An ac-dc hybrid cross-section construction method and system

Abstract

The application discloses a kind of AC-DC hybrid section construction method and system, the method is with power system short-circuit over-standard risk mitigation ability maximization principle, determine the combination mode of AC-DC line in the power transmission line, and with AC-DC hybrid power grid voltage support ability maximization principle, determine the type of converter station that DC line adopts, and with power system power imbalance tolerance determines the transmission capacity of AC line, and under DC line N-1 fault, with AC line carrying DC line transfer power flow ability determines the transmission capacity of DC line, the safety, stability, controllability of hybrid section are considered multidimensionally in this method, meet the requirement of future new type power system to power grid structure, can effectively promote power grid structure optimization and scale expansion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power systems, and particularly relates to a method and system for constructing an AC-DC hybrid section. BACKGROUND

[0002] Embedded HVDC technology refers to a new type of power transmission technology in which two-terminal HVDC systems are embedded in the main AC network framework of a power grid. By constructing embedded HVDC, the transmission capacity of a transmission section can be effectively improved without changing the existing AC main network framework. There are various transmission section structures in AC-DC hybrid power grids. If there are n transmission lines in a section, of which m are HVDC transmission lines, the uncontrollable dimension of power flow in the power grid is n-m-1. Therefore, to ensure the maximum controllability of an AC-DC hybrid power grid, an AC-DC hybrid transmission section structure containing a single AC line is selected to achieve complete controllability of power flow. However, how to construct a reasonable AC-DC hybrid transmission section is the focus of current research. In view of several security and stability problems that may exist in AC-DC hybrid networks, current scholars mostly start from control and propose many effective improved control strategies. For example, the rapid power regulation capability of flexible HVDC systems is used to improve the frequency and synchronization characteristics of AC-DC hybrid power systems, the power flow relationship between AC-DC parallel transmission channels is optimized to reduce the risk of AC line overload under single fault, and it is pointed out that transmission line opening can be used as a control means to avoid collapse of the hybrid system. However, only through these control strategies, the operation stability of the AC-DC hybrid section can be improved to a certain extent, but the security and stability risks of the AC-DC hybrid section cannot be completely avoided. Therefore, a reliable AC-DC hybrid section construction scheme needs to be proposed from multiple angles.

[0003] Therefore, how to propose a completely controllable AC-DC hybrid section construction method with controllability, security and stability is a problem to be solved by those skilled in the art. SUMMARY

[0004] To solve the problems in the prior art, the application provides an AC-DC hybrid section construction method and system.

[0005] The technical scheme of the application is as follows:

[0006] An AC-DC hybrid section construction method, the AC-DC hybrid section is provided with a single AC line and a plurality of DC lines, comprising:

[0007] The combination mode of AC and DC lines in the power transmission line is determined according to the principle of maximizing the short-circuit risk relief capability of the power system, the type of the converter station used by the DC line is determined according to the principle of maximizing the voltage support capability of the AC and DC hybrid power grid, the power transmission capacity of the AC line is determined according to the power imbalance tolerance of the power system, and the power transmission capacity of the DC line is determined according to the AC line's ability to transfer the transferred power of the DC line under the N-1 fault of the DC line.

[0008] Further, the specific method for determining the combination mode of AC and DC lines in the power transmission line according to the principle of maximizing the short-circuit risk relief capability of the power system comprises:

[0009] A combination mode set of AC and DC lines in the power transmission line is constructed, and the combination mode set includes a plurality of combination modes of AC and DC lines; the short-circuit current margin corresponding to each combination mode of AC and DC lines in the combination mode set is calculated respectively, and the combination mode of AC and DC lines corresponding to the maximum short-circuit current margin is selected.

[0010] The calculation formula of the short-circuit current margin is as follows:

[0011]

[0012] In the formula, K sci is the minimum margin of short-circuit current in the power system; I bmaxi is the maximum allowable short-circuit current of the i-th node; I sci is the actual short-circuit current of the i-th node, and min is the minimum value of the corresponding index of all nodes in the system.

