Flexible power distribution network multi-type remote control switch and soft switch combined planning method

Abstract

The invention discloses an elastic power distribution network multi-type remote control switch and soft switch combined planning method, which relates to the field of power distribution networks and comprises the following steps: step 1), establishing a target function with the minimum sum of investment cost of a soft switch and a multi-type remote control switch and power loss cost in a fault; 2) establishing a power distribution network operation model considering multiple stages of active island, degradation, fault isolation and fault recovery and protection constraints; and step 3), converting the operation model into a mixed second-order cone integer programming model by adopting a quadratic term linearization method to solve the mixed second-order cone integer programming model. According to the method, multiple actually existing remote control switches and protection constraints are innovatively coordinated in multiple stages, and the capability of the distribution network for resisting disasters is effectively improved.

Description

Technical Field

[0001] The invention relates to the field of distribution networks, and in particular to a method for jointly planning multiple types of remote-controlled switches and soft switches in a flexible distribution network. Background Art

[0002] In recent years, natural disasters and attacks on power systems have become more frequent, resulting in severe power outages and huge economic losses. Since distribution networks usually operate in a radial manner, redundancy is low. Therefore, power outages caused by distribution network failures account for the vast majority of the total power outages each year. In addition, the distribution network is directly connected to end users to support their electricity needs. Once a failure event occurs, it will have a greater impact on people's production and life. Therefore, it is of great significance to study the active improvement of the resilience of resilient distribution networks.

[0003] At present, the distribution network is equipped with a large number of remote control switches, which can achieve rapid fault isolation and recovery of the power grid, shorten the fault time, and reduce the inconvenience of end users. Compared with traditional remote control switches, soft switches can accurately control the active power and reactive power at both ends of the feeder, realize two-way regulation of system flow, and effectively deal with a series of new problems brought about by the access of distributed power sources. The realization of soft switches is mainly based on fully controlled power electronic devices, which have high investment and operation and maintenance costs. Therefore, reasonable planning of soft switches and remote control switches is very necessary.

[0004] Existing studies have used soft switches and remote switches in distribution networks to improve the resilience of the system in fault scenarios. In fact, there are many types of remote switches, mainly including: 1) Circuit breakers and reclosers: capable of connecting, carrying and disconnecting current under normal and abnormal current conditions. 2) Load circuit breaker switches: can connect or disconnect current under normal load conditions, but cannot connect or disconnect fault currents. 3) Sectionalizers: can only operate under no-load conditions. Existing studies only consider one type of remote switch, and do not plan the remote switch type, performance and restrictions based on actual conditions, nor do they consider protection constraints during faults. Summary of the invention

[0005] The object of the present invention is to provide a method for jointly planning multiple types of remote-controlled switches and soft switches in a flexible distribution network to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for joint planning of multiple types of remote-controlled switches and soft switches in a flexible distribution network comprises the following steps:

[0008] Step 1): Establish an objective function that minimizes the investment cost and power failure cost of soft switches and multi-type remote control switches;

[0009] Step 2): Establish a distribution network operation model that considers multiple stages of active islanding, degradation, fault isolation and fault recovery and protection constraints;

[0010] Step 3): Use methods such as quadratic term linearization to convert the original model into a mixed second-order cone integer programming model for solution.

[0011] Preferably, the step 1) is specifically as follows:

[0012] Taking the investment cost and power failure cost of soft switches and multi-type remote control switches as the minimum, the system objective function is established as follows:

[0013] min(C CoD (x)+C VoLL (x)) (1)

[0014]

[0015]

[0016]

[0017] Among them C CoD and C VoLL is the annual joint planning fee and load reduction fee; m represents the number of remote control switches used, S n Indicates the total capacity of the soft switches put into use; I RCS Represents the single investment cost of remote control switch, I SOP represents the cost per unit capacity of the soft switch; r 0 is the discount rate; τ is the expected life of the remote switch and soft switch; ζ om Annual operation and maintenance costs for remote switches and soft switches; is the unit price of load shedding; fault is the failure time of simulated investment distribution network within one year; P ω is the probability of the failure scenario ω occurring; T f , T ir , T rr , T im Respectively represent the fault occurrence time, fault isolation time, service recovery time, and fault repair time; represents the active load reduction of node i in the scenario; where c = 1, c = 2, and c = 3 are the degradation stage, isolation stage, and service recovery stage. i is the load weight of the node, Ω b is a node set;

