Contactless power supply device

Abstract

A contactless power supply device capable of improving power transmission efficiency with a simple structure is provided. A power transmission device (2) of the contactless power supply device (1) comprises: a transmitting coil (13) for supplying power to a power receiving device (3) via a receiving coil (21) provided in the power receiving device (3); a power supply circuit (10) for converting the DC power supplied from the power supply (11) into AC power and supplying the AC power to the transmitting coil (13) via a plurality of switch elements (12a to 12d) connected in a full bridge or half bridge between a power supply 11 for supplying DC power and the transmitting coil 13; an auxiliary coil (14) configured to be electromagnetically coupled with the transmitting coil (13); a variable capacitance circuit (15) connected to the auxiliary coil (14) and having an adjustable electrostatic capacitance; a second communicator (16) for receiving a signal containing a measured value of an output voltage from the power receiving device (3); and a control circuit (17) for controlling the electrostatic capacitance of the variable capacitance circuit (15) according to the measured value of the output voltage.

Description

Technical Field

[0001] The present invention relates to a contactless power supply device. Background Art

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

[0003] As one of such contactless power supply technologies, the following technology has been proposed: a resonant circuit is formed only in the secondary (power receiving) side coil, the phase information of the resonant current flowing in the resonant circuit is detected, and based on the phase information, a driving frequency is determined so that the current phase of the driving current flowing in the primary (power transmission) side coil is slightly delayed compared to the voltage phase, and the primary coil is driven (for example, refer to Patent Document 1). In addition, in this technology, the Q value determined by the leakage inductance of the secondary coil, the capacitance of the resonant capacitor, and the equivalent load resistance is set to Q = 2 / k 2 (k is the coupling coefficient). According to this technology, the heating in the primary coil is suppressed, and the frequency with the best power factor observed from the primary coil side can be automatically selected as the driving frequency. In addition, copper loss and switching loss are reduced.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2015 / 173850 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, in the above technology, in order to set an appropriate driving frequency, it is necessary to increase the Q value. In order to increase the Q value, it is necessary to increase the inductance of the coil on the power receiving side, and for this purpose, it is required to increase the size of the coil on the power receiving side. As a result, the entire device is increased in size.

[0009] Therefore, an object of the present invention is to provide a contactless power supply device capable of improving power transmission efficiency with a simple structure.

[0010] Solutions to Solve Problems

[0011] As one embodiment of the present invention, a contactless power supply device is provided, which includes a power transmission device and a power receiving device to which power is transmitted in a contactless manner from the power transmission device. In the contactless power supply device, the power receiving device includes: a resonant circuit, which includes a receiving coil and a resonant capacitor that resonates with the receiving coil, and receives power from the power transmission device; a rectifier circuit, which rectifies the power output from the resonant circuit; a voltage detection circuit, which measures the output voltage of the power output from the rectifier circuit and obtains the measured value of the output voltage; and a first communicator, which sends a signal containing the measured value of the output voltage to the power transmission device. The power transmitting device comprises: a transmitting coil, which supplies power to a power receiving device via a receiving coil; a power supply circuit, which has a plurality of switching elements connected in a full-bridge or half-bridge shape between a power supply supplying DC power and the transmitting coil, and is switched at a prescribed frequency by turning on and off the plurality of switching elements, so that the DC power supplied from the power supply is converted into AC power with a prescribed frequency and supplied to the transmitting coil; an auxiliary coil, which is configured to be electromagnetically coupled to the transmitting coil; a variable capacitance circuit, which is connected to the auxiliary coil and has an adjustable electrostatic capacitance; a second communicator, which receives a signal containing a measured value of an output voltage from the power receiving device; and a control circuit, which controls the electrostatic capacitance of the variable capacitance circuit according to the measured value of the output voltage.

[0012] By having such a structure, the contactless power supply device can improve the power transmission efficiency with a simple structure.

[0013] In the contactless power supply device, if the measured value of the output voltage is less than a specified lower limit threshold, or exceeds a specified upper limit threshold that is higher than the specified lower limit threshold, the control circuit of the power transmission device preferably controls the variable capacitor circuit with reference to a reference table representing the relationship between the current electrostatic capacitance of the variable capacitor circuit and the changed electrostatic capacitance, so that the changed electrostatic capacitance becomes corresponding to the current electrostatic capacitance.

[0014] Thus, the contactless power supply device can suppress the peak value of the current flowing in each switching element of the power supply circuit at the timing when the switching element is turned off, so the switching loss of each switching element can be reduced. In addition, the contactless power supply device can suppress the effective value of the current flowing in the auxiliary coil from being too high, and reduce the conduction loss caused by the current flowing in the auxiliary coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the configuration of a contactless power supply device according to one embodiment of the present invention.

