JP2021040465A - Transmission device and power transmission system - Google Patents

Abstract

To provide a transmission device and a power transmission system that can efficiently transmit power to a power receiving device.SOLUTION: A transmission device includes a power transmission coil L1 that transmits power to a power receiving device in a non-contact manner, and a protection circuit 130 that suppresses power transmission from the power transmission coil to the power receiving device when an overcurrent flowing through the power transmission coil is detected. The protection circuit changes a time from suppression of the transmission to release of the suppression of the transmission, depending on the frequency of suppression of the transmission. In low frequency, the protection circuit takes less time than that of high frequent.SELECTED DRAWING: Figure 2

Description

The present invention relates to a power transmission device and a power transmission system.

In a system that transmits power from a power transmitting device to a power receiving device in a non-contact manner, in order to protect the inverter in the power transmitting device, when the current flowing through the inverter exceeds the limit value, the transmitted power is reduced so that the current falls below the limit value. There is a technique for reducing the power (see, for example, Patent Document 1). Further, when the primary current flowing from the primary coil of the transformer to the GND exceeds a predetermined overcurrent threshold, the power supply to the primary coil is stopped to protect the load on the secondary side from overcurrent. (See, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2018-7509 Japanese Unexamined Patent Publication No. 2004-248365

By suppressing the transmission from the power transmitting device to the power receiving device, the power receiving device can be protected from overvoltage or overcurrent due to overtransmission. However, it may not be possible to efficiently transmit power to the power receiving device depending on the timing at which the suppression of power transmission from the power transmitting device to the power receiving device is released.

Therefore, the present disclosure provides a power transmission device and a power transmission system capable of efficiently transmitting power to a power receiving device.

This disclosure is
A power transmission coil that transmits power to the power receiving device in a non-contact manner,
When an overcurrent flowing through the power transmission coil is detected, a protection circuit for suppressing power transmission from the power transmission coil to the power receiving device is provided.
The protection circuit provides a power transmission device that changes the time from suppressing the power transmission to releasing the suppression of the power transmission according to the frequency of suppressing the power transmission.

In addition, this disclosure is
A power transmission system including a power transmission device and a power reception device.
The power transmission device
A power transmission coil that transmits power to the power receiving device in a non-contact manner,
When an overcurrent flowing through the power transmission coil is detected, a protection circuit for suppressing power transmission from the power transmission coil to the power receiving device is provided.
The protection circuit provides a power transmission system that changes the time from suppressing the power transmission to releasing the suppression of the power transmission according to the frequency of suppressing the power transmission.

According to the technique of the present disclosure, it is possible to provide a power transmission device and a power transmission system capable of efficiently transmitting power to a power receiving device.

It is a figure which shows one configuration example of the power transmission system in one Embodiment. It is a figure which shows one configuration example of a power transmission device. It is a figure which shows one configuration example of a control part. It is a timing chart which illustrates the waveform of each part of a power transmission apparatus. It is a timing chart which exemplifies the state which repeats suppressing and releasing the power transmission at the time of a light load. It is a timing chart which exemplifies the state which repeats suppressing and releasing the power transmission at the time of a heavy load.

Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a power transmission system according to an embodiment. The power transmission system 100 shown in FIG. 1 is a system that transmits power from the power transmission device 1 to the power reception device 2 in a non-contact manner by a magnetic field resonance method. The power transmission system 100 includes a power transmission device 1, a power receiving device 2, and a load 3.

The power transmission device 1 is a device that transmits electric power to the power receiving device 2 in a non-contact manner, and includes a resonance circuit 11, a drive circuit 12, a power supply 13, and a control circuit 14.

The resonance circuit 11 is a circuit that generates an alternating magnetic field, and includes a capacitive element C1 and a coil L1. The capacitive element C1 includes a first terminal and a second terminal. The first terminal of the capacitance element C1 is connected to the first output terminal of the drive circuit 12, and the second terminal of the capacitance element C1 is connected to the first terminal of the coil L1. The coil L1 is a power transmission coil and generates an alternating magnetic field. The coil L1 includes a first terminal and a second terminal. The first terminal of the coil L1 is connected to the second terminal of the capacitive element C1, and the second terminal of the coil L1 is connected to the second output terminal of the drive circuit 12.

The drive circuit 12 is a circuit that supplies an alternating current I1 to the resonant circuit 11 and generates an alternating magnetic field in the resonant circuit 11, and includes switch elements S1 and S2. The switch elements S1 and S2 are elements that can open and close the circuit, and each includes a first terminal, a second terminal, and a control terminal, respectively. The first terminal of the switch element S1 is connected to the first terminal of the power supply 13, the second terminal of the switch element S1 is connected to the first terminal of the switch element S2, and the control terminal of the switch element S1 is the control circuit 14. Connected to. The first terminal of the switch element S2 is connected to the second terminal of the switch element S1, the second terminal of the switch element S2 is connected to the second terminal of the power supply 13, and the control terminal of the switch element S2 is the control circuit 14. Connected to. The connection point between the second terminal of the switch element S1 and the first terminal of the switch element S2 corresponds to the first output terminal of the drive circuit 12. The second terminal of the switch element S2 corresponds to the second output terminal of the drive circuit 12.

