CONTACTLESS POWER SUPPLY DEVICE AND METHOD FOR ANOMALIC STOPPING

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 receiving device (3) comprises: a resonant circuit (20) having a receiving coil (21) which receives energy from the energy transmission device (2); and a rectifier circuit (25) which rectifies energy output from the resonance circuit (20), and wherein the energy transmission device (2) comprises: a transmission coil (14) which supplies energy to the energy receiving device (3); a power supply circuit (10) which supplies alternating current power to the transmission coil (14) at an adjustable switching frequency; and a control circuit (17) that stops a power supply from the power supply circuit (10) to the transmission coil (14) when the contactless power supply device (1) does not perform a constant voltage output operation in which an output voltage of the power output from the rectifier circuit (25) becomes a constant voltage even if a resistance value of a load circuit (27) connected to the rectifier circuit (25) changes, even if the switching frequency of the AC power supplied to the transmission coil (14) from the power supply circuit (10) is changed over a predetermined frequency range.

Description

AREA

[0001] The present invention relates to a contactless power supply device and a method for abnormal stopping in the 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 primary series and secondary 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 technique 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 such a technique is sometimes referred to as the SPL method. The method is also referred to herein as the SPL method.

[0006] In such various types of contactless power supply devices, a metal foreign object sometimes inadvertently penetrates between the transmitting coil on the power transmitting side and the receiving coil on the power receiving side. In such a case, the foreign object is heated by induction heating during power transfer, resulting in a malfunction such as ignition of the foreign object or deformation of the device cover. Therefore, a technique for detecting a metal foreign object that has penetrated between the transmitting coil and the receiving coil has been proposed (see, for example, NPL 2). [LIST OF DOCUMENTS][PATENT LITERATURE]

[0007] [PTL 1] Japanese Unexamined Patent Publication (Kokai) JP 2015 042 051 A [NON-PATENT LITERATURE] [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, Nr.7, S.707-713, 2013 [NPL 2] Komasaki et al., „Methods for Detecting Foreign Metallic Materials in the Air Gap of Contactless Battery Charger for Electric Vehicles“, IEE-Japan Industry Applications Society Conference, 2012

[0008] Weitere Stand der Technik Dokumente sind die US 2011 / 0 254 377 A1 und die US 2014 / 0 203 774 A1. KURZFASSUNG[TECHNISCHE AUFGABE]

[0009] In NPL 2, three methods are proposed as foreign matter detection methods, namely (I) a method for comparing a transformer efficiency estimated from a voltage ratio between the transmitting coil and the receiving coil with an actual efficiency, (II) a method for comparing current values ​​when a constant voltage is applied to the transmitting coil in a state where the device on the power receiving side is removed, and (III) a method for sampling a transmission loss at a specified period of time and comparing sampled transmission loss values. Of the three methods, methods (I) and (II) are methods for detecting a foreign matter that has entered before starting power transmission, and method (III) is a method for detecting a foreign matter that has entered during power transmission.However, the methods are based on the assumption that the coupling coefficient between the transmitting coil and the receiving coil does not change, and therefore, when the coupling coefficient changes during power transmission, for example, due to a change in the relative positional relationship between the device on the power transmitting side and the device on the power receiving side, it is impossible to distinguish between whether a foreign matter has penetrated or the coupling coefficient has changed.

[0010] Accordingly, it is an object of the present invention to provide a contactless power supply device capable of preventing a malfunction from occurring due to a foreign matter intruding between the transmitting coil and the receiving coil, even when the coupling coefficient between the transmitting coil of the power transmitting-side device and the receiving coil of the power receiving-side device changes. This object is achieved by the subject matter of the independent claims. Preferred embodiments and further developments are the subject matter of the dependent claims. The invention is defined by the claims, with embodiments of the invention being set forth below.

[0011] As an embodiment of the present invention, there is provided a contactless power supply device comprising 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 receiving device includes a resonance circuit having a receiving coil that receives power from the power transmitting device, and a rectifier circuit that rectifies power output from the resonance circuit, and the power transmitting device includes a transmitting coil that supplies power to the power receiving device, a power supply circuit that supplies AC power to the transmitting coil at an adjustable switching frequency, and a control circuit that stops power supply from the power supply circuit to the transmitting coil when the contactless power supply device does not perform a constant voltage output operation, even if the switching frequency of the AC power supplied to the transmitting coil from the power supply circuit is changed over a predetermined frequency range.

[0012] Against the background of such a configuration, the contactless power supply device is capable of preventing a malfunction from occurring due to a foreign matter having entered between the transmitting coil and the receiving coil even if a coupling coefficient between the transmitting coil of the device on the power transmitting side and the receiving coil of the device on the power receiving side changes.

[0013] In the contactless power supply device, the power receiving device preferably further comprises a coil connected in series with the receiving coil between the resonance circuit and the rectifier circuit, and the resonance circuit of the power receiving device preferably further comprises a resonance capacitor connected in parallel with the receiving coil, and the control circuit of the power transmitting device preferably controls the power supply circuit in such a manner that AC power is supplied to the transmitting coil at a switching frequency at which the transmitting coil does not resonate.

[0014] With such a configuration, the contactless power supply device can determine whether or not a foreign matter has entered between the transmitting coil and the receiving coil based on whether or not the constant voltage output operation is performed, and the contactless power supply device is capable of accurately determining whether or not a foreign matter has entered between the transmitting coil and the receiving coil.

[0015] Alternatively, in the contactless power supply device, the resonance circuit of the power receiving device preferably further comprises a resonance capacitor connected in series with the receiving coil.

[0016] With such a configuration, the contactless power supply device can determine whether or not a foreign matter has entered between the transmitting coil and the receiving coil based on whether or not the constant voltage output operation is performed, and the contactless power supply device is capable of accurately determining whether or not a foreign matter has entered between the transmitting coil and the receiving coil.

[0017] In the contactless power supply device, the power receiving device preferably further comprises a voltage detection circuit that measures an 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 a measured value of the output voltage, whether the contactless power supply device performs the constant voltage output operation or not and whether a 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 transmission device a signal having determination information indicatingwhether the contactless power supply device performs the constant voltage output operation and whether a measured value of the output voltage 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 the control circuit of the power transmission device preferably stops power supply from the power supply circuit to the transmission coil if the control circuit of the power transmission device does not receive the determination information indicating that the contactless power supply device performs the constant voltage output operation, even if the switching frequency of the AC power supplied from the power supply circuit to the transmission coil is varied over the predetermined frequency range.

[0018] Against the background of such a configuration, the contactless power supply device is able to reliably prevent a malfunction from occurring due to a foreign matter having penetrated between the transmitting coil and the receiving coil.

[0019] In this case, the constant-voltage determination circuit of the power receiving device preferably calculates a change amount of measured values ​​of the output voltage during a lapse of a predetermined period of time, and the transmitter of the power receiving device preferably includes the change amount of measured values ​​of the output voltage in the determination information. If the change amount of measured values ​​of the output voltage included in the determination information indicates that the measured values ​​of the output voltage increase when the switching frequency of the AC power supplied to the transmission coil from the power supply circuit is changed in such a way as to increase it by a predetermined amount, the control circuit of the power transmission device preferably stops power supply from the power supply circuit to the transmission coil.

[0020] Against the background of such a configuration, the contactless power supply device is able to reliably prevent a malfunction from occurring due to a foreign matter having penetrated between the transmitting coil and the receiving coil.

[0021] Furthermore, in the contactless power supply device, when measured values ​​of the output voltage become substantially constant even if a resistance value of a circuit connected to the resonance circuit is changed, the constant voltage determining circuit of the power receiving device preferably determines that the contactless power supply device performs the constant voltage output operation.

[0022] Against the background of such a configuration, the contactless power supply device is capable of accurately determining whether the contactless power supply device performs the constant voltage output operation or not when no foreign matter has entered between the transmitting coil and the receiving coil.

[0023] Alternatively, in the contactless power supply device, the power transmission device preferably further comprises a current detection circuit that measures current flowing through the transmission coil and obtains a measured value of the current, and the control circuit of the power transmission device preferably monitors measured values ​​of the current while changing the switching frequency over the predetermined frequency range, and thereby determines whether or not a switching frequency at which measured values ​​of the current have a local maximum is detected, and stops power supply from the power supply circuit to the transmission coil when no switching frequency at which measured values ​​of the current have a local maximum is detected.

[0024] Against the background of such a configuration, the contactless power supply device is able to reliably prevent a malfunction from occurring due to a foreign matter having penetrated between the transmitting coil and the receiving coil.

