A power distribution network distributed power supply recovery method considering energy storage system

Abstract

The present disclosure belongs to the technical field of power supply recovery, and particularly relates to a power distribution network distributed power supply recovery method considering an energy storage system, comprising the following steps: after fault isolation of a power distribution network, taking an intelligent terminal at a disconnected switch downstream of a fault point as a search starting root node, searching for a non-fault outage area of the power distribution network; constructing an energy storage system model for power supply recovery based on self attributes of the energy storage system; formulating an adjustment strategy of the energy storage system in a power distribution network distributed power supply recovery process according to constraint conditions of the constructed energy storage system model for power supply recovery, solving output power of the energy storage system based on the formulated adjustment strategy, determining a recoverable power supply range of the non-fault outage area of the power distribution network, and realizing power distribution network distributed power supply recovery.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of power supply recovery, and particularly relates to a power distribution network distributed power supply recovery method considering an energy storage system. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute the prior art.

[0003] Fault self-healing is an important feature of smart distribution networks, and power supply recovery is an important technical link to achieve fault self-healing. As the scale of smart distribution networks continues to expand, the operation mode becomes more flexible and variable, the allowed power outage time is continuously shortened, and the topology and electrical quantity information of the power grid increases dramatically, which brings great pressure to centralized information collection, interaction and calculation, and also leads to rapid expansion of the solution scale of optimization problems. These factors make it more and more difficult for centralized power supply recovery strategies to meet the requirements.

[0004] With the development of smart distribution networks, more and more energy storage systems (ESS) and distributed generators (DG) are introduced into the distribution network system, which improves the flexible adjustment and control capability of the distribution network, and at the same time, greatly changes the operation structure and form of the distribution network. After a fault occurs, different fault characteristics from traditional distribution networks will inevitably appear.

[0005] The application scenarios of ESS in distribution networks are increasingly rich. When a fault occurs in the distribution network, the upper power grid suspends power supply to the power-off area, and the ESS connected to the distribution network can continue to supply power to the distribution network by using its own energy storage, which shows that the ESS has important research significance in enhancing the power supply recovery capability of the distribution network and improving the power supply reliability.

[0006] After the DG is connected to the distribution network, it can maintain the voltage level and improve the voltage stability of the distribution network; it can reduce network loss because it does not need long-distance power transmission; and it can generate current harmonics through the inverter to affect power quality. The connection and output regulation of ESS can better promote the consumption of DG in the distribution network.

[0007] After the ESS and DG devices are connected to the distribution network, their diverse operating characteristics provide good support for power supply recovery, but at the same time, make the power supply recovery problem after a fault more complex; therefore, a distributed power supply recovery method that is suitable for the new structure and operating characteristics of the distribution network, fast, and has strong adaptability to new devices needs to be researched.

[0008] According to the understanding of the inventors, after the ESS and DG devices are connected to the distribution network, new characteristics and demands may appear during the process of power supply recovery of the distribution network:

[0009] (1) The access of multiple devices expands the scale of the power distribution network, and the topology structure is more complex when realizing the radial operation and closed-loop operation. The power distribution network operation information increases, and the scale and difficulty of power supply restoration problems rapidly expand;

[0010] (2) After the introduction of ESS and distributed power in the new form of power distribution network, the controllability of ESS and DG devices will bring frequent output adjustment, which will affect the electrical quantity change of related nodes in the power distribution network, further increasing the complexity of the power supply restoration problem. SUMMARY

[0011] To solve the above problems, the present disclosure proposes a power distribution network distributed power supply restoration method considering energy storage system, which flexibly adjusts the output power of the adjustable and controllable device such as ESS according to the power characteristics of the load to be restored, so that the available power capacity in the power distribution network outage area and the node load power characteristics in the power supply restoration path cooperate with each other, and realize fast and as large as possible range power supply restoration.

[0012] According to some embodiments, the scheme of the present disclosure provides a power distribution network distributed power supply restoration method considering energy storage system, which adopts the following technical scheme:

[0013] A power distribution network distributed power supply restoration method considering energy storage system, comprising the following steps:

[0014] After the fault isolation of the power distribution network, the intelligent terminal at the downstream disconnected switch of the fault point is taken as the search starting root node, and the search of the non-fault outage area of the power distribution network is performed;

[0015] Based on the attributes of the energy storage system, an energy storage system model for power supply restoration is constructed;

[0016] According to the constraint conditions of the constructed energy storage system model for power supply restoration, an adjustment strategy of the energy storage system in the process of power distribution network distributed power supply restoration is formulated, the output power of the energy storage system is solved based on the formulated adjustment strategy, the range of the power supply restoration of the non-fault outage area of the power distribution network is determined, and the power distribution network distributed power supply restoration is realized.

