Contactless energy supply device

Abstract

Contactless energy supply device (1) comprising an energy transmission device (2) and an energy reception device (3) to which energy is transmitted from the energy transmission device (2) without contact, wherein the energy reception device (3) comprises: a resonance circuit (20) comprising a receiving coil (21) which receives energy from the energy transmission device (2), a resonance capacitor (22) connected in parallel to the receiving coil (21), and a first coil (23) connected in series with or in parallel to the receiving coil (21); a rectifier circuit (26) which rectifies energy output from the resonant circuit (20); and a second coil (24) connected in series with the receiving coil (21) between the resonant circuit (20) and the rectifier circuit (26), and wherein the energy transmission device (2) comprises: a transmission coil (14) which supplies energy to the energy receiving device (3); a third coil connected in series with the transmission coil (14); and a power supply circuit (10) supplying AC power to the transmission coil (14) at an adjustable switching frequency at which the transmission coil (14) does not resonate and at an adjustable voltage, the power receiving device further comprising (3): a voltage detection circuit (29) that measures an output voltage of a power output from the resonance circuit (20) and obtains a measured value of the output voltage; a constant voltage determination circuit (30) which, based on the measured value of the output voltage, determines whether the contactless power supply device (1) performs a constant voltage output operation in which measured values ​​of the output voltage do not change even if a resistance value of a load circuit (28) connected to the rectifier circuit (26) of the power receiving device (3) changes, and whether the measured value of the output voltage is within a predetermined allowable voltage range; and a transmitter (33) transmitting to the power transmission device (2) a signal having determination information indicating whether or not the contactless power supply device (1) is performing a constant voltage output operation and whether or not the measured value of the output voltage is within the predetermined allowable voltage range, and wherein the power transmission device (2) further comprises: a receiver (16) receiving the signal comprising the destination information; and a control circuit (18) which controls the switching frequency and the voltage of the alternating current power supplied to the transmission coil (14) from the power supply circuit (10) in accordance with the determination information.

Description

AREA

[0001] The present invention relates to a contactless power supply device. STATE OF THE ART

[0002] To date, technologies for transmitting electrical energy through space without the use of metal contacts or the like, or so-called contactless power supply technologies (also called wireless power supply technologies), have been conventionally investigated.

[0003] As one of the contactless power supply technologies, a method of supplying power by electromagnetic induction is known. The method of supplying power by electromagnetic induction uses a method of connecting primary capacitors in series and secondary capacitors in parallel (hereinafter referred to as the SP method) (see, for example, NPL 1). According to the SP method, a capacitor is connected in series with a transmission coil serving as a part of a transformer on the primary side (power transmission side), and a capacitor is connected in parallel with a reception coil serving as another part of the transformer on the secondary side (power reception side).

[0004] In the SP method, since the resonance circuit formed by the receiving coil and the capacitor on the power receiving side causes parallel resonance, the output from the resonance circuit is a constant current output. Therefore, the SP method is generally more difficult to control than the method of primarily connected in series and secondarily connected in series capacitors (hereinafter referred to as the SS method), in which the output on the power receiving side is a constant voltage output. This is because electronic devices are generally controlled by constant voltage.

[0005] Furthermore, a technology for arranging a choke coil connected in series with the coil in the resonant circuit on the power receiving side in the SP method has been proposed (see, for example, NPL 1 and PTL 1). Note that the method using this technology is sometimes referred to as the SPL method. The method is also referred to herein as the SPL method. [LIST OF DOCUMENTS][PATENT LITERATURE]

[0006] [PTL 1] Japanese Unexamined Patent Publication (Kokai) JP 2015-042051 A [NON-PATENT LITERATURE]

[0007] [NPL 1] Watanabe et al., “Bidirectional Contactless Power Transfer System expandable from Unidirectional Systems,” The transactions of the Institute of Electrical Engineers of Japan. D, IEEJ Transactions on Industry Applications, Vol.133, No.7, pp.707-713, 2013

[0008] Further prior art is formed by US 9 561 730 B2 and US 2014 / 0 203 774 A1. US 9 561 730 B2 discloses a device comprising: a conductive charging interface (CCI); an antenna circuit configured to wirelessly receive an electromagnetic field from a transmitting device to provide charging energy at a level sufficient to provide a second AC signal based on the received charging energy; a power factor correction (PFC) circuit shared by the CCI and the antenna circuit via a switching circuit configured to selectively couple the PFC circuit to one of the CCI and the antenna circuit; a power converter circuit operatively coupled between the PFC circuit and the switching circuit; and a rectifier circuit operatively coupled between the antenna circuit and the switching circuit, wherein the PFC circuit is configuredwhen operatively coupled to the antenna circuit, to receive the DC output signal from the rectifier circuit and to reduce harmonics in the second AC power signal provided by the antenna circuit by providing a variable impedance to the rectifier circuit. US 2014 / 0 203 774 A1 discloses a charging control device comprising a chopper circuit, a primary-side coil, a primary-side inverter circuit, and a control unit, and a charged device comprising a secondary-side coil and a secondary-side rectifier circuit configured to be connected to a storage cell, wherein the control unit samples a secondary-side signal on a second cycle, samples a primary-side signal on a first cycle that is shorter than the second cycle,estimates the secondary-side signal at a time of the primary-side signal sampled at that time based on the secondary-side signal, the primary-side signal obtained when the secondary-side signal is sampled, and the primary-side signal sampled at that time, and performs feedback control of a control signal so that a predetermined signal of the secondary-side rectifier circuit becomes constant. SUMMARY[TECHNICAL TASK]

[0009] In a contactless power supply device using the SPL method, a power factor is improved because harmonic components of transmitted power are reduced and ideal transformer characteristics are obtained, and consequently, a power transmission efficiency is increased.

[0010] It is preferable that, even when the SPL method is employed, the contactless power supply device be used in such a way that it performs a constant voltage output operation. Furthermore, depending on the application, an adjustable frequency range of an AC power supplied to the transmitting coil is sometimes limited even when the coupling coefficient between a transmitting coil and a receiving coil is not constant. In such a case, it is preferable that a deviation in the resonance frequency of the resonant circuit including the receiving coil due to a change in the coupling coefficient is suppressed.

[0011] Accordingly, an object of the present invention is to provide a contactless power supply device capable of suppressing a deviation of the resonance frequency of the resonance circuit of the device on the receiving side due to a change in the coupling coefficient between the transmission coil of the device on the power transmission side and the reception coil of the device on the power reception side.

[0012] This object is achieved by the subject matters of independent claims 1, 5, and 7. Preferred embodiments of the invention are subject matters of the dependent claims. The invention is defined by the claims, with aspects of the invention being explained below: According to one aspect of the present invention, a contactless power supply device is provided, comprising a power transmitting device and a power receiving device to which power is transmitted from the power transmitting device without contact. In the contactless power supply device, the power transmitting device comprises a transmitting coil that supplies power to the power receiving device, and a power supply circuit that supplies alternating current power to the transmitting coil at an adjustable switching frequency, at which the transmitting coil does not resonate, and at an adjustable voltage.On the other hand, the power receiving device includes a resonance circuit including a receiving coil that receives power from the power transmitting device, a resonance capacitor connected in parallel to the receiving coil, a first coil connected in series with or in parallel to the receiving coil, a rectifier circuit that rectifies power output from the resonance circuit, and a second coil connected in series with the receiving coil between the resonance circuit and the rectifier circuit.

[0013] In the contactless power supply device, the first coil included in the resonance circuit of the power receiving device is preferably not coupled to the transmission coil even while power is transmitted from the power transmission device to the power receiving device.

[0014] In addition, the energy transmission device in the contactless energy supply device preferably further comprises a third coil connected in series with the transmission coil.

[0015] Furthermore, in the contactless power supply device, the power receiving device preferably further comprises a voltage detection circuit that measures the output voltage of a power output from the resonance circuit and obtains a measured value of the output voltage, a constant voltage determination circuit that determines, based on the measured value of the output voltage, whether the contactless power supply device performs a constant voltage output operation or not and whether a measured value of the output voltage is within a predetermined allowable voltage range or not, and a transmitter that transmits to the power transmitting device a signal having determination information indicatingwhether the contactless power supply device is performing a constant voltage output operation and whether the measured value of the output voltage is within the predetermined allowable voltage range. Furthermore, the power transmission device preferably further comprises a receiver that receives a signal containing the determination information and a control circuit that controls the switching frequency and voltage of the AC power supplied to the transmission coil from the power supply circuit in accordance with the determination information.

[0016] Furthermore, in the contactless power supply device, when the determination information indicates that the contactless power supply device does not perform a constant voltage output operation, the control circuit of the power transmission device preferably controls the switching frequency of the AC power supplied to the transmission coil from the power supply circuit in such a manner that measured values ​​of the output voltage do not change even if the resistance value of a load circuit connected to the rectifier circuit of the power reception device changes.

[0017] In addition, in this case, when the determination information indicates that the contactless power supply device performs a constant voltage output operation and the measured value of the output voltage is not within the predetermined allowable voltage range, the control circuit of the power transmission device preferably controls the voltage of the AC power supplied to the transmission coil from the power supply circuit in such a manner that measured values ​​of the output voltage are within the allowable range.

[0018] According to another aspect of the present invention, in the contactless power supply device, the power supply circuit can adjust the switching frequency and voltage of AC power supplied to the transmission coil, and the power transmission device preferably further comprises a current detection circuit that measures a current flowing through the transmission coil and obtains a measured value of the current, and a control circuit that controls the switching frequency and voltage of the AC power supplied to the transmission coil from the power supply circuit depending on the measured value of the current.

[0019] In this case, the control circuit of the power transmission device preferably monitors measured values ​​of the current while changing the switching frequency, and thereby detects a switching frequency at which measured values ​​of the current have a local maximum, and controls the power supply circuit in such a manner that an AC power having the detected switching frequency is supplied to the transmission coil.

[0020] Furthermore, according to another aspect of the present invention, a contactless power supply device is provided, which includes a power transmission device and a power reception device to which power is transmitted from the power transmission device without contact. In the contactless power supply device, the power reception device includes a resonance circuit including a reception coil that receives power from the power transmission device and a resonance capacitor connected in parallel with the reception coil, a rectifier circuit that rectifies power output from the resonance circuit, and a first coil connected in series with the reception coil between the resonance circuit and the rectifier circuit.On the other hand, the power transmission device comprises a transmission coil that supplies power to the power reception device, a second coil that is connected in series with the transmission coil and is not coupled to the reception coil even while power is being transmitted from the power transmission device to the power reception device, and a power supply circuit that supplies AC power to the transmission coil at an adjustable switching frequency at which the transmission coil does not resonate and at an adjustable voltage.

