Magnetic resonance wireless power transfer device

Abstract

[Problem] To enable stable transmission of substantially constant electric power even when the transmission distance varies in a PT-symmetric wireless power transfer device. [Solution] Provided is a magnetic resonance wireless power transfer device configured such that PT symmetry is maintained between a transmitting-side circuit 100, in which a self-excited oscillating inverter 120 is connected to a transmitting-side resonant circuit 110, and a receiving-side circuit 200, in which a load RL is connected to a receiving-side resonant circuit 210, wherein the transmitting-side circuit 100 has a built-in filtering circuit 130 comprising a frequency-to-voltage converter circuit 131 that converts the oscillation frequency of the inverter 120 into a voltage and outputs the voltage, a voltage limiter circuit 133 that cuts the portion of the voltage outputted from the frequency-to-voltage converter circuit 131 that is not within a prescribed range, and a voltage control oscillator 134 that converts the voltage outputted from the voltage limiter circuit 133 into a frequency proportional to said voltage and outputs the frequency to the inverter 120, and the inverter 120 is configured not to oscillate outside a prescribed frequency range.

Description

Magnetic resonance type wireless power supply device

[0001] The present invention relates to a magnetic resonance type wireless power feeder that feeds power in a contactless manner by magnetically resonating a power feeding coil and a power receiving coil.

[0002] Wireless power feeders that supply power to electronic devices in a non-contact (wireless) manner without using a power cord, etc. Known power feed methods for wireless power feeders include electromagnetic induction and magnetic resonance.

[0003] In an electromagnetic induction-based wireless power transfer device, power is transferred from the power transfer coil to the power receiving coil by passing an alternating current through a power transfer coil, which changes the magnetic flux passing through the power transfer coil, thereby changing the magnetic flux passing through a power receiving coil located near the power transfer coil and causing an induced current to flow through the power receiving coil. However, as shown in Figure 1(a), electromagnetic induction-based wireless power transfer devices have the disadvantage that the transmitted power decreases significantly as the transmission distance increases. For this reason, while the electromagnetic induction method can be adopted for applications in which a power receiving device incorporating a power receiving coil can be placed in close proximity to a power transfer device incorporating a power transfer coil (such as charging a mobile terminal), it has been difficult to adopt the electromagnetic induction method for applications in which the power receiving device cannot be placed in close proximity to the power transfer device (such as charging an electric vehicle).

[0004] In contrast, a magnetic resonance wireless power feeder includes a power feeder resonant circuit including a power feeder coil and a power receiver resonant circuit including a power receiver coil with the same resonant frequency. An AC magnetic field generated when an AC current flows through the power feeder coil resonates the power feeder resonant circuit and the power receiver resonant circuit, thereby transmitting power. Compared to an electromagnetic induction wireless power feeder, a magnetic resonance wireless power feeder has the advantage of being able to transmit power with high efficiency even over long transmission distances. However, as shown in FIG. 1( b ), a magnetic resonance wireless power feeder has the disadvantage that the transmitted power drops significantly if the transmission distance deviates from the peak of the transmitted power. Therefore, a magnetic resonance wireless power feeder has the problem that highly efficient power transmission is not possible unless the power receiver device is accurately positioned relative to the power feeder device.

[0005] As described above, although there is a difference between the electromagnetic induction method and the magnetic resonance method in the transmission distance over which power can be transmitted with high efficiency, they are the same in that the power receiving device cannot be moved relative to the power transmitting device. This defeats the original purpose of wireless power transmission. In a wireless power supply device using the magnetic resonance method, it is theoretically possible to maintain a constant transmission power regardless of the transmission distance by using a computer or the like for control, but other problems arise, such as the need for a high-performance computer and increased power consumption.

[0006] In light of this situation, a magnetic resonance wireless power feeder based on the principle of PT (Parity-Time) symmetry has been proposed in recent years (see Non-Patent Document 1) and has attracted attention. Here, PT symmetry refers to a combination of two symmetries: spatial inversion symmetry, which means that the laws of physics do not change even when spatial coordinates are inverted, and time reversal symmetry, which means that the laws of physics do not change even when the direction of time is inverted. Hereinafter, a magnetic resonance wireless power feeder based on the principle of PT symmetry will be referred to as a "PT-symmetric wireless power feeder," and a magnetic resonance wireless power feeder that is not based on the principle of PT symmetry will be referred to as a "non-PT-symmetric wireless power feeder."

