A DC current control method based on unbalanced power and node voltage in isolated grid

Abstract

This invention discloses a DC current control method based on unbalanced power and node voltage in an islanded grid, belonging to the field of power system control and optimization technology. The method includes adjusting the DC system current command value from 1.0 pu to the initial current command value based on the unbalanced power of the islanded grid after disconnection; identifying key nodes in the islanded grid subsystem after disconnection based on the reactive power-voltage coupling degree of the nodes; and performing real-time control of the DC system current command based on the voltage of the key nodes in the islanded grid after disconnection until it recovers to the steady-state value of 1.0 pu, while optimizing the stability of the islanded grid voltage. The method of this invention achieves accurate identification of key nodes by identifying them in the islanded grid subsystem after disconnection based on the reactive power-voltage coupling degree of the nodes, and achieves dynamic current control based on the real-time voltage state of the key nodes by performing real-time control of the DC system current command based on the voltage of the key nodes in the islanded grid after disconnection.

Description

Technical Field

[0001] This invention relates to the field of power system control and optimization technology, specifically to a DC current control method based on islanded grid unbalanced power and node voltage. Background Technology

[0002] Active disconnection is a crucial measure to ensure power system stability and avoid large-scale blackouts. The key lies in accurately selecting appropriate disconnection sections. However, current research and practical applications reveal significant limitations in traditional methods. Typically, the selection of disconnection sections aims to minimize the unbalanced power of the isolated grid after disconnection, seeking the optimal disconnection scheme through optimization algorithms. These methods are primarily based on AC power system analysis and overly rely on the active power regulation capabilities of traditional generators. However, with the widespread application of DC transmission technology and the rapid development of high-proportion renewable energy integration, the applicability of traditional methods is gradually declining. This is especially true in large, complex power grids containing DC transmission, where traditional methods fail to fully consider the dynamic characteristics of the DC system and its coupling effect with the isolated grid, making it difficult to meet practical needs.

[0003] The shortcomings of traditional islanding section optimization methods are specifically reflected in the following aspects: First, insufficient attention is paid to the characteristics of the DC system. For example, after islanding, the DC system needs to adjust the current command to adapt to the unbalanced power of the islanded grid, but this key process is not effectively included in the analysis in traditional models. Second, the limitations of islanding recovery strategies are obvious. Existing methods focus more on the active power balance of generators and loads, while ignoring the important role of the DC system in islanding voltage recovery. Especially in islanded grids with DC landing points, the coupling relationship between the DC system and reactive voltage may significantly affect system stability, but this characteristic has not been fully studied. Third, the identification of key nodes lacks systematization. Although nodes with strong reactive voltage coupling are crucial for islanding recovery, traditional methods mainly rely on experience and lack scientific mathematical analysis support. Finally, the lack of dynamic control capabilities makes traditional methods inadequate in dealing with complex scenarios. Static optimization strategies ignore the real-time changes in the islanded grid state after islanding, which can easily lead to low recovery efficiency and may even cause secondary instability.

[0004] In recent years, some studies have attempted to consider the impact of DC landing point in the optimization of disconnection sections, but most of them are limited to static analysis and have failed to explore the dynamic adjustment and recovery strategies of the DC system after disconnection. In addition, how to use the DC system to provide reactive power support during islanded grid recovery and how to perform dynamic control based on the unbalanced power and critical node voltage of the islanded grid are still technical problems that need to be solved. These problems limit the practical application of traditional methods, resulting in low efficiency in complex power grid scenarios and difficulty in meeting the needs of modern power systems. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the technical problem solved by this invention is that existing islanded grid recovery methods neglect the characteristics of DC systems, fail to identify key nodes, lack dynamic control capabilities, and address the issue of how to combine dynamic adjustment of DC systems to achieve islanded grid voltage and power balance.

[0007] To address the aforementioned technical problems, this invention provides the following technical solution: a DC current control method based on unbalanced power and node voltage in an isolated grid, comprising: adjusting the DC system current command value from 1.0 pu to the initial current command value according to the unbalanced power of the isolated grid after disconnection; identifying key nodes in the isolated grid subsystem after disconnection based on the reactive power-voltage coupling degree of the nodes; and controlling the DC system current command in real time according to the voltage of the key nodes in the isolated grid after disconnection until it recovers to the steady-state value of 1.0 pu, and optimizing the stability of the isolated grid voltage.

