Interconnected power grid cascading failure multi-stage blocking control method and system

Abstract

The invention relates to the technical field of interconnected power grid control, and particularly discloses a multi-stage blocking control method and system for interconnected power grid cascading failures, and the method comprises the steps: determining a high-risk failure chain under each initial failure through the simulation of a failure chain of the interconnected power grid cascading failures; propagation path control constraints are designed for the high-risk fault chain, coordination characteristics and tie line constraints of the regional power grids are considered, and a multi-region blocking control problem is constructed with the purpose of minimizing the sum of the occurrence probability, the control cost and the load loss risk of cascading faults of the regional power grids at all stages; solving a multi-region blocking control problem to obtain a control plan of active power and load shedding capacity of a generator in each regional network; therefore, the active power and the load shedding capacity of the generator in each regional network are controlled according to the control plan of each stage, and multi-stage blocking control is realized. According to the method, cascading failures can be more safely blocked, meanwhile, the needed load shedding amount is remarkably reduced, and the error-tolerant rate of a dispatching department is greatly increased.

Description

Technical Field

[0001] The present invention relates to the technical field of interconnected power grid control, and particularly to a multi-stage blocking control method and system for cascading failures in an interconnected power grid. Background Art

[0002] Inter-regional interconnected power grids are an important method for improving energy use efficiency and also the main trend of current power grid development. With the rapid advancement of power grid interconnection projects, the power system has developed from regional power grids to large-scale inter-regional interconnected power grids, and the degree of interconnection and complexity of the power grid have been continuously improved. Interconnected power grids have the characteristic of coordinating power resources in each region and can effectively solve the problem of imbalance between energy distribution and demand. However, at the same time, they have many components, a large scale, and are vulnerable to small-probability failures. Once a cascading failure occurs, it will bring great harm to the safety of the power system. Therefore, how to make good use of the regional coordination characteristics of interconnected power grids to block the propagation of cascading failures is of great significance for maintaining its stable operation.

[0003] Most of the existing research on emergency control of cascading failures takes a single regional power grid as the research object. Some research focuses on overload-dominated cascading failures and adopts a control scheme at the link with the highest risk in the cascading failure path based on a risk assessment model. Some research considers the line outage probability, screens out high-risk paths according to risk indicators, formulates the blocking of cascading failures as a multi-stage optimal power flow problem, and proves that the multi-stage control scheme is superior to the single-stage control. Some research considers the outage probability during the operation of components and proposes a multi-stage game defense model for cascading failures based on the bounded rationality of participants. Some research considers the complementary characteristics of preventive control and emergency control in the defense of cascading failures, takes into account the constraints of the tolerable degree of the consequences of cascading failures by dispatchers and the goal of economic optimality, and establishes a large power grid cascading failure defense model based on preventive-emergency coordinated control. The above research has laid a solid foundation for the blocking control of cascading failures from different perspectives of control means and influencing factors, but all of them take the regional power grid as the object of research, do not consider the connection between interconnected power grids, and do not apply the coordination effect between regional power grids to the blocking of cascading failures. Therefore, the above research cannot be fully applied to the blocking of cascading failures in interconnected power grids, and it is necessary to invent a more perfect multi-stage blocking model for cascading failures in interconnected power grids. Summary of the Invention

[0004] The present invention provides a multi-stage blocking control method and system for cascading failures in an interconnected power grid, and the technical problem to be solved is: how to quickly block the fault link when a cascading failure occurs in the interconnected power grid.

[0005] To solve the above technical problems, the present invention provides a multi-stage blocking control method for cascading failures in an interconnected power grid, including the steps:

[0006] Traverse each initial fault to simulate cascading faults in the interconnected power grid, and determine the high-risk fault chains under each initial fault;

[0007] Detect a primary fault, and based on the corresponding relationship between the simulated initial faults and high-risk fault chains, obtain the high-risk fault chain corresponding to the primary fault;

[0008] Determine the propagation path control constraints based on the high-risk fault chain corresponding to the primary fault;

[0009] Determine the generator down-ramp constraints, load shedding constraints, tie-line down-ramp constraints, and node power balance constraints that the interconnected power grid still needs to satisfy at each stage;

[0010] Determine the objective function that minimizes the sum of the occurrence probabilities, control costs, and load shedding risks of each stage of cascading faults in each regional power grid by controlling the active power of generators and the amount of load shedding within each regional power grid;

[0011] Construct a multi-region blocking control problem based on the objective function and the determined constraints;

[0012] Solve the multi-region blocking control problem to obtain the active power of generators and the amount of load shedding within each regional power grid;

[0013] Perform multi-region blocking control on the interconnected power grid according to the active power of generators and the amount of load shedding within each regional power grid obtained by the solution.

[0014] Furthermore, traversing each initial fault to simulate cascading faults in the interconnected power grid and determining the high-risk fault chain under each initial fault specifically includes the steps of:

[0015] A1. Construct an interconnected power grid model and initialize it, and calculate the power exchange value between regional power grids in the interconnected power grid model in the initial state;

[0016] A2. Confirm an initial fault from the initial fault set, and disconnect the corresponding line according to the initial fault;

[0017] A3. Judge whether the power exchange value between regional power grids is changed. If so, go to the next step; otherwise, go to step A5;

[0018] A4. The transmission power of tie-lines between regional power grids ramps up to the maximum feasible power;

[0019] A5. Judge whether the regional power grid is disconnected or the power flow fails to converge due to the disconnected line. If so, go to the next step; otherwise, go to step A7;

[0020] A6. Re-balance the power of each regional power grid;

[0021] A7. Determine whether the fault chain termination condition is reached. If so, go to step A9; otherwise, calculate the DC power flow and proceed to the next step.

