Power reception device and non-contact power supply system

Abstract

The present invention appropriately suppresses an excessive increase in current flowing through a battery.　A power reception device (3) comprises: a resonance circuit (33) having a power reception coil (34) and a resonance capacitor (35); a rectification circuit (36); a second smoothing capacitor (45b); a battery (80) connected to the second smoothing capacitor; a current detection unit (51) that detects the current flowing through the battery; and an adjustment unit (52) that adjusts the current flowing through the battery on the basis of the detected current.

Description

Power receiving device and wireless power supply system

[0001] The present invention relates to a power receiving device and a contactless power supply system.

[0002] Patent Document 1 discloses a contactless power transfer device. The power receiving device of this contactless power transfer device includes a sub-coil arranged to be electromagnetically coupled to the receiving coil, a second rectifier circuit connected to the sub-coil, a smoothing capacitor, and a voltage detection circuit. The second rectifier circuit outputs power to the smoothing capacitor when the rectified voltage is higher than the voltage across the smoothing capacitor. The voltage detection circuit measures the output voltage from the smoothing capacitor to the load circuit, and when the output voltage exceeds a threshold, the power receiving device shorts the sub-coil.

[0003] Japanese Patent Publication No. 2020-072604

[0004] In the configuration of Patent Document 1, an excessive increase in output voltage is prevented by monitoring the output voltage from the smoothing capacitor to the load circuit.

[0005] On the other hand, if a battery, rather than a load, is directly connected to the smoothing capacitor of the power receiving device, the output voltage of the smoothing capacitor is clamped by the battery. Therefore, even if the power supplied from the power transmitting device increases excessively, the output voltage of the smoothing capacitor hardly increases, and instead a large current flows into the battery. The configuration of Patent Document 1 cannot prevent excessive current from flowing into the battery.

[0006] An object of one embodiment of the present invention is to provide a power receiving device that can appropriately suppress an excessive increase in current flowing to a battery.

[0007] A power receiving device for contactless power supply according to aspect 1 of the present invention comprises a resonant circuit having a receiving coil that receives power from a power transmitting device and a resonant capacitor connected in series to the receiving coil, a rectifier circuit that rectifies the AC voltage generated in the resonant circuit, a smoothing capacitor connected to the rectifier circuit and smoothing the voltage output from the rectifier circuit, a battery connected to the smoothing capacitor, a current detection unit that detects the current flowing to the battery, and an adjustment unit that adjusts the current flowing to the battery based on the detected current.

[0008] According to the above configuration, even when the output voltage of the smoothing capacitor is clamped by the battery, the current flowing through the battery is detected and the current flowing through the battery is adjusted based on the detected current, thereby making it possible to appropriately prevent the current flowing through the battery from increasing excessively.

[0009] A power receiving device according to a second aspect of the present invention may be configured in the above-described first aspect such that the adjustment unit reduces the current flowing through the battery by changing the resonant frequency of the resonant circuit.

[0010] A power receiving device according to aspect 3 of the present invention may be configured in the above-described aspect 1 to include a transformer having a primary coil connected between one end and the other end of the power receiving coil, a secondary coil having a number of turns less than that of the primary coil, and a switching circuit connected between both ends of the secondary coil and capable of short-circuiting the two ends of the secondary coil, and the adjustment unit may be configured to reduce the current flowing to the battery by conducting the switching circuit.

[0011] According to the above configuration, the resonant frequency of the resonant circuit can be changed by shorting both ends of the secondary coil whose voltage is stepped down by the switching circuit, and therefore the current flowing to the battery can be adjusted by the operation of the power receiving device.

[0012] A power receiving device according to aspect 4 of the present invention may be configured in the above-described aspect 1 to include a switching circuit connected between one end and the other end of the power receiving coil and capable of short-circuiting both ends of the power receiving coil, and the adjustment unit may reduce the current flowing to the battery by conducting the switching circuit.

[0013] According to the above configuration, the resonant frequency of the resonant circuit can be changed by short-circuiting both ends of the power receiving coil using the switching circuit.

[0014] A power receiving device according to aspect 5 of the present invention may be configured in accordance with aspect 1 above, further comprising a transformer having an auxiliary coil electromagnetically coupled to the power receiving coil, a primary coil connected between one end and the other end of the auxiliary coil, and a secondary coil having fewer turns than the primary coil, and a switching circuit connected between both ends of the secondary coil and capable of short-circuiting both ends of the secondary coil, wherein the adjustment unit reduces the current flowing to the battery by conducting the switching circuit.

[0015] According to the above configuration, by short-circuiting both ends of the secondary coil by the switching circuit, the resonant frequency of the resonant circuit can be changed via the auxiliary coil.

[0016] A power receiving device according to aspect 6 of the present invention may be configured in the above-described aspect 1, further comprising an auxiliary coil electromagnetically coupled to the power receiving coil, and a switching circuit connected between both ends of the auxiliary coil and capable of short-circuiting the both ends of the auxiliary coil, and the adjustment unit reduces the current flowing to the battery by conducting the switching circuit.

