Impedance estimation method for low-voltage transmission lines with weak synchronization

Abstract

The present invention provides an impedance estimation method for a weakly synchronous low-voltage line, comprising: performing area broadcast time synchronization on a first acquisition device and a second acquisition device at the head and end of a target line to be measured, so that the synchronization error does not exceed a preset error duration; the first acquisition device and the second acquisition device respectively acquire voltage information and power information according to a preset freezing time, and screen and obtain voltage effective data and power effective data; according to the voltage effective data and the power effective data, a first calculation matrix is ​​established based on a voltage drop relationship equation deduced by the trigonometric cosine theorem; according to the phase angle relationship between active power and reactive power, the first calculation matrix is ​​screened based on the validity of the voltage drop relationship equation to obtain a second calculation matrix; based on the second calculation matrix, a multivariate linear minimum equation group is established, and the impedance of the target line to be measured is calculated using a least squares method, thereby providing an impedance estimation scheme that is less affected by a mutual inductor error and can be used for light-load lines.

Description

Technical Field

[0001] The present invention relates to the technical field of power system electricity management, and in particular to an impedance estimation method for a weakly synchronous low-voltage line. Background Art

[0002] Due to the complexity of the lines, the small impact of faults and cost issues, the flow calculation and line impedance analysis of low-voltage distribution networks have always been in a blind spot. However, with the increasing requirements for lean management, real-time analysis of the impedance changes of distribution network lines can play a positive role in early detection of line aging, short-circuit and open-circuit fault prediction, and line loss management, which can effectively improve power supply reliability.

[0003] There are currently two main technical routes for impedance estimation of low-voltage lines: The first technical route is to install a micro PMU device, namely a synchronous phasor measurement unit (PMU), to collect the voltage and current vectors at the same time, calculate the voltage phase angle difference at both ends of the line, and then calculate the line impedance. This method requires high-precision synchronization and has a high investment cost. In addition, since the voltage drop in the distribution network is often small, the accuracy error caused by the mutual inductor is even larger than the actual value, which brings about the error drowning problem. The second technical route is to calculate the line impedance using the voltage and current amplitudes collected by the smart meter. This method is simple to calculate, but is greatly affected by the current phase angle, and can only calculate the modulus of the line impedance, and cannot accurately calculate the resistance and reactance of the line, which has certain limitations.

[0004] Therefore, it is necessary to provide an impedance estimation technology solution that can accurately calculate the resistance and reactance, i.e., impedance, of a low-voltage distribution line while avoiding the error flooding problem caused by a transformer error. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an impedance estimation method for a weakly synchronous low-voltage line, comprising the following specific steps:

[0006] Performing broadcast time synchronization on the first acquisition device and the second acquisition device at the head and end of the target line to be tested, so that the time synchronization error between the first acquisition device and the second acquisition device does not exceed a preset error duration;

[0007] The first acquisition device and the second acquisition device respectively acquire voltage information and power information according to a preset freezing time to obtain voltage sampling data and power sampling data;

[0008] Filtering the voltage sampling data and the power sampling data to obtain voltage valid data and power valid data;

[0009] According to the voltage effective data and the power effective data, a first calculation matrix is ​​established based on a voltage drop relationship equation deduced from the trigonometric cosine theorem;

[0010] According to the phase angle relationship between the active power and the reactive power, the first calculation matrix is ​​screened based on the validity of the voltage drop relationship equation to obtain a second calculation matrix;

[0011] A multivariate linear minimum equation group is established based on the second calculation matrix, and the impedance of the target line to be measured is calculated using the least squares method.

[0012] In a possible implementation, the preset error duration is 1 second within 24 hours.

[0013] In a possible implementation, the freezing time is any value of 1 minute, 5 minutes, 15 minutes, and 30 minutes.

[0014] In a possible implementation, the screening rule for screening the voltage sampling data and the power sampling data is:

[0015] ΔU <V set ;

[0016]

[0017] |T1-T2|≤T set ;

[0018] Among them, ΔU represents the voltage amplitude difference between the beginning and the end of the line, V set represents the voltage amplitude difference threshold, P represents the active power measured at the head end of the line, Q represents the reactive power measured at the head end of the line, S set represents the apparent power threshold, T1 represents the freezing time at the beginning of the line, T2 represents the freezing time at the end of the line, T set Indicates the time difference threshold.

