A direct current landing point optimization method considering sending and receiving end fault transfer

Abstract

The application relates to a DC landing point optimization method considering fault transmission of sending and receiving ends, comprising the following steps: constructing a fault transmission process of the sending and receiving ends considering AC / DC superposition interaction; constructing a landing point optimization index set considering fault transmission of the sending and receiving ends of multiple DC systems based on the transmission process; and optimizing a DC landing point from the landing point optimization index set based on a DC landing point optimization method improved based on a Vague set satisfaction limit. Compared with the prior art, the application has the advantages of effectively relieving the fault transmission problem of the sending and receiving ends and the like.

Description

Technical Field

[0001] This invention relates to the field of DC construction planning technology for multi-infeed power grids, and in particular to a method for optimizing DC landing points that takes into account fault propagation at the sending and receiving ends. Background Technology

[0002] In a DC power system, the DC current is transmitted through transmission lines or cables to the terminal or load. In a DC transmission system, DC current is delivered from the power plant or converter station to a specific terminal via DC transmission lines or cables to supply the load at that terminal. This terminal location is the DC point of connection. The DC point of connection typically uses specialized equipment, such as converter stations or DC substations, to convert alternating current (AC) to DC and then transmit it to the designated location via DC transmission lines or cables. In DC power systems, DC transmission has lower transmission losses and higher transmission capacity, thus enabling long-distance, high-power transmission. The DC point of connection is the final access point of the DC transmission system.

[0003] Due to spatial differences in energy and load distribution, large-scale long-distance energy transmission has developed rapidly to meet the demands of load growth, resulting in a hybrid AC / DC transmission pattern. The increasing output of new energy sources in the west and the continuous growth rate of load in the east have led to a dense concentration of DC landing points in both the sending-end energy bases and the receiving-end load-dense areas, affecting safe and stable operation.

[0004] Patent applications CN103617556A and CN108631290A both disclose a DC landing point selection method based on the receiving end. With the increasing number of high-voltage direct current (HVDC) lines in operation, the problem of fault transmission between the sending and receiving ends of DC lines has become apparent, seriously affecting the safe and stable operation of the power grids at both ends. The aforementioned patents are based on one-sided screening, therefore existing DC planning studies lack consideration for the problem of fault transmission between the sending and receiving ends. Summary of the Invention

[0005] The purpose of this invention is to provide an optimal DC landing point method that takes into account the transmission of faults at both the transmitting and receiving ends, thus effectively mitigating the transmission of faults at both ends.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for optimizing the DC landing point considering fault propagation at both the sending and receiving ends includes the following steps:

[0008] Construct a fault transmission process at the sending and receiving ends that considers AC / DC superposition and interaction;

[0009] Based on the transmission process, a set of optimal landing point indexes is constructed to consider the fault transmission at the sending and receiving ends of multiple DC systems;

[0010] The DC landing point optimization method based on Vague set satisfaction limit optimizes the DC landing point from the landing point optimization index set.

[0011] Furthermore, the fault transmission at the sending and receiving ends manifests as fluctuations in DC transmission power, which are determined by DC voltage and DC current.

[0012] Furthermore, the process of constructing the landing point optimization index set specifically includes:

[0013] Based on the aforementioned transmission process, we propose an AC / DC superposition interaction factor and an AC / DC short-circuit ratio to reflect the superposition and interaction of AC and DC, as well as an overall indicator and an interference indicator to reflect the planned DC transmission and reception end, in order to characterize the AC / DC superposition and interaction mechanism at the transmission and reception end.

[0014] The degree of fault propagation at the sending and receiving ends is characterized by the near-zone stability coefficient of the sending and receiving ends, the impact energy of multiple DC power, and the frequency of commutation failure pulses.

[0015] Based on the AC / DC superposition interaction mechanism and fault propagation degree of the sending and receiving ends, the fault propagation problem of the sending and receiving ends under AC / DC superposition interaction is evaluated, and the optimal index set of DC landing point is obtained.

