CONTACTLESS ENERGY TRANSFER DEVICE

Abstract

Contactless energy transfer device (1), comprising: a transmitter (2); and a receiver (3) which is configured to receive electrical energy from the transmitter (2) in a contactless manner, where the transmitter (2) has: a transmitting coil (14) which is set up to supply electrical energy to the receiver (3), a power supply circuit (10) which is set up to supply alternating current energy to the transmitting coil (14) with an adjustable switching frequency and an adjustable voltage, a current sensing circuit (16) which is set up to measure a current through the transmitting coil (14) and to determine a measured value of the current, a control circuit (19) which is set up to control the switching frequency and the voltage of the alternating current energy which is supplied to the transmitting coil (14) by the power supply circuit (10), and a first communication device (17) that is set up to communicate with the receiver (3), where the receiver (3) has: a resonant circuit (20) comprising a receiving coil (21) configured to receive electrical energy from the transmitter (2) and a resonant capacitor (22) configured to resonate with the receiving coil (21) in response to electrical energy from the transmitter (2), a rectifier circuit (24) which is set up to rectify electrical energy output by the resonant circuit (20), a short-circuit circuit (30) which is configured to switch between short-circuiting and opening the resonant circuit (20), a voltage detection circuit (28) which is set up to measure an output voltage of an electrical energy output by the resonant circuit (20) and to determine a measured value of the output voltage, a second communication device (31) which is set up to communicate with the transmitter (2), and a determination circuit (29) configured to determine whether the measured output voltage is within a predetermined permissible voltage range, and to cause the short-circuiting circuit (30) to short-circuit the resonant circuit (20), and to cause the second communication device (31) to transmit determination information indicating that the contactless power transfer device (1) is not performing a constant voltage output operation in which the output voltage from the rectifier circuit (24) is a constant voltage, even if a resistance of a load circuit (27) connected to the rectifier circuit (24) changes when the measured output voltage is outside the predetermined permissible voltage range, and wherein the control circuit (19) in the transmitter (2) detects a switching frequency of the alternating current energy in response to the determination information received by the receiver (3) through the first communication device (17), which indicates that the contactless energy transfer device (1) is not performing a constant voltage output operation, at which the contactless energy transfer device (1) performs the constant voltage output operation according to the measured current.

Description

AREA

[0001] The present invention relates to a contactless energy transfer device. STATE OF THE ART

[0002] Techniques for contactless energy transfer (also called wireless energy transfer) or for transmitting electrical energy across a space without the use of metal contacts or other connections were investigated.

[0003] In contactless energy transfer, the frequency of an alternating current applied to a transmitting coil varies according to the coupling degree between the transmitting coil on a primary side (transmitter side) and a receiving coil on a secondary side (receiver side) in order to achieve high energy transfer efficiency. The coupling degree between the transmitting and receiving coils varies according to the positional relationship between the two coils. Therefore, a technique was developed to obtain a frequency response corresponding to the frequency response of the transfer efficiency simply and accurately by processing on the transmitter side (see, for example, patent literature 1).

[0004] An energy transfer device described in patent literature 1 supplies alternating current energy to a transmitting coil at a constant voltage or with a constant current while changing the drive frequency of an inverter. The energy transfer device then obtains the frequency response of a current value corresponding to a current through the transmitting coil receiving the alternating current energy, or of a voltage value corresponding to a voltage applied to the transmitting coil. LIST OF DOCUMENT PATENT LITERATURE

[0005] Patent Literature 1: Japanese Unexamined Patent Application Publication JP 2015-12 748 A

[0006] Further prior art is provided by US 2013 / 0 313 893 A1. US 2013 / 0 313 893 A1 discloses a method for setting a resonant frequency and the impedance of a resonant system in contactless energy transfer by means of a resonance method, wherein a variable capacitor sets the resonant frequency of a secondary self-resonant coil, a matching box sets an input impedance of a resonant system, and an ECU first sets the resonant frequency of the secondary self-resonant coil by controlling the variable capacitor, and after setting the resonant frequency, sets the input impedance of the resonant system by controlling the matching box. SUMMARY TECHNICAL TASK

[0007] A contactless power transfer device can perform a constant voltage output operation to allow a receiver to output a constant voltage. Electronic devices are typically controlled with a constant voltage. Therefore, a contactless power transfer device is intended to supply a constant voltage to a load circuit.

[0008] Although the technique described in patent literature 1 can determine the frequency of an alternating current energy applied to the transmitting coil on the transmitter side to achieve high energy transfer efficiency, this frequency could differ from the frequency at which the contactless energy transfer device outputs a constant voltage. Furthermore, the frequency of an alternating current energy applied to the transmitting coil at which the contactless energy transfer device outputs a constant voltage varies according to the coupling degree between the transmitting coil and the receiving coil. Therefore, the frequency of the alternating current energy applied to the transmitting coil at which the contactless energy transfer device outputs a constant voltage is to be determined.

[0009] Against this background, the invention is based on the objective of providing a contactless energy transmission device which can correctly detect the frequency of an alternating current energy applied to the transmitting coil, at which a constant voltage output is given. SOLUTION TO THE TASK

[0010] This problem is solved by the subject matter of independent claim 1. Preferred embodiments of the invention are the subject matter of the dependent claims. The invention is defined by the claims, aspects of which are explained below: A contactless energy transmission device according to one aspect of the present invention comprises a transmitter and a receiver, which receives electrical energy from the transmitter in a contactless manner. The transmitter comprises a transmitting coil that supplies electrical energy to the receiver, a power supply circuit that supplies alternating current energy to the transmitting coil with an adjustable switching frequency and an adjustable voltage, a current sensing circuit that measures a current through the transmitting coil and determines a measured value of the current, and a control circuit that controls the switching frequency and the voltage of the alternating current energy.which is supplied to the transmitting coil by the power supply circuit, and a first communication device that communicates with the receiver. The receiver has a resonant circuit comprising a receiving coil that receives electrical energy from the transmitter and a resonant capacitor that resonates with the receiving coil in response to electrical energy from the transmitter, a rectifier circuit that rectifies electrical energy output by the resonant circuit, a short-circuit circuit that switches between short-circuiting and opening the resonant circuit, a voltage sensing circuit that measures the output voltage of electrical energy output by the resonant circuit and determines a reading of the output voltage, a second communication device that communicates with the transmitter, and a determining circuit that determines,The first communication device detects whether the measured output voltage is within a predetermined permissible voltage range, and the short-circuiting circuit is triggered to short-circuit the resonant circuit. The second communication device is also triggered to transmit determination information indicating that the contactless power transfer device does not output a constant voltage when the measured output voltage is outside the predetermined permissible voltage range. In response to the determination information received by the receiver from the first communication device, indicating that the contactless power transfer device does not output a constant voltage, the control circuit in the transmitter detects a switching frequency of the AC power at which the contactless power transfer device outputs a constant voltage according to the measured current.

[0011] The contactless energy transmission device with the aforementioned structure can correctly detect the frequency of an alternating current energy applied to the transmitting coil, at which a constant voltage output is produced.

[0012] In the contactless energy transfer device, the receiver may further include a coil connected in series with the receiving coil between the resonant circuit and the rectifier circuit. The receiving coil and the resonant capacitor in the receiver's resonant circuit may be connected in parallel. The short-circuiting circuit in the receiver may have one end connected between the coil connected in series with the receiving coil and the rectifier circuit. The determining circuit in the receiver may cause the short-circuiting circuit to short-circuit the resonant circuit via the coil connected in series with the receiving coil when the measured output voltage is outside the predetermined permissible voltage range.

[0013] The contactless energy transmission device with the aforementioned structure can correctly detect the frequency of an alternating current energy applied to the transmitting coil, at which a constant voltage output is produced.

[0014] In the contactless energy transfer device, the receiving coil and the resonant capacitor can be connected in series in the resonant circuit in the receiver.

[0015] The contactless energy transfer device with the aforementioned structure can exhibit higher energy transfer efficiency at a lower output voltage.

[0016] In the contactless energy transfer device, the control circuit in the transmitter can determine that the contactless energy transfer device outputs a constant voltage at a switching frequency of the alternating current energy at which the measured current is greater than or equal to a predetermined threshold.

[0017] The contactless energy transmission device with the aforementioned structure can correctly detect the frequency of an alternating current energy applied to the transmitting coil, at which a constant voltage output is produced.

[0018] In the contactless energy transfer device, the control circuit in the transmitter can determine that the contactless energy transfer device outputs a constant voltage at a switching frequency of the alternating current energy, at which an absolute value of a difference between a phase of the measured current and a phase of the voltage of the alternating current energy supplied to the transmitting coil is less than or equal to a predetermined threshold.

