Resistance type superconducting current limiter optimization configuration method in distributed power supply access scene

Abstract

The invention discloses an optimal configuration method for a resistance-type superconducting current limiter in a distributed power supply access scene. The method comprises the following steps: S1, carrying out site selection on a resistance-type superconducting current limiter mounting branch; s2, establishing a target function F1 by taking the lowest cost of the resistance type superconducting current limiter as a target; s3, establishing a target function F2 by taking the optimal matching degree of the resistance type superconducting current limiter and current protection as a target; s4, normalizing the objective functions of the F1 and the F2, and constructing a single objective function; s5, establishing constraint conditions of the optimization configuration model of the resistance type superconducting current limiter; and S6, solving the configuration model to obtain an optimal configuration scheme. According to the method, the possible access positions of the RSFCL are screened through sensitivity analysis, then the length, the installation positions and the installation number of the superconducting tape of the RSFCL are taken as decision variables, the cost of the current limiter and the cooperation degree with protection are comprehensively considered, a 10kV distribution network optimal configuration model of the RSFCL in a DG access scene is established, and an optimal configuration scheme of the RSFCL is obtained through solving.

Description

Technical Field

[0001] The present invention relates to the field of resistive superconducting fault current limiters, and an optimized configuration method for resistive superconducting fault current limiters in the scenario of distributed power source access. Background Art

[0002] A resistive superconducting fault current limiter (RSFCL) has almost no loss during normal power grid operation due to the zero-resistance characteristic of the superconducting material, and quickly quenches and introduces impedance to limit the short-circuit current during a fault. Its excellent performance has broad application prospects. In the context of large-scale access of distributed power sources (such as wind power, photovoltaic power, etc.) to the distribution network, the resistive superconducting fault current limiter has become one of the key technologies to improve the security of the distribution network due to its fast response, low loss, and self-adaptive current limiting characteristics. The resistive superconducting fault current limiter is often configured at the transformer outlet of the distribution network, the grid connection point of the new energy power station, or the load center to cope with the problem of excessive short-circuit current caused by the access of distributed power sources.

[0003] The configuration of the resistive superconducting fault current limiter in the scenario of distributed power source access has moved from laboratory research to demonstration applications, but it still needs to solve problems such as material cost and loss optimization. How to achieve the optimized configuration of the resistive superconducting fault current limiter is the main goal of technical personnel. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an optimized configuration method for resistive superconducting fault current limiters in the scenario of distributed power source access.

[0005] One technical solution to achieve the above purpose is: an optimized configuration method for resistive superconducting fault current limiters in the scenario of distributed power source access, including the following steps:

[0006] S1, use sensitivity analysis to select the location of the branch where the resistive superconducting fault current limiter is installed;

[0007] S2, establish an objective function F1 with the lowest cost of the resistive superconducting fault current limiter as the goal;

[0008] S3, establish an objective function F2 with the best cooperation degree between the resistive superconducting fault current limiter and the current protection as the goal;

[0009] S4, normalize the objective functions of F1 and F2 to construct a single-objective function;

[0010] S5, establish the constraint conditions of the optimized configuration model of the resistive superconducting fault current limiter;

[0011] S6, solve the optimized configuration model of the resistive superconducting fault current limiter to obtain the optimized configuration scheme of the resistive superconducting fault current limiter.

[0012] Further, in S1, the specific steps for selecting the installation branch of the resistive superconducting fault current limiter using sensitivity analysis are as follows:

[0013] S11, Establish a distribution network operation model: An electrical model of the distribution network is established through power flow calculation of the power grid. The distributed power source is regarded as a controlled current source, enabling the model to reflect the current, voltage, and power flow of each node in the distribution network;

[0014] S12, Distribution network fault simulation: Considering three-phase short-circuit faults, simulate the effect of a unit-length resistive superconducting fault current limiter on limiting the three-phase short-circuit current on different lines;

[0015] S13, Selection of key nodes: Select the nodes at the outlet of the distributed power source and the nodes at the protection installation location as key nodes to participate in the calculation of sensitivity indicators;

[0016] S14, Calculation of sensitivity indicators: Calculate the ratio of the change in fault current before and after connecting a unit resistive superconducting fault current limiter to the fault current of the connected resistive superconducting fault current limiter as the sensitivity indicator;

[0017] S15, Screening of the optimal installation location: Calculate the sensitivity of each key node after connecting the resistive superconducting fault current limiter to each branch respectively, sum up the sensitivities of each key node, then sort them from large to small, and select the top n branches, where n is determined according to the scale of the distribution network, as the preferred locations of the resistive superconducting fault current limiter in the distribution network under the scenario of this distributed power source access.

[0018] Further, in S11, the electrical model of the power grid is described by the following power flow calculation formula:

[0019]

[0020] In the formula, P i and Q i are the active power and reactive power of node i respectively, V i is the voltage, Y ij is the admittance between nodes, and θ ij is the phase angle difference between nodes.

