CN107769252B - Island detection method, device and system of distributed power generation system - Google Patents
Island detection method, device and system of distributed power generation system Download PDFInfo
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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
- H02J3/381—Dispersed generators
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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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Abstract
The invention provides an island detection method, equipment and a system of a distributed power generation system, and relates to the technical field of island detection, wherein the island detection method comprises the following steps: the method comprises the steps of sequentially sending pseudo-random disturbance signals to a plurality of inverters in a distributed power generation system according to a preset time interval, receiving an offset returned by the inverters according to the received pseudo-random disturbance signals, obtaining a preset offset threshold value, and outputting a detection result according to the offset and the preset offset threshold value. The island detection method, the device and the system for the distributed power generation system can realize island detection of the distributed power generation system with multiple inverters.
Description
Technical Field
The invention relates to the technical field of island detection, in particular to an island detection method, equipment and a system of a distributed power generation system.
Background
The quality and safety reliability of power supply in the present society are higher and higher, and a centralized power supply system which is mainly characterized by a large unit, a large power grid and high voltage cannot meet the requirements due to the defects of the centralized power supply system. At present, a centralized power supply system and a distributed power generation system are combined, and a smaller generator set (generally lower than 30MW) is configured at a user site or close to a power utilization site, so that the requirements of specific users can be met, and the quality and safety and reliability of power supply can be improved.
However, if the distributed power generation system continues to supply power to the blackout area after the centralized power supply system stops supplying power, at this time, the lines in the blackout area still maintain the live state, and a power island is formed. After the centralized power supply system stops supplying power, the voltage and the frequency of a cable in the power island cannot be controlled, so that serious safety accidents of power equipment, maintenance personnel and even a power grid are easily caused, and serious potential safety hazards are brought to power supply. Therefore, islanding detection is required for a distributed power generation system accessing a centralized power supply system.
In the existing islanding detection technology (for example, an active frequency offset method), a current signal with a constant waveform and a variable frequency is injected into a power grid through an inverter, and the islanding detection is performed on a distributed power generation system according to the current signal. However, the existing island detection technology is only suitable for island detection of a distributed power generation system with a single inverter, and when the existing island detection technology is applied to island detection of a distributed power generation system with multiple inverters, current signals of the island detection technology are mutually offset, so that the island detection requirement of the distributed power generation system with multiple inverters cannot be met.
Disclosure of Invention
In order to solve the problem that the existing island detection technology cannot perform island detection on a multi-inverter distributed power generation system, the invention provides an island detection method, equipment and a system of a distributed power generation system.
One of the objects of the present invention is to provide an island detection method for a distributed power generation system, the distributed power generation system including a plurality of inverters, the island detection method including:
sending pseudo-random disturbing signals to the plurality of inverters in sequence according to a preset time interval;
receiving the offset returned by the inverter according to the received pseudo-random disturbing signal;
acquiring a preset offset threshold;
and outputting a detection result according to the offset and the preset offset threshold.
Optionally, the preset time interval is smaller than or equal to a time interval threshold, and the time interval threshold is determined by a maximum detection period and the number of inverters in the distributed power generation system.
Optionally, outputting an island detection result according to the offset and the preset offset threshold includes:
judging whether the offset is greater than or equal to the preset offset threshold;
when the judgment result is yes, outputting a detection result of the island existence;
and when the judgment result is negative, outputting the detection result without island.
Optionally, the island detection method further includes:
and when the detection result is that the island exists, sending a disconnection instruction to the power generation device in the distributed power generation system so as to stop feeding the power generation device.
Optionally, the island detection method further includes:
acquiring the total offset amount of the grid-connected buses of the plurality of inverters;
and adjusting the preset time interval according to the total offset amount so as to reduce the total offset amount.
One of the objects of the present invention is to provide an island detection device of a distributed power generation system, the island detection device including:
the disturbance signal sending module is used for sequentially sending pseudo-random disturbance signals to a plurality of inverters in the distributed power generation system according to a preset time interval;
the offset receiving module is used for receiving the offset which is returned by the inverter and is determined according to the received pseudo-random disturbing signal;
the offset threshold acquisition module is used for acquiring a preset offset threshold;
and the result output module is used for outputting a detection result according to the offset and the preset offset threshold.