The alternating current I1 is supplied to the resonance circuit 11 by alternately opening and closing the switch elements S1 and S2. The switch elements S1 and S2 are, for example, bipolar transistors or MOSFETs (Metal Oxide Semiconductor Field Effect Transistor), but are not limited thereto. As the switch elements S1 and S2, any element capable of opening and closing the circuit can be used.

The power supply 13 is a constant voltage source and includes a first terminal and a second terminal. The first terminal (high voltage side terminal) of the power supply 13 is connected to the first terminal of the switch element S1, and the second terminal (low voltage side terminal) of the power supply 13 is connected to the second terminal of the switch element S2.

The control circuit 14 is a circuit that controls the opening and closing of the switch elements S1 and S2 to control the frequency of the alternating current I1 supplied to the resonant circuit 11 and controls the frequency of the alternating magnetic field generated by the resonant circuit 11. The control circuit 14 detects the overvoltage generated by the power receiving device 2 based on the alternating current I1 flowing through the resonance circuit 11. When the control circuit 14 detects the overvoltage generated by the power receiving device 2, the control circuit 14 controls the operation of at least one of the switch elements S1 and S2 so that the non-contact power transmission from the power transmitting device 1 to the power receiving device 2 is suppressed. .. For example, when the control circuit 14 detects the overvoltage generated by the power receiving device 2, at least one of the switch elements S1 and S2 is turned off, and the power transmission from the power transmitting device 1 to the power receiving device 2 is stopped.

The configuration of the power transmission device 1 is not limited to the example of FIG. For example, the power transmission device 1 may include a wireless communication module for wirelessly communicating with the power receiving device 2 by a predetermined communication method such as Bluetooth (registered trademark) or Wi-Fi (registered trademark), or may provide electric power to an external power source. May be supplied from.

The power receiving device 2 is a device that receives the electric power transmitted from the power transmitting device 1 in a non-contact manner, and includes a resonance circuit 21, a rectifier circuit 22, an overvoltage detection circuit 23, and a control circuit 24.

The resonant circuit 21 is a circuit that receives electric power from the resonant circuit 11 in a non-contact manner. The resonant circuit 21 includes a capacitive element C2 and a coil L2. The capacitive element C2 includes a first terminal and a second terminal. The first terminal of the capacitance element C2 is connected to the first terminal of the coil L2, and the second terminal of the capacitance element C2 is connected to the first input terminal of the rectifier circuit 22. The coil L2 is a power receiving coil, and an alternating current is generated by an alternating magnetic field generated by the coil L1 and input to the rectifier circuit 22. The coil L2 includes a first terminal and a second terminal. The first terminal of the coil L2 is connected to the first terminal of the capacitive element C2, and the second terminal of the coil L2 is connected to the second input terminal of the rectifier circuit 22.

The rectifier circuit 22 is a circuit that rectifies the alternating current input from the resonance circuit 21 and outputs the voltage obtained by the rectification as the output voltage V1 from the first output terminal. The output voltage V1 is input to the overvoltage detection circuit 23. The rectifier circuit 22 includes a first input terminal, a second input terminal, a first output terminal, and a second output terminal. The first input terminal of the rectifier circuit 22 is connected to the second terminal of the capacitive element C2, and the second input terminal of the rectifier circuit 22 is connected to the second terminal of the coil L2. Further, the first output terminal of the rectifier circuit 22 is connected to the first input terminal of the overvoltage detection circuit 23, and the second output terminal of the rectifier circuit 22 is connected to the second input terminal of the overvoltage detection circuit 23. The rectifier circuit 22 is, for example, a diode bridge, but is not limited to this. As the rectifier circuit 22, any circuit capable of rectifying alternating current can be used.

The overvoltage detection circuit 23 is a circuit that detects an overvoltage. The overvoltage referred to here means that the output voltage V2 of the overvoltage detection circuit 23 becomes the threshold voltage Vth1 or higher. The overvoltage detection circuit 23 includes a first input terminal, a second input terminal, a first output terminal, and a second output terminal. The first input terminal of the overvoltage detection circuit 23 is connected to the first output terminal (high voltage side output terminal) of the rectifier circuit 22, and the second input terminal of the overvoltage detection circuit 23 is the second output terminal (low voltage) of the rectifier circuit 22. It is connected to the side output terminal). Further, the first output terminal of the overvoltage detection circuit 23 is connected to the first terminal (high voltage side terminal) of the load 3, and the second output terminal of the overvoltage detection circuit 23 is the second terminal (low voltage side terminal) of the load 3. Connected to. That is, the overvoltage detection circuit 23 is connected between the rectifier circuit 22 and the load 3. The overvoltage detection circuit 23 outputs an output voltage V2 corresponding to the output voltage V1 input from the rectifier circuit 22. The output voltage V2 is input to the load 3. The overvoltage detection circuit 23 includes a switch element S3, a capacitance element C3, a capacitance element C4, and a control circuit 24.

