A new energy grid-connected system subsynchronous oscillation risk assessment method and system

Abstract

This invention discloses a method and system for assessing the risk of subsynchronous oscillation in a new energy grid-connected system, belonging to the field of electrical engineering, including: step S1, establishing A for each new energy power station. i The complex frequency domain equations of the access point system side, where i = 1, 2, ..., m, m is the total number of new energy power stations; Step S2: Perform matrix transformation on the complex frequency domain equations of the system side to obtain the system side relative to the new energy power station A. i The equivalent admittance matrix Y of the access point si To obtain the equivalent impedance Z in the complex frequency domain on the system side. si Step S3: If the complex frequency domain equivalent impedance Z si and the aforementioned new energy power station A i Complex frequency domain self-impedance Z of the access point ii If the amplitude curves intersect and the phase difference is greater than 180°, then it is determined that the new energy power station A... i The system is susceptible to subsynchronous oscillations. This invention can determine the impact of any new energy generator unit's connection on system stability, enabling subsynchronous oscillation risk assessment for complex power systems.

Description

Technical Field

[0001] This invention belongs to the field of electrical engineering technology, and more specifically, relates to a method and system for assessing the risk of subsynchronous oscillation in a new energy grid-connected system. Background Technology

[0002] With the continuous advancement of energy transformation, the installed capacity of new energy power generation is constantly increasing. In the future, new energy power generation will be connected to the grid on a large scale, and new energy will replace traditional fossil energy as the main source of energy supply. The development of the power system shows a "double high" trend, namely, a high proportion of new energy power generation and a high proportion of power electronic equipment.

[0003] The extensive integration of power electronic equipment has brought significant challenges to the safe and stable operation of power systems. Power electronic equipment on the generation side and in the transmission network are interconnected, and the control interactions between these devices, as well as the interactions between them and the power grid, can cause more complex electromagnetic oscillation problems. These oscillations often originate from small-signal negative damping instability, and their frequencies are mostly in the subsynchronous / supersynchronous band. For example, the subsynchronous interaction between the doubly-fed induction generator (DFIG) converter and the series compensation device of the transmission line, the interaction between direct-drive wind turbines and weak AC networks, and the interaction between the DC transmission inverter side and weak AC networks can all cause novel subsynchronous oscillation problems.

[0004] Currently, the main methods for assessing the subsynchronous oscillation stability of power systems include short-circuit ratio-based, state-space analysis, and impedance analysis-based methods. Among these, the short-circuit ratio-based method uses the ratio of the AC system's short-circuit capacity to the capacity of renewable energy grid-connected equipment to reflect the relative strength of the AC system, thereby assessing grid stability. However, there is no unified and precise standard for the specific calculation details of the short-circuit ratio, such as the calculation of the short-circuit ratio at each wind farm port in a multi-wind farm grid-connected system, and the impact of dynamic reactive power compensation devices configured in the wind power grid-connected system on the short-circuit ratio. Therefore, the description of system stability is not very precise. The state-space analysis-based method typically uses a continuous state-space model, which involves a large amount of computation for complex networks, leading to the "curse of dimensionality." Furthermore, the algebraic variable elimination process during calculation results in the final state-space model of the entire system failing to display the topological information of the entire system. For complex power systems, existing stability assessment methods based on impedance analysis mainly rely on aggregated impedances of the overall model and the RLC resonance principle to determine the stability of the system. However, the aggregation of impedance networks requires following a specific oscillation path and cannot intuitively identify which specific renewable energy equipment has an oscillation problem, which has certain limitations. Summary of the Invention

[0005] To address the shortcomings and improvement needs of existing technologies, this invention provides a method and system for assessing the risk of subsynchronous oscillations in a new energy grid-connected system. Its purpose is to determine the impact of any new energy generator unit on the system stability, thereby achieving the assessment of the risk of subsynchronous oscillations in complex power systems.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for assessing the risk of subsynchronous oscillation in a new energy grid-connected system is provided, comprising: Step S1: Establish A for each new energy power station. i The complex frequency domain equations on the access point system side, where i = 1, 2, ..., m, and m is the total number of new energy power stations; Step S2: Perform a matrix transformation on the complex frequency domain equations of the system side to obtain the system side relative to the new energy power station A. i Equivalent admittance matrix of the access point To obtain the equivalent impedance in the complex frequency domain on the system side. ; Step S3: If the complex frequency domain equivalent impedance and the aforementioned new energy power station A i Complex frequency domain self-impedance of the access point If the amplitude curves intersect and the phase difference is greater than 180°, then it is determined that the new energy power station A... i There is a risk of subsynchronous oscillation in the access system.

