Heterogeneous new energy grid-connected system transient stability assessment method and system
By establishing the power angle characteristic equation and energy function, the evaluation error of converter dynamic interaction in heterogeneous new energy grid-connected systems was solved, and accurate transient stability assessment was achieved, providing a guarantee for the safe and stable operation of the new energy grid.
Patent Information
- Application Number
- CN202511679838.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-17
- Publication Date
- 2026-02-17
AI Technical Summary
Existing transient stability analysis methods cannot accurately characterize the dynamic interaction between grid-connected and grid-connected converters in heterogeneous renewable energy grid-connected systems, leading to inaccurate evaluation results and affecting the safe and stable operation of high-proportion renewable energy power grids.
By establishing the power angle characteristic equation of the grid converter and combining it with the energy function, the critical energy value at the unstable equilibrium point is solved to evaluate the transient stability of the system. The model is directly based on the electrical quantity relationship, which avoids the model distortion problem of equating the grid converter with constant impedance in the traditional method.
It improves the accuracy of transient stability assessment of heterogeneous new energy grid-connected systems, provides operable assessment standards, and can quickly and accurately determine the stability status of the system.
Smart Images
Figure CN121543873A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of power system stability analysis and control, and more specifically, to a transient stability assessment method and system for heterogeneous new energy grid-connected systems. Background Technology
[0002] With the rapid development of new energy bases in the Gobi Desert and offshore wind power, grid-connected control technology is becoming increasingly popular, and new energy grid-connected systems are forming a new heterogeneous form where grid-connected and grid-connected converters coexist. However, existing transient stability analysis methods are mostly for systems with a single control strategy, and when dealing with grid-connected converters, they are often simplified to a constant impedance model. This simplification distorts the essential characteristics of the current source and cannot accurately characterize its true dynamics during transient processes.
[0003] When two types of converters coexist in a system, the complex dynamic interaction renders traditional evaluation theories ineffective. Currently, there is a lack of effective methods to accurately analyze such heterogeneous systems and quickly assess their transient stability, which restricts the safe and stable operation of power grids with a high proportion of new energy sources.
[0004] Therefore, this application provides a transient stability assessment method and system for heterogeneous new energy grid-connected systems to solve one of the aforementioned technical problems. Summary of the Invention
[0005] The purpose of this application is to provide a transient stability assessment method and system for heterogeneous renewable energy grid-connected systems, which can solve at least one of the aforementioned technical problems. The specific solution is as follows: According to a specific embodiment of this application, in a first aspect, this application provides a transient stability assessment method for a heterogeneous renewable energy grid-connected system, applicable to a heterogeneous renewable energy grid-connected system including a grid-connected converter, a grid-connected converter, and a receiving-end system, comprising the following steps: Based on the electrical quantity relationship between the grid-connected converter and the grid-connected converter, and combined with the electrical quantity characteristics of the heterogeneous renewable energy grid-connected system, the power angle characteristic equation of the grid-connected converter is established. Using the power angle characteristic equation, the energy function of the heterogeneous renewable energy grid-connected system is determined, and by combining the power angle characteristic equation and the energy function, the critical energy value at the unstable equilibrium point is solved. The system energy of the heterogeneous renewable energy grid-connected system at the fault clearing moment is calculated, and the transient stability of the system is evaluated based on the comparison between the system energy and the critical energy value.
[0006] In one embodiment, establishing the power angle characteristic equation of the grid-type converter based on the electrical quantity relationship between the grid-type converter and the grid-connected converter, combined with the electrical quantity characteristics of the heterogeneous new energy grid-connected system, includes: solving for the output current of the grid-type converter based on the electrical quantity relationship between the grid-type converter and the grid-connected converter; based on the output current of the grid-type converter, and according to the electrical quantity characteristics of the heterogeneous new energy grid-connected system, solving for the voltage amplitude and phase angle of the grid-connected converter at the grid connection point; and establishing the power angle characteristic equation of the grid-type converter based on the voltage amplitude and the phase angle.
[0007] In one embodiment, the voltage amplitude of the grid-connected converter at the grid connection point and phase angle It can be expressed using the following formula: ; ; in, This indicates the voltage amplitude at the grid connection point of the grid-connected converter. This represents the equivalent output reactance of a grid-connected converter. Indicates the equivalent reactance of the line. It represents the magnitude of the equivalent internal potential of the power grid. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the voltage phase angle at the grid connection point of the grid-connected converter. This indicates the magnitude of the reactive current injected by the grid-connected converter into the grid connection point. , , , , These are intermediate coefficients introduced to simplify the expression, and are represented as follows: ; ; ; ; .
