Contactless power supply device

Abstract

To provide a non-contact power supply device that can improve power transmission efficiency while enabling a constant voltage output operation.SOLUTION: A power transmitting device 2 included in a non-contact power supply device has: a power supply circuit 10 that supplies AC power having a predetermined drive frequency to a transmitting coil 14 supplying power to a power receiving device 3; a first coil 17 and a first capacitor 15 that are connected between the power supply circuit 10 and the transmitting coil 14; a second capacitor 16 that is connected with the first capacitor 15 at one end and connected with the transmitting coil 14 at the other end; and a control circuit 19. The power receiving device 3 has a resonant circuit 20 having a receiving coil 21 that receives power, and a resonant capacitor 22 that resonates with the receiving coil 21. The control circuit 19 of the power transmitting device 2 controls the power supply circuit 10 so that the predetermined drive frequency is included within a predetermined frequency range including the resonant frequency of the resonant circuit 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a contactless power supply device. [Background technology]

[0002] Conventionally, research has been conducted into so-called non-contact power supply (also called wireless power supply) technology, which transmits power through space without going through metal contacts or the like.

[0003] One known contactless power transfer technology is a technology that transmits power from a power transmitting device to a power receiving device via a power transmitting coil and a power receiving coil. In particular, a technology has been proposed that achieves high efficiency and miniaturization while reducing harmonic components that are undesirably radiated from a primary coil (see Patent Document 1). In the contactless power transfer device disclosed in Patent Document 1, a capacitor that resonates with the primary coil is connected in series to the primary coil to form a primary series resonant circuit. An L-shaped resonant circuit having another coil and a capacitor that resonates with the other coil is inserted between the primary series resonant circuit and a drive circuit. This L-shaped resonant circuit is then connected in series with the primary series resonant circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2006 / 022365 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the above technology, it can be difficult to maintain a constant voltage output operation, i.e., to keep the voltage output from the power receiving device substantially constant even when the resistance of the load circuit connected to the power receiving device fluctuates. Furthermore, as the distance between the power transmitting coil and the power receiving coil increases, the phase delay of the current flowing through the power transmitting coil relative to the phase of the AC voltage applied to the power transmitting coil becomes significant. As a result, switching loss in the inverter circuit that supplies AC power to the power transmitting coil increases, reducing power transmission efficiency.

[0006] Therefore, an object of the present invention is to provide a contactless power supply device that is capable of improving power transmission efficiency while enabling constant voltage output operation. [Means for solving the problem]

[0007] One aspect of the present invention provides a contactless power supply device including a power transmission device and a power receiving device to which power is wirelessly transmitted from the power transmission device. In this contactless power supply device, the power transmission device includes a transmission coil that supplies power to the power receiving device, a power supply circuit that supplies AC power having a predetermined drive frequency to the transmission coil, a first capacitor connected between the power supply circuit and one end of the transmission coil, the first coil connected between the power supply circuit and one end or the other end of the transmission coil and the power supply circuit, a second capacitor having one end connected to the first capacitor and the other end connected to the other end of the transmission coil, and a control circuit that controls the power supply circuit so that AC power having the predetermined drive frequency is supplied to the transmission coil. The power receiving device also includes a reception coil that receives power via the transmission coil of the power transmission device and a resonant circuit that includes a resonant capacitor that resonates with the reception coil. The control circuit of the power transmission device controls the power supply circuit so that the predetermined drive frequency is within a predetermined frequency range that includes the resonant frequency of the resonant circuit. With this configuration, the contactless power supply device can improve power transmission efficiency while enabling constant voltage output operation.

[0008] In the power transmission device of this contactless power supply device, the inductance of the transmission coil, the capacitance of the first capacitor, and the capacitance of the second capacitor are set so that the closed-loop resonant frequency of the closed loop formed by the transmission coil, the first capacitor, and the second capacitor is higher than a predetermined drive frequency. By having such a configuration, this contactless power supply device can appropriately adjust the amount of phase delay of the current flowing through the transmitting coil relative to the phase of the voltage of the AC power supplied to the transmitting coil, and as a result, can reduce switching loss in the power supply circuit. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a contactless power supply device according to an embodiment of the present invention. [Figure 2] FIG. 10 is a schematic diagram illustrating an example of frequency characteristics of gain related to transmitted power in a contactless power supply device. [Figure 3] 3 is an equivalent circuit diagram of a transmission coil, a first capacitor, a second capacitor, and a first coil of a power transmission device, and a resonant circuit of a power reception device. FIG. [Figure 4] FIG. 10 is a diagram showing an example of a simulation result of the frequency characteristic of the output voltage of the contactless power supply device according to the present embodiment. [Figure 5] FIG. 10 is a schematic configuration diagram of a power receiving device according to a modified example. [Figure 6] 10 is a diagram illustrating an example of the positional relationship of connections between an inverter, a transmission coil, a first capacitor, a second capacitor, and a first coil in a power transmission device according to a modified example. FIG. [Figure 7] FIG. 10 is a diagram illustrating an example of the positional relationship of connections between an inverter, a transmission coil, a first capacitor, a second capacitor, and a first coil in a power transmission device according to another modification. [Figure 8] FIG. 10 is a diagram showing an example of the positional relationship of connections between an inverter in a power transmitting device, a transmitting coil, a first capacitor, a second capacitor, and a first coil according to yet another modification. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a contactless power supply device according to an embodiment of the present invention will be described with reference to the drawings. In a contactless power transfer device according to the present invention, a power transmission device (hereinafter simply referred to as a power transmission device) has a first capacitor connected between one end of a power transmission coil (hereinafter simply referred to as a transmission coil) and a power supply circuit that supplies AC power to the transmission coil, a first coil connected in series with the first capacitor, and a second capacitor having one end connected between the first capacitor and the first coil and the other end connected to the other end of the transmission coil. In this contactless power transfer device, the frequency of the AC power supplied to the transmission coil is controlled to be within a predetermined frequency range that includes the resonant frequency of a resonant circuit having a power receiving coil (hereinafter simply referred to as a receiving coil) in a power receiving device (hereinafter simply referred to as a power receiving device). Hereinafter, the frequency of the AC power supplied to the transmission coil may be simply referred to as the drive frequency.

