Urban medium voltage distribution network load balancing method

Abstract

The invention discloses an urban medium-voltage power distribution network load balancing method, which comprises the following steps of: S1, determining optional path information of load transfer of each transformer substation in a hot spot region on the basis of a power system topological graph in a power production management system, and establishing a load transfer power system incidence matrix among the transformer substations in the hot spot region according to the optional path information; and S2, pre-judging a heavy overload transformer substation of the regional electrical system in a normal operation mode, and calculating a daily load rate prediction curve of the heavy overload transformer substation and related feeder lines. And S3, on the basis of the daily load rate prediction curve of the heavy and overload transformer substation and the related feeder line, determining all load transfer paths with feasibility of being brought into the hot spot region load balancing scheme. And S4, carrying out transfer according to all the load transfer paths included in the feasibility of the load balancing scheme of the hot spot region, calculating the maximum value and the average value of the peak load rate of each transformer substation after transfer, and selecting the optimal load transfer path to obtain the load balancing scheme of the hot spot region. The method is simple in logic and easy to implement.

Description

Technical Field

[0001] The invention relates to the field of load balancing of a city medium-voltage distribution network, and in particular to a method for load balancing of a city medium-voltage distribution network. Background Art

[0002] In the urban medium-voltage distribution network, 110kV and 35kV substations are the core of grid-based regional power conversion. Due to cable channel constraints and lack of power supply points, the operating risks of urban distribution networks caused by insufficient capacity or uneven load have already emerged. In summer and winter every year, affected by extreme natural weather such as high temperatures and cold waves, the air-conditioning load rises sharply, and some substations may be overloaded, which seriously affects the safe and stable operation of the power grid. For this reason, before the summer and winter load peaks approach, the power grid dispatching department needs to predict the overloaded substations, adjust the power grid operation mode, and transfer the load of the overloaded substations in advance, thereby reducing the load-bearing pressure of the overloaded substations during the load peak and balancing the load of each substation.

[0003] With the acceleration of urbanization and the agglomeration of industries, the same load characteristics between the same industrial blocks and the differences between different industrial blocks are becoming more and more obvious. As the power supply aggregation center for the loads in the jurisdiction blocks, the daily load characteristics (mainly including curves, peaks and valleys, etc.) of the substation are also similar or significantly different. This is both an opportunity and a challenge for the dispatching department to carry out the load transfer work of the heavily overloaded substation before the peak load.

[0004] Before the peak load approaches, the general practice of the power grid dispatching department is to predict the load peak of substations and feeders in the hot spot area, lock in the substations that may be overloaded or heavily loaded, and then select the appropriate load transfer path, and then arrange the operation mode adjustment for the heavily overloaded substations in advance to solve the heavy overload problem of the substation in advance. At present, the load transfer of substations mainly relies on manual experience prediction of their load rate peak and simple addition and subtraction, without taking into account the daily load characteristics of the transfer-related substations and feeders, and lacks consideration of factors such as equipment utilization, which urgently needs to be optimized and improved. Summary of the invention

[0005] The purpose of the present invention is to provide a method for load balancing in a city medium-voltage distribution network, which is used for balanced distribution of regional loads among associated substations to achieve regional load balancing.

[0006] In order to achieve the above objectives, the present invention is implemented by the following technical solutions:

[0007] A method for load balancing of a city medium-voltage distribution network comprises: step S1, selecting a load hotspot area of ​​a city medium-voltage distribution network, determining optional path information of load transfer of each substation in the hotspot area based on the power system topology map in the power production management system, and establishing a load transfer system association matrix between each substation in the hotspot area according to the optional path information. Step S2, predicting the heavily overloaded substations in the normal operation mode of the regional power system, and calculating the daily load rate prediction curve of the heavily overloaded substation and related feeders. Step S3, based on the daily load rate prediction curve of the heavily overloaded substation and related feeders, determining all load transfer paths with feasibility of being included in the hotspot area load balancing solution. Step S4, the heavily overloaded substation transfers according to all load transfer paths included in the feasibility of the hotspot area load balancing solution, calculating the maximum value and average value of the peak load rate of each substation after the transfer, and selecting the optimal load transfer path from all load transfer paths included in the feasibility of the hotspot area load balancing solution according to the maximum value and average value of the peak load rate of each substation after the transfer, and obtaining the load balancing solution for the hotspot area.

[0008] Optionally, the step S1 includes: judging and restoring the substations in temporary operation mode in the power system of the hot spot area, and correcting the load-to-power-transfer system association matrix thereof to obtain the load-to-power-transfer system association matrix.

[0009] Optionally, the step S2 includes: calculating a daily load rate prediction curve of each substation in the normal operation of the regional power system, and predicting a heavily overloaded substation based on the daily load rate prediction curve of each substation in the normal operation of the regional power system.

[0010] Optionally, the load-to-power system association matrix A i,j as follows:

[0011]

[0012] In the formula, A i,j Indicates substation T i With substation T j The load-to-power system correlation matrix; K i and K j Respectively represent substation T i and T j The number of feeders; L i,m Indicates T i The mth feeder, L j,n Indicates T j The nth feeder of m,n Indicates L i,m and L j,n The electrical topological correlation between m,n 1 means Li,m and L j,n There is a load transfer path between m,n 0 means L i,m and L j,n There is no load transfer path between them.

