A method and system for identifying small disturbance stability of wind power grid-connected system

Abstract

The present invention belongs to the field of wind power grid connection, and provides a method and system for identifying the small disturbance stability of a wind power grid connection system. The method includes obtaining the real-time operating state of the wind power grid connection system, constructing a dynamic model of a wind turbine generator set; calculating the equivalent voltage and equivalent impedance of the Thevenin equivalent model based on the real-time operating state of the wind power grid connection system and the Thevenin equivalent model; associating the Thevenin equivalent model with the dynamic model of the wind turbine generator set, obtaining the balance point of the wind power grid connection system as an initial value, and forming a state equation matrix; based on the eigenvalue of the state equation matrix, identifying the small disturbance stability of the wind power grid connection system, so as to determine whether to generate a wind power grid connection system control instruction to stabilize the output of the wind power grid connection system.

Description

Technical Field

[0001] The present invention belongs to the field of wind power grid connection, and in particular relates to a small disturbance stability identification method and system for a wind power grid connection system. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] At present, with the widespread access of renewable energy such as wind power to the power grid and its increasing year by year, the structure and operation mode of the power system have changed, and the small disturbances encountered have also increased. Small disturbances may cause the system to continue to oscillate or even cause the system to collapse, and the volatility and uncertainty of wind power have a great impact on the small disturbance stability of the power grid. Among them, small disturbances refer to the equations that describe the system response in the analysis can be linearized.

[0004] Traditional small disturbance stability analysis often uses precise system modeling for small disturbance calculations. However, wind farms are connected to the grid through power electronic equipment, and the control links are complex. The small disturbance model has a large number of orders, which may cause the "curse of dimensionality" problem of the state matrix when facing large-scale wind power grid connection. At this time, in order to study the small disturbance problem of a wind farm or a wind turbine in the system, since there may be other wind farms in the external system, it is necessary to perform equivalence on the external dynamic system of wind power to solve the problem of difficult modeling and analysis of wind power grid-connected systems.

[0005] Relevant scholars have conducted evaluations on the small disturbance analysis of wind power grid-connected equivalent systems. The prior art proposes to treat the external system as an infinite system, accurately model the inside of the wind turbine, ignore the impact of the external system, and directly perform small disturbance analysis on the dynamic process inside the wind turbine. The prior art also proposes to treat the wind farm contained in the external network as a load with a negative active power at the boundary bus, ignore the dynamic characteristics of the wind farm, and reduce the scale of the system. The prior art method for using wind turbine group equivalence divides the wind farm into several wind turbine groups with similar dynamic characteristics according to the similarity of the dynamic characteristics of each wind turbine in the wind farm, such as input wind speed, output power, terminal voltage, rotor speed, etc., and then performs single-machine equivalence on the wind turbine group. The prior art practical method for wind farm model parameter aggregation based on weighted method, which includes the synchronization equivalence of large-scale wind farm power grids, completes the synchronization equivalence of wind farm concentrated areas from four aspects: synchronization group identification, synchronization bus aggregation, synchronization group parameter aggregation, and network simplification. The existing method of dynamic equivalent modeling of wind farms uses a time series clustering method to group wind turbines, and aggregates each group into a wind turbine equivalent sub-model. Based on the sensitivity and correlation analysis method, the key parameters to be identified in the wind turbine body parameters and related control module parameters in the equivalent model are selected. Based on the multi-objective optimization algorithm and hybrid dynamic simulation technology, the key parameters of each wind turbine equivalent sub-model are step-by-step decoupled and identified under the conditions of wind speed fluctuations and external system failures. The existing method of analyzing the small disturbance stability of the power system containing wind farms implements the contraction processing of the system node admittance matrix based on the wind farm equivalent admittance model, converts the output power characteristics of the wind farm into the influence on the electromagnetic power of each synchronous machine, and then integrates the influence of the wind farm into the system state equation, and then implements the quantitative analysis of the influence of wind farm access on the system small disturbance stability based on the characteristic root analysis method. This method does not need to list the state equation of the doubly fed wind turbine, which reduces the computational complexity to a certain extent.

