Transient attractive domain stability analysis method for hybrid systems
Patent Information
- Application Number
- CN202611444226.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-17
- Publication Date
- 2026-10-23
Smart Images
Figure CN122964403A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of new energy grid connection technology in power systems, and in particular to a method for analyzing the stability of transient attraction domains in hybrid systems. Background Technology
[0002] As the proportion of new energy power generation equipment and power electronic equipment connected to the power system continues to increase, the mixed connection of grid-connected converters and grid-connected converters to the power grid is gradually becoming an operating mode in new energy power systems.
[0003] Grid-connected converters typically rely on grid voltage for synchronization, while grid-connected converters have different synchronization and power control characteristics. Therefore, when the power system is subjected to large disturbances such as faults, the two types of converters exhibit differences in power angle, power, and voltage transient responses. At the same time, grid-connected and grid-connected converters are electrically coupled through the power grid and their respective grid-connected branches. Changes in the operating state of one type of converter will affect the other type of converter through network relationships, giving the transient dynamic process of the hybrid system strong coupling characteristics.
[0004] Therefore, when existing transient stability analysis methods are applied to hybrid systems of grid-connected and grid-connected converters, it is difficult to provide a unified and complete characterization of the actual transient stability boundary of the system under the combined influence of different stability constraints and the coupling effect of the two types of converters. Consequently, it is difficult to accurately analyze the influence of different system parameters and control parameters on the transient stability performance of the hybrid system based on a unified stability analysis benchmark.
[0005] The information disclosed in this background section is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention
[0006] This invention provides a method for analyzing the stability of the transient attraction domain of a hybrid system, which can effectively solve the problems in the background art.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for transient attraction domain stability analysis of a hybrid system, the hybrid system including grid-connected converters and grid-connected converters, comprising: Construct the transient energy function of the hybrid system of grid-connected converter and grid-connected converter, and obtain the static potential energy function used to characterize the transient stability boundary of the system; The transient attraction domain and phase trajectory of the hybrid system are determined based on the static potential energy function. By introducing the static stability boundary and equipment current limiting constraint of the grid-connected converter into the transient attraction domain, a modified transient attraction domain that simultaneously considers the static stability boundary and equipment current limiting constraint is obtained. Based on the modified transient attraction domain and phase trajectory, the parameters affecting the transient stability of the hybrid system and their influence laws are analyzed.
[0008] Furthermore, the transient energy function of the hybrid system is constructed to obtain the static potential energy function, including: The transient energies of the grid-connected converter and the grid-connected converter are obtained respectively based on the transient dynamic equations of the grid-connected converter and the grid-connected converter. Ignoring the damping terms related to angular velocity, conservative terms related to the power angle of the grid-type converter and the power angle of the grid-type converter are extracted respectively to obtain the self-synchronization potential energy components of the grid-type converter and the grid-type converter. Based on the cross-coupling relationship between grid-type converters and network-type converters through the impedance network, the mutual synchronization potential energy components between the two types of converters are obtained. Based on the Lyapunov direct method, the self-synchronization potential energy components of the grid-type converter, the self-synchronization potential energy components of the grid-following converter, and the mutual synchronization potential energy components are superimposed to construct the static potential energy function of the hybrid system with the power angles of the grid-following converter and the grid-type converter as state variables.
[0009] Furthermore, determining the transient attraction domain of the hybrid system based on the static potential energy function includes: Based on the static potential energy function, the stable equilibrium point and corresponding potential energy boundary of the hybrid system are determined, and the transient attraction domain is determined in the two-dimensional state space composed of the power angle of the grid-type converter and the power angle of the grid-type converter. The phase trajectory is calculated based on the changes in system state before, during, and after the fault is cleared, and the phase trajectory is mapped to the transient attraction domain to determine the transient stable state of the system after the fault. When the output current of the grid converter exceeds the preset current limit, the static potential energy function is corrected according to the change in the relationship between the output voltage of the grid converter and the system power after current limiting, and the transient attraction domain and phase trajectory are re-determined according to the corrected static potential energy function.
[0010] Furthermore, the static stability boundary and equipment current limiting constraint of the grid-connected converter are introduced into the transient attraction domain, including: Using the fact that the damping power of the grid-connected converter is greater than zero as the static stability criterion, the static stability boundary of the grid-connected converter in the hybrid system is determined. Determine the current limiting constraint boundary based on the equipment current limit value, and divide the current limiting area beyond the current limit constraint; By superimposing the static stability boundary and current limiting constraint boundary with the transient energy boundary, a modified transient attraction domain that simultaneously considers the transient energy boundary, the static stability boundary of the grid-connected converter, and the current limiting constraint of the equipment is obtained.
[0011] Furthermore, the parameters affecting the transient stability of the hybrid system and their influence laws are analyzed, including: Based on the modified transient attraction domain and phase trajectory, the parameters to be analyzed are changed respectively to obtain the transient response of the system under different parameters, and the corresponding modified transient attraction domain is plotted. Based on the changes in the transient attraction domain area and phase trajectory, the influence of the parameters to be analyzed on the transient stability range and stability performance of the hybrid system is determined.
[0012] Furthermore, the parameters to be analyzed include line impedance; By changing the impedance of the power grid line, the impedance of the grid-connected converter branch, and the impedance of the grid-connected converter branch, the transient responses of the system power, power angle, and voltage under different line impedances are obtained, and the corresponding modified transient attraction domains are plotted to determine the influence of line impedance on the transient stability performance of the hybrid system.
[0013] Furthermore, the parameters to be analyzed include system operating parameters; By changing the grid voltage sag depth, the capacity ratio of grid-connected converters, and the equipment current limit, the modified transient attraction domain under different system operating parameters is plotted and its area ratio is calculated to determine the influence of grid voltage sag depth, grid ratio, and current limit on the transient stability range of the hybrid system.
[0014] Furthermore, the parameters to be analyzed include the control parameters of the grid-type converter; By changing the equivalent moment of inertia, equivalent damping coefficient, reactive power control parameters, and active power reference values of the grid-type converter, the influence of the grid-type converter control parameters on the transient stability performance of the hybrid system is determined based on the changes in the area of the corrected transient attraction domain and the phase trajectory.
