CN116539940A - Current measuring device and method - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention belongs to the technical field of equipment, and particularly relates to a current measuring device and a current measuring method, wherein the current measuring device comprises a current sensor, a magnetic field detecting component and a differential amplifier, wherein the current sensor is in a circular ring structure, a conductor passes through a hollow round hole, and a magnetic field is generated and measured by the magnetic field detecting component; the magnetic field detection assembly comprises a TMR three-dimensional magnetic field sensor; the sensor output signal is output in a differential mode, and the subsequent signal processing circuit is used for converting the output signal into a single-ended signal through differential amplification and then outputting the single-ended signal in a differential mode; the differential amplifier comprises a first amplifier for converting a double-ended signal into a single-ended signal; the second amplifier converts the single-ended signal into a double-ended signal and outputs the double-ended signal in a differential mode; the current sensor is connected with the data acquisition card, and the data acquisition card is connected with the upper computer. The magnetic core is not contained, so that the problem of signal distortion caused by magnetic core saturation is effectively avoided; the structure is simple, the volume is small, and the installation is convenient; the method belongs to a non-contact measurement method and is installed without power failure.
Description
Technical Field
The invention belongs to the technical field of equipment, and particularly relates to a current measuring device and a current measuring method.
Background
Current is an indispensable electrical parameter in many application fields, such as current calculation, relay protection and fault diagnosis. Conventional current measurement methods are based on electromagnetic measurement of the law of electromagnetic induction, i.e. current transformers (Current Transformer, CT). However, due to the presence of the iron core, the saturation phenomenon of the magnetic core may cause distortion of the secondary detection signal, even ferromagnetic resonance of the power system, resulting in instability of the system. In recent years, current measurement methods based on magnetic field sensor arrays have been attracting attention of students, and current measurement methods for a single conductor and a plurality of conductors have been studied. However, in most of the reported methods, assuming that the conductors are perpendicular to the plane of the magnetic field sensor array, there is little consideration if the current measurement error is far beyond an acceptable error range when not perpendicular.
Disclosure of Invention
In order to solve or improve the problems, the invention provides a current measuring device and a method, and the specific technical scheme is as follows:
the present invention provides a current measuring apparatus including:
the current sensor comprises a magnetic field detection assembly and a differential amplifier, wherein the magnetic field detection assembly and the differential amplifier are arranged on a PCB (printed circuit board), the current sensor is of a circular ring structure, a plurality of conductors penetrate through hollow round holes, and a magnetic field generated by conductor current in space is measured by the magnetic field detection assembly;
the magnetic field detection assembly comprises 6 TMR three-dimensional magnetic field sensors which are uniformly distributed in a circumference manner, correspondingly, a three-dimensional Cartesian coordinate system is established by taking the center of the current sensor as a coordinate origin, and three magnetic field components measured by the TMR three-dimensional magnetic field sensors face to the directions of x, y and z axes respectively;
the output signal of the TMR three-dimensional magnetic field sensor is output in a differential mode, and in order to inhibit common mode interference, the subsequent signal processing circuit differentially amplifies and converts the sensor output signal into a single-ended signal and then outputs the single-ended signal in a differential mode, so that the signals are transmitted in a differential mode;
the differential amplifier comprises 2 operational amplifiers, which are respectively marked as a first amplifier and a second amplifier, wherein the output signal of the magnetic field sensor is in a differential mode, and the first amplifier receives the output signal in a differential mode and amplifies the output signal with a certain gain so as to convert a double-ended signal into a single-ended signal; the second amplifier converts the single-ended signal into a double-ended signal and outputs the double-ended signal in a differential mode;
the current sensor is connected with the data acquisition card, and the data acquisition card is connected with the upper computer.
Preferably, the upper computer system performs data transmission with the data acquisition card, and then performs inverse problem calculation by using the acquired magnetic field data to solve the current flowing through each phase of conductor, and at the same time, visualizes the data.
Preferably, the data acquisition card is 32 paths of single-ended or 16 paths of differential analog input, the sampling rate is 100kS/s, and a 16 paths of differential analog input mode is adopted;
acquiring 18 paths of output signals of 6 TMR magnetic field sensors through 2 data acquisition cards, and displaying the signals on the upper computer;
the upper computer solves the current flowing through each phase conductor based on inverse problem calculation and is also used for visualizing data.
