Power reception device and non-contact power supply system

Abstract

The present invention appropriately suppresses an excessive increase in voltage generated in a power reception coil.　A power reception device (3) comprises: a resonance circuit (33) having a power reception coil (34) and a resonance capacitor (35); a first rectification circuit (36) that rectifies an AC voltage generated in the resonance circuit; a smoothing capacitor (37) connected to the first rectification circuit; a transformer (38) having a primary coil connected between one end and the other end of the power reception coil; and a second rectification circuit (39) that is connected to a secondary coil and outputs the rectified voltage to the smoothing capacitor.

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 supply device. The power receiving device of this contactless power supply device includes a sub-coil arranged to be electromagnetically coupled to a receiving coil, a second rectifier circuit connected to the sub-coil, and a smoothing capacitor. The second rectifier circuit outputs power to the smoothing capacitor when the rectified voltage is higher than the voltage across the smoothing capacitor.

[0003] Japanese Patent Publication No. 2020-072604

[0004] In the configuration of Patent Document 1, under normal circumstances, the voltage rectified by the second rectifier circuit needs to be lower than the voltage rectified by the first rectifier circuit, and therefore, in order to realize the configuration of Patent Document 1, the number of turns of the receiving coil needs to be very large, which has the problem of limiting the cases in which it can be applied.

[0005] An object of one embodiment of the present invention is to provide a power receiving device that can appropriately suppress an excessive increase in voltage generated in a power receiving coil.

[0006] A power receiving device for contactless power supply according to aspect 1 of the present invention comprises a resonant circuit having a first power receiving coil that receives power from a power transmitting device and a first resonant capacitor connected in series to the first power receiving coil, a first rectifier circuit that rectifies the AC voltage generated in the resonant circuit, a smoothing capacitor connected to the first rectifier circuit and smoothing the voltage output from the first rectifier circuit, a transformer having a primary coil connected between one end and the other end of the first power receiving coil or the first resonant capacitor and a secondary coil with fewer turns than the number of turns of the primary coil, and a second rectifier circuit connected to the secondary coil and outputting the rectified voltage to the smoothing capacitor.

[0007] According to the above configuration, when the smoothing capacitor is not sufficiently charged, the voltage stepped down by the transformer is output to the smoothing capacitor via the second rectifier circuit, which changes the resonant frequency of the resonant circuit. This makes it possible to prevent the voltage generated in the first power receiving coil from increasing excessively.

[0008] 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 inductance of the primary coil is 10 times or more the inductance of the first power receiving coil.

[0009] According to the above configuration, it is possible to suppress the influence of the transformer on the resonant frequency of the resonant circuit during constant voltage output operation.

[0010] A power receiving device for contactless power supply according to aspect 3 of the present invention comprises a resonant circuit having a first power receiving coil that receives power from a power transmitting device and a first resonant capacitor connected in series to the first power receiving coil, a first rectifier circuit that rectifies the AC voltage generated in the resonant circuit, a smoothing capacitor connected to the first rectifier circuit and smoothing the voltage output from the first rectifier circuit, an auxiliary coil electromagnetically coupled to the first 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 with fewer turns than the number of turns of the primary coil, and a second rectifier circuit connected to the secondary coil and outputting the rectified voltage to the smoothing capacitor.

[0011] A power receiving device according to a fourth aspect of the present invention may be configured in the third aspect described above, such that the inductance of the primary coil is 10 times or more the inductance of the auxiliary coil.

[0012] A power receiving device according to a fifth aspect of the present invention may be configured in any one of the first to fourth aspects above, further comprising a switching circuit connected across the secondary coil and capable of short-circuiting the two ends of the secondary coil.

[0013] According to the above configuration, the switching circuit can short-circuit the secondary side of the transformer, where the voltage is stepped down. Therefore, when an abnormality occurs, the resonant frequency of the resonant circuit can be changed by short-circuiting the secondary side of the transformer. This reduces the received power and suppresses overvoltage.

[0014] A power receiving device according to a sixth aspect of the present invention may be configured in accordance with the fifth aspect described above, further comprising a short-circuit control circuit that short-circuits the switching circuit based on an output voltage from the smoothing capacitor.