[0016] Figure 2 It is a diagram showing another example of the inverter circuit.

[0017] Figure 3(a) is a diagram showing an example of current flowing through each switching element when the degree of coupling between the transmission coil and the auxiliary coil is lower than the degree of coupling between the transmission coil and the reception coil. Figure 3 (b) is a diagram showing an example of current flowing through each switching element when the degree of coupling between the transmission coil and the auxiliary coil is equal to the degree of coupling between the transmission coil and the reception coil. Figure 3 (c) is a diagram showing an example of current flowing through each switching element when the coupling degree between the transmission coil and the auxiliary coil is greater than the coupling degree between the transmission coil and the reception coil.

[0018] Figure 4 This is a diagram showing an example of the relationship between the electrostatic capacitance of the variable capacitance circuit and the current flowing through each switching element of the inverter circuit and the current flowing through the auxiliary coil based on a simulation.

[0019] Figure 5 This is a diagram showing an example of the relationship between the coupling degree between the transmission coil and the reception coil, the output voltage output from the power receiving device, and the current flowing through the switching element of the inverter circuit when the power transmitting device has no LC circuit based on a simulation.

[0020] Description of symbols

[0021] 1. Contactless power supply device

[0022] 2 Power transmission device

[0023] 10 Power supply circuit

[0024] 11 Power Supply

[0025] 12 Inverter Circuit

[0026] 12a~12d switching element

[0027] 12e Capacitor

[0028] 13 Transmitter coil

[0029] 14 Auxiliary coil

[0030] 15 Variable Capacitor Circuit

[0031] 151-1~151-n Capacitor

[0032] 152-1~152-n Switching elements

[0033] 16 communicator

[0034] 17 Control Circuit

[0035] 3 Power receiving device

[0036] 20 Resonance Circuit

[0037] 21 Receiving coil

[0038] 22 Resonant capacitor

[0039] 23 Rectification and smoothing circuit

[0040] 24 Voltage detection circuit

[0041] 25 Communicator DETAILED DESCRIPTION

[0042] Hereinafter, a contactless power supply device according to an embodiment of the present invention will be described with reference to the drawings.

[0043] In the contactless power supply device based on the present invention, the device on the power transmission side (hereinafter referred to as the power transmission device) has: an LC circuit composed of an auxiliary coil configured to be electromagnetically coupled with a coil for power transmission (hereinafter referred to as a transmitting coil) and a variable capacitance circuit connected to the auxiliary coil; and a control circuit that controls the electrostatic capacitance of the variable capacitance circuit. On the other hand, the device on the power receiving side (hereinafter referred to as the power receiving device) measures the output voltage generated by the power received from the power transmission device via the coil for power reception (hereinafter referred to as a receiving coil) included in the resonant circuit, and sends the measured value of the output voltage to the power transmission device. The output voltage changes according to the coupling degree between the transmitting coil and the receiving coil, and according to the coupling degree, the phase of the current flowing in each switching element of the power supply circuit changes with respect to the phase delay amount of the voltage applied to each switching element of the power supply circuit that supplies AC power to the transmitting coil. Therefore, the control circuit of the power transmission device controls the electrostatic capacitance of the variable capacitance circuit based on the measured value of the output voltage received from the power receiving device. Thus, the contactless power supply device sets the delay amount of the phase of the current flowing through each switching element of the power supply circuit relative to the phase of the voltage applied to each switching element of the power supply circuit to an appropriate delay amount, thereby improving the power transmission efficiency. In addition, since the Q value of the resonance circuit of the power receiving device does not need to be increased, the contactless power supply device does not need to enlarge the receiving coil included in the resonance circuit, and as a result, the entire device can be simplified.

[0044] Figure 1 FIG. 1 is a schematic diagram of a contactless power supply device including a power transmission device according to an embodiment of the present invention. Figure 1As shown, the contactless power supply device 1 includes: a power transmission device 2; and a power receiving device 3 to which power is transmitted from the power transmission device 2 via space in a contactless manner. The power transmission device 2 includes: a power supply circuit 10; a transmission coil 13; an auxiliary coil 14; a variable capacitance circuit 15; a communicator 16; and a control circuit 17. On the other hand, the power receiving device 3 includes: a resonant circuit 20 composed of a reception coil 21 and a resonant capacitor 22; a rectification and smoothing circuit 23; a voltage detection circuit 24; and a communicator 25. The contactless power supply device 1 according to this embodiment transmits power by a method (NS method) in which the resonant circuit 20 on the power receiving side performs series resonance with respect to the AC power supplied to the transmission coil 13, without using the resonance on the power transmission side. Furthermore, the contactless power supply device 1 may also transmit power by a method (NP method) in which the resonant circuit 20 on the power receiving side performs parallel resonance with respect to the AC power supplied to the transmission coil 13, without using the resonance on the power transmission side.

