Power reception device and non-contact power supply system

Abstract

Provided is a power reception device capable of adequately obtaining a voltage gain within an intended range.　In a resonance circuit (30) of a power reception device (3), a first resonance capacitor (321) and a second resonance capacitor (322) are connected in series to a resonance coil (31), and a first switching circuit (331) is connected in parallel to the second resonance capacitor (322). A control unit (42) changes the resonance frequency of the resonance circuit (30) by switching the first switching circuit (331) in accordance with the output voltage of a smoothing capacitor (45).

Description

Power receiving device and contactless power supply system

[0001] The present invention relates to a power receiving device and a contactless power supply system.

[0002] Patent Document 1 discloses a contactless power supply device. The power receiving device of this contactless power supply device includes a resonant circuit having a receiving coil and a variable capacitance circuit. The power receiving device reduces the capacitance of the variable capacitance circuit as the output voltage from the resonant circuit increases.

[0003] Japanese Patent Publication No. 2018-148640

[0004] In conventional contactless power supply systems, the operating frequency was changed to alter the voltage gain when the load or the degree of coupling between the transmitting and receiving coils changed. Patent Document 1 proposes a contactless power supply device that can suppress the decrease in energy transmission efficiency even when the degree of coupling changes dynamically.

[0005] In the variable capacitance circuit of Patent Document 1, there are multiple capacitors, each connected in parallel to the receiving coil. A switching element is connected in series to each capacitor constituting the variable capacitance circuit. When this switching element is off, the output voltage of the receiving coil is applied across the switching element. In contactless power supply with a heavy load, the output voltage of the receiving coil may exceed the withstand voltage of the switching element.

[0006] One aspect of the present invention aims to appropriately obtain a voltage gain within an intended range.

[0007] A power receiving device for contactless power supply according to Embodiment 1 of the present invention comprises a resonant circuit having a resonant coil, a first resonant capacitor connected in series with the resonant coil, a second resonant capacitor connected in series with the first resonant capacitor, and a first switching circuit connected in parallel with the second resonant capacitor; a rectifier circuit for rectifying the received AC current; a smoothing capacitor connected to the rectifier circuit for smoothing the voltage output from the rectifier circuit; a first detection unit for detecting the output voltage of the smoothing capacitor; and a control unit for changing the resonant frequency of the resonant circuit by switching the first switching circuit on or off according to the output voltage, and is configured for contactless power supply.

[0008] According to the above configuration, the control unit changes the resonant frequency of the resonant circuit by switching the first switching circuit on and off according to the output voltage of the smoothing capacitor. Therefore, a voltage gain within the intended range can be obtained appropriately.

[0009] Furthermore, the second resonant capacitor is connected in series with the first resonant capacitor, and the first switching circuit is connected in parallel with the second resonant capacitor. Therefore, when the first switching circuit is switched off, it is unlikely that the voltage across the first switching circuit will exceed the voltage rating of the first switching circuit.

[0010] The power receiving device according to aspect 2 of the present invention may be configured such that, in aspect 1 above, it is electromagnetically coupled with the resonant coil and includes a power receiving coil that receives power from a power transmitting device, and the rectifier circuit is connected to the power receiving coil and receives the alternating current from the power receiving coil.

[0011] The voltage across the resonant coil can be significantly higher than the output voltage of the smoothing capacitor. According to the above configuration, a receiving coil is provided that electromagnetically couples with the resonant coil, and an alternating current is input from this receiving coil to the rectifier circuit. This makes it easy to obtain the desired voltage gain.

[0012] In the power receiving device according to embodiment 3 of the present invention, the resonant coil may be configured to receive power from the power transmitting device, as described in embodiment 1 above.

[0013] In the power receiving device according to embodiment 4 of the present invention, the control unit may be configured to perform hysteresis control so that the output voltage falls within a predetermined range, as described in embodiment 1 above.

[0014] The above configuration reduces the possibility of excessive stress being applied to the switching circuit of the resonant circuit.

[0015] A power receiving device according to embodiment 5 of the present invention, in embodiment 3 above, comprises a transformer having a primary coil connected between one end and the other end of the resonant coil, and a secondary coil with fewer turns than the primary coil, wherein the rectifier circuit is connected to the secondary coil and receives the alternating current from the secondary coil.

[0016] A contactless power supply system according to embodiment 6 of the present invention comprises a power receiving device described in any of embodiments 1 to 5 above, and a power transmission device equipped with a power transmission coil that supplies power to the power receiving device.

[0017] A contactless power supply system according to embodiment 7 of the present invention may be configured such that the power transmission device comprises an inverter, an inductor connected to the inverter, a first power transmission capacitor disposed between the inductor and the power transmission coil and connected in series with the power transmission coil, and a second power transmission capacitor connected in parallel with the first power transmission capacitor and the power transmission coil.