Optionally, the preset time interval is smaller than or equal to a time interval threshold, and the time interval threshold is determined by a maximum detection period and the number of inverters in the distributed power generation system.
Optionally, the output module includes:
the judging unit is used for judging whether the offset is greater than or equal to the preset offset threshold;
the first output unit is used for outputting the detection result of the island when the judgment result of the judgment unit is yes;
and the second output unit is used for outputting the detection result of the island when the judgment result of the judgment unit is negative.
Optionally, the island detection device further includes:
and the disconnection instruction sending module is used for sending a disconnection instruction to the power generation device in the distributed power generation system to stop feeding the power generation device when the detection result shows that the island exists.
Optionally, the island detection device further includes:
the offset total amount acquisition module is used for acquiring the offset total amount of the grid-connected buses of the inverters;
and the time interval adjusting module is used for adjusting the preset time interval according to the total offset amount so as to reduce the total offset amount.
One of the objects of the present invention is to provide an island detection system, which includes a distributed power generation system and an island detection device of the distributed power generation system.
The island detection method, the device and the system of the distributed power generation system have the advantages that the pseudo-random disturbance signals are sequentially sent to the inverters according to the preset time interval, the offset returned by the inverters is received, the detection result is output according to the offset and the preset offset threshold, and when the detection result shows that an island exists, a disconnection instruction is sent to the power generation device, so that the power generation device stops feeding. And meanwhile, acquiring the total offset of the grid-connected buses of the inverters, and adjusting a preset time interval according to the total offset to reduce the total offset. The island detection method, the device and the system of the distributed power generation system provided by the invention not only can realize island detection and island control on the distributed power generation system with multiple inverters, but also can adjust the power quality of a power grid.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a block diagram of a first embodiment of an island detection system provided by the present invention;
fig. 2 is a structural block diagram of a second embodiment of an island detection system provided by the present invention;
fig. 3 is a block diagram of a third embodiment of an island detection system according to the present invention;
fig. 4 is a block diagram of an island detection device of a distributed power generation system according to a first embodiment of the present invention;
FIG. 5 is a block diagram illustrating the structure of the result output module 240 in FIG. 4;
fig. 6 is a block diagram of a second embodiment of an island detection device of a distributed power generation system according to the present invention;
fig. 7 is a block diagram of a third embodiment of an island detection device of a distributed power generation system according to the present invention.
Fig. 8 is a flowchart of a first embodiment of an island detection method for a distributed power generation system according to the present invention;
FIG. 9 is a detailed flowchart of step S240 in FIG. 8;
fig. 10 is a flowchart of a second embodiment of an island detection method for a distributed power generation system according to the present invention;
fig. 11 is a flowchart of a third embodiment of an island detection method for a distributed power generation system according to the present invention;
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As will be appreciated by one skilled in the art, embodiments of the present invention may implement a system, apparatus, device, method or computer program. Thus, the present invention may be embodied in the form of: entirely hardware, entirely software (including firmware, resident software, micro-code, etc.), or a combination of hardware and software.
Moreover, any number of elements in the drawings are by way of example and not by way of limitation, and any nomenclature is used solely for differentiation and not by way of limitation.
The principles and spirit of the present invention are explained in detail below with reference to several representative embodiments of the invention.
Summary of The Invention
In the existing islanding detection technology (for example, an active frequency offset method), a current signal with a constant waveform and a variable frequency is injected into a power grid through an inverter, and the islanding detection is performed on a distributed power generation system according to the current signal. However, the existing island detection technology is only suitable for island detection of a distributed power generation system with a single inverter, and when the existing island detection technology is applied to island detection of a distributed power generation system with multiple inverters, current signals of the island detection technology are mutually offset, so that the island detection requirement of the distributed power generation system with multiple inverters cannot be met.
In order to solve the problem that the existing island detection technology cannot perform island detection on a multi-inverter distributed power generation system, the invention provides an island detection method, equipment and a system of a distributed power generation system.
Having described the general principles of the invention, various non-limiting embodiments of the invention are described in detail below.
Exemplary System
In the following, with reference to the accompanying drawings, an island detection method, device and system of a distributed power generation system according to the present invention are described with reference to the above application scenarios. It should be noted that the above application scenarios are merely illustrated for the convenience of understanding the spirit and principles of the present invention, and the embodiments of the present invention are not limited in this respect. Rather, embodiments of the present invention may be applied to any scenario where applicable.
