CN117175520A - Micro-grid current and voltage protection method and system adopting grid side short-circuit current constraint - Google Patents
Micro-grid current and voltage protection method and system adopting grid side short-circuit current constraint Download PDFInfo
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Abstract
The application discloses a micro-grid current and voltage protection method and system adopting grid side short-circuit current constraint, and the method is suitable for micro-grids containing high-proportion new energy sources. The current-limiting power electronic switch is arranged at the joint (PCC point) of the micro-grid and the large power grid, so that the large power grid provides certain short-circuit current for the micro-grid and the operation safety of power electronic equipment in the micro-grid is considered; according to the micro-grid current and voltage protection method, the current limiting type power electronic switch is arranged at the PCC point, so that the short-circuit current from the large power grid can be restrained to a certain extent, the relay protection characteristic quantity requirement is met, and meanwhile, the safety of power electronic devices inside the micro-grid can be ensured.
Description
Technical Field
The application relates to a micro-grid current and voltage protection method and system adopting grid side short-circuit current constraint, and belongs to the field of micro-grid relay protection.
Background
The method has important significance in the application of the electric power system by pushing new energy. In various aspects of improving the permeability of the distributed power supply, improving the power supply reliability, guaranteeing stable power supply in remote areas, meeting the power supply requirements of special power users and the like, the micro-grid has incomparable advantages of a large power grid, so that the micro-grid is increasingly favored by people.
However, the micro-grid has significant differences from the large grid in terms of network morphology, output characteristics, spatial characteristics, and the like, so that the conventional protection method applied to the large grid is difficult to directly apply in the micro-grid. After a short-circuit fault occurs in the micro-grid, the protection schemes of the existing micro-grid can be roughly divided into two types. One is to keep it in grid-tie mode, i.e. to keep the micro-grid and the large grid connected. By utilizing the amount of short-circuit current from the large power grid with obvious fault characteristics, the selective identification of internal faults of the micro power grid is realized, but the short-circuit current with high enough amplitude from the large power grid can pose a great threat to the operation safety of power electronic equipment in the micro power grid.
Another is to keep it in island mode, i.e. disconnect the micro-grid from the large grid. Because a large amount of new energy sources contained in the micro-grid generally keep amplitude limiting output after faults, which is generally 1.2-1.5 times of rated current, the short-circuit current after amplitude limiting can ensure the operation safety of power electronic equipment in the micro-grid, but can not provide enough obvious fault characteristic quantity for relay protection.
In addition, the micro-grid range is smaller, so that the electrical distance between the electrical devices is shorter, and further the short-circuit current change under faults between different points of the line is smaller, and therefore the current protection widely applied in the large-scale grid is difficult to continuously apply to the micro-grid.
Therefore, the significant differences between the micro-grid in terms of network morphology, operation mode, spatial characteristics and the like and the large grid make the traditional protection method applied to the large grid difficult to directly apply in the micro-grid. How to design a relay protection method aiming at a micro-grid is a difficult problem to be solved in the current micro-grid relay protection field, wherein the factors comprise the requirements of the micro-grid relay protection fault characteristics, the operation safety of internal power electronic equipment, the unique characteristics of the micro-grid and the like.
Disclosure of Invention
The application aims to provide a micro-grid current and voltage protection method and system adopting grid side short-circuit current constraint, wherein a current-limiting type power electronic switch is arranged at the joint of a large grid and the micro-grid, and a three-section type low-voltage protection method started by current quantity is arranged in the micro-grid by referring to a traditional three-section type overcurrent protection method, so that the selective removal of faults in the micro-grid and the running safety of the micro-grid can be realized, and the reliability of regional power supply can be effectively improved.
In order to achieve the above purpose, the application is realized by adopting the following technical scheme:
in a first aspect, the present application provides a method for protecting a micro-grid current and voltage using a grid-side short-circuit current constraint, based on a current-limiting power electronic switch provided at a junction of the micro-grid and a large grid, comprising:
collecting current at the joint of the micro power grid and the large power grid;
if the current at the joint of the micro power grid and the large power grid is smaller than the limiting value, the current-limiting power electronic switch is in a zero impedance state and does not act;
if the current at the joint of the micro-grid and the large grid is larger than the limiting value, the current-limiting power electronic switch is in a high-impedance state, enters a current-limiting state and restrains short-circuit current from the side of the grid.
