Contactless power supply device

Abstract

To provide a non-contact power supply device that can suppress a decline in power transmission efficiency even when a load connected to a device on a power receiving side fluctuates.SOLUTION: A non-contact power supply device 1 has a relay circuit 4 that relays power transmitted in a non-contact manner from a power transmitting device 2 to a power receiving device 3. The power transmitting device 2 has a transmitting coil 12 that transmits AC power having a predetermined frequency supplied from a power supply circuit 11 to the relay circuit 4. The relay circuit 4 has a first coil 31 that is arranged in electromagnetic coupling with the transmitting coil 12 and receives AC power from the transmitting coil 12, a second coil 32 that transmits the received AC power to the power receiving device 3, and a resonant capacitor 33 that, together with the first coil 31 and the second coil 32, resonates with the AC power supplied to the transmitting coil 12. The power receiving device 3 has a resonant circuit 20 having a receiving coil 21 that receives the AC power from the second coil 32 by electromagnetic coupling with the second coil 32 of the relay circuit 4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a non-contact power supply device.

Background Art

[0002] Conventionally, so-called non-contact power supply (also called wireless power supply) technology that transmits power through space without using metal contacts or the like has been studied.

[0003] As one of the non-contact power supply technologies, a method of supplying power by electromagnetic induction is known. In the method of supplying power by electromagnetic induction, generally, by driving an inverter provided in a power transmission side device at a switching frequency lower than 1 MHz, AC power is supplied to a coil on the power transmission side to generate electromagnetic induction with a coil on the power reception side. On the other hand, a technique has been proposed that enables switching at a frequency of 6.78 MHz by configuring a power transmission machine for power supply as an E-class amplifier (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a device on the power transmission side of a non-contact power supply device, in order for a power supply circuit that supplies power to a coil on the power transmission side to be configured as an E-class amplifier, the following conditions are required to be satisfied for a switching element provided in the power supply circuit. • The voltage applied to the switching element is zero when switching from on to off or off to on (Zero-Voltage Switching, sometimes referred to as ZVS below). • The slope of the voltage applied to the switching element with respect to time change at the moment the switching element switches from off to on is zero (i.e., dV / dt = 0) (Zero-Voltage-Derivative-Switching, sometimes referred to as ZDS below).

[0006] When the above ZVS and ZDS conditions are met, switching losses in the switching elements are reduced as much as possible, resulting in improved power transmission efficiency. However, the conditions for achieving ZVS and ZDS fluctuate depending on the load connected to the receiving device.

[0007] Therefore, the present invention aims to provide a contactless power supply device that can suppress a decrease in power transmission efficiency even when the load connected to the power receiving device fluctuates. [Means for solving the problem]

[0008] One embodiment of the present invention is a contactless power supply device. This contactless power supply device includes a power transmission device, a power receiving device, and a relay circuit that relays power transmitted contactlessly from the power transmission device to the power receiving device. The power transmission device includes a transmitting coil that transmits supplied AC power to the relay circuit, and a power supply circuit that converts DC power supplied from a DC power source into AC power having a predetermined frequency and supplies the converted AC power to the transmitting coil. The relay circuit includes a first coil arranged to be electromagnetically coupled with the transmitting coil and to receive AC power from the transmitting coil, a second coil that transmits the AC power received via the first coil to the power receiving device, and a resonant capacitor that resonates with the AC power supplied to the transmitting coil together with the first and second coils. The power receiving device includes a resonant circuit having a receiving coil that receives AC power from the second coil by electromagnetic coupling with the second coil of the relay circuit, and a rectifier and smoothing circuit that rectifies the AC power output from the resonant circuit into DC power and outputs the DC power to a load circuit. By having such a configuration, this contactless power supply device can suppress a decrease in power transmission efficiency even when the load connected to the power receiving device fluctuates.

[0009] In this contactless power supply device, it is preferable that the second coil of the relay circuit be arranged so as not to be electromagnetically coupled with the first coil of the relay circuit and the transmitting coil of the power transmission device. With this configuration, the contactless power supply device can more reliably suppress the decrease in power transmission efficiency in response to fluctuations in the load connected to the power receiving device.