The switch element S3 is an element capable of opening and closing a circuit, and includes a first terminal, a second terminal, and a control terminal. The first terminal of the switch element S3 is connected to the first output terminal of the rectifier circuit 22 and the first terminal of the capacitance element C3, and the second terminal of the switch element S3 is the first terminal of the load 3 and the first terminal of the capacitance element C3. It is connected to two terminals and the first terminal (high voltage side terminal) of the capacitance element C4. That is, the switch element S3 is connected in series between the rectifier circuit 22 and the load 3. A control signal for controlling the opening and closing of the switch element S3 is input to the control terminal of the switch element S3. The first terminal of the switch element S3 corresponds to the first input terminal of the overvoltage detection circuit 23, and the second terminal of the switch element S3 corresponds to the first output terminal of the overvoltage detection circuit 23. Hereinafter, the connection point between the first terminal of the switch element S3 and the first terminal of the capacitance element C3 will be referred to as a node N1. Further, the connection points of the second terminal of the switch element S3, the second terminal of the capacitance element C3, and the first terminal of the capacitance element C4 are referred to as nodes N2. The voltage of the node N1 corresponds to the output voltage V1 of the rectifier circuit 22, and the voltage of the node N2 corresponds to the output voltage V2 of the overvoltage detection circuit 23. The switch element S3 is, for example, a bipolar transistor or a MOSFET, but is not limited thereto. As the switch element S3, any element capable of opening and closing the circuit can be used.

The capacitive element C3 includes a first terminal and a second terminal. The first terminal of the capacitance element C3 is connected to the node N1, and the second terminal of the capacitance element C3 is connected to the node N2. That is, the capacitance element C3 is connected in parallel with the switch element S3.

The capacitive element C4 includes a first terminal and a second terminal. The first terminal of the capacitance element C4 is connected to the node N2, and the second terminal (low voltage side terminal) of the capacitance element C4 is connected to the second output terminal of the rectifier circuit 22 and the second terminal of the load 3. That is, the capacitive element C4 is connected in parallel with the load 3. The second terminal of the capacitive element C4 corresponds to the second input terminal and the second output terminal of the overvoltage detection circuit 23. Hereinafter, the connection point of the second terminal of the capacitance element C4, the rectifier circuit 22, and the load 3 will be referred to as a node N3. Node N3 may be connected to ground.

The control circuit 24 is a circuit that detects the overvoltage and controls the opening and closing of the switch element S3 to suppress the output voltage V2 and notify the power transmission device 1 of the overvoltage detection result. The control circuit 24 normally turns on the switch element S3, and turns off the switch element S3 when it detects an overvoltage. When the switch element S3 is turned off, the load capacitance of the overvoltage detection circuit 23 becomes small, and the output voltage V1 rises sharply. When the output voltage V1 rises, the alternating current I1 supplied by the power transmission device 1 sharply increases. Therefore, the power transmission device 1 can detect the overvoltage generated by the power receiving device 2 based on the magnitude of the alternating current I1.

The configuration of the power receiving device 2 is not limited to the example of FIG. For example, the power receiving device 2 may include a wireless communication module, a filter circuit, an amplifier circuit, or the like for wireless communication with the power transmission device 1 by a predetermined communication method such as Bluetooth or Wi-Fi.

The load 3 is supplied with the electric power received by the power receiving device 2 in a non-contact manner. The load 3 includes a first terminal and a second terminal. The first terminal of the load 3 is connected to the node N2, and the second terminal of the load 3 is connected to the node N3. The load 3 is, for example, an IC (Integrated Circuit), a battery, or a sensor, but is not limited thereto.

Next, the operation of the power transmission system 100 will be described.

First, the power transmission device 1 starts non-contact power transmission. Specifically, the control circuit 14 starts driving the drive circuit 12 (open / close control of the switch elements S1 and S2). As a result, an alternating current I1 having a predetermined frequency is supplied to the resonance circuit 11. When the alternating current I1 is supplied to the resonant circuit 11, the coil L1 generates an alternating magnetic field having the same frequency as the alternating current I1.

When the power receiving device 2 approaches the power transmitting device 1 during power transmission, the coil L2 generates an alternating current by an alternating magnetic field, and the alternating current is input to the rectifier circuit 22. When an alternating current is input, the rectifier circuit 22 rectifies the alternating current and generates an output voltage V1. When the output voltage V1 is input from the rectifier circuit 22, the overvoltage detection circuit 23 outputs the output voltage V2 corresponding to the output voltage V1. This output voltage V2 is applied to the load 3, and power corresponding to the output voltage V2 is supplied to the load 3.

Here, the operation of the overvoltage detection circuit 23 will be described in detail. When the output voltage V2 is not output, the switch element S3 of the overvoltage detection circuit 23 is off until the power receiving device 2 starts receiving power. When the power receiving device 2 starts receiving power, the capacitance elements C3 and C4 are charged, and the output voltages V1 and V2 rise.

The control circuit 24 turns on the switch element S3 when the output voltage V1 becomes the threshold voltage Vth2 or more. As a result, the capacitance element C3 is removed from the load capacitance of the overvoltage detection circuit 23, and the load capacitance becomes large. The threshold voltage Vth2 is set lower than the threshold voltage Vth1.

After that, the output voltages V1 and V2 corresponding to the load 3 are output from the rectifier circuit 22 and the overvoltage detection circuit 23, respectively. The output voltage V2 fluctuates with the output voltage V1 while the switch element S3 is on.

When the load 3 fluctuates while the power receiving device 2 is receiving power and the output voltage V2 becomes the threshold voltage Vth1 or more (overvoltage is detected), the control circuit 24 turns off the switch element S3.

