Power transmission system and power receiving device

Abstract

To provide a technique capable of reducing interference between power transmission to a main battery and power transmission to an auxiliary battery.SOLUTION: A power transmission system in which power is transmitted from a power transmission-side device to a power reception-side device, the power transmission-side device including a power transmission-side coil, the power reception-side device including a power reception-side coil, an AC / DC converter, a first battery, a transformer, and a second battery, the transformer including a primary-side winding connected to the AC / DC converter via a filter and a secondary-side winding connected to the second battery, the power transmission system comprising: Operating the AC / DC converter at a first operation frequency not included in a frequency band of a filter in a first mode in which power is transmitted from the power reception-side coil to the first battery, and operating the AC / DC converter at a second operation frequency included in the frequency band in a second mode in which power is transmitted from the first battery to the second battery.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power transmission system and a power receiving device. [Background technology]

[0002] In recent years, wireless power transfer (WPT), which wirelessly transmits power to electric vehicles via power-transmitting coils embedded in roads and parking lots, has been attracting attention. This wireless power transfer technology allows the main battery that supplies power to the traction motor to be charged while the electric vehicle is in motion, dramatically extending the driving range of the electric vehicle. However, the circuit systems installed in electric vehicles for wireless power transfer typically operate only while power is being supplied, resulting in low facility utilization and increased costs for the electric vehicle.

[0003] In addition to a main battery, an electric vehicle is generally equipped with an auxiliary battery that stores power to be supplied to the air conditioner, lights, etc. Non-Patent Document 1 proposes a technology that aims to improve facility utilization rate and reduce costs by integrating a function for controlling power transfer from the main battery to the auxiliary battery in a circuit for controlling power transfer to the main battery by dynamic wireless power transfer (DWPT). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Z. Zhang, R. Ota, R. Okada and N. Hoshi, “Multi-port Inductive PowerTransfer System Considering Charging Auxiliary Battery in EVs,” in 2019 24thEuropean Conference on Power Electronics and Applications (EPC'22 ECCE Europe),2022, pp.1-9. [Non-patent document 2] R. Okada, R. Ota, and N. Hoshi, “Novel soft-switching active-bridge converter for bi-directional inductive power transfer system,” IEEJ Journal ofIndustry Applications, vol.11, no.1, pp.97-107, 2022. Summary of the Invention [Problem to be solved by the invention]

[0005] The configuration proposed in Non-Patent Document 1 may cause a problem in that power transmission to the main battery by wireless power supply during driving may interfere with power transmission from the main battery to the auxiliary battery.

[0006] Therefore, an object of the present invention is to provide a technique capable of reducing interference between power transmission to a main battery and power transmission to an auxiliary battery. [Means for solving the problem]

[0007] In order to achieve the above object, one aspect of the present invention provides a power transfer system that transfers power from a power transmitting side device to a power receiving side device, wherein the power transmitting side device includes a power transmitting side coil, and the power receiving side device includes a power receiving side coil that generates power in response to a magnetic field generated by the power transmitting side coil, an AC / DC converter connected to the power receiving side coil, a first battery connected to the AC / DC converter, a transformer, and a second battery, wherein the transformer has a primary winding connected to the AC / DC converter via a filter that passes power in a predetermined frequency band, and a secondary winding connected to the second battery, and is characterized in that in a first mode in which power is transferred from the power receiving side coil to the first battery, the AC / DC converter is operated at a first operating frequency that is not included in the predetermined frequency band, and in a second mode in which power is transferred from the first battery to the second battery, the AC / DC converter is operated at a second operating frequency that is included in the predetermined frequency band. [Effects of the Invention]

