CN107908846B - Magnetic field analysis method of magnetic resonance type wireless power supply technology in high-voltage power line monitoring - Google Patents
Magnetic field analysis method of magnetic resonance type wireless power supply technology in high-voltage power line monitoring Download PDFInfo
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Abstract
The invention discloses a magnetic field analysis method of a magnetic resonance type wireless power supply technology in high-voltage power line monitoring. The method comprises the steps of designing the whole framework of the wireless power supply device of the high-voltage line on-line monitoring terminal, building a module of the wireless power supply device of the high-voltage line on-line monitoring terminal, building a cylindrical coordinate system for carrying out distribution calculation of a magnetic field of a transmitting end and building 1 for an axial equal-diameter single-layer close-wound coil based on a coil structure: and (3) solving the magnetic field distribution around the wireless power supply device, calculating the integral synthetic magnetic field, calculating the alternating current magnetic field and building an experimental platform for verification by using the simulation model with the size of 1. Compared with the conventional electromagnetic calculation simulation software Ansoft Maxwell, the calculation method provided by the invention has the advantages of high solving speed and approximate calculation accuracy. By using the method, a common computer can perform complex electromagnetic calculation, and the method has important significance for design optimization of the high-voltage wireless power supply device and the electromagnetic safety thereof.
Description
Technical Field
The invention relates to a wireless power transmission technology, in particular to a magnetic field analysis method of magnetic resonance type wireless power supply in high-voltage power line monitoring.
Background
The high-voltage power transmission aims at medium-distance and long-distance power transmission, and a combined power system is constructed through interconnection among long-distance systems. In order to save the cultivated land area, most of transmission lines are tested in various severe operating environments, and the electric power line patrol is very difficult. Therefore, on the high-voltage transmission line, a system formed by a plurality of composite technologies such as an online monitoring technology, a charged detection technology state monitoring technology and the like is mostly adopted as a supplement to replace manpower to monitor the line, so that accident potential hazards can be found as soon as possible and eliminated in time, the high-voltage transmission line can always run in a good state, and reliable operation guarantee measures are provided for the transmission line.
In the existing literature, theoretical analysis about a magnetic resonance wireless power transmission system mainly utilizes the biot saxael law and an ellipse integral formula to solve the magnetic field of a single-turn coil at a certain point in space, and a multi-turn coil is equivalent to the superposition of a plurality of single-turn coils or Ansoft Maxwell, Ansoft HFSS and CST EM are adopted
Carrying out simulation calculation by using an isoelectric magnetic field finite element simulation software and a COMSOL Multiphysics multi-physical field coupling simulation software. For finite element simulation, if higher solving precision is required, finer mesh division is required, and at the moment, if the solving area is larger, the simulation time is longer, and even the simulation cannot be performed.
Disclosure of Invention
On the basis of the research, the magnetic vector potential at any position around the wireless power supply device is obtained by combining a reciprocal distance method, so that the analytic solution of a magnetic field around the device and an induced electric field thereof is obtained, the simulation result of Ansoft Maxwell finite element simulation software is combined, the distribution of the magnetic field around the device is analyzed, in addition, the electric field caused by the potential difference of the transmission coil is taken into account, the distribution of the electromagnetic field around the wireless power supply device is integrally analyzed, so that a theoretical basis is provided for the feasibility analysis of the wireless power supply device in a high-voltage environment, and the method has high accuracy and high solving speed.
In order to realize the purpose of the invention, the following technical scheme is adopted for realizing the purpose:
a magnetic field analysis method of a magnetic resonance type wireless power supply technology in high-voltage power line monitoring is characterized in that a magnetic vector potential at any position around a wireless power supply device is obtained by combining a reciprocal distance method, and magnetic field distribution around the device is analyzed by combining a simulation result of Ansoft Maxwell finite element simulation software; the simulation result comprises a magnetic induction distribution diagram in simulation software, a magnetic induction distribution diagram around the transmitting end working coil only in a resonance state, and a magnetic induction instantaneous value distribution diagram of the transmission coil working at a frequency point.
And (3) calculating the distribution of the magnetic field of the transmitting end by using the reciprocal distance in combination with Neumann addition theorem and Lipshitz integral, and performing simulation calculation and analysis.