[0011] FIG. 1 is a schematic diagram of a contactless power transfer device according to one embodiment of the present invention. As shown in FIG. 1, the contactless power transfer device 1 includes a power transfer device 2 and a power receiving device 3 to which power is transferred contactlessly from the power transfer device 2 via space. The power transfer device 2 includes a power supply circuit 10, a transmission coil 14, a first capacitor 15, a second capacitor 16, a first coil 17, a communicator 18, and a control circuit 19. The power receiving device 3 includes a resonant circuit 20 including a reception coil 21 and a resonant capacitor 22, a first rectifier circuit 23, a smoothing capacitor 24, a sub-coil 25, a second rectifier circuit 26, a voltage detection circuit 27, a resistor 28, a switching element 29, a determination circuit 30, and a communicator 31. The power receiving device 3 is connected to a load circuit 32. The power receiving device 3 receives power, converts it into direct current, and outputs the power to the load circuit 32.

[0012] First, the power transmitting device 2 will be described. The power supply circuit 10 supplies AC power having a predetermined drive frequency and an adjustable voltage to the transmission coil 14. To this end, the power supply circuit 10 includes a full-wave rectifier circuit 11, a power factor correction circuit 12, and an inverter 13.

[0013] The full-wave rectifier circuit 11 supplies power with a predetermined pulsating voltage. To this end, the full-wave rectifier circuit 11 has four diodes connected in a bridge configuration and is connected to a commercial AC power supply. The full-wave rectifier circuit 11 then rectifies the AC power supplied from the AC power supply, converts it into power with a pulsating voltage, and outputs the power to the power factor correction circuit 12.

[0014] The power factor correction circuit 12 converts the voltage of the power output from the full-wave rectifier circuit 11 into DC power having a voltage according to the control from the control circuit 19 and outputs it. Therefore, the AC power supply, the full-wave rectifier circuit 11, and the power factor correction circuit 12 constitute a DC power supply.

[0015] The power factor correction circuit 12 may have a configuration similar to any of various power factor correction circuits capable of adjusting the output voltage under control of the control circuit 19. In this embodiment, the power factor correction circuit 12 includes a coil connected in series at one end to the positive terminal of the full-wave rectifier circuit 11, and a diode connected between the other end of the coil and the inverter 13 so that the direction from the coil toward the inverter 13 is the forward direction. The power factor correction circuit 12 also includes a switching element connected at one end between the coil and the diode and at the other end connected to the negative terminal of the full-wave rectifier circuit 11, and a smoothing capacitor connected in parallel with the switching element and the diode. The control circuit 19 controls the on / off duty ratio of the switching element to control the voltage output from the power factor correction circuit 12. The power factor correction circuit 12 may have a configuration similar to that of the power factor correction circuit of a power transmission device described in Japanese Patent No. 6390808.

[0016] Inverter 13 converts the DC power output from power factor correction circuit 12 into AC power having a drive frequency corresponding to the on / off switching cycle of switching elements 13-1 to 13-2. Inverter 13 then outputs the AC power to transmission coil 14 via first capacitor 15, second capacitor 16, and first coil 17.

[0017] For this purpose, the inverter 13 has two switching elements 13-1 and 13-2. Each of the two switching elements 13-1 and 13-2 may be, for example, an n-channel MOSFET. The inverter 13 is configured as a so-called half-bridge circuit. That is, the switching elements 13-1 and 13-2 are connected in series between the positive and negative terminals of the full-wave rectifier circuit 11 via the power factor correction circuit 12. In this embodiment, the switching element 13-1 is connected to the positive terminal of the full-wave rectifier circuit 11, and the switching element 13-2 is connected to the negative terminal of the full-wave rectifier circuit 11. The drain terminal of the switching element 13-1 is connected to the positive terminal of the full-wave rectifier circuit 11 via the power factor correction circuit 12, and the source terminal of the switching element 13-1 is connected to the drain terminal of the switching element 13-2. The source terminal of the switching element 13-2 is connected to the negative terminal of the full-wave rectifier circuit 11 via the power factor correction circuit 12. The source terminal of the switching element 13-1 and the drain terminal of the switching element 13-2 are connected to one end of the transmitting coil 14 via the first coil 17 and the first capacitor 15, and the source terminal of the switching element 13-2 is connected to the other end of the transmitting coil 14.

