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

Abstract

To achieve both impedance adjustment and switching loss reduction functions.SOLUTION: A power receiving device 10 includes: a rectifier circuit 100 including switching elements sw11 to sw14 as rectifier elements; first to fourth impedance adjusting units 111-114 including capacitors C1 to C4 connected in parallel with the switching elements sw11 to sw14 and switching elements S1 to S4 for connecting / disconnecting the capacitors C1 to C4 with / from the rectifier circuit 100 and for adjusting an impedance of the rectifier circuit 100 according to charge amounts of the capacitors C1 to C4; and first to fourth rectification control sections 121 to 124 for maintaining the switching elements sw11 to sw14 OFF when the voltage of the capacitors C1 to C4 is higher than 0, and turning the switching elements sw11 to sw14 ON when the voltage of the capacitors C1 to C4 is equal to or less than 0 and a forward current flows in the switching elements sw11 to sw14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rectifier device, a power receiving device of a non-contact power supply system, and a non-contact power supply system.

Background Art

[0002] As a power receiving device of a non-contact power supply system, there is known one that rectifies AC power generated in a power receiving coil into DC power and supplies it to a load unit (for example, see Patent Documents 1 to 3). In the power receiving devices described in Patent Documents 1 and 2, variable capacitance capacitors are connected in parallel to two of the four diodes of 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 capacitance capacitor. Further, in the power receiving device described in Patent Document 3, instead of the above variable capacitance capacitor, a fixed capacitor and a switching element connected in series to this fixed capacitor are provided. In this power receiving device, impedance adjustment of the power receiving device is performed by turning on / off the switching element.

[0003] Also, as a power receiving device of a non-contact power supply system, there is known one that rectifies AC power into DC by a full-bridge type synchronous rectifier circuit including a MOS-FET (Metal Oxide Semiconductor Field-Effect Transistor) as a rectifying element (for example, see Patent Document 4). In the synchronous rectifier circuit described in Patent Document 4, switching loss can be reduced by turning on the MOS-FET when a forward current flows through the body diode of the MOS-FET. >

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] This paper examines a rectifier circuit that incorporates both impedance adjustment and synchronous rectification functions. In this rectifier circuit, if a voltage remains in the capacitor used for impedance adjustment and the MOS-FET is turned ON, the capacitor will discharge, hindering the impedance adjustment function. Therefore, this rectifier circuit requires measures to achieve both impedance adjustment and switching loss reduction.

[0006] In view of the above circumstances, the present invention aims to provide a rectifier, a power receiving device for a contactless power supply system, and a contactless power supply system that can achieve both impedance adjustment and switching loss reduction functions. [Means for solving the problem]

[0007] The rectifier of the present invention comprises a rectifier circuit that converts AC power to DC power, with a first switching element as the rectifier element; a capacitor connected in parallel with the first switching element; a second switching element that connects / disconnects the capacitor to the rectifier circuit; an impedance adjustment unit that adjusts the impedance of the rectifier circuit according to the charge amount of the capacitor; and a rectifier control unit that keeps the first switching element OFF when the voltage of the capacitor is higher than 0, and turns the first switching element ON when the voltage of the capacitor is 0 or less and a forward current flows through the first switching element.

[0008] The power receiving device of the contactless power supply system of the present invention comprises a power receiving coil that generates AC power, a rectifier circuit that includes a first switching element as a rectifier element and converts the AC power generated by the power receiving coil into DC power, a capacitor connected in parallel with the first switching element, a second switching element that connects / disconnects the capacitor to the rectifier circuit, an impedance adjustment unit that adjusts the impedance of the rectifier circuit according to the charge amount of the capacitor, and a rectifier control unit that keeps the first switching element OFF when the voltage of the capacitor is higher than 0, and turns the first switching element ON when the voltage of the capacitor is 0 or less and a forward current flows through the first switching element.

[0009] The contactless power supply system of the present invention comprises a power transmission coil that resonates when AC power is supplied to it, a power receiving coil that generates AC power due to the resonance of the power transmission coil, a rectifier circuit that converts the AC power generated in the power receiving coil into DC power, with a first switching element as a rectifier element, a capacitor connected in parallel with the first switching element, a second switching element that connects / disconnects the capacitor to the rectifier circuit, an impedance adjustment unit that adjusts the impedance of the rectifier circuit according to the charge amount of the capacitor, and a rectifier control unit that keeps the first switching element OFF when the voltage of the capacitor is higher than 0, and turns the first switching element ON when the voltage of the capacitor is 0 or less and a forward current flows through the first switching element. [Effects of the Invention]

[0010] According to the present invention, it is possible to achieve both impedance adjustment and switching loss reduction functions. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows a contactless power supply system according to one embodiment of the present invention. [Figure 2]FIG. 2 is a graph showing the relationships between the load current [A], charging power [kW], and power supply voltage [V] during constant-voltage charging of the battery and the capacitance [μF] of the first to fourth capacitors. [Figure 3] FIG. 3 is a block diagram showing the functions of the control unit shown in FIG. 1. [Figure 4] FIG. 4 is a diagram showing the relationship between the ON / OFF signals of the switching elements of the first and second impedance adjustment units and the load voltage. [Figure 5] FIG. 5 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 6] FIG. 6 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 7] FIG. 7 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 8] FIG. 8 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 9] FIG. 9 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 10] FIG. 10 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 11] FIG. 11 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 12] FIG. 12 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 13] FIG. 13 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit. [Figure 14] FIG. 14 is a circuit diagram for explaining the operation of the synchronous rectification control executed by the first rectification control unit.

