Vibration power generation device

Abstract

To provide a vibration power generation device which can stabilize output by automatically following frequency change of environmental vibration.SOLUTION: A vibration power generation device according to one embodiment of the present invention comprises: a vibration power generation element with an electret type movable part, in which a resonance frequency changes according to change of load resistance; phase comparison means of outputting control voltage according to phase difference by performing phase comparison between a phase of an external vibration and a phase of a vibration of the movable part; and resonance adjustment means that includes a load resistance and adjusts resonance of the vibration power generation element by change of the load resistance according to the control voltage.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a vibration power generation device.

Background Art

[0002] Conventionally, as one of energy harvesting technologies for harvesting energy from environmental vibration, a vibration power generation device provided with a vibration power generation element is known. The vibration power generation device can obtain a large output when the resonance frequency of the vibration power generation element is synchronized with the environmental vibration, but if the environmental vibration deviates from the resonance frequency, the output will be significantly reduced.

[0003] Patent Document 1 (see paragraphs

[0034] to

[0048] , Figure 3) discloses that in a vibration power generation device provided with a frequency detection circuit for detecting a vibration frequency, feedback is performed to an output control circuit while monitoring the vibration frequency, and the impedance of the output control circuit is controlled based on the detected frequency so that the output power is maximized. The vibration power generation device of Patent Document 1 aims to efficiently extract electric power even when the vibration frequency changes by such a configuration.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as described above, the vibration power generation device described in Patent Document 1 requires impedance control based on the vibration frequency detected by the frequency detection circuit, and cannot automatically follow the frequency change of environmental vibration to stabilize the output.

[0006] This disclosure has been made in view of such problems and aims to provide a vibration power generation device that can automatically track changes in the frequency of environmental vibrations and stabilize its output. [Means for solving the problem]

[0007] A vibration power generation device according to one aspect of the present disclosure is a vibration power generation element having an electret-type movable part, characterized by comprising: a vibration power generation element whose resonant frequency changes in response to a change in load resistance; a phase comparison means that performs a phase comparison between the phase of external vibration and the phase of vibration of the movable part and outputs a control voltage corresponding to the phase difference; and a resonance adjustment means that includes the load resistance and adjusts the resonance of the vibration power generation element by changing the load resistance in response to the control voltage.

[0008] Furthermore, according to one aspect of the present disclosure, the load resistance is raised or lowered in accordance with the control voltage so that the resonance conditions are met, thereby adjusting the resonance.

[0009] Furthermore, according to one aspect of this disclosure, the resonance condition is characterized by including the fact that the amplitude of the resonance frequency is maximized.

[0010] Furthermore, according to one aspect of this disclosure, the phase comparison means is characterized by performing the phase comparison using an exclusive OR circuit.

[0011] Furthermore, according to one aspect of the present disclosure, the phase comparison means further comprises a charge / discharge circuit that repeatedly charges and discharges according to the pulse signal output from the exclusive OR circuit and outputs the control voltage.

[0012] Furthermore, according to one aspect of this disclosure, the on-period and off-period of the pulse signal are equal to those when the resonance condition is met.

[0013] Furthermore, according to one aspect of the present disclosure, the resonance adjustment means includes a field-effect transistor in which the control voltage is the gate voltage and the load resistance is the ON resistance, characterized in that the ON resistance changes according to the gate voltage. [Effects of the Invention]

[0014] According to this disclosure, it is possible to provide a vibration power generation device that can automatically track changes in the frequency of environmental vibrations and stabilize the output. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows the power generation frequency characteristics of an electret-type vibration power generation device. [Figure 2] This is a schematic diagram of a vibration power generation device according to one embodiment. [Figure 3] This figure illustrates an example configuration of a resonance adjustment circuit and a phase comparator according to one embodiment. [Figure 4] This diagram illustrates an example of operation when the phase difference between external vibration and movable part vibration is 90 degrees. [Figure 5] This diagram illustrates an example of operation when the phase difference between external vibration and movable part vibration is greater than 90 degrees. [Figure 6] This diagram illustrates an example of operation when the phase difference between external vibration and movable part vibration is less than 90 degrees. [Figure 7] This diagram shows the relationship between gate voltage and ON resistance. [Figure 8] This figure compares the power generation amount of the vibration power generation device disclosed in this disclosure with the power generation amount of a conventional vibration power generation device. [Modes for carrying out the invention]

[0016] Embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The same elements are denoted by the same reference numerals throughout this specification and the accompanying drawings, and redundant descriptions are omitted.

