CN108919003B - Sensitive equipment voltage sag tolerance characteristic testing and data processing method - Google Patents
Sensitive equipment voltage sag tolerance characteristic testing and data processing method Download PDFInfo
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Abstract
A voltage sag tolerance characteristic test and data processing method for sensitive equipment is characterized in that the sag duration time is set in a sectional variable step length mode, the density of test points is increased at the transition part of a tolerance curve to ensure that the obtained tolerance curve is finer, and the test times are ensured to be in a reasonable range; testing under various influence factors to obtain a large number of tolerance curves, enveloping, and performing broken line processing on the envelope line by using a least square method; dividing a non-rectangular uncertain region of the equipment into two regions, then taking the determined probability values of the upper envelope line, the lower envelope line and the region boundary line as reference values, describing the rectangular regions in uniform distribution, and adopting a line segment ratio method between related points for the non-rectangular regions to realize the quantification of the influence degree of the voltage sag event on the equipment. The method can provide a reasonable test method and a simple and convenient data processing method for power grids, governing manufacturers and sensitive equipment users, and realizes quantitative description of the non-rectangular uncertain area of the equipment.
Description
Technical Field
The invention belongs to the technical field of power quality analysis, and particularly relates to a voltage sag tolerance characteristic testing and data processing method for sensitive equipment.
Background
In recent years, power supply companies and power consumers pay more and more attention to the problem that the voltage sag event affects the normal operation of typical equipment, and a large amount of monitoring, evaluation and treatment work is carried out. Typical devices, such as ac contactors, frequency converters, Programmable Logic Controllers (PLCs), PCs, etc., commonly used in the modern industry are sensitive to voltage sag events, and may cause severe loss due to the influence of the voltage sag events, such as shutdown, control command disorder, efficiency reduction, or life reduction. For example, the running state of a PC depends on the severity of the sag event, the operating conditions, the power structure, the software and hardware configuration performance, and the like. For an early PC with a high CPU utilization rate and a passive power factor correction structure adopted by a power supply, the phenomena of sudden shutdown, operating system damage and the like are likely to occur due to the voltage amplitude falling of 50% and the sag event lasting only 80 ms.
The voltage sag tolerance characteristic of the sensitive equipment is usually described by a Voltage Tolerance Curve (VTC), which identifies the voltage sag of critical tolerance of the equipment on a sag amplitude-duration (V-T) plane, the voltage sag below the curve causes the equipment to malfunction, the sag above the curve has substantially no influence on the equipment, and the tolerance capability of the sensitive equipment to sag events can be intuitively understood through the tolerance curve. In the existing sensitive equipment tolerance curve standard, an ITIC curve suitable for the information technology industry and a SEMI F47 curve suitable for the semiconductor industry are commonly used; the working report of CIGRE/CIRED/UIE combined working group C4.110 on the voltage sag immunity of the equipment gives tolerance curves of five immunity grades, and one curve can be used for describing the tolerance of general equipment; the upper limit, the lower limit and the average value of tolerance curves of a variable frequency speed regulator, an alternating current relay, a PC (personal computer) and a PLC (programmable logic controller) are given in early IEEE std 1346-1998; the national electric power industry standard DL/T1648-. However, the sag tolerance curve of the device is affected by various factors, such as the load of the device, the operating condition, the protection threshold, the sag type, the phase jump, the starting point, the harmonic wave, etc., and the tolerance curve standard in the early stage does not indicate the applicable condition, etc., and does not necessarily accurately describe the tolerance characteristics of the sensitive device in the present day. Therefore, extensive testing studies are necessary to obtain sag tolerance characteristics of a certain class of devices under a variety of influences.
The sag tolerance curve of a typical sensitive device is approximately rectangular, but in practical situations, the vertical and horizontal portions of the tolerance curve of the device often have a transition portion, and are not completely rectangular. The conventional testing method, such as IEEE P1668, only roughly determines several fixed time duration points, 2s, 1s, 0.5s, 0.2s, 0.05s, etc., tests the corresponding critical tolerance amplitude, the transition part of each tolerance curve is different, and how to dynamically change the testing step size is a question to be studied. According to the IEEE P1668 test standard, the endurance curve test of a device is typically within 2s in duration, while a short interruption time (set at T) of the critical endurance of the device is obtained by the test0) If at T0When the test is carried out in equal step length within the range of 2s, the tolerance characteristic at the transition part of the tolerance curve can be lost when the step length is too large, and the test times of testing one tolerance curve can be large when the step length is too small. In order to keep the number of tests within a reasonable range and to describe the tolerance characteristics of the device in a more detailed manner, the duration of the sag (test) should be reduced in the horizontal part of the tolerance curveInter-points) are set sparsely, and test time points should be set densely at tolerance curve transitions.