[0017] According to the above configuration, the resonant frequency of the resonant circuit can be changed by short-circuiting both ends of the auxiliary coil using the switching circuit.

[0018] A power receiving device according to aspect 7 of the present invention may be configured in the above-mentioned aspect 1 such that the adjustment unit reduces the current flowing through the battery by instructing the power transmitting device to reduce the power to be transmitted.

[0019] According to the above configuration, the state in which the power supply is excessive can be resolved by changing the operation of the power transmitting device.

[0020] A power receiving device according to aspect 8 of the present invention may be configured in the above-described aspect 1 to include a resistive element connected between one end of the smoothing capacitor and the battery, and the current detection unit detects the current flowing to the battery by detecting the voltage between both ends of the resistive element.

[0021] A power receiving device according to aspect 9 of the present invention may be configured in the above-described aspect 1 to include a transistor connected between one end of the smoothing capacitor and the battery, and the current detection unit may detect the current flowing to the battery by detecting the voltage between both ends of the transistor in the on state.

[0022] According to the above configuration, the current flowing through the battery can be detected by utilizing the on-resistance of the transistor having another function.

[0023] A power receiving device according to Aspect 10 of the present invention may be configured in the above-described Aspect 1, such that the battery is connected to the smoothing capacitor without passing through a DC-DC converter.

[0024] A contactless power supply system according to an eleventh aspect of the present invention may be configured as in any one of the first to tenth aspects, further comprising the power receiving device and a power transmitting device including a power transmitting coil that supplies power to the power receiving device.

[0025] According to one embodiment of the present invention, an excessive increase in current flowing through a battery can be appropriately suppressed.

[0026] Fig. 1 is a circuit diagram showing the configuration of a contactless power supply system according to an embodiment of the present invention. Fig. 2 is a circuit diagram showing the configuration of a contactless power supply system according to an embodiment of the present invention. Fig. 3 is a circuit diagram showing the configuration of a contactless power supply system according to an embodiment of the present invention. Fig. 4 is a circuit diagram showing the configuration of a contactless power supply system according to an embodiment of the present invention. Fig. 5 is a circuit diagram showing the configuration of a contactless power supply system according to an embodiment of the present invention.

[0027] [First Embodiment] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described with reference to the drawings.

[0028] 1 is a circuit diagram showing the configuration of a contactless power supply system 1 according to this embodiment. The contactless power supply system 1 includes a power transmitting device 2 and a power receiving device 3. The power transmitting device 2 supplies power to the power receiving device 3 in a contactless manner.

[0029] One way to prevent excessive current from flowing into the battery is to install a DC-DC converter between the smoothing capacitor and the battery, but installing a DC-DC converter would increase the size of the power receiving device.

[0030] The power receiving device 3 of this embodiment includes a current detection unit 51 and an adjustment unit 52. The current detection unit 51 detects the current flowing to the battery 80. The adjustment unit 52 adjusts the current flowing to the battery 80 based on the detected current. As a result, even if the power supplied from the power transmission device 2 becomes excessive, the power receiving device 3 can appropriately suppress an excessive increase in the current flowing to the battery 80. The power receiving device 3 does not require a DC-DC converter between the smoothing capacitor and the battery 80. This allows the power receiving device 3 to be made smaller.

[0031] §2 Configuration Example (Configuration of Power Transmission Device 2) The power transmission device 2 includes a first communication unit 21, a power transmission control unit 22, a power source 23, an inverter 24, a coil 25, a first capacitor 26, a second capacitor 27, and a power transmission coil 28. The power source 23 is a DC power source. The inverter 24 is connected to the power source 23 and converts DC voltage into AC voltage. The inverter 24 includes a plurality of switching elements 24a to 24d.

[0032] One end of the coil 25 is connected to one output terminal of the inverter 24. One end of the first capacitor 26 is connected to the other end of the coil 25, and the other end of the first capacitor 26 is connected to the other output terminal of the inverter 24. One end of the second capacitor 27 is connected to the other end of the coil 25.

[0033] One end of the power transmission coil 28 is connected to the other end of the second capacitor 27, and the other end of the power transmission coil 28 is connected to the other output terminal of the inverter 24. The power transmission coil 28 generates an AC magnetic field to supply power to the power receiving device 3 in a wireless manner.

[0034] The first communication unit 21 performs wireless communication with the second communication unit 32 of the power receiving device 3. The first communication unit 21 receives operation information of the power receiving device 3 from the power receiving device 3. The first communication unit 21 outputs the operation information received from the power receiving device 3 to the power transmission control unit 22.

[0035] The power transmission control unit 22 controls the frequency and / or power of the AC voltage output by the inverter 24 by controlling the multiple switching elements 24a to 24d based on operation information of the power receiving device 3. For example, the power transmission control unit 22 controls the average voltage applied to the power transmitting coil 28 by performing phase shift control. In this way, the power transmission control unit 22 controls the power supplied from the power transmitting coil 28 to the power receiving device 3.

