CN102565598A - Island detection method based on negative sequence voltage divider - Google Patents

Island detection method based on negative sequence voltage divider Download PDF

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CN102565598A
CN102565598A CN2012100325288A CN201210032528A CN102565598A CN 102565598 A CN102565598 A CN 102565598A CN 2012100325288 A CN2012100325288 A CN 2012100325288A CN 201210032528 A CN201210032528 A CN 201210032528A CN 102565598 A CN102565598 A CN 102565598A
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sequence voltage
common connection
negative sequence
points
island
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马静
米超
王彤
彭明法
王增平
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North China Electric Power University
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North China Electric Power University
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Abstract

The invention discloses an island detection method based on a negative sequence voltage divider in a distributed power generation system detection technology field. The method is characterized by: firstly extracting an effective value of the negative sequence voltage at a position of a micro-grid common connection point; then calculating a ratio of the effective value to the effective value of a negative sequence voltage source which is added on the common connection point; when the ratio is less than a set threshold, determining that the island is not generated; when the ratio is greater than or equal to the set threshold, determining that the island is generated. By using the method of the invention, under various kinds of fault conditions and other scurviness situations, the island can be effectively detected. The detection is only related to a network topology structure and a pseudo island can not influence the detection. An on-site application requirement can be satisfied and the method possesses actual engineering significance.

