CONTACTLESS POWER TRANSMISSION DEVICE

Abstract

Device for contactless power transmission (1), comprising: a transmitter (2); and a receiver (3) configured to receive power contactlessly from the transmitter (2), wherein the transmitter (2) has a transmitting coil (14) configured to supply current to the receiver (3), and a power supply circuit (10) designed to supply current to the transmitting coil (14), where the receiver (3) has a resonant circuit (20) comprising a receiving coil (21) configured to receive current from the transmitter (2) and a resonant capacitor (22) connected in parallel with the receiving coil (21), a rectifier circuit (24) configured to rectify the current supplied by the resonant circuit (20), and a first coil (23, 23-1) which is connected in parallel to the resonant circuit (20) between the resonant circuit (20) and the rectifier circuit (24), wherein the power supply circuit (10) sets a switching frequency and a voltage of an alternating current power supplied to the transmitting coil (14), wherein the transmitter (2) further exhibits a first communicator (15) configured to receive from the receiver (3) a signal containing determination information indicating whether the contactless power transmission device (1) is operating in constant voltage output mode and whether a measured value of an output voltage of the resonant circuit (20) is within a specified permissible voltage range, and a control circuit (17) configured to control, according to the destination information, the switching frequency and the voltage of the AC power supplied by the power supply circuit (10) to the transmitting coil (14), and where the recipient (3) further exhibits a voltage detection circuit (28) configured to measure the output voltage of an electrical power output from the resonant circuit (20) and to determine the measured value of the output voltage, a constant voltage circuit (29) configured to determine, on the basis of the measured output voltage, whether the contactless power transfer device (1) is operating at constant voltage output and whether the measured output voltage of the resonant circuit (20) is within the specified permissible voltage range, and a second communicator (32) configured to transmit the signal including the destination information to the transmitter (2).

Description

AREA

[0001] The present invention relates to a device for contactless power transmission. BACKGROUND

[0002] Techniques for contactless power transmission (also known as wireless power transmission) or for transmitting electrical energy through space without the use of metal contacts or other connections have been investigated.

[0003] A well-known technique for contactless power transmission is the transfer of energy by electromagnetic induction. One method for power supply by electromagnetic induction can use primary series / secondary parallel capacitors (hereinafter referred to as SP topology) (see, e.g., non-patent literature 1). According to the SP method, a capacitor is connected in series with a transmitting coil, which serves as part of a transformer on the primary side (power transmission side), and a capacitor is connected in parallel with a receiving coil, which serves as the other part of the transformer on the secondary side (power reception side).

[0004] In the SP topology, a resonant circuit with the receiver coil and the capacitor in the receiver creates a parallel resonance and outputs a constant current.

[0005] In the SP topology, an inductor can be connected in series to the coil in the receiver's resonant circuit (see, for example, non-patent literature 1 and patent literature 1). This technique can be referred to as the SPL topology. A contactless power transmission device with an SPL topology reduces harmonic components in the transmitted power to enable ideal transformer behavior, thereby increasing the power factor and improving power transmission efficiency.

[0006] Patent literature 1: JP 2015 - 42 051 A

[0007] Non-patent literature 1: Watanabe et al., “Bidirectional contactless power transfer system expandable from unidirectional systems”, IEEJ Transactions D, IEEJ Transactions on Industry Applications, Vol. 133, No. 7, pp. 707–713, 2013. Further prior art is provided by US 2017 / 0 288 463 A1 and US 2013 / 0 313 893 A1. US 2017 / 0 288 463 A1 describes a contactless power transfer device comprising a resonant coil and a resonant capacitor, as well as impedance-variable circuits whose impedance can be changed.In the contactless power transmission device, a power transmission-side controller changes the impedance of one of the variable-impedance circuits, a power reception-side controller changes the impedance of the other of the variable-impedance circuits, and the output impedance on a power supply side with respect to a power transmission coil unit and the input impedance on a load side with respect to the power transmission coil unit are matched. US 2013 / 0 313 893 A1 discloses a method for adjusting the resonant frequency and impedance of a resonant system in a contactless power transmission by means of a resonance method. In this method, a variable capacitor sets the resonant frequency of a secondary self-resonant coil. An impedance matching box sets the input impedance of a resonant system.An ECU first sets the resonant frequency of the secondary self-resonant coil by controlling the variable capacitor, and after setting the resonant frequency, it sets the input impedance of the resonant system by controlling the impedance matching box. While the resonant frequency is being set by the variable capacitor, the ECU sets the impedance of the impedance matching box to a predetermined fixed value. OVERVIEW Technical Problem

[0008] Electronic devices are typically controlled with a constant voltage. For example, contactless power transmission devices can output a constant voltage from the receivers. A contactless power transmission device comprising primary series and secondary series capacitors (hereafter referred to as the SS topology) is also investigated for outputting a constant voltage from the receiver. In the SS topology, one capacitor is connected in series with a transmitting coil, which acts as part of a transformer in the transmitter, and another capacitor is connected in series with a receiving coil, which acts as another part of the transformer in the receiver.

[0009] However, the SS topology cannot sufficiently reduce fluctuations in the voltage output of a device in the receiver due to load fluctuations in a load circuit connected to a device in the receiver.

[0010] In view of the problems mentioned above, the present invention aims to provide a device for contactless power transmission that reduces fluctuations in an output voltage caused by load fluctuations in a load circuit connected to a device in the receiver. This problem is solved by the subject matter of independent claim 1. Preferred embodiments are the subject matter of the dependent claims. The invention is defined by the claims, aspects of which are explained below:

[0011] A device for contactless power transmission according to one aspect of the present invention comprises a transmitter and a receiver that receives current contactlessly from the transmitter. In the device for contactless power transmission, the transmitter comprises a transmitting coil that supplies current to the receiver and a power supply circuit that supplies the transmitting coil with alternating current. The receiver comprises a resonant circuit including a receiving coil that receives current from the transmitter and a resonant capacitor connected in series with the receiving coil, a rectifier circuit that rectifies the electrical output power of the resonant circuit, and a coil connected in parallel to the resonant circuit between the resonant circuit and the rectifier circuit.

[0012] The contactless power transmission device with the above structure reduces fluctuations in output voltage caused by load fluctuations in a load circuit connected to a device in the receiver.

[0013] In the contactless power transmission device, the power supply circuit in the transmitter can set a switching frequency and an AC voltage supplied to the transmitting coil. The transmitter can also include a first communicator, which receives a signal from the receiver containing determination information indicating whether the contactless power transmission device is operating in constant voltage output mode and whether the output voltage of the resonant circuit is within a predetermined permissible voltage range, and a control circuit that, according to the determination information, controls the switching frequency and the voltage of the AC supply supplied to the transmitting coil from the power supply circuit.The receiver may also include a voltage detection circuit that measures the output voltage of an electrical power output from the resonant circuit and determines a measured value of the output voltage, a constant voltage determination circuit that uses the measured value of the output voltage to determine whether the contactless power transfer device is operating in constant voltage output mode and whether the measured value is within the specified permissible voltage range, and a second communicator that transmits the signal to the transmitter, which includes the determination information indicating whether the contactless power transfer device is operating in constant voltage output mode and whether the measured value is within the specified permissible voltage range.

