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); a resonance suppression coil (27) disposed so as to be electromagnetically coupleable to the reception coil (21); a switching circuit (28) capable of switching the resonance suppression coil (27) to be short-circuited or open; and a switching control circuit (29) that controls the switching circuit (28) so as to repeat short-circuiting and opening of the resonance suppression coil (27). A control circuit (19) of a power transmission device (2) determines the presence or absence of foreign matter on the basis of the average value of the current flowing to a first switching element (13-2) of an inverter (13) detected by a current detection circuit (18) during a period in which a resonance suppression coil (27) of a power reception device (3) is short-circuited.

Description

Technical Field

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

[0002] Conventional research has explored so-called contactless power supply (also known as wireless power supply) technologies, which transmit power through space without metallic contacts or other means. One known method for this type of contactless power supply is electromagnetic induction. In this method, power is transferred from the transmitting coil to the receiving coil through electromagnetic coupling between a primary-side (power-transmitting or power-supplying) coil (hereinafter referred to as the transmitting coil) and a secondary-side (power-receiving) coil (hereinafter referred to as the receiving coil).

[0003] In power transmission systems utilizing this type of contactless power supply technology, foreign objects such as metal may become lodged between the transmitting and receiving coils. In such cases, during power transmission, these foreign objects can be inductively heated, igniting fires or causing system failures due to heat buildup. Therefore, technologies for detecting these foreign objects have been proposed (see Patent Document 1 and Non-Patent Document 1).

[0004] The contactless power supply device disclosed in Patent Document 1 monitors the phases of the voltage and current output from the inverter to the power transmission coil, and detects metallic foreign matter mixed in the power supply based on changes in the phases.

[0005] Furthermore, the power supply loss comparison method disclosed in Non-Patent Document 1 detects foreign objects during power supply by regularly sampling and comparing transmission loss power.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2015 / 037291

[0009] Non-patent literature

[0010] Non-Patent Document 1: Komazaki et al., "Method for Detecting Foreign Objects in the Gap of a Contactless Power Supply Device for Electric Vehicles," Proceedings of the Industrial Application Division Meeting of the Institute of Electrical Engineers, No. 4-10, pp. 115-120, 2012 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] Foreign matter that gets between the transmitting and receiving coils poses a high risk, and therefore there is a demand for further improvement in the accuracy of detecting such foreign matter.

[0013] Therefore, an object of the present invention is to provide a contactless power supply device capable of accurately detecting a foreign object that affects power transmission from a power transmitting-side device to a power receiving-side device.

[0014] Technical means to solve the problem

[0015] As one aspect 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 for supplying power to the power receiving device; a power supply circuit comprising 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 current flowing through a first switching element among the plurality of switching elements in the inverter; and a control circuit for determining, based on the detected current, the presence of a foreign object that could affect power transmission from the power transmitting device to the power receiving device. The power receiving device further comprises: a resonant circuit having a receiving coil and a resonant capacitor connected to the receiving coil, which resonates with current flowing through the transmitting coil of the power transmitting device, thereby receiving power from the transmitting coil; a rectifier circuit that rectifies the power received via the resonant 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 between short-circuiting and opening the resonance suppression coil; and a switch control circuit that controls the switch circuit based on power output from the rectifier circuit to repeatedly short-circuit and open the resonance suppression coil. Furthermore, the control circuit of the power transmitting device determines the presence of a foreign object based on an average value of current flowing through a first switching element during a period in which the resonance suppression coil of the power receiving device is short-circuited.

[0016] With this configuration, the contactless power supply device can accurately detect a foreign object that affects power transmission from a power transmitting device to a power receiving device.

[0017] In the contactless power supply device, the control circuit of the power transmitting device preferably determines that a foreign object is present when an average value of the current flowing to the first switching element over a period corresponding to a predetermined number of repeated cycles of short-circuiting and opening the resonance suppression coil of the power receiving device exceeds a predetermined detection threshold.

