JP7422554B2 - Contactless power transfer system - Google Patents

Description

The present invention relates to a contactless power supply system that can supply power to a load in a contactless manner.

BACKGROUND ART Conventionally, a non-contact power supply system that uses magnetic resonance is known as a non-contact power supply system that transfers power to devices such as portable electronic devices and robot vacuum cleaners in a non-contact manner. As shown in Patent Document 1, for example, this magnetic resonance type non-contact power supply system includes a power transmission unit having a primary coil connected to a power source, and a secondary coil connected to a battery (also referred to as a load). By making the primary coil and secondary coil resonate at a resonant frequency, power is transmitted from the power transmitting unit to the power receiving unit, thereby charging the battery built into the device. can.

By the way, in such a magnetic resonance type non-contact power supply system, in order to increase the power transmission efficiency, the resonance frequency (also called operating frequency) of the primary coil and the secondary coil is set to a high frequency of, for example, 10 kHz or higher. sometimes used. In this case, for example, if a metallic foreign object is present between the power transmitting unit and the power receiving unit during charging, the foreign object will be rapidly heated by the high-frequency magnetic field, potentially causing burns or fire.

Therefore, in recent years, contactless power supply systems in which the operating frequency is set to a low frequency (for example, 3 kHz or less) have been developed. This makes it possible to reduce the influence of heat generated by the above-mentioned metal foreign matter.

Japanese Patent Application Publication No. 2014-90617

However, when the operating frequency is set to a low frequency, the wire diameters of the conductive wires that make up the primary and secondary coils become thicker than those with a high operating frequency, resulting in increased heat generation due to the skin effect. This limits the ability to incorporate it into devices.

The present invention has been made to solve the above problems, and has the object of suppressing heat generation due to the skin effect of the primary coil and secondary coil in a magnetic resonance type non-contact power supply system, and contributing to the miniaturization of the system. The main issue is:

That is, the contactless power transfer system according to the present invention includes a power transmission unit having a primary coil connected to a power source, and a power receiving unit having a secondary coil connected to a load, the primary coil and the primary coil being connected to a load. The magnetic resonance type transmits power from the power transmitting unit to the power receiving unit by causing the secondary coil disposed opposite to the side coil to resonate, wherein the primary coil and the secondary coil are It is a solenoid type constructed by winding a conductive wire around a magnetic core, and the magnitude of the current flowing through the secondary coil is determined by controlling the load resistance value when looking at the load from the secondary side resonant circuit. an impedance conversion unit that suppresses the impedance to a value below a value, and is configured such that the number of conductive wires wound around the magnetic core of the primary coil is greater than the number of conductive wires wound around the magnetic core of the secondary coil. It is characterized by being

With this configuration, the magnitude of the current flowing through the conductor of the secondary coil can be suppressed to a predetermined value or less by the impedance conversion section, so the diameter of the conductor of the secondary coil can be reduced and the skin effect can be reduced. It is possible to reduce heat generation in the secondary coil.
Furthermore, when the current flowing through the secondary coil is reduced by the impedance conversion section, the current flowing through the primary coil increases, but in the wireless power transfer system of the present invention, the number of conductors in the primary coil is reduced. By making the number of conductors larger than the number of conductors in the secondary coil and creating a structure in which multiple conductors are wound, the wire diameter of each conductor in the primary coil can be reduced, and the primary coil due to the skin effect. heat generation can be reduced.
Since heat generation due to the skin effect in the primary coil and the secondary coil can be reduced in this way, the thermal influence on adjacent components can be reduced, contributing to system downsizing.

In the contactless power supply system, it is preferable that the primary coil and the secondary coil have a resonance frequency of 3 kHz or less.
With such a device, even if a metal foreign object is present between the power transmitting unit and the power receiving unit during charging, the metal foreign object can be prevented from being rapidly heated, and the occurrence of burns or fire can be suppressed.

In the non-contact power supply system, it is preferable that each magnetic core of the primary coil and the secondary coil has a plate shape, and the areas of opposing surfaces thereof are equal.
With such a configuration, the opposing areas of the magnetic cores included in the primary coil and the secondary coil are equal, so it is possible to improve the power transmission efficiency.