[0019] In a possible implementation, the pressure drop relationship equation is:

[0020]

[0021] Among them, U1 represents the voltage measured at the beginning of the line, U2 represents the voltage measured at the end of the line, P represents the active power measured at the beginning of the line, Q represents the reactive power measured at the beginning of the line, R represents the line resistance, and X represents the line reactance.

[0022] In a possible implementation, the first calculation matrix is:

[0023]

[0024] Among them, ΔUn Indicates the voltage difference between the beginning and the end of the line during the nth freezing, P n Indicates the active power at the head end of the line during the nth freezing, Q n Indicates the reactive power at the head end of the line during the nth freezing, U 1n represents the voltage at the beginning of the line at the time of the nth freezing; R represents the line resistance, X represents the line reactance, and β is the intercept coefficient.

[0025] In a possible implementation, the screening condition when screening the first calculation matrix based on the validity of the pressure drop relationship equation is:

[0026]

[0027] Among them, R mse Represents the standard deviation of the power ratio, R mseset represents the standard deviation threshold, δ i =Q i / P i , δ i represents the i-th power phase angle, and δ represents the average power phase angle.

[0028] The technical solution provided by the present invention has at least the following beneficial effects:

[0029] By screening the voltage sampling data and the power sampling data, and further screening the first calculation matrix, the influence of bad data and bad measurement team calculation can be effectively eliminated, and the estimation accuracy of the impedance estimation method can be improved; at the same time, the voltage drop relationship equation is deduced from the trigonometric cosine theorem to establish the first calculation matrix, which completely avoids the error flooding problem caused by subtracting similar numbers and reduces the influence of transformer errors on the calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flowchart of an impedance estimation method for a weakly synchronous low-voltage line provided by an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the installation of the substation equipment provided by the embodiment of the present invention;

[0032] Figure 3 A schematic diagram of line voltage drop provided by an embodiment of the present invention;

[0033] Figure 4 This is a diagram of the fitting estimation effect provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only used to explain the present invention and do not limit the protection scope of the present invention.

[0035] Please refer to Figures 1 to 4 The present invention provides a method for estimating impedance of a weakly synchronous low-voltage line, comprising the following specific steps:

[0036] S100: Performing area broadcast timing synchronization on a first acquisition device and a second acquisition device at the head and end of a target line to be measured, so that the timing error between the first acquisition device and the second acquisition device does not exceed a preset error duration.

[0037] In this embodiment, Figure 2 , the data acquisition equipment for collecting information is installed at the beginning and end of the target line to be tested. The target line to be tested can be the line between any two adjacent nodes. Figure 2 The device at the upper end of the line is the first acquisition device, which is installed at the end of the line (such as Figure 2 The device at the lower end of the control line is the second acquisition device. The acquisition device communicates with the master station via wireless or carrier. The master station performs the time synchronization of the area broadcast. In the specific implementation, the time synchronization error between the first and second acquisition devices does not exceed 1s / 24h, that is, the time error between the first acquisition device and the second acquisition device does not exceed 1s within 24h.

[0038] In a possible implementation, the preset error duration is 1 second within 24 hours.

[0039] In this embodiment, the impedance estimation method does not require precise synchronization, and the calculation can be completed as long as the timing error of each measuring device (i.e., the first acquisition device and the second acquisition device) is less than 1s / 24h. It should be noted that the 24-hour timekeeping error of less than 1s is the basic standard for power distribution devices.

[0040] S200: The first acquisition device and the second acquisition device respectively acquire voltage information and power information according to a preset freezing time to obtain voltage sampling data and power sampling data.

[0041] In this embodiment, the first acquisition device is used to collect voltage and power information (including active power and reactive power), and the second acquisition device is used to collect voltage information. The two devices simultaneously send the electrical quantity information (i.e., voltage sampling data and power sampling data) collected at the same time section, i.e., at the same time, to the master station through wireless or carrier, and the master station estimates the line impedance. The voltage sampling data and the power sampling data are frozen data corresponding to the freezing time.

[0042] In a possible implementation, the freezing time is any value of 1 minute, 5 minutes, 15 minutes, and 30 minutes.

[0043] In this embodiment, the master station sets a freezing time for the device (the first acquisition device and the second acquisition device), which can be 1min, 5min, 15min, or 30min. After the setting is completed, each device freezes the collected voltage information and power information at the whole second. For example, when the freezing time is set to 1min, a set of data (including voltage, current, power, etc.) is collected every 1min, and 100 sets of data will take 100min; when the freezing time is set to 5min, a set of data is collected every 5min, and 100 sets of data will take 500min.