[0018] With this configuration, the contactless power supply device can accurately detect a foreign object that affects power transmission from a power transmitting device to a power receiving device.

[0019] Furthermore, in the contactless power supply device, the power receiving device preferably further includes a periodic signal generating circuit that generates a periodic signal having a repetitive cycle based on the power output from the rectifier circuit. Furthermore, the switch control circuit preferably controls the switch circuit based on the periodic signal so that the resonance suppression coil is repeatedly short-circuited and opened at the repetitive cycle.

[0020] With this configuration, the contactless power supply device can reliably short-circuit the resonance suppression coil at a fixed repetition cycle, thereby preventing the period during which foreign object detection is impossible from becoming excessively prolonged. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] [ 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.

[0022] [ Figure 2A ] Figure 2A This is a diagram showing an example of the waveform of the current flowing through the switching element of the inverter when the resonance suppression coil is short-circuited and the waveform of the current flowing through the switching element of the inverter when the resonance suppression coil is open.

[0023] [ Figure 2B ] Figure 2B This is a diagram showing an example of the waveform of the current flowing through the switching element of the inverter when the resonance suppression coil is short-circuited and the waveform of the current flowing through the switching element of the inverter when the resonance suppression coil is open.

[0024] [ Figure 3A ] Figure 3A This is a diagram showing an example of the relationship between the output voltage from the rectifying and smoothing circuit, the short circuit and opening of the resonance suppression coil, and the average value of the current flowing through the switching element of the inverter when no foreign matter is present.

[0025] [ Figure 3B ] Figure 3B This is a diagram showing an example of the relationship between the output voltage from the rectifying and smoothing circuit, the short circuit and opening of the resonance suppression coil, and the average value of the current flowing through the switching element of the inverter when a foreign object is present.

[0026] [ Figure 4 ] Figure 4 This is the circuit diagram of the current detection circuit.

[0027] [ Figure 5 ] Figure 5 This is a flowchart of the foreign object detection process.

[0028] [ Figure 6 ] Figure 6This 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

[0029] Below, while referring to Figure 1 A 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 receiving coil and a resonance suppression coil (hereinafter referred to as the resonance suppression coil) configured to electromagnetically couple with the receiving coil. The power receiving device repeatedly short-circuits and opens the resonance suppression coil to maintain the output voltage within a fixed range. Meanwhile, a device on the power transmitting side (hereinafter referred to as the power transmitting device) determines the presence of foreign objects that could affect power transmission between the transmitting and receiving coils based on the average value of the current flowing through any switching element of the inverter that supplies AC power to the transmitting coil while the resonance suppression coil is short-circuited.

[0030] 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 DC-DC (Direct Current-Direct Current) converter 24, a smoothing capacitor 25, a periodic signal generating circuit 26, a resonance suppression coil 27, a switching circuit 28, and a switching control circuit 29. 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.

[0031] First, the power transmission device 2 will be described.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 .

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 whose current is detected by the current detection circuit 18 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. When the switching element 13-2 is turned on, the current detection circuit 18 detects the current flowing through the transmitting coil 14 and outputs the detected current value to the control circuit 19. In other words, 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.

[0047] 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.

[0048] 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 determines the presence of foreign objects that could affect the transmission of power from the transmitting coil 14 to the receiving coil 21 based on the current value detected by the current detection circuit 18. Details of how the control circuit 19 determines the presence of foreign objects will be described later.

[0049] 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.

[0050] Next, the power receiving device 3 will be described.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The rectifying and smoothing circuit 23 is an example of a rectifying circuit and includes a full-wave rectifying 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 rectifying circuit. The rectifying and smoothing circuit 23 rectifies and smoothes the AC power output from the resonant circuit 20, converting it into DC power. The rectifying and smoothing circuit 23 then outputs this DC power to the DC-DC converter 24.

[0055] The DC-DC converter 24 converts the voltage output from the rectifier-smoothing circuit 23 into a voltage sufficient to operate the load circuit 4 and outputs the converted voltage. The DC-DC converter 24 can be either a step-up or step-down DC-DC converter. However, the DC-DC converter 24 is preferably a fixed-output DC-DC converter. This provides a stable output voltage. The DC-DC converter 24 outputs the converted power to the load circuit 4 via the smoothing capacitor 25.