[0018] According to the above configuration, the power transmission device of the contactless power supply system is equipped with a resonant circuit consisting of an inductor, a first power transmission capacitor, and a second capacitor. By providing a resonant circuit in the power transmission device, it becomes possible to adjust the peak value of the current flowing to the inverter when the inverter's switching element is switched off.

[0019] According to one aspect of the present invention, a voltage gain within the intended range can be appropriately obtained.

[0020] This is a circuit diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention. This figure shows the peak value of the received voltage when the conditions change. This figure shows the peak value of the received voltage when the conditions change. This figure shows the peak value of the received voltage when the conditions change. This is a circuit diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention.

[0021] [Embodiment 1] Hereinafter, an embodiment relating to one aspect of the present invention (hereinafter also referred to as "this embodiment") will be described based on the drawings.

[0022] §1 Application Example Figure 1 is a circuit diagram showing the configuration of the contactless power supply system 1 of this embodiment. The contactless power supply system 1 comprises a power transmission device 2 and a power receiving device 3. The power transmission device 2 supplies power to the power receiving device 3 in a contactless manner.

[0023] The power receiving device 3 is used for contactless power supply and includes a resonant circuit 30, a first detection unit 41, a resonant control unit 42 (control unit), a rectifier circuit 44, and a smoothing capacitor 45. The resonant circuit 30 of the power receiving device 3 includes at least a resonant coil 31, a first resonant capacitor 321, a second resonant capacitor 322, and a first switching circuit 331.

[0024] The first resonant capacitor 321 is connected in series with the resonant coil 31. The second resonant capacitor 322 is connected in series with the first resonant capacitor 321. The first switching circuit 331 is connected in parallel with the second resonant capacitor 322.

[0025] The rectifier circuit 44 rectifies the received AC current. For example, it rectifies the output current received from both ends of the receiving coil 43. The smoothing capacitor 45 is connected to the rectifier circuit 44 and smooths the voltage output from the rectifier circuit 44. The first detection unit 41 detects the output voltage of the smoothing capacitor 45. The resonance control unit 42 changes the resonance frequency of the resonance circuit 30 by switching the first switching circuit 331 and the like on and off according to the output voltage of the smoothing capacitor 45.

[0026] The smoothing capacitor 45 outputs its output voltage to the load 80. The output voltage of the smoothing capacitor 45 can increase as the load resistance of the load 80 increases. That is, the higher the load resistance of the load 80, the higher the voltage gain between the transmitting coil 28 and the receiving coil 43 can become. The resonance control unit 42 switches the first switching circuit 331 on and off, for example, so that the resonant frequency of the resonant circuit 30 increases as the output voltage of the smoothing capacitor 45 increases. By switching the first switching circuit 331 off, the resonance control unit 42 increases the resonant frequency of the resonant circuit 30, the output voltage of the smoothing capacitor 45 falls within a predetermined range, and a voltage gain within the intended range is obtained.

[0027] When the first switching circuit 331 is switched off, the voltage across the second resonant capacitor 322 is applied across the first switching circuit 331. Since the second resonant capacitor 322 is connected in series with the first resonant capacitor 321, the voltage applied across the first switching circuit 331 is reduced compared to the voltage across the resonant coil 31.

[0028] Therefore, the contactless power supply system 1 can obtain a voltage gain within the intended range while reducing the voltage applied across the first switching circuit 331 of the resonant circuit 30.

[0029] §2 Configuration Example (Configuration of Power Transmission Device 2) The power transmission device 2 comprises a power transmission control unit 22, a power supply 23, an inverter 24, a coil 25 (inductor), a first capacitor 26 (second power transmission capacitor), a second capacitor 27 (first power transmission capacitor), and a power transmission coil 28. The power supply 23 is a DC power supply. The inverter 24 is connected to the power supply 23 and converts the DC voltage to an AC voltage. The inverter 24 includes a plurality of switching elements 24a to 24d. The power transmission control unit 22 operates the inverter 24 by controlling the plurality of switching elements 24a to 24d.

[0030] One end of coil 25 is connected to one output terminal of inverter 24. One end of first capacitor 26 is connected to the other end of coil 25, and the other end of first capacitor 26 is connected to the other output terminal of inverter 24. One end of second capacitor 27 is connected to the other end of coil 25. One end of power transmission coil 28 is connected to the other end of second capacitor 27, and the other end of power transmission coil 28 is connected to the other output terminal of inverter 24. Second capacitor 27 is positioned between coil 25 and power transmission coil 28. First capacitor 26 is connected in parallel to second capacitor 27 and power transmission coil 28. Power transmission coil 28 supplies power to power receiving device 3 non-contact by generating an alternating current magnetic field.

