Wireless Power Supply System

Abstract

To provide a wireless power supply system and method and a wireless power transmission system that mitigate reduction in power transmission efficiency even when impedance of a load side circuit has varied.SOLUTION: A wireless power supply system comprises: a power transmission device 3 comprising a power transmission side resonance circuit including a power transmission coil 32; a power reception device comprising a power reception side resonance circuit including a power reception coil; a load to which power received via the power reception coil is supplied; and an impedance matching mechanism 9 that mitigates a difference between load side impedance, impedance of a circuit on the load side from an input end IE of the power transmission device 3, and input side impedance, impedance of a circuit on the AC power supply 5 side from the input end IE of the power transmission device 3. The power transmission device 3 further comprises a plurality of power supply coils 31A, 31B, 31C that are connected in parallel with one another to transmit power to the power transmission coil 32. The impedance matching mechanism 9 supplies power to at least one of the plurality of power supply coils 31A, 31B, 31C.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a wireless power supply system. Mu It is related to. [Background technology]

[0002] In recent years, research and development of wireless power transfer systems using magnetic fields has been progressing. Known power transfer methods using such magnetism include an electromagnetic coupling (electromagnetic induction) method and a magnetic resonance method. The magnetic resonance method transmits power via a state in which magnetic fields generated by the coils of the resonant circuits are tightly coupled (magnetic resonance coupling) by transmitting magnetic field vibrations generated by the flow of AC current through a resonant circuit of a power transmitting device to a resonant circuit of a power receiving device, causing resonance. Wireless power transfer using the magnetic resonance method has the advantage of a longer power transfer distance compared to wireless power transfer using electromagnetic coupling (see, for example, Patent Document 1). While the magnetic resonance method also uses magnetic coupling, the method using resonance is referred to as the magnetic resonance method in this invention for ease of understanding.

[0003] In such a wireless power supply system, in order to transmit power efficiently, it is necessary to set the impedance of the load side circuit, including the power receiving device and load, as viewed from the power transmitting device to be equivalent to the impedance of the power source side as viewed from the power transmitting device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-505369 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the load-side circuit described above is connected to a driving member such as a battery or a motor, and the battery or the motor serves as a load. Therefore, the current flowing through the load-side circuit may fluctuate depending on the driving state of the battery or the motor. In a wireless power transfer system, the impedance of the load-side circuit fluctuates in response to fluctuations in the current flowing through the load-side circuit. This causes a mismatch between the impedance of the load-side circuit as seen from the power transmitting device and the impedance of the power source as seen from the power transmitting device, resulting in a significant decrease in power transmission efficiency and a decrease in transmitted power, which may result in a system failure.

[0006] Therefore, even if the impedance of the load side circuit fluctuates, a technical problem arises that must be solved in order to reduce the decrease in power transmission efficiency, and an object of the present invention is to solve this problem. [Means for solving the problem]

[0007] In order to achieve the above object, the wireless power supply system of the present invention is a wireless power supply system that transmits and receives power using magnetism, and includes: a power transmitting device having a power transmitting-side resonant circuit including a power transmitting coil; a power receiving device having a power receiving-side resonant circuit including a power receiving coil; a load to which the power received via the power receiving coil is supplied; and an impedance matching mechanism that performs impedance processing to reduce the difference between a load-side impedance, which is the impedance of a circuit from an input end of the power transmitting device to a load side, and an input-side impedance, which is the impedance of a circuit from the input end of the power transmitting device to a power supply device side, wherein the power transmitting device further includes a plurality of power supply coils that are arranged to be magnetically coupled with the power transmitting coil, each of which has a different coupling strength in magnetic field coupling with the power transmitting coil, and are connected in parallel to each other to supply power to the power transmitting coil, and the impedance matching mechanism supplies power to at least one of the plurality of power supply coils. [Effects of the Invention]

[0010] The present invention reduces the difference between the input impedance and the load impedance even when the impedance of the load side circuit fluctuates, thereby suppressing the generation of reflected waves at the input terminal and avoiding a decrease in power transmission efficiency and the resulting risk of system failure. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating a configuration of a wireless power supply system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of an impedance matching mechanism. [Figure 3] FIG. 2 is a circuit diagram corresponding to the wireless power supply system. [Figure 4] FIG. 4 is an equivalent circuit diagram corresponding to the circuit diagram shown in FIG. [Figure 5] 1 is a graph showing the relationship between a load voltage and a load current. [Figure 6] 1 is a graph showing the relationship between a load current and a load-side impedance. [Figure 7] 10 is a schematic diagram showing the positional relationship between a power transmission coil and three power supply coils arranged offset in the axial direction of the coil axis. FIG. [Figure 8] 10 is a graph showing the relationship between the distance from the power feeding coil to the power transmitting coil and the load resistance. [Figure 9] 10 is a schematic diagram illustrating a state in which the coil moving mechanism slides the power supply coil in a direction perpendicular to the coil axis. FIG. [Figure 10] 10A and 10B are schematic diagrams illustrating a state in which the coil moving mechanism slides the power supply coil in parallel to the coil axis. [Figure 11] 10 is a schematic diagram showing the positional relationship between a power transmission coil and three power supply coils that are arranged offset in a direction perpendicular to the axial direction of the coil axis. FIG. [Figure 12] 10 is a schematic diagram showing the positional relationship between a power transmission coil and eight power supply coils arranged in a substantially spherical shape and tilted relative to the power transmission coil. FIG. [Figure 13]FIG. 10 is a schematic diagram showing the positional relationship between a power transmission coil and three power supply coils arranged in a spiral. [Figure 14] FIG. 1 is a schematic diagram showing the positional relationship between a power transmission coil and three power supply coils arranged on the same plane. DETAILED DESCRIPTION OF THE INVENTION

[0012] A wireless power supply system 1 according to one embodiment of the present invention and a wireless power supply method using the wireless power supply system 1 will be described with reference to the drawings. Note that, hereinafter, when referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when it is clearly limited to a specific number in principle, the number is not limited to that specific number and may be more or less than the specific number.

[0013] Furthermore, when referring to the shape or positional relationship of components, etc., it includes things that are substantially similar or approximate to those shapes, etc., unless otherwise specified or when it is clearly considered otherwise in principle.

[0014] In addition, the drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional proportions of the components may not be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

[0015] <Wireless power supply system configuration> FIG. 1 is a schematic diagram showing the configuration of a wireless power supply system 1. The wireless power supply system 1 uses magnetic field resonance to supply power to a power supply target 2 in a contactless manner. The power supply target 2 is, for example, a vehicle, a robotic air vehicle, an underwater robot, a capsule endoscope, a cardiac pacemaker, etc., and may be either a mobile device or an immobile device. Furthermore, when power is supplied, the power supply target 2 may be either moving or stationary. The wireless power supply system 1 includes a power transmitting device 3 and a power receiving device 4.

[0016] <Configuration of power transmission device> The power transmitting device 3 includes a power feeding coil 31, a power transmitting coil 32, and capacitors 33 and .

[0017] The power supply coil 31 and the power transmission coil 32 are formed by circularly winding a copper wire or the like with high electrical conductivity. Note that the current flowing through the copper wire flows more near the surface than in the center due to the influence of internal resistance. Therefore, when a litz wire made of multiple twisted copper wires is used as the wire material for the power supply coil 31 and the power transmission coil 32, the surface area of ​​the litz wire is larger than that of a single copper wire of the same diameter, allowing for a larger current to flow and reducing current loss.

[0018] The power feeding coil 31 is supplied with AC power from an AC power source 5. The AC power is set to, for example, a frequency of 150 kHz and a voltage of 10 V, but the frequency and voltage of the AC power source 5 can be changed as desired. Hereinafter, the contact point of the power feeding coil 31 on the AC power source 5 side will be referred to as the "input end IE." Note that in this embodiment, the power feeding coil 31 and the AC power source 5 are described as being directly connected to each other via the input end IE. However, the power feeding coil 31 and the AC power source 5 may be directly connected to each other via the input end IE or indirectly connected to each other via a coaxial cable or the like provided between the AC power source 5 and the input end IE. In this case, if the impedance of the power source matches the impedance of the coaxial cable or the like, the power source end of the coaxial cable or the like does not cause power reflection or the like and therefore does not pose a problem. Therefore, the input end IE refers to the load end of the coaxial cable or the like.

