Intertripping prevention method and system for alternating-current and direct-current hybrid power grid

Abstract

The invention discloses a cascading trip prevention method and system for an AC-DC hybrid power grid, and the method comprises the steps: determining a comprehensive index of the cascading trip of the AC-DC hybrid power grid based on an index for judging whether the cascading trip occurs after an AC system has an initial fault and an index for judging whether a DC system normally operates after the initial fault is cut off; calculating branch network loss cost and a risk value of non-fault branch shutdown caused by power flow transfer, constructing a target function by taking minimization of the branch network loss cost and the risk value as a target, constructing a constraint condition based on a comprehensive index, and solving the cascading trip prevention model to obtain a cascading trip prevention result. According to the method, the influence of various factors in the alternating-current and direct-current hybrid power grid on the cascading trip is more comprehensively considered, the occurrence probability and the propagation path of the cascading trip are more accurately predicted, the branch outage risk and the network loss cost are considered, the stability change of the alternating-current and direct-current hybrid power grid under the cascading trip condition is more accurately evaluated, and the stability of the cascading trip is improved. And the intertripping phenomenon of the alternating-current and direct-current hybrid power grid can be comprehensively and effectively prevented.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method and system for preventing cascading trips in AC / DC hybrid power grids. Background Technology

[0002] Due to their unique structure and operating characteristics, AC / DC hybrid power grids, while meeting the demands for long-distance, high-capacity power transmission, also pose severe challenges to the safe and stable operation of the power grid. The possibility of a cascading failure of an individual component evolving into a large-scale power outage is increasing. Therefore, studying the cascading failure evolution characteristics of AC / DC hybrid power grids and developing cascading trip prevention measures undoubtedly has significant practical and theoretical value.

[0003] Currently, traditional protection models are not comprehensive enough and cannot fully take into account the various needs of AC / DC hybrid power grids under cascading tripping conditions. They cannot effectively cope with complex fault scenarios and therefore cannot effectively prevent cascading tripping. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for preventing cascading tripping in AC / DC hybrid power grids, which can comprehensively and effectively prevent cascading tripping in AC / DC hybrid power grids.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preventing cascading tripping in an AC / DC hybrid power grid includes the following steps: A comprehensive index for determining whether a cascading trip occurs in an AC / DC hybrid power grid is determined based on a first index and a second index. The first index is used to determine whether a cascading trip occurs in the AC system after an initial fault, and the second index is used to determine whether the DC system operates normally after the initial fault is disconnected. Calculate the cost of branch network loss and the risk of non-faulty branch outages caused by power flow transfer after a faulty branch disconnects; An objective function is constructed with the goal of minimizing the branch network loss cost and the risk value, and constraints are constructed based on the comprehensive index. The cascading trip prevention model, which includes the objective function and the constraints, is solved to obtain a prevention scheme.

[0006] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is as follows: A cascading trip prevention system for an AC / DC hybrid power grid includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it performs the following steps: A comprehensive index for determining whether a cascading trip occurs in an AC / DC hybrid power grid is determined based on a first index and a second index. The first index is used to determine whether a cascading trip occurs in the AC system after an initial fault, and the second index is used to determine whether the DC system operates normally after the initial fault is disconnected. Calculate the cost of branch network loss and the risk of non-faulty branch outages caused by power flow transfer after a faulty branch disconnects; An objective function is constructed with the goal of minimizing the branch network loss cost and the risk value, and constraints are constructed based on the comprehensive index. The cascading trip prevention model, which includes the objective function and the constraints, is solved to obtain a prevention scheme.

