Energy storage optimization configuration method and system for AC / DC hybrid system

Abstract

The present invention relates to the technical field of AC / DC hybrid systems, and discloses a method and system for optimizing energy storage configuration of an AC / DC hybrid system, including S1, establishing a power flow over-limit risk index in combination with the branch disconnection distribution factor, and then finding the shortest path between the converter station and several designated nodes according to the Dijkstra algorithm, and judging the sensitivity and vulnerability of the AC lines on all the shortest paths to DC power transfer by the power flow over-limit risk index; S2, screening out candidate lines for energy storage access to the AC / DC hybrid system from all the AC lines; S3, establishing a multi-objective mathematical model for the candidate lines with the maximum power flow over-limit risk index and the minimum energy storage investment cost; S4, using the PSO algorithm to obtain the capacity of energy storage in each energy storage configuration position, and selecting the optimal energy storage configuration position from the candidate lines. The present invention avoids setting energy storage on the sensitive and vulnerable line, causing grid instability.

Description

Technical Field

[0001] The present invention relates to the technical field of AC / DC hybrid systems, and in particular to an energy storage optimization configuration method and system for an AC / DC hybrid system. Background Art

[0002] As a long-distance and large-capacity power transmission method across large regions, DC transmission can achieve optimal resource allocation between regions. In order to meet the development of large hydropower bases, large thermal power bases, and large new energy power bases and the demand for "west-to-east power transmission", China has successively built and put into operation a number of ultra-high voltage DC transmission lines, such as Fufeng DC, Qishao DC, Zhaqing DC, Jiquan DC, etc. At the same time, in order to achieve the dual carbon goals, multiple DC lines are also planned. However, after a DC lockout fault occurs in ultra-high voltage DC transmission, it faces a large power transfer, that is, the DC power will flow into the AC channel, causing the power of the AC channel to increase sharply, which will lead to the following problems: 1) The power of the AC channel exceeds the limit and continues to oscillate, and the node voltage exceeds the maximum range; 2) The power of the AC channel exceeds the limit, which will cause chain failures, such as chain tripping and other accidents. In order to solve the problems of AC channel over-limit and system instability caused by the DC lockout fault of the AC / DC hybrid system, the current main method is to cut the machine and load to eliminate the over-limit power of the AC channel and improve the stability of the power grid. However, the system takes a long time to cut off the power supply, which may cause the system to become unstable before the power supply is completely cut off, which is not conducive to the stability of the system. At the same time, it will take a long time to start the power supply, which greatly increases the operating cost of the power supply. At the same time, the system also needs to cut off a certain amount of load when cutting off the power supply, which will further increase the operating cost of the power supply, and may reduce the quality of power and affect the reliability of power supply. Energy storage has good dynamic active and reactive power regulation capabilities, and can adapt to the operation control requirements of different time scales. In addition, the AC / DC hybrid system can eliminate the flow limit caused by the DC high power transfer of the AC / DC hybrid system through the configured energy storage, reduce the amount of machine cutting and load cutting after the system failure, improve the system operation flexibility and stability, and ensure the safe, reliable and efficient operation of the AC / DC hybrid system. Therefore, by connecting energy storage near the converter station of the DC transmission line in the AC / DC hybrid system, after a DC locking fault occurs, the AC channel over-limit can be eliminated by absorbing active power through energy storage, and the amount of machine cutting and load shedding can be reduced. However, when using energy storage near the converter station to eliminate power transfer, some sensitive and fragile AC lines still have power flow over-limit problems, which may cause chain failures and reduce the safe and stable operation capabilities of the AC / DC hybrid system. Summary of the invention

[0003] Aiming at the problem that after a fault occurs in an AC / DC hybrid system, the sensitive and fragile lines in the system still exceed the static stability limit, the present invention provides an energy storage optimization configuration method and system for an AC / DC hybrid system to solve the problem that the sensitive and fragile AC lines have a power flow exceeding the limit and may cause a cascading failure, thereby improving the safe and stable operation capability of the system.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for optimizing energy storage configuration of an AC / DC hybrid system, comprising:

