Low-frequency current signal detection method and device

Abstract

The invention discloses a low-frequency current signal detection method and device, and the method comprises the steps: collecting and detecting a first voltage signal, carrying out the switching when the first voltage signal is at an upper zero-crossing moment or a lower zero-crossing moment, and generating a first current signal with a characteristic frequency; acquiring a second current signal, and performing adjacent period subtraction on the second current signal according to the sampling frequency; collecting and detecting a second voltage, extracting a third current signal when the second voltage is at an upper zero-crossing moment or a lower zero-crossing moment, and obtaining a characteristic frequency of the third current signal to obtain a real part value of a characteristic frequency component; cyclically caching the real part value of each voltage during upper zero passage or lower zero passage, obtaining a plurality of real part values at intervals when the caching number reaches a preset number, and performing correlation operation on the real part values and a preset local sequence to obtain correlation values; and whether the characteristic signal arrives or not is judged according to the correlation value and a preset correlation value threshold, so that accurate detection of the low-frequency characteristic current is realized.

Description

Technical Field

[0001] The present application relates to the technical field of low-voltage substation topological relationship identification, and specifically to a low-frequency current signal detection method and device. Background Art

[0002] Clear topological relationships between low-voltage substations can ensure that the power grid can smoothly carry out abnormal damage investigation, fault repair and other tasks, which is conducive to the lean management and digital construction of the power grid.

[0003] At present, the identification of low-voltage substation topological relationships mainly adopts the characteristic current communication method, which can more efficiently and accurately sort out the low-voltage substation topological relationships. However, the characteristic current communication method usually uses high-frequency (800Hz-2kHz) current signal communication methods, and high-frequency current signals have the problem of excessive shunting under certain working conditions, which is prone to signal detection anomalies, resulting in errors in the topological relationship results. Summary of the invention

[0004] To this end, the present application provides a low-frequency current signal detection method and device to solve the problem that the low-voltage substation topology relationship identification method in the prior art is prone to signal detection anomalies.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] In a first aspect, a low-frequency current signal detection method comprises:

[0007] Step 1: Collect and detect a first voltage signal, and switch the first voltage signal when the first voltage signal is at an upper zero crossing or a lower zero crossing to generate a first current signal with a characteristic frequency;

[0008] Step 2: collecting a second current signal, and performing a difference calculation on adjacent cycles of the second current signal according to a sampling frequency;

[0009] Step 3: collecting and detecting the second voltage, extracting the third current signal when the second voltage is at the moment of crossing zero upward or crossing zero downward, and obtaining the characteristic frequency of the third current signal to obtain the real part value of the characteristic frequency component;

[0010] Step 4: Circularly cache the real part value of each voltage when it crosses zero or below zero. When the number of cached values ​​reaches a preset number, obtain multiple real part values ​​at intervals and perform correlation operations with a preset local sequence to obtain a correlation value.

[0011] Step 5: Determine whether the characteristic signal has arrived based on the correlation value and a preset correlation value threshold.

[0012] Preferably, in step 1, the frequency of the first current signal is 175 Hz.

[0013] Preferably, in step 2, when the adjacent cycles of the second current signal are differentiated according to the sampling frequency, specifically: adjacent 50 Hz cycles of the second current signal are differentiated according to the sampling frequency.

[0014] Preferably, in step 3, a DFT algorithm is used to obtain the characteristic frequency of the third current signal.

[0015] Preferably, in step 3, the extraction time of the third current signal is 40 ms, and the total duration is 10.24 s.

[0016] Preferably, in step 4, the preset number is 2N, wherein N is the sequence length, and the sequence length is 256.

[0017] Preferably, in step 4, N real part values ​​are obtained at intervals.

[0018] Preferably, in step 4, the local sequence is a pseudo-random sequence of 1 and -1.

[0019] Preferably, in step 5, the correlation value threshold is 20.

[0020] In a second aspect, a low-frequency current signal detection device comprises:

[0021] A sending module, used for collecting and detecting a first voltage signal, switching when the first voltage signal is at an upper zero crossing or a lower zero crossing moment, and generating a first current signal with a characteristic frequency;

[0022] A receiving module, used for collecting a second current signal, and performing a difference operation on adjacent cycles of the second current signal according to a sampling frequency;

[0023] A real value calculation module is used to collect and detect the second voltage, extract the third current signal when the second voltage is at an upper zero crossing or a lower zero crossing moment, and obtain the characteristic frequency of the third current signal to obtain the real value of the characteristic frequency component;

[0024] A correlation value calculation module is used to cyclically cache the real part value of each voltage when it crosses zero upward or downward. When the number of cached values ​​reaches a preset number, multiple real part values ​​are obtained at intervals and correlated with a preset local sequence to obtain a correlation value.

