CN102928666A - Digital measurement method for phase difference of alternating current - Google Patents

Abstract

The invention discloses a digital measurement method for the phase difference of alternating current. For continuous digital sampling signals, sampling points P1, P2 and P3 are sequentially selected after the signal exceeds the negative peak value. Make the negative value of the P1 sampling value in the interval [P2 sampling value, P3 sampling value]. Calculate a point P4 on the line segment composed of P2 and P3 by interpolation method, so that the value of P4 is equal to the negative value of the sampling value of P1, and obtain the virtual occurrence time of point P4. The zero point of the electrical signal is calculated from the sampling occurrence time of P1 and the virtual occurrence time of P4, and the period of the electrical signal is calculated from a series of zero-crossing points of the electrical signal. Finally, according to the difference between the zero-crossing time of different signals and the signal period, the phase difference between the acquired signals is calculated. The invention overcomes the disadvantage of poor anti-interference ability of the traditional zero-crossing point detection, and is especially suitable for the phase difference measurement of low-frequency signals; the data is accurate and reliable when realized, and has wider application prospects.

Description

A Digital Measuring Method of Phase Difference of Alternating Current

technical field

The invention relates to a digitized measurement technology of the phase difference of alternating current, which can also be used for the phase difference measurement of other low-frequency signals. the

Background technique

In daily life and production process, it is often necessary to measure the phase difference of AC signals. The more accurate the measured phase difference is, the better the application effect is. In the existing phase difference measurement methods, most of them convert the signal into a square wave, and then measure the time difference between the rising edges of the two square waves, so as to obtain the phase difference of the two signals, but this algorithm is easy to implement but Requires additional hardware and is susceptible to interference. the

Contents of the invention

The technical problem to be solved by the present invention is to propose a digital measurement method for the phase difference of the alternating current in view of the inaccurate measurement accuracy of the phase difference of the alternating current signal in the prior art. the

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

A digital measurement method of the phase difference of alternating current, comprising the following steps:

Step 1), sampling the electrical signal under test to obtain the sampling value of the electrical signal under test, and then generate a sampling signal;

Step 2), in the sampling signal of the measured electrical signal, when the cycle of the measured electrical signal exceeds the negative peak value and does not reach the zero point, a sampling point is selected as the first sampling point P1 _i , and the first sampling point P1 _i is set as The sampling time is T1 _i , and the sampling value is S1 _i ;

Step 3), when the cycle of the electrical signal under test does not reach the positive peak value after crossing the zero point, select two consecutive sampling points in the sampling signal, that is, the second sampling point P2 _i and the third sampling point P3 _i , set The sampling times of these two points are T2 _i and T3 _i respectively, and the sampling values are S2 _i and S3 _i respectively, where the sampling values S2 _i and S3 _i need to satisfy |S2 _i |≤|S1 _i |≤|S3 _i | and | _S2i |<| _S3i |;

Step 4), take the point corresponding to the opposite value of the sampling value of the first sampling point P1 _i as the virtual sampling point P4 _i , and calculate the virtual occurrence time of the virtual sampling point P4 _i ${T4}_i={T2}_i+\frac{({T3}_i-{T2}_i)\&times;({S1}_i+{S2}_i)}{{S2}_i-{S3}_i};$

Step 5), calculate the zero-crossing time: $T_{\mathrm{the\; zi}}=\frac{{T1}_i+{T4}_i}{2};$

Step 6), repeat step 2) to step 5) to obtain several zero-crossing times: T _z1 , T _z2 , T _z3 ... T _zi , T _zi+1 , T _zi+2 ... T _zn , where, i=1, 2,...n, n is a positive integer; then the cycle of the electrical signal to be measured: T _pi =T _zi+1 -T _zi , so the cycle of the obtained signal is T _p1 , T _p2 , T _p3 , ...Tpn _-1 ;

Step 7), for two measured electrical signals with the same frequency, according to step 1) to step 6), get the zero-crossing time of the two measured electrical signals respectively; then according to the difference of the zero-crossing time of the two measured electrical signals , and the periods of the two measured electrical signals, the phase difference between the two measured electrical signals is calculated. the