[0025] According to another embodiment of the present invention, there is provided a method for abnormal stopping in a non-contact power supply device having a power transmission device and a power reception device to which power is transmitted from the power transmission device without contact.In the abnormal stopping method, the power receiving device of the contactless power supply device includes a resonance circuit having a receiving coil that receives power from the power transmitting device, a rectifier circuit that rectifies power output from the resonance circuit, and a coil connected in series with the receiving coil between the resonance circuit and the rectifier circuit, and the power transmitting device includes a transmitting coil that supplies power to the power receiving device, and a power supply circuit that supplies AC power to the transmitting coil at an adjustable switching frequency.The abnormal stopping method includes a step of changing the switching frequency of the AC power supplied to the transmission coil from the power supply circuit over a predetermined frequency range, and a step of stopping power supply from the power supply circuit to the transmission coil when the contactless power supply device does not perform a constant voltage output operation even if the switching frequency of the AC power is changed over the predetermined frequency range.

[0026] Against the background of such a configuration, the abnormal stopping method is capable of preventing a malfunction from occurring due to a foreign matter having entered between the transmitting coil and the receiving coil even if the coupling coefficient between the transmitting coil of the power transmitting-side device and the receiving coil of the power receiving-side device changes. 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 the output voltage from the contactless power supply device according to the SPL method at the time of foreign matter intrusion. Fig. 4A is a diagram illustrating another example of simulation results of frequency characteristics of the output voltage from the contactless power supply device according to the SPL method at the time of foreign matter intrusion. Fig. 4B is another diagram illustrating another example of the simulation results of frequency characteristics of the output voltage from the contactless power supply device according to the SPL method at the time of foreign matter intrusion. Fig. 5 is a schematic view of a configuration of a contactless power supply device according to an embodiment of the present invention. 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 a voltage applied to the transmission coil is varied according to a coupling coefficient in the manner shown in Fig. 6 illustrated simulation is changed. Fig. 8 is an operation flowchart of abnormal stop processing. Fig. 9 is a diagram illustrating an example of simulation results of frequency characteristics of the output voltage from the contactless power supply device at the time of intrusion of a foreign matter. Fig. 10 is an operation flowchart of abnormal stop processing according to a modification. Fig. 11 is a diagram showing an example of simulation results of frequency characteristics of the output voltage when a voltage applied to a resonance circuit on the power transmission side is varied according to the coupling coefficient in the manner shown in Fig. 2, which relates to the contactless power supply device according to the SPL method. Fig. 12 is a diagram showing an example of simulation results of frequency characteristics of the output voltage when the voltage applied to the resonance circuit on the power transmission side is varied according to the coupling coefficient at the time of intrusion of a foreign matter in the Fig. 11 illustrated simulation is changed. Fig. 13 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage when a voltage applied to a resonance circuit on the power transmission side is changed according to the coupling coefficient with respect to a contactless power supply device according to the SL method. Fig. 14 is a diagram showing an example of simulation results of frequency characteristics of the output voltage when the voltage applied to the resonance circuit on the power transmission side is varied according to the coupling coefficient at the time of intrusion of a foreign matter in the Fig. 13 illustrated simulation is changed. Fig. 15 is a diagram showing 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 according to the Fig. 5 illustrated embodiment. Fig. 16 is a schematic view of a configuration of a contactless power supply device according to a modification. Fig. 17 is a schematic view of a configuration of a contactless power supply device according to another modification. Fig. 18 is a diagram showing an example of simulation results of frequency characteristics of an output voltage when a voltage applied to the transmission coil is varied according to the coupling coefficient with respect to the contactless power supply device according to the Fig. 17 is modified. Fig. 19 is a diagram showing an example of simulation results of frequency characteristics of the output voltage with respect to the contactless power supply device according to the Fig. 17 illustrates the modification at the time of penetration of a foreign body. Fig. 20A is a circuit diagram of a power transmission device according to a modification. Fig. 20B is a circuit diagram of a power supply circuit according to another modification. DESCRIPTION OF EMBODIMENTS

[0027] A contactless power supply device according to an embodiment of the present invention will be described below with reference to the drawings. The contactless power supply device includes a coil connected in series with a receiving coil of a resonant circuit on the power receiving side, as in the SPL method. However, unlike the SPL method, the contactless power supply device can perform a constant voltage output operation even when a coupling coefficient between a transmitting coil on the power transmitting side and the receiving coil changes, by supplying AC power at a frequency at which the transmitting coil does not resonate to the transmitting coil and, in conjunction with this, adjusting the frequency.In addition, when the constant voltage output operation is not achieved even if the frequency of the AC power supplied to the transmitting coil is adjusted, the non-contact power supply device determines that a metal foreign object has entered between the transmitting coil and the receiving coil and stops power transmission.

[0028] To better understand the contactless power supply device according to the present invention, a relationship between a constant voltage output operation performed by a contactless power supply device according to the SPL method and an intrusion of a foreign matter will first be described.

[0029] 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 an 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 transmission side and a winding resistance on the power reception side. Cp is a capacitance of a capacitor connected in parallel with the receiving coil in the resonant circuit on the power reception side. Lop is an inductance of a coil connected in series with the receiving coil. Rac is an AC equivalent resistance of a load circuit and is calculated using a resistance Ro of the load circuit as Rac = (8 / π). 2 ) × Ro.

[0030] 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⋅Ctrl01]⋅[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 = j2 πf. 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.

[0031] 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)0.0⋅Vin2⋅1n In the preceding equation, Vin is the voltage (amplitude) of the AC power supplied to the resonance circuit on the power transmission side, and Fspl(s, k, Rac)0,0 represents the upper left element of the F matrix expressed by equation (1).

[0032] 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 example assumes that Lp = 174 µH, Cr1 = Cp = 20 nF, Lop = 3Lp, Ri = Ris = 0.04 Ω, n = 1, Vin = 200 V, and Ro = 200 Ω (Rac ≅ 162.1 Ω).

[0033] 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.Note that, since in the SPL method, the resonance circuit on the power transmission side is also generally caused to resonate, AC power having frequencies as illustrated by points 211 to 213 is necessarily supplied to the resonance circuit on the power transmission side in order to cause the contactless power supply device to perform a constant voltage output operation.

[0034] Now, assume that a metal foreign matter has entered between the transmitting coil and the receiving coil. Such foreign matter intrusion affects the leakage inductance Lr, the winding resistance Ri on the power transmitting side, and the winding resistance Ris on the power receiving side. For example, assume that due to the intrusion of a foreign matter, the leakage inductance Lr decreases by 50 µH, and the winding resistance Ri on the power transmitting side and the winding resistance Ris on the power receiving side each increase by 3 Ω. In this case, an F-matrix Fp5(s, k, Rac) of the contactless power supply device according to the SPL method at the time of foreign matter intrusion is expressed by the following equation. Fp5(s,k,Rac)=[1Ri+301]⋅[11s⋅Crl01]⋅[1s⋅(Lr(k)−0.00005)01]⋅[101s⋅Lm(k)1]⋅[1s ⋅(Lr(k)−0.00005)01]⋅[1n2⋅(Ris+3)01]⋅[10s⋅1n2⋅Cp1]⋅[1s⋅Lop⋅n201]⋅[101n2⋅Rac1]

[0035] Therefore, an output gain Gp5(s, k, Rac) at the time of foreign matter intrusion is expressed by the following equation. Gp5(s,k,Rac)=1Fp5(s,k,Rac)0.0⋅Vin2⋅1n

[0036] In the previous equation, Fp5(s, k, Rac)0,0 represents the upper left element of the F-matrix expressed by equation (3).

[0037] Fig. 3 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 at the time of foreign matter intrusion, which are calculated according to equation (4). Fig. 3, a frequency is plotted along the horizontal axis and an output voltage is plotted along the vertical axis. Graph 301 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 is set to Rac. In addition, graph 302 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 is set to (10 * Rac). In addition, graph 303, as a comparison example, represents a frequency characteristic of the output voltage when no foreign matter has entered (ie, the frequency characteristic is calculated according to equation (2)), the coupling coefficient k is set to k = 0.15 and the AC equivalent resistance of the load circuit is set to Rac.Furthermore, as another comparison example, Graph 304 represents a frequency response of the output voltage when no foreign matter has entered, the coupling coefficient k is set to k = 0.15, and the AC equivalent resistance of the load circuit is set to (10*Rac). Note that in this example, the same values ​​were used as the parameters of the respective circuit elements as those used in the simulation in . Fig. 2.

[0038] As indicated by points 311 and 312 in Fig. 3, when no foreign matter has entered, there are frequencies at which the output voltage becomes substantially constant even when the resistance of the load circuit changes. In contrast, when a foreign matter has entered, there is no frequency at which the output voltage becomes substantially constant regardless of a change in the resistance of the load circuit. Furthermore, as illustrated by a point 313, a frequency at which a difference in the output voltage when the resistance of the load circuit changes has a minimum value is different from frequencies at which the output voltage becomes substantially constant when no foreign matter has entered, as indicated by points 311 and 312.