[0013] Optionally, the step S3 includes: step S31, selecting a substation with the highest predicted load rate from the heavily overloaded substations as an initial target substation T h According to the load-to-power system association matrix, the initial target substation T is determined h Step S32: Analyze all the load transfer paths in the first optional load transfer path group to determine the initial target substation T h All load transfer paths that are feasible for the load balancing solution in the hot spot area are included to obtain the second optional load transfer path group.

[0014] Optionally, the step S32 includes: step S321, according to the initial target substation T h The daily load rate prediction curve, the initial target substation T h After the load is transferred through the current load transfer path, the initial target substation T is determined. h Whether there is an overload in the opposite substation or feeder. If yes, the current load transfer path is not included in the second optional load transfer path group. If not, the current load transfer path is included in the second optional load transfer path group. Step S322, select the next load transfer path from the first optional load transfer path group for transfer. Repeat steps S321-S322 until all load transfer paths in the first optional load transfer path group are preferentially determined to obtain the second optional load transfer path group.

[0015] Optionally, the step S4 includes: step S41, for each load transfer path R in the second optional load transfer path group, hi , the following formula is used to calculate the initial target substation T after the load transfer path is transferred. h and the opposite side substation T g The daily load factor prediction curve η Thi and η Tgi and peak load factor η Thi,P and η Tgi,P :

[0016] R hi :T h -L h,m -Lg,n -T g (1)

[0017] η Thi,P =max(η Thi ) (2)

[0018] η Tgi,P =max(η Tgi ) (3)

[0019] In the formula, R hi represents the initial target substation T h and the opposite side substation T g The i-th load transfer path between h,m T h The mth feeder, L g,n T g The nth feeder line.

[0020] Step S42: Calculate η using the following formula: Thi,P and η Tgi,P The maximum value η in T,i,max , and η Thi,P and η Tgi,P The average value η T,i,ave :

[0021] η T,i,max =max(η Thi,P ,η Tgi,P ) (4)

[0022] η T,i,ave =ave(η Thi,P ,η Tgi,P ) (5)

[0023] And select a minimum value using the following formula:

[0024] η T,min =min(η T,1,max ,η T,2,max , ...,η T,M,max ) (6)

[0025] Where η T,min represents the η corresponding to all load transfer paths T,i,max The minimum value between

[0026] Step S43: Set parameter ɑ according to actual needs and determine the interval [η T,min , η T,min +ɑ]; wherein η in the interval T,i,max The corresponding load transfer path is the load transfer path that meets the actual demand. Select η from all load transfer paths that meet the actual demand.T,i,ave The minimum load transfer path is used to obtain the optimal load transfer path.

[0027] Optionally, the step S4 further includes: step S44, determining the initial target substation T h After the load is transferred via the optimal load transfer path, whether there is an overload situation, if yes, proceed to step S45. If no, proceed to step S46.

[0028] Step S45: Pair all the load transfer paths in the second optional load transfer path group to obtain multiple load transfer path combinations, and the multiple load transfer path combinations constitute a first optional load transfer path set; calculate the initial target substation T after transfer pair by pair. h , the first associated substation T g and the second associated substation T f The daily load rate prediction curve and peak value, and according to the initial target substation T after the transfer h , the first association T g Substation and the second associated substation T f The daily load rate prediction curve and peak value determine the optimal load transfer path combination and proceed to step S46.

[0029] Step S46: The optimal load transfer path or the optimal load transfer path combination is the initial target substation T h The load balancing scheme; the initial target substation T h The process proceeds to step S47 after transferring via the optimal load transfer path or the optimal load transfer path combination.

[0030] Step S47, selecting the next heavily overloaded substation in the hot spot area, and repeating steps S31 to S46 until there is no heavily overloaded substation in the hot spot area or the loads between the substations are balanced.

[0031] Optionally, the step S45 includes: step S451, for each load transfer path combination in the first optional load transfer path set, calculating the initial target substation T h After the load is transferred through the corresponding load transfer path combination, the initial target substation T h The peak load rate of the first associated substation T g The peak load rate of the second associated substation T f The peak load rate is the maximum value among the three and the average value of the three.

[0032] Step S452: According to the initial target substation T h After the load is transferred through the corresponding load transfer path combination, the initial target substation Th The peak load rate of the first associated substation T g The peak load rate of the second associated substation T f The maximum value of the three peak load rates and the average value of the three are used to determine the optimal load transfer path combination.

[0033] Optionally, the step S4 also includes: step S48, calculating the daily load rate prediction curve of the substation after the optimal transfer path or the optimal transfer path combination. Step S49, judging whether the daily load rate prediction curve of each substation in the hot spot area after the optimal transfer path or the optimal transfer path combination meets the preset requirements according to the daily load rate prediction curve of the substation after the optimal transfer path or the optimal transfer path combination. If so, the load balancing process of each substation in the hot spot area ends, if not, repeating steps S31 to S47.

