Rectifier, power receiving device for contactless power supply system, and contactless power supply system

Abstract

To provide a rectification device that expands a range of impedance adjustment of the rectification device.SOLUTION: In a non-contact power supply system 1, a power reception device 10 comprises a diode bridge rectifier circuit 13 in which a first diode D1 and a second diode D2 are serially connected and further a third diode D3 and a fourth diode D4 are serially connected, and which rectifies AC power to DC power and supplies the DC power to a load. The diode bridge rectifier circuit 13 comprises: a first variable capacitance capacitor VC1 that is connected to the first diode D1 in parallel and allows adjustment to an amount of charging; a second variable capacitance capacitor VC2 that is connected to the second diode D2 in parallel and allows adjustment to the amount of charging; a third variable capacitance capacitor VC3 that is connected to the third diode D3 in parallel and allows adjustment to the amount of charging; and a fourth variable capacitance capacitor VC4 that is connected to the fourth diode D4 in parallel and allows adjustment to the amount of charging.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rectifier device, a power receiving device of a contactless power supply system, and a contactless power supply system. [Background technology]

[0002] Known power receiving devices for contactless power transfer systems rectify AC power generated in a power receiving coil into DC power and supply it to a load (see, for example, Patent Documents 1 to 3). In the power receiving devices described in Patent Documents 1 and 2, a variable capacitor is connected in parallel to two of the four diodes in a diode bridge rectifier circuit. In this power receiving device, impedance adjustment of the power receiving device is performed by changing the capacitance of the variable capacitor. Furthermore, the power receiving device described in Patent Document 3 is provided with a fixed capacitor and a switching element connected in series to the fixed capacitor, instead of the variable capacitor. In this power receiving device, impedance adjustment is performed by turning the switching element on and off. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6309503 [Patent Document 2] Patent No. 6814642 [Patent Document 3] Japanese Patent Application Publication No. 2019-58035 Summary of the Invention [Problem to be solved by the invention]

[0004] In the power receiving devices described in Patent Documents 1 to 3, the current that flows back from the diode bridge rectifier circuit to the power receiving coil is at most half the input current, and the range of impedance adjustment is determined accordingly.

[0005] In view of the above circumstances, an object of the present invention is to provide a rectifier that can widen the range of impedance adjustment of the rectifier, a power receiving device of a contactless power transfer system, and a contactless power transfer system. [Means for solving the problem]

[0006] The rectifier device of the present invention is a rectifier device including a diode bridge rectifier circuit in which a first diode and a second diode are connected in series and a third diode and a fourth diode are connected in series, rectifying AC power to DC power and supplying the DC power to a load, wherein the diode bridge rectifier circuit includes a first capacitor connected in parallel to the first diode and having an adjustable charge amount, a second capacitor connected in parallel to the second diode and having an adjustable charge amount, a third capacitor connected in parallel to the third diode and having an adjustable charge amount, and a fourth capacitor connected in parallel to the fourth diode and having an adjustable charge amount.

[0007] A power receiving device of a contactless power supply system of the present invention is a power receiving device of a contactless power supply system comprising: a receiving coil that generates AC power; and a diode bridge rectifier circuit in which a first diode and a second diode are connected in series and a third diode and a fourth diode are connected in series, and which rectifies the AC power generated in the receiving coil into DC power and supplies the DC power to a load, wherein the diode bridge rectifier circuit comprises a first capacitor connected in parallel to the first diode and having an adjustable charge amount, a second capacitor connected in parallel to the second diode and having an adjustable charge amount, a third capacitor connected in parallel to the third diode and having an adjustable charge amount, and a fourth capacitor connected in parallel to the fourth diode and having an adjustable charge amount.

[0008] The contactless power supply system of the present invention includes a power transmission coil that resonates when supplied with AC power, a power receiving coil that generates AC power through resonance of the power transmission coil, and a diode bridge rectifier circuit in which a first diode and a second diode are connected in series and a third diode and a fourth diode are connected in series, rectifying the AC power generated in the power receiving coil to DC power and supplying the DC power to a load, wherein the diode bridge rectifier circuit includes a first capacitor connected in parallel to the first diode and having an adjustable charge amount, a second capacitor connected in parallel to the second diode and having an adjustable charge amount, a third capacitor connected in parallel to the third diode and having an adjustable charge amount, and a fourth capacitor connected in parallel to the fourth diode and having an adjustable charge amount. [Effects of the Invention]

[0009] According to the present invention, the range of impedance adjustment of the rectifier can be widened. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a contactless power supply system according to one embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing the relationship between the load current [A], charging power [kW], and power supply voltage [V] and the capacitance [μF] of the first to fourth variable capacitors VC1 to VC4 during constant voltage charging of the battery. [Figure 3] FIG. 3 is a waveform diagram showing the voltage and current at each point when the capacitance of the first and second variable capacitors is 0 [μF] and the capacitance of the third and fourth variable capacitors is 0.6 [μF]. [Figure 4] Figures 4(1) to (4) are diagrams showing the relationship between current, voltage, and charging and discharging of the first to fourth variable capacitors when the capacitance of the first and second variable capacitors is 0 [μF] and the capacitance of the third and fourth variable capacitors is 0.6 [μF]. [Figure 5]FIG. 5 is a waveform diagram showing the voltage and current at each point when the capacitance of the first and second variable capacitors is 0 [μF] and the capacitance of the third and fourth variable capacitors is 1.2 [μF]. [Figure 6] FIG. 6 is a waveform diagram showing the current at each point when the capacitance of the first and second variable capacitors is 0.6 [μF] and the capacitance of the third and fourth variable capacitors is 1.2 [μF]. [Figure 7] FIG. 7 is a waveform diagram showing the voltages at each point when the capacitance of the first and second variable capacitors is 0.6 [μF] and the capacitance of the third and fourth variable capacitors is 1.2 [μF]. [Figure 8] Figures 8(1) to (4) are diagrams showing the relationship between current, voltage, and charging and discharging of the first to fourth variable capacitors when the capacitance of the first and second variable capacitors is 0.6 [μF] and the capacitance of the third and fourth variable capacitors is 1.2 [μF]. [Figure 9] FIG. 9 is a diagram showing a contactless power supply system according to another embodiment of the present invention. [Figure 10] FIG. 10 is a block diagram showing the functions of the control unit shown in FIG. [Figure 11] FIG. 11 is a diagram showing the relationship between the switch-on / switch-off signal and the load voltage in the embodiment shown in FIG. [Figure 12] FIG. 12 is a block diagram showing a modified example of the functions of the control unit shown in FIG. [Figure 13] FIG. 13 is a sequence chart showing an example of the operation of the third and fourth switches in the modified example shown in FIG. [Figure 14] FIG. 14 is a diagram showing a contactless power supply system according to another embodiment of the present invention. [Figure 15] FIG. 15 is a graph showing the relationship between the capacitance of the capacitor of the impedance adjustment unit of the power receiving device and the voltage-current phase difference of the power transmitting device. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described below in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below and can be modified as appropriate without departing from the spirit of the present invention. In addition, in the embodiments shown below, some components are omitted from illustration and description, but for the details of the omitted technologies, publicly known or well-known technologies are applied as appropriate within the scope of not causing any contradictions with the content described below.

[0012] Fig. 1 is a diagram showing a contactless power supply system 1 according to one embodiment of the present invention. As shown in this figure, the contactless power supply system 1 includes a power receiving device 10 and a power transmitting device 20. The contactless power supply system 1 of this embodiment is a contactless charging system that charges a battery 3 as a load.

[0013] The power transmitting device 20 includes a power transmitting coil 21, a resonant capacitor 22, an inverter circuit 23, and a DC power supply 2. The DC power supply 2 outputs DC power to the inverter circuit 23. The inverter circuit 23 converts the DC power input from the DC power supply 2 into AC power by turning on / off switching elements sw1 to sw4, and supplies the AC power to the power transmitting coil 21 and the resonant capacitor 22. The power transmitting coil 21 and the resonant capacitor 22 are connected in series to form a resonant circuit.

[0014] The power receiving device 10 includes a power receiving coil 11, a resonant capacitor 12, a diode bridge rectifier circuit 13, a smoothing capacitor 14, a current sensor 15, a voltage sensor 16, and a control unit 100. The power receiving coil 11 and the resonant capacitor 12 are connected in series to form a resonant circuit. The power receiving coil 11 is disposed opposite a power transmitting coil 21.

[0015] When the power transmitting coil 21 and the resonance capacitor 22 resonate, a magnetic field is generated in the power transmitting coil 21, and a part of the magnetic field interlinks with the power receiving coil 11. As a result, an induced current is generated in the power receiving coil 11. That is, AC power is transmitted from the power transmitting coil 21 to the power receiving coil 11 by magnetic field resonance.

