Method and system for evaluating equivalent damping coefficient of regional power grid

Abstract

The invention provides a regional power grid equivalent damping coefficient evaluation method and system based on data collected by a synchronous phasor measurement device, and belongs to the technical field of power system parameter identification. The method comprises the following steps: firstly, selecting a frequency measurement result with relatively high data quality before and after a large disturbance event, and analyzing the influence of a determined component and a noise component of an active unbalance amount on a system frequency dynamic state in the large disturbance event; secondly, performing curve fitting on discrete frequency measurement results, and estimating a frequency response component caused by a noise component effect after a large disturbance event based on a superposition principle; on the basis, the equivalent damping coefficient of the regional power grid is estimated by combining the active power sudden change amplitude caused by the large disturbance event, the occurrence time of the large disturbance event and the inertia coefficient of the regional power grid.

Description

Technical Field

[0001] The present disclosure relates to the technical field of power system parameter identification, and in particular to a method and system for evaluating an equivalent damping coefficient of a regional power grid. Background Art

[0002] As a large number of load resources are connected to the power grid through power electronic devices, the system load characteristics have changed significantly, and the range of variation of the system equivalent damping coefficient has increased. The equivalent damping coefficient is one of the key parameters in the power system frequency response model. For the stability analysis and optimal control of the power system, the identification of the system equivalent damping coefficient is of great significance.

[0003] The key parameters of the frequency response model, such as the system equivalent damping coefficient, can be identified based on the system frequency measurement value after a large disturbance event. However, such methods usually only focus on the active power mutation caused by a large disturbance event, and believe that its amplitude is much larger than the net load disturbance amplitude under normal operation. In large regional power grids with large scale and high penetration of renewable energy, the amplitude of active unbalance caused by large disturbance events such as DC interlocking and unit tripping is of similar order of magnitude to the amplitude of active unbalance under normal operation of the system. The use of such simplified methods will lead to large errors in the identification of the equivalent damping coefficient of the regional power grid.

[0004] Therefore, there is an urgent need for a regional power grid equivalent damping coefficient evaluation method with smaller error to more accurately characterize the dynamic characteristics of the system frequency response. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and to propose a method and system for evaluating the equivalent damping coefficient of a regional power grid based on synchronized phasor data.

[0006] The technical solution of the present invention discloses a method for evaluating the equivalent damping coefficient of a regional power grid, comprising:

[0007] Select frequency data from the frequency measurement results of synchronized phasor data, analyze the influence of the determined component and noise component of active unbalance quantity on the system frequency dynamics in large disturbance events, and obtain the frequency response of the system;

[0008] Curve fitting is performed on the selected frequency data to estimate the frequency response components caused by the noise components after a large disturbance event, and further estimate the equivalent damping coefficient of the regional power grid.

[0009] Furthermore, the selected frequency data is screened in the synchronized phasor data frequency measurement results of the nodes near the location where the large disturbance event occurs, and samples that are not near the nodes of the frequency measurement result group or have obviously inconsistent frequency change trends are removed.

[0010] Furthermore, the system frequency dynamics is expressed as:

[0011]

[0012] Among them, H is the equivalent inertia level of the regional power grid, which is estimated by statistical method or inertia parameter identification method, D is the equivalent damping coefficient of the regional power grid, Δf(t) represents the frequency deviation of the regional power grid at time t, ΔP(t) represents the net load active power of the regional power grid at time t, that is, the active unbalance. Before and after the large disturbance event, the net load active power of the regional power grid ΔP(t) is divided into the determined component ΔP d (t) and the noise component ΔP r (t).

[0013] Furthermore, the sudden change of active unbalance caused by the large disturbance event is expressed as:

[0014]

[0015] Where t0 represents the time when the large disturbance event occurs, L represents the power loss amplitude caused by the large disturbance event, ΔP d (t) represents the determined component.

