Power system economic dispatching method considering line dynamic capacity increase and related device

Abstract

The invention provides a power system economic dispatching method considering dynamic capacity increase of a line and a related device. The method comprises the following steps: establishing a target function taking the minimum unit operation cost of a power system as a target; determining constraint conditions of the target function according to parameters of the power system; solving the economic dispatching model to obtain a current square term of each line in the power system; performing thermal stability verification on each line according to the current square term of each line, and determining an out-of-limit line; and carrying out iterative solution on the electric power economic dispatching model to obtain an economic dispatching scheme of the electric power system. According to the method, the power adjustment rate constraint is determined, the unit climbing dynamic process is considered in detail, the calculation precision of the line temperature rise is improved, thermal stability verification is carried out on the solving result of the economic dispatching model, constraint iteration generation is carried out aiming at a high-dimensional constraint set caused by considering the unit climbing dynamic process, and the calculation precision of the line temperature rise is improved. The calculation complexity of the economic dispatching model of the power system is reduced, and the solving speed and efficiency of the model are improved.

Description

Technical Field

[0001] This application relates to the technical field of electrical engineering, and particularly to an economic dispatch method and related devices for a power system considering line dynamic capacity increase. Background Art

[0002] The economic dispatch problem is one of the basic problems in the operation of a power system. Its goal is to dispatch units to meet the total demand at the minimum cost on the premise of meeting the balance between supply and demand and various constraint conditions.

[0003] Traditional economic dispatch methods usually stipulate the transmission capacity of a line with a conservative constant, which only represents the safe transmission capacity under multiple typical working conditions. Under actual working conditions, there is room for improvement in the transmission capacity of the line, that is, the transmission capacity of the line has not been fully exploited. If the power system is economically dispatched according to a fixed transmission capacity, the actual situation of the power system is not considered, and the role of each line in the power system cannot be fully exerted, making the economic dispatch effect of the power system to be further optimized. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide an economic dispatch method and related devices for a power system considering line dynamic capacity increase, which can release the transmission capacity of the line. On the basis of ensuring safety, the economic dispatch model is optimized through line dynamic capacity increase, the power adjustment rate constraint considering the unit ramp dynamic is taken into account, and a constraint iteration generation strategy is adopted, which can improve the solution accuracy, solution speed and efficiency of the economic dispatch model considering dynamic capacity increase. The specific technical solutions are as follows: In the first aspect, this application provides an economic dispatch method for a power system considering line dynamic capacity increase, and the method includes: Establish an objective function with the minimum operating cost of the units in the power system as the goal; Determine the constraint conditions of the objective function according to the parameters of the power system, and the constraint conditions include unit constraints, network variable constraints, power adjustment rate constraints and linearized AC power flow constraints; Solve the economic dispatch model to obtain the square term of the current of each line in the power system, and the economic dispatch model includes the objective function and the constraint conditions; Conduct thermal stability verification on each line according to the square term of the current of each line to determine the over-limit lines. The over-limit lines are the lines that do not pass the thermal stability verification, and the over-limit lines are used to determine the linearized line thermal stability constraints; Iteratively solve the power economic dispatch model to obtain the economic dispatch plan of the power system. The power economic dispatch model is obtained by adding the linearized line thermal stability constraint to the economic dispatch model.

[0005] In a possible implementation manner, performing thermal stability verification on each of the lines according to the square terms of the currents of the lines to determine the over-limit lines includes: Performing steady-state thermal stability verification on each of the lines according to the square terms of the currents of the lines to obtain steady-state over-limit lines, where the steady-state over-limit lines are the lines that fail the steady-state thermal stability verification; Performing transient thermal balance calculation by using the square terms of the currents of the steady-state over-limit lines to obtain the final temperatures of the lines of the steady-state over-limit lines; Performing transient thermal stability verification on the steady-state over-limit lines according to the final temperatures of the lines of the steady-state over-limit lines to obtain the over-limit lines.

[0006] In a possible implementation manner, determining the power adjustment rate constraint according to the parameters of the power system includes: Constructing a power adjustment rate equation for accounting for the ramp dynamic process according to the parameters of the power system; Performing linearization processing on the power adjustment rate equation to obtain the power adjustment rate constraint.