Preferably, the relation between the conductor current and the magnetic field it generates is:wherein, when the coefficient matrix is determined, the current I is obtained by multiplying the magnetic field B by the pseudo-inverse of the coefficient matrix M.
Preferably, the calibration process comprises: step S1, according to the relation between a magnetic field generated by an infinitely long conductor in space and current, when a single conductor and a magnetic field sensor array incline, establishing a mathematical model of the current flowing through the conductor and the space magnetic field;
s2, obtaining a mathematical model of the three-phase inclined conductor and the space magnetic field by utilizing the superposition principle according to the result obtained in the step S1;
step S3, measuring three-dimensional magnetic field components of 6 points in space by the magnetic field detection assembly;
s4, reversely pushing the coordinate position, the inclination angle and the current flowing through the conductors by using the magnetic field value measured in the step S3 and combining the inverse problem model in the step S2 by adopting an evolutionary algorithm;
and S5, calculating a coefficient matrix M by the conductor coordinate position and the inclination angle obtained in the step S4, and finally completing the calibration process of the current sensor.
Preferably, in the step S1, the calculation formula is:
wherein B is s ,B s，x ,B s，y ,B s，z The magnetic field components of the combined magnetic field at a certain point in space in the x, y and z directions, x s ,y s For the coordinate position, x, of the plane in which the magnetic field sensor array is located c ,y c The intersection point coordinates of the plane where the conductor and the magnetic field sensor array are located are that I is current flowing through the conductor, m=sin (alpha) cos (beta), n=sin (alpha) sin (beta), p=cos (alpha), and alpha and beta are included angles between the inclined conductor and the z-axis direction respectively, and an included angle between the projection of the inclined conductor on the xoy plane and the x-axis direction.
Preferably, in the step S2, the calculation formula of the mathematical model is:
wherein alpha is 1 ，β 1 (i=1, 2, 3) is the tilt angle of the three-phase conductor, x ci ,y ci (i=1, 2, 3) are the coordinate positions of the three-phase conductors, I i (i=1, 2, 3) are the currents flowing through the three-phase conductors, respectively; f (F) i (X),G i (X),H i Expression of (X):
wherein, the liquid crystal display device comprises a liquid crystal display device,
f (i, j) expression:
parameters related to tilt angle:
preferably, in said steps S1 and S2, a mathematical model of the relationship of the inclined three-phase conductor currents to the magnetic field they generate in space is obtained; from equation (2), the number of unknown variables contained is 15, which are the conductor tilt angles αi, βi (i=1, 2, 3), respectively, the coordinate position x of the conductor ci ,y ci Current I of each phase conductor i The method comprises the steps of carrying out a first treatment on the surface of the Measuring to obtain 18 magnetic field components by adopting 6 three-dimensional magnetic field sensors, and determining 18 equations by a superposition theorem; when the evolutionary algorithm is adopted to carry out multi-objective optimization, constraint conditions met by the nonlinear problem are as follows:
wherein MAX current ,MAX current The maximum radius of the limiting area where the conductor is located is the current which the conductor is allowed to flow through;
the objective function involved is
Wherein B is i，x ,B i，y ，B i，z Adding a penalty term for the calculated magnetic field measured value, and setting the penalty factor to 1000 so as to require that the calculated current cannot exceed an allowable value; the purpose of the evolutionary algorithm is to obtain the optimal individual through the evolutionary iteration of the population, so that the value of the objective function is as small as possible.
Preferably, in the step S4, the geometric parameter α is determined 1 ,β 1 ,x c1 ,y c1 ,α 2 ,β 2 ,x c2 ,y c2 ,α 3 ,β 3 ,x c3 ,y c3 Thereafter, the current was calculated:
[I] 3×1 ＝pseudo([M] 18×3 )[B] 18×1 the method comprises the steps of carrying out a first treatment on the surface of the Wherein [ B ]] 18×1 For magnetic flux density measured by magnetic field, [ I ]] 3×1 To be a current flowing through the conductor, [ M ]] 18×3 Is a coefficient matrix.
