JP7802280B2 - Wireless Power Supply System - Google Patents

Description

The present invention relates to a wireless power supply system .

In recent years, research and development of wireless power transfer systems that utilize magnetic fields has been progressing. Known power transfer methods that utilize such magnetism include electromagnetic coupling (electromagnetic induction) and magnetic resonance. In magnetic resonance, magnetic field vibrations generated by AC current flowing through a resonant circuit in a power transmitting device are transmitted to a resonant circuit in a power receiving device, causing resonance, resulting in the magnetic fields generated by the coils of each resonant circuit being tightly coupled (magnetic resonance coupling), thereby transmitting power. Wireless power transfer using magnetic resonance has the advantage of a longer power transfer distance compared to wireless power transfer using electromagnetic coupling (see, for example, Patent Document 1). While magnetic resonance also utilizes magnetic coupling, this invention refers to the method that utilizes resonance as magnetic resonance for ease of understanding.

In such a wireless power transfer system, in order to transmit power efficiently, the impedance of the load-side circuit, including the power receiving device and load, as seen from the power transmitting device, must be set equivalent to the impedance of the power source side as seen from the power transmitting device.

JP 2018-505369 A

However, a driving component such as a battery or motor is connected to the load-side circuit, and the battery or motor acts as a load. Therefore, the current flowing through the load-side circuit can fluctuate depending on the driving state of the battery or 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 drop in transmitted power, which could potentially lead to system failure.

This presents a technical challenge that must be overcome to mitigate the decline in power transmission efficiency even when the impedance of the load-side circuit fluctuates, and the present invention aims to solve this challenge.

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

This invention reduces the difference between the input impedance and the load impedance even when the impedance of the load circuit fluctuates, thereby suppressing the generation of reflected waves at the input terminal and avoiding a decrease in power transmission efficiency and the associated risk of system failure.

1 is a schematic diagram illustrating a configuration of a wireless power supply system according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of an impedance matching mechanism. FIG. 2 is a circuit diagram corresponding to the wireless power supply system. FIG. 4 is an equivalent circuit diagram corresponding to the circuit diagram shown in FIG. 3 . 1 is a graph showing the relationship between a load voltage and a load current. 1 is a graph showing the relationship between a load current and a load-side impedance. 10 is a schematic diagram illustrating the positional relationship between a power transmission coil and three power supply coils arranged offset in the axial direction of the coil axis. FIG. 10 is a graph showing the relationship between the distance from the power feeding coil to the power transmitting coil and the load resistance. 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. 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. 10 is a schematic diagram illustrating 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. 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. FIG. 10 is a schematic diagram showing the positional relationship between a power transmission coil and three power supply coils arranged in a spiral. FIG. 10 is a schematic diagram showing the positional relationship between a power transmission coil and three power supply coils arranged on the same plane.

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.

In addition, when referring to the shape or positional relationship of components, etc., this includes things that are substantially similar or approximate to that shape, etc., unless otherwise specified or when it is clearly considered otherwise in principle.

In addition, drawings may exaggerate characteristic parts to make their 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.

<Configuration of wireless power supply system>
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, during power supply, 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.

<Configuration of power transmission device>
The power transmission device 3 includes a power supply coil 31 , a power transmission coil 32 , and capacitors 33 and 34 .

The power supply coil 31 and the power transmission coil 32 are formed by winding a highly conductive copper wire or similar material into a circular shape. Due to the influence of internal resistance, the current flowing through the copper wire flows more near the surface than in the center of the wire. Therefore, if a litz wire made by twisting together multiple copper wires is used 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.

The power supply coil 31 is supplied with AC power from the AC power source 5. The AC power is set, for example, to 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 supply 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 supply coil 31 and the AC power source 5 are described as being directly connected via the input end IE. However, the power supply coil 31 and the AC power source 5 may be connected directly via the input end IE or indirectly 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 supply matches the impedance of the coaxial cable or the like, the power supply end of the coaxial cable or the like does not cause power reflections or other problems, and the input end IE refers to the load end of the coaxial cable or the like.

