A method for analyzing transient stability of AC-DC system based on VSC-HVDC

Abstract

The application discloses a kind of based on VSC-HVDC AC-DC system transient stability analysis method, first constructs the steady-state model and transient model of AC-DC system based on VSC-HVDC, determines stable equilibrium point before and after fault, then constructs the energy function of AC-DC system based on VSC-HVDC, and based on fault trajectory, determine the maximum value of system energy, as escape point, take escape point as initial value, based on stable boundary tracking determines the norm of reduced system integral process, find out the norm minimum point, take norm minimum point as initial value to determine leading unstable equilibrium point, finally determine the energy at leading unstable equilibrium point, and the energy of this point is as critical energy, determine system limit cut-off time, complete AC-DC system transient stability analysis.The scheme of the application can determine the minimum gradient point and leading unstable equilibrium point in the transient stability analysis of AC-DC system containing VSC-HVDC, improve the precision of direct method transient stability analysis, and is beneficial to the stability of flexible HVDC transmission system.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of transient stability analysis of flexible DC power transmission, and particularly relates to a VSC-HVDC-based AC / DC system transient stability analysis method. BACKGROUND

[0002] As the main body of the world's energy structure, fossil energy is becoming increasingly depleted due to its non-renewability and the increasing demand for energy along with the rapid economic development of countries around the world. On the other hand, environmental problems such as abnormal changes in global climate and frequent extreme weather have affected the sustainable development of mankind. Due to the above two major reasons, it is imperative to develop renewable new energy and reform the existing energy structure.

[0003] China has explicitly proposed the goals of carbon peak and carbon neutrality in the "14th Five-Year Plan", and requires promoting green and low-carbon energy transformation and high-quality development. As an important lever for reducing carbon emissions, China's renewable energy has ushered in a development stage. However, due to the vast territory and uneven energy distribution in China, the main power consumption areas in East China and the coastal areas are far away from the northwest region where most of the new energy is distributed, so the development of flexible DC power transmission is of great significance. Flexible DC power transmission has advantages over AC power transmission in long-distance power transmission, such as no capacitive current, no need for synchronous operation of the system at both ends of the line, and good economy.

[0004] At the same time, with the growth of the economy and the development of society, the public's demand for power system power supply stability and safety is also increasing, so the transient stability evaluation of the AC / DC system with VSC-HVDC is becoming increasingly important. Among them, the two most important analysis methods are time-domain simulation method and direct method.

[0005] In comparison, the direct method makes a system stability judgment faster than the time-domain simulation method and can provide stability margin information, while the dominant unstable equilibrium point method based on stability boundary tracking technology as the latest method in the direct method has greatly improved the calculation accuracy compared to other existing direct methods, but at the same time, the technical requirements have become higher. SUMMARY

[0006] In view of the above problems, the purpose of the present application is to provide a VSC-HVDC-based AC / DC system transient stability analysis method.

[0007] The specific technical scheme to achieve the purpose of the present application is as follows:

[0008] A VSC-HVDC-based AC / DC system transient stability analysis method, comprising the following steps:

[0009] Step 1, a steady-state model of an AC-DC system based on VSC-HVDC is constructed, and a stable equilibrium point before fault is determined;

[0010] Step 2, a transient-state model of the AC-DC system based on VSC-HVDC is constructed, and simulation is carried out by using a time-domain simulation method, a fault trajectory is obtained, the stable equilibrium point before fault is taken as an initial value, and a stable equilibrium point after fault is determined based on a projected voltage and the system after fault;

[0011] Step 3, an energy function of the AC-DC system based on VSC-HVDC is constructed, and a maximum value of system energy is determined as an escape point based on the fault trajectory obtained in step 2;

[0012] Step 4, the escape point is taken as an initial value, a norm of an integral process of a reduced-order system is determined based on stable boundary tracking, and a minimum value point of the norm is found out;

[0013] Step 5, the minimum value point of the norm is taken as an initial value to determine a dominant unstable equilibrium point;

[0014] Step 6, energy at the dominant unstable equilibrium point is determined, the energy at the point is taken as critical energy, a system limit clearing time is determined, and transient-state stability analysis of the AC-DC system is completed.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] (1) The scheme of the present application determines a stable equilibrium point after fault, an escape point, a minimum value point of a norm and a dominant unstable equilibrium point in sequence based on a steady-state model and a transient-state model of the AC-DC system based on VSC-HVDC, and finally determines a system limit clearing time, so that the transient-state stability state of the AC-DC system is determined according to the system limit clearing time in the actual AC-DC system;

[0017] (2) The scheme of the present application can determine a minimum gradient point and a dominant unstable equilibrium point in the transient-state stability analysis of the AC-DC system containing VSC-HVDC, and further improves the precision of the direct method transient-state stability analysis, which is beneficial to the stability of the flexible HVDC transmission system. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The figure is a step flow chart of the transient-state stability analysis method of the AC-DC system based on VSC-HVDC of the present application.