[0036] (Configuration of power receiving device 3) The power receiving device 3 includes a current detection unit 51, an adjustment unit 52, a second communication unit 32, a resonant circuit 33, a rectifier circuit 36, a first smoothing capacitor 45a, a second smoothing capacitor 45b, a smoothing coil 46, a resistive element 47, a transformer 38, a switching circuit 40, and a battery 80.

[0037] The resonant circuit 33 has a power receiving coil 34 and a resonant capacitor 35. The power receiving coil 34 receives power from the power transmitting coil 28 of the power transmitting device 2. The resonant capacitor 35 is connected in series to the power receiving coil 34.

[0038] The rectifier circuit 36 ​​rectifies the AC voltage generated in the resonant circuit 33 into a DC voltage. Here, the rectifier circuit 36 ​​is a bridge circuit including multiple diodes, but is not limited to this and may be a circuit including multiple switching elements. The rectifier circuit 36 ​​has a first AC terminal 36a connected to one end of the resonant capacitor 35, a second AC terminal 36b connected to one end of the power receiving coil 34, a positive terminal 36c, and a negative terminal 36d. The rectifier circuit 36 ​​outputs a full-wave rectified DC (pulsating) voltage from the positive terminal 36c and the negative terminal 36d. The negative terminal 36d is connected to ground.

[0039] The first smoothing capacitor 45a is connected between the positive terminal 36c and the negative terminal 36d of the rectifier circuit 36. One end of the smoothing coil 46 is connected to the positive terminal 36c of the rectifier circuit 36 ​​and one end of the first smoothing capacitor 45a. One end of the second smoothing capacitor 45b is connected to the other end of the smoothing coil 46. The other end of the second smoothing capacitor 45b is connected to the positive terminal 36c and the negative terminal 36d of the rectifier circuit 36 ​​and the other end of the first smoothing capacitor 45a. The first smoothing capacitor 45a, the second smoothing capacitor 45b, and the smoothing coil 46 form a smoothing circuit. The smoothing circuit smoothes the voltage output from the rectifier circuit 36. In the smoothing circuit, the first smoothing capacitor 45a and the second smoothing capacitor 45b smooth the voltage output from the rectifier circuit 36. The second smoothing capacitor 45b outputs the smoothed output voltage to the battery 80.

[0040] The battery 80 is a chargeable and dischargeable secondary battery. The positive terminal of the battery 80 is connected to one end of the second smoothing capacitor 45b and the other end of the smoothing coil 46. The negative terminal of the battery 80 is connected to the other end of the second smoothing capacitor 45b via a resistor element 47. The battery 80 is connected to the second smoothing capacitor 45b without going through a DC-DC converter.

[0041] The resistive element 47 is connected between the other end of the second smoothing capacitor 45b and the battery 80. The resistive element 47 is a resistive element for measuring a current flowing through the battery 80.

[0042] The transformer 38 has a primary coil and a secondary coil. The primary coil is connected between one end and the other end of the power receiving coil 34. The number of turns in the secondary coil is smaller than the number of turns in the primary coil. The transformer 38 is a transformer that transforms the voltage input to the primary side to a lower voltage and outputs it to the secondary side.

[0043] The switching circuit 40 is connected across the secondary coil of the transformer 38. The switching circuit 40 switches between a cutoff state (non-conducting) and a short-circuit state (conducting) across the secondary coil of the transformer 38. For example, the switching circuit 40 includes a first switching element 41, which is a transistor, and a second switching element 42, which is also a transistor. The first switching element 41 and the second switching element 42 are connected in series with each other. One end of the first switching element 41 is connected to one end of the secondary coil of the transformer 38. The other end of the first switching element 41 is connected to one end of the second switching element 42. The other end of the second switching element 42 is connected to the other end of the secondary coil of the transformer 38. A node between the first switching element 41 and the second switching element 42 is connected to ground.

[0044] The current detection unit 51 detects the current flowing through the battery 80. Specifically, the voltage of the node between the resistive element 47 and the battery 80 is input to the current detection unit 51. The current detection unit 51 detects the input voltage (= the voltage across the resistive element 47) to detect the current flowing through the resistive element 47, i.e., the current flowing through the battery 80. The current detection unit 51 outputs the value of the detected current to the adjustment unit 52.

[0045] The adjustment unit 52 adjusts the current flowing through the battery 80 based on the detected current. The adjustment unit 52 shorts (conducts) the switching circuit 40 based on the detected current. For example, when the current flowing through the battery 80 is equal to or greater than a current threshold, the adjustment unit 52 switches the first switching element 41 and the second switching element 42 to a conductive state. When the current flowing through the battery 80 is less than the current threshold, the adjustment unit 52 switches the first switching element 41 and the second switching element 42 to a non-conductive state.

