CN110687350A - Power grid voltage and current harmonic analysis method and system - Google Patents
Power grid voltage and current harmonic analysis method and system Download PDFInfo
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Abstract
A power grid voltage and current harmonic analysis method and a system thereof are provided, wherein an AD converter samples an input voltage signal, a secondary virtual sampling unit performs secondary sampling on first sampling data by a virtual sampling period s, and a spectrum analysis unit performs data secondary sampling by using an FFT algorithmAnalyzing to obtain a frequency spectrum of the voltage signal, scanning and accumulating all spectral lines except the power frequency signal and harmonic thereof in the frequency spectrum by a frequency spectrum leakage estimation unit to obtain total energy leakage d of the frequency spectrum, and adjusting a virtual sampling period s by a virtual sampling period adjusting unit according to the frequency spectrum leakage; the invention realizes the self-adaption to the frequency drift of the power frequency signal by utilizing a simple fixed hardware circuit, thereby ensuring the minimum frequency spectrum leakage of an analysis result.
Description
Technical Field
The invention belongs to the technical field of power grid signal detection and signal analysis, and particularly relates to a power grid voltage and current harmonic analysis method and a power grid voltage and current harmonic analysis system.
Background
Harmonic analysis of power grid signals is an important content of power supply quality monitoring of a power system, and is widely applied to various links of power transmission and transformation, power distribution and the like. Currently, the basic approach for online harmonic analysis of grid signals is the Fast Fourier Transform (FFT) algorithm. There is a fundamental limitation in the application of this algorithm, the amount of input data must be 2N. However, the frequency of the power grid is not constant, and the maximum allowable power grid frequency in the current national power grid standard is 0.5Error in Hz. Therefore, under the condition of a certain sampling period, the sampling data corresponds to 2NThe sub-sampling time window may not be an integer multiple of the input signal period, and especially when the grid signal frequency fluctuates, even a carefully adjusted sampling system may be mismatched with the input signal. The FFT using such sampled data necessarily generates a certain spectrum leakage, resulting in harmonic analysis errors.
In order to reduce spectrum leakage and improve analysis accuracy, a common solution includes: a certain sampling window function is used to replace a simple rectangular window function. Generally, selectable window functions include a hanning window, a hamming window, a match window and the like, and for different signal forms, the form of the window function is reasonably selected to improve the spectrum leakage to a certain extent and improve the analysis precision, but the problem of the spectrum leakage cannot be fundamentally solved, and the degree of performance improvement is limited.
Obtaining a reference signal with the same frequency as the fundamental component of the input signal by utilizing the narrow-band tracking capability of a phase-locked loop (PLL), and performing 2NThe frequency of the signal is multiplied by m and then is used as a sampling trigger signal, so that 2 is ensuredNThe time of the sub-sampling window is always m times of the period of the fundamental wave of the input signal, so that the minimum spectrum leakage is obtained. The method can fundamentally solve the problem of frequency spectrum leakage, but the PLL structure is more complex, and the system cost is increased. When the frequency of the input signal changes, the tracking speed of the PLL is low, the dynamic error of the frequency spectrum analysis is large, and due to the limitation of the tracking speed and the range of the PLL frequency, when the frequency change range of the input signal is large, the PLL loses lock and loses the automatic tracking capability.
Disclosure of Invention
Aiming at the defects and limitations in the harmonic analysis process in the prior art, the method and the system for analyzing the voltage and current harmonic of the power grid provided by the invention realize the harmonic analysis of synchronous sampling by carrying out secondary equivalent sampling on the sampling data, and realize the self-adaption to the frequency drift of the power frequency signal by utilizing a simple fixed hardware circuit, thereby ensuring the minimum frequency spectrum leakage of the analysis result.
The technical scheme adopted by the invention is as follows:
a power grid voltage and current harmonic analysis method comprises the following steps:
s1, controlling the AD converter to sample the input voltage signal by using the fixed-frequency sampling signal, wherein the first sampling data is D ═ D0,D1,…,Dn-1]；
S2, the secondary virtual sampling unit performs secondary sampling on the first sampling data by a virtual sampling period S, and the data obtained after the virtual sampling is
S3, the spectrum analysis unit uses FFT algorithm to data
Analyzing to obtain frequency spectrum of voltage signal
P＝[P0,P1,…,Pm-1]；
S4, the frequency spectrum leakage estimation unit scans and accumulates all spectral lines except the power frequency signal and the harmonic thereof in the frequency spectrum to obtain total energy leakage d of the frequency spectrum;
s5, the virtual sampling period adjusting unit adjusts the virtual sampling period S according to the total energy leakage;
s6, after the virtual sampling period S is adjusted, repeating the steps S1-S5, the end condition of the circulation is | Sk|＜ΔsthWherein, Δ sthIs a preset error limit.
Further, the virtual sampling performs virtual sampling according to the following formula:
wherein the content of the first and second substances,
for the ith dummy sample data, i ═ 1,2, …, m-1, m being an integer power of 2; int (. beta.) is a rounding function, Dint(is)And Dint(is)+1The data in the first sampling data are respectively, and the serial numbers of the data are respectively the rounding result and the rounding plus 1 of the is.