[0019] Figure 2 The figure is a steady-state model schematic diagram of the AC-DC system in the embodiment of the present application.

[0020] Figure 3 The figure is a stable boundary tracking schematic diagram in the embodiment of the present application.

[0021] Figure 4A schematic diagram of a norm minimum point in an embodiment of the present application. DETAILED DESCRIPTION

[0022] A VSC-HVDC-based AC / DC system transient stability analysis method, comprising the following steps:

[0023] Step 1, constructing a VSC-HVDC-based AC / DC system steady-state model, determining a pre-fault stable equilibrium point, specifically:

[0024]

[0025] In the above formula, the first row is the active power balance of the system, and the second row is the reactive power balance;

[0026] Where, P Gi and Q Gi are the active power and reactive power of the generator; P ldi and Q ldi are the active power and reactive power of the load; P dcr and Q dcr are the active power and reactive power of the rectifier; P dcI and Q dcI are the active power and reactive power of the inverter; V i and V j are node voltages, i, j = 1, 2,..., n+m+3; θ ij is the node phase angle; G ij and B ij are the node conductance and susceptance, n is the number of generators; m is the number of loads; a i , b i , c i and d i are the coefficients of the generator, load, rectifier and inverter respectively.

[0027] Step 2, constructing a VSC-HVDC-based AC / DC system transient model, and simulating it by using a time-domain simulation method to obtain a fault trajectory, projecting it onto the post-fault system, based on the pre-fault stable equilibrium point as the initial value, and using the projected voltage and the post-fault system to determine the post-fault stable equilibrium point, specifically:

[0028]

[0029] In the formula, L c1 , L c2 and R c1 , R c2 are the AC side resistance and inductance of the rectifier VSC1 and the inverter VSC2 respectively; I s1d , I s1q and I s2d , Is2q These are the d and q components of the AC side current of rectifier VSC1 and inverter VSC2, respectively; U s1d U s1q and U s2d U s2q These are the d and q components of the AC side voltages of rectifier VSC1 and inverter VSC2, respectively; U c1d U c1q and U c2d U c2q These are the d and q components of the AC output voltages of rectifier VSC1 and inverter VSC2, respectively; u d1 and u d2 These are the DC-side voltages of rectifier VSC1 and inverter VSC2, respectively; d It is direct current; P c1 and P c2 These are the DC-side active power values ​​of rectifier VSC1 and inverter VSC2, respectively; R dB It is the resistance reference value; C d It is a DC capacitor.

[0030] Step 3: Construct the AC / DC system energy function based on VSC-HVDC, and determine the system energy maximum as the escape point based on the fault trajectory obtained from the simulation in Step 2.

[0031] W(δ,ω,V,θ)=W k (ω)+W p (δ,V,θ)

[0032] =W k (ω)+W g (δ,V,θ)+W net (V,θ)+W ld (V,θ)+W dc (V,θ)

[0033] Among them, W k It is kinetic energy; W p It is potential energy; W g It is the potential energy of the generator; W net It is network potential energy; W ld It is the load potential energy; W dc It is DC potential energy;

[0034] The energy at the unstable equilibrium point after the fault is set to 0. Based on the above-mentioned AC / DC system energy function based on VSC-HVDC, the maximum point of potential energy in the fault is determined according to the potential energy of the fault trajectory obtained in step 2, and it is taken as the escape point of the fault trajectory.

[0035] Step 4, taking the escape point as the initial value, the norm of the reduced system integral process is determined based on the stable boundary tracking, and the norm minimum point is found, which is:

[0036] First, determine the norm in the integral process of the reduced system:

[0037]

[0038] Where N is the norm; P Gi and P mi are the active power and mechanical power of the i-th generator, respectively;

[0039] Then, compare the adjacent norms in the integral process two by two, when the first norm is smaller than its previous norm and the next norm, the norm is the norm minimum value.

