A Feature Current Discrimination Method for Substation Area Topology Identification

Abstract

The present invention relates to the technical field of low-voltage distribution network automation, and discloses a characteristic current discrimination method for substation topology identification, comprising the following steps: setting a characteristic frequency, a characteristic sequence S_1, a characteristic signal strength threshold, and the duration Tc of each code element at a signal receiving end; detecting S_1 with a sliding Fourier transform at the signal receiving end to obtain a sequence S_2 with the same number of bits as S_1; calculating the true signal strength P1 of the first 16 bits of S_2 with a sliding Fourier transform at the signal receiving end; comparing S_2 with S_1, if the deviation does not exceed m bits and P1 is greater than a threshold, the characteristic current is identified and the process ends; otherwise, the characteristic current is not identified and the calculation continues. The present invention reduces the probability of misidentification of the characteristic sequence without occupying too much chip resources and having almost no effect on the bit error rate, thereby reducing the reporting frequency of the receiving end, ensuring the reliability of micro-current communication, and thus ensuring the normal use of the master station and the accuracy of topology identification.

Description

Technical Field

[0001] The present invention relates to the technical field of low-voltage distribution network automation, and in particular to a characteristic current discrimination method for substation topology identification, which is mainly used for detecting and analyzing characteristic current signals in a low-voltage distribution system. Background Art

[0002] In recent years, power grid technology has developed rapidly, and power companies have increasingly higher requirements for power grid technology. State Grid Corporation of China has proposed the strategic goal of "three types and two networks, world-class", which has put forward new requirements for the operation and distribution connection and the topological relationship of "station-line-transformer-user" in the power grid. The application of topology identification solutions based on microcurrent communication technology has also become a consensus among many manufacturers.

[0003] The topology recognition technology based on micro-current communication sends characteristic current signals at locations such as users and branches, receives signals at branches and terminal locations, determines the relative positions of the sent and received signals, and then determines the affiliation of meter-branch-transformer.

[0004] The receiving device receives the characteristic sequence sent by the transmitting device, parses the received sequence through frequency demodulation, and reports the received information to the master station. Since the receiving device is always receiving signals and the background noise is of varying magnitude, it is easy to mistakenly identify the background noise as a characteristic signal during the process, resulting in frequent reporting of erroneous information to the master station, which in turn affects the normal use of the master station and the accuracy of topology recognition. Summary of the Invention

[0005] In view of the shortcomings and defects of the prior art, the present invention provides a characteristic current discrimination method for substation topology identification.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A characteristic current discrimination method for substation topology identification includes the following steps:

[0008] S1: According to the signals to be identified sent by each signal transmitting device in the line, the characteristic frequency f1, characteristic sequence S_1, characteristic signal strength threshold T and the duration Tc of each code element are set at the signal receiving device;

[0009] S2: The receiving device collects the signal to be identified in the line at a sampling frequency Fs. Based on a window of duration Tc and a sliding step size Ts, it uses a sliding Fourier transform to detect the received S_1, and obtains a characteristic sequence S_2 with the same number of bits as S_1.

[0010] S3: Based on the window duration Tc1 and the sliding step size Ts, the real signal strength P1 of the first 16 bits of S_2 is calculated at the signal receiving device using the sliding Fourier transform method;

[0011] S4: Compare S_2 and S_1. If the difference between the two does not exceed m bits, jump to step S5; otherwise, jump to step S2.

[0012] S5: If P1 is greater than the threshold T, it is considered that the characteristic current signal has been identified and the process ends; otherwise, it is considered that the characteristic current signal has not been identified and the process jumps to step S2.

[0013] Preferably, the characteristic sequence S_1 is set as follows: add two 0s at the end of the sequence to be judged S_0 as the characteristic sequence S_1, that is, set .

[0014] Preferably, Ts=0.1Tc.

[0015] Preferably, the specific calculation method of the real signal strength P1 of the first 16 bits of S_2 in step S3 is:

[0016]

[0017] Where N is the number of 1s in the first 16 bits of S_2, and P is the signal strength of the first 16 bits of S_2 calculated using the sliding Fourier transform.

[0018] Preferably, m=1.

