Variable capacitor and power supply device

Abstract

To provide a variable capacitance capacitor capable of reducing a control voltage.SOLUTION: A variable capacitance capacitor C1 is used in a control circuit 73 for controlling an operation of a device 70. The variable capacitance capacitor includes: first control electrode layers 21; second control electrode layers 22 that face the first control electrode layers; a dielectric layer 32 that is disposed at least between the first control electrode layers and the second control electrode layers; and a first extraction electrode layer 11 and a second extraction electrode layer 12 that face each other with the dielectric layer therebetween. The first extraction electrode layer and the second extraction electrode layer are positioned so as to generate an electric field in a direction that intersects an electric field vector generated between the first control electrode layers and the second control electrode layers when a voltage is applied between the first control electrode layers and the second control electrode layers; and the voltage applied between the first control electrode layers and the second control electrode layers is adjusted to adjust a capacitance value of a capacitance stored between the first extraction electrode layer and the second control electrode layers.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a variable capacitor and a power supply device. [Background technology]

[0002] Conventionally, there is a capacitor with variable capacitance in which a dielectric layer is disposed between a pair of electrodes for applying a DC bias (for example, Patent Document 1). In the conventional capacitor, a dielectric layer is disposed between an earth electrode and a DC bias electrode, and a capacitance acquisition electrode is disposed between the earth electrode and the DC bias electrode via the dielectric layer. When a DC bias is applied between the earth electrode and the DC bias electrode, the dielectric properties of the dielectric layer change, and the capacitance of the capacitor changes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-344845 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional capacitors, the earth electrode, DC bias electrode, and capacitance acquisition electrode are stacked in the same direction with a dielectric layer interposed between them, which makes it necessary to set the distance between the earth electrode and the DC bias electrode and the distance between the earth electrode and the capacitance acquisition electrode in conjunction with each other. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] According to a first aspect of the present disclosure, there is provided a variable capacitor (C1) used in a control circuit (73) that controls the operation of a device (70). The variable capacitor includes a first control electrode layer (21), a second control electrode layer (22) facing the first control electrode layer, at least a dielectric layer (32) disposed between the first control electrode layer and the second control electrode layer, and a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other across the dielectric layer, wherein the first extraction electrode layer and the second extraction electrode layer are disposed at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when a voltage is applied between the first control electrode layer and the second control electrode layer, and the voltage applied between the first control electrode layer and the second control electrode layer is adjusted to adjust the capacitance value of the electrostatic capacitance stored between the first extraction electrode layer and the second control electrode layer. The device is a power supply device that has a resonant circuit (72) composed of the variable capacitor and a primary coil (L1) and that wirelessly supplies power to a power receiving device, and the control circuit has a control voltage application circuit (76, 276, 376, 476) that applies a control voltage between the first control electrode layer and the second control electrode layer to change the dielectric constant of the dielectric layer, and the control voltage application circuit performs a power supply operation of setting the resonant circuit to a resonant state when AC power of a predetermined operating frequency is applied to the resonant circuit by setting the control voltage to a first control voltage, and and a standby operation of setting the resonant circuit to a non-resonant state when the AC power of the operating frequency is applied to the resonant circuit by setting a second control voltage different from the first control voltage, wherein the variable capacitor adjusts the resonant frequency of the resonant circuit by adjusting its capacitance using the control voltage, and is set to a first capacitance value when the first control voltage is applied, and is set to a second capacitance value different from the first capacitance value when the second control voltage is applied, and application of the second control voltage starts around the time when the voltage of the AC power applied to the primary side coil is zero volts. According to another aspect of the present disclosure, there is provided a variable capacitor (C1) for use in a control circuit (73) that controls the operation of a device (70). This variable capacitor comprises a first control electrode layer (21), a second control electrode layer (22) facing the first control electrode layer, at least a dielectric layer (32) arranged between the first control electrode layer and the second control electrode layer, and a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other across the dielectric layer, wherein the first extraction electrode layer and the second extraction electrode layer are arranged at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when a voltage is applied between the first control electrode layer and the second control electrode layer, and the voltage applied between the first control electrode layer and the second control electrode layer is adjusted to adjust the capacitance value of the electrostatic capacitance stored between the first extraction electrode layer and the second control electrode layer, and the dielectric layer has dielectric properties such that the relative dielectric constant at temperatures higher than a predetermined operating temperature is smaller than the relative dielectric constant at the operating temperature.

[0007] According to this embodiment, the direction of the electric field applied to the dielectric layer by applying a DC voltage between the first control electrode layer and the second control electrode layer can be made different from the direction of the electric field applied to the dielectric layer by applying an AC voltage between the first and second extraction electrodes. The distance between the first control electrode layer and the second control electrode layer and the distance between the first and second extraction electrodes can be set independently. Therefore, by shortening the distance between the first and second control electrode layers, the electric field applied to the dielectric layer can be increased even with the same DC voltage, thereby reducing the DC voltage. Furthermore, because the capacitance value of the variable capacitor C1 changes depending on the magnitude of the control voltage, the circuit size can be reduced compared to using a circuit consisting of multiple capacitors and switches to change the capacitance value of the capacitor.

[0008] According to a second aspect of the present disclosure, there is provided a power supply device (70) that wirelessly supplies power to a power receiving device (80). The power supply device includes a resonant circuit (72) configured with a variable capacitor (C1) and a primary coil (L1), and a control voltage application circuit (76) that applies a control voltage to the variable capacitor. The variable capacitor includes a first control electrode layer (21), a second control electrode layer (22) facing the first control electrode layer, at least a dielectric layer (32) disposed between the first control electrode layer and the second control electrode layer, and a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other across the dielectric layer. The first extraction electrode layer and the second extraction electrode layer are positioned so as to generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when the control voltage is applied between the first control electrode layer and the second control electrode layer. the control voltage application circuit is capable of executing a power supply operation of setting the resonant circuit to a resonant state when AC power of a predetermined operating frequency is applied to the resonant circuit by setting the control voltage to a first control voltage and setting the variable capacitor to a first capacitance value, and a standby operation of setting the resonant circuit to a non-resonant state when AC power of the operating frequency is applied to the resonant circuit by setting the control voltage to a second control voltage different from the first control voltage and setting the variable capacitor to a second capacitance value different from the first capacitance value. Thus, application of the second control voltage begins around the time when the voltage of the AC power applied to the primary coil is zero volts.

