Method and device for evaluating transient synchronous stability of phase-locked synchronous converter system under energy perspective

Abstract

The invention relates to a transient synchronization stability evaluation method and device of a phase-locked synchronous converter system under an energy perspective, belongs to the field of new energy grid connection, and solves the problem of transient synchronization stability evaluation of a phase-locked synchronous converter at the present stage. The method comprises the following steps: establishing a port energy function of each element in the phase-locked synchronous converter system; according to the law of conservation of energy, establishing a phase-locked synchronous converter system branch energy function considering the transient synchronization influence of the phase-locked loop; branch energy and port energy indexes based on information entropy are constructed, and stability margins of key branches and phase-locked synchronous converter elements in the network are quantitatively estimated based on local network measurement information. According to the method, the stability margin of the key branch and the key phase-locking synchronous converter of the system can be accurately and quantitatively identified, and a new visual angle and a new tool are provided for transient synchronous stability evaluation of a high-permeability renewable resource system.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method and apparatus for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective. Background Technology

[0002] With the ongoing low-carbon energy transition, renewable energy and auxiliary resources are being connected to the power grid via power electronic converters and synchronized through phase-locked loop (PLL) control. However, this also brings new control interaction and instability issues. As the proportion of renewable energy continues to grow, ensuring the transient synchronization stability of the power system based on PLL-based synchronous converters becomes crucial.

[0003] The equal-area criterion, Lyapunov's direct method, phase diagram method, and energy function method are commonly used to analyze and evaluate the transient synchronization stability of systems dominated by synchronous generators. While the equal-area criterion is effective, it is highly conservative because it neglects impedance fluctuations and damping effects caused by frequency variations. Lyapunov's method has a well-developed theoretical framework and is widely applicable to high-order nonlinear systems, but constructing the corresponding function is challenging, and the results are often overly conservative. The phase diagram method is intuitive but cannot provide a standard for evaluating transient synchronization stability. These methods have inherent limitations in evaluating the transient synchronization stability of phase-locked synchronous converter systems.

[0004] Furthermore, due to the complex interactions between numerous phase-locked synchronous converters and the power system, assessing the transient synchronization stability of power systems with high renewable resource penetration is challenging. Although some measurement-based transient synchronization stability assessment methods have been proposed, their application is limited by the difficulty in measuring and obtaining the internal parameters of phase-locked synchronous converters.

[0005] Application content

[0006] Based on the above analysis, this invention aims to provide a method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective, enabling quantitative evaluation of the transient synchronization stability of the phase-locked synchronous converter using only local network measurement information. This addresses the issue of stable system operation after new energy sources are connected to the grid.

[0007] The objective of this invention is mainly achieved through the following technical solutions:

[0008] This invention discloses a method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective, comprising:

[0009] Step S1: Construct the port energy function of each component in the phase-locked synchronous converter system;

[0010] Step S2: Based on the law of conservation of energy, establish the branch energy function of the phase-locked loop synchronous converter system considering the transient synchronization effect of the phase-locked loop;

[0011] Step S3: Branch energy and port energy indices based on information entropy were constructed, and the stability margin of key branches and phase-locked synchronous converter components in the network was quantitatively evaluated based on local network measurement information.

[0012] Preferably, according to at least one embodiment of the present invention, the phase-locked synchronous converter system described in step S1 can be considered as a complex system formed by a phase-locked synchronous converter and its control subsystem, a synchronous machine subsystem, a load subsystem, and the interconnection of a power network. During the process of the system recovering from a three-phase short-circuit fault to a stable equilibrium point, the port energies of the phase-locked synchronous converter, generator, load, and branch oscillate, but the total energy of these four components remains conserved. In actual system analysis, the boundary of the target system is defined according to the port interconnection structure, and the port energy is defined as:

[0013]

[0014] In the formula, They represent the flow through The active and reactive power of the port. These represent the voltage and phase angle of the corresponding node, respectively.