As an aspect of the non-contact power supply system, the power transmission unit includes a primary side resonance circuit including the primary side coil and a primary side resonance capacitor connected in series to the primary side coil, and the power receiving unit includes the secondary side resonance circuit. One example includes a secondary resonant circuit including a secondary coil and a secondary resonant capacitor connected in series to the secondary coil.

The impedance conversion unit may include a current detector that detects a current flowing through the secondary coil, a semiconductor switch connected in series to the secondary resonant circuit, and a semiconductor switch connected to the secondary resonant circuit and the secondary resonant circuit. A coil connected in series to the semiconductor switch and provided between the semiconductor switch and the load controls a duty ratio of a switching operation of the semiconductor switch according to a current value detected by the current detector. An example of this is a device equipped with a control section.

According to the present invention configured in this manner, in a magnetic resonance type non-contact power supply system, heat generation due to the skin effect of the primary coil and the secondary coil can be suppressed, contributing to miniaturization of the system.

FIG. 1 is a diagram schematically showing a circuit configuration of a non-contact power supply system according to the present embodiment. FIG. 3 is a diagram schematically showing a circuit configuration of a power receiving unit according to the embodiment. The figure which shows roughly the structure of the primary side coil and the secondary side coil of the same embodiment. The figure which shows roughly the structure of the primary side coil and the secondary side coil of the same embodiment. 7 is a graph showing changes in power feeding efficiency and coil current when the load resistance value of the power receiving unit is controlled using the impedance conversion section of the embodiment.

A contactless power supply system 100 according to an embodiment of the present invention will be described below with reference to the drawings.

<Overall configuration>
The contactless power supply system 100 of this embodiment is for contactlessly charging a battery (load) 4 built into an electronic device such as a robot vacuum cleaner using a charger. Specifically, as shown in FIG. 1, this contactless power supply system 100 includes a power transmission unit 2 built into a charger connected to a power source 1, and a power reception unit built into a robot vacuum cleaner and connected to a load 4. 3. This contactless power supply system 100 has a primary coil 231 provided in the power transmission unit 2 and a secondary coil 311 provided in the power reception unit 3 facing each other, and also connects the primary coil 231 and the secondary coil 311 at a frequency of 3 kHz or less. This is a so-called magnetic resonance method in which power is transmitted from the power transmission unit 2 to the power reception unit 3 by resonating at a low frequency resonance frequency (preferably a commercial power supply frequency). This will be explained in detail below.

<Power transmission unit 2>
The power transmission unit 2 transmits power from the power source 1 to the power reception unit 3. Specifically, this power transmission unit 2 includes a rectifying and smoothing circuit 21 that rectifies and smoothes the AC voltage supplied from the power source 1 into a DC voltage, and is connected in parallel to the rectifying and smoothing circuit 21 to convert the DC voltage to any frequency. It includes an inverter circuit 22 that converts into an alternating current voltage and outputs it, a primary side resonant circuit 23 connected in parallel to the inverter circuit 22, and a control section 24.

As the rectifying and smoothing circuit 21, a known configuration may be applied, and includes, for example, a diode bridge, a smoothing capacitor, and the like. Further, a known configuration may be used as the inverter circuit 22, and for example, a full bridge type inverter circuit configured from four switching elements can be mentioned. The control unit 24 physically includes a CPU, memory, input means, etc., and controls the frequency of the AC voltage output by the inverter circuit 22 by operating according to a predetermined program stored in the memory. functions to control the

The primary side resonant circuit 23 is applied with an alternating current voltage from the inverter circuit 22 and generates an oscillating magnetic field. Specifically, this primary side resonant circuit 23 is an LC series resonant circuit composed of a primary side coil 231 and a primary side resonant capacitor 232 that are connected in series with each other.

As shown in FIGS. 3 and 4, the primary coil 231 is of a solenoid type in which a conducting wire 231L is wound around a substantially plate-shaped primary magnetic core 231C. The primary magnetic core 231C has a plate shape and is made of a magnetic material such as ferrite. The primary magnetic core 231C includes a wound portion 231C ₁ around which the conducting wire 231L is wound, and a pair of protruding portions 231C ₂ and 231C ₃ that protrude from the wound portion 231C ₁ to both ends of the coil 231 in the axial direction. Be prepared. The protrusions 231C ₂ and 231C ₃ are exposed without the conductive wire 231L being wound thereon, and have a rectangular facing surface 231Cs facing the secondary coil 311. The protrusions 231C ₂ and 231C ₃ are formed to have a uniform thickness along the axial direction.

