CN105044458A - TT transformation-based electric power system harmonic detection method - Google Patents

Abstract

The invention discloses a TT transformation-based electric power system harmonic detection method, and is specifically implemented according to the steps of: 1. sampling and discretizing a signal of an electric power system to be detected, and feeding the acquired discrete signal to be detected into a central processing unit; 2. performing TT transformation on the discrete signal in the Step 1 in the central processing unit, and analyzing a result after TT transformation to obtain segment information of the signal; and 3. according to the segment information obtained in the Step 2, obtaining harmonic components in the signal to be detected and start-stop moments of each harmonic component. The TT transformation-based electric power system harmonic detection method can detect weak higher harmonics, and can also detect a time range where harmonics exist.

Description

A kind of trend of harmonic detection method of power based on TT conversion

Technical field

The invention belongs to Measurement of Harmonics in Power System technical field, be specifically related to a kind of trend of harmonic detection method of power based on TT conversion.

Background technology

Harmonic wave has very large harm to utility network and related system, and can produce interference to neighbouring communication system, reduce communication quality, higher hamonic wave environment also has a great impact people, animal and ecologic environment.Harmonic detecting is the prerequisite of harmonics restraint, under current electric grid load day by day complicated situation, good harmonic detecting method is beneficial to effective analysis and the supervision of mains by harmonics disturbance regime, therefore the method studying harmonic detecting is necessary, early stage harmonic detecting method is all based on frequency domain theory, namely adopts the principle of analog filtering, but when needs detect multiple harmonic component, realizing circuit becomes complicated, and design difficulty increases thereupon; The people such as Japanese scholars H.Akagi propose based on the instantaneous reactive power theory under time domain and nonsinusoidal condition, namely the P-Q based on instantaneous real power P and instantaneous reactive power Q is theoretical, at present in Active Power Filter-APF, this method is widely used, but this theory proposes based on three-phase three-wire circuit, complicated on the contrary for single-phase circuit application; It is also increasing that domestic and international application neural network detects harmonic wave, namely utilizes the Function approximation capabilities of Multi-layered Feedforward Networks, by constructing special multilayer feedforward neural network, carry out harmonic detecting, this method calculated amount is little, and real-time is good, but also has a lot of problem in engineer applied; FFT is most widely used a kind of harmonic detecting method in current harmonic detecting, is usually used in detecting first-harmonic and integral frequency harmonizing wave, and the method can obtain amplitude and the phase place of harmonic wave simultaneously, and function is more, convenience of calculation.But FFT also has its limitation: be first extract whole spectrum information from simulating signal, need the time quantum getting endless in theory, next is that testing result does not reflect time dependent frequency, and when people need when understanding the spectrum information of non-stationary signal, FFT is no longer applicable.For this shortcoming of FFT method, people utilize short time discrete Fourier transform (ShortTimeFourierTransformation, and wavelet transformation (wavelettransform STFT), WT) harmonic wave is detected, but the time frequency resolution of STFT is fixing, although WT has adaptive multiresolution, but it still needs to trade off between time frequency resolution on the one hand, WT is time scale transformation on the other hand, and the harmonic wave that different Wavelet Detection goes out all will be converted into frequency yardstick.Therefore be necessary to find new harmonic detecting method, new method preferably have FFT concurrently with the advantage of wavelet transformation.

Summary of the invention

The object of this invention is to provide a kind of trend of harmonic detection method of power based on TT conversion, solve the problem that the inspection of existing harmonic detecting method does not measure the time range of faint higher hamonic wave and harmonic wave existence.

The technical solution adopted in the present invention is, a kind of trend of harmonic detection method of power based on TT conversion, specifically implements according to following steps:

Step 1, the signal of electric system to be detected to be sampled and discretize, obtain discrete signal to be detected and send into central processing unit;

Step 2, in central processing unit, TT conversion is carried out to the discrete signal in step 1, carry out analyzing the segment information obtaining signal to the result after TT conversion;

Step 3, according to the segment information obtained in step 2, obtain the start/stop time of harmonic components in signal to be detected and often kind of harmonic components.

