A baseband power quality fault embedded detection method based on cepstrum analysis

Abstract

The application discloses a fundamental frequency power quality fault embedded detection method based on cepstrum analysis, and relates to the technical field of power detection. The method comprises the following steps: setting a sampling frequency, sampling voltage according to the sampling frequency to obtain sampling voltage data; analyzing a time domain signal, and performing real cepstrum calculation on the sampling voltage data according to an analysis result; and analyzing the characteristics of the signal according to the frequency spectrum obtained by cepstrum calculation.

Description

Technical Field

[0001] The present invention relates to the technical field of power quality detection, and in particular to a fundamental frequency power quality fault embedded detection method based on cepstrum analysis. Background Art

[0002] As power grids gradually transition to smart grids, combining large grids with microgrids powered by clean energy, the power supply structure is changing, leading to increasingly severe distortion of voltage and current waveforms within the grid. Furthermore, the increasing variety of user loads is severely impacting power quality. These power quality issues not only undermine the safe and stable operation of the grid but also negatively impact user electricity consumption and industrial and agricultural production. One approach to addressing power quality monitoring and diagnosis in power grids is to build distributed power quality monitoring systems using low-power embedded devices as power quality detection nodes.

[0003] Due to the computing and power limitations of distributed platforms, a simple and accurate algorithm is needed to detect power quality faults. The traditional cycle or half-cycle effective value method is computationally simple. However, this method lacks accuracy when dealing with complex disturbances such as harmonics. Currently, power quality detection algorithms using time-frequency analysis methods such as wavelet transform and S transform have been gradually researched and applied. However, these algorithms are mostly targeted at the needs of complex power quality disturbance detection and are computationally complex, making them unsuitable for deployment on distributed platforms.

[0004] In view of this, an embedded detection method for fundamental frequency power quality faults based on cepstrum analysis is needed. Summary of the Invention

[0005] The embodiment of the present invention provides an embedded detection method for fundamental frequency power quality faults based on cepstrum analysis, so as to at least solve the technical problem of complex power quality analysis in related technologies.

[0006] According to one aspect of an embodiment of the present invention, a method for embedded detection of fundamental frequency power quality faults based on cepstrum analysis is provided, comprising:

[0007] Setting a sampling frequency, and sampling the voltage according to the sampling frequency to obtain sampled voltage data;

[0008] Analyzing the time domain signal, and performing real cepstrum calculation on the sampled voltage data according to the analysis result;

[0009] The characteristics of the signal are analyzed based on the spectrum obtained by cepstrum calculation.

[0010] Optionally, the sampling frequency is set according to the characteristic of analyzing only the baseband signal.

[0011] Optionally, the real cepstrum calculation includes:

[0012] Calculate the sampled voltage spectrum using the FFT algorithm;

[0013] Calculate the logarithm of the real part of the voltage spectrum;

[0014] Perform IFFT calculation on the calculated spectrum logarithm to obtain the real cepstrum.

[0015] Optionally, the spectrum obtained by cepstrum calculation can analyze the envelope characteristics of the signal.

[0016] Optionally, analyzing the envelope characteristic of the signal includes: finding a maximum value in the middle of the cepstrum, and analyzing the envelope characteristic of the signal based on this value.

[0017] Optionally, the sampling frequency =3.2kHz.

[0018] Compared with the existing technology, the present invention has the following beneficial effects:

[0019] The present invention provides an embedded detection method for fundamental frequency power quality faults based on cepstrum analysis. By setting a sampling frequency, the voltage is sampled according to the sampling frequency to obtain sampled voltage data. The method then analyzes the time domain signal and, based on the analysis results, performs real cepstrum calculations on the sampled voltage data. The signal characteristics are analyzed based on the spectrum obtained from the cepstrum calculations. This method makes cepstrum analysis simple and fast, and is highly effective in identifying voltage sags. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 is a flow chart of an embedded detection method for fundamental frequency power quality faults based on cepstrum analysis according to an embodiment of the present invention;

[0022] Figure 2 is a schematic diagram of a simulation of a voltage sag according to an embodiment of the present invention;

[0023] Figure 3 is a voltage drop cepstrum diagram according to an embodiment of the present invention;

[0024] Figure 4 is a schematic diagram of a simulation of a no-fault voltage according to an embodiment of the present invention;

[0025] Figure 5 is a real cepstrum diagram of a no-fault voltage according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0028] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0029] Example 1

[0030] According to an embodiment of the present invention, an embodiment of an embedded detection method for fundamental frequency power quality faults based on cepstrum analysis is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0031] like Figure 1 FIG. 1 is a flow chart of an embedded detection method for fundamental frequency power quality faults based on cepstrum analysis according to an embodiment of the present invention. Figure 1 As shown, the detection method includes the following steps:

[0032] S1. Set a sampling frequency. According to the sampling frequency, the embedded platform samples the voltage through the ADC module to obtain sampled voltage data.

