CN111983307A - SOGI-based rapid and accurate frequency detection method - Google Patents
SOGI-based rapid and accurate frequency detection method Download PDFInfo
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- CN111983307A CN111983307A CN201910423714.6A CN201910423714A CN111983307A CN 111983307 A CN111983307 A CN 111983307A CN 201910423714 A CN201910423714 A CN 201910423714A CN 111983307 A CN111983307 A CN 111983307A
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Abstract
The application discloses a quick and accurate frequency detection method based on SOGI, which comprises the steps of sampling and normalizing a single-phase voltage signal, and carrying out IIR low-pass filtering on obtained normalized floating point data so as to eliminate the influence caused by harmonic waves and inter-harmonic waves; separating out in-phase and orthogonal components of the filtered signal by using an SOGI module, obtaining active and reactive components according to dq transformation, obtaining the reactive component of 0 according to physical significance, and correcting according to the physical significance to obtain accurate phase and frequency information; the obtained frequency is a fluctuation amount, and a stable frequency detection result can be obtained by utilizing an average filtering algorithm; the filter adopts a lower order, the coefficient of the filter is obtained by a computer and is stored in Flash for calling; the average filtering can adopt three stages in series to enlarge the detection range of the frequency.
Description
Technical Field
The invention belongs to the field of electric energy quality of an electric power system, and mainly aims to accurately detect the frequency of a power grid, particularly to consider the condition of high harmonic component in the voltage of the power grid.
Background
With the rapid development of power electronic technology and information technology, the wide application of various nonlinear devices, the enlargement of the scale of a power grid and the improvement of complexity, harmonic current can be inevitably generated in the power grid. Harmonic voltages are generated by harmonic currents and grid impedance, so harmonic voltages are unavoidable, and are particularly severe in weak grids.
The zero-crossing detection of the voltage of the power grid is a frequency locking mode adopted by many products, and has the advantages of being fast, simple and the like, however, when the harmonic content of the power grid is high, the superposition of harmonics can cause zero-crossing point offset, further the result of frequency locking can have great errors, and even frequency out-of-limit misjudgment can be generated.
The phase-locking algorithm is a widely applied detection mode of the frequency and the phase of the power grid, and three-phase frequency locking is a main research content. However, the voltage source of the transformer is also three-phase, so the grid voltage frequency of each phase is different, even when each phase is only 0.01Hz, the obtained frequency locking result will fluctuate, and the frequency locking error is very high, so under the condition of high frequency requirement, the result obtained by three-phase frequency locking cannot represent the frequency result of each phase or one phase, and for the electric energy quality analyzer, the standard is the grid frequency of the reference phase, so single-phase frequency locking is also essential.
Single-phase lock has been studied in recent years and is roughly classified into two categories: a phase-locking algorithm based on power (e.g., LPF-PLLs/MAF-PLLs/DFAC-PLLs algorithms, etc.) and a phase-locking algorithm based on quadrature signals (e.g., TD-PLLs/APF-PLLs/SOGI-PLLs algorithms, etc.). Among the algorithms, the orthogonal signal-based SOGI/FFSOGI phase-locked algorithm has higher performance, high accuracy, fast frequency tracking and simple realization, and is suitable for locking the frequency and the phase of the power grid. However, the SOGI phase-locked algorithm has disadvantages, and when the power grid harmonic is high, a plurality of SOGI modules are required to be combined for use to form an m-SOGI algorithm, which not only increases the calculation amount, but also causes long time delay, and especially when the power grid voltage harmonic content is complex, even when the power grid voltage contains inter-harmonics, the calculation complexity is greatly increased. It follows that the simple SOGI phase-lock algorithm behaves generally for grid voltage harshness conditions.
Disclosure of Invention
The invention aims to provide a quick and accurate frequency detection method based on the SOGI, the method is single-phase frequency detection, is not influenced by three-phase frequency difference, has wide frequency application range, resists harmonic wave and inter-harmonic wave interference, adopts a simple mode to realize high precision, and meets the requirements of an electric energy quality analyzer on frequency for operation time and operation precision.