[0018] The gate terminals of the switching elements 13-1 to 13-2 are connected to the control circuit 19. Furthermore, the gate terminals of the switching elements 13-1 to 13-2 may be connected to the source terminals of the switching elements via resistors, respectively, to ensure that the switching elements are turned on when a voltage that turns them on is applied. The switching elements 13-1 and 13-2 are alternately switched on and off in accordance with a control signal from the control circuit 19. In this embodiment, the switching elements 13-1 and 13-2 are alternately switched on and off such that while the switching element 13-1 is on, the switching element 13-2 is off, and conversely, while the switching element 13-2 is on, the switching element 13-1 is off. As a result, the DC power supplied from the power factor correction circuit 12 is converted into AC power having a drive frequency corresponding to the on / off switching cycle of each switching element, and is supplied to the transmission coil 14.

[0019] The inverter 13 is not limited to the above embodiment, but may be configured as a full-bridge circuit in which four switching elements are connected in a full-bridge configuration.

[0020] The first coil 17 is connected in series with the first capacitor 15 between the inverter 13 and the transmitting coil 14. That is, one end of the first coil 17 is connected to one of the two output terminals of the inverter 13, i.e., the connection between the source terminal of the switching element 13-1 and the drain terminal of the switching element 13-2, and the other end of the first coil 17 is connected to one end of the first capacitor 15. In addition, the other end of the first capacitor 15 is connected to one end of the transmitting coil 14. Note that the first coil 17 is preferably arranged so as not to be electromagnetically coupled to the transmitting coil 14 and each coil of the power receiving device 3.

[0021] Furthermore, one end of the second capacitor 16 is connected between the other end of the first coil 17 and one end of the first capacitor 15, and the other end is connected to the other end of the transmitting coil 14 and the other output terminal of the inverter 13, i.e., the source terminal of the switching element 13-2.

[0022] By providing the first capacitor 15, the second capacitor 16, and the first coil 17 as described above, the phase delay of the current flowing through the transmitting coil 14 relative to the phase of the voltage supplied to the transmitting coil 14 is adjusted so as to reduce switching loss in each switching element of the inverter 13. Furthermore, the contactless power supply device 1 can operate to output a constant voltage. Details regarding the setting of the capacitances of the first capacitor 15 and the second capacitor 16 and the inductance of the first coil 17 will be described later.

[0023] The transmission coil 14 transmits AC power supplied from the inverter 13 of the power supply circuit 10 via the first coil 17 and the first capacitor 15 to the resonant circuit 20 of the power receiving device 3 through space.

[0024] Every time the communicator 18 receives a wireless signal from the communicator 31 of the power receiving device 3, it extracts output voltage information indicating the output voltage from the power receiving device 3 from the wireless signal and outputs the output voltage information to the control circuit 19. To this end, the communicator 18 has, for example, an antenna that receives the wireless signal in accordance with a predetermined wireless communication standard and a communication circuit that demodulates the wireless signal. Note that the predetermined wireless communication standard may be, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0025] The control circuit 19 includes, for example, a non-volatile memory circuit, a volatile memory circuit, an arithmetic circuit, an interface circuit for connecting to other circuits, and a drive circuit for outputting control signals to each switching element. Each time the control circuit 19 receives output voltage information from the communicator 18, it controls the voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14 in accordance with the output voltage information.

[0026] The control circuit 19 controls the power factor correction circuit 12 so that the output voltage from the power receiving device 3 falls within a preset allowable range of output voltages. For example, when the output voltage from the power receiving device 3, as represented by the output voltage information, is higher than the upper limit of the allowable range, the control circuit 19 reduces the duty ratio of the switching elements of the power factor correction circuit 12. Conversely, when the output voltage from the power receiving device 3, as represented by the output voltage information, is lower than the lower limit of the allowable range, the control circuit 19 increases the duty ratio of the switching elements of the power factor correction circuit 12. Furthermore, when the output voltage from the power receiving device 3, as represented by the output voltage information, falls within the allowable range, the control circuit 19 keeps the duty ratio of the switching elements of the power factor correction circuit 12 constant without changing it.

[0027] Furthermore, control circuit 19 controls the on / off of two switching elements 13-1 and 13-2 of inverter 13 so that the frequency of AC power supplied from inverter 13 to transmission coil 14 becomes a predetermined drive frequency. That is, control circuit 19 controls switching elements 13-1 to 13-2 so that switching element 13-1 and switching element 13-2 are alternately turned on and the on period of switching element 13-1 and the on period of switching element 13-2 become equal within one cycle corresponding to the predetermined drive frequency. Note that, to prevent switching elements 13-1 and 13-2 from being turned on simultaneously and short-circuiting the AC power supply, control circuit 19 may provide a dead time during which both switching elements are off when switching switching elements 13-1 and 13-2 on / off.

[0028] Next, the power receiving device 3 will be described. The resonant circuit 20 is an LC resonant circuit in which a receiving coil 21 and a resonant capacitor 22 are connected in series. One end of the receiving coil 21 of the resonant circuit 20 is connected to one input terminal of a first rectifier circuit 23 via the resonant capacitor 22. The other end of the receiving coil 21 is connected to the other input terminal of the first rectifier circuit 23.