[0016] Furthermore, the expression for the AC / DC superposition interaction factor is:

[0017]

[0018]

[0019] Among them, A ADSIFjk The AC / DC superposition interaction factor; k refers to any AC line; ΔU' j To superimpose the impact of an AC line fault k on the DC converter bus voltage j under the superimposed interactive conditions, ΔU jk The direct impact of an AC line fault (k) on the DC converter bus voltage (j); ΔU jik The combined effect of a fault in AC line k on converter bus i, and the subsequent impact of converter bus i on converter bus j, is determined by the multi-feed interaction factor M. MIIFji The value can be obtained from the definition as ΔU jik =ΔU ik ·M MIIFji N represents the set of DC nodes.

[0020] Furthermore, the expression for the AC / DC short-circuit ratio is:

[0021]

[0022] In the formula, A ADSCRk The short-circuit ratio is defined as AC / DC; k represents any AC line; S ac,kP represents the short-circuit capacity of AC line k; k P represents the active power equivalent to all DC power passing through AC line k; dc,i The active power of DC i; A ADSIFik The AC / DC superposition interaction factor for AC line fault k on DC line i.

[0023] Furthermore, the process of constructing the overall performance index of the sending and receiving ends specifically includes:

[0024] Select the AC / DC target node set based on the AC / DC short-circuit ratio;

[0025] The overall index of the sending and receiving ends is constructed by summing and averaging the target node set, and the expression is:

[0026]

[0027] In the formula, I wholeness A represents the overall performance index value for both the sending and receiving ends. ADSCRi Let be the AC / DC short-circuit ratio of the i-th node.

[0028] Furthermore, the expression for the interference index is:

[0029]

[0030] In the formula, I interference A is a disruptive indicator value. ADSCRi0 For, A ADSCRi Let be the AC / DC short-circuit ratio of the i-th node.

[0031] Furthermore, the expression for the near-field stability coefficient of the sending and receiving ends is as follows:

[0032]

[0033] In the formula, S SRNSFS and S SRNSFR These are the near-field stability coefficients at the sending and receiving ends, respectively; ∑P S and ∑P R These represent the total active power output of nearby power plants at both the sending and receiving ends; S Sac,i and S Rac,i These are the short-circuit capacities of the feeder and receiver station busbars, respectively; P Si and P Ri These represent the active power generated by the sending and receiving stations, respectively; Z Sij and Z Rij These are the mutual impedances between the sending and receiving end station's collection busbar and other station collection buses, respectively; Z Sii and Z Rii These are the self-impedances of the station's collection busbars at the sending and receiving ends, respectively; U Si and U RiThese are the voltages of the station's collection bus at the sending and receiving ends, respectively; U Sj and U Rj These are the bus voltages of other stations at the sending and receiving ends, respectively; P Sj and P Rj These represent the active power generated by the j-th power station at both the sending and receiving ends.

[0034] Furthermore, the sum of the multiple DC power surge energies caused by the AC fault is defined as follows:

[0035]

[0036] In the formula, J sum For multi-DC power impact energy, J Si and J Ri N represents the DC power surge energy at the sending and receiving ends, respectively. S and N R These are the DC node sets for the sending and receiving ends, respectively.

[0037] Furthermore, the specific steps for selecting the optimal DC landing point include:

[0038] Establish a target preference matrix based on the aforementioned landing point optimization index set;

[0039] The subjective and objective weight coefficients for each indicator are determined based on the entropy weight method;

[0040] Satisfaction limits were obtained based on the interquartile range method.

[0041] An evaluation function is constructed based on the Vague set, and each landing point is evaluated according to the evaluation function and the satisfaction threshold to optimize the DC landing point at the DC transmitter and receiver. The expression of the evaluation function is as follows:

[0042] e i =(∑w s1 +∑w s2 -∑w o1 -∑w o2 ) / 2

[0043] In the formula, e i Let ∑w be the evaluation function for landing scheme i; s1 and ∑w s2 These represent the upper and lower bounds of the support set weight interval, respectively; ∑w o1 and ∑w o2 These represent the upper and lower limits of the weight range for the opposition set, respectively.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) This invention fully considers the problem of fault transmission between the sending and receiving ends under the superposition and interaction of AC and DC. Starting from the superposition and interaction of AC and DC, it proposes an optimal index set and, based on the obtained index, optimizes the DC landing point of each landing point scheme by Vague set satisfaction, effectively alleviating the problem of fault transmission between the sending and receiving ends from the planning level.

