Subsynchronous oscillation analysis method and system for direct-driven wind power multi-station grid-connected system

Abstract

The invention discloses a subsynchronous oscillation analysis method and system for a direct-driven wind power multi-station grid-connected system. The subsynchronous oscillation analysis method comprises the following steps: establishing a small signal model of each link of the direct-driven wind power multi-station grid-connected system; determining an expression of a generalized damping coefficient suitable for analyzing the subsynchronous oscillation mode; converting the small signal model of each link into transfer function description, constructing a first closed-loop transfer function model of the system based on the transfer function description, and performing aggregation blocking processing on the first closed-loop transfer function model to obtain a second closed-loop transfer function model; based on the second closed-loop transfer function model, separating interaction paths between subsystems into interaction paths between wind power plant stations and an alternating current system and between wind power plant stations, and performing quantitative analysis on damping characteristics of various dynamic interaction paths existing in the system based on an expression of a generalized damping coefficient; and determining a subsynchronous oscillation analysis result.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, and more particularly, to a method and system for analyzing sub-synchronous oscillation of a direct-drive wind power multi-station grid-connected system. BACKGROUND

[0002] New energy power generation represented by wind power has developed rapidly. However, the large-scale wind power access leads to frequent sub-synchronous oscillation (SSO) accidents, which seriously threatens the safe and stable operation of the power grid. It is of great practical significance to comprehensively and deeply analyze the SSO problem of the direct-drive wind power multi-station grid-connected system.

[0003] The existing mainstream SSO analysis method is difficult to be directly applied to the direct-drive wind power multi-station grid-connected system with multi-machine characteristics, and it is also difficult to reveal the dynamic process of system instability, which is not conducive to in-depth analysis of the SSO mechanism. In addition, there is also a DC capacitor link dominated SSO mode in the wind power station grid-connected system with multi-machine characteristics, which is more likely to be unstable under various dynamic interactions and weak AC grid strength conditions.

[0004] Therefore, there is a need for a novel method for analyzing sub-synchronous oscillation of a direct-drive wind power multi-station grid-connected system. SUMMARY

[0005] The present application proposes a method and system for analyzing sub-synchronous oscillation of a direct-drive wind power multi-station grid-connected system to solve the problem of how to analyze sub-synchronous oscillation of a direct-drive wind power multi-station grid-connected system.

[0006] In order to solve the above problems, according to one aspect of the present application, a method for analyzing sub-synchronous oscillation of a direct-drive wind power multi-station grid-connected system is provided, the method comprising:

[0007] establishing a small-signal model of each link of the direct-drive wind power multi-station grid-connected system;

[0008] determining an expression of a generalized damping coefficient suitable for analyzing a sub-synchronous oscillation mode;

[0009] converting the small-signal model of each link into a transfer function description, constructing a first closed-loop transfer function model of the system based on the transfer function description, and performing aggregated block processing on the first closed-loop transfer function model to obtain a second closed-loop transfer function model;

[0010] separating the interaction paths between subsystems into interaction paths between wind power stations and AC systems and between wind power stations based on the second closed-loop transfer function model, and quantitatively analyzing the damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient to determine a sub-synchronous oscillation analysis result.

[0011] Preferably, the small signal model of each link of the direct-drive wind power plant grid-connected system is established, comprising:

[0012]

[0013] Wherein, ΔX n , ΔU n and ΔY n are the state variable, input variable and output variable of link n respectively; A n , B n , C n and D n are the state matrix, input matrix, output matrix and pass-through matrix of link n respectively.

[0014] Preferably, the small signal model of each link is converted into a transfer function description, comprising:

[0015]

[0016] Wherein, I is an identity matrix; G n (s) is the transfer function of link n; ΔU n (s) and ΔY n (s) are the input variable and output variable of link n respectively; ΔY n (s) is the output variable of link n; s is a complex frequency domain variable introduced by Laplace transform.

[0017] Preferably, the first closed-loop transfer function model is aggregated and blocked to obtain a second closed-loop transfer function model, comprising:

[0018] A direct-drive wind power plant is selected as the target research object, the dominant oscillation link DC capacitor of the target direct-drive wind power plant is retained, the remaining links in the subsystem of the direct-drive wind power plant are aggregated and blocked, and the remaining wind power plants in the system are also aggregated;

[0019] Based on the aggregation and blocking processing result, the first closed-loop transfer function model is further derived to determine the second closed-loop transfer function model of the system; wherein the second closed-loop transfer function model can describe the oscillation transmission path and various dynamic interaction relationships of the system.

[0020] Preferably, based on the second closed-loop transfer function model, the interaction path between the subsystems is separated into the interaction path between the wind power plants and the AC system and the interaction path between the wind power plants, and the damping characteristics of various dynamic interaction paths existing in the system are quantitatively analyzed based on the expression of the generalized damping coefficient to determine the subsynchronous oscillation analysis result, comprising:

[0021] Solving a damping transfer function including two interaction paths based on the second closed-loop transfer function model, and then disconnecting the connection between the wind power plants except the target wind power plant and the AC system to obtain a damping transfer function of the interaction path between the wind power plant and the AC system, and subtracting the damping transfer function of the interaction path between the wind power plant and the AC system from the damping transfer function including the two interaction paths to obtain a damping transfer function of the interaction path between the wind power plants according to the superposition principle of linear systems;

[0022] Solving the damping transfer functions of the interaction paths in the system, and determining the expression of the damping coefficient of each interaction path based on the expression of the generalized damping coefficient;

[0023] Based on the expression of the damping coefficient of various dynamic interactions, drawing the frequency characteristic curves of the damping coefficients, and positioning the frequency band with negative damping coefficients for simulation analysis to quantitatively evaluate the damping characteristics of various interaction paths and determine the subsynchronous oscillation analysis result.

