Dynamic simulation models, screening methods, equipment and media for cascading faults in power systems

Abstract

This invention discloses a dynamic simulation model, screening method, equipment, and medium for power system cascading failures, relating to the field of power system cascading failure technology. The invention includes sampling line fault rate data under severe weather conditions, considering latent faults caused by misoperation during major power outages, and incorporating time parameters to characterize line breaks, fault repair, and fault maintenance models under power system impacts; establishing a system frequency simulation model around the power system, and establishing transient characteristics of synchronous generators, distributed power sources, and load nodes; establishing fault models and judgment methods in a hybrid simulation model, classifying these fault types, and incorporating them into the hybrid simulation model; acquiring real-time power system operating data, inputting it into the hybrid simulation model, and then screening cascading failure types according to fault type classification for assessing and preventing power system cascading failure risks.

Description

Technical Field

[0001] This invention relates to the field of power system cascading failure technology, specifically to dynamic simulation models, screening methods, equipment, and media for power system cascading failures. Background Technology

[0002] With the rapid development of my country's economy, the demand for electricity will continue to increase, and the interconnection and complexity of the power system will also continue to improve. This undoubtedly increases the risk of cascading failures in the power system. In the past few decades, cascading failures have triggered several major power outages, causing huge economic losses to society. Therefore, the key to preventing and mitigating low-probability, high-impact disasters and improving the safety performance and resilience of the power system lies in cascading failures. In other words, the study of the occurrence process of cascading failures and the formulation of corresponding defense strategies are of great significance.

[0003] In power systems, cascading faults refer to a series of fault events triggered by one or more initial faults, which then lead to the successive failures of other components in the system. The occurrence of cascading faults may originate from factors such as aging faults, protection malfunctions, and human error within the power system, or from factors outside the power system such as natural disasters and vegetation contact with lines. Therefore, relying solely on safety checks based on a given set of anticipated faults is insufficient to effectively reduce the risk of cascading faults. In fact, after the initial triggering stage of a cascading fault, the factors that exacerbate the propagation of the cascading process in the system mainly come from within the system. These factors include, but are not limited to, line overload outages caused by power flow transfer, protection malfunctions or failures to operate, latent faults, and system disconnection. Given the different mechanisms exhibited by cascading faults in the initial triggering stage and the subsequent propagation stage, the analysis and handling of faults in the two stages will also differ.

[0004] To prevent cascading failures and mitigate their propagation, targeted modeling of the complex processes involved in cascading failures is necessary. This requires reliable control over the behavior of power system components and power flow changes to identify potential faults that may be triggered in cascading failures and the reasons for such triggering. This is essential for predicting cascading failures. After constructing the corresponding cascading failure model, multiple random sampling simulations of the power system are required. This allows for the assessment of cascading failure risks and provides targeted data for cascading failure prevention, which is of great significance for power system planning and construction. Summary of the Invention

[0005] The purpose of this invention is to provide a dynamic simulation model, screening method, equipment and medium for power system cascading failures, for assessing the risk of power system cascading failures, and for providing targeted data for cascading failure prevention.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a dynamic simulation model for cascading faults in power systems, as detailed below:

[0007] We sampled line fault rate data under severe weather conditions, considered hidden faults caused by misoperation in major power outages, and added time parameters to characterize line disconnection, fault repair, and fault repair models under power system impact.

[0008] A transient-steady-state hybrid simulation model was established for the power system, and the transient characteristics of synchronous generators, distributed power sources, and load nodes were established.

[0009] Establish fault models and judgment methods in the transient steady-state hybrid simulation model, classify these fault forms, and add them to the hybrid simulation model;

[0010] By acquiring real-time operating data of the power system and inputting it into a transient-steady-state hybrid simulation model, cascading fault types can be filtered according to fault type classification, which can be used to assess and prevent the risk of cascading faults in the power system.

[0011] Furthermore, the line failure rate data is sampled to establish a simulation process and determine the corresponding time parameters. The specific steps are as follows:

[0012] 1) Initialize the relevant parameters of the power system network based on the power system model data;

[0013] 2) Sample line faults caused by severe weather and set them as the initial faults of the system;

[0014] 3) Detect whether an island has been generated in the power system. If no island has been generated, continue sampling the faulty line; if there is only one island, proceed to step 4); if the number of islands is greater than or equal to two, proceed to step 6.

