CN107508322B - A kind of short-circuit fault of power system computational methods for considering photovoltaic electric station grid connection - Google Patents
A kind of short-circuit fault of power system computational methods for considering photovoltaic electric station grid connection Download PDFInfo
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- CN107508322B CN107508322B CN201710866407.6A CN201710866407A CN107508322B CN 107508322 B CN107508322 B CN 107508322B CN 201710866407 A CN201710866407 A CN 201710866407A CN 107508322 B CN107508322 B CN 107508322B
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- H02J3/383—
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The present invention relates to a kind of short-circuit fault of power system computational methods for considering photovoltaic electric station grid connection, for the electric system of access photovoltaic plant, when carrying out analysis of Short Circuit Fault, photovoltaic plant is equivalent to current source, according to measured test data, functional relation of the photovoltaic plant between the short circuit current and grid entry point Voltage Drop size that electric system injects when obtaining short trouble by Mathematical Fitting, in actual short calculation of fault, situation is fallen according to the virtual voltage of photovoltaic electric station grid connection point, the short circuit current of photovoltaic plant output is quickly obtained by look-up table, and then calculate the distribution of the whole network short circuit current and voltage, suitable for the Practical Calculation Analysis field of short-circuit fault of power system.
Description
Technical Field
The invention relates to the field of short circuit calculation and analysis of power systems, in particular to a power system short circuit fault calculation method considering grid connection of photovoltaic power stations.
Background
According to the existing grid-connected power generation rule of the photovoltaic power station, a large-scale grid-connected power generation system of the photovoltaic power station needs to have certain low-voltage ride through capability, namely, the grid-connected power generation system still runs for a period of time when the power grid fails, and certain dynamic reactive current is output to the power grid. With the continuous expansion of the scale of the photovoltaic power station, when the short circuit fault occurs to the power grid, the influence of the photovoltaic power station on the power grid is not negligible. Therefore, when the short-circuit fault analysis and calculation of the power system are carried out, the influence of the photovoltaic power station on the power system is considered, and the method has very important significance for the work of power grid fault calculation and the like of new energy power generation access.
However, in the conventional power system relay protection fault calculation and setting calculation method, a corresponding graph library and mathematical model of the photovoltaic power station are not available, and the short-circuit current injected after the photovoltaic power station is connected to the grid cannot be calculated and considered, so that the short-circuit calculation requirement and the relay protection setting requirement after more and more photovoltaic power stations are connected to the power system are difficult to meet.
Disclosure of Invention
The invention overcomes the technical defect of short circuit calculation analysis when the existing photovoltaic power station is connected into a power grid, provides the power system short circuit fault calculation method considering photovoltaic power station grid connection, and fills the blank that the existing relay protection fault calculation lacks a photovoltaic power station short circuit fault calculation model and a short circuit calculation method.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a method for calculating short-circuit faults of an electric power system considering grid connection of photovoltaic power stations comprises the following implementation steps:
s1, establishing a short-circuit fault analysis calculation model of a power system;
s2, through the experimental results of short-circuit current and voltage drop of the photovoltaic power station under various alternating current faults, the short-circuit current of the photovoltaic power station under the short-circuit fault is approximately obtained by adopting a mathematical fitting methodi sc And grid point voltage drop valueu drop The functional relationship of (a);
s3, performing fault calculation on the power system without considering the photovoltaic power station to obtain the voltage of the grid-connected pointu i ；
S4, passing through the voltage of the grid connection pointu i Calculating voltage drop value of grid-connected pointu drop Voltage drop value of grid-connected pointu drop The following formula is used to solve:
u
drop
=U
n
-u
i
wherein,U n the rated voltage of a grid-connected point of the photovoltaic power station;
s5, calculating the short-circuit current output by the photovoltaic power station under the short-circuit fault according to the table corresponding to the functional relation obtained in the step S2 and the voltage drop value of the grid-connected pointi sc ；
S6, passing short-circuit currenti sc Calculating the voltage correction quantity delta of the grid-connected point after the action of the output short-circuit current of the superimposed photovoltaic power stationu；
S7, correcting quantity delta is passeduComparing with a predetermined threshold value epsilon, if deltauIf < ε, then S8 is executed; if ΔuEqual to epsilon, then executeu i =u i +ΔuAnd will be updatedu i Substituting and returning to S4 for iterative calculation;
and S8, calculating the short-circuit current and voltage distribution of the whole network by using a node voltage method and a node impedance matrix according to the short-circuit current output by the photovoltaic power station under the short-circuit fault.
In a preferred embodiment, the specific process of S1 is as follows:
the method comprises the steps that a short-circuit fault model is established for an electric power system except a photovoltaic power station by a short-circuit current calculation method based on a symmetric component method, the photovoltaic power station is approximately equivalent to a current source, and the current source injects short-circuit current into the electric power system from a grid-connected point.
In a preferred embodiment, in S2, the photovoltaic power station injects the short-circuit current into the power system from the grid-connected point, and the functional relationship exists between the short-circuit current and the grid-connected point voltage drop value, and the functional relationship is approximately expressed as:
i sc =f(u drop )
in the formula,fthe functional relationship obtained for mathematical fitting may be calculated by a table look-up method.