[0018] Preferably, the step 2) is specifically as follows:

[0019] (1) The soft switch is modeled as follows:

[0020]

[0021]

[0022]

[0023]

[0024] in: is the active / reactive power injection of the soft switch at node i in the recovery phase c,ω scenario; Ω S is the set of branches with soft switches installed; Ω s,ω,c The set of branches with soft switches installed in the recovery phase c,ω scenario; is the capacity of the converter at node i; is the reactive power boundary of the converter at node i; b ij is a binary variable indicating whether a soft switch is installed on branch (i; j); n i,ω,c is a binary variable indicating whether node i is located in the fault area. If node i is located in the fault area, it is equal to 1, indicating that node i has a closed path with any fault point, otherwise it is 0;

[0025] (2) The linear power flow model is used to model the distribution network as follows:

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] Where: P i,ω,c and Q i,ω,c is the sum of active and reactive power injection at node i in scenario c during the recovery phase; P ij,ω,c and Q ij,ω,c is the active and reactive power of branch (i; j) in scenario c during the recovery phase; Ω l is the set of branches; r ij and x ij is the resistance and reactance of branch (i; j); U i,ω,c is the voltage at node i in the recovery phase c scenario; ij,ω,c is a binary variable, which takes the value 1 if the branch (i; j) is closed, and 0 otherwise; is the active and reactive load consumption of node i; is the active and reactive load reduction of node j in scenario ω; is the active and reactive power output of distributed generation at node i in scenario ω of phase c; is the active and reactive power injected from the substation; Ω G A collection of substations;

[0032] (3) Set the safety constraints as follows:

[0033]

[0034]

[0035] Where: S ij is the apparent power capacity of branch (i; j); and U The upper and lower limits are defined for the voltage; constraints (13) and (14) represent the limits on the node voltage and line power, respectively;

[0036] (4) Distributed generation constraints are as follows:

[0037]

[0038]

[0039]

[0040] in: is the minimum active and reactive power output by distributed generation at node i; is the rated active and reactive power output by distributed generation at node i; is the up / down ramp rate of distributed generation at node i;

[0041] (5) Set the load reduction constraints as follows:

[0042]

[0043]

[0044] (6) Set the equipment installation constraints as follows:

[0045]

[0046]

[0047] Among them: a ijis a binary variable, which takes the value of 1 if the branch (i; j) is equipped with a remote switch, and 0 otherwise; constraint (20) indicates that the remote switch and the soft switch cannot be installed in the branch at the same time; constraint (21) indicates that the parallel switch should always remain in the open state after the soft switch is installed;

[0048] (7) Set topological constraints:

[0049] The topology constraints include substation constraints and phase constraints, where substation constraints (22)-(23) are set to ensure that each node can only belong to one substation and should be satisfied in all four restoration phases of the multi-substation distribution network:

[0050]

[0051]

[0052] in: represents the indication of the substation supplying power to node i in the scenario ω of phase c; represents the index of substation i; constraint (22) indicates that if a substation is not affected by the fault, then the substation is the main power source; constraint (23) indicates that the nodes at both ends of the closed line are powered by the same substation, that is, the nodes electrically connected to a substation belong to the same power supply area;

[0053] (8) Set protection constraints:

[0054] The switching current must meet the following requirements:

[0055] I n ·OLF<I p (twenty four)

[0056] I p <I f,min (25)

[0057] Where: I n is the current flowing through the switch, calculated by the power flow equation of the distribution network, OLF is the overload factor, I p is the minimum trigger current of the protection device; I f,min is the minimum fault current;

[0058] (9) Set up the constraints for step-by-step fault recovery:

[0059] ① Active island

[0060] Before an accident occurs, prepare active islands based on planned remote switches and soft switches, taking into account topological constraints and operational constraints:

[0061]

[0062]

[0063]

[0064] Where: X ij,ω,c A binary variable representing the connection status between nodes i and j at stage c, which takes the value 1 when i is the parent node of j and 0 otherwise; g j is a binary variable, which takes the value of 1 if node j is a substation, otherwise 0; π(j) / δ(j) is the set of parent nodes / child nodes of node j;

[0065] ②Degeneration stage

[0066] The fault area is formed after an extreme fault event. At this stage, the following constraints are considered:

[0067]

[0068]

[0069]

[0070]