[0019] Preferably, the signal receiving device is an intelligent circuit breaker, a line terminal unit (LTU), or an energy controller.

[0020] Preferably, Tc1=16Tc.

[0021] Preferably, T=0.25A.

[0022] The beneficial effects of the present invention are as follows: by optimizing the characteristic current judgment method at the receiving device, the probability of misidentification of the characteristic sequence is greatly reduced without occupying too much chip resources and almost without affecting the bit error rate, thereby significantly reducing the reporting frequency of the receiving device, ensuring the reliability of microcurrent communication, and thus ensuring the normal use of the master station and the accuracy of topology recognition. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0024] Figure 1 It is the overall flow chart of the present invention.

[0025] Figure 2 2 is a comparison chart of the bit error rates of the Tc-S-1 scheme and the Tc-S-0 scheme in an embodiment of the present invention.

[0026] Figure 3 2 is a comparison chart of the misrecognition rates of the Tc-S-1 scheme and the Tc-S-0 scheme in an embodiment of the present invention.

[0027] Figure 4 2 is a comparison chart of the bit error rates of the Tc1-S-1 scheme and the Tc-S-0 scheme in an embodiment of the present invention.

[0028] Figure 5 2 is a comparison chart of the misrecognition rates of the Tc1-S-1 scheme and the Tc-S-0 scheme in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example

[0031] like Figure 1 As shown in FIG, a characteristic current discrimination method for substation topology identification, denoted as Tc1-S-1, includes the following process:

[0032] S1: According to the signal to be identified sent by the signal sending end device in the line, set the characteristic frequency 783Hz and characteristic sequence at the energy controller of the signal receiving end device , characteristic signal strength threshold 25mA and duration of each symbol 600ms;

[0033] The sequence S_0 to be determined in the signal to be determined consists of 16 code elements, and the code elements are divided into two types: 1 and 0. When the code element is 1, the frequency of the signal to be determined is 783 Hz and the effective value of the current is 100 mA; when the code element is 0, there is no signal.

[0034] S2: The energy controller collects the signal to be identified in the circuit at a sampling frequency of 5kHz. Based on a short window duration of 600ms and a sliding step of 60ms, it uses the sliding Fourier transform (SDFT) to detect the sequence to be identified S_1, and obtains the characteristic sequence S_2 with the same number of bits as S_1.

[0035] The sliding step size of SDFT is set to Ts=0.1Tc=60ms to ensure smaller data storage space and higher calculation accuracy. The SDFT step size of S3 is set similarly.

[0036] S3: Based on a long window of 9600ms duration and a sliding step of 60ms, the sliding Fourier transform (SDFT) is used at the energy controller to calculate the true signal strength P1 of the first 16 bits of S_2. The specific calculation method of P1 is:

[0037]

[0038] Where N is the number of 1s in the first 16 bits of S_2, and P is the signal strength of the first 16 bits of S_2 calculated using the sliding Fourier transform.

[0039] S4: Compare S_2 and S_1. If the difference between the two does not exceed 1 bit, jump to step S5; otherwise, jump to step S2.

[0040] S5: If P1 is greater than the threshold value of 25mA, it is considered that the characteristic current signal has been identified and the process ends; otherwise, it is considered that the characteristic current signal has not been identified and the process jumps to step S2.

[0041] The Tc1-S-1 scheme was adopted, and the signal-to-noise ratio range was set to -23dB~-16dB. 2000 groups of experiments were simulated at each signal-to-noise ratio. For each signal-to-noise ratio condition, the number of experimental groups with accurate signal recognition was counted, and the bit error rate at each signal-to-noise ratio was obtained according to the bit error rate calculation method.

[0042] The Tc1-S-1 scheme was adopted, and the signal-to-noise ratio range was set to -23dB~-16dB. 2000 groups of experiments were simulated at each signal-to-noise ratio. For each signal-to-noise ratio condition, the number of experimental groups with signal misidentification was counted, and the misrecognition rate at each signal-to-noise ratio was obtained according to the misrecognition rate calculation method.