[0010] In this case, it is preferable that the outer circumference of the second coil of the relay circuit is larger than the outer circumference of the first coil of the relay circuit. Having such a configuration, this contactless power supply device makes it easy to arrange the receiving coil of the power receiving device so that it is electromagnetically coupled to the second coil of the relay circuit, but not to the transmitting coil and the first coil.

[0011] Furthermore, it is preferable that the first coil of the relay circuit is formed on one surface of the substrate, and the transmitting coil of the power transmission device is formed on the other surface of the substrate such that the central axis of the first coil and the central axis of the transmitting coil are coaxial. By having such a configuration, this contactless power supply device can increase the degree of coupling between the transmitting coil and the first coil, thereby suppressing a decrease in power transmission efficiency.

[0012] Alternatively, it is preferable that the first coil of the relay circuit and the transmitting coil of the power transmission device are wound around the same core. By having such a configuration, this contactless power supply device can increase the degree of coupling between the transmitting coil and the first coil, thereby suppressing a decrease in power transmission efficiency. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram of a contactless power supply device according to one embodiment of the present invention. [Figure 2] This is an equivalent circuit diagram of a contactless power supply device in a comparative example where no relay circuit exists. [Figure 3] This is an equivalent circuit diagram of the contactless power supply device according to this embodiment. [Figure 4] This diagram shows an example of the arrangement of the transmitting coil, the first coil, and the second coil. [Figure 5] This figure shows another example of the arrangement of the transmitting coil, the first coil, and the second coil. [Modes for carrying out the invention]

[0014] Hereinafter, a contactless power supply device and a power transmission method performed by the contactless power supply device according to one embodiment of the present invention will be described with reference to the figures. This contactless power supply device drives the switching elements of a power supply circuit that supplies AC power to a coil on the transmitting side at a switching frequency included in the ISM band, which has fewer restrictions on use. Furthermore, the inventors have found that even if ZDS is not achieved, if ZVS is achieved and the difference between the timing when the switching element changes from off to on and the timing when the voltage applied to the switching element becomes sufficiently small, the switching loss of the switching element can be reduced to a level that does not pose a practical problem, even if the switching element is driven at a switching frequency included in the ISM band.

[0015] Therefore, this contactless power supply device has a relay circuit between the power-transmitting device and the power-receiving device for relaying AC power transmitted from the power-transmitting device to the power-receiving device. This relay circuit has a first coil that is electromagnetically coupled to a power-transmitting coil provided in the power-transmitting device, a second coil that is electromagnetically coupled to a power-receiving coil provided in the power-receiving device, and a resonant capacitor that resonates with the AC power transmitted from the power-transmitting device together with the first and second coils. As a result, this contactless power supply device is able to achieve ZVS even when the load connected to the power-receiving device fluctuates, and to sufficiently reduce the difference between the timing when the switching element changes from off to on and the timing when the voltage applied to the switching element becomes. Consequently, this contactless power supply device is able to reduce switching losses in the switching element and suppress a decrease in power transmission efficiency.

[0016] FIG. 1 is a schematic configuration diagram of a non-contact power supply device according to an embodiment of the present invention. As shown in FIG. 1, the non-contact power supply device 1 includes a power transmission device 2, a power reception device 3 that receives power non-contactingly through space from the power transmission device 2, and a relay circuit 4 that relays AC power transmitted from the power transmission device 2 to the power reception device 3. The power transmission device 2 includes a power supply circuit 11, a transmission coil 12, a capacitor 13, and a control circuit 14. On the other hand, the power reception device 3 includes a resonance circuit 20 including a reception coil 21 and a resonance capacitor 22, and a rectifying and smoothing circuit 23. And the power reception device 3 is connected to a load circuit 5. The load circuit 5 is, for example, a secondary battery, a charging circuit for a secondary battery, or a circuit that operates using DC power. Further, the relay circuit 4 includes a first coil 31, a second coil 32, and a resonance capacitor 33.

[0017] First, the power transmission device 2 will be described. The power supply circuit 11 converts the DC power supplied from the DC power source 10 into AC power having a frequency included in the ISM band, and supplies the converted AC power to the transmission coil 12. For this purpose, the power supply circuit 11 includes a coil 15, a capacitor 16, and a switching element 17, and is configured as a DC-AC converter.

