CN105977970B - A kind of power distribution network intelligent trouble restoration methods containing distributed generation resource - Google Patents

Abstract

The invention discloses an intelligent fault recovery method for a distribution network containing distributed power sources. The method aims at most of the temporary faults occurring in the distribution network at present, and considering that the penetration rate of distributed power sources in the distribution network is gradually increased, The fault recovery method selects a recovery method based on distributed power or topology reconfiguration based on the scope of the fault, based on the primary load and the total recovery rate of the load. In the fault recovery process, in order to isolate the fault point and restore the non-fault loads that have lost power, the load in the distribution network is gradually restored with the minimum fault recovery time, the minimum load rate of the fault recovery affected branch and the maximum possible recovery load as the objective functions. The present invention provides a detailed algorithm description by using a 53-node network as a test system, and proves that the proposed method improves the fault recovery speed and effectively improves the recovery speed of the primary load through a series of experiments.

Description

An Intelligent Fault Restoration Method for Distribution Network Containing Distributed Power

technical field

The invention relates to the field of distributed power supply and fault recovery, in particular to an intelligent fault recovery method for distribution network with distributed power supply.

Background technique

In recent years, in order to reduce greenhouse gas emissions caused by fossil fuel combustion and improve the stability of distribution networks, the penetration rate of various forms of distributed power has been significantly increased. However, due to the two-way power flow brought by the access of distributed power to the distribution network, it may cause problems such as increased system failure rate and protection failure, which puts forward new requirements for the operation control and fault recovery speed of the distribution network. At the same time, in a distribution network with a high penetration rate of distributed power, distributed power can also provide energy for fault recovery and speed up fault recovery.

Generally speaking, fault recovery is to restore the supply of the lost load to the greatest extent in the shortest possible time, especially the primary load. However, the commonly used fault recovery methods do not consider the impact range of the fault, and the method of topology reconstruction is used for fault recovery when a fault occurs. However, because there are many temporary faults in the distribution network, the power flow changes caused by frequent topology reconfiguration are also unfavorable to the security and stability of the system. In addition, the topology reconfiguration method needs to operate the associated switch, and generally speaking, the operation time of the associated switch is more time-consuming than the operation of the circuit breaker on the branch. Therefore, considering the time of fault recovery, in the case of a small-scale fault, it is also unfavorable to adopt the method of changing the system topology for fault recovery.

In the distribution network under the high penetration rate of distributed generation, some small-scale faults can rely on nearby distributed generation to restore power supply to the lost load without changing the system topology. However, due to the limited capacity of distributed power in the distribution network, it is necessary to find a suitable fault recovery method after a reasonable trade-off between the scope of the fault and the distributed power supply capacity in the process of fault recovery in order to maximize the use of distributed power. power supply to improve the speed of fault recovery. Therefore, in view of the above problems, in order to realize the intelligent fault recovery strategy in the distribution network, it is necessary to have a reasonable criterion to distinguish the fault recovery method based on distributed power supply and the fault recovery method based on topology reconstruction. The fault recovery rate is an important indicator for judging the fault recovery. Therefore, the fault recovery rate of the primary load and the recovery rate of all power-off loads are used to distinguish the scope of use of the two methods. At the same time, after determining the method of fault recovery, when selecting the recovery path, it is necessary to consider the time of fault recovery, the speed of fault recovery, and the impact of fault recovery on other normal lines in the distribution network. Based on this understanding, the present invention establishes a fault recovery model that simultaneously considers these three factors, so as to achieve as much load as possible in the shortest possible time during the fault recovery process, especially the primary load, and To ensure the minimum impact on other lines in the distribution network during the recovery process, that is, to finally realize the optimal compromise between the rapidity and safety of fault recovery.

Contents of the invention

Aiming at the deficiency of existing fault recovery strategies, the object of the present invention is to propose an intelligent fault recovery method for distribution network including distributed power sources.

The purpose of the present invention is achieved through the following technical means, and the specific implementation steps are as follows: A method for recovering intelligent faults of distribution networks containing distributed power sources, the method comprising the following steps:

Step (1): Detect whether all nodes in the distribution network system are faulty at intervals Δt;

Step (2): When a fault occurs, according to the topological structure of the distribution network system, disconnect the branch circuit isolation switch affected by the fault, and calculate the power flow distribution at the time of the fault;

Step (3): According to the power flow distribution, judge whether the capacity of the distributed power source in the power-off area can meet the supply of the power-off load; specifically: if the capacity of the distributed power source can meet all the primary loads in the power-off state and the power-off 80% of the state's non-Level 1 load, that meets:

∑P _DGs ≥∑P _{critical loads} +80%×∑P _{noncritical loads}

Among them, ∑P _DGs represents the available capacity of all distributed power sources in the de-energized area; ∑P _{critical loads} represents the primary load in the de-energized state, and ∑P _{noncritical loads} represents the non-primary load in the de-energized area; During the recovery process, the fault recovery method based on distributed power is used to recover; otherwise, the system's associated switch state is changed to recover from the fault.

