WO2019176358A1 - Power reception device - Google Patents

Abstract

In order to suppress occurrence of unnecessary leakage flux even when the operation of a power conversion unit stops while current is flowing through a coil of a power reception device, a power reception device 200 is provided with: a secondary coil L2; a resonance coil Lx and a resonance capacitor Cx which are connected to the secondary coil L2 and which constitute, along with the secondary coil L2, a resonance circuit having a prescribed resonance frequency; a power conversion unit 250 that controls AC current i flowing through the resonance circuit, by causing MOS transistors Q1-Q4 to separately execute switching operations; and a buffer coil Ly that is a closed circuit element for selectively forming a closed circuit including the secondary coil L2 but being different from the resonance circuit.

Description

Power receiving device

The present invention relates to a power receiving device used in wireless power feeding.

In recent years, in an electric vehicle or the like, a wireless power feeding system that feeds power wirelessly from a power transmitting device provided on the ground side to a power receiving device provided on the vehicle side is being realized. In such a wireless power feeding system, a wireless power feeding technique using magnetic field resonance or magnetic field induction has attracted attention. In magnetic field induction, a magnetic field (magnetic flux) is generated by flowing an alternating current through a coil provided in a ground-side power transmission device, and this magnetic field is received by a coil provided in a vehicle-side power receiving device to generate an alternating current. By doing so, wireless power feeding from the power transmitting device to the power receiving device is realized. On the other hand, magnetic resonance is the same as magnetic field induction in that a coil is provided in each of the power transmission device and the power reception device, but by matching the frequency of the current flowing in the coil of the power transmission device with the resonance frequency of the coil of the power reception device, Resonance is generated between the power transmission device and the power reception device. As a result, the coil of the power transmission device and the coil of the power reception device are magnetically coupled to achieve highly efficient wireless power feeding.

Regarding the wireless power feeding technology described above, the following Patent Document 1 is known. Patent Document 1 discloses a source-side resonator coil and a device-side resonator coil that is inductively coupled to the source-side resonator coil in a wireless energy transmission system for transmitting energy between a power source and a load. A tunable switching amplifier driven by the power source and driving the source-side resonator coil through a source-side impedance matching network, the switching amplifier having an electronically controllable switching element A tunable switching rectifier that drives the load and receives energy from the device-side resonator coil via a device-side impedance matching network, the switching rectifier having an electronically controllable switching element And switching of the switching element in the amplifier Control the characteristics and adjust the power extracted from the power source, control the switching characteristics of the switching element in the rectifier and the amplifier control section on the source side, and adjust the characteristics of the output appearing in the load A rectifier controller configured to communicatively couple to the source-side amplifier controller, wherein the amplifier controller has a substantially fixed switching frequency in the amplifier. Supplying to the switching element is described.

Special table 2014-5277793 gazette

In a wireless power feeding system used for an electric vehicle or the like, a switching rectifier that is a power conversion unit in spite of the fact that a magnetic field is being emitted from a coil of a power transmission device when an unexpected malfunction occurs in a power reception device May stop, and the current flowing through the coil of the power receiving apparatus may be suddenly interrupted. In such a case, in the system described in Patent Document 1, the magnetic coupling between the power transmission device and the power reception device is disturbed, and unnecessary leakage magnetic flux may be generated.

A power receiving device according to the present invention receives an AC magnetic field emitted from a primary coil installed on the ground side and is wirelessly fed, and is connected to a secondary coil and the secondary coil to have a predetermined resonance frequency. A power conversion unit that controls the alternating current flowing in the resonance circuit by switching each of the plurality of switching elements. A closed circuit element that selectively forms a closed circuit different from the resonant circuit including the secondary coil.

According to the present invention, it is possible to suppress generation of unnecessary leakage magnetic flux even when the operation of the power conversion unit is stopped when a current is flowing through the coil of the power receiving device.

