CN103424622B - A kind of detection of fractional harmonic source and determination methods - Google Patents

Abstract

The invention discloses a kind of detection and determination methods of fractional harmonic source, by measurements and calculations fractional harmonic active power, detect one or more fractional harmonic source in systems in which.When there is multiple fractional harmonic source, can the responsibility that each fractional harmonic source should be shared be quantized.Comprise the following steps: in electric system, utilize voltage transformer (VT) to obtain substation bus bar voltage signal, utilize current transformer to obtain each bar line current signal being connected to bus, be converted to numerical data through AC data acquisition device.Calculate effective value and the phase place of each frequency component, select the fractional harmonic component that wherein effective value is maximum, calculate the fractional harmonic active power on each bar circuit.Judge that the side of fractional harmonic active power as negative is as fractional harmonic source.If there is multiple fractional harmonic source, then the influence degree that the ratio accounting for total active power according to respective active power size causes to quantize each fractional harmonic source.

Description

A kind of detection of fractional harmonic source and determination methods

Technical field

The present invention relates to for electric power quality monitoring field, particularly relate to a kind of detection and determination methods of fractional harmonic source.

Background technology

Fractional harmonic refers to that frequency is the spectrum component of fundamental frequency point several times (instead of integral multiple).Fractional harmonic source refers to the power equipment producing fractional harmonic.

In recent years, on the one hand along with the extensive application of power electronic equipment and the increase of nonlinear-load, the quality of power supply in electric system has the trend of deterioration, and causes occurring the power quality problem that fractional harmonic etc. is new.On the other hand, the consumer of extensively universal various complex precises is more responsive to the quality of power supply, and the bad quality of power supply can cause subscriber equipment to go out substandard products, shut down and even damage, and therefore society is more and more higher to the requirement of the quality of power supply.Strengthen for the quality of power supply detection, to administer be an important and urgent problem.

Current people are more deep for the research of traditional (integral multiple) harmonic wave, but understand less for emerging fractional harmonic.At present, fractional harmonic has become the research field that in developed country, is enlivened very much, and people's mechanism of production, harm, measuring method etc. started fractional harmonic is carried out many-side and inquired into, and promotes the formulation of its standard limit.

Fractional harmonic in electric system; there is a lot of harm; as produced added losses, causing equipment heating, reducing equipment life; measuring instrument is made to produce error; cause protective relaying maloperation etc.; can also voltage fluctuation and flicker be caused in addition, cause traditional harmonic filter normally to work and even damage.The equipment such as the generator in electric system, transformer, transmission line of electricity seldom produce fractional harmonic when normal operation, in a lot of situation, fractional harmonic is produced by subscriber equipment (as frequency converter, electric arc furnaces and rolling mill etc.), therefore when there is fractional harmonic problem, electric power enterprise and user are concerned about how fractional harmonic is from where, identify that fractional harmonic disturbing source is this very corn of a subject very much.Only have and correctly find out fractional harmonic source, fractional harmonic source position can be judged, thus targetedly control measures is taked to fractional harmonic disturbing source, the electric system of development green non-pollution.

At present, obtain some progress at harmonic source detection field both at home and abroad, but little in the achievement in research of fractional harmonic source detection field.The present invention uses for reference the concept of electric system fundamental active power supply, be applied to the detection of fractional harmonic source, with fractional harmonic active power for index, thus the fractional harmonic power source in system can be detected, particularly can multiple fractional harmonic source in recognition system, and can quantize according to the impact of size on each fractional harmonic source of respective fractional harmonic active power.

Generally speaking, the technical matters needing those skilled in the art urgently to solve at present is: how to identify and to assess fractional harmonic disturbing source.

Summary of the invention

Object of the present invention is exactly that provide a kind of detection and determination methods of fractional harmonic source, it can detect one or more fractional harmonic source in electric system in order to solve the problem.When there is multiple fractional harmonic source, each fractional harmonic source can also be quantized and impact degree.

