Offshore wind farm composite ring power collection system topology planning method based on n-1 safety criterion

Abstract

A kind of offshore wind farm composite ring power collection system topology planning method based on N-1 safety criterion, including steps as follows: S1 obtains wind farm basic data, including wind turbine and substation node coordinates, wind turbine rated power, cable electrical parameter etc.;S2 generates candidate cable set based on basic data and cable intersection avoidance constraint set;S3 constructs scene set containing normal scene and all single cable fault scene, establishes optimization model with minimum total cost in whole life cycle as target, integrates cable construction / operation variable and direct current power flow power balance, node degree, cable intersection avoidance constraint;S4 obtains initial topology scheme by solving model;S5 carries out N-1 safety check to initial scheme for whole fault set, and illegal scene is included in fault set and is resolved again, until scheme meets N-1 criterion.The present application considers reliability and economy by non-predefined topology optimization and planning, reduces calculation complexity, and can also be extended to cross substation scene.

Description

TECHNICAL FIELD

[0001] The present application relates to offshore wind farm technology, in particular to a method for planning a composite ring power collection system topology of an offshore wind farm based on an N-1 safety criterion. BACKGROUND

[0002] In recent years, driven by the global renewable energy development goal, offshore wind power has become an important direction of energy transformation due to its abundant resources, gradually mature technology, and huge development potential. As the installed capacity continues to expand and the development of wind farms gradually extends to deeper waters, the planning of the power collection system of offshore wind farms will face increasingly high reliability requirements.

[0003] As the key link connecting wind turbines and offshore booster stations, the investment cost of the power collection system accounts for about 15%-30% of the total construction cost of the wind farm, and the rationality of the planning and design directly affects the economy and stability of the system. However, this type of optimization problem has NP-hard and non-convex characteristics, and as the scale of the wind farm expands, the problem complexity rises sharply, making it difficult to obtain a globally optimal solution. At the same time, the harsh environmental conditions at sea also result in much higher operating and maintenance costs than on land. Once the power collection system fails, it may cause serious economic and social consequences. Therefore, how to achieve a reasonable balance between economy and reliability is a problem that needs to be solved urgently.

[0004] The existing power collection system topology mainly includes radial, single-sided ring, double-sided ring, and star structures. Among them, the radial structure is widely used due to its simple structure, low cost, and easy control, but its reliability is insufficient and lacks effective fault recovery capability in the event of a fault. In contrast, the ring structure can achieve automatic switching through the setting of backup circuits after a fault occurs, improving the stability of the system, but correspondingly increasing the investment in cables and switchgear, resulting in a significant increase in construction costs. Therefore, the ring structure is usually used only in large or offshore wind farms and other scenarios with extremely high reliability requirements.

[0005] In terms of research methods, most existing power collection system planning is based on pre-defined topologies, such as using the CMST-based modeling method for radial power collection systems or the CVRP-based modeling method for ring-shaped power collection systems. At the same time, due to the high complexity of the problem, many studies rely on heuristic or meta-heuristic algorithms. Although such methods have high computational efficiency, they lack global optimality guarantees and the quality of the solution is difficult to evaluate. In contrast, the planning method can obtain a globally optimal solution through precise modeling, but its application in the field of power collection system planning is limited.

[0006] In addition, the research on non-predefined topologies is still not in-depth. For example, existing work proposes a multi-ring structure of partial redundant ring topology or a cross-boosting station grid connection mechanism, which balances economy and reliability to some extent, but these methods still rely on heuristic solutions and cannot achieve global optimal solutions, and lack sufficient characterization of the N-1 safety criterion. In power transmission network planning, the N-1 safety criterion has become a standard requirement, that is, the system can still operate safely after any unit failure. However, existing research on offshore wind power collection system planning that meets the N-1 criterion is still limited to traditional double-sided ring structures, and lacks exploration of more flexible and economical topologies.

[0007] In summary, the prior art has the following shortcomings:

[0008] 1. Most research is limited to predefined topologies (especially double-sided rings), which lack flexibility;

[0009] 2. The planning method relies on heuristic or meta-heuristic algorithms, which lack global optimality guarantees;

[0010] 3. The research on non-conventional topologies and their N-1 criterion is still insufficient.

[0011] It should be noted that the information disclosed in the above background section is only for understanding the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0012] The main purpose of the present application is to overcome the defects in the background art, and to provide a topology planning method for a composite ring power collection system of an offshore wind farm based on the N-1 safety criterion.

