JP2024048208A - Wireless power transmission system, power supply station, and wireless power supply program - Google Patents

Abstract

[Problem] To provide a wireless power transmission system and a power supply station capable of grasping the positional relationship between a power transmission coil and a power receiving coil with a simple configuration. [Solution] The power supply station 10 includes a power supply station 10 having power supply units 11A, 11B and a processor 12, and a mobile object wirelessly supplied with power from the power supply station. Each power supply unit includes a power transmission section 111 having a plurality of power transmission coils and a capacitor, and a power conversion section 112 that converts DC power to AC power. The mobile object includes a power receiving coil and a capacitor. Each power transmission coil is disposed so that cross-coupling is smaller than the coupling coefficient between each power transmission coil and the power receiving coil. The processor 12 includes a switching control section 121 that controls the power conversion section so that the phase difference between the output voltage and output current of the power conversion section becomes zero, and a power receiving coil position grasping section 122 that grasps the position of the power receiving coil relative to the power transmission coil based on the switching frequency. [Selected Figure] Figure 2

Description

The present invention relates to a wireless power transmission system, a power supply station, and a wireless power supply program, and more specifically to a wireless power transmission system, a power supply station, and a wireless power supply program for wirelessly charging a mobile object using a magnetic field resonance method.

Various technologies have been proposed for transmitting power contactlessly, such as by electromagnetic induction (Patent Documents 1 to 4, Non-Patent Document 1).

Patent Document 1 discloses a non-contact power transmission device that creates a magnetic field beat by varying the excitation frequencies of adjacent primary (transmission) coils, thereby achieving high output and stable power transmission over a wide range.

Patent document 2 describes a device that uses a pair of planar coils set at a point where all interlinkage magnetic flux cancels each other out and the degree of coupling becomes zero, to continuously monitor items such as local pressure within the body via resonant frequency.

Patent document 3 describes a wireless power transmission device that includes a coupling adjustment unit that adjusts the inductance or capacitance components in the first and second power receiving units by substantially maintaining the resonant frequencies of the first and second power receiving units in a state in which cross-coupling is canceled.

Patent document 4 describes a non-contact power supply system for power supply and position detection of a transmitting/receiving coil in real time. In this system, power is supplied by resonating a power supply circuit connected to each of the transmitting and receiving coils at a certain resonant frequency, and the position detection circuit is resonated at a resonant frequency different from the resonant frequency of the power supply circuit to detect the relative positions of both coils.

Non-Patent Document 1 is a paper by the present inventors that describes a wireless power transmission system based on two receiving coils with reduced cross-coupling, and discusses the resonant frequency characteristics of the system.

JP 2009-164293 A JP 2018-000901 A JP 2015-154543 A JP 2015-002641 A

Shohei Komeda, Rin Arai, “Resonant Frequency Characteristics of a Wireless Power Transfer System based on Dual-Receiver Configuration without Cross Coupling”, IECON 2021 - 47th Annual Conference of the IEEE Industrial Electronics Society

To achieve efficient wireless power transfer, it is important to understand the positional relationship between the power transmitting coil and the power receiving coil. However, in the past, a resonant circuit and a power source for position detection were required, as described in Patent Document 4.

The present invention has been made based on the above technical understanding, and aims to provide a wireless power transmission system, a power supply station, and a wireless power supply program that are capable of grasping the positional relationship between a power transmission coil and a power receiving coil with a simple configuration.

A wireless power transmission system according to an aspect of the present invention includes:
a power supply station having a plurality of power supply units and a control unit;
a moving object to which power is wirelessly supplied from the power supply station,
Each of the power supply units is
a power transmitting unit including a power transmitting coil and a resonant capacitor connected to the power transmitting coil;
a power conversion unit that converts DC power into AC power and outputs the AC power to the power transmission unit,
The moving body is
a power receiving unit having a power receiving coil and a resonance capacitor connected to the power receiving coil;
a rectifier that rectifies the AC voltage induced in the power receiving coil;
a battery electrically connected to an output of the rectifier;
the plurality of power transmitting coils of the plurality of power supply units are arranged such that cross-coupling is smaller than any of coupling coefficients between the respective power transmitting coils and the power receiving coils;
The control unit of the power supply station
a switching control unit that controls a switching frequency of the power conversion unit so that a phase difference between an output voltage and an output current of the power conversion unit becomes zero for each of the power supply units;
and a power receiving coil position determining unit that determines a position of the power receiving coil relative to the power transmitting coils based on switching frequencies of the power conversion units.

In the wireless power transmission system,
The receiving coil position grasping unit may be configured to determine that the distance between the transmitting coil of the power supply unit and the receiving coil has decreased when the switching frequency of the power conversion unit of a power supply unit among the multiple power supply units increases, and to determine that the distance between the transmitting coil of the power supply unit and the receiving coil has increased when the switching frequency of the power conversion unit decreases.

In the wireless power transmission system,
The power receiving coil position ascertaining unit may be configured to ascertain a direction of misalignment of the power receiving coil with respect to the power transmitting coils, based on a change in switching frequency of the power conversion units.

In the wireless power transmission system,
The power receiving coil position ascertaining unit may ascertain a position of the power receiving coil relative to the plurality of power transmitting coils without using information from the moving object.

