Online hierarchical control method, device, equipment and medium for isolated microgrid

Abstract

The present invention belongs to the technical field of power system automation, and specifically relates to an online hierarchical control method, device, equipment and medium for an isolated microgrid. The method includes, after a distribution network failure occurs, constructing each isolated microgrid based on energy storage equipment and distributed photovoltaics; constructing a hierarchical voltage / reactive power control model based on a three-phase unbalanced distribution network model of the isolated microgrid; the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function; introducing an auxiliary variable vector to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraints, using the quasi-Newton ADMM method to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated microgrid. This scheme uses the inherent photovoltaic resources in the island to solve the voltage safety problem of the isolated microgrid after photovoltaic grid connection, and realizes voltage autonomy.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system automation, and in particular relates to an online hierarchical control method, device, equipment and medium for an isolated island microgrid. Background Art

[0002] In recent years, the frequency of extreme weather has increased, resulting in frequent large-scale power outages. Compared with urban power grids, distribution networks are more vulnerable to extreme weather, and secondary disasters such as waterlogging, mudslides, and landslides in extreme weather such as heavy rain will lead to road and communication interruptions, greatly increasing the difficulty of power grid repair. The above factors make the power outage time of distribution networks under disasters far longer than that of urban distribution networks, and residents' lives are facing huge impacts.

[0003] To address the above problems, existing emergency repair work often connects mobile generators, mobile energy storage, etc. to planned microgrids after disasters to restore some of the users' electricity needs. However, distributed photovoltaics in mountainous areas are less utilized. This is because under isolated operation, the output of distributed photovoltaics fluctuates frequently, and the existing reactive power compensation equipment is difficult to respond quickly to reactive power demand. There is a lack of effective voltage control measures, which leads to frequent fluctuations in the voltage and frequency of the isolated island system, increasing the risk of system instability. Summary of the invention

[0004] The purpose of the present invention is to provide an online hierarchical control method, device, equipment and medium for an isolated island microgrid. In view of the limited emergency power supply resources of the isolated island power grid under extreme disasters and the intermittent and volatile nature of distributed photovoltaics that limit their restoration and grid connection, the inherent photovoltaic resources in the isolated island are used to solve the voltage safety problem of the isolated island microgrid after photovoltaic grid connection, thereby achieving voltage autonomy.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an online hierarchical control method for an isolated island microgrid, which is applied to a distribution network in a mountainous area, comprising:

[0007] After a distribution network failure occurs, each isolated island microgrid is constructed based on energy storage equipment and distributed photovoltaics;

[0008] Construct a three-phase unbalanced distribution network model based on an island microgrid;

[0009] Based on the three-phase unbalanced distribution network model, a hierarchical voltage / reactive power control model is constructed; wherein the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function;

[0010] An auxiliary variable vector is introduced to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraints, the quasi-Newton ADMM method is used to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated island microgrid.

[0011] Furthermore, each isolated island microgrid is constructed based on energy storage equipment and distributed photovoltaics, including:

[0012] Obtain various data parameters of the distribution network; the various data parameters include topology information, node load, distributed photovoltaic output range and energy storage equipment parameters;

[0013] An energy storage output model is constructed based on the energy storage device parameters, and the maximum active power of the energy storage device is determined based on the energy storage output model; a distributed photovoltaic output model is constructed based on the distributed photovoltaic output range, and the output prediction value of the photovoltaic device is determined based on the distributed photovoltaic output model;

[0014] Based on the topology information, the node where the energy storage device is located is taken as the root node, and the baseline power circle is constructed with the maximum active power of the energy storage device as the radius. The breadth-first search algorithm is used to determine the actual range of the baseline power circle in the distribution network.

[0015] Based on the topological information, a dotted power circle is constructed with the node where the distributed photovoltaic power is located as the root node and 80% of the predicted output value of the photovoltaic equipment as the radius, and the actual range of the dotted power circle in the distribution network is determined using the breadth-first search algorithm.

[0016] When two baseline power circles intersect, or when the baseline power circle intersects with the dashed power circle, the corresponding root node regions are merged into an island; when two dashed power circles intersect, islands are not merged;

[0017] Based on the node load, the recovery status of the target load in the distribution network is determined, and the node where the target load that has not restored power supply is located is used as the root node; based on the breadth-first search algorithm, the node where the target load that has not restored power supply is located is merged into the nearest island that meets the power demand, and the load in the nearest island is reduced or connected to mobile power generation resources; the power constraint of the nearest island is checked, and when the power constraint is not met, part of the load is removed according to the distance between the load and the root node and the importance of the load until the power constraint is met.

[0018] Furthermore, a three-phase unbalanced distribution network model based on an island microgrid is constructed, including:

[0019] An unbalanced linearized power flow model of the distribution network is determined, the unbalanced linearized power flow model is rewritten into a compact form model, and the compact form model is simplified to obtain a three-phase unbalanced distribution network model.

