JP7139857B2 - WIRELESS POWER RECEIVING DEVICE AND WIRELESS POWER TRANSMISSION SYSTEM USING THE SAME - Google Patents

Description

The present invention relates to a wireless power receiving device that receives power wirelessly transmitted from a power transmission side, and a wireless power transmission system using the same.

In recent years, wireless power transmission technology has attracted attention as a technology for charging rechargeable batteries of electric vehicles. In this wireless power transmission technology, there is a problem that the power transmission efficiency decreases due to changes in impedance that occur according to the state of the load. In order to solve this problem, for example, Patent Document 1 detects the impedance of the charging section, selects the bridge rectifier circuit when the detected impedance is relatively low, and selects a bridge rectifier circuit when the detected impedance reaches a relatively high value. In such a case, it has been proposed to suppress the decrease in power transmission efficiency by selecting a voltage doubler rectifier circuit.

However, in the technology disclosed in Patent Document 1, hardware such as a switch that switches between the bridge rectifier circuit and the voltage doubler rectifier circuit, a detection unit that detects impedance related to the charging unit, and a control circuit that controls on/off of the switch is required. necessary. In particular, when a large amount of power is handled, a large-sized switch is required, which raises the problem of high cost and securing installation space. In terms of software, an active control algorithm is required to detect the impedance of the load and control the on/off timing of the switch, which complicates the system.

By the way, in a wireless power transmission system, an abnormality such as an overvoltage may occur on the power receiving side during power transmission, and it is known to mount a protection circuit to protect circuit elements from such an abnormality. For example, Patent Document 2 proposes a protection circuit using a switching element that protects a rectifier circuit from overvoltage. The protection circuit disclosed in Patent Document 2 has a switching element and a rectifying element connected between the output section of the power receiving side resonant circuit and the output section of the rectifying circuit. When the value of the output voltage exceeds a preset reference voltage value, the switching element is operated to short-circuit the circuit and protect the circuit element from overvoltage.

WO2013/136409 WO2016/159093

When the protection circuit of Patent Document 2 is applied to the wireless power transmission system of Patent Document 1, it is possible to prevent a decrease in power transmission efficiency due to a change in impedance and to protect circuit elements constituting a rectifier circuit and the like from overvoltage. is possible.

However, simply incorporating a protection circuit in a wireless power receiving device that combines a bridge rectifier circuit and a voltage doubler rectifier circuit may cause excessive current to flow through the switching elements that make up the protection circuit, depending on the operation timing of the protection circuit. can cause problems with flow. A method of selecting an element that can withstand an excessively large current is also conceivable, but in that case, there is a possibility that it will lead to an increase in the size and cost of the device. Therefore, there is a demand for a technique for suppressing excessive current flow to the elements forming the protection circuit without increasing the size and cost of the device.

The present invention has been made in view of the above circumstances. An object of the present invention is to provide a power transmission system.

In order to solve the above problems, the wireless power receiving device according to the present invention includes a power receiving unit including a power receiving coil, a first diode having an anode connected to one output terminal of the power receiving unit, and a cathode connected to the one output terminal. a third diode having an anode connected to the other output terminal of the power receiving unit; a fourth diode having a cathode connected to the other output terminal; and a fourth diode connected in parallel, respectively, a rectifier circuit for converting AC power received by the power receiving coil into DC power, and the other output terminal of the power receiving unit. and a protection circuit including a first switching element connected between the rectifier circuit and the output terminal of the rectifier circuit; and the first and a control circuit for controlling the on/off operation of the switching element.

According to the present invention, it is possible to prevent excessive current from flowing through the first switching element or the like that forms the protection circuit while protecting the circuit elements that form the rectifier circuit or the like when an overvoltage occurs. , the circuit elements themselves constituting the protection circuit can be protected.

In the present invention, the protection circuit further includes a second switching element connected between the one output terminal of the power receiving unit and the output terminal of the rectifier circuit, and the control circuit controls the output terminal of the rectifier circuit. It is preferable to control on/off operations of the first and second switching elements based on the output voltage and the voltage across the terminals of the first or second capacitor. According to this configuration, it is possible to quickly protect the circuit elements forming the protection circuit.

In the present invention, the protection circuit is connected between the other output terminal of the power receiving unit and the first switching element, or between the first switching element and the output terminal of the rectifier circuit. It is preferable to further include a first rectifying element. According to this configuration, it is possible to prevent the operation of the wireless power receiving device from becoming unstable due to the influence of the parasitic capacitance of the first switching element of the protection circuit during normal operation when the protection circuit is not operating.

In the present invention, the protection circuit is connected between the other output terminal of the power receiving unit and the first switching element, or between the first switching element and the output terminal of the rectifier circuit. and the one output terminal of the power receiving unit and the second switching element, or between the second switching element and the output terminal of the rectifier circuit It is preferable to further include a second rectifying element. According to this configuration, it is possible to prevent the operation of the wireless power receiving device from becoming unstable due to the influence of the parasitic capacitance of the first and second switching elements of the protection circuit during normal operation when the protection circuit is not operating. can.

In the present invention, the protection circuit includes: a first rectifying element connected between the other output terminal of the power receiving unit and the first switching element; a second rectifying element connected between the first switching element, the first switching element being connected to the other output terminal via the first rectifying element, It is preferable to connect to said one output terminal through said 2nd rectifying element. According to this configuration, it is possible to prevent the operation of the wireless power receiving device from becoming unstable due to the influence of the parasitic capacitance of the first switching element of the protection circuit during normal operation when the protection circuit is not operating. In addition, since the protection circuit is constructed using a single switching element, it is possible to reduce costs and stabilize control.

In the present invention, the first switching element is a first field effect transistor, the second switching element is a second field effect transistor, and the fourth diode is the first electric field transistor. Preferably, it is a parasitic diode of an effect transistor and said second diode is a parasitic diode of said second field effect transistor. According to this configuration, some elements of the rectifier circuit can be shared with the protection circuit, and an independent protection circuit can be omitted to achieve size reduction and cost reduction.

The present invention further comprises a first voltage detection circuit that detects the output voltage of the rectifier circuit, and a second voltage detection circuit that detects the voltage across the terminals of the first capacitor or the second capacitor. , The control circuit preferably controls the ON/OFF operation of the first switching element based on detection results of the first voltage detection circuit and the second voltage detection circuit. According to this configuration, the on/off operation of the first switching element can be controlled based on the output voltage of the rectifier circuit and the voltage across the terminals of the first or second capacitor.

In the present invention, the second voltage detection circuit is configured to detect a voltage between terminals of the second capacitor, and the control circuit detects the voltage detected by the first voltage detection circuit as a first voltage. Preferably, the first switching element is turned on when the threshold voltage is exceeded and the voltage detected by the second voltage detection circuit is below the second threshold voltage. According to this configuration, it is possible to further suppress an excessive current flowing to the elements forming the protection circuit.

In the present invention, it is preferable that the second threshold voltage is set based on the rated current of the first switching element. With this configuration, it is possible to further suppress an excessive current flowing to the elements forming the protection circuit.

In the present invention, the second voltage detection circuit is configured to detect a voltage across terminals of the first capacitor, and the control circuit detects the voltage detected by the first voltage detection circuit as a first voltage. Preferably, the first switching element is turned on when the threshold voltage is exceeded and the voltage detected by the second voltage detection circuit exceeds a third threshold voltage. According to this configuration, it is possible to further suppress an excessive current flowing to the elements forming the protection circuit.

In the present invention, it is preferable that the third threshold voltage is set based on the rated current of the first switching element. With this configuration, it is possible to further suppress an excessive current flowing to the elements forming the protection circuit.

In the present invention, it is preferable that the control circuit outputs a power transmission stop signal instructing to stop the power transmission operation when the voltage detected by the first voltage detection circuit exceeds a first threshold voltage. According to this configuration, the elements forming the protection circuit can be quickly protected.

