CN110945746A - Power transmission device and non-contact power supply system - Google Patents

Abstract

The power transmitting device wirelessly transmits power to a power receiving device having a power receiving coil. The power transmission device includes: an inverter circuit; a power transmission coil connected to the inverter circuit; and a controller for controlling the output voltage of the inverter circuitAnd (5) manufacturing a circuit. The control circuit calculates mutual inductance (L) of the power transmission coil and the power receiving coil in a predetermined positional relationship based on an AC resistance value of the power receiving coil estimated or calculated based on a distance between the power transmission coil and the power receiving coil, an input impedance of the power transmission coil, and the AC resistance value of the power transmission coil_m). Thereby, the output voltage of the inverter circuit is determined.

Description

Power transmission device and non-contact power supply system

Technical Field

The present application relates to a contactless power supply system and a power transmission device used in the contactless power supply system.

Background

Development of a non-contact power supply system (also referred to as a wireless power transmission system) that wirelessly transmits power from a power transmitting apparatus to a power receiving apparatus is being advanced. Patent document 1 discloses an example of a contactless power supply system. In the system of patent document 1, information such as a reception voltage is fed back from a power receiving device to a power transmitting device by wireless communication, and the power transmitting device controls the transmission power based on the information.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2015-089267

Non-patent document

Non-patent document 1: lammerner, M.Stafl, "Eddy currents", life books,1966

Disclosure of Invention

Problems to be solved by the invention

The prior art has the following problems: when power transmission is started or when the distance between the power transmitting apparatus and the power receiving apparatus changes during power transmission, a long time is required until a desired voltage or current is supplied to the power receiving apparatus. The present disclosure provides a novel power transmission control technique capable of shortening this time.

Means for solving the problems

A power transmission device according to an aspect of the present disclosure is a power transmission device that wirelessly transmits power to a power receiving device having a power receiving coil, the power transmission device including: an inverter circuit; a power transmission coil connected to the inverter circuit; and a control circuit that controls an output voltage of the inverter circuit. The control circuit determines the output voltage of the inverter circuit based on an alternating current resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an alternating current resistance value of the power transmitting coil estimated or calculated from a distance between the power transmitting coil and the power receiving coil.

The general or specific aspects described above can be implemented by an apparatus, a system, a method, an integrated circuit, a computer program, or a recording medium. Alternatively, it may be realized by any combination of systems, apparatuses, methods, integrated circuits, computer programs, and recording media.

Effects of the invention

According to an aspect of the present disclosure, when power transmission is started or when the distance between a power transmitting device and a power receiving device changes during power transmission, the time required until a desired voltage or current is supplied to the power receiving device can be shortened.

Drawings

Fig. 1 is a diagram for explaining an outline of a mobile body system in an exemplary embodiment of the present disclosure.

Fig. 2 is a perspective view schematically showing an example of a moving body 200 in an exemplary embodiment of the present disclosure.

Fig. 3 is a perspective view showing a state in which the power transmitting resonator 103 and the power receiving resonator 203 are opposed to each other in the exemplary embodiment of the present disclosure.

Fig. 4A is a block diagram showing the structure of a mobile body system in an exemplary embodiment of the present disclosure.

Fig. 4B is a block diagram showing a more detailed structure of the mobile unit system in the exemplary embodiment of the present disclosure.

Fig. 5A is a block diagram illustrating a configuration example of a mobile body system capable of maximizing efficiency by adjusting power-receiving-side impedance in an exemplary embodiment of the present disclosure.

Fig. 5B is a block diagram illustrating a configuration example of a mobile body system having a representative distance measuring device capable of maximizing efficiency by adjusting power-receiving-side impedance in the exemplary embodiment of the present disclosure.

Fig. 6 is a diagram showing an equivalent circuit of the power transmitting resonator 103 and the power receiving resonator 203 of the contactless power supply system in the exemplary embodiment of the present disclosure.

Fig. 7 is a diagram for explaining a case where the power receiving voltage deviates from a desired value when the distance between coils is different from an assumed distance.

Fig. 8A is a diagram illustrating an example of a change in the resistance component 1032 of the power transmitting resonator 103 when the distance between the power transmitting resonator 103 and the power receiving resonator 203 changes. The plotted points are actual values and the curves are calculated values.

Fig. 8B is a diagram showing another example of a change in the resistance component 1032 of the power transmitting resonator 103 when the distance between the power transmitting resonator 103 and the power receiving resonator 203 is changed.

Fig. 8C is a diagram showing another example of a change in the resistance component 1032 of the power transmitting resonator 103 when the distance between the power transmitting resonator 103 and the power receiving resonator 203 is changed.

Fig. 9 is a graph showing the dependency of the calculated value of the power transmission efficiency on the secondary-side input impedance in the coil combination example shown in fig. 8A. The results of the calculations are shown for three cases: obtaining the actual variation resistance value and calculating the power transmission efficiency; determining the power transmission efficiency without knowing the actual variation of the resistance value; and calculating the power transmission efficiency after calculating the actually varying resistance value.

FIG. 10 is a graph showing the consumption current I of the load 202 in the case where the feedforward control in the embodiment shown in FIG. 4A is performed_12DCA schematic diagram of the effect of reducing the time until the convergence to the predetermined value.

Fig. 11 is a flow chart illustrating operations in the illustrative embodiment shown in fig. 4B.

Fig. 12 is a diagram showing the definition of constants in the spiral coil.

Fig. 13 is a schematic diagram showing a coil through which current flows and a coil through which magnetic flux passes in two opposing spiral coils.

Fig. 14 is a schematic diagram showing a state in which the spiral coil is opposed to a dissimilar metal. An example of the case where the thickness of the dissimilar metal is close to the radius of the coil wire is shown.

Detailed Description

Prior to the description of the embodiments of the present disclosure, the knowledge that forms the basis of the present disclosure will be described.

In a conventional non-contact power supply system that performs feedback control, information such as a voltage or a current supplied to a load in a power receiving device is wirelessly transmitted from the power receiving device to the power transmitting device during power transmission. The power transmission device controls the output voltage of the inverter circuit so that the value of the voltage or current supplied to the load becomes a desired value. For example, in a system in which a DC-DC converter is disposed at a preceding stage of an inverter circuit, the output voltage of the inverter circuit can be controlled by controlling the output voltage of the DC-DC converter input to the inverter circuit. Thus, even when the operating state of the load changes or the distance between the power transmitting device and the power receiving device changes, the transmission power can be appropriately controlled in accordance with the change.

However, in such feedback control, there is a problem that an optimum control gain value changes when the distance between the coils changes. When the distance between the coils varies, various parameters vary, and particularly, the power transmission efficiency greatly varies. In general, when the power transmission efficiency is low, for example, a Proportional gain value in PID control (Proportional-Integral-Differential Controller) needs to be set large. However, when the power transmission efficiency is high in such a gain value setting, there is a problem that the received power overshoots. When designing a power receiving apparatus capable of quickly setting a desired value of received power in response to a variation in the distance between coils, it is difficult to set the gain. Therefore, a small gain value is generally set in terms of safety of the product. However, when the gain value is small, there is a problem that a long time is required until a desired voltage or current is supplied to a load in the power receiving device.

Therefore, a design combining feedforward control and feedback control is considered. Such a design is effective when the power receiving coil is found to be present at a predetermined position in terms of the rating of the product. For example, a control circuit of a power transmission device calculates and supplies a voltage to be applied to an inverter circuit (hereinafter, may be simply referred to as an "inverter") or an output voltage of the inverter circuit (hereinafter, also referred to as a power transmission voltage). If an appropriate initial value of the power transmission voltage can be provided according to the state of the distance between the coils, the power transmission voltage can be adjusted to an appropriate value by the feedback control thereafter, and the time until a desired voltage or current is supplied to the load in the power receiving device can be shortened. The present disclosure proposes a better method in terms of the process of calculating the initial value of the transmission voltage.

For calculating the initial value of the transmission voltage, a method using an equation derived from an effect circuit of the power transmission coil is considered. By this equation, the ratio of the power reception voltage to the power transmission voltage can be obtained. Therefore, when the voltage to be applied to the load or the current to be flowed is known, the transmission voltage to be applied can be obtained by calculation. The equation includes the mutual inductance between the coils, the resonance frequency of the power transmission coil, the resonance frequency of the power reception coil, the power transmission-side input impedance, the power reception-side input impedance, the ac resistance value of the power transmission coil, and the ac resistance value of the power reception coil. Variations in these values can be calculated or estimated by a variety of methods.

The present inventors paid attention to variations in the ac resistance value of the power transmission coil, the ac resistance value of the power reception coil, and the mutual inductance. In the embodiment of the present disclosure, when inverting the value of the varying mutual inductance, the ac resistance value of the power transmission coil and the ac resistance value of the power reception coil are used. It is known that the ac resistance value varies due to the proximity of metals to which a high frequency is applied, and this effect is called the proximity effect. By taking into account the variation in the ac resistance value due to the adjacent effect, the value of the initial value of the mutual inductance and/or the transmission voltage can be accurately calculated. Furthermore, the disadvantage of the feedback control can be compensated, and the gain value of the feedback controller can be set to be small, but an appropriate initial power transmission voltage can be supplied. As a result, the time required to supply a desired voltage or current to the load in the power receiving device can be shortened. If the distance between the coils is within the rated value, the time until the desired voltage or current is supplied can be sufficiently shortened regardless of whether the coils are separated or close to each other.