[0039] Fig. 4A and Fig. 4B are diagrams illustrating another example of simulation results of frequency characteristics of the output voltage from the contactless power supply device according to the SPL method at the time of foreign matter intrusion, which are calculated according to equation (4). Fig. 4A and Fig. In Figure 4B, a frequency is plotted along the horizontal axis and an output voltage is plotted along the vertical axis. Note that Fig. 4A illustrates frequency responses of the output voltage in a frequency band in which the resonance circuit on the power transmission side resonates, and Fig. 4B illustrates frequency characteristics of the output voltage in a frequency band higher than the frequency band in which the resonant circuit on the power transmission side resonates. Graph 401 represents a frequency characteristic 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. In addition, graph 402 represents a frequency characteristic 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). In addition, as a comparison example, graph 403 represents a frequency characteristic of the output voltage when no foreign matter has entered (ie, the frequency characteristic is calculated according to equation (2)), the coupling coefficient k is set to k = 0.6, and the AC equivalent resistance of the load circuit is set to Rac.Furthermore, as another comparison example, Graph 404 represents a frequency response of the output voltage when no foreign matter has entered, 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 in this example, the same values ​​were used as the parameters of the respective circuit elements as those used in the simulation in . Fig. 2.

[0040] As indicated by points 411 and 412 in Fig. 4A and Fig. 4B illustrates that when no foreign matter has entered, there are frequencies at which the output voltage becomes substantially constant even when the resistance of the load circuit changes. In contrast, when a foreign matter has entered, there is no frequency at which the output voltage becomes substantially constant regardless of a change in the resistance of the load circuit. Moreover, as illustrated by a point 413, a frequency at which a difference in the output voltage when the resistance of the load circuit changes has a minimum value is different from frequencies at which the output voltage becomes substantially constant when no foreign matter has entered, as indicated by points 411 and 412.

[0041] As in Fig. 3, Fig. 4A and Fig. As illustrated in Figure 4B, when no foreign matter has entered between the transmitting coil and the receiving coil and the coupling coefficient between the transmitting coil and the receiving coil changes, adjusting the frequency of the AC power supplied to the transmitting coil enables the contactless power supply device to continue a constant voltage output operation. In contrast, when a foreign matter has entered between the transmitting coil and the receiving coil, the contactless power supply device is unable to perform a constant voltage output operation even if the frequency of the AC power supplied to the transmitting coil is adjusted.

[0042] Therefore, a contactless power supply device according to an embodiment of the present invention, when unable to continue a constant-voltage output operation, adjusts a frequency of AC power supplied to a transmitting coil, thereby searching for a frequency at which the contactless power supply device performs the constant-voltage output operation. If no frequency at which the contactless power supply device performs the constant-voltage output operation is found, the contactless power supply device determines that a foreign matter has entered between the transmitting coil and a receiving coil and stops power transmission.On the other hand, when a frequency at which the contactless power supply device performs the constant voltage output operation is found, the contactless power supply device determines that the coupling coefficient between the transmitting coil and the receiving coil has changed, and continues power transfer at the frequency at which the contactless power supply device performs the constant voltage output operation. This configuration enables the contactless power supply device to detect a foreign object that has penetrated between the transmitting coil and the receiving coil, even if the coupling coefficient between the transmitting coil and the receiving coil changes.

[0043] Note that, as used herein, the constant voltage output operation is an operation in which the contactless power supply device operates 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.

[0044] Fig. 5 is a schematic view of a configuration of the contactless power supply device according to the embodiment of the present invention. As shown in Fig. As illustrated in Figure 5, 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 receiver 15, gate drivers 16-1 and 16-2, and a control circuit 17. On the other hand, the power reception device 3 includes a resonance circuit 20 including a reception coil 21 and a resonance capacitor 22, a coil 23, a rectifying and smoothing circuit 24, a load circuit 27, a voltage detection circuit 28, a constant voltage determination circuit 29, and a transmitter 32.

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

[0046] 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.

[0047] 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.

[0048] 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 17 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 16-1.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 17 as a measurement representing a voltage output from the diode D.

[0049] The power factor improvement circuit 12 performs a power factor improvement operation through the gate driver 16-1, which controls switching of the switching element SW between an on and off state according to a duty cycle determined by the control circuit 17, 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.

[0050] 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.

[0051] Note that the power factor improvement circuit 12 is not limited to the above-described configuration and may have another configuration capable of adjusting an output voltage controlled by the control circuit 17.

[0052] 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, 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.

[0053] 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.

[0054] In addition, the gate terminals of the switching elements 13-1 to 13-4 are connected to the control circuit 17 via the gate driver 16-2. 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 17.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 off while switching elements 13-1 and 13-4 are on, and conversely, switching elements 13-1 and 13-4 are off while switching elements 13-2 and 13-3 are 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.

[0055] 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.

[0056] The receiver 15 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 32 of the power receiving device 3, and outputs the determination information to the control circuit 17. For this purpose, the receiver 15 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).

[0057] The gate driver 16-1 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 17 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 16-1 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 16-1 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 16-1 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 17.

[0058] The gate driver 16-2 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 17 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 16-2 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 16-2 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 16-2 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.

[0059] The control circuit 17 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 17 receives the destination information from the receiver 15, the control circuit 17 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.

[0060] For this purpose, in the present embodiment, the control circuit 17 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 17 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.

[0061] Furthermore, the control circuit 17 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 17 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 16-1.

[0062] Furthermore, when the receiver 15 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 is able to receive power 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 17 may set the duty cycle for the on / off control of the switching element SW to 0 and stop power supply from the power supply circuit 10 to the transmitting coil 14. This control makes it possible to suppress power loss while the power transmitting device 2 is in the standby state.In addition, as will be described later, when it is determined that a foreign matter made of metal has entered between the transmitting coil 14 and the receiving coil 21, the control circuit 17 also sets the duty ratio for the on / off control of the switching element to 0 and stops a power supply from the power supply circuit 10 to the transmitting coil 14.

[0063] Note that details of the control of the switching frequency and the voltage applied to the transmission coil 14 and the processing of stopping due to a foreign matter performed by the control circuit 17 will be described later.

[0064] Next, the power receiving device 3 will be described.

[0065] The resonant circuit 20 is an LC resonant circuit formed by the receiving coil 21 and the resonant capacitor 22 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 and, in connection therewith, to an input terminal of the rectifying and smoothing circuit 24 via the coil 23. 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 24.

[0066] 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 24 via the resonant capacitor 22 and the coil 23. 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.

[0067] The resonant capacitor 22 is connected at one end to one end of the receiving coil 21 and the coil 23, and at the other end to the other end of the receiving coil 21 and the rectifying and smoothing circuit 24. The resonant capacitor 22 outputs the energy received by the receiving coil 21 to the rectifying and smoothing circuit 24 via the coil 23.

[0068] The coil 23 is connected between the resonant circuit 20 and the rectifying and smoothing circuit 24. In the present embodiment, the coil 23 is connected at one end to the receiving coil 21 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 at the other end to the rectifying and smoothing circuit 24. The coil 23 outputs the energy received by the resonant circuit 20 to the rectifying and smoothing circuit 24. Note that arranging the coil 23 as in the SPL method makes it possible to suppress harmonic components of the received energy.

[0069] The rectifying and smoothing circuit 24 is an example of a rectifying circuit. It includes a full-wave rectifying circuit 25, which includes four diodes connected in a bridge circuit, and a smoothing capacitor 26. It rectifies and smooths the energy received via the resonant circuit 20 and the coil 23 to convert the energy into DC energy. The rectifying and smoothing circuit 24 outputs the DC energy to the load circuit 27.

[0070] The voltage detection circuit 28 detects an output voltage between both terminals of the rectifying and smoothing circuit 24 at every predetermined period. Since the output voltage between both terminals of the rectifying and smoothing circuit 24 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 24 indirectly represents a measured value of the output voltage of the resonant circuit 20. For the voltage detection circuit 28, for example, any of various known voltage detection circuits capable of detecting DC voltage can be used. The voltage detection circuit 28 outputs a voltage detection signal representing a measured value of the output voltage to the constant voltage determination circuit 29.

[0071] The constant-voltage determination circuit 29 determines, based on the measured value of the output voltage received from the voltage detection circuit 28, 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 29 notifies the transmitter 32 of a determination result. For this purpose, the constant-voltage determination circuit 29 includes, for example, a memory circuit configured to store an allowable voltage range and a determination circuit 30 comprising an arithmetic operation circuit configured to compare a measured value of the output voltage with the allowable voltage range.

[0072] Furthermore, the constant-voltage determination circuit 29 includes a switching element 31, such as a MOSFET, connected between the rectifying and smoothing circuit 24 and the load circuit 27. When off, the switching element 31 prevents current from flowing from the rectifying and smoothing circuit 24 to the load circuit 27 (i.e., Rac = ∞), while when on, the switching element 31 allows current to flow from the rectifying and smoothing circuit 24 to the load circuit 27. The determination circuit 30 of the constant-voltage determination circuit 29 switches the switching element 31 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 27 connected to the rectifying and smoothing circuit 24, to change within the predetermined period. Therefore, the determination circuit 30 is able to determine whether the contactless power supply device 1 is performing a constant-voltage output operation by determining whether the measured values ​​of the output voltage become substantially constant or not while the switching element 31 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 30 switches the switching element 31 between an on and an off state in a predetermined period of time, the determination circuit 30 notifies the transmitter 32 that the contactless power supply device 1 performs the constant voltage output operation.