[0013] Further, the specific method for determining the type of the converter station used by the DC line according to the principle of maximizing the voltage support capability of the AC and DC hybrid power grid comprises:

[0014] The system voltage stiffness is calculated by the following formula:

[0015] K vtg = U sys / U sys0

[0016]

[0017] In the formula, λ SCR is the short-circuit ratio of the corresponding grid-connected device at any point in the power grid; U sys0 is the no-load voltage at any point when the grid-connected device is not connected to the power grid.

[0018] When the calculated system voltage stiffness is greater than 0.95, a conventional DC converter station type is selected; otherwise, a converter station type with voltage support capability is selected.

[0019] Further, the specific method for determining the AC line transmission capacity based on the power imbalance tolerance of the power system comprises:

[0020] calculating the maximum power shortage that may occur in the AC / DC hybrid power grid, and taking the maximum power shortage as the AC line transmission capacity:

[0021]

[0022]

[0023] wherein P acsum is the total transmission power of the AC line in the AC / DC hybrid section; P acj is the active power transmitted by the jth AC line in the AC channel; ΔP is the maximum power shortage allowed in the section; P sum is the total power transmitted in the section; P dci is the power transmitted by the ith DC line; n ac is the number of AC lines; m is the number of DC lines; RoCoF is the maximum frequency change rate of the system; f N is the frequency under normal operating conditions of the system; H sys is the inertia value of the system; β is the frequency oscillation amplitude; ζ is the damping ratio parameter of the system; ω n is the natural oscillation angular frequency of the system; T is the equivalent inertia time constant of the system; Δf max is the maximum frequency deviation; D is the load damping coefficient of the system; K is the speed gain of the unit governor; t1 is the time from the start of the fault to the maximum frequency deviation; Δf st is the quasi-steady-state frequency deviation.

[0024] Further, the specific method for determining the DC line transmission capacity based on the AC line carrying the DC line transferred power capacity under the N-1 fault of the DC line comprises:

[0025] The DC line capacity constraint formula of the AC / DC hybrid section under the N-1 fault is constructed as follows:

[0026] P dcmax = n ac × P acmax -P acsum

[0027] wherein P dcmax is the maximum transmission power of a single DC line; P acmax is the maximum transmission power of a single AC line; P acsum is the maximum power shortage that may occur in the AC / DC hybrid power grid; n ac is the number of AC lines.

[0028] Further, the method further comprises: determining the operation state of the AC line in the hybrid connection section through the phase angle difference of the power grids at both ends of the transmission line.

[0029] Further, the specific method for determining the operation state of the AC line in the hybrid connection section through the phase angle difference of the power grids at both ends of the transmission line comprises:

[0030] An active splitting strategy is adopted in the system, the phase difference of the AC power grids at both ends of the transmission line is measured, and the measured phase difference of the power grids at both ends is compared with a phase difference threshold value. If the phase difference of the AC power grids at both ends of the transmission line is less than the phase difference threshold value, i.e. the phase difference constraint formula of the sending and receiving power grids of the AC / DC hybrid power grid is met, the AC line is in normal operation, and the single-AC multi-DC hybrid connection structure is maintained. Otherwise, the phase difference of the AC power grids at both ends of the transmission line is greater than or equal to the phase difference threshold value. Based on the active splitting strategy of the AC tie line, the AC line is disconnected, and the sending and receiving power grids are operated asynchronously to avoid instability, thereby ensuring the operation synchronization stability of the power grid.

[0031] A system for constructing an AC / DC hybrid connection section, the AC / DC hybrid connection section being provided with a single AC line and a plurality of DC lines of a transmission line, the system comprising a combination mode determination module of AC / DC lines, a converter station type determination module, an AC line transmission capacity determination module, and a DC line transmission capacity determination module.

[0032] The combination mode determination module of AC / DC lines is configured to determine the combination mode of the AC / DC lines in the transmission line according to the principle of maximizing the short-circuit risk mitigation capability of the power system.

[0033] The converter station type determination module is configured to determine the type of the converter station for the DC line according to the principle of maximizing the voltage support capability of the AC / DC hybrid power grid.

[0034] The AC line transmission capacity determination module is configured to determine the transmission capacity of the AC line according to the power imbalance tolerance of the power system.