[0007] 2 shows an example of the circuit configuration of a PT symmetrical type wireless power feeder. As shown in FIG. 2, the PT symmetrical type wireless power feeder is composed of a power feeding side device and a power receiving side device. The power feeding side device is provided with a circuit in which a power feeding side resonant circuit 110 is connected to an inverter 120, and the power receiving side device is provided with a load R Ｌ A circuit is provided in which a power receiving-side resonant circuit 210 is connected to a load (such as a battery or a motor that consumes power). A self-oscillating inverter (called a "self-oscillating inverter") is used as the inverter 120. The power supplying-side resonant circuit 110 and the power receiving-side resonant circuit 210 are configured by combining a coil and a capacitor. In all of Figures 2(a) to 2(c), the power supplying-side resonant circuit 110 has a coil and a capacitor connected in series, and while there is no difference in the power supplying-side resonant circuit 110, the power receiving-side resonant circuit 210 is different.

[0008] That is, in the power receiving side resonant circuit 210 shown in FIG. 2(a), a coil and a capacitor are connected in parallel. Also, in the power receiving side resonant circuit 210 shown in FIG. 2(b), a coil and a capacitor connected in series are connected in parallel to another capacitor. Furthermore, in the power receiving side resonant circuit 210 shown in FIG. 2(c), a coil and a capacitor are connected in series. The circuit configuration shown in FIG. 2(a) is called an "S-P topology," the circuit configuration shown in FIG. 2(b) is called an "S-SP topology," and the circuit configuration shown in FIG. 2(c) is called an "S-S topology."

[0009] Whether to adopt the S-P topology (FIG. 2(a)), S-SP topology (FIG. 2(b)), or S-S topology (FIG. 2(c)) depends on the application of the wireless power supply device. When a self-oscillating inverter is used to configure a PT symmetric wireless power supply device, immittance conversion is performed in the S-P topology (FIG. 2(a)) and S-SP topology (FIG. 2(b)), whereas immittance conversion is not performed in the S-S topology (FIG. 2(c)). That is, in the S-S topology (FIG. 2(c)), when a constant voltage power supply is used to supply power to the inverter, the load RＬ A constant voltage is supplied to the power supply. Therefore, in applications where power is supplied at a constant voltage and received at a constant voltage (such as an application for charging an electric vehicle), the S-S topology (Figure 2(c)) is the basis.

[0010] The principles of a PT symmetric wireless power feeder are explained in detail in the above-mentioned Non-Patent Document 1 as well as Patent Document 1, and therefore a detailed explanation of the principles will be omitted in this application. However, power is transmitted from a power feeding device to a power receiving device by the interaction (resonance) between the power feeding resonant circuit 110 and the power receiving resonant circuit 210. In this PT symmetric wireless power feeder, the oscillation frequency is automatically adjusted so that the transmitted power is always kept constant even when the transmission distance changes. Therefore, as shown in FIG. 1(c), high transmitted power can be obtained over a wide range of transmission distances without incorporating a computer as described above. The property of a wireless power feeder that allows transmitted power to be kept constant even when the transmission distance changes is called "robustness."

[0011] Japanese Patent Application Laid-Open No. 2022-121324

[0012] S. Assawaworrarit, X. Yu, and S. Fan, “Rоbust wireless power transfer using a nonlinear parity-time symmetric circuit” Nature, 546, 387 (2017)

[0013] However, in a PT symmetric type wireless power feeder, the inverter operates at a frequency ω ｈ The self-oscillation mode and the frequency ω ｌ In the following equations 1 and 2, ０ is the resonant frequency of the power supply resonant circuit and the power receiving resonant circuit, κ is the coupling rate between the couplers, and Γ ２０ is the intrinsic loss rate of the receiving resonant circuit, and Γ Ｌ is the load loss rate.

[0014] These frequencies ωｈ , ω ｌ The relationship between the frequency ω and the transmission distance is shown in Figure 3. ｈ is the resonant frequency ω ０ is higher than the frequency ω ｌ is the resonant frequency ω ０ In order to perform highly efficient power transmission in a PT symmetric wireless power transfer device, the above PT symmetry must be maintained. ｈ and frequency ω ｌ and the resonant frequency ω ０ However, this PT symmetry is not preserved even if the transmission distance becomes infinitely long, and is no longer preserved once a certain transmission distance (critical transmission distance) is exceeded. In order to achieve highly efficient power transmission with a PT symmetric wireless power transfer device, power transmission must be performed within the critical transmission distance.

[0015] However, in a PT symmetric type wireless power feeder, even if power is transmitted within the critical transmission distance, as shown in FIG. 4, the oscillation frequency is ｈ and frequency ω ｌ 3(d) in Non-Patent Document 1, the oscillation frequency changes from ω ｌ From ω ｈ As in Non-Patent Document 1, when the transmission power is as small as 0.01 W, the oscillation frequency is switched to the frequency ω ｌ and frequency ω ｈ Even if the oscillation frequency is switched between 1000 and 2000 Hz, no major problems will occur in terms of hardware. However, when the transmission power is large, if such a switch in the oscillation frequency occurs, the inverter's switching frequency will change suddenly, causing a short-circuit current to flow through the inverter, which may damage the switching elements (field-effect transistors, etc.) that make up the inverter. Even if no damage occurs, the transmission power will fluctuate every time the oscillation frequency is switched, which will defeat the original purpose of the wireless power supply device.

