Method and system for determining characteristics of UHV DC blocking fault

Abstract

The present invention provides a method and system for determining the characteristics of a UHV DC blocking fault. After simulating and calculating the unbalanced power of the UHV AC-DC power grid at multiple different times when the DC blocking fault occurs, the frequency and section power flow after the fault at each time are calculated respectively based on the unbalanced power at each time; the fault information in the UHV AC-DC power grid is calculated based on the section power flow; and the fault information is screened based on the distance and physical quantities to obtain the fault characteristics. The present invention explores the relationship between DC fault characteristics, screens and preprocesses the power grid environment information and DC fault characteristics, obtains accurate and specific fault characteristics, provides accurate model data for the deep learning training architecture, and can directly perform fault analysis using the deep learning method. It overcomes the shortcomings of the prior art that do not consider the power grid fault environment information and only model the physical characteristics of the power grid fault.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system automation, and particularly relates to a method and system for determining the characteristics of UHVDC blocking faults. Background Art

[0002] With the rapid development of UHV AC / DC interconnected power grids, the construction process of UHVDC has been accelerating continuously. The operation mode and dynamic behavior of the power grid are complex and changeable, and the degree of interdependence and coupling among regional power grids is also increasing. UHVDC effectively saves the corridor width of transmission lines and improves the transmission capacity, but at the same time brings new challenges to the safe and stable operation of the power grid. Once a blocking fault occurs in the UHVDC transmission system, a large amount of power surplus will be generated in the sending-end power grid, causing power imbalance and frequency increase in the regional power grid, resulting in unstable operation or even disconnection of the entire power system, affecting the safe operation of the entire power grid.

[0003] Currently, the dispatcher's regulation and control of the power grid after UHVDC blocking faults mainly rely on their own regulation and control experience, and use the formulated fault handling plans to handle power grid faults. However, due to the prominent characteristics of integrated power grid operation, the difficulty of real-time operation control by the dispatcher is increasing day by day. The previous dispatching control systems have deficiencies in supporting real-time monitoring and fault decision-making of UHV power grids. In this regard, many scholars have conducted a lot of research on the operation control of UHV AC / DC power grids. However, due to the complexity of the power grid structure, the physical characteristics of the power grid cannot be well modeled and simulated during simulation calculations, and the calculation results cannot meet the actual requirements. Therefore, the method based on the physical characteristics of the power grid has strong limitations. The existing technologies only model the physical characteristics of power grid faults, do not consider the power grid fault environment information, lack the influence of the environment information before and after the power grid fault on the power grid fault modeling, ignore some fault environment factors, and lack the effective information extraction and analysis of power grid fault characteristics. Summary of the Invention

[0004] To overcome the deficiencies of the above-mentioned prior art, the present invention proposes a method for determining the characteristics of UHVDC blocking faults, which is improved in that it includes:

[0005] Simulating and calculating the unbalanced power of the UHV AC / DC power grid after the occurrence of DC blocking faults at multiple different times;

[0006] Based on the unbalanced power at each moment, calculating the frequency and section power flow after the fault at each moment respectively;

[0007] Calculating the fault information in the UHV AC / DC power grid based on the section power flow;

[0008] Screening the fault information based on distance and physical quantities to obtain fault characteristics;

[0009] Among them, the fault information includes: the changes in the active power and reactive power of each branch in the UHV AC / DC power grid, the AC node voltages, and the DC node voltages before and after the fault.

[0010] The first preferred technical solution provided by the present invention is improved in that, based on distance and physical quantities, the fault information is screened to obtain fault characteristics, including:

[0011] Statistically count all fault information at all times;

[0012] For the same fault information at different times, determine whether the number of fault information not greater than the first threshold at different times exceeds the quantity threshold: if so, delete the fault information, otherwise retain the fault information;

[0013] For each retained item of fault information, calculate the ratio of the average value of the fault information at each time to the corresponding value before the fault;

[0014] Divide the ratio by the electrical distance to obtain a fault characteristic value;

[0015] For each item of fault information, determine whether the fault characteristic value corresponding to the fault information is greater than the second threshold: if so, retain the fault information and the values before and after the occurrence of the corresponding fault as fault characteristics, otherwise delete the fault information.