[0035] The DC line transmission capacity determination module is configured to determine the transmission capacity of the DC line according to the DC line capacity constraint formula of the AC / DC hybrid connection section under N-1 fault.

[0036] An electronic device, comprising a memory and a processor, the memory storing a computer program, and the processor being configured to invoke and run the computer program stored in the memory to execute the method according to any one of the above.

[0037] A computer readable storage medium, storing a computer program, the computer program being executed by a processor to implement the steps of the method according to any one of the above.

[0038] Compared with the prior art, the present application has the following beneficial effects:

[0039] The present application provides a method and system for constructing an AC-DC hybrid section, which determines the combination of AC and DC lines in the power transmission line according to the principle of maximizing the risk mitigation capability of short-circuit over-standard in the power system, determines the type of converter station used by the DC line according to the principle of maximizing the voltage support capability of the AC-DC hybrid power grid, determines the power transmission capacity of the AC line according to the power imbalance tolerance of the power system, and determines the power transmission capacity of the DC line according to the ability of the AC line to carry the transferred power of the DC line under N-1 fault of the DC line. This method considers the safety, stability and controllability of the hybrid section in multiple dimensions, meets the requirements of future new power systems for power grid structure, and can effectively promote the optimization and expansion of power grid structure. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Flowchart of the method for constructing an AC-DC hybrid section in the embodiment;

[0041] Figure 2 Typical structure diagram of the AC-DC hybrid section in the embodiment;

[0042] Figure 3 Voltage stiffness variation characteristic curve diagram with short-circuit ratio in the embodiment;

[0043] Figure 4 Typical structure diagram of three power transmission channel interconnection in the embodiment;

[0044] Figure 5 Frequency response curve diagram of each unit under HVDC1 blocking in the embodiment. DETAILED DESCRIPTION

[0045] The present application will be further illustrated below in conjunction with the drawings and specific embodiments, and it should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. After reading the present application, those skilled in the art can make various modifications to the present application, and all such modifications fall within the scope defined by the appended claims.

[0046] Embodiment one:

[0047] The present application provides a method for constructing an AC-DC hybrid section, which is provided with a single AC line and a plurality of DC lines, as shown in Figure 1 and Figure 2 The method comprises the following specific steps:

[0048] S1, determining the combination of AC and DC lines in the power transmission line according to the principle of maximizing the risk mitigation capability of short-circuit over-standard in the power system;

[0049] S2, determine the type of converter station used by the DC line according to the principle of maximizing the voltage support capability of the AC-DC hybrid power grid;

[0050] S3, determine the AC line transmission capacity according to the power imbalance tolerance of the power system, and determine the DC line transmission capacity according to the AC line's ability to carry the transferred flow of the DC line under the N-1 fault of the DC line.

[0051] Embodiment two:

[0052] The embodiment is further designed on the basis of embodiment one, and in this embodiment, the specific method for determining the combination mode of AC-DC lines in the power transmission line according to the principle of maximizing the short-circuit risk mitigation capability of the power system includes:

[0053] A combination mode set of AC-DC lines in the power transmission line is constructed, and the combination mode set includes a plurality of combination modes of AC-DC lines; the short-circuit current margin corresponding to each combination mode of AC-DC lines in the combination mode set is calculated, and the combination mode of AC-DC lines corresponding to the maximum short-circuit current margin is selected.

[0054] The calculation formula of the short-circuit current margin is as follows:

[0055]

[0056] In the formula, K sci is the minimum margin of short-circuit current in the power system; I bmaxi is the maximum allowable short-circuit current of the i-th node; I sci is the actual short-circuit current of the i-th node, and min is the minimum value of the corresponding index of all nodes in the system. When K sci < 0, it indicates that the line short-circuit current is out of limit, reflecting the short-circuit current level of the AC-DC hybrid power grid.