[0015] Preferably, according to at least one embodiment of the present invention, the transient energy function of each component of the phase-locked synchronous converter system during a transient fault;

[0016] The first Port energy of Taiwan-locked synchronous converter and its control subsystem It can be represented as:

[0017]

[0018] The first Port energy of the synchronous machine and its control subsystem It can be represented as

[0019]

[0020] The first Port energy of each load subsystem

[0021]

[0022] Apart from phase-locked synchronous converters and synchronous machine nodes, all other nodes in the power grid are considered as load nodes.

[0023] The power network Including all in the power grid Each node and its connecting lines, and its port energy It can be represented as:

[0024]

[0025] Preferably, according to at least one embodiment of the present invention, step S2 includes:

[0026] Step S201: Analyze a power system consisting of n nodes using the law of conservation of energy. The nodal current equations can be expressed according to Kirchhoff's current law:

[0027]

[0028] in, Representing branch roads From node To the node The real-time currents represent the currents entering the system from the phase-locked synchronous converter and the synchronous machine, respectively, and the current entering the load from the system. A complex vector of dimension 1. These represent the number of nodes, the number of phase-locked synchronous converters, the number of synchronous machines, and the number of loads in the network, respectively, and are satisfied at any time during system operation.

[0029] Step S202: Based on the research objective, the dynamic system described by the port energy structure can be arbitrarily divided into the target system and the external system acting on the target system. However, regardless of the division in the power grid, the ports between subsystems are inevitably branches connecting nodes or segments composed of branches, and the port energy represents the transient energy flow at a certain point on the branch. In order to accurately map the transient synchronous stability characteristics of the phase-locked synchronous converter within the system, the transient synchronous stability characteristics of the phase-locked synchronous converter within the system are... Divided into steady-state components and transient components At this point, the steady-state node current equation can be expressed as:

[0030]

[0031] In the formula,

[0032] Representing branches From node To the node The current entering the system from the phase-locked synchronous converter and the synchronous machine, as well as the steady-state current entering the load.

[0033] Due to transient components The growth of potential energy is decisive, therefore the nodal transient current equation can be derived from... get:

[0034]

[0035] In step S203, the total transient energy of the four types of network elements is always conserved, satisfying the law of conservation of energy. During the transient stabilization process of the system, there is energy interaction between the phase-locked synchronous converter and the branch.

[0036] In step S204, the ports between subsystems are inevitably interconnected through branches, and the port energy represents the transient energy flow at a certain point on the branch. Therefore, based on identifying the critical branches in the network, the transient synchronization stability of the phase-locked synchronous converter is evaluated.

[0037] Preferably, according to at least one embodiment of the present invention, the transient stability characteristics of the internal components of the phase-locked synchronous converter are preserved. Due to the energy interaction between the phase-locked synchronous converter and the branches, the instability characteristics of the converter are mapped into the network. By utilizing port energy to characterize the transient energy accumulation effect, complex control process calculations are avoided, the modeling process is simplified, and the difficulty of constructing the energy function is reduced.

[0038] Preferably, according to at least one embodiment of the present invention, step S3 includes:

[0039] Step S301: We revealed the transient behavior of the phase-locked synchronous converter by observing the accumulation effect of port energy and the distribution characteristics of branch energy. Therefore, based on the forms of port energy and branch energy, we proposed two transient synchronization stability evaluation indices based on information entropy.

[0040] Step S302: Information entropy reflects the evolutionary order of natural phenomena and is widely used to describe the uncertainty and stability of systems. For complex nonlinear systems, information entropy can measure the disorder and chaos of the system state, and the equilibrium state of the system can be judged by the change in information entropy value. Based on the entropy balance principle and the distribution characteristics of network branch potential energy and branch energy during transient processes, a quantitative information entropy branch energy stability index (IEBSI) for transient synchronization stability is proposed, expressed as:

[0041]

[0042] In the formula The magnitude of IEBSI reflects the impact of disturbances and faults on the network energy distribution. Therefore, the magnitude of IEBSI indicates the severity of interference in the GFL-VSC system.