Fig. 7 is a diagram for explaining a case where the power voltage deviates from a desired value when the distance between coils is different from an assumed distance in a system that does not take into account the adjacency effect. Here, a system is assumed that takes into account the change in mutual inductance that occurs with a change in distance between coils, but does not take into account the effect of adjacency between coils. Let the effective value of the transmission voltage be V_rms1Assuming that the effective value of the receiving voltage is V_rms2. The transmission voltage is a voltage applied to the transmission coil. The power receiving voltage is a voltage supplied to a load in the power receiving device. The solid curve in FIG. 7 represents actual V_rms2To V_rms1The dashed curve represents V calculated without taking into account the adjacency effect_rms2To V_rms1The dependence of (c). The difference between these curves can be said to be a value calculated in consideration of the above-described variation of the parameter such as the mutual inductance between the coils, the resonance frequency of the power transmission coil, the resonance frequency of the power reception coil, the power transmission-side input impedance, the power reception-side input impedance, the ac resistance value of the power transmission coil, and the ac resistance value of the power reception coil, or a value calculated without consideration of the variation of the above-described parameter. The system was designed on the premise of the ac resistance value of each coil when the coil-to-coil distance was 35mm, and the actual coil-to-coil distance was 19 mm. The dashed curve in fig. 7 represents the determination of the transmission voltage V without taking into account the adjacency effect_rms1Time target receiving voltage V_rms2Is connected with the target receiving voltage V_rms2Corresponding transmission voltage V_rms1The relationship between them. The solid line curve shows the transmission voltage V when the distance between the coils is 19mm_rms1And a receiving voltage V_rms2The actual relationship between them.

In the system, the power is receivedThe command value of pressure being, for example, V_rms2In the case of 30V, the transmission voltage is set to V_rms1170V (dashed line in fig. 7). However, since the coil-to-coil distance is not 35mm but 19mm in practice, the received voltage is only about 24V (solid line in fig. 7) even if a transmission voltage of 170V is applied. In order to set the reception voltage to 30V, it is necessary to set the transmission voltage to about 210V according to the solid curve in fig. 7.

If the distance between the power transmission coil and the power receiving coil is shortened, the ac resistance values of the power transmission coil and the power receiving coil increase due to the proximity effect. If the influence of this increase is not taken into consideration, the reception voltage or the reception current cannot be set to the target value quickly. However, in the conventional non-contact power feeding system, the influence of the increase in the ac resistance values of the power transmission coil and the power reception coil has not been considered.

According to the technique of the present disclosure, by considering the increase in the ac resistance values of the power transmission coil and the power reception coil due to the proximity effect, the time until a desired voltage or current is supplied to the power reception device can be shortened.

Hereinafter, an outline of the embodiment of the present disclosure will be described.

A power transmitting device according to an aspect of the present disclosure wirelessly transmits power to a power receiving device having a power receiving coil. The power transmission device includes: an inverter circuit; a power transmission coil connected to the inverter circuit; and a control circuit for controlling the output voltage of the inverter circuit. The control circuit determines the output voltage of the inverter circuit based on an alternating current resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an alternating current resistance value of the power transmitting coil estimated or calculated from a distance between the power transmitting coil and the power receiving coil.

According to the above configuration, the time until the voltage or the current in the power receiving device reaches the target value can be shortened.

The power transmission device may further include a measurement device that measures an output voltage and an output current of the inverter circuit. In this case, the control circuit calculates the input impedance of the power transmission coil and the ac resistance value of the power transmission coil from the output voltage and the output current measured by the measuring device.

In one embodiment, the power transmission device estimates an ac resistance value of the power receiving coil based on a distance measured by the sensor. The power transmission device may also have such a sensor. Alternatively, the power receiving device or the external control device may have a sensor for measuring the distance between the coils.

The control circuit may estimate a distance between the power transmission coil and the power receiving coil based on the input impedance of the power transmission coil, the ac resistance value of the power transmission coil, and the effective operating frequency, and estimate the ac resistance value of the power receiving coil based on the estimated distance. In this case, a sensor for measuring the distance between the coils can be omitted. The effective operating frequency is a frequency at which the input impedance to the power transmission coil is minimum when the frequency of the ac power output from the inverter circuit (hereinafter, sometimes referred to as "operating frequency") is swept.

The power transmission device may further include a recording medium storing a table or a function of a correspondence relationship between the predetermined distance and the ac resistance value of the power receiving coil. In this case, the control circuit estimates the ac resistance value of the power receiving coil with reference to the table or the function.

The control circuit can adjust the output voltage of the inverter circuit (hereinafter, sometimes referred to as "transmission voltage") by various methods. For example, the transmission voltage can be adjusted by changing the duty ratio, phase, or frequency of a control signal supplied to a switching element among a plurality of switching elements included in the inverter circuit or by changing the dc voltage input to the inverter circuit. In a system in which the power transmission device includes a DC-DC converter connected between the inverter circuit and the DC power supply, the DC voltage input to the inverter circuit can be controlled. In such an aspect, the control circuit can change the direct-current voltage input to the inverter circuit by controlling on/off of the switching element included in the DC-DC converter.

The non-contact power supply system in the present disclosure has the power transmitting device and the power receiving device in the present disclosure. The power receiving device is, for example, a mobile body. The "movable body" refers to a movable object that is driven or charged by electric power. The moving body may be, for example, an Automated Guided Vehicle (AGV), an Electric Vehicle (EV), a mobile robot or an Unmanned Aerial Vehicle (UAV, so-called drone). The power receiving device may be a device that moves autonomously, such as a portable device.

The present disclosure includes a control device having a control circuit used in the power transmission device, a control program executed by the control circuit, and a control method.

Hereinafter, exemplary embodiments of the present disclosure will be described. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid unnecessary redundancy in the following description, which will be readily understood by those skilled in the art. The present inventors have provided drawings and the following description in order to fully understand the present disclosure by those skilled in the art, and do not intend to limit the subject matter described in the claims. In the following description, the same or similar components are denoted by the same reference numerals.

(embodiment mode)

< Structure >

Fig. 1 is a diagram for explaining an outline of a mobile body system in the present embodiment. The mobile body system is an example of the contactless power supply system in the present disclosure. The mobile body system can be used as a system for transporting articles in a factory, for example. The mobile body system has at least one wireless power transmission device (hereinafter, simply referred to as "power transmission device") 100 and at least one mobile body 200. The mobile body 200 is an example of a power receiving device. The mobile unit 200 may be, for example, an unmanned carrier that autonomously moves in a factory and carries an article to a required place. Fig. 1 illustrates four power transmission devices 100 and four mobile units 200. The number of power transmission devices 100 and mobile object 200 is not limited to four, and is arbitrary.

The power transmission device 100 wirelessly transmits power to the mobile unit 200. The power transmission device 100 includes a power transmission resonator 103 including a power transmission coil that transmits ac power to a space. The moving body 200 has a power receiving resonator 203 including a power receiving coil. By the power transmitting resonator 103 and the power receiving resonator 203 being coupled by magnetic field resonance, power is wirelessly transmitted from the power transmitting coil to the power receiving coil. As described above, in the present embodiment, wireless power transmission by magnetic field resonance coupling (also sometimes referred to as "magnetic field resonance coupling" or "resonant magnetic field coupling") is used. According to wireless power transmission of the magnetic field resonance coupling method, power transmission over a longer distance is possible than in the method using electromagnetic induction. The technique of the present disclosure is not limited to the magnetic field resonance coupling method, and can be applied to wireless power transmission by an electromagnetic induction method. Thus, the present disclosure also includes structures by electromagnetic induction.

The movable body 200 includes a capacitor and a motor. The power received by the power receiving resonator in the power receiving resonator 203 is rectified and stored in a capacitor. As the capacitor, a large-capacity and low-resistance capacitor such as an electric double layer capacitor or a lithium ion capacitor can be used. The movable body 200 can move by driving the motor with the electric power stored in the capacitor.

When the mobile unit 200 moves, the amount of stored electricity (i.e., the amount of charged electricity) in the capacitor decreases. Therefore, in order to continue the movement, recharging is required. Therefore, when the amount of charge is lower than the predetermined threshold value during movement, the mobile unit 200 moves to the vicinity of the power transmission device 100 and is charged. As shown in fig. 1, when the power transmission devices 100 are provided at a plurality of locations, the moving body 200 only needs to move to the vicinity of the nearest power transmission device 100, and thus the moving distance can be shortened.

As described above, such a system can be used as a system for transporting articles in a factory, for example. The mobile unit 200 typically has a stage on which an article is mounted, and functions as a carriage that autonomously moves in a factory and transports the article to a necessary place. The mobile system is not limited to use in a factory, and can be used in, for example, a store, a hospital, a home, and any other places. The moving object 200 is not limited to the AGV, and may be another industrial machine or a service robot. The moving body 200 may be any device having a movable mechanism, such as a manned vehicle, an unmanned aerial vehicle, or a sweeping robot. The power receiving device in the present disclosure is not limited to a mobile body. The technique of the present disclosure can be applied even when the relative position of the power transmission coil and the power reception coil has an error within the rated range during power transmission. The technique of the present disclosure can be applied to any non-contact power supply system in which there is a possibility that the relative position of the power transmission coil and the power reception coil changes during power transmission.

Fig. 2 is a perspective view schematically showing an example of the moving body 200 in the present embodiment. The moving body 200 includes: a power receiving resonator 203 provided on the side surface; a plurality of wheels including a drive wheel 207 driven by a motor; and a stage 206 on which the article is placed. The power receiving resonator 203 includes a power receiving coil.

Fig. 3 is a perspective view showing an example of the arrangement relationship between the power transmitting resonator 103 and the power receiving resonator 203 during charging. XYZ coordinates representing directions X, Y, Z perpendicular to each other are shown in fig. 3. In the following description, the illustrated coordinate system is used. The XY plane is parallel to the horizontal plane or the ground, and the forward direction of the moving body 200 is the positive direction of the X axis, and the vertically upward direction is the positive direction of the Z axis. Fig. 3 shows the DC-DC converter 101, the inverter circuit 102, and the rectifier circuit 201, and other components are not shown. The power transmitting resonator 103 includes a power transmitting coil 1031, and the power receiving resonator 203 includes a power receiving coil 2031.

The orientation of the structure shown in the drawings of the present application is set for convenience of explanation, and is not intended to limit the orientation in which the embodiments of the present disclosure are actually implemented. The shape and size of the whole or a part of the structure shown in the drawings are not limited to actual shapes and sizes.