[0024] According to another aspect of the present application, a subsynchronous oscillation analysis system for a direct-drive wind power multi-plant grid-connected system is provided, and the system comprises:

[0025] A model establishing unit is configured to establish small-signal models of each link of the direct-drive wind power multi-plant grid-connected system.

[0026] An expression determining unit is configured to determine the expression of the generalized damping coefficient suitable for analyzing the subsynchronous oscillation mode.

[0027] A closed-loop transfer function model obtaining unit is configured to convert the small-signal models of each link into a transfer function description, construct a first closed-loop transfer function model of the system based on the transfer function description, and obtain a second closed-loop transfer function model by aggregating and blocking the first closed-loop transfer function model.

[0028] An analysis unit is configured to separate the interaction paths between the subsystems into the interaction paths between the wind power plants and the AC system and the interaction paths between the wind power plants based on the second closed-loop transfer function model, quantitatively analyze the damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient, and determine the subsynchronous oscillation analysis result.

[0029] Preferably, the model establishing unit establishes the small-signal models of each link of the direct-drive wind power multi-plant grid-connected system, including:

[0030]

[0031] wherein ΔX n , ΔU n , and ΔY nThese are the state variables, input variables, and output variables of stage n, respectively; A n B n C n and D n These are the state matrix, input matrix, output matrix, and through matrix of link n, respectively.

[0032] Preferably, the closed-loop transfer function model acquisition unit converts the small-signal models of each stage into transfer function descriptions, including:

[0033]

[0034] Where I is the identity matrix; G n (s) is the transfer function of link n; ΔU n (s) and ΔY n (s) represent the input and output variables ΔY of the link n, respectively. n (s) represents the output variable of element n; s represents the complex frequency domain variable introduced by the Laplace transform.

[0035] Preferably, the closed-loop transfer function model acquisition unit performs aggregation and block processing on the first closed-loop transfer function model to obtain the second closed-loop transfer function model, including:

[0036] A direct-drive wind farm is selected as the target research object. The DC capacitor of the dominant oscillation link of the target direct-drive wind farm is retained. The remaining links in the subsystem of the direct-drive wind farm are aggregated and segmented. The remaining wind farms in the system are also aggregated.

[0037] Based on the aggregation and block processing results, the first closed-loop transfer function model is further derived to determine the second closed-loop transfer function model of the system; wherein, the second closed-loop transfer function model can describe the oscillation propagation path and various dynamic interaction relationships of the system.

[0038] Preferably, the analysis unit, based on the second closed-loop transfer function model, separates the interaction paths between subsystems into interaction paths between the wind farm and the AC system, and between wind farms, and quantitatively analyzes the damping characteristics of various dynamic interaction paths in the system based on the expression of the generalized damping coefficient, determining the subsynchronous oscillation analysis results, including:

[0039] Solving a damping transfer function including two interaction paths based on the second closed-loop transfer function model, and then disconnecting the connection between the wind power plants except the target wind power plant and the AC system to obtain a damping transfer function of the interaction path between the wind power plants and the AC system, and subtracting the damping transfer function of the interaction path between the wind power plants and the AC system from the damping transfer function including the two interaction paths to obtain a damping transfer function of the interaction path between the wind power plants;

[0040] Solving the damping transfer functions of the interaction paths in the system, and determining the expression of the damping coefficient of each interaction path based on the expression of the generalized damping coefficient;

[0041] Based on the expression of the damping coefficient representing various dynamic interactions, the frequency characteristic curves of the damping coefficients are drawn, and the frequency band in which the damping coefficient is negative is located for simulation analysis, so as to quantitatively evaluate the damping characteristics of the various interaction paths and determine the subsynchronous oscillation analysis result.

[0042] Based on another aspect of the present application, the present application provides a computer readable storage medium, which stores a computer program, and the program is executed by a processor to realize the steps of any one of the subsynchronous oscillation analysis methods of the direct-drive wind power multi-plant grid-connected system.

[0043] Based on another aspect of the present application, the present application provides an electronic device, which comprises:

[0044] The above computer readable storage medium; and

[0045] One or more processors for executing the program in the computer readable storage medium.

[0046] The present application provides a subsynchronous oscillation analysis method and system of a direct-drive wind power multi-plant grid-connected system, which comprises: establishing a small-signal model of each link of the direct-drive wind power multi-plant grid-connected system; determining an expression of a generalized damping coefficient suitable for analyzing a subsynchronous oscillation mode; converting the small-signal model of each link into a transfer function description, constructing a first closed-loop transfer function model of the system based on the transfer function description, and performing aggregation and block processing on the first closed-loop transfer function model to obtain a second closed-loop transfer function model; separating the interaction paths between the subsystems into the interaction paths between the wind power plants and the AC system and the interaction paths between the wind power plants based on the second closed-loop transfer function model, and quantitatively analyzing the damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient to determine a subsynchronous oscillation analysis result. The present application considers the dynamic interaction between the wind power plants, can more comprehensively and deeply reveal the SSO mechanism and various dynamic interaction relationships, and efficiently performs the subsynchronous oscillation analysis of the direct-drive wind power multi-plant grid-connected system. BRIEF DESCRIPTION OF DRAWINGS

