JP5794203B2 - Power transmission device, power reception device, vehicle, and non-contact power supply system - Google Patents

Description

  The present invention relates to a power transmission device, a power reception device, a vehicle, and a non-contact power feeding system, and more particularly to a technique for improving power transmission efficiency in a non-contact power feeding system.

  In recent years, non-contact wireless power transmission without using a power cord or a power transmission cable has attracted attention, and an electric vehicle, a hybrid vehicle, or the like that can charge an in-vehicle power storage device with a power source outside the vehicle (hereinafter also referred to as “external power source”). Application to is proposed.

  In a non-contact power supply system, in order to improve power transmission efficiency, it is important to match impedances between a power transmission unit that transmits power and a power reception unit that receives power.

  Japanese Patent Laying-Open No. 2010-233354 (Patent Document 1) adjusts the impedance of a power receiving side circuit by a variable capacitor connected in series to a power receiving coil in a non-contact power feeding device that performs power transmission using electromagnetic induction. A configuration is disclosed.

JP 2010-233354 A JP2012-039692A

  In the non-contact power supply system, matching the impedance between the power transmission unit and the power reception unit, that is, bringing the resonance frequencies closer to each other leads to an improvement in power transmission efficiency. And the resonant frequency can be adjusted by providing the variable capacitor connected in series with the coil as disclosed by Unexamined-Japanese-Patent No. 2010-233354 (patent document 1).

  However, simply matching the impedance between the power transmission unit and the power reception unit may not necessarily optimize the power transmission efficiency. For example, even if the resonance frequency is the same, the power transmission efficiency can change if the mutual coupling degree is different.

  Therefore, in the non-contact power supply system, in order to further improve the power transmission efficiency, it is desired to be able to adjust the impedance over a wider range.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an impedance adjustment method for improving power transmission efficiency in a non-contact power feeding system.

  A power receiving device according to the present invention is a power receiving device for receiving power supplied to an electric load from a power transmission device in a contactless manner, and includes a power receiving unit that receives power from the power transmission device in a contactless manner. The power receiving unit includes a coil electrically connected to the electric load, a first variable capacitance unit connected in series with the coil between the coil and the electric load, and a second connected in parallel to the coil. Including a variable capacitance section.

  Preferably, the power reception device further includes a control device that controls the power reception unit. The control device adjusts the capacities of the first and second variable capacitor parts while maintaining the combined capacity of the first and second variable capacitor parts.

  Preferably, the control device determines a combined capacity of the first and second variable capacitance units in which the power transmission efficiency between the power transmitting device and the power receiving device is larger in the adjustable range, and then determines the determined combined capacity While maintaining the above, the capacities of the first and second variable capacitor sections are adjusted so that the power transmission efficiency is further increased.

  Preferably, the power reception device further includes a control device that controls the power reception unit. The control device adjusts the capacities of the first and second variable capacitance units according to the power transmission efficiency between the power transmitting device and the power receiving device.

  Preferably, the control device adjusts the capacities of the first and second variable capacitance units so that the power transmission efficiency exceeds a predetermined threshold value.

  Preferably, the power transmission device includes a power transmission unit for supplying power in a contactless manner. The difference between the natural frequency of the power transmission unit and the natural frequency of the power reception unit is ± 10% or less of the natural frequency of the power transmission unit or the natural frequency of the power reception unit.

  Preferably, the power transmission device includes a power transmission unit for supplying power in a contactless manner, and a coupling coefficient between the power transmission unit and the power reception unit is 0.1 or less.

  Preferably, the power transmission device includes a power transmission unit for supplying power in a contactless manner. The power receiving unit, through at least one of a magnetic field that vibrates at a specific frequency formed between the power receiving unit and the power transmitting unit, and an electric field that vibrates at a specific frequency formed between the power receiving unit and the power transmitting unit, Receives power from the power transmission unit.

  A vehicle according to the present invention includes the above power receiving device and a power storage device that stores electric power received by the power receiving device.

  A power transmission device according to the present invention is a power transmission device that supplies power from a power source to a power receiving device in a contactless manner, and includes a power transmission unit that transmits power to the power receiving device in a contactless manner. The power transmission unit includes a coil electrically connected to the power source, a first variable capacitor unit connected in series with the coil between the power source and the coil, and a second variable capacitor connected in parallel to the coil. Part.

  The non-contact power feeding system according to the present invention transmits electric power from the power transmission device to the vehicle in a non-contact manner. The non-contact power supply system is included in a power transmission device, a power transmission unit having a power transmission coil electrically connected to a power source, a power reception unit included in a vehicle and having a power reception coil electrically connected to an electrical load, And a control device for controlling the power transmission unit and the power reception unit. At least one of the power transmission coil and the power receiving coil has a first variable capacitor connected in series to the coil and a second variable capacitor connected in parallel to the coil. The control device adjusts the first and second variable capacitance units so that the power transmission efficiency between the power transmission unit and the power reception unit is larger within the adjustable range.

  The non-contact power feeding system according to the present invention transmits electric power from the power transmission device to the vehicle in a non-contact manner. The non-contact power supply system is included in a power transmission device, a power transmission unit having a power transmission coil electrically connected to a power source, a power reception unit included in a vehicle and having a power reception coil electrically connected to an electrical load, And a control device for controlling the power transmission unit and the power reception unit. The power transmission coil includes a first variable capacitance portion connected in series with the power transmission coil and a second variable capacitance portion connected in parallel with the power transmission coil between the power transmission coil and the power source. The power receiving coil includes a third variable capacitor connected in series with the power receiving coil and a fourth variable capacitor connected in parallel with the power receiving coil between the power receiving coil and the electric load. The control device performs the first and second operations so that the power transmission efficiency between the power transmission unit and the power reception unit is larger within the adjustable range without changing the third and fourth variable capacitance units in the power reception coil. Adjust the variable capacity section. Thereafter, the control device adjusts the third and fourth variable capacitance units so that the power transmission efficiency becomes larger within the adjustable range without changing the first and second variable capacitance units in the power transmission coil. .