[0056] Smoothing capacitor 25 is connected between the DC-DC converter 24 and the load circuit 4, and between the positive and negative sides of the DC-DC converter 24. Smoothing capacitor 25 smoothes the voltage output from the DC-DC converter 24 and outputs the smoothed output voltage to the load circuit 4.

[0057] Based on the voltage output from the smoothing capacitor 25, the periodic signal generating circuit 26 generates a periodic signal whose voltage varies at a predetermined period. The periodic signal can be a rectangular wave periodic signal. However, the periodic signal is not limited to a rectangular wave and can also be a sine wave or triangular wave periodic signal. Furthermore, the predetermined period is preferably a sufficiently long period corresponding to the drive frequency of the inverter 13 of the power transmission device 2 and the resonant frequency of the resonant circuit 20, for example, a period of approximately 0.1 seconds to several seconds. The periodic signal generating circuit 26 can be any of various known circuits capable of generating the periodic signal described above. The periodic signal generating circuit 26 then outputs the generated periodic signal to the switching control circuit 29.

[0058] The resonance suppression coil 27 is provided so as to be electromagnetically coupled to the receiving coil 21 of the resonant circuit 20. For example, the resonance suppression coil 27 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 27 may be equal or different. Furthermore, both ends of the resonance suppression coil 27 are connected to a switching circuit 28. When the resonance suppression coil 27 is short-circuited by the switching circuit 28, the resonance suppression coil 27 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 of the resonant circuit 20 increases excessively, short-circuiting the resonance suppression coil 27 reduces the power transmitted from the power transmitting device 2 to the power receiving device 3, thereby reducing the output voltage of the resonant circuit 20.

[0059] On the other hand, when the switch circuit 28 opens both ends of the resonance suppression coil 27 , the resonance suppression coil 27 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 28 is connected to both ends of resonance suppression coil 27 and switches between short-circuiting and opening resonance suppression coil 27 in response to a control signal from switch control circuit 29. Specifically, while receiving an on-control signal from switch control circuit 29, switch circuit 28 short-circuits resonance suppression coil 27. On the other hand, while receiving an off-control signal from switch control circuit 29, switch circuit 28 opens both ends of resonance suppression coil 27.

[0061] The switch circuit 28 includes, for example, a relay circuit. When the switch control circuit 29 turns on the relay circuit, the resonance suppression coil 27 is short-circuited. On the other hand, when the switch control circuit 29 turns off the relay circuit, both ends of the resonance suppression coil 27 are opened.

[0062] Alternatively, the switching circuit 28 may include two n-channel MOSFETs connected in series between the two ends of the resonance suppression coil 27. 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 27. Furthermore, the gate terminals of the two MOSFETs are connected to the switching control circuit 29. 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 29, current flows between the source and drain of each MOSFET, short-circuiting the resonance suppression coil 27. 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 29, 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 27 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 27. 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 29, the resonance suppression coil 27 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 29, both ends of the resonance suppression coil 27 are opened.

[0064] Switch control circuit 29 controls the on / off state of switch circuit 28 based on the periodic signal received from periodic signal generation circuit 26. Specifically, switch control circuit 29 controls switch circuit 28 in response to the power output from rectifier circuit 23, causing the circuit to repeatedly short-circuit and open resonance suppression coil 27. To this end, switch control circuit 29 includes, for example, a memory circuit that stores upper and lower threshold values, a calculation circuit that compares the voltage of the periodic signal with these threshold values, and a control circuit that controls the on / off state of switch circuit 28.