Further, in the step 3, the fault recovery method based on distributed power supply is specifically:

(A1) Calculate the load recovery capability of all recoverable branches in the current state, including the size of the direct recovery load and the positional relationship of each recoverable branch to the remaining load to be restored; the recoverable branches do not include system-associated switches ,Specifically:

(A1.1) Assuming that there are a total of n branches that can be restored in the current state, if one of the branches is restored, a part of the load can be restored to supply, then this part of the load is the direct recovery load of the branch; the i can The direct restoration load of the restoration branch is calculated by expression (1):

Among them, k is the number of direct recovery loads of the i-th recoverable branch; ρ _j is the weight of the j-th direct recovery load, if it is a primary load ρ _j =100; otherwise, ρ _j =1; P _j is the size of the jth direct recovery load;

(A1.2) The indirect restoration load P _{indirect loads} (i) of the i-th restorable branch is calculated by expression (2):

Among them, m is the number of remaining loads to be restored after restoring the i-th recoverable branch; P _{indirect loads,ij} is the size of the q-th load to be restored after restoring the i-th recoverable branch; distance _iq After restoring the i-th recoverable branch, the number of branches to be restored to restore the q-th load to be restored;

(A1.3) Considering the direct/indirect restoration load comprehensively, the load restoration capacity of the i-th restorable branch is calculated by expression (3):

P _{recover loads} (i)＝P _{direct loads} (i)+P _{indirect loads} (i) (3)

(A2) Weight the normalized value of the load recovery capability and time cost of each recoverable branch according to the importance level, and then use it as the recovery cost matrix element of the recoverable branch, and each time from the matrix Select a branch with the least cost; among them, the recovery cost of the recoverable branch is calculated by expression (5):

(A3) Weight the normalized value of the load recovery capability and time cost of each recoverable branch according to the importance level, and then use it as the recovery cost matrix element of the recoverable branch, and each time from the matrix Select a branch with the least cost; among them, the recovery cost of the recoverable branch is calculated by expression (5):

Cost(i)＝β ₁ φ(f _1i )+β ₃ φ(f _3i ) (5)

Among them, f _1i is the normalized value of time cost; f _3i is the normalized value of branch load restoration ability; β ₁ is the weight of time cost, β ₁ = 1; β ₃ is the weight of branch load restoration ability , β ₃ =5; and φ is a penalty function, for x∈[0,1]

(A4) Calculate and check whether the system meets the power flow operation constraints and line safety constraints after restoring this branch; for all branches, the line safety constraints are:

Among them, V is the lower limit of the line voltage; is the lower limit of the line voltage; V is the line voltage; Is the upper limit of the line current; I is the line current;

(A5) If not satisfied, then exclude the current branch that does not satisfy the constraint from the recoverable branch; repeat steps (A3) and (A4), until finding the minimum recoverable branch that meets the constraint condition; restore the constraint condition The minimum recoverable branch of , update the topology of the system.

(A6) Repeat steps (A1) to (A5) until all recoverable loads are recovered.

Further, in the step 3, the system topology is changed to restore the failure, specifically:

(B1) Calculating the load recovery capabilities of all recoverable branches in the current state, including the size of the direct recovery load and the positional relationship of each recoverable branch to the remaining load to be restored; the recoverable branches include system-associated switches, Specifically:

(B1.1) Assuming that there are a total of n branches that can be restored in the current state, if one of the branches is restored, a part of the load can be restored to supply, and this part of the load is the direct recovery load of the branch; The direct restoration load of the restoration branch is calculated by expression (1):

Among them, k is the number of direct recovery loads of the i-th recoverable branch; ρ _j is the weight of the j-th direct recovery load, if it is a primary load ρ _j =100; otherwise, ρ _j =1; P _j is the size of the jth direct recovery load;

(B1.2) The indirect restoration load P _{indirect loads} (i) of the i-th restorable branch is calculated by expression (2):

Among them, m is the number of remaining loads to be restored after restoring the i-th recoverable branch; P _{indirect loads,ij} is the size of the q-th load to be restored after restoring the i-th recoverable branch; distance _iq After restoring the i-th recoverable branch, the number of branches to be restored to restore the q-th load to be restored;

(B1.3) Considering the direct/indirect restoration load comprehensively, the load restoration capacity of the i-th restorable branch is calculated by expression (3):

P _{recover loads} (i)＝P _{direct loads} (i)+P _{indirect loads} (i) (3)

(B2) Calculate the risk coefficient of all recoverable branches in the current state, which is the normalized weighted value that may cause the load rate increase of other non-faulty branches due to the restoration of a certain branch; specifically:

The risk coefficient of the i-th recoverable branch is calculated by expression (4):

Among them, L is the number of branches that cause power flow changes after restoring the i-th recoverable branch; I _l is the actual current of the l-th branch; I _limit,l is the current capacity of the l-th branch;

(B3) Calculate the operating time cost of all recoverable branches in the current state; divide all nodes in the system into different areas according to the bus they are connected to, if the switch on the branch is an associated switch, the time cost is 0.4; if the switch on the branch It is not an associated switch. The time cost is judged according to whether the nodes connected at both ends of the branch are in the same area. If they are in the same area, the time cost of the circuit breaker is 0.1; if they are not in the same area, the time cost of the circuit breaker is 0.2;