[0073] 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 30 suspends switching of switching element 31 between an on and off state and maintains switching element 31 in the on state. Determination circuit 30 determines whether the measured output voltage value is within the allowable voltage range and notifies transmitter 32 of the determination result.

[0074] 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 30 notifies the transmitter 32 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.

[0075] Note that, according to a modification, the constant-voltage determination circuit 29 may include a resistor connected to the rectifying and smoothing circuit 24 in parallel with the load circuit 27. In this case, the switching element 31 may be arranged in series with the resistor and in parallel with the load circuit 27. In this case, the determination circuit 30 turns off the switching element 31 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 30 may switch the switching element 31 between an on and an off state in the predetermined period of time.According to the modification, the power supply to the load circuit 27 is maintained even if the contactless power supply device 1 does not perform a constant voltage output operation.

[0076] 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 27. In this case, while measured values ​​of the output voltage are within the allowable voltage range, the determination circuit 30 turns on the second switching element, thereby enabling power supply to the load circuit 27. On the other hand, when a measured value of the output voltage is outside the allowable voltage range, the determination circuit 30 may turn off the second switching element and suspend power supply to the load circuit 27. 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 27.

[0077] The transmitter 32 generates, at each predetermined transmission period, a wireless signal including determination information indicating whether or not the contactless power supply device 1 performs the 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 30 of the constant voltage determination circuit 29, and transmits the wireless signal to the receiver 15 of the power transmission device 2. For this purpose, the transmitter 32 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 15, the predetermined wireless communication standard may be, for example, ISO / IEC 15693, ZigBee (registered trademark) or Bluetooth (registered trademark).

[0078] An operation of the contactless power supply device 1 will be described in detail below.

[0079] In the present embodiment, the control circuit 17 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 15 in such a manner that the contactless power supply device 1 continues the output operation at a constant voltage.

[0080] The contactless power supply device of the present embodiment differs from the contactless power supply device according to the SPL method in that resonance of the resonant circuit on the power transmission side is not used. Therefore, the frequency characteristic of the output voltage from the contactless power supply device 1 is similar to the frequency characteristic of the output voltage from the contactless power supply device according to the SPL method when the equivalent circuit in Fig. 1 the capacitance Cr1 of the capacitor connected in series with the transmission coil in the resonance circuit on the power transmission side is increased and the resonance frequency of the resonance circuit on the power transmission side is thereby lowered to prevent the resonance of the resonance circuit on the power transmission side from affecting the power supply.

[0081] 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 according to the present embodiment. In Fig. 6, a frequency is plotted along the horizontal axis and an output voltage 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. 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 27 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 27 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 27 is set to Rac. In addition, graph 604 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 27 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 27 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 27 is set to (10*Rac).

[0082] In Fig. 6, since the transmission coil 14 does not resonate, extreme values ​​of the output voltage on the low frequency side are compared to Fig. 2 in which Fig. 6 has disappeared. 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 27 changes under the condition that the coupling coefficient k does not change (there are three combinations, which are illustrated by points 611 to 613 in the figure). Therefore, it can be understood that even if 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 the constant voltage output operation against a change in the resistance value of the load circuit 27.Furthermore, although, as illustrated by points 611 to 613, output voltages differ from each other depending on the coupling coefficient when a constant voltage is output against a variation in the resistance value of the load circuit 27, 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.

[0083] 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 27 is set to Rac, and the voltage applied to the transmission coil 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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to Vin.In addition, graph 703 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 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.47*Vin). In addition, graph 704 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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to (0.47*Vin). Furthermore, graph 705 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.19*Vin).Furthermore, 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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to (0.19*Vin).

[0084] 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 27 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.

[0085] As described above, it is clear that, as long as no foreign matter has entered between the transmitting coil 14 and the receiving coil 21, appropriate adjustment of the switching frequency and the voltage of the AC power applied to the transmitting coil 14 makes it possible to keep the output voltage substantially constant even if either the resistance value of the load circuit 27 or the coupling coefficient changes.

[0086] Consequently, in order to achieve the constant voltage output operation, the control circuit 17 controls the switching frequency and the voltage of the AC power applied to the transmission coil 14 as described below.

[0087] When determination information included in a wireless signal received by the power receiving device 3 via the receiver 15 indicates that the contactless power supply device 1 is not performing the constant voltage output operation, the control circuit 17 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 set to a frequency at which a constant voltage is output at the minimum of the expected values ​​of the coupling coefficient between the transmitting coil 14 and the receiving coil 21, and a frequency at which a constant voltage is output at the minimum of the expected values ​​of the coupling coefficient between the transmitting coil 14 and the receiving coil 21, respectively.a frequency at which a constant voltage is output at a maximum of the expected values ​​of the coupling coefficient between the transmitting coil 14 and the receiving coil 21 when power is supplied to the power receiving device 3 from the power transmitting device 2.

[0088] When changing the switching frequency, the control circuit 17 may 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 29 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 17 gradually change the switching frequency in such a manner that the same switching frequency is maintained for a period longer than a period during which the determination circuit 30 of the constant-voltage determination circuit 29 switches the switching element 31 between an on and an off state.

[0089] Note that it is preferable that, while adjusting the switching frequency, the control circuit 17 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.

[0090] If the determination information included in the wireless signal received by the power receiving device 3 via the receiver 15 does not indicate that the constant voltage output operation is performed even if the switching frequency is changed over the entire predetermined frequency range, the control circuit 17 determines that a foreign matter has entered between the transmitting coil 14 and the receiving coil 21. Then, the control circuit 17 stops power supply from the power supply circuit 10 to the transmitting coil 14, thereby suspending power transmission.

[0091] On the other hand, if the determination information included in the wireless signal received by the power receiving device 3 via the receiver 15 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 changes, that is, the constant-voltage output operation is performed, the control circuit 17 keeps the switching frequency constant thereafter. Next, the control circuit 17 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 17 controls the gate driver 16-1 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 15 indicates that measured values ​​of the output voltage are within the allowable voltage range, the control circuit 17 keeps the switching frequency and the voltage of the AC power supplied to the transmission coil 14 constant.

[0092] Note that, instead of determining a duty ratio with reference to the above-described reference table, the control circuit 17 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 15 indicates that measured values ​​of the output voltage are within the allowable voltage range.

[0093] Fig. 8 is an operation flowchart of abnormal stop processing performed by the control circuit 17.

[0094] When determination information received from the power receiving device 3 indicates that a constant voltage output operation is not performed, the control circuit 17 controls the power supply circuit 10 to lower a voltage of an alternating current power supplied to the transmission coil 14 to a predetermined amount (step S101).

[0095] The control circuit 17 controls the power supply circuit 10 to gradually increase the switching frequency from the lower limit to the upper limit of a predetermined setting range within which the switching frequency is set (step S102). The control circuit 17 determines, based on determination information received from the power receiving device 3, whether or not it is indicated that the constant voltage output operation is performed at an arbitrary switching frequency (step S103).

[0096] If it is specified that the constant voltage output operation is performed at any switching frequency (Yes in step S103), the control circuit 17 controls the power supply circuit 10 such that AC power having the switching frequency is supplied to the transmission coil 14. Further, the control circuit 17 controls the power supply circuit 10 to increase the voltage of the AC power supplied to the transmission coil 14 until an output voltage from the resonance circuit 20 of the power receiving device 3 falls within a predetermined allowable voltage range (step S104).

[0097] On the other hand, if it is not specified that the constant voltage output operation is performed at any switching frequency (No in step S103), the contactless power supply device 1 is unable to perform the constant voltage output operation within the predetermined frequency range, that is, within an expected range of a coupling coefficient. Therefore, it is determined that a metal foreign matter has entered between the transmitting coil 14 and the receiving coil 21. Therefore, the control circuit 17 stops power supply from the power supply circuit 10 to the transmitting coil 14, thereby stopping power transmission from the power transmitting device 2 to the power receiving device 3 (step S105).Furthermore, the control circuit 17 can output an abnormality signal indicating that a foreign metal object has been detected to another device via an unillustrated interface.

[0098] After step S104 or S105, the control circuit 17 terminates the abnormal stop processing.

[0099] As described above, when the contactless power supply device stops performing a constant-voltage output operation, it changes the switching frequency of the AC power supplied to the transmitting coil of the power transmitting device within a frequency range according to the expected coupling coefficient between the transmitting coil and the receiving coil. If the constant-voltage output operation is not achieved even if the frequency is changed over the entire frequency range, the contactless power supply device determines that a metal foreign object has penetrated between the transmitting coil and the receiving coil and stops power transmission from the power transmitting device to the power receiving device.This configuration enables the contactless power supply device to detect a metal foreign object that has entered between the transmitting coil and the receiving coil even if the coupling coefficient between the transmitting coil and the receiving coil changes, and prevent a malfunction from occurring due to the foreign object that has entered.