MODE FOR CARRYING OUT THE INVENTION

[0012] Hereinafter, the present invention will be described in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be appropriately modified without departing from the gist of the present invention. Further, in the embodiments shown below, there are some places where the illustration and description of some configurations are omitted. Regarding the details of the omitted technology, publicly known or well-known technologies are appropriately applied within the range where there is no contradiction with the content described below.

[0013] FIG. 1 is a diagram showing a non-contact power supply system 1 according to an embodiment of the present invention. As shown in this figure, the non-contact power supply system 1 includes a power receiving device 10 and a power transmitting device 20. The non-contact power supply system 1 of the present embodiment is a non-contact charging system and charges a battery 3 as a load.

[0014] The power transmitting device 20 includes a power transmitting coil 21, a resonance 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 and off switching elements sw1 to sw4, and supplies it to the power transmitting coil 21 and the resonance capacitor 22. The power transmitting coil 21 and the resonance capacitor 22 are connected in series to form a resonance circuit.

[0015] The power receiving device 10 includes a power receiving coil 11, a resonance capacitor 12, a current sensor 13, a smoothing capacitor 1, a current sensor 15, a voltage sensor 16, a rectifier circuit 100, and a control unit 200. The power receiving coil 11 and the resonance capacitor 12 are connected in series to form a resonance circuit. The power receiving coil 11 is arranged to face the power transmitting coil 21.

[0016] 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 links 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.

[0017] The current sensor 13 is a resistance-detection type or magnetic field-detection type current sensor installed between the power receiving coil 11 and the rectifier circuit 100, and detects the current value of the alternating current between the power receiving coil 11 and the rectifier circuit 100. Here, the current sensor 13 has the function of detecting the direction of the current between the power receiving coil 11 and the rectifier circuit 100 from the positive or negative sign of the detected current value. In the following description, the direction of the current flowing from the rectifier circuit 100 through the current sensor 13 to the power receiving coil 11 is considered the positive direction, and the direction of the current flowing from the power receiving coil 11 through the current sensor 13 to the rectifier circuit 100 is considered the negative direction.

[0018] When the current sensor 13 detects a current flowing in the positive direction, it outputs a High level to AND gates &1 and &4, which will be described later. On the other hand, when the current sensor 13 detects a current flowing in the negative direction, it outputs a High level to AND gates &2 and &3, which will be described later.

[0019] The smoothing capacitor 14 is connected in parallel with the battery 3 and constitutes a smoothing circuit. This smoothing capacitor 14 smooths the pulsating current flowing from the rectifier circuit 100 to the battery 3.

[0020] The current sensor 15 detects the current value of the DC current supplied to the battery 3 and outputs it to the control unit 200. The voltage sensor 16 also detects the voltage value of the battery 3 (hereinafter referred to as the load voltage) and outputs it to the control unit 200.

[0021] The rectifier circuit 100 is a full-bridge rectifier circuit (full-wave rectifier circuit) and comprises first to fourth rectifier sections 101 to 104. The first rectifier section 101 comprises a switching element sw11, a first impedance adjustment section 111, and a first rectifier control section 121. The second rectifier section 102 comprises a switching element sw12, a second impedance adjustment section 112, and a second rectifier control section 122. The third rectifier section 103 comprises a switching element sw13, a third impedance adjustment section 113, and a third rectifier control section 123. Furthermore, the fourth rectifier section 104 comprises a switching element sw14, a fourth impedance adjustment section 114, and a fourth rectifier control section 124.

[0022] Switching elements sw11 and sw12 are connected in series, and switching elements sw13 and sw14 are connected in series. Switching elements sw11 and sw12, which are connected in series, and switching elements sw13 and sw14, which are connected in series, are connected in parallel. One end 11A of the power receiving coil 11 is connected between switching elements sw11 and sw12 via a resonant capacitor 12. On the other hand, the other end 11B of the power receiving coil 11 is connected between switching elements sw13 and sw14.

[0023] The switching elements sw11 to sw14 are power semiconductors such as MOS-FETs and IGBTs (Insulated Gate Bipolar Transistors), and are equipped with body diodes. When a forward current flows through the body diodes of the switching elements sw11 to sw14 while they are OFF, a voltage drop occurs across the body diodes, resulting in power loss equivalent to the product of the voltage drop and the current. Therefore, the power receiving device 10 of this embodiment is equipped with a synchronous rectification function, described later, to reduce power loss in the rectifier circuit 100.

[0024] The rectifier circuit 100 converts the AC power output from the receiving coil 11 into DC power and supplies it to the battery 3. When the battery 3 is charged with a constant current, the current output from one end 11A of the receiving coil 11 flows sequentially through the resonant capacitor 12, the switching element sw11, the battery 3, and the switching element sw14, and returns to the other end 11B of the receiving coil 11. On the other hand, when the battery 3 is charged with a constant current, the current output from the other end 11B of the receiving coil 11 flows sequentially through the switching element sw13, the battery 3, the switching element sw12, and the resonant capacitor 12, and returns to the one end 11A of the receiving coil 11.