[0031] (Configuration of the power receiving device 3) The power receiving device 3 comprises a resonant circuit 30, a first detection unit 41, a resonant control unit 42 (control unit), a power receiving coil 43, a rectifier circuit 44, a smoothing capacitor 45, and a load 80.

[0032] The resonant circuit 30 includes a resonant coil 31 and a variable capacitance circuit 32. The resonant coil 31 generates an AC voltage from the AC magnetic field of the power transmission coil 28 of the power transmission device 2. The variable capacitance circuit 32 is a circuit whose capacitance can be adjusted and is connected in series with the resonant coil 31.

[0033] The variable capacitance circuit 32 includes a first resonant capacitor 321, a second resonant capacitor 322, a third resonant capacitor 323, a fourth resonant capacitor 324, a first switching circuit 331, a second switching circuit 332, and a third switching circuit 333.

[0034] The first resonant capacitor 321 is connected in series with the resonant coil 31. One end of the first resonant capacitor 321 is connected to one end of the resonant coil 31, and the other end is connected to one end of the second resonant capacitor 322. The second resonant capacitor 322 is connected in series with the first resonant capacitor 321. The third resonant capacitor 323 is connected in series with the second resonant capacitor 322. The fourth resonant capacitor 324 is connected in series with the third resonant capacitor 323.

[0035] The first switching circuit 331 is connected in parallel to the second resonant capacitor 322. By switching the on (conductive) / off (non-conductive) state of the first switching circuit 331, the short-circuit state / open-circuit state between both ends of the second resonant capacitor 322 is switched. The second switching circuit 332 is connected in parallel to the third resonant capacitor 323. By switching the on (conductive) / off (non-conductive) state of the second switching circuit 332, the short-circuit state / open-circuit state between both ends of the third resonant capacitor 323 is switched. The third switching circuit 333 is connected in parallel to the fourth resonant capacitor 324. By switching the on (conductive) / off (non-conductive) state of the third switching circuit 333, the short-circuit state / open-circuit state between both ends of the fourth resonant capacitor 324 is switched. The first switching circuit 331, the second switching circuit 332, and the third switching circuit 333 include transistors such as MOSFETs.

[0036] In the variable capacitance circuit 32, the capacitance of the variable capacitance circuit 32 can be changed by switching the on / off states of the first switching circuit 331, the second switching circuit 332, and the third switching circuit 333 respectively. Among the first switching circuit 331, the second switching circuit 332, and the third switching circuit 333, as the number of switching circuits switched to off increases, the capacitance of the variable capacitance circuit 32 becomes smaller. When the capacitance of the variable capacitance circuit 32 becomes smaller, the resonant frequency of the resonant circuit 30 becomes larger.

[0037] The capacitances of the second resonance capacitor 322, the third resonance capacitor 323, and the fourth resonance capacitor 324 can be determined to be arbitrary capacitances at the design stage of the resonance circuit 30. For example, the capacitances of the second resonance capacitor 322, the third resonance capacitor 323, and the fourth resonance capacitor 324 may be determined to be the same capacitance as that of the first resonance capacitor 321, or may be determined to be different capacitances respectively. For example, the capacitances of the second resonance capacitor 322, the third resonance capacitor 323, and the fourth resonance capacitor 324 may be determined to be larger than the capacitance of the first resonance capacitor 321 respectively.

[0038] The power receiving coil 43 receives power from the power transmitting coil 28 of the power transmitting device 2. The power receiving coil 43 is electromagnetically coupled with the resonance coil 31. For example, the power receiving coil 43 and the resonance coil 31 share a core and are electromagnetically coupled with a high degree of coupling. The number of turns of the power receiving coil 43 is less than the number of turns of the resonance coil 31.

[0039] The rectifier circuit 44 rectifies the alternating current input from the power receiving coil 43. Here, the rectifier circuit 44 is a bridge circuit including a plurality of diodes, but is not limited thereto, and may be a circuit including a plurality of switching elements. The rectifier circuit 44 has a first AC terminal 44a connected to one end of the power receiving coil 43, a second AC terminal 44b connected to the other end of the power receiving coil 43, a positive terminal 44c, and a negative terminal 44d. The rectifier circuit 44 outputs a full-wave rectified DC (pulsating) voltage from the positive terminal 44c and the negative terminal 44d. The negative terminal 44d is connected to the ground.

[0040] The smoothing capacitor 45 is connected between the positive terminal 44c and the negative terminal 44d of the rectifier circuit 44. The smoothing capacitor 45 smooths the voltage output from the rectifier circuit 44. The smoothing capacitor 45 outputs the smoothed output voltage to the load 80.

[0041] The load 80 is an arbitrary load device. The positive terminal of the load 80 is connected to one end of the smoothing capacitor 45 and the positive terminal 44c of the rectifier circuit 44. The negative terminal of the load 80 is connected to the other end of the smoothing capacitor 45.

