CN114498760A - Island detection method and device and electronic equipment thereof - Google Patents
Island detection method and device and electronic equipment thereof Download PDFInfo
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- CN114498760A CN114498760A CN202210238979.0A CN202210238979A CN114498760A CN 114498760 A CN114498760 A CN 114498760A CN 202210238979 A CN202210238979 A CN 202210238979A CN 114498760 A CN114498760 A CN 114498760A
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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
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
Abstract
The embodiment of the invention discloses an island detection method, an island detection device and electronic equipment thereof. The island detection method comprises the following steps: injecting disturbance into the power grid in sequence by each of the plurality of inverters according to the disturbance sequence until N disturbances are injected, and repeatedly injecting each inverter according to a fixed period; after each inverter injects disturbance to the power grid once, detecting the change of the frequency or the phase of the power grid in the disturbance stage compared with the frequency or the phase of the power grid in the previous disturbance stage; and if the change of the frequency or the phase exceeds a first preset threshold value, resetting the disturbance sequence, and if the change of the frequency or the phase exceeds a second preset threshold value, judging that the power grid has an island. Through the mode, the single machine disturbance in the inverter parallel system can be synchronized, the mutual interference of disturbance quantities of different machines when multiple machines are connected in parallel is effectively avoided, and the reliability of island protection is improved.
Description
Technical Field
The embodiment of the invention relates to a distributed power system, in particular to an island detection method, an island detection device and electronic equipment thereof.
Background
Distributed power generation has been increasingly widely used in the domestic power generation market at present. The photovoltaic grid-connected inverter is one of key components of a photovoltaic power generation system, converts direct current in a solar photovoltaic module square matrix into alternating current through electric power and feeds the alternating current back to a power grid, and grid-connected power generation is achieved. In a photovoltaic power generation system, when a power grid is disconnected, a distributed power generation system and a local load easily form an island system without power grid support, which brings challenges to the safe and stable operation of a power system.
At present, most of island detection methods mainly comprise two island detection methods based on remote communication and island detection methods based on local information, wherein the island detection methods depend on communication technology, have no detection blind area and are high in cost; the latter may be further divided into a passive island detection method and an active island detection method. The passive type is mainly carried out based on the change of local information quantity before and after the island, is simple and easy to realize, but has larger blind area, and the island detection fails when the distributed power generation system is approximately matched with the local load power; the active island detection is based on the disturbance injected into the system by the grid-connected inverter, and the island detection is realized by measuring the response of the grid-connected point to the disturbance. In addition, when multiple machines work in parallel, the mutual interference of disturbance quantities occurs in probability, and island protection is caused to fail. Therefore, a novel disturbance method and a novel detection method are provided, and stable and reliable island protection is achieved when multiple machines are connected in parallel.
Disclosure of Invention
The technical problem mainly solved by the embodiment of the invention is to provide an island detection method, device and electronic equipment thereof, which can synchronize single machine disturbance in an inverter parallel system and effectively avoid mutual interference of disturbance quantities of different machines when multiple machines are connected in parallel, thereby improving the reliability of island protection.
In order to solve the above technical problem, one technical solution adopted by the embodiment of the present invention is: the island detection method is applied to a distributed power grid formed by connecting a plurality of inverters in parallel, and comprises the following steps: injecting disturbance into the power grid by a plurality of inverters according to a disturbance sequence, wherein the disturbance is injected into the power grid by the plurality of inverters respectively according to the disturbance sequence in sequence until N disturbances are injected, and the injection of each inverter is repeated according to a fixed period; after each inverter injects disturbance to the power grid once, detecting the change of the frequency or the phase of the power grid in the disturbance stage compared with the frequency or the phase of the power grid in the previous disturbance stage; and if the change of the frequency or the phase exceeds a first preset threshold value, resetting the disturbance sequence, and if the change of the frequency or the phase exceeds a second preset threshold value, judging that the power grid has an island, wherein the second preset threshold value is larger than the first preset threshold value.
It can be understood that, in the present invention, the change of the grid frequency or phase in the disturbance phase from the grid frequency or phase in the previous disturbance phase refers to the change of the grid frequency in the disturbance phase from the grid frequency in the previous disturbance phase, or the change of the grid phase in the disturbance phase from the grid phase in the previous disturbance phase.