[0015] 4) Calculate the power flow based on the new system topology after the line breakage, determine whether the power flow of each line is overloaded, and for overloaded lines, calculate their fault probability according to the following formula fault probability model and update the line status information.

[0016]

[0017] in p is the probability of failure for line l. l This is the current load rate of line l. It is the rated load rate of line l. It is the maximum load factor of line l;

[0018] If a new line experiences an overload fault, determine the number of islands. If it is still one, repeat step 4). If it is greater than or equal to two, proceed to step 6. If no new line experiences an overload fault, proceed to step 5.

[0019]

[0020] Among them, t i a is the time interval between the previous line disconnection and the current line i disconnection. i b is a constant i c is the time coefficient. i Let x be the reciprocal of the expected value, and x be a random positive number greater than or equal to 0;

[0021] 5) Perform latent fault sampling on the line. Sample whether a latent fault has occurred on the adjacent line of the previously faulted line. If a new latent fault occurs, proceed to step 4). If no latent fault occurs, proceed to the optimal load shedding model. The goal of this model is to minimize the total load shedding of the system under the constraints of power balance and no line power flow overload. Proceed to step 7).

[0022] 6) For each island, determine its island type. For the number and type of nodes in each island, perform load shedding, calculate and record the total load loss. This cascading failure simulation ends. Increment the simulation test count and proceed to step 7).

[0023] 7) Power system recovery fault sampling: For lines disconnected after a fault, set their recovery time as shown in the following formula. After the fault development process, line recovery and load shedding recovery, complete the cascading fault simulation. The simulation test data is incremented and proceeds to step 8).

[0024]

[0025] Among them, t ri Let a be the recovery time of line i. ri b is a constant ri c is the time coefficient. ri Let x be the reciprocal of the expected value, where x is a positive number greater than or equal to 0.

[0026] 8) Calculate and record the faulty line, number of trips, load loss and fault development curve data in each simulation test. If the data obtained from the simulation test does not meet the convergence condition, proceed to step 2); otherwise, the simulation test is completed.

[0027] Cv n >Cv0

[0028] Among them, Cv nIt is the coefficient of variation obtained from n simulation test data, and its reference value Cv0 is set to 0.05. The simulation test ends when the above formula is satisfied.

[0029] Furthermore, a system frequency simulation model is established, and the transient characteristics of synchronous generators, distributed power sources, and load nodes are established. The specific steps are as follows:

[0030] 1) Establish a transient frequency model: Establish a system frequency simulation model around the power system. Considering that the load nodes are constant loads and that neither distributed power sources nor load nodes participate in frequency regulation, the node inertia is set to H=0. The synchronous generator has frequency regulation function: The synchronous generator is set to consider frequency changes. The frequency is determined by the rotational speed, inertia, mechanical power and electromagnetic power. Nodes other than the synchronous generator are regarded as having the same frequency.

[0031] For n lines in a power system The N fault chains {L1, L2, ..., L...} obtained through N simulations will be... N The propagation relationship of} can be represented by an undirected graph. This means, that is:

[0032]

[0033]

[0034] The above two equations are the equations for the changes in the node frequency of the synchronous generator and the system frequency, respectively.

[0035] In the formula, the subscript i refers to the i-th synchronous generator, and δ i To change the phase angle at the node, P is the node angular frequency. mi P ei These refer to the nodal mechanical power and electromagnetic power, respectively, γ i H is the nodal damping coefficient. i Let P be the nodal inertia, where each term in the following formula represents a system value. loss This refers to system line losses.

[0036] 2) Power flow calculation in transient model iteration: After the phase angle iteration of each node in the system is completed, the power from time t to time t+1 is obtained by the following formula;

[0037]

[0038] in, This refers to the apparent power injected by the node, P m (t+1) and Q m (t+1) represents its active and reactive components, the values ​​of which are determined by the node voltage V. m V n Phase angle θm ,θ n The above equation is obtained by combining the grid impedance admittance parameters G and B. In the equation, S... m It refers to the set of nodes connected to m nodes in the power grid topology.

[0039] 3) Iterative solution process for node phase angle and frequency data: After solving the power flow based on the voltage and phase angle of the previous moment, the phase angle of each node in the system is iterated and the frequency change rate is calculated. Then, the voltage of the node where the renewable energy motor of the same type is located is iterated, thereby updating the state of the entire network at time t+1.

[0040] Furthermore, the fault model and judgment method in the system frequency simulation model are established as follows:

[0041] 1) Initial Fault

[0042] Power system failures caused by severe weather are classified as line outages.

