CN103364634B - Three-phase alternating-current supply frequency measurement method - Google Patents

Abstract

The present invention discloses a kind of three-phase alternating-current supply frequency measurement method, and it comprises step: the three-phase voltage signal V gathering three-phase supply _a, V _band V _c, gather the three-phase voltage signal V of three-phase supply _a, V _band V _c, by three-phase voltage signal V _a, V _band V _cchange the instantaneous value V of two phase coordinate systems into _αand V _β, ask the modulus value V of current voltage rotating vector _m; According to the instantaneous value V of two phase coordinate systems _αand V _β, and modulus value V _m, obtain the tangent value of the rotating vector angle θ of 1/2nd; Look into tangent table and ask for corresponding angle, and then obtain rotating vector angle θ; Angular frequency is calculated, by angular frequency divided by the frequency values that namely can obtain line voltage to rotating vector angle θ computing of differentiating.The present invention has the advantages that antijamming capability is strong, precision is high, can be used for the rugged surroundings such as jitter, imbalance, harmonic content be large, is especially suitable in frequency and phase sequence measurement mechanism.

Description

Three-phase alternating-current supply frequency measurement method

Technical field

The present invention relates to a kind of supply frequency measuring technique, especially relate to a kind of three-phase alternating-current supply frequency measurement method.

Background technology

The frequency measurement of existing three-phase alternating-current supply and judging phase order method, the zero crossing that adopts judges more, and need hardware circuit to be detected zero-signal, soldier calculates the time interval T between adjacent two zero cross signals, and then obtains frequency.

Existing method relies on hardware circuit accuracy of detection, and, when mains harmonics is larger, or shake back and forth near zero-crossing point, multiple zero crossing certainly will be there is, cause frequency to be judged by accident, and be difficult to find suitable solution to this erroneous judgement.

Summary of the invention

Technical matters to be solved by this invention proposes that a kind of antijamming capability is strong, precision is high, the stability in detected three-phase signal source does not affect the three-phase alternating-current supply frequency measurement method of measurement result.

The present invention adopts following technical scheme to realize: a kind of three-phase alternating-current supply frequency measurement method, and it comprises step:

Gather the three-phase voltage signal V of three-phase supply _a, V _band V _c, by three-phase voltage signal V _a, V _band V _cchange the instantaneous value V of two phase coordinate systems into _αand V _β, ask the modulus value V of current voltage rotating vector _m;

According to the instantaneous value V of two phase coordinate systems _αand V _β, and modulus value V _m, obtain the tangent value tan (θ/2) of the rotating vector angle θ of 1/2nd;

Look into tangent table and ask for corresponding angle θ/2, and then obtain rotating vector angle θ;

Angular frequency is calculated to rotating vector angle θ computing of differentiating, namely can obtain the frequency values of line voltage by angular frequency divided by 2 π.

Wherein, by three-phase voltage signal V _a, V _band V _cchange the instantaneous value V of two phase coordinate systems into _αand V _β, and modulus value V _mcomputing formula as follows:

$\left\{\begin{array}{c}{V}_{\mathrm{\α}}=\left(\frac{2}{3}\right)\×(V_a\×1-V_b\×0.5-V_c\×0.5)\\ V_{\mathrm{\β}}=\left(\frac{2}{3}\right)\×(V_a\×0+V_b\×\frac{\sqrt{3}}{2}-V_c\×\frac{\sqrt{3}}{2})\\ V_m=\sqrt{V_{\mathrm{\α}}\×V_{\mathrm{\α}}+V_{\mathrm{\β}}\×V_{\mathrm{\β}}}\end{array}\right..$

Wherein, the formula obtaining the tangent value tan (θ/2) of the rotating vector angle θ of 1/2nd is $\tan \frac{\mathrm{\θ}}{2}=\frac{V_m\sin \mathrm{\θ}}{V_m+V_m\cos \mathrm{\θ}}=\frac{V_{\mathrm{\β}}}{V_m+V_{\mathrm{\α}}}.$

In one embodiment, also comprising step: judge current phase sequence according to the positive and negative values of frequency, is positive sequence when frequency values is greater than 0, is negative phase-sequence when frequency values is less than 0.

Wherein, when rotating vector angle θ value is between-45 ° ~ 45 °, angular frequency is calculated to rotating vector angle θ computing of differentiating.

