JP2012170271A - Wireless power transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless power transmission device that can detect the relative position between a primary coil and a secondary coil.SOLUTION: A wireless power transmission device comprises: a primary coil 19 supplying a power to a secondary coil 21 by electromagnetic induction; a driving circuit 17 supplying AC power to the primary coil 19; a current detection circuit 11 detecting an input current Iin supplied to the driving circuit 17; and a control circuit 15 to which the detection result of the current detection circuit 11 is supplied. The control circuit 15 drives the driving circuit 17 by a predetermined driving frequency fdr and detects the relative position between the primary coil 19 and the secondary coil 21 based on the input current Iin flowing during the driving.

Description

  The present invention relates to a wireless power transmission apparatus.

  In recent years, a method for transmitting power in a contactless manner to an electronic device such as a mobile phone, a digital camera, or a laptop computer has become widespread. Electric power is transmitted to a secondary coil built in a power receiver such as an electronic device by an alternating magnetic field generated from a primary coil built in the power transmitter.

  If the relative positions of the primary coil and the secondary coil are shifted, the coupling coefficient between the coils is reduced, so that desired power cannot be transmitted or the power transmission efficiency is lowered. In order to avoid this problem, the relative position between the primary and secondary coils must be within a certain range. Therefore, a means for detecting that the relative position between the primary and secondary coils is within a predetermined range is required.

  Patent Document 1 describes means for detecting the position of a secondary coil built in a power receiver such as an electronic device. When the position of a power receiver such as an electronic device with respect to the power transmitter is deviated from the normal set position, the electromagnetic coupling between the primary coil and the secondary coil is reduced, the equivalent impedance of the primary coil is changed, and the power consumption of the primary coil is reduced. . Thus, the power consumption of the primary coil, the current flowing through the primary coil, the resonance frequency of the primary coil, and the impedance of the primary coil vary depending on the relative positions of the primary coil and the secondary coil. By detecting these changes, the position of a power receiver such as an electronic device with respect to the power transmitter is detected.

JP 2008-141940 A

  However, such a position detection method only detects whether the position of the secondary coil with respect to the primary coil is at a normal set position. Patent Document 1 does not describe a specific detection method or a method for obtaining a positional deviation amount. Further, there is a problem that the position detection error is not taken against various fluctuation factors such as the input voltage, and the position detection accuracy is poor.

  The present invention has been made in view of such a problem, and an object thereof is to provide a wireless power transmission device capable of detecting a relative position between a primary coil and a secondary coil.

  In order to achieve such an object, the present invention provides a primary coil that supplies electric power to a secondary coil by electromagnetic induction, a drive circuit that supplies AC power to the primary coil, and an input that is supplied to the drive circuit. A current detection circuit for detecting a current and a control circuit to which a detection result of the current detection circuit is supplied; the control circuit drives the drive circuit at a predetermined drive frequency; Based on this, a relative position between the primary coil and the secondary coil is detected.

  ADVANTAGE OF THE INVENTION According to this invention, the wireless power transmission apparatus which can detect the relative position between a primary-secondary coil can be provided.

1 is a block diagram of a wireless power transmission device according to a first embodiment of the present invention. The perspective view which shows the positional relationship of a primary coil and a secondary coil Cross section of transmitter and receiver Circuit diagram showing an example of drive circuit Drive signal pulse pattern Timing chart showing an example of the operation of the switching element Waveform diagram of input current when current is supplied to the primary coil Detected voltage with respect to the horizontal distance between the central axes of the primary and secondary coils Coupling coefficient for horizontal distance between the central axes of primary and secondary coils Detection voltage with respect to the horizontal distance between the central axis of the primary coil and the secondary coil when the drive frequency is constant and the secondary resonance frequency for detection fluctuates Detection voltage with respect to the horizontal distance between the central axis of the primary coil and the secondary coil when the difference between the secondary resonance frequency for detection and the drive frequency is constant and the secondary resonance frequency for detection fluctuates Block diagram of a wireless power transmission apparatus in a second embodiment of the present invention Detection voltage for the horizontal distance between the central axes of the primary and secondary coils when the input voltage fluctuates Detection voltage after correction for the horizontal distance between the central axis of the primary and secondary coils when the input voltage fluctuates Block diagram of a wireless power transmission apparatus in a third embodiment of the present invention The perspective view which shows an example of the wireless power transmission apparatus in 3rd Example of this invention. The perspective view which shows an example of the wireless power transmission device which provided the detection means of the position shift direction.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 shows a block diagram of a wireless power transmission apparatus according to a first embodiment of the present invention. The power transmitter 10 includes a current detection circuit 11, a control circuit 15, an input smoothing capacitor 16, a drive circuit 17, a primary capacitor 18, and a primary coil 19. The current detection circuit 11 includes a current detection resistor 12, an error amplifier 13, and an analog / digital converter 14. The power receiver 20 includes a secondary coil 21, a secondary capacitor 22, a detection capacitor 23, a rectifier circuit 24, an output smoothing capacitor 25, an impedance element 26, a control circuit 27, a load open / close switch 28, and a load 29.

  First, the configuration of the power transmitter 10 will be described. The drive circuit 17 is supplied with the input voltage Vin from the DC power source DC via the current detection resistor 12. An input current Iin flows through the current detection resistor 12. The error amplifier 13 amplifies the voltage across the current detection resistor 12 and supplies the amplified voltage signal to the control circuit 15 via the analog / digital converter 14. The operation of the drive circuit 17 is controlled by a drive signal Sdr supplied from a control circuit 15 constituted by a microcomputer as an example. An input smoothing capacitor 16 is connected to the input end of the drive circuit 17, and a primary coil 19 and a primary capacitor 18 are connected in series to the output end of the drive circuit 17. The drive circuit 17 supplies AC power to the primary coil 19 and the primary capacitor 18. As an example, the drive circuit 17 is configured by a full bridge circuit, a half bridge circuit, or the like.