[0018] The coil 15 is connected between the positive terminal of the DC power source 10 and one end of the transmission coil 12. Also, the capacitor 16 is connected at one end between the coil 15 and one end of the transmission coil 12, and at the other end to the negative terminal of the DC power source 10. And the coil 15 and the capacitor 16 convert the DC power output from the DC power source 10 into AC power having a switching frequency at which the on and off of the switching element 17 are switched.

[0019] The switching element 17 is connected in parallel with the capacitor 16 between the capacitor 16 and the coil 15. That is, one end of the switching element 17 is connected to the positive terminal of the DC power source 10 through the coil 15, and the other end of the switching element 17 is connected to the negative terminal of the DC power source 10.

[0020] Furthermore, the switching element 17 can be an element capable of switching between on and off at a switching frequency included in the ISM band, for example, a field effect transistor (GaN FET) formed of gallium nitride. The switching terminal of the switching element 17 (for example, the gate terminal of the GaN FET) is connected to the control circuit 14, and is switched between on and off by a control signal from the control circuit 14. As described above, when the switching element 17 is switched between on and off at the switching frequency, the DC power output from the DC power supply 10 is converted into AC power having that switching frequency by the coil 15 and the capacitor 16. Then, the converted AC power is output to the transmission coil 12.

[0021] Note that the power supply circuit 11 may have a DC-DC converter for boosting or降压 the DC power output from the DC power supply 10 between the DC power supply 10 and the coil 15.

[0022] The transmission coil 12 generates a periodically changing magnetic field around the transmission coil 12 in response to the AC power supplied from the power supply circuit 11. Then, the magnetic field generated by the transmission coil 12 causes electromagnetic coupling between the transmission coil 12 and the first coil 31 of the relay circuit 4. Thereby, the AC power supplied to the transmission coil 12 is transmitted to the relay circuit 4.

[0023] The capacitor 13 is connected in series with the transmission coil 12 between the positive output terminal of the power supply circuit 11 and one end of the transmission coil 12. Then, the AC power output from the power supply circuit 11 is supplied to the transmission coil 12 via the capacitor 13.

[0024] It should be noted that the "降压" in the translation of item is a literal translation of the Chinese "降压", and it may be more appropriate to use "buck" in a more professional context. You can adjust it according to the actual situation.The control circuit 14 includes a processor, memory, and a gate driver. The control circuit 14 switches the switching elements 17 of the power supply circuit 11 on and off via the gate driver at a switching frequency included in the ISM band (e.g., 6.78 MHz or 13.56 MHz) and a predetermined duty cycle (e.g., 0.5).

[0025] Next, we will describe the power receiving device 3.

[0026] The resonant circuit 20 is an LC resonant circuit in which a receiving coil 21 and a resonant capacitor 22 are connected in series. One end of the receiving coil 21 of the resonant circuit 20 is connected to one input terminal of the rectifier-smoothing circuit 23 via the resonant capacitor 22. The other end of the receiving coil 21 is connected to the other input terminal of the rectifier-smoothing circuit 23. Note that the resonant circuit 20 is not limited to this example, and may also be an LC parallel resonant circuit in which the receiving coil 21 and the resonant capacitor 22 are connected in parallel.

[0027] The receiving coil 21, together with the resonant capacitor 22, resonates with the alternating current flowing through the second coil 32 of the relay circuit 4, thereby receiving power from the power transmission device 2 via the relay circuit 4. The receiving coil 21 then outputs the received power to the rectifier and smoothing circuit 23 via the resonant capacitor 22. In other words, the inductance of the receiving coil 21 and the capacitance of the resonant capacitor 22 are set so that the resonant frequency of the resonant circuit 20 is approximately equal to the switching frequency.

[0028] The resonant capacitor 22 is connected in series with the receiving coil 21. That is, one end of the resonant capacitor 22 is connected to one end of the receiving coil 21, and the other end is connected to the rectifier and smoothing circuit 23. The resonant capacitor 22 then resonates together with the receiving coil 21, outputting the received AC power to the rectifier and smoothing circuit 23.