[0043] Comparative solution Tc-S-1 includes the following process:

[0044] S1: According to the signal to be identified sent by the signal sending end device in the line, set the characteristic frequency 783Hz and characteristic sequence at the energy controller of the signal receiving end device , characteristic signal strength threshold 25mA and duration of each symbol 600ms;

[0045] The sequence S_0 to be determined in the signal to be determined consists of 16 code elements, and the code elements are divided into two types: 1 and 0. When the code element is 1, the frequency of the signal to be determined is 783 Hz and the effective value of the current is 100 mA; when the code element is 0, there is no signal.

[0046] S2: The energy controller collects the signal to be identified in the circuit at a sampling frequency of 5kHz. Based on a short window duration of 600ms and a sliding step of 60ms, the sliding Fourier transform (SDFT) is used to detect the sequence to be identified S_1, and the characteristic sequence S_2 with the same number of bits as S_1 is obtained.

[0047] S3: Compare S_2 and S_1. If the deviation between the two does not exceed 1 bit, it is considered that the characteristic current signal has been identified and the process ends. Otherwise, it is considered that the characteristic current signal has not been identified and jump to step S2.

[0048] The Tc-S-1 scheme was adopted, and the signal-to-noise ratio range was set to -23dB~-16dB. 2000 groups of experiments were simulated at each signal-to-noise ratio. For each signal-to-noise ratio condition, the number of experimental groups with accurate signal recognition was counted, and the bit error rate at each signal-to-noise ratio was obtained according to the bit error rate calculation method.

[0049] The Tc-S-1 scheme was adopted, and the signal-to-noise ratio range was set to -23dB~-16dB. 2000 groups of experiments were simulated at each signal-to-noise ratio. For each signal-to-noise ratio condition, the number of experimental groups with signal misidentification was counted, and the misrecognition rate at each signal-to-noise ratio was obtained according to the misrecognition rate calculation method.

[0050] The comparative scheme Tc-S-0 includes the following process:

[0051] S1: Based on the signal to be identified sent by the signal transmitting device in the line, the energy controller of the signal receiving device is set to 783Hz, the characteristic frequency, S_0, the characteristic signal strength threshold, 25mA, and the duration of each code element, 600ms.

[0052] The sequence S_0 to be determined in the signal to be determined consists of 16 code elements, and the code elements are divided into two types: 1 and 0. When the code element is 1, the frequency of the signal to be determined is 783 Hz and the effective value of the current is 100 mA; when the code element is 0, there is no signal.

[0053] S2: The energy controller collects the signal to be identified in the circuit at a sampling frequency of 5kHz. Based on a short window duration of 600ms and a sliding step of 60ms, the sliding Fourier transform (SDFT) is used to detect the sequence to be identified S_0, and the characteristic sequence S_2 with the same number of bits as S_0 is obtained.

[0054] S3: Compare S_2 and S_0. If the deviation between the two does not exceed 1 bit, it is considered that the characteristic current signal has been identified and the process ends. Otherwise, it is considered that the characteristic current signal has not been identified and jump to step S2.

[0055] The Tc-S-0 scheme was adopted, and the signal-to-noise ratio range was set to -23dB~-16dB. 2000 groups of experiments were simulated at each signal-to-noise ratio. For each signal-to-noise ratio condition, the number of experimental groups with accurate signal recognition was counted, and the bit error rate at each signal-to-noise ratio was obtained according to the bit error rate calculation method.

[0056] The Tc-S-0 scheme was adopted, and the signal-to-noise ratio range was set to -23dB~-16dB. 2000 groups of experiments were simulated at each signal-to-noise ratio. For each signal-to-noise ratio condition, the number of experimental groups with signal misidentification was counted, and the misrecognition rate at each signal-to-noise ratio was obtained according to the misrecognition rate calculation method.

[0057] The bit error rate (BER) is calculated as 1 minus the correct recognition rate (CRR). The CRR is the probability of identifying a characteristic signal at the correct location when noise is superimposed on the signal. It is the ratio of the number of correctly identified signals to the total amount of data.

[0058] The false recognition rate (FAR) refers to the probability of misidentifying a feature signal when there is only background noise, that is, the ratio of the number of misidentified signals to the total amount of data.