In one embodiment of the invention, the value of N is chosen according to the disturbance variable of the disturbance sequence and the number of inverters, so that the total disturbance variable of the grid does not remain unchanged until N disturbances are co-injected.
In an embodiment of the present invention, the injecting the disturbance into the grid by the plurality of inverters according to the pre-action sequence further comprises: and increasing the number of nested circulation layers, and enabling the plurality of inverters to inject disturbance into the power grid according to the disturbance sequence of the layers through hierarchical circulation.
In one embodiment of the invention, said resetting said perturbation sequence if said change in frequency or phase exceeds a first preset threshold comprises: judging whether the change exceeds a first preset threshold value; if the change exceeds a first preset threshold, adding 1 to a first count value of a preset filter; if the change does not exceed a first preset threshold, setting a first count value to be 0; if the number of times the change continuously exceeds the first preset threshold value makes the first count value greater than or equal to the reset threshold value, the disturbance sequence is reset.
In one embodiment of the invention, the reset perturbation sequence comprises: resetting the disturbance quantity to be injected next time to be a first disturbance quantity; and injecting disturbance to the power grid again according to the disturbance sequence.
In an embodiment of the present invention, the determining that the power grid is islanded if the change in the frequency or the phase exceeds a second preset threshold includes: judging whether the change exceeds a second preset threshold value; if the change exceeds a second preset threshold, adding 1 to a second count value of a preset filter; if the change does not exceed a second preset threshold, setting a second count value to be 0; and if the second count value is larger than or equal to the island threshold value due to the times that the change continuously exceeds the second preset threshold value, judging that the island is formed.
In an embodiment of the present invention, the first preset threshold and the second preset threshold each include a frequency threshold or a phase threshold.
In order to solve the above technical problem, another technical solution adopted by the embodiment of the present invention is: an islanding detection apparatus is provided, the apparatus including: the injection module is used for injecting disturbance into the power grid by the plurality of inverters according to the disturbance sequence, and comprises the steps that the plurality of inverters respectively inject the disturbance into the power grid in sequence according to the disturbance sequence until N disturbances are injected, and each inverter repeatedly injects the disturbance according to a fixed period; the detection module is used for detecting the change of the frequency or the phase of the power grid in the disturbance stage compared with the frequency or the phase of the power grid in the previous disturbance stage after each inverter injects disturbance to the power grid for one time; the judging module is used for resetting the disturbance sequence if the change of the frequency or the phase exceeds a first preset threshold value, and judging that the power grid has an island if the change of the frequency or the phase exceeds a second preset threshold value, wherein the second preset threshold value is larger than the first preset threshold value.
The embodiment of the invention adopts another technical scheme that: provided is an electronic device including: at least one processor; and a memory communicatively coupled to the at least one processor; wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform a method of islanding detection as described above.
Embodiments of the present invention also provide a non-transitory computer storage medium storing computer-executable instructions that, when executed by one or more processors, cause the one or more processors to perform one of the above-described islanding detection methods.
The beneficial effects of the embodiment of the invention are as follows: in contrast to the prior art, an embodiment of the present invention employs an island detection method, which includes: injecting disturbance into the power grid sequentially by a plurality of inverters according to a preset disturbance sequence until N disturbances are injected, and repeatedly injecting each inverter according to a fixed period; after each inverter injects disturbance to the power grid once, detecting the change of the frequency or the phase of the power grid in the disturbance stage compared with the frequency or the phase of the power grid in the previous disturbance stage; and if the change of the frequency or the phase exceeds a first preset threshold value, resetting the disturbance sequence, and if the change of the frequency or the phase exceeds a second preset threshold value, judging that the power grid has an island. Through the mode, the single machine disturbance in the inverter parallel system can be synchronized, the mutual interference of disturbance quantities of different machines when multiple machines are connected in parallel is effectively avoided, and the reliability of island protection is improved.
Drawings
Fig. 1 is a schematic flow chart of an island detection method provided by the present invention;
FIG. 2 is a software flow diagram of an island detection method provided by the present invention;
fig. 3 is a schematic structural diagram of an islanding detection apparatus provided in the present invention;
fig. 4 is a schematic diagram of a hardware structure of an electronic device according to the present invention.