[0046] (2) This invention performs multi-objective decision optimization on the Vague set, effectively avoiding the "long / short board effect" in the traditional weighted method, and improves the satisfaction limit determination method. It proposes a method based on interquartile range to obtain the satisfaction limit, improves the credibility of the satisfaction limit, and avoids the satisfaction being completely affected by subjective factors.

[0047] (3) This invention analyzes the fault transmission process of the sending and receiving ends under the superposition and interaction of AC and DC in a dense landing point system, and proposes the AC / DC superposition interaction factor and AC / DC short-circuit ratio to reflect the impact of planned DC on the integrity and interference of the sending and receiving ends from the perspective of AC nodes; considering the energy stability of the sending and receiving ends near the energy source, it proposes the near-area stability coefficient of the sending and receiving ends to measure the near-area fault risk of the planned DC; based on the time-domain simulation results of the actual power grid model, it proposes the multi-DC power impact energy and the fuzzy index commutation failure pulse frequency to reflect the degree of fault transmission at the sending and receiving ends; for the proposed optimization index, it constructs a DC sending and receiving end landing point optimization method based on Vague set satisfaction limit improvement, which uses support, exclusion and neutral sets to avoid the "long / short board effect" and can include fuzzy indexes in the consideration without distorting the results. Based on the interquartile range, the improvement of the satisfaction limit fills the gap of the optimization method in dealing with threshold-free indexes, making the optimization results more objective and accurate. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0049] Figure 2 This is a schematic diagram of the single-end AC / DC superposition interaction in an embodiment of the present invention, taking the sending end as an example;

[0050] Figure 3 This is a schematic diagram of the fault transmission process at the DC transmitting and receiving ends of the present invention.

[0051] Figure 4 This is a flowchart illustrating the process of obtaining the satisfaction threshold based on the interquartile range in this invention.

[0052] Figure 5 This invention provides a flowchart for selecting the DC landing point to consider fault transmission at both the sending and receiving ends. Detailed Implementation

[0053] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0054] This embodiment provides a method for optimizing the DC landing point considering fault propagation at the sending and receiving ends, such as... Figure 1 As shown, the method includes the following steps:

[0055] Step 1: Analyze the fault transmission process at the sending and receiving ends under the superposition and interaction of AC and DC.

[0056] This step involves analyzing the fault propagation process at the sending and receiving ends, considering the superposition and interaction of AC and DC, and modeling the DC fault propagation at the sending and receiving ends as a dynamic propagation process that includes the superposition and interaction of AC and DC under dense DC landing points and the DC fault propagation at the sending and receiving ends. It fully considers the coupling effect between AC and DC and between the sending and receiving end systems to obtain the key factors affecting the stability of the sending and receiving end power grids.

[0057] The superposition and interaction of AC and DC at dense DC landing points, such as Figure 2 As shown, the analysis takes the impact of an AC fault on the sending end on the DC power supply as an example. An AC fault will affect the rectifier-side converter bus voltage U. L The drop caused the DC transmission active power P to be reduced. dc Instantaneous drop. Due to U L When changes occur, the rectifier-side controller activates to stabilize the DC voltage, thus reducing the reactive power demand Q of the DC system. absorb The rise in reactive power impacts the near-terminal area. When DC transmission lines are densely distributed, this leads to a deterioration of reactive power balance in the near-term area, causing overlapping and interactive fault effects, exacerbating the impact of AC faults on any single DC line, and increasing U... L and P dc Increased instantaneous drop amplitude, DC system recovery time T r Extended. Similarly, when a DC fault occurs in a densely populated system, the AC nodes will also suffer greater negative impacts due to the superimposed interaction, which is more detrimental to the stable operation of the sending and receiving end power grids.

[0058] The transmission of faults at both the sending and receiving ends manifests directly as fluctuations in DC power transmission, which are determined by DC voltage and DC current. Taking a 12-pulse converter as an example, the DC current I... dc The calculation formula is:

[0059]

[0060] In the formula: U dc,R and U dc,I These are the DC voltages across the rectifier and inverter, respectively; R dc N is the equivalent resistance of a DC line. cNumber of converters per pole; U ac,R and U ac,I These represent the AC voltages on the rectifier side and inverter side, respectively; α is the rectifier firing angle; γ is the inverter turn-off angle; U T This refers to the commutation pressure drop of the converter valve. In R... dc and U T When I remains constant dc The size depends on U ac,R U ac,I Changes in α and γ.

