CN117420344A - Voltage sag characteristic calculation method based on goodness-of-fit test - Google Patents

Voltage sag characteristic calculation method based on goodness-of-fit test Download PDF

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Publication number
CN117420344A
CN117420344A CN202311371417.4A CN202311371417A CN117420344A CN 117420344 A CN117420344 A CN 117420344A CN 202311371417 A CN202311371417 A CN 202311371417A CN 117420344 A CN117420344 A CN 117420344A
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voltage
voltage sag
point
calculating
sag
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杨帆
胡伟
蔡勇
沈煜
杨志淳
董明齐
雷杨
陈鹤冲
胡成奕
闵怀东
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State Grid Hubei Electric Power Co Ltd
Electric Power Research Institute of State Grid Hubei Electric Power Co Ltd
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State Grid Hubei Electric Power Co Ltd
Electric Power Research Institute of State Grid Hubei Electric Power Co Ltd
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Priority to CN202311371417.4A priority Critical patent/CN117420344A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/04—Measuring peak values or amplitude or envelope of ac or of pulses
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R25/00—Arrangements for measuring phase angle between a voltage and a current or between voltages or currents

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention provides a voltage sag characteristic calculation method based on a goodness-of-fit test, which comprises the following steps: sliding the reference window and the detection window rightward by taking one sampling point as a step length, and calculating fitting goodness test statistics between the two windows so as to detect a transition section of voltage sag; calculating a voltage sag type based on the number of detected transition sections; calculating a starting point and an ending point of the voltage sag based on the transition section, and obtaining the duration time of the voltage sag; calculating phase angles of a starting point and an ending point according to the obtained starting point and ending point of the voltage sag, taking a sampling point with a fundamental wave voltage zero crossing point and a derivative being positive as a reference, and determining a voltage sag waveform point; in the phase angle calculation process, the transition section is excluded to avoid calculation artifacts generated by the transition section, and the phase jump of the voltage sag is obtained. Compared with the prior art, the method and the device can realize the single event feature of once calculating the voltage sag, and improve the calculation efficiency of the power quality monitoring equipment.

Description

Voltage sag characteristic calculation method based on goodness-of-fit test
Technical Field
The invention relates to the field of power systems, in particular to a voltage sag characteristic calculation method based on fitting goodness test.
Background
Residual voltage, duration, dip type, waveform point, phase jump are five typical single event features of voltage dips that can affect the proper operation of many sensitive devices. Accurate calculation of voltage sag single event characteristics is critical to accurately compensating for voltage sag in a power system or a user. The residual voltage is considered as the lowest value of the three-phase voltage effective value in the voltage sag process, and is easy to calculate, so the invention is not discussed. Furthermore, with the development of new power systems, distributed power sources may be off-grid due to short circuit faults, resulting in more complex multi-stage voltage sags. The multi-stage voltage sag presents new basic characteristics compared with the traditional rectangular voltage sag, and the calculation of single event characteristics such as the sag type is influenced.
At present, some researches are carried out on the calculation method of each characteristic of the voltage sag at home and abroad, such as calculating the voltage sag type based on three-phase voltage symmetry; calculating duration based on a valid value thresholding method; calculating waveform points based on a time domain analysis method, a frequency domain analysis method and a time-frequency combination analysis method; phase jumps are calculated based on the delta voltage quantities, etc. However, there is no unified and systematic method for calculating the single event characteristics of the voltage sag, and it is difficult for the existing method to calculate the single event characteristics of the multi-stage voltage sag in the context of the novel power system. In an electric power system, the electric energy quality monitoring device needs to adopt a plurality of different methods to calculate different voltage sag characteristics, so that one voltage sag needs to be calculated for a plurality of times, and memory occupation and calculation time are more. Therefore, in practical engineering applications, a method capable of calculating all these characteristics and compatible with the multi-stage voltage sag in the context of a novel power system needs to be proposed, so as to improve the calculation efficiency of the power quality monitoring device.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a voltage sag characteristic calculation method based on a goodness-of-fit test.