[0100] Note that there is a possibility that, depending on a foreign matter that has entered between the transmitting coil and the receiving coil, the output voltage from the resonance circuit of the power receiving device hardly changes due to a deviation of the leakage inductance and the winding resistance value.

[0101] Fig. Figure 9 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage from the contactless power supply device at the time of foreign object intrusion. Fig. 9, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Graph 901 represents a frequency characteristic of the output voltage when a foreign matter has entered between the transmitting coil 14 and the receiving coil 21, 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 902 represents a frequency characteristic of the output voltage when a foreign matter has entered between the transmitting coil 14 and the receiving coil 21, the coupling coefficient k is set to k = 0.15, and the AC equivalent resistance of the load circuit is set to (10*Rac). In addition, graph 903 represents a frequency characteristic of the output voltage when no foreign matter has entered, 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 904 represents a frequency response of the output voltage when no foreign matter has entered, the coupling coefficient k is set to k = 0.15, and the AC equivalent resistance of the load circuit is set to (10*Rac). Note that in the example, with respect to graphs 901 and 902, the values ​​of the parameters used in the simulation are shown in . Fig. 2 were used, except for the value of the leakage inductance Lr, which is 30 µH lower than that used in the simulation in Fig. 2, and the winding resistance value Ri on the power transmission side and the winding resistance value Ris on the power reception side, each of which is 3 Ω lower than those in the simulation in Fig. 2 were reduced, were used as parameters of the respective circuit elements.

[0102] Comparing graphs 901 and 903, it can be seen that the intrusion of a foreign matter causes a peak value and the waveform of the output voltage to change little, and the waveform shifts slightly toward the high frequency side. Therefore, at a frequency at which a constant voltage output is performed when no foreign matter has entered, indicated by a point 911, the output voltage, in the case where the AC equivalent resistance of the load circuit 27 is Rac, hardly changes between when a foreign matter has entered and when it has not entered.Therefore, measured values ​​of the output voltage from the resonant circuit 20 of the power receiving device 3 remain within the allowable voltage range, and unless the resistance value of the load circuit 27 changes, there is a possibility of erroneously determining that a constant-voltage output operation is being continued. In reality, as illustrated by graphs 901 and 902, the intrusion of a foreign matter causes the output voltage from the resonant circuit 20 to vary in response to a variation in the resistance value of the load circuit 27, and the contactless power supply device 1 therefore does not perform the constant-voltage output operation.

[0103] Furthermore, the inventors found that a frequency at which a constant voltage output operation is performed is included in a frequency range where the output voltage decreases with increasing frequency. Therefore, it is estimated that a foreign matter has entered when, as illustrated by graph 901, the output voltage increases when the switching frequency is increased from a switching frequency (the point 911 in Fig. 9), in which an output process with constant voltage appears to be continued, is increased.

[0104] Therefore, according to a modification, each time a measured value of an output voltage measured by the voltage detection circuit 28 is detected, the determination circuit 30 of the constant-voltage determination circuit 29 stores the measured value for a predetermined period (for example, several tens of milliseconds). The determination circuit 30 calculates a change amount Δv of the output voltage by subtracting a stored measured value of the output voltage the predetermined period earlier from a last measured value of the output voltage. The determination circuit 30 incorporates the change amount Δv of the output voltage into the determination information and transmits the determination information to the power transmission device 2 via the transmitter 32.On the other hand, even if the control circuit 17 of the power transmission device 2 continuously receives determination information indicating that measured values ​​of the output voltage are within the allowable voltage range from the power reception device 3, the control circuit 17 periodically increases the switching frequency only by a predetermined amount Δf and determines that a foreign matter made of metal has entered between the transmission coil 14 and the reception coil 21, and stops power transmission when a change amount Δv of the output voltage at that moment indicates an increase.

[0105] Fig. 10 is a process flowchart of abnormal stop processing performed by the control circuit 17 according to the modification. The control circuit 17 can perform abnormal stop processing according to the process flowchart described below.

[0106] The control circuit 17 determines whether or not determination information received from the power receiving device 3 indicates that measured values ​​of an output voltage from the resonant circuit 20 are within an allowable voltage range (step S201). If the determination information indicates that measured values ​​of the output voltage from the resonant circuit 20 are outside the allowable voltage range (No in step S201), there is a possibility that the coupling coefficient has changed or a foreign matter has entered between the transmitting coil 14 and the receiving coil 21. Therefore, the control circuit 17 performs processing of step S101 and subsequent steps in Fig. 8 through.

[0107] On the other hand, if the determination information indicates that measured values ​​of the output voltage from the resonance circuit 20 are within the allowable voltage range (Yes in step S201), the control circuit 17 determines whether or not the control circuit 17 has continuously received determination information indicating that a constant-voltage output operation is being performed from the power receiving device 3 for a predetermined period of time (step S202). If the duration for which the determination information indicating that the constant-voltage output operation is being performed has not reached the predetermined period of time (No in step S202), the control circuit 17 enters the standby state for a predetermined period of time and then repeats the processing in step S202.

[0108] On the other hand, when the duration for which the determination information indicating that the constant voltage output operation is being performed has been received has reached the set duration (Yes in step S202), the control circuit 17 increases the switching frequency of the AC power supplied to the transmission coil 14 from the power supply circuit 10 by only a predetermined amount Δf (step S203). The control circuit 17 refers to a change amount Δv of the output voltage included in determination information received from the power receiving device 3 after increasing the switching frequency, and determines whether Δv / Δf has a negative value or not (step S204). If Δv / Δf has a negative value, that is,If the output voltage from the resonance circuit 20 of the power receiving device 3 decreases in response to the increase in the switching frequency (Yes in step S204), the control circuit 17 determines that no foreign matter has entered between the transmitting coil 14 and the receiving coil 21. Therefore, the control circuit 17 lowers the switching frequency of the AC power supplied to the transmitting coil 14 from the power supply circuit 10 by only the predetermined amount Δf (step S205). In other words, the control circuit 17 resets the switching frequency to the original switching frequency. The control circuit 17 further repeats the processing from step S201.

[0109] On the other hand, when Δv / Δf has a positive value, that is, the output voltage from the resonance circuit 20 of the power receiving device 3 increases in response to the increase in the switching frequency (No in step S204), the control circuit 17 determines that a foreign matter has entered between the transmitting coil 14 and the receiving coil 21. Therefore, the control circuit 17 stops power supply from the power supply circuit 10 to the transmitting coil 14, thereby stopping power transmission from the power transmitting device 2 to the power receiving device 3 (step S206). Note that according to the modification, the control circuit 17 may also output an abnormality signal indicating that a metal foreign matter has been detected to another device via an unillustrated interface.

[0110] After step S206, the control circuit 17 terminates the abnormal stop processing. Note that if not only a foreign object has entered but also the coupling coefficient has changed, the output voltage sometimes hardly changes. Therefore, even if the output voltage from the resonance circuit 20 of the power receiving device 3 increases in response to an increase in the switching frequency in step S204, the control circuit 17, instead of immediately stopping power transmission, may continue the processing of step S101 and subsequent steps in Fig. 8 and determine whether it stops energy transfer or not.

[0111] According to a modification, even if the output voltage from the resonance circuit 20 of the power receiving device 3 hardly changes when a metal foreign matter has entered between the transmitting coil 14 and the receiving coil 21, the non-contact power supply device is capable of detecting the foreign matter that has entered and preventing a malfunction from occurring due to the foreign matter that has entered.

[0112] Note that the contactless power supply device capable of determining intrusion of a foreign matter is not limited to the above-described embodiment and may be a contactless power supply device capable of performing a constant voltage output operation within a certain deviation of an allowable voltage range by adjusting the switching frequency and the voltage of an AC power supplied to the transmission coil.

[0113] For example, the contactless power supply device may be a contactless power supply device according to the SPL method. In this case, the power transmission device 2 may be in the Fig. 5, the contactless power supply device includes a capacitor connected in series with the transmission coil 14. The power supply circuit 10 can supply alternating current power to the power transmission-side resonance circuit at a switching frequency at which a resonance circuit formed by the transmission coil 14 and the capacitor (hereinafter referred to as the power transmission-side resonance circuit to distinguish it from the resonance circuit 20 of the power reception device 3) resonates.

[0114] Fig. 11 is a diagram showing an example of simulation results of frequency characteristics of the output voltage when a voltage applied to the resonance circuit on the power transmission side is varied according to the coupling coefficient in the Fig. 2, which relates to the contactless power supply device according to the SPL method. In Fig. 11, a frequency is plotted along the horizontal axis and an output voltage 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. Graph 1101 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 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.4*Vin). Furthermore, graph 1102 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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to (0.4*Vin). In addition, graph 1103 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 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.67*Vin).In addition, graph 1104 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 27 is set to (10 * Rac), and the voltage applied to the transmission coil is set to (0.67 * Vin). Furthermore, graph 1105 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to Vin. In addition, graph 1106 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to (10 * Rac), and the voltage applied to the transmission coil is set to Vin.