[0043] 2) Transient power flow exceeding limits

[0044] The occurrence of this phenomenon in transient simulations demonstrates that power flow limits can be determined at each step of the transient simulation by calculating the phase angle of the node voltages, indicating that conventional cascading fault simulations cannot address power flow limits.

[0045] The fault triggering conditions are as follows:

[0046]

[0047] Among them, Sl m,t Let m be the apparent power of line m at time t. For the rated apparent power of line m, k tsl This is the coefficient for judging the limit of the current trend;

[0048] 3) Frequency change rate exceeds the limit

[0049] In each transient simulation step, the fault screening for transient frequency change rate exceeding the limit is achieved by comparing the frequency change rate of the synchronous generator node with the reference value of the node other than the synchronous generator node.

[0050] The fault triggering conditions are as follows:

[0051]

[0052] Among them, RoCoF n,t Let RoCoF be the rate of change of the frequency of node n at time t. min ,RoCoF max These are the upper and lower limits of the rate of change of node frequency, respectively.

[0053] 4) Frequency exceeding limits

[0054] In each transient simulation step, fault screening for transient frequency exceeding limits is achieved by comparing the frequency of the synchronous generator node with the reference value of other nodes.

[0055] The fault triggering conditions are as follows:

[0056]

[0057] Among them, fr n,t Let fr be the frequency of node n at time t. min ,fr max These represent the upper and lower limits of the node frequency, respectively.

[0058] 5) Generator voltage exceeds limit

[0059] In each transient simulation step, transient generator voltage fault screening is achieved by comparing the voltage of each generator node at each step with the lowest and highest normal operating voltages.

[0060] The fault triggering conditions are as follows:

[0061]

[0062] Among them, V n,t Let k be the node voltage of node n at time t. V,min k V,max This is the threshold voltage judgment coefficient.

[0063] 6) Phase shift exceeding limits at distributed power generation nodes

[0064] Modeling phase-shifting protection of distributed generation sources on the power system side, extracting phase angle changes under different phase lengths of distributed generation nodes in transient simulation, and comparing them with power system constraint values ​​to achieve screening of such faults;

[0065] The fault triggering conditions are as follows:

[0066] Ph l,t -Ph l,t-tph -fr0·tph>Ph Δ

[0067] Among them, Ph l,t Let fr0 be the phase angle at node t where the l-th new energy generator is located, tph be the rated frequency, and tph be the time interval for judging phase shift protection. Δ To determine the phase angle of the phase-shifting protection.

[0068] 7) Steady-state power flow exceeding limits

[0069] This indicates a power flow exceeding the limit triggered in steady-state simulation;

[0070] The fault triggering conditions are as follows:

[0071]

[0072] in p is the probability of failure for line l. l This is the current load rate of line l. It is the rated load rate of line l. It is the maximum load factor of line l;

[0073] 8) Steady-state latent faults

[0074] This represents a latent fault in the power system triggered during steady-state simulation.

[0075] Among them, latent faults are a type of fault that is difficult to detect during the operation of the power system. Once the power grid experiences an operational failure or the load fluctuates to a certain extent, the latent fault will be exposed, which will cause the relay protection system to fail to work normally. This process will be reflected in the cascading fault process.

[0076] 9) Classify the faults described in 1)-8) according to whether they occur in transient or steady state, whether the load is cut off after the fault, and whether the fault causes a line break fault.

[0077] According to one aspect of the present invention, the present invention provides a method for screening cascading faults in a power system, which uses the aforementioned dynamic simulation model of cascading faults in a power system to screen for cascading fault types.

[0078] According to another aspect of the present invention, the present invention provides an apparatus comprising:

[0079] One or more processors;

[0080] Memory, used to store one or more programs;

[0081] When the one or more programs are executed by the one or more processors, the one or more processors implement the power system cascading fault screening method.

[0082] According to another aspect of the present invention, the present invention provides a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform the aforementioned power system cascading fault screening method.