Also comprise step in one embodiment: use low-pass filter to carry out noise filtering process and carry out stabilized frequency value.

Compared with prior art, the present invention has following beneficial effect:

The present invention has the advantages that antijamming capability is strong, precision is high, can be used for the rugged surroundings such as jitter, imbalance, harmonic content be large, be especially suitable in frequency and phase sequence measurement mechanism, such as three-phase alternating-current powered equipment, three-phase alternating current measuring instrument and three-phase alternating current pick-up unit.

Accompanying drawing explanation

Fig. 1 is schematic flow sheet of the present invention;

The change schematic diagram of rotating vector angle θ when Fig. 2 is electrical network positive sequence;

The change schematic diagram of rotating vector angle θ when Fig. 3 is electrical network negative phase-sequence;

Fig. 4 is the signal schematic representation that rotating vector angle θ causes noise when discontinuous.

Embodiment

As shown in Figure 1, a preferred embodiment of the invention comprises following performing step:

Step S1, use sensor gather the three-phase voltage signal V of three-phase supply _a, V _band V _c.

Step S2, the three-phase voltage signal V that sensor is gathered _a, V _b, V _cby three-phase to the coordinate transform of two-phase, change the instantaneous value V of two-phase (static) coordinate system into _αand V _β, and obtain the modulus value V of current voltage rotating vector _m, transformational relation is as shown in the formula shown in (1-1).

$\left\{\begin{array}{c}{V}_{\mathrm{\α}}=\left(\frac{2}{3}\right)\×(V_a\×1-V_b\×0.5-V_c\×0.5)\\ V_{\mathrm{\β}}=\left(\frac{2}{3}\right)\×(V_a\×0+V_b\×\frac{\sqrt{3}}{2}-V_c\×\frac{\sqrt{3}}{2})\\ V_m=\sqrt{V_{\mathrm{\α}}\×V_{\mathrm{\α}}+V_{\mathrm{\β}}\×V_{\mathrm{\β}}}\end{array}\right.---(1-1)$

Wherein, V _mfor instantaneous value V _αor V _βamplitude.

Step S3, instantaneous value V according to two phase coordinate systems _αand V _β, and instantaneous value V _αor V _βamplitude V _m, obtain the tangent value tan (θ/2) of the voltage rotating vector angle θ of 1/2nd.

According to trigonometric function relation:

$\tan \frac{\mathrm{\θ}}{2}=\frac{\sin \mathrm{\θ}}{1+\cos \mathrm{\θ}}---(1-2)$

Wherein known: $\left\{\begin{array}{c}{V}_{\mathrm{\α}}=V_m\cos \mathrm{\θ}\\ V_{\mathrm{\β}}=V_m\sin \mathrm{\θ}\end{array}\right.---(1-3)$

In order to simplified operation, (1-2) formula molecule denominator is multiplied by V simultaneously _αor V _βamplitude V _m, then:

$\tan \frac{\mathrm{\θ}}{2}=\frac{V_m\sin \mathrm{\θ}}{V_m+V_m\cos \mathrm{\θ}}=\frac{V_{\mathrm{\β}}}{V_m+V_{\mathrm{\α}}}---(1-4)$

Step S4, basis (1-4) formula obtain tan (θ/2) value, then need to look into tangent table and ask for corresponding angle θ/2, and then obtain rotating vector angle θ.

This step needs to make tangent table, and the field of definition due to tan is-90 ° ~ 90 ° changes, and corresponding tangent value is from minus infinity to positive infinity, in order to the convenience of tabling look-up has made-89 ° ~ 89 ° forms.

Step S5, computing of differentiating to rotating vector angle θ calculate angular frequency, namely can obtain the frequency values of line voltage by angular frequency divided by 2 π.

From Fig. 2 and Fig. 3, find out that rotating vector angle θ is from-180 ° ~ 180 ° changes when electrical network is positive sequence, and slope is greater than 0; When electrical network is negative phase-sequence, rotating vector angle θ is from 180 ° ~-180 ° changes, and slope is less than 0.Wherein, the horizontal ordinate of Fig. 2 is the time, and unit is second, and ordinate is positive sequence rotating vector angle value (-180 ° ~ 180 °); The horizontal ordinate of Fig. 3 is the time, and unit is second, and ordinate is negative phase-sequence rotating vector angle value (-180 ° ~ 180 °).