[0014] The device for contactless power transmission with the above-mentioned structure can continue operation with constant voltage output with varying coupling levels between the transmitter coil and the receiver coil.

[0015] In the aforementioned contactless power transmission devices, the control circuit in the transmitter can, in response to the determination information indicating that the contactless power transmission device is not operating in constant voltage output mode, control the switching frequency of the AC power supplied to the transmitting coil from the power supply circuit in order to allow the measured output voltage to remain unchanged for a varying resistance of a load circuit connected to the rectifier circuit in the receiver.

[0016] The contactless power transmission device with the above-mentioned structure can correctly detect the AC frequency of the transmitting coil to enable operation with constant voltage output.

[0017] In the aforementioned contactless power transmission device, the control circuit in the transmitter can control the AC supply voltage delivered from the power supply to the transmitting coil in response to the determination information indicating that the contactless power transmission device is operating with constant voltage output and the measured output voltage is outside the specified permissible voltage range, so that the measured output voltage is within the specified permissible voltage range.

[0018] The device for contactless power transmission with the above-mentioned structure can output a constant voltage from the resonant circuit in the receiver with variable coupling levels between the transmitter coil and the receiver coil.

[0019] In the contactless power transmission device, the receiver may also include a second coil connected in parallel to the resonant circuit between the resonant circuit and the rectifier circuit, and a short-circuit circuit switchable between short-circuiting or opening the second coil. In this contactless power transmission device, the constant-voltage detection circuit can receive the switching frequency of the AC power supply, which is fed to the transmitter coil from the power supply circuit, from the transmitter via the communicator when the contactless power transmission device is operating in constant-voltage mode, and control the short-circuit circuit according to the switching frequency.

[0020] The contactless power transmission device with the above structure can efficiently reduce fluctuations in output voltage caused by load fluctuations in a load circuit, with varying coupling levels between the transmitting coil and the receiving coil. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a device for contactless power transmission according to an embodiment of the present invention. Fig. Figure 2 is an equivalent circuit diagram of a receiver according to the embodiment. Fig. Figure 3 is a diagram showing example simulation results for the frequency response of the output voltage of the contactless power transmission device according to the embodiment. Fig. Figure 4 is a diagram with example simulation results for the frequency response of the output voltage for a varying voltage, which in the simulation is in Fig. 3 is applied to a transmitting coil, according to the coupling degree. Fig. Figure 5 is a table showing the relationship between the resistance of a load circuit and the output voltage for each coupling level in the simulation. Fig. 4 at a switching frequency that allows operation with constant voltage output. Fig. Figure 6 is a table as a comparative example in which a coil between a resonant circuit and a rectifier smoothing circuit has been removed, showing the relationship between the resistance of the load circuit and the output voltage for each coupling degree in the simulation. Fig. 4 at a switching frequency that allows operation with constant voltage. Fig. Figure 7 is a schematic representation of a receiver according to a modification. Fig. 8A is a circuit diagram of a power supply circuit according to a modification. Fig. 8B is a circuit diagram of a power supply circuit according to a modification. DETAILED DESCRIPTION

[0021] The following describes a contactless power transmission device according to an embodiment of the present invention with reference to the drawings. The inventors noticed that a contactless power transmission device using primary series and secondary series capacitors (SS topology) might not be able to sufficiently reduce fluctuations in an alternating current (AC) voltage output by a resonant circuit in the receiver (hereinafter simply referred to as the output voltage) against load fluctuations in a load circuit if the AC power from the resonant circuit is rectified by a rectifier circuit before being supplied to the load circuit. The inventors then discovered that fluctuations in the output voltage arise from the parasitic capacitance of diodes included in the rectifier circuit.

[0022] In this contactless power transfer device, the receiver can include a coil connected in parallel to the resonant circuit between the rectifier circuit and the resonant circuit, including a receiving coil and a resonant capacitor to generate series resonance. The contactless power transfer device thus reduces the parasitic capacitance of the diodes in the rectifier circuit, which affects resonance with the transferred power, and therefore reduces fluctuations in the output voltage caused by load variations in a load circuit.

[0023] Constant voltage output operation refers here to operation of the contactless power transfer device in which fluctuations in the output voltage are within a permissible range (e.g., a range corresponding to ±10% of a specified reference voltage), e.g., according to the specifications of a load circuit connected to the contactless power transfer device.

[0024] Fig. Figure 1 is a schematic representation of a device for contactless power transmission according to an embodiment of the present invention. As shown in Fig. Figure 1 shows a contactless power transmission device 1 comprising a transmitter 2 and a receiver 3 for the contactless reception of power from the transmitter 2 through space. The transmitter 2 includes a power supply circuit 10, a transmitting coil 14, a communicator 15, gate drivers 16-1 and 16-2, and a control circuit 17. The receiver 3 comprises a resonant circuit 20 with a receiving coil 21 and a resonant capacitor 22, a coil 23, a rectifier smoothing circuit 24, a load circuit 27, a voltage detection circuit 28, a constant voltage detection circuit 29, and a communicator 32. The contactless power transmission device according to the present embodiment uses a topology referred to as a non-resonant series with L (NSL) topology.

[0025] Transmitter 2 is described below.

[0026] The power supply circuit 10 supplies the transmitting coil 14 with alternating current at an adjustable switching frequency and voltage. The power supply circuit 10 thus comprises a current source 11, a reactive power compensation circuit 12, and four switching elements 13-1 to 13-4.

[0027] Power source 11 supplies current with a predetermined pulsating voltage. Power source 11 is thus connected to an AC power source of the utility company and contains a full-wave rectifier circuit for rectifying the AC power supplied by the utility company's AC power source.

[0028] The reactive power compensation circuit 12 converts the voltage supplied by the power source 11 into a voltage controlled by the control circuit 17 and outputs the resulting voltage. The reactive power compensation circuit 12 therefore comprises, for example, an inductor L and a diode D connected in series from the positive terminal of the power source 11, a switching element SW, which is an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET) whose drain terminal is connected between the inductor L and the diode D and whose source terminal is connected to the negative terminal of the power source 11, and a smoothing capacitor C connected in parallel to the switching element SW via the diode D. The switching element SW has a gate terminal connected to the gate driver 16-1.The reactive power compensation circuit 12 contains two resistors R1 and R2, which are connected in series between the positive and negative electrode terminals of the power source 11. Resistors R1 and R2 are connected in parallel with the smoothing capacitor C between the diode D and the smoothing capacitor C. The voltage across resistors R1 and R2 is measured by the control circuit 17 as the output voltage of diode D.

[0029] The gate driver 16-1 controls the on / off state of the switching element SW according to a duty cycle specified by the control circuit 17, so that the current output of the diode D has the same waveform as the voltage supplied by the current source 11. The reactive power compensation circuit 12 thus performs a power factor correction. Since the duty cycle that causes the switching element SW to be on is higher, the diode D outputs a higher voltage.