[0045] First, the power transmission device 2 will be described.

[0046] The power supply circuit 10 supplies AC power to the transmission coil 13. To this end, the power supply circuit 10 includes a power supply 11 and an inverter circuit 12.

[0047] The power supply 11 supplies DC power. For this purpose, for example, the power supply 11 includes: a full-wave rectifier circuit connected to a commercial AC power source for rectifying the AC power supplied from the AC power source; and a smoothing capacitor for smoothing the pulsating power output from the full-wave rectifier circuit. In addition, the power supply 11 converts the AC power supplied from the commercial AC power source into DC power, and outputs the converted DC power to the inverter circuit 12. Furthermore, the power supply 11 may also be a DC power source such as a battery.

[0048] The inverter circuit 12 converts the DC power supplied from the power supply 11 into AC power having a predetermined frequency, and supplies the converted AC power to the transmitting coil 13. The predetermined frequency can be set to a frequency at which the resonant circuit 20 of the power receiving device 3 resonates at an assumed coupling degree between the transmitting coil 13 and the receiving coil 21. In the present embodiment, the inverter circuit 12 is a full-bridge inverter in which four switching elements 12a to 12d are connected in a full-bridge shape. In addition, each switching element can be set to, for example, an n-channel MOSFET.

[0049] That is, among the four switching elements 12a to 12d, the switching element 12a and the switching element 12b are connected in series between the positive terminal and the negative terminal of the power supply 11. In addition, in the present embodiment, the switching element 12a is connected to the positive side of the power supply 11, and the switching element 12b is connected to the negative side of the power supply 11. Similarly, among the four switching elements 12a to 12d, the switching element 12c and the switching element 12d are connected in parallel with the switching element 12a and the switching element 12b, and are connected in series between the positive terminal and the negative terminal of the power supply 11. In addition, the switching element 12c is connected to the positive side of the power supply 11, and the switching element 12d is connected to the negative side of the power supply 11. Moreover, one end of the transmission coil 13 is connected between the switching element 12a and the switching element 12b, and the other end of the transmission coil 13 is connected between the switching element 12c and the switching element 12d.

[0050] like Figure 2 As shown, the inverter circuit 12 may also be a half-bridge inverter in which two switching elements 12a and 12b are connected in a half-bridge shape relative to the power supply 11. In this case, one end of the transmission coil 13 is connected between the switching element 12a and the switching element 12b via the capacitor 12e, and the other end of the transmission coil 13 may be grounded.

[0051] Furthermore, the power transmission device 2 may further include a DC-DC converter (not shown) between the power source 11 and the inverter circuit 12 .

[0052] The transmission coil 13 transmits the AC power supplied from the power supply circuit 10 to the receiving coil 21 of the power receiving device 3 via space. The power transmission device 2 may include a capacitor connected in series with the transmission coil 13 between the transmission coil 13 and the inverter circuit 12 of the power supply circuit 10 and used to cut off the DC power.

[0053] The auxiliary coil 14 is configured to be electromagnetically coupled with the transmitting coil 13. For this purpose, for example, the auxiliary coil 14 is wound around the same axis as the transmitting coil 13. Furthermore, the number of turns of the auxiliary coil 14 may be the same as or different from the number of turns of the transmitting coil 13. Furthermore, the auxiliary coil 14 acts on the AC power supplied to the transmitting coil 13 together with the capacitor 15, and the delay amount of the phase of the current flowing in the switching element relative to the phase of the voltage applied to the switching element is set to an appropriate delay amount for each switching element 12a to 12d of the inverter circuit 12 of the power supply circuit 10. As a result, the peak value of the current flowing in each switching element 12a to 12d when the switching element is turned off is close to 0. Therefore, the switching loss caused by each switching element 12a to 12d is reduced.

[0054] The variable capacitance circuit 15 has an adjustable electrostatic capacitance, is connected to the auxiliary coil 14, and together with the auxiliary coil 14 constitutes an example of a phase adjustment circuit, namely an LC circuit (hereinafter, sometimes referred to as an LC circuit). Moreover, in the LC circuit, namely the phase adjustment circuit, constituted by the auxiliary coil 14 and the variable capacitance circuit 15, for each switching element 12a~12d, the delay amount of the phase of the current flowing in the switching element relative to the phase of the voltage applied to the switching element is set to an appropriate delay amount. Furthermore, the resonant frequency of the LC circuit constituted by the auxiliary coil 14 and the variable capacitance circuit 15 may be different from the frequency of the AC power supplied to the transmitting coil 13. That is, the LC circuit constituted by the auxiliary coil 14 and the variable capacitance circuit 15 may not resonate with the AC power flow flowing in the transmitting coil 13.

