CN102809687A - Digital measurement method for alternating-current frequency - Google Patents

Abstract

The invention discloses a digital measurement method for an alternating-current frequency. According to the digital measurement method, aiming at continuous digital sampling signals, a sampling point P1 is selected after the signals passing through a positive peak and a negative peak; two continuous points P2 and P3 are selected from subsequent sampling points; the selection condition of the P2 and P3 is that the negative value of the sampling value P1 is within the interval [sampling value P2, sampling value P3]; a point P4 is solved on a line segment formed by the P2 and P3 by an interpolation method, so that the numerical value of the P4 is equal to the negative value of the sampling value P1; simultaneously, the virtual occurrence time of the P4 can be acquired; the zero point of an electric signal is calculated by the sampling occurrence time P1 and the virtual occurrence time of the P4; and the frequency or the period of the electric signal is calculated by zero-crossing points of a series of electric signals. A low-frequency signal is not required to be converted into square wave, so that the method is particularly suitable for the frequency measurement of low-frequency sinusoidal signals, the system detection is convenient, the hardware overhead is low, the anti-interference capacity of the system is high, the method is implemented easily and reasonably, and the data are accurate and reliable.

Description

A kind of digital measuring method of ac frequency

Technical field

The present invention relates to a kind of digital measuring method of ac frequency, also can be used for fixing the frequency measurement of the little low frequency sinusoidal signal of frequency or change of frequency, triangular signal etc.

Background technology

In daily life, production run, usually need the frequency of monitor signal, the frequency of measurement is accurate more, and application results is often better.In the frequency measurement method of existing low frequency signal, be mostly low frequency signal is formed square wave through shaping circuit earlier, the time interval T of adjacent two rising edges of detection side's phase of wave or negative edge asks inverse to draw frequency.In addition the method that also has some software measurement frequencies, such as: zero friendship method, analytical method, error minimize principle class algorithm, DFT class algorithm, quadrature remove modulation method or the like.But these algorithms are easy to a bit realize but precision is lower, and the operand of some algorithm is excessive.

Prior art one: application number is measuring method and the device that 02107167 Chinese patent discloses a kind of three-phase alternating current frequency; Through sampled voltage or current signal; Ask for the angular velocity of voltage or electric current rotating vector, and then utilize rotating vector angular velocity reduced frequency.Though this measurement mechanism antijamming capability is strong; But shortcoming is the computing that needs large amount of complex when utilizing rotating vector angular velocity reduced frequency; And this measurement mechanism is exclusively used in the three-phase alternating current frequency measurement; Can not be used for the frequency measurement of civilian single-phase alternating current, more can not be used for the frequency measurement of common non-three phase low frequency signal.

Prior art two: the Chinese patent of application number 201010150157 discloses a kind of frequency measurement method of low-frequency signals, and its essence also is a kind of zero crossing detection method, but possibly there is the bigger situation of operand in this method.

Summary of the invention

Technical matters to be solved by this invention is the excessive shortcoming of operand in the not accurate enough or measuring process to the frequency measurement accuracy of AC signal in the prior art; Propose a kind of digital measuring method of ac frequency, this method also can be used for fixing the frequency measurement of the little low frequency sinusoidal signal of frequency or change of frequency.

The present invention adopts following technical scheme for solving the problems of the technologies described above:

A kind of digital measuring method of ac frequency may further comprise the steps:

Step 1) is sampled to tested electric signals, obtains the sampled value of tested electric signals, generates sampled signal then;

Step 2), in the sampled signal of tested electric signals, no show selects a sampled point as the first sampled point P1 during zero point after the cycle of tested electric signals is crossed any peak value _i, establish this first sampled point P1 _iSampling time be T1 _i, sampled value is S1 _i

Step 3) during the next peak value of no show, is chosen two continuous sampled points, i.e. the second sampled point P2 in this section sampled signal after sampled signal is crossed zero point _iWith the 3rd sampled point P3 _i, the sampling time of establishing these two points is respectively T2 _iAnd T3 _i, sampled value is respectively S2 _iAnd S3 _i, sampled value S2 wherein _iAnd S3 _iNeed to satisfy | S2 _i|≤| S1 _i|≤| S3 _i|;

Step 4) is with the first sampled point P1 _iThe inverse value of sampled value is pairing as virtual sampled point P4 _i, calculate virtual sampled point P4 _iVirtual time of origin ${T4}_i={T2}_i+\frac{({T3}_i-{T2}_i)\×({S1}_i+{S2}_i)}{{S2}_i-{S3}_i};$