The power transmission is performed with the power transmission coil 1031 facing the power reception coil 2031. More specifically, the charging is performed in a state where a surface defined by the winding of the power transmission coil 1031 and a surface defined by the winding of the power reception coil 2031 (in the illustrated example, both surfaces are parallel to the XZ plane) face each other. Charging can be performed not only when these surfaces are perfectly parallel but also when they are inclined to each other.

The mobile unit 200 can grasp the position and orientation of the mobile unit and the position and orientation of the power transmission coil 1031 using various sensors. This makes it possible to specify the power transmission device 100 closest to the device itself, move the device to the vicinity of the power transmission device 100, and assume an attitude in which efficient power transmission is possible, that is, an attitude in which the power receiving coil 2031 is opposed to the power transmission coil 1031 in proximity to the power transmission coil 1031. When the nearest power transmission apparatus 100 is supplying power to another mobile unit 200, the mobile unit 200 may move to the next nearest power transmission apparatus 100.

The structure of the moving body system according to the present embodiment will be described in more detail below.

Fig. 4A is a block diagram showing the structure of the mobile body system of the present embodiment. The mobile body system includes a power transmission device 100 and a mobile body (power reception device) 200.

The power transmission device 100 includes a DC-DC converter 101, an inverter circuit 102, a power transmission resonator 103, and a control circuit 104. In the example of fig. 4A and 4B, the power transmission device 100 further includes the power source 105, but the power source 105 may be an external component of the power transmission device 100. The DC-DC converter 101 is connected between the power supply 105 and the inverter circuit 102. The inverter circuit 102 is connected between the DC-DC converter 101 and the power transmission resonator 103. The control circuit 104 controls the DC-DC converter 101 to control the ac power output from the inverter circuit 102. Similarly, the control circuit 104 controls the inverter circuit 102 to control the frequency of the output ac power.

The sensor 300 in the present embodiment is provided in the power receiving device 200. The sensor 300 includes a position detector that detects the position and/or movement of the moving body 200 and measures the distance between the coils. The sensor 300 may be provided outside the power receiving device 200.

The power transmission resonator 103 includes the aforementioned power transmission coil 1031. The moving body 200 includes a power receiving resonator 203, a rectifier circuit 201 connected to the power receiving resonator 203, and a load 202 connected to the rectifier circuit 201. The power receiving resonator 203 includes the power receiving coil 2031 described above. The load 202 includes an electric double layer capacitor, a battery, or the like. Further, the power transmission device 100 and the mobile object 200 may have other components not shown. The moving body system does not necessarily have to include all the components shown in fig. 4A, and can be omitted as appropriate. For example, the DC-DC converter 101 may be omitted. In this case, the control circuit 104 controls the output voltage of the inverter circuit 102 by controlling the inverter circuit 102.

The power transmission resonator 103 has not only an inductance component but also a capacitance component C1 and a resistance component R₁. Likewise, the power receiving resonator 203 has not only an inductance component but also a capacitance component C₂And a resistance component R₂. When the distance between the power transmission coil and the power reception coil is shortened, a resistance component (hereinafter, also referred to as an ac resistance value) R is generated₁And R₂Increased by the abutment effect. The voltage and current used to provide the desired voltage and current to the power delivery side of the load 202 also vary. Therefore, in the present embodiment, the distance between coils is detected by the sensor 300, and the control circuit 104 appropriately controls the DC-DC converter 101 and the inverter 102 in accordance with the distance. Thus, even if the distance between the resonators changes during power transmission, a desired voltage and current can be quickly supplied to the load 202.

Fig. 4B is a diagram showing a more detailed example of the structure of the mobile body system shown in fig. 4A. Hereinafter, each component will be described in more detail with reference to fig. 4B.

< Power supply >

The power supply 105 is a power supply circuit that outputs a dc voltage of a predetermined magnitude. Power supply 105 may include, for example, a converter that converts commercial ac power into dc power having an operating voltage of power transmission device 100 and outputs the dc power. The power source 105 can include a circuit for improving a power factor of the commercial power, for example. In the example shown in fig. 4A and 4B, the power supply 105 includes a converter that converts three-phase ac power into dc power. The power supply 105 may include a converter that converts single-phase ac power to dc power.

< DC-DC converter >

The DC-DC converter 101 steps up or down an input direct-current voltage. The DC-DC converter 101 can be, for example, a boost chopper circuit or a buck-boost chopper circuit. In the example of fig. 4B, the DC-DC converter 101 is a boost chopper circuit having a switching element S5. The switching element S5 is controlled by the control circuit 104, thereby adjusting the direct-current voltage output from the DC-DC converter 101. The layout of the DC-DC converter 101 may be either an insulating type or a non-insulating type as long as it has a voltage conversion function. The DC-DC converter 101 can change an output voltage by switching on/off of a switching element in a circuit according to a control signal supplied from the control circuit 104.

< inverter circuit and power transmission side control circuit >

The inverter circuit 102 converts direct-current power supplied from the DC-DC converter 101 into alternating-current power. The inverter circuit 102 may be a full-bridge inverter circuit, for example. The full-bridge inverter circuit includes four switching elements, and can output ac power of a desired frequency and voltage value by adjusting the timing of switching of each switching element. Each switching element is switched between a conductive state and a non-conductive state in accordance with a pulse signal supplied from the control circuit 104.

The inverter circuit 102 shown in fig. 4B has a full-bridge inverter circuit configuration including four switching elements S1 to S4. Each switching element may be a Transistor such as an IGBT (Insulated-gate bipolar Transistor), a MOSFET (metal oxide Semiconductor Field-Effect Transistor), or a hemt (high Electron mobility Transistor), for example.

The control circuit 104 includes a recording medium 1041 such as a memory, a controller 1042, a plurality of gate drivers 1043, a plurality of voltage/current measuring devices 1044, and a communication device 1045. The plurality of gate drivers 1043 includes: a gate driver that drives the switching element S5 in the DC-DC converter 101; and gate drivers that drive the switching elements S1, S2, S3, S4 in the inverter 102, respectively. The measuring unit 1044 includes: a measuring device that measures a voltage and a current output from the DC-DC converter 101 and input to the inverter circuit 102; and a measuring device for measuring the voltage and current output from the inverter circuit 102 and input to the power transmission resonator 103. The controller 1042 includes, for example, a microprocessor, and controls each drive 1043 according to a computer program stored in the recording medium 1041. Each driver 1043 switches the on/off state of the switching element by supplying a control signal (for example, a pulse signal) to the gate of the switching element connected to each driver 1043 in accordance with an instruction from the controller 1042.

The controller 1042 acquires measured values of the voltage and the current supplied to the load 202 of the power receiving apparatus 200 via the communication device 1045 during the power transmission operation. The controller 1042 also acquires the measured values of the voltage and the current supplied to the power transmitting resonator 103 from the voltage/current measurer 1044. The controller 1042 controls each driver 1043 so that a desired voltage and current are supplied to the load 202 based on the two measurement values.

< control circuit on power receiving side >

The power-receiving-side control circuit 204 includes a controller 2042, a voltage/current measuring unit 2044, and a communication device 2045. The measuring device 2044 measures the voltage and the current output from the rectifier circuit 201 and input to the load 202. The controller 2042 includes, for example, a microprocessor, and operates according to a computer program stored in a recording medium, not shown. The controller 2042 acquires data representing measured values of the voltage and current input to the load 202 from the measurer 2044. The controller 2042 also acquires data representing the distance between the power transmitting resonator 103 and the power receiving resonator 203 from the sensor 300. The controller 2042 transmits the two types of data to the communication device 1045 in the power transmission side control circuit 104 via the communication device 2045.

< rectifier circuit >

The rectifier circuit 201 in the power receiving device 200 is a circuit that converts ac power output from the power receiving resonator 203 into dc power and supplies the dc power to the load 202. In the example shown in fig. 4B, the rectifier circuit 201 has a diode bridge and a smoothing capacitor. The layout of the rectifier circuit 201 is not limited to the illustrated layout, and can be changed as appropriate.

< modification of power receiving side Circuit >

The circuit on the power receiving side may have the structure shown in fig. 5A or 5B. Fig. 5A and 5B show a modification in which the power receiving device 200 includes an impedance conversion converter (hereinafter, simply referred to as a DC-DC converter) 205. Fig. 5A shows an example of a configuration in which the power receiving apparatus 200 and the power receiving-side control circuit 204 shown in fig. 4A are replaced with the power receiving apparatus 200 and the power receiving-side control circuit 204 shown in fig. 5A, respectively. Fig. 5B shows an example of a configuration in which sensor 300 in the configuration of fig. 5A is replaced with sensor 300 mounted on power transmission device 100 and having a distance measuring device. Details of the sensor 300 will be described later.

In the non-contact power feeding using the magnetic field resonance coupling method and the electromagnetic induction method, the input impedance Z observed from the power receiving resonator 203 is determined based on parameters specific to the power transmitting resonator 103 and the power receiving resonator 203_in2(hereinafter, simply referred to as "input impedance Z_in2") to determine power transfer efficiency. Therefore, in the contactless power supply system of fig. 5A and 5B, the power receiving device 200 has a function for converting the input impedance Z_in2Set to a desired value, DC-DC converter 205. The layout of the DC-DC converter 205 is not limited to the illustrated layout, and can be changed as appropriate. The DC-DC converter 205 may be a step-down chopper circuit, a step-up chopper circuit, an insulating circuit, or a resonant circuit. The DC-DC converter 205 may also be a multi-phase converter. The DC-DC converter 205 has an input impedance Z_in2The changed function.

In this example, the power-receiving-side control circuit 204 measures the voltage and current input to the load 202, and measures the input impedance of the DC-DC converter 205. The power-receiving-side control circuit 204 controls each switching element of the DC-DC converter 205 according to the input impedance of the DC-DC converter 205 to set the input impedance Z_in2Set to the desired value.