[0019] The contactless energy transmission device with the aforementioned structure can correctly detect the frequency of an alternating current energy applied to the transmitting coil, at which a constant voltage output is produced.

[0020] In the contactless power transmission device, the control circuit in the transmitter, after detecting the switching frequency of the alternating current power at which the contactless power transmission device outputs a constant voltage, can cause the first communication device to transmit detection information indicating the detection of the switching frequency. The determining circuit in the receiver can cause the short-circuiting circuit to open the resonant circuit after receiving the detection information from the second communication device.

[0021] The contactless energy transfer device with the aforementioned structure can quickly resume power supply to a load circuit.

[0022] In this case, after causing the first communication device to transmit the acquisition information, the control circuit in the transmitter can control the power supply circuit to regulate the voltage of the alternating current energy supplied to the transmitting coil to a voltage at which the contactless power transmission device outputs a constant voltage.

[0023] The contactless energy transfer device with the aforementioned structure can resume a constant voltage output process. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a contactless energy transfer device according to an embodiment of the present invention. Fig. Figure 2 is an equivalent circuit diagram of the contactless energy transfer device. Fig. Figure 3 is a graph showing example simulation results for the frequency response of the output voltage of the contactless energy transfer device according to the embodiment. Fig. Figure 4 is a graph showing example simulation results for the frequency response of the output voltage for a varying voltage applied to a transmitting coil, according to the coupling coefficient in the Fig. The simulation shown in section 3 illustrates this. Fig. Figure 5 is a graph showing example simulation results for the frequency response of the output voltage for a varying impedance of a circuit connected to a resonant circuit at a constant coupling degree. Fig. Section 6 includes graphs showing an example relationship between the frequency response of the output voltage and the frequency response of the input impedance in the contactless energy transfer device. Fig. Figure 7 includes graphs showing an example relationship between the frequency response of the output voltage of the contactless energy transfer device and the frequency response of a phase delay of the current relative to the voltage of the AC energy applied to the transmitting coil. Fig. Figure 8 is a schematic representation of a receiver according to a modification. Fig. Figure 9 is a schematic representation of a receiver according to another modification. Fig. Figure 10 is a schematic representation of a receiver according to yet another modification. Fig. Figure 11 is a graph showing example simulation results for the frequency response of the output voltage of the contactless power transfer device, which has a Fig. 1 shown channel and the one in Fig. The 10 receivers shown are shown. Fig. Figure 12 is a graph showing example simulation results for the frequency response of the output voltage of the contactless power transfer device, which is described in Fig. 1 shown channel and the one in Fig. Figure 10 shows the receiver for a varying impedance of a circuit connected to a resonant circuit at a constant coupling degree. Fig. Figure 13 is a graph which shows an example relationship between the frequency response of the output voltage of the contactless energy transfer device, which is in Fig. 1 shown channel and the one in Fig. 10 shown receivers, and shows the frequency response of a phase delay of the current relative to the voltage of the alternating current energy applied to the transmitting coil. DETAILED DESCRIPTION

[0024] A contactless energy transfer device according to an embodiment of the present invention is now described with reference to the drawings. The contactless energy transfer device can output a constant voltage based on the same structure as the SPL topology, which includes an inductor connected in series with a receiving coil, which resonates in parallel with a resonant capacitor. The contactless energy transfer device uses resonance on the receiver side to transfer energy without using resonance on the transmitter side, thus avoiding a reduction in energy transfer efficiency at a low coupling degree between the transmitting coil and the receiving coil.

[0025] In this contactless energy transfer device, the inventors of the present application have found that the current through the transmitting coil reaches its maximum at the frequency of an alternating current applied to the transmitting coil, at which the contactless energy transfer device outputs a constant voltage, when a load circuit connected to a resonant circuit on the receiver side has a very small, negligible impedance. The inventors have also found that the voltage of the alternating current has the same phase as the current through the transmitting coil.

[0026] If the contactless power transfer device can no longer output a constant voltage, for example, because the positional relationship between the transmitting and receiving coils has changed, the device shorts out the resonant circuit on the receiver side via a coil connected in series with the receiving coil in the resonant circuit. The contactless power transfer device then measures the current through the transmitting coil while varying the frequency of the AC power applied to the transmitting coil. The device detects the frequency at which the measured current reaches its maximum or the voltage applied to the transmitting coil has the same phase as the current through the transmitting coil. The device then applies AC power at the detected frequency to the transmitting coil to output a constant voltage.

[0027] Fig. Figure 1 is a schematic representation of a contactless energy transfer device according to an embodiment of the present invention. As shown in Fig. As shown in Figure 1, a contactless energy transfer device 1 comprises a transmitter 2 and a receiver 3 for contactlessly receiving energy from the transmitter 2 through a space. The transmitter 2 includes a power supply circuit 10, a transmitting coil 14, a capacitor 15, a current sensing circuit 16, a communication device 17, a gate driver 18, and a control circuit 19. The receiver 3 includes a resonant circuit 20, which comprises a receiving coil 21 and a resonant capacitor 22, a coil 23, a rectifier-smoothing circuit 24, which comprises a full-wave rectifier circuit 25 and a smoothing capacitor 26, a load circuit 27, a voltage sensing circuit 28, a determining circuit 29, a relay 30, a communication device 31, and a charge storage circuit 32.

[0028] The power supply circuit 10 supplies alternating current energy to the transmitting coil 14 with an adjustable switching frequency and an adjustable voltage. Therefore, the power supply circuit 10 comprises a variable voltage power source 11, a DC-DC converter 12, and three switching elements 13-1 to 13-3.

[0029] The variable-voltage power source 11 supplies direct current energy at a voltage adjustable by the control circuit 19. The variable-voltage power source 11 can have any circuit design that allows for adjustment of the supply voltage. While the contactless power transfer device 1 outputs a constant voltage, the direct current energy supplied by the variable-voltage power source 11 is converted to alternating current energy via the switching elements 13-1 and 13-2 before being supplied to the transmitting coil 14. While the switching frequency is being adjusted to allow the contactless power transfer device 1 to output a constant voltage, the direct current energy supplied by the variable-voltage power source 11 is supplied to the transmitting coil 14 via the DC-DC converter 12 and the switching element 13-3.

[0030] The input terminal of the DC-DC converter 12 is connected to one terminal of the positive electrode of the variable-voltage power source 11, and its output terminal is connected to one end of the capacitor 15 via a diode D and the switching element 13-3. The DC-DC converter 12 reduces the voltage of the DC energy supplied by the variable-voltage power source 11 to a predetermined voltage (e.g., 5 V).

[0031] While the switching frequency is being adjusted to allow the contactless power transfer device 1 to output a constant voltage, the voltage output by the DC converter 12 is supplied to the transmitting coil 14 via the diode D, the switching element 13-3 and the capacitor 15.

[0032] The switching elements 13-1 to 13-3 are, for example, n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). Switching elements 13-1 and 13-2 are connected in series between the positive and negative terminals of the variable-voltage power source 11. The positive terminal of the variable-voltage power source 11 is connected to switching element 13-1, and its negative terminal is connected to switching element 13-2. The drain terminal of switching element 13-1 is connected to the positive terminal of the variable-voltage power source 11, and its source terminal is connected to the drain terminal of switching element 13-2. 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 via capacitor 15.The source terminal of the switching element 13-2 is connected to the terminal of the negative electrode of the variable voltage energy source 11 and the other end of the transmitting coil 14 via the current sensing circuit 16.

[0033] The drain terminal of switching element 13-3 is connected to the output terminal of the DC-DC converter 12, and its source terminal is connected to one end of the transmitting coil 14 via the capacitor 15. Switching elements 13-1 to 13-3 have gate terminals that are connected to the gate driver 18.

[0034] The switching elements 13-1 to 13-3 are controlled by the control circuit 19 and switched on and off by the gate driver 18. The on / off control for the switching elements 13-1 to 13-3 will be described later.

[0035] The transmitting coil 14 transmits alternating current energy supplied by the power supply circuit 10 through a space to the resonant circuit 20 in the receiver 3.