[0030] The voltage output by the diode D is smoothed by the smoothing capacitor C and fed to the transmitting coil 14 via the four switching elements 13-1 to 13-4.

[0031] The reactive power compensation circuit 12 is not limited to the above structure and can have a different structure to output a voltage that is adjustable as controlled by the control circuit 17.

[0032] The four switching elements 13-1 to 13-4 are, for example, n-channel MOSFETs. Of the four switching elements 13-1 to 13-4, switching elements 13-1 and 13-2 are connected in series between the positive and negative electrode terminals of the power source 11 via the reactive power compensation circuit 12. In the present embodiment, the power source 11 has a positive electrode connected to switching element 13-1 and a negative electrode connected to switching element 13-2. Switching element 13-1 has a drain terminal connected to the positive electrode terminal of the power source 11 via the reactive power compensation circuit 12, and a source terminal connected to the drain terminal of switching element 13-2. The switching element 13-2 has a source terminal which is connected to the negative electrode terminal of the power source 11 via the reactive power compensation circuit 12.The source terminal of switching element 13-1 and the drain terminal of switching element 13-2 are connected to one end of the transmitting coil 14, and the source terminal of switching element 13-2 is connected to the other end of the transmitting coil 14 via switching element 13-4.

[0033] Similarly, of the four switching elements 13-1 to 13-4, switching elements 13-3 and 13-4 are connected in parallel with switching element 13-1 and switching element 13-2, respectively, and are connected in series between the positive and negative electrode terminals of the power source 11 via the reactive power compensation circuit 12. At the power source 11, the positive electrode is connected to switching element 13-3 and the negative electrode to switching element 13-4. Switching element 13-3 has a drain terminal connected via the reactive power compensation circuit 12 to the positive electrode terminal of the power source 11, and a source terminal connected to the drain terminal of switching element 13-4. Switching element 13-4 has a source terminal connected via the reactive power compensation circuit 12 to the negative electrode terminal of the power source 11.The source terminal of switching element 13-3 and the drain terminal of switching element 13-4 are connected to the other end of the transmitting coil 14.

[0034] The gate terminals of switching elements 13-1 to 13-4 are connected to the control circuit 17 via the gate driver 16-2. Each of the switching elements 13-1 to 13-4 can have its gate terminal connected to its source terminal via a resistor to ensure reliable activation in response to a voltage. The switching elements 13-1 to 13-4 are switched on and off at an adjustable switching frequency in response to a control signal from the control circuit 17. In the present embodiment, a pair of switching elements 13-1 and 13-4 and a pair of switching elements 13-2 and 13-3 are alternately switched on and off so that the switching elements 13-2 and 13-3 can be switched off while the switching elements 13-1 and 13-4 are switched on, and the switching elements 13-1 and 13-4 can be switched off while the switching elements 13-2 and 13-3 are switched on.This allows the direct current (DC) power supplied by the power source 11 via the reactive power compensation circuit 12 to be converted into alternating current at the switching frequency of the switching elements and delivered to the transmitting coil 14.

[0035] The transmitting coil 14 transmits alternating current, which is supplied by the power supply circuit 10 to the resonant circuit 20 of the receiver 3, through the room.

[0036] In contrast to a contactless power transmission device with an SS topology, the transmitter 2 in the present embodiment does not include a capacitor connected in series or parallel to the transmitter coil 14. The contactless power transmission device 1 according to the present embodiment therefore does not use resonance in the transmitter. More precisely, the transmitter coil 14 receives alternating voltage at a switching frequency at which the transmitter coil 14 does not resonate. The transmitter 2 can thus reduce Joule losses resulting from an increase in the current flowing through the transmitter coil 14.

[0037] The communicator 15, which is an example of a first communicator, extracts determination information from each radio signal received by the communicator 32 of the receiver 3. This information indicates, for example, whether the contactless power transmission device 1 is operating in constant voltage output mode, and outputs the information to the control circuit 17. Thus, the communicator 15 includes, for example, an antenna that receives a radio signal according to a predefined wireless communication standard and a communication circuit that demodulates the radio signal. The predefined wireless communication standard is, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0038] The gate driver 16-1 receives a control signal from the control circuit 17 to switch the switching element SW in the reactive power compensation circuit 12 on and off. In response to the control signal, it changes a voltage applied to the gate terminal of the switching element SW. More precisely: Upon receiving a control signal to switch on the switching element SW, the gate driver 16-1 applies a relatively high voltage to the gate terminal of the switching element SWan to turn the switching element SW on. Upon receiving a control signal to turn off the switching element SW, the gate driver 16-1 applies a relatively low voltage to the gate terminal of the switching element SWan to turn the switching element SW off. This allows the gate driver 16-1 to switch the switching element SW in the reactive power compensation circuit 12 on and off at the time specified by the control circuit 17.

[0039] The gate driver 16-2 receives a control signal from the control circuit 17 to switch each of the switching elements 13-1 to 13-4 on and off and changes the voltage applied to the gate terminal of each of the switching elements 13-1 to 13-4 in response to the control signal. More precisely: Upon receiving a control signal to switch on the switching elements 13-1 and 13-4, the gate driver 16-2 applies a relatively high voltage to the gate terminals of the switching elements 13-1 and 13-4 to switch them on. This allows a current from the current source 11 to flow through the switching element 13-1, the transmitting coil 14, and the switching element 13-4.Upon receiving a control signal to switch off switching elements 13-1 and 13-4, the gate driver 16-2 applies a relatively low voltage to the gate terminals of switching elements 13-1 and 13-4 to switch them off and prevent current from the current source 11 from flowing through them. Similarly, the gate driver 16-2 controls a voltage applied to the gate terminals of switching elements 13-2 and 13-3. When switching elements 13-1 and 13-4 are off and switching elements 13-2 and 13-3 are on, current from the current source 11 flows through switching element 13-3, the transmitting coil 14, and switching element 13-2.

[0040] The control circuit 17 includes, for example, non-volatile and volatile memory circuits, an arithmetic circuit, and an interface circuit for connection to another circuit. Upon receiving destination information from the communicator 15, the control circuit 17 controls the switching frequency and the voltage of the AC power supply, which is delivered to the transmitting coil 14 by the power supply circuit 10 in accordance with the destination information.

[0041] In the present embodiment, the control circuit 17 controls the pair of switching elements 13-1 and 13-4 and the pair of switching elements 13-2 and 13-3 to switch them on alternately for the same duration within a cycle according to the switching frequency. To prevent the pair of switching elements 13-1 and 13-4 and the pair of switching elements 13-2 and 13-3 from being switched on simultaneously and the power source 11 from being short-circuited, the control circuit 17 can provide a dead time during which both pairs of switching elements are switched off between the on and off states.