(B4) Weight the normalized value of the load recovery ability, risk coefficient and time cost of each recoverable branch according to the importance level, and then use it as the restoration cost matrix element of the recoverable branch, each time Select a branch with the least cost from the matrix; among them, the recovery cost of the recoverable branch is calculated by expression (5):

Cost(i)＝β ₁ φ(f _1i )+β ₂ φ(f _2i )+β ₃ φ(f _3i ) (5)

Among them, f _1i is the normalized value of time cost; f _2i is the normalized value of branch risk coefficient; f _3i is the normalized value of branch load recovery ability; β ₁ is the weight of time cost, β ₁ = 1; β ₂ is the weight of branch risk coefficient, β ₂ = 3; β ₃ is the weight of branch load recovery ability, β ₃ = 5; and φ is the penalty function, for x∈[0,1]

(B5) Calculate and check whether the system meets the power flow operation constraints and line safety constraints after restoring this branch; for all branches, the line safety constraints are:

Among them, V is the lower limit of the line voltage; is the lower limit of the line voltage; V is the line voltage; Is the upper limit of the line current; I is the line current;

(B6) If not satisfied, then exclude the current branch that does not satisfy the constraint from the recoverable branch; repeat steps (B4) to (B5) until the minimum recoverable branch that meets the constraint is found; restore the satisfying constraint The minimum recoverable branch of , update the topology of the system.

(B7) Steps (B1) to (B6) are repeated until all recoverable loads are recovered.

The beneficial effect of the present invention is that: the present invention fully considers the importance of the primary load and the impact on system security and stability during the recovery process according to the scope of the fault and the recovery ability of the distributed power supply within the fault to the power-off load, and realizes Intelligent fault recovery algorithm. This intelligent recovery algorithm can realize the selective recovery of some non-level one loads by making full use of the distributed power supply in the fault area under the premise of satisfying the fast recovery of the first level load, which can effectively reduce the time cost of fault recovery and the frequent system topology The impact of structural changes on system stability and security.

Description of drawings

Fig. 1 is a process flowchart of the present invention;

Fig. 2 is the test system (53 node network) topological schematic diagram of this method;

Figure 3 is the active power and reactive power of each node in the test system;

Fig. 4 is a graph showing the variation of primary load/all load recovery rates under two fault recovery methods in Embodiment 1 of the present invention;

Fig. 5 is the node overvoltage rate curve under two fault recovery methods in Embodiment 1 of the present invention;

Fig. 6 is in embodiment 1 of the present invention, under two kinds of fault recovery methods, line current margin curve;

Fig. 7 is the recovery cost curve under two fault recovery methods in Embodiment 1 of the present invention;

Fig. 8 is a graph showing the variation of primary load/all load recovery rates under two fault recovery methods in Embodiment 2 of the present invention;

Fig. 9 is the node overvoltage rate curve under two fault recovery methods in Embodiment 2 of the present invention;

Fig. 10 is the line current margin curve under two fault recovery methods in Embodiment 2 of the present invention;

Fig. 11 is a recovery cost curve under two fault recovery methods in Embodiment 2 of the present invention.

specific implementation plan

Below in conjunction with accompanying drawing, the present invention is described in further detail:

What Fig. 1 shows is the processing flowchart of this invention. Its specific implementation will be described as follows in conjunction with specific examples. The specific steps are described with a 53-node test network, and its topology is shown in Figure 2.

The load data curve of each node in the system is shown in Figure 3. Among them, nodes 8, 9, 12, 18, 22, 30, 33, 39, and 40 are primary load nodes; and nodes 19, 24, 35, 49, 28, 37, 39, and 27 have distributed power sources.

(1) Detect every time Δt, at the current moment, whether all nodes in the distribution network system are faulty.

(2) When a fault occurs, according to the topological structure of the distribution network system, the disconnector of the branch affected by the fault is disconnected, and the power flow distribution at the time of the fault is calculated.

(3) In order to reduce the frequent changes of system power flow caused by frequent changes of system topology and the frequent operation of associated switches in the system, before the fault is restored, according to the power flow distribution, it is judged whether the distributed power supply capacity in the power-off area can meet the power-off load supply. Specifically: if the capacity of the distributed power supply can meet 80% of all primary loads in a power-off state and non-primary loads in a power-off state, then:

∑P _DGs ≥∑P _{critical loads} +80%×∑P _{noncritical loads}

Among them, ∑P _DGs represents the available capacity of all distributed power sources in the de-energized area; ∑P _{critical loads} represents the primary load in the de-energized state, and ∑P _{noncritical loads} represents the non-primary load in the de-energized area; During the recovery process, the fault recovery method based on distributed power is used to recover; otherwise, the system's associated switch state is changed to recover from the fault.