[0034] The present invention has at least one of the following technical effects:

[0035] The method of the present invention scientifically selects a load transfer path to achieve balanced distribution of regional loads among associated substations. The logic is simple and easy to implement, and the problem of inaccurate calculation in traditional methods is avoided.

[0036] The present invention rationally utilizes daily load characteristics such as load differences and peak-valley complementarity among different substations, scientifically selects load transfer paths, and realizes balanced distribution of regional loads among related substations.

[0037] The present invention can simply and accurately select the optimal load transfer path for the target substation, thereby realizing the priority transfer of the target heavy-load substation load to the substation with lighter load or peak-valley characteristic complementary substation, without the need to reconstruct the power grid topology on a large scale, and providing an effective basis and method for improving the utilization rate of power grid equipment and reducing the power grid capacity-load ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A flow chart of a method for load balancing in a city medium voltage distribution network provided by one embodiment of the present invention;

[0039] Figure 2 A schematic diagram of a load transfer path provided by an embodiment of the present invention;

[0040] Figure 3 The maximum load day L in summer of a certain year provided by an embodiment of the present invention i,m , L j,n Daily load current curve;

[0041] Figure 4 The initial target substation T provided by an embodiment of the present inventionh Schematic diagram of all load transfer paths that can be included in the plan. DETAILED DESCRIPTION

[0042] The following is a further detailed description of a method for load balancing of a city medium-voltage distribution network proposed by the present invention in combination with the accompanying drawings and specific implementation methods. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the implementation method of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the accompanying drawings. It should be noted that the structure, proportion, size, etc. illustrated in the drawings of this specification are only used to match the content disclosed in the specification, so that people familiar with this technology can understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so it has no technical substantive significance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effect that the present invention can produce and the purpose that can be achieved, should still fall within the scope of the technical content disclosed by the present invention.

[0043] Figure 1 The present invention provides a flow chart of a method for load balancing of a city medium voltage distribution network according to an embodiment of the present invention. Figure 1 As shown, this embodiment provides a method for load balancing of a city medium-voltage distribution network, including: step S1, selecting a load hotspot area of ​​a city medium-voltage distribution network, determining the optional path information of the load transfer of each substation in the hotspot area based on the power system topology map in the power production management system, and establishing a load transfer system association matrix between each substation in the hotspot area according to the optional path information. Step S2, predicting the heavy overload substation in the normal operation mode of the regional power system, and calculating the daily load rate prediction curve of the heavy overload substation and related feeders. Step S3, based on the daily load rate prediction curve of the heavy overload substation and related feeders, determining all load transfer paths with feasibility of being included in the hotspot area load balancing solution. Step S4, the heavy overload substation transfers according to all load transfer paths included in the feasibility of the hotspot area load balancing solution; calculating the maximum and average values ​​of the peak load rates of each substation after the transfer, and selecting the optimal load transfer path from all load transfer paths included in the feasibility of the hotspot area load balancing solution according to the maximum and average values ​​of the peak load rates of each substation after the transfer, to obtain the load balancing solution for the hotspot area.

[0044] The method of this embodiment scientifically selects the load transfer path to achieve balanced distribution of the load in the hot spot area among the associated substations. The logic is simple and easy to implement, avoiding the problem of inaccurate calculation of traditional methods.

[0045] In order to facilitate understanding of this embodiment, Figure 2 and Figure 3 The basic definition of the load transfer path involved in the substation is as follows:

[0046] like Figure 2 As shown, T i 、T j are any two substations in a certain area, L i,m T i The mth feeder, L j,n T j The nth feeder, S i,m , S j,n L i,m , L j,n For switches in the substation, if L i,m With L j,n There is a circuit breaker B between the open i,m-j,n , and L i,m The supplied load can be i,m-j,n , open S i,m The operation is transferred to L j,n Powered by, proven T i The feeder load can be supplied through the path T i -L i,m -L j,n -T j Transferred from T j Power supply, this path is regarded as substation T i A load transfer path.

[0047] For example, Figure 2 and Figure 3 As shown, T i It is a 35kV heavy-load substation during the summer load peak period. j There is a line like Figure 2 The optional load transfer path T shown i -L i,m -L j,n -T j , and the feeder L i,m and L j,n The rated current of L is 400A. i,m and L j,n The daily load current curve is as follows Figure 3 As shown. Figure 3 It can be seen that on that day, L i,m , L j,n The current peaks are 136A and 224A respectively. According to the traditional load transfer path selection method, i,m , L j,n The sum of the current peaks is 360A, reaching 90% of the rated current. Therefore, after selecting this load transfer path, Lj,n The load will be seriously overloaded and there will be operational risks. Therefore, the dispatching department usually does not select it as the optimal load transfer path. Figure 3 It can be seen that L i,m , L j,n The load peak moments are different, indicating that although it is relatively simple to select the load transfer path by simply summing the load peaks, the accuracy is low.