[0016] The diode bridge rectifier circuit 13 includes first to fourth diodes D1 to D4 and an impedance adjuster 131. The first diode D1 and the second diode D2 are connected in series, and the third diode D3 and the fourth diode D4 are connected in series. The first diode D1 and the second diode D2 connected in series are connected in parallel to the third diode D3 and the fourth diode D4 connected in series. One end 11A of the power receiving coil 11 is connected between the first diode D1 and the second diode D2 via the resonant capacitor 12. On the other hand, the other end 11B of the power receiving coil 11 is connected between the third diode D3 and the fourth diode D4.

[0017] Diode bridge rectifier circuit 13 converts AC power output from receiving coil 11 into DC power and supplies it to battery 3. When battery 3 is being charged with a constant current, the current output from one end 11A of receiving coil 11 flows sequentially through resonant capacitor 12, first diode D1, battery 3, and fourth diode D4, before returning to other end 11B of receiving coil 11. On the other hand, when battery 3 is being charged with a constant current, the current output from other end 11B of receiving coil 11 flows sequentially through third diode D3, battery 3, second diode D2, and resonant capacitor 12, before returning to one end 11A of receiving coil 11.

[0018] The impedance adjustment unit 131 includes a first impedance adjustment unit 131A and a second impedance adjustment unit 131B. The first impedance adjustment unit 131A includes a first variable capacitor VC1 and a second variable capacitor VC2. The first variable capacitor VC1 is connected in parallel to the first diode D1, and the second variable capacitor VC2 is connected in parallel to the second diode D2. The second impedance adjustment unit 131B includes a third variable capacitor VC3 and a fourth variable capacitor VC4. The third variable capacitor VC3 is connected in parallel to the third diode D3, and the fourth variable capacitor VC4 is connected in parallel to the fourth diode D4. The first to fourth variable capacitors VC1 to VC4 are capacitors with adjustable capacitance (varicon: variable capacitors). Examples of the first to fourth variable capacitors VC1 to VC4 include voltage-adjusted capacitors whose capacitance is adjusted by an applied voltage and mechanically adjusted capacitors whose capacitance is mechanically adjusted.

[0019] The capacitances of the first to fourth variable capacitors VC1 to VC4 are adjusted by the control unit 100. In this embodiment, during constant current charging in CCCV (Constant Current, Constant Voltage) charging of the battery 3, the capacitances of the first to fourth variable capacitors VC1 to VC4 are adjusted to 0 μF. On the other hand, during constant voltage charging in CCCV charging of the battery 3, the capacitances of the first to fourth variable capacitors VC1 to VC4 are adjusted between 0 and an upper limit value (for example, 1.2 μF). As the capacitances of the first to fourth variable capacitors VC1 to VC4 increase, the current supplied to the battery 3 (hereinafter referred to as load current) decreases.

[0020] The smoothing capacitor 14 is connected in parallel with the battery 3 and forms a smoothing circuit. The smoothing capacitor 14 smoothes the pulsating current flowing from the diode bridge rectifier circuit 13 to the battery 3.

[0021] The current sensor 15 detects the current value of the direct current supplied to the battery 3 and outputs it to the control unit 100. The voltage sensor 16 detects the voltage value of the battery 3 (hereinafter referred to as the load voltage) and outputs it to the control unit 100.

[0022] The control unit 100 controls the capacitances of the first to fourth variable capacitors VC1 to VC4. Specifically, the control unit 100 sets the first to fourth variable capacitors VC1 to VC4 to 0 μF during constant current charging of the battery 3. At this time, the output current of the power receiving coil 11 (hereinafter referred to as the coil current) is entirely supplied to the battery 3. Furthermore, when the load voltage detected by the voltage sensor 16 increases with an increase in the charging rate of the battery 3, the control unit 100 increases the capacitances of the first to fourth variable capacitors VC1 to VC4. In other words, when the load voltage increases to a predetermined value or more, the control unit 100 shifts the charging mode of the battery 3 from constant current charging to constant voltage charging.

[0023] 2 is a graph showing the relationship between the load current [A], charging power [kW], and power supply voltage [V] and the capacitance [μF] of the first to fourth variable capacitors VC1 to VC4 during constant voltage charging of the battery 3. The load current [A] shown in this graph is the average value of the charging current supplied to the battery 3. The charging power [kW] is the product of the load current [A] and the load voltage. The power supply voltage [V] is the effective value of the output voltage of the power transmitting device 20.

[0024] In this graph, the point at which the capacitance [μF] of the first to fourth variable capacitors VC1 to VC4 reaches 0 [μF] is the point at which the charging mode of the battery 3 shifts from constant current charging to constant voltage charging. Also, in this graph, the point at which the capacitance [μF] of the first to fourth variable capacitors VC1 to VC4 reaches 1.2 [μF] is the end point of constant voltage charging (end point of CCCV charging) of the battery 3. Note that 1.2 [μF], which is the maximum value of the capacitance [μF] of the first to fourth variable capacitors VC1 to VC4, is just an example, and this maximum value can be set appropriately.

[0025] As shown in this graph, during constant voltage charging of battery 3, control unit 100 first gradually increases the capacitance [μF] of third and fourth variable capacitors VC3 and VC4 of second impedance adjustment unit 131B from 0 [μF] to a maximum value (1.2 [μF]). At this time, the load current [A] gradually decreases from the value during constant current charging of battery 3 to half the value during constant current charging of battery 3. Furthermore, as the load current [A] decreases, the charging power [kW] gradually decreases from the value during constant current charging of battery 3 to half the value during constant current charging of battery 3. Note that during constant voltage charging of battery 3, the power supply voltage [V] is constant, and the voltage of power transmission device 20 is not controlled.

[0026] From the middle of the constant voltage charging of the battery 3 to the end of the constant voltage charging, the control unit 100 gradually increases the capacitance [μF] of the first and second variable capacitors VC1 and VC2 of the first impedance adjustment unit 131A from 0 [μF] to a maximum value (1.2 [μF]). During this time, the load current [A] gradually decreases from half its value during constant current charging of the battery 3 to 0 [A]. Furthermore, as the load current [A] decreases, the charging power [kW] gradually decreases from half its value during constant current charging of the battery 3 to 0 [kW].

[0027] Fig. 3 is a waveform diagram showing the voltage and current of each part when the capacitance of the first and second variable capacitors VC1, VC2 is 0 [μF] (lower limit) and the capacitance of the third and fourth variable capacitors VC3, VC4 is 0.6 [μF] (half the upper limit). Also, Figs. 4(1) to (4) are diagrams showing the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 when the capacitance of the first and second variable capacitors VC1, VC2 is 0 [μF] and the capacitance of the third and fourth variable capacitors VC3, VC4 is 0.6 [μF].

[0028] Figure 4(1) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing of (1) in Figure 3. Also, Figure 4(2) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing of (2) in Figure 3. Also, Figure 4(3) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing of (3) in Figure 3. Furthermore, Figure 4(4) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing of (4) in Figure 3.

[0029] In Figures 4(1) to (4), current is indicated by a solid black arrow, and voltage is indicated by a hollow arrow. Also, in Figures 4(1) to (4), current A, indicated by a thick solid black arrow, is twice as large as current B, indicated by a thin solid black arrow. Also, in Figures 4(1) to (4), the length of the hollow arrow indicates the level of voltage. That is, voltage C is the highest, and voltage E is the lowest.

[0030] The timing of (1) in Figure 3 is the timing immediately after the coil current changes from negative to positive. At this timing of (1) in Figure 3, the current flowing through the third variable capacitor VC3 (hereinafter referred to as the VC3 current) changes from 0 to positive, and the current flowing through the fourth variable capacitor VC4 (hereinafter referred to as the VC4 current) changes from 0 to negative. Also, at the timing of (1) in Figure 3, the load current changes from a decrease to an increase. Furthermore, at the timing of (1) in Figure 3, the voltage of the third variable capacitor VC3 (hereinafter referred to as the VC3 voltage) changes from 0 to an increase, and the voltage of the fourth variable capacitor VC4 (hereinafter referred to as the VC4 voltage) changes from a load voltage to a decrease.

[0031] As shown in FIG. 4(1), at timing (1) in FIG. 3, the coil current (current A) passes through the first diode D1 and branches into a load current (current B) and a VC3 current (current B). The VC3 current, which is half the magnitude of the coil current, charges the third variable capacitor VC3 and flows back to the receiving coil 11. On the other hand, the fourth variable capacitor VC4, which is in a charged state, discharges, and the VC4 current, which is a discharge current, flows back to the receiving coil 11.