[0016] The second preferred technical solution provided by the present invention is improved in that the average value of the fault information is the average value after removing one maximum value and one minimum value.

[0017] The third preferred technical solution provided by the present invention is improved in that, based on the unbalanced power at each time, the frequency and section power flow after the fault at each time are calculated respectively, including:

[0018] Based on the unbalanced power at each time, use the dynamic power flow algorithm to calculate the frequency and section power flow after the fault at each time respectively.

[0019] The fourth preferred technical solution provided by the present invention is improved in that the inequality constraints of the AC system of the dynamic power flow algorithm are shown as the following formula:

[0020]

[0021] Among them, N ss represents the set of AC nodes in the UHV AC / DC power grid, and N G represents the set of all generator nodes in the UHV AC / DC power grid; the superscript min represents the minimum value of the corresponding value, and the superscript max represents the maximum value of the corresponding value; U siDenotes the voltage of the AC node i, S ij Denotes the apparent power between the AC nodes i and j, Q si Denotes the reactive power of the AC node i; P Gi Denotes the active power generation of the generator node i, Q Gi Denotes the reactive power generation of the generator node i.

[0022] The fifth preferred technical solution provided by the present invention is improved in that the DC system inequality constraints of the dynamic power flow algorithm are shown as follows:

[0023]

[0024] Wherein, N d Denotes the set of DC nodes in the UHV AC / DC power grid, N C Denotes the set of virtual synchronous machines; the superscript min represents the minimum value of the corresponding value, and the superscript max represents the maximum value of the corresponding value; U dk Denotes the voltage of the DC node k, U cn Denotes the AC-side voltage of the converter of the virtual synchronous machine n, M n Denotes the modulation ratio of the virtual synchronous machine n, I n Denotes the thermal capacity of the virtual synchronous machine n, I kv Denotes the current between the DC nodes k and v.

[0025] The sixth preferred technical solution provided by the present invention is improved in that after screening the fault information based on the distance and physical quantities to obtain the fault characteristics, it further includes:

[0026] For each fault characteristic, respectively obtain the out-of-limit type corresponding to the fault characteristic or frequency according to the fault characteristic and the post-fault value corresponding to the frequency according to the preset standard;

[0027] Use the field of the number of out-of-limit types to record whether the fault characteristic or frequency is the corresponding out-of-limit type, and jointly form a fault model with the pre-fault and post-fault values corresponding to the fault characteristic or frequency.

[0028] The seventh preferred technical solution provided by the present invention is improved in that the pre-fault and post-fault values corresponding to the fault characteristic or frequency in the fault model are normalized values.

[0029] Based on the same inventive concept, the present invention also provides a system for generating a continuous operation simulation section of a power grid, including: a simulation calculation module, a frequency and section module, a fault information module, and a fault characteristic module;

[0030] The simulation calculation module is used to simulate and calculate the unbalanced power of the UHV AC / DC power grid after the occurrence of a DC blocking fault at multiple different times.

[0031] The frequency and section module is used to calculate the frequency and section power flow after the fault at each time based on the unbalanced power at each time.

[0032] The fault information module is used to calculate the fault information in the UHV AC / DC power grid based on the section power flow.

[0033] The fault feature module is used to screen the fault information based on distance and physical quantities to obtain fault features.

[0034] Among them, the fault information includes: the active power and reactive power of each branch in the UHV AC / DC power grid, and the change amounts of the voltages of each AC node and each DC node before and after the fault.

[0035] The eighth preferred technical solution provided by the present invention is improved in that the fault feature module includes: a statistics unit, a first screening unit, a ratio unit, a fault feature value unit, and a second screening unit;

[0036] The statistics unit is used to respectively count all the fault information at all times.

