JP2004248365A - Method and apparatus for contactless power transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for contactless power transmission capable of stabilizing an output voltage, without requiring feedback from the secondary side. <P>SOLUTION: The contactless power transmission apparatus has a transformer TR70 for transmitting power in contactless manner to a load 90 on the secondary side from the primary side. The drive frequency of an oscillation means 10 that generates pulse signals supplied to feeding means 20, 30, Q1, and Q2 is determined, with a control means 60, through adaptation to the value of the load 90 acquired, by estimating the value of the load 90 on the secondary side, by referencing to a preset characteristics, based on the primary current flowing to a GND from a primary side coil of the transformer TR70 which is detected by a current-detecting means 40. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-contact power transmission device and a non-contact power transmission method for transmitting power in a non-contact manner using electromagnetic induction by a transformer, and particularly to stabilizing a secondary-side output voltage without providing a feedback circuit. The present invention relates to a contactless power transmission device and a contactless power transmission method.
[0002]
[Prior art]
As one of the methods for transmitting electric power without contact, there is a method using electromagnetic induction by a transformer. In this method, when the load connected to the secondary side fluctuates, how to stabilize the output voltage on the secondary side becomes an issue. In this regard, there is a method in which the secondary output voltage is fed back to the primary drive circuit to perform adaptive control to stabilize the secondary output voltage. For example, in Patent Document 1, the feedback control is performed by the load information detection unit 24 and the secondary information input unit 14 shown in FIG.
[0003]
[Patent Document 1]
JP-A-11-187852 (pages 3-5, FIG. 1)
[0004]
[Problems to be solved by the invention]
However, in the above method disclosed in, for example, Patent Document 1 for stabilizing the output voltage on the secondary side, it is necessary to convert the load information from the secondary side into light and feed it back to the primary side. Therefore, when the optical system is used as a communication line, it must be separated from the feedback signal (light) in some form. When it is desired to reduce the size of the secondary side, the feedback circuit becomes an obstacle. Further, there is a problem that the structure becomes complicated in order to provide the feedback circuit without contact between the primary and secondary sides.
[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is intended to estimate a secondary output voltage only by a primary drive circuit and stabilize the output voltage without requiring feedback from a secondary side. It is an object of the present invention to provide a non-contact power transmission device and a non-contact power transmission method capable of performing the following.
[0006]
[Means for Solving the Problems]
In order to achieve this object, the invention according to claim 1 has a non-contact power supply having a transformer TR70 for transmitting power from a primary side to a load 90 on a secondary side in a contactless manner, as shown in FIG. In the transmission device, the switching element connected in series with the DC power supply is switched at a predetermined on / off frequency, and the DC power from the DC power supply is converted into AC power and supplied to the primary coil of the transformer TR70. Power supply means 20, 30, Q1, and Q2; an oscillating means 10 that oscillates a signal at a drive frequency set from the outside and supplies the signal to the power supply means 20, 30, Q1, and Q2; A current detecting means for detecting a primary current flowing from the side coil to GND, and a value of the load on the secondary side estimated based on the primary current detected by the current detecting means; And control means 60 for determining a drive frequency adapted to the value of the load 90 and setting the drive frequency in the oscillating means 10. The characteristic between the primary current and the value of the load 90 determined in advance for each frequency and the characteristic between the value of the load 90 determined in advance and the driving frequency adapted to the value of the load 90 are held. The driving frequency to be set in the oscillating means 10 is determined with reference to these characteristics.
[0007]
Therefore, according to the first aspect of the present invention, in the contactless power transmission device having the transformer TR70 for transmitting the power from the primary side to the load 90 on the secondary side in a contactless manner, the power supply means 20, 30, Q1 , Q2, the drive frequency of the oscillating means 10 that generates a pulse signal is determined in advance by the control means 60 based on the primary current flowing from the primary coil of the transformer TR70 to the GND detected by the current detection means 40. By referring to the set characteristics and estimating the value of the load 90 on the secondary side and determining it in accordance with the value of the load 90, the primary load can be obtained without providing a feedback circuit from the secondary side. The output voltage to the load 90 can be stabilized with a simple configuration on the side. Further, the circuit on the secondary side can be configured very simply.