[0019] The power feeding coil 31 and the capacitor 33 are connected in series to form a power feeding side resonant circuit 35. When an AC voltage having a frequency corresponding to a resonant frequency set by the inductance of the power feeding coil 31 and the capacitance of the capacitor 33 flows through the power feeding coil 31, an oscillating magnetic field is generated that penetrates the power feeding coil 31. The detailed configuration of the power feeding coil 31 will be described later.

[0020] The power feed coil 31 and the power transmission coil 32 are magnetically coupled, and the power feed coil 31 supplies power to the power transmission coil 32 using magnetic resonance. That is, the power feed coil 31 and the power transmission coil 32 are designed to resonate at a resonant frequency set according to the inductance of the power feed coil 31 and the capacitance of the capacitor 33, which is approximately equal to a resonant frequency set according to the inductance of the power transmission coil 32 and the capacitance of the capacitor 34. As a result, magnetic field oscillations at a specific frequency (resonant frequency) generated by an AC current flowing through the power feed coil 31 are transmitted to the power transmission coil 32, which resonates at the same specific frequency, generating an electromotive force in the power transmission coil 32. Note that, although the magnetic resonance method is preferable for supplying power from the power feed coil 31 to the power transmission coil 32, which reduces the influence of the relative positions of the coils, an electromagnetic coupling method may also be used, in which an electromotive force is generated in the power transmission coil 32 via a magnetic flux that is generated to penetrate the power feed coil 31 in the coil axial direction when an AC current flows through the power feed coil 31. Furthermore, the magnetic field resonance method and the electromagnetic coupling method may be used in combination.

[0021] The power transmitting coil 32 and the capacitor 34 are connected in series to form a power transmitting-side resonant circuit 36. When an AC voltage having a frequency corresponding to a resonant frequency set by the inductance of the power transmitting coil 32 and the capacitance of the capacitor 33 flows through the power transmitting coil 32, the power receiving coil 41 (described later) resonates, generating an electromotive force.

[0022] <Configuration of power receiving device> The power receiving device 4 is provided inside the power supply target 2. The power receiving device 4 includes a power receiving coil 41 and a capacitor .

[0023] The power receiving coil 41 is provided at a distance from the power transmitting coil 32 in the coil axial direction. The power receiving coil 41 is formed by circularly winding a copper wire or the like having high electrical conductivity. As with the power feeding coil 31 and the power transmitting coil 32, the power receiving coil 41 also preferably uses a Litz wire as the wire material.

[0024] The power receiving coil 41 and capacitor 42 are connected in series to form a power receiving-side resonant circuit 43. The resonant frequency, which is set by the inductance of the power receiving coil 41 and the capacitance of the capacitor 42, is set to approximately match the resonant frequency of the power transmitting coil 32 and capacitor 33. As a result, an induced current flows in the power receiving coil 41 due to oscillations of the magnetic field that are generated so as to penetrate the power transmitting coil 32 in the coil axial direction, and an oscillating magnetic field is generated so as to penetrate the power receiving coil 41 in the coil axial direction. At this time, the magnetic fields of the power transmitting coil 32 and the power receiving coil 41 resonate and are strongly coupled together.

[0025] The AC power received by the power receiving coil 41 through resonance is supplied to a load 8 via a rectifier circuit (AC-DC converter) 6 and a DC-DC converter 7. The load 8 is a motor, a battery, or the like that constitutes the power supply target 2.

[0026] The rectifier circuit 6 has four diodes 61 arranged on a bridge, performs full-wave rectification on the AC power received by the power receiving coil 41, and outputs a DC voltage. Reference numeral 62 denotes a capacitor that smoothes the DC voltage output by the rectifier circuit 6.

[0027] DC-DC converter 7 converts the rectified DC voltage into a preset constant voltage (for example, 12 V). The voltage output from DC-DC converter 7 is applied to load 8. Note that DC-DC converter 7 may be provided according to the required voltage, and may be omitted as appropriate.

[0028] <Configuration of impedance matching mechanism> Next, an impedance matching mechanism 9 that performs impedance matching processing to reduce the difference between the impedance of the circuit (load side circuit) from the input terminal IE to the power receiving device 4 side, i.e., the impedance of the circuit including the power transmitting device 3, the power receiving device 4, the rectifier circuit 6, the DC-DC converter 7, and the load 8 (hereinafter referred to as "load side impedance"), and the impedance of the circuit from the input terminal IE to the AC power source 5 side (hereinafter referred to as "input side impedance") will be described with reference to Fig. 2. The power transmitting device 3 and the impedance matching mechanism 9 constitute a wireless power transmitting system 11.

[0029] The impedance matching mechanism 9 supplies power to at least one of the three power supply coils 31 (31A, 31B, 31C) by controlling the switching of the switches 91a and 91b. Note that other configurations may be used instead of the switches 91a and 91b as long as they are capable of selectively supplying power to any one of the power supply coils 31A, 31B, 31C.

[0030] The power feeding coil 31 includes three power feeding coils 31A, 31B, and 31C arranged in parallel to one another. In a normal state, the coil axes 31a, 31b, and 31c of the power feeding coils 31A, 31B, and 31C are positioned approximately coaxially with the coil axis 32a of the power transmitting coil 32. Note that the following description will be given taking as an example a case where the power feeding coil 31 is divided into three power feeding coils 31A, 31B, and 31C, but the number of power feeding coils may be two, four, or more.

[0031] The power supply coils 31A, 31B, and 31C are arranged such that the power supply coil 31A is closest to the power transmission coil 32, and the power supply coils 31B, 31C are arranged in this order so that the power supply coil 31A is farther away from the power transmission coil 32. Therefore, the strength of magnetic field coupling with the power transmission coil 32 is set to be strongest for the power supply coil 31A and weakest for the power supply coil 31C. When power is transmitted between the power supply coil 31 and the power transmission coil 32 using magnetic field resonance, efficient power transmission can be achieved by setting the inductances of the power supply coils 31A, 31B, and 31C to be equal to each other.

[0032] The switches 91a and 91b are three-way switches for supplying current to the power supply coils 31A, 31B, and 31C. One end of the switch 91a and one end of the power supply coils 31A, 31B, and 31C are connected to the AC power supply 5. The switch 91a is configured to be switchable between the other end of the power supply coil 31C and the switch 91b. The switch 91b is configured to be switchable between the other end of the power supply coil 31A and the other end of the power supply coil 31B.

[0033] When power is to be supplied to the power feeding coil 31A, the switch 91a is switched to the switch 91b side, and the switch 91b is switched to the other end of the power feeding coil 31A. When power is to be supplied to the power feeding coil 31B, the switch 91a is switched to the switch 91b side, and the switch 91b is switched to the other end of the power feeding coil 31B. When power is to be supplied to the power feeding coil 31C, the switch 91a is switched to the power feeding coil 31C side.

[0034] The switching of the switches 91a and 91b is controlled by a controller 92. The controller 92 is configured by, for example, a CPU, a memory, etc. The functions of the controller 92 may be realized by control using software, or may be realized by operation using hardware. The controller 92 is functionally divided into a storage unit 93 and a control unit 94 (see FIG. 1).

[0035] By supplying power to at least one of the power supply coils 31A, 31B, and 31C, the load-side impedance, which is the circuit impedance from the input terminal IE of the power transmitting device 3 to the load side, can be adjusted according to the distance from the power transmitting coil 32.

[0036] This will be explained in more detail with reference to Figs. 3 and 4. Fig. 3 is a circuit diagram corresponding to the wireless power supply system 1. "V" in Fig. 3 represents the voltage of the power supply 5, and "Z s" is the impedance of the power supply 5 (input impedance), "R0" is the parasitic resistance of the power feeding coil 31, "L0" is the inductance of the power feeding coil 31, "C0" is the capacitance of the capacitor 33, "I0" is the current flowing through the power feeding coil 31, "R1" is the parasitic resistance of the power transmitting coil 32, "L1" is the inductance of the power transmitting coil 32, "C1" is the capacitance of the capacitor 34, "I1" is the current flowing through the power transmitting coil 32, "k 01 " is the coupling coefficient between the power feeding coil 31 and the power transmitting coil 32, "R2" is the parasitic resistance of the power receiving coil 41, and "R L " is the load resistance of the load 8, "L2" is the inductance of the receiving coil 41, "C2" is the capacitance of the capacitor 42, "I2" is the current flowing through the receiving coil 41, and "k 12 ' is the coupling coefficient between the power transmitting coil 32 and the power receiving coil 41.