The island detection system comprises a distributed power generation system 100 and island detection equipment 200 of the distributed power generation system. The distributed power generation system 100 includes a plurality of inverters 110 and a power generation device 120, and the inverters 110 are connected to the power generation device 120 through power lines. In the present description, the number of inverters is 4, for example, and those skilled in the art may select other numbers of inverters according to actual needs, but the present invention is not limited thereto.
Fig. 1 is a block diagram of a first embodiment of an island detection system according to the present invention, and as shown in fig. 1, an island detection device 200 of a distributed power generation system 100 is disposed in the distributed power generation system 100, and is connected to an inverter 110 and a power generation apparatus 120 in the distributed power generation system 100 through a power line, so as to perform island detection on the distributed power generation system 100.
Fig. 2 is a block diagram of a second embodiment of an island detection system according to the present invention, and as shown in fig. 2, an island detection device 200 is disposed outside a distributed power generation system 100, and is connected to an inverter 110 and a power generation apparatus 120 in the distributed power generation system 100 through a power line, so as to perform island detection on the distributed power generation system 100.
Fig. 3 is a block diagram of a third embodiment of an island detection system according to the present invention, and as shown in fig. 3, for an inverter 110 that is inconvenient for island detection due to factors such as geographical location in a distributed power generation system 100, an island detection device 200 may be disposed in a power generation apparatus 120, and connected to the inverter 110 in the distributed power generation system 100 through a power line, so as to perform island detection on the distributed power generation system 100.
The island detection system provided by the invention is not limited to the above three embodiments, and those skilled in the art can select other embodiments according to actual situations, and the invention is not limited.
Exemplary devices
After the island detection system provided by the invention is introduced, the island detection equipment of the distributed power generation system of the invention is specifically introduced below.
Fig. 4 is a block diagram of a first embodiment of an island detection device of a distributed power generation system, where as shown in fig. 4, the island detection device includes:
the disturbing signal sending module 210 is configured to send pseudo-random disturbing signals to a plurality of inverters in the distributed power generation system in sequence according to a preset time interval.
In a specific embodiment, the disturbance signal sending module 210 continuously sends the pseudo-random disturbance signals to the plurality of inverters 110 in a polling manner, and this specification takes a polling cycle as an example, and in a polling cycle, the disturbance signal sending module 210 sequentially sends the pseudo-random disturbance signals to the plurality of inverters 110 according to a preset time interval. For example, in one polling cycle, the disturbance signal sending module 210 sends pseudo-random disturbance signals to the first inverter 110, the second inverter 110, the third inverter 110 and the fourth inverter 110 sequentially according to a preset time interval, and thereafter, the disturbance signal sending module 210 sends pseudo-random disturbance signals to the first inverter 110, the second inverter 110, the third inverter 110 and the fourth inverter 110 sequentially according to the preset time interval again, and so on, that the disturbance signal sending module 210 continuously sends pseudo-random disturbance signals to the plurality of inverters 110 in a polling manner.
The pseudo-random disturbing signal is a signal whose amplitude is unpredictable but obeys a certain statistical characteristic, and may be a current pseudo-random disturbing signal, a frequency pseudo-random disturbing signal or a phase pseudo-random disturbing signal, and is usually generated by a gaussian random function or a sinusoidal random function, or may be generated by other random functions, which is not limited in the present invention.
The preset time interval is less than or equal to a time interval threshold, and the time interval threshold is determined by a maximum detection period and the number of inverters in the distributed power generation system.
In a specific embodiment, if the preset time interval is too large, when the distributed power generation system 100 forms an island, the island cannot be detected in time, so that a major safety accident of power equipment, maintenance personnel and even a power grid is caused, and a serious potential safety hazard is brought to power supply. In order to ensure the timeliness of the islanding detection and improve the reliability of the islanding detection, the preset time interval is less than or equal to a time interval threshold, and the time interval threshold is a ratio of the maximum detection period to the number of inverters 110 in the distributed power generation system 100. The maximum detection period is the longest time for all inverters 110 in the distributed power generation system 100 to complete one islanding detection. The maximum detection period may be preset according to various indexes such as the type and scale of the distributed power generation system 100, or may be preset in combination with relevant standards established by the country, which is not limited in the present invention. For example, according to the national standard, the maximum detection period is 2s, the number of inverters in the distributed power generation system 100 is 4, the time interval threshold is 2 s/4-0.5 s, and the setting of the subsequent preset time interval is less than or equal to 0.5 s. When the preset time interval is equal to the time interval threshold, the mutual offset or superposition of the offsets can be effectively prevented, and the reliability of island detection is improved; and when the preset time interval is smaller than the time interval threshold, the island detection speed can be increased, and the island can be detected more quickly.