[0046] When the current flowing through the battery 80 is less than the current threshold, the adjustment unit 52 notifies the second communication unit 32 that an overcurrent is not occurring. When the current flowing through the battery 80 is equal to or greater than the current threshold, the adjustment unit 52 notifies the second communication unit 32 that an overcurrent is occurring. The adjustment unit 52 may notify the second communication unit 32 of the current flowing through the battery 80. As a result, the adjustment unit 52 instructs the power transmitter 2, via the second communication unit 32, to reduce the power to be transmitted.

[0047] The second communication unit 32 communicates wirelessly with the first communication unit 21 of the power transmission device 2. Based on a notification from the adjustment unit 52, the second communication unit 32 generates operation information for the power receiving device 3 indicating whether an overcurrent is occurring in the power receiving device 3. The second communication unit 32 wirelessly transmits the operation information for the power receiving device 3 to the power transmission device 2. The operation information indicating the occurrence of an overcurrent means an instruction to reduce the power to be transmitted. The operation information may include information about the current flowing through the battery 80.

[0048] (Operation of Contactless Power Transfer System 1) The output of the resonant circuit 33 may increase due to, for example, a change in the relative position between the power transmitting coil 28 and the power receiving coil 34. The output voltage from the second smoothing capacitor 45b is clamped to a substantially constant value by the battery 80, and instead the current flowing to the battery 80 increases.

[0049] In the contactless power transfer system 1 of the present embodiment, when the current flowing through the battery 80 is equal to or greater than the current threshold, the adjustment unit 52 switches the first switching element 41 and the second switching element 42 to the conductive state. This allows the switching circuit 40 to short-circuit both ends of the secondary coil of the transformer 38.

[0050] When both ends of the secondary coil of the transformer 38 are short-circuited, the resonant frequency of the resonant circuit 33 changes. This reduces the power received by the power receiving device 3 from the power transmitting device 2, and also reduces the current flowing from the resonant circuit 33 to the battery 80 via the smoothing circuit. This makes it possible to appropriately prevent the current flowing to the battery 80 from increasing excessively. In the contactless power transfer system 1, the transformer 38 is connected in parallel to the power receiving coil 34. Therefore, the power receiving device 3 can reliably change the resonant frequency of the resonant circuit 33 by using the switching circuit 40 provided on the secondary side of the transformer 38.

[0051] For example, when the contactless power transfer system 1 is used in an automated guided vehicle (AGV) or an autonomous guided vehicle (AMR), a voltage of several kV may be generated across the power receiving coil 34. On the other hand, the voltage across the second smoothing capacitor 45b during normal operation is approximately several tens of volts.

[0052] In the power receiving device 3, the voltage on the secondary side is lowered from the voltage on the primary side by the transformer 38. Therefore, even if the voltage on the primary side (i.e., the voltage across the power receiving coil 34) is high enough that it cannot be controlled by a transistor, the secondary coil can be short-circuited by the switching circuit 40 using a transistor.

[0053] Adjustment of the supplied power via communication causes a delay (for example, about 10 ms) due to the communication. In the contactless power transfer system 1, although the power transmission device 2 controls the amount of power to be supplied, the occurrence of an overcurrent can be prevented by control on the power receiving device 3 side without waiting for adjustment of the supplied power by the power transmission device 2. Therefore, the occurrence of failures due to an overcurrent can be reduced.

[0054] When the current flowing through the battery 80 is less than the current threshold, the adjustment unit 52 turns the first switching element 41 and the second switching element 42 off. That is, while a current within the normal range is supplied to the battery 80, the switching circuit 40 is in an off state. Therefore, no current flows through the secondary coil of the transformer 38. In this case, if the inductance of the primary coil of the transformer 38 is sufficiently larger than the inductance of the receiving coil 34, the transformer 38 has almost no effect on the resonant frequency of the resonant circuit 33. The inductance of the primary coil of the transformer 38 may be 10 times or more the inductance of the receiving coil 34. More preferably, the inductance of the primary coil of the transformer 38 may be 100 times or more the inductance of the receiving coil 34.

[0055] Furthermore, when the current flowing through the battery 80 is equal to or greater than the current threshold, the adjustment unit 52 transmits, via the second communication unit 32, operation information indicating that an overcurrent is occurring in the power receiving device 3 to the power transmitting device 2. That is, the adjustment unit 52 instructs the power transmitting device 2, via the second communication unit 32, to reduce the power to be transmitted.

[0056] When the first communication unit 21 receives operation information indicating that an overcurrent is occurring, the power transmission control unit 22 reduces the voltage (average voltage) applied to the power transmission coil 28 or shifts the frequency from the resonant frequency. As a result, the power transmission control unit 22 reduces the power supplied to the power receiving device 3. This makes it possible to prevent an overcurrent from occurring again when the adjustment unit 52 of the power receiving device 3 returns the switching circuit 40 to the cut-off state.

