Method for suppressing dc overvoltage of static var generator

Abstract

The application provides a static var generator DC overvoltage suppression method, comprising the following steps: establishing a state space model of static var generator grid connection based on device control parameters and network topology parameters; substituting control variables of a current input static var generator in a power system into the state space model, analyzing key variables affecting DC overvoltage and corresponding suppression strategies of the key variables by solving the state space model; when the key variables meet preset response conditions, simulating the suppression strategies, and determining selected suppression strategies and executing according to simulation results. The application establishes a detailed state space model from fault recovery to the time when DC voltage reaches a peak value, so that key factors leading to DC overvoltage can be quickly and accurately determined based on the mechanism of SVG DC overvoltage, and corresponding suppression strategies can be determined, which is beneficial to eliminating the threat of very serious DC overvoltage to devices and power grid stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrical engineering, and particularly relates to a method for suppressing DC overvoltage of a static var generator. BACKGROUND

[0002] The gradual withdrawal of traditional energy needs to be based on the safe and reliable foundation of new energy. The fact is that with the high popularity of new energy, the strength of the power grid has been declining. Static var generators are widely used as reactive power compensation devices to provide fast reactive power and voltage support for the power grid. However, during the short-circuit fault recovery process, the SVG will be affected by the DC overvoltage and may be disconnected from the power grid.

[0003] In the steady state, the static var generator (SVG) operates at 0 power factor, and the DC voltage remains constant. However, field experiments show that the SVG absorbs active power during fault recovery. Since the DC side capacitor of the SVG is very small, and the SVG is usually not equipped with hardware protection devices, the absorption of active power during fault recovery may cause very serious DC overvoltage, which threatens the stability of the device and the power grid. SUMMARY

[0004] In order to solve the problem that the static var generator absorbs active power during fault recovery, which may cause very serious DC overvoltage and threaten the stability of the device and the power grid, the application proposes a method for suppressing DC overvoltage of a static var generator, establishes a state space model of a grid-connected SVG during short-circuit fault recovery, analyzes the mechanism of DC overvoltage using the model, analyzes the key influencing factors of DC overvoltage, and proposes a DC overvoltage suppression strategy based on simulation analysis results.

[0005] The method for suppressing DC overvoltage of a static var generator comprises the following steps:

[0006] Based on the device control parameters and network topology parameters, a state space model of a grid-connected static var generator is established;

[0007] The control variables of the current input static var generator in the power system are substituted into the state space model, and the key variables affecting the DC overvoltage and the corresponding suppression strategy of the key variables are analyzed by solving the state space model;

[0008] When the key variables meet the preset response conditions, the suppression strategy is simulated, and the selected suppression strategy is determined and executed according to the simulation results.

[0009] Optionally, the state space model is:

[0010]

[0011] wherein, state vector x = [V d V q x1 x2 x5 I sd I sq I gd I gq U dc x3 x4] T , denotes derivative of x, V d , V q are d, q axis components of static var generator terminal voltage; I sd , I sq are d, q axis components of filter inductor current; I gd , I gq are d, q axis components of transmission line current, U dc is DC voltage, x1, x2 are integral terms of current control input, x5 is integral term of DC voltage control input, x3, x4 are state variables corresponding to voltage feedforward control; A is state transition matrix of power system where static var generator is located, B is control transition matrix of power system where static var generator is located, u is control variable input to power system where static var generator is located.

[0012] Optionally, when A and B in the state space model are determined, A and B are simulated and calculated based on device control parameters and network topology parameters through Simulink tool of matlab.

[0013] Optionally, the key variable affecting DC overvoltage is analyzed by solving the state space model, including:

[0014] Based on modal analysis theory, an analytical solution of the state space model is solved, and is decomposed according to characteristic roots as follows:

[0015]

[0016] wherein, λ i is the i th characteristic value of state transition matrix A in the power system, v i and q i T are corresponding right eigenvector and left eigenvector, x(t) represents state variable of the power system at t time, x(t0) represents state variable of the power system at initial time t0, and n represents total number of characteristic values.

[0017] Optionally, when the suppression strategy corresponding to the key variable is determined, the influencing factor affecting the key variable is analyzed through participation factor, and the corresponding suppression strategy is generated based on the influencing factor.