The invention provides a current measurement method, which is suitable for the device and comprises the following steps: acquiring a magnetic field generated by a conductor to be tested when the conductor to be tested is electrified through the current sensor; and acquiring data output by the current sensor through a data acquisition card and uploading the data to the upper computer.
The beneficial effects of the invention are as follows: the magnetic core is not contained, so that the problem of signal distortion caused by magnetic core saturation is effectively avoided; the structure is simple, the volume is small, and the installation is convenient; the method belongs to a non-contact measurement method and is installed without power failure.
Drawings
FIG. 1 is a schematic illustration of a magnetic field provided by an embodiment of the present invention with a single conductor passing through a magnetic field sensor array;
FIG. 2 is a schematic diagram of a three-phase conductor passing through a magnetic field sensor array according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a current measurement device according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be understood that the terms "comprises" and "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.
An embodiment of the present invention provides a current measurement apparatus, including: the current sensor comprises a magnetic field detection assembly and a differential amplifier, wherein the magnetic field detection assembly and the differential amplifier are arranged on a PCB (printed circuit board), the current sensor is of a circular ring structure, a plurality of conductors penetrate through hollow round holes, and a magnetic field generated by conductor current in space is measured by the magnetic field detection assembly;
the magnetic field detection assembly comprises 6 TMR three-dimensional magnetic field sensors which are uniformly distributed in a circumference manner, correspondingly, a three-dimensional Cartesian coordinate system is established by taking the center of the current sensor as a coordinate origin, and three magnetic field components measured by the TMR three-dimensional magnetic field sensors face to the directions of x, y and z axes respectively; the output signal of the TMR three-dimensional magnetic field sensor is output in a differential mode, and in order to inhibit common mode interference, the subsequent signal processing circuit differentially amplifies and converts the sensor output signal into a single-ended signal and then outputs the single-ended signal in a differential mode, so that the signals are transmitted in a differential mode; the differential amplifier comprises 2 operational amplifiers, which are respectively marked as a first amplifier and a second amplifier, wherein the output signal of the magnetic field sensor is in a differential mode, and the first amplifier receives the output signal in a differential mode and amplifies the output signal with a certain gain so as to convert a double-ended signal into a single-ended signal; the second amplifier converts the single-ended signal into a double-ended signal and outputs the double-ended signal in a differential mode; the current sensor is connected with the data acquisition card, and the data acquisition card is connected with the upper computer.
And the upper computer system and the data acquisition card perform data transmission, and then the acquired magnetic field data are used for performing inverse problem calculation to solve the current flowing through each phase of conductor, and meanwhile, the data are visualized.
The data acquisition card is in 32 paths of single-ended or 16 paths of differential analog input, the sampling rate is 100kS/s, and a 16 paths of differential analog input mode is adopted; acquiring 18 paths of output signals of 6 TMR magnetic field sensors through 2 data acquisition cards, and displaying the signals on the upper computer; the upper computer solves the current flowing through each phase conductor based on inverse problem calculation and is also used for visualizing data.
The relation between the conductor current and the magnetic field generated by the conductor current:wherein, when the coefficient matrix is determined, the current I is obtained by multiplying the magnetic field B by the pseudo-inverse of the coefficient matrix M.
The calibration process includes: step S1, according to the relation between a magnetic field generated by an infinitely long conductor in space and current, when a single conductor and a magnetic field sensor array incline, establishing a mathematical model of the current flowing through the conductor and the space magnetic field; s2, obtaining a mathematical model of the three-phase inclined conductor and the space magnetic field by utilizing the superposition principle according to the result obtained in the step S1; step S3, measuring three-dimensional magnetic field components of 6 points in space by the magnetic field detection assembly; s4, reversely pushing the coordinate position, the inclination angle and the current flowing through the conductors by using the magnetic field value measured in the step S3 and combining the inverse problem model in the step S2 by adopting an evolutionary algorithm; and S5, calculating a coefficient matrix M by the conductor coordinate position and the inclination angle obtained in the step S4, and finally completing the calibration process of the current sensor.
