CN102830307A - Virtual inductance based positive feedback island detection method - Google Patents
Virtual inductance based positive feedback island detection method Download PDFInfo
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- CN102830307A CN102830307A CN2012102944757A CN201210294475A CN102830307A CN 102830307 A CN102830307 A CN 102830307A CN 2012102944757 A CN2012102944757 A CN 2012102944757A CN 201210294475 A CN201210294475 A CN 201210294475A CN 102830307 A CN102830307 A CN 102830307A
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Abstract
The invention discloses a virtual inductance based positive feedback island detection method. In the method, action generated by error signals is enhanced by means of a relation formula shown in the description, and output current of a grid-connected inverter is perturbed in a positive feedback manner, and accordingly, the purpose of island detection is achieved. In the relation formula, i indicates a perturbance current signal to the output current, and u indicates an error voltage signal. By adding an integrator into the positive feedback process to form virtual inductance, so that voltage at a PCC (point of common coupling) no matter what kind of load the voltage is applied to can make change quickly, and detection dead zones can be reduced greatly. In the virtual inductance based positive feedback island detection method, no complicated algorithm is involved due to the fact that the virtual inductance is added into the feedback process only, so that construction can be realized favorably.
Description
Technical field
The invention belongs to the electricity generation system technical field, relate to a kind of distributed grid-connected system, relate in particular to a kind of positive feedback island detection method based on virtual inductor.
Background technology
At present, the most electric load in the whole world is provided by big electrical network.But Along with people's requires increasingly highly to the quality of power supply and power supply reliability, and large-scale power grid also shows out its fragile one side gradually especially.Large area blackout several times took place in the world wide especially in the last few years in succession, and its defective fully comes out.
(1) in the interconnected pattern of large scale electric network, the disturbance of breaking down and produced in its any point will have an immense impact on to whole electrical network, even can cause the collapse of whole electrical network, causes catastrophic effect.
(2) because big electrical network inertia is very big, can not follows the tracks of electric load flexibly and change.
(3) can not carry out desirable power supply for remote districts.For example: certain areas are far away from electric system, and are and sparsely populated, but it is bigger to build the distribution system investment, and cost is very high.Perhaps some regional natural conditions are abominable, at all can't the construction of line.
On the other hand, along with the exhaustion of primary energy, the deterioration of environment, People more and more is paid close attention to the protection of ecologic environment and the development of renewable new forms of energy.Like this, impelled the distributed power generation technology to become new research focus.
But distributed generating electricity by way of merging two or more grid systems when satisfying people's need for electricity also brought many potential safety hazards and accident to electrical network, and be wherein also particularly outstanding by the caused safety problem of isolated island.So-called island effect just is meant when electrical network for a certain reason during interruption of power supply the still peripherad electric of grid-connected photovoltaic system, thereby the isolated island (see figure 1) of the uncontrollable self-energizing of formation-individual Utilities Electric Co..Like this, isolated island is in case after forming, will cause significant damage to power equipment and personnel, so will avoid the generation of island effect.Linked groups stipulates that grid-connected system must possess the island detection ability both at home and abroad.Therefore, become the indispensable key link of distributed grid-connected system.