[0040] Step 5, taking the norm minimum point as the initial value to determine the dominant unstable equilibrium point, which is:

[0041]

[0042] Where P Gi and Q Gi are the active power and reactive power of the generator; P ldi and Q ldi are the active power and reactive power of the load; P dcr and Q dcr are the active power and reactive power of the rectifier; P dcI and Q dcI are the active power and reactive power of the inverter; V i and V j are node voltages, i, j = 1, 2,..., n+m+3; θ ij is the node phase angle; G ij and B ij are the node conductance and susceptance, n is the number of generators; m is the number of loads; a i , b i , c i and d i are the coefficients of the generator, load, rectifier and inverter, respectively.

[0043] Step 6, determine the energy at the dominant unstable equilibrium point, and take the point energy as the critical energy to determine the system limit cut-off time, complete the transient stability analysis of the AC / DC system, which is:

[0044]

[0045] Where P dcr and P dcIP and P are active power of rectifier side and inverter side respectively; Q dcr and Q dcI Q and Q are reactive power of rectifier side and inverter side respectively; φ r and φ I φ and φ are phase angle of rectifier side and inverter side respectively; v r and v I v and v are voltage logarithm of rectifier side and inverter side respectively;

[0046] Then, the time when the total energy of the system in the system simulation fault process is the critical energy is found, and the time is the critical switching time;

[0047] When the switching time of the system is greater than the critical switching time, the system is in an unstable state; otherwise, the system remains stable.

[0048] A VSC-HVDC-based AC / DC system transient stability analysis system, comprising the following modules:

[0049] An AC / DC system steady-state model construction module: used for constructing a VSC-HVDC-based AC / DC system steady-state model and determining a stable equilibrium point before a fault;

[0050] An AC / DC system transient model construction module: used for constructing a VSC-HVDC-based AC / DC system transient model and simulating by a time-domain simulation method to obtain a fault trajectory, projecting the fault trajectory to a post-fault system, determining a stable equilibrium point after the fault based on the stable equilibrium point before the fault as an initial value and the projected voltage and the post-fault system;

[0051] An escape point determination module: used for constructing an energy function of the VSC-HVDC-based AC / DC system and determining a maximum value of the system energy as an escape point based on the fault trajectory obtained by simulation;

[0052] A norm minimum point determination module: used for determining a norm of an integral process of a reduced-order system based on stable boundary tracking with the escape point as an initial value and determining a norm minimum point;

[0053] A dominant unstable equilibrium point determination module: used for determining a dominant unstable equilibrium point with the norm minimum point as an initial value;

[0054] A system limit switching time determination module: used for determining an energy at the dominant unstable equilibrium point, taking the energy at the point as a critical energy, and determining a system limit switching time to complete transient stability analysis of the AC / DC system.

[0055] A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program:

[0056] Step 1, construct a steady-state model of the AC / DC system based on VSC-HVDC, and determine the stable equilibrium point before the fault;

[0057] Step 2, construct a transient-state model of the AC / DC system based on VSC-HVDC, and simulate using the time-domain simulation method to obtain the fault trajectory, project it onto the post-fault system, and determine the stable equilibrium point after the fault based on the stable equilibrium point before the fault as the initial value and the projected voltage and the post-fault system;

[0058] Step 3, construct an energy function of the AC / DC system based on VSC-HVDC, and determine the maximum value of the system energy as the escape point based on the fault trajectory obtained in Step 2;

[0059] Step 4, take the escape point as the initial value, determine the norm of the integral process of the reduced-order system based on the stable boundary tracking, and find the minimum value point of the norm;

[0060] Step 5, take the minimum value point of the norm as the initial value to determine the dominant unstable equilibrium point;

[0061] Step 6, determine the energy at the dominant unstable equilibrium point, take the energy of the point as the critical energy, determine the limit clearing time of the system, and complete the transient stability analysis of the AC / DC system.