[0071] Among them: When branch (i; j) is in scene ω, f ij,ω The value is 1, otherwise it is 0; Constraint (29) indicates that if there is a fault on the closed line, the two nodes at both ends of the branch will involve the fault area;

[0072] ③Isolation stage

[0073] After the degradation stage, the fault is isolated by remote control and soft switching, thereby isolating the smallest fault area. The isolation stage is divided into the recloser isolation stage and the sectionalizer isolation stage according to the different switches:

[0074] During the recloser isolation phase, the following constraints are set:

[0075] (1-f ij,ω )(z ij,ω,0 -a ij,REC )≤z ij,ω,2 ≤(1-f ij,ω ) ij,ω,0 (33)

[0076]

[0077]

[0078]

[0079] During the segmenter isolation phase, set the following constraints:

[0080] (1-f ij,ω )(z ij,ω,0 -a ij,SEC )≤z ij,ω,2 ≤(1-f ij,ω ) ij,ω,0 (37)

[0081]

[0082]

[0083]

[0084] where a ij,REC 、a ij,SEC Respectively indicate whether a recloser and a sectionalizer are installed on the branch (i; j);

[0085] ④Recovery phase

[0086] After the fault is isolated, rapid service recovery will be achieved based on remote control switches and soft switches, so that the offline area affected by the fault can be restored to its maximum load, and the faulty area can be isolated and repaired. The following constraints are used in the recovery phase:

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094] The load breaker switch only acts during the recovery phase, with the following constraints:

[0095] (1-f ij,ω )(z ij,ω,3 -a ij,REC -b ij,LBS )<=z ij,ω,3 (48)

[0096] z ij,ω,3 <=(1-f ij,ω )(z ij,ω,3 +a ij,REC +bij,LBS ) (49)

[0097] a ij,LBS =b ij,LBS if f ij,ω =1 (50)

[0098] where a ij,LBS Indicates whether a load circuit breaker is installed on the branch (i; j), b ij,LBS Indicates whether the load circuit breaker on branch (i; j) is activated.

[0099] Preferably, the step 3) is specifically:

[0100] (1) The method to realize the linearization of quadratic terms is as follows:

[0101] Use variable substitution to linearize the quadratic term, that is, use V i,ω,c replace Equations (10) and (13) are transformed into the following linear constraints by replacing the above variables:

[0102]

[0103]

[0104] (2) The method to achieve absolute term linearization is as follows:

[0105] An auxiliary variable is introduced to handle the absolute term in the constraint (17), and the linearization process is expressed as:

[0106]

[0107] in: is an auxiliary variable defined to represent the output change of distributed generation at node i between phase c and phase c-1.

[0108] (3) For equivalent linearization, the following constraints are obtained based on the big M method:

[0109]

[0110]

[0111] Where: M is a sufficiently large number, take 50000000000; P ij,ω,c and Q ij,ω,c Also affected by ij,ω,c Constraints;

[0112]

[0113]

[0114]

[0115] (4) Perform second-order cone relaxation

[0116] Using relaxation, equations (7) and (14) can be relaxed to a rotational second-order cone constraint, which is expressed as:

[0117]

[0118]

[0119] (5) Establish evaluation indicators

[0120] After relaxation, the original optimization problem is transformed into a mixed integer second-order cone model and solved efficiently using existing solvers (such as CPLEX). In order to evaluate the resilience level of the distribution network, the following evaluation indicators are calculated:

[0121]

[0122] Where: R overall is the percentage of expected power supply during the restoration phase of all fault conditions, t c Indicates the duration of phase c.

[0123] Compared with the prior art, the present invention has the following beneficial effects:

[0124] 1. Compared with the previous remote control switch planning that only considers the recovery stage, the present invention divides the distribution network fault recovery into multiple stages: islanding, degradation, fault isolation and fault recovery, making full use of the functional characteristics of power electronic soft switching devices and the switch protection coordination mechanism to enhance the flexibility of the system;

[0125] 2. Compared with the previous consideration of only one type of remote control switch, the present invention innovatively considers the multiple types, performances and operating restrictions of remote control switches that actually exist, gives full play to the coordination effect of various types of switches, and has strong practical application value;

[0126] 3. The optimization model established by the present invention is a mixed integer nonlinear programming problem. Currently, there is no reliable solution method. By further adopting the second-order cone method to transform the mixed integer nonlinear programming into mixed integer second-order cone programming, an effective and fast solution can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0127] Figure 1 Flow chart of the remote control switch and soft switch joint planning scheme of the present invention

[0128] Figure 2 It is a schematic diagram of the joint planning scheme of the remote control switch and the soft switch in the preferred embodiment of the present invention.