  The non-contact power feeding system according to the present invention transmits electric power from the power transmission device to the vehicle in a non-contact manner. The non-contact power supply system is included in a power transmission device, a power transmission unit having a power transmission coil electrically connected to a power source, a power reception unit included in a vehicle and having a power reception coil electrically connected to an electrical load, And a control device for controlling the power transmission unit and the power reception unit. The power transmission coil includes a first variable capacitance portion connected in series with the power transmission coil and a second variable capacitance portion connected in parallel with the power transmission coil between the power transmission coil and the power source. The power receiving coil includes a third variable capacitor connected in series with the power receiving coil and a fourth variable capacitor connected in parallel with the power receiving coil between the power receiving coil and the electric load. In the state where the first and second variable capacitors in the power transmission coil are not changed, the control device performs the third and fourth so that the power transmission efficiency between the power transmission unit and the power reception unit is larger within the adjustable range. Adjust the variable capacity section. Thereafter, the control device adjusts the first and second variable capacitance units so that the power transmission efficiency becomes larger within the adjustable range without changing the third and fourth variable capacitance units in the power receiving coil. .

  ADVANTAGE OF THE INVENTION According to this invention, in a non-contact electric power feeding system, more extensive impedance adjustment can be performed and electric power transmission efficiency can be improved.

1 is an overall configuration diagram of a vehicle power feeding system according to an embodiment of the present invention. It is a functional block diagram explaining the structure of the vehicle and power transmission apparatus which are shown in FIG. 1 in detail. It is an equivalent circuit diagram at the time of power transmission from the power transmission device to the vehicle. It is a figure which shows the simulation model of an electric power transmission system. It is a figure which shows the relationship between the shift | offset | difference of the natural frequency of a power transmission part and a power receiving part, and electric power transmission efficiency. It is a graph which shows the relationship between the electric power transmission efficiency when changing an air gap in the state which fixed the natural frequency, and the frequency of the electric current supplied to a power transmission part. It is the figure which showed the relationship between the distance from an electric current source (magnetic current source), and the intensity | strength of an electromagnetic field. It is a figure which shows an example of the simulation about the relationship between the resonant frequency and electric power transmission efficiency at the time of changing the capacity | capacitance of two variable capacitors, maintaining a synthetic capacity in a coil unit. FIG. 5 is a diagram showing changes in combined impedance and power transmission efficiency with respect to frequency when the ratio of the combined capacitance and reactance is changed while maintaining the multiplication value of the combined capacitance of the variable capacitor and the reactance of the coil in the coil unit. is there. In this Embodiment, it is a flowchart for demonstrating the impedance adjustment control performed by ECU. It is a figure which shows the 1st modification which has the variable capacitor connected to the coil of the coil unit by the side of the power transmission apparatus in parallel and series. It is a figure which shows the 2nd modification which has the variable capacitor connected to the coil of the coil unit by the side of the power transmission apparatus in parallel and in series. It is a figure which shows the 3rd modification which has the variable capacitor connected to the coil of the coil unit by the side of the power transmission apparatus in parallel and in series. It is a figure which shows the 1st modification which has the variable capacitor connected to the coil of the coil unit by the side of a receiving device in parallel and in series. It is a figure which shows the 2nd modification which has the variable capacitor connected to the coil of the coil unit by the side of a receiving device in parallel and in series. It is a figure which shows the 3rd modification which has the variable capacitor connected to the coil of the coil unit by the side of a receiving device in parallel and in series. It is a figure which shows an example of the detailed structure of the variable capacitor in a coil unit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Configuration of wireless power supply system]
FIG. 1 is an overall configuration diagram of a vehicle power supply system (non-contact power supply system) 10 according to an embodiment of the present invention. Referring to FIG. 1, vehicle power feeding system 10 includes a vehicle 100 and a power transmission device 200. Vehicle 100 includes a power reception unit 110 and a communication unit 160. The power transmission device 200 includes a power supply device 210, a power transmission unit 220, and a communication unit 230.

  The power receiving unit 110 is installed on the bottom surface of the vehicle body, for example, and receives high-frequency AC power output from the power transmitting unit 220 of the power transmitting device 200 in a contactless manner via an electromagnetic field. The detailed configuration of power reception unit 110 will be described later together with the configuration of power transmission unit 220 and power transmission from power transmission unit 220 to power reception unit 110. Communication unit 160 is a communication interface for vehicle 100 to communicate with power transmission device 200.

  The power supply apparatus 210 in the power transmission apparatus 200 generates AC power having a predetermined frequency. As an example, the power supply device 210 receives power from a system power supply (not shown), generates high-frequency AC power, and supplies the generated AC power to the power transmission unit 220.

  The power transmission unit 220 is installed, for example, on the floor of a parking lot and receives supply of high-frequency AC power from the power supply device 210. Then, power transmission unit 220 outputs electric power in a non-contact manner to power reception unit 110 of vehicle 100 via an electromagnetic field generated around power transmission unit 220. The detailed configuration of the power transmission unit 220 will be described later together with the configuration of the power reception unit 110 and the power transmission from the power transmission unit 220 to the power reception unit 110. Communication unit 230 is a communication interface for power transmission device 200 to communicate with vehicle 100.

  In the vehicle power supply system 10, power is transmitted in a non-contact manner from the power transmission unit 220 of the power transmission device 200 to the power reception unit 110 of the vehicle 100.

  FIG. 2 is a detailed configuration diagram of the vehicle power supply system 10 shown in FIG. Referring to FIG. 2, power transmission device 200 includes power supply device 210 and power transmission unit 220 as described above. In addition to communication unit 230, power supply device 210 further includes a power transmission ECU 240 that is a control device, and a power supply unit 250. The power transmission unit 220 includes a coil unit having a resonance coil 221 (also referred to as a primary coil) and variable capacitors 222 and 223.

  Power supply unit 250 is controlled by control signal MOD from power transmission ECU 240, and converts power received from an AC power supply such as commercial power supply 400 into high-frequency power. Then, the power supply unit 250 supplies the converted high frequency power to the power transmission unit 220.

  In addition, power supply unit 250 outputs power transmission voltage Vtr and power transmission current Itr detected by a voltage sensor and a current sensor (not shown) to power transmission ECU 240, respectively.

  The resonance coil 221 transfers electric power to the resonance coil 111 included in the power reception unit 110 of the vehicle 100 in a non-contact manner.

  The variable capacitor 222 is connected in series with the resonance coil 221 between the resonance coil 221 and the power supply unit 250. The variable capacitor 223 is connected to the resonance coil 221 in parallel. The variable capacitors 222 and 223 are controlled by the control signal SIG <b> 2 from the power transmission ECU 240 and adjust the impedance of the power transmission unit 220.

  Note that power transmission between the power reception unit 110 and the power transmission unit 220 will be described later with reference to FIG.