[0062] A computer storable medium storing a computer program, on which the following steps are implemented by a processor:

[0063] Step 1, construct a steady-state model of the AC / DC system based on VSC-HVDC, and determine the stable equilibrium point before the fault;

[0064] Step 2, construct a transient-state model of the AC / DC system based on VSC-HVDC, and simulate using the time-domain simulation method to obtain the fault trajectory, project it onto the post-fault system, and determine the stable equilibrium point after the fault based on the stable equilibrium point before the fault as the initial value and the projected voltage and the post-fault system;

[0065] Step 3, construct an energy function of the AC / DC system based on VSC-HVDC, and determine the maximum value of the system energy as the escape point based on the fault trajectory obtained in Step 2;

[0066] Step 4, take the escape point as the initial value, determine the norm of the integral process of the reduced-order system based on the stable boundary tracking, and find the minimum value point of the norm;

[0067] Step 5, take the minimum value point of the norm as the initial value to determine the dominant unstable equilibrium point;

[0068] Step 6, determine the energy at the dominant unstable equilibrium point, take the energy of the point as the critical energy, determine the limit clearing time of the system, and complete the transient stability analysis of the AC / DC system.

[0069] Embodiments

[0070] In combination Figure 1 A VSC-HVDC-based AC / DC system transient stability analysis method, comprising the following steps:

[0071] Step 1, constructing a VSC-HVDC-based AC / DC system steady-state model, as shown in Figure 2 determining the pre-fault stable equilibrium point, specifically:

[0072]

[0073] In the above formula, the first row is the active power balance of the system, and the second row is the reactive power balance;

[0074] Where, P Gi and Q Gi are the active power and reactive power of the generator; P ldi and Q ldi are the active power and reactive power of the load; P dcr and Q dcr are the active power and reactive power of the rectifier; P dcI and Q dcI are the active power and reactive power of the inverter; V i and V j are node voltages, i, j = 1, 2,..., n+m+3; θ ij is the node phase angle; G ij and B ij are the node conductance and susceptance, n is the number of generators; m is the number of loads; a i , b i , c i and d i are the coefficients of the generator, load, rectifier and inverter, respectively.

[0075] Step 2, constructing a VSC-HVDC-based AC / DC system transient model, and simulating it with a time-domain simulation method to obtain the fault trajectory, projecting it onto the post-fault system, using the pre-fault stable equilibrium point as the initial value, and using the projected voltage and the post-fault system to determine the post-fault stable equilibrium point, specifically:

[0076]

[0077]

[0078] In the formula, L c1 , L c2 and R c1 , R c2are the resistance and inductance of the AC side of rectifier VSC1 and inverter VSC2, respectively; I s1d , s1q and I s2d , s2q are the d, q components of the AC side current of rectifier VSC1 and inverter VSC2, respectively; U s1d , U s1q and U s2d , U s2q are the d, q components of the AC side voltage of rectifier VSC1 and inverter VSC2, respectively; U c1d , U c1q and U c2d , U c2q are the d, q components of the AC side outlet voltage of rectifier VSC1 and inverter VSC2, respectively; u d1 and u d2 are the DC side voltage of rectifier VSC1 and inverter VSC2, respectively; i d is the DC current; P c1 and P c2 are the DC side active power of rectifier VSC1 and inverter VSC2, respectively; R dB is the resistance reference value; C d is the DC capacitor.

[0079] Step 3, construct the energy function of the AC / DC system based on VSC-HVDC, and determine the maximum value of the system energy as the escape point based on the fault trajectory obtained by simulation in step 2:

[0080] W(δ,ω,V,θ)=W k (ω)+W p (δ,V,θ)

[0081] =W k (ω)+W g (δ,V,θ)+W net (V,θ)+W ld (V,θ)+W dc (V,θ)

[0082] Wherein, W k is kinetic energy; W p is potential energy; W g is generator potential energy; W net is network potential energy; W ld is load potential energy; W dc is DC potential energy;

[0083] The energy at the post-fault unstable equilibrium point is set to 0, based on the energy function of the VSC-HVDC-based AC / DC system, the maximum point of the potential energy in the fault is determined according to the potential energy of the fault trajectory obtained in step 2, and the maximum point is taken as the escape point of the fault trajectory.

[0084] Step 4, taking the escape point as the initial value, determining the norm of the reduced-order system integral process based on the stable boundary tracking, and finding the norm minimum point, specifically:

[0085] First, determine the norm in the reduced-order system integral process:

[0086]

[0087] Where N is the norm; P mi and P Gi are the electromagnetic power and mechanical power of the i th generator;

[0088] Then, compare the adjacent norms in the integral process two by two, when the first norm is smaller than the previous and the next norm, the norm is the norm minimum value.

[0089] Where the stable boundary tracking diagram is shown in Figure 3 , and the norm minimum value in the embodiment is shown in Figure 4 .