[0009] According to this embodiment, the direction of the electric field applied to the dielectric layer by applying a DC voltage between the first control electrode layer and the second control electrode layer can be made different from the direction of the electric field applied to the dielectric layer by applying an AC voltage between the first and second extraction electrodes. The distance between the first control electrode layer and the second control electrode layer and the distance between the first and second extraction electrodes can be set independently. Therefore, by shortening the distance between the first and second control electrode layers, the electric field applied to the dielectric layer can be increased even with the same DC voltage, thereby reducing the DC voltage. Furthermore, because the capacitance value of the variable capacitor C1 changes depending on the magnitude of the control voltage, the circuit size of the resonant circuit and the control voltage application circuit can be reduced compared to using a circuit composed of multiple capacitors and switches to change the capacitance value of the capacitor. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a contactless power supply system. [Figure 2] Circuit diagram of a wireless power supply system. [Figure 3] FIG. [Figure 4] 4 is a cross-sectional view of the variable capacitor shown in FIG. 3 taken along line IV-IV. [Figure 5] FIG. 10 is a diagram showing the relationship between a control electric field and a relative dielectric constant. [Figure 6] FIG. [Figure 7] FIG. 10 is a circuit diagram of a power supply device according to a second embodiment. [Figure 8] FIG. 10 is a circuit diagram of a power supply device according to a third embodiment. [Figure 9] FIG. 10 is a circuit diagram of a power supply device according to a fourth embodiment. [Figure 10] FIG. 4 is a diagram showing the relationship between the start timing of application of a control voltage and a coil voltage. [Figure 11] FIG. 11 is a graph showing the dielectric properties of a dielectric layer according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A. First embodiment: A1. Wireless power transfer system configuration: As shown in FIG. 1, the contactless power supply system 1 includes a power supply device 70 and a power receiving device 80. In this embodiment, the power supply device 70 is buried under a road RS. The power receiving device 80 is mounted on a vehicle VE, which is a moving body that travels on the road RS. While the vehicle VE is traveling, power is supplied to the power receiving device 80 from the power supply device 70. Here, "traveling" includes a case where the vehicle VE is moving and a case where the vehicle is stopped, such as waiting at a traffic light. The vehicle VE is configured as, for example, an electric vehicle or a hybrid vehicle.

[0012] The power supply device 70 has a primary side resonant circuit 72, which is a series resonant circuit having a primary side coil L1 and a variable capacitance capacitor C1, and an AC power supply 71 that supplies power to the primary side resonant circuit 72. The AC power supply 71 supplies power to the multiple primary side resonant circuits 72. The multiple primary side coils L1 are arranged along the extension direction of the road RS. The power receiving device 80 has a secondary side coil L2.

[0013] The moving body on which the power receiving device 80 is mounted is not limited to a vehicle VE traveling on the road RS, but may be, for example, an AGV (automated guided vehicle), a traveling robot, etc. Furthermore, the power supply device 70 may be installed not under the road RS, but on a sidewalk or parking lot adjacent to the road RS, or on a route along which the AGV travels.

[0014] A2.Circuit configuration of the wireless power transfer system: 2, in addition to the above configuration, the power supply device 70 also includes a control circuit 73 and a primary-side detection circuit 78. The control circuit 73 has a control voltage application circuit 76 and a primary-side control circuit 77. A primary-side coil L1 and a variable capacitor C1 are connected in series to form a primary-side resonant circuit 72 as a resonant circuit.

[0015] The control circuit 73 controls the operation of the power supply device 70 by adjusting the electric field applied between the first control electrode layer 21 and the second control electrode layer 22 and adjusting the capacitance value of the electrostatic capacitance stored between the first extraction electrode layer 11 and the second control electrode layer 22. The control voltage application circuit 76 applies a control voltage between the first control electrode layer 21 and the second control electrode layer 22. The control voltage is a voltage for changing the dielectric constant of the second dielectric layer 32. The variable capacitor C1 adjusts the capacitance value using the control voltage, thereby adjusting the resonant frequency of the primary-side resonant circuit 72.

[0016] The AC power supply 71 includes a DC power supply 74 and an inverter 75. The inverter 75 converts DC power supplied from the DC power supply 74 into AC power at a predetermined operating frequency and applies the AC power to the primary-side resonant circuit 72. In this embodiment, the operating frequency is 85 kHz. The variable capacitor C1 functions to place the primary-side resonant circuit 72 in a resonant state at the operating frequency and to place the primary-side resonant circuit 72 in a non-resonant state at the operating frequency. In this embodiment, the variable capacitor C1 is configured to be switchable between a first capacitance value and a second capacitance value smaller than the first capacitance value. The capacitance value of the variable capacitor C1 is switched between the first capacitance value and the second capacitance value by a switching signal Sig1 output from the control voltage application circuit 76. When the primary-side coil L1 and the secondary-side coil L2 are magnetically coupled and the variable capacitor C1 has the first capacitance value, the primary-side resonant circuit 72 is in a resonant state at the operating frequency. That is, the first capacitance value of the variable capacitor C1 is set to a value that makes the resonant frequency of the primary-side resonant circuit 72 match the operating frequency. On the other hand, when the variable capacitor C1 has the second capacitance value, the resonant frequency of the primary-side resonant circuit 72 deviates from the operating frequency, and the primary-side resonant circuit 72 enters a non-resonant state at the operating frequency.