Further, the limiting value is the maximum short-circuit current value limited to flow by the current-limiting type power electronic switch arranged at the PCC point, and is taken as 3-5 times of the rated current of the line.
Further, the method further comprises:
three-stage low-voltage protection is provided inside the micro-grid.
Further, three-stage low voltage protection is provided inside the micro-grid, including:
setting a three-section low-voltage protection fixed value;
and performing three-section type low-voltage protection based on the set three-section type low-voltage protection fixed value.
Further, the method for setting the three-section low-voltage protection fixed value comprises the following steps:
the operation voltage value of the low-voltage protection I section of the protection 1 must be smaller than the residual voltage at the bus A when the short circuit occurs on the bus B, and then the operation setting value of the low-voltage protection I section of the protection 1 is as follows
Wherein I is S Representing normal current transmitted by a large power grid to a micro power grid before failure; i 1 Indicating the normal current flowing through the protection 1 before the fault; k (k) 1 Representing the limiting multiple of the current-limiting power electronic switch arranged at the PCC point; k (k) 2 Representing the limiting multiple of the new energy power supply connected to the bus A after the fault; z is Z AB The full length impedance of the line between the buses A, B;the reliability matching coefficient of the I-stage protection is 1 for protection;
the low voltage protection II section of the protection 1 is matched with the low voltage protection I section of the next line, so that the action setting value of the low voltage protection II section of the protection 1The method comprises the following steps:
in the method, in the process of the application,the reliability matching coefficient for the protection of the low-voltage II section is 1; />Setting value for low voltage protection I section action of next line protection 2.
The low voltage III section protection of the protection 1 aims at overload setting, and the residual voltage at the bus A is required to be smaller than the maximum load, so that the low voltage III section protection action setting value of the protection 1The method comprises the following steps:
in the method, in the process of the application,the reliability matching coefficient of the protection of the section III for the protection 1 low voltage; i L.max Is an overload current that may occur on the line; z is Z BC The full length impedance of the line between the buses B, C; z is Z CD Is the full length impedance of the line between the bus bars C, D.
Further, the method comprises the steps of,
k 1 taking 3-5;
k 2 taking 1.2-1.5;
taking 0.8-0.9;
taking 0.8-0.9;
taking 0.8-0.9.
Further, based on the three-stage low voltage protection fixed value after setting, the three-stage low voltage protection is performed, including:
step A: measuring the current at the protection installation position to obtain a current measurement value;
and (B) step (B): if the current measured value is larger than the protection starting value, measuring the residual voltage of the bus, otherwise, jumping to the step A;
step C: if the residual voltage of the bus is smaller than the fixed value of the low-voltage I section protection action of the line, the short circuit fault is located in the low-voltage I section protection range of the line, and the corresponding protection action is performed; otherwise, the low-voltage I section protection of the local line does not act, and the step D is skipped.
Step D: if the residual voltage of the bus is smaller than the fixed value of the low-voltage section II protection of the line, starting timing of the low-voltage section II protection of the line; if the residual voltage of the bus rises to the vicinity of the rated value before the timing moment arrives, the step A is skipped; if the timing time arrives, the residual voltage of the bus is still smaller than the fixed value of the low-voltage section II protection of the line, and the fault is removed by the protection of the low-voltage section II of the line.
Step E: if the residual voltage of the bus is smaller than the low-voltage III section protection fixed value, starting timing; if the residual voltage of the bus is still lower after the timing time is reached, tripping; and (C) if the residual voltage of the bus is larger than the low-voltage III section protection fixed value before the timing time is reached, indicating that the fault or overload is disappeared, and returning to the step (A).
Further, the protection start value is set to be 1.2-1.5 times of the rated line current.
Furthermore, the III-section time delay is smaller than the II-section time delay, and the II-section time delay is smaller than the I-section time delay, so that sequential selective actions of low-voltage protection of different circuits are realized.
In a second aspect, the present application provides a micro-grid current-voltage protection system employing grid-side short-circuit current constraint, comprising:
a current limiting type power electronic switch arranged at the joint of the micro power grid and the large power grid;
the current-limiting power electronic switch is used for collecting current at the joint of the micro-grid and the large grid, if the current at the joint of the micro-grid and the large grid is smaller than a limiting value, the current-limiting power electronic switch is in a zero-impedance state and does not act, and if the current at the joint of the micro-grid and the large grid is larger than the limiting value, the current-limiting power electronic switch is in a high-impedance state, enters a current-limiting state and restrains short-circuit current from the side of the grid.