[0008] According to the present invention, for example, it is possible to provide a technique capable of reducing interference between power transmission to a main battery and power transmission to an auxiliary battery. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a conceptual diagram of a power transmission system according to an embodiment; [Figure 2] FIG. 1 is a diagram illustrating an example of a circuit configuration of a power transmission system according to an embodiment; [Figure 3] FIG. 10 is a circuit diagram illustrating the operation of the power receiving device in the MBC mode. [Figure 4] 1 is a timing chart showing the operating waveforms of each switch element in MBC mode, as well as the waveforms of each voltage value and each current value. [Figure 5] Circuit diagram showing the operation of the power receiving device in ABC mode [Figure 6] 1 is a timing chart showing the operating waveforms of each switch element in ABC mode, as well as the waveforms of each voltage value and each current value. [Figure 7] 1 is a timing chart showing waveforms of voltage values ​​and current values ​​in an embodiment of a power transmission system; [Figure 8] Frequency response in ABC mode [Figure 9] Efficiency characteristics in MBC mode DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and includes modifications and variations of the configuration within the scope of the present invention. Furthermore, not all of the combinations of features described in the present embodiments are necessarily essential to the present invention. Note that the same reference numerals are used to designate the same components, and their description will be omitted.

[0011] [Conceptual diagram of power transmission system] FIG. 1 shows a conceptual diagram of a power transmission system 100 according to one embodiment of the present invention. The power transmission system 100 is a system that performs wireless power transfer, transmitting power wirelessly to an electric vehicle EV via a power transmission coil 11 buried in a road RD (road surface). The wireless power transfer may include dynamic wireless power transfer (DWPT), which wirelessly transfers power to an electric vehicle EV while it is moving, and static wireless power transfer (STPT), which wirelessly transfers power to an electric vehicle EV while it is stopped. The power transmission system 100 of this embodiment may also include a power transmitting device 10 having a power transmitting coil 11 buried in the road RD, and a power receiving device 20 mounted on the electric vehicle EV.

[0012] In this embodiment, an electric vehicle EV is described as an example of a vehicle to which power is transmitted by the power transmission system 100, but the invention is not limited to this and may be, for example, a hybrid vehicle. Furthermore, a four-wheeled vehicle is described as an example of an electric vehicle EV, but the invention is not limited to this and may be any moving body, such as a saddle-type vehicle (two-wheeled vehicle, three-wheeled vehicle) or an unmanned guided vehicle used in a factory.

[0013] The power transmitting side device 10 includes, for example, a power transmitting coil 11, a resonant circuit 12, a DC / AC converter 13, and a control unit 14, and a plurality of such devices are arranged along the traveling direction of the electric vehicle EV on the road RD. In each power transmitting side device 10, the power transmitting coil 11 is supplied with power (AC) from the DC / AC converter 13 via the resonant circuit 12. The DC / AC converter 13 is supplied with power (DC) from the power grid via an AC / DC converter 30. The AC / DC converter 30 may include, for example, a PFC (Power Factor Correction) circuit.

[0014] The control unit 14 of the power transmitting side device 10 controls the on / off of each switching element included in the DC / AC converter 13, thereby controlling the DC / AC conversion in the DC / AC converter 13. The control unit 14 can be configured by a computer including a processor represented by a CPU (Central Processing Unit), a storage device such as a semiconductor memory, an interface with an external device, and the like.

[0015] In the example of FIG. 1 , not only the power transmitting side coil 11 of each power transmitting side device 10 but also the resonant circuit 12 and the DC / AC converter 13 are illustrated as being buried in the road RD, but the resonant circuit 12 and the DC / AC converter 13 do not have to be buried in the road RD. Moreover, the AC / DC converter 30 does not have to be buried in the road RD either. The power transmitting side coil 11 may be installed on the road RD. Furthermore, the power transmitting side coil 11 may be buried or installed not only in the power transmitting side road RD but also in the ground or floor. That is, the power transmitting side coil 11 may be buried or installed in at least one of the road RD, the ground, and the floor.

[0016] The power receiving side device 20 may include, for example, a power receiving side coil 21, a resonant circuit 22, an AC / DC converter 23, a control unit 24, a filter 25, a transformer 26, a rectifier 27, a main battery BT1 (first battery), and an auxiliary battery BT2 (second battery). The main battery BT1 may be a battery having a rated voltage in the range of, for example, 200 to 800 V, and the auxiliary battery BT2 may be a battery having a rated voltage in the range of, for example, 12 to 48 V. In other words, the rated voltage of the main battery BT1 is higher than the rated voltage of the auxiliary battery BT2.

