Regional power grid inertia evaluation method and system based on synchronous phasor measurement

Abstract

The invention provides a regional power grid inertia evaluation method and system based on synchronous phasor measurement, and belongs to the technical field of power system parameter identification. The method comprises the following steps: firstly, selecting a frequency measurement result of a synchronous phasor measurement unit (PMU), and analyzing the influence of sudden power change caused by large disturbance on the frequency change rate of a system; secondly, converting the selected PMU frequency measurement result into an analog quantity by adopting a polynomial fitting method, and positioning the occurrence time of large disturbance; and finally, estimating the inertia of the regional power grid according to the power sudden change amplitude caused by the large disturbance, the large disturbance occurrence time and the frequency fitting curve.

Description

Technical Field

[0001] The present disclosure relates to the field of power system control, and in particular to a method and system for evaluating inertia of a regional power grid based on synchronized phasor measurement. Background Art

[0002] With the global energy transformation, the proportion of renewable energy power generation represented by wind power and photovoltaic power in the power system has continued to rise in recent years. Renewable energy is often connected to the power grid through power electronic equipment. Under the current conventional control strategy, its power output is decoupled from the grid frequency and does not have the inertial support capacity of synchronous generators. In this context, system inertia assessment is of vital importance for in-depth research on the dynamic characteristics of system frequency and guiding the access of renewable energy to the power grid.

[0003] Existing invention patents have proposed related methods, such as the invention patent "A method for evaluating system inertia in different regions based on disturbance data" (CN110943451A), which uses easily available measurement parameters to evaluate the inertia level of the power system. However, this method regards the power change caused by large disturbances as the only source of power imbalance in the system, while ignoring the impact of other power generation and load fluctuations in the system before and after the large disturbance, and fails to fully consider the measurement error of frequency data.

[0004] Therefore, a regional power grid inertia assessment method with smaller error is urgently needed. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem of large errors in the prior art and to propose a method for evaluating the inertia of a regional power grid based on synchronized phasor measurement data of disturbance events.

[0006] Technical solution: The present invention discloses a method for evaluating the inertia of a regional power grid based on synchronized phasor measurement, comprising:

[0007] Selecting measurement data representing frequency changes of the regional power system power grid before and after a large disturbance event from the measurement nodes of the synchronized phasor measurement device, and calculating the frequency change rate difference of the regional power grid before and after the large disturbance event;

[0008] The measurement data of the synchronous phasor measurement device is converted from digital to analog to obtain a fitting curve of the frequency deviation; different values ​​of the fitting curve parameters are traversed, and the frequency curve is fitted under different parameter combinations. The optimal parameter combination is selected to estimate the inertia of the regional power grid.

[0009] Furthermore, the measurement data representing the frequency change of the regional power system power grid before and after the large disturbance event is frequency measurement data without obvious peaks and burrs before and after the large disturbance event.

[0010] Furthermore, the frequency change rate of the regional power grid is expressed as:

[0011]

[0012] Where H represents the inertia of the regional power grid, D represents the load damping coefficient of the regional power grid, Δf(t) represents the change of the frequency deviation of the regional power grid with time t, and ΔP l (t) represents the change of net load active power of regional power grid with time t.

[0013] Furthermore, the net load active power ΔP of the regional power grid l (t) can be divided into active power mutation ΔP caused by large disturbance l1 (t) and other active unbalanced quantities ΔP in the system when a large disturbance occurs l2 (t), as follows:

[0014] ΔP l (t) = ΔP l1 (t)+ΔP l2 (t)

[0015] The active power mutation ΔP caused by the large disturbance l1 (t) satisfies the following formula:

[0016]

[0017]

[0018] When the large disturbance occurs, other active unbalanced quantities ΔP in the system l2 (t) satisfies the following formula:

[0019]

[0020] Among them, t0 is the time when the large disturbance occurs, and They are the moments before and after t0 respectively, and L is the amplitude of active power mutation caused by large disturbance.