[0057] Embodiment three:

[0058] The embodiment is further designed on the basis of embodiment two, and in this embodiment, the specific method for determining the type of converter station used by the DC line according to the principle of maximizing the voltage support capability of the AC-DC hybrid section includes:

[0059] The system voltage stiffness is calculated by the following formula, and the voltage support strength of any point in the power grid is defined as the ability to maintain the voltage modulus of the access point close to the no-load voltage of the access point, which is called voltage stiffness K vtg :

[0060]

[0061] In the formula, λ SCR is the short-circuit ratio of the corresponding grid-connected equipment at any point in the power grid; and U sys0The no-load voltage at any point when the connected equipment is not connected to the power grid;

[0062] Voltage stiffness K vtg The value range of Z is [0,1]. th When the voltage stiffness K is equal to zero, vtg Equals 1; when Z th When the voltage stiffness K is equal to infinity, vtg It equals zero.

[0063] For voltage stiffness K vtg Compared to the short-circuit ratio λ SCR By comparison, it can be seen that K vtg The reflected power grid information and grid-connected equipment information are compared with λ SCR More comprehensive, λ SCR It only reflects and The magnitude information does not reflect the phase angle information of the two; in addition, the short-circuit ratio λ SCR The range of values ​​for is [0,∞], while K vtg The value range is [0,1].

[0064] If the calculated system voltage stiffness is greater than 0.95, a conventional DC converter station type should be selected; otherwise, a converter station type with voltage support capability should be selected.

[0065] like Figure 3 As shown, when the short-circuit ratio λ SCR When the short-circuit ratio is 3, the voltage stiffness is 0.95. It is generally believed that when the short-circuit ratio is greater than 3, that is, when the voltage stiffness is greater than 0.95, the connection point SYS is a relatively strong connection point because its voltage drop after being loaded is less than 5% of the rated voltage, the system voltage support capability is strong, and the system voltage can be kept stable under fault conditions.

[0066] During the planning phase, by calculating the system voltage stiffness index, it can be determined whether the system voltage support capability is sufficient to ensure system voltage stability. If it does not meet the requirements, it is necessary to consider adopting a DC converter station type with voltage support capability.

[0067] Example 4:

[0068] This embodiment, based on Embodiment 3, further incorporates the following design: The specific method for determining the AC line transmission capacity based on the power system power imbalance tolerance includes:

[0069] For the AC-DC hybrid grid structure containing only one AC line, when the DC transmission system occurs any N-1 or N-2 fault, the power shortage of the sending and receiving end power grid will not be caused, and the power transmitted by the DC will be transferred to the AC line, so that the DC line fault will not affect the frequency stability of the AC-DC hybrid grid; when the AC transmission line occurs N-1 or N-2 fault, the sending and receiving end power grid will completely lose the AC tie, and the power transmitted by the original AC line will not be borne by the DC system, so that the power shortage of the sending and receiving end power grid will be caused, and the frequency fluctuation will be caused.

[0070] Considering the system frequency stability constraint, the system frequency stability is checked by the maximum power imbalance that may occur in the system under fault, and the maximum transmission power of the AC line under the system allowed maximum frequency deviation is determined.

[0071] The maximum power shortage that may occur in the AC-DC hybrid grid is calculated, and the maximum power shortage is taken as the AC line transmission power:

[0072]

[0073] In the formula, P acsum is the maximum power shortage that may occur in the AC-DC hybrid grid; P acj is the active power transmitted by the jth AC line in the AC channel; P sum is the total power transmitted at the section; P dci is the power transmitted by the ith DC line; n ac is the total number of AC lines in the hybrid section; and m is the number of DC lines.

[0074] For the frequency impact caused by the power imbalance of the two-end power grid under fault, the maximum frequency change rate, the maximum frequency deviation and the quasi-steady frequency deviation indexes are commonly used to check the frequency stability in the actual power grid.

[0075]

[0076] In the formula, RoCoF is the maximum frequency change rate of the system; f N is the frequency under normal working condition of the system; H sys is the inertia value of the system; β is the frequency oscillation amplitude; ζ is the damping ratio parameter of the system; ω n is the natural oscillation angular frequency of the system; T is the equivalent inertia time constant of the system; Δf max is the maximum frequency deviation; D is the load damping coefficient of the system; K is the speed gain of the unit governor; t1 is the time from the beginning of the fault to the maximum frequency deviation; Δf st is the quasi-steady frequency deviation.

[0077] The maximum power shortage of the sending and receiving system caused by the AC line N-1 / N-2 fault is used to check the frequency stability of the system, so as to determine the maximum allowed transmission power of the AC line, and thus the distribution capacity of the AC line can be determined.

