Power distribution network electric energy quality treatment method and device based on flexible multi-state switch

Abstract

The invention relates to the technical field of electric power systems, in particular to a power distribution network electric energy quality treatment method and device based on a flexible multi-state switch, and the method comprises the steps: enabling the flexible multi-state switch FMS to be installed on a node in an electric power system according to an actual demand; according to the actual operation data of the three-phase unbalanced power system, a mathematical model of a power distribution network accessed to the FMS is established, the mathematical model of the power distribution network accessed to the FMS comprises an objective function, the objective function takes the minimum total network loss including line loss and FMS operation loss as a reference, and a control strategy and an operation mode of the flexible multi-state switch FMS are determined; the method is applied to FMS-based power distribution network optimization control. A simulation experiment is carried out in an IEEE 33-node power distribution network model, and the result shows that the FMS can effectively reduce the system network loss, improve the voltage level and improve the three-phase unbalance degree. The method provides powerful technical support for application of the flexible multi-state switch in an actual power system.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method and device for managing power quality in a distribution network based on a flexible multi-state switch. Background Art

[0002] With the growth of global energy demand and the pressure of environmental protection, distributed energy is increasingly used in power systems. Distributed energy such as photovoltaic, wind power and other renewable energy sources are clean and sustainable, but the randomness and volatility of their output power have brought new challenges to the stability and reliability of traditional power systems. Especially in the case of high penetration, the power grid faces a series of problems such as voltage fluctuations, frequency deviations and three-phase imbalance. These problems not only affect the quality of power, but may also cause equipment damage and system collapse.

[0003] Power quality problems mainly include voltage sag, voltage fluctuation, voltage imbalance, harmonic pollution, etc. These problems have a negative impact on the reliability and safety of power supply for industrial and residential users. Traditional power quality management methods mainly rely on reactive power compensation equipment and filters, but these devices often fail to achieve the expected results when faced with complex power quality problems.

[0004] In order to meet the above challenges, flexible multi-state switches, as a new type of power electronic device, have gradually attracted widespread attention. Flexible multi-state switches (FMS) have the characteristics of flexible control and efficient operation. They can improve voltage distribution, reduce power loss and solve power imbalance problems by adjusting active and reactive power. The core component of flexible multi-state switches (FMS) is the back-to-back voltage source converter, whose bidirectional power flow and independent power control capabilities give it significant advantages in modern power systems.

[0005] In practical applications, FMS can not only supply power to the load, but also feed back the power of distributed power sources to the grid. Its advanced control strategies, such as vector control and DC voltage control, ensure the independent regulation of active and reactive power, significantly enhancing the dynamic response capability and operational stability of the system. FMS achieves effective management of power quality by flexibly adjusting the power flow.

[0006] The application of flexible multi-state switches in distribution networks has been widely studied. For example, FMS has shown good results in reducing system losses, improving voltage levels, and solving voltage fluctuations and three-phase unbalanced problems. However, existing research mainly focuses on the application of FMS in single-phase multi-node systems, and fails to fully consider the situation of three-phase unbalanced systems. In order to further explore the application of FMS in three-phase systems, based on the optimization model of distributed generators and FMS in three-phase unbalanced distribution networks, the comprehensive management of the power quality of the system has been studied through optimization algorithms such as second-order cone programming and multi-objective optimization models, and certain results have been achieved. However, when dealing with optimization problems with higher complexity, these traditional optimization algorithms often face problems such as high difficulty in solving and long calculation time, making it difficult to obtain ideal optimization results.

[0007] In addition, heuristic algorithms are a type of optimization algorithms based on empirical inspiration and natural phenomena. They have strong global search capabilities and flexibility, and can find optimal solutions in complex high-dimensional search spaces. The application of these algorithms in power systems covers many aspects, such as optimizing the power flow distribution of power systems, improving system stability, and optimizing resource allocation. Compared with traditional optimization methods, heuristic algorithms have the advantages of short development time and strong system robustness, especially when dealing with incomplete or noisy data. With the development of smart grids, heuristic algorithms play an increasingly important role in the optimization and control of power systems. Realizing adaptive control and optimized operation of power systems through intelligent means will be an important direction for the development of future power systems.

[0008] Publication number CN118300197A discloses a distribution network dispatching method, device, electronic device and storage medium, which dispatches flexible multi-state switches based on an optimized dispatching strategy. However, there are certain limitations in the dispatching of distribution networks containing flexible multi-state switches. Its technology mainly focuses on voltage optimization and switch dispatching, and does not involve more complex distribution network problems, such as three-phase imbalance and comprehensive power quality management. In addition, although the patent proposes constraints on active and reactive power, it does not conduct in-depth research on the impact of the converter loss of the flexible multi-state switch itself on the overall performance. Moreover, the patent does not clearly provide actual verification of the application scenario, especially the adaptability analysis of dynamic operating environments such as load fluctuations and distributed energy access is insufficient. Summary of the invention

[0009] Purpose of the invention: In view of the shortcomings of the prior art in dealing with power quality issues when distributed energy is connected to the power grid, the present invention provides a distribution network power quality management method based on a flexible multi-state switch. The present invention also discloses a distribution network power quality management device based on a flexible multi-state switch.