When the switch element S3 is turned off, the capacitance element C3 is connected in series with the capacitance element C4, so that the load capacitance of the overvoltage detection circuit 23 becomes small and the output voltage V1 rises sharply. When the output voltage V1 rises, the AC voltage of the resonance circuit 21 rises, and the AC current I1 supplied by the power transmission device 1 sharply increases. At this time, the output voltage V2 output to the load 3 rises more slowly than the output voltage V1 according to the capacitance ratio of the capacitance elements C3 and C4, so that the overvoltage to the load side is suppressed. The capacitance of the capacitance element C3 is set to be smaller than the capacitance of the capacitance element C4.

When the control circuit 14 of the power transmission device 1 detects that the AC current I1 is equal to or higher than the threshold current Is (for example, the voltage corresponding to the AC current I1 is equal to or higher than the threshold voltage corresponding to the threshold current Is), It is determined that an overvoltage has occurred in the power receiving device 2. When the control circuit 14 determines that an overvoltage has occurred in the power receiving device 2, for example, at least one of the switch elements S1 and S2 is turned off, and power transmission from the coil L1 to the coil L2 is stopped. Instead of stopping the power transmission, the power transmission device 1 may reduce the amount of power supplied to the power receiving device 2 by changing the power transmission frequency or lowering the voltage of the power supply 13.

When the power transmission from the power transmission device 1 is suppressed, the output voltages V1 and V2 of the power receiving device 2 decrease. Therefore, the power receiving device 2 can be protected from overvoltage or overcurrent due to overtransmission from the power transmitting device 1 to the power receiving device 2. It should be noted that the suppression of power transmission may include the suspension of power transmission (the same applies to other explanations).

As described above, when the power receiving device 2 in one embodiment detects an overvoltage, the switch element S3 is turned off, the load capacitance of the overvoltage detection circuit 23 is reduced, and the output voltage V2 output to the load 3 is set to the threshold voltage Vth1. Suppress so that it does not exceed the above. Then, the power receiving device 2 notifies the power transmission device 1 of the occurrence of the overvoltage by increasing the output voltage V1 and increasing the AC current I1. As a result, the power receiving device 2 can instantly notify the power transmission device 1 of the occurrence of overvoltage (in a time shorter than the communication interval of wireless communication). As a result, when an overvoltage is generated in the power receiving device 2, the power transmission device 1 can quickly suppress the power transmission and suppress the generation of the overvoltage in the power receiving device 2.

Next, one configuration example of the power transmission device 1 in one embodiment will be described.

The power transmission device 1 includes a coil L1 and a control circuit 14. The coil L1 is a power transmission coil that transmits power to the power receiving device 2 in a non-contact manner. The control circuit 14 provides a protection circuit 130 (see FIG. 2, details described later) that suppresses power transmission from the coil L1 to the power receiving device 2 when an overcurrent (excessive alternating current I1) flowing through the coil L1 is detected. Have. The protection circuit 130 protects the power receiving device 2 from overvoltage or overcurrent due to overtransmission by suppressing power transmission from the coil L1 to the power receiving device 2.

In FIG. 1, when the protection circuit 130 suppresses non-contact power transmission from the power transmission device 1 to the power reception device 2, the voltage generated on the power reception device 2 side (power reception side voltage) decreases, so that the protection circuit 130 is a power reception device. 2 can be protected from overvoltage or overcurrent due to overtransmission. The power receiving side voltage is, for example, an output voltage V1 or an output voltage V2. If the power receiving side voltage drops too much, the operation of the load 3 such as the load 3 stopping will be affected. Therefore, before the power receiving side voltage drops too much, the suppression of power transmission from the power transmitting device 1 to the power receiving device 2 is released. There is a need to.

However, depending on the timing at which the suppression of power transmission from the power transmission device 1 to the power reception device 2 is released, it may not be possible to efficiently transmit power to the power reception device 2. For example, if the timing of releasing the suppression of power transmission from the power transmitting device 1 to the power receiving device 2 is released too late, the power required by the power receiving device 2 may be insufficient. On the contrary, if the timing of releasing the suppression of power transmission from the power transmission device 1 to the power reception device 2 is too early, there is a possibility that more power than necessary is transmitted from the power transmission device 1 to the power reception device 2.

Further, when the weight of the load 3 (that is, the resistance value of the load 3) changes, the rate of decrease of the power receiving side voltage also changes due to the difference in the time constant, so that the suppression of power transmission from the power transmitting device 1 to the power receiving device 2 is released. Depending on the timing, the power receiving side voltage may become excessive or too small. For example, when the load 3 is heavy (that is, the resistance value of the load 3 is small), if the timing of releasing the suppression of power transmission from the power transmission device 1 to the power receiving device 2 is too late, the voltage on the power receiving side may drop too much. .. On the contrary, when the load 3 is light (that is, the resistance value of the load 3 is large), if the timing of releasing the suppression of power transmission from the power transmission device 1 to the power receiving device 2 is too early, the voltage on the receiving side at the time of releasing is too high. There is a risk. That is, when the load 3 is relatively heavy, it is required to quickly release the suppression of power transmission, while when the load 3 is relatively light, the suppression of power transmission is released later than when the load 3 is heavy. May be good.

