A Multi-Mode Oscillation Analysis Method for a Multi-Energy Power Generation and Transmission System

Abstract

The present invention discloses a multi-mode oscillation analysis method for a multi-energy power generation and transmission system, which relates to the technical field of power systems. The main purpose is to construct a full operating mode set of the multi-energy power generation and transmission system, taking into account various oscillation forms and their coupling effects, capable of evaluating the oscillation risk of the system under a wide range of operating modes, effectively identifying potential risk operating modes, and playing an important role in risk avoidance and system protection. The main technical solutions adopted are: S1, construction of the full operating mode set; S2, screening of multi-oscillation forms and their grouping mode sets; S3, analysis of grouped oscillation modes based on the impedance network model; S4, coupling analysis of multi-oscillation forms; S5, identification of risk operating modes; S6, output of information.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and particularly to a multi-mode oscillation analysis method for a multi-energy power generation and transmission system. Background Art

[0002] The power system is developing towards a trend with new energy as the main body, and the installed capacity of new energy represented by wind power and photovoltaic power is growing rapidly. New energy is usually bundled with existing thermal power and then connected to the grid for transmission together, forming a multi-energy power generation and transmission system. Such systems face complex sub- / supra-synchronous oscillation problems, which are manifested as: (1) there are various types of sub- / supra-synchronous oscillation forms, including shaft torsional vibration caused by the interaction between thermal power units and series-compensated power grids / HVDC transmission systems, and electrical oscillations caused by the interaction between new energy units such as wind power and photovoltaic power and series-compensated power grids / weak AC power grids; (2) the system topology and equipment types are complex, and the operation modes of the machine and the grid vary widely, and the operation modes of the machine and the grid have a great influence on the oscillation characteristics.

[0003] The prior art proposes a broadband oscillation risk assessment method and device for a power system with a new energy power station connected to the grid. The method includes: obtaining the grid connection impedance of the power system under various first working conditions, and obtaining the grid connection impedance of the new energy power station under various second working conditions; obtaining the impedance characteristic band of the power system, and obtaining the impedance characteristic band of the new energy power station; locking the frequency range of potential broadband oscillation risks; traversing the frequency range of potential broadband oscillation risks to obtain the damping ratio of the oscillation mode under each combined working condition; and evaluating the broadband oscillation risk of the power system with the new energy power station connected to the grid according to the damping ratio of the oscillation mode under various combined working conditions.

[0004] Most of the existing analysis techniques for the sub- / supra-synchronous oscillation stability of power systems focus on analyzing one or two oscillation forms in the system, lacking a comprehensive analysis of multiple oscillation forms; in addition, specific operation modes are generally selected for analysis, or only the changes of a few operation parameters are considered, making it difficult to evaluate the oscillation risks of the system under a wide range of operation modes. In order to analyze the oscillation stability problem of the multi-energy power generation and transmission system, a feasible and effective method and system are urgently needed, which can take into account multiple oscillation forms and consider the changes of various operation parameters of the system to effectively identify potential risk operation modes and provide important information for the prevention and control of oscillations. Summary of the Invention

[0005] In view of this, the present invention provides a multi-mode oscillation analysis method for a multi-energy power generation and transmission system, and the main purpose is to construct a full operation mode set of the multi-energy power generation and transmission system, consider multiple oscillation forms and their coupling effects, be able to evaluate the oscillation risks of the system under a wide range of operation modes, effectively identify potential risk operation modes, and play an important role in risk avoidance and system protection.