[0021] Further, in S12, the distribution network fault simulation is specifically as follows:

[0022] The three-phase short-circuit current is calculated by the following formula:

[0023]

[0024] In the formula, I i is the three-phase short-circuit current of the bus, E i is the normal operating bus voltage, and Z iiis the self-impedance of node i; the self-impedance of the node after a fault is associated with the access position of the resistive superconducting fault current limiter per unit length. After a fault occurs, the additional branch method is used to determine the new self-impedance Z’ of node i ii , the resistive superconducting fault current limiter per unit length is connected to any line mn in the distribution network, which is equivalent to connecting an impedance with a magnitude of Z N in parallel on branch mn, where Z N can be calculated by the following formula:

[0025] Z N =(Z mn +Z RSFCL ) / / (-Z mn )

[0026] where, Z mn is the original line impedance magnitude of branch mn, Z RSFCL is the impedance magnitude corresponding to the resistive superconducting fault current limiter per unit length. According to the branch addition method, when the resistive superconducting fault current limiter per unit length is connected to any line mn, the self-impedance of node i will become:

[0027]

[0028] where, Z im is the impedance from node i to m, Z in is the impedance from node i to n, Z mm is the impedance of point m, Z nn is the impedance of point n, △Z ii is the impedance change amount.

[0029] Furthermore, in S14, the sensitivity index S is specifically:

[0030]

[0031] Furthermore, in S2, the cost of the resistive superconducting fault current limiter includes the cost of the external device and the cost of the superconducting tape:

[0032] F1 = C out + C HTS

[0033] where: F1 is the total cost of the resistive superconducting fault current limiter; C out is the cost of the external device, including the costs of the inner and outer dewars and the bushing. In a fixed application scenario, the cost of the external device takes a constant value; C HTS is the cost of the superconducting tape, which is proportional to the length of the superconducting tape and is 100 yuan / meter.

[0034] Furthermore, in S3, the protection coordination objective function of the resistive superconducting fault current limiter is defined as:

[0035]

[0036] Wherein:

[0037] The short-circuit current at the installation location i of the protection after the current limiter is connected, A;

[0038] The setting current value of the first section of the protection device, A;

[0039] F2: The sum of the ratios of each protection setting value to the short-circuit current after limitation. The smaller the value, the higher the protection sensitivity.

[0040] Further, in S4, the normalization formula for establishing the objective function with the lowest cost of the resistive superconducting current limiter as the goal and the objective function with the optimal coordination degree between the resistive superconducting current limiter and the current protection as the goal is:

[0041]

[0042] Wherein: l is the sum of the lengths of the superconducting tapes of all installed current limiters, l max is the sum of the maximum lengths of the superconducting tapes of all installed current limiters. F′1 is the cost objective function after normalization, and the smaller the better; the value of F2 is already in the range of [0, 1], and it is also the smaller the better, so no processing is required. There is

[0043] F′2 = F2

[0044] The single-objective function of the weighted summation method is defined as:

[0045] F′ = α·F′1 + β·F′2

[0046] Wherein: α and β are weight coefficients specified by the user, satisfying α + β = 1, and are used to reflect the importance of the current limiter cost and the protection coordination degree.

[0047] Further, in S5, the constraint conditions for the distributed power access scenario are specifically:

[0048] S5.1, the short-circuit current flowing through the protection after the resistive superconducting current limiter is connected is greater than the operating current of the first section of the relay protection device. Generally, it is stipulated that the ratio to the operating current should be 1.3 - 1.8 times to meet the sensitivity requirements;

[0049]

[0050] Wherein: I RSFCL is the magnitude of the short-circuit current after the RSFCL is installed, is the setting value of the first section of the relay protection;

[0051] S5.2, the pressure borne by the tape per unit length of the superconducting fault current limiter is within the allowable range.

[0052]

[0053] Where: U RSFCL is the voltage across the RSFCL, L is the length of the superconducting tape, and U safe is the voltage that the superconducting tape per unit length can withstand.

[0054] Furthermore, the peacock optimization algorithm is used to solve the optimization configuration model of the resistive superconducting fault current limiter, and the optimal limiter configuration scheme is output, including the tape length, installation quantity, and installation location.