[0048] In this embodiment or some other embodiments, the step S1 also includes: judging and restoring the substations in temporary operation mode in the hot spot area power system, and correcting the load-to-power-transfer system association matrix to obtain the load-to-power-transfer system association matrix.

[0049] Specifically, the temporary operating modes that exist within the regional power system due to planned maintenance, fault repairs, etc. are restored, and existing load forecasting methods are used to predict heavily overloaded substations under future normal operating modes.

[0050] More specifically, for changes in the transfer path caused by planned maintenance, fault repairs, etc., combined with the power system changes, signboard prompts and other operations completed simultaneously in the relevant diagrams of the power production management system, the changes in the transfer path caused by the power grid work are correctly judged and restored, and the load transfer power system association matrix A is corrected simultaneously, and finally the load transfer power system association relationship under normal operation is obtained.

[0051] In this embodiment or some other embodiments, the load-to-power system association matrix A i,j as follows:

[0052]

[0053] In the formula, A i,j Indicates substation T i With substation T j The load-to-power system correlation matrix K i and K j Respectively represent substation T i and T j The number of feeders; L i,m Indicates T i The mth feeder, L j,n Indicates T j The nth feeder of m,n Indicates L i,m and L j,n The electrical topological correlation between m,n 1 means L i,m and L j,n There is a load transfer path between m,n 0 means L i,mand L j,n There is no load transfer path between them.

[0054] Specifically, the regional substation load-to-power system association matrix A can be derived by programming in the background environment of the power production management system, as follows:

[0055]

[0056] Where: N is the number of substations in the hotspot area; A i,j is the i-th substation T in the hotspot area i With the jth substation T j The load-to-power system association matrix.

[0057]

[0058] Where: K i , K j They are hotspot area substation T i , T j The number of feeders; a m,n Characterization L i,m and L j,n The electrical topological correlation between m,n 1 indicates that L i,m and L j,n There is a load transfer path between m,n 0 means L i,m and L j,n There is no load transfer path between them.

[0059] It should be noted that, assuming that due to the planned maintenance of the power grid, the substation T i The first feeder and substation T j The tie switch between the second feeder and the second feeder is out of service, and there is no feasible load transfer path. 1,2 = 0, after the planned maintenance is completed, the above-mentioned tie switch is restored to service, and there is a feasible load transfer path, then a 1,2 =1.

[0060] In this embodiment or some other embodiments, the step S2 includes: after restoring the temporary operation mode existing in the regional power system due to planned maintenance, fault repair, etc., use the existing load forecasting means to predict the heavily overloaded substations under the future normal operation mode. Specifically, calculate the daily load rate prediction curve of each substation in the regional power system under the normal operation mode, and then predict the regional heavily overloaded substation; that is, calculate the daily load rate prediction curve of each substation in the regional power system under the normal operation mode, and predict the regional heavily overloaded substation according to the daily load rate prediction curve of each substation in the regional power system under the normal operation mode. In this embodiment or some other embodiments, such as Figure 4 As shown, the step S3 includes: based on the daily load rate prediction curve of the heavily overloaded substation and related feeders, a safety check is simultaneously performed to determine all load transfer paths that are feasible for inclusion in the hot spot area load balancing solution.

[0061] Step S31: Select the substation with the highest predicted load rate from the heavily overloaded substations as the initial target substation T h According to the load-to-power system association matrix, the initial target substation T is determined h All optional load transfer paths are selected to obtain the first optional load transfer path group.

[0062] Step S32: Analyze all load transfer paths in the first optional load transfer path group to determine the initial target substation T h All load transfer paths that are feasible for the load balancing solution in the hot spot area are included to obtain the second optional load transfer path group.

[0063] The step S32 includes: step S321, according to the initial target substation T h The daily load rate prediction curve, the initial target substation T h After the load is transferred through the current load transfer path, the initial target substation T is determined. h Whether the opposite side substation or feeder is overloaded. If so, the current load transfer path is not included in the second optional load transfer path group. If not, the current load transfer path is included in the second optional load transfer path group.

[0064] Step S322: Select the next load transfer path from the first optional load transfer path group for transfer. Repeat the steps S321 to S322 until all load transfer paths in the first optional load transfer path group are selected and determined to obtain the second optional load transfer path group.

[0065] It should be noted that step S32 is the specific process of safety verification. h All optional load transfer paths are analyzed one by one. According to the daily load rate prediction curve, if the opposite substation or feeder is overloaded after transfer via a certain path, this path will no longer be considered in the plan; if the opposite substation or feeder is overloaded after transfer via a certain path, although this path is included in the plan, its priority is lower than other paths.

[0066] In this embodiment or some other embodiments, the step S4 includes: step S41, for each of the load transfer paths R in the second optional load transfer path group, hi, the following formula is used to calculate the initial target substation T after the load transfer path is transferred. h and the opposite side substation T g The daily load factor prediction curve η Thi and η Tgi and peak load factor η Thi,P and η Tgi,P :

[0067] R hi :T h -L h,m -L g,n -T g (1)

[0068] η Thi,P =max(η Thi ) (2)

[0069] η Tgi,P =max(η Tgi ) (3)

[0070] In the formula, R hi represents the initial target substation T h and the opposite side substation T g The i-th load transfer path between h,m T h The mth feeder, L g,n T g The nth feeder line.

