CN112152190B - Micro-grid interphase short-circuit fault protection method and system - Google Patents
Micro-grid interphase short-circuit fault protection method and system Download PDFInfo
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- 238000004364 calculation method Methods 0.000 claims description 32
- 238000000605 extraction Methods 0.000 claims description 7
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- 238000004146 energy storage Methods 0.000 description 24
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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Abstract
Provided are a micro-grid interphase short-circuit fault protection method and system, the micro-grid interphase short-circuit fault protection method may include: for a micro-grid with a neutral point not grounded, which is operated in an island mode, calculating a negative sequence voltage component and a negative sequence current component of a branch in the micro-grid; calculating the negative sequence active power of the branch according to the negative sequence voltage component and the negative sequence current component of the branch; and determining whether interphase short circuit faults occur to the branch circuit according to the polarity of the negative sequence active power of the branch circuit, wherein the micro-grid is a medium-voltage micro-grid or a low-voltage micro-grid.
Description
Technical Field
The invention relates to the field of micro-grid protection of power systems, in particular to a micro-grid interphase short-circuit fault protection method and system.
Background
The micro-grid is a small power generation and distribution system composed of a distributed power supply, an energy storage device, a load, an energy conversion device and the like.
The proposal of the micro-grid aims to realize flexible and efficient application of the distributed power supply and solve the problem of grid connection of the distributed power supply with huge quantity and various forms. After the micro-grid is connected into the power distribution network and has short-circuit faults in a grid-connected operation mode, the fault current of the micro-grid is larger because of the short-circuit current provided by the large power grid, so that the fault protection can be carried out by adopting the conventional three-section current protection and utilizing the conventional means such as directional elements. However, when the micro grid is operated in the island mode or the micro grid is an independent micro grid, after the micro grid has a short-circuit fault, the short-circuit current of the micro grid is mainly provided by various distributed power sources inside the micro grid, and the distributed power sources inside the micro grid are mainly classified into a converter type, a synchronous motor type, and an asynchronous motor type according to interface classification. The three types of distributed power supplies have different contributions to the short-circuit current, and the maximum output current of the converter type distributed power supply is not more than 2 times of the rated current due to the limitation of power electronic devices. Therefore, the conventional three-stage current protection means may fail in the micro grid island mode.
Accordingly, there is a need to cope with various faults including an inter-phase short circuit fault occurring in a micro grid operating in an island mode with a new protection method.
Disclosure of Invention
In order to at least solve the problems in the prior art, the invention provides a micro-grid interphase short-circuit fault protection method and system.
An aspect of the present invention provides a method for protecting a micro-grid interphase short-circuit fault, including: for a micro-grid with a neutral point not grounded, which is operated in an island mode, calculating a negative sequence voltage component and a negative sequence current component of a branch in the micro-grid; calculating the negative sequence active power of the branch according to the negative sequence voltage component and the negative sequence current component of the branch; and determining whether interphase short circuit faults occur to the branch circuit according to the polarity of the negative sequence active power of the branch circuit, wherein the micro-grid is a medium-voltage micro-grid or a low-voltage micro-grid.
The step of calculating the negative sequence voltage component and the negative sequence current component of the branch may comprise: the negative sequence voltage alpha component v_alpha, the negative sequence voltage beta component v_beta, the negative sequence current alpha component i_alpha and the negative sequence current beta component i_beta of the branch are calculated through a positive and negative sequence extraction method based on a generalized second-order integrator.
The step of calculating the negative sequence active power of the branch may comprise: the negative-sequence active power p of the branch is calculated according to the following equation:
p＝(v_α×i_α+v_β×i_β)×1.5。
the step of determining whether the branch has an interphase short circuit fault may include: if the polarity of the negative sequence active power of the branch is positive, determining that the branch has low possibility of inter-phase short circuit fault occurrence; and if the polarity of the negative sequence active power of the branch is negative, determining that the branch has a high possibility of inter-phase short circuit fault occurrence.
The micro-grid interphase short-circuit fault protection method can further comprise the following steps: when it is determined that the branch has a high possibility of occurrence of an inter-phase short-circuit fault, the following operations are performed: directly determining that an inter-phase short-circuit fault occurs in a branch having a high possibility of occurrence of the inter-phase short-circuit fault; alternatively, the negative-sequence reactive power of the branch having a high possibility of occurrence of the inter-phase short-circuit fault is calculated, and if the polarity of the calculated negative-sequence reactive power of the branch is negative, it is determined that the inter-phase short-circuit fault has occurred in the branch.