[0055] The optimization configuration method of the resistive superconducting fault current limiter in the distributed power supply access scenario of the present invention proposes a pre-site selection method for the installation branch of the RSFCL based on sensitivity analysis. By performing sensitivity analysis to screen the possible access positions of the RSFCL, it helps to improve the calculation efficiency of the optimization process, shorten the optimization time, and provide a more practical scheme for the configuration of the limiter in actual engineering; the present invention takes the superconducting tape length, installation location, and installation quantity of the RSFCL as decision variables, comprehensively considers the cost of the limiter and the degree of coordination with protection, establishes an optimization configuration model of the 10kV distribution network for the RSFCL in the DG access scenario, and uses the peacock optimization algorithm to solve it, and can obtain the optimization configuration scheme of the RSFCL. Description of the Drawings

[0056] Figure 1 is the flow chart of the optimization configuration method of the resistive superconducting fault current limiter in the distributed power supply access scenario of the present invention;

[0057] Figure 2 is the flow chart of selecting the installation branch of the resistive superconducting fault current limiter by using sensitivity analysis;

[0058] Figure 3 is the logic diagram of using the peacock optimization algorithm to solve the model;

[0059] Figure 4 is the actual 10kV distribution network diagram of a certain area with multi-point DG access;

[0060] Figure 5 is the schematic diagram of the convergence curve comparison. Detailed Embodiment

[0061] In order to better understand the technical solution of the present invention, the following is a detailed description through specific embodiments:

[0062] In order to optimize the configuration of the RSFCL in the scenario of the protection coordination problem of multiple access points of distributed generation (DG), the present invention proposes an optimal configuration method for a resistive superconducting fault current limiter in the scenario of distributed generation access, as Figure 1 shown, including the following steps:

[0063] S1. Use sensitivity analysis to select the location of the branch where the resistive superconducting fault current limiter is installed;

[0064] S2. Establish an objective function F1 with the lowest cost of the resistive superconducting fault current limiter as the goal;

[0065] S3. Establish an objective function F2 with the optimal coordination degree between the resistive superconducting fault current limiter and the current protection as the goal;

[0066] S4. Normalize the objective functions of F1 and F2 to construct a single-objective function;

[0067] S5. Establish the constraint conditions of the optimal configuration model of the resistive superconducting fault current limiter;

[0068] S6. Solve the optimal configuration model of the resistive superconducting fault current limiter to obtain the optimal configuration scheme of the resistive superconducting fault current limiter.

[0069] For S1, sensitivity analysis is a mathematical method for evaluating the impact of changes in system input variables on system output. In the fault analysis and risk analysis of the distribution network, sensitivity analysis can help identify key areas in the power grid, thus providing a theoretical basis for the pre-location of the RSFCL. In the operation of the distribution network with DG access, the installation location of the RSFCL will directly affect the limiting effect of the fault current. Therefore, sensitivity analysis provides a pre-location for the research on the configuration problem of the RSFCL and can improve the optimization efficiency.

[0070] The core idea of using sensitivity analysis for pre-locating the branch where the RSFCL is installed is to select the optimal installation location by evaluating the responsiveness of the current flowing through important nodes in the distribution network to the change in the installation location of the RSFCL. This method is based on the operation model of the distribution network, combines mathematical formulas and simulation analysis, calculates the magnitude change of the current flowing through important nodes under multiple optional installation locations of the RSFCL, and thus finds the key points that can significantly improve the system performance. The calculation results are used as the input conditions of the optimization configuration model, which can greatly shorten the solution time of the optimization configuration model of the RSFCL. By changing the installation location of the RSFCL on different lines, analyze its contribution to the limiting effect of the short-circuit current flowing through the protection installation. Through this systematic analysis method, not only can the configuration rationality of the RSFCL be improved, but also the safety and stability of the distribution network can be fully guaranteed.

[0071] Assume that the system output is y and the installation location is x, then the sensitivity S can be expressed as:

[0072]

[0073] Among them, represents the sensitivity of the current y to the change in the installation position x, reflecting the influence of the installation of the RSFCL at different positions on the magnitude of the current flowing through the key node.

[0074] The basic process of using sensitivity analysis to screen the installation position of the RSFCL is as follows: Assume that three-phase short circuits occur on each line. By installing the RSFCL with a unit length on each line and setting the sensitivity index to observe the short-circuit current limiting effect, the optimal installation position of the RSFCL is then screened out. The specific process of pre-site selection is as Figure 2 shown:

[0075] S11, establish a distribution network operation model: Establish an electrical model of the distribution network through power flow calculation of the power grid. Treat the distributed power source as a controlled current source so that the model can reflect the current, voltage, and power flow conditions of each node in the distribution network. The electrical model of the distribution network is usually described by the following power flow calculation formula:

[0076]

[0077] In the formula, P i and Q i are the active power and reactive power of node i respectively, V i is the voltage, Y ij is the admittance between nodes, and θ ij is the phase angle difference between nodes.

[0078] S12, distribution network fault simulation: Consider a three-phase short circuit fault and simulate the effect of a unit-length resistive superconducting fault current limiter on limiting the three-phase short circuit current on different lines. Although most faults in the distribution network are asymmetric faults, since the influence of single-phase grounding faults is relatively small, the present invention only considers the influence of the most severe three-phase short circuit on the system.