[0006] To achieve the above object, the present invention mainly provides the following technical solutions:

[0007] An embodiment of the present invention provides a multi-mode oscillation analysis method for a multi-energy power generation and transmission system. The method includes the following steps:

[0008] S1. Construction of the full operation mode set: The multi-energy power generation and transmission system includes m operation variables, and a discrete value set A i (i = 1, 2,..., m) is set for each operation variable. The discrete values of the m operation variables are combined to form operation modes, where card(A i ) represents the number of elements in the set A i . All operation modes are numbered to construct the full operation mode set of the system. Among them, the multi-energy power generation and transmission system is a multi-energy power generation and transmission system in which new energy and thermal power units are bundled and then connected to the grid for transmission together;

[0009] S2. Screening of multi-oscillation forms and their branch mode sets: Screen out the grouping mode sets with relatively high oscillation risks from the full operation mode set. If n oscillation forms are considered to exist in the multi-energy power generation and transmission system, a total of n grouping mode sets are screened. The grouping mode set corresponding to the Kth oscillation form is denoted as S K (K = 1, 2,..., n);

[0010] S3. Analysis of grouped oscillation modes based on the impedance network model: For the n grouped mode sets screened in S2, analyze the oscillation modes of all operation modes of the n grouped mode sets based on the impedance network model to obtain whether there are risk oscillation modes in the grouped mode set corresponding to the kth oscillation form;

[0011] S4. Coupling analysis of multi-oscillation forms: If there is an electrical oscillation risk caused by the interaction between the power grids of new energy and thermal power units in an operation mode, and the frequency f P of the risk oscillation mode and the shaft torsional vibration frequency f TG of the thermal power unit meet the following relationship:

[0012] |f p - |f0 - f TG || ≤ f coupling or |f p - |f0 + f TG || ≤ f coupling ;

[0013] Then it is determined that there is a coupling between electrical oscillation and shaft torsional vibration in this operation mode; where fcoupling is a preset threshold according to the actual situation, and f0 is the power frequency;

[0014] S5. Discrimination of risk operation modes: Evaluate the oscillation risk level of the operation mode and discriminate the risk operation modes;

[0015] S6. Output information: Output the number, oscillation mode, and risk level information of the operation mode to provide guidance for further oscillation prevention and control.

[0016] As mentioned above, the new energy includes wind farms and photovoltaic power stations. The wind farms include doubly-fed wind turbines and direct-drive wind turbines, and the photovoltaic power stations include photovoltaic power generation unit groups;

[0017] The m operation variables include: thermal power unit grid structure type, unit commissioning type, and unit output type; the thermal power unit grid structure type includes the number of lines and the line series compensation degree; the unit commissioning type includes the number of commissioned thermal power units, the number of grid-connected wind turbines in the wind farm, and the number of grid-connected photovoltaic power generation units in the photovoltaic power station; the unit output type includes the output of a single thermal power unit, the output of a single wind turbine, and the output of a single photovoltaic power generation unit;

[0018] The m operation variables constitute an m-dimensional parameter space, and each operation mode can be represented by a unique m-dimensional vector.

[0019] As mentioned above, the discrete value set A of each operation variable i (i = 1, 2,..., m) is in the form of

[0020] A i ={a i1 , a i2 ,..., a ij}

[0021] Each element in A i represents a value of the i-th operation variable, where the element a ij represents the j-th possible value of the i-th operation variable.

[0022] As mentioned above, in S2, the multi-energy power generation and transmission system has 4 oscillation forms: doubly-fed wind turbine - series-compensated power grid, direct-drive wind turbine - weak power grid, photovoltaic power generation unit - weak power grid, and thermal power unit shafting - series-compensated power grid. When screening the grouping mode set corresponding to a specific oscillation form, some relatively severe operation modes should be selected according to its oscillation characteristics. The following screening principles can be used but are not limited to:

[0023] For the oscillation of doubly-fed wind turbine - series-compensated power grid: Several operation modes with a relatively high line series compensation degree, most of the grid-connected new energy units being doubly-fed wind turbines, and a relatively low single-unit output level of the doubly-fed wind turbines can be selected to form the grouping mode set S1;

[0024] For the direct-drive wind turbine-weak grid oscillation: Several operation modes with relatively weak grid strength, a large number of grid-connected new energy units being direct-drive wind turbines, and a relatively high total output level of direct-drive wind turbines can be selected to form a grouping mode set S2;

[0025] For the photovoltaic power generation unit-weak grid oscillation: Several operation modes with relatively weak grid strength, a large number of grid-connected new energy units being photovoltaic power generation units, and a relatively high total output level of photovoltaics can be selected to form a grouping mode set S3;

[0026] For the steam turbine shafting-series compensated grid oscillation: Several operation modes with the steam turbine output close to no-load can be selected to form a grouping mode set S4.