On the basis of solving the magnetic field distribution of the transmitting end by using the reciprocal distance, the calculation of the integral synthetic magnetic field is carried out, wherein the calculation comprises the steps of determining the working frequency, calculating the alternating current magnetic field and designing a calculation program to realize theoretical calculation.
The method specifically comprises the following steps;
step 1, designing an integral framework of a wireless power supply device of a high-voltage line online monitoring terminal, and building a module design model of the wireless power supply device of the high-voltage line online monitoring terminal;
step 2, establishing a cylindrical coordinate system for carrying out distribution calculation of the magnetic field of the transmitting end based on the coil structure as an axial equal-diameter single-layer close-wound coil;
step 3, in Ansoft Maxwell software, the same parameters are adopted, Ansoft Maxwell electromagnetic field finite element software is compared, and 1: 1, obtaining the magnetic field distribution around the wireless power supply device under the excitation of the same current by using a simulation model with the size of 1;
and 4, calculating the integral synthetic magnetic field: when the frequency splitting phenomenon occurs, selecting a frequency point at the maximum transmitting power position of a transmitting end with obvious distinguishing characteristics as a working frequency point of the wireless power supply device, carrying out Ansoft Maxwell software simulation analysis on an electromagnetic field of the device in the working frequency point state, and obtaining a theoretical calculation formula of an alternating current magnetic field, wherein the formula is as follows:
the transmitting coil and the receiving coil work at the same time at a frequency point f corresponding to the maximum transmitting power of the device0The magnetic vector potential in the state is: a ═ A1+A2
Wherein, I(λ,μ,ν)(R, R, | u |) is a Bezier Laplace integral corresponding to the magnetic induction expressions in the R-direction and z-direction. Mu.s0Is vacuum magnetic conductance, R is coil radius, R is the distance between any source point and field point in the magnetic field, the length of wire turn is 2h, N is the number of coil turns,
is the unit vector of the magnetic vector potential direction, I1、I2Current, i.e. voltage, effective values of the transmitter and receiver coils, respectivelySAnd the ratio of the resistances.
Step 5, designing a program for calculating a magnetic field around the wireless power supply device and a magnetic field induced electric field, and completing theoretical calculation in the steps 2, 3 and 4 by using MATLAB programming;
and 6, according to the parameters of the calculation example, establishing an experimental platform of the wireless power supply device of the high-voltage line online monitoring terminal, and verifying the accuracy and the effectiveness of the magnetic field distribution calculation method.
The procedure in step 5 comprises the following steps:
step 5.1, setting parameters of the material, the winding radius, the number of turns, the width and the transmission distance of the coil;
step 5.2, carrying out frequency sweep analysis on the current of the transmitting end, determining the working frequency of the device and corresponding current excitation, and determining the solving range of the magnetic field under the column coordinate;
step 5.3, respectively determining the magnetic induction intensities of the transmitting coil and the receiving coil in the r direction and the z direction under the condition according to the value range of the longitudinal height z;
and 5.4, combining all the conditions, superposing the r-direction magnetic induction intensity and the z-direction magnetic induction intensity of the transmitting coil and the receiving coil respectively, and drawing a graph.
The purpose of the invention is: in order to promote the application of the wireless power transmission technology in high-voltage power monitoring, the influence of a wireless power supply device based on the technology on the normal operation of a high-voltage power transmission and distribution line and the influence of the high-voltage power transmission and distribution line on the wireless power supply device need to be analyzed. Furthermore, the influence of the wireless power supply device on the monitoring device and other electronic devices around the monitoring device, which are the power supply objects of the wireless power supply device, needs to be analyzed, the influence of the electronic devices on the normal operation of the wireless power supply device needs to be analyzed, and the problem of the mutual influence between the wireless power supply device and the human body also exists. The influence is controlled within the range of relevant standard limit values, so that the wireless power supply device, namely the lines and equipment around the wireless power supply device can continuously and normally work, and the safety of nearby personnel is ensured.
Drawings
Fig. 1 is a general structure diagram of a wireless power supply device of a high-voltage line online monitoring terminal.