Feature of the present invention is also:

In step 1, the signal of electric system to be detected to be sampled and the equipment of discretize adopts mutual inductor or Hall element.

In step 1, central processing unit adopts DSP or FPGA.

Carrying out analyzing the segment information obtaining signal to the result after TT conversion in step 2, being specially: when being mixed into Instantaneous Harmonic in discrete signal, the result of TT conversion will be undergone mutation, and will be judged to be the start time of transient harmonics the moment of undergoing mutation; When the Instantaneous Harmonic be mixed in discrete signal disappears, the result of TT conversion also will be undergone mutation again, and the moment of again undergoing mutation judges the finish time being decided to be Instantaneous Harmonic; Continue to judge that the result that TT converts is undergone mutation the moment, until the result that TT converts all has been judged; According to start time and the finish time of Instantaneous Harmonic, by discrete signal segmentation; If the result of TT conversion is not undergone mutation, then there is no Instantaneous Harmonic in discrete signal, without the need to discrete signal segmentation.

In step 3, the acquisition of the start/stop time of harmonic components and often kind of harmonic components is specially:

If discrete signal 1. to be detected does not have segmentation, directly from the result of TT conversion, extract diagonal element, then fast connect is carried out to diagonal element, detect that the maximum value number of amplitude spectrum is exactly harmonic wave number, corresponding frequency is exactly harmonic frequency, namely obtain harmonic components, its harmonic wave initial time of discrete signal without segmentation is sampling start time, and end time is sampling end time;

If 2. carried out segmentation to discrete signal to be detected, according to the segment information of step 2 pair signal, the diagonal element in the result of TT conversion is extracted in every section, then fast connect is carried out to diagonal element, every section detects that the maximum value number of amplitude spectrum is exactly the harmonic wave number of this section, corresponding frequency is exactly the harmonic frequency of this section, namely obtains harmonic components, draws the start/stop time of often kind of harmonic components from the harmonic components obtained.

The invention has the beneficial effects as follows: the present invention proposes a kind of trend of harmonic detection method of power based on TT conversion, faint higher hamonic wave can be detected, and can be applicable to the harmonic detecting of the block signal of stationary signal and non-stationary, also can detect the time range that harmonic wave exists, effect is good.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of a kind of trend of harmonic detection method of power based on TT conversion of the present invention;

Fig. 2 is the TT transformation results figure of block signal;

Fig. 3 is the FFT transformation results figure of signal to be detected without segmentation;

Fig. 4 is the S-transformation result figure of signal to be detected without segmentation;

Fig. 5 is the detection method result figure of signal to be detected without segmentation;

Fig. 6 is the FFT transformation results figure that signal to be detected has segmentation;

Fig. 7 is the S-transformation result figure that signal to be detected has segmentation;

Fig. 8 is the detection method result figure that signal to be detected has segmentation.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

A kind of trend of harmonic detection method of power based on TT conversion (Time-TimeTransform) of the present invention, flow process as shown in Figure 1, is specifically implemented according to following steps:

Step 1, employing mutual inductor or Hall element or other sample devicess are sampled and discretize to the current signal of electric system to be detected or voltage signal, obtain discrete signal to be detected and send into central processor CPU (can be DSP or FPGA or other process chip);

Step 2, in central processing unit, TT conversion is carried out to the discrete signal in step 1, carry out analyzing the segment information obtaining signal to the result after TT conversion;

