JP2010028934A - Power reception control device, power receiving device and contactless power transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a power transmitting device to unfailingly detect an inserted foreign substance without inhibiting normal power transmission, and imposing excessive burden on the power transmitting device and a power receiving device in a contactless power transmission system. <P>SOLUTION: A power reception control circuit 52 uses a driving clock DRCK of a primary coil in a normal power transmission period as a reference of timing to control a load demodulation section 46, thereby causing the power transmitting device to transmit regular authentication data including a 010 pattern. The period of one bit of the regular authentication data is set at, e.g. a period equivalent to 16 of driving clocks of the primary coil, and the period of one bit of a communication packet is set at, e.g. a period equivalent to 32 of driving clocks of the primary coil. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power reception control device, a power reception device, a contactless power transmission system, and the like.

  In recent years, contactless power transmission (non-contact power transmission) that uses electromagnetic induction and enables power transmission even without a contact of a metal part has been in the spotlight. As an application example of this non-contact power transmission, charging of a mobile phone or a household device (for example, a handset of a phone) has been proposed.

  A non-contact power transmission device using a primary coil and a secondary coil is described in Patent Document 1, for example. In the non-contact power transmission system described in Patent Literature 1, data can be transmitted from a power transmission device to a power reception device by frequency modulation. In addition, data can be transmitted from the power receiving apparatus to the power transmitting apparatus by load modulation.

  The power receiving device described in Patent Document 1 includes a variable load unit (load modulation unit), and turns on / off a MOS transistor for load modulation provided in the variable load unit (load modulation unit). Thus, data is transmitted to the power transmission device via the secondary coil and the primary coil.

When the load state of the power receiving device changes due to the on / off of the MOS transistor, for example, the voltage amplitude at the coil end of the primary coil increases or decreases. Therefore, the power transmission device monitors the coil end voltage of the primary coil, and compares the amplitude of the coil end voltage with a threshold value, for example, to “0” and “1” of data sent from the power receiving device. Can be distinguished.
JP 2006-60909 A

  After the power transmission device starts normal power transmission to the power reception device, for example, when a conductive foreign object (for example, a large metal thin plate) is inserted between the primary coil and the secondary coil, the transmitted power Most of this is consumed in conductive foreign matter. For this reason, a state (takeover state) in which the power transmission device regards the conductive foreign matter as a load and continues normal power transmission occurs. When the takeover state occurs, the conductive foreign matter generates heat, which is not preferable for safety.

  In the conventional non-contact power transmission system, the power transmission device cannot accurately detect the hijacking state. Therefore, effective measures are required.

  The detection of the hijacking state needs to be executed during the normal power transmission period. Therefore, when detecting the hijacking state, it is necessary to give sufficient consideration so that normal power transmission is not hindered and an excessive burden is not placed on the power transmission device and the power reception device.

  In addition, it is important that the power transmission device can reliably detect the hijacking state.

  The present invention has been made based on such consideration. According to some embodiments of the present invention, for example, a power transmission device can reliably insert a foreign object (particularly takeover) without impeding normal power transmission and without imposing an excessive burden on the power transmission device and the power reception device. State) can be detected.

  (1) In one aspect of the power reception control device of the present invention, the primary coil and the secondary coil are electromagnetically coupled to transmit power from the power transmission device to the power reception device, and the power reception during the power transmission period A power receiving control device provided in the power receiving device in a contactless power transmission system in which a load modulation unit included in the device modulates a load of the power receiving device and transmits a load modulation signal to the power transmitting device. A power reception control circuit for controlling the operation of the device, wherein the power reception control circuit controls the load modulation unit during the power transmission period to cause periodic load modulation of the power reception device, thereby , 010 is transmitted to the power transmission device.

  In the normal power transmission period, the power reception control device controls the load modulation unit provided in the power reception device, and transmits the load modulation signal to the power transmission device periodically (periodically). When a foreign object (conductive foreign object) is inserted between the primary coil and the secondary coil, communication is interrupted by the foreign object, so that the power transmitting device periodically transmits a load modulation signal transmitted from the power receiving device. Cannot receive. Therefore, if the power transmission device can receive the load modulation signal periodically transmitted from the power receiving device, it can determine that there is no foreign object inserted and can perform normal power transmission. For example, measures such as stopping normal power transmission can be taken.

  The load modulation signal periodically transmitted by the power receiving device includes a data pattern of 010 (or 101). The load modulation signal transmitted periodically is a communication signal (communication data) for detecting a foreign matter (conductive foreign matter) inserted between the primary coil and the secondary coil. In this specification, a communication signal having a data pattern of 010 (or 101) for detecting a foreign object may be referred to as “periodic authentication data”. The periodic authentication data can be transmitted from the power receiving side to the power transmitting side, for example, every second.

  The periodic authentication data includes a data pattern of 010 (or 101). For example, “1” corresponds to a state where the power receiving device has a heavy load (a state where the load current is large), and “0” corresponds to a state where the power receiving device has a light load (a state where the load current is small or the load current is zero). Make it correspond. The reverse is also possible. The pattern 010 and the pattern 101 are equivalent.

  The periodic authentication data can be constituted by, for example, a single pattern (isolated pattern) of “010 (or 101)”, and a pattern in which “010 (or 101)” is repeated k times (k is an integer of 2 or more). It may be. For example, when k = 2, the pattern “01010” or “010010” may be employed.

  Further, as a pattern of the periodic authentication data, a pattern applying the pattern 010 (or 101) can be adopted. For example, a special pattern such as “0101000010” may be employed.

  The power receiving device of the non-contact power transmission system can originally perform communication by load modulation during normal power transmission. In this aspect, this communication function is used for foreign object detection. Therefore, it is easy to realize without adding a special circuit, and there is no problem of cost increase.

  Therefore, the power transmission device can reliably detect a foreign object without impeding normal power transmission and without placing a burden on the power transmission device or the power reception device. Therefore, when a hijacking state occurs, the power transmission device can reliably take measures such as stopping normal power transmission (or reducing the power of normal power transmission to low power), and the reliability of the contactless power transmission system Will improve.

  (2) In another aspect of the power reception control device of the present invention, the periodic authentication data is configured by a single pattern of 010 or 101.

  In this aspect, the simplest pattern is adopted as the pattern of the periodic authentication data. In order to simplify the detection processing of the periodic authentication data by the power transmission device, it is desirable that the periodic authentication data has a pattern as simple as possible.