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

The power supply coil 31 and the power transmission coil 32 are magnetically coupled, and the power supply coil 31 supplies power to the power transmission coil 32 using magnetic resonance. Specifically, the power supply coil 31 and the power transmission coil 32 are designed to resonate at a resonant frequency set according to the inductance of the power supply coil 31 and the capacitance of the capacitor 33, which is approximately equal to the 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 AC current flowing through the power supply coil 31 are transmitted to the power transmission coil 32, resonating at the same specific frequency, generating an electromotive force in the power transmission coil 32. Note that while magnetic resonance is preferred for power supply from the power supply coil 31 to the power transmission coil 32, as this reduces the influence of the relative positions of the coils, an electromagnetic coupling method may also be used, in which an electromotive force is also generated in the power transmission coil 32 via a magnetic flux that penetrates the power supply coil 31 in the coil axial direction when AC current flows through the power supply coil 31. Additionally, the magnetic resonance method and the electromagnetic coupling method may be used together.

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

<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 42.

The receiving coil 41 is spaced apart from the transmitting coil 32 in the coil axial direction. The receiving coil 41 is formed by winding a highly electrically conductive copper wire or the like in a circular shape. Like the feeding coil 31 and transmitting coil 32, the receiving coil 41 preferably uses Litz wire as the wire material.

The receiving coil 41 and capacitor 42 are connected in series to form the receiving-side resonant circuit 43. The resonant frequency, set by the inductance of the receiving coil 41 and the capacitance of the capacitor 42, is set to approximately match the resonant frequency of the transmitting coil 32 and capacitor 33. As a result, an induced current flows in the receiving coil 41 due to the oscillation of the magnetic field that penetrates the transmitting coil 32 in the coil axial direction, generating an oscillating magnetic field that penetrates the receiving coil 41 in the coil axial direction. At this time, the magnetic fields of the transmitting coil 32 and the receiving coil 41 resonate and are strongly coupled.

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

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

The DC-DC converter 7 converts the rectified DC voltage into a preset constant voltage (e.g., 12 V). The voltage output from the DC-DC converter 7 is applied to the load 8. Note that the DC-DC converter 7 only needs to be placed according to the required voltage, and may be omitted as appropriate.

<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, 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 the "load side impedance"), and the impedance of the circuit from the input terminal IE to the AC power source 5 (hereinafter referred to as the "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 transmission system 11.

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 switches 91a and 91b. Note that other configurations may be used in place of switches 91a and 91b as long as they are capable of selectively supplying power to one of power supply coils 31A, 31B, and 31C.

The power supply coil 31 consists of three power supply coils 31A, 31B, and 31C arranged in parallel to one another. Under normal conditions, the coil axes 31a, 31b, and 31c of the power supply coils 31A, 31B, and 31C and the coil axis 32a of the power transmission coil 32 are positioned approximately coaxially. The following description will be given using an example in which the power supply coil 31 is divided into three power supply coils 31A, 31B, and 31C, but the number of power supply coils may be two, four, or more.

The power supply coils 31A, 31B, and 31C are arranged so 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 they are further away from the power transmission coil 32. Therefore, the strength of the 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.

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

When power is supplied to the power supply 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 supply coil 31A. When power is supplied to the power supply 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 supply coil 31B. When power is supplied to the power supply coil 31C, the switch 91a is switched to the power supply coil 31C side.

Switching control of switches 91a and 91b is controlled by controller 92. Controller 92 is composed of, for example, a CPU, memory, etc. The functions of 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 memory unit 93 and a control unit 94 (see Figure 1).

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 transmission device 3 to the load side, can be adjusted according to the distance from the power transmission coil 32.

This will be described in more detail with reference to Figures 3 and 4. Figure 3 is a circuit diagram corresponding to the wireless power supply system 1. In FIG. 3 , “V” is the voltage of the power supply 5, “Z _s ” is the impedance (input side impedance) of the power supply 5, “R ₀ ” is the parasitic resistance of the power feeding coil 31, “L ₀ ” is the inductance of the power feeding coil 31, “C ₀ ” is the capacitance of the capacitor 33, “I ₀ ” is the current flowing through the power feeding coil 31, “R ₁ ” is the parasitic resistance of the power transmitting coil 32, “L ₁ ” is the inductance of the power transmitting coil 32, “C ₁ ” is the capacitance of the capacitor 34, “I ₁ ” 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, “R ₂ ” is the parasitic resistance of the power receiving coil 41, “R _L ” is the load resistance of the load 8, “L ₂ ” is the inductance of the power receiving coil 41, “C ₂ ” is the capacitance of the capacitor 42, “I ₂ ” is the current flowing through the power receiving coil 41, and “ _k ” is the coupling coefficient between the power transmitting coil 32 and the power receiving coil 41.