[0020] Furthermore, the hierarchical voltage / reactive power control model specifically includes:

[0021] Objective function:

[0022] Constraints:

[0023] in, Indicates the power flow voltage of the distribution network; Indicates the reactive power generated by distributed photovoltaics during period k; Represents the weight coefficient of voltage deviation; The weight coefficient representing the reactive power cost generated by distributed photovoltaic inverters; , They represent the lower and upper limits of reactive power generated by distributed photovoltaics respectively; represents a vector consisting of square terms of voltage reference values; represents a diagonal matrix; The transpose of the matrix representing the node connectivity, A vector representing the connection relationship between the first node and the remaining nodes, Indicates the reference voltage value, and All are standard correlation matrices for distribution networks; , Represent active power flow and reactive power flow respectively.

[0024] Furthermore, an auxiliary variable vector is introduced to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model, including:

[0025] Based on auxiliary variable vector The hierarchical voltage / reactive power control model is reconstructed to obtain the reconstructed model:

[0026]

[0027]

[0028]

[0029] in, M and μ All are defined intermediate parameters; represents the objective function of the reconstruction model; auxiliary variable vector , auxiliary variable vector , z n is the auxiliary variable vector z Elements in

[0030] Determine the equivalent representation model of the reconstructed model as follows:

[0031]

[0032]

[0033] in, Reactive power generated by distributed photovoltaics; is the defined parameter, representing the auxiliary variable vector The indicator function ;

[0034]

[0035] Z For the defined parameters, .

[0036] Furthermore, the quasi-Newton ADMM method is used to solve the equivalent model of the problem, including:

[0037] The augmented Lagrangian function L that determines the equivalent representation of the reconstructed model is:

[0038]

[0039] in, is the augmented Lagrangian parameter; is the defined parameter, indicating Related dual variables;

[0040] Set up a positive definite matrix for the local agent , define the parameters ;

[0041] Defining parameters : ;

[0042] The equivalent description model of the equivalent representation model is determined as follows:

[0043]

[0044]

[0045] The augmented Lagrangian function that equivalently describes the model is as follows:

[0046]

[0047] Defining parameters , and ,as follows:

[0048]

[0049]

[0050]

[0051] in, ;

[0052] right To solve, the steps are as follows:

[0053] Step 1: Update

[0054]

[0055] Step 2: Update

[0056]

[0057] Step 3: Update

[0058]

[0059] in, represents the number of iterations, the update z in step 1 is handled by the local agent; in step 2 Updates are handled by central agents.

[0060] Furthermore, define the parameters , and In the step of , the parameter B is diagonalized.

[0061] In a second aspect, the present invention provides an online hierarchical control device for an isolated microgrid, comprising:

[0062] Microgrid construction module, used to build each island microgrid based on energy storage equipment and distributed photovoltaics after a distribution network failure occurs;

[0063] The distribution network model building module is used to build a three-phase unbalanced distribution network model based on an island microgrid;

[0064] An optimization model building module is used to build a hierarchical voltage / reactive power control model based on the three-phase unbalanced distribution network model; wherein the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function;

[0065] The model solving module is used to introduce an auxiliary variable vector to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraints, the quasi-Newton ADMM method is used to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated island microgrid.

[0066] According to a third aspect of the present invention, an electronic device is provided, comprising a processor and a memory, wherein the processor is configured to execute a computer program stored in the memory to implement the above-mentioned online hierarchical control method for an isolated island microgrid.

[0067] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores at least one instruction, and when the at least one instruction is executed by a processor, the online hierarchical control method for an isolated island microgrid as described above is implemented.

[0068] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0069] A quasi-Newton ADMM algorithm is proposed. By diagonalizing the Hessian matrix of the objective function, it can accelerate the convergence ability of ADMM and improve the convergence performance of the voltage / reactive power control strategy.

[0070] An online hierarchical voltage / reactive power control strategy in unbalanced distribution networks is designed using the quasi-Newton ADMM. This strategy can utilize the good convergence performance of the quasi-Newton ADMM and has good tracking ability for rapidly changing environments.

[0071] It can be effectively applied in isolated island scenarios, and the voltage fluctuation problem caused by photovoltaic grid connection can be solved through the reactive power adjustment capability of the photovoltaic inverter itself, so that the isolated island microgrid can obtain more power resources, reduce the power outage losses after the disaster, and reduce the layout capacity or output power of mobile resources, so as to reduce the scheduling cost of mobile resources.

