JP7637970B2 - Wireless power supply device - Google Patents

Description

The present invention relates to a wireless power supply device. In particular, the present invention relates to a device that wirelessly supplies power to an electric body on a road surface within a wireless power supply area using electric field coupling, regardless of the position of the electric body.

It is known that in wireless power transfer technology, the efficiency of power transfer decreases due to standing waves of the transmitted power generated in power transmitters such as electrodes and coils in infrastructure facilities. In particular, when supplying power to a power receiver attached to a moving electric vehicle, it is important to be able to supply power without depending on the relative positions of the power receiver and power transmitter.

Wireless power supply technologies that use electric field coupling include the following:

For example, Patent Documents 1 and 2 disclose the structure of a power transmission electrode for planar power supply (hereinafter sometimes referred to as "two-dimensional power supply"). However, they do not take into consideration the effect of a decrease in power supply due to standing waves generated in the power transmission electrode.

In addition, Non-Patent Documents 1 and 2 show systems for power supply while moving. In Non-Patent Document 1, standing waves can be cancelled by inserting a so-called left-handed circuit in the middle of the power transmission electrode at a constant interval with respect to the wavelength of the wave of the transmitted power, thereby making it possible to maintain the power supply at a constant level. Furthermore, Non-Patent Document 2 shows a system in which the phase of the standing wave is changed according to the position of the electric body by terminating the transmission line including the power transmission electrode using a variable reactance.

Non-Patent Documents 1 and 2 solve the problems of power transfer while moving, namely the decrease in power transmission efficiency and the increase in reflected power due to standing waves, but Non-Patent Document 1 has a problem that the number of so-called left-handed circuits required to be inserted increases as the power transmission electrode becomes longer, which leads to the complication of the wireless power transfer system and increased costs. Also, Non-Patent Document 2 has a problem that the variably controlled termination reactance is constantly required during wireless power transfer, which leads to the complication of the wireless power transfer system and increased costs.

JP 2016-32425 A JP 2020-43686 A

Yoshiteru Suzuki and 5 others, "Right-hand and left-hand hybrid electrified road for battery-less electric carts running continuously with power supply," IEICE Transactions on Information and Communication Engineers, vol.J99-C, no.4, pp.133-141, Mar.2016. Sonshu Sakihara, and 3 others, “Far-end reactor matching to a traveling load along an RF power transmission line,” IEICE Trans. Electron., vol.E101-A, no.2, pp.396-401, Feb. 2018.

The present invention has been made in consideration of the above-mentioned problems related to wireless power supply, and aims to provide a wireless power supply device that supplies power to an electric body with high efficiency regardless of the relative positions of an electric body equipped with a power receiver and a power transmitter.

A first wireless power supply device according to the present invention is a wireless power supply device that transmits power in a non-contact manner to an electric body that moves along a power transmitting electrode,
A power source for supplying high frequency power, a gyrator, and at least four power receiving electrodes;
At least four power transmitting electrodes using transmission lines;
The power transmitting electrode has a physical length that is a positive integer multiple of half the wavelength of the wave of the power to be transmitted, and the power transmitting electrode is of two types, the ends of which are appropriately open or short-circuited;
The gyrator is mounted between the high frequency power source and the power transmitting electrode whose end is short-circuited,
The input impedance of the power transmitting electrode is changed from a short circuit to an open circuit.

The second wireless power supply device according to the present invention is the first wireless power supply device according to the present invention, characterized in that the power received by the power receiving electrode is combined using at least four electrodes.

A third wireless power supplying device according to the present invention is the first and second wireless power supplying devices according to the present invention,
a first matching circuit that is installed between the high frequency power source and the start ends of at least four of the power transmitting electrodes;
a second matching circuit that is connected between the power transmitting electrode having an open end and a first load that is connected to the open end;
a third matching circuit that is loaded between the power transmitting electrode whose end is short-circuited and a second load connected to the end;
The second and third matching circuits of the matching circuits are characterized in that they are configured with the same inductor element and capacitor element.

According to the wireless power supply device of the present invention, it is possible to transmit power with high efficiency without being affected by the fluctuation of the transmitted power. Furthermore, since the circuit configuration does not require active elements or complex control circuits and control software, it is possible to implement a wireless power supply device that operates stably at low cost.