[0017] As will be described in detail later, the control voltage application circuit 76 applies a switching signal Sig1 generated using AC power output from the AC power supply 71 to the variable capacitor C1.

[0018] The primary-side detection circuit 78 is a magnetic sensor that detects the magnitude of magnetic flux near the primary-side coil L1, specifically, a magnetic sensor with a built-in coil disposed near the primary-side coil L1. The primary-side detection circuit 78 detects magnetic flux density and outputs a signal indicating the detected magnetic flux density to the primary-side control circuit 77. The primary-side control circuit 77 uses the signal output from the primary-side detection circuit 78 to instruct the control voltage application circuit 76 to switch the voltage value of the switching signal Sig1 to the variable capacitor C1. Specifically, when the magnetic flux density indicated by the signal is greater than a predetermined threshold, the primary-side control circuit 77 instructs the control voltage application circuit 76 to switch the voltage value of the switching signal Sig1 to the variable capacitor C1.

[0019] In addition to the above configuration, the power receiving device 80 has a secondary-side resonant circuit 81, a rectifier 82, and a battery 83. A secondary-side coil L2 and a secondary-side capacitor C2 are connected in series to form the secondary-side resonant circuit 81. The rectifier 82 converts AC power output from the secondary-side resonant circuit 81 into DC power and supplies it to the battery 83. The battery 83 is charged by the supplied DC power.

[0020] When the primary coil L1 and the secondary coil L2 are magnetically coupled, the resonant frequency of the primary resonant circuit 72 and the resonant frequency of the secondary resonant circuit 81 are set to be substantially the same. This allows contactless power supply to the power receiving device 80 by magnetic field resonance between the primary coil L1 and the secondary coil L2.

[0021] A3. Standby and power transmission states: The state in which the variable capacitor C1 is set to a first capacitance value, a transmission current flows through the primary coil L1, and power is being supplied is called the power supply state.The state in which the variable capacitor C1 is set to a second capacitance value, a standby current smaller than the transmission current flows through the primary coil L1, and power is not being supplied is called the standby state.

[0022] The primary coils L1 are arranged in the direction in which the road RS extends, and the secondary coils L2 receive contactless power from the nearest primary coil L1. In a standby state, a standby current flows through the primary coil L1, causing the primary coil L1 to generate magnetic flux. The power receiving device 80 includes a magnetic sensor (not shown). When the power receiving device 80 approaches the target primary resonant circuit 72, the magnetic sensor detects the magnetic flux generated by the primary coil L1. Upon detecting the magnetic flux, the power receiving device 80 passes an AC current through the secondary coil L2, generating magnetic flux. When the magnetic flux generated by the secondary coil L2 is detected by the primary detection circuit 78, the primary control circuit 77 commands the control voltage application circuit 76 to switch the voltage value of the switching signal Sig1. The variable capacitor C1 switches its capacitance value from the second capacitance value to the first capacitance value using the voltage value of the switching signal Sig1. This puts the primary side resonant circuit 72 into a resonant state, and power supply begins.

[0023] The method by which the power supply device 70 detects the presence of the secondary coil L2 is not limited to the above. As another embodiment, the power supply device 70 may detect a current flowing through the primary coil L1 and detect an increase in the current, or may detect a voltage across the primary coil L1 and detect an increase in the voltage.

[0024] A4. Structure of a variable capacitor: 3, the variable capacitor C1 has a first extraction electrode layer 11, a second extraction electrode layer 12, a first control electrode layer 21, a second control electrode layer 22, a first dielectric layer 31, a second dielectric layer 32, a first extraction electrode common layer 41, and a second extraction electrode common layer 42. The first extraction electrode layer 11 and the second extraction electrode layer 12 are also collectively referred to as extraction electrode layers 10. The first control electrode layer 21 and the second control electrode layer 22 are also collectively referred to as control electrode layers 20.

[0025] Figure 3 depicts three mutually orthogonal spatial axes, the X, Y, and Z axes. The directions of the X, Y, and Z arrows indicate the positive directions along the X, Y, and Z axes, respectively. The positive directions along the X, Y, and Z axes are the +X direction, +Y direction, and +Z direction, respectively. The directions opposite to the directions of the X, Y, and Z arrows are the negative directions along the X, Y, and Z axes, respectively. The negative directions along the X, Y, and Z axes are the -X direction, -Y direction, and -Z direction, respectively. The directions along the X, Y, and Z axes, regardless of whether they are positive or negative, are called the X direction, Y direction, and Z direction, respectively. This also applies to the following figures and explanations.

[0026] 4, the first control electrode layer 21 and the second control electrode layer 22 are electrode layers for adjusting the capacitance of the variable capacitor C1. The first extraction electrode layer 11 and the second extraction electrode layer 12 are electrode layers for utilizing the capacitance of the variable capacitor C1. Typically, the variable capacitor C1 is used by applying a control voltage, which is a DC voltage, to the first control electrode layer 21 and the second control electrode layer 22, and applying AC power between the first extraction electrode layer 11 and the second extraction electrode layer 12.

[0027] The variable capacitor C1 further has a first terminal ACp, a second terminal ACn, a third terminal DCp, and a fourth terminal DCn for electrically connecting to an external circuit. The first terminal ACp is electrically connected to the first extraction electrode layer 11. The second terminal ACn is electrically connected to the second extraction electrode layer 12. The third terminal DCp is electrically connected to the first control electrode layer 21. The fourth terminal DCn is electrically connected to the second control electrode layer 22.

