Direct current control method based on isolated network unbalanced power and node voltage

Abstract

The invention discloses a direct current control method based on the unbalanced power and node voltage of an isolated network, and relates to the technical field of power system control and optimization, and the method comprises the steps: adjusting a current instruction value of a direct current system from 1.0 pu to an initial current instruction value according to the unbalanced power of the isolated network after splitting; based on the node reactive voltage coupling degree, key nodes in the isolated network subsystem after splitting are identified; and according to the key node voltage of the separated isolated network, performing real-time control on the current instruction of the direct-current system until a steady-state value 1.0 pu is recovered, and optimizing the voltage stability of the isolated network. According to the method, based on the node reactive voltage coupling degree, the key nodes in the isolated network subsystem after splitting are recognized, accurate recognition of the key nodes is achieved, the current instruction of the direct current system is controlled in real time according to the voltage of the key nodes of the isolated network after splitting, and the reliability of the system is improved. And current dynamic control based on the real-time voltage state of the key node is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power system control and optimization, and in particular to a direct current control method based on unbalanced power of an isolated grid and node voltage. Background Art

[0002] Active disconnection is an important measure to ensure the stability of the power system and avoid large-scale power outages. The key lies in accurately selecting the appropriate disconnection section. However, in current research and practical applications, traditional methods have obvious limitations. Usually, the selection of the disconnection section aims to minimize the unbalanced power of the isolated network after disconnection, and the optimal disconnection solution is sought through optimization algorithms. These methods are mainly based on the analysis of AC power systems and overly rely on the active regulation capabilities of traditional generators. However, with the widespread application of DC transmission technology and the rapid development of a high proportion of new energy access, the applicability of traditional methods is gradually declining, especially in large and complex power grids with DC transmission. Traditional methods fail to fully consider the dynamic characteristics of the DC system and its coupling with the isolated network, and it is difficult to meet actual needs.

[0003] The shortcomings of traditional disconnection 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 disconnection, the DC system needs to adjust the current command to adapt to the unbalanced power of the isolated grid, but this key process has not been effectively included in the analysis in the traditional model. Second, the limitations of the isolated grid recovery strategy are obvious. The existing methods focus more on the active power balance of generators and loads, but ignore the important role of the DC system in the voltage recovery of the isolated grid. Especially in the isolated grid with DC drop points, the coupling relationship between the DC system and the reactive voltage may significantly affect the 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 to the recovery of the isolated grid, traditional methods mainly rely on experience and lack scientific mathematical analysis support. Finally, the lack of dynamic control capabilities makes the traditional method inadequate in dealing with complex scenarios. The static optimization strategy ignores the real-time changes in the state of the isolated grid after disconnection, 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 influence of DC drop points in the optimization of disconnection sections, but most of them are limited to static analysis and have failed to deeply 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 the restoration of the isolated grid, and how to dynamically control the unbalanced power and key node voltages of the isolated grid are still technical problems that need to be solved urgently. These problems limit the practical application capabilities of traditional methods, resulting in their 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 the present invention is: the existing isolated grid recovery method ignores the characteristics of the DC system, insufficiently identifies key nodes, lacks dynamic control capabilities, and how to combine the dynamic adjustment of the DC system to achieve the voltage and power balance of the isolated grid.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: a DC current control method based on unbalanced power and node voltage of an isolated network, comprising adjusting the DC system current command value from 1.0pu to the initial current command value according to the unbalanced power of the isolated network after decoupling; identifying the key nodes in the isolated network subsystem after decoupling based on the degree of node reactive voltage coupling; and controlling the DC system current command in real time according to the key node voltage of the isolated network after decoupling until it recovers to the steady-state value of 1.0pu, and optimizing the voltage stability of the isolated network.

[0008] As a preferred solution of the DC current control method based on unbalanced power and node voltage of an isolated network according to the present invention, the unbalanced power of the isolated network after decoupling includes incorporating the DC system feeding node into the isolated network subsystem where the active output of the generator is less than the active load when the DC feed-in power system is in the active decoupling section, and calculating the initial unbalanced power of the isolated network subsystem after decoupling, which is expressed as:

[0009] ΔP G-L =P G -P L

[0010] Where ΔP G-L is the initial unbalanced power of the isolated grid subsystem after decoupling, P G is the active power output of the generator in the isolated grid subsystem, P L It is the active load in the isolated grid subsystem.