(4) According to the conditions in step 3, select the corresponding topology reconfiguration method. If it is a fault recovery method based on distributed power supply, specifically:

(4.1) Calculate the load recovery capability of all recoverable branches in the current state, including the size of the direct recovery load and the positional relationship of each recoverable branch to the remaining load to be restored; the recoverable branch includes a system associated switch, Specifically:

(4.1.1) Assuming that there are a total of n branches that can be restored in the current state, if one of the branches is restored, a part of the load can be restored to supply, then this part of the load is the direct recovery load of the branch; the i item can be The direct restoration load of the restoration branch is calculated by expression (1):

Among them, k is the number of direct recovery loads of the i-th recoverable branch; ρ _j is the weight of the j-th direct recovery load, if it is a primary load ρ _j =100; otherwise, ρ _j =1; P _j is the size of the jth direct recovery load;

(4.1.2) The indirect restoration load P _{indirect loads} (i) of the i-th restorable branch is calculated by expression (2):

Among them, m is the number of remaining loads to be restored after restoring the i-th recoverable branch; P _{indirect loads,ij} is the size of the q-th load to be restored after restoring the i-th recoverable branch; distance _iq After restoring the i-th recoverable branch, the number of branches to be restored to restore the q-th load to be restored;

(4.1.3) Considering the direct/indirect recovery load comprehensively, the load recovery capacity of the i-th recoverable branch is calculated by the expression (3):

P _{recover loads} (i)＝P _{direct loads} (i)+P _{indirect loads} (i) (3)

(4.2) Calculate the operating time cost of all recoverable branches in the current state; divide all nodes in the system into different areas according to the bus they are connected to, if the switch on the branch is an associated switch, the time cost is 0.4; if the switch on the branch It is not an associated switch. The time cost is judged according to whether the nodes connected at both ends of the branch are in the same area. If they are in the same area, the time cost of the circuit breaker is 0.1; if they are not in the same area, the time cost of the circuit breaker is 0.2;

(4.3) Weight the normalized value of the load recovery ability, risk coefficient and time cost of each recoverable branch according to the importance level, and then use it as the recovery cost matrix element of the recoverable branch, each time Select a branch with the least cost from the matrix; among them, the recovery cost of the recoverable branch is calculated by expression (5):

Cost(i)＝β ₁ φ(f _1i )+β ₂ φ(f _2i )+β ₃ φ(f _3i ) (5)

Among them, f _1i is the normalized value of time cost; f _2i is the normalized value of branch risk coefficient; f _3i is the normalized value of branch load recovery ability; β ₁ is the weight of time cost, β ₁ = 1; β ₂ is the weight of branch risk coefficient, β ₂ = 3; β ₃ is the weight of branch load recovery ability, β ₃ = 5; and φ is the penalty function, for x∈[0,1]

(4.4) Calculate and check whether the system meets the power flow operation constraints and line safety constraints after restoring this branch; for all branches, the line safety constraints are:

Among them, V is the lower limit of the line voltage; is the lower limit of the line voltage; V is the line voltage; Is the upper limit of the line current; I is the line current;

(4.5) If not satisfied, then exclude the current branch that does not satisfy the constraint from the recoverable branch, repeat steps (4.3), (4.4) until the minimum recoverable branch that meets the constraint is found; restore the satisfying constraint The minimum recoverable branch updates the topology of the system.

(4.6) Repeat steps (4.1) to (4.5) until all recoverable loads are restored.

(5) Select the corresponding topology reconstruction method according to the conditions in step 3. If it is a fault recovery method based on topology reconstruction, it is specifically:

(5.1) Calculate the load recovery capability of all recoverable branches in the current state, including the size of the direct recovery load and the positional relationship of each recoverable branch to the remaining load to be restored; the recoverable branch includes a system-associated switch, Specifically:

(5.1.1) Assuming that there are a total of n branches that can be restored in the current state, if one of the branches is restored, a part of the load can be restored to supply, and this part of the load is the direct recovery load of the branch; the i item can be The direct restoration load of the restoration branch is calculated by expression (1):

Among them, k is the number of direct recovery loads of the i-th recoverable branch; ρ _j is the weight of the j-th direct recovery load, if it is a primary load ρ _j =100; otherwise, ρ _j =1; P _j is the size of the jth direct recovery load;

(5.1.2) The indirect restoration load P _{indirect loads} (i) of the i-th restorable branch is calculated by expression (2):

Among them, m is the number of remaining loads to be restored after restoring the i-th recoverable branch; P _{indirect loads,ij} is the size of the q-th load to be restored after restoring the i-th recoverable branch; distance _iq After restoring the i-th recoverable branch, the number of branches to be restored to restore the q-th load to be restored;

(5.1.3) Considering the direct/indirect restoration load comprehensively, the load restoration capacity of the i-th restorable branch is calculated by expression (3):

P _{recover loads} (i)＝P _{direct loads} (i)+P _{indirect loads} (i) (3)

(5.2) Calculate the risk coefficient of all recoverable branches in the current state, that is, the normalized weighted value that may cause the load rate increase of other non-faulty branches due to the restoration of a certain branch; specifically:

The risk coefficient of the i-th recoverable branch is calculated by expression (4):

Among them, L is the number of branches that cause power flow changes after restoring the i-th recoverable branch; I _l is the actual current of the l-th branch; I _limit,l is the current capacity of the l-th branch;

(5.3) Calculate the operating time cost of all recoverable branches in the current state; divide all nodes in the system into different areas according to the bus they are connected to, if the switch on the branch is an associated switch, the time cost is 0.4; if the switch on the branch It is not an associated switch. The time cost is judged according to whether the nodes connected at both ends of the branch are in the same area. If they are in the same area, the time cost of the circuit breaker is 0.1; if they are not in the same area, the time cost of the circuit breaker is 0.2;