And an offset receiving module 220, configured to receive an offset, which is returned by the inverter and determined according to the received pseudo-random disturbance signal.
In a specific embodiment, when the inverter 110 receives the pseudo-random disturbance signal, first, the pseudo-random disturbance signal is added to the output current of the inverter 110 to obtain a disturbed output current, then, the inverter 110 obtains an offset corresponding to the pseudo-random disturbance signal according to the disturbed output current and the rated output current, and finally, the inverter 110 sends the offset to the offset receiving module 220. When the pseudo-random disturbing signal is a current pseudo-random disturbing signal, the corresponding offset is a voltage offset; when the pseudo-random disturbing signal is a frequency pseudo-random disturbing signal, the corresponding offset is a frequency offset; when the pseudo-random disturbing signal is a phase pseudo-random disturbing signal, the corresponding offset is a power offset.
An offset threshold obtaining module 230, configured to obtain a preset offset threshold.
In a specific implementation, the preset offset threshold may be preset according to various indexes such as the type and the scale of the distributed power generation system 100, or may be preset in combination with related standards established by the country, which is not limited in the present invention. For example, the preset voltage offset threshold is 10% of the rated voltage for a distributed power generation system of 35Kv and above, and 7% of the rated voltage for a distributed power generation system of 10Kv or below.
And a result output module 240, configured to output a detection result according to the offset and the preset offset threshold.
In a specific embodiment, when the distributed power generation system 100 does not form an island, the disturbance of the pseudorandom disturbance signal to the output current of the inverter 110 is limited by the power grid balance, the disturbance effect is small, the offset is small, when the distributed power generation system 100 forms an island, the disturbance effect of the pseudorandom disturbance signal to the output current of the inverter 110 is large, the offset is large, by comparing the offset with a preset offset threshold, whether the distributed power generation system 100 forms an island can be determined, and a corresponding detection result is output through the result output module 240.
In the above embodiment, the pseudo-random disturbance signal is used to perform island detection on the distributed power generation system 100, so that the influence of the local load property on the offset in the existing island detection technology can be avoided, and meanwhile, the pseudo-random disturbance signal is sent at intervals, so that mutual cancellation or superposition of the offset on the power line can be effectively prevented, and island detection on the multi-inverter distributed power generation system is realized.
Fig. 5 is a block diagram illustrating a specific structure of the result output module 240 in fig. 4, where the result output module 240 includes:
a determining unit 241, configured to determine whether the offset is greater than or equal to the preset offset threshold.
And a first output unit 242, configured to output a detection result of the island existence when the determination result of the determination unit is yes.
A second output unit 243, configured to output a detection result of no island when the determination result of the determination unit is negative.
In a specific embodiment, the determining unit 241 compares the absolute value of the offset with a preset offset threshold, and when the offset is greater than or equal to the preset offset threshold, it indicates that the pseudo-random disturbance signal has a large disturbance effect on the output current of the inverter 110, the distributed power generation system 100 forms an island, and the first output unit 242 outputs a detection result that the island exists. When the offset is smaller than the preset offset threshold, it is indicated that the disturbance effect of the pseudorandom disturbance signal on the output current of the inverter 110 is small, the distributed power generation system 100 does not form an island, and the second output unit 243 outputs a detection result that no island exists. The output result may be output through a display, or may be output through an alarm device, which is not limited in the present invention.
In the above embodiment, when the offset is greater than or equal to the preset offset threshold, the display or the alarm device may output the detection result that an island exists, and remind the staff of the distributed power generation system 100 to process the island at the first time of island formation in real time. Otherwise, outputting a detection result without the island, and subsequently continuing to perform island detection.
