Fault identification method and system for renewable energy island power grid connected to flexible direct current grid

Abstract

The present invention provides a method and system for distinguishing faults of a renewable energy island power grid via a flexible direct current grid-connected system, and relates to the technical field of fault distinguishing of a grid-connected system. The method and system obtain voltage data of each measuring point under a grid-connected system fault signal; the voltage data of each measuring point is substituted into a fault distinguishing index system of a renewable energy island via a flexible direct current transmission system. The fault distinguishing index system of a renewable energy island via a flexible direct current transmission system is constructed in the following process: electrical quantity data under different historical working conditions and different faults are obtained, a fault database is constructed, and based on the fault database, the data of the lowest voltage drop point and the data of the maximum voltage drop slope of each measuring point under different fault locations and fault types are quantitatively analyzed. Based on the laws shown by the data of the lowest voltage drop point and the data of the maximum voltage drop slope of each measuring point, a fault type distinguishing index and a fault location distinguishing index are constructed, and the fault distinguishing index is used to complete the fault distinguishing of the renewable energy island via a flexible direct current transmission system.

Description

Technical Field

[0001] The present disclosure relates to the technical field of grid-connected system fault determination, and in particular to a method and system for determining faults in a renewable energy island power grid connected to a flexible direct current grid. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] Due to the reverse distribution of resources and demand in some regions, the transmission system of some large renewable energy bases connected to the grid through flexible direct current has become one of the typical forms of the new power system. The renewable energy island connected to the grid through flexible direct current system has significant differences in topology and operating characteristics from the traditional power system with synchronous generators as the main body. It does not have any traditional power supply support and is a highly dynamic and complex power network that fully integrates various renewable energy sources. At the same time, compared with the high-penetration renewable energy system, the renewable energy penetration rate of the renewable energy island connected to the grid through flexible direct current system reaches 100%, and its requirements for operating stability are more stringent. Therefore, it is of great significance to carry out relevant research on the operating characteristics of the renewable energy island grid connected to the grid through flexible direct current system, especially the electrical quantity response characteristics of the island grid after the fault, to optimize the system control and ensure the level of renewable energy transmission.

[0004] At present, the identification and research methods of isolated power grid systems are mainly aimed at faults occurring on the power grid side, and there are few methods for the identification and research of internal faults in isolated power grid systems. Moreover, the existing identification and research methods of isolated power grid systems after faults are based on a relatively simple basis, without a detailed analysis of the propagation mechanism and propagation path of the fault from the renewable energy system through the flexible direct current system after the fault occurs, and a complete fault identification system is formed according to the different fault locations and fault types within the renewable energy island system; in addition, the existing identification and research methods of isolated power grid systems after faults cannot realize the identification of the fault type and fault location of the isolated power grid system without communication. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a fault identification method and system for a renewable energy island power grid connected to a flexible direct current grid, a fault database is constructed based on electrical quantity data measured under different fault conditions of the system under various working conditions, and a fault type and fault location identification index system is constructed based on two identification indicators. The fault type and fault location are identified, which can guide renewable energy stations and flexible direct current converter stations to adjust control strategies in a timely manner and optimize control parameters.

[0006] According to some embodiments, the present disclosure adopts the following technical solutions:

[0007] A method for identifying faults in a renewable energy island power grid connected to a flexible direct current grid, including:

[0008] Obtain voltage data of each measuring point under grid-connected system fault signal;

[0009] Substituting the voltage data of each measuring point into the fault identification index system of the renewable energy island flexible direct current transmission system to identify the fault type and fault location;

[0010] Among them, the process of constructing the fault discrimination index system of the renewable energy island through flexible direct current transmission system is as follows: obtaining historical electrical quantity data under different working conditions and different faults, constructing a fault database, and based on the fault database, quantitatively analyzing the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point under different fault locations and fault types, and based on the laws expressed by the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point, constructing the fault type discrimination index and the fault location discrimination index, and completing the construction of the fault discrimination index system of the renewable energy island through flexible direct current transmission system.

[0011] According to some embodiments, the present disclosure adopts the following technical solutions:

[0012] Fault identification system for renewable energy isolated power grid via flexible direct current grid connection system, including:

[0013] A data acquisition module is used to obtain voltage data of each measuring point under a grid-connected system fault signal;

[0014] A discrimination module, used for substituting the voltage data of each measuring point into the fault discrimination index system of the renewable energy island flexible direct current transmission system to discriminate the fault type and fault location;

[0015] Among them, the process of constructing the fault discrimination index system of the renewable energy island through flexible direct current transmission system is as follows: obtaining historical electrical quantity data under different working conditions and different faults, constructing a fault database, and based on the fault database, quantitatively analyzing the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point under different fault locations and fault types, and based on the laws expressed by the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point, constructing the fault type discrimination index and the fault location discrimination index, and completing the construction of the fault discrimination index system of the renewable energy island through flexible direct current transmission system.

