Power reception device and wireless power supply system

Abstract

To provide a power reception device and a wireless power supply system in which capacity control can be performed more easily.SOLUTION: A power reception device includes a first capacitor that is included with a power reception coil in a resonance circuit and has a variable capacity, a second capacitor that is connected in parallel with the first capacitor and has a fixed capacity, a switching circuit that is connected in series with both ends of the first capacitor and includes a switch that can be bidirectionally turned on / off, an AGC (Automatic Gain Control) circuit that converts, as an input, an AC voltage from both ends of the second capacitor to an AC voltage of a fixed amplitude value by increasing / decreasing an amplitude rate, and a switch control circuit that controls the switch of the switching circuit on the basis of comparison between the AC voltage of the fixed amplitude value outputted from the AGC circuit and a reference voltage.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power receiving device for wireless power supply and a wireless power supply system.

Background Art

[0002] Electrical devices using rechargeable batteries have become widespread, ranging from small electronic devices such as mobile devices and toys to large electric mobility such as electric vehicles and electric propulsion ships. Attention has been paid to the convenience of wireless power supply by the magnetic resonance method, which is one of the power supply methods for these devices. By making wireless power supply safe and faster, it is possible to reduce the trouble of forgetting to charge and the hassle of attaching and detaching cables.

[0003] In the magnetic resonance method, the power transmission device and the power receiving device each include a resonance circuit, and power is transmitted by utilizing the resonance phenomenon of these resonance circuits. Power can be transmitted most efficiently if the resonance frequencies of the resonance circuits provided in the power transmission device and the power receiving device are equal to the frequency of the transmission signal. However, there are cases where a flexible coil can be used to obtain a non-fixed resonance frequency, such as when the power receiving device side is a soft object or when it is necessary to attach it to products of various shapes. The inventors have proposed to realize capacitance control with a simple configuration in order to maintain resonance even in such cases (Patent Document 1, etc.).

[0004] In Patent Document 1, a control circuit for continuously adjusting the capacitance of a capacitor to match the phase of the frequency was proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a power receiving device and a wireless power supply system capable of more easily performing capacity control. **Means for Solving the Problems**

[0007] A power receiving device according to an embodiment of the present disclosure includes a variable-capacitance first capacitor included in a resonance circuit together with a power receiving coil, a fixed-capacitance second capacitor connected in parallel to the first capacitor, and a switching circuit including switches that are respectively connected in series to both ends of the first capacitor and can be turned on / off bidirectionally, an AGC (Automatic Gain Control) circuit that takes the AC voltage across both ends of the second capacitor as an input and converts it into an AC voltage with a constant amplitude value by increasing or decreasing the amplification factor, and a switch control circuit that controls the switches of the switching circuit based on a comparison between the AC voltage with the constant amplitude value output from the AGC circuit and a reference voltage.

[0008] Note that the AGC circuit may also be referred to as an AVC circuit (Automatic Volume Control).

[0009] In the power receiving device according to an embodiment of the present disclosure, after adjusting the AC voltage with the AGC circuit so as to have a constant maximum amplitude without dividing the applied AC voltage, it is used for comparison. The fixed reference voltage is output using a processor based on the phase difference between the current and the voltage, so that the capacitance of the resonance circuit can be controlled without being affected by changes in the impedance of the power receiving device. **Advantages of the Invention**

[0010] According to the present disclosure, it is possible to provide a wireless power supply system that can continuously adjust the capacitance of the capacitor in the resonance circuit with a simpler configuration and maintain the power transmission efficiency under various conditions. **Brief Description of the Drawings**

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0012] The present disclosure will be specifically described with reference to the drawings showing its embodiments. In the following embodiments, a wireless power supply system to which the power receiving device of the present disclosure is applied will be described.

[0013] FIG. 1 is a block diagram showing the configuration of a wireless power supply system 100 in the present embodiment. The wireless power supply system 100 includes a power supply device 1 and a power receiving device 2 provided in an electric device including a battery B. The power supply device 1 rectifies and smoothes the power from the AC power supply E, converts it into a high-frequency signal using a MOS-FET (Metal-Oxide-Semiconductor Field Effect Transistor), and wirelessly transmits it from the power supply coil 11. The power receiving device 2 receives the high-frequency signal (for example, on the order of several kHz to several hundreds of MHz) emitted from the power supply coil 11 with the power receiving coil 21, rectifies and smoothes it, and outputs it to the battery B.

