A system and method for diagnosing inter-turn faults of a doubly-fed generator

Abstract

The present invention provides a doubly-fed generator turn-to-turn fault diagnosis system and method, comprising the following steps: collecting the three-phase current waveform of the generator stator in a given time particle; converting the three-phase current to a dq plane and fitting an ellipse; calculating the eccentricity of the fitted ellipse; judging whether the doubly-fed generator turn-to-turn fault is faulty according to the obtained eccentricity; the present invention can effectively avoid diagnostic errors caused by differences between different motors and improve diagnostic accuracy.

Description

Technical Field

[0001] The invention belongs to the field of power generation, and in particular relates to a system and method for diagnosing inter-turn faults of a doubly-fed generator. Background Art

[0002] When a stator winding inter-turn short circuit occurs in a doubly-fed wind turbine, if the fault is relatively minor, the change in the three-phase stator current is very small. At this time, it is impossible to identify whether there is a stator inter-turn short circuit fault only from the time domain waveform. The three-phase current Park vector trajectory changes significantly with the fault. The shape of the vector trajectory and the eccentricity of the elliptical ring can be used to determine whether there is a short circuit and estimate the severity of the inter-turn short circuit. It is generally believed that when a 1% inter-turn short circuit occurs, the elliptical eccentricity will change significantly (increase from 0.009 to 0.213). However, during the actual operation of the generator, the initial elliptical eccentricity is already quite obvious, and the eccentricity cannot be directly used for fault diagnosis. Therefore, it is necessary to adopt a new analysis method. Summary of the invention

[0003] The purpose of the present invention is to provide a doubly-fed generator inter-turn fault diagnosis system and method, which solves the above-mentioned shortcomings in the prior art; the present invention aims at the weak ability of doubly-fed generator time domain waveform to identify inter-turn faults; and uses Park vector to characterize the inter-turn state of the equipment to realize equipment fault diagnosis.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides a method for diagnosing inter-turn faults of a doubly-fed generator, comprising the following steps:

[0006] Collect the three-phase current waveform of the generator stator in the particle at a given time;

[0007] Convert the three-phase currents to the dq plane and fit an ellipse;

[0008] Calculate the eccentricity of the fitted ellipse;

[0009] Whether there is a fault between turns of the doubly-fed generator is determined based on the obtained eccentricity.

[0010] Preferably, the three-phase current is converted to the dq plane and an ellipse is fitted, and the specific method is:

[0011] According to the collected three-phase current waveform, a waveform data matrix S is obtained;

[0012] Divide the waveform data matrix S equally by row to obtain multiple sub-matrices;

[0013] Each submatrix is ​​transformed to the dq plane using Park's vector transformation equation, and multiple points are obtained corresponding to each submatrix;

[0014] Each sub-matrix constructs a corresponding matrix based on the multiple points obtained;

[0015] The matrix and the quadratic parametric form of the conic section are combined to fit the ellipse, and each submatrix obtains the corresponding ellipse.

[0016] Preferably, each submatrix is ​​converted to the dq plane using the Park vector transformation equation, and each submatrix corresponds to a plurality of points. The specific method is:

[0017] Set the loop condition corresponding to each sub-matrix;

[0018] According to the loop conditions, each submatrix is ​​transformed into the dq plane in combination with the Park vector transformation equation, and each submatrix corresponds to multiple points.

[0019] Preferably, the loop condition corresponding to each submatrix is:

[0020] The initial value is 1; the step size is 1000; and the final value is 1000×L, where L is the number of rows of each submatrix divided by 1000 and rounded down.

[0021] Preferably, a nonlinear fitting method is used to transform the matrix O L Combined with the quadratic parametric form of conic sections to fit ellipses.

[0022] Preferably, judging whether there is a fault between turns of the doubly-fed generator according to the obtained eccentricity is specifically performed as follows:

[0023] Calculate the eccentricity of the ellipse corresponding to each submatrix;

[0024] A plurality of ellipse eccentricities are used to form a matrix, wherein the elements in the matrix satisfy a normal distribution;

[0025] The distribution variance of the matrix is ​​calculated and used to diagnose the inter-turn fault of the doubly-fed generator.

[0026] Preferably, the matrix distribution variance is calculated by:

[0027] Taking 0.95 as the confidence interval, the maximum likelihood estimate is calculated for the elements in the matrix to obtain the distribution variance of the matrix.

[0028] Preferably, the distribution variance is used to diagnose the inter-turn fault of the doubly-fed generator, and the specific method is:

[0029] If σ>0.1, it indicates that the eccentricity change is too large and there is a turn-to-turn fault. Otherwise, it indicates that it is normal.