The following is a description of the drawings:
100: an injection module; 200: a detection module; 300: a decision module;
600: an electronic device; 601: a processor; 602: a memory.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
It should be noted that, if not conflicted, the various features of the embodiments of the invention may be combined with each other within the scope of protection of the present application. Additionally, while functional block divisions are performed in apparatus schematics, with logical sequences shown in flowcharts, in some cases, steps shown or described may be performed in sequences other than block divisions in apparatus or flowcharts. Further, the terms "first," "second," "third," and the like, as used herein, do not limit the data and the execution order, but merely distinguish the same items or similar items having substantially the same functions and actions.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Referring to fig. 1, fig. 1 is a method for detecting an island according to an embodiment of the present invention, where the method includes:
step S100: injecting disturbance into the power grid by a plurality of inverters according to the disturbance sequence;
in the embodiment of the present invention, the disturbance amounts are set as disturbance sequences in order of empirical values obtained through a plurality of experiments as disturbance amounts. If the first disturbance quantity is set to be 0, the injection disturbance is 0; the second disturbance amount is 1, which represents that positive disturbance is injected, so that the frequency of the grid-connected point of the inverter is shifted upwards; the third disturbance amount is-1, indicating that negative disturbance is injected, shifting the frequency of the inverter grid-connected point downward. I.e. R1=0, R2=1, R3= -1 is a perturbation sequence.
In the embodiment of the invention, the plurality of inverters respectively and sequentially inject the disturbance into the power grid according to the preset disturbance sequence until the disturbance is injected for N times, and each inverter is repeatedly injected according to a fixed period.
For example, N =3 has been preset, the disturbance sequence R1=0, R2=1, R3= -1, assuming that there are 3 inverters in parallel. Since the disturbance periods of the inverters are not synchronous, at the same time point, a first disturbance amount R1 can be injected into the grid by inverter No. 1, a second disturbance amount R2 can be injected into the grid by inverter No. 2, and a third disturbance amount R3 can be injected into the grid by inverter No. 3, each inverter periodically injects the next disturbance amount into the grid according to a preset disturbance sequence R1=0, R2=1, and R3= -1, and the period continuous injection is repeated for detection. At the same time, although the inverter No. 1 may inject R2, the inverter No. 2 may inject R3, and the inverter No. 3 may inject R1, the inverter No. 1 may inject R3, the inverter No. 2 may inject R3, and the inverter No. 3 may inject R2 into the grid, the inverters inject disturbances into the grid according to a preset disturbance sequence, but the disturbances injected by the inverters at the same time point are random.
The N value is selected according to the disturbance quantity of the disturbance sequence and the number of the inverters, and the total disturbance quantity of the power grid is required to be kept unchanged until N disturbances are injected into the power grid. In the embodiment of the present invention, in order to avoid that the system disturbance amount remains unchanged when finite machines are connected in parallel, the value of N should be reasonably selected, as described above, N =3, R1=0, R2=1, R3= -1, if the number of inverters is 3, since the disturbance period of each inverter is asynchronous, if inverter 1 injects disturbance according to the period of R1=0, R2=1, R3= -1, if inverter 2 injects disturbance according to the period of R2=1, R3= -1, R1=0, and if inverter 3 injects disturbance according to the period of R3= -1, R1=0, R2=1, the total disturbance amount of the grid is unchanged at that time node regardless. The choice of N here is therefore not reasonable.
It is known that the preset N value enables the repetitive injection of the disturbance sequence to avoid the system disturbance amount from remaining unchanged when the finite machines are connected in parallel, so that the disturbance interference when a greater number of inverters are connected in parallel can be avoided as much as possible by increasing the cycle period, i.e., increasing the value of N, or periodically changing the value of N.
In the embodiment of the invention, the disturbance is injected into the power grid by the plurality of inverters according to the disturbance sequence, the disturbance is injected into the power grid by the plurality of inverters respectively according to the preset disturbance sequence in sequence until N disturbances are injected, each inverter is repeatedly injected according to a fixed period, the number of nested circulation layers is increased, and the disturbance is injected into the power grid by each inverter according to the disturbance sequence of the layer through hierarchical circulation. For example, the first layer cycle control disturbances are numbered in accordance with R1, R2, and R3, and the second layer cycle controls the cycle period of the first layer, and may be the R1 and R2 cycles, or the R1, R2, and R3 cycles.