[0016] As shown in FIG. ｈ and frequency ωｌ The region where the difference between the frequency and the frequency is small is an unstable region where the above-mentioned switching of the oscillation frequency can occur frequently. However, this unstable region is a region of high utility value in terms of application, as long as the switching of the oscillation frequency can be suppressed. This is because this region has a long transmission distance and a small range of frequency fluctuation relative to the transmission distance. In addition, in Japan, the Radio Law stipulates that the frequency band that can be used for wireless power supply is 79 to 90 kHz, and the frequency ω in Figure 4 ａ (The frequency ω when the transmission distance is shortest in the unstable region ｈ The value of ω is 90 kHz, and the resonant frequency ω ０ In this application, in order to use a highly useful range for power transmission, it is necessary to reliably prevent the oscillation frequency from switching in this range.

[0017] In this regard, one possible way to prevent the oscillation frequency from switching is to incorporate a high-pass filter into the inverter to reduce the resonant frequency ω ０ In other words, as shown in FIG. 5(a), when the oscillation frequency is within the range of the resonant frequency ω ０ By filtering the region where the frequency is lower than ０ However, since the gain of a high-pass filter has a frequency gradient, in an actual high-pass filter, the threshold (resonant frequency ω ０ ) cannot be clearly filtered, and as shown in Figure 5(b), the threshold (resonant frequency ω ０ ) filtering becomes ambiguous near this frequency. For this reason, this method cannot reliably prevent switching of the oscillation frequency. In addition, when a high-pass filter is incorporated, a phase difference occurs in the waveforms on the input and output sides of the high-pass filter. This phase difference causes a change in the inverter's output power, defeating the original purpose of the wireless power transfer device.

[0018] The present invention has been made to solve the above-mentioned problems, and provides a PT symmetrical wireless power feeder that prevents switching of the oscillation frequency and maintains a frequency ω ｈ and frequency ω ｌ It is an object of the present invention to stably oscillate at a desired frequency and to stably transmit a substantially constant amount of power. Another object of the present invention is to provide a power supply circuit for use in the magnetic resonance type wireless power feeder.

[0019] The above problem is solved by providing a magnetic resonance type wireless power feeder configured to preserve PT symmetry between a power feed circuit in which a self-oscillating inverter is connected to a power feed resonant circuit including a power feed coil, and a power receiving circuit having a power receiving resonant circuit including a power receiving coil, wherein the power feed circuit is equipped with a filtering circuit including: a frequency-voltage conversion circuit that converts the oscillation frequency of the inverter into a voltage proportional to the oscillation frequency and outputs the voltage; a voltage limiting circuit that cuts out voltages that are not within a predetermined range from the voltages output from the frequency-voltage conversion circuit, while outputting voltages that are within the predetermined range as is; and a voltage-controlled oscillator that converts the voltage output from the voltage limiting circuit into a frequency proportional to the voltage and outputs the voltage to the inverter, preventing the inverter from oscillating outside the predetermined frequency range.

[0020] As already mentioned, in the method of directly filtering the inverter's oscillation frequency by incorporating a high-pass filter in the inverter, it is difficult to clearly filter the oscillation frequency at the target frequency (threshold). In contrast, in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention, the inverter's oscillation frequency is not directly filtered, but the oscillation frequency is first converted to a voltage, filtered, and then converted back to frequency. It is easy to clearly filter the voltage at the threshold. For example, by using a Zener diode, a reference voltage diode, a shunt regulator, an ideal diode, or the like, it is possible to clearly filter the voltage with the threshold voltage as a boundary. Therefore, even if the relative position of the receiving-side resonant circuit with respect to the supplying-side resonant circuit changes, such as when the transmission distance changes, switching of the inverter's oscillation frequency is prevented, and the above frequency ω ｈ and frequency ω ｌ Therefore, even if the relative position of the power receiving side resonant circuit with respect to the power supply side resonant circuit changes, the transmitted power can be kept approximately constant.

[0021] However, in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention, if the voltage waveform and current waveform of the frequency signal (oscillating frequency of the inverter) input to the inverter are perfectly aligned in phase, power loss in the switching elements (field effect transistors, etc.) constituting the inverter increases. Furthermore, the switching elements may generate heat, potentially damaging the inverter. These problems are particularly likely to occur when the transmission power is large.