[0078] Embodiment five:

[0079] The embodiment is further designed on the basis of embodiment four, and the reasonable distribution relationship between the AC and DC transmission power can be selected by using the power flow constraints under normal conditions and N-1 fault, so as to ensure that the AC line will not be overloaded under N-1 fault of the DC system, and thus the distribution capacity of each DC line can be determined. Under N-1 fault of the AC-DC hybrid power grid, the power transmission capacity on the fault DC line will be transferred to the AC transmission line, and the DC power transmission line capacity constraint can be determined by the power flow transfer amount. For the AC-DC hybrid cross-section structure containing one AC line, when the AC channel has only one line, the maximum transmission power P dcmax of the single DC line should be less than the maximum transmission power P acmax of the single AC line. When the AC channel has parallel double-circuit lines, the maximum transmission power of the AC line should be twice the maximum transmission power of the single-circuit AC line. The specific method of determining the DC power transmission capacity by using the AC line to bear the transferred power flow capacity of the DC line under N-1 fault of the DC line in this example includes:

[0080] The DC line capacity constraint formula of the AC-DC hybrid cross-section under N-1 fault is as follows:

[0081] P dcmax = n ac × P acmax -P acsum

[0082] In the formula, P dcmax is the maximum transmission power of the single DC line; P acmax is the maximum transmission power of the single-circuit AC line; P acsum is the maximum power shortage that may occur in the AC-DC hybrid power grid, i.e. the total power transmitted by the AC line; and n ac is the number of AC lines.

[0083] Embodiment six:

[0084] The embodiment is further designed on the basis of embodiment five, and the method in this embodiment further includes: determining the operating state of the AC line in the hybrid cross-section by the phase angle difference of the power grids at both ends of the transmission line.

[0085] Embodiment seven:

[0086] The embodiment is further designed on the basis of embodiment six, and the specific method for determining the operation state of the AC line in the hybrid connection section by the phase angle difference of the power grids at both ends of the transmission line in this embodiment includes:

[0087] The active splitting strategy is adopted in the system, the phase difference of the AC power grids at both ends of the transmission line is measured, and the measured phase difference of the power grids at both ends is compared with the phase difference threshold value, if the phase difference of the AC power grids at both ends of the transmission line is less than the phase difference threshold value, that is, the sending and receiving end power grid phase difference constraint formula of the AC-DC hybrid power grid is met, the AC line is normally operated, and the single AC multi-DC hybrid connection structure is maintained, otherwise, the phase difference of the AC power grids at both ends of the transmission line is greater than or equal to the phase difference threshold value, based on the active splitting strategy of the AC tie line, the AC line is disconnected, and the sending and receiving end power grids are operated asynchronously to avoid instability, thereby ensuring the operation synchronization stability of the power grid. The sending and receiving end power grid phase difference constraint formula of the AC-DC hybrid power grid: Δθ ac <θ th . Wherein, the real-time detection of the phase difference at both ends of the AC tie line is Δθ ac , the system phase difference threshold value is θ th , when the phase difference Δθ ac of the AC-DC hybrid transmission system at both ends of the power grid reaches the threshold value θ th , the AC circuit between the two AC power grids is disconnected, and asynchronous operation is realized.

[0088] Embodiment eight:

[0089] The AC-DC hybrid connection section construction system of the application, the AC-DC hybrid connection section is provided with a single AC line and a plurality of DC lines of the transmission line, the system comprises an AC-DC line combination mode determination module, a converter station type determination module, an AC line transmission capacity determination module and a DC line transmission capacity determination module;

[0090] The AC-DC line combination mode determination module is used to determine the combination mode of the AC-DC line in the transmission line according to the principle of maximizing the short-circuit risk mitigation capacity of the power system;

[0091] The converter station type determination module is used to determine the type of the converter station adopted by the DC line according to the principle of maximizing the voltage support capacity of the AC-DC hybrid power grid;

[0092] The AC line transmission capacity determination module is used to determine the AC line transmission capacity according to the power imbalance tolerance of the power system;

[0093] The DC line transmission capacity determination module is used to determine the DC line transmission capacity according to the DC line capacity constraint formula of the AC-DC hybrid connection section under N-1 fault

[0094] Embodiment nine:

[0095] An electronic device comprising a memory storing a computer program and a processor configured to invoke and run the computer program stored in the memory to perform the method according to any one of the preceding method embodiments.