[0008]
According to a second aspect of the present invention, in the first aspect of the present invention, it is detected whether or not the primary current exceeds a predetermined overcurrent threshold. And the oscillating unit 10 supplies power to the power supply units 20, 30, Q1, and Q2 upon receiving a notification of an overcurrent from the overcurrent detection unit 50. Is output.
[0009]
Therefore, according to the second aspect of the present invention, when the overcurrent detection means 50 detects a primary current exceeding a predetermined overcurrent threshold, the overcurrent detection means 50 notifies the oscillation means 10 of the overcurrent detection, and the oscillation means 10 Since the power supply means 20, 30, Q1, and Q2 output a signal for stopping the power supply, when an overcurrent is supplied to the load 90, the power supply to the load 90 can be stopped immediately to protect the circuit. be able to.
[0010]
According to a third aspect of the present invention, in the first or second aspect, the control unit 60 sets the highest drive frequency that can be set to the oscillation unit 10 as an initial value when power is turned on. I have.
[0011]
Therefore, according to the third aspect of the present invention, the control means 60 sets the highest drive frequency that can be set as the initial value in the oscillation means 10 when the power is turned on, thereby suppressing the output voltage by the high drive frequency, Unnecessarily high output voltage to the secondary side can be prevented.
[0012]
According to a fourth aspect of the present invention, based on an output signal of the oscillator 10 oscillating at an externally set drive frequency, a switching element connected in series with a DC power supply is switched at a predetermined on / off frequency, and In a contactless power transmission method for converting DC power from a DC power supply to AC power, supplying the AC power to a primary coil of a transformer TR70, and transmitting the power to a secondary load 90 without contact, A primary current flowing from the primary coil to GND is detected, and a value of the secondary load 90 is determined in advance for each drive frequency that can be set in the oscillator 10 based on the detected primary current. The driving frequency adapted to the estimated value of the load 90 is estimated with reference to the characteristic between the primary current and the value of the load 90, and the driving frequency adapted to the estimated value of the load 90 and the value of the load 90 are determined in advance. Drives that adapt to Determined with reference to the characteristics between the frequency and the driving frequency and the determined and sets the oscillator 10.
[0013]
Therefore, according to the present invention, the value of the load 90 on the secondary side is estimated on the primary side without referring to the feedback signal from the secondary side, and the oscillator 10 is adaptively controlled based on the estimated value. By doing so, the output voltage to the secondary side can be stabilized.
[0014]
According to a fifth aspect of the present invention, in the fourth aspect of the present invention, it is detected whether or not the primary current exceeds a predetermined overcurrent threshold value. The power supply to the primary coil of the transformer TR70 is stopped when the notification is made and the oscillator 10 receives the notification that the overcurrent occurs.
[0015]
Therefore, according to the fifth aspect of the present invention, when the primary current exceeds the predetermined overcurrent threshold, the oscillator is notified to notify the oscillator that the overcurrent is supplied to the load immediately. Power supply can be stopped, and the circuit can be protected.
[0016]
A sixth aspect of the present invention is characterized in that, in the invention of the fourth or fifth aspect, when the power is turned on, the highest drive frequency that can be set is set in the oscillator 10 as an initial value.
[0017]
Therefore, according to the invention of claim 6, when the power is turned on, the highest drive frequency that can be set is set as the initial value in the oscillator 10, so that the output voltage is suppressed by the high drive frequency, and the unnecessarily high secondary The generation of the output voltage to the side can be prevented.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0019]
FIG. 1 is a block diagram illustrating a configuration of a contactless power transmission device according to an embodiment of the present invention. In the following description of the present embodiment, the contactless power transmission device of the present invention is mounted on a vehicle and is used for non-contact power transmission between a vehicle body (body) as a primary side and a steering as a secondary side. An example applied will be described.
[0020]
The contactless power transmission device according to the present embodiment includes a transformer TR70, and a voltage controlled oscillator (VCO: Voltage Controlled Oscillator) 10, a Hi-side driver 20, a Hi-side field effect transistor FETQ1, a Low-side driver 30, on its primary side. It includes a low-side field effect transistor FETQ2, a current detection resistor R40, an overcurrent detection circuit 50, and an arithmetic circuit 60. A rectifying / smoothing circuit 80 and a load 90 are provided on the secondary side of the transformer TR70.