[0008] In one embodiment, determining the energy function of the heterogeneous new energy grid-connected system using the power angle characteristic equation includes: deriving the second-order rotor motion equation of the grid-connected converter based on the power angle characteristic equation; and performing an initial integration on the second-order rotor motion equation to obtain the energy function of the heterogeneous new energy grid-connected system.
[0009] In one embodiment, the second-order rotor motion equation is expressed by the following formula: ; ;in, This indicates the phase angle of the internal potential of a grid-connected converter. For the electric angular velocity of the grid-type converter, The rated electric angular velocity of the system, , For the virtual inertial time constant of the grid-type converter, This is a reference value for the active power of a grid-type converter. For grid-type converters to output active power, The damping coefficient is used; the energy function of the heterogeneous new energy grid-connected system is expressed by the following formula: ;in, The relative power angle between the grid-type converter and the system at the time of fault clearing. This refers to the power angle value at the stable equilibrium point of the grid-type converter after fault clearance. The electrical angular velocity of the grid-type converter at the moment of fault clearing. The electric angular velocity of the grid-type converter at time t after the fault is cleared.
[0010] In one embodiment, the step of combining the power angle characteristic equation and the energy function to solve for the critical energy value at the unstable equilibrium point includes: for the power angle characteristic equation, setting the output active power of the grid-type converter equal to the active power reference value of the grid-type converter, and in... Within the interval, the stable equilibrium point power angle and the unstable equilibrium point power angle are calculated; for the energy function, combined with the stable equilibrium point power angle and the unstable equilibrium point power angle, and using the fact that the electric angular velocity of the grid-type converter at the unstable equilibrium point is 0, the energy function is solved for the unstable equilibrium point to obtain the critical energy value at the unstable equilibrium point.
[0011] In one embodiment, the work angle characteristic equation is expressed by the following formula: ;in, This indicates the output active power of the grid-connected converter. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. It represents the magnitude of the equivalent internal potential of the power grid. This represents the equivalent output reactance of a grid-connected converter. Indicates the equivalent reactance of the line. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the magnitude of the reactive current injected by the grid-connected converter into the grid connection point. , , , , These are intermediate coefficients introduced to simplify the expression, and are represented as follows: ; ; ; ; .
[0012] In one embodiment, assessing the transient stability of the system based on the comparison between the system energy and the critical energy value includes: if the system energy is less than or equal to the critical energy value, then assessing that the heterogeneous new energy grid-connected system can maintain transient stability; if the system energy is greater than the critical energy value, then assessing that the heterogeneous new energy grid-connected system is about to become transiently unstable.
[0013] In one embodiment, the formula for solving the critical energy value is expressed as follows: ;in, This represents the critical energy value at the unstable equilibrium point. Angle of work at an unstable equilibrium point Stable equilibrium point work angle This indicates the output active power of the grid-connected converter. The phase angle of the internal potential of the grid-connected converter is represented by the following formula: The system energy of the heterogeneous new energy grid-connected system at the moment of fault clearing is calculated using the following formula: ;in, This represents the system energy of a heterogeneous renewable energy grid-connected system at the moment of fault clearing. , For the virtual inertial time constant of the grid-type converter, The rated electric angular velocity of the system, The electrical angular velocity of the grid-type converter at the moment of fault clearing. The relative power angle between the grid-type converter and the system at the time of fault clearing. This refers to the power angle value at the stable equilibrium point of the grid-type converter after fault clearance. For grid-type converters to output active power, This indicates the phase angle of the internal potential of a grid-type converter.
[0014] According to a specific embodiment of this application, in a second aspect, this application provides a transient stability assessment system for a heterogeneous renewable energy grid-connected system, characterized in that it is applied to a heterogeneous renewable energy grid-connected system including a grid-connected converter, a grid-connected converter, and a receiving-end system, comprising: The power angle characteristic equation establishment module is used to establish the power angle characteristic equation of the grid-type converter based on the electrical quantity relationship between the grid-type converter and the grid-connected converter, combined with the electrical quantity law of the heterogeneous new energy grid-connected system; the critical energy solution module is used to determine the energy function of the heterogeneous new energy grid-connected system using the power angle characteristic equation, and to solve for the critical energy value at the unstable equilibrium point by combining the power angle characteristic equation and the energy function; the stability evaluation module is used to calculate the system energy of the heterogeneous new energy grid-connected system at the fault clearing time, and to evaluate the transient stability of the system based on the comparison result of the system energy and the critical energy value.