The electric power received by the power receiving device 2 from the power transmitting device 1 may fluctuate each time the positional relationship such as the gap distance and the center position between the power transmitting device 1 and the power receiving device 2 deviates. Therefore, as the load 3 becomes lighter, the power required by the power receiving device 2 and the load 3 becomes smaller, so that the power is excessively transmitted from the power transmitting device 1 to the power receiving device 2 (excessive power required by the power receiving device 2 and the load 3). Power supply) is likely to occur. Therefore, the lighter the load 3, the higher the frequency with which the overcurrent flowing through the coil L1 is detected (that is, the frequency with which power transmission is suppressed). On the contrary, as the load 3 becomes heavier, the electric power required by the power receiving device 2 and the load 3 increases, so that overtransmission from the power transmitting device 1 to the power receiving device 2 is less likely to occur. Therefore, the heavier the load 3, the lower the frequency with which the overcurrent flowing through the coil L1 is detected (that is, the frequency with which power transmission is suppressed).

The protection circuit 130 according to the present disclosure changes the time from suppressing the power transmission to releasing the suppression of the power transmission (hereinafter, also referred to as "time T") according to the frequency of suppressing the power transmission. As a result, the protection circuit 130 can release the suppression of power transmission at an appropriate timing according to the weight of the load 3, so that power can be efficiently transmitted to the power receiving device 2.

For example, the protection circuit 130 shortens the time T as the frequency of suppressing power transmission is reduced, so that when the load 3 is relatively heavy (heavy load state), the power shortage and the power receiving side voltage required by the power receiving device 2 are insufficient. It is possible to suppress an excessive decrease in power. On the contrary, the protection circuit 130 lengthens the time T as the frequency of suppressing power transmission increases, so that excessive power transmission from the power transmission device 1 to the power receiving device 2 in a state where the load 3 is relatively light (light load state). It is possible to suppress the power and the excessive voltage on the receiving side at the time of release. As described above, the protection circuit 130 can efficiently transmit power to the power receiving device 2 by shortening the time T when the frequency of suppressing power transmission is low as compared with the case where the frequency of suppressing power transmission is high.

Next, an example of one configuration of the power transmission device will be described.

FIG. 2 is a diagram showing a configuration example of a power transmission device. The power transmission device 1 shown in FIG. 2 includes a resonance circuit 11, a drive circuit 12, a pre-driver 110, and a protection circuit 130.

The resonance circuit 11 has a circuit in which the capacitance element C1 and the coil L1 are connected in series, but when a desired resonance state is formed, the capacitance element C1 may be omitted, or other circuit forms may be used. Good.

The drive circuit 12 is a circuit that drives the coil L1. In this example, the drive circuit 12 is a half-bridge circuit in which the switch element S1 and the switch element S2 are connected in series. However, the drive circuit 12 may be a full bridge circuit in which four switch elements are connected in an H shape, or a bridge circuit of another drive type.

The pre-driver 110 is an integrated circuit that has an enable terminal 111 to which an enable signal F is input and controls the operation of the drive circuit 12. The enable signal F is generated by the signal generation unit 80 described later based on the power control signal E supplied from the outside of the protection circuit 130 and the detection result of the overcurrent by the protection circuit 130. The enable signal F is an example of a control signal that controls suppression of power transmission. The pre-driver 110 is a gate driver that drives the respective gates of the switch elements S1 and S2 when the switch elements S1 and S2 are MOSFETs. The pre-driver 110 switches whether or not to suppress power transmission from the coil L1 to the power receiving device 2 by controlling the operation of the drive circuit 12 based on the enable signal F.

When the enable signal F input to the enable terminal 111 becomes negate (for example, low level), the predriver 110 stops the switching operation of the drive circuit 12 and suppresses power transmission from the coil L1 to the power receiving device 2.

On the other hand, when the enable signal F input to the enable terminal 111 becomes asserted (for example, high level), the predriver 110 releases the suppression of power transmission from the coil L1 to the power receiving device 2. The predriver 110 controls the switching operation of the drive circuit 12 with the drive frequency (switching frequency) controlled by the frequency control signal J in a state where the suppression of power transmission from the coil L1 to the power receiving device 2 is released, and the coil Power is transmitted from L1.

The power transmission device 1 may include a control unit that supplies a frequency control signal J for controlling the drive frequency of the drive circuit 12 to the pre-driver 110.

FIG. 3 is a diagram showing a configuration example of the control unit. The control unit 120 shown in FIG. 3 outputs the frequency control signal J and the power control signal E, and the frequency output signal G is input. The frequency control signal J is a signal for controlling the drive frequency of the drive circuit 12. The power control signal E is a signal that controls the magnitude of the transmitted power in power transmission. The frequency output signal G is a signal that changes according to the frequency with which the protection circuit 130 suppresses power transmission, and is supplied from the protection circuit 130.

The control unit 120 is, for example, a microcomputer including a processor 124, a memory 125, a first PWM (Pulse Width Modulation) module 121, a second PWM module 122, and an AD (Analog to Digital) converter 123.

The first PWM module 121 generates a frequency control signal J, which is a PWM signal having a constant duty ratio (for example, 50%) and a variable frequency, based on arithmetic processing by the processor 124. The first PWM module 121 changes the frequency of the frequency control signal J so that the drive circuit 12 switches at a drive frequency that causes the resonance circuit 11 to resonate at a desired resonance frequency.