[0036] Capacitor 15 is connected between the transmitting coil 14 and the power supply circuit 10. Capacitor 15 repeatedly charges and discharges in response to the switching on and off of each switching element at the switching frequency, supplying alternating current energy to the transmitting coil 14 at the switching frequency. To prevent the transmitting coil 14 and capacitor 15 from operating as a resonant circuit within the adjustable switching frequency range, the capacitance of capacitor 15 can be set such that sympathetic resonance of the transmitting coil 14 and capacitor 15 is permitted at a frequency lower than the resonant frequency of the resonant circuit 20 in the receiver 3 and lower than the lower cutoff frequency within the adjustable switching frequency range.

[0037] The current sensing circuit 16 is connected between the transmitting coil 14 and the power supply circuit 10 to measure the current through the transmitting coil 14. The current sensing circuit 16 outputs the measured current value to the control circuit 19. The current sensing circuit 16 can be connected in parallel to the capacitor 15 connected to the transmitting coil 14, along with a parallel capacitor (not shown) connected in series with the current sensing circuit 16. In this case, the current sensing circuit 16 indirectly measures the current through the transmitting coil 14.

[0038] The communication device 17 extracts determination information from each radio signal received by the communication device 31 in the receiver 3. This information indicates, for example, whether the contactless power transfer device 1 outputs a constant voltage, and outputs this information to the control circuit 19. The communication device 17 also generates a radio signal containing detection information received from the control circuit 19, indicating that the switching frequency at which the contactless power transfer device 1 outputs a constant voltage has been detected, and transmits this radio signal to the communication device 31 in the receiver 3.The communication device 17 therefore includes, for example, an antenna that transmits and receives a radio signal conforming to a predetermined wireless communication standard, and a communication circuit that modulates a radio signal before transmission or demodulates a received radio signal. The predetermined wireless communication standard is, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0039] The gate driver 18 receives a control signal from the control circuit 19 to switch each of the switching elements 13-1 to 13-3 on and off. In response to the control signal, the gate driver 18 changes the voltage applied to the gate terminal of each of the switching elements 13-1 to 13-3. Specifically, when a control signal to switch on switching element 13-1 is received, the gate driver 18 applies a relatively high voltage to the gate terminal of switching element 13-1 to turn it on. When a control signal to switch off switching element 13-1 is received, the gate driver 18 applies a relatively low voltage to the gate terminal of switching element 13-1 to turn it off. This allows the gate driver 18 to switch switching element 13-1 on and off at times specified by the control circuit 19.Similarly, the gate driver 18 switches the switching elements 13-2 and 13-3 on and off by changing a voltage applied to the gate terminals of the switching elements 13-2 and 13-3.

[0040] The control circuit 19 includes, for example, non-volatile and volatile memory circuits, an arithmetic circuit, and an interface circuit for connection to another circuit. Each time it receives destination information from the communication device 17, the control circuit 19 controls the switching frequency and the voltage of the alternating current power supplied to the transmitting coil 14 by the power supply circuit 10, according to the destination information.

[0041] In the present embodiment, while the contactless power transfer device 1 outputs a constant voltage, the control circuit 19 outputs a control signal to the gate driver 18, instructing it to maintain the off state of the switching element 13-3. The control circuit 19 also outputs a control signal to the gate driver 18, instructing it to switch the switching elements 13-1 and 13-2 on and off at the switching frequency at which a constant voltage is output. More precisely, when the switching element 13-1 is on and the switching element 13-2 is off, current flows through the transmitting coil 14, while the capacitor 15 is charged with the energy supplied by the variable-voltage power source 11 via the switching element 13-1. When the switching element 13-1 is switched off and the switching element 13-2 is switched on, the capacitor 15 discharges, causing current to flow through the transmitting coil 14.

[0042] The control circuit 19 controls the switching elements 13-1 and 13-2 to alternately switch them on for the same duration within a cycle, according to the switching frequency. To prevent the switching elements 13-1 and 13-2 from being switched on simultaneously and short-circuiting the variable voltage power source 11, the control circuit 19 can have a dead time during which the switching elements 13-1 and 13-2 are both switched off when they are switched on and off.

[0043] While the switching frequency is being set to allow the contactless power transfer device 1 to output a constant voltage, the control circuit 19 outputs a control signal to the gate driver 18, which instructs it to keep the off state of the switching element 13-1 and to alternately switch the switching elements 13-3 and 13-2 on and off at the switching frequency.

[0044] If the communication device 17 does not receive a radio signal from the receiver 3, the receiver 3 may be located outside the range for receiving energy from the transmitter 2, or, in other words, the transmitter 2 may be in a standby state. In this case, the control circuit 19 can set the voltage output by the variable-voltage power source 11 to its lowest possible value. During the standby state of the transmitter 2, the lowest possible voltage is applied to the transmitting coil 14 to minimize energy loss.

[0045] The control of the voltage and switching frequency of an alternating current energy applied to the transmitting coil 14, in order to enable the contactless energy transmission device 1 to output a constant voltage, will be described in detail later.

[0046] Receiver 3 will now be described.

[0047] The resonant circuit 20 is an LC resonant circuit comprising the receiving coil 21 and the resonant capacitor 22, which are connected in parallel. One end of the receiving coil 21 in the resonant circuit 20 is connected to one end of the resonant capacitor 22 and also to an input terminal of the rectifier-smoothing circuit 24 via the coil 23. The other end of the receiving coil 21 is connected to the other end of the resonant capacitor 22 and also to the other input terminal of the rectifier-smoothing circuit 24.

[0048] The receiving coil 21 oscillates with an alternating current flowing through the transmitting coil 14 in the transmitter 2 in order to receive energy from the transmitting coil 14. The receiving coil 21 outputs the received energy to the rectifier-smoothing circuit 24 via the resonant capacitor 22 and the coil 23. The receiving coil 21 and the transmitting coil 14 in the transmitter 2 can have the same or different numbers of turns.

[0049] One end of the resonant capacitor 22 is connected to the receiving coil 21 and the coil 23, and its other end is connected to the other end of the receiving coil 21 and the rectifier-smoothing circuit 24. The resonant capacitor 22 outputs the energy received by the receiving coil 21 to the rectifier-smoothing circuit 24 via the coil 23.

[0050] The coil 23 is connected between the resonant circuit 20 and the rectifier-smoothing circuit 24. In the present embodiment, the coil 23 is connected at one end to the receiving coil 21 and the resonant capacitor 22 in the resonant circuit 20, so that it is in series with the receiving coil 21, and at the other end to the rectifier-smoothing circuit 24. The coil 23 outputs energy from the resonant circuit 20 to the rectifier-smoothing circuit 24. The coil 23 reduces harmonic components contained in the received energy in the same way as in the SPL topology. The receiving coil 21 and the coil 23 can have the same or different numbers of turns.

[0051] The rectifier-smoothing circuit 24, which represents an example of a rectifier circuit, features the full-wave rectifier circuit 25 with four bridge-connected diodes and a smoothing capacitor 26. The rectifier-smoothing circuit 24 rectifies and smooths the energy received by the resonant circuit 20 and output by the coil 23 in order to convert the energy into direct current energy. The rectifier-smoothing circuit 24 outputs the resulting direct current energy to the load circuit 27.

[0052] The voltage sensing circuit 28 measures the output voltage across the rectifier-smoothing circuit 24 at predetermined intervals. The output voltage across the rectifier-smoothing circuit 24 corresponds one-to-one to the output voltage of the resonant circuit 20. The measured value of the output voltage across the rectifier-smoothing circuit 24 therefore indirectly represents the measured value of the output voltage of the resonant circuit 20. The voltage sensing circuit 28 can be any known voltage sensing circuit capable of detecting a DC voltage. The voltage sensing circuit 28 outputs a voltage detection signal to the reference circuit 29, which represents the measured value of the output voltage.

[0053] The determination circuit 29 determines, based on the measured output voltage received by the voltage sensing circuit 28, whether the contactless power transfer device 1 outputs a constant voltage and whether the measured output voltage during a constant voltage output operation is within the permissible voltage range. The determination circuit 29 provides the determination result to the communication device 31. The determination circuit 29 therefore includes, for example, a memory circuit that stores the permissible voltage range and an arithmetic circuit that compares the measured output voltage with the permissible voltage range.

[0054] While the measured output voltage is outside the permissible voltage range, the detection circuit 29 switches on the relay 30 to short-circuit the two ends of the resonant circuit 20 via the coil 23, and maintains the short-circuited state across the resonant circuit 20 until it receives detection information from the transmitter 2 indicating that the switching frequency has been detected at which the contactless power transfer device 1 outputs a constant voltage. The impedance of any circuit connected to the resonant circuit 20 decreases to a negligible value, while the control circuit 19 in the transmitter 2 adjusts the switching frequency and the voltage of the AC power applied to the transmitting coil 14 to enable the contactless power transfer device 1 to output a constant voltage.