The wireless power receiving device according to the present invention further includes a first voltage detection circuit that detects an output voltage of the rectifier circuit, and a second voltage detection circuit that detects a voltage across terminals of the second capacitor, When the voltage detected by the first voltage detection circuit exceeds a first threshold voltage, the control circuit turns on the second switching element and detects the voltage detected by the first voltage detection circuit. Preferably, the first switching element is turned on when the first threshold voltage is exceeded and the voltage detected by the second voltage detection circuit is below the second threshold voltage. By turning on the second switching element immediately after detecting the overvoltage of the output voltage, the rise of the output voltage is mitigated even when the first and second capacitors are operating as a voltage doubler circuit. In addition, when the current load is released, a path for discharging the charge of the second capacitor can be secured to facilitate discharge. Therefore, the voltage across the terminals of the second capacitor can be immediately lowered.

The wireless power receiving device according to the present invention further includes: a first voltage detection circuit that detects an output voltage of the rectifier circuit; and a second voltage detection circuit that detects a voltage between terminals of the first capacitor, When the voltage detected by the first voltage detection circuit exceeds a first threshold voltage, the control circuit turns on the second switching element and detects the voltage detected by the first voltage detection circuit. It is also preferable to turn on the first switching element when the first threshold voltage is exceeded and the voltage detected by the second voltage detection circuit exceeds a third threshold voltage. By turning on the second switching element immediately after detecting the overvoltage of the output voltage, the rise of the output voltage is mitigated even when the first and second capacitors are operating as a voltage doubler circuit. In addition, when the current load is released, a path for discharging the charge of the second capacitor can be secured to facilitate discharge. Therefore, the voltage across the terminals of the second capacitor can be immediately lowered.

When the frequency of the AC power is f and the maximum resistance value of the load is _RLmax , the capacitance C1 of the _first capacitor and the capacitance C2 of the _second capacitor are C1, _{C 2} <1/(2fR _Lmax ) is preferably satisfied. According to this, the rectifier circuit can be operated as a bridge rectifier circuit or a voltage doubler rectifier circuit, and the rectifier circuit operates as a bridge rectifier circuit in accordance with a change in the impedance of the load connected to the output of the rectifier circuit. It is possible to passively change the duty ratio between the rectification mode and the voltage doubler rectification mode operating as a voltage doubler rectifier circuit. That is, the operation time in the bridge rectification mode can be lengthened when the load impedance is low, and the operation time in the voltage doubler rectification mode can be lengthened when the load impedance is high. Therefore, it is possible to suppress variations in the impedance of the load viewed from the input side of the rectifier without separately providing an impedance converter that requires active control.

It is preferable that the capacitance C ₁ of the first capacitor and the capacitance C ₂ of the second capacitor satisfy 1/(80×2fR _Lmax )<C ₁ , C ₂ . According to this configuration, the upper limit value of the duty ratio of the voltage doubler rectification mode to the half cycle of the AC power input to the rectifier circuit can be made larger than 10%. Therefore, the two modes can be operated at an appropriate duty ratio within the load impedance variation range, and the effect of suppressing load impedance variation can be further enhanced.

The wireless power receiving device according to the present invention preferably further includes a smoothing capacitor connected in parallel to the output terminal of the rectifier circuit, and a choke coil provided between the output terminal of the rectifier circuit and the smoothing capacitor. . According to this configuration, it is possible to suppress excessive current flow to the circuit elements that constitute the protection circuit.

In the wireless power receiving device according to the present invention, between a connection point between the anode of the third diode and the cathode of the fourth diode and a connection point between the first switching element and the output terminal of the rectifier circuit, Preferably, it further comprises an inductor element provided. According to this configuration, overcurrent when the first switching element is turned on can be mitigated, and damage to the switching element can be prevented.

Further, a wireless power transmission system according to the present invention includes a wireless power transmission device and the above-described wireless power reception device according to the present invention, wherein the wireless power transmission device includes an inverter that converts DC power into AC power, and an inverter that receives the AC power. a power transmission unit that includes a power transmission coil that generates an alternating magnetic field with a power transmission unit; a current detection circuit that detects a current output from the inverter; and a power transmission control circuit that controls the operation of the inverter, wherein the power transmission control circuit The operation of the inverter is stopped when the current detected by the current detection circuit exceeds a threshold current.

According to the present invention, it is possible to prevent excessive current from flowing through the first switching element or the like that forms the protection circuit while protecting the circuit elements that form the rectifier circuit or the like when an overvoltage occurs. , the circuit elements themselves constituting the protection circuit can be protected. In addition, since the wireless power transmission device detects an abnormality and stops the power transmission operation, it is possible to more quickly protect the elements forming the protection circuit on the wireless power reception device side.

According to the present invention, it is possible to provide a wireless power receiving device and a wireless power transmission system that are capable of protecting the circuit elements that make up the device and also protecting the circuit elements themselves that make up the protection circuit when an overvoltage occurs. can.

FIG. 1 is an overall circuit diagram of a wireless power transmission system according to a first embodiment of the invention. 2A and 2B are diagrams for explaining the operation of the protection circuit 25. FIG. FIGS. 3A and 3B are diagrams for explaining the actions of the diodes D5 and D6. FIG. 4 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage _vC2 across the terminals of the second capacitor Cd2, and the control signal SG1 output from the control circuit . 5A and 5B are explanatory diagrams of the bridge rectification mode of the rectifier circuit 23. FIG. 6A and 6B are explanatory diagrams of the voltage doubler rectification mode of the rectifier circuit 23. FIG. FIG. 7 is a graph showing an example of temporal changes in the power transmission efficiency of the bridge rectifier circuit and the voltage doubler rectifier circuit. FIG. 8 is an equivalent circuit diagram of the rectifier circuit 23. As shown in FIG. FIG. 9 is a waveform diagram showing input and output currents of the rectifier circuit 23. As shown in FIG. 10A and 10B are equivalent circuit diagrams, where (a) shows an equivalent circuit in the bridge rectification operation mode and (b) shows an equivalent circuit in the voltage doubler rectification operation mode. FIG. 11 is a waveform diagram showing the input voltage v _rect of the rectifier circuit 23. As shown in FIG. FIGS. 12A and 12B are waveform diagrams showing the input voltage v _rect depending on the position of the mode switching point. Each shows the case where the timing is fast (D is small). FIG. 13 is a graph showing the relationship between the load impedance |Z _ac | viewed from the input side of the rectifier circuit 23 and the actual load impedance R _L . FIG. 14 is a circuit diagram showing the configuration of the wireless power receiving device according to the second embodiment. FIG. 15 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage _vC1 across the terminals of the first capacitor Cd1, and the control signal SG1 output from the control circuit . FIG. 16 is a circuit diagram showing the configuration of the wireless power receiving device according to the third embodiment. FIG. 17 is a circuit diagram showing the configuration of the wireless power receiving device according to the fourth embodiment. FIG. 18 is a circuit diagram showing the configuration of the wireless power receiving device according to the fifth embodiment. FIG. 19 is a circuit diagram showing the configuration of a wireless power receiving device according to the sixth embodiment of the invention. FIG. 20 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage vC2 across the terminals of the second capacitor Cd2, and the control signals _SG11 and S12 output from the control circuit . FIG. 21 is a circuit diagram showing the configuration of a wireless power receiving device according to the seventh embodiment of the invention. FIG. 22 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage vC1 across the terminals of the first capacitor Cd1, and the control signals _SG11 and S12 output from the control circuit . FIG. 23 is a circuit diagram showing the configuration of the wireless power receiving device according to the eighth embodiment of the invention.

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is an overall circuit diagram of a wireless power transmission system according to a first embodiment of the invention.

As shown in FIG. 1 , the wireless power transmission system 1 includes a combination of a wireless power transmission device 10 and a wireless power reception device 20 and wirelessly transmits power from the wireless power transmission device 10 to the wireless power reception device 20 .

The wireless power transmission device 10 includes an inverter 12 that converts DC power supplied from a DC power supply 11 into AC power, and a power transmission unit 13 that receives AC voltage and generates magnetic flux. The inverter 12 is a full-bridge switching circuit in which four switching elements SW11 to SW14 are bridge-connected. For example, MOSFETs can be used for the switching elements SW11 to SW14. The on/off operations of the switching elements SW11 to SW14 are controlled by switching control signals supplied from the power transmission control circuit 15, and by controlling the on/off of the switching elements SW11 to SW14, DC power is converted into AC power of 100 KHz, for example.