[0044] S300: Filter the voltage sampling data and the power sampling data to obtain voltage valid data and power valid data.

[0045] In this embodiment, the master station can Figure 2 The topological information in the circuit is read, the frozen data at the beginning and end of the line are read, and the data is filtered according to certain rules to obtain the effective voltage data and power data for inclusion in the calculation matrix.

[0046] In a possible implementation, the screening rule for screening the voltage sampling data and the power sampling data is:

[0047] ΔU <V set ;

[0048]

[0049] |T1-T2|≤T set ;

[0050] Among them, ΔU represents the voltage amplitude difference between the beginning and the end of the line, V set represents the voltage amplitude difference threshold, P represents the active power measured at the head end of the line, Q represents the reactive power measured at the head end of the line, S set represents the apparent power threshold, T1 represents the freezing time at the beginning of the line, T2 represents the freezing time at the end of the line, T set Indicates the time difference threshold.

[0051] In this embodiment, by adding screening rules, the influence of bad data and bad measurement groups on the calculation can be effectively eliminated.

[0052] S400: Establishing a first calculation matrix according to the voltage effective data and the power effective data based on a voltage drop relationship equation deduced from the trigonometric cosine theorem.

[0053] In this embodiment, the impedance is calculated by geometric method using trigonometric cosine formula, which completely avoids the error drowning problem caused by subtracting similar numbers and reduces the influence of mutual inductor error on the calculation. In specific implementation, the line voltage drop vector diagram involved in the voltage drop relationship equation is as follows: Figure 3As shown. In the process of solving the line voltage drop, in order to avoid the error amplification problem caused by subtracting large numbers, only the voltage and power amplitude are used in the algorithm. According to the trigonometric cosine theorem, the voltage drop generated on the line can be expressed by the initial voltage drop equation as follows:

[0054] U1 2 =U2 2 +dU 2 +2dU·U2cosθ;

[0055] Among them, U1 represents the voltage measured at the beginning of the line, U2 represents the voltage measured at the end of the line, dU represents the voltage drop generated on the line, and θ represents the phase difference between dU and U2.

[0056] dU can also be expressed as:

[0057]

[0058] Among them, P represents the active power measured at the head end of the line, Q represents the reactive power measured at the head end of the line, R represents the line resistance, and X represents the line reactance.

[0059] It can be seen that dU is composed of the product of current and impedance, so θ can be expressed as θ = θ l +θ I ,θ l = atan(X / R),θ I =atan(-Q / P).

[0060] From this we can get:

[0061]

[0062] Finally, the simplified pressure drop relationship equation is obtained:

[0063]

[0064] Among them, U1 represents the voltage measured at the beginning of the line, U2 represents the voltage measured at the end of the line, P represents the active power measured at the beginning of the line, Q represents the reactive power measured at the beginning of the line, R represents the line resistance, and X represents the line reactance.

[0065] According to the voltage drop relationship equation and the screened voltage effective data and power effective data, the first calculation matrix can be expressed as:

[0066]

[0067] Among them, ΔU n Indicates the voltage difference between the beginning and the end of the line during the nth freezing, P n Indicates the active power at the head end of the line during the nth freezing, Q nIndicates the reactive power at the head end of the line during the nth freezing, U 1n represents the voltage at the beginning of the line at the time of the nth freezing; R represents the line resistance, X represents the line reactance, and β is the intercept coefficient.

[0068] S500: According to the phase angle relationship between active power and reactive power, the first calculation matrix is ​​screened based on the validity of the voltage drop relationship equation to obtain a second calculation matrix.

[0069] In this embodiment, the validity of the equation is verified in the first calculation matrix. Since the impedance angle is estimated by relying on multiple groups of different active power and reactive power, the phase angle of each group of measured power cannot be completely consistent.

[0070] In a possible implementation, the screening condition when screening the first calculation matrix based on the validity of the pressure drop relationship equation is:

[0071]

[0072] Among them, R mse Represents the standard deviation of the power ratio, R mseset represents the standard deviation threshold, δ i =Q i / P i , δ i represents the i-th power phase angle, and δ represents the average power phase angle.

[0073] In this embodiment, by adding screening conditions, the influence of bad data and bad measurement groups on the calculation can be further eliminated.

[0074] S600: Establishing a multivariate linear minimum equation group based on the second calculation matrix, and using the least squares method to calculate the impedance of the target line to be measured.

[0075] In this embodiment, after the validity is verified, the least square method is used to solve the multivariate linear minimum equation system Ax=b to obtain the line equivalent resistance reactance, that is, the impedance of the target line to be measured.