[0037] The first screening unit is used to, for the same fault information at different times, judge whether the number of fault information not greater than the first threshold at different times exceeds the quantity threshold: if so, delete the fault information, otherwise retain the fault information;

[0038] The ratio unit is used to, for each retained item of fault information, calculate the ratio of the average value of the fault information at each time to the corresponding value before the fault.

[0039] The fault feature value unit is used to divide the ratio by the electrical distance to obtain the fault feature value.

[0040] The second screening unit is used to, for each item of fault information, judge whether the fault feature value corresponding to the fault information is greater than the second threshold: if so, retain the fault information and the values before and after the occurrence of the fault corresponding to the fault information as fault features, otherwise delete the fault information.

[0041] Compared with the closest prior art, the beneficial effects of the present invention are as follows:

[0042] The present invention provides a method and system for determining the characteristics of UHV DC blocking faults. After simulating and calculating the unbalanced power of the UHV AC-DC power grid at multiple different times after the occurrence of a DC blocking fault, the frequency and section power flow after the fault at each time are calculated based on the unbalanced power at each time. Based on the section power flow, the fault information in the UHV AC-DC power grid is calculated. Based on the distance and physical quantities, the fault information is screened to obtain the fault characteristics. The present invention explores the relationships between DC fault characteristics, screens and preprocesses the grid environment information and DC fault characteristics to obtain accurate and specific fault characteristics, providing accurate model data for the deep learning training architecture, and can directly perform fault analysis using deep learning methods. It overcomes the shortcomings of the prior art that do not consider the grid fault environment information and only models the physical characteristics of grid faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 FIG. is a schematic flow chart of a method for determining the characteristics of UHV DC blocking faults provided by the present invention;

[0044] Figure 2 FIG. is a schematic basic structure diagram of a system for determining the characteristics of UHV DC blocking faults provided by the present invention;

[0045] Figure 3 FIG. is a schematic detailed structure diagram of a system for determining the characteristics of UHV DC blocking faults provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0047] Embodiment 1:

[0048] A schematic flow chart of a method for determining the characteristics of UHV DC blocking faults provided by the present invention is as Figure 1 shown and includes:

[0049] Step 1: After simulating and calculating the unbalanced power of the UHV AC-DC power grid at multiple different times after the occurrence of a DC blocking fault;

[0050] Step 2: Based on the unbalanced power at each time, calculate the frequency and section power flow after the fault at each time respectively;

[0051] Step 3: Based on the section power flow, calculate the fault information in the UHV AC-DC power grid;

[0052] Step 4: Based on the distance and physical quantities, screen the fault information to obtain the fault characteristics;

[0053] Among them, the fault information includes: the changes in the active power and reactive power of each branch in the UHV AC-DC power grid, the voltages of each AC node, and the voltages of each DC node before and after the fault.

[0054] Specifically, in order to overcome the shortcomings of the prior art that only the physical characteristics of power grid faults are modeled, the prior art does not consider the power grid fault environment information, lacks the influence of the environmental information before and after the power grid fault on the power grid fault modeling, ignores some fault environment factors, lacks effective information extraction and analysis of power grid fault characteristics, and the modeling of the prior art cannot be directly applied to subsequent deep learning functional decision-making. The present invention proposes a method and system for determining the characteristics of UHV DC locking faults, mines the relationship between DC fault characteristics, screens and pre-processes the power grid environment information and DC fault characteristics before and after the fault, obtains accurate and specific fault characteristics, provides accurate model data for the deep learning training architecture, and can directly perform fault analysis.

[0055] First, the power grid fault environment information is described.