1 is a diagram illustrating a configuration of a wireless power feeding system according to an embodiment of the present invention. It is a figure which shows the structural example of the power receiving apparatus which concerns on one Embodiment of this invention. It is an equivalent circuit diagram of a resonance circuit and a closed circuit. It is a figure which shows the processing flow of the wireless power feeding system which concerns on one Embodiment of this invention.

Hereinafter, embodiments of a power receiving device according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a wireless power feeding system 1 according to an embodiment of the present invention. A wireless power feeding system 1 shown in FIG. 1 is used in wireless power feeding to a vehicle such as an electric vehicle, and includes a power transmission device 100 installed on the ground side in the vicinity of the vehicle and a power receiving device respectively mounted on the vehicle side. 200, a battery 300, and a load 400.

The power transmission device 100 includes a power transmission control unit 110, a communication unit 120, an AC power source 130, a power conversion unit 140, and a primary coil L1. The power transmission control unit 110 controls the power transmission apparatus 100 as a whole by controlling the operations of the communication unit 120 and the power conversion unit 140.

The communication unit 120 performs wireless communication with the communication unit 220 included in the power receiving device 200 under the control of the power transmission control unit 110. Various information necessary for wireless power feeding is exchanged between the power transmitting apparatus 100 and the power receiving apparatus 200 by wireless communication between the communication unit 120 and the communication unit 220. For example, information such as the frequency of the alternating current flowing through the primary coil L1, that is, the frequency of the alternating magnetic field emitted from the primary coil L1, is transmitted from the communication unit 120 to the communication unit 220. In addition, information such as the state of charge (SOC) and deterioration state of battery 300 and the allowable current during charging is transmitted from communication unit 220 to communication unit 120.

AC power supply 130 is a commercial power supply, for example, and supplies predetermined AC power to the power conversion unit 140. The power conversion unit 140 outputs an alternating current having a predetermined frequency and current value to the primary coil L <b> 1 using the alternating current power supplied from the alternating current power supply 130 under the control of the power transmission control unit 110. Primary coil L1 is installed on the ground side located under the vehicle, and emits an alternating magnetic field corresponding to the alternating current flowing from power conversion unit 140 toward the vehicle. Thereby, wireless power feeding to the vehicle is performed.

The power receiving apparatus 200 includes a power reception control unit 210, a communication unit 220, an alternating current detection unit 230, a drive control unit 240, a power conversion unit 250, a secondary coil L2, a resonance coil Lx, a resonance capacitor Cx, and a buffer coil Ly. Two resonant coils Lx and two resonant capacitors Cx are connected to the secondary coil L2, respectively, and constitute a resonant circuit together with the secondary coil L2. The resonance frequency of the resonance circuit is determined according to the inductances of the secondary coil L2 and the resonance coil Lx and the capacitance value of the resonance capacitor Cx. Note that the resonance coil Lx and the resonance capacitor Cx may each be composed of one or three or more elements. Further, part or all of the resonance coil Lx may be substituted by the inductance of the secondary coil L2.

The buffer coil Ly acts to alleviate a change in the magnetic field generated in the secondary coil L2 when the alternating current flowing through the resonance circuit including the secondary coil L2 is suddenly interrupted. One end of the buffer coil Ly is connected between one resonance coil Lx and the resonance capacitor Cx, and the other end of the buffer coil Ly is connected between the other resonance coil Lx and the resonance capacitor Cx. In other words, the buffer coil Ly is connected to both ends of the secondary coil L2 with the two resonance capacitors Cx interposed therebetween without passing through the power converter 250. Thereby, according to the operation state of the power converter 250, a closed circuit including the secondary coil L2 and the buffer coil Ly is selectively formed. The selective formation of the closed circuit by the buffer coil Ly will be described later in detail with reference to FIG.