[0007] In a possible implementation manner, determining the linearized line thermal stability constraint includes: Calculating a linearized transient thermal balance equation based on the square terms of the currents of the over-limit lines to obtain the linearized line thermal stability constraint, where the linearized transient thermal balance equation is constructed according to the parameters of the power system.

[0008] In a possible implementation manner, before performing thermal stability verification on each of the lines according to the square terms of the currents of the lines to determine the over-limit lines, the method further includes: Constructing a transient thermal balance equation for accounting for the dynamic change of the line temperature according to the parameters of the power system; Performing linearization processing on the transient thermal balance equation to obtain a linearized transient thermal balance equation.

[0009] In a second aspect, the present application further provides an economic dispatch device for a power system considering line dynamic capacity increase, where the device includes: An establishment module, configured to establish an objective function with the minimum operating cost of the units of the power system as the goal; A determination module, configured to determine the constraint conditions of the objective function according to the parameters of the power system, where the constraint conditions include unit constraints, network variable constraints, power adjustment rate constraints, and linearized AC power flow constraints; A model solving module, configured to solve the economic dispatch model to obtain the square terms of the currents of the lines in the power system, where the economic dispatch model includes the objective function and the constraint conditions; A verification module, configured to perform thermal stability verification on each of the lines according to the square term of the current of each line, determine the out-of-limit lines, where the out-of-limit lines are the lines that fail the thermal stability verification, and the out-of-limit lines are used to determine the thermal stability constraints of the linearized lines; An iterative solution module, configured to perform iterative solution on the power economic dispatch model to obtain the economic dispatch plan of the power system, where the power economic dispatch model is obtained by adding the thermal stability constraints of the linearized lines to the economic dispatch model.

[0010] In a possible implementation manner, the verification module includes: A steady-state verification unit, configured to perform steady-state thermal stability verification on each of the lines according to the square term of the current of each line, and obtain steady-state out-of-limit lines, where the steady-state out-of-limit lines are the lines that fail the steady-state thermal stability verification; A transient calculation unit, configured to perform transient thermal balance calculation by using the square term of the current of the steady-state out-of-limit lines to obtain the final temperature of the lines of the steady-state out-of-limit lines; A transient verification unit, configured to perform transient thermal stability verification on the steady-state out-of-limit lines according to the final temperature of the lines of the steady-state out-of-limit lines to obtain the out-of-limit lines.

[0011] In a possible implementation manner, the determination module includes: A ramp dynamic construction unit, configured to construct a power adjustment rate equation for considering the ramp dynamic process according to the parameters of the power system; A ramp dynamic linearization unit, configured to perform linearization processing on the power adjustment rate equation to obtain the power adjustment rate constraint.

[0012] In a third aspect, the present application further provides a computer device, including: a memory and a processor; wherein, the memory is used to store a computer program; The processor is configured to execute the computer program in the memory to implement the method described in the first aspect or any item of the first aspect above.

[0013] In a fourth aspect, the present application further provides a computer-readable storage medium, storing instructions, which when running on a computer, cause the computer to execute the method described in the first aspect or any item of the first aspect above.