[0030] A doubly-fed generator turn-to-turn fault diagnosis system based on Park vector ellipse change rate, the system can run the method described, including:

[0031] A collection unit, used for collecting the three-phase current waveform of the generator stator in the particle at a given time;

[0032] A data fitting unit converts the three-phase currents to the dq plane and fits an ellipse;

[0033] A calculation unit, used for calculating the eccentricity of the fitted ellipse;

[0034] The diagnosis unit is used to determine whether there is a turn-to-turn fault in the double-fed generator according to the obtained eccentricity.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The invention provides a method for diagnosing inter-turn faults of a doubly-fed generator. The method realizes the diagnosis of inter-turn faults of a doubly-fed generator by determining the rate of change of the ellipse eccentricity within a particle at a given time. Theoretical analysis shows that when the generator is operating normally, the lengths of the major and minor semi-axes of the Park vector are substantially equal, and the eccentricity is very small. At this time, the Park vector diagram is approximately a circle. When an inter-turn short circuit fault occurs in the stator winding, the major semi-axle of the Park vector ellipse increases, the minor semi-axle shortens, and the eccentricity value increases significantly. Therefore, it can be theoretically considered that the Park vector eccentricity value can be used for inter-turn fault diagnosis. However, in the actual operation of the motor, it is possible that the initial values ​​of the eccentricity of different motors do not completely meet the theoretical interval, so the diagnostic accuracy of the absolute value of the eccentricity is not high. The eccentricity matrix that varies with time is obtained by using the Park vector transformation, and the eccentricity change is obtained by using the maximum likelihood estimation, that is, the change rate is used to carry out diagnosis, which can effectively avoid diagnostic errors caused by differences between different motors and improve the diagnostic accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the process of the present invention;

[0038] Figure 2 It is a three-phase current waveform diagram;

[0039] Figure 3 is the fitted ellipse graph. DETAILED DESCRIPTION

[0040] The present invention provides a method for diagnosing inter-turn faults of a doubly-fed generator, which realizes inter-turn fault diagnosis by collecting three-phase current waveforms in particles at a given time, converting the three-phase current to d and q axes, fitting an ellipse, and analyzing the change rate of the eccentricity of the ellipse in the particles at a given time.

[0041] like Figure 1 As shown, the specific steps include:

[0042] Step 1: Collect the three-phase current waveform data of the generator stator in the particle at a fixed time (such as Figure 2As shown in the figure, the acquisition frequency is 12800 Hz, and the acquisition time granularity is 10s. Then the waveform data matrix S can be obtained, S is a 128000-row, 4-column matrix, the first column is the sampling time, and the 2nd to 4th columns are the instantaneous values ​​of the three-phase currents A, B, and C respectively.

[0043] Step 2: Divide the waveform data matrix S into 10 sub-matrices by row, then the matrix A 1 ,A 2 ,A 3 ,A 4 ,A 5 ,...,A 10 Both are 12800 rows and 4 columns matrices, which can be expressed as:

[0044] S=[A 1 ,A 2 ,A 3 ,A 4 ,A 5 ,...,A 10 ] T

[0045] Step 3, set the loop conditions corresponding to each sub-matrix, specifically:

[0046] Divide the number of rows of each of the 10 sub-matrices obtained in step 2 by 1000 and round down to get the value L;

[0047] Set the loop conditions according to the value L: the initial value is 1, the step size is 1000, and the end value is 1000×L.

[0048] Take A in step 2 1 Assume that the number of matrix rows is 12800 as an example, then L=12.

[0049] Step 4: Start the loop according to the loop condition set in step 3, and transform the three-phase current data in each matrix to the plane composed of the d and q axes according to the following Park vector transformation equation. Assume that the d axis coincides with the a axis of the A phase current. Each time the loop is repeated, each submatrix obtains a point (i d ,i q ), the point (i d ,i q ) corresponds to a point O on the (dq) plane; where the Park vector transformation equation is:

[0050]

[0051] (i d ,i q ) is the current coordinate in the (dq) plane, then:

[0052]

[0053] i a 、i b 、i c A 1 The instantaneous values ​​of the three-phase currents of the generator corresponding to the matrix.

[0054] After the loop is completed, each submatrix corresponds to a series of points on the (dq) plane, and the series of points are used to construct the matrix O corresponding to each submatrix. L .

[0055]

[0056] Wherein, m represents the number of cycles.

[0057] Step 5: Using a nonlinear fitting method, the matrix O obtained in step 4 is L The quadratic parameter form of the conic section is combined to fit the ellipse, and the coefficient matrix p corresponding to each submatrix is ​​calculated using the nonlinear regression method (such as Figure 3 As shown); the ellipse secondary parameter form is:

[0058] f(xy)=p 1 x 2 +p 2 xy+p 3 y 2 +p 4 x+p 5 y+1

[0059]

[0060] The coefficient matrix p is:

[0061] p=[p 1 , p 2 , p 3 , p 4 , p 5 , 1] T

[0062] Step 6: Calculate the center of the ellipse according to the coefficient matrix p, where the geometric center of the ellipse is (X c , Y c ), calculated using the following formula:

[0063]

[0064] Among them, p 1 , p 2 , p 3 , p 4 , p 5 is the corresponding value in the coefficient matrix p.

