JP7301706B2 - Power receiving device and wireless power supply system - Google Patents

Description

The present invention relates to a power receiving device and a wireless power supply system.

2. Description of the Related Art In recent years, development of a wireless power feeding system that wirelessly transmits power from a power transmitting device to a power receiving device has been progressing. For example, Patent Literature 1 discloses a wireless power supply measuring device in which a power receiving device receives power output from a power transmitting device in a contactless manner and a voltage corresponding to the power is supplied to a load.

WO2017/141340

In such a wireless power supply system, a voltage generated across the power receiving coil by electromagnetic induction between the power transmitting coil and the power receiving coil is applied to the load. At this time, since the power receiving coil behaves as a constant voltage source when viewed from the load, even if the power received by the power receiving coil is constant, the amount of current supplied to the load varies according to the load impedance. For example, when the load impedance is high, the amount of current flowing through the load is relatively small, but when the load impedance is low, a large amount of current may flow through the load. Therefore, it becomes necessary to select components of the power receiving device in consideration of such a large current, which causes a problem of cost increase. In order to deal with this problem, it is preferable that the amount of current flowing through the load be constant regardless of the load impedance.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a power receiving device and a wireless power supply system that make the amount of current flowing through a power supply target constant regardless of the impedance of the power supply target.

A power receiving device according to an aspect of the present invention includes a power receiving coil that receives power transmitted from a power transmitting coil, a voltage-current conversion circuit that converts a voltage corresponding to the power received by the power receiving coil into a current, and a voltage-current conversion circuit. and a smoothing circuit for smoothing the output current of the rectifying circuit and supplying it to a power supply target.

According to this aspect, by providing the voltage-current conversion circuit, the voltage generated across the power receiving coil is converted into a current and supplied to the power supply target. Therefore, the receiving coil acts as a constant current source when viewed from the power supply target, and the amount of current flowing through the power supply target can be made constant regardless of the impedance of the power supply target.

In the above aspect, the voltage-current conversion circuit includes a first element having one end connected to the first terminal, and a second element having one end connected to the other end of the first element and the other end connected to the second terminal. , and a third element having one end connected to the other end of the first element and one end of the second element, and having the other end connected to the third terminal and the fourth terminal, the first element and the impedance of the third element may be zero, and the sum of the impedance of the second element and the impedance of the third element may be zero.

According to this aspect, the voltage-to-current conversion circuit can be composed of three passive elements. Therefore, compared to a configuration using a DC-DC converter, an active element, etc., for example, the power receiving device can be downsized and stabilized, and the cost can be reduced.

In the above aspect, where VL is the supply voltage to the power supply target and IL is the supply current to the power supply target, the absolute values of the impedances of the first to third elements are in the range of 10 to 50% of VL/IL, respectively. may be included.

According to this aspect, since the impedances of the first to third elements are designed in consideration of the voltage loss in the rectifier circuit and the smoothing circuit, the accuracy of controlling the current supplied to the power supply target is improved.

In the above aspect, the voltage-current conversion circuit includes a fourth element having one end connected to the first terminal and the other end connected to the second terminal, and a fourth element having one end connected to the first terminal and the other end connected to the third terminal. and a sixth element having one end connected to the second terminal and the other end connected to the fourth terminal, wherein the impedance of the fourth element and the fifth element may be zero, and the sum of the impedance of the fourth element and the impedance of the sixth element may be zero.

According to this aspect, the voltage-to-current conversion circuit can be composed of three passive elements. Therefore, compared to a configuration using a DC-DC converter, an active element, etc., for example, the power receiving device can be downsized and stabilized, and the cost can be reduced.

In the above aspect, if the supply voltage to the power supply object is VL and the supply current to the power supply object is IL, the absolute values of the impedances of the fourth to sixth elements are in the range of 10 to 50% of VL/IL, respectively. may be included.

According to this aspect, since the impedances of the fourth to sixth elements are designed in consideration of the voltage loss in the rectifier circuit and the smoothing circuit, the accuracy of controlling the current supplied to the power supply target is improved.

A wireless power supply system according to an aspect of the present invention includes the power receiving device described above, and a power transmitting device including a power transmitting coil and a power supply circuit that supplies power supply voltage to the power transmitting coil.

According to this aspect, since the power receiving device includes the voltage-current conversion circuit, the voltage generated across the power receiving coil is converted into a current and supplied to the power supply target. Therefore, power can be transmitted from the power transmitting device to the power receiving device while keeping the amount of current flowing through the power feeding target constant regardless of the impedance of the power feeding target.