Step S200: detecting a change in the frequency or phase of the power grid;
in an embodiment of the invention, after each inverter has injected a disturbance into the grid, a change in the grid frequency or phase during the disturbance phase compared to the grid frequency or phase during the previous disturbance phase is detected.
In the embodiment of the present invention, the frequency change amount is represented by Δ F, and the phase change amount is represented by Δ P. Δ F = FI-FI-1，FIIndicating the grid frequency, F, of the disturbance phase after one inverter has injected a disturbance into the gridI-1Representing the power grid frequency after the inverter injects disturbance into the power grid in the previous disturbance stage of the disturbance stage; Δ F = PI-PI-1，PIIndicating the phase, P, of the grid at the stage of a disturbance, after an inverter has injected a disturbance into the gridI-1And the inverter injects the disturbed power grid phase into the power grid in the previous disturbance phase representing the previous disturbance phase.
Step S300: judging whether to reset the disturbance sequence or judge the island according to whether the change exceeds a set threshold value;
in the embodiment of the present invention, a first preset threshold and a second preset threshold are preset and determined, where the first preset threshold is an empirical value obtained through a plurality of experiments, and the value includes a frequency threshold and a phase threshold.
In the embodiment of the invention, a reset threshold is also preset, the reset threshold is a value used for judging whether to reset the disturbance sequence, so that the multi-machine disturbance synchronization is realized, and similarly, the reset threshold is also an empirical value obtained by multiple experiments, and the reset threshold is a constant and represents the times.
In the embodiment of the invention, a filter is provided, and when Δ F or Δ P is greater than a first preset threshold, the filter count value is increased by 1, which is called a first count value. If Δ F or Δ P is not greater than the first preset threshold, the first count value is set to 0. And when the first count value is greater than or equal to the reset threshold value, resetting the disturbance sequence, resetting the next injection disturbance as the first disturbance quantity of the disturbance sequence, injecting the disturbance again according to the disturbance sequence, and simultaneously adjusting the disturbance quantity of each disturbance time point.
If the above disturbance sequence N =3, R1=0, R2=1, R3= -1, and if there are 3 inverters connected in parallel, the known N value is selected to be 3, R1=0, R2=1, R3= -1, as described above, the possibility may arise that the total disturbance amount of the grid is constant regardless of the node at that time, so that the sequence of N =5, R1=0, R2=1, R3= -1, R4=1, R5= -1, inverter 1 is injected in the sequence of R2=1, R3= -1, R4=1, R5= -1, R1=0, inverter 2 is injected in the sequence of R3= -1, R4=1, R5= -1, R462 =0, R2=1, inverter 3 is injected in the sequence of R =1, R1= 1, R1= -1, R1= -1, and R1 is selected here. It should be noted that, here, only an example of injecting the disturbance into each inverter is given, and the injection into each inverter is random. When the inverter 1 is injected into the R2, the inverter 2 is injected into the R3, the inverter 3 is injected into the R1, the injection disturbance of the inverter 3 is 0, the inverter 1 and the inverter 2 cancel each other out, the total disturbance amount is not changed, when the inverter 1 is injected into the R3 at the next time point, the inverter 2 is injected into the R4, and the inverter 3 is injected into the R2, the total disturbance amount injected by the inverter 1, the inverter 2 and the inverter 3 is 1, during the subsequent detection process, if the first count value is greater than or equal to the reset threshold value, the inverter 1, the inverter 2 and the inverter 3 are reset, the disturbance sequence is reset back to the R1, and the subsequent disturbances are injected in the sequence of R1=0, R2=1, R3= -1, R4=1, and R5= -1.
In the embodiment of the present invention, a first preset threshold is preset and determined, where the first preset threshold is an empirical value obtained through a plurality of experiments, and the value includes a frequency threshold and a phase threshold.
In the embodiment of the present invention, an island threshold is also preset, where the island threshold is a value used for determining whether the island is present, and similarly, the island threshold is also an empirical value obtained through multiple experiments, and the island threshold is a constant and represents the number of times.