[0033] As an optional embodiment, the sampling frequency is set based on the characteristic of only analyzing the fundamental frequency signal. Since only the fundamental frequency is analyzed, the sampling frequency can be set lower. =3.2kHz.

[0034] S2. Analyze the time domain signal, and perform real cepstrum calculation on the sampled voltage data according to the analysis result.

[0035] As an optional embodiment, the time domain signal , its complex cepstrum for:

[0036]

[0037] in, for To simplify the calculation, only the real cepstrum can be analyzed.

[0038] Therefore, the real cepstrum for:

[0039]

[0040] Compared to the complex cepstrum, the real cepstrum only needs to process the real part of the frequency domain, which can save computing time and space. Therefore, the real cepstrum calculation includes:

[0041] S21. Calculate the sampled voltage spectrum using the FFT algorithm. In this example, 2560 data points are selected, corresponding to 20 power frequency cycles.

[0042] S22. Calculate the logarithm of the real part of the voltage spectrum. FFT data in embedded systems typically stores the real and imaginary parts in two separate arrays. Perform the logarithm operation on the real array.

[0043] S23. Perform IFFT calculation on the calculated spectrum logarithm to obtain the real cepstrum.

[0044] S3. Analyze the characteristics of the signal based on the frequency spectrum obtained by cepstrum calculation.

[0045] As an optional embodiment, the envelope characteristics of the signal can be analyzed according to the spectrum obtained by cepstrum calculation.

[0046] Specifically, the cepstrum converts multiplication relationships into addition and subtraction relationships through logarithmic calculations, thus effectively decomposing the signal envelope. In a fundamental frequency power quality fault, voltage fluctuations are equivalent to changes in the voltage envelope, and therefore manifest as peaks at specific points in the cepstrum. The cepstrum and frequency spectrum are both symmetrical, with high-frequency signals corresponding to the two ends of the cepstrum and low-frequency envelopes corresponding to the middle of the cepstrum. Therefore, the maximum value in the middle of the cepstrum can be found and used to analyze the signal envelope characteristics. In this embodiment, a search is performed for the maximum absolute value of the cepstrum (i.e., the horizontal coordinate of the cepstrum) between 500 and 1000 in the cepstrum. If the maximum absolute value is greater than 0.07, a fundamental frequency fault is determined.

[0047] In order to verify the effect of the present invention, the voltage sag and normal voltage signals were simulated by software, such as Figure 2 and Figure 4 As shown, white noise is added to simulate the interference in actual situations. The cepstrum of the two signals are calculated separately, as shown in Figure 3 and Figure 5 As shown. Figure 3 and Figure 5 It can be seen that the cepstrum of the voltage sag signal has an obvious peak point compared with the normal signal, which corresponds to the voltage sag. This shows that the cepstrum analysis has a good recognition effect on voltage sag.

[0048] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for embedded detection of fundamental frequency power quality faults based on cepstrum analysis, characterized in that: include: Setting a sampling frequency, and sampling the voltage according to the sampling frequency to obtain sampled voltage data; According to the characteristics of only analyzing the fundamental frequency signal, the sampling frequency is set; Analyzing the time domain signal, and performing real cepstrum calculation on the sampled voltage data according to the analysis result of the time domain signal; The real cepstrum calculation includes: calculating the sampled voltage spectrum by using the FFT algorithm; calculating the logarithm of the real part of the voltage spectrum; performing IFFT calculation on the calculated spectrum logarithm to obtain the real cepstrum; The spectrum obtained from the cepstrum calculation can analyze the envelope characteristics of the signal. Analyzing the envelope characteristics of the signal includes: finding the maximum value in the middle of the cepstrum and using it to analyze the signal envelope characteristics; searching for the maximum absolute value between 500 and 1000 of the cepstrum in the cepstrum. If the maximum absolute value is greater than 0.07, it is determined that a fundamental frequency fault exists.

2. The embedded detection method for fundamental frequency power quality faults based on cepstrum analysis according to claim 1 is characterized in that: The sampling frequency f s =3.2kHz.

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