Method and system for evaluating severity of low-frequency oscillation of new energy direct current sending-out system

Abstract

The present application relates to the technical field of power system stability analysis, and is a low-frequency oscillation severity evaluation method and system for a new energy direct current sending system, which comprises the following steps: calculating correlation factors affecting the low-frequency oscillation severity of the new energy direct current sending system; determining the weights between the correlation factors based on stability simulation analysis; calculating a comprehensive evaluation index reflecting the low-frequency oscillation severity of the new energy direct current sending system based on the correlation factors and the weights between the correlation factors; and obtaining the threshold value of the comprehensive evaluation index based on data simulation driving. The present application can directly evaluate the possibility and severity of low-frequency oscillation of the system by using system steady-state operation state data such as new energy power generation output, direct current sending power and operating voltage, and compared with the traditional low-frequency oscillation evaluation method, the present application does not need to perform transient simulation or stability analysis each time, has small calculation amount and strong operability, and has guiding significance for evaluating the stability of the new energy direct current sending system.

Description

Technical Field

[0001] This invention relates to the field of power system stability analysis technology, and in particular to a method and system for assessing the severity of low-frequency oscillations in a new energy DC transmission system. Background Technology

[0002] Low-frequency oscillations are prone to occur in power systems transmitting new energy via DC, posing a challenge to the safe and stable operation of the system. Traditional methods for assessing the severity of low-frequency oscillations require evaluation based on information such as the frequency and amplitude of the oscillation waveform after monitoring the fault waveform, which falls into the category of post-assessment; or they require transient stability simulation analysis for each instance, which is computationally complex. However, the operating state of new energy DC transmission systems is time-varying and has a significant impact on the probability and severity of low-frequency oscillations. Therefore, directly assessing the probability and severity of low-frequency oscillations through highly correlated operating states has become a critical problem that urgently needs to be solved.

[0003] To address the aforementioned issues, this invention provides a method for assessing the severity of low-frequency oscillations in a DC renewable energy transmission system. By analyzing the correlation factors affecting low-frequency oscillations, determining the weights of these factors, obtaining a comprehensive evaluation index, and setting a threshold for the comprehensive evaluation index, the severity of low-frequency oscillations in the renewable energy DC transmission system is assessed based on this threshold, providing a reference for the safe operation and risk warning of the power system. Summary of the Invention

[0004] This invention provides a method and system for assessing the severity of low-frequency oscillations in a new energy DC transmission system, overcoming the shortcomings of the prior art. It effectively solves the problems of traditional low-frequency oscillation assessment methods requiring transient simulation or stability analysis each time, which involve large computational loads and difficult operation.

[0005] To address the above problems, one of the technical solutions of this invention is achieved through the following method: a method for assessing the severity of low-frequency oscillations in a new energy DC transmission system, comprising the following steps: Calculate the correlation factors affecting the severity of low-frequency oscillations in new energy DC transmission systems; Based on stability simulation analysis, the weights among the correlation factors are determined. Based on the correlation factors and the weights between them, a comprehensive evaluation index reflecting the severity of low-frequency oscillations in the new energy DC transmission system is calculated. Based on data simulation, the threshold of the comprehensive evaluation index is obtained; The severity of low-frequency oscillations in the new energy DC transmission system under different operating conditions is assessed based on threshold values.

[0006] The factors affecting the severity of low-frequency oscillations in the above-mentioned new energy DC transmission system include: The ratio of the total output of all renewable energy power plants in the renewable DC transmission system to the total output of all types of power sources is calculated and denoted as the correlation factor. I 1; The ratio of the total DC power transmitted to the total rated DC power in a new energy DC transmission system is calculated and denoted as the correlation factor. I 2; Taking the difference between the highest and lowest steady-state operating voltages of the new energy DC transmission system as the benchmark value, the average per-unit value of the difference between the operating voltage and the lowest operating voltage of all new energy power stations in the system is calculated and denoted as the correlation factor. I 3.

[0007] The above-mentioned stability simulation analysis determines the weights between correlation factors, including: While keeping the other two correlation factors at 0.5 and constant, calculate the change in the system's minimum damping ratio when the third correlation factor changes from 0.2 to 0.8; determine the weights of the three correlation factors by the proportion of the changes, denoted as . ; (1) In the formula, Correlation factors I 1, I 2, I 3. Change in damping ratio before and after the change.

[0008] The above-mentioned comprehensive evaluation index, based on correlation factors and their weights, reflects the severity of low-frequency oscillations in the new energy DC transmission system; including: The comprehensive evaluation index is obtained by weighting three related factors, denoted as . I : (2).