[0037] Fig. 4 is an equivalent circuit diagram based on the circuit diagram shown in Fig. 3. The equivalent circuit diagram shown in Fig. 4 shows a state in which the power feeding coil 31 and the power transmitting coil 32 are resonating, and the power transmitting coil 32 and the power receiving coil 41 are resonating. The mutual inductance L0 between the power feeding coil 31 and the power transmitting coil 32 is expressed as k 01 √(L0L1), and the mutual inductance L2 between the power transmitting coil 32 and the power receiving coil 41 is k 12 √(L1L2). "Z0" in FIG. 4 is the impedance of the circuit between the power supply 5 and the power feeding coil 31, that is, from the input end IE of the power transmitting device 3 to the load 8 side (load-side impedance). "Z1" is the impedance of the circuit between the power feeding coil 31 and the power transmitting coil 32 to the load 8 side. "Z2" is the impedance of the circuit between the power feeding coil 31 and the power transmitting coil 32 to the load 8 side. The following formulas 1 to 3 are obtained from the equivalent circuit shown in FIG. 4.

[0038]

number

[0039]

number

[0040]

number

[0041] In the present invention, impedance matching is defined as the load resistance R L When the load impedance Z0 of the circuit when viewed from the input terminal IE of the power transmission device 3 to the load 8 side changes, the input impedance Z s This means that the temperature is matched to the temperature and kept approximately constant.

[0042] Specifically, in the wireless power supply system 1, when the power of the load 8 is large and the impedance of the load 8 is small, the impedance Z2 of the circuit between the power supply coil 31 and the power transmission coil 32 on the load 8 side becomes small, as can be seen from equation (1). At this time, the impedance Z1 of the circuit between the power supply coil 31 and the power transmission coil 32 on the load 8 side becomes large, as can be seen from equation (2), and the load-side impedance Z0 becomes small, as can be seen from equation (3). In other words, while the load-side impedance Z0 becomes small, the input-side impedance Z s does not change.

[0043] Therefore, by controlling the switches 91a to 91d to supply power to the power feeding coil 31A that is closest to the power transmitting coil 32, the magnetic field coupling with the power transmitting coil 32 becomes closer, and the coupling coefficient k 01 The coupling coefficient k between the power feeding coil 31 and the power transmitting coil 32 increases at the same rate as the rate at which the impedance Z1 of the circuit on the load 8 side increases from between the power feeding coil 31 and the power transmitting coil 32. 01 By increasing the load impedance Z0, the load impedance Z0 can be kept constant. s By continuing to control the impedance to be approximately equal to the power reflection, it is possible to suppress the power reflection and realize an efficient system operation state.

[0044] Furthermore, when the power of the load 8 is small and the impedance of the load 8 is large, the impedance Z2 of the circuit between the power feeding coil 31 and the power transmitting coil 32 on the side of the load 8 increases, as can be seen from equation (1). At this time, the impedance Z1 of the circuit between the power feeding coil 31 and the power transmitting coil 32 on the side of the load 8 decreases, as can be seen from equation (2), and the load-side impedance Z0 increases, as can be seen from equation (3). In other words, while the load-side impedance Z0 increases, the input-side impedance Z s does not change.

[0045] Therefore, by controlling the switching of the switches 91a to 91d to supply power to one of the power feeding coils 31B and 31C, the magnetic field coupling with the power feeding coil 32 becomes weaker depending on the distance between the power feeding coil 32 and the power feeding coils 31B and 31C, and the coupling coefficient k 01 The coupling coefficient k between the power feeding coil 31 and the power transmitting coil 32 decreases at the same rate as the rate at which the impedance Z1 of the circuit between the power feeding coil 31 and the power transmitting coil 32 on the load 8 side decreases. 01 By reducing the load impedance Z0, the load impedance Z0 can be kept constant. s By continuing to control the impedance to be approximately equal to the power reflection, it is possible to suppress the power reflection and realize an efficient system operation state.

[0046] The memory unit 93 stores a function indicating the relationship between the load voltage and load current output from the DC-DC converter 7 and supplied to the load 8, and a function indicating the relationship between the load current and load-side impedance. The load voltage and load current supplied to the load 8 are continuously measured in real time by a measurement unit 95 provided between the DC-DC converter 7 and the load 8. The measurement unit 95 is not limited to measuring the load voltage, but may also measure the load current, or both. The load voltage and load current in this embodiment are the output voltage and output current from the DC-DC converter 7, or in other words, the input voltage and input current of the load 8. The measurement unit 95 can be provided between the capacitor 62 and the DC-DC converter 7. In this case, the load voltage and load current are the input voltage and input current of the DC-DC converter 7. Furthermore, if the DC-DC converter 7 is not provided, the load voltage and load current are the input voltage and input current of the load 8.

[0047] Specifically, as shown in FIG. 5, the function showing the relationship between the load voltage and the load current includes a function showing the relationship between the load voltage and the load current in an idling state (converter OFF) in which the input voltage to the DC-DC converter 7 (e.g., 15 V) is equal to or lower than the operating power (e.g., 12 V) of the DC-DC converter 7 and the DC-DC converter 7 is not operating, and a function showing the relationship between the load voltage and the load current in a state (converter ON) in which the input voltage to the DC-DC converter 7 exceeds the operating power of the DC-DC converter 7 and the DC-DC converter 7 is operating.

[0048] As shown in FIG. 6, the function showing the relationship between the load current and the load side impedance includes a function showing the relationship between the load current and the load side impedance when the DC-DC converter 7 is idling (converter OFF), and a function showing the relationship between the load current and the load side impedance when the DC-DC converter 7 is not operating (converter ON).

[0049] The function showing the relationship between the load voltage and the load current and the function showing the relationship between the load current and the load side impedance may be calculated in advance by experiments or the like, and are not limited to the graphs of linear functions exemplified in Figures 5 and 6.

[0050] The control unit 94 controls the switching of the switches 91a and 91b based on the measurement values ​​of the measurement unit 95 and various functions stored in the storage unit 93. The switching control of the switches 91a and 91b by the control unit 94 will be described in detail later.

[0051] In this way, the wireless power supply system 1 according to this embodiment can instantly change the positional relationship between the power supply coil 31 and the power transmission coil 32 using the impedance matching mechanism 9 in response to fluctuations in the load-side impedance measured by the measuring unit 95, and can reduce the difference between the input-side impedance and the load-side impedance at the input terminal IE in real time.

[0052] <Impedance matching processing> Next, the impedance matching process performed by the impedance matching mechanism 9 will be described with reference to the drawings.

[0053] First, we will explain why the load-side impedance varies depending on whether the DC-DC converter 7 is on or off. In this embodiment, we will explain an example in which the load-side impedance varies depending on whether the DC-DC converter 7 is on or off, but the load-side impedance can vary not only due to whether the DC-DC converter 7 is on or off, but also due to, for example, changes in the relative position between the transmitting coil 32 and the receiving coil 41, changes in the driving status (output) of the load 8, etc., and it goes without saying that this can be used to suppress variations in the load-side impedance due to these various factors.

[0054] As shown in FIG. 5, when the DC-DC converter 7 is idling (converter OFF), the output voltage of the DC-DC converter 7 is, for example, below 12 V, which is the operating power, and the load current is also very small. When the measuring unit 95 is placed between the DC-DC converter 7 and the load 8, the load current (the output current of the DC-DC converter 7) is almost zero. When the measuring unit 95 is placed between the capacitor 62 and the DC-DC converter 7, the load current (the input current of the DC-DC converter 7) increases slightly until it reaches the operating voltage (for example, 12 V). At this time, the load-side impedance becomes extremely large, as shown in FIG. 6. When the measuring unit 95 is placed between the DC-DC converter 7 and the load 8, the load-side impedance is almost constant (a value equivalent to the power of the load intended by the device), but when the measuring unit 95 is placed between the capacitor 62 and the DC-DC converter 7, the load-side impedance decreases slightly.

[0055] Next, as shown in Fig. 5, when the DC-DC converter 7 starts operating (converter ON) and power is supplied to the load 8, the output voltage (load voltage) of the DC-DC converter 7 increases to, for example, 12 V, and the output current (load current) of the DC-DC converter 7 increases rapidly. Then, as shown in Fig. 6, the load-side impedance at this time decreases rapidly and gradually approaches a predetermined value over time. In order to reliably suppress fluctuations in the load-side impedance from the point at which power supply to the load 8 starts, the value of the load-side impedance is adjusted in advance while the engine is idling, before the DC-DC converter 7 starts operating.