< sensor >

The sensor 300 measures the relative distance between the power transmitting resonator 103 and the power receiving resonator 203. The sensor 300 may detect the position or movement of the mobile body 200. The sensor 300 may be, for example, a sensor using visible light or near infrared light. The sensor 300 may be a distance measuring device such as a laser distance meter or a device capable of measuring a distance such as a stereo camera.

The sensor 300 may have any one of the power transmission device 100 and the mobile object 200 (power receiving device). Sensor 300 may be provided outside power transmission device 100 or mobile object 200. For example, the mobile body 200 may have a sensor such as a laser range finder. In this case, data indicating the distance between the coils measured by the sensor is transmitted to the power transmission device 100, and the power transmission device 100 performs power transmission control based on the data.

When the mobile body system includes a control device that manages the positions and movements of all the mobile bodies 200, the control device may include a sensor. Such sensors measure or estimate the position and orientation of each mobile body 200, and transmit the data to power transmission device 100. The control circuit 104 in the power transmission device 100 can know the coil-to-coil distance from the received data.

As in the example shown in fig. 5B, the control circuit 104 may be configured to estimate the inter-coil distance from the output of the sensor 300 having a distance measuring device. For example, the distance between the power transmission coil and the power receiving coil 2031 can be estimated using the input impedance of the power transmission coil 1031 and the ac resistance value of the power transmission coil 1031 estimated from the output of the distance measuring instrument. The distance measuring instrument includes, for example: a light source that emits visible light or near infrared light (collectively referred to as "light"); and a detector that detects light emitted from the light source.

In the present embodiment, the voltage or frequency with the highest efficiency is determined according to the values of the voltage V1 and the current I1 measured by the measurer 1044 shown in fig. 4B, in particular. The details of this operation will be described later. The gate driver 1043 supplies a pulse signal having a frequency and a duty ratio determined by the controller 1042 to the gates of the switching elements S1 to S5. In addition, a part or all of the controller 1042 can be actually demonstrated by an integrated circuit such as a microcomputer.

< Power transmitting resonator and Power receiving resonator >

Fig. 6 is a diagram showing an equivalent circuit of the power transmitting resonator 103 and the power receiving resonator 203. The power transmission resonator 103 has an inductance component (L) generated by the power transmission coil 1031₁) A capacitance component (C) generated by the resonance frequency adjusting capacitor 1033₁) And mainly the resistance component of the power transmission coil 1031: (Hereinafter, simply referred to as resistance component) 1032 (R)₁) The series resonant circuit of (1). The power receiving resonator 203 has an inductance component (L) generated by the power receiving coil 2031₂) Capacitance component (C) generated by the resonance frequency adjusting capacitance 2033₂) And a resistance component 2032 (R) mainly included in the power receiving coil 2031 (hereinafter, simply referred to as a resistance component)₂) The series resonant circuit of (1). The capacitance components (C1 and C2) may be parasitic capacitance components of the power transmission coil 1031 and the power reception coil 2031, respectively, or may be generated by a separately provided capacitor.

The resonance frequency of the power transmitting resonator 103 and the resonance frequency of the power receiving resonator 203 are set to substantially the same value. The resonance frequency is not particularly limited, but may be set to, for example, 5 kilohertz (kHz) or more and 50 megahertz (MHz) or less. The resonance frequency is more preferably 10kHz to 20 MHz. Each resonator is not limited to the series resonant circuit, and may be a parallel resonant circuit. For example, a primary coil coupled to the power transmitting resonator 103 by electromagnetic induction and a secondary coil coupled to the power receiving resonator 203 by electromagnetic induction may be provided.

Resistance component 1032 (R)₁) And a resistance component 2032 (R)₂) Is increased by the proximity of the power transmission coil 1031 and the power reception coil 2031. And, a resistance component 1032 (R)₁) And a resistance component 2032 (R)₂) But also according to the heat change. The resistance component 1032 (R)₁) And a resistance component 2032 (R)₂) Both the magnetic field resonance coupling method and the electromagnetic induction method are used as variables in a calculation formula required for a non-contact power supply system. Embodiments of the present disclosure may actually measure the resistance component 1032 (R)₁) And a resistance component 2032 (R)₂) The amount of change due to the respective heat amounts may be stored in a storage device in the control circuit 104, or the amount of change in the resistance component due to the proximity effect may be calculated from the distance change actually measured by the sensor 300 (R) for the resistance component 1032₁) And a resistance component 2032 (R)₂) A change in (c). In addition, the embodiment of the present disclosure may actually measure the distance change by the sensor 300, and the control circuit 10 may control the distance change4 actual measurement of input impedance Z to the power transmitting resonator 103_in1The high-frequency resistance of the power transmitting resonator 103 is actually measured by the control circuit 104, and the heat change of the power receiving resonator 203 is actually measured by the power receiving-side control circuit 204, whereby the current resistance component 2032 (R) is calculated from each actual measurement value₂). Further, since it takes several seconds or more to actually measure the ac resistance value, when the mobile body 200 operates as shown in fig. 1, the method of calculating and obtaining the resistance component 1032 using the distance information acquired by the sensor 300 is quick. Alternatively, the value of the resistance component 1032 corresponding to the information of the sensor 300 may be recorded in advance in the storage device of the control circuit 104 and called.

< AC resistance value of coil >

In the present embodiment, the output voltage of the inverter circuit 102 is determined in consideration of an increase in the ac resistance value of each coil due to the adjacent effect. The ac resistance value of each coil and the adjacent effect will be described in detail below. In the following description, it is assumed that the power transmission coil and the power reception coil are spiral coils or solenoid coils. Each coil is assumed to be formed of a litz wire obtained by bundling a plurality of bare wires (a thin wire). However, each coil is not limited to such a configuration.

AC resistance value R of coil_acCan be defined approximately as follows.

[ equation 1]

R_dcIndicating the dc resistance value of the coil. F_RThe frequency of the ac power output from the inverter circuit 102 and the skin effect coefficient of the bare wire material of the coil are shown. R_{prox_a}Which represents an ac resistance value due to the adjacent effect that a plurality of coil wires present at different turns of a spiral coil or a solenoid coil have. R_{prox_v}The ac resistance value is represented by an adjacent effect caused by the power transmission coil 1031 and the power reception coil 2031 facing each other and affecting each other by their proximity. R_{prox_other}Represents an ac resistance value due to an abutting effect generated between the coil and a metal existing at a position distant from the coil. And, R_{prox_other}But also includes the effect when forming a coil after litz wire is bundled and wound. Let the resistance value when forming the coil be R_{prox_a}The relationship between the wires after the litz wires are bundled and the metallic foreign matter is set to F_a-1And U is adopted. The metal can be, for example, a magnetic flux shielding metal or a metal foreign matter required in designing the coil.

The skin effect is a phenomenon in which current flows only on the surface of the coil wire as the frequency increases. In this phenomenon, the distribution of the current density is concentrated only on the peripheral portion of the coil wire. In other words, the resistance of the central portion of the coil wire becomes large. F in equation 1_RCan be calculated by known methods. Here, F_RAs represented by the following formula,

[ equation 2]

R_dcIs a direct current resistance value r_sIs the bare wire radius of the twisted coil, delta is the skin effect coefficient, R_condRepresents a passing coefficient F_RAnd increased R_dc. Here, in the case where the skin effect is sufficiently small, F_RIs approximately 1, R_condAnd R_dcClose to equal values.

Next, assume a case where an alternating current flows through the coil wire. A magnetic field generated by a current flowing through a part of the coil wire may enter a part of another coil wire opposite to the coil wire, for example. Eddy current is generated in this portion, and loss occurs. As a result, the density distribution of the current flowing through a part where the magnetic field enters becomes disturbed. This increases the ac resistance value of the other coil wire opposite to the coil wire. This is called the abutment effect. Non-patent document 1 describes the principle of the adjacency effect. In the present embodiment, a process related to the magnetic field described in non-patent document 1 is expanded, and a spiral coil used for non-contact power supply is described.

In equation 1, R is calculated when the distance between the power transmission coil and the power reception coil facing each other is shortened_{prox_v}When the distance between the coil and the metal is shortened, R is increased_{prox_other}And (4) increasing. Hereinafter, for the AC resistance value R_{prox_v}And R_{prox_ohter}The calculation method of (2) will be explained.

First, to R_{prox_v}The calculation method of (2) will be explained. Consider a case where a magnetic field is generated by a current I flowing through a helical coil having n turns. The magnetic field is expressed by equation 3 below using vector expressions shown in fig. 12 and 13 according to the Biot-savart (Biot-savart) law.

[ equation 3]

Wherein the content of the first and second substances,

[ equation 4]

R＝P-S (4)

H_nRepresenting the magnetic field vector generated from a helical coil with n turns. ds represents a component current (vector), and s is a position vector representing a part of the coil. P is a position vector indicating a position where a magnetic field is generated. C_iThe path on the coil wire of the ith turn is represented, representing the box integral. Equation 4 represents a vector from a part of the coil to a position where the magnetic field is generated. Fig. 12 shows the element current ds in equation 3. Fig. 13 shows the expression of the vector in equation 4.

The eddy current loss is calculated from the magnetic field of equation 3, and the increased ac resistance value is obtained by dividing the loss by the square of the current. The eddy current loss P is expressed by the following equation 5_n。

[ equation 5]

σ is the intrinsic conductivity of a substance, and the reciprocal represents the resistivity. Gamma is the natural frequency response of a substanceThe ratio of the characteristic coefficient δ to the radius r1 of the coil wire (γ r1/δ). The current density distribution in the coil wire varies according to the frequency and by the skin effect. γ represents a ratio of the actual radius of the coil wire to the variation of the current density. If I is used as the effective value of the alternating current_rms＝I/(2^1/2) Then, R in formula 1 is calculated_{prox_v}Expressed by the following equation.

[ equation 6]

Where n is the number of bare litz wires, P_nThe bare wire, which is a litz wire, has a resistive loss. The resistance value is obtained by dividing the loss by the square of the current.

When equations 3 and 5 are used, R in equation 6_{prox_v}Expressed by equation 7 below.