[0025] The first impedance adjustment unit 111 includes a capacitor C1 and a switching element S1. Capacitor C1 is connected in parallel with the switching element sw11, and capacitor C1 and switching element S1 are connected in series. The second impedance adjustment unit 112 includes a capacitor C2 and a switching element S2. Capacitor C2 is connected in parallel with the switching element sw12, and capacitor C2 and switching element S2 are connected in series. The third impedance adjustment unit 113 includes a capacitor C3 and a switching element S3. Capacitor C3 is connected in parallel with the switching element sw13, and capacitor C3 and switching element S3 are connected in series. Furthermore, the fourth impedance adjustment unit 114 includes a capacitor C4 and a switching element S4. Capacitor C4 is connected in parallel with the switching element sw14, and capacitor C4 and switching element S4 are connected in series.

[0026] Capacitors C1 to C4 are capacitors with fixed (non-adjustable) capacitance. Switching elements S1 to S4 are power semiconductors such as MOS-FETs and IGBTs, and are equipped with body diodes. Switching element S1 connects / disconnects (ON / OFF) capacitor C1 to the rectifier circuit 100. Switching element S2 connects / disconnects (ON / OFF) capacitor C2 to the rectifier circuit 100. Switching element S3 connects / disconnects (ON / OFF) capacitor C3 to the rectifier circuit 100. Furthermore, switching element S4 connects / disconnects (ON / OFF) capacitor C4 to the rectifier circuit 100.

[0027] The first rectifier control unit 121 comprises a comparator Cp1, an AND circuit &1, and a driver 121D. The second rectifier control unit 122 comprises a comparator Cp2, an AND circuit &2, and a driver 122D. The third rectifier control unit 123 comprises a comparator Cp3, an AND circuit &3, and a driver 123D. Furthermore, the fourth rectifier control unit 124 comprises a comparator Cp4, an AND circuit &4, and a driver 124D.

[0028] The + input terminals of comparators Cp1 to Cp4 are connected between capacitors C1 to C4 and switching elements S1 to S4, respectively, while the - input terminals of comparators Cp1 to Cp4 are connected between capacitors C1 to C4 and battery 3 or power receiving coil 11, respectively. Furthermore, the output terminals of comparators Cp1 to Cp4 are connected to input terminal A of AND gates &1 to &4, respectively.

[0029] Comparators Cp1 to Cp4 output a Low level to input terminal A of AND gates &1 to &4, respectively, when the input voltage of the + input terminal is higher than the input voltage of the - input terminal. On the other hand, comparators Cp1 to Cp4 output a High level to input terminal A of AND gates &1 to &4, respectively, when the input voltage of the + input terminal is lower than the input voltage of the - input terminal.

[0030] The input terminal B of AND gates &1 to &4 is connected to the current sensor 13. The output terminals of AND gates &1 to &4 are connected to drivers 121D to 124D, respectively. AND gates &1 to &4 output a high level to drivers 121D to 124D when a high level is input from both comparators Cp1 to Cp4 and the current sensor 13. On the other hand, AND gates &1 to &4 output a low level to drivers 121D to 124D when a low level is input from at least one of comparators Cp1 to Cp4 and the current sensor 13.

[0031] Drivers 121D to 124D control the ON / OFF state of switching elements sw11 to sw14 according to the output of AND gates &1 to &4, respectively. Specifically, drivers 121D to 124D turn on switching elements sw11 to sw14 when a High level is input from AND gates &1 to &4, respectively. On the other hand, drivers 121D to 124D turn off switching elements sw11 to sw14 when a Low level is input from AND gates &1 to &4, respectively.

[0032] The control unit 200 adjusts the charge amount of capacitors C1 to C4 by controlling the ON / OFF state of switching elements S1 to S4 of the first to fourth impedance adjustment units 111 to 114. Specifically, during constant current charging, the control unit 200 turns off switching elements S1 to S4 to adjust the charge amount of capacitors C1 to C4 to 0 (lower limit). At this time, the output current of the power receiving coil 11 (hereinafter referred to as coil current) is supplied entirely to the battery 3. Furthermore, if the load voltage detected by the voltage sensor 16 rises above a predetermined value as the charge rate of the battery 3 increases, the control unit 200 turns on switching elements S1 to S4 to increase the charge amount of capacitors C1 to C4. In other words, when the load voltage rises above a predetermined value, the control unit 200 switches the charging mode of the battery 3 from constant current charging to constant voltage charging.

[0033] Figure 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 capacitors C1 to C4 during constant voltage charging of battery 3. The load current [A] shown in this graph is the average value of the charging current supplied to 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 transmission device 20.

[0034] In this graph, the point at which the capacitance [μF] of capacitors C1 to C4 is 0 [μF] corresponds to the point at which the charging mode of battery 3 transitions from constant current charging to constant voltage charging. Furthermore, in this graph, the point at which the capacitance [μF] of capacitors C1 to C4 is 1.2 [μF] corresponds to the end of constant voltage charging of battery 3 (the end of CCCV (Constant Current, Constant Voltage) charging). Note that the maximum value of 1.2 [μF] for the capacitance [μF] of capacitors C1 to C4 is just an example; this maximum value can be set as appropriate.

