Interconnected Substation Area Regulation Method and System Based on the Collaboration of F-SOP and Phase Converter

Abstract

The present invention discloses an interconnection substation area regulation method and system based on the cooperation of F-SOP and phase changer. The method includes the following steps: S1, collecting the operation parameters of the low-voltage distribution substation area; S2, calculating the three-phase unbalance degree, load rate of the transformer output power and the voltage of each node of each phase, and judging whether it is within the constraint interval; if it meets the standard, the phase changer and F-SOP do not act, and return to S1; if not, start the phase changer; S3, determining the first optimal action state of the phase changer, and secondly judging whether the index meets the standard; if it meets the standard, the phase changer acts according to the first optimal state, otherwise start the F-SOP; S4, constructing an economic optimal objective function for collaborative action; S5, solving the function, determining the second optimal action state of the phase changer and the F-SOP power scheduling instruction, and sending them to the phase changer and F-SOP. The present invention effectively solves the problems of three-phase unbalance and heavy and light load of the substation area transformer, and at the same time solves the problem of three-phase unbalance of the substation area line.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and particularly to an interconnection substation area regulation method and system based on the coordination of F-SOP and a phase converter. Background Art

[0002] Distributed energy has rapidly increased its penetration rate in the distribution network due to its characteristics such as cleanliness and flexibility. However, with the large-scale and high-proportion access of distributed energy and the widespread existence of random loads, the safe and economic operation of the distribution network faces unprecedented challenges. Especially in distribution substations, their network structures are complex, user types are diverse, and single-phase and three-phase loads are randomly mixed and connected, greatly increasing the complexity of operation. The rapid changes of these random loads have exacerbated problems such as three-phase imbalance phenomena, heavy and light loading of transformers, and prominent line losses in distribution substations, posing great potential hazards to the safe and stable operation of the low-voltage distribution network.

[0003] In recent years, the four-leg soft open point (F-SOP) and phase converters have been applied to address the above problems; currently, scholars have conducted some research on the separate applications of F-SOP and phase converters in distribution substations. For example, Chinese patent document CN116054210A discloses a flexible interconnection distribution substation three-phase imbalance optimization regulation method based on F-SOP, which uses F-SOP to achieve internal imbalance management in the substation area and power mutual assistance between different substations, greatly reducing the problems of heavy and light loading operation of substation transformers and three-phase imbalance. However, F-SOP is usually connected to the low-voltage bus side of the substation area, and it can only address the three-phase imbalance and heavy and light loading problems of the substation transformer itself, but cannot alleviate the three-phase imbalance problems on the line side of the substation area and problems such as line overload and increased losses. In the field of phase converters, Chinese patent document CN114977225A discloses a method for managing three-phase imbalance in a distribution substation area, proposing to connect a phase converter on the load side to achieve phase conversion operation of the load, thereby reducing the imbalance problem of the line. However, as a discrete-action device, the phase converter can only completely switch the connected load to the other two phases and cannot achieve continuous adjustment of three-phase imbalance power. Therefore, it can only alleviate the three-phase imbalance problem of the line to a certain extent and cannot completely eliminate the three-phase imbalance problem in the substation area.

[0004] In summary, the F-SOP has the advantages of real-time continuous power adjustment and interconnection between substations, and the phase converter has the advantage of alleviating the three-phase imbalance of the line from the load side. Therefore, the coordinated control of the F-SOP with continuous adjustment ability and the discrete-action phase converter can effectively solve the problems of global three-phase imbalance and heavy / light load in the distribution substation area, improve the economic efficiency and reliability of system operation, and realize the complementary advantages of the two. However, how to establish a dynamic phase converter model and a comprehensive model of three-phase four-wire network loss in the distribution substation area without changing the power flow network architecture, and design a coordinated operation control strategy for the phase converter and the F-SOP are urgent problems to be solved at present. Summary of the Invention

[0005] To overcome the above technical defects, the present application provides an interconnection substation area regulation method and system based on the coordination of the F-SOP and the phase converter.

[0006] The object of the present invention is achieved by at least one of the following technical solutions.

[0007] An interconnection substation area regulation method based on the coordination of the F-SOP and the phase converter, wherein the phase converter includes three parallel arms each containing upper and lower power electronic switch devices, the three arms are respectively connected to the three phases of the transmission line, and the output end after parallel connection is connected to the phase conversion user; multiple low-voltage distribution substations are interconnected through a multi-port F-SOP, and the F-SOP includes multiple three-phase four-arm converters in parallel with a common DC side. The output end of each three-phase four-arm converter is used as a port of the F-SOP, and the a, b, and c phase arms of each converter are respectively connected to the three busbars of a low-voltage distribution substation.

[0008] The F-SOP controls the three-phase output power of each low-voltage distribution substation to achieve interconnection substation area regulation, including the following steps:

[0009] Step S1: Collect the operation-related parameters of each low-voltage distribution substation interconnected through the multi-port F-SOP for the first time, where the operation-related parameters of the low-voltage distribution substation include the normal operation data of the low-voltage distribution substation and the equipment parameters of the transformer, F-SOP, and phase converter.

[0010] Step S2: According to the operation-related parameters of the low-voltage distribution substation collected for the first time, calculate the three-phase imbalance degree of the output power of the transformer in each low-voltage distribution substation, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation for the first time, and determine whether the three-phase imbalance degree of the output power of the transformer in each low-voltage distribution substation, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation are simultaneously within the constraint interval.

[0011] If so, the phase converter and the F-SOP do not act, and return to step S1 to continue real-time monitoring.

[0012] If not, start the phase converter and go to step S3;

[0013] Step S3: According to the pre - constructed large - model of losses in the low - voltage distribution sub - area with the phase converter connected, construct the economic - optimal objective function of the low - voltage distribution sub - area with only the phase converter connected, and determine the first optimal action state of the phase converter; the large - model of losses in the low - voltage distribution sub - area with the phase converter connected includes the transformer loss characteristic model, the phase - converter loss characteristic model, and the three - phase four - wire independent power - flow network loss characteristic model;

[0014] Make the phase converter act according to the first optimal action state;

[0015] Second - time collect the operation - related parameters of each low - voltage distribution sub - area;

[0016] According to the operation - related parameters of each low - voltage distribution sub - area collected for the second time, second - time calculate the three - phase unbalance degree of the output power of the transformer in each low - voltage distribution sub - area, the load rate of the transformer, and the voltage of each phase at each node in each low - voltage distribution sub - area, and second - time judge whether the three - phase unbalance degree of the output power of the transformer, the load rate of the transformer, and the voltage of each phase at each node in each low - voltage distribution sub - area are simultaneously within the constraint intervals;

[0017] If so, F - SOP does not act, and return to step S1 to continue real - time monitoring;

[0018] If not, start F - SOP and go to step S4;

[0019] Step S4: Based on the large - model of losses in the low - voltage distribution sub - area with the phase converter connected and the pre - constructed F - SOP loss characteristic model, construct the economic - optimal objective function of the low - voltage interconnected sub - area regulation strategy with F - SOP and the phase converter acting in coordination;

[0020] Step S5: Solve the economic - optimal objective function of the low - voltage interconnected sub - area regulation strategy with F - SOP and the phase converter acting in coordination, determine the second optimal action state of the phase converter and the optimal power - scheduling instruction of F - SOP, and send them to the phase converter and F - SOP respectively.

[0021] Furthermore, the load rate of the th transformer phase is obtained by dividing the apparent power sent out by the th transformer phase by the capacity of the th transformer phase, specifically as follows:

[0022]

[0023] Among them, represents the load rate of the th transformer phase, , respectively represent Three-phase; is the th transformer apparent power transmitted by the phase; is the th transformer capacity of the phase;

[0024] The unbalance degree of the three-phase output power of the th transformer is obtained by subtracting the average value of the three-phase output power of the th transformer from the maximum value of the three-phase output power of the th transformer and then dividing by the average value of the three-phase output power of the th transformer, as follows: subtracting the average value of the three-phase output power of the th transformer from the maximum value of the three-phase output power of the th transformer and then dividing by the average value of the three-phase output power of the th transformer, as follows: th transformer th transformer, and the specific is as follows:

[0025]

[0026] Among them, represents the unbalance degree of the three-phase output power of the th transformer, is the maximum value of the three-phase output power of the th transformer, is the average value of the three-phase output power of the th transformer.