Compared with the prior art, the application has the beneficial effects that:
1. according to the micro-grid current and voltage protection method and system adopting the grid side short-circuit current constraint, the current-limiting type power electronic switch is arranged at the joint of the micro-grid and the large grid, so that the current-limiting type power electronic switch is in a zero-impedance state when normal so as not to influence normal exchange of power, and is in a high-impedance state when fault so as to achieve the purpose of constraining the short-circuit current from the grid side, and the running safety of power electronic equipment in the micro-grid and the relay protection characteristic quantity requirement of the micro-grid can be effectively considered.
2. Aiming at the micro-grid containing a large amount of new energy sources, the application provides a micro-grid current and voltage protection method adopting grid side short-circuit current constraint, and a three-section type low-voltage protection method is arranged inside the micro-grid by referring to the traditional three-section type overcurrent protection method. Aiming at the characteristic that the electrical distance between the electrical devices in the micro-grid is short, the voltage quantity with larger variation is used as the relay protection characteristic quantity, and the protection performance is effectively improved.
3. The micro-grid current and voltage protection method adopting the grid side short-circuit current constraint provided by the application is designed based on the inverter components contained in the new energy power supply, can be widely applied to micro-grids containing different new energy types, and has higher universality.
4. The micro-grid current and voltage protection method adopting the grid side short-circuit current constraint is suitable for micro-grids with high new energy occupation, and has important economic significance and civilian significance for guaranteeing the power supply reliability of remote areas (such as islands and remote mountain areas) powered by the micro-grids.
Drawings
FIG. 1 is a schematic illustration of a method and system for protecting a micro-grid current and voltage using grid side short circuit current constraints;
FIG. 2 is a flow chart illustrating the operation of a method and system for protecting a micro-grid current and voltage using grid side short circuit current constraints;
Detailed Description
The application will be explained in further detail below with reference to the drawings and the specific embodiments, but it should be understood that the scope of protection of the application is not limited to the specific embodiments.
Embodiment one:
the embodiment provides a micro-grid current and voltage protection method adopting grid side short-circuit current constraint, and a schematic illustration diagram of the micro-grid current and voltage protection method is shown in fig. 1. The micro-grid contains a high proportion of new energy power supply, is limited by the internal self-control characteristic, and has obvious nonlinear amplitude limiting characteristic after faults. In general, a micro-grid has two modes of grid-connected operation and island operation. After a line short-circuit fault occurs in the micro-grid, if the micro-grid is in a grid-connected operation mode, the short-circuit current with higher amplitude from the large power grid can meet the requirements of the micro-grid relay protection characteristic quantity, but the internal power electronic device is damaged easily; when the micro-grid is in the island operation mode, the short-circuit current is provided by an internal new energy power supply, the amplitude is smaller (usually only 1.2-1.5 times of rated current), the safety of power electronic devices can be ensured, but enough fault characteristic quantity cannot be provided to meet relay protection requirements.
According to the application, the current-limiting type power electronic switch is arranged at the joint (PCC point) of the micro-grid and the large grid, and the short-circuit current from the large grid is limited, so that the requirements of the relay protection characteristic quantity of the micro-grid and the operation safety of internal power electronic equipment are both realized. The current-limiting power electronic switch is normally in a zero-impedance state (so as not to influence the normal exchange of power), and is in a high-impedance state (so as to achieve the purpose of restraining short-circuit current from the power grid side) when in fault.
The general scope of the micro-grid is smaller, so that the electrical distance between the devices inside is shorter, the short-circuit current change under different faults of the dotted lines is smaller, and the selectivity of the protection action is difficult to ensure; and the residual voltage of the bus under different line faults has larger change, so that the fault positions can be effectively distinguished. The application refers to a traditional three-section type overcurrent protection method, and a three-section type low-voltage protection method is arranged in a micro-grid. Meanwhile, the increased current amount is adopted as a protection starting value, and the starting value can be set to be 1.2-1.5 times of the rated current of the line for the reliable starting of protection.
The application provides a micro-grid current and voltage protection method and system adopting grid side short-circuit current constraint, which are characterized in that a current-limiting type power electronic switch is arranged at the joint (PCC point) of a micro-grid and a large grid to constrain short-circuit current from the large grid.