[0071] Step S42: Calculate η using the following formula: Thi,P and η Tgi,P The maximum value η in T,i,max , and η Thi,P and η Tgi,P The average value η T,i,ave :

[0072] η T,i,max =max(η Thi,P ,η Tgi,P ) (4)

[0073] η T,i,ave =ave(η Thi,P ,η Tgi,P ) (5)

[0074] And select a minimum value using the following formula:

[0075] η T,min =min(η T,1,max ,η T,2,max , …,η T,M,max ) (6)

[0076] Where η T,min represents the η corresponding to all load transfer paths T,i,max The minimum value between .

[0077] Step S43: Set parameter ɑ according to actual needs and determine the interval [η T,min , η T,min +ɑ]; wherein η in the interval T,i,max The corresponding load transfer path is a load transfer path that meets actual needs.

[0078] Select η from all load transfer paths that meet actual needs. T,i,ave The minimum load transfer path is used to obtain the optimal load transfer path.

[0079] Step S44: Determine the initial target substation T h After the load is transferred via the optimal load transfer path, whether there is an overload situation, if yes, proceed to step S45. If no, proceed to step S46.

[0080] Step S45: Pair all the load transfer paths in the second optional load transfer path group to obtain multiple load transfer path combinations, and the multiple load transfer path combinations constitute a first optional load transfer path set; calculate the initial target substation T after transfer pair by pair. h , the first associated substation T g and the second associated substation T f The daily load rate prediction curve and peak value, and according to the initial target substation T after the transfer h , the first associated substation T g and the second associated substation T f The daily load rate prediction curve and peak value determine the optimal load transfer path combination and proceed to step S46.

[0081] Step S46: The optimal load transfer path or the optimal load transfer path combination is the initial target substation T h The load balancing scheme; the initial target substation T h The process proceeds to step S47 after transferring via the optimal load transfer path or the optimal load transfer path combination.

[0082] Step S47, selecting the next heavily overloaded substation in the hot spot area, and repeating steps S31 to S46 until there is no heavily overloaded substation in the hot spot area or the loads between the substations have been balanced to the maximum extent.

[0083] In this embodiment or some other embodiments, step S45 includes:

[0084] Step S451: For each load transfer path combination in the first optional load transfer path set, calculate the initial target substation T h After the load is transferred through the corresponding load transfer path combination, the initial target substation T h The peak load rate of the first associated substation T g The peak load rate of the second associated substation T f The peak load rate is the maximum value among the three and the average value of the three.

[0085] Step S452: According to the initial target substation T h After the load is transferred through the corresponding load transfer path combination, the initial target substation T h The peak load rate of the first associated substation T g The peak load rate of the second associated substation T f The maximum value of the three peak load rates and the average value of the three are used to determine the optimal load transfer path combination.

[0086] It should be noted that, in step S451, for each load transfer path combination R in the first optional load transfer path set, hi , Calculate the initial target substation T h After the load is transferred through the i-th and j-th load transfer paths at the same time, the target substation T h The peak load rate of the first associated substation Tg, the peak load rate of the second associated substation T f The peak load rate is the maximum value among the three and the average value of the three.

[0087] In this embodiment or some other embodiments, the step S4 also includes: step S48, calculating the daily load rate prediction curve of the substation after transfer via the optimal load transfer path or the optimal transfer path combination.

[0088] Step S49, according to the daily load rate prediction curve of the substation after the optimal load transfer path or the optimal transfer path combination, determine whether the daily load rate prediction curve of each substation in the hot spot area after the optimal load transfer path or the optimal transfer path combination meets the preset requirements, if so, the load balancing process of each substation in the hot spot area ends, if not, repeat steps S31 to S47. It should be noted that each substation includes the initial target substation and the opposite substation or each substation includes the initial target substation, the first associated substation and the second associated substation.

[0089] In order to better understand step S3 and step S4, step S3 and step S4 are further explained as follows:

[0090] The step S3 comprises: 1) selecting the substation T with the highest predicted load rate h As the initial goal, according to the load-to-power system association matrix A, determine T from the perspective of power system topology. h All optional load transfer paths, namely the first optional load transfer path group.

[0091] 2) For T h All optional load transfer paths are analyzed one by one. According to the daily load rate prediction curve, if the opposite substation or feeder is overloaded after transfer via a certain path, this path will no longer be considered; if the opposite substation or feeder is overloaded after transfer via a certain path, this path will be considered but its priority will be lower than other paths.

[0092] 3) Based on the above reliability constraints, all M load transfer paths R that are feasible to be included in the regional distribution network load balancing solution can be identified. hi (i∈[1,M]). This is the second optional load transfer path group.

[0093] The step S4 comprises: selecting the optimal load transfer path according to the maximum value and average value of the peak load rate of each substation after the transfer, and forming a load balancing plan.

