Mismatch risk setting discrimination method for new active distribution network protection based on distributed power output analysis

Abstract

The application discloses a novel active power distribution network protection mismatch risk setting value discrimination method based on distributed power output analysis, and is suitable for a high proportion of new energy grid connection scene. The method constructs a typical topology structure of a power distribution network containing a high proportion of distributed new energy, analyzes the influence mechanism of distributed power access on protection action performance, and clearly defines the reasons for protection misoperation and refusal; constraint conditions that should be met by correct protection action are established, and a quantitative mapping relationship between distributed power output and protection mismatch risk setting value is constructed; a double-loop iteration method based on a backbone particle swarm algorithm is used to solve the protection failure action boundary; a protection mismatch risk setting value discrimination overall process is formulated, and risk setting values that may cause protection misoperation and refusal are screened out according to the current distributed power output condition. The application can effectively discriminate the protection mismatch risk setting value, and improve the reliability and stability of the power distribution network protection system.

Description

Technical Field

[0001] This invention relates to the field of power system protection technology, specifically to a method for identifying protection mismatch risk settings applicable to scenarios with a high proportion of renewable energy grid connection. Background Technology

[0002] With the increasing penetration of distributed photovoltaic and wind turbine systems into distribution networks, the distribution network is transforming from a traditional passive unidirectional radial network to an active bidirectional interactive system. The amplitude and distribution of short-circuit currents under fault scenarios in these new active distribution networks differ significantly from those in traditional distribution networks. This can lead to performance degradation of current protection devices that rely on line fault characteristics for triggering, posing a risk of incorrect operation. In recent years, research on current protection for new active distribution networks has focused primarily on optimizing and verifying setting values, in addition to exploring new protection principles.

[0003] Regarding the optimization of protection settings, some scholars have conducted in-depth research on adaptive adjustment of settings. Some scholars have obtained short-circuit current values ​​online by collecting operating data of distributed generation sources and dynamically adjusted the protection settings of each segment based on this, but this research only focused on instantaneous overcurrent protection and only involved single IIDG access scenarios; some scholars have introduced differential evolution algorithms to change protection settings in real time in combination with the current electrical quantity information of the distribution network, but have not fully considered the impact of distributed generation output fluctuations; some scholars have identified fault types based on the measured short-circuit current sequence components and selected corresponding protection settings for different fault types to improve reliability, but such methods have high requirements for the speed, accuracy, and synchronization of communication devices.

[0004] The core idea of ​​adaptive setting adjustment is to dynamically adjust protection settings or switch setting zones based on real-time operating parameters of the distribution network. However, due to the lack of effective risk setting identification methods, it is impossible to fully distinguish whether there is a risk of mismatch in the current protection settings at the initial moment of protection setting adjustment. At present, in the actual operation of the distribution network, switching protection settings requires a series of procedures such as issuing setting orders, and frequent changes to protection settings affect the safe and stable operation of the power system.

[0005] In the area of ​​protection setting verification, some scholars have focused on optimizing the verification order, sorting each protection unit by importance and verifying their settings sequentially to ensure that protection units with higher importance are verified first. Some scholars use the relative entropy combination weighting method to weight and sum a series of indicators to obtain a comprehensive protection importance index; others use a breadth-first search algorithm to combine risk assessment theory with the risk of grid cascading failures to measure protection importance. Furthermore, some scholars have conducted research aimed at improving the speed of setting verification, dividing large-scale power grids into several sub-regions using multi-level graph partitioning and characteristic matrix partitioning equivalence methods, allowing parallel verification calculations in each region to increase the verification rate. However, existing protection setting verification methods lack necessary screening mechanisms and cannot promptly screen and verify risk settings based on the output status of distributed generation sources. This results in a lack of specificity in the setting verification process, requiring verification of the entire network's settings each time, leading to a massive workload and low efficiency.

[0006] To address this, this invention proposes a novel method for identifying protection mismatch risk settings in active distribution networks based on distributed generation output analysis. This method first analyzes the impact mechanism of distributed generation access on protection performance in typical distribution network scenarios with a high proportion of renewable energy sources, combined with distributed generation grid-connected control strategies, clarifying the causes of protection maloperation and failure to operate. Based on this, it establishes the constraints that the correct protection operation should satisfy, constructs a quantitative mapping relationship between distributed generation output and protection mismatch risk settings, and solves the protection failure action boundary using a double-loop iterative method based on the backbone particle swarm optimization algorithm. Finally, it formulates an overall process for identifying protection mismatch risk settings, screening out risk settings that may lead to protection maloperation and failure to operate based on the current distributed generation output status. This method can combine the actual operating status of the distribution network to promptly identify and distinguish risk settings, improving the reliability and security of the protection system. Summary of the Invention

[0007] This invention addresses the risk of protection maloperation and failure to operate caused by a high proportion of distributed generation (DG) power sources integrated into the distribution network in existing technologies. It proposes a novel method for identifying protection mismatch risk settings in active distribution networks based on DG output analysis. By establishing a quantitative mapping relationship between DG output and protection mismatch risk settings, and combining this with intelligent optimization algorithms to solve for protection failure action boundaries, a complete risk setting identification process is developed, thereby achieving accurate identification and early warning of protection mismatch risk settings.