[0017] (overview) FIG. 1 is a diagram showing power generation frequency characteristics of an electret-type vibration power generator using an electret electrode for a power generation element. The horizontal axis of the graph represents frequency (Hz), and the vertical axis of the graph represents generated power (μW). Here, simulation results of the relationship between frequency and generated power when the load resistance is set to 1 to 15 MΩ are shown.

[0018] As illustrated, when the load resistance of the power generation element changes, its power generation frequency characteristics also change. For example, as the load resistance changes from 1 MΩ to 5 MΩ and then to 15 MΩ, the peak of the generated power also changes from approximately 102 Hz to the latter half of 103 Hz. This is due to the hard spring effect caused by electrostatic force. The frequency at the peak is the resonant frequency of the power generation element.

[0019] In the vibration power generator according to the present disclosure, the characteristic that the resonant frequency varies with the magnitude of the load resistance is utilized to change the power generation frequency characteristic of the vibration power generator, so that the resonant frequency automatically tracks the frequency of ambient vibration. By doing so, the vibration power generator according to the present disclosure can perform stable power generation even when the frequency of ambient vibration fluctuates.

[0020] (Embodiment) FIG. 2 is a schematic configuration diagram of a vibration power generator according to an embodiment. A vibration power generator 100 includes a power generation element 10, a rectifier circuit 20, a resonance adjustment circuit 30, and a phase comparator 40. The vibration power generator 100 is also connected to an external device 50 and an external load 60.

[0021] The power generation element 10 is a capacitive vibration power generation element equipped with an electret electrode. It generates electricity when the movable electrode 11 vibrates relative to the fixed electrodes 12 and 13 in response to vibrations from the external equipment 50, i.e., environmental vibrations. An electret is formed on at least one of the movable electrode 11 and the fixed electrodes 12 and 13 near the surface of the faces of the movable electrode 11 and the fixed electrodes 12 and 13. Note that the configuration of the movable electrode 11 and the fixed electrodes 12 and 13 is not limited to the illustrated configuration. Thus, the power generation element 10 is equipped with an electret-type movable part. The output power of the power generation element 10 is greatest at the resonance frequency with the environmental vibration and decreases significantly when it deviates from the vibration frequency of the environmental vibration. The power generation element 10 constitutes the power generation mechanism of the vibration power generation device 100. The rectifier circuit 20 rectifies the AC power output from the power generation element 10 and converts it into DC power, which is then output to the resonance adjustment circuit 30. The rectifier circuit 20 can be configured with four diodes, as shown in the figure, but is not limited to this configuration.

[0022] The phase comparator 40 compares the phase of vibrations from external equipment 50, i.e., environmental vibrations, with the phase of movement of the power generation mechanism, and outputs a control voltage for adjusting the resonance in the resonance adjustment circuit 30. Details of the phase comparator 40 will be described later.

[0023] The resonance adjustment circuit 30 adjusts the resonance, that is, the phase difference between external vibrations and the movement of the power generation mechanism, according to the control voltage from the phase comparator 40. Details of the resonance adjustment circuit 30 will be described later.

[0024] The vibration power generation device according to this disclosure can automatically track changes in the vibration frequency of environmental vibrations by using a resonance adjustment circuit 30 and a phase comparator 40, thereby stabilizing the output. The above-described schematic configuration is merely illustrative and does not limit the configuration of the vibration power generation device according to this disclosure.

[0025] Next, an example of the configuration of the resonance adjustment circuit 30 and phase comparator 40 of the vibration power generation device according to this disclosure will be described. Figure 3 is a diagram illustrating an example of the configuration of the resonance adjustment circuit 30 and phase comparator 40 of the vibration power generation device according to one embodiment. Note that the rectifier circuit 20 is not shown.

[0026] The phase comparator 40 includes an exclusive OR (EXOR) circuit 41 and a charge / discharge circuit 42. The EXOR circuit 41 takes the phase of the vibration of the movable part, i.e., the movement of the power generation mechanism, and the phase of the vibration of the external equipment, as input and outputs a pulse signal. In this embodiment, when reading the external vibration, the timing of reading the external vibration by a vibration sensor (not shown) is tuned so that when the resonant frequencies of the external vibration and the movable part match, the phase of the signal of the vibration of the movable part and the external vibration are shifted by 90 degrees. When the phase difference between the vibration of the movable part and the external vibration is 90 degrees, i.e., when the power generation mechanism is resonating, the on period and the off period of the pulse signal are equal. If the phase difference is greater than 90 degrees, the on period becomes shorter than the off period, and if the phase difference is less than 90 degrees, the on period becomes longer than the off period. Note that a flip-flop circuit may be used as the EXOR circuit 41.