[0021]
The voltage controlled oscillator 10 is a circuit that controls the oscillation frequency based on the input voltage. The voltage controlled oscillator 10 determines the oscillation frequency based on the voltage control signal input from the arithmetic circuit 60, and converts the rectangular wave having a duty ratio of 50% into the Hi side driver 20 and Output to the Low side driver 30. When the occurrence of an overcurrent is detected by an overcurrent protection signal, which will be described later, from the overcurrent detection circuit 50, both the Hi-side field effect transistor FETQ1 and the Low-side field effect transistor FETQ2 are turned off to apply a load to the load 90 on the secondary side. In order to stop power supply, a low rectangular wave is output to both the Hi side driver 20 and the Low side driver 30.
[0022]
The Hi-side driver 20 is a driver for driving the Hi-side field effect transistor FETQ1 ON / OFF, and drives the gate of the FET Q1 with a voltage equal to or higher than VCC. Except for the dead time, it is driven in the opposite phase to the Low side driver 30. The low side driver 30 is a driver for driving the low side field effect transistor FETQ2 ON / OFF, and is driven in the opposite phase to the Hi side driver 20 except for the dead time.
[0023]
The Hi-side field effect transistor FETQ1 and the Low-side field effect transistor FETQ2 are connected between a battery or other power supply and ground, and function as switching elements. The Hi-side field effect transistor FETQ1 and the Low-side field effect transistor FETQ2 alternately switch the DC input voltage, and transmit power to the secondary-side rectifying and smoothing circuit 80 via the transformer TR70. Hi-side field effect transistor FETQ1 may be a P-channel FET or an N-channel FET. The low-side field effect transistor FETQ2 is preferably an N-channel FET.
[0024]
The current detection resistor R40 is a resistor of several tens mΩ to several Ω which is provided between the primary coil of the transformer TR70 and the ground. The overcurrent detection circuit 50 amplifies a minute voltage generated in the current detection resistor R40 and outputs a primary current value (analog signal) to the arithmetic circuit 60. When the arithmetic circuit 60 is realized by microcomputer control, a primary current value is input to an A / D input terminal of the microcomputer. Also, the overcurrent detection circuit 50 compares a predetermined threshold value with the primary current value, and for example, outputs an overcurrent protection signal (binary “Hi” when exceeding the threshold value and “Low” when within the threshold value). Signal) to the voltage controlled oscillator 10.
[0025]
The arithmetic circuit 60 determines an optimal frequency to be oscillated by the voltage controlled oscillator 10 based on the primary current value input from the overcurrent detection circuit 50, and sends a voltage control signal corresponding to the frequency to the voltage controlled oscillator 10. Output. The arithmetic circuit 60 can be realized by microcomputer control. The relationship between the drive frequency of the voltage controlled oscillator 10, the load 90, and the primary current appearing in the primary coil of the transformer TR70 (see FIGS. 5 to 7) is built in an EEPROM (Electrically Erasable and Programmable ROM) or the like. The microcomputer may refer to the database to be determined to determine an optimum frequency.
[0026]
Further, the arithmetic circuit 60 is not limited to being realized by microcomputer control, and the control of the present invention may be realized using an ASIC (Application Specific Integrated Circuit) or a DSP (Digital Signal Processor).
[0027]
In the description of the present embodiment, for example, the transformer TR70 is configured such that the primary coil side is disposed in a column on the vehicle body (body) side, the secondary side coil is disposed on the steering side, and both coils are relatively rotatable. The detailed structure of the rotary transformer will be described later.
[0028]
The rectifying and smoothing circuit 80 rectifies and smoothes AC power transmitted in a non-contact manner by electromagnetic induction in the transformer TR, and converts the AC power into DC power. Then, the converted DC power is supplied to the load 90. For example, a rectifier circuit may use a diode, and a smoothing circuit may use a capacitor and a coil. The load 90 applied to the contactless power transmission device of the present invention is a load whose value varies. For example, an airbag is used.
[0029]
2 and 3 are diagrams illustrating a structural example of the transformer TR70. The transformer TR70 is composed of a rotary transformer composed of a rotating part side member (secondary side) P1, a fixed part side member (primary side) P2, and a light guide P3 arranged between these members. .
[0030]
FIG. 2 is a view showing a state in which the transformer TR70 is mounted on a connecting portion between the steering and the column on the vehicle body (body) side. As shown in FIG. The fixed rotating unit side member (secondary side) P1 and the fixed unit side member (primary side) P2 fixed to the column side are connected and arranged facing each other.