[0090] Step 5, taking the norm minimum point as the initial value to determine the dominant unstable equilibrium point, specifically:

[0091]

[0092] Where P Gi and Q Gi are the active power and reactive power of the generator; P ldi and Q ldi are the active power and reactive power of the load; P dcr and Q dcr are the active power and reactive power of the rectifier; P dcI and Q dcI are the active power and reactive power of the inverter; V i and V j are node voltages, i, j = 1, 2, …, n+m+3; θ ij is the node phase angle; G ij and B ij are the node conductance and susceptance, n is the number of generators; m is the number of loads; a i , b i , c i and d i are the coefficients of the generator, load, rectifier and inverter respectively.

[0093] Step 6, determine the energy at the dominant unstable equilibrium point, and take the point energy as the critical energy, determine the system limit cutting time, complete the transient stability analysis of the AC-DC system, specifically:

[0094]

[0095] Where, P dcr and P dcI are the active power of the rectifier side and the inverter side respectively; Q dcr and Q dcI are the reactive power of the rectifier side and the inverter side respectively; φ r and φ I are the phase angles of the rectifier side and the inverter side respectively; v r and v I are the voltage logarithms of the rectifier side and the inverter side respectively.

[0096] Then, find the time when the total energy of the system in the system simulation fault process is the critical energy, which is the critical cutting time;

[0097] When the cutting time of the system is greater than the critical cutting time, the system is in an unstable state; otherwise, it is less than or equal to the critical time, the system remains stable, and the transient stability analysis of the AC-DC system is completed.

[0098] The above examples show and describe the basic principles and main features of the present application. Those skilled in the art should understand that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A transient stability analysis method for AC / DC systems based on VSC-HVDC, characterized in that, Includes the following steps: Step 1: Construct a steady-state model of the AC / DC system based on VSC-HVDC and determine the stable equilibrium point before the fault. Step 2: Construct a transient model of the AC / DC system based on VSC-HVDC and perform simulation using the time-domain simulation method to obtain the fault trajectory. Project the trajectory onto the post-fault system. Using the pre-fault stable equilibrium point as the initial value, determine the post-fault stable equilibrium point using the projected voltage and the post-fault system. Step 3: Construct the AC / DC system energy function based on VSC-HVDC, and determine the system energy maximum value as the escape point based on the fault trajectory obtained from the simulation in Step 2. Step 4: Using the escape point as the initial value, determine the norm of the integration process of the reduced-order system based on stability boundary tracking, and find the norm minimum point; Step 5: Use the norm minimum point as the initial value to determine the dominant unstable equilibrium point; Step 6: Determine the energy at the dominant unstable equilibrium point and use this energy as the critical energy to determine the system's limit cut-off time, thus completing the transient stability analysis of the AC / DC system.

2. The transient stability analysis method for AC / DC systems based on VSC-HVDC according to claim 1, characterized in that, The steady-state model of the AC / DC system based on VSC-HVDC in step 1 is specifically as follows: Among them, P Gi and Q Gi It refers to the active and reactive power of the generator; P ldi and Q ldi It refers to the active and reactive power of the load; P dcr and Q dcr It refers to the active and reactive power of the rectifier; P dcI and Q dcI It refers to the active and reactive power of the inverter; V i and V j These are the node voltages, i, j = 1, 2, ..., n+m+3; θ ij It is the nodal phase angle; G ij and B ij These are the node conductance and susceptance, where n is the number of generators; m is the number of loads; and a i b i c i and d i These are the generator, load, rectifier, and inverter coefficients, respectively.

3. The transient stability analysis method for AC / DC systems based on VSC-HVDC according to claim 1, characterized in that, The transient model of the AC / DC system based on VSC-HVDC in step 2 is specifically as follows: In the formula, L c1 L c2 and R c1 R c2 These are the AC side resistances and inductors of rectifier VSC1 and inverter VSC2, respectively; I s1d I s1q and I s2d I s2q These are the d and q components of the AC side current of rectifier VSC1 and inverter VSC2, respectively; U s1d U s1q and U s2d U s2q These are the d and q components of the AC side voltages of rectifier VSC1 and inverter VSC2, respectively; U c1d U c1q and U c2d U c2q These are the d and q components of the AC output voltages of rectifier VSC1 and inverter VSC2, respectively; u d1 and u d2 These are the DC-side voltages of rectifier VSC1 and inverter VSC2, respectively; d It is direct current; P c1 and P c2 These are the DC-side active power values ​​of rectifier VSC1 and inverter VSC2, respectively; R dB It is the resistance reference value; C d It is a DC capacitor.