<Power receiving unit 3>
The power receiving unit 3 receives the power transmitted from the power transmitting unit 2 and outputs the power to the load 4. Specifically, the power receiving unit 3 includes a secondary resonant circuit 31 that magnetically resonates with the primary resonant circuit 23 and generates an alternating current voltage, and a rectifier circuit 32 that rectifies the alternating current voltage output from the secondary resonant circuit 31. , a first smoothing circuit 33 that smoothes the DC voltage output from the rectifier circuit 32, a voltage conversion circuit 34 that adjusts the voltage value of the smoothed DC voltage, and a DC voltage output from the voltage conversion circuit 34. It includes a second smoothing circuit 35 for smoothing and a control section 36. These circuits included in the power receiving unit 3 are connected in parallel with each other and in parallel with the load 4.

The secondary side resonant circuit 31 is an LC series resonant circuit composed of a secondary side coil 311 and a secondary side resonant capacitor 312 that are connected in series with each other.

As shown in FIGS. 3 and 4, the secondary coil 311 is of a solenoid type in which a conducting wire 311L is wound around a substantially plate-shaped secondary magnetic core 311C. The secondary magnetic core 311C has a plate shape and is made of a magnetic material such as ferrite. The secondary magnetic core 311C includes a wound portion 311C ₁ around which the conducting wire 311L is wound, and a pair of protruding portions 311C ₂ and 311C ₃ that protrude from the wound portion 311C ₁ to both ends of the coil 311 in the axial direction. Equipped with. The protrusions 311C ₂ and 311C ₃ are exposed without the conductive wire 311L being wound thereon, and have a rectangular opposing surface 311Cs that faces the primary coil 231. The protrusions 311C ₂ and 311C ₃ are formed to have a uniform thickness along the axial direction.

As the rectifier circuit 32, a known configuration may be applied, such as a diode bridge composed of four diodes. The rectifier circuit 32 is connected in parallel to the secondary coil 311 and the secondary resonant capacitor 312, and rectifies (that is, converts into pulsating voltage) the alternating current voltage generated in the secondary coil 311 and the secondary resonant capacitor 312. .

The first smoothing circuit 33 includes a first smoothing capacitor 331 connected in parallel to the rectifier circuit 32, and generates a DC voltage by smoothing the pulsating voltage output from the rectifier circuit 32. The first smoothing capacitor 331 has one end connected to the output end of the rectifier circuit 32 and the other end connected to the input end of the rectifier circuit 32 .

In this embodiment, the voltage conversion circuit 34 is a so-called step-down circuit including a first switching element 341, a second switching element 342, and a coil 343, and steps down the DC voltage, as shown in FIG. When viewed from the secondary coil 311, the first switching element 341 and the second switching element 342 are connected in parallel to the first smoothing capacitor 331. One end of the first switching element 341 is connected to the output end of the rectifier circuit 32 . The coil 343 is connected in series to the first switching element 341 and in parallel to the second switching element 342. The coil 343 has one end connected to the first switching element 341 and the second switching element 342, and the other end connected to the load 4. The first switching element 341 and the second switching element 342 are, for example, semiconductor switches such as MOSFETs and IGBTs, and are switched between on and off states based on a control signal from the control unit 36. Note that although the voltage conversion circuit 34 of this embodiment is provided between the first smoothing circuit 33 and the second smoothing circuit 35, the present invention is not limited thereto. The voltage conversion circuit 34 only needs to be provided between the rectifier circuit 32 and the load 4.

The second smoothing circuit 35 includes a second smoothing capacitor 351 connected in series to the coil 343 and in parallel to the second switching element 342 . The second smoothing circuit 35 smoothes the DC voltage stepped down by the voltage conversion circuit 34.

The control unit 36 physically includes a CPU, a memory, input means, etc., and operates according to a predetermined program stored in the memory to control the first switching element 341 and the step-down circuit included in the step-down circuit. It functions to control the switching operation of the second switching element 342. The control unit 36 outputs a pulse signal of a predetermined period to the first switching element 341 and the second switching element 342 to control the duty ratio (ratio of On time and Off time) of these switching operations. (PWM control).