The power transmission unit 13 has a power transmission coil L1 and capacitors C11 and C12. The power transmission coil L1 is, for example, a planar coil or a solenoid coil configured using a litz wire or a single wire obtained by twisting a plurality of thin conductor wires. The power transmission coil L1 constitutes an LC resonance circuit together with the capacitors C11 and C12. The capacitors C11 and C12 are ceramic capacitors, for example, and have the function of adjusting the resonance frequency of the LC resonance circuit. In this embodiment, the capacitors C11 and C12 are connected in series to one end and the other end of the power transmission coil L1, respectively, but at least one of the capacitors C11 and C12 may be connected in parallel with the power transmission coil L1, or the capacitor C11 may be connected in parallel. , C12 may be omitted. The power transmission coil L1 of the power transmission unit 13 configured in this manner receives AC power supplied from the inverter 12 and generates an AC magnetic field.

The wireless power transmission device 10 according to this embodiment also includes a current detection circuit 14 that detects the current output from the inverter 12 . The current detection circuit 14 outputs an abnormality detection signal when an overcurrent exceeding a threshold is detected, and the abnormality detection signal is supplied to the power transmission control circuit 15 . When the abnormality detection signal is input, the power transmission control circuit 15 stops the switching operations of the four switching elements SW11 to SW14 that constitute the inverter. can. In addition, since the wireless power transmission device 10 detects an abnormality and stops the power transmission operation, it is possible to more quickly protect the elements constituting the protection circuit in the wireless power reception device 20, which will be described later.

Next, the wireless power receiving device 20 will be described. The wireless power receiving device 20 includes a power receiving unit 21 that takes in AC power via a magnetic field generated by a power transmission coil L1, a rectifier circuit 23 that converts the AC power received by the power receiving unit 21 into DC power, and the rectifier circuit 23 from overvoltage. a protection circuit 25 for protection; a first voltage detection circuit 26 for monitoring the output voltage of the rectifier circuit 23; A second voltage detection circuit 27 monitors the voltage at the other input terminal P2 of the rectifier circuit 23, and the operation of the protection circuit 25 is controlled based on the detection results of the first and second voltage detection circuits 26 and 27. and a control circuit 28 .

The power receiving unit 21 has a power receiving coil L2 and capacitors C21 and C22. The power receiving unit 21 can be configured similarly to the power transmitting unit 13 , and may have the same configuration as the power transmitting unit 13 or a different configuration from the power transmitting unit 13 . The power receiving coil L2 generates AC power by magnetically coupling with the power transmitting coil L1 of the power transmitting unit 13 .

The rectifier circuit 23 includes four bridge-connected diodes D1 to D4 and capacitors Cd1 and Cd2 connected in parallel to the diodes D3 and D4, respectively. The diodes D1 to D4 form a full bridge rectifier circuit. Although the details will be described later, the capacitors Cd1 and Cd2 constitute a voltage doubler rectifier circuit together with the diodes D1 and D2.

The anode of the diode D1 and the cathode of the diode D2 form one input terminal P1 of the rectifier circuit 23 and are connected to one output terminal of the power receiving unit 21 . The anode of the diode D3 and the cathode of the diode D4 constitute the other input terminal P2 of the rectifier circuit 23 and are connected to the other output terminal of the power receiving unit 21 . The cathodes of the diodes D1 and D3 form one output terminal P3 of the rectifier circuit 23, and the anodes of the diodes D2 and D4 form the other output terminal P4 of the rectifier circuit 23. FIG. When the other output end P4 of the rectifier circuit 23 is grounded, the one output end P3 becomes the plus side output end, and the other output end P4 becomes the minus side output end. A smoothing capacitor Cs is connected in parallel between the pair of output terminals P3 and P4 of the rectifier circuit 23 . A battery, for example, is connected as a load 30 between the pair of output terminals P3 and P4 of the rectifier circuit 23, and is charged with power received by the wireless power receiving device 20. FIG.

The protection circuit 25 has two switching elements SW21, SW22 and two diodes D5, D6. The switching element SW21 (first switching element) is provided between the other input terminal P2 of the rectifier circuit 23 (the other output terminal of the power receiving unit 21) and the other output terminal P4 of the rectifier circuit 23, and performs switching. The element SW22 (second switching element) is provided between one input terminal P1 of the rectifier circuit 23 (one output terminal of the power receiving unit 21) and the other output terminal P4 of the rectifier circuit 23. FIG. On/off operations of the switching elements SW21 and SW22 are controlled by a control signal SG1 from the control circuit .

The diode D5 (first rectifying element) is connected in series with the switching element SW21. The anode of the diode D5 is the other input terminal P2 of the rectifying circuit 23 (the other output terminal of the power receiving unit 21), and the cathode is the rectifying element. It is connected so as to face the other output terminal P4 side of the circuit 23 . That is, the diode D5 is forward-connected toward the other output terminal P4 of the rectifier circuit 23 . In this embodiment, the diode D5 is provided closer to the input end of the rectifier circuit 23 than the switching element SW21 is, but it may be provided closer to the output end of the rectifier circuit 23 .

The diode D6 (second rectifying element) is connected in series with the switching element SW22, the anode of the diode D6 is one input terminal P1 (one output terminal of the power receiving unit 21) of the rectifying circuit 23, and the cathode is rectifying. It is connected so as to face the other output terminal P4 side of the circuit 23 . That is, the diode D6 is forward-connected toward the other output terminal P4 of the rectifier circuit 23. As shown in FIG. In this embodiment, the diode D6 is provided closer to the input end of the rectifier circuit 23 than the switching element SW22 is, but it may be provided closer to the output end of the rectifier circuit 23 .

The first voltage detection circuit 26 is a circuit that monitors the output voltage of the rectifier circuit 23. When the output voltage of the rectifier circuit 23 exceeds a predetermined threshold voltage (first threshold voltage), the first detection signal SGa is detected. to output The first threshold voltage is set based on the rated voltage of the circuit elements forming the rectifier circuit 23 . The second voltage detection circuit 27 is a circuit for monitoring the voltage across the terminals of the second capacitor Cd2, and detects a second detection signal when the voltage across the terminals of the capacitor Cd2 falls below a predetermined threshold voltage (second threshold voltage). Output SGb. The second threshold voltage is set based on the rated current of the first switching element SW21.

The control circuit 28 outputs the control signal SG1 when both the first detection signal and the second detection signal are active. As a result, both the switching elements SW21 and SW22 are turned on, and the input terminals P1 and P2 and the output terminal P4 of the rectifier circuit 23 are short-circuited. Therefore, circuit elements such as the diodes D1 to D4 that constitute the rectifier circuit 23 can be protected from overvoltage. Further, the control circuit 28 outputs the power transmission stop signal SG2 at least when the first detection signal is active. The power transmission stop signal SG2 is wirelessly transmitted to the wireless power transmission device 10 side, and the power transmission control circuit 15 of the wireless power transmission device 10 that receives the power transmission stop signal SG2 stops the operation of the switching elements SW11 to SW14. can prevent the operation of the system and enhance the safety of the system.

2A and 2B are diagrams for explaining the operation of the protection circuit 25. FIG. 3(a) and 3(b) are diagrams for explaining the action of the diodes D5 and D6.

As shown in FIG. 2A, when the switching elements SW21 and SW22 of the protection circuit 25 are off, the protection circuit 25 can be ignored. Therefore, when the rectifier circuit 23 operates in a bridge rectification mode, which will be described later, one current path from one input terminal P1 of the rectifier circuit 23 to the other input terminal P2 passes through the diode D1, the load 30, and the diode D4 in this order. It becomes a return path to The other current path from the other input terminal P2 of the rectifier circuit 23 to the one input terminal P1 is a feedback path that passes through the diode D3, the load 30, and the diode D2 in this order. At this time, no current flows through the switching elements SW21 and SW22 of the protection circuit 25 due to the action of the diodes D5 and D6.