[0022] To prevent such problems from occurring, it is necessary to create a state in which the phase of the voltage waveform of the frequency signal (oscillating frequency of the inverter) input to the inverter slightly leads the phase of the current waveform (this state is called an "inductive state") and achieve soft switching (this soft switching is also called zero voltage switching (ZVS)). For this reason, in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention, it is preferable to incorporate a phase shift circuit in the power feed side circuit that shifts the phase so that the voltage waveform of the frequency signal input to the inverter leads the current waveform of the same frequency signal. This creates an inductive state and makes it possible to achieve soft switching.

[0023] However, as the oscillation frequency of the inverter, the above frequency ω ｌ In order to simultaneously achieve preservation of PT symmetry and soft switching in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention, the frequency ω ｌ Instead, the frequency ω ｈ Therefore, in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention, it is preferable that the voltage limiting circuit cuts off voltages that do not reach a predetermined threshold voltage, while outputting voltages equal to or greater than the threshold voltage as they are. As a result, for example, the threshold voltage can be set to a value that is smaller than the resonant frequency ω ０ If the value is set to a value corresponding to the inverter oscillation frequency, the frequency ω ｈ can be reliably selected.

[0024] Incidentally, in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention, it is preferable to use a phase-locked loop circuit (PLL circuit) as the filtering circuit. This is because a PLL circuit includes many of the elements necessary to configure a filtering circuit. That is, PLL circuits are known that include a phase detector (PFD) that detects the phase difference between two output signals, a charge pump (CP) that converts the phase difference detected by the phase detector into a voltage and outputs it, and a voltage-controlled oscillator (VCO) that converts the voltage into a frequency proportional to the voltage and outputs it. The phase detector and charge pump in the PLL circuit can function as a frequency-to-voltage conversion circuit in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention, and the voltage-controlled oscillator in the PLL circuit can function as a voltage-controlled oscillator in the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention.

[0025] Furthermore, in a PLL circuit, the output (frequency) from the voltage-controlled oscillator is negatively fed back to the phase detector, thereby aligning the phase of the signal (frequency) input to the PLL circuit with the phase of the signal (frequency) output from the PLL circuit, thereby synchronizing these signals. Therefore, using a PLL circuit in a filtering circuit can also prevent the output power of the inverter from changing. Furthermore, even though the input signal and the output signal are the same in a PLL circuit, the output signal is generated by the voltage-controlled oscillator, and therefore the input signal and the output signal are electrically separated. Therefore, noise contained in the input signal can also be removed. In addition, because PLL circuits are very inexpensive, using a PLL circuit can also reduce the manufacturing cost of the magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder) of the present invention.

[0026] As described above, according to the present invention, in a PT symmetrical wireless power feeder, even if the relative position of the power receiving side resonant circuit with respect to the power supply side resonant circuit changes due to a change in the transmission distance or the like, the switching of the oscillation frequency is prevented, and the frequency ω ｈand frequency ω ｌ It is possible to stably oscillate at the desired frequency and stably transmit a substantially constant amount of power. It is also possible to provide a power supply circuit for use in the magnetic resonance type wireless power supply device.

[0027] 1 is a graph showing the relationship between transmission distance and transmission power in (a) an electromagnetic induction type wireless power feeder, (b) a magnetic resonance type (non-PT symmetric type) wireless power feeder, and (c) a magnetic resonance type (PT symmetric type) wireless power feeder. It is a diagram showing circuit configuration examples of a PT symmetric type wireless power feeder, each showing (a) an S-P topology, (b) an S-SP topology, and (c) an S-S topology. It is a graph showing the relationship between transmission distance and transmission power in (a) an electromagnetic induction type wireless power feeder, (b) a magnetic resonance type (non-PT symmetric type) wireless power feeder, and (c) a magnetic resonance type (PT symmetric type) wireless power feeder. It is a diagram showing circuit configuration examples of a PT symmetric type wireless power feeder, each showing (a) an S-P topology, (b) an S-SP topology, and (c) an S-S topology. ｈ and frequency ω ｌ 1 is a graph showing the relationship between the frequency and the transmission distance in a PT symmetric type wireless power feeder. ｈ and frequency ω ｌ 1 is a diagram illustrating a state in which the inverter oscillation frequency is switched between (a) an ideal state and (b) an actual state after filtering the inverter oscillation frequency. FIG. 2 is a diagram illustrating an example of an electric circuit of a magnetic resonance type wireless power feeder according to the present invention. FIG. 3 is a diagram illustrating an example of the configuration of a filtering circuit. FIG. 4 is a graph illustrating the relationship between the input voltage and the output voltage of a voltage limiting circuit. Ｌ ) and the voltage detected by the shunt resistor (V ｉｎ ) and the voltage detected by the super-barrier rectifier diode (V ＳＢＲ ) is a graph showing the relationship between

[0028] 1. Overview of the Magnetic Resonance-Type Wireless Power Supply Apparatus Preferred embodiments of the magnetic resonance-type wireless power supply apparatus of the present invention will be described in more detail with reference to the drawings.