[0079] The simplified three-phase short circuit current is calculated by the following formula:

[0080]

[0081] In the formula, I i is the three-phase short circuit current of the bus, E i is the normal operating bus voltage, and Z ii is the self-impedance of node i.

[0082] As can be seen from the above formula, the fault current of a certain node is closely related to the self-impedance of that node, and the self-impedance of the node after a fault is associated with the access position of the RSFCL per unit length. Therefore, after a fault occurs, the additional branch method is used to determine the new self-impedance Z ii ’ of node i.

[0083] When the RSFCL per unit length is connected to any line mn in the distribution network, it is equivalent to connecting an impedance of size Z N in parallel to the branch mn, where Z N can be calculated by the following formula:

[0084] Z N =(Z mn +Z RSFCL ) / / (-Z mn )

[0085] Wherein, Z mn is the original line impedance size of the branch mn, and Z RSFCL is the impedance size corresponding to the resistive superconducting fault current limiter per unit length. According to the branch addition method, when the resistive superconducting fault current limiter per unit length is connected to any line mn, the self-impedance of node i will become:

[0086]

[0087] Wherein, Z im is the impedance from node i to m, Z in is the impedance from node i to n, Z mm is the impedance at point m, Z nn is the impedance at point n, and △Z ii is the impedance change amount.

[0088] S13, Key node selection: The present invention pre-locates the RSFCL for the DG multi-point access application scenario. Since the introduction of the RSFCL is mainly to solve the problem of misoperation of current protection in the case of DG access, the short-circuit current flowing through the node at the DG outlet and the short-circuit current flowing through the node at the protection installation location are the key points of concern in the present invention and are selected as the key nodes in the pre-location.

[0089] S14, Calculation of sensitivity index: As can be obtained from the above steps, the fault short-circuit current of a certain node is closely related to the self-impedance of that node. Therefore, the sensitivity S can be calculated by the ratio of the change in the fault current before and after connecting a unit RSFCL to the fault current of the connected RSFCL:

[0090]

[0091] S15. Optimal installation location screening: In the distribution network, there are often multiple nodes that need to limit the short-circuit current. Therefore, the screening of the installation branch of the RSFCL is a global problem. Calculate the sensitivity of each key node after connecting the RSFCL to each branch respectively, sum up the sensitivities of each key node, then sort them from large to small, and select the top n (n depends on the scale of the distribution network) branches as the preferred locations of the RSFCL in this application scenario of the distribution network.

[0092] This pre-site selection method can screen out the locations that are more effective in reducing the fault current flowing through the DG outlet and the fault current flowing through the protection installation location in the case of multi-point DG access, which not only improves the action reliability of the protection, but also reduces the time required for subsequent optimization.

[0093] When configuring the RSFCL, the optimization objectives include two aspects: the economy of the limiter cost and the best coordination with the relay protection. The design of the objective function needs to fully reflect the requirements of the actual problem: on the one hand, reduce the cost by reducing the length of the limiter strip and the number of installations, etc.; on the other hand, ensure that the ratio of the limited current to the protection setting value is as large as possible within the allowable range, so as to improve the protection sensitivity. The optimal parameters of the limiter should be optimized and determined by comprehensively considering the economic cost and the relay protection sensitivity.

[0094] Specifically, in the present invention, S2 establishes an objective function F1 with the lowest cost of the resistive superconducting fault current limiter as the goal.

[0095] The cost function of the RSFCL includes the cost of external devices and the cost of superconducting tapes:

[0096] F1 = C out + C HTS

[0097] Where: F1 is the total cost of the RSFCL; C out is the cost of external devices, including the costs of internal and external dewars and bushings, etc. In a fixed application scenario, the cost of external devices takes a constant value; C HTS is the cost of superconducting tapes, which is proportional to the length of the superconducting tapes and is taken as 100 yuan / m; the cost of the parallel resistance of the RSFCL can be ignored compared with the costs of external devices and superconducting tapes. Therefore, the present invention does not consider the cost of parallel resistance.

[0098] Specifically, in the present invention, S3 establishes an objective function F2 with the best coordination between the resistive superconducting fault current limiter and the current protection as the goal.

[0099] Degree of coordination with current protection:

[0100] In the DG access scenario, the purpose of connecting the RSFCL is to ensure that the protection does not refuse to operate when a fault occurs. Therefore, the current at the protection location should be greater than the setting value of its section I after the RSFCL is connected to ensure the rapid operation of the protection. Moreover, the ratio of the current flowing through the protection location to the setting value of protection section I should be as large as possible within the allowable range, which is generally taken as 1.3 - 1.8, so as to improve the sensitivity of the protection.