[0055] In response to the detection information received by the communication device 31 from the transmitter 2, the determining circuit 29 switches off the relay 30 and opens both ends of the resonant circuit 20. This causes the impedance of the circuit connected to the resonant circuit 20 to have a value corresponding to the resistance of the load circuit 27. If the measured output voltage is within the permissible voltage range, or more precisely, if the contactless power transmission device 1 outputs a constant voltage, the determining circuit 29 keeps the relay 30 in the off state, or more precisely, keeps both ends of the resonant circuit 20 in the open state. The determining circuit 29 provides the communication device 31 with the determination result, indicating that the measured output voltage is within the permissible voltage range.

[0056] Relay 30 is an example of a short-circuit circuit. One end of relay 30 is connected between coil 23 and one input terminal of rectifier-smoothing circuit 24, and its other end is connected between resonant circuit 20 and the other input terminal of rectifier-smoothing circuit 24. In the present embodiment, relay 30, which is normally a switched-off relay, is switched on according to a control by the determining circuit 29. When relay 30 is switched on, the resonant circuit 20 is short-circuited via coil 23. The impedance of the circuit connected to the resonant circuit 20 decreases to a negligible value.

[0057] The communication device 31 generates a radio signal at predetermined intervals, based on the determination result from the determination circuit 29. This signal contains determination information indicating whether the contactless energy transfer device 1 outputs a constant voltage and whether the measured output voltage is within the permissible voltage range. The communication device 31 then transmits the radio signal to the communication device 17 in the transmitter 2. The communication device 31 receives the radio signal, which contains detection information, from the communication device 17 in the transmitter 2 and outputs the detection information to the determination circuit 29.The communication device 31 therefore comprises, for example, an antenna that transmits and receives a radio signal conforming to a predetermined wireless communication standard, and a communication circuit that modulates a radio signal before transmission and demodulates a received radio signal. As in the communication device 17, the predetermined wireless communication standard is, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0058] The charge storage circuit 32 charges itself with the energy output via the rectifier-smoothing circuit 24. The charge storage circuit 32 supplies energy to the receiving circuit 29 to keep the relay 30 in the on state. The charge storage circuit 32 therefore includes, for example, a capacitor, one end of which is connected to the output terminal of the positive electrode of the rectifier-smoothing circuit 24 via a diode for forward bias, and the other end of which is grounded. While the receiver 3 receives energy from the transmitter 2, the capacitor in the charge storage circuit 32 charges itself with the energy output via the rectifier-smoothing circuit 24.When the contactless energy transfer device 1 does not output a constant voltage and the relay 30 is switched on to block the energy output via the rectifier smoothing circuit 24, the determining circuit 29 uses the energy supplied by the capacitor in the charge storage circuit 32 to keep the relay 30 in the on state.

[0059] The charge storage circuit 32 can include a circuit other than a capacitor that can store energy. For example, the charge storage circuit 32 can include an accumulator instead of a capacitor. In this case, the energy stored in the charge storage circuit 32 can be used to power the control circuit 29 and the communication device 31.

[0060] The operation of the contactless energy transfer device 1 is described in detail.

[0061] In the present embodiment, the control circuit 19 in the transmitter 2 sets the switching frequency and the voltage of the alternating current energy supplied to the transmitting coil 14 in order to enable the contactless energy transfer device 1 to output a constant voltage when the determination information received by the communication device 17 indicates that the measured value of the output voltage is outside a predetermined permissible range or, more precisely, that the contactless energy transfer device 1 is not outputting a constant voltage.

[0062] The contactless power transfer device 1 according to the present embodiment does not use resonance on the transmitter side. The frequency response of the output voltage from the contactless power transfer device 1 is therefore similar to the frequency response of the output voltage for the increased capacitance of the capacitor connected in series with the transmitting coil and the reduced resonant frequency of the resonant circuit on the transmitter side in a contactless power transfer device that uses the SPL topology, including an inductor connected in series with the coil in the resonant circuit on the receiver side.

[0063] Fig. Figure 2 is an equivalent circuit diagram of the contactless energy transfer device 1. In an equivalent circuit 100, the transmitting coil 14 on the transmitter side is coupled to the receiving coil 21 in the resonant circuit 20 on the receiver side to form an ideal n:1 transformer. In this circuit, Lr is the leakage inductance of the transmitting coil 14 on the transmitter side, and Lm is the magnetizing inductance of the transmitting coil 14. The inductance Lp of the transmitting coil 14 on the transmitter side is equal to (Lm + Lr), and Lr = (1-k)Lp and Lm = kLp, where k is the coupling coefficient between the transmitting coil 14 and the receiving coil 21. Ri is the coil resistance on the transmitter side, and Ris is the coil resistance on the receiver side. Cp is the capacitance of the resonant capacitor 22, which is connected in parallel to the receiving coil 21 in the resonant circuit 20 on the receiver side. Lop is the inductance of the coil 23, which is connected in series with the receiving coil 21.Rac is the equivalent AC resistance of the load circuit 27 and Rac = (8 / π. 2 ) × Ro.

[0064] Fig. Figure 3 is a graph showing example simulation results for the frequency response of the output voltage of the contactless energy transfer device 1 according to the present embodiment. Fig. Figure 3 shows the horizontal axis as the frequency and the vertical axis as the output voltage. In this simulation, Lp = 174 µH, Cp = 20 nF, Lop = 3Lp, Ri = Ris = 0.3 Ω, n = 1, Vin = 200 V and Ro = 200 Ω (Rac ≈ 162.1 Ω). Graph 301 shows the frequency response of the output voltage when the coupling coefficient k = 0.15 and the AC equivalent resistance of the load circuit is 27 Rac. Graph 302 shows the frequency response of the output voltage when the coupling coefficient k = 0.15 and the AC equivalent resistance of the load circuit is 27 (10 * Rac). Graph 303 shows the frequency response of the output voltage when the coupling factor k = 0.3 and the AC equivalent resistance of the load circuit is 27 Rac. Graph 304 shows the frequency response of the output voltage when the coupling factor k = 0.3 and the AC equivalent resistance of the load circuit is 27 (10 * Rac).Graph 305 shows the frequency response of the output voltage when the coupling factor k = 0.6 and the AC equivalent resistance of the load circuit is 27 Rac. Graph 306 shows the frequency response of the output voltage when the coupling factor k = 0.6 and the AC equivalent resistance of the load circuit is 27 (10 * Rac).

[0065] As in Fig. As shown in Figure 3, the graph for each coupling degree k (at three points 311 to 313 in the figure) includes the combination of frequency and output voltage that results in an essentially constant output voltage (or causes a constant voltage output), as opposed to a varying AC equivalent resistance of the load circuit 27 at a constant coupling degree k. This shows that the contactless power transfer device 1 can output a constant voltage for a varying resistance of the load circuit 27 when the transmitting coil 14 receives AC power at a switching frequency at which the transmitting coil 14 does not oscillate.Although the output voltage, which is constant in contrast to the varying resistance of the load circuit 27, varies depending on the degree of coupling, as indicated by points 311 to 313, adjusting the voltage applied to the transmitting coil 14 can eliminate this difference in the output voltage and allow the output voltage to be essentially constant at any degree of coupling.

[0066] Fig. Figure 4 is a graph showing example simulation results for the frequency response of the output voltage for a varying voltage applied to the transmitting coil 14, according to the coupling coefficient in the Fig. The simulation shown in section 3 illustrates this. Fig. In Figure 4, the horizontal axis represents the frequency and the vertical axis represents the output voltage. Graph 401 shows the frequency response of the output voltage when the coupling coefficient k = 0.15, the equivalent AC resistance of the load circuit is 27 Rac, and the voltage Vin applied to the transmitting coil is . Graph 402 shows the frequency response of the output voltage when the coupling coefficient k = 0.15, the equivalent AC resistance of the load circuit is 27 (10 * Rac), and the voltage Vin applied to the transmitting coil is . Graph 403 shows the frequency response of the output voltage when the coupling coefficient k = 0.3, the equivalent AC resistance of the load circuit is 27 Rac, and the voltage Vin applied to the transmitting coil is 0.47 * Vin. A graph 404 represents the frequency response of the output voltage when the coupling factor k = 0.3, the AC equivalent resistance of the load circuit is 27 (10* Rac) and a voltage applied to the transmitting coil is (0.47* Vin).Graph 405 shows the frequency response of the output voltage when the coupling coefficient k = 0.6, the equivalent AC resistance of the load circuit is 27 * Rac, and the voltage applied to the transmitting coil is (0.19 * Vin). Graph 406 shows the frequency response of the output voltage when the coupling coefficient k = 0.6, the equivalent AC resistance of the load circuit is (10 * Rac), and the voltage applied to the transmitting coil is (0.19 * Vin).