[0017] The power receiving coil 21 is provided on the bottom surface of the electric vehicle EV, and generates electric power (AC) in response to a magnetic field M generated by the power transmitting coil 11 of each power transmitting device 10. The electric power generated by the power receiving coil 21 is supplied to an AC / DC converter 23 via a resonance circuit 22. The electric power (DC) converted by the AC / DC converter 23 is supplied to the main battery BT1. This charges the main battery BT1.

[0018] Electric power from main battery BT1 is supplied to traction motor 32 via three-phase inverter 31. Traction motor 32 is a drive source for electric vehicle EV, and three-phase inverter 31 is a motor driver for driving traction motor 32. Electric power from main battery BT1 is also used to charge auxiliary battery BT2, which stores power to be supplied to the air conditioner, lights, etc. Electric power from main battery BT1 is supplied to auxiliary battery BT2 via AC / DC converter 23, filter 25, transformer 26, and rectifier 27. This charges auxiliary battery BT2.

[0019] The AC / DC converter 23 in the power receiving side device 20 of this embodiment is configured to be able to operate in an MBC (Main Battery Charging) mode and an ABC (Auxiliary Battery Charging) mode. The MBC mode is an operation mode (first mode) in which the main battery BT1 is charged by transmitting power from the power receiving side coil 21 to the main battery BT1, and can operate in a state where wireless power feeding is being performed. For example, the MBC mode can be executed in a state where the electric vehicle EV is traveling on a road RD on which the power transmitting side device 10 (power transmitting side coil 11) is installed. On the other hand, the ABC mode is an operation mode (second mode) in which the auxiliary battery BT2 is charged by transmitting power from the main battery BT1 to the auxiliary battery BT2, and can operate in a state where wireless power feeding is not being performed. For example, the ABC mode can be executed in a state where the electric vehicle EV is traveling on an ordinary road on which the power transmitting side device 10 (power transmitting side coil 11) is not installed, or in a state where the electric vehicle EV is stopped.

[0020] Switching between the MBC mode and the ABC mode can be controlled by a control unit 24 of the power receiving side device 20. Specifically, the control unit 24 can switch between the MBC mode and the ABC mode by controlling the on / off of each switching element included in the AC / DC converter 23. Here, the control unit 24 can be configured by a computer including a processor represented by a CPU (Central Processing Unit), a storage device such as a semiconductor memory, an interface with an external device, etc. The control unit 24 may be configured as part of an external control device such as an ECU (Electronic Control Unit) provided in the electric vehicle EV.

[0021] [Circuit configuration of power transmission system] As described above, in the power transmission system 100 of this embodiment, the AC / DC converter 23 is configured to be able to execute (switch between) the MBC mode and the ABC mode. That is, a portion of the AC / DC converter 23 is used in common between the MBC mode and the ABC mode. This makes it possible to improve the facility utilization rate and reduce costs in the power receiving side device 20. On the other hand, if the AC / DC converter 23 is used in common between the MBC mode and the ABC mode, a problem may arise in that operation in the MBC mode (charging operation of the main battery BT1) interferes with operation in the ABC mode (charging operation of the auxiliary battery BT2).

[0022] Therefore, in power receiving device 20 of this embodiment, the primary winding of transformer 26 is connected to AC / DC converter 23 via filter 25, which passes power in a predetermined frequency band. In MBC mode, AC / DC converter 23 operates at a first operating frequency that is not included in the predetermined frequency band, and in ABC mode, AC / DC converter 23 operates at a second operating frequency that is included in the predetermined frequency band. This reduces interference between operations in MBC mode and ABC mode.

[0023] A specific configuration example of the power transmission system 100 of this embodiment will be described below. Fig. 2 shows an example of the circuit configuration of the power transmission system 100 of this embodiment.