[0065] When the voltage of the periodic signal exceeds a predetermined upper threshold, the switch control circuit 29 turns on the switch circuit 28, short-circuiting the resonance suppression coil 27. This changes the resonant frequency of the resonance circuit 20, thereby lowering the output voltage. On the other hand, when the voltage of the periodic signal falls below a predetermined lower threshold, the switch control circuit 29 turns off the switch circuit 28, opening the resonance suppression coil 27. This restores the resonant frequency of the resonance circuit 20, thereby increasing the output voltage. By controlling the on / off state of the switch circuit 28 in this manner, the resonance suppression coil 27 is repeatedly short-circuited and opened. The upper threshold is set to a value obtained by multiplying the maximum voltage of the periodic signal by a safety factor less than 1 (e.g., 0.9 to 0.97). Furthermore, the lower threshold is set to a value lower than the upper threshold and obtained by multiplying the minimum voltage of the periodic signal by a safety factor greater than 1 (e.g., 1.03 to 1.1). Furthermore, by controlling the switch circuit 28 based on the periodic signal generated by the periodic signal generating circuit 26, the switch control circuit 29 can reliably short-circuit the resonance suppression coil at a fixed repetition cycle, thereby preventing the period during which foreign object detection is impossible from becoming excessively prolonged.

[0066] The following describes in detail how the control circuit 19 determines whether a foreign object is present. To this end, the relationship between the short-circuiting and opening of the resonance suppression coil 27 and the power consumption will be described first.

[0067] Figure 2A and Figure 2B 1 and 2 are diagrams showing examples of the waveform of the current flowing through the switching element of the inverter 13 when the resonance suppression coil 27 is short-circuited and the waveform of the current flowing through the switching element of the inverter 13 when the resonance suppression coil 27 is open. Figure 2A and Figure 2B In the figure, the horizontal axis represents time and the vertical axis represents current value. Figure 2A The waveform 201 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 27 is short-circuited. Figure 2B Waveform 202 shows the waveform of the current flowing through the first switching element when the resonance suppression coil 27 is open. Waveforms 201 and 202 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.

[0068] While resonance suppression coil 27 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 201, the average value of the current flowing through the first switching element is approximately zero while resonance suppression coil 27 is short-circuited.

[0069] In contrast, when power is transmitted from power transmitting device 2 to power receiving device 3 via open resonance suppression coil 27, power is consumed on the receiving side. Consequently, the effective power on the transmitting side also increases. As a result, as shown in waveform 202, the average value of the current flowing through the first switching element is positive during power transmission via open resonance suppression coil 27.

[0070] If a conductive foreign object (e.g., a small metal piece) is present at a location that affects power transmission from the transmitting coil 14 to the receiving coil 21, the magnetic field generated by the transmitting coil 14 will cause current to flow to the foreign object, resulting in power consumption. However, if the foreign object is small, the power consumed by the foreign object during the period when the resonance suppression coil 27 is open will be relatively small compared to the power consumed by the power receiving device 3. Therefore, the change in the current flowing to the first switching element due to the presence or absence of the foreign object will be minimal. In contrast, if the resonance suppression coil 27 is short-circuited, and power consumption in the power receiving device 3 is essentially zero, the change in the current flowing to the first switching element due to the presence or absence of the foreign object will be relatively large.

[0071] For example, if the input voltage applied to the transmitting coil 14 by the facility is 200 V, and the resonance suppression coil 27 is open, and the power receiving device 3 receives power, the power consumption is 200 W. In this case, the average current flowing through the first switching element is 1 A. Now, suppose a foreign object is introduced between the transmitting coil 14 and the receiving coil 21, and the foreign object causes a power consumption of 2 W. In this case, the total power consumption is 202 W, and the average current flowing through the first switching element is 1.01 A. Thus, the average value of the current flowing through the first switching element varies by only 1% overall depending on the presence or absence of the foreign object. Therefore, when the resonance suppression coil 27 is open and the power receiving device 3 receives power, it is difficult to accurately determine the presence of a foreign object based on the current flowing through the first switching element.

