CN103364634A - Three-phase alternating-current power supply frequency measuring method - Google Patents

Abstract

The invention discloses a three-phase alternating-current power supply frequency measuring method. The method includes the following steps that a three-phase voltage signal Va, a three-phase voltage signal Vb and a three-phase voltage signal Vc of a three-phase power supply are collected and converted into a real-time value V alpha and a real-time value V beta of a two-phase coordinate system, and a module value Vm of a current voltage rotating vector is evaluated; according to the real-time value V alpha and the real-time value V beta of the two-phase coordinate system and the module value Vm, the tangent value of a 1 / 2 rotating vector angle theta is evaluated; the angle corresponding to the tangent value is evaluated through check of a tangent table to further evaluate the rotating vector angle theta; differentiation operation is carried out on the rotating vector angle theta to calculate angular frequency omega, and the frequency value of network voltage can be obtained by dividing the angular frequency omega by 2*pi. The three-phase alternating-current power supply frequency measuring method has the advantages of being high in antijamming capability and precision, can be used in severe environments with unstable signals, imbalance, large harmonic contents and the like, and is especially suitable for frequency and phase sequence measuring devices.

Description

The 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 adopt zero crossing to judge more, need hardware circuit to detect zero cross signal, and the soldier calculates the time interval T between adjacent two zero cross signals, and then obtains frequency.

Existing method relies on the hardware circuit accuracy of detection, and, when mains harmonics is larger, perhaps shake back and forth near zero-crossing point, certainly will there be a plurality of zero crossings, cause the frequency erroneous judgement, and this erroneous judgement is difficult to find suitable solution.

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, with 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 mould value V of current voltage rotating vector _m

Instantaneous value V according to two phase coordinate systems _αAnd V _β, and mould value V _m, obtain the tangent value tan (θ/2) of 1/2nd rotating vector angle θ;

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

The computing of differentiating calculates angular frequency to rotating vector angle θ, namely can obtain the frequency values of line voltage divided by 2 π with angular frequency.

Wherein, with three-phase voltage signal V _a, V _bAnd V _cChange the instantaneous value V of two phase coordinate systems into _αAnd V _β, and mould 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 of obtaining the tangent value tan (θ/2) of 1/2nd rotating vector angle θ 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 comprise step: the positive negative value according to frequency is judged current phase sequence, when frequency values is positive sequence greater than 0, when frequency values is negative phase-sequence less than 0 the time.

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

Also comprise in one embodiment step: carry out noise filtering with low-pass filter and process the 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, especially be suitable in frequency and the 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.

Description of drawings

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

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

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

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

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 the coordinate transform of three-phase to two-phase, change the instantaneous value V of two-phase (static) coordinate system into _αAnd V _β, and obtain the mould 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 _mBe instantaneous value V _αOr V _βAmplitude.

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

Concern according to trigonometric function:

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

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

For simplified operation, (1-2) formula molecule denominator be multiply 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 are obtained tan (θ/2) value, then need to look into the tangent table and ask for corresponding angle θ/2, and then obtain rotating vector angle θ.

This step need to be made the tangent table, because the field of definition of tan is-90 °～90 ° variations, corresponding tangent value is from the minus infinity to positive infinity, for the convenience of tabling look-up has been made-89 °～89 ° forms.

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

From Fig. 2 and Fig. 3, find out when electrical network is positive sequence rotating vector angle θ from-180 °～180 ° variations, and slope is greater than 0; When electrical network was negative phase-sequence, rotating vector angle θ was from 180 °～-180 ° variations, 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 is asked for differential in-π～π transient process can introduce noise, causes asking for frequency values unstable.In order to reduce noise, the method that please take to dwindle the θ region of variation in this, namely when the θ value is between-45 °～45 °, carry out again the computing of differential, although this method can't fundamentally be eliminated noise, but noise can be reduced, and namely can filter noise by the low-pass filter that uses 1Hz, reach the purpose 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, among Fig. 4: straight line (1) expression frequency 50Hz;

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

To sum up, instantaneous value V α and the V β of the present invention by three-phase voltage signal being changed into two phase coordinate systems, and then asking for rotating vector angle θ, θ asks for derivative to the rotating vector angle, converts out frequency values, frequency signal is carried out low-pass filtering, filter the noise signal in the frequency signal, thereby obtain stable frequency signal, judge current phase sequence according to the positive negative value of frequency simultaneously, when frequency is positive sequence greater than 0, when frequency is negative phase-sequence less than 0 the time.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, especially be suitable in frequency and the 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 above only is preferred embodiment of the present invention, not in order to limiting the present invention, all any modifications of doing within the spirit and principles in the present invention, is equal to and replaces and improvement etc., all should be included within protection scope of the present invention.

Claims (6)

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, with 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 mould value V of current voltage rotating vector _m

Instantaneous value V according to two phase coordinate systems _αAnd V _β, and mould value V _m, obtain the tangent value tan (θ/2) of 1/2nd rotating vector angle θ;

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

The computing of differentiating calculates angular frequency to rotating vector angle θ, namely can obtain the frequency values of line voltage divided by 2 π with angular frequency.

2. described three-phase alternating-current supply frequency measurement method according to claim 1 is characterized in that, with three-phase voltage signal V _a, V _bAnd V _cChange the instantaneous value V of two phase coordinate systems into _αAnd V _β, and mould 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. described three-phase alternating-current supply frequency measurement method according to claim 1 is characterized in that, the formula of obtaining the tangent value tan (θ/2) of 1/2nd rotating vector angle θ 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. described three-phase alternating-current supply frequency measurement method according to claim 1 is characterized in that, also comprise step: the positive negative value according to frequency is judged current phase sequence, when frequency values is positive sequence greater than 0, when frequency values is negative phase-sequence less than 0 the time.

5. according to claim 1 and 2 or 3 or 4 described three-phase alternating-current supply frequency measurement methods, it is characterized in that, when rotating vector angle θ value was between-45 °～45 °, the computing of differentiating calculated angular frequency to rotating vector angle θ.

6. described three-phase alternating-current supply frequency measurement method according to claim 5 is characterized in that, also comprises step: carry out noise filtering with low-pass filter and process the stabilized frequency value.

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