[0042] The first detection unit 41 detects the output voltage of the smoothing capacitor 45. The first detection unit 41 can be, for example, any of the various known voltage detection circuits capable of detecting DC voltage.

[0043] The resonance control unit 42 changes the resonant frequency of the resonant circuit 30 by changing the combined capacitance of the variable capacitance circuit 32 according to the output voltage of the smoothing capacitor 45 detected by the first detection unit 41. At this time, the resonance control unit 42 performs hysteresis control so that the output voltage of the smoothing capacitor 45 detected by the first detection unit 41 falls within a predetermined range. For example, as the output voltage of the smoothing capacitor 45 increases, the resonance control unit 42 gradually switches off the first switching circuit 331, the second switching circuit 332, and the third switching circuit 333 of the variable capacitance circuit 32. The resonance control unit 42 is connected, for example, to the gate electrodes of the first switching circuit 331, the second switching circuit 332, and the third switching circuit 333. The resonance control unit 42 performs hysteresis control by outputting a control signal generated by the comparator circuit to the gate electrodes of the first switching circuit 331, the second switching circuit 332, and the third switching circuit 333.

[0044] (Operation of the contactless power supply system 1) Before power supply begins, the smoothing capacitor 45 of the power receiving device 3 is not charged. At this time, the first switching circuit 331, the second switching circuit 332, and the third switching circuit 333 of the variable capacitance circuit 32 are all turned on. When the power transmitting device 2 and the power receiving device 3 move closer to each other, the power transmitting coil 28 and the resonant coil 31 become electromagnetically coupled, and the degree of coupling increases. At this time, an AC voltage is generated in the resonant coil 31, and an AC voltage (receiving voltage) is also generated in the power receiving coil 43 according to the degree of coupling with the resonant coil 31 and the turns ratio. When the induced current in the power receiving coil 43 is rectified by the rectifier circuit 44 and flows to the smoothing capacitor 45, charging of the smoothing capacitor 45 begins, and the output voltage of the smoothing capacitor 45 rises.

[0045] The resonance control unit 42 switches the first switching circuit 331 to the off state when the output voltage of the smoothing capacitor 45 detected by the first detection unit 41 becomes higher than a predetermined first off threshold. This reduces the combined capacitance of the variable capacitance circuit 32 and increases the resonant frequency of the resonant circuit 30. The resonance control unit 42 keeps the first switching circuit 331 in the off state until the output voltage of the smoothing capacitor 45 falls below a predetermined first on threshold. The first on threshold is lower than the first off threshold. When the second switching circuit 332 is on and the output voltage of the smoothing capacitor 45 falls below a predetermined first on threshold, the resonance control unit 42 switches the first switching circuit 331 to the on state. When the first switching circuit 331 is switched on, the combined capacitance of the variable capacitance circuit 32 increases and the resonant frequency of the resonant circuit 30 decreases.

[0046] The resonance control unit 42 switches off the second switching circuit 332 when the output voltage of the smoothing capacitor 45 detected by the first detection unit 41 becomes higher than a predetermined second off threshold while the first switching circuit 331 is in the off state. This further reduces the combined capacitance of the variable capacitance circuit 32 and increases the resonant frequency of the resonant circuit 30. The second off threshold may be the same as the first off threshold or higher than the first off threshold. The resonance control unit 42 keeps the second switching circuit 332 in the off state until the output voltage of the smoothing capacitor 45 becomes lower than or equal to a predetermined second on threshold. The second on threshold is lower than the second off threshold. The second on threshold may be the same as the first on threshold or lower than the first on threshold. The resonance control unit 42 switches on the second switching circuit 332 when the output voltage of the smoothing capacitor 45 becomes lower than or equal to a predetermined second on threshold while the third switching circuit 333 is in the on state. When the second switching circuit 332 is switched on, the combined capacitance of the variable capacitance circuit 32 increases, and the resonant frequency of the resonant circuit 30 decreases.

[0047] When the second switching circuit 332 is in the off state, the resonance control unit 42 switches the third switching circuit 333 to the off state when the output voltage of the smoothing capacitor 45 detected by the first detection unit 41 becomes higher than a predetermined third off threshold. This further reduces the combined capacitance of the variable capacitance circuit 32 and increases the resonant frequency of the resonant circuit 30. The third off threshold may be the same as the second off threshold or higher than the second off threshold. The resonance control unit 42 keeps the third switching circuit 333 in the off state until the output voltage of the smoothing capacitor 45 falls below a predetermined third on threshold. The third on threshold is lower than the third off threshold. The third on threshold may be the same as the second on threshold or lower than the second on threshold. When the output voltage of the smoothing capacitor 45 falls below a predetermined third on threshold, the resonance control unit 42 switches the third switching circuit 333 to the on state. When the third switching circuit 333 is switched on, the combined capacitance of the variable capacitance circuit 32 increases and the resonant frequency of the resonant circuit 30 decreases.