[0016] In the noise component ΔP r (t) acts alone, the frequency response of the system is Δf r (t), then determine the component ΔP d (t) Under the single action, the frequency response of the system is Δf d (t) is expressed as:

[0017] Δf d (t) = Δf(t) - Δf r (t)

[0018] When the component acts alone, the frequency response of the system is Δf d (t) is expressed as:

[0019]

[0020] Furthermore, the selected frequency data is subjected to curve fitting, and the fitting result is expressed as:

[0021]

[0022] in, represents the fitting result of the system frequency deviation before and after the large disturbance event, which is regarded as the estimated value of the system's true frequency response Δf(t), where are the frequency fitting curves before and after the disturbance, Δt - , Δt +They are the lengths of the interval fitting intervals before and after the disturbance occurs, respectively.

[0023] Further, before the large disturbance event occurs, the component ΔP d (t) and the resulting frequency deviation component Δf d (t) are always 0. Therefore, when t < t0, the system frequency deviation is completely caused by the noise component, and there is Δf r (t) = Δf(t);

[0024] After the large disturbance event occurs, the system deviation is caused by the combined action of ΔP d (t) and ΔP r (t). Based on the frequency deviation fitting curve before the disturbance occurs Trend extrapolation is performed on the frequency deviation component caused by the action of the noise component ΔP r (t) after the disturbance occurs to obtain its estimated value

[0025] Further, under the action of the component ΔP d (t) alone, the estimated value of the frequency response Δf d (t) of the system is expressed as:

[0026]

[0028] Further, the equivalent damping coefficient of the regional power grid is expressed as:

[0029]

[0030] Among them, H is estimated by the statistical method or the inertia parameter identification method, and the estimated value of the equivalent damping coefficient of the regional power grid is expressed as:

[0031]

[0032] In the range of [t0, t0 + Δt + , multiple time points are taken for calculation, and the average value of multiple estimated values is used as the final estimated result of the equivalent damping coefficient of the regional power grid.

[0033] The present invention also discloses a regional power grid equivalent damping coefficient evaluation system, including:

[0034] A sampling module for selecting frequency data from the frequency measurement results of synchronous phasor data and analyzing the influence of the determined component and the noise component of the active power imbalance amount on the system frequency dynamics in a large disturbance event;

[0035] A digital-to-analog conversion module for estimating the frequency response component caused by the action of the noise component after a large disturbance event;

[0036] Evaluation module, used to estimate the equivalent damping coefficient of the regional power grid.

[0037] The present invention considers the digital quantity characteristics of the actual measurement data of the synchronous phasor measurement unit (PMU) in the real power system, and converts it into analog quantity by using a curve fitting method, which helps to reduce the quantization noise in the PMU frequency measurement signal, restore the real system frequency change, improve the frequency change rate calculation accuracy, and further improve the accuracy of the identification of the equivalent damping coefficient of the regional power grid.

[0038] The present invention comprehensively considers the determined component and the noise component of the active unbalance in a large disturbance event, and based on the linear system superposition principle, filters out the influence of the noise component on the system frequency, which helps to reduce the error of identifying the equivalent damping coefficient of the regional power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a curve diagram of the evaluation results obtained in Example 1 of the embodiment of the present invention;

[0040] Figure 2 is a curve chart of evaluation results obtained in Example 2 of an embodiment of the present invention;

[0041] Figure 3 3 is a curve chart of the evaluation results obtained in Example 3 of the embodiment of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0043] The present invention proposes a method and system for evaluating equivalent damping coefficient of a regional power grid based on synchronized phasor data. The method involved in the present invention will be described in detail below in conjunction with the steps of a specific embodiment.

[0044] 1) Select representative frequency data. Screen the PMU frequency measurement results of nodes near the location where the large disturbance event occurred, remove samples with serious data problems (nodes not near the frequency measurement result group or frequency change trends are obviously inconsistent), and select measurement data without obvious data quality problems before and after the large disturbance event.

