A self-compensating button type current detection device and detection method thereof

Abstract

The present invention belongs to the technical field of current measurement, and specifically relates to a self-compensating button-type current detection device and a detection method thereof, wherein an upper end cover, a positioning plate and a package are fixed by bolts, and the upper end cover, the positioning plate and the package each have an arc-shaped groove to realize the positioning of a measured cable; a plurality of bosses with different heights are provided on the lower bottom surface inside the package, and each boss has a different distance from the inner wall surface of the package, a piezoelectric layer is fixed on the boss, a permanent magnet is fixed on the piezoelectric layer, all structures fixed on each boss are completely the same in size, and a single-chip microcomputer is fixed on the inner surface parallel to the central axis of a circular hole formed by four arc-shaped grooves; the present invention can measure direct current and alternating current, and can be self-powered, and has the characteristics of high linearity, high precision, simple structure, easy maintenance, wide application range, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of current measurement, and in particular relates to a self-compensating button type current detection device and a detection method thereof. Background Art

[0002] With the rapid development of my country's smart grid and the proposal of "Made in China 2025", the importance of high-precision dynamic measurement technology has become more prominent. Transmission cables and various high-precision equipment increasingly require dynamic measurement of current while also meeting the requirements of measurement accuracy. Therefore, it is of great significance to develop a high-precision current detection device that can dynamically measure;

[0003] The current detection device needs current to work. If it is equipped with a separate power supply, it will not only waste resources, but also require manual battery replacement. It cannot perform long-term current measurement in places where it is not convenient to maintain, such as underground or high altitude. Therefore, developing a self-powered current detection device not only saves manpower and material resources, but can also be upgraded to a node of a wireless sensor network in the future.

[0004] The conventional current detection devices in the prior art mainly include capacitive current sensors, Hall current sensors, all-fiber current sensors, fluxgate current sensors, Rogowski coil current sensors, giant magnetoresistance current sensors, etc., which have good accuracy and linearity, but also have problems in processing, cost, application scope, etc. For new current detection devices, such as passive current detection devices developed with piezoelectric cantilever beam structures, current measurement of dual-core cables can be performed without driving power or stripping of protective layers, but the accuracy is slightly lower than that of conventional current sensors, because the magnetic field excited by the cable is not uniform around it, and the relative position change of the permanent magnet at one end of the piezoelectric cantilever beam and the cable during vibration cannot be ignored, resulting in the force on the permanent magnet not being proportional to the current, so that the output voltage of the sensor is not linearly related to the measured current, that is, there is a nonlinear error. At the same time, due to the limitation of installation accuracy during the installation of the cantilever beam resonant current sensor, the uncertainty between the initial position between the piezoelectric cantilever beam and the measured cable, that is, the installation error of the sensor, has a certain influence on the measurement accuracy of the sensor. Summary of the invention

[0005] In order to overcome the above problems, the present invention provides a self-compensating button-type current detection device and a detection method thereof; the output linearity is very high, the accuracy is greatly improved, the manufacturing accuracy of its positioning structure and the installation process during use are not required to be high, the cost is reduced, and the operation is simpler; the current detection device proposed in the present invention has a response range that depends on the electrical parameters of the piezoelectric layer, and its sensitivity depends on the residual magnetism of the permanent magnet. By optimizing the device, its response range can be further expanded and its sensitivity can be further improved.

[0006] A self-compensating button-type current detection device comprises an upper end cover 1, a positioning plate 2, a package 3, a permanent magnet 4, a piezoelectric layer 5 and a single-chip computer 6, wherein the positioning plate 2 and the upper end cover 1 are arranged in sequence above the package 3, the upper end cover 1, the positioning plate 2 and the package 3 are fixed together by connecting bolts 7, and the first arc-shaped groove 101 provided at the bottom of the upper end cover 1, the second arc-shaped groove 201 provided on the positioning plate 2 and the third arc-shaped groove 307 provided on the top of the package 3 together constitute a circular through hole for placing a cable to be tested, a plurality of bosses of different heights located below the circular through hole are provided inside the package 3, and each boss has a different distance from the inner side surface 308 of the front wall of the package 3, each boss is fixed with a piezoelectric layer 5 of the same shape and size as the top surface of the corresponding boss, the piezoelectric layer 5 is fixed with a permanent magnet 4 of the same shape and size as the top surface of the corresponding piezoelectric layer 5, and the single-chip computer 6 is fixed on the inner side surface 308 of the front wall of the package 3 parallel to the center axis of the circular through hole.