[0025] The characteristic signal judging module is used to judge whether the characteristic signal has arrived according to the correlation value and a preset correlation value threshold.

[0026] Compared with the prior art, this application has at least the following beneficial effects:

[0027] The present application provides a low-frequency current signal detection method and device, which collects and detects a first voltage signal, switches when the first voltage signal is at the moment of crossing zero or crossing zero, and generates a first current signal with a characteristic frequency; collects a second current signal, and makes a difference between adjacent cycles of the second current signal according to the sampling frequency; collects and detects a second voltage, extracts a third current signal when the second voltage is at the moment of crossing zero or crossing zero, and obtains the characteristic frequency of the third current signal, and obtains the real value of the characteristic frequency component; cyclically caches the real value of each voltage crossing zero or crossing zero, and when the number of caches reaches a preset number, obtains multiple real values ​​at intervals, and performs correlation operations with a preset local sequence to obtain a correlation value; judges whether the characteristic signal has arrived according to the correlation value and the preset correlation value threshold. The present application performs frequency discrimination on the characteristic current signal through the synchronization of voltage crossing zero or crossing zero, and performs correlation operations with the local sequence, and realizes the accurate detection of the low-frequency characteristic current through correlation peak judgment, which effectively overcomes the problem of incorrect combing of the topological relationship of the low-voltage substation caused by abnormal shunt of high-frequency current signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more intuitively illustrate the prior art and the present application, exemplary drawings are given below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing the present application; for example, those skilled in the art are capable of easily making conventional adjustments or further optimizations to the addition / reduction / attribution division, specific shapes, positional relationships, connection methods, dimensional ratios, etc. of certain units (components) based on the technical concepts and exemplary drawings disclosed in the present application.

[0029] Figure 1 A basic flow chart of a low-frequency current signal detection method provided in Example 1 of the present application;

[0030] Figure 2 A judgment flow chart of a low-frequency current signal detection method provided in Example 1 of the present application;

[0031] Figure 3 A partial schematic diagram of a current signal of a characteristic frequency transmitted according to the first embodiment of the present application;

[0032] Figure 4 A schematic diagram of performing correlation operations on a transmitted signal provided in Embodiment 1 of the present application;

[0033] Figure 5 A schematic diagram of performing correlation operation on a transmitted signal superimposed with 30A background noise provided in Embodiment 1 of the present application;

[0034] Figure 6 A schematic diagram of performing correlation operation on a transmitted signal superimposed with 300A background noise provided in Example 1 of the present application;

[0035] Figure 7 This is a schematic diagram of performing correlation operations on a transmitted signal with a phase shift of 30° and superimposed with 300A background noise, provided in Example 1 of the present application. DETAILED DESCRIPTION

[0036] The present application is further described below in detail through specific embodiments in conjunction with the accompanying drawings.

[0037] In the description of this application: unless otherwise specified, the meaning of "plurality" is two or more. The terms "first", "second", "third", etc. in this application are intended to distinguish the objects referred to, and do not have special meanings in terms of technical connotations (for example, they should not be understood as emphasizing the importance or order, etc.). Expressions such as "including", "comprising", "having", etc. also mean "not limited to" (certain units, components, materials, steps, etc.).

[0038] The terms such as "upper", "lower", "left", "right", "middle", etc. cited in this application are usually used to indicate the general relative position relationship for the purpose of intuitive understanding by referring to the drawings, and are not absolute limitations on the position relationship in the actual product.

[0039] Embodiment 1

[0040] This embodiment provides a low-frequency current signal detection method, which sends a current signal of a characteristic frequency when the voltage crosses zero or below zero, and uses the voltage crossing zero or below zero as synchronization, and uses frequency domain detection and correlation operation methods to perform signal detection, effectively overcoming the interference of low-frequency noise, solving the problem of topological relationship errors caused by abnormal high-frequency signal shunting in the topology identification process, and realizing the detection of low-frequency current signals.

[0041] See also Figure 1 and Figure 2 , this embodiment provides a low-frequency current signal detection method, including:

[0042] S1: Collect and detect a first voltage signal, and switch the first voltage signal when it is at an upper zero crossing or a lower zero crossing to generate a first current signal with a characteristic frequency;

[0043] Specifically, this step generates a square wave current signal with a characteristic frequency of 175 Hz by switching a circuit having MOS, according to complementary PWM switching signals when the voltage is positive and when the voltage is negative. The voltage zero crossing or zero crossing moment refers to the moment when the voltage is <0 or ≥0, and the frequency f of the first current signal is 175 Hz.

