Parallel and cooperative recovery method for AC-DC hybrid system

Abstract

The application discloses a parallel and cooperative recovery method for an AC-DC hybrid system, takes internal MMC-HVDC as an immune node, corrects an infection matrix, then updates the infection matrix according to the relationship between a node infection rate and a node infection threshold, obtains a reasonable partition scheme according to whether the infection matrix satisfies a partition constraint condition, rationally allocates available recovery resources of subintervals under the premise of guaranteeing relative independence and controllability of recovery of each subintervals, shortens the recovery time difference of different subintervals, and improves the overall recovery efficiency, for the recovery process of the node, updates a recovery matrix according to whether a recovery path satisfies a recovery constraint condition, obtains a unit recovery sequence scheme after all nodes are recovered, and realizes fast parallel and cooperative recovery of the AC-DC hybrid power system under the consideration of MMC-HVDC, and improves the technical effect of the recovery performance of the AC-DC hybrid system.

Description

Technical Field

[0001] This invention relates to the field of AC / DC hybrid system technology, and in particular to a parallel collaborative recovery method for AC / DC hybrid systems. Background Technology

[0002] As power system structures gradually evolve towards a hybrid AC / DC configuration, the role of DC transmission in power system operation and restoration will become increasingly crucial. For areas experiencing large-scale power outages, implementing parallel restoration strategies can effectively reduce the difficulty of restoration and further improve the overall restoration efficiency of the power grid.

[0003] Existing methods for parallel power system restoration focus on pure AC power systems and hybrid systems with LCC-HVDC (Line Commuted Converter High Voltage Direct Current) feeds. However, in current AC / DC deeply hybrid power system structures, MMC-HVDC (Modular Multilevel Converter High Voltage Direct Current) participates in the parallel power system restoration process. Therefore, how to rapidly perform parallel and coordinated restoration of AC / DC hybrid power systems, taking MMC-HVDC into account, and improve the restoration performance of AC / DC hybrid systems, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] This invention provides a parallel collaborative recovery method for AC / DC hybrid power systems, which can be used to quickly perform parallel collaborative recovery of AC / DC hybrid power systems while taking MMC-HVDC into account, thereby improving the recovery performance of AC / DC hybrid power systems.

[0005] In view of this, the present invention provides a parallel cooperative recovery method for AC / DC hybrid systems, comprising:

[0006] S1. Obtain the topology and node parameters of the AC / DC hybrid system;

[0007] S2. Construct the initial infection matrix based on the topology and node parameters;

[0008] S3. Based on the actual power outage scenario, set the pre-planned MMC-HVDC as an immune node and correct the infection matrix;

[0009] S4. For each node in the infection matrix other than the immune node, calculate the node infection rate based on the infection rate between adjacent nodes.

[0010] S5. Update the infection matrix based on the relationship between node infection rate and node infection threshold;

[0011] S6. Determine whether the infection state nodes in the infection matrix meet the partitioning constraints. If yes, proceed to step S7; otherwise, proceed to the next infection and return to step S5.

[0012] S7. Determine if any new crew members have been infected. If so, proceed to step S11; otherwise, proceed to step S8.

[0013] S8. Determine whether all power-depleted nodes have been infected. If so, obtain the partitioning scheme and jump to step S9. Otherwise, proceed to the next infection and return to step S5.

[0014] S9. Determine whether the unit recovery sequence plan has been obtained. If yes, output the partitioning plan and the unit recovery sequence plan. Otherwise, jump to step S10.

[0015] S10. Determine whether the conditions for interval coordinated recovery using MMC-HVDC as the interval connection line are met. If yes, perform partitioned interconnection using MMC-HVDC as the interval connection line, adjust the unit recovery order, and jump to step S11. Otherwise, jump directly to step S11.

[0016] S11. Based on the objective function of power restoration of the AC / DC hybrid system, sort the restoration order of the infected units in each partition in ascending order and number the target restoration units.

[0017] S12. Extract the recovery path of the current target recovery unit, determine whether the recovery path meets the recovery constraints, if so, update the recovery matrix according to the recovery path; otherwise, find the recovery path for the next target recovery unit.

[0018] S13. Determine whether all units in the partition have been restored. If so, obtain the unit restoration order plan and jump to step S14. Otherwise, proceed to the next infection and return to step S5.

[0019] S14. Determine whether a partitioning scheme has been obtained. If so, output the partitioning scheme and the unit recovery order scheme. Otherwise, proceed to the next infection and return to step S5.

