A power optimization method for piezoelectric energy harvesting device based on series-parallel connection of piezoelectric sheets

Abstract

The present invention relates to a power optimization method of a piezoelectric energy harvesting device based on a series-parallel connection of piezoelectric sheets, comprising the following steps: 1. Fixing a bi-crystal piezoelectric sheet on a fixture, determining the connection mode of the bi-crystal piezoelectric sheet, and performing subsequent measurements using a test device; 2. Measuring the open circuit voltage of each bi-crystal piezoelectric sheet, thereby obtaining its resonant frequency, grouping the bi-crystal piezoelectric sheets according to the principle of similar resonant frequencies, and combining the bi-crystal piezoelectric sheets in the group using different series-parallel connection modes in each group; 3. Measuring the open circuit voltage of each bi-crystal piezoelectric sheet combination under different series-parallel connection modes, and performing a load test, measuring the load voltage and calculating the load power; 4. Comparing the load voltage and load power of each bi-crystal piezoelectric sheet combination obtained under different series-parallel connection modes, and determining the optimal series-parallel connection mode, which is the optimal power combination mode of the piezoelectric energy harvesting device. The method is conducive to obtaining the optimal power combination mode of the piezoelectric energy harvesting device.

Description

Technical Field

[0001] The present invention belongs to the field of piezoelectric energy harvesting, and specifically relates to a power optimization method for a piezoelectric energy harvesting device based on a series-parallel connection of piezoelectric sheets. Background Art

[0002] Mechanical vibrations that are ubiquitous in the natural environment can generate electrical energy in the microwatt to milliwatt range, which is sufficient to meet the power supply requirements of micro-power wireless sensor networks. Currently, there are three main methods for vibration energy recovery: electrostatic, electromagnetic, and piezoelectric. The electrostatic method uses the principle of electrostatic induction to convert mechanical energy into electrical energy, the electromagnetic method uses the principle of electromagnetic induction to convert mechanical energy into electrical energy, and the piezoelectric method uses the positive piezoelectric effect of piezoelectric materials to convert mechanical energy into electrical energy. Among them, the piezoelectric vibration energy recovery method has the highest energy density, and the piezoelectric energy recovery system has a simple structure, is easy to integrate and miniaturize, and can be widely used in life and production practice, which has great advantages over electromagnetic and electrostatic methods.

[0003] Piezoelectric energy harvesting devices generally use a traditional cantilever beam structure to generate electrical energy using the piezoelectric effect. When an external force is applied to the piezoelectric crystal, the positive and negative charges are no longer symmetrically distributed, and polarized charges of opposite signs will be generated on the surface of the crystal, resulting in a positive piezoelectric effect. The piezoelectric chip is pasted on the upper surface of the cantilever beam. When mechanical vibration occurs in the outside world, the beam swings up and down, and drives the piezoelectric sheet attached to it to bend and deform, thereby converting the mechanical vibration energy in the external environment into electrical energy. The thickness, length and width of the piezoelectric chip are linked to the power generation performance of the bimorph piezoelectric sheet. The length and width of the cantilever beam can affect the resonant frequency of the bimorph piezoelectric sheet.

[0004] Therefore, it is feasible to realize self-powering of micro-power sensors by converting vibration energy in the environment into electrical energy through piezoelectric sheets, which can improve the power supply problem of current micro-electromechanical devices such as wireless sensor nodes. Compared with single-crystal piezoelectric sheets, dual-crystal piezoelectric sheets can obtain higher output voltages. Through the combination of series and parallel, the load capacity and load power of piezoelectric sheets can be effectively improved, thereby maximizing the efficiency of converting mechanical energy into electrical energy. Summary of the invention

[0005] The object of the present invention is to provide a method for optimizing the power of a piezoelectric energy harvesting device based on series-parallel connection of piezoelectric sheets, which method is conducive to obtaining the optimal power combination of the piezoelectric energy harvesting device.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a power optimization method of a piezoelectric energy harvesting device based on a series-parallel connection of piezoelectric sheets, comprising the following steps:

[0007] Step 1: Fix the bimorph piezoelectric sheet on the fixture, determine the connection method of the bimorph piezoelectric sheet, and use the test device for subsequent measurements;