[0021] In the contactless power supply device, the power receiving device preferably further comprises a voltage detection circuit that measures the output voltage of a power output from the resonance circuit and obtains a measured value of the output voltage, a constant voltage determination circuit that determines, based on the measured value of the output voltage, whether the contactless power supply device performs a constant voltage output operation or not and whether the measured value of the output voltage from the resonance circuit is within a predetermined allowable voltage range or not, and a transmitter that transmits to the power transmitting device a signal having determination information indicatingwhether the contactless power supply device performs a constant voltage output operation or not, and whether the measured value of the output voltage from the resonant circuit is within the predetermined allowable voltage range. On the other hand, the power transmission device preferably further comprises a receiver that receives the signal containing the determination information, and a control circuit that controls the switching frequency and voltage of the AC power supplied to the transmission coil from the power supply circuit depending on the determination information. [ADVANTAGEOUS EFFECTS OF THE INVENTION]

[0022] A contactless power supply device according to the present invention has an advantageous effect of suppressing a deviation of the resonance frequency of the resonance circuit of the receiving-side device due to a change in the coupling coefficient between the transmitting coil of the power transmitting-side device and the receiving coil of the power receiving-side device. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an equivalent circuit diagram of a contactless power supply device according to an SPL method. Fig. 2 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the SPL method. Fig. 3 is a diagram illustrating an example of simulation results of frequency characteristics of an input impedance of the contactless power supply device according to the SPL method. Fig. 4 is a schematic view of a configuration of a contactless power supply device according to an embodiment of the present invention. Fig. 5 is an equivalent circuit diagram of the contactless power supply device according to the present embodiment. Fig. 6 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the present embodiment. Fig. 7 is a diagram showing an example of simulation results of frequency characteristics of the output voltage when voltage applied to the transmission coil is varied according to a coupling coefficient in the Fig. 6 illustrated simulation is changed. Fig. 8 is a diagram illustrating frequency characteristics of a delay of a phase of current with respect to a phase of voltage with respect to an alternating current power applied to the transmission coil in the contactless power supply device according to the present embodiment. Fig. 9 is an equivalent circuit diagram of a contactless power supply device according to a modification. Fig. 10 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the modification when the voltage applied to the transmission coil is changed according to the coupling coefficient. Fig. 11 is an equivalent circuit diagram of a contactless power supply device according to another modification. Fig. 12 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the further modification when the voltage applied to the transmission coil is changed according to the coupling coefficient. Fig. 13 is an equivalent circuit diagram of a contactless power supply device according to still another modification. Fig. 14 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the still further modification when the voltage applied to the transmission coil is changed according to the coupling coefficient. Fig. 15 is a diagram illustrating an example of a relationship between frequency characteristics of the output voltage and frequency characteristics of an input impedance of the contactless power supply device. Fig. 16 is a schematic view of a configuration of a contactless power supply device according to a modification. Fig. 17A is a circuit diagram of a power transmission device according to a modification. Fig. 17B is a circuit diagram of a power supply circuit according to another modification. DESCRIPTION OF EMBODIMENTS

[0023] Hereinafter, a contactless power supply device according to an embodiment of the present invention will be described with reference to the drawings.

[0024] For a better understanding of the contactless power supply device according to the present invention, a constant voltage output operation performed by the contactless power supply device according to the SPL method will first be described.

[0025] Fig. Figure 1 is an equivalent circuit diagram of the contactless power supply device according to the SPL method. It is assumed that, in an equivalent circuit 100 in the circuit diagram, a transmitting coil of a resonant circuit on the power transmitting side is coupled to a receiving coil of a resonant circuit on the power receiving side to form an ideal transformer with a ratio of n:1. Cr1 is a capacitance of a capacitor connected in series with the transmitting coil in the resonant circuit on the power transmitting side. Lr and Lm are the leakage inductance and excitation inductance of the resonant circuit on the power transmitting side, respectively.Note that the inductance Lp of the transmitting coil of the resonant circuit on the power transmitting side is equal to (Lm + Lr), and assuming a coupling coefficient between the transmitting coil and the receiving coil is denoted by k, Lr = (1 - k)Lp and Lm = kLp. In addition, Ri and Ris are respectively a winding resistance on the power transmitting side and a winding resistance on the power receiving side. Cp is a capacitance of a capacitor connected in parallel to the receiving coil in the resonant circuit on the power receiving side. Lop is an inductance of a coil connected in series with the receiving coil. Rac is an equivalent AC resistance of a load circuit Ro and is represented as Ras = (8 / π). 2 ) × Ro.

[0026] From the equivalent circuit 100, an F-matrix Fspl(s, k, Rac) of the contactless power supply device according to the SPL method is expressed by the following equation. Fspl(s,k,Rac):=[1Ri01]⋅[11s⋅Crl01]⋅[1s⋅Lr(k)01]⋅[101s⋅Lm(k)1]⋅[ 1s⋅Lr(k)01]⋅[1n2⋅Ris01]⋅[10s⋅1n2⋅Cp1]⋅[1s⋅Lop⋅n201]⋅[101n2⋅Rac1] In the equation above, s is expressed as s = j2πf. Note that f is the frequency of an alternating current power supplied to the resonant circuit on the power transmission side. Furthermore, k denotes a coupling coefficient between the transmitting coil and the receiving coil.

[0027] From the definition of the F-matrix, an output gain Gspl(s, k, Rac) of the contactless power supply device according to the SPL method is expressed by the following equation. Gspl(s,k,Rac)=1Fspl(s,k,Rac)⋅Vin2⋅1n

[0028] In the previous equation, Vin is the voltage of the AC power supplied to the resonant circuit on the power transmission side, and Fspl(s, k, Rac)0,0 represents the upper left element of the F matrix expressed in equation (1).

[0029] Fig. Figure 2 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the SPL method, which are calculated according to equation (2). Fig. 2, a frequency is plotted along the horizontal axis and an output voltage is plotted along the vertical axis. Graph 201 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15 and the AC equivalent resistance of the load circuit is set to Rac. In addition, graph 202 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15 and the AC equivalent resistance of the load circuit is set to (10 * Rac). Graph 203 also represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit is set to Rac. In addition, graph 204 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit is set to (10 * Rac).Furthermore, graph 205 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6 and the AC equivalent resistance of the load circuit is set to Rac. Furthermore, graph 206 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6 and the AC equivalent resistance of the load circuit is set to (10*Rac). Note that the simulation assumes that Lp = 174 µH, Cr1 = Cp = 20 nF, Lop = 3Lp, Ri = Ris = 0.3 Ω, n = 1, Vin = 200 V, and Ro = 200 Ω (Rac ≅ 162.1 Ω).

[0030] As in Fig. 2, as illustrated by points 211 to 216, there are six combinations of a frequency and an output voltage at which the output voltage becomes substantially constant even if the AC equivalent resistance of the load circuit changes under the condition that the coupling coefficient k is constant (that is, a constant-voltage output is obtained when the coupling coefficient k is constant). Of points 211 to 216, points 211 to 213 on the low-frequency side are close to the resonance frequency of the resonance circuit on the power transmission side and are affected by the resonance of the resonance circuit on the power transmission side. On the other hand, points 214 to 216 on the high-frequency side are higher than the resonance frequency of the resonance circuit on the power transmission side by a certain amount and are slightly affected by the resonance of the resonance circuit on the power transmission side.Since in the SPL method, the resonance circuit on the power transmission side is also generally caused to resonate, AC power is necessarily supplied to the resonance circuit on the power transmission side at frequencies as illustrated by points 211 to 213 in order to cause the contactless power supply device to perform a constant voltage output operation.

[0031] Fig. Figure 3 is a diagram illustrating an example of simulation results of frequency responses of an input impedance Zinspl(s, k, Rac) of the contactless power supply device according to the SPL method. Fig. 3, a frequency is plotted along the horizontal axis and an input impedance is plotted along the vertical axis. Graphs 301 to 304 represent frequency responses of the input impedance Zinspl(s, k, Rac) when the AC equivalent resistance of the load circuit is fixed to Rac and the coupling coefficients k are set to 0.001, 0.15, 0.3, and 0.6, respectively. Note that the frequency responses of the input impedance Zinspl(s, k, Rac) illustrated by graphs 301 to 304 can be obtained by entering values ​​of the respective parameters obtained in the Fig. 2, into an equation of the input impedance Zinspl(s, k, Rac), which is expressed by the following equation. Zinspl(s,k,Rac)=Fspl(s,k,Rac)0.0Fspl(s,k,Rac)1.0 In the previous equation, Fspl(s, k, Rac)1,0 represents the lower left element of the F-matrix expressed by equation (1).

[0032] As in Fig. As illustrated in Figure 3, in a frequency range near the resonance frequency of the resonant circuit on the power transmission side, as the coupling coefficient decreases, the input impedance becomes lower at frequencies where a constant voltage is output. For example, at a frequency f1 illustrated by point 211, at which the contactless power supply device can perform the constant voltage output operation when the coupling coefficient k = 0.15, the input impedance has a value less than 10 Ω at the coupling coefficient k = 0.15. This is because energy stored in the transmission coil increases due to an increase in current flowing through the resonant circuit on the power transmission side due to resonance of the resonant circuit.Therefore, in the SPL method, supplying AC power to the resonant circuit on the power transmission side when the coupling coefficient is low results in increased power loss. Furthermore, as can be seen from items 211 to 213, the output gain does not necessarily improve even when the coupling coefficient increases.

[0033] On the other hand, the input impedance decreases in a frequency range that is higher than the resonance frequency of the resonance circuit on the power transmission side and does not cause the resonance circuit on the power transmission side to resonate and in which the contactless power supply device can perform the output operation with a constant voltage even if the coupling coefficient changes (for example, a range from a frequency f3 corresponding to the point 214 in Fig. 2, to a frequency f4 corresponding to point 216), to a certain level, and energy loss is therefore suppressed. However, the frequency range becomes wider than a frequency range in which the resonance circuit on the power transmission side resonates, and the constant voltage output operation can be performed (a range from frequency f2 to frequency f1).

[0034] It is assumed that this is due to the fact that the resonance frequency of the resonant circuit on the power receiving side varies depending on the coupling coefficient.

[0035] Thus, the contactless power supply device according to the embodiment of the present invention supplies power from a power transmission device configured to supply AC power to a transmission coil at a frequency at which the transmission coil does not resonate, to a power receiving device comprising a resonant circuit that causes parallel resonance and a coil connected in series with a reception coil included in the resonant circuit. In the resonant circuit of the power receiving device, a coil that is not coupled to the transmission coil, even at the time of power transmission, is arranged separately from the reception coil.Due to this configuration, the contactless power supply device can suppress an increase in power loss due to a deviation of the coupling coefficient and narrow a frequency adjustment range of AC power supplied to the transmitting coil at the time of performing a constant voltage output operation by suppressing the deviation of the resonance frequency of the resonance circuit of the power receiving device due to a change in the coupling coefficient between the transmitting coil and the receiving coil.

[0036] Furthermore, the contactless power supply device measures the output voltage from the resonance circuit on the power receiving side and controls the switching frequency and the voltage of the AC power supplied to the transmitting coil in such a manner that the measured value is within an allowable voltage range at the time of a constant voltage output operation, and thereby maintains the constant voltage output operation even if the coupling coefficient between the transmitting coil and the receiving coil or the resistance value of the load circuit changes.

[0037] Note that, as used herein, the constant voltage output operation is an operation in which the contactless power supply device is operated in such a manner that an output voltage is maintained within an allowable voltage range (for example, within ±10% of a predetermined voltage reference value) determined according to the specification of a load circuit connected to the contactless power supply device, and the like.

[0038] Fig. 4 is a schematic view of a configuration of a contactless power supply device according to an embodiment of the present invention. As shown in Fig. As illustrated in Figure 4, a contactless power supply device 1 includes a power transmission device 2 and a power reception device 3 to which power is transmitted from the power transmission device 2 through space without contact. The power transmission device 2 includes a power supply circuit 10, a transmission coil 14, a capacitor 15, a receiver 16, gate drivers 17-1 and 17-2, and a control circuit 18. On the other hand, the power reception device 3 includes a resonance circuit 20 including a reception coil 21, a resonance capacitor 22, and a coil 23, a coil 24, a rectifying and smoothing circuit 25, a load circuit 28, a voltage detection circuit 29, a constant voltage determination circuit 30, and a transmitter 33.

[0039] First, the energy transmission device 2 will be described.

[0040] The power transmission device 10 supplies alternating current power to the transmission coil 14 at an adjustable switching frequency and an adjustable voltage. For this purpose, the power supply circuit 10 comprises a power source 11, a power factor improvement circuit 12, and four switching elements 13-1 to 13-4.

[0041] The power source 11 supplies power at a predetermined pulsating voltage. For this purpose, the power source 11 is connected to a commercial AC power source and includes a full-wave rectifier circuit for rectifying the AC power supplied by the AC power source.

