Non-contact power supply device

Abstract

A power reception device (3) of a non-contact power supply device is provided with: a resonance circuit (20) that includes a reception coil (21) and receives power from a transmission coil (14) of a power transmission device (2) of the non-contact power supply device; a rectifier circuit (23) that rectifies the power output from the resonant circuit (20); and a resonance suppression coil (25) disposed so as to be electromagnetically coupleable with the reception coil (21). A switching control circuit (27) of the power receiving device (3) controls the short circuit and opening of the resonance suppression coil (25) in accordance with the voltage output from the rectifier circuit (23). A control circuit (19) of a power transmission device (2) controls the voltage of AC power supplied from a power supply circuit (10) to a transmission coil (14) such that a duty ratio related to a period during which a resonance suppression coil (25) is short-circuited, which is estimated on the basis of a current flowing to a first switching element (13-2) of an inverter (13) detected by a current detection circuit (18), is within a predetermined allowable range.

Description

Technical Field

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

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

[0003] In power supply devices utilizing contactless power supply technology (hereinafter referred to as contactless power supply devices), if the positional relationship between the primary (transmitting) coil and the secondary (receiving) coil changes, the degree of coupling between the two coils changes. As a result, the output voltage from the receiving device to the load circuit also fluctuates. In some cases, the output voltage to the load circuit may increase excessively, potentially causing failures in the receiving device or load circuit. Therefore, a technology has been proposed that simultaneously suppresses excessive increases in output voltage and reduces energy loss (see Patent Document 1).

[0004] In the contactless power transmission device disclosed in Patent Document 1, a device on the power receiving side is provided with a resonance suppression coil configured to electromagnetically couple with a receiving coil used to receive power from a transmitting coil of a device on the power transmitting side. Furthermore, when the output voltage, obtained by rectifying the power output from a resonant circuit including the receiving coil using a rectifier circuit, exceeds a predetermined upper threshold, the resonance suppression coil is short-circuited, and an output voltage abnormality signal is transmitted to the device on the power transmitting side. Furthermore, upon receipt of the output voltage abnormality signal, the device on the power transmitting side changes at least one of the switching frequency and voltage of the AC power supplied to the transmitting coil.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-176565 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] In this technology, in order to maintain a so-called constant voltage output operation, which keeps the output voltage from the power-receiving device substantially constant even if the resistance of the load circuit connected to the power-receiving device fluctuates, both the frequency and voltage of the AC power supplied to the transmitting coil must be controlled. Therefore, in operating environments where the positional relationship between the transmitting and receiving coils frequently changes during power transmission, there is a risk that the frequency and voltage of the AC power supplied to the transmitting coil will not be controlled in time. Consequently, it is impossible to maintain a constant output voltage, making it difficult to maintain sufficient power transmission efficiency.

[0010] Therefore, an object of the present invention is to provide a contactless power supply device that can maintain an output voltage on a power receiving side within a fixed range while improving power transmission efficiency.

[0011] Technical means to solve the problem

[0012] As one embodiment of the present invention, a contactless power supply device is provided, comprising a power transmitting device and a power receiving device that transmits power contactlessly from the power transmitting device. The contactless power supply device comprises: a transmitting coil that supplies power to the power receiving device; a power supply circuit that includes an inverter having multiple switching elements connected in a full-bridge or half-bridge configuration and supplies AC power to the transmitting coil; a current detection circuit that detects current flowing through a first switching element among the multiple switching elements of the inverter; and a control circuit that controls the voltage of the AC power supplied from the power supply circuit to the transmitting coil. The power receiving device further comprises: a resonant circuit comprising a receiving coil and a resonant capacitor connected to the receiving coil, which resonates with current flowing through a transmitting coil of a power transmitting device, thereby receiving power from the transmitting coil; a rectifier circuit that rectifies the power received via the resonant circuit; a voltage detection circuit that measures the output voltage of the power outputted from the rectifier circuit; a resonance suppression coil arranged to be electromagnetically coupled to the receiving coil; a switch circuit connected to the resonance suppression coil and capable of switching between short-circuiting and opening the resonance suppression coil; and a switch control circuit that controls the switch circuit to short-circuit the resonance suppression coil when a measured output voltage value exceeds a predetermined upper threshold value, and controls the switch circuit to open the resonance suppression coil when the measured output voltage value falls below a predetermined lower threshold value that is lower than the predetermined upper threshold value. Furthermore, the control circuit of the power transmitting device estimates a duty ratio associated with a period during which the resonance suppression coil is short-circuited based on the current detected by the current detection circuit, and controls the voltage of the AC power supplied from the power supply circuit to the transmitting coil so that the estimated duty ratio falls within a predetermined allowable range.

[0013] With this configuration, the contactless power supply device can maintain the output voltage on the power receiving side within a fixed range while improving power transmission efficiency.

[0014] Preferably, the power transmission device of the contactless power supply device further comprises: a first capacitor connected between the power supply circuit and one end of the transmitting coil; a first coil connected between the power supply circuit and one end or the other end of the transmitting coil and the power supply circuit; and a second capacitor having one end connected to the first capacitor and the other end connected to the other end of the transmitting coil. Furthermore, preferably, the frequency of the AC power supplied from the power supply circuit to the transmitting coil is set to be within a predetermined frequency range that includes the resonant frequency of the resonant circuit of the power receiving device.

[0015] With this configuration, the contactless power supply device can perform a constant voltage output operation even if the degree of coupling between the transmitting coil and the receiving coil fluctuates.

[0016] Furthermore, it is preferred that the control circuit of the power transmitting device controls the power supply circuit so as to increase the voltage of the AC power supplied from the power supply circuit to the transmitting coil when the period during which the resonance suppression coil of the power receiving device is open is longer than a predetermined threshold value, and that, on the other hand, the control circuit controls the power supply circuit so as to decrease the voltage of the AC power supplied from the power supply circuit to the transmitting coil when the duty ratio is greater than an upper limit of a predetermined allowable range and the period during which the resonance suppression coil is open is less than a predetermined threshold value.

[0017] With this configuration, the contactless power supply device can maintain the output voltage within a fixed range and reduce the power consumed when the resonance suppression coil is short-circuited.

[0018] Furthermore, preferably, the control circuit of the power transmitting device determines that there is a foreign object affecting power transmission from the transmitting coil to the receiving coil when the average value of the current flowing to the first switching element during a period in which the resonance suppression coil of the power receiving device is short-circuited is greater than a predetermined detection threshold.

[0019] With this configuration, the contactless power supply device can accurately detect foreign objects that affect power transmission.

[0020] Furthermore, preferably, the power receiving device is mounted on a moving object, and the transmission coil of the power transmitting device is provided on a moving path of the moving object.