[0007] The piezoelectric layer 5 includes an upper electrode plate 502 , a piezoelectric material 501 and a lower electrode plate 503 which are sequentially connected from top to bottom.

[0008] The inner side surface 308 of the front wall of the package 3 is parallel to the central axis of the circular through hole formed by the first arc-shaped groove 101 , the second arc-shaped groove 201 and the third arc-shaped groove 307 .

[0009] The upper plate 502, the piezoelectric material 501, the lower plate 503 and the permanent magnet 4 are cubes, cuboids or cylinders.

[0010] The positioning plate 2 is composed of two half positioning plates spliced ​​together.

[0011] A self-compensating button current detection method comprises the following steps:

[0012] Step 1: fix the current detection device on the cable under test through the circular through hole, that is, pass the cable under test through the circular through hole, and then use the connecting bolt 7 to lock the upper end cover 1, the positioning plate 2 and the package 3 to press the cable under test into the circular through hole;

[0013] Step 2: The magnetic field generated by the current in the measured cable causes the permanent magnet 4 to be subjected to electromagnetic force, and then the piezoelectric layer 5 produces a micro deformation. The output voltage of each piezoelectric layer 5 is linearly related to the measured current value. For the voltage U output by any piezoelectric layer 5 in the current detection device, the formula is as follows:

[0014] For DC current:

[0015]

[0016] For AC current:

[0017]

[0018] in:

[0019]

[0020]

[0021]

[0022] where k p is the Young's modulus of the piezoelectric layer 5, m p is the mass of the piezoelectric layer 5, ω n is the natural frequency of the piezoelectric layer 5, ω is the frequency of the alternating current, ξ is the mechanical damping of the piezoelectric layer 5, C p is the capacitance of the piezoelectric layer 5, d 33 is the piezoelectric constant, I is the amplitude of the current to be measured, the straight line passing through the centroid of the permanent magnet 4 and perpendicular to the upper surface of the permanent magnet 4 is taken as the z-axis, the straight line passing through the centroid of the permanent magnet 4, perpendicular to the z-axis and orthogonal to the central axis of the third arc-shaped slot 307 is taken as the x-axis to establish the coordinate system of the current detection device, the central axis of the double-core cable to be measured is taken as the u-axis, the cable cross section passing through the centroid of the permanent magnet 4 is taken, the centroid of each core conductor cross section is taken as the v-axis, the w-axis is orthogonal to the u-axis and the v-axis, and the coordinate system of the cable to be measured is established, B r is the residual magnetic flux of permanent magnet 4, F v is the magnetic field force generated by the tested cable on the permanent magnet 4 along the v-axis direction, H v is the component of the magnetic field intensity generated by the measured cable along the v-axis direction, H u is the component of the magnetic field intensity generated by the measured cable along the u axis direction, a is the distance between the central axes of the two conductors in the cable; u, v, w are the coordinates of the center of mass of the permanent magnet 4 along the u, v, w axes respectively, Δx, Δy are the displacement errors generated by the current detection device along the x, y coordinate axes respectively, c, s are the abbreviations of cos and sin respectively, c1, c2, c3 represent the cosine values ​​of the angular errors generated by the rotation of the current detection device along the x, y, z coordinate axes respectively, s1, s2, s3 represent the sine values ​​of the angular errors generated by the rotation of the current detection device along the x, y, z coordinate axes respectively;

[0023] Step three, since the output voltage U0 of the single-chip microcomputer 6 is linearly related to the current amplitude I in the measured cable, the output voltages of all piezoelectric layers 5 are solved by the single-chip microcomputer 6 to compensate for the non-uniform magnetic field and the nonlinear error caused by the bending moment of the permanent magnet 4 and the installation error generated during the installation process, wherein the single-chip microcomputer 6 calculates the current amplitude in the measured cable according to the following formula, and converts the calculated current amplitude into its own output voltage for output:

[0024] For DC current:

[0025]

[0026] U0=k0I

[0027] For AC current:

[0028]

[0029] U0=k0I

[0030] Where k0 is the amplification factor in the single chip microcomputer 6, U0 is the output voltage of the single chip microcomputer 6, and U i is the output voltage of each piezoelectric layer 5.