[0027] Furthermore, the constraint condition of the load rate of the transformer is that the load rate of each phase of each transformer does not exceed the economic operation range of the transformer specified in the national standard (Economic Operation of Power Transformers), as follows:

[0028]

[0029] Among them, represents the load rate of the th transformer phase, , and respectively represent the upper and lower limits of the economic operation range;

[0030] The constraint condition of the unbalance degree of the three-phase output power of the transformer is that the unbalance degree of the output power of each transformer does not exceed the unbalance degree threshold specified in the Distribution Network Operation and Maintenance Regulations, as follows:

[0031]

[0032] Among them, is the unbalance degree threshold of the load three-phase; represents the unbalance degree of the three phases of the th transformer;

[0033] The constraint conditions for the voltage of each phase of each node are that the voltage of each phase of each node in each low-voltage distribution substation area does not exceed the upper and lower limits of the node voltage specified for the safe operation of the low-voltage distribution substation area, specifically as follows:

[0034]

[0035] Among them, is the set composed of all nodes in the low-voltage distribution substation area; is the th node of the phase, respectively represent and are the upper and lower limits of the amplitude of the node voltage of the th node of the

[0036] Furthermore, in the transformer loss characteristic model, calculating the transformer loss includes the no-load loss of the comprehensive power of each phase of each transformer, the rated load loss of the comprehensive power, and the zero-sequence loss generated when the three-phase loads of each transformer are unbalanced, specifically as follows:

[0037]

[0038] Among them, is the transformer loss, is the no-load loss of the comprehensive power of the th transformer of the phase, is the rated load loss of the comprehensive power of the th transformer of the is the zero-sequence loss generated when the three-phase loads of the th transformer are unbalanced; represents the th transformer of the

[0039] In the commutation device loss characteristic model, calculating the commutation device loss is obtained by multiplying the commutation device resistance coefficient by the sum of the apparent power of the a-phase load of each group of commutation devices connected to the node, specifically as follows:

[0040]

[0041] Among them, is the commutation device loss, is the set commutation device resistance coefficient, represents the Phase load apparent power at the connection node of the phase converter Phase load apparent power;

[0042] In the three-phase four-wire independent power flow network loss characteristic model, the total line loss of the three-phase four-wire network is calculated by multiplying the current of each phase of each branch by the resistance of the corresponding phase of the corresponding branch, as follows:

[0043]

[0044] Wherein, Is the total line loss of the three-phase four-wire network, Is The current of phase Of branch , The branch is the line between the th node and the th node in the low-voltage distribution substation area; Is The resistance of phase Of branch Is the set composed of all branches in the low-voltage distribution substation area.

[0045] Furthermore, the economic optimal objective function of the low-voltage distribution substation area with only the phase converter connected is the minimum value of the sum of the transformer loss cost, the comprehensive operation cost of the phase converter, and the three-phase four-wire network line loss cost, as follows:

[0046]

[0047] Wherein, Is the comprehensive operation cost of the low-voltage distribution substation area with only the phase converter connected;

[0048] According to the transformer loss characteristic model, the transformer loss cost Is obtained by multiplying the grid electricity price by the transformer loss, as follows:

[0049]

[0050] Wherein, Is the grid electricity price; Is the transformer loss;

[0051] The comprehensive operation cost of the phase converter Includes the phase converter loss cost and the phase converter operation cost, as follows:

[0052]

[0053] According to the phase converter loss characteristic model, the phase converter loss cost Is obtained by multiplying the grid electricity price by the phase converter loss, as follows:

[0054]

[0055] Among them, is the commutation loss;

[0056] Commutation action cost is obtained by multiplying the commutation action cost coefficient by the sum of all commutation action times, specifically as follows:

[0057]

[0058] Among them, is the commutation action cost coefficient, is the action status scalar indicating the th group of commutation;

[0059] Based on the three-phase four-wire independent power flow network loss characteristic model, the three-phase four-wire network line loss cost is obtained by multiplying the grid electricity price by the total three-phase four-wire network line loss, specifically as follows:

[0060]

[0061] Among them, is the total three-phase four-wire network line loss.

[0062] Furthermore, the constraint condition of the transformer loss characteristic model is that the apparent power output of each phase of each transformer cannot exceed the capacity of the corresponding phase of the corresponding transformer, and the total apparent power output of the three phases of each transformer cannot exceed the three-phase total capacity of the corresponding transformer, specifically as follows:

[0063]

[0064] Among them, is the apparent power transmitted by the th transformer phase, , is the active power output by the th transformer phase, is the reactive power output by the th transformer phase, is the capacity of the th transformer phase, is the total transmitted apparent power of the th transformer, is the three-phase total capacity of the th transformer;

[0065] The constraint conditions of the commutation loss characteristic model are that the sum of the active power and reactive power output by the three-phase bridge arms of the th group of commutation devices should be equal to 0 respectively. The active power and reactive power output by the th group of commutation devices phase bridge arm are respectively equal to the opposite of the state scalar and the product of the active power and reactive power of the phase load at the node where the th group of commutation devices is connected. The product of the active power output by the th group of commutation devices and phase bridge arms is 0. The product of the reactive power output by the th group of commutation devices and phase bridge arms is also 0, specifically as follows:

[0066]

[0067] Among them, is the active power injected by the th group of commutation devices phase bridge arm into a certain node phase. is the reactive power injected by the th group of commutation devices phase bridge arm into a certain node phase; and are the active power and reactive power of the th group of commutation devices connected to the node phase load. represents the action state scalar of the th group of commutation devices;

[0068] The operating safety constraint conditions for each phase of the three-phase four-wire loss characteristic model are that the voltage amplitude of each phase at each node in the low-voltage distribution substation area does not exceed the upper and lower limits of the node voltage specified for the safe operation of the low-voltage distribution substation area; the current amplitude of each phase in each branch of the low-voltage distribution substation area does not exceed the upper limit of the branch current specified for the safe operation of the low-voltage distribution substation area; the amplitude of the active power injected into each phase at each node in the low-voltage distribution substation area does not exceed the upper and lower limits of the node injection power, specifically as follows:

[0069]

[0070] Among them, is the set composed of all nodes in the low-voltage distribution substation area; is the node voltage of the th node phase in the low-voltage distribution substation area. , respectively represent three phases and the neutral phase; and are the upper and lower limits of the node voltage amplitude of the th node in the low-voltage distribution substation area for the th phase respectively. is the current of the th phase of the branch. The branch is the line between the th node and the th node in the low-voltage distribution substation area. is the upper limit of the amplitude of is the set composed of all branches in the low-voltage distribution substation area; is the power of the th node in the low-voltage distribution substation area for the th phase. and are respectively the upper and lower limits of the amplitude;

[0071] The power flow constraint condition of the three-phase four-wire loss characteristic model is that each phase of each low-voltage distribution substation area needs to satisfy the optimal power flow constraint after second-order cone relaxation respectively (Gao Hongjun, Liu Junyong, Shen Xiaodong, Xu Rui. Research on Optimal Power Flow in Active Distribution Network and Its Application Examples [J]. Proceedings of the CSEE, 2017, 37(6): 1634-1645. DOI: 10.13334 / j.0258-8013.pcsee.152839), which is specifically as follows:

[0072] Let , , there is:

[0073]

[0074] In the formula, represents the set composed of all upstream nodes that inject power into the th node through the power grid, and represents the set composed of all downstream nodes that the power flowing out from the th node reaches through the power grid; and respectively represent the active power and reactive power injected into the th node for the th phase; and respectively represent the active power and reactive power of the th phase of the branch; represents the branch​ The resistance of the phase indicates branch The reactance of the phase.