[0029] The rectifier-smoothing circuit 23 is composed of, for example, a full-wave rectifier circuit having four bridge-connected diodes and a smoothing capacitor. One of the two input terminals of the full-wave rectifier circuit is connected to the resonant capacitor 22, and the other of the two input terminals is connected to the receiving coil 21. Also, one of the two output terminals of the full-wave rectifier circuit is connected to one end of the smoothing capacitor, and the other of the two output terminals is connected to the other end of the smoothing capacitor. The rectifier-smoothing circuit 23 rectifies the AC power output from the resonant circuit 20 and converts it into DC power. The rectifier-smoothing circuit 23 outputs the converted DC power to the load circuit 5. Note that the rectifier-smoothing circuit 23 may include a half-wave rectifier circuit instead of a full-wave rectifier circuit.

[0030] Furthermore, the power receiving device 3 may further include a DC-DC converter for boosting or lowering the voltage of the DC power output from the rectifier and smoothing circuit 23.

[0031] Next, we will explain relay circuit 4.

[0032] The first coil 31, together with the second coil 32 and the resonant capacitor 33, constitutes an LC series resonant circuit. The first coil 31 is positioned to be electromagnetically coupled to the transmitting coil 12, and together with the second coil 32 and the resonant capacitor 33, it resonates with the alternating current flowing through the transmitting coil 12 of the power transmission device 2, thereby receiving power from the power transmission device 2.

[0033] The second coil 32 generates a magnetic field using the alternating current power received from the power transmission device 2 via the first coil 31. Therefore, by positioning the receiving coil 21 of the power receiving device 3 in a location where it can electromagnetically couple with the second coil 32, the alternating current power received by the relay circuit 4 from the power transmission device 2 is transmitted to the power receiving device 3.

[0034] The resonant capacitor 33 is connected in series with the first coil 31 and the second coil 32. That is, one end of the resonant capacitor 33 is connected to one end of the first coil 31, and the other end is connected to one end of the second coil 32. The resonant capacitor 33, together with the first coil 31 and the second coil 32, resonates with the current flowing through the transmitting coil 12 of the power transmission device 2, thereby receiving AC power from the power transmission device 2. In other words, the inductances of the first coil 31 and the second coil 32 and the capacitance of the resonant capacitor 33 are set so that the resonant frequency of the relay circuit 4 is approximately equal to the switching frequency. The inductances of the first coil 31 and the second coil 32 may be equal or different. Details regarding the arrangement of each coil in the relay circuit 4 and the transmitting coil 12 will be described later.

[0035] The following describes the operation of the contactless power supply device 1 in detail. Figure 2 is an equivalent circuit diagram of a comparative example of a contactless power supply device in which the relay circuit 4 does not exist. That is, the equivalent circuit 200 shown in Figure 2 is an equivalent circuit diagram of a comparative example in the contactless power supply device 1 in which the relay circuit 4 is omitted and AC power is directly transmitted from the power supply device 2 to the power receiving device 3 by electromagnetic coupling between the transmitting coil 12 of the power transmission device 2 and the receiving coil 21 of the power receiving device 3. Here, Lf, Ltx, and Lrx are the inductances of the coil 15, transmitting coil 12, and receiving coil 21 of the power supply circuit 11, respectively, and Csh, Cs, and C2 are the capacitances of the capacitor 16, capacitor 13, and resonant capacitor 22 of the power supply circuit 11, respectively. Rac is the load resistance of the power receiving device 3. And M is the mutual inductance between the transmitting coil 12 and the receiving coil 21.

[0036] When the resonant circuit 20 of the power receiving device 3 is in resonance, the equivalent circuit 200 can be rewritten as equivalent circuit 210 or equivalent circuit 220. In this case, the impedance Z of the entire contactless power supply device of the comparative example, that is, the impedance seen from the power transmitting device 2 side during power transmission, is expressed as follows.

number

[0037] As is clear from equation (1), when the load resistance Rac of the power receiving device 3 decreases, the overall load resistance Ro of the contactless power supply device increases. Conversely, when the load of the power receiving device 3 decreases and the load resistance Rac increases, the overall load resistance Ro of the contactless power supply device decreases. If the load resistance Ro becomes too small, ZVS will not be achieved, or the timing at which the voltage applied to the switching element 17 becomes zero will be too early relative to the timing at which the switching element 17 turns on. If the timing at which the voltage applied to the switching element 17 becomes zero is too early relative to the timing at which the switching element 17 turns on, a loss will occur due to the current flowing through the body diode of the switching element 17. Thus, in the contactless power supply device of the comparative example, the power transmission efficiency may decrease due to fluctuations in the load of the load circuit 5 connected to the power receiving device 3. For further details on this matter, see, for example, Zhang, Lujie, “Load-Independent Class-E Power Conversion”, https: / / vtechworks.lib.vt.edu / handle / 10919 / 97601, 2020, Chapter 2.

