JP2015156741A - Power transmission system, power receiver, and power transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power transmission system, a power receiver, and a power transmitter, capable of performing power transmission of high power while suppressing a conductor loss and increase in apparatus size.

SOLUTION: A power transmission system 1 for transmitting a power from a power transmitter 101 to a power receiver 201 by using magnetic field coupling comprises: the power transmitter 101 comprising an inverter circuit 12, a piezoelectric transformer 14 for stepping up AC voltage from the inverter circuit 12 to apply the stepped-up voltage to a power transmission side coil 15, and resonant circuits 141, 142, 143 including a capacity component of the transmission side coil 15; and the power receiver 201 comprising a piezoelectric transformer 24 for stepping down a voltage induced in a power reception side coil 25, a rectifying and smoothing circuit 23 for rectifying and smoothing a voltage from the piezoelectric transformer 24 to supply the rectified and smoothed voltage to a load, and resonant circuits 241, 242, 243 including a capacity component of the power reception side coil 24. The respective resonant circuits are set to have the same resonant frequency. The power transmitter drives the inverter 12 with the resonant frequency.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention relates to a power transmission system that transmits power from a power transmission device to a power reception device by a magnetic field coupling method, and a power reception device and a power transmission device included in the power transmission system.

  Patent Document 1 discloses a power transmission system that wirelessly transmits power from a power transmission device to a power reception device using magnetic field coupling. The power transmission system described in Patent Document 1 increases the reliability of power transmission to an electronic device while suppressing a decrease in efficiency of power transmission by widening the power receiving range of the coil on the power receiving device side. Can do.

JP 2013-225961 A

  By the way, when transmitting a large amount of power in a magnetic field coupling type power transmission system, if the current is increased, the conductor loss increases. On the other hand, when the voltage is increased, a step-up winding transformer is required for the power transmission device, and a step-down winding transformer is required for the power receiving device, which increases the size of the device.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a power transmission system, a power receiving device, and a power transmitting device capable of transmitting a large amount of power while suppressing conductor loss and an increase in size of the device.

  The present invention provides a power transmission system that transmits power from a power transmission device to a power reception device by magnetically coupling a power transmission side coil included in the power transmission device and a power reception side coil included in the power reception device. An inverter circuit that converts the DC voltage output from the inverter into an AC voltage, a step-up transformer that boosts the AC voltage converted by the inverter circuit and applies the boosted voltage to the power transmission side coil, and a power transmission side first including the power transmission side coil. A resonance circuit, and the power receiving device includes a step-down transformer that steps down the voltage induced in the power receiving side coil, a rectifying and smoothing circuit that rectifies and smoothes the voltage stepped down by the step-down transformer, and supplies the voltage to a load; A power-receiving-side first resonance circuit including the power-receiving-side coil, and at least one of the step-up transformer or the step-down transformer is a piezoelectric transformer, When the pressure transformer is a piezoelectric transformer, the power transmission side first resonance circuit is set to be substantially the same as the resonance frequency of the piezoelectric transformer, and when the step-down transformer is a piezoelectric transformer, the power receiving side The first resonance circuit is set to be substantially the same as the resonance frequency of the piezoelectric transformer, the power transmission device includes a control circuit that drives the inverter circuit at the resonance frequency, and the step-up transformer is a piezoelectric transformer. The power transmission side first resonance circuit includes a capacitance component of the piezoelectric transformer, and when the step-down transformer is a piezoelectric transformer, the power reception side first resonance circuit includes a capacitance component of the piezoelectric transformer. It is characterized by.

  According to this configuration, in order to suppress the conductor loss due to the flow of a large current, a piezoelectric transformer is used for the step-up transformer or the step-down transformer that is required when power is transmitted at a high voltage. Large power can be transmitted while suppressing an increase in size.

  The step-down transformer is a piezoelectric transformer, the power-receiving-side first resonance circuit includes an input capacitance component of the piezoelectric transformer and the power-receiving-side coil, and the power receiving device includes the piezoelectric transformer, the rectifying and smoothing circuit, and A power-receiving-side inductor connected between the power-receiving-side inductor, the power-receiving-side inductor, and an output capacitance component of the piezoelectric transformer, and a power-receiving-side second resonance circuit having substantially the same resonance frequency as the power-receiving-side first resonance circuit. It is preferable to comprise.

  In this configuration, a resonance circuit is configured with the output capacitance component of the piezoelectric transformer and the power receiving side inductor, and the loss due to the output capacitance component of the piezoelectric transformer is suppressed by matching the resonance frequency of the resonance circuit with the drive frequency of the power transmission device. it can. As a result, power can be transmitted with high transmission efficiency.