Fig. 4 is an equivalent circuit diagram based on the circuit diagram shown in Fig. 3. The equivalent circuit diagram shown in Fig. 4 illustrates a state in which the power feeding coil 31 and the power transmitting coil 32 resonate and the power transmitting coil 32 and the power receiving coil 41 resonate. The mutual inductance _L0 between the power feeding coil 31 and the power transmitting coil ₃₂ is _k01√ ( _L0L1 ), and the mutual inductance _L2 between the power transmitting coil 32 and the power receiving coil 41 is _k12√ ( _L1L2 ). " _Z0 " in Fig. 4 is _the impedance of the circuit between the power source 5 and the power feeding coil 31, i.e., the impedance of the circuit from the input end IE of the power transmitter 3 to the load 8 (load-side impedance). " _Z1 " is the impedance of the circuit from the power feeding coil 31 and the power transmitting coil 32 to the load 8. " _Z2 " is the impedance of the circuit from the power feeding coil 31 and the power transmitting coil 32 to the load 8. The following formulas 1 to 3 are obtained from the equivalent circuit shown in FIG.

In the present invention, impedance matching means that when the load resistance _RL changes, the load side impedance Z0 of the circuit when looking at the load 8 side from the input terminal IE of the power transmission device ₃ is matched to the input side impedance _Zs of the power source 5 and kept approximately constant.

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 on the load 8 side between the power supply coil 31 and the power transmission coil 32 decreases, as can be seen from equation (1). At this time, the impedance _Z1 of the circuit on the load 8 side between the power supply coil 31 and the power transmission coil 32 increases, as can be seen from equation (2), and the load-side impedance _Z0 decreases, as can be seen from equation (3). In other words, while the load-side impedance _Z0 decreases, the input-side impedance _Zs does not change.

Therefore, by controlling the switches 91a to 91d to supply power to the power feeding coil 31A that is closest to the power feeding coil 32, the magnetic field coupling with the power feeding coil 32 becomes closer and the coupling coefficient _k01 increases. Then, by increasing the coupling coefficient _k01 between the power feeding coil 31 and the power feeding coil 32 at a rate equal to the rate at which the impedance _Z1 of the circuit on the load 8 side between the power feeding coil ₃₁ and the power feeding coil 32 increases, the load impedance Z0 can be kept constant. In this way, by continuing to control the load impedance _Z0 to be approximately equal to the input impedance _Zs , power reflection is suppressed, and an efficient system operating state can be achieved.

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). In this case, 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 _Zs does not change.

Therefore, by supplying power to one of the power feeding coils 31B and 31C through switching control of the switches 91a to 91d, 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 _k01 decreases. The load-side impedance _Z0 can be kept constant by reducing the coupling coefficient _k01 between the power feeding coil 31 and the power transmitting coil 32 at a rate equal to the rate at which the impedance _Z1 of the circuit on the load 8 side between the power feeding coil 31 and the power transmitting coil 32 decreases. By continuing to control the load-side impedance _Z0 to be approximately equal to the input-side impedance _Zs in this way, power reflection is suppressed, and an efficient system operating state can be achieved.

The memory unit 93 stores a function showing 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 showing the relationship between the load current and the 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. Note that the measurement unit 95 is not limited to measuring the load voltage, but may also measure the load current, or both. Note that 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.

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

Furthermore, as shown in Figure 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).

The function showing the relationship between load voltage and load current and the function showing the relationship between load current and load-side impedance may be calculated in advance through experiments, etc., and are not limited to the linear function graphs shown in Figures 5 and 6.

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 memory unit 93. Details of the switching control of the switches 91a and 91b by the control unit 94 will be described later.

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 measurement unit 95, thereby reducing the difference between the input-side impedance and the load-side impedance at the input terminal IE in real time.

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

First, we will explain why the load-side impedance fluctuates 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 fluctuates depending on whether the DC-DC converter 7 is on or off. However, fluctuations in the load-side impedance can occur not only due to the on/off of the DC-DC converter 7, 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. It goes without saying that this can be used to suppress fluctuations in the load-side impedance due to these various factors.