Fig. 2 is a relationship diagram of the overall structure of the wireless power supply device of the high-voltage line online monitoring terminal.
Fig. 3 is a schematic structural view of a high-voltage electricity-taking device.
Fig. 4 is a diagram of a transmitting end circuit.
Fig. 5 is a schematic diagram of the arrangement of the transmitting coils in a cylindrical coordinate system.
Fig. 6 is an equivalent circuit diagram of the wireless power supply device.
Fig. 7 is a schematic diagram of the arrangement of the transmitting coil and the receiving coil.
Fig. 8 is a flowchart of a procedure for calculating the magnetic field induced electric field around the wireless power supply device.
Detailed Description
In order to facilitate the understanding and implementation of the present invention for those of ordinary skill in the art, the present invention is further described in detail with reference to the accompanying drawings and examples, it is to be understood that the embodiments described herein are merely illustrative and explanatory of the present invention and are not restrictive thereof.
Step 1, designing an integral framework of the wireless power supply device of the high-voltage line online monitoring terminal, and building a module design model of the wireless power supply device of the high-voltage line online monitoring terminal. The general structure of the wireless power supply device of the high-voltage line online monitoring terminal is shown in fig. 1. The architecture mainly comprises three parts: the high-voltage power taking device comprises a high-voltage power taking device, a high-frequency energy transmitting device and a high-frequency energy receiving device. The relationship between these three parts is shown in fig. 2. The high-voltage electricity taking device and the high-frequency energy transmitting device are fixed at a position, close to an insulator, of the high-voltage line, the high-voltage electricity taking device obtains power-frequency alternating current from the high-voltage line, the power-frequency alternating current is rectified and converted into direct current through a control circuit of the high-voltage electricity taking device, and the high-voltage electricity taking device supplies power to the high-frequency energy transmitting device. A control circuit in the high-frequency energy transmitting device converts direct current into high-frequency alternating current by using an inverter, then transmits the electric energy to a high-frequency energy receiving device at the other end of the insulator in a wireless mode, and a receiving end converts the high-frequency alternating current into direct current by using a rectification control device after receiving the energy, and the direct current is filtered and stabilized by an electric energy output circuit to supply power for line monitoring equipment on a tower. In order to meet the requirements of engineering application, each part of the device uses a high-reliability packaging shell to package the device, so that the device can meet the related mechanical performance requirements and electrical performance requirements.
The high-voltage power taking device consists of a high-voltage power taking coil and a power taking device control circuit; the high-frequency energy transmitting device is composed of a transmitting end control circuit, a transmitting end capacitor and a transmitting end transmission coil; the high-frequency energy receiving device consists of a receiving end transmission coil, a receiving end capacitor, a receiving end rectification control device and an electric energy output circuit.
The high-voltage electricity taking device consists of a high-voltage electricity taking structure and an electricity taking device control circuit. The control circuit comprises an energy taking power control circuit, an energy storage device and a voltage stabilizing and adjusting circuit. The electricity taking structure converts a magnetic field around the high-voltage wire into alternating-current voltage, and the alternating-current voltage is converted into direct current through the rectifying and filtering circuit. If the obtained electric energy exceeds the consumed electric energy, the voltage of the device is increased, the voltage comparator outputs a control signal, the release switch S is opened, and the redundant energy is released in a current mode. The high-voltage electricity taking device is designed as shown in figure 3.
Step 2, the equivalent circuit of the transmitting end is shown in fig. 4, and the natural angular frequency omega of the series circuit is obtained according to the resonance condition of the RLC series circuit1Corresponding natural frequency f1And calculates a transient expression of the supply voltage.
And establishing a cylindrical coordinate system for solving for the axial equal-diameter single-layer close-wound coil based on the coil structure. The radius of the coil is R, the length of a turn is 2h, the number of turns of the coil is N, and the Litz wire is wound by a single layer of 0.01mmx500 strands. The center of the coil is placed at the origin of coordinates, and the distance parameter between any source point in the coil and the field point is set, as shown in fig. 5.