  Next, the configuration of the power receiver 20 will be described. The secondary coil 21 receives power from the primary coil 19 by electromagnetic induction. A detection capacitor 23 is connected to both ends of the secondary coil 21 via a secondary capacitor 22. The voltage applied to the detection capacitor 23 is rectified by the rectifier circuit 24. An output smoothing capacitor 25, an impedance element 26, and a control circuit 27 are connected in parallel to the output terminal of the rectifier circuit 24. The output smoothing capacitor 25 removes a ripple of the output voltage Vout. The impedance element 26 is an element such as an LED or a voltage regulator provided in the power receiver 20. A load 29 such as a secondary battery is connected to the output terminal of the rectifier circuit 24 via a load opening / closing switch 28. The operation of the impedance element 26 and the load opening / closing switch 28 provided in the power receiver 20 is controlled by a control circuit 27 configured by a microcomputer or the like as an example. The load 29 can be disconnected from the circuit of the power receiver 20 by the load opening / closing switch 28. When the electric power obtained by the secondary coil 21 is supplied to the load 29, the load opening / closing switch 28 is closed and the output voltage Vout is applied to the load 29.

  Hereinafter, the frequency of AC power supplied to the primary coil 19 is referred to as a drive frequency fdr. In addition, the resonance frequency of the primary LC resonance circuit composed of the primary coil 19 and the primary capacitor 18 is defined as a primary resonance frequency fp. Further, the resonance frequency of the secondary LC resonance circuit composed of the secondary coil 21 and the secondary capacitor 22 is defined as a secondary resonance frequency fs. Further, the resonance frequency of the resonance circuit composed of the secondary coil 21, the secondary capacitor 22, and the detection capacitor 23 is defined as a detection secondary resonance frequency fd.

  FIG. 2 is a perspective view showing the positional relationship between the primary coil 19 and the secondary coil 21. The primary coil 19 and the secondary coil 21 each have a flat and thin structure, and are arranged so as to face each other. The distance between the central axes of the primary coil 19 and the secondary coil 21 is a horizontal distance D, and the distance between the opposing surfaces of the primary coil 19 and the secondary coil 21 is a gap G.

  FIG. 3 is a cross-sectional view of the power transmitter 10 and the power receiver 20. The primary coil 19 is housed in the case 41 of the power transmitter 10, and the secondary coil 21 is housed in the case 51 of the power receiver 20. Magnetic bodies 42 and 52 are provided on the surfaces of the primary coil 19 and the secondary coil 21 opposite to the surfaces facing each other. The case 51 of the power receiver 20 is placed on the surface of the case 41 of the power transmitter 10. A distance between the central axes of the primary coil 19 and the secondary coil 21 is a horizontal distance D. Even when the central axes of the primary coil 19 and the secondary coil 21 are shifted, the gap G has a substantially constant value due to the thickness of each case.

  Next, the operation of detecting the relative position between the primary coil 19 and the secondary coil 21 will be specifically described. Here, it is assumed that a full bridge circuit is used as the drive circuit 17. FIG. 4 is a circuit diagram illustrating an example of a drive circuit. The drive circuit 17 includes switching elements Q1 to Q4 that form a full bridge circuit.

  First, when performing position detection, the load opening / closing switch 28 provided in the power receiver 20 is opened. Then, the control circuit 15 supplies a predetermined drive signal Sdr to the drive circuit 17 for a time determined in a certain cycle. Here, an example of the pulse pattern of the drive signal Sdr is shown in FIG. At time ta, supply of a pulse wave with a predetermined frequency is started. At the time tb when the on period Ton has elapsed, the supply of the pulse wave stops. Further, at time tc when the off period Toff has elapsed, supply of a pulse wave with a predetermined frequency is started again. As described above, the drive circuit 17 is supplied with the pulse wave from the control circuit 15 for the ON period Ton determined at a certain period Ts. As an example, the period Ts is set to 200 ms, and the on period Ton is set to 3 ms. During the on period Ton, the switching elements Q <b> 1 to Q <b> 4 are on / off controlled according to the drive signal Sdr, and AC power is supplied to the primary coil 19. On the other hand, during the off period Toff, the switching elements Q1 and Q4 are switched on and the switching elements Q2 and Q3 are switched off, and no AC power is supplied to the primary coil 19. Alternatively, the switching elements Q1 and Q4 are turned off and the switching elements Q2 and Q3 are turned on. The reason why all the switching elements Q1 to Q4 are not turned off during the off period Toff is to suppress the generation of a large flyback voltage in the primary coil 19. The cycle Ts and the on period Ton are determined by the control circuit 15. During the on period Ton, the switching elements Q1 to Q4 in the drive circuit 17 are on / off controlled by such a drive signal Sdr.

  Here, FIG. 6 shows a timing chart showing an example of the operation of the switching elements Q1 to Q4 in the ON period Ton of the drive signal Sdr. At time t0, switching element Q4 is switched on, and switching elements Q1, Q4 are turned on. At time t1, switching element Q1 is switched off, and current is regenerated by the body diode of switching element Q2 and switching element Q4. At time t2, switching element Q2 is turned on, and current regeneration is continued in switching element Q2 and switching element Q4. At time t3, the switching element Q4 is switched off, and current regeneration is continued by the body diodes of the switching element Q2 and the switching element Q4. At time t4, the switching element Q3 is turned on, and the switching elements Q2, Q3 are turned on. At time t5, the switching element Q2 is switched off, and current is regenerated by the body diode of the switching element Q1 and the switching element Q3. At time t6, the switching element Q1 is switched on, and current is regenerated by the switching element Q1 and the switching element Q3. At time t7, the switching element Q3 is turned off, and current is regenerated by the body diodes of the switching element Q1 and the switching element Q3. At time t8, the switching element Q4 is turned on again, and the switching elements Q1, Q4 are turned on. By repeating such an operation, AC power is supplied to the primary coil 19 and the primary capacitor 18. A period between times t1 and t4 and between times t5 and t8 represents a dead time DT. By providing the dead time DT, the switching elements Q1 and Q2 or the switching elements Q3 and Q4 are prevented from being turned on simultaneously, and the DC power source DC is prevented from being short-circuited. The ratio of the time for which the switching element is turned on with respect to the period T is defined as the on duty. The control circuit 15 determines the period T and the on-duty of the switching elements Q1 to Q4. The dead time DT is determined by the drive frequency fdr and the on-duty.

  As described above, the control circuit 15 determines the drive frequency fdr, the on-duty of the switching elements Q1 to Q4, and the like. Here, the drive frequency fdr is set to 700 kHz. The secondary resonance frequency for detection fd is 1 MHz.