  The step-up transformer is a piezoelectric transformer, the power transmission-side first resonance circuit is composed of an output capacitance component of the piezoelectric transformer and the power transmission-side coil, and the power transmission device includes the inverter circuit and the piezoelectric transformer. A power transmission side inductor connected between them, the power transmission side inductor, and an input capacitance component of the piezoelectric transformer, and a power transmission side second resonance circuit having substantially the same resonance frequency as the power transmission side first resonance circuit; It is preferable to provide.

  In this configuration, a resonance circuit is configured with the input capacitance component of the piezoelectric transformer and the power transmission-side inductor, and the resonance frequency of the resonance circuit is matched to the drive frequency of the power transmission device to suppress loss due to the input capacitance component of the piezoelectric transformer. it can. As a result, power can be transmitted with high transmission efficiency.

  According to the present invention, since a piezoelectric transformer is used as a step-up transformer or a step-down transformer that is required when power is transmitted at a high voltage in order to suppress a conductor loss due to a large current flowing, a conductor loss and a device are reduced. Therefore, large power transmission is possible.

Circuit diagram of power transmission system according to Embodiment 1 Equivalent circuit diagram of power transmission equipment provided in power transmission system Equivalent circuit diagram of power receiving device provided in power transmission system Perspective view for explaining the structure of a piezoelectric transformer Circuit diagram of power transmission system according to Embodiment 2 Equivalent circuit diagram of the power receiving device shown in FIG. Circuit diagram of power transmission system according to Embodiment 3 Circuit diagram of power transmission system according to Embodiment 4

(Embodiment 1)
FIG. 1 is a circuit diagram of a power transmission system 1 according to the first embodiment. FIG. 2 is an equivalent circuit diagram of the power transmission device 101 included in the power transmission system 1. FIG. 3 is an equivalent circuit diagram of the power receiving device 201 included in the power transmission system 1.

  The power transmission system 1 includes a power transmission device 101 and a power reception device 201. The power receiving apparatus 201 includes a load circuit RL. The load circuit RL includes a charging circuit and a secondary battery. And the power receiving apparatus 201 is a portable electronic device provided with the secondary battery, for example. Examples of the portable electronic device include a mobile phone, a PDA (Personal Digital Assistant), a portable music player, a notebook PC, and a digital camera. The power transmission device 101 is a charging stand for charging the secondary battery of the power receiving device 201 placed thereon.

  The power transmission apparatus 101 includes a DC power supply 11 that outputs a DC voltage. The DC power source 11 is an AC adapter connected to a commercial power source.

  An inverter circuit 12 is connected to the DC power supply 11. The inverter circuit 12 includes MOS-FET switching elements Q1, Q2, Q3, and Q4. In the inverter circuit 12, switch elements Q1 and Q2 are connected in series, and switch elements Q3 and Q4 are connected in series. The inverter circuit 12 is switching-controlled by the control circuit 13.

  The control circuit 13 controls the drive of the inverter circuit 12 at a predetermined drive frequency. Specifically, the control circuit 13 outputs a PWM signal to the gates of the switch elements Q1 to Q4, and alternately turns on and off the switch elements Q1 and Q4 and the switch elements Q2 and Q3. Thereby, the inverter circuit 12 converts a DC voltage into an AC voltage.

  The power transmission device 101 includes a piezoelectric transformer 14. The piezoelectric transformer 14 includes a first electrode E11, a second electrode E12, a third electrode E13, and a fourth electrode E14. The first electrode E11 is connected to the connection point of the switch elements Q1, Q2 of the inverter circuit 12. The second electrode E12 is connected to the connection point of the switch elements Q3, Q4 of the inverter circuit 12. The third electrode E13 and the fourth electrode E14 are connected to the power transmission side coil 15. The piezoelectric transformer 14 boosts the voltage input from the first electrode E11 and the second electrode E12, and outputs the boosted voltage from the third electrode E13 and the fourth electrode E14 to the power transmission side coil 15. That is, the piezoelectric transformer 14 is a step-up transformer that boosts the AC voltage output from the inverter circuit 12 and applies the boosted voltage to the power transmission side coil 15.

  By using the piezoelectric transformer 14 for boosting, the power transmission device 101 can be reduced in size and thickness as compared with the case where a winding transformer is used. Further, by boosting the voltage applied to the power transmission side coil 15 by the piezoelectric transformer 14, the amount of current necessary for transmitting large power from the power transmission apparatus 101 to the power reception apparatus 201 is reduced. For this reason, a conductor loss can be suppressed and the line | wire width or wire diameter of the power transmission side coil 15 can be made small.

  As shown in FIG. 2, the piezoelectric transformer 14 is represented by capacitors C11 and C12, a capacitor Cp1, an inductor Lp1, a resistor Rp1, and the like. The capacitor C11 is an equivalent input capacity of the piezoelectric transformer 14, and the capacitor C12 is an equivalent output capacity of the piezoelectric transformer 14. The capacitor Cp1 and the inductor Lp1 are electromechanical parameters. Each capacitor C11, C12, Cp1 is a capacitance generated between the electrodes E11 to E14.