[0007] Furthermore, it also includes: if the new energy power station A i If the access system has a risk of subsynchronous oscillation, the frequency corresponding to the intersection of the amplitude curves will be identified as the subsynchronous oscillation frequency.

[0008] Furthermore, the equivalent impedance in the complex frequency domain for:

[0009] in, This indicates that the system side is relative to the new energy power station A. i The nodal equivalent admittance matrix.

[0010] Further, step S1 includes: Step S11: Establish the port equivalent admittance matrix model of each component of the new energy grid-connected system in the same coordinate system in the complex frequency domain; Step S12: Based on the complex frequency domain port equivalent admittance matrix model, calculate the new energy power station A using the branch addition method. i Admittance matrix on the system side of the access point; Step S13: For a specific new energy power station A iThe access point, based on the access point current, voltage, and the new energy power station A... i The relationship between the admittance matrices on the access point system side is used to establish the relationship between the admittance matrices of the new energy power station A. i Complex frequency domain equations on the access point system side.

[0011] Furthermore, in step S13, the current and voltage at the access point and the new energy power station A... i The relationship between the admittance matrices on the access point system side is as follows:

[0012] In the formula, I 1. U 1 represents the new energy power station A. i Current matrix and voltage matrix at the connection point; U 2 represents the node voltage matrix on the system side. This indicates that the node injection current on the system side is all 0. , , , These respectively represent the new energy power station A i The access point system side admittance matrix is ​​based on the new energy power station A. i The four sub-blocks after dividing the access point and the remaining N-1 nodes are represented by the content in the brackets of the subscripts, which indicate the size of the matrix. N represents the total number of nodes in the new energy grid-connected system.

[0013] Further, in step S11, each component includes grid-connected new energy sources, and establishing the complex frequency domain port equivalent admittance matrix model for the grid-connected new energy sources includes: Establish a state-space model of new energy power generation equipment in a two-phase rotating dq coordinate system; Based on the transformation relationship between the two-phase rotating dq coordinate system of the power generation equipment and the two-phase synchronous rotating xy coordinate system of the power grid, the coordinate transformation relationship between the connection point voltage and the output current is obtained through linearization. Substituting the coordinate transformation relationship into the state space model under the two-phase rotating dq coordinate system, we obtain the state space model of the new energy power generation equipment under the two-phase synchronous rotating xy coordinate system of the power grid, so as to obtain the complex frequency domain port equivalent admittance matrix model of the new energy grid connection.

[0014] Furthermore, in step S11, the same coordinate system is a positive-negative order coordinate system; Step S2 also includes the step of obtaining the positive-sequence complex frequency domain equivalent impedance of the system side through positive-sequence and negative-sequence decoupling analysis; Step S3 further includes the step of: if the positive sequence complex frequency domain equivalent impedance and the new energy power station A iIf the amplitude curves of the positive-sequence complex frequency domain self-impedance of the access point intersect and the phase difference is greater than 180°, then the new energy power station A... i There is a risk of subsynchronous oscillation in the access system.

[0015] According to another aspect of the present invention, a subsynchronous oscillation risk assessment system for a new energy grid-connected system is provided, comprising: The complex frequency domain equation construction module is used to establish A for each new energy power station. i The complex frequency domain equations on the access point system side, where i = 1, 2, ..., m, and m is the total number of new energy power stations; The equivalent impedance calculation module is used to perform matrix transformations on the complex frequency domain equations of the system side to obtain the system side relative to the new energy power station A. i Equivalent admittance matrix of the access point To obtain the equivalent impedance in the complex frequency domain on the system side. ; The subsynchronous oscillation risk assessment module is used to assess the risk of the new energy power station A. i Does the access system have a risk of subsynchronous oscillation? If the complex frequency domain equivalent impedance... and the aforementioned new energy power station A i Complex frequency domain self-impedance of the access point If the amplitude curves of the two energy power stations intersect and the phase difference is greater than 180°, then the energy power station A... i There is a risk of subsynchronous oscillation in the access system.

[0016] According to another aspect of the present invention, an electronic device is provided, characterized in that it includes: a processor and a memory, wherein the memory stores a computer-executable program, which, when executed by the processor, causes the processor to perform the evaluation method as described in any one of the first aspects.

[0017] According to another aspect of the invention, a computer-readable storage medium is provided having a computer program stored thereon, characterized in that the program, when executed by a processor, implements the evaluation method as described in any of the first aspects.