[0032] Timing (2) in Figure 3 is the timing immediately after the coil current starts to decrease from its maximum positive value. Just before timing (2) in Figure 3, the VC3 current changes from its maximum positive value to zero, and the VC4 current changes from its maximum negative value to zero. That is, at timing (2) in Figure 3, the VC3 current and VC4 current are both zero. Also, just before timing (2) in Figure 3, the load current changes from half the magnitude of the coil current to the magnitude of the coil current. That is, at timing (2) in Figure 3, the load current is equal to the coil current. Furthermore, at timing (2) in Figure 3, the VC3 voltage is equal to the load voltage, and the VC4 voltage is zero.

[0033] As shown in Fig. 4(2), at the timing of Fig. 3(2), all of the coil current becomes a load current (current A) and flows back to the power receiving coil 11 without flowing to the third and fourth variable capacitors VC3 and VC4. At this time, the VC3 voltage is equal to the load voltage.

[0034] Timing (3) in Figure 3 is the timing immediately after the coil current changes from positive to negative. At timing (3) in Figure 3, the VC3 current changes from 0 to negative, and the VC4 current changes from 0 to positive. Also, at timing (3) in Figure 3, the load current changes from a decrease to an increase. Furthermore, at timing (3) in Figure 3, the VC3 voltage changes from the load voltage to a decrease, and the VC4 voltage changes from 0 to an increase.

[0035] As shown in Figure 4 (3), at timing (3) in Figure 3, the coil current (current A) branches into a load current (current B) and a VC4 current (current B). The VC4 current, which is half the magnitude of the coil current, charges the fourth variable capacitor VC4, passes through the second diode D2 and the resonant capacitor 12, and returns to the receiving coil 11. On the other hand, the third variable capacitor VC3, which is in a charged state, discharges, and the VC3 current, which is a discharge current, becomes the load current.

[0036] Timing (4) in Figure 3 is the timing immediately after the coil current starts to decrease from its negative maximum value. Just before timing (4) in Figure 3, the VC3 current changes from its negative maximum value to zero, and the VC4 current changes from its positive maximum value to zero. That is, at timing (4) in Figure 3, the VC3 current and VC4 current are both zero. Also, just before timing (4) in Figure 3, the load current changes from half the magnitude of the coil current to the magnitude of the coil current. That is, at timing (4) in Figure 3, the load current (absolute value) is equal to the coil current. Furthermore, at timing (4) in Figure 3, the VC3 voltage is zero, and the VC4 voltage is equal to the load voltage.

[0037] As shown in Figure 4 (4), at timing (4) in Figure 3, all of the coil current becomes load current (current A) and flows back to the receiving coil 11 without flowing to the third and fourth variable capacitors VC3 and VC4. At this time, the VC4 voltage is equal to the load voltage.

[0038] 5 is a waveform diagram showing the voltages and currents of various parts when the capacitances of the first and second variable capacitors VC1 and VC2 are 0 μF and the capacitances of the third and fourth variable capacitors VC3 and VC4 are 1.2 μF (upper limit). As shown in this waveform diagram, when the capacitances of the third and fourth variable capacitors VC3 and VC4 are 1.2 μF, the waveforms of the VC3 current, VC4 current, VC3 voltage, and VC4 voltage are sinusoidal.

[0039] The amplitude of the VC3 current and VC4 current is always half the amplitude of the coil current. Furthermore, the VC3 current is in phase with the coil current, and the VC4 current is in opposite phase to the coil current. The amplitude of the load current is also always half the amplitude of the coil current. Furthermore, the waveform of the load current has a profile in which positive half waves of a sine wave are repeated.

[0040] The VC3 voltage and the VC4 voltage are in opposite phase. During a half cycle in which the coil current shifts in the positive direction, the VC3 voltage rises from 0 to the load voltage, and the VC4 voltage decreases from the load voltage to 0. That is, while the coil current is shifting in the positive direction, the third variable capacitor VC3 is charged to the load voltage, and the fourth variable capacitor VC4 is discharged. On the other hand, while the coil current is shifting in the negative direction, the third variable capacitor VC3 is discharged, and the fourth variable capacitor VC4 is charged to the load voltage.

[0041] In other words, when the capacitance of the first and second variable capacitors VC1 and VC2 is set to 0 [μF] and the capacitance of the third and fourth variable capacitors VC3 and VC4 is set to 1.2 [μF], half of the coil current always becomes the load current, and the remaining half of the coil current is not supplied to the battery 3 but flows back to the receiving coil 11.

[0042] Fig. 6 is a waveform diagram showing the current at each point when the capacitance of the first and second variable capacitors VC1 and VC2 is 0.6 μF (half the upper limit) and the capacitance of the third and fourth variable capacitors VC3 and VC4 is 1.2 μF. Fig. 7 is a waveform diagram showing the voltage at each point when the capacitance of the first and second variable capacitors VC1 and VC2 is 0.6 μF and the capacitance of the third and fourth variable capacitors VC3 and VC4 is 1.2 μF. Furthermore, Figs. 8(1) to 8(4) are diagrams showing the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 when the capacitance of the first and second variable capacitors VC1 and VC2 is 0.6 μF and the capacitance of the third and fourth variable capacitors VC3 and VC4 is 1.2 μF.

[0043] Figure 8(1) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing (1) in Figures 6 and 7. Figure 8(2) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing (2) in Figures 6 and 7. Figure 8(3) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing (3) in Figures 6 and 7. Figure 8(4) shows the relationship between the current, voltage, and charge / discharge of the first to fourth variable capacitors VC1 to VC4 at the timing (4) in Figures 6 and 7.

[0044] In Figures 8(1) to (4), current is indicated by a solid black arrow, and voltage is indicated by a hollow arrow. Also, in Figures 8(1) to (4), current A, indicated by a thick solid black arrow, is twice as large as current B, indicated by a thin solid black arrow. Also, in Figures 8(1) to (4), the length of the hollow arrow indicates the level of voltage. That is, voltage C is the highest, and voltage E is the lowest.

[0045] As shown in Fig. 6, the waveform of the VC3 current has a profile that can be roughly called a sine curve, and the VC3 current has the same phase and amplitude as the VC3 current shown in Fig. 5. Furthermore, the waveform of the VC4 current has a profile that can be roughly called a sine curve, and the V4 current has the same phase and amplitude as the VC4 current shown in Fig. 5.

[0046] As shown in Fig. 7, the waveforms of the VC3 voltage and the VC4 voltage are sinusoidal. The VC3 voltage has the same phase and amplitude as the VC3 voltage shown in Fig. 5, and the VC4 voltage has the same phase and amplitude as the VC4 voltage shown in Fig. 5.

[0047] The timing (1) in Figures 6 and 7 is the timing immediately after the coil current changes from negative to positive. At the timing (1) in Figure 6, the current flowing through the first variable capacitor VC1 (hereinafter referred to as the VC1 current) changes from 0 to negative, and the current flowing through the second variable capacitor VC2 (hereinafter referred to as the VC2 current) changes from 0 to positive. Also, at the timing (1) in Figure 6, the load current is 0. Also, at the timing (1) in Figure 7, the voltage of the first variable capacitor VC1 (hereinafter referred to as the VC1 voltage) changes from a load voltage to a decrease, and the voltage of the second variable capacitor VC2 (hereinafter referred to as the VC2 voltage) changes from 0 to an increase.

[0048] As shown in FIG. 8(1), at the timing (1) in FIGS. 6 and 7, the coil current (current A) passes through resonance capacitor 12 and branches. One of the branched currents passes through first variable capacitor VC1 and third variable capacitor VC3 and returns to receiving coil 11. On the other hand, the other branched current passes through second variable capacitor VC2 and fourth variable capacitor VC4 and returns to receiving coil 11. That is, at the timing (1) in FIGS. 6 and 7, not all of the coil current is supplied to battery 3 but circulates in diode bridge rectifier circuit 13 and returns to receiving coil 11.

[0049] 6 and 7, the first variable capacitor VC1 in a charged state is discharged, and the second variable capacitor VC2 is charged with a VC2 current that is half the coil current. Also, at the timing (1) in Fig. 6 and 7, the third variable capacitor VC3 is charged with a VC3 current that is half the coil current, and the fourth variable capacitor VC4 in a charged state is discharged.