[0029] The receiving coil 21, together with the resonant capacitor 22, resonates with the AC current flowing through the transmitting coil 14 of the power transmitting device 2, thereby receiving power from the transmitting coil 14. The receiving coil 21 then outputs the received power to the first rectifier circuit 23 via the resonant capacitor 22. The number of turns of the receiving coil 21 and the number of turns of the transmitting coil 14 of the power transmitting device 2 may be the same or different.

[0030] The resonant capacitor 22 is connected in series with the receiving coil 21. That is, one end of the resonant capacitor 22 is connected to one end of the receiving coil 21, and the other end is connected to the first rectifier circuit 23. The resonant capacitor 22 resonates with the receiving coil 21, and outputs the received power to the first rectifier circuit 23.

[0031] The first rectifier circuit 23 can be, for example, a full-wave rectifier circuit having four bridge-connected diodes. One of the two input terminals of the first rectifier circuit 23 is connected to the resonant capacitor 22, and the other of the two input terminals is connected to the receiving coil 21. One of the two output terminals of the first rectifier circuit 23 is connected to one end of the smoothing capacitor 24, and the other of the two output terminals is connected to the other end of the smoothing capacitor 24 and is also grounded. The first rectifier circuit 23, together with the smoothing capacitor 24, rectifies the AC power output from the resonant circuit 20 and converts it into DC power.

[0032] The smoothing capacitor 24, together with the first rectifier circuit 23 or the second rectifier circuit 26, converts AC power received via the resonant circuit 20 or the sub-coil 25 into DC power. The smoothing capacitor 24 then outputs the DC power to the load circuit 32. To this end, one end of the smoothing capacitor 24 is connected to one of the two output terminals of the first rectifier circuit 23, one of the two output terminals of the second rectifier circuit 26, and one end of the load circuit 32. The other end of the smoothing capacitor 24 is connected to the other of the two output terminals of the first rectifier circuit 23, the other of the two output terminals of the second rectifier circuit 26, and the other end of the load circuit 32.

[0033] The subcoil 25 is arranged to be electromagnetically coupled to the receiving coil 21 of the resonant circuit 20. For example, the subcoil 25 and the receiving coil 21 are wound around the same core wire. Both ends of the subcoil 25 are connected to two input terminals of the second rectifier circuit 26, respectively. Providing such a subcoil 25 prevents an excessive increase in the voltage applied to the resonant circuit 20. For example, when the load of the load circuit 32 increases, the contactless power transfer device 1 attempts to maintain a constant voltage output operation, causing the voltage across the receiving coil 21 to increase. As the voltage increases, the voltage across the subcoil 25 also increases. If the voltage from the subcoil 25 becomes higher than the output voltage of the power receiving device 3, a portion of the transmitted power flows from the subcoil 25 to the smoothing capacitor 24 via the second rectifier circuit 26, thereby preventing an excessive voltage from being applied to the resonant circuit 20. On the other hand, when the voltage output from the resonant circuit 20 to the load circuit 32 via the first rectifier circuit 23 and the smoothing capacitor 24 reaches a certain level, the voltage across the terminals of the smoothing capacitor 24 becomes higher than the voltage across the two output terminals of the second rectifier circuit 26, which is caused by the voltage across the terminals of the sub-coil 25. Therefore, no current flows from the sub-coil 25 to the smoothing capacitor 24. Therefore, when the contactless power supply device 1 continues to operate in a constant voltage output mode, the sub-coil 25 does not affect the constant voltage output mode.

[0034] Preferably, the number of turns ns of the sub-coil 25 is set so that it is smaller than the number of turns nm of the receiving coil 21. Furthermore, the ratio (nm / ns) of the number of turns nm of the receiving coil 21 to the number of turns ns of the sub-coil 25 is set so that the expected maximum voltage peak value of the sub-coil 25 is equal to or less than the output voltage from the smoothing capacitor 24 when the contactless power supply device 1 is performing a constant voltage output operation. This output voltage is set according to the specifications of the load circuit 32.

[0035] The second rectifier circuit 26 may be, for example, a full-wave rectifier circuit having four bridge-connected diodes. However, the second rectifier circuit 26 may be another type of rectifier circuit. One of the two input terminals of the second rectifier circuit 26 is connected to one end of the sub-coil 25, and the other of the two terminals is connected to the other end of the sub-coil 25. One of the two output terminals of the second rectifier circuit 26 is connected to one end of the smoothing capacitor 24, and the other of the two output terminals is grounded. The second rectifier circuit 26 outputs the power output from the sub-coil 25 to the smoothing capacitor 24 when the voltage across the two output terminals of the second rectifier circuit 26, which corresponds to the voltage across the two terminals of the sub-coil 25, is higher than the voltage across the smoothing capacitor 24.

[0036] The voltage detection circuit 27 measures the voltage across the smoothing capacitor 24, i.e., the output voltage from the power receiving device 3 to the load circuit 32, at predetermined intervals. The voltage detection circuit 27 may be, for example, any of various known voltage detection circuits capable of detecting DC voltage. The voltage detection circuit 27 then outputs a voltage detection signal representing the measured value of the output voltage to the determination circuit 30.