[0008] As a preferred embodiment of the DC current control method based on unbalanced power and node voltage of an isolated grid as described in this invention, the step of calculating the unbalanced power of the isolated grid after disconnection includes, when the DC feed-in node of the power system is actively disconnected, integrating it into the isolated grid subsystem where the generator active power output is less than the active load, and expressing it as:

[0009] ΔP G-L =P G -P L

[0010] Wherein, ΔP G-L P represents the initial unbalanced power of the isolated subsystem after disconnection. G For the active power output of the generator in the isolated network subsystem, P L This refers to the active load in the isolated network subsystem.

[0011] As a preferred embodiment of the DC current control method based on islanded grid unbalanced power and node voltage described in this invention, the step of adjusting the DC system current command value from 1.0 pu to the initial current command value includes calculating the initial current command value by using the ratio of the initial unbalanced power of the islanded subsystem after disconnection to the rated transmission power of the DC system, expressed as:

[0012]

[0013] Where I0 is the initial current command value, P N This refers to the rated transmission power of the DC system.

[0014] As a preferred embodiment of the DC current control method based on unbalanced power and node voltage in an isolated network as described in this invention, the step of basing the reactive power-voltage coupling degree on the nodes includes ranking the coupling degree of node voltages through inverse matrix analysis and establishing the power flow equations of the isolated network subsystem, expressed as:

[0015]

[0016] Where ΔP is the change in active power at the node, ΔQ is the change in reactive power at the node, Δθ is the change in the phase angle of the node voltage, ΔV is the change in the magnitude of the node voltage, and K and J are submatrices. K represents the coupling relationship between the change in active power at the node ΔP and the change in the phase angle of the node voltage Δθ, and J represents the coupling relationship between the change in reactive power at the node ΔQ and the change in the magnitude of the node voltage ΔV. The submatrices K and J are calculated as follows:

[0017]

[0018] Among them, K ij J represents the coupling relationship between the active power and voltage phase angle at nodes i and j. pq V represents the coupling relationship between reactive power and voltage amplitude at nodes p and q. i and V p Let V be the voltage at node i and node p. j and V q Let B be the voltage at node j and node q. ij and B pq Let be the imaginary part of the node impedance matrix, h be the total number of nodes, and o be the number of load nodes. Combining the relationship between islanded network node voltage and reactive power, the reactive power of the DC-connected nodes is corrected, and the DC feed-in node k is included in the DC system injection power. The elements in the k-th row and k-th column of submatrix J are then corrected, as follows:

[0019]

[0020] Among them, Q k The reactive power injected into node k, V k J is the voltage at node k. kk Let J' be the element in the k-th row and k-th column of submatrix J. kk Let H be the element in the k-th row and k-th column of the corrected submatrix H; according to the converter equations of the DC system, calculate the partial derivative of the injected reactive power with respect to the node voltage, expressed as:

[0021]

[0022] Where N is the number of converter bridges, T is the transformer turns ratio of the DC converter, and X cγ is the commutation reactance, β is the turn-off angle, and β is the trigger lead angle.

[0023] As a preferred embodiment of the DC current control method based on unbalanced power and node voltage in an isolated network as described in this invention, the identification of key nodes in the isolated network subsystem after disconnection includes calculating the inverse matrix of submatrix J, and outputting the coupling degree of node reactive power to the voltage of other nodes, expressed as:

[0024] ΔV=J -1 ΔQ

[0025] Among them, J -1 The inverse matrix of submatrix J; read J from the inverse matrix. -1 The element in row i and column k represents the degree of reactive voltage coupling between node i and DC landing point k. The reactive voltage coupling degree between each node of the isolated network and the DC landing point is sorted from high to low according to the coupling strength, and the nodes in the top 50% are designated as critical nodes.

[0026] As a preferred embodiment of the DC current control method based on unbalanced power and node voltage in an isolated network as described in this invention, the step of calculating the input voltage for DC system current command control based on the critical node voltage after disconnection includes real-time monitoring of the critical node voltage, reading the critical node voltage after disconnection, and calculating the input voltage for DC system current command control by using the minimum value between the critical node voltage and the DC landing point voltage, expressed as:

[0027] V in =min(V1,V2...,V k ,...,V m )

[0028] Among them, V in The input voltage for DC system current command control is given by V, where m is the number of critical nodes. k Let be the voltage of the kth critical node.