  As described above, communication unit 230 is a communication interface for performing wireless communication between power transmission device 200 and vehicle 100, and exchanges information INFO with communication unit 160. Communication unit 230 receives vehicle information transmitted from communication unit 160 on vehicle 100 side, a signal for instructing start and stop of power transmission, and the like, and outputs the received information to power transmission ECU 240. Communication unit 230 transmits information including power transmission voltage Vtr and power transmission current Itr from power transmission ECU 240 to vehicle 100.

  Although not shown in FIG. 1, the power transmission ECU 240 includes a CPU (Central Processing Unit), a storage device, and an input / output buffer, and inputs signals from each sensor and outputs control signals to each device. Each device in the power supply device 210 is controlled. Note that these controls are not limited to processing by software, and can be processed by dedicated hardware (electronic circuit).

  In addition to power receiving unit 110 and communication unit 160, vehicle 100 includes a charging relay CHR 170, a rectifier 180, a power storage device 190, a system main relay SMR 115, a power control unit PCU (Power Control Unit) 120, and a motor generator 130. Power transmission gear 140, drive wheel 150, vehicle ECU (Electronic Control Unit) 300 as a control device, voltage sensor 195, and current sensor 196. Power reception unit 110 includes a coil unit having a resonance coil 111 (also referred to as a secondary coil) and variable capacitors 112 and 113.

  The resonance coil 111 receives power from the resonance coil 221 included in the power transmission device 200 in a contactless manner. The variable capacitor 112 is connected in series with the resonance coil 111 between the resonance coil 111 and the rectifier 180. The variable capacitor 113 is connected to the resonance coil 111 in parallel. Variable capacitors 112 and 113 are controlled by control signal SIG <b> 1 from vehicle ECU 300 to adjust the impedance of power reception unit 110.

  In this embodiment, an electric vehicle is described as an example of vehicle 100, but the configuration of vehicle 100 is not limited thereto as long as the vehicle can travel using electric power stored in the power storage device. Other examples of the vehicle 100 include a hybrid vehicle equipped with an engine and a fuel cell vehicle equipped with a fuel cell.

  Rectifier 180 rectifies the AC power received from resonance coil 112, and outputs the rectified DC power to power storage device 190 via CHR 170. For example, the rectifier 180 may include a diode bridge and a smoothing capacitor (both not shown). As the rectifier 180, a so-called switching regulator that performs rectification using switching control may be used. When the rectifier 180 is included in the power receiving unit 110, it is more preferable to use a static rectifier such as a diode bridge in order to prevent a malfunction of the switching element due to the generated electromagnetic field.

  CHR 170 is electrically connected between rectifier 180 and power storage device 190. CHR 170 is controlled by a control signal SE2 from vehicle ECU 300, and switches between supply and interruption of power from rectifier 180 to power storage device 190.

  The power storage device 190 is a power storage element configured to be chargeable / dischargeable. The power storage device 190 includes, for example, a secondary battery such as a lithium ion battery, a nickel metal hydride battery, or a lead storage battery, and a power storage element such as an electric double layer capacitor.

  Power storage device 190 is connected to rectifier 180. Power storage device 190 stores the power received by power reception unit 110 and rectified by rectifier 180. The power storage device 190 is also connected to the PCU 120 via the SMR 115. Power storage device 190 supplies power for generating vehicle driving force to PCU 120. Further, power storage device 190 stores the electric power generated by motor generator 130. The output of power storage device 190 is, for example, about 200V.

  Although not shown in FIG. 2, when the power reception voltage and the charging voltage of the power storage device 190 are different, a power conversion device such as a DC-DC converter is provided between the rectifier 180 and the power storage device 190. You may make it provide.

  Although not shown, power storage device 190 is provided with a voltage sensor and a current sensor for detecting voltage VB of power storage device 190 and input / output current IB. These detection values are output to vehicle ECU 300. Vehicle ECU 300 calculates the state of charge of power storage device 190 (also referred to as “SOC (State Of Charge)”) based on voltage VB and current IB.

  SMR 115 is electrically connected between power storage device 190 and PCU 120. SMR 115 is controlled by control signal SE <b> 1 from vehicle ECU 300, and switches between supply and interruption of power between power storage device 190 and PCU 120.

  Although not shown, the PCU 120 includes a converter and an inverter. The converter is controlled by a control signal PWC from vehicle ECU 300 to convert the voltage from power storage device 190. The inverter is controlled by a control signal PWI from vehicle ECU 300 and drives motor generator 130 using electric power converted by the converter.

  Motor generator 130 is an AC rotating electric machine, for example, a permanent magnet type synchronous motor including a rotor in which permanent magnets are embedded.

  The output torque of motor generator 130 is transmitted to drive wheel 150 via power transmission gear 140. The vehicle 100 travels using this torque. The motor generator 130 can generate electric power by the rotational force of the drive wheels 150 during the regenerative braking operation of the vehicle 100. Then, the generated power is converted by PCU 120 into charging power for power storage device 190.

  Further, in a hybrid vehicle equipped with an engine (not shown) in addition to motor generator 130, necessary vehicle driving force is generated by operating engine and motor generator 130 in a coordinated manner. In this case, the power storage device 190 can be charged using the power generated by the rotation of the engine.

  As described above, communication unit 160 is a communication interface for performing wireless communication between vehicle 100 and power transmission device 200, and exchanges information INFO with communication unit 230 of power transmission device 200. Information INFO output from communication unit 160 to power transmission device 200 includes vehicle information from vehicle ECU 300 and a signal for instructing start and stop of power transmission.

  Although not shown in FIG. 1, vehicle ECU 300 includes a CPU, a storage device, and an input / output buffer, and inputs a signal from each sensor and outputs a control signal to each device. Control. Note that these controls are not limited to processing by software, and can be processed by dedicated hardware (electronic circuit).

  The voltage sensor 195 is connected in parallel to the resonance coil 112 and detects the received voltage Vre received by the power receiving unit 110. The current sensor 196 is provided on a power line connecting the resonance coil 111 and the rectifier 180, and detects the received current Ire. The detected power reception voltage Vre and power reception current Ire are transmitted to the vehicle ECU 300 and used for calculation of transmission efficiency and the like.

[Principle of power transmission]
FIG. 3 is an equivalent circuit diagram when power is transmitted from the power transmission device 200 to the vehicle 100. Referring to FIG. 3, power transmission unit 220 of power transmission device 200 includes a resonance coil 221 and variable capacitors 222 and 223.