[0009] The thresholds for obtaining the comprehensive evaluation indicators based on data simulation include: Perform M small-disturbance stability simulations, randomly changing the values ​​of three correlation factors in each simulation to obtain M pairs of minimum damping ratios and comprehensive evaluation indices, denoted as... to ; By performing correlation fitting on M array pairs, the mapping relationship between them can be obtained. ; Based on the minimum damping ratio threshold requirements of 0.03, 0, and -0.01, the low threshold of the comprehensive evaluation index is obtained by substituting these values ​​into the mapping formula. Medium threshold and high threshold .

[0010] The above-mentioned threshold-based assessment of the severity of low-frequency oscillations in new energy DC transmission systems under different operating conditions includes: When the comprehensive evaluation index is ≥ When the system is deemed unstable, the low-frequency oscillation is severe and the risk level is red. when ≤Comprehensive evaluation index< When the system is deemed unstable, the low-frequency oscillation severity is low, and the low-frequency oscillation risk level is orange. when ≤Comprehensive evaluation index< When the system is in a state of reduced amplitude oscillation, damping needs to be increased, and the risk level of low-frequency oscillation is yellow. When the comprehensive evaluation index < At that time, the system was deemed stable, and the low-frequency oscillation risk level was green.

[0011] The second technical solution of this invention is achieved through the following method: a low-frequency oscillation severity assessment system for a new energy DC transmission system, comprising: The correlation factor calculation unit calculates the correlation factors that affect the severity of low-frequency oscillations in the new energy DC transmission system; The weight determination unit determines the weights between related factors based on stability simulation analysis. The comprehensive evaluation index unit calculates a comprehensive evaluation index reflecting the severity of low-frequency oscillations in the new energy DC transmission system based on the correlation factors and the weights between the correlation factors. The threshold acquisition unit, driven by data simulation, obtains the threshold of the comprehensive evaluation index. The severity assessment unit evaluates the severity of low-frequency oscillations in the new energy DC transmission system under different operating conditions based on a threshold.

[0012] Compared with the prior art, the present invention has the following advantages: This invention can analyze the steady-state operating data of the system, such as the output of new energy power generation, DC transmission power, and operating voltage, and determine the weights of the factors affecting low-frequency oscillations to obtain a comprehensive evaluation index. Based on this comprehensive evaluation index threshold, the severity of low-frequency oscillations in the new energy DC transmission system can be assessed. This directly evaluates the probability and severity of low-frequency oscillations in the system. Compared with traditional low-frequency oscillation assessment methods, it does not require transient simulation or stability analysis for each instance, has a smaller computational load, and is highly operable. This method has guiding significance for assessing the stability of new energy DC transmission systems. Attached Figure Description

[0013] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0014] Figure 1 This is a flowchart of the method in Embodiment 1 of the present invention.

[0015] Figure 2 This is a system block diagram of Embodiment 2 of the present invention.

[0016] Figure 3 This is a schematic diagram of the simulation model of the new energy DC transmission system in Embodiment 3 of the present invention. Detailed Implementation

[0017] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0018] Example 1: As Figure 1 As shown in the figure, this invention discloses a method for assessing the severity of low-frequency oscillations in a new energy DC transmission system, comprising the following steps: S101, Calculate the correlation factors affecting the severity of low-frequency oscillations in the new energy DC transmission system; S102, Based on stability simulation analysis, determine the weights between the correlation factors; S103, based on the correlation factors and the weights between the correlation factors, calculates a comprehensive evaluation index that reflects the severity of low-frequency oscillations in the new energy DC transmission system; S104, based on data simulation, obtains the threshold of the comprehensive evaluation index; S105, based on threshold judgment, assess the severity of low-frequency oscillations in the new energy DC transmission system under different operating conditions.

[0019] In step S101 above, the correlation factors affecting the severity of low-frequency oscillations in the new energy DC transmission system are calculated, including: The ratio of the total output of all renewable energy power plants in the renewable DC transmission system to the total output of all types of power sources is calculated and denoted as the correlation factor. I 1; The ratio of the total DC power transmitted to the total rated DC power in a new energy DC transmission system is calculated and denoted as the correlation factor. I 2; Taking the difference between the highest and lowest steady-state operating voltages of the new energy DC transmission system as the benchmark value, the average per-unit value of the difference between the operating voltage and the lowest operating voltage of all new energy power stations in the system is calculated and denoted as the correlation factor. I 3.

[0020] In step S102 above, the weights between correlation factors are determined based on stability simulation analysis; including: While keeping the other two correlation factors at 0.5 and constant, calculate the change in the system's minimum damping ratio when the third correlation factor changes from 0.2 to 0.8; determine the weights of the three correlation factors by the proportion of the changes, denoted as . ; (1) In the formula, Correlation factors I 1, I 2, I 3. Change in damping ratio before and after the change.