In the embodiment of the invention, a filter is provided, and when Δ F or Δ P is greater than a second preset threshold, the filter count value is increased by 1, which is called a second count value. If Δ F or Δ P is not greater than the second predetermined threshold, the second count value is set to 0. And when the second count value is greater than or equal to the islanding threshold value, judging the islanding.
In the embodiment of the present invention, step S410 and step S420 are executed successively, that is, after it is determined whether to reset the disturbance sequence according to whether the change exceeds a first preset threshold, it is determined whether to be an islanding according to whether the change exceeds a second preset threshold. In addition, the method can also be implemented firstly to judge whether the island is an island according to whether the change exceeds a second preset threshold value, and then to judge whether the disturbance sequence is reset according to whether the change exceeds a first preset threshold value. The determination of whether to reset the disturbance sequence according to whether the variation exceeds a first preset threshold and the determination of whether to be islanding according to whether the variation exceeds a second preset threshold may also be performed simultaneously.
Different from the prior art, the invention adds the disturbance sequence, injects disturbance for multiple times according to the disturbance sequence, and sets the disturbance sequence reset mechanism at the same time, creates conditions to enable the inverter parallel system to achieve multi-machine disturbance synchronization, effectively avoids the mutual interference of disturbance quantities of different machines when the multiple machines are connected in parallel, and further improves the reliability of island protection.
Referring to fig. 2, fig. 2 is a software flowchart of an island detection method according to an embodiment of the present invention, where a specific operation flow is as follows:
cnt1 represents the perturbation value, injected number of times for perturbation; cnt2 represents a first count value representing the number of times that the frequency or phase of the grid changes continuously by more than a first preset threshold value compared with the frequency or phase of the grid in the previous disturbance phase after each inverter injects a disturbance into the grid; cnt3 represents a second count value representing the number of times the grid frequency or phase changes continuously over a second preset threshold compared to the grid frequency or phase of the previous disturbance phase after each inverter injected a disturbance into the grid.
Firstly, judging whether the injection disturbance frequency reaches N times, if the N times of disturbance are injected, resetting Cnt1 to be 0, injecting the next disturbance injection again according to the disturbance sequence, wherein the injection disturbance value is R [ Cnt1], if the injection disturbance frequency does not reach N times, adding 1 to the disturbance value, namely Cnt1+ +, injecting the next disturbance value according to the current disturbance sequence, and wherein the injection disturbance value is R [ Cnt1 ].
After the disturbance is injected, the change of the grid frequency or phase in the disturbance stage compared with the grid frequency or phase in the previous disturbance stage after the disturbance is injected into the grid once by each inverter is detected, i.e., Δ F or Δ P, determining whether Δ F or Δ P is greater than a first predetermined threshold D1, if so, D1, the first count Cnt2 is incremented by 1, the first count Cnt2 is incremented by 1 to determine whether Cnt2 is greater than or equal to F1, F1 indicates a reset threshold, and if Cnt2 is greater than or equal to F1, resetting the disturbance sequence to reset the next injection disturbance to the first disturbance quantity of the disturbance sequence, injecting the disturbance again according to the disturbance sequence, and performing the next step, judging after each inverter injects the disturbance once to the power grid, whether the change of the frequency or the phase of the power grid in the disturbance stage compared with the frequency or the phase of the power grid in the previous disturbance stage is larger than a second preset threshold value or not; if the Cnt2 is smaller than F1, the next step is carried out, and whether the change of the frequency or the phase of the power grid in the disturbance stage is larger than a second preset threshold value or not compared with the frequency or the phase of the power grid in the previous disturbance stage after each inverter injects disturbance to the power grid for one time is judged;
if the Δ F or the Δ P is not greater than the first preset threshold, resetting the first count value Cnt2 to 0, and performing the next step to determine whether the change of the grid frequency or the phase in the disturbance stage compared with the grid frequency or the phase in the previous disturbance stage is greater than a second preset threshold D2 after each inverter injects a disturbance to the grid once. If Δ F or Δ P is greater than a second preset threshold D2, adding 1 to a second count value Cnt3, and determining whether Cnt3 is greater than or equal to F2, where F2 represents an islanding threshold, if Cnt3 is greater than or equal to F2, determining that islanding is achieved, and ending the process; if Cnt3 is less than F2, the process ends;
if Δ F or Δ P is not greater than the second preset threshold D2, the second count value Cnt3 is reset to 0, and the process ends.