[0008] Step 2: Measure the open circuit voltage of each bimorph piezoelectric sheet to obtain its resonant frequency, group the bimorph piezoelectric sheets according to the principle of similar resonant frequencies, and combine the bimorph piezoelectric sheets in each group using different series-parallel methods;

[0009] Step 3: Measure the open circuit voltage of each bimorph piezoelectric sheet combination under different series-parallel combinations, and perform a load test to measure the load voltage and calculate the load power;

[0010] Step 4: Compare the load voltage and load power of each dual-crystal piezoelectric sheet combination obtained under different series-parallel combinations to determine the optimal series-parallel combination, which is the optimal power combination of the piezoelectric energy harvesting device.

[0011] Furthermore, in step 1, the bimorph piezoelectric film is a PMN-PT piezoelectric ceramic doped with Sm synthesized by high-temperature solid-state treatment; the center frequency of the excitation source vibration is taken as the target frequency, and the target frequency is taken as the resonant frequency of the bimorph piezoelectric film to design the thickness, length and width of the bimorph piezoelectric film to capture the maximum power at the target frequency.

[0012] Furthermore, in step 1, the clamp is an insulating clamp to prevent the bimorph piezoelectric sheets from being at the same potential when connected in series and parallel.

[0013] Furthermore, in step 1, it is determined that the connection mode of the bimorph piezoelectric film is that the electrodes of the bimorph piezoelectric film are connected in series.

[0014] Furthermore, in step 1, the test device includes a signal generator, a power amplifier, an exciter, an oscilloscope, and a load resistor box. A sinusoidal signal with adjustable frequency and amplitude is input from the signal generator, the signal is amplified by the power amplifier, and then the amplified signal is provided to the exciter. The vibration excitation signal acting on the exciter drives the dual-crystal piezoelectric combination to vibrate; the dual-crystal piezoelectric combination converts mechanical vibration energy into electrical energy based on the piezoelectric effect, connects the output electrical energy to the load resistor box, observes the open-circuit voltage of the dual-crystal piezoelectric combination through an oscilloscope, and records the voltage and power output by the load resistor.

[0015] Furthermore, in step 2, each bi-crystal piezoelectric sheet group has N bi-crystal piezoelectric sheets, satisfying N=A*B, where B represents the number of parallel groups, and A represents the number of bi-crystal piezoelectric sheets connected in series in each group, that is, every A bi-crystal piezoelectric sheets with similar resonance frequencies are connected in series, and then connected in parallel to form a group.

[0016] Furthermore, a specific method for grouping the bimorph piezoelectric sheets according to the principle of similar resonance frequencies is: the piezoelectric sheets with similar resonance frequencies are grouped together for series connection, and the piezoelectric groups after series connection are connected in parallel.

[0017] Furthermore, the condition that the series-parallel combination of the bimorph piezoelectric sheets can improve the output power and broaden the frequency domain is that the resonant frequency difference of the bimorph piezoelectric sheets is within a set range.

[0018] Furthermore, in step 4, the optimal series-parallel combination is to increase the number of parallel groups of bi-crystal piezoelectric sheets as much as possible while the output voltage of the series-connected bi-crystal piezoelectric sheets in each group meets the activation voltage of the back-end circuit.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the method provides guidance for the optimal power combination of the piezoelectric energy harvesting device by comparing the load open circuit voltage and load power obtained by different series-parallel combinations of bimorph piezoelectric plates, thereby obtaining the optimal power combination of the piezoelectric energy harvesting device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a principle block diagram of the test device in the embodiment of the present invention.

[0021] Figure 2 Schematic diagram of different connection modes of bimorph piezoelectric films in an embodiment of the present invention; wherein (a) is a series connection of electrodes of the bimorph piezoelectric films, and (b) is a parallel connection of electrodes of the bimorph piezoelectric films.

[0022] Figure 3 1 is a comparison of open circuit voltages under different connection modes in the embodiment of the present invention.