[0075] Furthermore, in the F-SOP loss characteristic model, the comprehensive operating cost of F-SOP is calculated, including the loss cost and operation and maintenance cost of F-SOP, as follows:

[0076]

[0077] The loss cost of F-SOP is obtained by multiplying the grid electricity price by the transmission power loss of F-SOP, as follows:

[0078]

[0079] F-SOP power transmission loss is obtained by subtracting the product of the transmission efficiency and the transmission power from the transmission power of each phase arm of each port, as follows:

[0080]

[0081] In the formula, is the power transmission loss of F-SOP, indicates the th port transmission power of the phase arm of F-SOP; indicates the th port power transmission efficiency of the phase arm of F-SOP;

[0082] The operation and maintenance cost of F-SOP is obtained by multiplying the operation and maintenance cost coefficient by the total transmission power of each phase arm of each port of F-SOP, as follows:

[0083]

[0084] In the formula, is the operation and maintenance cost coefficient, indicates the th port apparent power transmitted by the phase arm of F-SOP, ;

[0085] Based on the F-SOP comprehensive operating cost and the large model of the high loss of the converter-connected distribution area, the economic optimal objective function of the coordinated operation strategy of F-SOP and the converter is the minimum value of the sum of the transformer loss cost, the converter comprehensive operating cost, the three-phase four-wire network line loss cost, and the F-SOP comprehensive operating cost, as follows:

[0086]

[0087] Wherein, is the comprehensive operation cost of the low-voltage distribution substation area under the collaborative strategy.

[0088] Furthermore, the power transmission conservation constraint condition of the F-SOP loss characteristic model is that the sum of the active power transmitted by each bridge arm of each port of the F-SOP is 0, specifically as follows:

[0089]

[0090] Wherein, represents the active power flowing out of the th port phase bridge arm of the F-SOP;

[0091] The capacity constraint condition of the F-SOP loss characteristic model is that the apparent power transmitted by each bridge arm of each port of the F-SOP should be less than or equal to the capacity of the corresponding port corresponding bridge arm; the total apparent power transmitted by the F-SOP should also be less than or equal to the overall capacity of the F-SOP:

[0092]

[0093] Wherein, represents the apparent power flowing through the th port phase bridge arm of the F-SOP; represents the capacity of the th port phase bridge arm of the F-SOP, is the total transmission power of the F-SOP, is the overall capacity of the F-SOP.

[0094] Furthermore, in step S5, after solving the economic optimal objective function of the low-voltage interconnected substation area regulation strategy for the coordinated action of the F-SOP and the phase converter, the optimal power scheduling instruction of the F-SOP is obtained, including the active power and reactive power transmitted by each phase bridge arm of each port of the F-SOP.

[0095] The interconnected substation area regulation system based on the coordination of the F-SOP and the phase converter includes the following modules:

[0096] Data acquisition module: Firstly, collect the operation-related parameters of each low-voltage distribution substation area interconnected through the multi-port F-SOP. Among them, the operation-related parameters of the low-voltage distribution substation area include the normal operation data of the low-voltage distribution substation area and the equipment parameters of the transformer, F-SOP, and phase converter;

[0097] The first calculation and judgment module: According to the operation-related parameters of the low-voltage distribution area collected once, calculate the three-phase imbalance degree of the output power of the transformer in each low-voltage distribution area, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution area once, and judge once whether the three-phase imbalance degree of the output power of the transformer in each low-voltage distribution area, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution area are simultaneously within the constraint interval;

[0098] If so, the phase changer and F-SOP do not act, and return to the start data acquisition module to continue real-time monitoring;

[0099] If not, start the phase changer and start the second calculation and judgment module;

[0100] The second calculation and judgment module: According to the pre-constructed large model of the loss of the phase changer-connected distribution area, construct the economic optimal objective function of the low-voltage distribution area with only the phase changer connected, and determine the first optimal action state of the phase changer; the large model of the loss of the phase changer-connected distribution area includes the transformer loss characteristic model, the phase changer loss characteristic model, and the three-phase four-wire independent power flow network loss characteristic model;

[0101] Make the phase changer act according to the first optimal action state;

[0102] Collect the operation-related parameters of each low-voltage distribution area for the second time;

[0103] According to the operation-related parameters of each low-voltage distribution area collected for the second time, calculate the three-phase imbalance degree of the output power of the transformer in each low-voltage distribution area, the load rate of the transformer, and the voltage of each phase of each node for the second time, and judge for the second time whether the three-phase imbalance degree of the output power of the transformer in each low-voltage distribution area, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution area are simultaneously within the constraint interval;

[0104] If so, F-SOP does not act, and return to the start data acquisition module to continue real-time monitoring;

[0105] If not, start F-SOP and start the instruction acquisition module;

[0106] The instruction acquisition module: Based on the large model of the loss of the phase changer-connected distribution area and the pre-constructed F-SOP loss characteristic model, construct the economic optimal objective function of the low-voltage interconnected distribution area regulation strategy with the coordinated action of F-SOP and the phase changer; solve the economic optimal objective function of the low-voltage interconnected distribution area regulation strategy with the coordinated action of F-SOP and the phase changer, determine the second optimal action state of the phase changer and the optimal power scheduling instruction of F-SOP, and send them to the phase changer and F-SOP respectively.

[0107] Compared with the prior art, the present invention has the following beneficial effects:

[0108] The interconnected substation area regulation method based on the cooperation of F-SOP and the phase converter proposed by the present invention can effectively solve the problems of three-phase imbalance and heavy / light load of the substation transformer while effectively solving the three-phase imbalance problem of the substation lines. Compared with the existing technical solutions, the total loss of the method proposed by the present invention is effectively reduced, the operation safety of the low-voltage distribution substation area is improved, the service life of the equipment is extended, and the long-term operation economy of the low-voltage distribution substation area is also improved. Description of the Drawings

[0109] Figure 1 It is a structural topology diagram of the four-leg intelligent soft switch in the embodiment of the present invention.

[0110] Figure 2 It is a topology diagram of the phase converter in the embodiment of the present invention.

[0111] Figure 3 It is a flow diagram of the interconnected substation area regulation method based on the cooperation of F-SOP and the phase converter in the embodiment of the present invention.

[0112] Figure 4 It is a diagram of the flexible interconnected substation area based on the two-port F-SOP and four groups of phase converters in the embodiment of the present invention.

[0113] Figure 5 It is a node architecture diagram of two low-voltage distribution substation areas in the embodiment of the present invention.

[0114] Figure 6a 、 Figure 6b 、 Figure 6c and Figure 6d It is a comparison diagram of the transformer load rates under four schemes in the embodiment of the present invention.

[0115] Figure 7a 、 Figure 7b 、 Figure 7c and Figure 7d It is a comparison diagram of the three-phase imbalance degree of the transformer output power in the embodiment of the present invention.

[0116] Figure 8a 、 Figure 8b 、 Figure 8c and Figure 8d It is a comparison diagram of the total loss and loss composition of the low-voltage distribution substation area under four schemes in the embodiment of the present invention.

[0117] Figure 9 It is a curve diagram of the comprehensive operation cost of the low-voltage distribution substation area in the embodiment of the present invention. Detailed Embodiments

[0118] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0119] In order to enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the protection scope of this application.

