CN116299027A - Island detection method and device for distributed power supply - Google Patents
Island detection method and device for distributed power supply Download PDFInfo
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Abstract
The invention provides an island detection method and device of a distributed power supply, wherein the method comprises the following steps: acquiring three-phase voltage and current at a public connection position of a distributed power supply, and performing dq conversion of positive sequence and negative sequence on the three-phase voltage and current to obtain three-phase voltage and current under a dq coordinate system; injecting M% negative sequence current into the public connection part; calculating the voltage unbalance degree of the public connection part according to the three-phase voltage and current under the dq coordinate system; judging whether the voltage unbalance exceeds a first threshold value; if the voltage unbalance exceeds a first threshold, injecting N% negative sequence current into the public connection; calculating the voltage unbalance and the current unbalance of the common connection part; judging whether the voltage unbalance exceeds a second threshold value; if the voltage unbalance exceeds the second threshold value, judging whether the voltage unbalance is equal to the current unbalance; and if the voltage unbalance is equal to the current unbalance, confirming that the distributed power supply is in island operation.
Description
Technical Field
The invention relates to the technical field of island detection, in particular to an island detection method and an island detection device of a distributed power supply.
Background
With the rapid growth of world economy and the increasing level of living of people, the demand of human beings for energy is increasing, and the development of society and economy is often accompanied by the massive utilization and consumption of energy. In order to realize sustainable development of society and economy, the country is always accelerating optimization and adjustment of energy structures, and clean renewable energy sources are greatly developed. After the renewable energy source is generated, the renewable energy source is mainly connected into the power distribution network in the form of a distributed power source. In addition to the elimination of new energy sources, distributed power sources have many advantages: the distributed power supply can effectively perform peak clipping and valley leveling on the power grid, and has stronger flexibility; the distributed power supply is connected near the local load, so that loss caused by long-distance power transmission is avoided, and the distributed power supply has a good economical type; the distributed power supply can also improve the safety of the power system, and when unexpected disasters such as earthquake, typhoon, ice disaster, flood or artificial damage occur and the power grid collapses, the distributed power supply can continuously supply power to important users, so that the adverse effect caused by large-area power failure is reduced.
The distributed power supply operation mode is divided into grid-connected operation and island operation according to whether the distributed power supply operation mode is connected with a power distribution network or not. In normal conditions, the distributed power supply is connected with the power distribution network through PCC (Point of Common Coupling, public connection point) for operation, and the distributed power generation equipment and the power distribution network are combined to supply power to user electric equipment, namely grid-connected operation; when the power distribution network fails, the distributed power supply is disconnected from the electrical appliances of the power distribution network, the distributed power supply can independently supply power to users, the reliability of the power consumption of the users is improved, the operation can be stopped, and the damage of user equipment caused by insufficient capacity is avoided. Whether the distributed power supply continues to operate in island or not, the island state needs to be detected in time to decide whether to shut down the distributed power supply or switch the distributed power supply control mode from the grid-connected operation mode to the island operation mode. Therefore, the method for detecting the island of the distributed power supply in the power distribution network has strong engineering display significance.
Whether the distributed power supply operates in an island is always a hot spot for research at home and abroad can be effectively and timely judged, at present, island detection methods can be divided into two main types of remote monitoring detection and local detection, and the defects and shortages of the prior art are mainly expressed in the following aspects:
and firstly, the remote monitoring method utilizes communication signals between the power distribution network and the distributed power supply to judge whether the circuit breaker is opened or not. The carrier signal is sent by the power grid side, the receiver is arranged on the distributed power source side, the receiver judges whether island occurs according to the change of the carrier signal, the device has the advantages of NDZ (Non Detection Zone, no detection blind area), high detection accuracy, no interference to the normal operation of the power grid and the like, and the device has the defects of being required to be added, being complex in operation and low in economical efficiency.