[0027] As described above, in S3, for the n grouping mode sets screened for S2, based on the impedance network model, analyze the oscillation modes of all operation modes of the n grouping mode sets, and obtain whether there is a risk oscillation mode in the grouping mode set corresponding to the kth oscillation form, including the following steps:

[0028] SⅠ. In any operation mode of the grouping mode set S k (k = 1, 2,..., n), use the small-signal model derivation or external characteristic identification method to calculate the impedance models of each power equipment in the multi-energy power generation and transmission system;

[0029] SⅡ. Piece together the impedance models of each power equipment into an impedance network model according to the system topology structure, and use methods such as series-parallel operation or impedance matrix transformation calculation to simplify the impedance network model into an aggregated impedance;

[0030] SⅢ. Identify the oscillation mode of the system according to the aggregated impedance, and calculate the damping σ x ;

[0031] SⅣ. Judge whether the stability margin of each oscillation mode meets the requirements, and record the risk flag risk p , and the criterion is as follows:

[0032]

[0033] Among them, the positive parameter σ risk is the preset stability margin; if the damping σ p of the pth oscillation mode is less than σ risk , then let the risk flag risk p = 1, and it is considered that this mode has the risk of divergent or weakly damped oscillation, denoted as a risk oscillation mode. If there is a risk oscillation mode in the current operation mode, it means that the system has the risk of the kth oscillation form;

[0034] SV, repeat SⅠ to SⅣ, and analyze the oscillation modes of all operation modes of n grouping mode sets.

[0035] As described above, in SⅠ, for the convenience of analyzing and calculating the impedance models of various power equipment in the multi-energy power generation and transmission system, when analyzing the electrical oscillations caused by the grid connection of wind farms / solar photovoltaic power stations, the dynamic of the thermal power unit shafting is not considered temporarily, and the single-rigid-body model can be adopted for the thermal power unit shafting.

[0036] When analyzing the torsional vibration caused by the thermal power unit shafting - series compensation power grid, the multi-mass model is adopted for the thermal power unit shafting.

[0037] As described above, in SⅢ, the oscillation modes of the multi-energy power generation and transmission system are identified according to the aggregated impedance, and the damping σ of this oscillation mode is calculated. x , and a method that can be adopted is:

[0038] Obtain the frequency characteristic curve of the aggregated impedance, and denote the real part and the imaginary part of the aggregated impedance as the equivalent resistance R and the equivalent reactance X respectively. If the equivalent reactance - frequency curve has a zero crossing at a frequency of ω X , it is considered that the system has an oscillation mode with a frequency of ω X , and the damping σ of this oscillation mode X can be calculated as:

[0039]

[0040] where k X (jω X ) is the slope of the equivalent reactance at the frequency ω X , k R (jω X ) is the slope of the equivalent resistance at the frequency ω X , R(jω X ) is the equivalent resistance at the frequency ω X . The damping of a stable oscillation mode is positive, and the damping of an unstable oscillation mode is negative.

[0041] As described above, in S5, according to the oscillation severity, the oscillation risks of the operation modes are divided into three levels, which are arranged in descending order of severity as follows:

[0042] If there is a risk oscillation mode and there is a coupling between electrical oscillation and shafting torsional vibration, it is determined that the oscillation risk is the highest, and the risk level is the first level;

[0043] If there is a risk oscillation mode but there is no coupling between electrical oscillation and shafting torsional vibration, it is determined that there is a certain oscillation risk, and the risk level is the second level;

[0044] If there is no risk oscillation mode, it is determined that there is basically no oscillation risk, and the risk level is the third level;

[0045] Among them, the operation modes with the first-level and second-level risk levels belong to the risk operation modes.