Furthermore, the present invention provides a digital measurement method for the phase difference of alternating current, the sampling in step 1) is equal time interval sampling or unequal time interval sampling. the

Further, the present invention provides a digital measurement method for the phase difference of alternating current, the sampling in step 1) is sampling the entire cycle. the

Further, the present invention is a digital measurement method of the phase difference of alternating current, the specific steps of the step 7) are as follows:

或者以弧度表示为： $P_r=\frac{{T2}_{\mathrm{zi}}-{T1}_{\mathrm{zi}}}{T_p}\&times;2\&times;\mathrm{\&pi;},$ 其中，T_p是依步骤6）计算得出的被测电信号周期的瞬时值，或者是依步骤6）计算得出的被测电信号的前若干个周期值的平均值。  Assuming that the zero-crossing time of the first measured electrical signal calculated from step 1) to step 6) is T1 _zi , and the zero-crossing time of the second measured electrical signal is T2 _zi , then the two measured electrical signals The value of the phase difference is expressed in degrees as:

Or expressed in radians as: $P_r=\frac{{T2}_{\mathrm{the\; zi}}-{T1}_{\mathrm{the\; zi}}}{T_p}\&times;2\&times;\mathrm{\&pi;},$ Wherein, T _p is the instantaneous value of the period of the electrical signal under test calculated according to step 6), or the average value of the previous several periods of the electrical signal under test calculated according to step 6).

Further, in the digital measurement method of the phase difference of alternating current of the present invention, in the step 3), when the sampling values of the selected first to third sampling points meet |S2 _i |=|S1 _i |=| S3 _i |condition, take any one of the following two processing schemes:

a), reselect the second sampling point P2 _i and the third sampling point P3 _i , so that the sampling value S2 _i of the second sampling point and the sampling value S3 _i of the third sampling point must satisfy |S2 _i |<|S3 _i | , and then proceed to step 4) to step 7);

b) Select any point on the sampling time interval [T2 _i , T3 _i ] between the second sampling point P2 _i and the third sampling point P3 _i as the virtual sampling time T4 _i corresponding to the virtual sampling point P4 _i , and then proceed to step 5 ) to step 7).

Furthermore, in the method for digitally measuring the phase difference of alternating current of the present invention, in the scheme b), the sampling time interval [T2 _i , T3 _i ] of the second sampling point P2 _i and the third sampling point P3 _i is taken Calculate the virtual occurrence time of the virtual sampling point P4 _i at the midpoint on ${T4}_i=\frac{{T3}_i+{T2}_i}{2}.$

Compared with the prior art by adopting the above technical scheme, the present invention has the following technical effects:

1) The traditional zero-crossing method uses two consecutive points with opposite signs to determine the zero point. Although the physical concept of the algorithm is clear, it is easily disturbed by harmonics and measurement errors, and the measurement accuracy is low. Only by accurately locating the zero point can the precise phase difference be calculated. In the present invention, the zero-crossing point can be obtained through calculation from the three selected sampling points. After determining the zero crossing point of the signal, the frequency and period of the AC signal can be calculated. Finally, according to the difference between the zero-crossing time of different signals and the signal period, the phase difference between the acquired signals is calculated. Compared with the traditional zero-crossing method, the amount of calculation has increased, but the measurement accuracy and anti-interference performance have been greatly improved. the

2) The sampling involved in the present invention may be sampling at equal time intervals or sampling at unequal time intervals. the

Description of drawings

Fig. 1 is a schematic diagram of obtaining P4 _i by means of interpolation from P1 _i , P2 _i , and P3 _i in Fig. 1 , and further calculating the zero-crossing point by T1 _i and T4 _i ;

Fig. 2 is the schematic diagram of calculating signal period;

Fig. 3 is a schematic diagram of calculating the phase difference of two signals. the

Detailed ways

Below in conjunction with accompanying drawing technical scheme of the present invention is described in further detail:

The essence of the present invention is to select a sampling point P1 after the signal crosses the negative peak value, then select two consecutive points P2 and P3 after the signal zero crossing point, the selection condition of P2 and P3 is that the negative value of the P1 sampling value is in the interval [P2 Sampled value, within P3 sampled value]. Then, a point P4 can be calculated on the line segment composed of P2 and P3 by interpolation method, so that the value of P4 is equal to the negative value of the sampling value of P1, and the virtual occurrence time of point P4 can be obtained at the same time. The zero point of the electrical signal is calculated from the sampling occurrence time of P1 and the virtual occurrence time of P4, and the period of the electrical signal is calculated from a series of zero-crossing points of the electrical signal. Finally, according to the difference between the zero-crossing time of different signals and the signal period, the phase difference between the acquired signals is calculated. The selected P1 should not be too close to the zero point, if it is close to the zero point, it is easy to be interfered by noise and the measurement result is not accurate enough. the

In order to obtain a more accurate measurement result, the suggested selection scheme of the sampling point P1 is: it should not be too close to the zero point. the

The features and advantages of the present invention will be described in detail by way of example with reference to the accompanying drawings. The principle of the present invention is illustrated by measuring the phase difference of the low-frequency signal. As the sampling speed increases, the sampling times within one cycle increase. The specific implementation process of the present invention is as follows:

1. Sampling the signal under test, the sampling mentioned here is the sampling of the whole cycle. It can be sampling at equal time intervals or sampling at unequal time intervals. the

2. Select a sampling point P1 _i after the electrical measurement signal crosses the negative peak value, set the sampling time of this sampling point as T1 _i , and the sampling value is S1 _i ; when the sampling signal crosses the zero point, select continuous sampling points in the subsequent sampling values Two points P2 _i and P3 _i , assuming the sampling time of these two points are T2 _i and T3 _i respectively, the sampling values of the two points are S2 _i and S3 _i respectively, these two points have the following characteristics: S1 _i is Negative numbers, S2 _i and S3 _i are both positive numbers, and satisfy |S2 _i |≤|S1 _i |≤|S3 _i , |S2 _i |<|S3 _i |.

根据计算获得的T4_i，过零点时间的计算如下：  3. The process of obtaining the zero-crossing point is as follows. First, the virtual occurrence time T4 _i of point P4 _i needs to be calculated. Since the value of P4 _i is equal to the negative value of the sampling value of P1 _i , then: T4 _i can be expressed as ${T4}_i={T2}_i+\frac{({T3}_i-{T2}_i)\&times;({S1}_i+{S2}_i)}{{S2}_i-{S3}_i};$ When the sampling value of the selected sampling point meets the condition of |S2 _i |=|S1 _i |=|S3 _i |, two processing methods can be adopted: one method is to reselect P2 _i and P3 _i and recalculate; the other The first method is that T4 _i takes any point on the interval [T2 _i , T3 _i ], for the convenience of calculation, take the midpoint of the interval, then

According to the calculated T4 _i , the zero-crossing time is calculated as follows:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; zi</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span>$

4. Refer to Figure 1 for specific operations. The hollow circle points P1 _i , P2 _i , and P3 _i in Figure 1 are three points selected according to the requirements, and the hollow triangle point P4 _i is a virtual point obtained after interpolation, and the value of point P4 _i is the sampling value of point P1 _i negative value. T1 _i is the sampling time of P1 _i , T4 _i is the virtual occurrence time of P4 _i , and the hollow circle point T _zi on the horizontal axis is the zero-crossing point obtained after calculation.

5. After obtaining several zero-crossing times, the signal period can be calculated. The low-frequency signal in Figure 2 has three negative peaks in total, so after the negative peaks appear, a total of three interpolation and calculations have been performed. The times on the horizontal axis are respectively The hollow circle points of T _z1 , T _z2 , and T _z3 are the calculated three zero-crossing points. Since the period of the measured signal can be expressed as: T _pi =T _zi+1 -T _zi , the signal period in Figure 2 can be Expressed as: T _p2 =T _z3 -T _z2 , T _p1 =T _z2 -T _z1 .