  Since the periodic authentication data is transmitted from the power receiving apparatus to the power transmitting apparatus via the secondary coil and the primary coil, a certain amount of waiting time (delay is required) until the periodic authentication data can be accurately received by the power transmitting apparatus. Time). Further, since the voltage at the coil end of the primary coil has a distorted waveform, the power transmission device needs to carefully detect the periodic authentication data.

  When the periodic authentication data is long or complicated, the detection load of the periodic authentication data in the power transmission device increases, and the time until detection tends to increase.

  Therefore, in this aspect, a single (isolated) pattern of 010 or 101 is adopted as the pattern of the periodic authentication data. That is, in the period in which the periodic authentication is executed, 010 is transmitted from the power receiving side to the power transmission side only once. Since the pattern of the periodic authentication data is simplified, the process for detecting the periodic authentication data in the power transmission device is easy, and the time required for detecting the periodic authentication data can be the shortest time.

  (3) In another aspect of the power reception control device of the present invention, the power reception side control circuit uses the drive clock of the primary coil reproduced based on the coil end voltage or coil current of the secondary coil as a reference for timing. Are used to turn on / off the load modulation switch included in the load modulation section.

  The periodic authentication data detection process by the power transmission device is executed, for example, every second. If the power transmission device can predict the timing for receiving the periodic authentication data, the reception process of the periodic authentication data is facilitated, and the reliability of the detected periodic authentication data is increased.

  Therefore, in this aspect, the power reception control device performs on / off control of the load modulation switch using the primary coil drive clock (primary coil drive signal used on the power transmission side) as a timing reference.

  That is, when the primary coil is AC driven by the drive clock, the coil end voltage (coil current) of the secondary coil also varies in synchronization with the drive clock of the primary coil. Therefore, on the power receiving side, the drive clock of the primary coil can be reproduced based on the coil end voltage (coil current) of the secondary coil. The power reception control device uses the load modulation switch based on the reproduced drive clock of the primary coil (that is, in synchronization with the drive clock or in synchronization with the clock generated based on the drive clock). ON / OFF control. Thereby, the periodic authentication data is transmitted from the power receiving side to the power transmitting side at a timing determined based on the drive clock of the primary coil.

  The periodic authentication data is detected on the power transmission side after a certain delay time has elapsed, but the delay time can be predicted. Further, the timing of the drive clock of the primary coil (for example, the timing of the positive edge) is known for the power transmission device. Therefore, the power transmission side can predict the timing at which the periodic authentication data is received based on the timing of the drive clock of the primary coil.

  Therefore, the reception process of the periodic authentication data in the power transmission device is facilitated, and the reliability of the detected periodic authentication data is increased. In addition, in order to synchronize communication between the power reception side and the power transmission side, it is not necessary to use a special control signal, and the implementation is easy.

  (4) In another aspect of the power reception control device of the present invention, the power reception side control circuit is transmitted when the load modulation unit is controlled to transmit the periodic authentication data during the power transmission period. A 1-bit period of “0” or “1” is set to a time that is p times (p is an integer of 1 or more) one cycle of the drive clock of the primary coil, and during the power transmission period, When transmitting a communication packet by controlling the load modulation unit, the transmitted 1-bit “0” or “1” period is q times the cycle of the drive clock of the primary coil (q is 1). It is the above integer and is set to p ≠ q).

  During the normal power transmission period, a communication packet may be transmitted from the power receiving side to the power transmission side. For example, information indicating the charge state of the load to be fed may be transmitted irregularly from the power reception side to the power transmission side. Therefore, the periodical authentication period and the communication packet transmission period may overlap.

  Therefore, the power transmission device needs to distinguish whether the received data is a communication packet or periodic authentication data. For example, when the received data is 010, it is important that the power transmission side can distinguish whether the 010 data is a communication packet or periodic authentication data.

  Therefore, in this aspect, by changing the 1-bit period (1 bit length), the power transmission side can distinguish between the periodic authentication data and the communication packet. That is, for the periodic authentication data, a 1-bit period of “0” or “1” is set to a time that is p times (p is an integer of 1 or more) one cycle of the drive clock of the primary coil. For communication packets, the 1-bit period of “0” or “1” is set to q times the cycle of the drive clock of the primary coil (q is an integer of 1 or more and p ≠ q). Set.

  On the power transmission side, when bit synchronization is established and data is received, it is detected whether the 1-bit period continues for a period p times or q times the period of the drive clock of the primary coil. As a result, the transmission side can distinguish whether the received data is a communication packet or periodic authentication data.

  (5) In another aspect of the power reception control device of the present invention, the power reception side control circuit transmits one bit when the load modulation unit is controlled to transmit a communication packet during the power transmission period. Is set to q times (q = β × p, β is an integer of 2 or more) one cycle of the drive clock of the primary coil.

  In this aspect, the 1-bit period of the transmission packet is set to β times the 1-bit period of the periodic authentication data (β is an integer of 2 or more). On the transmitting side, one bit period of the periodic authentication data is defined as one unit time, and it is detected whether one bit continues for the unit time or a period that is β times the unit time. Thereby, the power transmission side can distinguish the periodic authentication data from the communication packet. On the power transmission side, since the reception process can be performed with one bit period of the periodic authentication data as one unit time, the data reception process is simplified.

  (6) In another aspect of the power reception control device of the present invention, p = 16 and q = 32 (thus β = 2).

  If the 1-bit period is too long, the time required to determine 1-bit received data becomes longer. Therefore, in this aspect, β = 2 is set.

  (7) In another aspect of the power reception control device of the present invention, when the power reception control circuit performs the periodic load modulation, first, the power supply to the power supply target load is temporarily reduced or stopped, During the period when the power supply to the power supply target load is temporarily reduced or stopped, the load modulation unit is controlled to periodically modulate the load of the power receiving device.

  When the power receiving side performs load modulation in a state where there is a large amount of current supplied to a power supply target load (for example, a battery such as a secondary battery), the amount of current changed by the load modulation is the current supplied to the power supply target load. Since it is small with respect to quantity, it may become difficult for the power transmission side to detect a load modulation signal.

  Therefore, in this aspect, when the power receiving side performs load modulation, the power receiving control device controls, for example, a power control switch provided in the power feeding path to temporarily reduce power feeding to the load to be fed (power feeding). Reduce the current) or stop. Accordingly, the power transmission side can always reliably detect the load modulation signal regardless of the state of the load to be fed. Therefore, the reliability of the non-contact power transmission system is further improved.