[0129] Figure 3 This is a schematic diagram of a solution that only plans remote control switches.

[0130] Figure 4 Schematic diagram of the solution where only soft switching is planned. DETAILED DESCRIPTION

[0131] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0132] In an embodiment of the present invention, a method for jointly planning multiple types of remote-controlled switches and soft switches in a flexible distribution network includes the following steps:

[0133] Step 1): Establish an objective function that minimizes the sum of the investment cost of soft switches and multiple types of remote control switches and the power loss cost during a fault;

[0134] Step 2) establishing a distribution network operation model that considers multiple stages of active islanding, degradation, fault isolation and fault recovery and protection constraints;

[0135] Step 3): The operating model is converted into a mixed second-order cone integer programming model for solving by using a quadratic linearization method.

[0136] As a further solution of the present invention, the step 1) is specifically:

[0137] Taking the investment cost and power failure cost of soft switches and multi-type remote control switches as the minimum, the system objective function is established as follows:

[0138] min(C CoD (x)+C VoLL (x)) (1)

[0139]

[0140]

[0141]

[0142] Among them C CoD and C VoLL is the annual joint planning cost and load shedding cost; m represents the number of remote control switches used, S n Indicates the total capacity of the soft switches put into use; I RCS Represents the single investment cost of remote control switch, I SOP represents the cost per unit capacity of the soft switch; r0 is the discount rate; τ is the expected life of the remote switch and soft switch; ζ om is the annual operation and maintenance cost of the remote switch and soft switch; is the unit price of load shedding; fault Simulate the failure time of the investment distribution network within one year; P ω is the probability of the failure scenario ω occurring; T f , T ir , T rr , T im Respectively represent the fault occurrence time, fault isolation time, service recovery time, and fault repair time; represents the active load reduction of node i in the scenario; where c = 1, c = 2, and c = 3 are the degradation stage, isolation stage, and service recovery stage. i is the load weight of the node, Ω b is a node set;

[0143] As a further solution of the present invention, the step 2) is specifically:

[0144] (1) The soft switch is modeled as follows:

[0145]

[0146]

[0147]

[0148]

[0149] in: is the active / reactive power injection of the soft switch at node i in the recovery phase c,ω scenario; Ω S is the set of branches with soft switches installed; Ω s,ω,c is the set of branches with soft switches installed in the recovery phase c,ω scenario; is the capacity of the converter at node i; is the reactive power boundary of the converter at node i; b ij is a binary variable indicating whether a soft switch is installed on branch (i; j); n i,ω,c is a binary variable indicating whether node i is located in the fault zone. If node i is located in the fault zone, it is equal to 1, indicating that node i has a closed path with any fault point, otherwise it is 0;

[0150] (2) The linear power flow model is used to model the distribution network as follows:

[0151]

[0152]

[0153]

[0154]

[0155]

[0156] Where: P i,ω,c and Q i,ω,c is the sum of active and reactive power injection at node i in scenario c during the recovery phase; P ij,ω,c and Q ij,ω,c is the active and reactive power of branch (i; j) in scenario c during the recovery phase; Ω l is the set of branches; r ij and x ij is the resistance and reactance of branch (i; j); U i,ω,c is the voltage at node i in the recovery phase c scenario; ij,ω,c is a binary variable, which takes the value 1 if the branch (i; j) is closed, and 0 otherwise; is the active and reactive load consumption of node i; is the active and reactive load reduction of node j in scenario ω; is the active and reactive power output of distributed generation at node i in scenario ω of phase c; is the active and reactive power injected from the substation; Ω G A collection of substations;

[0157] (3) Set the safety constraints as follows:

[0158]

[0159]

[0160] Where: S ij is the apparent power capacity of branch (i; j); and U The upper and lower limits are defined for the voltage; constraints (13) and (14) represent the limits on the node voltage and line power, respectively;

[0161] (4) Distributed generation constraints are as follows:

[0162]

[0163]

[0164]

[0165] in: is the minimum active and reactive power output by distributed generation at node i; is the rated active and reactive power output by distributed generation at node i; is the up / down ramp rate of distributed generation at node i;