[0059] like Figure 2 、 3 As shown, the bit error rate of the Tc-S-1 scheme is slightly higher than that of the Tc-S-0 scheme, but the difference is generally small. When the signal-to-noise ratio is below -19dB, the bit error rates of the two schemes are almost the same. When the signal-to-noise ratio is above -18dB, the bit error rate difference only becomes small. The error recognition rate of the Tc-S-1 scheme is 2% to 3%, while the error recognition rate of the Tc-S-0 scheme is about 5% to 7%, which is about 1 / 2 to 1 / 3 of the error recognition rate of the Tc-S-1 scheme. In summary, the Tc-S-1 scheme can effectively reduce the error recognition rate without affecting recognition accuracy (that is, almost without increasing the bit error rate), thus verifying that increasing code bits can help improve communication reliability.

[0060] like Figure 4 、 5As shown, compared with the Tc-S-0 scheme, the Tc1-S-1 scheme has a slightly lower bit error rate. When the signal-to-noise ratio is below -19dB, the bit error rate performance gain of Tc1-S-1 is approximately 0.2dB~0.3dB. When the signal-to-noise ratio is above -18dB, the Tc1-S-1 scheme will increase the bit error rate by less than 0.1% compared with the Tc-S-0 scheme. In general, it can be considered that the Tc1-S-1 scheme and the Tc-S-0 scheme have similar bit error rate performance. In terms of error recognition rate, the Tc1-S-1 scheme can reduce the error recognition rate by more than one order of magnitude, to no more than 1%, while the error recognition rate of the Tc-S-0 scheme is about 5%~7%. In summary, the scheme described in this application has the advantages of both low bit error rate and low error recognition rate, ensuring the best overall performance.

[0061] The above embodiments are illustrations of specific implementation methods of the present invention, rather than limitations of the present invention. Technicians in the relevant technical fields may make various transformations and changes to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should be included in the scope of patent protection of the present invention.

Claims

1. A characteristic current discrimination method for substation topology identification, characterized in that: The steps are as follows: S1: According to the signals to be identified sent by each signal transmitting device in the line, the characteristic frequency f1, characteristic sequence S_1, characteristic signal strength threshold T and the duration of each code element Tc are set at the signal receiving device; The sequence S_0 to be determined in the signal to be determined consists of 16 code elements, which are divided into two types: 1 and 0. When the code element is 1, the frequency of the signal to be determined is f1 and the current intensity is A. When the code element is 0, there is no signal; S2: The receiving device collects the signal to be identified in the line at a sampling frequency Fs. Based on a window duration of 600ms and a sliding step size Ts, it uses a sliding Fourier transform to detect the received S_1, and obtains a characteristic sequence S_2 with the same number of bits as S_1. S3: Based on a window duration of 9600ms and a sliding step size Ts, the real signal strength P1 of the first 16 bits of S_2 is calculated at the signal receiving device using a sliding Fourier transform method; S4: Compare S_2 and S_1. If the difference between the two does not exceed m bits, jump to step S5; otherwise, jump to step S2. S5: If P1 is greater than the threshold T, it is considered that the characteristic current signal has been identified and the process ends; otherwise, it is considered that the characteristic current signal has not been identified and the process jumps to step S2.

2. A characteristic current discrimination method for substation topology identification according to claim 1, characterized in that: The characteristic sequence S_1 is set as follows: two 0s are added to the end of the sequence to be judged S_0 as the characteristic sequence S_1, that is, S_1=[S_0 0 0].

3. The characteristic current discrimination method for substation topology identification according to claim 1, wherein the characteristic value is Ts=0.1Tc.

4. A characteristic current discrimination method for substation topology identification according to claim 1, characterized in that: The specific calculation method of the real signal strength P1 of the first 16 bits of S_2 in step S3 is: P1=16P / N; Where N is the number of 1s in the first 16 bits of S_2, and P is the signal strength of the first 16 bits of S_2 calculated using the sliding Fourier transform.

5. The characteristic current discrimination method for substation topology identification according to claim 1, characterized in that: The m=1.

6. The characteristic current discrimination method for substation topology identification according to claim 1, characterized in that: The signal receiving end device is an intelligent circuit breaker, a line terminal unit (LTU), or an energy controller.

7. The characteristic current discrimination method for substation topology identification according to claim 1, characterized in that: The T=0.25A.

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