[0067] The combinations of frequency and output voltage at three points 411 to 413 correspond to the combinations at the three points 311 to 313, which are described in Fig. Figure 3 shows how the output voltage is essentially constant (or causes a constant voltage output), in contrast to a varying AC equivalent resistance of the load circuit 27 at a constant coupling factor k. The output voltages at points 411 to 413 are essentially equal to each other.

[0068] This shows that by appropriately adjusting the switching frequency and the voltage of the AC energy applied to the transmitting coil 14, the output voltage remains essentially constant regardless of the varying resistance of the load circuit 27 or the varying coupling degree k.

[0069] The inventors have also determined that the contactless power transfer device 1 has a minimum input impedance at the frequency at which the contactless power transfer device 1 outputs a constant voltage when the load circuit 27 in the receiver 3 has a preset resistance. The inventors have also determined that the frequency at which the contactless power transfer device 1 outputs a constant voltage has the same phase as the frequency at which the output voltage reaches its maximum when the load circuit 27 has a small, negligible resistance, and also the frequency at which the input impedance of the contactless power transfer device 1 reaches its minimum.

[0070] Fig. Figure 5 is a graph showing example simulation results for the frequency response of the output voltage for a varying impedance of the circuit connected to the resonant circuit 20, with a constant coupling degree. Fig. In Figure 5, the horizontal axis represents the frequency and the vertical axis represents the output voltage. Graph 501 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 * Rac. Graph 502 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 * (10 * Rac). Graph 503 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 * (0.1 * Rac). Graph 504 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 * (0.01 * Rac). The same parameter values ​​were used in the simulation as in the simulation in Fig. The 3 circuit elements shown are used.

[0071] As in Fig. As shown in Figure 5, when the AC equivalent resistance of the load circuit 27 is reduced to extremely small values, as indicated by graphs 503 and 504, the output voltage reaches its maximum at a frequency f0 at which essentially the same output values ​​for the AC equivalent resistances of the load circuit 27, Rac and (10 * Rac), are observed. This is based on the following set of formulas, which applies when the load circuit 27 has an AC equivalent resistance of essentially 0. Formula 1: 11ωLr2+ωCp+ωLop=0ω=2πf,Lr2=L2(1−k2) where Lop is the inductance of coil 23 connected in series with receiving coil 21, Cp is the capacitance of resonant capacitor 22, L2 is the self-inductance of receiving coil 21, k is the coupling coefficient, Lr2 is the inductance of receiving coil 21 when transmitting coil 14 is short-circuited, and f is the frequency of the AC energy applied to transmitting coil 14. Therefore, the output voltage reaches its maximum at frequency f0, which is represented by the following formula, obtained by solving formula (1) for frequency f. Formula 2: f0=Lr2+LopLr2LopCp2π

[0072] The output voltage is lower at frequency f0 when the AC equivalent resistance of the load circuit 27 is (0.1 * Rac) or (0.01 * Rac) than when it is Rac. This is because the load circuit 27, with its much smaller AC equivalent resistance, allows more current to flow, thus increasing the probability of a voltage drop.

[0073] Fig. Section 6 comprises graphs that show an example relationship between the frequency response of the output voltage and the frequency response of the input impedance in the contactless power transfer device. The upper graph in Fig. In figure 6, the horizontal axis represents the frequency and the vertical axis represents the output voltage. In the lower graph in Fig. Figure 6 represents the frequency on the horizontal axis and the input impedance on the vertical axis. The same parameter values ​​were used in the simulation as in the simulation in Fig. The circuit elements shown in the diagram are used. In the upper diagram, graph 601 (which corresponds to graph 501 in the diagram) represents the circuit element shown. Fig. 5 is identical) represents the frequency response of the output voltage from the contactless power supply device 1 when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 Rac. A graph 602 (which corresponds to graph 502 in Fig. 5 is identical) represents the frequency response of the output voltage from the contactless power transfer device 1 when the coupling factor k = 0.15 and the AC equivalent resistance 27 of the load circuit is (10 * Rac). A graph 603 (which corresponds to graph 503 in Fig. 5 is identical) represents the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance 27 of the load circuit is (0.1 * Rac). A graph 604 (which corresponds to graph 504 in Fig. 5 is identical) represents the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance 27 of the load circuit is (0.01 * Rac).

[0074] In the lower diagram, graph 611 represents the frequency response of the input impedance of the contactless power transfer device 1 when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is Rac. Graph 612 represents the frequency response of the input impedance of the contactless power transfer device 1 when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (10 * Rac). Graph 613 represents the frequency response of the input impedance of the contactless power transfer device 1 when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (0.1 * Rac). Graph 614 represents the frequency response of the input impedance of the contactless power transfer device 1 when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (0.01 * Rac).

[0075] As in Fig. As shown in Figure 6, with a smaller equivalent AC resistance of the load circuit 27, the frequency at which the input impedance reaches its minimum is closer to the frequency f0 at which the contactless power transfer device 1 outputs a constant voltage. Specifically, if the load circuit 27 has an equivalent AC resistance of (0.01 * Rac), the input impedance reaches its minimum at the frequency f0. In other words, the current through the transmitting coil 14 reaches its maximum at the frequency f0.

[0076] Fig. Figure 7 comprises graphs showing an example relationship between the frequency response of the output voltage of the contactless energy transfer device and the frequency response of a phase delay of the current relative to the voltage of the AC energy applied to the transmitting coil 14. In the upper graph in Fig. In figure 7, the horizontal axis represents the frequency and the vertical axis represents the output voltage. In the lower graph in Fig. Figure 7 shows the horizontal axis representing the frequency and the vertical axis representing the phase delay. In the graph, a positive phase delay indicates that the phase of the current is delayed relative to the phase of the voltage. The same parameter values ​​were used in the simulation as in the simulation in Fig. The circuit elements shown in the diagram are used. In the upper diagram, graph 701 (which corresponds to graph 501 in the diagram) represents the circuit element shown. Fig. 5 is identical) represents the frequency response of the output voltage from the contactless power supply device 1 when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 Rac. A graph 702 (which corresponds to graph 502 in Fig. 5 is identical) represents the frequency response of the output voltage from the contactless power transfer device 1 when the coupling factor k = 0.15 and the AC equivalent resistance 27 of the load circuit is (10 * Rac). A graph 703 (which corresponds to graph 503 in Fig. 5 is identical) represents the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance 27 of the load circuit is (0.1 * Rac). A graph 704 (which corresponds to graph 504 in Fig. 5 is identical) represents the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance 27 of the load circuit is (0.01 * Rac).

[0077] Graph 711 in the lower diagram represents the frequency response of a current phase delay relative to the voltage for the AC energy applied to the transmitting coil 14, obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is Rac. Graph 712 represents the frequency response of a current phase delay relative to the voltage for the AC energy applied to the transmitting coil 14, obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (10 * Rac). Graph 713 represents the frequency response of a current phase delay relative to the voltage for the AC energy applied to the transmitting coil 14, obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (0.1 * Rac).A graph 714 represents the frequency response of a phase delay of the current relative to the voltage for the AC energy applied to the transmitting coil 14, which is obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (0.01 * Rac).

[0078] As in Fig. As shown in Figure 7, for a smaller equivalent AC resistance of the load circuit 27, the frequency at which the phase delay of the current relative to the voltage of the AC energy applied to the transmitting coil 14 is 0 is closer to the frequency f0 at which the contactless power transmission device 1 outputs a constant voltage. Specifically, when the equivalent AC resistance of the load circuit 27 is (0.01 * Rac), the phase delay of the current relative to the voltage for the AC energy applied to the transmitting coil 14 at frequency f0 is 0, or more precisely, the power factor is 1. More precisely, at frequencies higher than frequency f0, the phase delay of the current relative to the voltage for the AC energy applied to the transmitting coil 14 is positive when the equivalent AC resistance of the load circuit 27 is (0.01 * Rac). This represents inductive driving.The contactless energy transfer device 1 therefore enables the power supply circuit 10 and the transmitting coil 14 to perform a soft-switching operation in a frequency band with a phase delay of 0 to 90°. At frequencies lower than the frequency f0, the phase delay of the current relative to the voltage for the AC energy applied to the transmitting coil 14 is negative. This represents capacitive drive. The contactless energy transfer device 1 therefore causes the power supply circuit 10 and the transmitting coil 14 to perform a hard-switching operation, especially in a frequency band with a phase delay of 0 to -90°, which reduces the energy transfer efficiency.