The second PWM module 122 generates a power control signal E which is a PWM signal having a variable duty ratio and a constant frequency based on arithmetic processing by the processor 124. The power control signal E has a frequency lower than the frequency of the frequency control signal J, and is a signal asynchronous with the frequency control signal J. The second PWM module 122 changes the duty ratio of the power control signal E based on the power request received from the power receiving device 2 via wireless communication. The second PWM module 122 adjusts the duty ratio of the power control signal E to the duty ratio according to the power request value from the power receiving device 2, and if there is no power request from the power receiving device 2, the duty ratio of the power control signal E is adjusted. Minimize.

Each function of the control unit 120 is realized by operating a processor 124 such as a CPU (Central Processing Unit) by a program readable and stored in the memory 125.

In FIG. 2, the protection circuit 130 changes the time T from the stop of the power transmission to the release of the stop of the power transmission according to the frequency with which the protection circuit 130 stops the power transmission. In this example, the protection circuit 130 has a time T from stopping the operation of the drive circuit 12 to releasing the stop of the operation of the drive circuit 12, depending on the frequency with which the protection circuit 130 stops the operation of the drive circuit 12. To change.

The protection circuit 130 includes a current detection unit 30, a peak hold unit 40, a comparison unit 70, a signal generation unit 80, a threshold value setting circuit 60, a time adjustment circuit 50, and a frequency output unit 90.

The current detection unit 30 is a circuit that outputs a current detection signal A that changes according to the magnitude of the alternating current I1 flowing through the coil L1. By converting the alternating current I1 into a current and a voltage, the current detection signal A Detect as voltage. The current detection unit 30 includes, for example, a series circuit in which the resistance element 31 and the capacitance element 32 are connected in series, and a diode 33 in which the capacitance element 32 is connected in parallel. The series circuit of the resistance element 31 and the capacitance element 32 is connected in parallel to the coil L1, and the cathode of the diode 33 is connected to the intermediate connection point between the resistance element 31 and the capacitance element 32. The voltage of the current detection signal A corresponds to the voltage across the capacitive element 32 and fluctuates periodically in a sinusoidal manner.

The peak hold unit 40 is a circuit that holds the peak value of the current detection signal A, and holds the positive peak value of the current detection signal A in the capacitor 47 by the action of negative feedback and outputs it as a voltage signal B. The peak hold portion 40 shown in FIG. 2 is a well-known circuit having resistors 43 and 44, operational amplifiers 41 and 42, diodes 45 and 46, and a capacitor 47. The peak hold unit 40 detects the peak value of the current detection signal A by the operational amplifier 41, and holds the detected peak value in the capacitor 47 via the operational amplifier 42. The operational amplifier 42 functions as a buffer.

The comparison unit 70 compares the voltage signal B corresponding to the peak value held by the peak hold unit 40 with the threshold value C, and outputs a binary overcurrent detection signal D representing the comparison result. The comparison unit 70 has resistors 71 and 72 and a comparator 73. The threshold value C is a voltage obtained by dividing the threshold value setting voltage generated by the threshold value setting circuit 60 by the resistors 71 and 72. The comparison unit 70 compares the voltage signal B input to the non-inverting input terminal with the threshold C input to the inverting input terminal, and when the voltage signal B exceeds the threshold C, the comparison unit 70 forcibly operates the drive circuit 12. A high-level overcurrent detection signal D for stopping is output. The high-level overcurrent detection signal D indicates that the overcurrent flowing through the coil L1 has been detected due to the generation of the overvoltage in the power receiving device 2.

The signal generation unit 80 generates an enable signal F based on the power control signal E that adjusts the magnitude of the transmitted power and the overcurrent detection signal D that represents the overcurrent detection result. The signal generation unit 80 includes resistors 81, 84, 85, a Schottky barrier diode 82, and a transistor 83. When the overcurrent detection signal D becomes high level, the transistor 83 is turned on, so that the enable signal F becomes low level regardless of the logic level of the power control signal E. The pre-driver 110 forcibly stops the operation of the drive circuit 12 and stops the power transmission when the enable signal F becomes low level.

Further, when the transistor 83 of the signal generation unit 80 is turned on and the enable signal F becomes low level, the transistor 61 of the threshold setting circuit 60 is turned off.

The threshold value setting circuit 60 raises or lowers the threshold value C based on the enable signal F. The threshold setting circuit 60 includes a transistor 61, resistors 62 to 64, 66, and a shunt diode 65. When the transistor 61 is turned from on to off, the threshold setting voltage generated by the shunt diode 65 is lowered, so that the threshold C is also lowered. That is, when the overcurrent detection signal D output from the comparator 73 reaches a high level, the transistor 61 is turned off and the threshold value C is lowered, so that the overcurrent detection signal D is maintained at a high level.

When the overcurrent detection signal D becomes high level, the operation of the drive circuit 12 is stopped, and the current flowing through the coil L1 becomes zero. As a result, the voltage of the voltage signal B output from the peak hold unit 40 gradually decreases due to the time constants of the transistor 55 (which functions as a variable resistor), the discharge resistor 56, and the capacitor 47.