[0006] S1. Obtain the branch disconnection distribution factor of the converter station of the DC transmission line in the AC / DC hybrid system where DC blocking occurs, establish a power flow over-limit risk index in combination with the branch disconnection distribution factor, and then find the shortest path between the converter station and several designated nodes according to the Dijkstra algorithm, and judge the sensitivity and vulnerability of the AC lines on all the shortest paths to DC power transfer by the power flow over-limit risk index;

[0007] S2, selecting candidate lines for energy storage access to the AC / DC hybrid system from all the AC lines;

[0008] S3. Based on the safe and stable operation capability of the candidate line, a multi-objective mathematical model is established for the candidate line with the maximum risk index of power flow crossing and the minimum investment cost of energy storage, so as to achieve the optimal configuration of energy storage of the candidate line;

[0009] S4. Taking the input end of the candidate line as the energy storage configuration position, the PSO algorithm is used to obtain the energy storage capacity in each energy storage configuration position, and the optimal energy storage configuration position is selected from the candidate line, thereby eliminating the over-limit power of the candidate line to improve the safe and stable operation capability of the AC / DC hybrid system.

[0010] As an optimization, the power flow over-limit risk index is as follows:

[0011]

[0012] Among them, A and R are lines in the AC / DC hybrid system, A is the DC transmission line, R is the AC line, ΔP′ is the power flow over-limit capacity margin of line R when the power flow of line R changes after line A is disconnected, D R-A represents the branch disconnection distribution factor that causes the change in active power flow of line R after line A is disconnected, P A,max It is the thermal stability limit value of breaking line A.

[0013] As an optimization, the formula for the power flow over-limit capacity margin ΔP′ of line R under the power flow change of line R caused by line A disconnection is as follows:

[0014] When DR-A <0, the expression of the line power flow over-limit capacity margin ΔP′ is as follows:

[0015]

[0016] When D R-A When >0, the expression of line power flow over-limit capacity margin ΔP′ is as follows:

[0017]

[0018] Among them, P R,max is the thermal stability limit of line R, P R Represents the steady-state initial active power of line R.

[0019] As an optimization, the AC line whose absolute value of the power flow over-limit risk index is less than the set limit value is the candidate line.

[0020] As an optimization, in S3, the multi-objective mathematical model includes a first objective function of minimizing the energy storage investment cost for energy storage to eliminate the over-limit power of the AC channel after a fault occurs in the AC / DC hybrid system, a second objective function of minimizing the penalty cost for cutting generators and loads, and a third objective function of maximizing the line flow over-limit risk index;

[0021] Among them, the expression of the first objective function is as follows:

[0022]

[0023] The expression of the second objective function is as follows:

[0024]

[0025] The expression of the third objective function is as follows:

[0026]

[0027] Among them, F ERI is the power flow over-limit risk index of the AC / DC hybrid system; ΔP′ is the line power flow over-limit capacity margin; D k,x is the branch breaking distribution factor; P dc-max is the thermal stability limit of the DC line; G inv The investment cost and operation and maintenance cost of energy storage; c p 、c e are the unit power cost and capacity cost of energy storage respectively; P rate,n 、E rate,n are the maximum charging and discharging power and capacity of energy storage respectively; r is the annual interest rate of funds; y is the life cycle of energy storage; G cut is the penalty cost of shedding the load; c Gcut,m 、cLcut,n are the penalty cost per unit of machine shedding and the penalty cost per unit of load shedding respectively; M and N are the number of generators and loads in the system respectively; K is the number of lines in the shortest path.

[0028] As an optimization, the branch breaking distribution factor D k,x The specific expression is as follows:

[0029]

[0030] Among them, P k is the power of line x at the initial moment; △P is the power increment on line x after the AC / DC hybrid system is connected to the energy storage.