Further, the method for calculating the total energy leakage d of the frequency spectrum comprises the following steps:
wherein, PjThe power frequency fundamental wave signal is the jth spectral line amplitude, k is a positive integer, and the power frequency fundamental wave signal is located in the ith spectral line;
further, the method for adjusting the virtual sampling period s comprises the following steps:
Δsk＝sign[(dk-1-dk)×Δsk-1]×α×dk
sk＝sk-1+Δsk
wherein, Δ skIs the k-th adjustment quantity, s, of the virtual sampling periodkFor the adjusted virtual sampling period of the k-th time, dkFor the spectral leakage of the k-th virtual sampling data, alpha is an adjustment coefficient, and sign (·) is a sign function;
based on the power grid voltage and current harmonic analysis method, the invention also provides a power grid voltage and current harmonic analysis system which comprises an AD converter, a primary sampling data buffer area, a secondary virtual sampling unit, a secondary sampling data buffer area and a spectrum analysis unit which are sequentially connected, wherein the spectrum analysis unit is connected with the secondary virtual sampling unit through a spectrum leakage estimation unit and a virtual sampling period regulation unit which are sequentially connected, and the virtual sampling period regulation unit regulates a virtual sampling period s according to the spectrum leakage calculated by the spectrum leakage estimation unit.
The invention has the beneficial effects that:
1. according to the method for analyzing the voltage and current harmonic waves of the power grid, secondary virtual sampling is introduced, the virtual sampling frequency is continuously and automatically corrected in the analyzing process, and the frequency deviation of input signals is tracked, so that the synchronous sampling of the signals is realized, and the frequency spectrum analyzing result with the minimum frequency spectrum leakage is obtained.
2. According to the invention, an additional signal fundamental wave frequency detection or phase locking link is not needed, and only a simple AD conversion hardware circuit with a fixed sampling rate is needed, the system can automatically select the optimal secondary sampling rate to adapt to the frequency drift of the signal, namely, the sampling rate is ensured to be integral multiple of the signal fundamental wave frequency, a complete sampling window always contains integral multiple of the signal fundamental wave and harmonic wave period, and a spectrum analysis result with minimum spectrum leakage is obtained.
3. Compared with the traditional synchronous sampling harmonic analysis based on a phase-locked loop and a method for performing frequency spectrum correction by adopting a window function, the method has the advantages of simple system structure, automatic tracking of frequency drift of a power frequency signal and wider application field.
Drawings
FIG. 1 is a flow diagram of a harmonic analysis method;
fig. 2 shows a basic structure of a harmonic analysis system.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to realize a hardware system of the analysis method of the invention, as shown in fig. 2, the MCU is used as a data processing core, and STM32F407 is adopted, specifically, the MCU carries a 12-bit AD converter on chip; and sampling the input signal by using the MCU chip-carried AD converter. The input signal of the AD converter is the measured power grid signal, and the output of the AD converter is connected with the input of the primary sampling data buffer area; the output of the primary sampling data buffer area is connected with the input of the secondary virtual sampling unit; the output of the secondary virtual sampling unit is connected with the input of the secondary sampling data buffer area; the output of the secondary sampling data buffer area is connected with the input of the spectrum analysis unit; the output of the spectrum analysis unit is connected with the input of the spectrum leakage estimation unit, and the output of the spectrum leakage estimation unit is connected with the input of the virtual sampling period regulation unit; the output of the virtual sampling period adjusting unit is connected with the control end of the secondary virtual sampling unit, and the virtual sampling period s can be adjusted by the whole system according to the total energy leakage of the frequency spectrum through a closed loop formed among the secondary virtual sampling unit, the secondary sampling data buffer area, the frequency spectrum analyzing unit, the frequency spectrum leakage estimating unit and the virtual sampling period adjusting unit, so that a signal harmonic analysis result is finally output. The primary sampling data buffer area and the secondary sampling data buffer area are respectively used for storing signal data collected by the AD converter and the secondary virtual sampling unit; in the initialization process of the harmonic analysis system, hardware peripherals such as needed ADC, a timer, a memory and the like are set, the sampling rate of the ADC1 is set to be about 3.2kHz, and the sampling window time is 50 ms.
Referring to fig. 1, a method for analyzing voltage and current harmonics of a power grid specifically includes the following steps:
s1, using fixed frequency sampling signal to control AD converter to sample input voltage signal, completing 160 times sampling under the condition of ensuring sampling rate satisfying basic requirement of sampling theorem, making sampling window time greater than 2 times of signal base frequency period, first time sampling data being D ═ D [ -D [0,D1,…,D159]。
S2, after sampling is completed 160 times, setting the initial virtual sampling period S to be 1, performing secondary sampling on the first sampled data by the secondary virtual sampling unit with the virtual sampling period S, and performing secondary sampling according to the following formula:
obtaining 128 secondary sampling data after secondary virtual samplingAnd stored in a subsampled data buffer, where 128 is an integer power of 2, int (·) is an integer function, Dint(is)And Dint(is)+1Respectively, the data in the first sampling data, the serial numbers of which are respectively the fetching of isAnd adding 1 to the integer and the integer.