[0015] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects: This application provides a transient stability assessment method for heterogeneous renewable energy grid-connected systems. By establishing the power angle characteristic equation of the grid-connected converter and solving for the critical energy value using an energy function, it can accurately reflect the dynamic interaction characteristics between devices with different control strategies in the heterogeneous renewable energy grid-connected system. This method is directly based on electrical quantity relationships for modeling, avoiding the model distortion problem caused by equating the grid-connected converter with constant impedance in traditional methods. This solves the transient stability assessment error caused by differences in control strategies in the prior art and improves the accuracy of the assessment results. Simultaneously, by comparing the system energy at the fault clearing moment with the critical energy value, it achieves a quantitative judgment of the system stability state, providing an operable assessment standard for heterogeneous systems. Attached Figure Description
[0016] Figure 1 A schematic diagram of a heterogeneous new energy grid-connected system is shown; Figure 2 A flowchart of a transient stability assessment method for a heterogeneous renewable energy grid-connected system is shown; Figure 3 A simplified topology diagram of a heterogeneous new energy grid-connected system is shown; Figure 4 This diagram illustrates the electrical quantity relationships of a heterogeneous new energy grid-connected system after fault clearance. Figure 5 The power angle characteristic diagram of the grid-type converter in the application example is shown; Figure 6 A schematic diagram of the critical energy value for an application example is shown; Figure 7 The graphs show the power angle variation curves of the grid-type converter under two operating conditions in the application example. Figure 8 A block diagram of a transient stability assessment system for a heterogeneous new energy grid-connected system is shown. Detailed Implementation
[0017] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0018] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the application. The singular forms “a,” “said,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.
[0019] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.
[0020] It should be understood that although the terms first, second, third, etc., may be used in the embodiments of this application, these descriptions should not be limited to these terms. These terms are only used to distinguish the descriptions. For example, first may also be referred to as second without departing from the scope of the embodiments of this application, and similarly, second may also be referred to as first.
[0021] Depending on the context, the words “if” or “suppose” as used here can be interpreted as “when” or “in response to determination” or “in response to detection.” Similarly, depending on the context, the phrases “if determination” or “if detection (of the stated condition or event)” can be interpreted as “when determination” or “in response to determination” or “when detection (of the stated condition or event)” or “in response to detection (of the stated condition or event).”
[0022] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.
[0023] It should be noted that any symbols and / or numbers present in the specification that are not marked in the accompanying drawings are not reference numerals.
[0024] The optional embodiments of this application are described in detail below with reference to the accompanying drawings.
[0025] The embodiments provided in this application are embodiments of a transient stability assessment method for heterogeneous new energy grid-connected systems.
[0026] Figure 1 A schematic diagram of a heterogeneous new energy grid-connected system is shown.
[0027] like Figure 1 As shown, the heterogeneous new energy grid-connected system includes grid-connected converters, grid-connected converters, and receiving-end systems.
[0028] Figure 2 A flowchart of a transient stability assessment method for heterogeneous renewable energy grid-connected systems is shown, such as... Figure 2 As shown, this method is applied to, for example Figure 1 The heterogeneous new energy grid-connected system shown includes the following steps S201 to S203: S201. Based on the electrical quantity relationship between grid-connected converters and grid-connected converters, and combined with the electrical quantity law of heterogeneous new energy grid-connected systems, establish the power angle characteristic equation of grid-connected converters.
[0029] S202. Using the power angle characteristic equation, determine the energy function of the heterogeneous new energy grid-connected system, and combine the power angle characteristic equation and the energy function to solve for the critical energy value at the unstable equilibrium point.
[0030] S203. Calculate the system energy of the heterogeneous new energy grid-connected system at the fault clearing time, and evaluate the transient stability of the system based on the comparison results of the system energy and the critical energy value.
[0031] In this embodiment, by establishing the power angle characteristic equation of the grid-connected converter and solving for the critical energy value using an energy function, the dynamic interaction characteristics between devices with different control strategies in a heterogeneous renewable energy grid-connected system can be accurately reflected. This method directly models based on electrical quantity relationships, avoiding the model distortion problem caused by equating the grid-connected converter to a constant impedance in traditional methods. This solves the transient stability assessment error caused by differences in control strategies in the background technology, improving the accuracy of the assessment results. Simultaneously, by comparing the system energy at the fault clearing moment with the critical energy value, a quantitative judgment of the system stability state is achieved, providing an operable assessment standard for heterogeneous systems.