The power reception control unit 210 controls the power reception apparatus 200 as a whole by controlling the operations of the communication unit 220 and the drive control unit 240. The communication unit 220 performs wireless communication with the communication unit 120 included in the power transmission device 100 under the control of the power reception control unit 210, and stores various types of information as described above exchanged between the power transmission device 100 and the power reception device 200. Send and receive. Information such as the frequency of the alternating current flowing through the primary coil L1 received by the communication unit 220 is output from the communication unit 220 to the power reception control unit 210.

The alternating current detection unit 230 detects the alternating current flowing through the resonance circuit including the secondary coil L2 when the secondary coil L2 receives the alternating magnetic field emitted from the primary coil L1. Then, an AC voltage whose frequency and amplitude change according to the detected AC current is generated and output to the drive control unit 240. The drive control unit 240 can acquire the frequency and magnitude of the alternating current flowing through the resonance circuit based on the alternating voltage input from the alternating current detection unit 230.

The drive control unit 240 controls the switching operations of the plurality of switching elements included in the power conversion unit 250 under the control of the power reception control unit 210. At this time, the drive control unit 240 changes the timing of the switching operation of each switching element based on the alternating current flowing through the resonance circuit detected by the alternating current detection unit 230. A specific method for changing the timing of the switching operation will be described later.

The power conversion unit 250 has a plurality of switching elements, and controls the AC current flowing through the resonance circuit and rectifies by switching each of the plurality of switching elements, thereby converting AC power to DC power. Do. The power conversion unit 250 is connected to a chargeable / dischargeable battery 300, and the battery 300 is charged using DC power output from the power conversion unit 250. Note that a smoothing capacitor C0 for smoothing an input voltage to the battery 300 is connected between the power conversion unit 250 and the battery 300.

A load 400 is connected to the battery 300. The load 400 provides various functions related to the operation of the vehicle using the DC power charged in the battery 300. The load 400 includes, for example, an AC motor for driving a vehicle, an inverter that converts DC power of the battery 300 into AC power, and supplies the AC power to the AC motor.

Next, details of the power receiving apparatus 200 to which the present invention is applied in the wireless power feeding system 1 of FIG. 1 will be described. FIG. 2 is a diagram illustrating a configuration example of the power receiving device 200 according to an embodiment of the present invention.

As shown in FIG. 2, the alternating current detection unit 230 is configured using, for example, a transformer Tr. When the magnetic flux generated by the alternating magnetic field emitted from the primary coil L1 is linked to the secondary coil L2, an electromotive force is generated in the secondary coil L2, and an alternating current i flows through the resonance circuit including the secondary coil L2.
When this alternating current i flows through the primary coil of the transformer Tr, an alternating voltage Vg whose frequency and amplitude change according to the alternating current i is generated at both ends of the secondary coil of the transformer Tr. Thereby, the alternating current detection part 230 can detect the alternating current i. Note that the AC current detection unit 230 may be configured by using a device other than the transformer Tr as long as the AC current i flowing through the resonance circuit can be detected.

The power conversion unit 250 includes two MOS transistors (MOSFETs) Q1 and Q2 connected in series, and two MOS transistors Q3 and Q4 connected in series. The series circuit of the MOS transistors Q1, Q2 and the series circuit of the MOS transistors Q3, Q4 are connected in parallel to the smoothing capacitor C0. The MOS transistors Q1 to Q4 perform a switching operation for switching between the source and the drain from the conductive state to the disconnected state or from the disconnected state to the conductive state in accordance with the gate drive signal from the drive control unit 240. By this switching operation, the MOS transistors Q1 and Q3 can function as switching elements for the upper arm, and the MOS transistors Q2 and Q4 can function as switching elements for the lower arm, respectively. A resonance circuit including the secondary coil L2 is connected to a connection point O1 between the MOS transistors Q1 and Q2 and a connection point O2 between the MOS transistors Q3 and Q4. Therefore, the alternating current i flowing through the resonance circuit can be controlled and rectified by switching the MOS transistors Q1 to Q4 at appropriate timings.