[0072] An isolated microgrid online hierarchical control device, electronic device and computer-readable storage medium provided by the present invention also solve the problems raised in the background technology section. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0074] Figure 1 A schematic flow chart of an online hierarchical control method for an isolated island microgrid according to an embodiment of the present invention;

[0075] Figure 2 Schematic diagram of an isolated island microgrid according to an embodiment of the present invention;

[0076] Figure 3 A schematic diagram of communication between a central agent and a local agent in an embodiment of the present invention;

[0077] Figure 4 Schematic diagram of online hierarchical voltage / reactive power control process in an embodiment of the present invention;

[0078] Figure 5 Schematic diagram of the convergence of the quasi-Newton ADMM in the embodiment of the present invention; wherein (a) the convergence of reactive power output of the photovoltaic inverter on phase C of node 18 at 18h; (b) the convergence of phase B voltage of node 93 at 18h;

[0079] Figure 6 Schematic diagram of the voltage situation of the system in 24 hours with and without the hierarchical voltage / reactive power control strategy in the embodiment of the present invention; wherein, (a) the maximum voltage of the system without voltage / reactive power control; (b) the minimum voltage of the system without voltage / reactive power control; (c) the maximum voltage of the system with voltage / reactive power control; (d) the minimum voltage of the system with voltage / reactive power control;

[0080] Figure 7 Schematic diagram of 24h real-time voltage of the system with and without online hierarchical voltage / reactive power control strategy in the embodiment of the present invention; wherein (a) online control is not used; (b) online control is used;

[0081] Figure 8 It is a schematic diagram of the convergence situation under non-ideal communication conditions in an embodiment of the present invention;

[0082] Fig. 9 This is a structural block diagram of an online hierarchical control device for an isolated island microgrid according to an embodiment of the present invention;

[0083] Fig.10 The present invention is a structural block diagram of an electronic device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0084] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0085] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit exemplary embodiments according to the present invention.

[0086] Glossary:

[0087] Alternating Direction Method of Multipliers (ADMM) is a method for solving decomposable convex optimization problems.

[0088] Breadth First Search (BFS) is a search algorithm for graphs.

[0089] Example 1

[0090] like Figure 1 As shown, an online hierarchical control method for an island microgrid is applied to a distribution network in a mountainous area, comprising:

[0091] S1. After a distribution network failure occurs, each isolated island microgrid is constructed based on energy storage equipment and distributed photovoltaics.

[0092] After a fault occurs, when the fault condition has been identified, an island generation strategy is studied based on energy storage equipment and distributed photovoltaics to quickly restore the electricity demand of users in some areas and reduce power outage losses, such as Figure 2 shown.

[0093] In one embodiment, each isolated island microgrid is constructed based on energy storage equipment and distributed photovoltaics, including:

[0094] S10, obtaining various data parameters of the distribution network; wherein the various data parameters include topology information, node load, distributed photovoltaic output range and energy storage equipment parameters;

[0095] S11. construct an energy storage output model based on the energy storage device parameters, and determine the maximum active power of the energy storage device based on the energy storage output model; construct a distributed photovoltaic output model based on the distributed photovoltaic output range, and determine the photovoltaic device output prediction value based on the distributed photovoltaic output model;

[0096] S12. Based on the topology information, the node where the energy storage device is located is taken as the root node, a baseline power circle is constructed with the maximum active power of the energy storage device as the radius, and a breadth-first search algorithm is used to determine the actual range of the baseline power circle in the distribution network;

[0097] S13. Based on the topological information, a dotted power circle is constructed with the node where the distributed photovoltaic is located as the root node and 80% of the predicted output value of the photovoltaic equipment as the radius, and the breadth-first search algorithm BFS is used to determine the actual range of the dotted power circle in the distribution network; when two baseline power circles intersect, or the baseline power circle intersects with the dotted power circle, the corresponding root node area is merged into an island; when two dotted power circles intersect, no island merging is performed;

[0098] S14. Based on the node load, determine the recovery status of the target load in the distribution network, and use the node where the target load that has not restored power supply is located as the root node; based on the breadth-first search algorithm, merge the node where the target load that has not restored power supply is located into the nearest island that meets the power demand, and reduce the load in the nearest island or connect to mobile power generation resources; check the power constraint of the nearest island, and when the power constraint is not met, cut off part of the load according to the distance between the load and the root node and the importance of the load until the power constraint is met.

[0099] S2. Construct a three-phase unbalanced distribution network model based on an island microgrid.

[0100] In one embodiment, the present solution takes into account the non-full-phase grid-connected situation of photovoltaics in the distribution network and constructs a three-phase unbalanced distribution network model based on an island microgrid, including: determining an unbalanced linearized power flow model of the distribution network, rewriting the unbalanced linearized power flow model into a compact form model, and simplifying the compact form model to obtain a three-phase unbalanced distribution network model.