[0016] According to some embodiments, the present disclosure adopts the following technical solutions:

[0017] A non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the method for determining faults of a renewable energy island power grid connected to a flexible direct current grid is implemented.

[0018] According to some embodiments, the present disclosure adopts the following technical solutions:

[0019] An electronic device comprises: a processor, a memory and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory, so that the electronic device executes the method for determining faults of a renewable energy island power grid connected to a flexible direct current grid.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The disclosed method for distinguishing the fault of the renewable energy island power grid through the flexible direct current grid-connected system establishes a fault library of the renewable energy island power grid through the flexible direct current grid-connected system, which contains various electrical quantity data of different fault locations, different fault types, and different measurement points under different working conditions. Based on the fault library data, the influence of the fault location and fault type on the voltage drop degree and drop speed of each measurement point is quantitatively analyzed. Based on the analysis results that the voltage response characteristics measured at each measurement point are different when different types of faults occur or the faults occur at different locations, the voltage data features are extracted, a fault distinction index system is constructed, and the effectiveness of the fault distinction index in distinguishing the fault type and fault location is verified. When a fault is detected in the renewable energy island power grid, the control layer of each renewable energy station and the flexible direct current converter station can quickly determine the fault type and fault location through the fault distinction index, providing guidance for the selection of control strategies and optimization of control parameters during the fault.

[0022] The disclosed method for distinguishing faults in an isolated renewable energy power grid via a flexible direct current grid-connected system extracts the lowest point of voltage drop and the maximum value of the slope during the voltage drop as distinguishing indicators. This is because the lowest point of voltage drop and the maximum value of the slope during the voltage drop are the most obvious features describing voltage changes during system faults. The lowest points of voltage drops at different positions can be used to determine the severity and type of faults in the system, while the maximum value of the drop slope can be used to determine the propagation path of the fault and thus the location of the fault. The combination of the two can provide an effective reference for distinguishing faults, and can ensure that when a fault occurs in an isolated renewable energy power grid via a flexible direct current grid-connected system, the fault location and the type of fault that has occurred can be quickly determined based on the distinguishing indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings constituting a part of the present disclosure are used to provide a further understanding of the present disclosure. The illustrative embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation on the present disclosure.

[0024] Figure 1 A topological structure diagram of a renewable energy island power grid connected to a flexible direct current grid in accordance with a disclosed embodiment;

[0025] Figure 2 It is a comparison diagram of the lowest voltage drop points measured at nine fault points and six measurement points under working condition 1 of the embodiment of the present disclosure;

[0026] Figure 3 It is a comparison diagram of the lowest voltage drop points measured at nine fault points and six measurement points under working condition 5 of the embodiment of the present disclosure;

[0027] Figure 4 It is a comparison diagram of the lowest voltage drop points measured at nine fault points and six measurement points under working condition 9 of the embodiment of the present disclosure;

[0028] Figure 5 This is a comparison diagram of the maximum voltage drop slope values ​​measured at nine fault points and six measurement points under working condition 1 of an embodiment of the present disclosure;

[0029] Figure 6 This is a comparison diagram of the maximum voltage drop slope values ​​measured at nine fault points and six measurement points under working condition 5 of an embodiment of the present disclosure;

[0030] Figure 7 This is a comparison diagram of the maximum voltage drop slope values ​​measured at nine fault points and six measurement points under working condition 9 of an embodiment of the present disclosure;

[0031] Figure 8 This is a comparison diagram of the lowest voltage drop points measured at nine fault points and six measurement points under working condition 1 of the embodiment of the present disclosure;

[0032] Fig. 9 This is a comparison diagram of the lowest voltage drop points measured at nine fault points and six measurement points under working condition 5 of the embodiment of the present disclosure;

[0033] Fig.10 This is a comparison diagram of the lowest voltage drop points measured at nine fault points and six measurement points under working condition 9 of the embodiment of the present disclosure;

[0034] Fig.11 This is a comparison diagram of the maximum voltage drop slope values ​​measured at nine fault points and six measurement points under working condition 1 of an embodiment of the present disclosure;

[0035] Fig.12 This is a comparison diagram of the maximum voltage drop slope values ​​measured at nine fault points and six measurement points under working condition 5 of an embodiment of the present disclosure;

[0036] Fig.13 This is a comparison diagram of the maximum voltage drop slope values ​​measured at nine fault points and six measurement points under working condition 9 of an embodiment of the present disclosure;

[0037] Fig.14 This is the application architecture of the fault identification indicator system of the embodiment of the present disclosure. DETAILED DESCRIPTION

[0038] The present disclosure is further described below in conjunction with the accompanying drawings and embodiments.