(5.4) Weight the normalized value of the load recovery ability, risk coefficient and time cost of each recoverable branch according to the importance level, and then use it as the recovery cost matrix element of the recoverable branch, each time Select a branch with the least cost from the matrix; among them, the recovery cost of the recoverable branch is calculated by expression (5):

Cost(i)＝β ₁ φ(f _1i )+β ₂ φ(f _2i )+β ₃ φ(f _3i ) (5)

Among them, f _1i is the normalized value of time cost; f _2i is the normalized value of branch risk coefficient; f _3i is the normalized value of branch load recovery ability; β ₁ is the weight of time cost, β ₁ = 1; β ₂ is the weight of branch risk coefficient, β ₂ = 3; β ₃ is the weight of branch load recovery ability, β ₃ = 5; and φ is the penalty function, for x∈[0,1]

(5.5) Calculate and check whether the system meets the power flow operation constraints and line safety constraints after restoring this branch; for all branches, the line safety constraints are:

Among them, V is the lower limit of the line voltage; is the lower limit of the line voltage; V is the line voltage; Is the upper limit of the line current; I is the line current;

(5.6) If not satisfied, then exclude the current branch that does not satisfy the constraint from the recoverable branch, repeat steps (5.1), (5.5) until the minimum recoverable branch that meets the constraint is found; restore the satisfying constraint The minimum recoverable branch updates the topology of the system.

(5.7) Repeat steps (5.1) to (5.6) until all recoverable loads are restored.

Below in conjunction with accompanying drawing and embodiment, the embodiment of the present invention is described in detail, in the following embodiment, under the consideration based on the method for recovering failure intelligently, emphasize the limitation of primary load, realize the fast recovery of primary load (implementation Example 1); under the premise of considering the primary load, consider the intelligent recovery method, and realize the utilization maximization (embodiment 2) of distributed energy resources on fault recovery, and realize that the points and characteristics of the present invention are easy to be understood by those skilled in the art Personnel understand, thereby make more clear and definite definition to the scope of protection of the present invention.

Example 1

In this embodiment, under the premise of considering the primary load, when a single node failure occurs, the recovery degree of the primary load and all loads, the recovery cost and the impact on system stability and security during the recovery process are analyzed.

The system runs under the condition of whether to consider the first-level load priority and partition, and analyzes the recovery situation of each single node failure in the system. Taking the failure of node 1 as an example, the specific process is as follows:

(1) Detect every time Δt, at the current moment, whether all nodes in the distribution network system are faulty.

(2) When a fault occurs at node 1, according to the topological structure of the distribution network system, disconnect the branch isolation switches 1-9 affected by the fault to prevent the distributed power from running in an island state, and calculate the power flow at the time of the fault distributed.

(3) In order to reduce the frequent changes of the system power flow caused by the frequent changes of the system topology and the frequent operation of the associated switches in the system, before the fault is restored, according to the topology structure at the time of the fault in step (2), the distribution in the power-off area is judged Whether the distributed power supply capacity can meet the supply of power-off loads; through judgment, it can be seen that the distributed power supply capacity cannot meet the supply of all primary loads and 80% of power-off loads, and the topology of the system must be changed, that is, the associated switch status of the system must be changed .

(4) First calculate the load restoration capacity of all recoverable branches (branches 6, 7, 51, 52 and 57) in the current state.

(5) Calculate the risk coefficient of each recoverable branch in the current state.

(6) Calculate the recovery time cost of each recoverable branch in the current state.

(7) Weight the normalized value of the load recovery ability, risk coefficient and time cost of each recoverable branch according to the importance level, and then use it as the restoration cost matrix element of the recoverable branch, each time Choose a branch with the least cost from the matrix.

(8) Calculate and verify the system's power flow operation constraints and line safety constraints after restoring this branch;

(9) If all constraints are not satisfied, repeat steps (7), (8) until a recoverable branch that satisfies the constraints is found; if all constraints are satisfied, update the topology of the system

(10) Repeat steps (1) to (9) until all recoverable loads are recovered.

Considering all single-node failures in the system, repeat the above experimental steps (1)-(10). Compare the experimental results of the two groups, as shown in Figures 4 to 7. It can be seen from Example 1 that when considering the priority of the primary load and the difference in road operation time cost due to partitioning, the recovery speed of the primary load is significantly improved, but it has no effect on the overall fault recovery speed. The security and stability of the system are also slightly improved. Due to the priority of the first-level load, the recovery cost increases in the case of a small number of single-node failures. However, due to the consideration of partitions, the non-faulty nodes in the same area can be effectively used to restore power supply, which has a significant effect on reducing the system failure recovery cost.

Example 2

This embodiment analyzes on the premise of the intelligent fault recovery method, when a single node fault occurs, the recovery degree of the primary load and all loads, the recovery cost and the impact on system stability and security during the recovery process.

The system runs separately under the condition of considering whether to adopt the intelligent fault recovery method, and analyzes the recovery situation of each node in the system when a fault occurs. Taking the fault of node 1 as an example, the specific process is as follows:

(1) Detect every time Δt, at the current moment, whether all nodes in the distribution network system are faulty.