[0008] This invention provides a novel method for identifying the risk setting of protection mismatch in active distribution networks based on distributed generation output analysis, comprising the following steps:

[0009] S1: Define the distribution network topology and protection configuration, and construct a typical topology model containing distributed power sources;

[0010] S2: Analyze the impact mechanism of distributed power supply access on protection operation performance, reveal the root causes of protection maloperation and failure to operate, and establish the constraints that protection must meet for correct operation;

[0011] S3: Based on constraints, construct a quantitative mapping relationship between distributed power output and protection mismatch risk setting;

[0012] S4: Design a double-loop iterative method based on the backbone particle swarm algorithm to solve the protection failure action boundary;

[0013] S5: Establish a complete protection mismatch risk setting identification process, and based on the real-time monitoring of distributed power output, screen out risk settings that may cause protection to malfunction or fail to operate and trigger an early warning mechanism.

[0014] In S1, the distribution network topology model includes two feeders, L1 and L2, which are connected to inverter-type distributed generation sources (IIDG1 and IIDG2) respectively, with their grid connection points located at bus B and C. The system power supply equivalent potential Es and equivalent impedance Zs constitute the main power supply part. Protection devices P1 to P6 are distributed in different locations, with P1, P2, P3, and P5 configured with complete three-stage current protection, while P4 and P6 are only configured with stage I and stage III current protection; P1 and P2 are equipped with directional elements to avoid maloperation caused by reverse current. The distribution network lines are divided into upstream lines of IIDG, lines between IIDG, downstream lines of IIDG, and adjacent lines, with impedances Zs of each line being Zs. AB Z BC Z CD Z AF Z FG .

[0015] Furthermore, in S2, the impact mechanism of IIDG access on protection operation performance is analyzed, including external suction effect and amplification effect. When an upstream line fault occurs, the short-circuit current output by the IIDG may lead to reduced protection sensitivity or failure to operate; when a fault occurs between IIDGs, the protection range may expand or shrink due to changes in IIDG output, posing a risk of false operation or failure to operate; when a downstream line fault occurs, the superposition effect of the short-circuit current provided by the IIDG may cause the protection range to extend to the downstream line, triggering false operation; when an adjacent line fault occurs, the amplification effect of the IIDG may increase the short-circuit current flowing through the protection, affecting protection selectivity. Based on the above analysis, the constraints that the protection must meet for correct operation are clarified, including the protection range of current stage I, the sensitivity of stage II, and the sensitivity of stage III remote backup protection.

[0016] Specifically, in S3, taking the I-stage protection of P3 as an example, a quantitative mapping relationship between the output of distributed power sources and the protection mismatch risk setting is established, which is specifically expressed as follows:

[0017] λ1PIIDG1 +λ2P IIDG2 +C set

[0018] Where λ1 and λ2 are influence factors used to quantify the contribution of IIDG output to the short-circuit current; C is a constant term; I set To ensure protection setpoints, linearization is used to define the protection failure action boundary as a sequence of maximum output boundary values ​​for each IIDG, further simplifying the solution process.

[0019] Furthermore, in S4, a dual-loop iterative method based on the backbone particle swarm optimization algorithm is designed to solve the protection failure action boundary. The outer loop iteration module is responsible for the overall optimization process, finding the optimal solution through the particle swarm optimization algorithm and updating the global particle leader; the inner loop iteration module focuses on solving the node voltage equations and short-circuit currents to ensure calculation accuracy. The iteration termination condition is reaching the maximum number of iterations or satisfying the convergence condition, and finally outputting the swarm optimal solution to obtain the protection failure action boundary.

[0020] Specifically, S5 establishes a complete protection mismatch risk assessment process, which includes the following steps:

[0021] S501: Define the distribution network topology, IIDG and line parameters, protection configuration, solve the failure action boundary corresponding to each protection setting and store it in the protection device;

[0022] S502: Real-time monitoring of the output sequence of each IIDG to determine whether there is a continuous increasing trend and to initiate risk assessment;

[0023] S503: Compare the current IIDG output with the failure action boundary, and mark the protection setting that exceeds the boundary as the risk setting;

[0024] S504: Further determine whether the mapping relationship is valid and trigger the early warning mechanism.

[0025] The advantages of this invention compared to the prior art are as follows:

[0026] By quantitatively analyzing the mapping relationship between distributed power source output and protection mismatch risk settings, this invention can promptly identify risk settings that may lead to protection maloperation or failure to operate, significantly improving the operational reliability of protection devices. In terms of adaptive setting adjustment, it can serve as a criterion for initiating setting adjustments, avoiding frequent setting changes. Regarding protection setting verification, targeted verification is performed by identifying risk settings, greatly reducing workload and improving verification efficiency. Traditional methods typically involve directly accumulating the output values ​​of each IIDG, ignoring the differences in the impact of unit output of IIDGs at different locations on protection, which may lead to missed risk settings. This invention effectively solves this problem by introducing an influence factor to quantify the degree of influence of each IIDG output on protection operation performance.​

[0027] In summary, the protection mismatch risk setting identification method proposed in this invention has significant engineering application value. It can promptly identify risk settings that may lead to protection maloperation or failure to operate based on the real-time output status of distributed power sources, providing theoretical support for related research. Attached Figure Description

[0028] Figure 1 This is a topology diagram of a distribution network containing multiple IIDGs;

[0029] Figure 2 A flowchart for solving the model;

[0030] Figure 3 To protect the mismatch risk assessment flowchart;

[0031] The attached figures are labeled as follows:

[0032] Es—Equivalent potential of the system power supply; Zs—Equivalent impedance of the system; L1, L2—Feeders;

[0033] P1~P6——Protection device number; ZAB~ZFG——Line impedance;

[0034] IIDG1, IIDG2 — Inverter-type distributed power sources; f1~f3 — Fault location;

[0035] P IIDG1 P IIDG2 — Output value of distributed power sources. Detailed Implementation

[0036] This invention provides a novel method for identifying the risk setting of protection mismatch in active distribution networks based on distributed generation output analysis, combined with the appendix. Figure 1 To be continued Figure 3 The specific implementation process is explained in detail. This method is applicable to distribution network scenarios with a high proportion of distributed power sources. By analyzing the impact mechanism of distributed power source output on protection operation performance, a quantitative mapping relationship between distributed power source output and protection mismatch risk setting is constructed. A double-loop iterative method based on the backbone particle swarm algorithm is used to solve the protection failure action boundary, and finally a complete risk setting identification process is formulated.