[0056] In this way, while the load side impedance varies depending on the operating state of the DC-DC converter 7, the input side impedance is fixed at a predetermined value (for example, 50Ω). As a result, the input side impedance and the load side impedance do not match, and reflected waves are generated at the input terminal IE, which may reduce the transmission efficiency or may cause a system failure due to insufficient transmitted power.

[0057] Therefore, the controller 92 increases or decreases the impedance of the circuit in the power transmitting device 3 in accordance with the fluctuation of the load side impedance.

[0058] Specifically, first, the control unit 94 calculates the load current based on the load voltage measured by the measurement unit 95 and the function shown in Fig. 5. The control unit 94 also calculates the load-side impedance based on the calculated load current and the function shown in Fig. 6.

[0059] Next, the control unit 94 switches the switches 91a and 91b to determine to which of the power supply coils 31A, 31B, and 31C power should be supplied so that the load-side impedance matches the input-side impedance, and adjusts the impedance of the circuit within the power transmission device 3.

[0060] For example, when the DC-DC converter 7 is idling and the load impedance is large relative to the input impedance, supplying power to the power feed coil 31A as shown in Fig. 7(a) strengthens the magnetic coupling between the power feed coil 31 and the power transmission coil 32, increasing the coupling coefficient. As a result, the load impedance at the input terminal IE decreases, as described above, and the difference with the input impedance is alleviated.

[0061] On the other hand, when the DC-DC converter 7 is operating and the load impedance is lower than the input impedance, as shown in Fig. 7(b), power is supplied to the power feed coil 31B, which is farther from the power transmitting coil 32 than the power feed coil 31A, so that the magnetic field coupling between the power feed coil 31 and the power transmitting coil 32 becomes weaker and the coupling coefficient decreases. As a result, the load impedance at the input terminal IE increases, and the difference with the input impedance is alleviated.

[0062] 7(c), when the load impedance further decreases, power is supplied to the power feeding coil 31C, which is farthest from the power transmitting coil 32, and the magnetic field coupling between the power feeding coil 31 and the power transmitting coil 32 becomes weaker, and the coupling coefficient decreases. As a result, the load impedance at the input terminal IE becomes larger, and the difference with the input impedance is alleviated.

[0063] The function of the distance between the power feeding coils 31A, 31B, and 31C and the power transmitting coil 32 and the change in the coupling coefficient is obtained in advance through experiments or the like.

[0064] In this way, the wireless power supply system 1 according to this embodiment is a wireless power supply system 1 that transmits and receives power using magnetism, and includes a power transmitting device 3 having a power transmitting-side resonant circuit 36 ​​including a power transmitting coil 32, a power receiving device 4 having a power receiving-side resonant circuit 43 including a power receiving coil 41, a load 8 to which the power received via the power receiving coil 41 is supplied, and an impedance matching mechanism 9 that reduces the difference between the load-side impedance, which is the impedance of the circuit from the input terminal IE of the power transmitting device 3 to the load 8, and the input-side impedance, which is the impedance of the circuit from the input terminal IE of the power transmitting device 3 to the AC power source 5, and the power transmitting device 3 further includes a plurality of power supply coils 31A, 31B, and 31C that are arranged to be magnetically coupled to the power transmitting coil 32, each of which has a different coupling strength in magnetic field coupling with the power transmitting coil 32, are connected in parallel to each other, and supply power to the power transmitting coil 32, and the impedance matching mechanism 9 supplies power to at least one of the plurality of power supply coils 31A, 31B, and 31C.

[0065] With this configuration, when the load-side impedance does not match the input-side impedance, the impedance matching mechanism 9 supplies power to one of the power supply coils 31A, 31B, and 31C, and changes the strength of the magnetic field coupling (the density of the magnetic field coupling) between the power supply coil 31 and the power transmission coil 32. This increases or decreases the impedance of the circuit within the power transmission device 3, and reduces the difference between the input-side impedance and the load-side impedance. This suppresses the generation of reflected waves at the input terminal IE, making it possible to avoid a decrease in power transmission efficiency and a system failure due to a decrease in transmitted power.

[0066] Furthermore, the wireless power supply system 1 according to this embodiment is configured such that the multiple power supply coils 31A, 31B, and 31C each have coil axes 31a, 31b, and 31c that are arranged approximately coaxially with one another, and are set at different distances from the power transmission coil 32.

[0067] With this configuration, the strength of the magnetic field coupling between the power supply coils 31A, 31B, and 31C and the power transmission coil 32 weakens in inverse proportion to the distance of the power supply coils 31A, 31B, and 31C from the power transmission coil 32. Therefore, by supplying power to one of the power supply coils 31A, 31B, and 31C that has a different magnetic field coupling strength with the power transmission coil 32, the impedance of the circuit in the power transmission device 3 can be increased or decreased.

[0068] Furthermore, in the wireless power supply system 1 according to this embodiment, power is supplied from the power supply coil 31 to the power transmission coil 32 by a magnetic field resonance method, and the inductance values ​​of the power supply coils 31A, 31B, and 31C are set to be approximately equal.

[0069] This configuration allows efficient power supply from the power feeding coils 31A, 31B, and 31C, which are positioned differently relative to the power transmitting coil 32, to the power transmitting coil 32 by magnetic field resonance.

[0070] Moreover, the wireless power supply system 1 according to this embodiment further includes a measuring unit 95 that measures the load current or load voltage in the load 8, and the impedance matching mechanism 9 is configured to perform impedance matching processing according to the measurement result of the measuring unit 95.

[0071] With this configuration, even if the load-side impedance fluctuates due to factors such as turning the DC-DC converter 7 on and off, the difference between the input-side impedance and the load-side impedance is mitigated, thereby suppressing the generation of reflected waves at the input terminal IE and avoiding system failures due to reduced power transmission efficiency and reduced transmitted power.

[0072] Furthermore, the wireless power supply system 1 according to this embodiment is configured so that power is supplied from the power transmitting coil 32 to the power receiving coil 41 by a magnetic field resonance method.

[0073] This configuration allows for efficient power supply from the power transmitting coil 32 to the power receiving coil 41.

[0074] Furthermore, a wireless power feeding method using the wireless power feeding system 1 according to this embodiment is a wireless power feeding method using the wireless power feeding system 1, which includes: a power transmitting device 3 having a power transmitting-side resonant circuit 36 ​​including a power transmitting coil 32; a power receiving device 4 having a power receiving-side resonant circuit 43 including a power receiving coil 41; a load 8 to which power received via the power receiving coil 41 is supplied; and an impedance matching mechanism 9 that performs impedance processing to reduce the difference between a load-side impedance, which is the impedance of a circuit from an input terminal IE of the power transmitting device 3 to the load 8, and an input-side impedance, which is the impedance of a circuit from the input terminal IE of the power transmitting device 3 to the AC power source 5. The power transmitting device 3 further includes a plurality of power feeding coils 31A, 31B, and 31C that are arranged to be magnetically coupled to the power transmitting coil 32, have different coupling strengths in the magnetic field coupling with the power transmitting coil 32, are connected in parallel to each other, and feed power to the power transmitting coil 32, and the impedance matching mechanism 9 supplies power to at least one of the plurality of power feeding coils 31A, 31B, and 31C.

[0075] With this configuration, when the load-side impedance does not match the input-side impedance, the impedance matching mechanism 9 supplies power to one of the power supply coils 31A, 31B, and 31C, and changes the strength of the magnetic field coupling (the density of the magnetic field coupling) between the power supply coil 31 and the power transmission coil 32. This increases or decreases the impedance of the circuit within the power transmission device 3, and reduces the difference between the input-side impedance and the load-side impedance. This suppresses the generation of reflected waves at the input terminal IE, making it possible to avoid a decrease in power transmission efficiency and a system failure due to a decrease in transmitted power.