[0035] As shown in this graph, during constant voltage charging of battery 3, the control unit 200 first gradually increases the capacitance [μF] of capacitors C3 and C4 of the third and fourth impedance adjustment units 113 and 114 from 0 [μF] to the 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 of the value during constant current charging of battery 3. Also, the charging power [kW] gradually decreases from the value during constant current charging of battery 3 to half of the value during constant current charging of battery 3 as the load current [A] decreases. Note that during constant voltage charging of battery 3, the power supply voltage [V] is constant, and the voltage of the power transmission device 20 is not controlled.

[0036] From the middle of the constant-voltage charging of battery 3 until the end of the constant-voltage charging, the control unit 200 gradually increases the capacitance [μF] of capacitors C1 and C2 of the first and second impedance adjustment units 111 and 112 from 0 [μF] to the maximum value (1.2 [μF]). During this time, the load current [A] gradually decreases from half the value during constant-current charging of battery 3 to 0 [A]. Also, the charging power [kW] gradually decreases from half the value during constant-current charging of battery 3 to 0 [kW] as the load current [A] decreases.

[0037] Figure 3 is a block diagram showing the functions of the control unit 200 shown in Figure 1. Figure 4 is a diagram showing the relationship between the ON / OFF signals of the switching elements S1 and S2 of the first and second impedance adjustment units 111 and 112 and the load voltage. As shown in Figure 3, the control unit 200 includes a voltage detection unit 201, a current detection unit 202, an operational amplifier 203, a charging current setting unit 211, and an adder 212. The control unit 200 also includes a set capacitor capacity holding unit 213, a set capacitor capacity calculation unit 214, a maximum capacitor capacity setting unit 215, a capacitor capacity ratio calculation unit 216, a threshold voltage calculation unit 217, a plurality of first comparators 218, and a second comparator 219.

[0038] The voltage detection unit 201 is connected in parallel to the battery 3 via an operational amplifier 203. The voltage detection unit 201 detects the voltage of the battery 3 based on the voltage signal output from the operational amplifier 203, which is a differential amplifier circuit. The current detection unit 202 is connected between the smoothing capacitor 14 and the positive terminal side of the battery 3 and detects the current flowing from the smoothing capacitor 14 to the battery 3. The current detection unit 202 is connected to the set capacitor capacity calculation unit 214 via an adder 212 together with the charging current setting unit 211. The adder 212 subtracts the output of the charging current setting unit 211 from the output of the current detection unit 202 and outputs the result to the set capacitor capacity calculation unit 214.

[0039] The control unit 200 adjusts the amount of charge charged to capacitors C1 to C4 based on the detected voltage detected by the voltage detection unit 201 and the detected current detected by the current detection unit 202. That is, the control unit 200 adjusts the amount of charge charged to capacitors C1 to C4 in accordance with the change in the charging current of the battery 3. For example, if the charging current of the battery 3 increases, the control unit 200 relatively increases the amount of charge charged to capacitors C1 to C4, and if the charging current of the battery 3 decreases, it relatively decreases the amount of charge charged to capacitors C1 to C4. Through this control, the control unit 200 can maintain the impedance of the rectifier circuit 100 at an optimal value and arbitrarily adjust the charging current.

[0040] The control unit 200 is provided with a set of circuits consisting of the voltage detection unit 201, current detection unit 202, operational amplifier 203, charging current setting unit 211, adder 212, set capacitor capacity holding unit 213, set capacitor capacity calculation unit 214, maximum capacitor capacity setting unit 215, capacitor capacity ratio calculation unit 216, threshold voltage calculation unit 217, first comparator 218, and second comparator 219. One circuit implements the function of adjusting the amount of charge charged to capacitors C1 and C2 of the first and second impedance adjustment units 111 and 112. The other circuit implements the function of adjusting the amount of charge charged to capacitors C3 and C4 of the third and fourth impedance adjustment units 113 and 114. The following describes the function of adjusting the amount of charge charged to capacitors C1 and C2 of the first and second impedance adjustment units 111 and 112. Although the explanation of the function of adjusting the amount of charge charged to capacitors C3 and C4 in the third and fourth impedance adjustment units 113 and 114 is omitted, both functions are the same.

[0041] The set capacitor capacity calculation unit 214 is a circuit that calculates the capacities of capacitors C1 and C2. The set capacitor capacity calculation unit 214 calculates the set capacitor capacity, which is the capacity of capacitors C1 and C2, by, for example, reducing the absolute value of the difference between the output value of the adder 212 and the set value of the charging current setting unit 211. Specifically, the set capacitor capacity calculation unit 214 obtains the previous value of the set capacitor capacity from the set capacitor capacity retention unit 213, and performs PID (Proportional Integral Differential) control, increasing the set capacitor capacity from the previous value when the output of the adder 212 is positive, and decreasing the set capacitor capacity from the previous value when the output of the adder 212 is negative. The set capacitor capacity calculation unit 214 is connected to the capacitor capacity ratio calculation unit 216 and the set capacitor capacity retention unit 213, and outputs the calculated set capacitor capacity to the capacitor capacity ratio calculation unit 216 and the set capacitor capacity retention unit 213.