[0015] Furthermore, the parameters to be analyzed include the control parameters of the grid-type converter; By changing the proportional gain, integral gain, and active current command of the phase-locked loop (PLL) of the grid-connected converter, the changes in the area of the corrected transient attraction domain and the phase trajectory caused by the changes in different control parameters are compared, and key control parameters that have a significant impact on the transient stability performance of the hybrid system are screened.
[0016] Furthermore, the method also includes: By changing the line impedance, system operating parameters, and converter control parameters respectively, calculate the critical cut-off time and critical cut-off angle of the hybrid system under the change of each parameter. Plot the relationship between parameters and critical cut-off time and critical cut-off angle to quantify the impact of different parameters on the transient stability margin of the hybrid system.
[0017] The technical solution of this invention can achieve the following technical effects: This invention constructs the transient energy function and static potential energy function of a hybrid system of grid-connected and grid-connected converters to determine the system's transient attraction domain and phase trajectory. Furthermore, it introduces the static stability boundary of the grid-connected converter and equipment current limiting constraints to form a modified transient attraction domain that better reflects actual operating constraints, thereby improving the completeness and accuracy of the transient stability boundary analysis of the hybrid system. Simultaneously, based on the modified transient attraction domain and phase trajectory, the influence of line impedance, system operating parameters, and converter control parameters on transient stability can be analyzed in a unified manner, providing a theoretical basis for transient stability assessment, parameter optimization, and coordinated control design of hybrid systems.
[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0020] Figure 1 A schematic diagram of the process for analyzing the stability of the transient attraction domain in a hybrid system; Figure 2 A schematic diagram of the transient attraction domain and phase trajectory of a hybrid system, wherein: (a) is a schematic diagram of the transient attraction domain and phase trajectory of a hybrid system without considering current limiting; (b) Schematic diagram of transient attraction domain and phase trajectory of a hybrid system with current limiting; Figure 3 A schematic diagram of the modified transient attraction domain for a hybrid system is provided, in which: (a) is the transient attraction domain partition considering the statically stable boundary of GFL under the condition of no current limiting; (b) The modified transient attraction domain considering the statically stable boundary and current-limiting constraint of GFL under the triggered current-limiting condition; Figure 4 The diagram illustrates the transient characteristics of a hybrid system with different grid-connected converter branch impedances, where: (a) shows the power angle transient response of the hybrid system under different GFL branch impedances. (b) The transient response of braking power of the hybrid system under different GFL branch impedances. (c) The damping power transient response of the hybrid system under different GFL branch impedances; (d) shows the voltage transient response of the hybrid system under different GFL branch impedances; Figure 5 This diagram illustrates the transient characteristics of a hybrid system under different converter branch impedances and grid line impedances, where: (a) Transient power angle, power and voltage response of the hybrid system under different GFM branch impedances; (b) Transient power angle, power and voltage response of the hybrid system under different power grid line impedances; Figure 6 A schematic diagram of the modified transient attraction region for a hybrid system under different line impedances, wherein: (a) The change of the transient attraction domain under different GFL branch impedances; (b) Correcting the transient attraction domain variation under different power grid line impedances; (c) shows the change in the corrected transient attraction domain under different GFM branch impedances; Figure 7 This is a schematic diagram of the power angle transient characteristics of a hybrid system under different system operating parameters, where: (a) The transient power angle response of the hybrid system under different grid voltage drop depths; (b) The transient power angle response of the hybrid system under different grid-type converter capacity ratios; (c) shows the power angle transient response of the hybrid system under different GFM current limiting values; Figure 8 A schematic diagram of the modified transient attraction domain for a hybrid system under different system operating parameters, wherein: (a) The change of the corrected transient attraction domain under different grid voltage drop depths; (b) Correcting the transient attraction domain variation under different network proportions; (c) shows the change in the corrected transient attraction domain under different GFM current limiting values; Figure 9 This diagram illustrates the transient characteristics of the power angle of a hybrid system under different grid-type converter control parameters, where: (a) Power angle response of the hybrid system under different GFM equivalent inertia parameters; (b) shows the power angle response of the hybrid system under different GFM damping coefficients; (c) is the power angle response of the hybrid system under different reactive power control parameters; (d) is the power angle response of the hybrid system under different GFM active power reference values; Figure 10 The diagram shows the transient attraction domain and phase trajectory of a hybrid system under different grid-type converter control parameters, where: (a) shows the transient phase trajectory changes under different GFM equivalent inertia; (b) shows the transient phase trajectory changes under different GFM damping coefficients; (c) Correction of transient attraction domain variation under different GFM active power reference values; (d) shows the change in the corrected transient attraction domain under different reactive power control parameters; Figure 11 The diagram illustrates the transient characteristics of the power angle of a hybrid system under different grid-connected converter control parameters, where: (a) shows the power angle transient response of the hybrid system under different phase-locked loop proportional coefficients; (b) shows the power angle transient response of the hybrid system under different phase-locked loop integral coefficients; (c) is the transient response of the power angle of the hybrid system under different active current commands; Figure 12 The diagram shows the transient attraction domain and phase trajectory of a hybrid system under different grid-connected converter control parameters, where: (a) shows the transient phase trajectory of the hybrid system under different phase-locked loop proportional coefficients; (b) shows the transient phase trajectory of the hybrid system under different phase-locked loop integral coefficients; (c) Correcting the transient attraction domain change under different active current commands; Figure 13 This diagram illustrates the influence of different parameters on the critical clearance time of the hybrid system, where: ① The influence of power grid line impedance on critical clearing time; ② The effect of GFL branch impedance on critical resection time; ③ The effect of GFM branch impedance on critical clearance time; ④ is the effect of the GFM damping coefficient on the critical resection time; ⑤ The effect of GFM equivalent inertia on critical resection time; ⑥ is the effect of reactive power control parameters on critical cut-off time; ⑦ shows the effect of the GFM active power reference value on the critical clearance time; ⑧ The impact of the capacity ratio of grid-type converters on the critical cut-off time; ⑨ represents the effect of the GFM current limiting value on the critical cut-off time; Figure 14 This is a schematic diagram illustrating the influence of different parameters on the critical cut-off angle of the hybrid system, where: ① The effect of power grid line impedance on the critical cut-off angle; ② The effect of GFL branch impedance on the critical cut-off angle; ③ The effect of GFM branch impedance on the critical cut-off angle; ④ is the effect of the GFM damping coefficient on the critical cut-off angle; ⑤ The effect of GFM equivalent inertia on the critical cut angle; ⑥ is the effect of reactive power control parameters on the critical cut-off angle; ⑦ shows the effect of the GFM active power reference value on the critical cut-off angle; ⑧ The influence of the capacity ratio of grid-type converters on the critical cut-off angle; ⑨ represents the effect of the GFM current limiting value on the critical cut-off angle. Detailed Implementation
[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0023] The hybrid system in this embodiment includes a grid-connected converter (GFL) and a grid-connected converter (GFM). The grid-connected converter and the grid-connected converter are connected to a common coupling point through corresponding grid-connected branches and connected to the power grid through power grid lines. The two types of converters form electrical coupling through an impedance network.