[0017] As a further technical limitation, during the search of the non-fault outage area of the power distribution network, the forward relay search and reverse information confirmation method is adopted.

[0018] Further, the process of forward relay search of the non-fault outage area of the power distribution network is:

[0019] Starting from the search starting root node, the adjacent nodes and their corresponding intelligent terminals are searched according to the common branches of the power distribution network topology, and the adjacent intelligent terminals are triggered to start topology search;

[0020] When the adjacent intelligent terminal receives the search starting instruction, it is determined whether the search stopping condition is met according to the attribute of the switch corresponding to the adjacent intelligent terminal; if the search stopping condition is met, the search is stopped, otherwise a topology search instruction is sent to the downstream intelligent terminal in the power distribution network topology;

[0021] The searched node is marked, and after the search is completed, the marked node and the set of related branches are the non-fault outage area of the power distribution network.

[0022] Further, the search stopping condition is that a plurality of switches are marked in the node attribute information stored by the intelligent terminal, and the plurality of switches include an end node switch, a main power supply switch, a energy storage system switch, a distributed power grid-connected switch, or a switch in a split position that is prohibited to close.

[0023] Further, after the search of the non-fault outage area of the power distribution network is completed, the confirmation information is returned in the reverse direction along the topology search path of the power distribution network from the end node of the power distribution network, directly communicates with the adjacent intelligent terminal, and does not need to search the topology of the power distribution network again, and gradually returns to the search starting root node.

[0024] As a further technical limitation, in the process of determining the recoverable power supply range of the non-fault outage area of the power distribution network, for the searched non-fault outage area, if there is a recoverable power supply point in the non-fault outage area, the search starting root node sends a power supply recovery calculation instruction to each power supply in the power distribution network, and each power supply receives the instruction and performs power supply recovery calculation, and sends the calculation instruction and network equivalent parameters to the connected nodes; after the intermediate node receives the information, it performs power supply recovery calculation according to the local electrical quantity information and the network equivalent parameters, verifies the constraint condition, and if the constraint condition is met, regenerates the network equivalent parameters and continues to calculate, otherwise the calculation is stopped.

[0025] As a further technical limitation, the energy storage system model for power supply recovery includes at least a linear characteristic energy storage system power supply recovery model, a circular characteristic energy storage system power supply recovery model, and a rectangular characteristic energy storage system power supply recovery model.

[0026] Further, the linear characteristic energy storage system power supply recovery model is applicable to a power distribution network with sufficient reactive power; the reactive power constraint is not considered, and the linear characteristic energy storage system model is simplified to a left-direction active power broken line to provide active power support to the power supply recovery path.

[0027] The operating power constraint of the energy storage system charging state is:

[0028]

[0029] wherein, and These represent the lower and upper limits of the charging power of the energy storage system at node i, respectively. Let be the charging decision variable of the energy storage system at node i at time t. This indicates that the energy storage system installed at node i is in a charging state at time t. This indicates that the energy storage system installed at node i at time t is not in a charging state;

[0030] Operating power constraints of energy storage systems in discharge state:

[0031]

[0032] in, and Let be the charging power and discharging power of the energy storage system at node i at time t, respectively. and These represent the lower and upper limits of the discharge power of the energy storage system at node i, respectively. Let i be the discharge decision variable of the energy storage system at node i at time t; This indicates that the ESS installed at node i is in a discharging state at time t; This indicates that the ESS installed at node i at time t is not in a charging state;

[0033] Energy storage systems cannot be in a charging and discharging state simultaneously:

[0034]

[0035] Output power of the energy storage system:

[0036] P i ESS =P i ch η ch -P i dis / η dis

[0037] in, η is the output power of the energy storage system at node i during operation. ch and η dis , respectively, represent the charging and discharging efficiency of the energy storage system at node i.

[0038] Furthermore, the power regulation capability of the circular energy storage system power recovery model satisfies the power constraint:

[0039]

[0040] Among them, Q i,max S represents the maximum reactive power generated by the energy storage system at node i. i,maxis the maximum capacity of the energy storage system device itself on the node i.

[0041] Further, the rectangular characteristic power supply recovery model of the energy storage system installs a reactive compensation device in the energy storage system to realize the power supply recovery range of the non-fault outage area; the adjustment capability range of the installed reactive compensation device is limited by the rated capacity constraint of the connected inverter, and the reactive power constraint is:

[0042] Q i,min ≤Q i,SVC ≤Q i,max

[0043] Q i,min is the maximum reactive power generated by the additional reactive compensation device of the energy storage system on the node i, and Q i,max is the minimum reactive power generated by the reactive compensation device on the node i.