[0056] In large-scale UHV AC and DC transmission networks, the UHV DC transmission and receiving systems interact with each other. The UHV DC transmission system is connected to a large number of AC lines. The two are coupled with each other, and the impact of local failures in the DC system is relatively large. For example, more than 250 AC lines in the main grid of the East China Power Grid can cause seven DC commutation failures. If continuous commutation failures occur in the DC transmission to East China during the flood season, the 500 kV section of the sending grid may exceed the limit of stability. After a DC failure, joint control is required at all levels and local control centers to fully recover.

[0057] The data information of the normal operation of the power grid before the failure includes the total output of the power grid units at the DC sending and receiving ends, the total load network loss, the frequency limit, the voltage limit and the power shortage, the control mode and reactive power compensation of the DC sending and receiving ends before the failure, the transmission power of the interconnection line to obtain the unbalanced power of the receiving end power grid, and the voltage amplitude, voltage phase angle, line active power and line reactive power of all AC electrical islands connected to the DC lines.

[0058] After a UHV DC fault occurs, due to a sudden large power loss in the power grid, calculate the unbalanced power ΔP at the time of fault t = 0 (0) :

[0059] ΔP (0) =P G(0) -P L(0) -P Loss

[0060] Among them, P G(0) is the total power output of the grid, P L(0) is the total load of the power grid, P Loss is the total grid loss.

[0061] After a DC blocking fault occurs in the power grid, the post-fault frequency f is calculated using the dynamic power flow algorithm. (i+1)And the main cross-section tidal current. The frequency change amount at t = 0 is as follows:

[0062] Δf (0) =f (N) -f (0)

[0063] where f (N) =50Hz, f (0) is the system frequency at t = 0, i.e., the fault moment. The iterative formula is as follows:

[0064]

[0065] The frequency change amount Δf at t = i is calculated from the above formula (i) , where Δt is the iterative time interval, and Δf (i-1) is the frequency change amount at t = i - 1. The system dynamic primary frequency regulation frequency is calculated according to the following formula:

[0066] f (i+1) =f (i) +Δf (i)

[0067] where f (i+1) is the system dynamic primary frequency regulation frequency at t = i + 1, and f (i) is the system dynamic primary frequency regulation frequency at t = i.

[0068] During the dynamic power flow calculation, in order to ensure the convergence of the system after the fault, the threshold values of voltage and power can be appropriately increased. The inequality constraint conditions of the AC system after the fault are:

[0069]

[0070] where N ss represents the set of AC nodes in the UHV AC / DC power grid, and N G represents the set of all generator nodes in the UHV AC / DC power grid; the superscript min represents the minimum value of the corresponding value, and the superscript max represents the maximum value of the corresponding value; U si represents the voltage of AC node i, S ij represents the apparent power between AC nodes i and j, Q si represents the reactive power of AC node i; P Gi represents the active power generation of generator node i, and Q Gi represents the reactive power generation of generator node i.

[0071] The DC system inequality constraints include: DC node voltage constraint, converter AC side voltage constraint, modulation ratio constraint, VSC thermal capacity constraint, and DC line maximum allowable current constraint, i.e.:

[0072]

[0073] Among them, N d represents the set of DC nodes in the UHV AC-DC power grid, and N C represents the set of virtual synchronous machines; the superscript min represents the minimum value of the corresponding value, and the superscript max represents the maximum value of the corresponding value; U dk represents the voltage of DC node k, and U cn represents the AC-side voltage of the converter of virtual synchronous machine n, M n represents the modulation ratio of virtual synchronous machine n, I n represents the thermal capacity of virtual synchronous machine n, I kv represents the current between DC nodes k and v.

[0074] According to the results of the dynamic power flow calculation, judge the specific states of the frequency, voltage or line power of the actual power grid after the fault, and record them as different types. For the bus voltage, different type flags are recorded as different numbers, as shown in the following table:

[0075] Table 1 Types of bus voltages after the fault

[0076] Flag bit 0 1 2 3 4 5 Type Normal Below lower limit Above upper limit Maximum voltage rise Maximum voltage drop Highest voltage

[0077] For power over-limit, as shown in the following table:

[0078] Table 2 Types of power over-limit after the fault

[0079] Flag 0 1 2 Type Normal Below lower limit Above upper limit

[0080] For frequency over-limit, as shown in the following table:

[0081] Table 3 Types of frequency over-limit after the fault

[0082] Flag 0 1 2 Type Normal Below lower limit Above upper limit

[0083] Secondly, perform fault information screening.