  (8) According to one aspect of the power receiving device of the present invention, the power received from the power transmitting device via the electromagnetically coupled primary coil and secondary coil is received, and the load modulation signal is received during the power receiving period. A power receiving device for transmitting to a power transmitting device, wherein the secondary coil, a power receiving unit including a rectifier circuit, a load modulating unit that modulates a load of the power receiving device to generate the load modulation signal, and a power supply target A power supply control unit that controls power supply to a load, and the power reception control device according to any one of the above.

  As a result, a highly reliable power receiving device that enables reliable foreign object detection is realized.

  (9) One aspect of the contactless power transmission system of the present invention is a primary coil, a secondary coil, a power transmission unit that drives the primary coil to transmit power, and power transmission that controls the operation of the power transmission unit. A power transmission device having the control device, and the power reception device.

  As a result, a non-contact power transmission system capable of reliably detecting foreign matter and having high safety and reliability is realized.

  (10) In one aspect of the contactless power transmission system of the present invention, the power transmission device stops power transmission to the power reception device when the power reception device fails to receive the load modulation signal periodically transmitted. Or reduce transmission power.

  During the normal power transmission period, foreign object detection is performed periodically. When a foreign object is detected, power transmission is stopped or power transmission power is reduced. Thereby, problems, such as heat_generation | fever of a conductive foreign material, do not arise, but the reliability of a non-contact power transmission system improves markedly.

  In addition, as a countermeasure when a foreign object is detected, either power transmission stop or power transmission power reduction can be executed. However, by stopping the power transmission, the problem of heat generation of foreign matters is completely solved. If priority is given to ensuring the reliability of the non-contact power transmission system over the charging of the secondary battery, it is preferable to take a measure of stopping power transmission.

  (11) In another aspect of the contactless power transmission system of the present invention, the power transmission device continuously receives the load modulation signal periodically transmitted by the power reception device n times (n is an integer of 2 or more). In the case of failure, power transmission to the power receiving apparatus is stopped or power transmission power is reduced.

  When the periodic authentication data is transmitted from the power receiving side to the power transmission side, for example, noise may occur accidentally, and the power transmission side may not be able to receive the periodic authentication data.

  Therefore, in this aspect, the power transmission side stops normal power transmission to the power receiving device when n times (n is an integer of 2 or more) consecutive periodic authentication data reception has failed, or the power of normal power transmission is reduced. Reduce. As a result, there is no inconvenience that the normal power transmission is erroneously stopped even though no foreign matter is inserted.

  (12) In another aspect of the contactless power transmission system of the present invention, n = 3.

  If the value of n is too large, a quick foreign matter countermeasure cannot be executed. On the other hand, when n = 2, for example, a state in which noise is likely to be generated continues, and there may be a situation where accurate reception cannot be performed twice consecutively. Therefore, in this aspect, n = 3 is set. The reception process on the power transmission device side is executed at intervals of 1 second, for example. Even if a state with a lot of noise continues for a certain period of time, it is considered that the probability of failure of receiving a load modulation signal executed at intervals of 1 second, for example, three times consecutively is low due to the noise. That is, when a situation occurs in which reception of the periodic load modulation signal fails three times in succession, it may be determined that there is a high possibility that a conductive foreign object has been inserted between the primary coil and the secondary coil. it can. Therefore, it is possible to achieve both accurate detection of foreign object insertion and rapid detection.

  (13) In another aspect of the non-contact power transmission system of the present invention, the power transmission device performs reception processing of the load modulation signal periodically transmitted by the power reception device X times (X is an integer of 2 or more). As a result, if the load modulation signal is received Y times (Y is an integer satisfying 1 ≦ Y ≦ X), the power transmission to the power receiving apparatus is stopped or the power transmission power is reduced.

  In this aspect, when the number of reception failures with respect to a given number of reception processes reaches a given value, the power transmission device determines that a foreign object has been inserted, and executes power transmission stop or power transmission power reduction. For example, the power transmission apparatus executes the periodic load modulation signal reception process 10 times. During this series of ten reception processes, for example, when reception fails five times, the power transmission device stops power transmission or reduces power transmission power.

  For example, it may be difficult for the primary side to detect the periodic load modulation signal due to the relative positional relationship between the primary side and the secondary side. In such a case, it may be difficult to determine whether the reception failure is due to a foreign object or due to the relative positional relationship between the primary side and the secondary side. However, if the number of reception processing times to be determined is increased to some extent, the probability that the cause of reception failure can be distinguished increases, and the accuracy of foreign object detection improves. Therefore, according to this aspect, highly reliable foreign object detection is realized.

  As described above, according to some embodiments of the present invention, for example, the power transmission device can reliably prevent foreign objects without impeding normal power transmission and without excessively burdening the power transmission device and the power reception device. Insertion (especially a takeover state) can be detected.

  Hereinafter, preferred embodiments of the present invention will be described in detail. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are indispensable as means for solving the present invention. Not always.

(First embodiment)
In the present embodiment, a configuration example of a contactless power transmission system and main operations, periodic authentication, a data configuration for distinguishing periodic authentication data from communication packets, and the like will be described.

(Configuration of electronic equipment)
FIG. 1A to FIG. 1C are diagrams illustrating a configuration of an example of a contactless power transmission system. FIG. 1A shows an example of an electronic device to which the contactless power transmission method of this embodiment is applied. A charger 500 (cradle) which is one of electronic devices has a power transmission device 10. A mobile phone 510 that is one of the electronic devices includes a power receiving device 40. The mobile phone 510 includes a display unit 512 such as an LCD, an operation unit 514 including buttons and the like, a microphone 516 (sound input unit), a speaker 518 (sound output unit), and an antenna 520.

  Electric power is supplied to the charger 500 via the AC adapter 502, and this electric power is transmitted from the power transmitting device 10 to the power receiving device 40 by contactless power transmission. Thereby, the battery of the mobile phone 510 can be charged or the device in the mobile phone 510 can be operated.

  The electronic device to which this embodiment is applied is not limited to the mobile phone 510. For example, the present invention can be applied to various electronic devices such as wristwatches, cordless telephones, shavers, electric toothbrushes, wrist computers, handy terminals, portable information terminals, electric bicycles, and IC cards.