[0042] The power factor improvement circuit 12 converts the voltage of the power output from the power source 11 into a voltage determined under control from the control circuit 18 to output the converted voltage. For this purpose, the power factor improvement circuit 12 includes, for example, a coil L and a diode D connected in series in this order from the positive electrode terminal of the power source 11; a switching element SW whose drain and source are connected between the coil L and the diode D and to the negative electrode terminal of the power source 11, respectively, and which is an n-channel MOSFET; and a smoothing capacitor C connected in parallel to the switching element SW with the diode D interposed therebetween. Furthermore, the gate of the switching element SW is connected to the gate driver 17-1.Furthermore, the power factor improvement circuit 12 includes two resistors R1 and R2 connected in series between the positive electrode terminal and the negative electrode terminal of the power source 11. The resistors R1 and R2 are connected in parallel between the diode D and the smoothing capacitor C. A voltage between the resistor R1 and the resistor R2 is measured by the control circuit 18 as a measurement representing a voltage output from the diode D.

[0043] The power factor improvement circuit 12 performs a power factor improvement operation through the gate driver 17-1, which controls switching of the switching element SW between an on and off state according to a duty cycle determined by the control circuit 18, and in such a manner that a trajectory of a current waveform output from the diode D coincides with a trajectory of voltage supplied from the power source 11. The higher the duty cycle at which the switching element SW is turned on, the higher the voltage output from the diode D becomes.

[0044] The voltage output by the diode D is smoothed by the smoothing capacitor C and supplied to the transmission coil 14 via the four switching elements 13-1 to 13-4.

[0045] Note that the power factor improvement circuit 12 is not limited to the configuration described above and may have another configuration capable of adjusting an output voltage controlled by the control circuit 18.

[0046] For the four switching elements 13-1 to 13-4, for example, n-channel MOSFETs can be used. Of the four switching elements 13-1 to 13-4, the switching element 13-1 and the switching element 13-2 are connected in series between the positive electrode terminal and the negative electrode terminal of the power source 11 via the power factor improvement circuit 12. Furthermore, in the present embodiment, the switching element 13-1 is connected to the positive electrode side of the power source 11, while the switching element 13-2 is connected to the negative electrode side of the power source 11. The drain terminal of the switching element 13-1 is connected to the positive electrode terminal of the power source 11 via the power factor improvement circuit 12, and the source terminal of the switching element 13-1 is connected to the drain terminal of the switching element 13-2.In addition, the source terminal of the switching element 13-2 is connected to the negative electrode terminal of the power source 11 via the power factor improvement circuit 12. Furthermore, the source terminal of the switching element 13-1 and the drain terminal of the switching element 13-2 are connected to one end of the transmission coil 14 via the capacitor 15, and the source terminal of the switching element 13-2 is connected to the other end of the transmission coil 14 via the switching element 13-4.

[0047] Similarly, of the four switching elements 13-1 to 13-4, switching element 13-3 and switching element 13-4 are connected in parallel to switching element 13-1 and switching element 13-2, and are connected in series between the positive electrode terminal and the negative electrode terminal of power source 11 via power factor improvement circuit 12. Furthermore, switching element 13-3 is connected to the positive electrode side of power source 11, while switching element 13-4 is connected to the negative electrode side of power source 11. The drain terminal of switching element 13-3 is connected to the positive electrode terminal of power source 11 via power factor improvement circuit 12, and the source terminal of switching element 13-3 is connected to the drain terminal of switching element 13-4.In addition, the source terminal of the switching element 13-4 is connected to the negative electrode terminal of the power source 11 via the power factor improvement circuit 12. Furthermore, the source terminal of the switching element 13-3 and the drain terminal of the switching element 13-4 are connected to the other end of the transmission coil 14.

[0048] In addition, the gate terminals of the switching elements 13-1 to 13-4 are connected to the control circuit 18 via the gate driver 17-2. Furthermore, each of the switching elements 13-1 to 13-4 can have its gate terminal connected to its own source terminal via a resistor to ensure that the switching element is turned on when the voltage for turning on the switching element is applied. The switching elements 13-1 to 13-4 are switched between an on and an off state at an adjustable switching frequency according to a control signal from the control circuit 18.In the present embodiment, a pair of switching elements 13-1 and 13-4, and a pair of switching elements 13-2 and 13-3 are alternately switched between an on-state and an off-state in such a manner that switching elements 13-2 and 13-3 are turned off while switching elements 13-1 and 13-4 are turned on, and conversely, switching elements 13-1 and 13-4 are turned off while switching elements 13-2 and 13-3 are turned on. This configuration causes DC power supplied from power source 11 via power factor improvement circuit 12 to be converted into AC power at the switching frequency of the switching elements and supplied to transmission coil 14.

[0049] The transmission coil 14 transmits the alternating current power supplied from the power supply circuit 10 to the resonance circuit 20 of the power receiving device 3 through space.

[0050] The capacitor 15 is connected in series with the transmission coil 14 and cuts off direct current flowing to the transmission coil 14. Note that it is preferable that the capacitance of the capacitor 15 be set in such a manner that the resonance frequency of the transmission coil 14 and the capacitor 15 is lower than the resonance frequency of the resonance circuit 20 of the power receiving device 3 and the lower limit of the frequency of a frequency range in which the switching frequency is set, so that the transmission coil 14 and the capacitor 15 do not operate as a resonance circuit in the frequency range in which the switching frequency is set.

[0051] The receiver 16 extracts determination information indicating whether or not the contactless power supply device 1 is performing a constant voltage output operation, etc., from the wireless signal each time it receives a wireless signal from the transmitter 33 of the power receiving device 3, and outputs the determination information to the control circuit 18. For this purpose, the receiver 16 includes, for example, an antenna for receiving a wireless signal and a communication circuit for demodulating the wireless signal according to a predetermined wireless communication standard. Note that the predetermined wireless communication standard may be, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0052] The gate driver 17-1 receives a control signal for switching the switching element SW of the power factor improvement circuit 12 between an on and an off state from the control circuit 18 and, in accordance with the control signal, changes a voltage applied to the gate terminal of the switching elements SW. In other words, upon receiving a control signal for turning on the switching element SW, the gate driver 17-1 applies a relatively high voltage to the gate terminal of the switching element SW such that the switching element SW is turned on. On the other hand, upon receiving a control signal for turning off the switching element SW, the gate driver 17-1 applies a relatively low voltage to the gate terminal of the switching element SW such that the switching element SW is turned off.This configuration causes the gate driver 17-1 to switch the switching element SW of the power factor improvement circuit 12 between an on and an off state at times specified by the control circuit 18.

[0053] The gate driver 17-2 receives a control signal for switching the switching elements 13-1 to 13-4 between an on and an off state from the control circuit 18 and, in accordance with the control signal, changes a voltage applied to the gate terminals of the switching elements 13-1 to 13-4. In other words, upon receiving a control signal for turning on the switching element 13-1 and the switching element 13-4, the gate driver 17-2 applies a relatively high voltage to the gate terminal of the switching element 13-1 and the gate terminal of the switching element 13-4 such that the switching element 13-1 and the switching element 13-4 are turned on. This operation causes current from the power source 11 to flow through the switching element 13-1, the transmission coil 14, and the switching element 13-4.On the other hand, upon receiving a control signal to turn off the switching element 13-1 and the switching element 13-4, the gate driver 17-2 applies a relatively low voltage to the gate terminal of the switching element 13-1 and the gate terminal of the switching element 13-4 such that the switching element 13-1 and the switching element 13-4 are turned off and current from the power source 11 is prevented from flowing through the switching element 13-1 and the switching element 13-4. Similarly, the gate driver 17-2 controls a voltage applied to the gate terminals of the switching element 13-2 and the switching element 13-3. Therefore, when the switching element 13-1 and the switching element 13-4 are turned off and the switching element 13-2 and the switching element 13-3 are turned on, current starts to flow from the power source 11 through the switching element 13-3, the transmission coil 14 and the switching element 13-2.

[0054] The control circuit 18 includes, for example, a non-volatile memory circuit and a volatile memory circuit, an arithmetic operation circuit, and an interface circuit for connecting to other circuits. Each time the control circuit 18 receives the destination information from the receiver 16, the control circuit 18 controls the switching frequency and voltage of the AC power supplied to the transmission coil 14 from the power supply circuit 10 according to the destination information.

[0055] For this purpose, in the present embodiment, the control circuit 18 controls the switching elements 13-1 to 13-4 in such a manner that the pair of the switching element 13-1 and the switching element 13-4 and the pair of the switching element 13-2 and the switching element 13-3 are alternately turned on, and that a duration for which the pair of the switching element 13-1 and the switching element 13-4 is in the on-state and a duration for which the pair of the switching element 13-2 and the switching element 13-3 is in the on-state are equal to each other in a period corresponding to the switching frequency.Note that in order to prevent the pair of the switching element 13-1 and the switching element 13-4 and the pair of the switching element 13-2 and the switching element 13-3 from being in the on state at the same time and the power source 11 from being short-circuited, the control circuit 18 may set a dead time during which both pairs of switching elements are turned off when the pair of the switching element 13-1 and the switching element 13-4 and the pair of the switching element 13-2 and the switching element 13-3 are switched between an on state and an off state.

[0056] Furthermore, the control circuit 18 selects a duty ratio corresponding to a desired switching frequency by referring to a reference table, each entry of which indicates a relationship between a switching frequency and a duty cycle. The duty cycle corresponds to a voltage applied to the transmission coil 14, which causes a constant voltage to be output at the switching frequency and is used in the on / off control of the switching element SW of the power factor improvement circuit 12. The control circuit 18 determines times at which the switching element SW is switched between an on and off state based on the duty cycle and a change in the output voltage from the diode D of the power factor improvement circuit 12, and outputs control signals representing the times to the gate driver 17-1.

[0057] Furthermore, when the receiver 16 is unable to receive a wireless signal from the power receiving device 3, it is judged that the power receiving device 3 is not present at a position where the power receiving device 3 can receive a power supply from the power transmitting device 2, that is, the power receiving device 2 is in a standby state. Therefore, in this case, the control circuit 18 can set the duty cycle for the on / off control of the switching element SW to a minimum settable value.Alternatively, the control circuit 18 may control the power supply circuit 10 in a so-called burst mode, which repeats control for causing the power supply circuit 10 to operate with the duty cycle set to a preset value for the on / off control of the switching element SW for a relatively short, fixed period (for example, approximately several seconds), and then suspending the power supply from the power supply circuit 10 to the transmission coil 14, with the switching elements maintained in the off state, for a relatively long period (for example, approximately several minutes). Since this control causes the voltage applied to the transmission coil 14 to be set to a minimum, definable value while the power transmission device 2 is in the standby state, power loss can be suppressed.

[0058] Note that details of the control of the switching frequency and the voltage applied to the transmission coil 14 by the control circuit 18 will be described later.

[0059] Next, the power receiving device 3 will be described.

[0060] The resonant circuit 20 is an LC resonant circuit in which the receiving coil 21 and the coil 23 are connected in series, and the resonant capacitor 22 are connected in parallel. One end of the receiving coil 21 included in the resonant circuit 20 is connected to one end of the resonant capacitor 22 via the coil 23 and, in connection therewith, to an input terminal of the rectifying and smoothing circuit 25 via the coil 24. Furthermore, the other end of the receiving coil 21 is connected to the other end of the resonant capacitor 22 and, in connection therewith, to the other input terminal of the rectifying and smoothing circuit 25.

[0061] The receiving coil 21 receives energy from the transmitting coil 14 by resonating with the alternating current flowing through the transmitting coil 14 of the power transmission device 2. The receiving coil 21 outputs the received energy to the rectifying and smoothing circuit 25 via the coil 23, the resonant capacitor 22, and the coil 24. Note that the number of turns in the winding of the receiving coil 21 and the number of turns in the winding of the transmitting coil 14 of the power transmission device 2 may be identical or different.