[0166] (5) Set the load reduction constraints as follows:

[0167]

[0168]

[0169] (6) Set the equipment installation constraints as follows:

[0170]

[0171]

[0172] Among them: a ij is a binary variable, which takes the value of 1 if the branch (i; j) is equipped with a remote switch, and 0 otherwise; constraint (20) indicates that the remote switch and the soft switch cannot be installed in the branch at the same time; constraint (21) indicates that the parallel switch should always remain in the open state after the soft switch is installed;

[0173] (7) Set topological constraints:

[0174] The topology constraints include substation constraints and phase constraints, where substation constraints (22)-(23) are set to ensure that each node can only belong to one substation and should be satisfied in all four restoration phases of the multi-substation distribution network:

[0175]

[0176]

[0177] in: represents the indication of the substation supplying power to node i in the scenario ω of phase c; represents the index of substation i; constraint (22) indicates that if a substation is not affected by the fault, then the substation is the main power source; constraint (23) indicates that the nodes at both ends of the closed line are powered by the same substation, that is, the nodes electrically connected to a substation belong to the same power supply area;

[0178] (8) Set protection constraints:

[0179] The switching current must meet the following requirements:

[0180] I n ·OLF<I p (twenty four)

[0181] I p <I f,min (25)

[0182] Where: I n is the current flowing through the switch, calculated by the power flow equation of the distribution network, OLF is the overload factor, I p is the minimum trigger current of the protection device; I f,min is the minimum fault current;

[0183] (9) Set up the constraints for step-by-step fault recovery:

[0184] ① Active island

[0185] Before an accident occurs, prepare active islands based on planned remote switches and soft switches, taking into account topological constraints and operational constraints:

[0186]

[0187]

[0188]

[0189] Where: X ij,ω,c A binary variable representing the connection status between nodes i and j at stage c, which takes the value 1 when i is the parent node of j and 0 otherwise; g j is a binary variable, which takes the value of 1 if node j is a substation, otherwise 0; π(j) / δ(j) is the set of parent nodes / child nodes of node j;

[0190] ②Degeneration stage

[0191] The fault area is formed after an extreme fault event. At this stage, the following constraints are considered:

[0192]

[0193]

[0194]

[0195]

[0196] Among them: When branch (i; j) is in scene ω, f ij,ω The value is 1, otherwise it is 0; Constraint (29) indicates that if there is a fault on the closed line, the two nodes at both ends of the branch will involve the fault area;

[0197] ③Isolation stage

[0198] After the degradation stage, the fault is isolated by remote control and soft switching, thereby isolating the smallest fault area. The isolation stage is divided into the recloser isolation stage and the sectionalizer isolation stage according to the different switches:

[0199] During the recloser isolation phase, the following constraints are set:

[0200] (1-f ij,ω )(z ij,ω,0 -a ij,REC )≤z ij,ω,2 ≤(1-f ij,ω ) ij,ω,0 (33)

[0201]

[0202]

[0203]

[0204] During the segmenter isolation phase, set the following constraints:

[0205] (1-f ij,ω )(z ij,ω,0 -a ij,SEC )≤z ij,ω,2 ≤(1-f ij,ω ) ij,ω,0 (37)

[0206]

[0207]

[0208]

[0209] where a ij,REC 、a ij,SEC Respectively indicate whether a recloser and a sectionalizer are installed on the branch (i; j);

[0210] ④Recovery phase

[0211] After the fault is isolated, rapid service recovery will be achieved based on remote control switches and soft switches, so that the offline area affected by the fault can be restored to its maximum load, and the faulty area can be isolated and repaired. The following constraints are used in the recovery phase:

[0212]

[0213]

[0214]

[0215]

[0216]

[0217]

[0218]

[0219] The load breaker switch only acts during the recovery phase, with the following constraints:

[0220] (1-f ij,ω )(z ij,ω,3 -a ij,REC -b ij,LBS )<=z ij,ω,3 (48)

[0221] z ij,ω,3 <=(1-f ij,ω )(z ij,ω,3 +a ij,REC +b ij,LBS ) (49)

[0222] a ij,LBS =b ij,LBS if f ij,ω =1 (50)

[0223] where a ij,LBS Indicates whether a load circuit breaker is installed on the branch (i; j), b ij,LBS Indicates whether the load circuit breaker on branch (i; j) is activated.