[0028] The second control electrode layer 22 faces the first control electrode layer 21. The second dielectric layer 32 is disposed at least between the first control electrode layer 21 and the second control electrode layer 22. The first extraction electrode layer 11 and the second extraction electrode layer 12 face each other with the second dielectric layer 32 interposed therebetween. The first extraction electrode layer 11 and the second extraction electrode layer 12 are disposed at positions that generate an electric field along a direction intersecting with the electric field vector generated between the first control electrode layer 21 and the second control electrode layer 22 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22. In this embodiment, the first control electrode layer 21 and the second control electrode layer 22 face each other in the X direction. Furthermore, the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction.

[0029] As shown in Fig. 4, the variable capacitor C1 has a layered structure. Specifically, a first dielectric layer 31 is disposed on a first extraction electrode layer 11. A first control electrode layer 21, a second control electrode layer 22, and a second dielectric layer 32 are disposed on the first dielectric layer 31. The second dielectric layer 32 covers the first control electrode layer 21 and the second control electrode layer 22. A second extraction electrode layer 12 is disposed on the second dielectric layer 32. The film surface directions of each layer are the XY directions. The stacking direction of each layer is the Z direction.

[0030] 3, the first control electrode layer 21 and the second control electrode layer 22 each have a flat plate shape with the long axis in the Y direction. The first control electrode layers 21 and the second control electrode layers 22 are alternately arranged at intervals in the X direction. The -Y direction end of each first control electrode layer 21 is electrically connected to the first extraction electrode common layer 41. The +Y direction end of each second control electrode layer 22 is electrically connected to the second extraction electrode common layer 42.

[0031] A structure formed by alternately arranging the first control electrode layers 21 and the second control electrode layers 22 with the second dielectric layer 32 sandwiched between them in the X direction is also referred to as a first structure ST1. By alternately arranging the first control electrode layers 21 and the second control electrode layers 22, the capacitors formed between the first control electrode layers 21 and the second control electrode layers 22 are connected in parallel with each other, thereby making it possible to increase the capacitance value of the variable capacitor C1.

[0032] 4, the second dielectric layer 32 is disposed at least between the first control electrode layer 21 and the second control electrode layer 22. Specifically, the second dielectric layer 32 is disposed in a control region RG1 sandwiched in the X direction between the first control electrode layer 21 and the second control electrode layer 22. As a result, when a control voltage that is a DC voltage is applied between the first control electrode layer 21 and the second control electrode layer 22, an electric field vector that is approximately parallel to the X direction is generated in the control region RG1.

[0033] The first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction with the second dielectric layer 32 interposed therebetween. As a result, an electric field vector generated in the control region RG1 when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12 roughly intersects with a voltage vector generated in the control region RG1 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22. In this embodiment, the electric field vector generated in the control region RG1 when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12 roughly intersects with a voltage vector generated in the control region RG1 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22.

[0034] The direction in which the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other is different from the direction in which the first control electrode layer 21 and the second control electrode layer 22 face each other. This allows the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12 and the distance between the first control electrode layer 21 and the second control electrode layer 22 to be set independently. The distance between the first control electrode layer 21 and the second control electrode layer 22 can be shortened without shortening the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12. Therefore, by shortening the distance between the first control electrode layer 21 and the second control electrode layer 22 while maintaining a distance between the first extraction electrode layer 11 and the second extraction electrode layer 12 that can withstand the voltage applied between the first extraction electrode layer 11 and the second extraction electrode layer 12, the electric field applied between the first control electrode layer 21 and the second control electrode layer 22 can be increased. This allows the control voltage to be reduced.

[0035] In this embodiment, the first dielectric layer 31 and the second dielectric layer 32 contain the same ferroelectric material. Specifically, the first dielectric layer 31 and the second dielectric layer 32 contain PVDF (polyvinylidene fluoride). Alternatively, the first dielectric layer 31 and the second dielectric layer 32 may contain a ferroelectric polymer such as a fluororesin such as P(VDF-TrFE) (poly(vinylidene fluoride-trifluoroethylene)). By including a ferroelectric in the first dielectric layer 31, the first dielectric layer 31 can also function as a variable capacitance capacitor.

[0036] As another embodiment of the first dielectric layer 31 and the second dielectric layer 32, the first dielectric layer 31 and the second dielectric layer 32 may include dielectrics made of different materials.

[0037] PVDF molecules have hydrogen and fluorine atoms bonded to carbon chains. Because hydrogen atoms are positively charged and fluorine atoms are negatively charged, PVDF molecules have a dipole moment. When PVDF molecules aggregate due to intermolecular forces, the carbon chains of each PVDF molecule align. The hydrogen and fluorine atoms are positioned perpendicular to the carbon chain extension direction. Therefore, PVDF crystals undergo spontaneous polarization. When an electric field is applied to a PVDF crystal, the polarization direction changes, rotating around the X-axis, which is the carbon chain extension direction. Therefore, even when a control voltage is applied, the polarization direction changes when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12. Therefore, by using PVDF for the second dielectric layer 32, a variable capacitor C1 can be provided whose relative permittivity changes when the control voltage value is changed.

[0038] 5 is a diagram showing the relationship between the magnitude of the control electric field Ed generated by applying a control voltage between the first control electrode layer 21 and the second control electrode layer 22, and the relative dielectric constant εr when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12. The variable capacitor C1 has dielectric characteristics in which the relative dielectric constant εr has two peaks.

[0039] Ferroelectrics are spontaneously polarized when the control electric field is zero V / m. When the control electric field is increased up to the coercive electric field Ec, the polarization becomes zero and the relative dielectric constant εr reaches a maximum. Near the coercive electric field Ec, the dipole moment tends to move in a direction corresponding to the AC voltage applied between the first extraction electrode layer 11 and the second extraction electrode layer 12, which is thought to increase the relative dielectric constant εr.