[0055] In this embodiment, the variable capacitance circuit 15 includes: a plurality of capacitors 151-1 to 151-n (n is an integer greater than or equal to 2) connected in parallel to the auxiliary coil 14; and a plurality of switching elements 152-1 to 152-n. Moreover, the capacitor 151-k (k = 1, 2, ..., n) and the switching element 152-k are connected in series. Furthermore, one of the plurality of capacitors 151-1 to 151-n may be connected to the auxiliary coil 14 without passing through the switching element.

[0056] Each of the plurality of switch elements 152-1 to 152-n can be, for example, a relay or an n-channel MOSFET. When each switch element is an n-channel MOSFET, the drain terminal of each switch element is connected to one end of the auxiliary coil 14 via a corresponding capacitor, and the source terminal of each switch element is connected to the other end of the auxiliary coil 14. In addition, the gate terminal of each switch element is connected to the control circuit 17.

[0057] The plurality of switch elements 152-1 to 152-n are switched on / off by the control circuit 17, respectively. Moreover, among the plurality of capacitors 151-1 to 151-n, the capacitor connected in series with the switched-on switch element contributes to the operation of the LC circuit. That is, among the plurality of switch elements 152-1 to 152-n, the more the number of switched-on switch elements is, the more the electrostatic capacitance of the variable capacitance circuit 15 increases. Therefore, the effective value of the current flowing in the LC circuit increases. The phase of the current flowing in the LC circuit leads the phase of the voltage applied to the transmitting coil 13, so the more the effective value of the current flowing in the LC circuit increases, the greater the influence of the current flowing in the LC circuit on the phase of the current flowing in the inverter circuit 12 of the power supply circuit 10. As a result, the delay amount of the phase of the current flowing in each switch element relative to the phase of the voltage applied to each switch element of the inverter circuit 12 becomes smaller.

[0058] Whenever a wireless signal is received from the communicator 25 of the power receiving device 3, the communicator 16 extracts voltage information indicating the measured value of the output voltage from the wireless signal and outputs it to the control circuit 17. To this end, the communicator 16 has, for example, an antenna for receiving wireless signals according to a predetermined wireless communication standard and a communication circuit for demodulating the wireless signals. The predetermined wireless communication standard can be, for example, ISO / IEC15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0059] The control circuit 17 includes, for example, a nonvolatile memory circuit and a volatile memory circuit; a calculation circuit; an interface circuit for connecting to other circuits; the switching elements 12a to 12d of the inverter circuit 12 of the power supply circuit 10; and a drive circuit for outputting control signals to the switching elements 152-1 to 152-n of the variable capacitance circuit 15. The control circuit 17 controls the switching elements 12a to 12d of the inverter circuit 12 so that the frequency of the AC power supplied from the power supply circuit 10 to the transmission coil 13 is a predetermined frequency. As described above, the predetermined frequency can be set to a frequency at which the resonance circuit 20 of the power receiving device 3 resonates with an assumed coupling degree between the transmission coil 13 and the reception coil 21.

[0060] In the present embodiment, the control circuit 17 turns on the group of switch elements 12a and switch elements 12d and the group of switch elements 12b and switch elements 12c alternately. Moreover, the control circuit 17 makes the period during which the group of switch elements 12a and switch elements 12d is turned on equal to the period during which the group of switch elements 12b and switch elements 12c is turned on within one cycle corresponding to the frequency of the AC power supplied to the transmitting coil 13. Furthermore, it is preferred that the control circuit 17 turns on the group of switch elements 12a and switch elements 12d and the group of switch elements 12b and switch elements 12c at the same time to prevent the power supply 11 from being short-circuited. For this purpose, when the control circuit 17 switches on / off the group of switch elements 12a and switch elements 12d and the group of switch elements 12b and switch elements 12c, a dead time during which the groups of switch elements on both sides are turned off may also be set. In addition, when the inverter circuit 12 is Figure 2 In the case of the half-bridge inverter shown, the control circuit 17 may turn on the switching element 12 a and the switching element 12 b alternately at the frequency of the AC power supplied to the transmission coil 13 .

[0061] Then, the control circuit 17 controls the electrostatic capacitance of the variable capacitance circuit 15 based on the measured value of the output voltage indicated in the voltage information. The details of the control of the electrostatic capacitance of the variable capacitance circuit 15 will be described later.

[0062] Next, the power receiving device 3 will be described.