As shown in Figure 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 (output current of the DC-DC converter 7) is nearly zero. When the measuring unit 95 is placed between the capacitor 62 and the DC-DC converter 7, the load current (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 Figure 6. Furthermore, when the measuring unit 95 is placed between the DC-DC converter 7 and the load 8, the load-side impedance is nearly 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.

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

As a result, while the load-side impedance fluctuates depending on the operating state of the DC-DC converter 7, the input-side impedance is fixed at a predetermined value (e.g., 50 Ω). This means that the input-side impedance and the load-side impedance do not match, which can result in reflected waves at the input terminal IE, reducing power transmission efficiency, or insufficient transmitted power, potentially causing a system failure.

The controller 92 therefore increases or decreases the impedance of the circuit within the power transmission device 3 in response to fluctuations in the load-side impedance.

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 Figure 5. The control unit 94 also calculates the load-side impedance based on the calculated load current and the function shown in Figure 6.

Next, the control unit 94 switches the switches 91a and 91b to determine to which of the power supply coils 31A, 31B, and 31C to supply power, adjusting the impedance of the circuit within the power transmission device 3 so that the load impedance matches the input impedance.

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 supply coil 31A as shown in FIG. 7(a) tightens the magnetic field coupling between the power supply coil 31 and the power transmission coil 32, increasing the coupling coefficient. As a result, as described above, the load impedance at the input terminal IE decreases, reducing the difference with the input impedance.

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 Figure 7(b), power is supplied to the power supply coil 31B, which is farther from the power transmission coil 32 than the power supply coil 31A. This loosens the magnetic field coupling between the power supply coil 31 and the power transmission coil 32, and reduces the coupling coefficient. As a result, the load impedance at the input end IE increases, reducing the difference with the input impedance.

Furthermore, when the load-side impedance decreases further, as shown in Figure 7(c), by supplying power to the power supply coil 31C, which is farthest from the power transmission coil 32, the magnetic field coupling between the power supply coil 31 and the power transmission coil 32 becomes weaker and the coupling coefficient decreases. As a result, the load-side impedance at the input end IE increases further, and the difference with the input-side impedance is alleviated.

The function of the distance between the power supply coils 31A, 31B, and 31C and the power transmission coil 32 and the change in the engagement coefficient is obtained in advance through experiments, etc.

In this way, the wireless power transfer system 1 according to this embodiment is a wireless power transfer system 1 that transmits and receives power using magnetism and includes a power transmitter 3 having a power transmitter-side resonant circuit 36 including a power transmitter coil 32; a power receiver 4 having a power receiver-side resonant circuit 43 including a power receiver coil 41; a load 8 to which the power received via the power receiver 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 transmitter 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 transmitter 3 to the AC power source 5. The power transmitter 3 is arranged to be magnetically coupled to the power transmitter coil 32, and further includes multiple power feed coils 31A, 31B, and 31C that are set to have different coupling strengths in the magnetic field coupling with the power transmitter coil 32 and are connected in parallel to transfer power to the power transmitter coil 32. The impedance matching mechanism 9 supplies power to at least one of the multiple power feed coils 31A, 31B, and 31C.

With this configuration, when the load impedance and input impedance do not match, 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 between the power supply coil 31 and the power transmission coil 32 (how tight or loose the magnetic field coupling). This increases or decreases the impedance of the circuit within the power transmission device 3, reducing the difference between the input impedance and the load impedance. This suppresses the generation of reflected waves at the input terminal IE, and avoids system failures due to reduced power transmission efficiency or reduced transmitted power.

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.

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 within the power transmission device 3 can be increased or decreased.

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 using a magnetic field resonance method, and the inductance values of the power supply coils 31A, 31B, and 31C are set to be approximately equal.

This configuration enables efficient power supply from power supply coils 31A, 31B, and 31C, which are positioned differently relative to the power transmission coil 32, to the power transmission coil 32 using magnetic field resonance.

The wireless power supply system 1 according to this embodiment further includes a measurement 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 in accordance with the measurement results of the measurement unit 95.

With this configuration, even if the load-side impedance fluctuates due to factors such as the on/off switching of the DC-DC converter 7, the difference between the input-side impedance and the load-side impedance is mitigated, suppressing the occurrence of reflected waves at the input terminal IE and preventing system failures due to reduced power transmission efficiency and reduced transmitted power.