[0010] Technical solution: The present invention is a distribution network power quality management method based on a flexible multi-state switch. The back-to-back voltage source converter is used as one of the implementation forms of the multi-state switch, and has bidirectional power flow and independent power control capabilities. The efficient transmission of electric energy is achieved through AC-DC and DC-AC conversion. The two-terminal flexible multi-state switch adopts the PQ-VdcQ control mode in normal operation to adjust power transmission and maintain DC voltage. The multi-terminal flexible multi-state switch stabilizes the AC voltage through the VdcQ mode to ensure the overall stability of the system. The method includes:

[0011] Installing the flexible multi-state switch FMS on a node in the power system according to actual needs, the power system is a single-phase and / or three-phase unbalanced distribution network;

[0012] According to the actual operation data of the three-phase unbalanced power system, a mathematical model of the distribution network connected to the FMS is established, wherein the mathematical model of the distribution network connected to the FMS includes an objective function, wherein the objective function is based on minimizing the total network loss taking into account the line loss and the FMS operation loss, and determining the control strategy and operation mode of the flexible multi-state switch FMS;

[0013] Based on the mathematical model of the distribution network connected to the FMS and the control strategy and operation mode of the flexible multi-state switch FMS, the operation constraints of the FMS, the distribution network flow balance constraints, the voltage and current amplitudes and the system three-phase imbalance constraints in the distribution network containing the flexible multi-state switch are determined.

[0014] The walking difference algorithm HOA-DE is adopted, based on the control strategy and operation mode of the flexible multi-state switch FMS, and considering the constraints in the distribution network containing the flexible multi-state switch, the system network loss including the line loss and the FMS operation loss is optimized; the walking difference algorithm adopts the walking difference optimization algorithm HOA for preliminary search, and then uses the mutation and crossover strategy of the differential evolution algorithm DE for optimization;

[0015] Verify the effect of using the walking difference algorithm HOA-DE to optimize the system network loss.

[0016] Further, including:

[0017] The optimization objective function of the walking difference algorithm HOA-DE is to minimize the system network loss taking into account the line loss and FMS operation loss. The objective function is expressed as:

[0018]

[0019] Among them, Ω b is the set of all nodes in the power system, Inject into node i The active power of the phase, is a set of three phases, the three phases are phase a, phase b and phase c, Ω FMS A collection of FMSs connected to the power system, is the kth FMS on the jth line Power losses inside the phase inverter.

[0020] Further, including:

[0021] The step of determining the control strategy and operation mode of the flexible multi-state switch FMS includes:

[0022] Establishing a FMS operation balance constraint based on the balance between the active power injected into the associated feeder by the FMS and the internal losses of the converter formed by the flexible multi-state switch;

[0023] According to the stable operation of the power system, active and reactive power between nodes in the power system are kept balanced, and a power flow balance constraint is established;

[0024] Constraining node voltage and current amplitudes;

[0025] The voltage unbalance degree in the system is defined according to the ratio of the deviation of the square of the three-phase voltage amplitude to the square of the average voltage amplitude, and the three-phase voltage unbalance degree is constrained;

[0026] The root node current unbalance is defined by the ratio of the root node negative-sequence current amplitude to the positive-sequence current amplitude, and a constraint on the root node three-phase current unbalance is established.

[0027] Further, including:

[0028] The FMS operation balance constraint is expressed as:

[0029]

[0030] in, The active power injected into the jth branch by the kth FMS;

[0031] The active power injected into the jth branch by the kth FMS is There is a constraint relationship, expressed as:

[0032]

[0033] in, The reactive power injected into the jth branch by the kth FMS, is the converter loss coefficient;

[0034] To constrain the operation of FMS, The upper and lower bound constraints are expressed as:

[0035]

[0036] In the formula, The kth FMS is on the j branch. The maximum and minimum values ​​of reactive power allowed to pass through the phase converter.

[0037] Further, including:

[0038] The power flow balance constraint is expressed as:

[0039]

[0040] S ij =V i I ij ; (6)

[0041]

[0042] In the formula, I ij represents the current flowing from node i to node j, S ij is the complex power from node i to node j, Z ij Indicates the impedance of the line, S j Table Node j injection power, Ω REF is the reference node, S ij Calculated from the voltage of node i and the current of line (i, j), S j It consists of distributed generation, multi-state switches and line loads.