[0018] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: (1) The subsynchronous oscillation risk assessment method of the new energy grid-connected system of the present invention is based on establishing A for each new energy power station. i The complex frequency domain equations on the access point system side enable the analysis of the complex frequency domain equivalent impedance of the remaining network excluding a single renewable energy power station, taking that single power station as the research object. The complex frequency domain self-impedance of this single renewable energy power station The impedance curve relationship is used to determine whether there is an oscillation risk when a single renewable energy power station is connected. This invention performs impedance analysis on the stability of each renewable energy connection point, which can intuitively and accurately analyze the impact of each renewable energy generator unit on system stability. The criteria are simple, clear, and easy to implement. This invention can achieve a comprehensive assessment of the subsynchronous oscillation risk of complex power systems, making subsequent subsynchronous oscillation suppression work more targeted.

[0019] (2) Furthermore, according to the criterion of the present invention, the oscillation frequency that causes the subsynchronization of the system can be further obtained, which facilitates the subsequent work of suppressing the subsynchronization oscillation problem.

[0020] (3) Furthermore, the present invention also provides a new energy power station A i Admittance matrix of the access point system side and equivalent admittance matrix of the node The specific calculation method is simple and easy to obtain through calculation of the nodal equivalent admittance matrix. Further, the equivalent impedance in the complex frequency domain is obtained. .

[0021] (4) This invention adopts a modular component modeling method and utilizes node analysis to determine the connection point current, voltage, and new energy power station A. i The relationship between the admittance matrices on the system side of the access point can be used to easily establish the complex frequency domain equations of the network to obtain the equivalent impedance of the remaining network. Furthermore, the complex frequency domain equations of the network can be easily modified when the network structure changes due to operations such as switching on / off of system components. It is easy to implement through programming and is suitable for evaluating the grid connection stability of new energy sources under complex network structure conditions.

[0022] (5) In the process of establishing the equivalent admittance matrix model of the port of the new energy grid connection, the state space model of the new energy power generation equipment established by the present invention can better reflect the dynamic characteristics of the new energy grid connection system. Therefore, it can accurately judge the subsynchronous oscillation stability of the new energy grid connection system.

[0023] (6) As a preferred option, the port equivalent admittance matrix model of each component established under a unified positive and negative order coordinate system ignores the coupling effect between positive and negative order variables and performs approximately decoupled analysis of positive and negative order, which can reduce the computational load of the system. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the subsynchronous oscillation risk assessment method for new energy grid-connected systems according to the present invention.

[0025] Figure 2 This is a flowchart of the subsynchronous oscillation risk assessment method for new energy grid-connected systems according to the present invention.

[0026] Figure 3 This is a vector diagram showing the relationship between the dq coordinate system and the xy synchronous rotating coordinate system of new energy power generation equipment.

[0027] Figure 4 This is a schematic diagram of the test system structure provided in an embodiment of the present invention.

[0028] Figures 5(a) and 5(b) are respectively the impedance analysis amplitude curve and phase curve at the port of the direct-drive wind farm in the test system provided in the embodiment of the present invention.

[0029] Figure 6 The active power waveform output by the test system provided in this embodiment of the invention is shown in the figure after a disturbance at a wind farm. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] like Figure 1 , Figure 2 As shown, the subsynchronous oscillation risk assessment method for new energy grid-connected systems of the present invention mainly includes: Step S1: Establish A for each new energy power station. i The complex frequency domain equations on the access point system side, where i = 1, 2, ..., m, and m is the total number of new energy power stations; Specifically, step S1 includes: Step S11: Establish a complex frequency domain port equivalent admittance matrix model for each component of the new energy grid-connected system in the same coordinate system; and calculate the complex frequency domain self-impedance of any new energy power station grid connection point (access point) based on the complex frequency domain port equivalent admittance matrix model. Step S12: Based on the complex frequency domain port equivalent admittance matrix model, calculate the new energy power station A using the branch addition method. i Admittance matrix of the access point system side; among which, new energy power station A i The access point system side is the new energy grid-connected system to be studied, excluding the new energy power station A. i The remaining network outside; Step S13, based on new energy power station A i The admittance matrix on the system side of the access point is obtained using nodal analysis for a specific new energy power station A. i The connection point, based on the current and voltage of the connection point and the new energy power station A iThe relationship between the admittance matrices on the access point system side is used to establish the new energy power station A. i Complex frequency domain equations on the access point system side.