  A current is supplied to the primary coil 19 during the ON period Ton of the drive signal Sdr. The input current Iin at this time is detected by the current detection circuit 11. Here, a waveform diagram of the input current Iin when a current is supplied to the primary coil 19 is shown in FIG. The horizontal axis represents time, and the vertical axis represents the input current Iin. FIG. 7 shows the input current Iin waveform when the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 is set to 0 mm, 4 mm, 10 mm, and 20 mm, respectively. At time ta, supply of a pulse wave with a predetermined frequency to the drive circuit 17 is started, and current is supplied to the primary coil 19 and the primary capacitor 18. Then, the input current Iin gradually increases as shown in FIG. When the horizontal distance D is 0 mm, 4 mm, and 10 mm, a peak appears at the rising edge of the input current Iin. When the horizontal distance D is 20 mm, the input current Iin increases monotonously, but the current peak value is smaller than when the horizontal distance D is 10 mm. Thus, it can be seen that the peak value of the input current Iin increases as the horizontal distance D decreases. At time tb, the supply of the pulse wave supplied to the drive circuit 17 is stopped. Then, no current is supplied to the primary coil 19 and the primary capacitor 18, and the input current Iin decreases.

  Next, the detection voltage with respect to the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 is shown in FIG. The horizontal axis indicates the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21. The vertical axis represents the detection voltage. The detection voltage is detected by amplifying the voltage at both ends of the current detection resistor 12 through which the input current Iin flows with the error amplifier 12 and detecting the peak value of the input current Iin. When the horizontal distance D is 0 mm, the detection voltage, that is, the input current Iin becomes the maximum value. The input current Iin decreases as the horizontal distance D increases.

  Next, the relationship between the drive frequency fdr and the detection secondary resonance frequency fd will be described. The resonance circuit composed of the secondary coil 21, the secondary capacitor 22, and the detection capacitor 23 has the minimum impedance at the detection secondary resonance frequency fd. When the drive frequency fdr of the primary coil 19 is brought close to the secondary resonance frequency for detection fd, the impedance of the primary coil 19 decreases, so that the current flowing through the primary coil 19 increases. As the current supplied to the primary coil 19 increases, the current supplied to the drive circuit 17 also increases and the input current Iin increases. Conversely, when the drive frequency fdr of the primary coil 19 is moved away from the secondary resonance frequency for detection fd, the impedance of the primary coil 19 increases, so that the current flowing through the primary coil 19 decreases. As the current supplied to the primary coil 19 decreases, the current supplied to the drive circuit 17 also decreases, and the input current Iin decreases. As described above, when the drive frequency fdr changes, the value of the input current Iin changes.

  Therefore, when the drive frequency fdr of the primary coil 19 is fixed and the secondary coil 21 is brought close to the primary coil 19, the coupling coefficient between the primary coil 19 and the secondary coil 21 increases, and the input current Iin increases. Further, when the drive frequency fdr of the primary coil 19 is fixed and the secondary coil 21 is moved away from the primary coil 19, the coupling coefficient between the primary coil 19 and the secondary coil 21 decreases, and the input current Iin decreases.

  Thus, the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 and the input current Iin are in a correlation. The relative position between the primary coil 19 and the secondary coil 21 can be obtained by fixing the drive frequency fdr with respect to the secondary resonance frequency for detection fd and measuring the input current Iin. Specifically, the detection result of the input current Iin is converted into a digital value by the analog / digital converter 14 and calculated by the control circuit 15 using the digital value and a conversion table or conversion formula created in advance. The relative positions of the primary coil 19 and the secondary coil 21 can be obtained. The reason why the load opening / closing switch 28 is opened first is to prevent the measurement result of the input current Iin from changing when the load 29 varies.

  Next, the coupling coefficient between the primary coil 19 and the secondary coil 21 will be described. The primary coil 19 and the secondary coil 21 are coupled with a certain coupling coefficient. FIG. 9 shows the coupling coefficient with respect to the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21. The horizontal axis indicates the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21. The vertical axis represents the coupling coefficient. The coupling coefficient is maximum when the horizontal distance D is 0 mm, that is, when the central axes of the primary coil 19 and the secondary coil 21 coincide. At this time, the power transmission efficiency from the primary coil 19 to the secondary coil 21 is maximized. As the horizontal distance D becomes longer, the coupling coefficient decreases. The coupling coefficient between the primary coil 19 and the secondary coil 21 and the input current Iin are correlated. This can also be seen from the fact that the curves shown in FIGS. 8 and 9 have substantially similar shapes. Therefore, the coupling coefficient between the primary coil 19 and the secondary coil 21 can be obtained by a method similar to that for obtaining the relative position between the primary coil 19 and the secondary coil 21.

  If the drive frequency fdr is set to a lower frequency side than the secondary resonance frequency for detection fd, a peak appears at the rising edge of the input current Iin when the secondary coil 21 is brought close to the primary coil 19. Therefore, the detection sensitivity of the input current Iin is good, and the relative position between the primary coil 19 and the secondary coil 21 can be obtained with high accuracy. As the drive frequency fdr is closer to the detection secondary resonance frequency fd, the voltage induced in the secondary coil 19 also increases, so that the reverse withstand voltage of the rectifier circuit 24 may be exceeded. In order to prevent this, an element for preventing overvoltage such as a Zener diode may be provided at the input terminal of the rectifier circuit 24. By setting the drive frequency fdr somewhat apart from the detection secondary resonance frequency fd, it is possible to prevent the occurrence of overvoltage and at the same time suppress the increase in power consumption. The degree of separation between the drive frequency fdr and the detection secondary resonance frequency fd is determined in consideration of the detection sensitivity of the input current Iin, the output voltage Vout, power consumption, and the like.

  Further, the detection sensitivity can be further adjusted by changing the duty ratio of the drive circuit 17, that is, the on-duty of the switching elements Q1 to Q4. Increasing the on-duty of the drive circuit 17 increases the input current Iin, thereby improving the detection sensitivity.