  The resonance coil 221 forms an LC resonance circuit together with the variable capacitors 222 and 223. As will be described later, an LC resonance circuit is also formed in the power receiving unit 110 of the vehicle 100. The difference between the natural frequency of the LC resonant circuit formed by the resonant coil 221 and the variable capacitors 222 and 223 and the natural frequency of the LC resonant circuit of the power receiving unit 110 is ± 10% or less of the former natural frequency or the latter natural frequency. It is. Resonant coil 221 receives power from power supply unit 250 and transmits power to power receiving unit 110 of vehicle 100 in a contactless manner.

  Power receiving unit 110 of vehicle 100 includes a resonance coil 111 and variable capacitors 112 and 113.

  The resonance coil 111 forms an LC resonance circuit together with the variable capacitors 112 and 113. As described above, the natural frequency of the LC resonance circuit formed by the resonance coil 111 and the variable capacitors 112 and 113 and the LC resonance formed by the resonance coil 221 and the variable capacitors 112 and 113 in the power transmission unit 220 of the power transmission device 200. The difference from the natural frequency of the circuit is ± 10% of the natural frequency of the former or the natural frequency of the latter. Then, the resonance coil 111 receives power from the power transmission unit 220 of the power transmission device 200 in a non-contact manner.

  In power transmission device 200, when power is supplied from power supply device 210 to resonance coil 221, energy (power) from resonance coil 221 to resonance coil 111 through a magnetic field formed between resonance coil 221 and resonance coil 111 of vehicle 100. ) Moves. The energy (electric power) moved to the resonance coil 111 is transmitted to the electric load device 118 of the vehicle 100. The electrical load device 118 is an electrical device that uses the power received by the power receiving unit 110, and specifically represents the electrical devices after the rectifier 180 (FIG. 2).

  As described above, in this power transmission system, the difference between the natural frequency of power transmission unit 220 of power transmission device 200 and the natural frequency of power reception unit 110 of vehicle 100 is the natural frequency of power transmission unit 220 or the specific frequency of power reception unit 110. It is ± 10% or less of the frequency. By setting the natural frequencies of the power transmission unit 220 and the power reception unit 110 in such a range, the power transmission efficiency can be increased. On the other hand, if the difference between the natural frequencies is larger than ± 10%, there is a possibility that the power transmission efficiency becomes smaller than 10% and the power transmission time becomes longer.

  In addition, the natural frequency of the power transmission unit 220 (power reception unit 110) means a vibration frequency when the electric circuit (resonance circuit) constituting the power transmission unit 220 (power reception unit 110) freely vibrates. In the electric circuit (resonance circuit) constituting the power transmission unit 220 (power reception unit 110), the natural frequency when the braking force or the electrical resistance is substantially zero is the resonance frequency of the power transmission unit 220 (power reception unit 110). Also called.

  A simulation result obtained by analyzing the relationship between the natural frequency difference and the power transmission efficiency will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram illustrating a simulation model of the power transmission system. FIG. 5 is a diagram illustrating the relationship between the deviation of the natural frequency of the power transmission unit and the power reception unit and the power transmission efficiency.

  Referring to FIG. 4, power transmission system 89 includes a power transmission unit 90 and a power reception unit 91. The power transmission unit 90 includes a resonance coil 94 and a capacitor 95 provided in the resonance coil 94. Power reception unit 91 includes a resonance coil 99 and a capacitor 98 connected to resonance coil 99.

  The inductance of the resonance coil 94 is defined as an inductance Lt, and the capacitance of the capacitor 95 is defined as a capacitance C1. Further, the inductance of the resonance coil 99 is an inductance Lr, and the capacitance of the capacitor 98 is a capacitance C2. When each parameter is set in this way, the natural frequency f1 of the power transmission unit 90 is represented by the following equation (1), and the natural frequency f2 of the power reception unit 91 is represented by the following equation (2).

f1 = 1 / {2π (Lt × C1) ^1/2 } (1)
f2 = 1 / {2π (Lr × C2) ^1/2 } (2)
Here, when the inductance Lr and the capacitances C1 and C2 are fixed and only the inductance Lt is changed, the relationship between the deviation of the natural frequency of the power transmission unit 90 and the power reception unit 91 and the power transmission efficiency is shown in FIG. In this simulation, the relative positional relationship between the resonance coil 94 and the resonance coil 99 is fixed, and the frequency of the current supplied to the power transmission unit 90 is constant.

  In the graph shown in FIG. 5, the horizontal axis indicates the deviation (%) of the natural frequency, and the vertical axis indicates the power transmission efficiency (%) at a constant frequency current. The deviation (%) in natural frequency is expressed by the following equation (3).

(Deviation of natural frequency) = {(f1−f2) / f2} × 100 (%) (3)
As is clear from FIG. 5, when the deviation (%) of the natural frequency is 0%, the power transmission efficiency is close to 100%. When the deviation (%) in natural frequency is ± 5%, the power transmission efficiency is about 40%. When the deviation (%) in natural frequency is ± 10%, the power transmission efficiency is about 10%. When the deviation (%) in natural frequency is ± 15%, the power transmission efficiency is about 5%. That is, the natural frequency of the power transmission unit 90 and the power reception unit 91 is set so that the absolute value of the deviation (%) in natural frequency (difference in natural frequency) is within a range of 10% or less of the natural frequency of the power reception unit 91. Thus, it can be seen that the power transmission efficiency can be increased to a practical level. Furthermore, if the natural frequency of the power transmission unit 90 and the power reception unit 91 is set so that the absolute value of the deviation (%) of the natural frequency is 5% or less of the natural frequency of the power reception unit 91, the power transmission efficiency can be further increased. It is more preferable. The simulation software employs electromagnetic field analysis software (JMAG (registered trademark): manufactured by JSOL Corporation).

  Referring again to FIG. 2, power transmission unit 220 of power transmission device 200 and power reception unit 110 of vehicle 100 are formed between power transmission unit 220 and power reception unit 110, and a magnetic field that vibrates at a specific frequency and power transmission Power is exchanged in a non-contact manner through at least one of an electric field that is formed between the unit 220 and the power receiving unit 110 and vibrates at a specific frequency. The coupling coefficient κ between the power transmission unit 220 and the power reception unit 110 is preferably 0.1 or less, and power is transmitted from the power transmission unit 220 to the power reception unit 110 by causing the power transmission unit 220 and the power reception unit 110 to resonate with each other by an electromagnetic field. Is transmitted.