[0024] like Figure 1 As shown, this application provides a method for transient attraction domain stability analysis of a hybrid system, which includes a grid-connected converter and a grid-connected converter, comprising: S1: Construct the transient energy function of the hybrid system of grid-connected converter and grid-connected converter, and obtain the static potential energy function used to characterize the transient stability boundary of the system; First, based on the synchronous control characteristics of grid-connected and network-type converters, corresponding transient dynamic equations are established. The power angle, angular frequency, output power, damping power of the two types of converters, as well as the coupling power formed by the two through the impedance network, are incorporated into the transient mathematical model.
[0025] By multiplying both sides of the corresponding transient dynamic equations by the angular velocities of the grid-type and mesh-type converters respectively, the transient energy expressions of the two types of converters are obtained. Conservative terms related to the power angle are extracted from the transient energy, and the cross-coupling effect between the grid-type and mesh-type converters caused by the impedance network is considered to form potential energy components that describe the self-synchronization effect and mutual synchronization effect of the two types of converters.
[0026] Combining the above potential energy components, we obtain δ GFL and δ GFM For hybrid systems with state variables, the static potential function of the GFM and GFL can be compared accordingly. The specific results are as follows: (1); In the formula, δ GFM For the GFM angle, δ GFL For GFL power angle, δ d ω is the relative angle of attack between GFL and GFM. GFL ω is the angular frequency of the GFL. GFM Let ω be the angular frequency of the GFM. d k is the relative angular frequency between GFL and GFM. p-PLL k is the proportional gain of the phase-locked loop. i-PLL J is the integral coefficient of the phase-locked loop. GFM D is the inertia coefficient of the GFM. GFM P is the GFM damping coefficient. GFM-ref For GFM power commands, P GFL-ref For GFL power commands, U GFM X represents the output voltage amplitude of the GFM. GFL X is the GFL line impedance. GFM Let q be the GFM line impedance, q be the capacity ratio of the grid-type converter, a and b be simplification factors, and P be the line impedance. D-GFM and P D-GFL The damping power of GFM and GFL are respectively, P GFM and P GFL The braking power of GFM and GFL are respectively, I GFL-d and I GFL-q These are the d-axis and q-axis current components of the GFL, respectively.
[0027] Multiply both sides of equation (1) by the angular velocity ω of the strain gauge. GFM and ω GFL Then the transient energy E of GFM can be obtained. k-GFM and the transient energy E of GFL k-GFL , means as follows: (2); (3); Ignore ω GFM and ω GFL The damping term is used to extract the GFM work angle δ. GFM and GFL power angle δ GF The relevant conservative term W GFM and W GFL In the formula P GFL-ref=abI GFL-d .
[0028] (4); Meanwhile, GFM and GFL are cross-coupled through an impedance network, and their mutual synchronization constraint term W GFL+GFM You can first solve it using the integration rule, and then supplement I. GFL-d To meet the same benchmark: (5); The transient energy function and global static potential V are constructed based on the Lyapunov direct method. p It is the linear superposition of the self-synchronization potential energy of each node in the system and the mutual synchronization potential energy between nodes. Adding the conservative components derived in the above three steps and taking the negative sign, we obtain the static potential energy function V of the hybrid system. p (δ GFL δ GFM As shown in the following formula: (6); Equation (6) describes the static potential energy function of the hybrid system, which can only describe the stability boundary constraints under a single fault condition. However, I in this function... GFL-d I GFL-q U GFM Since it is related to the current limiting constraint, it is necessary to explore the transient attraction domain and phase trajectory after current limiting separately.
[0029] S2: Determine the transient attraction domain and phase trajectory of the hybrid system based on the static potential energy function; Based on the static potential energy function V obtained in step S1 p Determine the stable equilibrium point of the hybrid system and the potential energy boundary corresponding to the stable equilibrium point, and use δ GFL and δ GFM A two-dimensional state space is constructed for the coordinates; in the two-dimensional state space, a transient attraction domain of the hybrid system is formed based on the stable equilibrium point and the potential energy boundary. The transient attraction domain represents the state region where the system can recover to a stable operating state under the corresponding operating conditions.
[0030] Further, system disturbance conditions were set up to obtain δ values before the fault, during the fault, and after the fault was cleared. GFL and δ GFM The corresponding state points are mapped to the two-dimensional state space in chronological order, thereby forming the phase trajectory corresponding to the fault process. By comparing the positional relationship between the phase trajectory and the transient attraction domain, it can be determined whether the system can return to a stable state after experiencing a fault disturbance.
[0031] Since the current limiting of the equipment changes the relationship between the output voltage of the grid-type converter and the system power, the static potential energy function, transient attraction domain and phase trajectory are calculated for the operating states of no current limiting and current limiting respectively, so as to obtain the system stability boundary considering the influence of equipment current limiting.
[0032] S3: Introduce the static stability boundary and equipment current limiting constraint of the grid-connected converter into the transient attraction domain to obtain the modified transient attraction domain that simultaneously considers the static stability boundary and equipment current limiting constraint; Based on the transient attraction domain obtained in step S2, the static stability boundary of the grid-connected converter is further determined. For the case of considering only a single grid-connected converter, the static stability range can be determined according to the relationship between its power angle and damping power. For the grid-connected / grid-connected hybrid system in this embodiment, since the damping power P of the grid-connected converter... D-GFL It is also affected by the operating status of the grid-type converter, therefore, the P under the condition of hybrid system is adopted. D-GFL Make a judgment.