[0043] Further, including:

[0044] The constraining of the node voltage amplitude and the node current amplitude respectively includes:

[0045] The node voltage in the system is constrained, and the voltage amplitude of each node and each phase is expressed as:

[0046]

[0047] In the formula, are the upper and lower limits of the voltage amplitude of node i, respectively. This constraint applies to the set of all nodes except the reference node;

[0048] The branch current in the line is constrained, which can be expressed as:

[0049]

[0050] In the formula, is the maximum current of line (i, j).

[0051] Further, including:

[0052] The constraining of the three-phase voltage unbalance includes:

[0053]

[0054]

[0055] In the formula, i-node Phase voltage unbalance parameter, is the average value of the square of the voltage amplitude at node i.

[0056] Further, including:

[0057] The step of establishing a constraint on the unbalance degree of the three-phase current of the root node includes:

[0058]

[0059] Among them, C I is the root node three-phase current unbalance parameter, is the maximum value of this parameter, They are respectively the positive and negative sequence current amplitudes of the root node in the system, and are calculated as follows:

[0060]

[0061]

[0062] a=e j2π / 3 ; (15)

[0063] In the formula, They are the root node a, b, and c phase currents respectively.

[0064] Further, including:

[0065] The HOA-DE algorithm is used to optimize the system network loss taking into account the line loss and the FMS operation loss, including:

[0066] Initialize the pedestrians and generate a set of initial candidate solutions based on the reactive power of FMS. As a hiker population X i ;

[0067] Write in the relevant FMS converter internal loss parameters, and based on the operating characteristics of the FMS, write in constraints such as node voltage amplitude, three-phase voltage imbalance, and root node current imbalance;

[0068] Taking the system network loss f taking into account the line loss and FMS operation loss as the optimization target, calculate the fitness F(x) value;

[0069] Calculate the walker's speed W according to the Tobler walking function i t , and based on the hiker X i t Current speed W i t Update its location and get Evaluate new fitness;

[0070] After the initial search, the mutation and crossover strategies of the DE algorithm are used for optimization, the quality of the solution after each mutation and crossover is evaluated, solutions that do not meet the FMS operation constraints and voltage and current amplitude constraints are discarded, and solutions that do not meet the three-phase unbalance constraints are penalized;

[0071] According to the evaluation results after crossover mutation, select the individual X with the highest fitness best , extract its corresponding Update the objective function fitness value as the final optimization result.

[0072] On the other hand, the present invention also provides a distribution network power quality management device based on a flexible multi-state switch, comprising:

[0073] A configuration module, used to install the flexible multi-state switch FMS on a node in the power system according to actual needs, wherein the power system is a single-phase and / or three-phase unbalanced distribution network;

[0074] A model building module, for establishing a mathematical model of a distribution network connected to the FMS according to actual operation data of the three-phase unbalanced power system, wherein the mathematical model of the distribution network connected to the FMS includes an objective function, wherein the objective function is based on minimizing the total network loss taking into account the line loss and the FMS operation loss, and determining the control strategy and operation mode of the flexible multi-state switch FMS;

[0075] An optimization module is used to optimize the system network loss taking into account the line loss and the FMS operation loss by using the walking difference algorithm HOA-DE; the walking difference algorithm is to use the walking difference optimization algorithm HOA to perform a preliminary search and then use the mutation and crossover strategy of the differential evolution algorithm DE to perform optimization;

[0076] The verification module is used to verify the effect of using the pedestrian difference algorithm HOA-DE to optimize the system network loss.

[0077] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0078] The present invention proposes a power quality management method for a distribution network based on a flexible multi-state switch. By combining the walking optimization algorithm with the differential evolution algorithm, a walking differential algorithm is proposed, and it is successfully applied to the optimization control of an actual power system. The simulation experimental results of the present invention verify the remarkable effect of the method in reducing system network losses, increasing voltage levels, and improving three-phase imbalance. This method not only improves the optimization control effect of FMS in the distribution network, but also provides strong support for the stable operation and efficient management of future power systems, and has broad application prospects and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 This is a schematic diagram of a multi-terminal flexible multi-state switch according to an embodiment of the present invention;

[0080] Figure 2 This is a flow chart of the HOA-DE algorithm described in an embodiment of the present invention;

[0081] Figure 3 This is a schematic diagram of the FMS access position in the single-phase 33-node distribution network according to an embodiment of the present invention;

[0082] Figure 4 A voltage curve diagram of the FMS connected to different positions according to an embodiment of the present invention;

[0083] Figure 5 A schematic diagram of the FMS access position in the three-phase 33-node distribution network according to an embodiment of the present invention;

[0084] Figure 6 Schematic diagram of voltage level curves in three scenarios described in an embodiment of the present invention. DETAILED DESCRIPTION

[0085] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0086] The present invention discloses a method for managing power quality of a distribution network based on a flexible multi-state switch, the method comprising:

[0087] S1 installs the flexible multi-state switch FMS on a node in the power system according to actual needs, and the power system is a single-phase and / or three-phase unbalanced distribution network.