Advantageous Effects of Invention According to the present invention, it is possible to provide a power receiving device and a wireless power supply system that make the amount of current flowing through a power supply target constant regardless of the impedance of the power supply target.

1 is a circuit diagram of a wireless power feeding system according to one embodiment of the present invention; FIG. 4 is a diagram for explaining functions of a voltage-current conversion circuit 23A; FIG. It is a figure which shows the structural example of 23 A of voltage current conversion circuits. It is a figure which shows the structural example of 23 A of voltage current conversion circuits. 4 is a diagram for explaining functions of a voltage-current conversion circuit 23B; FIG. It is a figure which shows the structural example of the voltage current conversion circuit 23B. It is a figure which shows the structural example of the voltage current conversion circuit 23B.

Embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that, in each figure, the same reference numerals have the same or similar configurations.

FIG. 1 is a circuit diagram of a wireless power feeding system according to one embodiment of the present invention. As shown in the figure, the wireless power feeding system 1 includes a power transmitting device 10 that transmits power and a power receiving device 20 that receives the power in a contactless manner.

The power transmission device 10 includes, for example, a power supply circuit 11, a power transmission coil 12, and a resonance capacitor 13.

The power supply circuit 11 generates an AC power supply voltage with a predetermined frequency (for example, several kHz to several hundred MHz) and supplies it to the power transmission coil 12 .

The power transmission coil 12 is, for example, a spirally wound coil, and is supplied with an AC power supply voltage from the power supply circuit 11 . The resonance capacitor 13 is connected in series with the power transmission coil 12 and forms a resonance circuit together with the power transmission coil 12 . The resonance circuit has a resonance frequency f expressed by f=1/2π√LC (Hz), where L is the inductance value of the power transmission coil 12 and C is the capacitance value of the resonance capacitor 13 .

The power receiving device 20 includes a power receiving coil 21 , a resonance capacitor 22 , a voltage-current conversion circuit 23A, a rectifying circuit 24 , a smoothing circuit 25 , and a power supply target 26 .

The power receiving coil 21 is, for example, a spirally wound coil, is magnetically coupled with the power transmitting coil 12 , and receives power transmitted from the power transmitting coil 12 . The resonance capacitor 22 is connected in series with the power receiving coil 21 and constitutes a resonance circuit together with the power receiving coil 21 . Power is transmitted from the power transmitting device 10 to the power receiving device 20 by the resonance of the resonant circuit on the power transmitting device 10 side and the resonant circuit on the power receiving device 20 side at the same resonance frequency (magnetic field resonance method).

The voltage-current conversion circuit 23A is provided between the power receiving coil 21 and the rectifier circuit 24, converts a voltage corresponding to the power received by the power receiving coil 21 into a current, and outputs the current. In this embodiment, the voltage-to-current conversion circuit 23A comprises three elements 230-232 forming a so-called T-shaped circuit. The details of the configuration of the voltage-current conversion circuit 23A will be described later.

The rectifier circuit 24 full-wave rectifies the AC current output from the voltage-current conversion circuit 23A and outputs DC power. Rectifier circuit 24 includes two sets of diodes 240, 241 and diodes 242, 243 connected in series with each other. These two sets of diodes 240, 241 and diodes 242, 243 are connected in parallel. Note that the circuit configuration of the rectifier circuit 24 is an example, and is not limited to this. For example, the rectifier circuit 24 may be a half-wave rectifier circuit.

The smoothing circuit 25 reduces variations in the output current of the rectifier circuit 24 and supplies the smoothed DC current to the power supply target 26 . The smoothing circuit 25 is a so-called L-type filter circuit composed of a coil 250 and a capacitor 251 .

The power supply target 26 is a target to which the DC power smoothed by the smoothing circuit 25 is supplied. The power supply target 26 is not particularly limited, but in this embodiment, it is assumed that electric power is stored in a storage device such as a battery or a capacitor, and a capacitor 260 is shown. Note that the power supply target 26 may be a load that consumes electric power, such as an actuator such as a motor, instead of the capacitor 260 . In addition, although FIG. 1 shows a configuration in which the power supply target 26 is included in the power receiving device 20 , the power supply target may not be included in the power receiving device 20 and may be provided outside the power receiving device 20 .