At present, basic island detection method has two big types: active island detection and passive island detection.Passive island detection method mainly is to locate to such an extent that the variation of voltage, frequency and phase place is judged and had or not isolated island to produce through observing point of common coupling (PCC).But this method has significant limitation, and promptly this method can only detect when the output power of distributed power source and island load demand differ greatly, PCC point place voltage.Frequency and phase change.When if the output power of distributed power source and island load demand are more or less the same, to detect with this method, blind area (NDZ) will appear detecting.The active detecting rule is through in the control signal of inverter, adding very little voltage, electric current or phase perturbation signal; When being incorporated into the power networks; Because receiving big electrical network clamps down on, the disturbing signal effect is very little: and after isolated island took place, the effect that disturbing signal produced will be clearly; Have or not isolated island to take place through detecting the system responses that PCC is ordered, judging then.Because initiatively method of perturbation has been broken the equilibrium relation between distributed generation system output and the load, it is very little to detect the blind area, thereby has remedied the deficiency of passive detection method.Thereby the active detecting method has obtained widespread use in the distributed power generation grid-connected system.The active detecting method mainly contains three types: magnitude shift method, frequency deviation method and phase shift method.Commonly used has: Sandia variation method (SVS), active shift frequency method (AFD) and slip frequency drift method (SMS).Sandia variation method (SVS) is exactly that PCC point voltage amplitude is introduced positive feedback; When isolated island takes place; Utilize the drastic change of PCC point voltage small variation causing combining inverter output current; From and cause the PCC point voltage to change, circulation is so always gone down and is exceeded the detection threshold value until the PCC point voltage, isolated island is detected.But this complex algorithm is not easy to Project Realization.Initiatively shift frequency method (AFD) and Sandia frequency deviation method (SFS) all are through the angular frequency that changes the inverter output current PCC point voltage frequency to be produced disturbance; To remain on power frequency stable for voltage when being incorporated into the power networks; And the PCC point voltage is changed by the influence of inverter output current frequency during islet operation; When exceeding threshold, then think to have produced isolated island.But initiatively the shortcoming of frequency displacement method is obvious: when the phase differential that causes when active shift frequency (AFD) equates when the angle of impedance of load is near power frequency or power frequency just, isolated island can not be detected.And, under the situation of many DG, must make the frequency shift (FS) direction of inverter consistent, otherwise can influence each other, cause detecting failure.And slip frequency method (SMS) also need ceaselessly be revised the phase place of inverter output current, and is therefore bigger to the influence of the quality of power supply.
Summary of the invention
The objective of the invention is to overcome the shortcoming of above-mentioned prior art; Provide a kind of positive feedback island detection algorithm based on virtual inductor guaranteeing when isolated island takes place, the detecting isolated island phenomenon effectively and quickly, and can effectively avoid because the detection blind area that the inverter output power is caused when taking place to mate with bearing power.
The objective of the invention is to solve through following technical scheme:
This positive feedback island detection method based on virtual inductor; Utilize relational expression
to enlarge the effect that error signal produces; And the output current of combining inverter is carried out disturbance with the form of positive feedback, to reach the purpose of island detection; The i representative is to the current perturbation signal of output current in the formula, and u represents error voltage signal, and L is an inductance value, and t is the time.
Further, above method following steps:
1) extracts load side voltage through the voltage subtraction device, be designated as U, extract the load side electric current, be designated as I through the current draw device;
2) U is the BPF. of power frequency through centre frequency, obtains voltage signal U
*, with the voltage signal U that obtains
*Voltage signal U process subtracter with extracting obtains error voltage signal, i.e. harmonic signal U
eLet error voltage signal U
eThrough integrator, obtain current perturbation signal I
e
3) will pass through multiplier through voltage signal and the amplitude A that obtains behind the BPF., obtain the current signal I identical with the line voltage amplitude
*Then with I
*With current perturbation signal I
eThrough totalizer, obtain combining inverter output current reference signal I
Ref
4) with inverter output current I that extracts and reference current signal I
RefThrough subtracter, produce current controling signal I
cWith I
cImprove the stability of system through matrix current adjustment circuit, at last through PWM generator, and then control combining inverter output current.
Further, above-mentioned steps 3) in, said amplitude A is determined by load impedance value; Obtain the current signal I identical with the line voltage amplitude
*Be through voltage signal U
*Obtain, then, by formula
Can know,
So A gets
| Z| is impedance.
The present invention has following beneficial effect:
(1) the positive feedback island detection method that the present invention is based on virtual inductor forms virtual inductor directly at positive feedback link adding integrator, makes PCC place voltage no matter from which kind of its load form, can both make variation rapidly, has reduced the detection blind area greatly.
(2) the present invention has just added virtual inductor at the feedback element place, does not relate to very complicated algorithm, so, be beneficial to Project Realization.
Description of drawings
Back distributed power generation power supply state figure takes place for isolated island in Fig. 1;
Fig. 2 is virtual inductor island detection control block diagram of the present invention;
The variation of front and back PCC place's electric voltage frequency and amplitude takes place in Fig. 3 for virtual inductor island detection method resistive load isolated island of the present invention;
The variation of front and back PCC place's electric voltage frequency and amplitude takes place in Fig. 4 for virtual inductor island detection method inductive load isolated island of the present invention;
The variation of front and back PCC place's electric voltage frequency and amplitude takes place in Fig. 5 for virtual inductor island detection method capacitive load isolated island of the present invention.