And establishing a cylindrical coordinate system by taking three variables of the radius r, the angle phi and the height z as coordinate axes. In the column coordinates, for the reciprocal of the distance between two points of an arbitrary field point P (coordinates: r1, phi 1 and z1) and an arbitrary source point Q (coordinates: r2, phi 2 and z2) in the graph, namely the reciprocal distance, a summation integral formula of the reciprocal distances can be obtained by utilizing Lipshitz integral and Neumann addition theorem. The vector of magnetic vector potential and current density at any field point in the magnetic field is calculated. The coil is symmetrically wound around the z axis, so that the magnetic field distribution around the coil is irrelevant to the phase phi, an integral expression of the magnetic vector potential is obtained by utilizing the orthogonality of a trigonometric function, and the magnetic induction intensity is obtained by solving the degree of rotation of the magnetic vector potential. A point in the magnetic field is taken and its coordinate is (r, phi, z). The magnetic induction intensities in the r direction and the z direction can be respectively obtained by utilizing the Bessel function recursion relation when z is less than or equal to-h, -h is less than z and less than h, and z is more than or equal to h. The magnetic induction intensities in the r-direction and the z-direction are further solved by a Bezier Laplace integral expression. After the r-direction and z-direction magnetic induction intensity distribution around the coil during coil resonance is respectively obtained, the instantaneous value of the magnetic induction intensity at any moment can be deduced by utilizing a superposition formula and the relation between the electromagnetic wave time domain and the frequency domain.
And 3, simulating, calculating and analyzing the magnetic field of the transmitting end. To verify the above theoretical calculations on magnetic field distribution, the same parameters were used to compare Ansoft Maxwell electromagnetic field finite element software to establish 1: 1, and obtaining the magnetic field distribution around the wireless power supply device under the same current excitation. The magnetic induction intensity distribution of the wireless power supply device at time t-0 is taken as an example for analysis. For comparison, the magnetic induction intensity values at typical field points around the wireless power supply device at the time t-0 are taken as an example, and the simulation calculated values and the theoretical calculated values are listed in the table respectively. The table records calculated values of magnetic induction at different distances (i.e. different r) and experimental test values at a certain ordinate z. Wherein the ordinate z is changed from-0.6 m to 0.6m, the coordinate r is changed from 0 to 0.5m, and the results are uniformly recorded by taking points in the range.
And 4, calculating the integral synthetic magnetic field. An equivalent circuit diagram of the wireless power supply apparatus is shown in fig. 6. When the device is used for a 10kV high-voltage line, due to the limitation of field installation conditions (on the premise of ensuring the insulation strength, the distance between transmission coils of the wireless power supply device is related to the position of a fixed support in order to ensure the construction and installation stability of the device), the axial distance between the outer edges of the coils of the transmitting end and the receiving end in the on-line operation process is 0.5m, and the capacitor CsAnd Cd435pF, 24v of output voltage of the high-voltage power taking device, 50% of duty ratio of the transmitting end circuit and equivalent resistance R of the transmitting ends3.8 omega, receiving end equivalent resistance Rd2 omega, and the equivalent resistance R of the online monitoring equipment (load)LIs 14.5 omega.
When the working frequency of the wireless power supply device is gradually increased, the current of the transmitting end successively generates two peak points and one valley point, namely, the frequency splitting phenomenon. In the application of a high-voltage environment, under the condition of no bilateral communication, in order to ensure that the receiving end on-line monitoring device can obtain enough power to stably operate, a frequency point at the maximum transmitting power position of a transmitting end with obvious distinguishing characteristics is selected as a working frequency point of the wireless power supply device, and the electromagnetic field of the device in the state of the working frequency point is analyzed.
Working frequency f corresponding to current peak point of transmitting end of device0The angular frequency of (a) is denoted as ω0And calculating the currents of the transmitting end and the receiving end. To facilitate the analysis of the electromagnetic field distribution when the dual coils are used, the coils of the transmitting end and the receiving end are placed in cylindrical coordinates, and the two coils are symmetrically arranged along the zero point of the coordinates, as shown in fig. 7. According to the installation requirement of the transmission line in the practical engineering project, the axial distance between the outer edges of the coils at the transmitting end and the receiving end of the device is 0.5m, namely 2a is 500mm in the figure.