[0014] The power receiving device 2 includes a resonance capacitor 22 connected in series to the power receiving coil 21. The power receiving coil 21 and the resonance capacitor 22 constitute an LC series resonance circuit. The power receiving coil 21 is powered from the power supply coil 11, a voltage Vr is generated, and a current Ir flows through the LC series resonance circuit. The voltage-current detector 220 detects the voltage Vr and the current Ir and outputs the phase difference therebetween as Δθ.

[0015] The power receiving device 2 includes a rectifying and smoothing circuit 23. The rectifying and smoothing circuit 23 converts the AC power received by the LC series resonance circuit composed of the power receiving coil 21 and the resonance capacitor 22 into DC power and outputs it. The rectifying and smoothing circuit 23 is a circuit that combines a rectifying circuit for rectifying when converting the received AC power into DC power and a smoothing circuit for smoothing the pulsating current included in the DC power. The output of the rectifying and smoothing circuit 23 is connected to the battery B.

[0016] The power receiving device 2 includes a control board 24. The control board 24 is a microcontroller including a processor and a memory, is connected to the output terminal of the rectifying and smoothing circuit 23, and controls the ON / OFF of the power to the battery B. A converter may be provided between the rectifying and smoothing circuit 23 and the battery B, and the control board 24 may be configured to control the output of the converter. When the power receiving device 2 is connected to the battery B via an AC / DC converter, a DC / AC converter may be provided between the rectifying and smoothing circuit 23 and the battery B.

[0017] In the wireless power supply system 100 of the present embodiment, even if a deviation occurs between the resonance frequency in the power supply coil 11 and the resonance frequency in the power receiving coil 21 in the power receiving device 2, the resonance frequency in the power receiving coil 21 is adjusted to maintain the transmission efficiency. For this reason, the resonance capacitor 22 is connected to the control board 24 and adjusts the resonance frequency using the capacity control circuit 200 described later and the signal output from the control board 24. The resonance capacitor 22 is connected to the control board 24 and adjusts the resonance frequency using the capacity control circuit 200 described later and the signal output from the control board 24.

[0018] The resonance frequency f in the LC series resonance circuit is generally expressed as f = 1 / (2π√LC), where L is the inductance value of the coil and C is the capacitance of the capacitor. The resonance capacitor 22 is a capacitor adopted to adjust the resonance frequency f and has an adjustable capacitor capacitance.

[0019] The resonance capacitor 22 is a capacitor whose capacitance value can be controlled by a capacitance control circuit 200 described below. FIG. 2 is a block diagram showing the control system of the capacitance control circuit 200. The capacitance control circuit 200 includes a resonance circuit 210, a voltage-current detector 220, a reference voltage generation circuit 230, an AGC circuit 240, a switch control circuit 250, and a switching circuit 260.

[0020] The resonance circuit 210 includes the power receiving coil 21 and the resonance capacitor 22 shown in FIG. 1. As shown in FIG. 1, a voltage-current detector 220 is connected to the resonance circuit 210. The voltage-current detector 220 detects the voltage Vr applied to the resonance circuit 210 and the current Ir flowing through the resonance circuit 210, and outputs the phase difference Δθ therebetween. The voltage-current detector 220 may be constituted by one detector, or may be constituted by including detectors for voltage and current respectively.

[0021] The reference voltage generation circuit 230 is partly constituted by the control board 24, and is a circuit that outputs a reference voltage ±Vref with reference to the phase difference Δθ from the voltage-current detector 220. The reference voltage generation circuit 230 adjusts the voltage value of the reference voltage ±Vref to increase or decrease it under the control of the processor of the control board 24.

[0022] The AGC circuit 240 is a circuit that inputs the terminal voltage Vc of the capacitor Cs to be controlled included in the resonance circuit 210, adjusts it so that the maximum amplitude becomes a fixed value, and outputs a voltage Vc´.

[0023] The switch control circuit 250 compares the reference voltage ±Vref output from the reference voltage generation circuit 230 with the Vc´ output from the AGC circuit 240, and outputs control voltages Vg1 and Vg2 for controlling the switching circuit 260 provided at both ends of the capacitor Cs to be controlled.