[0037] The resistor 28 is connected to the first rectifier circuit 23 and the second rectifier circuit 26 so as to be in parallel with the load circuit 32 together with the switching element 29. That is, one end of the resistor 28 is connected between one of the two output terminals of the first rectifier circuit 23 and one of the two output terminals of the second rectifier circuit 26 and one end of the smoothing capacitor 24, and the other end of the resistor 28 is grounded via the switching element 29. When the switching element 29 is turned on, a current output from the first rectifier circuit 23 or the second rectifier circuit 26 flows through the resistor 28. Therefore, by switching the switching element 29 on and off, it is possible to obtain an effect similar to that of a change in the resistance of the load circuit 32 connected to the power receiving device 3.

[0038] The switching element 29 is, for example, a MOSFET, and is connected to the first rectifier circuit 23 and the second rectifier circuit 26 so as to be in parallel with the load circuit 32 together with the resistor 28. When the switching element 29 is turned off, it prevents current from flowing from the first rectifier circuit 23 and the second rectifier circuit 26 to the resistor 28, and when it is turned on, it allows current to flow from the first rectifier circuit 23 and the second rectifier circuit 26 to the resistor 28.

[0039] At predetermined intervals, the determination circuit 30 determines whether the measured output voltage is within the allowable range of the output voltage, based on the measured output voltage value received from the voltage detection circuit 27. Furthermore, at predetermined intervals, the determination circuit 30 generates output voltage information representing the measured output voltage, and notifies the generated output voltage information to the communication device 31. To this end, the determination circuit 30 includes, for example, a memory circuit that stores the allowable range of the output voltage, an arithmetic circuit that compares the measured output voltage value with the allowable range, and a control circuit that controls the on / off of the switching element 29.

[0040] The determination circuit 30 switches the switching element 29 on and off at regular intervals while the measured value of the output voltage is outside the allowable range of the output voltage. As a result, the resistance value of the entire circuit, including the load circuit 32, connected to the power receiving device 3, changes at the regular intervals. Therefore, the determination circuit 30 can determine whether the contactless power supply device 1 is operating at a constant voltage by determining whether the measured value of the output voltage is approximately constant while switching the switching element 29 on and off. Therefore, the determination circuit 30 switches the switching element 29 on and off while the measured value of the output voltage is outside the allowable range of the output voltage. On the other hand, if the measured value of the output voltage is within the allowable range of the output voltage, the determination circuit 30 keeps the switching element 29 in the off state.

[0041] The communicator 31 generates a wireless signal including the output voltage information received from the determination circuit 30 at every predetermined transmission period, and transmits the wireless signal to the communicator 18 of the power transmitting device 2. To this end, the communicator 31 has, for example, a communication circuit that generates a wireless signal in accordance with a predetermined wireless communication standard, and an antenna that outputs the wireless signal. Note that the predetermined wireless communication standard, like the communicator 18, can be, for example, ISO / IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

[0042] The operation of the contactless power supply device 1 will be described in detail below.

[0043] In this embodiment, the control circuit 19 of the power transmitting device 2 controls the voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14 based on the output voltage information received from the communication device 18 so that the contactless power feeding device 1 continues to output a constant voltage and the output voltage from the power receiving device 3 falls within an allowable range. Hereinafter, the output voltage from the power receiving device 3 may be simply referred to as the output voltage.

[0044] Here, it is preferable that the output voltage fluctuates little with respect to changes in the drive frequency near the drive frequency of the AC power supplied from the power supply circuit 10 to the transmitter coil 14 so that the contactless power transfer device 1 operates to output a constant voltage. If the output voltage fluctuates greatly with changes in the drive frequency, the efficiency of power transfer will fluctuate even with a slight change in the positional relationship between the transmitter coil 14 and the receiver coil 21 or a slight change in the circuit constants of individual elements of the power transmitter 2 or the power receiver 3. Furthermore, in order to improve power transfer efficiency, it is preferable that the frequency characteristics of the output voltage have a maximum value at or near the drive frequency.

[0045] FIG. 2 is a schematic diagram showing an example of the frequency characteristic of the gain related to the transmitted power in the contactless power transfer device 1. In FIG. 2, the horizontal axis represents frequency, and the vertical axis represents gain. Graph 200 shows an example of the frequency characteristic of the gain. In the frequency characteristic 200, the gain has maximum values ​​at three different frequencies. Among the frequencies at which the gain has maximum values, the gain fluctuates more slowly with respect to frequency changes near frequency f0 than near the other frequencies at which the gain has maximum values. Therefore, it is preferable to control the inverter 13 of the power supply circuit 10 so that the drive frequency is at or near frequency f0. This frequency f0 is the resonant frequency of the resonant circuit 20 of the power receiving device 3. Therefore, the fact that frequency f0 is the resonant frequency of the resonant circuit 20 will be described below.