  As schematically shown in FIG. 1B, power transmission from the power transmission device 10 to the power reception device 40 is performed on the primary coil L1 (power transmission coil) provided on the power transmission device 10 side and on the power reception device 40 side. This is realized by electromagnetically coupling the secondary coil L2 (power receiving coil) formed to form a power transmission transformer. Thereby, non-contact power transmission becomes possible.

  In FIG. 1B, the primary coil L1 and the secondary coil L2 are, for example, air-core planar coils formed by winding a coil wire spirally on a plane. However, the coil of the present embodiment is not limited to this, and any shape, structure, or the like may be used as long as the primary coil L1 and the secondary coil L2 can be electromagnetically coupled to transmit power.

  For example, in FIG. 1C, the primary coil L1 is formed by winding a coil wire around the X-axis around the magnetic core in a spiral shape. The same applies to the secondary coil L2 provided in the mobile phone 510. The present embodiment can also be applied to a coil as shown in FIG. In the case of FIG. 1 (C), as the primary coil L1 and the secondary coil L2, in addition to the coil wound around the X axis, a coil wound around the Y axis may be combined. .

(Example of configuration of contactless power transmission system)
FIG. 2 is a diagram illustrating an example of a configuration of a contactless power transmission system. The power transmission device 10 includes a primary coil L1, a power transmission unit 12, and a power transmission control device (power transmission control IC) 20. The power transmission control device 20 includes a waveform monitor circuit 14, a waveform detection circuit 28, a power transmission side control circuit 22 that controls the operation of the power transmission device, and a driver control circuit 26.

  The power reception device 40 includes a secondary coil L2, a power reception unit 42, a load modulation unit 46, a power supply control unit 48, and a power reception control device (power reception control IC) 50.

  The power receiving unit 42 includes a rectifier circuit 43, a smoothing capacitor CB1, and voltage dividing resistors RB4 and RB5.

  The load modulation unit 46 includes a load modulation transistor (load modulation switch) M1 and a current limiting resistor RB3. On / off of the load modulation transistor (load modulation switch) M1 is controlled by a load modulation signal P3Q output from the power receiving side control circuit 52.

  The power supply control unit 48 includes a regulator (LDO) 49, a power supply control transistor M2, and a bias resistor RU2.

  The power reception control device (power reception control IC) 50 includes a power reception side control circuit 52. The power receiving side control circuit 52 controls the operation of the power receiving device 40.

  The power receiving side control circuit 52 is supplied with a voltage obtained by dividing the coil end voltage of the secondary coil L2 by the voltage dividing resistors RB1 and RB2. The power receiving side control circuit 52 is supplied with a voltage VD4 obtained by dividing the rectified voltage VDC by the voltage dividing resistors RB4 and RB5.

  The power receiving side control circuit 52 monitors the voltage VD5 at the output node of the regulator (LDO) 49 via the monitoring line LP1. Further, the power receiving side control circuit 52 outputs a load modulation signal P3Q to the control line LP3, thereby controlling on / off of the load modulation transistor (load modulation switch) M1.

  In addition, the power reception side control circuit 52 supplies a power supply control signal (ICUTX) to the charging device 90 via the terminals TA3 and TA4. When the power supply control signal (ICUTX) becomes active level (H level), the power supply to the load (secondary battery) 94 to be supplied is temporarily stopped. Alternatively, the current supplied to the load (secondary battery) 94 to be supplied can be temporarily reduced.

  The charging device (charger) 90 manages charging of a load (secondary battery 94 in this case) to be fed. The charging device 90 includes a power supply control transistor (power supply control switch) M3, a pull-down resistor R16, a charge control device (charge control IC) 92, a power supply control transistor M5, and a current sense resistor R15.

  When the power supply control signal (ICUTX) output from the power receiving side control circuit 52 is at an inactive level (L level), the power supply control transistor (power supply control switch) M3 is in an on state, and is supplied to the load 94 to be fed. Power can be supplied. When the power supply control signal (ICUTX) is at the active level (H level), the power supply control transistor (power supply control switch) M3 is turned off, and the power supply to the power supply target load 94 is temporarily stopped, or The feeding current is reduced.

  The power receiving device 40 performs load modulation during normal power transmission (continuous power transmission after authentication of the secondary device), and periodically (periodically) periodically authentication data PT1 for foreign object detection to the power transmission device 10. Send. The power transmission side control circuit 22 included in the power transmission control device 20 detects the load modulation signal PT1 transmitted from the power reception device 40 side during normal power transmission. When the load modulation signal PT1 cannot be detected, the power transmission side control circuit 22 determines that the foreign object AR has been inserted, and stops normal power transmission (or can reduce the power of normal power transmission).

(Communication method and periodic authentication between power transmission device and power reception device)
3A and 3B are diagrams for explaining data communication between the power transmission device and the power reception device.

  As shown in FIG. 3A, the power transmission device includes a power transmission control device 20 including a power transmission side control circuit 22, a driver control circuit 26, a power transmission unit (power transmission driver) 12, a waveform monitor circuit 14, and 1 A secondary coil L1 and a capacitor C1 connected in series to the primary coil L1 are included. The power transmission control device 20 comprehensively controls the operation of the power transmission device. The power transmission side control circuit 22 included in the power transmission control device 20 executes various determination processes, controls the operation of the driver control circuit 26 based on the results, and determines the data sent from the power receiving apparatus. Execute. The power transmission unit (power transmission driver) 12 AC-drives the primary coil L1 based on a primary coil drive clock (hereinafter sometimes simply referred to as a drive clock or a driver clock) DRCK.

  Communication from the power transmitting apparatus to the power receiving apparatus is performed by frequency modulation (switching the frequency of the drive clock between f1 and f2). On the other hand, communication from the power receiving apparatus to the power transmitting apparatus is executed by load modulation (forcibly changing the load state of the power receiving apparatus).

The frequency detection circuit 60 included in the power receiving apparatus includes a drive clock (DRCK) reproducing unit 61. In FIG. 3A, the power receiving unit 42 divides the coil end voltage of the secondary coil by the voltage dividing resistors RB1 and RB2. Press. A sine wave having the same frequency as that of the drive clock DRCK is obtained from the common connection point of the voltage dividing resistors RB1 and RB2. The sine wave is waveform-shaped by the DRCK reproducing unit 61, and thereby the driving clock is reproduced. In FIG. 3A, the regenerated drive clock is denoted as DRCK (RE).