[0044] More specifically, the first current signal is sent according to a 128-point sequence with pseudo-random characteristics (composed of ±1). When the sequence is 1, the current is generated by switching with an initial phase of 0° according to the characteristic frequency, and the current is sent for 0.04s. When the sequence is -1, the current is generated by switching with an initial phase of 180° according to the characteristic frequency, and the current is sent for 0.04s.

[0045] S2: collecting the second current signal, and performing difference calculation on adjacent cycles of the second current signal according to the sampling frequency;

[0046] Specifically, this step performs subtraction of adjacent 50 Hz periods of the current signal according to the sampling frequency Fs. This step can eliminate periodic components, such as fundamental wave components, by subtracting the current signal, thereby highlighting characteristic signals with higher frequencies.

[0047] S3: collecting and detecting the second voltage, extracting the third current signal when the second voltage is at an upper zero crossing or a lower zero crossing moment, and obtaining the characteristic frequency of the third current signal to obtain the real part value of the characteristic frequency component;

[0048] Specifically, this step detects the voltage zero crossing or zero crossing point, extracts the current signal of time T at the voltage zero crossing or zero crossing moment, and uses discrete Fourier transform (DFT algorithm) to extract the characteristic frequency f of the current signal, and outputs the real value RI of the characteristic frequency f component. Among them, the extraction time T is 40ms, and the total duration of the characteristic signal is 10.24s.

[0049] S4: cyclically cache the real part value of each voltage when it crosses zero upward or downward, and when the number of cached values ​​reaches a preset number, obtain multiple real part values ​​at intervals, and perform correlation operation with a preset local sequence to obtain a correlation value;

[0050] Specifically, this step caches the real value RI of each voltage crossing zero or below zero. When the cache reaches 2N numbers, N real value RIs are extracted at intervals and correlated with the local sequence S to calculate the correlation value C_V. If the cache does not reach 2N numbers, the cache continues. The local sequence is a pseudo-random sequence with elements of 1 and -1, and the sequence length N is set to 256.

[0051] S5: Determine whether the characteristic signal has arrived based on the correlation value and a preset correlation value threshold.

[0052] Specifically, the correlation value threshold ThV is set to 20. If the correlation value C_V>ThV is satisfied, it is determined that the characteristic signal has arrived, otherwise, steps S2 to S5 are repeated.

[0053] See also Figure 3 , Figure 3This is a partial diagram of the current signal of the sending characteristic frequency of this embodiment, wherein the actual characteristic current is a square wave signal generated by switching the MOS, the amplitude of the square wave current signal is 360mA, the duty cycle is 1 / 3, and a 175Hz current signal is generated according to the positive and negative 175Hz PWM switching. The current signal peak is about 200mA, and each bit of information contains 40ms.

[0054] See also Figure 4 , Figure 4 A diagram of correlation operation on the transmitted signal provided for this embodiment, in which the signal is superimposed to the 201st cycle. It can be seen that when the complete characteristic signal is not detected, the result of the correlation operation is very small, and the maximum correlation value is within 10. When the complete characteristic signal is detected, the correlation value is about 40. The characteristic signal can be determined by correlation value detection.

[0055] See also Figure 5 , Figure 5 The graph provided for the present embodiment shows the correlation operation of the transmitted signal superimposed with 30A background noise. It can be seen that after superimposing 30A background noise, it still has the characteristic of obvious correlation. This proves that when a certain background noise is superimposed, the method is still feasible.

[0056] See also Figure 6 , Figure 6 The diagram provided for the present embodiment shows the correlation operation of the transmitted signal with 300A background noise superimposed. It can be seen that after the 300A background noise is superimposed, the highest correlation peak remains basically unchanged, but the correlation value before the signal arrives has a certain increase, but the correlation value is still significantly lower than 20, so this method is still feasible when a larger background noise is superimposed.

[0057] See also Figure 7 , Figure 7 From the graph provided for this embodiment, which shows the correlation operation of the transmitted signal with a phase shift of 30° and superimposed 300A background noise, it can be seen that even if the received characteristic signal has a certain phase shift and is superimposed with a higher background noise, it still has obvious correlation characteristics, and the highest correlation peak is weakened, but it still meets the conditions that the correlation value is >20 when the signal is detected and the correlation value is <20 when the signal is not detected. Therefore, this method is still feasible when the phase is shifted and a large background noise is superimposed.

[0058] A low-frequency current signal detection method provided in this embodiment performs frequency discrimination on a characteristic current signal through synchronization of voltage crossing zero or crossing zero, performs correlation operation with a local sequence, and realizes accurate detection of low-frequency characteristic current through correlation peak judgment, thereby effectively overcoming the problem of errors in combing the topological relationship of low-voltage substations caused by abnormal shunt of high-frequency current signals.