In the wireless power transmission system,
At least the power transmitting coils of the plurality of power supply units in the power supply station may be arranged below the water surface.

In the wireless power transmission system,
The moving body may be an underwater moving body.

In the wireless power transmission system,
The power transmission coils of the multiple power supply units may be arranged so that adjacent ones partially overlap each other.

In the wireless power transmission system,
When the switching frequency of a power supply unit among the plurality of power supply units increases, the switching control unit may control the power conversion unit of the other power supply unit so that the switching frequency of the other power supply unit matches the switching frequency of the one power supply unit.

A power supply station according to one aspect of the present invention includes:
A power supply station that wirelessly supplies power to a mobile object,
A plurality of power supply units;
A control unit,
Each of the power supply units is
a power transmitting unit including a power transmitting coil and a resonant capacitor connected to the power transmitting coil;
a power conversion unit that converts DC power into AC power and outputs the AC power to the power transmission unit,
the plurality of power transmitting coils of the plurality of power supply units are arranged such that cross-coupling is smaller than any of coupling coefficients between the respective power transmitting coils and the power receiving coil of the moving object,
The control unit is
a switching control unit that controls a switching frequency of the power conversion unit so that a phase difference between an output voltage and an output current of the power conversion unit becomes zero for each of the power supply units;
The power converter further includes a power receiving coil position determining unit that determines a position of the power receiving coil relative to the power transmitting coils based on a plurality of switching frequencies of the power conversion units.

A wireless power supply program according to an aspect of the present invention includes:
A wireless power supplying program executed in a power supplying station that wirelessly supplies power to a moving object,
Each of the plurality of power supply units included in the power supply station includes:
a power transmitting unit including a power transmitting coil and a resonant capacitor connected to the power transmitting coil;
a power conversion unit that converts DC power into AC power and outputs the AC power to the power transmission unit,
The wireless power supply program causes a computer of the power supply station to
Each power supply unit is operated as a switching control unit that controls the switching frequency of the power conversion unit so that the phase difference between the output voltage and output current of the power conversion unit becomes zero, and a receiving coil position determination unit that determines the position of the receiving coil relative to the multiple transmitting coils based on the multiple switching frequencies of the multiple power conversion units.

The present invention provides a wireless power transmission system, a power supply station, and a wireless power supply program that can grasp the positional relationship between a power transmission coil and a power receiving coil with a simple configuration.

1 is a diagram showing a schematic configuration of a wireless power transmission system according to an embodiment. FIG. 2 is a functional block diagram of a power supply station according to the embodiment. 2 is a diagram showing an example of a circuit configuration of a power supply station (two power supply units 11A, 11B) and a mobile object (a power receiving unit 21, a rectifier 22, and a battery 23). FIG. FIG. 2 is a diagram showing an example of the arrangement of two power transmitting coils, the upper side being a plan view and the lower side being a side view. 13 is a graph showing the relationship (actual measured value) between the center distance of two power transmitting coils and the coupling coefficient. FIG. 2 is a plan view showing an example of the arrangement of three power transmitting coils. FIG. 2 is a functional block diagram of a moving object according to the embodiment. 1 is a side view showing the positional relationship between two power transmitting coils (power transmitting coil units) and one power receiving coil. FIG. 13 is a graph showing the relationship (actual measured values) between the distance between two transmitting coils and one receiving coil and the coupling coefficient. FIG. 2 is a diagram showing a T-type equivalent circuit of a system consisting of one power supply unit and one receiving coil. 11 is a graph showing a relationship between a coupling coefficient between one power transmitting coil and one power receiving coil and a switching frequency in resonant frequency tracking control. 5A to 5C are diagrams showing an example of measurement results of voltage and current waveforms in each power supply unit and power receiving unit. 5A to 5C are diagrams showing an example of measurement results of voltage and current waveforms in each power supply unit and power receiving unit. 13 is a graph showing the relationship (actual measured values) between the distance between two power transmitting coils and one power receiving coil and the resonant frequency.

Embodiments of the present invention will be described below with reference to the drawings. Note that in each drawing, components having equivalent functions are given the same reference numerals.

<Wireless power transmission system 1>
First, a schematic configuration of a wireless power transfer system (Wireless Power Transfer: WPT) 1 according to an embodiment will be described with reference to Fig. 1. Note that, although Fig. 1 shows only four power transmission coils in the power supply station 10, more power transmission coils may be provided. For example, a large number of power transmission coils may be arranged so as to cover a predetermined charging area on the upper surface of the power supply station 10. In this embodiment, two power transmission coils function as one power transmission coil unit. A plurality of power transmission coil units may be arranged across the charging area.

The wireless power transmission system 1 according to this embodiment is a system for wirelessly supplying power to a mobile body 20. In the embodiment described below, the wireless power transmission system 1 is configured to wirelessly supply power to a mobile body in water, such as an autonomous underwater vehicle (AUV). However, the mobile body 20 is not limited to this, and may be a land mobile body such as an automobile or motorcycle, or an air mobile body such as a drone or unmanned aerial vehicle.

As shown in FIG. 1, the wireless power transmission system 1 includes a power supply station 10 having multiple power transmission coils L1 and L2, and a mobile object 20 having a power receiving coil L3. The mobile object 20 is charged by an AC voltage induced in the power receiving coil L3.