[0046] 3 is an equivalent circuit diagram of the transmission coil 14, the first capacitor 15, the second capacitor 16, and the first coil 17 of the power transmission device 2, and the resonant circuit 20 of the power reception device 3. In this equivalent circuit 300, the parameter L in represents the inductance of the first coil 17. Furthermore, the parameters C1 and C p represent the capacitance of the first capacitor 15 and the capacitance of the second capacitor 16, respectively. Furthermore, the parameter L p and parameter L s represent the inductance of the transmitting coil 14 and the inductance of the receiving coil 21, respectively, and the parameter C s represents the capacitance of the resonant capacitor 22. Furthermore, the parameter M is the mutual inductance between the transmitting coil 14 and the receiving coil 21. If the degree of coupling between the transmitting coil 14 and the receiving coil 21 is k, then M=k(L p L s ) 1 / 2 is.

[0047] The F matrix of this equivalent circuit 300 is expressed by the following equation.

number

[0048] Therefore, the terminal constant A is expressed by the following equation: The terminal constant A represents the transfer characteristic of the ratio (V1 / V2) of the voltage V1 of the AC power applied to the transmitting coil 14 via the first capacitor 15, the second capacitor 16, and the first coil 17 (hereinafter referred to as the input voltage for convenience) to the output voltage V2 from the resonant circuit 20 when the output current I2 from the resonant circuit 20 is set to 0.

number

[0049] Furthermore, a terminal constant B that represents the transfer characteristic of the ratio (V1 / I2) of the input voltage V1 to the output current I2 when the output voltage V2 from the resonant circuit 20 is set to 0 is expressed by the following equation.

number

[0050] The gain G of the output voltage from the resonant circuit 20 is expressed by the following equation:

number

[0051] As shown in equation (4), the gain G is determined by the terminal constant A, the terminal constant B, and the AC equivalent resistance value of the load circuit 32. Of these, the terminal constant A is determined only according to the circuit constants of the individual elements on the power transmission device 2 side, as shown in equation (2), and there are two angular frequencies ω at which the terminal constant A becomes 0. Furthermore, the two angular frequencies at which the terminal constant A becomes 0 are angular frequencies determined by the fourth-order or second-order terms of the angular frequency ω, so that in the vicinity of these two angular frequencies, the terminal constant A changes abruptly as the angular frequency changes.

[0052] On the other hand, as shown in Equation (3), there are third-order or higher terms of the angular frequency ω for the terminal constant B, so there are at least three angular frequencies ω at which the terminal constant B is zero. One of the angular frequencies at which the terminal constant B is zero corresponds to frequency f0 in FIG. 2. It is preferable to set the circuit constants of the coils and capacitors of the power transmitting device 2 and the circuit constants of the receiving coil 21 and resonant capacitor 22 of the power receiving device 3 so that the terminal constant B is greater than the terminal constant A at any angular frequency at which the terminal constant B is not zero. By setting the circuit constants of each element in this manner, the term of the terminal constant A becomes dominant with respect to the gain G at angular frequencies sufficiently away from the angular frequency at which the terminal constant A is zero and in the vicinity of the angular frequency at which the terminal constant B is zero. At other angular frequencies at which the terminal constant B is not zero, the term of the terminal constant B becomes dominant with respect to the gain G. Therefore, the difference between the gain value at frequency f0 in FIG. 2 and the gain at nearby frequencies becomes relatively large.

[0053] In equation (3), terminal constant B = 0 and 1>>k 2 Assuming that holds, k 2 If we ignore the term and solve equation (3) for the square of the angular frequency, we get the following solution:

number

[0054] Furthermore, as is clear from equation (4), at the angular frequency where the terminal constant B is 0, the gain G is no longer dependent on the resistance of the load circuit 32. Therefore, by setting the drive frequency to a frequency corresponding to the angular frequency where the terminal constant B is 0 or a frequency in the vicinity thereof, the contactless power supply device 1 operates to output a constant voltage.

[0055] Therefore, by setting the drive frequency to a frequency included in a predetermined frequency range including the resonant frequency of the resonant circuit 20, the contactless power supply device 1 can perform constant voltage output operation and improve power transmission efficiency. Note that the predetermined frequency range may be set so that fluctuations in output voltage due to fluctuations in the resistance of the load circuit 32 are included in the allowable range of the output voltage in the system in which the contactless power supply device 1 is implemented, for example.

[0056] Furthermore, the degree of coupling k between the transmitting coil 14 and the receiving coil 21 is 1>>k 2 As long as this condition is satisfied (for example, when the degree of coupling k is 0.2 or less), the drive frequency for the contactless power supply device 1 to perform constant voltage output operation does not change even if the positional relationship between the transmitting coil 14 and the receiving coil 21 changes slightly. Therefore, the control circuit 19 of the power transmission device 2 does not need to change the cycle for switching on / off the switching elements 13-1 to 13-2 of the inverter 13 even if the positional relationship between the transmitting coil 14 and the receiving coil 21 changes slightly.

[0057] Furthermore, in order for the inverter 13 to perform soft switching, it is necessary to set an appropriate value for the phase delay of the current flowing through the transmitting coil 14 relative to the phase of the AC power supplied to the transmitting coil 14. For this purpose, it is preferable that the resonant frequency Fp of a closed loop formed by the transmitting coil 14, the first capacitor 15, and the second capacitor 16 in the power transmitting device 2 is higher than the drive frequency Fsw. The resonant frequency Fp of this closed loop is expressed by the following equation:

number

[0058] Therefore, by setting the inductance of the transmitting coil 14 and the capacitances of the first capacitor 15 and the second capacitor 16 to satisfy equation (6), it is possible to prevent the phase delay of the current flowing through the transmitting coil 14 from becoming too large relative to the phase of the voltage of the AC power supplied to the transmitting coil 14. As a result, the switching loss in each switching element of the inverter 13 is reduced.