[0023] Figure 4 1 is a comparison of load voltage and load power obtained under different combinations in the embodiments of the present invention; wherein (a) is a comparison of load voltage, and (b) is a comparison of load power. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0025] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0027] This embodiment provides a method for optimizing the power of a piezoelectric energy harvesting device based on a series-parallel connection of piezoelectric sheets, comprising the following steps:

[0028] Step 1: Fix the bimorph piezoelectric sheet on the fixture, determine the connection method of the bimorph piezoelectric sheet, and use the test device for subsequent measurements.

[0029] In this embodiment, the bimorph piezoelectric film is a PMN-PT piezoelectric ceramic doped with Sm synthesized by high temperature solid state treatment, with a high pCN -1 Ultra-high piezoelectric coefficient d 33 and a dielectric constant greater than 13,000 ε 33 / ε 0.

[0030] The center frequency of the excitation source vibration is taken as the target frequency, and the target frequency is taken as the resonant frequency of the bimorph piezoelectric film to design the thickness, length, and width of the bimorph piezoelectric film to capture the maximum power at the target frequency. By changing the length, width, and thickness of the piezoelectric film substrate and the piezoelectric chip, its resonant frequency will also change accordingly. The maximum power can be obtained by designing the resonant frequency of the piezoelectric film according to the center frequency of the excitation source vibration. Because the piezoelectric film can output the highest voltage at the resonant frequency. The length, width, and thickness of the piezoelectric film are designed with the target frequency as the resonant frequency of the piezoelectric film (the resonant frequency of the piezoelectric film can be roughly determined by simulation when making the piezoelectric film), and then a sweep frequency test is performed to finally determine its resonant frequency. In this embodiment, the thickness, length, and width of the piezoelectric crystal are selected as 2mm, 10mm, and 10mm, respectively. The resonant frequency is an inherent characteristic of the piezoelectric film, and it will not change after the length, width, and thickness of the piezoelectric film are determined, and it has nothing to do with the electrode connection method of the bimorph piezoelectric film.

[0031] In this embodiment, the clamp is an insulating clamp to prevent the bimorph piezoelectric sheets from being at the same potential when connected in series or parallel.

[0032] In this embodiment, the connection mode of the bimorph piezoelectric sheet is determined to be that the electrodes of the bimorph piezoelectric sheet are connected in series. Figure 2 As shown. Figure 3 As shown in the figure, compared with the parallel connection of the bimorph piezoelectric electrodes, the series connection of the electrodes can output a higher voltage. Because the bimorph piezoelectric has two piezoelectric chips bonded to the upper and lower ends of the piezoelectric substrate, there are three electrodes (piezoelectric chip, piezoelectric chip, substrate). When the bimorph piezoelectric electrodes are connected in parallel, there is voltage cancellation, and the output voltage is extremely low (more than ten mV), so the highest voltage can be output by connecting the bimorph piezoelectric electrodes in series.

[0033] In this embodiment, the test device includes a signal generator, a power amplifier, an exciter, an oscilloscope, and a load resistor box. A sinusoidal signal with adjustable frequency and amplitude is input from the signal generator, the signal is amplified by the power amplifier, and the amplified signal is provided to the exciter. The vibration excitation signal acting on the exciter drives the bimorph piezoelectric sheet combination to vibrate; the bimorph piezoelectric sheet combination (i.e., piezoelectric array) converts mechanical vibration energy into electrical energy based on the piezoelectric effect, connects the output electrical energy to the load resistor box, observes the open circuit voltage of the bimorph piezoelectric sheet combination through the oscilloscope, and records the voltage and power output by the load resistor.

[0034] Step 2: Use the bi-crystal piezoelectric strips in series to measure the open circuit voltage of each bi-crystal piezoelectric strip, and then obtain its resonant frequency (record the open circuit voltage of each bi-crystal piezoelectric strip through a sweep frequency test, and the frequency corresponding to the highest point of the open circuit voltage is the resonant frequency of the bi-crystal piezoelectric strip). Group the bi-crystal piezoelectric strips according to the principle of similar resonant frequencies, and use different series-parallel methods to combine the bi-crystal piezoelectric strips in each group.