[0088] S2 establishes a mathematical model of the distribution network connected to the FMS based on the actual operating data of the three-phase unbalanced power system. The mathematical model of the distribution network connected to the FMS includes an objective function. The objective function takes the minimum total network loss taking into account the line loss and the FMS operating loss as a benchmark, and determines the control strategy and operating mode of the flexible multi-state switch FMS.

[0089] In this embodiment, the present invention analyzes the architecture of the FMS and establishes an optimization model taking into account the three-phase unbalanced constraints of the system operation, including: establishing a voltage, current and power distribution model of each node according to the actual operation data of the power system;

[0090] Consider the electrical connections and power flows between different nodes and determine the electrical parameters in the system.

[0091] Set the optimization objective function to reduce system network losses and improve voltage distribution as the main goals, while taking into account the improvement of three-phase imbalance;

[0092] Further, in this embodiment, the control strategy and operation mode of the flexible multi-state switch are determined;

[0093] The FMS operation balance constraint is established based on the balance between the active power injected by the FMS into the associated feeder and the internal losses of its converter;

[0094] Establishing power flow balance constraints based on the balance of active and reactive power between nodes in the power system when the system is running stably;

[0095] To ensure the superiority of system power quality, the node voltage amplitude is constrained;

[0096] In order to prevent the circuit temperature from being too high, which may cause problems such as material aging, circuit damage or short circuit, the current amplitude is constrained;

[0097] The voltage unbalance degree in the system is defined according to the ratio of the deviation of the square of the three-phase voltage amplitude to the square of the average voltage amplitude, and the three-phase voltage unbalance degree is constrained;

[0098] The root node current unbalance is defined by the ratio of the root node negative-sequence current amplitude to the positive-sequence current amplitude, and a constraint on the root node three-phase current unbalance is established.

[0099] S3 uses the walking difference algorithm HOA-DE to optimize the system network loss taking into account the line loss and FMS operation loss; the walking difference algorithm uses the walking difference optimization algorithm HOA for preliminary search and then uses the mutation and crossover strategy of the differential evolution algorithm DE for optimization.

[0100] Hiking Optimization Algorithm (HOA) is a metaheuristic optimization algorithm inspired by the experience of hiking. Hikers consciously or unconsciously take into account the steepness of the terrain as they attempt to reach the top of a mountain, hill, or rock, a popular recreational activity that recognizes the similarities between the search landscape of an optimization problem and the mountainous terrain that hikers traverse. The mathematical model of HOA is premised on the Tobler hiking function, which determines the walking speed of a hiker (i.e., the agent) by taking into account the elevation of the terrain and the distance traveled. The Tobler hiking function (THF) is used to determine the position of the hiker during the solution of the optimization problem.

[0101] Initialize the pedestrians and generate a set of initial candidate solutions based on the reactive power of FMS. As a hiker population X i , and write the relevant FMS converter internal loss parameters, write the node voltage amplitude, three-phase voltage imbalance, root node current imbalance and other constraints based on the FMS operation characteristics. Take the system network loss f including line loss and FMS operation loss as the optimization target, calculate the fitness F(x) value, and calculate the pedestrian's travel speed W according to the Tobler walking function i t , and based on the hiker Current speed W i t Update its location and get Evaluate the new fitness.

[0102] After the initial search, the DE algorithm mutation and crossover strategies are used for optimization, and the quality of the solution after each mutation and crossover is evaluated. The solutions that do not meet the FMS operation constraints and voltage and current amplitude constraints are discarded, and the solutions that do not meet the three-phase unbalance constraints are penalized. According to the evaluation results after crossover and mutation, the individual with the highest fitness X is selected. best , extract its corresponding Update the objective function fitness value as the final optimization result.

[0103] S4 verifies the effect of using the walking difference algorithm HOA-DE to optimize the system network loss.

[0104] In this embodiment, the present invention optimizes the operation of a distribution network containing a flexible multi-state switch by using the proposed algorithm with the main goals of reducing system network losses and improving voltage distribution, including:

[0105] Set up a single-phase distribution network system with IEEE33 nodes;

[0106] FMS is connected to different locations of the single-phase 33-bus system, and the proposed HOA-DE algorithm is used to optimize the total network loss of the system.

[0107] The network loss results after optimization of the distribution network with flexible multi-state switches connected at different positions of the single-phase system are compared to obtain the difference in the optimization effect of the same capacity FMS on network loss.

[0108] The optimized voltage curves of the distribution network connected to the flexible multi-state switch at different positions of the single-phase system are compared to obtain the difference in the voltage drop management capabilities of the same capacity FMS;

[0109] Furthermore, the single-phase is extended to three-phase, and the FMS is connected to the three-phase 33-node distribution network;

[0110] Based on the mathematical model of flexible multi-state switch and the constraint of three-phase imbalance in the system, the proposed HOA-DE algorithm is used to optimize the network loss of the system.