  The resonance frequency of the piezoelectric transformer 14 is determined mainly by the resonance of the series resonance circuit 141 by the capacitor Cp1 and the inductor Lp1. Since electrical energy conversion is via elastic vibration, it has a natural resonance frequency determined by the elastic wave propagation velocity and dimensions of the piezoelectric ceramic.

  An inductor L1 is connected between the connection point of the switching elements Q1 and Q2 of the inverter circuit 12 and the first electrode E11 of the piezoelectric transformer 14. The inductor L1 is an example embodiment that corresponds to the “power transmission side inductor” according to the present invention. The inductor L1 is a filter inductor, which suppresses the harmonic component of the rectangular wave output from the inverter circuit 12 to be a sine wave and inputs it to the piezoelectric transformer 14. When a rectangular wave is input to the piezoelectric transformer 14, the piezoelectric transformer 14 may generate heat due to the influence of harmonic components. However, by providing the inductor L1, a sine wave is input to the piezoelectric transformer 14, and the piezoelectric transformer. The heat generation of 14 is suppressed.

  A capacitor C11, which is an equivalent input capacitance of the piezoelectric transformer 14, constitutes a series resonance circuit 142 together with the inductor L1. The series resonance circuit 142 has a circuit constant set so that the resonance frequency is substantially the same as that of the series resonance circuit 141. The series resonance circuit 142 is an example embodiment that corresponds to the “power transmission side second resonance circuit” according to the present invention.

  The capacitor C12, which is an equivalent output capacity of the piezoelectric transformer 14, forms a parallel resonant circuit 143 together with the power transmission side coil 15. The circuit constants of the parallel resonance circuit 143 are also set so that the resonance frequency is substantially the same as that of the series resonance circuit 141. In other words, the series resonant circuits 141 and 142 and the parallel resonant circuit 143 have substantially the same resonant frequency. The parallel resonance circuit 143 is an example embodiment that corresponds to the “power transmission side first resonance circuit” according to the present invention.

  The control circuit 13 performs PWM control of the inverter circuit 12 using a drive frequency that is substantially the same as the resonance frequency of the series resonance circuits 141 and 142 and the parallel resonance circuit 143.

  The power receiving device 201 includes a power receiving side coil 25. When the power receiving device 201 is placed on or close to the power transmitting device 101, the power receiving side coil 25 is close to the power transmitting side coil 15. Then, when a voltage is applied to the power transmission side coil 15 of the power transmission device 101, the power transmission side coil 15 and the power reception side coil 25 are magnetically coupled, and power is transmitted from the power transmission device 101 to the power reception device 201 via this coupling. Is done.

  The power receiving device 201 includes a piezoelectric transformer 24. The piezoelectric transformer 24 includes a first electrode E21, a second electrode E22, a third electrode E23, and a fourth electrode E24. The first electrode E21 and the second electrode E22 are connected to the rectifying and smoothing circuit 23. The third electrode E23 and the fourth electrode E24 are connected to the power receiving side coil 25. When the voltage induced in the power receiving side coil 25 by the magnetic field coupling is input to the third electrode E23 and the fourth electrode E24, the piezoelectric transformer 24 steps down the voltage and outputs it from the first electrode E21 and the second electrode E22. To do.

  By using the piezoelectric transformer 24 for step-down, the power receiving apparatus 201 can be made smaller and thinner than when a winding coil is used. Further, as described above, in order to transmit large power from the power transmitting apparatus 101 to the power receiving apparatus 201, no large current is transmitted from the power transmitting apparatus 101, conductor loss can be suppressed, and no large current flows. Therefore, the line width or wire diameter of the power receiving side coil 25 can be reduced.

  As shown in FIG. 3, the piezoelectric transformer 24 is represented by capacitors C21 and C22, a capacitor Cp2, an inductor Lp2, a resistor Rp2, and the like. The capacitor C21 is an equivalent input capacity of the piezoelectric transformer 24, and the capacitor C22 is an equivalent output capacity of the piezoelectric transformer 24. The capacitor Cp2 and the inductor Lp2 are electromechanical parameters. Each of the capacitors C21, C22, Cp2 is a capacitance generated between the electrodes E21 to E24.

  The resonance frequency of the piezoelectric transformer 24 is determined mainly by the resonance of the series resonance circuit 241 by the capacitor Cp2 and the inductor Lp2. Since electrical energy conversion is via elastic vibration, it has a natural resonance frequency determined by the elastic wave propagation velocity and dimensions of the piezoelectric ceramic. The resonance frequency of the series resonance circuit 241 is substantially the same as the resonance frequency of the piezoelectric transformer 14 included in the power transmission apparatus 101, that is, the resonance frequency of the series resonance circuit 141.