(2) When a fault occurs at node 1, according to the topological structure of the distribution network system, disconnect the branch isolation switches 1 to 9 affected by the fault to prevent the distributed power from running in an island state, and calculate the power flow at the time of the fault distributed.

(3) If the intelligent restoration method is considered, before the fault is restored, it is judged according to the power flow distribution whether the distributed power supply capacity in the power-off area can meet the supply of power-off loads; through the judgment, it can be seen that the distributed power supply capacity cannot meet all primary loads As well as supplying 80% of the dead loads, the topology of the system has to be changed, ie change the associated switch states of the system. If the intelligent recovery method is not considered, the fault recovery method based on topology reconstruction is adopted directly.

(4) Firstly calculate the load restoration capacity of all recoverable branches (branches 6, 7, 51, 52 and 57) in the current state, the calculation steps are as follows:

(5) Calculate the risk coefficient of each recoverable branch in the current state.

(6) Calculate the recovery time cost of each recoverable branch in the current state.

(7) Weight the normalized value of the load recovery ability, risk coefficient and time cost of each recoverable branch according to the importance level, and then use it as the restoration cost matrix element of the recoverable branch, each time Choose a branch with the least cost from the matrix.

(8) Calculate and verify the system's power flow operation constraints and line safety constraints after restoring this branch;

(9) If all constraints are not satisfied, repeat steps (7), (8) until a recoverable branch that satisfies the constraints is found; if all constraints are satisfied, update the topology of the system.

(10) Repeat steps (1) to (9) until all recoverable loads are recovered.

Considering the failure of all single nodes in the system, repeat the above experimental steps (1)-(10), and compare the experimental results of the two groups, as shown in Figures 8 to 11. It can be seen from Example 2 that when the intelligent fault recovery method is adopted, the recovery rate and recovery speed of the primary load are obviously improved, but it has no effect on the overall fault recovery speed, and the security and stability of the system are also slightly improved . Since the intelligent recovery algorithm can effectively use the distributed power supply within the fault range to restore power supply, it has a significant effect on reducing the cost of fault recovery.

Claims (1)

1. A method for recovering intelligent faults of a power distribution network with distributed power supplies is characterized by comprising the following steps:

step (1): detecting whether all nodes in the power distribution network system have faults at intervals of delta t;

step (2): when a fault occurs, disconnecting the branch isolating switch affected by the fault according to a topological structure in the power distribution network system, and calculating the load flow distribution at the moment of the fault;

and (3): judging whether the capacity of the distributed power supply in the power loss region can meet the supply of the power loss load or not according to the power flow distribution; the method specifically comprises the following steps: if the capacity of the distributed power supply can satisfy 80% of all the primary loads in the power loss state and the non-primary loads in the power loss state, that is, the following conditions are satisfied:

∑P_DGs≥∑P_{critical loads}+80％×∑P_{noncritical loads}

wherein, Sigma P_DGsRepresenting the available capacity of all distributed power sources in the power loss area; sigma P_{critical loads}First-order load, SIG P, representing a power-loss condition_{noncritical loads}A non-primary load representing a power loss condition; in the fault recovery process, a fault recovery method based on a distributed power supply is adopted for recovery; otherwise, changing the topological structure of the system to recover the fault;

in the step (3), the fault recovery method based on the distributed power supply specifically includes:

(A1) calculating the load recovery capacity of all recoverable branches in the current state, wherein the load recovery capacity comprises the size of a direct recovery load and the position relation of each recoverable branch to the residual load to be recovered; the recoverable branch does not include a system association switch, and specifically comprises:

(A1.1) assuming that n branches can be recovered in the current state, if one branch is recovered, a part of load can be recovered and supplied, and the part of load is the direct recovery load of the branch; the direct recovery load of the i-th recoverable branch is calculated using the expression (A-1):

<mrow> <msub> <mi>P</mi> <mrow> <mi>d</mi> <mi>i</mi> <mi>r</mi> <mi>e</mi> <mi>c</mi> <mi>t</mi> <mi>l</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mi>s</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>k</mi> </munderover> <msub> <mi>&amp;rho;</mi> <mi>j</mi> </msub> <mo>&amp;times;</mo> <msub> <mi>P</mi> <mi>j</mi> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>A</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow>

wherein k is the number of direct recovery loads of the ith recoverable branch; rho_jFor the weight of the jth direct recovery load, if it is the first-order load ρ_j100; otherwise, ρ_j＝1；P_jThe magnitude of the direct recovery load for the jth;

(A1.2) Indirect restoration load P of i-th recoverable Branch_{indirect loads}(i) Calculated using expression (A-2):

<mrow> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> <mi>e</mi> <mi>c</mi> <mi>t</mi> <mi>l</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mi>s</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>q</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>m</mi> </munderover> <mfrac> <mrow> <msub> <mi>&amp;rho;</mi> <mi>q</mi> </msub> <mo>&amp;times;</mo> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> <mi>e</mi> <mi>c</mi> <mi>t</mi> <mi>l</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mi>s</mi> <mo>,</mo> <mi>i</mi> <mi>q</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>distance</mi> <mrow> <mi>i</mi> <mi>q</mi> </mrow> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>A</mi> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow>

wherein m is the number of the residual loads to be recovered after the ith recoverable branch is selected to be recovered; p_{indirect loads,iq}After the ith recoverable branch is recovered, the size of the qth load to be recovered; distance_iqRecovering the number of the branch circuits required to be recovered for the q-th load to be recovered after recovering the ith recoverable branch circuit;