In the step S1, the calculation formula is as follows:
wherein B is s ,B s，x ,B s，y ,B s，z The magnetic field components of the combined magnetic field at a certain point in space in the x, y and z directions, x s ,y s For the coordinate position, x, of the plane in which the magnetic field sensor array is located c ,y c The intersection point coordinates of the plane where the conductor and the magnetic field sensor array are located are that I is current flowing through the conductor, m=sin (alpha) cos (beta), n=sin (alpha) sin (beta), p=cos (alpha), and alpha and beta are included angles between the inclined conductor and the z-axis direction respectively, and an included angle between the projection of the inclined conductor on the xoy plane and the x-axis direction.
In step S2, the calculation formula is:
wherein alpha is 1 ，β 1 (i=1, 2, 3) is the tilt angle of the three-phase conductor, x ci ,y ci (i=1, 2, 3) are the coordinate positions of the three-phase conductors, I i (i=1, 2, 3) are the currents flowing through the three-phase conductors, respectively; f (F) i (X),G i (X),H i The expression of (X) is shown as formula (3)
The expression f (i, j) in the formula (3) is represented by the formula (4); the parameter related to the tilt angle is shown in formula (5);
in said steps S1 and S2, a mathematical model of the relationship of the inclined three-phase conductor currents and the magnetic fields they produce in space is obtained; from equation (2), the number of unknown variables contained is 15, which are the conductor tilt angles αi, βi (i=1, 2, 3), respectively, the coordinate position x of the conductor ci ,y ci Each phaseCurrent I of conductor i The method comprises the steps of carrying out a first treatment on the surface of the Measuring to obtain 18 magnetic field components by adopting 6 three-dimensional magnetic field sensors, and determining 18 equations by a superposition theorem; when the evolutionary algorithm is adopted to carry out multi-objective optimization, constraint conditions met by the nonlinear problem are as follows: i 1 |,|I 2 |,|I 3 |＜MAX current (6)
Wherein MAX current ,MAX current The maximum radius of the limiting area where the conductor is located is the current which the conductor is allowed to flow through;
the objective function involved is:
wherein B is i，x ,B i，y ，B i，z Adding a penalty term for the calculated magnetic field measured value, and setting the penalty factor to 1000 so as to require that the calculated current cannot exceed an allowable value; the purpose of the evolutionary algorithm is to obtain the optimal individual through the evolutionary iteration of the population, so that the value of the formula (9) is as small as possible.
In the step S4, a geometric parameter alpha is determined 1 ,β 1 ,x c1 ,y c1 ,α 2 ,β 2 ,x c2 ,y c2 ,α 3 ,β 3 ,x c3 ,y c3 Thereafter, the current was calculated:
[I] 3×1 ＝pseudo([M] 18×3 )[B] 18×1 the method comprises the steps of carrying out a first treatment on the surface of the Wherein [ B ]] 18×1 For magnetic flux density measured by magnetic field, [ I ]] 3×1 To be a current flowing through the conductor, [ M ]] 18×3 Is a coefficient matrix.
The invention provides a current measurement method, which is suitable for the device and comprises the following steps: acquiring a magnetic field generated by a conductor to be tested when the conductor to be tested is electrified through the current sensor; and acquiring data output by the current sensor through a data acquisition card and uploading the data to the upper computer.
The method proposed by the present invention uses a magnetic field sensor array to measure the current of a tilted multi-conductor system. The measurement method of the single inclined conductor is analyzed first.
FIG. 1 is a schematic diagram of a single conductor passing through a hollow region of a magnetic field sensor array and generating a magnetic field at a three-dimensional magnetic field sensor. In FIG. 1, A (x c ,y c 0) is the intersection point coordinate of the inclined conductor and the array, and alpha and beta are the included angles of the inclined conductor and the z axis respectively, and the included angles of the projection of the conductor on the magnetic field sensor array and the x axis direction. S (x) s ,y s 0) is the coordinates of the three-dimensional magnetic field sensor. B (B) s ,B sx ,B sy ,B sz The resultant magnetic field at point S, the magnetic field components in the x, y, z directions, respectively. I is the current flowing through the conductor. According to electromagnetic theory, the relation between the current and the magnetic field can be deduced, as shown in formula (1). When the conductor and the magnetic field sensor array have a certain inclination angle, the magnetic field measured in an array manner contains components in the Z-axis direction, and if the conductor current is still measured by the two-dimensional magnetic field sensor array at this time, the obtained error is far beyond an acceptable range, and the invention can perform detailed error analysis later. As can be seen from the formula (1), the unknown parameters are alpha, beta, x c ,y c And I, in order to solve the five parameters, five independent equations must be established, and in order to avoid the occurrence of a multi-solution problem, two three-dimensional magnetic field sensors can be adopted, so as to obtain an overdetermined equation set consisting of 6 equations.
