CN117054737B - Method and device for calculating power supply frequency through autocorrelation filtering - Google Patents
Method and device for calculating power supply frequency through autocorrelation filtering Download PDFInfo
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- CN117054737B CN117054737B CN202311026967.2A CN202311026967A CN117054737B CN 117054737 B CN117054737 B CN 117054737B CN 202311026967 A CN202311026967 A CN 202311026967A CN 117054737 B CN117054737 B CN 117054737B
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- 230000003111 delayed effect Effects 0.000 claims description 4
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
- G01R19/2503—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques for measuring voltage only, e.g. digital volt meters (DVM's)
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E40/40—Arrangements for reducing harmonics
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Abstract
The invention provides a method and a device for calculating power supply frequency by autocorrelation filtering, which belong to automatic monitoring methods for various power quality detection equipment and power wave recording devices. Firstly, filtering an AD sampled voltage signal, multiplying the AD sampled voltage signal by signals with time delays of m and 2m respectively, and obtaining a current instantaneous frequency value according to a formula after the multiplied data passes through a low-pass filter. The instantaneous frequency values of a plurality of power frequency periods are averaged to obtain the accurate value of the frequency. The invention has the advantages that the delay is much smaller than that of the conventional method, the calculation accuracy is high, and the invention is suitable for various computers, DSPs or FPGAs.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a method and a device for calculating power supply frequency by autocorrelation filtering, which are used for frequency measurement of power quality detection equipment.
Background
With the development of power electronics technology, power quality monitoring is increasingly used in power systems, and frequency measurement is an important component of power quality. High-precision measurement of power frequency is the basis for measurement of many other parameters of power quality.
Common frequency measurement methods include a gate method, a period method, and an equal accuracy method. However, these methods have the following disadvantages: 1. the voltage needs to be converted into a square wave using a regulating circuit, and then the frequency is calculated using a timer/counter; 2. frequency information point by point with the AD sampling rate cannot be provided; 3. sufficient accuracy can be obtained by measuring a plurality of power frequency periods, and the resolution and accuracy of instantaneous measurement are not ideal.
With the development of computer hardware level, the limitation of the calculation complexity on the algorithm is smaller, so that the use of a more complex algorithm can be considered to calculate the numerical value after the AD conversion into frequency information.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method and a device for calculating power supply frequency by autocorrelation filtering, which are used for various power quality detection equipment and power wave recording devices.
The technical scheme adopted by the invention for achieving the purpose is as follows: a method of calculating a power supply frequency by autocorrelation filtering, comprising the steps of:
sampling the analyzed voltage signal with a sampling period Ts to obtain V (n);
filtering harmonic waves and direct current components of V (n) to obtain V' (n);
multiplying V '(n) by V' (n) after delaying mTs and 2mTs respectively, wherein m is a shaping constant;
filtering high-frequency components in the multiplication result;
obtaining instantaneous frequency according to the multiplication result of the filtered high-frequency components;
the voltage frequency over a period of time is obtained from the instantaneous frequency.
The V 'n is multiplied by V' n after being respectively delayed by mTs and 2mTs, and the method specifically comprises the following steps: the multiplication S1 (n) and S2 (n) results are expressed as:
S1(n)＝V`(n)V`(n+m)
S2(n)＝V`(n)V`(n+2m)
the voltage signal V (n) is represented as follows:
V(n)＝Ucos(2π×n×Ts×f(n))
wherein U is fundamental voltage, and f (n) is instantaneous frequency;
substituting V (n) into S1 (n) and S2 (n) and performing triangular decomposition to obtain:
where ρ=2pi×ts×f (n).
The multiplication result of the filtered high-frequency components is as follows:
the instantaneous frequency is:
the voltage frequency over the period of time is:
wherein N is the number of sampling points corresponding to the time period.
An apparatus for calculating a power supply frequency by autocorrelation filtering, comprising:
a sampling module for sampling the analyzed voltage signal V (n) with a sampling period Ts; the band-pass filter is used for filtering harmonic waves and direct current components of V (n) to obtain V' (n);
the delay module is used for respectively delaying V' (n) to mTs and 2mTs, wherein m is a shaping constant;
the multiplication module is used for multiplying the delayed result with V' (n);
a low-pass filter for filtering out high-frequency components in the multiplication result;
the processing module is used for obtaining the instantaneous frequency according to the multiplication result of the filtered high-frequency components;
the determining module is used for obtaining the voltage frequency in a period of time according to the instantaneous frequency.