[0032] Figure 3 A simplified topology diagram of a heterogeneous new energy grid-connected system is shown.
[0033] For example, when performing electrical quantity analysis on a heterogeneous renewable energy grid-connected system, it can be done according to the following... Figure 3The simplified topology of the system is shown in the diagram. Here, GFL represents a grid-connected generator, and GFM represents a network-connected generator. This represents the electromotive force and phase angle of the GFM generator. This represents the voltage and phase angle at grid connection point b. This represents the electromotive force of the power grid and its phase angle. This represents the reactance from GFL to grid connection point b. This represents the reactance from GFM to grid connection point b. This represents the reactance from grid connection point b to the power grid. This represents the output current from GFL to grid connection point b, where For active current components, This is the reactive current component. This represents the output current from grid connection point b to the power grid, where For active current components, This is the reactive current component. This represents the output current from the GFM to the grid connection point b, where For active current components, This represents the reactive current component.
[0034] In this embodiment, the rotor angle of the equivalent synchronous machine in the power grid is used. Since it is a reference value, the phase angle is 0, that is, based on... Alternative express.
[0035] In some embodiments, step S201 involves establishing the power angle characteristic equation of the grid-connected converter based on the electrical quantity relationship between the grid-connected converter and the grid-connected converter, combined with the electrical quantity characteristics of the heterogeneous new energy grid-connected system. This includes: solving for the output current of the grid-connected converter based on the electrical quantity relationship between the grid-connected converter and the grid-connected converter; solving for the voltage amplitude and phase angle of the grid-connected converter at the grid connection point based on the output current of the grid-connected converter and according to the electrical quantity characteristics of the heterogeneous new energy grid-connected system; and establishing the power angle characteristic equation of the grid-connected converter based on the voltage amplitude and phase angle. For ease of understanding, a specific implementation flow for establishing the power angle characteristic equation is shown below.
[0036] Figure 4 A schematic diagram of the electrical quantity relationships of a heterogeneous new energy grid-connected system after fault clearance is shown.
[0037] For example, see reference. Figure 3 The simplified topology shown, when the fault is cleared, has a phase angle with the grid-connected converter's voltage at the grid connection point, which is then equal to the voltage within the grid-connected converter. The output active and reactive power of the grid-connected converter continues to increase, and the relationships between various electrical quantities in the heterogeneous renewable energy grid-connected system are as follows: Figure 4As shown.
[0038] In some embodiments, the output current of a grid-type converter includes active current and reactive current.
[0039] At the system's sending end, the output current of the grid-type converter can be... along as well as The normal vector is decomposed into active current and reactive current. Among them, the active current... Amplitude reactive current Amplitude Assume the active current output of the grid-type converter is... In the positive direction, that is, when the grid-type converter absorbs active current, It is a negative value. (By...) Figure 4 The amplitude of the output active current of the grid-connected converter can be obtained as follows: ; in, This represents the amplitude of the active current output by the grid-connected converter. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the voltage phase angle at the grid connection point of the grid-connected converter. This represents the equivalent output reactance of a grid-type converter.
[0040] Based on a similar approach, a grid-type converter is designed to inject reactive current into grid connection point b. For the positive direction, that is, when reactive current is injected into the grid-connected converter at grid connection point b, For negative values, by Figure 4 The magnitude of the reactive current injected by the grid-connected converter into grid connection point b is: ; in, This indicates the magnitude of the reactive current injected by the grid-connected converter into the grid connection point. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the voltage phase angle at the grid connection point of the grid-connected converter. This indicates the voltage amplitude at the grid connection point of the grid-connected converter. This represents the equivalent output reactance of a grid-type converter.
[0041] Furthermore, based on the output current of the grid-connected converter and in accordance with the electrical quantity rules of the heterogeneous new energy grid-connected system, the voltage amplitude and phase angle of the grid-connected converter at the grid connection point can be solved.
[0042] For example, in the receiving end of the system, the current... It can be decomposed into reactive current. Active current Its amplitude is .