[0031] As an optimization, the constraints of the multi-objective mathematical model include power balance constraints, line loss constraints, generator power constraints, generator ramp constraints, line power constraints, energy storage capacity constraints, and energy storage charging and discharging power constraints, wherein:

[0032] The power balance constraint is as follows:

[0033]

[0034] Where P G,m , P L,n , P B,r are the output of generator m, the required power of load n, and the absorbed power of energy storage r respectively; R is the amount of energy storage configured in the AC / DC hybrid system;

[0035] The line loss constraint is as follows:

[0036]

[0037] In the formula, P′ k , Q′ k are respectively the active power and reactive power transmitted by the receiving end of the kth line; R k is the resistance of the kth circuit; U′ k is the voltage amplitude of the receiving node of the kth line;

[0038] The generator power constraint is as follows:

[0039]

[0040] In the formula, P G.m are the upper and lower limits of the generator output respectively;

[0041] The generator climbing constraint is as follows:

[0042] -rd,m Δt≤P G,m,t -P G,m,t-1 ≤r u,m Δt;

[0043] Where P G,m,t , P G,m,t-1 are the output power of generator m at time t and time t-1 respectively; r d,m 、r u,m are the maximum decreasing rate and the maximum increasing rate of the generator m respectively; Δt is the time interval;

[0044] The line power constraint is as follows:

[0045]

[0046] In the formula, P L.m are the upper and lower limits of the active power of the transmission line respectively;

[0047] The capacity constraint of the energy storage is as follows:

[0048] S rmin ≤S r,t ≤S rmax ;

[0049] In the formula, S r,t , S r,t-1 are the capacities of energy storage r at time t and time t-1 respectively; are the charging power and discharging power of energy storage r at the tth moment respectively; S rmin , S rmax are the minimum and maximum capacities of energy storage r respectively;

[0050] The energy storage charging and discharging power constraint is as follows:

[0051]

[0052] Where P r,max is the maximum value of the energy storage discharge power, The charging power for energy storage, is the energy storage discharge power.

[0053] As an optimization, the limit is 0.5.

[0054] As an optimization, among the candidate lines, if there is a flow reversal and the flow of the line satisfies |P′ R |≤|P R |, then remove the line from the candidate lines, where P′ R is the branch power flow after the line is disconnected, P Ris the steady-state initial active power of line R.

[0055] The present invention also discloses an energy storage optimization configuration system for an AC / DC hybrid system, which is used to execute the above-mentioned energy storage optimization configuration method for an AC / DC hybrid system, comprising:

[0056] A power flow over-limit risk evaluation module is used to obtain the branch disconnection distribution factor of the DC lockout of the converter station of the DC transmission line in the AC / DC hybrid system, establish a power flow over-limit risk index in combination with the branch disconnection distribution factor, and then find the shortest path between the converter station and several designated nodes according to the Dijkstra algorithm, and evaluate the sensitivity and vulnerability of the AC lines on all the shortest paths to DC power transfer through the power flow over-limit risk index;

[0057] A screening module, used to screen candidate lines for energy storage access to the AC / DC hybrid system from all the AC lines;

[0058] A modeling module, for establishing a multi-objective mathematical model of the candidate line with a maximum flow over-limit risk index and a minimum energy storage investment cost in combination with the safe and stable operation capability of the candidate line, so as to achieve an optimal configuration of energy storage of the candidate line;

[0059] The configuration module is used to use the input end of the candidate line as the energy storage configuration position, adopt the PSO algorithm to obtain the energy storage capacity in each energy storage configuration position, and select the optimal energy storage configuration position from the candidate line, thereby eliminating the over-limit power of the candidate line to improve the safe and stable operation capability of the AC / DC hybrid system.

[0060] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0061] 1. Aiming at the problem that the sensitive and vulnerable lines in the AC / DC hybrid system still exceed the static stability limit after a fault occurs in the AC / DC hybrid system, the present invention establishes a multi-objective model with the minimum energy storage investment cost, the minimum generator and load shedding penalty cost, and the maximum line flow over-limit risk index, so as to achieve the optimal configuration of energy storage and thus improve the stability of the power grid;

[0062] 2. The present invention takes into account the power transfer amount of the line and the thermal stability limit of the line, and evaluates the sensitivity of the line. Since the more sensitive the line is to the power transfer amount, the more fragile the line is, and the easier it is to exceed the thermal stability limit of the line, the power input node of the line is more likely to be connected to the energy storage;