The negative sequence reactive power q of the branch is calculated according to the following equation:
q＝(v_β×i_α－v_α×i_β)×1.5。
the micro-grid interphase short-circuit fault protection method can further comprise the following steps: and when the interphase short-circuit fault occurs to the branch circuit, cutting off the branch circuit with the interphase short-circuit fault.
Another aspect of the present invention provides a micro-grid interphase short-circuit fault protection system, including: the computing unit is used for computing a negative sequence voltage component and a negative sequence current component of a branch in the micro-grid aiming at the micro-grid with a neutral point which is not grounded and running in an island mode, and computing the negative sequence active power of the branch according to the negative sequence voltage component and the negative sequence current component of the branch; and the fault determining unit is used for determining whether interphase short circuit faults occur to the branch circuit according to the polarity of the negative sequence active power of the branch circuit, wherein the micro-grid is a medium-voltage micro-grid or a low-voltage micro-grid.
The calculation unit may calculate the negative sequence voltage α component v_α, the negative sequence voltage β component v_β, the negative sequence current α component i_α, and the negative sequence current β component i_β of the branch by a positive and negative sequence extraction method based on a generalized second-order integrator.
The calculation unit may calculate the negative-sequence active power p of the branch according to the following equation:
p＝(v_α×i_α+v_β×i_β)×1.5。
the fault determination unit may determine that the branch has a low possibility of occurrence of an inter-phase short fault if the polarity of the negative sequence active power of the branch is positive; and if the polarity of the negative-sequence active power of the branch is negative, the fault determination unit may determine that the branch has a high possibility of occurrence of an inter-phase short fault.
When it is determined that the branch has a high possibility of occurrence of an inter-phase short-circuit fault: the fault determining unit may directly determine that an inter-phase short fault has occurred in a branch having a high possibility of an inter-phase short fault, or the calculating unit may calculate negative-sequence reactive power of the determined branch having a high possibility of an inter-phase short fault, and if the polarity of the calculated negative-sequence reactive power of the branch is negative, the fault determining unit may determine that an inter-phase short fault has occurred in the branch.
The calculation unit may calculate the negative sequence reactive power q of the branch according to the following equation:
q＝(v_β×i_α－v_α×i_β)×1.5。
the micro-grid interphase short-circuit fault protection system may further include: and the fault processing unit is used for cutting off the branch circuit with the interphase short circuit fault when determining that the branch circuit has the interphase short circuit fault.
The number of the calculation units, the number of the fault determination units, and the number of the fault handling units may be the same as the number of branches in the micro grid, and each branch may correspond to one calculation unit, one fault determination unit, and one fault handling unit.
Alternatively, the number of the calculation units, the number of the failure determination units, and the number of the failure processing units may be 1.
An aspect of the present invention is to provide a computer-readable storage medium storing a program including instructions for executing the above-described micro grid inter-phase short-circuit fault protection method.
An aspect of the present invention is to provide a computer comprising a readable medium storing a computer program comprising instructions for performing the above-described micro grid inter-phase short circuit fault protection method.
Drawings
A full understanding of the present invention will be gained by a study of the following detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings in which:
FIG. 1 shows a microgrid topology operating in island mode;
fig. 2 is a flowchart illustrating a micro grid interphase short-circuit fault protection method according to an exemplary embodiment of the present invention;
FIG. 3 shows a block diagram of a generalized second order integrator;
fig. 4 is a block diagram illustrating a micro grid interphase short-circuit fault protection system according to an exemplary embodiment of the present invention.
Fig. 5 to 7 are negative sequence power waveforms of the energy storage branch, the load branch and the photovoltaic branch, respectively, when the energy storage branch in the discharging mode suffers from an inter-phase short circuit fault;
fig. 8 to 10 are negative sequence power waveforms of the energy storage branch, the load branch and the photovoltaic branch, respectively, when the energy storage branch in the charging mode suffers from an inter-phase short circuit fault;
FIGS. 11-13 are negative sequence power waveforms of the load branch, the energy storage branch, and the photovoltaic branch, respectively, when an inter-phase short circuit fault occurs in the load branch;
fig. 14-16 are negative sequence power waveforms of the photovoltaic branch, the energy storage branch, and the load branch, respectively, when an inter-phase short circuit fault occurs in the photovoltaic branch.