[0046] By means of the above technical solution, the multi-mode oscillation analysis method of the multi-energy power generation and transmission system of the present invention has at least the following advantages:

[0047] The multi-mode oscillation analysis method of the multi-energy power generation and transmission system of the present invention constructs a full operation mode set of the multi-energy power generation and transmission system, considers various oscillation forms and their coupling effects, can evaluate the oscillation risk of the system under a wide range of operation modes, effectively identify potential risk operation modes, plays an important role in risk avoidance and system protection, and can greatly improve the efficiency and accuracy of the wide-screen oscillation assessment of the multi-energy power generation system, provides certain help for effectively suppressing power system failures caused by broadband oscillation problems, and at the same time, also provides certain support for improving the new energy transmission rate of the system.

[0048] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following will be described in detail with reference to the preferred embodiments of the present invention and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic flow chart of the multi-mode oscillation analysis method of the multi-energy power generation and transmission system of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following will be described in detail with reference to the accompanying drawings and preferred embodiments regarding the specific implementation manners, structures, features and effects of the present invention application.

[0051] As Figure 1 shown, a multi-mode oscillation analysis method of a multi-energy power generation and transmission system proposed in an embodiment of the present invention includes the following steps:

[0052] S1. Construction of the full operation mode set: The multi-energy power generation and transmission system includes m operation variables, and a discrete value set Ai (i = 1, 2,..., m) of each operation variable is set. The discrete values of the m operation variables are combined to form operation modes, where card(Ai) represents the number of elements in the set Ai. All operation modes are numbered to construct the full operation mode set of the system. Among them, the multi-energy power generation and transmission system is a multi-energy power generation and transmission system in which new energy and thermal power units are bundled and connected to the grid for transmission together;

[0053] S2. Screening of multiple oscillation patterns and their branching methods: From the full set of operating modes, screen out the grouped mode sets with relatively high oscillation risks. If there are n oscillation patterns in the multi-energy power generation and transmission system, then a total of n grouped mode sets are screened. The grouped mode set corresponding to the Kth oscillation pattern is denoted as S K (K = 1, 2,..., n);

[0054] S3. Analysis of grouped oscillation modes based on impedance network model: For the n grouped mode sets screened in S2, analyze the oscillation modes of all operating modes of the n grouped mode sets based on the impedance network model to obtain whether there are risk oscillation modes in the grouped mode set corresponding to the kth oscillation pattern;

[0055] S4. Coupling analysis of multiple oscillation patterns: If there is an electrical oscillation risk caused by the interaction between the power grids of new energy and thermal power units under an operating mode, and the frequency f of the risk oscillation mode P and the torsional vibration frequency f of the thermal power unit shafting TG meet the following relationship:

[0056] |f p - |f0 - f TG || ≤ f coupling or |f p - |f0 + f TG || ≤ f coupling ;

[0057] Then it is determined that there is a coupling between electrical oscillation and shafting torsional vibration under this operating mode; where fcoupling is a preset threshold based on actual conditions, and f0 is the power frequency;

[0058] S5. Identification of risk operating modes: Evaluate the oscillation risk level of the operating mode and identify the risk operating modes;

[0059] S6. Output information: Output the number, oscillation mode, and risk level information of the operating mode to provide guidance for further oscillation prevention and control.

[0060] Furthermore, in the present invention, the new energy includes wind farms and photovoltaic power stations. The wind farm includes doubly-fed wind turbines and direct-drive wind turbines, and the photovoltaic power station includes photovoltaic power generation unit groups.

[0061] Furthermore, the purpose of S1 is to sort out various operating variables of the multi-energy power generation and transmission system and construct the full set of operating modes of the system. In specific implementation, wind power, photovoltaic power, and thermal power are bundled and sent out through a series-compensated line. A total of m operating variables of the multi-energy power generation and transmission system are considered, including:

[0062] (1) Grid structure type: number of circuit lines, series compensation degree of lines, etc.;

[0063] (2) Unit commissioning category: the number of commissioned thermal power units, the number of grid-connected wind turbines in a wind farm, the number of grid-connected photovoltaic power generation units in a photovoltaic power station, etc.;

[0064] (3) Unit output category: the output of a single thermal power unit, the output of a single wind turbine, the output of a single photovoltaic power generation unit, etc.