And secondly, the local detection method does not need to add an additional transformer and other measuring equipment, and mainly relies on analyzing the electrical parameters of the distributed power supply side to judge whether island operation occurs. Local detection methods are classified into passive detection methods and active detection methods. The passive island detection method judges whether island occurs or not according to whether the voltage amplitude, frequency, harmonic wave, phase and the like exceed a given threshold value, has the advantages of good economy, simple principle and no influence on the electric energy quality, but the island detection time is long, the threshold value is difficult to set, and when the distributed power capacity is matched with a load, the electric quantity at the public connection point before and after the island is kept unchanged or changes little in the threshold value, the passive detection method cannot detect, and a larger detection blind area exists.
Third, for the active island detection method based on the positive feedback principle, since the three-phase system is balanced under the ideal condition of complete power matching, and negative sequence voltage and negative sequence power do not exist, positive feedback of the negative sequence voltage and the negative sequence power cannot occur, island detection relying on positive feedback of the negative sequence voltage and island detection relying on positive feedback of the negative sequence power will fail under such island detection blind areas. And then, considering the ideal condition that a filter connected with the inverter filters all high-frequency and low-frequency components, the inverter outputs ideal three-phase symmetrical sine waves, and positive feedback based on harmonic distortion rate cannot occur, so island detection by means of the positive feedback of the harmonic distortion rate also fails.
Disclosure of Invention
The invention provides a method and a device for detecting the island of a distributed power supply, which can improve the reliability of the island detection of the distributed power distribution network.
The technical scheme adopted by the invention is as follows:
an island detection method of a distributed power supply comprises the following steps: acquiring three-phase voltage and current at a public connection position of the distributed power supply, and performing dq conversion of positive sequence and negative sequence on the three-phase voltage and current to obtain three-phase voltage and current under a dq coordinate system; injecting M% negative sequence current into the public connection part, wherein M is more than 0 and less than or equal to 2; calculating the voltage unbalance degree of the public connection part according to the three-phase voltage and current in the dq coordinate system; judging whether the voltage unbalance exceeds a first threshold value; if the voltage unbalance exceeds the first threshold, injecting N% negative sequence current into the public connection part, wherein N is more than 2 and less than or equal to 4; calculating the voltage unbalance and the current unbalance of the public connection part; judging whether the voltage unbalance exceeds a second threshold value; if the voltage unbalance exceeds the second threshold value, judging whether the voltage unbalance is equal to the current unbalance or not; and if the voltage unbalance is equal to the current unbalance, confirming that the distributed power supply is in island operation.
The distributed power supply is connected to the power distribution network after being inverted into alternating current through a three-phase voltage type inverter, wherein the three-phase voltage type inverter adopts feedforward decoupling control.
The calculation formula of the voltage unbalance degree is as follows:
wherein U is - pcc For the negative sequence voltage, U + pcc Is the positive sequence voltage.
The calculation formula of the current unbalance degree is as follows:
wherein, the liquid crystal display device comprises a liquid crystal display device,I - pcc for the negative sequence current, I + pcc Is the positive sequence current.
When the distributed power supply performs island operation, the calculation formulas of the positive sequence voltage and the negative sequence voltage at the public connection part are as follows:
wherein Z is L Is the local load negative sequence impedance.
An islanding detection device of a distributed power supply, comprising: the acquisition module is used for acquiring three-phase voltage and current at a public connection position of the distributed power supply and performing dq conversion of positive sequence and negative sequence on the three-phase voltage and current to obtain three-phase voltage and current under a dq coordinate system; the first injection module is used for injecting M% negative sequence current to the public connection part, wherein M is more than 0 and less than or equal to 2; the first calculation module is used for calculating the voltage unbalance degree of the public connection part according to the three-phase voltage and current in the dq coordinate system; the first judging module is used for judging whether the voltage unbalance exceeds a first threshold value or not; the second injection module is used for injecting N% negative sequence current to the public connection part if the voltage unbalance exceeds the first threshold value, wherein N is more than 2 and less than or equal to 4; the second calculation module is used for calculating the voltage unbalance degree and the current unbalance degree of the public connection part; the second judging module is used for judging whether the voltage unbalance exceeds a second threshold value or not; a third judging module, configured to judge whether the voltage unbalance is equal to the current unbalance if the voltage unbalance exceeds the second threshold; and the confirmation module is used for confirming that the distributed power supply runs as an island if the voltage unbalance is equal to the current unbalance.