Detailed Description
Reference will now be made in detail to the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments will be described below in order to explain the present invention by referring to the figures. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present disclosure.
Prior to the detailed description, technical terms involved in the present disclosure are described to facilitate understanding of the specific content of the present disclosure:
equivalent network: when a short circuit occurs in the power system, a set of asymmetric electromotive forces are generated, and each phase potential of the electromotive forces is equal to each phase asymmetric voltage in magnitude and opposite in direction, which is equivalent to the occurrence of an asymmetric fault. When an asymmetric fault occurs in the network, a group of asymmetric potential sources can be connected to the fault point to replace the asymmetric electromotive force generated after the asymmetric fault occurs, and the group of asymmetric potential sources can be decomposed into three groups of symmetric components of positive sequence, negative sequence and zero sequence, so that an equivalent network can be obtained.
Interphase short circuit: a short circuit between the two phases;
three-phase short circuit: short circuit among the three phases;
medium voltage microgrid: a micro grid at 6-35 kV;
forward and reverse faults: as seen from the protective installation, a fault occurring in the direction of the "bus-bar-to-line" is called a forward fault, and vice versa.
The present invention will be described in the following description taking a medium voltage micro grid of 10kV, the neutral point of which is not grounded, as an example, but the present invention is not limited thereto, and the present invention may be applied to medium voltage micro grids of other voltage levels, the neutral point of which is not grounded, and may also be generalized to low voltage micro grids (e.g., 400v low voltage micro grids).
Fig. 1 shows a topology diagram of a micro-grid operating in island mode.
As shown in fig. 1, the micro-grid is a radiating topology that includes three branches, i.e., a load branch, an energy storage branch, and a photovoltaic branch, and a common connection point between the micro-grid and a large grid is in an off state, so the micro-grid operates in an island mode.
When an inter-phase short circuit occurs in the micro grid, a negative sequence voltage and a negative sequence current can occur in the micro grid. A micro grid interphase short-circuit fault protection method according to an exemplary embodiment of the present invention will be described in detail with reference to fig. 2.
Fig. 2 is a flowchart illustrating a micro grid interphase short-circuit fault protection method according to an exemplary embodiment of the present invention.
As shown in fig. 2, in step S100, for a micro grid in which a neutral point operating in an island mode is not grounded, a negative sequence voltage component and a negative sequence current component of a branch in the micro grid are calculated.
Specifically, the negative sequence voltage alpha component v_alpha, the negative sequence voltage beta component v_beta, the negative sequence current alpha component i_alpha and the negative sequence current beta component i_beta of the branch are calculated by a positive and negative sequence extraction method based on a generalized second-order integrator. Specifically, in the case where the micro grid as shown in fig. 1 includes three branches, a negative sequence voltage α component v_α, a negative sequence voltage β component v_β, a negative sequence current α component i_α, and a negative sequence current β component i_β are calculated for each of the three branches, respectively. This calculation process will be described in detail with reference to fig. 3.
FIG. 3 shows a block diagram of a generalized second order integrator, where v represents the input signal; k represents a gain coefficient; omega 0 Is undamped natural frequency; e and e q All represent the output signals of the second-order generalized integrator, the phases of the two signals differ by 90 degrees, e q The phase lags e by 90 °. Since the calculation process of the negative sequence voltage and the negative sequence current of each branch are the same, the load branch is taken as an example for explanation.
First, three instantaneous values in the abc coordinate system are transformed into the αβ0 coordinate system by Clark transformation.
Then, the negative sequence voltage alpha component v_alpha is taken as the input signal v of the second-order generalized integrator, and the output signals e and e are taken as the output signals q Respectively defined as D α 、Q α Wherein Q is α Phase lag D α Phase 90 deg..
Then, the negative sequence voltage beta component v_beta is taken as the input signal v of the second-order generalized integrator, and signals e and e are output q Respectively defined as D β 、Q β Wherein Q is β Phase lag D β Phase 90 deg..