[0063] 3. In order to accurately obtain the location of the optimal configuration of energy storage and the speed of solving the optimal energy storage solution, the present invention adopts the Dijkstra algorithm to find the shortest path between the two nodes of the disconnected line composed of the open and disconnected lines, and uses the flow over-limit index to evaluate the lines in the shortest path, so as to find out the sensitive and fragile lines in the lines, avoiding setting the energy storage on the sensitive and fragile lines, which will cause instability in the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0065] Figure 1 Solve the flow chart for optimal energy storage configuration. DETAILED DESCRIPTION

[0066] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0067] Example 1

[0068] The specific process of the energy storage optimization configuration method of the AC / DC hybrid system disclosed in the present invention is as follows: Figure 1 As shown, the solution steps are as follows:

[0069] (1) The graph obtained by abstracting the power grid is G0, and the reactance value of each line in the power grid is used as the weight of each edge;

[0070] (2) When a DC block occurs at the UHV DC converter station at the sending end, the Dijkstra algorithm is used to find the shortest path from the converter station to the specified node; for example, the connection line between node A and node B is L AB Node A can also reach node B through other connected nodes. If line LAB fails and the line is disconnected, it is necessary to find the shortest path from node A to node B through other nodes, and all nodes are converter stations.

[0071] (3) Taking the union of the branch sets consisting of the shortest paths between the target source point and the end point (two nodes of the DC transmission line, for example, the target source point is the power flow input converter station node, and the end point is the power flow output converter station node) to obtain the power flow transfer branch set;

[0072] (4) Calculate the flow over-limit risk index of all branches in the flow transfer branch set, and select branches with absolute values ​​of flow over-limit risk index less than 0.5 to form a main branch set. The main branch set is the candidate line;

[0073] (5) For the lines in the main branch set, if there is a flow reversal and the branch flow satisfies |P′ R |≤|P R |, then remove it from the main branch set (P′ R is the branch power flow after the line is disconnected);

[0074] (6) Establish a multi-objective mathematical model to maximize the risk index of power flow over-limit and minimize the energy storage investment cost;

[0075] (7) The PSO algorithm is used to solve the problem and obtain the optimal configuration location and capacity of the energy storage. The optimal node for connecting to the energy storage is selected from the nodes in the candidate lines, that is, the optimal configuration location.

[0076] In the present invention, the power flow over-limit risk index takes into account the impact of power transfer on other lines and the line power flow over-limit capacity margin. After considering the line power flow over-limit capacity margin, there is no need to consider separately the problem of power flow reversal in other lines caused by power flow transfer, which reduces unnecessary calculations. At the same time, it can better reflect the sensitivity and fragility of other lines and identify sensitive and fragile lines in AC / DC hybrid systems.

[0077] For example, when the DC transmission line A is disconnected and causes the AC line R power flow change, the power flow over-limit capacity margin of line R can be expressed as follows:

[0078] When D R-A When <0, the line power flow over-limit capacity margin expression is as follows:

[0079]

[0080] When D R-A When >0, the expression of line power flow over-limit capacity margin ΔP′ is as follows:

[0081]

[0082] P R,max is the thermal stability limit of line R, P R Represents the steady-state initial active power of line R.

[0083] Combined with the branch disconnection distribution factor, the flow over-limit risk index expression for judging the sensitivity and vulnerability of other lines to the transferred flow after the branch is disconnected is given as follows:

[0084]

[0085] Where P A,max is the thermal stability limit value of the disconnected line (usually a certain value), D R-A It represents the branch disconnection distribution factor that causes the change of active power flow of line R after line A is disconnected.

[0086] After a DC locking fault occurs in an AC / DC hybrid system, the sensitivity and vulnerability (sensitivity and vulnerability) of each AC line can be effectively judged by calculating the power flow over-limit risk index of each AC line. The smaller the power flow over-limit risk index of the AC line, the lower its ability to receive and transfer power flow, and the higher the risk of power flow over-limit (the factors affecting the power flow over-limit risk index are: power flow over-limit capacity margin and branch disconnection factor. If the power flow over-limit capacity margin is smaller, the power flow over-limit risk index is smaller, and it is easier to over-limit; the larger the branch disconnection factor, the smaller the power flow over-limit risk index is, and it is easier to over-limit).