[0050] Timing (2) in Figures 6 and 7 is the timing immediately after the coil current starts to decrease from its maximum positive value. Just before timing (2) in Figure 6, the VC1 current changes from its maximum negative value to zero, and the VC2 current changes from its maximum positive value to zero. Also, just before timing (2) in Figure 6, the VC3 current reaches its maximum positive value, and the VC4 current reaches its maximum negative value. Furthermore, just before timing (2) in Figure 6, the load current changes from zero to half the magnitude of the coil current. In other words, the load current is zero from just before (1) to just before (2) in Figure 6.

[0051] At the timing (2) in Figure 7, the VC1 voltage is 0 and the VC2 voltage is equal to the load voltage. Also, at the timing (2) in Figure 7, the VC3 voltage is rising and the VC4 voltage is falling.

[0052] As shown in Figure 8(2), at timing (2) in Figures 6 and 7, the coil current (current A) passes through the first diode D1 and branches. One of the branched currents (current B) passes through the battery 3 and fourth variable capacitor VC4 and returns to the receiving coil 11. On the other hand, the other branched current passes through the third variable capacitor VC3 and returns to the receiving coil 11.

[0053] 6 and 7, the first and second variable capacitors VC1 and VC2 are not charged or discharged, the third variable capacitor VC3 is charged by a VC3 current that is half the coil current, and the fourth variable capacitor VC4, which is in a charged state, is discharged. Also, from (2) to (3) in FIG. 7, the VC1 voltage is maintained at 0, and the VC2 voltage is maintained at the load voltage.

[0054] The timing (3) in Figures 6 and 7 is the timing immediately after the coil current changes from positive to negative. At the timing (3) in Figure 6, the VC1 current changes from 0 to positive, and the VC2 current changes from 0 to negative. Also, at the timing (3) in Figure 6, the load current is 0. Furthermore, at the timing (3) in Figure 7, the VC1 voltage starts to increase from 0, and the VC2 voltage starts to decrease from the load voltage.

[0055] 8(3), at the timing (3) in FIGS. 6 and 7, the coil current (current A) branches between the third variable capacitor VC3 and the fourth variable capacitor VC4. One of the branched currents (current B) passes through the third variable capacitor VC3, the first variable capacitor VC1, and the resonance capacitor 12, before returning to the receiving coil 11. On the other hand, the other branched current passes through the fourth variable capacitor VC4, the second variable capacitor VC2, and the resonance capacitor 12, before returning to the receiving coil 11. That is, at the timing (3) in FIGS. 6 and 7, not all of the coil current is supplied to the battery 3, but circulates in the diode bridge rectifier circuit 13 and returns to the receiving coil 11.

[0056] 6 and 7, the third variable capacitor VC3 in a charged state is discharged, and the first variable capacitor VC1 is charged with a VC1 current that is half the coil current. Also, at the timing (3) in Figures 6 and 7, the fourth variable capacitor VC4 is charged with a VC4 current that is half the coil current, and the second variable capacitor VC2 in a charged state is discharged.

[0057] Timing (4) in Figures 6 and 7 is the timing immediately after the coil current starts to decrease from its negative maximum value. Just before timing (4) in Figure 6, the VC1 current changes from its positive maximum value to zero, and the VC2 current changes from its negative maximum value to zero. Also, just before timing (4) in Figure 6, the VC3 current reaches its negative maximum value, and the VC4 current reaches its positive maximum value. Furthermore, just before timing (4) in Figure 6, the load current changes from zero to half the magnitude of the coil current. In other words, the load current is zero from just before (3) to just before (4) in Figure 6.

[0058] At the timing (4) in Figure 7, the VC1 voltage is equal to the load voltage, and the VC2 voltage is 0. Also, at the timing (4) in Figure 7, the VC3 voltage is decreasing, and the VC4 voltage is increasing.

[0059] 8(4), at timing (4) in FIGS. 6 and 7, the coil current (current A) branches between the third variable capacitor VC3 and the fourth variable capacitor VC4. One branched current (current B) passes through the third variable capacitor VC3, the battery 3, and the second diode D2, and then flows back to the power receiving coil 11. On the other hand, the other branched current (current B) passes through the fourth variable capacitor VC4 and the second diode D2, and then flows back to the power receiving coil 11.

[0060] 6 and 7, the first and second variable capacitors VC1 and VC2 are not charged or discharged, the third variable capacitor VC3, which is in a charged state, is discharged, and the fourth variable capacitor VC4 is charged by a VC4 current that is half the magnitude of the coil current. Also, from (4) to (1) in Fig. 7, the VC1 voltage is maintained at the load voltage, and the VC2 voltage is maintained at 0.

[0061] As described above, the power receiving device 10 of this embodiment includes the first to fourth variable capacitors VC1 to VC4, which are capacitors with adjustable charge amounts, in the diode bridge rectifier circuit 13. In the diode bridge rectifier circuit 13, the first diode D1 and the second diode D2 are connected in series, and the third diode D3 and the fourth diode D4 are connected in series. The third variable capacitor VC3 is connected in parallel with the third diode D3, and the fourth variable capacitor VC4 is connected in parallel with the fourth diode D4. By adjusting the charge amounts of these third and fourth variable capacitors VC3 and VC4, the impedance of the diode bridge rectifier circuit 13 can be adjusted, and the load current can be adjusted.

[0062] Here, the power receiving device 10 includes first and second variable capacitors VC1 and VC2 in addition to third and fourth variable capacitors VC3 and VC4. The first variable capacitor VC1 is connected in parallel with the first diode D1, and the second variable capacitor VC2 is connected in parallel with the second diode D2. Adjusting the charge amounts of the first and second variable capacitors VC1 and VC2 expands the impedance adjustment range of the diode bridge rectifier circuit 13. This allows the load current to be appropriately reduced during constant-voltage charging of the battery 3 in CCCV charging. In particular, since the load current can be arbitrarily reduced to zero, the load current can be appropriately reduced without reducing the output of the power transmitting device 20 using communication or using a DC / DC converter. This eliminates the need for an antenna for communication or an additional coil on the power receiving device 10 side, thereby avoiding increased costs and a larger power receiving device 10.

[0063] Furthermore, the control unit 100 of the power receiving device 10 of this embodiment adjusts the charge amounts of the first to fourth variable capacitors VC1 to VC4, thereby adjusting the impedance of the diode bridge rectifier circuit 13 and adjusting the load current. This makes it possible to arbitrarily adjust the load current without adjusting the output on the power transmitting device 20 side, i.e., without requiring communication with the power transmitting device 20 side.

[0064] Furthermore, the control unit 100 of the power receiving device 10 of this embodiment sets the first to fourth variable capacitors VC1 to VC4 to a state where they cannot be charged, and executes a first current supply process to supply a constant current from the diode bridge rectifier circuit 13 to the battery 3. In this first current supply process, the first to fourth variable capacitors VC1 to VC4 are not charged, thereby minimizing the current circulating to the power receiving coil 11 via the diode bridge rectifier circuit 13. This makes it possible to maximize the load current without adjusting the output of the power transmitting device 20.

[0065] Then, the control unit 100 executes a second current supply process that reduces the load current by setting the first and second variable capacitors VC1 and VC2 to a state where they cannot be charged and the third and fourth variable capacitors VC3 and VC4 to a state where they can be charged. In this second current supply process, the amount of charge in the third and fourth variable capacitors VC3 and VC4 increases, thereby increasing the current circulating to the power receiving coil 11 via the diode bridge rectifier circuit 13. This makes it possible to reduce the load current without adjusting the output of the power transmitting device 20. The second current supply process is suitable for constant-voltage CCCV charging of the battery 3, and this process makes it possible to reduce the load current during constant-voltage charging.

[0066] Furthermore, the control unit 100 executes a third current supply process that sets the first to fourth variable capacitors VC1 to VC4 to a state where they can be charged and further reduces the load current. In this third current supply process, the charge amounts of the first and second variable capacitors VC1 and VC2, as well as the third and fourth variable capacitors VC3 and VC4, are increased, thereby further increasing the current circulating to the power receiving coil 11 via the diode bridge rectifier circuit 13. This allows the load current to be arbitrarily reduced to zero without adjusting the output of the power transmitting device 20. The third current supply process is suitable for the final stage of constant-voltage CCCV charging of the battery 3, and allows the load current to be appropriately reduced to zero during constant-voltage charging of the battery 3.

[0067] Furthermore, the control unit 100 gradually increases the maximum charge amounts of the third and fourth variable capacitors VC3 and VC4 in the second current supply process, i.e., the first stage of constant voltage charging. This allows the impedance of the diode bridge rectifier circuit 13 to be adjusted in stages and the load current to be gradually reduced in the first stage of constant voltage charging of the battery 3. Note that the maximum charge amounts of the third and fourth variable capacitors VC3 and VC4 may also be increased in stages in the second current supply process.