Description

Island detection method based on the negative phase-sequence voltage divider
Technical field
The invention belongs to distributed generation system detection technique field, relate in particular to a kind of island detection method based on the negative phase-sequence voltage divider.
Background technology
In recent years, along with the development of distributed power generation technology, (distributed generation DG) with the local microgrid system that loads and form, becomes the useful of big electrical network and replenishes by distributed power source.Microgrid can link to each other with big electrical network, to mains supply, again can islet operation, and independent of this locality load power supply.Because the control mode of microgrid when being incorporated into the power networks with islet operation be different, microgrid by and net state when transferring island state to, require inner DG can obtain signal quickly and accurately, realize the smooth switching of control model.Therefore, island detection has crucial meaning.
At present, island detection method is divided three classes: (1) on off state detection method, and this method need be by communication facilities, complex structure, cost is higher.(2) passive detection method, the generation of isolated island is judged in the voltage through detecting microgrid and the variation of frequency, this method has bigger blind area, and threshold value is difficult to confirm.(3) active detecting method, this method adds disturbing signal to system, amplifies some inner electric parameters of microgrid, thereby judges isolated island, and this method can cause certain influence to the quality of power supply.
Summary of the invention
To the existing island detection complex structure of mentioning in the above-mentioned background technology, the high deficiency of cost the present invention proposes a kind of island detection method based on the negative phase-sequence voltage divider.
Technical scheme of the present invention is based on the island detection method of negative phase-sequence voltage divider, to it is characterized in that this method may further comprise the steps:
Step 1: extract microgrid points of common connection place negative sequence voltage effective value, and calculate this value and the ratio that is attached to the effective value in negative sequence voltage source on the points of common connection;
Step 2:, then judge isolated island does not take place when said ratio during less than setting threshold; When said ratio during, then judge isolated island takes place more than or equal to setting threshold.
The negative sequence voltage effective value of said microgrid points of common connection with the computing formula that is attached to the ratio of the effective value in negative sequence voltage source on the points of common connection is:
K = U 2 ( 2 ) U G ( 2 ) = Z 2 ( 2 ) Z 1 ( 2 ) + Z 2 ( 2 )
Wherein:
K is the negative sequence voltage effective value of microgrid points of common connection and is attached to negative phase-sequence on the points of common connection
The ratio of the effective value of voltage source;
Figure BDA0000135578900000022
is the negative sequence voltage effective value of microgrid points of common connection;
is for being attached to the effective value in negative sequence voltage source on the points of common connection;
is the equivalent negative sequence impedance in points of common connection place;
Figure BDA0000135578900000025
is the negative phase-sequence value of negative sequence voltage source institute series impedance.
The computing formula of said
Figure BDA0000135578900000026
is:
Z 2 ( 2 ) = Z s ( 2 ) Z DG ( 2 ) Z s ( 2 ) + Z DG ( 2 )
Wherein:
Figure BDA0000135578900000028
is the equivalent negative sequence impedance of power distribution network;
Figure BDA0000135578900000031
is the equivalent negative sequence impedance of microgrid.
Said setting threshold is 0.2.
Beneficial effect of the present invention is that the method for utilizing negative phase-sequence power supply voltage divider to propose island detection has the following advantages:
(1) the present invention can correctly detect isolated island in 30 milliseconds under the most abominable situation of IEEE Std.1547 prescribed by standard;
When (2) island detection was successful, the quality of power supply was not damaged, and has the advantage of non-destructive and non-blind area;
(3) single-phase open circuit with situation that two open circuit mutually under still can correctly judge the generation of isolated island;
(4) when pseudo-isolated island takes place, it is disconnected erroneous judgement can not occur.
This method principle is simple, applied widely, under various fault conditions and other abominable situation, all can detect isolated island effectively, and is only relevant with network topology structure, and do not receive the influence of pseudo-isolated island, can satisfy on-the-spot application requirements, has practical meaning in engineering.
Description of drawings
Fig. 1 is for being applied to main circuit system synoptic diagram of the present invention and each preface net figure;
Fig. 1 a is the main circuit system synoptic diagram; Fig. 1 b is the whole network circuit; Fig. 1 c is the positive sequence network circuit;
Fig. 1 d is the negative sequence network circuit;
Each characteristic quantity oscillogram of island detection of isolated island takes place in Fig. 2 under the symmetric fault for three-phase opens circuit;
Fig. 2 a is the three-phase voltage curve map in negative sequence voltage source; Fig. 2 b is a points of common connection place ratio K oscillogram; Fig. 2 c is the microgrid voltage curve; Fig. 2 d is a microgrid frequency oscillogram;
The points of common connection place ratio K curve map of isolated island takes place down in Fig. 3 for asymmetric fault;
Fig. 3 a is a points of common connection place ratio K curve map under the single-phase open circuit conditions; Fig. 3 b is a points of common connection place ratio K curve map under the two phase open circuit conditions;
Fig. 4 is under the pseudo-isolated island situation, and the present invention detects each characteristic quantity oscillogram of isolated island;
Fig. 4 a is grid voltage waveform figure; Fig. 4 b is a points of common connection place ratio K curve map.
Embodiment
Below in conjunction with accompanying drawing, preferred embodiment is elaborated.Should be emphasized that following explanation only is exemplary, rather than in order to limit scope of the present invention and application thereof.
The objective of the invention is to overcome the deficiency that prior art exists, a kind of island detection method based on the negative phase-sequence voltage divider is provided.Isolated island be the microgrid system that is incorporated into the power networks under the situation that big electric network fault takes place, break off with big electrical network and continue situation to local electric, independent operating.
Microgrid inside can be reduced to DG and local model of loading, and microgrid links to each other with power distribution network through points of common connection.The capacity of power distribution network is bigger, and equivalent impedance is less, and the capacity of microgrid is less, equivalent impedance is bigger.When microgrid is incorporated into the power networks, link to each other with power distribution network, what the equivalent impedance of public junction was the microgrid impedance with the power distribution network impedance is parallelly connected, very little usually.And when piconet island moved, points of common connection place switch broke off, and equivalent impedance is the microgrid impedance, and numerical value is bigger.In order to reflect the Changing Pattern of isolated island this measurement impedance of front and back; Add the negative sequence voltage source at the points of common connection place; Negative sequence voltage effective value through the points of common connection place comes the reflected measurement impedance variation of (referring to negative sequence impedance here) with the variation of the ratio of the effective value in additional negative sequence voltage source, thereby judges the generation of isolated island.Concrete steps are following:
At first; Extract negative sequence voltage effective value
Figure BDA0000135578900000041
usefulness of points of common connection and the ratio K of the effective value
Figure BDA0000135578900000043
in the negative sequence voltage source that is added, as the decision content of island detection.The computing formula of K is:
K = U 2 ( 2 ) U G ( 2 ) = Z 2 ( 2 ) Z 1 ( 2 ) + Z 2 ( 2 ) - - - ( 1 )