[0087] A multi-objective mathematical model is established to minimize the energy storage investment cost, minimize the generator and load shedding penalty cost, and maximize the line flow over-limit risk index after the AC / DC hybrid system fails. The expression is as follows:

[0088]

[0089] In the formula, F ERI is the system power flow over-limit risk index; △P′ is the line power flow over-limit capacity margin; D k,x is the branch breaking distribution factor; P dc-max is the thermal stability limit of the DC line; G inv are the investment cost and operation and maintenance cost of energy storage respectively; c p 、c e are the unit power cost and capacity cost of energy storage respectively; P rate,n 、E rate,n are the maximum charging and discharging power and capacity of energy storage respectively; r is the annual interest rate of funds; y is the life cycle of energy storage; G cut is the penalty cost of shedding the load; c Gcut,m 、c Lcut,n are the penalty cost per unit of machine shedding and the penalty cost per unit of load shedding respectively; M and N are the number of generators and loads in the system respectively; K is the number of lines in the shortest path.

[0090] The branch circuit breaking distribution factor is calculated as follows:

[0091]

[0092] Where P k is the power at the initial moment of the line; △P is the power increment on the line after the system is connected to the energy storage.

[0093] The constraints of the multi-objective mathematical model are as follows:

[0094] (1) Power balance constraints

[0095]

[0096] Where P G,m , P L,n , P B,r They are respectively the output of generator m, the required power of load n, and the absorbed power of energy storage r; R is the amount of energy storage configured in the system.

[0097] (2) Line loss constraints

[0098]

[0099] Where P′ and Q′ are the active power and reactive power transmitted by the receiving end of the kth line respectively; R k is the resistance of the kth line; U′ is the voltage amplitude of the receiving node of the kth line.

[0100] (3) Generator power constraints

[0101]

[0102] In the formula, P G,m are the upper and lower limits of the generator output respectively.

[0103] (4) Generator climbing constraints

[0104] -r d,m △t≤P G,m,t -P G,m,t-1 ≤r u,m △t

[0105] Where P G,m,t , P G,m,t-1 are the output power of generator m at time t and time t-1 respectively; r d,m 、r u,m are the maximum decreasing rate and maximum increasing rate of the generator respectively; △t is the time interval.

[0106] (5) Line power constraints

[0107]

[0108] In the formula, P L,m They are the upper and lower limits of the active power of the transmission line respectively.

[0109] (6) Energy storage capacity constraints:

[0110] S rmin ≤S r,t ≤S rmax

[0111] In the formula, S r,t , S r,t-1 are the capacities of energy storage r at time t and time t-1 respectively; are the charging power and discharging power of energy storage r at the tth moment respectively; S rmin , S rmax are the minimum and maximum capacities of the energy storage r respectively.

[0112] (7) Energy storage charging and discharging power constraints

[0113]

[0114]

[0115] Where P r,max is the maximum value of the energy storage discharge power.

[0116] In order to reasonably obtain the location for configuring energy storage, the PSO algorithm is used to solve the optimal energy storage capacity, and the optimal energy storage configuration location is selected from the candidate nodes (some lines on the shortest path are selected as vulnerability sensitive lines, and the input nodes of the sensitive lines are candidate nodes). Then, the optimally configured energy storage is used to quickly eliminate the over-limit power on the AC line, improve system stability, and prevent major accidents.

[0117] Example 2

[0118] The present invention also discloses an energy storage optimization configuration system for an AC / DC hybrid system, which is used to execute the above-mentioned energy storage optimization configuration method for an AC / DC hybrid system, comprising:

[0119] A power flow over-limit risk evaluation module is used to obtain the branch disconnection distribution factor of the DC transmission line in the AC / DC hybrid system where DC blocking occurs, establish a power flow over-limit risk index in combination with the branch disconnection distribution factor, and then find the shortest path between the converter station and several designated nodes according to the Dijkstra algorithm, and evaluate the sensitivity and vulnerability of the AC lines on all the shortest paths to DC power transfer through the power flow over-limit risk index;

[0120] A screening module, used to screen candidate lines for energy storage access to the AC / DC hybrid system from all the AC lines;

[0121] A modeling module, for establishing a multi-objective mathematical model of the candidate line with a maximum flow over-limit risk index and a minimum energy storage investment cost in combination with the safe and stable operation capability of the candidate line, so as to achieve an optimal configuration of energy storage of the candidate line;

[0122] The configuration module is used to use the input end of the candidate line as the energy storage configuration position, adopt the PSO algorithm to obtain the energy storage capacity in each energy storage configuration position, and select the optimal energy storage configuration position from the candidate line, thereby eliminating the over-limit power of the candidate line to improve the safe and stable operation capability of the AC / DC hybrid system.