[0083] This invention has at least the following beneficial effects:

[0084] This invention, in the area of ​​cascading fault simulation, samples line fault rate data under severe weather conditions, considers latent faults caused by misoperation during major power outages, and incorporates time parameters to characterize line breaks, fault repair, and fault maintenance models under power system impact. It establishes a system frequency simulation model around the power system, and establishes transient characteristics of synchronous generators, distributed power sources, and load nodes. It establishes fault models and judgment methods in a hybrid simulation model, classifies these fault types, and incorporates them into the hybrid simulation model. Through steps such as acquiring real-time power system operating data and inputting it into the hybrid simulation model, it can filter cascading fault types according to fault type classification. This not only assesses the risk of power system cascading faults but also provides targeted data for cascading fault prevention, which is of great significance for power system planning and construction. Attached Figure Description

[0085] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0086] Figure 2 This is a topology diagram of the simulation test system of the present invention;

[0087] Figure 3 The curve showing the change of system load rate over time obtained from the simulation of this invention is shown. Detailed Implementation

[0088] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0089] Please see Figure 1-3 This invention provides a technical solution: a dynamic simulation model for cascading faults in a power system, as detailed below:

[0090] (1) Sample the line fault rate data under the influence of severe weather, consider the hidden faults caused by misoperation in major power outages, and add time parameters to characterize the line breakage, fault repair and fault repair model under power system impact. The specific steps are as follows:

[0091] 1) Initialize the relevant parameters of the power system network based on the power system model data;

[0092] The power system data includes node loads, generator output limits, and grid line capacity. The power system model is a physical model that includes the above data.

[0093] 2) Sample line faults caused by severe weather and set them as the initial faults of the system;

[0094] 3) Detect whether an island has been generated in the power system. If no island has been generated, continue sampling the faulty line; if there is only one island, proceed to step 4); if the number of islands is greater than or equal to two, proceed to step 6.

[0095] 4) Calculate the power flow based on the new system topology after the line breakage, determine whether the power flow of each line is overloaded, and for overloaded lines, calculate their fault probability according to the following formula fault probability model and update the line status information.

[0096]

[0097] in p is the probability of failure for line l. l This is the current load rate of line l. It is the rated load rate of line l. It is the maximum load factor of line l;

[0098] If a new line experiences an overload fault, determine the number of islands. If it is still one, repeat step 4). If it is greater than or equal to two, proceed to step 6. If no new line experiences an overload fault, proceed to step 5.

[0099]

[0100] Among them, t i a is the time interval between the previous line disconnection and the current line i disconnection. i b is a constant i c is the time coefficient. i Let x be the reciprocal of the expected value, and x be a random positive number greater than or equal to 0;

[0101] 5) Perform latent fault sampling on the line. Sample whether a latent fault has occurred on the adjacent line of the previously faulted line. If a new latent fault occurs, proceed to step 4). If no latent fault occurs, proceed to the optimal load shedding model. The goal of this model is to minimize the total load shedding of the system under the constraints of power balance and no line power flow overload. Proceed to step 7).

[0102] The expression for the optimal load shedding model is as follows:

[0103]

[0104]

[0105] Where Min. represents the minimum value, NB is the total number of nodes in the system model. If there are no islands in the current power system network, the system model is the previous power system network. If there are islands in the current power system network, and each island contains a generator, the system model is the island model. If there are n islands with generators in the previous power system network, the optimal load shedding model is used to calculate the optimal load shedding amount for each island, and then the n optimal load shedding amounts are added together to obtain the final optimal load shedding amount; PDcut j Let NG represent the load shedding amount at the j-th node, NG represent the total number of generators in the system model, and PG represent the load shedding amount at the j-th node. i PD represents the output of the i-th generator in the system model. j PG represents the total load of the j-th node. i,min With PG i,max Let represent the upper and lower limits of the output of the i-th generator, respectively. LS is the limit load rate of line l in the system model, PL is the state matrix of the line in the system model, and LS is the limit load rate of line l in the system model. max PL represents the upper limit of power flow for the lines in the system model.

[0106] 6) For each island, determine its island type. For the number and type of nodes in each island, perform load shedding, calculate and record the total load loss. This cascading failure simulation ends. Increment the simulation test count and proceed to step 7).

[0107] 7) Power system recovery fault sampling: For lines disconnected after a fault, set their recovery time as shown in the following formula. After the fault development process, line recovery and load shedding recovery, complete the cascading fault simulation. The simulation test data is incremented and proceeds to step 8).

[0108]

[0109] Among them, t ri Let a be the recovery time of line i. ri b is a constant ri c is the time coefficient. ri Let x be the reciprocal of the expected value, where x is a positive number greater than or equal to 0.