[0043] First, consider a grid-type converter that only outputs active power, i.e. and If they are in phase, then the sine value for: ; The voltage amplitude at grid connection point b can be obtained further. for: ; Based on this, if we consider the simultaneous output of reactive power with the grid-type converter, then the current... along as well as Normal decomposition into active current Its amplitude is reactive current Its amplitude is sine value With voltage amplitude The formula can be updated as follows: ; ; Substituting the formula for calculating the active current amplitude output by the grid-type converter into the sine value... The calculation formula yields: ; After simplification, we get: ; Substituting the formula for calculating the magnitude of the reactive current injected by the grid-connected converter into the voltage magnitude calculation formula... The calculation formula yields: ; After sorting, we get: ; Based on this, intermediate coefficients are introduced to simplify the expression. , , , , , means as follows: ; ; ; ; ; Based on the intermediate coefficients, the simplified sine value The calculation formula can be further simplified as follows: ; Based on this, further solutions can be found. , as well as The specific expression is as follows: ; ; ; in, This indicates the voltage amplitude at the grid connection point of the grid-connected converter. This represents the equivalent output reactance of a grid-connected converter. Indicates the equivalent reactance of the line. It represents the magnitude of the equivalent internal potential of the power grid. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the voltage phase angle at the grid connection point of the grid-connected converter. This indicates the magnitude of the reactive current injected by the grid-connected converter into the grid connection point.
[0044] In some embodiments, the power angle characteristic equation of the grid-type converter can be established based on the voltage amplitude and phase angle.
[0045] In some specific embodiments, the output power of a grid-type converter can be expressed as: ; Among them, factor items and The output power of the grid-type converter can be obtained by substituting the values obtained through the above embodiments. With grid-type converter power angle The relationship between them is used in this application as the power angle characteristic equation of a grid-type converter, as follows: ; in, This indicates the output active power of the grid-connected converter. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. It represents the magnitude of the equivalent internal potential of the power grid. This represents the equivalent output reactance of a grid-connected converter. Indicates the equivalent reactance of the line. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the magnitude of the reactive current injected by the grid-connected converter into the grid connection point. , , , , These are intermediate coefficients introduced to simplify the expression, and are represented as follows: ; ; ; ; .
[0046] In some embodiments, step S202 involves determining the energy function of the heterogeneous new energy grid-connected system using the power angle characteristic equation, including: deriving the second-order rotor motion equation of the grid-connected converter based on the power angle characteristic equation; and performing the first integration of the second-order rotor motion equation to obtain the energy function of the heterogeneous new energy grid-connected system.
[0047] In some specific embodiments, based on the power angle characteristic equation of the grid-type converter obtained from the above embodiments, its second-order rotor motion equation can be obtained as follows: ; ; in, This indicates the phase angle of the internal potential of a grid-connected converter. For the electric angular velocity of the grid-type converter, The rated electric angular velocity of the system, , For the virtual inertial time constant of the grid-type converter, This is a reference value for the active power of a grid-type converter. For grid-type converters to output active power, The damping coefficient; Furthermore, by performing the first integration of the second-order rotor motion equations, the energy function of the heterogeneous new energy grid-connected system can be obtained, expressed by the following formula: ; in, The relative power angle between the grid-type converter and the system at the time of fault clearing. This refers to the power angle value at the stable equilibrium point of the grid-type converter after fault clearance. The electrical angular velocity of the grid-type converter at the moment of fault clearing. The electric angular velocity of the grid-type converter at time t after the fault is cleared.
[0048] In some embodiments, step S202, combining the power angle characteristic equation and the energy function, solves for the critical energy value at the unstable equilibrium point, including: for the power angle characteristic equation, setting the output active power of the grid-type converter equal to the active power reference value of the grid-type converter, and in... Within the interval, the power angles at the stable equilibrium point and the unstable equilibrium point are calculated. For the energy function, combining the power angles at the stable equilibrium point and the unstable equilibrium point, and taking advantage of the fact that the electric angular velocity of the grid-type converter at the unstable equilibrium point is 0, the energy function is solved for the energy at the unstable equilibrium point to obtain the critical energy value at the unstable equilibrium point.
[0049] In some specific embodiments, for the power angle characteristic equation of the grid-type converter obtained in the above embodiments, let ,exist The work angle at the stable equilibrium point is calculated within the interval. Work angle at unstable equilibrium point And there are = At the unstable equilibrium point Then the unstable equilibrium point ( The critical energy value of (,0) is expressed as follows: ; in, This represents the critical energy value at the unstable equilibrium point. Angle of work at an unstable equilibrium point Stable equilibrium point work angle This indicates the output active power of the grid-connected converter. This indicates the phase angle of the internal potential of a grid-type converter.