[0031]
FIG. 3 is a cross-sectional view of the transformer TR70, showing details of a connecting portion between the rotating unit side member (secondary side) P1 and the fixed unit side member (primary side) P2. Light guide paths P3a and P3b, which form a part of the light guide P3, are arranged on the rotating part side member P1 and the fixed part side member P2, respectively, facing each other. In order to supply power from the column side to the steering side in a non-contact manner by electromagnetic induction, a primary side coil 70a is provided on the fixed part side member P2, and a secondary side coil is provided on the rotating part side member P1. 70b are provided.
[0032]
Next, the operation of the contactless power transmission device according to the embodiment of the present invention will be outlined. In FIG. 1, a voltage-controlled oscillator 10 generates an oscillation output pulse signal having a set frequency, and a Hi-side driver 20 and a Low-side driver 30 perform a predetermined operation based on a pulse signal supplied from the voltage-controlled oscillator 10. To generate an alternate pulse signal having an appropriate pause period.
[0033]
The alternating pulse signal is input to the gates of the Hi-side field-effect transistor FETQ1 and the Low-side field-effect transistor FETQ2, so that the Hi-side field-effect transistor FETQ1 and the Low-side field-effect transistor FETQ2 are turned on and off at predetermined times. Switching control is performed so as to turn on and off at a frequency.
[0034]
The DC input voltage of a battery or the like is alternately switched on and off by the Hi-side field-effect transistor FETQ1 and the Low-side field-effect transistor FETQ2 to be converted into a pulsed voltage. Transformer TR70 transmits electric power from the primary coil to the secondary coil. The rectifying and smoothing circuit 80 rectifies and smoothes the power transmitted to the secondary coil and supplies the rectified and smoothed power to the load 90.
[0035]
FIG. 4 is a flowchart for describing an operation related to adaptive control of the contactless power transmission device according to the embodiment of the present invention. First, when the non-contact power device is powered on, the arithmetic circuit 60 outputs a voltage control signal corresponding to the highest frequency that can be set to the voltage controlled oscillator 10, and the voltage controlled oscillator 10 Oscillate at the highest frequency based on the signal (step S1).
[0036]
Next, the overcurrent detection circuit 50 amplifies the minute voltage generated in the current detection resistor R40 and outputs a primary current value (primary coil current) to the arithmetic circuit 60 (Step S2). The arithmetic circuit 60 calculates the current load based on the current drive frequency and the primary current value input from the overcurrent detection circuit 50, referring to the graph showing the relationship between the load and the primary current in FIG. The weight of 90 is estimated (step S3).
[0037]
Next, the arithmetic circuit 60 obtains the optimum drive frequency corresponding to the estimated weight of the load 90 with reference to the graph of FIG. 7 showing the relationship between the load and the optimum drive frequency. Then, the arithmetic circuit 60 determines whether or not the current drive frequency matches the obtained optimum drive frequency (step S4). If the current driving frequency matches the obtained optimum driving frequency (step S4 / YES), the process proceeds to step S2 while maintaining the current driving frequency. If the current driving frequency is different from the obtained optimum driving frequency (step S4 / NO), the current driving frequency is changed to the newly obtained optimum driving frequency (step S5). And it changes to step S2. The arithmetic circuit 60 outputs a voltage control signal corresponding to the new drive frequency to the voltage controlled oscillator 10, and the voltage controlled oscillator 10 oscillates at the drive frequency based on the voltage control signal.
[0038]
Thereafter, the secondary output voltage can be stabilized by repeating steps S2 to S5. The setting range of the drive frequency is determined in advance based on the fluctuation range of the load 90. The data of the graphs shown in FIGS. 5 to 7 are stored in a database in a microcomputer (for example, a controller other than the microcomputer) by actual measurement or calculation. Further, an approximate expression may be obtained from the data of the graph, and the approximate expression may be formed into a circuit.
[0039]
Next, a specific example of the operation of the above-described contactless power transmission device will be described. Here, an example for generating a stable secondary output voltage of 14 V with respect to the unknown load 90 will be described. First, referring to the graph of FIG. 5 showing the relationship between the load and the output voltage, it can be seen that the output voltage is highest when the load resistance is large, and that the output voltage is lower as the drive frequency is higher. Therefore, immediately after the power is turned on, first, the voltage-controlled oscillator 10 is oscillated at the highest frequency that can be set (166 kHz in FIG. 5) (step S1).