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 using a magnetic field resonance method.

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

Furthermore, the wireless power supply method using the wireless power supply system 1 according to this embodiment 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 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 side, 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 side. The wireless power supply method uses the wireless power supply system 1 that transmits and receives power using magnetism, and the power transmitting device 3 is further provided with a plurality of power supply coils 31A, 31B, and 31C that are arranged to be capable of magnetically coupling with the power transmitting coil 32, are set to have different coupling strengths in the 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.

With this configuration, when the load impedance and input impedance do not match, 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 between the power supply coil 31 and the power transmission coil 32 (how tight or loose the magnetic field coupling). This increases or decreases the impedance of the circuit within the power transmission device 3, reducing the difference between the input impedance and the load impedance. This suppresses the generation of reflected waves at the input terminal IE, and avoids system failures due to reduced power transmission efficiency or reduced transmitted power.

The wireless power transmission system 11 according to this embodiment 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 the load 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 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, depending on the load current or load voltage of the load 8. The power transmitting device 3 further includes multiple power supply coils 31A, 31B, and 31C that are capable of magnetically coupling with the power transmitting coil 32, have different coupling strengths in the magnetic field coupling with the power transmitting coil 32, are connected in parallel, and transmit power to the power transmitting coil 32. The impedance matching mechanism 9 supplies power to at least one of the multiple power supply coils 31A, 31B, and 31C.

With this configuration, when the load impedance and input impedance do not match, 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 between the power supply coil 31 and the power transmission coil 32 (how tight or loose the magnetic field coupling). This increases or decreases the impedance of the circuit within the power transmission device 3, reducing the difference between the input impedance and the load impedance. This suppresses the generation of reflected waves at the input terminal IE, and avoids system failures due to reduced power transmission efficiency or reduced transmitted power.

Furthermore, in the above-described embodiment, the cause of fluctuations in the load-side impedance was explained as being fluctuations in the load current caused by turning the DC-DC converter 7 on and off, but the cause of fluctuations in the load-side impedance is not limited to this.

For example, it is conceivable that the load-side impedance may fluctuate as the power supply target 2 moves. This is because, as the power receiving coil 41 approaches the power transmitting coil 32, the strength of the magnetic coupling between the power transmitting coil 32 and the power receiving coil 41 increases, and as the power receiving coil 41 moves away from the power transmitting coil 32, the strength of the magnetic coupling between the power transmitting coil 32 and the power receiving coil 41 decreases, causing the magnetic coupling state between the power transmitting coil 32 and the power receiving coil 41 to fluctuate. Therefore, in such cases, the distance between the power transmitting coil 32 and the power receiving coil 41 may be monitored, and a determination may be made 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 in accordance with changes in the distance between the power transmitting coil 32 and the power receiving coil 41.

Furthermore, in this embodiment, a configuration has been illustrated in which the input side impedance and the load side impedance are pre-matched when the DC-DC converter 7 is idling. However, it is also possible to configure the input side impedance and the load side impedance to be pre-matched, for example, when the DC-DC converter 7 transitions from idling to ON, or when the load side impedance stabilizes after the DC-DC converter 7 is turned ON.

<Experimental Example>
Next, a simulation was performed to verify the effects and feasibility of the wireless power transfer system 1 according to this embodiment. 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 distance L between the centers of the power transfer coil 31 and the power transmission coil 32 in the axial direction of the coil axes 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 the load resistance R and the vertical axis represents the 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 R 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.

As shown in FIG. 8 , when power supply coil 31A is positioned 300 mm from power transmission coil 32, power supply coil 31B is positioned 400 mm from power transmission coil 32, and power supply coil 31C is positioned 500 mm from power transmission coil 32, the load current is measured by measurement unit 95 to calculate the drive power of load 8, and power supply coils 31A, 31B, and 31C are switched by switching switches 91a to 91d according to the calculated drive power of load 8. Specifically, power supply coil 31A is activated when the drive power of load 8 is 200 W or more, power supply coil 31B is activated when the drive power of load 8 is 20 W or more but less than 200 W, and power supply coil 31C is activated when load 8 is OFF or the drive power of load 8 is less than 20 W.