[0123] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for optimizing energy storage configuration of an AC / DC hybrid system, characterized in that: include: S1. Obtain the first branch disconnection distribution factor of the converter station of the DC transmission line in the AC / DC hybrid system where DC blocking occurs, establish a power flow over-limit risk index in combination with the first branch disconnection distribution factor, then find the shortest path between the converter station and the designated node according to the Dijkstra algorithm, and judge the sensitivity and vulnerability of all AC lines on the shortest path to DC power transfer through the power flow over-limit risk index; S2, selecting candidate lines for energy storage access to the AC / DC hybrid system from all the AC lines; S3. Based on the safe and stable operation capability of the candidate line, a multi-objective mathematical model is established for the candidate line with the maximum risk index of power flow crossing and the minimum investment cost of energy storage, so as to achieve the optimal configuration of energy storage of the candidate line; The multi-objective mathematical model includes a first objective function to minimize the energy storage investment cost and operation and maintenance cost of energy storage to eliminate the over-limit power of the AC channel after a fault occurs in the AC / DC hybrid system, a second objective function to minimize the penalty cost of cutting generators and loads, and a third objective function to maximize the line power flow over-limit risk index; Among them, the expression of the first objective function is as follows: ； The expression of the second objective function is as follows: ； The expression of the third objective function is as follows: ； in, is the power flow over-limit risk index of the AC / DC hybrid system; is the line power flow over-limit capacity margin; is the second branch breaking distribution factor; is the thermal stability limit of the DC line; The investment cost and operation and maintenance cost of energy storage; , They are the unit power cost and capacity cost of energy storage respectively; , They are the maximum charging and discharging power and capacity of energy storage respectively; r is the annual interest rate of the funds; y The life cycle of energy storage; Penalty cost for cutting the machine to cut load; , are the penalty cost per unit of power cut and the penalty cost per unit of load cut respectively; M and N are the number of power generation and load in the system respectively; K is the number of lines in the shortest path; , They are machine cutting amount and load cutting amount respectively; S4. Taking the input end of the candidate line as the energy storage configuration position, the PSO algorithm is used to obtain the energy storage capacity in each energy storage configuration position, and the optimal energy storage configuration position is selected from the candidate line, thereby eliminating the over-limit power of the candidate line to improve the safe and stable operation capability of the AC / DC hybrid system.

2. The energy storage optimization configuration method of an AC / DC hybrid system according to claim 1, characterized in that: The current over-limit risk index is as follows: ； in, A , R All of them are lines in AC / DC hybrid system. A For DC transmission lines, R For AC lines, For line A After disconnection, the line R Flow Change Down Line R The power flow over-limit capacity margin, The first branch disconnection distribution factor representing the change in active power flow of line R caused by disconnection of line A, It is the thermal stability limit value of breaking line A.

3. The energy storage optimization configuration method of an AC / DC hybrid system according to claim 2 is characterized in that: line A After disconnection, the line R Flow Change Down Line R The power flow capacity margin The formula is as follows: when When the line power flow exceeds the capacity limit The expression is as follows: ； when When the line power flow exceeds the capacity limit, the expression of the margin is as follows: ； in, is the thermal stability limit of line R, Represents the steady-state initial active power of line R.

4. The energy storage optimization configuration method of an AC / DC hybrid system according to claim 1, characterized in that: The AC line whose absolute value of the power flow over-limit risk index is less than the set limit value is a candidate line.

5. The energy storage optimization configuration method of an AC / DC hybrid system according to claim 1, characterized in that: The second branch breaking distribution factor The specific expression is as follows: ； in, is the power of line x at the initial moment; is the power increment on line x after the AC / DC hybrid system is connected to energy storage.