[0084] The amount of information on the frequency, voltage and line power of the power grid involved before and after the UHVDC blocking fault is huge, and it is necessary to pick out the effective information among them, that is, to find the information of the buses, units and lines affected by the DC blocking fault in the huge power grid environment information. These information that can fully reflect the DC fault are the screened fault characteristics.

[0085] Select the real-time power flow data of DC operation at different times to perform the above DC fault simulations. The simulations are carried out m times in total, and m sets of data before and after the fault are obtained. Analyze the power flow data before and after the DC blocking fault. There are n nodes in the AC-DC power transmission system. Then, the active power change ΔP ij and reactive power change ΔQ ij of the line ij (i, j = 1, 2, 3,..., n) (i.e., the line between nodes i and j) before and after the DC blocking fault are as shown in the following formula:

[0086]

[0087]

[0088] Among them, and respectively represent the active and reactive power transmission values of the ij branch before the fault, and respectively represent the active and reactive power transmission values of the ij branch after the fault.

[0089] Similarly, the voltage amplitude changes ΔU i and ΔU k of the i-th (i = 1, 2, 3,..., n) AC node and the k-th (k = 1, 2, 3,..., d) DC node before and after the DC blocking fault are as shown in the following formula:

[0090]

[0091]

[0092] Among them, and respectively represent the voltage values of the AC node and the DC node before the fault, and respectively represent the voltage values of the AC node and the DC node after the fault.

[0093] If in the simulation results exceeding the quantity threshold, the above four change quantities ΔP ij , ΔQ ij , ΔU i and ΔU k of the AC-DC power grid are not greater than their respective first thresholds, then the corresponding ΔP ij , ΔQ ij , ΔU i or ΔU k data do not reflect the characteristics of DC faults and are directly excluded. Among them, the quantity threshold can be set to 2 / 3m.

[0094] The remaining data is still m groups. For the same type of data, one maximum value is removed, and after removing one minimum value, the average value is taken. Then, the average value is divided by the data before the fault to obtain a ratio, and the ratio is divided by the electrical distance to obtain the fault characteristic value, denoted as ΔP ij as an example:

[0095]

[0096]

[0097] Among them, is the average value corresponding to ΔP ij , and is the corresponding fault characteristic value, D is the electrical distance of the node, that is, the number of branches of the fault line on node i. For and , they are sorted from large to small respectively. The larger the ratio, the greater the impact of the fault. Take the second threshold. If and are each greater than the second threshold, then the or that is greater than the second threshold is retained, and the corresponding ΔP ij , ΔQ ij , ΔU i and ΔU k are also retained, as well as the corresponding original data and and

[0098] Finally, perform fault characteristic processing to build a model.

[0099] After reading the m groups of fault characteristic data after screening, data preprocessing is required before using deep learning methods for training and learning. Organize the characteristic data before and after the fault for each group, and the explanations of each field are shown in the following table:

[0100] Table 4 Explanation of Fault Characteristic Fields (Partial)

[0101]

[0102]

[0103] Table 4 lists the bus voltage of node 33 and the active power of branch 13. For each selected bus voltage and active power, reactive power, frequency, voltage and other fault characteristics, they are listed as characteristic fields. Among them, Number is the serial number field of each fault simulation data, which has little association with the dispatching decision we want to train and generate, so we ignore and delete it, and only select the fields useful for the dispatching decision. If several data field values are null, the null values must be changed to the average value of m groups of this fault characteristic data. The Type type field is a classification characteristic field. If there are n classifications, it is converted into n fields. For example, the No.33_bus_voltage_type field is converted into 6 fields, as shown in Table 5 respectively:

[0104] Table 5 Preprocessing of Classification Characteristic Fields

[0105] Classification field Data description No.33_bus_voltage_type_0 The normal value of the voltage at bus No. 33 is 1, otherwise 0 No.33_bus_voltage_type_1 The voltage at bus No. 33 is 1 when it is below the lower limit, otherwise 0 No.33_bus_voltage_type_2 The voltage at bus No. 33 is 1 when it is above the upper limit, otherwise 0 No.33_bus_voltage_type_3 The maximum voltage rise of the voltage at bus No. 33 is 1, otherwise 0 No.33_bus_voltage_type_4 The maximum voltage drop of the voltage at bus No. 33 is 1, otherwise 0 No.33_bus_voltage_type_5 The highest voltage of the voltage at bus No. 33 is 1, otherwise 0

[0106] After processing the classification characteristic fields, because the unit of the numerical characteristic fields is different and the numerical differences will be very large, and there are per-unit values and nominal values in the power system fault characteristic data, with large numerical differences, it is necessary to standardize the characteristic fields so that all numerical values are in the same interval, giving the numerical characteristic fields a common standard, thereby improving the accuracy of the trained model.

[0107] Standardization scales the data proportionally so that it falls into a small specific interval. It does not change the feature distribution and will not cause the data to lose its feature information. Since the data has different evaluation indicators, their dimensions or dimension units are different and they are at different orders of magnitude. Therefore, it is necessary to remove the unit limitation of the data and convert it into a dimensionless pure numerical value, so that indicators with different units or magnitudes can be compared and weighted, making the features between different dimensions comparable numerically and greatly improving the accuracy of the classifier. Moreover, the process of finding the optimal solution will become smoother and it is easier to converge correctly, that is, it can improve the iteration speed when using gradient descent to find the optimal solution. In addition, when it comes to some algorithms involving distance calculation, standardization can make each feature contribute equally to the result, effectively reducing the loss of accuracy. So standardization is very necessary, and the most typical one is the linear normalization processing of the data, that is, mapping the data uniformly to the [0,1] interval.

[0108]

[0109] Among them, X scaled is the normalization result, X is the sample value, X min is the difference of the minimum sample, X max -X min is the sample span, (max-min) is the scaling range, and min is the scaling minimum value.

[0110] For the retained or the corresponding ΔP ij , ΔQ ij , ΔU i and ΔU k , and the corresponding original data and Furthermore, by performing the above processing on the frequencies before and after the fault and the frequency over-limit type, a fault model is jointly constructed.

[0111] Finally, each fault model is a one-dimensional array, including the pre- and post-fault characteristic quantities and characteristic fields of the nodes and branches after filtering the fault information, as well as the characteristic quantities and characteristic fields of the frequencies before and after the fault.

[0112] Embodiment 2:

[0113] Based on the same inventive concept, the present invention also provides a system for determining the characteristics of a UHV DC blocking fault. Since the principles of these devices for solving technical problems are similar to those of the method for determining the characteristics of a UHV DC blocking fault, the repeated parts will not be elaborated herein.

[0114] The basic structure of this system is as Figure 2 shown, including: a simulation calculation module, a frequency and section module, a fault information module, and a fault characteristic module;

[0115] Among them, the simulation calculation module is used to simulate and calculate the unbalanced power of the UHV AC / DC power grid after the occurrence of a DC blocking fault at multiple different times;

[0116] The frequency and section module is used to calculate the frequency and section power flow after the fault at each moment based on the unbalanced power at each moment;

[0117] The fault information module is used to calculate the fault information in the UHV AC / DC power grid based on the section power flow;

[0118] The fault characteristic module is used to screen the fault information based on the distance and physical quantity to obtain the fault characteristics;

[0119] Among them, the fault information includes: the changes in the active power and reactive power of each branch in the UHV AC / DC power grid, the AC node voltages, and the DC node voltages before and after the fault.