[0110] 8) Calculate and record the faulty line, number of trips, load loss and fault development curve data in each simulation test. If the data obtained from the simulation test does not meet the convergence condition, proceed to step 2); otherwise, the simulation test is completed.

[0111] Cv n >Cv0

[0112] Among them, Cv nIt is the coefficient of variation obtained from n simulation test data, and its reference value Cv0 is set to 0.05. The simulation test ends when the above formula is satisfied.

[0113] 9) The expression for the optimal load shedding model in step 5) is as follows:

[0114]

[0115]

[0116] Where Min. represents the minimum value, NB is the total number of nodes in the system model. If there are no islands in the current power system network, the system model is the previous power system network. If there are islands in the current power system network, and each island contains a generator, the system model is the island model. If there are n islands with generators in the previous power system network, the optimal load shedding model is used to calculate the optimal load shedding amount for each island, and then the n optimal load shedding amounts are added together to obtain the final optimal load shedding amount; PDcut j Let NG represent the load shedding amount at the j-th node, NG represent the total number of generators in the system model, and PG represent the load shedding amount at the j-th node. i PD represents the output of the i-th generator in the system model. j PG represents the total load of the j-th node. i,min With PG i,max Let represent the upper and lower limits of the output of the i-th generator, respectively. LS is the limit load rate of line l in the system model, PL is the state matrix of the line in the system model, and LS is the limit load rate of line l in the system model. max PL represents the upper limit of power flow for the lines in the system model.

[0117] (2) Establish a transient-steady-state hybrid simulation model for the power system, and establish the transient characteristics of synchronous generators, distributed generation sources, and load nodes. The specific steps are as follows:

[0118] 1) Establish a transient frequency model: Establish a system frequency simulation model around the power system. Considering that the load nodes are constant loads and that neither distributed power sources nor load nodes participate in frequency regulation, the node inertia is set to H=0. The synchronous generator has frequency regulation function: The synchronous generator is set to consider frequency changes. The frequency is determined by the rotational speed, inertia, mechanical power and electromagnetic power. Nodes other than the synchronous generator are regarded as having the same frequency.

[0119] For n lines in a power system The N fault chains {L1, L2, ..., L...} obtained through N simulations will be... N The propagation relationship of} can be represented by an undirected graph. This means, that is:

[0120]

[0121]

[0122] The above two equations are the equations for the changes in the node frequency of the synchronous generator and the system frequency, respectively.

[0123] In the formula, the subscript i refers to the i-th synchronous generator, and δ i To change the phase angle at the node, P is the node angular frequency. mi P ei These refer to the nodal mechanical power and electromagnetic power, respectively, γ i H is the nodal damping coefficient. i Let P be the nodal inertia, where each term in the following formula represents a system value. loss For system line losses;

[0124] 2) Power flow calculation in transient model iteration: After the phase angle iteration of each node in the system is completed, the power from time t to time t+1 is obtained by the following formula;

[0125]

[0126] in, This refers to the apparent power injected by the node, P m (t+1) and Q m (t+1) represents its active and reactive components, the values ​​of which are determined by the node voltage V. m V n Phase angle θ m ,θ n The above equation is obtained by combining the grid impedance admittance parameters G and B. In the equation, S... m It refers to the set of nodes connected to m nodes in the power grid topology.

[0127] 3) Iterative solution process for node phase angle and frequency data: After solving the power flow based on the voltage and phase angle of the previous moment, the phase angle of each node in the system is iterated and the frequency change rate is calculated. Then, the voltage of the node where the renewable energy motor of the same type is located is iterated, thereby updating the state of the entire network at time t+1.

[0128] (3) Establish fault models and judgment methods in the metastable state hybrid simulation model, classify these fault forms, and add them to the hybrid simulation model, as follows:

[0129] 1) Initial Fault

[0130] Power system failures caused by severe weather are classified as line outages.

[0131] 2) Transient power flow exceeding limits

[0132] The occurrence of this phenomenon in transient simulations demonstrates that power flow limits can be determined at each step of the transient simulation by calculating the phase angle of the node voltages, indicating that conventional cascading fault simulations cannot address power flow limits.

[0133] The fault triggering conditions are as follows:

[0134]

[0135] Among them, Sl m,t Let m be the apparent power of line m at time t. For the rated apparent power of line m, k tsl This is the coefficient for judging the limit of the current trend;

[0136] 3) Frequency change rate exceeds the limit

[0137] In each transient simulation step, the fault screening for transient frequency change rate exceeding the limit is achieved by comparing the frequency change rate of the synchronous generator node with the reference value of the node other than the synchronous generator node.