[0101] Specifically, this scheme considers a radial distribution network with N+1 nodes, where the nodes contain unbalanced three-phase .use Represents the index set of nodes, 0 represents the head end node of the distribution network, It is other non-head-end nodes. There are N feeders in the radial distribution network, and each feeder can be single-phase, two-phase or three-phase. is the node in the distribution network The node that was previously directly connected to it. represents the set of all nodes strictly behind node j along the radial distribution network. represents the set of all different feeders in the distribution network, is a collection of energy management time periods. and each feeder , the unbalanced linearized power flow model of the distribution network can be expressed as follows:

[0102] (1a)

[0103] (1b)

[0104] (1c)

[0105] in, Indicates feeder The three-phase active power; Indicates feeder The three-phase reactive power; Indicates the square value of the three-phase voltage at node j; represents the active power of node j; represents the reactive power of node j; ; ; ; and ; Indicates the corresponding phase sequence, , Indicates three phases. , Respectively represent the active and reactive power between nodes j and m, represents the voltage at node i, , Represent the resistance and reactance between nodes i and j respectively, is a column vector representing the phase relationship between the three phases. for The three-phase resistance per unit value matrix, for The three-phase resistance per unit value matrix, , for The conjugate transpose of , , is the multiplication operator.

[0106] All the above items are expressed in per unit value (pu), based on three-phase Sort.

[0107] The unbalanced linearized power flow model of formula (1) can be written as the following compact form model at any time k:

[0108] (2)

[0109] in, , , ; represents the power flow voltage of the distribution network, The transpose of the matrix representing the node connectivity, A vector representing the connection relationship between the first node and the remaining nodes, Indicates the reference voltage value, , Respectively represent active power flow and reactive power flow; , , All are standard correlation matrices for distribution networks;

[0110] and are all block diagonal matrices, express bp (N) and the resistance between node N, express bp (N) and the reactance between node N, bp(N) For the node N Before and with node N Directly connected nodes.

[0111] Use vector and They represent the reactive power generated by distributed photovoltaic power generation and the reactive power consumed by the distribution network in period k, respectively. .Will Substitute into (2), then any energy management period ,have:

[0112] (3)

[0113] Defining intermediate parameters , , then formula (3) can be written as the following three-phase unbalanced distribution network model:

[0114] (4)

[0115] The purpose of the conversion of equations (3) and (4) is to support variable updates in the offline process, and the voltage information in the online process can be directly obtained by the measurement device.

[0116] In the optional embodiment, when the energy storage device is connected or the isolated microgrid itself has a certain scale of energy storage, it can support the operation of the isolated microgrid and meet part of the load demand. The recovery and grid connection of distributed photovoltaic can further make up for the electricity demand of residents. However, since the output of distributed photovoltaic is affected by the environment and is intermittent and volatile, after the grid connection is restored based on energy storage support, the active balance in the isolated microgrid also needs the support of energy storage equipment:

[0117] (5)

[0118] in, P PV is the active output of distributed photovoltaics. P BESS is the active power of the energy storage device. P Load is the load. When the load is greater than the active output of distributed photovoltaics, the energy storage device discharges; when the load is less than the active output of distributed photovoltaics, the energy storage device charges. In order to ensure the load demand of the system, only active power is balanced through energy storage devices, and only fixed reactive power is provided. Dynamic reactive power adjustment is undertaken by the photovoltaic inverter. In order to take into account active power balance and extend the battery storage life of energy storage equipment, the following charging and discharging control scheme is set:

[0119] (6)

[0120] Among them, SOC is the remaining power; SOClow and SOCup are the lower limit and upper limit of the remaining power, and Pbattset is the reference active power output of the battery.

[0121] S3. Based on the three-phase unbalanced distribution network model, a hierarchical voltage / reactive power control model is constructed; wherein the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function.

[0122] The hierarchical voltage / reactive power control model constructed above formulates the reactive power output plan of each distributed photovoltaic inverter through information interaction between the central agent and the local agent. Compared with the distributed voltage control between adjacent users, it can have a better convergence speed.

[0123] The goal of voltage / var control is to reduce voltage deviations and the cost of producing reactive power through distributed generation resources.

[0124] In one embodiment, the hierarchical voltage / reactive power control model specifically includes:

[0125] The objective function is expressed as follows:

[0126] (7a)

[0127] The constraints are expressed as follows:

[0128] (7b)

[0129] in, Indicates the reactive power generated by distributed photovoltaics during period k; Indicates the power flow voltage of the distribution network; Represents the weight coefficient of voltage deviation; The weight coefficient representing the reactive power cost generated by distributed photovoltaic inverters; and They represent the lower and upper limits of the reactive power generated by distributed photovoltaics, i.e. the reactive power response capability of photovoltaic inverters; represents a vector consisting of square terms of voltage reference values; represents a diagonal matrix. The first term in formula (7a) is used to calculate the voltage deviation, and the second term is used to describe the cost of reactive power control through distributed generation resources.

[0130] S4. Introduce an auxiliary variable vector to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraints, use the quasi-Newton ADMM method to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated island microgrid.