For a particular tolerance curve, the tests are refined to accurately describe the tolerance characteristics. In addition, when the test data volume is large, the treatment tolerance curve is properly simplified in a comprehensive mode, and the method is also necessary for establishing a general mathematical model of the equipment tolerance curve. Since each device cannot be tested experimentally, the problem of quantitative description of uncertain zones of sag tolerance of typical sensitive devices arises. At present, related researchers have proposed a normal distribution probability density function method, a fuzzy random method, an interval method and the like, but all the methods are suitable for rectangular planes with equipment sag tolerance capability, and cannot reflect the actual influence degree of voltage sag events on sensitive equipment. However, the sag tolerance test of the sensitive equipment finds that the sag tolerance characteristic of certain typical sensitive equipment is changed, and the obtained uncertain region is in a non-rectangular shape, such as the current PLC, the current AC contactor and the like. The equipment fault probability evaluation model established for the rectangular uncertain region is likely to have difficulty in obtaining a quantitative result which accords with the actual sag tolerance of the equipment.
In view of this, the invention provides a voltage sag tolerance characteristic testing and data processing method for a sensitive device. In the process of testing the equipment sag test, setting the sag duration by adopting sectional variable step length, and increasing the density of a test point for the transition part of the tolerance curve to ensure that the obtained tolerance curve is finer; testing under various influence factors to obtain a large number of tolerance curves, enveloping the tolerance curves, and then performing folding processing on the envelope curve, so that a mathematical model can be conveniently established; the non-rectangular uncertain regions with typical equipment sag tolerance capacity are subjected to regional processing, then the upper envelope line, the lower envelope line and the boundary line definite probability value are used as references, rectangular regions in the regions are described according to uniform distribution, and the line segment ratio between relevant points is adopted for the non-rectangular regions, so that the quantification of the influence degree of voltage sag on the equipment is realized. The method is simple and clear, and has better universality.
Disclosure of Invention
In order to solve the above problems, the present invention provides a voltage sag tolerance characteristic testing and data processing method for a sensitive device. The method sets sag test points for testing the duration sectional variable step length, so that the test times are in a reasonable range, and the sparse and dense degree distribution of the test points is more reasonable; testing under various influence factors to obtain a large number of tolerance curves, enveloping the tolerance curves, and then performing folding processing on the envelope curve, so that a mathematical model can be conveniently established; for a non-rectangular uncertain region of the sag tolerance of the conventional typical equipment, the non-rectangular uncertain region is divided into regions, and then different quantitative description methods are adopted for different regions, so that the evaluation of the influence degree of the voltage sag on the equipment is realized.
In order to achieve the purpose, the invention adopts the following technical scheme.
A voltage sag tolerance characteristic testing and data processing method for sensitive equipment comprises the following steps:
A. setting the sag duration time segment variable step length to sag test points;
B. enveloping and folding the equipment tolerance curve;
C. the non-rectangular uncertainty region of the equipment's transient drop tolerance was quantitatively described.
Further, step a includes:
A1. setting short-time interruption and finding critical endurance time T of equipment0；
A2. Setting a voltage sag amplitude by adopting a bisection method;
A3. test duration of T0Critical withstand voltage U of time device0Selecting several fixed test time points, testing their correspondent critical endurance voltages according to T0In relation to the magnitude of the fixed test time point, T0-2 s into three sections: fixed test section T22s, coarse test segment T1～T2And a fine test section T0～T1Wherein, 0<T0<T1<T2<2 s; the fixed test section is not provided with more fixed test pointsOther test points; by step Δ T in the coarse test section1＝(T2-T1)/n1Setting a test point, n1Is a positive integer; base in fine test section (T)0,U0)、(T1,U1) The slope between the two points changes the step length to set the test point.
Further, the step length Δ T is measured when the slope is too large or too small0Should be large, but not larger than the step size of the coarse test segment, i.e., Δ T0<ΔT1(ii) a When (T)0,U0)、(T1,U1) When the included angle between the connecting line and the horizontal axis is 45 degrees, the testing step length delta T0And minimum.
Further, n is15 to 10.
Further, step B includes:
B1. equipment tolerance curve enveloping processing
Counting the maximum value and the minimum value of the tolerance time under a certain voltage amplitude, and respectively connecting the maximum value and the minimum value of the tolerance time into a line to obtain the upper envelope line and the lower envelope line of the tolerance curve of the equipment;
B2. extracting slope catastrophe points on tolerance curve envelope line
Calculating a broken line processing section, namely a transition curve section connecting a horizontal edge and a vertical edge of the tolerance curve and the slope between every two adjacent points in the vertical edge, and judging whether the broken line processing section is a catastrophe point according to the sign and size change relationship of any point on the curve and the slopes of the two points before and after the point;
B3. linear fitting of sample points between adjacent mutation points
According to the mutation points extracted in the step B2, fitting a straight line between two adjacent mutation points by utilizing least square fitting to approximately describe the tolerance characteristics of the equipment, wherein the straight line with the minimum sum of the distances from all sample points among the mutation points is the required straight line; is { (T)j,Uj) J is 1,2 …, m is a sample data point, m is a sample point number between two adjacent mutation points, and the function S (T) is calculatedj)＝a0+a1T，a0、a1Is a parameter to be solved, and a1Not equal to 0, so that an error is generatedThe sum of squares is minimized, as shown in formula (1), and this is converted into the solution of the function I (a) shown in formula (2)0,a1) The minimum value of (a) is,
the function I (a)0,a1) At its extreme point with respect to a0、a1Is equal to 0, represented by the formula (3)
Can deduce a0、a1The expression (4) of (a),
further, the method for determining the mutation point in step B1 includes: let any point be { (T)i,Ui) I is 2,3 …, p, and p points are set on the envelope line in total for comparison (T)i,Ui) Two points (T) in front and at the backi-1,Ui-1)、(Ti+1,Ui+1) Whether the signs of the slopes between are the same or not, let ki＝(Ui-Ui-1)/(Ti-Ti-1) I.e. determine ki×ki+1Whether greater than 0; if k isi×ki+1<0, then (T)i,Ui) Is a mutation point; if k isi×ki+1When the value is 0, (T)i,Ui) If the point is not a mutation point, i is i +1, and whether the next point is a mutation point is continuously judged; if k isi×ki+1>0, judging whether the relative change rate delta k of the slope shown in the formula (5) exceeds a certain value; if Δ k>Then (T)i,Ui) If the point is a mutation point, otherwise, if i is i +1, continuously judging whether the next point is a mutation point,
further, 10% was taken.