[0020] Optionally, the partitioning constraints include partition number constraints and active power balance constraints;

[0021] The number of partitions is constrained as follows:

[0022] H≤Z

[0023] Where H represents the number of partitions, and Z represents the number of black boot power supplies within each partition;

[0024] The active power balance constraint is:

[0025]

[0026] Where, τ i C is the minimum technical output factor for the node unit. Gi N represents the maximum output active power of node unit i. g P represents the total number of nodes that have been restored. Dj For the active power support from the j-th DC system to the receiving AC system, N D P represents the number of DC landing points. Ls For the active load of node s, N s This represents the total number of nodes that have been restored.

[0027] Optionally, the objective function for power restoration in an AC / DC hybrid system is:

[0028]

[0029] Where F1 is the total recovery time of the target unit, F2 is the total output power of the non-black start units within the specified recovery time, F3 is the total charging reactive power of the recovery path, and T l To restore the charging time of route l in the path, T starti P is the start-up time of unit i. Gi For the active power output of unit i, N i To restore unit i, the number of lines that need to be restored, N G T represents the total number of units restored, and T represents the grid connection time of the last unit.

[0030] Optionally, the recovery constraints include unit start-up power constraints, system reactive power constraints, and power flow constraints;

[0031] The unit's starting power constraint is:

[0032]

[0033] Among them, P starti P is the starting power required by unit i. Dk This represents the active power output at the DC landing point k.

[0034] The system reactive power constraint is:

[0035]

[0036] Among them, Q Pl To restore the charging reactive power of line l, N l Q represents the total number of lines that have been restored. Lk N is the reactive power for restoring load to unit k. k Q represents the total number of units that were restored. GiTo restore the phase advance capability of unit i, c l c k c d and c i These are binary variables of 0 and 1; when the value is 0, no input is made, and when the value is 1, input is made.

[0037] Current constraints are:

[0038]

[0039] Among them, P Gi,max and P Gi,min These are the upper and lower limits of the active power of unit i, respectively, Q. Gi,max and Q Gi,min These are the upper and lower limits of reactive power for unit i, respectively. l P is the active power on branch l. l,max To transmit the maximum active power, U k U is the voltage at node k. k,max and U k,min Let P be the upper and lower limits of the voltage at node k, respectively. Di P is the transmission power at DC landing point i. Di,max The maximum transmission power is the DC landing point i.

[0040] Optionally, the conditions for obtaining the partitioning scheme are:

[0041]

[0042] Where h is the h-th partition, E S Let f be the set of power-out nodes. hj This represents the existence status of the j-th power-out node in the h-th partition, where 0 indicates existence and 1 indicates non-existence.

[0043] The conditions for obtaining the unit recovery sequence plan are:

[0044]

[0045] Among them, E I Let r be the set of infected nodes that have been infected by the virus. hj This represents the presence status of the j-th infected node in the h-th partition, where 0 indicates its presence and 1 indicates its absence.

[0046] Optionally, the formula for calculating the infection rate between adjacent nodes is:

[0047]

[0048] Where, α ij Let k be the infection rate between adjacent nodes i and j. i and kj P represents the importance of node i and node j, respectively. ij P represents the transmission power between node i and node j. max β1 and β2 are the maximum transmission power of all nodes, and are weighting coefficients.

[0049] Optionally, the formula for calculating the node infection rate is:

[0050]

[0051] Where, α i Let E be the node infection rate of node i. S Let E be the set of power-loss nodes. i Let i be the set of nodes that are adjacent to node i and are infected by the same virus.

[0052] Optionally, the node infection threshold is:

[0053] η=min{α i ,α i ≠0} i=1,2,...N

[0054] Where N is the number of infected nodes.

[0055] Optionally, the Dijkstra algorithm can be used to extract the recovery path of the target recovery unit.

[0056] Optionally, the conditions for using MMC-HVDC as the inter-interval tie line for inter-interval coordinated recovery are as follows:

[0057] The recovery progress of the two partitions is inconsistent;

[0058] After the two partitions are restored in a coordinated manner by using MMC-HVDC as the inter-partition connection line, they remain relatively independent and controllable.

[0059] Compared with existing technologies, the parallel cooperative recovery method for AC / DC hybrid systems provided by this invention has the following advantages:

[0060] The parallel collaborative recovery method for AC / DC hybrid power systems provided by this invention uses the internal MMC-HVDC as an immune node to correct the infection matrix. Then, the infection matrix is ​​updated based on the relationship between the node infection rate and the node infection threshold. A reasonable partitioning scheme is obtained by considering whether the infection matrix meets the partitioning constraints. Considering the collaborative recovery effect of sub-intervals, the available recovery resources of sub-intervals are reasonably allocated under the premise of ensuring that the recovery of each sub-interval is relatively independent and controllable, thereby shortening the recovery time difference between different sub-intervals and improving the overall recovery efficiency. For the node recovery process, the recovery matrix is ​​updated based on whether the recovery path meets the recovery constraints. After all nodes have been recovered, the unit recovery sequence scheme is obtained. This method achieves the technical effect of rapidly performing parallel collaborative recovery of AC / DC hybrid power systems while considering MMC-HVDC, thus improving the recovery performance of AC / DC hybrid power systems. Attached Figure Description

[0061] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0062] Figure 1 This is a flowchart illustrating a parallel collaborative recovery method for an AC / DC hybrid system provided in this invention.