[0039] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanation of the present disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present disclosure belongs.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] Example 1

[0042] In one embodiment of the present disclosure, a method for determining faults in a renewable energy island power grid connected to a flexible direct current grid is provided, comprising:

[0043] Step 1: Obtain voltage data of each measuring point under the fault signal of the grid-connected system;

[0044] Step 2: Substituting the voltage data of each measuring point into the fault identification index system of the renewable energy island flexible direct current transmission system to identify the fault type and fault location;

[0045] Among them, the process of constructing the fault discrimination index system of the renewable energy island through flexible direct current transmission system is as follows: obtaining historical electrical quantity data under different working conditions and different faults, constructing a fault database, and based on the fault database, quantitatively analyzing the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point under different fault locations and fault types, and based on the laws expressed by the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point, constructing the fault type discrimination index and the fault location discrimination index, and completing the construction of the fault discrimination index system of the renewable energy island through flexible direct current transmission system.

[0046] As an embodiment, the construction process of the fault identification index system of the renewable energy island through the flexible direct current transmission system in the method for identifying the fault of the renewable energy island power grid through the flexible direct current grid-connected system disclosed in the present invention is as follows:

[0047] Step 1: Construct the topology of the renewable energy island power grid through flexible direct current grid-connected system, build a model simulation test, and form a fault database;

[0048] Based on the renewable energy island grid-connected flexible direct current system, a variety of fault types are set for different operating conditions and fault locations. Through simulation tests, the electrical quantity data of each data measurement point are obtained, forming a complete renewable energy island grid-connected flexible direct current system fault database.

[0049] Specifically, based on the different access ratios of wind power and photovoltaic stations, nine operating conditions are formed as shown in Table 1. Figure 1 The simulation tests were conducted on three different fault types, namely, single-phase grounding fault, two-phase grounding fault and three-phase grounding fault, at nine fault points, including the AC side of the flexible DC sending end converter station (fault point 1), the 220kV grid connection point of wind farm station A and wind farm station B (fault point 2), the 220kV grid connection point of photovoltaic station C and photovoltaic station D (fault point 3), the 220kV grid connection point of photovoltaic station E (fault point 4) and the 35kV grid connection points of each renewable energy station (fault points 5~9). Finally, the electrical quantity data of six electrical measurement points, including the AC side of the flexible DC sending end converter station (measurement point 1) and the 35kV grid connection points of each renewable energy station (measurement points 2~6), were obtained to form a fault database of the renewable energy island power grid through the flexible DC grid connection system.

[0050] Table 1 Detailed parameters of nine different operating conditions

[0051]

[0052] Step 2: Based on the constructed fault database, conduct quantitative analysis of voltage waveform data for different types of faults occurring at the same location and the same type of fault occurring at different fault locations, so as to clarify the changing characteristics of voltage data under different fault conditions.

[0053] In the traditional power system dominated by synchronous generators, the concept of grid strength is usually used to measure the strength of the interaction between the grid itself and the primary equipment connected to the grid. It mainly includes two aspects: voltage support strength and frequency support strength. On the one hand, the frequency support strength of the traditional power grid is represented by the kinetic energy stored in the rotor of the synchronous machine of the whole network, and the commonly used unit is MWs. However, in the renewable energy island through flexible direct current transmission system, since there is no traditional synchronous machine power supply, that is, there is no inertia entity, it can be considered that the system inertia level is close to 0. In this case, the frequency of the system is completely dominated by the sending-end converter station using grid-type control. The change of frequency after the system fault is closely related to the selection of the control strategy and parameter setting of the converter station, but has little to do with the fault type and location. On the other hand, the system voltage level and stability directly affect the reliability of the grid-connected operation of renewable energy sites. Different fault types and fault locations will cause different degrees of voltage drop on each bus of the system. The degree and speed of voltage drop will directly determine whether the renewable energy site or even the entire system can operate safely and stably. Therefore, the obtained fault library data is used to analyze the voltage waveform data for different types of faults occurring at the same location and the same type of fault occurring at different fault locations, so as to clarify the changing characteristics of the voltage data under different fault conditions, thereby providing a sufficient theoretical basis for the establishment of the subsequent fault identification index system.

[0054] First, the common fault types of renewable energy island power grids include single-phase grounding, two-phase grounding and three-phase grounding faults. When different types of faults occur at the same location, the voltage drop degree and speed of each grid connection point of the island power grid show different characteristics. In order to clarify the impact of fault types on the operating characteristics of the island power grid, this paper selects fault library data of three typical working conditions, namely working conditions 1, working conditions 5 and working conditions 9, and analyzes the voltage data detected at each measurement point when different types of faults occur at the same fault location by extracting indicators such as the lowest point of voltage drop and the maximum slope during the drop process.