Furthermore, if the ratio of the number M of samples separated between two mutation points to the total number M of samples in the broken line processing section is less than a certain range, the mutation points close to the right side of the time axis are removed.
Further, the certain range is 20% to 25%.
Further, step C includes:
C1. partitioning a non-rectangular uncertainty region of a device into regions
The device operation state uncertain region between the upper envelope line and the lower envelope line is in a non-rectangular shape, the non-rectangular shape uncertain region is divided into a rectangular region and a non-rectangular region in the direction of a transverse axis, probability values corresponding to the upper envelope line and the lower envelope line are determined, and a determined value can be obtained after the boundary line of the longitudinal axis of the rectangular region is uniformly distributed;
C2. quantitative description of non-rectangular-shaped uncertainty regions
The rectangular area in the transverse axis direction in the non-rectangular uncertain area is only related to amplitude values, the probability values of upper and lower envelope lines are determined, and the influence degree of the voltage sag event falling in the area can be measured by the proportion of the sag amplitude value to the corresponding amplitude value interval of the upper and lower envelope lines, namely, uniform distribution is obeyed;
and for the non-rectangular region in the non-rectangular uncertain region, determining the equipment fault probability value corresponding to each boundary line, enabling the voltage sag tolerance curve to be oblique lines near the catastrophe point, taking the probability value determined by the boundary lines as a reference value, and obtaining a quantized value corresponding to the voltage sag event by using the line segment ratio relation of relevant points after determining the sag amplitude value and the curve inclination.
Description of the figures
FIG. 1 is a general flowchart of a voltage sag tolerance testing and data processing method for a sensitive device according to the present invention;
FIG. 2 is a schematic diagram of a non-rectangular tolerance curve in an embodiment of the present invention;
FIG. 3 is a schematic diagram of a duration segment test according to an embodiment of the present invention;
FIG. 4 is a graph illustrating the number of test intervals as a function of slope in accordance with one embodiment of the present invention;
FIG. 5 is a graph of the number of test intervals as a function of slope in one embodiment of the present invention;
FIG. 6 is a PLC tolerance curve envelope based on measured data in an embodiment of the present invention;
FIG. 7 is a flowchart of the extraction of the mutation points on the envelope of the tolerance curve according to an embodiment of the present invention;
FIG. 8 is a graph of a PLC tolerance curve envelope after a polyline process in accordance with an embodiment of the present invention;
fig. 9 is an explanatory diagram of a method for quantizing a non-rectangular uncertainty area of a device according to an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
Detailed inferential analysis methods and exemplary analysis examples are disclosed below. However, the specific reasoning and analysis process details disclosed herein are for purposes of describing example analysis examples only.
It should be understood, however, that the intention is not to limit the invention to the particular exemplary embodiments disclosed, but to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure. Like reference numerals refer to like elements throughout the description of the figures.
As shown in fig. 1, a voltage sag tolerance characteristic testing and data processing method for a sensitive device includes the following steps:
A. setting a sag test point by segmenting the duration and changing the step length;
B. enveloping and folding the equipment tolerance curve;
C. the non-rectangular uncertain region of the device is reasonably and quantitatively described.
In the step A, the step-down duration segment variable-step-size setting test point comprises the following steps:
A1. setting short-time interruption and finding critical endurance time T of equipment0；
A2. Setting a voltage sag
The voltage sag amplitude is set by a bisection method so as to reduce the test times. And for each test time point, changing the voltage amplitude from large to small, and reducing the change range of the voltage amplitude each time to ensure that the equipment fluctuates between action and non-action and gradually approaches the critical withstand voltage until the minimum change interval of the amplitude is reached.