[0037] First, this embodiment studies the correlation between the output power of the IIDG and its output current, and finds that changes in the output power of the IIDG directly affect the magnitude and phase of its output current, thereby affecting the protection action performance.

[0038] This embodiment uses inverter-interfaced distributed generation (IIDG) as an example for analysis. The output characteristics of IIDG are closely related to its inverter control strategy. During grid-connected operation, IIDG generally adopts a positive and negative sequence dual dq current control strategy. To suppress the negative sequence component in the output current, the reference value of the dq axis negative sequence current is usually set to 0. Based on the positive sequence voltage at the IIDG grid connection point... With the rated voltage U of the distribution network N The ratio γ can be used to divide the operation of the IIDG into constant power mode and low voltage ride-through (LVRT) mode. When the IIDG is running normally in grid-connected mode, it is in constant power mode and adopts a constant power control strategy dominated by positive sequence voltage component, outputting constant power and three-phase symmetrical current, as shown in equation (1).

[0039]

[0040] In the formula: P out Q out P ref Q ref — Output and reference values ​​of active and reactive power, in MW; i d-ref i q-ref —Reference value of dq-axis positive sequence current output of the outer loop of power frequency, kA; —dq-axis component of the positive sequence voltage at the grid connection point, kV; the same applies below.

[0041] When a fault occurs in the distribution network, the voltage drop at the IIDG grid connection point may cause the grid to disconnect, affecting the safe and stable operation of the distribution network. GB / T37408-2019 "Technical Requirements for Photovoltaic Power Generation Grid-Connected Inverters" points out that IIDGs need to have a certain low voltage ride-through capability. When a fault occurs, reactive current should be injected into the system first to provide reactive power support, thereby increasing the voltage drop at the grid connection point to maintain system voltage stability. Therefore, when a fault occurs, the IIDG switches to LVRT mode, and the reference value of its output dq-axis positive sequence current is shown in equation (2).

[0042]

[0043] In the formula: P max —Maximum output active power of IIDG, MW.

[0044] Substituting equation (2) into equation (3) and solving, we can obtain the amplitude and phase angle of the IIDG output current during the fault period:

[0045]

[0046] As can be seen from equation (3), the amplitude and phase angle of the IIDG output current are affected by the changes in the IIDG operation mode under different fault conditions, and have typical nonlinear controlled characteristics. Therefore, in the subsequent analysis, it is equivalent to a voltage-controlled current source.

[0047] Based on the above correlation between IIDG output and its output current, the mechanism of protection action performance degradation caused by IIDG grid connection is further analyzed.

[0048] First, clarify the distribution network topology and protection configuration, and construct a system as follows: Figure 1 The typical topology of a distribution network containing multiple IIDGs is shown. The mechanism of protection performance degradation caused by IIDG access to the distribution network is analyzed, and the constraints that protection must follow for correct operation in new active distribution networks are given in response to the root causes of protection maloperation and failure to operate.

[0049] As attached Figure 1 As shown, the distribution network includes two feeders, L1 and L2, which are connected to inverter-type distributed power sources IIDG1 (photovoltaic power station) and IIDG2 (permanent magnet direct-drive wind turbine), respectively. Their grid connection points are located at busbars B and C. The system's equivalent potential Es and equivalent impedance Zs constitute the main power supply portion of the grid. The impedances of each line are Z... AB Z BC Z CD Z AF Z FG .

[0050] DL / T584-2017, "Operation and Setting Regulations for 3kV~110kV Power Grid Relay Protection Devices," stipulates that 10kV distribution network lines generally adopt three-stage current protection, while terminal lines can adopt two-stage current protection. Therefore, protection devices P1, P2, P3, and P5 are configured with complete three-stage current protection, while protection devices P4 and P6 are configured with stage I and stage III current protection. Furthermore, to prevent excessive reverse current from the IIDG output from causing maloperation of the protection, directional elements are added to protection devices P1 and P2.

[0051] Based on the location of the IIDG grid connection point, the distribution network feeders are divided into IIDG upstream lines, IIDG inter-line lines, IIDG downstream lines, and adjacent lines. According to the location and type of the fault, the following scenarios are summarized. Taking the most serious fault, three-phase short circuit, as an example, the operation of each protection in different scenarios is discussed as follows.

[0052] 1) A fault occurred at point f1 on the upstream line of IIDG.

[0053] At this time, the short-circuit currents measured at protection points P1 and P2 are respectively:

[0054]

[0055] Where: α—the ratio of the distance from the fault point to the protection device to the length of the line at this level; Z f — Transition resistance at the fault location, Ω; I IIDG1 I IIDG2 —Short-circuit current output by IIDG1 and IIDG2, kA.

[0056] As can be seen from equation (4): when a fault occurs on the upstream line, if the fault type is a metallic short circuit, the system power supply is decoupled from IIDG1 and IIDG2, and only the short-circuit current from the system power supply flows through protection P1. The protection device can reliably operate and disconnect the faulty line. If the fault type is a non-metallic short circuit and the output of IIDG is large, since IIDG1, IIDG2 and the system power supply jointly inject short-circuit current into the fault point, the short-circuit current at the fault point will increase significantly, and the voltage at the short-circuit point will rise significantly. As a result, the short-circuit current flowing through protection P1 will decrease, and its protection range and sensitivity will be reduced. In severe cases, it may cause the I and II stages of protection of P1 to fail to operate.