[0065] The above m operating variables constitute an m-dimensional parameter space, and each operating mode of the system can be represented by a unique m-dimensional vector. Further, set the discrete value set A i (i = 1, 2,..., m), in the form of

[0066] A i ={a i1 , a i2 ,..., a ij}

[0067] Each element in A i represents a value of the i-th operating variable, where the element a ij represents the j-th possible value of the i-th operating variable.

[0068] Combining the discrete values of the m operating variables will form types of operating modes, where card(A i ) represents the number of elements in the set A i . Finally, number all the operating modes to construct the full operating mode set of the system.

[0069] Furthermore, in S2, various oscillation forms that may exist in the multi-energy power generation and transmission system are considered. According to the characteristics of each oscillation form, a set of grouped modes with relatively high oscillation risks is screened out from the full operating mode set. If there are n possible oscillation forms in the multi-energy power generation and transmission system, then a total of n grouped mode sets are screened out, and the grouped mode set corresponding to the k-th oscillation form is denoted as S k (k = 1, 2,..., n).

[0070] In specific implementation, there may be 4 oscillation forms in the multi-energy power generation and transmission system, such as doubly-fed wind turbines - series-compensated power grid, direct-drive wind turbines - weak power grid, photovoltaic power generation units - weak power grid, and thermal power unit shafting - series-compensated power grid. When screening the grouped mode set corresponding to a specific oscillation form, some relatively severe operating modes should be selected according to its oscillation characteristics. The following screening principles can be used but are not limited to:

[0071] (1) For the oscillation of the doubly-fed wind turbine - series-compensated power grid: Several operation modes can be selected, where the series compensation degree of the line is relatively high, most of the grid-connected new energy units are doubly-fed wind turbines, and the single-unit output level of the doubly-fed wind turbine is relatively low (considering that the equivalent negative resistance of the doubly-fed wind turbine is relatively large at low output), to form a grouping mode set S1;

[0072] (2) For the oscillation of the direct-drive wind turbine - weak power grid: Several operation modes can be selected, where the power grid strength is relatively weak (the number of line circuits is small and the series compensation degree is low), most of the grid-connected new energy units are direct-drive wind turbines, and the total output level of the direct-drive wind turbines is relatively high, to form a grouping mode set S2;

[0073] (3) For the oscillation of the photovoltaic power generation unit - weak power grid: Several operation modes can be selected, where the power grid strength is relatively weak (the number of line circuits is small and the series compensation degree is low), most of the grid-connected new energy units are photovoltaic power generation units, and the total output level of the photovoltaic power is relatively high, to form a grouping mode set S3;

[0074] (4) For the oscillation of the steam turbine shafting - series-compensated power grid: Considering that when the unit output decreases, the mechanical damping will decrease accordingly, and the risk of shafting torsional vibration will be higher. Therefore, several operation modes where the steam turbine output is close to no-load can be selected to form a grouping mode set S4.

[0075] Furthermore, the purpose of S3 is to perform grouped oscillation mode analysis on the n grouped mode sets screened from S2 based on the impedance network model, including the following steps:

[0076] (1) In any operation mode of the grouped mode set S k (k = 1, 2,..., n), methods such as small-signal model derivation or external characteristic identification are used to calculate the impedance models of various power equipment in the system. For the convenience of analysis and calculation, when analyzing the electrical oscillation caused by the grid connection of wind power / photovoltaic units, the dynamic of the steam turbine shafting is not considered temporarily, and the steam turbine shafting can adopt a single-rigid-body model; when analyzing the torsional vibration caused by the steam turbine shafting - series-compensated power grid, the steam turbine shafting adopts a multi-mass model.

[0077] (2) The impedance models of various power equipment are spliced into an impedance network model according to the system topology structure, and then methods such as series-parallel operation or impedance matrix transformation calculation are used to simplify the impedance network model into an aggregated impedance.