[0015] According to the above configuration, an excessive increase in the output voltage of the smoothing capacitor can be suppressed.

[0016] A power receiving device according to aspect 7 of the present invention may be configured in the above-mentioned aspect 1 or 2 such that the resonant circuit has a second power receiving coil connected in series to the first power receiving coil and receiving power from the power transmitting device, and the primary coil is connected between one end and the other end of the first power receiving coil.

[0017] According to the above configuration, the voltage applied to the primary coil of the transformer can be reduced, thereby enabling the transformer to be made smaller.

[0018] A power receiving device according to an eighth aspect of the present invention may be configured in the seventh aspect above, wherein the resonant circuit includes a second resonant capacitor connected between the first power receiving coil and the second power receiving coil.

[0019] According to the above configuration, the maximum voltage generated in the resonant circuit can be reduced, thereby increasing the degree of freedom in wiring design.

[0020] A power receiving device according to aspect 9 of the present invention may be configured in the above-mentioned aspect 1 or 2 such that the resonant circuit has a second resonant capacitor connected in series to the first resonant capacitor, and the primary coil is connected between one end and the other end of the first resonant capacitor.

[0021] The power receiving device according to Aspect 10 of the present invention may be configured in accordance with Aspects 3 or 4 above, further comprising a switching circuit connected across both ends of the auxiliary coil and capable of short-circuiting both ends of the auxiliary coil.

[0022] According to the above configuration, the current flowing through the switching circuit can be reduced, thereby preventing failure of the switching circuit.

[0023] 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 fourth 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.

[0024] According to one aspect of the present invention, it is possible to appropriately prevent the voltage generated in the power receiving coil from increasing excessively.

[0025] Fig. 1 is a circuit diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention. Fig. 2 is a circuit diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention. Fig. 3 is a diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention. Fig. 4 is a diagram showing the results of a simulation of voltage changes immediately after power supply starts in the contactless power supply system. Fig. 5 is a diagram showing the relationship between output voltage and output current in a simulation when the supplied power is increased during normal operation. Fig. 6 is a circuit diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention.

[0026] [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.

[0027] 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.

[0028] Before power supply starts, the smoothing capacitor 37 of the power receiving device 3 is not charged. When power is supplied from the power transmitting device 2 at the resonant frequency of the resonant circuit 33 while the smoothing capacitor 37 is not charged, a very large voltage is generated across the power receiving coil 34 and across the resonant capacitor 35 due to resonance.

[0029] The contactless power transfer system 1 includes a transformer 38 connected in parallel to the power receiving coil 34. When the smoothing capacitor 37 is not sufficiently charged, the voltage stepped down by the transformer 38 is output to the smoothing capacitor 37 via a second rectifier circuit 39. This changes the resonant frequency of the resonant circuit 33. This makes it possible to prevent the voltage generated in the power receiving coil 34 from rising excessively. Because the transformer 38 can step down the voltage, the design freedom of the power receiving coil 34 is also increased.

[0030] §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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] (Configuration of Power Receiving Device 3 ) The power receiving device 3 includes a voltage determining unit 31 , a second communication unit 32 , a resonant circuit 33 , a first rectifying circuit 36 ​​, a smoothing capacitor 37 , a transformer 38 , a second rectifying circuit 39 , a switching circuit 40 , and a load 90 .

[0036] 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.

[0037] The first rectifier circuit 36 ​​rectifies the AC voltage generated in the resonant circuit 33 into a DC voltage. Here, the first rectifier circuit 36 ​​is a bridge circuit including a plurality of diodes, but is not limited to this and may be a circuit including a plurality of switching elements. The first 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 first rectifier circuit 36 ​​outputs a full-wave rectified DC (pulsating) voltage from the positive terminal 36c and the negative terminal 36d.

[0038] The smoothing capacitor 37 is connected between the positive terminal 36c and the negative terminal 36d of the first rectifier circuit 36. The smoothing capacitor 37 smoothes the voltage output from the first rectifier circuit 36. The smoothing capacitor 37 outputs the smoothed output voltage to the load 90.