The wireless power transmission system 1 according to this embodiment, which will be described in detail later, is configured to grasp the position of the mobile object 20 relative to the power supply station 10 based on the switching frequency of the power supply unit 11A including the power transmission coil L1 and the switching frequency of the power supply unit 11B including the power transmission coil L2. More precisely, it is configured to grasp the position of the power receiving coil L3 relative to the power transmission coil unit consisting of the power transmission coil L1 and the power transmission coil L2 based on the switching frequencies of the power supply units 11A and 11B. Based on the grasped position of the power receiving coil L3, wireless power is supplied from the power supply station 10 to the mobile object 20.

<Power Supply Station 10>
Next, the power supply station 10 will be described in detail with reference to FIGS.

The power supply station 10 has a power supply unit 11A including a power transmission coil L1, a power supply unit 11B including a power transmission coil L2, and a processor (controller) 12 that controls the power supply units 11A and 11B. In this embodiment, the power supply station 10 wirelessly supplies power to the underwater moving object, so at least the power transmission coils L1 and L2 of the components of the power supply station 10 are placed below the water surface.

In this embodiment, the power supply unit 11A and the power supply unit 11B have the same configuration. That is, each of the power supply units 11A and 11B has a power transmission unit 111 including an LC resonant circuit and a power conversion unit 112 that converts DC power to AC power. FIG. 3 shows an example of the configuration of the power transmission unit 111 and the power conversion unit 112.

As shown in FIG. 3, the power transmission section 111 of the power supply unit 11A has a power transmission coil L1 and a capacitor C1 connected in series to the power transmission coil L1. This forms an LC resonant circuit. Similarly, the power transmission section 111 of the power supply unit 11B has a power transmission coil L2 and a capacitor C2 connected in series to the power transmission coil L2. The capacitors C1 and C2 are resonant capacitors that form a resonant circuit together with the power transmission coils L1 and L2. Note that the capacitor C1 may be connected in parallel to the power transmission coil L1. Similarly, the capacitor C2 may be connected in parallel to the power transmission coil L2.

In this embodiment, the inductance of the power transmission coil L1 is the same as the inductance of the power transmission coil L2, and the capacitance of the capacitor C1 is also the same as the capacitance of the capacitor C2. In addition, the power transmission coil L1 and the power transmission coil L2 are annular and have approximately the same size (diameter).

The power conversion unit 112 converts DC power supplied from a DC power source _Vdc into AC power and outputs the AC power to the power transmission unit 111. In the configuration example of Fig. 3, the power conversion unit 112 is an inverter composed of four semiconductor switches Q1 to Q4. Here, IGBTs are used as the semiconductor switches, but other elements such as MOS-FETs may also be used.

The configuration of the power conversion unit 112 is not limited to that shown in FIG. 3. For example, the power conversion unit 112 may include an AC/DC converter or a DC/DC converter in front of the inverter circuit made up of the semiconductor switches Q1 to Q4, or may include an AC/DC converter and a DC/DC converter.

Furthermore, the DC power supply _Vdc is not limited to a battery, but may be constituted by a converter that inputs commercial AC and converts it to DC.

The processor 12 functions as a control unit that controls the power supply station 10. The processor 12 has a switching control unit 121 that controls the semiconductor switches Q1 to Q4 of the power conversion unit 12, and a power receiving coil position grasping unit 122 that grasps the position of the power receiving coil L3. The processor 12 is composed of a microcomputer, a CPU, an FPGA, an ASIC, etc.

In this embodiment, the switching control unit 121 and the power receiving coil position determination unit 122 are realized by software (programs) that can be executed by the processor 12. However, this is not limited to this, and at least a part of the switching control unit 121 and the power receiving coil position determination unit 122 may be realized by hardware.

The switching control unit 121 controls the on/off of the semiconductor switches Q1 to Q4. The semiconductor switches Q1 to Q4 are controlled to be on/off at a high frequency of about several tens of kHz. This converts the DC power input from the DC power source _Vdc to the power conversion unit 112 into AC power. In the case of the circuit shown in Fig. 3, power conversion is performed by repeating a first state in which the semiconductor switches Q1 and Q4 are turned on and the semiconductor switches Q2 and Q3 are turned off, and a second state in which the semiconductor switches Q1 and Q4 are turned off and the semiconductor switches Q2 and Q3 are turned on.

The switching control unit 121 performs resonance frequency tracking control on the power conversion unit 112. That is, the switching control unit 121 controls the power conversion unit 112 so that the phase difference between the output voltage V inv1 and the output current I inv1 of the power conversion unit 112 of the power supply unit 11A becomes zero. In detail, the switching control unit 121 controls the switching frequency (f _sw ) of the semiconductor switches Q1 to Q4 of the power conversion unit 112 of the power supply unit 11A so that the phase difference between the output voltage V _inv1 and the output current I _inv1 of the power conversion unit 112 of the power supply unit 11A becomes zero. Similarly, the switching control unit 121 controls the switching frequency of the semiconductor switches Q1 to Q4 of the power conversion unit 112 of the power supply unit 11B so that the phase difference between the output voltage V _inv2 and the output current I _inv2 of the power conversion unit 112 of the power supply unit 11B becomes zero.