[0063] The receiving coil 21 and the resonant capacitor 22 together constitute a resonant circuit 20, and receive power from the transmitting coil 13 by resonating with the AC power flow flowing in the transmitting coil 13 of the power transmission device 2. In the present embodiment, the resonant capacitor 22 is connected in series with the receiving coil 21, but the resonant capacitor 22 may be connected in parallel with the receiving coil 21. In addition, in the resonant circuit 20, a coil connected in series with the receiving coil 21 may be provided between the receiving coil 21 and the rectifying and smoothing circuit 23. Then, the AC power output from the resonant circuit 20 is converted into DC power by the rectifying and smoothing circuit 23, and then output to a load circuit (not shown) connected to the power receiving device 3. Furthermore, the number of turns of the receiving coil 21 may be the same as the number of turns of the transmitting coil 13, or they may be different from each other.

[0064] The rectifying and smoothing circuit 23 is an example of a rectifying circuit, and includes, for example, a full-wave rectifying circuit including four bridge-connected diodes and a smoothing capacitor, and rectifies and smoothes the power output from the resonance circuit 20 to convert it into direct current power. Then, the rectifying and smoothing circuit 23 outputs the direct current power to the load circuit.

[0065] The voltage detection circuit 24 measures the output voltage between the two terminals of the rectifier and smoothing circuit 23. The output voltage between the two terminals of the rectifier and smoothing circuit 23 corresponds to the output voltage of the resonant circuit 20 one-to-one, so the measured value of the output voltage between the two terminals of the rectifier and smoothing circuit 23 indirectly becomes the measured value of the output voltage of the resonant circuit 20. The voltage detection circuit 24 can be set to one of various known voltage detection circuits that can detect DC power voltage, for example. Then, the voltage detection circuit 24 outputs voltage information indicating the measured value of the output voltage to the communicator 25.

[0066] The communicator 25 generates a wireless signal including the voltage information received from the voltage detection circuit 24 at each predetermined transmission cycle, and transmits the wireless signal to the communicator 16 of the power transmission device 2. To this end, the communicator 25 has, for example, a communication circuit that generates a wireless signal according to a predetermined wireless communication standard, and an antenna that outputs the wireless signal. In addition, similar to the communicator 16, the predetermined wireless communication standard can be, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0067] The following describes details of the operation of the contactless power supply device 1 and the relationship between parameter settings of each circuit element of the power transmission device 2 and the degree of coupling between each coil for reducing switching loss of each switching element of the inverter circuit 12 of the power supply circuit 10 .

[0068] In the present embodiment, when the coupling degree between the transmission coil 13 and the reception coil 21 is low, for example, when the power receiving device 3 is far away from the power transmitting device 2 and can hardly receive power from the power transmitting device 2, the phase of the current flowing in the transmission coil 13 is delayed from the phase of the voltage applied to each switching element of the inverter circuit 12 of the power supply circuit 10. The same is true when the current flowing in the load circuit connected to the power receiving device 3 is small. Therefore, it is preferable to set the inductance of the auxiliary coil 14 and the electrostatic capacitance of the variable capacitor 15 so that the phase of the current flowing in the LC circuit composed of the auxiliary coil 14 and the variable capacitor 15 is ahead of the phase of the voltage applied to each switching element of the power supply circuit 10. For this reason, it is preferable to set the inductance of the auxiliary coil 14 and the electrostatic capacitance of the variable capacitor 15 so that the resonant frequency of the LC circuit is higher than the frequency of the AC power supplied to the transmission coil 13.

[0069] In addition, the larger the inductance of the auxiliary coil 14, the better. This is because the larger the inductance of the auxiliary coil 14, the smaller the current flowing in the LC circuit. For example, it is preferable to set the inductance of the auxiliary coil 14 so that the current flowing in the LC circuit is smaller than the excitation current component of the current flowing in the transmitting coil 13 that does not depend on the load of the power receiving circuit 23 and the load circuit connected to the resonance circuit 20. In other words, it is preferable that the inductance of the auxiliary coil 14 is larger than the value obtained by multiplying the maximum value kmax of the coupling degree assumed between the transmitting coil 13 and the receiving coil 21 by the self-inductance of the power transmission side when the transmitting coil 13 and the receiving coil 21 are electromagnetically coupled.

[0070] Furthermore, it is preferable to arrange the transmission coil 13 and the auxiliary coil 14 so that the coupling degree between the transmission coil 13 and the auxiliary coil 14 is higher than the maximum value kmax of the coupling degree assumed between the transmission coil 13 and the receiving coil 21. For example, the transmission coil 13 and the auxiliary coil 14 are wound around the same axis and arranged at a distance such that the coupling degree between the transmission coil 13 and the auxiliary coil 14 is higher than the maximum value kmax of the coupling degree assumed between the transmission coil 13 and the receiving coil 21. As a result, the phase delay of the current flowing through the transmission coil 13 with respect to the phase delay of the voltage applied to the transmission coil 13 is reduced, and as a result, the peak value of the current when each switching element of the inverter circuit 12 is turned off is easily reduced.

