A method and device for evaluating the severity of voltage sag

Abstract

The present invention discloses a method and device for assessing the severity of voltage sags, belonging to the technical field of power quality research in distribution networks. The present invention considers the impact of different transformer types on the propagation of different voltage sag events, solving the problem of difficulty in converting data between the grid system side and the user side data; uses a nonlinear least squares method to establish a fusion tolerance curve to comprehensively assess the severity level of voltage sags on the user side, solving the problem that there are multiple load devices on the user side and the severity of the user side cannot be comprehensively assessed based on grid side data; uses an improved hierarchical analysis method to calculate the influence coefficient of the characteristic values ​​of the voltage sag, namely the sag amplitude and duration, and establishes a hierarchical assessment benchmark based on energy indicators, which can quantitatively reflect the more realistic sag degree on the user side and achieve a reasonable and accurate assessment of the severity of the voltage sag event on the user side.

Description

Technical Field

[0001] The present invention relates to a method and a device for evaluating the severity of a voltage sag, and belongs to the technical field of power quality research in distribution networks. Background Art

[0002] With the widespread use of new power electronic equipment in power systems, voltage sags are becoming increasingly prominent, becoming a major power quality issue affecting reliable power supply and the normal operation of equipment, resulting in significant economic losses for sensitive users. A reasonable and accurate assessment of voltage sag severity not only serves as a measure of system power quality, serving as an important basis for quality-based pricing in power market environments, but also serves as a key indicator for the production of sensitive user equipment. Therefore, developing a method for assessing the severity of user-side voltage sags has become a key topic in power quality research. Summary of the Invention

[0003] The present invention provides a method and device for evaluating the severity of a voltage sag, so as to realize the evaluation of the severity of a voltage sag.

[0004] The technical solution of the present invention is:

[0005] According to one aspect of the present invention, a method for assessing the severity of a voltage sag is provided, comprising:

[0006] Step 1: Calculate the voltage sag characteristic value on the user side;

[0007] Step 2: Based on the tolerance curves of different devices on the user side, establish integrated tolerance curves for different voltage sag types;

[0008] Step 3: Calculate the influence coefficient of the voltage sag characteristic value; wherein the influence coefficient of the voltage sag characteristic value includes the influence coefficient of the sag amplitude and the influence coefficient of the duration;

[0009] Step 4: Combine the fusion tolerance curve and the influence coefficient to obtain the corrected sag amplitude and duration;

[0010] Step 5: Calculate the energy index on the user side based on the corrected sag amplitude and duration, and establish an energy index grading assessment benchmark to assess the severity of the voltage sag on the user side.

[0011] The step 2 comprises:

[0012] Step 2.1: Based on the tolerance curves of multiple different devices on the user side, establish a comprehensive tolerance curve based on different sag types;

[0013] Step 2.2: Based on the comprehensive tolerance curve, establish the fusion tolerance curve function u=ae of the improved exponential function model where t is the duration, u is the sag amplitude, and a, b, c, and d are unknown parameters. b*t +ce d*t ;

[0014] Step 2.3: Use the nonlinear least squares method to directly take the fitting data for the overlapping part of the comprehensive tolerance curve. For the non-overlapping part of the comprehensive tolerance curve, take the intermediate data value of the comprehensive tolerance curve as the fitting data, and fit the integrated tolerance curve for different voltage sag types on the user side.

[0015] The step 3 comprises:

[0016] Step 3.1: Divide the voltage sag amplitude into 9 intervals and the duration into 8 intervals. Use the nine-scale method to construct the voltage sag amplitude judgment matrix A. u and duration judgment matrix A t ;

[0017] Step 3.2: Based on the judgment matrix, establish a judgment matrix for the sag amplitude and duration, and solve the maximum eigenvalue λ of the sag amplitude of the judgment matrix. umax and the maximum eigenvalue of duration λ tmax The corresponding eigenvector is used as the weight vector W of the sag amplitude u and the weight vector W of the duration t ;

[0018] Step 3.2: Introduce the consistency ratio value CR to perform consistency test on the judgment matrix;

[0019] Step 3.4: Weight vector W for the sag amplitude u and the weight vector W of the duration t Normalized calculation is performed to obtain the influence coefficient of the sag amplitude and the influence coefficient of the duration.