Thereafter, negative sequence voltage α components v_α and β components v_β are obtained by a positive-negative sequence extraction method according to the following equations (1) and (2):
v_α＝0.5D α +0.5Q β (1)
v_β＝-0.5Q α +0.5D β (2)
in addition, the calculation equations of the negative sequence current α component i_α and the negative sequence current β component i_β are the same as those of the negative sequence voltage α component v_α and the negative sequence voltage β component v_β, and only the negative sequence current α component i_α and the negative sequence current β component i_β need be used as the input signal v of the second-order generalized integrator, respectively, and therefore, a repetitive description is not made here.
The negative sequence voltage component and the negative sequence current component of the branch may be obtained through step S100, after which the negative sequence active power of the branch is calculated from the negative sequence voltage component and the negative sequence current component of the branch in step S200. Since the calculation process of the negative sequence active power of each branch is the same, the load branch is taken as an example for the following description.
Specifically, the negative-sequence active power p of the load branch is calculated according to the following equation (3):
p＝(v_α×i_α+v_β×i_β)×1.5 (3)
where v_α, v_β, i_α and i_β are the negative sequence voltage α component, the negative sequence voltage β component, the negative sequence current α component and the negative sequence current β component of the load branch, respectively.
In step S300, it may be determined whether the branch has an inter-phase short fault according to the polarity of the negative-sequence active power of the branch.
In particular, in determining whether an inter-phase short fault has occurred in a branch, if the polarity of the negative-sequence active power of the branch is positive, it is determined that the branch has a low possibility of occurrence of the inter-phase short fault, in which case it may be determined that the branch has not occurred in the inter-phase short fault, which is also referred to as a reverse fault, and the branch may be locked back.
If the polarity of the negative sequence active power of a branch is negative, it is determined that the branch has a high likelihood of occurrence of an inter-phase short fault.
In particular, when it is determined that a branch has a high possibility of occurrence of an inter-phase short-circuit fault, it can be directly determined that an inter-phase short-circuit fault has occurred in a branch having a high possibility of occurrence of an inter-phase short-circuit fault. In this case, it can be determined very quickly that an inter-phase short fault has occurred in the branch, which is also called a forward fault, with a certain degree of accuracy ensured.
Optionally, when it is determined that the branch has a high possibility of occurrence of the inter-phase short-circuit fault, the accuracy of the inter-phase short-circuit fault determination may be further improved according to the polarity of the negative-sequence reactive power of the branch. Specifically, the negative-sequence reactive power of the determined branch having a high possibility of occurrence of the inter-phase short-circuit fault may be further calculated, and it may be determined whether the polarity of the negative-sequence reactive power of the branch is negative, and if the polarity of the negative-sequence reactive power of the branch is also negative, it may be determined that the inter-phase short-circuit fault has indeed occurred in the branch. By such further operations, it is possible to quickly and accurately determine whether an inter-phase short fault has occurred in a branch, wherein the negative-sequence reactive power q of the branch (e.g., a branch having a high possibility of an inter-phase short fault occurrence) can be calculated according to the following equation (4).
q＝(v_β×i_α－v_α×i_β)×1.5 (4)
Through step S300, it is finally determined quickly and accurately whether the branch has an inter-phase short-circuit fault, i.e. whether the branch has a forward fault.
Alternatively, before step S200 is described above, the effective values r of the negative sequence voltages of the branches may be calculated according to the following equation (5), and then it is determined that the effective values r of the negative sequence voltages of the branches are greater than or equal to a predetermined threshold value, if the effective values r of the negative sequence voltages of the branches are greater than or equal to the predetermined threshold value, step S200 is performed for the corresponding branch, otherwise, step S100 is returned, where the predetermined threshold value may be set by the user according to the actual situation.
In addition, the micro-grid interphase short-circuit fault protection method may perform further protection work according to the determination result in step S300. Specifically, when the inter-phase short-circuit fault of the branch is determined, the micro-grid inter-phase short-circuit fault protection method can cut off the branch with the inter-phase short-circuit fault, and if the inter-phase short-circuit fault of the branch is determined not to occur, locking returns.
The micro grid inter-phase short-circuit fault protection method described above with reference to fig. 2 and 3 may be performed simultaneously for all branches in the micro grid in parallel, so that a rapid response may be performed independently and in a targeted manner for each branch.