[0040] When the control field Ed is larger than the coercive field Ec, the relative permittivity εr decreases. This is thought to be because the electric dipoles are constrained by the control field Ed and are less likely to move in response to the AC voltage.

[0041] In this embodiment, the direction of the control electric field Ed intersects with the direction of the electric field generated by the application of an AC voltage. Furthermore, the polarization direction of the PVDF contained in the second dielectric layer 32 rotates around the carbon chain as the axis of rotation. Therefore, a peak in the relative dielectric constant εr appears even in a region where the control electric field Ed is smaller than the coercive electric field Ec. This is thought to be because the application of the control electric field Ed makes the electric dipoles more likely to move in response to the application of the AC voltage than when the control electric field Ed is not applied.

[0042] The dielectric characteristics of the variable capacitor C1 have an assist region, a polarization inversion region, and a saturation region. When a control voltage in the assist region is applied, the polarization movement of the second dielectric layer 32 is assisted. Specifically, the assist region is a region where the control electric field Ed is smaller than the coercive electric field Ec, and the relative dielectric constant εr is larger than the relative dielectric constant ε1 and smaller than the relative dielectric constant ε2. Here, the relative dielectric constant εr is the relative dielectric constant εr when the control electric field Ed is zero. The relative dielectric constant ε2 is the minimum point between the two peaks of the relative dielectric constant εr.

[0043] When a control voltage for the polarization inversion region including the voltage of the coercive field Ec is applied, the polarization of the second dielectric layer 32 is more likely to be reversed in response to the AC voltage than in the assist region. Specifically, the polarization inversion region is an electric field range in which the control field Ed includes the coercive field Ec, and is a region in which the relative dielectric constant εr is larger than the peak value ε3 of the relative dielectric constant εr in the assist region.

[0044] When a control voltage in the saturation region is applied, the movement of polarization in the second dielectric layer 32 is constrained. Specifically, the saturation region is a region where the control field Ed is greater than the coercive field Ec, and the control field Ed is greater than the coercive field Ec.

[0045] As described above, by applying the control electric field Ed in the assist region, the polarization can be made to move more easily than when the control electric field Ed is not applied. Therefore, by applying the control electric field Ed in the assist region to the variable capacitor C1, the capacitance of the variable capacitor C1 can be made larger than the capacitance when the control electric field Ed is not applied.

[0046] Furthermore, by applying the control electric field Ed in the polarization inversion region, the polarization can be made to move more easily than in the assist region. Therefore, by applying the control electric field Ed in the polarization inversion region to the variable capacitor C1, the capacitance of the variable capacitor C1 can be made larger than the capacitance when the control electric field Ed in the assist region is applied.

[0047] Furthermore, applying a control electric field Ed in the saturation region makes it difficult for polarization to move. Therefore, by applying a control electric field Ed in the saturation region to the variable capacitor C1, the capacitance of the variable capacitor C1 can be made smaller than the capacitance when the control electric field Ed in the assist region is not applied. Therefore, with the variable capacitor C1, the capacitance value of the variable capacitor C1 can be set to a desired capacitance value by adjusting the magnitude of the control electric field Ed.

[0048] A5. Circuit configuration of control voltage application circuit: As shown in FIG. 6, the control voltage application circuit 76 includes a rectifier 79, a smoothing capacitor C10, and a switch SW. The rectifier 79 rectifies the AC current output from the AC power supply 71 and outputs a DC voltage to the wiring N1 and the wiring N2. For example, a diode bridge circuit can be used as the rectifier 79. The voltage applied to the wiring N1 is higher than the voltage applied to the wiring N2. The switch SW is disposed on the wiring N1. The switch SW is, for example, a transistor. The smoothing capacitor C10 is connected between the wiring N1 and the wiring N2. The switching signal Sig1 is specifically the voltage between the wiring N1 and the wiring N2.

[0049] The wiring N1 is connected to a third terminal DCp of the variable capacitor C1. The wiring N2 is connected to a fourth terminal DCn of the variable capacitor C1. The wiring connected to one output terminal of the inverter 75 is connected to a first terminal ACp of the variable capacitor C1. The wiring connected to the other output terminal of the inverter 75 is connected to a second terminal ACn of the variable capacitor C1.

[0050] The primary-side control circuit 77 outputs a signal to the control voltage application circuit 76 to set the switch SW to an open state or a conductive state. Specifically, when the power supply device 70 is set to a power supply state, the primary-side control circuit 77 outputs a signal to set the switch SW to an open state. When the signal is input from the primary-side control circuit 77, the control voltage application circuit 76 performs a supply operation to set the switch SW to an open state. In the supply operation, the control voltage application circuit 76 sets the control voltage to zero volts as a first control voltage. As a result, the control voltage Vd applied between the first control electrode layer 21 and the second control electrode layer 22 of the variable capacitor C1 becomes zero volts. The capacitance value of the variable capacitor C1 is set to a first capacitance value when the relative dielectric constant εr of the second dielectric layer 32 is the relative dielectric constant ε1. Therefore, the primary-side resonant circuit 72 is in a resonant state.

[0051] On the other hand, when the power supply device 70 is set to a standby state, the primary-side control circuit 77 outputs a signal to set the switch SW to a conductive state. When the control voltage application circuit 76 receives a signal from the primary-side control circuit 77, it performs a standby operation to set the switch SW to a conductive state. In the standby operation, the control voltage application circuit 76 sets the control voltage to a voltage value that provides a control electric field Ed in the saturation region as the second control voltage. As a result, the control electric field Ed applied between the first control electrode layer 21 and the second control electrode layer 22 of the variable capacitor C1 becomes an electric field in the saturation region. The capacitance value of the variable capacitor C1 is set to a second capacitance value when the relative dielectric constant εr in the saturation region of the second dielectric layer 32 is set. As described above, the second capacitance value is smaller than the first capacitance value. As a result, the primary-side resonant circuit 72 is in a non-resonant state.