[0018] Optionally, when the key variable meets the preset response condition, the simulation is performed on the suppression strategy, and the selected suppression strategy is determined and executed according to a simulation result, comprising:

[0019] The setting parameter corresponding to the influence factor is adjusted based on the suppression strategy;

[0020] The U in the state vector x is simulated based on the adjusted setting parameter by using the Simulink tool of matlab; dc The U is selected according to a simulation effect. dc The suppression strategy with the fastest suppression response speed is executed.

[0021] The technical scheme provided by the application has the beneficial effects that:

[0022] The application establishes a detailed state space model of SVG from fault recovery to the time when the DC voltage reaches a peak value, so that the key factor causing the DC overvoltage can be quickly and accurately determined based on the mechanism of the SVG DC overvoltage, and the corresponding suppression strategy is determined, which is beneficial to eliminating the threat of very serious DC overvoltage to the equipment and the stability of the power grid. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical scheme of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 A flowchart of a static var generator DC overvoltage suppression method according to an embodiment of the application is shown in the figure.

[0025] Figure 2 A topological structure diagram of a power system in which the static var generator is located according to an embodiment of the application is shown in the figure.

[0026] Figure 3 A simulation result diagram of a DC voltage curve under different voltage feedforward time constants according to an embodiment of the application is shown in the figure.

[0027] Figure 4 A simulation result diagram of an I curve under different voltage feedforward time constants according to an embodiment of the application is shown in the figure. sd

[0028] Figure 5 A simulation result diagram of a DC voltage curve under different K according to an embodiment of the application is shown in the figure. p ​​

[0029] Figure 6 For the current control of different K in the embodiment of the present application p The simulation result schematic diagram of I sd The simulation result schematic diagram of I

[0030] Figure 7 The simulation result schematic diagram of I

[0031] Figure 8 The simulation result schematic diagram of I sd The simulation result schematic diagram of I DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the scope of protection of the present application.

[0033] The terms "first", "second", "third", "fourth" and the like in the description, claims, and drawings of the present application (if any) are used to distinguish between similar objects, and do not necessarily have to describe a particular sequential or chronological order. It should be understood that the data thus used can be interchanged, so that the embodiments of the present application described herein can be implemented in sequences other than those illustrated or described herein.

[0034] It should be understood that in various embodiments of the present application, the magnitude of the serial number of each process does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0035] It should be understood that in the present application, "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0036] It should be understood that in the present application, "a plurality of" means two or more. "And / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. The character " / " generally represents that the associated objects before and after it are in an "or" relationship. "Including A, B and C", "including A, B, C" means that A, B and C are all included, "including A, B or C" means that one of A, B and C is included, and "including A, B and / or C" means that any one or any two or three of A, B and C is included.

[0037] It should be understood that in the present application, "B corresponding to A", "B corresponding to A", "A corresponding to B" or "B corresponding to A" means that B is associated with A, and B can be determined according to A. Determining B according to A does not mean that B is determined only according to A, but also can be determined according to A and / or other information. The matching of A and B means that the similarity of A and B is greater than or equal to a preset threshold.

[0038] Depending on the context, "if" as used herein can be interpreted as "when" or "when" or "in response to determining" or "in response to detecting".

[0039] The technical solutions of the present application will be described in detail below with specific examples. The following specific examples can be combined with each other, and the same or similar concepts or processes may not be described in some examples.

[0040] Example 1

[0041] As shown in the figure, the embodiment provides a method for suppressing DC overvoltage of static var generator, comprising: Figure 1

[0042] S1: Based on the device control parameters and network topology parameters, a state space model of static var generator grid connection is established;

[0043] S2: Substitute the control variables of the current input static var generator in the power system into the state space model, analyze the key variables affecting the DC overvoltage through solving the state space model, and the corresponding suppression strategy of the key variables;

[0044] S3: When the key variables meet the preset response condition, simulate the suppression strategy, and determine the selected suppression strategy according to the simulation result and execute.

[0045] ​This embodiment establishes a detailed state-space model of the SVG from fault recovery to the time when the DC voltage reaches its peak. This allows for the rapid and accurate identification of key factors leading to DC overvoltage based on the mechanism of SVG DC overvoltage, and the determination of corresponding suppression strategies. This is beneficial for eliminating the threat posed by very severe DC overvoltage to equipment and grid stability.

