CN207472983U - A kind of electric network impedance on-line identification device based on PRBS disturbance injections - Google Patents
A kind of electric network impedance on-line identification device based on PRBS disturbance injections Download PDFInfo
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Abstract
The utility model is related to electrical engineering technical fields, disclose a kind of electric network impedance on-line identification device based on PRBS disturbance injections, are mainly made of gird-connected inverter, current loop controller, sampling apparatus and impedance identification unit, it is characterised in that：The gird-connected inverter is connected with current loop controller, carry out the injection of PRBS disturbances to power grid using gird-connected inverter in stability of grid connection, in PRBS signal injection process, built-in output voltage THD feedback controllers with ensure the THD values of inverter output voltage be less than 5%；At the sampling apparatus connection power grid PCC, the voltage and current at PCC is sampled and recorded；Sampling apparatus the data obtained is carried out DFT analyses by the impedance identification unit, and the amplitude and phase of each harmonic component of voltage and current under the sampling period can be averaged.The utility model precision is high, stablize, speed is fast, real-time, frequency range is wide, reduces measurement cost and difficulty.
Description
Technical field
The utility model is related to electrical engineering, computer controls and Power Electronic Technique technical field, more particularly, to
A kind of electric network impedance on-line identification device based on PRBS disturbance injections.
Background technology
With the extensive renewable distributed generation resource access power grid such as wind-power electricity generation and photovoltaic generation, extensive electric vehicle
Access and the continuous improvement for being supported on power grid total load accounting with Technics of Power Electronic Conversion interface, the power supply of power grid and negative
Significant change has occurred in lotus characteristic, and the power electronics feature of electric system is more and more apparent, is transported to the safety and stability of power grid
Row brings new challenge.It puts into operation when institute since wind-powered electricity generation and photovoltaic are difficult in the design phase to obtain inverter in advance when gird-connected inverters
In the electric network impedance information of power grid, and forethought may make designed gird-connected inverter to other gird-connected inverters and load
Into influence, therefore (particularly low and medium voltage distribution network) between gird-connected inverter and gird-connected inverter, parallel network reverse in the power grid
It, may when reciprocation occurs by grid-connected common point (point of common coupling, PCC) between device and power grid
Cause the harmonic oscillation of grid-connected common point, so as to generate a large amount of harmonic waves, it gently then influences the power quality of power grid, heavy then entail dangers to
The safe and stable operation of power grid.Current domestic and international research have shown that its be mainly gird-connected inverter output impedance with it is grid-connected
The electric network impedance of common point PCC mismatches, and causes the harmonic oscillation of DC/AC inverters.
Currently, in order to solve the problems, such as the harmonic oscillation of gird-connected inverter, usually there are two types of solutions：1st, in inverter simultaneously
Before net, the output impedance and electric network impedance of sweep generator off-line measurement gird-connected inverter are first passed through, judges that power grid is with direct impedance
No matching decides whether grid-connected again；2nd, gird-connected inverter obtains the impedance information of power grid in real time, automatically adjusts gird-connected inverter
Output impedance, it is automatic to adapt to the variation of electrical network parameter, and then achieve the purpose that improve power grid quality and stability.
But the operability in practical application of scheme 1 is not strong, it is difficult to the automatic variation for adapting to electrical network parameter；Scheme 2
Crucial difficult point is that the on-line identification of electric network impedance.Traditional impedance discrimination method is broadly divided into passive the resonance method and active
Injection method.Wherein, passive approach is passed through Fourier transformation and is extracted one using power grid distortion or the intrinsic harmonic wave of gird-connected inverter
Simultaneously electric network impedance is calculated in fixed harmonic component.Passive approach is non-invasive, and identification process will not normally transport power grid
Row impacts, but a major defect of this method is that distortion amplitude in real power grid and repetitive rate are all difficult to correctly survey
Amount, therefore, it is difficult to accurate measurement is made to electric network impedance.And common active method needs to set by additional power electronics
It is standby that certain voltage or current disturbing are injected to power grid, and frequency analysis is carried out to disturbance and response signal to obtain respective frequency
Rate ingredient, by electric network impedance is calculated.The shortcomings that active method is maximum is to need an additional electrical in series or in parallel
Power electronic device brings huge limitation to practical implementation method.Active injection method is still most common method, however when needs
When measuring the impedance operator under multiple frequencies, need to inject multiple characteristic signals simultaneously (such as：Sine wave), this to realize difficulty
It greatly improves, that is, needs multiple sine signal sources of connecting, be very unpractical in engineering practice.