Specifically, considering the requirements of the relay protection characteristic quantity of the micro-grid and the safety of power electronic equipment in the micro-grid, the limiting multiple of the current-limiting power electronic switch is set to be 3-5 times of the rated current of the line.
Specifically, referring to the three-stage overcurrent protection, a three-stage low voltage protection is provided inside the micro grid.
Specifically, the short-circuit current increased after short-circuit is used as the starting value of the three-stage low-voltage protection.
In particular, to ensure reliable start-up of the protection, the start-up value may be set to 1.2-1.5 times the line rated current.
Specifically, the setting method of the three-section type low-voltage protection of the micro-grid comprises the following steps:
as shown in FIG. 1, taking the protection 1 as an example, the operation voltage value of the low-voltage protection I section of the protection 1 must be smaller than the residual voltage at the bus A when the short circuit occurs on the bus B, and the operation setting value of the low-voltage protection I section of the protection 1 is that
Wherein I is S Representing normal current transmitted by a large power grid to a micro power grid before failure; i 1 Indicating the normal current flowing through the protection 1 before the fault; k (k) 1 Is shown inThe limiting multiple of the current-limiting power electronic switch set by the PCC point can be 3-5 (recommended value, and dynamically adjusted according to requirements during engineering application); k (k) 2 The limiting multiple of the new energy power supply connected to the bus A after the fault is indicated, and the limiting multiple can be generally 1.2-1.5; z is Z AB The full length impedance of the line between the buses A, B;for the reliability matching coefficient of the protection of the low-voltage I section 1, 0.8 to 0.9 is preferable;
the low voltage protection II section of the protection 1 is matched with the low voltage protection I section of the next line, so that the action setting value of the low voltage protection II section of the protection 1The method comprises the following steps:
in the method, in the process of the application,for the reliability matching coefficient of the protection of the low-voltage II section 1, 0.8 to 0.9 can be taken; />Setting value for low voltage protection I section action of next line protection 2.
The low voltage III section protection of the protection 1 aims at overload setting, and the residual voltage at the bus A is required to be smaller than the maximum load, so that the low voltage III section protection action setting value of the protection 1The method comprises the following steps:
in the method, in the process of the application,reliable mating system for protection of protection 1 low voltage III segmentThe number is 0.8-0.9; i L.max Is an overload current that may occur on the line; z is Z BC The full length impedance of the line between the buses B, C; z is Z CD Is the full length impedance of the line between the bus bars C, D.
Specifically, after the protection is started, the bus voltage is detected, and when the residual bus voltage is smaller than the setting value set by the low-voltage protection, each section of protection selectively acts through corresponding delay.
Specifically, the three-stage low-voltage protection action includes the following steps:
if the residual voltage of the bus is smaller than the fixed value of the low-voltage I section protection action of the line, the short circuit fault is located in the low-voltage I section protection range of the line, and the corresponding protection action is performed; otherwise, the low-voltage I section of the local line is protected from action.
If the residual voltage of the bus is smaller than the fixed value of the low-voltage section II protection of the line, starting timing of the low-voltage section II protection of the line; if the timing moment arrives, the residual voltage of the bus is increased to be near the rated value, which indicates that the fault occurs on the next line and the fault is protected and cut off by the low-voltage I section of the next line; if the timing time arrives, the residual voltage of the bus is still smaller than the fixed value of the low-voltage section II protection of the line, which indicates that the fault occurs in the line or the next line protection refuses to act, so that the fault is removed by the low-voltage section II protection of the line, and the full-line protection of the line and the backup protection of the next line outlet are realized.
The low-voltage I section protection and the low-voltage II section protection of all the circuits sequentially form a complete protection range.
In addition, a low voltage III-section protection is required. If the residual voltage of the bus is smaller than the low-voltage III section protection fixed value, starting timing; if the residual voltage of the bus is still lower after the timing time is reached, indicating that the fault or overload still exists, and tripping the bus; and if the residual voltage of the bus is larger than the low-voltage III section protection fixed value before the timing time is reached, indicating that the fault or overload is disappeared, returning. In addition, because the nonlinearity of the power supply is stronger, the fixed value difference of the low-voltage III-section protection action of each line is not large, different delay time can be adopted at the moment, namely the delay time of the next line is smaller than the delay time deltat of the last line, and the sequential selective action of the low-voltage III-section protection of different lines is realized.