[0043] Step S303: The port energy of each component in the system does not depend on the internal electrical quantities of the phase-locked synchronous converter, but only on the output power of the phase-locked synchronous converter and the voltage and phase angle of the bus. To locate the position of the transiently unstable phase-locked synchronous converter, the Information Entropy Port Energy Stability Index (IEPSI) is proposed based on the port energy accumulation effect, as follows:

[0044]

[0045] In the formula The magnitude of IEBSI reflects the impact of disturbances and faults on the port energy of a phase-locked synchronous converter. Therefore, the magnitude of IEBSI indicates whether the port energy of the phase-locked synchronous converter exceeds a critical threshold.

[0046] Preferably, according to at least one embodiment of the present invention, the calculation of IEBSI and IEPSI is crucial for identifying key branches in the system oscillation center region and evaluating the contributions of different phase-locked synchronous converters. Before calculating these two indices, it is necessary to calculate the energy of each branch of the system and the port energy of the phase-locked synchronous converters separately.

[0047] The invention discloses an apparatus for evaluating the transient synchronization stability of a phase-locked synchronous converter system using the aforementioned energy-perspective method, comprising:

[0048] The data acquisition module is used to obtain electrical quantity data of each generator in the system required for subsequent calculations; by monitoring lines and nodes, it determines whether a three-phase short-circuit fault exists in the power system. After fault detection, power supply and voltage phase angle signals are acquired through PMUs distributed in the network;

[0049] The calculation module is used to process and calculate the electrical quantity data of each generator in the system acquired by the acquisition module. It uses the energy equation to calculate the branch energy in the system after a fault, as well as the port energy of the synchronous machine and phase-locked synchronous converter, and obtains the IEBSI and IEPSI indices of each component and branch.

[0050] The comparison module is used to compare and analyze the calculation results of the calculation module and sort the results in descending order. The stability margins of key system branches and key phase-locked synchronous converters are quantitatively identified using the IEBSI and IEPSI indices shown in Table 1.

[0051] The feedback module provides useful feedback to the decision support system.

[0052] Beneficial effects

[0053] This invention enables quantitative assessment of the stability margin of phase-locked synchronous converters (PLCs) based on local network measurement information. By constructing branch energy and port energy indices based on information entropy, the stability margins of critical branches and PLCs in the network are quantitatively estimated. This method provides a new perspective and tool for assessing the transient synchronization stability of PLC systems with high penetration of renewable resources.

[0054] Those skilled in the art should understand that the above embodiments are merely illustrative of the specific content of this disclosure and do not limit its scope. System capacity, voltage, line parameters, etc., will vary depending on the specific circumstances of the power electronic grid-connected generator set and its grid connection. Based on this disclosure, those skilled in the art can make other changes or adjustments, and these changes still fall within the scope of this disclosure. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings involved in the embodiments or the prior art are briefly described below. Obviously, these drawings illustrate several embodiments of the present invention, and those skilled in the art can derive other possible drawings based on these drawings without creative effort. The purpose of the drawings is limited to illustrating specific embodiments and does not limit the scope of the present invention.

[0056] Figure 1 This is a flowchart of the transient synchronization stability evaluation method for a phase-locked synchronous converter system in Embodiment 1 of the present invention;

[0057] Figure 2 This is a detailed model block diagram of the phase-locked synchronous converter in Embodiment 1 of the present invention;

[0058] Figure 3 This is a schematic diagram of the energy accumulation effect at the ports of various components in the phase-locked synchronous converter system according to Embodiment 1 of the present invention;

[0059] Figure 4 This is a schematic diagram of energy conservation in a phase-locked synchronous converter system according to Embodiment 1 of the present invention;

[0060] Figure 5 This is a schematic diagram of the transient synchronization stability evaluation device for a phase-locked synchronous converter system in Embodiment 2 of the present invention;

[0061] Figure 6 This is a system diagram of the IEEE 10 machine 39-node phase-locked synchronous converter in Embodiment 3 of the present invention;

[0062] Figure 7 This is the branch energy diagram in scenario A of the 10-machine 39-node system in Embodiment 3 of the present invention;

[0063] Figure 8This is the energy diagram of the key branch in the AE system of a 10-machine, 39-node system in Embodiment 3 of the present invention;

[0064] Figure 9 This is the energy diagram of the phase-locked synchronous converter port in case A of the 10-machine 39-node system in Embodiment 3 of the present invention;

[0065] Figure 10 This is a diagram of an actual Chinese power system containing a phase-locked synchronous converter, as shown in Embodiment 4 of the present invention.