Embodiment
The positive feedback island detection side that the present invention is based on virtual inductor utilizes relational expression
to enlarge the effect that error signal produces; And the output current of combining inverter is carried out disturbance with the form of positive feedback; To reach the purpose of island detection, the i representative is to the current perturbation signal of output current in the formula; U represents error voltage signal.
Below in conjunction with accompanying drawing the present invention is done and to describe in further detail:
The inventive method mainly is to carry out disturbance through frequency and amplitude to the combining inverter output current, makes isolated island generation back PCC place's electric voltage frequency and amplitude send out variation and takes place until definite isolated island.
Concrete control flow is shown in accompanying drawing 2.
(1) extracts load side (being the PCC place) voltage through the voltage subtraction device, be designated as U, extract load side (being the PCC place) electric current, be designated as I through the current draw device.
(2) U is the BPF. of power frequency through centre frequency, obtains voltage signal U
*, with the voltage signal U that obtains
*Voltage signal U process subtracter with extracting obtains error voltage signal, i.e. harmonic signal U
eLet error voltage signal U
eThrough integrator, obtain current perturbation signal I
e
(3) will be through the voltage signal U that obtains behind the BPF.
*Pass through multiplier with amplitude A, obtain the current signal I identical with the line voltage amplitude
*Then with I
*With I
eThrough totalizer, obtain combining inverter output current reference signal I
RefSaid amplitude A is determined by load impedance value; Obtain the current signal I identical with the line voltage amplitude
*Be through voltage signal U
*Obtain, then, by formula
Can know,
So A gets
| Z| is impedance.
(4) will extract inverter output current I and reference current signal I
RefThrough subtracter, produce current controling signal I
cWith I
cImprove the stability of system through matrix current adjustment circuit, at last through PWM generator, and then control combining inverter output current.
Above selection of parameter scope is following:
Relate to following parameter in the virtual inductor island detection method: BPF. centre frequency f
0, amplitude A, quality factor q
f
The specific requirement of selection of parameter scope is following on the common engineering:
f
0Generally get local power-frequency voltage frequency, domestic is 50Hz.
A is generally determined by the load impedance value and the magnitude of voltage that is incorporated into the power networks jointly.
Be quality factor, generally satisfy Q
f≤2.5.
Through Matlab software island detection method of the present invention is carried out simulating, verifying below.Concrete simulation parameter is following: the grid-connected inverting system output rating is 7.5kW; The line voltage effective value is 220V; Mains frequency f
Grid=BPF. centre frequency f
0=50Hz.
Embodiment 1
For parallelly connected RLC load, if its resonance frequency equals the line voltage frequency, be resistive load, R=3 Ω is then arranged, L=4mH, C=2535.6 μ F, the switch that is incorporated into the power networks broke off in the time of 0.2 second.At this moment, the variation of virtual inductor island detection method PCC place's voltage and frequency before and after isolated island takes place is shown in accompanying drawing 3.
Embodiment 2
If it is inductive load, i.e. f that parallelly connected RLC loads on line voltage frequency place
0>f
Grid, the parameter of choosing load is: R=3 Ω, and L=4mH, C=2000 μ F, the switch that is incorporated into the power networks broke off in the time of 0.2 second.At this moment, the variation of virtual inductor island detection method PCC place's voltage and frequency before and after isolated island takes place is shown in accompanying drawing 4.
Embodiment 3
If it is capacitive load, i.e. f that parallelly connected RLC loads on line voltage frequency place
0<f
Grid, the parameter of choosing load is: R=3 Ω, and L=4mH, C=3000 μ F, the switch that is incorporated into the power networks broke off in the time of 0.2 second.The variation of virtual inductor island detection method this moment PCC place electric voltage frequency before and after isolated island takes place is shown in accompanying drawing 5.
Can know by above analysis of simulation result,, and can detect the isolated island generation in the detection method proposed by the invention next cycle after isolated island takes place in case after isolated island took place, PCC place voltage magnitude and frequency will great changes will take place.When even load characteristic changes in addition, also can the accurate detection isolated island.Therefore, compared with prior art, the detection method that this paper proposed has not only reduced the detection blind area greatly, and it when guaranteeing under most severe condition that isolated island takes place accurate detection go out isolated island, guarantee system's security of operation.