Step 5) is calculated the zero crossing time:

Step 6), repeating step 2) obtains several zero crossings time, T to step 5) _Z1, T _Z2, T _Z3... T _Zi, T _Zi+1, T _Zi+2... T _Zn, wherein, i=1,2 ... N, n are positive integer; The cycle of tested electric signals: T then _Pi=T _Zi+2-T _ZiPerhaps T _Pi=2 * (T _Zi+1-T _Zi), the frequency of tested electric signals: $F_i=\frac{1}{T_{\mathrm{Pi}}}=\frac{1}{T_{\mathrm{Zi}+2}-T_{\mathrm{Zi}}}$ Perhaps: $F_i=\frac{1}{T_{\mathrm{Pi}}}=\frac{1}{2\×(T_{\mathrm{Zi}+1}-T_{\mathrm{Zi}})}.$

Further, the digital measuring method of a kind of ac frequency of the present invention, said tested electric signals is sampled of step 1) is constant duration sampling or not constant duration sampling.

Further, the digital measuring method of a kind of ac frequency of the present invention, described being sampled as of step 1) sampled to the complete cycle ripple of tested electric signals.

Further, the digital measuring method of a kind of ac frequency of the present invention also comprises according to step 2) principle choose the different sampled point of sampled value respectively as the first sampled point P1 _i, repeating step 3 then) carry out averaging after the several times zero crossing calculates to step 5), obtain the zero crossing time.

Further; The digital measuring method of a kind of ac frequency of the present invention; Further comprising the steps of: as repeating step 1) to step 6), to measure several cycles or the frequency values of tested electric signals, adopt the method for average to calculate final frequency to several cycles or the frequency values that obtains then.

Further, the digital measuring method of a kind of ac frequency of the present invention, in said step 3), when the sampled value of first to the 3rd sampled point of choosing meets | S2 _i|=| S1 _i|=| S3 _i| during condition, take in following two kinds of processing schemes any one:

A), choose the second sampled point P2 again _iWith the 3rd sampled point P3 _i, make the sampled value S2 of second sampled point _iSampled value S3 with the 3rd sampled point _iMust satisfy | S2 _i|<| S3 _i|, continue step 4) then to step 6);

B), at the second sampled point P2 _iWith the 3rd sampled point P3 _iInterval [T2 of sampling time _i, T3 _i] take up an official post and get a bit as virtual sampled point P4 _iPairing virtual sampling time T4 _i, continue step 5) then to step 6).

Further, the digital measuring method of a kind of ac frequency of the present invention is in said scheme b) in, the second sampled point P2 got _iWith the 3rd sampled point P3 _iInterval [T2 of sampling time _i, T3 _i] on mid point, calculate virtual sampled point P4 _iVirtual time of origin ${T4}_i=\frac{{T3}_i+{T2}_{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="120726140945.png"\; state="\{\{state\}\}">i</figure-callout>}}}{2}.$

The present invention adopts above technical scheme compared with prior art, has following technique effect:

1) traditional two opposite continuity points of zero friendship method symbolization are confirmed zero crossing, though the algorithm clear physics conception receives the interference of harmonic wave, measuring error etc. easily, measuring accuracy is low.Can through by 3 sampled points choosing and calculating zero crossing.Confirmed after the cycle signal zero-cross point, can calculate the frequency and the cycle of AC signal.Traditional zero friendship method of comparing, operand is roughly the same, but the antijamming capability of system increases.

2) calculated amount of the present invention is less, is fit to use under the embedded system.

Description of drawings

Fig. 1 is near the detailed maps that some zero points of ac signal, calculates and obtain zero crossing;

Fig. 2 carries out zero crossing to calculate also the further synoptic diagram of calculated rate near each zero point after ac signal is sampled.

Embodiment

Below in conjunction with accompanying drawing technical scheme of the present invention is done further detailed description:

Essence of the present invention is to continuous digital sampled signal;, signal chooses a sampled point P1 after crossing positive negative peak; In follow-up sampled point, choose continuous two some P2 and P3, the condition of choosing of P2 and P3 is: the negative value of P1 sampled value is in interval [P2 sampled value, P3 sampled value].Then can on the line segment that P2 and P3 formed, ask for 1 P4, make the numerical value of P4 equal the negative value of P1 sampled value, can obtain the virtual time of origin that P4 is ordered simultaneously through the method for interpolation.The zero point that the virtual time of origin of being ordered by sampling time of origin and the P4 of P1 calculates electric signal is by the frequency of calculating electric signal the zero point of series of electrical signals or cycle.If the P1 that chooses should not too near zero point, then possibly make that because of the reason of noise the accuracy of measuring is not high enough too near zero point.Step 2 in the claims of the present invention) and step 3) choosing P1, P2, P3 is last to have adopted a kind of mode more strict than said method, this method has stronger noiseproof feature.