The invention provides a quick and accurate frequency detection method based on an SOGI (short-range optical waveguide), which comprises the following steps:
sampling single-phase voltage, processing a sampling result to enable the maximum instantaneous value to be about floating point type data between 1 and 2, filtering out harmonic waves and inter-harmonic waves of the floating point type data by adopting a low-pass filtering mode, performing IIR filtering by utilizing coefficients of a Chebyshev II type filter, effectively improving the attenuation performance of a stop band, having shorter time delay, lower operation amount and less storage amount relative to an FIR filter, and enabling the result after the low-pass filtering to be regarded as a pure fundamental component so as to be convenient for directly adopting a single SOGI module to perform frequency detection;
the method comprises the steps that an SOGI module is adopted to extract input signals and orthogonal signals of the input signals, d-axis and q-axis components of a rotating coordinate system are obtained through dq transformation, wherein the q-axis component is used as input of PI control, the control aims are to enable the q-axis component to be 0, the PI control is utilized to obtain angular frequency, power grid frequency can be obtained according to the angular frequency, the current phase of a power grid can also be obtained through an integral mode, and then the power grid frequency is obtained according to sampling frequency;
The mode of obtaining the power grid frequency by using the mode can lead the frequency result to fluctuate, the fluctuation periodicity is good, generally, the direct current component is the actual frequency result, and therefore, the mean value filtering mode is adopted to filter the frequency locking result, and the stable frequency locking result is obtained.
Wherein, still include:
the IIR filter coefficient is designed by using MATLAB, the filter type is a Chebyshev II type 3-order low-pass filter, the possibly required filter coefficient is obtained according to the possibly adopted switching frequency, the designed coefficient is stored in Flash, the required filter coefficient is called by a table look-up method, compared with the method for designing the filter coefficient in real time in a program, the operation amount can be greatly reduced, the program implementation is simplified, and the RAM memory space is not occupied.
In order to expand the frequency adaptation range, the frequency obtained by utilizing the phase of the power grid is locked by adopting a three-level mean filtering mode, filters with different lengths are adopted in different frequency ranges, and mean filtering with corresponding lengths of 50Hz, 42.5Hz and 57.5Hz is respectively carried out according to the requirements of the power quality analyzer.
Further comprising:
caching and replacing the mean value filtered data by using a ring buffer;
the sampling frequency can be changed according to the requirement, so that the environment at 50Hz is equivalent to the environment regardless of the change of the grid frequency.
The SOGI-based rapid and accurate frequency detection method comprises the steps of sampling and normalizing single-phase voltage, carrying out IIR low-pass filtering, carrying out second-order generalized integral on the filtered signal, carrying out dq transformation by using a phase locking result, carrying out PI control by using a q-axis signal as a deviation, carrying out operation with a reference angular frequency to obtain a current phase, obtaining the current power grid frequency according to a differential relation and the phase and the sampling frequency, and obtaining a stable frequency value according to a three-level low-pass filtering algorithm.
The method relates to filter selection, and aims at the characteristics of simple operation, small time delay, harmonic filtering and low phase requirement, a third-order Chebyshev II type filter is adopted to filter a voltage signal, an average value filter is adopted to filter according to the characteristic of periodic fluctuation of frequency locking, and a three-level average value filter is adopted to enlarge the frequency detection range. The method also relates to an SOGI phase-locking algorithm, and the SOGI frequency locking can quickly and accurately lock the phase and the frequency. The method mainly utilizes an SOGI phase locking mode to lock frequency, and uses IIR low-pass filtering and mean filtering as assistance, so that accurate power grid frequency can be obtained when the power grid environment is poor.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a three-phase frequency-locking simulation result when the frequencies provided by the embodiment of the invention are consistent;
FIG. 2 is a three-phase frequency-locking simulation result when the frequency difference is 0.01Hz according to the embodiment of the present invention;
fig. 3 is a flowchart of a frequency locking algorithm based on LPF + SOGI according to an embodiment of the present invention;
fig. 4 is a frequency locking simulation result based on the SOGI module according to the embodiment of the present invention;
fig. 5 is a simulation result of frequency locking based on LPF + SOGI according to an embodiment of the present invention;
fig. 6 is a diagram illustrating an IIR low-pass filter structure according to an embodiment of the present invention;
FIG. 7 is a block diagram of an SOGI module according to an embodiment of the present invention;
FIG. 8 is a block diagram of a mean filtering module according to an embodiment of the present invention;
Detailed Description
The core of the invention is to provide a fast and accurate frequency detection method based on the SOGI, the method has simple operation, less resource occupation and high detection accuracy, is suitable for a complex power grid, and meets the detection requirement of a power quality analyzer on frequency parameters.
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 3 is a flowchart of a method for fast and accurate frequency detection based on the SOGI according to an embodiment of the present invention, where the method includes amplitude normalization of voltage signals, low-pass filtering of grid voltage, phase locking of fundamental component SOGI, and frequency-mean filtering of phase locking.
