transmitting coil 26. Therefore, the power receiving coil 32 can be easily arranged within the opening 262 of the power transmitting coil 26.

[0055] Furthermore, it is preferable that the area of ​​the opening 262 (air core portion) of the power transmission coil 26 be made to a predetermined extent (several times) larger than the area in the axial direction of the winding of the coil conductor 321 of the power receiving coil 32 (the axial direction of the magnetic core 329). This improves the degree of freedom in positioning the power receiving coil 32 on the power transmission coil 26.

[0056] Here, the power transmission resonant circuit 25, which includes the power transmission coil 26, utilizes the electromagnetic field resonance phenomenon, so it can achieve a high electromagnetic field strength over a wide area within the opening 262.

[0057] Furthermore, the receiving coil 32 has a magnetic core 329 with high relative permeability. Therefore, the magnetic flux generated in the transmitting coil 26 is formed to pass through the magnetic core 329, forming a magnetic path that passes through both ends of the magnetic core 329.

[0058] The coil conductors 321 of the receiving coil 32 are arranged on the circumferential surface of the magnetic core 329. Therefore, the entire wound coil conductor 321 constituting the receiving coil 32 is linked with the magnetic flux generated by the transmitting coil 26.

[0059] This increases the coupling between the power transmission coil 26 and the power receiving coil 32. Therefore, the power receiving device 30 can improve the power receiving efficiency from the power transmission device 20.

[0060] Furthermore, even if the position of the power receiving device 30 changes or differs within the opening 262 of the power transmitting coil 26, the power receiving coil 32 stably links with the magnetic flux generated by the power transmitting coil 26 due to the magnetic flux utilizing the electromagnetic field resonance described above.

[0061] In this way, by using the combination of the transmitting coil 26 and the receiving coil 32, the wireless power supply system 10 can reliably and efficiently transmit power from the transmitting device 20 to the receiving device 30.

[0062] Furthermore, the wireless power supply system 10 achieves power supply over a wide area by configuring the transmitting coil 26 as a planar spiral loop coil, thereby improving the flexibility of placement for the receiving coil 32. In addition, by configuring the receiving coil 32 as a cored helical solenoid coil with a magnetic core 329 at its center, the receiving coil 32 can be miniaturized. Therefore, the wireless power supply system 10 can stably and efficiently transmit power to the small receiving coil 32 at any position within the opening 262 of the transmitting coil 26, which is formed over a wide area.

[0063] Furthermore, the receiving coil 32 is constructed in a three-dimensional helical shape with a coil conductor 321 wound around a magnetic core 329. On the other hand, the transmitting coil 26 is constructed in a planar spiral shape. Therefore, the number of turns in the receiving coil 32 can be greater than the number of turns in the transmitting coil 26.

[0064] As a result, the receiving coil 32 can increase the resonant voltage generated in the receiving coil 32 by utilizing the electromagnetic induction phenomenon caused by the difference in turns ratio between it and the transmitting coil 26, in relation to the electromagnetic field created by the resonant current flowing through the coil conductor 261 of the transmitting coil 26. Therefore, the wireless power supply system 10 can increase the resonant current flowing through the receiving coil 32. Furthermore, the wireless power supply system 10 can increase the resonant voltage generated in the receiving coil 32, enabling stable and efficient power transmission from the transmitting coil 26 to the receiving coil 32.

[0065] Therefore, even when the voltage consumed by the load is high, the wireless power supply system 10 can stably supply an output voltage of a height corresponding to this consumption voltage to the load.

[0066] More specifically, the number of turns of the receiving coil 32 is set to a natural number close to the value obtained by dividing the output voltage of the receiving device 30 by the input DC voltage of the transmitting device 20 and multiplying by the number of turns of the transmitting coil 26. As a result, the wireless power supply system 10 can stably supply the load with an output voltage value that the load desires.

[0067] 10: Wireless power supply system 20: Power transmission device 21: DC power supply 22: Input capacitor 23: Power transmission control circuit 24: Power conversion circuit 25: Power transmission resonant circuit 26: Power transmission coil 27: Power transmission resonant capacitor 30: Power receiving device 31: Power receiving resonant circuit 32: Power receiving coil 33: Power receiving resonant capacitor 34: Power receiving rectifier circuit 35: Smoothing capacitor 260: Dielectric substrate 261: Coil conductor 262: Aperture 321: Coil conductor 329: Magnetic core QH, QL: Switching elements

Claims

1. A wireless power supply system comprising a power transmission device including a power transmission coil and a power receiving device including a power receiving coil, wherein the power transmission device comprises a power conversion circuit that converts an input DC voltage into AC current by switching operation and supplies it to the power transmission coil, and a power transmission resonant circuit including the power transmission coil and a power transmission resonant capacitor, the power receiving device comprises a power receiving resonant circuit including the power receiving coil and a power receiving resonant capacitor, a power receiving rectifier circuit that rectifies the AC current received by the power receiving coil, and a power receiving smoothing circuit that smooths the rectified current and outputs a DC voltage, wherein the power transmission coil is composed of an air-cored, planar spiral loop coil without a magnetic core, the power receiving coil is composed of a cored, helical solenoid coil with a magnetic core having a relative permeability of 100 or more, and has more turns than the power transmission coil, and the power transmission resonant capacitor is set to a capacitance value such that the impedance seen on the power receiving device side is near minimum at the switching frequency in which the switching operation is performed. The receiving resonant capacitor has a capacitance value set such that the receiving resonant frequency of the receiving resonant circuit is approximately the same as the switching frequency. The transmitting coil and the receiving coil each constitute the transmitting resonant circuit and the receiving resonant circuit, respectively, thereby forming an electromagnetic field resonant coupling to transmit electromagnetic field energy as power. The transmitting resonant circuit transmits power by increasing the resonant current flowing through the transmitting coil using the electromagnetic field resonance phenomenon. The receiving resonant circuit receives power by increasing the resonant current flowing through the receiving coil using the electromagnetic field resonance phenomenon. The receiving coil receives power by increasing the resonant voltage generated in the receiving coil with respect to the electromagnetic field created by the resonant current flowing through the transmitting coil, using the electromagnetic induction phenomenon due to the difference in turns ratio with the transmitting coil.

2. The wireless power supply system according to claim 1, wherein the winding shape of the power transmission coil, when viewed in the axial direction, is larger than the winding shape of the power receiving coil, and is sized to allow the power receiving coil to be placed in the air core portion of the power transmission coil.

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

4. The number of turns of the receiving coil is set to a natural number close to the value obtained by dividing the output voltage of the receiving device by the input DC voltage of the transmitting device and multiplying by the number of turns of the transmitting coil, according to claim 3.

5. The wireless power supply system according to any one of claims 1 to 4, wherein the magnetic core is made of ferrite.

6. The wireless power supply system according to any one of claims 1 to 4, wherein the magnetic core is made of a metallic magnetic material.

7. The wireless power supply system according to any one of claims 1 to 6, wherein the switching frequency is the 6.78 MHz band or the 13.56 MHz band of the ISM band.

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