The aim of the invention can be achieved by the following technical scheme:
a voltage sag characteristic calculation method based on a goodness-of-fit test comprises the following steps:
sliding the reference window and the detection window rightward by taking one sampling point as a step length at the same time, and calculating the fitting goodness-of-fit test statistic between the two windowsThereby detecting a transition segment of the voltage sag;
calculating a voltage sag type based on the number of detected transition sections;
calculating a starting point and an ending point of the voltage sag based on the transition section, and obtaining the duration time of the voltage sag;
calculating phase angles of a starting point and an ending point according to the obtained starting point and ending point of the voltage sag, taking a sampling point with a fundamental wave voltage zero crossing point and a derivative being positive as a reference, and determining a voltage sag waveform point;
in the phase angle calculation process, the transition section is excluded to avoid calculation artifacts generated by the transition section, and the phase jump of the voltage sag is obtained.
Further, the definitions of the reference window and the detection window specifically include:
the data in the reference window is used as the reference of the transition section of the impending voltage sag, the probability distribution corresponding to the composed vector is the steady-state voltage or the fluctuation of the voltage due to noise in the sag process, and the probability distribution is regarded as the target probability distribution; the detection window is adjacent to the reference window, and the length of the detection window is the same as that of the reference window, so that the detection window is a working window for fitting goodness-of-fit detection.
Further, the calculation of the goodness-of-fit test statistic between two windowsThereby detecting a transition of the voltage dip, comprising: calculating a goodness-of-fit test statistic between the two windows using a chi-square test in the goodness-of-fit test>Test statistic +.>Will exceed the critical value +.>
Further, the calculating the voltage sag type based on the detected number of transition sections specifically includes: when only one transition is detected, the voltage sag is classified as a slow recovery voltage sag; when two transition sections are detected, the voltage sag is classified as a rectangular voltage sag; a voltage dip is considered a multi-stage voltage dip when it has three or more transitions.
Further, the calculating the starting point and the ending point of the voltage dip based on the transition section, to obtain the duration of the voltage dip specifically includes: the actual duration of the voltage dip is the time interval from the start point to the end point, after the transition section is detected, the rectangular voltage dip start point is the first sampling point of the first transition section, and the end point is the first sampling point of the second transition section; the starting point of the multi-stage voltage sag is the first sampling point of the first transition section, and the ending point is the first sampling point of the last transition section; the starting point of the slow recovery voltage sag is the first sampling point of the transition section, and the ending time is the time when the effective value voltage is recovered to 0.9p.u.
Further, the phase angles of a starting point and an ending point are calculated by taking a sampling point with a zero crossing point and a positive derivative of the fundamental voltage as a reference, wherein for rectangular voltage sag and multi-stage voltage sag, the moments corresponding to the starting point and the ending point can be calculated through the detected transition section; for slow recovery voltage sag, there is no waveform end point parameter and only waveform start point parameter, since there is no fault clearing instant.
Further, in the phase angle calculation process, the transition section is excluded to avoid calculation artifact generated by the transition section, so as to obtain phase jump of voltage sag, which specifically includes: for voltage sag caused by common faults, excluding a transition section, and enabling the phase jump to be the maximum absolute value of a phase angle measured by any phase of the three-phase voltage in the sag event process; for the multi-stage voltage sag caused by the multi-stage fault, since no evidence indicates that the phase jump of the second stage can affect the sensitive equipment, the phase jump of the first stage of the multi-stage voltage sag is taken as the phase jump parameter.
Compared with the prior art, the invention has the following beneficial effects:
1. the voltage sag characteristic calculating method based on the goodness-of-fit test solves the problems that one voltage sag needs to be calculated for many times and memory occupation and calculation time are high due to the fact that the power quality monitoring device needs to adopt various different methods to calculate different characteristics of the voltage sag, achieves one-time calculation of all single event characteristics of the voltage sag, and improves the calculation efficiency of power quality monitoring equipment.