[0029] Fig. 6 is a diagram showing an example of an electric circuit of a magnetic resonance type wireless power feeder according to the present invention. As shown in Fig. 6, the magnetic resonance type wireless power feeder of this embodiment includes a power feeding circuit 100 and a power receiving circuit 200. The power feeding circuit 100 is provided in a power feeding side device, and the power receiving side circuit 200 is provided in a power receiving side device. The specific specifications of the power feeding side device and the charging side device vary depending on the application of the magnetic resonance type wireless power feeder, etc. The magnetic resonance type wireless power feeder of this embodiment is intended for use in wireless charging of electric vehicles, and a charging stand is assumed as the power feeding side device and an electric vehicle is assumed as the power receiving side device.

[0030] The power supplying device 100 includes a power supplying resonant circuit 110 , an inverter 120 , a filtering circuit 130 , and a phase shift circuit 140 .

[0031] The power supply side resonant circuit 110 is a power supply side coil (L １ ) and the power supply capacitor (C １ ) are connected in series. The power supply side resonant circuit 110 interacts (resonates) with a power receiving side resonant circuit 210 (described later) to wirelessly transmit power to the power receiving side circuit 200.

[0032] The inverter 120 is a self-excited inverter including a gate driver 121 and two switching elements (two field effect transistors (FET1 and FET12) in this embodiment). The inverter 120 receives an input signal S １０ In response to this, a signal S is input to the gates of FET1 and FET2. １１ , S １２ By switching the DC voltage (V ＣＣ In the magnetic resonance type wireless power feeder of this embodiment, the inverter 120 is used as a constant voltage source.

[0033] The filtering circuit 130 filters the input signal S (oscillation frequency of the inverter 120) to the inverter 120 so that the inverter 120 does not oscillate outside a predetermined frequency range. １０The filtering circuit 130 is provided on a path that detects the AC current flowing through the power supply side resonant circuit 110 and provides positive feedback to the input side of the inverter 120. The AC current flowing through the power supply side resonant circuit 110 is detected by a current detection circuit 150.

[0034] The phase shift circuit 140 receives the frequency signal S ２６ and the frequency signal S １０ (the oscillation frequency of the inverter 120), an inductive state is created in which the phase of the voltage waveform leads the phase of the current waveform.

[0035] On the other hand, the power receiving side circuit 200 includes a power receiving side resonant circuit 210, an AC-DC converter 220, a DC-DC converter 230, and a load (R Ｌ ) and is equipped with.

[0036] The power receiving side resonant circuit 210 is connected to the power supply side coil (L ２ ) and the power supply capacitor (C ２ ) are connected in series. １ ) and the power supply capacitor (C １ ) are also connected in series, the magnetic resonance type wireless power feeder of this embodiment forms an S-S topology (FIG. 2(c)). The receiver-side resonant circuit 210 interacts (resonates) with the feed-side resonant circuit 110 to wirelessly receive power from the feed-side circuit 100. Because of the S-S topology, the constant voltage power supplied by the inverter 120 is transmitted to the load (R Ｌ ) is transmitted at a constant voltage.

[0037] The AC-DC converter 220 converts the AC power received by the power receiving side resonant circuit 210 into DC power. As the AC-DC converter 220, various known circuits can be used.

[0038] The DC-DC converter 230 converts the DC power output from the AC-DC converter 220 into a voltage at a target voltage (load (R ＬThe DC-DC converter 230 converts the input voltage into DC power (voltage according to the specifications of the power supply). Various known circuits can be used as the DC-DC converter 230.

[0039] Load (R Ｌ ) is an electrical device that consumes power, such as a battery or a motor. Ｌ The type of load (R Ｌ ) is used as a battery for electric vehicles.

[0040] In this magnetic resonance type wireless power feeder, power is transmitted wirelessly based on the principle of PT symmetry by self-excited oscillation of the inverter 120. In this magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder), １ ) to the receiving coil (L ２ ) changes, and the distance (transmission distance) to the power supply coil (L １ ) with respect to the receiving coil (L ２ 1(c), the oscillation frequency of the inverter 120 is automatically adjusted so that the transmitted power is always kept constant even if the relative positions of the inverter 120 and the inverter 121 change. Therefore, as shown in FIG. 1(c), high transmitted power can be obtained over a wide transmission distance.