[0014] In this application, an objective function is established with the goal of minimizing the operating cost of the units in the power system; the constraint conditions of the objective function are determined according to the parameters of the power system, and the constraint conditions include unit constraints, network variable constraints, power adjustment rate constraints, and linearized AC power flow constraints; the economic dispatch model is solved to obtain the square terms of the currents of each line in the power system, and the economic dispatch model includes the objective function and the constraint conditions; the thermal stability of each line is verified according to the square terms of the currents of each line, and the over-limit lines are determined. The over-limit lines are the lines that fail the thermal stability verification, and the over-limit lines are used to determine the linearized line thermal stability constraints; the power economic dispatch model is iteratively solved to obtain the economic dispatch plan of the power system. The power economic dispatch model is obtained by adding the linearized line thermal stability constraints to the economic dispatch model. By determining the power adjustment rate constraints and considering the unit ramp-up dynamic process in detail, this application can improve the calculation accuracy of the line temperature rise. By constructing the power system economic dispatch model into a mixed-integer linear programming model and performing thermal stability verification on the solution results of the economic dispatch model, and generating constraint iterations for the high-dimensional constraint set caused by considering the unit ramp-up dynamic process, the model solution can be accelerated. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 The flowchart of a power system economic dispatch method considering line dynamic capacity increase provided by an embodiment of the present application is shown; Figure 2 The schematic diagram of the unit ramp-up process provided by an embodiment of the present application is shown; Figure 3 The schematic diagram of the piecewise linearization strategy of the function curve provided by an embodiment of the present application is shown; The schematic diagram of the piecewise linearization strategy of the square term of the square of the voltage difference provided by an embodiment of the present application is shown; Figure 4 The schematic diagram of the piecewise linearization strategy of the square term of the square of the voltage difference provided by an embodiment of the present application is shown; Figure 5 The schematic diagram of the line temperature curve obtained by the steady-state heat balance equation and the transient heat balance equation provided by an embodiment of the present application is shown; Figure 6 The flowchart of the constraint iteration generation strategy provided by an embodiment of the present application is shown; Figure 7 The network topology schematic diagram of the IEEE 39-node system provided by an embodiment of the present application is shown; Figure 8 It shows a schematic diagram of the line temperature rise curve considering and not considering the climbing process provided by the embodiments of the present application; Figure 9 It shows a schematic structural diagram of a power system economic dispatch device considering line dynamic capacity increase provided by the embodiments of the present application. Specific embodiments

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of them. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0018] Power system economic dispatch refers to a dispatch method that, on the premise of meeting safety and power quality, rationally utilizes energy and equipment to ensure reliable power supply to users at the lowest power generation cost or fuel cost. Economic dispatch is a typical optimization problem that requires reasonable allocation of unit power under the conditions of meeting demand and various constraints to ensure the lowest operating cost.

[0019] During the operation of the power system, the system operating state often fluctuates and changes strongly, and the line transmission capacity limit will affect the position of the system operating point. However, in existing economic dispatch methods, the transmission capacity limit of the line is usually stipulated by a conservative constant, and the conservative constant only represents the safe transmission capacity under multiple typical working conditions. Under specific working conditions, there is still room for improvement in the transmission capacity limit, that is, the transmission capacity of the line has not been fully exploited. Therefore, dynamically increasing the capacity of the line can optimize the economic dispatch strategy, which is of great significance for the safe, economic, and flexible operation of the power system.

[0020] The line dynamic capacity increase technology utilizes the thermal inertia effect of the transmission line, and according to the meteorological data obtained by the micro-meteorological sensor and the actual operating conditions of the power system, uses the heat balance equation to describe and track the temperature change of the transmission line, and sets the transmission capacity of the transmission line on the basis of ensuring that the transmission line meets the thermal stability constraint. Applying the line dynamic capacity increase technology to power system operation scenarios such as economic dispatch can release the potential of the line transmission capacity, optimize the economic dispatch strategy on the basis of ensuring safety, and enhance the flexibility of the power system operation.

[0021] In the prior art, an overload control strategy for an AC-DC hybrid power grid is proposed to ensure the economic operation and safety of the power grid and effectively avoid the occurrence of cascading tripping accidents in the hybrid power grid. The specific steps of the proposed control strategy are as follows: Step 1: Judging the over-limit of power flow and selecting the variables to be controlled, determining the set of power flow over-limit lines, and further determining the variables to be controlled for emergency control.

[0022] For the set of power flow over-limit lines, introduce the line current over-limit index to make a judgment: .

[0023] In the formula, is the active power of the line corresponding to nodes and after the accident, and is the rated active power of the line. The larger the value, the more active power flows through the line. When , it indicates that the line current is over-limit.

[0024] Based on , after the accident in the AC / DC hybrid power grid, by quickly estimating the power flow and comparing it with the upper limit of the power flow, all AC line sets in the power grid can be screened and divided into two types: the set of lines with over-limit power flow SL1 and the set of non-over-limit lines SL0.