[0063] Figure 2 This is a block diagram of the execution logic of a parallel collaborative recovery method for an AC / DC hybrid system provided in this invention;

[0064] Figure 3 This is a schematic diagram of the virus recovery iteration process provided in this invention;

[0065] Figure 4 This is a schematic diagram of a 12-node test example containing MMC-HVDC provided in this invention;

[0066] Figure 5 for Figure 4 A diagram showing the corresponding infection zoning results;

[0067] Figure 6 for Figure 4 The corresponding collaborative recovery result diagram. Detailed Implementation

[0068] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] Basic definition explanation:

[0070] S-class nodes: also known as power outage nodes, are all equivalent nodes in the power outage area except for immune nodes, including substations, power plants, and load nodes.

[0071] Type I nodes: Nodes carrying virus information. Nodes infected by different viruses are divided into different sub-regions (partitions), and infected nodes spread by infecting their neighboring nodes.

[0072] R-class nodes: Recovered nodes, that is, nodes that have gone from a power failure state to a power restoration state, and the nodes will not fail again.

[0073] Immune nodes: Nodes that are not infected by viruses, meaning they cannot perform recovery operations normally.

[0074] Node infection rate: The probability that a node is infected.

[0075] Node recovery rate: The probability that a node can be recovered.

[0076] For easier understanding, please refer to Figure 1 and Figure 2 This invention provides an embodiment of a parallel cooperative recovery method for AC / DC hybrid systems, comprising:

[0077] Step S1: Obtain the topology and node parameters of the AC / DC hybrid system.

[0078] It should be noted that the number of nodes in the topology parameters of the AC / DC hybrid system should be obtained first.

[0079] Step S2: Construct the initial infection matrix based on the topology and node parameters.

[0080] It should be noted that after obtaining the topology and node parameters of the AC / DC hybrid system, the infection matrix I is initialized based on the number and location of the black-start generators. Simultaneously, the virus propagation matrix P can be initialized based on the topology and physical characteristics of the AC / DC hybrid system.

[0081] Step S3: Based on the actual power outage scenario, set the pre-planned MMC-HVDC as an immune node and correct the infection matrix.

[0082] It should be noted that the infection matrix I is a matrix of dimension H×N, where H is the number of virus types, equivalent to the number of partitions, and N is the number of infected nodes. The infection matrix I can be defined as:

[0083]

[0084] Among them, f hi Let be the i-th node of the h-th partition, and let be an element of the infection matrix I, where h = 1, 2, ..., H, and i = 1, 2, ..., N.

[0085] A virus propagation matrix P is defined to represent the connectivity of nodes in an AC / DC hybrid system and the infection rate between nodes. The virus propagation matrix P is an N×N matrix, and can be defined as follows:

[0086]

[0087] Where, p ij For the virus transmission matrix P elements, α ij Let E be the infection rate between adjacent nodes i and j, i.e., the probability that node i is infected by node j. M This is a set of immune nodes.

[0088] Step S4: For each node in the infection matrix other than the immune node, calculate the node infection rate based on the infection rate between adjacent nodes.

[0089] It should be noted that the formula for calculating the infection rate between adjacent nodes is:

[0090]

[0091] Where, α ij Let k be the infection rate between adjacent nodes i and j. i and k j P represents the importance of node i and node j, respectively. ij P represents the transmission power between node i and node j. max β1 and β2 are the maximum transmission power of all nodes, and are weighting coefficients.

[0092] The formula for calculating the node infection rate is:

[0093]

[0094] Where, α i Let E be the node infection rate of node i. S Let E be the set of power-loss nodes. i Let i be the set of nodes that are adjacent to node i and are infected by the same virus.

[0095] To ensure that every node can be infected and the spread is continuously expanded, the infection threshold for each node is set as the minimum infection rate of all nodes at each infection. That is, the node infection threshold is:

[0096] η=min{α i ,α i ≠0} i=1,2,...N

[0097] Where N is the number of infected nodes.

[0098] Step S5: Update the infection matrix based on the relationship between node infection rate and node infection threshold.