The drive control unit 240 includes a voltage acquisition unit 241, a drive signal generation unit 243, and a gate drive circuit 244.

The voltage acquisition unit 241 acquires the AC voltage Vg output from the AC current detection unit 230 (transformer Tr) and outputs the AC voltage Vg to the drive signal generation unit 243.

The drive signal generation unit 243 receives the basic drive signal Sr from the power reception control unit 210 in addition to the AC voltage Vg acquired by the voltage acquisition unit 241. The basic drive signal Sr is an AC signal that is output from the drive control unit 240 to the power conversion unit 250 and is a source of a gate drive signal that controls the switching operation of the MOS transistors Q1 to Q4. It is determined according to the frequency of the current flowing through the coil L1. Specifically, when the communication unit 220 receives information representing the frequency f of the alternating current flowing through the primary coil L1 of the power transmission device 100 from the communication unit 120, the communication unit 220 outputs the information to the power reception control unit 210. When the information on the frequency f is input from the communication unit 220, the power reception control unit 210 generates a basic drive signal Sr corresponding to the frequency f and outputs it to the drive control unit 240. The basic drive signal Sr is, for example, a combination of four rectangular waves respectively corresponding to the MOS transistors Q1 to Q4, and has an H level corresponding to ON (conducting state) and an L level corresponding to OFF (disconnected state). Are alternately repeated at the frequency f. However, in order to prevent the MOS transistors Q1 and Q2 and Q3 and Q4 from being turned on at the same time, a predetermined protection period is provided between the H levels of the two rectangular waves in each combination of the rectangular waves corresponding thereto.

The drive signal generation unit 243 adjusts the phase of the basic drive signal Sr input from the power reception control unit 210 based on the AC voltage Vg input from the voltage acquisition unit 241, and generates the charge drive signal Sc. Then, the generated charge drive signal Sc is output to the gate drive circuit 244.

The gate drive circuit 244 outputs a gate drive signal based on the charge drive signal Sc input from the drive signal generation unit 243 to the gate terminals of the MOS transistors Q1 to Q4, respectively, and causes the MOS transistors Q1 to Q4 to perform a switching operation. As a result, in the power conversion unit 250, the MOS transistors Q1 to Q4 function as switching elements, respectively, and control of the alternating current i flowing in the resonance circuit according to the alternating magnetic field emitted from the primary coil L1, or the alternating current power to the direct current power. Conversion to

The power receiving device 200 of the present embodiment can charge the battery 300 by receiving wireless power feeding from the power transmitting device 100 by performing the operation described above.