[0068] Furthermore, the control unit 100 gradually increases the maximum charge amounts of the first and second variable capacitors VC1 and VC2 in the third current supply process, i.e., the second stage of constant voltage charging. This allows the impedance of the diode bridge rectifier circuit 13 to be adjusted in stages and the load current to be gradually reduced in the second stage of constant voltage charging of the battery 3. Note that the maximum charge amounts of the first and second variable capacitors VC1 and VC2 may also be increased in stages in the third current supply process.

[0069] Fig. 9 is a diagram showing a contactless power supply system 1' according to another embodiment of the present invention. As shown in this figure, the contactless power supply system 1' includes a power receiving device 110 and a power transmitting device 20. The contactless power supply system 1' of this embodiment is a contactless charging system, and charges a battery 3 as a load. Note that the same components as those in the above embodiment are denoted by the same reference numerals, and the description of the above embodiment is incorporated herein.

[0070] The power receiving device 110 includes an impedance adjustment unit 1131 instead of the impedance adjustment unit 131 of the above embodiment. The impedance adjustment unit 1131 includes a first impedance adjustment unit 1131A and a second impedance adjustment unit 1131B. The first impedance adjustment unit 1131A includes a first capacitor C1, a second capacitor C2, a first switch S1, and a second switch S2. The first capacitor C1 is connected in parallel with the first diode D1, and the second capacitor C2 is connected in parallel with the second diode D2. The second impedance adjustment unit 1131B includes a third capacitor C3, a fourth capacitor C4, a third switch S3, and a fourth switch S4. The third capacitor C3 is connected in parallel with the third diode D3, and the fourth capacitor C4 is connected in parallel with the fourth diode D4. The first to fourth capacitors C1 to C4 are capacitors with fixed (non-adjustable) capacitances.

[0071] The first switch S1 is a switch that connects / disconnects (ON / OFF) the first capacitor C1 to / from the diode bridge rectifier circuit 13. The second switch S2 is a switch that connects / disconnects (ON / OFF) the second capacitor C2 to / from the diode bridge rectifier circuit 13. The third switch S3 is a switch that connects / disconnects (ON / OFF) the third capacitor C3 to / from the diode bridge rectifier circuit 13. The fourth switch S4 is a switch that connects / disconnects (ON / OFF) the fourth capacitor C4 to / from the diode bridge rectifier circuit 13.

[0072] The power receiving device 110 includes a control unit 200 instead of the control unit 100 of the above embodiment. The control unit 200 controls the ON / OFF of the first to fourth switches S1 to S4. In this embodiment, during constant current charging in CCCV charging of the battery 3, the first to fourth switches S1 to S4 are turned OFF, and the charge amounts of the first to fourth capacitors C1 to C4 are adjusted to 0 (lower limit value). On the other hand, during the first stage of constant voltage charging in CCCV charging of the battery 3, the first and second switches S1 and S2 are kept OFF, and the third and fourth switches S3 and S4 are turned ON / OFF. Then, during the second stage of constant voltage charging in CCCV charging of the battery 3, the third and fourth switches S3 and S4 are kept ON, and the first and second switches S1 and S2 are turned ON / OFF. As the charge amounts of the first to fourth capacitors C1 to C4 connected to the diode bridge rectifier circuit 13 increase, the load current decreases.

[0073] Specifically, in the first stage of constant-voltage charging of battery 3 in CCCV charging, the first and second switches S1 and S2 are kept OFF, and the charge amounts of the first and second capacitors C1 and C2 are adjusted to 0 (lower limit). In this first stage, the current and voltage states shown in the waveform diagram of FIG. 3 are first established, and then the ON / OFF of the third and fourth switches S3 and S4 is controlled so that the current and voltage states shown in the waveform diagram of FIG. 5 are established. The current flowing through the third capacitor C3 (hereinafter referred to as the C3 current) corresponds to the VC3 current in FIGS. 3 and 5, and the current flowing through the fourth capacitor C4 (hereinafter referred to as the C4 current) corresponds to the VC4 current in FIGS. 3 and 5. The voltage of the third capacitor C3 (hereinafter referred to as the C3 voltage) corresponds to the VC3 voltage in FIGS. 3 and 5, and the voltage of the fourth capacitor C4 (hereinafter referred to as the C4 voltage) corresponds to the VC4 voltage in FIGS. 3 and 5.

[0074] 3, the third and fourth switches S3 and S4 are ON. During this period, the C3 current changes in a positive direction, and the C3 voltage rises from 0 to the load voltage, increasing the charge amount of the third capacitor C3 (the third capacitor C3 is charged). Also, the C4 current changes in a negative direction, and the C4 voltage drops from the load voltage, decreasing the charge amount of the fourth capacitor C4 (the fourth capacitor C4 is discharged). During this period, half of the coil current is supplied to the battery 3 as the load current, and half of the coil current flows back to the power receiving coil 11 without being supplied to the battery 3.

[0075] 3, the third and fourth switches S3 and S4 are OFF. During this period, the C3 current and C4 current become 0, the C3 voltage is maintained at the load voltage, and the C4 voltage is maintained at 0. In other words, during this period, all of the coil current is supplied to the battery 3 as the load current.

[0076] 3, the third and fourth switches S3 and S4 are ON. During this period, the C3 current changes in the negative direction, and the C3 voltage drops from the load voltage, decreasing the charge amount of the third capacitor C3 (the third capacitor C3 is discharged). Also, the C4 current changes in the positive direction, and the C4 voltage rises from 0 to the load voltage, increasing the charge amount of the fourth capacitor C4 (the fourth capacitor C4 is charged). During this period, half of the coil current is supplied to the battery 3 as the load current, and half of the coil current flows back to the power receiving coil 11 without being supplied to the battery 3.

[0077] 3, the third and fourth switches S3 and S4 are OFF. During this period, the C3 current and C4 current become 0, the C3 voltage is maintained at 0, and the C4 voltage is maintained at the load voltage. In other words, during this period, the entire coil current is supplied to the battery 3 as the load current.

[0078] The current and voltage states shown in the waveform diagram of Fig. 5 are formed by maintaining the third and fourth switches S3, S4 ON. While the current and voltage states shown in the waveform diagram of Fig. 5 are formed, half of the coil current is supplied to the battery 3 as a load current, and half of the coil current flows back to the receiving coil 11 without being supplied to the battery 3.

[0079] In the second stage of constant-voltage charging in CCCV charging of battery 3, first, the ON / OFF of first to fourth switches S1 to S4 is controlled so that the current and voltage states shown in the waveform diagrams of Figures 6 and 7 are formed. Note that the current flowing through first capacitor C1 (hereinafter referred to as C1 current) corresponds to the VC1 current in Figure 6, and the current flowing through second capacitor C2 (hereinafter referred to as C2 current) corresponds to the VC2 current in Figure 6. Also, C3 current corresponds to the VC3 current in Figure 6, and C4 current corresponds to the VC4 current in Figure 6. Also, the voltage of first capacitor C1 (hereinafter referred to as C1 voltage) corresponds to the VC1 voltage in Figure 7, and the voltage of second capacitor C2 (hereinafter referred to as C2 voltage) corresponds to the VC2 voltage in Figure 7. Also, C3 voltage corresponds to the VC3 voltage in Figure 7, and C4 voltage corresponds to the VC4 voltage in Figure 7.

[0080] In the second stage of constant voltage charging in CCCV charging of the battery 3, the third and fourth switches S3 and S4 are maintained ON, while the first and second switches S1 and S2 are turned ON / OFF as described below.

[0081] 6 and 7, the first and second switches S1 and S2 are ON from just before (1) to just before (2). During this period, the C1 current changes in the negative direction, and the C1 voltage drops from the load voltage to 0, thereby decreasing the charge amount of the first capacitor C1 (the first capacitor C1 is discharged). Furthermore, the C2 current changes in the positive direction, and the C2 voltage rises from 0 to the load voltage, thereby increasing the charge amount of the second capacitor C2 (the second capacitor C2 is charged). During this period, the load current becomes 0, and the coil current is not supplied to the battery 3, but instead flows back to the power receiving coil 11.

[0082] 6 and 7, the first and second switches S1 and S2 are OFF. During this period, the C1 current and C2 current become 0, the C1 voltage is maintained at 0, and the C2 voltage is maintained at the load voltage. During this period, half of the coil current is supplied to the battery 3 as the load current, and half of the coil current flows back to the receiving coil 11 without being supplied to the battery 3.