[0006] The above research has been conducted on the equivalence of systems containing wind power. However, the inventors have found that in the existing technology, when analyzing the small disturbance problem of a wind farm in the system, the external system is equivalent to a single-machine infinite system, ignoring the impact of the external system on wind power. The dynamic process of the system is still complicated after only the wind turbine group in the external system is equivalent, which makes it impossible to accurately determine the stability of the wind power grid-connected system under small disturbances, thereby affecting the stable operation of the wind power grid-connected system. Summary of the invention

[0007] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a small disturbance stability identification method and system for a wind power grid-connected system, which can accurately determine the small disturbance stability of the wind power grid-connected system and improve the stable operation of the wind power grid-connected system.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A first aspect of the present invention provides a method for identifying small disturbance stability of a wind power grid-connected system, comprising:

[0010] Obtain the real-time operating status of the wind power grid-connected system and build a dynamic model of the wind turbine;

[0011] Based on the real-time operating status of the wind power grid-connected system and the Thevenin equivalent model, the equivalent voltage and equivalent impedance of the Thevenin equivalent model are calculated;

[0012] The Thevenin equivalent model is associated with the dynamic model of the wind turbine generator system to obtain the equilibrium point of the wind power grid-connected system as the initial value and form a state equation matrix;

[0013] Based on the eigenvalues ​​of the state equation matrix, the small disturbance stability of the wind power grid-connected system is identified to determine whether to generate a wind power grid-connected system control instruction to stabilize the output of the wind power grid-connected system.

[0014] A second aspect of the present invention provides a small disturbance stability identification system for a wind power grid-connected system, comprising:

[0015] A wind turbine dynamic model building module, which is used to obtain the real-time operating status of the wind power grid-connected system and build a wind turbine dynamic model;

[0016] An equivalent voltage and equivalent impedance calculation module, which is used to calculate the equivalent voltage and equivalent impedance of the Thevenin equivalent model based on the real-time operating status of the wind power grid-connected system and the Thevenin equivalent model;

[0017] A state equation matrix forming module, which is used to associate the Thevenin equivalent model with the wind turbine dynamic model, obtain the equilibrium point of the wind power grid-connected system as an initial value, and form a state equation matrix;

[0018] The system small disturbance stability identification module is used to identify the small disturbance stability of the wind power grid-connected system based on the eigenvalue of the state equation matrix, so as to determine whether to generate a wind power grid-connected system control instruction to stabilize the output of the wind power grid-connected system.

[0019] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the method for identifying small disturbance stability of a wind power grid-connected system as described above.

[0020] A fourth aspect of the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps in the method for identifying small disturbance stability of a wind power grid-connected system as described above are implemented.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention constructs a dynamic model of the wind turbine generator set based on the real-time operating status of the wind power grid-connected system, and then performs real-time Thevenin equivalent on the system outside the wind farm, combines the dynamic model of the wind turbine generator set with the Thevenin equivalent system to model, obtains the equilibrium point of the wind power grid-connected system as an initial value, forms a state equation matrix, solves the eigenvalues ​​of the state matrix, and can analyze the degree to which the system state variables participate in the system oscillation through participating factors, thereby providing a theoretical basis for the small disturbance analysis of the wind power grid-connected system, and improving the accuracy of determining the small disturbance stability of the wind power grid-connected system and the stability of the operation of the wind power grid-connected system.

[0023] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 is a coupled multi-port network according to an embodiment of the present invention;

[0026] Figure 2 is the Thevenin equivalent model of an embodiment of the present invention;

[0027] Figure 3 This is a flow chart of a method for identifying small disturbance stability of a wind power grid-connected system according to an embodiment of the present invention;

[0028] Figure 4 is a flow chart of obtaining eigenvalues ​​of a state equation matrix according to an embodiment of the present invention;

[0029] Figure 5 It is a schematic diagram of the structure of a small disturbance stability identification system for a wind power grid-connected system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0031] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0033] Embodiment 1

[0034] according to Figure 1 According to circuit theory, the system node voltage equation can be expressed as

[0035]

[0036] L, T, and G represent load nodes, connection nodes, and generator nodes, respectively. In the admittance matrix, Represents the admittance matrix between load nodes, and the symbols of other admittance matrices are similar; I L and I G are the currents of the load node and the generator node respectively; V L 、V T 、V G They represent the voltages of the load node, interconnection node, and generator node respectively.

[0037] The grid node voltage equation after eliminating the tie node can be expressed as

[0038]

[0039] Among them, Y LL It represents the equivalent admittance matrix between load nodes after eliminating the connection nodes. The symbols of other admittance matrices are similar.

[0040] According to the above formula, the load node voltage vector can be expressed as

[0041]

[0042] Among them, K, Z LL They are the coefficient matrices before the node voltage phasor and the load current phasor respectively.