[0046] In this embodiment, the topology of the power system where the static var generator is located is as follows: Figure 2 As shown, the static var generator is a three-phase converter, which is connected to L... fs L g C f The reactor is connected to the AC power grid.

[0047] In this embodiment, within the DC overvoltage time scale, a detailed state-space model of the grid-connected SVG during short-circuit fault recovery is established by approximating some variables. The state-space model is as follows:

[0048]

[0049] Wherein, the state vector x = [V d V q x1 x2 x5 I sd I sq I gd I gq U dc x3 x4] T , V represents the derivative of x. d V q I represents the d-axis and q-axis components of the static var generator terminal voltage. sd I sq These are the d-axis and q-axis components of the filter inductor current; I gd I gq U represents the d-axis and q-axis components of the transmission line current. dc x1 and x2 are the integral terms of the current control input, x5 is the integral term of the DC voltage control input, and x3 and x4 are the state variables corresponding to the voltage feedforward control; A is the state transition matrix of the power system where the static var generator is located, B is the control transition matrix of the power system where the static var generator is located, and u is the control variable input to the power system where the static var generator is located.

[0050] The state transition matrix A and the control transition matrix B are usually determined by modeling the system. In the modeling process, the working principle of the system needs to be analyzed, and the state equation is derived accordingly. The specific method of determining the state transition matrix and the control transition matrix varies with the system and needs to be determined according to the characteristics of the system. Sometimes, experimental or measured data need to be used to verify and correct the modeling results.

[0051] In this embodiment, when determining A and B in the state space model, A and B are simulated and calculated based on device control parameters and network topology parameters by using the Simulink tool of matlab.

[0052] In this embodiment, the key variables affecting the DC overvoltage are analyzed by solving the state space model, including: based on the modal analysis theory, the analytical solution of the state space model is solved, and is decomposed into according to the eigenvalues:

[0053]

[0054] where λ i is the i-th eigenvalue of the state transition matrix A of the power system, v i and q i T are the corresponding right eigenvector and left eigenvector, x(t) represents the state variable of the power system at time t, x(t0) represents the state variable of the power system at the initial time t0, and n represents the total number of eigenvalues.

[0055] In this embodiment, the dynamic of the DC side capacitor can be represented as: approximate U dc in the above formula as a constant, the active power P E is approximated as: P E ≈I sd , and it can be seen that the increment of the DC voltage U dc is proportional to the negative integral of the d-axis current. As long as the d-axis current remains negative, the DC voltage will increase, and the d-axis current is dominated by the low-frequency component.

[0056] In determining the corresponding suppression strategy of the key variables, the influencing factors affecting the key variables are analyzed by using the participation factor, and the corresponding suppression strategy is generated based on the influencing factors.

[0057] Participation factor is an index of matrix eigenvalue analysis, which establishes the relationship between different modes (eigenvalues) of the matrix and state variables. The participation factor of the eigenvalue of the matrix measures the net participation degree of a certain state variable to the eigenvalue: the larger the participation factor, the greater the influence of the state variable on the eigenvalue. Participation factor analysis can obtain the state variable that has the greatest influence on the dominant eigenvalue, thereby effectively identifying the main control link of the overvoltage problem.

[0058] In this embodiment, through participation factor analysis, it can be obtained that the most important factor affecting the d-axis current is the d-axis current control, the dynamic of the DC side capacitor, the voltage feedforward control and the DC voltage control. The above factors are the key factors causing the SVG DC overvoltage problem. Further, the corresponding DC overvoltage suppression strategy is as follows:

[0059] (1) Improve the current tracking performance, for example, reduce the time constant of the voltage feedforward control, and increase the PI gain of the d-axis current control.

[0060] (2) Improve the DC voltage tracking performance, for example, increase the PI gain of the DC voltage control.

[0061] (3) Increase the DC side capacitor to reduce the volatility of the DC voltage.

[0062] For suppression strategy (1), the filter time constant of the voltage feedforward control is changed and other parameters are kept constant, Figure 3 the DC voltage is depicted, Figure 4 and the d-axis current of the SVG within 50 ms after the fault recovery is depicted. As Figure 3 shown, reducing the time constant of the voltage feedforward has a significant impact on the DC voltage. In Figure 4 , the reduction of the time constant makes the current reference track faster, while I sd is advanced to zero, and the DC overvoltage is alleviated.