  Next, the variation in the detection secondary resonance frequency fd will be described. The power transmitter 10 transmits power to the power receiver 20 incorporated in various electronic devices. At this time, the capacitance value of the detection capacitor 23 in the power receiver 20 of each electronic device and the inductance value of the secondary coil 21 may vary. Then, for each power receiver 20, a variation occurs in the detection secondary resonance frequency fd, which is the resonance frequency of the resonance circuit composed of the secondary coil 21, the secondary capacitor 22, and the detection capacitor 23. Therefore, the power receiver 20 changes the difference between the drive frequency fdr and the detection secondary resonance frequency fd. When the detection secondary resonance frequency fd varies, the impedances of the secondary coil 21, the secondary capacitor 22, and the detection capacitor 23 change with respect to the drive frequency fdr when the relative position of the primary-secondary coil is detected. Become. For this reason, it is conceivable that the input current Iin to be detected varies depending on the respective power receivers 20 and affects the detection result of the relative position between the primary coil 19 and the secondary coil 21.

  FIG. 10 is a graph showing the detection voltage with respect to the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 when the drive frequency fdr is constant and the secondary resonance frequency for detection fd fluctuates. The horizontal axis indicates the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21. The vertical axis represents the detection voltage. The driving frequency fdr at this time is 700 kHz. It can be seen that when the difference between the drive frequency fdr and the detection secondary resonance frequency fd changes, the input current Iin changes, and thus the detection voltage varies.

  When the detection secondary resonance frequency fd is 1.0 MHz, the detection voltage when the horizontal distance D is 6 mm is TH1, and the detection voltage when the horizontal distance D is 10 mm is TH2. Whether the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 is within 6 mm by detecting the range in which the detection voltage is relative to TH1 and TH2, or the range of 6 to 10 mm It is possible to detect whether it is within the range of 10 mm or more.

  When the detection secondary resonance frequency fd fluctuates to 900 kHz, the detection voltage is greater than TH1 when the horizontal distance D is within 6.3 mm, and the detection voltage when the horizontal distance D is within the range of 6.3 to 11.0 mm. Is smaller than TH1 and larger than TH2, and the detection distance is smaller than TH2 when the horizontal distance D is in the range of 11.0 mm or more. When the secondary resonance frequency for detection fd fluctuates to 1.1 MHz, the detection voltage becomes equal to TH1 when the horizontal distance D is 0 mm, and the detection voltage when the horizontal distance D is in the range of 0 to 8.4 mm. Is smaller than TH1 and larger than TH2, and when the horizontal distance D is in the range of 8.4 mm or more, the detection voltage becomes smaller than TH2.

  Thus, when the secondary resonance frequency for detection fd fluctuates, a large error occurs in the detection result of the relative position between the primary coil 19 and the secondary coil 21. In order to suppress this error, the drive frequency fdr may be set so as to cancel the change in the input current Iin due to the change in the detection secondary resonance frequency fd.

  FIG. 11 shows a horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 when the difference between the detection secondary resonance frequency fd and the drive frequency fdr is constant and the detection secondary resonance frequency fd varies. It is a graph which shows the detection voltage with respect to. The horizontal axis indicates the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21. The vertical axis represents the detection voltage. Here, the drive frequency fdr was set to a value lower by 300 kHz than the detection secondary resonance frequency fd.

  The characteristic curve when the secondary resonance frequency for detection fd is 1.0 MHz is the same as that shown in FIG. The drive frequency when the detection secondary resonance frequency fd is 900 kHz is 600 kHz, and the drive frequency fdr when the detection secondary resonance frequency fd is 1.1 MHz is 800 kHz.

  When the detection secondary resonance frequency fd fluctuates to 900 kHz, the detection voltage is greater than TH1 when the horizontal distance D is within 6.6 mm, and the detection voltage when the horizontal distance D is within the range of 6.6 to 9.8 mm. Is smaller than TH1 and larger than TH2, and when the horizontal distance D is in the range of 9.8 mm or more, the detection voltage becomes smaller than TH2. When the detection secondary resonance frequency fd fluctuates to 1.1 MHz, the detection voltage is larger than TH1 when the horizontal distance D is within 6.9 mm, and the horizontal distance D is within the range of 6.9 to 10.8 mm. Sometimes the detected voltage is smaller than TH2 when the detected voltage is smaller than TH1 and larger than TH2, and the horizontal distance D is in the range of 10.8 mm or more.

  From these measurement results, before and after the difference between the secondary resonance frequency for detection fd and the drive frequency fdr is adjusted to be constant, a comparison is made. When the secondary resonance frequency for detection fd fluctuates between 900 kHz and 1.1 MHz, the range of the horizontal distance D where the detection voltage is TH1 is 0 to 6.3 mm before adjustment, but after adjustment. Was 6 to 6.9 mm. The range of the horizontal distance D where the detection voltage becomes TH2 was 8.4 to 11.0 mm before the adjustment, and 10 to 10.8 mm after the adjustment. As described above, by making the difference between the detection secondary resonance frequency fd and the drive frequency fdr constant, it is possible to suppress fluctuations in the detection result of the input current Iin due to fluctuations in the detection secondary resonance frequency fd.

  When power is transmitted to various power receivers 20, variations occur in the secondary resonance frequency for detection fd. In order to compensate for this, the secondary resonance frequency fd for detection of the power receiver 20 is measured before detecting the relative position of each coil, that is, the input current Iin, and the drive frequency fdr is set based on the measurement result. That's fine. For example, the frequency of the drive signal Sdr supplied from the control circuit 15 to the drive circuit 17 is continuously changed before the relative position is detected, and the detection secondary resonance frequency fd is measured from the reaction of the input current Iin at that time. Keep it. Then, the drive frequency fdr for detecting the relative position may be set based on the measured secondary resonance frequency fd for detection. For example, a frequency that is a fixed value away from the measured secondary resonance frequency for detection fd is calculated. When the relative position is detected, the primary coil 19 is driven with the calculated frequency. By performing such control, fluctuations in the input current Iin can be suppressed even when the detection secondary resonance frequency fd of each power receiver 20 varies. Further, in order to suppress changes in the input current Iin due to fluctuations or variations in the impedance element 26, the drive frequency fdr is preferably set to a value closer to the detection secondary resonance frequency fd than the secondary resonance frequency fs.