In this embodiment, electromagnetic induction between the power transmitting coil 12 and the power receiving coil 21 generates a voltage across the power receiving coil 21 , and power corresponding to the voltage is supplied to the power supply target 26 . Here, if the power receiving device 20 does not include the voltage-to-current conversion circuit 23A, the power receiving coil 21 acts as a constant voltage source when viewed from the power supply target 26, so the voltage is supplied to the power supply target 26 according to the impedance of the power supply target 26. The amount of current applied will be different. For example, when the impedance of the power supply object 26 is high, the amount of current flowing through the power supply object 26 is relatively small. Therefore, it becomes necessary to select the components of the power receiving device 20 in consideration of such a large current, which causes a problem of cost increase.

In this respect, the power receiving device 20 according to the present embodiment includes the voltage-current conversion circuit 23A, so that the voltage generated across the power receiving coil 21 is converted into current and supplied to the power supply target 26 . In other words, the receiving coil 21 behaves as a constant current source when viewed from the power supply target 26 . This point will be further explained with reference to FIG.

FIG. 2 is a diagram for explaining the function of the voltage-current conversion circuit 23A. Note that, in FIG. 2 , the resonance capacitor 22, the rectifier circuit 24, and the smoothing circuit 25 among the components of the power receiving device 20 are omitted for the sake of simplicity of explanation.

In the voltage-current conversion circuit 23A, the element 230 (first element) has one end connected to the first terminal T1 and the other end connected to one end of the element 231 . The element 231 (second element) has one end connected to the other end of the element 230 and the other end connected to the second terminal T2. The element 232 (third element) has one end connected to the other end of the element 230 and one end of the element 231, and the other end connected to the third terminal T3 and the fourth terminal T4.

The impedances of the elements 230 to 232 are Z1 to Z3, respectively, and the impedance of the power supply target 26 is ZL (hereinafter also referred to as "load impedance ZL"). Also, the voltage generated across the power receiving coil 21 is V1, the current flowing through the power receiving coil 21 is I1, the voltage applied across the power supply target 26 is VL, and the current flowing through the power supply target 26 is IL. The voltage VL and the current IL are also obtained as the supply voltage and supply current to the power supply object 26 defined as specifications.

First, the constants of the elements 230 to 232 are determined so that the sum of the impedance Z1 of the element 230 and the impedance Z3 of the element 232 is zero, and the sum of the impedance Z2 of the element 231 and the impedance Z3 of the element 232 is zero. That is, impedances Z1 to Z3 satisfy equations (1) and (2).

Also, the voltage V1 is expressed as follows using the current I1 and the current IL.

From the above formula (1), the formula (3) is transformed as follows.

From this, it can be seen that the current amount of the current IL flowing through the power supply target 26 is proportional to the magnitude of the voltage V1 generated in the receiving coil 21, and the voltage is converted into current by the voltage-current conversion circuit 23A.

Moreover, the absolute values of the impedances Z1 to Z3 are all determined to be equal to the absolute value of the load impedance ZL, and satisfy equation (5).

Here, the minimum value of load impedance ZL satisfies equation (6).

Since the current IL flows through the element 231, the impedance Z2 of the element 231 is determined by the equation (7) from the above equation (5).

From the equations (1), (2) and (7) above, the impedance Z1 of the element 230 and the impedance Z3 of the element 232 are determined by the equations (8) and (9), respectively.

As shown in FIG. 1, the actual power receiving device 20 includes the rectifier circuit 24 and the smoothing circuit 25 after the voltage-to-current conversion circuit 23A, and voltage loss occurs in these circuits. Therefore, in order to allow a desired current to flow through the power supply target 26, it is necessary to estimate the load impedance ZL lower.

Specifically, when the voltage loss in the rectifying circuit 24 and the smoothing circuit 25 is considered, the voltage applied across the power supply target 26 is VL _X (VL _X <VL). Assuming that the alternating current supplied to the rectifier circuit 24 is a sine wave, the forward voltage of the diode included in the rectifier circuit 24 (the voltage drop of the diode when the forward current flows) is Vf, and the smoothing circuit 25 Assume that the input/output voltage ratio of the smoothing circuit 25 at the input frequency is α (0<α<1). The root mean square (RMS) of the voltage VL _X is represented by the following equation (10).