The amplitude normalization module is added because the SOGI module phase lock is accurate only if the signal amplitude is near 1. Because the voltage sampling circuit is unchanged, sampling is carried out by adopting a 12-bit or 16-bit AD chip, and the change range of the effective voltage value is relatively fixed, the voltage normalization coefficient can also be fixed. If sampling is performed by using a 12-bit AD chip, and the maximum sampling value is 3600, the coefficient is about:
k1＝1/(3600-2048)＝6.44×10-4 (1)
the digital filter is divided into a finite impulse response Filter (FIR) and an infinite impulse response filter (IIR), the FIR has no feedback link, can realize strict linear phase characteristics, the IIR filter has few orders, and the order of the IIR filter is 1/10 which is about the order of the FIR filter under the condition of realizing the same performance. The IIR filter is selected to perform low-pass filtering on the voltage signal in consideration of the advantages and the disadvantages of the IIR filter.
IIR Low pass Filter Structure As shown in FIG. 6, aiDenominator coefficient of filter response, biFor the molecular coefficients of the filter response, the transfer function and the difference equation of the IIR filter are:
the SOGI frequency locking module is shown in fig. 7, and the implementation steps are as follows: 1) the filtered voltage signals pass through an SOGI module to obtain mutually orthogonal signals; 2) carrying out dq conversion on the orthogonal signal by using the sine and cosine quantity of a phase locking result to obtain an active component and a reactive component of the orthogonal signal in a rotating coordinate system; 3) controlling the obtained reactive component signal, wherein when the reactive component signal is stable, the constant deviation is the difference between the actual angular frequency and the reference angular frequency, and the actual angular frequency of the power grid and the current phase of the power grid can be obtained according to the reference angular frequency; 4) according to the phase difference Delta theta and the sampling frequency fsThe frequency of the power grid can be obtained.
The voltage signal passes through the SOGI module to obtain mutually orthogonal signals, and the s-domain expression form of the signals is as follows:
vαis an angular frequency of ωnAnd a signal in phase with the voltage signal, vβIs and vαQuadrature angular frequency of omeganSince the phase lock is tracking the fundamental signal, ω isnHas an initial value of 100 pi.
Carrying out dq transformation on the orthogonal signal and a self phase locking result to obtain an active component and a reactive component of the signal:
Because the quadrature signal is dq converted under the self phase locking result, under the condition of accurate phase locking, the active component is the signal per se, the reactive component is 0, if the frequency of the power grid changes, the reactive component has a sudden change, the reactive component can be corrected by using the result of the reactive component as the input of control according to the physical significance, and when the input quantity tends to be stable, the accurate phase and the accurate frequency of the power grid can be obtained.
In the phase locking process, the angular frequency omega is obtainedgFrom this, the grid frequency f can be determinedgAnd the power grid frequency f can be obtained according to the phase after integration and correctiong。
The mean filtering module is shown in fig. 8, and the buffer amount N is the number of sampling points in one period. The mean filter is also called as a moving average filter, and is a special FIR filter, which has an inherent time delay N-1, and the frequency response and the difference equation are respectively:
the mean filter has the obvious characteristics of being capable of realizing recursion, improving the operation efficiency, and only needing two times of addition and one time of multiplication each time no matter how long the filtering length N is.
If variable sampling frequency is adopted for frequency detection, the number of points in the next period of different grid frequencies is a fixed value N, and the obtained frequency detection result is stable; if the frequency detection is carried out by adopting a fixed sampling frequency mode, the point number N of the next period of different power grid frequencies is an indeterminate value, the change of the point number N of one period cannot be ignored when the fluctuation range of the power grid frequency is large, if the cache length of the fixed point number N is still adopted, the obtained frequency result can generate small-range fluctuation (such as +/-0.03 Hz), and under the condition of not changing the cache length, two stages of mean value filtering modules which adapt to different frequencies can be added, so that the frequency detection range is expanded.
For an actual power grid, the frequency of the power grid fluctuates in real time, and the detected frequency inevitably fluctuates. Therefore, when the fluctuation range of the power grid frequency is small (such as 50 +/-1 Hz), only the mean value filtering of N-point cache is needed, the frequency detection error is within +/-0.005 Hz, the requirement of the power quality analyzer on the frequency detection precision is met, and the time delay caused by the mean value filtering can be reduced.