[0022] A8. Based on the calculated DC power flow, determine whether there is an overloaded line. If there is, select the line with the highest opening probability as the fault line in the next stage, disconnect it, and then return to step A3; otherwise, proceed to the next step.

[0023] A9. Determine whether all initial faults have been traversed. If so, end the cascading fault simulation process and obtain the high-risk fault chain composed of multi-stage fault lines; otherwise, return to step A2 to select the next initial fault.

[0024] Furthermore, step A6 specifically includes the following steps:

[0025] A61. Calculate the active power flow difference of each regional network.

[0026] A62. Based on the calculated active power flow differences of each regional network, uniformly adjust the generator loads of each regional network in proportion. The adjustment process is as follows:

[0027] For any regional network σ, the active power P G,i of generator i in this regional network is adjusted to P G,i ', which is the minimum value between the upper limit of the active power of generator i or P G,i ' and the lower limit of the active power of generator i. P G,i ' represents the theoretical value of the active power calculated based on ΔP σ and the initial active powers of all generators in this regional network. ΔP σ represents the active power flow difference of regional network σ. When P G,i ' is not between the lower limit and the upper limit , if ΔP σ ≥0, generator tripping is performed, and the tripping sequence is from the smallest to the largest according to the active power of the generators. If ΔP σ <0, the load is reduced in proportion.

[0028] Furthermore, ΔP σ is equal to P G,i 、P L,j 、P tl,ζ respectively represent the active power of generator i, the power of load j, and the transmission power of tie line ζ in regional network σ. v tl,ζ is the power transmission direction of tie line ζ, and v tl,ζ =1 indicates the sending power, and v tl,ζ =-1 indicates the receiving power;

[0029] P G,i 'The calculation process is as follows:

[0030] When ΔP σ ≥0, P G,i 'equals minus represents the initial power of generator i;

[0031] When ΔP σ <0, P G,i 'equals minus

[0032] The process of load shedding in proportion is as follows: represents the initial power of load j.

[0033] Furthermore, in step A7, the fault chain termination conditions are that the system load loss exceeds the load loss upper limit η, or reaches the maximum number of stages k of cascading failures max , or the probability P of the system fault chain is lower than the threshold;

[0034] In step A8, the line opening probability p is calculated as:

[0035] When the real-time line power flow F ≤ f Rated , p = p 0 , p 0 represents the preset low probability, and f Rated is the upper limit of the power flow when the line is operating normally;

[0036] When the real-time line power flow F > f max , p = p 1 , p 1 represents the preset high probability, and f max is the transmission limit power of the line;

[0037] When f Rated <F ≤ f max , e is the natural base.

[0038] Furthermore, the propagation path control constraints are:

[0039] When k = 1, 2, …, l - 1, the opening probability of the pre-opened line in the k-th stage is greater than the opening probability of the non-faulty line in the k-th stage The absolute value of the active power flow represents the upper limit of the power flow, γ is the control factor, and l is the length of the fault chain;

[0040] When k = l, the line outage probability ω in the k-th stage L k is 0, and the absolute value of the active power flow in the k-th stage line is not greater than

[0041] The generator down-ramp constraint is:

[0042]

[0043] where respectively represent the up-ramp and down-ramp amounts of the active power of generator i in the m-th stage among the first k stages, respectively represent the up-ramp and down-ramp amounts of the active power of generator i in the k-th stage, respectively represent the upper limits;

[0044] The load shedding constraint is:

[0045]

[0046] where represents the amount of load shedding of load j in the k-th stage, represents the amount of load shedding of load j in the m-th stage among the first k stages;

[0047] The tie-line down-ramp constraint is:

[0048]

[0049] where respectively represent the up-ramp and down-ramp amounts of tie-line ζ in the m-th stage among the first k stages, represents the upper limit of the transmission power of tie-line ζ, respectively represent the up-ramp and down-ramp amounts of tie-line ζ in the k-th stage, respectively represent the upper limits of the up-ramp and down-ramp amounts of tie-line ζ;

[0050] The node power balance constraint is:

[0051]

[0052] where represents the active power of all generators in regional network σ in the k-th stage, represents the transmission power of all tie-lines in regional network σ in the k-th stage, represents the power of all loads in the k-th stage, and respectively represent the set of lines with the head and tail being node n, denotes the power of node n in the regional network σ at the k-th stage respectively denote the output power and injection power of node n in the regional network σ at the k-th stage

[0053] Furthermore, the objective function is constructed as follows:

[0054]

[0055] where, ig represents the entire interconnected power grid, ω k denotes the opening probability of the faulty line at the k-th stage, and α and β respectively represent the adjustment cost of the generator and the cost coefficient of the load shedding

[0056] Furthermore, encoding is performed with the line disconnection probabilities at each stage of the cascading failure as chromosomes, decomposing the multi-region blocking control problem into an upper-level problem of optimizing the line opening probability, and a lower-level problem of optimizing the generator, tie-line scheduling, and load shedding under the condition that the line opening probabilities at each stage are known, and using the genetic algorithm to solve the upper-level problem and the lower-level problem

[0057] Furthermore, multi-region blocking control is performed on the interconnected power grid according to the active power of the generators and the load shedding amounts in each regional network obtained by the solution, specifically including the steps of:

[0058] Grant temporary scheduling authority to the tie-line to allow it to participate in fault blocking

[0059] Adjust the active power of the generators associated with the tie-line, shed the associated load, and adjust the active power of the remaining non-associated generators and shed the non-associated load according to the active power of the generators and the load shedding amounts obtained by the solution

[0060] The tie-line determines its transmission power based on the active power of the associated generators and supplies the associated load in the receiving-end network

[0061] The present invention also provides a multi-stage blocking control system for cascading failures in an interconnected power grid, applying the multi-stage blocking control method for cascading failures in an interconnected power grid, which is characterized in that it includes a fault simulation module, a fault detection module, a constraint determination module, an objective function determination module, a problem construction module, a problem solution module, and a multi-region blocking control module

[0062] The fault simulation module is used to traverse each initial fault to perform cascading fault simulation on the interconnected power grid and determine the high-risk fault chains under each initial fault

[0063] The fault detection module is used to detect the primary fault and obtain the high-risk fault chain corresponding to the primary fault based on the correspondence between the simulated initial faults and the high-risk fault chains

[0064] The constraint determination module is configured to determine propagation path control constraints based on the high-risk fault chains corresponding to the primary faults, and determine the generator down-ramp constraints, load shedding constraints, tie-line down-ramp constraints, and node power balance constraints that the interconnected power grid needs to satisfy at each stage;

[0065] The objective function determination module is configured to determine an objective function that minimizes the sum of the occurrence probabilities, control costs, and load shedding risks at each stage of the cascading faults in each regional power grid by controlling the active power of generators and the amount of load shedding within each regional power grid;

[0066] The problem construction module is configured to construct a multi-region blocking control problem based on the objective function and the determined constraints;

[0067] The problem solving module is configured to solve the multi-region blocking control problem to obtain the active power of generators and the amount of load shedding within each regional power grid;

[0068] The multi-region blocking control module is configured to perform multi-region blocking control on the interconnected power grid according to the active power of generators and the amount of load shedding within each regional power grid obtained by the solution.

[0069] A multi-stage blocking control method and system for cascading faults in an interconnected power grid provided by the present invention simulate the fault chains of cascading faults in the interconnected power grid to determine high-risk fault chains under each initial fault; design propagation path control constraints for high-risk fault chains, taking into account the coordination characteristics of regional power grids and tie-line constraints, so as to minimize the sum of the occurrence probabilities, control costs, and load shedding risks at each stage of cascading faults in each regional power grid, construct a multi-region blocking control problem; solve the multi-region blocking control problem to obtain a control plan for the active power of generators and the amount of load shedding within each regional power grid; and thus control the active power of generators and the amount of load shedding within each regional power grid according to the control plan at each stage to achieve multi-stage blocking control. The present invention takes into account the coordination effect among multiple regions of the interconnected power grid, and can perform cross-region support from a normal power grid to a faulty power grid to assist in blocking cascading faults; or multiple faulty regional power grids can cooperate in control to jointly prevent the spread of cascading faults. The present invention has a more excellent ability to protect the power supply of loads when blocking cascading faults, can significantly reduce the required amount of load shedding while blocking cascading faults more safely, and greatly increase the fault tolerance rate of the dispatching department. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 is a flowchart of a multi-stage blocking control method for cascading faults in an interconnected power grid provided by an embodiment of the present invention;

[0071] Figure 2 is a collaborative dispatching framework diagram of an interconnected power grid provided by an embodiment of the present invention;

[0072] Figure 3It is an example diagram of an interconnected power grid with two regions and three tie lines provided by an embodiment of the present invention;

[0073] Figure 4 It is a comparison diagram of the timing for enabling multi-region coordinated control provided by an embodiment of the present invention. Detailed implementation manners

[0074] The following specifically illustrates the implementation manners of the present invention in conjunction with the accompanying drawings. The given embodiments are only for illustrative purposes and should not be construed as limiting the present invention. The included drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from its spirit and scope.

[0075] A multi-stage blocking control method for cascading faults in an interconnected power grid provided by an embodiment of the present invention, as Figure 1 shown in the flowchart, includes the steps:

[0076] S1. Traverse each initial fault to perform cascading fault simulation on the interconnected power grid, and determine the high-risk fault chains under each initial fault;

[0077] S2. When a primary fault is detected, based on the correspondence between the simulated initial faults and the high-risk fault chains, obtain the high-risk fault chain corresponding to the primary fault;

[0078] S3. Determine the propagation path control constraints based on the high-risk fault chain corresponding to the primary fault;

[0079] S4. Determine the generator down-ramp constraints, load shedding constraints, tie line down-ramp constraints, and node power balance constraints that the interconnected power grid still needs to satisfy at each stage;

[0080] S5. Determine the objective function that minimizes the sum of the occurrence probabilities, control costs, and load shedding risks of cascading faults at each stage of each regional power grid by controlling the active power of generators and the amount of load shedding within each regional network;

[0081] S6. Based on the objective function and the determined constraints, construct a multi-region blocking control problem;

[0082] S7. Solve the multi-region blocking control problem to obtain the active power of generators and the amount of load shedding within each regional network;

[0083] S8. Perform multi-region blocking control on the interconnected power grid according to the active power of generators and the amount of load shedding within each regional network obtained by the solution.

[0084] In step S1, the initial fault types are divided into two types, namely single-region cascading faults caused by the disconnection of transmission lines and multi-region cascading faults caused by the disconnection of tie lines.