[0071] Figure 3 (a) is a diagram showing an example of current flowing through each switching element when the degree of coupling between the transmission coil 13 and the auxiliary coil 14 is lower than the degree of coupling between the transmission coil 13 and the reception coil 21 based on a simulation. Figure 3(b) is a diagram showing an example of current flowing through each switching element when the degree of coupling between the transmission coil 13 and the auxiliary coil 14 is equal to the degree of coupling between the transmission coil 13 and the reception coil 21 based on a simulation. Figure 3 (c) is a diagram showing an example of current flowing through each switching element when the degree of coupling between the transmission coil 13 and the auxiliary coil 14 is greater than the degree of coupling between the transmission coil 13 and the reception coil 21 based on a simulation.

[0072] exist Figure 3 (a)~ Figure 3 In the simulation shown in (c), it is assumed that the inverter circuit 12 is Figure 2 The half-bridge inverter shown. In addition, the inductance of the transmitting coil 13 is set to 91μH, and the electrostatic capacitance of the capacitor 12e is set to 220nF. In addition, the inductance of the auxiliary coil 14 is set to 100μH, and the electrostatic capacitance of the capacitor 15 is set to 30nF. In addition, the inductance of the receiving coil 21 is set to 121μF, and the electrostatic capacitance of the resonant capacitor 22 is set to 60nF. In addition, the resistance value Ro of the load circuit connected to the power receiving device 3 is set to 10Ω. In addition, Figure 3 In the simulation shown in (a), the coupling degree k12 between the transmitting coil 13 and the receiving coil 21 is set to 0.2, the coupling degree k13 between the transmitting coil 13 and the auxiliary coil 14 is set to 0.1, and the coupling degree k23 between the auxiliary coil 14 and the receiving coil 21 is set to 0.2. Figure 3 In the simulation shown in (b), the coupling degree k12 between the transmitting coil 13 and the receiving coil 21, the coupling degree k13 between the transmitting coil 13 and the auxiliary coil 14, and the coupling degree k23 between the auxiliary coil 14 and the receiving coil 21 are all set to 0.2. Figure 3 In the simulation shown in (c), the coupling degree k12 between the transmitting coil 13 and the receiving coil 21 and the coupling degree k23 between the auxiliary coil 14 and the receiving coil 21 are set to 0.2, and the coupling degree k13 between the transmitting coil 13 and the auxiliary coil 14 is set to 0.7.

[0073] exist Figure 3 (a)~ Figure 3 (c) In each graph, the horizontal axis represents time and the vertical axis represents current. Also, time t1 and time t2 represent the timing when the switch element 12a is turned off. Figure 3 In (a), waveform 301 represents the waveform of the current flowing in the switching element 12a when the coupling degree k12 is greater than the coupling degree k13. Figure 3 In (b), waveform 311 represents the waveform of the current flowing in the switching element 12a when the coupling degree k12 is equal to the coupling degree k13. Figure 3In (c), a waveform 321 shows a waveform of a current flowing through the switching element 12 a when the coupling degree k12 is smaller than the coupling degree k13 .

[0074] As shown in waveforms 301, 311, and 321, the greater the coupling degree k13 between the transmitting coil 13 and the auxiliary coil 14 is relative to the coupling degree k12 between the transmitting coil 13 and the receiving coil 21, the lower the peak value of the current when the switching element of the inverter circuit 12 is turned off and the effective value of the current flowing in the switching element. It can be seen that it is preferred that the coupling degree k13 is greater than the coupling degree k12.

[0075] Figure 4 1 is a diagram showing an example of the relationship between the electrostatic capacitance of the variable capacitance circuit 15 and the current flowing through each switching element of the inverter circuit 12 and the current flowing through the auxiliary coil 14 based on simulation. Figure 4 In the simulation shown, the parameter values ​​of each circuit element except the electrostatic capacitance of the variable capacitance circuit 15 are set to Figure 3 (a)~ Figure 3 The parameter values ​​in the simulation of (c) are the same. In addition, the coupling degree between the transmission coil 13 and the reception coil 21 and the coupling degree between the auxiliary coil 14 and the reception coil 21 are set to 0.2, and the coupling degree between the transmission coil 13 and the auxiliary coil 14 is set to 0.7.