In this way, the switching control unit 121 controls the switching frequency of the power conversion unit 112 for each of the power supply units 11A and 11B so that the phase difference between the output voltage and output current of the power conversion unit 112 becomes zero.

The processor 12 is not limited to being composed of a single chip such as a microcomputer. For example, the processor 12 may be composed of multiple individual chips (sub-controllers) that control each power supply unit, and a chip (main control unit) that oversees the sub-controllers.

The receiving coil position determination unit 122 determines the position of the receiving coil L3 relative to the transmitting coils L1 and L2 based on the switching frequency of each power supply unit 11A, 11B. When the switching frequency of the power conversion unit 112 of a power supply unit among the multiple power supply units 11A, 11B increases, the receiving coil position determination unit 122 determines that the distance between the transmitting coil of that power supply unit and the receiving coil L3 has decreased. Conversely, when the switching frequency of the power conversion unit 112 decreases, the receiving coil position determination unit 122 determines that the distance between the transmitting coil of that power supply unit and the receiving coil L3 has increased.

The receiving coil position grasping unit 122 grasps the direction of positional deviation of the receiving coil L3 relative to the multiple transmitting coils L1, L2 based on changes in the switching frequencies of the multiple power conversion units 112. For example, if the switching frequency of the power supply unit 11A increases and the switching frequency of the power supply unit 11B decreases, it is determined that the receiving coil L3 is misaligned in the direction from the transmitting coil L2 to the transmitting coil L1.

The power receiving coil position grasping unit 122 can grasp the positional relationship between the power transmission coil unit and the power receiving coil by monitoring the switching frequencies of the multiple power conversion units 112 under resonant frequency tracking control. The power receiving coil position grasping unit 122 may grasp the position of the power receiving coil relative to the power transmission coil unit consisting of three or more power transmission coils based on the resonant frequencies of three or more power supply units.

Next, the arrangement of the power transmission coil L1 of the power supply unit 11A and the power transmission coil L2 of the power supply unit 11B will be described with reference to FIG. 4. In this embodiment, the power transmission coil L1 and the power transmission coil L2 are arranged so that the coupling coefficient (cross-coupling) between the power transmission coil L1 and the power transmission coil L2 is a minimum value. As shown in FIG. 4, the power transmission coil L1 and the power transmission coil L2 are arranged so that a part of each of them overlaps with each other. Specifically, the power transmission coil L1 and the power transmission coil L2 are arranged so that the center-to-center distance d (the distance between the center _O1 of the power transmission coil L1 and the center _O2 of the power transmission coil L2) is 140 mm when the diameter of the annular power transmission coils L1 and L2 is 230 mm. In this arrangement, as can be seen from the graph of the measured cross-coupling values shown in FIG. 5, the coupling coefficient between the power transmission coil L1 and the power transmission coil L2 is a minimum value. By making the coupling coefficient between the power transmission coils as small as possible, the position of the power receiving coil can be accurately grasped. As described above, in this embodiment, the power transmitting coil unit is made up of the power transmitting coil L1 and the power transmitting coil L2 that are arranged so as to partially overlap each other.

The power transmitting coil L1 and the power transmitting coil L2 may be arranged in other ways as long as the cross-coupling is less than a predetermined level. That is, the arrangement may be such that the coupling coefficient between the power transmitting coil L1 and the power transmitting coil L2 is smaller than the coupling coefficient between the power transmitting coil L1 and the power receiving coil L3 and is smaller than the coupling coefficient between the power transmitting coil L2 and the power receiving coil L3. For example, the power transmitting coil L1 and the power transmitting coil L2 may be arranged such that the center-to-center distance d is greater than 140 mm. The power transmitting coils L1 and L2 may also be arranged so that their sides are in contact with each other.

In addition, the number of power transmission coils (the number of power supply units) is not limited to two, and may be three or more. FIG. 6 shows an example in which the power transmission coil unit is composed of three power transmission coils L1, L2, and L4. In this example, the centers _O1 , _O2 , and _O3 of the power transmission coils are arranged to form an equilateral triangle. By using such a power transmission coil unit, the planar position and distance of the power receiving coil relative to the power transmission coil unit can be grasped. When the power transmission coil unit is composed of three power transmission coils as shown in FIG. 6, it is desirable to position the power receiving coil directly above the center (center of gravity) of the equilateral triangle with the centers _O1 , _O2 , and _O3 as vertices in order to achieve high charging efficiency.

Furthermore, if the cross-coupling between the power transmitting coils is smaller than the coefficient between each power transmitting coil and the power receiving coil, the sizes of the power transmitting coils that make up the power transmitting coil unit may be different from each other.

<Mobile object 20>
Next, the moving body 20 to which power is wirelessly fed from the power feeding station 10 will be described in detail with reference to Fig. 7. The moving body 20 in this embodiment is an underwater exploration vehicle such as an AUV or a remotely operated vehicle (ROV).

The mobile body 20 includes a power receiving unit 21 including an LC resonant circuit, a rectifier 22 that rectifies the AC voltage induced in the power receiving coil L3, a battery 23 that is charged by the rectified DC voltage, one or more sensors 24, a drive unit 25 for driving the mobile body 20, and a processor 26 that controls the drive unit 25 and the like.