[0062] The resonant capacitor 22 is connected at one end to one end of the receiving coil 21 via the coil 23 and, in conjunction therewith, to the coil 24, and at the other end to the other end of the receiving coil 21 and the rectifying and smoothing circuit 25. The resonant capacitor 22 outputs the energy received by the receiving coil 21 to the rectifying and smoothing circuit 25 via the coil 24.

[0063] The coil 23 is connected between one end of the receiving coil 21 and one end of the resonance capacitor 22. The coil 23 forms an LC resonance circuit in conjunction with the receiving coil 21 and the resonance capacitor 22. Furthermore, unlike the receiving coil 21, the coil 23 is arranged in such a manner that it is not coupled to the transmitting coil 14 even during power transmission from the power transmitting device 2 to the power receiving device 3. For this reason, a resonance frequency f r2 of the resonance circuit 20 is expressed by the following equation. fr2=12πCp⋅(Lr2+L3)Lr2=L2(1−k)(1+k)

[0064] In the previous equation, Cp is a capacitance of the resonant capacitor 22 and L2 is an inductance of the receiving coil 21. L r2is an inductance of the receiving coil 21 when the transmitting coil 14 is short-circuited, and k denotes a coupling coefficient between the transmitting coil 14 and the receiving coil 21. In addition, L3 is an inductance of the coil 23. As is clear from the equation (4), it is clear that, compared to a case where the coil 23 is not included (ie, L3 = 0), a deviation of the resonance frequency f r2of the resonant circuit 20 when the coupling coefficient k varies is suppressed. Since a change in the resonant frequency becomes smaller with increasing inductance L3, a setting range of the switching frequency also becomes narrower. On the other hand, with increasing inductance L3, the gain of the output power decreases. Therefore, the inductance L3 of the coil 23 is set according to a setting range, which can be set with respect to the switching frequency of the AC power supplied to the transmission coil 14. For example, when the setting range is from about 80 kHz to about 90 kHz, it is preferable that the inductance L3 of the coil 23 be set to a value larger than the inductance L r2 of the receiving coil 21 when the transmitting coil 14 is short-circuited, and less than three times the inductance L r2 However, the inductance L3 of coil 23 is not limited to the example.

[0065] The coil 24 is connected between the resonant circuit 20 and the rectifying and smoothing circuit 25. In the present embodiment, the coil 24 is connected at one end to the coil 23 and the resonant capacitor 22 of the resonant circuit 20 in such a way as to be in series with the receiving coil 21 and the coil 23, and at the other end to the rectifying and smoothing circuit 25. The coil 24 outputs the energy received by the resonant circuit 20 to the rectifying and smoothing circuit 25. Note that arranging the coil 24 as in the SPL method makes it possible to suppress harmonic components of the received energy.

[0066] The rectifying and smoothing circuit 25 is an example of a rectifying circuit. It includes a full-wave rectifying circuit 26, which includes four diodes connected in a bridge circuit, and a smoothing capacitor 27. It rectifies and smooths the energy received via the resonant circuit 20 and the coil 24 to convert the energy into DC energy. The rectifying and smoothing circuit 25 outputs the DC energy to the load circuit 28.

[0067] The voltage detection circuit 29 detects an output voltage between both terminals of the rectifying and smoothing circuit 25 at every predetermined period. Since the output voltage between both terminals of the rectifying and smoothing circuit 25 corresponds one-to-one to the output voltage of the resonant circuit 20, a measured value of the output voltage between the two terminals of the rectifying and smoothing circuit 25 indirectly represents a measured value of the output voltage of the resonant circuit 20. For the voltage detection circuit 29, for example, any of various known voltage detection circuits capable of detecting DC voltage can be used. The voltage detection circuit 29 outputs a voltage detection signal representing a measured value of the output voltage to the constant voltage determination circuit 30.

[0068] The constant-voltage determination circuit 30 determines, based on the measured value of the output voltage received from the voltage detection circuit 29, whether the contactless power supply device 1 is performing a constant-voltage output operation and whether the measured value of the output voltage is within an allowable voltage range when the constant-voltage output operation is performed. The constant-voltage determination circuit 30 notifies the transmitter 33 of a determination result. For this purpose, the constant-voltage determination circuit 30 includes, for example, a memory circuit configured to store an allowable voltage range and a determination circuit 31 comprising an arithmetic operation circuit configured to compare a measured value of the output voltage with the allowable voltage range.

[0069] Furthermore, the constant-voltage determination circuit 30 includes a switching element 32, such as a MOSFET, connected between the rectifying and smoothing circuit 25 and the load circuit 28. When off, the switching element 32 prevents current from flowing from the rectifying and smoothing circuit 25 to the load circuit 28 (i.e., Rac = ∞), while when on, the switching element 32 allows current to flow from the rectifying and smoothing circuit 25 to the load circuit 28. The determination circuit 31 of the constant-voltage determination circuit 30 switches the switching element 32 between an on and an off state at a predetermined time while measured values ​​of the output voltage are outside the allowable voltage range.This operation causes the resistance value of the entire circuit, including the load circuit 28 connected to the rectifying and smoothing circuit 25, to change within the predetermined period. Therefore, the determination circuit 31 is able to determine whether the contactless power supply device 1 is performing the constant voltage output operation by determining whether the measured values ​​of the output voltage become substantially constant or not while the switching element 32 is switched between an on and an off state.Therefore, while measured values ​​of the output voltage are substantially constant, even if the determination circuit 31 switches the switching element 32 between an on and an off state in a predetermined period of time, the determination circuit 31 notifies the transmitter 33 that the contactless power supply device 1 performs the constant voltage output operation.

[0070] Furthermore, when measured output voltage values ​​indicate that contactless power supply device 1 performs the constant voltage output operation for a certain period longer than the predetermined period, determination circuit 31 suspends switching of switching element 32 between an on and off state and maintains switching element 32 in the on state. Determination circuit 31 determines whether the measured output voltage value is within the allowable voltage range and notifies transmitter 33 of the determination result.

[0071] When the measured values ​​of the output voltage are within the allowable voltage range for a certain period longer than the predetermined period, the determination circuit 31 notifies the transmitter 33 of a determination result indicating that the contactless power supply device 1 performs the constant voltage output operation and the measured values ​​of the output voltage are within the allowable voltage range.

[0072] Note that, according to a modification, the constant-voltage determination circuit 30 may include a resistor connected to the rectifying and smoothing circuit 25 in parallel with the load circuit 28. In this case, the switching element 32 may be arranged in series with the resistor and in parallel with the load circuit 28. In this case, the determination circuit 31 turns off the switching element 32 while measured values ​​of the output voltage are within the allowable voltage range. On the other hand, when a measured value of the output voltage is outside the allowable voltage range, as in the previously described embodiment, the determination circuit 31 may switch the switching element 32 between an on and an off state in the predetermined period of time.According to the modification, the power supply to the load circuit 28 is maintained even if the contactless power supply device 1 does not perform a constant voltage output operation.

[0073] Furthermore, according to a further modification, a second switching element, such as a MOSFET, may be arranged in parallel with the above-described resistor and in series with the load circuit 28. In this case, while measured values ​​of the output voltage are within the allowable voltage range, the determination circuit 31 turns on the second switching element, thereby enabling power supply to the load circuit 28. On the other hand, when a measured value of the output voltage is outside the allowable voltage range, the determination circuit 31 may turn off the second switching element and suspend power supply to the load circuit 28. Even if a received power voltage has risen to an excessively high level while the switching frequency is being adjusted in the power transmission device 2, this configuration prevents the excessively high voltage from being applied to the load circuit 28.

[0074] The transmitter 33 generates, at each predetermined transmission period, a wireless signal including determination information indicating whether or not the contactless power supply device 1 is performing a constant-voltage output operation and whether or not measured values ​​of the output voltage are within the allowable voltage range, based on a determination result received from the determination circuit 31 of the constant-voltage determination circuit 30, and transmits the wireless signal to the receiver 16 of the power transmission device 2. For this purpose, the transmitter 33 includes, for example, a communication circuit that generates a wireless signal according to a predetermined wireless communication standard and an antenna for outputting the wireless signal.Note that, as with the receiver 16, the predetermined wireless communication standard may be, for example, ISO / IEC 15693, ZigBee (registered trademark) or Bluetooth (registered trademark).

[0075] An operation of the contactless power supply device 1 will be described in detail below.

[0076] In the present embodiment, the control circuit 18 of the power transmission device 2 controls the switching frequency and the voltage of an alternating current power supplied to the transmission coil 14 from the power supply circuit 10 based on determination information received from the receiver 16 in such a manner that the contactless power supply device 1 continues a constant voltage output operation.

[0077] Fig. 5 is an equivalent circuit diagram of the contactless power supply device 1 according to the present embodiment. It is assumed that, in an equivalent circuit 500 in the circuit diagram, the transmitting coil 14 of the power transmitting device 2 is coupled to the receiving coil 21 of the resonant circuit 20 of the power receiving device 3 to form an ideal transformer with a ratio of n:1. Cr1 is a capacitance of the capacitor 15 connected in series to the transmitting coil 14. Lr and Lm are leakage inductance and excitation inductance of the transmitting coil 14, respectively. Note that an inductance Lp of the transmitting coil 14 is equal to (Lm + Lr), and assuming that a coupling coefficient between the transmitting coil 14 and the receiving coil 21 is denoted by k, Lr = (1 - k)Lp and Lm = kLp.In addition, Ri and Ris are each a winding resistance value on the power transmission side and a winding resistance value on the power reception side. Cp is a capacitance of the resonant capacitor 22 of the resonant circuit 20. L1 is an inductance of the coil 23 connected in series with the receiving coil 21 included in the resonant circuit 20. Furthermore, L2 is an inductance of the coil 24 connected between the resonant circuit 20 and the rectifying and smoothing circuit 25. Ro is a resistance value of the load circuit 28 (AC equivalent resistance Rac = (8 / π). 2 ) × Ro).

[0078] From the equivalent circuit 500, an F-matrix Fp(s, k, Rac) of the contactless power supply device 1 is expressed by the following equation. Fp(s,k,Rac):=[1Ri01]⋅[11s⋅Crl01]⋅[1s⋅Lr(k)01]⋅[101s⋅Lm(k)1]⋅[1s⋅Lr(k)01]⋅[1 s⋅n2⋅Lt01]⋅[1n2⋅Ris01]⋅[10s⋅1n2⋅Cp1]⋅[10s⋅1n2⋅Cp1]⋅[1s⋅L2⋅n201]⋅[101n2⋅Rac1]

[0079] Therefore, as in equation (2), an output gain Gp(s, k, Rac) of the contactless power supply device 1 is expressed by the following equation. Gp(s,k,Rac)=1Fp(s,k,Rac)0.0⋅Vin2⋅1n

[0080] In the preceding equation, Vin is a voltage (amplitude) of the AC power supplied to the resonance circuit on the power transmission side, and Fp(s, k, Rac)0,0 represents the upper left element of the F matrix expressed by equation (5).

[0081] Fig. Fig. 6 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device 1, which are calculated according to equation (6). Fig. 6, a frequency is plotted along the horizontal axis and an output voltage is plotted along the vertical axis. Graph 601 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15 and the AC equivalent resistance of the load circuit 28 is set to Rac. In addition, graph 602 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15 and the AC equivalent resistance of the load circuit 28 is set to (10*Rac). In addition, graph 603 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 28 is set to Rac. In addition, graph 604 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 28 is set to (10*Rac).Furthermore, graph 605 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6 and the AC equivalent resistance of the load circuit 28 is set to Rac. Furthermore, graph 606 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6 and the AC equivalent resistance of the load circuit 28 is set to (10*Rac). Note that the simulation assumes that Lp = 174 µH, Cr1 = 2 µF, Cp = 10 nF, L1 = 350 µH, L2 = 1300 µH, Ri = Ris = 0.3 Ω, n = 1, Ro = 150 Ω, and Vin = 800 V.