[0039] 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.

[0040] The second rectifier circuit 39 rectifies the AC voltage on the secondary side of the transformer 38 into a DC voltage. The second rectifier circuit 39 is connected to the secondary coil of the transformer 38. Here, the second rectifier circuit 39 is a bridge circuit including multiple diodes, but is not limited to this and may be a circuit including multiple switching elements. The second rectifier circuit 39 has a first AC terminal 39a connected to one end of the secondary coil of the transformer 38, a second AC terminal 39b connected to the other end of the secondary coil of the transformer 38, a positive terminal 39c, and a negative terminal 39d. The positive terminal 39c is connected to one end of the smoothing capacitor 37. The negative terminal 39d is connected to the other end of the smoothing capacitor 37. The second rectifier circuit 39 outputs a full-wave rectified DC (pulsating) voltage to the smoothing capacitor 37 from the positive terminal 39c and the negative terminal 39d.

[0041] 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. 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 the negative terminal 36d of the first rectifier circuit 36.

[0042] The voltage determination unit 31 detects the output voltage output from the smoothing capacitor 37 to the load 90 and determines whether the output voltage is equal to or greater than a voltage threshold. The voltage determination unit 31 (short-circuit control circuit) shorts (conducts) the switching circuit 40 based on the output voltage. For example, if the output voltage is equal to or greater than the voltage threshold, the voltage determination unit 31 switches the first switching element 41 and the second switching element 42 to a conductive state. If the output voltage is less than the voltage threshold, the voltage determination unit 31 switches the first switching element 41 and the second switching element 42 to a non-conductive state.

[0043] If the output voltage is less than the voltage threshold, the voltage determination unit 31 notifies the second communication unit 32 that no overvoltage is occurring. If the output voltage is equal to or greater than the voltage threshold, the voltage determination unit 31 notifies the second communication unit 32 that an overvoltage is occurring. The voltage determination unit 31 may notify the second communication unit 32 of the output voltage.

[0044] The second communication unit 32 performs wireless communication with the first communication unit 21 of the power transmission device 2. Based on the notification from the voltage determination unit 31, the second communication unit 32 generates operation information of the power reception device 3 indicating whether an overvoltage is occurring in the power reception device 3. The second communication unit 32 wirelessly transmits the operation information of the power reception device 3 to the power transmission device 2. The operation information may include information on the output voltage.

[0045] (Operation of Contactless Power Transfer System 1) Before power transfer begins, the smoothing capacitor 37 of the power receiving device 3 is not charged. As power transfer begins, charging of the smoothing capacitor 37 begins, and the output voltage rises. Therefore, immediately after power transfer begins, current from the first rectifier circuit 36 ​​flows into the smoothing capacitor 37, so the load resistance seen from the resonant circuit 33 approaches zero. In the case of a series resonant circuit in which the power receiving coil 34 and the resonant capacitor 35 are connected in series, the smaller the load resistance of the resonant circuit, the larger the Q value, which represents the sharpness of the resonance peak. When the load resistance of the power receiving device 3 approaches zero and the power transmitting device 2 transfers power at the resonant frequency of the resonant circuit 33, extremely large voltages are generated across the power receiving coil 34 and the resonant capacitor 35 due to resonance. To prevent this overvoltage, the power transmitting device 2 starts power transfer at a frequency different from the resonant frequency at the start of power transfer and gradually approaches the frequency to the resonant frequency, or gradually increases the voltage applied to the power transmitting coil 28 by controlling the phase shift amount.

[0046] However, there may be cases where the power transmitter 2 supplies power at the resonant frequency of the resonant circuit 33 when the load resistance of the power receiver 3 is close to zero for some reason, such as (i) when the positional relationship between the power transmitter 2 and the power receiver 3 changes, (ii) when the switching circuit in the power receiver 3 is short-circuited and then cut off again for overvoltage protection, and (iii) when a short circuit occurs in the load 90.