[0065] Step 7: Calculate the major axis a and minor axis b of the ellipse based on the calculation results of the previous step. The calculation method is:

[0066]

[0067] Step 8: According to the calculation results of the previous step, the eccentricity e of the fitting ellipse corresponding to each submatrix is ​​calculated. The calculation method is as follows:

[0068]

[0069] Step 9: All the fitted ellipse eccentricities e are combined into a matrix E, where the elements in the matrix E satisfy the normal distribution.

[0070] Step 10, calculate the maximum likelihood estimate for the elements in the matrix E with a confidence interval of 0.95, and obtain the variance σ of the distribution of the matrix E. If σ>0.1, it indicates that the eccentricity changes too much, and there may be a turn-to-turn fault. Otherwise, it indicates that it is normal.

[0071] Theoretical analysis shows that when the generator is operating normally, the lengths of the major and minor semi-axes of the Park vector are basically equal, and the eccentricity is very small. At this time, the Park vector diagram is approximately a circle. When a short-circuit fault occurs in the stator winding, the major semi-axis of the Park vector ellipse increases, the minor semi-axis shortens, and the eccentricity value increases significantly. Therefore, it can be theoretically believed that the Park vector eccentricity value can be used for turn-to-turn fault diagnosis. However, during the actual operation of the motor, it is possible that the initial values ​​of the eccentricity of different motors do not completely meet the theoretical range, so the absolute value of the eccentricity is not accurate enough for diagnosis. Therefore, the present invention uses Park vector transformation to obtain an eccentricity matrix that varies with time, and uses maximum likelihood estimation to obtain the change in eccentricity, that is, the change rate to carry out diagnosis, which can effectively avoid diagnostic errors caused by differences between different motors and improve diagnostic accuracy.

Claims

1. A method for diagnosing interturn faults of a doubly-fed generator, characterized in that: The following steps are involved: Collect the three-phase current waveform of the generator stator in the particle at a given time; Convert the three-phase currents to the dq plane and fit an ellipse; Calculate the eccentricity of the fitted ellipse; Judging whether there is a fault between turns of the doubly-fed generator according to the obtained eccentricity; According to the collected three-phase current waveform, a waveform data matrix S is obtained. The waveform data matrix S is a 4-column matrix, the first column is the sampling time, and the second to fourth columns are the instantaneous values ​​of the three-phase currents A, B, and C respectively; Divide the waveform data matrix S equally by row to obtain multiple sub-matrices; Each submatrix is ​​transformed to the dq plane using Park's vector transformation equation, and each submatrix corresponds to multiple points; Each sub-matrix constructs the corresponding matrix based on the obtained multiple points ; The matrix Combined with the quadratic parameter form of the conic section to fit the ellipse, each submatrix obtains the corresponding ellipse; According to the obtained eccentricity, it is judged whether there is a fault between the turns of the double-fed generator. The specific method is: Calculate the eccentricity of the ellipse corresponding to each submatrix; A plurality of ellipse eccentricities are used to form a matrix, wherein the elements in the matrix satisfy a normal distribution; Calculate the distribution variance of the matrix and use it to diagnose the inter-turn fault of the doubly-fed generator; Calculate the distribution variance of the matrix. The specific method is: Taking 0.95 as the confidence interval, calculate the maximum likelihood estimate for the elements in the matrix and obtain the distribution variance of the matrix; The variance is used to diagnose the inter-turn fault of the double-fed generator. The specific method is: If σ>0.1, it indicates that the eccentricity change is too large and there is a turn-to-turn fault. Otherwise, it indicates that it is normal.

2. A method for diagnosing interturn faults of a doubly-fed generator according to claim 1, characterized in that: Each submatrix is ​​converted to the dq plane using the Park vector transformation equation. Each submatrix corresponds to multiple points. The specific method is: Set the loop condition corresponding to each sub-matrix; According to the loop conditions, each submatrix is ​​transformed into the dq plane in combination with the Park vector transformation equation, and each submatrix corresponds to multiple points.

3. A method for diagnosing inter-turn faults of a doubly-fed generator according to claim 2, characterized in that: The loop condition corresponding to each submatrix is: The initial value is 1; the step size is 1000; and the final value is 1000×L, where L is the number of rows of each submatrix divided by 1000 and rounded down.

4. A method for diagnosing inter-turn faults of a doubly-fed generator according to claim 1, characterized in that: Using nonlinear fitting method, the matrix Combined with the quadratic parametric form of conic sections to fit ellipses.

5. A doubly-fed generator turn-to-turn fault diagnosis system, characterized in that: The system is capable of running the method according to any one of claims 1 to 4, including: A collection unit, used for collecting the three-phase current waveform of the generator stator in the particle at a given time; A data fitting unit converts the three-phase currents into a dq plane and fits an ellipse; A calculation unit, used for calculating the eccentricity of the fitted ellipse; The diagnosis unit is used to determine whether there is a turn-to-turn fault in the double-fed generator according to the obtained eccentricity.

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