[0045] 2) Analyze the influence of the determined component and noise component of active unbalance on the system frequency dynamics in large disturbance events. The specific method is as follows:

[0046] 2-1) The frequency dynamic characteristics of the regional power grid are expressed as follows:

[0047]

[0048] Among them, H is the equivalent inertia level of the regional power grid, which is estimated by statistical method or inertia parameter identification method, D is the equivalent damping coefficient of the regional power grid, Δf(t) represents the frequency deviation of the regional power grid at time t, and ΔP(t) represents the net load active power of the regional power grid at time t, that is, the active unbalance. Before and after the large disturbance event, the net load active power of the regional power grid ΔP(t) is divided into the determined component ΔP d (t) and the noise component ΔP r (t).

[0049] 2-2) Determine the component ΔP d (t) represents the sudden change of active unbalance caused by a large disturbance event, which has a step waveform and is expressed as follows:

[0050]

[0051] Among them, t0 represents the time when the large disturbance event occurs, and L represents the power loss amplitude caused by the large disturbance event, such as the active output power before the unit trips in the unit tripping event or the active power fed in before the DC line is locked, etc. This part of the active power has a large change amplitude and is easy to measure. Therefore, it is regarded as a deterministic component in the identification problem of the system equivalent damping parameters.

[0052] 2-3) Before and after a large disturbance event, in addition to the power change caused by the large disturbance event, there may be other active unbalanced components in the system, which are caused by factors such as load fluctuations, generator output changes, new energy output fluctuations, and active power regulation. This part of the component is more complex and difficult to measure, so it is regarded as a noise component in the system equivalent damping parameter identification problem, and is expressed by ΔP r (t) indicates.

[0053] 2-4) The frequency dynamic characteristics of the regional power grid described in step 2-1) are regarded as a linear system with ΔP(t) as input and Δf(t) as output. Therefore, according to the superposition principle, Δf(t) is decomposed into ΔP d (t) and ΔP r (t) Response under single action. Assuming the noise component ΔP r (t) acts alone, the frequency response of the system is Δf r (t), then determine the component ΔP d (t) Under the single action, the frequency response of the system is Δf d (t) is expressed as follows:

[0054] Δf d(t) = Δf(t) - Δf r (t)

[0055] 2 - 5) Determine the frequency response Δf of the system under the separate action of the components according to the dynamic characteristics of the regional grid frequency d (t) is expressed as the following formula:

[0056]

[0057] 3) Perform curve fitting on the PMU frequency measurement results in step 1), and estimate the frequency response components caused by the noise components after large disturbance events. The specific method is as follows:

[0058] 3 - 1) Considering that the PMU frequency measurement results are digital quantities and have discrete properties in both time and value, in order to improve the restoration degree of the original system frequency information and facilitate the calculation of the frequency change rate, first perform curve fitting on the PMU frequency data, using methods such as polynomial fitting and exponential fitting. Fit the PMU frequency data before and after large disturbance events respectively, and the fitting results are expressed as:

[0059]

[0060] Among them, represents the fitting results of the system frequency deviation before and after large disturbance events, regarded as the estimated value of the system true frequency response Δf(t), where are the frequency fitting curves before and after the disturbance respectively, and Δt - , Δt + are the lengths of the fitting intervals before and after the disturbance respectively, such as 1 to 5 seconds.

[0061] 3 - 2) Before the large disturbance event occurs, determine the component ΔP d (t) and the frequency deviation component Δf d (t) are always 0. Therefore, when t < t0, the system frequency deviation is completely caused by the noise component, and there is Δf r (t) = Δf(t).

[0062] 3 - 3) After the large disturbance event occurs, the system deviation is caused by the combined action of ΔP d (t) and ΔP r (t). In a large - scale regional grid, ΔP d (t) and ΔP r (t) may have similar orders of magnitude. Therefore, directly ignoring the noise component ΔP r (t) may cause large errors in the evaluation of the equivalent damping coefficient of the regional grid. Since the noise component ΔP r(t) is difficult to measure and its frequency response component cannot be accurately calculated, so it needs to be estimated. When no large disturbance event occurs in the system, only the noise component ΔP r At (t), the system is running relatively stably. Both the generator and the load have a certain inertia. Their output or power consumption maintains a certain trend in a short time. The frequency trend in the past few seconds can provide some effective information for the frequency change in the next few seconds. Therefore, based on the frequency deviation fitting curve before the disturbance occurs The noise component ΔP after the disturbance occurs r (t) The frequency deviation component caused by the action is extrapolated to obtain its estimated value