[0050] Furthermore, in some specific embodiments, the system energy of the heterogeneous renewable energy grid-connected system at the time of fault clearing is calculated using the following formula: ; in, This represents the system energy of a heterogeneous renewable energy grid-connected system at the moment of fault clearing. , For the virtual inertial time constant of the grid-type converter, The rated electric angular velocity of the system, The electrical angular velocity of the grid-type converter at the moment of fault clearing. The relative power angle between the grid-type converter and the system at the time of fault clearing. This refers to the power angle value at the stable equilibrium point of the grid-type converter after fault clearance. For grid-type converters to output active power, This indicates the phase angle of the internal potential of a grid-type converter.
[0051] In this embodiment, the critical energy value at the unstable equilibrium point can be calculated using the above-described method. And the system energy of heterogeneous new energy grid-connected systems at the time of fault clearing. To perform the numerical comparison in step S203.
[0052] As a feasible implementation method, in step S203, the transient stability of the system is evaluated based on the comparison result between the system energy and the critical energy value, including: if the system energy is less than or equal to the critical energy value, the heterogeneous new energy grid-connected system is evaluated as being able to maintain transient stability; if the system energy is greater than the critical energy value, the heterogeneous new energy grid-connected system is evaluated as being about to become transiently unstable.
[0053] To verify the effectiveness of the above embodiments of this application, a specific application example is shown below.
[0054] Figure 5 The diagram shows the power angle characteristics of a grid-type converter in an application example.
[0055] Figure 6 A schematic diagram of the critical energy value for an application example is shown.
[0056] Figure 7 The graphs showing the power angle variation of the grid-type converter under two operating conditions in the application example are shown.
[0057] As one specific implementation method, for Figure 3 The simplified topology of the heterogeneous new energy grid-connected system shown is configured as follows: =1.2, =1.2, =0.03, =0.4, =0.159, under different output power of the grid-type converter, the power angle characteristic of the grid-type converter is calculated according to the power angle characteristic equation of the grid-type converter as follows: Figure 5 As shown. According to the critical energy calculation formula, the critical energy value of the unstable equilibrium point is calculated as follows: Figure 6 The red box indicates the output power of the grid converter. Under the condition that =3, two operating conditions are set respectively. Operating condition 1 fault clearing time is... =1.2s, fault clearing time for operating condition 2 is =1.22s. Based on the calculation results of the critical energy value calculation formula, the critical energy value of the system is... The value is 3.74. Based on the system energy calculation formula, the energy at the fault clearing moment in condition 1 is calculated to be... The energy required to clear the fault in condition 2 is... The comparison results show that... Under operating condition 1, the system remains stable. Under operating condition 2, the system experiences transient instability. The power angle variation curves of the grid-type converter under the two operating conditions are as follows: Figure 7 As shown.
[0058] This application establishes a power angle characteristic equation for grid-connected converters that accurately reflects the dynamic interaction of the system by precisely solving the grid connection point voltage of grid-connected converters in heterogeneous renewable energy grid-connected systems. Based on this, the system's energy function is constructed, and a method for calculating the critical energy value is proposed, ultimately forming a complete transient stability assessment mechanism. This scheme overcomes the shortcomings of existing technologies that equate grid-connected converters to constant impedance models. It can quickly and accurately determine the transient stability of heterogeneous systems containing converters with different control strategies at fault clearance time, providing effective protection for the safe and stable operation of renewable energy-dominated power grids.
[0059] Based on the same concept, this application also provides a transient stability assessment system for heterogeneous new energy grid-connected systems. This system is used to perform the methods of the above embodiments and is applied to heterogeneous new energy grid-connected systems including grid-connected converters, grid-connected converters, and receiving-end systems.
[0060] Figure 8 A block diagram of a transient stability assessment system for a heterogeneous renewable energy grid-connected system is shown, such as... Figure 8 As shown, the system includes a power angle characteristic equation establishment module 801, a critical energy solution module 802, and a stability evaluation module 803.
[0061] The power angle characteristic equation establishment module 801 is used to establish the power angle characteristic equation of the grid-connected converter based on the electrical quantity relationship between the grid-connected converter and the grid-connected converter, combined with the electrical quantity law of the heterogeneous new energy grid-connected system.
[0062] The critical energy solution module 802 is used to determine the energy function of the heterogeneous new energy grid-connected system using the power angle characteristic equation, and to solve for the critical energy value at the unstable equilibrium point by combining the power angle characteristic equation and the energy function.