Fig. 3 is a schematic structural diagram of an island detection apparatus according to an embodiment of the present invention, where the apparatus includes: the injection module 100, the detection module 200 and the judgment module 300. The injection module 100 is configured to inject disturbance into the power grid by the plurality of inverters according to a disturbance sequence, and set an empirical value obtained through a plurality of experiments as a disturbance amount in the disturbance sequence in sequence. If the first disturbance quantity is set to be 0, the injection disturbance is 0; the second disturbance amount is 1, which represents that positive disturbance is injected, so that the frequency of the grid-connected point of the inverter is shifted upwards; the third disturbance amount is-1, indicating that negative disturbance is injected, shifting the frequency of the inverter grid-connected point downward. Namely R1=0, R2=1, R3= -1 is a perturbation sequence; and injecting disturbance into the power grid in sequence by the plurality of inverters according to the disturbance sequence respectively until N disturbances are injected, and repeatedly injecting the disturbance into each inverter according to a fixed period.
For example, N =3 has been preset, the disturbance sequence R1=0, R2=1, R3= -1, assuming there are 3 inverters. Since the disturbance periods of the inverters are not synchronous, at the same time point, a first disturbance amount R1 can be injected into the grid by inverter No. 1, a second disturbance amount R2 can be injected into the grid by inverter No. 2, and a third disturbance amount R3 can be injected into the grid by inverter No. 3, each inverter periodically injects the next disturbance amount into the grid according to a preset disturbance sequence R1=0, R2=1, and R3= -1, and the period continuous injection is repeated for detection. At the same time, the inverter No. 1 may inject R2 into the grid, the inverter No. 2 may inject R3 into the grid, and the inverter No. 3 may inject R1 into the grid; it is also possible that inverter No. 1 injects R3 into the grid, inverter No. 2 injects R3 into the grid, and inverter No. 3 injects R2 into the grid; that is, although each inverter injects disturbance into the grid according to a preset disturbance sequence, the disturbance injected by each inverter at the same time point is random.
In the embodiment of the invention, the disturbance is injected into the power grid by the plurality of inverters according to the disturbance sequence, the disturbance is injected into the power grid by the plurality of inverters respectively according to the preset disturbance sequence in sequence until N disturbances are injected, each inverter is repeatedly injected according to a fixed period, the number of nested circulation layers is increased, and the disturbance is injected into the power grid by each inverter according to the disturbance sequence of the layer through hierarchical circulation. For example, the first layer cycle control disturbances are numbered as R1, R2, and R3, and the second layer cycle control the cycle period (i.e., N times) of the first layer, and may be the R1 and R2 cycles, or the R1, R2, and R3 cycles.
The detection module 200 is configured to detect a change in the grid frequency or phase, and in an embodiment of the present invention, after each inverter injects a disturbance into the grid, the change in the grid frequency or phase in the disturbance phase is detected as compared to the grid frequency or phase in the previous disturbance phase.
In the embodiment of the present invention, the frequency change amount is represented by Δ F, and the phase change amount is represented by Δ P. Δ F = FI-FI-1，FIIndicating the grid frequency, F, of the disturbance phase after one inverter has injected a disturbance into the gridI-1Representing the power grid frequency after the inverter injects disturbance into the power grid in the previous disturbance stage of the disturbance stage; Δ P = PI-PI-1，PIIndicating the phase, P, of the grid at the stage of a disturbance, after an inverter has injected a disturbance into the gridI-1And the inverter injects the disturbed power grid phase into the power grid in the previous disturbance phase representing the previous disturbance phase.
The determining module 300 is configured to determine whether to reset the disturbance sequence or determine the islanding according to whether the variation exceeds a set threshold, and in an embodiment of the present invention, a first preset threshold is preset and determined, where the first preset threshold is an empirical value obtained through multiple experiments, and the value includes a frequency threshold and a phase threshold.
In the embodiment of the invention, a reset threshold is also preset, the reset threshold is a value used for judging whether to reset the disturbance sequence, so that the multi-machine disturbance synchronization is realized, and similarly, the reset threshold is also an empirical value obtained by a plurality of experiments, and the reset threshold is a constant and represents the times.