[0047] In the contactless power transfer system 1 of this embodiment, when power transfer from the power transmission device 2 begins, a voltage is generated across the power receiving coil 34. The same voltage across the power receiving coil 34 is applied to the primary coil of the transformer 38. The voltage across the primary coil is stepped down in accordance with the turns ratio of the transformer 38 and output from the secondary coil. The second rectifier circuit 39 outputs the stepped-down voltage to the smoothing capacitor 37. When the smoothing capacitor 37 is not sufficiently charged immediately after power transfer begins, the voltage output from the second rectifier circuit 39 is higher than the output voltage of the smoothing capacitor 37. Therefore, a current flows from the secondary coil of the transformer 38 to the smoothing capacitor 37 via the second rectifier circuit 39. That is, a current corresponding to the current flowing through the secondary coil also flows from the power receiving coil 34 to the primary coil of the transformer 38. In this state, the path of the transformer 38 and the second rectifier circuit 39 is added to the resonant circuit 33, so the resonant frequency of the resonant circuit 33 deviates from the original resonant frequency of the resonant circuit 33 itself. Therefore, even if the power transmitting device 2 supplies power at the resonant frequency of the resonant circuit 33 when the smoothing capacitor 37 is not sufficiently charged, resonance does not occur in the resonant circuit 33. Therefore, the contactless power transfer system 1 can appropriately suppress an excessive increase in the voltage generated across the power receiving coil 34.

[0048] Adjustment of the supplied power via communication involves 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 overvoltage 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 overvoltage can be reduced.

[0049] After a certain period of time has elapsed since the start of power supply, the smoothing capacitor 37 is sufficiently charged, and the power receiving device 3 performs normal constant voltage output operation to the load 90. When the smoothing capacitor 37 is sufficiently charged, the winding ratio of the transformer 38 is set so that the secondary voltage stepped down by the transformer 38 is lower than the output voltage of the smoothing capacitor 37. Therefore, during constant voltage output operation, power is not supplied from the second rectifier circuit 39 to the smoothing capacitor 37, and power is supplied only from the first rectifier circuit 36 ​​to the smoothing capacitor 37. Therefore, no current flows through the secondary coil of the transformer 38. If the inductance of the primary coil of the transformer 38 is sufficiently larger than the inductance of the power 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 power 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 power receiving coil 34 .

[0050] When the output voltage of the smoothing capacitor 37 is less than the voltage threshold, the voltage determination unit 31 turns off the first switching element 41 and the second switching element 42. That is, the switching circuit 40 is in the cut-off state while the normal constant voltage output operation is being performed immediately after the start of power supply.

[0051] On the other hand, a change in the relative position between the power transmitting coil 28 and the power receiving coil 34, for example, may increase the output of the resonant circuit 33, causing an overvoltage in the smoothing capacitor 37. When the output voltage is equal to or greater than a voltage threshold, the voltage determination unit 31 switches the first switching element 41 and the second switching element 42 to a conductive state. This allows the switching circuit 40 to short-circuit both ends of the secondary coil of the transformer 38. The voltage threshold is set to a value higher than the output voltage during constant voltage output operation.

[0052] 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 voltage output from the resonant circuit 33 to the smoothing capacitor 37. This reduces the output voltage of the smoothing capacitor 37, making it possible to suppress overvoltage. 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 a switching circuit 40 provided on the secondary side of the transformer 38.

[0053] Furthermore, when the output voltage of the smoothing capacitor 37 is equal to or greater than the voltage threshold, the second communication unit 32 transmits, to the power transmission device 2 , operation information indicating that an overvoltage is occurring in the power reception device 3 .

[0054] When the first communication unit 21 receives operation information indicating that an overvoltage has occurred, the power transmission control unit 22 reduces the 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 overvoltage from occurring again when the voltage determination unit 31 of the power receiving device 3 returns the switching circuit 40 to the cut-off state.

[0055] (Modification) The switching circuit 40 may have a relay instead of a transistor switching element.

[0056] [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.

[0057] 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.

[0058] The power receiving device 3 a includes a voltage determination unit 31 , a second communication unit 32 , a resonance circuit 33 a , a first rectifier circuit 36 ​​, a smoothing capacitor 37 , a transformer 38 , a second rectifier circuit 39 , a switching circuit 40 , and a load 90 .

[0059] 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.

[0060] 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.