[0079] The control circuit 19 controls the switching frequency and the voltage of the alternating current energy applied to the transmitting coil 14 in the manner described below in order to enable a constant voltage output process.

[0080] If the destination information contained in the radio signal received by receiver 3 via communication device 17 indicates that the contactless power transmission device 1 is not outputting a constant voltage, the control circuit 19, via the gate driver 18, holds switching element 13-1 in the off state and alternately switches switching elements 13-3 and 13-2 on and off to supply energy to the transmitting coil 14 via the DC-DC converter 12. The control circuit 19 controls the variable-voltage power source 11 so that it supplies a voltage of a predetermined value to the transmitting coil 14 via the DC-DC converter 12. The control circuit 19 reduces the energy supplied by transmitter 2 to receiver 3 by a degree that does not cause receiver 3 to fail.

[0081] The control circuit 19 then monitors the measured current through the transmitting coil 14 with the current sensing circuit 16 while the switching frequency is changed and detects the switching frequency at which the measured current reaches its maximum. As in the present embodiment, the resonant circuit 20 in the receiver 3 is short-circuited via the coil 23, while the contactless energy transfer device 1 does not output a constant voltage, thereby reducing the impedance of a circuit connected to the resonant circuit 20 to a negligible value. In this case, as in Fig. Figure 6 shows that, near the switching frequency at which the measured current through the transmitting coil 14 reaches its maximum, the measured current changes rapidly in response to a change in the switching frequency. The control circuit 19 can therefore detect the switching frequency at which the measured current reaches a predetermined threshold or a value greater than the threshold than the switching frequency at which the measured current reaches its maximum. The predetermined threshold can, for example, be a value corresponding to the current through the transmitting coil 14 at a switching frequency that is shifted by a predetermined tolerance from the switching frequency at which the current through the transmitting coil 14 reaches its maximum.

[0082] The switching frequency at which the measured current through the transmitting coil 14 reaches its maximum is the frequency at which the input impedance of the contactless energy transfer device 1 reaches its minimum, such as the one in Fig. The frequency f0 shown in Figure 6, or more precisely, the frequency at which the contactless power transfer device 1 outputs a constant voltage, is used. When the switching frequency is detected at which the measured current through the transmitting coil 14 reaches its maximum, the control circuit 19 controls the on / off state of the switching elements 13-1 and 13-2 via the gate driver 18 to supply energy from the variable-voltage power source 11 to the transmitting coil 14 at the switching frequency. The control circuit 19 switches off the switching element 13-3. In the manner described above, the control circuit 19 enables the contactless power transfer device 1 to output a constant voltage.The control circuit 19 then provides the communication device 17 with detection information indicating that the switching frequency at which the contactless power transmission device 1 outputs a constant voltage has been detected, and causes the communication device 17 to transmit a radio signal to the communication device 31 in the receiver 3, which includes the detection information.

[0083] The control circuit 19 then controls the variable-voltage energy source 11 in the power supply circuit 10, supplying a voltage to the transmitting coil 14 corresponding to the switching frequency and ensuring that the measured output voltage from the resonant circuit 20 in the receiver 3 lies within the predetermined permissible range. The control circuit 19 determines the voltage of the energy supplied by the variable-voltage energy source 11 by referring, for example, to a reference table that specifies the correspondence between each switching frequency and the voltage of the energy supplied by the variable-voltage energy source 11. The reference table is, for example, pre-stored in a memory located within the control circuit 19.

[0084] After the control circuit 19 receives information from the receiver 3 indicating that the measured output voltage is outside the predetermined permissible range, it cannot determine the switching frequency for a predetermined period from the transmission of the detection information to the receiver 3 until the voltage of the AC energy applied to the transmitting coil 14 changes to the voltage corresponding to the switching frequency. This prevents the control circuit 19 from repeatedly searching for the switching frequency after it has detected the switching frequency at which the contactless energy transfer device 1 outputs a constant voltage.

[0085] The control circuit 19 could not refer to the reference table, but instead gradually change the voltage of the energy supplied by the variable voltage energy source 11 until the determination information contained in the radio signal received by the receiver 3 through the communication device 17 indicates that the measured output voltage is within the permissible voltage range.

[0086] In one modification, while changing the switching frequency, the control circuit 19 can monitor the measured current through the transmitting coil 14 using the current sensing circuit 16 and detect the switching frequency at which the phase delay of the current relative to the voltage of the AC energy applied to the transmitting coil 14 is 0. In this case, the control circuit 19 can identify the phase of the voltage of the AC energy applied to the transmitting coil 14 based on, for example, the time of switching on and off of the switching elements 13-3 and 13-2 and the time constant corresponding to the inductance of the transmitting coil 14 and the capacitance of the capacitor 15. The control circuit 19 can determine the phase of the current through the transmitting coil 14 based on the time-varying measured current through the transmitting coil 14 obtained from the current sensing circuit 16.

[0087] As in Fig. As shown in Figure 7, the switching frequency at which the phase delay of the current relative to the voltage of the AC energy applied to the transmitting coil 14 is zero is the frequency at which the contactless energy transfer device 1 outputs a constant voltage. When the switching frequency at which the phase delay of the current relative to the voltage of the AC energy applied to the transmitting coil 14 is zero is detected, the control circuit 19, as in the preceding embodiment, controls the on / off state of the switching elements 13-1 and 13-2 and the switching element 13-3 to the off state by means of the gate driver 18 in order to supply energy from the variable-voltage energy source 11 to the transmitting coil 14 at the detected switching frequency.In this modification as well, the control circuit 19 can detect the switching frequency at which the absolute value of the difference between the phases of the voltage and the current of the AC energy applied to the transmitting coil 14 reaches the threshold or a value less than the threshold, as the switching frequency at which the phase delay of the current of the AC energy applied to the transmitting coil 14 is 0 relative to the voltage.

[0088] As previously described, the contactless power transfer device measures the current through the transmitting coil in the transmitter while the resonant circuit in the receiver is short-circuited via the coil connected in series with the receiving coil. It detects the switching frequency of the AC power applied to the transmitting coil at which the current reaches its maximum or the voltage across the transmitting coil is in phase with the current through the transmitting coil. The contactless power transfer device can therefore accurately detect the switching frequency at which a constant voltage is output. The contactless power transfer device then adjusts the voltage of the AC power applied to the transmitting coil to output a constant voltage at the detected switching frequency after the resonant circuit is open.The contactless energy transfer device can therefore output a constant voltage even with a non-constant coupling degree between the transmitting coil and the receiving coil, or with a non-constant resistance of the load circuit.

[0089] In one modification, the receiver 3, separate from the resonant circuit which oscillates with the alternating current energy applied to the transmitting coil 14, can have an output coil for outputting the transferred energy.

[0090] Fig. Figure 8 is a schematic representation of a receiver 4 according to a modification. As in Fig. As shown in Figure 8, the modified receiver 4 comprises a resonant circuit 20, which includes a receiving coil 21 and a resonant capacitor 22, a coil 23, a rectifier-smoothing circuit 24, which includes a full-wave rectifier circuit 25 and a smoothing capacitor 26, a load circuit 27, a voltage sensing circuit 28, a selection circuit 29, a relay 30, a communication device 31, a charge storage circuit 32, and an output coil 33. The modified receiver 4 differs from the receiver 3 in the preceding embodiment in that it includes the output coil 33 and outputs the transmitted energy from the output coil 33 instead of from the resonant circuit 20. The differences and related components will now be described.

[0091] The output coil 33 is arranged to be electromagnetically coupled to the receiving coil 21 in the resonant circuit 20. For example, the output coil 33 and the receiving coil 21 are wound around the same core wire. The output coil 33, together with the receiving coil 21, therefore forms a transformer, which allows energy received by the receiving coil 21 to be output by the output coil 33. One end of the output coil 33 is connected to an input terminal of the rectifier-smoothing circuit 24 via the coil 23. The other end of the output coil 33 is likewise connected to the other input terminal of the rectifier-smoothing circuit 24. The energy output by the output coil 33 via the resonant circuit 20 is supplied to the load circuit 27 via the coil 23 and the rectifier-smoothing circuit 24. In this modification, the resonant circuit 20 is not directly connected to the coil 23 and the rectifier-smoothing circuit 24.