In a preferred embodiment, the short-circuit current output by the photovoltaic power station under the short-circuit fault isi scThere is an upper limit due to the over-current capability of the photovoltaic inverter, i.e. the following mathematical relationship exists:
i sc≤I max
in the formula,I maxis the maximum output current of the photovoltaic inverter.
In a preferred embodiment, the specific process of S5 is as follows:
photovoltaic power station short-circuit current obtained through S2i sc And grid point voltage drop valueu drop And the photovoltaic power station short-circuit current corresponding to the current grid-connected point voltage drop value is obtained by adopting a table look-up method, and is used as the short-circuit current output to the power system by the photovoltaic power station in the short-circuit fault.
In a preferred embodiment, the grid-connected point voltage correction amount Δ in S6 isuThe following formula is used to solve:
Δu=g(i sc )
in the formula,gcorrection quantity delta for voltage of grid connection pointuAnd short-circuit currenti sc The functional relationship can be obtained according to the topological structure and the superposition principle of the power system.
The influence of the photovoltaic power station on the power system is approximately equal to that of the photovoltaic power station which is equivalent to a current source, and short-circuit current is injected into the power system from a grid-connected point. And the short-circuit current injected into the power system by the photovoltaic power station under the short-circuit fault has a functional relation with the grid-connected point voltage drop value, so that the output short-circuit current is calculated, and the current and voltage distribution under the whole network short-circuit fault is obtained.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
the method fills the blank that a photovoltaic power station short-circuit fault calculation model and a short-circuit calculation method are lacked in the conventional relay protection fault calculation, and further improves the relay protection setting calculation precision.
Drawings
FIG. 1 is a flow chart of an embodiment of a method.
FIG. 2 is a schematic diagram of the method of the present invention.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
The embodiment is the application of the invention in the short-circuit fault of an alternating current system.
As shown in fig. 1, a method for calculating a short-circuit fault of a power system considering photovoltaic power station grid connection includes the following steps:
the method comprises the following steps: establishing a short-circuit fault analysis calculation model of the power system: the electric power system except the photovoltaic power station adopts a short-circuit current calculation method based on a symmetric component method to establish a short-circuit fault model, the photovoltaic power station is approximately equivalent to a current source, and the current source injects short-circuit current into the electric power system from a grid-connected point, as shown in figure 2.
In the context of figure 2, it is shown,i sc is the short-circuit current of the photovoltaic power station under the short-circuit fault,u i is the voltage value of the grid-connected point, F is the fault point, IFIs the fault point current, VFIs the fault point voltage, ZFIs the point of failure resistance.
Step two: the short-circuit current of the photovoltaic power station under the short-circuit fault is approximately obtained by adopting a mathematical fitting method through the experimental results of the short-circuit current and the voltage drop of the photovoltaic power station under various alternating-current faultsi sc And grid point voltage drop valueu drop The functional relationship of (a); and the short-circuit current has an upper limit due to the limitation of the photovoltaic inverter, and the functional relation is approximately expressed as:
i sc =f(u drop ) (i sc≤I max)
in the formula,i scfor short-circuit current output by the photovoltaic power station under the condition of alternating-current short-circuit fault,u drop is the voltage drop value of the grid-connected point,fthe functional relationship obtained for fitting may be calculated by a table lookup.I maxIs the maximum output current of the photovoltaic inverter.
Step three: the fault calculation is carried out on the power system under the condition that the photovoltaic power station is not considered (namely the photovoltaic power station is opened), and the voltage of the grid-connected point is obtainedu i ；
Step four: by grid point voltageu i Calculating voltage drop value of grid-connected pointu drop Voltage drop value of grid-connected pointu drop The following formula is used to solve:
u
drop
=U
n
-u
i
wherein,U n the rated voltage of the grid-connected point of the photovoltaic power station.
Step five: obtaining the short-circuit current output by the photovoltaic power station according to the relation between the short-circuit current of the photovoltaic power station and the voltage drop value of the grid-connected pointi sc 。
Step six: calculating the voltage correction of the grid-connected point of the photovoltaic power station after the action of the short-circuit current output by the superimposed photovoltaic power station: photovoltaic power station grid-connected point voltage correction quantity deltauThe following formula is used to solve:
Δu=g(i sc )
in the formula,gcorrection quantity delta for voltage of grid connection pointuAnd short-circuit currenti sc The functional relationship can be obtained according to the topological structure and the superposition principle of the power system.
Step seven: comparing the voltage correction quantity of the photovoltaic power station grid-connected point obtained by calculation with a threshold value: if the voltage correction quantity delta of the grid-connected point of the photovoltaic power stationuIf the value is less than the threshold value, executing the step nine, otherwise executing the step eight.
Step eight: correcting the voltage of the grid connection point: grid point voltageu i The correction is made by the following formula:
u i =u i +Δu
the corrected grid-connected point voltageu i And substituting into the step four and continuing the calculation.