The power receiving unit 3 also includes a current detector 37 connected in series to a secondary coil 311 and a secondary resonance capacitor 312. This current detector 37 measures the value of the current flowing through the secondary coil 311 and transmits the measured value to the control unit 36. The current detector 37 may be of any type such as a CT type or a Hall element type.

Therefore, in the non-contact power supply system 100 of this embodiment, the number of conducting wires 231L forming the primary coil 231 is greater than the number of conducting wires 311L forming the secondary coil 311. Further, the wire diameter of the conducting wire 311L of the secondary coil 311 is configured to be smaller than the wire diameter of the conducting wire 231L of the primary coil 231. Specifically, a plurality of conductive wires 231L constituting the primary coil 231 are wound in parallel (here, bifilar winding), and the conductive wire 311L constituting the secondary coil 311 is wound in a single manner (that is, monofilar winding). . Below, the configurations of the primary coil 231 and the secondary coil 311 will be explained in more detail.

In the non-contact power supply system 100 of this embodiment, as shown in FIGS. 3 and 4, the coil length l ₁ along the axial direction of the primary coil 231 and the coil length along the axial direction of the secondary coil 311. _{The coil outer diameter d 2 of} the secondary coil 311 is smaller than the coil outer diameter d ₁ of the primary coil 231. Here, the coil length l ₁ along the axial direction of the primary coil 231 means the length along the winding axis direction of the conducting wire 231L that constitutes the primary coil 231. The same applies to the coil length _l2 along the axial direction of the secondary coil 311. Further, the coil outer diameter d ₁ of the primary coil 231 means the length along the radial direction of the wound conducting wire 231L that constitutes the primary coil 231. The same applies to the coil outer diameter _d2 of the secondary coil 311.

Further, in the contactless power supply system 100 of the present embodiment, as shown in FIGS. 3 and 4, the opposing surface 231Cs of the primary coil 231 and the opposing surface 311Cs of the secondary coil 311 are the same in plan view. They are configured to have the same shape and area. Here, the wire diameter of the conducting wire 311L of the secondary coil 311 is 0.5 mm, and the wire diameter of the conducting wire 231L of the primary coil 231 is 0.7 mm.

In order to realize such a shape of the secondary coil 311, the non-contact power supply system 100 of the present embodiment has a load resistance value (specifically, , which refers to the resistance component of the load impedance on the right side of the secondary side resonant capacitor 312 in the power receiving unit 3). The contactless power supply system 100 can limit the current value flowing through the secondary coil 311 during charging to a predetermined value (for example, 1 A) or less by adjusting the load resistance value of the power receiving unit 3 using the impedance converter 38. Can be done. Thereby, the wire diameter of the conducting wire 311L that constitutes the secondary coil 311 can be reduced, and the secondary coil 311 can be configured by winding a smaller number of conducting wires than the primary coil 231.

Specifically, this impedance conversion section 38 includes a current detector 37, a first switching element 341 and a coil 343 included in the voltage conversion circuit 34, and a control section 36. The control unit 36 variably controls the duty ratio of the switching operation of the first switching element 341 based on the current value (the value of the current flowing through the secondary coil 311) measured by the current detector 37. More specifically, while monitoring the current value, the control unit 36 variably controls the duty ratio of the switching operation of the first switching element 341 so that the current value does not exceed a predetermined value. Thereby, the magnitude of the current flowing through the secondary coil 311 can be controlled to be equal to or less than a predetermined value.

FIG. 5 shows the power feeding efficiency, the primary coil 231 (indicated as feeding coil), and the secondary coil 231 (indicated as feeding coil) when the load resistance value seen from the secondary coil 311 is controlled using the impedance conversion unit 38 of this embodiment. The current value of the current flowing through the next coil 311 (displayed as the receiving coil) is shown. As shown in FIG. 5, by controlling the impedance conversion unit 38 of this embodiment, the current value in the receiving coil can be suppressed to 1 A or less while maintaining a high power feeding efficiency of 90% or more, and the secondary The wire diameter of the conducting wire 311L of the side coil 311 can be reduced.