[0038] Figure 3 is an equivalent circuit diagram of the contactless power supply device 1 according to this embodiment. In this equivalent circuit 300, as in Figure 2, Lf, Ltx, and Lrx are the inductances of the coil 15, transmitting coil 12, and receiving coil 21 of the power supply circuit 11, respectively, and Csh, Cs, and C2 are the capacitances of the capacitor 16, capacitor 13 of the power supply circuit 11 and the resonant capacitor 22 of the power receiving device 3, respectively. Rac is the load resistance of the power receiving device 3. Furthermore, Lr1 and Lr2 are the inductances of the first coil 31 and the second coil 32 of the relay circuit 4, respectively. Also, Cr-1 and Cr-2 are the capacitance of the resonant capacitor 33 of the relay circuit 4 divided into two parts (i.e., the capacitance of the resonant capacitor 33 is ((Cr-1)*(Cr-2)) / ((Cr-1)+(Cr-2))). Rac is the load resistance of the power receiving device 3. Ma is the mutual inductance between the transmitting coil 12 and the first coil 31, and M is the mutual inductance between the second coil 32 and the receiving coil 21.

[0039] In the equivalent circuit 300, if the load resistance for the power transmission device 2 and the relay circuit 4 is Z1, then when the resonant circuit 20 of the power receiving device 3 is in resonance, the portion 300a of the equivalent circuit 300 on the power receiving side of the second coil 32 is represented by the equivalent circuit 310. In this case, the load resistance Z1 is expressed by the following equation.

number

number

[0040] As is clear from equation (3), unlike the comparative example, as the load of the power receiving device 3 decreases and the load resistance Rac increases, the overall load resistance Ro of the contactless power supply device also increases. Furthermore, as the degree of coupling k1 between the second coil 32 and the receiving coil 21 decreases, the overall load resistance Ro of the contactless power supply device increases. Therefore, the overall load resistance Ro of the contactless power supply device is minimized when the load resistance Rac of the power receiving device 3 is at its assumed minimum value and the degree of coupling k1 between the second coil 32 and the receiving coil 21 is at its assumed maximum value. Therefore, the values ​​of each circuit element of the contactless power supply device 1 and the maximum coupling degree between the second coil 32 and the receiving coil 21 are set so that when the load resistance Rac of the power receiving device 3 is at its expected minimum value and the coupling degree k between the second coil 32 and the receiving coil 21 is at its expected maximum value, the total load resistance Ro of the contactless power supply device is greater than or equal to the resistance value at which ZVS is achieved and the difference between the timing at which the voltage applied to the switching element 17 becomes zero relative to the timing at which the switching element 17 turns on is less than or equal to the allowable maximum value. As a result, even if the load of the power receiving device 3 fluctuates, ZVS is achieved and the difference between the timing at which the voltage applied to the switching element 17 becomes zero relative to the timing at which the switching element 17 turns on is less than or equal to the allowable maximum value. Furthermore, even if the power receiving device 3 is separated from the relay circuit 4 and unable to receive power, the coupling degree k between the second coil 32 and the receiving coil 21 becomes smaller, so ZVS is achieved, and the difference between the timing at which the switching element 17 turns on and the timing at which the voltage applied to the switching element 17 becomes zero is less than or equal to the allowable maximum value. Note that the conditions that the load resistance Ro must satisfy as described above may be referred to as the load resistance conditions below for the sake of explanation.