[0131] In one embodiment, an auxiliary variable vector is introduced to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model, including:

[0132] S401, introduce auxiliary variable vector ,set up , Indicates the reactive power generated by distributed photovoltaics; based on the auxiliary variable vector The hierarchical voltage / reactive power control model (i.e., formulas 7a and 7b) is reconstructed to obtain the reconstructed model:

[0133] (8a)

[0134] (8b)

[0135] (8c)

[0136] S402, set parameters for:

[0137] (9)

[0138] S403, use parameters Represents a closed convex set The indicator function :

[0139] (10)

[0140] S404. The equivalent representation model of the reconstructed model is as follows:

[0141] (11a)

[0142] (11b)

[0143] in, Indicates that it is constrained by z.

[0144] In one embodiment, the quasi-Newton ADMM method is used to solve the equivalent model of the problem, including:

[0145] S411, use Representation and The related dual variables can be reconstructed into an augmented Lagrangian function that is equivalent to the model for:

[0146] (12)

[0147] in, is the augmented Lagrangian parameter.

[0148] S412. Set a positive definite matrix for local agents , define the parameters , define the parameters respectively :

[0149] (13)

[0150] S413. The equivalent description model of the equivalent representation model is as follows:

[0151] (14a)

[0152] (14b)

[0153] S414. The augmented Lagrangian function of the equivalent description model is as follows:

[0154] (15)

[0155] S415, define parameters separately , and ,as follows:

[0156] (16a)

[0157] (16b)

[0158] (17)

[0159] in, ; Represents the augmented Lagrangian matrix after the introduction of parameter B, where B is a matrix.

[0160] Through the above conversion process, this scheme introduces the matrix B into the solution process of ADMM and forms a quasi-Newton ADMM.

[0161] S416, using quasi-Newton ADMM, augmented Lagrangian matrix To solve, the steps are as follows:

[0162] Step 10: Update

[0163] (18)

[0164] Step 20: Update

[0165] (19)

[0166] Step 30: Update

[0167] (20)

[0168] Among them, the superscript Indicates the number of iterations.

[0169] Step 20 The update of is processed by the central agent; the update of z in step 10 is processed by the local agent to establish a hierarchical voltage / reactive power control framework. According to the principle of hierarchical voltage / reactive power control strategy, Figure 3 As shown, no information exchange between local agents is required; data transfer only occurs between the central agent and the local agents.

[0170] Preferably, when the Hessian matrix is ​​used directly as the matrix B, its non-diagonal elements may be non-zero, which means information coupling between local agents. This coupling will require information exchange, cause privacy issues, and violate the principle of hierarchical strategy. Even if this scheme ignores the principle of hierarchical voltage / reactive power control strategy and assumes that users accept mutual information exchange, this setting will lead to additional communication overhead and slower calculation rate due to increased data transmission. In addition, directly solving the Hessian-based positive definite matrix F is a major challenge. To solve this problem, this scheme provides a method to diagonalize the Hessian matrix. Thereby ensuring that the voltage / reactive power control strategy based on quasi-Newton ADMM can be effectively implemented by interaction only between the central agent and the local agents. In addition, the obtained diagonal matrix allows the direct derivation of the positive definite matrix F, which can better analyze the optimal convergence of the quasi-Newton ADMM related to formula (17).

[0171] Based on the above, in the preferred solution, the matrix B is diagonalized as follows:

[0172] (21a)

[0173] (21b)

[0174] (21c)

[0175] (21d)

[0176] in, is a diagonal matrix, so this scheme can obtain the matrix B:

[0177] (twenty two)

[0178] The hierarchical voltage / reactive power control strategy based on quasi-Newton ADMM is shown in Algorithm 1. Through the above transformation, the hierarchical voltage / reactive power control strategy based on quasi-Newton ADMM can utilize second-order information to achieve algorithm acceleration without the need for information exchange between local users.

[0179] As an example, this scheme provides a hierarchical voltage / reactive power control strategy based on quasi-Newton ADMM as follows:

[0180]

[0181] The above voltage / reactive power control is performed offline. However, the environment in the planned island fluctuates rapidly after extreme disasters, and offline control cannot effectively cope with the frequently changing system operating conditions, and even deviates from the latest system operation control objectives. Therefore, in the preferred embodiment of the present invention, an online hierarchical voltage / reactive power control framework based on voltage information feedback is also provided to achieve effective voltage / reactive power control in a rapidly fluctuating environment, specifically including:

[0182] 1) Online implementation of quasi-Newton ADMM

[0183] In the online hierarchical voltage / reactive power control framework, the voltage The update no longer needs to follow the update based on equations (3) and (4). Instead, the online voltage on each bus can be obtained directly through the measurement device located at each local agent. , and transmitted to the central agent to generate online global voltage information Then, starting from equation (4), this solution will have:

[0184] (twenty three)

[0185] in, Indicates the value obtained based on actual measurement data. .