Fig. 6 is a structural block diagram of a second embodiment of an island detection device of a distributed power generation system provided by the present invention, and as shown in fig. 6, the island detection device further includes:
and a disconnection instruction sending module 250, configured to send a disconnection instruction to a power generation device in the distributed power generation system to stop feeding the power generation device when the detection result indicates that an island exists.
In a specific embodiment, when the detection result indicates that an island exists, the disconnection instruction sending module 250 sends a disconnection instruction to the power generation device 120, and the power generation device 120 stops feeding power after receiving the disconnection instruction.
Fig. 7 is a block diagram of a third embodiment of an island detection device of a distributed power generation system, where as shown in fig. 7, the island detection device further includes:
and an offset total amount obtaining module 260, configured to obtain an offset total amount at the multiple inverter grid-connected buses.
In a specific embodiment, when the plurality of inverters 110 of the distributed power generation system 100 receive the pseudo-random disturbance signal sent by the island detection device 200, offsets with different magnitudes and directions are generated. When the directions of the offsets of the inverters 110 are not consistent, the offsets of the inverters at the grid-connected bus are mutually offset, the total offset is small, and the power quality is good, and when the directions of the offsets of the inverters 110 are consistent, the offsets of the inverters at the grid-connected bus are mutually overlapped, the total offset is large, and the power quality is poor.
A time interval adjusting module 270, configured to adjust the preset time interval according to the total offset amount, so as to reduce the total offset amount.
In a specific embodiment, when the total offset is large and the power quality is poor, the preset time interval may be adjusted by the time interval adjustment module 270 to reduce the total offset and improve the power quality. For example: when the total offset is large, the preset time interval may be increased by the time interval adjustment module 270, and at this time, when the total offset continues to increase, the preset time interval may be decreased by the time interval adjustment module 270 until the total offset is minimum, and the power quality is best.
In the above embodiment, the time interval adjusting module 270 adjusts the preset time interval to reduce the total offset, improve the power quality, and prevent safety accidents caused by poor power quality.
Furthermore, although in the above detailed description several unit modules of the system are mentioned, this division is not mandatory only. Indeed, the features and functions of two or more of the units described above may be embodied in one unit, according to embodiments of the invention. Also, the features and functions of one unit described above may be further divided into embodiments by a plurality of units. The terms "module" and "unit" used above may be software and/or hardware that realizes a predetermined function. While the modules described in the following embodiments are preferably implemented in software, implementations in hardware, or a combination of software and hardware are also possible and contemplated.
Exemplary method
Having described the exemplary embodiment of the present invention, an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. The implementation of the device can be referred to the above overall implementation, and repeated details are not repeated.
Fig. 8 is a flowchart of a first embodiment of an island detection method for a distributed power generation system, where as shown in fig. 8, the island detection method includes:
s110: and sequentially sending pseudo-random disturbance signals to the plurality of inverters 110 according to a preset time interval.
In a specific embodiment, the island detection device 200 continuously sends the pseudo-random disturbance signals to the plurality of inverters 110 in a polling manner, and this specification takes a polling period as an example, and in a polling period, the island detection device 200 sequentially sends the pseudo-random disturbance signals to the plurality of inverters 110 according to a preset time interval.
The pseudo-random disturbing signal is a signal whose amplitude is unpredictable but obeys a certain statistical characteristic, and may be a current pseudo-random disturbing signal, a frequency pseudo-random disturbing signal or a phase pseudo-random disturbing signal, and is usually generated by a gaussian random function or a sinusoidal random function, or may be generated by other random functions, which is not limited in the present invention.
The preset time interval is less than or equal to a time interval threshold determined by a maximum detection period and the number of inverters 110 in the distributed power generation system 100.
In a specific embodiment, if the preset time interval is too large, when the distributed power generation system 100 forms an island, the island cannot be detected in time, so that a major safety accident of power equipment, maintenance personnel and even a power grid is caused, and a serious potential safety hazard is brought to power supply. In order to ensure the timeliness of the islanding detection and improve the reliability of the islanding detection, the preset time interval is less than or equal to a time interval threshold, and the time interval threshold is a ratio of the maximum detection period to the number of inverters 110 in the distributed power generation system 100. The maximum detection period is the longest time for all inverters 110 in the distributed power generation system 100 to complete one islanding detection. The maximum detection period may be preset according to various indexes such as the type and scale of the distributed power generation system 100, or may be preset in combination with relevant standards established by the country, which is not limited in the present invention. For example, according to the national standard, the maximum detection period is 2s, the number of inverters in the distributed power generation system 100 is 4, the time interval threshold is 2 s/4-0.5 s, and the setting of the subsequent preset time interval is less than or equal to 0.5 s. When the preset time interval is equal to the time interval threshold, the mutual offset or superposition of the offsets can be effectively prevented, and the reliability of island detection is improved; and when the preset time interval is smaller than the time interval threshold, the island detection speed can be increased, and the island can be detected more quickly.