[ equation 7]

Then, R in equation 1 is compared_{prox_other}The calculation method of (2) will be explained. When designing a coil, a metal plate may be disposed close to the coil in order to avoid leakage of a magnetic field or formation of an undesired magnetic path. Further, a metal foreign object such as a screw, a coin, or a beverage can may come close to at least one of the power transmission coil 1031 and the power receiving coil 2031. In this case, the ac resistance value of at least one of the power transmission coil 1031 and the power reception coil 2031 increases due to the proximity effect. A correspondence diagram between magnetic flux generated from the power transmission coil 1031 or the power receiving coil 2031 in such a case and metallic foreign matter is shown in fig. 14.

The loss Δ P of the coil due to the influence of the metal is expressed by the following equation 8_{prox_other}。

[ equation 8]

ΔP_{prox_other}＝ΔP_{prox_a}F_a-1U (8)

Wherein，ΔP_{prox_a}This is a loss when the coil is wound, and is represented by a magnetic flux incident transversely to the cylindrical coil. F_a-1Is expressed as follows.

[ equation 9]

At this time, r₁The radius of the coil wire is determined, and the approximate expression is divided according to conditions due to the magnitude relation between the radius of the coil wire and the skin effect coefficient delta. In this case, the division indicates a difference how the influence of the magnetic flux within the conductor is approximated. 1 is obtained by subtracting the loss when not affected by the metallic foreign matter from the loss when affected by the metallic foreign matter through the function U in addition to the influence by the magnetic flux in the conductor. Here, the skin effect coefficient δ is expressed by the following equation 10.

[ equation 10]

μ is the magnetic permeability, σ is the intrinsic conductivity of the material, and ω is the angular frequency of the alternating current. U is a coefficient indicating a positional relationship with the metallic foreign matter, and is an approximate function indicating a state in which magnetic flux generated from one of the adjacent cylinders generates magnetic flux at a position where the other cylinder is located. The loss Δ Pprox _ other affected by the metallic foreign matter is expressed by a relative relationship between the following three, which are: a loss Δ Pprox _ a generated when the coil is wound; skin effect coefficient when a single strand approximation is made to the coil; and a metallic foreign substance. Values corresponding to the material specific to the substance are substituted into the parameters in equations 7 to 9.

Next, the resistance value is derived from the actual coil shape according to the formula of equation 7. Loss per unit length Δ P of coil_{prox_other}Expressed by equation 11 below.

[ equation 11]

ΔP_{prox_other}＝ΔP_{prox_a}[F_a-1{1+12A}](11)

Equation 11 shows the loss Δ P_{prox_other}Delta P determined from design and manufacture of coil_{prox_a}To what extent it is increased. Where (1+12A) is an approximate expression of a natural logarithm, and a is expressed by the following expression 12.

[ equation 12]

r₂Is half the thickness of the disc-shaped metal opposite the coil. R represents the distance from the center of the cross section of one strand of coil wire to the center of the disk-shaped metal.

According to equation 11, R in equation 1_{prox_other}Expressed by the following equation 13.

[ equation 13]

Here, Δ Pprox _ a is an initial loss determined at the time of designing the coil, and will be described later. F_a-1Is the skin effect coefficient of the coil wire, influenced by (1+12A) as an approximation function of the natural logarithm. The calculation formula is a value obtained by performing a circular integral C of the length of a coil wire in a turn i through which a certain current flows_iThe amount corresponding to the number of turns of the coil is accumulated. The influence after winding the litz wire and the influence of the metal having a simple shape can be calculated by equation 13.

The amount of increase in the ac resistance value of at least one of the power transmission coil 1031 and the power reception coil 2031 can be calculated by the above equations 6 and 13.

Fig. 8A to 8C are diagrams showing an example of a change in the ac resistance value of the power receiving coil 2031 when the distance between the power transmission coil 1031 and the power receiving coil 2031 is changed. In the examples of fig. 8A to 8C, the combinations of the structures of the transmission coil 1031 and the power reception coil 2031 are different. The curves represent calculated values and the diamonds represent the median of the experimental values. The vertical straight line indicates the deviation of the experimental value. When the distance between the power transmission coil 1031 and the power reception coil 2031 is 70mm or more, the change in the ac resistance value of the power reception coil 2031 is relatively small. However, when the distance between the power transmission coil 1031 and the power reception coil 2031 is less than 70mm, the ac resistance value increases sharply when the distance becomes smaller.

Therefore, in the present embodiment, the control circuit 104 of the power transmission device appropriately controls the voltage input to the power transmission resonator 103, taking into account the influence of the increase in the ac resistance value with the approach between the coils. This control is performed by adjusting the magnitude of the DC voltage input from the DC-DC converter 101 to the inverter circuit 102. In the embodiment where the DC-DC converter 101 is not provided, the inverter circuit 102 may be directly controlled to perform the same adjustment. By preparing data (sometimes referred to as a library) specifying a correlation between the coil-to-coil distance and the ac resistance value or the variation amount of the transmission voltage due to the ac resistance value in advance, the voltage on the transmission side can be set to an appropriate value with reference to the data at the time of transmission.

The ac resistance value also increases due to heat generation of the coil. Therefore, the control circuit 104 of the power transmission device 100 may control the voltage input to the power transmission resonator 103 in consideration of the heat generation of the coil. The following shows a function for correcting the resistance value that increases due to heat generation of the coil. When the heat generation of the coil and the adjacent effect overlap, the calculation may be faster than the case of using the library. Δ P described in expressions 7 to 13₀The loss of the coil is determined by using the coil wire material and the frequency. Here, R is represented by formula 1_{prox_a}The description will be made. Generation of R_{prox_a}Loss per unit length of (Δ P)_{Rprox_a}Representing losses due to the adjacent effect caused by the magnetic flux incident into the coil wire through the transverse direction. The R is_{prox_a}The resistance value generated when the coil wire is wound in a spiral shape is shown. R_{prox_a}Although it is essentially a value that can be actually measured after design trial production, it is preferable to use R when correcting for a change in the amount of heat of the resistance value_{prox_a}The formula (2) is calculated.

In the following description, a conductive wire (for example, a copper wire) before being formed into a coil is referred to as a cylindrical conductor. The loss per unit length due to the adjacent effect caused by the magnetic flux incident in the lateral direction into the cylindrical conductor is expressed by equation 14.

[ equation 14]

σ in equation 14 represents conductivity, k is a coefficient depending on a substance and a frequency, which represents an epidermal effect, and r₀Is the radius of the wire, H₀Is a magnetic field generated when a coil is wound in a spiral shape and no foreign metal is present. G_RThe coefficients can be expressed by a bezier function, and are expressed by equation 15.

[ equation 15]

G_RBer and bei denote the real and imaginary parts, μ, of the Kelvin function, respectively₁Is the magnetic permeability, μ, of a substance existing in the space before incidence₂Is the permeability of the incident material. k is expressed by the following equation 16.

[ equation 16]

Using equations 14 to 16, the loss Δ P per unit length due to the adjacency effect generated by the incidence of the transverse magnetic flux into the cylindrical conductor as the base can be calculated_{prox_a}. The resistance value R representing the adjacency effect when winding the coil can be obtained by adding equation 14 to the number of adjacent strands of the coil wire and integrating the length of the coil by an amount corresponding to the length of the coil_{prox_a}。

[ equation 17]

[ equation 18]

Equations 17 and 18 are the first kelvin functions.

The resistance value of the adjacent effect included in equation 1 is described above. The frequency ω, the magnetic permeability μ, and the electric conductivity σ included in these calculation expressions can be corrected to correct the change due to heat, thereby obtaining the total resistance value more accurately. The change due to the heat may be called from the storage device of the control circuit 104 when the change of μ and σ corresponding to the heat is recorded in the library and the transmission voltage is controlled.

In the conventional non-contact power feeding system, it is considered that even if the ac resistance values of the power transmission coil 1031 and the power reception coil 2031 vary depending on the distance between the power transmission coil 1031 and the power reception coil 2031, the control of the system is not affected. However, it is understood that when the distance is shortened, the ac resistance value is significantly increased, and the influence on the control is increased. Therefore, in the present embodiment, power transmission control is performed in consideration of the proximity effect, that is, an increase in the ac resistance value of at least one of the power transmission coil 1031 and the power reception coil 2031. This enables more accurate and rapid supply of the power required by the power receiving device.

In the present embodiment, data such as a table or a function indicating a correspondence relationship between the inter-coil distance and the ac resistance value of the power receiving coil 2031 is recorded in advance in the recording medium 1041 attached to the control circuit 104. The control circuit 104 can calculate or estimate the ac resistance value of the power receiving coil 2031 from the inter-coil distance obtained from the sensor 300 with reference to the data. As will be described later, the estimated value of the ac resistance value is used when determining the output voltage of the inverter circuit 102.

The inter-coil distance can also be estimated from the resistance component 1032 of the power transmission resonator 103 without being acquired from the sensor 300. Since the ac resistance value increases due to the proximity effect, it is possible to estimate a general coil-to-coil distance from resistance component 1032 of power transmission resonator 103. In such a system, data of a table or a function defining a correspondence relationship between the resistance component 1032 of the power transfer resonator 103 and the coil-to-coil distance is recorded in advance in the recording medium 1041 attached to the control circuit 104. The control circuit 104 can also calculate or estimate the coil-to-coil distance with reference to this data.

< Transmission control method >

The power transmission device 100 in the present embodiment can appropriately determine the transmission power by the feedforward control without using information transmitted from the mobile body 200 when starting the power supply to the mobile body 200 or when the coil-to-coil distance changes during the power supply. After the transmission power is thus determined, power transmission device 100 performs feedback control based on information from mobile unit 200. This method will be specifically described below.

In the following description, an ac voltage and an ac current are expressed in terms of phasors (phasers). That is, the voltage and current are treated as a complex number. In the phasor display, the absolute values of the voltage and current represent the respective effective values.