Fig. 2 is a schematic diagram of a three-phase conductor passing through a hollow region of a magnetic field sensor array and generating a magnetic field at a three-dimensional magnetic field sensor. According to the superposition theorem, the magnetic fields of the sensor in the x, y and z directions are respectively superposition of three conductors in corresponding directions. Since the expressions of the calculated magnetic fields in the x, y, and z axis directions are different, three types of equations can be obtained from the superposition theorem, as shown in equation (2). In the equation expressed by the formula (2), the unknown parameter is alpha i ,β i ,x ci ,y ci ,I i (i=1, 2, 3) total 15 unknown parameters, 15 independent equations are required to determine the parameters. Considering the occurrence of the multiple solution problem, the patent adopts 6 three-dimensional magnetic field sensors to measure the magnetic field, thereby obtaining an overdetermined equation set consisting of 18 equations.
The measurement method of the inclined multi-conductor system provided by the invention is actually a nonlinear optimization problem. Constraints include equality constraints and inequality constraints. Equation (2) is an equality constraint that characterizes the relationship between the magnetic field and the current, and the inequality constraint is determined by equations (6) to (8). The nonlinear optimization problem is solved by adopting an evolutionary algorithm, and the obtained optimal individual minimizes the value of an objective function (shown in formula (9)) through evolutionary iteration of the population. The parameters to be optimized are alpha 1 ,β 1 ,x c1 ,y c1 ,I 1 ,Real,I 1 ,Imag,α 2 ,β 2 ,x c2 ,y c2 ,I 2 ,Real,I 2 ,Imag,α 3 ,β 3 ,x c3 ,y c3 ,I 3 ,Real,I 3 The number of imags is 18. Wherein I is 1 ,Real,I 1 ,Imag,I 2 ,Real,I 2 ,Imag,I 3 ,Real,I 3 Imag is the real and imaginary parts of the current flowing through conductor 1, conductor 2 and conductor 3, respectively. The dimension of the optimization problem is 18, however, as can be seen from equation (2), when the magnetic field is determined by measurement, and it is assumed that α i ,β i ,x ci ,y ci When (i=1, 2, 3) is known, the current of each phase conductor can be directly calculated. Thus, the dimension of the optimization problem is reduced from 18 to 12, i.e. α i ,β i ,x ci ,y ci (i=1, 2, 3), thereby greatly improving the computational efficiency of the evolutionary algorithm.
Currently, there are many evolutionary algorithms available. In order to research whether the type of the evolutionary algorithm affects the solving efficiency and accuracy of the nonlinear optimization problem, the invention compares and researches four evolutionary algorithms, namely an improved particle swarm algorithm, a frog-leaping algorithm, an empire evolutionary algorithm and a differential evolutionary algorithm. Because of the random nature of the evolutionary algorithm, each evolutionary iteration optimizing can not obtain an accurate result. Therefore, for 13 different cases that the three-phase conductor passes through the current sensor, the above four evolutionary algorithms are respectively adopted to solve the nonlinear optimization problem, and the obtained results are shown in table 1.
Table 1 four evolutionary algorithms solve the nonlinear optimization problem results table, the first behavioral three-phase conductor of table 1 passes through the index of different situations of the current sensor. For each case, the evolution algorithm was run 50 times, and the maximum, minimum and average values of the objective function values corresponding to the 50 runs are listed in the table. The average values of the above three types of objective function values are listed in the last column of table 1. Simulation researches show that when the objective function value is less than 5 e-5 When the three-phase current error is less than 2%, the objective function value is greater than 5 e-5 The calculation accuracy of the current is poor, so that the magnitude of the objective function value can be used as a basis for measuring whether the algorithm converges with higher accuracy. The introduced parameter VOF is the number of results converged to higher precision and is used for representing the convergence rate of each algorithm. The parameters VOF are also listed in Table 1. The configuration of the notebook computer used for simulation is 2.6GHz Intel core, 6700HQ CPU and 8GB memory. The objective function value in table 1 is of the order of 1 e-5 I.e. the actual objective function value is the value of the table multiplied by 1 e-5 . The average run time for each algorithm is listed in the first column of table 1. As can be seen from table 1, the empire evolutionary algorithm has a slightly longer calculation time than the other three algorithms, but has the smallest objective function value and the largest VOF, so that in practical application, the empire competition algorithm can be used to solve the nonlinear optimization problem.