[0044] Compared with the prior art, the beneficial effects of the present disclosure are:

[0045] (1) After obtaining the power outage area range, the present disclosure fully utilizes the limited information storage and calculation capability of each intelligent terminal, simplifies the centralized complex power supply recovery constraint condition of global optimization into a distributed power supply recovery constraint condition within the calculation capability range of the intelligent terminal, and performs fast electrical quantity calculation to obtain a power supply recovery scheme.

[0046] (2) Based on the peer-to-peer communication and distributed system working mode of the intelligent terminal, the present disclosure completes the topology search and simplification solution of the power supply recovery constraint condition of the non-fault outage area only under local information support.

[0047] (3) After the controllable device of the energy storage system is connected to the power distribution network, when the power distribution network adjusts the output of the controllable device such as the energy storage system, the related node electrical quantity at the device location will change, and the distributed algorithm can quickly complete the electrical quantity update calculation according to the local information, which can adapt to multiple parameter adjustments of the device.

[0048] (4) The present disclosure describes three different types of power supply recovery models of the energy storage system and their operating constraints, including a linear characteristic model of the energy storage system considering only active power output, a circular characteristic model of the energy storage system considering active and reactive power output, and a rectangular characteristic model of the energy storage system with additional reactive compensation devices.

[0049] (5) Based on different power supply recovery models of the energy storage system, the present disclosure considers the flexible operation and adjustable controllable characteristics of the energy storage system, proposes a distributed power supply recovery method considering the energy storage system and distributed power supply, and according to different simplified models, proposes adjustment strategies of the energy storage system and the energy storage system in the distributed power supply recovery method. BRIEF DESCRIPTION OF DRAWINGS

[0050] The accompanying drawings, which form a part of this disclosure, are intended to provide further understanding of the disclosure and are incorporated herein in their entirety, and together with the general description of the disclosure given above and the detailed description of the disclosure given below, serve to explain the present disclosure.

[0051] Figure 1 is a non-fault outage area topology search and information return confirmation process schematic diagram in the first embodiment of the present disclosure;

[0052] Figure 2 is a determination process schematic diagram of the actual recoverable power supply area in the first embodiment of the present disclosure;

[0053] Figure 3 is a capacity operating range schematic diagram of the circular characteristic ESS in the first embodiment of the present disclosure;

[0054] Figure 4 is a capacity operating range of the rectangular characteristic ESS in the first embodiment of the present disclosure;

[0055] Figure 5 is a local topology schematic diagram of the power distribution network in the first embodiment of the present disclosure;

[0056] Figure 6 is an output adjustment schematic diagram of the circular characteristic ESS in the power supply recovery path in the first embodiment of the present disclosure;

[0057] Figure 7 is an IEEE69 node power distribution network schematic diagram of the access ESS and DG in the second embodiment of the present disclosure;

[0058] Figure 8 is an ESS output adjustment and power supply recovery process schematic diagram in the second embodiment of the present disclosure;

[0059] Figure 9 is a comparison schematic diagram of the power supply recovery capability of the ESS with rectangular characteristic and circular characteristic in the second embodiment of the present disclosure. DETAILED DESCRIPTION

[0060] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0061] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present disclosure. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs.

[0062] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0063] The embodiments in the present disclosure and the features in the embodiments can be combined with each other in the case of no conflict.

[0064] Embodiment one

[0065] The embodiment one of the present disclosure introduces a power distribution network distributed power supply restoration method considering energy storage system.

[0066] The power distribution network distributed power supply restoration method considering energy storage system in the present embodiment takes the intelligent terminal STU installed at each switch of the power distribution network as the core, determines the non-fault outage area range and restores power supply to the area based on the local topology and electrical quantity information of the STU, and adopts peer-to-peer communication and distributed calculation mode.

[0067] The distributed power supply restoration scheme is completed in two steps: first, the non-fault outage area range is determined by adopting forward relay search and reverse information confirmation, and second, the network of the outage area is simplified and equivalent, and the constraint conditions are distributed and calculated to determine the actual recoverable power supply range.

[0068] First step: search of non-fault outage area

[0069] When the power distribution network completes fault isolation, the STU at the downstream disconnected switch of the fault point is taken as the search starting root node, and the relay search process of the non-fault outage area is started:

[0070] (1) Starting from the root node, the adjacent nodes and their corresponding STUs are searched according to the common branch in the stored topology information, and the adjacent STUs are triggered to start topology search;

[0071] (2) After the adjacent STU receives the search starting instruction, it first judges whether the search stopping condition is met according to the attribute of the corresponding switch, if the condition is met, the search is stopped, if not, the topology search instruction is sent to the downstream STU, and so on.

[0072] (3) The search stopping condition is: the end node switch, the main power supply TS, the ESS, the DG grid-connected switch or the switch in the split position and prohibited to close, the above switches will be marked in the node attribute information stored in the STU.