[0024] First, a description will be given of the circuit configuration of the power transmitting side device 10. As described above, the power transmitting side device 10 may include the power transmitting side coil 11, the resonant circuit 12, the DC / AC converter 13, and the control unit 14. The power supply PS connected to the DC / AC converter 13 may be an AC / DC converter 30 (PFC circuit) that is connected to a power grid and supplies power (direct current) to the DC / AC converter 13.

[0025] The power transmission coil 11 is, for example, a coil buried in the road RD, and generates a magnetic field M in response to power (AC) supplied from a DC / AC converter 13 via a resonance circuit 12. The resonance circuit 12 is, for example, an inductor L pt and capacitor C pt The filter may be configured by an LC filter in which the above-mentioned components are connected in series.

[0026] The DC / AC converter 13 includes a first power transmission leg L p1 , the second transmission leg L p2 and a capacitor C1. The first transmitting leg L p1 (3rd leg) is contact point b p1 Two switch elements S connected in series via the third contact pu1 ,S pl1 and the second transmitting leg L p2 (4th leg) is contact point b p2 Two switch elements S connected in series via the fourth contact pu2 ,S pl2 First transmitting leg L p1 Contact point b p1 One end of the power transmission coil 11 is connected to a capacitor C pt and the second transmitting leg L p2 Contact point b p2 The other end of the power transmitting coil 11 is connected to the terminal .

[0027] Here, each switch element S pu1 ,S pl1 ,S pu2 ,S pl2 As the switching element S, a transistor (power element) that performs a switching operation, such as an IGBT or a MOSFET, can be used. pu1 ,S pl1 ,S pu2 ,S pl2 The on (conduction) / off (non-conduction) of the first power transmission leg L can be controlled by the control unit 14 at a first operating frequency (for example, 85 kHz). p1 and the second transmitting leg L p2 are connected in parallel.

[0028] Next, we will explain the circuit configuration of the power receiving side device 20. As described above, the power receiving side device 20 may include the power receiving side coil 21, the resonant circuit 22, the AC / DC converter 23, the control unit 24, the filter 25, the transformer 26, the rectifier 27, the main battery BT1, and the auxiliary battery BT2.

[0029] The power receiving coil 21 is a coil provided on the bottom surface of the electric vehicle EV, and generates power in response to the magnetic field M generated by the power transmitting coil 11. The resonant circuit 22 is, for example, an inductor L st and capacitor C st The filter may be configured by an LC filter in which the above-mentioned components are connected in series.

[0030] The AC / DC converter 23 includes a first power receiving leg L connected in parallel to each other. s1 , the second receiving leg L s2 and a capacitor C2. s1 (1st leg) is contact point b s1 Two switch elements S connected in series via (first contact) su1 ,S sl1 and the second receiving leg L s2 (Second leg) is contact point b s2 Two switch elements S connected in series via (second contact) su2 ,S sl2 First receiving leg Ls1 Contact point b s1 One end of the power receiving coil 21 is connected to a capacitor C st and the second receiving leg L s2 Contact point b s2 The other end of the power receiving coil 21 is connected to the terminal .

[0031] Here, each switch element S su1 ,S sl1 ,S su2 ,S sl2 As the switching element S, a transistor (power element) that performs a switching operation, such as an IGBT or a MOSFET, can be used. su1 ,S sl1 ,S su2 ,S sl2 The on (conduction) / off (non-conduction) of the first power receiving leg L can be controlled by the control unit 24. s1 and the second receiving leg L s2 are connected in parallel.

[0032] The transformer 26 has a primary winding 26a and a secondary winding 26b wound around a common magnetic core 26c. The primary winding coil 26a of the transformer 26 is connected to the switch element S of the AC / DC converter 23 via a filter 25 that passes power in a predetermined frequency band. sl2 The filter 25 is connected in parallel to the inductor L f and capacitor C f The filter 25 of this embodiment has a cutoff frequency f lower than the first operating frequency (for example, 85 kHz). f The filter 25 may be configured as a low-pass filter having a cutoff frequency f f is the inductor L f and capacitor C f The filter 25 can be set by the value of the inductor L f and capacitor C fThe frequency band through which power passes in the filter 25 may be simply referred to as the "frequency band of the filter 25."