[0007] The beneficial effects of this invention are as follows: Based on indicators used to determine whether a cascading trip occurs in an AC system after an initial fault, and indicators used to determine whether a DC system operates normally after an initial fault is disconnected, a comprehensive indicator is determined to determine whether a cascading trip occurs in an AC / DC hybrid power grid. Branch network loss costs and the risk value of non-faulty branch outages caused by power flow transfer after a faulty branch is disconnected are calculated. An objective function is constructed with the goal of minimizing branch network loss costs and risk values. Constraints are constructed based on the comprehensive indicator. The cascading trip prevention model, including the objective function and constraints, is solved to obtain a prevention scheme. By using the first and second indicators, the impact of various factors on cascading trips in the AC / DC hybrid power grid is considered more comprehensively, namely AC system faults and DC commutation faults. This allows for more accurate prediction of the probability and propagation path of cascading trips. The constructed cascading trip prevention model considers branch outage risks and network loss costs, more accurately assesses the stability changes of the AC / DC hybrid power grid under cascading trip conditions, determines the comprehensive impact of complex faults on power grid stability, and the obtained prevention scheme can comprehensively and effectively prevent cascading trips in AC / DC hybrid power grids. Attached Figure Description

[0008] Figure 1 This is a flowchart illustrating the steps of a method for preventing cascading trips in an AC / DC hybrid power grid according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of a cascading trip prevention system for an AC / DC hybrid power grid according to an embodiment of the present invention. Detailed Implementation

[0009] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0010] Please refer to Figure 1 A method for preventing cascading tripping in an AC / DC hybrid power grid, comprising the following steps: A comprehensive index for determining whether a cascading trip occurs in an AC / DC hybrid power grid is determined based on a first index and a second index. The first index is used to determine whether a cascading trip occurs in the AC system after an initial fault, and the second index is used to determine whether the DC system operates normally after the initial fault is disconnected. Calculate the cost of branch network loss and the risk of non-faulty branch outages caused by power flow transfer after a faulty branch disconnects; An objective function is constructed with the goal of minimizing the branch network loss cost and the risk value, and constraints are constructed based on the comprehensive index. The cascading trip prevention model, which includes the objective function and the constraints, is solved to obtain a prevention scheme.

[0011] As can be seen from the above description, the beneficial effects of the present invention are as follows: Based on indicators used to determine whether a cascading trip occurs in an AC system after an initial fault, and indicators used to determine whether a DC system operates normally after an initial fault is disconnected, a comprehensive indicator is determined to determine whether a cascading trip occurs in an AC / DC hybrid power grid. Branch network loss costs and the risk value of non-faulty branch outages caused by power flow transfer after a faulty branch is disconnected are calculated. An objective function is constructed with the goal of minimizing branch network loss costs and risk values. Constraints are constructed based on the comprehensive indicator. The cascading trip prevention model, including the objective function and constraints, is solved to obtain a prevention scheme. By using the first and second indicators, the impact of various factors on cascading trips in the AC / DC hybrid power grid is considered more comprehensively, namely, AC system faults and DC commutation faults. This allows for more accurate prediction of the probability and propagation path of cascading trips. The constructed cascading trip prevention model considers branch outage risks and network loss costs, more accurately assesses the stability changes of the AC / DC hybrid power grid under cascading trip conditions, determines the comprehensive impact of complex faults on power grid stability, and the obtained prevention scheme can comprehensively and effectively prevent cascading trips in AC / DC hybrid power grids.

[0012] Furthermore, it also includes: After an initial fault occurs, the protection measurement values ​​and setting values ​​of all branches of the AC system are compared to obtain the first index, and the commutation voltage and critical voltage of the DC system under any operating state are compared to obtain the second index.

[0013] Furthermore, the protection measurement values ​​and setting values ​​of all branches of the AC system are compared to obtain the first indicator, which is as follows: ; In the formula, Indicates a branch L b of i Electrical distance on the side, Indicates a branch L b ofi Side current protection setting value, Indicates a branch L b of i Side current protection measurement value, Indicates a branch L b of j Electrical distance on the side, Indicates a branch L b of j Side current protection setting value, Indicates a branch L b of j Side current protection measurement value, I b This indicates the primary indicator.