As shown in the circuit diagram of FIG. 3, the power receiving unit 21 has a power receiving coil L3 and a capacitor C3 connected in series to the power receiving coil L3. The capacitor C3 is a capacitor that configures a resonant circuit together with the power receiving coil L3. The capacitor C3 may be connected in parallel to the power receiving coil L3.

In this embodiment, the inductance of the receiving coil L3 is the same as the inductance value of the transmitting coil L1 and the transmitting coil L2 (L3 = L1 = L2), and the capacitance of the capacitor C3 is the same as the capacitance of the capacitors C1 and C2 of the transmitting unit 111 (C3 = C1 = C2). In addition, the size (diameter) of the annular receiving coil L3 is approximately equal to the size of the transmitting coil L1 (transmitting coil L2).

The rectifier 22 has an input connected to the power receiving unit 21 and is configured to rectify the AC voltage induced in the power receiving coil L3. In this embodiment, as shown in Fig. 3, the rectifier 22 has a bridge diode composed of four diodes D1, D2, D3, and D4, and a smoothing capacitor _CO connected to the output end of the bridge diode.

The rectifier 22 may further include a DC/DC converter for voltage adjustment after the bridge diode. The rectifier 22 may also include an AC/DC converter instead of the bridge diode. Alternatively, the rectifier 22 may include an AC/DC converter before the bridge diode.

The battery 23 is connected to the output terminal of the rectifier 22 and is charged by the DC voltage rectified by the rectifier 22. The battery 23 is, for example, a secondary battery (lithium ion battery, etc.). The sensor 24, the drive unit 25, the processor 26, etc. operate using the power supplied by the battery 23. The battery 23 may have a battery management unit (BMU) for managing the battery.

The sensor 24 is a sensor provided for underwater exploration, and is a variety of sensors or measuring devices according to the observation purpose and observation target. The sensor 24 is, for example, a Doppler velocity log (DVL), a gyrocompass, or a depth finder. Note that an attitude and orientation sensor or an inertial navigation system may be provided instead of the gyrocompass. A multi-beam sonar may also be provided at the front of the main body of the moving body 20.

The drive unit 25 is configured to move or propel the moving body 20. In this embodiment, the drive unit 25 has a propeller provided at the stern of the main body and a motor that rotates and drives the propeller, although not shown. The drive unit 25 may be a water jet propulsion device that sprays pressurized water toward the outside by the rotation of an impeller provided inside the moving body 20.

The processor 26 controls the battery 23, the drive unit 25, etc. The processor 26 is composed of, for example, a CPU, a microcomputer, an FPGA, an ASIC, etc.

In addition to the above configuration, the mobile unit 20 may also be equipped with a communication device such as an acoustic communication transducer or a wireless communication antenna capable of receiving GPS signals.

<Positional relationship between coils and coupling coefficient>
Next, with reference to FIG. 8 and FIG. 9, the relationship between the positional relationship between the power transmitting coil unit (power transmitting coils L1, L2) and the power receiving coil, and the coupling coefficient between the coils will be described.

In the positional relationship I shown in the upper part of FIG. 8, the receiving coil L3 is located directly above the center of the power transmitting coil unit. At this time, the horizontal distance between the center of the receiving coil L3 and the center of the power transmitting coil unit is 0 mm. At this time, as can be seen from the graph of FIG. 9, the coupling coefficient _k13 between the power transmitting coil L1 and the receiving coil L3 and the coupling coefficient _k23 between the power transmitting coil L2 and the receiving coil L3 are almost equal. The coupling coefficient _k12 between the power transmitting coil L1 and the power transmitting coil L2 is smaller than the coupling coefficients _k13 and _k23 by devising the arrangement as described above. Note that, when wireless power supply is performed, it is desirable to position the receiving coil L3 directly above the power transmitting coil unit as in the positional relationship I in order to increase charging efficiency.

In positional relationship II shown in the middle of Fig. 8, the receiving coil L3 is located directly above the transmitting coil L1. In this case, the horizontal distance _d1 between the center of the receiving coil L3 and the center of the transmitting coil unit is 70 mm. In this case, as can be seen from the graph in Fig. 9, the coupling coefficient _k13 between the transmitting coil L1 and the receiving coil L3 becomes larger than that in positional relationship I and takes a maximum value. On the other hand, the coupling coefficient _k23 is a smaller value than that in positional relationship I.

In the positional relationship III shown in the lower part of Fig. 8, the center of the receiving coil L3 is located to the left of the center of the transmitting coil L1. In this case, the horizontal distance _d2 between the center of the receiving coil L3 and the center of the transmitting coil unit is 120 mm. In this case, as can be seen from the graph in Fig. 9, the coupling coefficient _k13 between the transmitting coil L1 and the receiving coil L3 is smaller than that in the positional relationship II. On the other hand, the coupling coefficient _k23 is approximately the same value as in the case of the positional relationship II.