[0063] The stability assessment module 803 is used to calculate the system energy of the heterogeneous new energy grid-connected system at the time of fault clearing, and to assess the transient stability of the system based on the comparison between the system energy and the critical energy value.
[0064] Although the operations are described in a specific order in the accompanying drawings, this should not be construed as requiring these operations to be performed in the specific order or serial order shown, or requiring all of the operations shown to obtain the desired result. In certain environments, multitasking and parallel processing may be advantageous.
[0065] The methods and systems of this application can be implemented using standard programming techniques, utilizing rule-based logic or other logic to implement various method steps. It should also be noted that the terms "system" and "module" as used herein and in the claims are intended to include implementations using one or more lines of software code and / or hardware implementations and / or devices for receiving input.
[0066] Any step, operation, or procedure described herein may be performed or implemented using one or more hardware or software modules, either alone or in combination with other devices. In one embodiment, the software module is implemented using a computer program product comprising a computer-readable medium containing computer program code, which is executable by a computer processor to perform any or all of the described steps, operations, or procedures.
[0067] The foregoing description of implementations of this application has been provided for illustrative and descriptive purposes. The foregoing description is not exhaustive and is not intended to limit this application to the exact forms disclosed. Various modifications and variations may exist in accordance with the foregoing teachings, or may arise from practice of this application. These embodiments were chosen and described to illustrate the principles of this application and its practical application, enabling those skilled in the art to utilize this application in various implementations and modifications to suit the specific purpose of the concept.
[0068] Regarding the system in the above embodiments, the specific ways in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated here.
[0069] It can be further understood that, unless otherwise specified, "connection" includes both direct connections where no other components exist between the two parties and indirect connections where other components exist between them.
[0070] It is further understood that although the operations are described in a specific order in the accompanying drawings in the embodiments of this application, this should not be construed as requiring these operations to be performed in the specific order or serial order shown, or requiring all the operations shown to be performed to obtain the desired result. In certain environments, multitasking and parallel processing may be advantageous.
[0071] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the field of this application that are not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.
[0072] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.
[0073] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A transient stability assessment method for a heterogeneous renewable energy grid-connected system, characterized in that, Applied to heterogeneous renewable energy grid-connected systems including grid-connected converters, grid-connected converters, and receiving-end systems, the following steps are included: Based on the electrical quantity relationship between the grid-type converter and the grid-connected converter, and combined with the electrical quantity law of the heterogeneous new energy grid-connected system, the power angle characteristic equation of the grid-type converter is established; Using the power angle characteristic equation, the energy function of the heterogeneous new energy grid-connected system is determined, and by combining the power angle characteristic equation and the energy function, the critical energy value at the unstable equilibrium point is solved. Calculate the system energy of the heterogeneous new energy grid-connected system at the fault clearing time, and evaluate the transient stability of the system based on the comparison result of the system energy and the critical energy value.
2. The method according to claim 1, characterized in that, The step of establishing the power angle characteristic equation of the grid-connected converter based on the electrical quantity relationship between the grid-connected converter and the grid-connected converter, combined with the electrical quantity characteristics of the heterogeneous new energy grid-connected system, includes: Based on the electrical quantity relationship between the grid-type converter and the root-type converter, the output current of the grid-type converter is calculated. Based on the output current of the grid-connected converter, and according to the electrical quantity law of the heterogeneous new energy grid-connected system, the voltage amplitude and phase angle of the grid-connected converter at the grid connection point are calculated. Based on the voltage amplitude and the phase angle, the power angle characteristic equation of the grid-type converter is established.
3. The method according to claim 2, characterized in that, The voltage amplitude of the grid-connected converter at the grid connection point and phase angle It can be expressed using the following formula: ； ； in, This indicates the voltage amplitude at the grid connection point of the grid-connected converter. This represents the equivalent output reactance of a grid-connected converter. Indicates the equivalent reactance of the line. It represents the magnitude of the equivalent internal potential of the power grid. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the voltage phase angle at the grid connection point of the grid-connected converter. This indicates the magnitude of the reactive current injected by the grid-connected converter into the grid connection point. , , , , These are intermediate coefficients introduced to simplify the expression, and are represented as follows: ； ； ； ； 。 4. The method according to claim 1, characterized in that, The process of determining the energy function of the heterogeneous renewable energy grid-connected system using the power angle characteristic equation includes: Based on the aforementioned power angle characteristic equation, the second-order rotor motion equation of the grid-type converter is derived. The energy function of the heterogeneous new energy grid-connected system is obtained by first integrating the second-order rotor motion equation.