[0013] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0014] A topology planning method for a composite ring power collection system of an offshore wind farm based on the N-1 safety criterion, comprising the following steps:

[0015] S1, obtaining wind farm basic data, including the spatial coordinates of wind turbine nodes and substation nodes, wind turbine rated power, cable electrical parameters, system life cycle parameters and electricity price information;

[0016] S2, based on the basic data, generating a candidate cable set and a set of cable intersection avoidance constraints;

[0017] S3, constructing a scenario set containing normal scenarios and all single-cable fault scenarios, establishing an optimization model with the minimum total cost of the entire life cycle as the target, the model integrates cable construction state variables and scenario-driven operation state variables, and introduces power balance constraints based on DC power flow, node degree constraints and cable intersection avoidance constraints;

[0018] S4, solving the optimization model to obtain an initial topology scheme;

[0019] S5, performing a full set of fault N-1 safety check on the initial topology scheme, if there is a scenario that violates the safety criterion, it is included in the fault set and re-solved until the scheme meets the N-1 safety criterion, and the final topology planning result is output.

[0020] Further, the generation of the candidate cable set in step S2 adopts a screening method based on spatial distance and clustering analysis, specifically including: first, calculating the Euclidean distance between each other according to the coordinate information of all nodes, then setting a distance threshold, and filtering out those potential cable connections whose length exceeds the threshold; further, using a clustering algorithm to divide the wind farm area into several partitions, and only keeping the node pairs located in the same partition as candidate cables, so as to effectively control the problem size while maintaining optimization potential.

[0021] Further, the objective function of the optimization model in step S3 is constructed by the following way:

[0022] Cable construction cost, calculated by accumulating the construction cost of each candidate cable and the product of its corresponding binary construction decision variable;

[0023] System operation and maintenance cost, calculated by multiplying the cable construction cost by a fixed proportion coefficient, and then uniformly distributing it to the entire system life cycle through the annuity discounting formula;

[0024] System loss cost, based on the assumption of direct current flow, the product of the resistance value of each cable and the square value of the transmission power is accumulated to obtain the annual network energy cost, and then it is extended to the whole life cycle through discounting calculation;

[0025] Wind curtailment cost, by introducing a large enough penalty coefficient, multiplied by the sum of wind curtailment power of all nodes in all scenarios, to ensure that the wind curtailment amount is zero in the process of minimizing the objective function.

[0026] Further, the constraint of the scenario-driven operating state variable in step S3 is realized by the following mechanism:

[0027] For any candidate cable and any scenario, the value of the operating state variable is constrained between the value of the construction state variable and zero, that is, the cable cannot be operated if it is not constructed, and the cable can choose to operate or not operate if it is constructed;

[0028] For any scenario predefined as a fault scenario, the operating state variable of the corresponding specific cable is forced to be zero to simulate the state of the cable failure and exit operation.

[0029] Further, the power balance constraint based on DC power flow in step S3 is established by the following process:

[0030] For each wind farm node and each scenario, its power balance equation constrains the sum of all cable power flowing out of the node to be equal to the difference between its wind power and possible curtailment power;

[0031] For each substation node and each scenario, its power balance equation constrains the sum of all cable power flowing into the node to be equal to its power aggregated to the grid;

[0032] For each candidate cable and each scenario, its DC power flow equation is established by introducing a node voltage phase angle variable and based on the cable susceptance value, while coupling this equation with the cable operation status variable by using the big M method, so that this constraint only takes effect when the cable is in operation;

[0033] The voltage phase angle of any one substation node in the system is set to zero, which is used as the reference phase of the entire network;

[0034] For each candidate cable and each scenario, the absolute value of its transmission power is constrained not to exceed the product of its carrying capacity and operation status variable, to ensure that only the cable in operation is allowed to transmit power, and the transmission power cannot exceed the limit;

[0035] For each wind farm node and each scenario, its curtailment power is constrained between zero and the wind power of the node.

[0036] Further, the node degree constraint in step S3 includes: in the final planning scheme, the total number of cables connected to any one wind farm node is greater than or equal to 2, to ensure that after any single cable failure, the wind farm can still remain connected to the grid through the remaining connections;

[0037] The cable cross-avoidance constraint includes: all candidate cable pairs that exist in cross in the two-dimensional plane are identified by geometric calculation, and a constraint is added for each pair of such cross cables to ensure that the sum of their corresponding construction status variables does not exceed 1, i.e. two cross cables are prohibited from being selected into the final scheme at the same time.

[0038] Further, the simplification and iteration verification process of the fault scenario set in step S3 includes:

[0039] When constructing the initial fault set of the main optimization model, only those scenarios in which the cables directly connected to the substation nodes fail are included, so as to greatly reduce the number of fault scenarios that need to be considered at the same time;

[0040] After the initial topology scheme is solved, a security check process including all possible single cable fault scenarios is started to comprehensively verify the N-1 safety of the scheme;

[0041] If it is found in the check process that some fault scenarios will cause system constraints to be violated, these scenarios are added to the fault set of the main optimization model, and the model is solved again;

[0042] The solving and checking process is repeatedly performed until the finally obtained topology scheme can pass the security check under all single cable fault scenarios and fully meet the N-1 safety criterion.

[0043] Further, the solving of the optimization model in step S4 is realized by using a mixed integer programming algorithm and by calling an external optimization solver; and the full fault set N-1 safety check in step S5 is realized by constructing an auxiliary verification model for the final topology scheme, which includes all single cable fault scenarios, and by solving the DC optimal power flow to check whether there is overload or wind curtailment, so as to confirm the N-1 compliance.