[0072] In contrast, if the resonance suppression coil 27 is short-circuited and the power receiving device 3 is not receiving power, the power consumption is due to losses caused by the windings of the transmitting coil 14 and the switching elements of the inverter 13, and is significantly smaller than the power consumption of the power receiving device 3 when receiving power. For example, if the input voltage applied to the transmitting coil 14 by the facility is 200 V, the windings of the transmitting coil 14 and the switching elements of the inverter 13 consume 2 W of power. In this case, if there is no foreign object, the average current flowing through the first switching element is 0.01 A. Here, assume that a foreign object has become lodged between the transmitting coil 14 and the receiving coil 21 as described above, and that the foreign object consumes 2 W of power. In this case, the total power consumption is 4 W, and the average current flowing through the first switching element is 0.02 A. Therefore, the average value of the current flowing through the first switching element varies by a factor of two depending on the presence or absence of the foreign object. Therefore, when the resonance suppression coil 27 is short-circuited and the power receiving device 3 is not receiving power, the presence or absence of a foreign object can be accurately determined based on the current flowing through the first switching element.

[0073] Figure 3A This is a diagram showing an example of the relationship between the output voltage from the rectifying and smoothing circuit 23 when no foreign matter exists, the short circuit and opening of the resonance suppression coil 27 , and the average value of the current flowing through the first switching element in a period corresponding to the driving frequency. Figure 3B This is a diagram showing an example of the relationship between the output voltage from the rectifying and smoothing circuit 23, the short circuit and opening of the resonance suppression coil 27, and the average value of the current flowing to the first switching element during a period corresponding to the drive frequency when a foreign object is present. Figure 3A and Figure 3B In the example, the horizontal axis represents time. Figure 3A In FIG. 1 , waveforms 301 and 302 respectively represent the time variation of the output voltage and the time variation of the short-circuited and open states of the resonance suppression coil 27. Furthermore, waveform 303 represents the time variation of the average current. Similarly, in FIG. Figure 3B In FIG, waveforms 311 and 312 respectively represent temporal changes in the output voltage and temporal changes in the short-circuited and open states of the resonance suppression coil 27. Furthermore, waveform 313 represents temporal changes in the average current.

[0074] In the absence of foreign matter, as shown in waveforms 301 and 302, during the off-period Toff (when the resonance suppression coil 27 is open), the power receiving device 3 receives power from the power transmitting device 2, causing the output voltage to gradually rise. Furthermore, as shown in waveform 303, the average current reaches a relatively high value. Meanwhile, during the on-period Ton (when the resonance suppression coil 27 is short-circuited), the power receiving device 3 no longer receives power, causing the output voltage to gradually decrease. Furthermore, the average current is approximately zero.

[0075] When a foreign object is present, as shown in waveforms 311 and 312, during the off-period Toff (when the resonance suppression coil 27 is open), the power receiving device 3 receives power from the power transmitting device 2, causing the output voltage to gradually rise. Furthermore, as shown in waveform 313, the average current reaches a relatively high value. Meanwhile, during the on-period Ton (when the resonance suppression coil 27 is short-circuited), the power receiving device 3 no longer receives power, causing the output voltage to gradually decrease. However, since power is consumed by the foreign object, the average current does not fully decrease and remains at a certain level.

[0076] As can be seen from this, the control circuit 19 can determine the presence or absence of foreign matter based on the average value of the current flowing through the first switching element while the resonance suppression coil 27 is short-circuited, as detected by the current detection circuit 18 .

[0077] Figure 4 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 .

[0078] 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 repetitive cycle of opening and short-circuiting resonance suppression coil 27 (i.e., one cycle of the periodic signal generated by periodic signal generation circuit 26), for example, a length of 1 / 100 to 1 / 1000 of the repetitive cycle. For each sampling period, control circuit 19 calculates the average voltage value output from current detection circuit 18 during that sampling period. Furthermore, control circuit 19 compares the average voltage value during each sampling period with a predetermined detection threshold. The detection threshold is set to a value that is smaller than the average voltage value estimated during the OFF period when resonance suppression coil 27 is open, and larger than the average voltage value during the ON period when resonance suppression coil 27 is short-circuited. More specifically, the detection threshold is set to a value obtained by adding an offset value to the average voltage value during the ON period, the offset value being smaller than the estimated voltage increase due to power consumption caused by foreign matter.