Fig. 4 is a block diagram illustrating a micro-grid interphase short-circuit fault protection system 10 according to an exemplary embodiment of the present invention.
As shown in fig. 4, the micro-grid interphase short-circuit fault protection system 10 may include a calculation unit 100 and a fault determination unit 200.
The calculation unit 100 may calculate a negative sequence voltage component and a negative sequence current component of a branch in the micro grid for a micro grid in which a neutral point operating in an island mode is not grounded. The microgrid may be a medium voltage or low voltage microgrid.
Specifically, the calculation unit 100 may calculate the negative sequence voltage α component v_α, the negative sequence voltage β component v_β, the negative sequence current α component i_α, and the negative sequence current β component i_β of the branch by a positive and negative sequence extraction method based on a generalized second-order integrator. Specifically, in the case where the micro grid as shown in fig. 1 includes three branches, a negative sequence voltage α component v_α, a negative sequence voltage β component v_β, a negative sequence current α component i_α, and a negative sequence current β component i_β are calculated for each of the three branches, respectively. Since this process has been described in detail above with reference to fig. 3, a detailed description thereof will be omitted herein.
After calculating the negative sequence voltage component and the negative sequence current component of the branch, the calculation unit 100 may calculate the negative sequence active power of the branch according to the negative sequence voltage component and the negative sequence current component of the branch. In particular, the at least one calculation unit 100 may calculate the negative-sequence active power of the branch according to equation (3) above. Since the above has been described in detail, a detailed description thereof will not be provided here.
The fault determining unit 200 may determine whether the phase-to-phase short fault occurs in the branch according to the polarity of the negative-sequence active power of the branch.
In particular, in determining whether an inter-phase short circuit fault has occurred in a branch, if the polarity of the negative-sequence active power of the branch is positive, the fault determination unit 200 may determine that the branch has a low possibility of occurrence of the inter-phase short circuit fault, in which case the fault determination unit 200 may determine that the branch has not occurred the inter-phase short circuit fault, which is also referred to as a reverse fault, and the branch may be locked back.
The fault determination unit 200 may determine that the branch has a high possibility of occurrence of an inter-phase short fault if the polarity of the negative sequence active power of the branch is negative.
In particular, when it is determined that the branch has a high possibility of occurrence of an inter-phase short-circuit fault, the fault determination unit 200 may directly determine that the branch having the high possibility of occurrence of the inter-phase short-circuit fault has occurred. In this case, it can be determined very quickly that an inter-phase short fault has occurred in the branch, which is also called a forward fault, with a certain degree of accuracy ensured.
Alternatively, when it is determined that the branch has a high possibility of occurrence of the inter-phase short fault, the fault determining unit 200 may further improve the accuracy of inter-phase short fault determination according to the polarity of the negative-sequence reactive power of the branch. Specifically, in this case, the calculation unit 100 may further calculate the determined negative-sequence reactive power of the leg having a high possibility of occurrence of the inter-phase short fault, and then the fault determination unit 200 may determine whether the polarity of the negative-sequence reactive power of the leg is negative, and if the polarity of the negative-sequence reactive power of the leg is also negative, the fault determination unit 200 may determine that the inter-phase short fault does occur in the leg. By such further operations, it is possible to quickly and accurately determine whether an inter-phase short fault has occurred in a branch, wherein the calculation unit 100 can calculate the negative-sequence reactive power q of a branch (e.g., a branch having a high possibility of occurrence of an inter-phase short fault) according to the above equation (4).
Accordingly, the micro-grid interphase short-circuit fault protection system 10 can finally and quickly determine whether interphase short-circuit faults occur in each branch, namely determine the branch with forward faults.
Alternatively, after calculating the negative sequence voltage component and the negative sequence current component of the branch, the calculating unit 100 may first calculate the effective values r of the negative sequence voltages of the branches according to equation (5) above, respectively, and then determine that the effective values r of the negative sequence voltages of the branches are greater than or equal to a predetermined threshold value, and if the effective values r of the negative sequence voltages of the branches are greater than or equal to the predetermined threshold value, the calculating unit 100 calculates the negative sequence active power of the corresponding branch according to the negative sequence voltage component and the negative sequence current component of the corresponding branch.