[0063] 3-4) According to steps 2-5) and 3-2), the component ΔP is determined d (t) Under the single action, the frequency response of the system is Δf d Estimated value of (t):

[0064]

[0065] 4) Estimate the equivalent damping coefficient of the regional power grid. The specific method is as follows:

[0066] 4-1) According to step 2-5), the equivalent damping coefficient of the regional power grid is expressed as:

[0067]

[0068] 4-2) In the expression of step 4-1), H is estimated by statistical method or inertia parameter identification method, ΔP d (t) As described in step 2-2), Δf d (t) is estimated by the method described in step 3). The estimated value of the equivalent damping coefficient of the regional power grid is as follows:

[0069]

[0070] 4-3) In [t0,t0+Δt + ] to select multiple time points within the range Calculations are performed and the average of multiple estimated values ​​is taken as the final estimated result of the equivalent damping coefficient of the regional power grid.

[0071] The present invention also discloses a regional power grid equivalent damping coefficient evaluation system based on synchronized phasor data, and running the system is to implement the aforementioned regional power grid equivalent damping coefficient evaluation method based on synchronized phasor data. The system includes:

[0072] The sampling module is used to select frequency data from the frequency measurement results of the synchronized phasor data and analyze the influence of the determined components of the active unbalance and the noise components on the system frequency dynamics in large disturbance events; the digital-to-analog conversion module is used to estimate the frequency response components caused by the noise components after large disturbance events; the evaluation module is used to estimate the equivalent damping coefficient of the regional power grid.

[0073] In an embodiment of the present invention, the scale of the power grid system is set to 300000MVA. Based on the frequency measurement data collected by PMU for large power grid disturbance events, the equivalent damping coefficient of the regional power grid is evaluated multiple times using the method of the present invention. Each evaluation is a calculation example, defined as Example 1, Example 2 and Example 3. Then, based on the power grid inertia H and the power grid damping coefficient D, three sets of power grid frequency deviation coefficients are calculated. The evaluation results obtained in this embodiment are shown in the following table.

[0074]

[0075] Figures 1 to 3 They are the graphs of the grid inertia H and the grid damping coefficient D of Examples 1 to 3, respectively. The left part of the figure represents the grid inertia H, and the right part represents the grid damping coefficient D; the horizontal axis represents time in seconds; the vertical axis represents the grid frequency in Hertz. In the left-hand grid inertia H curve, the green and red curves respectively represent the time before and after the disturbance occurs, and the intersection of different colors represents the time when the disturbance occurs; in the right-hand grid damping coefficient D curve, the orange and red curves respectively represent the time before and after the disturbance occurs, and the blue and green curves are the smooth curves of the orange and red curves, respectively, and the intersection of different colors represents the time when the disturbance occurs. Combined with the comparison of the curve graphs of each evaluation example, it can be seen that the one representing Example 3 Figure 3 There is an obvious turning point at the intersection of the two curves, indicating that the frequency of large disturbance events changes greatly. The evaluation value of Example 3 should be the most accurate.

[0076] The present invention performs curve fitting on the frequency values ​​measured by a synchronous phasor measurement device before and after a large disturbance event to achieve conversion from digital quantity to analog quantity; comprehensively considers the definite component and noise component of the active unbalanced quantity in the large disturbance event, and decomposes the system frequency response after the large disturbance event based on the superposition principle; extracts the frequency change component caused by the definite component acting alone, and calculates the identification result of the equivalent damping coefficient of the regional power grid.

Claims

1. A method for evaluating equivalent damping coefficient of a regional power grid, characterized in that: include: Select frequency data from the measurement nodes of the synchronized phasor measurement device, analyze the influence of the determined component and noise component of the active unbalance quantity on the system frequency dynamics in the large disturbance event, and obtain the frequency response of the system; The selected frequency data are curve fitted, and the frequency response components caused by the noise components after the large disturbance event are estimated, thereby obtaining the estimated value of the equivalent damping coefficient of the regional power grid.