[0021] Furthermore, at the moment before and after the large disturbance occurs, and The system frequency deviation satisfies the following formula:

[0022]

[0023] The frequency change rate before a large disturbance in the regional power grid occurs is expressed as:

[0024]

[0025] The frequency change rate after a large disturbance in the regional power grid is expressed as:

[0026]

[0027] Taking the difference between the above two equations, we get:

[0028]

[0029] Furthermore, the measurement data of the synchronized phasor measurement device is converted into digital-to-analog format, a time interval is selected near the time when the frequency curve has an obvious turning point, and the disturbance occurrence time is tested point by point with a certain step length. Each possible disturbance occurrence time t is selected. k , taking the frequency deviation measurement points within a short period of time before and after as samples, polynomial fitting is performed respectively, and the fitting result of the fitting curve of the frequency deviation is expressed as follows:

[0030]

[0031]

[0032] Where Δf - (t), Δf + (t) are respectively the time t k The frequency fitting polynomials before and after, is time t k The parameters of the front and back polynomials are selected based on the minimum sum of squares of the residuals, Δt - , Δt + is time t k The length of the front and back fitting intervals, o - , o + is time t k The order of the front and back fitting polynomials.

[0033] Furthermore, the optimal parameter combination is selected, and the selected parameter combination must meet the following conditions in sequence:

[0034] Condition 1:

[0035]

[0036] Where δ is a preset constant;

[0037] Condition 2:

[0038] min[Δf - (t k )-Δf + (t k )]

[0039] Select the parameter combination with the smallest difference among those that meet condition 1.

[0040] Furthermore, after traversing different values ​​of the parameters of the fitting curve, the time t0 of the occurrence of the large disturbance is obtained as t in the optimal parameter combination. k , and the polynomial fitting curve Δf of the system frequency before and after the disturbance - (t), Δf + (t).

[0041] Furthermore, the regional power grid inertia is estimated, and the regional power grid inertia H is expressed as:

[0042]

[0043] Estimation based on the system frequency fitting curve before and after the disturbance System frequency change rate at the moment, estimated value of regional power grid inertia It is expressed as:

[0044]

[0045] The present invention also discloses a regional power grid inertia assessment system based on synchronized phasor measurement, comprising:

[0046] A sampling module is used to select measurement data representing the frequency change of the regional power system power grid before and after the large disturbance event from the measurement nodes of the synchronous phasor measurement device, and calculate the frequency change rate difference before and after the large disturbance event of the regional power grid;

[0047] A digital-to-analog conversion module is used to perform digital-to-analog conversion on the measurement data of the synchronized phasor measurement device to obtain a fitting curve of the frequency deviation;

[0048] The evaluation module is used to traverse different values ​​of the fitting curve parameters, perform frequency curve fitting under different parameter combinations, select the optimal parameter combination, and estimate the inertia of the regional power grid.

[0049] Beneficial effects: The present invention takes into account the digital quantity characteristics of the actual measurement data of the synchronous phasor measurement device in the real system, and uses a polynomial fitting method to convert the digital quantity into an analog quantity, which helps to more accurately describe the frequency response of the system during large disturbances and improve the accuracy of the time location of large disturbances. The present invention comprehensively considers the power mutation caused by large disturbances and other active unbalanced quantities that may exist in the system when large disturbances occur, and filters out the influence of other unmeasurable active power disturbances on the system frequency except for the active power changes caused by measurable large disturbances, thereby improving the accuracy of inertia evaluation. In summary, the present invention discloses a method for evaluating the inertia of a regional power grid with smaller errors than the prior art. DETAILED DESCRIPTION

[0050] The present invention is further explained below in conjunction with specific implementation methods. It should be understood that the following specific implementation methods 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.

[0051] The present invention discloses a method and system for evaluating inertia of a regional power grid based on synchronized phasor measurement. The method involved in the present invention will be described in detail below in combination with specific implementation steps.

[0052] 1) Select representative data. In the Phasor Measurement Unit (PMU) measurement nodes near the location where the large disturbance event occurs, select frequency measurement data without obvious spikes, glitches and other abnormal values ​​before and after the large disturbance event to represent the frequency changes of the regional power system before and after the large disturbance.