After the current measurement principle is described, a current sensor for current measurement is described in detail below.
The 6 three-dimensional magnetic field sensors are welded on the circular ring-shaped PCB and are uniformly distributed in the circumference. Rc and Rs are the inner diameter and the outer diameter of the circular ring-shaped PCB respectively. The current carrying conductor passes through a hollow region of radius Rc, the conductor may be perpendicular to the PCB, or have a tilt angle.
The invention adopts a three-dimensional magnetic field sensor based on tunneling magneto-resistance effect, and adopts a TMR2301 magnetic field sensor produced by multidimensional science and technology company. The magnetic field components in the x, y, z axis directions can be measured simultaneously.
The three-dimensional magnetic field sensor adopted by the invention adopts a differential output mode, and in order to inhibit common-mode interference signals and improve the magnetic field measurement accuracy, the invention adopts a differential amplification mode. The operational amplifier ad8220 adopts a differential input mode, amplifies a differential output signal of the magnetic field sensor, converts the differential output signal into a single-ended signal, combines the single-ended signal with the operational amplifier ad8513, converts the single-ended signal into a differential signal, and then acquires the differential signal in a differential mode by the DAQ, thereby obtaining a magnetic field signal.
The invention provides a current measurement system. The 6 three-dimensional magnetic field sensors are uniformly distributed on the annular PCB, the three-phase conductors penetrate through the hollow area, the magnetic field generated by the conductor current in the surrounding space is measured by the magnetic field sensors, signals are acquired by the DAQ and transmitted to the upper computer, the currents of each phase are obtained through calculation by the inverse calculation method, and the data are visualized.
In order to prove the effectiveness and potential application value of the method, the current measurement method and the current measurement method based on the two-dimensional magnetic field sensor array are respectively adopted to calculate the current under the condition that the conductor and the current sensor incline, calculate the error of the current of each phase, and the superiority of the method is illustrated by the comparative analysis of the error.
Given parameters in simulation study:
the intersection point of the conductor 1 and the current sensor is (-0.2,0.2), alpha 1 ,β 1 Respectively 0-pi/4 and 0-pi/3, and the step length of the change is pi/180; the intersection point of the conductor 2 and the current sensor is (0.6,0.4), alpha 2 ,β 2 Pi/6, pi/3 respectively;
the intersection point of the conductor 3 and the current sensor is (0.4, -0.5), alpha 3 ,β 3 Pi/7, pi/9 respectively;
the currents carried by the conductors 1,2 and 3 are 15A,15 & lt-2 pi/3A and 15 & lt 2 pi/3A respectively.
The current error calculation method comprises the following steps of:
step S1: calculating a three-dimensional magnetic field of the position of the magnetic field sensor according to given parameters, considering that the magnetic field sensor is easily influenced by voltage offset and an environmental noise magnetic field in actual measurement, and applying 40dB Gaussian white noise in the calculated magnetic field so as to simulate an actual magnetic field measured value;
step S2: substituting the magnetic field value into a reverse push algorithm so as to calculate the current of each conductor, the intersection point of the current and the current sensor and the inclination angle;
step S3: altering alpha 1 ,β 1 Repeating steps S1, S2;
step S4: alpha is alpha 1 ,β 1 For x and y coordinates, the current error is taken as the z coordinate to draw the error of each phase current along with alpha 1 ,β 1 A three-dimensional map of the change;
the premise of realizing accurate current measurement based on the current measurement method of the two-dimensional magnetic field sensor array is that the conductor is vertical to the current sensor. However, it is sometimes difficult to secure the above-described vertical relationship in practical applications. The method provided by the invention well solves the problem that the inclination angle of the conductor brings large error to current measurement. The essential difference between the current measurement method based on the two-dimensional magnetic field sensor array and the method provided by the invention is that the solved parameter is x ci ,y ci ,I i (i=1, 2, 3), so that only 3 two-dimensional magnetic field sensors are needed to measure 9 magnetic field values, and 9 equations are constructed to solve the parameters. And (3) enabling alpha and beta in the inverse problem model provided by the invention to be zero, so that the constraint condition and the objective function of the corresponding inverse problem algorithm can be obtained.