[0066] Figure 11 This is a diagram showing the electrical quantities and energy of a phase-locked synchronous converter (PLC) in the actual Chinese power system as described in Embodiment 4 of the present invention. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0068] Example 1

[0069] This embodiment discloses a method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective.

[0070] like Figure 1 As shown, it includes the following steps:

[0071] Step S1: Construct the port energy function of each component in the phase-locked synchronous converter system;

[0072] Based on the block diagram of the phase-locked synchronous converter model, as follows: Figure 2 As shown, the phase-locked synchronous converter is divided into five parts: phase-locked loop, inner current loop, outer voltage loop, DC bus, and power grid.

[0073] Establish as Figure 3 The diagram shows the port energy functions of various components in a phase-locked synchronous converter system; where the first... The port energy of the synchronous machine and its control subsystem can be expressed as: , No. The port energy of a phase-locked synchronous converter and its control subsystem can be expressed as: The port energy of the i-th load can be expressed as: and power grid Including all in the power grid The port energy of a node and its connecting lines can be expressed as: .

[0074] During transient faults, the port energy functions of each component of the phase-locked synchronous converter system satisfy the following formula:

[0075]

[0076] In the formula, , They represent the flow through The active and reactive power of the port. These represent the voltage and phase angle of the corresponding node, respectively.

[0077] According to the second-order equation of motion of the phase-locked loop, the... One phase-locked synchronous converter port energy The mathematical expression is:

[0078]

[0079]

[0080] When the When the synchronous machine adopts the classic model, the port energy It can be represented as:

[0081]

[0082]

[0083] Eij represents the port energy under a constant power load model, and Eij represents the branch energy. The port energy is as follows:

[0084]

[0085]

[0086] Step S2: During the transient analysis process, establish the branch energy function of the phase-locked loop synchronous converter system considering the transient synchronization effect of the phase-locked loop;

[0087] Specifically, a power system consisting of n nodes can be analyzed based on the law of conservation of energy.

[0088] 1) The steady-state current equations at nodes can be expressed according to Kirchhoff's current law:

[0089]

[0090] Among them, I ij I GFLiI SGi I Li Representing branches From node To the node The real-time current.

[0091] 2) The transient current equations at nodes can be expressed according to Kirchhoff's current law:

[0092]

[0093] Since the transient component ΔI plays a decisive role in the growth of potential energy, the nodal transient current equation can be derived from... get.

[0094] 3) such as Figure 4 The verification of the 3-machine 9-node system shown demonstrates that the total transient energy of the four types of network elements is always conserved, satisfying the law of conservation of energy. During the system's transient stabilization process, there is energy interaction between the phase-locked synchronous converter and the branches.

[0095] 4) The total transient energy of a phase-locked synchronous converter system can be expressed as:

[0096]

[0097] The total transient energy is expressed as And expressed in the form of branch energy function. For total potential energy, for

[0098] Total kinetic energy This is for dissipating energy. It is the relative angular frequency of the node connected to the load. For nodes With nodes The difference in angular frequency, The relative angular frequency of the synchronous machine. This refers to the relative angular frequency of the phase-locked synchronous converter.

[0099] The specific S3 steps include the following:

[0100] Step S301 reveals the transient behavior of the phase-locked synchronous converter by analyzing the energy accumulation effect at the ports and the distribution characteristics of the energy in the branches. Therefore, based on the forms of port energy and branch energy, two transient synchronization stability evaluation indices based on information entropy are proposed.