[0094] 1) For each transfer path R hi :T h -L h,m -L g,n -T g , calculate the initial target T after transfer one by one h , Opposite Substation T g The daily load rate prediction curve and peak value are defined as follows:

[0095] η Thi,P =max(η Thi )

[0096] η Tgi,P =max(η Tgi )

[0097] Where: η Thi , η Tgi R hi After load transfer T h , T g Future daily load rate prediction curve; η Thi,P , η Tgi,P R hi After load transfer Th 、T g Future peak load factor.

[0098] 2) Define η T,i,ave is η Thi,P and η Tgi,P The average value, η T,i,max is η Thi,P and η Tgi,P The maximum value between , then for each transfer path R hi There exists an η T,i,ave and η T,i,max , η corresponding to all load transfer paths T,i,max The minimum value between T,min It can be calculated as follows:

[0099] η T,i,ave =ave(η Thi,P ,η Tgi,P )

[0100] η T,i,max =max(η Thi,P ,η Tgi,P )

[0101] η T,min =min(η T,1,max ,η T,2,max ,…,η T,M,max )

[0102] 3) Set the parameter ɑ according to actual needs to determine the interval [η T,min ,η T,min +ɑ].η T,i,max The transfer path within this interval is the transfer path that meets the demand, where η T,i,ave The smallest transfer path is the optimal transfer path. This is because compared with other transfer paths, T h 、T g The peak load rate is relatively low and the average value is the smallest, which drives the target substation load to transfer to the substation with sufficient margin or peak-valley complementarity.

[0103] 4) If the load transfer through the optimal path still cannot meet the requirements, all M load transfer paths are paired, that is, R hi , Calculate the daily load rate prediction curve and peak value of the associated substations after the transfer one by one, and then select the optimal transfer path combination according to the previous step.

[0104] 5) Select T hAfter the optimal load transfer path is found, the daily load rate prediction curve of the associated substation and feeder after the transfer is calculated. If the load rate of the regional substation meets the set requirements at this time, the load balancing process ends; if the load rate of the regional substation does not meet the set requirements at this time, T is selected. h After load transfer, the substation with the highest predicted load rate is taken as the new target and this process is repeated until the load rate of substations in the area meets the set requirements or reaches the optimal balance.

[0105] This embodiment aims at the situation that the substation is overloaded or the load is unevenly distributed during the peak load period of the urban medium-voltage distribution network, and takes into account the low accuracy of the traditional load transfer method, and proposes a load balancing method for the urban medium-voltage distribution network. This method is based on the regional substation load transfer system association matrix, the daily load rate prediction curve of the substation and the feeder, and takes the average value of the peak load rate of the associated substation after the transfer into consideration. The maximum value and average value of the peak load rate of the associated substation after the transfer are used as dual indicators. For the target substation, the optimal load transfer path is simply and accurately selected, thereby realizing the priority transfer of the target heavy-load substation load to the substation with lighter load or peak-valley characteristics complementary substation, without the need to reconstruct the power grid topology on a large scale, and provides an effective basis and method for improving the utilization rate of power grid equipment and reducing the power grid capacity-load ratio.

[0106] In order to better understand this embodiment, the specific implementation scheme is now described in conjunction with a certain city's medium-voltage distribution network area. There are 6 35kV substations in the area (see Table 1 for details). The air conditioning load rises sharply during the high temperature period in summer, and the load is heavy. The implementation method includes the following operations:

[0107] Table 1 Substation information

[0108]

[0109] First, establish the load transfer power supply system association matrix between substations T1 to T6. The transfer association matrix between substations T1 and T2 is as follows:

[0110]

[0111] Then, based on historical load and weather information, the daily load rate curves of the above substations and feeders during the summer peak are predicted. According to the prediction results, the peak load rate of substation T1 will reach 98.91%, and the peak load rates of the other five substations T2 to T6 are less than 80%, indicating that in this area, T1 faces the risk of overload and the load distribution between substations is extremely unbalanced. Load transfer is required to reduce the peak load rate of T1 while achieving load balance among substations.

[0112] Then, T1 is used as the initial target of load balancing, and all optional load transfer paths and the peak load rate information of the associated substations and feeders after transfer are shown in Table 2. It can be seen from Table 2 that:

[0113] 1) After the load is transferred through path 8 or 9, the opposite feeder may be overloaded. Considering that overloaded equipment operation is prone to cause failures and thus create new distribution network operation risks, the above paths are no longer considered in the load balancing solution.

[0114] 2) After the load is transferred through any other path, T1 may still be overloaded. Therefore, if the actual situation permits, at least two load transfer paths must be selected simultaneously to solve the overload problem of T1.

[0115] 3) After the load is transferred via path 5, 6 or 7, the opposite substation or feeder may be overloaded, causing new distribution network operation risks. Therefore, although the above paths are taken into consideration, their priority is lower than paths 1 to 4. In addition, after the load is transferred via path 5, the average and maximum values ​​of the peak load rate of its associated substation are the smallest, so path 5 has a higher priority than paths 6 and 7.

[0116] 4) The above analysis shows that the transfer paths that are feasible for inclusion in the load balancing plan are paths 1 to 7.