[0076] It should be pointed out that in order to calculate the resistance and reactance of the low-voltage distribution line in a lean manner, and to avoid the error flooding problem caused by the mutual inductor error, the present invention proposes an impedance estimation method for a weakly synchronized low-voltage line. It only requires a simple broadcast synchronization in the substation area, and the synchronization error of each upstream and downstream device is constrained within 1s / 24h. By collecting the voltage and power information of the upstream and downstream, and using a certain anti-error algorithm, the resistance and reactance of the low-voltage distribution line can be calculated in a lean manner.

[0077] The impedance estimation method for weakly synchronous low-voltage lines provided by the present invention does not require a costly timing device, but only uses an HPLC carrier for timing, and does not require additional hardware investment for GPS timing or Beidou timing; it completely avoids the error drowning problem caused by subtracting similar numbers in traditional line estimation methods, and at the same time has a certain degree of suppression on the mutual inductor error; the calculation consumes little resources and is convenient for transplantation into various types of embedded devices. In a specific implementation, the measurement data of a certain area is selected, the line type is YJV22, the measurement data is selected as 5-minute frozen data, and 500 groups of valid data, as shown in Table 1, Table 2, and Table 3 below:

[0078] Table 1:

[0079] U1 / V U2 / V P1 / V Q1 / V U1 / V U2 / V P1 / V Q1 / V U1 / V U2 / V P1 / V q1 / V U1 / V U2 / V P1 / V Q1 / V 226 226 3248 -1361 228 228 4389 -1559 226 227 3118 -1429 227 227 3634 -1566 226 227 2103 -1456 229 229 3540 -1591 226 224 4798 -1440 227 228 3577 -1228 226 226 4300 -1405 228 228 2443 -1432 224 227 4900 -1552 227 227 7194 -610 226 226 9039 -1508 227 228 5549 -1427 226 226 5632 -1213 227 227 6636 -1492 226 226 3471 -1545 228 228 8541 -1401 227 227 6152 -1579 227 227 2760 -1221 226 226 7628 -1620 227 227 6952 -1401 226 226 8437 -1531 226 227 3551 -1363 226 226 8866 -1551 227 226 9973 -617 227 227 7759 -1496 227 227 3421 -1441 226 226 11966 -1511 227 227 6148 -1456 227 227 5240 -1779 226 226 3577 -1321 226 225 18130 -1588 226 225 13104 -1454 224 227 5516 -1784 226 227 4994 -1424 226 227 4344 -1415 226 226 11097 -1325 226 226 8784 -1666 226 226 3227 -1433 226 227 4436 -1217 226 226 8542 -916 226 224 7117 -1762 226 226 3851 -1072 226 226 8230 -1550 226 226 6555 -1426 224 224 4292 -1715 226 226 3802 -1278 227 227 7675 -1540 226 226 3468 -1516 224 227 4482 -1852 227 224 4384 -1193 227 22 8443 -1491 226 227 2511 -1497 226 224 11178 -1632 226 226 3450 -1131 227 224 8057 -1556 226 226 4423 -1491 224 224 11050 -1559 226 226 5373 -1481 227 227 6025 -1718 225 225 7059 -1456 224 224 7394 -1528 226 226 4274 -1385 227 227 5606 -1843 225 226 4005 -1478 227 227 7327 -860 227 227 3518 -1561 226 227 7862 -1643 225 225 4164 -1488 227 227 6425 -1393 227 226 8635 -1463 226 226 10685 -1599 224 224 2982 -1353 227 224 10350 -1900 226 227 5724 -1571 227 227 7119 -1733 225 225 6532 -1413 228 228 6920 -1619 226 227 4180 -1474 227 227 5184 -1735 224 225 3139 -534 228 228 7152 -1274 227 227 4538 -1448 226 227 8042 -1709 225 225 4508 -1301 228 228 8459 -1243 227 227 2015 -1563 227 227 5001 -1886 225 225 3084 -688 228 228 8284 -1330 227 227 3441 -1547 227 228 5006 -1205 224 224 4718 -1095 228 227 11262 -1372 227 227 4653 -1462 227 227 6196 -1678 225 225 3129 -1558 228 228 8614 -1614 227 227 5225 -1341 227 228 5520 -1453 225 226 4950 -1601 228 228 11261 -1585 227 227 3698 -1334 228 228 6828 -1599 225 226 4061 -650 228 228 6930 -1627 227 227 3904 -1028 228 228 6384 -1588 225 226 2341 -1580 228 227 12432 -1481 227 227 4429 -1404 228 228 10023 -1706 225 226 3218 -1551 228 228 10579 -1386 227 227 6550 -1277 228 228 13271 -1764 225 225 4961 -1505 228 228 7075 -1487 227 227 4678 -963 228 228 12667 -1645 225 225 7178 -1494 228 228 6034 -1474 227 227 6142 -1368 228 228 10439 -1414 225 225 2925 -1451 228 228 6096 -1393 227 227 5920 -1405 228 228 6934 -1403 225 225 4388 -1380 229 229 4980 -1389 226 226 4221 -877 228 228 6150 -1346 225 225 2404 -1291 229 229 8125 -1488 226 227 2337 -1579 228 228 6651 -1396 225 225 3310 -1307 228 228 6538 -1468 226 226 4193 -1382 228 228 4938 -1494 225 225 2498 -1408 229 229 7049 -1615 226 226 7525 -1085 228 228 5774 -1483 225 225 4984 -1262 229 229 7144 -1253 226 226 4681 -1730 228 228 5437 -1438 225 225 4181 -1308 229 229 7155 -1608 226 226 1901 -1537 228 229 3358 -1449 225 226 3750 -1418 229 228 9385 -1575 226 227 4284 -1486 228 228 2381 -1502 225 226 4147 -1488 229 229 8908 -1522 227 227 6545 -1476 228 228 4929 -1475 225 226 4995 -1304 229 229 9039 -1478 226 226 6174 -1550 228 229 3439 -1472 226 226 6980 -1206 229 229 7245 -1485 226 227 3772 -1614 229 229 3953 -1576 226 226 5721 -1384 228 229 5533 -1422 227 227 6572 -1583 228 229 3368 -1537 226 226 6292 -1300 228 229 5736 -1379 227 227 6974 -1786 229 229 3273 -1598 225 225 7630 -1259 228 229 4627 -1321 227 227 6592 -1672 229 229 4516 -1570 225 225 8333 -1498 228 228 8883 -1377 227 227 4310 -1950 229 229 2403 -1479 226 226 7380 -1546 228 227 11570 -1320 227 227 5206 -1823 228 229 3876 -1533 226 226 7664 -1413 227 228 7057 -1344 227 227 4574 -1594 229 229 3304 -1566 226 226 4347 -1450 228 229 5210 -1561 227 227 2969 -1962 223 224 2515 -1586 226 226 5344 -1419 224 227 6212 -1496 226 227 6427 -1821