According to the arrangement in fig. 7, the magnetic induction intensities of the transmitting coil in the z direction and the r direction and the magnetic induction intensities of the receiving coil in the z direction and the r direction are calculated, and the expression of the magnetic induction intensities with respect to time can be obtained from the relation between the electromagnetic wave time domain and the frequency domain. Further, the frequency point f corresponding to the maximum transmitting power of the device when the transmitting coil and the receiving coil work at the same time can be obtained0Magnetic vector potential in the state.
According to the above analysis with a period T0(T0＝1/f0) Taking the inner 8 instantaneous values as an example, the transmitting coil and the receiving coil are simultaneously operated at a frequency point f corresponding to the maximum transmitting power of the device0The device induction intensity at 436kHz and the distribution of the instantaneous value of the electric field intensity of the induced electric field are plotted and analyzed.
And 5, designing a program for calculating the magnetic field around the wireless power supply device, and finishing theoretical calculation by using MATLAB programming. And (4) programming flow of theoretical calculation. On the basis of the above theoretical analysis, the specific calculation is completed by using MATLAB programming, and the programming flow of the calculation of the magnetic field around the wireless power supply device is shown in fig. 8:
step 5.1, setting parameters of the coil, such as material, winding radius, number of turns, width, transmission distance and the like;
step 5.2, carrying out frequency sweep analysis on the current of the transmitting end, determining the working frequency of the device and corresponding current excitation, and determining the solving range of the magnetic field under the column coordinate;
step 5.3, respectively determining the magnetic induction intensities of the transmitting coil and the receiving coil in the r direction and the z direction under the condition according to the value range of z;
and 5.4, combining all the conditions, superposing the r-direction magnetic induction intensity and the z-direction magnetic induction intensity of the transmitting coil and the receiving coil respectively, and drawing a graph.
And 6, building an experimental platform of the wireless power supply device of the high-voltage line on-line monitoring terminal according to the parameters of the example, and verifying the accuracy and the effectiveness of the magnetic field distribution calculation method.
In the experiment, a voltage-stabilized direct-current power supply is used as the power supply input of the high-frequency transmitting device, the input voltage is DC 24V (the power supply output of the high-voltage power taking device), and the duty ratio of the high-frequency transmitting device is set to be 50%. And when the wireless power supply device stably works at a frequency point corresponding to the current peak value of the transmitting end, the measuring work is started after 2 hours.
The transmission coil is axially and vertically arranged on a wooden table (the length of the table is 1.4m, the width of the table is 0.7m, and the height of the table is 1.2m) with the ground plane and horizontally arranged in the middle, the transmission coil is coaxially arranged, and the distance between the edges of the two coils is 0.5 m. The voltage-stabilizing direct-current power supply, the transmitting end control circuit, the transmitting end capacitor, the receiving end rectification control device and the electric energy output circuit are respectively arranged on two sides of the transmission coil.
In order to facilitate the analysis of the variation of the magnetic induction intensity and the electric field intensity at different positions around the transmission coil, a coordinate system is established, and an analysis grid is established by taking the axial midpoint o point of the transmission coil as the center. The calculated value is the root mean square value within a frequency period, which is convenient for comparison with the measured value. For the convenience of observation, the variation trend of the calculated value and the measured value of the electric field intensity is plotted.
Based on the theoretical calculation method, the electromagnetic field around a cylindrical two-coil magnetic resonance wireless power transmission system and other research objects can be solved and analyzed, and a good foundation is laid for subsequent electromagnetic safety research.