[0048] When the first switching circuit 331 is switched off, the voltage across the second resonant capacitor 322 is applied across the first switching circuit 331 (for example, between the drain and source). Since the second resonant capacitor 322 is connected in series with the first resonant capacitor 321, the voltage applied across the first switching circuit 331, which has been switched off, is lower than the AC voltage generated in the resonant coil 31. Therefore, even if the AC voltage generated in the resonant coil 31 increases, the voltage applied across the first switching circuit 331 is unlikely to exceed the withstand voltage of the transistor included in the first switching circuit 331. Similarly, when the second switching circuit 332 and the third switching circuit 333 are switched off, the voltages applied across the second switching circuit 332 and the third switching circuit 333 are unlikely to exceed the withstand voltage of the transistors included in the second switching circuit 332 and the third switching circuit 333. Therefore, the first switching circuit 331, the second switching circuit 332, and the third switching circuit 333 are less likely to be damaged.

[0049] To reduce the voltage applied across the first switching circuit 331, etc., which is switched off, it is necessary to reduce the AC voltage generated in the resonant coil 31, and to do so, it is necessary to increase the capacitance of the variable capacitance circuit 32. At this time, if the resonant frequency of the resonant circuit 30 is to be matched to the frequency of the transmission coil 28, it is necessary to reduce the inductance of the resonant coil 31. If the inductance of the resonant coil 31 is reduced, the inductance of the transmission coil 28 also needs to be reduced, and a large excitation current will flow through the transmission coil 28 regardless of the load resistance of the load 80. When each switching element 24a to 24d of the inverter 24 is switched off, the peak value of the current flowing through the power transmission device 2 becomes large, and switching losses can no longer be ignored. By providing a transmission-side resonant circuit including the coil 25, the first capacitor 26, and the second capacitor 27 in the power transmission device 2, the peak value of the current flowing through the inverter 24 can be adjusted.

[0050] (Relationship between control of the resonant control unit and voltage gain) Figure 2 shows the voltage gain when the capacitance of the resonant circuit 30 is not changed. Figure 3 shows the voltage gain when the capacitance of the resonant circuit 30 is changed. In Figures 2 and 3, the horizontal axis represents the frequency fq (Hz). The vertical axis represents the peak value of the received voltage Vo (V). The frequency of the transmission coil 28 is the frequency at the position indicated by the vertical line on the graph, which is 8.5 × 10⁻⁶. ４ The frequency is Hz. Using Figures 2 and 3, we will explain the effect of changing the capacitance of the variable capacitance circuit 32 on changing the resonant frequency of the resonant circuit 30 and thereby changing the voltage gain.

[0051] In Figure 2, the load resistance of the power receiving device 3 is RL, and the degree of coupling between the power transmission coil 28 and the resonant coil 31 is k. 12 The peak value of the received voltage when the capacitance of the resonant circuit 30 is C2 is |Vo(ω(fq), RL, k 12 The solid line shows the peak value of the received voltage when the transmission coil 28 and the resonant coil 31 are close together and the coupling degree doubles. |Vo(ω(fq), RL, 2k 12, |C2)| is indicated by a dashed line. The peak value of the received voltage |Vo(ω(fq), RL, 6k 12 , |C2)| is indicated by a dashed-dotted line.

[0052] In FIG. 3, the load resistance of the power receiving device 3 is RL, and the coupling degree between the power transmission coil 28 and the resonance coil 31 is k 12 , when the capacitance of the resonance circuit 30 is C2, the peak value of the received voltage |Vo(ω(fq), RL, k 12 , |C2)| is indicated by a solid line. When the power transmission coil 28 and the resonance coil 31 approach each other and the coupling degree becomes twice, and the capacitance of the variable capacitance circuit 32 is changed to change the capacitance of the resonance circuit 30 to 0.85 times of C2, the peak value of the received voltage |Vo(ω(fq), RL, 2k 12 , 0.85C2)| is indicated by a dashed line. When the power transmission coil 28 and the resonance coil 31 approach each other further and the coupling degree becomes six times, and the capacitance of the variable capacitance circuit 32 is changed to change the capacitance of the resonance circuit 30 to 0.6 times of C2, the peak value of the received voltage |Vo(ω(fq), RL, 6k 12 , 0.6C2)| is indicated by a dashed-dotted line.

[0053] In FIGS. 2 and 3, the value of |Vo(ω(fq), RL, k 12 , |C2)| is up to 40.605 V at maximum. Also, from FIG. 2, it can be seen that when the capacitance of the resonance circuit 30 is not changed, the higher the coupling degree, the larger the peak value Vo of the received voltage. That is, when the capacitance of the resonance circuit 30 is not changed, the higher the coupling degree, the higher the voltage gain.