[0011] As a preferred solution of the DC current control method based on unbalanced power and node voltage of isolated grid according to the present invention, wherein: the DC system current command value is adjusted from 1.0pu to the initial current command value, including calculating the initial current command value by the ratio of the initial unbalanced power of the isolated grid subsystem after decoupling to the rated transmission power of the DC system, which is expressed as:

[0012]

[0013] Among them, I0 is the initial current command value, P N is the rated transmission power of the DC system.

[0014] As a preferred solution of the DC current control method based on unbalanced power and node voltage of isolated grid according to the present invention, the coupling degree of node reactive voltage is based on the node reactive voltage, and the coupling degree is sorted by analyzing the node voltage through an inverse matrix, and the power flow equation of the isolated grid subsystem is established, which is expressed as:

[0015]

[0016] Among them, ΔP is the change of node active power, ΔQ is the change of node reactive power, Δθ is the change of node voltage phase angle, ΔV is the change of node voltage amplitude, K and J are sub-matrices, K is the coupling relationship between the change of node active power ΔP and the change of node voltage phase angle Δθ, J is the coupling relationship between the change of node reactive power ΔQ and the change of node voltage amplitude ΔV; calculate sub-matrices K and J, expressed as:

[0017]

[0018] Among them, K ij is the coupling relationship between the active power and voltage phase angle of node i and node j, J ij is the coupling relationship between the reactive power and voltage amplitude of nodes i and j, V i is the voltage at node i, V j is the voltage of node j, B is the imaginary part of the node impedance matrix, h is the total number of nodes, and o is the number of load nodes; combined with the relationship between the voltage and reactive power of the isolated grid node, the reactive power of the DC drop point node is corrected, the DC feed-in node k is included in the DC system injection power, and the elements of the kth row and kth column of the submatrix J are corrected, which is expressed as:

[0019]

[0020] Among them, Q k is the reactive power injected into node k, V k is the voltage at node k, J kk is the k-th row and k-th column element of submatrix J, J' kk is the k-th row and k-th column element of the modified submatrix J; according to the converter equation of the DC system, the partial derivative of the injected reactive power with respect to the node voltage is calculated, which is expressed as:

[0021]

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

[0023] As a preferred solution of the DC current control method based on unbalanced power and node voltage of isolated grid according to the present invention, the identification of key nodes in the isolated grid subsystem after decoupling includes calculating the inverse matrix of the submatrix J, and the coupling degree of the reactive power of the output node to the voltage of other nodes is expressed as:

[0024] ΔV=J -1 ΔQ

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

[0026] As a preferred solution of the DC current control method based on unbalanced power and node voltage of isolated grid according to the present invention, the key node voltage of the isolated grid after decoupling includes real-time monitoring of the key node voltage, reading the key node voltage of the isolated grid after decoupling, and calculating the input voltage of the DC system current command control through the minimum value of the key node voltage and the DC drop voltage, which is expressed as:

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

[0028] Among them, V in is the input voltage of the DC system current command control, m is the number of key nodes, V k is the voltage of the kth key node.

[0029] As a preferred solution of the DC current control method based on unbalanced power and node voltage of isolated grid according to the present invention, the real-time control of the DC system current command until it is restored 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, which is expressed as:

[0030]

[0031] Among them, I out is the per unit value of the current command output by the DC system; when V in ≥0.9, indicating that the input voltage is high, the system has tended to a steady state, and the current command is directly restored to the 1.0pu standard value; when 0.5 <V in <0.9, indicating that the input voltage is in the middle state, the system needs to adjust the current command by linear interpolation and gradually restore to the steady-state value; when Vin ≤0.5, indicating that the input voltage is low, the system is in an unstable state, and the current command maintains the initial current command value.