[0186] The problem expressed in equation (6) is updated as follows:

[0187] (24a)

[0188] (24b)

[0189] 2) Online Iteration Process

[0190] Figure 4The online execution of the hierarchical voltage / var control strategy is shown. In the figure, each local agent is equipped with a measuring device capable of measuring the voltage of the phase connected to the local bus. There is a two-way communication between the local agents and the central agent.

[0191] Step 1: The local measuring device records the voltage of the corresponding phase of its bus .

[0192] Step 2: The local distributor will provide the corresponding voltage and auxiliary variables Upload to central agent. represents the connection position of each local agent and k represents the time period.

[0193] Step 3: The central agent aggregates the information uploaded by the local agents to obtain online global voltage information and auxiliary variable vector , and then and to update.

[0194] Step 4: The central agent adjusts the data of the photovoltaic inverter Based on this command, the local agent adjusts the reactive power output of the PV inverter.

[0195] By repeatedly executing the above steps 10 to 40, the voltage changes of the system can be monitored in a near real-time manner, allowing rapid adjustments to ensure that the system operates in an optimal state. Considering the solution time of the sub-problems in each iteration and the limited data communication between the local agent and the central agent, this scheme sets the time window of each iteration to T seconds.

[0196] 3) Strategies for dealing with non-ideal communication

[0197] The above scheme is performed under ideal communication conditions. However, in real communication environments, problems such as random delays and packet loss are inevitable. How to use imperfect communication conditions to ensure the robustness of online algorithms is the focus of this section. Here, an iteration rule similar to asynchronous is introduced.

[0198] For the local agent, after each update of the operating status of the PV inverter, the local agent will not change the reactive power output of the PV inverter before receiving the instruction from the central agent. However, the local agent will perform an upload communication to the central agent every T seconds. For the central agent, after the kth iteration, the online global voltage information used in the calculation Also stored as , and Save As Before the central agent in iteration k+1 starts the calculation, the corresponding and will be updated according to the data uploaded by the local agent i. If the central agent does not receive the data, the information from the previous iteration will be retained. These steps constitute an approximate asynchronous iterative process, which can effectively alleviate the impact of communication failures in the online control process.

[0199] In order to verify the effectiveness of the method proposed in this solution, a simulation example is provided below:

[0200] The improved IEEE 123-node distribution network is selected for numerical simulation. The convergence of the quasi-Newton ADMM is shown in Figure 5 As shown, the static environment voltage control effect within 24 hours is as follows Figure 6 As shown, the dynamic control effect is as follows Figure 7 As shown in Figure 8 The case shows that this design can meet the voltage constraints of the distribution network based on photovoltaic inverter regulation.

[0201] Figure 5 The convergence of the quasi-Newton ADMM is shown in Figure 1. (a) The convergence of the reactive power output of the PV inverter on phase C at node 18 at 18 h; (b) The convergence of the voltage on phase B at node 93 at 18 h.

[0202] The convergence ability of the quasi-Newton ADMM is verified based on a set of load data. Figure 5 It can be seen that the quasi-Newton ADMM has better convergence ability than the ADMM algorithm.

[0203] Figure 6 Figure 24 shows the voltage conditions of the system with and without stratified voltage / reactive power control strategy for 24 hours: (a) the maximum voltage of the system without stratified voltage / reactive power control; (b) the minimum voltage of the system without stratified voltage / reactive power control; (c) the maximum voltage of the system with stratified voltage / reactive power control; (d) the minimum voltage of the system with stratified voltage / reactive power control.

[0204] The voltage control capability of the proposed method within 24 hours is verified by Figure 6 It can be observed that when the hierarchical voltage / reactive power control is not performed, the three-phase voltage of the system exceeds the limit at certain moments. After using the hierarchical voltage / reactive power control strategy proposed in this scheme, the voltage of the system is within a safe range within 24 hours.

[0205] Figure 7 Figure 24h real-time voltage of the system with and without online hierarchical voltage / reactive power control strategy: (a) without online control; (b) with online control.

[0206] Verify the effectiveness of the strategy when used online. Set the time window to 5s, which is the time required for one iteration. The environment updates the current situation every minute. The voltage situation within one hour is as follows: Figure 7 ,Depend on Figure 7 It can be seen that when online hierarchical voltage / reactive power control is not performed, the system's voltage exceeds the limit seriously within one hour and cannot meet the system operation requirements. However, after using the online hierarchical voltage / reactive power control strategy proposed in this solution, the voltage exceeding the limit problem in a rapidly changing environment can be solved.

[0207] Figure 8 The convergence speed of the algorithm under 30% communication failure rate is shown by Figure 8 It can be seen that compared with the ADMM algorithm, the quasi-Newton ADMM algorithm has good robustness in non-ideal communication environments.