  The power receiving side control circuit 52 turns on / off the load modulation transistor (NMOS transistor) M1 of the load modulation unit 46 in synchronization with the edge timing of the reproduced drive clock DRCK (RE). When the load modulation transistor M1 is turned on, the load modulation current Imod flows through the resistor RB3 and the load modulation transistor M1, and the load state of the power receiving device becomes heavy. When the load modulation transistor M1 is turned off, the load modulation current Imod does not flow, and the load state of the power receiving device becomes light.

  As shown in the lower side of FIG. 3A, when the power receiving device changes from a low load state to a high load state, for example, the voltage amplitude of the coil end voltage CSG of the primary coil increases. The waveform monitor circuit 14 can detect the load state of the power receiving device by comparing the coil end voltage CSG of the primary coil and the threshold voltage Vth. For example, if the low load state of the power receiving apparatus is associated with data “0” and the high load state is associated with data “1”, it is possible to determine “0” or “1” of the received data. However, in addition to the detection method that detects the peak voltage at the coil end, a detection method that focuses on the phase difference between the voltage and current can also be used.

  When the load state of the power receiving device 40 changes due to the modulation of the load of the power receiving device 40, the power transmitting device stably detects the change in the load state of the power receiving device from the timing of the change in the load state of the power receiving device 40. In general, there is a data indefinite period corresponding to the drive clocks of m primary coils (m is an integer of 1 or more) before it can be performed.

  For example, in FIG. 3B, the load modulation transistor TB3 in the power receiving device changes from the off state to the on state at time t1. However, the amplitude of the coil end voltage CSG of the primary coil L1 gradually increases from time t1 to time t6. After time t6, the change in the coil end voltage is stable, and as a result, highly reliable data determination is possible. A period from time t1 to time t6 is an indefinite period in which data is not fixed. The notation xxxxxx in FIG. 3B indicates that the five pieces of data obtained in the period corresponding to five drive clocks are indefinite. After time t6, the received data is stable, and the power transmission control device 20 can accurately determine the received data as “1”.

  As described above, in the present embodiment, during the normal power transmission period, the power reception control device (specifically, the power reception side control circuit) 50 controls the load modulation unit 46 provided in the power reception device 40 to control the load modulation signal ( 2 is transmitted to the power transmission device 10 periodically (periodically). When foreign matter (conductive foreign matter or non-conductive foreign matter) is inserted between the primary coil L1 and the secondary coil L2, communication is interrupted by the foreign matter, so that the power transmission device 10 is periodically connected to the power receiving device. Can not receive the load modulation signal transmitted from. Therefore, if the power transmission device can receive the load modulation signal periodically transmitted from the power receiving device, it can determine that there is no foreign object inserted and can perform normal power transmission. For example, measures such as stopping normal power transmission can be taken.

  Here, the load modulation signal periodically transmitted by the power receiving apparatus includes a data pattern of 010 (or 101). The periodic authentication data (load modulation signal) transmitted periodically is communication for detecting a foreign matter (conductive foreign matter or non-conductive foreign matter) inserted between the primary coil L1 and the secondary coil L2. It is data.

  The periodic authentication data includes a data pattern of 010 (or 101). For example, “1” corresponds to a state where the power receiving device 40 has a heavy load (a state where the load current is large), and “0” corresponds to a light state (a state where the load current is small or the load current is zero). To correspond. The reverse is also possible. The pattern 010 and the pattern 101 are equivalent.

  The periodic authentication data can be constituted by, for example, a single pattern (isolated pattern) of “010 (or 101)”, and a pattern in which “010 (or 101)” is repeated k times (k is an integer of 2 or more). It may be. For example, when k = 2, the pattern “01010” or “010010” may be employed.

  Further, as a pattern of the periodic authentication data, a pattern applying the pattern 010 (or 101) can be adopted. For example, a special pattern such as “0101000010” may be employed.

  The power receiving device 40 of the non-contact power transmission system can originally perform communication by load modulation during normal power transmission. In this embodiment, this communication function is used for foreign object detection. Therefore, it is easy to implement without adding a special circuit, and therefore there is no problem of cost increase.

  Therefore, the power transmission device can reliably detect a foreign object without impeding normal power transmission and without placing a burden on the power transmission device or the power reception device. Therefore, when a hijacking state occurs, the power transmission device 10 can reliably take measures such as stopping normal power transmission (or reducing the power of normal power transmission to low power). Therefore, the reliability of the non-contact power transmission system is improved.

  Further, the periodic authentication data can be composed of a single pattern (isolated pattern) of 010 or 101. That is, the simplest pattern can be adopted as the pattern of the periodic authentication data. In order to simplify the detection processing of the periodic authentication data by the power transmission device, it is desirable that the periodic authentication data has a pattern as simple as possible.

  Since the periodic authentication data is transmitted from the power receiving device to the power transmitting device via the secondary coil L2 and the primary coil L1, a certain amount of waiting time is required until the periodic authentication data can be accurately received by the power transmitting device. (Delay time) is required. Further, since the voltage at the coil end of the primary coil has a distorted waveform, the power transmission device needs to carefully detect the periodic authentication data.

  When the periodic authentication data is long or complicated, the detection load of the periodic authentication data in the power transmission device increases, and the time until detection tends to increase.

  Therefore, it is preferable to adopt a single (isolated) pattern of 010 or 101 as the pattern of the periodic authentication data. That is, in the period in which the periodic authentication is executed, 010 is transmitted from the power receiving side to the power transmission side only once. In this case, since the pattern of the periodic authentication data is simplified, the detection process of the periodic authentication data in the power transmission device is easy, and the time required for detecting the periodic authentication data can be the shortest time.

    In the present embodiment, as described above, the load included in the load modulation unit 46 using the primary coil drive clock regenerated based on the coil end voltage or coil current of the secondary coil L2 as a timing reference. The modulation switch (load modulation transistor) M1 is turned on / off.

  Periodic authentication data detection processing by the power transmission device 10 (specifically, the power transmission side control circuit 22) is executed, for example, every second. If the power transmission device 10 can predict the timing for receiving the periodic authentication data, the process for receiving the periodic authentication data is facilitated, and the reliability of the detected periodic authentication data is increased. Therefore, the power reception control device 50 performs on / off control of the load modulation switch (load modulation transistor) M1 using the drive clock DRCK of the primary coil as a timing reference.