[0021] With this configuration, the contactless power supply device can supply power to the moving body while the moving body moves along the moving path. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] [ Figure 1 ] Figure 1 This is a schematic diagram of the configuration of a contactless power supply device according to one embodiment of the present invention.

[0023] [ Figure 2 ] Figure 2 This is a diagram showing an example of simulation results of the frequency characteristics of the output voltage of the contactless power supply device according to the present embodiment.

[0024] [ Figure 3 ] Figure 3 This is a diagram showing an example of the relationship between the output voltage, the short-circuit and open state of the resonance suppression coil, the input voltage of the AC power supplied to the transmission coil, and the current flowing through the switching circuit.

[0025] [ Figure 4 ] Figure 4 This is a diagram showing an example of a waveform of a current flowing through a switching element of an inverter when the resonance suppression coil is short-circuited.

[0026] [ Figure 5A ] Figure 5A This is a diagram showing an example of the waveform of the current flowing to the transmission coil when the resonance suppression coil is short-circuited, and the waveform of the current flowing to the switching element of the inverter when the resonance suppression coil is open.

[0027] [ Figure 5B ] Figure 5B This is a diagram showing an example of the waveform of the current flowing to the transmission coil when the resonance suppression coil is short-circuited, and the waveform of the current flowing to the switching element of the inverter when the resonance suppression coil is open.

[0028] [ Figure 6 ] Figure 6 This is the circuit diagram of the current detection circuit.

[0029] [ Figure 7 ] Figure 7 This is an operation flow chart of input voltage control.

[0030] [ Figure 8 ] Figure 8 This is a system overview diagram when the contactless power supply device according to the embodiment or the modified example is used as a power supply system for a mobile object. DETAILED DESCRIPTION

[0031] Below, while referring to Figure 1A contactless power supply device according to one embodiment of the present invention will be described. In this contactless power supply device, a device on the power receiving side (hereinafter referred to as the power receiving device) includes both a power receiving coil (hereinafter referred to as the receiving coil) and a resonance suppression coil (hereinafter referred to as the resonance suppression coil) configured to electromagnetically couple with the receiving coil. When the output voltage from a rectifier circuit provided in the power receiving device exceeds a predetermined upper threshold, the power receiving device short-circuits the resonance suppression coil, changing the resonance conditions of the resonant circuit including the receiving coil, thereby reducing the output voltage. Conversely, when the output voltage falls below a predetermined lower threshold, the power receiving device opens the resonance suppression coil, restoring the resonance conditions of the resonant circuit and increasing the output voltage. Meanwhile, a device on the power transmission side (hereinafter referred to as the power transmission device) detects the current flowing through any switching element of the inverter that supplies AC power to a coil for power transmission (hereinafter referred to as the transmitting coil). Based on the detected current, it estimates the duty ratio (hereinafter sometimes referred to as the duty ratio related to the short-circuit of the resonance suppression coil or the duty ratio related to the period during which the resonance suppression coil is short-circuited), which is the ratio of the conduction period during which the resonance suppression coil is short-circuited to the repeated cycle of short-circuiting and opening the resonance suppression coil. The power transmission device then controls the voltage of the AC power supplied to the transmitting coil so that the estimated duty ratio falls within a predetermined allowable range, thereby reducing losses caused by a short-circuit of the resonance suppression coil. This allows the contactless power supply device to maintain the output voltage on the power receiving side within a fixed range while improving power transmission efficiency.

[0032] Figure 1 FIG is a schematic structural diagram of a contactless power supply device according to an embodiment of the present invention. Figure 1 As shown, a contactless power supply device 1 includes a power transmitting device 2 and a power receiving device 3 that transmits power contactlessly from the power transmitting device 2 through space. The power transmitting device 2 includes a power supply circuit 10, a transmitting coil 14, a first capacitor 15, a second capacitor 16, a first coil 17, a current detection circuit 18, and a control circuit 19. Meanwhile, the power receiving device 3 includes a resonant circuit 20 comprising a receiving coil 21 and a resonant capacitor 22, a rectifying and smoothing circuit 23, a voltage detection circuit 24, a resonance suppression coil 25, a switching circuit 26, and a switching control circuit 27. Furthermore, the power receiving device 3 is connected to a load circuit 4, and the power received and converted by the power receiving device 3 into DC is output to the load circuit 4.

[0033] First, the power transmission device 2 will be described.

[0034] The power supply circuit 10 supplies AC power having a predetermined driving frequency and an adjustable voltage to the transmission coil 14. To this end, the power supply circuit 10 includes a full-wave rectifier circuit 11, a power factor improvement circuit 12, and an inverter 13.

[0035] The full-wave rectifier circuit 11 supplies power with a predetermined pulsating current and voltage. To this end, the full-wave rectifier circuit 11 comprises four diodes connected in a bridge configuration and is connected to a commercial AC power source. Furthermore, the full-wave rectifier circuit 11 rectifies the AC power supplied from the AC power source, converting it into power with a pulsating current and voltage, and outputs this power to the power factor correction circuit 12.

[0036] The power factor correction circuit 12 converts the power output from the full-wave rectifier circuit 11 into DC power having a voltage according to the control of the control circuit 19 and outputs the DC power. Therefore, the AC power supply, the full-wave rectifier circuit 11, and the power factor correction circuit 12 constitute a DC power supply.

[0037] The structure of the power factor correction circuit 12 can be similar to any of various power factor correction circuits whose output voltage can be adjusted by control from the control circuit 19. In this embodiment, the power factor correction circuit 12 includes a coil having one end connected in series with the positive-side output terminal of the full-wave rectifier circuit 11; and a diode connected between the other end of the coil and the inverter 13, with the direction from the coil toward the inverter 13 being forward. The power factor correction circuit 12 also includes a switching element having one end connected between the coil and the diode and the other end connected to the negative-side output terminal of the full-wave rectifier circuit 11; and a smoothing capacitor connected in parallel with the switching element with the diode interposed therebetween. Furthermore, the control circuit 19 controls the on / off duty cycle of the switching element, thereby controlling the voltage output from the power factor correction circuit 12.

[0038] Inverter 13 converts the DC power output from power factor correction circuit 12 into AC power having a drive frequency corresponding to the on / off switching cycle of switching elements 13-1 to 13-4. Inverter 13 then outputs this AC power to transmitter coil 14 via first capacitor 15, second capacitor 16, and first coil 17.