[0052] According to the first embodiment described above, the first extraction electrode layer 11 and the second extraction electrode layer 12 are positioned to generate an electric field in a direction intersecting with the electric field vector generated when a control voltage is applied. This allows the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12 and the distance between the first control electrode layer 21 and the second control electrode layer 22 to be set independently. This allows the control voltage to be reduced. Furthermore, the variable capacitor C1 is used in the control voltage application circuit 76 in the contactless power supply system 1. The variable capacitor C1 adjusts the control electric field Ed applied between the first control electrode layer 21 and the second control electrode layer 22 to adjust the capacitance value of the electrostatic capacitance stored between the first extraction electrode layer 11 and the second control electrode layer 22, thereby controlling the operation of the contactless power supply system 1. This allows for a smaller circuit size compared to a configuration using multiple capacitors and switches to change the capacitance value of the capacitive component of the primary-side resonant circuit 72. Furthermore, the variable capacitor C1 can be made smaller than a capacitor whose capacitance value is mechanically adjusted.

[0053] The variable capacitor C1 is used to adjust the resonant frequency of the primary-side resonant circuit 72 and control the operation of the primary-side resonant circuit 72. This allows the circuit size to be smaller than a circuit configuration having multiple capacitors to change the capacitance value of the capacitance component of the primary-side resonant circuit 72.

[0054] The control voltage application circuit 76 also performs a power supply operation in which the primary-side resonant circuit 72 is set to a resonant state by setting the control voltage Vd to zero volts, and a standby operation in which the primary-side resonant circuit 72 is set to a non-resonant state by setting the control voltage to a voltage in the saturation region. The variable capacitor C1 is set to a first capacitance value by setting the control voltage Vd to zero volts, and is set to a second capacitance value by setting the control voltage Vd to the voltage value of the control electric field Ed in the saturation region. In a power supply device 70 that uses magnetic field resonance to supply power wirelessly, whether the power supply device is to supply power can be controlled by setting the primary-side resonant circuit 72 to a resonant state or a non-resonant state. The variable capacitor C1 of this embodiment can be suitably applied to such a power supply device 70.

[0055] Furthermore, the second capacitance value is smaller than the first capacitance value. This allows the impedance of the primary-side resonant circuit 72 to be small when the contactless power supply system 1 is in a standby state, thereby reducing the current flowing through the primary-side coil L1.

[0056] B. Second embodiment: 7, the power supply device 70 according to the second embodiment differs from the first embodiment in the configuration of the control voltage application circuit 276. The same components as those in the above embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0057] The control voltage application circuit 276 according to this embodiment includes a rectifier 79, a smoothing capacitor C10, and a DC-DC converter 100. The DC-DC converter 100 steps down or steps up the DC voltage output from the rectifier 79 and outputs it to the wiring N1 and the wiring N2. The control voltage output by the control voltage application circuit 276 is the same as that in the first embodiment. When stepping down or stepping up the voltage, the control voltage application circuit 276 outputs a voltage that is linear with respect to time. This suppresses sudden fluctuations in current, thereby making it possible to suppress surge voltages.

[0058] C. Third embodiment: 8, a power supply device 70 according to the third embodiment differs from the above-described embodiments in the configuration of a control voltage application circuit 376. The same components as those in the above-described embodiments are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0059] The control voltage application circuit 376 according to this embodiment includes a capacitor C30, a first diode D1, a second diode D2, a smoothing capacitor C10, and a DC-DC converter 100. The capacitor C30, the first diode D1, the second diode D2, and the smoothing capacitor C10 form a half-wave voltage doubler rectifier circuit, which allows a large control voltage Vd to be output. The control voltage output by the control voltage application circuit 376 is the same as that in the first embodiment.

[0060] D. Fourth embodiment: 9, a power supply device 70 according to a fourth embodiment differs from the above-described embodiments in the configuration of a control voltage application circuit 476. The same components as those in the above-described embodiments are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0061] The control voltage application circuit 476 according to this embodiment is connected to both terminals of the primary coil L1, and converts the coil voltage, which is an AC voltage applied to the primary coil L1, into a DC voltage and supplies it to the wiring N1 and the wiring N2.

[0062] As shown in FIG. 10 , when switching from power supply operation to standby operation, the control voltage application circuit 476 starts the standby operation around time t1 when the coil voltage is zero volts. Specifically, the control voltage application circuit 476 starts applying a control voltage Vd in the saturation region between the third terminal DCp and the fourth terminal DCn around time t1. Here, "around time t1" refers to the period around time t1 when the voltage of the AC power becomes 10% or less of its maximum voltage value. In this embodiment, the control voltage application circuit 476 starts the standby operation from time t1. As a result, the control electric field Ed is applied to the second dielectric layer 32 of the variable capacitor C1 in a state where the second dielectric layer 32 is not easily affected by the electric field caused by the application of AC power, and therefore the control electric field can be effectively applied to the second dielectric layer 32.

[0063] According to the fourth embodiment described above, the application of the control voltage to the variable capacitor C1 begins when the voltage of the AC power applied to the primary coil L1 approaches zero volts. As a result, the control electric field Ed is applied to the second dielectric layer 32 in a state where it is not easily affected by the electric field caused by the application of AC power, so that the control electric field can be applied to the second dielectric layer 32 effectively.

[0064] E. Fifth embodiment: As shown in FIG. 11 , in this embodiment, the second dielectric layer 32 has a dielectric characteristic in which the relative permittivity εr at temperatures higher than the phase transition temperature Tc, which is the operating temperature, is smaller than the relative permittivity εr at the phase transition temperature Tc. Specifically, the relative permittivity εr of the second dielectric layer 32 decreases as the temperature rises above the phase transition temperature Tc. In this embodiment, the dielectric used for the second dielectric layer 32 is fabricated so that the phase transition temperature Tc is lower than the operating temperature when the power supply device 70 enters an abnormal state. As a result, when the control circuit 73 becomes abnormally hot, the capacitance value of the variable capacitor C1 decreases. This makes it difficult for current to flow through the primary-side resonant circuit 72, thereby protecting the primary-side resonant circuit 72.

