Contactor contact wear on-line observation method

Abstract

The invention relates to a contactor contact wear on-line observation method, which comprises the following steps of: designing a movable iron core displacement observer and an electromagnetic suction observer by adopting a BP neural network model according to a binary one-to-one mapping relation of electromagnetic mechanism coil current i, magnetic circuit flux linkage psi, movable iron core displacement x and electromagnetic suction Fx; electromagnetic attraction and movable iron core displacement are directly observed according to coil current and coil voltage in the closing process of the contactor; calculating the electromagnetic attraction Fx and the movable iron core displacement x to obtain a counter-force integral waveform vf; and indirect identification of the counter-force step is carried out by observing the counter-force integral waveform, and a step signal is converted into an inflection point signal through integral operation, so that indirect identification of contact abrasion is realized. According to the technical scheme, the current contact abrasion condition is directly observed through the designed contact abrasion observer in the closing process of the contactor, and the contactor abrasion observer is used for guiding contact replacement and predictive maintenance of the contactor so as to ensure reliable operation of the contactor in the working period.

Description

Technical Field

[0001] The invention relates to the technical field of switch electrical appliances, in particular to an online observation method for contactor contact wear. Background Art

[0002] The power grid system is becoming more and more intelligent and complex, and the contactor is one of its core components. Its performance indicators directly affect the safety and stability of the entire power grid control system. During the operation of the contactor, the arc of opening and closing will continuously corrode the contacts, causing the end of its electrical life and leading to failures. In response to this problem, a large number of scholars have done a lot of research on the design of the body and life prediction. At present, in terms of body design, the electrical life of the contactor can be improved by replacing corrosion-resistant contact materials and improving arc extinguishing capabilities. However, since arc erosion is always difficult to avoid, the contacts are constantly worn, so real-time observation of contact wear is of great engineering significance.

[0003] At present, in the observation of contact wear of contactors, the more commonly used method is to obtain the direct relationship between contactor operating parameters such as pull-in time, arcing time, arcing energy, contact resistance and contactor contact usage time through experiments, and use feature extraction and artificial intelligence algorithms to indirectly observe the contact wear of contactors. This type of method constructs a prediction algorithm from the direct mapping relationship between the remaining usage time and operating characteristics, without prior knowledge, but the training process requires a large amount of data. In addition, some scholars use statistical methods to observe contact wear. By statistically analyzing the cumulative arc energy borne by the contactor contacts to satisfy the random model, the distribution function of the remaining usage time of the contacts is determined, and then the contact wear is determined. This method is suitable for large quantities of simple component products, and requires long-term and large-scale experiments and statistical analysis. The method does not take into account the complex operating environment, the performance degradation characteristics of the material, etc., resulting in low observation accuracy. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide an online observation method for contactor contact wear, which directly observes the current contact wear condition through the designed contact wear observer during the contactor closing process, so as to guide the contact replacement and predictive maintenance of the contactor, so as to ensure the reliable operation of the contactor during its operation.

[0005] To achieve the above object, the present invention adopts the following technical scheme: a contactor contact wear online observation method, according to the electromagnetic mechanism coil current i, magnetic circuit flux ψ, moving iron core displacement x, electromagnetic suction force F x The binary one-to-one mapping relationship is used to design the moving iron core displacement observer and the electromagnetic suction force observer using the BP neural network model; the electromagnetic suction force and the moving iron core displacement are directly observed according to the coil current and coil voltage during the contactor closing process; the electromagnetic suction force F x, the displacement of the moving iron core x is calculated to obtain the reaction force integral waveform v f ; The reaction force step is indirectly identified by observing the reaction force integral waveform, and the integral operation converts the step signal into an inflection point signal to achieve indirect identification of contact wear.