Referring to three-section type overcurrent protection, three-section type low-voltage protection is arranged inside a micro-grid; using the increased short-circuit current as a starting value of the low-voltage protection of the micro-grid; after the protection is started, three-section low-voltage protection is matched in sequence through corresponding time delay, and faults are selectively removed. With reference to the three-section type overcurrent protection, the three-section type low-voltage protection is arranged in the micro-grid, so that the selective fault removal can be effectively realized according to the characteristic that the electric distance between devices in the micro-grid is short, and the running safety of the micro-grid and the reliable power supply of the area are ensured.
Embodiment two:
the embodiment provides a micro-grid current-voltage protection system adopting grid side short-circuit current constraint, which comprises:
a current limiting type power electronic switch arranged at the joint of the micro power grid and the large power grid; the current-limiting power electronic switch is normally in a zero-impedance state (so as not to influence the normal exchange of power), and is in a high-impedance state (so as to achieve the purpose of restraining short-circuit current from the power grid side) when in fault.
The current-limiting power electronic switch is used for collecting current at the joint of the micro-grid and the large grid, if the current at the joint of the micro-grid and the large grid is smaller than a limiting value, the current-limiting power electronic switch is in a zero-impedance state and does not act, and if the current at the joint of the micro-grid and the large grid is larger than the limiting value, the current-limiting power electronic switch is in a high-impedance state, enters a current-limiting state and restrains short-circuit current from the side of the grid.
According to the application, the current-limiting type power electronic switch is arranged at the joint (PCC point) of the micro-grid and the large grid, and the short-circuit current from the large grid is limited, so that the requirements of the relay protection characteristic quantity of the micro-grid and the operation safety of internal power electronic equipment are both realized.
The system also includes a three-segment low voltage protection provided inside the microgrid with reference to the three-segment over-current protection.
Specifically, the three-stage low-voltage protection action includes the following steps:
if the residual voltage of the bus is smaller than the fixed value of the low-voltage I section protection action of the line, the short circuit fault is located in the low-voltage I section protection range of the line, and the corresponding protection action is performed; otherwise, the low-voltage I section of the local line is protected from action.
If the residual voltage of the bus is smaller than the fixed value of the low-voltage section II protection of the line, starting timing of the low-voltage section II protection of the line; if the timing moment arrives, the residual voltage of the bus is increased to be near the rated value, which indicates that the fault occurs on the next line and the fault is protected and cut off by the low-voltage I section of the next line; if the timing time arrives, the residual voltage of the bus is still smaller than the fixed value of the low-voltage section II protection of the line, which indicates that the fault occurs in the line or the next line protection refuses to act, so that the fault is removed by the low-voltage section II protection of the line, and the full-line protection of the line and the backup protection of the next line outlet are realized.
The low-voltage I section protection and the low-voltage II section protection of all the circuits sequentially form a complete protection range.
In addition, a low voltage III-section protection is required. If the residual voltage of the bus is smaller than the low-voltage III section protection fixed value, starting timing; if the residual voltage of the bus is still lower after the timing time is reached, indicating that the fault or overload still exists, and tripping the bus; and if the residual voltage of the bus is larger than the low-voltage III section protection fixed value before the timing time is reached, indicating that the fault or overload is disappeared, returning. In addition, because the nonlinearity of the power supply is stronger, the fixed value difference of the low-voltage III-section protection action of each line is not large, different delay time can be adopted at the moment, namely the delay time of the next line is smaller than the delay time deltat of the last line, and the sequential selective action of the low-voltage III-section protection of different lines is realized.
The general scope of the micro-grid is smaller, so that the electrical distance between the devices inside is shorter, the short-circuit current change under different faults of the dotted lines is smaller, and the selectivity of the protection action is difficult to ensure; and the residual voltage of the bus under different line faults has larger change, so that the fault positions can be effectively distinguished. The application refers to a traditional three-section type overcurrent protection method, and a three-section type low-voltage protection method is arranged in a micro-grid. Meanwhile, the increased current amount is adopted as a protection starting value, and the starting value can be set to be 1.2-1.5 times of the rated current of the line for the reliable starting of protection.
The application provides a micro-grid current and voltage protection method and system adopting grid side short-circuit current constraint, which are characterized in that a current-limiting type power electronic switch is arranged at the joint (PCC point) of a micro-grid and a large grid to constrain short-circuit current from the large grid.