  A capacitor C 21, which is an equivalent input capacitance of the piezoelectric transformer 24, forms a parallel resonance circuit 242 together with the power receiving side coil 25. The parallel resonant circuit 242 has circuit constants set so that the resonant frequency is substantially the same as that of the series resonant circuit 241. The parallel resonance circuit 242 is an example embodiment that corresponds to the “power-receiving-side first resonance circuit” according to the present invention.

  An inductor L2 is connected between the first electrode E21 of the piezoelectric transformer 24 and the rectifying / smoothing circuit 23. The inductor L2 is an example embodiment that corresponds to the “power receiving side inductor” according to the present invention. A capacitor C22, which is an equivalent output capacity of the piezoelectric transformer 24, forms a series resonance circuit 243 together with the inductor L2. The circuit constants of the series resonance circuit 243 are also set so that the resonance frequency is substantially the same as that of the series resonance circuit 241. Therefore, the series resonant circuits 241 and 243 and the parallel resonant circuit 242 and the series resonant circuits 141 and 142 and the parallel resonant circuit 143 on the power transmission apparatus 101 side have substantially the same resonant frequency. The series resonance circuit 243 is an example embodiment that corresponds to the “power-receiving-side second resonance circuit” according to the present invention.

  The rectifying / smoothing circuit 23 includes a diode bridge, a capacitor, an inductor, and the like, rectifies and smoothes the voltage stepped down by the piezoelectric transformer 24, and outputs it to the DC-DC converter 22. The DC-DC converter 22 converts the rectified voltage into a voltage having a predetermined value and outputs the voltage to the load circuit RL.

  Here, the structure of the piezoelectric transformers 14 and 24 will be described.

  FIG. 4 is a perspective view for explaining the structure of the piezoelectric transformers 14 and 24. Since the structures of the piezoelectric transformers 14 and 24 are the same, the piezoelectric transformer 14 will be described below, and the corresponding reference numerals are written in parentheses for the piezoelectric transformer 24, and description thereof will be omitted.

  The piezoelectric transformer 14 (24) includes a rectangular plate-shaped piezoelectric plate 30 (40). The piezoelectric plate 30 (40) is formed by laminating, for example, PZT ceramic sheets. The piezoelectric transformer 14 (24) vibrates in the length direction in the (3λ / 2) resonance mode. Here, λ is one wavelength of vibration in the length direction. Therefore, the length of the piezoelectric transformer 14 (24) is set to (3λ / 2). Here, the width and thickness of the piezoelectric plate 30 (40) are preferably less than (λ / 2). This is because the vibration in the width direction and the thickness direction are not coupled to the vibration in the length direction, and the vibration of the entire piezoelectric plate 30 (40) is not unstable.

  The piezoelectric plate 30 (40) is formed with a first region 31 (41), a second region 32 (42), and a third region 33 (43) along the length direction. Each of the lengths of the regions 31 (41) to 33 (43) is λ / 2. The first region 31 (41) and the third region 33 (43) are high voltage regions, and the second region 32 (42) is a low voltage region.

  As shown by the arrows in FIG. 4, the first region 31 (41) and the third region 33 (43) are polarized in the length direction. The second region 32 (42) is polarized in the thickness direction. Examples of the polarization treatment method include a method of applying a voltage of 2 kV / mm to the piezoelectric plate in insulating oil at 170 ° C.

  In the second region 32 (42), the first electrode E11 (E21) and the second electrode E12 (E22) are provided on the upper and lower surfaces of the piezoelectric plate 30 (40) so as to face each other in the thickness direction. In addition, a third electrode E13 (E23) and a fourth electrode E14 (E24) are provided on two side surfaces of the piezoelectric plate 30 (40) facing in the length direction.

  In the piezoelectric transformer 14 of the power transmission device 101 configured as described above, when an AC voltage is applied from the inverter circuit 12 to the first electrode E11 and the second electrode E12, a voltage is applied in the thickness direction of the piezoelectric plate 30. Applied. For this reason, an electric field is applied to the second region 32 in the polarization direction. Then, longitudinal vibration is excited in the direction orthogonal to the polarization direction by the inverse piezoelectric effect, that is, in the length direction of the piezoelectric plate 30. When longitudinal vibration is excited, mechanical strain is generated in the length direction in the first region 31 and the third region 33, and a potential difference is generated in the polarization direction due to the piezoelectric transverse effect. Due to this potential difference, the first region 31 and the third region 33 become a high voltage portion, and a high voltage is extracted from the third electrode E13 and the fourth electrode E14. The extracted high voltage is applied to the power transmission side coil 15.