[0057] (Modification) The switching circuit 40 may have a relay instead of a transistor switching element.

[0058] [Embodiment 2] Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0059] 2 is a circuit diagram showing the configuration of a contactless power supply system 1a according to this embodiment. The contactless power supply system 1a includes a power transmitting device 2 and a power receiving device 3a.

[0060] The power receiving device 3a includes a current detection unit 51, an adjustment unit 52, a second communication unit 32, a resonant circuit 33a, a rectifier circuit 36, a first smoothing capacitor 45a, a second smoothing capacitor 45b, a smoothing coil 46, a resistive element 47, a transformer 38, a switching circuit 40, and a battery 80.

[0061] The resonant circuit 33a includes a first power receiving coil 34a, a second power receiving coil 34b, a first resonant capacitor 35a, and a second resonant capacitor 35b. The first power receiving coil 34a and the second power receiving coil 34b receive power from the power transmitting coil 28 of the power transmitting device 2. For example, the first power receiving coil 34a and the second power receiving coil 34b share a common core. The first power receiving coil 34a, the second power receiving coil 34b, the first resonant capacitor 35a, and the second resonant capacitor 35b are connected in series with each other. The first resonant capacitor 35a is connected between the first power receiving coil 34a and the second power receiving coil 34b. The second power receiving coil 34b is connected between the first resonant capacitor 35a and the second resonant capacitor 35b.

[0062] The primary coil of the transformer 38 is connected in parallel to the first power receiving coil 34a, which is a part of the power receiving coil of the power receiving device 3a. That is, the primary coil is connected between one end and the other end of the first power receiving coil 34a.

[0063] In the wireless power supply system 1a of this embodiment, similarly to the above-described embodiment, when the current flowing through the battery 80 is equal to or greater than the current threshold, the adjustment unit 52 switches the switching circuit 40 to the conductive state. This changes the resonant frequency of the resonant circuit 33a. As a result, the power received by the power receiving device 3a from the power transmitting device 2 decreases, and the current flowing from the resonant circuit 33a to the battery 80 via the smoothing circuit also decreases. This makes it possible to appropriately prevent the current flowing through the battery 80 from increasing excessively.

[0064] For example, if the number of turns of the first power receiving coil 34a and the number of turns of the second power receiving coil 34b are each half the number of turns of the power receiving coil 34 in the first embodiment, the voltage applied to the primary side of the transformer 38 can be halved compared to the first embodiment. This reduces the voltage applied to the transformer 38, allowing the transformer 38 to be made smaller. Furthermore, when the switching circuit 40 is brought into a conductive state and both ends of the secondary coil of the transformer 38 are short-circuited, the current flowing through the switching circuit 40 and the secondary coil can be reduced. This prevents breakdowns in the switching circuit 40.

[0065] Furthermore, the voltage across the first power receiving coil 34a and the voltage across the first resonant capacitor 35a are in opposite phase. Therefore, the absolute value of the voltage across the first power receiving coil 34a and the first resonant capacitor 35a is smaller than the voltage across the first power receiving coil 34a. This makes it possible to reduce the maximum voltage in the resonant circuit 33a. This increases the degree of freedom in wiring design.

[0066] (Modification) In this way, the resonant circuit may have multiple pairs of receiving coils and resonant capacitors. Alternatively, the resonant circuit may have multiple receiving coils and a single resonant capacitor. Even in this case, it is possible to reduce the voltage applied to one receiving coil and the voltage applied to the primary side of the transformer 38.

[0067] [Embodiment 3] Another embodiment of the present invention will be described below. For the sake of convenience, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0068] 3 is a circuit diagram showing the configuration of a contactless power supply system 1b according to this embodiment. The contactless power supply system 1b includes a power transmitting device 2 and a power receiving device 3b.

[0069] The power receiving device 3b includes a current detection unit 51, an adjustment unit 52, a second communication unit 32, a resonant circuit 33a, a rectifier circuit 36, a first smoothing capacitor 45a, a second smoothing capacitor 45b, a smoothing coil 46, a resistive element 47, a switching circuit 40, and a battery 80.

[0070] The switching circuit 40 is connected in parallel to the first power receiving coil 34a. The switching circuit 40 switches between a cut-off state (non-conductive) and a short-circuit state (conductive) across both ends of the first power receiving coil 34a. One end of the first switching element 41 is connected to one end of the first power receiving coil 34a. The other end of the first switching element 41 is connected to one end of the second switching element 42. The other end of the second switching element 42 is connected to the other end of the first power receiving coil 34a. A node between the first switching element 41 and the second switching element 42 is connected to ground.

[0071] The resonant circuit 33a has a first power receiving coil 34a and a second power receiving coil 34b. Therefore, the maximum voltage generated across one first power receiving coil 34a is lower than the maximum voltage generated across the power receiving coil 34 in embodiment 1. Therefore, depending on the application of the contactless power transfer system 1b, conduction / non-conduction across the first power receiving coil 34a can be controlled by a transistor without stepping down the voltage using the transformer 38.