[0014] Furthermore, by comparing the commutation voltage and critical voltage under any operating state of the DC system, a second index is obtained, specifically: ; In the formula, U x This represents the commutation critical voltage. I d Indicates the current value of the DC system. X Indicates the commutation reactance on the inverter side. Indicates the minimum arc extinction angle. This indicates that a leading angle has been triggered. U This represents the effective value of the AC system voltage connected to the inverter side. U D This indicates the second indicator.

[0015] As described above, after an initial fault occurs, the protection measurement values ​​and setting values ​​of all branches of the AC system are compared to obtain the first index. The commutation voltage and critical voltage of the DC system under any operating state are compared to obtain the second index. This allows for consideration of the impact of AC faults on the AC and DC systems in the AC-DC hybrid power grid from both the characteristics of protection action and commutation failure, so as to determine whether the power grid will experience cascading tripping.

[0016] Furthermore, the comprehensive indicators for determining whether a cascading trip occurs in an AC / DC hybrid power grid, based on the first and second indicators, include: The minimum value between the first and second indicators is selected as the comprehensive indicator for judging whether a cascading trip has occurred in the AC / DC hybrid power grid.

[0017] As can be seen from the above description, when the first indicator is less than or equal to 0, it indicates that a cascading trip will be triggered. When the second indicator is less than or equal to 0, it indicates that the interruption of the AC fault will cause the DC system to fail to commutate and the DC system cannot operate stably. Selecting the minimum value of the first and second indicators as a comprehensive indicator for judging whether a cascading trip has occurred in the AC-DC hybrid power grid can more easily and quickly determine whether a cascading trip has occurred.

[0018] Furthermore, the calculation of branch network loss costs and the risk value of non-faulty branch outages caused by power flow transfer after a faulty branch disconnects include: Calculate the power flow impact rate of the branch circuit due to cascading tripping; Calculate the risk value of non-faulty branch outage caused by power flow transfer after the faulty branch is disconnected based on the power flow impact rate. Obtain the node voltage magnitude, node voltage phase angle difference, branch resistance, and branch reactance for all branches; The branch network loss cost is calculated based on the node voltage amplitude, the node voltage phase angle difference, the branch resistance, and the branch reactance.

[0019] Furthermore, the branch network loss cost is calculated based on the node voltage amplitude, the node voltage phase angle difference, the branch resistance, and the branch reactance, specifically as follows: ; In the formula, C Indicates the cost of branch network losses. Indicates the price coefficient. This represents the set of all branches. U i , U j Representing nodes respectively i , j voltage amplitude, Represents a node i and j The voltage phase angle difference, where R represents the resistance of the branch. This indicates the reactance of the branch circuit.

[0020] As described above, by calculating the risk value of non-faulty branches being out of service due to power flow transfer after a faulty branch is disconnected, the risk value reflects the safety of the AC / DC hybrid power grid. The branch network loss cost is calculated based on the node voltage amplitude, node voltage phase angle difference, branch resistance, and branch reactance. The branch network loss cost reflects the economy of the AC / DC hybrid power grid. This facilitates the consideration of both the safety and economy of the AC / DC hybrid power grid when preventing cascading tripping phenomena in the future.

[0021] Furthermore, the risk value of non-faulty branch outage caused by power flow transfer after the faulty branch is disconnected, calculated based on the power flow impact rate, includes: Obtain the load rate of non-faulty branches after a faulty branch triggers a cascading trip; Calculate the correlation index before and after the fault branch triggers a cascading trip based on the power flow impact rate and the load rate; The risk value of non-faulty branches being out of service due to power flow transfer after the faulty branch is disconnected is calculated based on the aforementioned correlation index.

[0022] As described above, the probability of branch outage caused by power flow transfer depends on the load of the branch and the impact of power flow changes on the power of other lines. Considering the branch's impact resistance and the system's active power flow transfer, the correlation index before and after the faulty branch triggers cascading trip is calculated based on the power flow impact rate and load rate. Based on the correlation index, the risk of branch outage caused by power flow transfer can be calculated more accurately.