As shown in Figure 4, rotating vector angle θ value asks for differential in-π ~ π transient process can introduce noise, causes asking for frequency values instability.In order to reduce noise, the method reducing θ region of variation please be take in this, the computing of differential is namely carried out again when θ value is between-45 ° ~ 45 °, although this method cannot fundamentally stress release treatment, but noise can be reduced, and by using the low-pass filter of 1Hz namely can filter noise, reach the object of stabilized frequency value.Wherein, the horizontal ordinate of Fig. 4 is the time, and unit is second, and ordinate is frequency and rotating vector angle, in Fig. 4: straight line (1) represents frequency 50Hz;

Curve (2) rotating vector angle is triangular wave; Curve (3) is frequency noise line, is spike.

To sum up, the present invention is by changing instantaneous value V α and the V β of two phase coordinate systems into by three-phase voltage signal, and then ask for rotating vector angle θ, derivative is asked for rotating vector angle θ, converts out frequency values, low-pass filtering is carried out to frequency signal, filter the noise signal in frequency signal, thus obtain stable frequency signal, judge current phase sequence according to the positive and negative values of frequency simultaneously, being positive sequence when frequency is greater than 0, is negative phase-sequence when frequency is less than 0.The present invention has the advantages that antijamming capability is strong, precision is high, can be used for the rugged surroundings such as jitter, imbalance, harmonic content be large, be especially suitable in frequency and phase sequence measurement mechanism, such as three-phase alternating-current powered equipment, three-phase alternating current measuring instrument and three-phase alternating current pick-up unit.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (4)

1. a three-phase alternating-current supply frequency measurement method, is characterized in that, comprises step:

Gather the three-phase voltage signal V of three-phase supply _a, V _band V _c, by three-phase voltage signal V _a, V _band V _cchange the instantaneous value V of two phase coordinate systems into _αand V _β, ask the modulus value V of current voltage rotating vector _m;

According to the instantaneous value V of two phase coordinate systems _αand V _β, and modulus value V _m, obtain the tangent value tan (θ/2) of the rotating vector angle θ of 1/2nd;

Look into tangent table and ask for corresponding angle θ/2, and then obtain rotating vector angle θ;

Angular frequency is calculated to rotating vector angle θ computing of differentiating, namely can obtain the frequency values of line voltage by angular frequency divided by 2 π;

When rotating vector angle θ value is between-45 ° ~ 45 °, angular frequency is calculated to rotating vector angle θ computing of differentiating;

Also comprise step: use the low-pass filter of 1Hz to carry out noise filtering process and carry out stabilized frequency value.

2. three-phase alternating-current supply frequency measurement method according to claim 1, is characterized in that, by three-phase voltage signal V _a, V _band V _cchange the instantaneous value V of two phase coordinate systems into _αand V _β, and modulus value V _mcomputing formula as follows:

$\left\{\begin{array}{c}{V}_{\mathrm{\α}}=\left(\frac{2}{3}\right)\×(V_a\×1-V_b\×0.5-V_c\×0.5)\\ V_{\mathrm{\β}}=\left(\frac{2}{3}\right)\×(V_a\×0+V_b\×\frac{\sqrt{3}}{2}-V_c\×\frac{\sqrt{3}}{2})\\ V_m=\sqrt{V_{\mathrm{\α}}\×V_{\mathrm{\α}}+V_{\mathrm{\β}}\×V_{\mathrm{\β}}}\end{array}\right..$

3. three-phase alternating-current supply frequency measurement method according to claim 1, it is characterized in that, the formula obtaining the tangent value tan (θ/2) of the rotating vector angle θ of 1/2nd is $\tan \frac{\mathrm{\θ}}{2}=\frac{V_m\sin \mathrm{\θ}}{V_m+V_m\cos \mathrm{\θ}}=\frac{V_{\mathrm{\β}}}{V_m+V_{\mathrm{\α}}}.$

4. three-phase alternating-current supply frequency measurement method according to claim 1, it is characterized in that, also comprise step: judge current phase sequence according to the positive and negative values of frequency, is positive sequence when frequency values is greater than 0, is negative phase-sequence when frequency values is less than 0.