[0031] Beneficial effects of the present invention:

[0032] (1) High linearity: Due to the limitation of the principle, the non-uniform magnetic field generated by the wire and the additional bending moment on the permanent magnet on the cantilever beam of the piezoelectric beam sensor make the cantilever beam vibrate nonlinearly, which affects the measurement accuracy and the linearity is not high. At the same time, the installation accuracy has a certain influence on the output. The sensitive element in the present invention is a piezoelectric ceramic. According to its principle, the output voltage generated is only related to the total load force on its surface. The additional bending moment generated by the non-uniform magnetic field on the permanent magnet in the sensor has no interference with the sensor output. The displacement of the permanent magnet in the non-uniform magnetic field is very small, which makes the sensor output linearity very high.

[0033] (2) High measurement accuracy: Due to the limitation of the principle, the installation accuracy of the piezoelectric beam sensor directly affects the measurement accuracy. The present invention determines the measured current size of the five installation degrees of freedom that directly affect the measurement accuracy as an unknown number, and uses the output of the six piezoelectric layers in the sensor to establish a set of equations. The measured current value is obtained by directly eliminating the influence of the installation error through the single-chip microcomputer, and the measurement accuracy is greatly improved.

[0034] (3) Strong practicability: The present invention can measure both direct current and alternating current without damaging the cable protective layer. At the same time, since the sensor is not limited by installation accuracy, the manufacturing accuracy of its positioning structure and the installation process during use are not required to be high, which reduces its cost and makes it easier to operate;

[0035] (4) Self-powered: The piezoelectric layer can realize self-powered power supply for subsequent processing circuits, without the need to regularly replace the power supply, which is convenient for long-term current measurement in places where maintenance is inconvenient, such as underground or in the air. In addition, in addition to using the piezoelectric layer as a self-powered element, various elements that can collect energy, such as capacitors, can also be used as self-powered elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of the self-compensating button type current detection device of the present invention;

[0037] Figure 2 It is a schematic diagram of the overall structure of Example 1 and Example 2 of the present invention;

[0038] Figure 3 For the present invention Figure 2 Axonometric drawing after sectioning on the AA and BB surfaces;

[0039] Figure 4 This is an axonometric diagram when the piezoelectric layer and the permanent magnet are rectangular parallelepipeds in Example 2 of the present invention;

[0040] Figure 5 This is an axonometric diagram when the piezoelectric layer and the permanent magnet are cylindrical in Example 3 of the present invention;

[0041] Figure 6 This is an axonometric diagram of different bosses with different distances from the inner wall surface in Example 2 of the present invention;

[0042] Figure 7 This is an axonometric view when the number of bosses is 1 in Example 3 of the present invention;

[0043] Figure 8 The schematic diagram of the present invention for detecting the current of a double-core cable. DETAILED DESCRIPTION

[0044] Example 1

[0045] A self-compensating button type current detection device, comprising an upper end cover 1, a positioning plate 2, a package 3, a permanent magnet 4, a piezoelectric layer 5 and a single chip computer 6, wherein the positioning plate 2 and the upper end cover 1 are arranged in sequence above the package 3, the upper end cover 1, the positioning plate 2 and the package 3 are fixed together by connecting bolts 7, and the first arc-shaped groove 101 provided at the bottom of the upper end cover 1, the second arc-shaped groove 201 provided on the positioning plate 2 and the third arc-shaped groove 307 provided on the top of the package 3 together constitute a circular passage for placing a cable to be tested. Hole, a plurality of bosses of different heights are provided inside the package 3 below the circular through hole, the number of the bosses is the same as the number of the piezoelectric layer 5 and the permanent magnet 4, and the distance between each boss and the inner side surface 308 of the front wall of the package 3 is different, a piezoelectric layer 5 with the same shape and size as the top surface of the corresponding boss is fixed on each boss, a permanent magnet 4 with the same shape and size as the top surface of the corresponding piezoelectric layer 5 is fixed on the piezoelectric layer 5, and a single-chip computer 6 is fixed on the inner side surface 308 of the front wall of the package 3 parallel to the central axis of the circular through hole.