[0023] Furthermore, the constraints constructed based on the comprehensive indicators include: Establish comprehensive indicator constraints based on comprehensive indicators; Establish active power injection constraints and reactive power injection constraints at nodes; Establish constraints on generator active power output, generator reactive power output, node voltage, and active power transmission through lines.

[0024] As described above, comprehensive index constraints are established based on comprehensive indices. In addition, constraints are also established for node injected active power, node injected reactive power, generator active output, generator reactive output, node voltage, and line transmission active power to ensure the reasonable operation of the AC / DC hybrid power grid during the solution process and to avoid cascading tripping.

[0025] Please refer to Figure 2 Another embodiment of the present invention provides a cascading trip prevention system for an AC / DC hybrid power grid, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements each step of the cascading trip prevention method for the AC / DC hybrid power grid described above.

[0026] The cascading tripping prevention method and system for AC / DC hybrid power grids described above are applicable to AC / DC hybrid power grid operation scenarios. The following detailed embodiments illustrate these methods: Please refer to Figure 1 Embodiment 1 of the present invention is as follows: A method for preventing cascading tripping in an AC / DC hybrid power grid includes the following steps: S1. After an initial fault occurs, the protection measurement values ​​and setting values ​​of all branches of the AC system are compared to obtain a first indicator, and the commutation voltage and critical voltage of the DC system under any operating state are compared to obtain a second indicator. The first indicator is used to determine whether the AC system experiences a cascading trip after the initial fault occurs, and the second indicator is used to determine whether the DC system operates normally after the initial fault is disconnected.

[0027] Assuming that each line in an AC / DC hybrid power grid is equipped with current-type backup protection, the first index is obtained by comparing the protection measurement values ​​and setting values ​​of all branches in the AC system, specifically: ; In the formula, Indicates a branch L b of i Electrical distance on the side, Indicates a branch L b of i Side current protection setting value, Indicates a branch L b of i Side current protection measurement value, Indicates a branch L b of j Electrical distance on the side, Indicates a branch L b of j Side current protection setting value, Indicates a branch L b of j Side current protection measurement value, I b This indicates the primary indicator.

[0028] when I b When >0, it indicates a branch L b It will not trigger a chain reaction of power outages, when I b When ≤0, it indicates a branch L b This will trigger a chain reaction of power outages.

[0029] The second index is obtained by comparing the commutation voltage and the critical voltage under any operating state of the DC system, specifically: ; In the formula, U xThis represents the commutation critical voltage. I d Indicates the current value of the DC system. X Indicates the commutation reactance on the inverter side. Indicates the minimum arc extinction angle. This indicates that a leading angle has been triggered. U This represents the effective value of the AC system voltage connected to the inverter side. U D This indicates the second indicator.

[0030] Inspired by the discriminant formula for whether a cascading fault occurs in the AC power grid, this paper presents a mathematical form (i.e., the formula above) to represent the commutation changes in the DC system, addressing the impact of AC faults on DC systems. U D A value >0 indicates that the DC system can operate stably and normally after the AC fault is disconnected by protection. U D When the value is ≤0, it indicates that the interruption of an AC fault will cause the DC system to fail to commutate, and the DC system will not be able to operate stably and normally.

[0031] S2. A comprehensive indicator for determining whether a cascading trip occurs in an AC / DC hybrid power grid, based on the first and second indicators.

[0032] Specifically, the minimum value between the first and second indicators is selected as the comprehensive indicator for judging whether a cascading trip has occurred in the AC / DC hybrid power grid. W =min( I b , U D ); In the formula, W A comprehensive indicator indicating whether a cascading trip occurs in an AC / DC hybrid power grid. When W When the value is >0, it indicates that the AC / DC hybrid power grid will not trigger a cascading trip. W When the value is ≤0, it means that the AC / DC hybrid power grid will trigger a cascading trip.