[0025] For the variables to be controlled, the following method is used for selection: After the accident in the AC / DC hybrid power grid, the PQ decoupling algorithm can be used to quickly estimate the power flow after the accident: ; .

[0026] In the formula, is the unbalanced vector of node active power, is the node voltage, is the coefficient matrix in the active power-phase angle (P-θ) iterative correction, is the correction vector of the node voltage phase angle, is the unbalanced vector of node reactive power, is the coefficient matrix in the reactive power-voltage (Q-U) iterative correction, is the increment, is the correction vector of the node voltage amplitude. Since the DC injection power has nothing to do with the phase angle of the node voltage, is the same as the calculation of the traditional AC system, but it will cause an increment , and the specific increment can be derived from the calculation formulas of different control modes of the DC system.

[0027] Furthermore, to improve the optimization efficiency of overload control, the power transmission distribution factor (PTDF) is introduced to reduce the control variables, and the generators and loads with good power flow control effects on the power flow over-limit line set SL1 are selected as control variables.

[0028] Then, the infinite norm set of the power transmission distribution factor vector is obtained. The nodes included in this set are the generator unit nodes and load nodes with the best power flow control effects on each over-limit line in the power flow over-limit line set SL1. The union of the infinite norm sets corresponding to multiple over-limit lines is taken to obtain the generator unit node set and load shedding node set with the optimal control effects on all over-limit lines in the power flow over-limit line set SL1.

[0029] Step 2: Taking the post-accident overload control as the research object, an AC / DC hybrid power grid overload control model is constructed.

[0030] The control objective is to adopt active power regulation of generator sets, sound DC power adjustment, and load shedding when necessary after the accident to achieve power balance and finally block the power flow transfer. The objective function is divided into the active power control cost of generator sets, the control cost of sound DC participation, and the load shedding control cost.

[0031] Among them, the active power control cost of generator sets is: .

[0032] In the formula, is the set of generator unit nodes participating in overload control, is the generator unit at the active power output at time, is the constant term coefficient of the active power control cost of generator sets, is the first-order term coefficient of the active power control cost of generator sets, is the second-order term coefficient of the active power control cost of generator sets, is the initial control time, is the end control time, , is the overload control time interval, is the differential of the time variable.

[0033] The control cost of sound DC participation is: .

[0034] In the formula, The set of generator unit nodes included in the DC system that still operates soundly after an accident is the active power output of a sound DC node or DC converter station at time is the control cost of DC active power. Generally, the control cost of a sound DC is less than the control cost of active power of generator units .

[0035] The control cost of load shedding is .

[0036] In the formula, is the set of load shedding nodes participating in overload control, is the load node at time, the amount of active power cut-off, is the equivalent cut-off cost of different load shedding nodes , which can reflect the economic losses and liability compensation caused by load shedding. A load node refers to all nodes connected to loads, and a load shedding node refers to a load node that takes load shedding measures

[0037] For the above multi-objective function, the weighted summation method is used to transform the multi-objective function into a single-objective function for processing, with the goal of minimizing the overall control cost, that is .

[0038] In the formula, represents the minimum value of the overall control cost, is the weight factor of the active power control cost of generator units, is the weight factor of the control cost participated by sound DCs, is the weight factor of the control cost of load shedding. The judgment matrix method can be used to assign different weights to the active power control cost of generator units, the control cost participated by sound DCs, and the control cost of load shedding

[0039] The constraint conditions of the objective function include equality constraints and inequality constraints. Among them, the equality constraints include the power balance equation of AC-DC hybrid power grid nodes, the resistance-current equation considering the dynamic thermal characteristics of transmission lines, and the dynamic thermal balance state equation of transmission lines; the inequality constraints include the security constraints of AC-DC hybrid power grid, overload control quantity constraints, safe operation constraints of transmission lines, and power adjustment rate constraints

[0040] By solving the optimization model composed of the objective function and constraint conditions, the overload control strategy of the AC-DC hybrid power grid can be obtained, so that the line meets the thermal stability constraints

[0041] Although the prior art takes into account the power adjustment rate constraint, it does not consider the detailed unit ramp-up dynamic process, and the calculation accuracy of line temperature rise needs to be improved. When considering the unit ramp-up dynamic process, the constraint iteration generation strategy is not considered, so it is difficult to obtain an accurate solution with a fast solution speed. Moreover, most of the models constructed by the prior art are non-convex and non-linear models, and often use non-linear interior point methods, heuristic algorithms, etc. to solve them, and it is difficult to obtain the global optimal solution.