[0043] Since the wind turbine to be analyzed does not have voltage support capability, the PCC bus node can be treated as a load node, and the voltage at the PCC bus can be expressed as

[0044]

[0045] Among them, m represents the number of generator nodes, and n represents the number of load nodes.

[0046] The first term of formula (4) is defined as the open-circuit voltage in the Thevenin equivalent circuit, and the remaining two terms are defined as the voltage drop due to the equivalent impedance. It is only applicable to large power grids where the voltage change at the generator node is not large. In fact, for a distribution network that is not very large, if a disturbance occurs in the system, it will affect the power output of the generator, thereby causing the generator voltage phase angle to change. This means that part of the generator terminal voltage is coupled with the load current, which needs to be considered in the Thevenin equivalent impedance. The analytical expression is:

[0047]

[0048] In formula (5), Δ represents the microvariable, ΔV Gj Indicates the voltage change of the generator node due to a slight change in the current at the PCC node i, ΔI Lqj It represents the change of current at load node j due to slight change of PCC node i.

[0049] According to Figure 2 , we can get the Thevenin equivalent potential

[0050] E eqi =V Li +I Li *Z eqi (6)

[0051] Through the above analysis, the power system is decomposed into a set of coupled single-port networks, in which the equivalent impedance includes the power supply coupling impedance, self-impedance, and load coupling impedance. The equivalent potential can be obtained through the equivalent impedance and PMU measurement values.

[0052] Combine the following Figure 3 As shown, a small disturbance stability identification method for a wind power grid-connected system of this embodiment is given in detail, which specifically includes the following steps:

[0053] S101: Acquire the real-time operating status of the wind power grid-connected system and construct a dynamic model of the wind turbine generator set.

[0054] The system admittance matrix is ​​obtained through SCADA, and the motor voltage phasor, load-side current phasor, and PCC bus voltage and current phasor are measured through PMUs.

[0055] Specifically, the wind turbine dynamic model includes a wind turbine transmission model, a double-fed wind turbine generator model, a filter dynamic model, a rotor-side converter and a grid-side converter.

[0056] Wind turbine transmission model:

[0057] The wind turbine and generator are equivalent to a mass block respectively, and their dynamic equations are:

[0058]

[0059] In the formula, ω t is the angular velocity of the wind turbine; s is the slip rate, s=(ω s -ω r ) / ω s ,ω s ,ω r are synchronous speed and rotor angular velocity respectively; ω B =2πf, which is the reference value of the system electrical angular velocity, θ tw is the angular displacement of the wind turbine relative to the generator rotor; D s is the damping coefficient between the wind turbine and the generator, the damping coefficients of the wind turbine and the generator themselves are negligible; K is the transmission chain stiffness coefficient.

[0060] Doubly-fed wind turbine generator model:

[0061] When the stator and rotor voltage and current directions are both in the generator convention, the mathematical model of the doubly-fed wind turbine generator can be described as

[0062]

[0063] Where: v' d 、v' q are the d-axis and q-axis components of the stator potential respectively; X' s is the stator equivalent winding transient inductance; X s , X' s are the stator circuit equivalent reactance and the stator equivalent winding transient reactance respectively; i ds 、i qs 、v dr 、v qr They are the stator d-axis and q-axis currents, and the rotor d-axis and q-axis voltages respectively.

[0064] Filter dynamic model:

[0065] The dynamic process of the filter can be described by the following differential equation:

[0066]

[0067] Among them, R g , L g are the resistance and inductance of the filter, v qg They are the d-axis and q-axis components of the grid-side inverter output voltage respectively.

[0068] Rotor-side inverter:

[0069] Introducing intermediate state variables x1, x2, x3, x4, the mathematical dynamic model of the rotor-side inverter is:

[0070]

[0071] Grid-side inverter:

[0072] The mathematical dynamic model of the grid-side inverter with the introduction of intermediate state variables x5, x6, x7, x8 is:

[0073]

[0074] From the above analysis, it can be concluded that the mathematical model of a wind turbine can be represented by a set of nonlinear mathematical equations.

[0075] S102: Based on the real-time operation status of the wind power grid-connected system and Figure 2 The Thevenin equivalent model is introduced, and the equivalent voltage and equivalent impedance of the Thevenin equivalent model are calculated.