[0044] Further, the method naturally supports the topology planning across substations by not presetting the ownership relationship of wind turbines and substations in modeling, allows the power flow under fault scenarios to be dynamically redistributed among multiple substations, and thus improves the reliability and economy of the system.

[0045] A computer program product comprising a computer program which, when executed by a processor, implements the offshore wind farm composite ring power collection system topology planning method.

[0046] The present application has the following beneficial effects:

[0047] The present application proposes an offshore wind farm composite ring power collection system topology planning method based on the N-1 safety criterion, which can realize flexible and non-traditional "N-1 composite ring" power collection system optimization planning under the N-1 safety criterion, so as to simultaneously consider economy and reliability, and effectively solve the limitations of the prior art.

[0048] The core of the method is to construct a scene set containing normal scenes and all single cable fault scenes, and to realize the optimization of non-predefined topology through a planning model. Specifically, the minimum full life cycle cost (covering investment, maintenance, power loss, wind abandonment cost, etc.) is taken as the target, the scene-driven cable operation state constraint (distinguishing between construction variables and operation variables), the power balance constraint based on direct current flow (including power balance of wind turbine nodes and substation nodes, voltage phase angle constraint, etc.), cable non-intersection constraint and reliability constraint of wind turbine node degree >=2 are designed, and then a composite ring topology meeting the N-1 safety criterion and being more economical is generated, thereby breaking through the limitations of traditional fixed topologies (such as double-sided ring, etc.).

[0049] The fixed topologies commonly used in the existing industry (such as double-sided ring, zoned multi-ring / CSI, etc.) are strongly limited by structural constraints when meeting the N-1 safety criterion, resulting in that the overall cable length, loss, maintenance cost, etc. are difficult to achieve global optimization; while the heuristic method (such as Sweep+CWS) has faster solving speed, but due to the zoning or regularization processing, the solution quality is further limited. Unlike the above, the present application proposes an N-1 composite ring model without presetting topology, which jointly considers direct current flow, node degree and non-intersection constraint on the basis of modeling based on fault scene set, and can optimize to obtain a topology which is more economical and meets the N-1 safety criterion. One of the major innovations is to propose a scene-driven non-predefined topology modeling method, which can explore a better N-1 structure in a larger solution space.

[0050] The specific advantages of the present application are reflected in many aspects: first, the model of the N-1 criterion fault scene is accurately completed; second, by deleting the topology constraint in the traditional planning problem, a solution better than the traditional ring structure can be found; third, the optimization scheme is used for solving, which ensures the stability and optimality of the solution; fourth, in view of the problem that the calculation complexity is usually too large, the present application reduces the solving complexity by screening the candidate submarine cables in advance and using the key fault set strategy of "first selecting the cables close to the substation, and then expanding through iteration".

[0051] In addition, the present application also has good scalability: since the model has flexibility in topology shape, it can be naturally extended to cross-substation scenarios to realize N-1 topology planning allowing power flow to be redistributed between multiple step-up stations after failure.

[0052] Other beneficial effects of the embodiments of the present application will be further described below. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 The vector cross product judgment schematic diagram for assisting in judging the cable geometric intersection relationship in the embodiments of the present application;

[0054] Figure 2 This is a flowchart of the topology planning scheme for the offshore wind farm power collection system according to an embodiment of the present invention;

[0055] Figure 3 A schematic diagram showing the coordinates of wind turbines and substations, and candidate submarine cables for a single-substation offshore wind farm.

[0056] Figure 4 This is a diagram showing the topology planning results of sweep+CWS in Comparative Example 1;

[0057] Figure 5 This is a diagram showing the results of the bilateral ring topology planning in Comparative Example 2;

[0058] Figure 6 This is a diagram showing the topology planning results for the multi-ring structure in Comparative Example 3;

[0059] Figure 7 This is a diagram showing the topology planning results of the N-1 composite ring in Embodiment 1 of the present invention;

[0060] Figure 8 This is a schematic diagram showing the coordinates of the wind turbines and substations, as well as the candidate submarine cables, for the Sheringham Shoal offshore wind farm (dual booster stations).

[0061] Figure 9 This is a diagram showing the results of the bilateral ring topology planning in Comparative Example 4;

[0062] Figure 10 This is a diagram showing the CSI structure topology planning results for Comparative Example 5;

[0063] Figure 11 This is a diagram showing the topology planning results of the N-1 composite ring in Embodiment 2 of the present invention;

[0064] Figure 12 This is a flowchart of the overall topology planning method for a composite ring collector system in an offshore wind farm based on the N-1 safety criterion. Detailed Implementation

[0065] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0066] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0067] The present application aims to solve the limitations of the traditional fixed topology (such as double-sided ring) in the planning of the existing offshore wind farm power collection system, such as insufficient flexibility, lack of global optimality of heuristic algorithms, and insufficient description of N-1 safety criteria, and proposes a compound ring power collection system topology planning method based on N-1 safety criteria. The method builds a scenario set containing normal scenarios and all single-cable fault scenarios, establishes a planning model with the minimum total life cycle cost (investment, maintenance, power loss, and wind power abandonment cost) as the target, integrates cable construction / operation variables, DC power flow power balance constraints, node degree constraints, and cable intersection avoidance constraints to realize non-predefined topology optimization, which not only guarantees N-1 reliability and global optimal solution, but also reduces computational complexity through candidate cable screening and key fault set dimension reduction, and can be naturally extended to the cross-substation scenario.