[0078] (3) Identify the oscillation mode of the system according to the aggregated impedance. One method that can be used is to obtain the frequency characteristic curve of the aggregated impedance, and record the real part and imaginary part of the aggregated impedance as the equivalent resistance R and the equivalent reactance X respectively. If the equivalent reactance - frequency curve has a zero crossing at a frequency of ω X then it is considered that the system has an oscillation mode with a frequency of ω X ; Further, the damping σ of this oscillation modeX Can be approximately calculated as:

[0079]

[0080] Where k X (jω X ) is the equivalent reactance slope at frequency ω X , k R (jω X ) is the equivalent resistance slope at frequency ω X , R(jω X ) is the equivalent resistance at frequency ω X . The damping of the stable oscillation mode is positive, and the damping of the unstable oscillation mode is negative. Then, record the frequencies and damping of all oscillation modes.

[0081] (4) Judge whether the stability margin of each oscillation mode meets the requirements, and record the risk flag risk p corresponding to each oscillation mode. The criterion formula is as follows:

[0082]

[0083] Where the positive parameter σ risk is the preset stability margin; if the damping σ p of the p-th oscillation mode is less than σ risk , then let the risk flag risk p = 1, and consider that this mode has the risk of divergent or weakly damped oscillation, denoted as "risk oscillation mode". If there is a risk oscillation mode in the current operating mode, it means that the system has the risk of the k-th oscillation form.

[0084] (5) Repeat (1) to (4) to analyze the oscillation modes of all operating modes in the n grouping mode sets.

[0085] Furthermore, the purpose of S4 is to analyze whether there is coupling between multiple oscillation forms. When there is an electrical oscillation between the wind power / photovoltaic units and the power grid, and it is close to complementary with the torsional vibration frequency of the thermal power unit shafting, it is easy to excite the strong torsional vibration of the thermal power unit shafting, and the system oscillation will be particularly serious. If the system has a risk of electrical oscillation caused by the interaction between the wind power / photovoltaic units and the power grid in an operating mode, and the frequency fp of the risk oscillation mode and the torsional vibration frequency f TG of the thermal power unit shafting meet the following relationship:

[0086] |f p -|f0 - f TG || ≤ f coupling or |f p -|f0 + f TG || ≤ f coupling

[0087] It is determined that there is a coupling between electrical oscillation and shafting torsional oscillation under this operation mode. Among them, f coupling is a threshold value preset according to the actual situation, and f0 is the power frequency.

[0088] The S5 evaluates the oscillation risk level of the operation mode and identifies the risk operation mode. According to the oscillation severity, the oscillation risk of the operation mode is divided into three levels, arranged in descending order of severity as follows:

[0089] (1) If there is a risk oscillation mode and there is a coupling between electrical oscillation and shafting torsional oscillation, it is determined that the oscillation risk is the highest and the risk level is the first level;

[0090] (2) If there is a risk oscillation mode but there is no coupling between electrical oscillation and shafting torsional oscillation, it is determined that there is a certain oscillation risk and the risk level is the second level;

[0091] (3) If there is no risk oscillation mode, it is determined that there is basically no oscillation risk and the risk level is the third level.

[0092] The operation modes with the first-level and second-level risk levels belong to the risk operation modes and need to be focused on.

[0093] The multi-mode oscillation analysis method of the multi-energy power generation and transmission system in the embodiment of the present invention constructs the full operation mode set of the multi-energy power generation and transmission system, considers various oscillation forms and their coupling effects, can evaluate the oscillation risk of the system under a wide range of operation modes, effectively identify potential risk operation modes, plays an important role in risk avoidance and system protection, and can greatly improve the evaluation efficiency and accuracy of the wide-screen oscillation of the multi-energy power generation system, provides certain help for effectively suppressing power system faults caused by broadband oscillation problems, and at the same time, also provides certain support for improving the new energy transmission rate of the system.