[0039] To this end, inverter 13 includes four switching elements 13-1 to 13-4. Each of the four switching elements 13-1 to 13-4 can be, for example, an n-channel metal oxide semiconductor field effect transistor (MOSFET). Inverter 13 is configured as a so-called full-bridge circuit. Specifically, switching element 13-1 and switching element 13-2 are connected in series between the positive and negative output terminals of full-wave rectifier circuit 11 via power factor correction circuit 12. In this embodiment, switching element 13-1 is connected to the positive side of full-wave rectifier circuit 11, while switching element 13-2 is connected to the negative side of full-wave rectifier circuit 11. The drain terminal of switching element 13-1 is connected to the positive output terminal of full-wave rectifier circuit 11 via power factor correction circuit 12, and the source terminal of switching element 13-1 is connected to the drain terminal of switching element 13-2. The source terminal of switching element 13-2 is connected to the negative output terminal of full-wave rectifier circuit 11 via power factor correction circuit 12. Furthermore, the source terminal of switching element 13-1 and the drain terminal of switching element 13-2 are connected to one end of transmitting coil 14 via first coil 17 and first capacitor 15.

[0040] Similarly, of the four switching elements 13-1 to 13-4, switching element 13-3 and switching element 13-4 are connected in parallel with switching element 13-1 and switching element 13-2 and are connected in series between the positive and negative output terminals of full-wave rectifier circuit 11 via power factor correction circuit 12. Furthermore, switching element 13-3 is connected to the positive side of full-wave rectifier circuit 11, while switching element 13-4 is connected to the negative side of full-wave rectifier circuit 11. The drain terminal of switching element 13-3 is connected to the positive output terminal of full-wave rectifier circuit 11 via power factor correction circuit 12, while the source terminal of switching element 13-3 is connected to the drain terminal of switching element 13-4. Furthermore, the source terminal of switching element 13-4 is connected to the negative output terminal of full-wave rectifier circuit 11 via power factor correction 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 transmitting coil 14 .

[0041] Furthermore, the gate terminals of each of the switching elements 13-1 to 13-4 are connected to the control circuit 19. Furthermore, to ensure that the switching elements remain conductive when a voltage is applied, the gate terminals of each switching element may be connected to the source terminal of the element itself via a resistor. Furthermore, each switching element alternately switches between on and off according to a control signal from the control circuit 19. In this embodiment, the on / off switching is performed alternately such that while switching elements 13-1 and 13-4 are on, switching elements 13-2 and 13-3 are off; conversely, while switching elements 13-2 and 13-3 are on, switching elements 13-1 and 13-4 are off. Thus, the DC power supplied by the power factor correction circuit 12 is converted into AC power having a drive frequency corresponding to the on / off switching cycle of each switching element and supplied to the transmitting coil 14.

[0042] In addition, the inverter 13 is not limited to the above embodiment. For example, the inverter 13 may be configured as a half-bridge circuit in which two switching elements are connected in a half-bridge shape.

[0043] The first coil 17 is connected in series with the first capacitor 15 between the inverter 13 and the transmitting coil 14. Specifically, one end of the first coil 17 is connected between one of the two output terminals of the inverter 13, namely, between the source terminal of the switching element 13-1 and the drain terminal of the switching element 13-2, while the other end of the first coil 17 is connected to one end of the first capacitor 15. Furthermore, the other end of the first capacitor 15 is connected to one end of the transmitting coil 14. Furthermore, the first coil 17 is preferably arranged so as not to be electromagnetically coupled with the transmitting coil 14 or the coils of the power receiving device 3.

[0044] Furthermore, one end of the second capacitor 16 is connected between the other end of the first coil 17 and one end of the first capacitor 15, and the other end is connected to the other end of the transmitting coil 14 and the other output terminal of the inverter 13, that is, the source terminal of the switching element 13-3 and the drain terminal of the switching element 13-4.

[0045] By providing first capacitor 15, second capacitor 16, and first coil 17 as described above, the phase delay of the current flowing to transmitting coil 14 relative to the phase of the voltage supplied to transmitting coil 14 is adjusted, thereby reducing switching losses in each switching element of inverter 13. Furthermore, contactless power supply device 1 can perform constant voltage output operation regardless of the degree of coupling between transmitting coil 14 and receiving coil 21.

[0046] The connection position of first coil 17 is not limited to the example described above. First coil 17 may also be connected between transmitting coil 14 and inverter 13, on the side opposite to the side connected to first capacitor 15. In other words, first coil 17 may be connected between the end of transmitting coil 14 opposite to the end connected to first capacitor 15 and switching elements 13-3 and 13-4 of inverter 13.

[0047] The transmitting coil 14 transmits the AC power supplied from the inverter 13 of the power supply circuit 10 via the first coil 17 and the first capacitor 15 to the resonant circuit 20 of the power receiving device 3 through space.

[0048] The current detection circuit 18 detects the current flowing through any of the multiple switching elements included in the inverter 13. For convenience, the switching element for which the current detection circuit 18 detects current is sometimes referred to as the first switching element. In this embodiment, the current detection circuit 18 is connected between the switching element 13-2 of the inverter 13 and the negative output terminal of the full-wave rectifier circuit 11. Furthermore, when the switching element 13-2 is turned on, the current detection circuit 18 detects the current flowing through the switching element 13-2 and outputs the detected current value to the control circuit 19. That is, in this embodiment, the switching element 13-2 serves as the first switching element. Details of the current detection circuit 18 will be described later.

[0049] Furthermore, the connection location of the current detection circuit 18 is not limited to the example described above. The current detection circuit 18 may also be connected between the switching element 13-4 of the inverter 13 and the negative-side output terminal of the full-wave rectifier circuit 11 to detect the current flowing through the switching element 13-4. In this case, the switching element 13-4 becomes the first switching element. Alternatively, the current detection circuit 18 may be connected between the switching element 13-1 of the inverter 13 and the positive-side output terminal of the full-wave rectifier circuit 11 to detect the current flowing through the switching element 13-1. In this case, the switching element 13-1 becomes the first switching element. Similarly, the current detection circuit 18 may be connected between the switching element 13-3 of the inverter 13 and the positive-side output terminal of the full-wave rectifier circuit 11 to detect the current flowing through the switching element 13-3. In this case, the switching element 13-3 becomes the first switching element. Furthermore, if inverter 13 is a half-bridge circuit including two switching elements, current detection circuit 18 can be connected between the switching element on the negative side of full-wave rectifier circuit 11 and the negative output terminal of full-wave rectifier circuit 11. In this case, the switching element on the negative side serves as the first switching element. Alternatively, current detection circuit 18 can be connected between the switching element on the positive side of full-wave rectifier circuit 11 and the positive output terminal of full-wave rectifier circuit 11. In this case, the switching element on the positive side serves as the first switching element.

[0050] The control circuit 19 includes, for example, nonvolatile and volatile memory circuits, a calculation circuit, an interface circuit for connecting to other circuits, and a drive circuit for outputting control signals to each switching element. Furthermore, the control circuit 19 estimates the duty cycle associated with a short circuit in the resonance suppression coil 25 of the power receiving device 3 based on the current value detected by the current detection circuit 18, and controls the voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14 based on the estimated duty cycle. Details of the duty cycle estimation and voltage control by the control circuit 19 will be described later.