2. The voltage sag characteristic calculation method based on the goodness-of-fit test provided by the invention is compatible with multi-stage voltage sag under the background of a novel power system on the basis of being capable of accurately calculating the single event characteristic of the traditional rectangular voltage sag.
Drawings
FIG. 1 is a schematic flow chart of a voltage sag characteristic calculation method based on a goodness-of-fit test according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a reference window and a detection window in a goodness-of-fit test;
FIG. 3 is a schematic diagram illustrating a measured voltage sag transition detection;
FIG. 4 is a schematic diagram of a measured multi-stage voltage sag waveform;
FIG. 5 is a schematic diagram of a measured slow recovery voltage sag waveform;
FIG. 6 is a schematic diagram of voltage sag duration calculation;
FIG. 7 is a schematic diagram of a phase angle calculation method;
FIG. 8 is a schematic diagram of a phase jump calculation method;
fig. 9 is a schematic diagram of a phase jump of a multi-stage voltage dip.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The embodiment of the invention provides a synchronous phasor measurement method based on a dynamic window length, which is shown in fig. 1 and comprises the following steps:
step S1, sliding a reference window and a detection window rightward by taking one sampling point as a step length at the same time, and calculating fitting goodness test statistics between the two windowsThereby detecting a voltage dipAnd a transition section.
In this embodiment, the data in the reference window is used as a reference of the transition section of the voltage sag that is about to occur, the probability distribution corresponding to the composed vector is the steady-state voltage or the fluctuation of the voltage due to noise in the sag process, and is regarded as the target probability distribution; the detection window is adjacent to the reference window, the length of the detection window is the same as that of the reference window, and the detection window is a working window for fitting goodness-of-fit detection, and the specific definition of the detection window is as follows.
W ref ＝{v(n)|(1≤n≤m)} (1)
W in the formula ref V (n) is a voltage instantaneous value, m is a reference window length, and m is the number of sampling points included in one period of the instantaneous value sampling signal, so that elements in the reference window can be in one-to-one correspondence with elements in a detection window defined below.
W det ＝{v(n)|(m+1≤n≤2m)} (2)
W in the formula det For the detection window v (n) is the instantaneous value of the voltage and m is the detection window length. A schematic diagram of the reference window and the detection window is shown in fig. 2.
In the detection of a voltage dip, a detection window W det The ith element W in (2) det (i) The observation frequency corresponding to the ith sampling point in the goodness-of-fit test, the reference window W ref W in (2) ref (i) Corresponding to the expected frequency of the ith sampling point in the goodness-of-fit test, there are:
wherein,for the goodness-of-fit test statistic in voltage sag detection, m is the number of sampling points contained in one sampling period of the sampled waveform, W det (i) Is a detection window W det The ith data, W ref (i) Is a reference window W ref I-th data of (a) in the database.
The reference window and the detection window are used as step sizes to the right at the same time by taking one sampling point as step sizeSliding while calculating goodness-of-fit test statistics between two windowsThereby detecting a transition of the voltage dip. Test statistic +.>Will exceed the critical value +.>Detection of the transition segment is achieved as shown in fig. 3.
FIG. 3 (a) shows an instantaneous voltage waveform of certain measured voltage sag data, wherein a solid line represents an instantaneous voltage in a steady state phase and a dotted line represents an instantaneous voltage during a sag; FIG. 3 (b) shows the trend of the goodness-of-fit test statistic for the measured voltage dip, where the solid line represents below the thresholdTest statistics of->The dashed line of the hatched area represents an excess of the critical value +.>Test statistics of->Test statistics->Does not exceed the critical value->Part of (2) corresponds to the steady-state voltage or the voltage during the voltage dip, and the test statistic +.>Exceeding the critical value->Corresponds to the transition voltage, and corresponds to the solid line portion and the broken line portion in the hatching of the voltage effective value waveform in fig. 3 (c), respectively.