[0053] 2) Analyze the impact of power mutation caused by large disturbance on the system frequency change rate. The specific steps are as follows:

[0054] 2-1) The frequency change rate of the regional power grid can be expressed as follows:

[0055]

[0056] Where H represents the inertia of the regional power grid, D represents the load damping coefficient of the regional power grid, Δf(t) represents the change of the frequency deviation of the regional power grid with time t, and ΔP l (t) represents the change of net load active power of regional power grid with time t.

[0057] 2-2) Regional power grid net load active power ΔP l (t) can be divided into active power mutation ΔP caused by large disturbance l1 (t) and other active unbalanced quantities ΔP in the system when a large disturbance occurs l2 (t), as follows:

[0058] ΔP l (t) = ΔP l1 (t)+ΔP l2 (t)

[0059] Among them, ΔP l1 (t) is usually caused by faults such as unit tripping and DC blocking, and presents a step-by-step change. Therefore, ΔP l1 (t) satisfies the following formula:

[0060]

[0061]

[0062] Among them, t0 is the time when the large disturbance occurs, and are the moments before and after t0 respectively, and L is the amplitude of the active power mutation caused by a large disturbance, such as the output active power before the unit trips, or the input or output active power before the DC line is locked, and its amplitude is easy to obtain.

[0063] ΔP l2 (t) is usually caused by load changes, unit participation in frequency regulation, etc. This part of the disturbance is difficult to measure, but the probability of a large amplitude mutation is small. Therefore, it can be assumed that other active unbalanced quantities ΔP in the system at the time of the large disturbance l2 (t) If no mutation occurs, the moment before and after the large disturbance occurs t0 and ΔP l2 (t) satisfies the following formula:

[0064]

[0065] 2-3) Since the frequency in the power system changes continuously, the frequency of the power system changes continuously in the instant before and after the large disturbance occurs. and The system frequency deviation satisfies the following formula:

[0066]

[0067] 2-4) In the moments before and after the large disturbance occurs t0 and The frequency change rate of the regional power grid can be expressed as:

[0068]

[0069]

[0070] Subtracting the above two equations yields:

[0071]

[0072] The above formula shows that the impact of the active power mutation caused by a large disturbance on the system frequency change rate is manifested as a sudden change in the frequency change rate.

[0073] 3) Convert the PMU frequency measurement results selected in step 1) into analog quantities, and locate the time when the large disturbance occurs based on the analysis results in step 2). The specific steps are as follows:

[0074] 3-1) The PMU frequency measurement result is a digital quantity with discrete time and amplitude. Direct linear interpolation of the sampling points will result in a step waveform, which cannot accurately calculate the frequency change rate. Therefore, the PMU measurement result needs to be converted from digital to analog. The approximate time when a large disturbance occurs is usually easy to obtain, but the accurate assessment of inertia requires precise positioning of the time when the large disturbance occurs. From step 2-4), it can be seen that the impact of the power mutation caused by a large disturbance on the system frequency change rate is manifested as a sudden change in the frequency change rate, that is, the frequency curve will turn at the moment after the large disturbance occurs. Therefore, based on the PMU frequency measurement results for a period of time before and after the large disturbance occurs, a time interval can be selected near the time when the frequency curve has an obvious turning point, and the time of the disturbance occurrence can be tested point by point with a certain step size, such as 0.02 seconds.

[0075] Each possible disturbance occurrence time t is selected k , taking the frequency deviation measurement points within a short period of time before and after as samples, polynomial fitting is performed to obtain the fitting curve of the frequency deviation, thereby realizing the conversion from digital quantity to analog quantity. The fitting result is expressed as the following formula:

[0076]

[0077]

[0078] Where Δf - (t), Δf + (t) are respectively the time t k The frequency fitting polynomials before and after, is time t k The parameters of the front and back polynomials can be selected based on the minimum sum of squares of the residuals, Δt - , Δt + is time t k The length of the fitting interval before and after, such as 1 to 10 seconds, o - , o + is time t k The order of the front and back fitting polynomials, i is one of the orders of the fitting polynomials. For example, if the single-order step size is 0.02 seconds, the total order in the 1-second interval is 50, and i is one of the orders.