9, regardless of the positional relationship between the receiving coil and the transmitting coil unit, the coupling coefficient _k12 between the transmitting coil L1 and the transmitting coil L2 is smaller than both the coupling coefficient _k13 and the coupling coefficient _k23 . In this manner, in the transmitting coil unit, the transmitting coil L1 and the transmitting coil L2 are arranged such that the cross-coupling (coupling coefficient _k12 ) is smaller than both the coupling coefficients ( _k13 , _k23 ) between the transmitting coils and the receiving coils. This makes it possible to accurately grasp the positional relationship of the receiving coil L3 with respect to the transmitting coil unit based on the coupling coefficient _k13 and the coupling coefficient _k23 (i.e., based on the switching frequencies of the power supply units 11A and 11B).

<Relationship between coupling coefficient and resonance frequency>
The relationship between the coupling coefficient between the coils and the switching frequency (resonant frequency) in the resonant frequency tracking control will be described with reference to Fig. 10 and Fig. 11. Here, a system consisting of one power supply unit and a power receiving coil will be considered.

FIG. 10 shows a T-type equivalent circuit of a system consisting of one power transmitting unit and one power receiving unit. In the case of a series-series compensation (SS) method in which a resonant capacitor is connected in series to each of the power transmitting coil and the power receiving coil as in this embodiment, the switching frequency (resonant frequency) is given by formulas (1) and (2). Here, it is assumed that the inductance and capacitance are equal between the transmitting and receiving coils, and that there is no winding resistance or iron loss resistance. For simplification, the input AC power source is a sinusoidal voltage source v _inv-f that takes into account only the fundamental wave component of the square wave of the inverter.

Here, L is the inductance of the transmitting coil and the receiving coil, C is the capacitance of the resonant capacitor, R _acS is the AC equivalent resistance, and k is the coupling coefficient between the transmitting coil and the receiving coil.

The AC equivalent resistance R _acS is given by equation (3) using the load resistance R _L.

Figure 11 shows the calculated (solid line) and measured (black circles) values of the switching frequency according to equations (1) and (2). Figure 11 also shows the calculated (solid line) and measured (white circles) values of the voltage induced in the receiving coil. The values of L = 135 μH, C = 1.76 μF, and R _L = 3 Ω were used in the calculation of the switching frequency.

As can be seen from FIG. 11, the switching frequency is constant in a region where the coupling coefficient k between the transmitting coil and the receiving coil is less than about 0.3. On the other hand, in a region where the coupling coefficient k is about 0.3 or more, the switching frequency f _SW increases as the coupling coefficient k increases. In other words, when the coupling coefficient is about 0.3 or more, the switching frequency increases as the coupling coefficient between the transmitting coil and the receiving coil increases. The positional relationship between the transmitting coil and the receiving coil is related to the coupling coefficient. Therefore, by monitoring the switching frequency (resonant frequency), the position of the receiving coil relative to the transmitting coil can be grasped.

In addition, even when the capacitors C1 and C2 are connected in parallel to the power transmission coils L1 and L2 in the power transmission unit 111 to form a resonant circuit, the switching frequency increases as the coupling coefficient between the power transmission coil and the power receiving coil increases, so the position of the power receiving coil relative to the power transmission coil can be determined by monitoring the switching frequency (resonant frequency).

As shown in Fig. 11, the voltage _Vrec generated in the power receiving coil is almost constant in a region where the coupling coefficient is about 0.3 or more. This is an advantageous characteristic for charging the battery of a mobile object. That is, in a typical contactless power transfer system, the voltage value on the power receiving side is fed back to the power transmitting side to adjust the switching frequency on the power transmitting side, but in this embodiment, since the voltage _Vrec is almost constant, such feedback is not necessary.

<Voltage and current waveforms>
Next, referring to Fig. 12 and Fig. 13, the voltage waveforms and current waveforms in the transmitting coil and the receiving coil actually measured in the circuit configuration of Fig. 3 will be described. Note that, in order to observe the change in the phase difference due to the change in the positional relationship between the coils, the resonance frequency tracking control is not performed. In Fig. 12 and Fig. 13, one division is 10 μSec.

12 shows the time waveforms of the voltage V _inv1 and current I _inv1 of the power supply unit 11A, the voltage V _inv2 and current I _inv2 of the power supply unit 11B, and the voltage V _rec and current I _rec of the power receiving unit 21, in positional relationship I (upper part of FIG. 8). As can be seen from this figure, the voltage V _inv1 and current I _inv1 , and the voltage V _inv2 and current I _inv2 are approximately in phase (phase difference is approximately 0).

FIG. 13 shows the time waveforms of the voltage V _inv1 and current I inv1 of the power supply unit 11A, the voltage V _inv2 and current I _inv2 of the power supply unit 11B, and the voltage V rec and current I _rec of the power receiving unit 21 when the power receiving coil L3 is moved horizontally toward the power transmitting coil L1 side in the positional relationship I (between the positional _relationship I and the positional relationship _II) .

Since the resonant frequency tracking control is not performed, the current of the power supply unit 11A leads in phase compared to the voltage, as can be seen from FIG. 13. This corresponds to the receiving coil L3 approaching the power transmission coil L1 of the power supply unit 11A and the coupling coefficient _k13 becoming larger. On the other hand, the current of the power supply unit 11B lags in phase compared to the voltage. This corresponds to the receiving coil L3 moving away from the power transmission coil L2 of the power supply unit 11B and the coupling coefficient _k23 becoming smaller. When the resonant frequency tracking control is performed, the power conversion unit 112 is controlled so that the phase difference becomes 0, so that the switching frequency of the power supply unit 11A increases in accordance with the phase lead, and the switching frequency of the power supply unit 11B decreases in accordance with the phase lag.