[0115] As illustrated by items 1111 to 1113, even if the AC equivalent resistance of the load circuit 27 changes under the condition that the coupling coefficient k does not change, output voltages are substantially equal to each other in respective combinations of a frequency and an output voltage at which the output voltage becomes substantially constant (i.e., a constant voltage is output). Therefore, it can be understood that the non-contact power supply device in the SPL method is also capable of performing a constant-voltage output operation and maintaining a substantially constant output voltage by adjusting the switching frequency and the voltage of the AC power applied to the resonance circuit on the power transmission side.In addition, in the example, frequencies exist at which an output process is carried out with a constant voltage, even within frequency ranges in which the output voltage decreases with increasing frequency.

[0116] Fig. 12 is a diagram showing an example of simulation results of frequency characteristics of the output voltage with respect to the contactless power supply device according to the SPL method when a voltage applied to the resonance circuit on the power transmission side is varied according to the coupling coefficient at the time of intrusion of a foreign matter in the Fig. 11 illustrated simulation is changed. In Fig. 12, a frequency is plotted along the horizontal axis and an output voltage is plotted along the vertical axis. Note that in the simulation, the values ​​of the parameters used in the simulation in Fig. 2 were used, except for the value of the leakage inductance Lr, which is 30 µH lower than that used in the simulation in Fig. 2, and the winding resistance value Ri on the power transmission side and the winding resistance value Ris on the power reception side, each of which is 3 Ω lower than those in the simulation in Fig. 2 were used as parameters of the respective circuit elements. 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 the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.4*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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to (0.4*Vin). In addition, graph 1203 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 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.67*Vin).In addition, 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 27 is set to (10 * Rac), and the voltage applied to the transmission coil is set to (0.67 * Vin). Furthermore, graph 1205 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to Vin. In addition, graph 1206 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to (10 * Rac), and the voltage applied to the transmission coil is set to Vin.

[0117] As in Fig. 12, it is understood that the output voltage varies significantly at any of the coupling coefficients due to a deviation of the AC equivalent resistance of the load circuit 27, and the contactless power supply device stops performing a constant voltage output operation.

[0118] Therefore, the contactless power supply device according to the SPL method is also capable of determining whether a metal foreign matter has penetrated between the transmitting coil and the receiving coil or not by having the control circuit of the power transmission device execute the abnormal stopping processing according to the operation flowchart shown in Fig. 8 or Fig. 10, and stops power transmission from the power transmission device to the power reception device when it determines that a foreign metal object has entered.

[0119] Furthermore, in the contactless power supply device according to the SPL method, the resonance capacitor of the resonance circuit on the power receiving side can be omitted. In this case, the contactless power supply device is also capable of performing a constant voltage output operation. In the modification, in the contactless power supply device according to Fig. 5, the power transmission device 2 may include a capacitor connected in series with the transmission coil 14, and the resonance capacitor 22 may be omitted from the resonance circuit 20 of the power reception device 3. A contactless power supply device according to the modification will hereinafter be referred to as a contactless power supply device according to the SL method for convenience.

[0120] Fig. Figure 13 is a diagram illustrating an example of simulation results of frequency characteristics of the output voltage when a voltage applied to the resonance circuit on the power transmission side is changed according to the coupling coefficient with respect to the contactless power supply device according to the SL method. Fig. 13, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Note that the simulation assumes that Lp = 174 µH, Cr1 = 20 nF, Lop = 3Lp, Ri = Ris = 0.04 Ω, n = 1, Vin = 200 V, and Ro = 200 Ω (Rac ≅ 162.1 Ω). Graph 1301 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.25*Vin). In addition, graph 1302 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to (0.25*Vin).In addition, graph 1303 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 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.5*Vin). In addition, graph 1304 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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to (0.5*Vin). Furthermore, graph 1305 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to Vin.Furthermore, graph 1306 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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to Vin.

[0121] As illustrated by items 1311 to 1313, even if the AC equivalent resistance of the load circuit 27 changes under the condition that the coupling coefficient k does not change, output voltages are substantially equal to each other in respective combinations of a frequency and an output voltage at which the output voltage becomes substantially constant (i.e., a constant voltage is output). Therefore, it can be understood that the non-contact power supply device in the SL method is also capable of performing a constant-voltage output operation and maintaining a substantially constant output voltage by adjusting the switching frequency and the voltage of the AC power applied to the resonance circuit on the power transmission side.In addition, in the example, frequencies exist at which an output process is carried out with a constant voltage, even within frequency ranges in which the output voltage decreases with increasing frequency.

[0122] Fig. 14 is a diagram showing an example of simulation results of frequency characteristics of the output voltage with respect to the contactless power supply device according to the SL method when a voltage applied to the resonance circuit on the power transmission side is varied according to the coupling coefficient at the time of intrusion of a foreign matter in the Fig. 13 illustrated simulation is changed. In Fig. 14, a frequency is plotted along the horizontal axis and an output voltage is plotted along the vertical axis. Note that in the simulation, the values ​​of the parameters used in the simulation in Fig. 13 were used, except for the value of the leakage inductance Lr, which is 30 µH lower than that used in the simulation in Fig. 13, and the winding resistance value Ri on the power transmission side and the winding resistance value Ris on the power reception side, each of which is 3 Ω lower than those in the simulation in Fig. 13 were used as parameters of the respective circuit elements. 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 the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.25*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 27 is set to (10*Rac), and the voltage applied to the transmission coil is set to (0.25*Vin). In addition, graph 1403 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 27 is set to Rac, and the voltage applied to the transmission coil is set to (0.5*Vin).In addition, 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 27 is set to (10 * Rac), and the voltage applied to the transmission coil is set to (0.5 * Vin). Furthermore, graph 1405 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil is set to Vin. Furthermore, graph 1406 represents a frequency characteristic of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to (10 * Rac), and the voltage applied to the transmission coil is set to Vin.

[0123] As in Fig. 14, it is understood that the output voltage varies significantly at any one of the coupling coefficients due to a deviation of the AC equivalent resistance of the load circuit 27, and the contactless power supply device stops performing a constant voltage output operation.

[0124] Therefore, the contactless power supply device according to the SL method is also capable of determining whether a foreign metal object has entered between the transmitting coil and the receiving coil or not by having the control circuit of the power transmission device execute the abnormal stopping processing according to the operation flowchart shown in Fig. 8 or Fig. 10, and stops power transmission from the power transmission device to the power reception device when it determines that a foreign metal object has entered.

[0125] 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 the constant voltage output operation.

[0126] Fig. 15 is a diagram showing an example of a relationship between frequency characteristics of the output voltage and frequency characteristics of the input impedance of the contactless power supply device 1 shown in Fig. 5. 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).

[0127] 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.

[0128] Therefore, according to a modification, the control circuit of the power transmission device can 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, and determine whether or not a foreign matter has entered depending on a result of the determination.

[0129] 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 4 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 and a resonance capacitor 62, a coil 63, a rectifying and smoothing circuit 64 including a full-wave rectifying circuit 65 and a smoothing capacitor 66, a load circuit 67, a voltage detecting circuit 68, a constant voltage determining circuit 69, a fixed load circuit 72, and a transmitter 73.

[0130] The contactless energy supply device 4 differs from the energy transmission device 1, which in Fig. 5, with respect to the power transmission device 42, the configuration of the power supply circuit 50 differs in that it includes the capacitor 55 and 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 4 differs from the contactless power supply device 1 in that it includes the fixed load circuit 72. Therefore, the above-described differences and the related matter will be explained below.

[0131] The power transmission device 50 supplies alternating current power with an adjustable switching frequency and an adjustable voltage to the transmission coil 54. 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.

[0132] 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 4 performs the 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 4 to perform the 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.

[0133] 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).

[0134] While the switching frequency adjustment for the contactless power supply device 4 is carried out to perform the 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.

[0135] 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.

[0136] 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.

[0137] While the contactless power supply device 4 performs the 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 the 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.

[0138] In addition, while performing the switching frequency adjustment for the contactless power supply device 4 to perform the 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.

[0139] 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 an on and off state 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.

[0140] 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.

[0141] In addition, the constant voltage determination circuit 69 of the power receiving device 43 includes a determination circuit 70 and a switching element 71, each of which is similar to the determination circuit 30 and the switching element 31 according to the above-described embodiment.

[0142] While measured values ​​of the output voltage from the resonant circuit 60, which is measured by the voltage detection circuit 68, are within the allowable voltage range, that is, the contactless power supply device 4 performs the constant voltage output operation, the determination circuit 70 of the constant voltage determination circuit 69 turns on the switching element 71, thereby causing the output voltage from the resonant circuit 60 to be supplied to the load circuit 67 via the rectifying and smoothing circuit 64. On the other hand, when measured values ​​of the output voltage are outside the allowable voltage range, the determination circuit 70 turns off the switching element 71, thereby causing the output voltage from the resonant circuit 60 to be supplied to the load circuit 67.