[0117] Table 2 T1 load transfer path and predicted peak load rate of associated stations and lines after transfer

[0118]

[0119]

[0120] Finally, after transferring the load through any two of the paths 1 to 7 at the same time, the maximum and average values ​​of the predicted peak load rates of all substations on this side and the opposite side are calculated, and the maximum values ​​are used as the basis for sorting from small to large. The top five transfer path combinations and the maximum and average values ​​of the predicted peak load rates of the relevant substations after the transfer are shown in Table 3. It can be seen from Table 3 that:

[0121] 1) Compared with path combinations 2 to 4, after adopting path combination 1, the maximum and average values ​​of the predicted peak load rate of the associated substations are both the smallest, that is, path combination 1 is better than path combinations 2 to 4.

[0122] 2) Compared with path combination 5, the maximum value of the predicted peak load rate of the associated substation after adopting path combination 1 is higher, but path combination 5 will cause the opposite substation T2 to be overloaded, which shows that path combination 1 is better than path combination 5.

[0123] Therefore, load transfer path combination 1 in Table 3 is selected to complete the load balancing of the regional distribution network, and the daily load rate prediction curve of the associated substation and feeder is recalculated accordingly. From the calculation results, it can be seen that after the load transfer is completed according to path combination 1, there is no more overloaded substation in the regional distribution network, so the load balancing process can be ended.

[0124] Table 3 The top 5 T1 load transfer path pairing combinations and the predicted peak load rate of the associated substations after transfer

[0125]

[0126]

[0127] In summary, this embodiment constructs a load transfer association matrix for each substation based on the power grid topology; locks the heavily overloaded substation based on the daily load rate prediction curve of the substation and its feeder, and identifies the optional load transfer path based on the reliability constraint condition; uses the maximum value and average value of the peak load rate of the transfer-associated substation as dual indicators, explores substations with lighter loads or complementary peak-valley characteristics, selects the optimal load transfer path, and achieves regional load balancing.

[0128] The method of this embodiment scientifically selects the load transfer path to achieve balanced distribution of regional load among related substations. The logic is simple and easy to implement, avoiding the problem of inaccurate calculation of traditional methods.

[0129] This embodiment rationally utilizes daily load characteristics such as load differences and peak-valley complementarity among different substations, scientifically selects load transfer paths, and realizes balanced distribution of regional loads among related substations.

[0130] This embodiment can simply and accurately select the optimal load transfer path for the target substation, thereby realizing the priority transfer of the target heavy-load substation load to the substation with lighter load or peak-valley characteristic complementary substation, without the need to reconstruct the power grid topology on a large scale, and providing an effective basis and method for improving the utilization rate of power grid equipment and reducing the power grid capacity-load ratio.

[0131] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0132] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for load balancing of a city medium voltage distribution network, characterized in that: include: Step S1, selecting a load hotspot area of ​​the urban medium-voltage distribution network, determining optional path information for load transfer of each substation in the hotspot area based on the power system topology in the power production management system, and establishing a load transfer power system association matrix between each substation in the hotspot area according to the optional path information; Step S2, predicting the heavily overloaded substations in the regional power system under normal operation, and calculating the daily load rate prediction curve of the heavily overloaded substations and related feeders; Step S3: Based on the daily load rate prediction curve of the heavily overloaded substation and related feeders, determine all load transfer paths that are feasible for inclusion in the hotspot area load balancing solution; Step S4, the heavily overloaded substation transfers load according to all load transfer paths included in the feasibility of the load balancing plan for the hot spot area; calculates the maximum and average values ​​of the peak load rates of each substation after the transfer, and selects the optimal load transfer path from all load transfer paths included in the feasibility of the load balancing plan for the hot spot area according to the maximum and average values ​​of the peak load rates of each substation after the transfer, so as to obtain the load balancing plan for the hot spot area.

2. The method for load balancing of a city medium voltage distribution network according to claim 1, characterized in that: The step S1 includes: judging and restoring the substations in temporary operation mode in the regional power system, and modifying the load-to-power-transfer system association matrix thereof to obtain the load-to-power-transfer system association matrix.

3. The method for load balancing of a city medium voltage distribution network according to claim 1, characterized in that: The step S2 comprises: calculating a daily load rate prediction curve of each substation in a normal operation mode of the regional power system, and predicting a heavily overloaded substation according to the daily load rate prediction curve of each substation in a normal operation mode of the regional power system.

4. The method for load balancing of a city medium voltage distribution network according to claim 1, characterized in that: The load-to-power system association matrix A i,j as follows: In the formula, A i,j Indicates substation T i With substation T j The load-to-power system correlation matrix; K i and K j Respectively represent substation T i and T j The number of feeders; L i,m Indicates T i The mth feeder, L j,n Indicates T j The nth feeder of m,n Indicates L i,m and L j,n The electrical topological correlation between m,n 1 means L i,m and L j,n There is a load transfer path between m,n 0 means L i,m and L j,n There is no load transfer path between them.