[0101] Define the protection coordination objective function in the DG access scenario as:

[0102]

[0103] Where:

[0104] The short - circuit current at the installation location i of the protection after the current limiter is connected, A;

[0105] The setting current value of protection section I of the protection device, A;

[0106] F2: The sum of the ratios of the setting values of each protection to the short - circuit current after limitation. The smaller the value, the higher the sensitivity of the protection.

[0107] S4. Normalize the objective functions of F1 and F2 to construct a single - objective function.

[0108] Due to different value ranges and dimensions, F1 and F2 need to be normalized to map the objective values to [0, 1]. Since the installed RSFCLs have the same structure type and the external device costs in the same scenario are the same, it can be considered that F1 is only related to the length of the superconducting tape. Therefore, use the length to normalize it. The normalization formula is:

[0109]

[0110] Where:

[0111] l is the sum of the lengths of the superconducting tapes of all installed current limiters, l max is the sum of the maximum lengths of the superconducting tapes of all installed current limiters. Currently, the maximum length of the superconducting tape of a single current limiter is taken as 204m. F′1 is the cost objective function after normalization, and the smaller the value, the better. In the case of DG access, the values of F2 are already within the range of [0, 1], and it is also of the type that the smaller the value, the better, so no processing is required.

[0112] F′2 = F2

[0113] Construct a single - objective function through the weighted - summation method:

[0114] F′ = α·F′1+β·F′2

[0115] Where: α, β: weight coefficients specified by the user, satisfying α + β = 1, which are used to reflect the importance of the limiter cost and the protection coordination degree. The weights are set according to the actual situation. If the actual distribution network has higher requirements for economy, then α is greater than β; conversely, if the actual distribution network has higher requirements for the reliability and sensitivity of relay protection, then β is greater than α. The weight coefficients can also be determined by means such as fuzzy membership functions. After the weight coefficients are determined, the optimal configuration problem is transformed into a single-objective optimization problem.

[0116] For S5, changing the series length of the superconducting tape, the installation location and the installation quantity of the RSFCL will cause different short-circuit current changes, power flow distributions and temperature rises on the tape in the system. It is also necessary to consider relevant technical constraints and establish the constraint conditions of the optimal configuration model of the resistive superconducting fault current limiter.

[0117] After the RSFCL is connected, the short-circuit current flowing through the protection is greater than the operating current of the first section of the relay protection device. Generally, it is stipulated that the ratio to the operating current should be between 1.3 and 1.8 times to meet the sensitivity requirements;

[0118]

[0119] Where: I RSFCL is the magnitude of the short-circuit current after the RSFCL is installed, is the setting value of the first section of the relay protection.

[0120] 2) The voltage per unit length of the superconducting tape of the superconducting fault current limiter is within the allowable range.

[0121]

[0122] Where: U RSFCL is the voltage across the RSFCL, L is the length of the superconducting tape, and U safe is the allowable voltage per unit length of the superconducting tape.

[0123] For S6, solve the optimal configuration model of the resistive superconducting fault current limiter to obtain the optimal configuration scheme of the resistive superconducting fault current limiter.

[0124] Considering that the established RSFCL optimal configuration model above belongs to a complex optimization problem with multiple constraints, having both 0-1 variables and continuous real variables, traditional optimization algorithms may be difficult to achieve satisfactory results when dealing with such problems. Compared with other swarm intelligence optimization algorithms, the peacock optimization algorithm can not only effectively handle high-dimensional and multi-constraint optimization problems, but also has the advantages of simple principle, few parameters and strong optimization ability. Based on these advantages, the present invention selects the peacock optimization algorithm as the solution algorithm for the limiter optimal configuration model.

[0125] The Peacock Optimization Algorithm (POA) is a heuristic optimization algorithm that simulates the courtship behavior of peacocks. This behavior embodies the combination of natural selection and sexual selection, that is, by demonstrating superior genetic traits to improve the adaptability of individuals, thus better transmitting genes in the population. Its basic process is as follows:

[0126] 1) Initialize the peacock population: Randomly initialize a certain number of peacock individuals in the solution space. Among them, the top 5 with the highest fitness are adult male peacocks, 30% are female peacocks, and the rest are juvenile peacocks. After each iteration, the identity of each individual needs to be re-assigned according to the fitness. Each individual represents a solution, and the decision variables of the individual are used as the solution to the optimization problem, expressed as:

[0127] X i =(x i1 ,x i2 ,...,x id )

[0128] where X i is the decision vector of the i-th peacock, and x ij is the decision variable of the i-th peacock in the j-th dimension.

[0129] 2) Fitness evaluation: Evaluate the solution of each peacock according to the objective function and calculate the fitness value. The fitness value represents the quality of the solution. The higher the fitness f(X i ), the more likely the individual is to guide the search of other individuals:

[0130] f(X i )=f(x i1 ,x i2 ,...,x id )

[0131] 3) Male peacocks display courtship: Male peacocks with higher fitness will show their superiority and attract other female peacock individuals through the behavior of "displaying their tails". During the display process, the optimal solution X best will attract other individuals to move in its direction, thereby improving the overall solution quality.