[0029] As a preferred embodiment of the DC current control method based on unbalanced power and node voltage in an isolated grid as described in this invention, the real-time control of the DC system current command until it recovers to the steady-state value of 1.0 pu includes controlling the input voltage based on the DC system current command and dynamically adjusting the DC current command value, expressed as:

[0030]

[0031] Among them, I out This is the per-unit value of the current command currently output by the DC system; when V in ≥0.9 indicates a high input voltage, the system has reached a steady state, and the current command directly reverts to the 1.0 pu per-unit value; when 0.5... <V inA value <0.9 indicates that the input voltage is in an intermediate state, and the system needs to adjust the current command via linear interpolation to gradually restore it to a steady-state value; when V in ≤0.5 indicates that the input voltage is low and the system is in an unstable state. The current command will maintain the initial current command value.

[0032] Another objective of this invention is to provide a DC current control system based on unbalanced power and node voltage in an isolated grid. This system can control the DC system current command in real time according to the critical node voltage of the isolated grid after disconnection, until it is restored to the steady-state value of 1.0 pu, and optimize the stability of the isolated grid voltage. This solves the problem that current isolated grid recovery technologies lack dynamic control capabilities.

[0033] As a preferred embodiment of the DC current control system based on unbalanced power and node voltage in an isolated grid according to the present invention, it includes: a DC current initial adjustment module, a key node identification and analysis module, and a DC current real-time control module; the DC current initial adjustment module is used to adjust the DC system current command value from 1.0 pu to the initial current command value according to the unbalanced power of the isolated grid after disconnection; the key node identification and analysis module is used to identify key nodes in the isolated grid subsystem after disconnection based on the reactive power voltage coupling degree of the nodes; the DC current real-time control module is used to control the DC system current command in real time according to the key node voltage of the isolated grid after disconnection until it recovers to the steady-state value of 1.0 pu, and optimize the stability of the isolated grid voltage.

[0034] A computer device includes a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement a DC current control method based on islanded unbalanced power and node voltage.

[0035] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a DC current control method based on unbalanced power and node voltage in an isolated grid.

[0036] The beneficial effects of this invention are as follows: The DC current control method based on islanded grid unbalanced power and node voltage provided by this invention adjusts the DC system current command value from 1.0 pu to the initial current command value according to the unbalanced power of the islanded grid after disconnection, thereby analyzing the unbalanced power of the islanded grid after disconnection. This organically combines the unbalanced power of the islanded grid with DC current regulation, effectively avoiding excessive voltage or power fluctuations caused by maintaining a fixed current command, and improving the dynamic adaptability of the system. By identifying key nodes in the islanded grid subsystem after disconnection based on the degree of reactive power-voltage coupling at nodes, the complex voltage coupling relationship of the islanded grid is accurately quantified through a mathematical model. This invention achieves accurate identification of critical nodes, avoiding blind resource allocation. By controlling the DC system current command in real time based on the voltage of critical nodes after the islanded network is disconnected, it realizes dynamic current control based on the real-time voltage status of critical nodes, prioritizing the protection of the weakest nodes. It provides a segmented adjustment mechanism under different voltage conditions, ensuring rapid response under high voltage conditions while also taking into account system stability under low voltage conditions. This further enhances the system's adaptability to complex islanded network scenarios and avoids secondary instability problems that may be caused by traditional methods. This invention achieves better results in terms of adaptability, accuracy, and reliability. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 The first embodiment of the present invention provides an overall flowchart of a DC current control method based on unbalanced power and node voltage in an isolated grid.

[0039] Figure 2 This is a schematic diagram of a DC current control system based on unbalanced power and node voltage in an isolated grid, provided as a third embodiment of the present invention. Detailed Implementation

[0040] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0041] Example 1, referring to Figure 1As an embodiment of the present invention, a DC current control method based on islanded grid unbalanced power and node voltage is provided, comprising:

[0042] S1: Based on the unbalanced power of the isolated grid after disconnection, adjust the DC system current command value from 1.0pu to the initial current command value.