S3, substituting the secondary sampling data into a spectrum analysis unit, the spectrum analysis unit utilizes FFT algorithm to dataAnalyzing to obtain frequency spectrum P ═ P of voltage signal0,P1,…,P127]；
S4, the frequency spectrum leakage estimation unit scans and accumulates all spectral lines except the power frequency signal and the harmonic thereof in the frequency spectrum to obtain total energy leakage d of the frequency spectrum;
according to the set conditions, the power frequency fundamental wave signal is located in the ith spectral line, all k multiplied by l spectral lines in the frequency spectrum are power frequency signals and harmonic components thereof, k is a positive integer, and l is greater than 1. The frequency spectrum leakage estimation unit scans and accumulates all spectral lines except the power frequency signal and the harmonic thereof in the frequency spectrum to obtain the total energy leakage of the frequency spectrum: in this embodiment, the power frequency fundamental component will be in the 2 nd spectral line, and all even spectral lines other than the 0 th spectral line are the power frequency signal and its harmonic component. The total energy leakage was calculated as follows:
wherein the initial spectral leakage is set to 0;
s5, the virtual sampling period adjusting unit adjusts the virtual sampling period S according to the total energy leakage, and the method for adjusting the virtual sampling period S comprises the following steps:
wherein, Δ skIs the k-th adjustment quantity, s, of the virtual sampling periodkFor the adjusted virtual sampling period of the k-th time, dkFor the spectral leakage of the k-th virtual sampling data, alpha is an adjustment coefficient, and sign (·) is a sign function;
s6, after the virtual sampling period S is adjusted, repeating the steps S1-S5, the end condition of the circulation is | Sk|＜ΔsthWherein，ΔsthIs a preset error limit.
The grid voltage and current harmonic analysis method provided by the invention does not need an additional signal fundamental frequency detection or phase locking link, and only needs a simple AD conversion hardware circuit with a fixed sampling rate, so that the system can automatically select the optimal secondary sampling rate to adapt to the frequency drift of the signal, namely, the sampling rate is ensured to be integral multiple of the signal fundamental frequency, a complete sampling window always contains integral multiple of the signal fundamental frequency and harmonic period, and a spectrum analysis result with minimum spectrum leakage is obtained.
The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.
Claims (5)
1. A power grid voltage and current harmonic analysis method is characterized by comprising the following steps:
s1, controlling the AD converter to sample the input voltage signal by using the fixed-frequency sampling signal, wherein the first sampling data is D ═ D0,D1,…,Dn-1]；
S2, secondary sampling is carried out on the first sampling data by a secondary virtual sampling unit in a virtual sampling period S, and the data obtained after virtual sampling is
S3, the spectrum analysis unit uses FFT algorithm to data
Analyzing to obtain frequency spectrum P ═ P of voltage signal0,P1,…,Pm-1]；
S4, the frequency spectrum leakage estimation unit scans and accumulates all spectral lines except the power frequency signal and the harmonic thereof in the frequency spectrum to obtain total energy leakage d of the frequency spectrum;
s5, the virtual sampling period adjusting unit adjusts the virtual sampling period S according to the total energy leakage;
s6, after the virtual sampling period S is adjusted, repeating the steps S1-S5, the end condition of the circulation is | Sk|＜ΔsthWherein, Δ sthIs a preset error limit.
2. The grid voltage current harmonic analysis method according to claim 1, wherein the virtual sampling is performed according to the following formula:
wherein the content of the first and second substances,
the ith virtual sample data is represented by i ═ 1,2, …, m-1, and m is an integer power of 2; int (. beta.) is a rounding function, Dint(is)And Dint(is)+1The data in the first sampling data are respectively, and the serial numbers of the data are respectively the rounding result and the rounding plus 1 of the is.
3. The grid voltage current harmonic analysis method according to claim 1, wherein the method for calculating the total energy leakage d of the frequency spectrum comprises the following steps:
wherein, PjThe power frequency fundamental wave signal is located in the ith spectral line.
4. The grid voltage current harmonic analysis method according to claim 1, wherein the method for adjusting the virtual sampling period s comprises:
Δsk＝sign[(dk-1-dk)×Δsk-1]×α×dk
sk＝sk-1+Δsk
wherein, Δ skIs the k-th adjustment quantity, s, of the virtual sampling periodkFor the adjusted virtual sampling period of the k-th time, dkFor the spectral leakage of the k-th virtual sampling data, α is an adjustment coefficient, and sign (·) is a sign function.
5. The utility model provides a grid voltage current harmonic analysis system, its characterized in that, is including AD converter, the first sampling data buffer, the virtual sampling unit of secondary, the second sampling data buffer and the spectral analysis unit that connect gradually, the spectral analysis unit is through the frequency spectrum leakage estimation unit, the virtual sampling cycle regulating unit that connect gradually connect the virtual sampling unit of secondary, and the virtual sampling cycle regulating unit leaks according to the frequency spectrum that the estimation unit calculated is leaked to the frequency spectrum, adjusts virtual sampling cycle s.
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