When the voltage of the decreasing voltage signal B becomes lower than the threshold value C, the overcurrent detection signal D output from the comparator 73 becomes low level, so that the transistor 83 is turned off. Therefore, the enable signal F becomes a high level, and the operation of the drive circuit 12 resumes. At this time, when the enable signal F becomes high level, the transistor 61 of the threshold value setting circuit 60 is turned on, so that the threshold value setting voltage generated by the shunt diode 65 rises and the threshold value C also rises. That is, when the overcurrent detection signal D output from the comparator 73 becomes low level, the threshold value C rises when the transistor 61 is turned on, so that the overcurrent detection signal D is maintained at low level.

As described above, the logic level of the enable signal F becomes a low level when the protection circuit 130 suppresses the power transmission and becomes a high level when the protection circuit 130 releases the power transmission suppression. In this way, by smoothing the enable signal F, which repeats low level and high level depending on the presence or absence of protection operation, by a low-pass filter, a signal whose voltage increases as the frequency of suppressing power transmission decreases (in this example, frequency). The detection signal H) can be generated.

The time adjustment circuit 50 adjusts the length of the time T based on the enable signal F. In this example, the time adjustment circuit 50 generates the frequency detection signal H by smoothing the enable signal F, and changes the speed at which the capacitor 47 is discharged according to the magnitude of the voltage of the frequency detection signal H. Adjust the length of time T. The time adjustment circuit 50 includes a frequency detection unit 57 that detects the frequency of suppressing power transmission, and a time adjustment unit 58 that adjusts the length of the time T.

The frequency detection unit 57 is a circuit that outputs a frequency detection signal H that changes according to the frequency of suppressing power transmission based on the enable signal F that changes according to the detection result of the overcurrent by the comparison unit 70. The frequency detection unit 57 outputs the frequency detection signal H by smoothing the enable signal F. The frequency detection unit 57 includes, for example, a low-pass filter having a filter resistor 51 and a filter capacitor 52, and a voltage dividing circuit having resistors 53 and 54. The frequency detection unit 57 outputs the frequency detection signal H by smoothing the enable signal F with a low-pass filter and dividing the smoothed enable signal F with a voltage dividing circuit.

The time adjustment unit 58 is a circuit that adjusts the length of the time T according to the frequency detection signal H. The time adjusting unit 58 has a transistor 55 that functions as a variable resistor and a discharge resistor 56 that discharges the capacitor 47. The time adjusting unit 58 changes the speed (falling speed) of changing the peak value (voltage signal B) held by the capacitor 47 of the peak holding unit 40 according to the frequency detection signal H, so that the length of the time T is long. To adjust. The speed at which the voltage signal B is lowered represents the speed at which the capacitor 47 is discharged.

The frequency output unit 90 is a circuit that outputs a frequency output signal G that changes according to the frequency of suppressing power transmission by smoothing the enable signal F. The frequency output unit 90 has, for example, a filter circuit of a filter resistor 91 and a filter capacitor 92, and an output resistor 93 that outputs an enable signal F smoothed by the filter circuit as a frequency output signal G.

FIG. 4 is a timing chart illustrating the waveforms of each part of the power transmission device. When the alternating current I1 flows, a current detection signal A whose amplitude changes periodically is generated in synchronization with the phase of the alternating current I1. The lower limit of the current detection signal A is slightly lower than the ground due to the diode 33. The voltage signal B captures the peak value of the sinusoidal current detection signal A, and the value is clamped. Note that FIG. 4 is a schematic diagram showing a situation in which the voltage signal B drops.

FIG. 5 is a timing chart illustrating a state in which power transmission is repeatedly suppressed and released when a light load is applied. FIG. 6 is a timing chart illustrating a state in which power transmission is repeatedly suppressed and released when a heavy load is applied.

The threshold value C becomes the voltage value VC1 by the action of the threshold value setting circuit 60 during the switching operation of the drive circuit 12, and becomes the voltage value VC1 by the action of the threshold value setting circuit 60 during the non-switching operation of the drive circuit 12 (when the operation is stopped). The voltage value is VC2, which is lower than that.

As the AC current I1 rises, the voltage signal B also rises, and when the voltage value of the voltage signal B exceeds the voltage value VC1, the overcurrent detection signal D output from the comparator 73 becomes a high level. As a result, the enable signal F becomes low level, and the switching of the drive circuit 12 is stopped. When the switching of the drive circuit 12 is stopped, the voltage signal B is lowered by the time constant of the transistor 55, the discharge resistor 56, and the capacitor 47.

When the voltage value of the voltage signal B becomes lower than the voltage value VC2, the overcurrent detection signal D output from the comparator 73 becomes low level. As a result, the power control signal E is reflected in the enable signal F, so that the switching of the drive circuit 12 is restarted. The power control signal E is a PWM signal having a variable duty ratio, and the drive circuit 12 is switched during a high level period. In the frequency output signal G and the frequency detection signal H, the enable signal F is smoothed by a CR filter.

The higher the voltage of the frequency detection signal H, the smaller the on-resistance of the transistor 55, so that the time constant of the capacitor 47, the transistor 55, and the discharge resistance 56 becomes smaller. That is, since the falling speed of the voltage signal B becomes faster, the period during which the overcurrent detection signal D is at a high level (that is, the operation stop time of the drive circuit 12) becomes shorter (see FIG. 6). The higher the voltage of the frequency detection signal H, the lower the frequency of suppressing the power transmission, and the lower the frequency indicates the state of heavy load. Therefore, the protection circuit 130 shortens the time T as the frequency of suppressing power transmission is reduced. Therefore, in a state where the load 3 is relatively heavy (heavy load state), the power shortage and the power receiving side voltage required by the power receiving device 2 are insufficient. Excessive reduction can be suppressed.