[0024] The switching circuit 260 includes switches SW1 and SW2 controlled by the control voltages Vg1 and Vg2 output from the switch control circuit 250, or their AND operation or the like. By turning on and off switches SW1 and SW2, the capacitance of the capacitor Cs to be controlled included in the resonance circuit 210 can be continuously changed.

[0025] FIG. 3 is a diagram showing the configuration of the variable capacitance circuit 201. The variable capacitance circuit 201 corresponds to the capacitor Cs to be capacitance-controlled included in the resonance circuit 210, the capacitor Cr with fixed capacitance connected in parallel to the capacitor Cs, and the switching circuit 260. The switching circuit 260 includes switches SW1 and SW2 each including transistors Tr1 and Tr2 connected in series to both ends of the capacitor Cs. Switches SW1 and SW2 can be turned on / off bidirectionally. As will be described later, the capacitor Cr functions as a reference element for the voltage Vc applied to the resonance capacitor 22.

[0026] The transistor of switch SW1 has its drain connected to one end of capacitor Cs, its source connected to one end of capacitor Cr, and the control voltage Vg1 supplied to its gate. The transistor of switch SW2 has its drain connected to the other end of capacitor Cs, its source connected to the other end of the capacitor Cr, and the control voltage Vg2 supplied to its gate.

[0027] In the variable capacitance circuit 201 shown in FIG. 3, the voltage Vcs applied to both ends of the capacitor Cs to be controlled changes in the same manner as the voltage Vc applied to the resonance capacitor 22 when both switches SW1 and SW2 at both ends are on (the control voltage is high). On the other hand, when either one of switches SW1 and SW2 is off, the voltage Vcs becomes constant. As a result, the apparent capacitance of the capacitor Cs decreases compared to the case where both ends of the capacitor Cs are always electrically conductive.

[0028] Figure 4 is a schematic diagram showing the configuration of the switch control circuit 250. The switch control circuit 250 is a circuit that generates a control voltage Vg1 and a control voltage Vg2. The switch control circuit 250 receives a reference voltage Vref and its inverted voltage -Vref, and a voltage Vc' obtained by adjusting the voltage Vc applied to the capacitor Cr shown in FIG. 3 by the AGC circuit 240.

[0029] Based on the voltage Vc' obtained by adjusting the voltage Vc and the input reference voltage ±Vref, the switch control circuit 250 functions as a phase control circuit that controls the phase of the power applied to the capacitor Cs to be controlled by switching the on and off states of the switch SW1 and the switch SW2.

[0030] The switch control circuit 250 includes a comparator OP1 that compares the reference voltage Vref with the voltage Vc', and a comparator OP2 that compares the reference voltage -Vref with the voltage Vc'. The comparator OP1 uses an operational amplifier and outputs a high-level voltage that turns on the switch SW1 as the control voltage Vg1 when the fixed voltage Vref is higher than the periodically varying voltage Vc. The comparator OP2 also uses an operational amplifier and outputs a high-level voltage that turns on the switch SW2 as the control voltage Vg2 when the varying voltage Vc' is higher than the fixed voltage -Vref.

[0031] Figure 5 is a time chart showing the waveforms of the reference voltage Vref, the adjusted reference voltage Vc', and the voltage Vcs. The switch control circuit 250 outputs a signal that periodically switches the on and off states of the switches SW1 and SW2 based on the reference voltage Vref and Vc'. As a result, the electrical conduction and non-conduction between one end and the other end of the capacitor Cs can be periodically switched. The voltage Vcs applied across the capacitor Cs varies periodically in the same manner as the voltage Vc when both switches SW1 and SW2 are on, but becomes constant when one of them is off. That is, when the amplitude of the voltage Vc' corresponding to the voltage Vc exceeds the magnitude of Vref, the switch control circuit 250 adjusts so that a voltage Vcs with the suppressed amplitude is applied to the capacitor Cs to be controlled.

[0032] By adjusting the height of the reference voltage Vref, the length of time (duty ratio) during which each of the control voltages Vg1 and Vg2 is at the high level can be adjusted. In FIG. 5, as described above, a time chart showing the relationship between the reference voltage Vref and the adjusted reference voltage Vc´, and the transitions of the control voltages Vg1 and Vg2 based thereon are shown. In FIG. 5, the transition of the voltage Vcs applied across the capacitor Cs is shown. From this, it can be seen that the higher the reference voltage Vref, the longer the time during which each of the control voltages Vg1 and Vg2 is at the high level, and the larger the apparent capacitance value of the capacitor Cs. Conversely, it can be seen that the lower the reference voltage Vref, the shorter the time during which each of the control voltages Vg1 and Vg2 is at the high level, and the smaller the apparent capacitance value of the capacitor Cs.