[0068] Referring to Figure 12 The embodiment of the present application provides a compound ring power collection system topology planning method for offshore wind farms based on N-1 safety criteria, comprising the following steps:

[0069] Step S1, obtaining wind farm basic data, including the spatial coordinates of wind turbine nodes and substation nodes, wind turbine rated power, cable electrical parameters, system life cycle parameters, and electricity price information.

[0070] Step S2, based on the basic data, generating a candidate cable set and a cable intersection avoidance constraint set.

[0071] In some embodiments, the generation of the candidate cable set in step S2 adopts a screening method based on spatial distance and clustering analysis, specifically including: first calculating the Euclidean distance between all nodes according to the coordinate information of all nodes, and then setting a distance threshold to filter out potential cable connections whose length exceeds the threshold; in some embodiments, a clustering algorithm is used to divide the wind farm area into several partitions, and only node pairs located in the same partition are retained as candidate cables, thereby effectively controlling the problem size while maintaining optimization potential.

[0072] Step S3, constructing a scenario set containing normal scenarios and all single-cable fault scenarios, establishing an optimization model with the minimum total life cycle cost as the target, the model integrates cable construction state variables and scenario-driven operation state variables, and introduces power balance constraints based on DC power flow, node degree constraints, and cable intersection avoidance constraints.

[0073] In some embodiments, the objective function of the optimization model in step S3 is constructed by: cable construction cost, calculated by summing the product of the construction cost of each candidate cable and its corresponding binary construction decision variable; system operation and maintenance cost, calculated by multiplying the cable construction cost by a fixed proportion coefficient, and then evenly distributing it to the entire system life cycle through the annuity discount formula; system network loss cost, based on the DC power flow assumption, the product of the resistance value of each cable and the square value of the transmission power is summed up to get the annual network loss energy cost, and then it is extended to the whole life cycle through discount calculation; wind curtailment cost, by introducing a large enough penalty coefficient, multiplied by the sum of wind curtailment power of all wind turbine nodes in all scenarios, to ensure that the wind curtailment is forced to zero in the process of minimizing the objective function.

[0074] In some embodiments, the scenario-driven operating state variable constraint in step S3 is achieved by the following mechanism: for any candidate cable and any scenario, the value of its operating state variable is constrained between the value of its construction state variable and zero, i.e. the cable cannot be operated if it is not constructed, and the cable can be operated or not operated if it is constructed; for any scenario predefined as a fault scenario, the operating state variable of the specific cable corresponding to the scenario is forced to zero to simulate the state of the cable failing to operate.

[0075] In some embodiments, the DC power flow-based power balance constraint in step S3 is established by the following process: for each wind turbine node and each scenario, its power balance equation constrains the sum of all cable power flowing into the node to be equal to the difference between its wind power generation and possible wind curtailment power; for each substation node and each scenario, its power balance equation constrains the sum of all cable power flowing out of the node to be equal to the power collected to the grid; for each candidate cable and each scenario, by introducing a node voltage phase angle variable and establishing its DC power flow equation based on the cable susceptance value, and coupling the equation with the operating state variable of the cable using the big M method, the constraint only takes effect when the cable is operating; the voltage phase angle of any substation node in the system is set to zero, which is used as the reference phase of the entire network; for each candidate cable and each scenario, the absolute value of its transmission power is constrained not to exceed the product of its carrying capacity and operating state variable, to ensure that only operating cables are allowed to transmit power, and the transmission power cannot exceed the limit; for each wind turbine node and each scenario, its wind curtailment power is constrained between zero and the wind power generation of the node.

[0076] In some embodiments, the node degree constraint in step S3 comprises: in the final planning scheme, the total number of cables connected to any one wind turbine node is greater than or equal to 2, to ensure that the wind turbine can remain connected to the grid through the remaining connections after any single cable failure; and the cable intersection avoidance constraint comprises: identifying all candidate cable pairs that intersect in a two-dimensional plane through geometric calculation, and adding a constraint for each such intersecting cable pair to ensure that the sum of their corresponding construction state variables is not greater than 1, i.e., to prohibit two intersecting cables from being selected into the final scheme at the same time.