<Effects of this embodiment>
According to the contactless power supply system 100 of the present embodiment configured in this way, the magnitude of the current flowing through the conductor 311L of the secondary coil 311 can be suppressed to a predetermined value or less by the impedance conversion unit 38, so that the The wire diameter of the conducting wire 311L of the side coil 311 can be reduced, and heat generation in the secondary coil 311 due to the skin effect can be reduced. Furthermore, when the impedance conversion unit 38 reduces the current flowing through the secondary coil 311, the current flowing through the conductor 231L of the primary coil 231 increases, but the contactless power supply system 100 of this embodiment Now, by increasing the number of conducting wires 231L of the primary coil 231 than the number of conducting wires 311L of the secondary coil 311 and using bifilar winding, the wire diameter of each conducting wire 231L of the primary coil 231 can be reduced. However, heat generation in the primary coil 231 due to the skin effect can be reduced. Since heat generation due to the skin effect in the primary coil 231 and the secondary coil 311 can be reduced in this way, the thermal influence on adjacent components can be reduced and the non-contact power supply system 100 can be downsized.

<Other modified embodiments>
Note that the present invention is not limited to the above embodiments.

In the embodiment described above, the conducting wire 231L constituting the primary coil 231 is formed by bifilar winding, but the present invention is not limited to this, and may be trifilar winding. Further, the conducting wire 311L constituting the secondary coil 311 may be configured with a plurality of windings such as bifilar winding. Even with such a configuration, the number of conductive wires 231L constituting the primary coil 231 may be greater than the number of conductive wires 311L constituting the secondary coil 311.

In the embodiment, the second switching element 342 is a semiconductor switch such as a MOSFET or an IGBT, but is not limited thereto and may be a diode.

Although the voltage conversion circuit 34 is a step-down circuit in the embodiment, the present invention is not limited to this. In other embodiments, the voltage conversion circuit 34 may be a so-called booster circuit.

The non-contact power supply system 100 in the embodiment described above may be used not only for charging a robot vacuum cleaner but also for charging other electronic devices such as a mobile phone or a smart phone.

In addition, various modifications and combinations of the embodiments may be made as long as they do not go against the spirit of the present invention.

100 ... Contactless power supply system 1 ... Power supply 231 ... Primary side coil 231L ... Primary side conductor 231C ... Primary side magnetic core 3 ... Power receiving unit 311 ... Secondary side coil 311L ...Secondary side conductor 311C...Secondary side magnetic core 37...Current sensor 38...Impedance conversion unit 4...Load

Claims (5)

A power transmission unit having a primary coil connected to a power source, and a power receiving unit having a secondary coil connected to a load, the primary coil and the secondary side disposed opposite to the primary coil. A magnetic resonance type contactless power supply system that transmits power from the power transmission unit to the power reception unit by causing resonance with a coil,
The primary coil and the secondary coil are of a solenoid type configured by winding a conductive wire around a magnetic core,
an impedance conversion unit that suppresses the magnitude of the current flowing through the secondary coil to a predetermined value or less by controlling a load resistance value when looking at the load from the secondary coil;
The primary coil is configured by bifilar winding or trifilar winding in which a plurality of conducting wires are wound in parallel around the magnetic core, and the number of conducting wires wound around the magnetic core of the primary coil is equal to the number of conducting wires wound around the magnetic core of the primary coil. A non-contact power supply system configured so that the number of conductors is greater than the number of conductors wound around the magnetic core of the next coil. The contactless power supply system according to claim 1, wherein the resonance frequency of the primary coil and the secondary coil is 3 kHz or less. The contactless power feeding system according to claim 1 or 2, wherein each of the magnetic cores of the primary coil and the secondary coil is plate-shaped, and the areas of opposing surfaces are equal. The power transmission unit includes a primary side resonant circuit including the primary side coil and a primary side resonant capacitor connected in series to the primary side coil,
The power receiving unit according to any one of claims 1 to 3, comprising a secondary side resonant circuit including the secondary side coil and a secondary side resonant capacitor connected in series to the secondary side coil. Contactless power supply system. The impedance conversion section is
a current detector that detects the current flowing through the secondary coil;
a semiconductor switch connected in series to the secondary side resonant circuit;
a coil connected in series to the secondary side resonant circuit and the semiconductor switch and provided between the semiconductor switch and the load;
The contactless power supply system according to claim 4 , further comprising a control unit that controls a duty ratio of a switching operation of the semiconductor switch according to a current value detected by the current detector.