  Here, a magnetic field having a specific frequency formed around the power transmission unit 220 will be described. The “magnetic field of a specific frequency” typically has a relationship with the power transmission efficiency and the frequency of the current supplied to the power transmission unit 220. First, the relationship between the power transmission efficiency and the frequency of the current supplied to the power transmission unit 220 will be described. The power transmission efficiency when power is transmitted from the power transmission unit 220 to the power reception unit 110 varies depending on various factors such as the distance between the power transmission unit 220 and the power reception unit 110. For example, the natural frequency (resonance frequency) of the power transmission unit 220 and the power reception unit 110 is f0, the frequency of the current supplied to the power transmission unit 220 is f3, and the air gap between the power transmission unit 220 and the power reception unit 110 is the air gap AG. And

  FIG. 6 is a graph showing the relationship between the power transmission efficiency when the air gap AG is changed and the frequency f3 of the current supplied to the power transmission unit 220 while the natural frequency f0 is fixed. With reference to FIG. 6, the horizontal axis indicates the frequency f3 of the current supplied to the power transmission unit 220, and the vertical axis indicates the power transmission efficiency (%). The efficiency curve L1 schematically shows the relationship between the power transmission efficiency when the air gap AG is small and the frequency f3 of the current supplied to the power transmission unit 220. As shown in the efficiency curve L1, when the air gap AG is small, the peak of power transmission efficiency occurs at frequencies f4 and f5 (f4 <f5). When the air gap AG is increased, the two peaks when the power transmission efficiency is increased change so as to approach each other. As shown in the efficiency curve L2, when the air gap AG is larger than the predetermined distance, the power transmission efficiency has one peak, and the power transmission efficiency is obtained when the frequency of the current supplied to the power transmission unit 220 is the frequency f6. Becomes a peak. When the air gap AG is further increased from the state of the efficiency curve L2, the peak of power transmission efficiency is reduced as shown by the efficiency curve L3.

  For example, the following method can be considered as a method for improving the power transmission efficiency. As a first method, the capacitance of the variable capacitors 112 and 113 and the variable capacitors 222 and 223 is changed in accordance with the air gap AG, with the frequency of the current supplied to the power transmission unit 220 being constant, thereby transmitting the power transmission unit 220. A method of changing the characteristic of power transmission efficiency between the power receiving unit 110 and the power receiving unit 110 is conceivable. Specifically, the capacitances of the variable capacitors 112 and 113 and the variable capacitors 222 and 223 are adjusted so that the power transmission efficiency reaches a peak in a state where the frequency of the current supplied to the power transmission unit 220 is constant. In this method, the frequency of the current flowing through the power transmission unit 220 and the power reception unit 110 is constant regardless of the size of the air gap AG. As a method for changing the characteristics of the power transmission efficiency, a method using a converter (not shown) provided between rectifier 180 and power storage device 190 in vehicle 100 may be employed.

  The second method is a method of adjusting the frequency of the current supplied to the power transmission unit 220 based on the size of the air gap AG. For example, when the power transmission characteristic is the efficiency curve L1, a current having a frequency f4 or f5 is supplied to the power transmission unit 220. When the frequency characteristic is the efficiency curves L2 and L3, the current having the frequency f6 is supplied to the power transmission unit 220. In this case, the frequency of the current flowing through power transmission unit 220 and power reception unit 110 is changed in accordance with the size of air gap AG.

  In the first method, the frequency of the current flowing through the power transmission unit 220 is a fixed constant frequency, and in the second method, the frequency flowing through the power transmission unit 220 is a frequency that changes as appropriate depending on the air gap AG. A current having a specific frequency set so as to increase the power transmission efficiency is supplied to the power transmission unit 220 by the first method, the second method, or the like. When a current having a specific frequency flows through the power transmission unit 220, a magnetic field (electromagnetic field) that vibrates at a specific frequency is formed around the power transmission unit 220. The power receiving unit 110 receives power from the power transmitting unit 220 through a magnetic field that is formed between the power receiving unit 110 and the power transmitting unit 220 and vibrates at a specific frequency. Therefore, the “magnetic field oscillating at a specific frequency” is not necessarily a magnetic field having a fixed frequency. In the above example, focusing on the air gap AG, the frequency of the current supplied to the power transmission unit 220 is set, but the power transmission efficiency is the horizontal direction of the power transmission unit 220 and the power reception unit 110. The frequency changes due to other factors such as a deviation, and the frequency of the current supplied to the power transmission unit 220 may be adjusted based on the other factors.

  In the above description, an example in which a helical coil is used as the resonance coil has been described. However, when an antenna such as a meander line is used as the resonance coil, a current having a specific frequency flows in the power transmission unit 220. Thus, an electric field having a specific frequency is formed around the power transmission unit 220. And electric power transmission is performed between the power transmission part 220 and the power receiving part 110 through this electric field.

  In this power transmission system, power transmission and power reception efficiency are improved by using a near field (evanescent field) in which the “electrostatic magnetic field” of the electromagnetic field is dominant.

  FIG. 7 is a diagram showing the relationship between the distance from the current source (magnetic current source) and the intensity of the electromagnetic field. Referring to FIG. 7, the electromagnetic field is composed of three components. The curve k1 is a component that is inversely proportional to the distance from the wave source, and is referred to as a “radiated electromagnetic field”. A curve k2 is a component inversely proportional to the square of the distance from the wave source, and is referred to as an “induction electromagnetic field”. The curve k3 is a component inversely proportional to the cube of the distance from the wave source, and is referred to as an “electrostatic magnetic field”. When the wavelength of the electromagnetic field is “λ”, the distance at which the strengths of “radiation electromagnetic field”, “induction electromagnetic field”, and “electrostatic magnetic field” are substantially equal can be expressed as λ / 2π.

  The “electrostatic magnetic field” is a region where the intensity of the electromagnetic wave suddenly decreases with the distance from the wave source. In the power transmission system according to this embodiment, the near field (evanescent field) in which the “electrostatic magnetic field” is dominant. ) Is used to transmit energy (electric power). That is, in the near field where the “electrostatic magnetic field” is dominant, by resonating the power transmitting unit 220 and the power receiving unit 110 (for example, a pair of LC resonance coils) having adjacent natural frequencies, the power receiving unit 220 and the other power receiving unit are resonated. Energy (electric power) is transmitted to 110. Since this “electrostatic magnetic field” does not propagate energy far away, the resonance method transmits power with less energy loss than electromagnetic waves that transmit energy (electric power) by “radiant electromagnetic field” that propagates energy far away. be able to.