[0061] The fault transmission process at the DC transmitting and receiving ends is as follows: Figure 3 As shown. Because AC faults, under the combined effects of superimposed interactions, can cause a significant voltage drop at the local converter station, therefore, when a sending-end fault occurs, U... dc,R It will drop instantaneously due to the DC voltage U across the inverter. dc,I The constant results in DC current I dc This decreases accordingly. Typically, the rectifier side uses a constant current controller (CCC), and the inverter side uses a constant extinction angle controller (CEAC). This is done when a DC current I is detected. dc When the current is reduced, the rectifier side will gradually decrease α to stabilize the DC current I. dc At the same time, the DC voltage U across the inverter was detected. dc,I After reduction, the commutation failure prediction function is activated and α acceleration decreases. If the fault has a high impact on DC, the DC current I... dc After α drops to its minimum value of 5° and continues to decrease, the rectifier side quickly switches to minimum α controller (MαC), while the inverter side switches to CCC to further raise γ to support the DC current I. dc At this point, commutation failure will not occur. However, the drop in DC current and voltage will inevitably lead to a momentary decrease in DC power, causing the fault at the sending end to be transmitted to the receiving end. The greater the voltage drop, the greater the momentary power decrease. If the fault has a significant impact on the rectifier, the rectifier-side converter valve will lose its conducting condition, and the DC voltage U across the rectifier will decrease. dc,R and DC current I dc During the fault, the voltage drops to 0, interrupting DC power transmission. After the fault at the sending end is cleared, the rectifier side switches back to CCC, and the inverter side switches back to CEAC. Voltage and current begin to recover, and the DC system absorbs a large amount of reactive power from the AC grid, causing the converter bus voltage to drop again, further deteriorating the AC / DC system's operating condition. During this process, the risk of commutation failure surges, especially under the superimposed interactive effect of multiple dense DC landing points, which can easily lead to multiple or consecutive commutation failures, exacerbating the severity of the fault propagation at both the sending and receiving ends.

[0062] Step 2: Based on the transmission process, construct a set of optimal landing point indexes that consider the fault transmission at the sending and receiving ends of multiple DC systems.

[0063] To address the problem of fault propagation at the sending and receiving ends under AC / DC superimposed interaction, this invention focuses on the AC / DC superimposed interaction and, based on the AC-DC-AC fault chain, reflects the grid strength of a multi-DC system under fault propagation from the perspective of AC nodes. Furthermore, for the fault propagation process at both the sending and receiving ends, corresponding optimal indicators are proposed for near-field stability at the fault landing point, multi-DC fault response, and planned DC fault propagation.

[0064] like Figure 3 As shown, the AC / DC superposition interaction factor, AC / DC short-circuit ratio, overall performance index of the sending and receiving ends, and interference index are used to characterize the AC / DC superposition interaction mechanism of the sending and receiving ends. The near-zone stability coefficient of the sending and receiving ends, the multi-DC power impact energy, and the commutation failure pulse frequency are used to characterize the fault propagation degree of the sending and receiving ends. The fault propagation problem of the sending and receiving ends under the AC / DC superposition interaction is evaluated in detail, and the optimal index set of DC landing point is obtained.

[0065] 1) AC / DC superposition interaction factor

[0066] In engineering practice, the multi-infeed interaction factor (MIIF) proposed by CIGRE WG B4-41 working group is commonly used to measure the strength of interactions between converter stations in multi-infeed DC transmission systems. However, it is difficult to reflect the interaction effects between AC and DC transmissions. Therefore, considering the superposition interaction between AC and DC transmissions, the AC-DC superposition interaction factor (ADSIF) is proposed, and its definition is as follows:

[0067]

[0068]

[0069] Where k refers to any AC line in the system; ΔU' j To superimpose the impact of an AC line fault k on the DC converter bus voltage j under the superimposed interactive conditions, ΔU jk The direct impact of an AC line fault (k) on the DC converter bus voltage (j); ΔU jik After a fault in AC line k affects converter bus i, the cumulative effect of converter bus i on converter bus j is determined by M. MIIFji The value can be obtained from the definition as ΔU jik =ΔU ik ·M MIIFji N represents the set of DC nodes in the system.