[0032] Step S2, for new energy power station A i The complex frequency domain equations at the access point system side are transformed by matrix to obtain the new energy power station A. i The access point system side is relative to the new energy power station A i Equivalent admittance matrix of the access point Thus, the new energy power station A was obtained. i Equivalent impedance in the complex frequency domain on the access point system side ; Step S3: According to the new energy power station A i Equivalent impedance in the complex frequency domain on the access point system side With the new energy power station A i Complex frequency domain self-impedance of grid connection point The amplitude and phase relationship is used to determine the new energy power station A. i Does connecting to a new energy grid system affect the system's stability, i.e., is there a risk of oscillation?

[0033] By following the steps above, it is possible to determine whether there is an oscillation risk in the connection system of all new energy power plants, thereby achieving a comprehensive assessment of the subsynchronous oscillation risk of the power system under study.

[0034] Specifically, in step S11, the main components in the new energy grid-connected power system include: transformers, AC transmission line components, synchronous generators, and new energy grid connection.

[0035] The process of establishing the port equivalent admittance matrix model of the transformer in the complex frequency domain in the xy coordinate system includes: In the abc three-phase coordinate system, the voltage equation of the transformer is established as shown in formula (1), where the transformer adopts the inductor-resistor series model; (1) In the formula, Represents a node voltage, Represents a node voltage, Indicates the nodes through which the flow passes. and nodes The current, This indicates the resistance of the transformer. Indicates the reactance of the transformer. This represents a differential operator.

[0036] Transforming formula (1) to the xy coordinate system, and after simplification, rearrangement, and linearization, the differential equation of the transformer model is obtained as follows: (2) In the formula, , Representing nodes respectively The x and y components of the voltage, , Representing nodes respectively The x and y components of the voltage, , Representing nodes and nodes The x and y axis components of the current.

[0037] Based on formula (2), the complex frequency domain port admittance matrix of the transformer is further obtained. for: (3) In the formula, This represents the complex frequency domain port admittance matrix of the transformer.

[0038] The process of establishing the port equivalent admittance matrix model of AC transmission line components in the complex frequency domain in the xy coordinate system includes: Transmission line components are considered as lumped parameter models (positive sequence networks), mainly including AC transmission line models (considering line charging capacitors) and series compensation capacitor branches; in the abc three-phase coordinate system, the equations for AC transmission lines and series compensation capacitor branches are established respectively: (4) (5) In the formula, This indicates the resistance of the transmission line. Indicates the reactance of the transmission line; This indicates the capacitance value of the compensation capacitor branch. This indicates the voltage of the compensation capacitor.

[0039] Transforming equations (4) and (5) into the xy coordinate system, and after simplification, rearrangement, and linearization, the differential equations of the AC transmission line and the series compensation capacitor branch are obtained as follows: (6) (7) In the formula, This indicates the reactance value of the compensation capacitor. , These represent the x and y axis components of the compensation capacitor voltage, respectively.

[0040] Based on formulas (6) and (7), the port admittance matrix of the transmission line and capacitor can be further obtained as follows: (8) (9) In the formula, , These represent the port equivalent admittance matrix of the AC transmission line in the complex frequency domain and the port equivalent admittance matrix of the compensation capacitor in the complex frequency domain, respectively.

[0041] The process of establishing the port equivalent admittance matrix model of a synchronous generator in the complex frequency domain in the xy coordinate system includes: Taking a generator set with a 6-winding electrical model as an example, without considering the effects of the excitation system and the power system stabilizer (PSS), for the dynamics of the shaft system, a segmented concentrated mass spring model is adopted. The torque transmission relationship between the shaft segments includes the prime mover torque or electromagnetic torque, the torque between adjacent mass blocks, and the damping torque.

[0042] The transformation relationship between the synchronous generator coordinate system dq and the system synchronous coordinate system xy is linearized, and after coordinate transformation matrix transformation, the following is obtained: (10) in, X G Let be the state vector of the synchronous generator. U Gxy , I Gxy These are the terminal voltage and terminal current vectors of the synchronous generator in the xy coordinate system, respectively. , , It is a coefficient matrix.

[0043] The complex frequency domain port admittance matrix of the synchronous generator is obtained by simplification. for: (11) In the formula, Represents the identity matrix.