[0076] exist Figure 4 In each curve, the horizontal axis represents time and the vertical axis represents the current. And time t1 represents the timing when the switch element 12b is disconnected. The waveforms 401 to 405 shown in the upper curve respectively represent the waveforms of the current flowing in the switch element 12b when the electrostatic capacitance of the variable capacitance circuit 15 is increased from 30nF in sequence by 2nF each time. The waveforms 411 to 415 shown in the lower curve respectively represent the waveforms of the current flowing in the auxiliary coil 14 when the electrostatic capacitance of the variable capacitance circuit 15 is increased from 30nF in sequence by 2nF each time.

[0077] As shown in waveforms 401 to 405, the more the electrostatic capacitance of the variable capacitance circuit 15 increases, the more the peak value of the current flowing in the switch element 12b at the timing when the switch element 12b is turned off decreases. On the other hand, as shown in waveforms 411 to 415, the more the electrostatic capacitance of the variable capacitance circuit 15 increases, the more the effective value of the current flowing in the auxiliary coil 14 increases.

[0078] Figure 5 This is a diagram showing an example of the relationship between the coupling degree between the transmission coil 13 and the reception coil 21, the output voltage output from the power receiving device 3, and the current flowing through the switching element 12b of the inverter circuit 12, based on a simulation, when the power transmission device 2 does not have an LC circuit. Figure 5In the simulation shown, the parameter values ​​of the circuit elements except the auxiliary coil 14 and the variable capacitance circuit 15 are omitted. Figure 3 (a)~ Figure 3 The parameter values ​​in the simulation of (c) are the same.

[0079] exist Figure 5 In each of the graphs, the horizontal axis represents time. Figure 5 In the upper curve, the vertical axis represents the current amount, and in the lower curve, the vertical axis represents the voltage. In addition, time t1 represents the timing when the switch element 12b is turned off. Waveforms 501 to 505 shown in the upper curve respectively represent the waveforms of the current flowing in the switch element 12b when the coupling degree between the transmitting coil 13 and the receiving coil 21 is increased from 0.1 by 0.1. Waveforms 511 to 515 shown in the lower curve respectively represent the waveforms of the output voltage output from the power receiving device 3 when the coupling degree between the transmitting coil 13 and the receiving coil 21 is increased from 0.1 by 0.1.

[0080] As shown in waveforms 501 to 505, the lower the coupling between the transmitting coil 13 and the receiving coil 21, the greater the delay of the phase of the current flowing in the switching element 12b relative to the phase of the voltage applied to the switching element 12b. Therefore, the lower the coupling between the transmitting coil 13 and the receiving coil 21, the greater the effective value of the current flowing in the switching element 12b, and the higher the peak value of the current flowing in the switching element 12b at the timing when the switching element 12b is turned off. On the other hand, as shown in waveforms 511 to 515, the output voltage from the power receiving device 3 changes with the change in the coupling between the transmitting coil 13 and the receiving coil 21.

[0081] As can be seen from this, in order to reduce the effective value of the current flowing through each switching element of the inverter circuit 12 and reduce the peak value of the current flowing through each switching element at the timing when each switching element of the inverter circuit 12 is turned off, the electrostatic capacitance of the variable capacitance circuit 15 can be changed according to the output voltage from the power receiving device 3. However, in order to reduce the conduction loss caused by the current flowing through the LC circuit including the auxiliary coil 14 and the variable capacitance circuit 15, it is preferable that the electrostatic capacitance of the variable capacitance circuit 15 is low.

[0082] Therefore, if the measured value of the output voltage represented by the voltage information received from the power receiving device 3 is less than the prescribed lower limit threshold, the control circuit 17 refers to the current electrostatic capacitance of the variable capacitance circuit 15 and the electrostatic capacitance of the variable capacitance circuit 15 after the change when the measured value of the output voltage is less than the lower limit threshold, which are pre-stored in the memory of the control circuit 17, that is, the control circuit 17 refers to a reference table for indicating the correspondence relationship between the combination of the switch elements to be turned on among the plurality of switch elements 152-1 to 152-n of the variable capacitance circuit 15. Then, the control circuit 17 determines the combination of the switch elements to be turned on corresponding to the current electrostatic capacitance of the variable capacitance circuit 15. The control circuit 17 controls the variable capacitance circuit 15 so that each switch element included in the determined combination is turned on and the other switch elements are turned off. Furthermore, for each electrostatic capacitance of the variable capacitance circuit 15, a combination of the following switching elements may be obtained by simulation or experiment in advance, and a reference table may be created based on the result, wherein the combination of the switching elements reduces the peak value of the current flowing through each switching element at the timing when each switching element of the inverter circuit 12 is turned off, and can suppress the increase in the effective value of the current flowing through each switching element, and can suppress the increase in the effective value of the current flowing through the auxiliary coil 14. As a result, the electrostatic capacitance of the variable capacitance circuit 15 changes, and as a result, the peak value of the current flowing through each switching element at the timing when each switching element of the inverter circuit 12 is turned off is reduced, the switching loss is reduced, and the increase in the effective value of the current flowing through each switching element is suppressed, and the increase in the conduction loss is suppressed. In addition, the increase in the effective value of the current flowing through the auxiliary coil 14 is suppressed, and the increase in the conduction loss caused by the LC circuit including the auxiliary coil 14 is suppressed.