The current calculation method based on the two-dimensional magnetic field sensor array comprises the following steps:
step S1: calculating magnetic fields in the x and y directions of the position of the two-dimensional magnetic field sensor by using a mathematical model of the inclined conductor current and the space magnetic field according to given parameters, ignoring Gaussian white noise without considering the magnetic field in the z direction, and directly simulating an actual magnetic field measured value by using a calculated value;
step S2: substituting the magnetic field value into a reverse-push algorithm in a current measurement method based on a two-dimensional magnetic field sensor array, so as to calculate the current of each conductor and the intersection point of the conductor and a current sensor;
step S3: altering alpha 1 ,β 1 Repeating steps S1, S2;
step S4: alpha is alpha 1 ,β 1 As a variable, the error of each phase current is plotted with alpha by taking the current error as a dependent variable 1 ,β 1 A three-dimensional map of the changes for analysis;
experiments show that the current errors of all phases calculated by the current measurement method provided by the invention are below 2%, namely the measurement errors are basically not influenced by the inclination of the conductor, and the stable measurement precision is realized; however, when a current calculation method based on a two-dimensional magnetic field sensor array is adopted, the error of the three-phase conductor current has different variation tendencies, and the error is large. The error of the a phase current can reach 40%, which is far more than the acceptable error range, and the same, b and c phase current errors are larger and the change is obvious. Thus demonstrating the effectiveness of the current measurement methods presented herein.
Those of ordinary skill in the art will appreciate that the elements of the examples described in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both, and that the elements of the examples have been described generally in terms of functionality in the foregoing description to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
In the embodiments provided in this application, it should be understood that the division of units is merely a logic function division, and there may be other manners of division in practical implementation, for example, multiple units may be combined into one unit, one unit may be split into multiple units, or some features may be omitted.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention, and are intended to be included within the scope of the appended claims and description.
Claims (9)
1. A current measurement device, comprising:
the current sensor comprises a magnetic field detection assembly and a differential amplifier, wherein the magnetic field detection assembly and the differential amplifier are arranged on a PCB (printed circuit board), the current sensor is of a circular ring structure, a plurality of conductors penetrate through hollow round holes, and a magnetic field generated by conductor current in space is measured by the magnetic field detection assembly;
the magnetic field detection assembly comprises 6 TMR three-dimensional magnetic field sensors which are uniformly distributed in a circumference manner, correspondingly, a three-dimensional Cartesian coordinate system is established by taking the center of the current sensor as a coordinate origin, and three magnetic field components measured by the TMR three-dimensional magnetic field sensors face to the directions of x, y and z axes respectively;
the output signal of the TMR three-dimensional magnetic field sensor is output in a differential mode, and in order to inhibit common mode interference, the subsequent signal processing circuit differentially amplifies and converts the sensor output signal into a single-ended signal and then outputs the single-ended signal in a differential mode, so that the signals are transmitted in a differential mode;
the differential amplifier comprises 2 operational amplifiers, which are respectively marked as a first amplifier and a second amplifier, wherein the output signal of the magnetic field sensor is in a differential mode, and the first amplifier receives the output signal in a differential mode and amplifies the output signal with a certain gain so as to convert a double-ended signal into a single-ended signal; the second amplifier converts the single-ended signal into a double-ended signal and outputs the double-ended signal in a differential mode;
the current sensor is connected with the data acquisition card, and the data acquisition card is connected with the upper computer;
and the upper computer system and the data acquisition card perform data transmission, and then the acquired magnetic field data are used for performing inverse problem calculation to solve the current flowing through each phase of conductor, and meanwhile, the data are visualized.
2. The current measurement device of claim 1, wherein the data acquisition card is a 32-way single-ended or 16-way differential analog input, the sampling rate is 100kS/s, and a 16-way differential analog input mode is adopted;
acquiring 18 paths of output signals of 6 TMR magnetic field sensors through 2 data acquisition cards, and displaying the signals on the upper computer;
the upper computer solves the current flowing through each phase conductor based on inverse problem calculation and is also used for visualizing data.