On the other hand, as the voltage of the frequency detection signal H becomes lower, the on-resistance of the transistor 55 becomes larger, so that the time constant of the capacitor 47, the transistor 55, and the discharge resistance 56 becomes larger. That is, since the falling speed of the voltage signal B becomes slower, the period during which the overcurrent detection signal D is at a high level (that is, the operation stop time of the drive circuit 12) becomes longer (see FIG. 5). The lower the voltage of the frequency detection signal H, the higher the frequency of suppressing power transmission, and the higher the frequency, the lighter the load. Therefore, the protection circuit 130 lengthens the time T as the frequency of suppressing power transmission increases, so that when the load 3 is relatively light (light load state), excessive power transmission from the power transmission device 1 to the power reception device 2 may occur. Excessive power receiving side voltage at the time of release can be suppressed. Even if the operating time of the drive circuit 12 is shortened, the power consumption of the power receiving device 2 is small when the load is light, so that the power receiving device 2 is not easily affected by the shortened operating time.

Although the power transmission device and the power transmission system have been described above by the embodiment, the present invention is not limited to the above embodiment. Various modifications and improvements, such as combinations and substitutions with some or all of the other embodiments, are possible within the scope of the present invention.
is there.

1 Transmission device 2 Power receiving device 11 Resonance circuit 12 Drive circuit 30 Current detection unit 40 Peak hold unit 50 Time adjustment circuit 57 Frequency detection unit 58 Time adjustment unit 60 Threshold setting circuit 70 Comparison unit 80 Signal generation unit 90 Frequency output unit 100 Power transmission System 110 Predriver 120 Control 130 Protection circuit

Claims (14)

A power transmission coil that transmits power to the power receiving device in a non-contact manner,
When an overcurrent flowing through the power transmission coil is detected, a protection circuit for suppressing power transmission from the power transmission coil to the power receiving device is provided.
The protection circuit is a power transmission device that changes the time from suppressing the power transmission to releasing the suppression of the power transmission according to the frequency of suppressing the power transmission. The power transmission device according to claim 1, wherein the protection circuit shortens the time when the frequency is low as compared with the case where the frequency is high. The protection circuit
A frequency detection unit that outputs a frequency detection signal that changes according to the frequency based on the overcurrent detection result, and a frequency detection unit.
The power transmission device according to claim 1 or 2, further comprising a time adjusting unit that adjusts the length of the time according to the frequency detection signal. The protection circuit
It has a signal generation unit that generates a control signal for controlling the suppression of power transmission based on the detection result of the overcurrent.
The power transmission device according to claim 3, wherein the frequency detection unit generates the frequency detection signal based on the control signal. The power transmission device according to claim 4, wherein the frequency detection unit generates the frequency detection signal by smoothing the control signal. The protection circuit
A current detection unit that outputs a current detection signal that changes according to the magnitude of the current flowing through the power transmission coil.
A peak hold unit that holds the peak value of the current detection signal and
It has a comparison unit that compares the peak value held in the peak hold unit with a threshold value.
The power transmission device according to claim 4 or 5, wherein the signal generation unit generates the control signal based on the comparison result by the comparison unit. The protection circuit
The power transmission device according to claim 6, further comprising a threshold value setting circuit for raising or lowering the threshold value based on the control signal. The sixth or seventh aspect of the present invention, wherein the time adjusting unit adjusts the length of the time by changing the speed at which the peak value held by the peak holding unit is changed according to the frequency detection signal. Power transmission equipment. The signal generation unit generates the control signal based on the power control signal for controlling the magnitude of the transmitted power in the power transmission and the detection result of the overcurrent, according to any one of claims 4 to 8. The power transmission device described. The drive circuit that drives the power transmission coil and
A pre-driver that controls the operation of the drive circuit based on a power control signal that controls the magnitude of the transmitted power in the power transmission is provided.
The power transmission device according to claim 9, wherein the pre-driver switches whether or not to suppress the power transmission based on the control signal by controlling the operation of the drive circuit. A control unit that outputs the power control signal is provided.
The power transmission device according to claim 10, wherein the control unit supplies a frequency control signal for controlling the drive frequency of the drive circuit to the pre-driver. The frequency is the frequency at which the protection circuit stops the power transmission.
The power transmission device according to any one of claims 1 to 11, wherein the time is a time from stopping the power transmission to releasing the stop of the power transmission. The frequency is the frequency at which the protection circuit stops the operation of the drive circuit that drives the power transmission coil.
The power transmission device according to any one of claims 1 to 12, wherein the time is a time from stopping the operation of the drive circuit to releasing the stop of the operation of the drive circuit. A power transmission system including a power transmission device and a power reception device.
The power transmission device
A power transmission coil that transmits power to the power receiving device in a non-contact manner,
When an overcurrent flowing through the power transmission coil is detected, a protection circuit for suppressing power transmission from the power transmission coil to the power receiving device is provided.
The protection circuit is a power transmission system that changes the time from suppressing the power transmission to releasing the suppression of the power transmission according to the frequency of suppressing the power transmission.