[0042] Therefore, the embodiment of the present application provides an economic dispatch method for a power system. For short-time scale scenarios, the minute-level unit ramp-up dynamic process is considered in detail and modeled in a linear form, and constraint iteration generation is performed for the high-dimensional line transient thermal balance constraint set caused by considering the unit ramp-up dynamic, that is, the line thermal stability constraint is iteratively added to the economic dispatch model that does not consider the line thermal stability constraint. In this way, while improving the calculation accuracy of line temperature rise, the model solution is accelerated.

[0043] Please refer to Figure 1 , which shows the flowchart of an economic dispatch method for a power system considering line dynamic capacity increase provided by the embodiment of the present application. The embodiment of the present application at least includes the following steps: S11, establish an objective function with the minimum operating cost of the units in the power system as the objective.

[0044] In the embodiment of the present application, an objective function with the minimum operating cost of the units in the power system as the objective can be established.

[0045] The expression of the objective function is as follows: (1) In formula (1), is the scheduling discretization period, is the set of scheduling discretization periods, is the unit at the active power output at the moment, is the set of units, is the quadratic term coefficient of the objective function, is the linear term coefficient of the objective function, is the constant term coefficient of the objective function. The discretization time interval of can be set according to the specific scenario. As an example, the discretization time interval of can be 15 minutes (min). The discretization time interval of The discretization time interval can be 1 min. If the discretization time interval is 15 min, the discretization time interval is 1 min, then within the scheduling period (i.e., within the period), there are 15 discretization moments.

[0046] In the embodiments of the present application, an objective function can be established according to the parameters of the power system. The , and corresponding to different units can be the same or different. The parameters of the power system can include the generator cost coefficients corresponding to different units (i.e., , and ).

[0047] The embodiments of the present application can adopt a piecewise linearization strategy to linearize the quadratic function curve of the objective function. The piecewise linearization strategy for the objective function can be set according to the actual scenario, and the embodiments of the present application do not make any limitations. It should be noted that the objective functions in the economic dispatch model and the power economic dispatch model of the embodiments of the present application are linearized objective functions.

[0048] S12. Determine the constraint conditions of the objective function according to the parameters of the power system.

[0049] After establishing the objective function, the constraint conditions of the objective function can be determined according to the parameters of the power system. In the embodiments of the present application, the constraint conditions without considering the line transient thermal stability constraint can include unit constraints, network variable constraints, power adjustment rate constraints, and linearized AC power flow constraints.

[0050] The parameters of the power system can include generator parameters, network parameters, and load parameters. The network parameters can include line parameters and node parameters. In the power system, nodes usually represent substations or load points, and these nodes are interconnected through transmission lines (i.e., lines) to jointly form the network structure of the power system.

[0051] The generator parameters can include the maximum active power output, minimum active power output, maximum reactive power output, and minimum reactive power output of each generator, all in megawatts (MW). The generator parameters can also include the generator cost coefficients corresponding to each generator.

[0052] The line parameters can include the conductance, susceptance, upper limit of phase angle difference, and lower limit of phase angle difference of each line. The units of conductance and susceptance are Siemens (S), and the units of the upper limit of phase angle difference and the lower limit of phase angle difference are radians (rad).

[0053] The node parameters may include the upper limit and the lower limit of the square of the voltage of each node.

[0054] The load parameters may include the active load and the reactive load, both in MW.

[0055] As a possible implementation manner, the embodiment of the present application determines the constraint conditions of the objective function according to the parameters of the power system, which may include the following steps: S121, determine the unit constraints.

[0056] The unit constraints involve the upper and lower limit constraints of the active power output and the reactive power output of the unit. The expressions of the unit constraints are as follows: (2) (3) In formulas (2) and (3), is the minimum active power output of the unit , is the active power output of the unit at time, is the maximum active power output of the unit , is the minimum reactive power output of the unit , is the reactive power output of the unit at time, is the maximum reactive power output of the unit .