[0051] Furthermore, control circuit 19 controls the on / off switching of the four switching elements 13-1 to 13-4 of inverter 13 so that the frequency of the AC power supplied from inverter 13 to transmitting coil 14 reaches a predetermined drive frequency. Specifically, control circuit 19 controls the switching elements so that the pair of switching elements 13-1 and 13-4 and the pair of switching elements 13-2 and 13-3 alternately turn on, and within a cycle corresponding to the predetermined drive frequency, the period during which the pair of switching elements 13-1 and 13-4 is on equals the period during which the pair of switching elements 13-2 and 13-3 is on. Furthermore, to prevent the AC power supply from short-circuiting due to simultaneous on-state switching of the switching element pairs, control circuit 19 may also include a dead time during which all switching elements are off when switching the switching element pairs on / off.

[0052] Next, the power receiving device 3 will be described.

[0053] Resonant circuit 20 is an LC resonant circuit comprising a receiving coil 21 and a resonant capacitor 22 connected in series. One end of receiving coil 21 included in resonant circuit 20 is connected to one input terminal of a rectifying and smoothing circuit 23 via resonant capacitor 22. The other end of receiving coil 21 is connected to the other input terminal of rectifying and smoothing circuit 23.

[0054] The receiving coil 21, along with the resonant capacitor 22, resonates with the AC current flowing through the transmitting coil 14 of the power transmitting device 2, thereby receiving power from the transmitting coil 14. The receiving coil 21 then outputs the power received via the resonant capacitor 22 to the rectifying and smoothing circuit 23. Therefore, the inductance of the receiving coil 21 and the capacitance of the resonant capacitor 22 are set so that the resonant frequency of the resonant circuit 20 is approximately equal to the driving frequency of the AC current flowing through the transmitting coil 14. The number of turns of the receiving coil 21 and the number of turns of the transmitting coil 14 of the power transmitting device 2 can be the same or different.

[0055] The resonant capacitor 22 is connected in series with the receiving coil 21. Specifically, one end of the resonant capacitor 22 is connected to one end of the receiving coil 21, and the other end is connected to the rectifying and smoothing circuit 23. The resonant capacitor 22 then resonates with the receiving coil 21 with respect to the current flowing through the transmitting coil 14, and outputs the received power to the rectifying and smoothing circuit 23.

[0056] The rectifier-smoothing circuit 23 is an example of a rectifier circuit and includes a full-wave rectifier circuit having four bridge-connected diodes connected to the resonant circuit 20, and a smoothing capacitor provided on the output side of the full-wave rectifier circuit. The rectifier-smoothing circuit 23 rectifies and smoothes the AC power output from the resonant circuit 20, converting it into DC power. The rectifier-smoothing circuit 23 then outputs this DC power to the load circuit 4.

[0057] The voltage detection circuit 24 measures the voltage between the two terminals on the output side of the rectifier-smoothing circuit 23, that is, the output voltage from the power receiving device 3 to the load circuit 4, at each predetermined cycle. For example, the voltage detection circuit 24 can be any of various known voltage detection circuits capable of detecting DC voltage. The voltage detection circuit 24 then outputs a voltage detection signal indicating the measured output voltage value to the switch control circuit 27.

[0058] The resonance suppression coil 25 is provided so as to be electromagnetically coupled to the receiving coil 21 of the resonant circuit 20. For example, the resonance suppression coil 25 and the receiving coil 21 are wound around the same core wire. The number of turns of the receiving coil 21 and the number of turns of the resonance suppression coil 25 may be equal or different. Furthermore, both ends of the resonance suppression coil 25 are connected to a switching circuit 26. When the resonance suppression coil 25 is short-circuited by the switching circuit 26, the resonance suppression coil 25 and the receiving coil 21 become electromagnetically coupled, causing the resonant frequency of the resonant circuit 20 to change. Therefore, even if the output voltage from the resonant circuit 20 increases excessively, short-circuiting the resonance suppression coil 25 reduces the power transmitted from the power transmitting device 2 to the power receiving device 3, thereby reducing the output voltage from the resonant circuit 20.

[0059] On the other hand, when the switch circuit 26 opens both ends of the resonance suppression coil 25 , the resonance suppression coil 25 no longer participates in the resonance between the transmitting coil 14 and the receiving coil 21 and no longer affects the power transmission from the power transmitting device 2 to the power receiving device 3 .

[0060] Switch circuit 26 is connected to both ends of resonance suppression coil 25 and switches between short-circuiting and opening resonance suppression coil 25 in response to a control signal from switch control circuit 27. Specifically, switch circuit 26 short-circuits resonance suppression coil 25 while receiving an on-control signal from switch control circuit 27. On the other hand, switch circuit 26 opens both ends of resonance suppression coil 25 while receiving an off-control signal from switch control circuit 27.

[0061] The switch circuit 26 includes, for example, a relay circuit. When the switch control circuit 27 turns on the relay circuit, the resonance suppression coil 25 is short-circuited. On the other hand, when the switch control circuit 27 turns off the relay circuit, both ends of the resonance suppression coil 25 are opened.

[0062] Alternatively, the switching circuit 26 may include two n-channel MOSFETs connected in series between the two ends of the resonance suppression coil 25. In this case, the two MOSFETs are configured so that their source terminals are connected to each other and their drain terminals are connected to each end of the resonance suppression coil 25. Furthermore, the gate terminals of the two MOSFETs are connected to the switching control circuit 27. When a relatively high voltage, equivalent to a control signal to turn on, is applied to the gate terminals of the two MOSFETs from the switching control circuit 27, current flows between the source and drain of each MOSFET, short-circuiting the resonance suppression coil 25. On the other hand, when a relatively low voltage, equivalent to a control signal to turn off, is applied to the gate terminals of the two MOSFETs from the switching control circuit 27, current no longer flows between the source and drain of each MOSFET. Furthermore, the body diodes of the two MOSFETs are in opposite directions, so even if current flows through the body diodes, no current flows. Consequently, the two ends of the resonance suppression coil 25 are open.

[0063] Alternatively, the two MOSFETs may be configured so that their drain terminals are connected to each other and their source terminals are connected to both ends of the resonance suppression coil 25. In this example, when a relatively high voltage, equivalent to a control signal for turning on, is applied to the gate terminals of the two MOSFETs from the switch control circuit 27, the resonance suppression coil 25 is also short-circuited. On the other hand, when a relatively low voltage, equivalent to a control signal for turning off, is applied to the gate terminals of the two MOSFETs from the switch control circuit 27, both ends of the resonance suppression coil 25 are opened.

[0064] The switch control circuit 27 controls the on / off state of the switch circuit 26 based on the output voltage measurement value received from the voltage detection circuit 24 at each predetermined cycle. To this end, the switch control circuit 27 includes, for example, a memory circuit for storing an upper threshold value and a lower threshold value of the output voltage; a calculation circuit for comparing the output voltage measurement value with these threshold values; and a control circuit for controlling the on / off state of the switch circuit 26.