[0027] The charge / discharge circuit 42 includes a resistor 43 and a capacitor 44. In the charge / discharge circuit 42, the capacitor 44 is charged and discharged according to the on / off state of the pulse signal output from the EXOR circuit 41, and the control voltage that changes accordingly is output to the resonance adjustment circuit 30. During the ON period of the pulse signal, the control voltage rises as the capacitor 44 is charged, and during the OFF period of the pulse signal, the control voltage decreases as the capacitor 44 is discharged.

[0028] In this way, the phase comparator 40 outputs a control voltage according to the phase difference between the external vibration and the movable part vibration, using the EXOR circuit 41 and the charge / discharge circuit 42.

[0029] The resonance adjustment circuit 30 is composed of a field-effect transistor (FET) for adjusting the ON resistance, and the ON resistance is adjusted using the control voltage from the phase comparator 40 as the gate voltage. As the ON resistance changes, the power generation frequency characteristics change as shown in Figure 1, and the resonance of the vibration power generation device 100 is controlled to follow external vibrations.

[0030] Figure 7 shows the relationship between the gate voltage and ON resistance of an FET. The horizontal axis of the graph represents the gate voltage (V), and the vertical axis represents the ON resistance (MΩ). As shown in the figure, the ON resistance decreases as the gate voltage increases, and increases as the gate voltage decreases. Furthermore, as shown in Figure 1, when the ON resistance (i.e., load resistance) increases, the peak frequency of the generated frequency characteristic shifts to the higher frequency side, and conversely, when the ON resistance decreases, the peak frequency of the generated frequency characteristic shifts to the lower frequency side.

[0031] Here, we will further explain the 90-degree phase difference. Generally, in a second-order resonant system, the mechanical amplitude is maximum at the resonant frequency, and the power output of the power generation element is also maximum at that frequency. Incidentally, the phase of the displacement lags the driving force by 90 degrees at this time. In the vibration power generation device according to this disclosure, this is used as an observable state variable in the feedback to maintain the resonant state. In other words, it can be called locking at the resonant point. The 90-degree phase difference is used as one indicator that the resonance condition (i.e., maximum amplitude) is met, and the phase difference is not necessarily 90 degrees; the value may vary depending on the circuit configuration. For example, the phase difference can be 89 degrees or 91 degrees. Also, depending on how the positive and negative signs of the voltage are taken, a 90-degree phase lag can also be said to be a 270-degree phase lead. The resonance condition may include the fact that the amplitude is maximum at the resonant frequency.

[0032] Next, with reference to Figures 4 to 6, we will explain in detail the mechanism by which resonance, that is, the phase difference between external vibrations and movable part vibrations, is adjusted.

[0033] Figure 4 shows an example of operation when the phase difference between external vibration and movable part vibration is 90 degrees.

[0034] As shown in the figure, when the phase difference between the external vibration and the movable part vibration is 90 degrees, the EXOR circuit 41 outputs a pulse signal with equally spaced on and off states. The charge / discharge circuit 42 also repeatedly charges and discharges at equal intervals according to the pulse signal output from the EXOR circuit 41. Therefore, the control voltage output from the charge / discharge circuit 42 remains approximately constant, and the ON resistance in the resonance adjustment circuit 30 is also maintained. Thus, the power generation frequency characteristics of the vibration power generation device are maintained, and the resonance state is also maintained.

[0035] Figure 5 shows an example of operation when the phase difference between external vibration and movable part vibration is greater than 90 degrees.

[0036] As shown in the figure, when the phase difference between the external vibration and the movable part vibration is greater than 90 degrees, the EXOR circuit 41 outputs a pulse signal with a short ON period and a long OFF period. In addition, in the charge / discharge circuit 42, the charging period becomes shorter and the discharge period becomes longer according to the pulse signal output from the EXOR circuit 41. Consequently, the control voltage output from the charge / discharge circuit 42 decreases, and the ON resistance in the resonance adjustment circuit 30 increases. Therefore, the power generation frequency characteristics of the vibration power generation device shift to the high-frequency side.

[0037] In this case, the control voltage rises until the phase difference reaches 90 degrees, and then remains constant. That is, the peak frequency of the resonant frequency characteristic of the generator shifts to the higher frequency side until it resonates with the external vibration.