2. The method for evaluating the equivalent damping coefficient of a regional power grid according to claim 1, characterized in that: The frequency data is selected by screening the synchronized phasor data frequency measurement results of the nodes near the location where the large disturbance event occurs, and removing the samples that are not near the nodes of the frequency measurement result group or whose frequency change trends are obviously inconsistent.

3. The method for evaluating equivalent damping coefficient of a regional power grid according to claim 2, characterized in that: The system frequency dynamics is expressed as: Among them, H is the equivalent inertia level of the regional power grid, which is estimated by statistical method or inertia parameter identification method, D is the equivalent damping coefficient of the regional power grid, Δf(t) represents the frequency deviation of the regional power grid at time t, ΔP(t) represents the net load active power of the regional power grid at time t, that is, the active unbalance. Before and after the large disturbance event, the net load active power of the regional power grid ΔP(t) is divided into the determined component ΔP d (t) and the noise component ΔP r (t).

4. The method for evaluating equivalent damping coefficient of a regional power grid according to claim 3, characterized in that: The sudden change of active unbalance caused by the large disturbance event is expressed as: Where t0 represents the time when the large disturbance event occurs, L represents the power loss amplitude caused by the large disturbance event, ΔP d (t) represents the determined component.

5. The method for evaluating equivalent damping coefficient of a regional power grid according to claim 4, characterized in that: In the noise component ΔP r (t) acts alone, the frequency response of the system is Δf r (t), then determine the component ΔP d (t) Under the single action, the frequency response of the system is Δf d (t) is expressed as: Δf d (t)=Δf(t)-Δf r (t) When the component acts alone, the frequency response of the system is Δf d (t) is expressed as:

6. The method for evaluating equivalent damping coefficient of a regional power grid according to claim 5, characterized in that: The selected frequency data is subjected to curve fitting, and the fitting result is expressed as: in, represents the fitting result of the system frequency deviation before and after the large disturbance event, which is regarded as the estimated value of the system's true frequency response Δf(t), where are the frequency fitting curves before and after the disturbance, Δt - , Δt + are the fitting interval lengths before and after the disturbance respectively.

7. The method for evaluating equivalent damping coefficient of a regional power grid according to claim 6, characterized in that: Before the large disturbance event occurs, determine the component ΔP d (t) and the resulting frequency deviation component Δf d (t) are always 0, that is, when t < t0, there is Δf r (t) = Δf(t); After a large disturbance event occurs, the system deviation changes from ΔP d (t) and ΔP r (t) The combined effect leads to the fitting curve based on the frequency deviation before the disturbance occurs. The noise component ΔP after the disturbance occurs r (t) The frequency deviation component caused by the action is extrapolated to obtain the estimated value of the frequency deviation t∈[t0,t0+Δt + ].

8. The method for evaluating equivalent damping coefficient of a regional power grid according to claim 7, characterized in that: Component ΔP d (t) Under the single action, the frequency response of the system is Δf d The estimated value of (t) is expressed as:

9. The method for evaluating equivalent damping coefficient of a regional power grid according to claim 8, characterized in that: The equivalent damping coefficient of the regional power grid is expressed as: Among them, H is estimated by statistical method or inertia parameter identification method, and the estimated value of the equivalent damping coefficient of the regional power grid is It is expressed as: In [t0,t0+Δt + ] to select multiple time points within the range Calculations are performed and the average of multiple estimated values ​​is taken as the final estimated result of the equivalent damping coefficient of the regional power grid.

10. A regional power grid equivalent damping coefficient evaluation system, characterized in that: include: The sampling module is used to select frequency data from the frequency measurement results of the synchronized phasor data and analyze the influence of the determination component and noise component of the active unbalance quantity on the system frequency dynamics in the large disturbance event; A digital-to-analog conversion module is used to estimate the frequency response component caused by the noise component after a large disturbance event; Evaluation module, used to estimate the equivalent damping coefficient of the regional power grid.

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