或者 

公式中的T_p是信号的周期，T_p可以是计算得出的信号周期的瞬时值，或者是计算得出的前几个周期值的平均值。公式也可以 写成弧度表达的形式。  6. The calculation of the phase difference can be seen in Figure 3. In the figure, the sine wave I has two zero-crossing points after the negative peak appears. The time of these two zero-crossing points is T1 _zi and T1 _zi+1 respectively, and the sine wave II is at the negative peak There are also two zero-crossing points after appearing, and the time of these two zero-crossing points is T2 _zi and T2 _zi+1 respectively, then the phase difference between sine wave I and sine wave II can be expressed as:

or

T _p in the formula is the period of the signal, and T _p can be the calculated instantaneous value of the signal period, or the calculated average value of the previous several period values. The formula can also be expressed in radians.

The preferred solution is that the sampling is equal time interval sampling. the

In summary, the digital measurement method of a phase difference of alternating current involved in the present invention does not need to convert the low-frequency signal into a square wave, overcomes the shortcomings of the traditional zero-crossing point detection and has poor anti-interference ability, and is especially suitable for low-frequency signal Phase difference measurement, system detection is convenient, hardware overhead is small; this method has a certain anti-interference ability; it is simple and reasonable to implement, and the data is accurate and reliable; it has a wider application prospect. Of course, the present invention can also be applied to phase difference measurement, power angle measurement and the like of civil three-phase alternating current. the

Claims (6)

1. the digital measuring method of the phase differential of an alternating current 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, then generates sampled signal;

Step 2), in the sampled signal of tested electric signals, select a sampled point as the first sampled point P1 when after the cycle of tested electric signals is crossed negative peak, not arriving zero point _i, establish this first sampled point P1 _iSampling time be T1 _i, sampled value is S1 _i

Step 3) when not arriving positive peak after the cycle of tested electric signals is crossed zero point, is chosen two continuous sampled points, i.e. the second sampled point P2 in this section sampled signal _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 corresponding as virtual sampled point P4 _i, calculate virtual sampled point P4 _iVirtual time of origin ${T4}_i={T2}_i+\frac{({T3}_i-T{2}_i)\&times;({S1}_i+{S2}_i)}{{S2}_i-S{3}_i};$

Step 5), calculate 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+1-T _Zi, the cycle of the signal that therefore obtains is followed successively by T _P1, T _P2, T _P3... T _Pn-1

Step 7) for two tested electric signals that frequency is identical, obtains respectively the zero crossing time of two tested electric signals according to step 1) to step 6); Again according to the difference of zero crossing time of two tested electric signals, and the cycle of two tested electric signals, calculate two phase differential between the tested electric signals.

2. the digital measuring method of the phase differential of a kind of alternating current according to claim 1 is characterized in that: the described sampling of step 1) is constant duration sampling or not constant duration sampling.

3. the digital measuring method of the phase differential of a kind of alternating current according to claim 1, it is characterized in that: described being sampled as of step 1) sampled to the complete cycle ripple.

4. the digital measuring method of the phase differential of a kind of alternating current according to claim 1, it is characterized in that: the concrete steps of described step 7) are as follows:

If the zero crossing time of the first via tested electric signals that is calculated by step 1) to step 6) is T1 _Zi, the second tunnel tested electric signals the zero crossing time be T2 _Zi, then the value of the phase differential of two-way tested electric signals is expressed as with the number of degrees:

Perhaps be expressed as with radian: $P_r=\frac{T{2}_{\mathrm{zi}}-{T1}_{\mathrm{zi}}}{T_p}\&times;2\&times;\mathrm{\&pi;},$ Wherein, T _pThe instantaneous value in tested electric signals cycle of calculating according to step 6), or the mean value of front several periodic quantities of the tested electric signals that calculates according to step 6).

5. the digital measuring method of the phase differential of a kind of alternating current according to claim 1 is characterized in that: in described step 3), when the sampled value of the 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), again choose the second sampled point P2 _iWith the 3rd sampled point P3 _i, so that the sampled value S2 of the second sampled point _iSampled value S3 with the 3rd sampled point _iMust satisfy | S2 _i|＜| S3 _i|, then continue step 4) to step 7);

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 _iCorresponding virtual sampling time T4 _i, then continue step 5) to step 7).

6. the digital measuring method of the phase differential of a kind of alternating current according to claim 5 is characterized in that: in described 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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