[0120] It should be noted that the terms "first", "second", etc. in the description and claims of this application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances for the embodiments of this application described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0121] In one embodiment, an interconnected substation area regulation method based on the cooperation of F-SOP and a phase converter. The phase converter includes three parallel arms with upper and lower power electronic switching devices. The three arms are respectively connected to the three phases of the transmission line, and the output end after parallel connection is connected to the phase-changing user. Multiple low-voltage distribution substations are interconnected through a multi-port F-SOP. The F-SOP includes multiple three-phase four-arm converters with a common DC side in parallel. The output end of each three-phase four-arm converter is used as a port of the F-SOP. The a, b, and c phase arms of each converter are respectively connected to the three busbars of a low-voltage distribution substation; In one embodiment, the structural topologies of the four-arm intelligent soft switch (Four-leg soft open point, F-SOP) and the phase converter are respectively as Figure 1 and Figure 2 shown.

[0122] The F-SOP controls the three-phase output power of each low-voltage distribution substation area to achieve interconnected substation area regulation, as Figure 3 shown, including the following steps:

[0123] Step S1: Collect the operation-related parameters of each low-voltage distribution substation area interconnected through the multi-port F-SOP at one time. Among them, the operation-related parameters of the low-voltage distribution substation area include the normal operation data of the low-voltage distribution substation area and the equipment parameters of the transformer, F-SOP, and phase converter;

[0124] In one embodiment, taking the two-port F-SOP and phase converter flexible interconnected substation area as an example, the loss characteristics of the F-SOP, transformer, and phase converter are analyzed respectively. The overall structure of the two-port F-SOP flexible interconnected substation area is as Figure 4 shown. The structure is as follows: The phase converter is formed by paralleling three arms each containing upper and lower power electronic switching devices. The three arms are respectively connected to the three phases of the transmission line, and the output end after parallel connection is connected to the phase-changing user. The substation area is interconnected through the two-port F-SOP. The F-SOP is formed by paralleling multiple three-phase four-arm converters with a common DC side. The output end of each three-phase four-arm converter serves as a port of the F-SOP. The a, b, and c phase arms of each converter are respectively connected to the three busbars of a low-voltage distribution substation area, and the F-SOP controls the three-phase output power of each low-voltage distribution substation area. Figure 4 In , both represent the 10 kV low-voltage distribution substation area, , respectively represent the distribution transformers with a turns ratio of 10 / 0.4 kV, is the th transformer phase output active power, is the th transformer phase output reactive power, , and the direction of flowing into the busbar is taken as the positive direction; The two ports of the F-SOP are respectively connected to the busbars of the two low-voltage distribution substation areas. and respectively represent the active power and reactive power flowing out of the th port phase arm of the F-SOP, , and the direction of flowing into the busbar is also taken as the positive direction; , respectively represent the active load and reactive load on the th substation area phase busbar, , and the direction of flowing out of the busbar is taken as the positive direction.

[0125] Select the 22-node three-phase low-voltage distribution substation area and the 15-node three-phase low-voltage distribution substation area as the first and second low-voltage distribution substation areas respectively to form an interconnected substation area. The specific three-phase node architecture diagram of the low-voltage distribution substation area and the access positions of the F-SOP and phase converter are as Figure 5 shown. For the same low-voltage distribution substation area, the upper, middle, and lower three layers are respectively the a, b, and c phases. The transformer nodes of the two low-voltage distribution substation areas (i.e., Figure 5 ​The 22-node and 37-node in ) are respectively connected to the two ports of the two-port F-SOP. The 12-node and 20-node of the first low-voltage distribution substation area, and the 12-node and 14-node of the second low-voltage distribution substation area are respectively connected to the phase shifter in the a-phase.

[0126] It is necessary to collect the operation-related parameters of the low-voltage distribution area at one time. The operation-related parameters of the low-voltage distribution substation area include the normal operation data of the low-voltage distribution substation area and the equipment parameters of the transformer, F-SOP, and phase shifter. The normal operation data of the low-voltage distribution substation area includes the impedance parameters of the three-phase and zero-sequence branches of the low-voltage distribution substation area, the three-phase load power of each node, the three-phase voltage, and the zero-sequence voltage. The transformer parameters include the capacity of each phase of the transformer, the zero-sequence impedance, the no-load loss of the comprehensive power, the rated load loss of the comprehensive power, the real-time three-phase output power of the secondary side, the three-phase voltage, and the three-phase current. The F-SOP parameters include the capacity, access position, and efficiency parameters of the F-SOP. The phase shifter equipment parameters include the access position and resistance coefficient of the phase shifter.

[0127] Step S2: According to the operation-related parameters of the low-voltage distribution substation area collected at one time, calculate the three-phase imbalance degree of the output power of the transformer in each low-voltage distribution substation area, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation area at one time;

[0128] The phase load rate of the transformer is obtained by dividing the apparent power sent out by the phase of the transformer by the capacity of the phase of the transformer, specifically as follows: Among them,

[0129]

[0130] where represents the load rate of the phase of the transformer, , respectively represent the three phases; is the apparent power transmitted by the phase of the transformer; is the capacity of the phase of the transformer;

[0131] The three-phase imbalance degree of the output power of the transformer is obtained by subtracting the average value of the three-phase output power of the transformer from the maximum value of the three-phase output power of the transformer and then dividing by the The average value of the three-phase output power of the transformer is obtained as follows:

[0132]

[0133] Among them, represents the three-phase output power unbalance degree of the th transformer, is the maximum value among the three-phase output powers of the th transformer, is the average value of the three-phase output powers of the th transformer.

[0134] The constraint condition of the load rate of the transformer is that the load rate of each phase of each transformer does not exceed the economic operation range of the transformer specified in the national standard (Economic Operation of Power Transformers), as follows:

[0135]

[0136] Among them, represents the load rate of the th transformer phase, , and respectively represent the upper and lower limits of the economic operation range;

[0137] The constraint condition of the three-phase output power unbalance degree of the transformer is that the unbalance degree of the output power of each transformer does not exceed the unbalance degree threshold specified in the Distribution Network Operation and Maintenance Regulations, as follows:

[0138]

[0139] Among them, is the load three-phase unbalance degree threshold; represents the three-phase unbalance degree of the th transformer;

[0140] The constraint condition of the voltage of each phase of each node is that the voltage of each phase of each node in each low-voltage distribution area does not exceed the upper and lower limits of the node voltage specified for the safe operation of the low-voltage distribution area, as follows:

[0141]

[0142] Among them, is the set composed of all nodes in the low-voltage distribution area; is the node voltage of the th node phase in the low-voltage distribution area, , respectively represent three phases and zero phase; and are respectively the upper and lower limits of the node voltage amplitude of the th node in each phase of the low-voltage distribution transformer area.

[0143] First, it is judged whether the three-phase imbalance degree of the output power, the load rate of the transformer, and the voltage of each phase of each node in the low-voltage distribution transformer area are simultaneously within the constraint intervals;

[0144] If it is satisfied, it means that the overall operation condition of the current area transformer is good and there is no need to adjust the operation instruction. At this time, the phase converter and F-SOP do not operate, and return to step S1 to continue real-time monitoring;

[0145] If it does not satisfy the above constraint conditions simultaneously, that is to say, at least one of the load rate of the area transformer, the three-phase imbalance degree of the output power of the area transformer, and the voltage of each phase of each node obtained does not satisfy the constraint conditions. At this time, it means that there is a problem with the operation of the area and adjustment is needed. Then, start the phase converter and enter step S3;

[0146] Step S3: According to the pre-constructed large model of the loss of the phase converter connected to the transformer area, construct the economic optimal objective function of the low-voltage distribution transformer area with only the phase converter connected, and determine the first optimal action state of the phase converter; the large model of the loss of the phase converter connected to the transformer area includes the transformer loss characteristic model, the phase converter loss characteristic model, and the three-phase four-wire independent power flow network loss characteristic model;

[0147] In the transformer loss characteristic model, calculating the transformer loss includes the comprehensive power no-load loss, the comprehensive power rated load loss of each phase of each transformer, and the zero-sequence loss generated when the three-phase load of each transformer is unbalanced. Specifically as follows:

[0148]

[0149] Among them, is the transformer loss, is the comprehensive power no-load loss of the th transformer in the phase, and is the comprehensive power rated load loss of the th transformer in the phase; is the zero-sequence loss generated when the three-phase load of the th transformer is unbalanced;

[0150] No-load loss refers to the loss caused by the exciting current and core loss in the iron core when the transformer is operating under no-load. It is related to factors such as the iron core material, structure, and supply voltage of the transformer, and is generally considered a relatively fixed loss. Load loss is the heat loss generated by the winding resistance when the load current passes through the transformer winding. It is proportional to the square of the load current and is also related to factors such as the material, structure, and temperature of the transformer winding. The zero-sequence loss of the transformer is the additional loss generated by the zero-sequence current caused by unbalanced three-phase currents in the winding and the iron core. When the three-phase load is asymmetric, the zero-sequence current flows through the neutral point or closed magnetic circuit, resulting in winding resistance heating and iron core eddy current loss. Its magnitude is directly related to the three-phase unbalance degree. The higher the unbalance degree, the more significant the zero-sequence loss. The transformer loss characteristic model is based on the generation mechanism of these losses and describes the relationship between transformer losses and various operating parameters through mathematical methods.