[0138] The fault triggering conditions are as follows:

[0139]

[0140] Among them, RoCoF n,t Let RoCoF be the rate of change of the frequency of node n at time t. min ,RoCoF max These are the upper and lower limits of the rate of change of node frequency, respectively.

[0141] 4) Frequency exceeding limits

[0142] In each transient simulation step, fault screening for transient frequency exceeding limits is achieved by comparing the frequency of the synchronous generator node with the reference value of other nodes.

[0143] The fault triggering conditions are as follows:

[0144]

[0145] Among them, fr n,t Let fr be the frequency of node n at time t. min ,fr max These represent the upper and lower limits of the node frequency, respectively.

[0146] 5) Generator voltage exceeds limit

[0147] In each transient simulation step, transient generator voltage fault screening is achieved by comparing the voltage of each generator node at each step with the lowest and highest normal operating voltages.

[0148] The fault triggering conditions are as follows:

[0149]

[0150] Among them, V n,t Let k be the node voltage of node n at time t. V,min k V,max This is the threshold voltage judgment coefficient.

[0151] 6) Phase shift exceeding limits at distributed power generation nodes

[0152] Modeling phase-shifting protection of distributed generation sources on the power system side, extracting phase angle changes under different phase lengths of distributed generation nodes in transient simulation, and comparing them with power system constraint values ​​to achieve screening of such faults;

[0153] The fault triggering conditions are as follows:

[0154] Ph l,t -Ph l,t-tph -fr0·tph>Ph Δ

[0155] Among them, Ph l,t Let fr0 be the phase angle at node t where the l-th new energy generator is located, tph be the rated frequency, and tph be the time interval for judging phase shift protection. Δ To determine the phase angle of the phase-shifting protection.

[0156] 7) Steady-state power flow exceeding limits

[0157] This indicates a power flow exceeding the limit triggered in steady-state simulation;

[0158] The fault triggering conditions are as follows:

[0159]

[0160] in p is the probability of failure for line l. l This is the current load rate of line l. It is the rated load rate of line l. It is the maximum load factor of line l;

[0161] 8) Steady-state latent faults

[0162] This represents a latent fault in the power system triggered during steady-state simulation.

[0163] Among them, latent faults are a type of fault that is difficult to detect during the operation of the power system. Once the power grid experiences an operational failure or the load fluctuates to a certain extent, the latent fault will be exposed, which will cause the relay protection system to fail to work normally. This process will be reflected in the cascading fault process.

[0164] 9) Classify the faults described in 1)-8) according to whether they occur in transient or steady state, whether the load is cut off after the fault, and whether the fault causes a line break fault;

[0165] 10) Based on the modeling of components such as generators, loads, grid frequency, and voltage, and the cascading fault screening method, simulations were conducted using IEEE-118 as the invention test system, with a new energy source ratio of 15%. IEEE-118 is an IEEE standard test system, and its topology is as follows: Figure 2 .

[0166] Table 1. Classification of Cascaded Faults in Power Systems

[0167]

[0168] Table 2. Statistical table of cascading failure data obtained from simulation calculations

[0169] Fault Type / Statistical Data Name Number of occurrences / statistics Transient current overrun 292 Frequency change rate exceeds limit 78 Frequency exceeding the limit 165 Generator voltage over-limit 286 Phase shift over-limit at distributed power nodes 276 Steady-state current overlimit 112 Steady-state hidden faults 45 Shear load percentage 1.073 Average number of broken lines 1.689

[0170] (4) Obtain real-time operating data of the power system and input it into the transient steady-state hybrid simulation model. Then, the cascading fault types can be screened according to the fault type classification, which can be used to assess and prevent the risk of cascading faults in the power system.

[0171] According to one aspect of the present invention, the present invention provides a method for screening cascading faults in a power system, which uses the aforementioned dynamic simulation model of cascading faults in a power system to screen for cascading fault types.

[0172] According to another aspect of the present invention, the present invention provides an apparatus comprising:

[0173] One or more processors;

[0174] Memory, used to store one or more programs;

[0175] When the one or more programs are executed by the one or more processors, the one or more processors implement the power system cascading fault screening method.

[0176] According to another aspect of the present invention, a storage medium comprising computer-executable instructions, which, when executed by a computer processor, are used to perform the aforementioned method for screening cascading faults in a power system.