Principle of the present invention describes through the frequency of two cycles of Measuring Alternating Current Signal.

Practical implementation process of the present invention is following:

1, tested electric signals is sampled, described here be sampled as the sampling that the complete cycle ripple is carried out.Can be the constant duration sampling, also can be not constant duration sampling.

2,, tested electric signals selects a sampled point P1 after crossing positive negative peak _i, the sampling time of establishing this sampled point is T1 _i, sampled value is S1 _i

3, after sampled signal is crossed zero point, in follow-up sampled value, choose two continuous some P2 _iAnd P3 _i, the sampling time of establishing these two points is respectively T2 _iAnd T3 _i, the sampled value of two points is respectively S2 _iAnd S3 _i, these two points have following characteristics: if S1 _iBe positive number, then S2 _iAnd S3 _iBe all negative; If S1 _iBe negative, then S2 _iAnd S3 _iBe all positive number, and satisfy | S2 _i|≤| S1 _i|≤| S3 _i| and | S2 _i|<| S3 _i|.

4, calculate P4 _iThe virtual time of origin T4 of point _i, because P4 _iNumerical value equal P1 _iThe negative value of sampled value, then: T4 _iCan be expressed as ${T4}_i={T2}_i+\frac{({T3}_i-{T2}_i)\&times;({S1}_i+{S2}_i)}{{S2}_i-{S3}_i};$

5, the sampled value when the sampled point of choosing meets | S2 _i|=| S1 _i|=| S3 _i| during condition, can take two kinds of disposal routes: a kind of method is to choose P2 again _iAnd P3 _iAnd recomputate; Another kind method is T4 _iAt interval [T2 _i, T3 _i] take up an official post and get a bit, calculate for convenient, get this interval mid point, then

Consider the up-down symmetry of ac signal, zero crossing time representation is:

Concrete operations can be referring to Fig. 1.The last hollow round spot P1 of Fig. 1 _i, P2 _i, P3 _iBe three points selecting as requested, hollow triangle point P4 _iBe virtual point through obtaining after the interpolation, T1 _iBe P1 _iSampling time, T4 _iBe P4 _iVirtual time of origin, the hollow round spot T on the transverse axis _ZiBe to calculate the zero crossing that the back obtains.

6, repeat above-mentioned steps, can obtain several zero crossing time, T _Z1, T _Z2, T _Z3... T _Zi, T _Zi+1, T _Zi+2... T _Zn, the cycle of tested ac signal: T then _Pi=T _Zi+2-T _ZiPerhaps T _Pi=2 * (T _Zi+1-T _Zi), the frequency of tested ac signal: $F_i=\frac{1}{T_{\mathrm{Pi}}}=\frac{1}{T_{\mathrm{Zi}+2}-T_{\mathrm{Zi}}}$ Perhaps: $F_i=\frac{1}{T_{\mathrm{Pi}}}=\frac{1}{2\&times;(T_{\mathrm{Zi}+1}-T_{\mathrm{Zi}})}.$

Can be in a signal period through choosing different P1 at some near zero-crossing points _iCarry out repeatedly zero crossing and measure, repeatedly the zero crossing effluxion can obtain the final zero crossing time after average.

The electric signal back of sampling is calculated near each zero point and figure such as Fig. 2 of survey frequency.There are 4 zero crossings in ac signal among Fig. 2, therefore after signal is crossed peak value, has carried out four times and has calculated.Soft dot among the figure on the transverse axis is the zero crossing that calculates, and zero crossing is successively: T _Zi-1, T _Zi, T _Zi+1, T _Zi+2Then the cycle of this signal can be expressed as T _p=T _Zi+1-T _Zi-1Perhaps T _p=T _Zi+2-T _ZiPerhaps T _p=2 * (T _Zi-T _Zi-1) or T _p=2 * (T _Zi+1-T _Zi) or T _p=2 * (T _Zi+2-T _Zi+1).Frequency F _pThen be T _pInverse.

After measuring several cycles or frequency values of tested electric signals, can adopt the method for average to calculate final frequency to several cycles or the frequency values that obtains.

Preferred version is that the above-mentioned constant duration that is sampled as is sampled the P1 that chooses _iShould not too also should not be too near peak value near zero point.