[0040]
Next, the overcurrent detection circuit 50 amplifies the minute voltage generated in the current detection resistor R40 and outputs a primary current value (primary coil current) to the arithmetic circuit 60 (Step S2). The arithmetic circuit 60 estimates the current resistance value of the load 90 based on the current drive frequency and the primary current value input from the overcurrent detection circuit 50 with reference to the graph shown in FIG. S3). Here, assuming that the primary current value is 1 A and the driving frequency is 166 kHz, the resistance value of the load 90 is about 21Ω.
[0041]
Next, the arithmetic circuit 60 obtains the optimum driving frequency corresponding to the estimated resistance value of the load 90 with reference to the graph shown in FIG. The graph shown in FIG. 7 shows characteristics for the output voltage to be 14 V. The characteristic at a required output voltage (for example, 14 V) is calculated from the graph shown in FIG. 5, and the graph shown in FIG. 7 is stored in a database in advance. Here, the optimum driving frequency for setting the output voltage to 14 V when the load resistance value is 21Ω is about 144 kHz.
[0042]
Since the current driving frequency (166 kHz) does not match the obtained optimum driving frequency (144 kHz) (step S4 / NO), the arithmetic circuit 60 determines the current driving frequency (166 kHz) by using the newly obtained optimum driving frequency (144 kHz). 144 kHz) (step S5). And it changes to step S2. The arithmetic circuit 60 outputs a voltage control signal corresponding to the new drive frequency to the voltage controlled oscillator 10, and the voltage controlled oscillator 10 oscillates at the drive frequency based on the voltage control signal. Thereafter, steps S2 to S5 are repeated.
[0043]
The embodiment described above is an example of a preferred embodiment of the present invention, and the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention.
[0044]
For example, the non-contact power transmission device of the present invention is applied not only to a rotating part such as a steering wheel of an automobile described above but also to a non-contact charging device of a mobile terminal such as a mobile phone, a PHS, a PDA, and a portable MD player. Applicable. When applied to a charging device, the state of the secondary load can be determined only on the primary side, so that the charging state can be monitored.
[0045]
In addition, the present invention is not sufficiently reliable in places where it is necessary to supply electric power in a non-contact manner, places where it is difficult to supply power by wire in rotating parts, places where rotation is infinite by power supply by a rotary transformer, and contacts. Good for places.
[0046]
【The invention's effect】
As is apparent from the above description, according to the first aspect of the present invention, there is provided a contactless power transmission device having a transformer for transmitting power from a primary side to a load on a secondary side in a contactless manner. The control means refers to a preset characteristic based on the primary current flowing from the primary coil of the transformer to the GND detected by the current detecting means, based on the driving frequency of the oscillating means for generating a pulse signal to be supplied to the power supply. Then, by estimating the value of the load on the secondary side and deciding it in accordance with the value of the load obtained, the load on the load can be reduced by a simple configuration on the primary side without providing a feedback circuit from the secondary side. Output voltage can be stabilized. Further, the circuit on the secondary side can be configured very simply.
[0047]
According to the second aspect of the invention, in addition to the effect of the first aspect, when the overcurrent detection means detects a primary current exceeding a predetermined overcurrent threshold, the oscillation means performs an overcurrent detection. The notifying unit outputs a signal for stopping the power supply to the power supply unit, so that when an overcurrent is supplied to the load, the power supply to the load can be stopped immediately to protect the circuit. it can.
[0048]
According to the invention of claim 3, in addition to the effect of the invention of claim 1 or 2, the control means sets the highest drive frequency that can be set to the oscillation means as an initial value when the power is turned on. In addition, the output voltage can be suppressed by the high driving frequency, and the occurrence of an unnecessary high output voltage to the secondary side can be prevented.
[0049]
According to the fourth aspect of the invention, the primary side estimates the value of the secondary side load without referring to the feedback signal from the secondary side, and adaptively controls the oscillator based on the estimated value. The output voltage to the secondary side can be stabilized.