Therefore, by monitoring the switching frequency (i.e., the resonant frequency) of the power supply units 11A and 11B under resonant frequency tracking control, the positional relationship between the receiving coil L3 and the transmitting coil unit can be grasped.

Next, the actual measured values of the change in switching frequency under resonant frequency tracking control will be described. FIG. 14 is a graph showing the relationship between the distance (horizontal distance, positional deviation) between the power transmission coil unit consisting of the power transmission coils L1 and L2 and one power receiving coil L3, and the resonant frequency of the power supply unit 11A having the power transmission coil L1. The resonant frequency is an actual measured value. As can be seen from this graph, the resonant frequency is maximum when the distance between the power transmission coil L1 and the power receiving coil L3 is 70 mm (positional relationship II, middle part of FIG. 8), at which the coupling coefficient between the power transmission coil L1 and the power receiving coil L3 is the largest. Although not shown, the resonant frequency of the power supply unit 11B decreases monotonically as the power receiving coil L3 moves away from the power transmission coil L2.

By monitoring the resonant frequencies of power supply unit 11A and power supply unit 11B in this manner, the power receiving coil position determination unit 122 of the processor 12 can detect in which direction the power receiving coil L3 (mobile body 20) has shifted relative to the power transmitting coil unit (towards the power transmitting coil L1 or towards the power transmitting coil L2). In other words, the power receiving coil position determination unit 122 determines the position of the power receiving coil L3 relative to the power transmitting coils L1 and L2 based on the switching frequencies of the power supply units 11A and 11B.

In addition, the movement direction of the receiving coil L3 can be grasped by monitoring the change in the switching frequency of both the power supply units 11A and 11B. In contrast, when only the switching frequency of one of the power supply units 11A and 11B is monitored, the movement direction of the receiving coil L3 cannot be grasped. For example, when only the switching frequency of the power supply unit 11A is monitored, it can be grasped that the receiving coil L3 is approaching (or moving away from) the transmitting coil L1, but it cannot be grasped from which direction of the transmitting coil L1 the receiving coil L3 is approaching (or moving away from). In other words, it cannot be grasped whether the receiving coil L3 is approaching from the transmitting coil L2 side or from the opposite side of the transmitting coil L2. In this embodiment, the movement direction of the receiving coil L3 can be grasped as described above by monitoring the switching frequencies of both the power supply units 11A and 11B.

In addition, in a situation where wireless power supply is performed in the positional relationship I shown in the upper part of FIG. 8, if the position of the moving body 20 is shifted due to the influence of ocean currents, etc., the switching frequencies of the power supply unit 11A and the power supply unit 11B will differ from each other. For example, if the receiving coil L3 approaches the transmitting coil L1 due to a positional shift, the switching frequency of the power supply unit 11A will increase and the switching frequency of the power supply unit 11B will decrease. As a result, the frequency components of the voltage induced in the receiving coil L3 will become multiple, and the charging efficiency of the battery 23 will decrease. In order to avoid this, the switching control unit 121 may perform control to match the switching frequency of the power supply units 11A and 11B to the higher one. For example, if the switching frequency of the power supply unit 11A increases, the power conversion unit of the power supply unit 11B is controlled so that the switching frequency of the power supply unit 11B matches the switching frequency of the power supply unit 11A. For example, if the frequency difference becomes equal to or greater than a predetermined value, it may be determined that the switching frequency of the power supply unit 11A has increased. By performing such cooperative control, it is possible to suppress a decrease in charging efficiency.

<Action and effect>
As described above, in this embodiment, the power receiving coil position determining unit 122 of the power supply station 10 determines the positional relationship between the power receiving coil and the power transmitting coil unit based on the resonance frequencies of multiple power supply units, and therefore does not require a circuit or the like for feeding back information about the moving object 20 to the power supply station 10. Therefore, for example, the switching control unit 121 and the power receiving coil position determining unit 122 can be realized by software of a microcomputer that controls the power conversion units 12 of the power supply units 11A and 11B, and no additional hardware is required. Therefore, according to this embodiment, the positional relationship between the power transmitting coil and the power receiving coil can be determined with a simple configuration.

Furthermore, according to this embodiment, the positional relationship can be grasped while power is being transmitted between the power transmitting coil and the power receiving coil. Therefore, there is no need to stop power transmission to grasp the position of the power receiving coil, and efficient wireless charging can be realized.

In addition, according to this embodiment, the power supply station 10 can grasp the position of the power receiving coil relative to the power transmission coil unit without using information from the moving body 20 (such as the voltage generated in the power receiving coil L3). Therefore, this embodiment can be applied even in situations where it is difficult to communicate information between the transmitter and receiver due to radio wave attenuation, such as wireless power supply underwater.

Underwater, the position of the moving body 20 fluctuates due to the influence of ocean currents and the like. In addition, because water is a viscous fluid, it is difficult to perform fine position control of the moving body 20. Even in such a situation, according to this embodiment, it is possible to select the power transmission coil unit to be used for power supply based on the grasped positional relationship, and efficient wireless power supply can be performed. Since efficient wireless power supply can be performed underwater in this way, it becomes possible to charge an underwater moving body such as an AUV without having to pull it up onto a mother ship, etc.