Specifically, considering the requirements of the relay protection characteristic quantity of the micro-grid and the safety of power electronic equipment in the micro-grid, the limiting multiple of the current-limiting power electronic switch is set to be 3-5 times of the rated current of the line.
Specifically, referring to the three-stage overcurrent protection, a three-stage low voltage protection is provided inside the micro grid.
Specifically, the short-circuit current increased after short-circuit is used as the starting value of the three-stage low-voltage protection.
In particular, to ensure reliable start-up of the protection, the start-up value may be set to 1.2-1.5 times the line rated current.
Specifically, the setting method of the three-section type low-voltage protection of the micro-grid comprises the following steps:
as shown in FIG. 1, taking the protection 1 as an example, the operation voltage value of the low-voltage protection I section of the protection 1 must be smaller than the residual voltage at the bus A when the short circuit occurs on the bus B, and the operation setting value of the low-voltage protection I section of the protection 1 is that
Wherein I is S Representing normal current transmitted by a large power grid to a micro power grid before failure; i 1 Indicating the normal current flowing through the protection 1 before the fault; k (k) 1 The limiting multiple of the current-limiting power electronic switch arranged at the PCC point can be 3-5 (recommended value, according to requirements in engineering applicationTo be dynamically adjusted); k (k) 2 The limiting multiple of the new energy power supply connected to the bus A after the fault is indicated, and the limiting multiple can be generally 1.2-1.5; z is Z AB The full length impedance of the line between the buses A, B;for the reliability matching coefficient of the protection of the low-voltage I section 1, 0.8 to 0.9 is preferable;
the low voltage protection II section of the protection 1 is matched with the low voltage protection I section of the next line, so that the action setting value of the low voltage protection II section of the protection 1The method comprises the following steps:
in the method, in the process of the application,for the reliability matching coefficient of the protection of the low-voltage II section 1, 0.8 to 0.9 can be taken; />Setting value for low voltage protection I section action of next line protection 2.
The low voltage III section protection of the protection 1 aims at overload setting, and the residual voltage at the bus A is required to be smaller than the maximum load, so that the low voltage III section protection action setting value of the protection 1The method comprises the following steps:
in the method, in the process of the application,for the reliability matching coefficient of the protection 1 low-voltage III section, 0.8 to 0.9 can be taken; i L.max Is an overload current that may occur on the line; z is Z BC Is a bus barB. The overall impedance of the line between C; z is Z CD Is the full length impedance of the line between the bus bars C, D.
Specifically, after the protection is started, the bus voltage is detected, and when the residual bus voltage is smaller than the setting value set by the low-voltage protection, each section of protection selectively acts through corresponding delay.
In the description of the present application, it should be understood that the terms "center," "longitudinal," "lateral," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, merely to facilitate description of the present application and simplify the description, and do not indicate or imply that the device or element being referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the protection of the present application.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The foregoing is merely a preferred embodiment of the present application, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present application, and such modifications and variations should also be regarded as being within the scope of the application.
Claims (10)
1. A micro-grid current-voltage protection method and system adopting grid side short-circuit current constraint are characterized by comprising the following steps of:
collecting current at the joint of the micro power grid and the large power grid;
if the current at the joint of the micro power grid and the large power grid is smaller than the limiting value, the current-limiting power electronic switch is in a zero impedance state and does not act;
if the current at the joint of the micro-grid and the large grid is larger than the limiting value, the current-limiting power electronic switch is in a high-impedance state, enters a current-limiting state and restrains short-circuit current from the side of the grid.
2. The method for protecting a micro-grid current and voltage by adopting grid side short-circuit current constraint according to claim 1, wherein the limiting value is a maximum short-circuit current value limited to flow by a current-limiting power electronic switch arranged at a PCC point, and the maximum short-circuit current value is taken as 3-5 times of a rated line current.
3. The method of protecting a micro-grid current from voltage using grid-side short-circuit current constraints of claim 1, further comprising:
three-stage low-voltage protection is provided inside the micro-grid.
4. A method of protecting a microgrid current and voltage using a grid side short circuit current constraint according to claim 3, wherein a three-stage low voltage protection is provided inside the microgrid, comprising:
setting a three-section low-voltage protection fixed value;
and performing three-section type low-voltage protection based on the set three-section type low-voltage protection fixed value.