(A1.3) comprehensively considering the direct/indirect recovery load, and calculating the load recovery capacity of the ith recoverable branch by using an expression (A-3):

P_{recover loads}(i)＝P_{direct loads}(i)+P_{indirect loads}(i) (A‐3)

(A2) calculating the operation time cost of all recoverable branches in the current state; dividing all nodes in the system into different areas according to buses connected with the nodes, wherein if the switches on the branches are related switches, the time cost is 0.4; if the switch on the branch is not the correlated switch, judging the time cost according to whether the nodes connected with the two ends of the branch are in the same region, and if the nodes are in the same region, the time cost of the breaker is 0.1; if the circuit breakers are not in the same area, the time cost of the circuit breaker is 0.2;

(A3) weighting the normalized values of the load recovery capacity and the time cost of each recoverable branch according to the importance level, taking the normalized values as recovery cost matrix elements of the recoverable branches, and selecting a branch with the minimum cost from the matrix each time; wherein, the recovery cost of the recoverable branch is calculated by an expression (A-5):

Cost(i)＝β₁φ(f_1i)+β₃φ(f_3i) (A‐5)

wherein f is_1iNormalized value for time cost; f. of_3iLoad recovery for a branchnormalized value of Complex ability,. beta₁as a weight of the time cost, β₁＝1；β₃weight of the load recovery capability of the branch, beta₃(ii) 5; and φ is a penalty function for x ∈ [0,1 ]]Is provided with

<mrow> <mi>&amp;phi;</mi> <mrow> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>0</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>1</mn> <mo>/</mo> <mn>3</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>3</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>1</mn> <mo>/</mo> <mn>3</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>2</mn> <mo>/</mo> <mn>3</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>10</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>2</mn> <mo>/</mo> <mn>3</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>9</mn> <mo>/</mo> <mn>10</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>70</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>9</mn> <mo>/</mo> <mn>10</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>1</mn> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>A</mi> <mo>-</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow>

(A4) Calculating and checking whether the system meets the load flow operation constraint and the line safety constraint after recovering the branch; for all branches, the line safety constraints are:

<mrow> <munder> <mi>V</mi> <mo>&amp;OverBar;</mo> </munder> <mo>&amp;le;</mo> <mi>V</mi> <mo>&amp;le;</mo> <mover> <mi>V</mi> <mo>&amp;OverBar;</mo> </mover> </mrow>

<mrow> <msup> <mi>I</mi> <mn>2</mn> </msup> <mo>&amp;le;</mo> <msup> <mover> <mi>I</mi> <mo>&amp;OverBar;</mo> </mover> <mn>2</mn> </msup> </mrow>

wherein,Vis the lower limit of the line voltage;is the upper limit of the line voltage; v is the line voltage;is the upper limit of the line current; i is line current;

(A5) if not, then excluding the branch which does not satisfy the constraint currently from the recoverable branch; repeating steps (A3) and (a4) until the smallest recoverable branch satisfying the constraint is found; recovering the minimum recoverable branch meeting the constraint condition, and updating the topological structure of the system;

(A6) repeating steps (a1) - (a5) until all recoverable loads are recovered;

in the step (3), the system topology is changed to recover the fault, specifically:

(B1) calculating the load recovery capacity of all recoverable branches in the current state, wherein the load recovery capacity comprises the size of a direct recovery load and the position relation of each recoverable branch to the residual load to be recovered; the recoverable branch comprises a system association switch, and specifically comprises:

(B1.1) assuming that n branches can be recovered in the current state, if one branch is recovered, a part of load can be recovered and supplied, and the part of load is the direct recovery load of the branch; the direct recovery load of the i-th recoverable branch is calculated using the expression (B-1):

<mrow> <msub> <mi>P</mi> <mrow> <mi>d</mi> <mi>i</mi> <mi>r</mi> <mi>e</mi> <mi>c</mi> <mi>t</mi> <mi>l</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mi>s</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>k</mi> </munderover> <msub> <mi>&amp;rho;</mi> <mi>j</mi> </msub> <mo>&amp;times;</mo> <msub> <mi>P</mi> <mi>j</mi> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>B</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow>

wherein k is the number of direct recovery loads of the ith recoverable branch; rho_jFor the weight of the jth direct recovery load, if it is the first-order load ρ_j100; otherwise, ρ_j＝1；P_jThe magnitude of the direct recovery load for the jth;

(B1.2) Indirect restoration load P of i-th recoverable Branch_{indirect loads}(i) Calculated using expression (B-2):

<mrow> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> <mi>e</mi> <mi>c</mi> <mi>t</mi> <mi>l</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mi>s</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>q</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>m</mi> </munderover> <mfrac> <mrow> <msub> <mi>&amp;rho;</mi> <mi>q</mi> </msub> <mo>&amp;times;</mo> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>d</mi> <mi>i</mi> <mi>r</mi> <mi>e</mi> <mi>c</mi> <mi>t</mi> <mi>l</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mi>s</mi> <mo>,</mo> <mi>i</mi> <mi>q</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>distance</mi> <mrow> <mi>i</mi> <mi>q</mi> </mrow> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>B</mi> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow>

wherein m is the number of the residual loads to be recovered after the ith recoverable branch is selected to be recovered; p_{indirect loads,iq}After the ith recoverable branch is recovered, the size of the qth load to be recovered; distance_iqTo recover the ith recoverable branch after recovering the ith recoverable branchq branches of the load to be recovered need to be recovered;