In addition, according to this embodiment, the direction of positional deviation of the receiving coil relative to the transmitting coil unit can be determined based on the change in the switching frequency of multiple power conversion units that are controlled to follow the resonant frequency.

In addition, in this embodiment, multiple power transmission coils function as one power transmission coil unit, so that even if one power supply unit fails, wireless charging can be continued by the other power supply unit. As a result, the reliability of the wireless power transmission system can be improved.

Based on the above description, a person skilled in the art may be able to conceive of additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the above-described embodiment. Various additions, modifications, and partial deletions are possible within the scope of the conceptual idea and intent of the present invention derived from the contents defined in the claims and their equivalents.

REFERENCE SIGNS LIST 1 Wireless power transmission system 10 Power supply stations 11A, 11B Power supply unit 111 Power transmission section 112 Power conversion section 12 Processor 121 Switching control section 122 Power receiving coil position determination section 20 Mobile body 21 Power receiving section 22 Rectifier 23 Battery 24 Sensor 25 Drive section 26 Processor C1, C2, C3 Capacitor D1, D2, D3, D4 Diode L1, L2 Power transmission coil L3 Power receiving coil Q1, Q2, Q3, Q4 Semiconductor switch

Claims (10)

a power supply station having a plurality of power supply units and a control unit;
a moving object to which power is wirelessly supplied from the power supply station,
Each of the power supply units is
a power transmitting unit including a power transmitting coil and a resonant capacitor connected to the power transmitting coil;
a power conversion unit that converts DC power into AC power and outputs the AC power to the power transmission unit,
The moving body is
a power receiving unit having a power receiving coil and a resonance capacitor connected to the power receiving coil;
a rectifier that rectifies the AC voltage induced in the power receiving coil;
a battery electrically connected to an output of the rectifier;
the plurality of power transmitting coils of the plurality of power supply units are arranged such that cross-coupling is smaller than any of coupling coefficients between the respective power transmitting coils and the power receiving coils;
The control unit of the power supply station
a switching control unit that controls a switching frequency of the power conversion unit so that a phase difference between an output voltage and an output current of the power conversion unit becomes zero for each of the power supply units;
a power receiving coil position determining unit that determines a position of the power receiving coil relative to the power transmitting coils based on switching frequencies of the power conversion units. The wireless power transmission system according to claim 1, wherein the receiving coil position grasping unit determines that the distance between the transmitting coil of a power supply unit and the receiving coil of the power supply unit is shortened when the switching frequency of the power conversion unit of a power supply unit among the plurality of power supply units increases, and determines that the distance between the transmitting coil of the power supply unit and the receiving coil of the power supply unit is shortened when the switching frequency of the power conversion unit decreases. The wireless power transmission system according to claim 2, wherein the power receiving coil position determination unit determines the direction of positional deviation of the power receiving coil relative to the power transmitting coils based on changes in the switching frequencies of the power conversion units. The wireless power transmission system according to claim 1, wherein the power receiving coil position determination unit determines the position of the power receiving coil relative to the multiple power transmitting coils without using information from the moving body. The wireless power transmission system according to claim 1, wherein at least the power transmission coils of the plurality of power supply units in the power supply station are placed below the water surface. The wireless power transmission system according to claim 5, wherein the moving body is an underwater moving body. The wireless power transmission system according to claim 1, wherein the power transmission coils of the multiple power supply units are arranged so that adjacent ones partially overlap each other. The wireless power transmission system according to claim 1, wherein, when the switching frequency of one of the plurality of power supply units increases, the switching control unit controls the power conversion unit of the other power supply unit so that the switching frequency of the other power supply unit matches the switching frequency of the one power supply unit. A power supply station that wirelessly supplies power to a mobile object,
A plurality of power supply units;
A control unit,
Each of the power supply units is
a power transmitting unit including a power transmitting coil and a resonant capacitor connected to the power transmitting coil;
a power conversion unit that converts DC power into AC power and outputs the AC power to the power transmission unit,
the plurality of power transmitting coils of the plurality of power supply units are arranged such that cross-coupling is smaller than any of coupling coefficients between the respective power transmitting coils and the power receiving coil of the moving object,
The control unit is
a switching control unit that controls a switching frequency of the power conversion unit so that a phase difference between an output voltage and an output current of the power conversion unit becomes zero for each of the power supply units;
a power receiving coil position determining unit that determines a position of the power receiving coil relative to the power transmitting coils based on a plurality of switching frequencies of the plurality of power conversion units. A wireless power supplying program executed in a power supplying station that wirelessly supplies power to a moving object,
Each of the plurality of power supply units included in the power supply station includes:
a power transmitting unit including a power transmitting coil and a resonant capacitor connected to the power transmitting coil;
a power conversion unit that converts DC power into AC power and outputs the AC power to the power transmission unit,
The wireless power supply program causes a computer of the power supply station to
a switching control unit that controls a switching frequency of the power conversion unit so that a phase difference between an output voltage and an output current of the power conversion unit becomes zero, and a receiving coil position determining unit that determines a position of the receiving coil relative to the transmitting coils based on a plurality of switching frequencies of the plurality of power conversion units.