A3. Test duration of T0Critical withstand voltage U of time device0. With reference to the IEEE P1668 test standard, several fixed test time points are selected to test the corresponding threshold withstand voltages. According to T0In relation to the magnitude of the fixed test time point, T0-2 s into three sections: fixed test segment (set to T)22s), coarse test segment (set to T)1～T2) And a fine test segment (set to T)0～T1). Wherein, 0<T0<T1<T2<2 s. The fixed test section is not provided with other test points except the fixed test point, and the rough test section is provided with a step length delta T1＝(T2-T1)/n1Setting a test point, n1The number of the positive integers is preferably 5 to 10. And in the fine test section according to (T)0,U0)、(T1,U1) (let T)0、T1Corresponding to a threshold withstand voltage of U0、U1) The slope between the two points changes the step length to set the test point. Too large or too small of a slope indicates that the curve is close to the vertical or horizontal part, at which time the test step Δ T0Should be large but should not be larger than the step size of the coarse test segment, i.e., Δ T0<ΔT1(ii) a When (T)0,U0)、(T1,U1) When the included angle between the connecting line and the horizontal axis is 45 degrees, the testing step length delta T0Should be minimal. Thus the test step length of the fine section follows (T)0,U0)、(T1,U1) The trend of the increase of the slope between the two should be decreasing and then increasing.
In step B, the enveloping and polygonal processing of the device tolerance curve includes:
B1. equipment tolerance curve enveloping processing
The influence of various factors on the tolerance curve of the equipment is considered, and the factors comprise the characteristics of the voltage sag (such as sag type, sag starting point, phase jump, harmonic distortion, sag pre-event supply voltage and the like) and equipment side factors (such as load level, protection threshold, direct current voltage stabilizing link capacity and the like). Testing the tolerance curves of the equipment under multiple factors, enveloping all the obtained tolerance curves, namely counting the maximum value and the minimum value of the tolerance time under a certain voltage amplitude, and respectively connecting the maximum value and the minimum value of the tolerance time into a line to obtain the upper envelope line and the lower envelope line of the tolerance curves of the equipment.
When the sag duration is longer, the endurance capacity of the device is generally only related to the voltage amplitude and appears as a horizontal edge of an endurance curve; when the sag amplitude is low, the endurance of the device is strongly correlated with the duration, represented by a vertical or near vertical edge of the endurance curve close to the voltage axis (vertical edge for short). However, a transition curve section is often arranged between the horizontal edge and the vertical edge, and the tolerance curve is not completely rectangular, so that slope catastrophe points on the curve need to be extracted before the polyline processing, and only the polyline processing is performed between the catastrophe points. Since the horizontal edge is a straight line and does not need to be broken, the broken line processing should be performed on the transition curve section and the vertical edge (called broken line processing section for short).
B2. Extraction of slope discontinuity points on tolerance curve envelope line
And calculating the slope between every two adjacent points in the broken line processing section on the upper envelope line and the lower envelope line of the tolerance curve. And judging whether the point is a catastrophe point according to the sign and size change relation between any point on the curve and the slopes of the two points before and after the point. In addition, if the ratio of the number M of samples separated between two mutation points to the number M of samples in the broken line processing section is less than a certain range, the mutation points close to the right side of the time axis are removed.
B3. Linear fitting of sample points between adjacent mutation points
In order to establish a mathematical model of the sag sensitivity of the equipment, the envelope curve needs to be subjected to a line folding process. And fitting a straight line between two adjacent abrupt change points according to the abrupt change points extracted in the step B2 to approximately describe the tolerance characteristic of the equipment. The straight line between all sample points between the discontinuities and whose sum of distances is the minimum is the solution, which is essentially a least squares fit. Is { (T)j,Uj) And j is 1,2 …, m (the number of sample points between two adjacent mutation points is m) is taken as a sample data point, and a function S (T) is calculatedj)＝a0+a1T(a0、a1Is a parameter to be solved, and a1Not equal to 0. ) So that the sum of squared errors is minimized as shown in equation (1). Converting the function into a function I (a) for solving the formula (2)0,a1) The minimum value of (a).
The function I (a)0,a1) At its extreme point with respect to a0、a1The partial derivative of (a) is equal to 0, as shown in equation (3).
Can deduce a0、a1The expression of (2) is shown in formula (4).
C. A reasonable quantitative description of the non-rectangular uncertainty region of the device includes:
C1. dividing a non-rectangular uncertain region of the equipment into regions:
after the sag tolerance curve of the equipment is enveloped, the upper envelope line and the lower envelope line divide the whole VTC plane into three types, namely, the inner side of the lower envelope line is a fault area determined by the equipment, the outer side of the upper envelope line is a non-fault area determined by the equipment, and the area between the upper envelope line and the lower envelope line is an uncertain area of the running state of the equipment. For an uncertain region, the early sag test finds that the variation range of sag tolerance capability of a typical device is approximately rectangular, and is divided into three parts, namely, only relevant to duration, only relevant to sag amplitude, and relevant to both sag amplitude and duration according to the correlation between amplitude and time in the quantitative description process. However, with the technology upgrade and performance improvement, the sag tolerance characteristics of the typical equipment are affected, and the uncertain region of the sag tolerance capability is in a non-rectangular shape. If the influence degree of the equipment is quantified by adopting the dividing method, a quantification result which accords with the actual sag tolerance of the equipment is difficult to obtain. Therefore, it is proposed that the non-rectangular uncertainty region is divided into two parts, namely a rectangular region and a non-rectangular region in the horizontal axis direction, the probability values corresponding to the upper and lower envelope lines are determined, and the boundary lines of the vertical axis of the rectangular region are uniformly distributed to obtain the determined values. The method has the advantages that when the quantitative description of the non-rectangular uncertain region is carried out, a reference value can be found, and the complexity can be greatly simplified.