[0041] For example, suppose the inductance of coil 15 in the power supply circuit 11 of power transmission device 2 is 1 μH, and the inductances of the transmitting coil 12 of power transmission device 2, the first coil 31 and the second coil 32 of relay circuit 4, and the receiving coil 21 of power receiving device 3 are each 3 μH. Furthermore, suppose the capacitor of capacitor 16 in the power supply circuit 11 of power transmission device 2 is 330.4 pF, and the capacitor of capacitor 13 is 201.9 pF. Also, suppose the capacitor of resonant capacitor 33 in relay circuit 4 is 91.8 pF, and the capacitor of resonant capacitor 22 in power receiving device 3 is 184 pF. At this time, when the switching element 17 is driven at a switching frequency of 6.78 MHz and a duty cycle of 0.5, ZVS is achieved, and the load resistance Ro of the entire contactless power supply device 1 is 41.4 Ω, such that the difference between the timing at which the switching element 17 turns on and the timing at which the voltage applied to the switching element 17 becomes zero is less than or equal to the allowable maximum value (see the above-mentioned document "Load-Independent Class-E Power Conversion"). Therefore, assuming that the coupling degree between the transmitting coil 12 and the first coil 31 is 0.5, and the assumed maximum coupling degree between the second coil 32 and the receiving coil 21 is 0.1, from equation (3), the minimum value Racmin of the load resistance of the power receiving device 3 that satisfies the load resistance condition is 1.65 Ω. Thus, with the load circuit 5 connected to the power receiving device 3, the contactless power supply device 1 should be configured such that the load resistance of the power receiving device 3 is the minimum value Racmin plus a predetermined offset, for example, 2 Ω.

[0042] For example, the longer the distance between the second coil 32 and the receiving coil 21 of the power receiving device 3, the smaller the coupling between the second coil 32 and the receiving coil 21. Therefore, in the housing that houses the relay circuit 4, the relay circuit 4 should be installed in such a way that the distance from the second coil 32 to the surface of the housing is equivalent to the distance corresponding to the maximum coupling between the second coil 32 and the receiving coil 21 of the power receiving device 3 that satisfies the load resistance condition. As a result, the coupling between the second coil 32 and the receiving coil 21 is always less than or equal to the maximum coupling value. In addition, a fixed load having a resistance value equivalent to the minimum load resistance of the power receiving device 3 that satisfies the load resistance condition should be provided in the load circuit 5, or on the wiring connecting the power receiving device 3 and the load circuit 5.

[0043] The arrangement of the transmitting coil 12 of the power transmission device 2 and the first coil 31 and second coil 32 of the relay circuit 4 will be described below.

[0044] Figure 4 shows an example of the arrangement of the transmitting coil 12, the first coil 31, and the second coil 32. In this example, the transmitting coil 12, the first coil 31, and the second coil 32 are each formed by conductive patterns provided on the substrate 400. Note that in Figure 4, the illustration of circuit elements other than the transmitting coil 12, the first coil 31, and the second coil 32 is omitted.

[0045] In order to maximize the efficiency of power transmission, it is preferable that the transmitting coil 12 and the first coil 31 be arranged so that their coupling degree is as high as possible. In this example, the first coil 31 is formed on one surface 400a of the substrate 400, and the transmitting coil 12 is formed on the surface 400b opposite to surface 400a, so that the central axis of the transmitting coil 12 and the central axis of the first coil 31 are coaxial.

[0046] It is preferable that the second coil 32 and the receiving coil 21 of the power receiving device 3, which is electromagnetically coupled to the second coil 32 and receives power via the second coil 32, are not electromagnetically coupled to the transmitting coil 12 and the first coil 31. For this reason, the second coil 32 is arranged on one surface 400a of the substrate 400, similar to the first coil 31. Furthermore, when viewed from the direction normal to surface 400a, the first coil 31 and the second coil 32 are arranged so as not to overlap with each other and at least a predetermined distance apart. The predetermined distance is such that the influence of the magnetic field generated by the transmitting coil 12 and the magnetic field generated by the first coil 31 on the second coil 32 and the receiving coil 21 that receives from the second coil 32 is negligible. This prevents the receiving coil 21 from receiving power from the transmitting coil 12 or the first coil 31 without going through the second coil 32. Therefore, even if the load of the power receiving device 3 fluctuates, a decrease in the overall load resistance of the non-contact power supply device 1 is suppressed.