[0055] In order to compare the voltage drop degree of each grid connection point of the isolated power grid when different types of faults occur at the same location, the data of the lowest voltage drop point under various fault conditions are extracted for comparative analysis.

[0056] When a single-phase grounding fault (fault type 1), a two-phase grounding fault (fault type 2), and a three-phase grounding fault (fault type 3) occur at the nine fault points, the comparison of the lowest voltage drop points measured at the six measurement points is as follows: Figure 2 Under three typical operating conditions, when the nine fault points have single-phase grounding fault, two-phase grounding fault and three-phase grounding fault respectively, the voltage drop lowest point data measured at the six measurement points basically show the same pattern, that is, the voltage drop lowest point is the highest under single-phase grounding fault, followed by two-phase grounding fault, and the voltage drop lowest point is the lowest when three-phase grounding fault occurs.

[0057] On the other hand, when different types of faults occur, the voltage drop speed after the fault will also show different characteristics. In order to compare the voltage drop speed of each grid connection point of the isolated power grid when different types of faults occur at the same location, the maximum value data of the voltage drop slope under various fault conditions are extracted for comparative analysis.

[0058] When a single-phase grounding fault (fault type 1), a two-phase grounding fault (fault type 2), and a three-phase grounding fault (fault type 3) occur at the nine fault points, the maximum voltage drop slopes measured at the six measurement points are compared. Figure 3 Under three typical operating conditions, when single-phase grounding fault, two-phase grounding fault and three-phase grounding fault occurred at nine locations respectively, the maximum voltage drop slopes detected by the six measuring points basically showed the same rule, that is, when a three-phase grounding fault occurred, its voltage drop speed was much faster than that of the other two types of faults, that is, when a single-phase grounding fault, a two-phase grounding fault and a three-phase grounding fault occurred respectively, the voltage drop speed detected by multiple measuring points under the three-phase grounding fault was faster than that when a single-phase grounding fault and a two-phase grounding fault occurred.

[0059] Furthermore, when a fault occurs at the same location, different fault types will cause the isolated power grid to produce different voltage response characteristics. On the other hand, when the same type of fault occurs at different locations, the voltage response characteristics generated by each grid connection point are also different. The nine fault locations set up in the present disclosure can be roughly divided into three categories: fault point 1 is the flexible direct current grid connection point of the renewable energy island power grid, fault points 2~4 are the 220kV grid connection points of the renewable energy station, and fault points 5~9 are the 35kV grid connection points of each renewable energy station.

[0060] The present disclosure also selected fault library data of three typical working conditions, namely working condition 1, working condition 5 and working condition 9, and analyzed the voltage data detected at each measuring point when the same fault type occurred at different locations by extracting indicators such as the lowest point of voltage drop and the maximum slope during the drop.

[0061] On the one hand, in order to compare the voltage drop degree of each grid connection point of the isolated power grid when the same fault type occurs at different fault locations, the present disclosure extracts the data of the lowest voltage drop under various fault conditions for comparative analysis. Under three typical working conditions, when three different types of faults occur at nine fault points, the comparison diagram of the lowest voltage drop measured at six measurement points is as follows: Figure 4As shown. The horizontal axis of the chessboard diagram represents nine fault points, and the vertical axis represents six measurement points. The color of the chessboard at the intersection of the horizontal and vertical axes represents the value of the lowest voltage drop measured at the corresponding measurement point when a fault occurs at a certain fault point. At the same time, the chessboard diagram uses black solid dots to mark the measurement point corresponding to the minimum value of the lowest voltage point measured by the six measurement points when a certain type of fault occurs at a certain location (that is, the measurement point with the most serious voltage drop), and marks the corresponding lowest voltage point value. By comparing and analyzing the data of the lowest voltage drop measured by the six measurement points when a fault occurs at each fault location, the following conclusions can be drawn:

[0062] (1) For the first type of fault point, i.e., the grid-connected point of the isolated renewable energy grid (fault point 1), regardless of the fault type, the measurement point corresponding to the minimum value of the lowest voltage point data measured at the six measurement points during the fault period under the three typical operating conditions is the AC side of the converter station at the flexible direct current sending end (measurement point 1).