[0076] If a disturbance occurs in the wind power grid-connected system, it will affect the power generated by the generator and cause the generator voltage phase angle to change. In this case, the disturbance will be taken into account in the Thevenin equivalent impedance and the corresponding Thevenin equivalent model will be constructed.

[0077] S103: Associating the Thevenin equivalent model with the dynamic model of the wind turbine generator system, obtaining the equilibrium point of the wind power grid-connected system as an initial value, and forming a state equation matrix.

[0078] Specifically, the Thevenin equivalent model is associated with the dynamic model of the wind turbine to obtain the wind power-Thevenin equivalent small perturbation equation. In the process of forming the state equation matrix, the wind power-Thevenin equivalent small perturbation equation is also linearized.

[0079] Combination Figure 3 and Figure 4 The Thevenin equivalent model and the wind turbine dynamic model can be linked together through the relationship between the export voltage, current and power, and finally the wind power-Thevenin equivalent small disturbance equation can be obtained.

[0080] The wind power-Thevenin small disturbance model can be described by the following differential algebraic equation:

[0081]

[0082] 0=g(x,z,u) (13)

[0083] Among them, x is the vector of state variables [ω t ,s,θ tw ,i qs ,i ds ,v' q ,v' d ,i dg ,i qg,x1,x2,x3,x4,x5,x6,x7,x8] T , z is a vector of algebraic variables [v qs ,v ds ,γ,Z eq ,E eq ,P eq ,Q eq ,I eq ] T , u is the vector of control variables [v qr ,v dr ,v qg ,v dg ] T , f and g correspond to the differential equation vector and the algebraic equation vector respectively. The state variable operating point can be obtained by solving f and g at the same time.

[0084] The impact of the Thevenin equivalent model on small disturbances in wind power is that it can change the balance point of wind power operation. Since there are also changes in the operating modes of wind farms and thermal power plants in the system performing the Thevenin equivalent, the Thevenin equivalent model is constantly changing, that is, the balance point of wind power is constantly changing.

[0085] By Taylor expanding (13)-(14) at the operating point and ignoring the second-order and higher-order terms, the linearized small-disturbance stability equation can be obtained. The linearized model is as follows:

[0086]

[0087] in,

[0088]

[0089]

[0090] Matrix A is the system state matrix.

[0091] S104: Based on the eigenvalues ​​of the state equation matrix, identifying the small disturbance stability of the wind power grid-connected system to determine whether to generate a wind power grid-connected system control instruction to stabilize the output of the wind power grid-connected system.

[0092] If the eigenvalue of the state equation matrix is ​​negative, the wind power grid-connected system is stable with small disturbances; otherwise, the wind power grid-connected system is unstable with small disturbances.

[0093] Specifically, the eigenvalue of matrix A represents the natural oscillation mode of the system and can be used to evaluate the stability of the system under small disturbances. If the eigenvalue is negative, the system is stable under small disturbances. The farther the eigenvalue is from the imaginary axis, the stronger the system's anti-disturbance ability is.

[0094] Embodiment 2

[0095] like Figure 5 As shown, this embodiment provides a small disturbance stability identification system for a wind power grid-connected system, which specifically includes the following modules:

[0096] A wind turbine dynamic model building module, which is used to obtain the real-time operating status of the wind power grid-connected system and build a wind turbine dynamic model;

[0097] An equivalent voltage and equivalent impedance calculation module, which is used to calculate the equivalent voltage and equivalent impedance of the Thevenin equivalent model based on the real-time operating status of the wind power grid-connected system and the Thevenin equivalent model;

[0098] A state equation matrix forming module, which is used to associate the Thevenin equivalent model with the wind turbine dynamic model, obtain the equilibrium point of the wind power grid-connected system as an initial value, and form a state equation matrix;

[0099] The system small disturbance stability identification module is used to identify the small disturbance stability of the wind power grid-connected system based on the eigenvalue of the state equation matrix, so as to determine whether to generate a wind power grid-connected system control instruction to stabilize the output of the wind power grid-connected system.

[0100] It should be noted here that each module in this embodiment corresponds to each step in Example 1 one by one, and the specific implementation process is the same, which will not be repeated here.

[0101] Embodiment 3

[0102] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps in the method for identifying small disturbance stability of a wind power grid-connected system as described above are implemented.

[0103] Embodiment 4

[0104] This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps in the method for identifying small disturbance stability of a wind power grid-connected system as described above are implemented.