  Further, in the piezoelectric transformer 24 of the power receiving device 201, the third electrode E 23 and the fourth electrode E 24 are connected to the power receiving side coil 25. When power is transmitted from the power transmitting apparatus 101 to the power receiving apparatus 201 and a voltage is induced in the power receiving coil 25, the voltage is applied in the length direction of the piezoelectric plate 40 by the third electrode E23 and the fourth electrode E24. For this reason, an electric field is applied to the first region 41 and the third region 43 in the polarization direction. Then, longitudinal vibration is excited in the direction orthogonal to the polarization direction by the inverse piezoelectric effect, that is, in the thickness direction of the piezoelectric plate 40. When longitudinal vibration is excited, mechanical distortion occurs in the polarization direction in the second region 42, and a potential difference occurs in the polarization direction due to the piezoelectric transverse effect. Due to this potential difference, the second region 42 becomes a low voltage portion, and a low voltage is extracted from the first electrode E21 and the second electrode E22.

  In the power transmission system 1 configured as described above, by setting the drive frequency of the inverter circuit 12 of the power transmission apparatus 101 to the resonance frequency of each resonance circuit, highly efficient power transmission is possible. As described above, the resonance circuits configured in the power transmission device 101 and the power reception device 201 have substantially the same resonance frequency. The drive frequency is determined by the resonance frequency. At the resonance frequency, the parallel resonance circuit 143 and the parallel resonance circuit 242 have high impedance (maximum), and the series resonance circuits 141 and 142 and the series resonance circuits 241 and 243 have low impedance (minimum). For this reason, the voltage drop in each resonance circuit, that is, the voltage drop between the inverter circuit 12 and the load circuit RL is small. Therefore, power can be transmitted from the power transmitting apparatus 101 to the power receiving apparatus 201 with high transmission efficiency.

  In addition, a resonant system having a high Q value can be configured on the path from the inverter circuit 12 to the load circuit RL when the power receiving device 201 is placed (close to) the power transmitting device 101. For this reason, EMI (Electro Magnetic Interference) due to harmonic components can be suppressed. And since the capacitive component of the piezoelectric transformers 14 and 24 and the power transmission side coil 15 and the power receiving side coil 25 are used to configure this resonance system, an increase in the number of parts for configuring the resonance circuit is suppressed. it can.

  Further, on the power transmission device 101 side, the piezoelectric transformer 14 and the power transmission side coil 15 constitute a resonance system, and on the power reception device 201 side, the piezoelectric transformer 24 and the power reception side coil 25 constitute a resonance system. Even in such a case, the resonance inside the piezoelectric transformer does not depend on the degree of coupling between the power transmission side coil 15 and the power reception side coil 25, so that the harmonic component is not related to the degree of coupling between the power transmission side coil 15 and the power reception side coil 25. Less power transmission is possible.

  Furthermore, resonance circuits 142 and 143 are configured for the capacitor C11 which is an equivalent input capacitance of the piezoelectric transformer 14 and the capacitor C12 which is an equivalent output capacitance, respectively. Therefore, since the loss generated in each of the capacitors C11 and C12 of the piezoelectric transformer 14 can be suppressed, it is not necessary to input and output a large voltage to the piezoelectric transformer 14.

  Similarly, resonance circuits 242 and 243 are respectively formed for the capacitor C21 which is an equivalent input capacitance and the capacitor C22 which is an equivalent output capacitance of the piezoelectric transformer 24, and the resonance frequencies of the resonance circuits 242 and 243 are determined by the power transmission system 1. The driving frequency is set to be substantially the same. Therefore, since the loss generated in each of the capacitors C21 and C22 of the piezoelectric transformer 24 can be suppressed, it is not necessary to input and output a large voltage to the piezoelectric transformer 14.

  In this embodiment, the resonance frequency of each resonance circuit is substantially the same. However, for the convenience of circuit design such as the number of windings of the power transmission side coil 15 and the power reception side coil 25, the resonance frequency of each resonance circuit is It does not have to be exactly the same. In addition, the drive frequency of the inverter circuit 12 may not completely match the resonance frequency of each resonance circuit, and is within a range of errors close to the resonance frequency, for example, about ± 10% of the resonance frequency. Good.

(Embodiment 2)
FIG. 5 is a circuit diagram of the power transmission system 2 according to the second embodiment. 6 is an equivalent circuit diagram of the power receiving device 202 shown in FIG. In this example, the resonance circuit configured in the power receiving device 202 included in the power transmission system 2 is different from that in the first embodiment. Hereinafter, the difference will be described. The power transmission device 101 included in the power transmission system 2 is the same as that in the first embodiment, and a description thereof will be omitted.

  An inductor L <b> 3 is connected between the piezoelectric transformer 24 included in the power receiving device 201 and the rectifying and smoothing circuit 23. The inductor L3 is an example embodiment that corresponds to the “power receiving side inductor” according to the present invention. The inductor L3 is connected in parallel to the capacitor C22 which is an equivalent output capacity of the piezoelectric transformer 24. The inductor L3 and the capacitor C22 constitute a parallel resonance circuit 244. The parallel resonance circuit 244 has circuit constants set so that the resonance frequency is substantially the same as the series resonance circuit 241 and the parallel resonance circuit 242. The parallel resonant circuit 244 is an example embodiment that corresponds to the “power receiving side second resonant circuit” according to the present invention.