  Thus, in this power transmission system, power is transmitted in a non-contact manner between the power transmission unit 220 and the power reception unit 110 by causing the power transmission unit 220 and the power reception unit 110 to resonate (resonate) with an electromagnetic field. The Such an electromagnetic field formed between the power reception unit and the power transmission unit may be referred to as a near-field resonance (resonance) coupling field, for example. And the coupling coefficient ((kappa)) between the power transmission part 220 and the power receiving part 110 is about 0.3 or less, for example, Preferably, it is 0.1 or less. As a matter of course, a coupling coefficient (κ) in the range of about 0.1 to 0.3 can also be adopted. The coupling coefficient (κ) is not limited to such a value, and may take various values that improve power transmission.

  Note that the coupling between the power transmission unit 220 and the power reception unit 110 in the power transmission is, for example, “magnetic resonance coupling”, “magnetic field (magnetic field) resonance coupling”, “magnetic field resonance (resonance) coupling”, “proximity” It is referred to as “field resonance (resonance) coupling”, “electromagnetic field (electromagnetic field) resonance coupling” or “electric field (electric field) resonance coupling”. The “electromagnetic field (electromagnetic field) resonance coupling” means a coupling including any of “magnetic resonance coupling”, “magnetic field (magnetic field) resonance coupling”, and “electric field (electric field) resonance coupling”.

  When the power transmission unit 220 and the power reception unit 110 are formed by coils as described above, the power transmission unit 220 and the power reception unit 110 are mainly coupled by a magnetic field (magnetic field), and are referred to as “magnetic resonance coupling” or “magnetic field”. (Magnetic field) resonance coupling "is formed. For example, an antenna such as a meander line may be employed for the power transmission unit 220 and the power reception unit 110. In this case, the power transmission unit 220 and the power reception unit 110 are mainly based on an electric field (electric field). The “electric field (electric field) resonance coupling” is formed.

  In the coil unit as shown in FIG. 2, if the capacitance of the capacitor connected in series with the coil is C11 and the capacitance of the capacitor connected in parallel with the coil is C12, the combined capacitance is C = C11 + C12. . And the resonance frequency F of a coil unit is represented by the following formula | equation (4) similarly to said formula (1), (2), when the reactance of a coil is set to L. FIG.

F = 1 / {2π (L × C) ^1/2 } (4)
By the way, in the coil unit having the above-described configuration, even if the combined capacitance C is the same, if the capacitance of each capacitor is different, the degree of coupling between the power transmission unit and the power reception unit is changed, so that the power transmission efficiency is improved. Can change.

  FIG. 8 is a diagram showing a result of simulating a change in power transmission efficiency when the capacitance of the variable capacitor is changed while maintaining the combined capacitance in the coil unit as shown in FIG.

  In FIG. 8, the horizontal axis represents frequency, and the vertical axis represents power transmission efficiency. As the curves W10, W11, W12, and W13 are obtained, the capacitance C11 of the variable capacitor connected in series with the coil gradually decreases, and conversely, the capacitance C12 of the variable capacitor connected in parallel with the coil increases gradually. Become.

  Regarding the relationship between the coupling coefficient κ and the power transmission efficiency, in general, when the coupling coefficient κ is κ> 1, the power transmission at the resonance frequency F0 is achieved as κ becomes larger (that is, the coupling becomes stronger) as κ increases. It is known that the power transmission efficiency is maximized when κ = 1, and the power transmission efficiency decreases as κ becomes smaller (that is, the coupling becomes weaker) when κ <1 and becomes unimodal. Yes.

  As can be seen from FIG. 8, even if the combined capacitance C of the capacitors is the same, when the capacitance of the capacitors connected in parallel to the coil is changed, the coupling coefficient κ changes and the power transmission efficiency changes. Therefore, by adopting the configuration of the coil unit as shown in FIG. 2, the power transmission efficiency can be adjusted without changing the resonance frequency.

Further, as described above, since the resonance frequency is defined by F = 1 / {2π (L × C) ^1/2 } as shown in Equation (4), in the design of the coil unit, a desired resonance frequency is used. Even if it exists, the combination of the reactance L of a coil and the synthetic capacity C of a capacitor can be made into a different aspect. That is, the ratio of the reactance L and the combined capacitance C can be changed while maintaining L × C.

  FIG. 9 is a diagram illustrating the frequency when the ratio of the combined capacitance C and the reactance L is changed while maintaining the multiplication value (L × C) of the combined capacitance C of the capacitor and the reactance L of the coil in the coil unit. This is a simulation of changes in synthetic impedance and power transfer efficiency.

  Referring to FIG. 9, with respect to the combined impedance, reactance L increases as curves W21, W22, W23, and W24, and conversely, combined capacitance C decreases. That is, at each frequency, the combined impedance increases as the reactance L increases.

  As for the power transmission efficiency, the curves W31, W32, W33, and W34 correspond to the power transmission efficiency in the case of the curves W21, W22, W23, and W24, respectively. The power transmission efficiency gradually increases with a single-peak characteristic as the reactance L increases (W31 → W32). However, if the reactance L becomes too large, it becomes a bimodal characteristic. (W32 → W33 → W44). One reason for this is that when the reactance L is increased, the resistance component of the coil increases.

  As described above, in order to improve the power transmission efficiency, it is important to appropriately set the relationship between the reactance L of the coil and the combined capacitance C at the time of design.

  In the present embodiment, the power transmission efficiency in the non-contact power feeding system is improved by executing impedance control for adjusting the variable capacitor having the configuration as shown in FIG. 2 according to the above-described characteristics.

  FIG. 10 is a flowchart for illustrating impedance adjustment control executed by vehicle ECU 300 and power transmission ECU 240 in the present embodiment. Each step in the flowchart shown in FIG. 10 is executed in response to a predetermined period or a predetermined condition being established when a program stored in advance in vehicle ECU 300 and power transmission ECU 240 is called from the main routine. It is realized by. Alternatively, for some steps, it is also possible to construct dedicated hardware (electronic circuit) and realize processing. In the following description, the process executed by vehicle ECU 300 will be described as an example, but the same applies to the case where it is executed by power transmission ECU 240, and the description thereof will not be repeated.

  Referring to FIGS. 2 and 10, in step 100 (hereinafter, step is abbreviated as “S”), vehicle ECU 300 first determines the frequency of the electromagnetic field determined in advance by the standard or the like (that is, the resonance frequency of power reception unit 110). F and reactance L in the design of the resonance coil 111 are acquired. These pieces of information are stored in advance in the vehicle ECU 300.