In addition, the micro grid interphase short-circuit fault protection system 10 may further include a fault handling unit 300. When the fault determining unit 200 determines that the interphase short-circuit fault has occurred in the branch, the fault processing unit 300 may cut off the branch in which the interphase short-circuit fault has occurred, and if the fault determining unit 200 determines that the interphase short-circuit fault has not occurred in the branch, the fault processing unit 300 latches back for the branch in which the interphase short-circuit fault has not occurred.
Although the micro grid inter-phase short-circuit fault protection system 10 shown in fig. 4 includes only one calculation unit 100, one fault determination unit 200, and one fault handling unit 300, that is, fault protection for all branches in the micro grid may be achieved with one calculation unit 100, one fault determination unit 200, and one fault handling unit 300, alternatively, the micro grid inter-phase short-circuit fault protection system 10 may include a plurality of calculation units 100, a plurality of fault determination units 200, and a plurality of fault handling units 300, and the number of calculation units 100, the number of fault determination units 200, and the number of fault handling units 300 may be the same as the number of branches in the micro grid, and each branch corresponds to one calculation unit 100, one fault determination unit 100, and one fault handling unit 100, in other words, fault protection for one branch may be formed with one calculation unit 100, one fault determination unit 200, and one fault handling unit 300, for example, in case that three branches exist in the micro grid, the micro grid inter-phase short-circuit protection system 10 may include 3 calculation units 100, 3 fault determination units 200, and 3 fault handling units 300.
Alternatively, the invention is not limited thereto, and any suitable number of the at least one calculation unit 200, the at least one fault determination unit 200 and the at least one fault handling unit 300 may be employed to achieve the above described fault protection of the branches in the micro grid.
Having described the inventive concepts of the micro-grid interphase short-circuit fault protection method and system, their application in branch fault determination will be further described below.
Fig. 5 to 16 show the negative sequence power waveforms of the respective branches in the micro grid shown in fig. 1 when an inter-phase short circuit fault occurs, and for the sake of comparing the negative sequence power waveforms of the respective branches more clearly, the negative sequence active power and the negative sequence reactive power of the respective branches are shown in fig. 5 to 16.
Fig. 5 to 7 are negative sequence power waveforms of the energy storage branch, the load branch and the photovoltaic branch, respectively, when the energy storage branch in the discharging mode suffers from an inter-phase short circuit fault. As can be seen from fig. 5 to 7, the polarities of the negative-sequence active power and the negative-sequence reactive power of the energy storage branch in the discharging mode shown in fig. 5 are both negative, and the negative-sequence active power of the load branch and the negative-sequence active power of the photovoltaic branch shown in fig. 6 and 7 respectively are both positive, according to this characteristic, it can be determined that the energy storage branch in the discharging mode corresponding to fig. 5 has an inter-phase short-circuit fault, and the load branch corresponding to fig. 6 and the photovoltaic branch corresponding to fig. 7 have no fault, so that the micro-grid inter-phase short-circuit fault protection method or system can cut off the energy storage branch having the inter-phase short-circuit fault according to the determined result.
Fig. 8 to 10 are negative sequence power waveforms of the energy storage branch, the load branch and the photovoltaic branch, respectively, when the energy storage branch in the charging mode suffers from an inter-phase short circuit fault. As can be seen from fig. 8 to 10, the polarities of the negative-sequence active power and the negative-sequence reactive power of the energy storage branch in the charging mode shown in fig. 8 are both negative, and the negative-sequence active power of the load branch and the negative-sequence active power of the photovoltaic branch shown in fig. 9 and 10 respectively are both positive, according to this characteristic, it can be determined that the energy storage branch in the charging mode corresponding to fig. 8 has an inter-phase short-circuit fault, and the load branch corresponding to fig. 9 and the photovoltaic branch corresponding to fig. 10 have no fault, so that the micro-grid inter-phase short-circuit fault protection method or system can cut off the energy storage branch having the inter-phase short-circuit fault according to the determined result.
As can be seen from fig. 5 to fig. 10 described above, the micro-grid inter-phase short-circuit fault protection method or system is applicable to both the charging mode and the discharging mode, and it is determined that an inter-phase short-circuit fault occurs in a certain branch without switching the protection policy according to the working mode, as long as it is determined that the polarity of the negative-sequence active power of the certain branch is negative or that the polarities of the negative-sequence reactive power and the negative-sequence active power of the certain branch are both negative, both in the charging mode and in the discharging mode.