[0032] Another object of the present invention is to provide a DC current control system based on unbalanced power and node voltage of an isolated network, which can perform real-time control of the DC system current command according to the key node voltage of the isolated network after decoupling until it is restored to a steady-state value of 1.0pu, and optimize the voltage stability of the isolated network, thereby solving the problem of the lack of dynamic control capability in the current isolated network recovery technology.

[0033] As a preferred solution of the DC current control system based on unbalanced power and node voltage of the isolated network described in 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 1.0pu to the initial current command value according to the unbalanced power of the isolated network after decoupling; the key node identification and analysis module is used to identify the key nodes in the isolated network subsystem after decoupling based on the node reactive voltage coupling degree; 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 network after decoupling until it recovers to the steady-state value of 1.0pu, and optimize the voltage stability of the isolated network.

[0034] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of a direct current control method based on unbalanced power of an isolated grid and node voltage.

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

[0036] Beneficial effects of the present invention: The DC current control method based on unbalanced power of isolated grid and node voltage provided by the present invention adjusts the DC system current command value from 1.0pu to the initial current command value according to the unbalanced power of the isolated grid after decoupling, thereby realizing the analysis of the unbalanced power of the isolated grid after decoupling, organically combining the unbalanced power of the isolated grid with the 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 the key nodes in the isolated grid subsystem after decoupling based on the node reactive voltage coupling degree, the complex voltage coupling relationship of the isolated grid is accurately quantified through a mathematical model. Accurate identification of key nodes is achieved, and blind resource allocation is avoided. By controlling the DC system current command in real time according to the key node voltage of the isolated network after decoupling, dynamic current control based on the real-time voltage state of the key nodes is achieved, and the nodes with the weakest voltage are protected first. A segmented adjustment mechanism under different voltage states is provided, which not only ensures a rapid response under high voltage states, but also takes into account the system stability under low voltage states, further enhances the system's adaptability to complex isolated network scenarios, and avoids the secondary instability problem that may be caused by traditional methods. The present invention achieves better results in terms of adaptability, accuracy and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

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

[0039] Figure 2 A module schematic diagram of a DC current control system based on unbalanced power and node voltage in an isolated grid provided by the third embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0041] Example 1, reference Figure 1, is an embodiment of the present invention, and provides a DC current control method based on unbalanced power and node voltage of an isolated grid, comprising:

[0042] S1: According to the unbalanced power of the isolated grid after decoupling, the DC system current command value is adjusted from 1.0pu to the initial current command value.

[0043] Furthermore, according to the unbalanced power of the isolated grid after decoupling, including the active decoupling section when the DC feed-in power system is in place, regardless of whether the optimization goal is the minimum unbalanced power or the minimum power flow impact, the DC system feed-in node is included in the isolated grid subsystem where the active output of the generator is less than the active load, and the initial unbalanced power of the isolated grid subsystem after decoupling is calculated, which is expressed as:

[0044] ΔP G-L =P G -P L

[0045] Where ΔP G-L is the initial unbalanced power of the isolated grid subsystem after decoupling, P G is the active power output of the generator in the isolated grid subsystem, P L It is the active load in the isolated grid subsystem.

[0046] It should be noted that adjusting the DC system current command value from 1.0pu to the initial current command value includes calculating the initial current command value by the ratio of the initial unbalanced power of the isolated grid subsystem after decoupling to the rated transmission power of the DC system, which is expressed as:

[0047]

[0048] Among them, I0 is the initial current command value, P N is the rated transmission power of the DC system.

[0049] It should also be noted that by calculating the initial unbalanced power after the isolated grid is disconnected, the current command value of the DC system is adjusted from 1.0pu to an initial value that is more suitable for the current state of the isolated grid. This process not only shortens the response time of the isolated grid recovery, but also reduces the risk of power oscillation caused by directly recovering to the steady-state value. In the traditional method, the correlation between the unbalanced power of the isolated grid and the characteristics of the DC system is not adjusted, which easily leads to instability in the initial recovery process. The present 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 node reactive voltage coupling, identify the key nodes in the isolated grid subsystem after decoupling.