And step S2, calculating the voltage sag type based on the number of the detected transition sections.
When a short circuit fault occurs in the power system, in most cases, the fault is cleared in a short time due to the relay protection device, and a rectangular voltage dip is formed, as shown in fig. 3 (a) and 3 (c). For this type of voltage dip, there are two transitions of the effective value voltage corresponding to the occurrence and clearing of a fault, respectively.
When a parameter of the power system changes during a short circuit fault, such as a protection relay isolation fault or the fault develops to another stage before being cleared, a multi-stage voltage sag may result, as shown in fig. 4. In fig. 4 (a) is a waveform of instantaneous value of a measured multi-stage voltage dip, wherein the steady-state voltage is marked as a solid line, the first stage voltage of the voltage dip event is marked as a dash-dot line, and the second stage voltage of the voltage dip is marked as a dashed line. In fig. 4 (b) is the effective voltage value of the measured multi-stage voltage dip having three transitions. For this type of voltage dip, there are more than two transitions in its effective value voltage. The first transition corresponds to the occurrence of a short circuit fault and the last transition corresponds to the clearing of the fault. The remaining transitions correspond to changes in power system parameters or the development of faults.
Slow recovery voltage sag refers to the event of a sudden drop in voltage caused by a large current generated by the excitation of an empty transformer or the start of a large induction motor. For this type of dip, the recovery process of the voltage is a slow process, rather than a step change. Thus, the slow recovery voltage dip has only one transition, as shown in fig. 5. The effective voltage value for the measured slow recovery voltage dip is shown in fig. 5, which is consistent with the above analysis, with only one transition segment. Since this type of voltage dip has no definite fault clearing moment, its waveform point parameter has only a starting point and no ending point. Moreover, the occurrence of the slow recovery voltage drop is not dependent on the change of the grid structure, so the slow recovery voltage dip has no phase jump characteristic.
From the above analysis, the voltage sag type can be calculated from the detected transition, as follows
The following is shown:
wherein N is T Is the number of voltage drop transitions. When only one transition is detected, the voltage drop is classified as a slow recovery voltage dip; when two transition sections are detected, the voltage sag is classified as a rectangular voltage sag; a voltage dip is considered a multi-stage voltage dip when it has three or more transitions.
And step S3, calculating a starting point and an ending point of the voltage sag based on the transition section, and obtaining the duration time of the voltage sag.
The actual duration of the voltage dip is the time interval from the start point to the end point. After detecting the transition, the duration of the different types of voltage dips can be calculated as follows:
1) Rectangular voltage sag (N) T =2). For a rectangular voltage dip, the starting point is the first sample point of the first transition and the ending point is the first sample point of the second transition, as shown in fig. 6 (a). The duration is the time interval between the start point and the end point, as shown in the following equation:
T＝t r -t i (5)
wherein T is the duration of the voltage sag, T r T is the time corresponding to the end point i The time corresponding to the starting point is the starting point.
2) Multi-stage voltage sag (N) T >2). For a multi-stage voltage sag, the starting point is the first
The first sample point of one transition, the end point is the first sample point of the last transition, as shown in fig. 6 (b). The duration is the time interval between the start point and the end point, calculated by equation (5).
3) Slow recovery type (N) T =1). For a slow recovery voltage dip, since there is no fault clearing instant, the present invention defines the end time of this type of voltage dip as the time at which the effective value voltage is recovered to 0.9p.u., the starting point is the first sampling point of the transition section, as shown in fig. 6 (c). The duration is the time interval between the start point and the end point, calculated by equation (5).
And S4, calculating phase angles of the starting point and the ending point according to the obtained starting point and the ending point of the voltage sag, taking the sampling point with the zero crossing point and the positive derivative of the fundamental wave voltage as a reference, and determining the waveform point of the voltage sag.