The embodiments are described in a progressive manner in the specification, each embodiment focuses on differences from other embodiments, and the same parts among the embodiments are referred to each other.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or the like. While the foregoing description has generally described various example compositions and steps in terms of their functionality, the manner in which such functionality is implemented should not be construed as exceeding the scope of the invention.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (4)
1. A quick and accurate frequency detection method based on SOGI is characterized in that the method takes power grid voltage as input quantity, and the accurate frequency detection result is finally obtained through digital signal processing and control algorithm and flexible processing according to actual conditions, and the method comprises the following specific steps:
1) analyzing the maximum sampling value range under normal grid voltage according to the AD sampling digit, and normalizing the sampled voltage signal;
2) filtering the voltage signal by adopting a Chebyshev II type IIR filter with low time delay and high filtering performance, filtering harmonic and inter-harmonic components, and only reserving fundamental wave components of a power grid;
3) an SOGI module is adopted to obtain voltage signal fundamental wave frequency in-phase signals and orthogonal signals thereof, active components and reactive components are obtained by dq conversion, the reactive components are controlled to obtain accurate grid angular frequency and phase, the grid frequency can be directly obtained through the angular frequency, and the grid frequency can also be obtained through differential values of the phase;
4) and stabilizing the frequency detected by the SOGI phase-locking method by adopting an average filter, eliminating the fluctuation of the frequency and obtaining a stable frequency result.
2. The SOGI-based fast and accurate frequency detection method according to claim 1, wherein filter parameters are designed by a computer, a plurality of parameters are designed according to a sampling frequency that may be adopted, and stored in Flash for calling; according to the estimated frequency range or in combination with the actual power grid condition, 1-stage or 3-stage mean filtering is adopted for frequency stabilization processing so as to eliminate the fluctuation of the frequency detection result caused by different frequencies as much as possible.
3. The SOGI-based fast and accurate frequency detection method according to claim 1, wherein when the sampling frequency is changed, the current frequency locking process is immediately ended, all the intermediate process values are restored to the initialization values, and the frequency locking process is restarted.
4. The SOGI-based fast and accurate frequency detection method according to claim 1, wherein the frequency is read and resampled every 10 cycles according to the requirement of the power quality analyzer, and if the sampling frequency is changed, the accurate and stable grid frequency detection result can be obtained only by one-stage mean filtering.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115015682A (en) * | 2022-08-09 | 2022-09-06 | 南京佑友软件技术有限公司 | Real-time online monitoring method for power quality |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH10132874A (en) * | 1996-11-01 | 1998-05-22 | Hioki Ee Corp | Frequency measuring device |
| CN102820884A (en) * | 2012-02-14 | 2012-12-12 | 上海大学 | Control method of single-phase phase locked loop based on second-order integrator |
| EP2623997A1 (en) * | 2012-02-03 | 2013-08-07 | Siemens Aktiengesellschaft | Determining a phase and a frequency of an electric quantity of an operating electrical device |
| CN103472302A (en) * | 2013-09-16 | 2013-12-25 | 宁夏隆基宁光仪表有限公司 | Method for using one-phase photovoltaic grid-connected inverter to detect network voltage phase |
| CN109510619A (en) * | 2018-11-09 | 2019-03-22 | 哈工大（张家口）工业技术研究院 | Enhanced phaselocked loop for the detection of single-phase mains voltage synchronizing information |
| CN109557365A (en) * | 2018-10-12 | 2019-04-02 | 西安电子科技大学 | Network voltage frequency and phase-angle detection method and system, single-phase power grid detection system |
-
2019
- 2019-05-21 CN CN201910423714.6A patent/CN111983307A/en not_active Withdrawn
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH10132874A (en) * | 1996-11-01 | 1998-05-22 | Hioki Ee Corp | Frequency measuring device |
| EP2623997A1 (en) * | 2012-02-03 | 2013-08-07 | Siemens Aktiengesellschaft | Determining a phase and a frequency of an electric quantity of an operating electrical device |
| CN102820884A (en) * | 2012-02-14 | 2012-12-12 | 上海大学 | Control method of single-phase phase locked loop based on second-order integrator |
| CN103472302A (en) * | 2013-09-16 | 2013-12-25 | 宁夏隆基宁光仪表有限公司 | Method for using one-phase photovoltaic grid-connected inverter to detect network voltage phase |
| CN109557365A (en) * | 2018-10-12 | 2019-04-02 | 西安电子科技大学 | Network voltage frequency and phase-angle detection method and system, single-phase power grid detection system |
| CN109510619A (en) * | 2018-11-09 | 2019-03-22 | 哈工大（张家口）工业技术研究院 | Enhanced phaselocked loop for the detection of single-phase mains voltage synchronizing information |
Non-Patent Citations (2)
| Title |
|---|
| 桂志国、陈友兴主编: "《数字信号处理原理及应用》", 30 June 2016, 国防工业出版社 * |
| 马明建: "《数据采集与处理技术》", 30 June 2012, 西安交通大学出版社 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115015682A (en) * | 2022-08-09 | 2022-09-06 | 南京佑友软件技术有限公司 | Real-time online monitoring method for power quality |
| CN115015682B (en) * | 2022-08-09 | 2022-11-08 | 南京佑友软件技术有限公司 | Real-time online monitoring method for power quality |
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