[0051] Furthermore, based on the node reactive voltage coupling degree, the node voltage is sorted by the inverse matrix analysis to establish the power flow equation of the isolated grid subsystem, which is expressed as:

[0052]

[0053] Among them, ΔP is the change of node active power, ΔQ is the change of node reactive power, Δθ is the change of node voltage phase angle, ΔV is the change of node voltage amplitude, K and J are sub-matrices, K is the coupling relationship between the change of node active power ΔP and the change of node voltage phase angle Δθ, J is the coupling relationship between the change of node reactive power ΔQ and the change of node voltage amplitude ΔV; calculate sub-matrices K and J, expressed as:

[0054]

[0055] Among them, K ij is the coupling relationship between the active power and voltage phase angle of node i and node j, J ij is the coupling relationship between the reactive power and voltage amplitude of nodes i and j, V i is the voltage at node i, V j is the voltage of node j, B is the imaginary part of the node impedance matrix, h is the total number of nodes, and o is the number of load nodes; combined with the relationship between the voltage and reactive power of the isolated grid node, the reactive power of the DC drop point node is corrected, the DC feed-in node k is included in the DC system injection power, and the elements of the kth row and kth column of the submatrix J are corrected, which is expressed as:

[0056]

[0057] Among them, Q k is the reactive power injected into node k, V k is the voltage at node k, J kk is the k-th row and k-th column element of submatrix J, J' kk is the k-th row and k-th column element of the modified submatrix J; according to the converter equation of the DC system, the partial derivative of the injected reactive power with respect to the node voltage is calculated, which is expressed as:

[0058]

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

[0060] It should be noted that identifying the key nodes in the isolated grid subsystem after decoupling includes calculating the inverse matrix of the submatrix J, and the coupling degree of the reactive power of the output node to the voltage of other nodes, which is expressed as:

[0061] ΔV=J -1 ΔQ

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

[0063] It should also be noted that based on the degree of reactive voltage coupling of the nodes and combined with the inverse matrix calculation of the power flow equation, the key nodes are dynamically sorted to ensure that the nodes with the greatest impact on the isolated grid voltage are restored first. The prior art lacks mathematical analysis methods to accurately identify the key nodes and relies on empirical judgment. The present invention quantifies and optimizes the identification of key nodes through the inverse matrix calculation of the submatrix J, thereby effectively enhancing the scientificity and accuracy of isolated grid recovery.

[0064] S3: Based on the voltage of key nodes 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 voltage stability of the isolated grid is optimized.

[0065] Furthermore, according to the key node voltage of the isolated network after the decoupling, the key node voltage is monitored in real time, the key node voltage of the isolated network after the decoupling is read, and the input voltage of the DC system current command control is calculated through the minimum value of the key node voltage and the DC drop voltage, which is expressed as:

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

[0067] Among them, V in is the input voltage of the DC system current command control, m is the number of key nodes, V k is the voltage of the kth key node.

[0068] It should be noted that the real-time control of the DC system current command until it returns 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, which is expressed as:

[0069]

[0070] Among them, I out is the per unit value of the current command output by the DC system; when V in≥0.9, indicating that the input voltage is high, the system has tended to a steady state, and the current command is directly restored to the 1.0pu standard value; when 0.5 <V in <0.9, indicating that the input voltage is in the middle state, the system needs to adjust the current command by linear interpolation and gradually restore to the steady-state value; when V in ≤0.5, indicating 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 isolated grid.

[0071] It should also be noted that the voltage of key nodes is monitored in real time, combined with the state of the input voltage, and the current command value is dynamically adjusted through a piecewise function to ensure the rapidity and stability of the recovery of the isolated network. The static recovery strategy of the traditional method is inefficient and has poor adaptability. The dynamic adjustment logic of the present 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] Embodiment 2 is an embodiment of the present invention, which provides a DC current control method based on unbalanced power of an isolated grid and node voltage. 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, verifies the advantages of the invented method in dynamically adjusting DC current instructions, identifying key nodes and optimizing grid stability, and designs two scenarios for comparison: Scenario 1 adopts a traditional isolated grid recovery strategy, and Scenario 2 implements a dynamic adjustment and optimization strategy based on the content of the present invention. The initial conditions are set as an unbalanced power of 50MW for the isolated grid system and an initial voltage deviation of 0.20pu for the key nodes. The key test parameters include the adjustment of the initial current instruction value, the recovery level of the key node voltage and the final stable voltage of the system.