The start point and end point of the waveform point are two parameters related to the occurrence and clearing of the fault. The determination of the time at which the fault occurs (the sampling point number corresponding to the start point) and the time at which the fault clears (the sampling point number corresponding to the end point) are key to calculating the waveform points. After the two moments are acquired, the phase angles of a starting point and an ending point are calculated by taking a sampling point of which the fundamental voltage passes through a zero crossing point and the derivative is positive as a reference,
a method of calculating the phase angles of the start point and the end point by crossing the zero upward will be described first with reference to fig. 7. The leftmost black point in the figure is the reference point for the starting point, the phase angle of which is considered to be 0 °. Based on the reference point, the phase angle of the starting point is calculated as 90 °; similarly, the right-most black point in the figure is the reference point for the end point, and the phase angle of this point is considered to be 0 °. Based on the reference point, the phase angle of the end point is calculated to be 180 °.
Then, for different types of dip, the waveform point characteristic calculation steps are as follows:
1) Rectangular voltage sag/multi-stage voltage sag (N) T 2). For rectangular voltage sag and multi-stage voltage sag, the moments corresponding to the start point and the end point can be calculated by the detected transition section. Thus (2)For both types of dips, the waveform start point and the waveform end point in the waveform points can be calculated according to equations (6) and (7).
POW-I＝Angle(t i ) (6)
POW-R＝Angle(t r ) (7)
Wherein POW-I is the waveform starting point in the waveform points, POW-R is the waveform ending point in the waveform points, angle is the phase Angle calculation method shown in FIG. 7, t i For the corresponding moment of the starting point, t r Corresponding to the ending point.
2) Slow recovery voltage sag (N) T =1). For a slow recovery voltage dip, there is no waveform end point parameter since there is no fault clearing instant. The waveform starting point parameters can be calculated according to the formula (6). As previously mentioned, the starting moment can be calculated from the detected transition piece.
And S5, in the phase angle calculation process, excluding the transition section to avoid calculation artifacts generated by the transition section, and obtaining the phase jump of the voltage sag.
The most important task of phase jump calculation is to exclude the transition segment to avoid calculation artifacts generated at the transition segment during the phase angle calculation. Fig. 8 illustrates calculation artifacts that may occur during the phase jump calculation process, where the true value of the phase jump and the maximum calculation artifact are marked with circles. The true value of the phase jump is the stable value during the voltage sag, -12.94 in fig. 8; in the process of calculating the voltage phase angle, if the transition section is not removed, calculation artifact therein can cause calculation error of phase jump, and the calculation artifact with the largest absolute value in fig. 8 is-23.92 degrees, which can cause calculation error of phase jump of 10.98 degrees, which is unacceptable in practical engineering.
Therefore, for voltage sag caused by common faults, after the transition section is detected by using the method provided by the invention, the transition section is excluded, and the phase jump can be calculated as the maximum absolute value of the phase angle measured by any phase of the three-phase voltage in the sag event process.
In addition, for the multi-stage voltage sag caused by the multi-stage fault, the power system parameter changes again due to the development of the fault, and when the voltage sag stage changes, the phase jump parameter also changes once, as shown in fig. 9. The phase jump in the first stage is-22.13 DEG, and the phase jump in the second stage is-14.28 deg. Since no evidence indicates that the phase jump of the second stage can affect the sensitive equipment, the phase jump of the first stage of the multi-stage voltage sag is used as a phase jump parameter in order to calculate the single event characteristic of the phase jump. As can be seen from fig. 9, if the phase jump in the second stage is required to be calculated, the method according to the present invention can be implemented by calculating the phase jump between the two transition sections.