[0047] The exemplary embodiments of this application can be more completely understood in consideration of the following drawings, in which:

[0048] Figure 1 Flow chart of the method 100 for analyzing subsynchronous oscillation of a direct-drive wind power multi-station grid-connected system according to an embodiment of the application;

[0049] Figure 2 Overall flow chart according to an embodiment of the application;

[0050] Figure 3 Structure diagram of a direct-drive wind power multi-station grid-connected system according to an embodiment of the application;

[0051] Figure 4 Schematic diagram of a closed-loop transfer function model of the entire system according to an embodiment of the application;

[0052] Figure 5 Schematic diagram of a closed-loop transfer function model of the system after aggregation and block processing according to an embodiment of the application;

[0053] Figure 6 Schematic diagram of a closed-loop transfer function model of the system after interaction separation according to an embodiment of the application;

[0054] Figure 7 Frequency characteristic curve of the damping coefficient D1 according to an embodiment of the application;

[0055] Figure 8 Frequency characteristic curve of the damping coefficient D2 according to an embodiment of the application;

[0056] Figure 9 Frequency characteristic curve of the damping coefficient D3 according to an embodiment of the application;

[0057] Figure 10 Result diagram of time-domain simulation verification according to an embodiment of the application;

[0058] Figure 11 Structure schematic diagram of a direct-drive wind power multi-station grid-connected system subsynchronous oscillation analysis system 1100 according to an embodiment of the application. DETAILED DESCRIPTION

[0059] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0060] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0061] In view of the fact that existing studies rarely consider the dynamic interaction between power stations and that mainstream analysis methods are unable to reveal the oscillation transmission path and various interaction relationships in the system, this invention proposes a subsynchronous oscillation analysis method for direct-drive wind power multi-power station grid-connected systems based on the combination of multivariable frequency domain control theory and damping torque.

[0062] Figure 1 This is a flowchart of a subsynchronous oscillation analysis method 100 for a direct-drive wind power multi-site grid-connected system according to an embodiment of the present invention. Figure 1 As shown, the subsynchronous oscillation analysis method for direct-drive wind power multi-site grid-connected systems provided by this invention considers the dynamic interactions between wind farms, and can more comprehensively and deeply reveal the SSO mechanism and various dynamic interaction relationships, and efficiently perform subsynchronous oscillation analysis of direct-drive wind power multi-site grid-connected systems. The subsynchronous oscillation analysis method 100 for direct-drive wind power multi-site grid-connected systems provided by this invention starts from step 101, in which small-signal models of each component of the direct-drive wind power multi-site grid-connected system are established.

[0063] Preferably, the establishment of small-signal models for each component of the direct-drive wind power multi-site grid-connected system includes:

[0064]

[0065] Where, ΔX n , ΔU n and ΔY n These are the state variables, input variables, and output variables of stage n, respectively; A n B n C n and D n These are the state matrix, input matrix, output matrix, and through matrix of link n, respectively.

[0066] CombinationFigure 2 In the present application, based on the modular modeling method, the small signal model of each link of the direct-drive wind power multi-station grid-connected system is established, so as to convert the state space description of each link into the transfer function description.

[0067] Specifically, the modular modeling method is adopted to linearize each link in the direct-drive wind power multi-station grid-connected system at the initial operating point, thereby establishing the small signal model of each link in the direct-drive wind power multi-station grid-connected system, and the small signal model of link n can be expressed as:

[0068]

[0069] wherein ΔX n , ΔU n , and ΔY n are the state variable, the input variable, and the output variable of link n respectively; A n , B n , C n , and D n are the state matrix, the input matrix, the output matrix, and the through matrix of link n respectively.

[0070] In step 102, an expression of the generalized damping coefficient suitable for analyzing the subsynchronous oscillation mode is determined.

[0071] In combination with Figure 2 In the present application, based on the analogy idea, the traditional damping torque method is extended to the field of SSO problem analysis, thereby the generalized damping torque method suitable for analyzing the SSO mode is proposed. The extension of the damping torque from the low-frequency oscillation to the subsynchronous oscillation analysis field in the present application is based on a certain type of oscillation mode expansion. The present application takes the DC capacitor dominant SSO mode most prone to instability in the direct-drive wind power multi-station grid-connected system as an example for derivation, and the specific steps include:

[0072] Step 2-1: The basic principle of the traditional damping torque method is described, which is commonly used to study the low-frequency oscillation problem, and its basis is the decomposition of the torque on the rotor motion equation of the generator. The dynamic equation of the generator rotor motion can be expressed as:

[0073]

[0074] wherein Δδ and Δω are the incremental changes of the rotor angular displacement and angular velocity respectively; ω0 is the synchronous angular velocity; M is the inertia coefficient; D is the damping coefficient; K1 is the synchronous coefficient; K2-K6 are constants related to the system characteristics.

[0075] The electromagnetic torque ΔT provided by the control device to the oscillation loop can be decomposed into the damping torque T d Δω and the synchronous torque T s Δδ. At this time, the dynamic equation of the generator rotor can be expressed as:

[0076] Ms 2 Δδ+(D+T d )sΔδ+(ω0K1+ω0T s )Δδ=0 (3)

[0077] From equation (3), it can be seen that the damping torque term affects the damping of the low-frequency oscillation mode. The above analysis constitutes the core theoretical framework of the damping torque method. When only considering the rotor dynamic characteristics, the rotor dynamic equation is:

[0078] Ms 2 Δδ+DsΔδ+ω0K1Δδ=0 (4)

[0079] Solving equation (4) gives:

[0080]

[0081] where a and b are constants; ω NOF is the natural oscillation frequency of the power angle.