[0047] Figure 5 shows another example of the arrangement of the transmitting coil 12, the first coil 31, and the second coil 32. In this example as well, the transmitting coil 12, the first coil 31, and the second coil 32 are each formed by conductive patterns provided on the substrate 500. Note that in Figure 5, circuit elements other than the transmitting coil 12, the first coil 31, and the second coil 32, as well as the wiring connecting each coil of the relay circuit 4, are not shown.

[0048] In this example as well, the first coil 31 is formed on one side 500a of the substrate 500, and the transmitting coil 12 is formed on the side 500b opposite to side 500a, so that the central axis of the transmitting coil 12 and the central axis of the first coil 31 are coaxial.

[0049] In this example as well, the second coil 32 is positioned on one surface 500a of the substrate 500, similar to the first coil 31. However, in this example, the second coil 32 is positioned such that, when viewed from the direction normal to surface 500a, it overlaps with the first coil 31 and the transmitting coil 12 to such an extent that they do not electromagnetically couple. That is, if the first coil 31 and the second coil 32 overlap to such an extent that the magnetic fields generated from each part of the first coil 31 and passing through the inside of the second coil 32 cancel each other out, then the first coil 31 and the second coil 32 do not electromagnetically couple. Similarly, if the transmitting coil 12 and the second coil 32 overlap to such an extent that the magnetic fields generated from each part of the transmitting coil 12 and passing through the inside of the second coil 32 cancel each other out, then the transmitting coil 12 and the second coil 32 do not electromagnetically couple. For example, the inventors have confirmed through simulation that when the first coil 31 and the second coil 32 are both formed in a substantially square shape and of the same size, electromagnetic coupling between the first coil 31 and the second coil 32 will cease when either side of the first coil 31 and either side of the second coil 32 lie on the same straight line and the first coil 31 and the second coil 32 are arranged to overlap by approximately 12%. It is preferable that an insulating layer be provided between the first coil 31 and the second coil 32 in the overlapping portion. Furthermore, in this example, it is preferable that the receiving coil 21 is positioned so that it does not electromagnetically couple with the transmitting coil 12 and the first coil 31 when the receiving coil 21 receives AC power from the second coil 32 through electromagnetic coupling between the second coil 32 and the receiving coil 21. Therefore, it is preferable that the first coil 31 and the second coil 32 be designed such that the outer circumference of the second coil 32 is larger than the outer circumference of the first coil 31.

[0050] The shapes of the transmitting coil 12, the first coil 31, and the second coil 32 are not limited to approximately circular shapes. For example, the transmitting coil 12, the first coil 31, and the second coil 32 may each be formed in an approximately square shape, or in other polygonal shapes. Furthermore, the shapes of the first coil 31 and the second coil 32 may be different from each other. Also, the first coil 31 and the second coil 32 may be arranged on different surfaces of the substrate. That is, in the example of Figure 4 or Figure 5 above, the second coil 32 may be provided on the surface of the substrate on which the transmitting coil 12 is located. In this case, the first coil 31 and the second coil 32 may be connected via vias provided on the substrate. Also, the arrangement of the transmitting coil 12, the first coil 31, and the second coil 32 is not limited to the above examples. For example, the transmitting coil 12 and the first coil 31 may be wound around the same core made of magnetic material. Furthermore, the second coil 32 may be wound around another core, which is provided separately from the core around which the transmitting coil 12 and the first coil 31 are wound. The core around which each coil is wound may be cylindrical or donut-shaped. Furthermore, in the example arrangement shown in Figure 4, the first coil 31 and the second coil 32 may be designed such that the outer circumference of the second coil 32 is larger than the outer circumference of the first coil 31.

[0051] As described above, this contactless power supply device drives the switching elements of a power supply circuit that supplies AC power to the transmitting coil at a switching frequency included in the ISM band, which has fewer usage restrictions. Furthermore, this contactless power supply device has a relay circuit between the transmitting device and the receiving device for relaying the AC power transmitted from the transmitting device to the receiving device. This relay circuit includes a first coil that electromagnetically couples with the transmitting coil, provided in the transmitting device; a second coil that electromagnetically couples with the receiving coil, provided in the receiving device; and a resonant capacitor that resonates with the AC power transmitted from the transmitting device, together with the first and second coils. As a result, this contactless power supply device can achieve ZVS (Zero Voltage Switching) even when the load connected to the receiving device fluctuates, and can sufficiently reduce the difference between the timing of the switching element changing from off to on and the timing of the voltage applied to the switching element. This allows the contactless power supply device to reduce switching losses in the switching elements and suppress a decrease in power transmission efficiency.