[0085] The cascading failure process has a time-sequence characteristic and can be clearly divided into multiple cascading stages. A fault in the upper level of the system will overload the normal line, thus inducing a fault in the lower level. Cascading failures are essentially conditional probability events. Denote the fault links as A 1 , A 2 , … A l (l represents the length of the fault chain). The probability of the fault chain occurring is calculated as shown in Equation (1):

[0086] P = p(A 1 ) p(A 2 | A 1 ) p(A l | A 1 , A 2 … A l-1 ) (1)

[0087] p(A 1 ) represents the occurrence probability of the first-stage fault A 1 . p(A 2 | A 1 ) represents the probability of the second-stage fault A 1 occurring based on the occurrence of the first-stage fault A 2 . And so on, p(A l | A 1 , A 2 … A l-1 ) represents the probability of the l-th stage fault A 1 , A 2 … A l-1 occurring based on the occurrence of the faults A l .

[0088] Analyzing the evolution of cascading fault paths requires considering the impact of the real-time operating state of the power grid on fault probabilities. The line outage probability model can make up for the deficiencies in the traditional research where the line failure rate uses long-term statistical values or steady-state probabilities. It comprehensively considers the impact of the system's real-time state and hidden faults, and quantifies the line opening probability at each stage using a piecewise function as shown in Equation (2):

[0089]

[0090] In Equation (2), F represents the real-time power flow of the line, f Rated is the upper limit of the power flow when the line is operating normally, f max is the transmission limit power of the line, p 0 represents a preset low probability, p 1 represents a preset high probability, and e is the natural base.

[0091] The cause of the evolution of overload-type cascading faults is usually the abnormal disconnection of transmission lines, which leads to power flow transfer and then causes successive line outages. Its evolution process includes selecting the initial fault, disconnecting the overloaded line, rebalancing the system power flow, calculating the DC power flow, and opening the overloaded line. Different from only considering the development process of single-region cascading faults, multi-region interconnected power grids need to consider the operating constraints of tie lines and the mutual connections between regional grids, and analyze the cross-region impact of faults.

[0092] Step S1 specifically includes the following steps:

[0093] A1. Construct an interconnected power grid model and initialize it, and calculate the power exchange value between regional grids in the interconnected power grid model under the initial state;

[0094] A2. Confirm an initial fault from the initial fault set, and disconnect the corresponding line according to the initial fault;

[0095] A3. Judge whether the power exchange value between regional grids is changed. If so, go to the next step; otherwise, go to step A5;

[0096] A4. The transmission power of tie lines between regional grids ramps up to the maximum feasible power, that is, its own transmission power limit or returns to the original planned exchange power between regions;

[0097] A5. Judge whether the regional grid is disconnected or the power flow fails to converge due to the disconnected line. If so, go to the next step; otherwise, go to step A7;

[0098] A6. Re-balance the power of each regional grid;

[0099] A7. Judge whether the fault chain termination condition is reached. If so, go to step A9; otherwise, calculate the DC power flow and go to the next step;

[0100] A8. Judge whether there is an overloaded line according to the calculated DC power flow. If there is an overloaded line, select the line with the largest opening probability (calculated according to formula (2)) as the fault line in the next stage and disconnect it, then go back to step A3; otherwise, go to the next step;

[0101] A9. Judge whether all initial faults have been traversed. If so, end the cascading fault simulation process and obtain the high-risk fault chain composed of multi-stage fault lines; otherwise, go back to step A2 to select the next initial fault.

[0102] Step A6 specifically includes the following steps:

[0103] A61. Calculate the active power flow difference of each regional grid. The active power flow difference of any regional grid σ is calculated by the following formula:

[0104]

[0105] P G,i 、P L,j 、P tl,ζ respectively represent the active power of generator i in the regional network σ, the load of load j, and the transmission power of tie line ζ. v tl,ζ is the power transmission direction of tie line ζ, v tl,ζ = 1 indicates power output, v tl,ζ = -1 indicates power reception;

[0106] A62. Uniformly adjust all generator loads in each regional network in proportion based on the calculated active power flow difference of each regional network.

[0107] In step S62, the present invention does not consider directly completing power balance by the power adjustment of the balancing machine, because sometimes it is difficult to complete the dispatching task only relying on the balancing machine, and it may also cause unnecessary power flow transfer and overload other lines. Therefore, the present invention uniformly adjusts all generator loads in the regional network. First, control the generator:

[0108]

[0109] Equations (4) and (5) indicate that for any regional network σ, the active power P G,i of generator i in this regional network is adjusted to the minimum value between P G,i ' and the upper limit of the active power of generator i or the maximum value between P G,i ' and the lower limit of the active power of generator i. P G,i ' represents the theoretical value of the active power calculated according to ΔP σ and the initial active power of all generators in this regional network. represents the initial power of generator i.

[0110] Meanwhile, when the generator cannot complete the subnet power flow balance plan (when P G,i ' is not between the lower limit and the upper limit ), if ΔP σ ≥0, the generator needs to be tripped, and the tripping sequence is from small to large according to the generator power; if ΔP σ <0, the power of the load to be reduced proportionally is:

[0111]

[0112] represents the initial power of load j.

[0113] It should be noted that in terms of strategy, power flow balance first adjusts the generator power and then performs generator tripping and load shedding operations. However, the specific implementation should be under the unified control of the dispatching center for each sub-network simultaneously.