[0046] The piezoelectric layer 5 includes an upper electrode plate 502 , a piezoelectric material 501 and a lower electrode plate 503 which are sequentially connected from top to bottom.

[0047] The inner side surface 308 of the front wall of the package 3 is parallel to the central axis of the circular through hole formed by the first arc-shaped groove 101 , the second arc-shaped groove 201 and the third arc-shaped groove 307 .

[0048] The upper plate 502, the piezoelectric material 501, the lower plate 503 and the permanent magnet 4 are cubes, cuboids or cylinders.

[0049] The distance between the boss and the inner side surface 308 of the front wall is any distance.

[0050] The number of the piezoelectric layers 5 and the permanent magnets 4 is 1, 2, 3, ... to n.

[0051] The positioning plate 2 is composed of two half positioning plates spliced ​​together.

[0052] A self-compensating button current detection method comprises the following steps:

[0053] Step 1: fix the current detection device on the cable under test through the circular through hole, that is, pass the cable under test through the circular through hole, and then use the connecting bolt 7 to lock the upper end cover 1, the positioning plate 2 and the package 3 to press the cable under test into the circular through hole;

[0054] Step 2: The magnetic field generated by the current in the measured cable causes the permanent magnet 4 to be subjected to electromagnetic force, and then the piezoelectric layer 5 produces a micro-deformation, and the six piezoelectric layers 5 generate output voltages U1, U2, U3, U4, U5, and U6. The output voltage of each piezoelectric layer 5 is linearly related to the measured current value. For the voltage U output by any piezoelectric layer 5 in the current detection device, the formula is as follows;

[0055] For DC current:

[0056]

[0057] For AC current:

[0058]

[0059] in:

[0060]

[0061]

[0062]

[0063] where k p is the Young's modulus of the piezoelectric layer 5, m p is the mass of the piezoelectric layer 5, ω n is the natural frequency of the piezoelectric layer 5, ω is the frequency of the alternating current, ξ is the mechanical damping of the piezoelectric layer 5, C p is the capacitance of the piezoelectric layer 5, d 33is the piezoelectric constant, I is the amplitude of the current to be measured, the straight line passing through the centroid of the permanent magnet 4 and perpendicular to the upper surface of the permanent magnet 4 is taken as the z-axis, the straight line passing through the centroid of the permanent magnet 4, perpendicular to the z-axis and orthogonal to the central axis of the third arc-shaped slot 307 is taken as the x-axis to establish the coordinate system of the current detection device, the central axis of the double-core cable to be measured is taken as the u-axis, the cable cross section passing through the centroid of the permanent magnet 4 is taken, the centroid of each core conductor cross section is taken as the v-axis, the w-axis is orthogonal to the u-axis and the v-axis, and the coordinate system of the cable to be measured is established, B r is the residual magnetic flux of permanent magnet 4, F v is the magnetic field force generated by the tested cable on the permanent magnet 4 along the v-axis direction, H v is the component of the magnetic field intensity generated by the measured cable along the v-axis direction, H u is the component of the magnetic field intensity generated by the measured cable along the u axis direction, a is the distance between the central axes of the two conductors in the cable; u, v, w are the coordinates of the center of mass of the permanent magnet 4 along the u, v, w axes respectively, Δx, Δy are the displacement errors generated by the current detection device along the x, y coordinate axes respectively, c, s are the abbreviations of cos and sin respectively, c1, c2, c3 represent the cosine values ​​of the angular errors generated by the rotation of the current detection device along the x, y, z coordinate axes respectively, s1, s2, s3 represent the sine values ​​of the angular errors generated by the rotation of the current detection device along the x, y, z coordinate axes respectively;

[0064] Step 3: Since the output voltage U0 of the single-chip microcomputer 6 is linearly related to the current amplitude I in the measured cable, the output voltages of all piezoelectric layers 5 are solved by the single-chip microcomputer 6 to compensate for the non-uniform magnetic field and the nonlinear error caused by the bending moment of the permanent magnet 4 and the installation error generated during the installation process, and converted into a DC voltage, wherein the single-chip microcomputer 6 calculates the current value in the measured cable according to the following formula:

[0065] For DC current:

[0066]

[0067] U0=k0I

[0068] For AC current:

[0069]

[0070] U0=k0I

[0071] Where k0 is the amplification factor in the single chip microcomputer 6, U0 is the output voltage of the single chip microcomputer 6, and U i is the output voltage of each piezoelectric layer 5.