[0151] In the commutation device loss characteristic model, the commutation device loss is calculated by multiplying the commutation device resistance coefficient by the sum of the apparent powers of the a-phase loads at the nodes where each group of commutation devices is connected, specifically as follows:

[0152]

[0153] Where, is the commutation device loss, is the set commutation device resistance coefficient, represents the th group of commutation devices connected to the node phase apparent power of the load;

[0154] The losses of commutation devices (such as grid-connected inverters, rectifiers) are mainly generated by the following mechanisms: Switching losses: Energy losses caused by the overlap of voltage and current during the turn-on and turn-off processes of semiconductor devices (such as IGBTs, MOSFETs). The higher the switching frequency, the greater the switching losses. Conduction losses: Power losses generated by the conduction resistance (such as the saturation voltage drop of IGBTs or the on-resistance of MOSFETs) when the device is conducting, which is proportional to the square of the current. Drive losses: The energy required for the control circuit to drive semiconductor devices, which is related to the drive circuit design and switching frequency. Stray losses: Additional losses caused by parasitic parameters (such as stray inductance, capacitance), electromagnetic radiation, or cooling system power consumption. The commutation device model correlates these losses with the operating parameters of the commutation device (such as current, voltage, switching frequency) through mathematical formulas or simulation methods to quantify the loss distribution and efficiency characteristics.

[0155] In the three-phase four-wire independent power flow network loss characteristic model, the total line loss of the three-phase four-wire network is calculated by multiplying the current of each phase of each branch by the resistance of the corresponding phase of the corresponding branch and then summing them up, specifically as follows:

[0156]

[0157] Among them, is the three-phase four-wire network bus loss, is the current of branch phase, , The branch is the line between the th node and the th node in the low-voltage distribution substation area; is the resistance of branch phase, is the set composed of all branches in the low-voltage distribution substation area.

[0158] The zero-sequence current of the neutral line is calculated as follows:

[0159]

[0160] In the formula, and are the zero-sequence voltages of the th node and the th node in the low-voltage distribution substation area respectively;

[0161] The formula for the zero-sequence voltage of the node is as follows:

[0162]

[0163] In the formula, , and are the voltages of phases a, b, and c of the th node in the low-voltage distribution substation area respectively;

[0164] The low-voltage distribution substation area with the three-phase four-wire structure characteristics includes three phase lines (phases a, b, and c) and a neutral line (N line), allowing single-phase, two-phase, or three-phase loads to be connected, resulting in unbalanced three-phase currents. The existence of the neutral line makes the neutral point may shift (the voltage is not zero), and the neutral line current further increases the line loss. Repeated grounding (the neutral point is connected to the ground through multiple grounding points) will introduce additional impedance and affect the power flow distribution.

[0165] The loss mechanism is as follows: Phase line loss: The product of the square of each phase current and the line resistance, which is directly related to the load distribution. Neutral line loss: The product of the square of the neutral line current and the neutral line resistance, which only occurs when the three phases are unbalanced. Earth wire loss: If the earth is considered as a conductive medium (such as a long-distance line), the loss caused by the earth impedance needs to be taken into account.

[0166] Characteristics of power flow calculation: It is necessary to simultaneously handle the asymmetry of three-phase voltages and currents, as well as the coupling effect between the neutral line and the ground. The traditional three-phase three-wire system model (ignoring the neutral line) cannot accurately reflect the unbalanced losses and needs to be corrected through a special model.

[0167] The economic optimal objective function of the low-voltage distribution substation area with only phase converters connected is the minimum value of the sum of the transformer loss cost, the comprehensive operation cost of the phase converters, and the line loss cost of the three-phase four-wire network, which is specifically as follows:

[0168]

[0169] Among them, is the comprehensive operation cost of the low-voltage distribution substation area with only phase converters connected;

[0170] According to the transformer loss characteristic model, the transformer loss cost is obtained by multiplying the grid electricity price by the transformer loss, which is specifically as follows:

[0171]

[0172] Among them, is the grid electricity price; is the transformer loss;

[0173] The comprehensive operation cost of the phase converters includes the phase converter loss cost and the phase converter operation cost, which is specifically as follows:

[0174]

[0175] According to the phase converter loss characteristic model, the phase converter loss cost is obtained by multiplying the grid electricity price by the phase converter loss, which is specifically as follows:

[0176]

[0177] Among them, is the phase converter loss;

[0178] The phase converter operation cost is obtained by multiplying the phase converter operation cost coefficient by the sum of all phase converter operation times, which is specifically as follows:

[0179]

[0180] Among them, is the phase converter operation cost coefficient, is the action status scalar representing the th group of phase converters;

[0181] Based on the three-phase four-wire independent power flow network loss characteristic model, the line loss cost of the three-phase four-wire network is obtained by multiplying the grid electricity price by the total line loss of the three-phase four-wire network, specifically as follows:

[0182]

[0183] where is the total line loss of the three-phase four-wire network.

[0184] The constraint condition of the transformer loss characteristic model is that the apparent power output of each phase of each transformer cannot exceed the capacity of the corresponding phase of the corresponding transformer, and the total apparent power output of the three phases of each transformer cannot exceed the three-phase total capacity of the corresponding transformer, specifically as follows:

[0185]

[0186] where is the apparent power transmitted by the th transformer phase, , is the active power output by the th transformer phase, is the reactive power output by the th transformer phase, is the capacity of the th transformer phase, is the total transmitted apparent power of the th transformer, is the three-phase total capacity of the th transformer;

[0187] The constraint condition of the phase converter loss characteristic model is that the sum of the active power and reactive power output by the three-phase bridge arms of the th group of phase converters should be equal to 0 respectively, and the active power and reactive power output by the th group of phase converters phase bridge arm are respectively equal to the opposite of the state scalar multiplied by the active power and reactive power of the th group of phase converter access node phase load, and the product of the active powers output by the th group of phase converters , phase bridge arms is 0, and the product of the reactive powers output by the th group of phase converters , phase bridge arms is also 0, specifically as follows:

[0188]

[0189] Among them, is the phase converter phase bridge arm's active power injected into a certain node ; is the phase converter phase bridge arm's reactive power injected into a certain node ; and are the active power and reactive power of the phase load connected to the node of the phase converter, represents the action status scalar of the phase converter;

[0190] The operating safety constraint conditions for each phase of the three-phase four-wire loss characteristic model are that the voltage amplitude of each phase at each node in the low-voltage distribution substation area does not exceed the upper and lower limits of the node voltage specified for the safe operation of the low-voltage distribution substation area; the current amplitude of each phase in each branch of the low-voltage distribution substation area does not exceed the upper limit of the branch current specified for the safe operation of the low-voltage distribution substation area; the amplitude of the active power injected into each phase at each node in the low-voltage distribution substation area does not exceed the upper and lower limits of the node injection power. Specifically, as follows:

[0191]