[0041] 2. Details of the Magnetic Resonance-Type Wireless Power Supply Apparatus Characteristic features of the magnetic resonance-type wireless power supply apparatus (PT symmetric wireless power supply apparatus) of this embodiment will be described in more detail.

[0042] 2.1 Filtering Circuit First, the filtering circuit 130 will be described. As already mentioned, the filtering circuit 130 is provided on a path that detects the AC current flowing through the power supply-side resonant circuit 110 using the current detection circuit 150 and provides positive feedback to the input side of the inverter 120. As shown in Fig. 6, the filtering circuit 130 includes a frequency-voltage conversion circuit 131, a loop filter 132, a voltage limiting circuit 133, and a voltage-controlled oscillator (VCO) 134. Fig. 7 shows an example configuration of the filtering circuit 130.

[0043] The filtering circuit 130 receives the signal S ２０ The frequency-voltage conversion circuit 131 receives this signal S ２０ In the magnetic resonance type wireless power feeder of this embodiment, the frequency-voltage conversion circuit 131 is configured with a phase detector (PFD) 131a and a charge pump (CP) 131b. The phase detector 131a converts the signal S ２０ and the signal S fed back from the voltage controlled oscillator 134. ２５ The phase difference is detected and the phase difference is output as a signal S ２１ The charge pump 131b outputs the phase difference (signal S ２１ The charge pump 131b converts the signal S ２０ A DC voltage proportional to the frequency of the signal S ２２ is output as

[0044] The frequency-voltage conversion circuit 131 (phase detector 131a and charge pump 131b) uses a commercially available phase-locked loop circuit (PLL circuit) including a voltage-controlled oscillator 134, which will be described later. ２５ This type of feedback circuit has a mechanism for feeding back (negative feedback) the signal S ２５ The phase of the signal ２０ For signal S ２５ If the phase of the output signal S of the charge pump 131b is reversed, the circuit will not be able to operate as designed. ２２ In the magnetic resonance type wireless power feeder of this embodiment, as shown in FIG. 7, a loop filter 132 is configured by a resistor and a grounded capacitor.

[0045] The voltage limiting circuit 133 limits the voltage (signal S ２３ ), the voltage outside the predetermined range is cut off, while the voltage within the predetermined range is output as is. In the magnetic resonance type wireless power feeder of this embodiment, the voltage limiting circuit 133 limits the input voltage (signal S ２３ ) is the threshold voltage V Ｔｈ If the input voltage does not reach the output voltage (signal S ２４ ) and the threshold voltage V Ｔｈ while outputting the input voltage (signal S ２３ ) is the threshold voltage V Ｔｈ If the input voltage is equal to or greater than the output voltage (signal S ２４ 8 shows the input voltage (signal S ２３ ) and output voltage (signal S ２４ ) is a graph showing the relationship between the threshold voltage V Ｔｈ is the resonant frequency ω ０ The values ​​are set to correspond to those shown in Figure 4.

[0046] In a PT symmetric type wireless power feeder such as the magnetic resonance type wireless power feeder of this embodiment, the oscillation frequency of the inverter 120 is set to a frequency ω ｈ (Figure 4) and frequency ω ｌ (FIG. 4) is selected, and the above threshold voltage V Ｔｈ By filtering with ０ higher frequencies than ω ｈ (FIG. 4) is selected as the oscillation frequency of the inverter 120. As described above, the frequency is converted into a voltage and then filtered, thereby obtaining a threshold voltage V Ｔｈ (i.e., the resonant frequency ω ０ ) can be clearly filtered. The voltage can be filtered by using a Zener diode, a reference voltage diode, a shunt regulator, an ideal diode, etc. Ｔｈ This is because filtering can be performed clearly at the boundary of frequency ω ｈ is the frequency ω ｌ6. Even in the unstable region where the oscillation frequency is likely to change (see "unstable region where the oscillation frequency is likely to change" in FIG. 4), the oscillation frequency of the inverter 120 (signal S １０ ) at frequency ω ｈ will be sure to be selected.

[0047] In the magnetic resonance type wireless power feeder of this embodiment, the voltage limiting circuit 133 is configured by combining a buffer amplifier 133a, an ideal diode 133b, and a Zener diode 133c, as shown in Fig. 7. The buffer amplifier 133a amplifies the output signal S ２３ The Zener diode 133c is connected to the power supply 131 and is isolated from the power supply 131 so as to extract only the voltage signal. Ｔｈ It may be replaced by various devices that can fix a voltage corresponding to the reference voltage IC, a reference voltage diode, a shunt regulator, etc.