[0042] The maximum capacitor capacity setting unit 215 is a circuit that sets the maximum capacitor capacity. The maximum capacitor capacity setting unit 215 pre-stores, for example, the maximum capacitor capacities of capacitors C1 and C2. The maximum capacitor capacity setting unit 215 also stores the capacities of capacitors C3 and C4. The maximum capacitor capacity setting unit 215 is connected to the capacitor capacity ratio calculation unit 216 and outputs the maximum capacitor capacities of capacitors C1 and C2, and the capacities of capacitors C3 and C4 to the capacitor capacity ratio calculation unit 216.

[0043] The capacitor capacitance ratio calculation unit 216 is a circuit that calculates the capacitor capacitance ratio. For example, the capacitor capacitance ratio calculation unit 216 calculates the capacitor capacitance ratio of capacitors C1 and C2 based on the set capacitor capacitance output from the set capacitor capacitance calculation unit 214, the maximum capacitor capacitances of capacitors C1 and C2 output from the maximum capacitor capacitance setting unit 215, and the capacitances of capacitors C3 and C4. The capacitor capacitance ratio calculation unit 216 is connected to the threshold voltage calculation unit 217 and outputs the calculated capacitor capacitance ratio of capacitors C1 and C2 to the threshold voltage calculation unit 217.

[0044] The threshold voltage calculation unit 217 is a circuit that calculates the threshold voltage Vth. The threshold voltage calculation unit 217 is connected to the capacitor capacitance ratio calculation unit 216 and the voltage detection unit 201. The capacitor capacitance ratio calculation unit 216 outputs the capacitor capacitance ratio of capacitors C1 and C2, and the voltage detection unit 201 outputs the detected voltage. The threshold voltage calculation unit 217 then calculates the threshold voltage Vth of capacitors C1 and C2 based on the capacitor capacitance ratio of capacitors C1 and C2 and the detected voltage. Specifically, let Cq be the set capacitor capacitance of capacitors C1 and C2, Cv be the maximum capacitor capacitance of capacitors C1 and C2, Cf be the capacitance of capacitors C3 and C4, and V be the detected voltage. In this case, the capacitor capacitance ratio of capacitors C1 and C2 is (Cq-Cf) / Cv, and the target charging voltage of capacitors C1 and C2, i.e., the threshold voltage Vth, can be obtained by the following equation (1). Vth = V × (Cq - Cf) / Cv ... (1)

[0045] The threshold voltage calculation unit 217 is connected to the first and second comparators 218 and 219, outputting the threshold voltage Vth of capacitor C1 to the first comparator 218 and the threshold voltage Vth of capacitor C2 to the second comparator 219.

[0046] The first and second comparators 218 and 219 are circuits that compare two voltages and output either a High or Low level. The first comparator 218 has its first input terminal 218A connected to the threshold voltage calculation unit 217, its second input terminal 218B connected to both sides of the switching element sw11 via the operational amplifier 218C, and its output terminal connected to the switching element S1. The first comparator 218 compares the threshold voltage Vth of the capacitor C1 output from the threshold voltage calculation unit 217 with the voltage V1 applied to the switching element sw11, and outputs an ON signal (High level) or an OFF signal (Low level) to the switching element S1.

[0047] The first comparator 218 outputs an OFF signal to the switching element S1 when the voltage V1 applied to the switching element sw11 (see Figure 5) is greater than or equal to the threshold voltage Vth of the capacitor C1, as shown in Figure 4. The first comparator 218 also outputs an ON signal to the switching element S1 when the voltage V1 applied to the switching element sw11 is less than the threshold voltage Vth of the capacitor C1.

[0048] The second comparator 219 has its first input terminal 219A connected to the threshold voltage calculation unit 217, its second input terminal 219B connected to both sides of the switching element sw12, and its output terminal connected to the switching element S2. The second comparator 219 compares the threshold voltage Vth of the capacitor C2 output from the threshold voltage calculation unit 217 with the voltage V1 applied to the switching element sw12, and outputs an ON signal or an OFF signal to the switching element S2. For example, as shown in Figure 4, the second comparator 219 outputs an OFF signal to the switching element S2 if the voltage V1 applied to the switching element sw12 is greater than or equal to the threshold voltage Vth of the capacitor C2. Also, for example, the second comparator 219 outputs an OFF signal to the switching element S2 if the voltage V1 applied to the switching element sw12 is less than the threshold voltage Vth of the capacitor C2.

[0049] As described above, the power receiving device 10 of this embodiment is equipped with an impedance adjustment function that adjusts the impedance of the rectifier circuit 100 in addition to the synchronous rectification function for adjusting the load current. However, if the corresponding switching elements sw11 to sw14 are turned ON while voltage remains in capacitors C1 to C4, discharge occurs from capacitors C1 to C4, impairing the effectiveness of the impedance adjustment function. Therefore, the power receiving device 10 of this embodiment is equipped with first to fourth rectifier control units 121 to 124 for the purpose of achieving both the synchronous rectification function and the impedance adjustment function. The operation of the synchronous rectification control performed by the first to fourth rectifier control units 121 to 124 will be described below.