Existing impedance network tester is it needs to be determined that parameter more than comparison, such as operating voltage of network etc., to realize
Testing impedance, and need tester sealing in the common point of grid-connected system to realize the measurement of the injection of disturbance and response, this
Sample can just measure the impedance value of some network.This method belongs to hardware injection method of perturbation, needs to add in grid-connected system
Additional power electronic equipment increases design difficulty and measurement cost, and the impedance measured belongs to external variable for system, can not
The shortcomings that incoming inverter carries out self adaptive control, this is undoubtedly impedance instrument.
In addition, in the electric network impedance test method and device that are proposed in patent CN104198843B, it is defeated by inverter
Go out non-characteristic frequency harmonic wave to obtain the impedance of non-characteristic frequency, then matched curve obtains impedance frequency characteristic, passes through again later
Curve calculates the impedance value under characteristic frequency.However this method is wanted to utilize think of of the power grid under non-characteristic frequency without corresponding response
Think, then the interpolation of voltage and current as measures obtained voltage and current in itself, is calculated correspond to by Ohm's law later
Impedance.This method is there is insufficient, because noise is ubiquitous, it means that even if under non-characteristic frequency,
Power grid remains many noises, this can seriously affect electric network impedance test result.
Utility model content
The utility model proposes it is a kind of based on PRBS disturbance injection electric network impedance on-line identification device,
A kind of electric network impedance on-line identification device based on PRBS disturbance injections, mainly by gird-connected inverter, electric current loop control
Device processed, sampling apparatus and impedance identification unit composition, it is characterised in that：The gird-connected inverter is connected with current loop controller,
The injection of PRBS disturbances is carried out to power grid using gird-connected inverter in stability of grid connection, in PRBS signal injection process
In, built-in output voltage THD feedback controllers with ensure the THD values of inverter output voltage be less than 5%；The sampling apparatus connects
It gets access to grid at PCC, the voltage and current at PCC is sampled and recorded；The impedance identification unit will be obtained by sampling apparatus
Data carry out DFT analyses, and the amplitude and phase of each harmonic component of voltage and current under the sampling period can be averaged,
Using obtained PRBS disturbances excitation and the amplitude and phase average of each harmonic component of voltage responsive, electric network impedance is calculated
Frequency sequence；The present apparatus predicts electric network impedance using least square curve fitting method, improves distinguishing in high band
Know precision.
Particularly, the gird-connected inverter is single-phase grid-connected inverter, and the injection mode that PRBS disturbances are carried out to power grid is
It is superimposed in the reference input of current loop controller.
Particularly, the gird-connected inverter is three-phase grid-connected inverter, and the injection mode that PRBS disturbances are carried out to power grid is
It is superimposed in the d axis reference inputs of current loop controller.
The method that electric network impedance on-line identification is carried out using above device, basic step are as follows：
(1) in the input of the amplitude reference of gird-connected inverter current loop controller, increase PRBS disturbing signal channels, carry out
The periodical superposition of PRBS disturbances；Wherein, the frequency of PRBS disturbing signals for power grid fundamental frequency frequency or according to specific requirement from
Row setting, number of bits N can voluntarily select the arbitrary integer between 5-11 according to the requirement of measurement accuracy；PRBS disturbing signals
Amplitude be inverter rated output less than 10%；
(2) gird-connected inverter output superposition PRBS disturbing signals, periodically carry out the injection of PRBS disturbing signals and stopping
PRBS disturbing signals are injected so that the inverter period is in containing disturbance and undisturbed two stable states；
(3) sampling apparatus is respectively containing disturbance and output voltage and output of undisturbed two stable states to PCC points
Electric current is measured and is sampled, and subsequent impedance identification unit carries out direct computation of DFT leaf analysis to sampled result and obtains voltage and current
Frequency domain sequence, to frequency domain sequence carry out vector difference operation, obtain under each frequency PRBS excitation disturbance and its power grid is drawn
The voltage responsive risen, and acquire the electric network impedance value of the period；Simultaneously to carrying out total harmonic distortion containing the voltage under state of disturbance
Analysis obtains the THD values of inverter output voltage, ensures the THD of output voltage<5%.
(4) the device plug-in carries out step (2) to (3) period, and constantly update measures obtained power grid in real time
Impedance frequency characteristic completes the on-line identification of electric network impedance.
Particularly, the gird-connected inverter is single-phase grid-connected inverter, and the stacked system of step (1) the PRBS disturbances is
PRBS disturbing signals are superimposed in the reference input of current loop controller.
Particularly, the gird-connected inverter is three-phase grid-connected inverter, the stacked system of step (1) PRBS disturbances
PRBS disturbing signals are superimposed in the d axis reference inputs of current loop controller.