[0080] Table 2:

[0081]

[0082] Table 3:

[0083] U1 / V U2 / V P1 / V Q1 / V U1 / V U2 / V P1 / V Q1 / V 226 226 3503 -1548 227 227 5497 -1568 225 225 3721 -1550 227 227 9693 -1657 225 225 5104 -1586 227 227 6818 -1402 224 224 7949 -1264 227 227 6657 -1540 224 224 8542 -708 227 227 8600 -1582 224 225 2029 -1079 227 228 7679 -1600 224 224 3011 -1401 227 228 3734 -1589 224 224 4484 -1299 228 228 6480 -1488 224 225 1455 -1313 228 229 5330 -1439 224 225 1566 -1345 228 228 7684 -1309 225 225 3027 -1278 228 228 6763 -1681 224 225 4241 -1223 228 228 4117 -1538 224 224 6318 -1493 228 228 4404 -1613 224 2.24 6483 -1494 228 228 3879 -1547 224 224 1643 -1466 228 228 3838 -1522 224 224 3106 -1469 228 228 2633 -1531 223 224 2301 -1421 228 228 4917 -1510 223 223 7333 -315 228 228 2523 -1431 223 224 3349 -1551 229 229 4095 -1481 223 223 3428 -1334 228 229 2714 -1433 223 223 2617 -1337 228 229 5351 -1526 223 223 2306 -1376 226 226 1667 -1521 225 225 2603 -1398 226 226 2258 -1607 225 226 3485 -1355 226 227 1359 -1614 22.5 226 2049 -1406 226 226 2470 -1611 225 226 2255 -14,9 227 227 1557 -1559 225 225 5369 -1412 226 227 1555 -1486 225 226 4257 -1442 226 227 1663 -1481 225 226 2288 -1562 226 227 1455 -1442 226 226 2059 -1533 226 227 1372 -1359 225 226 2859 -1587 226 227 2748 -1276 226 226 2324 -1592 226 227 3388 -1221 226 227 2681 -1448 226 226 2737 -1309 226 226 3528 -1439 226 226 4527 -1441 226 226 2644 -1378 225 226 3953 -1465 226 226 5937 -1436 225 226 4208 -1552 226 226 6441 -1418 225 225 7031 -1750 226 226 7344 -186 224 224 6524 -593 226 227 3597 -1584 224 225 1720 -1472 226 226 3542 -1613 224 224 5630 -467 226 226 5395 -1653 224 224 1683 -1317 226 226 5300 -1678 224 224 3276 -1321 226 226 5306 -1658 224 224 5237 -1117 227 227 5113 -1665 223 223 5756 -1175 227 227 4690 -1363 223 223 3011 -1318 227 227 6187 -1470 224 224 3898 -1241 227 227 5302 -1422 223 223 5320 -1439 227 227 5852 -1650 224 224 4495 -1429 227 226 8640 -1701 223 224 4877 -1364 227 227 6087 -1716 224 224 4193 -1394