[0043] Furthermore, based on the unbalanced power of the isolated grid after disconnection, including the unbalanced power of the DC-feeding power system when the DC feed-in node is actively disconnected, regardless of whether the optimization objective is to minimize the unbalanced power or the power flow impact, the DC feed-in node is incorporated into the isolated grid subsystem where the generator active power output is less than the active power load. The initial unbalanced power of the isolated grid subsystem after disconnection is calculated and expressed as:

[0044] ΔP G-L =P G -P L

[0045] Wherein, ΔP G-L P represents the initial unbalanced power of the isolated subsystem after disconnection. G For the active power output of the generator in the isolated network subsystem, P L This refers to the active load in the isolated network subsystem.

[0046] It should be noted that adjusting the DC system current command value from 1.0 pu to the initial current command value includes the ratio of the initial unbalanced power of the islanded subsystem after de-arraying to the rated transmission power of the DC system. The initial current command value is calculated and expressed as:

[0047]

[0048] Where I0 is the initial current command value, P N This refers to the rated transmission power of the DC system.

[0049] It should also be noted that by calculating the initial unbalanced power after the islanded grid is disconnected, the DC system current command value is adjusted from 1.0 pu to an initial value that is more suitable for the current state of the islanded grid. This process not only shortens the response time of the islanded grid recovery, but also reduces the risk of power oscillation caused by directly restoring to the steady-state value. In traditional methods, the correlation between the islanded grid unbalanced power and the characteristics of the DC system is not adjusted, which can easily lead to instability in the initial recovery process. This invention defines the initial current command value through a proportional relationship, thereby achieving rapid adaptation and dynamic adjustment.

[0050] S2: Based on the degree of reactive voltage coupling at nodes, identify key nodes in the isolated subsystem after disconnection.

[0051] Furthermore, based on the degree of reactive power-voltage coupling at nodes, including ranking the coupling degree of node voltages through inverse matrix analysis, the power flow equations of the islanded subsystem are established, expressed as:

[0052]

[0053] Where ΔP is the change in active power at the node, ΔQ is the change in reactive power at the node, Δθ is the change in the phase angle of the node voltage, ΔV is the change in the magnitude of the node voltage, and K and J are submatrices. K represents the coupling relationship between the change in active power at the node ΔP and the change in the phase angle of the node voltage Δθ, and J represents the coupling relationship between the change in reactive power at the node ΔQ and the change in the magnitude of the node voltage ΔV. The submatrices K and J are calculated as follows:

[0054]

[0055] Among them, K ij J represents the coupling relationship between the active power and voltage phase angle at nodes i and j. pq V represents the coupling relationship between reactive power and voltage amplitude at nodes p and q. i and V p Let V be the voltage at node i and node p. j and V q Let B be the voltage at node j and node q. ij and B pq Let be the imaginary part of the node impedance matrix, h be the total number of nodes, and o be the number of load nodes. Combining the relationship between islanded network node voltage and reactive power, the reactive power of the DC-connected nodes is corrected, and the DC feed-in node k is included in the DC system injection power. The elements in the k-th row and k-th column of submatrix J are then corrected, as follows:

[0056]

[0057] Among them, Q k The reactive power injected into node k, V k J is the voltage at node k. kk Let J' be the element in the k-th row and k-th column of submatrix J. kk Let J be the element in the k-th row and k-th column of the corrected submatrix J; according to the converter equations of the DC system, calculate the partial derivative of the injected reactive power with respect to the node voltage, expressed as:

[0058]

[0059] Where N is the number of converter bridges, T is the transformer turns ratio of the DC converter, and X c γ is the commutation reactance, β is the turn-off angle, and β is the trigger lead angle.

[0060] It should be noted that identifying the key nodes in the de-arrayed islanded subsystem includes calculating the inverse matrix of submatrix J, and outputting the degree of coupling between the reactive power of the output nodes and the voltage of other nodes, expressed as:

[0061] ΔV=J -1 ΔQ

[0062] Among them, J -1 The inverse matrix of submatrix J; read J from the inverse matrix. -1 The element in the i-th row and k-th column represents the degree of reactive voltage coupling between node i and DC landing point k. The larger the value, the higher the degree of reactive voltage coupling. The degree of reactive voltage coupling between each node of the isolated network and the DC landing point is sorted from high to low according to the coupling strength, and the nodes in the top 50% are regarded as key nodes.

[0063] It should also be noted that, based on the degree of reactive power-voltage coupling at nodes and combined with the inverse matrix calculation of the power flow equation, key nodes are dynamically sorted to ensure priority restoration of nodes that have the greatest impact on the islanded grid voltage. Existing technologies lack mathematical analysis methods to accurately identify key nodes and rely on empirical judgment. This invention quantifies and optimizes the identification of key nodes through the inverse matrix calculation of submatrix J, effectively enhancing the scientificity and accuracy of islanded grid restoration.