[0035] Among them, each bi-crystal piezoelectric sheet group has N bi-crystal piezoelectric sheets, satisfying N=A*B, where B represents the number of parallel groups, and A represents the number of bi-crystal piezoelectric sheets connected in series in each group, that is, every A bi-crystal piezoelectric sheets with similar resonance frequencies are connected in series to obtain B parallel groups, and then the B parallel groups are connected in parallel together to form a group.

[0036] The bimorph piezoelectric film electrodes in series can output higher voltage than the bimorph piezoelectric film electrodes in parallel. , the captured power reaches the maximum:

[0037]

[0038] in, is the piezoelectric voltage constant, E p is the Young's modulus of the piezoelectric chip, h is the thickness of the cantilever beam, L is the length of the cantilever beam, δ is the excitation displacement caused by the external force.

[0039] The specific method of grouping bimorph piezoelectric sheets according to the principle of similar resonance frequency is: those with similar frequencies are connected in series, and those with opposite frequencies are connected in parallel.

[0040] When the substrate material and size (length, width and thickness) are consistent, the resonant frequency of the piezoelectric sheets will not differ too much. In this case, when the piezoelectric sheets are combined, the number of piezoelectric sheets in series in each group remains the same. If the resonant frequencies of the piezoelectric sheets differ greatly, the piezoelectric sheets with similar resonant frequencies are grouped in series according to the principle of similar frequencies, and the groups are then connected in parallel.

[0041] Step 3: Measure the open circuit voltage of each bimorph piezoelectric sheet combination under different series-parallel combinations, and conduct a load test to measure the load voltage and calculate the load power.

[0042] The device is connected to an interface circuit at the back end. The interface circuit has an activation voltage. The function of the interface circuit is to convert the AC power output by the dual-crystal piezoelectric sheet combination into DC power, and then chop and filter it for use by the back-end load. The open circuit voltage is measured to see whether it meets the activation voltage of the interface circuit. If it does not meet the requirements, increase the number of dual-crystal piezoelectric sheets in series in each group; otherwise, increase the number of dual-crystal piezoelectric sheets in parallel as much as possible.

[0043] Step 4: Compare the load voltage and load power of each dual-crystal piezoelectric sheet combination obtained under different series-parallel combinations to determine the optimal series-parallel combination, which is the optimal power combination of the piezoelectric energy harvesting device.

[0044] The optimal series-parallel combination is to increase the number of parallel groups of bi-crystal piezoelectric sheets as much as possible while ensuring that the output voltage of the series-connected bi-crystal piezoelectric sheets in each group meets the activation voltage of the back-end circuit.

[0045] Piezoelectric energy harvesting devices use the piezoelectric effect of piezoelectric materials to generate electrical energy. When an external force is applied to a piezoelectric crystal, the mechanical force causes the piezoelectric crystal to bend and deform, polarization occurs inside the crystal, and charges of opposite polarity are generated on the two surfaces of the crystal, and the mechanical energy is converted into electrical energy.

[0046] In this embodiment, there are 3 groups in total. Each group has 12 bimorph piezoelectric sheets, which are grouped according to similar resonance frequencies. Different series-parallel combinations include:

[0047] 1) 12 bimorph piezoelectric sheets connected in series;

[0048] 2) Six bi-crystal piezoelectric sheets are connected in series into a group, a total of 2 groups, and each group of bi-crystal piezoelectric sheets is connected in parallel;

[0049] 3) Three bi-crystal piezoelectric sheets are connected in series into a group, with a total of 4 groups, and each group of bi-crystal piezoelectric sheets is connected in parallel.

[0050] Among them, the series group can play a role in widening the frequency domain and increasing the output voltage; the parallel group can increase the output current and further improve the output power of the bimorph piezoelectric film.

[0051] The condition for increasing the output power and broadening the frequency domain by combining bi-crystal piezoelectric pieces in series and parallel is that the resonant frequency difference of the bi-crystal piezoelectric pieces is within a certain range. By comparing the load open-circuit voltage and load power obtained by different combinations of bi-crystal piezoelectric pieces, the optimal power combination of the piezoelectric energy harvesting device is obtained.