[0082] In Fig. 6 disappear, since the transmission coil 14 does not resonate, extreme values ​​of the output voltage on the low frequency side compared to Fig. 2 in which Fig. 6. However, even in this case, for each coupling coefficient, there exists a combination of a frequency and an output voltage at which the output voltage becomes substantially constant (i.e., a constant voltage is output), even if the AC equivalent resistance of the load circuit changes under the condition that the coupling coefficient k does not change (there are three combinations, which in Fig. 6 by points 611 to 613). Therefore, it is clear that even when an AC power having a switching frequency at which the transmission coil 14 does not resonate is applied to the transmission coil 14, it is possible to cause the contactless power supply device 1 to perform a constant voltage output operation in view of a change in the resistance value of the load circuit 28.

[0083] Furthermore, although, as illustrated by points 611 to 613, when a constant voltage is output against a variation of the resistance value of the load circuit 28, the output voltages differ from each other depending on the coupling coefficient, the differences in the output voltages can be reduced to a substantially constant output voltage by adjusting a voltage applied to the transmission coil 14 regardless of the coupling coefficient.

[0084] Fig. Fig. 7 is a diagram showing an example of simulation results of frequency characteristics of the output voltage when the voltage applied to the transmission coil 14 is varied according to the coupling coefficient in the manner shown in Fig. 6 illustrated simulation is changed. In Fig. 7, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Graph 701 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to Vin. Furthermore, graph 702 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to Vin.Furthermore, graph 703 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.49*Vin). Furthermore, graph 704 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.49*Vin). Furthermore, graph 705 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.22*Vin).In addition, graph 706 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.22*Vin).

[0085] Combinations of a frequency and an output voltage that meet the Fig. 6 and at which the output voltage becomes substantially constant (ie, a constant voltage is output) even when the AC equivalent resistance of the load circuit 28 changes under the condition that the coupling coefficient k does not change, are three combinations indicated by points 711 to 713. The output voltages at the respective points 711 to 713 are substantially equal to each other.

[0086] From the foregoing description, it is clear that even if either the resistance value of the load circuit 28 or the coupling coefficient changes, appropriate adjustment of the switching frequency and the voltage of the AC power applied to the transmission coil 14 makes it possible to keep the output voltage substantially constant.

[0087] Furthermore, a frequency range from the frequency f1 corresponding to point 711 to the frequency f2 corresponding to point 713 is considerably narrower than the frequency range from the frequency f3 corresponding to point 214 to the frequency f4 corresponding to point 216, which in Fig. 2. Therefore, it is clear that the frequency adjustment range when the contactless power supply device 1 is caused to perform a constant voltage output operation can be narrowed further than the frequency adjustment range when the contactless power supply device according to the SPL method is caused to perform a constant voltage output operation at a frequency at which the resonance circuit on the power transmission side does not resonate.

[0088] Consequently, in order to achieve a constant voltage output, the control circuit 18 controls the switching frequency and the voltage of the AC power applied to the transmission coil 14 as described below.

[0089] When determination information included in a wireless signal received by the power receiving device 3 via the receiver 16 indicates that the contactless power supply device 1 does not perform a constant voltage output operation, the control circuit 18 changes the switching frequency of the AC power within a predetermined frequency range.The predetermined frequency range may be set, for example, as a frequency range whose lower limit and upper limit are respectively set to a frequency at which a constant voltage having the minimum of the expected values ​​of the coupling coefficient between the transmitting coil 14 and the receiving coil 21 is outputted, and a frequency at which a constant voltage having a maximum of the expected values ​​of the coupling coefficient between the transmitting coil 14 and the receiving coil 21 is outputted, when power is supplied to the power receiving device 3 from the power transmitting device 2.

[0090] When changing the switching frequency, the control circuit 18 can gradually increase the switching frequency from the lower limit to the upper limit of the predetermined frequency range, or conversely, gradually decrease the switching frequency from the upper limit to the lower limit of the predetermined frequency range. Furthermore, in order for the constant-voltage determination circuit 30 of the power receiving device 3 to be able to check whether the output voltage has become substantially constant, it is preferable that the control circuit 18 gradually change the switching frequency in such a way that the same switching frequency is maintained for a period longer than a period during which the determination circuit 31 of the constant-voltage determination circuit 30 switches the switching element 32 between an on and an off state.

[0091] Note that it is preferable that, while adjusting the switching frequency, the control circuit 18 reduces the voltage applied to the transmission coil 14 to a lower voltage limit. This configuration prevents the voltage of power supplied to the power receiving device 3 from increasing excessively.

[0092] When the determination information included in the wireless signal received by the power receiving device 3 via the receiver 16 indicates that measured values ​​of the output voltage, although not within the allowable voltage range, are substantially constant even if the resistance value of the load circuit 28 changes, that is, the constant-voltage output operation is performed, the control circuit 18 keeps the switching frequency constant thereafter. Next, the control circuit 18 determines a duty ratio by referring to the reference table, each entry of which indicates a relationship between a switching frequency and a duty ratio, which causes a constant voltage to be output at the switching frequency regardless of the coupling coefficient, and is used in the on / off control of the switching element SW of the power factor improvement circuit 12.The control circuit 18 controls the gate driver 17-1 in such a manner that the switching element SW of the power factor improvement circuit 12 is switched between an on and an off state according to the duty cycle. This operation causes the voltage applied to the transmission coil 14 to be adjusted in such a manner that the output voltage from the resonance circuit 20 is within the allowable voltage range, that is, a constant voltage is output regardless of the coupling coefficient. When the determination information included in a wireless signal received by the power receiving device 3 via the receiver 16 indicates that measured values ​​of the output voltage are within the allowable voltage range, the control circuit 18 keeps the switching frequency and the voltage of the AC power supplied to the transmission coil 14 constant.

[0093] Note that, instead of determining a duty ratio with reference to the above-described reference table, the control circuit 18 may gradually change the duty ratio until the determination information included in a wireless signal received from the power receiving device 3 via the receiver 16 indicates that measured values ​​of the output voltage are within the allowable voltage range.

[0094] Furthermore, in order to improve power transmission efficiency, it is preferable that the power supply circuit 10 and the transmission coil 14 of the power transmission device 2 continue to operate with soft switching (inductive operation). In order for the power supply circuit 10 and the transmission coil 14 to operate with soft switching, it is preferable that the phase of current flowing through the transmission coil 14 be delayed with respect to the phase of a voltage applied thereto. This configuration allows, for example, current to flow from the source terminal to the drain terminal of the switching element 13-1 when the switching element 13-1 and the switching element 13-4 are turned on, and the power supply circuit 10 and the transmission coil 14 thereby operate with soft switching, thereby suppressing the occurrence of switching loss.

[0095] Fig. Fig. 8 is a diagram illustrating frequency characteristics of a delay of the phase of current with respect to the phase of voltage with respect to an alternating current power applied to the transmission coil 14 in the contactless power supply device 1 according to the present embodiment. Fig. 8, a frequency is plotted along the horizontal axis, and a phase is plotted along the vertical axis. Note that, in the graph, a case where a phase has a positive value indicates that the phase of current is delayed with respect to the phase of voltage. Graph 801 represents a frequency characteristic of a phase delay when the coupling coefficient k is set to k = 0.15 and the AC equivalent resistance of the load circuit 28 is set to Rac. In addition, graph 802 represents a frequency characteristic of a phase delay when the coupling coefficient k is set to k = 0.15 and the AC equivalent resistance of the load circuit 28 is set to (10*Rac). In addition, graph 803 represents a frequency characteristic of a phase delay when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 28 is set to Rac.In addition, graph 804 represents a frequency characteristic of a phase delay when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 28 is set to (10 * Rac). Furthermore, graph 805 represents a frequency characteristic of a phase delay when the coupling coefficient k is set to k = 0.6 and the AC equivalent resistance of the load circuit 28 is set to Rac. In addition, graph 806 represents a frequency characteristic of a phase delay when the coupling coefficient k is set to k = 0.6 and the AC equivalent resistance of the load circuit 28 is set to (10 * Rac).

[0096] As illustrated by graphs 801 to 806, it is clear that in a frequency range containing the frequencies corresponding to points 711 to 713, which are shown in Fig. 7, that is, in a frequency range that causes the contactless power supply device 1 to perform a constant-voltage output operation, the phase delay constantly has a positive value regardless of the coupling coefficient. Therefore, it is apparent that the contactless power supply device 1 according to the present embodiment is capable of causing the power supply circuit 10 and the transmission coil 14 to operate with smooth switching.

[0097] As described above, by disposing, in the resonance circuit of the power receiving device, a coil connected in series with the receiving coil and not coupled with the transmitting coil, the contactless power supply device suppresses a change in the resonance frequency of the resonant circuit due to a change in the coupling coefficient between the transmitting coil and the receiving coil, even at the time of power transmission. This configuration enables the contactless power supply device to narrow the adjustment range of the switching frequency of an AC power supplied to the transmitting coil when performing a constant-voltage output operation in an environment where the coupling coefficient does not remain constant.Furthermore, the contactless power supply device suppresses an increase in current flowing through the transmitting coil by supplying the transmitting coil of the power transmitting device with AC power at a switching frequency at which the transmitting coil does not resonate, thereby causing an input impedance to have a certain magnitude even when the coupling coefficient decreases. Therefore, the contactless power supply device is capable of suppressing power loss even when the coupling coefficient between the transmitting coil and the receiving coil is low. Furthermore, the contactless power supply device monitors an output voltage from the resonant circuit of the power receiving device and controls the switching frequency and voltage of the AC power supplied to the transmitting coil according to the output voltage.This configuration enables the contactless power supply device to perform a constant voltage output operation even if the coupling coefficient between the transmitting coil and the receiving coil changes or the resistance value of the load circuit changes.

[0098] According to a modification, in a resonance circuit 20 of a power receiving device 3, a coil 23 that does not resonate with a transmission coil 14 even at the time of power transmission may be connected in series with a resonance capacitor 22 and in parallel with a reception coil 21.

[0099] Fig. Fig. 9 is an equivalent circuit diagram of a contactless power supply device according to the modification. An equivalent circuit 900 shown in Fig. 9 is different from the equivalent circuit 500 shown in Fig. 5, the coil 23 (corresponding to the inductance L1) is connected in series with the resonance capacitor 22 (corresponding to the capacitance Cp), and the coil 23 and the resonance capacitor 22 are connected in parallel to form an ideal transformer formed by the transmission coil 14 coupled to the reception coil 21. An F-matrix Fp2(s, k, Rac) of the contactless power supply device according to the modification is expressed by the following equation. Fp2(s,k,Rac):=[1Ri01]⋅[11s⋅Crl01]⋅[1s⋅Lr(k)01]⋅[101s⋅Lm(k)1]⋅[1s⋅L r(k)01]⋅[1n2⋅Ris01]⋅[10s⋅n2⋅Li+1s⋅n2⋅Cp1]⋅[1s⋅L2⋅n201]⋅[101n2⋅Rac1]

[0100] Therefore, as in equation (2), an output gain Gp2(s, k, Rac) of the contactless power supply device 1 is expressed by the following equation. Gp2(s,k,Rac)=1Fp2(s,k,Rac)⋅Vin2⋅1n

[0101] In the preceding equation, Vin is a voltage (amplitude) of an AC power supplied to the resonance circuit on the power transmission side, and Fp2(s, k, Rac)0,0 represents the upper left element of the F matrix expressed by equation (7).