[0076] Furthermore, the wireless power transmission system 11 according to this embodiment is a wireless power transmission system 11 that transmits power to a power receiving device 4 using magnetism, and includes a power transmitting device 3 that includes a power transmitting side resonant circuit 36 ​​including a power transmitting coil 32 and transmits power to a load 8 via the power receiving device 4, and an impedance matching mechanism 9 that reduces the difference between a load side impedance, which is the impedance of the circuit from the input terminal IE of the power transmitting device 3 to the load 8 side, and an input side impedance, which is the impedance of the circuit from the input terminal IE of the power transmitting device 3 to the AC power source 5 side, depending on the load current or load voltage in the load 8. The power transmitting device 3 further includes a plurality of power supply coils 31A, 31B, and 31C that are arranged to be magnetically coupled to the power transmitting coil 32, each of which has a different coupling strength in the magnetic field coupling with the power transmitting coil 32, and are connected in parallel to each other to transmit power to the power transmitting coil 32, and the impedance matching mechanism 9 supplies power to at least one of the plurality of power supply coils 31A, 31B, and 31C.

[0077] With this configuration, when the load-side impedance does not match the input-side impedance, the impedance matching mechanism 9 supplies power to one of the power supply coils 31A, 31B, and 31C, and changes the strength of the magnetic field coupling (the density of the magnetic field coupling) between the power supply coil 31 and the power transmission coil 32. This increases or decreases the impedance of the circuit within the power transmission device 3, and reduces the difference between the input-side impedance and the load-side impedance. This suppresses the generation of reflected waves at the input terminal IE, making it possible to avoid a decrease in power transmission efficiency and a system failure due to a decrease in transmitted power.

[0078] Furthermore, in the above-described embodiment, the cause of fluctuation in the load side impedance has been described as fluctuation in the load current due to the on / off switching of the DC-DC converter 7, but the cause of fluctuation in the load side impedance is not limited to this.

[0079] For example, it is conceivable that the load-side impedance may fluctuate as the power supply target object 2 moves. This is because the strength of the magnetic coupling between the power supply coil 32 and the power receiving coil 41 increases when the power receiving coil 41 approaches the power transmitting coil 32, and the strength of the magnetic coupling between the power supply coil 32 and the power receiving coil 41 decreases when the power receiving coil 41 moves away from the power transmitting coil 32, causing the magnetic coupling state between the power transmitting coil 32 and the power receiving coil 41 to fluctuate. Therefore, in such a case, the distance between the power transmitting coil 32 and the power receiving coil 41 may be monitored, and it may be determined to which of the power supply coils 31A, 31B, and 31C to supply power so that the input-side impedance and the load-side impedance match according to the change in the distance between the power transmitting coil 32 and the power receiving coil 41.

[0080] Furthermore, in the present embodiment, the input impedance and the load impedance are pre-matched when the DC-DC converter 7 is idling. However, the input impedance and the load impedance may be pre-matched, for example, when the DC-DC converter 7 transitions from idling to ON, or when the load impedance stabilizes after the DC-DC converter 7 is turned ON.

[0081] <Experimental Example> Next, a simulation performed to confirm the effects and feasibility of the wireless power transfer system 1 according to this embodiment will be described. In this simulation, the diameters of the power transfer coil 31 and the power transmission coil 32 were each set to 700 mm, and the power transfer coil 31 and the power transmission coil 32 maintained a resonant state, and the power transmission coil 32 and the power receiving coil 41 maintained a resonant state. The center-to-center distance L of the power transfer coil 31 and the power transmission coil 32 in the axial direction of the coil axis 31a (31b, 31c) at which impedances were matched was calculated when the load resistance RL of the load 8 was changed. The value of the load resistance RL included the values ​​of the load resistances of the rectifier circuit 6 and the DC-DC converter 7. The actual load resistance of the load 8 was also calculated, taking into account the load resistances of the rectifier circuit 6 and the DC-DC converter 7 when the output voltage of the DC-DC converter 7 was set to 48 V. The results are shown in Table 1 and FIG. 8. 8 is a graph in which the horizontal axis represents load resistance RL and the vertical axis represents center-to-center distance L between the power supply coil 31 and the power transmission coil 32 when impedance is matched. In Table 1 and Fig. 8, when the load 8 is OFF, the load resistance RL is set to 1000 Ω or more (the actual load resistance of the load 8 is 1000 Ω or more) for the sake of convenience, and the center-to-center distance L is set to 500 mm.

[0082] [Table 1]

[0083] 8, when power feeding coil 31A is located 300 mm from power transmitting coil 32, power feeding coil 31B is located 400 mm from power transmitting coil 32, and power feeding coil 31C is located 500 mm from power transmitting coil 32, measuring unit 95 measures the load current to calculate the value of the drive power of load 8, and switches 91a to 91d are operated to switch between power feeding coils 31A, 31B, and 31C in accordance with the calculated drive power of load 8. Specifically, power feeding coil 31A is operated when the drive power of load 8 is 200 W or more, power feeding coil 31B is operated when the drive power of load 8 is 20 W or more but less than 200 W, and power feeding coil 31C is operated when load 8 is off or the drive power of load 8 is less than 20 W.

[0084] Note that impedance matching can be performed with higher accuracy by increasing the number of power feeding coils 31. For example, the number of power feeding coils 31 is increased to six, and the installation positions of the power feeding coils 31 are set to 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, and 500 mm in terms of center-to-center distance L from the power transmitting coil 32. In this case, the power supply coil with a center distance L of 250 mm is activated when the drive power of the load 8 is 700 W or more, the power supply coil with a center distance L of 300 mm is activated when the drive power of the load 8 is 350 W or more and less than 700 W, the power supply coil with a center distance L of 350 mm is activated when the drive power of the load 8 is 200 W or more and less than 350 W, the power supply coil with a center distance L of 400 mm is activated when the drive power of the load 8 is 50 W or more and less than 200 W, the power supply coil with a center distance L of 450 mm is activated when the drive power of the load 8 is 10 W or more and less than 50 W, and the power supply coil with a center distance L of 500 mm is activated when the load 8 is off or the drive power of the load 8 is less than 10 W.

[0085] Furthermore, the multiple power feeding coils 31 do not necessarily need to be arranged at equal intervals, and the intervals between the arranged power feeding coils 31 may be changed as necessary. For example, the number of power feeding coils 31 arranged in a region where the drive power increases rapidly when the load 8 is started and the drive power is low may be greater than the number of power feeding coils 31 arranged in a region where the drive power of the load 8 is large and relatively stable. Specifically, when six power feeding coils 31 are provided, the power feeding coils 31 are arranged at center-to-center distances L from the power transmission coil 32 of 300 mm, 400 mm, 440 mm, 470 mm, 490 mm, and 500 mm. In this case, the power supply coil 31 with a center-to-center distance L of 300 mm operates when the drive power of the load 8 is 500 W or more; the power supply coil 31 with a center-to-center distance L of 400 mm operates when the drive power of the load 8 is 60 W or more and less than 500 W; the power supply coil 31 with a center-to-center distance L of 440 mm operates when the drive power of the load 8 is 30 W or more and less than 60 W; the power supply coil 31 with a center-to-center distance L of 470 mm operates when the drive power of the load 8 is 15 W or more and less than 30 W; the power supply coil 31 with a center-to-center distance L of 490 mm operates when the drive power of the load 8 is 5 W or more and less than 15 W; and the power supply coil 31 with a center-to-center distance L of 500 mm operates when the load 8 is OFF or the drive power of the load 8 is less than 5 W.

[0086] <Variation 1> Next, a modified example of this embodiment will be described. Note that the modified example has the same configuration as the above-described embodiment except for the configuration described below.

[0087] The impedance matching mechanism 9 may include a coil moving mechanism 96 that moves the power feeding coil 31 relative to the power transmitting coil 32, as shown in FIGS. 9(a) and 9(b).

[0088] The coil movement mechanism 96 is a solenoid including a plunger 96a and a case 96b. The tip of the plunger 96a is connected to the power supply coil 31. The plunger 96a moves forward and backward perpendicularly to the coil axes 31a, 31b, and 31c, thereby sliding the power supply coil 31 so that the coil axes 31a, 31b, and 31c move relatively away from or closer to (align with) the coil axis 32a of the power transmission coil 32 while maintaining the coil axes 31a, 31b, and 31c and the coil axis 32a of the power transmission coil 32 in a substantially parallel state.

[0089] Specifically, as shown in FIGS. 2(a) to 2(c), the position of the power supply coil 31 when the coil axes 31a, 31b, and 31c are coaxial with the coil axis 32a of the power transmission coil 32 is defined as the original position. As shown in FIG. 9(a), the plunger 96a retracts, and the power supply coil 31 moves away from the original position in a direction perpendicular to the coil axes 31a, 31b, and 31c. As shown in FIG. 9(b), the plunger 96a advances, and the power supply coil 31 moves away from the original position in a direction perpendicular to the coil axes 31a, 31b, and 31c.