[0061] In the wireless power transfer system 1a of this embodiment, similarly to the above-described embodiment, when the smoothing capacitor 37 is not sufficiently charged, a current flows from the transformer 38 to the smoothing capacitor 37 via the second rectifier circuit 39. This changes the resonant frequency of the resonant circuit 33a. Therefore, it is possible to appropriately prevent the voltages generated across the first power receiving coil 34a and the second power receiving coil 34b from increasing excessively.

[0062] 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.

[0063] 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.

[0064] (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.

[0065] [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.

[0066] 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.

[0067] The power receiving device 3 b includes a voltage determination unit 31 , a second communication unit 32 , a resonance circuit 33 , a first rectifier circuit 36 ​​, a smoothing capacitor 37 , a transformer 38 , a second rectifier circuit 39 , a switching circuit 40 , an auxiliary coil 44 , and a load 90 .

[0068] 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 first rectifier circuit 36 ​​rectifies the AC voltage generated in the resonant circuit 33 into a DC voltage.

[0069] 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 smaller than the number of turns of the primary coil. The second rectifier circuit 39 is connected to the secondary coil of the transformer 38. The switching circuit 40 is connected across the auxiliary coil 44.

[0070] 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.

[0071] When a voltage is generated in the auxiliary coil 44 by the AC magnetic field generated by the power transmitting coil 28, the voltage is further reduced by the transformer 38. If the voltage rectified by the second rectifier circuit 39 is higher than the voltage of the smoothing capacitor 37, a current flows from the secondary coil of the transformer 38 to the smoothing capacitor 37 via the second rectifier circuit 39. A current corresponding to the current flowing in the secondary coil also flows from the auxiliary coil 44 to the primary coil of the transformer 38. The auxiliary coil 44 is electromagnetically coupled to the power receiving coil 34. Therefore, in this state, the path of the auxiliary coil 44, the transformer 38, and the second rectifier circuit 39 is added to the resonant circuit 33, and the resonant frequency of the power receiving device 3b deviates from the resonant frequency of the resonant circuit 33 itself. Therefore, even if the power transmitting device 2 supplies power at the resonant frequency of the resonant circuit 33 when the smoothing capacitor 37 is not sufficiently charged, no resonance occurs in the resonant circuit 33. Therefore, according to the contactless power feeding system 1b, it is possible to appropriately prevent the voltage generated across the power receiving coil 34 from increasing excessively.

[0072] For example, when the contactless power transfer system 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 of the smoothing capacitor 37 during constant voltage output operation is approximately several tens of volts.

[0073] If the second rectifier circuit 39 is connected to the auxiliary coil 44 without using the transformer 38, the voltage generated in the auxiliary coil 44 needs to be reduced to several tens of volts depending on the ratio of the turns of the receiving coil 34 and the auxiliary coil 44. To suppress the above-mentioned overvoltage, a certain degree of coupling between the auxiliary coil 44 and the receiving coil 34 is necessary. Therefore, there is a lower limit to the number of turns of the auxiliary coil 44. In other words, it becomes necessary to increase the number of turns of the receiving coil 34, which results in an increase in the size of the resonant circuit.

[0074] In the contactless power transfer system 1b, a voltage lower than that of the power receiving coil 34 is generated by the electromagnetically coupled auxiliary coil 44, and this voltage is further stepped down by the transformer 38 and supplied to the smoothing capacitor 37. Because the voltage can be stepped down by the transformer 38, it is not necessary to make the turns ratio of the power receiving coil 34 and the auxiliary coil 44 extremely large. This makes it possible to prevent the power receiving coil 34 from becoming too large.

[0075] In the contactless power transfer system 1b, the switching circuit 40 is connected across the auxiliary coil 44. When the output voltage of the smoothing capacitor 37 is equal to or greater than the voltage threshold, the voltage determination unit 31 switches the first switching element 41 and the second switching element 42 to a conductive state. This allows the switching circuit 40 to short-circuit the auxiliary coil 44. When the auxiliary coil 44 is 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 also reduces the voltage output from the resonant circuit 33 to the smoothing capacitor 37. This makes it possible to suppress overvoltage across the smoothing capacitor 37. In the contactless power transfer system 1b, the voltage across the auxiliary coil 44 is lower than the voltage across the power receiving coil 34 (e.g., several kV), so it is possible to short-circuit the auxiliary coil 44 with a semiconductor switch.