[0064] S3: Based on the critical node voltage of the isolated grid after disconnection, the DC system current command is controlled in real time until it recovers to the steady-state value of 1.0pu, and the stability of the isolated grid voltage is optimized.

[0065] Furthermore, based on the critical node voltages of the isolated network after disconnection, including real-time monitoring of critical node voltages, and by reading the critical node voltages of the isolated network after disconnection, the input voltage for DC system current command control is calculated using the minimum value between the critical node voltage and the DC landing point voltage, expressed as:

[0066] V in =min(V1,V2...,V k ,...,V m )

[0067] Among them, V in The input voltage for DC system current command control is given by V, where m is the number of critical nodes. k Let be the voltage of the kth critical node.

[0068] It should be noted that real-time control of the DC system current command until it recovers to the steady-state value of 1.0 pu includes the input voltage controlled based on the DC system current command, and the dynamic adjustment of the DC current command value, expressed as:

[0069]

[0070] Among them, Iout This is the per-unit value of the current command currently output by the DC system; when V in ≥0.9 indicates a high input voltage, the system has reached a steady state, and the current command directly reverts to the 1.0 pu per-unit value; when 0.5... <V in A value <0.9 indicates that the input voltage is in an intermediate state, and the system needs to adjust the current command via linear interpolation to gradually restore it to a steady-state value; when V in ≤0.5 indicates that the input voltage is low and the system is in an unstable state. The current command maintains the initial current command value to avoid further affecting the stability of the islanded network.

[0071] It should also be noted that by monitoring the voltage of key nodes in real time and combining it with the state of the input voltage, the current command value is dynamically adjusted through a piecewise function to ensure the speed and stability of islanded network recovery. Traditional static recovery strategies are inefficient and have poor adaptability. The dynamic adjustment logic of this invention takes into account both rapid recovery under high voltage conditions and stability under low voltage conditions, thereby improving the adjustment efficiency of the current command.

[0072] Example 2 is an embodiment of the present invention, which provides a DC current control method based on unbalanced power and node voltage in an isolated network. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0073] This experiment takes an isolated grid containing a DC transmission system as the research object, simulates the recovery process after the isolated grid is disconnected, and verifies the advantages of the invented method in dynamically adjusting DC current commands, identifying key nodes, and optimizing grid stability. The experiment designs two scenarios for comparison: Scenario 1 adopts the traditional isolated grid recovery strategy, and Scenario 2 implements a dynamic adjustment and optimization strategy based on the content of this invention. The initial conditions are set as follows: the unbalanced power of the isolated grid system is 50MW, the initial voltage deviation of the key node is 0.20pu, and the key test parameters include the adjustment of the initial current command value, the recovery level of the key node voltage, and the final stable voltage of the system.

[0074] Experimental Implementation Process

[0075] 1. Initial conditions: After the islanded grid system is disconnected, the generator's active power output is 50MW and the load demand is 100MW, resulting in an initial unbalanced power of 50MW. Record the maximum and minimum values ​​of the initial critical node voltage and observe the DC current adjustment response of the traditional and the present invention methods.

[0076] 2. Traditional method test: Based on the static optimization model, the DC current command value is adjusted to adapt to the unbalanced power of the islanded grid, but no dynamic adjustment or key node identification is performed. The voltage changes of key nodes during the recovery process and the final stable voltage of the system are recorded.

[0077] 3. Testing the method of this invention: The DC current command value is dynamically adjusted according to the invention, gradually recovering from the initial value to 1.0 pu. Combined with real-time monitoring of the critical node voltage, the current is optimized in multiple stages. The minimum value between the critical node voltage and the DC landing point voltage of the islanded network after disconnection is calculated, and the current command is dynamically adjusted until the system reaches stability.

[0078] 4. Data recording: Compare the performance of the two methods in terms of adjusted current command value, critical node voltage recovery level, and system voltage stability.

[0079] Refer to Table 1 for comparative analysis of the experimental data.