[0111] The power management results before and after FMS configuration and before and after unbalance constraint setting are compared to verify the effect of FMS configuration on the comprehensive power quality management of three-phase unbalance.

[0112] Specifically, the multi-terminal flexible multi-state switch structure of the present invention is as follows Figure 1 As shown in the figure, each end of the flexible multi-state switch needs to have the function of transmitting active power flow and regulating power quality. It is mainly composed of back-to-back voltage source converters and connected to the power grid through feeders. The flexible multi-state switch realizes efficient transmission of electric energy through AC-DC and DC-AC conversion. The two-terminal FMS adopts the PQ-VdcQ control mode in normal operation to adjust power transmission and maintain DC voltage; the multi-terminal FMS stabilizes the AC voltage through the VdcQ mode to ensure the overall stability of the system.

[0113] Based on this, a mathematical model of the distribution network connected to the FMS is established, including:

[0114] The objective function is set to minimize the total network loss taking into account line loss and FMS operation loss, which can be expressed as:

[0115]

[0116] In the formula, Ω b is the set of all nodes in the distribution network, Inject into node i Active power of each phase, Ω FMS is the collection of FMSs connected to the distribution network, is the kth FMS on the jth line Power losses inside the phase inverter.

[0117] The FMS operation is constrained so that the active power injected into the associated feeder is balanced with the internal losses of its converter, which can be expressed as:

[0118]

[0119] In the formula, The active power injected into the jth branch is injected into the kth FMS.

[0120] To constrain the operation of FMS, the active power injected into the jth branch by the kth FMS is There is a constraint relationship, which can be expressed as:

[0121]

[0122] In the formula, The reactive power injected into the jth branch by the kth FMS, is the converter loss factor.

[0123] To constrain the operation of FMS, The upper and lower limit constraints can be expressed as:

[0124]

[0125] In the formula, The kth FMS is on the j branch. The maximum and minimum values ​​of reactive power allowed to pass through the phase converter.

[0126] To constrain the FMS operation and limit the apparent power of the converter, it can be expressed as:

[0127]

[0128] In the formula, is the maximum apparent power allowed to pass through the α-phase converter of the j-branch of the k-th FMS.

[0129] To constrain the system power flow balance, the voltage drop equation of the multi-phase distribution line can be expressed as:

[0130] ΔV i,j =Z·I

[0131] Where ΔV i,j is the voltage drop matrix between nodes i and j, Z is the line impedance matrix, and I is the line current matrix. The expression is as follows:

[0132]

[0133] Where V i,a 、V i,b 、V i,cis the three-phase complex voltage of nodes a, b, and c, Z aa , Z bb , Z cc is the self-impedance in the line, Z ab , Z bc , Z ac is the phase-to-phase mutual impedance, I a ,I b ,I c is the three-phase current vector between lines i and j.

[0134] To constrain the system power flow balance, the power relationship in the line can be expressed as:

[0135]

[0136] S ij =V i I ij ; (7)

[0137]

[0138] In the formula, S ij is the complex power from node i to node j, Z ij Indicates the impedance of the line, S j Table Node j injection power, Ω REF is the reference node, where S ij Calculated from the voltage of node i and the current of line (i, j), S j It consists of distributed generation, multi-state switches and line loads.

[0139] By constraining the node voltage in the system, the voltage amplitude of each node and each phase can be expressed as:

[0140]

[0141] In the formula, are the upper and lower limits of the voltage amplitude of node i, respectively. This constraint applies to the set of all nodes except the reference node.

[0142] The branch current in the line is constrained, and the thermal limit constraint can be expressed as:

[0143]

[0144] In the formula, is the maximum current of line (i, j).

[0145] The three-phase imbalance degree of the power grid is constrained, and the voltage imbalance constraint can be expressed as:

[0146]

[0147]

[0148] In the formula, i-node Phase voltage unbalance parameter, is the average value of the square of the voltage amplitude at node i.

[0149] The three-phase imbalance degree of the power grid is constrained, and the root node current imbalance degree constraint can be expressed as:

[0150]

[0151] In the formula, C I is the root node three-phase current unbalance parameter, is the maximum value of this parameter, They are respectively the positive and negative sequence current amplitudes of the root node in the system, and are calculated as follows:

[0152]

[0153]

[0154] a=e j2π / 3 ; (16)

[0155] In the formula, They are the root node a, b, and c phase currents respectively.

[0156] The pedestrian difference algorithm proposed in this invention is used to optimize the distribution network with flexible multi-state switches. The algorithm flow is as follows: Figure 2 shown.