[0073] The searched nodes are marked. After the search is completed, the set of marked nodes and related branches constitutes the power outage area.

[0074] by Figure 1 Taking a non-faulty power outage area topology search process as an example, node 1 is the root node, and the forward search process for the non-faulty power outage area begins (indicated by the blue arrows). STU1 searches for node 2 and STU2 based on branch 1-2, completing one relay search. Node 2 is a branch point, connecting multiple branches, so this embodiment adopts a breadth-first strategy, searching for the STUs corresponding to node 3 and node 7 based on the branches 2-3 and 2-7 connected to it, and so on, until the search stops. Among them, node 6 is the TS power supply point connected to the feeder, nodes 9 and 14 correspond to special marked power supply points such as ESS, node 11 corresponds to the end switch, node 15 corresponds to the DG grid-connected switch, and node 12 is the TS disconnected from the feeder. Node type 12 does not need to have its power restored.

[0075] After the search of non-faulty power outage areas is completed, a return information confirmation step is required. The main reasons are as follows:

[0076] (1) Since the search time for each branch is different, it is necessary to ensure that the search in the power outage area has been completed before the actual power restoration calculation begins;

[0077] (2) It is necessary to determine whether the conditions for power restoration are met in the power outage area;

[0078] (3) In order to meet the radial network topology constraints during the recovery process, nodes with branches must specify the number and type of downstream power sources.

[0079] Therefore, after completing the search for the power outage area, starting from the end node, the confirmation information is returned in the reverse direction along the topology search path, gradually returning to the root node.

[0080] The information return confirmation process also adopts a relay method, similar to the power outage area topology search process mentioned in this embodiment, but there is no need to perform a topology search again; it is only necessary to communicate directly with the adjacent STU.

[0081] Step 2: Searching for the actual recoverable area

[0082] If a recoverable power source exists in the non-faulty power outage area, the root node sends a "power restoration calculation" command to each power source. Upon receiving the command, each power source begins power restoration calculation, sending the calculation command and network equivalent parameters to its connected nodes. Intermediate nodes, upon receiving the information, verify the constraints based on local electrical quantity information and network equivalent parameters. If the constraints are met, the network equivalent parameters are regenerated and the calculation continues; otherwise, the calculation stops.

[0083] byFigure 2 To illustrate the determination of the actual recoverable power supply area, the power supply recovery process starts from the power supply point TS at node 6, and the blue arrow is the power supply recovery calculation path of the power supply point. When recovering to branch point 4, the branch where node 14 is located has an ESS, and the branch is recovered as a dominant branch. After recovering nodes 13 and 14, another branch node 3 is recovered, but the power supply recovery capability is insufficient to recover node 2, so the recovery calculation stops at another power supply point TS at node 9 along the blue dashed line path, and the power supply recovery calculation is started. The red arrow is the power supply recovery path with TS at node 9 as the power supply point.

[0084] Network equivalence calculation of distributed constraints

[0085] The distributed power supply recovery calculation starts from the power supply point that can recover power supply, and gradually recovers each node load. The recovered network equivalence is calculated as a Thevenin equivalent circuit, and the electrical quantity constraint condition of the node to be recovered is calculated. After calculating the relevant electrical quantities of node j to be recovered by using the network step-by-step Thevenin equivalence method, the following constraint conditions need to be met for the node to recover power supply:

[0086] Node voltage constraint:

[0087]

[0088] In the formula, and represent the lower limit and upper limit of the voltage of node j, respectively.

[0089] Power constraint and branch power flow constraint: i j ≤min(C S ,S jd ) (2)

[0091] In the formula, S j represents the node load of node j, C S represents the remaining available capacity of the power supply point when node j is recovered, and S jd represents the minimum value of the power margin of all branches between the node to be recovered j and the power supply point.

[0092] The corrected node voltage of the other recovered nodes satisfies the constraints (1)-(2).

[0093] ESS model for power supply recovery

[0094] (1) ESS power supply recovery model with linear characteristics:

[0095] ​ESS only has the ability to output active power during operation. This kind of ESS is suitable for operation in a power distribution network with sufficient reactive power. In this case, the operation adjustment of the ESS does not need to consider the reactive power constraint, and the operation constraint condition is shown in equations (3)-(6).

[0096] Operation power constraint of the charging state of the ESS:

[0097]

[0098] wherein, and are the lower and upper limits of the charging power of the ESS at node i, is the charging decision variable of the ESS at node i at time t, indicates that the ESS installed at node i at time t is in the charging state, indicates that the ESS installed at node i at time t is not in the charging state.