Illustrate for the transformation results of TT shown in Fig. 2, when being mixed into suddenly Instantaneous Harmonic in discrete signal, the result that its TT converts is obviously different from the TT transformation results before not containing Instantaneous Harmonic, known accordingly, if the result of TT conversion undergos mutation (near 130 sampled points), then must be mixed into Instantaneous Harmonic suddenly in its original discrete signal, is judged to be the initial time of transient harmonics the moment of undergoing mutation, in like manner, when the Instantaneous Harmonic be mixed in discrete signal suddenly disappears (near 250 sampled points), the result that its TT converts also will be undergone mutation, the moment of again undergoing mutation judges the end time being decided to be Instantaneous Harmonic.Continue to judge that the result that TT converts is undergone mutation the moment, until the result that TT converts all has been judged; According to initial time and the end time of Instantaneous Harmonic, by discrete signal segmentation; From the interval finding out the concrete time of origin of Instantaneous Harmonic that Fig. 2 can be clear and definite;

If the result of TT conversion is not undergone mutation, then there is no Instantaneous Harmonic in discrete signal, without the need to discrete signal segmentation.

Step 3, according to the segment information obtained in step 2, obtain the start/stop time of harmonic components in signal to be detected and often kind of harmonic components, preparation method is specially:

If discrete signal 1. to be detected does not have segmentation, show in discrete signal to be detected not containing Instantaneous Harmonic, then direct from TT conversion result extract diagonal element, then fast connect is carried out to diagonal element, detect that the maximum value number of amplitude spectrum is exactly harmonic wave number, corresponding frequency is exactly harmonic frequency, namely obtains harmonic components, its harmonic wave initial time of discrete signal without segmentation is sampling start time, and end time is sampling end time;

If 2. carried out segmentation to discrete signal to be detected, show in discrete signal to be detected containing Instantaneous Harmonic, according to the segment information of step 2 pair signal, the diagonal element in the result of TT conversion is extracted in every section, then fast connect is carried out to diagonal element, every section detects that the maximum value number of amplitude spectrum is exactly the harmonic wave number of this section, corresponding frequency is exactly the harmonic frequency of this section, namely obtain harmonic components, from the harmonic components obtained, draw the start/stop time of often kind of harmonic components.

The ultimate principle that TT conversion can be used for Measurement of Harmonics in Power System is as follows:

TT conversion be the people such as Pinnega based on short time discrete Fourier transform (STFT) and S-transformation put forward time m-time dimension conversion, the STFT of definition time territory signal h (t) is transformed to:

$STFT(t,f)={\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}h\left(\mathrm{\τ}\right)w(t-\mathrm{\τ})\exp (-2\mathrm{\π}if\mathrm{\τ})d\mathrm{\τ}---\left(1\right)$

In formula: τ and t represents the time, f represents frequency, and w is window function, general desirable Gaussian function.

Carry out inverse Fourier transform to above formula can obtain:

$\[h\left(\mathrm{\τ}\right)w(t-\mathrm{\τ})\]={\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}STFT(t,f)\exp (+2\mathrm{\π}if\mathrm{\τ})df---\left(2\right)$

Function [h (τ) w (t-τ)] is actually the function of a two-dimensional time, simplifies TT here _sTFT(t, τ), (2) formula can be rewritten as by we:

${\mathrm{TT}}_{STFT}(t,\mathrm{\τ})={\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}STFT(t,f)\exp (+2\mathrm{\π}if\mathrm{\τ})df---\left(3\right)$

Similar, also have corresponding TT to convert for S-transformation:

${\mathrm{TT}}_{ST}(t,\mathrm{\τ})={\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}S(t,f)\exp (+2\mathrm{\π}if\mathrm{\τ})df---\left(4\right)$

Wherein,

$S(t,f)=\underset{-\mathrm{\∞}}{\overset{+\mathrm{\∞}}{\∫}}h\left(\mathrm{\τ}\right)\frac{\left|f\right|}{\sqrt{2\mathrm{\π}}}{e}^{-\frac{{(\mathrm{\τ}-t)}^2{f}^2}{2}}{e}^{-i2\mathrm{\π}ft}d\mathrm{\τ}---\left(5\right)$

(5) formula is the S-transformation of signal h (τ).