[0044] The process of establishing the port equivalent admittance matrix model of new energy grid connection in the complex frequency domain under the xy coordinate system includes: A state-space model of new energy power generation equipment in a two-phase rotating dq coordinate system is established. This mathematical model can take into account various dynamic components and dynamic links in the new energy grid-connected system. For example, taking a direct-drive wind turbine as an example, it considers the wind turbine and its control link, permanent magnet motor, turbine-side converter and its control link, grid-side converter and its control link, phase-locked loop control, etc. It can better reflect the dynamic characteristics of the new energy grid-connected system, and thus can accurately judge the subsynchronous oscillation stability of the new energy grid-connected system.

[0045] The detailed state-space models of new energy power generation equipment such as direct-drive wind turbines, doubly-fed wind turbines, and photovoltaic power plants vary. However, since a single new energy power generation equipment is connected to the grid through only one node (grid connection point), the state-space model of the new energy power generation equipment can be expressed as the following general formula in the two-phase rotating dq coordinate system determined by its own phase-locked loop: (12) in, X S Let be the state vector of the new energy power generation equipment. u Sdq , i Sdq These are the grid-connected voltage vector and output current vector of the new energy power generation equipment in its own dq coordinate system, respectively. A 1. B 1. C 1 is the coefficient matrix.

[0046] like Figure 3 As shown, the dq coordinate axis is... PLL1 Angle rotation, the xy coordinate system rotates by an angle. E The transformation relationship between the power generation equipment's own dq rotating coordinate system and the power grid's two-phase synchronously rotating xy coordinate system is as follows: (13) In the formula, , Representing phasors respectively A The d-axis and q-axis components, This indicates the angle by which the q-axis leads the x-axis. , Representing phasors respectively A The x and y axis components.

[0047] Linearizing this conversion relationship and substituting the grid connection voltage and output current of the new energy power generation equipment into it, we can obtain: (14) in, u Sxy, i Sxy Let the voltage vector and output current vector at the grid connection point be defined in the synchronously rotating xy-coordinate system of the two phases of the power grid. T 0、 R V , R i All are coefficient matrices. , , , These represent the d-axis and q-axis components of the steady-state voltage at the grid connection point, respectively. , These represent the d-axis and q-axis components of the steady-state output current, respectively.

[0048] Substituting the coordinate transformation relationship between the grid connection point voltage and the output current into the state space model of the new energy power generation equipment in its own dq coordinate system, we can obtain the state space model of the new energy power generation equipment in the two-phase synchronous rotating xy coordinate system of the power grid as follows: (15) in, , , .

[0049] Furthermore, the complex frequency domain port equivalent admittance matrix model of new energy power generation equipment can be obtained: (16) To facilitate subsequent calculations, in step S11, the admittance matrix obtained above in the xy synchronous rotating coordinate system can be unified to the positive and negative sequence coordinate system; step S2 also includes the step of: obtaining the positive sequence complex frequency domain equivalent impedance of the remaining network except for the new energy power station A1 under study through positive sequence and negative sequence decoupling analysis, that is, the positive sequence complex frequency domain impedance of the equivalent network of the access point of the new energy power station A1 under study; step S3 also includes the step of: based on the positive sequence complex frequency domain equivalent impedance and the new energy power station A i The amplitude and phase relationship of the positive-sequence complex frequency domain self-impedance at the access point is used to determine the new energy power station A. i Does the access system exhibit subsynchronous oscillation?

[0050] In step S2, the new energy power station A i Equivalent impedance in the complex frequency domain on the access point system side With equivalent admittance matrix The following conditions must be met:

[0051] In this embodiment, when calculating the difference between a certain new energy power station A and... iBefore calculating the equivalent impedance in the complex frequency domain of the remaining network, the nodes of the power system under study are numbered. It is assumed that the power system under study has a total of [number missing]. N There are 1 independent nodes. Let the node where the port of the new energy power station under study is located be numbered 1, i.e., A1, and the remaining nodes be numbered sequentially to 1. N .

[0052] Based on the previously introduced complex frequency domain port admittance matrix model of each component, the branch addition method is used to obtain the new energy power station A. i Admittance matrix on the access point system side.

[0053] For each independent node, nodal analysis can be used, based on the current and voltage at the connection point and the new energy power station A. i The relationship between the admittance matrices on the access point system side, for the new energy power station A1 with node number 1, is such that the injected current equals the sum of the product of the node voltage and its self-admittance, and the product of the voltages and mutual admittances of adjacent nodes. This allows us to obtain the complex frequency domain equations for the remaining network excluding new energy power station A1. Specifically, the access point current, voltage, and new energy power station A1... i The relationship between the admittance matrices on the access point system side is as follows: (17) In the formula, I 1. U 1 represents the new energy power station A to be studied. i Current matrix and voltage matrix at the access point (port A1 in this embodiment); U 2 is for new energy power stations A i The node voltage matrix of the remaining network outside, Including the new energy power station A under study i The injected current at all nodes of the remaining network outside the network is 0. , , , These respectively represent the new energy power station A i The admittance matrix of the access point system side is based on the new energy power station A under study. i The node in question (node ​​1 in this example) and the four sub-blocks formed by dividing the remaining N-1 nodes are represented by the content within the brackets of the subscripts, indicating the size of the matrix.