[0033] The secondary winding 26b of the transformer 26 is connected to the auxiliary battery BT2 via a rectifier 27. In this embodiment, the rectifier 27 is configured as a diode rectifier including two diodes D1 and D2. A capacitor C3 is connected in parallel to the auxiliary battery BT2.

[0034] [Power transmission system operation] An example of the operation of the power transmission system 100 of this embodiment will be described below. As described above, the power receiving side device 20 of this embodiment can operate in the MBC mode and the ABC mode. The MBC mode and the ABC mode are determined by the switching of each switch element S of the AC / DC converter 23. su1 ,S sl1 ,S su2 ,S sl2 can be switched on (conducting) / off (non-conducting) by controlling the control unit 24.

[0035] First, the operation of the power transmission system 100 in the MBC mode will be described. Fig. 3 is a circuit diagram showing the operation of the power receiving side device 20 in the MBC mode. Fig. 4 is a timing chart showing the operating waveforms of each switch element and the waveforms of each voltage value and each current value when the power transmitting side device 10 and the power receiving side device 20 are operated in the MBC mode.

[0036] The transmission power P of the power transmitting device 10 in the MBC mode in which wireless power is supplied p [W] is controlled by the Triple Phase-Shift Control described in Non-Patent Document 2 and is expressed by the following equation (1): In equation (1), "ω" represents the switching angular frequency, and "δ" represents the phase difference between the power transmitting side coil 11 and the power receiving side coil 21. JPEG2026032675000002.jpg27170

[0037] In the MBC mode, as shown in FIG. 4, at a first operating frequency (for example, 85 kHz) that is not included in the frequency band of the filter 25, each switch element S pu1 ,S pl1 ,S pu2 ,S pl2 The control unit 14 controls the on / off of each switch element S of the AC / DC converter 23 of the power receiving side device 20. su1 ,S sl1 ,S su2 ,S sl2 The on / off of the power receiving coil 21 is controlled by the control unit 24. In this case, the power (voltage v s , current i s ) is supplied to the main battery BT1, so that the main battery BT1 is charged. m ) is brought to near zero by the action of filter 25. As a result, rectifier 27 (diodes D1 and D2) provided on the secondary side of transformer 26 does not conduct, and auxiliary battery BT2 is not charged.

[0038] Here, the primary winding 26a of the transformer 26 is supplied with a current i AB As shown in Fig. 1, a triangular waveform reactive current is generated by the action of the filter 25. This reactive current causes a s2 Each switch element S su2 ,S sl2 Immediately before turning on each switch element S su2 ,S sl2 As a result, a reverse current flows through each switch element S su2 ,S sl2 In other words, by providing the filter 25, a triangular waveform reactive current is generated in the MBC mode, and the charge accumulated in the parasitic capacitors of the switching elements S is released, thereby reducing switching loss and electromagnetic noise during switching. su2 ,Ssl2 This makes it possible to perform soft switching of the operation.

[0039] Next, the operation of the power transmission system 100 in the ABC mode will be described. Fig. 5 is a circuit diagram showing the operation of the power receiving side device 20 in the ABC mode. Fig. 6 is a timing chart showing the operating waveforms of each switch element and the waveforms of each voltage value and each current value when the power transmitting side device 10 and the power receiving side device 20 are operated in the ABC mode.

[0040] In the ABC mode, as described above, the power transmitting side device 10 can operate without wireless power supply. pu1 ,S pl1 ,S pu2 ,S pl2 is shown as an OFF state. In the AC / DC converter 23 of the power receiving side device 20, the first power receiving side leg L s1 Each switch element S su1 ,S sl1 Therefore, almost no voltage is applied to the power receiving coil 21 (resonant circuit 22), and the current i s As shown in Fig. 1, almost no current flows through the power receiving side coil 21. In other words, power is not transmitted from the power transmitting side device 10 to the power receiving side device 20, and the main battery BT1 is not charged.