[0177] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0178] For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on," "mounted on," "fixed to," or "set on" another element, it may be directly on the other element or there may be an intermediate element present. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

[0179] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0180] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A dynamic simulation model for cascading faults in a power system, characterized in that, The details are as follows; We sampled line fault rate data under severe weather conditions, considered hidden faults caused by misoperation in major power outages, and added time parameters to characterize line disconnection, fault repair, and fault repair models under power system impact. A transient-steady-state hybrid simulation model was established for the power system, and the transient characteristics of synchronous generators, distributed power sources, and load nodes were established. Establish fault models and judgment methods in the transient steady-state hybrid simulation model, classify these fault forms, and add them to the hybrid simulation model; By acquiring real-time operating data of the power system and inputting it into the transient steady-state hybrid simulation model, the cascading failure modes can be filtered according to the failure mode classification, which can be used to assess and prevent the risk of cascading failures in the power system. A transient steady-state hybrid simulation model is established to establish the transient characteristics of synchronous generators, distributed power sources, and load nodes. The specific steps are as follows: 1) Establish a transient frequency model: Establish a transient and steady-state hybrid simulation model around the power system. Considering that the load nodes are constant loads and that neither distributed power sources nor load nodes participate in frequency regulation, the node inertia is set to H=0. The synchronous generator has frequency regulation function: The synchronous generator is set to consider frequency changes. The frequency is determined by the rotational speed, inertia, mechanical power and electromagnetic power. Nodes other than the synchronous generator are regarded as having the same frequency. For power systems n Line The N fault chains obtained through N simulations The propagation relationship is represented by an undirected graph. This means, that is: The above two equations are the equations for the changes in the node frequency of the synchronous generator and the system frequency, respectively. In the formula, Subscript refers to the first One synchronous generator, To change the phase angle at the node, The node angular frequency, These refer to the mechanical power and electromagnetic power of the nodes, respectively. The nodal damping coefficient is... Let be the nodal inertia, and in the following formula, each term represents a system value. For system line losses; 2) Power flow calculation in transient model iteration: After the phase angle of each node in the system is iterated, the node injection power from time t to time t+1 is obtained by the following formula; in, This refers to the apparent power injected by the node. and It consists of active and reactive components, the values ​​of which are determined by the node voltage. Phase angle and grid impedance admittance parameters , We find that in the above formula, It refers to the set of nodes connected to m nodes in a power grid topology; 3) Iterative solution process for node phase angle and frequency data: After solving the power flow based on the voltage and phase angle of the previous moment, the phase angle of each node in the system is iterated and the frequency change rate is calculated. Then, the voltage of the node where the renewable energy motor of the same type is located is iterated, thereby updating the state of the entire network at time t+1.

2. The dynamic simulation model for cascading faults in a power system according to claim 1, characterized in that, Data on line fault rates under severe weather conditions are sampled. Considering latent faults caused by operational errors during major power outages, a time parameter is incorporated to characterize line breaks, fault repair, and fault repair models under power system impacts. The specific steps are as follows: 1) Initialize the relevant parameters of the power system network based on the power system model data; 2) Sample line faults caused by severe weather and set them as the initial faults of the system; 3) Detect whether islanding has occurred in the power system. If no islanding has occurred, continue sampling the faulty line. If there is one and only one isolated island, proceed to step 4); if the number of isolated islands is greater than or equal to two, proceed to step 6. 4) Calculate the power flow based on the new system topology after the line breakage, determine whether the power flow of each line is overloaded, and for overloaded lines, calculate their fault probability according to the following formula fault probability model and update the line status information. in It is a line l The probability of failure, It is a line l The current load rate, It is a line l Rated load rate, It is a line l The maximum load rate; If a new line experiences an overload fault, determine the number of islands. If it is still one, repeat step 4). If it is greater than or equal to two, proceed to step 6. If no new line overload fault occurs, proceed to step 5); in, It is the time from the previous broken line to the i-th broken line, which is a fixed time plus an exponential distribution with the time coefficient as the expected value; in, To transition from the previous line disconnection to the current line The time interval between disconnections It is a constant. For time coefficient, The reciprocal of the expected value A random positive number greater than or equal to 0; 5) Perform latent fault sampling on the line. Sample whether a latent fault has occurred on the adjacent line of the previously faulted line. If a new latent fault occurs, proceed to step 4). If no latent fault occurs, proceed to the optimal load shedding model. The goal of this model is to minimize the total load shedding of the system under the constraints of power balance and no line power flow overload. Proceed to step 7). 6) For each island, determine its island type. For the number and type of nodes in each island, perform load shedding, calculate and record the total load loss. This cascading failure simulation ends, and the simulation test count is incremented by one to proceed to step 7). 7) Power system recovery fault sampling: For lines disconnected after a fault, set their recovery time as shown in the following formula. After the fault development process, line recovery and load shedding recovery, complete the cascading fault simulation, and increment the simulation test data to enter step 8). in, For the line Recovery time It is a constant. For time coefficient, The reciprocal of the expected value A positive number greater than or equal to 0; 8) Calculate and record the faulty line, number of trips, load loss, and fault development curve data in each simulation test. If the data obtained from the simulation test does not meet the convergence condition, proceed to step 2); otherwise, the simulation test is complete. in, It is the coefficient of variation obtained from n simulation test data, and its reference value is... Set to 0.05, and the simulation test ends when the above formula is satisfied.