[0099] Operation power constraint of the discharging state of the ESS:

[0100]

[0101] wherein: and are the charging power and discharging power of the ESS at node i at time t, and are the lower and upper limits of the discharging power of the ESS at node i, is the discharging decision variable of the ESS at node i at time t. indicates that the ESS installed at node i at time t is in the discharging state; indicates that the ESS installed at node i at time t is not in the discharging state.

[0102] wherein, the ESS cannot be in the charging and discharging states at the same time:

[0103]

[0104] Output power of the ESS:

[0105] P i ESS = P i ch η ch -P i dis / η dis (6)

[0106] wherein: is the output power of the ESS during operation at node i, η ch and ηdis The charge-discharge efficiency of the ESS at node i, respectively.

[0107] In the power supply recovery process diagram of the distributed method, the ESS model with linear characteristics is simplified as a broken line of active power in the left direction, which provides active power support to the power supply recovery path.

[0108] (2) ESS power supply recovery model with circular characteristics:

[0109] The ESS has the ability to output active power and can also output and adjust reactive power during operation. Such ESSs have universal applicability in most distribution networks. When the distribution network connected with such ESSs is running, the ESSs provide active power and reactive power and can achieve flexible adjustment of operating power.

[0110] In such cases, the ESS needs to provide active power and reactive power while its power capacity is certain, so in the operation process, in addition to meeting the constraints of equations (3)-(6), its power regulation capability also needs to meet the power constraint (7):

[0111]

[0112] In the formula: Q i,max is the maximum reactive power output by the ESS at node i, S i,max is the maximum capacity of the ESS device at node i.

[0113] Such ESS devices with operating characteristics are applied to the distributed power supply recovery problem of the distribution network, and the operating adjustment range is similar to the SOP, and the operating characteristic is a capacity circle with a radius of S i,max is the maximum capacity of the ESS device at node i. Figure 3 As shown in , the capacity operating adjustment range of the ESS combination device is circular.

[0114] (3) ESS power supply recovery model with rectangular characteristics:

[0115] In the distribution network, all the capacity of the ESS is used to output active power to provide active power support for power restoration, and an additional reactive power compensation device is installed in the ESS device to compensate for the reactive power shortage of the ESS device in the power restoration path, so as to realize the power restoration range of the largest non-fault outage area. The regulation capacity range of the reactive power compensation device is limited by the rated capacity of the connected inverter. Taking the ESS additionally connected with the static var compensator SVC as an example, in addition to meeting the operation constraints of the device itself, the SVC also needs to meet the following reactive power constraints:

[0116] Q i,min ≤Q i,SVC ≤Q i,max (8)

[0117] In the formula: Q i,min is the maximum reactive power output by the additional reactive power compensation device of the ESS at node i, Q i,max is the minimum reactive power output by the reactive power compensation device at node i

[0118] The ESS device with such operation characteristics is applied to the distributed power restoration problem of the distribution network, and the operation adjustment range is no longer a circular characteristic. According to the active power and reactive power output constraints of the combined device, the capacity operation adjustment range of the ESS combined device is shown in Figure 4 As the ESS and the additional installed reactive power compensation device can realize respective control, in this case, the active power and the reactive power of the ESS combined device are respectively realized independently, and there is no coupling in the output adjustment, so the device can be adjusted and operated in the four quadrants in the operation rectangular range.

[0119] In addition to meeting various power constraints of different operation characteristics mentioned in the embodiment, due to the limitation of the operation capacity of the ESS, the ESS cannot realize long-term continuous stable output in the distribution network, so the state of charge constraint needs to be considered.

[0120] The relationship between the state of charge of the ESS and the charging and discharging power is:

[0121]

[0122] In the formula, SoC is the state of charge of the ESS at node i at t+1, η ch and η dis represent the charging and discharging efficiency of the ESS at node i, and Δt is the unit time step of the ESS.

[0123] The state of charge constraint of the ESS device itself is:

[0124]

[0125] wherein, and are the lower and upper limits of the state of charge of the ESS at node i, is the configured capacity of the ESS at node i.

[0126] It should be noted that the initial and final state of charge of the ESS is the same during normal operation of the ESS:

[0127]

[0128] wherein, and are the initial and final state of charge of the ESS.

[0129] As can be seen from the state of charge constraint condition of formula (10), when considering the state of charge constraint of the ESS, since the charging and discharging power of the ESS cannot be output stably for a long time to support the power supply restoration of the distribution network, the power support time of the ESS for the power supply restoration process is limited during the distributed power supply restoration process. The general processing method is to assume that the ESS is included in the distributed power supply restoration time for 30 minutes. If the power failure in the distribution network is removed in time within 30 minutes, the distribution network is switched to normal operation; if the power failure is not removed in time within 30 minutes, the ESS cannot continue to provide power output due to the constraint of the state of charge, and therefore exits operation, and the distribution network is switched to a standby power supply restoration scheme, i.e. a power supply restoration scheme of the distribution network without the ESS.