  In the above configuration, as in the first embodiment, the drive frequency of the inverter circuit 12 of the power transmission system 2 is determined to be substantially the same as the resonance frequency of each configured resonance circuit. As a result, the series resonant circuits 141 and 142 (see FIG. 2) configured in the power transmission apparatus 101 have low impedance (minimum), and the parallel resonant circuit 143 (see FIG. 2) has high impedance (maximum). Further, the series resonance circuit 241 configured in the power receiving apparatus 202 has a low impedance (minimum), and the parallel resonance circuits 242 and 244 have a high impedance (maximum). For this reason, the voltage drop in each resonance circuit, that is, the voltage drop between the inverter circuit 12 and the load circuit RL is small. Therefore, power can be transmitted from the power transmitting apparatus 101 to the power receiving apparatus 202 with high transmission efficiency.

  In addition, a parallel resonance circuit 244 is configured for the capacitor C22 of the piezoelectric transformer 24. For this reason, since the loss which generate | occur | produces in each of the capacitors C21 and C22 of the piezoelectric transformer 24 can be suppressed, it is not necessary to input / output a large voltage to the piezoelectric transformer 14.

  Further, the coupling can be strengthened, and power can be transmitted at a lower vibration speed. Driving the piezoelectric transformer with as little current as possible has better efficiency (efficiency of conversion between electric energy and mechanical energy). Further, when the current flowing through the piezoelectric plate 40 increases, the vibration speed of the piezoelectric plate 40 increases. Since the internal capacitors C21 and C22 also become a path through which current flows, if parallel resonance is performed at the vibration frequency of the piezoelectric plate 40 by paralleling the inductor L3 outside, the impedance of the LC parallel resonance becomes maximum, and the capacitor The current flowing through C21 and C22 is minimized. That is, the current can be minimized by making the current flowing through the piezoelectric transformer 24 flow only in the impedance of the load as much as possible. Therefore, the vibration speed can be further reduced and the efficiency of the piezoelectric transformer 24 can be maximized.

(Embodiment 3)
FIG. 7 is a circuit diagram of the power transmission system 3 according to the third embodiment. This example is different from the first and second embodiments in that the power transmission device 102 included in the power transmission system 3 does not include a piezoelectric transformer.

  The power transmission system 3 includes a power transmission device 102 and a power reception device 203. The power transmission device 102 includes a step-up transformer T1 that boosts the AC voltage output from the inverter circuit 12 and applies the boosted voltage to the power transmission side coil 15. The step-up transformer T1 includes a primary coil and a secondary coil. The primary coil of the step-up transformer T1 is connected to a connection point between the switch elements Q1 and Q2 of the inverter circuit 12 and a connection point between the switch elements Q3 and Q4. The secondary coil of the step-up transformer T1 is connected to the power transmission side coil 15 via the capacitor C3. The capacitor C3 constitutes a series resonance circuit 16 together with the power transmission side coil 15.

  The power receiving device 203 includes a piezoelectric transformer 26 that steps down the voltage induced in the power receiving side coil 25 and outputs the voltage to the rectifying and smoothing circuit 23. The piezoelectric transformer 26 is a Rosen type and includes a first electrode E31, a second electrode E32, and a third electrode E33. The first electrode E31 is connected to one end of the power reception side coil 25. The third electrode E <b> 33 is connected to the other end of the power receiving side coil 25. The second electrode E32 and the third electrode E33 are connected to the rectifying / smoothing circuit 23. The piezoelectric transformer 26 steps down the voltage applied between the first electrode E31 and the third electrode E33 and outputs it to the second electrode E32.

  The piezoelectric transformer 26 can be represented by an equivalent circuit shown in FIG. A capacitor having an equivalent input capacitance of the piezoelectric transformer 26 forms a parallel resonance circuit with the power receiving side coil 25. In this parallel resonant circuit, circuit constants are set so as to be substantially the same frequency as the resonant frequency of the piezoelectric transformer 26. The resonance frequency of the piezoelectric transformer 26 is the resonance frequency of the series resonance circuit 241 shown in FIG. The circuit constant is set so that the resonance frequency of the series resonance circuit 16 on the power transmission device 102 side is substantially the same as the resonance frequency of the piezoelectric transformer 26.

  The control circuit 13 of the power transmission apparatus 101 sets the drive frequency of the inverter circuit 12 to the resonance frequency of each resonance circuit, and performs PWM control of the inverter circuit 12.