[0065] When the measured output voltage value exceeds a predetermined upper threshold, switch control circuit 27 turns on switch circuit 26, short-circuiting resonance suppression coil 25. This causes switch control circuit 27 to change the resonant frequency of resonance circuit 20, thereby lowering the output voltage. On the other hand, when the measured output voltage value falls below a predetermined lower threshold, switch control circuit 27 turns off switch circuit 26, opening resonance suppression coil 25. This restores the resonant frequency of resonance circuit 20, thereby raising the output voltage. By controlling the on / off state of switch circuit 26 in this manner, the resonance suppression coil 25 is repeatedly short-circuited and opened, and the output voltage is adjusted to fall within the permissible range defined by the lower and upper thresholds. The upper threshold is set, for example, to a value obtained by multiplying the upper limit of the output voltage that does not interfere with the operation of load circuit 4 by a safety factor (e.g., 0.9 to 0.97) less than 1. The lower threshold is set to a value lower than the upper threshold and is obtained by multiplying the lower limit of the output voltage that does not hinder the operation of the load circuit 4 by a safety factor greater than 1 (eg, 1.03 to 1.1).

[0066] Hereinafter, the output voltage characteristics of the contactless power supply device 1 will be described.

[0067] Figure 2 1 is a diagram showing an example of simulation results of the frequency characteristics of the output voltage of the contactless power supply device 1 . Figure 2In this simulation, the horizontal axis represents frequency, and the vertical axis represents output voltage. Furthermore, in this simulation, the resonance suppression coil 25 of the power receiving device 3 is open, so it does not affect power transmission. Furthermore, the capacitance of the first capacitor 15 is set to 40.0 nF, and the capacitance of the second capacitor 16 is set to 45.6 nF. Furthermore, the inductance of the first coil 17 is set to 70.0 μH. Furthermore, the inductance of the transmitting coil 14 is set to 160 μH, and the inductance of the receiving coil 21 is set to 80.0 μH. Furthermore, the capacitance of the resonant capacitor 22 is set to 44.8 nF. Furthermore, the winding resistance values ​​on the power transmitting side and the power receiving side are set to 0.13 Ω. Furthermore, the voltage Vin of the AC power output by the inverter 13 and applied to the transmitting coil 14 is set to 310 V. Graph 201 shows the frequency characteristics of the output voltage when the coupling degree k between the transmitting coil 14 and the receiving coil 21 is 0.11 and the output load resistance value of the load circuit 4 is 20 Ω. Graph 202 shows the frequency characteristics of the output voltage when the coupling degree k is 0.11 and the output load resistance value of the load circuit 4 is 2 kΩ. Graph 203 shows the frequency characteristics of the output voltage when the coupling degree k is 0.22 and the output load resistance value of the load circuit 4 is 20 Ω. Graph 204 shows the frequency characteristics of the output voltage when the coupling degree k is 0.22 and the output load resistance value of the load circuit 4 is 2 kΩ. As shown in Graphs 201 to 204, at the resonant frequency f1 (84.6 kHz) of the resonant circuit 20 of the power receiving device 3, the output voltage remains constant even when the output load resistance value of the load circuit 4 changes. Furthermore, it can be seen that even when the coupling degree k changes, the frequency characteristics of the output voltage maintain a maximum value at the resonant frequency f1, and the output voltage fluctuates more gradually with frequency fluctuations than at other extreme frequencies. Therefore, by setting the drive frequency of the inverter 13 to a frequency within a predetermined frequency range (e.g., 0.97*f1 to 1.03*f1) that includes the resonant frequency f1 of the resonant circuit 20, the contactless power supply device 1 can achieve constant voltage output operation. Furthermore, during power transmission, even if the relative positional relationship between the transmitting coil 14 and the receiving coil 21 changes, causing the coupling degree between these coils to change, the contactless power supply device 1 can maintain a certain degree of power transmission efficiency by setting the drive frequency within this predetermined frequency range. Furthermore, even if the coupling degree between the transmitting coil 14 and the receiving coil 21 changes, the contactless power supply device 1 can maintain the output voltage within a fixed range by simply adjusting the voltage of the AC power supplied to the transmitting coil 14 without changing the drive frequency.

[0068] Next, we will describe in detail the duty cycle estimation performed by control circuit 19 related to the short-circuiting of resonance suppression coil 25 and the voltage control of the AC power supplied from power supply circuit 10 to transmitting coil 14. To this end, we will first explain the relationship between the short-circuiting and opening of resonance suppression coil 25 and power loss.

[0069] Figure 3 This is a diagram showing an example of the relationship between the output voltage, the short-circuiting and opening of the resonance suppression coil 25 , the voltage of the AC power supplied to the transmission coil 14 (hereinafter sometimes referred to as input voltage), and the current flowing to the switching circuit 26 . Figure 3 In the figure, the horizontal axis represents time. Waveforms 301 and 302 respectively represent the temporal variation of the output voltage and the temporal variation of the short-circuited and open states of resonance suppression coil 25. Furthermore, waveform 303 represents the temporal variation of the input voltage, and waveform 304 represents the temporal variation of the current flowing through switching circuit 26.

[0070] As shown in waveforms 301 to 303, the time required for the output voltage to rise from the lower threshold ThL to the upper threshold ThU, i.e., the off-period Toff during which the resonance suppression coil 25 is open, increases as the input voltage decreases. Furthermore, if the load of load circuit 4 is constant, the time required for the output voltage to fall from the upper threshold ThU to the lower threshold ThL, i.e., the on-period Ton during which the resonance suppression coil 25 is short-circuited, remains constant. Therefore, as the input voltage decreases, the repetition period T (=Toff+Ton) increases, and as a result, the duty cycle D (=Ton / T) associated with the short-circuiting of the resonance suppression coil 25 decreases. Furthermore, as shown in waveform 304, the smaller the duty cycle D, the shorter the ratio of the period during which current flows through the switching circuit 26 during the repetition period T. Consequently, as the input voltage decreases, the current flowing through the switching circuit 26 decreases. Therefore, the more the input voltage drops, the less loss caused by the current flowing through the resonance suppression coil 25 and the switching circuit 26 during the period when the resonance suppression coil 25 is short-circuited. Therefore, it is preferable to control the input voltage so that the duty cycle D is small. However, if the input voltage is dropped excessively, the output voltage may not exceed the lower threshold ThL, thereby hindering the operation of the load circuit 4. Furthermore, if the repetition period T becomes too long, it will be difficult for the input voltage to properly follow changes in the positional relationship between the transmitting coil 14 and the receiving coil 21. Therefore, it is preferable to control the input voltage so that the duty cycle D is at least a certain level.