[0048] The voltage controlled oscillator 134 is a voltage controlled oscillator (signal S ２４ ) is the frequency proportional to the output signal S ２６ The voltage (signal S ２４ ) is the frequency (signal S ２０ ), the signal S output from the voltage controlled oscillator 134 ２６ The frequency of the signal S input to the filtering circuit 130 ２０ and the frequency of the signal S ２５ and signal S ２０ The phase difference between the signals S ２６ is generated by the voltage controlled oscillator 134, and the signal S ２５ is electrically a signal S ２０ Therefore, the signal S ２６ So, signal S ２０ The noise contained in the

[0049] By configuring the filtering circuit 130 as described above, the oscillation frequency of the inverter 120 is adjusted to the resonant frequency ω ０ The oscillation frequency of the inverter 120 is set to a resonant frequency ω ０ Therefore, the oscillation frequency of the inverter 120 can be set to the frequency ω ｈ is reliably selected, and the oscillation frequency can be prevented from switching.

[0050] Also, the resonant frequency ω ０ (FIG. 4) is set to 79 kHz, and the inverter 120 is set to 90 kHz (frequency ω ａ If oscillation is prevented in a range exceeding the upper limit frequency (frequency ω ａ ) filtering at the lower limit frequency (resonant frequency ω ０ ), it can also be done in a state where the frequency is converted to a voltage. However, the lower limit frequency (resonant frequency ω ０ ) at frequency ω ｈ and frequency ω ｌ In addition to already preventing the switch to ａ Even if the filtering at the upper limit frequency (frequency ω ａ ) can be filtered by directly cutting frequencies using a low-pass filter or the like.

[0051] Incidentally, the current detection circuit 150 that detects the AC current flowing through the power supply side resonant circuit 110 is often configured with a shunt resistor, but in the magnetic resonance type wireless power supply device of this embodiment, the current detection circuit 150 is configured with a pair of super barrier rectifier diodes (SBR diodes).

[0052] This is because, when a shunt resistor is used in the current detection circuit 150, the current (i Ｌ ) and the voltage (V ｉｎ ) generates a slight phase difference. This phase difference is caused by the inductance component contained in the shunt resistor. If the frequency changes, the current (i Ｌ The phase difference between the current (i Ｌ ) and the voltage signal that is in phase with the current (i Ｌ ) with respect to voltage (V ｉｎ ) phase shift, the transmitted power fluctuates, and the purpose of wireless power supply is lost. In contrast, when a pair of super-barrier rectifier diodes is used in the current detection circuit 150, as shown in FIG. 9(b), the current (i Ｌ ) and the same phase voltage (V ＳＢＲ ) can be detected. Ｌ ) and the same phase voltage (V ＳＢＲ ) can be detected, the voltage (V ＳＢＲ ) the voltage signal V ＰＬＬ 9(d) (the gate signal S in FIG. 6) １１ The voltage V used as Ｇ１ , and the gate signal S in FIG. １２ The voltage V used as Ｇ２ ) can be produced, and the above problems can be solved.

[0053] Furthermore, the forward voltage of a super-barrier rectifier diode is lower than that of other diodes. Therefore, if a super-barrier rectifier diode is used in the current detection circuit 150, the power loss in the current detection circuit 150 can be reduced. Furthermore, what is desired to be detected by the current detection circuit 150 is the current (i Ｌ ) but the magnitude of the current (i Ｌ ) is the timing of zero crossing, the voltage (VＳＢＲ ) is the amplitude of the current (i Ｌ ) is not significantly affected by the magnitude of the current (i Ｌ ) can be small or large, allowing the circuit to operate over a wide range.

[0054] 2.2 Phase Shift Circuit The phase shift circuit 140 shifts the frequency signal S １０ In this case, the signal S output from the filtering circuit 130 is adjusted so as to generate an inductive state in which the phase of the voltage waveform is slightly ahead of the phase of the current waveform. ２６ The phase shift circuit 140 shifts the phase of the voltage waveform of the inverter 120. This phase shift circuit 140 enables soft switching in the inverter 120. Therefore, even when the transmission power is large (for example, 1 kW or more), not only can power loss be reduced and efficient power transmission be achieved, but also heat generation in the switching elements (FET1 and FET2 in FIG. 6) constituting the inverter 120 can be reduced, making the inverter 120 less likely to be damaged. A voltage-controlled phase shifter can be suitably used as the phase shift circuit 140.

[0055] However, the inductive state described above is caused by the oscillation frequency of the inverter 120 (signal S １０ The frequency of ０ (FIG. 4). In other words, when the oscillation frequency of the inverter 120 is higher than the resonant frequency ω ０ Therefore, in order to create an inductive state and realize soft switching, the oscillation frequency of the inverter 120 must be set to a value lower than the frequency ω ｌ (Fig. 4) but at frequency ω ｈ In this regard, in the magnetic resonance type wireless power feeder of this embodiment, as described above, the frequency ω ｈ Since the filtering circuit 130 is configured so that the PT symmetry is selected, it is possible to achieve both preservation of PT symmetry and soft switching.