[0079] 3-2) Follow step 3-1) to adjust the parameter t k , o - , o + traverse different values ​​of t k The traversal interval selection method is as shown in 3-1), o - , o +It can be selected between 1 and 5. Too high an order may lead to overfitting of the curve. Perform frequency curve fitting under different parameter combinations and select the optimal parameter combination based on the following criteria:

[0080] 3-2-1) At the moment of a large disturbance, the absolute value of the system frequency change rate should be the largest, so a parameter combination that satisfies condition 1 should be selected, and condition 1 is expressed as follows:

[0081]

[0082] Here, δ is selected to be a very small value, such as 0.02 seconds.

[0083] 3-2-2) Ideally, the two fitting curves are k The values ​​at the locations should be the same, so |Δf should be selected under the premise of satisfying condition 1 in 3-2-1). - (t k )-Δf + (t k )|The smallest parameter combination, that is, condition 2 is expressed as:

[0084] min[Δf - (t k )-Δf + (t k )]

[0085] 3-3) After completing the traversal described in 3-2), the time t0 of the occurrence of the large disturbance is obtained as t in the optimal parameter combination. k , and the polynomial fitting curve Δf of the system frequency before and after the disturbance - (t), Δf + (t).

[0086] 4) According to the large disturbance occurrence time obtained in step 3) and the system frequency fitting curve before and after the disturbance, the inertia of the regional power grid is estimated.

[0087] 4-1) According to 2-4), the regional power grid inertia H can be expressed as:

[0088]

[0089] 4-2) Estimation based on the system frequency fitting curve before and after the disturbance The estimated value of the regional power grid inertia is As follows:

[0090]

[0091] The present invention estimates the inertia of the regional power grid by only using the power mutation amplitude caused by large disturbances and the PMU frequency measurement results. The required data is less and easy to obtain, so it has strong practicability in actual systems.

[0092] The present invention also discloses a regional power grid inertia assessment system based on synchronized phasor measurement data, comprising:

[0093] A sampling module is used to select measurement data representing the frequency change of the regional power system power grid before and after the large disturbance event from the measurement nodes of the synchronous phasor measurement device, and calculate the frequency change rate difference before and after the large disturbance event of the regional power grid;

[0094] A digital-to-analog conversion module is used to perform digital-to-analog conversion on the measurement data of the synchronized phasor measurement device to obtain a fitting curve of the frequency deviation;

[0095] The evaluation module is used to traverse different values ​​of the fitting curve parameters, perform frequency curve fitting under different parameter combinations, select the optimal parameter combination, and estimate the inertia of the regional power grid.

[0096] The present invention comprehensively considers the active power mutation caused by a large disturbance and other active unbalanced quantities that may exist in the system when the large disturbance occurs, and adopts a difference method to extract the frequency change rate component corresponding to the power mutation caused by the large disturbance; for the PMU frequency measurement data before and after the large disturbance, a polynomial fitting method is adopted to convert the digital quantity into an analog quantity, and the time when the disturbance occurs is accurately located; according to the active power mutation amplitude caused by the large disturbance, the time when the large disturbance occurs and the frequency fitting result, the inertia assessment result of the regional power grid is calculated.

Claims

1. A method for evaluating inertia of a regional power grid based on synchronized phasor measurement, characterized in that: include: Selecting measurement data representing frequency changes of the regional power system power grid before and after the large disturbance event from the measurement nodes of the synchronized phasor measurement device, and calculating the frequency change rate difference of the regional power grid before and after the large disturbance event; Perform digital-to-analog conversion on the measurement data of the synchronous phasor measurement device to obtain a fitting curve of the frequency deviation; traverse different values ​​of the fitting curve parameters, perform frequency curve fitting under different parameter combinations, and select the optimal parameter combination; The inertia of the regional power grid is estimated according to the frequency change rate difference before and after the large disturbance event and the optimal parameter combination to obtain an estimated value of the inertia of the regional power grid.