[0057] The three-stage current protection setting principle states that the protection range of current stage I should be greater than 15% to 20% of the total length of the protected line; current stage II protection should be able to reliably protect the entire length of the line, and its sensitivity should be above 1.3. Based on this, the protection range of current stage I and the sensitivity constraints of current stage II should be established.

[0058]

[0059] In the formula: —Protecting the I and II segment settings of P1, kA; K sen —Sensitivity coefficient; —The fault current value flowing through protection P1 when a two-phase short circuit occurs at 20% of the AB line under the minimum operating conditions of the system, in kA; the same applies below.

[0060] Meanwhile, a reverse current flows through the output of IIDG2 at protection P2. However, because the upstream line protection of IIDG is equipped with a directional element, the P2 protection device reliably does not operate, and IIDG needs to rely on its own disconnection. If IIDG1 continues to operate in parallel after protection P1 trips, it cannot be isolated from the fault point, and its continuous output short-circuit current may cause reclosing failure. To avoid this situation, IIDG needs to be equipped with low-voltage, low-frequency automatic disconnection protection and anti-islanding protection.

[0061] 2) A fault occurred at point f2 on the line between IIDG1 and IIDG2.

[0062] At this time, the short-circuit currents measured at protection points P1 and P2 are respectively:

[0063]

[0064] As shown in equation (6), for protection P1, IIDG exhibits an external draining effect. When a fault occurs, IIDG preferentially injects reactive current into the short-circuit point, raising the voltage at the grid connection point and the fault point. This results in a decrease in the short-circuit current flowing through protection P1 and a reduction in sensitivity. At this time, the current stage III protection, as a remote backup protection, may fail to operate due to insufficient sensitivity. According to the setting principle of the three-stage current protection, the current stage III protection must be able to reliably protect the entire length of the current-level line and the downstream line, and its sensitivity should not be less than 1.2 when used as a remote backup.

[0065]

[0066] For protection P2, when a metallic fault occurs, IIDG1 has an amplifying effect. The short-circuit current flowing through protection P2 is formed by the superposition of the fault current provided by the main power grid and IIDG1. The protection sensitivity is improved and the original protection range is expanded. The protection range of current I stage may extend to the downstream line, causing the protection to trip over the level and resulting in protection mismatch. Therefore, it is necessary to establish the protection range constraint of current I stage.

[0067]

[0068] The current stage II protection is set in coordination with the downstream line stage I protection, i.e. in The operating value of stage II protection P2 is always greater than that of stage I protection P3. Therefore, the protection range of stage II protection P2 will not exceed the protection range of stage I protection P3. The sensitivity of stage II current protection is increased but the selectivity is not affected. As a backup protection for lower-level lines, stage III current protection relies on time difference to cooperate with the protection of lower-level lines. Although the sensitivity is improved, there is no problem of loss of selectivity.

[0069] When a non-metallic fault occurs, the trend of the short-circuit current flowing through protection P2 depends on the relative output of IIDG1 and IIDG2, and is therefore uncertain. If I... IIDG1 (Z s +Z AB )>I IIDG2 Z f If the short-circuit current flowing through protection P2 increases, the effect on protection P2 at this moment is consistent with the analysis results under the metallic fault condition; if I IIDG1 (Z s +Z AB ) < I IIDG2 Z f If the short-circuit current flowing through protection P2 decreases, it is equivalent to the output of IIDG1 being completely canceled out, and only IIDG2 acts alone. Protection P2 then becomes upstream line protection, similar to the operation of protection P1 in scenario 1).

[0070] 3) A fault occurred at point f3 on the downstream line of IIDG.

[0071] At this time, the short-circuit currents measured by protection devices P1, P2, P3, and P4 are respectively:

[0072]

[0073] As can be seen from equation (9), the short-circuit current flowing through protection P1 is decreasing, and the protection device can reliably not operate. The trend of short-circuit current flowing through protection P2 is difficult to determine, which is consistent with the response of the protection device in scenario 2). The short-circuit current flowing through protections P3 and P4 increases due to the superposition of fault current provided by IIDG1 and IIDG2. The protection range of current I section of P3 may be expanded to the DE line, thus losing the coordination with the protection of the lower-level line. The protection area of ​​current I section of P4 may cover the end of the line at this level. Therefore, it is necessary to constrain the protection range of current I section.

[0074]

[0075] The sensitivity of the P3 stage II protection is improved, but its protection range is always within the range of the P4 stage I protection. The stage III protection coordinates with the lower-level line protection through the action time limit difference, and the protection will not malfunction. The P4 stage III protection can reliably protect the terminal line and can meet the selectivity requirements.

[0076] 4) A fault occurred on the adjacent line of IIDG.

[0077] When a fault occurs on an adjacent line, the reverse short-circuit current flowing through the IIDG output at protection points P1 and P2 is unaffected by the directional elements installed at protection points P1 and P2. However, the amplifying effect of IIDG1 and IIDG2 increases the short-circuit current flowing through protection points P5 and P6, which is similar to the analysis of protection points P3 and P4 in scenario 3), and will not be repeated here.

[0078] Based on the correlation between IIDG output and its output current, the specific mechanism by which IIDG grid connection leads to the degradation of protection operation performance is analyzed. The results show that changes in IIDG output can cause a mismatch between the protection settings and the actual short-circuit current, thereby causing protection maloperation or failure to operate.

[0079] Based on clarifying the mechanism of protection action performance degradation caused by IIDG grid connection, a method for identifying protection mismatch risk settings is constructed.