[0033] Therefore, this invention analyzes the impact of faults on the operation of AC / DC hybrid power grids from two aspects: the characteristics of protection actions and commutation failures.

[0034] S3. Calculate the branch network loss cost and the risk value of non-faulty branch outages caused by power flow transfer after a faulty branch disconnects, specifically including S31-S34: S31. Calculate the power flow impact rate of the branch circuit on the cascading trip, specifically: ; In the formula, Indicates cascading trip to branch circuit Lb The trend impact rate P ab Indicates a branch L a After triggering a chain of power outages, the branch circuit L b The meritorious trend, P b0 Indicates a branch L a Branch before the fault L b The original trend, n This indicates the total number of branches in an AC / DC hybrid power grid.

[0035] S32. Calculate the risk value of non-faulty branch outage caused by power flow transfer after the faulty branch is disconnected, based on the power flow impact rate, specifically including S321-S323: S321. Obtain the load rate of non-faulty branches after the faulty branch triggers a cascading trip.

[0036] S322. Calculate the correlation index before and after the faulty branch triggers a cascading trip based on the power flow impact rate and the load rate, specifically: ; In the formula, V ab Indicates a branch L a Correlation indicators before and after triggering a cascading trip. Indicates a branch L a After triggering a chain of power outages, the branch circuit L b The load rate.

[0037] S323. Calculate the risk value of non-faulty branch outages caused by power flow transfer after the faulty branch disconnects, based on the aforementioned correlation index. Specifically: ; In the formula, F ab Indicates a branch L a Disconnection causes power flow transfer in branches L b Risk of shutdown V ai Indicates a branch L a Correlation indicators before and after triggering a cascading trip.

[0038] The probability of branch outage caused by power flow shift depends on the load of the branch and the impact of power flow changes on the power of other lines. Therefore, the above takes into account the branch's shock resistance and the system's active power flow shift.

[0039] S33. Obtain the node voltage amplitude, node voltage phase angle difference, branch resistance, and branch reactance of all branches.

[0040] S34. Calculate the branch network loss cost based on the node voltage amplitude, the node voltage phase angle difference, the branch resistance, and the branch reactance, specifically as follows: ; In the formula, C Indicates the cost of branch network losses. Indicates the price coefficient. This represents the set of all branches. U i , U j Representing nodes respectively i , j voltage amplitude, Represents a node i and j The voltage phase angle difference, where R represents the resistance of the branch. This indicates the reactance of the branch circuit.

[0041] S4. Construct an objective function with the goal of minimizing the branch network loss cost and the risk value, and construct constraints based on the comprehensive index.

[0042] The constraints constructed based on the comprehensive indicators include: Establish comprehensive indicator constraints based on comprehensive indicators; Establish active power injection constraints and reactive power injection constraints at nodes; Establish constraints on generator active power output, generator reactive power output, node voltage, and active power transmission through lines.

[0043] The comprehensive indicator constraints are as follows: W >0; Node-injected active power constraints are as follows: ; In the formula, Represents a node i The injected active power, Represents a node i voltage amplitude, Represents a node j voltage amplitude, Represents a node i , j The real part of the corresponding admittance matrix, Represents a node i voltage phase angle With nodes j voltage phase angle The difference, that is , Represents a node i , j The imaginary part of the corresponding admittance matrix, n This represents the total number of nodes in a hybrid AC / DC power grid.

[0044] The node injects reactive power constraints, specifically: ; In the formula, Represents a node i The injected reactive power.

[0045] The generator has active power output constraints, specifically: ; In the formula, P Gi.Min Indicates the first i The lower limit of the active power output of a generator. P Gi.Max Indicates the first i The generator has an upper limit on its active power output. r Indicates the operating status of the AC / DC hybrid power grid. r =0 corresponds to the initial fault condition. r =1 corresponds to the initial fault.