[0065] According to the fifth embodiment described above, the second dielectric layer 32 has a dielectric characteristic in which the relative dielectric constant εr decreases at temperatures higher than the phase transition temperature Tc. When the power supply device 70 is in an abnormal state, the capacitance value of the variable capacitor C1 decreases, thereby reducing the current flowing through the primary coil L1 and protecting the primary resonant circuit 72.

[0066] F. Other Embodiments: (F1) In the first embodiment, the second dielectric layer 32 includes a ferroelectric polymer. In another embodiment, the second dielectric layer 32 may include an inorganic ferroelectric material such as barium titanate (BaTiO3). The relative dielectric constant εr of an inorganic ferroelectric material also changes depending on the magnitude of the control voltage. This allows it to be used as the dielectric layer of the variable capacitor C1. It is even better if the inorganic ferroelectric material is polarized in multiple directions. This is because, even when the direction in which the control voltage is applied differs from the direction in which the AC voltage is applied, the relative dielectric constant changes depending on the magnitude of the control voltage, making it possible to provide a variable capacitor C1 with an excellent variability.

[0067] (F2) In the first embodiment, the control voltage application circuit 76 applies a control voltage in the saturation region when the power supply device 70 is in a standby state, and does not apply a control voltage when the power supply device 70 is in a power transmission state. As another example, the control voltage application circuit 76 may apply a control voltage in the polarization inversion region or the assist region when the power supply device 70 is in a standby state, and not apply a control voltage when the power supply device 70 is in a power transmission state.

[0068] (F3) In the first embodiment, the primary-side resonant circuit 72 has a variable capacitor C1 connected in series to the primary coil L1, and the secondary-side resonant circuit 81 has a secondary capacitor C2 connected in series to the secondary coil L2, which is a so-called SS-type circuit configuration. The circuit configurations of the primary-side resonant circuit 72 and the secondary-side resonant circuit 81 are not limited to the SS-type. (a) For example, the primary-side resonant circuit 72 may have a so-called PS-type circuit configuration in which the variable capacitor C1 is connected in parallel to the primary coil L1, and the secondary-side resonant circuit 81 has a secondary capacitor C2 connected in series to the secondary coil L2. (b) Furthermore, the secondary-side resonant circuit 81 may have a so-called P-SS-type circuit configuration in which, in addition to the variable capacitor C1 connected in series to the primary coil L1, a capacitor is connected in parallel to the primary coil L1, and two secondary capacitors C2 are connected in series to each terminal of the secondary coil L2. (c) The primary-side resonant circuit 72 may also include a closed circuit in which a coil and a capacitor are connected in series. The coil of this closed circuit is positioned so that it can be magnetically coupled to the secondary-side coil L2 when the primary-side coil L1 and secondary-side coil L2 are magnetically coupled. (d) The capacitor of the closed circuit may also be connected in parallel to the coil rather than in series. (e) The primary-side resonant circuit 72 may also include a coil connected in series to the primary-side coil L1, and a capacitor connected in parallel to the coil. This coil is positioned so that it can be magnetically coupled to the secondary-side coil L2 when the primary-side coil L1 and secondary-side coil L2 are magnetically coupled.

[0069] (F4) In the first embodiment, the variable capacitor C1 is applied to the power supply device 70. The device to which the variable capacitor C1 is applied is not limited to the power supply device 70. For example, the variable capacitor C1 can be used in a device that includes a circuit for converting frequencies.

[0070] The present disclosure is not limited to the above-described embodiments and modifications, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and modifications corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0071] Other forms: The features of the present disclosure are as follows: (Form 1) A variable capacitor (C1) used in a control circuit (73) that controls the operation of the device (70), a first control electrode layer (21); a second control electrode layer (22) facing the first control electrode layer; a dielectric layer (32) disposed at least between the first control electrode layer and the second control electrode layer; a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other with the dielectric layer interposed therebetween, the first extraction electrode layer and the second extraction electrode layer are disposed at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when a voltage is applied between the first control electrode layer and the second control electrode layer, A variable capacitance capacitor in which the capacitance value of the electrostatic capacitance stored between the first extraction electrode layer and the second control electrode layer is adjusted by adjusting the voltage applied between the first control electrode layer and the second control electrode layer. (Form 2) The variable capacitor according to aspect 1, The device further includes a resonant circuit (72) configured with the variable capacitor and a primary coil (L1), the control circuit further includes a control voltage application circuit (76, 276, 376, 476) that applies a control voltage between the first control electrode layer and the second control electrode layer to change the dielectric constant of the dielectric layer; The variable capacitor adjusts the resonant frequency of the resonant circuit by adjusting the capacitance value using the control voltage. (Form 3) The variable capacitor according to aspect 2, the device is a power supply device that wirelessly supplies power to a power receiving device, The control voltage application circuit a power supply operation of setting the control voltage to a first control voltage, thereby setting the resonant circuit to a resonant state when AC power of a predetermined operating frequency is applied to the resonant circuit; a standby operation of setting the resonant circuit to a non-resonant state when the AC power of the operating frequency is applied to the resonant circuit by setting the control voltage to a second control voltage different from the first control voltage; The variable capacitor is set to a first capacitance value when the first control voltage is applied, and is set to a second capacitance value different from the first capacitance value when the second control voltage is applied. (Form 4) The variable capacitor according to aspect 3, the resonant circuit is a series resonant circuit, The second capacitance value is smaller than the first capacitance value. (Form 5) The variable capacitor according to aspect 3 or 4, A variable capacitor in which application of the second control voltage begins around the time when the voltage of the AC power applied to the primary coil is zero volts. (Form 6) The variable capacitor according to any one of aspects 1 to 5, The variable capacitor has a dielectric characteristic in which the dielectric constant at a temperature higher than a predetermined operating temperature is smaller than the dielectric constant at the operating temperature. (Form 7) A power supply device (70) that wirelessly supplies power to a power receiving device (80), a resonant circuit (72) consisting of a variable capacitor (C1) and a primary coil (L1); a control voltage application circuit (76) that applies a control voltage to the variable capacitor; The variable capacitor is a first control electrode layer (21); a second control electrode layer (22) facing the first control electrode layer; a dielectric layer (32) disposed at least between the first control electrode layer and the second control electrode layer; a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other with the dielectric layer interposed therebetween, the first extraction electrode layer and the second extraction electrode layer are disposed at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when the control voltage is applied between the first control electrode layer and the second control electrode layer, The control voltage application circuit a power supply operation of setting the control voltage to a first control voltage and setting the variable capacitor to a first capacitance value, thereby setting the resonant circuit to a resonant state when AC power of a predetermined operating frequency is applied to the resonant circuit; a standby operation of setting the resonant circuit to a non-resonant state when the AC power of the operating frequency is applied to the resonant circuit by setting the control voltage to a second control voltage different from the first control voltage and setting the variable capacitor to a second capacitance value different from the first capacitance value. [Explanation of symbols]