[0006] In a preferred embodiment, after the step signal is converted into an inflection point signal, the inflection point is identified by an inflection point identification method based on function approximation; specifically, for discrete data containing an inflection point, a function with an inflection point is used to perform a difference-free approximation on the data; if there is a function that approximates the original data and its approximation error is minimized, then the inflection point of this function is the inflection point of the original data;

[0007] Through v f (t) The waveform is observed and analyzed, and a piecewise quadratic function is used to approximate it, so the fitting function is:

[0008]

[0009] The constraints are:

[0010] x0≤w slip ≤x n (2)

[0011] The optimization goal is:

[0012] min mse(f(x j )-y(x j ))x j ∈(x0,x n )j∈(0,n)(3)

[0013] Where: p1, p2, p4 and p5 are constraint function coefficients; w parameter is the independent variable of the function; w slip is the function segmentation point independent variable; z slip is the function segmentation point dependent variable; x0, x n is the range of the original discrete data independent variable; mse represents the mean square error; f is the fitting function, f(x j ) is the fitting function output when the original discrete data is used as the variable, y(x j ) is the original discrete data; j is the original discrete data index;

[0014] By traversing the constraints one by one, the optimization problem with constraints is transformed into multiple optimization problems without constraints. For a single optimization problem without constraints, the Nelder-Mead simplex optimization algorithm is used to solve it, and then the optimization problem with constraints is solved.

[0015] In a preferred embodiment, the inflection point identification specifically includes the following steps: first, the discrete data (x j,y(x j )) Input this algorithm and fit the segment points (w slip ,z slip ) are set as the original discrete data points (x j ,y(x j )), use the Nelder-Mead optimization algorithm to optimize the fitting function parameters p1, p2, p4, p5 at each segment point to make it close to the original discrete data. When the optimal approximation is reached, calculate and record the fitting function f(x j ) and the original discrete data y(x j )’s mean square error loss j , and then determine whether all discrete data have been traversed. If not, the segmentation points (w slip ,z slip ) is set as the next discrete data (x j+1 ,y(x j+1 )) Repeat the above process until all discrete data are traversed; after the traversal is completed, find the index j of the minimum value of the mean square error loss, and the original discrete data point x corresponding to this index j This is the inflection point of the original discrete data.

[0016] In a preferred embodiment, a flux observer is constructed to perform indirect measurement of the coil flux, and the contactor operation process follows the voltage balance equation:

[0017]

[0018] Where: u is the coil voltage; i is the coil current; R is the coil resistance; ψ is the magnetic flux

[0019] By rewriting equation (4), a voltage-integrated flux observer is constructed. The magnetic flux can be indirectly obtained by simply collecting the coil voltage and coil current and integrating them:

[0020] ψ=∫(u-iR)dt (5)

[0021] For an electromagnetic mechanism with a fixed structure, its coil current i, magnetic flux ψ, moving iron core displacement x, and electromagnetic suction force F x There exists (i,ψ)→x, (i,ψ)→F x The nonlinear mapping relationship of the contactor is established based on the mapping relationship; the suction observer and displacement observer of the contactor are designed by using a multi-layer BP neural network;

[0022] Finite element simulation experiments are performed on the electrical, magnetic and mechanical parameters of the contactor to obtain (i,ψ)→x, (i,ψ)→F xBinary mapping data, taking the static data of the electromagnetic system (i, ψ) as binary input, the electromagnetic attraction F x and the displacement of the moving iron core x as the expected output, and the BP neural network is trained offline. After the training is completed, the displacement observer and the suction observer can be constructed. When the observer is running, the (ψ, i) data pair is used as input, and the flux observer is used to map the output x and F through the neural network model. x , and ultimately achieve the purpose of estimating the displacement of the moving iron core and the electromagnetic attraction in real time through the coil voltage and coil current that are easily measured by the contactor.