[0042] The control circuit 17 selects a duty cycle corresponding to a switching frequency by referring to a reference table that specifies the correspondence between each switching frequency and the duty cycle for controlling the on / off state of the switching element SW in the reactive power compensation circuit 12, in order to provide a constant output voltage at the corresponding switching frequency for a voltage applied to the transmitting coil 14. The control circuit 17 determines the switching-on and off times of the switching element SW in accordance with the duty cycle and the change in the output voltage of the diode D in the reactive power compensation circuit 12 and outputs a control signal indicating the timing to the gate driver 16-1.

[0043] If the communicator 15 does not receive a radio signal from receiver 3, receiver 3 may be outside the reception range for the power supply of transmitter 2, i.e., transmitter 2 may be in standby mode. In this case, the control circuit 17 can set the duty cycle for controlling the on / off state of switching element SW to its minimum possible value. Alternatively, the control circuit 17 can control the power supply circuit 10 in a burst mode, or more precisely, repeat the control cycle of the power supply circuit 10 to operate with a predetermined duty cycle to control the on / off state of switching element SW for a relatively short predetermined duration (e.g., several seconds) and then interrupt the power supply to the transmitting coil 14, maintaining the off state of each switching element for a relatively long duration (e.g., several minutes).In the standby state of transmitter 2, the minimum possible voltage is applied to the transmitting coil 14 in order to reduce energy loss.

[0044] The control of the switching frequency and the voltage applied to the transmitting coil 14 by the control circuit 17 is described in detail below.

[0045] The following describes recipient 3.

[0046] The resonant circuit 20 is an LC resonant circuit with the receiving coil 21 and the resonant capacitor 22 connected in series. The receiving coil 21 in the resonant circuit 20 has one end connected via the resonant capacitor 22 to one input terminal of the rectifier circuit 24 and the other end connected to the other input terminal of the rectifier circuit 24.

[0047] The receiving coil 21, together with the resonant capacitor 22, resonates with an alternating current flowing through the transmitting coil 14 in the transmitter 2, in order to receive power from the transmitting coil 14. The receiving coil 21 outputs the received power via the resonant capacitor 22 to the rectifier-smoothing circuit 24. The receiving coil 21 and the transmitting coil 14 in the transmitter 2 can have the same or a different number of turns.

[0048] The resonant capacitor 22 is connected at one end to an end of the receiving coil 21 and at the other end to an end of the coil 23 and to an input terminal of the rectifier-smoothing circuit 24. The resonant capacitor 22 oscillates with the received power along with the receiving coil 21 and outputs the received power to the rectifier-smoothing circuit 24.

[0049] The coil 23 is connected between the resonant circuit 20 and the rectifier-smoothing circuit 24. In the present embodiment, one end of the coil 23 is connected to the resonant capacitor 22 in the resonant circuit 20 and to one input terminal of the rectifier-smoothing circuit 24, and the other end is connected to the receiving coil 21 and to the other input terminal of the rectifier-smoothing circuit 24 in parallel with the resonant circuit 20, or in this example, in parallel with the receiving coil 21. The coil 23 reduces the parasitic capacitance of diodes contained in the rectifier-smoothing circuit 24 that influence the resonance with the transmitted power.

[0050] The rectifier smoothing circuit 24, which is an example of a rectifier circuit, contains a full-wave rectifier circuit 25 with four bridge-connected diodes and a smoothing capacitor 26. The rectifier smoothing circuit 24 equalizes and smooths the power received via the resonant circuit 20 to convert the power into DC voltage. The rectifier smoothing circuit 24 delivers the resulting DC power to the load circuit 27.

[0051] The voltage detection circuit 28 detects an output voltage through the rectifier smoothing circuit 24 at predetermined time intervals. The output voltage at the rectifier smoothing circuit 24 corresponds to the output voltage of the resonant circuit 20. The measured value of the output voltage across the rectifier smoothing circuit 24 thus indirectly represents the measured value of the output voltage of the resonant circuit 20. The circuit for determining constant voltage 29 can, for example, be any known circuit capable of detecting DC voltage. The voltage detection circuit 28 outputs a voltage signal, representing the measured value of the output voltage, to the circuit for determining constant voltage 29.

[0052] The constant voltage detection circuit 29 uses the measured output voltage received from the voltage detection circuit 28 to determine whether the contactless power transmission device 1 is operating in constant voltage mode and whether the measured output voltage is within a permissible voltage range for constant voltage operation. The constant voltage detection circuit 29 then transmits the result of this determination to the communicator 32. Therefore, the constant voltage detection circuit 29 includes a determination circuit 30, which contains, for example, a storage circuit that stores the permissible voltage range, and an arithmetic circuit that compares the measured output voltage with the permissible voltage range.

[0053] The constant voltage detection circuit 29 also includes a switching element 31, such as a MOSFET, connected between the rectifier smoothing circuit 24 and the load circuit 27. The switching element 31 prevents current flow from the rectifier smoothing circuit 24 to the load circuit 27 in the off state (i.e., the AC equivalent resistance Rac of the load circuit 27 = ∞) and allows current flow from the rectifier smoothing circuit 24 to the load circuit 27 in the on state. The detection circuit 30 in the constant voltage detection circuit 29 switches the switching element 31 on and off at predetermined intervals while the measured output voltage is outside the permissible voltage range. This causes the resistance of the entire circuit, including the load circuit 27 connected to the rectifier smoothing circuit 24, to change at the predetermined intervals.The detection circuit 30 can thus determine whether the contactless power transmission device 1 is operating with constant voltage output by determining whether the measured output voltage remains essentially constant when the switching element 31 is switched on and off. The detection circuit 30 sends a message to the communicator 32 indicating that the contactless power transmission device 1 is operating with constant voltage output if the measured output voltage remains essentially constant when the switching element 31 is switched on and off at the specified intervals.

[0054] If the measured output voltage indicates that the contactless power transmission device 1 has been operating at a constant voltage output for a period of time longer than a predetermined interval, the detection circuit 30 stops the switching element 31 from switching on and off and maintains the on state. The detection circuit 30 determines whether the measured output voltage is within the permissible voltage range and transmits the result to the communicator 32.

[0055] If the measured output voltage is within the permissible voltage range for a certain period of time that is longer than the specified interval, the determining circuit 30 provides the communicator 32 with the measurement result indicating that the contactless power transmission device 1 is operating in constant voltage output mode and that the measured output voltage is within the permissible voltage range.

[0056] In one variation, the constant voltage detection circuit 29 can include a resistor connected in parallel to the load circuit 27 and then to the rectifier smoothing circuit 24. In this case, the switching element 31 can be connected in series with the resistor and in parallel with the load circuit 27. The detection circuit 30 switches off the switching element 31 as long as the measured output voltage is within the permissible voltage range. If the measured output voltage is outside the permissible voltage range, the detection circuit 30 switches the switching element 31 on and off at predetermined intervals in the same manner as in the embodiment described above. In this modification, the load circuit 27 is continuously energized, while the contactless power transmission device 1 is not operating in constant voltage output mode.