[0071] Furthermore, control circuit 19 preferably controls input voltage Vin so that the length of off-period Toff is less than or equal to a fixed value. This prevents excessive duration of the output voltage from exceeding the acceptable range due to, for example, changes in the positional relationship between transmitter coil 14 and receiver coil 21 during power transmission.

[0072] Figure 4 This is a diagram showing an example of a waveform of a current flowing through a switching element of the inverter 13 when the resonance suppression coil 25 is short-circuited. Figure 4 , the horizontal axis represents time, and the vertical axis represents current value. Also, waveform 400 represents the temporal change of the current flowing through the switching element.

[0073] In this embodiment, power transmission device 2 includes first coil 17, first capacitor 15, and second capacitor 16 between power supply circuit 10 and transmitting coil 14. This allows waveform 400 to have two poles within the repetition cycle of the current waveform. This reduces the peaks of the current waveform and reduces power loss on the transmission side.

[0074] As described above, the control circuit 19 controls the input voltage of the AC power supplied from the power supply circuit 10 to the transmission coil 14 based on the duty cycle D, thereby maintaining the output voltage within a constant range and reducing power loss.

[0075] Next, estimation of the duty ratio D will be described.

[0076] Figure 5A and Figure 5B Graphs each show an example of a waveform of a current flowing through the switching element of the inverter 13 when the resonance suppression coil 25 is short-circuited and an example of a waveform of a current flowing through the switching element of the inverter 13 when the resonance suppression coil 25 is open. Figure 5A and Figure 5B In the figure, the horizontal axis represents time and the vertical axis represents current value. Figure 5A The waveform 501 shown represents the waveform of the current flowing to the switching element 13 - 2 (in this example, corresponding to the first switching element) of the inverter 13 when the resonance suppression coil 25 is short-circuited. Figure 5B Waveform 502 shows the waveform of the current flowing through the first switching element when the resonance suppression coil 25 is open. Waveforms 501 and 502 are waveforms during the period when the first switching element is on, that is, waveforms corresponding to half the period corresponding to the drive frequency of the inverter 13.

[0077] While resonance suppression coil 25 is short-circuited, power transmission from power transmitting device 2 to power receiving device 3 is stopped. Consequently, power consumption on the power receiving side is approximately zero. Consequently, the effective power on the power transmitting side is also approximately zero. As a result, as shown in waveform 501, the average value of the current flowing through the first switching element is approximately zero while resonance suppression coil 25 is short-circuited.

[0078] In contrast, when power is transmitted from power transmitting device 2 to power receiving device 3 via open resonance suppression coil 25, power is consumed on the receiving side. Consequently, the effective power on the transmitting side also increases. As a result, as shown in waveform 502, the average value of the current flowing through the first switching element is positive during power transmission via open resonance suppression coil 25.

[0079] Thus, control circuit 19 measures the period during which the average value of the current flowing through the first switching element is less than a predetermined threshold as the on-period Ton during which resonance suppression coil 25 is short-circuited. Furthermore, control circuit 19 measures the period during which the average value of the current flowing through the first switching element is greater than or equal to the predetermined threshold as the off-period Toff during which resonance suppression coil 25 is open. Control circuit 19 can estimate duty ratio D (=Ton / (Ton+Toff)) associated with the short-circuit of resonance suppression coil 25 based on the measured on-period Ton and off-period Toff.

[0080] Figure 6 This is a circuit diagram of current detection circuit 18. Current detection circuit 18 includes four resistors R1 to R4, a capacitor C1, and an operational amplifier AMP. Resistor R1 is connected between switching element 13-2 of inverter 13 and the negative output terminal of full-wave rectifier circuit 11 via power factor correction circuit 12. Furthermore, one end of resistor R2 is connected between resistor R1 and switching element 13-2, and the other end is connected to the positive input terminal of operational amplifier AMP. Furthermore, one end of capacitor C1 is connected between the other end of resistor R2 and the positive input terminal of operational amplifier AMP, and the other end is connected to the negative output terminal of full-wave rectifier circuit 11 via power factor correction circuit 12. Furthermore, one end of resistor R3 is connected to the negative input terminal of operational amplifier AMP, and the other end is connected to the negative output terminal of full-wave rectifier circuit 11 via power factor correction circuit 12. Furthermore, the resistor R4 is connected between one end of the resistor R3 and the negative input terminal of the operational amplifier AMP, and the other end is connected to the output terminal of the operational amplifier AMP. The output terminal of the operational amplifier AMP is connected to the control circuit 19 .

[0081] While switching element 13-2 is on, the current flowing through transmitting coil 14 is converted into a voltage by resistor R1. The converted voltage then passes through an integrating circuit comprising resistor R2 and capacitor C1, filtering out high frequencies. The voltage is then integrated over a predetermined sampling period and input to the positive input terminal of the operational amplifier AMP. The operational amplifier AMP, resistors R3, and resistor R4 form a non-inverting amplifier circuit that amplifies the input voltage at an amplification factor corresponding to resistors R3 and R4. The amplified voltage is then output from the output terminal of the operational amplifier AMP to the control circuit 19. In this manner, the current detection circuit 18 outputs a voltage corresponding to the current flowing through transmitting coil 14. Therefore, the average value of the voltage output from the current detection circuit 18 over the sampling period corresponds to the average value of the current flowing through transmitting coil 14 over that sampling period. The sampling period is set to a length equal to or greater than half the period of the drive frequency of the inverter 13. More preferably, the sampling period is set to a period sufficiently shorter than the repetition cycle of resonance suppression coil 25, for example, a length of 1 / 100 to 1 / 1000 of the minimum assumed repetition cycle. For each sampling period, control circuit 19 calculates the average value of the voltage output from current detection circuit 18 within that sampling period. Furthermore, control circuit 19 can estimate that resonance suppression coil 25 is open during sampling periods where the average value is above a predetermined threshold, and estimate that resonance suppression coil 25 is short-circuited during sampling periods where the average value is below the predetermined threshold. Control circuit 19 can simply define the period during which the resonance suppression coil 25 is estimated to be open as the off period, and define the period during which the resonance suppression coil 25 is estimated to be short-circuited as the on period. This allows control circuit 19 to accurately measure on period Ton and off period Toff, and, as a result, accurately estimate the duty ratio associated with the short-circuit of resonance suppression coil 25.

[0082] Figure 7 This is an operation flowchart of input voltage control performed by the control circuit 19. The control circuit 19 may control the power supply circuit 10 according to the following operation flowchart.