The distributed power supply is connected to the power distribution network after being inverted into alternating current through a three-phase voltage type inverter, wherein the three-phase voltage type inverter adopts feedforward decoupling control.
The calculation formula of the voltage unbalance degree is as follows:
wherein U is - pcc For the negative sequence voltage, U + pcc Is the positive sequence voltage.
The calculation formula of the current unbalance degree is as follows:
wherein I is - pcc For the negative sequence current, I + pcc Is the positive sequence current.
When the distributed power supply performs island operation, the calculation formulas of the positive sequence voltage and the negative sequence voltage at the public connection part are as follows:
wherein Z is L Is the local load negative sequence impedance.
The invention has the beneficial effects that:
according to the invention, the negative sequence current is injected into the public connection part and the voltage unbalance degree is judged, if the voltage unbalance degree exceeds the first threshold value, the negative sequence current is continuously injected into the public connection part and whether the voltage unbalance degree exceeds the second threshold value is judged, if the voltage unbalance degree exceeds the second threshold value, whether the voltage unbalance degree is equal to the current unbalance degree is continuously judged, and if the voltage unbalance degree exceeds the second threshold value, the distributed power supply is confirmed to operate as an island, so that the reliability of island detection of the distributed power distribution network can be improved.
Drawings
FIG. 1 is a flowchart of a method for detecting islanding of a distributed power supply according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a negative sequence network circuit according to an embodiment of the present invention;
FIG. 3 is a flow chart of a method for island detection of a distributed power supply according to an embodiment of the present invention;
fig. 4 is a block diagram of an island detection device of a distributed power supply according to an embodiment of the invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Fig. 1 is a flowchart of an island detection method of a distributed power supply according to an embodiment of the present invention.
As shown in fig. 1, the island detection method of the distributed power supply according to the embodiment of the invention includes the following steps:
s1, three-phase voltage and current at a public connection position of a distributed power supply are obtained, and dq conversion of positive sequence and negative sequence is carried out on the three-phase voltage and current to obtain the three-phase voltage and current under a dq coordinate system.
In one embodiment of the invention, the distributed power supply can be connected into the power distribution network after being inverted into alternating current through a three-phase voltage type inverter, wherein the three-phase voltage type inverter can adopt feedforward decoupling control to realize separate control of d-axis and q-axis components.
Specifically, firstly, three-phase voltage and current at a public connection position of a distributed power supply can be sampled by utilizing a voltage transformer and a current transformer, the three-phase voltage and current at the public connection position of the distributed power supply are obtained, positive sequence Park conversion is carried out on the three-phase voltage and current, positive sequence direct current and negative sequence double frequency quantity are obtained, then a filter is adopted to filter out the negative sequence double frequency quantity so as to obtain positive sequence direct current, and finally Park-Clarke conversion is carried out on the positive sequence direct current so as to obtain positive sequence direct current under a Clarke coordinate system, namely, dq component under a dq coordinate system. And similarly, carrying out negative sequence Park change on the three-phase voltage and current to obtain negative sequence direct current and positive sequence double frequency quantity, filtering the negative sequence double frequency quantity by adopting a filter for resisting to obtain negative sequence direct current, and finally carrying out Park-Clarke conversion on the negative sequence direct current to obtain negative sequence direct current under a Clarke coordinate system, namely the dq component under the dq coordinate system.