The contravariant of TT conversion is changed to:

${\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}TT(t,\mathrm{\τ})dt=h\left(\mathrm{\τ}\right)---\left(6\right)$

Because S-transformation corresponding TT conversion there is good character, in order to simplify discussion, utilize TT to represent TT _sT(t, τ).Discrete TT conversion is as follows

$TT\[jT,kT\]=\underset{n=-N/2}{\overset{N/2-1}{\Σ}}S\[jT,\frac{n}{NT}\]\exp \[\frac{+2\mathrm{\π}ink}{N}\]---\left(7\right)$

The diagonal element that convert referred to as TT of diagonal line unit of TT conversion, namely in formula (4), make t=τ just can obtain diagonal element, although TT is converted and introduced by S-transformation, TT is converted and directly can be calculated by following formula:

$TT(t,\mathrm{\τ})={\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}h\left(\mathrm{\θ}\right){\mathrm{\ψ}}_k(\mathrm{\θ}-t,\mathrm{\θ}-\mathrm{\τ})d\mathrm{\θ}---\left(8\right)$

Wherein h (θ) is signal, ψ _kas shown in the formula:

${\mathrm{\ψ}}_k(t,\mathrm{\τ})=\underset{-\mathrm{\∞}}{\overset{+\mathrm{\∞}}{\∫}}\frac{\left|f\right|}{k\sqrt{2\mathrm{\π}}}{e}^{-\frac{{\mathrm{\τ}}^2{f}^2}{2k^2}}{e}^{-i2\mathrm{\π}ft}df---\left(9\right)$

CarineSimon derived TT conversion diagonal element calculating formula as follows:

In above formula represent inverse Fourier transform, H (f), Ψ (f) are signal h (t) and ψ respectively _kthe Fourier transform of (equaling τ at t), wherein Ψ (f)=-2p _k(1) π ²| f|, erfi is error function, can find out that diagonal element is for the high frequency effect of haveing a certain upgrade, so the diagonal element that TT can be utilized to convert detects weak higher hamonic wave signal.

Simulation comparison result

1. signal to be detected is without segmentation testing result

Original signal expression formula is

$\begin{array}{c}{h}_1=\cos (100\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})+0.5\×\cos (200\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})+0.05\×\cos (300\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})+\\ 0.03\×\cos (400\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})+0.01\×\cos (500\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})+0.005\×\cos (600\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})\end{array}$

Original signal is made up of first-harmonic and 2 subharmonic, 3 subharmonic, 4 subharmonic, 5 subharmonic and 6 subharmonic, and the amplitude of harmonic wave reduces successively, and the peak value of 6 subharmonic only has 0.5% of first-harmonic.The sample frequency of signal is 1KHz.

Fig. 3-5 is respectively FFT conversion, S-transformation and harmonic detecting method result figure of the present invention.

Known by the contrast of three result figure:

FFT conversion can detect first-harmonic, 2 subharmonic, 3 subharmonic, and other subharmonic content are less, is difficult to differentiate; S-transformation can detect first-harmonic, 2 subharmonic, and the harmonic wave of more than 3 times is distinguished because aliasing is also very difficult; Harmonic detecting method of the present invention has good amplification effect to high-frequency harmonic, very clearly can tell 6 kinds of harmonic waves.

2. signal to be detected has segmentation Detection results

Given non-stationary block signal:

$\left\{\begin{array}{c}{h}_{11}=\cos (100\mathrm{\π}\×t_1)\\ h_{12}=0.5\×\cos (200\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})\\ h_{13}=0.5\×\cos (300\mathrm{\π}\×t_1)\\ h_{14}=0.1\×\cos (400\mathrm{\π}\×t_1)\\ h_{15}=0.03\×\cos (500\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})\\ h_{16}=0.03\×\cos (600\mathrm{\π}\×t_1+\frac{\mathrm{\π}}{3})\end{array}\right.$

h ₁＝[h ₁₁(1:128)h ₁₁(129:256)+h ₁₂(129:256)+h ₁₃(129:256)+h ₁₄(129:256)h ₁₁(257:512)+h ₁₅(257:512)+h ₁₆(257:512)]

Fig. 6-8 is respectively FFT conversion, S-transformation and harmonic detecting method result figure of the present invention.