1 is a schematic diagram showing an embodiment of a wireless power supply device according to the present invention; FIG. 2 is a schematic diagram showing a matching circuit according to the present invention. 1 is a Smith chart showing a change in input impedance depending on a ratio (conversion ratio) of a capacitor and an inductor of a gyrator in an embodiment of a wireless power supply device according to the present invention. FIG. 2 is a schematic diagram of a circuit topology for performing impedance matching of two ports with an input and a short-circuit termination in one embodiment of a wireless power supply device according to the present invention. 5 is a graph showing simultaneous impedance matching of two ports by matching circuits on the input side and the output side in one embodiment of a wireless power supply device according to the present invention. FIG. 2 is a schematic diagram of a circuit topology for impedance matching with an input and open and short-circuit terminations in one embodiment of a wireless power supply device according to the present invention. 1 is a schematic diagram showing an embodiment in which the positions of the start ends of transmission lines used in power transmitting electrodes in a wireless power supply device according to the present invention are not aligned. FIG. FIG. 1 is a schematic diagram showing an embodiment in which a phase adjustment circuit is used in a wireless power supply device according to the present invention. 11 is a graph showing the results of a physical simulation regarding the position dependency of power transmission efficiency by a wireless power supply device according to the present invention. 11 is a graph showing the results of a physical simulation regarding the position dependency of power reflection rate by a wireless power supply device according to the present invention.

Embodiments of the present invention will be described below with reference to the drawings. However, the drawings used in the description and the following description are provided to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

By preparing power transmission lines (power transmission electrodes) with different termination conditions or lengths, the position where the node of the standing wave of the transmitted power wave occurs is moved. By arranging a power receiving electrode on each of the power transmission transmission lines to receive power, wireless power supply that avoids the influence of the nodes of the transmitted power wave can be realized. In this case, there is no need to control the variable termination conditions.

Figure 1 shows an overview of the wireless power supply device according to the present invention.

The wireless power supply device according to the present invention is composed of a power source, a gyrator, four receiving electrodes, and a power transmission line with open or short termination. In this wireless power supply device, an electric body equipped with a receiving electrode is placed on a power transmission line with a physical length of nλ/2, where n is a natural number and the wavelength of the wave of the transmitted power is λ. At this time, a standing wave is generated on the transmission line according to the wavelength of the transmitted power. The shape of the standing wave differs depending on the termination condition; under open termination conditions, the node of the power wave is in the center of the transmission line, while under short termination conditions, the node of the power wave is generated at both ends of the transmission line.

The reflection rate of transmitted power is the ratio of the power reflected back to the power source to the transmitted power (input power). A large reflected power not only reduces the power transmission efficiency, but can also cause the power source to fail. Therefore, it is necessary to keep the power reflection rate low.

This physical simulation uses a transmission line with different termination conditions, a gyrator, and four receiving electrodes. The gyrator is loaded on the input section of the transmission line with a short-circuit termination, and serves to change the input impedance of the transmission line from short-circuit to open. This suppresses the occurrence of overcurrent due to a virtual short circuit at the input section of the transmission line on the short-circuit termination side.

The electric field distribution that occurs on a power transmission line generates a standing wave node in the center of the line at an open termination, and a standing wave node at the end of the line at a short termination.

When the electric body is located in the center of the transmission line, the power transmission efficiency decreases due to the nodes of the standing wave that occur on the open-ended transmission line. On the other hand, on a short-ended transmission line, the standing wave that occurs becomes an antinode. Therefore, the received power is combined from the four receiving electrodes. By combining the received power, the effect of the nodes of the standing wave that occur is reduced.

Figure 2 shows the matching circuit according to the present invention. Three matching circuits are required: one on the power transmission side, one on the open termination side, and one on the short termination side (hereinafter referred to as the first, second and third matching circuits). The matching circuits are loaded for impedance matching, assuming that a port with a resistance value of 50 Ω and a power source are installed on the power transmission/reception electrode, and a 50 Ω load is installed on the other end of the power transmission electrode opposite the power source side (i.e., the termination).

The matching circuit must be designed for each termination condition. The second matching circuit for open termination is designed based on the results of a physical simulation in which the electric body, i.e., the receiving electrode, is placed at a corner of the power transmission line. The third matching circuit for short termination is designed based on the results of a physical simulation in which the electric body, i.e., the receiving electrode, is placed in the center of the power transmission line.

The design steps for a matching circuit are as follows:

Step 1: Place the receiving electrode at the antinode of the power standing wave for open and short circuit termination conditions.

Step 2: Adjust the gyrator element values to match the input impedance for each termination condition.

Step 3: Simultaneous impedance matching of two ports under one termination condition.

Step 4: Load a matching circuit on the other receiving electrode to determine the position dependence of the power transfer efficiency.