[0092] In this modification, the receiving coil 21 and the output coil 33 can have the same or different numbers of turns. For example, the output energy can have a lower voltage with high energy transfer efficiency if the receiving coil 21 has more turns than the output coil 33. In this modification, if the receiving coil 21 has more turns than the output coil 33, a voltage-reducing circuit, such as a DC-DC converter, is used for the load circuit 27 with a low upper limit for the receiveable voltage.

[0093] In this modification, one end of relay 30 can be connected between coil 23 and one input terminal of rectifier-smoothing circuit 24, and its other end can be connected between resonant circuit 20 and the other input terminal of rectifier-smoothing circuit 24. If the output voltage measured by voltage sensing circuit 28 is outside the predetermined permissible range, the determining circuit 29 can switch on relay 30 to short-circuit the two ends of output coil 33 via coil 23. The resonant circuit 20 is therefore short-circuited via coil 23. The impedance of any circuit connected to the resonant circuit 20 decreases to a negligible value.The contactless power transfer device according to this modification can correctly detect the switching frequency at which a constant voltage is output in the same way as the contactless power transfer device in the embodiment.

[0094] In another modification, relay 30 can be a normally switched-on relay.

[0095] Fig. Figure 9 is a schematic representation of a receiver 5 according to another modification. As in Fig. As shown in Figure 9, receiver 5, according to this modification, comprises a resonant circuit 20, which includes a receiving coil 21 and a resonant capacitor 22, a coil 23, a rectifier-smoothing circuit 24, which includes a full-wave rectifier circuit 25 and a smoothing capacitor 26, a load circuit 27, a voltage sensing circuit 28, a determining circuit 29, a relay 30, a communication device 31, a charge storage circuit 32, and an output coil 33. Receiver 5 in this modification differs from receiver 4 in the preceding modification in that it has a different type of relay 30 and the position of the energy source that supplies energy to the charge storage circuit 32 is different. The differences and related components will now be described.

[0096] In this modification, relay 30, which is normally switched on, is controlled by the control circuit 29 so that it is switched off when the contactless power transfer device outputs a constant voltage, or more precisely, when the output voltage value measured by the voltage sensing circuit 28 is within the predetermined permissible range. If the output voltage measured by the voltage sensing circuit 28 is outside the predetermined permissible range, the control circuit 29 switches relay 30 on. If the control circuit 29 subsequently receives a notification from transmitter 2 via the communication device 31, indicating that the transmitter has detected the switching frequency at which the contactless power transfer device outputs a constant voltage, it switches relay 30 off using energy stored in the charge storage circuit 32.

[0097] The charge storage circuit 32 charges with energy supplied from both ends of the output coil 33 and rectified by a diode, while the receiver 5 receives energy from the transmitter 2. In this example, when the relay 30 is switched on and short-circuits the two ends of the output coil 33, the charge storage circuit 32, which is connected immediately after the output coil 33, can continue to charge with the transferred energy while the switching frequency is being searched. The energy stored in the charge storage circuit 32 is used to switch off the relay 30, as described above.

[0098] The contactless energy transfer device according to this modification can also short-circuit the resonant circuit 20 via the coil 23 while searching for the switching frequency of the energy applied to the transmitting coil 14 at which a constant voltage is output. The contactless energy transfer device according to this modification can therefore correctly detect the switching frequency at which a constant voltage is output, similar to the contactless energy transfer device in the preceding embodiment.

[0099] In yet another modification, the receiving coil and the resonant capacitor in the receiver's resonant circuit can be connected in series. In this case as well, the contactless power transfer device can perform a constant voltage output operation. As in the preceding embodiment and modifications, in this modification, the contactless power transfer device can detect the switching frequency at which a constant voltage is output by measuring the current through the transmitting coil while the resonant circuit is short-circuited.

[0100] Fig. Figure 10 is a schematic representation of a receiver 6 according to this modification. As in Fig. As shown in Figure 10, the receiver 6 according to this modification comprises a resonant circuit 20a, which includes a receiving coil 21 and a resonant capacitor 22, a rectifier-smoothing circuit 24, which includes a full-wave rectifier circuit 25 and a smoothing capacitor 26, a load circuit 27, a voltage sensing circuit 28, a determining circuit 29, a relay 30, a communication device 31, a charge storage circuit 32, and an output coil 33. The receiver 6 according to this modification differs from the one shown in Figure 10. Fig. The receiver shown in Figure 1 differs in that the resonant circuit 20a uses a different design and the coil 23 is omitted. The differences and related components are now described.

[0101] In the resonant circuit 20a, the receiving coil 21 and the resonant capacitor 22 are connected in series. The energy received via the receiving coil 21 is output to the rectifier-smoothing circuit 24 via the resonant capacitor 22. In this case, the contactless power transfer device, which includes the transmitter 2 and the receiver 6, has the same design as primary and secondary capacitors connected in series (hereafter SS topology) to perform a constant voltage output operation. In contrast to the contactless power transfer device based on the SPL topology, the resonant circuit 20a in this example causes a series resonance, thereby eliminating the coil 23.In contrast to a system based on the SS topology, the contactless energy transfer device, which has the transmitter 2 and the receiver 6, cannot use the resonance of the transmitting coil 14 on the transmitter side.

[0102] The energy transfer efficiency in contactless energy transfer is expressed as the product of the coupling degree k between a transmitting coil and a receiving coil and the quality factor (Q-factor), which is an index of the resonant strength. To improve the energy transfer efficiency, the Q-factor must be increased. In this modification, receiver 6 operates, as described above, as an RLC series resonant circuit. In this case, the Q-factor is written using the following formula. Formula 3: Q=1RLC where C is the capacitance of the resonant capacitor 22, L is the inductance of the receiving coil 21, and R is the impedance of a circuit connected to the resonant circuit 20a. From equation (3), it follows that the Q-factor is lower the greater the impedance of the load circuit 27. For the load circuit 27, which consumes energy at a constant rate, the voltage output by the resonant circuit 20a and the impedance of the load circuit 27 must be reduced to increase the Q-factor. Conversely, compared to the resonant circuit 20 in the preceding embodiment and the modifications in which the receiving coil 21 and the resonant capacitor 22 resonate in parallel, the receiver 6 can have a larger inductance of the receiving coil 21 and a smaller capacitance of the resonant capacitor 22 to increase the Q-factor, as is evident from equation (3).

[0103] Fig. Figure 11 is a graph showing example simulation results for the frequency response of the output voltage of the contactless energy transfer device comprising transmitter 2 and receiver 6. Fig. In Figure 11, the horizontal axis represents the frequency and the vertical axis represents the output voltage. In this simulation, Lp = 174 µH, Cp = 20 nF, Ri = Ris = 0.1 Ω, n = 1, Vin = 300 V, and Ro = 200 Ω (Rac ≈ 162.1 Ω). Graph 1101 shows the frequency response of the output voltage when the coupling coefficient k = 0.15 and the AC equivalent resistance of the load circuit is 27 Rac. Graph 1102 shows the frequency response of the output voltage when the coupling coefficient k = 0.15 and the AC equivalent resistance of the load circuit is 27 (10 * Rac). A graph 1103 represents the frequency response of the output voltage when the coupling factor k = 0.3, the AC equivalent resistance of the load circuit 27 Rac and the voltage applied to the transmitting coil 14 is (0.5 * Vin).Graph 1104 shows the frequency response of the output voltage when the coupling coefficient k = 0.3, the equivalent AC resistance of the load circuit 27 (10 * Rac), and the voltage applied to the transmitting coil 14 (0.5 * Vin). Graph 1105 shows the frequency response of the output voltage when the coupling coefficient k = 0.6, the equivalent AC resistance of the load circuit 27 (Rac), and the voltage applied to the transmitting coil 14 (0.25 * Vin). Graph 1106 shows the frequency response of the output voltage when the coupling coefficient k = 0.6, the equivalent AC resistance of the load circuit 27 (10 * Rac), and the voltage applied to the transmitting coil 14 (0.25 * Vin).

[0104] As in Fig. As shown in Figure 11, the graph for each coupling degree k (at three points 1111 to 1113 in the figure) includes the combination of frequency and output voltage that results in an essentially constant output voltage (or causes a constant voltage output), as opposed to a varying AC equivalent resistance of the load circuit 27 at a constant coupling degree k. Therefore, according to this modification, the contactless power transfer device can also provide an essentially constant output voltage at any coupling degree by adjusting the switching frequency and the voltage of the AC power applied to the transmitting coil 14.