[0057] In a further modification, a second switching element, such as a MOSFET, can be connected in parallel to the resistor mentioned above and in series with the load circuit 27. In this case, the control circuit 30 switches on the second switching element while the measured output voltage is within the permissible voltage range, in order to supply current to the load circuit 27. If the measured output voltage is outside the permissible voltage range, the control circuit 30 can switch off the second switching element to interrupt the power supply to the load circuit 27. This design prevents an excessively high voltage from being applied to the load circuit 27, even though the voltage of the received power may rise excessively during the setting of the switching frequency in the transmitter 2.

[0058] Communicator 32, which is an example of a second communicator, generates a radio signal in accordance with the determination result from the determination circuit 30 in the constant voltage determination circuit 29. This radio signal contains determination information indicating whether the contactless power transmission device 1 is operating in constant voltage output mode and whether the measured output voltage is within the permissible voltage range at predetermined intervals. Communicator 32 then transmits the radio signal to communicator 15 in transmitter 2. Communicator 32 therefore includes, for example, a communication circuit that generates a radio signal according to a predetermined radio transmission standard and an antenna that transmits the radio signal. As with communicator 15, the predetermined wireless communication standard is, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0059] The contactless power transmission device 1 reduces fluctuations in the output voltage in the manner described below.

[0060] Fig. Figure 2 is an equivalent circuit diagram of receiver 3. In an equivalent circuit 100, L is the inductance of the receiving coil 21 in the resonant circuit 20, Cs is the capacitance of the resonant capacitor 22 connected in parallel to the receiving coil 21 in the resonant circuit 20 in receiver 3, Lp is the inductance of the coil 23, and Cd is the parasitic capacitance of the diodes contained in the rectifier smoothing circuit 24. Typically, Cd << Cs. Rac is the AC equivalent resistance of the load circuit 27 for a resistance Ro, and Rac = (8 / π²) × Ro.

[0061] The efficiency of power transmission in contactless power transmission varies depending on the coupling degree k between a transmitting coil and a receiving coil and the quality factor (Q), which is an index of the resonance intensity. More precisely, the power factor approaches 1 as the coupling degree k increases, thus improving the efficiency of the power transmission. As the quality factor (Q factor) increases, the power factor approaches 1, thereby improving the efficiency of the power transmission. As shown in equivalent circuit 100, the receiving coil 21 and the parasitic capacitance Cd of the diodes in the rectifier-smoothing circuit 24 form a parallel connection and thus operate together as an RLC parallel resonant circuit for the transmitted power. In this case, the RLC parallel resonant circuit formed by the receiving coil 21 and the parasitic capacitance Cd has the Q factor, which is expressed by the formula below.Formula 1. Q=RaccdL

[0062] Formula (1) shows that the Q-factor increases with increasing AC equivalent resistance Rac of the load circuit 27. Without the inductor 23, the parasitic capacitance Cd has a more direct effect on the power transfer, since the AC equivalent resistance Rac of the load circuit 27 increases and thus causes more fluctuations in the output voltage.

[0063] In the present embodiment, the coil 23 is connected in parallel to each resonant circuit 20 and the rectifier circuit 24. The coil 23 and the parasitic capacitance Cd together form a parallel resonant circuit that generates an impedance. This impedance increases with a frequency closer to the resonant frequency, which is determined by the product of the inductance Lp of the coil 23 and the parasitic capacitance Cd. At the resonant frequency, the impedance is theoretically infinite. This reduces the current flowing through the coil 23 and the parasitic capacitance Cd in the parallel resonant circuit. The circuit in the receiver 3 can thus be approximated to a series resonant circuit formed by the receiving coil 21, the resonant capacitor 22, and the load circuit 27. At the resonant frequency of the series resonant circuit, the probability that the AC equivalent resistance Rac of the load circuit 27 has a lesser influence on the Q-factor is reduced.The output voltage approaches a value determined by the coupling coefficient k and the voltage applied to the transmitting coil 14. This reduces any increase in the output voltage resulting from an increase in the AC equivalent resistance Rac of the load circuit 27. This, in turn, reduces fluctuations in the output voltage caused by fluctuations in the AC equivalent resistance Rac of the load circuit 27.

[0064] The operation of the device for contactless power transmission 1 is described in detail below.

[0065] In the present embodiment, the control circuit 17 of the transmitter 2 controls, on the basis of the destination information received via the communicator 15, the switching frequency and the alternating voltage supplied to the transmitting coil 14 by the power supply circuit 10, so that the contactless power transmission device 1 can continue to operate with constant voltage output.

[0066] Fig. Figure 3 is a diagram showing exemplary simulation results for the frequency response of the output voltage of the contactless power transmission device 1 according to the present embodiment. Fig. Figure 3 represents the horizontal axis as the frequency and the vertical axis as the output voltage. In the simulation, the transmitting coil 14 and the receiving coil 21 form an ideal 1:1 transformer. The transmitting coil 14 has an inductance L1 of 174 µH, the resonant capacitor 22 has a capacitance Cs of 20 nF, the transmitter has a coil resistance Ri of 0.1 Ω, the receiver has a coil resistance Ris of 0.1 Ω, the coil 23 has an inductance Lp of 160 µH, the diodes in the rectifier-smoothing circuit 24 have a parasitic capacitance Cd of 1 nF, a voltage Vin of 300 V is applied to the transmitting coil 14, and the load circuit 27 has a resistance Ro of 10 Ω (Rac ≈ 8.1 Ω). Furthermore, line 301 represents a frequency response of the output voltage when the coupling factor k is set to k = 0.15 and the AC equivalent resistance of the load circuit 27 is set to Rac.Furthermore, line 302 represents a frequency response of the output voltage when the coupling factor k is set to k = 0.15 and the AC equivalent resistance of the load circuit 27 is set to (100 * Rac). Line 303 represents a frequency response of the output voltage when the coupling factor k is set to k = 0.3 and the AC equivalent resistance of the load circuit 27 is set to Rac. Line 304 represents a frequency response of the output voltage when the coupling factor k is set to k = 0.3 and the AC equivalent resistance of the load circuit 27 is set to (100 * Rac). Line 305 represents a frequency response of the output voltage when the coupling factor k is set to k = 0.6 and the AC equivalent resistance of the load circuit 27 is set to Rac.Furthermore, a line 306 represents a frequency response of the output voltage when the coupling factor k is set to k = 0.6 and the AC equivalent resistance of the load circuit 27 is set to (100 * Rac).

[0067] As in Fig. As shown in Figure 3, the diagram illustrates, for each coupling degree k (in three graphs 311 to 313 in the figure), the combination of frequency and output voltage that causes the output voltage to be essentially constant (or constant) for each variable AC equivalent resistance Rac of the load circuit 27 under the constant coupling degree k. It follows that the contactless power transmission device 1 can operate with a constant voltage output for each variable resistance of the load circuit 27. Furthermore, although the constant output voltage varies for each varying AC equivalent resistance Rac of the load circuit 27 depending on the degree of coupling, as shown in graphs 311 to 313, adjusting the voltage at the transmitting coil 14 can eliminate this difference in the output voltage, and the output voltage can be essentially constant at each coupling degree.