[0077] In some embodiments, the simplification and iterative verification process for the set of failure scenarios in step S3 comprises: when constructing the initial failure set of the main optimization model, only including scenarios in which the cables directly connected to the substation node fail, to greatly reduce the number of failure scenarios that need to be considered at the same time; after obtaining the initial topology scheme, starting a security check process including all possible single cable failure scenarios to comprehensively verify the N-1 safety of the scheme; if it is found in the verification process that there are certain failure scenarios that will cause system constraints to be violated, then adding these scenarios to the failure set of the main optimization model and re-solving the model; repeatedly performing the solving and verification process until the final topology scheme can pass the safety check under all single cable failure scenarios and fully meet the N-1 safety criterion.

[0078] Step S4, solving the optimization model to obtain an initial topology scheme.

[0079] In some embodiments, the solving of the optimization model in step S4 is achieved by using a mixed integer programming algorithm and by calling an external optimization solver; and the full failure set N-1 safety check in step S5 is achieved by constructing an auxiliary verification model for the final topology scheme that includes all single cable failure scenarios, which checks whether there is overload or curtailment by solving a direct current optimal power flow, to confirm N-1 compliance.

[0080] Step S5, performing a full failure set N-1 safety check on the initial topology scheme, if there is a scenario that violates the safety criterion, then adding it to the failure set and re-solving, until the scheme meets the N-1 safety criterion, and outputting the final topology planning result.

[0081] In some embodiments, the method naturally supports cross-substation topology planning by not presetting the ownership relationship between wind turbines and substations in modeling, allowing the power flow under failure scenarios to be dynamically redistributed between multiple substations, thereby improving the reliability and economy of the system.

[0082] The offshore wind farm composite ring power collection system topology planning method based on the N-1 safety criterion comprises the following steps: constructing a scenario set comprising normal and all single-cable fault scenarios, and establishing an optimization model with the minimum total cost in the whole life cycle as the target.

[0083] The specific embodiments of the present application, algorithm examples and experimental verification are further described below.

[0084] A kind of offshore wind farm composite ring power collection system topology planning method based on N-1 safety criterion, the following model is constructed:

[0085] Objective function

[0086] Suppose a complete weighted directed graph , wherein including substation node And fan node , Represent all candidate cables connecting nodes, the cost of each candidate cable , , Binary decision variable representing whether candidate cable Is built, candidate cable When it is built. At the same time, set the resistance of each candidate cable , , the power flow of each cable is represented by variable . Set the wind curtailment as , in order to ensure that the power collection system meets the "N-1" safety constraint, multiply the cost by a maximum number , such as To ensure that the wind curtailment cost term in the objective function is 0. The objective function of the economic planning model of the power collection system meeting the "N-1" safety constraint is as follows:

[0087] (1) ​

[0088] where , , , are the cable construction cost, system operation and maintenance cost, system network loss cost and wind curtailment cost of the collection system, respectively, which can be expressed as

[0089] (2)

[0090] (3)

[0091] (4)

[0092] (5)

[0093] (6)

[0094] where the cable construction cost is the cost of each candidate cable multiplied by the sum of the construction decision variables; the system operation and maintenance cost can be regarded as the construction cost multiplied by a fixed coefficient; in the system network loss cost, represents the network loss cost of the wind farm throughout its life cycle, is the annual inflation rate. Meanwhile, the direct current flow assumption is adopted in the model, and the per-unit value of each node voltage is 1, so , and thus the network loss cost of each cable is written as . The wind curtailment cost takes M as a maximum number to ensure that the value of this term is 0.

[0095] Fault set constraints

[0096] When modeling the “N-1” fault set, we use to represent the set of all scenarios, and use binary variables to represent whether candidate cable is in normal operation in scenario t , which is distinguished from the variable representing whether candidate cable is constructed. represents that cable t is in normal operation in scenario . The fault set constraint determined in this way is:

[0097] (7)

[0098] (8)

[0099] where constraint (7) represents that the value of is between 0 and , i.e., the condition for the cable to be constructed to be in normal operation; constraint (8) is the fault cable constraint, which represents that in the fault scenario In particular, the corresponding pre-set fault cable cannot operate normally.

[0100] Power balance constraint based on DC power flow

[0101] The DC power flow based transmission planning model is in the following form:

[0102] (9)

[0103] (10)

[0104] (11)

[0105] (12)

[0106] (13)

[0107] (14)

[0108] Constraint (9) is the power balance constraint of point i, which represents the power balance equation of each wind turbine node i in each scenario; constraint (10) is the power balance constraint of the substation node j in each scenario; constraint (11) represents the transmission power of each candidate cable The DC power flow constraint considering phase angle, constraint (12) is the reference node constraint of the substation node for the power flow model; constraints (13) and (14) limit the transmission power of each candidate cable and the abandoned wind power of each wind turbine node i; due to the introduction of scenario variable t, the size of the model is much larger than that of the traditional two-sided ring planning model.

[0109] Cable non-intersection and node degree constraint

[0110] Similarly, the model describes the constraints of cable intersection avoidance and wind turbine node degree.