[0157] Based on this, the main steps of the walking difference algorithm include:

[0158] A set of candidate solutions is generated in the initialization phase of the algorithm, and the initial position in the search space is expressed as follows:

[0159]

[0160] In the formula, is the initial position of the i-th group of candidate solutions, are the upper and lower limits of the decision variables, and μ is a random constant between [0,1].

[0161] In the HOA algorithm, the terrain slope is expressed as:

[0162]

[0163] In the formula, is the terrain slope matrix of the t-th iteration of the i-th group of candidate solutions, dh and dl represent the altitude difference and distance difference respectively, is the terrain inclination angle, ranging from [0,50°].

[0164] The walking speed is calculated based on the Tobler walking function. Describe it as:

[0165]

[0166] The current speed of the hiker in the HOA algorithm is expressed as:

[0167]

[0168] Where W i t is the traveler’s current speed, W i t-1 is the speed in the previous iteration, is a constant uniformly distributed in the interval [0,1], X best To position the leading hiker, is the current hiker position, is the scan factor of the hiker, which is a constant in the interval [1,3].

[0169] Based on the population movement speed, the position of the particles in the algorithm is updated as follows:

[0170]

[0171] After the initial search using the HOA algorithm, the DE algorithm's mutation and crossover strategies are used for further optimization. The relevant formula is as follows

[0172] N i =X best +F·(X r1 -X r2 ); (twenty two)

[0173] Where N i is the mutation vector, X best is the optimal solution vector, X r1 , X r2 are two random individuals in the population, and F is the variation factor, which is used to control the amplitude of variation.

[0174] The mutation vector is combined with the current individual using the crossover formula to generate a new candidate solution.

[0175]

[0176] In the formula, m i,j is the jth decision variable of the crossover vector, n i,j is the jth decision variable of the mutation vector, x i,jis the jth decision variable of the current candidate solution, R j is a random number uniformly distributed in the interval [0,1], c is the crossover probability, J R is a randomly chosen dimension that ensures that at least one component is obtained from the mutation vector.

[0177] The present invention uses the HOA-DE algorithm in MATLAB to verify the effect of FMS in reducing network loss in the power system. The FMS access location is as follows: Figure 3 shown.

[0178] An IEEE 33-node system is set up, and FMS is connected between nodes 12-22, 18-33, and 9-15, respectively, with the capacity set to 500kW.

[0179] Based on this, the control effects of FMS at different nodes are compared.

[0180] When FMS is not connected, the system network loss is 204kW. When FMS is connected to nodes 12-22, the network loss is 119.15kW. When it is connected to nodes 18-33, the network loss is 120.73kW. When it is connected to nodes 9-15, the network loss is 139.5kW. It can be seen that the different positions of FMS in the distribution network have different effects on the control of system network loss.

[0181] The present invention uses the HOA-DE algorithm in MATLAB to verify the effect of FMS in reducing network loss in the power system. The voltage curves of FMS connected at different locations in the distribution network are as follows: Figure 4 shown.

[0182] It can be seen that the proposed algorithm has an obvious optimization effect in this example. The access of FMS has a certain improvement on the voltage level in the distribution network. Compared with the case without FMS, the overall system voltage level has increased to a certain extent. The same capacity FMS has a slightly different effect on the voltage level.

[0183] The present invention expands the single-phase 33-node distribution network into a three-phase model to verify the effect of FMS on the three-phase imbalance management in the power system. Figure 5 shown.

[0184] The 33-node distribution network is expanded into a three-phase model, and a three-phase load is set at each node. To simulate the impact of distributed power access on the operation of the distribution network, single-phase photovoltaic systems are connected to nodes 4, 19, and 26, with access capacities of 150kW each, and the FMS capacity is set to 500kVA.

[0185] Based on this, this study sets the following scenario:

[0186] Case 1: No FMS is configured and no three-phase unbalance constraint is set;

[0187] Case 2: Configure FMS without setting three-phase unbalance constraints;

[0188] Case 3: Configure FMS to constrain the three-phase voltage and current imbalance.

[0189] The present invention uses the HOA-DE algorithm to optimize the network with the goal of minimizing the total network loss taking into account the line loss and FMS operation loss for three scenarios. The optimization results are as follows: Figure 6 shown.

[0190] Based on this, it can be seen that the HOA-DE algorithm has a significant effect in optimizing the three-phase unbalanced operation of the power distribution network configured with FMS. Compared with the three-phase unbalanced system without FMS, the three-phase voltage level of the system is significantly improved after FMS is configured; Figure 6 (b) and Figure 6 In (c), after taking into account the three-phase unbalance constraint, the three-phase unbalance level of Case 3 is significantly reduced.