[0082] From equation (5), it can be seen that the damping of the low-frequency oscillation mode in the single-machine infinite system is related to both D and M, and the ratio of the two determines whether the active power output of the generator will experience low-frequency oscillation.

[0083] Step 2-2: Derive a second-order equation similar in structure to the rotor dynamic equation, define G x (s) as the transfer function of Δx dc to the grid-side converter input power ΔP e , and Δx dc = Δu dc / s, then:

[0084] ΔP e = G x (s)Δx dc (6)

[0085] When the system is stable, the DC capacitor dynamic equation can be expressed as:

[0086]

[0087] where u dc0 is the initial value of the DC capacitor voltage.

[0088] When the dominant oscillation mode of the DC capacitor is weakly damped, it is considered that s≈jω, ω is the system oscillation frequency, then:

[0089]

[0090] Substituting equation (8) into equation (7) gives:

[0091]

[0092] Step 2-3: Similar to the second-order dynamic equation (4) of the generator rotor motion and the second-order dynamic equation (9) of the DC capacitor, define Im[G x (s)] / ω as the generalized damping coefficient, and obtain the characteristic root expression of (9) by solving (9):

[0093]

[0094] As can be seen from the real part of the characteristic root in (10), D can be used as an evaluation index of the dominant oscillation mode damping of the DC capacitor. When D>0, the system shows positive damping characteristics, and the system is stable; when D<0, the system shows negative damping characteristics, and the oscillation mode has the risk of instability.

[0095] In step 103, the small-signal model of each link is converted into a transfer function description, a first closed-loop transfer function model of the system is constructed based on the transfer function description, and the first closed-loop transfer function model is aggregated and processed in blocks to obtain a second closed-loop transfer function model.

[0096] Preferably, the conversion of the small-signal model of each link into a transfer function description includes:

[0097]

[0098] where I is an identity matrix; G n (s) is the transfer function of link n; ΔU n (s) and ΔY n (s) are the input variable and output variable of link n, respectively; ΔY n (s) is the output variable of link n; and s is a complex frequency domain variable introduced by Laplace transform.

[0099] Preferably, the aggregation and block processing of the first closed-loop transfer function model to obtain the second closed-loop transfer function model includes:

[0100] A direct-drive wind power station is selected as a target research object, the dominant oscillation link DC capacitor of the target direct-drive wind power station is retained, the remaining links in the direct-drive wind power station subsystem are aggregated and processed in blocks, and the remaining wind power stations in the system are also aggregated.

[0101] Based on the aggregation and block processing result, the first closed-loop transfer function model is further derived to determine the second closed-loop transfer function model of the system; wherein the second closed-loop transfer function model can describe the oscillation transmission path and various dynamic interaction relationships of the system.

[0102] In combination with Figure 2As shown, in the present application, a system closed-loop transfer function model is constructed based on the multivariable frequency domain control theory, and then further derivation is made through aggregation and block processing, so as to depict the oscillation transmission path and various dynamic interaction relationships of the system, and thus reveal the SSO mechanism of the system. The specific steps include:

[0103] Step 3-1: Based on the multivariable frequency domain control theory, the state space description of each link of the system constructed in step 1 is converted into a first transfer function description, and the specific conversion process is realized through equation (11), so as to construct a first closed-loop transfer function model of the entire system:

[0104]

[0105] Wherein, I is a unit matrix; G n (s) is the transfer function of link n.

[0106] Step 3-2: Select a direct-drive wind power station as the target research object, retain the dominant oscillation link DC capacitor of the target direct-drive wind power station, and aggregate and block process the remaining links in the subsystem of the wind power station. The remaining wind power stations are all aggregated.

[0107] Step 3-3: According to the aggregation and block processing result in step 3-2, the closed-loop transfer function model of the entire system constructed in step 3-1 is further derived to obtain a second closed-loop transfer function model. At this time, the second closed-loop transfer function model of the system can clearly reveal the oscillation transmission path and various dynamic interaction relationships of the system, so as to describe the SSO mechanism of the direct-drive wind power multi-station grid-connected system.

[0108] In step 104, the interaction paths between subsystems are separated into the interaction paths between wind power stations and the AC system and between wind power stations based on the second closed-loop transfer function model, and the damping characteristics of various dynamic interaction paths existing in the system are quantitatively analyzed based on the expression of the generalized damping coefficient, so as to determine the subsynchronous oscillation analysis result.

[0109] Preferably, wherein the interaction paths between subsystems are separated into the interaction paths between wind power stations and the AC system and between wind power stations based on the second closed-loop transfer function model, and the damping characteristics of various dynamic interaction paths existing in the system are quantitatively analyzed based on the expression of the generalized damping coefficient, so as to determine the subsynchronous oscillation analysis result, including:

[0110] Based on the second closed-loop transfer function model, a damping transfer function including two interaction paths is solved, and the connection between the wind power stations other than the target wind power station and the AC system is disconnected, so as to obtain the damping transfer function of the interaction path between the wind power station and the AC system, and according to the superposition principle of the linear system, the damping transfer function of the interaction path between the wind power stations is obtained by subtracting the damping transfer function of the interaction path between the wind power station and the AC system from the damping transfer function including the two interaction paths.