[0076] The switching circuit 40 may be provided across the secondary coil of the transformer 38, as in the above-described embodiment. However, the current is larger on the secondary side of the transformer 38 than on the primary side. Therefore, short-circuiting the primary side of the transformer 38, as in the contactless power transfer system 1b, can reduce the short-circuit current flowing through the switching circuit 40.

[0077] In order to suppress the influence on the resonant frequency of the resonant circuit 33 during normal constant voltage output operation, the inductance of the primary coil of the transformer 38 may be made 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.

[0078] 4 shows simulation results of voltage changes immediately after the start of power supply in the contactless power supply system 1b. The graph indicated by reference numeral 401 shows voltage changes in a comparative example in which the auxiliary coil 44, transformer 38, second rectifier circuit 39, and switching circuit 40 are removed from the contactless power supply system 1b. The graph indicated by reference numeral 402 shows voltage changes in the contactless power supply system 1b. The blackened areas in the graph represent the AC voltage generated across the power receiving coil 34. The horizontal axis represents the time (ms) from the start of power supply. The vertical axis represents voltage (kV). The output voltage of the smoothing capacitor 37 is also shown in solid line at the top of the graph, but the scale of the vertical axis is different.

[0079] The simulation was performed under the conditions that the smoothing capacitor 37 was not charged before the start of power feeding, and that the power transmitting device 2 started power transmission at the resonant frequency of the resonant circuit 33 from the beginning.

[0080] In the comparative example indicated by reference numeral 401, the voltage across the receiving coil 34 rose sharply immediately after the start of power supply. The difference between the maximum and minimum voltage amplitudes was approximately 7 kV. Accordingly, 10 ms after the start, the output voltage of the smoothing capacitor 37 also rose to a value higher than the voltage during constant voltage output operation.

[0081] In the contactless power transfer system 1b of this embodiment, indicated by the reference numeral 402, an excessive rise in the voltage occurring across the power receiving coil 34 immediately after the start of power transfer is suppressed. The difference between the maximum and minimum amplitudes of this voltage is approximately 2.6 kV. The output voltage of the smoothing capacitor 37 also rises gently without exceeding the voltage during constant voltage output operation. In this way, the contactless power transfer system 1b suppresses an excessive rise in the voltage of the power receiving coil 34 and the smoothing capacitor 37 at the start of power transfer, achieving the effect of soft starting.

[0082] 5 is a diagram showing the relationship between output voltage and output current in a simulation in which the supply power is increased during normal operation. The graph indicated by reference numeral 501 shows the voltage-current characteristics of a comparative example in which the auxiliary coil 44, transformer 38, second rectifier circuit 39, and switching circuit 40 are removed from the contactless power transfer system 1b. The graph indicated by reference numeral 502 shows the voltage-current characteristics of the contactless power transfer system 1b. The horizontal axis represents the output current (A) output by the first rectifier circuit 36. The vertical axis represents the output voltage (V) output by the first rectifier circuit 36.

[0083] The simulation was performed under the conditions that the power supply from the power transmission device 2 was gradually increased from that during normal operation, that the power transmission device 2 transmitted power at the resonant frequency of the resonant circuit 33, and that the switching circuit 40 was not operating (was in a cut-off state).

[0084] In the comparative example indicated by reference numeral 501, as the supplied power was increased, the output current increased without limit.

[0085] In the contactless power transfer system 1b of this embodiment, indicated by the reference numeral 502, as the supply power is increased, current begins to flow from the auxiliary coil 44 via the second rectifier circuit 39 at a certain point. This changes the resonance conditions, causing the output voltage from the first rectifier circuit 36 ​​to drop sharply, and the output current no longer flows above a certain value. In other words, the circuit including the auxiliary coil 44, transformer 38, and second rectifier circuit 39 in the contactless power transfer system 1b also serves to protect the power receiving device 3b from overcurrent. In this way, the contactless power transfer system 1b can suppress overcurrent on the power receiving device 3b side without adjusting the supply power on the power transmitting device 2 side through communication. In other words, overcurrent can be suppressed even in a configuration that omits the switching circuit 40.