[0072] Example 2

[0073] like Figure 1 and Figure 2As shown, the upper end cover 1, the positioning plate 2 and the package 3 are fixed by connecting bolts 7. The upper end cover 1, the positioning plate 2 and the package 3 each have a first arc-shaped groove 101, a second arc-shaped groove 201 and a third arc-shaped groove 307 to achieve the positioning of the cable under test. Figure 3 As shown, there are 6 bosses of different heights on the bottom surface of the package 3, namely the first boss 301, the second boss 302, the third boss 303, the fourth boss 304, the fifth boss 305, and the sixth boss 306, and each boss is at a different distance from the inner wall surface 308 of the package. A piezoelectric layer 5 is fixed on the boss, including an upper plate 502, a piezoelectric material 501, and a lower plate 503. A permanent magnet 4 is fixed on the piezoelectric layer 5. All structures and sizes fixed on each boss are exactly the same. A single-chip computer 6 is fixed on the inner wall surface parallel to the central axis of the circular through hole formed by the first arc-shaped groove 101, the second arc-shaped groove 201, and the third arc-shaped groove 307.

[0074] The self-compensating button type current detection device described in the present invention has an upper plate 502, a piezoelectric material 501, a lower plate 503 and a permanent magnet 4 in the form of a cube, a cuboid, a cylinder and other cylinders of various cross sections, such as Figure 4 , Figure 5 shown.

[0075] In the self-compensating button current detection device described in the present invention, the distance between all bosses and the inner wall surface 308 is any distance, such as Figure 6 shown.

[0076] The self-compensating button type current detection device of the present invention is characterized in that the number of the piezoelectric layer 5 and the permanent magnet 4 is 1, 2, 3 ... to n, such as Figure 7 , Figure 8 shown.

[0077] A self-compensating button current detection method, characterized by comprising the following steps:

[0078] Step (1), fix the current detection device on the cable to be tested through the first arc-shaped groove 101, the second arc-shaped groove 201, and the third arc-shaped groove 307, and lock the upper end cover 1, the positioning plate 2, and the package 3 with the connecting bolts 7;

[0079] Step (2), at this time, the magnetic field generated by the current in the measured cable causes the permanent magnet 4 to be subjected to electromagnetic force, and the piezoelectric layer 5 produces a micro deformation. The output voltages generated by the six piezoelectric layers 5 are U1, U2, U3, U4, U5, and U6 respectively. The output voltage of each piezoelectric layer 5 is linearly related to the measured current value. For any piezoelectric layer 5 in the current detection device, the formula is as follows;

[0080] For DC current

[0081] For DC current

[0082]

[0083] For AC current

[0084]

[0085] in:

[0086]

[0087]

[0088] Wherein k1 and k2 are constants related to the physical parameters of the structure of the piezoelectric layer 5 itself, I is the amplitude of the current to be measured, and the straight line passing through the centroid of the permanent magnet 4 and perpendicular to the upper surface of the permanent magnet 4 is taken as the z-axis, and the straight line passing through the centroid of the permanent magnet 4, perpendicular to the z-axis and orthogonal to the central axis of the third arc-shaped slot 307 is taken as the x-axis to establish the coordinate system of the current detection device, and the central axis of the double-core cable to be measured is taken as the u-axis, and the cross section of the cable passing through the centroid of the permanent magnet 4 is taken, and the centroid line of each core conductor cross section is taken as the v-axis, and the w-axis is orthogonal to the u-axis and the v-axis, and the coordinate system of the cable to be measured is established, B r is the residual magnetic flux of permanent magnet 4, F v is the magnetic field force in the direction v generated by the tested cable on the permanent magnet 4, H v is the component of the magnetic field intensity generated by the measured cable along the v direction, H u is the component of the magnetic field intensity generated by the measured cable along the u direction, and a is the distance between the central axes of the two conductors in the cable. u, v, and w are the coordinates of the center of mass of the permanent magnet 4 along the u, v, and w axes respectively. Δx and Δy are the displacement errors generated along the x and y coordinate axes respectively, c and s are the abbreviations of cos and sin respectively, c1, c2, and c3 represent the cosine values ​​of the angular errors generated by the rotation along the x, y, and z coordinate axes, and s1, s2, and s3 represent the sine values ​​of the angular errors generated by the rotation along the x, y, and z coordinate axes.