[0050] Figures 5 to 13 are circuit diagrams illustrating the operation of synchronous rectification control performed by the first rectification control unit 121. Although the operation of synchronous rectification control performed by the first rectification control unit 121 is used as an example for explanation, the operation of synchronous rectification control performed by the second to fourth rectification control units 122 to 124 is similar.

[0051] Figure 5 shows the state of the first rectifier unit 101 when the voltage Vc across capacitor C1 rises to the threshold voltage Vth due to the execution of the impedance control function. The case in which rectification by the rectifier circuit 100 (see Figure 1) starts from this state will be explained. In this state, both the switching element sw11 and the switching element S1 of the first impedance adjustment unit 111 are OFF.

[0052] Figure 6 shows the state of the first rectifier section 101 when rectification of the rectifier circuit 100 begins from the state shown in Figure 5, and current is flowing through the first rectifier section 101 and the fourth rectifier section 104 (see Figure 1). As shown in this figure, the current passing through the first rectifier section 101 passes through the body diode and capacitor C1 of the switching element S1 of the first impedance adjustment section 111. At this time, the capacitor C1 discharges, and the voltage Vc of the capacitor C1 decreases. Also, the output from the current sensor 13 to the AND circuit &1 is at a high level, the output from the comparator Cp1 to the AND circuit &1 is at a low level, and the output from the AND circuit &1 to the driver 121D is at a low level.

[0053] Figure 7 shows the state of the first rectifier 101 when the load voltage V1 applied to the switching element sw11 drops below the threshold voltage Vth of the capacitor C1. As shown in this figure, when the load voltage V1 applied to the switching element sw11 drops below the threshold voltage Vth of the capacitor C1, the switching element S1 turns ON. In this state, the capacitor C1 is connected by the switching element S1 with a small ON resistance, and the current passing through the first rectifier 101 passes through the switching element S1 and the capacitor C1 of the first impedance adjustment unit 111. During this time, the discharge of the capacitor C1 continues. Also, the output from the current sensor 13 to the AND circuit &1 is at a high level, the output from the comparator Cp1 to the AND circuit &1 is at a low level, and the output from the AND circuit &1 to the driver 121D is at a low level.

[0054] Figure 8 shows the state of the first rectifier 101 when the discharge of capacitor C1 has progressed further from the state shown in Figure 7, and the voltage Vc of capacitor C1 has dropped to the forward voltage drop -Vf of the body diode of switching element sw11. In this state, the discharge of capacitor C1 stops, and the current passing through the first rectifier 101 passes through the body diode of switching element sw11. At this time, the output from current sensor 13 to AND circuit &1 is at a high level, the output from comparator Cp1 to AND circuit &1 is at a low level, and the output from AND circuit &1 to driver 121D is at a low level.

[0055] Figure 9 shows the state of the first rectifier section 101 when synchronous rectification is initiated. During the transition from the state shown in Figure 7 to the state shown in Figure 8, the polarity of the voltage applied to capacitor C1 reverses, causing the output of comparator Cp1 to change from a low level to a high level. At this time, both inputs of AND circuit &1 become high levels, and the output from AND circuit &1 to driver 121D becomes high level. As a result, the switching element sw11 turns ON, and the first rectifier section 101 is connected with a small ON resistance.

[0056] Figure 10 shows the state of the first rectifier 101 when synchronous rectification is maintained. In this state, similar to the state shown in Figure 9, the first rectifier 101 is connected by a switching element sw11 with a small ON resistance. In this state, a small voltage drop Vf occurs in the switching element sw11 due to its small ON resistance. At this time, since both ends of the capacitor C1 are connected to the switching element sw11, the voltage Vc across the capacitor C1 becomes a slightly negative voltage equal to the voltage drop Vf across the switching element sw11. The output from the current sensor 13 to the AND circuit &1, the output from the comparator Cp1 to the AND circuit &1, and the output from the AND circuit &1 to the driver 121D are all maintained at a high level.

[0057] Figure 11 shows the state of the first rectifier unit 101 at the point when rectification of the rectifier circuit 100, through which the current passes via the first rectifier unit 101 and the fourth rectifier unit 104, is completed. In this state, the output from the current sensor 13 to the AND circuit &1 becomes low, and the output from the AND circuit &1 to the driver 121D also becomes low. As a result, the switching element sw11 turns OFF, and the synchronous rectification of the first rectifier unit 101 is completed. The output from the comparator Cp1 to the AND circuit &1 is maintained at a high level.

[0058] Figure 12 shows the state of the first rectifier unit 101 at the start of rectification in the rectifier circuit 100, where the current passes through the second rectifier unit 102 and the third rectifier unit 103. In this state, a portion of the current flowing through the rectifier circuit 100 flows back into the first rectifier unit 101, charging the capacitor C1. At this time, the output from the current sensor 13 to the AND circuit &1 and the output from the AND circuit &1 to the driver 121D are maintained at a low level. In addition, the output from the comparator Cp1 to the AND circuit &1 is maintained at a high level.

[0059] Figure 13 shows the state of the first rectifier 101 when the charging of capacitor C1 has progressed from the state shown in Figure 12, and the voltage Vc of capacitor C1 has become 0 or greater. In this state, the output of the first comparator Cp1 changes to a low level. The output from the current sensor 13 to the AND circuit &1 and the output from the AND circuit &1 to the driver 121D are maintained at a low level.