Step nine: and (3) calculating the distribution of the current and voltage of the whole network short-circuit fault: and calculating the short-circuit current and voltage distribution of the whole network by using a node voltage method and a node impedance matrix according to the short-circuit current output by the photovoltaic power station under the short-circuit fault.
The same or similar reference numerals correspond to the same or similar parts;
the terms describing positional relationships in the drawings are for illustrative purposes only and are not to be construed as limiting the patent;
it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (6)
1. A method for calculating short-circuit faults of an electric power system considering grid connection of photovoltaic power stations is characterized by comprising the following implementation steps:
s1, establishing a short-circuit fault analysis calculation model of a power system;
s2, through the experimental results of short-circuit current and voltage drop of the photovoltaic power station under various alternating current faults, the short-circuit current i of the photovoltaic power station under the short-circuit fault is approximately obtained by adopting a mathematical fitting methodscAnd grid point voltage dip udropThe functional relationship of (a);
s3, carrying out non-examination on the electric power systemCalculating the faults of the photovoltaic power station to obtain the voltage u of the grid-connected pointi；
S4, passing through the voltage u of the grid-connected pointiCalculating voltage drop value u of grid-connected pointdropVoltage dip u of grid-connected pointdropThe following formula is used to solve:
udrop＝Un-ui
wherein, UnThe rated voltage of a grid-connected point of the photovoltaic power station;
s5, calculating the short-circuit current i output by the photovoltaic power station under the short-circuit fault according to the table corresponding to the functional relation obtained in the step S2 and the voltage drop value of the grid-connected pointsc；
S6, passing a short-circuit current iscCalculating the voltage correction quantity delta u of the grid-connected point after the action of the short-circuit current output by the superposed photovoltaic power station;
s7, comparing the correction quantity delta u with a preset threshold value epsilon, and if the delta u is less than the epsilon, executing S8; if Δ u ≧ ε, u is executedi＝ui+ Δ u, and updated uiSubstituting and returning to S4 for iterative calculation;
and S8, calculating the short-circuit current and voltage distribution of the whole network by using a node voltage method and a node impedance matrix according to the short-circuit current output by the photovoltaic power station under the short-circuit fault.
2. The method according to claim 1, wherein the specific process of S1 is as follows:
the method comprises the steps that a short-circuit fault model is established for an electric power system except a photovoltaic power station by a short-circuit current calculation method based on a symmetric component method, the photovoltaic power station is approximately equivalent to a current source, and the current source injects short-circuit current into the electric power system from a grid-connected point.
3. The method according to claim 2, wherein in S2, the short-circuit current injected from the grid-connected point to the power system by the photovoltaic power station has a functional relationship with the grid-connected point voltage sag value, and the functional relationship is approximately expressed as:
isc＝f(udrop)
in the formula, f is a function relation obtained by mathematical fitting and is calculated by a table look-up method.
4. The power system short-circuit fault calculation method according to claim 3, wherein the short-circuit current i output by the photovoltaic power station under the short-circuit fault isscThere is an upper limit due to the over-current capability of the photovoltaic inverter, i.e. the following mathematical relationship exists:
isc≤Imax
in the formula ImaxIs the maximum output current of the photovoltaic inverter.
5. The method for calculating the short-circuit fault of the power system according to any one of claims 1 to 4, wherein the specific process of S5 is as follows:
short-circuit current i of photovoltaic power station obtained through S2scAnd grid point voltage dip udropAnd the photovoltaic power station short-circuit current corresponding to the current grid-connected point voltage drop value is obtained by adopting a table look-up method, and is used as the short-circuit current output to the power system by the photovoltaic power station in the short-circuit fault.
6. The method according to claim 5, wherein the grid-connected point voltage correction Δ u in S6 is obtained by the following formula:
Δu＝g(isc)
wherein g is the correction amount of the grid-connected point voltage Δ u and the short-circuit current iscThe functional relation between the two is obtained according to the topological structure and the superposition principle of the power system.
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| CN109449982A (en) * | 2018-12-07 | 2019-03-08 | 国网山西省电力公司临汾供电公司 | The operation and maintenance method of power distribution network containing multiple photovoltaic micros |
| CN110378597B (en) * | 2019-07-19 | 2022-02-15 | 广东电网有限责任公司 | Photovoltaic power generation equipment fault current online calculation method and device |
| CN110336327B (en) * | 2019-07-29 | 2020-10-16 | 国网上海市电力公司 | Distribution network short-circuit current acquisition method considering distributed photovoltaic low-voltage ride through |
| CN113742907B (en) * | 2021-08-24 | 2023-09-15 | 国网河南省电力公司电力科学研究院 | Unified calculation method for short-circuit current of photovoltaic power station |
| CN114977305B (en) * | 2022-06-24 | 2024-07-23 | 广东电网有限责任公司电力调度控制中心 | Short-circuit current influence factor analysis method after photovoltaic access to power grid |
| CN115207920B (en) * | 2022-09-13 | 2023-03-14 | 国网江西省电力有限公司电力科学研究院 | Photovoltaic power supply-containing power distribution network short-circuit current calculation method and system based on factor table |
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