The foregoing is merely illustrative embodiments of the present invention, and the present invention is not limited thereto, and any changes or substitutions that may be easily contemplated by those skilled in the art within the scope of the present invention should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (7)

1. The voltage sag characteristic calculation method based on the goodness-of-fit test is characterized by comprising the following steps of:
sliding the reference window and the detection window rightward by taking one sampling point as a step length at the same time, and calculating the fitting goodness-of-fit test statistic between the two windowsThereby detecting a transition segment of the voltage sag;
calculating a voltage sag type based on the number of detected transition sections;
calculating a starting point and an ending point of the voltage sag based on the transition section, and obtaining the duration time of the voltage sag;
calculating phase angles of a starting point and an ending point according to the obtained starting point and ending point of the voltage sag, taking a sampling point with a fundamental wave voltage zero crossing point and a derivative being positive as a reference, and determining a voltage sag waveform point;
in the phase angle calculation process, the transition section is excluded to avoid calculation artifacts generated by the transition section, and the phase jump of the voltage sag is obtained.
2. The method for calculating the voltage sag characteristics based on the goodness-of-fit test according to claim 1, wherein the definition of the reference window and the detection window specifically comprises:
the data in the reference window is used as the reference of the transition section of the impending voltage sag, the probability distribution corresponding to the composed vector is the steady-state voltage or the fluctuation of the voltage due to noise in the sag process, and the probability distribution is regarded as the target probability distribution; the detection window is adjacent to the reference window, and the length of the detection window is the same as that of the reference window, so that the detection window is a working window for fitting goodness-of-fit detection.
3. The method for calculating voltage dip characteristics based on goodness-of-fit test of claim 1, wherein said calculating goodness-of-fit test statistics between two windowsThereby detecting a transition of the voltage dip, comprising: calculating a goodness-of-fit test statistic between the two windows using a chi-square test in the goodness-of-fit test>Test statistic +.>Will exceed the critical value +.>
4. The method for calculating the voltage sag characteristics based on the goodness-of-fit test according to claim 1, wherein the calculating the voltage sag type based on the number of detected transition sections specifically comprises: when only one transition is detected, the voltage sag is classified as a slow recovery voltage sag; when two transition sections are detected, the voltage sag is classified as a rectangular voltage sag; a voltage dip is considered a multi-stage voltage dip when it has three or more transitions.
5. The method for calculating voltage dip characteristics based on goodness-of-fit test according to claim 4, wherein calculating a start point and an end point of a voltage dip based on the transition section, obtaining a voltage dip duration, comprises: the actual duration of the voltage dip is the time interval from the start point to the end point, after the transition section is detected, the rectangular voltage dip start point is the first sampling point of the first transition section, and the end point is the first sampling point of the second transition section; the starting point of the multi-stage voltage sag is the first sampling point of the first transition section, and the ending point is the first sampling point of the last transition section; the starting point of the slow recovery voltage sag is the first sampling point of the transition section, and the ending time is the time when the effective value voltage is recovered to 0.9p.u.
6. The method for calculating voltage sag characteristics based on goodness-of-fit test according to claim 4, wherein the phase angles of the start point and the end point are calculated with reference to sampling points where the fundamental voltage crosses zero and the derivative is positive, wherein for rectangular voltage sag and multi-stage voltage sag, the time points corresponding to the start point and the end point can be calculated from the detected transition; for slow recovery voltage sag, there is no waveform end point parameter and only waveform start point parameter, since there is no fault clearing instant.
7. The method for calculating voltage sag characteristics based on goodness-of-fit test according to claim 4, wherein the phase angle calculation process excludes transition sections to avoid calculation artifacts generated thereby, and the step of obtaining a phase jump of the voltage sag specifically comprises: for voltage sag caused by common faults, excluding a transition section, and enabling the phase jump to be the maximum absolute value of a phase angle measured by any phase of the three-phase voltage in the sag event process; for the multi-stage voltage sag caused by the multi-stage fault, since no evidence indicates that the phase jump of the second stage can affect the sensitive equipment, the phase jump of the first stage of the multi-stage voltage sag is taken as the phase jump parameter.
CN202311371417.4A 2023-10-23 2023-10-23 Voltage sag characteristic calculation method based on goodness-of-fit test Pending CN117420344A (en)

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