[0084] The results of fitting based on the above 500 sets of valid data are as follows Figure 4 As shown, it can be calculated that the line resistance is about 0.016 ohms and the reactance is about 0.015 ohms, which is consistent with the actual situation. 2 is 0.7182. It should be noted that the fitting function used in the fitting is the first calculation matrix. 2 It is a statistical indicator. The larger its value is, the better the explanation of the model is and the higher the degree of fit is.

[0085] The above embodiments should not limit the present invention in any way, and any technical solutions obtained by equivalent replacement or equivalent conversion shall fall within the protection scope of the present invention.

Claims

1. A method for estimating impedance of a weakly synchronous low-voltage line, characterized in that: The specific steps include: Performing broadcast time synchronization on the first acquisition device and the second acquisition device at the head and end of the target line to be tested, so that the time synchronization error between the first acquisition device and the second acquisition device does not exceed a preset error duration; The first acquisition device and the second acquisition device respectively acquire voltage information and power information according to a preset freezing time to obtain voltage sampling data and power sampling data; Filtering the voltage sampling data and the power sampling data to obtain voltage valid data and power valid data; According to the voltage effective data and the power effective data, a first calculation matrix is ​​established based on a voltage drop relationship equation deduced from the trigonometric cosine theorem; According to the phase angle relationship between the active power and the reactive power, the first calculation matrix is ​​screened based on the validity of the voltage drop relationship equation to obtain a second calculation matrix; A multivariate linear minimum equation group is established based on the second calculation matrix, and the impedance of the target line to be measured is calculated using the least squares method.

2. The impedance estimation method according to claim 1, characterized in that: The preset error duration is 1 second within 24 hours.

3. The impedance estimation method according to claim 1, characterized in that: The freezing time is any value among 1 min, 5 min, 15 min and 30 min.

4. The impedance estimation method according to claim 1, characterized in that: The screening rules for screening the voltage sampling data and the power sampling data are: ΔU <V set ; |T1-T2|≤T set ; Among them, ΔU represents the voltage amplitude difference between the beginning and the end of the line, V set represents the voltage amplitude difference threshold, P represents the active power measured at the head end of the line, Q represents the reactive power measured at the head end of the line, S set represents the apparent power threshold, T1 represents the freezing time at the beginning of the line, T2 represents the freezing time at the end of the line, T set Indicates the time difference threshold.

5. The impedance estimation method according to claim 1, characterized in that: The pressure drop relationship equation is: Among them, U1 represents the voltage measured at the beginning of the line, U2 represents the voltage measured at the end of the line, P represents the active power measured at the beginning of the line, Q represents the reactive power measured at the beginning of the line, R represents the line resistance, and X represents the line reactance.

6. The impedance estimation method according to claim 1, characterized in that: The first calculation matrix is: Among them, ΔU n Indicates the voltage difference between the beginning and the end of the line during the nth freezing, P n Indicates the active power at the head end of the line during the nth freezing, Q n Indicates the reactive power at the head end of the line during the nth freezing, U 1n represents the voltage at the beginning of the line at the time of the nth freezing; R represents the line resistance, X represents the line reactance, and β is the intercept coefficient.

7. The impedance estimation method according to claim 1, characterized in that: The screening condition for screening the first calculation matrix based on the effectiveness of the pressure drop relationship equation is: Among them, R mse Represents the standard deviation of the power ratio, R mseset represents the standard deviation threshold, δ i =Q i / P i , δ i represents the i-th power phase angle, and δ represents the average power phase angle.

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