The phasors of the voltage and current at the power transmission side are shown as V₁And I₁The effective values of the voltage and current on the power transmission side are V_rms1＝|V₁I and I_rms1＝|I₁L. Similarly, the phasors of the voltage and current at the power receiving side are shown as V₂And I₂When, V_rms2＝|V₂I and I_rms2＝|I₂|。

Fig. 6 is a diagram showing an equivalent circuit of the contactless power supply system in the present embodiment. In fig. 6, components such as the inverter circuit 102 connected to the power transmitting resonator 103 (see fig. 4A and the like) are omitted, and components such as the rectifier circuit 201 connected to the power receiving resonator 203 are omitted. Here, let the input impedance of the power transmission coil 1031 be Z_in1。Z_in1Through V₁/I₁And obtaining the compound. Let the input impedance of the circuit connected to the power receiving resonator 203 be Z_in2。Z_in2Through V₂/I₂And obtaining the compound. Let mutual inductance be L_m. Let the AC resistance value of the power transmission coil 103 be R₁Is provided with a power receiving coil2031 has an alternating current resistance of R₂. The angular frequency ω of the transmitted ac power is the same as the driving angular frequency of the inverter circuit 102.

According to the circuit equation, V, of the circuit shown in FIG. 6₁、I₁、V₂And I₂The following equations 19 and 20 are satisfied.

[ equation 19]

[ equation 20]

Here, j is an imaginary unit.

In the following description, ω is related to the resonance angular frequency ω₀＝1/(L₁C₁)^1/2＝1/(L₂C₂)^1/2Are equal. In addition, ω may also be related to ω₀Not strictly equal.

The following I is obtained from equations 14 and 15₁And I₂。

[ equation 21]

[ equation 22]

When equation 21 is used, the input impedance Z is expressed by equation 23 below_in1。

[ equation 23]

When equation 23 is modified, ω is₀L_mExpressed by equation 24 below.

[ equation 24]

According to equation 24, X ═ ω₀L_mCan pass through Z_in1、R₁、Z_in2And R₂And (4) showing.

Therefore, control circuit 104 in power transmission device 100 measures the voltage and current output from inverter 102 by measuring instrument 1044, and calculates Z from the measured values_in1And R₁(refer to fig. 4B). This is because the control circuit 104 measures the Z based on weak power in order to confirm whether the relative distance between the power transmitting resonator 103 and the power receiving resonator 203 is within the design rating while confirming the effective operating frequency_in1The function of (a). When the inverter 102 outputs power while sweeping the operating frequency, at Z_in1The transmission current actually peaks at the smallest frequency. This frequency is set as the effective operating frequency. The control circuit 104 measures Z by this function_in1And according to V₁And I₁Finding R₁. Impedance Z in a powered device_in2Held constant by the power receiving side converter. From equation 24, in Z_in2Ratio R₂When the ratio of (A) to (B) is small by several times, R is₂May vary for X ═ ω₀L_mThe calculation of (2) brings a large influence. The control circuit 104 estimates R calculated in consideration of the proximity effect from the inter-coil distance measured by the sensor 300₂The value of (c). This estimation is performed based on data such as a table stored in the recording medium 1041 in the control circuit 104. The control circuit 104 utilizes these Z_in1、R₁、Z_in2And R₂And calculates X ω from equation 24₀L_m。

The control circuit 104 can also calculate X ═ ω from the calculated X ═ ω₀L_mThe receiving voltage and the receiving current are estimated.

Receiving voltage V₂And the transmission voltage V₁Ratio A of_vEquation of utilization 22And is expressed by equation 25 below.

[ equation 25]

Receiving a voltage I₂And the transmission current I₁Ratio A of_IThe following equation 26 is expressed by equations 21 and 22.

[ equation 26]

By using equations 25 and 26, control circuit 104 can obtain effective value V from the transmission voltage_rms1And the effective value I of the transmission current_rms1Obtaining an effective value V of the receiving voltage_rms2And the effective value I of the receiving current_rms2. For example, V can be obtained from equation 25_rms1And V_rms2The relationship of (1), i.e. V_rms2＝|A_V|V_rms1. V can be obtained from equation 26_rms1And I_rms2The relationship of (1), I_rms2＝(|A_I|/|Z_in1|)V_rms1. As long as these relationships are utilized, the implementation instruction value V can be determined_rms2Or the instruction value I_rms2Required V_rms1。

In this way, the control circuit 104 in the present embodiment estimates the mutual inductance between the power transmission coil 1031 and the power reception coil 2031 from the ac resistance value of the power reception coil 2031, the input impedance of the power transmission coil 1031, and the ac resistance value of the power transmission coil 1031. Then, the control circuit 104 determines the value of the voltage output from the inverter circuit 102 from the estimated value of the mutual inductance. In more detail, the control circuit 104 calculates ω according to equation 24₀L_mAnd determining the output voltage V of the inverter circuit 102 by using equation 25₁Or its effective value V_rms1。

Fig. 9 shows calculated values of power transfer efficiency and secondary-side input impedance Z_in2Off between (omega)In the magnetic field resonance coupling system, the power transfer efficiency η depends on the secondary-side input impedance Z_in2(omega). In the present embodiment, it is estimated in which state a certain system is in order to control the system. If the distance between the coils is close to the lowest value or the highest value among the power transmission distances defined as the design rated values, it is necessary to appropriately calculate the parameter that fluctuates.

Based on equations 25 and 26, the power transfer efficiency η is expressed by equation 27 below.

[ equation 27]

FIG. 9 shows that R is not considered₁And R₂Calculating transmission efficiency by using the variation of R₁And R₂The transmission efficiency is calculated from the measured value of (a) and R obtained by the method of the present embodiment is used₁And R₂The difference of the respective results of the cases of transmission efficiency is calculated. As shown in FIG. 9, in the present embodiment, R is not considered₁And R₂Can reduce errors compared to the case of variation of (2).

Fig. 10 shows the applied voltage V applied to the inverter 102 in the present embodiment_1DCConsumption current I with load 202_2DCSchematic of an example of the relationship between. According to the studies of the present inventors, the power transmission by the magnetic field resonance coupling method can obtain a longer power transmission distance than the electromagnetic induction method, and each parameter is likely to vary. As shown in fig. 10, the voltage changes according to changes in parameters such as mutual inductance, ac resistance value, and resonance frequency. Not determining V in power transmission apparatus_1DCIn the case of feed forward control of (2), to obtain a certain I_2DCOperating V according to control rules_1DC. However, the gain of the appropriate control law varies depending on the variation of the above parameters. Although there is a method of changing the gain of the control rule, the present embodiment proposes a method of calculating the changed parameter more appropriately.

For example, in a method capable of changing the gain of the control rule, the PID gain of the feedback control is selected for each inter-coil distance. When the power transmission efficiency decreases, the transmission voltage may need to be set to a larger value, and the transmission current may also increase. By being able to change the amount of time change of the transmitted power in accordance with the distance between the coils, robust control independent of the distance between the coils can be achieved. Further, there can be control having the following time-varying characteristics: when the receiving current rises, the receiving current has a large P gain, a small D gain and the like only in the initial period of time. However, it is very difficult to add an appropriate PID gain according to various inter-coil distances in terms of product design.

The feed-forward proposed in the present embodiment provides an initial voltage when the receiving current is increased from 0 to the command value. By the PID control, the reception current can be increased at a high speed, unlike the case where the amount of change in the reception current is read and the transmission voltage is operated. However, the power transmission characteristics differ depending on the variation in the distance between the coils. Therefore, when the initial power transmission voltage is applied, the power reception current may not smoothly rise or the power reception current may overshoot. The present proposal determines a power transmission voltage suitable for the inter-coil distance by acquiring the characteristic change in the inter-coil distance, and further determines a power transmission voltage with higher accuracy by acquiring the resistance value change due to the adjacency effect in the characteristic change in the inter-coil distance.

FIG. 10 shows V without control by feedforward_1DCDetermination of V by conventional feedforward control_1DCAnd V is determined by the feedforward control in the present embodiment_1DCThe respective results of the cases (a). As shown in FIG. 10, without feed forward, I_2DCSlowly rises until V_1DCIt takes a long time to converge to an appropriate value. In contrast, in the case of feedforward, I_2DCRapid rise, V_1DCConvergence is relatively fast. In the present embodiment, V at the time of feedforward is calculated more appropriately than before_1DC. Therefore, the surge current can be applied from the initial stageV closer to the convergence value within a range not exceeding the limit of hardware_1DC。

Next, an operation of setting the voltage value of the ac power output from the inverter circuit 102 in the power transmission device 100 to a desired voltage value by the estimation method according to the present embodiment will be described with reference to fig. 11.

Fig. 11 is a flowchart illustrating an example of a power feeding operation from the power transmission device 100 to the mobile body 200 in the present embodiment. The processing within the dotted line box in fig. 11 represents estimation of the state of the mobile body 200 to determine the initial power transmission voltage V_1initialThe method can be performed.

When power transmission is started, power transmission device 100 monitors the presence or absence of a power transmission stop signal (step S112). For example, when charging is completed or a failure occurs during charging, a power transmission stop signal is transmitted to power transmission device 100. Upon receiving the power transmission stop signal, power transmission device 100 ends charging (step S113). When the power transmission stop signal is not output, power transmission device 100 performs the following operation.