[0132] 4) Female peacocks adaptively approach male peacocks: According to the display behavior of peacocks with higher fitness, individuals will imitate the optimal solution to update their positions. The specific update formula is:

[0133] x h =x h (t)+3θ(x c，N -x h (t))

[0134] where: x his the position of the female peacock, x c，N is the position of the Nth male peacock, and θ is an operator that balances the local exploration and global search of the female peacock.

[0135] 5) Adaptive food search for juvenile peacocks: Juvenile peacocks randomly select a male peacock to move, and at the same time, randomly optimize in the search space by means of the Levy flight mechanism.

[0136] 6) Convergence condition: When the change of the solution tends to be stable or reaches the maximum number of iterations, the algorithm stops. Finally, the optimal solution in the peacock population is output.

[0137] The application in the solution of the optimal configuration model of the superconducting fault current limiter considering protection coordination is as follows.

[0138] After reading the basic data such as the initial distribution network topology structure and current protection settings, it enters the solution layer of the optimal configuration model. This layer uses the superconducting strip length of the fault current limiter, the installation position of the fault current limiter, and the installation quantity as decision variables. The dimension of the decision variables is determined by the number of alternative installation positions, the number of fault current limiters, and the parameter setting range. When using the peacock optimization algorithm for solution, each iteration of each peacock individual needs to go through steps such as fitness calculation and constraint condition judgment. Subsequently, the optimized fault current limiter configuration parameters are input into the system simulation model to calculate the corresponding optimized objective function value. Finally, the population evolution is carried out according to the fitness value of the individual until the given maximum number of iterations or convergence condition is met.

[0139] When using the peacock optimization algorithm for solution in the case of DG access, since some decision variables (such as strip length) are continuous, while the installation position and the switching quantity used to judge whether the RSFCL is accessed are discrete, therefore, continuous variables and discrete variables need to be processed separately during the optimization process. Specifically, continuous variables are directly represented by real numbers, discrete variables represent the installation position through integer values, and the switching quantity is encoded by 0-1 variables. To avoid excessive increase in the amount of calculation, after each iteration, the decision vector of the peacock individual is discretized and then input into the simulation model for optimization calculation to ensure the calculation efficiency. For the DG access scenario, the fitness calculation in the optimization process includes two main objectives: on the one hand, it is the cost of the RSFCL (determined by the external device cost and the strip length of the fault current limiter), and on the other hand, it is to improve the protection sensitivity. When evaluating the fitness, for individuals that do not meet the constraint conditions, they will be corrected by the penalty function to ensure the effective maintenance of the constraint conditions during the optimization process.

[0140] In each iteration, the fitness of the peacock individuals is calculated by weighting according to the weights of the optimization objective function, and the position update is completed by imitating and displaying behaviors. The optimization process will continue until the maximum number of iterations or the convergence condition is met. Finally, the peacock optimization algorithm will output the optimal fault current limiter configuration scheme, including the strip length, installation quantity, and installation location.

[0141] The specific process of using the peacock optimization algorithm for model solution is as Figure 3 shown.

[0142] Next, taking an actual 10 kV distribution network as an example, the effectiveness of the method of the present invention for the optimized configuration of the RSFCL considering current protection coordination in the 10 kV distribution network is verified.

[0143] Taking Figure 4 an actual 10 kV distribution network in a certain area shown as an example.

[0144] In this distribution network, 3 DGs are connected, with capacities of 5 MW, 3 MW, and 4 MW respectively, and the parallel resistance of the RSFCL is taken as 5 Ω. First, current protection configuration is carried out for this distribution network without DG connection, and the protection setting values are obtained by scanning the whole network. The specific results are shown in Table 1.

[0145] Table 1 Protection setting values for each

[0146]

[0147] After connecting the DGs, pre-site selection is carried out according to S1. In this example, the key nodes are selected as the nodes where the DG outlets are located, namely nodes 15, 35, and 49. Five branches with the largest sum of sensitivities of these 3 nodes are selected according to the network scale and recorded in Table 2 as the preselected branches for RSFCL installation.

[0148] Table 2 Candidate branches

[0149]

[0150] Since protection refusal may only occur when the fault point is downstream of the DG connection point, for this example, as DG1 has the largest capacity and has the worst impact on protection, the fault is set to occur at the end of line 3-4. The current at the outlet of node 1 is affected by 3 DGs simultaneously. After simulation tests, protection refusal occurs. In this scenario, the optimization model is solved according to the peacock optimization algorithm. On the premise of ensuring the optimization ability, the optimization time is minimized as much as possible. In this example, 50 peacock individuals are set, and the number of iterations is 200. During the optimization process, the upper limit of the superconducting strip length of any RSFCL is set to 204m, and the lower limit is 0m (i.e., the RSFCL is not connected), and the upper limit of the number of installed RSFCLs is 5. Since this example attaches more importance to the coordination between DG and relay protection, the weights in the objective function are taken as: α = 0.4, β = 0.6. The optimization results are shown in Table 3.