[0083] Similarly, if the measured value of the output voltage represented by the voltage information received from the power receiving device 3 exceeds a specified upper threshold value higher than the above-mentioned lower threshold value, the control circuit 17 refers to the current electrostatic capacitance of the variable capacitance circuit 15 and the electrostatic capacitance of the variable capacitance circuit 15 after the measured value of the output voltage exceeds its upper threshold value, which are pre-stored in the memory of the control circuit 17, that is, the control circuit 17 refers to a reference table for indicating the correspondence relationship between the combination of the switch elements to be turned on among the multiple switch elements 152-1 to 152-n of the variable capacitance circuit 15. Then, the control circuit 17 determines the combination of the switch elements to be turned on corresponding to the current electrostatic capacitance of the variable capacitance circuit 15. The control circuit 17 controls the variable capacitance circuit 15 so that each switch element included in the determined combination is turned on and the other switch elements are turned off.

[0084] As described above, in the contactless power supply device, in order to adjust the delay of the phase of the current flowing in each switching element relative to the phase of the voltage applied to each switching element of the inverter circuit of the power supply circuit that supplies AC power to the transmitting coil, the power transmission device has a variable capacitance circuit that forms an LC circuit together with an auxiliary coil configured to be electromagnetically coupled with the transmitting coil. In addition, the control circuit of the power transmission device controls the electrostatic capacitance of the variable capacitance circuit according to the voltage output from the power receiving device. Therefore, even if the coupling degree between the transmitting coil and the receiving coil changes, the contactless power supply device can maintain the delay amount of the phase of the current flowing in each switching element relative to the phase of the voltage applied to each switching element of the inverter circuit at an appropriate delay amount, and as a result, the switching loss of each switching element and the conduction loss of the LC circuit can be reduced.

[0085] According to a modified example, a control circuit for controlling the electrostatic capacitance of the variable capacitance circuit 15 may be provided separately from the control circuit 17 for controlling the inverter circuit 12 .

[0086] Thus, those skilled in the art can make various modifications in accordance with the embodiments within the scope of the present invention.

Claims

1. A contactless power supply device comprising a power transmission device and a power receiving device to which power is transmitted in a contactless manner from the power transmission device, The power receiving device comprises: a resonant circuit having a receiving coil and a resonant capacitor that resonates with the receiving coil, and receiving electric power from the power transmission device; a rectifier circuit for rectifying the power output from the resonant circuit; a voltage detection circuit for measuring an output voltage of the electric power output from the rectifier circuit and obtaining a measured value of the output voltage; as well as a first communicator that transmits a signal including a measured value of the output voltage to the power transmission device; The power transmission device comprises: a transmitting coil for supplying electric power to the power receiving device via the receiving coil; A power supply circuit, comprising a plurality of switch elements connected in a full-bridge or half-bridge configuration between a power supply supplying DC power and the transmitting coil, wherein the DC power supplied from the power supply is converted into AC power having the prescribed frequency and supplied to the transmitting coil by switching on and off the plurality of switch elements at a prescribed frequency; an auxiliary coil configured to be electromagnetically coupled to the transmitting coil; a variable capacitance circuit connected to the auxiliary coil, forming a phase adjustment circuit together with the auxiliary coil, and having an adjustable electrostatic capacitance, wherein the phase adjustment circuit is configured to adjust a delay amount of a phase of a current flowing through the plurality of switching elements of the power supply circuit relative to a phase of a voltage applied to the plurality of switching elements; a second communicator receiving a signal including a measured value of the output voltage from the power receiving device; and a control circuit that controls the electrostatic capacitance of the variable capacitance circuit according to the measured value of the output voltage, If the measured value of the output voltage is less than a specified lower limit threshold, or exceeds a specified upper limit threshold that is higher than the specified lower limit threshold, the control circuit of the power transmitting device controls the variable capacitor circuit with reference to a reference table representing the relationship between the current electrostatic capacitance of the variable capacitor circuit and the changed electrostatic capacitance, so that the changed electrostatic capacitance becomes corresponding to the current electrostatic capacitance.

2. The contactless power supply device according to claim 1, wherein: The resonant frequency of the phase adjustment circuit is higher than the frequency of the AC power supplied to the transmitting coil.

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