The control circuit 104 acquires data indicating the relative positional relationship between the power transmission coil 1031 and the power reception coil 2031 from the sensor 300, and measures the positional shift between the coils (step S102). Step S102 includes a process of obtaining a three-dimensional positional displacement amount, for example. When the positional deviation is read (yes in step S103), the control circuit 104 measures the temperature of the power transmission coil 1031 (step S104). Next, the control circuit 104 calculates or estimates the resistance component 2032 of the power transmission coil 1031 from the data representing the positional shift amount (step S105). The control circuit 104 estimates the resistance component 2032 (R) of the power receiving coil 2031 by referring to a table or the like defining the correspondence relationship between data indicating the three-dimensional positional shift amount and the resistance component 2032 of the power receiving coil 2031, or using a calculation expression₂) In this case, the resistance component may be acquired with higher accuracy by correcting the calculation formula using the measured value of the temperature measured in step S104 or by correcting the value acquired from the table. Before step S106, control circuit 104 performs power transmission in the weak power mode, acquires the measured values of voltage and current from measurement device 1044, and acquires input impedance Z of power transmission coil 1031_in1Heyu (Chinese character) transfusion systemAC resistance value R of electric coil 1031₁(step S101). This step S101 is performed at an arbitrary timing before step S106. In addition, when it is difficult to actually measure the resistance component 1032 with high accuracy, Z may be obtained from the table or the calculation formula in step S105 in the same manner_in1And R₁。

Then, the control circuit 104 estimates the ac resistance value R on the power receiving side based on the measured ac resistance value R₂And Z obtained_in1And R₁To estimate ω in the current relationship between the power transmitting resonator 103 and the power receiving resonator 203₀L_m(step S106). Then, the voltage ratio Av and the current ratio a in the current relationship between the power transmitting resonator 103 and the power receiving resonator 203 are obtained_I(step S107). The control circuit 104 determines the initial voltage V of the ac power to be output from the inverter circuit 102 according to the voltage ratio Av_1initial(step S107).

The control circuit 104 causes the inverter circuit 102 to output the ac power having the specified voltage value, and starts power transmission (step S109). Then, the power reception side control circuit 204 measures the payload current and transmits the measured payload current to the power transmission side control circuit 104 by wireless communication. The control circuit 104 performs PID control by obtaining a difference between the effective load current and the load current command value. The control circuit 104 determines whether a predetermined time has elapsed since the last measurement (step S111). When a certain time has elapsed, the operations of steps S112 to S111 are executed again. Thus, even if characteristic fluctuations such as fluctuations in the distance between coils during movement occur, fluctuations in the load voltage can be suppressed. In particular, the loop of step S111 is configured to acquire the output value of step S105 again at a predetermined time interval. When there is a system failure or the power receiving device is fully charged, a power transmission stop signal is output, and power transmission is stopped in step S113.

With the above operation, the target receiving voltage or receiving current can be reached more accurately and more quickly than before. In particular, the accuracy and robustness of feedforward with respect to the variation in the distance between coils are dramatically improved, and it is not necessary to change the feedback gain depending on the situation. Further, instantaneous rise and overshoot of the transmission power can be reduced by such characteristics, and derating (derating) of the power plant can be easily performed.

The above-described operation is an example, and can be appropriately changed. The processing according to each expression in the above description is an example, and can be used in a suitably modified manner. For example, the formula may be corrected as necessary to reduce the error.

As described above, the present disclosure includes the power transmission device, the non-contact power supply system, the program, and the method described in the following items.

[ item 1]

A power transmitting device wirelessly transmits power to a power receiving device having a power receiving coil,

the power transmission device includes:

an inverter circuit;

a power transmission coil connected to the inverter circuit; and

a control circuit which controls an output voltage of the inverter circuit,

the control circuit determines the output voltage of the inverter circuit from an ac resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an ac resistance value of the power transmitting coil estimated or calculated based on a distance between the power transmitting coil and the power receiving coil.

[ item 2]

The power transmission device according to item 1, wherein,

the power transmission device further includes a measuring device that measures an output voltage and an output current of the inverter circuit,

the control circuit calculates an input impedance of the power transmission coil and an alternating current resistance value of the power transmission coil from the measured output voltage and the output current.

[ item 3]

The power transmission device according to item 1 or 2, wherein,

and estimating an ac resistance value of at least one of the power receiving coil and the power transmission coil based on the distance measured by the sensor.

[ item 4]

The power transmission device according to item 3, wherein,

the power transmission device also has the sensor.

[ item 5]

The power transmission device according to item 1 or 2, wherein,

the control circuit estimates a distance between the power transmission coil and the power receiving coil from the input impedance of the power transmission coil, the AC resistance value of the power transmission coil, and an effective operating frequency, and estimates the AC resistance value of the power receiving coil from the estimated distance.

[ item 6]

The power transmission device according to any one of items 1 to 5,

the power transmission device further includes a recording medium that stores a table or a function that specifies a correspondence relationship between the distance and the ac resistance value of the power receiving coil, and the control circuit estimates the ac resistance value of the power receiving coil with reference to the table or the function.

[ item 7]

The power transmission device according to any one of items 1 to 6,

the control circuit estimates mutual inductance between the power transmission coil and the power reception coil from the alternating current resistance value of the power reception coil, the input impedance of the power transmission coil, and the alternating current resistance value of the power transmission coil, and determines a value of a voltage output from the inverter circuit from the estimated value of the mutual inductance.

[ item 8]

The power transmission device according to any one of items 1 to 7,

the angular frequency of the power transmission coil and the power receiving coil is omega₀Setting the input impedance of the power transmission coil to be Z_in1And the alternating current resistance value of the power transmission coilIs R₁And setting the input impedance of a circuit connected to the power receiving coil to Z_in2Let the AC resistance value of the receiving coil be R₂Let the mutual inductance be L_mSetting the output voltage of the inverter circuit to be V₁Setting an initial output voltage of the AC power output from the inverter circuit to V_1initialSetting a target value of an output voltage of the power receiving coil to V₂When the temperature of the water is higher than the set temperature,

the control circuit calculates ω by the following equation 28₀L_mAnd for Z_in2Acquiring or selecting a fixed value through wireless communication,

determining the output voltage V of the inverter circuit using the relationship of equation 29 below_1initial，

[ equation 28]

[ equation 29]

[ item 9]

The power transmission device according to any one of items 1 to 8,

at the AC resistance value R1 of the power transmission coil or the AC resistance value R of the power receiving coil₂In the case where the variation occurs due to the proximity effect or the temperature change, the control circuit corrects the output voltage by changing a calculation formula or a recorded value used for determining the output voltage.

[ item 10]

The power transmission device according to item 8, wherein,

the control circuit utilizes R calculated by the following equation 30_acTo correct the value of (d) for determining the output voltage V_1initialThe alternating current resistance value R of the power transmission coil₁And an alternating current resistance value R of the power receiving coil₂，

[ equation 30]

R_ac≈R_cond+R_{pro_v}+R_{prox_other}

＝R_dcF_R+R_{prox_v}+R_{prox_a}F_a-1U，

R_dcIs a direct current resistance value of the wire of each coil,

F_Ris a skin effect coefficient obtained by using the wire rod, the wire diameter of each coil and the frequency of the AC power output from the inverter circuit,

R_{prox_a}is a resistance value which is obtained when each coil is designed and manufactured and which indicates an adjacent effect obtained when the coil wire is wound in a spiral or solenoid shape,

R_{prox_v}is a resistance value representing an abutting effect generated by the proximity of the power transmission coil and the power reception coil,

R_{prox_other}is a resistance value representing an adjacency effect increased by a metal located in the vicinity of each coil,

R_{prox_v}as calculated by the following equation 31,

[ equation 31]

n is the number of bare strands of the litz wire constituting each coil,

gamma is a coefficient determined by the bare wire diameter and the skin effect coefficient of the litz wire,

sigma is the electrical conductivity of the copper alloy,

Σ n denotes the number of turns of the coil,

i denotes the current-generating turn or turns,

∫C_irepresenting the integral of the wrap for each turn of the coil,

ds represents the cell current, and is,

r represents a vector from the current generating turns until the magnetic flux reaches the turns,

R_{prox_other}when the current I flows through the coil, it is calculated by the following equation 32，F_a-1Is an approximate expression representing the skin effect in a cylindrical conductor,

[ equation 32]

[ equation 33]

r₁Is the approximate radius of the cylinder after bundling the litz wires of the coil,

delta is the skin effect coefficient determined from the frequency and the material properties of the litz wire,

coefficient F representing the skin effect produced in the bare litz wire_RIs the following formula 34, which is given below,

[ equation 34]

r_sIs the bare wire radius of the litz wire, R_dcIs a direct current resistance, R_condRepresents a passing coefficient F_RAnd increased R_dc，

(1+12A) is an approximation of the natural logarithm,

as calculated by the following equation 35,

[ equation 35]

r₂Is the radius of the thickness of the disc-shaped metal opposite the coil,

r represents a distance from the center of the cross section of one strand of coil wire to the center of the disc-shaped metal,

ΔP₀is the initial loss per unit length of the coil.

[ item 11]

The power transmission device according to any one of items 1 to 10,

the power transmission device further includes a measuring device that measures a change in heat of the power transmission coil and the power receiving coil.

[ item 12]

The power transmission device according to item 10, wherein,

the control circuit also determines the AC resistance value R of the power transmission coil using the following equations 36 and 37₁And an alternating current resistance value R of the power receiving coil₂，

[ equation 36]

[ equation 37]

k is a substance and frequency dependent coefficient representing the skin effect,

r₀is the radius of the wire rod,

H₀is a magnetic field generated when a coil is wound in a spiral shape and no foreign metal is present,

ber and bei denote the real and imaginary parts of the kelvin function respectively,

μ₁is the magnetic permeability of the material present in the space before the magnetic field is incident,

μ₂is the magnetic permeability of the material upon which the magnetic field is incident.

[ item 13]

The power transmission device according to any one of items 1 to 12,

the power transmission device further has a DC-DC converter connected between a direct-current power source and the inverter circuit,

the control circuit controls the output voltage of the inverter circuit by controlling a direct-current voltage output from the DC-DC converter.

[ item 14]

A contactless power supply system having:

the power transmission device according to any one of items 1 to 13; and

the power receiving device.

[ item 15]

The contactless power supply system according to item 14, wherein,

the power receiving device includes:

a DC-DC converter; and

a power receiving side control circuit that controls the DC-DC converter,

the power reception side control circuit controls an input impedance from the power reception coil to a circuit connected to the power reception coil to be constant by controlling the DC-DC converter.

[ item 16]

The contactless power supply system according to item 14 or 15, wherein,

the power receiving device is a mobile body.