[0099] It should be noted that if the node infection rate is greater than the node infection threshold, the node will be infected; otherwise, it will not be infected. Therefore, the infection matrix can be updated:

[0100]

[0101] Among them, I (t) Let be the infection matrix for the t-th infection.

[0102] Step S6: Determine whether the infected state nodes in the infection matrix meet the partitioning constraints. If yes, proceed to step S7; otherwise, proceed to the next infection and return to step S5.

[0103] It should be noted that the partitioning constraints are embedded into the partitioning process. These partitioning constraints include the number of partitions and the active power balance constraints.

[0104] The partition number constraint requires that each partition must include at least one power supply with black boot capability, i.e., the partition number constraint is:

[0105] H≤Z

[0106] Where H represents the number of partitions, and Z represents the number of black boot power supplies within each partition;

[0107] Power supply and demand balance is a prerequisite for maintaining voltage and frequency stability in the power system. Therefore, it is essential to ensure that each zone has sufficient load to maintain power balance. In this invention, the active power balance constraint is defined as follows:

[0108]

[0109] Where, τ i C is the minimum technical output coefficient of node unit i. Gi N represents the maximum output active power of node unit i. g P represents the total number of units that have been restored. Dj For the active power support from the j-th DC system to the receiving AC system, ND The number of DC landing points, including the number of DC landing points fed in from outside the power outage area and the number of DC landing points interconnected between sub-sections using MMC-HVDC, P Ls For the active load of node s, N s This represents the total number of nodes that have been restored.

[0110] If the partition constraints are not met, the system proceeds to the next infection cycle, i.e., t = t + 1, and returns to step S5 to update the infection matrix again. The generators are continuously outputting power; if the system's active power is unbalanced at this time, it will proceed to the next infection cycle until the system meets the partition constraints.

[0111] If the partition constraints are met, proceed to step S7.

[0112] Step S7: Determine if any new crew members have been infected. If so, proceed to step S11; otherwise, proceed to step S8.

[0113] It should be noted that the process involves determining whether any new unit nodes have been infected. If so, the process proceeds to step S11; otherwise, it proceeds to step S8.

[0114] Step S8: Determine whether all power-depleted nodes have been infected. If so, obtain the partitioning scheme and jump to step S9. Otherwise, proceed to the next infection and return to step S5.

[0115] It should be noted that if no new node units are infected, the system checks whether all power-out nodes, i.e., Class S nodes, have been completely infected. If so, a partitioning scheme is obtained. Whether a partitioning scheme has been obtained can be indicated by the flag bit Flag2. Flag2 is 0, indicating that no partitioning scheme has been obtained, and Flag2 is 1, indicating that a partitioning scheme has been obtained.

[0116] Besides immune nodes, any node can belong to only one partition and cannot exist in two partitions simultaneously. Therefore, in the last infection iteration, each column of the infection matrix has exactly one 1, with the rest being 0. That is, the condition for obtaining the partitioning scheme is:

[0117]

[0118] Where h is the h-th partition, E s Let f be the set of power-out nodes. hj This represents the existence status of the j-th power-out node in the h-th partition, where 0 indicates existence and 1 indicates non-existence.

[0119] Step S9: Determine whether the unit recovery sequence plan has been obtained. If yes, output the partitioning plan and the unit recovery sequence plan. Otherwise, proceed to step S10.

[0120] It should be noted that whether a unit recovery order scheme has been obtained can be represented by a flag bit Flag1. Flag1 of 0 indicates that no unit recovery order scheme has been obtained, and Flag1 of 1 indicates that a unit recovery order scheme has been obtained. Except for immune nodes, any node will be recovered according to its priority. At the end of the last iteration, each column of the recovery matrix will have exactly one 1, with the rest being 0. That is, the condition for obtaining a unit recovery order scheme is:

[0121]

[0122] Among them, E I Let r be the set of infected nodes that have been infected by the virus. hj This represents the presence status of the j-th infected node in the h-th partition, where 0 indicates its presence and 1 indicates its absence.

[0123] Step S10: Determine whether the conditions for inter-regional coordinated recovery using MMC-HVDC as the inter-regional tie line are met. If yes, then use MMC-HVDC as the inter-regional tie line for inter-regional interconnection, adjust the unit recovery order, and jump to step S11. Otherwise, jump directly to step S11.