[0101] Step S302: Information entropy reflects the evolutionary order of natural phenomena and is widely used to describe the uncertainty and stability of systems. For complex nonlinear systems, information entropy can measure the disorder and chaos of the system state, and the equilibrium state of the system can be judged by the change in information entropy value. Based on the entropy balance principle and the distribution characteristics of network branch potential energy and branch energy during transient processes, a quantitative information entropy branch energy stability index (IEBSI) for transient synchronization stability is proposed, expressed as:

[0102]

[0103] In the formula The magnitude of IEBSI reflects the impact of disturbances and faults on the network energy distribution. Therefore, the magnitude of IEBSI indicates the severity of interference in the GFL-VSC system.

[0104] Step S303: The port energy of each component in the system does not depend on the internal electrical quantities of the phase-locked synchronous converter, but only on the output power of the phase-locked synchronous converter and the voltage and phase angle of the bus. To locate the transient instability of the phase-locked synchronous converter, the Information Entropy Port Energy Stability Index (IEPSI) is proposed based on the port energy accumulation effect, as follows:

[0105]

[0106] In the formula The magnitude of IEBSI reflects the impact of disturbances and faults on the port energy of a phase-locked synchronous converter. Therefore, the magnitude of IEBSI indicates whether the port energy of the phase-locked synchronous converter exceeds a critical threshold.

[0107] Example 2

[0108] This embodiment discloses a transient synchronization stability evaluation device for a phase-locked synchronous converter system, such as... Figure 5 As shown, it includes a data acquisition module, a calculation module, a comparison module, and a feedback module.

[0109] The data acquisition module is used to acquire electrical quantity data of each generator in the system required for subsequent calculations; by monitoring lines and nodes, it determines whether a three-phase short-circuit fault exists in the power system. After fault detection, power supply and voltage phase angle signals are acquired through PMUs distributed in the network;

[0110] The calculation module processes and calculates the electrical quantity data of each generator in the system acquired by the acquisition module. It uses energy equations to calculate the branch energy and port energy of the synchronous machine and phase-locked synchronous converter after a fault. It obtains the IEBSI and IEPSI indices for each component and branch.

[0111] The comparison module is used to compare and analyze the calculation results of the calculation module and sort the results in descending order. The stability margins of key system branches and key phase-locked synchronous converters are quantitatively identified using the IEBSI and IEPSI indices shown in Table 1.

[0112] Table 1 Performance of Branch and Port Indicators

[0113]

[0114] The feedback module provides useful feedback to the decision support system.

[0115] Example 3

[0116] use Figure 6 A transient synchronous stability assessment method was validated for an IEEE 10-machine 39-bus system containing phase-locked synchronous converters. The system includes 4 GFL-VSCs nodes, 6 generator nodes, 19 load nodes, 12 bus nodes, 12 transformer branches, and 34 transmission line branches. Classical generator modeling neglects the prime mover, governor, and excitation system, while the loads are modeled as constant impedance. Nonlinear simulations were performed using DIgSILENT / PowerFactory.

[0117] To verify the correctness and effectiveness of this method, this embodiment selects case AE to verify the identification of key branches and the quantitative evaluation of phase-locked synchronous converters.

[0118] 1) Critical Branch Identification: In scenario A, a three-phase short-circuit fault occurs on busbar 3 within 1 second and lasts for 100 ms. Branch energy calculation uses the branch energy expression, such as... Figure 7 As shown in the figure. Then, the calculated branch energy is used to determine the IEBSI, thereby identifying the critical branches in the region near the oscillation center. Furthermore, the branch stability index (SBI) and branch transient transmission capacity index (sBTTC) are calculated to verify the effectiveness of the IEBSI. The ranking results of each index are listed in Table 2. Clearly, the top three branches are 06-31, 09-39, and 03-04. Therefore, these branches are considered the most vulnerable and mark the critical branches in the system. This is consistent with... Figure 7 The branch with the largest transient energy increment is consistent.