[0143] The fixed load circuit 72 is connected to the rectifying and smoothing circuit 64 in parallel with the load circuit 67 and, while the adjustment of the switching frequency 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 67 (in the case of Fig. 9, for example, Rac). For this purpose, the fixed load circuit 72 is connected to the rectifying and smoothing circuit 64 in parallel with the load circuit 67 and includes a resistor R1 having a resistance value corresponding to the load serving as a reference for the load circuit 67. 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 64, the fixed load circuit 72 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 64 via a resistor R3 and a reverse-biased Zener diode ZD.

[0144] While the contactless power supply device 4 performs the 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, 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.

[0145] 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 adjustment is being performed so that the contactless power supply device 4 performs the constant voltage output operation, the power supplied to the transmitting coil 54 from the DC-DC converter 52 is low. 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.

[0146] 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 4 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 the constant voltage output operation is performed via the gate driver 58.

[0147] 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 4 is not performing the 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 72 of the power receiving device 43.

[0148] 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 4 has a local minimum value, that is, a frequency at which the contactless power supply device 4 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 4 to perform the 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.

[0149] Note that when a foreign metal object has entered between the transmitting coil 54 and the receiving coil 61, the contactless power supply device 4 stops performing a constant voltage output operation, and as a result, a local minimum value of the input impedance, as shown by the graph 1511 in the lower diagram in Fig. 15, disappears. In other words, the input impedance is caused to increase in response to an increasing switching frequency, for example. Therefore, if no switching frequency at which measured values ​​of a current flowing through the transmitting coil 54 measured by the current detecting circuit 56 have a local maximum is detected, even if measured values ​​of the current at the time of adjusting the switching frequency are monitored, it is determined that a metal foreign matter has penetrated between the transmitting coil 54 and the receiving coil 61.

[0150] Therefore, according to the modification in step S103 in the process flowchart in Fig. 8, the control circuit 59 can determine that the contactless power supply device 4 is performing a constant-voltage output operation when a switching frequency at which measured values ​​of the current flowing through the transmitting coil 54, which is measured by the current detection circuit 56, have a local maximum is detected. Conversely, the control circuit 59 can determine that the contactless power supply device 4 is not performing the constant-voltage output operation and a metal foreign object has penetrated between the transmitting coil 54 and the receiving coil 61 when a switching frequency at which measured values ​​of the current flowing through the transmitting coil 54, which is measured by the current detection circuit 56, have a local maximum is not detected.

[0151] Note that in the modification, the control circuit 59 may also determine whether or not a foreign metal has penetrated between the transmitting coil 54 and the receiving coil 61 according to the operation flowchart shown in Fig. 10 is illustrated.

[0152] Note that the contactless power supply device used in Fig. 16, as in the contactless power supply device shown in Fig. 5, may also be set up according to the SPL method or the SL method.

[0153] According to the modification, the control circuit of the power transmission device is capable of detecting a switching frequency at which the contactless power transmission device performs the constant voltage output operation by monitoring current flowing through the transmission coil of the power transmission device and, in conjunction therewith, detecting that a foreign metal has penetrated between the transmission coil and the reception coil.

[0154] Furthermore, according to another modification, in the resonance circuit of the power receiving device, the receiving coil and the resonance capacitor may be connected in series with each other, as in the contactless power supply device according to the SS method. In this case, since the contactless power supply device can perform a constant voltage output operation, the contactless power supply device, as in the above-described embodiment or any of its modifications, is also capable of detecting a switching frequency at which the contactless power supply device performs the constant voltage output operation, and, in conjunction with this, detecting that a metal foreign matter has penetrated between the transmitting coil and the receiving coil.

[0155] Fig. 17 is a schematic view of a configuration of a contactless power supply device according to the modification. As shown in Fig. 17, a contactless power supply device 5 according to the modification includes a power transmission device 2 and a power reception device 44 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 receiver 15, gate drivers 16-1 and 16-2, and a control circuit 17. On the other hand, the power reception device 44 includes a resonance circuit 20a including a reception coil 21 and a resonance capacitor 22, a rectifying and smoothing circuit 24, a load circuit 27, a voltage detection circuit 28, a constant voltage determination circuit 29, and a transmitter 32. The contactless power supply device 5 differs from the contactless power supply device 1 shown in Fig. 5, in the configuration of the resonant circuit 20a and in that the coil 23 is omitted. Therefore, the differences described above and the related facts are explained below.

[0156] In the resonance circuit 20a, the receiving coil 21 and the resonance capacitor 22 are connected in series. Power received via the receiving coil 21 is output to the rectifying and smoothing circuit 24 via the resonance capacitor 22. Since the contactless power supply device 5 has a configuration similar to that of the SS method as described above, the contactless power supply device 5 is capable of performing a constant voltage output operation. Furthermore, in the modification, since the resonance circuit 20a performs series resonance, unlike the contactless power supply device according to the SPL method, the coil 23 can be omitted. Note that, unlike the SS method, the contactless power supply device 5 does not need to utilize resonance of the transmitting coil 14 on the power transmitting side.In other words, as in the above-described embodiment, the control circuit 17 of the power transmission device 2 can control the power supply circuit 10 to supply AC power to the transmission coil 14 at a switching frequency at which the transmission coil 14 does not resonate.

[0157] Fig. 18 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage when a voltage applied to the transmission coil 14 is changed according to the coupling coefficient with respect to the contactless power supply device 5 according to the modification. In Fig. 18, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Note that the simulation assumes that Lp = 174 µH, Cp = 20 nF, Ri = Ris = 0.1 Ω, n = 1, Vin = 300 V, and Ro = 10 Ω (Rac ≅ 8.1 Ω). Graph 1801 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil 14 is set to Vin. In addition, graph 1802 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 27 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to Vin.Furthermore, graph 1803 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 27 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.5*Vin). Furthermore, graph 1804 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 27 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.5*Vin). Furthermore, graph 1805 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 27 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.25*Vin).Furthermore, graph 1806 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 27 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.25*Vin).

[0158] As indicated by points 1811 to 1813 in Fig. As illustrated in Figure 18, in the modification, for each value of the coupling coefficient, there also exists a combination of a frequency and an output voltage at which the output voltage becomes substantially constant (ie, a constant voltage is output) even if the AC equivalent resistance of the load circuit 27 changes under the condition that the coupling coefficient k does not change. The output voltages at the respective points 1811 to 1813 are substantially equal to each other.

[0159] As described above, it is clear that with respect to the contactless power supply device 5, as long as no foreign matter has entered between the transmitting coil 14 and the receiving coil 21, appropriately adjusting the switching frequency and the voltage of the AC power applied to the transmitting coil 14 also makes it possible to keep the output voltage substantially constant even if either the resistance value of the load circuit 27 or the coupling coefficient changes.

[0160] Fig. 19 is a diagram illustrating an example of simulation results of frequency characteristics of an output voltage with respect to the contactless power supply device 5 at the time of intrusion of a foreign object. Fig. In FIG. 19, a frequency is plotted along the horizontal axis, and an output voltage is plotted along the vertical axis. Graph 1901 represents a frequency characteristic of the output voltage at the time of foreign matter intrusion when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmission coil 14 is set to Vin. Furthermore, graph 1902 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 27 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to Vin.Furthermore, graph 1903 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 27 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.5*Vin). Furthermore, graph 1904 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 27 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.5*Vin). Furthermore, graph 1905 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 27 is set to Rac, and the voltage applied to the transmission coil 14 is set to (0.25*Vin).Furthermore, graph 1906 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 27 is set to (10*Rac), and the voltage applied to the transmission coil 14 is set to (0.25*Vin). Note that in the example, to represent an influence due to the intrusion of a foreign matter, the values ​​of the parameters used in the simulation in . Fig. 18 were used, except for the value of the leakage inductance Lr, which is 50 µH lower than that used in the simulation in Fig. 18, and the winding resistance value Ri on the power transmission side and the winding resistance value Ris on the power reception side, each of which is 3 Ω lower than those in the simulation in Fig. 18 were increased, were used as parameters of the respective circuit elements.

[0161] As in Fig. As illustrated in Figure 19, it is apparent that the output voltage varies significantly at any of the coupling coefficients due to a variation in the AC equivalent resistance of the load circuit 27, and the contactless power supply device 5 ceases to perform a constant voltage output operation. Furthermore, it is apparent that the intrusion of a foreign matter causes the output voltage waveforms to shift toward the high frequency side regardless of the coupling coefficient.

[0162] Therefore, the contactless power supply device 5 is also capable of determining whether or not a foreign metal object has penetrated between the transmitting coil 14 and the receiving coil 21 by having the control circuit 17 of the power transmission device 2 execute the abnormal stop processing according to the operation flowchart shown in Fig. 8 or Fig. 10, and stops power transmission from the power transmission device 2 to the power reception device 44 when it determines that a foreign metal object has entered.