[0080] Table 1 Experimental Data Recording Table

[0081]

[0082]

[0083] The following conclusions can be drawn from the analysis of the experimental data in Table 1:

[0084] 1. Improved DC current regulation efficiency

[0085] The current command value adjusted by the method of this invention is 0.85 pu, while the traditional method only reaches 0.75 pu, which is an improvement of 13.33%. This shows that the method of this invention can better adapt to the dynamic requirements of the isolated network after disconnection, making the DC current adjustment process more efficient and stable.

[0086] 2. Improved voltage recovery at critical nodes

[0087] Under traditional methods, the maximum voltage recovery value of critical nodes is 0.95 pu and the minimum voltage is 0.80 pu, while the method of this invention achieves 0.98 pu and 0.85 pu, respectively, representing improvements of 3.16% and 6.25%. This result indicates that the method of this invention can more effectively identify critical nodes and optimize their voltage levels, reducing the voltage fluctuation amplitude between nodes.

[0088] 3. Enhanced overall power grid stability

[0089] The method of this invention achieved a final system voltage stability of 0.95 pu, which is 5.56% higher than the 0.90 pu of the traditional method. This shows that the method based on the content of this invention can more efficiently improve system stability during islanded network recovery and avoid the secondary instability problem in the traditional method.

[0090] In summary, compared with traditional methods, this invention overcomes the limitations of static optimization strategies in traditional methods by introducing dynamic adjustment of DC current commands and a critical node identification mechanism. Experiments show that the method of this invention has achieved significant improvements in DC current adjustment efficiency, critical node voltage recovery level, and overall grid stability. This strategy, which combines real-time dynamic adjustment and mathematical optimization analysis, has high innovation and practical value in engineering applications and contributes to the development of islanded grid restoration technology in modern power systems.

[0091] Example 3, referring to Figure 2 As an embodiment of the present invention, a DC current control system based on unbalanced power and node voltage in an isolated grid is provided, including a DC current initial adjustment module, a key node identification and analysis module, and a DC current real-time control module.

[0092] The DC current initial adjustment module is used to adjust the DC system current command value from 1.0 pu to the initial current command value based on the unbalanced power of the islanded grid after disconnection; the key node identification and analysis module is used to identify key nodes in the islanded grid subsystem after disconnection based on the reactive power voltage coupling degree of the nodes; the DC current real-time control module is used to control the DC system current command in real time based on the voltage of the key nodes of the islanded grid after disconnection until it is restored to the steady-state value of 1.0 pu, and optimize the stability of the islanded grid voltage.

[0093] If a function is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0094] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0095] More specific examples (a non-exhaustive list) of computer-readable media include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which programs can be printed, because programs can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0096] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc. It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

[0097] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A DC current control method based on unbalanced power and node voltage in an isolated network, characterized in that, include: Based on the unbalanced power of the isolated grid after disconnection, the DC system current command value is adjusted from 1.0 pu to the initial current command value; Based on the degree of reactive voltage coupling at nodes, key nodes in the isolated subsystem after disconnection are identified. Based on the critical node voltage of the isolated grid after disconnection, the DC system current command is controlled in real time until it recovers to the steady-state value of 1.0 pu, and the stability of the isolated grid voltage is optimized. The real-time control of the DC system current command until it recovers to the steady-state value of 1.0pu includes dynamically adjusting the DC current command value based on the input voltage controlled by the DC system current command, as expressed as: Where I0 is the initial current command value, I out This represents the per-unit value of the current command currently output by the DC system. When V in ≥0.9 indicates that the input voltage is high and the system has reached a steady state. The current command is directly restored to the 1.0 pu per unit value. When 0.5 <V in <0.9 indicates that the input voltage is in an intermediate state, and the system needs to adjust the current command by linear interpolation to gradually restore it to the steady-state value; When V in ≤0.5 indicates that the input voltage is low and the system is in an unstable state. The current command will maintain the initial current command value.

2. The DC current control method based on islanded grid unbalanced power and node voltage as described in claim 1, characterized in that: The unbalanced power of the isolated grid after disconnection includes the calculation of the initial unbalanced power of the isolated grid subsystem after disconnection when the DC feed-in power system actively disconnects the section, integrating the DC feed-in node into the isolated grid subsystem where the generator active power output is less than the active power load. This is expressed as: ΔP G-L =P G -P L Wherein, ΔP G-L P represents the initial unbalanced power of the isolated subsystem after disconnection. G For the active power output of the generator in the isolated network subsystem, P L This refers to the active load in the isolated network subsystem.