[0119] Table 2 Comparison of critical branch sortings defined by IEBSI, SBI, and SBTTC

[0120]

[0121] Four additional cases (BE) were considered to further test the effectiveness of the proposed method in identifying critical branches. Cases B and C had the same fault location as Case A, but the fault clearing time increased by 40 ms and 60 ms, respectively. Case D involved a three-phase fault on bus 17, lasting 100 ms. Case E involved a power load surge fault, with the load on bus 18 being 0.4 times the existing load, lasting 500 ms. Figure 8 As the critical branch, the critical branch remains similar regardless of the scenario. The results show that the system's critical branch is independent of fault location, fault type, and fault clearing time, and remains unchanged throughout.

[0122] 2) Quantitative evaluation of different phase-locked synchronous converters: By calculating the IEPSI during instantaneous faults, the contribution of phase-locked synchronous converters to the test system can be evaluated. Figure 9 Let represent the port energy of the phase-locked synchronous converter under condition a. During this period, the port energy of the phase-locked synchronous converter gradually increases and returns to its steady-state value, indicating that the system is stable. Figure 9 The contribution of phase-locked synchronous converters (PLCs) to the AE of the case study is shown. It can be seen that as the fault clearing time increases, the IEPSI values ​​of each PLC decrease continuously, and the closer the IEPSI value of GFL1 is to 0, the more unstable the system becomes. In conclusion, the quantitative evaluation method for PLCs proposed in this paper is effective.

[0123] Table 3. Determining the contribution of the phase-locked synchronous converter to transient energy under AE conditions.

[0124]

[0125] Example 4

[0126] use Figure 10 Taking a real-world power system in China containing phase-locked synchronous converters as an example, the system includes 4 phase-locked synchronous converters, 7 wind turbine generators, 9 photovoltaic systems, 10 generators, and 4 DC lines, verifying the effectiveness of the method in real-world scenarios.

[0127] 1) Identifying critical branches of the system: Scenario F, assuming a three-phase short-circuit fault lasting 100ms occurs on the BUS1B-5 bus within 1 second. In Scenario GI, the fault location changes, but the fault clearing time remains unchanged. The fault locations are BUS1B-10, BUS1B-4, and Gen1B-1, respectively. Figure 11 (a) is a fragile branch in case F, according to... Figure 11(b) is the time-domain trajectory of the active power of the system branches. Based on the obtained branch energy, the IEBSI of the critical vulnerable branches in the system was calculated. Table 4 lists the branch ranking results under IEBSI for case FI. The most obvious finding from the analysis of Table 4 is that the top three branches are AC42, AC41, and AC47. Therefore, these branches are considered the most vulnerable and mark the critical branches in the system. This is consistent with... Figure 11 (b) The branch with the largest transient energy increment is consistent with the branch in the diagram. The results further confirm that transient energy in the system always flows to the oscillation center region, regardless of the fault location.

[0128] Table 4. Ranking of the top 8 transmission lines in scenario F (IEBSI)

[0129]

[0130] Table 5. IEPSI values ​​of phase-locked synchronous converters under FI conditions

[0131]

[0132] 2) Quantitative evaluation of different phase-locked synchronous converters: By calculating the IEPSI during transient faults, the contribution of phase-locked synchronous converters to the test system can be evaluated. Figure 11 (c) Port energy of the phase-locked synchronous converter under case F. During this period, the port energy of phase-locked synchronous converter 1 and phase-locked synchronous converter 4 decreases monotonically. Figure 11 (d) The time-domain characteristic curves of the phase-locked loop phase angle of the phase-locked synchronous converter are given, which are consistent with the port energy characteristics. Table 5 lists the quantitative parameters of different phase-locked synchronous converters based on IEPSI under Case FI. These characteristics indicate that the stability of phase-locked synchronous converters 1 and 4 is always the worst.