[0050]
According to the invention of claim 5, in addition to the effect of the invention of claim 4, when the primary current exceeds a predetermined overcurrent threshold, the oscillator is notified to supply the overcurrent to the load. In this case, power supply to the load can be stopped immediately, and the circuit can be protected.
[0051]
According to the invention described in claim 6, in addition to the effect of the invention described in claim 4 or 5, the highest drive frequency that can be set is set as an initial value in the oscillator when the power is turned on. The output voltage can be suppressed, and the occurrence of an output voltage to the secondary side that is unnecessarily high can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a contactless power transmission device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a structural example of a transformer TR in the contactless power transmission device of the present invention, and is a diagram illustrating a state in which the transformer TR is mounted on a connection portion between a steering wheel and a column on a vehicle body side. is there.
FIG. 3 is a cross-sectional view illustrating a structural example of a transformer TR.
FIG. 4 is a flowchart illustrating an operation related to adaptive control of the contactless power transmission device according to the embodiment of the present invention.
FIG. 5 is a graph showing a relationship between a load and an output voltage according to the embodiment of the present invention.
FIG. 6 is a graph showing a relationship between a load and a primary current according to the embodiment of the present invention.
FIG. 7 is a graph showing a relationship between a load and an optimum driving frequency according to the embodiment of the present invention.
[Explanation of symbols]
10. Voltage controlled oscillator (VCO)
20 Hi side driver 30 Low side driver Q1 Hi side field effect transistor FET
Q2 Low side field effect transistor FET
40 Current detection resistor R
50 Overcurrent detection circuit 60 Operation circuit 70 Transformer TR
80 Rectifying smoothing circuit 90 Load

Claims (6)

In a contactless power transmission device having a transformer for transmitting power from a primary side to a load on a secondary side in a contactless manner,
Power supply means for switching a switching element connected in series with a DC power supply at a predetermined ON / OFF frequency, converting DC power from the DC power supply into AC power, and supplying the AC power to a primary coil of the transformer;
Oscillating means for oscillating a signal at a drive frequency set from the outside and supplying the signal to the power supply means;
Current detection means for detecting a primary current flowing from the primary coil of the transformer to GND;
Based on the primary current detected by the current detecting means, the value of the load on the secondary side is estimated, a drive frequency adapted to the value of the load is determined, and the drive frequency is set in the oscillating means. Control means, and
The control means adapts to the characteristic between the primary current and the value of the load determined in advance for each drive frequency that can be set in the oscillation means, and to the value of the load and the value of the load determined in advance. A non-contact power transmission device characterized by holding characteristics between a driving frequency and a driving frequency to be set in the oscillating means with reference to these characteristics. An overcurrent detection unit that detects whether the primary current exceeds a predetermined overcurrent threshold, and, if so, notifies the oscillation unit that an overcurrent is present.
2. The non-contact power transmission device according to claim 1, wherein the oscillating unit outputs a signal for stopping the power supply to the power supply unit when receiving a notification of an overcurrent from the overcurrent detection unit. . 3. The non-contact power transmission device according to claim 1, wherein the control unit sets the highest drive frequency that can be set as an initial value to the oscillation unit when power is turned on. Based on an output signal of an oscillator that oscillates at an externally set drive frequency, a switching element connected in series with a DC power supply is switched at a predetermined ON / OFF frequency, and DC power from the DC power supply is converted to AC power. In the non-contact power transmission method, the power is transmitted to the primary side coil of the transformer, and the power is transmitted to the secondary side load in a non-contact manner.
Detecting a primary current flowing from the primary side coil of the transformer to GND,
The value of the load on the secondary side based on the detected primary current is referred to by referring to a characteristic between the primary current and the value of the load previously obtained for each drive frequency that can be set in the oscillator. Presumed,
A drive frequency adapted to the estimated load value is determined with reference to a characteristic between a previously determined load value and a drive frequency adapted to the load value,
A non-contact power transmission method, wherein the determined drive frequency is set in the oscillator. Detects whether the primary current exceeds a predetermined overcurrent threshold, and if so, notifies the oscillator that there is an overcurrent,
5. The non-contact power transmission method according to claim 4, wherein when the oscillator is notified of the overcurrent, the power supply to the primary coil of the transformer is stopped. 6. The non-contact power transmission method according to claim 4, wherein the highest drive frequency that can be set is set as an initial value in the oscillator when the power is turned on.

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