[0063] (2) For the second type of fault point, i.e., the 220 kV grid connection point of the renewable energy station (fault points 2-4), when a single-phase grounding fault occurs, consistent conclusions can be drawn under the three typical working conditions: the measurement point corresponding to the minimum value of the lowest voltage point data measured by the six measurement points during the fault period is measurement point 1; and when a two-phase grounding fault or a three-phase grounding fault occurs, there is no unified conclusion as to the measurement point corresponding to the minimum value of the lowest voltage point data measured by the six measurement points during the fault period, but the lowest voltage point data measured by each measurement point are not much different.

[0064] (3) For the third type of fault point, i.e., the 35kV grid connection point of the renewable energy station (fault points 5-9), when a single-phase grounding fault occurs, consistent conclusions can be drawn under the three typical working conditions: the measurement point corresponding to the minimum value of the lowest voltage point data measured by the six measurement points during the fault period is measurement point 1 or the measurement point corresponding to the fault point (fault points 5-9 correspond to measurement points 2-6, respectively). At the same time, except for the lowest voltage point data measured by measurement point 1, the minimum values ​​of the lowest voltage point data measured by the other five measurement points all appear at the measurement point corresponding to the fault point. When a two-phase grounding fault or a three-phase grounding fault occurs, under the three typical working conditions, the minimum value of the lowest voltage point data measured by the six measurement points during the fault period also appears at the measurement point corresponding to the fault point.

[0065] On the other hand, the maximum value of the voltage drop slope during the voltage drop reflects the speed of the voltage drop. This paper extracts the maximum value data of the voltage drop slope under various fault conditions for comparative analysis. Under three typical working conditions, when three different types of faults occur at nine fault points, the comparison of the maximum values ​​of the voltage drop slope measured at six measurement points is shown in the figure below: Figure 5As shown. The horizontal axis of the chessboard diagram represents nine fault points, and the vertical axis represents six measurement points. The color of the chessboard at the intersection of the horizontal and vertical axes represents the value of the maximum voltage drop slope measured at the corresponding measurement point when a fault occurs at a certain fault point. At the same time, the chessboard diagram uses black solid dots to mark the measurement point corresponding to the maximum value of the maximum drop slope data measured by the six measurement points when a certain type of fault occurs at a certain location (that is, the measurement point with the fastest voltage drop speed), and marks the corresponding voltage minimum point value.

[0066] Finally, by comparing and analyzing the maximum voltage drop slope data measured at the six measurement points when a fault occurs at each fault location, the following conclusions can be drawn:

[0067] (1) For the first type of fault point, i.e., the grid connection point of the renewable energy island grid flexible direct current transmission (fault point 1), when a single-phase grounding fault occurs, the maximum value of the maximum voltage drop slope measured by the six measurement points under the three typical working conditions corresponds to different measurement points; however, when a two-phase grounding fault or a three-phase grounding fault occurs, the maximum value of the maximum voltage drop slope measured by the six measurement points under the three typical working conditions corresponds to measurement point 1.

[0068] (2) For the second type of fault point, i.e., the 220 kV grid connection point of the renewable energy station (fault points 2-4), when a single-phase grounding fault occurs, under the three typical working conditions, the measurement point corresponding to the maximum value of the maximum voltage drop slope data measured by the six measurement points during the fault period is basically measurement point 5; and when a two-phase grounding fault or a three-phase grounding fault occurs, under the three typical working conditions, the measurement point corresponding to the maximum value of the maximum voltage drop slope data measured by the six measurement points during the fault period is basically measurement point 6.

[0069] (3) For the third type of fault point, i.e., the 35 kV grid connection point of the renewable energy station (fault points 5-9), regardless of the fault type, under the three typical operating conditions, the maximum value of the voltage drop slope data measured at the six measurement points during the fault period basically appears at the measurement point corresponding to the fault point.

[0070] Step 3: Based on the voltage response characteristics measured at each measurement point when different types of faults occur in the renewable energy island power grid or the faults occur in different locations, a fault discrimination index is constructed to form a fault discrimination index system for the renewable energy island flexible direct current transmission system.

[0071] When different types of faults occur in the renewable energy island power grid or the faults occur in different locations, the voltage response characteristics measured at each measurement point are different. When different types of faults occur in the island power grid, regardless of the fault location, the lowest voltage drop point and the maximum voltage drop slope measured at each measurement point show the same rule, that is, when a three-phase grounding fault occurs, the voltage drop is the most serious and the drop speed is the fastest; when a single-phase grounding fault occurs, the voltage drop is the slightest and the drop speed is slow. When the same fault type occurs at different fault locations, the measurement point with the most serious voltage drop and the fastest voltage drop speed is generally the measurement point corresponding to the fault point.

[0072] Therefore, the lowest point of voltage drop and the maximum value of voltage drop slope during fault are used as effective data indicators to reflect the fault type and fault location, based on which a fault identification index system for renewable energy islands through flexible direct current transmission systems can be constructed.