[0111] (15)

[0112] Where the cable pair (AB, CD) belongs to if and only if and as shown in Figure 1 .

[0113] Under the condition of meeting the "N-1" safety constraint, it is easy to obtain that the degree of each wind turbine node at this time should be greater than or equal to 2:

[0114] (16)

[0115] Since, the modeling of the collection system optimization model for the "N-1" full fault set is completed, a large-scale MIQP model is obtained:

[0116]

[0117] In the model, the number of variables is of the order of and will become very large with the increase of the number of candidate cables |L|. Taking a wind farm with more than forty wind turbines as an example, the number of variables will reach one million, which brings great difficulty to the solution, and the following simplification technique can be used:

[0118] Fault scenario set simplification: in the model of the method of the application, the fault scenario set contains the scenario of the failure of each cable alone, which will lead to an excessively large model size when the number of wind turbines is large, so that the model is not suitable for direct solution. Considering that in the actual collection system, the cables close to the substation node have a higher carrying capacity, that is, the scenario of the failure of the cable close to the substation can be considered as the most serious failure scenario. If a cable planning result can keep normal operation under these most serious failure scenarios, it should also be able to meet the constraint conditions under all failure scenarios. Therefore, the range of the fault set is narrowed, and the scenario of the failure of the cable directly connected to the substation is focused on, so that the size of the fault set is reduced from the number of all candidate cables to the number of cables directly connected to the substation , so that the size of the solution model can be significantly reduced, the reliability of the planning result is ensured, and the consumption of computing resources is reduced.

[0119] The simplified model is in principle in line with the "N-1" safety constraint, and further strict checking is carried out. The main program for solving the method of the application is based on the model after the simplified fault set, and after the program solves the planning result, the model considering the complete fault scenario set is used as subsequent safety checking to verify the feasibility of the planning result. If there is a scenario that violates the constraint condition, the scenario is included in the fault set of the main program, and the main program is solved again until the final solution passes the safety checking, which can prove that the final planning result completely meets the "N-1" safety constraint.

[0120] The overall planning scheme flow of the embodiment of the application is shown in Figure 2 .

[0121] The application has good scalability. Due to the flexibility of the model in the topological shape, the model can be naturally extended to the scenario across the substation, realizing the N-1 topology planning allowing the power flow to be redistributed among multiple booster stations after failure.

[0122] Alternative embodiments:

[0123] (1) N-1 compound ring without crossing stations

[0124] Under the premise that the scenario modeling of the main scheme and the power balance constraint based on direct current flow, node degree constraint and cable non-crossing constraint remain unchanged, the cross-station connection edge is limited (only the compound ring of the nearest substation of each wind turbine is allowed to be closed). This is still a non-predefined topology and meets N-1.

[0125] (2) Degree constraint is tightened to “wind turbine degree = 2”

[0126] The local multi-ring / bridge freedom is converged to a single loop or quasi-loop, making the network form more regular and the engineering implementation more intuitive.

[0127] (3) Line loss term is not included in the target, only as a feasibility constraint

[0128] In order to quickly output a preliminary scheme, the network loss cost can be temporarily ignored, and only the upper limit of line transmission and the voltage phase angle difference is kept within the safety boundary. It still meets N-1 and engineering constraints.

[0129] Experimental verification

[0130] Experiment 1:

[0131] 36 wind turbines, single booster station, wind farm wind turbine and substation coordinates, candidate sea cable schematic diagram as shown in Figure 3 .

[0132] This experiment compares a variety of examples, as shown in Table 1.

[0133] Table 1

[0134]

[0135] Planning results: Figure 4 The sweep+CWS topology planning results of Comparative Example 1 are shown; Figure 5 The double-ring topology planning results of Comparative Example 2 are shown; Figure 6 The multi-ring structure topology planning results of Comparative Example 3 are shown; Figure 7 The N-1 compound ring topology planning results of Embodiment 1 of the present application are shown.

[0136] Cost comparison results (unit: 100,000 yuan RMB), as shown in Table 2.

[0137] Table 2

[0138]

[0139] The experimental results show that the cost of the present application (Example 1) is reduced by 18.2%, 16.4%, and 16.6% compared with the traditional method (Comparative Examples 1-3), respectively.

[0140] Experiment 2:

[0141] 88 wind turbines, double voltage boosting station, actual Sheringham Shoal offshore wind farm, wind turbine and substation coordinates, candidate submarine cable schematic diagram as Figure 8 .

[0142] Various examples are compared in the experiment, as shown in Table 3.

[0143] Table 3

[0144]

[0145] Planning results: Figure 9 The planning results of the bilateral ring topology of Comparative Example 4 are shown; Figure 10 The planning results of the CSI structure topology of Comparative Example 5 are shown; Figure 11 The planning results of the N-1 composite ring topology of Example 2 of the present application are shown.

[0146] The cost comparison results (unit: million RMB) are shown in Table 4.