[0090] When the coil axes 31a, 31b, and 31c are coaxial with the coil axis 32a of the power transmitting coil 32, the magnetic field coupling with the power transmitting coil 32 becomes tight (the coupling strength (coupling coefficient) becomes large). On the other hand, when the coil axes 31a, 31b, and 31c are offset from the coil axis 32a of the power transmitting coil 32 in a direction perpendicular to the coil axis 31a, the magnetic field coupling with the power transmitting coil 32 becomes loose (the coupling strength (coupling coefficient) becomes small).

[0091] The function of the offset amount (stroke amount of the plunger 96a) between the coil axis 31a of the power feeding coil 31 and the coil axis 32a of the power transmitting coil 32 and the change amount of impedance of the circuit in the power transmitting device 3 is obtained in advance by experiment or the like.

[0092] The stroke range (one side) of the plunger 96a is set to, for example, equal to or less than the radius of the power feeding coil 31. This allows at least a portion of the power feeding coil 31 to remain overlapped with at least a portion of the power transmitting coil 32 when viewed from the axial direction of the coil axes 31a, 31b, and 31c, even when the power feeding coil 31 moves to its maximum extent in any direction perpendicular to the coil axes 31a, 31b, and 31c.

[0093] Such a mechanism for moving the power feed coil 31 relative to the power transmission coil 32 using the coil movement mechanism 96 has poorer responsiveness than a configuration for electrically switching the switches 91a and 91b, so the impedance can be smoothly optimized by, for example, roughly adjusting the impedance by controlling the switching of the switches 91a and 91b, and then fine-tuning the impedance by moving the power feed coil 31 relative to the power transmission coil 32. Note that the impedance may also be optimized by roughly adjusting the impedance by moving the power feed coil 31 relative to the power transmission coil 32, and then fine-tuning the impedance by controlling the switching of the switches 91a and 91b.

[0094] <Variation 2> In the above-described first modification, the coil moving mechanism 96 moves the power supply coil 31 so that the coil axis 31a of the power supply coil 31 is offset in a direction perpendicular to the coil axis 32a of the power transmission coil 32. However, the coil moving mechanism 96 may be configured to move the power supply coil 31 in a direction parallel to the axial directions of the coil axes 31a, 31b, 31c and the coil axis 32a.

[0095] For example, as shown in FIGS. 2(a) to 2(c), the position of the power supply coil 31 when the coil axes 31a, 31b, and 31c are positioned coaxially with the coil axis 32a of the power transmission coil 32 is taken as the original position. As shown in FIG. 10(a), the plunger 96a may be retracted to move the power supply coil 31 from the original position in a direction parallel to the coil axes 31a, 31b, and 31c and away from the power transmission coil 32, and as shown in FIG. 10(b), the plunger 96a may be advanced to move the power supply coil 31 from the original position in a direction parallel to the coil axes 31a, 31b, and 31c and closer to the power transmission coil 32.

[0096] As described above, the closer the power supply coils 31A, 31B, and 31C are to the power transmission coil 32, the closer the magnetic field coupling between the power supply coils 31A, 31B, and 31C and the power transmission coil 32 becomes (the larger the coupling coefficient becomes), and the farther the power supply coils 31A, 31B, and 31C are from the power transmission coil 32, the looser the magnetic field coupling between the power supply coils 31A, 31B, and 31C and the power transmission coil 32 becomes (the smaller the coupling coefficient becomes).

[0097] The function of the amount by which the coil moving mechanism 96 moves the power supply coil 31 (stroke amount of the plunger 96a) and the amount of change in impedance of the circuit in the power transmission device 3 is obtained in advance by an experiment or the like.

[0098] Such a mechanism for moving the power supply coil 31 relative to the power transmission coil 32 using the coil movement mechanism 96 is less responsive than a configuration for electrically switching the switches 91a to 91d. Therefore, even if the impedance value changes significantly, smooth optimization can be achieved by, for example, roughly adjusting the impedance by controlling the switching of the switches 91a to 91d, and then fine-tuning the impedance by moving the power supply coil 31 relative to the power transmission coil 32.

[0099] Specifically, first, power feed coil 31A is arranged at a center-to-center distance L of 300 mm from power transmission coil 32, power feed coil 31B is arranged at a center-to-center distance L of 400 mm from power transmission coil 32, and power feed coil 31C is arranged at a center-to-center distance L of 500 mm from power transmission coil 32, power feed coils 31A, 31B, and 31C are configured as a single unit, and coil moving mechanism 96 is configured to be able to move power feed coils 31A, 31B, and 31C parallel to coil axes 31a, 31b, and 31c within a range of ±50 mm. That is, power feed coil 31A is movable within a center-to-center distance L range of 250 to 350 mm, power feed coil 31B is movable within a center-to-center distance L range of 350 to 450 mm, and power feed coil 31C is movable within a center-to-center distance L range of 450 to 550 mm.

[0100] For example, when the drive power of the load 8 is 300 W or more and less than 1000 W, the power supply coil 31A is used; when the drive power of the load 8 is 30 W or more and less than 300 W, the power supply coil 31B is used; when the load 8 is OFF or the drive power of the load 8 is less than 50 W, the power supply coil 31C is used; and then, the power supply coils 31A, 31B, and 31C are moved relative to the power transmission coil 32 to optimize the impedance.

[0101] Alternatively, the impedance may be optimized by roughly adjusting the impedance by moving the power feeding coil 31 relative to the power transmitting coil 32 using the coil moving mechanism 96, and then fine-tuning the impedance by controlling the switches 91a to 91d. In this case, the impedance can be finely adjusted at high speed, allowing smooth optimization even when the impedance changes suddenly.

[0102] Specifically, the power supply coil 31, which is made up of power supply coils 31A, 31B, and 31C arranged at a distance of 50 mm from one another, is treated as one unit, and the coil moving mechanism 96 is configured to be able to move the power supply coils 31A, 31B, and 31C by 100 mm or 200 mm in a direction away from the power transmission coil 32 in parallel with the coil axes 31a, 31b, and 31c.

[0103] For example, in a state where power supply coil 31A is arranged at a position with a center-to-center distance L of 200 mm, power supply coil 31B is arranged at a position with a center-to-center distance L of 250 mm, and power supply coil 31C is arranged at a position with a center-to-center distance L of 300 mm, when the drive power of load 8 is 700 W or more, power supply coil 31B is used, and when the drive power of load 8 is 350 W or more and less than 700 W, power supply coil 31C is used, thereby optimizing the impedance.

[0104] Furthermore, the coil moving mechanism 96 moves each of the power supply coils 31A, 31B, and 31C by 100 mm in a direction away from the power transmission coil 32, so that the power supply coil 31A is positioned at a center-to-center distance L of 300 mm, the power supply coil 31B is positioned at a center-to-center distance L of 350 mm, and the power supply coil 31C is positioned at a center-to-center distance L of 400 mm.In this state, the impedance is optimized by using the power supply coil 31A when the drive power of the load 8 is 350 W or more and less than 700 W, the power supply coil 31B when the drive power of the load 8 is 200 W or more and less than 350 W, and the power supply coil 31C when the drive power of the load 8 is 50 W or more and less than 200 W.

[0105] Furthermore, the coil moving mechanism 96 moves each of the power supply coils 31A, 31B, and 31C by 200 mm in a direction away from the power transmission coil 32, so that the power supply coil 31A is positioned at a position with a center-to-center distance L of 400 mm, the power supply coil 31B is positioned at a position with a center-to-center distance L of 450 mm, and the power supply coil 31C is positioned at a position with a center-to-center distance L of 500 mm.In this state, the impedance is optimized by using the power supply coil 31A when the drive power of the load 8 is 50 W or more and less than 200 W, the power supply coil 31B when the drive power of the load 8 is 10 W or more and less than 50 W, and the power supply coil 31C when the load 8 is OFF or the drive power of the load 8 is less than 10 W.

[0106] <Variation 3> In the above-described embodiment, the power supply coil 31 is illustrated as being made up of power supply coils 31A, 31B, and 31C whose coil axes 31a, 31b, and 31c are arranged substantially coaxially. However, the configuration of the power supply coil 31 is not limited to this.