Claims (2)
1. A magnetic field analysis method of a magnetic resonance type wireless power supply technology in high-voltage power line monitoring is characterized in that: the magnetic vector potential at any position around the wireless power supply device is obtained by combining a reciprocal distance method, and the magnetic field distribution around the wireless power supply device is analyzed by combining a simulation result of Ansoft Maxwell finite element simulation software; the simulation result comprises a magnetic induction intensity distribution diagram in simulation software, a magnetic induction intensity distribution diagram around a transmitting end working coil only in a resonance state, and a magnetic induction intensity instantaneous value distribution diagram of a transmission coil working at a frequency point;
establishing a cylindrical coordinate system by taking Rad, Theta and Height as coordinate axes, wherein the Rad, Theta and Height are in cylindrical coordinates; rad is the radius direction of a regular section of a cylindrical coordinate system, Theta is an angle value relative to a zero-angle reference point on the regular section of the cylindrical coordinate system, and Height is the vertical distance between two regular sections of the cylindrical coordinate system; for any field point P (Rad1, Theta1, Height1) and any source point Q (Rad2, Theta2, Height2), the reciprocal of the distance between the two points, namely the reciprocal distance;
calculating the distribution of the magnetic field of the transmitting end by utilizing the reciprocal distance in combination with Neumann addition theorem and Lipshitz integral, and carrying out simulation calculation and analysis;
on the basis of solving the magnetic field distribution of a transmitting end by utilizing the reciprocal distance, the calculation of the integral synthetic magnetic field is carried out, including the determination of working frequency, the calculation of an alternating-current magnetic field and the design of a calculation program to realize theoretical calculation;
the method specifically comprises the following steps;
step 1, designing an integral framework of a wireless power supply device of an online monitoring terminal of a high-voltage power line, and building a module design model of the wireless power supply device of the online monitoring terminal of the high-voltage power line;
step 2, establishing a cylindrical coordinate system for carrying out distribution calculation of the magnetic field of the transmitting end based on the coil structure as an axial equal-diameter single-layer close-wound coil;
step 3, in Ansoft Maxwell software, establishing a model 1 by adopting the same parameters as theoretical calculation: 1, obtaining the magnetic field distribution around the wireless power supply device under the excitation of the same current by using a simulation model with the size of 1;
and 4, calculating the integral synthetic magnetic field: when the frequency splitting phenomenon occurs, selecting a frequency point at the maximum transmitting power position of a transmitting end with obvious distinguishing characteristics as a working frequency point of the wireless power supply device, carrying out Ansoft Maxwell software simulation analysis on an electromagnetic field of the wireless power supply device in the working frequency point state, and researching a theoretical calculation formula of an alternating current magnetic field, wherein the formula is as follows:
the transmitting coil and the receiving coil work at the same time at a frequency point f corresponding to the maximum transmitting power of the wireless power supply device0The magnetic vector potential in the state is: a ═ A1+A2；
Wherein, I(λ,μ,ν)(R, | u |) is a bezier laplacian integral corresponding to the radial and axial magnetic induction expressions; mu.s0Is vacuum magnetic conductance, R is coil radius, R is the distance between any source point and field point in the magnetic field, the length of wire turn is 2h, N is the number of coil turns,
is the unit vector of the magnetic vector potential direction, I1、I2Current, i.e. voltage, effective values of the transmitter and receiver coils, respectivelySAnd the ratio of the resistance;
step 5, designing programs for calculating the magnetic field around the wireless power supply device and the magnetic field induced electric field, and completing theoretical calculation in the steps 2, 3 and 4 by using MATLAB programming;
and 6, according to the parameters of the calculation example, establishing an experimental platform of the wireless power supply device of the high-voltage line online monitoring terminal, and verifying the accuracy and the effectiveness of the magnetic field distribution calculation method.
2. The magnetic field analysis method of the magnetic resonance wireless power supply technology in the high-voltage power line monitoring as claimed in claim 1, characterized in that:
the procedure in step 5 comprises the following steps:
step 5.1, setting parameters of the material, the winding radius, the number of turns, the width and the transmission distance of the coil;
step 5.2, frequency sweeping is carried out to analyze the current of the transmitting end, the working frequency of the wireless power supply device and the corresponding current excitation are determined, and the solving range of the magnetic field is determined under the column coordinate;
step 5.3, respectively determining the radial and axial magnetic induction intensities of the transmitting coil and the receiving coil according to the value range of z;
and 5.4, superposing the radial and axial magnetic induction intensities of the transmitting coil and the receiving coil respectively, and drawing a three-dimensional graph, wherein x and y coordinates of the three-dimensional graph are radial and axial values of a field point respectively, and a z coordinate is the magnetic induction intensity of the field point.
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