Fig. 11 to 13 are negative sequence power waveforms of the load branch, the energy storage branch and the photovoltaic branch, respectively, when the load branch suffers from an inter-phase short circuit fault. As can be seen from fig. 11 to 13, the polarities of the negative-sequence active power and the negative-sequence reactive power of the load branch shown in fig. 11 are both negative, and the negative-sequence active power of the energy storage branch and the negative-sequence active power of the photovoltaic branch shown in fig. 12 and 13 are both positive, according to this characteristic, it can be determined that the load branch corresponding to fig. 11 has an inter-phase short-circuit fault, and the energy storage branch corresponding to fig. 12 and the photovoltaic branch corresponding to fig. 13 have no fault, so that the micro-grid inter-phase short-circuit fault protection method or system can cut off the load branch having the inter-phase short-circuit fault according to the determined result.
Fig. 14-16 are negative sequence power waveforms of the photovoltaic branch, the energy storage branch, and the load branch, respectively, when an inter-phase short circuit fault occurs in the photovoltaic branch. As can be seen from fig. 14 to 16, the polarities of the negative-sequence active power and the negative-sequence reactive power of the photovoltaic branch shown in fig. 14 are both negative, and the negative-sequence active power of the energy storage branch and the load branch shown in fig. 15 and 16 respectively are both positive, according to this characteristic, it can be determined that the photovoltaic branch corresponding to fig. 14 has an inter-phase short-circuit fault, while the energy storage branch corresponding to fig. 15 and the load branch corresponding to fig. 16 have no fault, and further the micro-grid inter-phase short-circuit fault protection method or system can cut off the photovoltaic branch having the inter-phase short-circuit fault according to the determined result.
According to the micro-grid interphase short-circuit fault protection method and the micro-grid interphase short-circuit fault protection system, the phase angles of the negative sequence voltage and the negative sequence current do not need to be calculated, whether interphase short-circuit faults occur in the branches can be determined only according to the polarity of the negative sequence active power of each branch, and the complexity of fault judgment is greatly reduced.
Furthermore, the present invention provides a computer-readable storage medium storing a program, which may include instructions for performing various operations in the above-described micro grid interphase short-circuit fault protection method. In particular, the program may include instructions for performing the steps described with reference to fig. 2.
Furthermore, the present invention provides a computer including a readable medium storing a computer program including instructions for performing various operations in the above-described micro grid inter-phase short-circuit fault protection method. In particular, the program may include instructions for performing the steps described with reference to fig. 2.
The foregoing description of exemplary embodiments of the invention has been presented only to be understood as illustrative and not exhaustive, and the invention is not limited to the exemplary embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Therefore, the protection scope of the present invention shall be subject to the scope of the claims.
Claims (14)
1. The micro-grid interphase short-circuit fault protection method is characterized by comprising the following steps of:
for a micro-grid with a neutral point not grounded, which is operated in an island mode, calculating a negative sequence voltage component and a negative sequence current component of a branch in the micro-grid;
calculating the negative sequence active power of the branch according to the negative sequence voltage component and the negative sequence current component of the branch;
determining whether the branch circuit has interphase short circuit fault according to the polarity of the negative sequence active power of the branch circuit,
wherein the microgrid is a medium voltage or low voltage microgrid,
wherein, the step of determining whether the branch circuit has interphase short circuit fault comprises the following steps:
if the polarity of the negative sequence active power of the branch is positive, determining that the branch has low possibility of inter-phase short circuit fault occurrence; and
if the polarity of the negative sequence active power of a branch is negative, it is determined that the branch has a high likelihood of occurrence of an inter-phase short fault,
wherein when it is determined that the branch has a high possibility of occurrence of an inter-phase short-circuit fault, the following operations are performed:
directly determining that an inter-phase short-circuit fault occurs in a branch having a high possibility of occurrence of the inter-phase short-circuit fault; or alternatively
And calculating the negative sequence reactive power of the branch with high possibility of inter-phase short-circuit fault occurrence, and if the polarity of the calculated negative sequence reactive power of the branch is negative, determining that the inter-phase short-circuit fault occurs in the branch.