[0107] For example, as shown in FIGS. 11(a) to 11(c), the power supply coil 31 may include power supply coils 31A, 31B, and 31C in which coil axes 31a, 31b, and 31c are arranged offset from each other and spaced apart from each other, and are substantially parallel to each other.

[0108] In this case, the magnetic field coupling between the power feed coil 31 and the power transmission coil 32 becomes stronger as the opposing area increases. Therefore, as shown in FIG. 11(a), the power feed coil 31A has the closest magnetic field coupling with the power transmission coil 32 because its coil axis 31a and coil axis 32a are coaxial. As shown in FIG. 11(b), the power feed coil 31B has the weakest magnetic field coupling with the power transmission coil 32 because its coil axis 31b is farther from the coil axis 32a. Furthermore, as shown in FIG. 11(c), the power feed coil 31C has the weakest magnetic field coupling with the power transmission coil 32 because its coil axis 31c is farthest from the coil axis 32a. With this configuration, power is selectively supplied to at least one of the power feed coils 31A, 31B, and 31C by controlling the switching of the switches 91a and 91b, so the strength of coupling (coupling coefficient) between the power feed coil 31 and the power transmission coil 32 can be adjusted.

[0109] <Variation 4> The power supply coil 31 may include eight power supply coils 31A to 31H arranged in a spherical shape, as shown in FIGS. 12(a) to 12(c), for example.

[0110] The power feeding coil 31 is made up of power feeding coils 31A to 31H that are inclined to each other with their centers aligned. The power feeding coils 31A to 31H are each one coil divided into eight sections, and are connected substantially in series. Although detailed descriptions of the connections between the power feeding coils 31A to 31H are omitted, similar to FIG. 2, the power feeding coils 31A to 31H are connected by a switch or the like (not shown) so that power from the AC power supply 5 can be supplied to at least one of the power feeding coils 31A to 31H.

[0111] 12(a), the power feeding coil 31A is housed within the power feeding coil 32 with its coil axis 31a substantially aligned with the coil axis 32a of the power feeding coil 32, i.e., without being tilted relative to the power feeding coil 32. As shown in FIG. 12(b), the power feeding coil 31C is housed within the power feeding coil 32 with a portion thereof tilted at approximately 45 degrees relative to the power feeding coil 32. As shown in FIG. 12(c), the power feeding coil 31E is housed within the power feeding coil 32 with a portion thereof tilted at approximately 90 degrees relative to the power feeding coil 32. Furthermore, the power feeding coils 31B, 31D, and 31F to 31H are housed within the power feeding coil 32 with a portion thereof tilted at approximately 22.5 degrees, approximately 67.5 degrees, approximately 112.5 degrees, approximately 135 degrees, and approximately 157.5 degrees relative to the power feeding coil 32, respectively.

[0112] In this case, the magnetic field coupling between the power feed coil 31 and the power transmission coil 32 becomes denser as the opposing area increases. That is, the power feed coil 31A has the coil axis 31a and the coil axis 32a positioned coaxially, and therefore has the densest magnetic field coupling with the power transmission coil 32. The power feed coil 31E has the loosest magnetic field coupling with the power transmission coil 32.

[0113] With this configuration, impedance matching can be performed by appropriately switching between, for example, the three power feeding coils 31A, 31C, and 31E. That is, when the DC-DC converter 7 is idling and the load impedance is large relative to the input impedance, supplying power to the power feeding coil 31A as shown in Fig. 12(a) increases the magnetic field coupling between the power feeding coil 31 and the power transmitting coil 32, thereby reducing the impedance of the circuit within the power transmitter 3. As a result, the load impedance at the input terminal IE decreases, and the difference with the input impedance is alleviated.

[0114] 12(b), when the DC-DC converter 7 is operating and the load impedance is lower than the input impedance, power is supplied to the power feed coil 31C, which is inclined relative to the power transmission coil 32 compared to the power feed coil 31A, thereby reducing the magnetic field coupling between the power feed coil 31 and the power transmission coil 32 and increasing the impedance of the circuit in the power transmitter 3. As a result, the load impedance at the input terminal IE increases, and the difference with the input impedance is alleviated.

[0115] Furthermore, when the load-side impedance is further reduced, as shown in FIG. 12(c), supplying power to the power supply coil 31E, which is orthogonal to the power transmission coil 32, further weakens the magnetic field coupling between the power supply coil 31 and the power transmission coil 32, further increasing the impedance of the circuit within the power transmission device 3. As a result, the negative impedance at the input terminal IE increases, and the difference with the input-side impedance is alleviated.

[0116] With this configuration, power is selectively supplied to at least one of the power feeding coils 31A to 31H, so that the coupling strength between the power feeding coil 31 and the power transmitting coil 32 can be adjusted.

[0117] Furthermore, the number of power supply coils constituting the spherical power supply coil 31 according to this modification is not limited to 8, and may be any number equal to or greater than 2. Furthermore, the inclination of the power supply coils 31A to 31H relative to the power transmission coil 32 according to this modification is set in the range of 0 to 180 degrees, but may be set in the range of −90 to +90 degrees in consideration of the phase of the coils.

[0118] Furthermore, the power feeding coil 31 is not limited to being housed within the power transmitting coil 32, but may be arranged outside the power transmitting coil 32. Furthermore, some of the power feeding coils 31A to 31H may be arranged inside the power transmitting coil 32, and the other power feeding coils 31A to 31H may be arranged outside the power transmitting coil 32. Note that the inclination of the power feeding coil 31 with respect to the power transmitting coil 32 is determined by the coupling coefficient k 01 is a geometric progression, the impedance adjustment range at the angle of each power feeding coil 31 becomes substantially constant, and impedance matching can be performed more stably.

[0119] <Variation 5> In the above-described embodiment, the power supply coil 31 is made up of power supply coils 31A, 31B, and 31C formed in substantially the same shape, but the power supply coils 31A, 31B, and 31C may have different shapes.

[0120] 13(a) to 13(c), the power supply coils 31A, 31B, and 31C may have a spiral shape in which the coil diameter increases and decreases on approximately the same plane. In this case, the coil axes 31a, 31b, and 31c are arranged approximately coaxially, and the power supply coils 31A, 31B, and 31C are formed so that their coil diameters gradually decrease and their coil heights increase in this order. Specifically, the power supply coil 31A has approximately the same coil diameter as the power transmission coil 32, and the power supply coils 31B and 31C are arranged on the inner periphery of the power supply coil 31A, and the power supply coil 31C is arranged on the inner periphery of the power supply coil 31B. Furthermore, when power is transmitted between the power supply coil 31 and the power transmission coil 32 using the magnetic field resonance method, it is preferable to gradually increase the number of turns of the power supply coils 31A, 31B, and 31C in this order so that the inductances of the power supply coils 31A, 31B, and 31C, which have different coil diameters, are equal to each other.

[0121] In this case, the magnetic field coupling between the power feed coil 31 and the power transmission coil 32 becomes tighter as the difference in coil diameter between them decreases. Therefore, as shown in FIG. 13(a), the power feed coil 31A has approximately the same coil diameter as the power transmission coil 32, and therefore the magnetic field coupling with the power transmission coil 32 is the tightest. As shown in FIG. 13(b), the power feed coil 31B has a smaller coil diameter than the power transmission coil 32, and therefore the magnetic field coupling with the power transmission coil 32 is looser. Furthermore, as shown in FIG. 13(c), the power feed coil 31C has an even smaller coil diameter than the power transmission coil 32, and therefore the magnetic field coupling with the power transmission coil 32 is the loosest. With this configuration, power is selectively supplied to at least one of the power feed coils 31A, 31B, and 31C by switching control of the switches 91a and 91b, so the strength of the coupling between the power feed coil 31 and the power transmission coil 32 can be adjusted.

[0122] <Variation 6> 14(a) to 14(c), the power feeding coil 31 may be configured so that the coil diameter gradually decreases from the outer periphery toward the center on the same plane. In this case, coil axes 31a, 31b, and 31c are arranged substantially coaxially, and power feeding coils 31A, 31B, and 31C are arranged substantially on the same plane, with the coil diameters of power feeding coils 31A, 31B, and 31C gradually decreasing in this order. Specifically, the power feeding coil 31A has substantially the same coil diameter as the power transmission coil 32, and power feeding coils 31B and 31C are arranged on the inner periphery of power feeding coil 31A, and power feeding coil 31C is arranged on the inner periphery of power feeding coil 31B. Furthermore, when power is transmitted between the power supply coil 31 and the power transmission coil 32 using the magnetic field resonance method, it is preferable to gradually increase the number of turns of the power supply coils 31A, 31B, and 31C in this order so that the inductances of the power supply coils 31A, 31B, and 31C, which have different coil diameters, are equal to each other.