[0114] In step A7, the fault chain termination conditions are that the system load loss exceeds the upper limit of load loss η, or reaches the maximum number of stages k of cascading failures max , or the probability P of the system fault chain (calculated according to Equation (1)) is lower than the threshold.

[0115] In an interconnected power grid, tie lines play a role in coordinating the power supply and demand balance between the sending and receiving end power grids and improving the overall operating efficiency of the power grid. The regional power grids are coupled through tie lines, and cross-regional power dispatching needs to meet the operating constraints of the tie lines. There are mainly three ways to transmit power across regions through tie lines: the constant power transmission mode, the mode considering the upper limit of the operating range, and the mode considering both the upper and lower limits of the operating range. This invention mainly considers the operating mode of the upper limit of the tie line operating range and gives the following operating model:

[0116]

[0117] Equations (7)-(9) respectively represent the tie line down-ramp rate constraint, the tie line power reverse limit constraint, and the equivalent external network operation constraint. P tl,k represents the tie line transmission power at the k-th stage, r tl,up and r tl,down respectively represent the up-ramp and down-ramp rates of the tie line. v tl,k is the forward and reverse direction of the tie line transmission power at the k-th stage, with the forward direction being 1 and the reverse direction being -1. c tl,k-1 is the sign of the tie line power flow change. When the power flow changes from the reverse direction to the forward direction, the value is 1. When the power flow changes from the forward direction to the reverse direction, the value is -1. When the power flow remains unchanged within adjacent stages, the value is 0. λ set represents the maximum number of reversals of the tie line power flow. Additionally, the equivalent external network operation constraint means that the transmission power of the tie line cannot exceed the maximum output power or the maximum power absorption capacity provided by the interconnected external network. In Equation (9) represents the transmission power of tie line h, represents the set of tie lines within the sub-network, the sub-network can provide the maximum power to the tie line.

[0118] The tie line operating state model is shown as follows:

[0119]

[0120] An auxiliary variable M is introduced to characterize the three operating modes of the tie line in the form of mixed-integer linear programming. v is a binary number representing the transmission direction of the tie line. When v 1,tl takes 1, it means that the transmission direction of the tie line is the same as the assumed direction of the system. When v 2,tl takes 1, it means that the transmission direction of the tie line is opposite to the assumed direction of the system; when equals it means that the tie line operates in a constant power transmission mode; when equals 0, it means that the tie line operates in a mode that only considers the upper limit of the operating interval. When it is not equal to 0, the tie line operates in a way that considers both the upper and lower limits of the interval; when v 1,tl constantly takes 1, it means that reverse power transmission of the tie line is not allowed.

[0121] The cross-regional power transmission of interconnected power grids is a coordinated dispatch, and there is a coordination relationship among various sets of generating units. The tie line is the channel for transmitting power between regional grids, and the active adjustment of the tie line power flow will simultaneously involve the sending-end grid and the receiving-end grid. As shown in the coordinated dispatch framework of the interconnected power grid Figure 2 shown, the sending-end grid supplies power to the tie line on the basis of ensuring its own load demand by planning the power of its own generating units; the load associated with the receiving-end grid tie line receives the support of the tie line transmitted power, and its own generating units supply other non-associated loads.

[0122] Referring to the commonly used objective function of the existing multi-stage blocking model for cascading failures, the blocking objective is to minimize the sum of the occurrence probabilities of each stage of cascading failures in each regional power grid, the control cost, and the load shedding risk. The calculation formula is as follows:

[0123]

[0124] ig represents the entire interconnected power grid, σ is the regional grid in the interconnected power grid, l is the length of the fault chain, k is the current fault stage, and ω k represents the opening probability of the fault line in the k-th stage; and respectively represent the ramp-up amount and ramp-down amount of the active power of generator i in the k-th stage, represents the reduction amount of load j in the k-th stage, and α and β respectively represent the adjustment cost of the generator and the cost coefficient of load shedding.

[0125] While blocking the propagation of cascading failures, it is necessary to control the evolution of the fault along the predicted fault path to avoid the phenomenon of taking one thing into consideration while neglecting another, where the fault probability of the non-fault path is greater than that of the fault line. The propagation path control constraint of the present invention is established as follows:

[0126]

[0127] Equations (12) and (13) indicate that when k = 1, 2, …, l - 1, the opening probability of the k-th stage pre-opened line is greater than the opening probability of the non-faulty line in the k-th stage The active power flow of the line in the k-th stage The absolute value of is not greater than represents the upper limit of the power flow, γ is the control factor (representing the degree of line over-limit, usually taking the value 1.4, indicating that the line power flow cannot exceed its transmission limit power), l is the length of the fault chain, L c and L n respectively represent the set of pre-opened lines and non-faulty paths in the k-th stage; when k = l, the opening probability ω of the line in the k-th stage L k is 0, and the absolute value of the active power flow of the line in the k-th stage is not greater than The meanings of the above two equations are as follows: First, the blocking control needs to ensure that the fault path evolves according to the expected fault chain. Limited over-limit of the line is allowed in the first l - 1 stages, but the propagation of the cascading fault must be blocked in the l-th stage; Second, the line power flow constraint is appropriately relaxed, which can be understood as the appropriate compromise of the defender to the fault party to minimize the total risk of the blocking.