[0052] Those skilled in the art can make various modifications within the scope of the present invention to suit the embodiment being implemented. [Explanation of symbols]

[0053] 1. Contactless power supply device 2. Power transmission equipment 10 DC power supply 11 Power supply circuit 12 Transmitting coil 13 Capacitors 14 Control circuits 15 coils 16 Capacitors 17 Switching elements 3. Power receiving device 20 Resonant circuit 21 Receiving coil 22 Resonant Capacitors 23 Rectifier smoothing circuit 4. Relay Circuit 31. The first coil 32. The second coil 33 Resonant Capacitor 5 Load circuit 400, 500 circuit boards

Claims

1. Power transmission equipment and Power receiving device and A relay circuit that relays power transmitted non-contactually from the power transmission device to the power receiving device, It has, The aforementioned power transmission device is A transmitting coil that transmits the supplied AC power to the relay circuit, A power supply circuit that converts DC power supplied from a DC power source into AC power having a predetermined frequency, and supplies the converted AC power to the transmitting coil, It has, The aforementioned relay circuit is A first coil is arranged to be electromagnetically coupled to the transmitting coil and to receive AC power from the transmitting coil, A second coil transmits the AC power received via the first coil to the power receiving device, A resonant capacitor that resonates with the AC power supplied to the transmitting coil, together with the first coil and the second coil, It has, The power receiving device is A resonant circuit having a receiving coil that receives AC power from the second coil by electromagnetic coupling with the second coil of the relay circuit, A rectifier and smoothing circuit that rectifies the AC power output from the resonant circuit to convert it into DC power and outputs the DC power to a load circuit, It has, The first coil of the relay circuit and the transmitting coil of the power transmission device are wound around the same core. Contactless power supply device.

2. The contactless power supply device according to claim 1, wherein the second coil of the relay circuit is arranged so as not to be electromagnetically coupled with the first coil of the relay circuit and the transmitting coil of the power supply device.

3. The contactless power supply device according to claim 2, wherein the outer circumference of the second coil is larger than the outer circumference of the first coil.

4. Power transmission device and Power receiving device and A relay circuit that relays power transmitted non-contactually from the power transmission device to the power receiving device, It has, The aforementioned power transmission device is A transmitting coil that transmits the supplied AC power to the relay circuit, A power supply circuit that converts DC power supplied from a DC power source into AC power having a predetermined frequency, and supplies the converted AC power to the transmitting coil, It has, The aforementioned relay circuit is A first coil is arranged to be electromagnetically coupled to the transmitting coil and to receive AC power from the transmitting coil, A second coil transmits the AC power received via the first coil to the power receiving device, A resonant capacitor that resonates with the AC power supplied to the transmitting coil, together with the first coil and the second coil, It has, The power receiving device is A resonant circuit having a receiving coil that receives AC power from the second coil by electromagnetic coupling with the second coil of the relay circuit, A rectifier and smoothing circuit that rectifies the AC power output from the resonant circuit to convert it into DC power and outputs the DC power to a load circuit, It has, The first coil of the relay circuit is formed on one surface of the substrate, and the transmitting coil of the power transmission device is formed on the other surface of the substrate such that the central axis of the first coil and the central axis of the transmitting coil are coaxial. Contactless power supply device.

5. The non-contact power supply device according to claim 4, wherein the first coil and the second coil are arranged to partially overlap when viewed from the direction normal to the substrate to such an extent that the magnetic fields generated from each part of the first coil and passing through the inside of the second coil cancel each other out, preventing electromagnetic coupling between the first coil and the second coil, and the transmitting coil and the second coil are arranged to partially overlap when viewed from the direction normal to the substrate to such an extent that the magnetic fields generated from each part of the transmitting coil and passing through the inside of the second coil cancel each other out, preventing electromagnetic coupling between the transmitting coil and the second coil.

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