Increasing the number of power supply coils 31 can achieve more accurate impedance matching. For example, the number of power supply coils 31 can be increased to six, and the installation positions of the power supply coils 31 can be 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 transmission coil 32. In this case, a power supply coil with a center-to-center distance L of 250 mm is activated when the drive power of the load 8 is 700 W or more, a power supply coil with a center-to-center distance L of 300 mm is activated when the drive power of the load 8 is 350 W or more but less than 700 W, a power supply coil with a center-to-center distance L of 350 mm is activated when the drive power of the load 8 is 200 W or more but less than 350 W, a power supply coil with a center-to-center distance L of 400 mm is activated when the drive power of the load 8 is 50 W or more but less than 200 W, a power supply coil with a center-to-center distance L of 450 mm is activated when the drive power of the load 8 is 10 W or more but less than 50 W, and a power supply coil with a center-to-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.

Furthermore, the multiple power supply coils 31 do not necessarily need to be arranged at equal intervals, and the intervals between the arranged power supply coils 31 may be changed as needed. For example, the number of power supply coils 31 installed in a region where the drive power is low and where the drive power increases suddenly when the load 8 is started may be greater than the number of power supply coils 31 installed in a region where the drive power of the load 8 is high and relatively stable. Specifically, when six power supply coils 31 are provided, the installation positions of the power supply coils 31 are 300 mm, 400 mm, 440 mm, 470 mm, 490 mm, and 500 mm in center-to-center distance L from the power transmission coil 32. 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.

<Modification 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.

As shown in Figures 9(a) and 9(b), the impedance matching mechanism 9 may include a coil movement mechanism 96 that moves the power supply coil 31 relative to the power transmission coil 32.

The coil movement mechanism 96 is a solenoid equipped with 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, 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 substantially parallel to the coil axis 32a.

Specifically, as shown in Figures 2(a) to 2(c), if 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 taken as the original position, as shown in Figure 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, and as shown in Figure 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.

Here, when coil axes 31a, 31b, and 31c are positioned coaxially with coil axis 32a of power transmission coil 32, the magnetic field coupling with power transmission coil 32 becomes tight (the coupling strength (coupling coefficient) becomes large). On the other hand, when coil axes 31a, 31b, and 31c are offset from coil axis 32a of power transmission coil 32 in a direction perpendicular to coil axis 31a, the magnetic field coupling with power transmission coil 32 becomes loose (the coupling strength (coupling coefficient) becomes small).

The function between the offset amount (stroke amount of the plunger 96a) between the coil axis 31a of the power supply coil 31 and the coil axis 32a of the power transmission coil 32 and the change in impedance of the circuit within the power transmission device 3 is obtained in advance through experiments, etc.

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

This mechanism for moving the power supply coil 31 relative to the power transmission coil 32 using the coil movement mechanism 96 has poorer responsiveness than a configuration that electrically switches the switches 91a and 91b. Therefore, 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 supply coil 31 relative to the power transmission coil 32. It is also possible to optimize the impedance by roughly adjusting the impedance by moving the power supply 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.

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

For example, as shown in FIGS. 2(a) to 2(c), if the position of the power supply coil 31 is defined as the original position when the coil axes 31a, 31b, and 31c are coaxial with the coil axis 32a of the power transmission coil 32, the coil movement mechanism 96 may be configured such that, as shown in FIG. 10(a), the plunger 96a retracts, moving 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 advances, moving 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.

As mentioned above, the closer the power supply coils 31A, 31B, and 31C are to the power transmission coil 32, the closer the magnetic field coupling with 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 with the power transmission coil 32 becomes (the smaller the coupling coefficient becomes).

The function between the amount by which the coil movement mechanism 96 moves the power supply coil 31 (stroke amount of the plunger 96a) and the amount of change in impedance of the circuit within the power transmission device 3 is obtained in advance through experiments, etc.

This type of mechanism for moving the power supply coil 31 relative to the power transmission coil 32 using a coil movement mechanism 96 has poorer responsiveness than a configuration that electrically switches the switches 91a to 91d. Therefore, for example, by roughly adjusting the impedance using the switching control 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, smooth optimization can be achieved even when the impedance value changes significantly.

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

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; and 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.

In addition, the impedance can be optimized by roughly adjusting the impedance by moving the power supply coil 31 relative to the power transmission coil 32 using the coil movement mechanism 96, and then fine-tuning the impedance by controlling the switches 91a to 91d. In this case, the impedance can be fine-tuned quickly, allowing for smooth optimization even in the event of a sudden change in impedance.