As shown in FIG. 2B, when the switching elements SW21 and SW22 of the protection circuit 25 are on, the current path of the protection circuit 25 is prioritized. Therefore, one current path from one input terminal P1 of the rectifier circuit 23 to the other input terminal P2 is a feedback path that sequentially passes through the diode D6, the switching element SW22, and the diode D4. The other current path from the other input terminal P2 of the rectifier circuit 23 to the one input terminal P1 is a feedback path that passes through the diode D5, the switching element SW21, and the diode D2 in this order. In other words, since no current flows through the load 30, the rectifier circuit 23 and the circuit elements forming the subsequent circuits can be protected from overvoltage.

Here, as shown in FIG. 3A, when the protection circuit 25 is not provided with the diodes D5 and D6 and the switching elements SW21 and SW22 have parasitic capacitance, even if the switching elements SW21 and SW22 are A current flows through the parasitic capacitance of the switching elements SW21 and SW22 even in the OFF state. That is, the current supplied from the power receiving unit 21 flows not only through the rectifier circuit 23 but also through the path that returns to the power receiving unit 21 via the switching elements SW21 and SW22, thereby generating reactive power and degrading the power factor. do.

However, as shown in FIG. 3B, when the diodes D5 and D6 are provided, even if the switching elements SW21 and SW22 have parasitic capacitance, the current path through the switching elements SW21 and SW22 is completely cut off, which is equivalent to an open circuit, and parasitic capacitance is no longer discharged. Therefore, it is possible to suppress the generation of reactive power due to the parasitic capacitance of the switching elements SW21 and SW22.

The protection circuit 25 is a circuit that short-circuits the input terminal of the rectifier circuit 23 and the negative output terminal of the rectifier circuit 23 when the output voltage of the rectifier circuit 23 is extremely high, thereby preventing damage to circuit elements constituting the rectifier circuit 23 and the like. The output voltage of the rectifier circuit 23 is monitored, and when overvoltage is detected, the switching elements SW21 and SW22 are turned on to prevent overvoltage. Here, the voltage across the terminals of the capacitor Cd2 connected in parallel with the switching element SW21 is an AC voltage, and the peak level of the voltage across the terminals of the capacitor Cd2 becomes very high when the voltage is overvoltage. If the switching element SW21 is turned on at such a timing when the peak level is high, an excessive current may flow through the switching element SW21 and damage it. Therefore, in the present embodiment, on/off control of the switching elements SW21 and SW22 of the protection circuit 25 is performed based on both the output voltage Vo of the rectifier circuit 23 and the voltage _vC2 across the terminals of the capacitor Cd2.

FIG. 4 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage _vC2 across the terminals of the second capacitor Cd2, and the control signal SG1 output from the control circuit .

As shown in FIG. 4, the output voltage Vo of the rectifier circuit 23 is substantially a DC voltage, and here, it is assumed that the overvoltage state is progressing with the gradual increase over time. On the other hand, the voltage v _C2 across the terminals of the capacitor Cd2 is an AC voltage close to a sine wave, and its amplitude gradually increases like the output voltage Vo of the rectifier circuit 23 .

The first voltage detection circuit 26 monitors the output voltage Vo of the rectifier circuit 23, and outputs the first detection signal _SGa when the output voltage Vo exceeds the first threshold voltage _Vth1 at time ta. . The second voltage detection circuit 27 monitors the voltage _vC2 across the terminals of the capacitor Cd2, and outputs the second detection signal _SGb when the voltage _vC2 across the terminals falls below the threshold voltage Vth2.

After time t _a when the output voltage Vo of the rectifier circuit 23 exceeds the first threshold voltage V _th1 , it is necessary to operate the protection circuit 25 to stop the supply of the overvoltage. However, as shown in the figure, the voltage v _C2 across the terminals of the capacitor Cd2 exceeds the second threshold voltage V _th2 at time _ta , so the control signal SG1 remains at the low level, and the protection circuit 25 operates. is not started. Therefore, it is possible to prevent excessive current from flowing through the switching element SW22 of the protection circuit 25 .

After that, at time _tb when the terminal voltage v _C2 of the capacitor Cd2 changes and falls below the second threshold voltage V _th2 , the second detection signal SGb of the second voltage detection circuit 27 becomes high level, and the control signal SG1 also becomes become high level. As a result, since both the first and second switching elements SW21 and SW22 are turned on, it is possible to prevent the rectifier circuit 23 from outputting an overvoltage.

In this embodiment, the switching element SW22 is switched from on to off at the same timing as the switching element SW21, but it is also possible to switch at a timing different from that of the switching element SW21. Even if the switching element SW22 is turned on at the timing _ta when the output voltage Vo of the rectifier circuit 23 exceeds the first threshold voltage _Vth1 , an excessive current does not flow through the switching element SW22 and the diode D6. Early protection of the rectifier circuit 23 can be achieved by turning off the switching element SW22 before the element SW21.

Next, normal rectification operation by the rectification circuit 23 will be described. During normal operation when the output voltage is not overvoltage, the rectifier circuit 23 operates in a bridge rectification mode or a voltage doubler rectification mode, which will be detailed below.

5 and 6 are explanatory diagrams of the operation modes of the rectifier circuit 23. FIGS. 5(a) and 6(b) represent the bridge rectification mode, and FIGS. 6(a) and 6(b) represent the voltage doubler rectification mode, respectively. showing.

As shown in FIG. 5(a), when a voltage is applied in which one input terminal P1 of the rectifier circuit 23 is positive and the other input terminal P2 is negative, the four diodes forming the bridge rectifier circuit A current flows to turn on the fourth diodes D1 and D4 among D1 to D4 and turn off the second and third diodes D2 and D3. Conversely, as shown in FIG. 5B, when a voltage is generated in which the input terminal P1 of the rectifier circuit 23 is negative and the input terminal P2 is positive, the second and third diodes D2 and D3 are turned on, A current flows to turn off the first and fourth diodes D1 and D4. Therefore, one output terminal P3 of the rectifier circuit 23 is a positive terminal, and the other output terminal P4 is a negative terminal. A DC voltage of V _max is obtained.

The first and second capacitors Cd1 and Cd2 constitute a voltage doubler rectifier circuit together with the diodes D1 and D2. Also, when diodes D1 and D2 are operating as a bridge rectifier circuit with diodes D3 and D4, the first and second capacitors Cd1 and Cd2 act as harmonic filter elements for the bridge rectifier circuit. In order to reduce the ripple of the input current to the load 30, the capacitances of the first and second capacitors Cd1 and Cd2 are preferably the same, but they do not necessarily have to be the same.

As shown in FIG. 6(a), when a voltage is applied in which one input terminal P1 of the rectifier circuit 23 is positive and the other input terminal P2 is negative, the first diode D1 and the first capacitor Cd1 A current flows through the first capacitor Cd1, and a DC voltage corresponding to the maximum value _Vmax of the input AC voltage of the rectifier circuit 23 is generated across the first capacitor Cd1. Conversely, as shown in FIG. 6(b), when a voltage is applied such that the input end P1 of the rectifier circuit 23 is negative and the input end P2 is positive, the second diode D2 and the second capacitor Cd2 are A current flows through the second capacitor Cd2, and a DC voltage corresponding to the maximum value _Vmax of the input AC voltage of the rectifier circuit 23 is generated across the second capacitor Cd2.

Therefore, the rectified voltage between the pair of output terminals P3 and P4 of the rectifier circuit 23 is a DC voltage approximately twice the maximum value _Vmax of the input AC voltage of the rectifier circuit 23. FIG. Thus, even if the input AC voltage is the same, the voltage doubler rectifier circuit is a circuit that can obtain a DC output voltage about twice that of the bridge rectifier circuit, and the input impedance is also about half.

Here, the power transmission efficiency when the battery is charged when only the bridge rectifier circuit is used and when only the voltage doubler rectifier circuit is used will be described with reference to FIG.

FIG. 7 is a graph showing an example of temporal changes in the power transmission efficiency of the bridge rectifier circuit and the voltage doubler rectifier circuit.