  Thus, by setting the drive frequency fdr in accordance with the detection secondary resonance frequency fd of the power receiver 20, the relative position of the primary coil 19 and the secondary coil 21 can be obtained with high accuracy. Note that the above-described method for setting the drive frequency fdr is merely an example. Any value may be set as long as the drive frequency fdr is set so as to cancel the change in the input current Iin due to the change in the detection secondary resonance frequency fd. Further, it is not necessary to sweep the drive frequency fdr when measuring the detection secondary resonance frequency fd. It is also possible to set several frequencies in advance, obtain the detection secondary resonance frequency fd from the value of the input current Iin when the primary coil 19 is driven at each frequency, and set the drive frequency fdr.

  FIG. 12 shows a block diagram of a wireless power transmission apparatus according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the site | part which has the same function as a 1st Example, and description is abbreviate | omitted. The power transmitter 60 is obtained by further adding a voltage detection circuit 61 to the power transmitter 10 shown in the first embodiment. The voltage detection circuit 61 detects the input voltage Vin supplied from the DC power supply DC and supplies the detection result to the control circuit 15. The configuration of the power receiver 20 is the same as that shown in the first embodiment.

  The relative positions of the primary coil 19 and the secondary coil 21 are detected based on the input current Iin supplied to the drive circuit 17. Therefore, if the input voltage Vin supplied from the direct current power source DC fluctuates due to some external factor, the input current Iin fluctuates accordingly. For this reason, the detection result of the input current Iin varies, which may affect the detection result of the relative position between the primary coil 19 and the secondary coil 21.

  FIG. 13 is a graph showing the detected voltage with respect to the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 when the input voltage Vin fluctuates. The horizontal axis indicates the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21. The vertical axis represents the detection voltage. It can be seen that when the input voltage Vin increases, the input current Iin also increases, and when the input voltage Vin decreases, the input current Iin also decreases. Here, the positional deviation characteristics between the coils when the input voltage Vin was changed to 4.5V and 5.5V with the input voltage Vin being 5.2V as a standard value were measured.

  When the input voltage Vin is 5.2 V, the detection voltage when the horizontal distance D is 6 mm is TH3, and the detection voltage when the horizontal distance D is 10 mm is TH4. Whether the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 is within 6 mm by detecting in what range the detection voltage is in relation to TH3 and TH4, or in the range of 6 to 10 mm It is possible to detect whether it is within the range of 10 mm or more.

  When the input voltage Vin changes to 4.5 V, the detection voltage is greater than TH3 when the horizontal distance D is within 4.4 mm, and the detection voltage is TH3 when the horizontal distance D is within the range of 4.4 to 8.8 mm. When it is smaller and larger than TH4 and the horizontal distance D is in the range of 8.8 mm or more, the detected voltage becomes smaller than TH4. When the input voltage Vin changes to 5.5 V, the detection voltage is greater than TH3 when the horizontal distance D is within 8.2 mm, and the detection voltage when the horizontal distance D is within the range of 8.2 to 11.6 mm. Is smaller than TH3 and larger than TH4, and when the horizontal distance D is in the range of 11.6 mm or more, the detection voltage becomes smaller than TH4.

  Thus, when the input voltage Vin varies, a large error occurs in the detection result of the relative position between the primary coil 19 and the secondary coil 21. In order to suppress this error, the value of the detected voltage may be corrected by the control circuit 15 so as to cancel out the change in the input current Iin due to the change in the input voltage Vin.

  FIG. 14 is a graph showing the corrected detection voltage with respect to the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21 when the input voltage Vin fluctuates. The horizontal axis indicates the horizontal distance D between the central axes of the primary coil 19 and the secondary coil 21. The vertical axis represents the corrected detection voltage. Here, the correction coefficient k = (5.2 / Vin) ^ 1.3, and the corrected detection voltage is a value obtained by multiplying the detection voltage by this correction coefficient k. When the input voltage Vin is a standard value of 5.2V, the correction coefficient k is 1. When the input voltage Vin is larger than 5.2V, the correction coefficient k is smaller than 1, and when the input voltage Vin is smaller than 5.2V, the correction coefficient k is larger than 1.

  The characteristic curve when the input voltage Vin is 5.2 V is the same as that shown in FIG. The characteristic curve when the input voltage Vin is 4.5 V and 5.5 V is obtained by correcting the value of the detection voltage in accordance with the fluctuation of the input voltage Vin.

  When the input voltage Vin changes to 4.5 V, the detection voltage is greater than TH3 when the horizontal distance D is within 6.2 mm, and the detection voltage is TH3 when the horizontal distance D is within the range of 6.2 to 10.2 mm. When it is smaller and larger than TH4 and the horizontal distance D is in the range of 10.2 mm or more, the detected voltage becomes smaller than TH4. When the input voltage Vin changes to 5.5V, the detection voltage is greater than TH3 when the horizontal distance D is within 7.5 mm, and the detection voltage when the horizontal distance D is within the range of 7.5 to 11.2 mm. Is smaller than TH3 and larger than TH4, and when the horizontal distance D is in the range of 11.2 mm or more, the detection voltage becomes smaller than TH4.

  From these measurement results, before and after correcting the detection result of the input current Iin is compared. When the input voltage Vin fluctuates between 4.5 and 5.5 V, the range of the horizontal distance D where the detection voltage becomes TH3 is 4.4 to 8.2 mm before correction, but after correction. Was 6-7.5 mm. Further, the range of the horizontal distance D in which the detection voltage is TH4 was 8.8 to 11.6 mm before correction, but was 10 to 11.2 mm after correction. In this way, by correcting the detection voltage in accordance with the change in the input voltage Vin, the change in the detection result of the input current Iin due to the change in the input voltage Vin can be suppressed.

  The voltage detection circuit 61 detects the input voltage Vin, and the control circuit 15 corrects the detection result of the input current Iin so as to cancel out the change in the input current Iin due to the fluctuation of the input voltage Vin. Correction of the detection result of the input current Iin may be performed by the control circuit 15 configured by, for example, a microcomputer. In this way, by correcting the detection result of the input current Iin according to the change in the input voltage Vin, the relative position between the primary coil 19 and the secondary coil 21 can be obtained with high accuracy even when the input voltage Vin changes. it can. The correction coefficient k described above is merely an example. Any calculation may be performed as long as the correction cancels the change in the input current Iin due to the change in the input voltage Vin.