[0054] When starting non-contact power supply, since the power transmission coil 28 gradually approaches the resonance coil 31, the coupling degree between the power transmission coil 28 and the resonance coil 31 increases. From FIG. 3, it can be seen that by appropriately determining the frequency of the power transmission coil 28 in advance and changing the capacitance of the variable capacitance circuit 32 to change the capacitance of the resonance circuit 30 within a predetermined range, a voltage gain within a predetermined range can be obtained regardless of the coupling degree.

[0055] In contactless power supply, energy transmission efficiency is increased by matching the frequency of the transmitting coil 28 to the resonant frequency of the receiving side. The frequency of the transmitting coil 28 can be adjusted based on the resonant circuit of the transmitting side, which includes the coil 25, the first capacitor 26, and the second capacitor 27. The frequency of the transmitting coil 28 is such that, for example, the degree of coupling between the transmitting coil 28 and the resonant coil 31 is minimized (for example, the degree of coupling is k). 12 In this case, the resonant frequency of the resonant circuit 30 should be adjusted to match the resonant frequency of the resonant circuit 30 when the capacitance of the variable capacitance circuit 32 is equal to the capacitance of the first resonant capacitor 321.

[0056] Figure 4 shows the voltage gain when the load resistance of the power receiving device 3 changes. The horizontal axis represents the frequency fq (Hz). The vertical axis represents the peak value of the power receiving voltage Vo (V). The frequency of the power transmitting coil 28 is the frequency at the position indicated by the vertical line on the graph, which is 8.5 × 10⁻⁶. ４ The frequency is Hz. The load resistance of the power receiving device 3 is RL, and the degree of coupling between the power transmission coil 28 and the resonant coil 31 is k. 12 The peak value of the received voltage when the capacitance of the resonant circuit 30 is C2 is |Vo(ω(fq), RL, k 12 The line ,C2)| is shown as a solid line. The peak value of the received voltage when the load resistance of the power receiving device 3 is changed by 100 times is |Vo(ω(fq), 100RL,k 12 , C2)| is shown with a dashed line.

[0057] The peak value of the received voltage when the load resistance of the power receiving device 3 is changed by 100 times is |Vo(ω(fq), 100RL, k 12 ,C2)| is,|Vo(ω(fq),RL,k 12The frequency f1 of the resonant circuit 30 is lower than the frequency at which the voltage C2 reaches its maximum value V1. The resonance control unit 42 reduces the capacitance of the variable capacitance circuit 32 and raises the resonant frequency of the resonant circuit 30, so that this frequency f1 approaches the frequency of the power transmission coil 28. Therefore, if the resonance control unit 42 appropriately changes the capacitance of the variable capacitance circuit 32 according to the load resistance of the load 80, a voltage gain within a predetermined range can be obtained regardless of the load resistance of the load 80. As a result, even if the load resistance of the load 80 increases, the voltage across the ends of the resonant coil 31 will remain within a predetermined range, and it will be difficult for a voltage exceeding the withstand voltage of the first switching circuit 331, etc. to be applied across the ends of the first switching circuit 331, etc. of the variable capacitance circuit 32.

[0058] In Figure 4, the peak value of the received voltage when the load resistance of the power receiving device 3 is changed by 100 times is shown as follows: |Vo(ω(fq), 100RL, k 12 ,C2)| is,|Vo(ω(fq),RL,k 12 Even at frequencies higher than the frequency at which C2)| reaches its maximum value V1 (40.605V), the value remains V1. The power receiving device 3 may control this frequency to approach the frequency of the power transmitting coil 28. However, in this case, a larger current will flow through the resonant coil 31, reducing the energy transmission efficiency.

[0059] For example, the resonance control unit 42 may switch the first switching circuit 331 to ON when the output voltage of the smoothing capacitor 45 becomes higher than a predetermined first ON threshold. With the first switching circuit 331 ON, the resonance control unit 42 switches the second switching circuit 332 ON when the output voltage of the smoothing capacitor 45 becomes higher than a predetermined second ON threshold. With the second switching circuit 332 ON, the resonance control unit 42 switches the third switching circuit 333 ON when the output voltage of the smoothing capacitor 45 becomes higher than a predetermined third ON threshold. Conversely, the resonance control unit 42 switches the third switching circuit 333 OFF when the output voltage of the smoothing capacitor 45 becomes lower than or equal to a predetermined third OFF threshold. With the third switching circuit 333 OFF, the resonance control unit 42 switches the second switching circuit 332 OFF when the output voltage of the smoothing capacitor 45 becomes lower than or equal to a predetermined second OFF threshold. When the second switching circuit 332 is in the off state, the resonance control unit 42 switches the first switching circuit 331 to the off state when the output voltage of the smoothing capacitor 45 falls below a predetermined first off threshold. In this case, each off threshold is lower than each on threshold.