[0057] S122, determine the network variable constraints.

[0058] The network variable constraints involve voltage constraints and phase angle (hereinafter simply referred to as phase angle) constraints. The expressions of the network variable constraints are as follows: (4) (5) In formulas (4) and (5), is the lower limit of the square of the voltage of node , is the voltage of node at time, is the upper limit of the square of the voltage of node , is the lower limit of the phase angle difference from node to node , is at time the phase angle difference from node to node The phase angle difference is the upper limit of the phase angle difference from node to node .

[0059] S123, determine the linearized AC power flow constraints.

[0060] Conventional power flow constraints are non-convex and non-linear constraints, making it difficult to directly obtain the global optimal solution. Therefore, the embodiments of the present application construct a linearized AC power flow model with the square of the voltage as the variable.

[0061] The expressions of the linearized AC power flow constraints are as follows: (6) (7) In equations (6) and (7), is the set of generators affiliated with node , is the active power output of unit at time , is the set of loads affiliated with node , is the active power load of load d at time , is the conductance of line , is the voltage of node at time , is the voltage of node at time , is the susceptance of line , is the phase angle difference from node to node to node at time is the reactive power output of unit at time , is the reactive power load of load d at time , is the total number of nodes, line is the line flowing from node to node . Node n is any node in the power system, and node i and node j are a pair of nodes in the power system connected by a line.

[0062] S124, determine the power adjustment rate constraints.

[0063] For real-time scheduling on a short time scale, a series of processes such as formulating a dispatching instruction, issuing the dispatching instruction, adjusting the unit output, and maintaining the unit output need to be gone through. The time scale of each process is at the minute level. Generally speaking, the time constant of the line transient thermal balance equation is about 10 minutes, which is also at the minute level. Therefore, it is necessary to consider the specific ramping process of the unit to make it match the time scale of the line temperature rise.

[0064] In real-time scheduling, the specific ramping process of the unit is as Figure 2 shown. For the real-time scheduling scenario, when the dynamic ramping process of the unit is not considered, at each dispatching instruction execution moment, the unit output changes stepwise, which does not conform to the actual situation. Among them, the dispatching instruction execution moment is as Figure 2 in the moment. The dynamic ramping process of the unit refers to the process in which the unit changes from the initial output value to the given output value, and can also be understood as the process in which the unit transitions from one steady state to another steady state. In this process, the output power of the unit needs to increase gradually. When the dynamic ramping process of the unit is considered, the dynamic ramping process of the unit can be divided into the following two stages: Output adjustment stage: After the dispatching instruction is issued and executed, the unit adjusts its output. Due to the existence of ramping rate limitations, the unit needs to go through a period of time to ramp up to the target output value set by the dispatching instruction.

[0065] Output holding stage: After the active power output of the unit is adjusted to the target output value, the unit enters the output steady state stage. At this time, the active power output of the unit no longer changes until the next dispatching instruction is issued.

[0066] Combining the output adjustment stage and the output holding stage, the power adjustment rate constraint can include: S1241, construct a power adjustment rate equation considering the dynamic ramping process according to the parameters of the power system.

[0067] The expression of the power adjustment rate equation considering the dynamic ramping process is as follows: (8) (9) (10) In equations (8) to (10), is the lower limit of the unit ramping slope, is the unit in the ramping slope during the period, is the upper limit of the unit ramping slope, is the unit in the active power output during the period, For the active power output of the unit during the time period, for the active power output of the unit at the moment. It can be understood as the target output value set in the dispatching instruction. In the embodiment of the present application, during the output adjustment stage in the time period, the ramp rate of each unit remains unchanged. Taking the discretization time interval of 15 min as an example, within the 15-min output adjustment stage, the unit has the same ramp rate per minute.

[0068] For the real-time dispatching time period , the total time experienced in the output adjustment stage is , the total time experienced in the output holding stage is . If the discretization time interval is 15 min, then takes 15 min. Equation (8) is the ramp rate range constraint of the unit, Equation (9) is the ramp power constraint of the unit at each moment, and Equation (10) is the critical moment constraint between the output adjustment stage and the output holding stage.