C2. Quantitative description of non-rectangular-shaped uncertainty regions
On a VTC plane, the outer side area of an upper envelope line of a device sag tolerance curve is a device determined non-failure area, and the device failure probability is determined to be 0; the inner side of the lower envelope line determines a fault area for equipment, and the fault probability of the equipment is determined to be 1; the area between the upper envelope line and the lower envelope line is an uncertain area of the running state of the equipment, the probability distribution of the equipment faults is between 0 and 1, the sag events fall on different positions in the uncertain area, and the corresponding equipment fault probabilities are different. Based on step C1, the rectangular-shaped region in the horizontal axis direction in the non-rectangular-shaped uncertainty region is associated with only the amplitude value, and its upper and lower envelope probability values are determined. For the influence degree of the voltage sag event falling in the region, the influence degree can be measured by the proportion of the sag amplitude value to the corresponding amplitude interval of the upper envelope line and the lower envelope line, namely uniform distribution is obeyed.
And for the non-rectangular areas in the non-rectangular uncertain areas, determining the equipment fault probability values corresponding to the boundary lines. The voltage sag tolerance curve of the current typical device is no longer horizontal and vertical, but is inclined near a curve abrupt point, and the voltage sag tolerance curve represents that the sag tolerance capacity of the device changes along with the change of the sag amplitude and duration. In order to quantify the influence degree of the voltage sag on the running state of the equipment more accurately, the probability value determined by the boundary line is used as a reference value, and after the sag amplitude and the curve inclination are determined, the quantitative value corresponding to the voltage sag event is obtained by utilizing the line segment ratio relation of relevant points.
The process of the present invention is described below in one embodiment. A voltage sag tolerance characteristic testing and data processing method for sensitive equipment comprises the following steps:
A. setting a sag test point by segmenting the duration and changing the step length;
B. enveloping and folding the tolerance curve of the equipment;
C. the non-rectangular uncertain region of the device is reasonably and quantitatively described.
In general, the tolerance curve of the device is not completely rectangular, as shown in fig. 2, with a transition curve segment AB. The test should be refined in the transition part of the curve, so that the coordinates of the two points need to be determined A, B first. The abscissa T of the point A can be tested by setting a short-time interrupt0Resetting the duration to T0The voltage sag of the point A is tested to obtain a vertical coordinate U of the point A0(ii) a And because the horizontal edge of the tolerance curve and the transition part have no definite demarcation point, the B point is difficult to be accurately obtained through twice tests, so that a fixed B point can be set, the AB section is subjected to a more precise test, and the adjacent section of the AB section is subjected to a more rough test, so that the tolerance curve of the equipment can be tested more completely and the test times are saved.
A1. Setting a short-time interrupt, setting the voltage amplitude to be 0p.u., and finding the critical endurance time T of the equipment from small increase of the duration0；
A2. Setting a voltage sag
The voltage sag amplitude is set by a bisection method so as to reduce the test times. And for each test time point, the test starting point of the corresponding voltage amplitude is 0.7p.u., the voltage amplitude is changed from large to small, the change range of the voltage amplitude is narrowed every time, the equipment fluctuates between action and non-action, the critical withstand voltage is gradually approached until the minimum change interval of the amplitude is reached, and the minimum interval can be 0.01 p.u..
Test duration of T0Critical withstand voltage U of time device0. Referring to IEEE P1668 test standard, selecting 0.1s, 0.5s, 1s and 2s as fixed test time points, and testing corresponding critical withstand voltage U0.1s、U0.5s、U1s、U2s. According to T0In relation to the magnitude of the fixed test time point, T0-2 s into three sections: fixed test segment (set to T)22s), coarse test segment (set to T)1～T2) And a fine test segment (set to T)0～T1). The following cases are distinguished:
1)T0<at 0.1s, T00.1s is the fine test segment, i.e. T1＝0.1s，U1＝U0.1sThe step size is according to (T)0,U0)、(T1,U1) The slope between them is determined, but its maximum value should not be greater than the step size of the coarse test segment; 0.1 s-0.5 s is a rough test segment, i.e. T2When n is 0.5s, n may be selected1Step size Δ T, 51＝(T2-T1)/n1(ii) a 0.5 s-2 s are fixed test sections, and other test points are not selected to test except the fixed test points.
2)0.1s<T0<At 0.5s, T00.5s is the fine test segment, i.e. T1＝0.5s，U1＝U0.5sThe step size is according to (T)0,U0)、(T1,U1) The slope between them is determined, but its maximum value should not be greater than the step size of the coarse test segment; 0.5 s-1 s is a rough test segment, i.e. T21s, and its step length Delta T is taken1＝(T2-T1)/n1(ii) a And 1 s-2 s are fixed test sections, and other test points are not selected for testing.