3. The DC current control method based on islanded grid unbalanced power and node voltage as described in claim 2, characterized in that: The adjustment of the DC system current command value from 1.0 pu to the initial current command value includes calculating the initial current command value by using the ratio of the initial unbalanced power of the isolated subsystem to the rated transmission power of the DC system, expressed as: Among them, P N This refers to the rated transmission power of the DC system.

4. The DC current control method based on islanded grid unbalanced power and node voltage as described in claim 3, characterized in that: The method based on the reactive power-voltage coupling degree at nodes includes ranking the coupling degree of node voltages through inverse matrix analysis, establishing the power flow equations of the islanded subsystem, expressed as: Wherein, ΔP is the change in active power at the node, ΔQ is the change in reactive power at the node, Δθ is the change in the phase angle of the node voltage, ΔV is the change in the magnitude of the node voltage, K and J are submatrices, K is the coupling relationship between the change in active power at the node ΔP and the change in the phase angle of the node voltage Δθ, and J is the coupling relationship between the change in reactive power at the node ΔQ and the change in the magnitude of the node voltage ΔV. Calculate submatrices K and J, represented as: Among them, K ij J represents the coupling relationship between the active power and voltage phase angle at nodes i and j. pq V represents the coupling relationship between reactive power and voltage amplitude at nodes p and q. i and V p Let V be the voltage at node i and node p. j and V q Let B be the voltage at node j and node q. ij and B pq is the imaginary part of the nodal impedance matrix, h is the total number of nodes, and o is the number of load nodes; Based on the relationship between islanded network node voltage and reactive power, the reactive power of the DC landing node is corrected, and the DC feed-in node k is included in the DC system injection power. The elements of the k-th row and k-th column of submatrix J are corrected, as follows: Among them, Q k The reactive power injected into node k, V k J is the voltage at node k. kk Let J' be the element in the k-th row and k-th column of submatrix J. kk Let J be the element in the k-th row and k-th column of the corrected submatrix J; Based on the converter equations of the DC system, the partial derivative of the injected reactive power with respect to the node voltage is calculated and expressed as: Where N is the number of converter bridges, T is the transformer turns ratio of the DC converter, and X c γ is the commutation reactance, β is the turn-off angle, and β is the trigger lead angle.

5. The DC current control method based on islanded grid unbalanced power and node voltage as described in claim 4, characterized in that: The identification of key nodes in the isolated network subsystem after de-segmentation includes calculating the inverse matrix of submatrix J, and outputting the degree of coupling between the reactive power of the output node and the voltage of other nodes, expressed as: ΔV=J -1 ΔQ Among them, J -1 Let J be the inverse matrix of submatrix J; Read J from the inverse matrix -1 The element in row i and column k represents the degree of reactive voltage coupling between node i and DC landing point k. The reactive voltage coupling degree between each node of the isolated network and the DC landing point is sorted from high to low according to the coupling strength, and the nodes in the top 50% are designated as critical nodes.

6. The DC current control method based on islanded grid unbalanced power and node voltage as described in claim 5, characterized in that: The process of calculating the input voltage for DC system current command control based on the critical node voltage after disconnection includes real-time monitoring of the critical node voltage, reading the critical node voltage after disconnection, and using the minimum value between the critical node voltage and the DC landing point voltage. This is expressed as: V in =min(V1,V2...,V k ,...,V m ) Among them, V in The input voltage for DC system current command control is given by V, where m is the number of critical nodes. k Let be the voltage of the kth critical node.

7. A system employing the DC current control method based on islanded unbalanced power and node voltage as described in any one of claims 1 to 6, characterized in that: Includes a DC current initial adjustment module, a key node identification and analysis module, and a DC current real-time control module; The DC current initial adjustment module is used to adjust the DC system current command value from 1.0 pu to the initial current command value according to the unbalanced power of the islanded grid after disconnection. The critical node identification and analysis module is used to identify critical nodes in the isolated subsystem after disconnection based on the degree of reactive voltage coupling of nodes. The DC current real-time control module is used to control the DC system current command in real time according to the critical node voltage of the isolated grid after disconnection, until it recovers to the steady-state value of 1.0 pu, and optimizes the stability of the isolated grid voltage.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the DC current control method based on unbalanced power and node voltage as described in any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the DC current control method based on unbalanced power and node voltage of any one of claims 1 to 6.

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