[0147] Table 4

[0148]

[0149] The experimental results show that the cost of the present application (Example 2) is reduced by 6.7% and 13.3% compared with the traditional method (Comparative Examples 4-5), respectively.

[0150] The present application also provides a storage medium for storing a computer program, which is executed to perform at least the method described above.

[0151] The present application also provides a control device comprising a processor and a storage medium for storing a computer program; wherein the processor is used to execute the computer program to perform at least the method described above.

[0152] The present application also provides a processor which executes a computer program to perform at least the method described above.

[0153] The storage medium can be implemented by any type of nonvolatile storage device, or a combination thereof. The nonvolatile memory can be a Read Only Memory (ROM), a Programmable Read-Only Memory (PROM), an Erasable Programmable Read-Only Memory (EPROM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a Ferromagnetic Random Access Memory (FRAM), a Flash Memory, a magnetic surface storage, an optical disc or a Compact Disc Read-Only Memory (CD-ROM). The magnetic surface storage can be a magnetic disc memory or a magnetic tape memory. The storage medium described in the embodiments of the present application is intended to include, but is not limited to, these and any other suitable type of memory.

[0154] In several embodiments provided by the present application, it should be understood that the disclosed system and method can be implemented in other manners. The described device embodiments are merely schematic, and the division of the units is merely a logical function division. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed coupling or direct coupling or communication connection between the components can be indirect coupling or communication connection through some interface, device or unit, and can be electrical, mechanical or other forms.

[0155] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place or distributed on a plurality of network units; some or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0156] In addition, each functional unit in the embodiments of the present application can be integrated into one processing unit, or each unit can be a separate unit, or two or more units can be integrated into one unit; the integrated unit can be implemented in the form of hardware, or in the form of hardware plus software functional units.

[0157] Those skilled in the art can understand that all or part of the steps of the above-mentioned method embodiments can be completed by program instruction related hardware, and the foregoing program can be stored in a computer readable storage medium, and the program performs the steps of the above-mentioned method embodiments when executed; and the foregoing storage medium includes a mobile storage device, a read-only memory (ROM), a random access memory (RAM), a magnetic disc or an optical disc and various storage medium capable of storing program codes.

[0158] Alternatively, the integrated unit of the present application can be stored in a computer readable storage medium if it is realized in the form of a software function module and sold or used as an independent product. Based on such understanding, the technical solutions of the embodiments of the present application can be embodied in the form of a software product, and the computer software product is stored in a storage medium, includes several instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute all or part of the methods described in the embodiments of the present application. The foregoing storage medium includes a mobile storage device, a ROM, a RAM, a magnetic disc or an optical disc and various storage medium capable of storing program codes.

[0159] The methods disclosed in the several method embodiments provided by the present application can be combined arbitrarily without conflict to obtain new method embodiments.

[0160] The features disclosed in the several product embodiments provided by the present application can be combined arbitrarily without conflict to obtain new product embodiments.

[0161] The features disclosed in the several method or device embodiments provided by the present application can be combined arbitrarily without conflict to obtain new method embodiments or device embodiments.

[0162] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For those skilled in the art of the present application, without departing from the concept of the present application, a number of equivalent substitutions or obvious modifications can be made, and the performance or use is the same, which should be regarded as belonging to the protection scope of the present application.

Claims

1. A method for topology planning of a composite ring power collection system for offshore wind farms based on N-1 security criterion, characterized in that, The method comprises the following steps: S1, obtaining wind farm basic data, including spatial coordinates of wind turbine nodes and substation nodes, wind turbine rated power, cable electrical parameters, system life cycle parameters and electricity price information; S2, based on the basic data, generating a candidate cable set and a cable intersection avoidance constraint set; Wherein the generation of the candidate cable set specifically comprises: first calculating the spatial distance between each other according to the coordinate information of all nodes, and then setting a distance threshold to filter out potential cable connections whose length exceeds the threshold; S3, constructing a scene set containing normal scenes and all single cable fault scenes, and establishing an optimization model according to the cable construction cost, system operation cost, system network loss cost and wind curtailment cost, the objective function of the optimization model aims to minimize the total cost in the whole life cycle, the optimization model integrates the construction state variables of the candidate cables and the operation state variables driven by the scene set, establishes the constraints of the scene-driven cable operation state variables, and distinguishes the construction state variables and the operation state variables; and introducing: power balance constraint based on direct current flow, including power balance and voltage phase angle constraint of wind turbine nodes and substation nodes; reliability constraint of wind turbine node degree ≥2; and cable intersection avoidance constraint; S4, solving the optimization model to obtain an initial topology scheme; S5, performing N-1 safety check on the initial topology scheme, if there is a scene that violates the safety criterion, it is included in the fault set and solved again until the scheme meets the N-1 safety criterion, and the final topology planning result is output.

2. The offshore wind farm composite ring power collection system topology planning method according to claim 1, characterized in that, In step S2, the spatial distance is Euclidean distance; further, a clustering algorithm is used to divide the wind farm area into several partitions, and only the node pairs located in the same partition are retained as candidate cables, so as to effectively control the problem size while maintaining optimization potential.