[0102] Fig. 10 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the modification when a voltage applied to the transmission coil 14 is changed according to the coupling coefficient, the frequency characteristics being calculated according to equation (8). Fig. 10, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Graph 1001 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of a load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to Vin. Furthermore, graph 1002 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to Vin.Furthermore, graph 1003 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.48*Vin). Furthermore, graph 1004 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.48*Vin). Furthermore, graph 1005 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.17*Vin).In addition, graph 1006 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to (10 * Rac), and the voltage applied to the transmission coil 14 is set to (0.17 * Vin). Note that the simulation assumes that Lp = 174 µH, Cr1 = 2 µF, Cp = 10 nF, L1 = 260 µH, L2 = 430 µH, Ri = Ris = 0.3 Ω, n = 1, Ro = 150 Ω, and Vin = 800 V.

[0103] As in Fig. 10, in the modification, for each coupling coefficient, there also exists a combination of a frequency and an output voltage at which the output voltage becomes substantially constant even if the AC equivalent resistance of the load circuit 28 changes under the condition that the coupling coefficient k does not change (there are three combinations, which are illustrated in the figure by points 1011 to 1013). In addition, a range from the frequency f1' corresponding to point 1011 to the frequency f2' corresponding to point 1013 in the modification is substantially equal to the range from the frequency f1 corresponding to point 711 to the frequency f2 corresponding to point 713 shown in Fig. 7. Therefore, the contactless power supply device according to the modification is also capable of performing a constant voltage output operation even if the coupling coefficient does not remain constant, and of narrowing a frequency adjustment range of an AC power supplied to the transmission coil 14. In addition, in the modification, as can be seen from the parameter values ​​of the respective circuit elements obtained during the simulation in Fig. 7 and the parameter values ​​of the respective circuit elements used in the simulation in Fig. 10, the inductance of the coil 23 and the inductance of the coil 24 are set lower than those of the coil 23 and the coil 24 in the previously described embodiment, respectively, in order to set the frequency setting ranges approximately equal to each other.

[0104] Furthermore, according to a further modification, instead of disposing a coil that is not coupled to the transmission coil 14 in a resonance circuit 20 of a power receiving device 3, a coil may be disposed in a power transmission device 2 that is connected in series to the transmission coil 14 and is not coupled to a receiving coil 21 even at the time of power transmission.

[0105] Fig. 11 is an equivalent circuit diagram of a contactless power supply device according to the modification. An equivalent circuit 1100 shown in Fig. 11 is different from the equivalent circuit 500 shown in Fig. 5, in that a coil corresponding to the inductance L1 and not coupled to the receiving coil 21 even at the time of power transmission is arranged in such a manner as to be connected in series with the transmitting coil 14.

[0106] In this case, a resonance frequency f r2 of the resonance circuit 20 is expressed by the following equation. fr2=12πCp⋅(Lr2×L3+Lr2(1−k)2×L3+Lr2)Lr2=L2(1−k)(1+k)

[0107] In the previous equation, Cp is a capacitance of a resonant capacitor 22 and L2 is an inductance of the receiving coil 21. L r2is the inductance of the receiving coil 21 when the transmitting coil 14 is short-circuited, and k denotes a coupling coefficient between the transmitting coil 14 and the receiving coil 21. In addition, L3 is an inductance of the coil connected in series with the transmitting coil 14. Since the coupling coefficient k is constantly 0 or more and 1 or less, the denominator on the right side of equation (9) is larger with increasing coupling coefficient k compared to a case where the coil connected in series with the transmitting coil 14 is not included (ie, L3 = 0), and as a result, an increase in the resonance frequency f r2 suppressed. Therefore, it is clear that a deviation of the resonance frequency f r2 the resonance circuit 20 when the coupling coefficient k changes is suppressed.

[0108] Fig. 12 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the modification when the voltage applied to the transmission coil 14 is changed according to the coupling coefficient. Fig. 12, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Graph 1201 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of a load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to Vin. Furthermore, graph 1202 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to Vin.Furthermore, graph 1203 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.48*Vin). Furthermore, graph 1204 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.48*Vin). Furthermore, graph 1205 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.22*Vin).In addition, graph 1206 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to (10 * Rac), and the voltage applied to the transmission coil 14 is set to (0.22 * Vin). Note that the simulation assumes that Lp = 174 µH, Cr1 = 2 µF, Cp = 25 nF, L1 = 240 µH, L2 = 1300 µH, Ri = Ris = 0.3 Ω, n = 1, Ro = 150 Ω, and Vin = 800 V.

[0109] In this case, although a variation in the output voltage due to a change in the resistance value of the load circuit 28 is larger than the variation in the above-described embodiment, there exists a frequency at which the variation in the output voltage is suppressed for each coupling coefficient, as illustrated by points 1211 to 1213. Furthermore, in the modification, a setting range of the switching frequency of an AC power supplied to the transmission coil 14 due to a variation in the coupling coefficient also becomes approximately the same as that in the above-described embodiment.

[0110] According to yet another modification, in conjunction with disposing a coil 23 which is not coupled to a transmitting coil 14 even at the time of power transmission in a resonance circuit 20 of a power receiving device 3, a coil may be disposed which is connected in series to the transmitting coil 14 of a power transmitting device 2 and is not coupled to a receiving coil 21 even at the time of power transmission.

[0111] Fig. 13 is an equivalent circuit diagram of a contactless power supply device according to the modification. An equivalent circuit 1300 shown in Fig. 13 is different from the equivalent circuit 900 shown in Fig. 9, which has, in the resonance circuit 20 of the power receiving device 3, a coil (corresponding to the inductance L1) connected in series with the resonance capacitor 22 and not coupled with the transmission coil 14, in that a coil corresponding to the inductance L3 and not coupled with the reception coil 21, even at the time of power transmission, is arranged in such a manner as to be connected in series with the transmission coil 14.

[0112] Fig. Fig. 14 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device according to the modification when the voltage applied to the transmission coil 14 is changed according to the coupling coefficient. Fig. 14, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Graph 1401 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of a load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to Vin. Furthermore, graph 1402 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to Vin.Furthermore, graph 1403 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.48*Vin). Furthermore, graph 1404 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 28 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.48*Vin). Furthermore, graph 1405 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.22*Vin).In addition, graph 1406 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 28 is set to (10 * Rac), and the voltage applied to the transmission coil 14 is set to (0.22 * Vin). Note that the simulation assumes that Lp = 174 µH, Cr1 = 2 µF, Cp = 9.2 nF, L1 = 260 µH, L2 = 1000 µH, L3 = 180 µH, Ri = Ris = 0.3 Ω, n = 1, Ro = 150 Ω, and Vin = 800 V.

[0113] In the modification, as illustrated by points 1411 to 1413, there also exists a frequency at which a deviation of the output voltage is suppressed for each coupling coefficient. Furthermore, in the modification, a setting range of the switching frequency of an AC power supplied to the transmission coil 14 from the frequency f1" corresponding to point 1411 to the frequency f2" corresponding to point 1413 due to a deviation of the coupling coefficient can be further narrowed than the setting range of the switching frequency according to the above-described embodiment (the range from the frequency f1 to the frequency f2 shown in Fig. 7 are illustrated).

[0114] Note that in the above-described respective modifications, as in the above-described embodiment, the control circuit 18 of the power transmission device 2 is also capable of causing the contactless power supply device to perform a constant voltage output operation by adjusting the switching frequency and the voltage of the AC power supplied to the transmission coil 14 from the power supply circuit 10 according to received determination information, even if the coupling coefficient does not remain constant.

[0115] Furthermore, the inventors have found that when the resistance value of the load circuit of the power receiving device has a preset value, the input impedance of the contactless power supply device according to the above-described embodiment or its modifications has a local minimum value at a frequency at which the contactless power supply device performs a constant voltage output operation.

[0116] Fig. Figure 15 is a diagram illustrating an example of a relationship between frequency characteristics of an output voltage and frequency characteristics of an input impedance of the contactless power supply device according to the SPL method. In the upper diagram in Fig. 15, a frequency is plotted along the horizontal axis and an output voltage is plotted along the vertical axis. Furthermore, in the lower diagram, Fig. 15 a frequency is plotted along the horizontal axis and an input impedance is plotted along the vertical axis. Note that the simulation uses the same values ​​as the values ​​of parameters of the respective circuit elements used in the Fig. 2. In the upper diagram, graph 1501 (the same as graph 203 in Fig. 2) a frequency response of the output voltage from the contactless power supply device 1 when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 27 is set to Rac. Furthermore, graph 1502 (the same as graph 204 in Fig. 2) A frequency characteristic of the output voltage from the contactless power supply device 1 when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 27 is set to (10*Rac). Furthermore, graph 1511 in the lower diagram represents a frequency characteristic of the input impedance of the contactless power supply device 1 when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 27 is set to Rac. Furthermore, graph 1512 represents a frequency characteristic of the input impedance of the contactless power supply device 1 when the coupling coefficient k is set to k = 0.3 and the AC equivalent resistance of the load circuit 27 is set to (100*Rac).

[0117] As in Fig. As illustrated in Figure 15, the input impedance has a local minimum value at the frequency f0 at which the contactless power supply device 1 performs a constant voltage output operation when the AC equivalent resistance of the load circuit 27 is set to Rac. In other words, the current flowing through the transmission coil 14 has a local maximum value at the frequency f0.

[0118] Therefore, according to a modification, the control circuit of the power transmission device may determine whether or not the contactless power supply device performs a constant voltage output operation based on a frequency characteristic of current flowing through the transmission coil.

[0119] Fig. 16 is a schematic view of a configuration of a contactless power supply device according to the modification. As shown in Fig. As illustrated in Figure 16, a contactless power supply device 41 includes a power transmission device 42 and a power reception device 43 to which power is transmitted from the power transmission device 42 through space without contact. The power transmission device 42 includes a power supply circuit 50, a transmission coil 54, a capacitor 55, a current detection circuit 56, a receiver 57, a gate driver 58, and a control circuit 59. On the other hand, the power receiving device 43 includes a resonance circuit 60 including a receiving coil 61, a resonance capacitor 62, and a coil 63, a coil 64, a rectifying and smoothing circuit 65 including a full-wave rectifying circuit 66 and a smoothing capacitor 67, a load circuit 68, a voltage detecting circuit 69, a constant voltage determining circuit 70, a fixed load circuit 73, and a transmitter 74.

[0120] The contactless energy supply device 41 differs from the energy transmission device 1, which in Fig. 4, with respect to the power transmission device 42, the configuration of the power supply circuit 50 differs in that it includes the current detection circuit 56, and a part of the control performed by the control circuit 59. Furthermore, with respect to the power receiving device 43, the contactless power supply device 41 differs from the contactless power supply device 1 in that it includes the fixed load circuit 73. Therefore, the above-described differences and the related matter will be explained below.

[0121] The power transmission device 50 supplies alternating current power to the transmission coil 54 at an adjustable switching frequency and an adjustable voltage. For this purpose, the power supply circuit 50 comprises a variable-voltage power source 51, a DC-DC converter 52, and three switching elements 53-1 to 53-3.

[0122] The variable-voltage power source 51 is a power source that supplies direct current power and is capable of adjusting the voltage of the direct current power according to control from the control circuit 59. Note that the variable-voltage power source 51 can have any of various circuit configurations capable of adjusting the supplied voltage. While the contactless power supply device 41 performs a constant-voltage output operation, the direct current power supplied from the variable-voltage power source 51 is converted into alternating current power by the switching elements 53-1 and 53-2 and supplied to the transmission coil 54.On the other hand, the DC power supplied from the variable voltage power source 51 while the switching frequency adjustment for the contactless power supply device 41 to perform a constant voltage output operation is carried out is supplied to the transmission coil 54 via the DC-DC converter 52 and the switching element 53-3.

[0123] The input terminal of the DC-DC converter 52 is connected to the positive electrode terminal of the variable-voltage power source 51, and the output terminal of the DC-DC converter 52 is connected to one end of the capacitor 55 via a diode D and the switching element 53-3. The DC-DC converter 52 reduces the voltage of the DC power supplied from the variable-voltage power source 51 to a predetermined voltage (for example, 5 V).