[0023] In a preferred embodiment, the moving iron core of the contactor conforms to the D'Alembert mechanical motion equation during movement:

[0024]

[0025] Where: m is the equivalent mass of the moving part; v is the speed of the moving iron core;

[0026] The reaction force is calculated according to formula (6):

[0027]

[0028] From formula (7), we can see that the reaction force observation requires the known electromagnetic attraction force F x , the displacement x of the moving iron core and the equivalent mass m of the moving parts; F x and x, and then complete the reaction force observation; f The signal is integrated using formula (8) to obtain the reaction force integral:

[0029]

[0030] After the integral operation, the reaction force step signal becomes an inflection point signal, and the reaction force step moment strictly corresponds to the inflection point moment. The inflection point moment t is extracted. ct , with the help of the inflection point and the initial contact opening distance x a The current contact wear value can be obtained; during the contactor closing process, the contactor coil voltage u and coil current i signals are collected, and the magnetic flux ψ is indirectly observed with the help of the integral flux observer. The (i, ψ) data is input into the moving iron core displacement observer and the electromagnetic suction force observer to observe the moving iron core displacement x and the electromagnetic suction force F. x , differentiate the displacement of the moving iron core to get the moving iron core velocity v; the electromagnetic attraction F x Divide by the equivalent mass m of the moving iron core to get the electromagnetic acceleration a x , integrating the electromagnetic acceleration gives the electromagnetic velocity v x ; Use electromagnetic velocity v x Subtract the total velocity v to resolve the reaction force integral v f, due to the reaction force F f At the moment when the contacts just close, t ct There is a step, so the reaction force integral v f There is an inflection point when the contacts just close; by identifying the inflection point, the contact just closing moment t ct , and t ct Corresponding to the closing moving iron core displacement x waveform, the current contact opening distance x can be observed a , then use the current contact distance minus the initial contact distance x a0 The current contact wear value x can be observed ct.ero .

[0031] Compared with the prior art, the present invention has the following beneficial effects: the present invention can directly analyze the coupling relationship between the electrical, magnetic and mechanical physical quantities during the contactor operation process, directly observe the contact wear, and plays a vital role in the stable and reliable operation of the contactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of an inflection point identification algorithm according to a preferred embodiment of the present invention;

[0033] Figure 2 It is a schematic diagram of the suction and displacement observer principle of a preferred embodiment of the present invention;

[0034] Figure 3 Schematic diagram of the contact wear observation principle of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0036] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0037] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0038] The present invention proposes an online observation method for contactor contact wear. According to the electromagnetic mechanism coil current i, magnetic circuit flux ψ, moving iron core displacement x, electromagnetic suction force F xThe binary one-to-one mapping relationship is used to design the moving iron core displacement observer and the electromagnetic suction force observer using the BP neural network model. The electromagnetic suction force and the moving iron core displacement can be directly observed according to the coil current and coil voltage during the contactor closing process. x , the displacement of the moving iron core x is calculated to obtain the reaction force integral waveform (denoted as v f ). Because the reaction force F on the moving iron core when the contacts are just closed f There is a step, and the displacement of the moving iron core at the step moment can directly observe the contact opening distance x a , this contact opening distance can reflect the contact wear. Since multiple differentiations are prone to spike interference, the present invention does not directly identify the reaction force step, but indirectly identifies the reaction force step by observing the reaction force integral waveform. The integral operation converts the step signal into an inflection point signal to achieve indirect identification of contact wear.

[0039] Inflection point identification principle:

[0040] After the step signal is converted into an inflection point signal, an inflection point identification algorithm is required. The present invention proposes an inflection point identification method based on function approximation. The core idea is that for discrete data with inflection points, a function with inflection points can be used to approximate it without difference; if there is a function that approximates the original data and its approximation error is minimized, then the inflection point of this function is the inflection point of the original data. Using this idea, the inflection point identification problem can be converted into a function extreme value problem, and then solved using existing optimization methods.

[0041] Through v f (t) The waveform can be observed and analyzed, and it can be considered that a piecewise quadratic function can be used to approximate it, so the fitting function is:

[0042]

[0043] The constraints are:

[0044] x0≤w slip ≤x n (2)

[0045] The optimization goal is:

[0046] min mse(f(x j )-y(x j ))x j ∈(x0,x n )j∈(0,n)(3)

[0047] Where: p1, p2, p4, p5 are constraint function coefficients; w slip is the function segmentation point independent variable; z slip is the function segmentation point dependent variable; x0, xn is the range of the original discrete data independent variable; mse represents the mean square error; f is the fitting function, f(x j ) is the output of the fitting function when the original discrete data is used as the variable, and j is the index of the original discrete data.