[0191] In the three scenarios, the total system loss is 228.61kW, 214.93kW, and 224.87kW respectively. It can be seen that in the three-phase network, FMS still has the effect of reducing network loss. When the three-phase unbalance constraint is taken into account, the optimization effect of FMS on network loss is weakened to a certain extent, but the network loss is still lower than Figure 6 The losses under (a) Case 1 in the figure show that in the distribution network connected to distributed power sources, the configuration of FMS has a significant effect on the comprehensive power quality management of three-phase unbalance.

[0192] This paper proposes and verifies an optimization algorithm that combines HOA and DE, and applies it to the optimization control of flexible multi-state switches (FMS) in distribution networks. First, the architecture of FMS is analyzed, and the optimization model is established by taking into account the three-phase unbalanced constraints of system operation; then, the HOA-DE algorithm is proposed, and through simulation experiments, the optimization effect of connecting FMS at different locations in the distribution network on the system power quality under the proposed algorithm is verified in a single-phase 33-node system. On this basis, the single-item model is extended to three phases, and it is verified that when considering the three-phase unbalanced constraints, the connection of FMS reduces system network losses, improves three-phase imbalance, and improves voltage levels. The effect provides theoretical support for the application of flexible multi-state switches in actual power systems, and demonstrates the important value of FMS in improving the power quality and system reliability of distribution networks.

[0193] On the other hand, the present invention also provides a distribution network power quality management device based on a flexible multi-state switch, comprising:

[0194] A configuration module, used to install the flexible multi-state switch FMS on a node in the power system according to actual needs, wherein the power system is a single-phase and / or three-phase unbalanced distribution network;

[0195] A model building module, for establishing a mathematical model of a distribution network connected to the FMS according to actual operation data of the three-phase unbalanced power system, wherein the mathematical model of the distribution network connected to the FMS includes an objective function, wherein the objective function is based on minimizing the total network loss taking into account the line loss and the FMS operation loss, and determining the control strategy and operation mode of the flexible multi-state switch FMS;

[0196] An optimization module is used to optimize the system network loss taking into account the line loss and the FMS operation loss by using the walking difference algorithm HOA-DE; the walking difference algorithm is to use the walking difference optimization algorithm HOA to perform a preliminary search and then use the mutation and crossover strategy of the differential evolution algorithm DE to perform optimization;

[0197] Verification module, used to verify the effect of using the pedestrian difference algorithm HOA-DE on the optimization of system network loss

[0198] Other technical features of the distribution network power quality management device based on flexible multi-state switches of the present invention are similar to the corresponding distribution network power quality management method based on flexible multi-state switches, and will not be repeated here.

[0199] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0200] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0201] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if these modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for power quality management of distribution network based on flexible multi-state switch, characterized in that: The method includes: Installing the flexible multi-state switch FMS on a node in the power system according to actual needs, the power system is a single-phase and / or three-phase unbalanced distribution network; According to the actual operation data of the three-phase unbalanced power system, a mathematical model of the distribution network connected to the FMS is established, wherein the mathematical model of the distribution network connected to the FMS includes an objective function, wherein the objective function is based on minimizing the total network loss taking into account the line loss and the FMS operation loss, and determining the control strategy and operation mode of the flexible multi-state switch FMS; Based on the mathematical model of the distribution network connected to the FMS and the control strategy and operation mode of the flexible multi-state switch FMS, the operation constraints of the FMS, the power flow balance constraints of the distribution network, the voltage and current amplitudes and the three-phase imbalance constraints of the system in the distribution network containing the flexible multi-state switch are determined; The walking difference algorithm HOA-DE is adopted, based on the control strategy and operation mode of the flexible multi-state switch FMS, and considering the constraints in the distribution network containing the flexible multi-state switch, the system network loss including the line loss and the FMS operation loss is optimized; the walking difference algorithm adopts the walking difference optimization algorithm HOA for preliminary search, and then uses the mutation and crossover strategy of the differential evolution algorithm DE for optimization; Verify the effect of using the walking difference algorithm HOA-DE to optimize the system network loss.

2. The method for power quality management of distribution network based on flexible multi-state switch according to claim 1 is characterized in that: The optimization objective function of the walking difference algorithm HOA-DE is to minimize the system network loss taking into account the line loss and FMS operation loss. The objective function is expressed as: Among them, Ω b is the set of all nodes in the power system, Inject into node i The active power of the phase, is a set of three phases, the three phases are phase a, phase b and phase c, Ω FMS A collection of FMSs connected to the power system, is the kth FMS on the jth line Power losses inside the phase inverter.

3. The method for power quality management of distribution network based on flexible multi-state switch according to claim 2 is characterized in that: The step of determining the control strategy and operation mode of the flexible multi-state switch FMS includes: Establishing a FMS operation balance constraint based on the balance between the active power injected into the associated feeder by the FMS and the internal losses of the converter formed by the flexible multi-state switch; According to the stable operation of the power system, active and reactive power between nodes in the power system are kept balanced, and a power flow balance constraint is established; Constraining node voltage and current amplitudes; The voltage unbalance degree in the system is defined according to the ratio of the deviation of the square of the three-phase voltage amplitude to the square of the average voltage amplitude, and the three-phase voltage unbalance degree is constrained; The root node current unbalance is defined by the ratio of the root node negative-sequence current amplitude to the positive-sequence current amplitude, and a constraint on the root node three-phase current unbalance is established.