[0124] It should be noted that conventional parallel recovery processes often involve interconnecting sub-regions after each sub-region has completed its corresponding recovery measures. However, this approach of restoring within a sub-region first and then interconnecting sub-regions cannot account for the coordinated recovery capabilities between sub-regions during the recovery process. If sub-regions with faster recovery progress can provide power support to sub-regions with slower recovery progress through pre-interconnection, the time interval between sub-regions will be shortened, indirectly accelerating the overall power grid recovery process. MMC-HVDC has excellent voltage and frequency regulation capabilities, strong controllability, and the AC systems connected at both ends can operate asynchronously. Therefore, using MMC-HVDC as a tie line between two sub-regions, and achieving mutual power support between sub-regions through pre-interconnection, can compensate for the inability of AC tie lines to pre-interconnect each sub-region. The conditions for determining whether MMC-HVDC can be used as a tie line for inter-regional coordinated recovery are: the recovery progress of the two sub-regions is inconsistent, and after inter-regional coordinated recovery using MMC-HVDC as the tie line, the two sub-regions remain relatively independent and controllable. If the conditions for inter-regional coordinated recovery using MMC-HVDC as the inter-regional tie line are met, then the MMC-HVDC is used as the inter-regional tie line for inter-regional interconnection. The unit recovery order is adjusted according to the result of the inter-regional interconnection, and then the process jumps to step S11.

[0125] Step S11: Based on the objective function of power restoration of the AC / DC hybrid system, sort the restoration order of the infected units in each partition in ascending order and number the target restoration units.

[0126] It should be noted that to obtain the node recovery status, it is necessary to solve for the objective function of determining the unit recovery order. The objective function for determining the unit recovery order is embedded into the recovery process. Upon entering the node recovery phase, the node recovery matrix is ​​first initialized. For example... Figure 3 As shown,

[0127] The corresponding infection matrix is:

[0128]

[0129] The corresponding initialization recovery matrix is:

[0130]

[0131] The ultimate goal of power system restoration is to restore all out-of-power loads as quickly and safely as possible. The total restoration time determines the speed of system restoration; a shorter time indicates a faster restoration speed, which is beneficial for accelerating the system restoration process. The total output active power determines the maximum power the system can supply within a specified time; a higher power indicates that more out-of-power loads can be restored, reducing economic losses. The total line charging reactive power determines the stability during the restoration process; a lower line charging reactive power reduces the possibility of overvoltage, avoiding secondary system faults. In this invention, the objective function for power restoration of an AC / DC hybrid system is:

[0132]

[0133] Where F1 is the total recovery time of the target unit, F2 is the total output power of the non-black start units within the specified recovery time, F3 is the total charging reactive power of the recovery path, and T l To restore the charging time of route l in the path, T starti P is the start-up time of unit i. Gi For the active power output of unit i, N i To restore unit i, the number of lines that need to be restored, N G T represents the total number of units restored, and T represents the grid connection time of the last unit.

[0134] The updated node recovery matrix can be represented as:

[0135]

[0136] Where R is the node recovery matrix, r hj Let j be an element in R, where j ∈ E I . λ hj This represents the node recovery rate.

[0137]

[0138] Based on the value of the objective function, the recovery order of the infected units in the partition is sorted from smallest to largest. The target recovery unit is numbered G. i i = 1, 2, ..., N G .

[0139] The objective function for power restoration in an AC / DC hybrid system can be solved using a greedy algorithm, decomposing the generator startup problem into a multi-step decision-making problem. The total restoration time can be decomposed into the sum of the time required to restore each generator and its restoration path. In each decision-making process, generators with shorter restoration times are prioritized for restoration, minimizing the total restoration time. Generators with faster ramp-up speeds are also prioritized for restoration, maximizing active power output within the specified restoration time. The total reactive power of the restoration path can be decomposed into the sum of the reactive power of the restoration path corresponding to each non-black-start generator. Therefore, the objective function for power restoration in an AC / DC hybrid system can be transformed into:

[0140]

[0141] Among them, T i C is the time it takes for unit i to reach maximum power. Gi f1 represents the maximum output power of generator point i, f2 represents the recovery time of each generator unit and its recovery path, f3 represents the ramp rate of each generator unit, and f4 represents the charging reactive power of the recovery path of each generator unit.

[0142] The multi-objective function is transformed into a single-objective function using a linear weighting method, defined as:

[0143] Ω=γ1f1+γ2f2+γ3f3

[0144] In the formula, γ1, γ2, and γ3 are the weights of each objective, which can be calculated using the combined weighting method. In each decision-making step, the unit with the largest Ω value is selected as the current decision objective. Through multi-step optimization, the overall result is approached as optimal.

[0145] Step S12: Extract the recovery path of the current target recovery unit, determine whether the recovery path meets the recovery constraints, if so, update the recovery matrix according to the recovery path, otherwise, for the next target recovery unit.