Particularly, the period of the gird-connected inverter output superposition PRBS disturbing signals can be chosen for 5 network waves, week
Phase is 0.1s.
The beneficial effects of the utility model：
PRBS is a kind of non-characteristic sequence, and major parameter is the number of bits N of sequence, and the number of bits of sequence is determined again
The step-length M of sequence is determined.Relationship between wherein step-length M and number of bits N is M=2N-1.In signal field, PRBS due to
The encoding characteristics of its own so that multiple harmonic present in its signal, wherein harmonic fundamental frequency depend on the frequency of PRBS.Cause
This, we can utilize the characteristic that PRBS includes multiple harmonic, be injected into grid-connected inverters point, then carry out electric network impedance
On-line identification.
The utility model is mainly characterized by the controller of inverter, periodically in the ginseng of inverter output amplitude
It examines and a PRBS disturbing signal is superimposed in input so that PRBS disturbing signals are included in inverter output voltage (or electric current), this
Output voltage (or electric current) is equivalent to there are multiple harmonic components, then to grid-connected common point (Point of Common
Coupling, PCC) the disturbing signal response of collected three-phase voltage and electric current carry out Fourier analysis, reality be calculated
When electric network impedance.The utility model belongs to Software Method injection, compared with traditional electric network impedance discrimination method, its not only precision
It is high, speed is fast, real-time, frequency range is wide, while also solves the shortcomings that needing to seal in additional power electronic device, significantly
Ground reduces measurement cost and difficulty so that the stability of gird-connected inverter is improved.
In the case of either for single-phase or three-phase, this patent is in the situation that need not add additional power electronic equipment
Under, the software and hardware resources of gird-connected inverter are reasonably utilized, by the modification to inverter internal programming module into line code,
Its own ability for having harmonic disturbance injection is realized, and utilizes the on-line identification for disturbing injection method realization electric network impedance.Separately
PRBS signals used in outer the utility model can change its number of bits according to actual conditions and disturbance amplitude is disturbed to control
The dynamic influence to grid-connected system.In electric network impedance identification process, the utility model can ensure certain electric network impedance identification
The influence of disturbed belt is reduced under the premise of precision, this is not available for other prior arts.Electric network impedance on-line identification
It realizes and its accuracy is the harmonic oscillation for realizing self adaptive control of the gird-connected inverter based on impedance with avoiding gird-connected inverter
It lays a good foundation.
In conclusion in the method to electric network impedance on-line identification, the on-line identification method based on PRBS disturbance injections
Have many advantages, such as that precision is high, at low cost, range is wide and easily realizes.And electric network impedance can online real-time identification, and to identification
Obtained electric network impedance carries out self adaptive control in inverter internal, to achieve the purpose that improve grid-connected inverters quality.
Description of the drawings
It in order to illustrate the embodiment of the utility model or the technical proposal in the existing technology more clearly, below will be to embodiment
Or attached drawing needed to be used in the description of the prior art is briefly described, it should be apparent that, the accompanying drawings in the following description is only
It is some embodiments of the utility model, for those of ordinary skill in the art, in the premise not made the creative labor
Under, it can also be obtained according to these attached drawings other attached drawings.
Fig. 1 is the electric network impedance identification system frame diagram of the utility model embodiment；
Fig. 2 is that the electric network impedance of the utility model embodiment recognizes decanting point schematic diagram；
Fig. 3 is that the three-phase grid-connected inverter powernet of the utility model embodiment recognizes topological diagram；
Fig. 4 is the flow chart of the power grid input impedance on-line identification method of the utility model embodiment；
Fig. 5 is matched curve of the utility model embodiment discrimination method to three-phase equilibrium power grid A phase of impedance models.
Specific embodiment
The preferred embodiment of the utility model is described in detail below in conjunction with the accompanying drawings, so that the advantages of the utility model
It can be easier to be readily appreciated by one skilled in the art with feature, it is apparent clear and definite so as to be made to the scope of protection of the utility model
Define.