[0123] In this case, the magnetic field coupling between the power feed coil 31 and the power transmission coil 32 becomes tighter as the difference in coil diameter between them decreases. Therefore, as shown in FIG. 14(a), the power feed coil 31A has approximately the same coil diameter as the power transmission coil 32, and therefore the magnetic field coupling with the power transmission coil 32 is the tightest. As shown in FIG. 14(b), the power feed coil 31B has a smaller coil diameter than the power transmission coil 32, and therefore the magnetic field coupling with the power transmission coil 32 is looser. Furthermore, as shown in FIG. 14(c), the power feed coil 31C has an even smaller coil diameter than the power transmission coil 32, and therefore the magnetic field coupling with the power transmission coil 32 is the loosest. With this configuration, power is selectively supplied to at least one of the power feed coils 31A, 31B, and 31C by switching control of the switches 91a and 91b, so the coupling strength (coupling coefficient) between the power feed coil 31 and the power transmission coil 32 can be adjusted.

[0124] In the above-described embodiment, the case where the power feeding coil 31, the power transmitting coil 32, and the power receiving coil 41 are all in a resonant state in order to reduce the imaginary part of the impedance to zero and suppress the generation of reactive power has been described as an example. However, even if the capacitor 33 is not connected to the power feeding coil 31, for example, reactive power occurs in the input impedance, but power transmission itself is possible, so only the power transmitting coil 32 and the power receiving coil 41 may be in a resonant state.

[0125] Furthermore, in the above-described embodiment, the wireless power supply system 1 has been described as an example of a three-coil system configuration including the power supply coil 31, the power transmitting coil 32, and the power receiving coil 41. However, the wireless power supply system may be a two-coil system having only the power transmitting coil 32 and the power receiving coil 41 without the power supply coil 31. In this case, the power transmitting coil 32 is divided into multiple power transmitting coil sections, and the relative positions of the power transmitting coil sections and the power receiving coil 41 are changed, thereby enabling control of the load-side impedance.

[0126] In a two-coil system consisting of the power transmitting coil 32 and the power receiving coil 41, if the position of the power transmitting coil 32 is moved to vary the load-side impedance, the coil axis 32a of the power transmitting coil 32 and the coil axis of the power receiving coil 41 will not be aligned coaxially, which may result in a decrease in power transmission efficiency. In contrast, in a three-coil system consisting of the power feeding coil 31, the power transmitting coil 32, and the power receiving coil 41, power is fed to the power transmitting coil 32 via the power feeding coil 31, and by adjusting the strength of the magnetic coupling between the power feeding coil 31 and the power transmitting coil 32 without changing the relative positions of the power transmitting coil 32 and the power receiving coil 41, the load-side impedance can be controlled and good power transmission efficiency can be maintained.

[0127] Furthermore, in the above-described embodiment, the wireless power transfer system 1 has been described as an example of a three-coil system configuration including the power transfer coil 31, the power transmitting coil 32, and the power receiving coil 41. However, the wireless power transfer system may also be configured as a four-coil system including a second power receiving coil in addition to the power receiving coil 41. In this case, the power receiving coil 41 is set to a resonance frequency approximately equal to that of the power transmitting coil 32, and power is transferred by magnetic field resonance. The power receiving coil 41 and the second power receiving coil are arranged in a non-contact manner, and power is transferred by electromagnetic coupling (electromagnetic induction) or magnetic field resonance. In a four-coil system, the power transmitting coil 32 and the power receiving coil 41 are resonant coils independent of other electric circuits, and therefore the resonance frequency does not change during operation, making the design easier and enabling a longer power transfer distance.

[0128] Furthermore, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention, and it goes without saying that the present invention also covers such modifications. [Explanation of symbols]

[0129] 1: Wireless power supply system 11: Wireless power transmission system 2: Power supply object 3: Power transmission equipment 31: Power supply coil 31A to 31H: Power supply coil 31a to 31c: Coil axis (of the power supply coil) 32: Transmission coil 32a: Coil axis (of the transmitting coil) 33, 34: Capacitor 35: Power supply side resonant circuit 36: Power transmission side resonant circuit 4: Power receiving device 41: Receiving coil 42: Capacitor 43: Receiving side resonant circuit 5: AC power supply (power supply device) 6: Rectifier circuit 61: Diode 62: Capacitor 7: DC-DC converter 8: Load 9: Impedance matching mechanism 91a, 91b: Switch 92: Controller 93: Storage section 94: Control unit 95: Measuring part 96: Linear motion mechanism 96a: Plunger 96b: Case IE: Input terminal

Claims

1. A wireless power supply system that transmits and receives power using magnetism, a power transmitting device including: a power transmitting-side resonant circuit including a power transmitting coil; and a plurality of power feeding coils that are arranged to be magnetically coupled with the power transmitting coil and that feed power supplied from an input terminal to the power transmitting coil by a magnetic field resonance method; a power receiving device including a power receiving side resonant circuit including a power receiving coil, the power receiving device supplying the power received by the power receiving coil to a load; an impedance matching mechanism that performs impedance processing to reduce the difference between a load-side impedance, which is the impedance of a circuit from an input end of the power transmitting device to a load side, and an input-side impedance, which is the impedance of a circuit from the input end of the power transmitting device to a power supply device side; Equipped with the plurality of power supply coils are set to have different coupling strengths in magnetic field coupling with the power transmission coil, are connected in parallel with each other, and transmit power to the power transmission coil; the impedance matching mechanism supplies power to at least one of the plurality of power supply coils; a plurality of the power supply coils are oriented in different directions and have coil axes that are angled differently relative to the coil axis of the power transmission coil;

2. A wireless power supply system that transmits and receives power using magnetism, a power transmitting device including: a power transmitting-side resonant circuit including a power transmitting coil; and a plurality of power feeding coils that are arranged to be magnetically coupled with the power transmitting coil and that feed power supplied from an input terminal to the power transmitting coil by a magnetic field resonance method; a power receiving device including a power receiving side resonant circuit including a power receiving coil, the power receiving device supplying the power received by the power receiving coil to a load; an impedance matching mechanism that performs impedance processing to reduce the difference between a load-side impedance, which is the impedance of a circuit from an input end of the power transmitting device to a load side, and an input-side impedance, which is the impedance of a circuit from the input end of the power transmitting device to a power supply device side; Equipped with the plurality of power supply coils are set to have different coupling strengths in magnetic field coupling with the power transmission coil, are connected in parallel with each other, and transmit power to the power transmission coil; the impedance matching mechanism supplies power to at least one of the plurality of power supply coils; a plurality of the power supply coils each having a coil axis that is substantially parallel to a coil axis of the power transmission coil and offset by different distances from each other;

3. A wireless power supply system that transmits and receives power using magnetism, a power transmitting device including: a power transmitting-side resonant circuit including a power transmitting coil; and a plurality of power feeding coils that are arranged to be magnetically coupled with the power transmitting coil and that feed power supplied from an input terminal to the power transmitting coil by a magnetic field resonance method; a power receiving device including a power receiving side resonant circuit including a power receiving coil, the power receiving device supplying the power received by the power receiving coil to a load; an impedance matching mechanism that performs impedance processing to reduce the difference between a load-side impedance, which is the impedance of a circuit from an input end of the power transmitting device to a load side, and an input-side impedance, which is the impedance of a circuit from the input end of the power transmitting device to a power supply device side; Equipped with the plurality of power supply coils are set to have different coupling strengths in magnetic field coupling with the power transmission coil, are connected in parallel with each other, and transmit power to the power transmission coil; the impedance matching mechanism supplies power to at least one of the plurality of power supply coils; the plurality of power supply coils each have a coil axis that is arranged substantially coaxially, A wireless power supply system characterized in that the coil diameters and coil heights of the respective power supply coils are set to be different from one another.

4. 4. The wireless power supply system according to claim 1, wherein the inductance values ​​of the power supply coils are set to be approximately equal.

5. 4. The wireless power supply system according to claim 1, wherein the power supply coil is configured to be movable relative to the power transmission coil.

6. 4. The wireless power supply system according to claim 1, wherein power is supplied from the power transmitting coil to the power receiving coil by a magnetic field resonance method.

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