[0070] Taking a multi-infeed receiving-end power grid as an example, the impact of an AC line fault k on other nodes of the system:

[0071]

[0072] Therefore, we can conclude that:

[0073]

[0074] ΔU k =Z kk ·ΔI k (6)

[0075] Substituting equations (1), (3), (5), and (6) into equation (2), we get:

[0076]

[0077] In a single-infeed DC system Z ji =0, at this time A ADSIFjk =A ADIFjk When k specifically refers to the DC converter bus, i.e., when k = i, then A... ADSIFjk =M MIIFji M MIIF and A ADIF Substituting the definition into equation (7) yields its relationship with A. ADSIF The relationship between them is shown in equation (8).

[0078]

[0079] 2) AC / DC short-circuit ratio

[0080] To quantify the impact of multiple DC feeds on the AC / DC system strength at AC node k, the AC-DC Short Circuit Ratio (ADSCR) is defined as follows:

[0081]

[0082] In the formula: S ac,k For the short-circuit capacity of AC line k, P k For all DC equivalent active power passing through AC line k, P dc,i Let i be the active power of DC.

[0083] 3) Overall performance indicators and interference indicators of the sending and receiving ends

[0084] To reflect the overall strength of the AC / DC power grid at both the sending and receiving ends, a target node set K for AC / DC is selected, where K = {A}. ADSCR1 A ADSCR2 A ADSCRk A ADSCRn}, for all nodes A in K ADSCR Summing and averaging can obtain the overall level of influence of multiple DC lines on the target node after the planned DC line is connected, reflecting the grid strength at the sending and receiving ends under the current scheme. Therefore, the overall performance index I at the sending and receiving ends is important. wholeness As shown in equation (10):

[0085]

[0086] I wholeness A higher value indicates higher overall strength, and can also indicate a greater system safety margin.

[0087] After the DC connection is planned, the overall AC / DC level of the sending and receiving end systems will change, leading to changes in the A of the AC node. ADSCR Decrease, if A ADSCR An excessively large decrease indicates strong interference from the planned DC transmission line to the AC / DC system, significantly impacting system stability. Therefore, the interference index I is used. interference To assess the interference level of the AC / DC power grid after the planned DC connection, as shown in Equation (11):

[0088]

[0089] I interference The smaller the value, the stronger the interference of the planned DC to the AC / DC system.

[0090] 4) Near-field stability coefficient of the sending and receiving ends

[0091] To describe the stability of renewable energy and the support characteristics of traditional energy in the vicinity of the DC transmission and receiving end points, this paper proposes a near-field stability factor (SRNSF) based on the multiple renewable energy station short circuit ratio (MRSCR) and considering the participation of traditional energy. The grid connection points of various energy sources in the vicinity of the transmission and receiving ends are attributed to the station's assembly bus closest to the DC landing point. Therefore, SRNSF can be obtained from equation (12):

[0092]

[0093] In the formula S SRNSFS and S SRNSFR These are the near-field stability coefficients at the sending and receiving ends, respectively; ∑P S and ∑P R These represent the total active power output of nearby power plants at both the sending and receiving ends; S Sac,i and S Rac,i These are the short-circuit capacities of the feeder and receiver station busbars, respectively; P Si and P Ri These represent the active power generated by the sending and receiving stations, respectively; Z Sijand Z Rij These are the mutual impedances between the sending and receiving end station's collection busbar and other station collection buses, respectively; Z Sii and Z Rii These are the self-impedances of the station's collection busbars at the sending and receiving ends, respectively; U Si and U Ri These are the voltages of the station's collection bus at the sending and receiving ends, respectively; U Sj and U Rj These are the bus voltages of other stations at the sending and receiving ends, respectively; P Sj and P Rj These represent the active power generated by the j-th power station at both the sending and receiving ends.

[0094] SRNSF characterizes the overall voltage stability of new and traditional energy sources in the near-field of the transmitting and receiving ends. The larger the SRNSF, the stronger the anti-interference capability of the near-field of the DC transmitting and receiving ends, the less affected by new energy sources, and the better the corresponding terminal landing scheme.