[0128] The interconnected power grid also needs to satisfy the generator down-ramp constraint, load shedding constraint, tie-line down-ramp constraint, and node power balance constraint at each stage, as shown in the following equations (14)-(17) respectively:

[0129]

[0130] Among them, respectively represent the up-ramp and down-ramp amounts of the active power of generator i in the m-th stage among the first k stages, respectively represent the up-ramp and down-ramp amounts of the active power of generator i in the k-th stage, respectively represent The upper limits; among them, represents the reduction amount of load j in the k-th stage, represents the reduction amount of load j in the m-th stage among the first k stages; respectively represent the up-ramp and down-ramp amounts of tie-line ζ in the m-th stage among the first k stages, represents the upper limit of the transmission power of tie-line ζ, respectively represent the up-ramp and down-ramp amounts of tie-line ζ in the k-th stage, respectively represent the upper limits of the up-ramp and down-ramp amounts of tie-line ζ; represents the active power of all generators in regional network σ in the k-th stage, Denote the transmission power of all tie lines in the regional network σ at the k-th stage. Denote the power of all loads at the k-th stage. And Denote the sets of lines with the head and tail being node n respectively. Denote the power of node n in the regional network σ at the k-th stage. Denote the output power and injection power of node n in the regional network σ at the k-th stage respectively.

[0131] The multi-stage blocking model of the interconnected power grid proposed in the present invention is the interactive influence between blocking control and cascading failure evolution, which belongs to a non-linear problem and is difficult to solve directly. Therefore, a two-layer decomposition scheme is adopted in this paper, and the genetic algorithm is used for solving. The line disconnection probabilities at each stage of the cascading failure are encoded as chromosomes. The upper layer is the optimization of the line opening probabilities, and the lower layer is the optimization of generator, tie line scheduling and load shedding under the condition that the line opening probabilities at each stage are known.

[0132] Based on the collaborative scheduling framework of the interconnected power grid, aiming at the characteristics and propagation modes of cascading failures, a multi-region coordinated control strategy is proposed. Its purpose is to take the interconnected power grid as a scheduling whole, and each regional network exchanges electric power through tie lines, so that the normal regional power grid can provide power support for the fault area on the premise of ensuring its own safe operation, or rely on the redundancy capacity of the local region to share the heavy load line power flow in the fault area, thereby improving the safety and economy of the blocking measures. The specific steps for multi-region blocking control of the interconnected power grid according to the obtained active power of generators and load shedding amounts in each regional network are as follows:

[0133] Grant temporary scheduling authority to tie lines to allow them to participate in fault blocking;

[0134] Adjust the active power of generators associated with tie lines, shed associated loads, and adjust the active power of other non-associated generators and shed non-associated loads according to the obtained active power of generators and load shedding amounts;

[0135] The tie line determines its own transmission power based on the active power of the associated generator and supplies the associated loads in the receiving-end network.

[0136] It should be understood that various forms of processes shown above can be used, steps can be reordered, added or deleted. For example, the steps recorded in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved. This embodiment does not limit this here.

[0137] The present invention also provides a multi-stage blocking control system for cascading failures in an interconnected power grid, and a multi-stage blocking control method for cascading failures in an interconnected power grid, which includes a fault simulation module, a fault detection module, a constraint determination module, an objective function determination module, a problem construction module, a problem solving module, and a multi-region blocking control module;

[0138] The fault simulation module is used to traverse each initial fault to perform cascading fault simulation on the interconnected power grid and determine the high-risk fault chains under each initial fault;

[0139] The fault detection module is used to detect a primary fault and obtain the high-risk fault chain corresponding to the primary fault based on the correspondence between the simulated initial faults and the high-risk fault chains;

[0140] The constraint determination module is used to determine the propagation path control constraints based on the high-risk fault chain corresponding to the primary fault, and determine the generator down-ramp constraints, load shedding constraints, tie-line down-ramp constraints, and node power balance constraints that the interconnected power grid needs to satisfy at each stage;

[0141] The objective function determination module is used to determine an objective function that minimizes the sum of the occurrence probabilities, control costs, and load shedding risks of each stage of cascading failures in each regional power grid by controlling the active power of generators and the amount of load shedding within each regional grid;

[0142] The problem construction module is used to construct a multi-region blocking control problem based on the objective function and the determined constraints;

[0143] The problem solving module is used to solve the multi-region blocking control problem to obtain the active power of generators and the amount of load shedding within each regional grid;

[0144] The multi-region blocking control module is used to perform multi-region blocking control on the interconnected power grid according to the active power of generators and the amount of load shedding within each regional grid obtained by the solution.

[0145] The embodiments described in the present invention can be implemented in a computing system including a backend component (e.g., as a data server), or a computing system including a middleware component (e.g., an application server), or a computing system including a frontend component (e.g., a user computer with a graphical user interface or a web browser, through which the user can interact with the implementation manners of the systems and technologies described herein), or a computing system including any combination of such backend components, middleware components, or frontend components. The components of the system can be interconnected through digital data communication in any form or medium (e.g., a communication network). Examples of communication networks include: local area network (LAN), wide area network (WAN), blockchain network, and the Internet.