[0105] Fig. Figure 12 is a graph showing example simulation results for the frequency response of the output voltage of the contactless energy transfer device, which has transmitter 2 and receiver 6, for a varying impedance of a circuit connected to the resonant circuit 20a, at a constant coupling degree. Fig. In Figure 12, the horizontal axis represents the frequency and the vertical axis represents the output voltage. Graph 1201 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 Rac. Graph 1202 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 (10 * Rac). Graph 1203 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 (0.1 * Rac). Graph 1204 shows the frequency response of the output voltage when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit is 27 (0.01 * Rac). The same parameter values ​​were used in the simulation as in the simulation in Fig. The circuit elements shown in the 11 diagrams are used.

[0106] As in Fig. As shown in Figure 12, when the equivalent AC resistance of the load circuit 27 is reduced to extremely small values, as indicated by graphs 1203 and 1204, the output voltage reaches its maximum at the frequency f0, at which essentially the same output values ​​for the equivalent AC resistances of the load circuit 27, Rac and (10 * Rac), are observed. Therefore, with a smaller equivalent AC resistance of the load circuit 27, the frequency at which the input impedance reaches its minimum, or more precisely, the current through the transmitting coil 14 reaches its maximum, is closer to the frequency f0.

[0107] Fig. Figure 13 is a graph showing an example relationship between the frequency response of the output voltage of the contactless energy transfer device, which has transmitter 2 and receiver 6, and the frequency response of a phase delay of the current relative to the voltage of the alternating current energy applied to the transmitting coil 14. Fig. Figure 13 shows that the horizontal axis represents the frequency and the vertical axis represents the phase delay. In the graph, a positive phase delay indicates that the phase of the current is delayed relative to the phase of the voltage. The same parameter values ​​were used in this simulation as in the simulation in Fig. The circuit elements shown in the 11 diagrams are used.

[0108] Graph 1311 represents the frequency response of a current phase delay relative to the voltage for the AC energy applied to the transmitting coil 14, obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is Rac. Graph 1312 represents the frequency response of a current phase delay relative to the voltage for the AC energy applied to the transmitting coil 14, obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (10 * Rac). Graph 1313 represents the frequency response of a current phase delay relative to the voltage for the AC energy applied to the transmitting coil 14, obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (0.1 * Rac).A graph 1314 represents the frequency response of a phase delay of the current relative to the voltage for the AC energy applied to the transmitting coil 14, which is obtained when the coupling factor k = 0.15 and the AC equivalent resistance of the load circuit 27 is (0.01 * Rac).

[0109] As in Fig. As shown in Figure 13, for a smaller AC equivalent resistance of the load circuit 27, the frequency at which the phase delay of the current relative to the voltage of the AC energy applied to the transmitting coil 14 is 0 is closer to the frequency f0 at which the contactless power transfer device outputs a constant voltage. In particular, when the AC equivalent resistance of the load circuit 27 is (0.01 * Rac), the phase delay of the current relative to the voltage for the AC energy applied to the transmitting coil 14 at frequency f0 is essentially 0, or, more precisely, the power factor is essentially 1.

[0110] Therefore, in the contactless energy transmission device, which has the transmitter 2 and the receiver 6, the control circuit 19 in the transmitter 2 simply controls the switching frequency and the voltage of the alternating current energy applied to the transmitting coil 14 in the same way as in the contactless energy transmission device 1, which in Fig. Figure 1 shows that the determining circuit 29 in the receiver 6 also transmits in the same way as in the contactless energy transmission device 1, which is shown in Figure 1. Fig. As shown in Figure 1, the communication device 31 sends destination information to transmitter 2 and receives detection information from transmitter 2 to control relay 30.

[0111] In yet another modification, two MOSFETs connected in series can be used as a short-circuit circuit instead of a relay. In this case, the source or drain terminals of the two MOSFETs can be connected together. To short-circuit the resonant circuit 20 (or resonant circuit 20a), the control circuit 29 can apply a voltage to the gate terminals of the two MOSFETs to turn them on. To open the resonant circuit 20 (or resonant circuit 20a), the control circuit 29 can apply a voltage to the gate terminals of the two MOSFETs to turn them on.

[0112] As described above, experts in the field can make various modifications according to embodiments that are implemented within the scope of the present invention.

Claims

[1] Contactless energy transfer device (1), comprising: a transmitter (2); and a receiver (3) which is configured to receive electrical energy from the transmitter (2) in a contactless manner, where the transmitter (2) has: a transmitting coil (14) which is set up to supply electrical energy to the receiver (3), a power supply circuit (10) which is set up to supply alternating current energy to the transmitting coil (14) with an adjustable switching frequency and an adjustable voltage, a current sensing circuit (16) which is set up to measure a current through the transmitting coil (14) and to determine a measured value of the current, a control circuit (19) which is set up to control the switching frequency and the voltage of the alternating current energy which is supplied to the transmitting coil (14) by the power supply circuit (10), and a first communication device (17) that is set up to communicate with the receiver (3), where the receiver (3) has: a resonant circuit (20) comprising a receiving coil (21) configured to receive electrical energy from the transmitter (2) and a resonant capacitor (22) configured to resonate with the receiving coil (21) in response to electrical energy from the transmitter (2), a rectifier circuit (24) which is set up to rectify electrical energy output by the resonant circuit (20), a short-circuit circuit (30) which is configured to switch between short-circuiting and opening the resonant circuit (20), a voltage detection circuit (28) which is set up to measure an output voltage of an electrical energy output by the resonant circuit (20) and to determine a measured value of the output voltage, a second communication device (31) which is set up to communicate with the transmitter (2), and a determination circuit (29) configured to determine whether the measured output voltage is within a predetermined permissible voltage range, and to cause the short-circuiting circuit (30) to short-circuit the resonant circuit (20), and to cause the second communication device (31) to transmit determination information indicating that the contactless power transfer device (1) is not performing a constant voltage output operation in which the output voltage from the rectifier circuit (24) is a constant voltage, even if a resistance of a load circuit (27) connected to the rectifier circuit (24) changes when the measured output voltage is outside the predetermined permissible voltage range, and wherein the control circuit (19) in the transmitter (2) detects a switching frequency of the alternating current energy in response to the determination information received by the receiver (3) through the first communication device (17), which indicates that the contactless energy transfer device (1) is not performing a constant voltage output operation, at which the contactless energy transfer device (1) performs the constant voltage output operation according to the measured current. [2] Contactless energy transfer device (1) according to claim 1, wherein the receiver (3) further comprises a coil (23) which is connected in series with the receiving coil (21) between the resonant circuit (20) and the rectifier circuit (24), the receiving coil (21) and the resonant capacitor (22) are connected in parallel in the resonant circuit (20), the short-circuit circuit (30) has one end that is connected between the coil (23) and the rectifier circuit (24), and the determining circuit (29) causes the short-circuit circuit (30) to short-circuit the resonant circuit (20) via the coil (23) when the measured value of the output voltage is outside the predetermined permissible voltage range. [3] Contactless energy transfer device (1) according to claim 1, wherein the receiving coil (21) and the resonant capacitor (22) are connected in series in the resonant circuit (20). [4] Contactless energy transfer device (1) according to any one of claims 1 to 3, wherein the control circuit (19) in the transmitter (2) determines that the contactless energy transfer device (1) performs the output process with constant voltage at a switching frequency of the alternating current energy at which the measured value of the current is greater than or equal to a predetermined threshold. [5] Contactless energy transfer device (1) according to any one of claims 1 to 3, wherein the control circuit (19) in the transmitter (2) determines that the contactless energy transfer device (1) performs the output process with constant voltage at an alternating current switching frequency at which an absolute value of a difference between a phase of the measured current and a phase of the voltage of the alternating current supplied to the transmitting coil (14) is less than or equal to a predetermined threshold. [6] Contactless energy transfer device (1) according to any one of claims 1 to 5, wherein the control circuit (19) in the transmitter (2), after detecting the switching frequency of the alternating current energy, at which the contactless energy transmission device (1) performs the output process with constant voltage, causes the first communication device (17) to transmit detection information indicating the detection of the switching frequency, and the determining circuit (29) in the receiver (3) causes the short-circuit circuit (30) to open the resonant circuit (20) after it has received the detection information through the second communication device (31). [7] Contactless energy transfer device (1) according to claim 6, wherein the control circuit (19) in the transmitter (2), after causing the first communication device (17) to transmit the detection information, controls the power supply circuit (10) to regulate the voltage of the alternating current energy supplied to the transmitting coil (14) to a voltage at which the contactless energy transfer device (1) performs the output operation at a constant voltage.

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