[0041] On the other hand, in the AC / DC converter 23 of the power receiving side device 20, the second power receiving side leg L s2 Each switch element S su2 ,S sl2 The on / off of the second power receiving leg L of the AC / DC converter 23 is controlled by the control unit 24 at a second operating frequency (for example, a frequency less than 40 kHz) included in the frequency band of the filter 25. In this case, the transformer 26 operates at the second operating frequency, and the rectifier 27 (diodes D1 and D2) provided on the secondary side of the transformer 26 is turned on. That is, the second power receiving leg L of the AC / DC converter 23 is turned on. s2and the transformer 26 operate as a half-bridge LLC converter, and power is transmitted from the main battery BT1 to the auxiliary battery BT2, thereby charging the auxiliary battery BT2.

[0042] Charging power P of auxiliary battery BT2 in ABC mode AB is expressed by the following equation (2): In equation (2), the rectifier 27 (D1 to D2) provided on the secondary side of the transformer 26 and the auxiliary battery BT2 are connected to a resistor R AB It is modeled as '. JPEG2026032675000003.jpg40170

[0043] [Example] Hereinafter, an example (experimental results) of the power transmission system 100 will be described. In this example, the transmission power P p (rated power) is 1kW, and the charging power of the auxiliary battery is P AB (Rated power) 180W, input voltage E p 80V, output voltage E MB The voltage was set to 18.5V and the phase difference δ was set to π / 2. f and capacitor C f This results in a cutoff frequency of 40 kHz, f f The filter is configured as a low-pass filter having the following structure.

[0044] 7A and 7B are timing charts showing waveforms of voltage values ​​and current values ​​in the power transmission system 100 of this embodiment. FIG. 7A shows waveforms of voltage values ​​v when the power transmission system 100 is operated in the MBC mode. s ,v s2 and current value i s ,i AB 7(b) shows the waveform of the voltage value v when the power transmission system 100 is operated in the ABC mode. s2 and current value i AB The waveform of

[0045] When the power transmission system 100 of this embodiment is operated in the MBC mode, as shown in FIG. 7(a), a current value i of about ±25 A flows in the power receiving coil 21 (resonant circuit 22). s It was confirmed that the main battery BT1 was charged. In addition, the current value i AB was almost zero, and it was also confirmed that the auxiliary battery BT2 was not being charged. AB On the other hand, when the power transmission system 100 of this embodiment is operated in the ABC mode, a current value i of about ±15 A flows through the primary winding 26a of the transformer 26, as shown in FIG. AB It was confirmed that the auxiliary battery BT2 was being charged.

[0046] Fig. 8 shows the frequency characteristics in the ABC mode. In Fig. 8, the horizontal axis represents the operating frequency f, and the vertical axis represents the charging power P AB As shown in FIG. 8, in the power transfer system 100 (power receiving side device 20) of this embodiment, the cutoff frequency f f At around 40 kHz, the charging power P AB is about 180W, but at 85kHz, which is the operating frequency of MBC mode (first operating frequency), the charging power P AB It was confirmed that this hardly ever occurs.

[0047] Fig. 9 shows the efficiency characteristics in the MBC mode. In Fig. 9, the horizontal axis represents the coupling coefficient k between the power transmitting coil 11 and the power receiving coil 21, and the vertical axis represents the efficiency. Each measurement point in Fig. 9 represents the transmission power P s The data was acquired under control by Triple Phase-Shift Control so that the rated output was 1 kW. As shown in Fig. 9, a high efficiency of 94.5% was obtained when the coupling coefficient k = 0.25, confirming that the impact of losses that may occur in the transformer 26 is small.

