CN104569581B - Multi-level set and single-cycle estimation method of power grid frequency measuring - Google Patents
Multi-level set and single-cycle estimation method of power grid frequency measuring Download PDFInfo
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Abstract
The invention provides a multi-level set and single-cycle estimation method of power grid frequency measuring. The method includes: performing low-pass filter on an input signal, and then sampling the signal; setting more than two thresholds horizontally intersecting with a sinusoidal periodic signal, determining the adjacent intersection points, whose slope is identical with the slope of two tangent lines of the sinusoid, of each threshold and signal sampling points close to the two intersection points, directly calculating the fundamental frequency of the threshold if the two intersection points of the threshold coincide with the signal sampling points, or else respectively substituting the signal sampling points close to the intersection points into a Lagrange interpolation formula, and calculating the fundamental frequency estimation value corresponding to the threshold; determining the weight of the multi-level set fundamental frequency estimation value acquired by each threshold according to the absolute value of the tangent line slope of the intersection points of each threshold and the sinusoidal periodic signal, and using a weighted average method to obtain the final fundamental frequency estimation value. The method has the advantages that multi-level set and single-cycle estimation frequency is achieved by multiple thresholds, and the method is good in instantaneity and high in precision.
Description
Technical field
The invention belongs to power domain, and in particular to a kind of power grid frequency measurement method.
Background technology
In existing fundamental wave frequency measurement method, frequently with integer-period sampled counting method, the method determines fundamental wave first
Cycle, it is determined that after the primitive period, determining the frequency of fundamental wave further according to the time interval between sampled point in the primitive period.Should
, when the sampling period is less, measured frequency accuracy is very poor, and when the sampling period is longer, can not meet real-time again for method
Requirement, additionally, the method does not filter high frequency harmonic signals in measurement frequency, when harmonic wave serious interference, can affect whole
The determination of individual primitive period, ultimately results in measured frequency inaccurate.
The content of the invention
The invention aims to overcome the shortcomings of above-mentioned power grid frequency measurement method, a kind of grid frequency measurement is proposed
Multilevel collection monocycle method of estimation, the method can with the existing frequency measurement method of effectively solving measure mains frequency when
The problem that precision is poor and real-time is poor.
The present invention proposes a kind of multilevel collection monocycle method of estimation of grid frequency measurement, and methods described includes following
Step：
Step one：Low-pass filtering treatment is carried out with low pass filter to input signal；Eliminate the interference of high-frequency harmonic；
Step 2：Select suitable sample frequency fsWith sampling length N, equal interval sampling, sample frequency f are carried out to signals
2 times of the frequency of highest harmonic componentss contained by signal should be not less than, signal discrete sample sequence x (t are obtainedn), n=0,1,
2,…,N-1；
Step 3：Find out discrete sampling sequence x (tn) in maximum MAX and minimum value MIN, then arrange m threshold value Yi, m
It is the integer more than or equal to 2, i=1,2 ..., m；
Step 4：Determine each threshold value and sinusoidal 2 tangent slope identical adjoining nodes and close on this 2 friendships
The signal sampling point of point, the time interval of 2 tangent slope identical adjoining nodes are 1 primitive period of signal；If
2 intersection points of certain threshold value are overlapped with signal sampling point, then directly calculate fundamental frequency estimated value fi；If certain threshold value
2 intersection points are not overlapped with signal sampling point, then the signal sampling point by the threshold value with the above-mentioned near intersections of sinusoidal signal is substituted into
Lagrange formula for interpolations, calculate threshold value YiCorresponding fundamental frequency estimated value；After all threshold calculations are finished, the m of acquisition
Individual fundamental frequency estimated value is multilevel collection fundamental frequency estimated value fi；
Step 5：To multilevel collection fundamental frequency estimated value f is obtained in step 4iIt is weighted averagely, calculates final
Fundamental frequency estimated value f, wherein weights qiIt is exhausted with the sine curve tangent slope of sinusoidal intersection point according to each threshold value
To value | Ki| it is determined that, slope absolute value is bigger, and weights are less, final fundamental frequency estimated value f=q1f1+q2f2+…+qmfm。
Described method, in step 3, described threshold value YiDiscrete sampling sequence x (t should be less thann) in maximum and
More than discrete sampling sequence x (tn) in minima, and for ensure set by threshold value in rational scope, eliminate other do not know
The interference that factor causes so as to meet：0.9MIN+0.1MAX<Yi<0.9MAX+0.1MIN；
Described method, in step 4, if 2 intersection points of certain threshold value are not overlapped with signal sampling point, by the threshold
Value substitutes into Lagrange formula for interpolations with the signal sampling point of the above-mentioned near intersections of sinusoidal signal, calculates threshold value YiCorresponding base
Wave frequency estimated value, is simplified operation, by the threshold value and the sampled signal discrete data (t, x (t)) of sinusoidal signal near intersections
4 Lagrange formula for interpolations are substituted into, through being calculated threshold value YiCorresponding fundamental frequency estimated value fi。
Described method, in step 5, weights qiAccording to the sine curve tangent line of each threshold value and sinusoidal intersection point
Slope absolute value | Ki| it is determined that, fiCorresponding weights are：
Beneficial effect：The present invention realizes grid frequency measurement using multilevel collection, overcomes conventional single threshold method easily quilt
The defect of noise jamming, and the present invention can realize frequency measurement within the monocycle, with high precision, real-time is good the characteristics of.