[0033] When P D-GFL When P is greater than zero, the corresponding state is determined as the positive damped static steady state of the grid-connected converter; when P D-GFL When the positive damping condition is not met, the corresponding state is defined as the negative damping instability state, and the state boundary between the two is used as the static stability boundary of the grid-connected converter; at the same time, the equipment current limiting constraint is determined according to the preset current limiting value of the equipment, when the output current I of the grid-connected converter... GFM Reaching the corresponding current limit value I GFM-max At that time, the current limiting boundary is determined; the region exceeding the current limiting boundary is designated as the current limiting constraint region, and the transient energy boundary, the static stability boundary of the grid-connected converter, and the equipment current limiting boundary are uniformly mapped to δ. GFL -δ GFM In the two-dimensional state space, a modified transient attraction domain is formed, which simultaneously reflects transient energy constraints, static stability constraints of grid-connected converters, and equipment current limiting constraints.
[0034] S4: Based on the modified transient attraction domain and phase trajectory, analyze the parameters affecting the transient stability of the hybrid system and their influence laws.
[0035] The parameters affecting the operating state of the hybrid system are selected as the parameters to be analyzed. While keeping other operating conditions constant, the parameters to be analyzed are changed, and the transient response, static potential function, modified transient attraction domain, and phase trajectory of the system are recalculated for each set of parameters. The changes in the area of the modified transient attraction domain and the positional changes between the phase trajectory and the stability boundary are compared under different parameter conditions. Thus, the influence of the parameters to be analyzed on the transient stability range and transient stability performance of the hybrid system is analyzed.
[0036] In this embodiment, the parameters to be analyzed may include line impedance, system operating parameters, grid-type converter control parameters, and grid-connected converter control parameters. By comparing parameters under a unified modified transient attraction domain analysis framework, the problem of inconsistent analysis benchmarks caused by evaluating different parameters separately using different stability indices can be avoided.
[0037] Furthermore, constructing the transient energy function of the hybrid system and obtaining the static potential energy function includes: The transient energies of the grid-connected converter and the grid-connected converter are obtained respectively based on the transient dynamic equations. Ignoring the damping terms related to angular velocity, conservative terms related to the power angle of the grid-type converter and the power angle of the grid-type converter are extracted respectively to obtain the self-synchronization potential energy components of the grid-type converter and the grid-type converter. Based on the cross-coupling relationship between grid-type converters and network-type converters through the impedance network, the mutual synchronization potential energy components between the two types of converters are obtained. Based on the Lyapunov direct method, the self-synchronization potential energy components of the grid-type converter, the self-synchronization potential energy components of the follow-grid converter, and the mutual synchronization potential energy components are superimposed to construct the static potential energy function of the hybrid system with the power angles of the follow-grid converter and the grid-type converter as state variables.
[0038] First, based on the transient dynamic equations of the grid-type converter and the grid-connected converter, the transient energy E of the grid-type converter is obtained respectively. k-GFM Transient energy E of grid-connected converter k-GFL Secondly, neglecting the transient energy related to ω GFM and ω GFL The relevant damping term is extracted from δ. GFM The relevant conservative term W GFM and with δ GFL The relevant conservative term W GFL These are respectively taken as the self-synchronization potential energy components of the grid-type converter and the grid-connected converter; further considering the cross-coupling relationship formed by the two types of converters through the impedance network, the mutual synchronization potential energy component W between the grid-connected converter and the grid-type converter is obtained based on the coupling relationship. GFL+GFM The mutual synchronization potential energy component is used to describe the influence of the power angle state change of one type of converter on the synchronization state of another type of converter through the impedance network. Finally, based on the Lyapunov direct method, the self-synchronization potential energy components of the grid-type converter, the self-synchronization potential energy components of the mesh-type converter, and the mutual synchronization potential energy components are combined to obtain the global static potential energy function V of the hybrid system. p (δ GFL δ GFM ).
[0039] Therefore, the static potential energy function not only describes the synchronization relationship between a single converter and the power grid, but also includes the synchronization effect of the grid-connected converter, the grid-connected converter itself, and the coupling synchronization effect between the two types of converters.
[0040] Furthermore, determining the transient attraction domain of a hybrid system based on the static potential function includes: The stable equilibrium point and corresponding potential energy boundary of the hybrid system are determined based on the static potential energy function, and the transient attraction domain is determined in the two-dimensional state space composed of the power angles of the grid-type converter and the grid-type converter. The phase trajectory is calculated based on the changes in system state before, during, and after the fault is cleared, and then mapped to the transient attraction domain to determine the transient stable state of the system after the fault. When the output current of the grid converter exceeds the preset current limit, the static potential energy function is corrected according to the change in the relationship between the output voltage of the grid converter and the system power after current limiting, and the transient attraction domain and phase trajectory are re-determined according to the corrected static potential energy function.
[0041] Further, in step S2, according to V p (δ GFL δ GFM ) Obtain the corresponding stable equilibrium point and potential energy boundary, and at δ GFL -δ GFM A transient attraction domain is formed in the two-dimensional state space. After a system fault occurs, δ is recorded in chronological order: before the fault, during the fault, and after the fault is cleared. GFL and δ GFM The corresponding state points are connected to form a phase trajectory. When the phase trajectory after the fault is cleared remains in the stable region and approaches the stable equilibrium point again, it can be determined that the corresponding operating condition is in a transient stable state. When the phase trajectory crosses the corresponding stable boundary and cannot return to the stable equilibrium point, it can be determined that the corresponding operating condition has experienced transient instability.
[0042] Regarding the impact of equipment current limiting, in a specific operating condition, the voltage U after a power grid fault is set. g Set the fault duration T to 0.3 pu. s The transient attraction domains and phase trajectories are 0.6 s and 0.78 s, respectively, and the transient attraction domains and phase trajectories are compared with and without considering current limiting. When I GFM More than I GFM-max At this time, the grid-type converter enters the current-limiting state, U GFM It changes depending on the current limiting status. Because U GFM It participates in the static potential energy function and the system power relationship, therefore, according to the current-limited U... GFM The power relationship is redefined, and the static potential energy function V is modified accordingly. p Then, the transient attraction domain and phase trajectory are redefined.
[0043] Depend on Figure 2 The results show that the current-limited state will change the original transient attraction domain and phase trajectory. Therefore, when analyzing the transient stability of the hybrid system under the current-limited conditions, it is necessary to use the static potential energy function and attraction domain corresponding to the current-limited state, and not continue to use the potential energy boundary of the unlimited state.