S120: and receiving the offset returned by the inverter 110 according to the received pseudo-random disturbance signal.
In a specific implementation, when the inverter 110 receives the pseudo-random disturbance signal, first, the pseudo-random disturbance signal is added to the output current of the inverter 110 to obtain a disturbed output current, then, the inverter 110 obtains an offset corresponding to the pseudo-random disturbance signal according to the disturbed output current and the rated output current, and finally, the inverter 110 sends the offset to the island detection device 200. When the pseudo-random disturbing signal is a current pseudo-random disturbing signal, the corresponding offset is a voltage offset; when the pseudo-random disturbing signal is a frequency pseudo-random disturbing signal, the corresponding offset is a frequency offset; when the pseudo-random disturbing signal is a phase pseudo-random disturbing signal, the corresponding offset is a power offset.
S130: and acquiring a preset offset threshold.
In a specific embodiment, the preset offset threshold may be preset according to various indexes such as the type and the scale of the distributed power generation system 100, or may be preset in combination with related standards established by the country, which is not limited in the present invention. For example, the preset voltage offset threshold is 10% of the rated voltage for a distributed power generation system of 35Kv and above, and 7% of the rated voltage for a distributed power generation system of 10Kv or below.
S140: and outputting a detection result according to the offset and the preset offset threshold.
In a specific embodiment, when the distributed power generation system 100 does not form an island, the disturbance of the pseudo-random disturbance signal to the output current of the inverter 110 is limited by the power grid balance, the disturbance effect is small, the offset is small, when the distributed power generation system 100 forms an island, the disturbance effect of the pseudo-random disturbance signal to the output current of the inverter 110 is large, the offset is large, and by comparing the offset with a preset offset threshold, whether the distributed power generation system 100 forms an island or not can be judged, and a corresponding detection result is output.
In the above embodiment, the pseudo-random disturbance signal is used to perform island detection on the distributed power generation system 100, so that the influence of the local load property on the offset in the existing island detection technology can be avoided, and meanwhile, the pseudo-random disturbance signal is sent at intervals, so that mutual cancellation or superposition of the offset on the power line can be effectively prevented, and island detection on the multi-inverter distributed power generation system is realized.
Fig. 9 is a detailed flowchart of step S140 in fig. 8, and step S240 includes:
s141: judging whether the offset is greater than or equal to the preset offset threshold;
s142: when the judgment result is yes, outputting a detection result of the island existence;
s143: and when the judgment result is negative, outputting the detection result without island. In a specific embodiment, the absolute value of the offset is compared with a preset offset threshold, when the offset is greater than or equal to the preset offset threshold, it indicates that the disturbance effect of the pseudorandom disturbance signal on the output current of the inverter 110 is large, and the distributed power generation system 100 forms an island, and when the offset is less than the preset offset threshold, it indicates that the disturbance effect of the pseudorandom disturbance signal on the output current of the inverter 110 is small, and the distributed power generation system 100 does not form an island. The output result may be output through a display, or may be output through an alarm device, which is not limited in the present invention.
In the above embodiment, when the offset is greater than or equal to the preset offset threshold, the display or the alarm device may output the detection result that an island exists, and remind the staff of the distributed power generation system 100 to process the island at the first time of island formation in real time. Otherwise, outputting a detection result without the island, and subsequently continuing to perform island detection.
Fig. 10 is a flowchart of a second implementation manner of an island detection method for a distributed power generation system provided by the present invention, and as shown in fig. 10, the island detection method further includes:
s150: when the detection result is that an island exists, a disconnection instruction is sent to the power generation device 120 in the distributed power generation system 100, so that the power generation device 120 stops feeding power.
In the specific embodiment, when the detection result indicates that an island exists, the island detection device 200 sends a disconnection instruction to the power generation apparatus 120, and the power generation apparatus 120 stops feeding power after receiving the disconnection instruction.