[0192] Among them, is the set composed of all nodes in the low-voltage distribution substation area; is the th node phase voltage of the , respectively represent three phases and the neutral phase; and are respectively the upper and lower limits of the amplitude of the th node phase voltage of the branch phase current, the branch is the line between the th node and the th node in the low-voltage distribution substation area, is the upper limit of the amplitude of is the set composed of all branches in the low-voltage distribution substation area; is the th node phase power of the and are respectively the upper and lower limits of the amplitude;

[0193] The power flow constraint condition of the three-phase four-wire loss characteristic model is that each phase of each low-voltage distribution substation area needs to separately meet the optimal power flow constraint after second-order cone relaxation (Gao Hongjun, Liu Junyong, Shen Xiaodong, Xu Rui. Research on Optimal Power Flow in Active Distribution Network and Its Application Examples [J]. Proceedings of the Chinese Society for Electrical Engineering, 2017, 37(6): 1634-1645. DOI: 10.13334 / j.0258-8013.pcsee.152839), specifically as follows:

[0194] Let , , there are:

[0195]

[0196] In the formula, represents all the upstream nodes injecting power into the th node through the power grid forming a set, represents all the downstream nodes where the power flowing out of the th node reaches through the power grid forming a set; and respectively represent the active power and reactive power injected into the th node phase; and respectively represent the active power and reactive power of the branch phase; represents the resistance of the branch phase, represents the reactance of the

[0197] Make the commutator act according to the first optimal action state;

[0198] Secondarily collect the operation-related parameters of each low-voltage distribution substation area;

[0199] According to the operation-related parameters of each low-voltage distribution substation area collected secondarily, secondarily calculate the three-phase unbalance degree of the output power of each transformer, the load rate of the transformer, and the voltage of each phase of each node, and secondarily judge whether the three-phase unbalance degree of the output power, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation area are simultaneously within the constraint interval;

[0200] If so, the F-SOP does not operate, and return to step S1 to continue real-time monitoring;

[0201] If not, start the F-SOP and enter step S4;

[0202] The principle of the phase converter is to achieve a more balanced three-phase load by switching the load of one phase to another phase as a whole. At the same time, it does not change the original power flow network structure of the low-voltage distribution substation area and has the advantage of being convenient for installation and withdrawal. The phase converter used in the present invention can switch the phase load of the corresponding node to phase or phase as a whole to achieve the foregoing purpose. The three ports of the phase converter are respectively connected to the three phases of the same node;

[0203] The specific working mode of the phase converter is as follows:

[0204] Set a 0-1 state scalar , when = 1, the phase converter operates, and there are:

[0205]

[0206] Or:

[0207]

[0208] When = 0, the phase converter does not operate, and there are:

[0209]

[0210] In the formula, , , are the active powers injected by the three-phase bridge arms of the th group of phase converters into the three phases of a certain node; , , are the reactive powers injected by the three-phase bridge arms of the th group of phase converters into the three phases of a certain node; and are the active power and reactive power of the th group of phase converters connected to the node, represents the active power and reactive power of the th group of phase converters; represents the action status scalar of the

[0211] Step S4: Based on the loss large model of the substation area accessed by the phase converter and the pre-constructed F-SOP loss characteristic model, construct an economic optimal objective function for the low-voltage interconnected substation area regulation strategy of the coordinated action of the F-SOP and the phase converter;

[0212] In the F-SOP loss characteristic model, the comprehensive operating cost of the F-SOP is calculated, including the loss cost and the operation and maintenance cost of the F-SOP, as follows:

[0213]

[0214] Loss cost of F-SOP It is obtained by multiplying the grid electricity price by the transmission power loss of the F-SOP, as follows:

[0215]

[0216] F-SOP power transmission loss It is obtained by subtracting the product of the transmission efficiency and the transmission power from the transmission power of each phase bridge arm of each port, as follows:

[0217]

[0218] In the formula, is the power transmission loss of the F-SOP, represents the transmission power of the th port phase bridge arm of the F-SOP; represents the power transmission efficiency of the th port phase bridge arm of the F-SOP;

[0219] Operation and maintenance cost of F-SOP It is obtained by multiplying the operation and maintenance cost coefficient by the total transmission power of each phase of each port of the F-SOP, as follows:

[0220]

[0221] In the formula, is the operation and maintenance cost coefficient, represents the apparent power transmitted by the th port phase bridge arm of the F-SOP, ;

[0222] Based on the F-SOP comprehensive operating cost and the commutation device access substation area loss large model, the economic optimal objective function of the coordinated operation strategy of the F-SOP and the commutation device is the minimum value of the sum of the transformer loss cost, the commutation device comprehensive operating cost, the three-phase four-wire network line loss cost and the F-SOP comprehensive operating cost, as follows:

[0223]

[0224] In the formula, The comprehensive operating cost of the low-voltage distribution substation under the collaborative strategy.

[0225] The power transmission conservation constraint condition of the F-SOP loss characteristic model is that the sum of the active power transmitted by each bridge arm of each port of the F-SOP is 0, specifically as follows:

[0226]

[0227] In the formula, represents the active power flowing out of the th port phase bridge arm of the F-SOP;

[0228] The capacity constraint condition of the F-SOP loss characteristic model is that the apparent power transmitted by each bridge arm of each port of the F-SOP should be less than or equal to the capacity of the corresponding port and corresponding bridge arm; the total apparent power transmitted by the F-SOP should also be less than or equal to the overall capacity of the F-SOP:

[0229]

[0230] In the formula, represents the apparent power flowing through the th port phase bridge arm of the F-SOP; represents the th port phase bridge arm capacity of the F-SOP, is the total transmission power of the F-SOP, is the overall capacity of the F-SOP.

[0231] Step S5: In this embodiment, the Cplex commercial solver is used to solve the economic optimal objective function of the low-voltage interconnected substation regulation strategy for the collaborative action of the F-SOP and the phase converter, determine the second optimal action state of the phase converter and the optimal power scheduling instruction of the F-SOP, and send them to the phase converter and the F-SOP respectively.

[0232] The optimal power scheduling instruction of the F-SOP shown includes the active power and reactive power transmitted by each phase bridge arm of the F-SOP at each port.

[0233] The interconnected substation regulation system based on the collaboration of the F-SOP and the phase converter includes the following modules:

[0234] Data acquisition module: Firstly, collect the operation-related parameters of each low-voltage distribution substation interconnected by the F-SOP with multiple ports. Among them, the operation-related parameters of the low-voltage distribution substation include the normal operation data of the low-voltage distribution substation and the equipment parameters of the transformer, F-SOP, and phase converter;

[0235] The first calculation and judgment module: According to the operation-related parameters of the low-voltage distribution substation area collected once, calculate the three-phase imbalance degree of the output power of the transformers in each low-voltage distribution substation area, the load rate of the transformers, and the voltage of each phase of each node in each low-voltage distribution substation area once, and judge once whether the three-phase imbalance degree of the output power, the load rate of the transformers, and the voltage of each phase of each node in each low-voltage distribution substation area are simultaneously within the constraint interval;

[0236] If so, the phase changer and F-SOP do not act, and return to the start data acquisition module to continue real-time monitoring;

[0237] If not, start the phase changer and start the second calculation and judgment module;

[0238] The second calculation and judgment module: According to the pre-constructed large model of the loss of the low-voltage distribution substation area with the phase changer connected, construct the economic optimal objective function of the low-voltage distribution substation area with only the phase changer connected, and determine the first optimal action state of the phase changer; the large model of the loss of the low-voltage distribution substation area with the phase changer connected includes the transformer loss characteristic model, the phase changer loss characteristic model, and the three-phase four-wire independent power flow network loss characteristic model;

[0239] Make the phase changer act according to the first optimal action state;

[0240] Collect the operation-related parameters of each low-voltage distribution substation area again;

[0241] According to the operation-related parameters of each low-voltage distribution substation area collected again, calculate the three-phase imbalance degree of the output power of the transformers in each low-voltage distribution substation area, the load rate of the transformers, and the voltage of each phase of each node again, and judge again whether the three-phase imbalance degree of the output power, the load rate of the transformers, and the voltage of each phase of each node in each low-voltage distribution substation area are simultaneously within the constraint interval;

[0242] If so, F-SOP does not act, and return to the start data acquisition module to continue real-time monitoring;

[0243] If not, start F-SOP and start the instruction acquisition module;

[0244] The instruction acquisition module: Based on the large model of the loss of the low-voltage distribution substation area with the phase changer connected and the pre-constructed F-SOP loss characteristic model, construct the economic optimal objective function of the low-voltage interconnected substation area regulation strategy with F-SOP and the phase changer acting in coordination; Solve the economic optimal objective function of the low-voltage interconnected substation area regulation strategy with F-SOP and the phase changer acting in coordination, determine the second optimal action state of the phase changer and the optimal power dispatching instruction of F-SOP, and send them to the phase changer and F-SOP respectively.