[0054] Simplifying formula (17) yields the admittance matrix of the remaining network relative to the grid-connected node 1 of the new energy power station under study. satisfy: (18) Complex frequency domain equivalent impedance to the remaining networks excluding the new energy power station A1 : (19) Specifically, in step S4, the stability assessment of each new energy power station is performed. Based on the complex frequency domain port equivalent admittance matrix model of the new energy grid-connected system in step S11, the new energy power station A under study is obtained. i The self-impedance, in this embodiment, is the self-impedance of the new energy power station A1. Z 11 Then, combined Z s1 and Z 11 The impedance curves were analyzed for the new energy power station A1 under study to assess the impact of the station's connection on the system's stability.

[0055] Specifically, according to the new energy power station A i The equivalent impedance in the complex frequency domain on the access point system side and the new energy power station A i The amplitude and phase relationship of the complex frequency domain self-impedance at the grid connection point is used to determine the new energy power station A. i The specific method for determining whether connecting to the power system affects system stability is as follows: If the complex frequency domain equivalent impedance of the remaining network And the new energy power station A i Complex frequency domain self-impedance of grid connection point If the amplitude curves of the two impedances intersect and the phase difference between the two impedances is greater than 180°, then it can be determined that the new energy power station A... i Integrating into the system carries the risk of oscillation, and the oscillation frequency corresponds to the frequency at the intersection of the amplitude curves. Otherwise, this new energy power station A... i Integrating it into the system will not affect the system's stability.

[0056] By performing the same analysis on the remaining renewable energy power stations in sequence, the stability of all renewable energy power stations in the power system under study can be determined, and the risk assessment of subsynchronous oscillation of the system under study can be completed. Figure 2 In the above, if k=0, it means that the integration of all new energy power stations into the system will not affect the stability of the system. k represents the number of new energy power stations with the risk of subsynchronous oscillation.

[0057] by Figure 4 The method of the present invention will be further explained using the test system shown as an example. A direct-drive wind farm is connected to the 220kV main AC power grid after passing through a step-up transformer. The parameters of the direct-drive wind farm and the AC power grid in the test system are shown in Tables 1 and 2, respectively. Typical control parameters are used in the control loop of the direct-drive wind turbine. The AC network strength is represented by the short-circuit ratio (SCR), which is the ratio of the short-circuit capacity at the wind farm outlet to the wind farm capacity.

[0058] Table 1 Parameters of Direct-Drive Wind Farm

[0059] Table 2 AC power grid parameters

[0060] The above-mentioned method was used to assess the risk of subsynchronous oscillation in the test system. Taking the direct-drive wind farm in the test system as the object, its self-impedance was calculated, and the equivalent network complex frequency domain impedance to the wind farm port was calculated using nodal analysis. The results are shown in Figures 5(a) and 5(b). It can be seen that the amplitude curves of the two impedances intersect at a frequency of 42.1 Hz. At this frequency, the phase curves of the two impedances are -104.224° and 85.8541°, respectively, with a difference greater than 180°. Therefore, it can be clearly seen that the direct-drive wind farm has a risk of subsynchronous oscillation under this condition. The test system has only one new energy power station and has a risk of subsynchronous oscillation. Therefore, the assessment result of the subsynchronous oscillation problem of the test system can be obtained.

[0061] The above test system was verified using the eigenvalue calculation method, with all parameters kept consistent. The results show that the system possesses an unstable subsynchronous oscillation mode λ. 35,36 =7.06±j2π×42.581, which is consistent with the analysis results of this invention, and the oscillation frequency is also very close.

[0062] Further dynamic characteristic simulations of the test system were performed using the PSCAD / EMTDC electromagnetic transient simulation platform, with the following parameters: The wind speed at the wind farm was 6 m / s. At the 6th second, the system network resistance and inductance were changed, reducing the short-circuit ratio at the wind farm port from 4 to 1.6, while other parameters remained unchanged. The active power output of the wind farm was as follows: Figure 6 As shown, when the short-circuit ratio decreases to 1.6, the test system will exhibit obvious subsynchronous oscillation, which is consistent with the evaluation results of this invention, and further verifies the correctness of the method of this invention.