[0046] The generator reactive power output constraint is as follows: ; In the formula, Q Gi.Min Indicates the first i The lower limit of reactive power output of a generator. Q Gi.Max Indicates the first i The upper limit of reactive power output of the generator.

[0047] Node voltage constraints, specifically: ; In the formula, U i.Min Represents a node i The lower limit of voltage, U i.Max Represents a node i The upper limit of voltage.

[0048] The active power constraint for line transmission is as follows: ; In the formula, P1 represents the active power transmitted through the line. P 1max This indicates the limit of active power transmitted through the line.

[0049] By ensuring the rationality, accuracy, and effectiveness of the model through the above constraints, the input parameters of the model can be limited to a reasonable physical range, ensuring that the model conforms to the actual operating rules and logic of the system.

[0050] S5. Solve the cascading trip prevention model, which includes the objective function and the constraints, to obtain the prevention scheme.

[0051] The aforementioned prevention scheme is an AC / DC hybrid power grid operation mode or operating state designed to prevent cascading trips.

[0052] All the inequality constraints in the above conditions can be simplified as follows: g ( x If )≥0, all equality constraints are simplified to: m ( x If )=0, then the cascading trip prevention model is as follows: .

[0053] The cascading trip prevention model has two objective functions: the safety objective function is the risk value of non-faulty branches being out of service due to power flow shift after the faulty branch is disconnected. P ab The economic objective function is the cost of branch network losses. C .

[0054] Please refer to Figure 2 Embodiment two of the present invention is as follows: A cascading trip prevention system for an AC / DC hybrid power grid includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the various steps of the cascading trip prevention method for the AC / DC hybrid power grid in Embodiment 1.

[0055] In summary, this invention provides a method and system for preventing cascading trips in AC / DC hybrid power grids. It determines a comprehensive index for whether cascading trips will occur in the AC / DC hybrid power grid based on indicators used to determine whether cascading trips will occur after an initial fault in the AC system and indicators used to determine whether the DC system will operate normally after the initial fault is resolved. It calculates branch network loss costs and the risk value of non-faulty branch outages caused by power flow transfer after a faulty branch is disconnected. An objective function is constructed with the goal of minimizing branch network loss costs and risk values. Constraints are constructed based on the comprehensive index. The cascading trip prevention model, including the objective function and constraints, is solved to obtain a prevention scheme. The first and second indices more comprehensively consider the impact of various factors on cascading trips in the AC / DC hybrid power grid, namely AC system faults and DC commutation faults. This approach allows for more accurate prediction of the probability and propagation path of cascading trips. The constructed cascading trip prevention model considers branch outage risks and network loss costs, more accurately assesses the stability changes of AC / DC hybrid power grids under cascading trip conditions, determines the comprehensive impact of complex faults on grid stability, and provides a comprehensive and effective prevention scheme to prevent cascading trips in AC / DC hybrid power grids. Furthermore, after the initial fault occurs, the protection measurement values ​​and setting values ​​of all branches in the AC system are compared to obtain the first indicator, and the commutation voltage and critical voltage of the DC system under any operating state are compared to obtain the second indicator. This approach can simultaneously consider the impact of AC faults on both the AC and DC systems in the AC / DC hybrid power grid from the perspectives of protection action characteristics and commutation failure, so as to subsequently determine whether the power grid has experienced cascading trips.

[0056] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preventing cascading tripping in an AC / DC hybrid power grid, characterized in that, Including the following steps: A comprehensive index for determining whether a cascading trip occurs in an AC / DC hybrid power grid is determined based on a first index and a second index. The first index is used to determine whether a cascading trip occurs in the AC system after an initial fault, and the second index is used to determine whether the DC system operates normally after the initial fault is disconnected. Calculate the cost of branch network loss and the risk of non-faulty branch outages caused by power flow transfer after a faulty branch disconnects; An objective function is constructed with the goal of minimizing the branch network loss cost and the risk value, and constraints are constructed based on the comprehensive index. The cascading trip prevention model, which includes the objective function and the constraints, is solved to obtain a prevention scheme.