  FIG. 15 shows a block diagram of a wireless power transmission apparatus according to the third embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the site | part which has the same function as a 1st Example, and description is abbreviate | omitted. The power transmitter 70 is configured by further providing notification means 71 to the power transmitter 10 shown in the first embodiment. For example, the notification unit 71 includes an LED 71a, a buzzer 71b, a vibrating body 71c, and the like. The LED 71 a, the buzzer 71 b, and the vibrating body 71 c are driven by signals supplied from the control circuit 15. The configuration of the power receiver 20 and the operation of detecting the relative position of the primary coil 19 and the secondary coil 21 are the same as those in the above-described embodiment.

  The control circuit 15 controls the notification means 71 based on the detection result of the relative position between the primary coil 19 and the secondary coil 21. The control circuit 15 changes the operation of the notification means 71 depending on the relative position of the primary coil 19 and the secondary coil 21. The user can recognize the relative positions of the primary coil 19 and the secondary coil 21 by confirming the operation of the notification means 71 when placing the power receiver 20 on the power transmitter 70.

  FIG. 16 is a perspective view showing an example of a wireless power transmission apparatus according to the third embodiment of the present invention. The primary coil 19 is provided in the case 41 of the power transmitter 70. The secondary coil 21 is provided in the case 51 of the power receiver 20. A notification means 71 is provided on the surface of the case 41 of the power transmitter 70. The notification means 71 is composed of LEDs arranged in a cross shape. The notification means 71 is composed of nine LEDs, a central LED 81, four inner LEDs 82a to 82d, and four outer LEDs 83a to 83d. The nine LEDs are arranged in a cross shape with the central LED 81 as the center. The inner LEDs 82 a to 82 d are arranged at an equal distance from the central LED 81. Similarly, the outer LEDs 83 a to 83 d are arranged at an equal distance from the central LED 81. Inner LEDs 82a to 82d are arranged between the central LED 81 and the outer LEDs 83a to 83d, respectively. In order to efficiently transmit power from the primary coil 19 to the secondary coil 21, it is necessary to bring the relative positions of the primary coil 19 and the secondary coil 21 close to each other. Therefore, the user moves the power receiver 20 in the direction of the arrow P in the drawing, and aligns the power receiver 20 so that the relative positions of the primary coil 19 and the secondary coil 21 approach each other.

Next, the operation of each LED 81, 82a to 83d, 83a to 83d will be described. Here, based on the relative positions between the coils detected by the control circuit 15, the following four states (A) to (D) are notified by the notification means 71.
(A) When the power receiver 20 is far from the appropriate position of the power transmitter 70, when the power receiver 20 is not placed on the power transmitter 70, or when the power transmitter 70 cannot detect the power receiver 20.
(B) The power transmitter 70 can detect the power receiver 20, but the relative position between the primary coil 19 and the secondary coil 21 is far.
(C) When the power transmitter 70 can detect the power receiver 20 and the relative positions of the primary coil 19 and the secondary coil 21 are close, but the efficiency is low for power transmission.
(D) When the power transmitter 70 can detect the power receiver 20 and is in an optimal position for power transmission.
That is, as the relative position of the primary coil 19 and the secondary coil 21 approaches, the state changes from state (A) → state (B) → state (C) → state (D).

Depending on the relative positions of the primary coil 19 and the secondary coil 21, the LEDs 81, 82a to 83d, 83a to 83d operate as follows.
In the state (A), all the LEDs are turned off.
In the state (B), the outer LEDs 83a to 83d are turned on.
In the state (C), the inner LEDs 82a to 82d are turned on.
In the state (D), the central LED 81 is turned on.
As the relative position between the primary coil 19 and the secondary coil 21 approaches, first, the outer LEDs 83a to 83d are turned on. Furthermore, when the relative position of each coil approaches, inner LED82a-82d will light. Furthermore, when the relative position of each coil approaches and the power receiver 20 is placed at an optimal position for power transmission, the central LED 81 is lit. By operating each LED in this manner according to the relative position of the primary coil 19 and the secondary coil 21, the relative position between the coils can be notified to the user. Further, when positioning the power receiver 20, the relative position between the primary coil 19 and the secondary coil 21 is approached by the user by gradually reporting the relative position between the primary coil 19 and the secondary coil 21. Can be recognized. Therefore, when the power receiver 20 is aligned, the user can be guided so that the relative position between the coils becomes an optimal position for power transmission. Further, when the power receiver 20 is placed at an optimal position for power transmission, the central LED 81 is lit. In this way, by changing the operation of the notification means 71, the power receiver 20 can be easily placed at an optimum position for efficient power transmission.

  Further, by providing a means for detecting the direction of displacement of the secondary coil 21 relative to the primary coil 19, the direction of displacement can be notified by the inner LEDs 82a to 83d or the outer LEDs 83a to 83d. FIG. 17 shows an example of a wireless power transmission apparatus provided with a means for detecting the misalignment direction. The power transmitter 80 is provided with direction detection coils 85a to 85d in the case 41 as detection means for the direction of displacement. The direction detection coils 85a to 85d are arranged in a cross shape around the primary coil 19. Further, the central axes of the direction detection coils 85 a to 85 d are arranged so as to be equidistant from the central axis of the primary coil 19. The direction detection coils 85a to 85d are supplied with an alternating current from a direction detection drive circuit. When detecting the misalignment direction, an alternating current is sequentially supplied to the direction detection coils 85a to 85d. When an alternating current is supplied to the direction detection coils 85a to 85d, the current flowing through the direction detection drive circuit is detected. By comparing the detection results, the misalignment direction of the secondary coil 21 with respect to the primary coil 19 can be detected. For example, it is assumed that the detection result when the alternating current is supplied to the direction detection coil 85a is relatively larger than the detection result when the alternating current is supplied to the other direction detection coils 85b to 85d. In this case, it can be seen that the displacement direction of the secondary coil 21 with respect to the primary coil 19 is the direction a in the figure. It is assumed that the detection results when the alternating current is supplied to the direction detection coils 85b and 85c are approximately the same and are relatively larger than the detection results when the alternating current is supplied to the direction detection coils 85a and 85d. In this case, it can be seen that the displacement direction of the secondary coil 21 with respect to the primary coil 19 is the direction f in the figure. In this way, the direction in which the secondary coil 21 is displaced relative to the primary coil 19 with respect to the arrows a to h in the figure is detected by the detecting means for the displacement direction. In addition, an operation example of each LED at that time will be described.