[0020] Step 4 specifically involves reconstructing the voltage sag characteristic value on the user side by fusing the tolerance curve to obtain reconstructed sag amplitudes and durations for different voltage sag types, and multiplying the reconstructed sag amplitudes and durations by the corresponding sag amplitude influence coefficients and duration influence coefficients to obtain corrected sag amplitudes and durations.

[0021] The step 5 comprises:

[0022] Step 5.1: Substitute the corrected voltage sag characteristic value into the energy index formula to calculate the voltage sag energy index on the user side;

[0023] Step 5.2: Divide the energy index into multiple levels based on the divided sag amplitude and duration intervals;

[0024] Step 5.3: Establish an energy index grading assessment benchmark based on multiple levels of energy index values, and comprehensively assess the severity level of the voltage sag event based on the energy index on the user side.

[0025] The level is 5, when the energy index E vs ≤0.0073, the severity level is mild; when 0.0073 <E vs ≤0.0145, the severity level is moderate; when 0.0145 <E vs ≤0.0304, the severity level is relatively serious; when 0.0304 <E vs ≤0.3327, the severity level is severe; when 0.3327 <E vs , the severity level was assessed as extremely severe.

[0026] According to another aspect of the present invention, there is provided a device for assessing the severity of a voltage sag, comprising:

[0027] A first calculation module is used to calculate the voltage sag characteristic value on the user side;

[0028] Establish a module for establishing integrated tolerance curves for different voltage sag types based on the tolerance curves of different devices on the user side;

[0029] The second calculation module is used to calculate the influence coefficient of the voltage sag characteristic value; wherein the influence coefficient of the voltage sag characteristic value includes the influence coefficient of the sag amplitude and the influence coefficient of the duration;

[0030] An acquisition module is used to combine the fusion tolerance curve and the influence coefficient to obtain the corrected sag amplitude and duration;

[0031] The evaluation module is used to calculate the energy index on the user side according to the corrected sag amplitude and duration, and to establish an energy index grading evaluation benchmark to evaluate the severity of the voltage sag on the user side.

[0032] The beneficial effects of the present invention are:

[0033] The present invention takes into account the influence of different transformer types on the propagation of different voltage sag events, and solves the problem of difficult conversion between power grid system side data and user side data; uses the nonlinear least squares method to establish a fusion tolerance curve to comprehensively evaluate the severity level of the voltage sag on the user side, which solves the problem that there are multiple load devices on the user side and the severity of the user side cannot be comprehensively evaluated based on the power grid side data; uses the improved hierarchical analysis method to calculate the influence coefficient of the characteristic values ​​of the voltage sag, namely the sag amplitude and duration, and establishes a hierarchical evaluation benchmark based on energy indicators, which can quantitatively reflect the more realistic sag degree on the user side, and realize a reasonable and accurate evaluation of the severity of the voltage sag event on the user side. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the overall flow chart of the present invention;

[0035] Figure 2 It is a single-phase / two-phase fusion tolerance curve;

[0036] Figure 3 It is a three-phase fusion tolerance curve diagram;

[0037] Figure 4 This is the energy index calculation process. DETAILED DESCRIPTION

[0038] The invention will be further described below with reference to the accompanying drawings and embodiments, but the content of the present invention is not limited to the scope of the drawings.

[0039] Example 1: Figure 1-4 As shown, a voltage sag severity assessment method includes:

[0040] Step 1: Calculate the voltage sag characteristic value on the user side;

[0041] Step 2: Based on the tolerance curves of different devices on the user side, establish integrated tolerance curves for different voltage sag types;

[0042] Step 3: Calculate the influence coefficient of the voltage sag characteristic value; wherein the influence coefficient of the voltage sag characteristic value includes the influence coefficient of the sag amplitude and the influence coefficient of the duration;

[0043] Step 4: Combine the fusion tolerance curve and the influence coefficient to obtain the corrected sag amplitude and duration;

[0044] Step 5: Calculate the energy index on the user side based on the corrected sag amplitude and duration, and establish an energy index grading assessment benchmark to assess the severity of the voltage sag on the user side.