[0060] Figure 14 shows the state of the first rectifier unit 101 when the charging of capacitor C1 has progressed further from the state shown in Figure 13, and the voltage Vc of capacitor C1 has reached or exceeded the threshold voltage Vth. In this state, the switching element S1 is turned OFF by the control of the first impedance adjustment unit 111 of the control unit 200. At this time, the reverse flow of current to the first rectifier unit 101 stops, and the voltage Vc of capacitor C1 is maintained at the threshold voltage Vth. From this state, the system transitions to the state shown in Figure 5, and the transitions between the states shown in Figures 5 to 14 are repeated.

[0061] As described above, the power receiving device 10 of this embodiment comprises a rectifier circuit 100, first to fourth impedance adjustment units 111 to 114 that realize an impedance adjustment function, and first to fourth rectification control units 121 to 124 that realize a synchronous rectification function. The rectifier elements of the rectifier circuit 100 are switching elements sw11 to sw14, which are power semiconductors that perform switching such as MOSFETs and IGBTs, and are equipped with body diodes through which forward current flows. In contrast, the first to fourth impedance adjustment units 111 to 114 each comprise capacitors C1 to C4 connected in parallel with the switching elements sw11 to sw14, and switching elements S1 to S4 provided corresponding to the capacitors C1 to C4. The switching elements S1 to S4 are power semiconductors that perform switching such as MOSFETs and IGBTs, and connect / disconnect the capacitors C1 to C4 to the rectifier circuit 100. The ON / OFF state of the switching elements S1 to S4 adjusts the charge levels of capacitors C1 to C4, and the impedance of the rectifier circuit 100 is adjusted according to the charge levels of capacitors C1 to C4.

[0062] In this case, when the voltage across capacitors C1 to C4 is higher than zero, the synchronous rectification function is executed and switching elements sw11 to sw14 are turned ON, causing capacitors C1 to C4 to discharge. This impairs the impedance adjustment function of the rectifier circuit 100. In contrast, in the power receiving device 10 of this embodiment, the first to fourth rectification control units 121 to 124 each keep the switching elements sw11 to sw14, which are rectifier elements, OFF when the voltage across capacitors C1 to C4 is higher than zero. On the other hand, the first to fourth rectification control units 121 to 124 each turn on the switching elements sw11 to sw14 when the voltage across capacitors C1 to C4 is zero or less and forward current flows through the body diodes of the switching elements sw11 to sw14. This prevents the impedance adjustment function from being impaired by the execution of the synchronous rectification function.

[0063] Furthermore, the first to fourth rectifier control units 121 to 124 of this embodiment each include comparators Cp1 to Cp4 and AND circuits &1 to &4, and each includes a common current sensor 13. Comparators Cp1 to Cp4 output a Low level when the voltage of capacitors C1 to C4 is higher than 0, and output a High level when the voltage of capacitors C1 to C4 is 0 or less. The current sensor 13 outputs a High level to comparators Cp1 to Cp4 corresponding to switching elements S1 to S4 through which forward current flows. In response, AND circuits &1 to &4 each output a High level to drivers 121D to 124D when a High level is input from both comparators Cp1 to Cp4 and the current sensor 13. Drivers 121D to 124D each turn on switching elements sw11 to sw14 when a High level is input from AND circuits &1 to &4. This allows the switching elements sw11 to sw14, which are rectifier elements, to remain OFF when the voltage across capacitors C1 to C4 is higher than 0. On the other hand, when the voltage across capacitors C1 to C4 is 0 or less and forward current flows through the body diodes of the switching elements sw11 to sw14, the switching elements sw11 to sw14 can be turned ON.

[0064] Furthermore, the rectifier circuit 100 in this embodiment is a full-wave rectifier circuit equipped with switching elements sw11 to sw14 as rectifier elements, and the current sensor 13 determines which two of the AND gates (AND gates &1 to &4) are the destination of the high-level output according to the direction of the current flowing through the rectifier circuit 100. As a result, synchronous rectification control of the switching elements sw11 to sw14, which are rectifier elements, can be performed in the rectifier circuit 100, which is a full-wave rectifier circuit, and the effect of reducing switching losses can be realized.

[0065] Furthermore, the rectifier circuit 100 of this embodiment is equipped with a total of four impedance adjustment units (first to fourth impedance adjustment units 111 to 114), corresponding to each of the switching elements sw11 to sw14, which are rectifier elements. In other words, the first to fourth impedance adjustment units 111 to 114 are provided for all of the rectifier elements of the rectifier circuit 100. This allows for a wide range of impedance adjustment of the rectifier circuit 100. Consequently, the load current can be appropriately reduced during constant voltage charging when charging the battery 3 with a CCCV. In particular, since the load current can be arbitrarily reduced to 0, the load current can be appropriately reduced without using communication to reduce the output on the power transmission device 20 side or using a DC / DC converter. Therefore, an antenna for communication and additional coils on the power receiving device 10 side are not required, thus avoiding increased costs and the need to enlarge the power receiving device 10.

[0066] Although the present invention has been described above based on embodiments, the present invention is not limited to the above embodiments, and modifications may be made, or publicly known or well-known technologies may be combined as appropriate, without departing from the spirit of the present invention.