  The drive frequency of the inverter circuit 12 of the power transmission system 3 is determined to be substantially the same as the resonance frequency of the configured resonance circuit, as in the first and second embodiments. Thereby, the series resonant circuit 16 comprised in the power transmission apparatus 102 becomes a low impedance (minimum). Further, the series resonance circuit configured in the power receiving device 203 has low impedance (minimum), and the parallel resonance circuit has high impedance (maximum). For this reason, the voltage drop in each resonance circuit, that is, the voltage drop between the inverter circuit 12 and the load circuit RL is small. Therefore, power can be transmitted from the power transmitting apparatus 102 to the power receiving apparatus 203 with high transmission efficiency.

  In addition, the transformation ratio can be increased by using a Rosen type piezoelectric transformer. For example, the transformation ratio can be increased by reducing the area of the second electrode E32 and the third electrode E33 and increasing the equivalent output capacity from the equivalent input capacity of the piezoelectric transformer. This transformation ratio is appropriately changed according to the voltage supplied to the load circuit RL.

  Although the piezoelectric transformer 26 according to the present embodiment is a Rosen type, the structure thereof can be changed as appropriate. Further, although the piezoelectric transformer 26 is a Rosen type, it may be the same piezoelectric transformer as in the first and second embodiments, or may be a piezoelectric transformer having another structure.

(Embodiment 4)
FIG. 8 is a circuit diagram of the power transmission system 4 according to the fourth embodiment. This example is different from the first and second embodiments in that the power receiving device 204 included in the power transmission system 4 does not include a piezoelectric transformer.

  The power transmission system 4 includes a power transmission device 103 and a power reception device 204. The power transmission device 103 includes a piezoelectric transformer 17 that boosts the AC voltage output from the inverter circuit 12 and applies it to the power transmission side coil 15. The piezoelectric transformer 17 is a Rosen type as in the third embodiment, and includes a first electrode E41, a second electrode E42, and a third electrode E43. The first electrode E41 is connected to one end of the power receiving side coil 25. The third electrode E43 is connected to the other end of the power receiving coil 25. The second electrode E42 is connected to the connection point of the switch elements Q1 and Q2 of the inverter circuit 12, and the third electrode E43 is connected to the connection point of the switch elements Q3 and Q4. The piezoelectric transformer 17 steps down the voltage applied between the second electrode E42 and the third electrode E43 and outputs it to the first electrode E41.

  The piezoelectric transformer 17 can be represented by an equivalent circuit shown in FIG. The capacitor having an equivalent output capacity of the piezoelectric transformer 17 forms a parallel resonance circuit with the power transmission side coil 15. In this parallel resonant circuit, circuit constants are set so as to have substantially the same frequency as the resonant frequency of the piezoelectric transformer 17. The resonance frequency of the piezoelectric transformer 17 is the resonance frequency of the series resonance circuit 141 shown in FIG.

  The power receiving device 204 includes a step-down transformer T <b> 2 that steps down the voltage induced in the power receiving side coil 25 and outputs it to the rectifying and smoothing circuit 23. The step-down transformer T2 includes a primary coil and a secondary coil. The primary coil of the step-down transformer T2 is connected to the power receiving side coil 25 via the capacitor C4. The secondary coil of the step-down transformer T2 is connected to the rectifying and smoothing circuit 23. The capacitor C4 and the power receiving side coil 25 constitute a parallel resonance circuit. The circuit constant is set so that the resonance frequency of the parallel resonance circuit is substantially the same as the resonance frequency of the piezoelectric transformer 17.

  The control circuit 13 of the power transmission apparatus 103 sets the drive frequency of the inverter circuit 12 to the resonance frequency of each resonance circuit, and performs PWM control of the inverter circuit 12.

  The drive frequency of the inverter circuit 12 of the power transmission system 4 is determined to be substantially the same as the resonance frequency of the configured resonance circuit, as in the first and second embodiments. Thereby, the series resonance circuit comprised in the power transmission apparatus 103 becomes a low impedance (minimum), and a parallel resonance circuit becomes a high impedance (maximum). Further, the parallel resonant circuit configured in the power receiving device 204 has high impedance (maximum). For this reason, the voltage drop in each resonance circuit, that is, the voltage drop between the inverter circuit 12 and the load circuit RL is small. Therefore, power can be transmitted from the power transmitting apparatus 103 to the power receiving apparatus 204 with high transmission efficiency.