The concrete methods of realizing of the present embodiment is as follows：
(1) the present embodiment mainly carries out electricity using the three-phase grid-connected inverter or single-phase grid-connected inverter of dq domains current control
The realization of net on-line identification.First, in the output amplitude reference value I of inverter current control looprefIt is (inverse for three-phase grid
Become device, be then d axis reference values Idref) increase a PRBS disturbance channel：
The disturbance channel can according to plug-in to output reference value Iref(for three-phase grid-connected inverter, then join for d axis
Examine value Idref) it is superimposed or cancels disturbance.Therefore, which will be controlled there are one Enable Pin by En signals are enabled built in inverter
The conducting state of channel, schematic diagram are as shown in Figure 2.In addition, since grid-connected system is there is certain effect of inertia, and DFT
Analysis is necessarily required to just obtain a result by a sinusoidal cycles.Therefore, it is especially heavy that the selection in injection period is disturbed in PRBS
It wants, directly affects the accuracy of electric network impedance on-line identification result.The enabling pulse signal period selection of the utility model
For 10 power grid sine wave periods, wherein continuous 5 sinusoidal cycles Enable Pins put 1 injection disturbing signal, latter continuous 5 just
String period Enable Pin sets to 0 the injection of revocation disturbance.Here it is found that the waveform in preceding 5 periods is disturbed comprising PRBS, rear 5 periods
Undisturbed.
(2) cooperation disturbance is injected the period, and (monophase system can be considered in three-phase system the voltage and current at measurement PCC
A certain phase)：
Due to the difference there is connection type in three-phase system, by taking the connection of three phase network impedance Y types as an example, it is directed to
Voltage and electric current should be respectively phase voltage and line current.According to disturbance injection timing, after 4 periods are injected in disturbance, detection
Each phase phase voltage value u (t) in last 1 period and line current value i (t) carry out discrete Fu to the voltage and electric current that measure
In leaf analysis, the amplitude and phase of each harmonic component obtained later to current sample period are averaged, are denoted as Utilization index form can obtain the expression containing the voltage and current under state of disturbance
Formula, respectivelyThe voltage and electricity under undisturbed state can similarly be obtained
The average value of harmonic component amplitude and phase is flowed, is denoted asVoltage under the state
It is respectively with current index form
(3) it calculates and fits power grid input impedance frequency characteristic, and real-time period updates：
In the voltage for including disturbance that (2) step obtainsAnd electric currentWith undisturbed voltageAnd electric currentSubtraction is carried out to it, obtains corresponding voltage and current increment, as shown in (3) formula：
Then power grid input impedance value can be calculated, as shown in (4) formula：
The amplitude of its middle impedance and the calculating of phase angle are as follows, as shown in (5) formula：
The input impedance sequence of power grid can be obtained in this wayShown in its expression-form such as formula (11)：
Electric network impedance frequency domain seriesIn high band, since the impedance of inductance part increases, to the inhibition of system
Also increase therewith so that system response time lengthens, and is relatively inaccessible to stablize in electric network impedance identification period internal ratio.Therefore, at this time
There are large errors for the impedance that measurement obtains.In order to solve the disadvantage that electric network impedance identification is not high under high frequency condition,
The method that curve matching is utilized in the utility model is higher using low-frequency range identification as a result, fitting the frequency of electric network impedance
Rate characteristic curve, thus can using fit come impedance model curve it is not high to correct high band impedance identification
Point.
In long distance power transmission, since the presence of line impedance and transformer leakage reactance causes the power grid at PCC to hinder
Anti- is in perception, as shown in formula (7).
Zg(s)=Rg+sLg (7)
It utilizes Euler's formula (8)：
eix=cos (x)+isin (x) (8)
The identification result of low-frequency range is utilized respectively Euler's formula to separate out by real and imaginary parts, can be obtained (9)：
Wherein Rf is the power grid resistance of fitting, and Lf is the power grid inductance of fitting.The electric network impedance model being so fitted is
(10)：
Zf=Rf+sLf (10)
Therefore, the electric network impedance curve that we can be fitted as shown in figure 5, fit what is come as can be seen from this figure
Electric network impedance and theoretical calculation degree are higher, it can be seen that the effect of fitting is preferable.
The present embodiment attached drawing and experimental data are described as follows：
Fig. 1 is electric network impedance identification system frame diagram, and main thought is to disturb to obtain electricity by injection and revocation PRBS
Electric network impedance is calculated with voltage responsive and by impedance identification module in flow disturbance.
Fig. 2 recognizes decanting point schematic diagram for electric network impedance, if in single-phase inverter, should join in control loop current amplitude
Examine the superposition that PRBS is carried out in value；If in three-phase inverter, the folded of PRBS disturbances should be carried out in control loop d axis reference values
Add.
Fig. 3 recognizes topological diagram for three-phase grid-connected inverter powernet, is hindered in the larger dotted line frame of the area of pictural surface for power grid
Anti- identification module, the phase voltage of PCC points is sampled with line current, and PRBS forms are obtained by the Vector operation in frequency domain
Current disturbing and voltage responsive frequency sequence, electric network impedance finally is calculated using formula (1)~(6)；Area is larger
Decanting point schematic diagram is disturbed for PRBS in dotted line frame, it is corresponding with Fig. 2.