As shown in FIG. 7, the impedance of the battery at the beginning of charging is low, and the impedance gradually increases as charging progresses. The power transfer efficiency when only the bridge rectifier circuit is used deteriorates in the second half of the battery charging period. On the other hand, the power transfer efficiency when only the voltage doubler is used is lower than when the bridge rectifier is used at the beginning of battery charging, but the bridge rectifier is used later in the battery charging period. higher than the case.

Therefore, in this embodiment, the rectifying action by the bridge rectifier circuit is stronger at the beginning of charging of a battery with low impedance, and the rectifying action by the voltage doubler rectifier circuit gradually becomes stronger than that of the bridge rectifier circuit as the amount of charge increases. to operate both.

The rectifier circuit 23 operates in the voltage doubler rectification mode at the start of the half cycle of the input AC voltage, but switches from the voltage doubler rectification mode to the bridge rectification mode in the middle of the half cycle. Then, the bridge rectification mode is switched again to the voltage doubler rectification mode at the timing of moving to the next half cycle.

As shown in FIGS. 6A and 6B, the diodes D3 and D4 are off when the rectifier circuit 23 operates in the voltage doubler rectification mode. Switching from the voltage doubler rectification mode to the bridge rectification mode is performed by turning on the diode D3 or D4. For example, in the positive half cycle of the input AC voltage, the voltage across the second capacitor Cd2 of the rectifier circuit 23 (see FIG. 6A) operating in the voltage doubler rectification mode gives a reverse bias to the diode D4. However, due to the voltage doubler rectification operation, the capacitor Cd2 is gradually discharged, the voltage between the terminals gradually decreases, and after being completely discharged, the polarity of the voltage between the terminals of the capacitor Cd2 is reversed and charging starts. When the voltage across the terminals gives a forward bias to the diode D4, the diode D4 is turned on, thereby switching the rectifier circuit 23 from the voltage doubler rectification mode to the bridge rectification mode.

Switching from the bridge rectification mode to the voltage doubler rectification mode is performed at the timing when the polarity of the input AC voltage is reversed. At this time, the voltage across the terminals of the capacitor Cd2 (or Cd1) gives a reverse bias to the diode D4 (or D3), so the diode D4 (or D3) is turned off and switched to the voltage doubler rectification mode.

Switching from the voltage doubler rectification mode to the bridge rectification mode is affected by the magnitudes of the capacitances of the capacitors Cd1 and Cd2. If the capacitance is large, the time constant will be large, so the capacitors Cd1 and Cd2 cannot be completely discharged within the period of the half cycle of the input AC voltage. Capacitors Cd1 and Cd2 can be completely discharged within a short period of time and then charged to a voltage at which diodes D3 and D4 are turned on.

This means that the larger the capacity of the first and second capacitors Cd1 and Cd2, the later the timing of switching from the voltage doubler rectification mode to the bridge rectification mode, and conversely, the smaller the capacity, the faster the timing. . That is, when the capacitance of the first and second capacitors Cd1 and Cd2 is large, the operation ratio in the voltage doubler rectification mode is higher, and when the capacitance is small, the operation ratio in the bridge rectification mode is higher.

When the frequency of the input AC power is f and the maximum value of the load impedance of the battery is _RLmax , each of the capacitance C1 of the _first capacitor Cd1 and the capacitance C2 of the _second capacitor Cd2 is 1 /(2fR _Lmax ) (ie C ₁ , C ₂ <1/(2fR _Lmax )). With such a capacitance, the duty ratio of the voltage doubler rectification mode to the bridge rectification mode can be less than 100% even when the load impedance is maximum, and rectification by the bridge rectification circuit can be achieved within the load impedance fluctuation range. Actions can always be made.

Also, each of the capacitance C ₁ of the first capacitor Cd1 and the capacitance C ₂ of the second capacitor Cd2 is greater than 1/(80×2fR _Lmax ) (i.e., C ₁ , C ₂ >1 /(80×2fR _Lmax ) is preferably satisfied). With such a capacitance, the upper limit of the duty ratio of the voltage doubler rectification mode to the bridge rectification mode of the rectifier circuit 23 can be made larger than 10%. Therefore, the two modes can be operated at an appropriate duty ratio within the load impedance fluctuation range, and the effect of suppressing the load impedance fluctuation can be further enhanced.

When the load 30 is a battery, the ratio of rectification operation by the bridge rectifier circuit is highest at the start of charging. As the charging of the battery progresses and the load impedance gradually increases, the ratio of rectification operation by the bridge rectifier circuit gradually decreases, and conversely, the ratio of rectification operation by the voltage doubler rectifier circuit gradually increases. When the battery is fully charged and the load impedance is maximized, the ratio of the rectification operation by the bridge rectifier circuit becomes the lowest, and the rectification operation by the voltage doubler rectifier circuit becomes dominant. Therefore, variations in the impedance of the load viewed from the input side of the rectifier circuit 23 can be suppressed without separately providing an impedance converter that requires active control.

FIG. 8 is an equivalent circuit diagram of the rectifier circuit 23. As shown in FIG. 9 is a waveform diagram showing input/output currents of the rectifier circuit 23. As shown in FIG.

As shown in FIGS. 8 and 9, when the input current i _rect of the rectifier circuit 23 is a sine wave, the output current i _o of the rectifier circuit 23 is not a normal bridge rectified waveform but a discontinuously changing waveform. Become.

When the output current i _o of the rectifier circuit 23 is superimposed on the input current i _rect and the current −i _C2 flowing through the second capacitor Cd2, the output current i _o is always equal to either one of these two currents, and on the way You can see that the mode is switched. That is, the output current i _o is equal to the current −i _C2 before the mode switching point, and is equal to the input current i _rect after the mode switching point. Furthermore, the current i _C1 flowing through the first capacitor Cd1 and the current i _C2 flowing through the second capacitor Cd2 have the same magnitude and opposite signs (i _C1 =−i _C2 ). Therefore, it can be seen that the rectifier circuit 23 operates in the voltage doubler rectification mode in the first half of the half cycle bordering on the mode switching point, and operates in the bridge rectification mode in the second half of the half cycle. When each current is defined by the direction of the arrow in FIG. 8, the relationship among the currents i _rect , i _C1 and i _C2 in the voltage doubler rectification mode is i _rect =i _C1 -i _C2 =2i _C1 .

Switching between the two modes is also due to the on action of diode D4 connected in parallel with second capacitor Cd2. That is, when the fourth diode D4 is off, the voltage doubler rectification mode is entered, and the equivalent circuit of the voltage doubler rectifier circuit is as shown in FIG. 10(a). When the diode D4 is on, the bridge rectification mode is set, and the equivalent circuit of the bridge rectification circuit is as shown in FIG. 10(b).

The input voltage v _rect with respect to the sinusoidal input current i _rect of the rectifier circuit 23 has a distorted waveform as shown in FIG. When the voltages across the terminals of the first and second capacitors Cd1 and Cd2 are respectively v _C1 and v _C2 , the input voltage v _rect is v _C1 or v _C2 in positive and negative half waves, respectively. , the relationship between the output voltage V _o and the voltages v _C1 and v _C2 across the terminals of the capacitors Cd1 and Cd2 is v _C1 +v _C2 =V _o (constant).

The switching point between the two modes is the point at which the voltage across the terminals of one capacitor of the rectifier circuit 23 becomes zero. At this time, the voltage across the terminals of the other capacitor is equal to the output voltage Vo (DC voltage). Become. That is, v _C1 (t=0)=0 and v _C1 (t=t _d )=Vo (t _d : switching time).

FIG. 12 is a diagram for explaining the difference in mode switching points D. FIG.

As shown in FIG. 12A, when the mode switching timing is late (D is large), the input voltage v _rect increases because the influence of the voltage doubler rectification operation increases. On the other hand, as shown in FIG. 12(b), when the mode switching timing is fast (D is small), the effect of the bridge _{rectification} operation becomes large. _rect becomes smaller. This means that the later the mode switching timing, the smaller the input impedance due to the influence of the voltage doubler rectification mode. Conversely, it means that the faster the mode switching timing, the less the input impedance is reduced due to the influence of the bridge rectification mode.