Adopt this method in a signal period, can carry out repeatedly frequency measurement.

In sum, the digital measuring method of a kind of ac frequency involved in the present invention need not convert ac signal to square wave, is particularly suitable for the frequency measurement of low frequency sinusoidal signal, and system is easy to detect, and hardware spending is little; The antijamming capability of system is stronger; Implement advantages of simple, data accurately, reliably; Have than application prospects.

Claims (7)

1. the digital measuring method of an ac frequency is characterized in that may further comprise the steps:

Step 1) is sampled to tested electric signals, obtains the sampled value of tested electric signals, generates sampled signal then;

Step 2), in the sampled signal of tested electric signals, no show selects a sampled point as the first sampled point P1 during zero point after the cycle of tested electric signals is crossed any peak value _i, establish this first sampled point P1 _iSampling time be T1 _i, sampled value is S1 _i

Step 3) during the next peak value of no show, is chosen two continuous sampled points, i.e. the second sampled point P2 in this section sampled signal after sampled signal is crossed zero point _iWith the 3rd sampled point P3 _i, the sampling time of establishing these two points is respectively T2 _iAnd T3 _i, sampled value is respectively S2 _iAnd S3 _i, sampled value S2 wherein _iAnd S3 _iNeed to satisfy | S2 _i|≤| S1 _i|≤| S3 _i|;

Step 4) is with the first sampled point P1 _iThe inverse value of sampled value is pairing as virtual sampled point P4 _i, calculate virtual sampled point P4 _iVirtual time of origin ${T4}_i={T2}_i+\frac{({T3}_i-{T2}_i)\&times;({S1}_i+{S2}_i)}{{S2}_i-{S3}_i};$

Step 5) is calculated the zero crossing time:

Step 6), repeating step 2) obtains several zero crossings time: T to step 5) _Z1, T _Z2, T _Z3... T _Zi, T _Zi+1, T _Zi+2... T _Zn, wherein, i=1,2 ... N, n are positive integer; The cycle of tested electric signals: T then _Pi=T _Zi+2-T _ZiPerhaps T _Pi=2 * (T _Zi+1-T _Zi), the frequency of tested electric signals: $F_i=\frac{1}{T_{\mathrm{Pi}}}=\frac{1}{T_{\mathrm{Zi}+2}-T_{\mathrm{Zi}}}$ Perhaps: $F_i=\frac{1}{T_{\mathrm{Pi}}}=\frac{1}{2\&times;(T_{\mathrm{Zi}+1}-T_{\mathrm{Zi}})}.$

2. the digital measuring method of a kind of ac frequency according to claim 1 is characterized in that: said tested electric signals is sampled of step 1) is constant duration sampling or not constant duration sampling.

3. the digital measuring method of a kind of ac frequency according to claim 1, it is characterized in that: described being sampled as of step 1) sampled to the complete cycle ripple of tested electric signals.

4. the digital measuring method of a kind of ac frequency according to claim 1 is characterized in that: also comprise according to step 2) principle choose the different sampled point of sampled value respectively as the first sampled point P1 _i, repeating step 3 then) carry out averaging after the several times zero crossing calculates to step 5), obtain the zero crossing time.

5. according to the digital measuring method of each described a kind of ac frequency in the claim 1 to 3; It is characterized in that: further comprising the steps of: repeating step 1) to step 6); Measure several cycles or the frequency values of tested electric signals, adopt the method for average to calculate final frequency to several cycles or the frequency values that obtains then.

6. the digital measuring method of a kind of ac frequency according to claim 1 is characterized in that: in said step 3), when the sampled value of first to the 3rd sampled point of choosing meets | S2 _i|=| S1 _i|=| S3 _i| during condition, take in following two kinds of processing schemes any one:

A), choose the second sampled point P2 again _iWith the 3rd sampled point P3 _i, make the sampled value S2 of second sampled point _iSampled value S3 with the 3rd sampled point _iMust satisfy | S2 _i|<| S3 _i|, continue step 4) then to step 6);

B), at the second sampled point P2 _iWith the 3rd sampled point P3 _iInterval [T2 of sampling time _i, T3 _i] take up an official post and get a bit as virtual sampled point P4 _iPairing virtual sampling time T4 _i, continue step 5) then to step 6).

7. the digital measuring method of a kind of ac frequency according to claim 6 is characterized in that: in said scheme b) in, the second sampled point P2 got _iWith the 3rd sampled point P3 _iInterval [T2 of sampling time _i, T3 _i] on mid point, calculate virtual sampled point P4 _iVirtual time of origin

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