For example, at the cutoff frequency of the smoothing circuit 25 (that is, the frequency at which the pass characteristic is -3 dB), the voltage ratio α is about 0.7. In general, since a sufficient amount of attenuation cannot be ensured at the cutoff frequency, high frequencies are often attenuated in a range of, for example, -6 dB to -20 dB of pass characteristics. Therefore, for example, the attenuation rate is 50 to 90% (α≈0.5 to 0.1%), including the range of ±20%, based on the point where the pass characteristic is -10 dB (attenuation rate 70%, α≈0.3). ) is preferably _used to set the impedances Z1 to Z3.

That is, the absolute values of impedances Z1-Z3 are preferably designed to fall within a range of 10-50% of design value VL/IL. This improves the accuracy of controlling the current supplied to the power supply target 26 . In the above equation (10), the forward voltage Vf of the diode is a negligibly small value if the diode has sufficient performance or if the voltage VL is sufficiently high.

3A and 3B are diagrams showing configuration examples of the voltage-current conversion circuit 23A. The voltage-to-current conversion circuit 23A is a CLC T-type circuit in which elements 230 and 231 are composed of capacitors C1 and C2, respectively, and element 232 is composed of a coil L1, as shown in FIG. 3A, for example. may Alternatively, as shown in FIG. 3B, the voltage-to-current conversion circuit 23A is an LCL T-type circuit in which the elements 230 and 231 are composed of coils L2 and L3, respectively, and the element 232 is composed of a capacitor C3. There may be.

When the voltage-current conversion circuit 23A is configured by a CLC T-type circuit, for example, the capacitor C1 and the resonance capacitor 22 may be collectively formed as one capacitor.

As described above, the power receiving device 20 includes the voltage-current conversion circuit 23A, so that the voltage generated across the power receiving coil 21 is converted into a current and supplied to the power supply target 26 . As a result, in the present embodiment, the receiving coil 21 behaves as a constant current source when viewed from the power supply target 26 . That is, according to the present embodiment, the amount of current flowing through the power supply object 26 can be made constant regardless of the impedance of the power supply object 26 .

Also, the voltage-current conversion circuit 23A is composed of three passive elements without using active elements. Therefore, the power receiving device 20 can be downsized and stabilized, and the cost can be reduced, compared to a configuration in which the current flowing through the power supply target is controlled to be constant using a DC-DC converter, an arithmetic device, or the like. can be done.

Furthermore, for example, when the power supply target 26 is a battery, if a constant voltage is applied to the battery in an empty state, there is a risk that a large amount of current will momentarily flow through the battery. In this regard, according to the present embodiment, generation of such a large current is suppressed, and the safety of the power receiving device 20 is improved.

In addition, the voltage-to-current conversion circuit 23A has a configuration in which a high-pass filter circuit and a low-pass filter circuit are combined. Therefore, according to the present embodiment, it is possible to block the noise received by the power receiving coil 21 from flowing into the power supply target 26 .

FIG. 4 is a diagram for explaining the function of a voltage-current conversion circuit 23B, which is another configuration example of the voltage-current conversion circuit. 4, the resonance capacitor 22, the rectifier circuit 24, and the smoothing circuit 25 are omitted from the components of the power receiving device 20, as in FIG. Also, in the following description, the description of matters common to the above-described embodiment will be omitted, and only the points of difference will be described. In particular, similar actions and effects due to similar configurations will not be mentioned sequentially for each embodiment.

The voltage-to-current conversion circuit 23B has three elements 233 to 235 forming a so-called π-type circuit. Specifically, the element 233 (fourth element) has one end connected to the first terminal T1 and the other end connected to the second terminal T2. The element 234 (fifth element) has one end connected to the first terminal T1 and the other end connected to the third terminal T3. The element 235 (sixth element) has one end connected to the second terminal T2 and the other end connected to the fourth terminal T4.

Let the impedances of the elements 233 to 235 be Z4 to Z6, respectively. First, the constants of the elements 233 to 235 are determined so that the sum of the impedance Z4 of the element 233 and the impedance Z5 of the element 234 is zero, and the sum of the impedance Z4 of the element 233 and the impedance Z6 of the element 235 is zero. That is, impedances Z4 to Z6 satisfy equations (11) and (12).

Moreover, the absolute values of the impedances Z4 to Z6 are all determined to be equal to the absolute value of the load impedance ZL, satisfying equation (13).

Since the voltage VL is applied across the element 235, the impedance Z6 of the element 235 is determined by the following formula (14) from the above formula (13).