[0063] For suppression strategy (2), the proportional constant of the d-axis current control is changed and other parameters are kept constant, Figure 5 the DC voltage is depicted, Figure 6 and the d-axis current of the SVG within 50 ms after the fault recovery is depicted.

[0064] The reason for the DC overvoltage is the slow dynamic of the current control. As Figure 6 can be seen, increasing the proportional constant of the d-axis current control helps to speed up the tracking of the current reference value. The d-axis current is zero at the same time under different PI parameters, but the faster the PI parameter, the smaller the "acceleration zone" that causes the voltage to rise. Therefore, Figure 5 the DC voltage peak value in p decreases with the increase of K .

[0065] For the suppression strategy (3), the PI parameters of the DC voltage control are changed and other parameters remain unchanged, Figure 7 The DC voltage curve is depicted, Figure 8 The d-axis current of the SVG within 50 ms after fault recovery is depicted.

[0066] The DC voltage control with faster PI parameters can track the DC voltage faster and improve the d-axis current reference dynamics. The faster the PI parameters of the DC voltage control, the earlier the d-axis current returns to zero, as Figure 8 shown. Therefore, the DC overvoltage gradually decreases with the increase of the parameters in Figure 7 .

[0067] On the basis of the simulation results described above, in the present embodiment, when the key variable meets the preset response condition, the suppression strategy is simulated, and the selected suppression strategy is executed according to the simulation result, including:

[0068] The setting parameters corresponding to the influence factor are adjusted based on the suppression strategy;

[0069] The U dc in the state vector x is simulated based on the adjusted setting parameters by using the Simulink tool of matlab; and the suppression strategy with the fastest suppression response speed of U dc is selected for execution according to the simulation effect.

[0070] The serial numbers in the above embodiments are only for description, and do not represent the sequence in the assembling or using process of the components.

[0071] The above description is only an embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of suppressing a DC overvoltage of a static var generator, characterized by, The suppression method includes: A state-space model of a static var generator connected to the grid is established based on equipment control parameters and network topology parameters. Substitute the control variables of the power system where the current input static var generator is located into the state-space model, and analyze the key variables affecting DC overvoltage and the suppression strategies corresponding to the key variables by solving the state-space model. When the key variable meets the preset response conditions, the suppression strategy is simulated, and the selected suppression strategy is determined and executed based on the simulation results. The state-space model is as follows: Wherein, the state vector x = [V d V q x1 x2 x5 I sd I sq I gd I gq U dc x3 x4] T , V represents the derivative of x. d V q I represents the d-axis and q-axis components of the static var generator terminal voltage. sd I sq These are the d-axis and q-axis components of the filter inductor current; I gd I gq U represents the d-axis and q-axis components of the transmission line current. dc x1 and x2 are the integral terms of the current control input, x5 is the integral term of the DC voltage control input, and x3 and x4 are the state variables corresponding to the voltage feedforward control; A is the state transition matrix of the power system where the static var generator is located, B is the control transition matrix of the power system where the static var generator is located, and u is the control variable input to the power system where the static var generator is located. The analysis of key variables affecting DC overvoltage by solving the state-space model includes: obtaining the analytical solution of the state-space model based on modal analysis theory, and decomposing it according to characteristic roots: where λ i is the i-th eigenvalue of the state transition matrix A in the power system, v i and q i T are the corresponding right and left eigenvectors, x(t) represents the state variable of the power system at time t, x(t0) represents the state variable of the power system at the initial time t0, and n represents the total number of eigenvalues. After determining the suppression strategy corresponding to the key variable, the suppression strategy is generated based on the influencing factors that affect the key variable through factor analysis. The simulation of the suppression strategy is performed when the key variable meets the preset response condition, and the selected suppression strategy is determined and executed according to a simulation result, including: adjusting the setting parameter corresponding to the influence factor based on the suppression strategy; performing simulation on the U dc in the state vector x based on the adjusted setting parameter through the Simulink tool of matlab; and selecting the suppression strategy with the fastest suppression response speed of U dc for execution according to the simulation effect.

2. The method for suppressing DC overvoltage in a static var generator according to claim 1, characterized in that, When determining A and B in the state-space model, MATLAB's Simulink tool is used to simulate and calculate A and B based on device control parameters and network topology parameters.

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