[0130] Considering that the power loss of the ESS itself is small relative to the transmission power, the power loss of the ESS itself is ignored in the power supply restoration calculation process of the ESS in this embodiment. In the distributed power supply restoration of the distribution network, the ESS only provides power support for the power failure area and does not provide stable voltage as the main power supply. Therefore, the ESS performs power control according to the predetermined adjustment strategy during the power supply restoration process.

[0131] Output adjustment strategy of ESS

[0132] After the fault occurs, the distributed power supply restoration calculation starts from the power supply point, and the TS and the ESS exist in the power failure area at the same time. The TS starts the power supply restoration calculation as the main power supply, and when the restoration reaches the ESS node, the node where the ESS is located is equivalent to a negative load providing power support to the distribution network, and the power is adjusted according to the power supply restoration process in the power failure area. The loss of the converter is ignored, and the Thevenin equivalent impedance is zero.

[0133] The power supply recovery calculation stops because the power constraint is not met. The active and reactive power of the traditional TS cannot be flexibly adjusted, which results in the excess of active power and the shortage of reactive power in the power supply point, and the power supply recovery range is limited.

[0134] When the power supply recovery calculation does not meet the power constraint at node i, the calculation stops, and the information is returned to the ESS. The ESS sets the reference value according to the adjustment strategy in equation (10) based on its own operating characteristics to restore the power supply at node i:

[0135]

[0136] In the formula, P ref and Q ref are the reference values of the active and reactive power output by the ESS to the non-fault power supply area, S max is the maximum operating power of the ESS, P TS and Q TS are the active and reactive power output by the TS in the non-fault power supply area, and ∑P i and ∑Q i are the power and of the restored path and the load and line loss at node i.

[0137] The ESS needs to provide stable voltage for the power distribution network when it is the only power supply point for fault recovery. The droop control can be used to achieve this. On this basis, the power output in a reasonable proportion is achieved according to equation (10).

[0138] The power adjustment strategy is described by taking the ESS power supply recovery model with circular characteristics as an example.

[0139] The ESS capacity circle center operates at the TS output capacity point, and the operating point is at the initial output power E1. When the ESS is included in the power supply recovery path, the power supply recovery process is as follows. Figure 5 Taking the local topology of the power distribution network as an example, if the ESS capacity characteristics at STU13 are circular at this time, the cooperation process between the ESS and the DG during the distributed power supply recovery is introduced.

[0140] Figure 6 For the local topology of the power distribution network with both ESS and DG, the non-fault power supply area is searched from node 1 where STU1 is located as the root node. The distributed power supply recovery starts from the TS at node 9 to gradually restore the load at each node. After the nodes 8-6 and nodes 10-12 are restored, the ESS is included in the recovery path, and then the nodes 4-5 are restored. The load at node 3 exceeds the current power supply range of the ESS, but it is still within the capacity circle. After the output adjustment of the ESS, node 3 is restored, and then the DG at node 14 is included in the recovery path. After that, nodes 2 and 1 are restored.

[0141] The distributed power supply restoration method in this embodiment does not require coordination of global electrical quantities, reducing the time for information transmission and complex parameter calculations across the entire network, and exhibits good computational speed. As the scale of the distribution network expands and the complexity of the network topology increases, the distributed power supply restoration method increasingly demonstrates its superiority.

[0142] ESS has proven effective in power restoration in distribution networks. A reasonable control strategy provides power supplementation and voltage support to non-faulty outage areas, improving power restoration capabilities. Adjusting the ESS operating power according to the characteristics of the load to be restored expands the power restoration range.

[0143] This embodiment establishes three ESS models for power restoration: linear, circular, and rectangular characteristics. Based on the operational characteristics of these three models, operational and adjustment strategies for ESS in distributed power restoration are proposed to achieve the largest possible power restoration range. To better illustrate the adjustment strategies, the power restoration adjustment process of ESS in the distribution network is shown in the distributed power restoration path diagram. According to the power characteristics of the load to be restored, the output power of the adjustable and controllable ESS device is flexibly adjusted to ensure that the available power capacity in the distribution network matches the power characteristics of the node loads in the power restoration path, thereby achieving the maximum possible power restoration range.

[0144] Example 2

[0145] Embodiment 2 of this disclosure verifies the effectiveness of the method introduced in Embodiment 1 based on a computational example. A circular ESS device is connected to the IEEE 69-node system to verify the operation and adjustment of the ESS in distributed power restoration, and the power restoration range is obtained as large as possible.