  That is, when the primary coil L1 is AC driven by the drive clock DRCK, the coil end voltage (coil current) of the secondary coil L2 also varies in synchronization with the drive clock DRCK of the primary coil. Therefore, the DRCK reproducing unit 61 shown in FIG. 3A can reproduce the driving clock DRCK of the primary coil based on the coil end voltage (coil current) of the secondary coil L2. The power reception control device 50 is generated based on the reproduced drive clock (DRCK (RE)) of the primary coil (that is, in synchronization with the reproduced drive clock or based on the drive clock). The load modulation switch (load modulation transistor) M1 is turned on / off in synchronization with the clock. Thereby, the periodic authentication data is transmitted from the power receiving side to the power transmitting side at a timing determined based on the drive clock DRCK of the primary coil.

  The periodic authentication data is detected on the power receiving side after a certain delay time has elapsed, and the delay time can be predicted, for example, as shown in FIG. Further, the timing of the drive clock DRCK of the primary coil (for example, the timing of the positive edge) is known for the power transmission device 10. Therefore, the power transmission control device 20 (specifically, the power transmission side control circuit) 22 can predict the timing at which the periodic authentication data is received based on the timing of the drive clock DRCK of the primary coil.

  Therefore, the reception processing of the periodic authentication data by the power transmission control device 20 is facilitated, and the reliability of the detected periodic authentication data is increased. In addition, in order to synchronize communication between the power reception side and the power transmission side, it is not necessary to use a special control signal, and the implementation is easy.

(Sending and receiving periodic authentication data and communication packets)
4A to 4D are diagrams for explaining transmission / reception of periodic authentication data and communication packets.

  The power receiving apparatus can perform load modulation and transmit a communication packet to the power transmitting apparatus during the normal power transmission period. In addition, periodic authentication data of a predetermined pattern can be transmitted periodically (for example, every second).

  The power transmission control device needs to distinguish and receive whether the data transmitted from the power receiving device is periodic authentication data or a communication packet. Therefore, as shown in FIG. 4A to FIG. 4D, a difference is provided in the bit length of 1 bit of the periodic authentication data and the communication packet.

  That is, by changing the 1-bit period (1 bit length), the power transmission side can distinguish between the periodic authentication data and the communication packet.

  For the periodic authentication data, a 1-bit period of “0” or “1” is set to a time that is p times (p is an integer of 1 or more) one cycle of the drive clock DRCK of the primary coil. For the communication packet, a 1-bit period of “0” or “1” is q times the cycle of the drive clock DRCK of the primary coil (q is an integer of 1 or more and p ≠ q). Set to.

  On the power transmission side, when bit synchronization is established and data is received, it is detected whether the 1-bit period continues for a period p times or q times the period of the drive clock of the primary coil. As a result, the transmission side can distinguish whether the received data is a communication packet or periodic authentication data.

  As shown in FIGS. 4B and 4C, the periodic authentication data is composed of a pattern of 010. The period during which “1” or “0” continues is set to a period corresponding to 16 drive clocks DRCK. As described above, when the periodic authentication data cannot be received, the power transmission device 10 determines that the foreign object ME has been inserted and stops normal power transmission.

  As shown in FIG. 4D, 1-bit data constituting the communication packet continues for a period corresponding to 32 drive clocks DRCK. That is, in the example of FIG. 3D, the bit length of 1 bit is twice the bit length of the periodic authentication data.

  As shown in FIG. 4A, the power transmission control device 20 detects a waveform change in the received data obtained from the waveform monitor circuit 14, and after the first waveform change is detected, a period corresponding to 16 drive clocks. If the same level is detected continuously, it is determined as a communication packet, and if the received data level is reversed after a period of 16 drive clocks, it is periodic authentication data. judge. In this way, the power transmission control device can distinguish and detect the periodic authentication data and the communication packet.

  As described above, the 1-bit period of the transmission packet can be set to β times the 1-bit period of the periodic authentication data (β is an integer of 2 or more). On the transmitting side, one bit period of the periodic authentication data is defined as one unit time, and it is detected whether one bit continues for the unit time or a period that is β times the unit time. Thereby, the power transmission side can distinguish the periodic authentication data from the communication packet. On the power transmission side, since the reception process can be performed with one bit period of the periodic authentication data as one unit time, the data reception process is simplified.

  However, if the 1-bit period is too long, the time required to determine 1-bit received data becomes longer. Therefore, in the example of FIG. 4, β = 2 is set.

(Example of data structure of communication packet)
FIG. 5 is a diagram illustrating an example of a data structure of a communication packet. The communication packet can include a start code, a command code, data (communication data), and an error code. Further, in order to make it easy to detect the beginning of the communication packet in the power transmission apparatus, a 16-bit “L (= 0)” period is provided immediately before the communication packet.

(Second Embodiment)
In the present embodiment, an example of temporarily stopping power supply to a load to be supplied when transmitting periodic authentication data on the power receiving side, a condition for the power transmission device to stop normal power transmission, and the like will be described.

  When the power receiving side performs load modulation in a state where a large amount of current is supplied to a power supply target load (eg, a battery such as a secondary battery) 94, the amount of current that changes due to load modulation (the load modulation current Imod shown in FIG. 2) is Since the amount of current supplied to the load 94 to be fed is small, it may be difficult for the power transmission side to detect the load modulation signal.

  Thus, in the present embodiment, when the power receiving side performs load modulation, the power receiving control device 50 controls, for example, a power control transistor (power control switch: M3 in FIG. 2) provided in the power feeding path to supply power. The power supply to the load 94 is temporarily reduced (reduction of power supply current) or stopped. When power supply is temporarily stopped, the coil end voltage of the primary coil changes depending on only on / off of the load modulation current Imod. Therefore, the power transmission side can more easily detect the periodic authentication data (load modulation signal) sent from the power reception side. In the following description, a case will be described in which the power receiving side temporarily stops the power supply to the power supply target load 94 when transmitting the periodic authentication data.

  Hereinafter, a specific description will be given with reference to FIG. FIG. 6 is a diagram for explaining an example of the periodic authentication process.

  As shown in the upper side of FIG. 6, during the period from time t40 to time t43, the power supply control signal ICUTX (see FIG. 2) output from the power receiving side control circuit 52 is active level (becomes H level). Therefore, during that period, the power supply control transistor (power supply control switch) M3 shown in FIG. 2 is turned off, and the power supply to the load 94 to be supplied is temporarily stopped. Note that the period from time t40 to time t43 corresponds to, for example, 400 drive clocks DRCK of the primary coil.

  In a period T2 from time t41 to time t42, the load modulation signal P3Q output from the power receiving side control circuit 52 becomes an active level (H level). A period T2 from time t41 to time t42 corresponds to, for example, 16 drive clocks DRCK of the primary coil.