[0052] By comparing the load open-circuit voltage and load power obtained by different combinations of bi-crystal piezoelectric sheets, it is found that the optimal power combination of the piezoelectric energy harvesting device is 4 groups of bi-crystal piezoelectric sheets in parallel, with 3 piezoelectric sheets in series in each group. The specific load open-circuit voltage and load power are as follows: Figure 4 shown.

[0053] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for optimizing the power of a piezoelectric energy harvesting device based on series-parallel connection of piezoelectric sheets, characterized in that: The following steps are involved: Step 1: Fix the bimorph piezoelectric sheet on the fixture, determine the connection method of the bimorph piezoelectric sheet, and use the test device for subsequent measurements; Step 2: Measure the open circuit voltage of each bimorph piezoelectric sheet to obtain its resonant frequency, group the bimorph piezoelectric sheets according to the principle of similar resonant frequencies, and combine the bimorph piezoelectric sheets in each group using different series-parallel methods; Step 3: Measure the open circuit voltage of each bimorph piezoelectric sheet combination under different series-parallel combinations, and perform a load test to measure the load voltage and calculate the load power; Step 4: Compare the load voltage and load power of each bimorph piezoelectric sheet combination obtained under different series-parallel combination modes, and determine the optimal series-parallel combination mode, which is the optimal power combination mode of the piezoelectric energy harvesting device; In step 2, each bi-crystal piezoelectric sheet group has N bi-crystal piezoelectric sheets, satisfying N=A*B, where B represents the number of parallel groups, and A represents the number of bi-crystal piezoelectric sheets in series in each group, that is, each A bi-crystal piezoelectric sheets with similar resonance frequencies are connected in series, and then connected in parallel to form a group; The specific method of grouping the bimorph piezoelectric sheets according to the principle of similar resonance frequency is: the piezoelectric sheets with similar resonance frequency are grouped in series, and the piezoelectric groups after series connection are connected in parallel; The condition that the series-parallel combination of bimorph piezoelectric sheets can improve the output power and broaden the frequency domain is that the resonant frequency difference of the bimorph piezoelectric sheets is within the set range; In step 4, the optimal series-parallel combination is to increase the number of parallel groups of bi-crystal piezoelectric sheets as much as possible while ensuring that the output voltage of the series-connected bi-crystal piezoelectric sheets in each group meets the activation voltage of the back-end circuit.

2. The power optimization method of a piezoelectric energy harvesting device based on a series-parallel connection of piezoelectric sheets according to claim 1 is characterized in that: In step 1, the bimorph piezoelectric film is a PMN-PT piezoelectric ceramic doped with Sm synthesized by high-temperature solid-state treatment; the center frequency of the excitation source vibration is taken as the target frequency, and the target frequency is taken as the resonant frequency of the bimorph piezoelectric film to design the thickness, length and width of the bimorph piezoelectric film to capture the maximum power at the target frequency.

3. The power optimization method of a piezoelectric energy harvesting device based on a series-parallel connection of piezoelectric sheets according to claim 1 is characterized in that: In step 1, the clamp is an insulating clamp to prevent the bimorph piezoelectric sheets from being at the same potential when connected in series and parallel.

4. The power optimization method of a piezoelectric energy harvesting device based on series-parallel connection of piezoelectric sheets according to claim 1 is characterized in that: In step 1, it is determined that the connection mode of the bimorph piezoelectric film is that the electrodes of the bimorph piezoelectric film are connected in series.

5. The power optimization method of a piezoelectric energy harvesting device based on series-parallel connection of piezoelectric sheets according to claim 1 is characterized in that: In step 1, the test device includes a signal generator, a power amplifier, an exciter, an oscilloscope, and a load resistor box. A sinusoidal signal with adjustable frequency and amplitude is input from the signal generator, the signal is amplified by the power amplifier, and then the amplified signal is provided to the exciter. The vibration excitation signal acting on the exciter drives the dual-crystal piezoelectric combination to vibrate; the dual-crystal piezoelectric combination converts mechanical vibration energy into electrical energy based on the piezoelectric effect, connects the output electrical energy to the load resistor box, observes the open-circuit voltage of the dual-crystal piezoelectric combination through an oscilloscope, and records the voltage and power output by the load resistor.

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