From the above equations (11), (12) and (14), the impedance Z4 of the element 233 and the impedance Z5 of the element 234 are determined by the following equations (15) and (16) respectively.

As in the voltage-current conversion circuit 23A described above, the absolute values of the impedances Z4 to Z6 should be within the range of 10 to 50% of the design value VL/IL as calculated from the above equation (10). is preferably set to

5A and 5B are diagrams showing configuration examples of the voltage-current conversion circuit 23B. The voltage-to-current conversion circuit 23B is an LCL pi-type circuit in which the element 233 is composed of a capacitor C4 and the elements 234 and 235 are composed of coils L4 and L5, respectively, as shown in FIG. 5A, for example. may Alternatively, as shown in FIG. 5B, the voltage-to-current conversion circuit 23B is a CLC π-type circuit in which the element 233 is composed of a coil L6 and the elements 234 and 235 are composed of capacitors C5 and C6, respectively. There may be.

In this way, even when the power receiving device 20 includes the voltage-current conversion circuit 23B, it is possible to obtain the same effects as in the case of including the above-described voltage-current conversion circuit 23A.

The embodiments described above are for facilitating understanding of the present invention, and are not intended to limit and interpret the present invention. Each element included in the embodiment and its arrangement, materials, conditions, shape, size, etc. are not limited to those illustrated and can be changed as appropriate. Also, it is possible to partially replace or combine the configurations shown in different embodiments.

For example, in the power receiving device 20 described above, the power receiving coil 21 and the resonance capacitor 22 are connected in series, but the power receiving coil and the resonance capacitor may be connected in parallel. This also applies to the power transmission device 10 .

DESCRIPTION OF SYMBOLS 1... Wireless electric power feeding system 10... Power transmission apparatus 11... Power supply circuit 12... Power transmission coil 13... Resonance capacitor 20... Power receiving apparatus 21... Power receiving coil 22... Resonance capacitor 23A, 23B... Voltage current conversion circuit, 24 Rectifier circuit 25 Smoothing circuit 26 Power supply target 230 to 235 Elements 240 to 243 Diode 250 Coil 251 Capacitor 260 Capacitor C1 to C6 Capacitor L1 to L6 Coil , T1...first terminal, T2...second terminal, T3...third terminal, T4...fourth terminal

Claims (3)

a power receiving coil that receives power transmitted from the power transmitting coil;
a voltage-current conversion circuit that converts a voltage corresponding to the power received by the power receiving coil into a current;
a rectifier circuit that rectifies the output current of the voltage-current conversion circuit;
a smoothing circuit that smoothes the output current of the rectifier circuit and supplies it to a power supply target,
The voltage-current conversion circuit is
a first element having one end connected to a first terminal;
a second element having one end connected to the other end of the first element and the other end connected to a second terminal;
a third element having one end connected to the other end of the first element and one end of the second element and having the other end connected to a third terminal and a fourth terminal;
having a T-shaped circuit containing
The sum of the impedance of the first element and the impedance of the third element is zero, the sum of the impedance of the second element and the impedance of the third element is zero,
Assuming that the supply voltage to the power supply object is VL and the supply current to the power supply object is IL, the absolute values of the impedances of the first to third elements are included in the range of 10 to 50% of VL/IL, respectively. to be
Powered device. a power receiving coil that receives power transmitted from the power transmitting coil;
a voltage-current conversion circuit that converts a voltage corresponding to the power received by the power receiving coil into a current;
a rectifier circuit that rectifies the output current of the voltage-current conversion circuit;
a smoothing circuit that smoothes the output current of the rectifier circuit and supplies it to a power supply target,
The voltage-current conversion circuit is
a fourth element having one end connected to the first terminal and the other end connected to the second terminal;
a fifth element having one end connected to the first terminal and the other end connected to the third terminal;
a sixth element having one end connected to the second terminal and the other end connected to the fourth terminal;
has a π-type circuit containing
The sum of the impedance of the fourth element and the impedance of the fifth element is zero, and the sum of the impedance of the fourth element and the impedance of the sixth element is zero.
Assuming that the supply voltage to the power supply object is VL and the supply current to the power supply object is IL, the absolute values of the impedances of the fourth to sixth elements are each included in the range of 10 to 50% of VL/IL. to be
Powered device. The power receiving device according to claim 1 or 2 ;
a power transmission device including the power transmission coil and a power supply circuit that supplies power supply voltage to the power transmission coil;
Wireless power supply system.

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