2. The micro-grid interphase short-circuit fault protection method according to claim 1, wherein the step of calculating the negative sequence voltage component and the negative sequence current component of the branch includes:
the negative sequence voltage alpha component v_alpha, the negative sequence voltage beta component v_beta, the negative sequence current alpha component i_alpha and the negative sequence current beta component i_beta of the branch are calculated through a positive and negative sequence extraction method based on a generalized second-order integrator.
3. The micro-grid interphase short-circuit fault protection method according to claim 2, wherein the step of calculating the negative-sequence active power of the branch circuit comprises: the negative-sequence active power p of the branch is calculated according to the following equation:
p＝(v_α×i_α+v_β×i_β)×1.5。
4. the micro-grid interphase short-circuit fault protection method according to claim 1, characterized in that the negative-sequence reactive power q of the branch is calculated according to the following equation:
q＝(v_β×i_α－v_α×i_β)×1.5。
5. the micro grid interphase short-circuit fault protection method according to any one of claims 1 to 4, further comprising: and when the interphase short-circuit fault occurs to the branch circuit, cutting off the branch circuit with the interphase short-circuit fault.
6. A micro-grid interphase short-circuit fault protection system, comprising:
the computing unit is used for computing a negative sequence voltage component and a negative sequence current component of a branch in the micro-grid aiming at the micro-grid with a neutral point which is not grounded and running in an island mode, and computing the negative sequence active power of the branch according to the negative sequence voltage component and the negative sequence current component of the branch;
a fault determining unit for determining whether the phase-to-phase short circuit fault occurs in the branch circuit according to the polarity of the negative sequence active power of the branch circuit,
wherein the microgrid is a medium voltage or low voltage microgrid,
wherein if the polarity of the negative sequence active power of the branch is positive, the fault determination unit determines that the branch has a low possibility of occurrence of an inter-phase short circuit fault; and
if the polarity of the negative sequence active power of the branch is negative, the fault determination unit determines that the branch has a high probability of occurrence of an inter-phase short fault,
wherein, when it is determined that the branch has a high possibility of occurrence of an inter-phase short-circuit fault:
the fault determination unit directly determines that an inter-phase short fault has occurred in a branch having a high possibility of occurrence of the inter-phase short fault; or alternatively
The calculation unit calculates the determined negative-sequence reactive power of the branch having a high possibility of occurrence of the inter-phase short-circuit fault, and if the polarity of the calculated negative-sequence reactive power of the branch is negative, the fault determination unit determines that the inter-phase short-circuit fault has occurred in the branch.
7. The micro grid interphase short-circuit fault protection system according to claim 6, wherein the calculation unit calculates the negative sequence voltage α component v_α, the negative sequence voltage β component v_β, the negative sequence current α component i_α, and the negative sequence current β component i_β of the branch by a positive-negative sequence extraction method based on a generalized second-order integrator.
8. The micro-grid interphase short-circuit fault protection system according to claim 7, wherein the calculation unit calculates the negative-sequence active power p of the branch according to the following equation:
p＝(v_α×i_α+v_β×i_β)×1.5。
9. the micro-grid interphase short-circuit fault protection system according to claim 6, wherein: the calculation unit calculates the negative sequence reactive power q of the branch according to the following equation:
q＝(v_β×i_α－v_α×i_β)×1.5。
10. the micro-grid interphase short-circuit fault protection system according to any one of claims 6 to 9, further comprising: and the fault processing unit is used for cutting off the branch circuit with the interphase short circuit fault when determining that the branch circuit has the interphase short circuit fault.
11. The micro grid inter-phase short circuit fault protection system according to claim 10, wherein the number of the calculation units, the number of the fault determination units, and the number of the fault handling units are the same as the number of branches in the micro grid, and each branch corresponds to one calculation unit, one fault determination unit, and one fault handling unit.
12. The micro grid interphase short-circuit fault protection system according to claim 10, wherein the number of the calculation units, the number of the fault determination units and the number of the fault handling units are all 1.
13. A computer-readable storage medium storing a program, characterized in that the program comprises instructions for executing the micro grid inter-phase short circuit fault protection method according to any one of claims 1 to 5.
14. A computer comprising a readable medium storing a computer program, characterized in that the program comprises instructions for performing the micro grid interphase short circuit fault protection method according to any of claims 1-5.
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