6. The energy storage optimization configuration method of an AC / DC hybrid system according to claim 5, characterized in that: The constraints of the multi-objective mathematical model include power balance constraints, line loss constraints, generator power constraints, generator ramp constraints, line power constraints, energy storage capacity constraints, and energy storage charging and discharging power constraints, wherein: The power balance constraint is as follows: ； In the formula, , , are the output of generator m, the required power of load n, and the absorbed power of energy storage r respectively; R is the amount of energy storage configured in the AC / DC hybrid system; The line loss constraint is as follows: ； In the formula, , are respectively the active power and reactive power transmitted by the receiving end of the kth line; is the resistance of the kth circuit; is the voltage amplitude of the receiving node of the kth line; The generator power constraint is as follows: ； In the formula, , are the upper and lower limits of the generator output respectively; The generator climbing constraint is as follows: ； In the formula, , are the output power of generator m at time t and time t-1 respectively; , are the maximum decreasing rate and the maximum increasing rate of the generator m respectively; is the time interval; The line power constraint is as follows: ； In the formula, , are the upper and lower limits of the active power of the transmission line respectively; The capacity constraint of the energy storage is as follows: ； In the formula, is the capacity of energy storage r at time t; , are the minimum and maximum capacities of energy storage r, respectively; The energy storage charging and discharging power constraint is as follows: ； ； In the formula, is the maximum value of the energy storage discharge power, is the charging power of energy storage r at time t, is the discharge power of energy storage r at time t.

7. The energy storage optimization configuration method of an AC / DC hybrid system according to claim 4, characterized in that: The limit value is 0.

5.

8. The energy storage optimization configuration method of an AC / DC hybrid system according to claim 1, characterized in that: If there is a reverse flow in the candidate line and the flow of the line satisfies , then remove the line from the candidate lines, where is the branch power flow after the line is disconnected, For line R The steady-state initial active power.

9. An energy storage optimization configuration system for an AC / DC hybrid system, used to execute an energy storage optimization configuration method for an AC / DC hybrid system according to any one of claims 1 to 8, characterized in that: include: A power flow over-limit risk evaluation module is used to obtain the first branch disconnection distribution factor of the DC transmission line in the AC / DC hybrid system where DC blocking occurs, establish a power flow over-limit risk index in combination with the first branch disconnection distribution factor, and then find the shortest path between the converter station and a number of designated nodes according to the Dijkstra algorithm, and evaluate the sensitivity and vulnerability of the AC lines on all the shortest paths to DC power transfer through the power flow over-limit risk index; A screening module, used to screen candidate lines for energy storage access to the AC / DC hybrid system from all the AC lines; A modeling module, for establishing a multi-objective mathematical model of the candidate line with a maximum flow over-limit risk index and a minimum energy storage investment cost in combination with the safe and stable operation capability of the candidate line, so as to achieve an optimal configuration of energy storage of the candidate line; The multi-objective mathematical model includes a first objective function to minimize the energy storage investment cost and operation and maintenance cost of energy storage to eliminate the over-limit power of the AC channel after a fault occurs in the AC / DC hybrid system, a second objective function to minimize the penalty cost of cutting generators and loads, and a third objective function to maximize the line power flow over-limit risk index; Among them, the expression of the first objective function is as follows: ； The expression of the second objective function is as follows: ； The expression of the third objective function is as follows: ； in, is the power flow over-limit risk index of the AC / DC hybrid system; is the line power flow over-limit capacity margin; is the second branch breaking distribution factor; is the thermal stability limit of the DC line; The investment cost and operation and maintenance cost of energy storage; , They are the unit power cost and capacity cost of energy storage respectively; , They are the maximum charging and discharging power and capacity of energy storage respectively; r is the annual interest rate of the funds; y The life cycle of energy storage; Penalty cost for cutting the machine to cut load; , are the penalty cost per unit of power cut and the penalty cost per unit of load cut respectively; M and N are the number of power generation and load in the system respectively; K is the number of lines in the shortest path; The configuration module is used to use the input end of the candidate line as the energy storage configuration position, adopt the PSO algorithm to obtain the energy storage capacity in each energy storage configuration position, and select the optimal energy storage configuration position from the candidate line, thereby eliminating the over-limit power of the candidate line to improve the safe and stable operation capability of the AC / DC hybrid system.

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