[0111] The damping transfer functions of various interaction paths in the system are solved, and the expressions of the damping coefficients of various interaction paths are determined based on the expression of the generalized damping coefficient.

[0112] Based on the expressions of the damping coefficients representing various dynamic interactions, the frequency characteristic curves of the damping coefficients are drawn, and the frequency bands in which the damping coefficients are negative are located for simulation analysis, so as to quantitatively evaluate the damping characteristics of various interaction paths and determine the subsynchronous oscillation analysis result.

[0113] In combination with Figure 2 As shown in the drawings, in the present application, according to the superposition principle, the interaction paths between the subsystems are separated into the interaction paths between the wind power station and the AC system and the interaction paths between the wind power stations, and then the damping characteristics of various dynamic interaction paths existing in the system are quantitatively analyzed based on the generalized damping torque method, and the specific steps include:

[0114] Step 4-1: Based on the second closed-loop transfer function model of the system obtained in step 3-3, a damping transfer function including two interaction paths is solved, and the connection between the wind power stations other than the target wind power station and the AC system is disconnected, so as to obtain the damping transfer function of the interaction path between the wind power station and the AC system, and according to the superposition principle of the linear system, the damping transfer function of the interaction path between the wind power stations is obtained by subtracting the damping transfer function of the interaction path between the wind power station and the AC system from the damping transfer function including the two interaction paths.

[0115] Step 4-2: The damping transfer functions of various interaction paths in the system are obtained, and according to the definition of the generalized damping coefficient, the system damping coefficient G x (s) is calculated, which is directly related to the transfer function of Δu dc to ΔP e , so G x (s) = sG Dj (s), j = 1, 2, 3, respectively representing the interaction between the internal links of the wind power station, the interaction between the wind power station and the AC system, and the interaction between the wind power stations. The total damping coefficient D = D1 + D2 + D3 represents the system damping level.

[0116] Step 4-3: Based on the expression of the damping coefficient representing various dynamic interactions, the frequency characteristic curves of each damping coefficient are drawn, the frequency band with negative damping coefficient is located, and simulation analysis is carried out, so as to quantitatively evaluate the damping characteristics of various interaction paths.

[0117] The application can also establish a time-domain simulation model corresponding to the analyzed system to verify the effectiveness of the obtained conclusion.

[0118] The following specific examples illustrate the embodiments of the application

[0119] The application takes the direct-drive wind power multi-station grid-connected system as an example for further detailed description of the application, and the process is realized based on the process shown in Figure 3 Figure 2 The specific steps are as follows:

[0120] Step 1: Linearize each link in the test system, including DC capacitor, grid-side converter control link, LC filter, phase-locked loop, transmission line and AC grid-connected line.

[0121] Step 2: For the DC capacitor dominant SSO mode prone to instability in the direct-drive wind power multi-station grid-connected system, the dynamic equation of the DC capacitor is derived, so that it has a similar form of a second-order equation with the rotor in structure, and the derivation process is shown in formula (2)-(10). Finally, the expression of the generalized damping torque coefficient is obtained, which is Im[G x (s)] / ω for the test system. The stability criterion is D>0, the system shows positive damping characteristics, and the system is stable; D<0, the system shows negative damping characteristics, and the oscillation mode has the risk of instability.

[0122] Step 3: Based on the input-output relationship of the small-signal model of each link obtained in step 1, the closed-loop transfer function model of the entire system is constructed as shown in Figure 4 Taking wind power station 1 as the target research object, retaining its dominant oscillation link DC capacitor, and aggregating the remaining links into G(s), aggregating each link in wind power station 2 into G PMSG2 (s), then:

[0123]

[0124] G(s) and G AC (s) can be blocked according to formula (13) and (14).

[0125]

[0126] According to formula (12)-(14), further transformation is made on Figure 5 , and the result is shown in Figure 4 ​The system oscillation transmission paths and various dynamic interactions are clearly revealed by the figure. The Figure 5 It can be seen that there are two oscillation transmission paths in the test system, i.e. path 1 and path 2, and the transmission direction is shown by the arrows in the figure. Path 1 is only related to the subsystem of wind farm 1, and thus reflects the internal characteristics of the direct-drive wind farm; path 2 is related to wind farm station 1, wind farm station 2 and the AC system, and thus reflects the interaction characteristics among the three; in addition, path 2 internally includes two paths (paths a and b), which present an "∞" shape and represent the interaction characteristics among the three subsystems.

[0127] Therefore, the SSO mechanism of the direct-drive wind farm multi-station grid-connected system can be explained as follows: the interaction among wind farm station 1, wind farm station 2 and the AC system causes the circulating oscillation component Δu s at the common grid-connected point, which is fed back to wind farm station 1 along path 2, causes the grid-side electromagnetic power to oscillate under the action of various links in wind farm station 1, and the oscillation component is superimposed on the electromagnetic power oscillation component generated by path 1, which affects the output characteristics of the DC capacitor and further causes the system to have an SSO problem. s

[0128] Step 4: According to the superposition principle of linear systems, path 2 can be considered to include the interaction path between wind farms and the interaction path between wind farms and the AC system. In order to quantitatively analyze the interactions represented by the two paths, the two paths need to be separated, and the specific process is as follows:

[0129] Substituting equation (14) into equation (12) gives:

[0130]

[0131] It can be seen from equation (13) that the relationship among Δi l1 , Δu dc1 and Δu s is:

[0132] Δi l1 = G 21 (s)Δu dc1 + G 22 (s)Δu s (16)

[0133] Substituting equation (16) into equation (15) gives:

[0134] Δi l1 = G 21 (s)Δu dc1 + G 22 (s)Δu s (17)

[0135] In the equation: ​

[0136]

[0137] The transfer function from Δu dc1 to Δu s is G N (s), substituting formula (16) and (17) into formula (14) can obtain the expression of G N (s) as follows:

[0138]

[0139] G N (s) contains the interaction between the wind farm and the AC system and the interaction between the wind farms, in order to separate the transfer function representing the characteristics of the interaction between the wind farm and the AC system, define G N1 (s), let Δi l2 = 0, substituting formula (16) into formula (14) obtains:

[0140]

[0141] The transfer function G N2 (s) representing the interaction between the wind farms is G N (s)-G N1 (s), then the oscillation transmission path is shown in Figure 5 .

[0142] As can be seen from Figure 6 , there are three oscillation transmission paths in the system, and the corresponding damping transfer functions will also have three, the damping transfer functions representing the interaction between each link in the wind farm, the interaction between the wind farm and the AC system and the interaction between the wind farms are respectively denoted as G D1 (s), G D2 (s), G D3 (s), then:

[0143]

[0144] As can be seen from the definition of the generalized damping coefficient, the system damping coefficient is calculated by G x (s), which is directly related to the transfer function from Δu dc1 to ΔP e1 , then G x (s) = sG Dj (s), j = 1, 2, 3. The total damping coefficient D = D1+D2+D3 represents the damping level of the system.

[0145] For the test system, the oscillation frequency of the DC capacitor dominant SSO mode is 14.8 Hz. Based on the expression of damping coefficient D1, D1 in the frequency band around ω1 is calculated and the interaction among the internal components of the wind farm is analyzed, and the results are shown in Figure 7 . It can be seen that the oscillation frequency of the oscillation mode corresponds to a damping coefficient of 0.42, indicating that the interaction path among the internal components of the wind farm provides positive damping, which is beneficial to system stability. If only this interaction is considered, the system will not oscillate at the resonance point, that is, the direct-drive wind farm will not cause SSO when connected to the infinite grid.

[0146] Based on the expression of damping coefficient D2, D2 in the frequency band around the oscillation frequency is calculated and the interaction between the wind farm and the AC system is analyzed, and the results are shown in Figure 8 . It can be seen that the oscillation frequency of the oscillation mode corresponds to a damping coefficient of -0.06, indicating that the interaction path between the wind farm and the AC system provides negative damping, which is not conducive to system stability. If only this interaction is considered, the system will oscillate at the resonance point, that is, the direct-drive wind farm will cause this SSO mode when connected to the AC grid.

[0147] Based on the expression of damping coefficient D3, D3 in the frequency band around the oscillation frequency is calculated and the interaction between the wind farms is analyzed, and the results are shown in Figure 9 . It can be seen that the oscillation frequency of the oscillation mode corresponds to a damping coefficient of -1.07, which is smaller than the damping coefficient of the interaction path between the wind farm and the AC system at the resonance point, indicating that the interaction path between the wind farms provides greater negative damping, which is more detrimental to system stability. If only this interaction is considered, the system will oscillate more severely at the resonance point, that is, the direct-drive wind farm will cause this SSO mode when multiple wind farms are connected to the infinite grid, and the oscillation will be more severe.

[0148] The time domain simulation model corresponding to the test system is built, and three scenarios are set (scenario 1: wind farm 1 is connected to the infinite grid; scenario 2: wind farm 1 is connected to the AC grid; scenario 3: wind farm system, i.e. the time domain simulation model corresponding to the test system), which respectively correspond to the interaction among the internal components of the direct-drive wind farm, the interaction between the direct-drive wind farm and the AC system, and the interaction between the direct-drive wind farms. The parameters are set the same as in the theoretical analysis process, and the SSO mode is excited at 3s. The DC capacitor voltage u dc1 of wind farm 1 is shown in Figure 10 . It can be seen that the u dc1 waveform does not oscillate in scenario 1, the u dc1 waveform oscillates with a small amplitude in scenario 2, and the u dc1The waveform oscillation has a large amplitude. This is because the interaction between the internal links of the wind farm station provides positive damping, the interaction between the wind farm station and the AC system and the interaction between the wind farm stations all provide negative damping, and the latter provides greater negative damping, which is consistent with the size of the damping coefficient of the corresponding interaction path in the theoretical analysis process, verifying the effectiveness of the theoretical analysis.

[0149] In summary, the direct-drive wind power multi-farm grid-connected system subsynchronous oscillation analysis method based on the multivariable frequency domain control theory combined with damping torque according to the present application can comprehensively and deeply analyze the SSO problem.

[0150] Figure 11 A structure schematic diagram of the direct-drive wind power multi-farm grid-connected system subsynchronous oscillation analysis system 1100 according to the present application embodiment is shown in the figure. Figure 11 As shown in the figure, the direct-drive wind power multi-farm grid-connected system subsynchronous oscillation analysis system 1100 according to the present application embodiment includes a model establishing unit 1101, an expression determining unit 1102, a closed-loop transfer function model obtaining unit 1103 and an analysis unit 1104.

[0151] Preferably, the model establishing unit 1101 is configured to establish a small-signal model of each link of the direct-drive wind power multi-farm grid-connected system.