[0056] 3. Experiment In the magnetic resonance type wireless power feeder of this embodiment, the power feed coil (L １ ) with respect to the receiving coil (L ２ An experiment was conducted to confirm how the transmission power changes when the relative positions of the magnetic resonance type wireless power feeder and the PT symmetric type wireless power feeder are changed to change the transmission distance. For comparison, the same experiment was also conducted with an existing magnetic resonance type wireless power feeder (PT symmetric type wireless power feeder). The transmission power was set to 1 kW in both the magnetic resonance type wireless power feeder of this embodiment and the existing magnetic resonance type wireless power feeder.

[0057] In the existing magnetic resonance type wireless power feeder, the transmission power was kept approximately constant only when the transmission distance was in the range of 0 to 15 mm. In contrast, in the magnetic resonance type wireless power feeder of this embodiment, the transmission power was kept approximately constant even when the transmission distance was changed in the range of 0 to 200 mm. In other words, it was confirmed that the magnetic resonance type wireless power feeder of this embodiment has a transmission distance that is 10 times or more longer than that of the existing magnetic resonance type wireless power feeder. This demonstrates that the magnetic resonance type wireless power feeder of this embodiment can exhibit excellent robustness even when the transmission power is large.

[0058] 3. Applications The magnetic resonance type wireless power feeder of this embodiment can be used in various applications in which power is transmitted wirelessly. In particular, the magnetic resonance type wireless power feeder of this embodiment can transmit power even when the transmission power is large, and therefore can be suitably employed when the transmission power is large. For example, it can be suitably employed when the transmission power is 100 W or more, 500 W or more, or 1 kW or more. Furthermore, the magnetic resonance type wireless power feeder of this embodiment is also highly robust, and therefore can be suitably employed in applications in which the relative position of the power receiving device with respect to the power supplying device is not fixed. An example of such an application is charging an electric vehicle.

[0059] 100 Power supply side circuit 110 Power supply side resonant circuit 120 Inverter 121 Gate driver 130 Filtering circuit 131 Frequency-voltage conversion circuit 132 Loop filter 133 Voltage limiting circuit 133a Buffer amplifier 133b Ideal diode 133c Zener diode 134 Voltage controlled oscillator 140 Phase shift circuit 150 Current detection circuit 200 Power receiving side circuit 210 Power receiving side resonant circuit 220 AC-DC converter 230 DC-DC converter

Claims

1. A magnetic resonance type wireless power feeder configured to preserve PT symmetry between a power feed circuit in which a self-oscillating inverter is connected to a power feed resonant circuit including a power feed coil, and a power receiving circuit in which a power receiving resonant circuit including a power receiving coil is connected, wherein the power feed circuit is equipped with a filtering circuit including: a frequency-voltage conversion circuit that converts the inverter's oscillation frequency into a voltage proportional to the oscillation frequency and outputs it; a voltage limiting circuit that cuts out voltages that are not within a specified range from the voltage output from the frequency-voltage conversion circuit, while outputting voltages that are within the specified range as is; and a voltage-controlled oscillator that converts the voltage output from the voltage limiting circuit into a frequency proportional to the voltage and outputs it to the inverter, preventing the inverter from oscillating outside the specified frequency range.

2. A magnetic resonance type wireless power feeder as claimed in claim 1, in which a phase shift circuit is incorporated in the power supply circuit to shift the phase so that the voltage waveform of the frequency signal input to the inverter leads the current waveform of the same frequency signal, and a voltage limiting circuit cuts off voltages that do not reach a predetermined threshold voltage, while outputting voltages that are equal to or greater than the threshold voltage.

3. A magnetic resonance type wireless power feeder according to claim 1, wherein the filtering circuit is configured using a phase-locked loop circuit.

4. A power supply side circuit for a magnetic resonance type wireless power supply device, in which a self-oscillating inverter is connected to a power supply side resonant circuit including a power supply side coil, characterized in that it incorporates a filtering circuit including: a frequency-voltage conversion circuit that converts the oscillation frequency of the inverter into a voltage proportional to said oscillation frequency and outputs it; a voltage limiting circuit that cuts out voltages that are not within a specified range from the voltage output from the frequency-voltage conversion circuit, while outputting voltages that are within said specified range as is; and a voltage-controlled oscillator that converts the voltage output from the voltage limiting circuit into a frequency proportional to said voltage and outputs it to the inverter, preventing the inverter from oscillating outside the specified frequency range.

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