5. The method according to claim 4, characterized in that, The second-order rotor motion equation is expressed by the following formula: ； ； in, This indicates the phase angle of the internal potential of a grid-connected converter. For the electric angular velocity of the grid-type converter, The rated electric angular velocity of the system, , For the virtual inertial time constant of the grid-type converter, This is a reference value for the active power of a grid-type converter. For grid-type converters to output active power, The damping coefficient; The energy function of the heterogeneous new energy grid-connected system is expressed by the following formula: ； in, The relative power angle between the grid-type converter and the system at the time of fault clearing. This refers to the power angle value at the stable equilibrium point of the grid-type converter after fault clearance. The electrical angular velocity of the grid-type converter at the moment of fault clearing. The electric angular velocity of the grid-type converter at time t after the fault is cleared.
6. The method according to claim 1, characterized in that, The step of combining the work angle characteristic equation and the energy function to solve for the critical energy value at the unstable equilibrium point includes: Regarding the aforementioned power angle characteristic equation, let the output active power of the grid-type converter be equal to the active power reference value of the grid-type converter, and in... The work angles at stable equilibrium points and unstable equilibrium points are calculated within the interval. For the energy function, combining the power angle of the stable equilibrium point and the power angle of the unstable equilibrium point, and taking into account that the electric angular velocity of the grid-type converter at the unstable equilibrium point is 0, the energy function is solved for the energy at the unstable equilibrium point to obtain the critical energy value at the unstable equilibrium point.
7. The method according to claim 2, 4, or 6, characterized in that, The work angle characteristic equation is expressed by the following formula: ； in, This indicates the output active power of the grid-connected converter. This represents the amplitude of the equivalent internal electromotive force generated by the internal control of the grid-type converter. It represents the magnitude of the equivalent internal potential of the power grid. This represents the equivalent output reactance of a grid-connected converter. Indicates the equivalent reactance of the line. This indicates the phase angle of the internal potential of a grid-connected converter. This indicates the magnitude of the reactive current injected by the grid-connected converter into the grid connection point. , , , , These are intermediate coefficients introduced to simplify the expression, and are represented as follows: ； ； ； ； 。 8. The method according to claim 1, characterized in that, The step of evaluating the transient stability of the system based on the comparison result between the system energy and the critical energy value includes: If the system energy is less than or equal to the critical energy value, then the heterogeneous new energy grid-connected system can be assessed as being able to maintain transient stability. If the system energy exceeds the critical energy value, the heterogeneous new energy grid-connected system is expected to become transiently unstable.
9. The method according to claim 6 or 8, characterized in that, The formula for determining the critical energy value is as follows: ； in, This represents the critical energy value at the unstable equilibrium point. Angle of work at an unstable equilibrium point Stable equilibrium point work angle This indicates the output active power of the grid-connected converter. This indicates the phase angle of the internal potential of a grid-type converter; The system energy of the heterogeneous renewable energy grid-connected system at the time of fault clearing is calculated using the following formula: ； in, This represents the system energy of a heterogeneous renewable energy grid-connected system at the moment of fault clearing. , For the virtual inertial time constant of the grid-type converter, The rated electric angular velocity of the system, The electrical angular velocity of the grid-type converter at the moment of fault clearing. The relative power angle between the grid-type converter and the system at the time of fault clearing. This refers to the power angle value at the stable equilibrium point of the grid-type converter after fault clearance. For grid-type converters to output active power, This indicates the phase angle of the internal potential of a grid-type converter.
10. A transient stability assessment system for a heterogeneous new energy grid-connected system, characterized in that, Applicable to heterogeneous renewable energy grid-connected systems, including grid-connected converters, grid-connected converters, and receiving-end systems, including: The power angle characteristic equation establishment module is used to establish the power angle characteristic equation of the grid-type converter based on the electrical quantity relationship between the grid-type converter and the grid-connected converter, combined with the electrical quantity law of the heterogeneous new energy grid-connected system. The critical energy solution module is used to determine the energy function of the heterogeneous new energy grid-connected system using the power angle characteristic equation, and to solve for the critical energy value at the unstable equilibrium point by combining the power angle characteristic equation and the energy function. The stability assessment module is used to calculate the system energy of the heterogeneous new energy grid-connected system at the fault clearing time, and to assess the transient stability of the system based on the comparison result of the system energy and the critical energy value.