[0245] In one embodiment, to verify the feasibility and superiority of the method provided in this application, four scenarios were set up for comparative analysis, and verification was carried out based on the loads of a three-phase four-wire 22-node distribution area and a 15-node distribution area. The four comparative scenarios are as follows:

[0246] 1) Each low-voltage distribution area is not interconnected via F-SOP and no phase converter is connected.

[0247] 2) Each low-voltage distribution area is interconnected via F-SOP and no phase converter is connected.

[0248] 3) Each low-voltage distribution area is not interconnected via F-SOP and a phase converter is connected.

[0249] 4) Each low-voltage distribution area is interconnected via F-SOP and a phase converter is connected, that is, the interconnected substation regulation method based on the cooperation of F-SOP and phase converter proposed in the present invention.

[0250] The equipment installation conditions of the four scenarios are shown in Table 1.

[0251] Table 1 Equipment installation conditions of the four scenarios

[0252]

[0253] Comparing the four scenarios, the main features are as follows:

[0254] The transformers in the first low-voltage distribution area and the second low-voltage distribution area are the No. 1 transformer and the No. 2 transformer respectively. Figure 6a 、 Figure 6b 、 Figure 6c and Figure 6d give the comparison charts of the transformer load rates under the four scenarios respectively. As Figure 6a and Figure 6c show, in Scenario 1 and Scenario 3, there is a lack of power compensation of F-SOP at the transformer end, and during the peak electricity consumption period in the daytime, the load rates of the two transformers exceed the economic operation range; while in Scenario 2 and Scenario 4, as Figure 6b and Figure 6d show, the low-voltage busbars of the distribution area are incorporated into F-SOP, and the transformers operate within the economic operation range at all times.

[0255] Figure 7a 、 Figure 7b 、 Figure 7c and Figure 7d give the comparison charts of the three-phase unbalance degrees of the transformer output powers under the four scenarios respectively.

[0256] In Scenario 1, as Figure 7a shows, when there is no F-SOP and no phase converter for three-phase unbalance control, the three-phase unbalance problem of the transformer is serious, and the unbalance degree of the transformer output power can reach up to 50%.

[0257] Under Scheme 2, as Figure 7b shown, the low-voltage busbars of the two regions are incorporated into the F-SOP, and the three-phase imbalance of the output power of the transformer is significantly reduced. However, due to the capacity limitation of the F-SOP, the three-phase imbalance of the output power still fails to meet the standard for more than half of the time;

[0258] Under Scheme 3, as Figure 7c shown, the ability of the phase converter to control the three-phase imbalance at the transformer end is very limited, and the three-phase imbalance problem of the transformer remains obvious;

[0259] Under Scheme 4, as Figure 7d shown, the F-SOP and the phase converter act in coordination, acting respectively at the transformer end and the line load side, so that the three-phase imbalance at all times is within the threshold.

[0260] Figure 8a and Figure 8b and Figure 8c and Figure 8d give the total losses and loss compositions of the low-voltage distribution substation under the four schemes respectively.

[0261] Under Scheme 1, as Figure 8a shown, since the two regions are not interconnected by the F-SOP and the phase converter does not perform phase conversion, the transformer bears all the loads, which results in the prominent zero-sequence loss and line loss of the transformer and a large total loss;

[0262] Under Scheme 2, as Figure 8b shown, after incorporating the F-SOP, the three-phase imbalance and heavy / light load of the transformer are controlled, and the transformer loss is significantly reduced, but the line loss is still prominent;

[0263] Under Scheme 3, as Figure 8c shown, incorporating the phase converter significantly reduces the line loss. At the moments of large load at noon and in the evening, the line loss can be reduced by about 35%, and the line loss at other times can be reduced by 10% to 20%. However, the transformer loss of this scheme has not been controlled, and the total loss is still very high;

[0264] Under Scheme 4, as Figure 8d shown, under the comprehensive control of the F-SOP and the phase converter, both the transformer loss and the line loss are significantly reduced, and the total loss is the smallest among the three schemes, with good control effect.

[0265] Figure 9 gives the comprehensive operation cost curve of the low-voltage distribution substation under the four schemes. From Figure 9It can be seen that although the method proposed in this application increases the comprehensive operating cost of the F-SOP and the phase converter, since the total loss is less than that of the other solutions, the comprehensive operating cost of the low-voltage distribution substation area is also lower than that of the other solutions, and the economy is optimal. At the same time, in the long run, this strategy effectively addresses the three-phase imbalance and heavy / light load problems in the entire substation area, improving the operating safety of the low-voltage distribution substation area.

[0266] In summary, the interconnected substation area regulation method proposed in this application based on the cooperation of F-SOP and the phase converter effectively addresses the three-phase imbalance problem of the substation area transformer while also effectively solving the three-phase imbalance problem of the substation area line. Compared with the existing solutions, the total loss of the method proposed in this application is effectively reduced, the operating safety of the low-voltage distribution substation area is improved, the service life of the equipment is extended, and the economy of the long-term operation of the low-voltage distribution substation area is also improved.

[0267] The above are only the preferred embodiments of this application and are not used to limit this application. For those skilled in the art, various changes and modifications can be made to this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. An interconnected substation area regulation method based on the cooperation of F-SOP and commutation devices, characterized in that: It includes the following steps: Step S1: Collect the operation-related parameters of each low-voltage distribution substation interconnected by F-SOP once; Step S2: According to the operation-related parameters of the low-voltage distribution substation collected once, calculate and judge whether the three-phase unbalance degree of the output power of the transformer in each low-voltage distribution substation, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation are simultaneously within the constraint interval; if so, the phase converter and F-SOP do not act, and return to Step S1 to continue monitoring; if not, start the phase converter and enter Step S3; Step S3: According to the large model of the loss of the substation area connected with the phase converter, construct the economic optimal objective function of the low-voltage distribution substation area with only the phase converter connected, and determine the first optimal action state of the phase converter; the large model of the loss of the substation area connected with the phase converter includes the transformer loss characteristic model, the phase converter loss characteristic model, and the three-phase four-wire independent power flow network loss characteristic model; Make the phase converter act according to the first optimal action state; collect the operation-related parameters of each low-voltage distribution substation area twice; calculate and judge whether the three-phase unbalance degree of the output power of the transformer in each low-voltage distribution substation area, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation area are simultaneously within the constraint interval; if so, F-SOP does not act, and return to Step S1 to continue monitoring; If not, start F-SOP and enter Step S4; Step S4: Based on the large model of the loss of the substation area connected with the phase converter and the pre-constructed F-SOP loss characteristic model, construct the economic optimal objective function of the regulation strategy of the low-voltage interconnected substation area with the coordinated action of F-SOP and the phase converter; Step S5: Solve the economic optimal objective function of the regulation strategy of the low-voltage interconnected substation area with the coordinated action of F-SOP and the phase converter, determine the second optimal action state of the phase converter and the optimal power dispatching instruction of F-SOP, and send them to the phase converter and F-SOP respectively; 2. The interconnected substation area regulation method based on the cooperation of F-SOP and commutation device according to claim 1, characterized in that The load factor of a transformer phase is obtained by dividing the apparent power issued by a transformer phase by the capacity of a transformer phase; ​ The output power three-phase unbalance degree of the th transformer is obtained by subtracting the average value of the three-phase output power of the th transformer from the maximum value among the three-phase output powers of the th transformer and then dividing by the average value of the three-phase output power of the th transformer.