[0045] Furthermore, an optional implementation of the present invention is described in detail below.

[0046] For different types of transformers, the voltage transfer matrix is ​​different, and during the propagation of the voltage sag, the three-phase voltage values ​​of different types of voltage sag are also different. Therefore, in this application, the voltage sag type and the transformer type are considered during the propagation of the voltage sag.

[0047] First, according to the 10kV power grid system, the characteristic value of the voltage sag will change after it propagates through different types of transformers. Considering the influence of the transformer on the propagation of the voltage sag and the type of voltage sag, the transformation matrix T is determined. Then, combined with the characteristic value of the voltage sag on the grid side of the 10kV power grid system (i.e., U ABC ), and then calculate the voltage sag amplitude on the user side according to formula (1):

[0048] U abc =T*U ABC (1)

[0049] Where: U abc Represents the value of the secondary side of the transformer, T represents the transformation matrix of the primary or secondary side of the transformer, U ABC Represents the value of the primary side of the transformer.

[0050] Secondly, for the tolerance curves of multiple different devices on the user side, a comprehensive tolerance curve based on different sag types is established; according to the state that the comprehensive tolerance curve first rises rapidly, then rises slowly, and finally tends to be horizontal, a fusion tolerance curve u=ae of the improved exponential function model is established with t as the duration, u as the sag amplitude, and a, b, c, and d as unknown parameters. b*t +ce d*t ; Use the nonlinear least square method to establish a fusion tolerance curve function for the tolerance curves of different devices on the user side. Figure 2 、 Figure 3 As shown in Figure 1, the fused comprehensive tolerance curve combines the SEMIF47 voltage tolerance curve and the ITIC tolerance curve with the voltage sag single-phase / two-phase and three-phase tolerance curves given by the C4.110 working group. For the overlapping parts of the tolerance curves, data fitting is directly adopted; for the non-overlapping parts of the tolerance curves, the middle value of the curve data is taken as the fitting data. To make the fitting effect more accurate, as much data as possible is selected. The values ​​of the unknown control parameters a, b, c, and d are calculated by fitting the least squares exponential function, and the fused tolerance curve function shown in Equations (2) and (3) is obtained to comprehensively evaluate the severity of the voltage sag event on the user side.

[0051] u1=0.7104e 0.1811*t -0.7349e -13.47*t (2)

[0052] u2=0.6996e0.1708*t -0.7708e -20.52*t (3)

[0053] Wherein, u1 is the sag amplitude of the single-phase / two-phase integrated tolerance curve, u2 is the sag amplitude of the three-phase integrated tolerance curve, and t is the voltage sag duration.

[0054] Then, the improved analytic hierarchy process is used to calculate the influence coefficients of voltage sag amplitude and duration. The weight coefficients of each duration interval and sag amplitude interval are calculated with the help of analytic hierarchy process, and their relative importance is reflected by the ratio of the level numbers. Based on this, the judgment matrix A for duration and sag amplitude is constructed as shown in equations (4) and (5):

[0055] A t =(a is ) 8*8 (4)

[0056] A u =(a is ) 9*9 (5)

[0057] in: Represents a i Factors and a s The relative importance of factors, a i with a s Represents each interval of voltage sag amplitude and duration, a i For a s The preceding interval; A t where i, s = 1, 2, 3…8, A u In A, i and s = 1, 2, 3…9. t A represents the judgment matrix of duration, u The judgment matrix of the voltage sag amplitude is represented by the IEC61000-2-8 statistical table, which divides the voltage sag amplitude into 9 intervals and the duration into 8 intervals. The nine-scale method is used to construct the voltage sag amplitude judgment matrix A. u and duration judgment matrix A t ;

[0058] By solving, we can get the maximum eigenvalue λ of matrix A t max and λ u max and the corresponding eigenvector W t =[w t1 ,w t2 ,…,w t8 ] and W u =[w u1 ,w u2 ,…,w u9]. The consistency ratio value CR is introduced to perform consistency test on the judgment matrix. When the CR value is less than 0.1, the judgment matrix is ​​considered to be consistent. The calculation method of CR is shown in formula (6) and formula (7).