[0083] Based on the current flowing through the first switching element of inverter 13, detected by current detection circuit 18, control circuit 19 estimates the off-period Toff during which resonance suppression coil 25 is open and the duty cycle D associated with the short-circuiting of resonance suppression coil 25 (step S101). Control circuit 19 then determines whether the estimated length of off-period Toff during which resonance suppression coil 25 is open is longer than a predetermined threshold value Th (e.g., 1 second) (step S102). If off-period Toff is longer than threshold value Th (step S102 - yes), control circuit 19 controls power supply circuit 10 to increase input voltage Vin (step S103). In this embodiment, control circuit 19 increases the duty cycle of the switching element of power factor improvement circuit 12. This shortens off-period Toff and increases duty cycle D due to the shortened off-period Toff. After a predetermined time (e.g., 1 to several seconds), control circuit 19 repeats the process from step S101 onward.

[0084] On the other hand, if the length of off period Toff is less than or equal to threshold value Th (step S102 - No), control circuit 19 determines whether duty cycle D, estimated to be related to a short circuit in resonance suppression coil 25, is less than or equal to a preset upper limit (step S104). As described above, duty cycle D is preferably small, and therefore, the upper limit of duty cycle D is preferably set to 0.3 or less, preferably 0.2 or 0.15.

[0085] If the duty cycle D is below the permissible upper limit (step S104 - Yes), the control circuit 19 does not change the duty cycle of the switching elements in the power factor correction circuit 12. In other words, the input voltage Vin of the AC power supplied from the power supply circuit 10 to the transmitting coil 14 remains maintained. Furthermore, after a predetermined time has passed, the control circuit 19 repeats the processes from step S101 onwards. On the other hand, if the duty cycle D is greater than the permissible upper limit (step S104 - No), the control circuit 19 controls the power supply circuit 10 to reduce the input voltage Vin of the AC power supplied from the power supply circuit 10 to the transmitting coil 14 (step S105). In this embodiment, the control circuit 19 reduces the duty cycle of the switching elements in the power factor correction circuit 12. This is expected to reduce the duty cycle D due to a longer off-period Toff. Furthermore, after a predetermined time has passed, the control circuit 19 repeats the processes from step S101 onwards.

[0086] Furthermore, even when the input voltage Vin is set to the maximum voltage of the AC power that can be supplied from the power supply circuit 10, if the average value of the current detected by the current detection circuit 18 remains substantially zero for a period exceeding a predetermined time, it is estimated that the power receiving device 3 has moved to a location where it cannot receive power from the power transmitting device 2. Therefore, the control circuit 19 may reduce the input voltage Vin to a predetermined standby voltage value. The standby voltage value is set to a value lower than the input voltage during normal power transmission.

[0087] As described above, the contactless power supply device includes a resonance suppression coil on the power receiving device to suppress resonance in the resonant circuit. By switching between short-circuiting and opening the resonance suppression coil, the device maintains the output voltage within a fixed range even if the coupling between the power transmitting and receiving coils fluctuates during power transmission. Furthermore, the contactless power supply device estimates the duty ratio associated with short-circuiting the resonance suppression coil based on the current flowing through any switching element of the inverter that supplies AC power to the power transmitting coil and the current flowing through the transmitting coil. The contactless power supply device controls the input voltage of the AC power supplied to the power transmitting coil based on the estimated duty ratio, thereby reducing power loss when the resonance suppression coil is short-circuited. As a result, the contactless power supply device improves power transmission efficiency without requiring communication between the power transmitting and receiving devices.

[0088] Furthermore, when the load of load circuit 4 is reduced, the output voltage drop when resonance suppression coil 25 is short-circuited becomes more gradual, and the on-period Ton becomes longer. As a result, the period during which current flows to switch circuit 26 becomes longer, potentially causing excessive heating of switch circuit 26.

[0089] Therefore, according to a variation, the control circuit 19 may also control the duty cycle of the switching element of the power factor improvement circuit 12 of the power supply circuit 10 when the measured conduction period is longer than the prescribed allowable upper limit length, so as to reduce the input voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14 to a prescribed standby voltage value.

[0090] If the on-time is shortened to below the prescribed upper limit after the input voltage is lowered to the standby voltage value, the control circuit 19 only needs to Figure 7 The power supply circuit 10 and the input voltage may be controlled according to the operation flowchart shown.

[0091] Furthermore, if the measured on-period is longer than a predetermined allowable upper limit, the control circuit 19 may control the power supply circuit 10 to remove the restriction that the off-period Toff must be less than a fixed length, thereby reducing the input voltage Vin. Specifically, the control circuit 19 may reduce the input voltage Vin until the measured on-period becomes less than the predetermined allowable upper limit.

[0092] According to this modification, the contactless power supply device can suppress heat generation of the switching circuit 26 , and thus can safely continue power transmission even if the load of the load circuit 4 is reduced.

[0093] Furthermore, if there is a conductive foreign object (e.g., a small metal piece) that affects power transmission between the transmitting coil 14 and the receiving coil 21, even if the resonance suppression coil 25 is short-circuited, the foreign object will still cause power consumption. Consequently, during the on-period, the effective power generated by the current flowing through each switching element of the inverter 13 will increase. Therefore, according to another variation, the control circuit 19 compares the average value of the voltage output from the current detection circuit 18 for each sampling period included in the on-period with a predetermined detection threshold. This average voltage value corresponds to the average value of the current flowing through the first switching element of the inverter 13 during the on-period. The detection threshold is set to a value lower than the threshold used for determining on / off periods. If the average voltage value exceeds the detection threshold, the control circuit 19 determines that a foreign object is present and keeps each switching element of the inverter 13 off, thereby stopping the power supply from the power supply circuit 10 to the transmitting coil 14. Furthermore, the control circuit 19 may also transmit an abnormality signal indicating the detection of a foreign object to other equipment (not shown). According to this modified example, the control circuit 19 can accurately detect foreign objects that affect power transmission, and can prevent the non-contact power supply device from causing abnormalities due to the foreign objects. In addition, it is preferred that the higher the input voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14, the larger the detection threshold is set. Therefore, for example, in the memory possessed by the control circuit 19, a reference table representing the relationship between the duty cycle of the switching element of the power factor improvement circuit 12 and the second threshold is pre-stored. And the control circuit 19 only needs to determine the second threshold by referring to the reference table and the duty cycle of the switching element of the power factor improvement circuit 12. As a result, the control circuit 19 can further improve the detection accuracy of foreign objects.

[0094] Furthermore, in the resonant circuit 20 of the power receiving device 3, the receiving coil 21 and the resonant capacitor 22 may be connected in parallel to each other to achieve parallel resonance. Furthermore, in the power receiving device 3, another coil may be provided, connected in series with the receiving coil 21, between the resonant circuit 20 and the rectifying and smoothing circuit 23. Furthermore, if the positional relationship between the power transmitting device 2 and the power receiving device 3 fluctuates negligibly during power transmission, the first coil 17 and the second capacitor 16 may be omitted from the power transmitting device 2.