[0089] Step (3), all output voltages are solved by the single chip microcomputer 6, the output voltage U0 of the single chip microcomputer 6 is a DC voltage, and the output voltage U0 of the single chip microcomputer 6 is linearly related to the current amplitude I in the measured cable, and compensates for the non-uniform magnetic field and the nonlinear error caused by the bending moment generated by the permanent magnet and the installation error generated during the installation process, and the formula is as follows;

[0090] For DC current:

[0091]

[0092] U0=k0I

[0093] For AC current:

[0094]

[0095] U0=k0I

[0096] The equations for DC current and AC current respectively contain six unknowns (Δx, Δy, c1, c2, c3, I), k0 is the amplification factor in the single-chip microcomputer 6, and U0 is the output voltage of the single-chip microcomputer 6;

[0097] The relationship between the output voltage U0 of the single-chip microcomputer 6 of the above current detection device prototype and the amplitude I of the measured current is as follows:

[0098] The measured current can be obtained by the following method:

[0099] The device is fixed on the measured cable with a current i through the first arc groove 101, the second arc groove 201 and the third arc groove 307, and the upper end cover 1, the positioning plate 2 and the package 3 are locked with the connecting bolts 7, as shown in FIG. Figure 8 As shown, the magnetic field force exerted on the permanent magnet 4 causes stress deformation in the piezoelectric material through the magnetic field force, thereby causing the piezoelectric material to generate an output voltage. The output voltage of all piezoelectric materials in the package 3 enters the single-chip microcomputer 6 for equation solving to obtain the amplitude I of the current in the measured cable.

[0100] The formula for the magnetic field strength generated by the double-core cable around the cable in the cable xyz coordinate system is:

[0101]

[0102]

[0103] The coordinate conversion formula from the cable xyz coordinate system to the uvw coordinate system of the permanent magnet 4 under the condition of introducing installation error is:

[0104] x=c2c3u-c2s3v+s2w+Δx

[0105] y=(c1s3+s1s2c3)u+(c1c3-s1s2s3)v-s1c2w+Δy

[0106] Conversion formula of magnetic field intensity in uvw coordinate system:

[0107]

[0108]

[0109] The magnetic field force in the v direction generated by the double-core cable on any permanent magnet 4 is:

[0110]

[0111] For the output voltage U in any piezoelectric layer

[0112] For DC current

[0113]

[0114] For AC current

[0115]

[0116] where k p is the Young's modulus of the piezoelectric layer 5, m p is the mass of the piezoelectric layer 5, ω n is the natural frequency of the piezoelectric layer 5, ω is the frequency of the alternating current, ξ is the mechanical damping of the piezoelectric layer 5, C p is the capacitance of the piezoelectric layer 5, d 33 is the piezoelectric constant, I is the amplitude of the current to be measured, and the voltage U output by all piezoelectric layers 5 enters the single-chip microcomputer 6 for equation solving, the equation is:

[0117] For DC current:

[0118]

[0119] U0=k0I

[0120] For AC current:

[0121]

[0122] U0=k0I

[0123] The equations for DC current and AC current respectively contain six unknowns (Δx, Δy, c1, c2, c3, I), k0 is the amplification factor in the single-chip microcomputer 6, and U0 is the output voltage of the single-chip microcomputer 6;

[0124] Example 3

[0125] The same as the embodiment 1, the difference is that the piezoelectric layer 5 and the permanent magnet 4 are both cylindrical, and the number of bosses in the package 3 is 1.