Next, the derivation of the mode switching point D will be described.

Considering a half cycle from t = 0 to t = T/2, when the mode switching point is expressed as D: [0, 1], the time [μs] at the switching point is TD/2 [μs]. .

A mode switching point D is obtained from the following conditional expression.
i _C2 =-i _C1
i _rect =i _C1 -i _C2 =2i _C1
v _C1 +v _C2 =Vo (constant)
v _C1 (t=0)=0, v _C1 (t=TD/2)=Vo

Next, calculating v _{C1 yields} :

Next, the calculation of I _o (average value (DC value) of i _o ) is as follows.

Next, simultaneous v _C1 and I _o are as follows.

Here, since the domain in parentheses of Equation (3) is [−1, 1], π/(ωC _d R _L )>1 and R _L <π/(ωC _d ) are satisfied. i know i need it. This defines the range of load impedances _RL to which this calculation is applicable.

In order to satisfy D<1 when the load impedance R _L is maximum (R _L =R _Lmax ) as described above, it is necessary that R _Lmax <π/(ωC _d ). In other words, it is necessary to satisfy R _Lmax <1/(2fC _d ), and the capacitances C ₁ and C ₂ of the first and second capacitors Cd1 and Cd2, respectively, are less than 1/(2fR _Lmax ). Small is required. From the above calculation, it can be seen that C ₁ , C ₂ <1/(2fR _Lmax ) should be satisfied in order to satisfy D<1 when the load impedance R _L is maximum (R _L =R _Lmax ).

FIG. 13 is a graph showing the relationship between the load impedance |Z _ac | viewed from the input side of the rectifier circuit 23 and the actual load impedance R _L .

As shown in FIG. 13, in the case of the conventional bridge rectifier circuit, the load impedance viewed from the input side of the rectifier circuit 23 changes in proportion to the actual load impedance _RL . That is, when the actual load impedance R _L increases, for example, from approximately 0Ω to approximately 60Ω, the load impedance |Z _ac | seen from the input side of the rectifier circuit 23 increases from approximately 0Ω to approximately 50Ω.

On the other hand, in the case of the rectifier circuit 23 according to the present invention, the load impedance |Z _ac | seen from the input side of the rectifier circuit 23 changes less than the actual load impedance R _L . That is, even if the actual load impedance R _L increases from about 0Ω to about 60Ω, the load impedance |Z _ac | seen from the input side of the rectifier circuit 23 increases only from about 0Ω to about 15Ω. This means that in the wireless power transmission system, the rectifier circuit 23 suppresses fluctuations in the load impedance on the wireless power receiving device 20 side as seen from the wireless power transmitting device 10 side. Therefore, it is possible to suppress a decrease in power transmission efficiency due to impedance mismatch between the wireless power transmitting device 10 side and the wireless power receiving device 20 side.

As described above, the wireless power transmission system 1 according to the present embodiment includes the wireless power transmission device 10 that wirelessly supplies power, and the wireless power reception device 20 that receives the power wirelessly supplied from the wireless power transmission device 10. , the wireless power receiving device 20 includes a rectifier circuit 23 including diodes D1 to D4 and capacitors Cd1 and Cd2, and a protection circuit 25 including a first switching element SW21. Since the ON/OFF operation of the first switching element SW21 is controlled based on the voltage across the terminals of the capacitor Cd2 of 23, it is possible to suppress an excessive current from flowing through the first switching element SW21 and the like constituting the protection circuit 25. can. In addition, when an overvoltage occurs at the output end of the power receiving unit, both ends of the power receiving unit are short-circuited, so that circuits subsequent to the power receiving unit can be protected from overvoltage. Therefore, it is possible to protect the circuit elements forming the protection circuit while protecting the circuit elements forming the device when an overvoltage occurs.

Further, the wireless power receiving device 20 according to the present embodiment includes a rectifying circuit 23 that converts AC power received by the power receiving coil L2 into DC power and outputs the power to the load 30. The rectifying circuit 23 includes bridge-connected diodes D1 to D4, a first capacitor Cd1 connected in parallel with the diode D3 of the diodes D1 to D4 whose anode is connected to the other input terminal P2 of the rectifier circuit 23, and a cathode connected to the other input terminal P2 of the rectifier circuit 23. With the second capacitor Cd2 connected in parallel with the connected diode D4, the rectifier circuit 23 can be operated as a bridge rectifier circuit or a voltage doubler rectifier circuit, and the load connected to the output of the rectifier circuit 23 The duty ratio between the bridge rectification mode and the voltage doubler rectification mode of the rectifier circuit 23 can be passively changed according to the change of the impedance of 30 . Therefore, it is possible to suppress fluctuations in the impedance of the load 30 viewed from the input side of the rectifier circuit 23 without separately providing an impedance converter that requires active control. can be suppressed.

Further, in the wireless power receiving device 20, the capacitance of the first capacitor Cd1 is C ₁ , the capacitance of the second capacitor Cd2 is C ₂ , the frequency of the AC power is f, and the maximum resistance value of the load 30 is R _Lmax. Then, since the capacitance C1 of the _first capacitor Cd1 and the capacitance C2 of the _second capacitor Cd2 are smaller than 1/(2fR _Lmax ), the half cycle of the AC power input to the rectifier circuit 23 is Among them, the upper limit value of the duty ratio of the voltage doubler rectification mode to the bridge rectification mode of the rectifier circuit 23 can be set to less than 100%. Therefore, the two modes can be operated at an appropriate duty ratio within the impedance variation range of the load 30, thereby suppressing load impedance variation.

FIG. 14 is a circuit diagram showing the configuration of the wireless power receiving device according to the second embodiment.

As shown in FIG. 14, the feature of the wireless power receiving device 20 according to this embodiment is that the second voltage detection circuit 27 detects the voltage across the terminals of the first capacitor Cd1. That is, when the output voltage of the rectifier circuit 23 exceeds the first threshold voltage and the voltage across the terminals of the capacitor Cd1 exceeds the third threshold voltage, the control circuit 28 outputs the control signal SG1 to protect the protection circuit. 25 is configured to operate. Since the voltage v _C1 across the terminals of the first capacitor Cd1 is an AC voltage that is inverse in phase to the voltage v _C2 across the terminals of the second capacitor Cd2, the voltage v C1 across the terminals of the first capacitor Cd1 changes from the voltage v _C1 across the terminals of the first capacitor Cd1 to the second capacitor. The voltage v _C1 across Cd2 can be indirectly detected. The third threshold voltage is set based on the rated current of the first switching element SW21.

FIG. 15 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage _vC1 across the terminals of the first capacitor Cd1, and the control signal SG1 output from the control circuit .

As shown in FIG. 15, the output voltage Vo of the rectifier circuit 23 is substantially a DC voltage, and here it is assumed that the overvoltage state is progressing with the gradual increase over time. On the other hand, the voltage v _C1 between the terminals of the capacitor Cd1 is an AC voltage close to a sine wave, and its amplitude gradually rises like the output voltage Vo of the rectifier circuit.

The first voltage detection circuit 26 monitors the output voltage Vo of the rectifier circuit 23, and outputs the first detection signal _SGa when the output voltage Vo exceeds the first threshold voltage _Vth1 at time ta. . The second voltage detection circuit 27 monitors the terminal voltage v _C1 of the capacitor Cd1, and outputs the second detection signal SGb when the terminal voltage v _C1 exceeds the threshold voltage V _th3 .

After time t _a when the output voltage Vo of the rectifier circuit 23 exceeds the first threshold voltage V _th1 , it is necessary to operate the protection circuit 25 to stop the supply of the overvoltage. However, as shown in the figure, the voltage v _C1 between the terminals of the capacitor Cd1 is lower than the third threshold voltage V _th3 at time _ta , so the control signal SG1 remains at the low level, and the protection circuit 25 operates. is not started. A state in which the voltage v _C1 across the capacitor Cd1 is lower than the third threshold voltage V _th3 means that the voltage v _C1 across the capacitor Cd2 is high. Therefore, the protection circuit 25 does not start operating at this timing.