[0224] Preferably, the step 3) is specifically:

[0225] (1) The method to realize the linearization of quadratic terms is as follows:

[0226] Use variable substitution to linearize the quadratic term, that is, use V i,ω,c replace Equations (10) and (13) are transformed into the following linear constraints by replacing the above variables:

[0227]

[0228]

[0229] (2) The method to achieve absolute term linearization is as follows:

[0230] An auxiliary variable is introduced to handle the absolute term in the constraint (17), and the linearization process is expressed as:

[0231]

[0232] in: is an auxiliary variable defined to represent the output change of distributed generation at node i between phase c and phase c-1.

[0233] (3) For equivalent linearization, the following constraints are obtained based on the big M method:

[0234]

[0235]

[0236] Among them: M is 50000000000; P ij,ω,c and Q ij,ω,c Also affected by ij,ω,c Constraints;

[0237]

[0238]

[0239]

[0240] (4) Perform second-order cone relaxation

[0241] Using relaxation, equations (7) and (14) can be relaxed to a rotational second-order cone constraint, which is expressed as:

[0242]

[0243]

[0244] (5) Establish evaluation indicators

[0245] After relaxation, the original optimization problem is transformed into a mixed integer second-order cone model and solved efficiently using the existing solver. In order to evaluate the resilience level of the distribution network, the following evaluation indicators are calculated:

[0246]

[0247] Where: R overall is the percentage of power expected to be available during the restoration phase of all fault conditions. c Indicates the duration of phase c.

[0248] As a preferred embodiment of the present invention, the present invention adopts an improved IEEE 34-node system for testing, and by setting 7 different fault scenarios, three solutions are compared to verify the effectiveness of the present invention (the comparison results are shown in Table 1).

[0249] Table 1

[0250]

[0251] Solution 1 is a joint planning solution of remote control switch and soft switch proposed by the present invention; Solution 2 is a solution that only plans remote control switch. Solution 3 is a solution that only plans soft switch. The planning situations of the three solutions are as follows: Figure 1 , 2 , as shown in Figure 3.

[0252] In the fault setting, four fault points are set for each group of faults, and seven groups of fault points are set. The fault points set in the case are all located behind node 8, with a total of 28 faults. In the protection coordination process of each switch, lines 13-14, 18-19, 22-23, and 16-28 in scenario 1 fail. After line 13-14 fails, lines 18-19 and 17-18 isolate the fault. The remote switch on line 18-19 serves as the main protection for fuse, and 17-18 serves as the backup protection. Similarly, when line 13-14 fails, the remote switch on line 13-14 serves as the main protection, and the remote switches on lines 11-12 and 33-34 serve as the backup protection. After the remote switch is completed, there needs to be a minimum adjustment time for the sectionalizer to operate to further reduce the impact of the fault and restore the power supply at this stage. After the fault isolation of the system is completed, the feeder, soft switch and load circuit breaker switch in the system are used to further restore the power-off area to reduce the loss caused by the fault.

[0253] The above switch distribution results were obtained through optimization. Figure 1-Figure 3 It can be seen that the planning locations of remote switches and soft switches are generally located in the line sections where faults often occur, indicating that remote switches and soft switches can reduce the fault area and enhance the resilience of the distribution network. It can also be seen from the results that the scheme 1 using the joint planning of soft switches and remote switches has the lowest total cost, the highest power supply percentage, and the lowest power loss. Although the number of remote switches planned in schemes 1 and 2 is the same, the total costs of the two schemes are very different, indicating that the joint operation of remote switches and soft switches can greatly reduce node power loss. The indicators of schemes 1 and 3, which include soft switches, are better than those of scheme 2, which only considers remote switches, indicating that the investment of soft switches can significantly enhance the resilience of the distribution system. In general, compared with the other two single planning modes, the joint planning of remote switches and soft switches for elastic distribution networks can effectively improve the ability of distribution networks to resist disasters.

[0254] In summary, the present invention divides the distribution network fault recovery into multiple stages of islanding, degradation, fault isolation and fault recovery, and makes full use of the functional characteristics of power electronic soft switching devices and the switch protection coordination mechanism to enhance the resilience of the system; at the same time, the present invention innovatively considers the actual existence of a variety of remote control switch types, performance and operation restrictions, and gives full play to the coordination role of various switches, which has a strong practical application value; finally, the optimization model established by the present invention is a mixed integer nonlinear programming problem, and there is currently no reliable solution method. By further adopting the second-order cone method to transform the mixed integer nonlinear programming into the mixed integer second-order cone programming, an effective and fast solution can be achieved.