[0126] Application example: Taking six rectangular piezoelectric layers 5 as the output elements of the present invention to eliminate installation errors in five directions for measuring a two-wire AC cable as an example, the basic principle of the present invention is explained as follows:

[0127] There is a live wire and a neutral wire inside the two-core cable, and their current directions are opposite, such as Figure 8 shown.

[0128] The formula for the magnetic field strength generated by the double-core cable around the cable in the cable xyz coordinate system is:

[0129]

[0130]

[0131] The coordinate conversion formula from the cable xyz coordinate system to the uvw coordinate system of the permanent magnet 4 under the condition of introducing installation error is:

[0132] x=c2c3u-c2s3v+s2w+Δx

[0133] y=(c1s3+s1s2c3)u+(c1c3-s1s2s3)v-s1c2w+Δy

[0134] Conversion formula of magnetic field intensity in uvw coordinate system:

[0135]

[0136]

[0137] The magnetic field force in the v direction generated by the double-core cable on any permanent magnet 4 is:

[0138]

[0139] For the output voltage U in any piezoelectric layer

[0140] For DC current

[0141]

[0142] For AC current

[0143]

[0144] where k p is the Young's modulus of the piezoelectric layer, m p is the mass of the piezoelectric layer, ω n is the natural frequency of the piezoelectric layer, ω is the frequency of the alternating current, ξ is the mechanical damping of the piezoelectric layer, C p is the capacitance of the piezoelectric layer, d 33 is the piezoelectric constant, I is the amplitude of the current to be measured, and the voltage U output by all piezoelectric layers 5 enters the single-chip microcomputer 6 for equation solving, the equation is:

[0145] For DC current:

[0146]

[0147] U0=k0I

[0148] For AC current:

[0149]

[0150] U0=k0I

[0151] The equation groups of direct current and alternating current respectively contain six unknowns (Δx, Δy, c1, c2, c3, I), k0 is the amplification factor in the single-chip computer 6, and U0 is the output voltage of the single-chip computer 6.

Claims

1. A current detection method using a self-compensating button-type current detection device, wherein the self-compensating button-type current detection device comprises an upper end cover (1), a positioning plate (2), a package (3), a permanent magnet (4), a piezoelectric layer (5) and a single-chip computer (6), wherein the positioning plate (2) and the upper end cover (1) are sequentially arranged above the package (3), the upper end cover (1), the positioning plate (2) and the package (3) are fixed together by connecting bolts (7), and a first arc-shaped groove (101) is arranged at the bottom of the upper end cover (1), a second arc-shaped groove (201) is arranged on the positioning plate (2), and a piezoelectric layer (5) is arranged at the top of the package (3). Some third arc-shaped grooves (307) together form a circular through hole for placing the tested cable, a plurality of bosses of different heights are provided inside the package (3) and are located below the circular through hole, and each boss is at a different distance from the inner side surface (308) of the front wall of the package (3), a piezoelectric layer (5) having the same shape and size as the top surface of the corresponding boss is fixed on each boss, a permanent magnet (4) having the same shape and size as the top surface of the corresponding piezoelectric layer (5) is fixed on the piezoelectric layer (5), and a single-chip computer (6) is fixed on the inner side surface (308) of the front wall of the package (3) parallel to the central axis of the circular through hole; characterized in that: The current detection method includes the following steps: Step 1: fix the current detection device on the cable to be tested through the circular through hole, that is, pass the cable to be tested through the circular through hole, and then use the connecting bolt (7) to lock the upper end cover (1), the positioning plate (2) and the package (3) to press the cable to be tested into the circular through hole; Step 2: The magnetic field generated by the current in the measured cable causes the permanent magnet (4) to be subjected to electromagnetic force, thereby causing the piezoelectric layer (5) to produce a micro-deformation. The output voltage of each piezoelectric layer (5) is linearly related to the measured current value. For the voltage U output by any piezoelectric layer (5) in the current detection device, the formula is as follows: For DC current: For AC current: in: where k p is the Young's modulus of the piezoelectric layer (5), m p is the mass of the piezoelectric layer (5), ω n is the natural frequency of the piezoelectric layer (5), ω is the frequency of the alternating current, ξ is the mechanical damping of the piezoelectric layer (5), C p is the capacitance of the piezoelectric layer (5), d 33 is the piezoelectric constant, I is the amplitude of the current to be measured, a straight line passing through the centroid of the permanent magnet (4) and perpendicular to the upper surface of the permanent magnet (4) is taken as the z-axis, a straight line passing through the centroid of the permanent magnet (4), perpendicular to the z-axis and orthogonal to the central axis of the third arc-shaped slot (307) is taken as the x-axis to establish a coordinate system of the current detection device, the central axis of the double-core cable to be measured is taken as the u-axis, a cable cross section passing through the centroid of the permanent magnet (4), a line connecting the centroids of the cross section of each core conductor is taken as the v-axis, and the w-axis is orthogonal to the u-axis and the v-axis, to establish a coordinate system of the cable to be measured, B r is the residual magnetic flux of the permanent magnet (4), F v is the magnetic field force along the v-axis direction generated by the tested cable on the permanent magnet (4), H v H is the component of the magnetic field intensity generated by the measured cable along the v-axis direction, u is the component of the magnetic field intensity generated by the measured cable along the u axis direction, a is the distance between the central axes of the two conductors in the cable; u, v, w are the coordinates of the center of mass of the permanent magnet (4) along the u, v, w axes respectively, △x, △y are the displacement errors generated by the current detection device along the x, y coordinate axes respectively, c, s are the abbreviations of cos and sin respectively, c1, c2, c3 represent the cosine values ​​of the angular errors generated by the rotation of the current detection device along the x, y, z coordinate axes respectively, s1, s2, s3 represent the sine values ​​of the angular errors generated by the rotation of the current detection device along the x, y, z coordinate axes respectively; Step 3: Since the output voltage U0 of the single-chip microcomputer (6) is linearly related to the current amplitude I in the measured cable, the output voltages of all piezoelectric layers (5) are solved by the single-chip microcomputer (6) to compensate for the non-uniform magnetic field and the nonlinear error caused by the bending moment generated by the permanent magnet (4) and the installation error generated during the installation process, wherein the single-chip microcomputer (6) calculates the current amplitude in the measured cable according to the following formula, and converts the calculated current amplitude into its own output voltage for output: For DC current: For AC current: U0=k0I Where k0 is the amplification factor in the single chip microcomputer (6), U0 is the output voltage of the single chip microcomputer (6), and U i is the output voltage of each piezoelectric layer (5).