3)0.5s<T0<1s, T01s is a fine test segment, i.e. T1＝1s，U1＝U1sThe step size is according to (T)0,U0)、(T1,U1) The slope between them is determined, but its maximum value should not be greater than the step size of the coarse test segment; 1 s-2 s are rough test segments, i.e. T22s, the step size Δ T may be taken1＝(T2-T1)/n1(ii) a There is no fixed test segment at this time.
4)1s<T0<At 2s, T02s is a fine test segment, i.e. T1＝2s，U1＝U2sThe step size is according to (T)0,U0)、(T1,U1) Determining the slope of the sample; there is no coarse test segment and no fixed test segment.
FIG. 3 is a schematic of duration segment testing, wherein fine, coarse and fixed test segments are denoted as "fine", "coarse" and "fixed", T0The first serial numbers (i), (ii), (iii), and (iv) represent the above 4 cases, respectively.
Base in fine test section (T)0,U0)、(T1,U1) Slope k (k ═ U) between1-U0)/(T1-T0) Change step set test point. Let the step size of the fine test segment be Δ T0＝(T1-T0) N is the number of intervals, and n is more than or equal to n1The maximum value n of n can be takenmaxIs n1Twice if n is taken1When n is 5, nmaxThe test point of the fine test section is controlled to be 5-10 times. Too large or too small of a slope indicates that the curve is close to the vertical or horizontal part, and the number of test intervals n should be small, and when (T)0,U0)、(T1,U1) The test interval n should be larger when the included angle between the connecting line and the horizontal axis is 45 degrees. Therefore, the trend of n of the fine segment with increasing k should be increasing and then decreasing, and can be described by a function with a large middle and a small two ends as shown in fig. 4. When k is 1, (T)0,U0) And (T)1,U1) The angle between the connecting line and the horizontal axis is 45 degrees, and the step length should be minimum at the moment, namely n is maximum, n ismax10; when k is 0 or k → ∞, the step size should be maximum, i.e. n is minimum, nmin＝n 15. Since n is a positive integer and the difference between the maximum value and the minimum value is not large, if the change rule of the maximum value and the minimum value along with the slope is described by a curve with a large curvature, the difference between the result described by rounding n and a straight line is small, and therefore, a linear rule (y ═ cx + d) can be adopted to establish k ∈ [0,1 ∈]The functional relationship between k and n. And when k → ∞ n tends to be a constant (i.e. n)1) If the linear relationship is used, it is not reasonable to describe the relationship, so that an exponential function (y ═ exp (λ) is considered1x+λ2)+λ3) A description will be given.
From the above analysis, a functional relation between the slope k and n can be obtained, as shown in equation (5), and the functional graph is shown in fig. 5. Wherein lambda of the exponential function is taken1The curve with a relatively close linear trend is obtained by the method of 0.1.
In the step B, the enveloping and polygonal line processing of the device tolerance curve specifically includes:
B1. device tolerant curve envelopment processing
Testing the tolerance curves of the equipment under multiple factors, enveloping all the obtained tolerance curves, namely counting the maximum value and the minimum value of the tolerance time under a certain voltage amplitude, and respectively connecting the maximum value and the minimum value of the tolerance time into a line to obtain the upper envelope line and the lower envelope line of the tolerance curves of the equipment. FIG. 6 is the upper and lower envelope curves of PLC tolerance curves under various factors.
B2. Extraction of slope discontinuity points on tolerance curve envelope line
And calculating the slope between every two adjacent points in the broken line processing section on the upper envelope line and the lower envelope line of the tolerance curve. Let any point be { (T)i,Ui) I is 2,3 …, p, and there are p points on the envelope. Comparison (T)i,Ui) Two points (T) in front and at the backi-1,Ui-1)、(Ti+1,Ui+1) Whether the signs of the slopes between are the same or not, let ki＝(Ui-Ui-1)/(Ti-Ti-1) I.e. determine ki×ki+1Whether greater than 0. If k isi×ki+1<0, then (T)i,Ui) Is a mutation point; if k isi×ki+1When the value is 0, (T)i,Ui) If the point is not a mutation point, i is i +1, and whether the next point is a mutation point is continuously judged; if k isi×ki+1>0, judging whether the relative change rate Δ k of the slope (shown in the formula (6)) exceeds a certain value (10% is set) or not: if Δ k>Then (T)i,Ui) And (4) judging whether the next point is a mutation point or not, otherwise, judging whether the next point is the mutation point or not if the point is i + 1. The determination process is shown in fig. 7. In addition, if the ratio of the number M of samples separated between two mutation points to the total number M of samples in the broken line processing section is less than a certain range (such as 20-25%), the mutation points close to the right side of the time axis are removed. As shown in FIG. 8, the discontinuity A of the envelope on the PLC can be extracted1、B1、C1And the discontinuity A of the lower envelope2、B2、C2、D2。
B3. Linear fitting of sample points between adjacent mutation points
And B2, fitting a straight line between two adjacent mutation points by using a least square method according to the extracted mutation points to approximately describe the tolerance characteristic of the equipment. Is { (T)j,Uj) J-0, 1,2 …, m is the sample data point, and the function S (T) is calculatedj)＝a0+a1T(a0、a1Is a parameter to be solved, and a1Not equal to 0) so that the sum of squared errors is minimized, as shown in equation (7). It is converted into a function I (a) for solving the equation (8)0,a1) The minimum value of (a).