[0105] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for identifying small disturbance stability of a wind power grid-connected system, characterized in that: include: Obtain the real-time operating status of the wind power grid-connected system and build a dynamic model of the wind turbine; Based on the real-time operating status of the wind power grid-connected system and the Thevenin equivalent model, the equivalent voltage and equivalent impedance of the Thevenin equivalent model are calculated; The Thevenin equivalent model is associated with the dynamic model of the wind turbine generator system to obtain the equilibrium point of the wind power grid-connected system as the initial value and form a state equation matrix; Based on the eigenvalues ​​of the state equation matrix, identifying the small disturbance stability of the wind power grid-connected system, so as to determine whether to generate a wind power grid-connected system control instruction to stabilize the output of the wind power grid-connected system; Among them, if the disturbance of the wind power grid-connected system affects the power generated by the generator and causes the generator voltage phase angle to change, the disturbance is taken into account in the Thevenin equivalent impedance, and the corresponding Thevenin equivalent model is constructed; part of the generator terminal voltage is coupled with the load current, and the Thevenin equivalent impedance is taken into account, then the Thevenin equivalent impedance analytical expression is: ； in, represents a microvariable, It indicates the voltage change of the generator node due to a slight change in the current at the PCC node i. represents the change of the current of load node j due to a slight change in PCC node i; m represents the number of generator nodes, and n represents the number of load nodes; The Thevenin equivalent model is associated with the dynamic model of the wind turbine generator system to obtain the wind power-Thevenin equivalent small disturbance equation.

2. The small disturbance stability identification method of a wind power grid-connected system according to claim 1, characterized in that: If the eigenvalue of the state equation matrix is ​​negative, the wind power grid-connected system is stable with small disturbances; otherwise, the wind power grid-connected system is unstable with small disturbances.

3. The small disturbance stability identification method of a wind power grid-connected system according to claim 1, characterized in that: The wind turbine dynamic model includes a wind turbine transmission model, a double-fed wind turbine generator model, a filter dynamic model, a rotor-side frequency converter and a grid-side frequency converter.

4. The small disturbance stability identification method of a wind power grid-connected system according to claim 1, characterized in that: In the process of forming the state equation matrix, the wind power-Thevenin equivalent small perturbation equation is also linearized.

5. A small disturbance stability identification system for a wind power grid-connected system, characterized in that: include: A wind turbine dynamic model building module, which is used to obtain the real-time operating status of the wind power grid-connected system and build a wind turbine dynamic model; An equivalent voltage and equivalent impedance calculation module, which is used to calculate the equivalent voltage and equivalent impedance of the Thevenin equivalent model based on the real-time operating status of the wind power grid-connected system and the Thevenin equivalent model; A state equation matrix forming module, which is used to associate the Thevenin equivalent model with the wind turbine dynamic model, obtain the equilibrium point of the wind power grid-connected system as an initial value, and form a state equation matrix; A system small disturbance stability identification module, which is used to identify the small disturbance stability of the wind power grid-connected system based on the eigenvalue of the state equation matrix, so as to determine whether to generate a wind power grid-connected system control instruction to stabilize the output of the wind power grid-connected system; Among them, if the disturbance of the wind power grid-connected system affects the power generated by the generator and causes the generator voltage phase angle to change, the disturbance is taken into account in the Thevenin equivalent impedance, and the corresponding Thevenin equivalent model is constructed; part of the generator terminal voltage is coupled with the load current, and the Thevenin equivalent impedance is taken into account, then the Thevenin equivalent impedance analytical expression is: ； in, represents a microvariable, It indicates the voltage change of the generator node due to a slight change in the current at the PCC node i. represents the change of the current of load node j due to a slight change in PCC node i; m represents the number of generator nodes, and n represents the number of load nodes; The Thevenin equivalent model is associated with the dynamic model of the wind turbine generator system to obtain the wind power-Thevenin equivalent small disturbance equation.

6. The small disturbance stability identification system for wind power grid-connected system according to claim 5, characterized in that: In the system small disturbance stability identification module, if the eigenvalue of the state equation matrix is ​​negative, the wind power grid-connected system is stable with small disturbances; otherwise, the wind power grid-connected system is unstable with small disturbances.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps in the method for identifying small disturbance stability of a wind power grid-connected system according to any one of claims 1 to 4 are implemented.

8. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps in the method for identifying small disturbance stability of a wind power grid-connected system according to any one of claims 1 to 4 are implemented.

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