(B1.3) comprehensively considering the direct/indirect recovery load, and calculating the load recovery capacity of the ith recoverable branch by using an expression B- (3):

P_{recover loads}(i)＝P_{direct loads}(i)+P_{indirect loads}(i) (B‐3)

(B2) calculating risk coefficients of all recoverable branches in the current state, namely, calculating a normalized weighted value which is a normalized weighted value which can cause the increase of the load rate of other non-fault branches due to the recovery of a certain branch; the method specifically comprises the following steps:

the risk factor of the i-th recoverable branch is calculated by the expression (B-4):

<mrow> <mi>R</mi> <mi>i</mi> <mi>s</mi> <mi>k</mi> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>l</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>L</mi> </munderover> <mfrac> <mrow> <mo>|</mo> <msub> <mi>I</mi> <mi>l</mi> </msub> <mo>-</mo> <msub> <mi>I</mi> <mrow> <mi>lim</mi> <mi>i</mi> <mi>t</mi> <mo>,</mo> <mi>l</mi> </mrow> </msub> <mo>|</mo> </mrow> <msub> <mi>I</mi> <mrow> <mi>lim</mi> <mi>i</mi> <mi>t</mi> <mo>,</mo> <mi>l</mi> </mrow> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>B</mi> <mo>-</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow>

wherein, L is the number of branch circuits causing the trend change after the ith recoverable branch circuit is recovered; i is_lThe actual current of the l branch; i is_limit,lElectricity for the l branchA flow capacity;

(B3) calculating the operation time cost of all recoverable branches in the current state; dividing all nodes in the system into different areas according to buses connected with the nodes, wherein if the switches on the branches are related switches, the time cost is 0.4; if the switch on the branch is not the correlated switch, judging the time cost according to whether the nodes connected with the two ends of the branch are in the same region, and if the nodes are in the same region, the time cost of the breaker is 0.1; if the circuit breakers are not in the same area, the time cost of the circuit breaker is 0.2;

(B4) weighting the normalized values of the load recovery capacity, the risk coefficient and the time cost of each recoverable branch according to the importance level, further taking the normalized values as recovery cost matrix elements of the recoverable branches, and selecting a branch with the minimum cost from the matrix each time; wherein, the recovery cost of the recoverable branch is calculated by an expression (B-5):

Cost(i)＝β₁φ(f_1i)+β₂φ(f_2i)+β₃φ(f_3i) (B‐5)

wherein f is_1iNormalized value for time cost; f. of_2iThe normalized value of the branch risk coefficient is obtained; f. of_3iis a normalized value of the branch load recovery capacity, beta₁as a weight of the time cost, β₁＝1；β₂as a weight of the branch risk factor, β₂＝3；β₃weight of the load recovery capability of the branch, beta₃(ii) 5; and φ is a penalty function for x ∈ [0,1 ]]Is provided with

<mrow> <mi>&amp;phi;</mi> <mo>&amp;prime;</mo> <mrow> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <mn>1</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>0</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>1</mn> <mo>/</mo> <mn>3</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>3</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>1</mn> <mo>/</mo> <mn>3</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>2</mn> <mo>/</mo> <mn>3</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>10</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>2</mn> <mo>/</mo> <mn>3</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>9</mn> <mo>/</mo> <mn>10</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mn>70</mn> <mo>,</mo> </mrow> </mtd> <mtd> <mrow> <mn>9</mn> <mo>/</mo> <mn>10</mn> <mo>&amp;le;</mo> <mi>x</mi> <mo>&lt;</mo> <mn>1</mn> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>B</mi> <mo>-</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow>

(B5) Calculating and checking whether the system meets the load flow operation constraint and the line safety constraint after recovering the branch; for all branches, the line safety constraints are:

<mrow> <munder> <mi>V</mi> <mo>&amp;OverBar;</mo> </munder> <mo>&amp;le;</mo> <mi>V</mi> <mo>&amp;le;</mo> <mover> <mi>V</mi> <mo>&amp;OverBar;</mo> </mover> </mrow>

<mrow> <msup> <mi>I</mi> <mn>2</mn> </msup> <mo>&amp;le;</mo> <msup> <mover> <mi>I</mi> <mo>&amp;OverBar;</mo> </mover> <mn>2</mn> </msup> </mrow>

wherein V is the lower limit of the line voltage;is the upper limit of the line voltage; v is the line voltage;is the upper limit of the line current; i is line current;

(B6) if not, then excluding the branch which does not satisfy the constraint currently from the recoverable branch; repeating the steps (B4) to (B5) until the smallest recoverable branch meeting the constraint condition is found; recovering the minimum recoverable branch meeting the constraint condition, and updating the topological structure of the system;

(B7) repeating steps (B1) - (B6) until all recoverable loads are recovered.