[0255] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0256] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for joint planning of multiple types of remote-controlled switches and soft switches in a flexible distribution network, characterized in that: The steps include: Step 1): Establish an objective function that minimizes the sum of the investment cost of soft switches and multiple types of remote control switches and the power loss cost during a fault; Step 2): Establish a distribution network operation model that considers multiple stages of active islanding, degradation, fault isolation and fault recovery and protection constraints; Step 3): The operating model is converted into a mixed second-order cone integer programming model for solving by using a quadratic linearization method.

2. The method for joint planning of multiple types of remote-controlled switches and soft switches for a flexible distribution network according to claim 1 is characterized in that: The step 1) is specifically as follows: Taking the investment cost and power failure cost of soft switches and multi-type remote control switches as the minimum, the system objective function is established as follows: min(C CoD (x)+C VoLL (x)) (1) Among them C CoD and C VoLL is the annual joint planning fee and load reduction fee; m represents the number of remote control switches used, S n Indicates the total capacity of the soft switches put into use; I RCS Represents the single investment cost of remote control switch, I SOP represents the cost per unit capacity of the soft switch; r0 is the discount rate; τ is the expected life of the remote switch and the soft switch; ζ om Annual operation and maintenance costs for remote switches and soft switches; is the unit price for load shedding; Ψ fault is the failure time of simulated investment distribution network within one year; P ω is the probability of the failure scenario ω occurring; T f , T ir , T rr , T im Respectively represent the fault occurrence time, fault isolation time, service recovery time, and fault repair time; represents the active load reduction of node i in the scenario; where c = 1, the isolation stage (c = 2), and the service recovery stage (c = 3); θ i is the load weight of the node, Ω b A collection of nodes.