Description of the drawings
Fig. 1 is the theory diagram of handling process of the present invention；
Fig. 2 is single threshold Frequency Estimation schematic diagram of the present invention；
Fig. 3 is the Frequency Estimation schematic diagram that intersection point of the present invention is overlapped with sampled point；
Fig. 4 is intersection point of the present invention and the misaligned Frequency Estimation schematic diagram of sampled point；
Fig. 5 is multi thresholds Frequency Estimation schematic diagram of the present invention.
Specific embodiment
The present invention proposes a kind of multilevel collection monocycle method of estimation of grid frequency measurement.Enter traveling one to the present invention
Step is described in detail.It should be appreciated that specific embodiment described herein is not used to limit this only to explain the present invention
It is bright.
1. the embodiment of the present invention first carries out low-pass filtering treatment with low pass filter to the signal being input into, then with sample frequency
fs=1000Hz carries out periodic sampling to signal, finds out maximum MAX and minimum value MIN；
The model of fundamental wave sinusoidal periodic signal is:
X (t)=A sin (2 π ft+ θ)+B (1)
In formula, A represents the amplitude of sinusoidal periodic signal, and f represents the frequency of sinusoidal periodic signal, and θ represents sinusoidal periodic signal
Initial phase, B represents the DC component of sinusoidal periodic signal.As shown in Fig. 2 sinusoidal periodic signal x (t) and certain threshold value b phase
The time interval of friendship and 2 adjacent intersection points of sine curve tangent slope identical is 1 primitive period of signal.Therefore,
By this 2 intersection points, a fundamental frequency estimated value of signal can be just obtained.
2. with sample frequency fsEquidistant discrete sampling, ordinary circumstance are carried out to the cycle analogue signal shown in formula (1)
Under, in real process, threshold value b is typically difficult to overlap with signal sampling point with the intersection point of sinusoidal signal, therefore in two kinds of situation：
1. as shown in figure 3, the above-mentioned intersection point of threshold value b is overlapped with signal sampling point, it should directly calculate this threshold value corresponding
Fundamental frequency estimated value：
F in formulagIt is fundamental frequency estimated value corresponding with threshold value b；
2. as shown in figure 4, the intersection point of threshold value b is misaligned with signal sampling point, intersection point (t is obtained by samplingb, b) near
Sampled point [tk-2, x (tk-2)]、[tk-1, x (tk-1)]、[tk, x (tk)]、[tk+1, x (tk+1)] and [tk+2, x (tk+2)].Using
Lagrange interpolation methods, can obtain 4 interpolation polynomials L4T () is：
By (tb, b) substitute into (3) and obtain：
L4(tb)=b (4)
T is solved by formula (4)b, t can be obtained in the same mannerb', have：
F in formulagIt is fundamental frequency estimated value corresponding with threshold value b；So far, complete to fundamental frequency corresponding to threshold value b
The estimation of value.
3. for sake of convenience, only the situation that 5 threshold values are intersected with sinusoidal periodic signal is explained below：
5 threshold values Y intersected with sinusoidal cycles sampled signal are seti, and make which in the reasonable scope, there is 0.9MIN+
0.1MAX<Yi<0.9MAX+0.1MIN, wherein i=1,2,3,4,5.The fundamental wave corresponding with each threshold value can be obtained by above-mentioned principle
Frequency estimation, can obtain and threshold value Y1Corresponding fundamental frequency estimated value is f1；With threshold value Y2Corresponding fundamental frequency estimated value is
f2；With threshold value Y3Corresponding fundamental frequency estimated value is f3；With threshold value Y4Corresponding fundamental frequency estimated value is f4；With threshold value Y5It is right
The fundamental frequency estimated value answered is f5.According to each threshold value YiWith tangent line at the sine curve of sinusoidal cycles sampled signal intersection point place
Slope absolute value | Ki| size, wherein KiValue by YiWith 4 interpolation polynomials L of the above-mentioned intersection point of sine curve4T () leads
Number is obtained, i.e.,：
To fundamental frequency estimated value f corresponding to each threshold valueiWeighting, absolute value are bigger, and weights are less, fiCorresponding power
It is worth and isI=1,2,3,4,5；Calculated with weighted average method is recycled to obtain most
Whole frequency estimation：
In formula, f is final fundamental frequency estimated value.