[0208] Example 2

[0209] like Fig. 9 As shown, based on the same inventive concept as the above embodiment, the present invention also provides an online hierarchical control device for an isolated island microgrid, comprising:

[0210] Microgrid construction module, used to build each island microgrid based on energy storage equipment and distributed photovoltaics after a distribution network failure occurs;

[0211] The distribution network model building module is used to build a three-phase unbalanced distribution network model based on an island microgrid;

[0212] An optimization model building module is used to build a hierarchical voltage / reactive power control model based on the three-phase unbalanced distribution network model; wherein the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function;

[0213] The model solving module is used to introduce an auxiliary variable vector to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraints, the quasi-Newton ADMM method is used to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated island microgrid.

[0214] Example 3

[0215] like Fig.10 As shown, the present invention also provides an electronic device 100 for implementing an online hierarchical control method for an isolated island microgrid;

[0216] The electronic device 100 includes a memory 101 , at least one processor 102 , a computer program 103 stored in the memory 101 and executable on the at least one processor 102 , and at least one communication bus 104 .

[0217] The memory 101 can be used to store a computer program 103. The processor 102 implements the steps of an online hierarchical control method for an island microgrid in Example 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101.

[0218] The memory 101 may mainly include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function (such as a sound playback function, an image playback function, etc.), etc.; the data storage area may store data (such as audio data) created according to the use of the electronic device 100, etc. In addition, the memory 101 may include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other non-volatile solid-state storage devices.

[0219] At least one processor 102 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The processor 102 may be a microprocessor or any conventional processor, etc. The processor 102 is the control center of the electronic device 100, and uses various interfaces and lines to connect various parts of the entire electronic device 100.

[0220] The memory 101 in the electronic device 100 stores a plurality of instructions to implement an online hierarchical control method for an isolated island microgrid, and the processor 102 can execute the plurality of instructions to implement:

[0221] After a distribution network failure occurs, each isolated island microgrid is constructed based on energy storage equipment and distributed photovoltaics;

[0222] Construct a three-phase unbalanced distribution network model based on an island microgrid;

[0223] Based on the three-phase unbalanced distribution network model, a hierarchical voltage / reactive power control model is constructed; wherein the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function;

[0224] An auxiliary variable vector is introduced to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraints, the quasi-Newton ADMM method is used to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated island microgrid.

[0225] Example 4

[0226] If the module / unit integrated in the electronic device 100 is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. Computer-readable media may include: any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory and read-only memory (ROM, Read-Only Memory).

[0227] It will be appreciated by those skilled in the art 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. Furthermore, 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.

[0228] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0229] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0230] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0231] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0232] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An online hierarchical control method for an isolated island microgrid, applied to a distribution network in a mountainous area, characterized in that: include: After a distribution network failure occurs, each island microgrid is constructed based on energy storage equipment and distributed photovoltaics; Construct a three-phase unbalanced distribution network model based on an island microgrid; Based on the three-phase unbalanced distribution network model, a hierarchical voltage / reactive power control model is constructed; wherein the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function; An auxiliary variable vector is introduced to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraint conditions, the quasi-Newton ADMM method is used to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated island microgrid; The hierarchical voltage / reactive power control model specifically includes: Objective function: Constraints: in, Indicates the power flow voltage of the distribution network; Indicates the reactive power generated by distributed photovoltaics during period k; Represents the weight coefficient of voltage deviation; The weight coefficient representing the reactive power cost generated by distributed photovoltaic inverters; , They represent the lower and upper limits of reactive power generated by distributed photovoltaics respectively; represents a vector consisting of square terms of voltage reference values; represents a diagonal matrix; The transpose of the matrix representing the node connectivity, A vector representing the connection relationship between the first node and the remaining nodes, Indicates the reference voltage value, and All are standard correlation matrices for distribution networks; , Represent active power flow and reactive power flow respectively.

2. The online hierarchical control method for an isolated island microgrid according to claim 1, characterized in that: Each isolated island microgrid is built based on energy storage equipment and distributed photovoltaics, including: Obtain various data parameters of the distribution network; the various data parameters include topology information, node load, distributed photovoltaic output range and energy storage equipment parameters; An energy storage output model is constructed based on the energy storage device parameters, and the maximum active power of the energy storage device is determined based on the energy storage output model; a distributed photovoltaic output model is constructed based on the distributed photovoltaic output range, and the output prediction value of the photovoltaic device is determined based on the distributed photovoltaic output model; Based on the topology information, the node where the energy storage device is located is taken as the root node, and the baseline power circle is constructed with the maximum active power of the energy storage device as the radius. The breadth-first search algorithm is used to determine the actual range of the baseline power circle in the distribution network. Based on the topological information, a dotted power circle is constructed with the node where the distributed photovoltaic power is located as the root node and 80% of the predicted output value of the photovoltaic equipment as the radius, and the actual range of the dotted power circle in the distribution network is determined using the breadth-first search algorithm. When two baseline power circles intersect, or when the baseline power circle intersects with the dashed power circle, the corresponding root node regions are merged into an island; when two dashed power circles intersect, islands are not merged; Based on the node load, the recovery status of the target load in the distribution network is determined, and the node where the target load that has not restored power supply is located is used as the root node; based on the breadth-first search algorithm, the node where the target load that has not restored power supply is located is merged into the nearest island that meets the power demand, and the load in the nearest island is reduced or connected to mobile power generation resources; the power constraint of the nearest island is checked, and when the power constraint is not met, part of the load is removed according to the distance between the load and the root node and the importance of the load until the power constraint is met.