[0151] Table 3 Optimal Configuration Results of RSFCL under the Scenario of Distributed Generation Access

[0152]

[0153] It can be seen from the optimization results that installing 3 RSFCLs can achieve the best optimization effect. Analyzing the installation locations of the RSFCLs, RSFCLs are installed at the outlets of all 3 DGs, and the access length of the superconducting strip is relatively large. This optimization result shows that for the unreliable operation of current protection caused by DG access, installing RSFCLs at the outlets of DGs is the most direct and effective. The multi-point access of DGs makes the power flow direction extremely complex. In addition to DG1 on the same branch as the protection, which can cause unreliable protection operation, DG2 and DG3 not on the same branch as the protection can also cause power flow changes and affect the protection. Therefore, RSFCLs are installed at the outlets of all 3 DGs to limit the injected current. At this time, F1 in the objective function is normalized to 0.435, and F2 is 0.592, that is, the protection sensitivity at node 1 is 1.689. According to the set weights, the total objective function is 0.529.

[0154] To further illustrate the improvement of pre-site selection on the optimization speed, experiments are also carried out on the optimal configuration of RSFCL without considering sensitivity. Table 4 shows the optimization results in two cases, Figure 5 showing the convergence curves in two cases.

[0155] Table 4 Comparison of Optimal Configuration Results of RSFCL

[0156]

[0157] The above results show that whether pre-site selection is carried out or not, the obtained optimized configuration schemes of RSFCL are the same, and the only difference between the two is the number of iterations. On the one hand, it shows that pre-site selection has a certain effect on improving the optimization time, and this effect will be more obvious with the increase of the distribution network scale; at the same time, to a certain extent, it also shows the stability of the configuration scheme obtained by the optimization configuration model of the present invention.

[0158] Further adjust the values of α and β in the objective function, compare the optimization results under different weights, and display the results in Table 5.

[0159] Table 5 Optimized Configuration Results of RSFCL under Different Weights

[0160]

[0161] Analyze the optimization results under different weights. It can be seen that with the decrease of the value of α / β, the protection sensitivity is further improved. When the value of α / β is relatively high, that is, when more attention is paid to the cost of the current limiter, the number of installed branches of RSFCL decreases, which further leads to the reduction of the cost; when the value of α / β is relatively low (that is, when more attention is paid to the coordination of protection), the protection sensitivity increases greatly, approaching the upper limit value of 1.8. The above analysis shows that the value of α / β can be adjusted according to the actual situation to meet the actual needs, and the optimization model has universality.

[0162] In summary, the present invention optimizes the configuration of RSFCL in a 10kV distribution network with multiple DG points. First, pre-site selection is carried out through sensitivity analysis. It can be seen from the example results that most of the candidate branches appear near DG and protection, indicating that the limiting effect of installing RSFCL around DG and protection is relatively good. Secondly, multiple optimization configurations are carried out by changing the weights of the sub-functions in the objective function, verifying the universality of the optimization model.

[0163] Those of ordinary skill in the art in this technical field should recognize that the above embodiments are only used to illustrate the present invention, rather than to limit the present invention. As long as within the scope of the essential spirit of the present invention, changes and modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. An optimized configuration method for resistive superconducting fault current limiters in the scenario of distributed power source connection, characterized in that, It includes the following steps: S1. Use sensitivity analysis to select the installation branch of the resistive superconducting fault current limiter; S2. Establish the objective function F1 with the lowest cost of the resistive superconducting fault current limiter as the goal; S3. Establish the objective function F2 with the optimal coordination degree between the resistive superconducting fault current limiter and the current protection as the goal; S4. Normalize the objective functions of F1 and F2 to construct a single-objective function; S5. Establish the constraint conditions of the optimization configuration model of the resistive superconducting fault current limiter; S6. Solve the optimization configuration model of the resistive superconducting fault current limiter to obtain the optimization configuration scheme of the resistive superconducting fault current limiter.

2. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein S1. The specific steps of using sensitivity analysis to select the installation branch of the resistive superconducting fault current limiter are as follows: S11. Establish the operation model of the distribution network: Establish the electrical model of the distribution network through power flow calculation of the power grid, and regard the distributed power source as a controlled current source so that the model can reflect the current, voltage and power flow of each node in the distribution network; S12. Distribution network fault simulation: Consider the three-phase short-circuit fault and simulate the effect of the resistive superconducting fault current limiter with a unit length on limiting the three-phase short-circuit current on different lines; S13. Selection of key nodes: Select the nodes at the outlet of the distributed power source and the nodes at the protection installation location as key nodes to participate in the calculation of the sensitivity index; S14. Calculation of the sensitivity index: Calculate the ratio of the change in the fault current before and after connecting a unit resistive superconducting fault current limiter to the fault current of the connected resistive superconducting fault current limiter as the sensitivity index; S15. Screening of the optimal installation position: Calculate the sensitivity of each key node after connecting the resistive superconducting fault current limiter to each branch respectively, sum up the sensitivities of each key node, and then sort them from large to small, and select the top n branches, where n is determined according to the scale of the distribution network, as the preferred positions of the resistive superconducting fault current limiter in the distribution network under the scenario of accessing this distributed power source.

3. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 2, wherein In S11, the electrical model of the power grid is described by the following power flow calculation formula: where P i and Q i are the active power and reactive power of node i respectively, V i is the voltage, Y ij is the admittance between nodes, and θ ij is the phase angle difference between nodes.

4. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 2, wherein In S12, the distribution network fault simulation is specifically as follows: The three-phase short-circuit current is calculated by the following formula: Where I i is the three-phase short-circuit current of the busbar, E i is the busbar voltage under normal operation, and Z ii is the self-impedance of node i; the self-impedance of the post-fault node is associated with the connection position of the unit-length resistive superconducting fault current limiter. After the fault occurs, the additional branch method is used to determine the new self-impedance Z ii ’ of node i. The unit-length resistive superconducting fault current limiter is connected to any line mn in the distribution network, which is equivalent to connecting an impedance with a magnitude of Z N in parallel on branch mn, where Z N can be calculated by the following formula: Z N = (Z mn + Z RSFC ) / (-Z mn ) Among them, Z mn is the magnitude of the original line impedance of branch mn, and Z RSFCL is the magnitude of the impedance corresponding to the unit-length resistive superconducting fault current limiter. According to the branch addition method, when the unit-length resistive superconducting fault current limiter is connected to any line mn, the self-impedance of node i will become: Among them, Z im is the impedance from node i to m, Z in is the impedance from node i to n, Z mm is the impedance at point m, Z nn is the impedance at point n, and △Z ii is the impedance change amount.

5. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 2, wherein In S14, the sensitivity index S is specifically as follows:

6. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein In S2, the cost of the resistive superconducting fault current limiter includes the cost of external devices and the cost of superconducting tapes: F1 = C out + C' HTS Where: F1 is the total cost of the resistive superconducting fault current limiter; C out is the cost of the external device, including the costs of the inner and outer dewars and the casing. In a fixed application scenario, the cost of the external device is a constant; C HTS is the cost of the superconducting tape, which is proportional to the length of the superconducting tape and is taken as 100 yuan / meter.

7. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, characterized in that In S3, define the protection coordination objective function of the resistive superconducting fault current limiter as: Where: Short-circuit current at the protection installation location i after the current limiter is connected, A; Setting current value of the first stage of the protection device, A; F2: The sum of the ratios of each protection setting value to the short-circuit current after limitation, and the smaller the value, the higher the protection sensitivity.

8. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 7, wherein In S4, the formula for normalizing the objective function established with the lowest cost of the resistive superconducting fault current limiter as the goal and the objective function established with the optimal coordination degree between the resistive superconducting fault current limiter and the current protection as the goal is: where: l is the sum of the lengths of all superconducting tapes of the installed current limiters, l max is the sum of the maximum lengths of the superconducting tapes of all installed current limiters, F′1 is the cost objective function after normalization, and the smaller the better; the value of F2 is already in the range of [0,1], and it is also the smaller the better, so no processing is required. There is F′2 = F2 The single-objective function defined by the weighted summation method is: F' = α·F′1 + β·F′2 Where: α and β are the weight coefficients specified by the user, satisfying α + β = 1, and are used to reflect the importance of the limiter cost and the protection coordination degree.

9. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein In S5, the constraint conditions of the distributed power source access scenario are specifically as follows: S5.

1. After connecting the resistive superconducting fault current limiter, the short-circuit current flowing through the protection is greater than the operating current of the first section of the relay protection device. Generally, it is stipulated that the ratio to the operating current should be 1.3 - 1.8 times to meet the sensitivity requirements; Wherein: I RSFCL is the magnitude of the short-circuit current after the installation of the RSFCL; is the setting value of the first section of the relay protection; S5.2, the pressure on the strip per unit length of the superconducting fault current limiter is within the allowable range. Where: U RSFCL is the voltage across the RSFCL, L is the length of the superconducting tape, and U safe is the voltage that the superconducting tape per unit length can withstand.

10. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein S6 uses the peacock optimization algorithm to solve the optimization configuration model of the resistive superconducting fault current limiter, and outputs the optimal limiter configuration scheme, including the strip length, installation quantity and installation location.

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