5. The method for protecting a micro-grid current and voltage by adopting grid-side short-circuit current constraint according to claim 4, wherein the method for setting the three-stage low-voltage protection fixed value is as follows:
the operation voltage value of the low-voltage protection I section of the protection 1 must be smaller than the residual voltage at the bus A when the short circuit occurs on the bus B, and then the operation setting value of the low-voltage protection I section of the protection 1 is as follows
Wherein I is S Representing normal current transmitted by a large power grid to a micro power grid before failure; i 1 Indicating the normal current flowing through the protection 1 before the fault; k (k) 1 Representing the limiting multiple of the current-limiting power electronic switch arranged at the PCC point; k (k) 2 Representing the limiting multiple of the new energy power supply connected to the bus A after the fault; z is Z AB The full length impedance of the line between the buses A, B;the reliability matching coefficient of the I-stage protection is 1 for protection;
the low voltage protection II section of the protection 1 is matched with the low voltage protection I section of the next line, so that the action setting value of the low voltage protection II section of the protection 1The method comprises the following steps:
in the method, in the process of the application,the reliability matching coefficient for the protection of the low-voltage II section is 1; />Setting value for low-voltage protection I section action of the next line protection 2;
the low voltage III section protection of the protection 1 aims at overload setting, and the residual voltage at the bus A is required to be smaller than the maximum load, so that the low voltage III section protection action setting value of the protection 1The method comprises the following steps:
in the method, in the process of the application,the reliability matching coefficient of the protection of the section III for the protection 1 low voltage; i L.max Is an overload current that may occur on the line; z is Z BC The full length impedance of the line between the buses B, C; z is Z CD Is the full length impedance of the line between the bus bars C, D.
6. The method for protecting a micro-grid current and voltage using a grid-side short-circuit current constraint according to claim 5, wherein,
k 1 taking 3-5;
k 2 taking 1.2-1.5;
taking 0.8-0.9;
taking 0.8-0.9;
taking 0.8-0.9.
7. The method for protecting a micro-grid current and voltage using a grid-side short-circuit current constraint according to claim 5, wherein the performing the three-stage low-voltage protection based on the set three-stage low-voltage protection fixed value comprises:
step A: measuring the current at the protection installation position to obtain a current measurement value;
and (B) step (B): if the current measured value is larger than the protection starting value, measuring the residual voltage of the bus, otherwise, jumping to the step A;
step C: if the residual voltage of the bus is smaller than the fixed value of the low-voltage I section protection action of the line, the short circuit fault is located in the low-voltage I section protection range of the line, and the corresponding protection action is performed; otherwise, the low-voltage I section protection of the local line does not act, and the step D is skipped;
step D: if the residual voltage of the bus is smaller than the fixed value of the low-voltage section II protection of the line, starting timing of the low-voltage section II protection of the line; if the residual voltage of the bus rises to the vicinity of the rated value before the timing moment arrives, the step A is skipped; if the timing time arrives, the residual voltage of the bus is still smaller than the protection fixed value of the low-voltage section II of the line, and the fault is removed by the protection of the low-voltage section II of the line;
step E: if the residual voltage of the bus is smaller than the low-voltage III section protection fixed value, starting timing; if the residual voltage of the bus is still lower after the timing time is reached, tripping; and (C) if the residual voltage of the bus is larger than the low-voltage III section protection fixed value before the timing time is reached, indicating that the fault or overload is disappeared, and returning to the step (A).
8. The method for protecting a micro-grid current and voltage using a grid-side short-circuit current constraint according to claim 7, wherein the protection start value is set to be 1.2-1.5 times the rated line current.
9. The micro-grid current and voltage protection method adopting grid side short-circuit current constraint according to claim 8, wherein the III-stage delay time is smaller than the II-stage delay time, the II-stage delay time is smaller than the I-stage delay time, and sequential selective actions of different line low-voltage protection are realized.
10. A micro-grid current-voltage protection system employing grid-side short-circuit current constraint, comprising:
a current limiting type power electronic switch arranged at the joint of the micro power grid and the large power grid;
the current-limiting power electronic switch is used for collecting current at the joint of the micro-grid and the large grid, if the current at the joint of the micro-grid and the large grid is smaller than a limiting value, the current-limiting power electronic switch is in a zero-impedance state and does not act, and if the current at the joint of the micro-grid and the large grid is larger than the limiting value, the current-limiting power electronic switch is in a high-impedance state, enters a current-limiting state and restrains short-circuit current from the side of the grid.
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