The vehicle ECU 300 calculates an initial value of the required composite capacity C from these information and F = 1 / {2π (L × C) ^1/2 }.

  Then, vehicle ECU 300 outputs a command to cause power transmission device 200 to perform test power transmission. This test power transmission is a power transmission for adjusting the capacitances C11 and C12 of the variable capacitors 112 and 113. The power transmitted in the test power transmission may be the same magnitude as that in the normal power transmission in which the power storage device 190 is fully charged, but the transmission efficiency is low as the capacity of the variable capacitors 112 and 113 is adjusted. Since it can be in a state, it is preferable that the power be smaller than the power used for normal power transmission.

  Thereafter, the vehicle ECU 300 adjusts the combined capacitance C in order to eliminate fluctuations in the resonance frequency due to variations in the design reactance L of the resonance coil 110. In other words, the vehicle ECU 300 adjusts the composite capacity C to match the resonance frequency of the power reception unit 110 with the specified frequency F.

  Specifically, vehicle ECU 300 adjusts variable capacitors 112 and 113 in S125, and changes combined capacitance C within the variable range. For example, the capacitance value is sequentially set in a predetermined change step from the state in which the combined capacity C is minimized to the state in which the composite capacity C is maximized in the variable range.

  In step S130, the vehicle ECU 300 calculates the transmission efficiency EF in the set combined capacity C from the information related to the transmission power from the power transmission device 200 and the received power calculated from the detection values of the voltage sensor 195 and the current sensor 196. To do.

  In S140, vehicle ECU 300 determines whether or not the calculated transmission efficiency EF is the maximum within the variable range of combined capacity C. Note that whether or not the transmission efficiency EF is maximum may be determined using the result of calculating the transmission efficiency EF of the entire variable range of the combined capacity C. For example, the transmission efficiency EF is not necessarily maximum. Alternatively, it may be determined whether or not the transmission efficiency EF is larger than a predetermined threshold value.

  If transmission efficiency EF is not maximum (NO in S140), the process returns to S125, and combined capacity C is further adjusted so that transmission efficiency EF is maximum.

  If transmission efficiency EF is maximized (YES in S140), the process proceeds to S150 to determine the size of combined capacity C used for power transmission.

  Thereafter, as described in FIG. 8, the vehicle ECU 300 changes the degree of coupling between the power transmission unit 220 and the power reception unit 110 by adjusting the combination of the variable capacitors 112 and 113 that can achieve the determined combined capacity C. And the transmission efficiency EF is optimized.

  Specifically, vehicle ECU 300 adjusts the capacity of variable capacitors 112 and 113 in S155. At this time, while maintaining the relationship of C = C11 + C12 by the variable capacitors 112 and 113, for example, C11 is sequentially set to change from a small value to a large value.

  Then, vehicle ECU 300 calculates transmission efficiency EF after variable capacitor adjustment in S160, and determines whether or not transmission efficiency EF calculated in S170 is the maximum in combined capacity C. In the determination of the transmission efficiency EF in S170, it may be determined whether the transmission efficiency EF is larger than a predetermined threshold as in S140.

  If transmission efficiency EF is not maximum (NO in S170), the process returns to S155, and vehicle ECU 300 further adjusts the capacity of variable capacitors 112 and 113 so that transmission efficiency EF is maximum.

  If transmission efficiency EF is maximized (YES in S170), the process proceeds to S180, and vehicle ECU 300 determines the capacities of variable capacitors 112 and 113.

  Thereafter, vehicle ECU 300 advances the process to S190 and transmits a command to start power transmission for charging power storage device 190 to power transmission device 200. Thereby, the charging process to the power storage device 190 is started.

  In addition, when both the power transmission unit and the power reception unit are provided with variable capacitors connected in parallel and in series to the resonance coil as shown in FIG. 2, the variable capacitor for either the power transmission unit or the power reception unit is given priority. And then adjust the variable capacitor for the other.

  By using the coil unit including the variable capacitor connected in parallel and in series with the resonance coil as shown in FIG. Impedance adjustment is possible, thereby improving power transmission efficiency.

[Modification]
The configuration of the coil unit as in the present invention is not necessarily provided in both the power transmission unit and the power reception unit as illustrated in FIG. 2, and may be provided in at least one of the power transmission unit and the power reception unit.

  11-13 is a figure which shows the variation in the case where the coil unit provided with the variable capacitor connected in parallel and in series with the resonance coil only in the power transmission part 220 is provided. 14-16 is a figure which shows the variation in the case where the above coil units are provided only in the power receiving part 110. FIG.

  In power reception unit 110A in FIG. 11 and power transmission unit 220A in FIG. 14, fixed capacitors 113A and 223A are provided in parallel with resonance coils 111 and 221, respectively.

  In power reception unit 110B in FIG. 12 and power transmission unit 220B in FIG. 15, fixed capacitors 112A and 222A are provided in series with resonance coils 111 and 221, respectively.

  In power reception unit 110C in FIG. 13, fixed capacitors 113A and 113B are provided at both ends of resonance coil 111, respectively, and in power transmission unit 220C in FIG. 16, fixed capacitors 223A and 223B are provided at both ends of resonance coil 221, respectively. It is done.

Note that the fixed capacitors shown in FIGS. 11 to 16 may be variable capacitors.
Further, the variable capacitor may be capable of continuously changing the capacitance. For example, as shown in FIG. 17, a plurality of capacitors connected in parallel to each other are switched by a switch. The capacity may be changed by the above.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10, 89 Power transmission system, 90, 220, 220A to 220C Power transmission unit, 91, 110, 110A to 110C Power reception unit, 94, 99, 110, 111, 221 Resonance coil, 95, 98, 112, 112A, 112B, 113 , 113A, 113B, 222A, 223A, 223B capacitor, 100 vehicle, 118 electric load device, 130 motor generator, 140 power transmission gear, 150 driving wheel, 160, 230 communication unit, 180 rectifier, 190 power storage device, 195 voltage sensor, 196 Current sensor, 200 power transmission device, 210 power supply device, 240 power transmission ECU, 250 power supply unit, 300 vehicle ECU, 400 commercial power supply.