[0021] In step S103 above, a comprehensive evaluation index reflecting the severity of low-frequency oscillations in the new energy DC transmission system is calculated based on the correlation factors and their weights; including: The comprehensive evaluation index is obtained by weighting three related factors, denoted as . I : (2).

[0022] In step S104 above, based on data simulation, the threshold of the comprehensive evaluation index is obtained, including: Perform M small-disturbance stability simulations, randomly changing the values ​​of three correlation factors in each simulation to obtain M pairs of minimum damping ratios and comprehensive evaluation indices, denoted as... to ; By performing correlation fitting on M array pairs, the mapping relationship between them can be obtained. ; Based on the minimum damping ratio threshold requirements of 0.03, 0, and -0.01, the low threshold of the comprehensive evaluation index is obtained by substituting these values ​​into the mapping formula. Medium threshold and high threshold .

[0023] In step S105 above, based on the threshold judgment, the severity of low-frequency oscillation of the new energy DC transmission system under different operating conditions is evaluated, including: When the comprehensive evaluation index is ≥ When the system is deemed unstable, the low-frequency oscillation is severe and the risk level is red. when ≤Comprehensive evaluation index< When the system is deemed unstable, the low-frequency oscillation severity is low, and the low-frequency oscillation risk level is orange. when ≤Comprehensive evaluation index< When the system is in a state of reduced amplitude oscillation, damping needs to be increased, and the risk level of low-frequency oscillation is yellow. When the comprehensive evaluation index < At that time, the system was deemed stable, and the low-frequency oscillation risk level was green.

[0024] This invention can analyze the steady-state operating data of the system, such as the output of new energy power generation, DC transmission power, and operating voltage, and determine the weights of the factors affecting low-frequency oscillations to obtain a comprehensive evaluation index. Based on this comprehensive evaluation index threshold, the severity of low-frequency oscillations in the new energy DC transmission system can be assessed. This directly evaluates the probability and severity of low-frequency oscillations in the system. Compared with traditional low-frequency oscillation assessment methods, it does not require transient simulation or stability analysis for each instance, has a smaller computational load, and is highly operable. This method has guiding significance for assessing the stability of new energy DC transmission systems.

[0025] Example 2: As Figure 2 As shown in the figure, an embodiment of the present invention discloses a low-frequency oscillation severity assessment system for a new energy DC transmission system, comprising: The correlation factor calculation unit calculates the correlation factors that affect the severity of low-frequency oscillations in the new energy DC transmission system; The weight determination unit determines the weights between related factors based on stability simulation analysis. The comprehensive evaluation index unit calculates a comprehensive evaluation index reflecting the severity of low-frequency oscillations in the new energy DC transmission system based on the correlation factors and the weights between the correlation factors. The threshold acquisition unit, driven by data simulation, obtains the threshold of the comprehensive evaluation index. The severity assessment unit evaluates the severity of low-frequency oscillations in the new energy DC transmission system under different operating conditions based on a threshold.

[0026] Example 3: This example is based on the PSASP simulation software. The simulation model of the new energy DC transmission system is as follows: Figure 3 As shown, there are a total of 5 power sources (3 new energy power plants and 1 thermal power plant), and the relevant parameters are shown in Table 1. The rated transmission capacity of one DC transmission channel is 500MW. The steady-state maximum and minimum voltages are 0.95 and 1.05 pu, respectively.

[0027] Table 1 Parameter Table Perform M=10 simulation calculations, with the calculation parameters randomly set as shown in Table 2: Table 2 Calculation Parameter Settings (Power unit is MW, voltage is per unit value) Based on Equations 1, 2, and 3 from Case 1, the correlation factors for the 10th order are calculated as shown in Table 3: Table 3 Results of Correlation Factor Calculation Based on small-disturbance stability simulation analysis, the weights among the correlation factors are determined. While keeping the other two correlation factors constant at 0.5, the change in the system's minimum damping ratio is calculated when the third correlation factor changes from 0.2 to 0.8. The weights of the three correlation factors are determined by the proportion of these changes, and the results are obtained according to Equation 6. , , .

[0028] Ten small-disturbance stability simulations were performed, with parameters as shown in Table 2 remaining constant. Ten array pairs between the minimum damping ratio and the comprehensive evaluation index were obtained, denoted as... to The statistical results are shown in Table 4.

[0029] Table 4 shows the data and calculation results. Correlation fitting was performed on the 10 array pairs to obtain the mapping relationship between them: I = -16.489* D 2 -6.120* D +0.658, Based on the minimum damping ratio threshold requirements of 0.03, 0, and -0.01, the low threshold of the comprehensive evaluation index is obtained by substituting these values ​​into the mapping formula. =0.460, middle threshold =0.658 and high threshold =0.718.