[0146] like Figure 7 The diagram illustrates an IEEE 69-node distribution network with integrated ESS and DG connections. DG connections are established at nodes 24, 31, 40, 46, 55, 60, and 64, with specific parameters shown in Table 1. An ESS device is installed at node 73 to replace the original tie switch TS73, with its operating capacity shown in Table 2. The per-unit voltage fluctuation range for each node is [0.95, 1.05]. The maximum transmission capacity of the line is 2030 kVA, with a base voltage of 12.66 kV and a base power of 12.66 MVA. A fault is set to cause switches 6 and 7 to disconnect, disconnecting all DG connections within the outage area from the main grid.

[0147] The distributed power restoration in IEEE 69-bus system starts from node 7, the root node, and performs the non-faulted blackout area topology search step, and then triggers the STU at the adjacent node to start the relay search until the TS and ESS power points corresponding to nodes 69 and 73 are searched, and the DG nodes corresponding to the end nodes at the respective locations are searched. After the search is completed, the return confirmation information is sent from the end node where the search is stopped to the root node 7, and the number and type of power points in the blackout area and other information are sent to the root node 7. After the first search step is completed, it is determined that there is a power point that can be used for power restoration in the blackout area, and the condition for distributed power restoration calculation is met. Therefore, the second search step is started, and the distributed power restoration calculation is started from the power point.

[0148] Table 1 DG parameters in IEEE 69-bus system

[0149]

[0150] Table 2 Thevenin equivalent parameters at TS in IEEE 69-bus system

[0151]

[0152] The Thevenin equivalent parameters from the TS at nodes 69 and 73 in the standard distribution system are shown in Table 2.

[0153] Initially, the root node 7 sends the "priority power restoration calculation" instruction to the STU 69. The distributed power restoration calculation is started from the node where the main power supply point SOP 69 is located. The STU 69 sends the equivalent parameters to the STU 10, and the STU 10 calculates the Thevenin equivalent voltage after the power restoration (0.9985+j0.00058), which meets the power restoration constraint condition, and the load at this node can be restored.

[0154] The loads at the respective nodes are gradually restored along the topology in the blackout area. When the node 47 is gradually restored, the ESS at the node 73 is included in the power restoration path. The ESS output adjustment and the power restoration process are as shown in Figure 8 .

[0155] The ESS initially operates at the SS1 point, and at this time, the operating capacity can only be restored to the node 50. When the restoration calculation is performed to the node 51, the current power is insufficient, which causes the node to be unable to be restored, but the load at this node is still within the current capacity circle of the ESS. According to the adjustment strategy, the intersection SS2 (1643, 1337) of the current load characteristic straight line l and the ESS capacity circle is obtained as the operating point of the ESS after the adjustment, and at this time, the output active power P ESS = 307 kW, and the reactive power Q ESS=513.7kVar. After ESS adjustment, continue to restore other load nodes in the outage area until the load at node 53 is fully restored.

[0156] All nodes within the power outage area of ​​the IEEE 69-node system have been restored. The distributed power supply restoration results of the example in this embodiment are shown in Table 3.

[0157] Table 3 Power restoration results of the IEEE 69-node system

[0158]

[0159] As can be seen from the table above, the ESS output adjustment strategy and the distributed power supply restoration path in this embodiment complement each other. The example in this embodiment verifies that the distributed power supply restoration method of the distribution network considering the energy storage system in Embodiment 1 has good feasibility and effectiveness.

[0160] Furthermore, the impact of different power ESS models on power restoration in the distribution network varies. In the above example, the active power P output by the circular characteristic ESS at node 73 is... ESS =307kW, reactive power Q ESS =513.7kVar. If the circular characteristic of the ESS connected to node 73 is replaced with a rectangular characteristic ESS device, then the capacity constraint of the ESS device itself is the active power P. max =600kW, capacity constraint Q of reactive power compensation device max =800kVar. Therefore, the adjusted output active power P in the power restoration result is... ESS =600kW, output reactive power Q ESS =751.1kVar, such as Figure 9 As shown.

[0161] according to Figure 9 A comparison of the power restoration models of two different operating characteristics of ESS shows that, compared with the circular operating characteristic ESS power restoration model, even if the same range of loads in the outage area has been restored, the rectangular operating characteristic ESS power restoration model has more remaining power capacity, giving the distribution network a stronger power restoration capability.