4. The method for managing power quality of distribution network based on flexible multi-state switch according to claim 3 is characterized in that: The FMS operation balance constraint is expressed as: in, The active power injected into the jth branch by the kth FMS; The active power injected into the jth branch by the kth FMS is There is a constraint relationship, expressed as: in, The reactive power injected into the jth branch by the kth FMS, is the converter loss coefficient; To constrain the operation of FMS, The upper and lower bound constraints are expressed as: In the formula, The kth FMS is on the j branch. The maximum and minimum values ​​of reactive power allowed to pass through the phase converter.

5. The method for power quality management of distribution network based on flexible multi-state switch according to claim 4 is characterized in that: The power flow balance constraint is expressed as: S ij =V i I ij ;(6) In the formula, I ij represents the current flowing from node i to node j, S ij is the complex power from node i to node j, Z ij Indicates the impedance of the line, S j Table Node j injection power, Ω REF is the reference node, S ij Calculated from the voltage of node i and the current of line (i, j), S j It consists of distributed generation, multi-state switches and line loads.

6. The method for power quality management of distribution network based on flexible multi-state switch according to claim 4 is characterized in that: The constraining of the node voltage amplitude and the node current amplitude respectively includes: The node voltage in the system is constrained, and the voltage amplitude of each node and each phase is expressed as: In the formula, are the upper and lower limits of the voltage amplitude of node i, respectively. This constraint applies to the set of all nodes except the reference node; Constrain the branch current in the line, expressed as: In the formula, is the maximum current of line (i, j).

7. The method for managing power quality of distribution network based on flexible multi-state switch according to claim 4 is characterized in that: The constraining of the three-phase voltage unbalance degree includes: In the formula, i-node Phase voltage unbalance parameter, is the average value of the square of the voltage amplitude at node i.

8. The method for power quality management of distribution network based on flexible multi-state switch according to claim 4 is characterized in that: The step of establishing a constraint on the unbalance degree of the three-phase current of the root node includes: Among them, C I is the root node three-phase current unbalance parameter, is the maximum value of this parameter, are the positive and negative sequence current amplitudes of the root node in the system, respectively, and are calculated as follows: a=e j2π / 3 ; (15) In the formula, They are the root node a, b, and c phase currents respectively.

9. The method for power quality management of distribution network based on flexible multi-state switch according to claim 1 is characterized in that: The HOA-DE algorithm is used to optimize the system network loss taking into account the line loss and the FMS operation loss, including: Initialize the pedestrians and generate a set of initial candidate solutions based on the reactive power of FMS. As a hiker population X i ; Write in the relevant FMS converter internal loss parameters, and based on the operating characteristics of the FMS, write in constraints such as node voltage amplitude, three-phase voltage imbalance, and root node current imbalance; Taking the system network loss f taking into account the line loss and FMS operation loss as the optimization target, calculate the fitness F(x) value; Calculate the walker's speed W according to the Tobler walking function i t , and based on the hiker Current speed W i t Update its location and get and evaluate the new fitness; After the initial search, the mutation and crossover strategies of the DE algorithm are used for optimization, and the quality of the solution after each mutation and crossover is evaluated. Solutions that do not meet the FMS operation constraints and voltage and current amplitude constraints are discarded, and solutions that do not meet the three-phase unbalance constraints are penalized. According to the evaluation results after crossover mutation, select the individual X with the highest fitness best , extract its corresponding Update the objective function fitness value as the final optimization result.

10. A distribution network power quality management device based on flexible multi-state switch, characterized in that: include: A configuration module, used to install the flexible multi-state switch FMS on a node in the power system according to actual needs, wherein the power system is a single-phase and / or three-phase unbalanced distribution network; A model building module, for establishing a mathematical model of a distribution network connected to the FMS according to actual operation data of the three-phase unbalanced power system, wherein the mathematical model of the distribution network connected to the FMS includes an objective function, wherein the objective function is based on minimizing the total network loss taking into account the line loss and the FMS operation loss, and determining the control strategy and operation mode of the flexible multi-state switch FMS; An optimization module is used to optimize the system network loss taking into account the line loss and the FMS operation loss by using the walking difference algorithm HOA-DE; the walking difference algorithm is to use the walking difference optimization algorithm HOA to perform a preliminary search and then use the mutation and crossover strategy of the differential evolution algorithm DE to perform optimization; The verification module is used to verify the effect of using the pedestrian difference algorithm HOA-DE to optimize the system network loss.

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