[0095] 5) High DC power impact energy

[0096] When an AC / DC fault occurs in a densely populated power grid at the sending and receiving ends, it can easily trigger multiple DC power surges. Because this involves a large number of DC circuits and a large total capacity, the impact of multiple DC power surges on the stability of the sending and receiving end systems is as severe as, or even comparable to, a single DC circuit blocking. The impact energy is related to the area under the curve between the power curve during DC commutation failure and the initial DC power, and can be used to characterize the severity of fault propagation at the sending and receiving ends. The impact energy J during a single DC power surge is:

[0097]

[0098] In the formula, t0 is the DC instantaneous sag initiation time, t1 is the DC recovery stabilization time, and P d0 For DC starting active power, P d This represents the actual active power of DC.

[0099] The sum of the DC power transient impact energy caused by AC faults is defined as the DC power transient energy J. sum :

[0100]

[0101] In the formula, J Si and J Ri N represents the DC power surge energy at the sending and receiving ends, respectively. S and N R These are the DC node sets for the sending and receiving ends, respectively.

[0102] J sumIt reflects the dynamic stability of the multi-DC system under fault propagation at the sending and receiving ends, and its magnitude depends on the power change amplitude and recovery time of multiple DC lines under fault conditions.

[0103] 6) Commutation failure pulse frequency

[0104] To better reflect the impact and disturbance of fault transmission at the sending and receiving ends on the AC / DC system, this invention does not consider DC blocking and assumes that γ is less than γ min A single commutation failure is recorded as one failure, and the commutation failure pulse frequency (CFPF) is defined accordingly. This index is obtained based on the number of DC commutation failures during fault propagation. The corresponding relationships are shown in Table 1.

[0105] Table 1 Total number of commutation failures at the planned DC transmitting and receiving ends

[0106]

[0107] Step 3: Based on the Vague set satisfaction limit improved DC landing point selection method, select DC landing points from the landing point selection index set.

[0108] This step proposes an improved DC transmitter-receiver landing point optimization method based on Vague set satisfaction thresholds. Multi-objective decision-making based on Vague sets effectively avoids the "long / short board effect" in traditional weighted methods. The satisfaction threshold determination method is modified by proposing a method based on interquartile ranges to obtain the satisfaction threshold, improving its reliability and preventing satisfaction from being entirely influenced by subjective factors. Specifically:

[0109] 1) Multi-objective decision optimization method based on Vague sets

[0110] Vague sets are commonly used in fuzzy multi-objective decision-making problems. By calculating the support, rejection, and neutral sets of different alternatives, an evaluation function is obtained, thereby prioritizing the alternatives. This method effectively avoids the "long / short board effect" in traditional weighted methods. Furthermore, Vague sets can integrate fuzzy indicators without distortion or increasing the dimensionality of consideration for each alternative. The multi-objective decision-making method based on Vague sets consists of the following four steps: 1) establishing an objective priority matrix; 2) determining subjective and objective weights based on the entropy weight method; 3) determining the satisfaction threshold; 4) constructing an evaluation function based on the Vague set. Finally, the evaluation function is used to describe the merits of each alternative.

[0111] The Vague sets for each scheme are obtained from equation (15):

[0112] V i =[(∑w s1 , ∑w s2), (1-Σw o1 ,1-Σw o2 (15)

[0113] In the formula, V i Let e ​​be the interval Vague set of scheme i. i Let ∑w be the evaluation function for scheme i. s1 and ∑w s2 These represent the upper and lower bounds of the support set weight interval, ∑w o1 and ∑w o2 These represent the upper and lower limits of the weight range for the opposition set, respectively.