[0086] [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.

[0087] 6 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.

[0088] The power receiving device 3 c includes a voltage determination unit 31 , a second communication unit 32 , a resonance circuit 33 a , a first rectifier circuit 36 ​​, a smoothing capacitor 37 , a transformer 38 , a second rectifier circuit 39 , a switching circuit 40 , and a load 90 .

[0089] The primary coil of the transformer 38 is connected in parallel to the first resonant capacitor 35a, which is part of the resonant circuit 33a, i.e., between one end and the other end of the first resonant capacitor 35a.

[0090] In the wireless power transfer system 1c of this embodiment, similarly to the above-described embodiments, when the smoothing capacitor 37 is not sufficiently charged, a current flows from the transformer 38 to the smoothing capacitor 37 via the second rectifier circuit 39. This changes the resonant frequency of the resonant circuit 33a. This makes it possible to appropriately prevent the voltages generated across the first power receiving coil 34a and the second power receiving coil 34b from increasing excessively.

[0091] Furthermore, similarly to the second embodiment, the contactless power supply system 1c of the present embodiment can reduce the voltage applied to the primary side of the transformer 38 compared to the configuration of the first embodiment. Therefore, the transformer 38 can be made smaller.

[0092] (Modification) The resonant circuit may have multiple pairs of receiving coils and resonant capacitors. Alternatively, the resonant circuit may have a single receiving coil and multiple resonant capacitors. Even in this case, the voltage applied to one resonant capacitor and the voltage applied to the primary side of the transformer 38 can be reduced.

[0093] [Example of implementation by software] The functions of the contactless power supply systems 1, 1a, 1b (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 voltage determination unit 31, and the second communication unit 32).

[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 first power receiving coil that receives power from a power transmitting device and a first resonant capacitor connected in series to the first power receiving coil, a first rectifier circuit that rectifies the AC voltage generated in the resonant circuit, a smoothing capacitor connected to the first rectifier circuit and smoothing the voltage output from the first rectifier circuit, a transformer having a primary coil connected between one end and the other end of the first power receiving coil or the first resonant capacitor and a secondary coil with fewer turns than the number of turns of the primary coil, and a second rectifier circuit connected to the secondary coil and outputting the rectified voltage to the smoothing capacitor.

[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 inductance of the primary coil is 10 times or more the inductance of the first power receiving coil.

[0099] A power receiving device for contactless power supply according to aspect 3 of the present invention comprises a resonant circuit having a first power receiving coil that receives power from a power transmitting device and a first resonant capacitor connected in series to the first power receiving coil, a first rectifier circuit that rectifies the AC voltage generated in the resonant circuit, a smoothing capacitor connected to the first rectifier circuit and smoothing the voltage output from the first rectifier circuit, an auxiliary coil electromagnetically coupled to the first 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 with fewer turns than the number of turns of the primary coil, and a second rectifier circuit connected to the secondary coil and outputting the rectified voltage to the smoothing capacitor.

[0100] A power receiving device according to a fourth aspect of the present invention may be configured in the third aspect described above, such that the inductance of the primary coil is 10 times or more the inductance of the auxiliary coil.

[0101] A power receiving device according to a fifth aspect of the present invention may be configured in any one of the first to fourth aspects above, further comprising a switching circuit connected across the secondary coil and capable of short-circuiting the two ends of the secondary coil.

[0102] A power receiving device according to a sixth aspect of the present invention may be configured in accordance with the fifth aspect described above, further comprising a short-circuit control circuit that short-circuits the switching circuit based on an output voltage from the smoothing capacitor.

[0103] A power receiving device according to aspect 7 of the present invention may be configured as in aspect 1 or 2 above, wherein the resonant circuit has a second power receiving coil connected in series to the first power receiving coil, and the primary coil is connected between one end and the other end of the first power receiving coil.