[0059]

[0060]

[0061] Using formula (8) and formula (9), the eigenvector W corresponding to the maximum eigenvalue is t and W u After normalization, it is used as the impact value S of the voltage sag duration and sag amplitude.

[0062]

[0063]

[0064] Where: s t(i) is the influence coefficient of the duration of the i-th segment obtained by the hierarchical analysis, s u(i) is the influence coefficient of the sag amplitude finally obtained by the hierarchical analysis belonging to the i-th segment.

[0065] Then, the corrected sag characteristic value is calculated by combining the fusion tolerance curve and the influence coefficient.

[0066] Finally, the energy index on the user side is calculated based on the corrected voltage sag amplitude and duration, and a graded assessment benchmark for the energy index is established based on the IEC61000-2-8 table to comprehensively evaluate the severity of the voltage sag on the user side.

[0067] like Figure 4 As shown, the energy index is calculated by first calculating the sag amplitude and duration on the grid side and then transferring them through the transformer to obtain the sag amplitude and duration on the user side. Then, based on the fusion tolerance curve, the amplitudes of different voltage sag events are reconstructed. The reconstructed sag amplitude and duration are multiplied by their corresponding influence coefficients respectively. Finally, the voltage sag energy index on the user side is calculated according to the energy index formula.

[0068] The 8 duration intervals and 9 sag amplitude impact intervals divided by the IEC61000-2-8 recommended table are comprehensively divided into 5 levels from high to low (for the duration interval, the interval division can be from high to low, and the interval division can be 1-2, 3-4, 5-6, 7, and 8, a total of five intervals; the sag amplitude interval division can be 1-2, 3-4, 5-6, 7-8, and 9, a total of five intervals); the energy index is calculated according to the energy index formula shown in formula (10) and the fusion tolerance curve function, and is divided into the 5 voltage sag event severity levels shown in Table 1.

[0069]

[0070] Among them, u(t) is the voltage sag amplitude, U nom is the nominal voltage; t is the duration of the voltage sag;

[0071] Table 1 Classification of severity levels of voltage sag events

[0072]

[0073] By applying the above technical solution, it can be seen that the present invention analyzes the changes in characteristic values ​​caused by sag events of different types for different transformer types; then, in view of the presence of multiple load devices on the user side, a fusion tolerance curve is established to comprehensively calculate the sag characteristic values ​​of the user side load, and the improved hierarchical analysis method is used to calculate the influence of the sag characteristic values, and a hierarchical evaluation benchmark based on energy indicators is established to comprehensively judge the severity of the voltage sag event, thereby solving the problem of evaluating the severity of the user side voltage sag based on the grid side data, and realizing the construction of a method for evaluating the severity of the user side voltage sag.

[0074] Example 2, a voltage sag severity assessment device, comprising:

[0075] A first calculation module is used to calculate the voltage sag characteristic value on the user side;

[0076] Establish a module for establishing integrated tolerance curves for different voltage sag types based on the tolerance curves of different devices on the user side;

[0077] The second calculation module is used to calculate the influence coefficient of the voltage sag characteristic value; wherein the influence coefficient of the voltage sag characteristic value includes the influence coefficient of the sag amplitude and the influence coefficient of the duration;

[0078] An acquisition module is used to combine the fusion tolerance curve and the influence coefficient to obtain the corrected sag amplitude and duration;

[0079] The evaluation module is used to calculate the energy index on the user side according to the corrected sag amplitude and duration, and to establish an energy index grading evaluation benchmark to evaluate the severity of the voltage sag on the user side.

[0080] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages or disadvantages of the embodiments.

[0081] In the above embodiments of the present invention, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0082] The specific embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for assessing the severity of voltage sag, characterized in that: include: Step 1: Calculate the voltage sag characteristic value on the user side; Step 2: Based on the tolerance curves of different devices on the user side, establish integrated tolerance curves for different voltage sag types; Step 3: Calculate the influence coefficient of the voltage sag characteristic value; wherein the influence coefficient of the voltage sag characteristic value includes the influence coefficient of the sag amplitude and the influence coefficient of the duration; Step 4: Combine the fusion tolerance curve and the influence coefficient to obtain the corrected sag amplitude and duration; Step 5: Calculate the user-side energy index based on the corrected sag amplitude and duration, and establish an energy index grading assessment benchmark to assess the severity of the user-side voltage sag. Step 4 specifically involves reconstructing the voltage sag characteristic value on the user side by fusing the tolerance curve to obtain reconstructed sag amplitudes and durations for different voltage sag types, and multiplying the reconstructed sag amplitudes and durations by the corresponding sag amplitude influence coefficients and duration influence coefficients to obtain corrected sag amplitudes and durations.