[0114] e i =(∑w s1 +∑w s2 -∑w o1 -∑w o2 ) / 2 (16)

[0115] 2) Improvement of the method for determining the satisfaction threshold

[0116] This invention proposes a method based on interquartile range (ICM) to obtain satisfaction thresholds, improving the reliability of these thresholds, avoiding complete susceptibility to subjective factors, and enhancing the extraction of data information. The improved ICM-based method can determine the overall quality distribution of the data and accordingly define the satisfaction thresholds: when a set of data values ​​is generally good, accept a large amount of top-performing data and reject a small amount of bottom-performing data; when a set of data values ​​exhibits a polarized or near-normal distribution, accept or reject a suitable amount of top- and bottom-performing data; when a set of data values ​​is generally poor, accept a small amount of top-performing data and reject a large amount of bottom-performing data. The specific determination process is as follows: Figure 4 As shown, first calculate the quartiles Q1, Q2, and Q3 of the data. Then calculate the difference between the third quartile and the first quartile, also known as the interquartile range Q, and the mean. Determine if Q is less than 0.3:

[0117] (1) If it is less than 0.3, then determine whether Q2 is greater than 0.5. If it is, then let μ′ be the mean. Let μ″ be Q² - Q; if not, let μ′ be Q² + Q. Let μ″ be the mean.

[0118] (2) If it is greater than or equal to 0.3, then determine whether Q1 is greater than 0.9:

[0119] (21) If it is greater than 0.9, then further determine whether Q3 is less than 0.3. If it is, set μ′ to 0.9 and μ″ to 0.3. Otherwise, determine whether Q is less than 0.6. If it is, determine whether Q is less than 0.6. If it is, set μ′ to 0.9 and μ″ to Q2-Q / 2. Otherwise, set μ′ to Q2+Q / 2 and μ″ to 0.3.

[0120] (22) If it is less than or equal to 0.9, then further determine whether Q3 is less than 0.3. If it is, set μ′ to Q2+Q / 2 and μ″ to 0.3. Otherwise, set μ′ to Q1 and μ″ to Q3.

[0121] Based on the above-mentioned indicators, Vague set calculations are performed on each landing point scheme to construct an evaluation function. The optimal DC transmission and reception landing point scheme is obtained by comparing the evaluation function results of each scheme.

[0122] In summary, this embodiment addresses the DC landing point location problem in multi-DC landing point power grids, proposing a DC landing point optimization index and method to address fault propagation at both the sending and receiving ends. For example... Figure 5 The flowchart shown first analyzes the fault propagation process at the sending and receiving ends under the superposition and interaction of AC and DC, and proposes the AC / DC superposition interaction factor and AC / DC short-circuit ratio to reflect the impact of planned DC on the overall integrity and interference of the sending and receiving ends from the perspective of AC nodes. Second, it proposes the near-field stability coefficient of the sending and receiving ends to reflect the near-field energy stability, the multi-DC power impact energy to reflect the degree of fault propagation at the sending and receiving ends, and the fuzzy index commutation failure pulse frequency. Then, it constructs a DC sending and receiving end landing point optimization method based on Vague set satisfaction limit improvement to achieve accurate processing of optimization indicators. Finally, it constructs a DC landing point selection process that considers the fault propagation at the sending and receiving ends, effectively alleviating the fault propagation problem at the sending and receiving ends from the planning level.

[0123] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

Claims

1. A method for optimizing the DC landing point considering fault propagation at the sending and receiving ends, characterized in that, Includes the following steps: Construct a fault transmission process at the sending and receiving ends that considers AC / DC superposition and interaction; Based on the transmission process, a set of optimal landing point indicators is constructed to consider the fault transmission at the sending and receiving ends of multiple DC systems. The construction process of the optimal landing point indicator set specifically includes: Based on the transmission process, the AC / DC superposition interaction factor and AC / DC short-circuit ratio, which reflect the AC / DC superposition interaction, are calculated, as well as the overall performance index and interference index of the sending and receiving ends, which reflect the planned DC, are calculated to characterize the AC / DC superposition interaction mechanism of the sending and receiving ends. The degree of fault propagation at the sending and receiving ends is characterized by the near-zone stability coefficient of the sending and receiving ends, the impact energy of multiple DC power, and the frequency of commutation failure pulses. Based on the AC / DC superposition interaction mechanism and fault propagation degree of the sending and receiving ends, the fault propagation problem of the sending and receiving ends under AC / DC superposition interaction is evaluated, and the optimal index set of DC landing point is obtained. The expression for the near-field stability coefficient of the sending and receiving ends is: In the formula, S SRNSFS and S SRNSFR These are the near-field stability coefficients of the sending and receiving ends, respectively; ∑ P S and ∑ P R These represent the total active power output of power stations near the sending and receiving ends; S Sac,i and S Rac,i These are the short-circuit capacities of the combined busbars at the sending and receiving ends of the station; P Si and P Ri These are the active power generated by the sending and receiving stations, respectively. Z Sij and Z Rij These are the mutual impedances between the receiving and sending end station's aggregation busbar and other station aggregation buses, respectively. Z Sii and Z Rii These are the self-impedances of the station's collection busbar at the sending and receiving ends, respectively. U Si and U Ri These are the voltages of the station's collection bus at the sending and receiving ends, respectively. U Sj and U Rj These are the bus voltages of other stations at the sending and receiving ends, respectively. P Sj and P Rj The sending and receiving ends are respectively j The active power generated by each station The multi-DC power surge energy is defined as the sum of the multi-DC power instantaneous descent surge energies caused by AC faults, and its expression is: In the formula, J sum For high DC power surge energy, J Si and J Ri The sending and receiving ends are respectively i DC power surge energy, N S and N R These are the DC node sets for the sending and receiving ends, respectively. The DC landing point optimization method based on Vague set satisfaction limit optimizes the DC landing point from the landing point optimization index set.