[0048] For optimization problems with a single constraint, the present invention converts the optimization problem with constraints into multiple optimization problems without constraints by traversing the constraints in sequence. For a single optimization problem without constraints, the present invention uses the Nelder-Mead simplex optimization algorithm to solve it, thereby solving the optimization problem with constraints.

[0049] The process of the inflection point identification algorithm is as follows Figure 1 As shown: First, the discrete data (x j ,y(x j )) Input this algorithm and fit the segment points (w slip ,z slip ) are set as the original discrete data points (x j ,y(x j )), use the Nelder-Mead optimization algorithm to optimize the fitting function parameters p1, p2, p4, p5 at each segment point to make it close to the original discrete data. When the optimal approximation is reached, calculate and record the fitting function f(x j ) and the original discrete data y(x j )’s mean square error loss j , and then determine whether all discrete data have been traversed. If not, the segmentation points (w slip ,z slip ) is set as the next discrete data (x j+1 ,y(x j+1 )) Repeat the above process until all discrete data are traversed. After the traversal is completed, find the index j of the minimum value of the mean square error loss. The original discrete data point x corresponding to this index j This is the inflection point of the original discrete data.

[0050] Principles of flux observer, displacement observer and suction observer:

[0051] The dynamic flux of the contactor is difficult to measure directly, so it is necessary to build a flux observer to indirectly measure the coil flux. The working process of the contactor follows the voltage balance equation:

[0052]

[0053] Where: u is the coil voltage; i is the coil current; R is the coil resistance; ψ is the magnetic flux

[0054] By rewriting equation (4), a voltage-integrated flux observer can be constructed. The magnetic flux can be indirectly obtained by simply collecting the coil voltage and coil current and integrating them:

[0055] ψ=∫(u-iR)dt (5)

[0056] For an electromagnetic mechanism with a fixed structure, its coil current i, magnetic flux ψ, moving iron core displacement x, and electromagnetic suction force F x There exists (i,ψ)→x, (i,ψ)→F x Based on this mapping relationship, the suction observer and displacement observer of the contactor can be established. The present invention adopts a multi-layer BP neural network with strong fitting ability to design the observer. The principles of the displacement observer and the suction observer are as follows: Figure 2 shown.

[0057] Finite element simulation experiments are performed on the electrical, magnetic and mechanical parameters of the contactor to obtain (i,ψ)→x, (i,ψ)→F x Binary mapping data, taking the static data of the electromagnetic system (i, ψ) as binary input, the electromagnetic attraction F x and the displacement of the moving iron core x as the expected output, and the BP neural network is trained offline. After the training is completed, the displacement observer and the suction observer can be constructed. When the observer is running, the (ψ, i) data pair is used as input, and the flux observer is used to map the output x, F through the neural network model. x , and ultimately achieve the purpose of estimating the displacement of the moving iron core and the electromagnetic attraction in real time through the coil voltage and coil current that are easily measured by the contactor.

[0058] Contact wear observation principle:

[0059] Contactor contact wear can be divided into mechanical wear and electrical wear. Electrical wear is the main factor of contact wear during contactor operation. The root cause of electrical wear is the erosion of the contact material by the arc generated during contactor operation. Generally speaking, the amount of contact erosion is positively correlated with the contact opening distance. Therefore, contact wear can be observed by observing the contact opening distance. The contact opening distance of the contactor can be represented by the reaction force step position. Therefore, a reaction force step observation algorithm needs to be designed to indirectly realize contact wear observation.