[0163] Note that in the contactless power supply device 5, the power transmission device 2 may include a capacitor connected in series with the transmission coil 14, and the control circuit 17 may control the power supply circuit 10 in such a manner that the transmission coil 14 is supplied with alternating current power having a switching frequency at which the resonance circuit formed by the transmission coil 14 and the capacitor resonates. In this case, the contactless power supply device 5 operates as a contactless power supply device according to the SS method. In this case, the control circuit 17 is also capable of determining whether or not a foreign metal has penetrated between the transmission coil 14 and the reception coil 21 by executing the abnormal stop processing according to the operation flowchart shown in Fig. 8 or Fig. 10, and stops power transmission from the power transmission device 2 to the power reception device 44 when it determines that a foreign metal object has entered.

[0164] Furthermore, in the contactless energy supply device 4, which is shown in Fig. As illustrated in Figure 16, in the contactless power supply device 5, the power receiving device 43 may include a resonance circuit in which a receiving coil and a resonance capacitor are connected in series, instead of the resonance circuit 60 in which the receiving coil 61 and the resonance capacitor 62 are connected in parallel. The coil 63 connected between the resonance circuit and the rectifying and smoothing circuit 64 may be omitted. In this case, the contactless power supply device also performs a constant voltage output operation when no foreign matter has entered between the transmitting coil and the receiving coil, and stops performing the constant voltage output operation when a foreign matter has entered between the transmitting coil and the receiving coil.Therefore, the control circuit 59 of the power transmission device 42 is capable of determining whether or not a metal foreign matter has entered between the transmission coil and the reception coil by performing the abnormal stopping processing similar to that performed by the contactless power supply device 4 shown in FIG. Fig. 16, and stops power transmission from the power transmission device 42 to the power reception device 43 when it determines that a foreign metal object has entered.

[0165] Furthermore, according to another 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.

[0166] Fig. 20A and Fig. 20B are circuit diagrams of power supply circuits according to the modification, respectively.

[0167] A power supply circuit 110, which in Fig. 20A includes a power source 11, a power factor improvement circuit 12, two switching elements 13-1 and 13-2, and a capacitor 131 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.

[0168] 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 131. Furthermore, the gate terminals of the switching elements are connected to a gate driver 16-2.

[0169] In this modification, the gate driver 16-2 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 17. 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 131 is charged. On the other hand, when the switching element 13-1 is off and the switching element 13-2 is on, the capacitor 131 is discharged, and current flows from the capacitor 131 via the transfer coil 14 and the switching element 13-2.In this modification, therefore, the control circuit 17 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 16-2, depending on destination information received from a power receiving device 3.

[0170] A power supply circuit 120, which in Fig. 20B, 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 131 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 131.

[0171] In this modification, the gate driver 16-2 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 17.

[0172] In addition, in the Fig. 5 illustrated embodiment and the one in Fig. 17 and the modification shown in Fig. 20A and Fig. 20B, 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. 5 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.

[0173] Furthermore, in the above-described embodiment or any of the respective modifications thereof, when it is possible to connect the receiver of the power transmission device and the transmitter of the power reception device to each other in a wired manner, each of the receiver and the transmitter may include a communication circuit capable of transmitting a signal including destination information in a wired manner.

[0174] 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, 4, 5 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 55 Capacitor 56 Current detection circuit 15, 57 recipients 16-1, 16-2, 58 gate drivers 17, 59 Control circuit 3, 43, 44 Energy receiving device 20, 20a, 60 resonant circuit 21, 61 receiving coil 22, 62 Resonance capacitor 23, 63 coil 24, 64 Rectifier and smoothing circuit 25, 65 Full-wave rectifier circuit 26, 66 smoothing capacitor 27, 67 Powershift 28, 68 Voltage detection circuit 29, 69 Constant voltage determination circuit 30, 70 Determination circuit 31, 71 switching element 72 Circuit with fixed load 32, 73 channels 111 AC power source 131 Capacitor

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 receiving device (3) comprises: a resonant circuit (20) having a receiving coil (21) which receives energy from the energy transmission device (2); and a rectifier circuit (25) which rectifies energy output from the resonance circuit (20), and wherein the energy transmission device (2) comprises: a transmission coil (14) which supplies energy to the energy receiving device (3); a power supply circuit (10) which supplies alternating current power to the transmission coil (14) at an adjustable switching frequency; and a control circuit (17) that stops a power supply from the power supply circuit (10) to the transmission coil (14) when the contactless power supply device (1) does not perform a constant voltage output operation in which an output voltage of the power output from the rectifier circuit (25) becomes a constant voltage even if a resistance value of a load circuit (27) connected to the rectifier circuit (25) changes, even if the switching frequency of the AC power supplied to the transmission coil (14) from the power supply circuit (10) is changed over a predetermined frequency range. [2] Contactless power supply device (1) according to claim 1, wherein the energy receiving device (3) further comprises a coil (23) connected in series with the receiving coil (21) between the resonant circuit (20) and the rectifier circuit (25), wherein the resonance circuit (20) of the energy receiving device (3) further comprises a resonance capacitor (22) connected in parallel to the receiving coil (21), and wherein the control circuit (17) of the energy transmission device (2) controls the energy supply circuit (10) in such a manner that alternating current energy is supplied to the transmission coil (14) at a switching frequency at which the transmission coil (14) does not resonate. [3] The contactless power supply device (1) according to claim 1, wherein the resonance circuit (20) of the power receiving device (3) further comprises a resonance capacitor (22) connected in series with the receiving coil (21). [4] Contactless power supply device (1) according to one of claims 1 to 3, wherein the energy receiving device (3) further comprises: a voltage detection circuit (28) 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 (29) which, based on a measured value of the output voltage, determines whether the contactless power supply device (1) performs the constant voltage output operation or not and whether a measured value of the output voltage from the resonance circuit (20) is within a predetermined allowable voltage range or not; and a transmitter (32) which transmits to the power transmission device (1) a signal which has determination information indicating whether or not the contactless power supply device performs the constant voltage output operation and whether or not a measured value of the output voltage is within the predetermined permissible voltage range, and wherein the energy transmission device (2) further comprises a receiver (15) which receives the signal comprising the destination information, wherein the control circuit (17) stops a power supply from the power supply circuit (10) to the transmission coil (14) when the control circuit (17) does not receive the determination information indicating that the contactless power supply device (1) performs the constant voltage output operation even if the switching frequency of the AC power supplied to the transmission coil (14) from the power supply circuit (10) is changed over the predetermined frequency range. [5] Contactless power supply device (1) according to claim 4, wherein the constant voltage determining circuit (29) of the power receiving device (3) calculates an amount of change in measured values ​​of the output voltage during a lapse of a predetermined period of time, wherein the transmitter (32) of the energy receiving device (3) includes the amount of change of measured values ​​of the output voltage in the determination information, and wherein the control circuit (17) of the power transmission device (2) stops a power supply from the power supply circuit (10) to the transmission coil (14) when the amount of change of measured values ​​of the output voltage included in the determination information indicates that the measured values ​​of the output voltage increase when the switching frequency of the AC power supplied to the transmission coil (14) from the power supply circuit (10) is changed in such a way as to be increased by a predetermined amount. [6] The contactless power supply device (1) according to claim 4 or 5, wherein the constant voltage determining circuit (29) determines that the contactless power supply device (1) performs the constant voltage output operation when measured values ​​of the output voltage become substantially constant even if a resistance value of the load circuit (27) connected to the resonance circuit (25) changes. [7] Contactless power supply device according to one of claims 1 to 3, wherein the energy transmission device (42) further comprises a current detection circuit (56) which measures current flowing through the transmission coil (54) and obtains a measured value of the current, and wherein the control circuit (59) of the power transmission device (54) monitors measured values ​​of the current while changing the switching frequency over the predetermined frequency range, and thereby determines whether or not a switching frequency at which measured values ​​of the current have a local maximum is detected, and stops a power supply from the power supply circuit (50) to the transmission coil (54) when no switching frequency at which measured values ​​of the current have a local maximum is detected. [8] A method for abnormal stopping in a contactless power supply device (1) comprising a power transmission device (2) and a power reception device (3) to which power is transmitted from the power transmission device (2) without contact, wherein the energy receiving device (3) comprises: a resonant circuit (20) having a receiving coil (21) which receives energy from the energy transmission device (2); and a rectifier circuit (25) which rectifies energy output from the resonance circuit (20), and wherein the energy transmission device (2) comprises: a transmission coil (14) which supplies energy to the energy receiving device (3); and a power supply circuit (10) which supplies the transmission coil (14) with alternating current energy at an adjustable switching frequency, wherein the method for abnormal stopping comprises: a step of varying the switching frequency of the alternating current power supplied to the transmission coil (14) from the power supply circuit (10) over a predetermined frequency range; and a step of stopping a power supply from the power supply circuit (10) to the transmission coil (14) when the contactless power supply device (1) does not perform a constant voltage output operation in which an output voltage of the power output from the rectifier circuit (25) becomes a constant voltage even if a resistance value of a load circuit (27) connected to the rectifier circuit (25) changes, even if the switching frequency of the AC power is changed over the predetermined frequency range.

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