[0044] Furthermore, the static stability boundary and equipment current limiting constraint of the grid-type converter are introduced into the transient attraction domain, including: Using the fact that the damping power of the grid-connected converter is greater than zero as the static stability criterion, the static stability boundary of the grid-connected converter in the hybrid system is determined. Determine the current limiting constraint boundary based on the equipment current limit value, and divide the current limiting area beyond the current limit constraint; By superimposing the static stability boundary and the current limiting constraint boundary with the transient energy boundary, a modified transient attraction domain that simultaneously considers the transient energy boundary, the static stability boundary of the grid-connected converter, and the current limiting constraint of the equipment is obtained.
[0045] To determine the static stability region of the grid-connected converter, the damping power P of the grid-connected converter in the hybrid system is used. D-GFL The determination is made under conditions different from those for a single grid-connected converter. In this embodiment, P... D-GFL Simultaneously affected by both the state of the grid-connected converter and the state of the grid-connected converter, δ is often used in engineering. GFL Drawing the statically stable boundary of the GFL for π / 2 essentially involves considering only the damping power P of the GFL. D-GFL It is a function of cosines, and when it is greater than π / 2, the damping is zero, leading to instability. However, in a hybrid system, P... D-GFL Also related to GFM, redefining P D-GFL as follows: (7); GFL can only remain statically stable when the constant value of I in equation (7) is always greater than zero. Meanwhile, due to I... GFM-max and I GFL-q All of these will change U in equation (6) GFM δ d Therefore, in Figure 2 Based on this, the transient attraction domain considering the statically stable boundary is plotted, specifically as follows: Figure 3 As shown in the figure. The red area represents GFL negative damping instability, the green area represents GFL positive damping static stability, and the gray area represents triggered overcurrent constraints. The boundary between the red and green areas is the static stability boundary. Figure 3 The area percentages are plotted in Table 1 below.
[0046] Table 1. Percentage of Transient Attraction Domain Area in Hybrid Systems
[0047] according to Figure 3 As shown in Table 1, the statically stable boundary values are larger than π / 2 for both current limiting and non-current limiting considerations compared to the single GFL. Without current limiting, the total area, red area, and green area of the transient attraction domain account for 53.4%, 45.1%, and 8.3%, respectively. With current limiting, the total area, red area, and green area of the transient attraction domain decrease to 35.4%, 22.2%, and 1.98%, respectively, while the gray area accounts for 11.2%. Therefore, current limiting worsens the transient attraction domain of the hybrid system.
[0048] Specifically, satisfying P D-GFL The region with a resistance greater than 0 is designated as the positive damping static stability region of the grid-connected converter, and the region that does not meet the positive damping condition is designated as the negative damping instability region. The boundary between the two regions serves as the static stability boundary of the grid-connected converter. Simultaneously, I... GFM-max As the equipment current limiting value for grid-type converters, I GFM Reaching I GFM-max The corresponding state boundary is determined as the current limiting constraint boundary, and the state region exceeding the current limiting constraint is determined as the current limiting region, such as... Figure 3 As shown, in one specific representation, the positive damping static stability region, the negative damping instability region, and the region triggering overcurrent constraint are displayed separately. By combining the above regions with the transient energy boundary, the modified transient attraction domain can be obtained.
[0049] Furthermore, the analysis examines the parameters affecting the transient stability of the hybrid system and their influence patterns, including: Based on the modified transient attraction domain and phase trajectory, the parameters to be analyzed are changed respectively to obtain the transient response of the system under different parameters, and the corresponding modified transient attraction domain is plotted. Based on the changes in the transient attraction domain area and phase trajectory, the influence of the parameters to be analyzed on the transient stability range and stability performance of the hybrid system is determined.
[0050] Specifically, the parameters to be analyzed are changed one by one. For any parameter to be analyzed, with other operating parameters and fault conditions remaining unchanged, at least two different parameter values are set respectively. Steps S1 to S3 are executed for each parameter value to obtain the corresponding power, power angle and voltage transient response, corrected transient attraction domain and phase trajectory.
[0051] For those capable of changing the static potential function V pThe parameters are compared based on the area and boundary position of the modified transient attraction domain under different parameter conditions. For parameters that mainly change the dynamic process of the power angle without changing the static potential energy function, the influence of the phase trajectory on transient stability is judged by the change of the phase trajectory in the modified transient attraction domain. Specifically, the proportion of the area of the modified transient attraction domain to the two-dimensional analysis region can be calculated, and the change of the area proportion under different parameter conditions can be compared. At the same time, it is observed whether the phase trajectory crosses the boundary of the modified transient attraction domain and whether it can return to the stable equilibrium point after the fault is cleared. Thus, the influence law of the parameters to be analyzed on the transient stability range and stability performance of the hybrid system is obtained.
[0052] Furthermore, the parameters to be analyzed include line impedance; By changing the impedance of the power grid line, the impedance of the grid-connected converter branch, and the impedance of the grid-connected converter branch, the transient responses of the system power, power angle, and voltage under different line impedances are obtained, and the corresponding modified transient attraction domains are plotted to determine the influence of line impedance on the transient stability performance of the hybrid system.
[0053] Furthermore, when the parameter to be analyzed is the line impedance, the power grid line impedance X is changed respectively. g , and the branch impedance X of the grid converter GFL and the branch impedance X of the grid-type converter GFM .
[0054] With X GFL For example, X GFL The changes will first alter the braking power, mutual braking power, damping power, and power angle δ of the grid-connected converter. GFL ;δ GFL The changes further affect the power and δ of the grid converter. GFM And ultimately affect U GFM and the voltage at the common coupling point U PCC Therefore, changes in line impedance can alter the static potential energy function and transient attraction domain through the aforementioned coupling relationship.
[0055] Furthermore, the parameters to be analyzed include system operating parameters; By changing the grid voltage sag depth, the capacity ratio of grid-connected converters, and the equipment current limit, the modified transient attraction domain under different system operating parameters is plotted and its area ratio is calculated to determine the influence of grid voltage sag depth, grid ratio, and current limit on the transient stability range of the hybrid system.
[0056] Furthermore, when the parameters to be analyzed are system operating parameters, the voltage U during power grid faults is changed respectively. g The capacity ratio q of the grid-type converter and the current limiting value I of the grid-type converter GFM-max .
[0057] For each system operating parameter, keeping other operating conditions constant, calculate δ. GFL and δ GFM The transient response is then determined, and the modified transient attraction domain is reconstructed and the corresponding area percentage is calculated.