3. The current measurement device of claim 2, wherein the relationship between conductor current and magnetic field generated thereby:wherein, when the coefficient matrix is determined, the current I is obtained by multiplying the magnetic field B by the pseudo-inverse of the coefficient matrix M.
4. A current measurement device according to claim 3, wherein the calibration procedure comprises:
step S1, according to the relation between a magnetic field generated by an infinitely long conductor in space and current, when a single conductor and a magnetic field sensor array incline, establishing a mathematical model of the current flowing through the conductor and the space magnetic field;
s2, obtaining a mathematical model of the three-phase inclined conductor and the space magnetic field by utilizing the superposition principle according to the result obtained in the step S1;
step S3, measuring three-dimensional magnetic field components of 6 points in space by the magnetic field detection assembly;
s4, reversely pushing the coordinate position, the inclination angle and the current flowing through the conductors by using the magnetic field value measured in the step S3 and combining the inverse problem model in the step S2 by adopting an evolutionary algorithm;
and S5, calculating a coefficient matrix M by the conductor coordinate position and the inclination angle obtained in the step S4, and finally completing the calibration process of the current sensor.
5. The current measurement device according to claim 4, wherein in the step S1, a calculation formula is:
wherein B is s ,B s，x ,B s，y ,B s，z The magnetic field components of the combined magnetic field at a certain point in space in the x, y and z directions, x s ,y s For the coordinate position, x, of the plane in which the magnetic field sensor array is located c ,y c The intersection point coordinates of the plane where the conductor and the magnetic field sensor array are located are that I is current flowing through the conductor, m=sin (alpha) cos (beta), n=sin (alpha) sin (beta), p=cos (alpha), and alpha and beta are included angles between the inclined conductor and the z-axis direction respectively, and an included angle between the projection of the inclined conductor on the xoy plane and the x-axis direction.
6. The current measurement device according to claim 5, wherein in the step S2, the mathematical model has a calculation formula:
wherein alpha is 1 ，β 1 (i=1, 2, 3) is the tilt angle of the three-phase conductor, x ci ,y ci (i=1, 2, 3) are the coordinate positions of the three-phase conductors, I i (i=1, 2, 3) are currents flowing through the three-phase conductors, respectively.
7. The current measuring apparatus according to claim 6, wherein the mathematical model has a calculation formula containing an unknown variable number of 15, which is a conductor inclination angle α i ,β i (i=1, 2, 3), coordinates of the conductorPosition x ci ,y ci Current I of each phase conductor i ；
Measuring to obtain 18 magnetic field components by adopting 6 three-dimensional magnetic field sensors, and determining 18 equations by a superposition theorem;
when the evolutionary algorithm is adopted to carry out multi-objective optimization, constraint conditions met by the nonlinear problem are as follows: i 1 |,|I 2 |,|I 3 |＜MAX current ，
Wherein MAX current ,MAX current The maximum radius of the limiting area where the conductor is located is the current which the conductor is allowed to flow through;
the objective function involved:wherein B is i，x ,B i，y ，B i，z For the calculated magnetic field measurement a penalty term is added and the penalty factor is set to 1000, so that the calculated current cannot exceed the allowed value.
8. The current measurement device according to claim 7, wherein in step S4, the geometric parameter α is determined 1 ,β 1 ,x c1 ,y c1 ,α 2 ,β 2 ,x c2 ,y c2 ,α 3 ,β 3 ,x c3 ,y c3 Thereafter, the current was calculated:
[I] 3×1 ＝pseudo([M] 18×3 )[B] 18×1 the method comprises the steps of carrying out a first treatment on the surface of the Wherein [ B ]] 18×1 For magnetic flux density measured by magnetic field, [ I ]] 3×1 To be a current flowing through the conductor, [ M ]] 18×3 Is a coefficient matrix.
9. A method of measuring current, adapted for use in the apparatus of claim 1, comprising:
acquiring a magnetic field generated by a conductor to be tested when the conductor to be tested is electrified through the current sensor;
and acquiring data output by the current sensor through a data acquisition card and uploading the data to the upper computer.
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