2. The voltage sag severity assessment method according to claim 1, characterized in that: The step 2 comprises: Step 2.1: Based on the tolerance curves of multiple different devices on the user side, establish a comprehensive tolerance curve based on different sag types; Step 2.2: Based on the comprehensive tolerance curve, establish the fusion tolerance curve function u=ae of the improved exponential function model where t is the duration, u is the sag amplitude, and a, b, c, and d are unknown parameters. b*t +ce d*t ; Step 2.3: Use the nonlinear least squares method to directly take the fitting data for the overlapping part of the comprehensive tolerance curve. For the non-overlapping part of the comprehensive tolerance curve, take the intermediate data value of the comprehensive tolerance curve as the fitting data, and fit the integrated tolerance curve for different voltage sag types on the user side.

3. The voltage sag severity assessment method according to claim 1, wherein: The step 3 comprises: Step 3.1: Divide the voltage sag amplitude into 9 intervals and the duration into 8 intervals. Use the nine-scale method to construct the voltage sag amplitude judgment matrix A. u and duration judgment matrix A t ; Step 3.2: Based on the judgment matrix, establish a judgment matrix for the sag amplitude and duration, and solve the maximum eigenvalue λ of the sag amplitude of the judgment matrix. umax and the maximum eigenvalue of duration λ tmax The corresponding eigenvector is used as the weight vector W of the sag amplitude u and the weight vector W of the duration t ; Step 3.3: Introduce the consistency ratio value CR to perform consistency test on the judgment matrix; Step 3.4: Weight vector W for sag amplitude u and the weight vector W of the duration t Normalized calculation is performed to obtain the influence coefficient of the sag amplitude and the influence coefficient of the duration.

4. The voltage sag severity assessment method according to claim 1, wherein: The step 5 comprises: Step 5.1: Substitute the corrected voltage sag characteristic value into the energy index formula to calculate the voltage sag energy index on the user side; Step 5.2: Divide the energy index into multiple levels based on the divided sag amplitude and duration intervals; Step 5.3: Establish an energy index grading assessment benchmark based on multiple levels of energy index values, and comprehensively assess the severity level of the voltage sag event based on the energy index on the user side.

5. The voltage sag severity assessment method according to claim 4, characterized in that: The level is 5, when the energy index E vs ≤0.0073, the severity level is mild; when 0.0073 <E vs ≤0.0145, the severity level is moderate; when 0.0145 <E vs ≤0.0304, the severity level is relatively serious; when 0.0304 <E vs ≤0.3327, the severity level is severe; when 0.3327 <E vs , the severity level was assessed as extremely severe.

6. A voltage sag severity assessment device, characterized in that: include: A first calculation module is used to calculate the voltage sag characteristic value on the user side; Establish a module for establishing integrated tolerance curves for different voltage sag types based on the tolerance curves of different devices on the user side; The second calculation module is used to calculate the influence coefficient of the voltage sag characteristic value; wherein the influence coefficient of the voltage sag characteristic value includes the influence coefficient of the sag amplitude and the influence coefficient of the duration; An acquisition module is used to combine the fusion tolerance curve and the influence coefficient to obtain the corrected sag amplitude and duration; An evaluation module is used to calculate the energy index on the user side based on the corrected sag amplitude and duration, and to establish a grading evaluation benchmark for the energy index to assess the severity of the voltage sag on the user side; The obtaining module specifically reconstructs the voltage sag characteristic value on the user side by fusing the tolerance curve to obtain reconstructed sag amplitudes and durations for different voltage sag types, and multiplies the reconstructed sag amplitudes and durations by the corresponding sag amplitude influence coefficients and duration influence coefficients to obtain corrected sag amplitudes and durations.

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