[0120] The detailed structure of the system for determining the characteristics of a UHV DC blocking fault is as Figure 3 shown.

[0121] Among them, the fault characteristic module includes: a statistical unit, a first screening unit, a ratio unit, a fault characteristic value unit, and a second screening unit;

[0122] A statistical unit for separately counting all fault information at all times;

[0123] A first screening unit for, for the same fault information at different times, determining whether the number of fault information not greater than a first threshold at different times exceeds a quantity threshold: if so, deleting the fault information; otherwise, retaining the fault information;

[0124] A ratio unit for, for each retained fault information item, separately calculating the ratio of the average value of the fault information at each time to the corresponding value before the fault;

[0125] A fault eigenvalue unit for dividing the ratio by the electrical distance to obtain a fault eigenvalue;

[0126] A second screening unit for, for each item of fault information, determining whether the fault eigenvalue corresponding to the fault information is greater than a second threshold: if so, retaining the fault information and the values before and after the fault corresponding to the fault information as fault characteristics; otherwise, deleting the fault information.

[0127] Wherein, the average value of the fault information is the average value after excluding one maximum value and one minimum value.

[0128] Wherein, based on the unbalanced power at each time, the frequency and section power flow after the fault at each time are respectively calculated, including:

[0129] Based on the unbalanced power at each time, using the dynamic power flow algorithm, the frequency and section power flow after the fault at each time are respectively calculated.

[0130] Wherein, the system further includes a modeling module for establishing a fault model; the modeling module includes: an overlimit type unit and a fault model unit;

[0131] An overlimit type unit for, for each fault characteristic, respectively obtaining the overlimit type corresponding to the fault characteristic or frequency according to the fault characteristic and the value after the fault corresponding to the frequency according to a preset standard;

[0132] A fault model unit for using a field of the number of overlimit types to record whether the fault characteristic or frequency is the corresponding overlimit type, and jointly forming a fault model with the values before and after the fault corresponding to the fault characteristic or frequency.

[0133] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0134] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows 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 the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing device generate means for implementing the functions specified in one or more of the flows Figure 1 one or more of the flows and / or blocks Figure 1 one or more of the blocks.

[0135] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means for implementing the functions specified in one or more of the flows Figure 1 one or more of the flows and / or blocks Figure 1 one or more of the blocks.

[0136] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more of the flows Figure 1 one or more of the flows and / or blocks Figure 1 one or more of the blocks.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the scope of its protection. Although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: after reading the present application, those skilled in the art can still make various changes, modifications, or equivalent replacements to the specific implementation manners of the application, but these changes, modifications, or equivalent replacements are all within the scope of the protection of the claims pending for the application.

Claims

1. A method for determining the characteristics of a UHV DC blocking fault, characterized in that including: simulating and calculating the unbalanced power of the UHV AC / DC power grid after the occurrence of a DC blocking fault at multiple different times; respectively calculating the frequency and section power flow after the fault at each moment based on the unbalanced power at each moment; calculating the fault information in the UHV AC / DC power grid based on the section power flow; screening the fault information based on distance and physical quantities to obtain fault characteristics; wherein the fault information includes: the changes in the active power and reactive power of each branch in the UHV AC / DC power grid, the voltages of each AC node, and the voltages of each DC node before and after the fault; the screening the fault information based on distance and physical quantities to obtain fault characteristics includes: respectively counting all the fault information at all times; for the same fault information at different times, judging whether the number of fault information not greater than the first threshold at different times exceeds the quantity threshold: if so, deleting the fault information, otherwise retaining the fault information; for each retained fault information, respectively calculating the ratio of the average value of the fault information at each moment to the corresponding value before the fault; dividing the ratio by the electrical distance to obtain a fault characteristic value; for each item of fault information, judging whether the fault characteristic value corresponding to the fault information is greater than the second threshold: if so, retaining the fault information and the values before and after the occurrence of the fault corresponding to the fault information as fault characteristics, otherwise deleting the fault information.