[0068] Fig. Figure 4 is a diagram showing exemplary simulation results for the frequency response of the output voltage for a varying voltage applied to the transmitting coil 14 in accordance with the coupling coefficient in the Fig. The simulation shown in section 3 is created. Fig. Figure 4 represents the frequency on the horizontal axis and the output voltage on the vertical axis. Furthermore, line 401 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmitting coil is Vin. Line 402 also represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.15, the AC equivalent resistance of the load circuit 27 is set to (100 * Rac), and the voltage applied to the transmitting coil is Vin. Finally, line 403 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmitting coil 14 is (0.5 * Vin).Furthermore, line 404 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.3, the AC equivalent resistance of the load circuit 27 is set to (100 * Rac), and the voltage applied to the transmitting coil is (0.5 * Vin). Furthermore, line 405 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to Rac, and the voltage applied to the transmitting coil 14 is (0.25 * Vin). Furthermore, line 406 represents a frequency response of the output voltage when the coupling coefficient k is set to k = 0.6, the AC equivalent resistance of the load circuit 27 is set to (100 * Rac), and the voltage applied to the transmitting coil is (0.25 * Vin).

[0069] The combinations of frequency and output voltage in the three diagrams 411 to 413 correspond to those in diagrams 311 to 313 in Fig. The three combinations shown produce a substantially constant output voltage (or a constant voltage output) in response to a varying AC equivalent resistance Rac of the load circuit 27 under the constant coupling factor k. The output voltages in the respective graphs 411 to 413 are substantially the same.

[0070] This shows that by appropriately adjusting the switching frequency and the voltage of the AC voltage applied to the transmitting coil 14, it is possible to keep the output voltage essentially constant, regardless of the varying AC equivalent resistance Rac of the load circuit 27 or the varying coupling degree k.

[0071] Fig. Figure 5 is a table showing the relationship between the resistance of the load circuit 27 and the output voltage at each of the graphs 411 to 413. Table 500 shows that for each of the coupling coefficients k = 0.15, 0.3, and 0.6, the output voltage for the AC equivalent resistance Rac of the load circuit 27 is essentially 8.1 Ω (Ro = 10 Ω), and the output voltage for the AC equivalent resistance Rac is essentially 810 Ω (Ro = 1 kΩ). This is similar to the simulation in Fig. 4 The transmitting coil 14 receives a voltage Vin of 300 V for k = 0.15, a voltage of (0.5 * Vin) for k = 0.3 and a voltage of (0.25 * Vin) for k = 0.6.

[0072] Fig. Figure 6 is a table showing the relationship between the resistance of the load circuit 27 and the output voltage at each of the graphs 411 to 413 in a comparative example where the coil 23 has been omitted. Table 600 shows that for each of the coupling coefficients k = 0.15, 0.3, and 0.6, the output voltage for the AC equivalent resistance Rac of the load circuit 27 is essentially 8.1 Ω, and the output voltage for the AC equivalent resistance Rac is 810 Ω. This is similar to the simulation in Fig. 4 The transmitting coil 14 receives a voltage Vin of 300 V for k = 0.15, a voltage of (0.5 * Vin) for k = 0.3 and a voltage of (0.25 * Vin) for k = 0.6.

[0073] As can be seen from Tables 500 and 600, the coil 23 can reduce fluctuations in the output voltage resulting from fluctuations in the resistance of the load circuit 27.

[0074] In order to enable such operation with constant voltage output, the control circuit 17 controls the switching frequency and the voltage of the alternating voltage applied to the transmitting coil 14 in the manner described below.

[0075] If the destination information contained in the radio signal received by receiver 3 via communicator 15 indicates that the contactless power transmission device 1 is not operating in constant voltage output mode, the control circuit 17 changes the switching frequency of the alternating current within a predetermined frequency range. This predetermined frequency range extends from the frequency at which a constant voltage is output with an estimated minimum coupling degree between the transmitting coil 14 and the receiving coil 21, to the frequency at which a constant voltage is output with an estimated maximum coupling degree between the transmitting coil 14 and the receiving coil 21, for example, when transmitter 2 is transmitting power to receiver 3.

[0076] When changing the switching frequency, the control circuit 17 can successively increase or decrease the switching frequency from the lower to the upper limit of the specified frequency range or from the upper to the lower limit of the specified frequency range. To enable the constant voltage detection circuit 29 in the receiver 3 to determine whether the output voltage is essentially constant, the control circuit 17 can change the switching frequency in steps such that the constant switching frequency is maintained for longer than the interval in which the detection circuit 30 in the constant voltage detection circuit 29 switches the switching element 31 on and off.

[0077] The control circuit 17 can reduce the voltage applied to the transmitting coil 14 to its lowest value during the setting of the switching frequency. This prevents current with excessive voltage from being supplied to the receiver 3.

[0078] If the determination information contained in the radio signal received by receiver 3 via communicator 15 indicates that the measured output voltage is outside the permissible voltage range, but remains essentially constant in response to a varying resistance of the load circuit, or if constant voltage output operation is being carried out, the control circuit 17 subsequently maintains the constant switching frequency. The control circuit 17 selects the duty cycle based on the reference table, which specifies the correspondence between each switching frequency and the duty cycle that controls the on / off state of the switching element SW in the reactive power compensation circuit 12, in order to enable a constant output voltage with the corresponding switching frequency at each coupling level.The control circuit 17 controls the gate driver 16-1 to switch the switching element SW in the reactive power compensation circuit 12 on and off in accordance with the duty cycle. In this way, the voltage at the transmitting coil 14 is adjusted so that the output voltage of the resonant circuit 20 is within the permissible voltage range, or more precisely, to output a constant voltage at any degree of coupling. If the determination information contained in the radio signal from the receiver 3 via the communicator 15 indicates that the measured output voltage is within the permissible voltage range, the control circuit 17 maintains the constant switching frequency and the constant voltage of the alternating current at the transmitting coil 14.

[0079] The control circuit 17 can gradually change the duty cycle until the determination information contained in the radio signal received by the receiver 3 via the communicator 15 indicates that the measured output voltage is within the permissible voltage range, instead of referring to the above reference table and selecting the duty cycle.

[0080] As described above, the contactless power transfer device in the receiver includes a coil connected in parallel to the resonant circuit between the resonant circuit and the rectifier circuit. This configuration of the contactless power transfer device can reduce the parasitic capacitance of the diodes in the rectifier circuit, which affects power transfer, and thus reduce fluctuations in the output voltage caused by load variations in the load circuit.

[0081] As in the Fig. 3 and Fig. As shown in Figure 4, the switching frequency of the alternating current applied to the transmitting coil 14 varies with the degree of coupling between the transmitting coil 14 and the receiving coil 21, in order to enable the contactless power transmission device 1 to operate with a constant output voltage. The impedance of the LC parallel resonant circuit formed by the coil 23 and the parasitic capacitance of the diodes in the rectifier smoothing circuit 24 also vary with the changing switching frequency. To reduce fluctuations in the output voltage more effectively, the inductance of the coil 23 can therefore also vary depending on the degree of coupling or switching frequency of the alternating current applied to the transmitting coil 14.