  The monitor waveform on the power transmission side is L level during the period from time t40 to time t41, is H level during the period T2 from time t41 to time t42, and is L level during the period from time t42 to time t43. Therefore, if no foreign object is inserted, the power transmission side can receive periodic authentication data having a pattern of 010.

  In the continuous L period T1, the power receiving side is in a low load state. The primary side can confirm that there is no foreign material during this period. In the period T2, the power receiving side is in a high load state. The power transmission side can detect the presence of the power receiving side device when detecting a change from the L level to the H level of the monitor waveform (time t41).

  Further, when the power transmission side detects a change in the monitor waveform from the H level to the L level (time t42), the period during which the monitor waveform is at the H level corresponds to 16 drive clocks DRCK. Confirm by periodic authentication flow. Thereby, it is detected that the periodic authentication data has been received. The primary side can confirm that there is no foreign matter.

  As shown in the upper side of FIG. 6, when the power receiving device 40 outputs the periodic authentication data of 010, the power supply control signal (ICUTX) is at the active level, and inactive in other periods. It is a level. Therefore, the power transmission device 10 receives a signal xxxxxxxx010xxxx. Here, x indicates that the ICUTX signal is at an inactive level.

  On the power transmission side, when determining 1 (= H) or 0 (= L) of the received data, a so-called seven-continuous determination is performed. As a result, highly reliable data determination is possible. The 7-continuous match determination process determines the value of the received data for each cycle of the drive clock DRCK of the primary coil, and determines the value of the received data when the determination results match 7 times in succession It is. As described with reference to FIG. 3B, for example, there is a data indefinite period of 5 clocks.

  However, the fact that the determination values are consistent for seven consecutive times means that the determination based on highly reliable data is performed at least twice. Further, when the determination values coincide with each other seven times in succession, it can be estimated that the coil end voltage is surely at the H level (L level) (at least there is such a tendency). For this reason, the power transmission side can reliably detect the value of the received data by executing the 7-continuous match determination.

  In FIG. 6, at time t41, the power transmission side establishes bit synchronization for the received data. In the period T2, the power transmission side detects H (= 1) of the received data by the 7-continuous match determination. Further, in the period T3, the power transmission side detects L (= 0) of the received data based on the 7 consecutive match determination.

  Note that the 7 consecutive match determination is an example, and generally, the detection accuracy of the received data can be improved by executing the k continuous match determination. As shown in FIG. 2B, when a data indefinite period corresponding to m clocks exists, the value of k is preferably set to k = m + α, for example, α = 2 or α = 3. be able to.

  As described above, the power transmission device 10 periodically detects a foreign object during the normal power transmission period, and stops power transmission or reduces the transmission power when a foreign object is detected. Thereby, problems, such as heat_generation | fever of a conductive foreign material, do not arise, but the reliability of a non-contact power transmission system improves markedly. In addition, as a countermeasure when a foreign object is detected, either power transmission stop or power transmission power reduction can be executed. However, by stopping the power transmission, the problem of heat generation of foreign matters is completely solved. If priority is given to ensuring the reliability of the non-contact power transmission system over the charging of the secondary battery, it is preferable to take a measure of stopping power transmission.

  Next, conditions such as when normal power transmission is stopped will be described with reference to the lower diagram of FIG.

  During the period when the power transmission side receives and detects the periodic authentication data, for example, noise may occur accidentally, and the power transmission side may not be able to receive the periodic authentication data. Therefore, it is necessary for the power transmission side to carefully detect the periodic authentication data.

  Therefore, in this embodiment, the power transmission side stops normal power transmission to the power receiving apparatus when it fails to receive the periodic authentication data n times (n is an integer of 2 or more) continuously. As a result, there is no inconvenience that the normal power transmission is erroneously stopped even though no foreign matter is inserted.

  However, if the value of n is too large, a quick foreign matter countermeasure cannot be executed. On the other hand, when n = 2, for example, a state in which noise is likely to be generated continues, and there may be a situation where accurate reception cannot be performed twice consecutively. Therefore, in the example of FIG. 6, n = 3 is set. The reception process of the power transmission device 10 is executed at intervals of 1 second, for example. Even if a state with a lot of noise continues for a certain period of time, it is considered that the probability of failure of receiving a load modulation signal executed at intervals of 1 second, for example, three times consecutively is low due to the noise. That is, when a situation where the reception of the periodic load modulation signal fails three times in succession, it is determined that there is a high possibility that the conductive foreign object AR has been inserted between the primary coil and the secondary coil. Can do. Therefore, it is possible to achieve both accurate detection of foreign object insertion and rapid detection.

  In the lower diagram of FIG. 6, in the first periodical authentication data detection period (period T11), the power transmission side succeeds in detecting the periodical authentication data. However, after that, the power transmission side has failed to detect the periodic authentication data three times consecutively (second detection period T12, third detection period T13, and fourth detection period T14). In this case, at time t56, the power transmission device 10 stops normal power transmission.

  As described above, when the detection of the periodic authentication data has failed n times consecutively, the power transmission device can also take measures to reduce the power of normal power transmission. However, ensuring the safety of the contactless power transmission system is important. Therefore, it is more preferable to stop normal power transmission when a foreign object is detected.

  In addition, when the number of reception failures with respect to a given number of reception processes reaches a given value, the power transmission device 10 determines that a foreign object has been inserted, and may stop transmission or reduce transmission power. Is possible.

  For example, the power transmission apparatus 10 performs the process of receiving a periodic load modulation signal 10 times. During the series of ten reception processes, for example, when reception fails five times, the power transmission device 10 executes power transmission stop or power transmission power reduction.

  For example, it may be difficult for the primary side to detect the periodic load modulation signal due to the relative positional relationship between the primary side and the secondary side. In such a case, it may be difficult to determine whether the reception failure is due to a foreign object or due to the relative positional relationship between the primary side and the secondary side. However, if the number of reception processing times to be determined is increased to some extent, the probability that the cause of reception failure can be distinguished increases, and the accuracy of foreign object detection improves. Therefore, according to this embodiment, highly reliable foreign object detection is realized.

(Operation example of contactless power transmission system)
FIG. 7 is a diagram illustrating an operation example of the non-contact power transmission system. The power transmission device detects the landing (setting) of the power receiving side device, for example, once every 0.3 seconds (step S1). The landing (setting) of the power receiving device is detected (step S2).