[0146] In summary, the multi-stage blocking control method and system for interconnected power grid cascading faults provided by the embodiments of the present invention simulate the fault chain of the interconnected power grid cascading faults to determine the high-risk fault chains under each initial fault; design propagation path control constraints for the high-risk fault chains, taking into account the coordination characteristics of regional power grids and tie-line constraints, so as to construct a multi-region blocking control problem with the goal of minimizing the sum of the occurrence probabilities, control costs, and load shedding risks of each stage of the interconnected power grid cascading faults in each region; solve the multi-region blocking control problem to obtain the control plans for the active power of generators and the load shedding amounts within each regional grid; and thus control the active power of generators and the load shedding amounts within each regional grid according to the control plan of each stage to achieve multi-stage blocking control. The present invention takes into account the coordination effect among multiple regions of the interconnected power grid. The normal power grid can provide cross-region support to the faulty power grid to assist it in blocking cascading faults; or multiple faulty regional power grids can cooperate in control to jointly prevent the spread of cascading faults. This innovative method is expected to effectively cope with the cascading faults of the power system in practice and is more secure and economical.

[0147] To verify the effectiveness of the present invention, a two-region three-tie-line interconnected power grid composed of a double IEEE 39-node system as shown in Figure 3 is used to conduct simulation analysis and verification on the proposed method. The comparison results of the cascading fault blocking effects are shown in Table 1, and the comparison results of the timing of enabling multi-region coordinated control are as shown in Figure 4 . In Table 1, Strategy 1 represents implementing blocking separately for each regional grid, and Strategy 2 is the multi-region collaborative blocking designed by the present invention.

[0148] Table 1

[0149]

[0150] It can be seen from Table 1 that Strategy 2 can have less load shedding amount and control cost. It can be seen from Figure 4 that in the multi-region cascading faults caused by the disconnection of tie-lines, the later the timing of implementing multi-region coordinated control, the higher the load shedding amount and fault risk required to block the cascading faults. The experimental results verify that the present invention has a more excellent ability to protect the power supply of loads when blocking cascading faults, can significantly reduce the required load shedding amount while blocking the cascading faults more safely, and greatly increase the fault tolerance rate of the dispatching department.

[0151] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A multi-stage blocking control method for cascading failures in an interconnected power grid, characterized in that: Includes steps: Traversing each initial fault to simulate the cascading faults of the interconnected power grid and determine the high-risk fault chain under each initial fault; A primary fault is detected, and based on the correspondence between the simulated initial fault and the high-risk fault chain, a high-risk fault chain corresponding to the primary fault is obtained; Determine a propagation path control constraint based on a high-risk fault chain corresponding to the primary fault; Determine the generator ramp-down constraints, load shedding constraints, tie line ramp-down constraints and node power balance constraints that the interconnected power grid needs to meet at each stage; Determine the objective function that minimizes the sum of the probability of occurrence of cascading failures at each stage of each regional power grid, the control cost, and the risk of load loss by controlling the active power of generators and the amount of load shedding in each regional power grid; Constructing a multi-region blocking control problem based on the objective function and the determined constraints; Solving the multi-region blocking control problem, obtaining the active power and load shedding amount of the generators in each regional network; The multi-region blocking control of the interconnected power grid is carried out according to the solved active power and load shedding of the generators in each regional network.

2. The method for controlling cascading failures in an interconnected power grid in multiple stages according to claim 1, characterized in that: Traversing each initial fault to simulate the cascading fault of the interconnected power grid, and determining the high-risk fault chain under each initial fault, specifically including the following steps: A1. Construct an interconnected power grid model and initialize it, and calculate the power exchange value between the regional networks of the interconnected power grid model in the initial state; A2. Confirm an initial fault from the initial fault set, and disconnect the corresponding line according to the initial fault; A3, determine whether the power exchange value between the regional networks is changed, if so, proceed to the next step, otherwise go to step A5; A4. The transmission power of the interconnection lines between each area is ramped up to the maximum feasible power; A5, determine whether the regional network is disconnected or the power flow does not converge due to disconnection of the line. If so, proceed to the next step, otherwise go to step A7; A6. Rebalance the power of each regional network; A7, determine whether the fault chain termination condition is met, if so, go to step A9, otherwise calculate the DC power flow and go to the next step; A8. Determine whether there is an overloaded line based on the calculated DC power flow. If so, select the line with the highest probability of disconnection as the next stage fault line and disconnect it, then return to step A3. Otherwise, proceed to the next step. A9. Determine whether all initial faults have been traversed. If so, end the chain fault simulation process to obtain a high-risk fault chain consisting of multi-stage fault lines. Otherwise, return to step A2 to select the next initial fault.

3. The method for controlling cascading failures in an interconnected power grid in multiple stages according to claim 2, characterized in that: Step A6 specifically includes the following steps: A61. Calculate the active power flow difference of each regional network; A62. Based on the calculated active power flow difference of each regional network, all generator loads of each regional network are uniformly adjusted proportionally. The adjustment process is as follows: For any regional network σ, the active power P of generator i in the regional network is G,i Adjust to P G,i ' and the upper limit of the active power of generator i The minimum value between G,i ' and the lower limit of the active power of generator i The maximum value between G,i ' indicates that according to ΔP σ The theoretical active power value calculated by the initial active power of all generators in the regional network, ΔP σ represents the active power flow difference of the regional network σ; when P G,i 'Not at the lower limit With upper limit If ΔP σ ≥0, the generator is cut off, and the cutting order is from small to large according to the active power of the generator. If ΔP σ If <0, the load will be reduced proportionally.

4. The method for controlling cascading failures in an interconnected power grid in multiple stages according to claim 3, characterized in that: ΔP σ equal P G,i , P L,j , P tl,ζ They represent the active power of generator i, the power of load j and the transmission power of tie line ζ in the regional network σ, respectively. tl,ζ is the power transmission direction of the tie line ζ, v tl,ζ =1 indicates the output power, v tl,ζ =-1 means receiving power; P G,i 'The calculation process is as follows: When ΔP σ When ≥0, P G,i 'equal reduce represents the initial power of generator i; When ΔP σ When P < 0 G,i 'equal reduce The process of proportional load reduction is: represents the initial power of load j.