[0067] For example, in the above embodiment, the present invention was described using the contactless power supply system 1 as an example, but the present invention is applicable to any rectifier device in which the input side of the rectifier circuit 100 operates as a current source. A transformer can be an example of such a rectifier device. In other rectifier devices such as transformers, the first to fourth impedance adjustment units 111 to 114 and the first to fourth rectifier control units 121 to 124 can be incorporated into an AC-DC converter, and the voltage and current to the load can be controlled in the same manner as in the above embodiment.

[0068] Furthermore, although the present invention was described using a rectifier circuit 100, which is a full-wave rectifier circuit, as an example in the above embodiment, the present invention is also applicable to a half-wave rectifier circuit (half-bridge rectifier circuit). Moreover, in the above embodiment, the present invention was described using a rectifier circuit 100 that includes switching elements sw11 to sw14, which are switching elements equipped with body diodes through which forward current flows, as an example. However, the present invention is also applicable to a rectifier circuit that includes a rectifier element in which a diode through which forward current flows and a switching element are connected in parallel. [Explanation of Symbols]

[0069] 1: Contactless power supply system 10: Power receiving device (rectifier) 11: Power receiving coil 13: Current Sensor 20: Power transmission equipment 21: Power transmission coil 100: Rectifier circuit 111: First impedance adjustment section (impedance adjustment section) 112: Second impedance adjustment section (impedance adjustment section) 113: Third impedance adjustment section (impedance adjustment section) 114: Fourth impedance adjustment section (impedance adjustment section) 121: First rectifier control unit (rectifier control unit) 122: Second rectifier control unit (rectifier control unit) 123: Third Rectifier Control Unit (Rectifier Control Unit) 124: Fourth Rectification Control Unit (Rectification Control Unit) 121D: Driver (drive unit) 122D: Driver (drive unit) 123D: Driver (drive unit) 124D: Driver (drive unit) C1: Capacitor C2: Capacitor C3: Capacitor C4: Capacitor Cp1: Comparator Cp2: Comparator Cp3: Comparator Cp4: Comparator S1: Switching element (second switching element) S2: Switching element (second switching element) S3: Switching element (second switching element) S4: Switching element (second switching element) sw11: Switching element (first switching element) sw12: Switching element (first switching element) sw13: Switching element (first switching element) sw14: Switching element (first switching element) &1: AND circuit &2: AND circuit &3: AND circuit &4: AND circuit

Claims

1. A rectifier circuit is provided, which uses a first switching element as a rectifier element to convert AC power to DC power, The impedance adjustment unit comprises a capacitor connected in parallel with the first switching element, and a second switching element that connects / disconnects the capacitor to the rectifier circuit, and adjusts the impedance of the rectifier circuit according to the charge amount of the capacitor. A rectifier control unit that keeps the first switching element OFF when the voltage of the capacitor is higher than 0, and turns the first switching element ON when the voltage of the capacitor is 0 or less and a forward current flows through the first switching element. A rectifier equipped with the following features.

2. The rectifier control unit, A comparator that outputs a first signal when the voltage of the capacitor is greater than zero, and outputs a second signal when the voltage of the capacitor is zero or less, A current sensor that outputs a third signal when the forward current flows through the first switching element, An AND circuit outputs a fourth signal to the drive unit of the first switching element, which turns on the first switching element when the second signal is input from the comparator and the third signal is input from the current sensor. The rectifier according to claim 1, comprising:

3. The rectifier circuit is a full-wave rectifier circuit comprising four of the first switching elements as the rectifier elements, The system comprises a plurality of impedance adjustment units and a plurality of rectification control units, The rectifier according to claim 2, wherein the current sensor determines the AND circuit to which the third signal is output according to the direction of the current flowing through the rectifier circuit.

4. The rectifier according to claim 3, comprising four impedance adjustment units provided corresponding to the four first switching elements.

5. A receiving coil that generates AC power, A rectifier circuit comprising a first switching element as a rectifier element, which converts AC power generated by the power receiving coil into DC power, The impedance adjustment unit comprises a capacitor connected in parallel with the first switching element, and a second switching element that connects / disconnects the capacitor to the rectifier circuit, and adjusts the impedance of the rectifier circuit according to the charge amount of the capacitor. A rectifier control unit that keeps the first switching element OFF when the voltage of the capacitor is higher than 0, and turns the first switching element ON when the voltage of the capacitor is 0 or less and a forward current flows through the first switching element. A power receiving device for a contactless power supply system.

6. A power transmission coil that resonates when AC power is supplied, A receiving coil that generates AC power due to the resonance of the aforementioned transmitting coil, A rectifier circuit comprising a first switching element as a rectifier element, which converts AC power generated by the power receiving coil into DC power, The impedance adjustment unit comprises a capacitor connected in parallel with the first switching element, and a second switching element that connects / disconnects the capacitor to the rectifier circuit, and adjusts the impedance of the rectifier circuit according to the charge amount of the capacitor. A rectifier control unit that keeps the first switching element OFF when the voltage of the capacitor is higher than 0, and turns the first switching element ON when the voltage of the capacitor is 0 or less and a forward current flows through the first switching element. A contactless power supply system equipped with the following features.

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