[0058] By using the above parameter scanning methods, the changes in the corrected transient attraction domain caused by changes in grid fault voltage, grid capacity ratio, and equipment current limiting capability can be obtained respectively. Based on the area ratio and phase trajectory, the impact of the corresponding system operating parameters on the transient stability range can be determined.
[0059] Furthermore, the parameters to be analyzed include the control parameters of the grid-type converter; By changing the equivalent moment of inertia, equivalent damping coefficient, reactive power control parameters, and active power reference values of the grid-type converter, the influence of the grid-type converter control parameters on the transient stability performance of the hybrid system is determined based on the changes in the area of the corrected transient attraction domain and the phase trajectory.
[0060] Furthermore, when the parameters to be analyzed are the control parameters of a grid-type converter, the equivalent moment of inertia J of the grid-type converter is changed respectively. GFM Equivalent damping coefficient D GFM Reactive power control parameter k q and active power reference value P GFM-ref .
[0061] For P GFM-ref Its change can directly alter the static potential energy function V. p For k q Its changes affect U GFM Indirectly changing the static potential energy function V p Therefore, for P GFM-ref and k q The analysis can be mainly based on the correction of the transient attraction domain area and phase trajectory under different parameter conditions.
[0062] For J GFM and D GFM Its changes mainly affect δ GFM The transient dynamic process, without directly changing the static potential energy function V p Therefore, the evaluation mainly utilizes phase trajectories. This is achieved by changing J... GFM and D GFM By comparing whether the phase trajectory crosses the boundary of the modified transient attraction domain during and after the fault is cleared, and whether it can return to the stable equilibrium point, the influence of inertia parameters and damping parameters on the transient stability performance of the system can be determined.
[0063] Furthermore, the parameters to be analyzed include the control parameters of the grid-type converter; By changing the proportional gain, integral gain, and active current command of the phase-locked loop (PLL) of the grid-connected converter, the changes in the area of the corrected transient attraction domain and the phase trajectory caused by the changes in different control parameters are compared, and key control parameters that have a significant impact on the transient stability performance of the hybrid system are screened.
[0064] Furthermore, when the parameters to be analyzed are the control parameters of a grid-type converter, the proportional coefficient k of the phase-locked loop is changed respectively. p-PLL Phase-locked loop integral coefficient k i-PLL and active current command I GFL-d .
[0065] δ is obtained for each control parameter. GFL and δ GFM The transient response is obtained, and the corresponding modified transient attraction domain and phase trajectory are re-obtained.
[0066] Parameter Analysis Based on the Quasi-Stable Attraction Domain Method 1) Line impedance Using GFL line impedance X GFL For example, X GFL It will change the braking power P of the GFL GFL Inter-braking power P GFL+GFM Damping power P D-GFL Mutual damping power P D-GFL+GFM and work angle δ GFL Due to δ GFL The change affects the braking power P of the GFM GFM Inter-braking power P GFM+GFL and work angle δ GFM Ultimately, this affects the output voltage amplitude U of the GFM converter. GFM and grid connection point voltage amplitude U PCC .
[0067] Figure 4 Showcasing different X GFL Transient power, power angle, and voltage characteristics of a GFL / GFM hybrid system under specified parameters. The simulation time is 15 seconds, with 7-8 seconds representing the fault phase. g The price dropped to 0.41 PU, and X was taken from each. GFL =0.1pu, 0.15pu and 0.2pu. Figure 4 Zhong Sui X GFL Increase, δ in (a) GFL and δ GFM The transient deviation increases, and the state changes from transient stability to stability. (b) X in braking power GFL Changes directly affect P GFL and P GFL+GFM The total size of the entire stage, and its impact on P after fault recovery. GFM Dynamic. Wherein, PGFM The situation before and during the fault was basically the same, while P GFM+GFL There are differences. When X GFL When δ is large GFL and δ GFM Instability occurs, and the braking power also fluctuates with the power angle. (c) The damping power is basically zero before the fault, and fluctuates with the X angle during the fault. GFL Increases with power angle, and fluctuates according to the power angle after the fault. (d) Voltage before and during the fault varies with X. GFL Slight changes, followed by oscillations with the power angle after a fault.
[0068] Similarly, X GFM and X GFL Changes can also affect the transient characteristics of hybrid systems. Figure 5 Showcasing different X GFM and X g The power angle transient characteristics of the hybrid system, where U g Dropped to 0.47 PU, selected X GFM and X g They are 0.1 pu, 0.2 pu, and 0.3 pu, respectively. (By...) Figure 5 It can be known that X GFM and X g It directly affects the system's transient power angle and voltage stability.
[0069] Figure 6 The transient attraction domain of the hybrid system under different impedances is given. As can be seen from the figure, the change in line impedance affects the transient attraction domain, which essentially changes the potential energy function V. p Different X GFL X g and X GFM The percentage of transient attraction domain area is shown in Table 2 below.
[0070] Table 2. Percentage of transient attraction region area under impedance changes of each line.
[0071] X in the table g and X GFL and X GFM As X increases, its attractive field tends to decrease. In summary, a smaller X... g X GFL and X GFM The magnitude of the impedance is beneficial to improving the transient stability of the system.
[0072] 2) System parameters System parameters affect the transient characteristics of a hybrid system. This section will explore the grid voltage U. g Drop depth, network coverage ratio q, and current limiting amplitude I GFM-max Impact on system transients.
[0073] Figure 7 Showcasing different U g q and I GFM-max The transient power angle characteristics of the hybrid system change, q and I GFM-max Middle U g It dropped to 0.47 pu. Figure 7 (a) U in g During the fall, δ GFM and δ GFL It tends to shift from stability to instability and volatility. Figure 7 (b) When q increases, δ GFL δ GFM It tends to become unstable from a transient state of stability. Figure 7 (c) I GFM-max When it decreases, δ GFM and δ GFM From stability to instability.
[0074] Figure 8 The transient attraction domain of the hybrid system under different system parameters is shown. Different U g q and I GFM-max The percentage of transient attraction domain area is shown in Table 3 below.
[0075] Table 3. Percentage of transient attraction domain area under changes in various system parameters.
[0076] Figure 8 Middle U g q and I GFM-max The effect of changes in system parameters on the transient attractive domain is essentially a change in the potential energy function V. p U in the table g , q and I GFM-max As q decreases, the attraction domain tends to decrease as well. Therefore, larger q and I... GFM-max and smaller U g It is beneficial to the transient stability of the system.