After that, at time _tb when the terminal voltage v _C1 of the capacitor Cd1 changes and exceeds the third threshold voltage V _th3 , the detection signal SGb of the second voltage detection circuit 27 becomes high level, and the control signal SG1 also becomes become high level. As a result, since both the first and second switching elements SW21 and SW22 are turned on, it is possible to prevent the rectifier circuit 23 from outputting an overvoltage.

In this embodiment, the second voltage detection circuit 27 detects only the voltage across the terminals of the first capacitor Cd1, and the control circuit switches based on the output voltage of the rectifier circuit 23 and the voltage across the terminals of the first capacitor Cd1. Although the ON/OFF operations of the elements SW21 and SW22 are controlled, the second voltage detection circuit 27 detects both the terminal voltage of the first capacitor Cd1 and the terminal voltage of the second capacitor Cd2, It is also possible to control the on/off operations of the switching elements SW21 and SW22 using both the output voltage and the voltage across the terminals of the first and second capacitors Cd1 and Cd2.

FIG. 16 is a circuit diagram showing the configuration of the wireless power receiving device according to the third embodiment.

As shown in FIG. 16, the feature of the wireless power receiving device 20 according to this embodiment is that the protection circuit 25 is configured using a single switching element SW21. The protection circuit 25 has a switching element SW21 and two diodes D5 and D6. One end of the switching element SW21 is connected to the other input terminal P2 of the rectifier circuit 23 via a diode D5 and to one input terminal P1 of the rectifier circuit 23 via a diode D6. The other end of the switching element SW21 is connected to the other output end P4 of the rectifier circuit 23 . Other configurations are the same as those of the first embodiment.

The wireless power receiving device 20 according to this embodiment can achieve the same effects as those of the first embodiment. In addition, since the protection circuit 25 is configured using a single switching element SW21, it is possible to reduce costs and stabilize control.

FIG. 17 is a circuit diagram showing the configuration of the wireless power receiving device according to the fourth embodiment.

As shown in FIG. 17, the feature of the wireless power receiving device 20 according to the present embodiment is that the diodes D2 and D4 of the rectifier circuit 23 in the first embodiment are replaced with switching elements SW22 and SW21 made of field effect transistors. at the point. As a result, the rectifier circuit 23 also functions as the protection circuit 25, and the body diodes of the field effect transistors forming the switching elements SW22 and SW21 function as the diodes D2 and D4 of the rectifier circuit 23 in the first embodiment. do. MOSFETs and IGBTs can be used for the switching elements SW21 and SW22. A control signal SG1 from the control circuit 28 is input to input terminals of the switching elements SW21 and SW22 forming the rectifier circuit 23 . According to this embodiment, not only can the same effects as in the first embodiment be obtained, but also the independent protection circuit can be omitted to achieve miniaturization and cost reduction.

FIG. 18 is a circuit diagram showing the configuration of the wireless power receiving device according to the fifth embodiment.

As shown in FIG. 18, the wireless power receiving device 20 according to this embodiment is characterized in that a choke coil L3 is inserted in series with one output terminal P3 of the rectifier circuit 23. As shown in FIG. Other configurations are the same as those of the first embodiment. Thus, in this embodiment, since the smoothing capacitor Cs and the choke coil L3 are provided after the rectifier circuit 23, when the protection circuit 25 operates, , it is possible to suppress an excessive current from flowing from the smoothing capacitor Cs to the first switching element SW21 and the like constituting the protection circuit 25 .

FIG. 19 is a circuit diagram showing the configuration of a wireless power receiving device according to the sixth embodiment of the invention. 20 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage vC2 across the terminals of the second capacitor Cd2, and the control signals _SG11 and S12 output from the control circuit .

As shown in FIGS. 19 and 20, the feature of the wireless power receiving device 20 according to this embodiment is that the first and second switching elements SW21 and SW22 are separately controlled by the control signals SG11 and SG12 output from the control circuit 28. at the point of being controlled. The control circuit 28 outputs the control signal SG12 even when only the first detection signal SGa is active, thereby turning on the switching element SW22. On the other hand, the control signal SG11 is output when both the first detection signal SGa and the second detection signal SGb are active, thereby turning on the switching element SW21.

As shown in FIG. 20, the control circuit 28 turns on the second switching element SW22 when the output voltage Vo of the rectifier circuit 23 detected by the first voltage detection circuit 26 exceeds the first threshold voltage _Vth1 . to In addition, the control circuit 28 detects that the output voltage Vo detected by the first voltage detection circuit 26 exceeds the first threshold voltage _Vth1 , and the voltage between the terminals of the second capacitor Cd2 detected by the second voltage detection circuit 27 is controlled. When the voltage v _C2 falls below the second threshold voltage V _th2 , the first switching element SW21 is turned on.

In this way, by turning on the second switching element SW22 immediately after detecting an overvoltage of the output voltage Vo, the first and second capacitors Cd1 and Cd2 are in a state of operating as a voltage doubler circuit. In addition, a path for discharging the second capacitor Cd2 when the current load is released can be secured to facilitate discharge. Therefore, the voltage across the terminals of the second capacitor Cd2 can be immediately lowered.

FIG. 21 is a circuit diagram showing the configuration of a wireless power receiving device according to the seventh embodiment of the invention. 22 is a signal waveform diagram showing the output voltage Vo of the rectifier circuit 23, the voltage vC1 across the terminals of the first capacitor Cd1, and the control signals _SG11 and S12 output from the control circuit .

As shown in FIGS. 21 and 22, the wireless power receiving device 20 according to this embodiment is a modification of the sixth embodiment (FIGS. 19 and 20), and is characterized in that the second voltage detection circuit 27 is The point is that the voltage _vC1 across the terminals of the first capacitor Cd1 is monitored instead of the voltage _vC2 across the terminals of the second capacitor Cd2. As in the sixth embodiment, the control signals SG11 and SG12 output from the control circuit 28 separately control the first and second switching elements SW21 and SW22, respectively. The control circuit 28 outputs the control signal SG12 even when only the first detection signal SGa is active, thereby turning on the switching element SW22. On the other hand, the control signal SG11 is output when both the first detection signal SGa and the second detection signal SGb are active, thereby turning on the switching element SW21.

As shown in FIG. 22, the control circuit 28 turns on the second switching element SW22 when the output voltage Vo of the rectifier circuit 23 detected by the first voltage detection circuit 26 exceeds the first threshold voltage _Vth1 . to In addition, the control circuit 28 detects that the output voltage Vo detected by the first voltage detection circuit 26 exceeds the first threshold voltage _Vth1 and that the voltage between the terminals of the first capacitor Cd1 detected by the second voltage detection circuit 27 is detected. When the voltage v _C1 exceeds the third threshold voltage V _th3 , the first switching element SW21 is turned on.

In this way, by turning on the second switching element SW22 immediately after detecting an overvoltage of the output voltage Vo, the first and second capacitors Cd1 and Cd2 are in a state of operating as a voltage doubler circuit. In addition, a path for discharging the second capacitor Cd2 when the current load is released can be secured to facilitate discharge. Therefore, the voltage across the terminals of the second capacitor Cd2 can be immediately lowered.

FIG. 23 is a circuit diagram showing the configuration of the wireless power receiving device according to the eighth embodiment of the invention.

As shown in FIG. 23, the wireless power receiving device 20 according to this embodiment is characterized by a connection point P5 between the anode of the third diode D3 and the cathode of the fourth diode D4, the first switching element SW21, and the rectifier circuit. 23 and the connection point P6 with the inductor element L4. Although the illustrated inductor element L4 is inserted between the connection point P5 and the diode D5, it may be inserted between the diode D5 and the first switching element SW21. It may be inserted between P6. According to this configuration, overcurrent when the first switching element SW21 is turned on can be alleviated, and damage to the switching element can be prevented.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. Needless to say, it is included within the scope.

For example, in the above embodiment, a battery was used as the load 30, but the present invention is not limited to such a case, and can target various loads whose impedance can fluctuate. In addition, the present invention has exemplified the rectifier circuit employed on the power receiving device side of the wireless power transmission device, but the application of the rectifier circuit is not limited to wireless power transmission technology, and can be used for various purposes. can be done.