S2, injecting M% negative sequence current into the public connection part, wherein M is more than 0 and less than or equal to 2.
In one embodiment of the invention, 2% of the negative sequence current can be injected into the common junction by the inverter, and the negative sequence voltage at the common junction remains approximately 0 due to the large grid impedance.
And S3, calculating the voltage unbalance degree of the common connection part according to the three-phase voltage and the current under the dq coordinate system.
Specifically, after the positive and negative sequence Park change and Park-Clarke change, the positive and negative sequence quantity under Clarke transformation can be obtained. Taking three-phase voltage as an example, the positive sequence voltage can be obtained through positive and negative sequence Park change and Park-Clarke change
And->
Negative sequence voltage->
And->
Because the modulus value of the positive and negative sequence voltage space vector is respectively equal to the amplitude value of the positive and negative sequence three-phase voltage, and U under the alpha beta 0 coordinate system is obtained by Clarke equal amplitude conversion α And U β The resultant vector in space is the voltage space vector U ori . This can be achieved by:
thus, the voltage unbalance degree of the public connection part at any time can be calculated, namely:
wherein U is - pcc Is the negative sequence voltage of the common connection part, U + pcc Is the positive sequence voltage at the common junction.
S4, judging whether the voltage unbalance degree exceeds a first threshold value.
In one embodiment of the present invention, since the voltage unbalance degree at the common connection point does not exceed 2% for a long time when the distributed power supply is in grid-connected operation, the first threshold value may be set to 1%, and then it is determined whether the voltage unbalance degree exceeds the first threshold value.
S5, if the voltage unbalance exceeds a first threshold value, injecting N% negative sequence current into the public connection part, wherein N is more than 2 and less than or equal to 4.
In one embodiment of the invention, when the voltage imbalance exceeds a first threshold, 4% negative sequence current may be injected by the inverter into the common junction.
And S6, calculating the voltage unbalance degree and the current unbalance degree of the common connection.
In one embodiment of the present invention, the calculation formula for the current imbalance is known from the calculation formula for the voltage imbalance as follows:
wherein I is - pcc For the negative sequence current, I + pcc Is the positive sequence current.
S7, judging whether the voltage unbalance degree exceeds a second threshold value.
In one embodiment of the present invention, the second threshold may be set to 4% because the voltage imbalance at the common connection is no more than 2% for long periods of time and no more than 4% for short periods of time when the distributed power source is operating in grid-tie.
And S8, if the voltage unbalance exceeds a second threshold value, judging whether the voltage unbalance is equal to the current unbalance or not.
And S9, if the voltage unbalance is equal to the current unbalance, confirming that the distributed power supply is in island operation.
In one embodiment of the present invention, as shown in fig. 2, when the switch S is closed, i.e., the distributed power grid-connected operation, the negative sequence voltage at the common junction can be calculated by the following formula:
wherein Z is S(2) Is equivalent negative sequence impedance of the power distribution network, Z L(2) Is the local load negative sequence impedance.
Due to Z S(2) Far less than Z L(2) So U is PCC(2) The voltage of the positive sequence at the public connection is clamped by the power distribution network and is equal to the rated voltage of the power grid, so that the voltage unbalance degree is approximately 0 during grid-connected operation, and the current unbalance degree is far greater than the voltage unbalance degree. When the switch S is open, i.e. the distributed power island is running, the positive and negative sequence voltages at the common junction can be calculated using the following formula:
due to Z L(1) ＝Z L(2) The voltage imbalance during island operation is equal to the current imbalance.
As shown in fig. 3, in one embodiment of the present invention, the island detection method of the distributed power supply may include the following steps:
s201, three-phase voltage and current at a public connection position of the distributed power supply are obtained, and dq conversion of positive sequence and negative sequence is carried out on the three-phase voltage and current.
S202, 2% negative sequence current is injected into the public connection part.