[0124] While the switching frequency adjustment for the contactless power supply device 41 is carried out to perform a constant voltage output operation, the voltage output from the DC-DC converter 52 is supplied to the transmission coil 54 via the diode D, the switching element 53-3 and the capacitor 55.

[0125] For each of the switching elements 53-1 to 53-3, for example, an n-channel MOSFET can be used. The switching elements 53-1 and 53-2 are connected in series between the positive electrode terminal and the negative electrode terminal of the variable-voltage power source 51. Furthermore, the switching element 53-1 is connected to the positive electrode side of the variable-voltage power source 51, while the switching element 53-2 is connected to the negative electrode side of the variable-voltage power source 51. The drain terminal of the switching element 53-1 is connected to the positive electrode terminal of the variable-voltage power source 51, and the source terminal of the switching element 53-1 is connected to the drain terminal of the switching element 53-2. In addition, the source terminal of the switching element 53-1 and the drain terminal of the switching element 53-2 are connected to one end of the transmission coil 54 via the capacitor 55.Furthermore, the source terminal of the switching element 53-2 is connected to the negative electrode terminal of the variable voltage power source 51 and the other end of the transmission coil 54 via the current detection circuit 56.

[0126] In addition, the drain terminal of the switching element 53-3 is connected to the output terminal of the DC-DC converter 52, and the source terminal of the switching element 53-3 is connected to one end of the transmission coil 54 via the capacitor 55. The gate terminals of the switching elements are connected to the gate driver 58.

[0127] While the contactless power supply device 41 performs a constant-voltage output operation, the gate driver 58 maintains the switching element 53-3 in the off state according to a control signal from the control circuit 59. Furthermore, the gate driver 58 alternately switches the switching elements 53-1 and 53-2 between an on and an off state at a switching frequency at which a constant-voltage output operation is performed, according to a control signal from the control circuit 59. In other words, when the switching element 53-1 is turned on and the switching element 53-2 is turned off, current flows to the transmission coil 54 in association with power supplied to the capacitor 55 from the variable-voltage power source 51 through the switching element 53-1, and the capacitor 55 is charged.On the other hand, when the switching element 53-1 is turned off and the switching element 53-2 is turned on, the capacitor 55 is discharged and current flows from the capacitor 55 to the transmission coil 54.

[0128] In addition, while performing the switching frequency adjustment for the contactless power supply device 41 to perform a constant voltage output operation, the gate driver 58 maintains the switching element 53-1 in the off state according to a control signal from the control circuit 59 and alternately switches the switching element 53-3 and the switching element 53-2 between an on and an off state at the switching frequency according to a control signal from the control circuit 59.

[0129] The capacitor 55 is connected between the transmission coil 54 and the power supply circuit 50. The capacitor 55 supplies AC power to the transmission coil 54 at the switching frequency by repeatedly charging and discharging in response to switching the switching elements between on and off states at the switching frequency. Note that it is preferable that the capacitance of the capacitor 55 be set in such a manner that the resonance frequency of the transmission coil 54 and the capacitor 55 is lower than the resonance frequency of the resonance circuit 60 of the power receiving device 43 and the lower limit frequency of a frequency range in which the switching frequency is set, so that the transmission coil 54 and the capacitor 55 do not operate as a resonance circuit in the frequency range in which the switching frequency is set.

[0130] The current detection circuit 56 is connected between the transmission coil 54 and the power supply circuit 50 and measures the current flowing through the transmission coil 54. The current detection circuit 56 outputs a measured current value to the control circuit 59. Note that the current detection circuit 56 can be connected to the transmission coil 54 in parallel with the capacitor 55 in conjunction with a capacitor for deflection (not shown) connected in series with the current detection circuit 56. In this case, the current detection circuit 56 is able to indirectly measure the current flowing through the transmission coil 54.

[0131] In addition, the constant voltage determination circuit 70 of the power receiving device 43 includes a determination circuit 71 and a switching element 72, each of which is similar to the determination circuit 30 and the switching element 31 according to the above-described embodiment.

[0132] While measured values ​​of the output voltage from the resonant circuit 60, which is measured by the voltage detection circuit 69, are within the allowable voltage range, that is, the contactless power supply device 40 performs a constant voltage output operation, the determination circuit 71 of the constant voltage determination circuit 70 turns on the switching element 72, thereby causing the output voltage from the resonant circuit 60 to be supplied to the load circuit 68 via the rectifying and smoothing circuit 65. On the other hand, when measured values ​​of the output voltage are outside the allowable voltage range, the determination circuit 71 turns off the switching element 72, thereby causing the output voltage from the resonant circuit 60 to be supplied to the load circuit 68.

[0133] The fixed load circuit 73 is connected to the rectifying and smoothing circuit 65 in parallel with the load circuit 68 and, while the switching frequency adjustment is being performed, provides the power receiving device 43 with a load substantially equal to a load serving as a reference for the load circuit 68 (in the case of Fig. 15, for example, Rac). For this purpose, the fixed load circuit 73 is connected to the rectifying and smoothing circuit 65 in parallel with the load circuit 68 and includes a resistor R1 having a resistance value corresponding to the load serving as a reference for the load circuit 68. The resistor R1 is connected in series with a switching element SW1, which is an n-channel MOSFET. Furthermore, between the two output terminals of the rectifying and smoothing circuit 65, the fixed load circuit 73 includes a resistor R2 and a switching element SW2, which is an npn bipolar transistor, connected in series in this order from the positive electrode side. In addition, the resistor R2 and the switching element SW2 are connected in parallel with the resistor R1.The gate terminal of switching element SW1 is connected between resistor R2 and one end (in this example, the collector terminal) of switching element SW2. Furthermore, the base terminal of switching element SW2 is connected to the positive electrode terminal of rectifying and smoothing circuit 65 via a resistor R3 and a reverse-biased Zener diode ZD.

[0134] While the contactless power supply device 41 performs a constant voltage output operation, the output voltage from the resonant circuit 60 is higher than the breakdown voltage of the Zener diode ZD, and as a result, current is supplied to the base terminal of the switching element SW2 via the Zener diode ZD and the resistor R3, thereby turning on the switching element SW2. Consequently, the voltage applied to the gate terminal of the switching element SW1 decreases, turning off the switching element SW1. Therefore, the output voltage from the resonant circuit 60 is not applied to the resistor R1.

[0135] On the other hand, since the voltage of the power supplied to the power receiving device 43 from the power transmitting device 42 is low while the switching frequency is being adjusted so that the contactless power supply device 41 performs a constant-voltage output operation, the power supplied to the transmitting coil 54 from the DC-DC converter 52 is low, the power also decreases. Therefore, the output voltage from the resonant circuit 60 also decreases to a voltage lower than the breakdown voltage of the Zener diode ZD. As a result, the switching element SW2 is turned off, and in conjunction with this, the voltage applied to the gate terminal of the switching element SW1 increases, thereby turning the switching element SW1 on. Therefore, the output voltage from the resonant circuit 60 is applied to the resistor R1.As a result, a fixed load comprising the resistor R1 is provided to the power receiving device 43.

[0136] The following describes an operation of the control circuit 59 of the power transmission device 42 according to the modification. As in the previously described embodiment, while the contactless power supply device 41 is performing a constant voltage output operation, the control circuit 59 controls the variable voltage power source 51 of the power supply circuit 50 to supply DC voltage to the transmission coil 54 at a voltage corresponding to the switching frequency, in such a manner that a measured value of the output voltage from the resonance circuit 60 of the power reception device 43 is within a predetermined allowable range.In addition, the control circuit 59 maintains the switching element 53-3 in the off state and, in conjunction therewith, switches the switching elements 53-1 and 53-2 between an on state and an off state at a switching frequency at which a constant voltage output operation is performed via the gate driver 58.

[0137] On the other hand, when determination information included in a wireless signal received by the power receiving device 43 via the receiver 57 indicates that the contactless power supply device 41 is not performing a constant-voltage output operation, the control circuit 59 maintains the switching element 53-1 in the off state and, in conjunction with this, alternately switches the switching elements 53-3 and 53-2 between an on and an off state via the gate driver 58, thereby supplying power from the DC-DC converter 52 to the transmission coil 54. Furthermore, the control circuit 59 controls the variable-voltage power source 51 in such a manner that the voltage supplied from the DC-DC converter 52 to the transmission coil 54 has a predetermined value.Through this control, the control circuit 59 reduces the power supplied to the power receiving device 43 from the power transmitting device 42 to a level at which voltage is applied to the resistor R1 of the fixed load circuit 73 of the power receiving device 43.

[0138] The control circuit 59 monitors measured values ​​of current flowing through the transmission coil 54, which are measured by a current detection circuit 56, while changing the switching frequency, and detects a switching frequency at which the measured values ​​of the current have a local maximum. The switching frequency at which the measured values ​​of the current flowing through the transmission coil 54 have a local maximum is a frequency at which the input impedance of the contactless power supply device 41 has a local minimum value, that is, a frequency at which the contactless power supply device 41 performs a constant voltage output operation, such as the frequency shown in Fig. 15. Therefore, when a switching frequency at which the measured values ​​of the current flowing through the transmission coil 54 have a local maximum is detected, the control circuit 59 controls the switching of the switching elements 53-1 and 53-2 between an on and an off state via the gate driver 58 at the switching frequency in such a manner that power is supplied to the transmission coil 54 from the variable-voltage power source 51. Furthermore, the control circuit 59 turns off the switching element 53-3. This operation enables the control circuit 59 to cause the contactless power supply device 41 to perform a constant-voltage output operation.In addition, as described above, the control circuit 59 controls the variable voltage power source 51 of the power supply circuit 50 to supply DC voltage having a voltage according to the switching frequency to the transmission coil 54 in such a manner that measured values ​​of the output voltage from the resonance circuit 60 of the power receiving device 43 are within a predetermined allowable range.

[0139] According to the modification, the control circuit of the power transmission device is capable of detecting a switching frequency at which the contactless power supply device performs a constant voltage output operation by monitoring current flowing through the transmission coil.

[0140] Note that in the Fig. 16 illustrated modification, as in the Fig. 9, the coil 63, which is not coupled to the transmission coil 54, even at the time of energy transmission, may be connected in series with the resonance capacitor 62 and in parallel with the reception coil 61 in the resonance circuit 60 of the energy receiving device 43. Alternatively, as in the embodiment shown in Fig. 11 or Fig. 13, in conjunction with disposing a coil that is not coupled to the transmission coil 54, or instead of disposing a coil in the resonance circuit 60 of the power receiving device 43, a coil may be disposed in the power transmission device 42 that is connected in series with the transmission coil 54 and is not coupled to the reception coil 61, even at the time of power transmission. In this case, the control circuit of the power transmission device is also capable of detecting a switching frequency at which the contactless power supply device performs a constant-voltage output operation by monitoring the current flowing through the transmission coil of the power transmission device.

[0141] According to a further modification, in the power transmission device, the power supply circuit that supplies AC power to the transmission coil may have a circuit configuration different from that in the above-described embodiment and its modifications, insofar as the power supply circuit is a circuit that can variably adjust the switching frequency and the voltage applied to the transmission coil.

[0142] Fig. 17A and Fig. 17B are circuit diagrams of power supply circuits according to the modification, respectively.

[0143] A power supply circuit 110, which in Fig. 17A, includes a power source 11, a power factor improvement circuit 12, two switching elements 13-1 and 13-2, and a capacitor 15 connected in series with a transmission coil 14 for blocking a direct current. Note that in this modification, n-channel MOSFETs, for example, can also be used for the switching elements. Furthermore, the power factor improvement circuit 12 can be configured, for example, identically to the power factor improvement circuit 12 in the previously described embodiment.