Known by the contrast of three result figure:

FFT conversion can only detect first-harmonic, 2 subharmonic and 3 subharmonic, cannot detect the initial time of other harmonic waves and harmonic wave.S-transformation result shows this signal can be divided into 3 sections, but every section of specific features is not obvious; Harmonic detecting method of the present invention can detect that first paragraph Fig. 8 (a) (corresponding sampled point 1 to 128) only has first-harmonic clearly, second segment Fig. 8 (b) (corresponding sampled point 129 to 256) has four kinds of ripples, and the 3rd section of Fig. 8 (c) (corresponding sampled point 257 to 512) has first-harmonic and 5 times, 6 subharmonic respectively.

Claims (5)

1., based on a trend of harmonic detection method of power for TT conversion, it is characterized in that, specifically implement according to following steps:

Step 1, the signal of electric system to be detected to be sampled and discretize, obtain discrete signal to be detected and send into central processing unit;

Step 2, in central processing unit, TT conversion is carried out to the discrete signal in step 1, carry out analyzing the segment information obtaining signal to the result after TT conversion;

Step 3, according to the segment information obtained in step 2, obtain the start/stop time of harmonic components in signal to be detected and often kind of harmonic components.

2. a kind of trend of harmonic detection method of power based on TT conversion according to claim 1, is characterized in that, samples and the equipment of discretize adopts mutual inductor or Hall element in described step 1 to the signal of electric system to be detected.

3. a kind of trend of harmonic detection method of power based on TT conversion according to claim 1, it is characterized in that, in described step 1, central processing unit adopts DSP or FPGA.

4. a kind of trend of harmonic detection method of power based on TT conversion according to claim 1, it is characterized in that, carry out analyzing the segment information obtaining signal to the result after TT conversion in described step 2, be specially: when being mixed into Instantaneous Harmonic in discrete signal, the result of TT conversion will be undergone mutation, and will be judged to be the initial time of transient harmonics the moment of undergoing mutation; When the Instantaneous Harmonic be mixed in discrete signal disappears, the result of TT conversion also will be undergone mutation again, and the moment of again undergoing mutation judges the end time being decided to be Instantaneous Harmonic; Continue to judge that the result that TT converts is undergone mutation the moment, until the result that TT converts all has been judged; According to start time and the finish time of Instantaneous Harmonic, by discrete signal segmentation; If the result of TT conversion is not undergone mutation, then there is no Instantaneous Harmonic in discrete signal, without the need to discrete signal segmentation.

5. a kind of trend of harmonic detection method of power based on TT conversion according to claim 4, it is characterized in that, in described step 3, the acquisition of the start/stop time of harmonic components and often kind of harmonic components is specially:

If discrete signal 1. to be detected does not have segmentation, directly from the result of TT conversion, extract diagonal element, then fast connect is carried out to diagonal element, detect that the maximum value number of amplitude spectrum is exactly harmonic wave number, corresponding frequency is exactly harmonic frequency, namely obtain harmonic components, its harmonic wave initial time of discrete signal without segmentation is sampling start time, and end time is sampling end time;

If 2. carried out segmentation to discrete signal to be detected, according to the segment information of step 2 pair signal, the diagonal element in the result of TT conversion is extracted in every section, then fast connect is carried out to diagonal element, every section detects that the maximum value number of amplitude spectrum is exactly the harmonic wave number of this section, corresponding frequency is exactly the harmonic frequency of this section, namely obtains harmonic components, draws the start/stop time of often kind of harmonic components from the harmonic components obtained.