And S203, calculating the voltage unbalance degree of the common connection.
S204, judging whether the voltage unbalance degree exceeds a first threshold value. If yes, step S205 is performed; otherwise, step S201 is performed.
S205, 4% negative sequence current is injected into the common connection.
S206, calculating the voltage unbalance degree and the current unbalance degree of the common connection.
S207, judging whether the voltage unbalance degree exceeds a second threshold value. If yes, go to step S208; otherwise, step S201 is performed.
S208, judging whether the voltage unbalance is equal to the current unbalance. If yes, go to step S209; otherwise, step S201 is performed.
S209, confirming island operation.
In summary, according to the method for operating the distributed power island according to the embodiment of the present invention, by injecting the negative sequence current into the public connection and determining the voltage unbalance, if the voltage unbalance exceeds the first threshold, then continuously injecting the negative sequence current into the public connection and determining whether the voltage unbalance exceeds the second threshold, if the voltage unbalance exceeds the second threshold, then continuously determining whether the voltage unbalance is equal to the current unbalance, and if so, confirming that the distributed power island is operated, thereby improving the reliability of the distributed power distribution network island detection.
In order to realize the distributed power island detection method of the embodiment, the invention also provides a distributed power island detection device.
Fig. 4 is a block diagram of a distributed power island detection apparatus according to an embodiment of the invention.
As shown in fig. 4, the distributed power island detection apparatus according to the embodiment of the present invention includes: the acquisition module 10, the first injection module 20, the first calculation module 30, the first determination module 40, the second injection module 50, the second calculation module 60, the second determination module 70, the third determination module 80, and the confirmation module 90. The acquisition module 10 is used for acquiring three-phase voltage and current at a public connection position of the distributed power supply, and performing dq conversion of positive sequence and negative sequence on the three-phase voltage and current to obtain the three-phase voltage and current under a dq coordinate system; the first injection module 20 is configured to inject an M% negative sequence current into the common junction, where M is greater than 0 and less than or equal to 2; the first calculation module 30 is configured to calculate a voltage imbalance at the common connection according to the three-phase voltages and currents in the dq coordinate system; the first determining module 40 is configured to determine whether the voltage imbalance exceeds a first threshold; the second injection module 50 is configured to inject an N% negative sequence current to the common connection if the voltage imbalance exceeds a first threshold, where N is greater than 2 and less than or equal to 4; the second calculation module 60 is used for calculating the voltage unbalance and the current unbalance at the common connection; the second determining module 70 is configured to determine whether the voltage imbalance exceeds a second threshold; the third judging module 80 is configured to judge whether the voltage unbalance is equal to the current unbalance if the voltage unbalance exceeds a second threshold; the confirmation module 90 is configured to confirm that the distributed power supply is operating in island if the voltage imbalance is equal to the current imbalance.
In one embodiment of the invention, the distributed power supply can be connected into the power distribution network after being inverted into alternating current through a three-phase voltage type inverter, wherein the three-phase voltage type inverter adopts feedforward decoupling control to realize separate control of d-axis and q-axis components.
Specifically, firstly, three-phase voltage and current at a public connection position of a distributed power supply can be sampled by utilizing a voltage transformer and a current transformer, the three-phase voltage and current at the public connection position of the distributed power supply are obtained, positive sequence Park conversion is carried out on the three-phase voltage and current, positive sequence direct current and negative sequence double frequency quantity are obtained, then a filter is adopted to filter out the negative sequence double frequency quantity so as to obtain positive sequence direct current, and finally Park-Clarke conversion is carried out on the positive sequence direct current so as to obtain positive sequence direct current under a Clarke coordinate system, namely, dq component under a dq coordinate system. And similarly, carrying out negative sequence Park change on the three-phase voltage and current to obtain negative sequence direct current and positive sequence double frequency quantity, filtering the negative sequence double frequency quantity by adopting a filter for resisting to obtain negative sequence direct current, and finally carrying out Park-Clarke conversion on the negative sequence direct current to obtain negative sequence direct current under a Clarke coordinate system, namely the dq component under the dq coordinate system.