[0095] Furthermore, the power supply circuit 10 of the power transmission device 2 may include a direct current-direct current (DC-DC) converter with a variable step-up / step-down ratio, instead of the power factor correction circuit 12. Furthermore, DC power may be directly input to the DC-DC converter. Furthermore, as in the previously described embodiment, the control circuit 19 may control the step-up / step-down ratio of the DC-DC converter based on the duty cycle associated with the short-circuiting of the resonance suppression coil 25, thereby controlling the input voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14.

[0096] The contactless power supply device according to the embodiment or the modified example can be preferably used to supply power to a mobile object such as an automatic guided vehicle (AGV).

[0097] Figure 8 This is a schematic diagram of a case where a contactless power supply device based on the embodiment or modification is used as a power supply system for a mobile body. The power receiving device 3 is mounted on the mobile body 800. On the other hand, the power transmitting device 2 is arranged along the moving path of the mobile body 800. For example, the transmitting coil 14 is provided on the floor surface on the moving path 810 of the mobile body 800. In addition, it is preferred that the transmitting coil 14 is provided at a position where the mobile body 800 temporarily stops, or at a position where the moving speed of the mobile body 800 becomes less than a predetermined speed. On the other hand, the receiving coil 21 is mounted on the lower part of the mobile body in a manner facing the floor surface. The power transmitting device 2 is not limited to one, and a plurality of power transmitting devices 2 may also be provided at different positions on the moving path 810. Figure 8 In the illustrated example, three power transmitting devices 2 are shown, and the transmitting coils 14 of each power transmitting device 2 are arranged in a row along the direction in which the movement path 810 extends. Furthermore, when multiple power transmitting devices 2 are provided, the transmitting coils 14 of each power transmitting device 2 may be arranged in a direction perpendicular to the direction in which the movement path 810 extends, or may be arranged in a grid or zigzag pattern.

[0098] When the mobile object 800 passes through a location where the transmitting coil 14 of any power transmitting device 2 is located, the transmitting coil 14 and the receiving coil 21 become electromagnetically coupled, enabling power transmission from the power transmitting device 2 to the power receiving device 3. The power received by the power receiving device 3 is then used to operate various devices onboard the mobile object 800, or to operate the mobile object 800 itself. In this case, the control circuit 19 simply controls the input voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14 in accordance with the aforementioned embodiment or variations. This allows the power transmitting device 2 to transmit power to the power receiving device 3 onboard the mobile object 800 with high power transmission efficiency, even when the mobile object 800 is moving during power transmission.

[0099] Thus, those skilled in the art can make various changes in accordance with the embodiments within the scope of the present invention.

[0100] Explanation of Figure Numbers

[0101] 1: Contactless power supply device

[0102] 2: Power transmission device

[0103] 10: Power supply circuit

[0104] 11: Full-wave rectifier circuit

[0105] 12: Power factor improvement circuit

[0106] 13: Inverter

[0107] 13-1 to 13-4: Switching elements

[0108] 14: Transmitting coil

[0109] 15: First capacitor

[0110] 16: Second capacitor

[0111] 17: First coil

[0112] 18: Current detection circuit

[0113] 19: Control circuit

[0114] 3: Power receiving device

[0115] 20: Resonance Circuit

[0116] 21: Receiving coil

[0117] 22: Resonant capacitor

[0118] 23: Rectification and smoothing circuit

[0119] 24: Voltage detection circuit

[0120] 25: Resonance suppression coil

[0121] 26: Switching Circuit

[0122] 27: Switch control circuit

[0123] 4: Load circuit

[0124] 800: Mobile

Claims

1. A contactless power supply device comprising a power transmitting device and a power receiving device for transmitting power contactlessly from the power transmitting device, wherein The power transmission device comprises: a transmitting coil for supplying power to the power receiving device; a power supply circuit including an inverter having a plurality of switching elements connected in a full-bridge or half-bridge configuration, for supplying AC power to the transmitting coil; a current detection circuit for detecting a current flowing to a first switching element among the plurality of switching elements; as well as a control circuit for controlling the voltage of the AC power supplied from the power supply circuit to the transmitting coil; The power receiving device comprises: a resonant circuit including a receiving coil and a resonant capacitor connected to the receiving coil, and receiving electric power from the transmitting coil by resonating with respect to a current flowing in the transmitting coil of the power transmitting device; a rectifier circuit for rectifying the power received via the resonant circuit; a voltage detection circuit for measuring an output voltage of the power output from the rectifier circuit; a resonance suppression coil configured to be electromagnetically coupled to the receiving coil; a switch circuit connected to the resonance suppression coil and capable of switching the resonance suppression coil between short circuit and open circuit; as well as a switch control circuit that controls the switch circuit to short-circuit the resonance suppression coil when the measured value of the output voltage becomes equal to or greater than a predetermined upper threshold, and controls the switch circuit to open the resonance suppression coil when the measured value of the output voltage becomes lower than the predetermined upper threshold and equal to or less than a predetermined lower threshold. The control circuit of the power transmission device estimates a duty ratio associated with a period during which the resonance suppression coil is short-circuited based on the current detected by the current detection circuit, and controls the voltage of the AC power supplied from the power supply circuit to the transmitting coil so that the estimated duty ratio falls within a predetermined allowable range.

2. The contactless power supply device according to claim 1, wherein the power transmission device further comprises: a first capacitor connected between the power supply circuit and one end of the transmitting coil; a first coil connected between the power supply circuit and one end or the other end of the transmitting coil and the power supply circuit; as well as A second capacitor, one end of which is connected to the first capacitor, and the other end of which is connected to the other end of the transmitting coil. The frequency of the AC power supplied from the power supply circuit to the transmission coil is set to be within a predetermined frequency range including the resonant frequency of the resonant circuit of the power receiving device.

3. The contactless power supply device according to claim 1 or 2, wherein the control circuit of the power transmitting device controls the power supply circuit to increase the voltage of the AC power supplied from the power supply circuit to the transmitting coil when the period during which the resonance suppression coil of the power receiving device is open is longer than a predetermined threshold value, and, on the other hand, controls the power supply circuit to decrease the voltage of the AC power supplied from the power supply circuit to the transmitting coil when the duty ratio is greater than an upper limit of the predetermined allowable range and the period during which the resonance suppression coil is open is less than or equal to the predetermined threshold value.

4. The contactless power supply device according to claim 1 or 2, wherein the control circuit of the power transmitting device determines that there is a foreign object that affects power transmission from the transmitting coil to the receiving coil when the average value of the current flowing to the first switching element during a period in which the resonance suppression coil of the power receiving device is short-circuited is greater than a predetermined detection threshold. 5 . The contactless power supply device according to claim 1 , wherein the power receiving device is mounted on a moving object, and the transmitting coil of the power transmitting device is provided on a moving path of the moving object.

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