Claims (14)

A power receiving device for receiving power supplied to an electric load from a power transmitting device in a contactless manner,
A power receiving unit that receives power from the power transmission device in a contactless manner;
A control device for controlling the power reception unit,
The power receiving unit
A coil electrically connected to the electrical load;
A first variable capacitor connected in series with the coil between the coil and the electrical load;
A second variable capacitor connected in parallel to the coil,
The control device determines a combined capacity of the first and second variable capacitance units so that power transmission efficiency between the power transmitting device and the power receiving device is larger in an adjustable range, and is then determined. In addition, the power receiving device adjusts the capacities of the first and second variable capacity units so that the power transmission efficiency is further increased while maintaining the combined capacity.   The power receiving device according to claim 1, wherein the control device adjusts the capacities of the first and second variable capacitance units according to power transmission efficiency between the power transmitting device and the power receiving device.   The power receiving device according to claim 2, wherein the control device adjusts the capacities of the first and second variable capacitance units such that the power transmission efficiency exceeds a predetermined threshold value. The power transmission device includes a power transmission unit for supplying power in a contactless manner,
The power receiving device according to claim 1, wherein a difference between a natural frequency of the power transmission unit and a natural frequency of the power reception unit is ± 10% or less of the natural frequency of the power transmission unit or the natural frequency of the power reception unit. The power transmission device includes a power transmission unit for supplying power in a contactless manner,
The power receiving device according to claim 1, wherein a coupling coefficient between the power transmitting unit and the power receiving unit is 0.1 or less. The power transmission device includes a power transmission unit for supplying power in a contactless manner,
The power reception unit includes a magnetic field that vibrates at a specific frequency formed between the power reception unit and the power transmission unit, and an electric field that vibrates at a specific frequency formed between the power reception unit and the power transmission unit. The power receiving device according to claim 1, wherein the power receiving device receives power from the power transmission unit through at least one of the two.   2. The power receiving device according to claim 1, wherein each of the first and second variable capacitance units includes a capacitor, and is configured to change a capacitance of the capacitor. A power receiving device according to claim 1;
A vehicle comprising: a power storage device that stores electric power received by the power receiving device. A power transmission device that supplies power from a power source to a power receiving device in a contactless manner,
A power transmission unit that transmits power to the power receiving device in a contactless manner;
A control device for controlling the power transmission unit,
The power transmission unit
A coil electrically connected to the power source;
A first variable capacitor connected in series with the coil between the power source and the coil;
A second variable capacitor connected in parallel to the coil,
The control device determines a combined capacity of the first and second variable capacitance units so that power transmission efficiency between the power transmitting device and the power receiving device is larger in an adjustable range, and is then determined. A power transmission device that adjusts the capacities of the first and second variable capacity units so that the power transmission efficiency is further increased while maintaining the combined capacity.   The power transmission device according to claim 9, wherein the first and second variable capacitance units include a capacitor, and are configured to be able to change a capacitance of the capacitor. A non-contact power supply system that transmits electric power from a power transmission device to a vehicle in a non-contact manner,
A power transmission unit included in the power transmission device and having a power transmission coil electrically connected to a power source;
A power receiving unit included in the vehicle and having a power receiving coil electrically connected to an electrical load;
A control device for controlling the power transmission unit and the power reception unit,
At least one of the power transmission coil and the power receiving coil has a first variable capacitor connected in series to the coil and a second variable capacitor connected in parallel to the coil,
The control device determines a combined capacity of the first and second variable capacitance units so that power transmission efficiency between the power transmission unit and the power reception unit is larger within an adjustable range, and then determines A non-contact power feeding system that adjusts the capacities of the first and second variable capacity sections so as to further increase the power transmission efficiency while maintaining the combined capacity.   The contactless power feeding system according to claim 11, wherein the first and second variable capacitance units include a capacitor, and are configured to change a capacitance of the capacitor. A non-contact power supply system that transmits electric power from a power transmission device to a vehicle in a non-contact manner,
A power transmission unit included in the power transmission device and having a power transmission coil electrically connected to a power source;
A power receiving unit included in the vehicle and having a power receiving coil electrically connected to an electrical load;
A control device for controlling the power transmission unit and the power reception unit,
The power transmission coil includes a first variable capacitance unit connected in series with the power transmission coil and a second variable capacitance unit connected in parallel to the power transmission coil between the power transmission coil and the power source. Have
The power receiving coil includes a third variable capacitor connected in series with the power receiving coil and a fourth variable capacitor connected in parallel to the power receiving coil between the power receiving coil and the electric load. Have
The control device is configured so that the power transmission efficiency between the power transmission unit and the power reception unit is larger within the adjustable range without changing the third and fourth variable capacitance units in the power reception coil. Determining a combined capacity of the first and second variable capacitance sections, and then maintaining the determined combined capacity while further increasing the power transmission efficiency of the first and second variable capacitance sections; Adjust the capacity,
Thereafter, the control device is configured to change the third and fourth variable so that the power transmission efficiency becomes larger within the adjustable range without changing the first and second variable capacitance portions in the power transmission coil. Non-contact power supply that determines a combined capacity of the capacity unit, and then adjusts the capacity of the third and fourth variable capacity units so as to further increase the power transmission efficiency while maintaining the determined combined capacity system. A non-contact power supply system that transmits electric power from a power transmission device to a vehicle in a non-contact manner,
A power transmission unit included in the power transmission device and having a power transmission coil electrically connected to a power source;
A power receiving unit included in the vehicle and having a power receiving coil electrically connected to an electrical load;
A control device for controlling the power transmission unit and the power reception unit,
The power transmission coil includes a first variable capacitance unit connected in series with the power transmission coil and a second variable capacitance unit connected in parallel to the power transmission coil between the power transmission coil and the power source. Have
The power receiving coil includes a third variable capacitor connected in series with the power receiving coil and a fourth variable capacitor connected in parallel to the power receiving coil between the power receiving coil and the electric load. Have
The control device is configured such that the power transmission efficiency between the power transmission unit and the power reception unit is larger within the adjustable range without changing the first and second variable capacitance units in the power transmission coil. Determining a combined capacity of the third and fourth variable capacitors, and then maintaining the determined combined capacity so that the power transmission efficiency is further increased. Adjust the capacity,
Thereafter, the control device does not change the third and fourth variable capacitance units in the power receiving coil, and the first and second variable variables so that the power transmission efficiency becomes larger within an adjustable range. Non-contact power supply that determines a combined capacity of the capacitor unit, and then adjusts the capacities of the first and second variable capacitor units so as to further increase the power transmission efficiency while maintaining the determined combined capacity system.

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