In one embodiment of the present invention, the first injection module 10 may inject 2% of the negative sequence current into the common junction by the inverter, and the negative sequence voltage at the common junction remains approximately 0 due to the large grid impedance.
In one embodiment of the present invention, the first calculation module 30 obtains the positive sequence voltage through the positive and negative sequence Park change and Park-Clarke change
And->
Negative sequence voltage->
And->
Because the modulus value of the positive and negative sequence voltage space vector is respectively equal to the amplitude value of the positive and negative sequence three-phase voltage, and U under the alpha beta 0 coordinate system is obtained by Clarke equal amplitude conversion α And U β The resultant vector in spaceIs the voltage space vector U ori . This can be achieved by:
thus, the voltage unbalance degree of the public connection part at any time can be calculated, namely:
wherein U is - pcc Is the negative sequence voltage of the common connection part, U + pcc Is the positive sequence voltage at the common junction.
In one embodiment of the present invention, since the voltage unbalance at the common connection does not exceed 2% for a long time when the distributed power source is in grid-connected operation, the first threshold value may be set to 1%, and then the first judgment module 40 judges whether the voltage unbalance exceeds the first threshold value.
In one embodiment of the invention, when the voltage imbalance exceeds a first threshold, 4% negative sequence current may be injected by the inverter to the common connection through the second injection module 50.
In one embodiment of the present invention, the calculation formula for the current imbalance is known from the calculation formula for the voltage imbalance as follows:
wherein I is - pcc For the negative sequence current, I + pcc Is the positive sequence current.
According to the distributed power island operation method, the negative sequence current is injected into the public connection part and the voltage unbalance degree is judged, if the voltage unbalance degree exceeds the first threshold value, the negative sequence current is continuously injected into the public connection part and whether the voltage unbalance degree exceeds the second threshold value is judged, if the voltage unbalance degree exceeds the second threshold value, whether the voltage unbalance degree is equal to the current unbalance degree is continuously judged, and if the voltage unbalance degree exceeds the second threshold value, the distributed power island operation is confirmed, so that the reliability of the distributed power distribution network island detection can be improved.
In the description of the present invention, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. The meaning of "a plurality of" is two or more, unless specifically defined otherwise.
In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
In the present invention, unless expressly stated or limited otherwise, a first feature "up" or "down" a second feature may be the first and second features in direct contact, or the first and second features in indirect contact via an intervening medium. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily for the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and further implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.
Logic and/or steps represented in the flowcharts or otherwise described herein, e.g., a ordered listing of executable instructions for implementing logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). In addition, the computer readable medium may even be paper or other suitable medium on which the program is printed, as the program may be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory.
It is to be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above-described embodiments, the various steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, may be implemented using any one or combination of the following techniques, as is well known in the art: discrete logic circuits having logic gates for implementing logic functions on data signals, application specific integrated circuits having suitable combinational logic gates, programmable Gate Arrays (PGAs), field Programmable Gate Arrays (FPGAs), and the like.
Those of ordinary skill in the art will appreciate that all or a portion of the steps carried out in the method of the above-described embodiments may be implemented by a program to instruct related hardware, where the program may be stored in a computer readable storage medium, and where the program, when executed, includes one or a combination of the steps of the method embodiments.