[0080] Based on the above analysis, the constraints that must be met after IIDG grid connection to ensure correct protection operation are discussed. On this basis, the mapping relationship between IIDG output and protection mismatch risk setting is quantitatively analyzed. Furthermore, the boundary of protection failure action is clarified using a double-loop iterative method based on the backbone particle swarm optimization algorithm. Finally, a protection mismatch risk setting identification process is formulated, with specific steps shown in S110 to S140:

[0081] S110: Mapping relationship between IIDG output and protection mismatch risk setting

[0082] Taking the I-stage protection of P3 as an example, based on the above analysis, it can be seen that in order for the I-stage protection of P3 to operate correctly after IIDG grid connection, its protection settings must be... It should be able to avoid the fault current value flowing through protection P3 when the three-phase short circuit occurs at the end of the CD line, which is shown in equation (11).

[0083]

[0084] Will Solving the equations simultaneously with the above equations, we can obtain the constraint relationship that the output current value of IIDG and the protection setting value should satisfy when protection P3 operates correctly:

[0085]

[0086] Based on the correlation between the IIDG output current and its output power, equation (3) I IIDG =f(P IIDG U PCC Substituting into equation (12), we get:

[0087]

[0088] In the formula: λ1, λ2 — influence factors, kA / MW; used to quantify the contribution of IIDG output to short-circuit current, that is, when the output of IIDG1 and IIDG2 increases by 1MW, the short-circuit current increases by λ1 and λ2kA respectively.

[0089] As can be seen from the above equation, the expressions for λ1 and λ2 are related to the line impedance and the voltage at the IIDG grid connection point, exhibiting nonlinear characteristics. To simplify the solution process, this invention performs linearization and equivalent processing on them. The sequence of maximum output boundary values ​​of each IIDG at that time Defined as the failure action boundary of the I-segment protection of P3, the formula for solving the influence factor can be expressed as follows: Equation (13) can be converted to:

[0090]

[0091] This establishes a quantitative mapping relationship between the output of the distributed power source and the I-stage setting of protection P3. If the output power of IIDG1 and IIDG2 causes this mapping relationship to fail, it indicates that protection P3 is at risk of maloperation and an early warning mechanism needs to be triggered to mark the I-stage protection setting of P3 as a risk setting.

[0092] S120: Method for Solving Boundary Determination of Protection Failure Actions

[0093] This embodiment uses an intelligent algorithm to generate IIDG output values. By calculating the short-circuit current corresponding to the constraint conditions and combining iterative optimization, the IIDG output state is continuously corrected until the short-circuit current reaches the constraint threshold. At this point, the IIDG output is its boundary value, and the sequence of IIDG output boundary values ​​constitutes the protection failure action boundary.

[0094] S130: Boundary Determination Model for Protection Failure Action

[0095] Design optimization variable x k For each IIDG output sequence, the objective function f(x) is to maximize the output of each IIDG. k In addition to the constraints listed in step 2 of this invention, the variable constraint st should also include the upper and lower limits of the IIDG output force, as shown in equation (15):

[0096]

[0097] In the formula: P IIDGi —The output value of the i-th IIDG, MW; P min P max —Minimum and maximum limits of IIDG output, MW; g(I k ,I set — The constraints corresponding to each protection setting listed in step 2.

[0098] S140: Model Solving Process

[0099] The model solution process is as follows: Figure 2 As shown, the system is divided into two main modules: outer loop iteration and inner loop iteration. The core function of the inner loop iteration module is to solve the node voltage equations considering the nonlinear coupling relationship between the IIDG output current and its grid connection point voltage, and further calculate the short-circuit current flowing through the protection. The outer loop iteration module uses the output results of the inner loop iteration module as variable constraints and optimizes the protection failure action boundary using a backbone particle swarm optimization algorithm. The specific solution steps are as follows:

[0100] 1) Set the initial parameters of the algorithm at the initial time of the outer loop iteration, including the initial particle swarm size popsize and the maximum number of iterations T. max Feasible reserve set N and infeasible reserve set N* Capacity; then read the distribution network architecture, line parameters, and protection settings; randomly generate the IIDG output particle swarm, with each particle x k Covering n-dimensional IIDG output value P IIDGi The algorithm finds the population optimum by evaluating the fitness value of each particle, using it as the initial value. It then calculates the output current values ​​of each IIDG under normal system conditions through power flow calculations, and uses these values ​​as the initial values ​​for the inner loop iterative module.

[0101] 2) The inner loop iterative module sets corresponding fault scenarios based on the constraints of each protection setting, including fault location, fault type, and system operation mode. It solves for the voltage of each node using the node voltage equation U = ZI, and calculates the voltage at the grid connection point U. PCC The output current of each IIDG is continuously adjusted according to the degree of drop. The condition is satisfied when the output current converges. Stop the iteration, export the voltage and output current values ​​at the IIDG grid connection point, calculate the short-circuit current flowing through the protection, and return to the outer loop iteration module after completion.

[0102] In the formula: —The output current value of the i-th IIDG at iteration number k and k+1, kA; — Voltage at the i-th IIDG grid connection point when the number of iterations is k, kV.

[0103] 3) The outer loop iteration module calculates cv(x) based on the inner loop iteration output using equation (16). k ), evaluate the output particle x k The degree of constraint violation is used to determine whether the particle satisfies all the constraint dominance conditions.

[0104]

[0105] In the formula: K—the total number of constraints; h j (x) and g j (x) – Equality and inequality constraints; δ – Tolerance coefficient for violating equality constraints, usually taken as 0.001. If dc j If cv(x) is greater than 0, it means that the particle violates the j-th constraint. When cv(x) is equal to 0, the particle satisfies all the constraints.