2. The method for evaluating the inertia of a regional power grid according to claim 1, characterized in that: The measurement data representing the frequency change of the regional power system power grid before and after the large disturbance event is the frequency measurement data without abnormal values ​​before and after the large disturbance event.

3. The method for evaluating the inertia of a regional power grid according to claim 1 or 2, characterized in that: The frequency change rate of the regional power grid is expressed as: Where H represents the inertia of the regional power grid, D represents the load damping coefficient of the regional power grid, Δf(t) represents the change of the frequency deviation of the regional power grid with time t, and ΔP l (t) represents the change of net load active power of regional power grid with time t.

4. The method for evaluating the inertia of a regional power grid according to claim 3, characterized in that: The net load active power of the regional power grid ΔP l (t) can be divided into active power mutation ΔP caused by large disturbance l1 (t) and other active unbalanced quantities ΔP in the system when a large disturbance occurs l2 (t), as follows: ΔP l (t)=ΔP l1 (t)+ΔP l2 (t) The large disturbance causes a sudden change in active power ΔP l1 (t) satisfies the following formula: When the large disturbance occurs, other active unbalanced quantities ΔP in the system l2 (t) satisfies the following formula: Among them, t0 is the time when the large disturbance occurs, and They are the moments before and after t0 respectively, and L is the amplitude of active power mutation caused by large disturbance.

5. The method for evaluating the inertia of a regional power grid according to claim 4, characterized in that: In the moments before and after the large disturbance occurs, and The system frequency deviation satisfies the following formula: The frequency change rate before a large disturbance in the regional power grid occurs is expressed as: The frequency change rate after a large disturbance in the regional power grid is expressed as: Taking the difference between the above two equations, we get:

6. The method for evaluating the inertia of a regional power grid according to claim 5, characterized in that: The measurement data of the synchronous phasor measurement device is converted into digital-to-analog format, a time interval is selected near the time when the frequency curve has an obvious turning point, and the disturbance occurrence time is tested point by point with a certain step length. Each possible disturbance occurrence time t is selected. k , taking the frequency deviation measurement points within a short period of time before and after as samples, polynomial fitting is performed respectively, and the fitting result of the fitting curve of the frequency deviation is expressed as follows: Where Δf - (t), Δf + (t) are respectively the time t k The frequency fitting polynomials before and after, is time t k The parameters of the front and back polynomials are selected based on the minimum sum of squares of the residuals, Δt - , Δt + is time t k The length of the front and back fitting intervals, o - , o + is time t k The order of the front and back fitting polynomials.

7. The method for evaluating the inertia of a regional power grid according to claim 6, characterized in that: The optimal parameter combination is selected, and the selected parameter combination must meet the following conditions in sequence: Condition 1: Where δ is a preset constant; Condition 2: min[Δf - (t k )-Δf + (t k )] Select the parameter combination with the smallest difference among those that meet condition 1.

8. The method for evaluating regional power grid inertia according to claim 7, characterized in that: After traversing different values ​​of the parameters of the fitting curve, the time t0 of the occurrence of the large disturbance is obtained as t in the optimal parameter combination. k , and the polynomial fitting curve Δf of the system frequency before and after the disturbance - (t), Δf + (t).

9. The method for evaluating the inertia of a regional power grid according to claim 5 or 8, characterized in that: The regional power grid inertia is estimated, and the regional power grid inertia H is expressed as: Estimation based on the system frequency fitting curve before and after the disturbance System frequency change rate at the moment, estimated value of regional power grid inertia It is expressed as:

10. A regional power grid inertia assessment system based on synchronized phasor measurement, characterized in that: include: A sampling module is used to select measurement data representing the frequency change of the regional power system power grid before and after the large disturbance event from the measurement nodes of the synchronous phasor measurement device, and calculate the frequency change rate difference before and after the large disturbance event of the regional power grid; A digital-to-analog conversion module is used to perform digital-to-analog conversion on the measurement data of the synchronized phasor measurement device to obtain a fitting curve of the frequency deviation; Traverse different values ​​of fitting curve parameters, perform frequency curve fitting under different parameter combinations, and select the optimal parameter combination; Evaluation module to estimate the inertia of the regional power grid.

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