3. The interconnection substation area regulation method based on the cooperation of F-SOP and commutation device according to claim 1, characterized in that The constraint condition of the load rate of the transformer is that the load rate of each phase of each transformer does not exceed the specified economic operation interval of the transformer; The constraint condition of the three-phase unbalance degree of the output power of the transformer is that the unbalance degree of the output power of each transformer does not exceed the specified unbalance degree threshold; The constraint condition of the voltage of each phase of each node is that the voltage of each phase of each node in each low-voltage distribution substation area does not exceed the upper and lower limits of the node voltage specified for the safe operation of the low-voltage distribution substation area; 4. The interconnected substation area regulation method based on the cooperation of F-SOP and commutation device according to claim 1, wherein In the transformer loss characteristic model, calculating the transformer loss includes the comprehensive power no-load loss of each phase of each transformer, the comprehensive power rated load loss, and the zero-sequence loss generated when the three-phase load of each transformer is unbalanced; In the phase converter loss characteristic model, calculating the phase converter loss is obtained by multiplying the phase converter resistance coefficient by the sum of the apparent power of the a-phase load of each group of nodes where the phase converter is connected; In the three-phase four-wire independent power flow network loss characteristic model, calculating the total line loss of the three-phase four-wire network is obtained by multiplying the current of each phase of each branch by the resistance of the corresponding phase of the corresponding branch and then summing; 5. The interconnection substation area regulation method based on the cooperation of F-SOP and commutation device according to claim 4, wherein The economic optimal objective function of the low-voltage distribution substation area with only the phase converter connected is the minimum value of the sum of the transformer loss cost, the comprehensive operation cost of the phase converter, and the three-phase four-wire network line loss cost; According to the transformer loss characteristic model, the transformer loss cost is obtained by multiplying the grid electricity price by the transformer loss; The comprehensive operating cost of the phase converter includes the phase converter loss cost and the phase converter operation cost; According to the phase converter loss characteristic model, the phase converter loss cost is obtained by multiplying the grid electricity price by the phase converter loss; The phase converter operation cost is obtained by multiplying the phase converter operation cost coefficient by the sum of the operation times of all phase converters; Based on the three-phase four-wire independent power flow network loss characteristic model, the three-phase four-wire network line loss cost is obtained by multiplying the grid electricity price by the total three-phase four-wire network line loss.

6. The interconnected substation area regulation method based on the cooperation of F-SOP and phase converter according to claim 1, characterized in that The constraint conditions of the commutation loss characteristic model are that the sum of the active power and reactive power output by the three-phase bridge arms of the th group of commutation devices should be equal to 0 respectively. The active power and reactive power output by the th group of commutation devices phase bridge arm are respectively equal to the opposite of the state scalar and the product of the active power and reactive power of the phase load at the connection node of the th group of commutation devices. The product of the active power output by the th group of commutation devices and phase bridge arms is 0. The product of the reactive power output by the th group of commutation devices and phase bridge arms is also 0. Specifically as follows: Among them, is the th group of phase converters phase bridge arm's active power injected into a certain node , is the th group of phase converters phase bridge arm's reactive power injected into a certain node ; And is the th group of phase converters' active and reactive powers of the load at the connected node , represents the action status scalar of the th group of phase converters.

7. The interconnected substation area regulation method based on the cooperation of F-SOP and phase converter according to claim 1, characterized in that The constraint condition of the transformer loss characteristic model is that the apparent power output of each phase of each transformer cannot exceed the capacity of the corresponding phase of the corresponding transformer, and the total apparent power output of the three phases of each transformer cannot exceed the three-phase total capacity of the corresponding transformer; The operating safety constraint condition of each phase of the three-phase four-wire independent power flow network loss characteristic model is that the voltage amplitude of each phase of each node in the low-voltage distribution substation area does not exceed the upper and lower limits of the node voltage specified for the safe operation of the low-voltage distribution substation area; The current amplitude of each phase of each branch in the low-voltage distribution substation area does not exceed the upper limit of the branch current specified for the safe operation of the low-voltage distribution substation area; The amplitude of the active power injected into each phase of each node in the low-voltage distribution substation area does not exceed the upper and lower limits of the node injection power; The constraint condition of the power flow of the three-phase four-wire independent power flow network loss characteristic model is that each phase of each low-voltage distribution substation area needs to satisfy the optimal power flow constraint after second-order cone relaxation respectively.

8. The interconnected substation area regulation method based on the cooperation of F-SOP and commutation device according to any one of claims 1 to 7, characterized in that In the F-SOP loss characteristic model, calculating the comprehensive operating cost of F-SOP includes the loss cost and operation and maintenance cost of F-SOP; The loss cost of F-SOP is obtained by multiplying the grid electricity price by the transmission power loss of F-SOP; The F-SOP power transmission loss is obtained by subtracting the product of the transmission efficiency and the transmission power from the transmission power of each phase of the bridge arm at each port; The operation and maintenance cost of F-SOP is obtained by multiplying the operation and maintenance cost coefficient by the total transmission power of each port and each bridge arm of F-SOP; Based on the F-SOP comprehensive operating cost and the phase converter access substation area loss large model, constructing the economic optimal objective function of the low-voltage interconnected substation area regulation strategy of the coordinated action of F-SOP and phase converter is the minimum value of the sum of the transformer loss cost, the phase converter comprehensive operating cost, the three-phase four-wire network line loss cost and the F-SOP comprehensive operating cost.

9. The interconnected substation area regulation method based on the cooperation of F-SOP and commutation device according to claim 1, wherein: In step S5, after solving the economic optimal objective function of the low-voltage interconnected substation area regulation strategy of the coordinated action of F-SOP and phase converter, the optimal power dispatching instruction of F-SOP is obtained, including the active power and reactive power transmitted by each phase of the bridge arm of F-SOP at each port.

10. A system for implementing the interconnected substation area regulation method based on the cooperation of F-SOP and commutation device according to claim 1, characterized in that: Including the following modules: Data acquisition module: Firstly, acquire the operation-related parameters of each low-voltage distribution substation area interconnected by F-SOP through multiple ports; The first calculation and judgment module: Based on the operation-related parameters of the low-voltage distribution substation area collected once, calculate and judge whether the three-phase imbalance degree of the output power of the transformer, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation area are simultaneously within the constraint interval; The second calculation and judgment module: Based on the pre-constructed large model of the loss of the commutation device accessing the substation area, construct the economic optimal objective function of the low-voltage distribution substation area with only the commutation device connected, determine the first optimal action state of the commutation device; make the commutation device act according to the first optimal action state; Collect the operation-related parameters of each low-voltage distribution substation area for the second time, calculate and judge whether the three-phase imbalance degree of the output power of the transformer, the load rate of the transformer, and the voltage of each phase of each node in each low-voltage distribution substation area are simultaneously within the constraint interval; The instruction acquisition module: Based on the large model of the loss of the commutation device accessing the substation area and the pre-constructed F-SOP loss characteristic model, construct the economic optimal objective function of the low-voltage interconnected substation area regulation strategy with the coordinated action of the F-SOP and the commutation device; solve the economic optimal objective function of the low-voltage interconnected substation area regulation strategy with the coordinated action of the F-SOP and the commutation device, determine the second optimal action state of the commutation device and the optimal power scheduling instruction of the F-SOP, and send them to the commutation device and the F-SOP respectively.

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