[0106] 4) Based on 3), cv(x) k The calculation results will output the force of particle x. k Store in feasible reserve set N or infeasible reserve set N * In the middle, the global particle leader is further updated via equation (17).

[0107] The global facilitator is selected using a dynamic allocation strategy. During algorithm iterations, it is assigned probabilities p. sl and (1-p) sl) The selection probability formula for choosing from the infeasible reserve set and the feasible reserve set is:

[0108]

[0109] Where, 0≤p sl2 <p sl1 ≤1

[0110] In the formula: t—the current iteration number, T max — The number of iterations at which the algorithm terminates; p sl1 and p sl2 As a constant, the literature

[18] shows that p sl1 and p sl2 The algorithm exhibits good performance when the values ​​are 0.7 and 0.6 respectively.

[0111] 5) Determine if the maximum number of iterations T has been reached. max If the target is not reached, the particle position is updated using equation (18) in conjunction with the current global particle leader, and the process jumps to the next iteration. This process continues until the maximum number of iterations T is reached. max Output the population optimal solution x k and the corresponding objective functions f(x) k This yields the failure action boundary P corresponding to the protection setting. IIDG.lim =[f1(x k f2(x) k )…f n (x k )).

[0112]

[0113] Where: i∈(1,popsize), j∈(1,n)

[0114] In the formula: x i,j —The position of the i-th particle in the j-th dimension; popsize —the swarm size; xp i,j (t) and xg i,j (t)——The individual optimal solution and the population optimal solution of the particle. r3~U(0,1), the introduction of r3 further increases the search range of the algorithm, which is conducive to the rapid construction of modules by particles and the development of a global leader with a 50% probability, thus ensuring the diversity of the particle swarm.

[0115] S340: Protection Mismatch Risk Assessment Process

[0116] Based on the above steps, a complete process for identifying and determining the protection mismatch risk setting is established, such as... Figure 3 As shown, the specific steps are as follows:

[0117] 1) After clarifying the new active distribution network topology, IIDG and line parameters, and protection configuration, the failure action boundary P corresponding to each protection setting is solved using the method in S320 of this embodiment. lim =[P IIDG1.max P IIDG2.max ], store it in the protection device and set it as a threshold.

[0118] 2) Construct risk setting threshold identification trigger criteria as shown in equation (19), and monitor the output sequence P of each IIDG during the operation of the distribution network in real time. IIDG =[P IIDG1 P IIDG2 If IIDG exists i Output P IIDGi If the risk level continues to rise, risk assessment will be initiated; otherwise, the process will be terminated.

[0119]

[0120] In the formula: P IIDGi (t1), P IIDGi (t2), P IIDGi (t3) — IIDG measured at times t1, t2, and t3 i Output value, MW.

[0121] 3) Compare the IIDG one by one i Output P IIDGi Failure action boundary P corresponding to each protection setting IIDGi.max Filter out the current P IIDGi Protection values ​​exceeding the boundary are marked as risk values ​​and risk warnings are issued; the remaining current P IIDGi The protection setting that does not exceed the boundary needs to be jumped to 4).

[0122] 4) Further assess the current output of each IIDG and P IIDGi The mapping relationship between the boundary protection settings is not exceeded, if λ1P IIDG1 +λ2P IIDG2 +C<I set If the condition is not met, it is marked as a risk value, and an early warning mechanism must be triggered immediately; otherwise, the value is determined to be risk-free.

[0123] Simulation verification:

[0124] To verify the effectiveness of this method, simulations were performed using PSCAD / EMTDC and MATLAB / Simulink platforms.

[0125] S210: System Parameters

[0126] This embodiment is based on the PSCAD / EMTDC simulation platform and builds... Figure 1 The 10kV novel active distribution network model shown has IIDG1 and IIDG2, each with a maximum output of 20MW; the positive sequence impedance per unit length of the distribution network line is Z. l =0.069+j0.099Ω / km, the lengths of lines AB~DE and AF~FG are 6km, 8km, 5km, 5km, 8km, and 6km respectively; the load capacities at the ends of feeders L1 and L2 are 5MW and 10MW respectively.

[0127] Based on the three-stage current protection setting principle, the protection settings are calculated using equation (20), and the results are shown in Table 1.

[0128]

[0129] In the formula: —The reliability coefficients for protected sections I, II, and III, taking into account the influence of aperiodic components and allowing for a certain margin, are respectively set to 1.2, 1.1, and 1.2 in this invention; K ss K re — Self-starting coefficient and return coefficient; I L.max —The maximum load current of the system during normal operation, in kA.

[0130] Table 1 Protection Settings

[0131]

[0132] S220: Protect the boundary of failed actions

[0133] Set the optimization variable to x. k =[P IIDG1 ,P IIDG2 The objective function is f1(x) k ) = max(P IIDG1 f2(x) k ) = max(P IIDG2 In addition to the constraints listed above, the maximum and minimum limits of IIDG output 0MW ≤ P should also be considered. IIDGi For models ≤20MW, the double-loop iterative method based on the backbone particle swarm optimization algorithm was implemented using the MATLAB / Simulink platform to solve the model in this embodiment. The results are shown in Table 2.

[0134] Table 2. Results of the protection failure action boundary calculation

[0135]

[0136] As shown in Table 2:

[0137] 1) For upstream protection P1, P IIDG1 =8.01MW or P IIDG2 When the power output reaches 9.02MW, the failure threshold of the second-stage protection is reached, at which point its sensitivity drops to the critical value of 1.3. For the first-stage and third-stage protections, their failure thresholds both exceed the maximum output limit of the IIDG by 20MW. It can be seen that within the output range of the IIDG, the range of the first-stage protection of P1 is always greater than 20% of the AB line. The sensitivity of the third-stage protection, due to its lower setting, is always above 1.2 when used as a remote backup protection, and it can overcome the influence of the IIDG grid connection.