[0060] According to the contactless power supply system 1 of this embodiment, communication between the power receiving device 3 and the power transmitting device 2 is not required to adjust the supplied power. Therefore, the supplied power can be adjusted without delay in environments where the relative position of the power receiving device 3 with respect to the power transmitting device 2 changes. For this reason, the contactless power supply system 1 can also be used for wireless power supply while driving (DWPT), etc.

[0061] [Embodiment 2] Another embodiment of the present invention will be described below. For the sake of convenience of explanation, components having the same function as those described in the above embodiment will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0062] Figure 5 is a circuit diagram showing the configuration of the contactless power supply system 1a of this embodiment. The contactless power supply system 1a comprises a power transmission device 2 and a power receiving device 3a. The power receiving device 3a comprises a resonant circuit 30, a transformer 55, a first detection unit 41, a resonant control unit 42 (control unit), a rectifier circuit 44, a smoothing capacitor 45, and a load 80.

[0063] The primary coil 55a of the transformer 55 is connected between one end and the other end of the resonant coil 31. One end of the secondary coil 55b of the transformer 55 is connected to the first AC terminal 44a of the rectifier circuit 44. The other end of the secondary coil 55b of the transformer 55 is connected to the second AC terminal 44b of the rectifier circuit 44. The number of turns of the secondary coil 55b of the transformer 55 is less than the number of turns of the primary coil 55a.

[0064] (Operation of the contactless power supply system 1a) In the power receiving device 3a, the resonant coil 31 receives power from the power transmitting device 2. Resonance in the resonant circuit 30 generates an AC voltage (receiving voltage) in the resonant coil 31. The receiving voltage generated in the resonant coil 31 is reduced in pressure by the transformer 55. The reduced receiving voltage is generated in the secondary coil of the transformer 55. The power received by the resonant coil 31 is supplied to the smoothing capacitor 45 via the transformer 55.

[0065] (Modification) In the above embodiments 1 and 2, the variable capacitance circuit 32 is provided with a first resonant capacitor 321, a second resonant capacitor 322, a third resonant capacitor 323, a fourth resonant capacitor 324, a first switching circuit 331, a second switching circuit 332, and a third switching circuit 333. However, the variable capacitance circuit 32 only needs to include at least the first resonant capacitor 321, the second resonant capacitor 322, and the first switching circuit 331.

[0066] In embodiments 1 and 2 described above, the threshold values ​​of the output voltage of the smoothing capacitor 45 are set to be different when the resonance control unit 42 switches the first switching circuit 331 etc. from on to off and when it switches it from off to on. By performing hysteresis control on the on / off switching of each switching circuit of the variable capacitance circuit 32, the possibility of each switching circuit switching frequently is reduced, and the possibility of excessive stress being applied to the switching circuits can be reduced. However, the threshold values ​​of the output voltage of the smoothing capacitor 45 may be set to be the same when the resonance control unit 42 switches the first switching circuit 331 etc. from on to off and when it switches it from off to on.

[0067] The load 80 may be, for example, a rechargeable secondary battery. The load 80 may be connected to the smoothing capacitor 45 without going through a DC-DC converter.

[0068] In the power receiving device 3a of the above embodiment 2, the transformer 55 may be omitted. When the AC voltage generated in the resonant coil 31 and the target voltage of the output voltage are far apart, it is preferable to reduce the voltage using the transformer 55.

[0069] In embodiments 1 and 2 described above, the power transmission control unit 22 may perform phase shift control. The power transmission control unit 22 may perform phase shift control by communicating wirelessly with the resonance control unit 42 and performing phase shift control based on information received from the resonance control unit 42. Examples of information received from the resonance control unit 42 include information about the resonant capacitor that is in a short-circuit state in the variable capacitance circuit 32 and the output voltage of the smoothing capacitor 45 detected by the first detection unit 41. By performing phase shift control, the power transmission control unit 22 can reduce the capacitance that needs to be changed in the variable capacitance circuit 32.

[0070] [Example of implementation by software] The functions of the contactless power supply system 1, 1a (hereinafter referred to as "device") can be realized by a program that causes a computer to function as the device, and by a program that causes a computer to function as each control block of the device (especially the power transmission control unit 22, the first detection unit 41, the resonance control unit 42, etc.).

[0071] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., memory) as hardware for executing the program. By executing the program using this control device and storage device, the functions described in each of the embodiments are realized.

[0072] The above program may be recorded on one or more computer-readable recording media, not temporary ones. These recording media may or may not be provided by the above device. In the latter case, the program may be supplied to the above device via any wired or wireless transmission medium.