2. The method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 1, characterized in that, Also includes: After an initial fault occurs, the protection measurement values ​​and setting values ​​of all branches of the AC system are compared to obtain the first index, and the commutation voltage and critical voltage of the DC system under any operating state are compared to obtain the second index.

3. The method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 2, characterized in that, The first indicator is obtained by comparing the protection measurement values ​​and setting values ​​of all branches of the AC system, specifically: ； In the formula, Indicates a branch L b of i Electrical distance on the side, Indicates a branch L b of i Side current protection setting value, Indicates a branch L b of i Side current protection measurement value, Indicates a branch L b of j Electrical distance on the side, Indicates a branch L b of j Side current protection setting value, Indicates a branch L b of j Side current protection measurement value, I b This indicates the primary indicator.

4. The method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 2, characterized in that, The second index is obtained by comparing the commutation voltage and the critical voltage under any operating state of the DC system, specifically: ； In the formula, U x This represents the commutation critical voltage. I d Indicates the current value of the DC system. X Indicates the commutation reactance on the inverter side. Indicates the minimum arc extinction angle. This indicates that a leading angle has been triggered. U This represents the effective value of the AC system voltage connected to the inverter side. U D This indicates the second indicator.

5. The method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 1, characterized in that, The comprehensive indicators for determining whether a cascading trip has occurred in an AC / DC hybrid power grid, based on the first and second indicators, include: The minimum value between the first and second indicators is selected as the comprehensive indicator for judging whether a cascading trip has occurred in the AC / DC hybrid power grid.

6. The method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 1, characterized in that, The calculation of branch network loss costs and the risk of non-faulty branch outages caused by power flow shifting after a faulty branch disconnects include: Calculate the power flow impact rate of the branch circuit due to cascading tripping; Calculate the risk value of non-faulty branch outage caused by power flow transfer after the faulty branch is disconnected based on the power flow impact rate. Obtain the node voltage magnitude, node voltage phase angle difference, branch resistance, and branch reactance for all branches; The branch network loss cost is calculated based on the node voltage amplitude, the node voltage phase angle difference, the branch resistance, and the branch reactance.

7. A method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 6, characterized in that, The branch network loss cost is calculated based on the node voltage amplitude, the node voltage phase angle difference, the branch resistance, and the branch reactance, specifically as follows: ； In the formula, C Indicates the cost of branch network losses. Indicates the price coefficient. This represents the set of all branches. U i , U j Representing nodes respectively i , j voltage amplitude, Represents a node i and j The voltage phase angle difference, where R represents the resistance of the branch. This indicates the reactance of the branch circuit.

8. A method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 6, characterized in that, The risk value of non-faulty branch outage caused by power flow transfer after faulty branch disconnection, calculated based on the power flow impact rate, includes: Obtain the load rate of non-faulty branches after a faulty branch triggers a cascading trip; Calculate the correlation index before and after the fault branch triggers a cascading trip based on the power flow impact rate and the load rate; The risk value of non-faulty branches being out of service due to power flow transfer after the faulty branch is disconnected is calculated based on the aforementioned correlation index.

9. A method for preventing cascading tripping in an AC / DC hybrid power grid according to claim 1, characterized in that, The constraints constructed based on the aforementioned comprehensive indicators include: Establish comprehensive indicator constraints based on comprehensive indicators; Establish active power injection constraints and reactive power injection constraints at nodes; Establish constraints on generator active power output, generator reactive power output, node voltage, and active power transmission through lines.

10. A cascading trip prevention system for an AC / DC hybrid power grid, 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 each step of the method for preventing cascading trips in an AC / DC hybrid power grid as described in any one of claims 1 to 9.

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