3. The method for joint planning of multiple types of remote-controlled switches and soft switches for a flexible distribution network according to claim 1 is characterized in that: The step 2) is specifically as follows: (1) The soft switch is modeled as follows: in: is the active / reactive power injection of the soft switch at node i in the recovery phase c,ω scenario; Ω S is the set of branches with soft switches installed; Ω s,ω,c The set of branches with soft switches installed in the recovery phase c,ω scenario; is the capacity of the converter at node i; is the reactive power boundary of the converter at node i; b ij is a binary variable indicating whether a soft switch is installed on branch (i; j); n i,ω,c is a binary variable indicating whether node i is located in the fault area. If node i is located in the fault area, it is equal to 1, indicating that node i has a closed path with any fault point, otherwise it is 0; (2) The linear power flow model is used to model the distribution network as follows: Where: P i,ω,c and Q i,ω,c is the sum of active and reactive power injection at node i in scenario c during the recovery phase; P ij,ω,c and Q ij,ω,c is the active and reactive power of branch (i; j) in scenario c during the recovery phase; Ω l is the set of branches; r ij and x ij is the resistance and reactance of branch (i; j); U i,ω,c is the voltage at node i in the recovery phase c scenario; ij,ω,c is a binary variable, which takes the value 1 if the branch (i; j) is closed, and 0 otherwise; is the active and reactive load consumption of node i; is the active and reactive load reduction of node j in scenario ω; is the active and reactive power output of distributed generation at node i in scenario ω of phase c; is the active and reactive power injected from the substation; Ω G A collection of substations; (3) Set the safety constraints as follows: Where: S ij is the apparent power capacity of branch (i; j); and U The upper and lower limits are defined for the voltage; constraints (13) and (14) represent the limits on the node voltage and line power, respectively; (4) Distributed generation constraints are as follows: in: is the minimum active and reactive power output by distributed generation at node i; is the rated active and reactive power output by distributed generation at node i; is the up / down ramp rate of distributed generation at node i; (5) Set the load reduction constraints as follows: (6) Set the equipment installation constraints as follows: Among them: a ij is a binary variable, which takes the value of 1 if the branch (i; j) is equipped with a remote switch, and 0 otherwise; constraint (20) indicates that the remote switch and the soft switch cannot be installed in the branch at the same time; constraint (21) indicates that the parallel switch should always remain in the open state after the soft switch is installed; (7) Set topological constraints: The topology constraints include substation constraints and phase constraints. Substation constraints (22)-(23) are set to ensure that each node belongs to only one substation and are satisfied in all four restoration phases of the multi-substation distribution network: in: represents the indication of the substation supplying power to node i in the scenario ω of phase c; represents the index of substation i; constraint (22) indicates that if a substation is not affected by the fault, then the substation is the main power source; constraint (23) indicates that the nodes at both ends of the closed line are powered by the same substation, that is, the nodes electrically connected to a substation belong to the same power supply area; (8) Set protection constraints: The switching current must meet the following requirements: I n ·OLF<I p (24) I p <I f,min (25) Where: I n is the current flowing through the switch, calculated by the power flow equation of the distribution network, OLF is the overload factor, I p is the minimum trigger current of the protection device; I f,min is the minimum fault current; (9) Set up the constraints for step-by-step fault recovery: ① Active island Before an accident occurs, prepare active islands based on planned remote switches and soft switches, taking into account topological constraints and operational constraints: Where: X ij,ω,c A binary variable representing the connection status between nodes i and j at stage c, which takes the value 1 when i is the parent node of j and 0 otherwise; g j is a binary variable, which takes the value of 1 if node j is a substation, otherwise 0; π(j) / δ(j) is the set of parent nodes / child nodes of node j; ②Degeneration stage The fault area is formed after an extreme fault event. At this stage, the following constraints are considered: Among them: When branch (i; j) is in scene ω, f ij,ω The value is 1, otherwise it is 0; Constraint (29) indicates that if there is a fault on the closed line, the two nodes at both ends of the branch will involve the fault area; ③Isolation stage After the degradation stage, the fault is isolated by remote control and soft switching, thereby isolating the smallest fault area. The isolation stage is divided into the recloser isolation stage and the sectionalizer isolation stage according to the different switches: During the recloser isolation phase, the following constraints are set: (1-f ij,ω )(z ij,ω,0 -a ij,REC )≤z ij,ω,2 ≤(1-f ij,ω )z ij,ω,0 (33) During the segmenter isolation phase, set the following constraints: (1-f ij,ω )(z ij,ω,0 -a ij,SEC )≤z ij,ω,2 ≤(1-f ij,ω )z ij,ω,0 (37) where a ij,REC 、a ij,SEC Respectively indicate whether a recloser and a sectionalizer are installed on the branch (i; j); ④Recovery phase After the fault is isolated, rapid service recovery will be achieved based on remote control switches and soft switches, so that the offline area affected by the fault can be restored to its maximum load, and the faulty area can be isolated and repaired. The following constraints are used in the recovery phase: The load breaker switch only acts during the recovery phase, with the following constraints: (1-f ij,ω )(z ij,ω,3 -a ij,REC -b ij,LBS )<=z ij,ω,3 (48) z ij,ω,3 <=(1-f ij,ω )(z ij,ω,3 +a ij,REC +b ij,LBS ) (49) a ij,LBS =b ij,LBS if f ij,ω =1 (50) where a ij,LBS Indicates whether a load circuit breaker is installed on the branch (i; j), b ij,LBS Indicates whether the load circuit breaker on branch (i; j) is activated.

4. The method for joint planning of multiple types of remote-controlled switches and soft switches for a flexible distribution network according to claim 1, characterized in that: The step 3) is specifically as follows: (1) The method to realize the linearization of quadratic terms is as follows: Use variable substitution to linearize the quadratic term, that is, use V i,ω,c replace Equations (10) and (13) are transformed into the following linear constraints by replacing the above variables: (2) The method to achieve absolute term linearization is as follows: An auxiliary variable is introduced to handle the absolute term in the constraint (17), and the linearization process is expressed as: in: is the auxiliary variable defined, which represents the output change of distributed generation at node i between stage c and stage c-1; (3) For equivalent linearization, the following constraints are obtained based on the big M method: Where: M is a sufficiently large number, take 50000000000; P ij,ω,c and Q ij,ω,c Also affected by ij,ω,c Constraints; (4) Perform second-order cone relaxation Using relaxation, equations (7) and (14) can be relaxed to a rotational second-order cone constraint, which is expressed as: (5) Establish evaluation indicators After relaxation, the original optimization problem is transformed into a mixed integer second-order cone model and solved efficiently using the existing solver. In order to evaluate the resilience level of the distribution network, the following evaluation indicators are calculated: Where: R overall is the percentage of expected power supply during the restoration phase of all fault conditions, t c Indicates the duration of phase c.

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