[0162] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A method for restoring distributed power supply in a distribution network considering an energy storage system, characterized in that, Includes the following steps: After the distribution network fault is isolated, the search for the non-fault outage area of ​​the distribution network is carried out with the intelligent terminal at the downstream disconnect switch of the fault point as the search starting root node; Construct an energy storage system model for power restoration based on the inherent properties of the energy storage system; Based on the constraints of the constructed energy storage system model for power restoration, the energy storage system model for power restoration includes at least three types: linear energy storage system power restoration model, circular energy storage system power restoration model, and rectangular energy storage system power restoration model; the power regulation capability of the circular energy storage system power restoration model satisfies the power constraint. in, Let be the maximum active power generated by the energy storage system at node i. Q i,max For nodes i The maximum reactive power generated by the energy storage system. S i,max For nodes i The maximum capacity of the energy storage system itself; the rectangular characteristic energy storage system power supply recovery model installs a reactive power compensation device in the energy storage system to realize the power supply recovery range of non-fault outage areas; the adjustment capability range of the installed reactive power compensation device is limited by the rated capacity constraint of the connected inverter, and its reactive power constraint is: in, The reactive power generated by the reactive power compensation device additionally installed on the energy storage system at node i. Q i,min For nodes i The maximum reactive power generated by the reactive power compensation device additionally installed on the energy storage system. Q i,max For nodes i The minimum reactive power generated by the reactive power compensation device; An adjustment strategy for the energy storage system during the distributed power supply restoration process of the distribution network is formulated. Based on the formulated adjustment strategy, the output power of the energy storage system is calculated to determine the range of restoreable power supply in non-faulty outage areas of the distribution network, thereby realizing the distributed power supply restoration of the distribution network. In the process of determining the range of restoreable power supply in non-faulty outage areas of the distribution network, for the searched non-faulty outage areas, if there are restoreable power sources in the non-faulty outage areas, the search starting root node sends a power supply restoration calculation command to each power source in the distribution network. After receiving the command, each power source performs power supply restoration calculation and sends the calculation command and network equivalent parameters to the connected nodes. After receiving the information, the intermediate nodes perform power supply restoration calculation based on local electrical quantity information and network equivalent parameters, and verify the constraints. If the constraints are met, the network equivalent parameters are regenerated and the calculation continues; otherwise, the calculation stops.

2. The method for restoring distributed power supply in a distribution network considering an energy storage system as described in claim 1, characterized in that, During the search for non-fault outage areas in the power distribution network, a forward relay search and reverse information confirmation method is adopted.

3. The method for restoring distributed power supply in a distribution network considering an energy storage system as described in claim 2, characterized in that, The forward relay search process for the non-fault outage area of ​​the distribution network is as follows: Starting from the root node of the search, the adjacent nodes and their corresponding smart terminals are searched according to the common branches of the distribution network topology, and the adjacent smart terminals are triggered to start the topology search. When an adjacent smart terminal receives a search start command, it determines whether the search stop condition is met based on the attributes of the switch corresponding to the adjacent smart terminal. If the search stop condition is met, the search is stopped; otherwise, a topology search command is sent to the downstream smart terminal in the distribution network topology. The searched nodes are marked. After the search is completed, the set of marked nodes and related branches is the non-fault outage area of ​​the distribution network.

4. The method for restoring distributed power supply in a distribution network considering an energy storage system as described in claim 3, characterized in that, The search stopping condition is that multiple switches are marked in the node attribute information stored in the smart terminal. The multiple switches include end node switches, main power supply switches, energy storage system switches, distributed power grid-connected switches, or switches that are in the open position and prohibited from being closed.

5. The method for restoring distributed power supply in a distribution network considering an energy storage system as described in claim 2, characterized in that, After the search of the non-fault outage area of ​​the distribution network is completed, starting from the end node of the distribution network, the confirmation information is returned in the reverse direction along the distribution network topology search path, and the system communicates directly with the adjacent smart terminal without having to search the distribution network topology again, gradually returning to the search starting root node.

6. The method for restoring distributed power supply in a distribution network considering an energy storage system as described in claim 1, characterized in that, The linear energy storage system power restoration model is applicable to distribution networks with sufficient reactive power. It does not require consideration of reactive power constraints and simplifies the linear energy storage system model into a left-hand active power polygonal line, providing active power support to the power restoration path. Operating power constraints of energy storage systems during charging: in, Let be the charging power of the energy storage system at node i at time t. and They are nodes i The lower and upper limits of charging power for energy storage systems. for t Time Node i Charging decision variables for energy storage systems =1 means t Installed on nodes at all times i The energy storage system is in a charging state. =0 means t Installed on nodes at all times i The energy storage system is not in a charging state; Operating power constraints of energy storage systems in discharge state: in, Let be the discharge power of the energy storage system at node i at time t. and They are nodes i The lower and upper limits of the discharge power of the energy storage system. for t Time Node i Discharge decision variables for the energy storage system; =1 means t Installed on nodes at all times i The ESS is in a discharged state; =0 means t Installed on nodes at all times i The ESS is not in a discharged state; Energy storage systems cannot be in a charging and discharging state simultaneously: Output power of the energy storage system: in, and These represent the charging power and discharging power of the energy storage system at node i, respectively. For nodes i The output power of the energy storage system during operation and They are nodes i The charging and discharging efficiency of the energy storage system.

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