  In the state (A), all the LEDs are turned off. In the state (D), the central LED 81 is turned on. In these states (A) and (D), it is not necessary to notify the direction of displacement of the secondary coil 21 with respect to the primary coil 19. When the state (B) is shifted in the direction a in the figure, the outer LED 83a is turned on. When the state (B) is shifted in the direction d in the figure, the outer LED 83d is turned on. When the state (B) is shifted in the direction of e in the figure, the outer LEDs 83a and 83b are turned on. When the state (C) is shifted in the direction a in the figure, the inner LED 82a is turned on. When the state (C) is shifted in the direction of g in the figure, the inner LEDs 82c and 82d are turned on. When the state (C) is shifted in the direction h in the figure, the inner LEDs 82d and 82a are turned on. As described above, one of the inner LEDs 82a to 82d or the outer LEDs 83a to 83d is equidistant from the central LED 81 according to the position shift direction of the secondary coil 21 with respect to the primary coil 19, and is positioned 90 degrees. Turn on the two LEDs. According to the position shift direction, one or two of the LEDs arranged at the same distance from the central LED 81 arranged in the center are turned on to notify the eight position shift directions of 45 degrees each. Can do. Note that the above-described detection method of the misalignment direction is merely an example. The detection of the misalignment direction is not limited to eight directions.

  As described above, the function of detecting the displacement direction of the secondary coil 21 with respect to the primary coil 19 is provided, and the LEDs are arranged in a cross shape as the notification means 71. Then, the LED to be lit is controlled according to the position shift direction. Thereby, the user can recognize the position shift direction of the secondary coil 21 with respect to the primary coil 19 simultaneously with the relative position between each coil.

  Note that the operation of each LED as described above is merely an example. As long as the user can recognize the relative position of the primary coil 19 and the secondary coil 21, the operation of the LED may be changed in any way. Moreover, although the four states (A) to (D) are detected according to the relative positions of the primary coil 19 and the secondary coil 21, this is merely an example. The number of LEDs used may be arbitrarily changed depending on how many states are detected.

  Hereinafter, another embodiment of the notification means 71 will be described.

As another first example of the notification means 71, the notification means 71 is constituted by one LED.
In the state (A), the LED is turned off.
When in state (B), the LED blinks slowly.
In the state (C), the LED blinks faster than in the state (B).
In the state (D), the LED is turned on.
Thus, according to the relative position of the primary coil 19 and the secondary coil 21, LED can be light-extinguished, blinking, and making it light, and a user can alert | report the relative position between each coil. By replacing the relative position of the primary coil 19 and the secondary coil 21 with the blinking speed of the LED, the user can easily recognize the relative position between the coils. Moreover, you may make it change continuously according to the relative position of the primary coil 19 and the secondary coil 21 instead of changing the blinking speed of LED in steps.

Further, when the notification means 71 is constituted by one LED, an LED whose color can be changed may be used.
In the state (A), the LED is turned off.
In the state (B), the LED is lit in red.
In the state (C), the LED is lit in orange.
In the state (D), the LED is lit in green.
Thus, the relative position between each coil can be notified to the user by changing the color of the LED according to the relative position between the primary coil 19 and the secondary coil 21.

Moreover, when comprising as one alerting | reporting means 71, you may change the brightness of LED. For example, the LED is driven by PWM control.
In the state (A), the LED is turned off.
In the state (B), the LED is driven with a predetermined duty ratio.
In the state (C), the LED is driven with a larger duty ratio than in the state (B).
In the state (D), the LED is driven with a duty ratio of 100%.
Thus, the relative position between each coil can be notified to the user by changing the brightness of the LED in accordance with the relative position between the primary coil 19 and the secondary coil 21. Moreover, you may make it change continuously according to the relative position of the primary coil 19 and the secondary coil 21 instead of changing the brightness of LED stepwise.

As another second example of the notifying unit 71, the notifying unit 71 includes a plurality of LEDs. For example, the notification unit 71 is configured by three LEDs.
In the state (A), all the LEDs are turned off.
In the state (B), only one LED is turned on.
In the state (C), two LEDs are turned on.
In the state (D), three LEDs are turned on.
In this way, a plurality of LEDs are provided as the notification means 71, and the relative position between the coils is notified to the user by changing the number of LEDs that are turned on in accordance with the relative positions of the primary coil 19 and the secondary coil 21. be able to.

Further, when the notification means 71 is constituted by a plurality of LEDs, a plurality of LEDs having different colors may be used. For example, three LEDs of red, orange and green are used.
In the state (A), all the LEDs are turned off.
In the state (B), only the red LED is turned on.
In the state (C), only the orange LED is turned on.
In the state (D), only the green LED is turned on.
In this way, by providing a plurality of LEDs having different colors and changing the color of the LED to be lit according to the relative positions of the primary coil 19 and the secondary coil 21, the relative position between the coils is notified to the user. be able to.

As another third example of the notification means 71, the notification means 71 is constituted by a sound source. For example, a buzzer is provided as a sound source, and a sound output interval is changed according to the relative position of the primary coil 19 and the secondary coil 21.
In state (A), the sound source is muted.
In the state (B), a beep sound is emitted from the sound source at a predetermined interval.
When in state (C), a beep sound is emitted at a shorter interval than in state (B).
In the state (D), a continuous beep sound is generated from the sound source for a predetermined time.
Thus, by providing the sound source and changing the interval of the sound generated from the sound source according to the relative position of the primary coil 19 and the secondary coil 21, the relative position between the coils can be notified to the user. The sound source may be any sound source such as a buzzer or a speaker. Any sound may be used. As a modified example, a predetermined sound such as a melody or a voice announcement is output from the sound source for a certain period only in the state (D), that is, when it is in an optimal position for power transmission from the power transmitter 70 to the power receiver 20. Also good. Thereby, the user can easily recognize that the relative position of the power transmitter 70 and the power receiver 20 is in an optimum position for power transmission.