[0096] A computer readable storage medium storing a computer program, the computer program being configured to perform the steps of the method according to any one of the preceding method embodiments when executed by a processor.

[0097] Application Embodiments:

[0098] In this example, the method of the present application is implemented for a certain power grid, which is an AC-DC hybrid power grid with one AC line constructed by an IEEE two-area four-machine system, the power grid structure is shown in Figure 4 and includes synchronous machine 1 to synchronous machine 8.

[0099] The frequency response curves of each unit under the HVDC1 blocking are shown in Figure 5 It can be seen that under the AC-DC hybrid power transmission construction scheme, after the HVDC1 DC blocking, the frequency deviation of each unit in the sending and receiving end power grid is very small, and after small amplitude fluctuation, it returns to the rated value, which can effectively avoid the impact of DC blocking on the frequency of the sending and receiving end system, and has high review stability. Under short-circuit fault, the phase difference between the sending and receiving end units may continuously increase and eventually lose step, but the AC line can be actively disconnected by detecting the phase difference to realize asynchronous operation of the sending and receiving end, and maintain the synchronous stability of the power grid. The method of the present application can meet the safe and stable operation condition of the power grid, and is feasible in engineering.

[0100] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for constructing an AC / DC hybrid transmission line, wherein the AC / DC hybrid transmission line comprises a single AC line and several DC lines, characterized in that, include: Based on the principle of maximizing the short-circuit risk mitigation capability of the power system, the combination mode of AC and DC lines in the transmission line is determined. Based on the principle of maximizing the voltage support capability of the AC and DC hybrid section, the type of converter station adopted for the DC line is determined. Based on the power system power imbalance tolerance, the AC line transmission capacity is determined. Under the N-1 fault of the DC line, the DC line transmission capacity is determined based on the AC line's ability to carry the DC line's power flow transfer capability. The specific method for determining the AC line transmission capacity based on the power system power imbalance tolerance includes: Calculate the maximum potential power deficit in an AC / DC hybrid power grid and use this maximum power deficit as the AC transmission capacity: ； ； ； ； ； ； In the formula, This represents the total transmission power of the AC lines in a hybrid AC / DC section. To deliver active power to the j-th AC line in the AC channel; This represents the maximum allowable power deficit for the cross-section. To deliver total power to the cross-section; To deliver power to the i-th DC line; m represents the number of AC lines; m represents the number of DC lines. This represents the system's maximum rate of frequency change. This refers to the frequency under normal system operating conditions. This represents the system inertia value. This refers to the frequency oscillation amplitude. The system damping ratio parameter; This is the natural angular frequency of the system's oscillation. T is the system's equivalent inertial time constant; This represents the maximum frequency deviation. This is the system load damping coefficient; The speed control gain of the unit's speed governor; The time from the onset of the fault to the frequency deviation reaching its maximum value; This refers to the quasi-steady-state frequency deviation.

2. The method for constructing an AC / DC hybrid cross-section according to claim 1, characterized in that, The specific method for determining the combination of AC and DC lines in the transmission lines based on the principle of maximizing the short-circuit risk mitigation capability of the power system includes: Construct a set of AC / DC line combination methods in a transmission line, wherein the set of combination methods includes several AC / DC line combination methods; calculate the short-circuit current margin corresponding to each AC / DC line combination method in the set of combination methods, and select the AC / DC line combination method corresponding to the maximum short-circuit current margin; The formula for calculating the short-circuit current margin is as follows: ； In the formula, This represents the minimum margin of short-circuit current in a power system. This represents the maximum permissible short-circuit current at the i-th node; Let be the actual short-circuit current of the i-th node, and min be the minimum value of the corresponding index among all nodes in the system.