[0072] 11...first extraction electrode layer, 12...second extraction electrode layer, 21...first control electrode layer, 22...second control electrode layer, 32...second dielectric layer, 70...power supply device, 73...control circuit, 76, 276, 376, 476...control voltage application circuit, C1...variable capacitance capacitor, L1...primary side coil

Claims

1. A variable capacitor (C1) used in a control circuit (73) that controls the operation of a device (70), a first control electrode layer (21); a second control electrode layer (22) facing the first control electrode layer; a dielectric layer (32) disposed at least between the first control electrode layer and the second control electrode layer; a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other with the dielectric layer interposed therebetween; the first extraction electrode layer and the second extraction electrode layer are disposed at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when a voltage is applied between the first control electrode layer and the second control electrode layer, a voltage applied between the first control electrode layer and the second control electrode layer is adjusted to adjust a capacitance value of an electrostatic capacitance stored between the first extraction electrode layer and the second control electrode layer; The device is a power supply device that has a resonant circuit (72) configured with the variable capacitor and a primary coil (L1) and that wirelessly supplies power to a power receiving device, the control circuit has a control voltage application circuit (76, 276, 376, 476) that applies a control voltage between the first control electrode layer and the second control electrode layer to change the dielectric constant of the dielectric layer, The control voltage application circuit a power supply operation of setting the control voltage to a first control voltage, thereby setting the resonant circuit to a resonant state when AC power having a predetermined operating frequency is applied to the resonant circuit; a standby operation of setting the resonant circuit to a non-resonant state when the AC power of the operating frequency is applied to the resonant circuit by setting the control voltage to a second control voltage different from the first control voltage; The variable capacitor is adjusting a capacitance value using the control voltage to adjust a resonant frequency of the resonant circuit; When the first control voltage is applied, the capacitance is set to a first capacitance value, and when the second control voltage is applied, the capacitance is set to a second capacitance value different from the first capacitance value; A variable capacitor, wherein application of the second control voltage begins around the time when the voltage of the AC power applied to the primary coil is zero volts.

2. 2. The variable capacitor according to claim 1, the resonant circuit is a series resonant circuit, The second capacitance value is smaller than the first capacitance value.

3. A variable capacitor (C1) used in a control circuit (73) that controls the operation of a device (70), a first control electrode layer (21); a second control electrode layer (22) facing the first control electrode layer; a dielectric layer (32) disposed at least between the first control electrode layer and the second control electrode layer; a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other with the dielectric layer interposed therebetween; the first extraction electrode layer and the second extraction electrode layer are disposed at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when a voltage is applied between the first control electrode layer and the second control electrode layer, a voltage applied between the first control electrode layer and the second control electrode layer is adjusted to adjust a capacitance value of an electrostatic capacitance stored between the first extraction electrode layer and the second control electrode layer; The variable capacitor has a dielectric characteristic in which the dielectric constant at a temperature higher than a predetermined operating temperature is smaller than the dielectric constant at the operating temperature.

4. A power supply device (70) that contactlessly supplies power to a power receiving device (80), a resonant circuit (72) consisting of a variable capacitance capacitor (C1) and a primary coil (L1); a control voltage application circuit (76) that applies a control voltage to the variable capacitor; The variable capacitor is a first control electrode layer (21); a second control electrode layer (22) facing the first control electrode layer; a dielectric layer (32) disposed at least between the first control electrode layer and the second control electrode layer; a first extraction electrode layer (11) and a second extraction electrode layer (12) facing each other with the dielectric layer interposed therebetween; the first extraction electrode layer and the second extraction electrode layer are disposed at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode layer and the second control electrode layer when the control voltage is applied between the first control electrode layer and the second control electrode layer, The control voltage application circuit a power supply operation of setting the control voltage to a first control voltage and setting the variable capacitor to a first capacitance value, thereby setting the resonant circuit to a resonant state when AC power of a predetermined operating frequency is applied to the resonant circuit; a standby operation of setting the resonant circuit to a non-resonant state when the AC power of the operating frequency is applied to the resonant circuit by setting the control voltage to a second control voltage different from the first control voltage and setting the variable capacitor to a second capacitance value different from the first capacitance value, The power supply device is configured such that application of the second control voltage begins around a point in time when the voltage of the AC power applied to the primary coil is zero volts.

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