Conventionally, high-frequency circuit networks have one input port and two output ports, requiring simultaneous impedance matching of three ports, but by following the steps above, a matching circuit designed with simultaneous impedance matching of two ports can be used, eliminating the need for simultaneous impedance matching of three ports. The same is true when there are three or more loads, and a matching circuit can be designed by performing simultaneous impedance matching of two ports.

As shown in Fig. 3, when the influence of inductance occurring at the short-circuited portion of the short-circuit termination cannot be ignored, the influence can be suppressed by adjusting the conversion ratio of the gyrator. The conversion ratio of the gyrator is the ratio between the characteristic impedance _Zc of the power transmission line and the reactance value of the inductor L and capacitor C mounted on the gyrator. In the embodiment according to the present invention, the conversion ratio is designed to be 1 in order to reduce the inductance.

Figure 4 shows a model for designing an impedance matching circuit with two input and two output ports. This model can be used as is even when expanding to three input and three output ports.

Figure 5 shows the calculation results for the impedance matching circuit shown in Figure 4. The matching state can be confirmed by the fact that S21, which represents the transmitted power, is high and S11, which represents the reflected power, is low.

By simultaneously matching the impedance of two ports in step 3 above, a power transmission efficiency of 99.1% was achieved.

In FIG. 6, the second and third matching circuits loaded at the open and short terminations are identical matching circuits with the same topology and the same element values.

In the above embodiment, both ends of all the transmitting electrodes are aligned and placed within a single virtual rectangle. However, as shown in FIG. 7, if the nodes of the standing waves of all the transmitting powers are in the same position, the start positions of the open-ended transmitting transmission lines may be shifted and placed within a single virtual parallelogram. Two open-ended transmission lines are treated as one pair, and multiple pairs are arranged in parallel with their positions shifted. In this way, the transmitting and receiving devices are coupled with a constant electric field strength regardless of the position of the electric body (receiver). In other words, fluctuations in transmission efficiency can be suppressed.

Furthermore, as shown in Figure 8, the same effect can be obtained by inserting a phase adjustment circuit instead of a matching circuit at the input/output stage of the power transmission line. The same effect can also be obtained by terminating with any phase adjustment circuit (e.g., a capacitor or inductor). Of the phase adjustment circuits close to the power source, the phase adjustment circuit located at the top in Figure 8 corresponds to the transmission line at the short-circuit end of the power transmission electrode in the wireless power supply device of the present invention, and the phase adjustment circuit located at the bottom in the figure corresponds to the gyrator in the wireless power supply device of the present invention.

The power transmission efficiency is defined as the ratio of the combined power P _out2 +P _out3 of the output power P _out2 to the load at the open termination and the output power P _out3 to the load at the short termination to the input power P _in . Figure 9 shows the results of a physical simulation regarding the position dependency of the power transmission efficiency by the wireless power supply device according to the present invention. It is shown that the wireless power supply device according to the present invention can stably transmit 95% or more of power regardless of the position of the electric body equipped with the power receiver.

Figure 10 shows the results of a physical simulation of the position dependency of the power reflection rate of the wireless power supply device according to the present invention. In the wireless power supply device according to the present invention, the power reflection rate is suppressed to within 5% regardless of the position of the electric body equipped with the receiver, and together with the results of Figure 9, it is clear that power can be transmitted with high efficiency.

Claims (3)

A wireless power supply device that transmits power in a non-contact manner to an electric body that moves along a power transmission electrode,
A power source for supplying high frequency power, a gyrator, and at least four power receiving electrodes;
At least four power transmitting electrodes using transmission lines;
The power transmitting electrode has a physical length that is a positive integer multiple of half the wavelength of the wave of the power to be transmitted, and the power transmitting electrode is of two types, the ends of which are appropriately open or short-circuited;
The gyrator is mounted between the high frequency power source and the power transmitting electrode whose end is short-circuited,
A wireless power supply device, characterized in that the input impedance of the power transmission electrode is changed from a short circuit to an open circuit. The wireless power supply device according to claim 1, characterized in that the power received by the power receiving electrode is combined using at least four electrodes. a first matching circuit that is installed between the high frequency power source and the start ends of at least four of the power transmitting electrodes;
a second matching circuit that is connected between the power transmitting electrode having an open end and a first load that is connected to the open end;
a third matching circuit that is loaded between the power transmitting electrode whose end is short-circuited and a second load connected to the end;
3. The wireless power supply device according to claim 1, wherein the second and third matching circuits of the matching circuits are configured with the same inductor element and capacitor element.

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