4. The transient stability analysis method for AC / DC systems based on VSC-HVDC according to claim 1, characterized in that, The construction of the AC / DC system energy function based on VSC-HVDC in step 3 is specifically as follows: W(δ,ω,V,θ)=W k (ω)+W p (d,V,i) =W k (ω)+W g (δ,V,θ)+W net (V,θ)+W ld (V,θ)+W dc (V,θ) Among them, W k It is kinetic energy; W p It is potential energy; W g It is the potential energy of the generator; W net It is network potential energy; W ld It is the load potential energy; W dc It is DC potential energy; The energy at the unstable equilibrium point after the fault is set to 0. Based on the above-mentioned AC / DC system energy function based on VSC-HVDC, the maximum point of potential energy in the fault is determined according to the potential energy of the fault trajectory obtained in step 2, and it is taken as the escape point of the fault trajectory.

5. The transient stability analysis method for AC / DC systems based on VSC-HVDC according to claim 1, characterized in that, The determination of the norm minimum point in step 4 specifically involves: First, determine the norm during the integration process of the reduced-order system: Where N is the norm; P Gi and P mi These are the active power and mechanical power of the i-th generator, respectively; Then, the adjacent norms in the integration process are compared pairwise. When the first norm is smaller than both its preceding and following norms, that norm is the norm minimum.

6. The transient stability analysis method for AC / DC systems based on VSC-HVDC according to claim 1, characterized in that, The determination of the dominant unstable equilibrium point in step 5 specifically involves: Among them, P Gi and Q Gi It refers to the active and reactive power of the generator; P ldi and Q ldi It refers to the active and reactive power of the load; P dcr and Q dcr It refers to the active and reactive power of the rectifier; P dcI and Q dcI It refers to the active and reactive power of the inverter; V i and V j These are the node voltages, i, j = 1, 2, ..., n+m+3; θ ij It is the nodal phase angle; G ij and B ij These are the node conductance and susceptance, where n is the number of generators; m is the number of loads; and a i b i c i and d i These are the generator, load, rectifier, and inverter coefficients, respectively, P. mi It is the mechanical power of the i-th generator.

7. The transient stability analysis method for AC / DC systems based on VSC-HVDC according to claim 1, characterized in that, The determination of the energy at the dominant unstable equilibrium point in step 6 specifically involves: Among them, P dcr and P dcI These are the active power on the rectifier side and the inverter side, respectively; Q dcr and Q dcI These are the reactive power on the rectifier side and the inverter side, respectively; φ r and φ I These are the phase angles of the rectifier side and the inverter side, respectively; v r and v I These are the logarithms of the rectifier and inverter sides, respectively, W. dc It is DC potential energy; Next, find the time when the total system energy reaches the critical energy during the system's simulated fault process; this time is the critical cut-off time. When the resection time of the system is greater than the critical resection time, the system is in an unstable state; conversely, when it is less than or equal to the critical time, the system remains stable.

8. A transient stability analysis system for AC / DC systems based on VSC-HVDC, characterized in that, Includes the following modules: AC / DC system steady-state model construction module: used to construct a steady-state model of an AC / DC system based on VSC-HVDC and determine the stable equilibrium point before the fault. AC / DC system transient model construction module: used to construct AC / DC system transient model based on VSC-HVDC, and to simulate it using time-domain simulation method to obtain the fault trajectory, project it onto the post-fault system, and use the pre-fault stable equilibrium point as the initial value, and use the projected voltage and the post-fault system to determine the post-fault stable equilibrium point; Escape point determination module: used to construct the energy function of AC / DC system based on VSC-HVDC, and determine the maximum energy value of the system based on the fault trajectory obtained from simulation, as the escape point; Norm Minimum Point Determination Module: Used to determine the norm of the integration process of the reduced-order system based on the escape point as the initial value and the stability boundary tracking, and to determine the norm minimum point; Dominant Unstable Equilibrium Point Determination Module: Used to determine the dominant unstable equilibrium point by taking the norm minimum point as the initial value; System limit cut-off time determination module: used to determine the energy at the dominant unstable equilibrium point, and use this energy as the critical energy to determine the system limit cut-off time, thus completing the transient stability analysis of the AC / DC system.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method steps specified in any one of claims 1 to 7.

10. A computer-storeable medium storing a computer program, characterized in that, The method steps as specified in any one of claims 1 to 7 are implemented by a processor on the computer program.

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