[0138] 2) For IIDG2, P2 is the upstream protection; the analysis is similar to 1). IIDG2 When the power consumption reaches 2.13 MW, the P2II stage protection fails to operate, and its sensitivity drops to the critical value of 1.3, posing a risk of protection failure. For IIDG1, P2 is the downstream protection. IIDG1 When the power reaches 11.96MW, the protection fails to operate at the boundary of the P2I segment, and its protection range extends to the lower-level line, posing a risk of maloperation.

[0139] 3) For downstream protection P3 and P4, Figure 1 IIDG1 and IIDG2 are relatively close to protection P3, and as shown in Table 2, the protection failure action boundaries of P3 and P4 are respectively The maximum output boundary values ​​of IIDG1 and IIDG2 are both greater than It can be seen that the impact of IIDG output on protection is related to the distance between IIDG and protection. As the distance between the two gradually increases, the impact of IIDG unit output on protection continues to decrease, and the protection failure action boundary value increases sequentially.

[0140] 4) For adjacent line protections P5 and P6, their failure boundaries both exceed the 20MW maximum output limit. It can be seen that within the IIDG output range, due to the current limiting control strategy of the inverter and the overcurrent withstand capability of the power electronic devices, the short-circuit current output by the IIDG exhibits weak feedback characteristics. The fault current flowing through the adjacent line protection is still dominated by the large power grid. Therefore, the response of protections P5 and P6 is basically unaffected.

[0141] S230: Simulation Verification of Protection Actions under Different IIDG Output Scenarios

[0142] Taking the protection of P1II and P3 and P4I segments as examples, the operation of each segment of the protection is simulated under different IIDG output scenarios to verify the effectiveness of the proposed method. The simulation results are shown in Table 3.

[0143] Table 3. Protective Actions under Different IIDG Output Scenarios

[0144]

[0145] Based on the S220 step described in this embodiment, the failure action boundary of each protection segment is clearly defined. On this basis, the corresponding influence factor λ of each protection segment is solved by equation (14). i As shown in Table 4.

[0146] Table 4. Corresponding Influence Factors for Each Protection Section

[0147]

[0148] Comparing Table 3, we can see that:

[0149] 1) When P IIDG1 =4MW, P IIDG2 =2MW, the failure action boundary of each protection device has not yet been reached; further determine the mapping relationship between the IIDG output and each protection setting, as shown in equation (21):

[0150]

[0151] Therefore, it can be seen that the protection sensitivity of P2II segment is greater than 1.3 at this time; the protection range of P3I segment and P4I segment does not exceed the line of this level, and all protection devices can respond normally; as shown by the data in Table 3, the theoretical analysis is consistent with the simulation results.

[0152] 2)P IIDG1 =6MW, P IIDG2 At 3MW, the failure action boundary of each protection has not yet been breached. At this time, the mapping relationship between the output of IIDG and the setting of each protection is as shown in equation (22):

[0153]

[0154] At this point, the protection sensitivity of segment P2II drops below 1.3, which no longer meets the protection sensitivity coefficient K. sen >1.3 Requirements: When a fault occurs at the end of the AB line, the P1II protection may fail to operate due to insufficient sensitivity; the protection range of the P3I section extends to the lower-level line, and when a fault occurs on the DE line, P3 may malfunction and trip synchronously with P4, thereby disrupting the coordination between protections; the protection area of ​​the P4I section is expanded to the end of the line at this level, increasing the probability of protection maloperation. The simulation results in Table 3 are consistent with this conclusion.

[0155] 3) IIDG output climbed to P IIDG1 =9MW, P IIDG2When the power output is 5MW, the output of IIDG1 exceeds the failure action boundary of the P1II protection stage, and the protection is at risk of not operating; the output of IIDG2 breaks the failure action boundary of the P3I and P4I protection stages, and the protection is at risk of false operation, which is consistent with the simulation verification results in Table 3.

[0156] 4) Analysis using S420 shows that within the IIDG output range, the response of protection stages I and III of P1 and protection stage I of adjacent lines P5 and P6 remains unaffected; a comparison with Table 3 shows that both IIDGs operate at their maximum output of 20MW. The protection range of section P1I is more than 20% of the line at this level; the protection sensitivity of section P1III is 2.10, which meets the requirement that the sensitivity of the remote backup protection is greater than 1.2. The protection range of P5 and P6 in section I does not exceed the level of the line, and there is no loss of selectivity, which is consistent with the analysis results above.

[0157] S240: Comparative Analysis of Existing Solutions

[0158] Existing research on the impact of IIDG output on protection performance typically involves simply summing the outputs of each IIDG, which has significant drawbacks. Distributed photovoltaic and wind turbine outputs are intermittent, random, and fluctuating. During nighttime, with weakened sunlight and increased wind speed, the output of IIDG1 decreases while the output of IIDG2 increases. If the output of IIDG1 decreases by ΔP... IIDG1 The increase in output ΔP of IIDG2 IIDG2 If the outputs of each IIDG are equal and the sum of their outputs remains unchanged, it means that the effects of the output fluctuations of IIDG1 and IIDG2 on protection are mutually "cancelled", thus making it impossible to identify the protection risk setting.

[0159] However, as can be seen from the analysis in step 3) of S220 above in this embodiment, the degree of influence of the unit output of IIDG at different locations on each protection varies. Under the above circumstances, the protection may be at risk of false operation or failure to operate, thus causing missed detection. The method of the present invention, through the influence factor λ, i The impact of each IIDG output on the protection action performance was quantified, which can effectively solve this problem.