[0059] 4 is a diagram showing an example of a simulation result of the frequency characteristic of the output voltage of the contactless power supply device 1. In FIG. 4, the horizontal axis represents frequency, and the vertical axis represents output voltage. In this simulation, the capacitance C1 of the first capacitor 15 is set to 40.1 nF, and the capacitance C p The inductance L of the first coil 17 is set to 45.6 nF. in The inductance of the transmitting coil 14 and the receiving coil 21 was set to 70.0 μH. Furthermore, the capacitance C s was set to 22.4 nF. The winding resistance value on the power transmission side and the winding resistance value on the power receiving side were set to 0.13 Ω. Furthermore, the voltage V inThe voltage was set to 440 V. Graph 401 shows the frequency characteristics of the output voltage when the degree of coupling k between the transmitter coil 14 and the receiver coil 21 is 0.11 and the AC equivalent resistance of the load circuit 32 is 20 Ω. Graph 402 shows the frequency characteristics of the output voltage when the degree of coupling k is 0.11 and the AC equivalent resistance of the load circuit 32 is 2 kΩ. As shown in graphs 401 and 402, the output voltage remains constant at the resonant frequency f1 (=84.1 kHz) of the resonant circuit 20, even when the AC equivalent resistance of the load circuit 32 changes. Furthermore, the frequency characteristics of the output voltage have a maximum value at the resonant frequency f1, and the output voltage fluctuates more slowly with respect to frequency fluctuations than at other frequencies with extreme values. Therefore, by setting the drive frequency fsw to a frequency within a predetermined frequency range including the resonant frequency f1 of the resonant circuit 20, the contactless power transfer device 1 can output a constant voltage and improve power transmission efficiency.

[0060] As described above, in this contactless power transfer device, the power transmission device is configured to have a first coil and a first capacitor connected in series between the inverter of the power supply circuit and one end of the transmission coil, and a second capacitor having one end connected between the first coil and the first capacitor and the other end connected to the other end of the transmission coil.The drive frequency supplied to the transmission coil is set within a predetermined frequency range that includes the resonant frequency of the resonant circuit of the power receiving device, so that this contactless power transfer device can improve power transmission efficiency while enabling constant voltage output operation.

[0061] Fig. 5 is a schematic diagram of a power receiving device according to a modified example. The power receiving device 4 according to this modified example differs from the power receiving device 3 shown in Fig. 1 in that it has a switch circuit 41 for switching between short-circuiting and open-circuiting the sub-coil 25, and that a determination circuit 30 controls the on / off switching of the switch circuit 41. Therefore, the switch circuit 41 and its related parts will be described below. For other components of the power receiving device 4, please refer to the descriptions of the corresponding components in the above embodiment.

[0062] The switch circuit 41 includes, for example, a relay or a MOSFET. One end of the switch circuit 41 is connected between one end of the sub-coil 25 and one terminal on the input side of the second rectifier circuit 26, and the other end of the switch circuit 41 is connected between the other end of the sub-coil 25 and the other terminal on the input side of the second rectifier circuit 26. When the switch circuit 41 is configured with MOSFETs, it is preferable that the switch circuit 41 include two MOSFETs connected in series with each other so that their body diodes are oriented in opposite directions.

[0063] The determination circuit 30 compares the measured value of the output voltage obtained by the voltage detection circuit 27 with an upper threshold (first upper threshold) and switches the switch circuit 41 on / off depending on the comparison result. That is, when the measured value of the output voltage is equal to or greater than the upper threshold, the determination circuit 30 turns on the switch circuit 41 to short-circuit the sub-coil 25. On the other hand, when the measured value of the output voltage is less than the upper threshold, the determination circuit 30 turns off the switch circuit 41 to open the sub-coil 25. Note that the upper threshold is preferably set to a value higher than the voltage applied to the load circuit 32 when the contactless power supply device operates in constant voltage output mode, particularly a value equal to or greater than the upper limit of the allowable range. Note that the determination circuit 30 may notify the communicator 18 of the power transmitting device 2 via the communicator 31 that the measured value of the output voltage is equal to or greater than the upper threshold. In this case, when the control circuit 19 of the power transmitting device 2 is notified by the communicator 18 that the measured value of the output voltage is equal to or greater than the upper threshold, the control circuit 19 may control the power factor correction circuit 12 to reduce the voltage of the AC power supplied from the power supply circuit 10 to the transmitting coil 14.

[0064] When the switch circuit 41 is turned on and the sub-coil 25 is short-circuited, the resonant frequency of the resonant circuit 20 changes. Therefore, even if the output voltage from the resonant circuit 20 increases excessively, the power transmitted from the power transmitter 2 to the power receiver 4 decreases because the sub-coil 25 is short-circuited, and the output voltage from the resonant circuit 20 also decreases. Therefore, according to this modification, the contactless power transfer device can suppress an increase in the voltage applied to the receiver coil 21 in accordance with a change in the degree of coupling between the transmitter coil 14 and the receiver coil 21. Therefore, this contactless power transfer device can prevent the output voltage from the resonant circuit from increasing excessively, which would cause a breakdown in the power receiver or the load circuit.