3. The dynamic simulation model for cascading faults in a power system according to claim 1, characterized in that, The fault model and judgment method in the metastable state hybrid simulation model are established as follows: 1) Initial Fault Power system failures caused by severe weather are classified as line outages; 2) Transient power flow exceeding limits The occurrence of this phenomenon in transient simulations demonstrates that power flow limits can be determined at each step of the transient simulation by calculating the phase angle of the node voltages, indicating that conventional cascading fault simulations cannot address power flow limits. The fault triggering conditions are as follows: in, Let m be the apparent power of line m at time t. The rated apparent power of line m. This is the coefficient for judging the limit of the current trend; 3) Frequency change rate exceeds the limit In each transient simulation step, the fault screening for transient frequency change rate exceeding the limit is achieved by comparing the frequency change rate of the synchronous generator node with the reference value of the node other than the synchronous generator node. The fault triggering conditions are as follows: in, Let n be the rate of change of frequency at time t. These are the upper and lower limits of the rate of change of node frequency, respectively. 4) Frequency exceeding limits In each transient simulation step, fault screening for transient frequency exceeding limits is achieved by comparing the frequency of the synchronous generator node with the reference value of other nodes. The fault triggering conditions are as follows: in, Let n be the frequency of node n at time t. These are the upper and lower limits of the node frequency, respectively; 5) Generator voltage exceeds limit In each transient simulation step, transient generator voltage fault screening is achieved by comparing the voltage of each generator node at each step with the lowest and highest normal operating voltages. The fault triggering conditions are as follows: in, Let be the node voltage of node n at time t. This is the threshold voltage judgment coefficient; 6) Phase shift exceeding limits at distributed power generation nodes Modeling phase-shifting protection of distributed generation sources on the power system side, extracting phase angle changes under different phase lengths of distributed generation nodes in transient simulation, and comparing them with power system constraint values ​​to achieve screening of such faults; The fault triggering conditions are as follows: in, Let be the phase angle at time t where the l-th new energy generator is located. For the rated frequency, To determine the time interval of phase-shifting protection, To determine the phase angle of the phase-shifting protection; 7) Steady-state power flow exceeding limits This indicates a power flow exceeding the limit triggered in steady-state simulation; The fault triggering conditions are as follows: in It is a line l The probability of failure, It is a line l The current load rate, It is a line l Rated load rate, It is a line l The maximum load rate; 8) Steady-state latent faults This represents a latent fault in the power system triggered during steady-state simulation. Among them, latent faults are a type of fault that is difficult to detect during the operation of the power system. Once the power grid experiences an operational fault or the load fluctuates to a certain extent, the latent fault will be exposed, which will cause the relay protection system to fail to work normally. This process will be reflected in the cascading fault process. 9) Classify the faults described in 1)-8) according to whether they occur in transient or steady state, whether the load is cut off after the fault, and whether the fault causes a line break fault.

4. A method for screening cascading faults in a power system, characterized in that, It uses the dynamic simulation model of power system cascading faults as described in any one of claims 1-3 to screen the types of cascading faults.

5. A device, characterized in that, include: One or more processors; Memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement a power system cascading fault screening method as described in claim 4.

6. A storage medium containing computer-executable instructions, characterized in that, The computer-executable instructions, when executed by a computer processor, are used to perform a power system cascading fault screening method as described in claim 4.

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