[0072] In the wireless power transfer system 1b of this embodiment, similarly to the above-described embodiment, when the current flowing through the battery 80 is equal to or greater than the current threshold, the adjustment unit 52 switches the switching circuit 40 to the conductive state. This shorts the two ends of the first power receiving coil 34a, changing the resonant frequency of the resonant circuit 33a. This reduces the power received by the power receiving device 3b from the power transmitting device 2, and also reduces the current flowing from the resonant circuit 33a to the battery 80 via the smoothing circuit. This makes it possible to appropriately prevent the current flowing through the battery 80 from increasing excessively.

[0073] [Embodiment 4] Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0074] 4 is a circuit diagram showing the configuration of a contactless power supply system 1c according to this embodiment. The contactless power supply system 1c includes a power transmitting device 2 and a power receiving device 3c.

[0075] The power receiving device 3c includes a current detection unit 51, an adjustment unit 52, a second communication unit 32, a resonant circuit 33, a rectifier circuit 36, a first smoothing capacitor 45a, a second smoothing capacitor 45b, a smoothing coil 46, a resistive element 47, an auxiliary coil 44, a transformer 38, a switching circuit 40, and a battery 80.

[0076] The primary coil of the transformer 38 is connected between one end and the other end of the auxiliary coil 44. The number of turns of the secondary coil is less than the number of turns of the primary coil. The switching circuit 40 is connected between both ends of the secondary coil.

[0077] The auxiliary coil 44 is electromagnetically coupled to the power receiving coil 34. The auxiliary coil 44 and the power receiving coil 34 share a core. That is, at least a portion of the magnetic flux generated in the power receiving coil 34 by the power transmitting coil 28 passes through the auxiliary coil 44. The number of turns of the auxiliary coil 44 is smaller than the number of turns of the power receiving coil 34. Therefore, the voltage generated in the auxiliary coil 44 by the power transmitting coil 28 is lower than the voltage generated in the power receiving coil 34.

[0078] When a voltage is generated in the auxiliary coil 44 by the AC magnetic field generated by the power transmission coil 28, the voltage is further stepped down to a lower voltage by the transformer 38. Because the voltage of the secondary coil is stepped down and low, the conduction / non-conduction can be easily controlled by the switching circuit 40 using a transistor.

[0079] In the wireless power transfer system 1c of this embodiment, similarly to the above-described embodiments, when the current flowing through the battery 80 is equal to or greater than the current threshold, the adjustment unit 52 switches the switching circuit 40 to the conductive state. This short-circuits the secondary coil, and a current also flows through the primary coil due to the voltage of the auxiliary coil 44. Because the auxiliary coil 44 is electromagnetically coupled to the power receiving coil 34, the resonant frequency of the resonant circuit 33 changes. As a result, the power received by the power receiving device 3c from the power transmitting device 2 decreases, and the current flowing from the resonant circuit 33 to the battery 80 via the smoothing circuit also decreases.

[0080] In order to suppress the influence on the resonant frequency of the resonant circuit 33 during normal operation, the inductance of the primary coil of the transformer 38 may be set sufficiently larger than the inductance of the auxiliary coil 44. The inductance of the primary coil of the transformer 38 may be 10 times or more the inductance of the auxiliary coil 44. More preferably, the inductance of the primary coil of the transformer 38 may be 100 times or more the inductance of the auxiliary coil 44.

[0081] [Embodiment 5] Another embodiment of the present invention will be described below. For the sake of convenience, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0082] 5 is a circuit diagram showing the configuration of a contactless power supply system 1d according to this embodiment. The contactless power supply system 1d includes a power transmitting device 2 and a power receiving device 3d.

[0083] The power receiving device 3d includes a current detection unit 51, an adjustment unit 52, a second communication unit 32, a resonant circuit 33, a rectifier circuit 36, a first smoothing capacitor 45a, a second smoothing capacitor 45b, a smoothing coil 46, a resistive element 47, an auxiliary coil 44, a switching circuit 40, and a battery 80.

[0084] In the contactless power transfer system 1d, the switching circuit 40 is connected across the auxiliary coil 44. When the current flowing through the battery 80 is equal to or greater than a current threshold, the adjustment unit 52 switches the switching circuit 40 to a conductive state. This allows the switching circuit 40 to short-circuit the two ends of the auxiliary coil 44. When the two ends of the auxiliary coil 44 are short-circuited, the resonant frequency of the resonant circuit 33, which includes the power receiving coil 34 electromagnetically coupled to the auxiliary coil 44, changes. This reduces the power received by the power receiving device 3d from the power transmitting device 2, and also reduces the current flowing from the resonant circuit 33 to the battery 80 via the smoothing circuit.

[0085] In the contactless power supply system 1d, the voltage generated across the auxiliary coil 44 is lower than the voltage (e.g., several kV) generated across the receiving coil 34, so it is possible to short-circuit the ends of the auxiliary coil 44 with a semiconductor switch.