[ item 17]

A computer program for controlling a power transmitting apparatus that wirelessly transmits power to a power receiving apparatus having a power receiving coil,

the power transmission device includes:

an inverter circuit;

a power transmission coil connected to the inverter circuit; and

a control circuit which controls an output voltage of the inverter circuit,

the computer program causes the control circuit to determine the output voltage of the inverter circuit based on an alternating current resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an alternating current resistance value of the power transmitting coil estimated or calculated from a distance between the power transmitting coil and the power receiving coil.

[ item 18]

A method for controlling a power transmitting device that wirelessly transmits power to a power receiving device having a power receiving coil,

the power transmission device includes:

an inverter circuit;

a power transmission coil connected to the inverter circuit; and

a control circuit which controls an output voltage of the inverter circuit,

the method causes the control circuit to determine the output voltage of the inverter circuit according to an ac resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an ac resistance value of the power transmitting coil estimated or calculated based on a distance between the power transmitting coil and the power receiving coil.

Industrial applicability

The technique of the present disclosure can be applied to a non-contact power supply system that supplies power to a moving body such as an Automated Guided Vehicle (AGV), for example. The techniques of this disclosure can also be applied to other industrial machines, multi-axis aircraft, service robots, and the like.

Description of the reference symbols

100 power transmission apparatus 101 DC-DC converter 102 inverter 103 power transmission resonator 1031 power transmission coil 1032 resistance component 1033 resonant frequency adjustment capacitance 104 power transmission side control circuit 1041 storage medium 1042 control circuit 1043 gate driver 1044 voltage current measurer 1045 communication device 105 power supply 200 mobile 201 rectifier circuit 202 load 203 power reception resonator 2031 power reception coil 2032 resistance component 2033 resonant frequency adjustment capacitance 204 power reception side control circuit 2042 control circuit 2044 voltage current measurer 2045 communication device 205 DC-DC converter stage 206 drive wheel 300 sensor 310 distance measurer

Claims (18)

1. A power transmitting device wirelessly transmits power to a power receiving device having a power receiving coil,

the power transmission device includes:

an inverter circuit;

a power transmission coil connected to the inverter circuit; and

a control circuit which controls an output voltage of the inverter circuit,

the control circuit determines the output voltage of the inverter circuit based on an alternating current resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an alternating current resistance value of the power transmitting coil estimated or calculated based on a distance between the power transmitting coil and the power receiving coil.

2. The power transmission device according to claim 1,

the power transmission device further includes a measuring device that measures an output voltage and an output current of the inverter circuit,

the control circuit calculates an input impedance of the power transmission coil and an alternating current resistance value of the power transmission coil from the measured output voltage and the output current.

3. The power transmission device according to claim 1 or 2,

and estimating an ac resistance value of at least one of the power receiving coil and the power transmission coil based on the distance measured by the sensor.

4. The power transmission device according to claim 3,

the power transmission device also has the sensor.

5. The power transmission device according to claim 1 or 2,

the control circuit estimates a distance between the power transmission coil and the power receiving coil based on the input impedance of the power transmission coil, the AC resistance value of the power transmission coil, and an effective operating frequency, and estimates the AC resistance value of the power receiving coil based on the estimated distance.

6. The power transmission device according to any one of claims 1 to 5,

the power transmission device further includes a recording medium that stores a table or a function that specifies a correspondence relationship between the distance and the ac resistance value of the power receiving coil, and the control circuit estimates the ac resistance value of the power receiving coil with reference to the table or the function.

7. The power transmission device according to any one of claims 1 to 6,

the control circuit estimates mutual inductance between the power transmission coil and the power reception coil based on the alternating current resistance value of the power reception coil, the input impedance of the power transmission coil, and the alternating current resistance value of the power transmission coil, and determines a value of a voltage output from the inverter circuit based on the estimated value of the mutual inductance.

8. The power transmission device according to any one of claims 1 to 7,

the angular frequency of the power transmission coil and the power receiving coil is omega₀Setting the input impedance of the power transmission coil to be Z_in1If the alternating current resistance value of the power transmission coil is R₁And setting the input impedance of a circuit connected to the power receiving coil to Z_in2Let the AC resistance value of the receiving coil be R₂Let the mutual inductance be L_mSetting the output voltage of the inverter circuit to be V₁Setting an initial output voltage of the AC power output from the inverter circuit to V_1initialSetting a target value of an output voltage of the power receiving coil to V₂When the temperature of the water is higher than the set temperature,

the control circuit calculates ω by the following equation 1₀L_mAnd for Z_in2Acquiring or selecting a fixed value through wireless communication,

determining the output voltage V of the inverter circuit using the relationship of equation 2 below_1initial，

[ equation 1]

[ equation 2]

9. The power transmission device according to any one of claims 1 to 8,

at the value of the alternating current resistance R of the power transmission coil₁Or the alternating current resistance value R of the power receiving coil₂In the case where the variation occurs due to the proximity effect or the temperature change, the control circuit corrects the output voltage by changing a calculation formula or a recorded value used for determining the output voltage.

10. The power transmission device according to claim 8,

the control circuit utilizes R calculated by the following equation 3_acTo correct the value of (d) for determining the output voltage V_1initialThe alternating current resistance value R of the power transmission coil₁And an alternating current resistance value R of the power receiving coil₂，

[ equation 3]

R_ac≈R_cond+R_{prox_v}+R_{prox_other}

＝R_dcF_R+R_{prox_v}+R_{prox_a}F_a-1U

R_dcIs a direct current resistance value of the wire of each coil,

F_Ris a skin effect coefficient obtained by using the wire rod, the wire diameter of each coil and the frequency of the AC power output from the inverter circuit,

R_{prox_a}is a resistance value which is obtained when each coil is designed and manufactured and which indicates an adjacent effect obtained when the coil wire is wound in a spiral or solenoid shape,

R_{prox_v}is a resistance value representing an abutting effect generated by the proximity of the power transmission coil and the power reception coil,

R_{prox_other}is a resistance value representing an adjacency effect increased by a metal located in the vicinity of each coil,

R_{prox_v}as calculated by the following equation 4,

[ equation 4]

n is the number of bare strands of the litz wire constituting each coil,

gamma is a coefficient determined by the bare wire diameter and the skin effect coefficient of the litz wire,

sigma is the electrical conductivity of the copper alloy,

Σ n denotes the number of turns of the coil,

i denotes the current-generating turn or turns,

∫C_irepresenting the integral of the wrap for each turn of the coil,

ds represents the cell current, and is,

r represents a vector from the current generating turns until the magnetic flux reaches the turns,

r is calculated by the following equation 5 when a current I flows through the coil_{prox_other}，

[ equation 5]

F_a-1Is an approximate expression representing the skin effect in a cylindrical conductor,

[ equation 6]

And is selected by the conditions described above,

r₁is the radius after a single strand approximation of the litz wire of the coil,

delta is the skin effect coefficient determined from the frequency and the material properties of the litz wire,

in bare litz wireCoefficient of the skin effect produced F_RIs the following equation 7, which is given below,

[ equation 7]

r_sIs the bare wire radius of the litz wire, R_dcIs a direct current resistance, R_condRepresents a passing coefficient F_RAnd increased R_dc，

(1+12A) is an approximation of the natural logarithm,

as calculated by the following equation 8,

[ equation 8]

r₂Is half the thickness of the disc-shaped metal opposite the coil,

r represents a distance from the center of the cross section of one strand of coil wire to the center of the disc-shaped metal,

ΔP₀is the initial loss per unit length of the coil.

11. The power transmission device according to any one of claims 1 to 10,

the power transmission device further includes a measuring device that measures a change in heat of the power transmission coil and the power receiving coil.

12. The power transmission device according to claim 10,

the control circuit also determines the AC resistance value R of the power transmission coil using the following equations 9 and 10₁And an alternating current resistance value R of the power receiving coil₂，

[ equation 9]

[ equation 10]

k is a substance and frequency dependent coefficient representing the skin effect,

r₀is the radius of the wire rod,

H₀is a magnetic field generated when a coil is wound in a spiral shape and no foreign metal is present,

ber and bei denote the real and imaginary parts of the kelvin function respectively,

μ₁is the magnetic permeability of the material present in the space before the magnetic field is incident,

μ₂is the magnetic permeability of the material at which the magnetic field is incident.

13. The power transmission device according to any one of claims 1 to 12,

the power transmission device further has a DC-DC converter connected between a direct-current power source and the inverter circuit,

the control circuit controls the output voltage of the inverter circuit by controlling a direct-current voltage output from the DC-DC converter.

14. A contactless power supply system having:

the power transmission device of any one of claims 1 to 13; and

the power receiving device.

15. The contactless power supply system according to claim 14, wherein,

the power receiving device includes:

a DC-DC converter; and

a power receiving side control circuit that controls the DC-DC converter,

the power reception side control circuit controls an input impedance from the power reception coil to a circuit connected to the power reception coil to be constant by controlling the DC-DC converter.

16. The contactless power supply system according to claim 14 or 15, wherein,

the power receiving device is a mobile body.

17. A computer program for controlling a power transmitting apparatus that wirelessly transmits power to a power receiving apparatus having a power receiving coil,

the power transmission device includes:

an inverter circuit;

a power transmission coil connected to the inverter circuit; and

a control circuit which controls an output voltage of the inverter circuit,

the computer program causes the control circuit to determine the output voltage of the inverter circuit from an alternating current resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an alternating current resistance value of the power transmitting coil estimated or calculated based on a distance between the power transmitting coil and the power receiving coil.

18. A method for controlling a power transmitting device that wirelessly transmits power to a power receiving device having a power receiving coil,

the power transmission device includes:

an inverter circuit;

a power transmission coil connected to the inverter circuit; and

a control circuit which controls an output voltage of the inverter circuit,

the method causes the control circuit to determine the output voltage of the inverter circuit according to an ac resistance value of the power receiving coil, an input impedance of the power transmitting coil, and an ac resistance value of the power transmitting coil estimated or calculated based on a distance between the power transmitting coil and the power receiving coil.

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