Wherein;
is the negative phase-sequence value of negative sequence voltage source institute series impedance;
Figure BDA0000135578900000046
Be the equivalent negative sequence impedance in points of common connection place, Z 2 ( 2 ) = Z s ( 2 ) Z DG ( 2 ) Z s ( 2 ) + Z DG ( 2 ) ;
Figure BDA0000135578900000051
is the equivalent negative sequence impedance of power distribution network;
Figure BDA0000135578900000052
is the equivalent negative sequence impedance of microgrid.
Secondly, set the threshold epsilon of K 1
Then, judge whether to take place isolated island according to the size of K, criterion is following:
(1) surpasses pre-set threshold ε as K 1, judge that then isolated island does not take place microgrid;
(2) surpass or equal pre-set threshold ε as K 1, then judge microgrid generation isolated island.
The present invention selects for use the negative phase-sequence power supply as additional power source, with certain value impedance series connection at the points of common connection place.Additional power source and microgrid, power distribution network are formed the island detection circuit.Microgrid inside can be reduced to DG and local model of loading, and microgrid links to each other with power distribution network through points of common connection, and microgrid and power distribution network can be regarded the branch of parallel circuit as.
In the positive sequence network of testing circuit, add the negative sequence voltage source and be output as zero, can not exert an influence to positive sequence network.In the negative sequence network of testing circuit, microgrid equivalent source and power distribution network equivalent source are output as zero, form only to contain the single simple network that adds the negative sequence voltage source.In this network, the equivalent negative sequence impedance in points of common connection place
Figure BDA0000135578900000053
forms the bleeder circuit of connecting with the negative phase-sequence value
Figure BDA0000135578900000054
of negative sequence voltage source institute series impedance.When microgrid is incorporated into the power networks; Link to each other with power distribution network; What the equivalent impedance at points of common connection place was the microgrid impedance with the power distribution network impedance is parallelly connected;
Figure BDA0000135578900000055
is less; Consider
Figure BDA0000135578900000056
simultaneously and be constant negative sequence impedance; Therefore, the K value that is calculated by formula (1) is less.When piconet island moves; Points of common connection breaks off; Equivalent impedance is the microgrid impedance;
Figure BDA0000135578900000057
is bigger, can know that by formula (1) the K value is also bigger.Judge the generation of isolated island through the K value.
The operating process that the present invention is concrete: on an inverter that adopts the TI DSPTMS320F240 of company to do the master control chip, experimentize.Like Fig. 1 (wherein, P L+ jQ LApplied power for local load in the microgrid; P+jQ is the output applied power of DG in the microgrid; Δ P+j Δ Q is the applied power that microgrid flows to power distribution network) shown in, and add the negative sequence voltage source, simulating, verifying under the most abominable defined situation in IEEE Std.1547 standard at the points of common connection place.Each component parameters is as follows: grid line voltage is 380V, frequency 50Hz (containing the very little higher hamonic wave of amplitude), and inverter nominal reference power is 50kW, DC bus-bar voltage is 800V, LC wave filter (L f=0.6mH, C f=1500 μ F, equivalent resistance R=0.01 Ω), load rating power is 50kW (R=2.904 Ω, L=3.698mH, C=2740.2 μ F, Q f=2.5).The line voltage effective value in negative sequence voltage source is 3.8V, series impedance Z 1=50 Ω.System inserts the utility grid of 220V through transformer.
The threshold epsilon of points of common connection place ratio K value 1Be taken as 0.2, China's standard GB/T 15543-1995 regulation, the points of common connection normal working voltage degree of unbalancedness permissible value of electric system is 2%, is no more than 4% in short-term.
When emulation began, microgrid was in the state of being incorporated into the power networks; In 0.5s points of common connection place switch disconnection constantly, microgrid gets into the islet operation state.In order to prevent that the excessive negative phase-sequence power supply that adds from damaging the microgrid quality of voltage, additional power source phase voltage effective value is merely 1% of microgrid phase voltage effective value, shown in Fig. 2 a.Fig. 2 b has provided K value change curve; Can find out; When microgrid is incorporated into the power networks; Because the equivalent negative sequence impedance at points of common connection place is minimum; Therefore to account for the proportion that adds negative phase-sequence power supply
Figure BDA0000135578900000063
also minimum for the negative phase-sequence measuring voltage
Figure BDA0000135578900000062
at this place, and the K value approaches 0; At 0.5s constantly; Microgrid gets into the islet operation state; The equivalent negative sequence impedance at points of common connection place increases; The proportion that
Figure BDA0000135578900000065
at this place accounts for
Figure BDA0000135578900000066
also increases; Cause the K value trend that rises to occur; And still very obvious behind a cycle, can judge the generation of isolated island thus.In the island detection process; Microgrid voltage magnitude and frequency shown in Fig. 2 c and Fig. 2 d, can be known by figure that respectively both all are in the normal range of operation of standard GB/T 14549-93 regulation; The quality of power supply is destroyed, and has realized that non-destructive and non-blind area detect.
Moreover the situation that a phase or two is broken off mutually possibly appear in points of common connection place isolating switch, under the both of these case; Shown in Fig. 3 a and Fig. 3 b, similar with the three-phase breaker disconnection, a phase or two phase isolating switchs are after 0.5s breaks off the change curve of K value respectively; The K value also demonstrates the trend of rising; And still very obvious behind a cycle, therefore, utilize this method still can realize island detection under the open-phase operation situation.
For wind generator system; Break down at electrical network and to cause under the situation that voltage reduces suddenly; Require the wind-powered electricity generation unit to continue to keep being connected with electrical network, have only when fault is serious, just to allow off-grid, this just requires wind power generating set to have stronger low voltage ride-through capability.Especially, when wind-powered electricity generation unit set end voltage drop to rated voltage 15% the time, require the wind-powered electricity generation unit to continue operation 0.625s.This has proposed new challenge just for the island detection technology, and traditional passive detection method passes through in low-voltage erroneous judgement possibly occur when phenomenon takes place, but the present invention can address this problem effectively.Fig. 4 has provided 0.5s constantly, and microgrid voltage is reduced to suddenly under 15% the situation of ratings, the change curve of K value.
After low-voltage is passed through the phenomenon generation; Because microgrid still links to each other with electrical network; The equivalent negative sequence impedance at points of common connection place does not change; Drop to after the fluctuation of K value through a cycle and approach a minimal value of zero; Less than threshold value, therefore, low-voltage is passed through phenomenon can not cause this method erroneous judgement.
Fig. 2～Fig. 4 shows that the island detection method based on the negative phase-sequence voltage divider provided by the present invention is in the IEEEStd.1547 standard under the most abominable defined situation; Can fast and effeciently detect the generation of isolated island; Still effective under the single-phase and two phase open circuit conditions at electrical network, and do not receive the influence of pseudo-isolated island problem.Can realize non-destructive non-blind area island detection, principle is simple, has good engineering practicability.
The above; Be merely the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, any technician who is familiar with the present technique field is in the technical scope that the present invention discloses; The variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claim.