[0059] Embodiment 2

[0060] This embodiment provides a low-frequency current signal detection device, including:

[0061] A sending module, used for collecting and detecting a first voltage signal, switching when the first voltage signal is at an upper zero crossing or a lower zero crossing moment, and generating a first current signal with a characteristic frequency;

[0062] A receiving module, used for collecting a second current signal, and performing a difference operation on adjacent cycles of the second current signal according to a sampling frequency;

[0063] A real value calculation module is used to collect and detect the second voltage, extract the third current signal when the second voltage is at an upper zero crossing or a lower zero crossing moment, and obtain the characteristic frequency of the third current signal to obtain the real value of the characteristic frequency component;

[0064] A correlation value calculation module is used to cyclically cache the real part value of each voltage when it crosses zero upward or downward. When the number of cached values ​​reaches a preset number, multiple real part values ​​are obtained at intervals and correlated with a preset local sequence to obtain a correlation value.

[0065] The characteristic signal judging module is used to judge whether the characteristic signal has arrived according to the correlation value and a preset correlation value threshold.

[0066] The specific implementation contents of each module in a low-frequency current signal detection device can be found in the above definition of a low-frequency current signal detection method, which will not be repeated here.

[0067] The technical features of the above embodiments may be arbitrarily combined (as long as there is no contradiction in the combination of these technical features). To make the description concise, not all possible combinations of the technical features in the above embodiments are described; these embodiments that are not explicitly written should also be considered to be within the scope of this specification.

Claims

1. A low-frequency current signal detection method, characterized in that: include: Step 1: Collect and detect a first voltage signal, and switch the first voltage signal when the first voltage signal is at an upper zero crossing or a lower zero crossing to generate a first current signal with a characteristic frequency; Step 2: Collect the second current signal, and perform difference calculation on adjacent cycles of the second current signal according to the sampling frequency; Step 3: collecting and detecting the second voltage, extracting the third current signal when the second voltage is at the moment of crossing zero upward or crossing zero downward, and obtaining the characteristic frequency of the third current signal to obtain the real part value of the characteristic frequency component; Step 4: Circularly cache the real part value of each voltage when it crosses zero or below zero. When the number of cached values ​​reaches a preset number, obtain multiple real part values ​​at intervals and perform correlation operations with a preset local sequence to obtain a correlation value. Step 5: Determine whether the characteristic signal has arrived based on the correlation value and a preset correlation value threshold.

2. The low-frequency current signal detection method according to claim 1, characterized in that: In step 1, the frequency of the first current signal is 175 Hz.

3. The low-frequency current signal detection method according to claim 1, characterized in that: In step 2, when the adjacent cycles of the second current signal are differentiated according to the sampling frequency, specifically: adjacent 50 Hz cycles of the second current signal are differentiated according to the sampling frequency.

4. The low-frequency current signal detection method according to claim 1, characterized in that: In step 3, a DFT algorithm is used to obtain the characteristic frequency of the third current signal.

5. The low-frequency current signal detection method according to claim 1, characterized in that: In step 3, the extraction time of the third current signal is 40 ms, and the total duration is 10.24 s.

6. The low-frequency current signal detection method according to claim 1, characterized in that: In step 4, the preset number is 2N, where N is the sequence length, and the sequence length is 256.

7. The low-frequency current signal detection method according to claim 6, characterized in that: In step 4, when multiple real part values ​​are obtained at intervals, N values ​​are obtained.

8. The low-frequency current signal detection method according to claim 1, characterized in that: In step 4, the local sequence is a pseudo-random sequence of 1 and -1.

9. The low-frequency current signal detection method according to claim 1, characterized in that: In step 5, the correlation value threshold is 20.

10. A low-frequency current signal detection device, characterized in that: include: A sending module, used for collecting and detecting a first voltage signal, switching when the first voltage signal is at an upper zero crossing or a lower zero crossing moment, and generating a first current signal with a characteristic frequency; A receiving module, used for collecting a second current signal, and performing a difference operation on adjacent cycles of the second current signal according to a sampling frequency; A real value calculation module is used to collect and detect the second voltage, extract the third current signal when the second voltage is at an upper zero crossing or a lower zero crossing moment, and obtain the characteristic frequency of the third current signal to obtain the real value of the characteristic frequency component; A correlation value calculation module is used to cyclically cache the real part value of each voltage when it crosses zero upward or downward. When the number of cached values ​​reaches a preset number, multiple real part values ​​are obtained at intervals and correlated with a preset local sequence to obtain a correlation value. The characteristic signal judging module is used to judge whether the characteristic signal has arrived according to the correlation value and a preset correlation value threshold.

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