3. The online hierarchical control method for an isolated island microgrid according to claim 1, characterized in that: Construct a three-phase unbalanced distribution network model based on an island microgrid, including: An unbalanced linearized power flow model of the distribution network is determined, the unbalanced linearized power flow model is rewritten into a compact form model, and the compact form model is simplified to obtain a three-phase unbalanced distribution network model.

4. The online hierarchical control method for an isolated island microgrid according to claim 1, characterized in that: An auxiliary variable vector is introduced to reconstruct the hierarchical voltage / reactive power control model to obtain an equivalent model of the problem, including: Define auxiliary variable vector , z n is the auxiliary variable vector z Elements in; define auxiliary variable vector , based on the auxiliary variable vector The hierarchical voltage / reactive power control model is reconstructed to obtain the reconstructed model: in, M and μ All are defined intermediate parameters; represents the objective function of the reconstruction model; Determine the equivalent representation model of the reconstructed model as follows: in, Reactive power generated by distributed photovoltaics; is the defined parameter, representing the auxiliary variable vector The indicator function ; Z For the defined parameters, .

5. The online hierarchical control method for an isolated island microgrid according to claim 4 is characterized in that: The quasi-Newton ADMM method is used to solve the equivalent model of the problem, including: The augmented Lagrangian function L that determines the equivalent representation of the reconstructed model is: in, is the augmented Lagrangian parameter; is the defined parameter, indicating Related dual variables; Set up a positive definite matrix for the local agent , define the parameters ; Defining parameters : ; The equivalent description model of the equivalent representation model is determined as follows: The augmented Lagrangian function that equivalently describes the model is as follows: Defining parameters , and ,as follows: in, ; right To solve, the steps are as follows: Step 1: Update Step 2: Update Step 3: Update in, represents the number of iterations, the update z in step 1 is handled by the local agent; in step 2 Updates are handled by central agents.

6. The online hierarchical control method for an isolated island microgrid according to claim 5, characterized in that: Defining parameters , and In the step of , the parameter B is diagonalized.

7. An online hierarchical control device for an isolated island microgrid, characterized in that: include: Microgrid construction module, used to build each island microgrid based on energy storage equipment and distributed photovoltaics after a distribution network failure occurs; The distribution network model building module is used to build a three-phase unbalanced distribution network model based on an island microgrid; An optimization model building module is used to build a hierarchical voltage / reactive power control model based on the three-phase unbalanced distribution network model; wherein the hierarchical voltage / reactive power control model includes: an objective function of minimizing the sum of voltage deviation and reactive power cost generated by distributed photovoltaic inverters, and constraints corresponding to the objective function; A model solving module is used to introduce an auxiliary variable vector to reconstruct the hierarchical voltage / reactive power control model to obtain a problem equivalent model; based on the constraint conditions, the quasi-Newton ADMM method is used to solve the problem equivalent model to obtain an online hierarchical control strategy for the isolated island microgrid; The hierarchical voltage / reactive power control model specifically includes: Objective function: Constraints: in, Indicates the power flow voltage of the distribution network; Indicates the reactive power generated by distributed photovoltaics during period k; Represents the weight coefficient of voltage deviation; The weight coefficient representing the reactive power cost generated by distributed photovoltaic inverters; , They represent the lower and upper limits of reactive power generated by distributed photovoltaics respectively; represents a vector consisting of square terms of voltage reference values; represents a diagonal matrix; The transpose of the matrix representing the node connectivity, A vector representing the connection relationship between the first node and the remaining nodes, Indicates the reference voltage value, and All are standard correlation matrices for distribution networks; , Represent active power flow and reactive power flow respectively.

8. An electronic device, characterized in that: It comprises a processor and a memory, wherein the processor is used to execute a computer program stored in the memory to implement the online hierarchical control method for an island microgrid as claimed in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores at least one instruction, and when the at least one instruction is executed by the processor, the online hierarchical control method for the isolated island microgrid is implemented as described in any one of claims 1 to 6.

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