[0146] It should be noted that for the target recovery unit with a number, Dijkstra's algorithm is used to extract the recovery path of the target recovery unit, for i≤G i If the recovery path satisfies the recovery constraints, then update the recovery matrix according to the recovery path; otherwise, determine the recovery path for the next target recovery unit, i.e., t = t + 1.

[0147] The recovery constraints include unit start-up power constraints, system reactive power constraints, and power flow constraints.

[0148] During system recovery, sufficient starting power is required to meet the power demands of non-black start units. If the starting power is insufficient at any point, the recovery time needs to be delayed to allow the units to ramp up or receive power support from adjacent sub-areas until the units meet their starting power requirements. Therefore, the unit starting power constraint is:

[0149]

[0150] Among them, P starti P is the starting power required by unit i. Dk This represents the active power output at the DC landing point k.

[0151] The system reactive power constraint is:

[0152]

[0153] Among them, Q Pl To restore the charging reactive power of line l, N l Q represents the total number of lines that have been restored. Lk N is the reactive power for restoring load to unit k. k Q represents the total number of units that were restored. Gi To restore the phase advance capability of unit i, c l c k c d and c i These are binary variables of 0 and 1; when the value is 0, no input is made, and when the value is 1, input is made.

[0154] Based on the power flow constraints of traditional AC systems, additional constraints on DC transmission power are added to ensure that the MMC-HVDC operates within a controllable range, and to achieve reasonable allocation of sub-interval recovery resources in the case of MMC-HVDC interconnection. Therefore, the power flow constraints are:

[0155]

[0156] Among them, P Gi,max and P Gi,min These are the upper and lower limits of the active power of unit i, respectively, Q. Gi,max and Q Gi,min These are the upper and lower limits of reactive power for unit i, respectively. l P is the active power on branch l. l,max To transmit the maximum active power, U k U is the voltage at node k. k,max and U k,min Let P be the upper and lower limits of the voltage at node k, respectively.Di P is the transmission power at DC landing point i. Dimax The maximum transmission power is the DC landing point i.

[0157] Step S13: Determine whether all units in the partition have been restored. If so, obtain the unit restoration order plan and jump to step S14. Otherwise, proceed to the next infection and return to step S5.

[0158] It should be noted that after updating and restoring the treatment, it is determined whether all units in the partition have been restored. If all nodes in the partition have been restored, the unit restoration order scheme can be obtained. If there are still nodes in the partition that have not been restored, the next infection will begin, t = t + 1, and the process will return to step S5.

[0159] Step S14: Determine whether a partitioning scheme has been obtained. If so, output the partitioning scheme and the unit recovery order scheme. Otherwise, proceed to the next infection and return to step S5.

[0160] It should be noted that after obtaining the unit recovery sequence plan and the partitioning plan, the partitioning plan and the unit recovery sequence plan are output.

[0161] The parallel collaborative recovery method for AC / DC hybrid power systems provided by this invention uses the internal MMC-HVDC as an immune node to correct the infection matrix. Then, the infection matrix is ​​updated based on the relationship between the node infection rate and the node infection threshold. A reasonable partitioning scheme is obtained by considering whether the infection matrix meets the partitioning constraints. Considering the collaborative recovery effect of sub-intervals, the available recovery resources of sub-intervals are reasonably allocated under the premise of ensuring that the recovery of each sub-interval is relatively independent and controllable, thereby shortening the recovery time difference between different sub-intervals and improving the overall recovery efficiency. For the node recovery process, the recovery matrix is ​​updated based on whether the recovery path meets the recovery constraints. After all nodes have been recovered, the unit recovery sequence scheme is obtained. This method achieves the technical effect of rapidly performing parallel collaborative recovery of AC / DC hybrid power systems while considering MMC-HVDC, thus improving the recovery performance of AC / DC hybrid power systems.

[0162] To more intuitively illustrate the effect of the parallel cooperative recovery method for AC / DC hybrid systems provided by this invention, a 12-node test example including MMC-HVDC is used for illustration. The 12-node test example including MMC-HVDC is as follows: Figure 4 As shown, there are 6 unit connection points: G1, G2, G3, G4, G5, and G6. G1 and G4 are equivalent to the external power grid via MMC-HVDC. Unit parameters are shown in Table 1-1, and line parameters are shown in Table 1-2. It is assumed that nodes 1 and 4 are connected to the faulty power grid via the external power grid through MMC-HVDC, and lines 8-9 are MMC-HVDC. The recovery optimization time is set to 1 hour.