3. The offshore wind farm composite ring power collection system topology planning method according to claim 1 or 2, characterized in that, In step S3: The cable construction cost is calculated by adding the construction cost of each candidate cable and the product of the corresponding binary construction decision variable; The system operation cost is calculated by multiplying the cable construction cost by a fixed proportion coefficient, and then uniformly distributing it to the entire system life cycle through the annuity discount formula; The system network loss cost is calculated by adding the product of the resistance value and the square value of the transmission power of each cable, obtaining the annual network loss energy cost, and then extending it to the whole life cycle through discount calculation; The wind curtailment cost is calculated by multiplying a large enough penalty coefficient with the sum of wind curtailment power of all wind turbine nodes in all scenarios, so as to ensure that the wind curtailment amount is zero in the process of minimizing the objective function.

4. The offshore wind farm composite ring power collection system topology planning method according to claim 1 or 2, characterized in that, The constraint of the scene-driven operation state variable in step S3 is realized by the following mechanism: For any candidate cable and any scene, the value of the operation state variable is constrained between the value of the construction state variable and zero, that is, the cable cannot run if it is not constructed, and the cable can choose to run or not run if it is constructed; For any scenario predefined as a fault scenario, the operating state variable of its corresponding specific cable is forced to be zero to simulate the state that the cable is out of operation due to failure.

5. The offshore wind farm composite ring power collection system topology planning method according to claim 1 or 2, characterized in that, The power balance constraint based on DC power flow in step S3 is established by the following process: For each wind farm node and each scenario, the power balance equation constrains the sum of all cable power flowing out of the node to be equal to the difference between its wind power generation and possible curtailed wind power; For each substation node and each scenario, the power balance equation constrains the sum of all cable power flowing into the node to be equal to its power aggregated to the grid; For each candidate cable and each scenario, the DC power flow equation is established by introducing the node voltage phase angle variable and based on the cable susceptance value, while the equation is coupled with the operating state variable of the cable by using the large M method, so that the constraint only takes effect when the cable is in operation; The voltage phase angle of any substation node in the system is set to zero, which is used as the reference phase of the entire network; For each candidate cable and each scenario, the absolute value of its transmission power is constrained to be less than the product of its carrying capacity and the operating state variable, to ensure that only the cable in operation is allowed to transmit power, and the transmission power cannot exceed the limit; For each wind farm node and each scenario, the curtailed wind power is constrained between zero and the wind power generation of the node.

6. The offshore wind farm composite ring power collection system topology planning method according to claim 1 or 2, characterized in that, The reliability constraint of the wind farm node degree ≥ 2 in step S3 specifically includes: in the final planning scheme, the total number of cables connected to any wind farm node is greater than or equal to 2, to ensure that the wind farm can still remain connected to the grid through the remaining connections after any single cable failure; The cable intersection avoidance constraint includes: all candidate cable pairs that intersect in the two-dimensional plane are identified through geometric calculation, and a constraint is added for each pair of such intersecting cables to ensure that the sum of their corresponding construction state variables is less than or equal to 1, i.e. two intersecting cables are prohibited from being selected into the final scheme at the same time.

7. The offshore wind farm composite ring power collection system topology planning method according to claim 1 or 2, characterized in that, In steps S3 to S5, the specific process of simplifying and iteratively verifying the fault scenario set includes: In the initial fault set for building the main optimization model, only those scenarios in which the cables directly connected to the substation nodes fail are included, thereby greatly reducing the number of fault scenarios that need to be considered simultaneously; After obtaining the initial topology scheme, a security verification process including all possible single cable fault scenarios is started to comprehensively verify the N-1 safety of the scheme; If it is found in the verification process that there are certain fault scenarios that will cause the system constraints to be violated, these scenarios are added to the fault set of the main optimization model, and the model is solved again; The solving and verification process is repeated until the final topology scheme can pass the safety verification under all single cable fault scenarios and fully meet the N-1 safety criterion.

8. The offshore wind farm composite ring power collection system topology planning method according to claim 1 or 2, characterized in that, The solution of the optimization model in step S4 is achieved by using a mixed integer programming algorithm and by calling an external optimization solver; the full fault set N-1 safety check in step S5 is achieved by constructing an auxiliary verification model for the final topology scheme, which contains all single-cable fault scenarios, and checking whether there is overload or wind curtailment by solving the DC optimal power flow, so as to confirm the N-1 compliance.

9. The offshore wind farm composite ring power collection system topology planning method according to claim 1 or 2, characterized in that, The method naturally supports cross-substation topology planning by not presetting the ownership relationship between the wind turbine and the substation in modeling, and allows the power flow under the fault scenario to be dynamically redistributed between multiple substations.

10. A computer program product comprising a computer program, characterized in that, The computer program, when executed by a processor, implements the offshore wind farm composite ring power collection system topology planning method according to any one of claims 1 to 9.

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