[0152] Preferably, the model establishing unit 1101 is configured to establish a small-signal model of each link of the direct-drive wind power multi-farm grid-connected system, including:

[0153]

[0154] wherein ΔX n , ΔU n and ΔY n are respectively the state variable, the input variable and the output variable of the link n; A n , B n , C n and D n are respectively the state matrix, the input matrix, the output matrix and the pass-through matrix of the link n.

[0155] Preferably, the expression determining unit 1102 is configured to determine an expression of the generalized damping coefficient suitable for analyzing the subsynchronous oscillation mode.

[0156] Preferably, the closed-loop transfer function model obtaining unit 1103 is configured to convert the small-signal model of each link into a transfer function description, construct a first closed-loop transfer function model of the system based on the transfer function description, and perform aggregated block processing on the first closed-loop transfer function model to obtain a second closed-loop transfer function model.

[0157] Preferably, the closed-loop transfer function model acquisition unit 1103 converts the small-signal model of each link into a transfer function description, including:

[0158]

[0159] wherein I is an identity matrix; G n (s) is the transfer function of link n; ΔU n (s) and ΔY n (s) are the input variable and output variable ΔY n (s) of link n, respectively; s is a complex frequency domain variable introduced by Laplace transform.

[0160] Preferably, the closed-loop transfer function model acquisition unit 1103 aggregates and blocks the first closed-loop transfer function model to obtain a second closed-loop transfer function model, including:

[0161] A direct-drive wind farm station is selected as a target research object, the dominant oscillation link DC capacitor of the target direct-drive wind farm station is retained, the remaining links in the direct-drive wind farm station subsystem are aggregated and blocked, and the remaining wind farm stations in the system are aggregated.

[0162] Based on the aggregation and blocking processing result, the first closed-loop transfer function model is further derived to determine a second closed-loop transfer function model of the system; wherein the second closed-loop transfer function model can describe the oscillation transmission path and various dynamic interaction relationships of the system.

[0163] Preferably, the analysis unit 1104 separates the interaction path between subsystems into the interaction path between wind farm stations and the alternating current system and the interaction path between wind farm stations based on the second closed-loop transfer function model, and quantitatively analyzes the damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient to determine the subsynchronous oscillation analysis result.

[0164] Preferably, the analysis unit 1104 separates the interaction path between subsystems into the interaction path between wind farm stations and the alternating current system and the interaction path between wind farm stations based on the second closed-loop transfer function model, and quantitatively analyzes the damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient to determine the subsynchronous oscillation analysis result, including:

[0165] Solving the damping transfer functions of the two interaction paths based on the second closed-loop transfer function model, and then disconnecting the connection between the wind power plants except the target wind power plant and the AC system to obtain the damping transfer function of the interaction path between the wind power plants and the AC system, and subtracting the damping transfer function of the interaction path between the wind power plants and the AC system from the damping transfer functions of the two interaction paths to obtain the damping transfer function of the interaction path between the wind power plants;

[0166] Solving the damping transfer functions of the interaction paths in the system, and determining the expression of the damping coefficient of each interaction path based on the expression of the generalized damping coefficient;

[0167] Based on the expression of the damping coefficient of various dynamic interactions, the frequency characteristic curves of the damping coefficients are drawn, and the frequency band with negative damping coefficients is located for simulation analysis, so as to quantitatively evaluate the damping characteristics of the interaction paths and determine the subsynchronous oscillation analysis result.

[0168] The subsynchronous oscillation analysis system 1100 of the direct-drive wind power multi-plant grid-connected system of the embodiment of the present application corresponds to the subsynchronous oscillation analysis method 100 of the direct-drive wind power multi-plant grid-connected system of another embodiment of the present application, and will not be described here.

[0169] Based on another aspect of the present application, the present application provides a computer readable storage medium, which stores a computer program, and the program is executed by a processor to realize the steps of any one of the subsynchronous oscillation analysis methods of the direct-drive wind power multi-plant grid-connected system.

[0170] Based on another aspect of the present application, the present application provides an electronic device, comprising:

[0171] The computer readable storage medium described above; and

[0172] One or more processors for executing the program in the computer readable storage medium.

[0173] The present application has been described by referring to a small number of embodiments. However, it is well known to those skilled in the art that other embodiments, etc. other than the above disclosed embodiments of the present application fall within the scope of the present application.

[0174] Generally, all the terms used in the present application are interpreted according to their usual meanings in the technical field, unless otherwise explicitly defined therein. All references to "a / the / that [device, component, etc.]" are interpreted as at least one instance of the device, component, etc., unless otherwise explicitly stated. The steps of any method disclosed herein do not necessarily have to be run in the exact order disclosed, unless explicitly stated.

[0175] Those skilled in the art will appreciate that embodiments of the application can be devised for a method, a system, or a computer program product. Accordingly, the present application can be embodied in the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application can take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) embodying computer readable program code.

[0176] The present application is described in reference to the flowchart illustrations and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart illustrations and / or block diagrams. Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams. Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams.

[0177] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the functions specified in the flowchart illustrations and / or block diagrams. Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams. Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams.

[0178] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart illustrations and / or block diagrams. Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams. Figure 1 Figure 1 one or more functions specified in the flowchart illustrations and / or block diagrams.

[0179] Finally, it should be noted that the above-mentioned embodiments are merely intended for describing and illustrating, not limiting the technical solutions of the present application. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, and any modifications or equivalent replacements without departing from the spirit and scope of the present application should be covered within the protection scope of the present application.