[0030] The actual operating conditions of the new energy DC transmission system to be evaluated are shown in Table 5: Table 5 Actual Operating Conditions Calculate three correlation factors, then calculate their weights and the comprehensive index to obtain the comprehensive index. I =0.637.

[0031] because( =0.460) ≤ Comprehensive index ( I =0.637) < ( =0.658), therefore it is determined to be a system-wide reduced-amplitude oscillation, which requires increasing damping, and the risk level of low-frequency oscillation is yellow.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the pending claims.

Claims

1. A method for assessing the severity of low-frequency oscillations in a new energy DC transmission system, characterized in that, Includes the following steps: Calculate the correlation factors affecting the severity of low-frequency oscillations in new energy DC transmission systems; Based on stability simulation analysis, the weights among the correlation factors are determined. Based on the correlation factors and the weights between them, a comprehensive evaluation index reflecting the severity of low-frequency oscillations in the new energy DC transmission system is calculated. Based on data simulation, the threshold of the comprehensive evaluation index is obtained; The severity of low-frequency oscillations in the new energy DC transmission system under different operating conditions is assessed based on threshold values.

2. The method for assessing the severity of low-frequency oscillations in a new energy DC transmission system according to claim 1, characterized in that, The factors affecting the severity of low-frequency oscillations in the new energy DC transmission system include: The ratio of the total output of all renewable energy power plants in the renewable DC transmission system to the total output of all types of power sources is calculated and denoted as the correlation factor. I 1; The ratio of the total DC power transmitted to the total rated DC power in a new energy DC transmission system is calculated and denoted as the correlation factor. I 2; Taking the difference between the highest and lowest steady-state operating voltages of the new energy DC transmission system as the benchmark value, the average per-unit value of the difference between the operating voltage and the lowest operating voltage of all new energy power stations in the system is calculated and denoted as the correlation factor. I 3.

3. The method for assessing the severity of low-frequency oscillations in a new energy DC transmission system according to claim 2, characterized in that, The determination of the weights between correlation factors based on stability simulation analysis includes: While keeping the other two correlation factors at 0.5 and constant, calculate the change in the system's minimum damping ratio when the third correlation factor changes from 0.2 to 0.8; determine the weights of the three correlation factors by the proportion of the changes, denoted as . ; （1） In the formula, Correlation factors I 1, I 2, I 3. Change in damping ratio before and after the change.

4. The method for assessing the severity of low-frequency oscillations in a new energy DC transmission system according to claim 3, characterized in that, The comprehensive evaluation index, based on correlation factors and their weights, reflects the severity of low-frequency oscillations in the new energy DC transmission system; including: The comprehensive evaluation index is obtained by weighting three related factors, denoted as . I : （2）。 5. The method for assessing the severity of low-frequency oscillations in a new energy DC transmission system according to claim 4, characterized in that, The threshold for obtaining the comprehensive evaluation index based on data simulation includes: Perform M small-disturbance stability simulations, randomly changing the values ​​of three correlation factors in each simulation to obtain M pairs of minimum damping ratios and comprehensive evaluation indices, denoted as... to ; By performing correlation fitting on M array pairs, the mapping relationship between them can be obtained. ; Based on the minimum damping ratio threshold requirements of 0.03, 0, and -0.01, the low threshold of the comprehensive evaluation index is obtained by substituting these values ​​into the mapping formula. Medium threshold and high threshold .

6. The method for assessing the severity of low-frequency oscillations in a new energy DC transmission system according to claim 5, characterized in that, The assessment of the severity of low-frequency oscillations in the renewable energy DC transmission system under different operating conditions, based on threshold judgment, includes: When the comprehensive evaluation index is ≥ When the system is deemed unstable, the low-frequency oscillation is severe and the risk level is red. when ≤Comprehensive evaluation index< When the system is deemed unstable, the low-frequency oscillation severity is low, and the low-frequency oscillation risk level is orange. when ≤Comprehensive evaluation index< When the system is in a state of reduced amplitude oscillation, damping needs to be increased, and the risk level of low-frequency oscillation is yellow. When the comprehensive evaluation index < At that time, the system was deemed stable, and the low-frequency oscillation risk level was green.

7. A low-frequency oscillation severity assessment system for a new energy DC transmission system, characterized in that, include: The correlation factor calculation unit calculates the correlation factors that affect the severity of low-frequency oscillations in the new energy DC transmission system; The weight determination unit determines the weights between related factors based on stability simulation analysis. The comprehensive evaluation index unit calculates a comprehensive evaluation index reflecting the severity of low-frequency oscillations in the new energy DC transmission system based on the correlation factors and the weights between the correlation factors. The threshold acquisition unit, driven by data simulation, obtains the threshold of the comprehensive evaluation index. The severity assessment unit evaluates the severity of low-frequency oscillations in the new energy DC transmission system under different operating conditions based on a threshold.

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