Fig. 4 is the flow chart of power grid input impedance on-line identification method, and gird-connected inverter is utilized in stability of grid connection
The injection of PRBS disturbances is carried out to power grid, after perturbed system to be implanted is waited to stablize, voltage and current PCC at is carried out sampling with
It records and carries out DFT analyses, the amplitude and phase of each harmonic component of voltage and current under the sampling period are averaged；It removes
After pin disturbance and waiting system are stablized again, each harmonic component width of voltage and current under undisturbed is obtained using same strategy
The frequency domain sequence of electric network impedance is calculated using inverter internal electric network impedance identification module for the average value of value and phase.
Fig. 5 gives matched curve of the discrimination method to three-phase equilibrium power grid A phase of impedance models, can from the figure
Go out to fit the A phase electric network impedance curves come and theoretical calculation degree be higher, solve the problems, such as that high band identification result is poor,
Curve-fitting method is demonstrated to correctness.
Table 1 is the experimental data of electric network impedance on-line identification：
Table 1
Table 1 gives the base that this method recognizes resistance R=5 Ω with the inductance L=2mL impedance models connected
The experimental data of electric network impedance under wave to 25 subharmonic, wherein mainly include 1. measure obtain the amplitude of impedance and phase angle, 2. pairs
The relative error that the theoretical value of impedance magnitude and phase angle, 3. measured values is answered to be compared with theoretical value.
From subordinate list 1：1. in the impedance identification of the subharmonic of fundamental wave~25, maximum relative error is no more than
1.869%, either amplitude or phase angle, relative error are generally less than 0.15%.2. with the increase of identification frequency, impedance is surveyed
The relative error brought is measured in increase tendency, but still in tolerance interval.
Although being described in conjunction with the accompanying the embodiment of the utility model, patent owner can want in appended right
Various deformations or amendments are made within the scope of asking, as long as no more than the described protection model of the claim of the utility model
It encloses, should all be within the protection scope of the utility model.
Claims (3)
1. a kind of electric network impedance on-line identification device based on PRBS disturbance injections, mainly by gird-connected inverter, current loop control
Device, sampling apparatus and impedance identification unit composition, it is characterised in that：The gird-connected inverter is connected with current loop controller,
Carry out the injection of PRBS disturbances in the case of stability of grid connection to power grid using gird-connected inverter, in PRBS signal injection process,
Built-in output voltage THD feedback controllers with ensure the THD values of inverter output voltage be less than 5%；The sampling apparatus connection electricity
It nets at PCC, the voltage and current at PCC is sampled and recorded；The impedance identification unit is by sampling apparatus the data obtained
DFT analyses are carried out, and the amplitude and phase of each harmonic component of voltage and current under the sampling period can be averaged, are utilized
Obtained PRBS disturbances excitation and the amplitude and phase average of each harmonic component of voltage responsive calculate the frequency of electric network impedance
Rate sequence.
2. device for identifying according to claim 1, it is characterised in that：The gird-connected inverter is single-phase grid-connected inverter,
The injection mode that PRBS disturbances are carried out to power grid is to be superimposed in the reference input of current loop controller.
3. device for identifying according to claim 1, it is characterised in that：The gird-connected inverter is three-phase grid-connected inverter,
The injection mode that PRBS disturbances are carried out to power grid is to be superimposed in the d axis reference inputs of current loop controller.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109030950A (en) * | 2018-08-06 | 2018-12-18 | 南方电网科学研究院有限责任公司 | Impedance scanning method and system for power electronic equipment |
| CN110045187A (en) * | 2019-05-07 | 2019-07-23 | 郑州轻工业学院 | Gird-connected inverter electric network impedance discrimination method based on high frequency electrocardiography |
| CN111103524A (en) * | 2019-12-06 | 2020-05-05 | 华帝股份有限公司 | Disturbance signal injection method based on linear circuit |
-
2017
- 2017-05-22 CN CN201720568317.4U patent/CN207472983U/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109030950A (en) * | 2018-08-06 | 2018-12-18 | 南方电网科学研究院有限责任公司 | Impedance scanning method and system for power electronic equipment |
| CN110045187A (en) * | 2019-05-07 | 2019-07-23 | 郑州轻工业学院 | Gird-connected inverter electric network impedance discrimination method based on high frequency electrocardiography |
| CN111103524A (en) * | 2019-12-06 | 2020-05-05 | 华帝股份有限公司 | Disturbance signal injection method based on linear circuit |
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