Claims

1. A method for analyzing subsynchronous oscillation of a direct-drive wind power multi-terminal station grid-connected system, characterized in that, The method comprises: establishing small signal models of each link of a direct-drive wind power multi-station grid-connected system; determining an expression of a generalized damping coefficient suitable for analyzing a subsynchronous oscillation mode; converting the small signal models of each link into transfer function descriptions, constructing a first closed-loop transfer function model of the system based on the transfer function descriptions, and performing aggregated block processing on the first closed-loop transfer function model to obtain a second closed-loop transfer function model; based on the second closed-loop transfer function model, separating interaction paths between subsystems into interaction paths between wind power stations and an alternating current system and interaction paths between wind power stations, and quantitatively analyzing damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient to determine a subsynchronous oscillation analysis result.

2. The method of claim 1, wherein, The method comprises: where ΔX n , ΔU n and ΔY n are the state variable, input variable and output variable of the link n, respectively; A n , B n , C n and D n are the state matrix, input matrix, output matrix and pass-through matrix of the link n, respectively.

3. The method of claim 1, wherein, The method comprises: where I is an identity matrix; G n (s) is a transfer function of the link n; ΔU n (s) and ΔY n (s) are an input variable and an output variable of the link n, respectively; ΔY n (s) is an output variable of the link n; s is a complex frequency domain variable introduced by Laplace transform.

4. The method of claim 1, wherein, The method comprises: The method comprises: The method comprises:

5. The method of claim 1, wherein, The method comprises: The system comprises: a model establishing unit configured to establish small signal models of each link of a direct-drive wind power multi-station grid-connected system; an expression determining unit configured to determine an expression of a generalized damping coefficient suitable for analyzing a subsynchronous oscillation mode; 6. A direct-drive wind power multi-station grid-connected system subsynchronous oscillation analysis system, characterized in that, an expression determining unit configured to determine an expression of a generalized damping coefficient suitable for analyzing a subsynchronous oscillation mode; ​ ​ The closed-loop transfer function model obtaining unit is configured to convert the small-signal models of the links into transfer function descriptions, construct a first closed-loop transfer function model of the system based on the transfer function descriptions, and aggregate and block the first closed-loop transfer function model to obtain a second closed-loop transfer function model. The analysis unit is configured to separate the interaction paths between the subsystems into interaction paths between the wind power stations and the AC system and interaction paths between the wind power stations based on the second closed-loop transfer function model, quantitatively analyze the damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient, and determine the subsynchronous oscillation analysis result.

7. The system of claim 6, wherein, The model establishing unit establishes small-signal models of links of a direct-drive wind power multi-station grid-connected system, including: where ΔX n , ΔU n and ΔY n are the state variable, input variable and output variable of the link n, respectively; A n , B n , C n and D n are the state matrix, input matrix, output matrix and pass-through matrix of the link n, respectively.

8. The system of claim 6, wherein, The closed-loop transfer function model obtaining unit converts the small-signal models of the links into transfer function descriptions, including: where I is an identity matrix; G n (s) is the transfer function of the link n; ΔU n (s) and ΔY n (s) are the input variable and the output variable ΔY n (s) of the link n, respectively; s is a complex frequency domain variable introduced by Laplace transform.

9. The system of claim 6, wherein, The closed-loop transfer function model obtaining unit aggregates and blocks the first closed-loop transfer function model to obtain a second closed-loop transfer function model, including: One direct-drive wind power station is selected as a target research object, the dominant oscillation link DC capacitor of the target direct-drive wind power station is retained, the remaining links in the subsystem of the direct-drive wind power station are aggregated and blocked, and the remaining wind power stations in the system are all aggregated; The first closed-loop transfer function model is further derived based on the aggregation and blocking result to determine a second closed-loop transfer function model of the system; the second closed-loop transfer function model can describe the oscillation transmission paths and various dynamic interaction relationships of the system.

10. The system of claim 6, wherein, The analysis unit separates the interaction paths between the subsystems into interaction paths between the wind power stations and the AC system and interaction paths between the wind power stations based on the second closed-loop transfer function model, quantitatively analyzes the damping characteristics of various dynamic interaction paths existing in the system based on the expression of the generalized damping coefficient, and determines the subsynchronous oscillation analysis result, including: The damping transfer functions of the two kinds of interaction paths are solved based on the second closed-loop transfer function model, the connection between the wind power stations other than the target wind power station and the AC system is disconnected, the damping transfer function of the interaction path between the wind power stations and the AC system is obtained, and the damping transfer function of the interaction path between the wind power stations is obtained by subtracting the damping transfer function of the interaction path between the wind power stations and the AC system from the damping transfer function of the two kinds of interaction paths according to the superposition principle of linear systems; The damping transfer functions of the interaction paths in the system are solved, and the expressions of the damping coefficients of the interaction paths are determined based on the expression of the generalized damping coefficient; Based on the expressions of the damping coefficients representing various dynamic interactions, frequency characteristic curves of the damping coefficients are drawn, and a frequency band in which the damping coefficients are negative is located for simulation analysis, so as to quantitatively evaluate the damping characteristics of the interaction paths and determine the subsynchronous oscillation analysis result.

11. A computer readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the steps of the method in any one of claims 1-5.

12. An electronic device, comprising: including: The computer readable storage medium in claim 11; and one or more processors to execute a program in the computer readable storage medium.

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