[0073] First, based on the voltage drop minimum point data and drop slope maximum value data detected at each measurement point, the fault discrimination index of each measurement point is constructed as follows:

[0074] (1)

[0075] Where: λ i For the i Fault identification index of each measuring point; v min i The lowest voltage drop data measured at each measuring point; k max i The maximum value data of voltage drop slope measured at each measuring point; a 1. a 2 are the weighting coefficients of the lowest voltage drop point and the maximum voltage drop slope, respectively, satisfying a 1+ a 2=1.

[0076] Furthermore, 1) fault type identification

[0077] When different types of faults occur, regardless of the fault location, the lowest voltage drop point and the maximum voltage drop slope measured at each measurement point show the same pattern, that is, the fault discrimination index of each measurement point also shows the same pattern. Therefore, the fault type discrimination index can be constructed as follows:

[0078] (2)

[0079] Where: μ It is the fault type identification index; nis the total number of measurement points. This index is the average value of the fault discrimination index of each measurement point. For various fault types, the fault type discrimination index has a corresponding value range. When the fault type discrimination index value falls within the corresponding value range, the fault type can be identified.

[0080] The discrimination principle can be expressed as follows:

[0081] (3)

[0082] Where: μ j down For the j The lower limit of the fault type identification index for the type of fault; μ j up For the j The upper limit of the fault type discrimination index for the type of fault; j =1, 2, 3 correspond to single-phase grounding fault, two-phase grounding fault and three-phase grounding fault respectively. When the fault discrimination index value meets the formula (3), it can be judged as the first j Types of failures.

[0083] 2) Fault location determination

[0084] When the same type of fault occurs at different locations, the lowest voltage drop point and the maximum voltage drop slope value measured at each measurement point are different, that is, when faults occur at different locations, the fault discrimination index values ​​of each measurement point are different. According to the analysis of the impact of the same type of fault occurring at different locations on the voltage drop, when a fault occurs at a certain location, the corresponding measurement point will have the minimum value of the lowest voltage drop point data and the maximum value of the maximum voltage drop slope data, that is, the measurement point corresponding to the minimum value of the fault discrimination index value of each measurement point is the measurement point corresponding to the fault point. Therefore, after a fault occurs, the fault location can be determined by comparing the fault index values ​​of different measurement points.

[0085] Simulation Verification

[0086] In order to verify the feasibility and effectiveness of the fault type discrimination index and the fault location discrimination index, the fault library data under two working conditions, working condition 1 and working condition 9, were extracted to verify the effectiveness of the fault type discrimination and fault location discrimination respectively.

[0087] (1) Fault type determination

[0088] Based on the voltage data under various fault conditions under two working conditions in the fault library, the voltage drop minimum point data and the drop slope maximum value data detected at each measurement point are extracted. According to formula (1) and formula (2), the fault type discrimination index values ​​can be calculated as shown in Table 2 and Table 3.

[0089] Table 2 Fault type identification index values ​​under working condition 1

[0090]

[0091] Table 3 Fault type identification index values ​​under working condition 9

[0092]

[0093] As shown in the table above, the vertical column for single-phase grounding fault and the vertical column for three-phase grounding fault in the table correspond to the maximum and minimum values ​​of the fault type index value when three types of faults occur at a certain fault point. It can be seen that under the two working conditions, regardless of the fault location, the fault discrimination index value is that the three-phase grounding fault is greater than the two-phase grounding fault and greater than the single-phase grounding fault. Similar to the above two operating conditions, the same conclusion can be obtained by analyzing and calculating the voltage data under other working conditions. Therefore, it is only necessary to select a reasonable fault discrimination index limit and combine it with formula (3) to achieve the discrimination of the fault type.

[0094] (2) Fault location determination

[0095] In the renewable energy island transmission system via flexible direct current, the degree of impact of faults at different locations on the system is different, and the sending-end converter station and each renewable energy station have different solutions for coping with faults. When the first type of fault point and the second type of fault point (fault point 1-4) fail, the fault has a wide impact range, so the sending-end converter station and each renewable energy station need to deal with it together; when the third type of fault point (fault point 5-9) fails, the corresponding renewable energy station should play the main control role and other renewable energy stations play an auxiliary control role. Therefore, the present disclosure selects fault point 1 and fault point 5-9 to correspond to the above two situations respectively, and verifies the effectiveness of the fault location discrimination index. According to the analysis in the previous article, for fault location discrimination, it is only necessary to compare the fault discrimination indexes of the six measurement points, find the measurement point corresponding to the minimum index value, and the fault point corresponding to the measurement point is the fault location. Taking the two-phase grounding fault under working conditions 1 and 9 as an example, when faults occur at different locations, the fault discrimination index values ​​of each measurement point calculated according to formula (1) are shown in Tables 4 and 5. In the table, measurement point 1 at fault point 1, measurement point 2 at fault point 5, measurement point 3 at fault point 6, measurement point 4 at fault point 7, measurement point 5 at fault point 8, and measurement point 6 at fault point 9 are the minimum values ​​of fault discrimination indicators of the six measurement points after a fault occurs at a certain point.