Here, when the resonance frequency fr1 is obtained by temporarily ignoring the self-inductances of L2 and Tr in the resonance circuit including the secondary coil L2, the equation (1) in FIG. 3 is obtained. Here, LT is a combined inductance obtained from the two resonance coils Lx and the buffer coil Ly, and is expressed by equation (2) in FIG. When the power conversion unit 250 is operating normally, a current i substantially conforming to the resonance frequency of the expression (1) flows.
Next, when an alternating current i is flowing, an abnormality has occurred in the drive control unit 240 or the power conversion unit 250, so that the operation of the power conversion unit 250 is stopped and the MOS transistors Q1 to Q4 are all turned off. Suppose that In this case, since the connection points O1 and O2 are disconnected, the current flowing through the resonance circuit including the resonance coil Lx is cut off, but the buffer coil Ly acts so as to keep the current flowing through the secondary coil L2. That is, a closed circuit including the secondary coil L2 and the buffer coil Ly is selectively formed without using the power conversion unit 250. Since this closed circuit does not include the resonance coil Lx, it is different from the resonance circuit formed when the power conversion unit 250 is operating. If the resonance frequency in this state is set to fr2, it can be expressed by equation (3) in FIG. As a numerical example, if the ratio of Lx to Ly is 1: 3, fr2 is approximately 1: 1.58 to the resonance frequency fr1.
Returning to the principle of magnetic field resonance, it is important for high efficiency to make the frequency of the current flowing in the coil of the power transmission device coincide with the resonance frequency of the coil of the power reception device, and the frequency of the above formula (1) is transmitted. The frequency is set approximately equal to the current flowing through the coil of the device. Next, in a situation where the MOS transistors Q1 to Q4 are all turned off and the buffer coil Ly continues to pass current through the secondary coil L2, the frequency fr2 in the expression (3) is approximately from the frequency of the current flowing through the coil of the original power transmission device. 1.58 times higher. The magnetic field resonance is originally operated near the resonance point of the circuit to obtain a high Q (a parameter representing the sharpness of resonance). When the frequency increases 1.58 times by the action of the buffer coil Ly, Q decreases, and the alternating current i also decreases in proportion thereto. This means that the current can be suppressed on the safe side in a situation where the power conversion unit 250 becomes abnormal. However, if the ratio of Ly is increased to 1:10 as compared with Lx, fr2 becomes several times as high as the original fr1, but this is because Q becomes very small, and it approaches the situation where AC current i does not flow. Not desirable.
Considering the case where there is no buffer coil Ly, when all the MOS transistors Q1 to Q4 are turned off, the current flowing through the secondary coil L2 loses its path, and as a result, the induced voltage L2 di / dt becomes an overvoltage. There is a risk of adding to the capacitor CX and destroying it. When the buffer coil Ly is present and the frequency fr2 is not too high and the alternating current i is reduced while lowering Q, the induced voltage falls within an appropriate value and the capacitor CX is not destroyed.

When the above closed circuit is formed, the buffer coil Ly continues to flow current to the secondary coil L2 according to a time constant corresponding to the inductance. Therefore, by appropriately setting the inductance of the buffer coil Ly, the buffer coil Ly can be operated as a constant current source that maintains a substantially constant current flowing in the closed circuit formed when the operation of the power conversion unit 250 is stopped. it can.

FIG. 3 is an equivalent circuit diagram of the above-described resonant circuit and closed circuit. In the equivalent circuit diagram of FIG. 3, the switch SW corresponds to the MOS transistors Q1 to Q4, and the constant current source VCS (abbreviation of variable current source) corresponds to the buffer coil Ly. The variable coil LM and the AC power source Vc correspond to the secondary coil L2.

Next, the flow of wireless power feeding using the wireless power feeding system 1 will be described. FIG. 4 is a diagram showing a processing flow of the wireless power feeding system 1 according to the embodiment of the present invention. When the vehicle on which the power receiving device 200, the battery 300, and the load 400 are mounted is parked at a predetermined charging position, the processing flow of FIG.

In step S10, the ground-side power transmission device 100 issues a charge inquiry to the vehicle-side power reception device 200. Here, for example, charging is inquired by transmitting a predetermined communication message from the communication unit 120 of the power transmission device 100 to the communication unit 220 of the power reception device 200.

In step S20, the power receiving device 200 that has received the charge inquiry in step S10 notifies the power transmitting device 100 of the allowable current of the battery 300 during charging. At this time, the power receiving apparatus 200 determines the allowable current based on, for example, the charge state or deterioration state of the battery 300 measured in advance, and transmits information indicating the value of the allowable current from the communication unit 220 to the communication unit 120 of the power transmission apparatus 100. Send. Note that, when charging is unnecessary, the power receiving apparatus 200 may notify the power transmitting apparatus 100 to that effect. In this case, the process flow of FIG. 3 is complete | finished, without performing the process after step S30.