[0086] Sixth Embodiment Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0087] 6 is a circuit diagram showing the configuration of a contactless power supply system 1e according to this embodiment. The contactless power supply system 1e includes a power transmitter 2 and a power receiver 3e.

[0088] The power receiving device 3e includes a current detection unit 51, an adjustment unit 52, a second communication unit 32, a resonant circuit 33, a rectifier circuit 36, a first smoothing capacitor 45a, a second smoothing capacitor 45b, a smoothing coil 46, a protection transistor 48, a transformer 38, a switching circuit 40, and a battery 80.

[0089] In the contactless power supply system 1e of this embodiment, a protection transistor 48 is connected between the other end of the second smoothing capacitor 45b and the battery 80, instead of the resistive element 47. The protection transistor 48 is, for example, an n-type transistor (MOSFET). The on-resistance of an n-type transistor (resistance in the on state) is relatively small.

[0090] The voltage of the node between the protection transistor 48 and the battery 80 is input to the current detection unit 51. The current detection unit 51 detects the voltage across the protection transistor 48 when the protection transistor 48 is in the on state (conducting state). The current detection unit 51 detects the current flowing through the protection transistor 48, i.e., the current flowing to the battery 80, from the voltage and the on resistance of the protection transistor 48.

[0091] When the current flowing through the battery 80 is equal to or greater than the first current threshold, the adjustment unit 52 switches the first switching element 41 and the second switching element 42 to the conductive state, thereby changing the resonant frequency of the resonant circuit 33. As a result, the power received by the power receiving device 3e from the power transmitting device 2 decreases, and the current flowing from the resonant circuit 33 to the battery 80 via the smoothing circuit also decreases.

[0092] The adjusting unit 52 switches the protection transistor 48 to the off state when the current flowing through the battery 80 is equal to or greater than a second current threshold that is greater than the first current threshold, thereby quickly preventing a large current from flowing through the battery 80 when an abnormality occurs.

[0093] [Example of Implementation by Software] The functions of the contactless power supply systems 1, 1a to 1e (hereinafter referred to as "devices") can be realized by a program for causing a computer to function as the device, and a program for causing a computer to function as each control block of the device (in particular, the first communication unit 21, the power transmission control unit 22, the second communication unit 32, the current detection unit 51, and the adjustment unit 52).

[0094] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The functions described in each of the above embodiments are realized by executing the program using the control device and storage device.

[0095] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0096] Furthermore, some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention. In addition, the functions of the control blocks can also be realized by, for example, a quantum computer.

[0097] [Summary] A power receiving device for contactless power supply according to aspect 1 of the present invention comprises a resonant circuit having a receiving coil that receives power from a power transmitting device and a resonant capacitor connected in series to the receiving coil, a rectifier circuit that rectifies the AC voltage generated in the resonant circuit, a smoothing capacitor connected to the rectifier circuit and smoothing the voltage output from the rectifier circuit, a battery connected to the smoothing capacitor, a current detection unit that detects the current flowing to the battery, and an adjustment unit that adjusts the current flowing to the battery based on the detected current.

[0098] A power receiving device according to a second aspect of the present invention may be configured in the above-described first aspect such that the adjustment unit reduces the current flowing through the battery by changing the resonant frequency of the resonant circuit.

[0099] A power receiving device according to aspect 3 of the present invention may be configured in accordance with aspect 1 or 2 above, to include a transformer having a primary coil connected between one end and the other end of the power receiving coil, a secondary coil having a number of turns less than that of the primary coil, and a switching circuit connected between both ends of the secondary coil and capable of short-circuiting the two ends of the secondary coil, and the adjustment unit may be configured to reduce the current flowing to the battery by conducting the switching circuit.

[0100] A power receiving device according to aspect 4 of the present invention may be configured in accordance with aspect 1 or 2 above, to include a switching circuit connected between one end and the other end of the power receiving coil and capable of short-circuiting both ends of the power receiving coil, and the adjustment unit may reduce the current flowing to the battery by conducting the switching circuit.

[0101] A power receiving device according to aspect 5 of the present invention may be configured in accordance with aspect 1 or 2 above, to include a transformer having an auxiliary coil electromagnetically coupled to the power receiving coil, a primary coil connected between one end and the other end of the auxiliary coil, and a secondary coil having fewer turns than the primary coil, and a switching circuit connected between both ends of the secondary coil and capable of short-circuiting both ends of the secondary coil, and the adjustment unit may be configured to reduce the current flowing to the battery by conducting the switching circuit.

[0102] A power receiving device according to aspect 6 of the present invention may be configured in accordance with aspect 1 or 2 above, to include an auxiliary coil electromagnetically coupled to the power receiving coil, and a switching circuit connected between both ends of the auxiliary coil and capable of short-circuiting the both ends of the auxiliary coil, and the adjustment unit reduces the current flowing to the battery by conducting the switching circuit.