[0133] In summary, the transient synchronization stability assessment method and apparatus for phase-locked synchronous converter (PLC) systems based on local area network measurements constructed in this invention solves the problems of assessment complexity and measurement difficulty caused by the numerous internal parameters of PLCs. Considering the dynamic influence of the PLC, Kirchhoff's current law is used to construct the port energy and branch energy functions of the PLC system. By identifying the critical branches and PLCs in the PLC system, IEBSI and IEPSI are derived for quantitatively assessing the transient stability margin of critical branches and PLCs. A convenient and accurate evaluation method is proposed. Finally, the effectiveness of the proposed method is verified through simulations of an improved IEEE 39-BUS system and a real power system. This method provides a new perspective and tool for transient synchronization stability assessment of PLC systems with high penetration renewable resources.

[0134] Those skilled in the art should understand that the above embodiments are merely illustrative of the content of this disclosure and do not limit its scope. The system capacity, voltage, line parameters, etc., shown may vary depending on the specific circumstances of the power electronic grid-connected generator set and its grid connection. Based on this disclosure, those skilled in the art can make other changes or adjustments, and these changes still fall within the scope of this disclosure.

Claims

1. A method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective, characterized in that, include: Step S1: Construct the port energy function of each component in the phase-locked synchronous converter system; Step S2: Based on the law of conservation of energy, establish the branch energy function of the phase-locked loop synchronous converter system considering the transient synchronization effect of the phase-locked loop; Step S3: Branch energy and port energy indices based on information entropy were constructed, and the stability margin of key branches and phase-locked synchronous converter components in the network was quantitatively evaluated based on local network measurement information.

2. The method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective according to claim 1, characterized in that, The phase-locked synchronous converter system described in step S1 can be viewed as a complex system formed by the phase-locked synchronous converter and its control subsystem, synchronous machine subsystem, load subsystem, and interconnection with the power network. During the process of the system recovering from a three-phase short-circuit fault to a stable equilibrium point, the port energy of the phase-locked synchronous converter, generator, load, and branch oscillates, but the total energy of these four parts remains conserved. In practical system analysis, the boundary of the target system is defined based on the port interconnection structure, and the port energy is defined as follows: In the formula, (P i ), (Q i (V) represent the active power and reactive power flowing through port i, respectively. i ), (θ i ) represent the voltage and phase angle of the corresponding node, respectively.

3. The method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective according to claim 2, characterized in that, Transient energy functions of each component of a phase-locked synchronous converter system during a transient fault; The port energy (E) of the i-th phase-locked synchronous converter and its control subsystem GFLi This can be represented as: The port energy (EsGi) of the i-th synchronous machine and its control subsystem can be expressed as: The port energy (E) of the i-th load subsystem Li This can be represented as: Apart from phase-locked synchronous converters and synchronous machine nodes, all other nodes in the power grid are considered as load nodes. The power network (ij) includes all n nodes in the power grid and their connecting lines, and its port energy (E) ij This can be represented as:

4. The method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective, as described in claim 1 or 3, is characterized in that... Step S2 includes: Step S201: Analyze a power system consisting of n nodes using the law of conservation of energy. The nodal current equations can be expressed according to Kirchhoff's current law: Among them, (I) ij ), (I GFLi ), (I SGi ), (I Li Let represent the real-time current of branch (ij) from node i to node j, respectively; let represent the current entering the system from the phase-locked synchronous converter and the synchronous machine, respectively; and let represent the current entering the load from the system. They are n-dimensional complex vectors. B ), (n GFL ), (n SG ), (n L These represent the number of nodes, the number of phase-locked synchronous converters, the number of synchronous machines, and the number of loads in the network, respectively, and are satisfied at any time during system operation. Step S202: Based on the research objective, the dynamic system described by the port energy structure can be arbitrarily divided into the target system and the external system acting on the target system. However, regardless of the division in the power grid, the ports between subsystems are inevitably branches connecting nodes or segments composed of branches, and the port energy represents the transient energy flow at a certain point on the branch. In order to accurately map the transient synchronous stability characteristics of the phase-locked synchronous converter in the system, I is divided into a steady-state component (I0). s The steady-state node current equation can then be expressed as: (The equation includes the transient component (ΔI) and the steady-state node current equation.) In the formula, These represent the current entering the system from node i to node j in the branch (ij), the current entering the system from the phase-locked synchronous converter and the synchronous machine, and the steady-state current entering the load, respectively. Since the transient component (ΔI) plays a decisive role in the growth of potential energy, the nodal transient current equation can be derived from (ΔI=II). s )get: In step S203, the total transient energy of the four types of network elements is always conserved, satisfying the law of conservation of energy. During the transient stabilization process of the system, there is energy interaction between the phase-locked synchronous converter and the branch. In step S204, the ports between subsystems are inevitably interconnected through branches, and the port energy represents the transient energy flow at a certain point on the branch. Therefore, based on identifying the critical branches in the network, the transient synchronization stability of the phase-locked synchronous converter is evaluated.