Claims (4)

1. based on the island detection method of negative phase-sequence voltage divider, it is characterized in that this method may further comprise the steps:
Step 1: extract microgrid points of common connection place negative sequence voltage effective value, and calculate this value and the ratio that is attached to the effective value in negative sequence voltage source on the points of common connection;
Step 2:, then judge isolated island does not take place when said ratio during less than setting threshold; When said ratio during, then judge isolated island takes place more than or equal to setting threshold.
2. the island detection method based on the negative phase-sequence voltage divider according to claim 1 is characterized in that the negative sequence voltage effective value of said microgrid points of common connection and the computing formula that is attached to the ratio of the effective value in negative sequence voltage source on the points of common connection are:
K = U 2 ( 2 ) U G ( 2 ) = Z 2 ( 2 ) Z 1 ( 2 ) + Z 2 ( 2 )
Wherein:
K is the negative sequence voltage effective value of microgrid points of common connection and is attached to negative phase-sequence on the points of common connection
The ratio of the effective value of voltage source;
Figure FDA0000135578890000012
is the negative sequence voltage effective value of microgrid points of common connection;
Figure FDA0000135578890000013
is for being attached to the effective value in negative sequence voltage source on the points of common connection;
Figure FDA0000135578890000014
is the equivalent negative sequence impedance in points of common connection place;
Figure FDA0000135578890000015
is the negative phase-sequence value of negative sequence voltage source institute series impedance.
3. the island detection method based on the negative phase-sequence voltage divider according to claim 2 is characterized in that the computing formula of said
Figure FDA0000135578890000016
is:
Z 2 ( 2 ) = Z s ( 2 ) Z DG ( 2 ) Z s ( 2 ) + Z DG ( 2 )
Wherein:
Figure FDA0000135578890000021
is the equivalent negative sequence impedance of power distribution network;
Figure FDA0000135578890000022
is the equivalent negative sequence impedance of microgrid.
4. the island detection method based on the negative phase-sequence voltage divider according to claim 1 is characterized in that said setting threshold is 0.2.
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Cited By (11)

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CN104218602A (en) * 2013-05-31 2014-12-17 阳光电源股份有限公司 Distributed power generation system and island detection device thereof, current converter thereof
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CN103869200A (en) * 2014-04-08 2014-06-18 国家电网公司 Method for power distribution network island detection based on wide-area information
CN104155576A (en) * 2014-08-04 2014-11-19 华北电力大学 Island detection method based on shunt principle
CN104155576B (en) * 2014-08-04 2017-01-18 华北电力大学 Island detection method based on shunt principle
CN106199228A (en) * 2015-04-29 2016-12-07 清华大学 For the determination methods of distributed generator islanding of network system with judge system
CN111463771A (en) * 2019-12-12 2020-07-28 华北电力大学 Multi-direct-current emergency modulation coordination strategy for improving transient stability of alternating current-direct current hybrid system
CN111463771B (en) * 2019-12-12 2023-10-27 华北电力大学 Multi-DC emergency modulation coordination method and system for improving transient stability of AC/DC series-parallel system

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Application publication date: 20120711