[0063] The subsynchronous oscillation risk assessment method for new energy grid-connected systems of the present invention establishes a complex frequency domain port equivalent admittance matrix model for each component in the new energy grid-connected system. Taking a single new energy power station as the research object, it compares and analyzes the equivalent input impedance of the system side at the access point of the new energy power station and the self-impedance of the new energy power station access network to clarify the impact of each new energy generator unit access on system stability, thereby realizing the assessment of the subsynchronous oscillation risk of complex power systems.

[0064] According to another aspect of the present invention, the present invention also provides a subsynchronous oscillation risk assessment system for a new energy grid-connected system, comprising: The complex frequency domain equation construction module is used to establish A for each new energy power station. i Complex frequency domain equations on the access point system side; The equivalent impedance calculation module is used to perform matrix transformations on the complex frequency domain equations of the system side to obtain the system side impedance relative to the new energy power station A. i Equivalent admittance matrix of the access point To obtain the equivalent impedance in the complex frequency domain on the system side. Where i = 1, 2, ..., m, and m is the total number of new energy power stations; The subsynchronous oscillation risk assessment module is used to assess the risk of secondary oscillations in new energy power plants A. i Does the access system pose a risk of subsynchronous oscillation? If the equivalent impedance in the complex frequency domain... and New Energy Power Station A i Complex frequency domain self-impedance of grid connection point If the amplitude curves intersect and the phase difference is greater than 180°, then it is determined that the new energy power station A... i There is a risk of subsynchronous oscillation in the access system.

[0065] For details on the implementation of each module, please refer to the specific steps corresponding to the above-mentioned risk assessment method for subsynchronous oscillations in new energy grid-connected systems.

[0066] According to another aspect of the present invention, the present invention also provides an electronic device, including: a processor and a memory, wherein the memory stores a computer-executable program, and when the program is executed by the processor, the processor performs the specific steps corresponding to the above-described risk assessment method for subsynchronous oscillation of new energy grid-connected systems, which will not be repeated here.

[0067] According to another aspect of the present invention, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the specific steps corresponding to the above-described risk assessment method for subsynchronous oscillations in new energy grid-connected systems, which will not be repeated here.

[0068] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for assessing the risk of subsynchronous oscillation in a new energy grid-connected system, characterized in that, include: Step S1: Establish A for each new energy power station. i The complex frequency domain equations on the access point system side, where i = 1, 2, ..., m, and m is the total number of new energy power stations; Step S2: Perform a matrix transformation on the complex frequency domain equations of the system side to obtain the system side relative to the new energy power station A. i Equivalent admittance matrix of the access point To obtain the equivalent impedance in the complex frequency domain on the system side. The equivalent impedance in the complex frequency domain for: , This indicates that the system side is relative to the new energy power station A. i The nodal equivalent admittance matrix; Step S3: If the complex frequency domain equivalent impedance and the aforementioned new energy power station A i Complex frequency domain self-impedance of the access point If the amplitude curves intersect and the phase difference is greater than 180°, then it is determined that the new energy power station A... i The access system is susceptible to subsynchronous oscillation; among them, the new energy power station A i Complex frequency domain self-impedance of the access point Determined based on its complex frequency domain port equivalent admittance matrix model; Step S1 includes: Step S11: Establish the port equivalent admittance matrix model of each component of the new energy grid-connected system in the same coordinate system in the complex frequency domain; Step S12: Based on the complex frequency domain port equivalent admittance matrix model, calculate the new energy power station A using the branch addition method. i Admittance matrix on the system side of the access point; Step S13: For a specific new energy power station A i The access point, based on the access point current, voltage, and the new energy power station A... i The relationship between the admittance matrices on the access point system side is used to establish the relationship between the admittance matrices of the new energy power station A. i Complex frequency domain equations on the access point system side; In step S13, the current and voltage at the access point and the new energy power station A i The relationship between the admittance matrices on the access point system side is as follows: In the formula, I 1. U 1 represents the new energy power station A. i Current matrix and voltage matrix at the connection point; U 2 represents the node voltage matrix on the system side. This indicates that the node injection current on the system side is all 0. , , , These respectively represent the new energy power station A i The admittance matrix on the access point system side is based on the new energy power station A. i The four sub-blocks after dividing the access point and the remaining N-1 nodes are represented by the subscripts in square brackets, which indicate the size of the matrix. N represents the total number of nodes in the new energy grid-connected system.