1, 2, 3, 4 ... Power transmission system 11 ... DC power supply 12 ... Inverter circuit 13 ... Control circuits 14, 17, 24, 26 ... Piezoelectric transformer 15 ... Power transmission side coil 16 ... Series resonance circuit 22 ... DC-DC converter 23 ... rectifying / smoothing circuit 25 ... receiving coil 30, 40 ... piezoelectric plates 31, 41 ... first region 32,42 ... second region 33,43 ... third region 101,102,103 ... power transmission device 141 ... series resonance circuit 142 ... Series resonance circuit (power transmission side second resonance circuit)
143 ... Parallel resonance circuit (first resonance circuit on the power transmission side)
201, 202, 203, 204 ... power receiving device 241 ... series resonance circuit 242 ... parallel resonance circuit (power receiving side first resonance circuit)
243 ... Series resonance circuit (power-receiving-side second resonance circuit)
244 ... Parallel resonant circuit (power-receiving-side second resonant circuit)
C11: Capacitor (input capacitance component)
C12: Capacitor (output capacitance component)
C21: Capacitor (input capacitance component)
C22: Capacitor (output capacitance component)
C3, C4 ... capacitors Cp1, Cp2 ... capacitors E11, E21, E31, E41 ... first electrodes E12, E22, E32, E42 ... second electrodes E13, E23, E33, E43 ... third electrodes E14, E24 ... fourth electrodes L1 ... Inductor (Inductor on the power transmission side)
L2, L3 ... Inductor (Receiver side inductor)
Lp1, Lp2 ... inductors Q1, Q2, Q3, Q4 ... switch element RL ... load circuit Rp1, Rp2 ... resistor T1 ... step-up transformer T2 ... step-down transformer

Claims (5)

In the power transmission system that transmits power from the power transmission device to the power reception device by magnetically coupling the power transmission side coil included in the power transmission device and the power reception side coil included in the power reception device,
The power transmission device is:
An inverter circuit for converting a DC voltage output from a DC power source into an AC voltage;
A step-up transformer that steps up the alternating voltage converted by the inverter circuit and applies the boosted voltage to the power transmission side coil;
A power transmission side first resonance circuit including the power transmission side coil;
With
The power receiving device is:
A step-down transformer for stepping down a voltage induced in the power receiving side coil;
Rectifying and smoothing the voltage stepped down by the step-down transformer and supplying the voltage to a load; and
A power-receiving-side first resonance circuit including the power-receiving-side coil;
With
At least one of the step-up transformer or the step-down transformer is a piezoelectric transformer,
When the step-up transformer is a piezoelectric transformer, the power transmission-side first resonance circuit is set to be substantially the same as the resonance frequency of the piezoelectric transformer, and when the step-down transformer is a piezoelectric transformer, the power receiving The first side resonance circuit is set to be substantially the same as the resonance frequency of the piezoelectric transformer,
The power transmission device includes a control circuit that drives the inverter circuit at the resonance frequency,
When the step-up transformer is a piezoelectric transformer, the power-transmission-side first resonance circuit includes a capacitive component of the piezoelectric transformer, and when the step-down transformer is a piezoelectric transformer, the power-receiving-side first resonance circuit is Including the capacitive component of the piezoelectric transformer,
Power transmission system. The step-down transformer is a piezoelectric transformer;
The power receiving side first resonance circuit is composed of an input capacitance component of the piezoelectric transformer and the power receiving side coil,
The power receiving device is:
A power receiving-side inductor connected between the piezoelectric transformer and the rectifying and smoothing circuit;
A power-receiving-side second resonance circuit composed of the power-receiving-side inductor and an output capacitance component of the piezoelectric transformer, and having substantially the same resonance frequency as the power-receiving-side first resonance circuit;
A power transmission system according to claim 1. The step-up transformer is a piezoelectric transformer;
The power transmission side first resonance circuit is composed of an output capacitance component of the piezoelectric transformer and the power transmission side coil,
The power transmission device is:
A power transmission side inductor connected between the inverter circuit and the piezoelectric transformer;
The power transmission side inductor and the input capacitance component of the piezoelectric transformer, the power transmission side second resonance circuit having substantially the same resonance frequency as the power transmission side first resonance circuit,
A power transmission system according to claim 1 or 2. In the power receiving device that transmits power from the power transmitting device by the magnetic field coupling method,
A power receiving side coil magnetically coupled to a power transmitting side coil included in the power transmission device;
A piezoelectric transformer that steps down the voltage induced in the power receiving coil;
A power receiving side first resonance circuit configured by the power receiving side coil and an input capacitance component of the piezoelectric transformer, and having substantially the same resonance frequency as the piezoelectric transformer;
A rectifying / smoothing circuit for rectifying and smoothing the voltage stepped down by the piezoelectric transformer and supplying the voltage to a load;
A power receiving device. In the power transmission device that transmits power to the power receiving device by the magnetic field coupling method,
A power transmission side coil magnetically coupled to a power reception side coil included in the power reception device;
An inverter circuit for converting a DC voltage output from a DC power source into an AC voltage;
A piezoelectric transformer that boosts the alternating voltage converted by the inverter circuit and applies the boosted voltage to the power transmission side coil;
An output capacitance component of the piezoelectric transformer and the power transmission side coil, a power transmission side first resonance circuit having substantially the same resonance frequency as the piezoelectric transformer,
A control circuit for driving the inverter circuit at a resonance frequency of the power transmission side first resonance circuit;
A power transmission device comprising:

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