[0060] The moving iron core of the contactor complies with the D'Alembert mechanical motion equation during movement:

[0061]

[0062] Where: m is the equivalent mass of the moving part; v is the speed of the moving iron core;

[0063] According to formula (6), the reaction force can be calculated:

[0064]

[0065] From formula (7), we can see that the reaction force observation requires the known electromagnetic attraction force F x , the displacement x of the moving iron core and the equivalent mass m of the moving parts. With the help of the displacement observer and the suction observer mentioned above, we can observe F x and x, and then complete the reaction force observation. Theoretically, the reaction force step signal can be obtained by differentially treating the displacement waveform twice according to formula (7), but the displacement observation signal has errors and interference, resulting in low signal accuracy after multiple differentiations. Therefore, the present invention is to use F f The signal is integrated using formula (8) to obtain the reaction force integral:

[0066]

[0067] After the integral operation, the reaction force step signal becomes an inflection point signal, and the reaction force step moment strictly corresponds to the inflection point moment, so the inflection point identification algorithm mentioned above can be used to extract the inflection point moment t ct , with the help of the inflection point and the initial contact opening distance x a You can get the current contact wear value

[0068] The contact wear observation principle finally constructed is as follows: Figure 3 shown.

[0069] During the contactor closing process, the coil voltage u and coil current i signals of the contactor are collected, and the magnetic flux ψ is indirectly observed with the help of the integral flux observer. The (i, ψ) data is input into the moving iron core displacement observer and the electromagnetic suction force observer to observe the moving iron core displacement x and the electromagnetic suction force F. x , differentiate the displacement of the moving iron core to get the moving iron core velocity v. x Divide by the equivalent mass m of the moving iron core to get the electromagnetic acceleration a x , integrating the electromagnetic acceleration gives the electromagnetic velocity v x Since the force on the moving iron core conforms to the superposition theorem, the electromagnetic velocity v is used. x Subtract the total velocity v to resolve the reaction force integral v f , due to the reaction force F f At the moment when the contacts just close, t ct There is a step, so the reaction force integral v f There is an inflection point when the contacts just close. The inflection point identification algorithm can be used to obtain the contact just closing moment t ct , and t ct Corresponding to the closing moving iron core displacement x waveform, the current contact opening distance x can be observed a , then use the current contact distance minus the initial contact distance x a0 The current contact wear value x can be observed ct.ero。

Claims

1. A method for online observation of contactor contact wear, characterized in that: According to the electromagnetic mechanism coil current i, magnetic circuit flux ψ, moving iron core displacement x, electromagnetic suction force F x The binary one-to-one mapping relationship is used to design the moving iron core displacement observer and the electromagnetic suction force observer using the BP neural network model; the electromagnetic suction force and the moving iron core displacement are directly observed according to the coil current and coil voltage during the contactor closing process; the electromagnetic suction force F x , the displacement of the moving iron core x is calculated to obtain the reaction force integral waveform v f ; The reaction force step is indirectly identified by observing the reaction force integral waveform, and the integral operation converts the step signal into an inflection point signal to achieve indirect identification of contact wear.

2. The method for online observation of contactor contact wear according to claim 1, characterized in that: After the step signal is converted into an inflection point signal, the inflection point is identified by an inflection point identification method based on function approximation; specifically, for discrete data with an inflection point, when a function with an inflection point is used to perform a difference-free approximation on it, if there is a function that approximates the original data and its approximation error is minimized, then the inflection point of this function is the inflection point of the original data; Through v f (t) The waveform is observed and analyzed, and a piecewise quadratic function is used to approximate it, so the fitting function is: The constraints are: x0≤w slip ≤x n (2) The optimization goal is: min mse(f(x j )-y(x j ))x j ∈(x0,x n )j∈(0,n)(3) Where: p1, p2, p4 and p5 are constraint function coefficients; w parameter is the independent variable of the function; w slip is the function segmentation point independent variable; z slip is the function segmentation point dependent variable; x0, x n is the range of the original discrete data independent variable; mse represents the mean square error; f is the fitting function, f(x j ) is the fitting function output when the original discrete data is used as the variable, y(x j ) is the original discrete data; j is the original discrete data index; By traversing the constraints one by one, the optimization problem with constraints is transformed into multiple optimization problems without constraints. For a single optimization problem without constraints, the Nelder-Mead simplex optimization algorithm is used to solve it, and then the optimization problem with constraints is solved.