[0096] According to the data in the table, when a fault occurs at a certain point, the fault discrimination index calculated at the corresponding measurement point will be smaller than the fault discrimination index of the remaining measurement points. Therefore, the fault location can be effectively identified by comparing the fault discrimination index of each measurement point.

[0097] Table 4 Fault discrimination index values ​​of each measurement point under working condition 1

[0098]

[0099] Table 5 Fault discrimination index values ​​of each measurement point under working condition 9

[0100]

[0101] As an embodiment, the fault identification index system constructed by the present disclosure can timely and accurately identify the type of fault and the location of the fault after the system fault occurs. According to different fault types and fault locations, each renewable energy station and flexible direct current converter station can select reasonable transient control strategies and control parameters in a targeted manner to achieve the best control effect. The control process after the fault identification index system is applied to the system transient control is as follows: Figure 6 shown.

[0102] First, before the system fails, the control center has issued and stored the default transient support control strategy to each renewable energy station and flexible DC converter station. After the system fails, each renewable energy station and flexible DC converter station immediately starts the default control strategy to suppress the impact of the initial fault on the system and prevent the fault from further deteriorating. At the same time, each measurement point synchronously measures the electrical quantity data and sends it to the control center. Based on the electrical quantity data, the control center extracts characteristic data such as the minimum voltage drop and the maximum drop slope, and uses the fault discrimination index to determine the fault location according to the fault discrimination index of each measurement point; on the other hand, the fault type index is calculated to determine the fault type. Finally, the control scheme is adjusted in a targeted manner according to the discrimination results, the control parameters are optimized, and sent to each renewable energy station and flexible DC converter station to achieve the best control effect.

[0103] This discrimination index system can be used to guide the selection and modification of control strategies and control parameters during faults.

[0104] Example 2

[0105] In one embodiment of the present disclosure, a system for identifying faults in a renewable energy island power grid connected to a flexible direct current grid is provided, comprising:

[0106] A data acquisition module is used to obtain voltage data of each measuring point under a grid-connected system fault signal;

[0107] A discrimination module, used for substituting the voltage data of each measuring point into the fault discrimination index system of the renewable energy island flexible direct current transmission system to discriminate the fault type and fault location;

[0108] Among them, the process of constructing the fault discrimination index system of the renewable energy island through flexible direct current transmission system is as follows: obtaining historical electrical quantity data under different working conditions and different faults, constructing a fault database, and based on the fault database, quantitatively analyzing the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point under different fault locations and fault types, and based on the laws expressed by the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point, constructing the fault type discrimination index and the fault location discrimination index, and completing the construction of the fault discrimination index system of the renewable energy island through flexible direct current transmission system.

[0109] Example 3

[0110] In one embodiment of the present disclosure, a non-transitory computer-readable storage medium is provided, wherein the non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the fault determination method of the renewable energy island power grid through the flexible direct current grid-connected system is implemented.

[0111] Example 4

[0112] In one embodiment of the present disclosure, an electronic device is provided, including: a processor, a memory, and a computer program; wherein the processor is connected to the memory, and the computer program is stored in the memory. When the electronic device is running, the processor executes the computer program stored in the memory, so that the electronic device executes the method for determining faults of a renewable energy island power grid through a flexible direct current grid-connected system.

[0113] The present disclosure is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present disclosure. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0114] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0115] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Technical personnel in the relevant field should understand that on the basis of the technical solution of the present disclosure, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present disclosure.

Claims

1. A method for identifying faults in a renewable energy island power grid connected to a flexible direct current grid, characterized in that: include: Obtain voltage data of each measuring point under grid-connected system fault signal; Substituting the voltage data of each measuring point into the fault identification index system of the renewable energy island flexible direct current transmission system to identify the fault type and fault location; Among them, the process of constructing the fault discrimination index system of the renewable energy island through flexible direct current transmission system is as follows: obtaining historical electrical quantity data under different working conditions and different faults, constructing a fault database, and based on the fault database, quantitatively analyzing the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point under different fault locations and fault types, and based on the laws expressed by the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point, constructing the fault type discrimination index and the fault location discrimination index, and completing the construction of the fault discrimination index system of the renewable energy island through flexible direct current transmission system.