2. The method for optimizing the DC landing point considering fault transmission at the sending and receiving ends according to claim 1, characterized in that, The fault transmission at the sending and receiving ends manifests as fluctuations in DC transmission power, which are determined by DC voltage and DC current.

3. The method for optimizing the DC landing point considering fault transmission at the sending and receiving ends according to claim 1, characterized in that, The expression for the AC / DC superposition interaction factor is: in, The interaction factor is the superposition of AC and DC. k Refers to any AC line; Δ U' j For overlay interactive communication lines k Fault on DC converter bus j The effect of voltage, Δ U jk For communication lines k Fault on DC converter bus j The direct effect of voltage; Δ U jik For communication lines k Fault to converter bus i After the impact occurs, the converter bus will... i Converter bus j The resulting cumulative effects are caused by multiple feed-in interaction factors. M MIIFji The value can be obtained from the definition as Δ U jik =Δ U ik • M MIIFji ; N This is a set of DC nodes.

4. The method for optimizing the DC landing point considering fault transmission at the sending and receiving ends according to claim 1, characterized in that, The expression for the AC / DC short-circuit ratio is: In the formula, AC / DC short-circuit ratio; k Refers to any communication line; S ac,k For communication lines k Short-circuit capacity; P k For all DC equivalents through AC lines k The active power; P dc,i DC i The active power; For communication lines k Fault to DC i AC / DC superposition interaction factor.

5. The method for optimizing the DC landing point considering fault transmission at the sending and receiving ends according to claim 1, characterized in that, The process of constructing the overall performance index of the sending and receiving ends specifically includes: Select the AC / DC target node set based on the AC / DC short-circuit ratio; The overall index of the sending and receiving ends is constructed by summing and averaging the target node set, and the expression is: In the formula, I wholeness For the overall index value of the sending and receiving ends, For the first i AC / DC short-circuit ratio of each node.

6. The method for optimizing the DC landing point considering fault transmission at the sending and receiving ends according to claim 1, characterized in that, The expression for the interference index is: In the formula, I interference These are interfering index values. For the first i AC / DC short-circuit ratio of each node.

7. The method for optimizing the DC landing point considering fault transmission at the sending and receiving ends according to claim 1, characterized in that, The specific steps for selecting the optimal DC landing point include: Establish a target preference matrix based on the aforementioned landing point optimization index set; The subjective and objective weight coefficients for each indicator are determined based on the entropy weight method; The satisfaction threshold was obtained based on the interquartile range method. An evaluation function is constructed based on the Vague set, and each landing point is evaluated according to the evaluation function and the satisfaction threshold to optimize the DC landing point at the DC transmitter and receiver. The expression of the evaluation function is as follows: In the formula, e i For landing point plan i The evaluation function; ∑ w s1 and ∑ w s2 These represent the upper and lower bounds of the support set weight interval, respectively; ∑ w o1 and ∑ w o2 These represent the upper and lower limits of the weight range for the opposition set, respectively.

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