To achieve these goals, the present invention adopts following technical scheme:

The detection of fractional harmonic source and a determination methods, comprise the following steps:

Step one: in the electric system comprising substation bus bar and circuit, utilize voltage transformer (VT) to obtain substation bus bar voltage signal at substation bus bar place, utilize current transformer to obtain the current signal of electric system side inlet wire and each load side outlet, and be converted to numerical data through AC data acquisition device;

Step 2: the effective value and the phase place that calculate each frequency component;

Step 3: choose the fractional harmonic component that effective value is maximum, calculates the fractional harmonic active power of electric system side and each load side;

Step 4: judge that the side of fractional harmonic active power as negative is as fractional harmonic source; If there is multiple fractional harmonic source, then the ratio accounting for total active power according to respective active power size impacts degree to quantize each fractional harmonic source.

In described step one, electric system comprises a substation bus bar, bus connects at least two circuits, described substation bus bar is provided with voltage transformer (VT) (PT), every bar circuit is equipped with current transformer (CT), described voltage transformer (VT) summation current transformer output terminal is all connected with AC data acquisition device, the voltage and current signal of input processes through AC data acquisition device by AC data acquisition device, finally be converted to the numerical data of applicable computer disposal, described AC data acquisition device comprises the signal conditioning circuit connected successively, sampling hold circuit, analog to digital converter, central signal processor.

Described step one is specially: in electric system, utilize voltage transformer (VT) to obtain the voltage signal of substation bus bar, utilizes current transformer to obtain the current signal being connected to each bar circuit of bus; All voltage and current signal demand continuous sampling 200ms, each current reference direction all selects outflow bus to be positive dirction; Through AC data acquisition device, carry out timing equal interval sampling, obtain voltage and current Wave data.

Described step 2 is specially: the voltage and current Wave data getting continuous 200ms length, calculates effective value and the phase place of each frequency component;

Suppose a busbar voltage u, an electric system side electric current and multiple load side electric current carry out continuous 200ms sampling, and sampling rate is 6400Hz.The Wave data that note measures the voltage u obtained is u={u ₁, u ₂, u ₃..., u _n, wherein N=1280.The then real part a of a wherein kth frequency component _kuwith imaginary part b _kuas follows:

Real part: $a_{\mathrm{ku}}=\frac{2}{N}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{u}_n\cos \left(\mathrm{kn}\frac{2\mathrm{\π}}{N}\right)$

Imaginary part: $b_{\mathrm{ku}}=\frac{2}{N}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{u}_n\sin \left(\mathrm{kn}\frac{2\mathrm{\π}}{N}\right)$

Can be calculated further:

Effective value U _ku: $U_{\mathrm{ku}}=\sqrt{{a_{\mathrm{ku}}}^2+{b_{\mathrm{ku}}}^2}/\sqrt{2}$

Phase theta _ku: θ _ku=arctan (-b _uk/ a _ku)

Wherein k=1,2,3 ..., 320.

Similarly, to current waveform data, carry out the effective value and the phase place that calculate each electric current as stated above.

Described step 3 is specially: select the maximum fractional harmonic frequency component of effective value (or user's certain fractional harmonic frequency component preassigned), carry out the detection of this frequency score harmonic source.The busbar voltage of this frequency is multiplied with electric system side electric current, calculates the fractional harmonic active power of electric system side.Several harmonic voltage effective value of scoring is U _s, phase place is θ _u, electric system side current effective value is I ₀, phase place is θ _i0, then electric system side fraction harmonic wave active power is: P ₀=U _si ₀cos (θ _u-θ _i0).

Similarly, to load side electric current, the fractional harmonic active power of each load side can be calculated as stated above.