5. The method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective according to claim 4, characterized in that, The transient stability characteristics of the internal components of the phase-locked synchronous converter (PLC) are preserved. Due to the energy interaction between the PLC and its branches, the instability characteristics of the converter are mapped into the network. By utilizing port energy to characterize transient energy accumulation effects, complex control process calculations are avoided, the modeling process is simplified, and the difficulty of constructing the energy function is reduced.

6. The method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective according to claim 1, characterized in that, Step S3 includes: Step S301: We revealed the transient behavior of the phase-locked synchronous converter by observing the accumulation effect of port energy and the distribution characteristics of branch energy. Therefore, based on the forms of port energy and branch energy, we proposed two transient synchronization stability evaluation indices based on information entropy. Step S302: Information entropy reflects the evolutionary order of natural phenomena and is widely used to describe the uncertainty and stability of systems. For complex nonlinear systems, information entropy can measure the disorder and chaos of the system state, and the equilibrium state of the system can be judged by the change in information entropy value. Based on the entropy balance principle and the distribution characteristics of network branch potential energy and branch energy during transient processes, a quantitative information entropy branch energy stability index (IEBSI) for transient synchronization stability is proposed, expressed as: In the formula (H) l The magnitude of IEBSI reflects the impact of disturbances and faults on the network energy distribution. Therefore, the magnitude of IEBSI indicates the severity of interference in the GFL-VSC system. Step S303: The port energy of each component in the system does not depend on the internal electrical quantities of the phase-locked synchronous converter, but only on the output power of the phase-locked synchronous converter and the voltage and phase angle of the bus. To locate the position of the transiently unstable phase-locked synchronous converter, the Information Entropy Port Energy Stability Index (IEPSI) is proposed based on the port energy accumulation effect, as follows: The magnitude of (H2) in the formula reflects the impact of disturbances and faults on the port energy of the phase-locked synchronous converter. Therefore, the magnitude of IEBSI indicates whether the port energy of the phase-locked synchronous converter exceeds the critical threshold.

7. The method for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective according to claim 6, characterized in that, Calculating IEBSI and IEPSI is crucial for identifying key branches in the system oscillation center region and evaluating the contributions of different phase-locked synchronous converters. Before calculating these two indices, it is necessary to calculate the energy of each branch of the system and the port energy of the phase-locked synchronous converters separately.

8. An apparatus for evaluating the transient synchronization stability of a phase-locked synchronous converter system from an energy perspective, as described in any one of claims 1 to 7, characterized in that, include: The data acquisition module is used to obtain electrical quantity data of each generator in the system required for subsequent calculations; by monitoring lines and nodes, it determines whether a three-phase short-circuit fault exists in the power system. After fault detection, power supply and voltage phase angle signals are acquired through PMUs distributed in the network; The calculation module is used to process and calculate the electrical quantity data of each generator in the system acquired by the acquisition module. It uses the energy equation to calculate the branch energy in the system after a fault, as well as the port energy of the synchronous machine and phase-locked synchronous converter, and obtains the IEBSI and IEPSI indices of each component and branch. The comparison module is used to compare and analyze the calculation results of the calculation module and sort the results in descending order. The stability margins of key system branches and key phase-locked synchronous converters are quantitatively identified using the IEBSI and IEPSI indices shown in Table 1. The feedback module provides useful feedback to the decision support system.

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