In the embodiment of the invention, a filter is provided, and when Δ F or Δ P is greater than a first preset threshold, the filter count value is increased by 1, which is called a first count value. If Δ F or Δ P is not greater than the first preset threshold, the first count value is set to 0. And when the first count value is greater than or equal to the reset threshold value, resetting the disturbance sequence, resetting the next injected disturbance as the first disturbance quantity of the disturbance sequence, injecting the disturbance again according to the disturbance sequence, and simultaneously adjusting the disturbance quantity of each disturbance time point.
If the above disturbance sequence N =3, R1=0, R2=1, R3= -1, and if there are 3 inverters connected in parallel, the known N value is selected to be 3, R1=0, R2=1, R3= -1, as described above, the possibility may arise that the total disturbance amount of the grid is constant regardless of the node at that time, so that the sequence of N =5, R1=0, R2=1, R3= -1, R4=1, R5= -1, inverter 1 is injected in the sequence of R2=1, R3= -1, R4=1, R5= -1, R1=0, inverter 2 is injected in the sequence of R3= -1, R4=1, R5= -1, R462 =0, R2=1, inverter 3 is injected in the sequence of R =1, R1= 1, R1= -1, R1= -1, and R1 is selected here. It should be noted that, here, only an example of injecting the disturbance into each inverter is given, and the injection into each inverter is random. When the inverter 1 injects R2, the inverter 2 injects R3, and the inverter 3 injects R1, at this time, the injection disturbance of the inverter 3 is 0, the inverter 1 and the inverter 2 cancel each other out, and the total disturbance quantity is unchanged; when the inverter 1 is injected into the R3 at the next time point, the inverter 2 is injected into the R4, and the inverter 3 is injected into the R2, at this time point, the total disturbance amount injected by the inverter 1, the inverter 2, and the inverter 3 is 1, in the subsequent detection process, if the first count value is greater than or equal to the reset threshold, the inverter 1, the inverter 2, and the inverter 3 are reset, the disturbance sequence is reset back to the R1, and the disturbances are injected subsequently according to the sequence of R1=0, R2=1, R3= -1, R4=1, and R5= -1.
In the embodiment of the present invention, a first preset threshold and a second preset threshold are preset and determined, where the first preset threshold and the second preset threshold both include a frequency threshold and a phase threshold.
In the embodiment of the present invention, an island threshold is also preset, where the island threshold is a value used for determining whether the island is present, and similarly, the island threshold is also an empirical value obtained through multiple experiments, and the island threshold is a constant and represents the number of times.
In the embodiment of the invention, a filter is provided, and when Δ F or Δ P is greater than a second preset threshold, the filter count value is increased by 1, which is called a second count value. If Δ F or Δ P is not greater than the second predetermined threshold, the second count value is set to 0. And when the second count value is greater than or equal to the islanding threshold value, judging the islanding.
Fig. 4 is a schematic diagram of a hardware structure of an electronic device according to an embodiment of the present invention, and as shown in fig. 4, the electronic device 600 includes:
one or more processors 601 and a memory 602, one processor 601 being illustrated in fig. 4.
The processor 601 and the memory 602 may be connected by a bus or other means, such as the bus connection shown in fig. 4.
The memory 602, which is a non-volatile computer-readable storage medium, may be used to store non-volatile software programs, non-volatile computer-executable programs, and modules. The processor 601 executes various functional applications and data processing of the electronic device by running nonvolatile software programs, instructions and units stored in the memory 602, that is, implements an islanding detection method of the above method embodiment.
The memory 602 may include a storage program area and a storage data area, wherein the storage program area may store an operating system, an application program required for at least one function; the storage data area may store data created according to the use of the electronic device, and the like. Further, the memory 602 may include high speed random access memory, and may also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid state storage device. In some embodiments, the memory 602 optionally includes memory located remotely from the processor 601, which may be connected to the electronic device via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
The one or more units are stored in the memory 602, and when executed by the one or more processors 601, perform an islanding detection method in any of the above-described method embodiments, for example, perform the above-described method steps S100 to S300 in fig. 1, and implement the functions of the module 100 and 300 in fig. 3.