[0033] The configuration of the switch control circuit 250 can take several modified examples. FIG. 6 shows another example of the switch control circuit 250. The switch control circuit 250 in the other example, similar to the switch control circuit 250 shown in FIG. 4, receives the reference voltage Vref and its inverted voltage -Vref, and the voltage Vc´ obtained by adjusting the voltage Vc applied to the capacitor Cr shown in FIG. 3 by the AGC circuit 240. The switch control circuit 250 in FIG. 6 includes a comparator OP1 that compares the reference voltage Vref with the voltage Vc´, and a comparator OP2 that compares the reference voltage -Vref with the voltage Vc´. The other switch control circuit 250 further includes an AND circuit 251 that outputs a signal (control voltage) corresponding to the logical product (AND) of the output from the comparator OP1 and the output from the comparator OP2. That is, the switch control circuit 250 outputs a control voltage that becomes high level only when both the output from the comparator OP1 and the output from the comparator OP2 are at the high level (true: 1). The switch control circuit 250 branches and outputs the control voltages output from the AND circuit 251 to both the control voltages Vg1 and Vg2. The transition of the voltage Vcs applied across the capacitor Cs controlled by the control voltages Vg1 and Vg2 output in this way is the same as that shown in FIG. 5.

[0034] Alternatively, the switch control circuit 250 may be configured to output the control voltage Vg1 and the control voltage Vg2 by comparing the voltage Vc´, its inverted voltage -Vc´, and the reference voltage Vref.

[0035] In the switch control circuit 250 configured as described above, as can be seen with reference to FIG. 5, by adjusting the height of the reference voltage Vref, the time during which the switches SW1 and SW2 are turned on can be adjusted, and the capacitance value of the capacitor Cs can be continuously adjusted. Next, the generation of the reference voltage Vref and its adjustment method will be described.

[0036] Conventionally, for the reference voltage Vref, a voltage divider circuit was connected in parallel to the voltage Vc that can be referenced from the capacitor Cr, and the voltage divided from the connection point of the two variable resistance elements included in the voltage divider circuit was taken out and used. However, the maximum amplitude of the voltage Vc that should theoretically be fixed changes according to the capacitance adjustment of the capacitor Cs by the above-described switch control. Specifically, when the capacitance of the capacitor Cs increases, the impedance decreases, so the referenced voltage Vc becomes smaller. Conversely, when the capacitance of the capacitor Cs decreases, the impedance increases, so the referenced voltage Vc becomes larger. By changing the capacitance, the amplitude of the reference voltage Vc that should be fixed also becomes indeterminate. Furthermore, the amplitude of the referenced voltage Vc also fluctuates due to various factors such as the transient characteristics of the circuit. In contrast, the conventional reference voltage generation method was a method of adjusting the gain by applying a digital potentiometer to the divided voltage. The inventors have obtained the knowledge that such reference voltage generation by gain adjustment is not suitable for power supply at high power.

[0037] Therefore, the power receiving device 2 in the present embodiment generates the reference voltages ±Vref by the function as a part of the reference voltage generation circuit 230 of the control board 24. The reference voltage generation circuit 230 adjusts the effective value (absolute value) of the reference voltages ±Vref based on the phase difference Δθ that can be referenced from the voltage-current detector 220 under microcomputer control, and outputs it to the switch control circuit 250 as shown in FIG. 2.

[0038] The uncertainty of the amplitude of the voltage Vc is adjusted by the AGC circuit 240. FIG. 7 is a block diagram showing the configuration of the AGC circuit 240. The AGC circuit 240 is a closed-loop feedback circuit composed of a variable gain device (gain amplifier) 241, a detection circuit 242, and a comparison circuit 243.