[0144] In this modification, the switching element 13-1 and the switching element 13-2 are connected in series between the positive electrode terminal and the negative electrode terminal of the power source 11. Furthermore, the switching element 13-1 is connected to the positive electrode side of the power source 11, while the switching element 13-2 is connected to the negative electrode side of the power source 11. The drain terminal of the switching element 13-1 is connected to the positive electrode terminal of the power source 11 via the power factor improvement circuit 12, and the source terminal of the switching element 13-1 is connected to the drain terminal of the switching element 13-2. Furthermore, the source terminal of the switching element 13-2 is connected to the negative electrode terminal of the power source 11 via the power factor improvement circuit 12.Furthermore, the source terminal of the switching element 13-1 and the drain terminal of the switching element 13-2 are connected to one end of the transmission coil 14, and the source terminal of the switching element 13-2 is connected to the other end of the transmission coil 14 via the capacitor 15. Furthermore, the gate terminals of the switching elements are connected to a gate driver 17-2.

[0145] In this modification, the gate driver 17-2 can alternately switch the switching element 13-1 and the switching element 13-2 between an on and an off state according to a control signal from a control circuit. In other words, when the switching element 13-1 is on and the switching element 13-2 is off, current flows from the power source 11 to the transfer coil 14 via the power factor improvement circuit 12 and the switching element 13-1, and the capacitor 15 is charged. On the other hand, when the switching element 13-1 is off and the switching element 13-2 is on, the capacitor 15 is discharged, and current flows from the capacitor 15 via the transfer coil 14 and the switching element 13-2.In this modification, therefore, the control circuit can control the switching frequency at which the switching element 13-1 and the switching element 13-2 are switched between an on state and an off state via the gate driver 17-2, depending on destination information received from a power receiving device 3.

[0146] A power supply circuit 120, which in Fig. 17B, ​​as in the power supply circuit 110, includes a power source 11, a power factor improving circuit 12, two switching elements 13-1 and 13-2, and a capacitor 15 connected in series with a transfer coil 14. Note that, in the power supply circuit 120, compared to the power supply circuit 110, one end of the transfer coil 14 is connected to the positive electrode terminal of the power source 11 via the power factor improving circuit 12, and the other end of the transfer coil 14 is connected to the source terminal of the switching element 13-1 and the drain terminal of the switching element 13-2 via the capacitor 15.

[0147] In this modification, the gate driver 17-2 may also alternately switch the switching element 13-1 and the switching element 13-2 between an on state and an off state according to a control signal from a control circuit.

[0148] Note that with respect to the power supply circuit 110 shown in Fig. 17A, and the power supply circuit 120 shown in Fig. 17B, ​​it is preferable that the capacitance of the capacitor 15 is set in such a manner that the resonance frequency of the transmission coil 14 and the capacitor 15 is lower than the resonance frequency of a resonance circuit 20 of the power receiving device 3, and as the lower limit of the frequency of a frequency range in which the switching frequency is set such that the transmission coil 14 and the capacitor 15 are not operated as a resonance circuit within the frequency range in which the switching frequency is set.

[0149] In addition, in the above-described embodiment or the modification described in Fig. 9, Fig. 11 or Fig. 13, the capacitor 15 connected in series with the transmission coil 14 for blocking a direct current is omitted.

[0150] Furthermore, in the Fig. 4 illustrated embodiment and the Fig. 9, Fig. 11, Fig. 17A and Fig. 17B, ​​modifications illustrated a variable voltage power source instead of the power source and the power factor improvement circuit as in Fig. 16. Conversely, in the Fig. 16 illustrates the energy source and the power factor improvement circuit in the Fig. 4 can be used instead of the variable voltage power source. Furthermore, in the embodiment shown in Fig.In the modification illustrated in Figure 16, the variable-voltage power source 51 may be configured to supply power to the transmission coil 54 at a predetermined voltage while adjusting the switching frequency. In this case, the DC-DC converter 52 and the switching element 53-3 may be omitted.

[0151] In addition, if it is possible to connect the receiver 16 of the power transmission device 2 and the transmitter 33 of the power reception device 3 to each other in a wired manner, each of the receiver 16 and the transmitter 33 may include a communication circuit capable of transmitting a signal including destination information in a wired manner.

[0152] As discussed above, one skilled in the art could make various changes suitable to the embodiments without departing from the scope of the present invention. LIST OF REFERENCE SYMBOLS 1, 41 Contactless energy supply device 2, 42 Energy transmission device 10, 110, 120 power supply circuit 11 Energy source 12 Power factor improvement circuit 51 Variable voltage power source 52 DC converters 13-1 to 13-4, 53-1 to 53-3 switching element 14, 54 transmission coil 15, 55 capacitor 56 Current detection circuit 16, 57 recipients 17-1, 17-2, 58 Gate drivers 18, 59 Control circuit 3, 43 Energy receiving device 20, 60 Resonance circuit 21, 61 receiving coil 22, 62 Resonance capacitor 23, 24, 63, 64 coil 25, 65 Rectifier and smoothing circuit 26, 66 Full-wave rectifier circuit 27, 67 smoothing capacitor 28, 68 Powershift 29, 69 Voltage detection circuit 30, 70 Constant voltage determination circuit 31, 71 Determination circuit 32, 72 switching element 73 Circuit with fixed load 33, 74 channels 111 AC power source

Claims

[1] Contactless energy supply device (1) comprising an energy transmission device (2) and an energy reception device (3) to which energy is transmitted from the energy transmission device (2) without contact, wherein the energy reception device (3) comprises: a resonance circuit (20) comprising a receiving coil (21) which receives energy from the energy transmission device (2), a resonance capacitor (22) connected in parallel to the receiving coil (21), and a first coil (23) connected in series with or in parallel to the receiving coil (21); a rectifier circuit (26) which rectifies energy output from the resonant circuit (20); and a second coil (24) connected in series with the receiving coil (21) between the resonant circuit (20) and the rectifier circuit (26), and wherein the energy transmission device (2) comprises: a transmission coil (14) which supplies energy to the energy receiving device (3); a third coil connected in series with the transmission coil (14); and a power supply circuit (10) supplying AC power to the transmission coil (14) at an adjustable switching frequency at which the transmission coil (14) does not resonate and at an adjustable voltage, the power receiving device further comprising (3): a voltage detection circuit (29) that measures an output voltage of a power output from the resonance circuit (20) and obtains a measured value of the output voltage; a constant voltage determination circuit (30) which, based on the measured value of the output voltage, determines whether the contactless power supply device (1) performs a constant voltage output operation in which measured values ​​of the output voltage do not change even if a resistance value of a load circuit (28) connected to the rectifier circuit (26) of the power receiving device (3) changes, and whether the measured value of the output voltage is within a predetermined allowable voltage range; and a transmitter (33) transmitting to the power transmission device (2) a signal having determination information indicating whether or not the contactless power supply device (1) is performing a constant voltage output operation and whether or not the measured value of the output voltage is within the predetermined allowable voltage range, and wherein the power transmission device (2) further comprises: a receiver (16) receiving the signal comprising the destination information; and a control circuit (18) which controls the switching frequency and the voltage of the alternating current power supplied to the transmission coil (14) from the power supply circuit (10) in accordance with the determination information. [2] Contactless power supply device (1) according to claim 1, wherein the first coil (23) is not coupled to the transmission coil (14) even while power is transmitted from the power transmission device (2) to the power reception device (3). [3] The contactless power supply device (1) according to claim 1 or 2, wherein the control circuit (18), when the determination information indicates that the contactless power supply device (1) does not perform the constant voltage output operation, controls the switching frequency of the AC power supplied to the transmission coil (14) from the power supply circuit (10) in such a manner that measured values ​​of the output voltage do not change even if a resistance value of a load circuit (28) connected to the rectifier circuit (26) of the power receiving device (3) changes. [4] The contactless power supply device (1) according to claim 3, wherein the control circuit (18), when the determination information indicates that the contactless power supply device (1) performs the constant voltage output operation and the measured value of the output voltage is not within the predetermined allowable voltage range, controls the voltage of the AC power supplied to the transmission coil (14) from the power supply circuit (10) in such a manner that measured values ​​of the output voltage are within the predetermined allowable voltage range. [5] A contactless energy supply device (41) comprising an energy transmission device (42) and an energy reception device (43) to which energy is transmitted from the energy transmission device (42) without contact, the energy reception device (43) comprising: a resonant circuit (60) comprising a receiving coil (61) receiving energy from the energy transmission device (42), a resonant capacitor (62) connected in parallel to the receiving coil (61), and a first coil (63) connected in series with or in parallel to the receiving coil (61); a rectifier circuit (66) which rectifies energy output from the resonant circuit (60); and a second coil (64) connected in series with the receiving coil (61) between the resonant circuit (60) and the rectifier circuit (66), and wherein the energy transfer device (42) comprises: a transmission coil (54) that supplies energy to the energy receiving device (43); a third coil connected in series with the transmission coil (54); and a power supply circuit (50) that supplies AC power to the transmission coil (54) at an adjustable switching frequency at which the transmission coil (54) does not resonate and at an adjustable voltage, wherein the power supply circuit (50) can adjust the switching frequency and the voltage of AC power supplied to the transmission coil (54), and wherein the energy transmission device (42) further comprises: a current detection circuit (56) that measures a current flowing through the transmission coil (54) and obtains a measured value of the current; and a control circuit (59) which controls the switching frequency and the voltage of the alternating current power supplied to the transmission coil (54) from the power supply circuit (50) in dependence on the measured value of the current. [6] A contactless power supply device (41) according to claim 5, wherein the control circuit (59) monitors measured values ​​of the current while changing the switching frequency, and thereby detects a switching frequency at which measured values ​​of the current have a local maximum, and controls the power supply circuit (50) in such a manner that an AC power having the detected switching frequency is supplied to the transmission coil (54). [7] Contactless energy supply device (1) comprising an energy transmission device (2) and an energy reception device (3) to which energy is transmitted from the energy transmission device (2) without contact, wherein the energy reception device (3) comprises: a resonance circuit (20) comprising a receiving coil (21) which receives energy from the energy transmission device (2) and a resonance capacitor (22) connected in parallel to the receiving coil (21); a rectifier circuit (26) which rectifies energy output from the resonant circuit (20); and a first coil (23) connected in series with the receiving coil (21) between the resonant circuit (20) and the rectifier circuit (26), and wherein the energy transmission device (2) comprises: a transmission coil (14) which supplies energy to the energy receiving device (3); a second coil connected in series with the transmitting coil (14) and not coupled to the receiving coil (21) even while energy is being transmitted from the energy transmitting device (2) to the energy receiving device (3); and a power supply circuit (10) supplying AC power to the transmission coil (14) at an adjustable switching frequency at which the transmission coil (14) does not resonate and at an adjustable voltage, the power receiving device (3) further comprising: a voltage detection circuit (29) that measures an output voltage of a power output from the resonance circuit (20) and obtains a measured value of the output voltage; a constant voltage determination circuit (30) which, based on the measured value of the output voltage, determines whether the contactless power supply device (1) performs a constant voltage output operation in which measured values ​​of the output voltage do not change even if a resistance value of a load circuit (28) connected to the rectifier circuit (26) of the power receiving device (3) changes, and whether the measured value of the output voltage is within a predetermined allowable voltage range; and a transmitter (33) transmitting to the power transmission device (2) a signal having determination information indicating whether or not the contactless power supply device (1) is performing a constant voltage output operation and whether or not the measured value of the output voltage is within the predetermined allowable voltage range, and wherein the power transmission device (2) further comprises: a receiver (16) receiving the signal comprising the destination information; and a control circuit (18) which controls the switching frequency and the voltage of the alternating current power supplied to the transmission coil (14) from the power supply circuit (10) in accordance with the determination information.

Images