The electronic device can execute the island detection method provided by the embodiment of the invention, and has the corresponding program module and beneficial effects of the execution method. For technical details that are not described in detail in the electronic device embodiment, reference may be made to an island detection method provided by the embodiment of the present invention.
An embodiment of the present invention further provides a nonvolatile computer-readable storage medium, which may be included in the device described in the above embodiment; or may be separate and not incorporated into the device. The non-transitory computer readable storage medium carries one or more programs which, when executed, implement the methods of embodiments of the present disclosure.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (10)
1. An island detection method is applied to a distributed power grid formed by connecting a plurality of inverters in parallel, and is characterized by comprising the following steps:
injecting disturbance into the power grid by a plurality of inverters according to a disturbance sequence, wherein the disturbance is injected into the power grid by the plurality of inverters respectively according to the disturbance sequence in sequence until N disturbances are injected, and the injection of each inverter is repeated according to a fixed period;
after each inverter injects disturbance to the power grid once, detecting the change of the frequency or the phase of the power grid in the disturbance stage compared with the frequency or the phase of the power grid in the previous disturbance stage;
and if the change of the frequency or the phase exceeds a first preset threshold value, resetting the disturbance sequence, and if the change of the frequency or the phase exceeds a second preset threshold value, judging that the power grid has an island, wherein the second preset threshold value is larger than the first preset threshold value.
2. The method of claim 1, wherein the value of N is selected based on the disturbance magnitude of the disturbance sequence and the number of inverters such that the total disturbance magnitude of the grid does not remain constant until N disturbances are co-injected.
3. The method of claim 1, wherein injecting the disturbance into the grid by the plurality of inverters in the disturbance sequence further comprises:
and increasing the number of nested circulation layers, and enabling the plurality of inverters to inject disturbance into the power grid according to the disturbance sequence of the layers through hierarchical circulation.
4. The method according to claim 1, wherein said resetting said perturbation sequence if said change in frequency or phase exceeds a first preset threshold comprises:
judging whether the change exceeds a first preset threshold value;
if the change exceeds a first preset threshold, adding 1 to a first count value of a preset filter;
if the change does not exceed a first preset threshold, setting the first count value to be 0;
resetting the disturbance sequence if the first count value is greater than or equal to a reset threshold value for the number of times that the change continuously exceeds the first preset threshold value.
5. The method of claim 4, wherein the reset perturbation sequence comprises:
resetting the disturbance quantity to be injected next time to be a first disturbance quantity;
and injecting disturbance to the power grid again according to the disturbance sequence.
6. The method according to claim 1, wherein the determining that the power grid is islanded if the change in the frequency or the phase exceeds a second preset threshold comprises:
judging whether the change exceeds a second preset threshold value;
if the change exceeds a second preset threshold, adding 1 to a second count value of a preset filter;
if the change does not exceed a second preset threshold, setting the second count value to be 0;
and if the second count value is larger than or equal to the island threshold value due to the times that the change continuously exceeds the second preset threshold value, judging that the island is formed.
7. The method of claim 1, wherein the first and second predetermined thresholds each comprise a frequency threshold or a phase threshold.
8. An island detection device, characterized by comprising
The injection module is used for injecting disturbance into the power grid by the plurality of inverters according to the disturbance sequence, and comprises the steps that the plurality of inverters respectively inject the disturbance into the power grid in sequence according to the disturbance sequence until N disturbances are injected, and each inverter repeatedly injects the disturbance according to a fixed period;
the detection module is used for detecting the change of the frequency or the phase of the power grid in the disturbance stage compared with the frequency or the phase of the power grid in the previous disturbance stage after each inverter injects disturbance to the power grid for one time;
the judging module is used for resetting the disturbance sequence if the change of the frequency or the phase exceeds a first preset threshold value, and judging that the power grid has an island if the change of the frequency or the phase exceeds a second preset threshold value, wherein the second preset threshold value is larger than the first preset threshold value.
9. An electronic device, comprising:
at least one processor; and the number of the first and second groups,
a memory communicatively coupled to the at least one processor; wherein the content of the first and second substances,
the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method of any one of claims 1-7.
10. A non-transitory computer storage medium storing computer-executable instructions that, when executed by one or more processors, cause the one or more processors to perform a method of islanding detection as claimed in any one of claims 1 to 7.
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