[0074] Experimental implementation process

[0075] 1. Initial condition setting: After the isolated grid system is disconnected, the active output of the generator is 50MW and the load demand is 100MW, resulting in an initial unbalanced power of 50MW. The maximum and minimum values ​​of the initial key node voltages are recorded to observe the DC current adjustment responses of the traditional and inventive 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 isolated grid, but no dynamic adjustment and key node identification are performed. The voltage changes of key nodes during the recovery process and the final system stable voltage are recorded.

[0077] 3. Test of the method of the present invention: According to the content of the invention, the DC current command value is dynamically adjusted, gradually restored from the initial value to 1.0pu, and the current is optimized in multiple stages in combination with the key node voltage monitored in real time. The minimum value of the key node voltage and the DC drop point voltage of the isolated grid after decoupling 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, key node voltage recovery level and system voltage stability.

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

[0080] Table 1 Experimental data record 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 the present invention is 0.85pu, while the traditional method only reaches 0.75pu, which is improved by 13.33%. This shows that the method of the present invention can better adapt to the dynamic needs of the isolated grid after decoupling, making the regulation process of the DC current more efficient and stable.

[0086] 2. Better voltage recovery at key nodes

[0087] Under the traditional method, the maximum voltage recovery value of the key node is 0.95pu and the minimum voltage is 0.80pu, while the method of the present invention reaches 0.98pu and 0.85pu respectively, which are improved by 3.16% and 6.25% respectively. This result shows that the method of the present invention can more effectively identify the key nodes and optimize their voltage levels, reducing the voltage fluctuation amplitude between nodes.

[0088] 3. Enhanced overall grid stability

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

[0090] In summary, compared with traditional methods, the present invention overcomes the limitations of static optimization strategies in traditional methods by introducing dynamic adjustment of DC current instructions and key node identification mechanisms. Experiments show that the method of the present invention has achieved significant improvements in DC current adjustment efficiency, key node voltage recovery level and overall grid stability. This strategy of combining real-time dynamic adjustment and mathematical optimization analysis has high innovation and practical value in actual engineering applications, and is conducive to the development of isolated grid recovery technology in modern power systems.

[0091] Example 3, reference Figure 2 , which is an embodiment of the present invention, provides a DC current control system based on unbalanced power and node voltage of an isolated grid, 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 1.0pu to the initial current command value according to the unbalanced power of the isolated network after decoupling; the key node identification and analysis module is used to identify the key nodes in the isolated network subsystem after decoupling based on the node reactive voltage coupling degree; 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 network after decoupling until it recovers to the steady-state value of 1.0pu, and optimize the voltage stability of the isolated network.

[0093] If the function is implemented in the form of 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 the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

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

[0095] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or processing in another suitable manner as necessary, and then stored in a computer memory.

[0096] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc. It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limited. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in 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 rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A DC current control method based on isolated grid unbalanced power and node voltage, characterized in that: include: According to the unbalanced power of the isolated grid after disconnection, the DC system current command value is adjusted from 1.0pu to the initial current command value; Based on the node reactive power and voltage coupling degree, identify the key nodes in the isolated grid subsystem after disconnection; According to the voltage of key nodes of the isolated grid after decoupling, the DC system current command is controlled in real time until it recovers to the steady-state value of 1.0pu, and the voltage stability of the isolated grid is optimized.

2. The DC current control method based on unbalanced power and node voltage of isolated grid according to claim 1, characterized in that: The unbalanced power of the isolated grid after decoupling includes incorporating the DC system feed-in node into the isolated grid subsystem where the active output of the generator is less than the active load when the DC feed-in power system is in the active decoupling section, and calculating the initial unbalanced power of the isolated grid subsystem after decoupling, which is expressed as: ΔP G-L =P G -P L Among them, ΔP G-L is the initial unbalanced power of the isolated grid subsystem after decoupling, P G is the active power output of the generator in the isolated grid subsystem, P L It is the active load in the isolated grid subsystem.