[0079] If you refer to it again Figure 3A and Figure 3B If no foreign matter is present, as shown in waveform 303, the average current becomes less than the current value Th corresponding to the detection threshold value during each on-period. In contrast, if a foreign matter is present, as shown in waveform 313, the average current does not fall below the current value Th even during the on-period.

[0080] Therefore, if the average voltage value does not fall below the detection threshold even once over a predetermined number of repetitions (e.g., 1 to 5 times), control circuit 19 determines that a foreign object is present. Furthermore, control circuit 19 keeps the switching elements of inverter 13 off, thereby halting the supply of power from power supply circuit 10 to transmitting coil 14. Furthermore, control circuit 19 may also notify other devices (not shown) of an abnormality signal indicating the detection of a foreign object. On the other hand, if the average voltage value falls below the detection threshold even once during this period, control circuit 19 has not detected a foreign object.

[0081] Figure 5 This is an operational flow chart of the foreign object detection process performed by the control circuit 19.

[0082] Control circuit 19 determines whether the average value of the voltage output from current detection circuit 18, corresponding to the average value of the current flowing through the first switching element of inverter 13 during sampling period P, is less than detection threshold Thv (step S101). As described above, during power transmission, the average value of the voltage does not fall below detection threshold Thv during the off-period when resonance suppression coil 27 is open. Therefore, the actual value to be determined in step S101 is the average value of the voltage during the on-period when resonance suppression coil 27 is short-circuited.

[0083] If the average voltage value is greater than the detection threshold Thv (step S101 – No), the control circuit 19 determines whether the duration C during which the average voltage value remains above the detection threshold Thv is greater than or equal to a predetermined time threshold Thp (step S102). If the duration C is greater than or equal to the time threshold Thp (step S102 – Yes), the control circuit 19 determines that a foreign object is present that is affecting the power transmission from the transmitting coil 14 to the receiving coil 21 (step S103). The control circuit 19 then stops the power supply from the power supply circuit 10 to the transmitting coil 14 (step S104). The control circuit 19 then terminates the foreign object detection process.

[0084] On the other hand, if the duration C is less than the time threshold Thp (step S102 —No), the control circuit 19 updates the duration C by adding the sampling period S to the duration C (step S105). The control circuit 19 then repeats the process from step S101 onwards during the next sampling period.

[0085] If the voltage average value is less than the detection threshold Thv in step S101 (step S101 —Yes), the control circuit 19 resets the duration C to 0 (step S106 ). The control circuit 19 then repeats the process from step S101 onwards in the next sampling period.

[0086] As described above, the contactless power supply device includes a resonance suppression coil in the power receiving device to suppress resonance in the resonant circuit. By switching between short-circuiting and opening the resonance suppression coil, the output voltage can be maintained within a fixed range. Furthermore, the contactless power supply device determines the presence of a foreign object based on the current flowing through the first switching element of the inverter that supplies AC power to the power transmission coil during the on-period when the resonance suppression coil is short-circuited. During the on-period, the current flowing through the first switching element varies significantly depending on the presence of a foreign object, enabling the contactless power supply device to accurately determine the presence of a foreign object.

[0087] 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 between the resonant circuit 20 and the rectifying and smoothing circuit 23, connected in series with the receiving coil 21. 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.

[0088] Furthermore, the switch control circuit 29 can also control the on / off state of the switch circuit 28 based on the output voltage from the rectifier-smoothing circuit 23. In this case, a voltage detection circuit for measuring the output voltage is provided on the output side of the rectifier-smoothing circuit 23. The switch control circuit 29 can simply turn on the switch circuit 28 when the voltage measured by the voltage detection circuit is above an upper threshold, and turn off the switch circuit 28 when the voltage measured by the voltage detection circuit is below a lower threshold. The upper threshold is set, for example, to a value obtained by multiplying the upper limit of the output voltage that does not impair the operation of the load circuit 4 by a safety factor less than 1 (e.g., 0.9 to 0.97). The lower threshold is set to a value lower than the upper threshold and obtained by multiplying the lower limit of the output voltage that does not impair the operation of the load circuit 4 by a safety factor greater than 1 (e.g., 1.03 to 1.1). Furthermore, in this variation, the DC-DC converter 24, smoothing capacitor 25, and periodic signal generating circuit 26 can be omitted.