The invention has the following advantages and beneficial effects:
1. the time delay of the frequency calculation of the invention depends on the AD sampling period and the order of the filter, and generally, high precision can be obtained in 1 to 2 power frequency periods, and the time delay of the calculation is greatly smaller than that of the conventional method.
2. The calculation accuracy is high.
3. Is suitable for various computer, DSP or FPGA.
Drawings
FIG. 1 is a flow chart of a method according to an embodiment of the present invention;
FIG. 2 is a block diagram of the computational principle of an embodiment of the present invention;
fig. 3 is a block diagram of an apparatus according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
As shown in fig. 1 and 2, a method for calculating an electric power supply frequency by autocorrelation filtering includes the following steps:
and a step a, sampling the analyzed voltage signal by taking a sampling period as Ts to obtain V (n), wherein n is a voltage sampling sequence number, directly obtaining the voltage signal of the power grid by using a voltage divider or from the PT secondary side of the voltage transformer, and sending the voltage signal to an AD sampling position through an anti-aliasing filter. Filtering harmonic wave and direct current component by using a band-pass filter to obtain V ' (n), and then multiplying the V ' (n) by mTs and 2mTs respectively to obtain the V ' (n):
S1(n)＝V ′ (n)V ′ (n+m)
S2(n)＝V ′ (n)V ′ (n+2m) (1)
where m is a shaping constant, generally 2mTS corresponds to about 1/8 cycle, and in practice the m > =1 algorithm is true. The voltage signal V (n) may be expressed as follows:
V(n)＝Ucos(2π×n×Ts×f(n)) (2)
wherein U is fundamental voltage, f (n) is instantaneous frequency, and the fundamental voltage is substituted into formula (1) and subjected to triangular decomposition to obtain:
where ρ=2pi×ts×f (n).
Step b, filtering high-frequency components of S1 (n) and S2 (n) by a low-pass filter to obtain:
step c, solving the equation to obtain
When the delay is less than pi/2, the plus sign is established, and then the instantaneous value of the frequency can be obtained:
where f (n) is the instantaneous frequency.
The arithmetic average of the instantaneous frequency over a period of time is the exact value of the frequency. Averaging the instantaneous frequency over a period of time, yielding an accurate value f of frequency:
wherein N is the number of sampling points corresponding to the period of time, and n=0 to N-1.
As shown in fig. 3, an apparatus for calculating an electric power supply frequency by autocorrelation filtering includes:
a sampling module for sampling the analyzed voltage signal V (n) with a sampling period Ts;
the band-pass filter is used for filtering harmonic waves and direct current components of V (n) to obtain V' (n), and the cut-off frequency of the band-pass filter is 90Hz;
the delay module is used for respectively delaying V' (n) to mTs and 2mTs, wherein m is a shaping constant;
the multiplication module is used for multiplying the delayed result with V' (n);
a low-pass filter for filtering out high-frequency components in the multiplication result, the cut-off frequency of the low-pass filter being 45Hz;
the processing module is used for obtaining the instantaneous frequency according to the multiplication result of the filtered high-frequency components;
the determining module is used for obtaining the voltage frequency in a period of time according to the instantaneous frequency.
Claims (2)
1. A method of calculating an electrical power supply frequency by autocorrelation filtering, comprising the steps of:
sampling the analyzed voltage signal with a sampling period Ts to obtain V (n);
filtering harmonic waves and direct current components of V (n) to obtain V' (n);
multiplying V '(n) by V' (n) after delaying mTs and 2mTs respectively, wherein m is a shaping constant;
filtering high-frequency components in the multiplication result;
obtaining instantaneous frequency according to the multiplication result of the filtered high-frequency components;
obtaining a voltage frequency within a period of time according to the instantaneous frequency;
the V 'n is multiplied by V' n after being respectively delayed by mTs and 2mTs, and the method specifically comprises the following steps:
the multiplication S1 (n) and S2 (n) results are expressed as:
S1(n)＝V`(n)V`(n+m)
S2(n)＝V`(n)V`(n+2m)
the voltage signal V (n) is represented as follows:
V(n)＝Ucos(2π×n×Ts×f(n))
wherein U is fundamental voltage, and f (n) is instantaneous frequency;
substituting V (n) into S1 (n) and S2 (n) and performing triangular decomposition to obtain:
wherein ρ=2pi×ts×f (n);
the multiplication result of the filtered high-frequency components is as follows:
the instantaneous frequency is:
2. the method of claim 1, wherein the voltage frequency over the period of time is:
wherein N is the number of sampling points corresponding to the time period.
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