[0083] 6 and 7, the first and second switches S1 and S2 are ON from just before (3) to just before (4). During this period, the C1 current changes in a positive direction, and the C1 voltage rises from 0 to the load voltage, increasing the charge amount of the first capacitor C1 (the first capacitor C1 is charged). Furthermore, the C2 current changes in a negative direction, and the C2 voltage drops from the load voltage to 0, decreasing the charge amount of the second capacitor C2 (the second capacitor C2 is discharged). During this period, the load current becomes 0, and the coil current is not supplied to the battery 3 but entirely flows back to the power receiving coil 11.

[0084] 6 and 7, the first and second switches S1 and S2 are OFF. During this period, the C1 current and C2 current become 0, the C1 voltage is maintained at the load voltage, and the C2 voltage is maintained at 0. During this period, half of the coil current is supplied to the battery 3 as the load current, and half of the coil current flows back to the power receiving coil 11 without being supplied to the battery 3.

[0085] The first to fourth switches S1 to S4 are maintained ON in the final stage of constant voltage charging in CCCV charging of the battery 3. In this final stage, the load current becomes zero, and all of the coil current flows back to the power receiving coil 11 without being supplied to the battery 3.

[0086] As described above, in the power receiving device 110 of this embodiment, the load current can be adjusted arbitrarily, similar to the above embodiment, without providing a variable capacitor in the diode bridge rectifier circuit 13. Therefore, the power receiving device 110 of this embodiment can preferably achieve current control during constant voltage charging when the battery 3 is CCCV charged, with a configuration that is less expensive than the above embodiment that provides a variable capacitor.

[0087] Fig. 10 is a block diagram showing the functions of the control unit 200 shown in Fig. 9. Fig. 11 is a diagram showing the relationship between the switch-on / switch-off signal and the load voltage in the embodiment shown in Fig. 10. As shown in Fig. 10, the control unit 200 includes a voltage detection unit 71, a current detection unit 72, an operational amplifier 73, a charging current setting unit 81, an adder 82, a set capacitor capacitance holding unit 83, a set capacitor capacitance calculation unit 84, a maximum capacitor capacitance setting unit 85, a capacitor capacitance ratio calculation unit 86, a threshold voltage calculation unit 87, a first comparator 88, and a second comparator 89.

[0088] The voltage detection unit 71 is connected in parallel to the battery 3 via, for example, an operational amplifier 73. The voltage detection unit 71 detects the voltage based on the voltage signal differentially output by the operational amplifier 73. The current detection unit 72 is provided between the smoothing capacitor 14 and the anode side of the battery 3, and detects the current flowing from the smoothing capacitor 14 to the battery 3. The current detection unit 72, together with a charging current setting unit 81, is connected to a set capacitor capacity calculation unit 84 via an adder 82. The adder 82 subtracts the output of the charging current setting unit 81 from the output of the current detection unit 72, and outputs the result to the set capacitor capacity calculation unit 84.

[0089] The control unit 200 adjusts the amount of charge stored in the first to fourth capacitors C1 to C4 based on the detected voltage detected by the voltage detection unit 71 and the detected current detected by the current detection unit 72. That is, the control unit 200 adjusts the amount of charge stored in the first to fourth capacitors C1 to C4 in accordance with changes in the charging current of the battery 3. For example, when the charging current of the battery 3 increases, the control unit 200 increases the amount of charge stored in the first to fourth capacitors C1 to C4 relatively, and when the charging current of the battery 3 decreases, the control unit 200 decreases the amount of charge stored in the first to fourth capacitors C1 to C4 relatively. Through this control, the control unit 200 can maintain the input impedance of the impedance adjustment unit 1131 at an optimal value and adjust the charging current as desired. A set of circuits is provided, each circuit comprising the voltage detection unit 71, current detection unit 72, operational amplifier 73, charging current setting unit 81, adder 82, set capacitor capacitance holding unit 83, set capacitor capacitance calculation unit 84, maximum capacitor capacitance setting unit 85, capacitor capacitance ratio calculation unit 86, threshold voltage calculation unit 87, first comparator 88, and second comparator 89. One circuit adjusts the amount of charge stored in the third and fourth capacitors C3 and C4, while the other circuit adjusts the amount of charge stored in the first and second capacitors C1 and C2. The following describes the function of adjusting the amount of charge stored in the third and fourth capacitors C3 and C4, and omits a description of the function of adjusting the amount of charge stored in the first and second capacitors C1 and C2, although both functions are similar.

[0090] The set capacitor capacitance calculation unit 84 is a circuit that calculates the capacitance of the capacitors. For example, the set capacitor capacitance calculation unit 84 calculates the set capacitor capacitances, which are the capacitances of the third and fourth capacitors C3 and C4, so as to reduce the absolute value of the difference between the output value of the adder 82 and the set value of the charging current setting unit 81. Specifically, the set capacitor capacitance calculation unit 84 obtains the previous value of the set capacitor capacitance from the set capacitor capacitance holding unit 83 and performs PID (Proportional Integral Differential) control to increase the set capacitor capacitance from the previous value when the output of the adder 82 is positive and decrease the set capacitor capacitance from the previous value when the output of the adder 82 is negative. The set capacitor capacitance calculation unit 84 is connected to the capacitor capacitance ratio calculation unit 86 and the set capacitor capacitance holding unit 83 and outputs the calculated set capacitor capacitances to the capacitor capacitance ratio calculation unit 86 and the set capacitor capacitance holding unit 83.

[0091] The maximum capacitor capacitance setting unit 85 is a circuit that sets the maximum capacitor capacitance. The maximum capacitor capacitance setting unit 85 stores, for example, the maximum capacitor capacitances of the third and fourth capacitors C3 and C4 in advance. The maximum capacitor capacitance setting unit 85 also stores the capacitances of the first and second capacitors C1 and C2. The maximum capacitor capacitance setting unit 85 is connected to the capacitor capacitance ratio calculation unit 86 and outputs the maximum capacitor capacitances of the third and fourth capacitors C3 and C4 and the capacitances of the first and second capacitors C1 and C2 to the capacitor capacitance ratio calculation unit 86.

[0092] The capacitor capacitance ratio calculation unit 86 is a circuit that calculates the capacitor capacitance ratio. The capacitor capacitance ratio calculation unit 86 calculates the capacitor capacitance ratio of the third and fourth capacitors C3 and C4 based on, for example, the set capacitor capacitance output from the set capacitor capacitance calculation unit 84, the maximum capacitor capacitance of the third and fourth capacitors C3 and C4 output from the maximum capacitor capacitance setting unit 85, and the capacitances of the first and second capacitors C1 and C2. The capacitor capacitance ratio calculation unit 86 is connected to the threshold voltage calculation unit 87 and outputs the calculated capacitor capacitance ratio of the third and fourth capacitors C3 and C4 to the threshold voltage calculation unit 87.

[0093] The threshold voltage calculation unit 87 is a circuit that calculates a first threshold voltage Vth. The threshold voltage calculation unit 87 is connected to the capacitor capacitance ratio calculation unit 86 and the voltage detection unit 71. The capacitor capacitance ratio calculation unit 86 outputs the capacitor capacitance ratio of the third and fourth capacitors C3 and C4, and the voltage detection unit 71 outputs the detected voltage. The threshold voltage calculation unit 87 then calculates a first threshold voltage Vth for the third and fourth capacitors C3 and C4 based on the capacitor capacitance ratio of the third and fourth capacitors C3 and C4 and the detected voltage. Specifically, the set capacitor capacitances of the third and fourth capacitors C3 and C4 are represented by Cp, the maximum capacitor capacitances of the third and fourth capacitors C3 and C4 are represented by Cv, the capacitances of the first and second capacitors C1 and C2 are represented by Cf, and the detected voltage is represented by V. In this case, the capacitance ratio of the third and fourth capacitors C3 and C4 is (Cp-Cf) / Cv, and the target charging voltage V1 of the third and fourth capacitors C3 and C4, i.e., the first threshold voltage Vth, can be calculated using the following equation (1): V1=V×(Cp-Cf) / Cv (1)

[0094] The threshold voltage calculation unit 87 is connected to the first and second comparators 88 and 89, and outputs the first threshold voltage Vth of the third capacitor C3 to the first comparator 88 and outputs the first threshold voltage Vth of the fourth capacitor C4 to the second comparator 89.