[0103] A power receiving device according to aspect 7 of the present invention may be configured in any one of aspects 1 to 6 above, such that the adjustment unit reduces the current flowing through the battery by instructing the power transmitting device to reduce the power to be transmitted.

[0104] A power receiving device according to aspect 8 of the present invention may be configured in any one of aspects 1 to 7 above, to include a resistive element connected between one end of the smoothing capacitor and the battery, and the current detection unit detects the current flowing to the battery by detecting the voltage between both ends of the resistive element.

[0105] A power receiving device according to aspect 9 of the present invention may be configured in any one of aspects 1 to 7 above, to include a transistor connected between one end of the smoothing capacitor and the battery, and the current detection unit detects the current flowing to the battery by detecting the voltage between both ends of the transistor in the on state.

[0106] A power receiving device according to Aspect 10 of the present invention may be configured in any one of Aspects 1 to 9 above, such that the battery is connected to the smoothing capacitor without passing through a DC-DC converter.

[0107] A contactless power supply system according to an eleventh aspect of the present invention may be configured as in any one of the first to tenth aspects, further comprising the power receiving device and a power transmitting device including a power transmitting coil that supplies power to the power receiving device.

[0108] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0109] REFERENCE SIGNS LIST 1, 1a, 1b, 1c, 1d, 1e Wireless power transfer system 2 Power transmitting device 3, 3a, 3b, 3c, 3d, 3e Power receiving device 21 First communication unit 22 Power transmission control unit 24 Inverter 28 Power transmitting coil 32 Second communication unit 33, 33a Resonant circuit 34 Power receiving coil 34a First power receiving coil 34b Second power receiving coil 35 Resonant capacitor 35a First resonant capacitor 35b Second resonant capacitor 36 Rectifier circuit 38 Transformer 40 Switching circuit 44 Auxiliary coil 45a First smoothing capacitor 45b Second smoothing capacitor 46 Smoothing coil 47 Resistance element 48 Protection transistor 51 Current detection unit 52 Adjustment unit 80 Battery

Claims

1. A power receiving device for contactless power supply, comprising: a resonant circuit having a receiving coil that receives power from a power transmitting device and a resonant capacitor connected in series to the receiving coil; a rectifying circuit that rectifies the AC voltage generated in the resonant circuit; a smoothing capacitor connected to the rectifying circuit and smoothing the voltage output from the rectifying circuit; a battery connected to the smoothing capacitor; a current detection unit that detects the current flowing to the battery; and an adjustment unit that adjusts the current flowing to the battery based on the detected current.

2. The power receiving device according to claim 1, wherein the adjustment unit reduces the current flowing to the battery by changing the resonant frequency of the resonant circuit.

3. A power receiving device as described in claim 1, comprising: a transformer having a primary coil connected between one end and the other end of the power receiving coil, and a secondary coil having a number of turns less than that of the primary coil; and a switching circuit connected between both ends of the secondary coil and capable of short-circuiting both ends of the secondary coil, wherein the adjustment unit reduces the current flowing to the battery by conducting the switching circuit.

4. The power receiving device according to claim 1, further comprising a switching circuit connected between one end and the other end of the power receiving coil and capable of short-circuiting both ends of the power receiving coil, wherein the adjustment unit reduces the current flowing to the battery by conducting the switching circuit.

5. The power receiving device according to claim 1, further comprising: an auxiliary coil electromagnetically coupled to the power receiving coil; a transformer having a primary coil connected between one end and the other end of the auxiliary coil; and a secondary coil having a number of turns less than that of the primary coil; and a switching circuit connected across both ends of the secondary coil and capable of short-circuiting both ends of the secondary coil, wherein the adjustment unit reduces the current flowing to the battery by conducting the switching circuit.

6. The power receiving device according to claim 1, further comprising: an auxiliary coil electromagnetically coupled to the power receiving coil; and a switching circuit connected across both ends of the auxiliary coil and capable of short-circuiting both ends of the auxiliary coil, wherein the adjustment unit reduces the current flowing to the battery by conducting the switching circuit.

7. The power receiving device according to claim 1, wherein the adjustment unit reduces the current flowing through the battery by instructing the power transmitting device to reduce the power to be transmitted.

8. The power receiving device according to claim 1, further comprising a resistive element connected between one end of the smoothing capacitor and the battery, wherein the current detection unit detects the current flowing through the battery by detecting the voltage across the resistive element.

9. The power receiving device according to claim 1, further comprising a transistor connected between one end of the smoothing capacitor and the battery, wherein the current detection unit detects the current flowing to the battery by detecting the voltage across the transistor in an on state.

10. The power receiving device according to claim 1, wherein the battery is connected to the smoothing capacitor without passing through a DC-DC converter.

11. A contactless power supply system comprising: a power receiving device according to any one of claims 1 to 10; and a power transmitting device having a power transmitting coil that supplies power to the power receiving device.

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