As another fourth example of the notification means 71, the notification means 71 is constituted by a vibrating body.
In the state (A), the vibrating body is not vibrated.
In the state (B), the vibrating body is vibrated with a predetermined vibration intensity.
In the state (C), the vibrating body is vibrated with a stronger vibration intensity than in the state (B).
In the state (D), the vibrating body is vibrated with a stronger vibration intensity than in the state (C).
In this way, the power transmitter 70 is provided with a vibrating body, and the vibration is transmitted to the user who has the charging device 20 by the vibration. By changing the vibration intensity of the vibrating body according to the relative position of the primary coil 19 and the secondary coil 21, the relative position between the coils can be notified to the user.

Further, when the notification means 71 is constituted by a vibrating body, the vibration interval may be changed according to the relative position of the primary coil 19 and the secondary coil 21.
In the state (A), the vibrating body is not vibrated.
In the state (B), the vibrating body is vibrated at a predetermined interval.
In the state (C), the vibrating body is vibrated at a shorter interval than in the state (B).
In the state (D), the vibrating body is continuously vibrated for a predetermined time.
In this way, by providing a vibrating body and changing the vibration pattern according to the relative position of the primary coil 19 and the secondary coil 21, the relative position between the coils can be notified to the user.

  In addition to the examples given above, the notification means 71 may be constituted by a monitor. The user is notified of the relative position of the primary coil 19 and the secondary coil 21 by displaying on the monitor screen. In addition, when the relative position between the power transmitter 70 and the power receiver 20 is in an optimal position for power transmission, the monitor screen displays that it is in an optimal state.

  As described above, the control circuit 15 controls the notification unit 71 based on the detection result of the relative position between the primary coil 19 and the secondary coil 21. Therefore, the operation of the notification unit 71 can be changed depending on the relative position of the primary coil 19 and the secondary coil 21. The user can recognize the relative positions of the primary coil 19 and the secondary coil 21 by confirming the operation of the notification means 71 when placing the power receiver 20 on the power transmitter 70. Further, it is possible to notify the notification means 71 that the relative position of the primary coil 19 and the secondary coil 21 is within a range suitable for power transmission. Thereby, the fall of the coupling coefficient by the position shift of the primary coil 19 and the secondary coil 21 can be suppressed, and electric power transmission can be performed efficiently.

  A method of suppressing the fluctuation of the input current Iin with respect to the variation in the detection secondary resonance frequency fd as shown in the first embodiment may be used in combination. Further, a detection method for correcting the fluctuation of the input current Iin relative to the fluctuation of the input voltage Vin as shown in the second embodiment may be used in combination. As a result, more accurate position detection can be performed, and power transmission can be performed with better transmission efficiency.

  In addition, the example of the alerting | reporting means 71 mentioned above and the operation example of the alerting | reporting means 71 are an example to the last. The operation example of the notification means 71 may be changed in any way as long as the user can recognize the relative position of the primary coil 19 and the secondary coil 21. Moreover, although the example using LED, a sound source, and a vibrating body was shown as the alerting | reporting means 71, you may use combining these. Moreover, you may use light emitting elements other than LED. Moreover, although the four states (A) to (D) are detected according to the relative positions of the primary coil 19 and the secondary coil 21, this is merely an example. It is only necessary to provide at least one threshold, detect whether the relative position between the coils is closer to or farther than a certain distance, and notify the notification means 71 of this. Moreover, it is also possible to change the brightness, blinking speed, and the like of the LED continuously rather than stepwise according to the relative positions of the primary coil 19 and the secondary coil 21. Thereby, the user can recognize in detail how far the relative positions between the coils are. In addition, the present invention can be implemented in various modifications without departing from the spirit thereof, or by combining the embodiments.

10, 60, 70, 80 Power transmitter 11 Current detection circuit 12 Current detection resistor 13 Error amplifier 14 Analog / digital converter 15 Control circuit 16 Input smoothing capacitor 17 Drive circuit 18 Primary capacitor 19 Primary coil 20 Power receiver 21 Secondary coil 22 Secondary capacitor 23 Detection capacitor 24 Rectifier circuit 25 Output smoothing capacitor 26 Impedance element 27 Control circuit 28 Load open / close switch 29 Load 41, 51 Case 42, 52 Magnetic body 61 Voltage detection circuit 71 Notification means 81, 82a to 82d, 83a to 83d LED
85a-85d direction detection coil

Claims (8)

A primary coil that supplies power to the secondary coil by electromagnetic induction, a drive circuit that supplies AC power to the primary coil, a current detection circuit that detects an input current supplied to the drive circuit, and the current detection A control circuit to which the detection result of the circuit is supplied;
Wireless power transmission characterized in that the control circuit drives the drive circuit at a predetermined drive frequency and detects a relative position between the primary coil and the secondary coil based on the input current flowing at that time apparatus. A secondary capacitor connected in series with the secondary coil; and a detection capacitor connected in parallel to the secondary coil and the secondary capacitor;
The wireless power transmission device according to claim 1, wherein the drive frequency is set to a lower frequency side than a resonance frequency of a resonance circuit including the secondary coil, the secondary capacitor, and the detection capacitor. A secondary capacitor connected in series with the secondary coil; and a detection capacitor connected in parallel to the secondary coil and the secondary capacitor;
The control circuit measures a resonance frequency of a resonance circuit including the secondary coil, the secondary capacitor, and the detection capacitor before the current detection circuit detects the input current, and based on the measurement result. The wireless power transmission device according to claim 1, wherein the driving frequency is set.   The wireless power transmission device according to claim 3, wherein the drive frequency is set to a value shifted to a lower frequency side than the resonance frequency.   5. The control circuit according to claim 1, wherein the control circuit corrects the detection result of the input current so as to cancel out a change in the input current due to a change in the input voltage supplied to the drive circuit. 6. Wireless power transmission device.   The wireless power transmission device according to any one of claims 1 to 5, further comprising notification means for notifying a relative position between the primary coil and the secondary coil according to a detection result of the current detection circuit.   The notification means is composed of a plurality of LEDs arranged in a cross shape, and lights in order from the LED arranged outside to the LED arranged in the center as the relative position between the primary coil and the secondary coil approaches. The wireless power transmission device according to claim 6. Detecting means for detecting a direction of displacement of the secondary coil with respect to the primary coil;
The wireless power transmission device according to claim 7, wherein one or two of the LEDs arranged at an equal distance from the LED arranged at the center are turned on according to the position shift direction.

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