[0095] The first and second comparators 88 and 89 are circuits that output the results of comparing two voltages. The first comparator 88 has a first input terminal 88A connected to a threshold voltage calculation unit 87, a second input terminal 88B connected to both sides of the third diode D3 via an operational amplifier 88C, and an output terminal connected to the third switch S3. The first comparator 88 compares the first threshold voltage Vth of the third capacitor C3 output from the threshold voltage calculation unit 87 with the load voltage applied to the third diode D3, and outputs the result (a switch-on signal or a switch-off signal) to the third capacitor C3. For example, as shown in FIG. 10, the first comparator 88 outputs a switch-off signal to the third switch S3 when the load voltage applied to the third diode D3 is equal to or greater than the first threshold voltage Vth of the third capacitor C3. Furthermore, for example, when the load voltage applied to the third diode D3 is less than the first threshold voltage Vth of the third capacitor C3, the first comparator 88 outputs a switch-on signal to the third switch S3.

[0096] The second comparator 89 has a first input terminal 89A connected to the threshold voltage calculation unit 87, a second input terminal 89B connected to both sides of the fourth diode D4, and an output terminal connected to the fourth switch S4. The second comparator 89 compares the first threshold voltage Vth of the fourth capacitor C4 output from the threshold voltage calculation unit 87 with the load voltage applied to the fourth diode D4, and outputs the result to the fourth switch S4. For example, as shown in FIG. 10, the second comparator 89 outputs a switch-off signal to the fourth switch S4 when the load voltage applied to the fourth diode D4 is equal to or greater than the first threshold voltage Vth of the fourth capacitor C4. Furthermore, the second comparator 89 outputs a switch-off signal to the fourth switch S4 when the load voltage applied to the fourth diode D4 is less than the first threshold voltage Vth of the fourth capacitor C4.

[0097] FIG. 12 is a block diagram illustrating a modified example of the function of the control unit 200 shown in FIG. 10. FIG. 13 is a sequence chart illustrating an example of the operation of the third and fourth switches S3 and S4 in the modified example shown in FIG. 12. In the power receiving device 110 shown in FIG. 12, the first comparator 88 controls the third switch S3 based on the load voltage applied to the fourth diode D4 instead of the load voltage applied to the third diode D3. Here, the load voltages applied to the third diode D3 and the fourth diode D4 change symmetrically such that an increase in one load voltage causes a decrease in the other load voltage, and a decrease in one load voltage causes an increase in the other load voltage. By utilizing this symmetric change, both the third and fourth switches S3 and S4 can be controlled based on one of the load voltages. In other words, the power receiving device 110 controls the third and fourth switches S3 and S4 based on the load voltage applied to either the third diode D3 or the fourth diode D4. The power receiving device 110 includes, for example, a calculator 88D that calculates a second threshold voltage Vthu for controlling the third switch S3 based on the load voltage applied to the fourth diode D4. The calculator 88D calculates the first threshold voltage Vth output from the threshold voltage calculation unit 87 from the detected voltage output from the voltage detection unit 71 to calculate the second threshold voltage Vthu (see FIG. 13 ). The calculator 88D outputs the calculated second threshold voltage Vthu to the first comparator 88.

[0098] The first comparator 88 has a first input terminal 88A connected to the connection point between the third diode D3 and the fourth diode D4, a second input terminal 88B connected to a calculator 88D, and an output terminal connected to the third switch S3. The first comparator 88 compares a second threshold voltage Vthu output from the calculator 88D with a load voltage applied to the fourth diode D4, and outputs the result to the third switch S3. For example, as shown in FIG. 13, the first comparator 88 outputs a switch-on signal to the third switch S3 when the load voltage is equal to or greater than the second threshold voltage Vthu (e.g., between times t4 and t5). Furthermore, the first comparator 88 outputs a switch-off signal to the third switch S3 when the load voltage is less than the second threshold voltage Vthu (e.g., between times t1 and t4).

[0099] The second comparator 89 has a first input terminal 89A connected to the threshold voltage calculation unit 87, a second input terminal 89B connected to the connection point between the third diode D3 and the fourth diode D4, and an output terminal connected to the fourth switch S4. The second comparator 89 compares the first threshold voltage Vth of the fourth capacitor C4 output from the threshold voltage calculation unit 87 with the load voltage applied to the fourth diode D4, and outputs the result to the fourth switch S4. For example, as shown in FIG. 13, the second comparator 89 outputs a switch-off signal to the fourth switch S4 when the load voltage is equal to or greater than the first threshold voltage Vth of the fourth capacitor C4 (e.g., between times t3 and t6). Furthermore, the second comparator 89 outputs a switch-on signal to the fourth switch S4 when the load voltage is less than the first threshold voltage Vth of the fourth capacitor C4 (e.g., between times t2 and t3).

[0100] FIG. 14 is a diagram showing a contactless power supply system 1″ according to another embodiment of the present invention. As shown in this figure, the contactless power supply system 1″ includes a power receiving device 10 and a power transmitting device 120. The contactless power supply system 1″ of this embodiment is a contactless charging system, and charges a battery 3 as a load. Note that the same components as those in the above embodiment are denoted by the same reference numerals, and the description of the above embodiment is applicable.

[0101] 14, the power transmitting device 120 includes a capacitor 24, an inductor 25, a voltage sensor 26, a current sensor 27, and a control unit 300 in addition to the configuration of the power transmitting device 20 of the above-described embodiment. The capacitor 24 is connected in parallel with the power transmitting coil 21. The inductor 25 is connected in series with the resonant capacitor 22, and the capacitor 24 is connected between the resonant capacitor 22 and the inductor 25.

[0102] Voltage sensor 26 detects the voltage of capacitor 24 and outputs the detected voltage to control unit 300. Current sensor 27 detects the current between resonant capacitor 22 and inductor 25 and outputs the detected current to control unit 300.

[0103] The control unit 300 includes a phase difference detection unit 301, a transmission power adjustment unit 302, and an inverter control unit 303. The phase difference detection unit 301 receives a detected voltage from the voltage sensor 26 and a detected current from the current sensor 27. The phase difference detection unit 301 calculates the phase difference between the detected voltage, which is the voltage applied to the capacitor 24, and the detected current, which is the current flowing through the resonant capacitor 22. The phase difference detection unit 301 outputs the calculated phase difference to the transmission power adjustment unit 302.

[0104] The transmission power adjusting unit 302 adjusts the transmission power based on the phase difference output from the phase difference detecting unit 301. Specifically, when the phase difference output from the phase difference detecting unit 301 exceeds threshold A (see FIG. 15 ), the transmission power adjusting unit 302 gradually reduces the transmission power until the phase difference falls to threshold A. On the other hand, when the phase difference output from the phase difference detecting unit 301 falls below threshold A, the transmission power adjusting unit 302 gradually increases the transmission power until the phase difference rises to threshold A. The transmission power adjusting unit 302 outputs a signal to adjust the transmission power to the inverter control unit 303. The inverter control unit 303 controls the ON / OFF of the switching elements sw1 to sw4 of the inverter circuit 23 based on the signal output from the transmission power adjusting unit 302.

[0105] In the power receiving device 10, the impedance adjusting unit 131 adjusts the input impedance to the diode bridge rectifier circuit 13 in accordance with the charge requirement of the battery 3, thereby adjusting the charge amount of the battery 3. At this time, the power not consumed in charging the battery 3 is returned to the power receiving coil 11 side. An increase in the amount of this returned power increases the reactive power on the power transmitting device 120 side. Then, the increase in the reactive power on the power transmitting device 120 side increases the phase difference (hereinafter referred to as the voltage-current phase difference) between the detected voltage, which is the voltage applied to the capacitor 24, and the detected current, which is the current flowing through the resonant capacitor 22.

[0106] 15 is a graph showing the relationship between the capacitor capacitance VC of the impedance adjuster 131 of the power receiving device 10 and the voltage-current phase difference of the power transmitting device 120. The capacitor capacitance VC shown in this graph can be calculated by the following equation (2) when the capacitance of the first variable capacitor VC1 is VC1, the capacitance of the second variable capacitor VC2 is VC2, the capacitance of the third variable capacitor VC3 is VC3, and the capacitance of the fourth variable capacitor VC4 is VC4. VC=VC1+VC3 (2) However, VC1=VC2 and VC3=VC4.

[0107] 15, an increase in the capacitor capacitance VC of the impedance adjuster 131 of the power receiving device 10, i.e., an increase or decrease in the amount of power returned to the power receiving coil 11, is reflected in the voltage-current phase difference on the power transmitting device 120 side. Therefore, the control unit 300 of the power transmitting device 120 can transmit power suited to the state of charge on the power receiving device 10 side without needing to communicate with the power receiving device 10 side by adjusting the transmitted power so as to keep the voltage-current phase difference constant.