Described step 4 is specially: if certain fractional harmonic active power is negative, then judge that this side is as fractional harmonic source.If when there is multiple fractional harmonic source, the impact that each fractional harmonic source causes can be quantified as the ratio of this fractional harmonic source active power and the total active power of all fractional harmonic source.Remember that all fractional harmonic source active power sums are P _h, then wherein any one active power is P _mfractional harmonic source to the influence degree Y of whole system _mcan quantum chemical method be: Y _m=P _m/ P _h, the wherein numbering of m to be integer be fractional harmonic source.

Key of the present invention is, for the fractional harmonic problem in electric system, fractional harmonic source is detected by calculating fractional harmonic active power, when particularly there is multiple fractional harmonic source in electric system, the active power proposing can to send by comparing each fractional harmonic source quantizes each fractional harmonic source and impacts degree.

The invention has the beneficial effects as follows: when detecting electric system fractional harmonic source, not needing to change electric system circuit, only utilizing the voltage of substation bus bar and each line current just can judge fractional harmonic source, technically easily realizing; Not only be applicable to the system containing a fractional harmonic source, be also applicable to the system containing multiple fractional harmonic source, and each fractional harmonic source can be quantized when there is multiple fractional harmonic source impact degree.Principle and the current existing power system of data acquisition device of AC data acquisition device are similar, but its improvements are continuous acquisition to reach the signal of 200ms at every turn, therefore have higher frequency resolution.

Accompanying drawing explanation

Fig. 1 process flow diagram of the present invention;

The electric system schematic diagram that Fig. 2 the present invention is suitable for;

Fig. 3 AC data acquisition device schematic diagram;

Fig. 4 electric system exemplary plot;

Fig. 5 substation bus bar voltage u waveform;

Fig. 6 system side current i 0 waveform;

Fig. 7 load 1 side (linear load) current i 1 waveform;

Fig. 8 load 2 side (fractional harmonic source) current i 2 waveform;

Fig. 9 load 3 side (fractional harmonic source) current i 3 waveform;

The spectrogram of Figure 10 load 3 side current i 3;

Wherein, the 1, first load, the 2, second load, the 3, the 3rd load.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the invention will be further described.

As shown in Figure 1, a kind of detection of fractional harmonic source and determination methods, comprise the following steps:

Step one: in the electric system comprising substation bus bar and circuit, utilize voltage transformer (VT) to obtain substation bus bar voltage signal at substation bus bar place, utilize current transformer to obtain the current signal of electric system side inlet wire and each load side outlet, and be converted to numerical data through AC data acquisition device;

Step 2: the effective value and the phase place that calculate each frequency component;

Step 3: choose the fractional harmonic component that effective value is maximum, calculates the fractional harmonic active power of electric system side and each load side;

Step 4: judge that the side of fractional harmonic active power as negative is as fractional harmonic source; If there is multiple fractional harmonic source, then the ratio accounting for total active power according to respective active power size impacts degree to quantize each fractional harmonic source.

As shown in Figure 2, in described step one, electric system comprises a substation bus bar, bus connects at least two circuits, described substation bus bar is provided with voltage transformer (VT) (PT), every bar circuit is equipped with current transformer (CT), described voltage transformer (VT) summation current transformer output terminal is all connected with AC data acquisition device, the voltage and current signal of input processes through AC data acquisition device by AC data acquisition device, is finally converted to the numerical data of applicable computer disposal.

As shown in Figure 3, described AC data acquisition device comprises the signal conditioning circuit, sampling hold circuit, analog to digital converter, the central signal processor that connect successively.