Specifically, the power supply coil 31, which is made up of power supply coils 31A, 31B, and 31C arranged 50 mm apart from one another, is treated as a single unit, and the coil movement 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 parallel to the coil axes 31a, 31b, and 31c and away from the power transmission coil 32.

For example, with power supply coil 31A positioned at a center distance L of 200 mm, power supply coil 31B positioned at a center distance L of 250 mm, and power supply coil 31C positioned at a center distance L of 300 mm, power supply coil 31B is used when the drive power of load 8 is 700 W or more, and power supply coil 31C is used when the drive power of load 8 is 350 W or more but less than 700 W, thereby optimizing impedance.

Furthermore, by using the coil movement mechanism 96 to move each of the power supply coils 31A, 31B, and 31C by 100 mm in a direction away from the power transmission coil 32, 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, 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.

Furthermore, the coil movement 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, thereby positioning the power supply coil 31A at a position with a center-to-center distance L of 400 mm, the power supply coil 31B at a position with a center-to-center distance L of 450 mm, and the power supply coil 31C at a position with a center-to-center distance L of 500 mm. Impedance is optimized by using power supply coil 31A when the drive power of the load 8 is 50 W or more but less than 200 W, power supply coil 31B when the drive power of the load 8 is 10 W or more but less than 50 W, and power supply coil 31C when the load 8 is OFF or the drive power of the load 8 is less than 10 W.

<Modification 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.

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

At this time, the magnetic field coupling between the power supply coil 31 and the power transmission coil 32 becomes denser as the opposing area increases. Therefore, as shown in FIG. 11( a), the power supply 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 supply 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 supply 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 supply coils 31A, 31B, and 31C by controlling the switching of the switches 91 a and 91 b, so the strength of coupling (coupling coefficient) between the power supply coil 31 and the power transmission coil 32 can be adjusted.

<Modification 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.

The power supply coil 31 is made up of power supply coils 31A to 31H that are inclined to each other with their centers aligned. Power supply coils 31A to 31H are each a single coil divided into eight sections, which are essentially connected in series. Details of the connections between power supply coils 31A to 31H are omitted, but similar to Figure 2, they are connected by switches (not shown) or the like so that power from the AC power supply 5 can be supplied to at least one of the power supply coils 31A to 31H.

As shown in FIG. 12(a), the power supply coil 31A is housed within the power transmission coil 32 with its coil axis 31a substantially aligned with the coil axis 32a of the power transmission coil 32, i.e., without tilting relative to the power transmission coil 32. As shown in FIG. 12(b), the power supply coil 31C is housed within the power transmission coil 32 with a portion thereof tilted at approximately 45 degrees relative to the power transmission coil 32. As shown in FIG. 12(c), the power supply coil 31E is housed within the power transmission coil 32 with a portion thereof tilted at approximately 90 degrees relative to the power transmission coil 32. Furthermore, the power supply coils 31B, 31D, and 31F to 31H are housed within the power transmission 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, respectively, relative to the power transmission coil 32.

At this time, the magnetic field coupling between the power supply coil 31 and the power transmission coil 32 becomes denser as the opposing area increases. That is, the power supply coil 31A has the closest magnetic field coupling with the power transmission coil 32 because the coil axes 31a and 32a are coaxial. The power supply coil 31E has the weakest magnetic field coupling with the power transmission coil 32.

With this configuration, impedance matching can be performed by appropriately switching between the three power supply coils 31A, 31C, and 31E, for example. 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 supply coil 31A as shown in FIG. 12(a) strengthens the magnetic field coupling between the power supply coil 31 and the power transmission coil 32, reducing the impedance of the circuit within the power transmission device 3. As a result, the load impedance at the input terminal IE decreases, reducing the difference with the input impedance.

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 Figure 12(b), by supplying power to the power supply coil 31C, which is inclined relative to the power transmission coil 32 compared to the power supply coil 31A, the magnetic field coupling between the power supply coil 31 and the power transmission coil 32 becomes weaker, and the impedance of the circuit within the power transmission device 3 increases. As a result, the load impedance at the input terminal IE increases, and the difference with the input impedance is alleviated.