[0065] According to another modification, if the positional relationship between the transmitter coil 14 and the receiver coil 21 is ensured by the respective structures of the device in which the power transmitter 2 is implemented and the device in which the power receiver 3 is implemented so as to prevent excessive voltage from being generated in the power receiver 3, the sub-coil 25 and the second rectifier circuit 26 may be omitted. This simplifies the circuit configuration of the power receiver 3.

[0066] Furthermore, the degree of coupling k between the transmitting coil 14 and the receiving coil 21 is not constant, and there is a possibility that the degree of coupling k may fluctuate with each power transmission or during the power transmission, and 1>>k 2 The coupling factor k may take such a large value that it does not satisfy the constraint. In such a case, the control circuit 19 of the power transmitting device 2 may adjust the drive frequency to search for a drive frequency at which the contactless power supply device 1 can perform a constant voltage output operation. In this case, when the output voltage falls outside the allowable range, the determination circuit 30 of the power receiving device 3 notifies the power transmitting device 2 via the communicator 31 of information indicating that the output voltage is not constant, while switching the switching element 29 on and off to simulate a change in the load connected to the power receiving device 3, until the output voltage becomes approximately constant. While receiving the information indicating that the output voltage is not constant from the power receiving device 3 via the communicator 18, the control circuit 19 changes the drive frequency by changing the on / off switching cycle of each switching element of the inverter 13, and when the control circuit 19 no longer receives such information, it may keep the drive frequency constant.

[0067] According to still another modification, in the power transmitting device 2, the connection positions of the transmitting coil 14, the first capacitor 15, the second capacitor 16, and the first coil 17 relative to the inverter 13 are not limited to the above example.

[0068] 6 to 8 are diagrams showing examples of the connection positional relationship between the inverter 13, the transmitting coil 14, the first capacitor 15, the second capacitor 16, and the first coil 17 in the power transmitting device 2 according to a modified example. Note that, below, differences from the power transmitting device 2 in the above embodiment will be described.

[0069] 6, the first coil 17 is connected between the transmitting coil 14 and the inverter 13 on the side opposite to the side to which the first coil 15 is connected. That is, the first coil 17 is connected between one end of the transmitting coil 14 opposite to the end to which the first coil 15 is connected and the source terminal of the switching element 13-2 of the inverter 13.

[0070] 7, the power factor correction circuit 12 has two smoothing capacitors C1 and C2 connected in series. One end of the transmission coil 14 opposite to the side to which the first coil 15 is connected and one end of the second capacitor 16 opposite to the side to which the first coil 15 is connected are connected between the smoothing capacitors C1 and C2.

[0071] 8, the first coil 17 is arranged such that one end is connected between the two switching elements 13-1 and 13-2 of the inverter 13, and the other end is connected to one end of the transmitting coil 14, as in the above embodiment. Meanwhile, the other end of the transmitting coil 14 is connected to the drain terminal of the switching element 13-1 via the first coil 15.

[0072] These modifications also provide the same effects as the above embodiment.

[0073] As described above, those skilled in the art can make various modifications to the embodiments within the scope of the present invention. [Explanation of symbols]

[0074] 1. Contactless power supply device 2. Power transmission equipment 10 Power supply circuit 11 Full wave rectifier circuit 12 Power factor correction circuit 13 Inverter 13-1~13-2 Switching elements 14 Transmitting coil 15 First Capacitor 16 Second capacitor 17 First Coil 18 Communication Device 19 Control circuit 3, 4 Power receiving device 20 Resonant circuit 21 receiving coil 22 Resonant Capacitor 23 First rectifier circuit 24 smoothing capacitor 25 subcoils 26 Second rectifier circuit 27 Voltage detection circuit 28 Resistance 29 Switching element 30 Judgment circuit 31 Communication device 32 Load circuit 41 Switch Circuit

Claims

[Claim 1] A contactless power supply device having a power transmission device and a power reception device to which power is transmitted contactlessly from the power transmission device, The power transmission device is a transmitting coil for supplying power to the power receiving device; a power supply circuit that supplies AC power having a predetermined drive frequency to the transmission coil; a first capacitor connected between the power supply circuit and one end of the transmitting coil; a first coil connected between the power supply circuit and the one end or the other end of the transmitting coil and the power supply circuit; a second capacitor having one end connected to the first capacitor and the other end connected to the other end of the transmitting coil; a control circuit that controls the power supply circuit so that AC power having the drive frequency is supplied to the transmission coil; The power receiving device is a receiving coil that receives power via the transmitting coil of the power transmitting device, and a resonant circuit that includes a resonant capacitor that resonates together with the receiving coil; the control circuit controls the power supply circuit so that the drive frequency is within a predetermined frequency range that includes a resonant frequency of the resonant circuit; a contactless power supply device in which the inductance of the transmitting coil, the capacitance of the first capacitor, and the capacitance of the second capacitor are set so that a closed-loop resonant frequency of a closed loop formed by the transmitting coil, the first capacitor, and the second capacitor is higher than the drive frequency.

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