(1) for the electric system exemplary plot of Fig. 4, electric system side supply frequency is 50Hz, substation bus bar has a system side inlet wire and three load outlets, wherein the first load 1 is linear load, and the second load 2 and the 3rd load 3 all contain 25Hz fractional harmonic source.Utilize voltage transformer (VT) to obtain the voltage u at substation bus bar place, utilize four current transformers to obtain current i 1, i2 and the i3 of electric system side current i 0 and three loads respectively.All voltage and current signal continuous sampling 200ms, sampling rate is 6400Hz, and it is positive dirction that bus is flowed out in the choosing of each current reference direction.Through AC data acquisition device (see Fig. 3, internal main will comprise signal condition, sampling maintenance, analog-digital converter circuit), carry out timing equal interval sampling, obtain voltage u as Fig. 5, system side current i 0 is shown in Fig. 6, the current i 1 of the first load 1 is shown in Fig. 7, and the current i 2 of the second load 2 is shown in Fig. 8, and the current i 3 of the 3rd load 3 is shown in Fig. 9.

(2) get the voltage and current Wave data of continuous 200ms length, calculate effective value and the phase place of each frequency component, the partial frequency spectrum that obtains is shown in Figure 10.

Circular is as follows, if measure the voltage that obtains or current waveform data is x={x ₁, x ₂, x ₃..., x _n, wherein N=1280.The then real part a of a kth frequency component _kwith imaginary part b _kas follows:

Real part: $a_k=\frac{2}{N}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{x}_n\cos \left(\mathrm{kn}\frac{2\mathrm{\π}}{N}\right)$

Imaginary part: $b_k=\frac{2}{N}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{x}_n\sin \left(\mathrm{kn}\frac{2\mathrm{\π}}{N}\right)$

Its effective value X _k: $X_k=\sqrt{{a_k}^2+{b_k}^2}/\sqrt{2}$

Its phase theta _k: θ _k=arctan (-b _k/ a _k).

Wherein k=1,2,3 ..., 320.

(3) select the maximum fractional harmonic frequency component of effective value (selecting 25Hz according to the frequency spectrum of Figure 10 here), carry out the detection of 25Hz fractional harmonic source.The busbar voltage of this frequency is multiplied with electric system side electric current, calculates the fractional harmonic active power of electric system side.If fractional harmonic voltage effective value is U _s, phase place is θ _u, electric system side current effective value is I ₀, phase place is θ _i0, then system side fractional harmonic active power calculating formula is: P ₀=U _si _i0cos (θ _u-θ _i0).

Similarly, the 25Hz fractional harmonic active-power P of each load side can be calculated ₁, P ₂and P ₃.

The 25Hz active power of the electric system side calculated and each load side is in table 1.

(4) from table 1, the 25Hz active power (P of electric system side and the first load 1 ₀=113.8W, P ₁=3.849W) be positive number, can judge that these two is not fractional harmonic source.And the 25Hz active power (P of the second load 2 and the 3rd load 3 ₂=-31.11W, P ₃=-86.50W) be negative, can judge they two be fractional harmonic source.Further can be as follows by calculating the impact quantizing to cause separately:

All two 25Hz fractional harmonic source active power sum: Ph=P ₂+ P ₃=-31.11-86.50=-117.61 (W)

The influence degree that second load 2 causes: Y ₂=P ₂/ P _h=-31.11/ (-117.61)=0.26=26%,

The influence degree that 3rd load 3 causes: Y ₃=P ₃/ P _h=-86.50/ (-117.61)=0.74=74%.

Table 1 experimental result

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (5)

1. the detection of fractional harmonic source and a determination methods, is characterized in that, comprise the following steps:

Step one: in the electric system comprising substation bus bar and circuit, utilize voltage transformer (VT) to obtain substation bus bar voltage signal at substation bus bar place, utilize current transformer to obtain the current signal of electric system side inlet wire and each load side outlet, and be converted to numerical data through AC data acquisition device;

Step 2: the effective value and the phase place that calculate each frequency component:

Get the voltage and current Wave data of continuous 200ms length, calculate effective value and the phase place of each frequency component;

Suppose a busbar voltage u, an electric system side electric current and multiple load side electric current carry out continuous 200ms sampling, and sampling rate is 6400Hz; The Wave data that note measures the voltage u obtained is u={u ₁, u ₂, u ₃..., u _n, wherein N=1280; The then real part a of a wherein kth frequency component _kuwith imaginary part b _kuas follows:

Real part: $a_{\mathrm{ku}}=\frac{2}{N}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{u}_n\cos \left(\mathrm{kn}\frac{2\mathrm{\π}}{N}\right)$

Imaginary part: $b_{\mathrm{ku}}=\frac{2}{N}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{u}_n\sin \left(\mathrm{kn}\frac{2\mathrm{\π}}{N}\right)$

Calculate further:

Effective value U _ku: $U_{\mathrm{ku}}=\sqrt{{a_{\mathrm{ku}}}^2+{b_{\mathrm{ku}}}^2}/\sqrt{2}$

Phase theta _ku: θ _ku=arctan (-b _uk/ a _ku)

Wherein k=1,2,3 ..., 320;

Similarly, to current waveform data, calculate effective value and the phase place of each electric current by the effective value of above-mentioned voltage and the computing method of phase place;

Step 3: choose the fractional harmonic component that effective value is maximum, calculates the fractional harmonic active power of electric system side and each load side;

Step 4: judge that the side of fractional harmonic active power as negative is as fractional harmonic source; If there is multiple fractional harmonic source, then the ratio accounting for total active power according to respective active power size impacts degree to quantize each fractional harmonic source.

2. the detection of a kind of fractional harmonic source as claimed in claim 1 and determination methods, is characterized in that,

In described step one, electric system comprises a substation bus bar, bus connects at least two circuits, described substation bus bar is provided with voltage transformer (VT), every bar circuit is equipped with current transformer, described voltage transformer (VT) summation current transformer output terminal is all connected with AC data acquisition device, the voltage and current signal of input processes by AC data acquisition device, finally be converted to the numerical data of applicable computer disposal, described AC data acquisition device comprises the signal conditioning circuit connected successively, sampling hold circuit, analog to digital converter, central signal processor.

3. the detection of a kind of fractional harmonic source as claimed in claim 1 and determination methods, is characterized in that,

Described step one is specially: in electric system, utilize voltage transformer (VT) to obtain the voltage signal of substation bus bar, utilizes current transformer to obtain the current signal being connected to each bar circuit of bus; All voltage and current signal demand continuous sampling 200ms, each current reference direction all selects outflow bus to be positive dirction; Through AC data acquisition device, carry out timing equal interval sampling, obtain voltage and current Wave data.

4. the detection of a kind of fractional harmonic source as claimed in claim 1 and determination methods, is characterized in that,

Described step 3 is specially: select the fractional harmonic frequency component that effective value is maximum, carry out the detection of this frequency score harmonic source; The busbar voltage of this frequency is multiplied with electric system side electric current, calculates the fractional harmonic active power of electric system side; Several harmonic voltage effective value of scoring is U _s, phase place is θ _u, electric system side current effective value is I ₀, phase place is θ _i0, then electric system side fraction harmonic wave active power is: P ₀=U _si ₀cos (θ _u-θ _i0);

Similarly, to load side electric current, calculate the fractional harmonic active power of each load side by the computing method of above-mentioned electric system side fraction harmonic wave active power.

5. the detection of a kind of fractional harmonic source as claimed in claim 1 and determination methods, is characterized in that,

Described step 4 is specially: if the fractional harmonic active power of system side is negative, then decision-making system side is fractional harmonic source; If the fractional harmonic active power of certain load side is negative, then judge that this load side is as fractional harmonic source; If when there is multiple fractional harmonic source, the influence amount that each fractional harmonic source causes turns to the ratio of this fractional harmonic source active power and the total active power of all fractional harmonic source; Remember that all fractional harmonic source active power sums are P _h, then wherein any one active power is P _mfractional harmonic source to the influence degree Y of whole system _mquantum chemical method is: Y _m=P _m/ P _h, the wherein numbering of m to be integer be fractional harmonic source.