In step S30, the power transmission device 100 determines the amount of current and starts power transmission to the power reception device 200. At this time, the power transmitting apparatus 100 compares the output current value corresponding to the allowable current notified from the power receiving apparatus 200 in step S20 and its own rated current value, and selects the smaller one to determine the current amount. . Then, the power transmission control unit 110 controls the power conversion unit 140 to cause an alternating current corresponding to the determined current amount to flow through the primary coil L1, thereby generating an alternating magnetic field in the primary coil L1 and starting power transmission. At this time, by further transmitting information representing the frequency f of the alternating current flowing through the primary coil L1 from the communication unit 120 to the communication unit 220 of the power reception device 200, the power reception control unit 210 of the power reception device 200 sets the frequency f to It is preferable that the above-described basic drive signal Sr can be generated. Alternatively, the frequency f may be notified from the power transmitting apparatus 100 to the power receiving apparatus 200 when an inquiry for charging is made in step S10.

In step S40, the power receiving device 200 performs drive control processing of the power conversion unit 250 according to the alternating current i that flows through the resonance circuit including the secondary coil L2 by receiving the alternating magnetic field emitted from the primary coil L1. Here, drive control of the power conversion unit 250 according to the alternating current received from the power transmission device 100 is performed by performing the above-described processing in each unit of the drive control unit 240. Thereby, the battery 300 is charged in the constant current (CC) mode. In addition, when the operation of the power conversion unit 250 is stopped due to an abnormality or the like when the drive control process of the power conversion unit 250 is performed in step S40, the resonance circuit and the resonance circuit are caused by the action of the buffer coil Ly as described above. Form different closed circuits to mitigate changes in the current flowing through the secondary coil L2.

In step S50, the power receiving device 200 determines whether or not the state of charge (SOC) of the battery 300 has reached a predetermined value, for example, 80% or more. As a result, if the SOC is less than 80%, the drive control process of step S40 is repeated. If the SOC becomes 80% or more, the constant current mode is changed to the constant voltage (CV) mode and the process proceeds to step S60.

In step S60, the power receiving device 200 notifies the power transmitting device 100 of a charging current corresponding to the current state of charge of the battery 300. At this time, the power receiving apparatus 200 determines a charging current with a value smaller than the allowable current notified in step S20 based on the current charging state of the battery 300, and receives information indicating the value of the charging current from the communication unit 220. It transmits to the communication part 120 of the power transmission apparatus 100.

In step S70, the power receiving device 200 performs the same drive control process as in step S40, thereby charging the battery 300 in the constant voltage (CV) mode. In Step S70 as well as Step S40, when the operation of the power converter 250 is stopped due to the occurrence of an abnormality or the like when the drive control process of the power converter 250 is being performed, the buffer coil Ly as described above is stopped. By the action, a closed circuit different from the resonance circuit is formed, and the change in the current flowing through the secondary coil L2 is alleviated.

In step S80, the power receiving device 200 determines whether the state of charge (SOC) of the battery 300 has reached 100% of full charge. As a result, if the SOC is less than 100%, the process returns to step S60 to continue charging the battery 300, and if the SOC reaches 100%, the process proceeds to step S90.

In step S90, charging of the battery 300 is terminated. Here, for example, by transmitting a predetermined communication message from the communication unit 220 of the power receiving device 200 to the communication unit 120 of the power transmission device 100, the power transmission stop is instructed. In the power transmission device 100, power transmission is stopped by interrupting the energization of the primary coil L1 in response to the power transmission stop instruction. When the power transmission from the power transmission device 100 is stopped, the operation of the power conversion unit 250 in the power reception device 200 is stopped, thereby completing the charging of the battery 300.

When the charging of the battery 300 is completed in step S90, the processing flow of FIG. Thereby, the wireless power supply of the wireless power supply system 1 is completed.

According to the embodiment of the present invention described above, the following operational effects are obtained.