[0163] Table 1-1 Unit Data for the 111-Node Test Case

[0164]

[0165]

[0166] Table 1-2 Line Data

[0167]

[0168] Consider using MMC-HVDC as the interval tie line to achieve sub-region interconnection. The partitioning result is as follows: Figure 5 As shown, the recovery result is as follows Figure 6 As shown in Table 1-3, the unit recovery order for each sub-area is as follows.

[0169] Table 1-3 Order of Unit Restoration for Each Sub-region

[0170]

[0171] Initially, viruses a and b infect G1 and G4 respectively. Since the MMC-HVDC is set as an immune node, the viruses cannot infect through this line. The resulting partitioning is as follows: nodes 1, 2, 6, and 7 belong to partition 1; nodes 3, 4, 5, 9, 10, 11, and 12 belong to partition 2; and node 8 is the DC landing point of the MMC-HVDC. In partition 1, the unit recovery order is G1, G2, and G6; in partition 2, the unit recovery order is G4, G5, and G3.

[0172] Section 1 and Section 2 are interconnected via MMC-HVDC, as shown in Table 1-3. The grid connection time of the last restored unit in both sections is 50 minutes, and the restoration time interval between sub-sections is 0 minutes. During the restoration process, Section 2 provides 50MW of restoration power to Section 1 via MMC-HVDC to start unit G3. Section 2 also absorbs the charging reactive power generated by restoration path 8-3 corresponding to restored unit G3 in Section 1 via MMC-HVDC, which is 78.02MVar. It is evident that MMC-HVDC plays a coordinating role between different sub-sections, rationally allocating restoration resources between sub-sections through MMC-HVDC, reducing the restoration time interval between sections, and accelerating the restoration progress of each sub-section.

[0173] Taking the MMC-HVDC inter-interconnection effect as a comparative example, the corresponding partitioning results and recovery results are shown in Table 1-4, and the results comparison is shown in Table 1-5.

[0174] Table 1-4 Unit Restoration Sequence for Each Sub-region

[0175]

[0176] Table 1-5 Comparison of Results

[0177]

[0178] As shown in Table 1-4, without considering the interconnection between MMC and HVDC, the resulting partitioning is as follows: Nodes 1, 2, 3, 6, 7, and 8 belong to partition 1, and nodes 4, 5, 9, 10, 11, and 12 belong to partition 2. In partition 1, the unit recovery order is G1, G2, G6, and G3; in partition 2, the unit recovery order is G4 and G5. The last unit in partition 1 was connected to the grid in 55 minutes, while the last unit in partition 2 was connected in 35 minutes, a time interval of 20 minutes, indicating a significant difference in the recovery process between the two partitions.

[0179] Comparing Tables 1-3 and 1-4 reveals that, considering the MMC-HVDC inter-regional interconnection, the grid connection time of Unit G3 is shortened by 5 minutes, assuming other unit grid connection times remain unchanged. As shown in Table 1-5, the scheme considering the inter-regional interconnection results in a 50-minute startup time for the last unit in the entire system, which is better than the 55-minute time without inter-regional interconnection. Furthermore, the maximum time interval difference between sub-regions is smaller, and the recovery processes of each zone are more similar. Within the optimized timeframe, the total output power of non-black-start units is 196.5MW, greater than 173.5MW, also better than the scheme without inter-regional interconnection. Therefore, considering the MMC-HVDC inter-regional interconnection helps reduce the difference in recovery time between sub-regions, shortens the grid connection time of some units, improves system output power, and accelerates the overall recovery process.

[0180] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A parallel cooperative recovery method for an AC / DC hybrid system, characterized in that, include: S1. Obtain the topology and node parameters of the AC / DC hybrid system; S2. Construct the initial infection matrix based on the topology and node parameters; S3. Based on the actual power outage scenario, set the pre-planned MMC-HVDC as an immune node and correct the infection matrix; S4. For each node in the infection matrix other than the immune node, calculate the node infection rate based on the infection rate between adjacent nodes. S5. Update the infection matrix based on the relationship between node infection rate and node infection threshold; S6. Determine whether the infection state nodes in the infection matrix meet the partitioning constraints. If yes, proceed to step S7; otherwise, proceed to the next infection and return to step S5. S7. Determine if any new crew members have been infected. If so, proceed to step S11; otherwise, proceed to step S8. S8. Determine whether all power-depleted nodes have been infected. If so, obtain the partitioning scheme and jump to step S9. Otherwise, proceed to the next infection and return to step S5. S9. Determine whether the unit recovery sequence plan has been obtained. If yes, output the partitioning plan and the unit recovery sequence plan. Otherwise, jump to step S10. S10. Determine whether the conditions for interval coordinated recovery using MMC-HVDC as the interval connection line are met. If yes, perform partitioned interconnection using MMC-HVDC as the interval connection line, adjust the unit recovery order, and jump to step S11. Otherwise, jump directly to step S11. S11. Based on the objective function of power restoration of the AC / DC hybrid system, sort the restoration order of the infected units in each partition in ascending order and number the target restoration units. S12. Extract the recovery path of the current target recovery unit, determine whether the recovery path meets the recovery constraints, if so, update the recovery matrix according to the recovery path; otherwise, find the recovery path for the next target recovery unit. S13. Determine whether all units in the partition have been restored. If so, obtain the unit restoration order plan and jump to step S14. Otherwise, proceed to the next infection and return to step S5. S14. Determine whether a partitioning scheme has been obtained. If so, output the partitioning scheme and the unit recovery order scheme. Otherwise, proceed to the next infection and return to step S5.

2. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 1, characterized in that, The zoning constraints include the number of zoning constraints and the active power balance constraints; The number of partitions is constrained as follows: H≤Z Where H represents the number of partitions, and Z represents the number of black boot power supplies within each partition; The active power balance constraint is: Where, τ i C is the minimum technical output factor for the node unit. Gi N represents the maximum output active power of node unit i. g P represents the total number of nodes that have been restored. Dj For the active power support from the j-th DC system to the receiving AC system, N D P represents the number of DC landing points. Ls For the active load of node s, N s This represents the total number of nodes that have been restored.

3. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 2, characterized in that, The objective function for power restoration in an AC / DC hybrid system is: Where F1 is the total recovery time of the target unit, F2 is the total output power of the non-black start units within the specified recovery time, F3 is the total charging reactive power of the recovery path, and T l To restore the charging time of route l in the path, T starti P is the start-up time of unit i. Gi For the active power output of unit i, N i The number of lines that need to be restored to restore unit i, N G T represents the total number of units restored, and T represents the grid connection time of the last unit.

4. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 3, characterized in that, Restoration constraints include unit start-up power constraints, system reactive power constraints, and power flow constraints; The unit's starting power constraint is: Among them, P starti P is the starting power required by unit i. Dk This represents the active power output at the DC landing point k. The system reactive power constraint is: Among them, Q Pl To restore the charging reactive power of line l, N l Q represents the total number of lines that have been restored. Lk N is the reactive power for restoring load to unit k. k Q represents the total number of units that were restored. Gi To restore the phase advance capability of unit i, c l c k c d and c i These are binary variables of 0 and 1; when the value is 0, no input is made, and when the value is 1, input is made. Current constraints are: Among them, P Gi,max and P Gi,min These are the upper and lower limits of the active power of unit i, respectively, Q. Gi,max and Q Gi,min These are the upper and lower limits of reactive power for unit i, respectively, P l P is the active power on branch l. l,max To transmit the maximum active power, U k U is the voltage at node k. k,max and U k,min Let P be the upper and lower limits of the voltage at node k, respectively. Di P is the transmission power at DC landing point i. Di,max The maximum transmission power is the DC landing point i.

5. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 1, characterized in that, The conditions for obtaining the partitioning scheme are: Where h is the h-th partition, E S Let f be the set of power-out nodes. hj This represents the existence status of the j-th power-out node in the h-th partition, where 0 indicates existence and 1 indicates non-existence. The conditions for obtaining the unit recovery sequence plan are: Among them, E I Let r be the set of infected nodes that have been infected by the virus. hj This represents the presence status of the j-th infected node in the h-th partition, where 0 indicates its presence and 1 indicates its absence.

6. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 1, characterized in that, The formula for calculating the infection rate between adjacent nodes is: Where, α ij Let k be the infection rate between adjacent nodes i and j. i and k j P represents the importance of node i and node j, respectively. ij P represents the transmission power between node i and node j. max β1 and β2 are the maximum transmission power of all nodes, and are weighting coefficients.

7. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 6, characterized in that, The formula for calculating the node infection rate is: Where, α i Let E be the node infection rate of node i. S Let E be the set of power-loss nodes. i Let i be the set of nodes that are adjacent to node i and are infected by the same virus.

8. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 7, characterized in that, The node infection threshold is: η=min{α i ,a i ≠0}i=1,2,...N Where N is the number of infected nodes.

9. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 1, characterized in that, Dijkstra's algorithm is used to extract the recovery path of the target recovery unit.

10. The parallel cooperative recovery method for AC / DC hybrid systems according to claim 1, characterized in that, The conditions for segmented coordinated recovery using MMC-HVDC as the segmental tie line are as follows: The recovery progress of the two partitions is inconsistent; After the two partitions are restored in a coordinated manner by using MMC-HVDC as the inter-partition connection line, they remain relatively independent and controllable.

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