[0160] Taking the I-stage protection of P3 as an example, when the system is running normally, P is set to... IIDG1 =5.5MW, P IIDG2 =1.5MW, P after power output fluctuation IIDG1 =4.5MW, P IIDG2 =2.5MW. The protection action was verified through simulation, as shown in Table 5.

[0161] Table 5. Protection Action of Stage I in P3

[0162]

[0163] When directly accumulating the output of each IIDG using the traditional method, the output of IIDG1 decreases by ΔP. IIDG1 The increase in output ΔP of IIDG2 IIDG2 All are 1MW. The sum of the outputs of each IIDG remains unchanged before and after the IIDG output fluctuation. At this time, the protection response should not be affected. However, the simulation results in Table 5 contradict this, indicating a missed detection. When using the method of this invention, the IIDG output fluctuation has not yet reached the P3I segment protection failure action boundary. Further judgment is needed regarding the IIDG output and its relationship with the protection response. The mapping relationship between them is At this point, there is a risk of malfunction in the protection system. The early warning mechanism should be activated immediately and the system should be marked as a risk value, which confirms the superiority of this method.

[0164] In summary, the protection mismatch risk setting identification method proposed in this invention has significant engineering application value. It can promptly identify risk settings that may lead to protection maloperation or failure to operate based on the real-time output status of distributed power sources, providing theoretical support for related research.

[0165] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A novel method for identifying the risk setting of protection mismatch in active distribution networks based on distributed generation output analysis, characterized in that, Includes the following steps: S1: Define the distribution network topology and protection configuration, and construct a typical topology model containing distributed generation sources; S2: Analyze the impact mechanism of distributed power source access on protection operation performance, and establish the constraints that the protection must meet for correct operation; S3: Based on constraints, construct a quantitative mapping relationship between distributed power output and protection mismatch risk setting; S4: Design a double-loop iterative method based on the backbone particle swarm algorithm to solve the protection failure action boundary; S5: Establish a complete process for identifying protection mismatch risk settings. Based on the real-time monitoring of distributed power output, screen out risk settings that may lead to protection malfunction or failure to operate and trigger an early warning mechanism.

2. The novel active distribution network protection mismatch risk setting identification method based on distributed power source output analysis according to claim 1, characterized in that, In step S1, the distribution network topology model includes two feeders, L1 and L2, which are connected to inverter-type distributed power sources IIDG1 and IIDG2, respectively. Their grid connection points are located at bus B and C. The system power equivalent potential Es and equivalent impedance Zs constitute the main power supply part of the grid. Protection devices P1, P2, P3, P4, P5, and P6 are distributed in different locations, and the impedances of each line are Zs. AB Z BC Z CD Z AF Z FG .

3. The novel active distribution network protection mismatch risk setting identification method based on distributed power source output analysis according to claim 2, characterized in that, The protection devices P1 and P2 are equipped with directional elements to prevent malfunctions caused by reverse current.

4. The novel active distribution network protection mismatch risk setting identification method based on distributed power generation output analysis according to claim 1, characterized in that, In step S2, the influence mechanism of distributed power supply access on protection operation performance is analyzed, including external suction effect and boosting effect, and the constraints that the protection must meet for correct operation are established, including the current I-stage protection range, II-stage sensitivity, and III-stage remote backup protection sensitivity.

5. The novel active distribution network protection mismatch risk setting identification method based on distributed power generation output analysis according to claim 4, characterized in that, The protection range constraints are used to prevent protection from malfunctioning or failing to activate.

6. The novel active distribution network protection mismatch risk setting identification method based on distributed power generation output analysis according to claim 1, characterized in that, In step S3, taking the P3I segment protection as an example, a quantitative mapping relationship is established between the output of distributed power sources and the protection mismatch risk setting, specifically expressed as follows: λ1P IIDG1 +λ2P IIDG2 +C<I set Where λ1 and λ2 are influence factors used to quantify the contribution of IIDG output to the short-circuit current; C is a constant term; I set To protect the set value.

7. The novel active distribution network protection mismatch risk setting identification method based on distributed power source output analysis according to claim 6, characterized in that, The protection failure action boundary is defined by linearization as a sequence of maximum output boundary values ​​of each IIDG.

8. The novel active distribution network protection mismatch risk setting identification method based on distributed power generation output analysis according to claim 1, characterized in that, In step S4, the design is based on the dual-loop iterative method of the backbone particle swarm algorithm to solve the protection failure action boundary. The outer loop iterative module is responsible for the overall optimization process, while the inner loop iterative module focuses on solving the node voltage equation and short-circuit current. The iteration termination condition is reaching the maximum number of iterations or satisfying the convergence condition.

9. The novel active distribution network protection mismatch risk setting identification method based on distributed power generation output analysis according to claim 1, characterized in that... In step S5, the process of establishing a complete protection mismatch risk assessment and identification procedure includes the following steps: S501: Define the distribution network topology, IIDG and line parameters, protection configuration, solve the failure action boundary corresponding to each protection setting and store it in the protection device; S502: Real-time monitoring of the output sequence of each IIDG to determine whether there is a continuous increasing trend and to initiate risk assessment; S503: Compare the current IIDG output with the failure action boundary, and mark the protection setting that exceeds the boundary as the risk setting; S504: Further determine whether the mapping relationship is valid and trigger the early warning mechanism.

10. The novel active distribution network protection mismatch risk setting identification method based on distributed power generation output analysis according to claim 9, characterized in that, In step S504, when monitoring the output sequence of each IIDG in real time, if the output of an IIDG shows a continuous increasing trend, the risk assessment process is initiated.

Images