3. The method for constructing an AC / DC hybrid cross-section according to claim 2, characterized in that, The specific method for determining the converter station type for DC lines based on the principle of maximizing the voltage support capacity of AC / DC hybrid sections includes: The system voltage stiffness is calculated using the following formula: ； ； in, The short-circuit ratio of the connected equipment at any point in the power grid; The no-load voltage at any point when the connected equipment is not connected to the power grid; If the calculated system voltage stiffness is greater than 0.95, a conventional DC converter station type should be selected; otherwise, a converter station type with voltage support capability should be selected.

4. The method for constructing an AC / DC hybrid cross-section according to claim 3, characterized in that, Under the N-1 fault condition of the DC line, the specific method for determining the transmission capacity of the DC line based on the AC line's ability to carry the power flow transfer from the DC line includes: The capacity constraint formula for AC / DC hybrid DC lines under N-1 fault conditions is as follows: ； In the formula, This represents the maximum power output of a single DC signal. This represents the maximum transmission power of a single-circuit AC line. This represents the maximum potential power deficit in a hybrid AC / DC power grid. This refers to the number of communication lines.

5. The method for constructing an AC / DC hybrid cross-section according to claim 4, characterized in that, The method further includes: determining the operating status of AC lines in a hybrid section by measuring the phase angle difference between the power grids at both ends of the transmission line.

6. The method for constructing an AC / DC hybrid cross-section according to claim 5, characterized in that, The specific method for determining the operating status of AC lines in a hybrid section by the phase angle difference between the power grids at both ends of the transmission line includes: The system employs an active disconnection strategy, measuring the phase difference between the AC grids at both ends of the transmission line and comparing the measured phase difference with a phase difference threshold. If the phase difference between the AC grids at both ends of the transmission line is less than the phase difference threshold, i.e., satisfying the phase difference constraint formula for the sending and receiving end grids of the AC / DC hybrid grid, the AC line operates normally, maintaining the single AC and multiple DC hybrid structure. Otherwise, if the phase difference between the AC grids at both ends of the transmission line is greater than or equal to the phase difference threshold, the AC line is disconnected based on the active disconnection strategy of the AC tie line, and the sending and receiving end grids operate asynchronously to avoid instability and thus ensure the synchronous stability of the grid operation.

7. A hybrid AC / DC transmission line system, wherein the hybrid AC / DC transmission line comprises a single AC line and several DC lines, characterized in that, The system includes a module for determining the combination of AC and DC lines, a module for determining the type of converter station, a module for determining the transmission capacity of AC lines, and a module for determining the transmission capacity of DC lines. The AC / DC line combination determination module is used to determine the combination of AC / DC lines in the transmission line based on the principle of maximizing the short-circuit risk mitigation capability of the power system. The converter station type determination module is used to determine the converter station type adopted by the DC line based on the principle of maximizing the voltage support capacity of the AC / DC hybrid section. The AC line transmission capacity determination module is used to determine the AC line transmission capacity based on the power system power imbalance tolerance. The DC line transmission capacity determination module is used to determine the DC line transmission capacity using the DC line capacity constraint formula under N-1 fault conditions for AC / DC hybrid sections. The specific method for determining the AC line transmission capacity based on the power system power imbalance tolerance includes: Calculate the maximum potential power deficit in an AC / DC hybrid power grid and use this maximum power deficit as the AC transmission capacity: ； ； ； ； ； ； In the formula, This represents the total transmission power of the AC lines in a hybrid AC / DC section. To deliver active power to the j-th AC line in the AC channel; This represents the maximum allowable power deficit for the cross-section. To deliver total power to the cross-section; To deliver power to the i-th DC line; m represents the number of AC lines; m represents the number of DC lines. This represents the system's maximum rate of frequency change. This refers to the frequency under normal system operating conditions. This represents the system inertia value. This refers to the frequency oscillation amplitude. The system damping ratio parameter; This is the natural angular frequency of the system's oscillation. T is the system's equivalent inertial time constant; This represents the maximum frequency deviation. This is the system load damping coefficient; The speed control gain of the unit's speed governor; The time from the onset of the fault to the frequency deviation reaching its maximum value; This refers to the quasi-steady-state frequency deviation.

8. An electronic device, characterized in that, The electronic device includes a memory and a processor, the memory storing a computer program, and the processor being configured to invoke and run the computer program stored in the memory to perform the method as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 6 above.

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