[0094] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A multi-mode oscillation analysis method for a multi-energy power generation and transmission system, characterized in that: It includes the following steps: S1. Construction of the full operating mode set: The multi - energy power generation and transmission system includes m operating variables, and a discrete value set A of each operating variable is set. i， For i = 1, 2, …, m, the discrete values of the m operating variables are combined to form operating modes, where card(A i ) represents the number of elements in the set A i . Number all the operating modes to construct the full operating mode set of the system, where the multi - energy power generation and transmission system is a multi - energy power generation and transmission system in which new energy and thermal power units are bundled and connected to the grid for transmission together. S2. Screening of multiple oscillation patterns and their grouping mode sets: Screen out the grouping mode sets with high oscillation risks from the full operation mode sets. If there are n oscillation patterns in the multi-energy power generation and transmission system, a total of n grouping mode sets are screened. The grouping mode set corresponding to the Kth oscillation pattern is denoted as S K， K = 1, 2, …, n; S3. Group oscillation mode analysis based on the impedance network model: For the n grouped mode sets screened in S2, analyze the oscillation modes of all operating modes of the n grouped mode sets based on the impedance network model to obtain whether there are risk oscillation modes in the grouped mode set corresponding to the kth oscillation form; In S3, for the n grouped mode sets screened in S2, analyze the oscillation modes of all operating modes of the n grouped mode sets based on the impedance network model to obtain whether there are risk oscillation modes in the grouped mode set corresponding to the kth oscillation form, including the following steps: SⅠ. In the grouping mode set S k , under any operating mode where k = 1, 2,..., n, use the small-signal model derivation or external characteristic identification method to calculate the impedance models of each power equipment in the multi-energy power generation and transmission system; SⅡ. Splice the impedance models of each power equipment into an impedance network model according to the system topology structure, and simplify the impedance network model into an aggregated impedance by using series-parallel operations or impedance matrix transformation calculation methods; SⅢ. Identify the oscillation mode of the system based on the aggregation impedance and calculate the damping σ of this oscillation mode x ; SⅣ. Determine whether the stability margins of each oscillation mode meet the requirements, and record the risk flag risk corresponding to each oscillation mode p , and the criterion is as follows: Among them, the positive parameter σ risk is the preset stability margin; if the damping σ p of the p-th oscillation mode is less than σ risk , then let the risk flag risk p = 1, and it is considered that this mode has the risk of divergence or weakly damped oscillation, which is recorded as the risk oscillation mode. If there is a risk oscillation mode under the current operating mode, it means that the multi-energy power generation and transmission system has the risk of the k-th oscillation form; SⅤ. Repeat SⅠ to SⅣ to analyze the oscillation modes of all operating modes of the n grouped mode sets; S4. Coupled analysis of multiple oscillation patterns: If there is a risk of electrical oscillation caused by the interaction between the new energy and thermal power unit power grids under a certain operation mode, and the frequency f of the risk oscillation mode P is consistent with the torsional vibration frequency f of the thermal power unit shafting TG satisfies the following relationship: |f p -|f0 - f TG || ≤ f coupling or |f p -|f0 + f TG || ≤ f coupling ; It is determined that there is a coupling between electrical oscillation and shafting torsional oscillation under this operating mode; where f coupling is a threshold value preset according to the actual situation, and f0 is the power frequency; S5. Discrimination of risk operating modes: Evaluate the oscillation risk level of the operating modes to discriminate risk operating modes; S6. Output information: Output the number, oscillation mode, and risk level information of the operating mode to provide guidance for further oscillation prevention and control.

2. The multi-mode oscillation analysis method for a multi-energy power generation and transmission system according to claim 1, wherein the new energy includes a wind farm and a photovoltaic power station. The wind farm includes doubly-fed wind turbines and direct-drive wind turbines. The photovoltaic power station includes a photovoltaic power generation unit group; the m operating variables include: thermal power unit grid structure type, unit commissioning type, and unit output type; the thermal power unit grid structure type includes the number of line circuits and the line series compensation degree; the unit commissioning type includes the number of commissioned thermal power units, the number of grid-connected wind turbines in the wind farm, and the number of grid-connected photovoltaic power generation units in the photovoltaic power station; the unit output type includes the output of a single thermal power unit, the output of a single wind turbine, and the output of a single photovoltaic power generation unit; the m operating variables constitute an m-dimensional parameter space, and each operating mode can be represented by a unique m-dimensional vector.