In addition, each functional unit in the embodiments of the present invention may be integrated in one processing module, or each unit may exist alone physically, or two or more units may be integrated in one module. The integrated modules may be implemented in hardware or in software functional modules. The integrated modules may also be stored in a computer readable storage medium if implemented in the form of software functional modules and sold or used as a stand-alone product.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (10)
1. The island detection method of the distributed power supply is characterized by comprising the following steps of:
acquiring three-phase voltage and current at a public connection position of the distributed power supply, and performing dq conversion of positive sequence and negative sequence on the three-phase voltage and current to obtain three-phase voltage and current under a dq coordinate system;
injecting M% negative sequence current into the public connection part, wherein M is more than 0 and less than or equal to 2;
calculating the voltage unbalance degree of the public connection part according to the three-phase voltage and current in the dq coordinate system;
judging whether the voltage unbalance exceeds a first threshold value;
if the voltage unbalance exceeds the first threshold, injecting N% negative sequence current into the public connection part, wherein N is more than 2 and less than or equal to 4;
calculating the voltage unbalance and the current unbalance of the public connection part;
judging whether the voltage unbalance exceeds a second threshold value;
if the voltage unbalance exceeds the second threshold value, judging whether the voltage unbalance is equal to the current unbalance or not;
and if the voltage unbalance is equal to the current unbalance, confirming that the distributed power supply is in island operation.
2. The island detection method of a distributed power supply according to claim 1, wherein the distributed power supply is connected to a power distribution network after being inverted into alternating current by a three-phase voltage type inverter, and wherein the three-phase voltage type inverter adopts feedforward decoupling control.
3. The island detection method of a distributed power supply according to claim 2, wherein the calculation formula of the voltage unbalance is:
wherein U is - pcc For the negative sequence voltage, U + pcc Is the positive sequence voltage.
4. The island detection method of a distributed power supply according to claim 3, wherein the calculation formula of the current unbalance is:
wherein I is - pcc For the negative sequence current, I + pcc Is the positive sequence current.
5. The island detection method of a distributed power supply according to claim 4, wherein when the distributed power supply performs island operation, a calculation formula of the positive sequence voltage and the negative sequence voltage at the common connection is:
wherein Z is L Is the local load negative sequence impedance.
6. Island detection device of distributed power source, characterized by comprising:
the acquisition module is used for acquiring three-phase voltage and current at a public connection position of the distributed power supply and performing dq conversion of positive sequence and negative sequence on the three-phase voltage and current to obtain three-phase voltage and current under a dq coordinate system;
the first injection module is used for injecting M% negative sequence current to the public connection part, wherein M is more than 0 and less than or equal to 2;
the first calculation module is used for calculating the voltage unbalance degree of the public connection part according to the three-phase voltage and current in the dq coordinate system;
the first judging module is used for judging whether the voltage unbalance exceeds a first threshold value or not;
the second injection module is used for injecting N% negative sequence current to the public connection part if the voltage unbalance exceeds the first threshold value, wherein N is more than 2 and less than or equal to 4;
the second calculation module is used for calculating the voltage unbalance degree and the current unbalance degree of the public connection part;
the second judging module is used for judging whether the voltage unbalance exceeds a second threshold value or not;
a third judging module, configured to judge whether the voltage unbalance is equal to the current unbalance if the voltage unbalance exceeds the second threshold;
and the confirmation module is used for confirming that the distributed power supply runs as an island if the voltage unbalance is equal to the current unbalance.
7. The island detection device of a distributed power supply according to claim 6, wherein the distributed power supply is connected to a power distribution network after being inverted into ac by a three-phase voltage type inverter, and wherein the three-phase voltage type inverter adopts feedforward decoupling control.
8. The island detection device of a distributed power supply of claim 7, wherein the formula for calculating the voltage imbalance is:
wherein U is - pcc For the negative sequence voltage, U + pcc Is the positive sequence voltage.
9. The island detection device of a distributed power supply of claim 8, wherein the current imbalance is calculated by the formula:
wherein I is - pcc For the negative sequence current, I + pcc Is the positive sequence current.
10. The island detection device of a distributed power supply according to claim 9, wherein when the distributed power supply performs island operation, a calculation formula of the positive sequence voltage and the negative sequence voltage at the common connection is:
wherein Z is L Is the local load negative sequence impedance.
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