[0082] Fig. Figure 7 is a schematic representation of a receiver according to a modification. As in Fig. As shown in Figure 7, a receiver 4 according to this modification comprises a resonant circuit 20 with a receiving coil 21 and a resonant capacitor 22, three coils 23-1 to 23-3, a rectifier smoothing circuit 24, a load circuit 27, a voltage detection circuit 28, a constant voltage detection circuit 29, a communicator 32, and two relays 33-1 and 33-2. The receiver 4, together with the transmitter 2 in the above embodiment, forms, for example, a device for contactless power transmission.

[0083] In this variation, receiver 4 differs from receiver 3 in that Fig. 1 in the three coils 23-1 to 23-3 between the resonant circuit 20 and the rectifier-smoothing circuit 24 and the two relays 33-1 and 33-2, as well as partially in the operation of the determining circuit 30 in the circuit for determining constant voltage 29 and the communicator 32. The differences and related sections are now described. For the other components of the receiver 4, the corresponding components are described in the embodiment above.

[0084] The three coils 23-1 to 23-3 are connected in series with each other and in parallel with the resonant circuit 20 and the rectifier-smoothing circuit 24 between the resonant circuit 20 and the rectifier-smoothing circuit 24. The coils 23-1 to 23-3 can have the same inductance or different inductances.

[0085] The two relays 33-1 and 33-2 each represent a short-circuit circuit. Relay 33-1 is connected in parallel to coil 23, and relay 33-2 is connected in parallel to coil 23-2. When switched on, relay 33-1 short-circuits coil 23-1. Similarly, relay 33-2 short-circuits coil 23-2 when switched on. The control circuit 30 controls the on / off states of relays 33-1 and 33-2. Relays 33-1 and 33-2 are switched on and off in the manner described above to change the resonant frequency of the parallel resonant circuit formed by coils 23-1 to 23-3 and the parasitic capacitance Cd of the diodes in the rectifier smoothing circuit 24. More precisely, when relay 33-1 and relay 33-2 are switched off, the resonant frequency of the parallel resonant circuit is determined by the product of the parasitic capacitance Cd and the sum of the inductances of coils 23-1 to 23.When relay 33-1 is off and relay 33-2 is on, the resonant frequency of the parallel resonant circuit is determined by the product of the parasitic capacitance Cd and the sum of the inductances of coils 23-1 and 23. When relay 33-1 is on and relay 33-2 is off, the resonant frequency of the parallel resonant circuit is determined by the product of the parasitic capacitance Cd and the sum of the inductances of coils 23-2 and 23. When both relay 33-1 and relay 33-2 are on, the resonant frequency of the parallel resonant circuit is determined by the product of the parasitic capacitance Cd and the inductance of coil 23. Thus, switching relays 33-1 and 33-2 on and off at the same frequency can change the impedance of the parallel resonant circuit formed by coils 23-1 to 23-3 and the parasitic capacitance Cd of the diodes in the rectifier smoothing circuit 24.

[0086] In the case of operation with constant voltage output of a device for contactless power transmission with the in Fig. In the transmitter 2 and receiver 4 shown in Figure 1, the communicator 32 receives a radio signal from the communicator 15 in the transmitter 2 containing information specifying the switching frequency of the alternating voltage supplied to the transmitting coil 14, and delivers this information to the control circuit 30. If the control information contained in the radio signal received by the receiver 4 via the communicator 15 indicates that the measured output voltage is within the permissible voltage range, the control circuit 17 in the transmitter 2 controls the communicator 15 to transmit a radio signal including the information indicating the switching frequency of the alternating current of the transmitting coil 14.

[0087] The control circuit 30 stores in its non-volatile semiconductor memory a reference table containing the correspondence between each switching frequency, enabling constant voltage output operation of the contactless power transmission device, and the on-off states of relays 33-1 and 33-2. The on-off states of relays 33-1 and 33-2 are specified for the reference table, for example, by simulations or experiments, in order to minimize fluctuations in the output voltage due to load variations in the load circuit 27 at the corresponding switching frequency. At higher switching frequencies, for example, more relays are switched on to increase the resonant frequency of the parallel resonant circuit formed by coils 23-1 to 23-3 and the parasitic capacitance Cd of the diodes in the rectifier smoothing circuit 24.In operation with constant voltage output of the contactless power transmission, the determining circuit 30 receives the switching frequency of the alternating current supplied to the transmitting coil 14 from the transmitter 2 via the communicator 32 and refers to the reference table for determining the on / off state of relays 33-1 and 33-2 for the received switching frequency. The determining circuit 30 controls the on / off states of relays 33-1 and 33-2 according to the determination.

[0088] The contactless power transmission device, including receiver 4 according to the modification, switches between short-circuiting and opening at least one of the coils connected between the resonant circuit and the rectifier smoothing circuit, depending on the switching frequency of the alternating current supplied to the transmitting coil during constant voltage output operation, or more precisely, depending on the degree of coupling between the transmitting coil and the receiver coil. The contactless power transmission device thus efficiently eliminates the parasitic capacitance of the diodes in the rectifier smoothing circuit, which affects the transmitted power, and thereby reduces fluctuations in the output voltage caused by load variations in the load circuit.

[0089] The coils 23-1 to 23-3 can be arranged in parallel to each other between the resonant circuit 20 and the rectifier-smoothing circuit 24. In this case as well, the parallel resonant circuit of the coils 23-1 to 23-3 and the parasitic capacitance Cd of the diodes in the rectifier-smoothing circuit 24 have different impedances for the same frequency, depending on whether the coils 23-1 and 23-2 are short-circuited. Thus, as in the modification described above, the control circuit 30 controls the on / off states of the relays 33-1 and 33-2 according to the switching frequency, thereby enabling operation with a constant voltage output of the device for contactless power transmission.

[0090] In another example, instead of three coils, two coils or four or more coils can be connected in series or in parallel to each other, and also in parallel to the receiving coil 21 in the resonant circuit 20 and to the rectifier-smoothing circuit 24 between the resonant circuit 20 and the rectifier-smoothing circuit 24. The coils, with the exception of one, are each connected in parallel to a relay. In the same way as in the modification described above, the control circuit 30 controls the on / off states of the relays depending on the switching frequency, thus enabling the device to operate for contactless power transmission with a constant voltage output.

[0091] In another variation, the power supply circuit that supplies the transmitting coil in the transmitter with alternating current may not have the circuit configuration described in the above embodiment or in the variations, but may have a different circuit configuration with which the switching frequency and the voltage applied to the transmitting coil can be adjusted.

[0092] Fig. 8A and Fig. 8B each represent a circuit diagram of a power supply circuit according to one modification.

[0093] A in Fig. The power supply circuit 110 shown in Figure 8A comprises a current source 11, a reactive power compensation circuit 12, two switching elements 13-1 and 13-2, and a capacitor 131 connected in series with a transmitting coil 14, which acts as a DC circuit breaker. In this modification as well, each switching element can be, for example, an n-channel MOSFET. The reactive power compensation circuit 12 can, for example, be the same as the reactive power compensation circuit 12 in the embodiment above.