(1) The power receiving device 200 is wirelessly powered by receiving an alternating magnetic field emitted from the primary coil L1 installed on the ground side. The power receiving apparatus 200 includes a secondary coil L2, a resonance coil Lx and a resonance capacitor Cx, which are resonance elements that are connected to the secondary coil L2 and constitute a resonance circuit having a predetermined resonance frequency together with the secondary coil L2. A resonance circuit including MOS transistors Q1 to Q4 which are switching elements and including a secondary coil L2 and a power conversion unit 250 that controls an alternating current i flowing through the resonance circuit by switching the MOS transistors Q1 to Q4. And a buffer coil Ly that is a closed circuit element that selectively forms a closed circuit different from the above. Since it did in this way, even when the operation | movement of the power converter 250 stops when the electric current is flowing into the secondary coil L2 of the power receiving apparatus 200, generation | occurrence | production of an unnecessary leakage magnetic flux can be suppressed.

(2) The buffer coil Ly acts as a constant current source that maintains the current flowing in the closed circuit substantially constant. Since it did in this way, when the operation | movement of the power converter 250 stops, the change of the electric current which flows into the secondary coil L2 can be relieve | moderated, and generation | occurrence | production of a leakage magnetic flux can be suppressed reliably.

(3) The buffer coil Ly does not form a closed circuit during the operation of the power conversion unit 250, and forms a closed circuit when the operation of the power conversion unit 250 is stopped. Since it did in this way, generation | occurrence | production of an unnecessary leakage magnetic flux can be suppressed when the operation | movement of the power conversion part 250 stops, implement | achieving efficient wireless electric power feeding using a resonance circuit during the operation | movement of the power conversion part 250. .

(4) Since the above closed circuit element is the buffer coil Ly connected to both ends of the secondary coil L2 without going through the power converter 250, a closed circuit different from the resonance circuit can be selectively selected with a simple configuration. The closed circuit element to be formed can be realized.

In the embodiment described above, each component included in the drive control unit 240 may be realized by software executed by a microcomputer or the like, or realized by hardware such as FPGA (Field-Programmable Gate Array). May be. These may be used in combination.

In the above-described embodiment, the wireless power feeding system 1 used for wireless power feeding to a vehicle such as an electric vehicle has been described. However, the present invention is not limited to wireless power feeding to a vehicle, but is applied to a wireless power feeding system for other uses. May be.

The embodiment and various modifications described above are merely examples, and the present invention is not limited to these contents as long as the features of the invention are not impaired. Moreover, although various embodiment and the modification were demonstrated above, this invention is not limited to these content. Other embodiments conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Wireless power supply system 100 Power transmission apparatus 110 Power transmission control part 120 Communication part 130 AC power supply 140 Power conversion part 200 Power receiving apparatus 210 Power reception control part 220 Communication part 230 AC current detection part 240 Drive control part 241 Voltage acquisition part 243 Drive signal generation part 244 Gate drive circuit 250 Power conversion unit 300 Battery 400 Load L1 Primary coil L2 Secondary coil Lx Resonant coil Ly Buffer coil Cx Resonant capacitor Tr Transformer Q1, Q2, Q3, Q4 MOS transistor

Claims (4)

A power receiving device that receives an alternating magnetic field emitted from a primary coil installed on the ground side and is wirelessly powered,
A secondary coil;
A resonant element connected to the secondary coil to form a resonant circuit having a predetermined resonant frequency together with the secondary coil;
A power converter that has a plurality of switching elements and controls the alternating current flowing in the resonance circuit by switching the plurality of switching elements, respectively;
And a closed circuit element that selectively forms a closed circuit that includes the secondary coil and is different from the resonant circuit. The power receiving device according to claim 1,
The closed circuit element is a power receiving device that acts as a constant current source that maintains a substantially constant current flowing in the closed circuit. The power receiving device according to claim 1 or 2,
The closed circuit element does not form the closed circuit during the operation of the power conversion unit, and forms the closed circuit when the operation of the power conversion unit is stopped. The power receiving device according to claim 1 or 2,
The power receiving device, wherein the closed circuit element is a coil connected to both ends of the secondary coil without passing through the power converter.

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