[0104] A power receiving device according to an eighth aspect of the present invention may be configured in the seventh aspect above, wherein the resonant circuit includes a second resonant capacitor connected between the first power receiving coil and the second power receiving coil.

[0105] A power receiving device according to aspect 9 of the present invention may be configured in the above-mentioned aspect 1 or 2 such that the resonant circuit has a second resonant capacitor connected in series to the first resonant capacitor, and the primary coil is connected between one end and the other end of the first resonant capacitor.

[0106] The power receiving device according to Aspect 10 of the present invention may be configured in accordance with Aspects 3 or 4 above, further comprising a switching circuit connected across both ends of the auxiliary coil and capable of short-circuiting both ends of the auxiliary coil.

[0107] A contactless power supply system according to an eleventh aspect of the present invention may be configured to include the power receiving device according to any one of the first to tenth aspects, 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 Wireless power transfer system 2 Power transmission device 3, 3a, 3b Power reception device 21 First communication unit 22 Power transmission control unit 24 Inverter 28 Power transmission coil 31 Voltage determination unit 32 Second communication unit 33, 33a Resonant circuit 34 Power reception coil 34a First power reception coil 34b Second power reception coil 35 Resonant capacitor 35a First resonant capacitor 35b Second resonant capacitor 36 First rectifier circuit 37 Smoothing capacitor 38 Transformer 39 Second rectifier circuit 40 Switching circuit 44 Auxiliary coil 90 Load

Claims

1. A power receiving device for contactless power transfer, comprising: a resonant circuit having a first receiving coil that receives power from a power transmitting device and a first resonant capacitor connected in series to the first receiving coil; a first rectifier circuit that rectifies the AC voltage generated in the resonant circuit; a smoothing capacitor connected to the first rectifier circuit and smoothing the voltage output from the first rectifier circuit; a transformer having a primary coil connected between one end and the other end of the first receiving coil or the first resonant capacitor and a secondary coil with fewer turns than the primary coil; and a second rectifier circuit connected to the secondary coil and outputting the rectified voltage to the smoothing capacitor.

2. The power receiving device according to claim 1, wherein the inductance of the primary coil is 10 times or more the inductance of the first power receiving coil.

3. A power receiving device for contactless power transfer, comprising: a resonant circuit having a first receiving coil that receives power from a power transmitting device and a first resonant capacitor connected in series to the first receiving coil; a first rectifier circuit that rectifies the AC voltage generated in the resonant circuit; a smoothing capacitor connected to the first rectifier circuit and smoothing the voltage output from the first rectifier circuit; an auxiliary coil electromagnetically coupled to the first receiving coil; a transformer having a primary coil connected between one end and the other end of the auxiliary coil and a secondary coil with fewer turns than the primary coil; and a second rectifier circuit connected to the secondary coil and outputting the rectified voltage to the smoothing capacitor.

4. The power receiving device according to claim 3, wherein the inductance of the primary coil is 10 times or more the inductance of the auxiliary coil.

5. A power receiving device according to any one of claims 1 to 4, further comprising a switching circuit connected across the secondary coil and capable of short-circuiting the two ends of the secondary coil.

6. The power receiving device according to claim 5, further comprising a short-circuit control circuit that short-circuits the switching circuit based on the output voltage from the smoothing capacitor.

7. A power receiving device as described in claim 1 or 2, wherein the resonant circuit has a second power receiving coil connected in series to the first power receiving coil and receiving power from the power transmitting device, and the primary coil is connected between one end and the other end of the first power receiving coil.

8. The power receiving device according to claim 7, wherein the resonant circuit has a second resonant capacitor connected between the first power receiving coil and the second power receiving coil.

9. A power receiving device as described in claim 1 or 2, wherein the resonant circuit has a second resonant capacitor connected in series to the first resonant capacitor, and the primary coil is connected between one end and the other end of the first resonant capacitor.

10. The power receiving device according to claim 3 or 4, further comprising a switching circuit connected across the auxiliary coil and capable of short-circuiting the ends of the auxiliary coil.

11. A contactless power supply system comprising: a power receiving device according to any one of claims 1 to 4; and a power transmitting device having a power transmitting coil that supplies power to the power receiving device.

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