[0089] Furthermore, the power supply circuit 10 of the power transmission device 2 may include a DC-DC converter instead of the power factor improvement circuit 12. Furthermore, direct current power may be directly input to the DC-DC converter.

[0090] 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).

[0091] Figure 6 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 600. On the other hand, the power transmitting device 2 is arranged along the moving path of the mobile body 600. For example, the transmitting coil 14 is arranged on the floor surface on the moving path 610 of the mobile body 600. In addition, it is preferred that the transmitting coil 14 is provided at a position where the mobile body 600 temporarily stops or at a position where the moving speed of the mobile body 600 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 610. Figure 6 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 610 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 610 extends, or may be arranged in a grid or zigzag pattern.

[0092] When the mobile object 600 passes through the 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, and power is transmitted 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 600, or to operate the mobile object 600 itself. In this case, the control circuit 19 can simply detect foreign objects according to the aforementioned embodiment or variations. Furthermore, when a foreign object is detected, the control circuit 19 notifies an external device, such as a management device for the equipment where the mobile object 600 is located, of the detection. Furthermore, when the administrator removes the foreign object and receives a signal from the external device to resume power supply, the control circuit 19 simply resumes the power supply from the power supply circuit 10 to the transmitting coil 14.

[0093] Thus, those skilled in the art can make various changes in accordance with the embodiments within the scope of the present invention.

[0094] Explanation of Figure Numbers

[0095] 1: Contactless power supply device

[0096] 2: Power transmission device

[0097] 10: Power supply circuit

[0098] 11: Full-wave rectifier circuit

[0099] 12: Power factor improvement circuit

[0100] 13: Inverter

[0101] 13-1 to 13-4: Switching elements

[0102] 14: Transmitting coil

[0103] 15: First capacitor

[0104] 16: Second capacitor

[0105] 17: First coil

[0106] 18: Current detection circuit

[0107] 19: Control circuit

[0108] 3: Power receiving device

[0109] 20: Resonance Circuit

[0110] 21: Receiving coil

[0111] 22: Resonant capacitor

[0112] 23: Rectification and smoothing circuit

[0113] 24: DC-DC converter

[0114] 25: Smoothing capacitor

[0115] 26: Periodic signal generation circuit

[0116] 27: Resonance suppression coil

[0117] 28: Switching Circuit

[0118] 29: Switch control circuit

[0119] 4: Load circuit

[0120] 600: 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 that determines the presence or absence of a foreign object that affects power transmission from the power transmitting device to the power receiving device based on the detected current, 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 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 to be short-circuited or open; as well as a switch control circuit that controls the switch circuit according to the power output from the rectifier circuit so as to repeatedly short-circuit and open the resonance suppression coil; The control circuit of the power transmitting device determines the presence or absence of the foreign object based on an average value of the current flowing through the first switching element during a period in which the resonance suppression coil of the power receiving device is short-circuited.

2. The contactless power supply device according to claim 1, wherein the control circuit of the power transmitting device determines that the foreign object is present when the average value of the current is greater than a predetermined detection threshold value over a period corresponding to a predetermined number of repeated cycles of short-circuiting and opening the resonance suppression coil of the power receiving device.

3. The contactless power supply device according to claim 2, wherein the power receiving device further comprises a periodic signal generating circuit configured to generate a periodic signal having the repetitive period based on the power output from the rectifier circuit. The switch control circuit controls the switch circuit based on the periodic signal so as to repeatedly short-circuit and open the resonance suppression coil in the repetitive cycle.

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