2. The method according to claim 1, wherein The average value of the fault information is the average value after removing one maximum value and one minimum value.

3. The method according to claim 1, characterized in that, The respectively calculating the frequency and section power flow after the fault at each moment based on the unbalanced power at each moment includes: based on the unbalanced power at each moment, using the dynamic power flow algorithm to respectively calculate the frequency and section power flow after the fault at each moment.

4. The method according to claim 3, wherein The inequality constraints of the AC system of the dynamic power flow algorithm are shown as follows: Among them, N ss represents the set of AC nodes in the UHV AC / DC power grid, and N G represents the set of all generator nodes in the UHV AC / DC power grid; the superscript min represents the minimum value of the corresponding value, and the superscript max represents the maximum value of the corresponding value; U si represents the voltage of AC node i, and S ij represents the apparent power between AC nodes i and j, and Q si represents the reactive power of AC node i; P Gi represents the active power generation of generator node i, and Q Gi represents the reactive power generation of generator node i.

5. The method according to claim 3, characterized in that, The inequality constraints of the DC system of the dynamic power flow algorithm are shown as follows: Among them, N d represents the set of DC nodes in the UHV AC / DC power grid, and N C represents the set of virtual synchronous machines; the superscript min represents the minimum value of the corresponding value, and the superscript max represents the maximum value of the corresponding value; U dk represents the voltage of DC node k, and U cn represents the AC-side voltage of the converter of virtual synchronous machine n, M n represents the modulation ratio of virtual synchronous machine n, I n represents the thermal capacity of virtual synchronous machine n, I kv represents the current between DC nodes k and v.

6. The method according to claim 1, characterized in that, After the screening the fault information based on distance and physical quantities to obtain fault characteristics, it further includes: for each fault characteristic, respectively obtaining the over-limit type corresponding to the fault characteristic or frequency according to the fault characteristic and the value after the fault corresponding to the frequency according to a preset standard; using a field of the number of over-limit types to record whether the fault characteristic or frequency is the corresponding over-limit type, and jointly forming a fault model with the values before and after the occurrence of the fault corresponding to the fault characteristic or frequency.

7. The method according to claim 6, wherein The values before and after the occurrence of the fault corresponding to the fault characteristic or frequency in the fault model are normalized values.

8. A characteristic determination system for UHVDC blocking faults, characterized in that, including: a simulation calculation module, a frequency and section module, a fault information module, and a fault characteristic module; the simulation calculation module is used to simulate and calculate the unbalanced power of the UHV AC / DC power grid after the occurrence of a DC blocking fault at multiple different times; the frequency and section module is used to respectively calculate the frequency and section power flow after the fault at each moment based on the unbalanced power at each moment; the fault information module is used to calculate the fault information in the UHV AC / DC power grid based on the section power flow; the fault characteristic module is used to screen the fault information based on distance and physical quantities to obtain fault characteristics; Among them, the fault information includes: the changes in the active power and reactive power of each branch in the UHV AC / DC power grid, the AC node voltages, and the DC node voltages before and after the fault; The fault feature module includes: a statistics unit, a first screening unit, a ratio unit, a fault feature value unit, and a second screening unit; The statistics unit is used to respectively count all the fault information at all times; The first screening unit is used to, for the same fault information at different times, determine whether the number of fault information not greater than the first threshold at different times exceeds the quantity threshold: if so, delete the fault information, otherwise retain the fault information; The ratio unit is used to, for each retained item of fault information, calculate the ratio of the average value of the fault information at each time to the corresponding value before the fault; The fault feature value unit is used to divide the ratio by the electrical distance to obtain the fault feature value; The second screening unit is used to, for each item of fault information, determine whether the fault feature value corresponding to the fault information is greater than the second threshold: if so, retain the fault information and the values before and after the corresponding fault occurrence of the fault information as the fault feature, otherwise delete the fault information.

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