2. The current detection method according to claim 1, characterized in that The invention comprises an upper end cover (1), a positioning plate (2), a package (3), a permanent magnet (4), a piezoelectric layer (5) and a single chip computer (6), wherein the positioning plate (2) and the upper end cover (1) are arranged in sequence above the package (3), the upper end cover (1), the positioning plate (2) and the package (3) are fixed together by connecting bolts (7), and a first arc-shaped groove (101) provided at the bottom of the upper end cover (1), a second arc-shaped groove (201) provided on the positioning plate (2) and a third arc-shaped groove (307) provided on the top of the package (3) together constitute A circular through hole for placing a cable to be tested, a package (3) is provided with a plurality of bosses of different heights located below the circular through hole, and each boss is at a different distance from an inner side surface (308) of a front wall of the package (3), a piezoelectric layer (5) having the same shape and size as the top surface of the corresponding boss is fixed on each boss, a permanent magnet (4) having the same shape and size as the top surface of the corresponding piezoelectric layer (5) is fixed on the piezoelectric layer (5), and a single-chip computer (6) is fixed on an inner side surface (308) of the front wall of the package (3) parallel to the central axis of the circular through hole.

3. The current detection method according to claim 1, characterized in that The piezoelectric layer (5) comprises an upper electrode plate (502), a piezoelectric material (501) and a lower electrode plate (503) which are connected in sequence from top to bottom.

4. The current detection method according to claim 2, characterized in that The inner side surface (308) of the front wall of the package (3) is parallel to the central axis of the circular through hole formed by the first circular arc groove (101), the second circular arc groove (201) and the third circular arc groove (307).

5. The current detection method according to claim 3, characterized in that The upper electrode plate (502), the piezoelectric material (501), the lower electrode plate (503) and the permanent magnet (4) are cubes, cuboids or cylinders.

6. The current detection method according to claim 1, characterized in that The positioning plate (2) is composed of two half positioning plates spliced ​​together.

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