  Next, various types of information are exchanged between the power transmission device and the power reception device (step S3). For example, the power transmission device can detect information transmitted from the power reception device with high accuracy by executing the 7-continuous matching determination. Normal power transmission (charging) is started after it is confirmed by ID authentication that the power receiving apparatus is an appropriate power transmission target.

  When full charge is detected during normal power transmission, a full charge notification is transmitted from the power receiving apparatus to the power transmission apparatus, and the power transmission apparatus that has received this notification stops normal power transmission (step S4). And it transfers to the standby phase after full charge detection (step S5).

  In a standby state after full charge detection, for example, removal detection is executed once every 5 seconds, and confirmation of the necessity of recharging is executed once every 10 minutes. When the power receiving device is removed after full charge, the process returns to the initial standby phase (step S6). If it is determined that recharging is necessary after full charging, the process returns to step S3 (step S7). Further, when removal of the power receiving device is detected in the state of step 3, the initial standby state is restored (step S8).

  As described above, according to some embodiments of the present invention, for example, the power transmission device can be reliably configured without obstructing normal power transmission and without excessively burdening the power transmission device and the power reception device. , Foreign object insertion (particularly a hijacking state) can be detected.

  In addition, it is possible to realize a high-performance power reception control device, a power reception device, and a contactless power transmission system with high reliability and a simplified circuit configuration. Although the embodiments of the present invention have been described in detail, those skilled in the art will readily understand that many modifications are possible without departing from the novel matters and effects of the present invention. Therefore, all such modifications are included in the present invention.

1A to 1C are diagrams illustrating an example of a configuration of a contactless power system. FIG. 2 is a diagram illustrating an example of a configuration of a contactless power transmission system 3A and 3B are diagrams for explaining data communication between the power transmission device and the power reception device. 4 (A) to 4 (D) are diagrams for explaining transmission / reception of periodic authentication data and communication packets. The figure which shows an example of the data structure of a communication packet Diagram for explaining an example of periodic authentication processing The figure which shows an example of operation | movement of a non-contact electric power transmission system

Explanation of symbols

10 power transmission device, 22 power transmission side control circuit, 40 power reception device, 42 power reception unit,
46 load modulation unit, 48 power supply control unit, 50 power reception control device, 52 power reception side control circuit,
90 charging device, 94 load to be charged, L1 primary coil, L2 secondary coil,
M1 load modulation transistor (load modulation switch),
M3 power supply control switch (power supply control transistor),
DRCK Primary coil drive clock (driver clock)

Claims (13)

The primary coil and the secondary coil are electromagnetically coupled to transmit power from the power transmission apparatus to the power reception apparatus, and the load modulation unit included in the power reception apparatus modulates the load of the power reception apparatus during the power transmission period In a contactless power transmission system that transmits a load modulation signal to the power transmission device, a power reception control device provided in the power reception device,
A power reception control circuit for controlling the operation of the power reception device;
The power reception control circuit includes:
During the power transmission period, by periodically controlling the load of the power receiving device by controlling the load modulation unit, the periodic authentication data including the pattern of 010 or 101 is transmitted to the power transmitting device. ,
A power reception control device characterized by that. The power reception control device according to claim 1,
The periodical authentication data is composed of a single pattern of 010 or 101. The power reception control device according to claim 1 or 2,
The power receiving side control circuit includes:
Turning on / off a load modulation switch included in the load modulation unit using a drive clock of the primary coil reproduced based on a coil end voltage or a coil current of the secondary coil as a timing reference; A power reception control device. The power reception control device according to any one of claims 1 to 3,
The power receiving side control circuit includes:
In the case of transmitting the periodic authentication data by controlling the load modulation unit during the power transmission period, the 1-bit “0” or “1” period to be transmitted is set as the drive clock of the primary coil. Set to a time that is p times (p is an integer greater than or equal to 1) of one cycle,
In addition, when the communication packet is transmitted by controlling the load modulation unit during the power transmission period, the transmitted 1-bit “0” or “1” period is set as the drive clock of the primary coil. Q times one period (q is an integer of 1 or more and p ≠ q)
A power reception control device characterized by that. The power reception control device according to claim 4,
The power receiving side control circuit includes:
When transmitting the communication packet by controlling the load modulation unit during the power transmission period, the transmitted 1-bit “0” or “1” period is set to one cycle of the drive clock of the primary coil. Q times (q = β × p, β is an integer of 2 or more),
A power reception control device characterized by that. The power reception control device according to claim 4 or 5, wherein
p = 16, q = 32 (therefore, β = 2). The power reception control device according to any one of claims 1 to 6,
The power reception control circuit includes:
When performing the periodic load modulation, first, temporarily reduce or stop the power supply to the power supply target load, in a period during which the power supply to the power supply target load is temporarily reduced or stopped, By periodically controlling the load of the power receiving device by controlling the load modulation unit,
A power reception control device characterized by that. A power receiving device that receives power transmitted from a power transmitting device via an electromagnetically coupled primary coil and secondary coil, and transmits a load modulation signal to the power transmitting device during a power receiving period,
The secondary coil;
A power receiving unit including a rectifier circuit;
A load modulation unit that modulates a load of the power receiving device to generate the load modulation signal;
A power supply control unit that controls power supply to the load to the power supply target;
The power reception control device according to any one of claims 1 to 7,
A power receiving device comprising: A primary coil;
A secondary coil;
A power transmission device having a power transmission unit that drives the primary coil to transmit power, and a power transmission control device that controls the operation of the power transmission unit;
A power receiving device according to claim 8;
A non-contact power transmission system comprising: The contactless power transmission system according to claim 9,
The power transmission device stops contact power transmission to the power receiving device or reduces power transmission power when the power receiving device fails to receive the load modulation signal periodically transmitted. Transmission system. The contactless power transmission system according to claim 10,
The power transmission device stops power transmission to the power reception device when the load modulation signal periodically transmitted by the power reception device fails n times (n is an integer of 2 or more) continuously, Or the non-contact electric power transmission system characterized by reducing power transmission power. The contactless power transmission system according to claim 11,
A non-contact power transmission system, wherein n = 3. The contactless power transmission system according to claim 10,
The power transmission device performs reception processing of the load modulation signal periodically transmitted by the power reception device X times (X is an integer of 2 or more). 1 ≦ Y ≦ X)) A contactless power transmission system that stops power transmission to the power receiving device or reduces power transmission power if it fails.

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