[0077] 3) Control parameters Control parameters also affect the transient characteristics of hybrid systems; the inertia parameter J of the GFM (Geostationary Mechanism) GFM Damping parameter D GFM droop coefficient k q and GFM active power reference value P GFM-ref Changes can affect the transient characteristics of a hybrid system.
[0078] Figure 9 Showing different J GFM D GFM k q and P GFM-refChanges in the transient power angle characteristics of the lower system. Figure 9 (a) J GFM When it increases, δ GFM and δ GFL It tends to stabilize after the first wave of instability. Figure 9 (b) D GFM When it increases, δ GFL δ GFM It tends to stabilize from transient instability. Figure 9 (c) k q When it increases, δ GFM and δ GFM From stable to unstable. Figure 9 (d) P GFM-ref When it increases, δ GFM and δ GFM Transient overshoot increases.
[0079] Figure 10 The transient attraction domain of the hybrid system under different GFM control parameters is shown. Figure 10 P was observed in (a) and (b) GFM-ref and k q The change affected the transient attraction domain, P GFM-ref It directly changed the potential energy function V p k q By changing U GFM Indirectly affecting V p . Figure 10 In (c) and (d), due to J GFM and D GFM Direct control δ GFM Change without changing V p It can only analyze the transient performance of phase trajectory parameters by judging the phase trajectory. Different P GFM-ref and k q The area ratio of the attraction domain is shown in Table 4 below.
[0080] Table 4P GFM-ref and k q Percentage of transient attraction domain area under change
[0081] P in Table 4 GFM-ref and k q Decreasing both increases the area of the attraction field, while J GFM and D GFM The phase trajectory changes from unstable to stable during the fault period. Therefore, in a hybrid system, the GFM active loop P GFM-ref J GFM D GFM and reactive power loop k q Changes in have a significant impact on its transient characteristics.
[0082] In addition, the PLL scaling parameter k in GFL p-PLL Integral parameter k i-PLL and instruction I GFL-d Changes can also affect the transient characteristics of hybrid systems. Figure 11 The changes in the transient characteristics of the system power angle under different GFL control parameters are shown. Figure 11 Chinese K p-PLL and k i-PLL Changes with δ GFL and δ GFM While there are dynamic differences, they have virtually no impact on stability. GFL-d Decrease, transient stability.
[0083] Figure 12 The transient attraction domain and phase trajectory of the hybrid system under different GFL control parameters are shown. Figure 12 It can be known that k p-PLL and k i-PLL The changes have virtually no impact on the change of the phase trajectory endpoint, while I GFL-d Reducing the size of the field of attraction is beneficial to increasing the transient attraction domain, which is consistent with the transient characteristics of the work angle.
[0084] In summary, only the GFL parameter I GFL-d GFM parameter J GFM D GFM k q and P GFM-ref Changes can affect the stability of hybrid systems, k p-PLL and k i-PLL No impact. GFM control parameters are key parameters for improving the transient performance of hybrid systems and can be used as a basis for designing coordinated control methods for hybrid systems.
[0085] Meanwhile, the effects of variations in line impedance, system parameters, and control parameters on critical clearing time (CCT) and critical clearing angle (CCA) were analyzed.
[0086] Figure 13 and Figure 14 The changes in CCT and CCA under different parameters are shown respectively. Figure 13 In the middle, the line impedance X g X GFM X GFL Increasing the value significantly reduces the CCT; control parameter D GFM J GFM Increase and k q and P GFM-ref Decreasing significantly improves CCT; system parameters q and I GFM-max Improving both can increase CCT. Figure 14 The trend of CCA in China is opposite to that of CCT.
[0087] Based on the qualitative and quantitative analysis above, the influence patterns on transient stability indices are summarized as shown in Table 5.
[0088] Table 5 Summary of Influence Patterns
[0089] Therefore, this invention provides a transient attraction domain stability analysis method for root / structure hybrid systems that considers static stability boundaries, solving the problem of insufficient consideration of GFL static stability boundaries and equipment current limiting constraints in existing transient attraction domain analyses. It systematically reveals the influence mechanism of line impedance, system parameters, and control parameters on the transient stability of root / structure hybrid systems, providing a theoretical basis and practical tools for transient stability assessment, parameter optimization, and coordinated control design of hybrid systems.
[0090] Furthermore, the methods also include: By changing the line impedance, system operating parameters, and converter control parameters respectively, calculate the critical cut-off time and critical cut-off angle of the hybrid system under the change of each parameter. Plot the relationship between parameters and critical cut-off time and critical cut-off angle to quantify the impact of different parameters on the transient stability margin of the hybrid system.
[0091] Furthermore, in order to evaluate the transient stability margin of the system based on the modified transient attraction domain analysis, the critical cut-off time (CCT) and critical cut-off angle (CCA) are calculated under different line impedances, system operating parameters, and converter control parameters.
[0092] For any parameter to be analyzed, first fix other operating parameters and fault conditions, gradually change the fault duration, and calculate the phase trajectory after fault clearance for each fault duration. When the phase trajectory after fault clearance can still remain within the stable range allowed by the modified transient attraction domain and return to the stable equilibrium point, increase the fault duration. When the phase trajectory crosses the corresponding stable boundary and enters the unstable state, continue to narrow the fault duration search range between the stable and unstable operating conditions until the critical fault duration between stability and instability is obtained. This time is determined as the critical clearing time CCT. After determining the CCT, read the system power angle state corresponding to the critical fault clearance time, and determine the corresponding critical clearing angle CCA according to the adopted power angle definition.
[0093] Change X in the manner described above. g X GFL X GFM J GFM D GFM k q PGFM-ref q and I GFM-max Then, calculate the corresponding CCT and CCA, and plot the relationship between the parameter to be analyzed and the changes in CCT and CCA.
[0094] Therefore, the modified transient attraction domain is used to characterize the system's stable range, the phase trajectory is used to characterize the evolution of a specific fault state within the stable range, and CCT and CCA are further used to characterize the system's margin from the critical instability state, thereby enabling a quantitative comparison of the effects of different parameters.
[0095] Through the above implementation methods, the transient energy coupling relationship between grid-connected converters and grid-connected converters, the static stability constraints of grid-connected converters, and the equipment current limiting constraints can be uniformly incorporated into the transient attraction domain analysis. Furthermore, the influence of different line, operation, and control parameters on the transient stability of the hybrid system can be analyzed by using the modified transient attraction domain, phase trajectory, critical cut-off time, and critical cut-off angle.