Furthermore, as the load-side impedance decreases further, as shown in Figure 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.

With this configuration, power is selectively supplied to at least one of the power supply coils 31A to 31H, making it possible to adjust the coupling strength between the power supply coil 31 and the power transmission coil 32.

Furthermore, the number of power supply coils constituting the spherical power supply coil 31 according to this modification is not limited to eight, and may be any number equal to or greater than two. 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, taking into account the phase of the coils.

Furthermore, the power feeding coil 31 is not limited to being housed within the power feeding coil 32, but may be arranged outside the power feeding coil 32. Alternatively, some of the power feeding coils 31A to 31H may be arranged inside the power feeding coil 32, and the other power feeding coils 31A to 31H may be arranged outside the power feeding coil 32. Note that by configuring the inclination of the power feeding coil 31 with respect to the power feeding coil 32 to be switchable so that the coupling coefficient _k01 is a geometric progression, the impedance adjustment range for each angle of the power feeding coil 31 becomes approximately constant, and impedance matching can be performed more stably.

<Modification 5>
In the above-described embodiment, the power supply coil 31 is illustrated as being 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.

13(a) to 13(c), the power supply coils 31A, 31B, and 31C may have a spiral shape in which the coil diameter expands and contracts 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 become gradually smaller 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.

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

<Modification 6>
14( a) to 14(c), the power supply 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, the coil axes 31a, 31b, and 31c are arranged substantially coaxially, the power supply coils 31A, 31B, and 31C are arranged substantially coaxially, and the power supply coils 31A, 31B, and 31C have gradually smaller coil diameters in this order. Specifically, the power supply coil 31A has substantially the same coil diameter as the power transmission coil 32, 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.

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

In the above-described embodiment, the power supply coil 31, power transmission coil 32, and power receiving coil 41 are all placed in a resonant state in order to reduce the imaginary part of the impedance to zero and suppress the generation of reactive power. However, even if the capacitor 33 is not connected to the power supply coil 31, for example, reactive power will be generated in the input impedance, but power transmission itself is still possible. Therefore, only the power transmission coil 32 and power receiving coil 41 may be placed in a resonant state.

In addition, in the above-described embodiment, the wireless power supply system 1 has been described as a three-coil system configuration including the power supply coil 31, the power transmission coil 32, and the power receiving coil 41. However, the wireless power supply system may also be a two-coil system having only the power transmission coil 32 and the power receiving coil 41 without the power supply coil 31. In this case, the load-side impedance can be controlled by dividing the power transmission coil 32 into multiple power transmission coil sections and changing the relative positions of each power transmission coil section and the power receiving coil 41.

In a two-coil system consisting of a power transmission coil 32 and a power receiving coil 41, if the position of the power transmission coil 32 is moved to vary the load-side impedance, the coil axis 32a of the power transmission coil 32 and the coil axis of the power receiving coil 41 will not be aligned coaxially, which could result in a decrease in power transmission efficiency. In contrast, a three-coil system consisting of a power supply coil 31, a power transmission coil 32, and a power receiving coil 41 transmits power to the power transmission coil 32 via the power supply coil 31, and by adjusting the strength of the magnetic coupling between the power supply coil 31 and the power transmission coil 32 without changing the relative positions of the power transmission coil 32 and the power receiving coil 41, it is possible to control the load-side impedance and maintain good power transmission efficiency.

In the above-described embodiment, the wireless power transfer system 1 has been described as a three-coil system including the power transfer coil 31, the power transmission 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 resonant frequency approximately equal to that of the power transmitting coil 32, and power is transferred using 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 using 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 electrical circuits, so the resonant frequency does not change during operation, making the design easier and enabling a longer power transmission distance.

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.

1: Wireless power feeding system 11: Wireless power transmission system 2: Power feeding target object 3: Power transmitting device 31: Power feeding coils 31A to 31H: Power feeding coils 31a to 31c: Coil axis (of power feeding coil) 32: Power transmitting coil 32a: Coil axis (of power transmitting coil) 33, 34: Capacitor 35: Power feeding side resonant circuit 36: Power transmitting side resonant circuit 4: Power receiving device 41: Power receiving coil 42: Capacitor 43: Power 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 unit 94: Control unit 95: Measuring unit 96: Linear motion mechanism 96a: Plunger 96b: Case IE: Input terminal

Claims (6)

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