[0048] As described above, in power transfer system 100 of the present embodiment, primary winding 26a of transformer 26 is connected to AC / DC converter 23 via filter 25, which passes power in a predetermined frequency band. In MBC mode, AC / DC converter 23 operates at a first operating frequency that is not included in the frequency band of filter 25, and in ABC mode, AC / DC converter 23 operates at a second operating frequency that is included in the frequency band of filter 25. This makes it possible to efficiently charge main battery BT1 in MBC mode and auxiliary battery BT2 in ABC mode, and to reduce interference between the charging operation in MBC mode and the charging operation in ABC mode.

[0049] The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0050] 10: power transmitting side device, 11: power transmitting side coil, 12: resonant circuit, 13: DC / AC converter, 20: power receiving device, 21: power receiving coil, 22: resonant circuit, 23: AC / DC converter, 25: filter, 26: transformer, BT1: Main battery, BT2: Auxiliary battery, 100: Power transmission system

Claims

1. A power transmission system that transmits power from a power transmitting side device to a power receiving side device, the power transmitting side device includes a power transmitting side coil; the power receiving side device includes a power receiving side coil that generates power in response to a magnetic field generated by the power transmitting side coil, an AC / DC converter connected to the power receiving side coil, a first battery connected to the AC / DC converter, a transformer, and a second battery; the transformer has a primary winding connected to the AC / DC converter via a filter that passes power in a predetermined frequency band, and a secondary winding connected to the second battery; a first operating frequency that is not included in the predetermined frequency band in a first mode in which power is transferred from the power receiving coil to the first battery, and a second operating frequency that is included in the predetermined frequency band in a second mode in which power is transferred from the first battery to the second battery.

2. the AC / DC converter has a first leg including two switch elements connected in series via a first contact, and a second leg including two switch elements connected in series via a second contact, The power transfer system according to claim 1 , wherein the power receiving coil is connected between the first contact and the second contact.

3. The power transmission system according to claim 2 , wherein the first battery is connected in parallel to the first leg and the second leg.

4. 3. The power transfer system according to claim 2, wherein the primary winding of the transformer is connected in parallel to one of two switch elements constituting the second leg via the filter.

5. The power transfer system according to claim 2 , wherein the power receiving coil is connected to the first contact point via a capacitor.

6. The power transmission system according to claim 1 , wherein the secondary winding of the transformer is connected to the second battery via a rectifier.

7. The power transmission system according to claim 1 , wherein a rated voltage of the first battery is higher than a rated voltage of the second battery.

8. The power transmission system according to claim 1 , wherein the filter is configured by an LC filter including an inductor and a capacitor.

9. The power transmission system according to claim 1 , wherein the primary winding and the secondary winding of the transformer are wound around a common core.

10. the power transmitting side device further includes a DC / AC converter that transmits power from a power source to the power receiving side coil; The power transmission system according to claim 1 , wherein the DC / AC converter operates at the first operating frequency.

11. the DC / AC converter has a third leg including two switch elements connected in series via a third contact, and a fourth leg including two switch elements connected in series via a fourth contact, The power transfer system according to claim 10 , wherein the power transmitting coil is connected between the third contact and the fourth contact.

12. The power transfer system according to claim 11 , wherein the power transmitting coil is connected to the third contact via a capacitor.

13. the power transmitting coil of the power transmitting side device is buried or installed in at least one of a road, the ground, and a floor, The power transmission system according to claim 1 , wherein the power receiving device is mounted on a mobile object.

14. A power receiving side device to which power is transmitted from a power transmitting side device including a power transmitting side coil, a power receiving side coil that generates power in response to a magnetic field generated by the power transmitting side coil; an AC / DC converter connected to the power receiving side coil; a first battery connected to the AC / DC converter; a transformer; and a second battery, the transformer has a primary winding connected to the AC / DC converter via a filter that passes power in a predetermined frequency band, and a secondary winding connected to the second battery; a power receiving side device configured to operate the AC / DC converter at a first operating frequency that is not included in the predetermined frequency band in a first mode in which power is transmitted from the power receiving side coil to the first battery, and to operate the AC / DC converter at a second operating frequency that is included in the predetermined frequency band in a second mode in which power is transmitted from the first battery to the second battery.

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