In the above embodiment, when it is detected that the distributed power generation system 100 has an island, the island detection device 200 sends a disconnection instruction to the power generation apparatus 120, and the power generation apparatus 120 stops feeding after receiving the disconnection instruction, so that a major safety accident of power equipment, maintenance personnel, and even a power grid due to the power island can be effectively prevented, and potential safety hazards can be effectively suppressed.
Fig. 11 is a flowchart of a third implementation manner of an island detection method of a distributed power generation system provided by the present invention, and as shown in fig. 11, the island detection method further includes:
s160: acquiring the total offset amount of the grid-connected buses of the plurality of inverters;
in a specific embodiment, when the plurality of inverters 110 of the distributed power generation system 100 receive the pseudo-random disturbance signal sent by the island detection device 200, offsets with different magnitudes and directions are generated. When the directions of the offsets of the inverters 110 are not consistent, the offsets of the inverters at the grid-connected bus are mutually offset, the total offset is small, and the power quality is good, and when the directions of the offsets of the inverters 110 are consistent, the offsets of the inverters at the grid-connected bus are mutually overlapped, the total offset is large, and the power quality is poor.
S170: and adjusting the preset time interval according to the total offset amount so as to reduce the total offset amount.
In a specific embodiment, when the total offset is large and the power quality is poor, the total offset can be reduced by adjusting the preset time interval, so that the power quality is improved. For example: when the total offset amount is larger, the preset time interval can be increased, and at this time, when the total offset amount continues to be increased, the preset time interval can be decreased until the total offset amount is minimum and the power quality is best.
In the above embodiment, the total offset is reduced by adjusting the preset time interval, so as to improve the power quality and prevent safety accidents caused by poor power quality.
As mentioned above for the distributed power generation system islanding detection method according to the present invention, it should be noted that although the operations of the method according to the present invention are depicted in the drawings in a specific order, this does not require or imply that these operations have to be performed in this specific order, or that all illustrated operations have to be performed in order to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step broken down into multiple step executions.
It will be understood by those skilled in the art that all or part of the processes of the methods of the above embodiments may be implemented by a computer program, which can be stored in a general computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The storage medium may be a Read-Only Memory (ROM) or a Random Access Memory (RAM).
Those skilled in the art will also appreciate that the various functions performed in the exemplary embodiments of the present invention are implemented as hardware or software, depending upon the particular application and design requirements of the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present embodiments.
The island detection method, device and system of the distributed power generation system provided by the invention are described in detail below with reference to specific embodiments:
(1) according to the maximum detection period 2s of the national regulation island detection, the number of the inverters 110 in the distributed power generation system is 4, the time interval threshold value is calculated to be 0.5s by workers according to the maximum detection period and the number of the inverters, and the preset time interval is also set to be 0.5s by the workers.
(2) The islanding detection device 200 sequentially sends pseudo-random disturbance signals to the inverter 110 according to a preset time interval, wherein the pseudo-random disturbance signals are current pseudo-random disturbance signals and are generated through a gaussian random function.
(3) When the inverter 110 receives the current pseudorandom disturbance signal, first, the current pseudorandom disturbance signal is added to the output current of the inverter 110 to obtain a disturbed output current, then, the inverter 110 obtains a voltage offset corresponding to the current pseudorandom disturbance signal according to the disturbed output current and the rated output current, and finally, the inverter 110 sends the voltage offset to the island detection device 200.
(4) After receiving the voltage offset returned by the inverter 110, the islanding detection device 200 compares the voltage offset with a preset offset threshold, and outputs a detection result that no islanding exists when the voltage offset is smaller than the preset offset threshold. At this time, the islanding detection device 200 continues to detect the next inverter 110, and if the inverter 110 is the last inverter, step (2) is performed.
(5) When the voltage offset is greater than or equal to the preset offset threshold, outputting a detection result of the island, and meanwhile, sending a disconnection instruction to the power generation device 120 in the distributed power generation system 100, and stopping feeding after the power generation device 120 receives the disconnection instruction.
(6) Island detection equipment 200 is carrying out island detection's in-process, acquires the skew total amount that a plurality of inverters incorporated into the power networks bus department in real time, when the skew total amount is great, will predetermine the time interval increase, at this moment, when the skew total amount continues to increase, then will predetermine the time interval and reduce, until the skew total amount is minimum, the electric energy quality is the best.