3. The multi-mode oscillation analysis method for a multi-energy power generation and transmission system according to claim 2, wherein The discrete value set A of each operating variable i , where i = 1, 2, …, m, in the form of A i = {a i1 , a i2 ,..., a ij} A i Each element in it represents a value of the \(i\)-th running variable, where element \(a\) ij represents the \(j\)-th value of the \(i\)-th running variable.

4. The multi-mode oscillation analysis method for a multi-energy power generation and transmission system according to claim 2, wherein In S2, there are 4 oscillation forms in the multi-energy power generation and transmission system: doubly-fed wind turbine - series-compensated power grid, direct-drive wind turbine - weak power grid, photovoltaic power generation unit - weak power grid, and thermal power unit shafting - series-compensated power grid. When screening the grouped mode set corresponding to a specific oscillation form, some severe operating modes should be selected according to its oscillation characteristics, including the following screening principles: For the oscillation of doubly-fed wind turbine - series-compensated power grid: Select several operating modes with a high line series compensation degree, most of the grid-connected new energy units being doubly-fed wind turbines, and a low single-unit output level of the doubly-fed wind turbines to form the grouped mode set S1; For the oscillation of direct-drive wind turbine - weak power grid: Select several operating modes with a weak power grid strength, most of the grid-connected new energy units being direct-drive wind turbines, and a high total output level of the direct-drive wind turbines to form the grouped mode set S2; For the photovoltaic power generation unit - weak grid oscillation: Select several operation modes with weak grid strength, a large number of grid-connected new energy units being photovoltaic power generation units, and a high total photovoltaic output level to form a grouping mode set S3; For the steam turbine shafting - series compensated grid oscillation: Select several operation modes with the steam turbine output being no-load to form a grouping mode set S4.

5. The multi-mode oscillation analysis method for a multi-energy power generation and transmission system according to claim 4, characterized in that, In SⅠ, to facilitate the analysis and calculation of the impedance models of various power equipment in the multi-energy power generation and transmission system, when analyzing the electrical oscillations caused by the grid connection of a wind farm / photovoltaic power station, the dynamics of the steam turbine shafting are temporarily not considered, and the steam turbine shafting adopts a single-rigid-body model; When analyzing the torsional vibration caused by the steam turbine shafting - series compensated grid, the steam turbine shafting adopts a multi-mass model.

6. The multi-mode oscillation analysis method for a multi-energy power generation and transmission system according to claim 4, characterized in that, In SⅢ, the oscillation mode of the multi-energy power generation and transmission system is identified based on the aggregation impedance, and the damping σ of this oscillation mode is calculated. x , and one method adopted is as follows: Obtain the frequency characteristic curve of the aggregated impedance. Denote the real part and the imaginary part of the aggregated impedance as the equivalent resistance R and the equivalent reactance X respectively. If the equivalent reactance - frequency curve has a zero crossing at a frequency of ω X then it is considered that the system has an oscillation mode at a frequency of ω X and the damping σ X of this oscillation mode is calculated as: where, kX(jωX) is the equivalent reactance slope at frequency ω X , kR(jωX) is the equivalent resistance slope at frequency ω X , R(jωX) is the equivalent resistance at frequency ω X , the damping of the stable oscillation mode is positive, and the damping of the unstable oscillation mode is negative; record the frequencies and damping of all oscillation modes.

7. The multi-mode oscillation analysis method for a multi-energy power generation and transmission system according to claim 1, characterized in that, In S5, according to the severity of the oscillation, the oscillation risks of the operation modes are divided into three levels, and arranged in descending order of severity as follows: If there is a risk oscillation mode and there is a coupling between electrical oscillation and shafting torsional vibration, it is determined that the oscillation risk is the highest and the risk level is the first level; If there is a risk oscillation mode but there is no coupling between electrical oscillation and shafting torsional vibration, it is determined that there is a certain oscillation risk and the risk level is the second level; If there is no risk oscillation mode, it is determined that there is no oscillation risk and the risk level is the third level; Among them, the operation modes with the risk levels of the first level and the second level belong to the risk operation modes.

Images