5. The method for controlling cascading failures in an interconnected power grid in multiple stages according to claim 4, characterized in that: In step A7, the fault chain termination condition is that the system load loss exceeds the load loss upper limit η, or reaches the maximum stage number k of the chain failure max , or the probability P of system failure chain occurrence is lower than the threshold; In step A8, the line start probability p is calculated as: When the line real-time power flow F≤f Rated When p=p0, p0 represents the preset low probability, f Rated It is the upper limit of power flow when the line is operating normally; When the line real-time power flow F>f max When p=p1, p1 represents the preset high probability, f max Transmit the maximum power for the line; When f Rated <F≤f max hour, e is the natural base.

6. A multi-stage blocking control method for interconnected power grid cascading failures according to claim 5, characterized in that: The propagation path control constraints are: When k=1,2,…,l-1, the probability of breaking the line in the kth stage Greater than the probability of disconnection of the non-fault line in stage k Active power flow of the line in the kth stage The absolute value of is not greater than represents the upper limit of the power flow, γ is the control factor, and l is the length of the fault chain; When k = l, the probability of line disconnection in the kth stage ω L k =0, the active power flow of the line in the kth stage The absolute value of is not greater than The generator climbing downhill constraint is: in, They represent the climbing and descending amount of the active power of generator i in the mth stage of the first k stages, respectively. They represent the climbing and descending amount of the active power of generator i in the kth stage, Respectively The upper limit of The load shedding constraint is: in, represents the reduction amount of load j in the kth stage, represents the reduction of load j in the mth stage among the first k stages; The climbing and descending constraints of the tie line are: in, They represent the climbing and descending amount of the tie line ζ in the mth stage in the first k stages, represents the upper limit of the transmission power of the tie line ζ, They represent the climbing and descending amount of the tie line ζ in the kth stage, They represent the upper limits of the climbing and descending slopes of the tie line ζ respectively; The node power balance constraint is: in, represents the active power of all generators in the regional network σ at the kth stage, represents the transmission power of all tie lines in the regional network σ at the kth stage, represents the power of all loads in the kth stage, and They represent the set of lines whose head and end are nodes n, represents the power of node n of the regional network σ at the kth stage, They represent the output power and injection power of node n in the regional network σ in the kth stage respectively.

7. A multi-stage blocking control method for cascading failures in interconnected power grids according to claim 6, characterized in that: The objective function is constructed as: Among them, ig represents the entire interconnected power grid, ω k represents the probability of disconnection of the fault line in the kth stage, α and β represent the adjustment cost of the generator and the cost coefficient of load shedding, respectively.

8. The method for controlling cascading failures in an interconnected power grid in multiple stages according to claim 7, characterized in that: The line disconnection probability at each stage of a cascading fault is used as the chromosome to encode the multi-area blocking control problem, which is decomposed into an upper-level problem of optimizing the line disconnection probability and a lower-level problem of optimizing the scheduling of generators, tie lines and load reduction when the line disconnection probability at each stage is known. Genetic algorithms are used to solve the upper and lower problems.

9. A multi-stage blocking control method for cascading failures in interconnected power grids according to any one of claims 1 to 8, characterized in that: The multi-region blocking control of the interconnected power grid is performed according to the solved active power and load shedding amount of the generators in each regional network, which specifically includes the following steps: Grant temporary dispatching authority to the tie line, allowing it to participate in fault blocking; According to the solved active power and load shedding amount of the generator, the active power of the tie-line associated generator is adjusted, the associated load is reduced, and the active power of the other non-associated generators is adjusted, and the non-associated load is reduced; The tie line determines its own transmission power based on the active power of the associated generators and supplies the associated loads of the receiving network.

10. A multi-stage blocking control system for cascading failures in an interconnected power grid, using a multi-stage blocking control method for cascading failures in an interconnected power grid as claimed in any one of claims 1 to 9, characterized in that: It includes fault simulation module, fault detection module, constraint determination module, objective function determination module, problem construction module, problem solving module and multi-area blocking control module; The fault simulation module is used to traverse each initial fault to simulate a chain failure of the interconnected power grid, and determine a high-risk fault chain under each initial fault; The fault detection module is used to detect a primary fault and obtain a high-risk fault chain corresponding to the primary fault based on a correspondence between a simulated initial fault and a high-risk fault chain; The constraint determination module is used to determine the propagation path control constraint based on the high-risk fault chain corresponding to the primary fault, and determine the generator climbing and descending constraints, load shedding constraints, tie line climbing and descending constraints and node power balance constraints that the interconnected power grid needs to meet at each stage; The objective function determination module is used to determine an objective function that minimizes the sum of the probability of occurrence of each stage of a cascading failure of each regional power grid, the control cost, and the risk of load loss by controlling the active power of the generators and the load shedding amount in each regional power grid; The problem construction module is used to construct a multi-region blocking control problem based on the objective function and the determined constraints; The problem solving module is used to solve the multi-region blocking control problem and obtain the active power and load shedding amount of the generators in each regional network; The multi-region blocking control module is used to perform multi-region blocking control on the interconnected power grid according to the solved active power and load shedding amount of the generators in each regional network.

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