[0096] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of the application as defined herein, and are to be considered as covering any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.
Claims
1. A method for transient attraction domain stability analysis of a hybrid system, wherein the hybrid system includes a grid-connected converter and a grid-connected converter, characterized in that, include: A transient energy function is constructed for a hybrid system of grid-connected and grid-connected converters, and a static potential energy function is obtained based on the transient energy function to characterize the transient stability boundary of the system. The transient attraction domain and phase trajectory of the hybrid system are determined based on the static potential energy function. By introducing the static stability boundary and equipment current limiting constraint of the grid-connected converter into the transient attraction domain, a modified transient attraction domain that simultaneously considers the static stability boundary and equipment current limiting constraint is obtained. Based on the modified transient attraction domain and phase trajectory, the parameters affecting the transient stability of the hybrid system and their influence laws are analyzed.
2. The method for analyzing the stability of the transient attraction domain of a hybrid system according to claim 1, characterized in that, Constructing the transient energy function of the hybrid system and obtaining the static potential energy function includes: The transient energies of the grid-connected converter and the grid-connected converter are obtained respectively based on the transient dynamic equations. Remove the damping terms related to the angular velocity of the grid-connected converter and the grid-type converter, and extract the conservative terms related to the power angle of the grid-type converter and the power angle of the grid-connected converter, respectively, to obtain the self-synchronization potential energy component of the grid-type converter and the self-synchronization potential energy component of the grid-connected converter. Based on the cross-coupling relationship between grid-type converters and network-type converters through the impedance network, the mutual synchronization potential energy components between the two types of converters are obtained. Based on the Lyapunov direct method, the self-synchronization potential energy components of the grid-type converter, the self-synchronization potential energy components of the grid-following converter, and the mutual synchronization potential energy components are superimposed to construct the static potential energy function of the hybrid system with the power angles of the grid-following converter and the grid-type converter as state variables.
3. The method for analyzing the stability of the transient attraction domain of a hybrid system according to claim 1, characterized in that, Determining the transient attraction region of the hybrid system based on the static potential energy function includes: Based on the static potential energy function, the stable equilibrium point and corresponding potential energy boundary of the hybrid system are determined, and the transient attraction domain is determined in the two-dimensional state space composed of the power angle of the grid-type converter and the power angle of the grid-type converter. The phase trajectory is calculated based on the changes in the power angle of the grid-connected converter and the grid-connected converter over time before, during, and after the fault is cleared. The phase trajectory is then mapped to the transient attraction domain to determine the transient stable state of the system after the fault. When the output current of the grid converter exceeds the preset current limit, the static potential energy function is corrected according to the change in the relationship between the output voltage of the grid converter and the system power after current limiting, and the transient attraction domain and phase trajectory are re-determined according to the corrected static potential energy function.
4. The method for analyzing the transient attraction domain stability of a hybrid system according to claim 1, characterized in that, Introducing the static stability boundary and equipment current limiting constraint of the grid-connected converter into the transient attraction domain includes: Using the fact that the damping power of the grid-connected converter is greater than zero as the static stability criterion, the static stability boundary of the grid-connected converter in the hybrid system is determined. Determine the current limiting constraint boundary based on the equipment current limit value, and divide the current limiting area beyond the current limit constraint; By superimposing the static stability boundary and current limiting constraint boundary with the transient energy boundary, a modified transient attraction domain that simultaneously considers the transient energy boundary, the static stability boundary of the grid-connected converter, and the current limiting constraint of the equipment is obtained.
5. The method for analyzing the stability of the transient attraction domain of a hybrid system according to claim 1, characterized in that, Analyze the parameters affecting the transient stability of the hybrid system and their influence laws, including: Based on the modified transient attraction domain and phase trajectory, the parameters to be analyzed are changed respectively to obtain the transient response of the system under different parameters, and the corresponding modified transient attraction domain is plotted. Based on the changes in the transient attraction domain area and phase trajectory, the influence of the parameters to be analyzed on the transient stability range and stability performance of the hybrid system is determined.
6. The method for analyzing the stability of the transient attraction domain of a hybrid system according to claim 5, characterized in that, The parameters to be analyzed include line impedance; By changing the impedance of the power grid line, the impedance of the grid-connected converter branch, and the impedance of the grid-connected converter branch, the transient responses of the system power, power angle, and voltage under different line impedances are obtained, and the corresponding modified transient attraction domains are plotted to determine the influence of line impedance on the transient stability performance of the hybrid system.
7. The method for analyzing the stability of the transient attraction domain of a hybrid system according to claim 5, characterized in that, The parameters to be analyzed include system operating parameters; By changing the grid voltage sag depth, the capacity ratio of grid-connected converters, and the equipment current limit, the modified transient attraction domain under different system operating parameters is plotted and its area ratio is calculated to determine the influence of grid voltage sag depth, grid ratio, and current limit on the transient stability range of the hybrid system.
8. The method for analyzing the stability of the transient attraction domain of a hybrid system according to claim 5, characterized in that, The parameters to be analyzed include the control parameters of the grid-type converter; By changing the equivalent moment of inertia, equivalent damping coefficient, reactive power control parameters, and active power reference values of the grid-type converter, the influence of the grid-type converter control parameters on the transient stability performance of the hybrid system is determined based on the changes in the area of the corrected transient attraction domain and the phase trajectory.
9. The method for analyzing the stability of the transient attraction domain of a hybrid system according to claim 5, characterized in that, The parameters to be analyzed include the control parameters of the grid-type converter; By changing the proportional gain, integral gain, and active current command of the phase-locked loop (PLL) of the grid-connected converter, the changes in the area of the corrected transient attraction domain and the phase trajectory caused by the changes in different control parameters are compared, and key control parameters that have a significant impact on the transient stability performance of the hybrid system are screened.
10. The method for analyzing the transient attraction domain stability of a hybrid system according to claim 1, characterized in that, The method further includes: By changing the line impedance, system operating parameters, and converter control parameters respectively, calculate the critical cut-off time and critical cut-off angle of the hybrid system under the change of each parameter. The relationship between parameters and critical cut-off time and critical cut-off angle is obtained, and the influence of different parameters on the transient stability margin of the hybrid system is quantified.