Claims (3)
1. positive feedback island detection method based on virtual inductor; It is characterized in that; Utilize relational expression
to enlarge the effect that error signal produces; And the output current of combining inverter is carried out disturbance with the form of positive feedback, to reach the purpose of island detection; The i representative is to the current perturbation signal of output current in the formula, and u represents error voltage signal, and L is an inductance value, and t is the time.
2. the positive feedback island detection method based on virtual inductor according to claim 1 is characterized in that, may further comprise the steps:
1) extracts load side voltage through the voltage subtraction device, be designated as U, extract the load side electric current, be designated as I through the current draw device;
2) U is the BPF. of power frequency through centre frequency, obtains voltage signal U
*, with the voltage signal U that obtains
*Voltage signal U process subtracter with extracting obtains error voltage signal, i.e. harmonic signal U
eLet error voltage signal U
eThrough integrator, obtain current perturbation signal I
e
3) will pass through multiplier through voltage signal and the amplitude A that obtains behind the BPF., obtain the current signal I identical with the line voltage amplitude
*Then with I
*With current perturbation signal I
eThrough totalizer, obtain combining inverter output current reference signal I
Ref
4) with inverter output current I that extracts and reference current signal I
RefThrough subtracter, produce current controling signal I
cWith I
cImprove the stability of system through matrix current adjustment circuit, at last through PWM generator, and then control combining inverter output current.
3. the positive feedback island detection method based on virtual inductor according to claim 2, in step 3), said amplitude A is determined by load impedance value; Obtain the current signal I identical with the line voltage amplitude
*Be through voltage signal U
*Obtain, then, by formula
Can know,
So A gets
| Z| is impedance.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103308806A (en) * | 2013-06-18 | 2013-09-18 | 江苏大学 | Islanding detection method based on fundamental frequency and switching-frequency sub-impedance |
| CN105182189A (en) * | 2015-10-29 | 2015-12-23 | 国家电网公司 | Inverter disturbance type island detection method based on combination of voltage frequency and measured impedance |
| CN106771860A (en) * | 2016-12-07 | 2017-05-31 | 中国人民解放军后勤工程学院 | A kind of current feed-forward disturbance island detection method |
Citations (4)
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| US20030098671A1 (en) * | 2001-11-26 | 2003-05-29 | Visteon Global Technologies, Inc. | Anti-islanding detection scheme for distributed power generation |
| CN101059555A (en) * | 2006-04-17 | 2007-10-24 | 盈正豫顺电子股份有限公司 | Distribution type electric power system island movement detection device and its method |
| TW200931751A (en) * | 2008-01-08 | 2009-07-16 | Wen-Yu Zhang | Island protective relaying system of grid-connected induction generators and detection method for island effect thereof |
| CN101976851A (en) * | 2010-10-27 | 2011-02-16 | 西安交通大学 | Method for improving wireless internet stability of multiple inverters in microgrid by utilizing virtual impedance |
-
2012
- 2012-08-17 CN CN2012102944757A patent/CN102830307A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20030098671A1 (en) * | 2001-11-26 | 2003-05-29 | Visteon Global Technologies, Inc. | Anti-islanding detection scheme for distributed power generation |
| CN101059555A (en) * | 2006-04-17 | 2007-10-24 | 盈正豫顺电子股份有限公司 | Distribution type electric power system island movement detection device and its method |
| TW200931751A (en) * | 2008-01-08 | 2009-07-16 | Wen-Yu Zhang | Island protective relaying system of grid-connected induction generators and detection method for island effect thereof |
| CN101976851A (en) * | 2010-10-27 | 2011-02-16 | 西安交通大学 | Method for improving wireless internet stability of multiple inverters in microgrid by utilizing virtual impedance |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103308806A (en) * | 2013-06-18 | 2013-09-18 | 江苏大学 | Islanding detection method based on fundamental frequency and switching-frequency sub-impedance |
| CN105182189A (en) * | 2015-10-29 | 2015-12-23 | 国家电网公司 | Inverter disturbance type island detection method based on combination of voltage frequency and measured impedance |
| CN105182189B (en) * | 2015-10-29 | 2017-12-12 | 国家电网公司 | The inverter combined based on electric voltage frequency and measurement impedance disturbs formula isolated island detection method |
| CN106771860A (en) * | 2016-12-07 | 2017-05-31 | 中国人民解放军后勤工程学院 | A kind of current feed-forward disturbance island detection method |
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Application publication date: 20121219 |