[0094] In this modification, the switching element 13-1 and the switching element 13-2 are connected in series between the positive and negative electrode terminals of the power source 11. The positive electrode of the power source 11 is connected to switching element 13-1 and the negative electrode to switching element 13-2. Switching element 13-1 has a drain terminal connected to the positive electrode terminal of the power source 11 via the reactive power compensation circuit 12, and a source terminal connected to the drain terminal of switching element 13-2. Switching element 13-2 has a source terminal connected to the negative electrode terminal of the power source 11 via the reactive power compensation circuit 12.The source terminal of switching element 13-1 and the drain terminal of switching element 13-2 are connected to one end of the transmitting coil 14, and the source terminal of switching element 13-2 is connected to the other end of the transmitting coil 14 via capacitor 131. Each switching element has a gate terminal that is connected to the gate driver 16.

[0095] In this modification, the gate driver 16-2 can alternately switch the switching elements 13-1 and 13-2 on and off in accordance with a control signal from a control circuit. More precisely, when switching element 13-1 is on and switching element 13-2 is off, a current flows through the reactive power compensation circuit 12 and switching element 13-1 from the power source 11 to the transmitter coil 14 to charge the capacitor 131. When switching element 13-1 is off and switching element 13-2 is on, the capacitor 131 discharges, allowing a current to flow through the transmitter coil 14 and switching element 13-2 from the capacitor 131. Thus, in this modification, the control circuit can use the gate driver 16-2 to control the switching frequency for turning switching elements 13-1 and 13-2 on and off according to the destination information received from the receiver 3.

[0096] Similar to power supply circuit 110, a [circuit] in [circuit] includes Fig. The power supply circuit 120 shown in Figure 8B comprises a power source 11, a reactive power compensation circuit 12, two switching elements 13-1 and 13-2, and a capacitor 131 connected in series to a transmitting coil 14. The power supply circuit 120 differs from the power supply circuit 110 in that the transmitting coil 14 has one end connected via the reactive power compensation circuit 12 to the positive electrode terminal of the power source 11, and another end connected via the capacitor 131 to the source terminal of switching element 13-1 and to the drain terminal of switching element 13-2.

[0097] In the present modification, the gate driver 16-2 can alternately switch the switching elements 13-1 and 13-2 on and off in accordance with a control signal from a control circuit.

[0098] To prevent the transmitting coil 14 and the capacitor 131 from operating in the adjustable switching frequency range in the power supply circuit 110 in Fig. 8A and in the power supply circuit 120 in Fig. Since 8B each operate as a resonant circuit, the capacitance of the capacitor 131 can be adjusted so that the transmitting coil 14 and the capacitor 131 oscillate at a frequency that is lower than the resonant frequency of the resonant circuit in the receiver and lower than the lower cutoff frequency in the adjustable switching frequency range.

[0099] In the Fig.In the embodiment shown in Figure 1, a capacitor can be connected in series with the transmitting coil 14 to act as a DC circuit breaker, as in the power supply circuits 110 and 120. To prevent the transmitting coil 14 and the capacitor from operating as a resonant circuit in the adjustable switching frequency range, the capacitance of the capacitor can be adjusted so that the transmitting coil 14 and the capacitor oscillate at a frequency lower than the resonant frequency of the resonant circuit 20 in the receiver 3 and lower than the lower cutoff frequency in the adjustable switching frequency range.

[0100] The communicator 15 in transmitter 2 and the communicator 32 in receiver 3 can be connected by a wire and can each contain a communication circuit that sends and receives a signal including destination information over the wire.

[0101] The rectifier circuit included in the receiver in each of the embodiments, and the modifications described above, can constitute a synchronous rectifier circuit.

[0102] As described above, the person skilled in the art can make modifications according to various embodiments within the scope of the present invention.

Claims

[1] Device for contactless power transmission (1), comprising: a transmitter (2); and a receiver (3) configured to receive power contactlessly from the transmitter (2), wherein the transmitter (2) has a transmitting coil (14) configured to supply current to the receiver (3), and a power supply circuit (10) designed to supply current to the transmitting coil (14), where the receiver (3) has a resonant circuit (20) comprising a receiving coil (21) configured to receive current from the transmitter (2) and a resonant capacitor (22) connected in parallel with the receiving coil (21), a rectifier circuit (24) configured to rectify the current supplied by the resonant circuit (20), and a first coil (23, 23-1) which is connected in parallel to the resonant circuit (20) between the resonant circuit (20) and the rectifier circuit (24), wherein the power supply circuit (10) sets a switching frequency and a voltage of an alternating current power supplied to the transmitting coil (14), wherein the transmitter (2) further exhibits a first communicator (15) configured to receive from the receiver (3) a signal containing determination information indicating whether the contactless power transmission device (1) is operating in constant voltage output mode and whether a measured value of an output voltage of the resonant circuit (20) is within a specified permissible voltage range, and a control circuit (17) configured to control, according to the destination information, the switching frequency and the voltage of the AC power supplied by the power supply circuit (10) to the transmitting coil (14), and where the recipient (3) further exhibits a voltage detection circuit (28) configured to measure the output voltage of an electrical power output from the resonant circuit (20) and to determine the measured value of the output voltage, a constant voltage circuit (29) configured to determine, on the basis of the measured output voltage, whether the contactless power transfer device (1) is operating at constant voltage output and whether the measured output voltage of the resonant circuit (20) is within the specified permissible voltage range, and a second communicator (32) configured to transmit the signal including the destination information to the transmitter (2). [2] Device for contactless power transmission (1) according to claim 1, wherein the control circuit (17), in response to the determination information indicating that the device for contactless power transmission (1) is not operating with constant voltage output, controls the switching frequency of the AC power supplied to the transmitting coil (14) from the power supply circuit (10) in order to allow the measured output voltage for a varying resistance of a load circuit (27) connected to the rectifier circuit (24) in the receiver (3) to remain unchanged. [3] Device for contactless power transmission (1) according to claim 2, wherein the control circuit (17) controls the voltage of the AC power supplied to the transmitting coil (14) from the power supply circuit (10) in response to the specified determination information indicating that the device for contactless power transmission (1) is in constant voltage output operation and the measured value of the output voltage of the resonant circuit (20) is outside the specified permissible voltage range, so that the measured value of the output voltage of the resonant circuit (20) is within the specified permissible voltage range. [4] Device for contactless power transmission (1) according to claim 1, wherein the recipient (3) further exhibits a second coil (23-2, 23-3) which is connected in parallel to the resonant circuit (20) between the resonant circuit (20) and the rectifier circuit (24), and a short-circuit circuit (33-1, 33-2) switchable between the short circuit or the opening of the second coil (23-2, 23-3), and wherein the constant voltage determination circuit (29) receives the switching frequency of the alternating current power supplied to the transmitter coil (14) by the power supply circuit (10) from the transmitter (2) via the communicator (15) when the contactless power transmission device (1) is operating with constant voltage output, and controls the short-circuit circuit (33-1, 33-2) according to the switching frequency.

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