The function I (a)0,a1) At its extreme point with respect to a0、a1The partial derivative of (a) is equal to 0, as shown in equation (9).
Can deduce a0、a1The expression of (2) is shown in formula (10).
The solid line in fig. 8 is the envelope of the endurance curve after being broken.
In the step C, reasonably and quantitatively describing the non-rectangular uncertain region of the equipment, specifically comprising the following steps:
C1. dividing a non-rectangular uncertain region of the equipment into regions:
in fig. 9, after crossing the lower envelope mutation point H with the upper envelope at point G, the boundary line HG divides the entire uncertainty region into a rectangular region B (right region of HG) and a non-rectangular region a (cdefghic). The division basis is that the region B is only related to the amplitude, the quantitative description obeys uniform distribution, and the voltage sag event quantitative description falling on the boundary line HG at the moment can be determined according to the proportional relation between the position of the voltage sag event quantitative description and the sag amplitude section; the device fault probability values represented by the boundary lines DEFG, GH and HIC of the area A are all determined values, and can provide reference values for quantitative description by adopting a line segment ratio algorithm.
C2. Quantitative description of uncertain region:
in FIG. 9, assume that a voltage sag event i is available (T)i,Ui) Indicates that the upper and lower inflection points of the curve are available (T) within the rectangular region Bmin,Tmax)、(Umin,Umax) Indicates that the sag event causes a device failure probability p(i)Can be represented by formula (11):
from this, the device failure probabilities represented by the upper envelope point G and the lower envelope point H are p(G)＝0、p(H)When HG segments are divided into 7 segments, point N is set to 10The corresponding equipment failure probability is
For voltage sag event points N (T, U) falling in the non-rectangular area A, intersecting line segments HG and EF at the points N respectively by using N as time axis parallel lines0(T0,U0)，N1(T1,U1)，U＝U0＝U1. Because the uncertain region of the equipment sag tolerance capacity is obtained based on a large amount of experimental data, the coordinate values of curve mutation points such as E, F, H, I are known, and then the inclined line L is formedEF、LHIThe functional relationship may be determined. Is not provided with LEFThe slope is k, UmFor the intercept, the sag value u is expressed in relation to the time t as follows:
u＝kt+Um(12)
then, at known event N1Temporarily decreasing amplitude value U1Then, T can be determined from equation (12)1The value is obtained.
With N0The point probability value is the reference value and falls into the line segment N0N1The upper voltage sag event point N can be quantitatively described by equation (13).
When the voltage sag event point N falls in different positions of the area A0In the case of a variation in the HG section,
the value can be determined by equation (11), i.e.
When point N0In the event of a change in the HIC zone,
the value being constant, i.e.
The voltage sag tolerance characteristic testing and data processing method for the sensitive equipment has the main advantages that the sag duration time is set in a sectional variable step length mode, the density of the test points is increased in the transition part of the tolerance curve to ensure that the obtained tolerance curve is finer, the test times are not too many, and the sparse and dense degree distribution of the test points is more reasonable; testing under various influence factors to obtain a large number of tolerance curves, enveloping the tolerance curves, and performing broken line processing on the envelope curve by using a least square method, so that a mathematical model is conveniently established; the non-rectangular uncertain regions with typical equipment sag tolerance capacity are subjected to regional processing, and then different quantitative description methods are adopted for different regions, so that the influence degree of voltage sag on the equipment is quantized, and the method is concise and clear and has better universality.
The voltage sag tolerance characteristic testing and data processing method for the sensitive equipment can provide a reasonable testing method and a simple and convenient data processing method for power grids, governing manufacturers and sensitive equipment users, is suitable for fine testing of a single tolerance curve, is suitable for building a comprehensive model of a large number of tolerance curves, and can be applied to voltage sag tolerance analysis of general sensitive equipment.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and should not be construed as limiting the scope of the present invention, and any minor changes and modifications to the present invention are within the scope of the present invention without departing from the spirit of the present invention.