3. The DC current control method based on isolated grid unbalanced power and node voltage according to claim 2, characterized in that: The 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 the ratio of the initial unbalanced power of the isolated grid subsystem after decoupling to the rated transmission power of the DC system, which is expressed as: Among them, I0 is the initial current command value, P N is the rated transmission power of the DC system.

4. The DC current control method based on isolated grid unbalanced power and node voltage according to claim 3, characterized in that: The method based on the node reactive voltage coupling degree includes sorting the coupling degree of the node voltage by inverse matrix analysis, and establishing the power flow equation of the isolated grid subsystem, which is expressed as: Among them, ΔP is the change of node active power, ΔQ is the change of node reactive power, Δθ is the change of node voltage phase angle, ΔV is the change of node voltage amplitude, K and J are sub-matrices, K is the coupling relationship between the change of node active power ΔP and the change of node voltage phase angle Δθ, J is the coupling relationship between the change of node reactive power ΔQ and the change of node voltage amplitude ΔV; Calculate the submatrices K and J, expressed as: Among them, K ij is the coupling relationship between the active power and voltage phase angle of node i and node j, J ij is the coupling relationship between the reactive power and voltage amplitude of nodes i and j, V i is the voltage at node i, V j is the voltage at node j, B is the imaginary part of the node impedance matrix, h is the total number of nodes, and o is the number of load nodes; Combined with the relationship between the voltage and reactive power of the isolated grid node, the reactive power of the DC drop point node is corrected, the DC feed-in node k is included in the DC system injection power, and the elements of the kth row and kth column of the submatrix J are corrected, which is expressed as: Among them, Q k is the reactive power injected into node k, V k is the voltage at node k, J kk is the k-th row and k-th column element of submatrix J, J' kk is the k-th row and k-th column element of the modified submatrix J; According to the converter equation 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 ratio of the DC converter, and X c is the commutation reactance, γ is the turn-off angle, and β is the trigger advance angle.

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

6. The DC current control method based on unbalanced power and node voltage of isolated grid according to claim 5, characterized in that: The key node voltage of the isolated network after the decoupling includes real-time monitoring of the key node voltage, reading the key node voltage of the isolated network after the decoupling, and calculating the input voltage of the DC system current command control through the minimum value of the key node voltage and the DC drop voltage, which is expressed as: V in =min(V1,V2...,V k ,...,V m ) Among them, V in is the input voltage of the DC system current command control, m is the number of key nodes, V k is the voltage of the kth key node.

7. The DC current control method based on unbalanced power and node voltage of isolated grid according to claim 6, characterized in that: The real-time control of the DC system current command until it returns to the steady-state value of 1.0 pu includes dynamically adjusting the DC current command value based on the input voltage controlled by the DC system current command, which is expressed as: Among them, I out It is the per unit value of the current command currently output by the DC system; When V in ≥0.9, indicating that the input voltage is high, the system has reached a steady state, and the current command is directly restored to the 1.0pu standard value; When 0.5 <V in <0.9, indicating that the input voltage is in an intermediate state, and the system needs to adjust the current command by linear interpolation to gradually restore to the steady-state value; When V in ≤0.5, indicating that the input voltage is low, the system is in an unstable state, and the current command maintains the initial current command value.

8. A system using the DC current control method based on unbalanced power and node voltage of an isolated grid as claimed in any one of claims 1 to 7, characterized in that: 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 1.0pu to the initial current command value according to the unbalanced power of the isolated grid after decoupling; The key node identification and analysis module is used to identify the key nodes in the isolated grid subsystem after decoupling based on the node reactive voltage coupling degree; 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 network after decoupling, until it recovers to the steady-state value of 1.0pu, and optimize the voltage stability of the isolated network.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the direct current control method based on unbalanced power and node voltage of an isolated grid are implemented as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the DC current control method based on unbalanced power and node voltage of an isolated grid are implemented as described in any one of claims 1 to 7.

Images