[0073] Furthermore, some or all of the functions of each of the above control blocks can also be realized by logic circuits. For example, an integrated circuit in which logic circuits functioning as each of the above control blocks are formed is also included in the scope of the present invention. In addition, it is also possible to realize the functions of each of the above control blocks by, for example, a quantum computer.

[0074] [Summary] The power receiving device according to embodiment 1 of the present invention is a resonant circuit comprising: a resonant coil; a first resonant capacitor connected in series with the resonant coil; a second resonant capacitor connected in series with the first resonant capacitor; and a first switching circuit connected in parallel with the second resonant capacitor; a rectifier circuit for rectifying the received AC current; a smoothing capacitor connected to the rectifier circuit for smoothing the voltage output from the rectifier circuit; a first detection unit for detecting the output voltage of the smoothing capacitor; and a control unit for changing the resonant frequency of the resonant circuit by switching the first switching circuit on or off according to the output voltage, and is for contactless power supply.

[0075] The power receiving device according to aspect 2 of the present invention may be configured such that, in aspect 1 above, it is electromagnetically coupled with the resonant coil and includes a power receiving coil that receives power from a power transmitting device, and the rectifier circuit is connected to the power receiving coil and receives the alternating current from the power receiving coil.

[0076] In the power receiving device according to embodiment 3 of the present invention, the resonant coil may be configured to receive power from a power transmitting device, as described in embodiment 1 above.

[0077] In the power receiving device according to embodiment 4 of the present invention, in any of embodiments 1 to 3 described above, the control unit may be configured to perform hysteresis control so that the output voltage falls within a predetermined range.

[0078] A power receiving device according to embodiment 5 of the present invention may be configured such that, in embodiment 1 or 3 above, it comprises a transformer having a primary coil connected between one end and the other end of the resonant coil, and a secondary coil with fewer turns than the primary coil, and the rectifier circuit is connected to the secondary coil and receives the alternating current from the secondary coil.

[0079] A contactless power supply system according to embodiment 6 of the present invention comprises the power receiving device described in any of embodiments 1 to 5 above, and a power transmission device equipped with a power transmission coil that supplies power to the power receiving device.

[0080] In the contactless power supply system according to embodiment 7 of the present invention, the power transmission device may be configured to include an inverter, an inductor connected to the inverter, a first power transmission capacitor disposed between the inductor and the power transmission coil and connected in series with the power transmission coil, and a second power transmission capacitor connected in parallel with the first power transmission capacitor and the power transmission coil.

[0081] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0082] 1, 1a Contactless power supply system 2 Power transmission device 3, 3a Power receiving device 22 Power transmission control unit 24 Inverter 28 Power transmission coil 30 Resonant circuit 31 Resonant coil 32 Variable capacitance circuit 321 First resonant capacitor 322 Second resonant capacitor 331 First switching circuit 41 First detection unit 42 Resonant control unit (control unit) 43 Power receiving coil 44 Rectifier circuit 45 Smoothing capacitor 55 Transformer 55a Primary coil 55b Secondary coil 80 Load

Claims

1. A power receiving device for contactless power supply, comprising: a resonant circuit having a resonant coil; a first resonant capacitor connected in series with the resonant coil; a second resonant capacitor connected in series with the first resonant capacitor; and a first switching circuit connected in parallel with the second resonant capacitor; a rectifier circuit for rectifying the received AC current; a smoothing capacitor connected to the rectifier circuit for smoothing the voltage output from the rectifier circuit; a first detection unit for detecting the output voltage of the smoothing capacitor; and a control unit for changing the resonant frequency of the resonant circuit by switching the first switching circuit on or off according to the output voltage.

2. The power receiving device according to claim 1, comprising a power receiving coil that is electromagnetically coupled to the resonant coil and receives power from a power transmission device, wherein the rectifier circuit is connected to the power receiving coil and receives the alternating current from the power receiving coil.

3. The power receiving device according to claim 1, wherein the resonant coil receives power from a power transmission device.

4. The power receiving device according to claim 1, wherein the control unit performs hysteresis control so that the output voltage falls within a predetermined range.

5. The power receiving device according to claim 3, comprising a transformer having a primary coil connected between one end and the other end of the resonant coil, and a secondary coil having fewer turns than the number of turns of the primary coil, wherein the rectifier circuit is connected to the secondary coil and receives the alternating current from the secondary coil.

6. A contactless power supply system comprising a power receiving device according to any one of claims 1 to 5, and a power transmission device equipped with a power transmission coil for supplying power to the power receiving device.

7. The contactless power supply system according to claim 6, wherein the power transmission device comprises an inverter, an inductor connected to the inverter, a first power transmission capacitor disposed between the inductor and the power transmission coil and connected in series with the power transmission coil, and a second power transmission capacitor connected in parallel with the first power transmission capacitor and the power transmission coil.

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