[0108] Therefore, in the power transmitting device 120 of this embodiment, the phase difference detection unit 301 detects the voltage-current phase difference, and the transmission power adjustment unit 302 adjusts the transmission power via the inverter control unit 303 so that the voltage-current phase difference approaches a certain threshold A. Specifically, as described above, when the voltage-current phase difference exceeds threshold A, the transmission power is gradually reduced until the voltage-current phase difference falls to threshold A. On the other hand, when the voltage-current phase difference falls below threshold A, the transmission power is gradually increased until the voltage-current phase difference rises to threshold A.

[0109] Furthermore, when charging of the battery 3 progresses and the voltage-current phase difference exceeds a certain threshold B (>threshold A) or when the transmitted power falls below a certain threshold C, the transmitted power adjustment unit 302 determines that charging of the battery 3 on the power receiving device 10 side has finished and stops the power transmission. This allows the power transmitting device 120 to detect the charging state of the battery 3 on the power receiving device 10 side and stop the power transmission without the need to communicate with the power receiving device 10 side.

[0110] According to the contactless power supply system 1" of this embodiment, the control unit 300 of the power transmission device 120 can detect the charging state of the battery 3 on the power receiving device 10 side without needing to communicate with the power receiving device 10 side. Therefore, even in a situation where communication from the power receiving device 10 side to the power transmitting device 120 side is not established, charging of the battery 3 can be performed. Therefore, stable charging can be performed regardless of the communication state between the power receiving device 10 side and the power transmitting device 120 side.

[0111] Furthermore, when the charging state of the battery 3 on the power receiving device 10 side is notified to the power transmitting device 120 side through communication, a time lag occurs. However, according to the wireless power supply system 1″ of this embodiment, the time lag can be eliminated, and the operation of the system can be speeded up. Furthermore, the cost of hardware required for communication can be reduced.

[0112] The presence of inductor 25 between the inverter circuit 23 and the voltage measurement points (on both sides of capacitor 24) and the current measurement points (between capacitor 24 and resonant capacitor 22) reduces the effect of noise from inverter circuit 23 on voltage and current measurements, thereby ensuring the accuracy of voltage and current measurements.

[0113] Furthermore, the voltage measurement point and the current measurement point are located between capacitor 24 and resonant capacitor 22, and the high voltage of power transmission coil 21 is divided between capacitor 24 and resonant capacitor 22. This reduces the voltage applied to the measurement circuit when performing measurements using a shunt resistor or the like, reducing the withstand voltage requirements of the components used and leading to lower costs.

[0114] The contactless power supply system 1" of this embodiment may include a power receiving device 110 instead of the power receiving device 10. The filter circuit (capacitor 24, inductor 25) on the power transmitting device 120 side is not essential.

[0115] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and modifications may be made within the scope of the spirit of the present invention, and publicly known or well-known technologies may be combined as appropriate.

[0116] For example, in the above embodiment, the present invention has been described using the contactless power supply systems 1, 1', and 1" as examples. However, the present invention is applicable to any rectifier device in which the input side of the diode bridge rectifier circuit 13 operates as a current source. An example of such a rectifier device is a transformer. In other rectifier devices such as a transformer, the impedance adjustment units 131 and 1131 can be incorporated into the AC-DC converter, and the voltage and current to the load can be controlled in the same way as in the above embodiment.

[0117] In the above embodiment, the first and second switches S1, S2 are turned OFF and the third and fourth switches S3, S4 are controlled ON / OFF during the first stage of constant voltage charging, and the first to fourth switches S1 to S4 are controlled ON / OFF during the second stage of constant voltage charging. However, the third and fourth switches S3, S4 may be turned OFF and the first and second switches S1, S2 are controlled ON / OFF during the first stage of constant voltage charging, and the first to fourth switches S1 to S4 may be controlled ON / OFF during the second stage of constant voltage charging. [Explanation of symbols]

[0118] 1,1',1": Contactless power supply system 3: Battery (load) 10: Power receiving device (rectifier) 11: Receiving coil 13: Diode bridge rectifier circuit 20: Power transmission equipment 21: Transmission coil 23: Inverter circuit (power supply section) 26: Voltage sensor (voltage detection part) 27: Current sensor (current detection section) 100: Control unit 110: Power receiving device (rectifier) 200: Control section 300: Control section 301: Phase difference detection unit 302: Transmission power adjustment section (power adjustment section) C1: First capacitor C2: Second capacitor C3: Third capacitor C4: Fourth capacitor D1: First diode D2: Second diode D3: Third diode D4: Fourth diode S1: First switch (first switch group) S2: Second switch (first switch group) S3: Third switch (second switch group) S4: 4th switch (2nd switch group) VC1: First variable capacitor (first capacitor) VC2: Second variable capacitor (second capacitor) VC3: Third variable capacitor (third capacitor) VC4: Fourth variable capacitor (fourth capacitor)

Claims

1. A rectifier device including a diode bridge rectifier circuit in which a first diode and a second diode are connected in series and a third diode and a fourth diode are connected in series, the rectifier circuit rectifying AC power into DC power and supplying the DC power to a load, The diode bridge rectifier circuit a first capacitor connected in parallel to the first diode and having an adjustable charge amount; a second capacitor connected in parallel to the second diode and having an adjustable charge amount; a third capacitor connected in parallel to the third diode and having an adjustable charge amount; a fourth capacitor connected in parallel to the fourth diode and having an adjustable charge amount; A rectifier comprising:

2. The rectifier according to claim 1 , further comprising a control unit that adjusts the charge amounts of the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor.

3. The control unit a first current supply process of setting the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor to a state in which they cannot be charged and supplying a constant current from the diode bridge rectifier circuit to the load; a second current supply process of reducing a current supplied from the diode bridge rectifier circuit to the load by setting the first capacitor and the second capacitor to a state in which they cannot be charged and setting the third capacitor and the fourth capacitor to a state in which they can be charged; a third current supply process in which the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are brought into a state in which they can be charged, and the current supplied from the diode bridge rectifier circuit to the load is further reduced compared to the second current supply process; The rectifier device according to claim 2 , which executes the following:

4. The control unit The rectifier device according to claim 3 , wherein in the second current supply process, the maximum values of the charge amounts of the third capacitor and the fourth capacitor are increased gradually or stepwise.

5. The control unit The rectifier device according to claim 4 , wherein in the third current supply process, the maximum values of the charge amounts of the first capacitor and the second capacitor are increased gradually or stepwise.

6. The control unit a first switch group that switches on / off the connection between the first capacitor and the second capacitor and the diode bridge rectifier circuit; a second switch group that switches on or off the connection between the third capacitor and the fourth capacitor and the diode bridge rectifier circuit; Equipped with controlling the first switch group based on a load voltage applied to either the first diode or the second diode; 6. The rectifier device according to claim 2, wherein the second group of switches is controlled based on a load voltage applied to either the third diode or the fourth diode.

7. a receiving coil that generates AC power; a diode bridge rectifier circuit in which a first diode and a second diode are connected in series and a third diode and a fourth diode are connected in series, the diode bridge rectifier circuit rectifying AC power generated in the power receiving coil into DC power and supplying the DC power to a load; A power receiving device of a contactless power supply system comprising: The diode bridge rectifier circuit a first capacitor connected in parallel to the first diode and having an adjustable charge amount; a second capacitor connected in parallel to the second diode and having an adjustable charge amount; a third capacitor connected in parallel to the third diode and having an adjustable charge amount; a fourth capacitor connected in parallel to the fourth diode and having an adjustable charge amount; A power receiving device of a contactless power supply system comprising:

8. a transmitting coil that resonates when supplied with AC power; a receiving coil that generates AC power by resonance of the transmitting coil; a diode bridge rectifier circuit in which a first diode and a second diode are connected in series and a third diode and a fourth diode are connected in series, the diode bridge rectifier circuit rectifying AC power generated in the power receiving coil into DC power and supplying the DC power to a load; A contactless power supply system comprising: The diode bridge rectifier circuit a first capacitor connected in parallel to the first diode and having an adjustable charge amount; a second capacitor connected in parallel to the second diode and having an adjustable charge amount; a third capacitor connected in parallel to the third diode and having an adjustable charge amount; a fourth capacitor connected in parallel to the fourth diode and having an adjustable charge amount; A contactless power supply system comprising:

9. a power supply unit that supplies AC power to the power transmitting coil; a voltage detection unit that detects a voltage at a predetermined measurement point of the power supply unit; a current detection unit that detects a current at a predetermined measurement point of the power supply unit; a phase difference detection unit that detects a phase difference between the voltage detected by the voltage detection unit and the current detected by the current detection unit; a power adjustment unit that adjusts the supply power of the power supply unit based on the phase difference detected by the phase difference detection unit; The contactless power supply system according to claim 8 , comprising:

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