The invention has the beneficial effects that:
(1) the pseudo-random disturbance signal is adopted to carry out island detection on the distributed power generation system 100, so that the influence of the local load property on the offset in the existing island detection technology can be avoided, and meanwhile, the pseudo-random disturbance signal is sent at intervals, so that the offset can be effectively prevented from being mutually offset or superposed on the power line, and the island detection of the distributed power generation system with multiple inverters can be realized.
(2) When the distributed power generation system 100 is detected to have the island, the island detection equipment 200 sends a disconnection instruction to the power generation device 120, and the power supply is stopped after the power generation device 120 receives the disconnection instruction, so that the major safety accidents of power equipment, maintenance personnel and even a power grid caused by the power island can be effectively prevented, and the potential safety hazard is effectively inhibited.
(3) Through adjusting the preset time interval, the total amount of deviation is reduced, the power quality is improved, and safety accidents caused by poor power quality are prevented.
The above embodiments are provided to further explain the objects, technical solutions and advantages of the present invention in detail, it should be understood that the above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like, which are outside the spirit and principle of the present invention, should be included in the scope of the present invention.
Claims (9)
1. An island detection method of a distributed power generation system, wherein the distributed power generation system comprises a plurality of inverters, the island detection method comprising:
sending pseudo-random disturbance signals to the plurality of inverters in sequence according to a preset time interval, wherein the preset time interval is smaller than or equal to a time interval threshold, the time interval threshold is determined by a maximum detection period and the number of the inverters in the distributed power generation system, and the maximum detection period is the longest time for completing one island detection of all the inverters in the distributed power generation system;
receiving the offset returned by the inverter according to the received pseudo-random disturbing signal;
acquiring a preset offset threshold;
and outputting a detection result according to the offset and the preset offset threshold.
2. The islanding detection method of claim 1, wherein outputting the islanding detection result according to the offset and the preset offset threshold comprises:
judging whether the offset is greater than or equal to the preset offset threshold;
when the judgment result is yes, outputting a detection result of the island existence;
and when the judgment result is negative, outputting the detection result without island.
3. The islanding detection method according to claim 2, further comprising:
and when the detection result is that the island exists, sending a disconnection instruction to the power generation device in the distributed power generation system so as to stop feeding the power generation device.
4. The islanding detection method according to claim 1, further comprising:
acquiring the total offset amount of the grid-connected buses of the plurality of inverters;
and adjusting the preset time interval according to the total offset amount so as to reduce the total offset amount.
5. An island detection device of a distributed power generation system, the island detection device comprising:
the disturbance signal sending module is used for sequentially sending pseudo-random disturbance signals to a plurality of inverters in the distributed power generation system according to a preset time interval, wherein the preset time interval is smaller than or equal to a time interval threshold value, the time interval threshold value is determined by a maximum detection period and the number of the inverters in the distributed power generation system, and the maximum detection period is the longest time for all the inverters in the distributed power generation system to complete one-time island detection;
the offset receiving module is used for receiving the offset which is returned by the inverter and is determined according to the received pseudo-random disturbing signal;
the offset threshold acquisition module is used for acquiring a preset offset threshold;
and the result output module is used for outputting a detection result according to the offset and the preset offset threshold.
6. The islanding detection device of claim 5, wherein the result output module comprises:
the judging unit is used for judging whether the offset is greater than or equal to the preset offset threshold;
the first output unit is used for outputting the detection result of the island when the judgment result of the judgment unit is yes;
and the second output unit is used for outputting the detection result of the island when the judgment result of the judgment unit is negative.
7. The islanding detection device of claim 6, further comprising:
and the disconnection instruction sending module is used for sending a disconnection instruction to the power generation device in the distributed power generation system to stop feeding the power generation device when the detection result shows that the island exists.
8. The islanding detection device of claim 5, further comprising:
the offset total amount acquisition module is used for acquiring the offset total amount of the grid-connected buses of the inverters;
and the time interval adjusting module is used for adjusting the preset time interval according to the total offset amount so as to reduce the total offset amount.
9. An island detection system, characterized in that the island detection system comprises a distributed power generation system and an island detection device of the distributed power generation system according to any one of claims 5 to 8.
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