Claims (7)
1. A voltage sag tolerance characteristic testing and data processing method for sensitive equipment comprises the following steps:
A. setting the sag duration time segment variable step length to sag test points;
B. enveloping and folding the equipment tolerance curve;
B1. equipment tolerance curve enveloping processing
Counting the maximum value and the minimum value of the tolerance time under a certain voltage amplitude, and respectively connecting the maximum value and the minimum value of the tolerance time into a line to obtain the upper envelope line and the lower envelope line of the tolerance curve of the equipment;
B2. extracting slope catastrophe points on tolerance curve envelope line
Calculating a broken line processing section, namely a transition curve section connecting a horizontal edge and a vertical edge of the tolerance curve and the slope between every two adjacent points in the vertical edge, and judging whether the broken line processing section is a catastrophe point according to the sign and size change relationship of any point on the curve and the slopes of the two points before and after the point;
B3. linear fitting of sample points between adjacent mutation points
According to the mutation points extracted in the step B2, fitting a straight line between two adjacent mutation points by utilizing least square fitting to approximately describe the tolerance characteristic of the equipment, wherein the straight line with the minimum sum of the distances from all sample points among the mutation points is the required straight line; is { (T)j,Uj) J is 1,2 …, m is a sample data point, m is a sample point number between two adjacent mutation points, and the function S (T) is calculatedj)＝a0+a1T，a0、a1Is a parameter to be solved, and a1Not equal to 0, so as to minimize the sum of squared errors, as shown in equation (1), and converting it into solving the function I (a) shown in equation (2)0,a1) The minimum value of (a) is,
the function I (a)0,a1) At its extreme point with respect to a0、a1Is equal to 0, represented by the formula (3)
Can deduce a0、a1The expression (4) of (a),
C. quantitatively describing a non-rectangular uncertain region of the equipment sag tolerance capacity;
the rectangular area in the transverse axis direction in the non-rectangular uncertain area is only related to amplitude values, the probability values of upper and lower envelope lines are determined, and the influence degree of the voltage sag event falling in the area can be measured by the proportion of the sag amplitude value to the corresponding amplitude value interval of the upper and lower envelope lines, namely, uniform distribution is obeyed;
and for the non-rectangular region in the non-rectangular uncertain region, determining the equipment fault probability value corresponding to each boundary line, enabling the voltage sag tolerance curve to be oblique lines near the catastrophe point, taking the probability value determined by the boundary lines as a reference value, and obtaining a quantized value corresponding to the voltage sag event by using the line segment ratio relation of relevant points after determining the sag amplitude value and the curve inclination.
2. The method for testing and processing the voltage sag tolerance characteristic of the sensitive equipment according to claim 1, wherein the step A comprises the following steps:
A1. setting short-time interruption and finding critical endurance time T of equipment0；
A2. Setting a voltage sag amplitude by adopting a bisection method;
A3. test duration of T0Critical withstand voltage U of time device0Selecting a fixed test time point, testing the corresponding critical withstand voltage according to T0In relation to the magnitude of the fixed test time point, T0-2 s into three sections: fixed test section T22s, coarse test segment T1～T2And a fine test section T0～T1Wherein, 0<T0<T1<T2<2 s; the fixed test section is not provided with other test points except the fixed test points; by step Δ T in the coarse test section1＝(T2-T1)/n1Setting a test point, n1Is a positive integer; base in fine test section (T)0,U0)、(T1,U1) The slope between the two points changes the step length to set the test point.
3. The method as claimed in claim 2, wherein the fine test section is based on (T)0,U0)、(T1,U1) The slope k of two-point calculation changes the step length to set the test point, k ═ U1-U0)/(T1-T0) When the slope is greater than 1 or less than 1, the test step length delta T0Should be increased, but not greater than the step size of the coarse test segment, Δ T0<ΔT1(ii) a When (T)0,U0)、(T1,U1) When the included angle between the connecting line and the horizontal axis is 45 degrees, namely the slope is equal to 1, the testing step length delta T0And minimum.
4. The method for voltage sag tolerance characteristic testing and data processing of sensitive equipment according to claim 2, wherein n is15 to 10.
5. The method for testing and processing voltage sag tolerance characteristics of sensitive equipment according to claim 1, wherein the method for determining the mutation point in the step B1 comprises the following steps: let any point be { (T)i,Ui) I is 2,3 …, p, and p points are set on the envelope line in total for comparison (T)i,Ui) Two points (T) in front and at the backi-1,Ui-1)、(Ti+1,Ui+1) Whether the signs of the slopes between them are the same or not is setki＝(Ui-Ui-1)/(Ti-Ti-1) I.e. determine ki×ki+1Whether greater than 0; if k isi×ki+1<0, then (T)i,Ui) Is a mutation point; if k isi×ki+1When the value is 0, (T)i,Ui) If the point is not a mutation point, i is i +1, and whether the next point is a mutation point is continuously judged; if k isi×ki+1>0, judging whether the relative change rate delta k of the slope shown in the formula (5) exceeds a certain value; if Δ k>Then (T)i,Ui) If the point is a mutation point, otherwise, if i is i +1, continuously judging whether the next point is a mutation point,
6. the method according to claim 5, wherein the voltage sag tolerance characteristic of the sensitive device is 10%.
7. The method as claimed in claim 5, wherein the discontinuities are removed if the ratio of the number M of samples separated between two discontinuities to the total number M of samples in the polygonal line processing section is less than 20% -25%.
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| CN110672951B (en) * | 2019-10-10 | 2021-08-03 | 国网电力科学研究院(武汉)能效测评有限公司 | Method and device for identifying voltage fragile region of power distribution network |
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