[0039] The variable gain device 241 is configured to receive the voltage Vc across the terminals of the capacitor Cr. Specifically, the variable gain device 241 receives the output of a differential amplifier circuit connected in parallel with the capacitor Cr, which is a voltage reference element. The variable gain device 241 amplifies the input voltage Vc with an amplification factor determined by the gain control voltage Vctrl input to the variable gain device 241, and outputs it as the voltage Vc'. The gain control voltage Vctrl is obtained in the comparison circuit 243 by comparing the reference voltage Vbase output from the control board 24 with the DC voltage Vdc corresponding to the effective value of Vc' output from the variable gain device 241 to detect and output the state of the loop. The DC voltage Vdc is output from a detection circuit 242 that detects the effective value of the AC voltage Vc' output from the variable gain device 241 and outputs a DC voltage. The reference voltage Vbase is output from the control board 24, which is a microcomputer. The control board 24 outputs the reference voltage Vbase as a constant DC voltage. As a result, Vc' output from the reference voltage generation circuit has a waveform with a constant amplitude that is not affected by the variation of the voltage Vc.

[0040] In this way, by inserting the AGC circuit 240 that makes the variation (amplitude fluctuation) of the voltage Vc constant, an AC waveform Vc' with a constant amplitude that is not affected by the variation of the voltage Vc can be obtained. By using the adjusted output voltage Vc' in the switch control circuit 250 of FIG. 3, the capacitance of the capacitor Cs can be controlled to improve the transmission efficiency as much as possible.

[0041] In the above embodiment, an automatic gain control circuit, that is, an AGC circuit is used to obtain an AC voltage Vc' with a constant amplitude. However, the present invention is not limited to this, and an automatic level control circuit, that is, an ALC (Automatic Level Control) circuit may also be used.

[0042] The embodiments disclosed as above are illustrative in all respects and not restrictive. The scope of the present invention is shown by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

Explanation of Signs

[0043] 100 Wireless power supply system 2 Power receiving device 21 Power receiving coil 22 Resonance capacitor 24 Control board 200 Capacitance control circuit 201 Variable capacitance circuit 210 Resonance circuit 220 Voltage-current detector 230 Reference voltage generation circuit 240 AGC circuit 241 Variable gain device 242 Detection circuit 243 Comparison circuit 250 Switch control circuit 260 Switching circuit Cr capacitor (first capacitor) Cx capacitor (second capacitor)

Claims

1. A first variable capacitor included in a resonant circuit together with a power receiving coil, A second fixed capacitor connected in parallel to the first capacitor, A switching circuit connected in series to both ends of the first capacitor respectively and including a switch that can be turned on / off bidirectionally, An AGC (Automatic Gain Control) circuit that takes the AC voltage at both ends of the second capacitor as an input, increases or decreases the amplification factor, and converts it into an AC voltage with a constant amplitude value, A switch control circuit that controls the switch of the switching circuit based on the comparison between the AC voltage with the constant amplitude value output from the AGC circuit and a reference voltage A power receiving device comprising the same.

2. Further comprising a voltage-current detector for detecting the voltage and current of the resonant circuit, The switch control circuit is controlled using, as the reference voltage, a value based on the phase difference between the voltage and current of the resonant circuit detected by the voltage-current detector The power receiving device according to claim 1.

3. The switching circuit compares the AC voltage with the constant amplitude value output from the AGC circuit and the reference voltage, and when the AC voltage with the constant amplitude value output from the AGC circuit is within the range of the reference voltage, turns on the switch The power receiving device according to claim 1 or 2.

4. A power feeding device comprising a power feeding side resonant circuit including a power feeding coil and feeding power from a power source as a high-frequency signal, A power receiving device comprising a power receiving side resonant circuit including a power receiving coil and receiving the power transmitted from the power feeding device, Including, The power receiving device is A first variable capacitor included in the power receiving side resonant circuit together with the power receiving coil, A second fixed capacitor connected in parallel to the first capacitor, A switching circuit connected in series to both ends of the first capacitor respectively and including a switch that can be turned on / off bidirectionally, An AGC circuit that takes the AC voltage at both ends of the second capacitor as an input, increases or decreases the amplification factor, and converts it into an AC voltage with a constant amplitude value, A voltage-current detector for detecting the voltage and current of the power receiving side resonant circuit, A switch control circuit that uses, as the reference voltage, a value based on the phase difference between the voltage and current of the power receiving side resonant circuit detected by the voltage-current detector, and turns on the switch when the AC voltage with the constant amplitude value output from the AGC circuit is within the range of the reference voltage A wireless power feeding system comprising the same.

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