[0038] Figure 6 shows an example of operation when the phase difference between external vibration and movable part vibration is less than 90 degrees.

[0039] As shown in the figure, when the phase difference between the external vibration and the movable part vibration is less than 90 degrees, the EXOR circuit 41 outputs a pulse signal with a long ON period and a short OFF period. Also, in the charge / discharge circuit 42, the charging period becomes longer and the discharge period becomes shorter according to the pulse signal output from the EXOR circuit 41. Consequently, the control voltage output from the charge / discharge circuit 42 increases, and the ON resistance in the resonance adjustment circuit 30 decreases. Therefore, the power generation frequency characteristics of the vibration power generation device shift to the low-frequency side.

[0040] In this case, the control voltage decreases until the phase difference reaches 90 degrees, and then becomes constant. That is, the peak frequency of the power generation frequency characteristic shifts to the lower frequency side until it resonates with the external vibration.

[0041] As described above, the vibration power generation device according to this disclosure can automatically track frequency changes of external vibrations and stabilize the output by adjusting the ON resistance so that the phase difference is 90 degrees (i.e., so that the resonance condition is met).

[0042] Figure 8 shows a comparison of the power generation amount of the vibration power generation device according to this disclosure with the power generation amount of a conventional vibration power generation device.

[0043] Figure 8(a) shows the effect of changes in the load state of external equipment on frequency. Here, changes in the load state of external equipment cause frequency fluctuations of several Hz.

[0044] Figure 8(b) shows the effect of the frequency fluctuations shown in Figure 8(a) on power generation. The upper part of Figure 8(b) shows the power generation when a tracking system is present, i.e., the power generation of the vibration power generation device according to this disclosure. On the other hand, the lower part of Figure 8(b) shows the power generation when a tracking system is not present, i.e., the power generation of a conventional vibration power generation device.

[0045] As shown in the figure, when the frequency of external vibration changes, conventional vibration power generators experience a significant decrease in power generation. However, in the vibration power generator according to this disclosure, although the power generation decreases slightly when the frequency of external vibration fluctuates, the decrease is only temporary, and the power generation can be recovered quickly.

[0046] According to the embodiments described above, the following effects and advantages are achieved.

[0047] (1) Even if the frequency of external vibrations changes, the optimal resonance state can be automatically maintained, thereby stabilizing the output of the vibration power generation device.

[0048] (2) Furthermore, since a significant decrease in power output due to resonance shifts can be avoided, a larger amount of power can be obtained when compared with conventional vibration power generation devices over the same period. In other words, the power generation efficiency of vibration power generation devices can be improved. [Explanation of symbols]

[0049] 10 Power generation element 20 Rectifier circuit 30 Resonance adjustment circuit 40 Phase comparator 41 EXOR circuit 42 Charge / discharge circuit 43 Resistors 44 Capacitors 50 External equipment 60 External load 100 Vibration power generation device

Claims

1. A vibration power generation element having an electret-type movable part, wherein the resonant frequency changes in response to a change in load resistance, A phase comparison means performs a phase comparison between the phase of external vibration and the phase of vibration of the movable part, and outputs a control voltage corresponding to the phase difference. A resonance adjustment means comprising the aforementioned load resistor, wherein the load resistor changes in accordance with the control voltage to adjust the resonance of the vibration power generation element, A vibration power generation device characterized by being equipped with the following features.

2. The vibration power generation device according to claim 1, characterized in that the load resistance increases or decreases in accordance with the control voltage so that the resonance conditions are met, thereby adjusting the resonance.

3. The vibration power generation device according to claim 2, characterized in that the resonance condition includes the amplitude of the resonance frequency being maximized.

4. The vibration power generation apparatus according to any one of claims 1 to 3, characterized in that the phase comparison means performs the phase comparison by an exclusive OR circuit.

5. The vibration power generation device according to claim 4, further comprising a charge / discharge circuit that repeatedly charges and discharges according to a pulse signal output from the exclusive OR circuit and outputs the control voltage, wherein the phase comparison means is further characterized by comprising a charge / discharge circuit.

6. The vibration power generation device according to claim 5, characterized in that the on-period and off-period of the pulse signal are equal to those when the resonance condition is met.

7. The vibration power generation device according to claim 1, wherein the resonance adjustment means includes a field-effect transistor in which the control voltage is the gate voltage and the load resistance is the ON resistance, and the ON resistance changes according to the gate voltage.

Images