So far, the multilevel collection monocycle for completing grid frequency measurement is estimated.The method calculates simple, by threshold value with
The sinusoidal tangent slope identical adjoining nodes of sampled signal just can measure electrical network fundamental frequency, and employ 4 times
Lagrange interpolation methods and the method for weighting, possess extraordinary real-time and accuracy.
Claims (4)
1. the multilevel collection monocycle method of estimation of a kind of grid frequency measurement, it is characterised in that methods described includes following steps
Suddenly：
Step one：Low-pass filtering treatment is carried out to input signal with low pass filter, the interference of high-frequency harmonic is eliminated；
Step 2：Select suitable sample frequency fsWith sampling length N, equal interval sampling, sample frequency f are carried out to signalsShould not
Less than 2 times of the frequency of highest harmonic componentss contained by signal, signal discrete sample sequence x (t are obtainedn), n=0,1,2 ..., N-
1；
Step 3：Find out discrete sampling sequence x (tn) in maximum MAX and minimum value MIN, then arrange m threshold value Yi, m is big
In the integer equal to 2, i=1,2 ..., m；
Step 4：Determine each threshold value and sinusoidal 2 tangent slope identical adjoining nodes and close on this 2 intersection points
Signal sampling point, the time interval of 2 tangent slope identical adjoining nodes are 1 primitive period of signal, if certain
2 intersection points of threshold value are overlapped with signal sampling point, then directly calculate fundamental frequency estimated value fiIf, 2 of certain threshold value
Intersection point is not overlapped with signal sampling point, then the signal sampling point by the threshold value with the above-mentioned near intersections of sinusoidal signal is substituted into
Lagrange formula for interpolations, calculate threshold value YiCorresponding fundamental frequency estimated value, after all threshold calculations are finished, the m of acquisition
Individual fundamental frequency estimated value is multilevel collection fundamental frequency estimated value fi；
Step 5：To multilevel collection fundamental frequency estimated value f is obtained in step 4iIt is weighted average, the final fundamental wave frequency of calculating
Rate estimated value f, wherein weights qiAccording to the sine curve tangent slope absolute value of each threshold value and sinusoidal intersection point | Ki|
It is determined that, slope absolute value is bigger, and weights are less, final fundamental frequency estimated value f=q1f1+q2f2+…+qmfm。
2. method according to claim 1, it is characterised in that in step 3, described threshold value YiDiscrete sampling should be less than
Sequence x (tn) in maximum and be more than discrete sampling sequence x (tn) in minima, and for ensure set by threshold value rational
In the range of, eliminate the interference that other uncertain factors cause so as to meet 0.9MIN+0.1MAX<Yi<0.9MAX+0.1MIN。
3. method according to claim 1, it is characterised in that in step 4, if 2 intersection points of certain threshold value not with letter
Number sampled point overlaps, then will the threshold value to substitute into Lagrange interpolation with the signal sampling point of the above-mentioned near intersections of sinusoidal signal public
Formula, calculates threshold value YiCorresponding fundamental frequency estimated value, is simplified operation, by adopting for the threshold value and sinusoidal signal near intersections
Sample signal discrete data (t, x (t)) substitute into 4 Lagrange formula for interpolations, through being calculated threshold value YiCorresponding fundamental wave
Frequency estimation fi。
4. method according to claim 1, it is characterised in that in step 5, weights qiAccording to each threshold value
With the sine curve tangent slope absolute value of sinusoidal intersection point | Ki| it is determined that, fiCorresponding weights are：
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| CN105403767A (en) * | 2015-10-21 | 2016-03-16 | 广东美的制冷设备有限公司 | Voltage frequency detection method of alternating current power supply input into air conditioner, system and the air conditioner |
| CN109633266B (en) * | 2019-02-26 | 2020-12-01 | 重庆新世杰电气股份有限公司 | Frequency measurement method, system, device and computer readable storage medium |
| CN112151065B (en) * | 2019-06-28 | 2024-03-15 | 力同科技股份有限公司 | Method, device, equipment and computer storage medium for detecting single-tone signal frequency |
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| CN102116798A (en) * | 2011-03-07 | 2011-07-06 | 深圳市锐能微科技有限公司 | Power grid frequency measurement method and device |
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