5. The method for load balancing of a city medium voltage distribution network according to claim 1, characterized in that: The step S3 further comprises: Step S31: Select the substation with the highest predicted load rate from the heavily overloaded substations as the initial target substation T h According to the load-to-power system association matrix, the initial target substation T is determined h all optional load transfer paths to obtain a first optional load transfer path group; Step S32: Analyze all load transfer paths in the first optional load transfer path group to determine the initial target substation T h All load transfer paths that are feasible for the load balancing solution in the hot spot area are included to obtain the second optional load transfer path group.

6. The method for load balancing of a city medium voltage distribution network according to claim 5, characterized in that: include: The step S32 comprises: Step S321: According to the initial target substation T h and the daily load rate prediction curve of the related feeders, the initial target substation T h After the load is transferred through the current load transfer path, the initial target substation T is determined. h Whether the opposite substation or feeder is overloaded; If so, the current load transfer path is not included in the second optional load transfer path group; If not, the current load transfer path is included in the second optional load transfer path group; Step S322: select the next load transfer path from the first optional load transfer path group for transfer, repeat steps S321-S322 until all load transfer paths in the first optional load transfer path group are preferentially determined to obtain the second optional load transfer path group.

7. The method for load balancing of a city medium voltage distribution network according to claim 5, characterized in that: The step S4 comprises: Step S41: for each load transfer path R in the second optional load transfer path group, hi , the following formula is used to calculate the initial target substation T after the load transfer path is transferred. h and the opposite side substation T g The daily load factor prediction curve η Thi and η Tgi and peak load factor η Thi,P and η Tgi,P : R hi :T h -L h,m -L g,n -T g (1) or Thi,P =max(η Thi ) (2) or Tgi,P =max(η Tgi ) (3) In the formula, R hi represents the initial target substation T h and the opposite side substation T g The i-th load transfer path between h,m T h The mth feeder, L g,n T g The nth feeder; Step S42: Calculate η using the following formula: Thi,P and η Tgi,P The maximum value of the two T,i,max , and η Thi,P and η Tgi,P The average value η T,i,ave ; or T,i,max =max(η Thi,P ,or Tgi,P ) (4) or T,i,ave =ave(η Thi,P ,or Tgi,P ) (5) And select a minimum value using the following formula: or T,min =min(η T,1,max ,or T,2,max ,...,or T,M,max ) (6) Where η T,min represents the η corresponding to all load transfer paths T,i,max The minimum value between Step S43: Set parameter ɑ according to actual needs and determine the interval [η T,min , η T,min +ɑ]; wherein η in the interval T,i,max The corresponding load transfer path is a load transfer path that meets actual needs; Select η from all load transfer paths that meet actual needs. T,i,ave The minimum load transfer path is used to obtain the optimal load transfer path.

8. The method for load balancing of a city medium voltage distribution network according to claim 7, characterized in that: The step S4 further comprises: Step S44: Determine the initial target substation T h Whether there is an overload situation after the optimal load transfer path is used for transfer, If yes, proceed to step S45; If not, proceed to step S46; Step S45: Pair all the load transfer paths in the second optional load transfer path group to obtain multiple load transfer path combinations, and the multiple load transfer path combinations constitute a first optional load transfer path set; calculate the initial target substation T after transfer pair by pair. h , the first associated substation T g and the second associated substation T f The daily load rate prediction curve and peak load rate, and according to the initial target substation T after the transfer h , the first association T g Substation and the second associated substation T f The daily load rate prediction curve and the peak load rate are used to determine the optimal load transfer path combination, and then proceed to step S46; Step S46: The optimal load transfer path or the optimal load transfer path combination is the initial target substation T h The load balancing scheme; the initial target substation T h Transferring via the optimal load transfer path or the optimal load transfer path combination, proceeding to step S47; Step S47, selecting the next heavily overloaded substation in the hot spot area, and repeating steps S31 to S46 until there is no heavily overloaded substation in the hot spot area or the loads between the substations are balanced.

9. The method for load balancing of a city medium voltage distribution network according to claim 8, characterized in that: The step S45 comprises: Step S451: For each load transfer path combination in the first optional load transfer path set, calculate the initial target substation T h After the load is transferred through the corresponding load transfer path combination, the initial target substation T h The peak load rate of the first associated substation T g The peak load rate of the second associated substation T f The maximum value of the three and the average value of the three for the peak load rate; Step S452: According to the initial target substation T h After the load is transferred through the corresponding load transfer path combination, the initial target substation T h The peak load rate of the first associated substation T g The peak load rate of the second associated substation T f The maximum value of the three peak load rates and the average value of the three are used to determine the optimal load transfer path combination.

10. The method for load balancing of a city medium voltage distribution network according to claim 8, characterized in that: The step S4 further comprises: Step S48, calculating a daily load rate prediction curve of the substation after the optimal load transfer path or the optimal transfer path combination transfer; Step S49, based on the daily load rate prediction curve of each substation after transfer via the optimal load transfer path or the optimal transfer path combination, determine whether the daily load rate prediction curve of each substation in the hot spot area after transfer via the optimal load transfer path or the optimal transfer path combination meets the preset requirements. If so, the load balancing process of each substation in the hot spot area ends; if not, repeat steps S31 to S47.

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