2. The evaluation method according to claim 1, characterized in that, Also includes: If the aforementioned new energy power station A i If the access system has a risk of subsynchronous oscillation, the frequency corresponding to the intersection of the amplitude curves will be identified as the subsynchronous oscillation frequency.

3. The evaluation method according to claim 1, characterized in that, In step S11, each component includes grid-connected new energy sources, and establishing the complex frequency domain port equivalent admittance matrix model for the grid-connected new energy sources includes: Establish a state-space model of new energy power generation equipment in a two-phase rotating dq coordinate system; Based on the transformation relationship between the two-phase rotating dq coordinate system of the power generation equipment and the two-phase synchronous rotating xy coordinate system of the power grid, the coordinate transformation relationship between the connection point voltage and the output current is obtained through linearization. Substituting the coordinate transformation relationship into the state space model under the two-phase rotating dq coordinate system, we obtain the state space model of the new energy power generation equipment under the two-phase synchronous rotating xy coordinate system of the power grid, so as to obtain the complex frequency domain port equivalent admittance matrix model of the new energy grid connection.

4. The evaluation method according to claim 1, characterized in that, In step S11, the same coordinate system is a positive and negative order coordinate system; Step S2 also includes the step of obtaining the positive-sequence complex frequency domain equivalent impedance of the system side through positive-sequence and negative-sequence decoupling analysis; Step S3 further includes the step of: if the positive sequence complex frequency domain equivalent impedance and the new energy power station A i If the amplitude curves of the positive-sequence complex frequency domain self-impedance of the access point intersect and the phase difference is greater than 180°, then the new energy power station A... i There is a risk of subsynchronous oscillation in the access system.

5. A risk assessment system for subsynchronous oscillation in a new energy grid-connected system, characterized in that, include: The complex frequency domain equation construction module is used to establish A for each new energy power station. i The complex frequency domain equations on the access point system side, where i = 1, 2, ..., m, and m is the total number of new energy power stations; The equivalent impedance calculation module is used to perform matrix transformations on the complex frequency domain equations of the system side to obtain the system side relative to the new energy power station A. i Equivalent admittance matrix of the access point To obtain the equivalent impedance in the complex frequency domain on the system side. The equivalent impedance in the complex frequency domain for: , This indicates that the system side is relative to the new energy power station A. i The nodal equivalent admittance matrix; The subsynchronous oscillation risk assessment module is used to assess the risk of the new energy power station A. i Does the access system have a risk of subsynchronous oscillation? If the complex frequency domain equivalent impedance... and the aforementioned new energy power station A i Complex frequency domain self-impedance of the access point If the amplitude curves of the two energy power stations intersect and the phase difference is greater than 180°, then the energy power station A... i The access system is susceptible to subsynchronous oscillation; among them, the new energy power station A i Complex frequency domain self-impedance of the access point Determined based on its complex frequency domain port equivalent admittance matrix model; The implementation of the complex frequency domain equation construction module specifically includes: Step S11: Establish the port equivalent admittance matrix model of each component of the new energy grid-connected system in the same coordinate system in the complex frequency domain; Step S12: Based on the complex frequency domain port equivalent admittance matrix model, calculate the new energy power station A using the branch addition method. i Admittance matrix on the system side of the access point; Step S13: For a specific new energy power station A i The access point, based on the access point current, voltage, and the new energy power station A... i The relationship between the admittance matrices on the access point system side is used to establish the relationship between the admittance matrices of the new energy power station A. i Complex frequency domain equations on the access point system side; In step S13, the current and voltage at the access point and the new energy power station A i The relationship between the admittance matrices on the access point system side is as follows: In the formula, I 1. U 1 represents the new energy power station A. i Current matrix and voltage matrix at the connection point; U 2 represents the node voltage matrix on the system side. This indicates that the node injection current on the system side is all 0. , , , These respectively represent the new energy power station A i The admittance matrix on the access point system side is based on the new energy power station A. i The four sub-blocks after dividing the access point and the remaining N-1 nodes are represented by the subscripts in square brackets, which indicate the size of the matrix. N represents the total number of nodes in the new energy grid-connected system.

6. An electronic device, characterized in that, include: A processor and a memory, wherein the memory stores a computer-executable program that, when executed by the processor, causes the processor to perform the evaluation method as described in any one of claims 1-4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the evaluation method as described in any one of claims 1-4.

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