2. The method for identifying faults in a renewable energy island power grid connected to a flexible direct current grid as claimed in claim 1, characterized in that: Based on the different access ratios of wind power and photovoltaic stations, various operating conditions are obtained, and simulation tests are carried out on various fault types under operating conditions. The electrical quantity data of multiple electrical measurement points on the AC side of the flexible DC sending-end converter station and the 35kV grid-connected points of each renewable energy station are obtained to form a fault database of the renewable energy island power grid through the flexible DC grid-connected system.

3. The method for identifying faults in a renewable energy island power grid connected to a flexible direct current grid as claimed in claim 1, characterized in that: Based on the fault database, a quantitative analysis of voltage waveform data is carried out for different types of faults occurring at the same location and the same type of fault occurring at different fault locations. When comparing the voltage drop degrees of each grid-connected point of the isolated power grid when different types of faults occur at the same location, the data of the lowest voltage drop under various fault conditions are extracted for comparative analysis. When a single-phase grounding fault, a two-phase grounding fault and a three-phase grounding fault occur at the fault point, the data of the lowest voltage drop measured at each measuring point show that the lowest voltage drop is the highest under a single-phase grounding fault, followed by a two-phase grounding fault, and the lowest voltage drop is the lowest when a three-phase grounding fault occurs.

4. The method for identifying faults in a renewable energy island power grid connected to a flexible direct current grid as claimed in claim 3, characterized in that: When a single-phase grounding fault, a two-phase grounding fault and a three-phase grounding fault occur respectively, the maximum voltage drop slope data under various fault conditions are extracted for comparative analysis. Among them, the voltage drop speed detected by multiple measuring points under a three-phase grounding fault is greater than the voltage drop speed when a single-phase grounding fault and a two-phase grounding fault occur.

5. The method for fault identification of renewable energy island power grid via flexible direct current grid connection system as claimed in claim 1, characterized in that: The lowest point of voltage drop and the maximum value of voltage drop slope during fault are taken as effective data indicators to reflect the fault type and fault location. Based on the lowest point of voltage drop and the maximum value of voltage drop slope during fault, a fault identification index system for renewable energy island flexible direct current transmission system is constructed.

6. The method for identifying faults in a renewable energy island power grid connected to a flexible direct current grid as claimed in claim 5, characterized in that: According to the voltage drop minimum point data and drop slope maximum value data detected at each measurement point, the fault identification index of each measurement point is constructed as follows: Where: λ i For the i Fault identification index of each measuring point; v min i The lowest voltage drop data measured at each measuring point; k max i The maximum value data of voltage drop slope measured at each measuring point; a 1. a 2 are the weighting coefficients of the lowest voltage drop point and the maximum voltage drop slope, respectively, satisfying a 1+ a 2=1.

7. The method for identifying faults in a renewable energy island power grid connected to a flexible direct current grid as claimed in claim 1, characterized in that: When different types of faults occur, regardless of the fault location, the lowest voltage drop point and the maximum voltage drop slope measured at each measurement point show the same pattern, that is, the fault discrimination index of each measurement point also shows the same pattern. The fault type discrimination index is constructed as follows: Where: μ It is the fault type identification index; n is the total number of measurement points. This indicator is the average value of the fault discrimination indicators of each measurement point. For various fault types, the fault type discrimination indicator has a corresponding value range. When the fault type discrimination indicator value falls within the corresponding value range, the fault type can be identified.

8. A fault identification system for renewable energy island power grid via flexible direct current grid connection system, characterized in that: include: A data acquisition module is used to obtain voltage data of each measuring point under a grid-connected system fault signal; A discrimination module, used for substituting the voltage data of each measuring point into the fault discrimination index system of the renewable energy island flexible direct current transmission system to discriminate the fault type and fault location; Among them, the process of constructing the fault discrimination index system of the renewable energy island through flexible direct current transmission system is as follows: obtaining historical electrical quantity data under different working conditions and different faults, constructing a fault database, and based on the fault database, quantitatively analyzing the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point under different fault locations and fault types, and based on the laws expressed by the voltage drop minimum point data and the voltage drop slope maximum value data of each measuring point, constructing the fault type discrimination index and the fault location discrimination index, and completing the construction of the fault discrimination index system of the renewable energy island through flexible direct current transmission system.

9. A non-transitory computer-readable storage medium, characterized in that: The non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by the processor, the fault identification method of the renewable energy island power grid through the flexible direct current grid-connected system as described in any one of claims 1 to 7 is implemented.

10. An electronic device, characterized in that: include: A processor, a memory and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory so that the electronic device executes the method for fault identification of a renewable energy island power grid through a flexible direct current grid-connected system as described in any one of claims 1 to 7.

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