1 wireless power transmission system 10 wireless power transmission device 11 DC power supply 12 inverter 13 power transmission unit 14 current detection circuit 15 power transmission control circuit 20 wireless power reception device 21 power reception unit 23 rectifier circuit 25 protection circuit 26 first voltage detection circuit 27 second voltage Detection circuit 28 Control circuit 30 Loads C11, C12 Capacitors C21, C22 Capacitors Cd1, Cd2 Capacitor Cs Smoothing capacitor D1 Diode D2 Diode D3 Diode D4 Diode D5 Diode (first rectifying element)
D6 diode (second rectifier)
L1 power transmitting coil L2 power receiving coil L3 choke coil L4 inductor element P1 one input terminal P2 of rectifier circuit 23 the other input terminal P3 of rectifier circuit 23 one output terminal P4 of rectifier circuit 23 the other output terminal P5 of rectifier circuit 23 Connection point P6 between the anode of the third diode and the cathode of the fourth diode Connection points SW11 to SW14 between the first switching element and the output terminal of the rectifier circuit Switching elements SW21 and SW22 Switching elements

Claims (21)

a power receiving unit including a power receiving coil;
A first diode having an anode connected to one output terminal of the power receiving unit, a second diode having a cathode connected to the one output terminal, and an anode connected to the other output terminal of the power receiving unit. a third diode connected to the other output terminal, a fourth diode having a cathode connected to the other output terminal, and first and second capacitors connected in parallel to the third and fourth diodes, respectively, a rectifier circuit that converts AC power received by the power receiving coil into DC power;
a first switching element connected between the other output terminal of the power receiving unit and the output terminal of the rectifier circuit, and between the one output terminal of the power receiving unit and the output terminal of the rectifier circuit; a protection circuit including a connected second switching element ;
a control circuit that controls on/off operations of the first and second switching elements based on the output voltage of the rectifier circuit and the voltage across the terminals of the first or second capacitor. Device. The protection circuit is connected between the other output terminal of the power receiving unit and the first switching element, or between the first switching element and the output terminal of the rectifier circuit. a rectifying element;
a second rectifying element connected between the one output terminal of the power receiving unit and the second switching element, or between the second switching element and the output terminal of the rectifying circuit; The wireless power receiving device of claim 1 , comprising: The first switching element is a first field effect transistor,
the second switching element is a second field effect transistor,
the fourth diode is a parasitic diode of the first field effect transistor;
The wireless power receiver according to claim 1 , wherein said second diode is a parasitic diode of said second field effect transistor. a first voltage detection circuit that detects the output voltage of the rectifier circuit;
a second voltage detection circuit that detects the voltage across the terminals of the second capacitor,
The control circuit is
When the voltage detected by the first voltage detection circuit exceeds the first threshold voltage, the second switching element is turned on, and the voltage detected by the first voltage detection circuit exceeds the first threshold voltage. 4. The first switching element is turned on when the threshold voltage is exceeded and the voltage detected by the second voltage detection circuit is below the second threshold voltage. The wireless power receiving device as described in . The wireless power receiving device according to claim 4 , wherein said second threshold voltage is set based on a rated current of said first switching element. a first voltage detection circuit that detects the output voltage of the rectifier circuit;
a second voltage detection circuit that detects the voltage across the terminals of the first capacitor,
The control circuit is
When the voltage detected by the first voltage detection circuit exceeds the first threshold voltage, the second switching element is turned on, and the voltage detected by the first voltage detection circuit exceeds the first threshold voltage. 4. The first switching element is turned on when the threshold voltage is exceeded and the voltage detected by the second voltage detection circuit exceeds a third threshold voltage. The wireless power receiving device as described in . The wireless power receiving device according to claim 6 , wherein said third threshold voltage is set based on a rated current of said first switching element. 8. The control circuit according to any one of claims 4 to 7 , wherein when the voltage detected by the first voltage detection circuit exceeds a first threshold voltage, the control circuit outputs a power transmission stop signal instructing to stop the power transmission operation. 11. The wireless power receiving device according to claim 1. a power receiving unit including a power receiving coil;
A first diode having an anode connected to one output terminal of the power receiving unit, a second diode having a cathode connected to the one output terminal, and an anode connected to the other output terminal of the power receiving unit. a third diode connected to the other output terminal, a fourth diode having a cathode connected to the other output terminal, and first and second capacitors connected in parallel to the third and fourth diodes, respectively, a rectifier circuit that converts AC power received by the power receiving coil into DC power;
a first switching element connected between the other output terminal of the power receiving unit and the output terminal of the rectifier circuit and between the one output terminal of the power receiving unit and the output terminal of the rectifier circuit. a protection circuit;
and a control circuit for controlling the on/off operation of the first switching element based on the output voltage of the rectifier circuit and the inter-terminal voltage of the first or second capacitor. The protection circuit includes a first rectifying element connected between the other output terminal of the power receiving unit and the first switching element;
a second rectifying element connected between the one output end of the power receiving unit and the first switching element;
10. The first switching element is connected to the other output terminal via the first rectifying element and is connected to the one output terminal via the second rectifying element. The wireless power receiving device as described in . a first voltage detection circuit that detects the output voltage of the rectifier circuit;
a second voltage detection circuit that detects the voltage across the terminals of the first capacitor or the second capacitor,
11. The wireless power receiving device according to claim 9 , wherein said control circuit controls on/off operations of said first switching element based on detection results of said first voltage detection circuit and said second voltage detection circuit. . The second voltage detection circuit is configured to detect a voltage across the terminals of the second capacitor,
When the voltage detected by the first voltage detection circuit exceeds a first threshold voltage and the voltage detected by the second voltage detection circuit falls below a second threshold voltage, the control circuit controls the 12. The wireless power receiver of claim 11 , turning on the first switching element. The wireless power receiving device according to claim 12 , wherein said second threshold voltage is set based on a rated current of said first switching element. the second voltage detection circuit is configured to detect a voltage across the terminals of the first capacitor;
When the voltage detected by the first voltage detection circuit exceeds a first threshold voltage and the voltage detected by the second voltage detection circuit exceeds a third threshold voltage, the control circuit controls the The wireless power receiver according to any one of claims 11 to 13 , which turns on the first switching element. The wireless power receiving device according to claim 14 , wherein said third threshold voltage is set based on a rated current of said first switching element. 16. The control circuit according to any one of claims 11 to 15 , wherein when the voltage detected by the first voltage detection circuit exceeds a first threshold voltage, the control circuit outputs a power transmission stop signal instructing to stop the power transmission operation. 11. The wireless power receiving device according to claim 1. When the frequency of the AC power is f and the maximum resistance value of the load is _RLmax , the capacitance C1 of the _first capacitor and the capacitance C2 of the _second capacitor are:
C ₁ , C ₂ <1/(2fR _Lmax )
The wireless power receiving device according to any one of claims 1 to 16 , wherein: The capacitance C1 of the _first capacitor and the capacitance C2 of the _second capacitor are
1/(80×2fR _Lmax )<C ₁ , C ₂
The wireless power receiving device according to claim 17 , wherein: 19. The apparatus according to any one of claims 1 to 18 , further comprising a smoothing capacitor connected in parallel to the output end of said rectifier circuit, and a choke coil provided between the output end of said rectifier circuit and said smoothing capacitor. A wireless powered device as described. An inductor element provided between a connection point between the anode of the third diode and the cathode of the fourth diode and a connection point between the first switching element and the output terminal of the rectifier circuit. 20. The wireless power receiver according to any one of claims 1 to 19 . a wireless power transmission device;
A wireless power receiving device according to any one of claims 1 to 20 ,
The wireless power transmission device
an inverter that converts DC power to AC power;
a power transmission unit including a power transmission coil that receives the AC power and generates an AC magnetic field;
a current detection circuit that detects the current output from the inverter;
a power transmission control circuit that controls the operation of the inverter,
The wireless power transmission system, wherein the power transmission control circuit stops the operation of the inverter when the current detected by the current detection circuit exceeds a threshold current.

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