3. The method for online observation of contactor contact wear according to claim 2, characterized in that: The inflection point identification specifically includes the following steps: First, the discrete data (x j ,y(x j )) Input this algorithm and fit the segment points (w slip ,z slip ) are set as the original discrete data points (x j ,y(x j )), use the Nelder-Mead optimization algorithm to optimize the fitting function parameters p1, p2, p4, p5 at each segment point to make it close to the original discrete data. When the optimal approximation is reached, calculate and record the fitting function f(x j ) and the original discrete data y(x j )’s mean square error loss j , and then determine whether all discrete data have been traversed. If not, the segmentation points (w slip ,z slip ) is set as the next discrete data (x j+1 ,y(x j+1 )) Repeat the above process until all discrete data are traversed; after the traversal is completed, find the index j of the minimum value of the mean square error loss, and the original discrete data point x corresponding to this index j This is the inflection point of the original discrete data.

4. The method for online observation of contactor contact wear according to claim 1, characterized in that: A flux observer is constructed to indirectly measure the coil flux. The contactor working process follows the voltage balance equation: Where: u is the coil voltage; i is the coil current; R is the coil resistance; ψ is the magnetic flux By rewriting equation (4), a voltage-integrated flux observer is constructed. The magnetic flux can be indirectly obtained by simply collecting the coil voltage and coil current and integrating them: ψ=∫(u-iR)dt (5) For an electromagnetic mechanism with a fixed structure, its coil current i, magnetic flux ψ, moving iron core displacement x, and electromagnetic suction force F x There exists (i,ψ)→x, (i,ψ)→F x The nonlinear mapping relationship of the contactor is established based on the mapping relationship; the suction observer and displacement observer of the contactor are designed by using a multi-layer BP neural network; Finite element simulation experiments are performed on the electrical, magnetic and mechanical parameters of the contactor to obtain (i,ψ)→x, (i,ψ)→F x Binary mapping data, taking the static data of the electromagnetic system (i, ψ) as binary input, the electromagnetic attraction F x and the displacement of the moving iron core x as the expected output, and the BP neural network is trained offline. After the training is completed, the displacement observer and the suction observer can be constructed. When the observer is running, the (ψ, i) data pair is used as input, and the flux observer is used to map the output x and F through the neural network model. x , and ultimately achieve the purpose of estimating the displacement of the moving iron core and the electromagnetic attraction in real time through the coil voltage and coil current that are easily measured by the contactor.

5. The method for online observation of contactor contact wear according to claim 1, characterized in that: The moving iron core of the contactor complies with the D'Alembert mechanical motion equation during movement: Where: m is the equivalent mass of the moving part; v is the speed of the moving iron core; The reaction force is calculated according to formula (6): From formula (7), we can see that the reaction force observation requires the known electromagnetic attraction force F x , the displacement x of the moving iron core and the equivalent mass m of the moving parts; F x and x, and then complete the reaction force observation; f The signal is integrated using formula (8) to obtain the reaction force integral: After the integral operation, the reaction force step signal becomes an inflection point signal, and the reaction force step moment strictly corresponds to the inflection point moment. The inflection point moment t is extracted. ct , with the help of the inflection point and the initial contact opening distance x a The current contact wear value can be obtained; during the contactor closing process, the contactor coil voltage u and coil current i signals are collected, and the magnetic flux ψ is indirectly observed with the help of the integral flux observer. The (i, ψ) data is input into the moving iron core displacement observer and the electromagnetic suction force observer to observe the moving iron core displacement x and the electromagnetic suction force F. x , differentiate the displacement of the moving iron core to get the moving iron core velocity v; the electromagnetic attraction F x Divide by the equivalent mass m of the moving iron core to get the electromagnetic acceleration a x , integrating the electromagnetic acceleration gives the electromagnetic velocity v x ; Use electromagnetic velocity v x Subtract the total velocity v to resolve the reaction force integral v f , due to the reaction force F f At the moment when the contacts just close, t ct There is a step, so the reaction force integral v f There is an inflection point when the contacts just close; by identifying the inflection point, the contact just closing moment t ct , and t ct Corresponding to the closing moving iron core displacement x waveform, the current contact opening distance x can be observed a , then use the current contact distance minus the initial contact distance x a0 The current contact wear value x can be observed ct.ero .

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