[0069] S1242. Linearize the power adjustment rate equation to obtain the power adjustment rate constraint.

[0070] Equations (9) and (10) of the power adjustment rate equation are non-linear terms. Therefore, it is necessary to linearize Equations (9) and (10).

[0071] Linearize Equation (9): Transform the expression of Equation (9) into: (11) (12) Introduce 0-1 auxiliary variables , , into Equation (11), and introduce 0-1 auxiliary variables , , into Equation (12) for equivalent transformation. , indicating that A is a sufficient condition for B.

[0072] Equation (11) is equivalently transformed into: (13) Equation (12) is equivalently transformed into: (14) Introduce minimum values, sufficiently large values, and sufficiently small values into equations (13) and (14) for further equivalent transformation.

[0073] Equation (13) is further equivalently transformed into:[[]] (15) Equation (14) is further equivalently transformed into:[[]] (16) In equations (15) and (16),[[]] is the minimum value, used to transform the less-than sign into a less-than-or-equal sign and the greater-than sign into a greater-than-or-equal sign. The value of can be set according to the actual scenario. As an example, can be taken as[[]] . , , , are sufficiently large values. , , , are sufficiently small values. , , , , , , , The values of can be set according to the actual scenario. As an example, in the embodiments of this application[[]] , , , , , , , The values are as follows:[[]] (17) Perform linearization processing on equation (10):[[]] Transform the expression of equation (10) into:[[]] (18) In equation (18),[[]] is the product of two continuous variables. There are clear upper and lower bounds, so perform binary expansion approximation on[[]] :[[]] (19) In equation (19),[[]] are all 0-1 auxiliary variables, used for[[]] Perform binary expansion approximation. The value of .

[0074] At this time, can be transformed into the sum of the products of several 0-1 auxiliary variables ( ) and continuous variables ( ): (20) For the product of the 0-1 auxiliary variable and the continuous variable in Equation (20), taking as an example, it can be linearized by the following strategy: (21) In Equation (21), is a sufficiently large value, is the auxiliary continuous variable introduced by linearization, The value of .

[0075] Combining the above process, the dynamic process of the unit ramp can be modeled to reach the minute level, so as to reach the same time scale as the transient thermal balance equation. In addition, the relevant constraints of the unit ramp dynamics are all modeled as linear constraints. The finally obtained power adjustment rate constraints can include Equation (8), Equation (15), Equation (16), Equation (17), Equation (20) and Equation (21).

[0076] S13. Solve the economic dispatch model to obtain the square term of the current of each line in the power system.

[0077] After S11 and S12, the economic dispatch model can be obtained in this embodiment of the present application. The economic dispatch model can include the objective function and the constraint conditions without considering the transient thermal stability constraints of the lines, that is, the economic dispatch model in this embodiment of the present application can include Equation (1) to Equation (5), Equation (8), Equation (15) to Equation (17), Equation (20) and Equation (21).

[0078] Through the construction of the objective function and the determination of the constraint conditions, the economic dispatch model in this embodiment of the present application is a mixed integer linear programming model (Mixed-Integer Linear Programming, MILP), which can handle complex problems that contain both continuous variables and integer variables, and can ensure that the solution satisfies the integer constraints, thereby improving the accuracy of decision-making.

[0079] By solving the economic dispatch model in this embodiment of the present application, the square term of the current of the line in the power system can be obtained. , thereby obtaining the square terms of the currents of each line. The solution method for the economic dispatch model can be set according to the actual scenario. As an example, in the embodiments of the present application, an optimization solver can be used to solve the economic dispatch model, and the optimization solver can be Cplex, Gurobi, etc. Both Cplex and Gurobi can efficiently solve problems such as linear programming, mixed integer programming, quadratic programming, quadratic constraint programming, and constraint programming.

[0080] S14. Perform thermal stability verification on each line according to the square terms of the currents of each line, and determine the over-limit lines.

[0081] After obtaining the square terms of the currents of each line, in the embodiments of the present application, thermal stability verification can be performed on each line according to the square terms of the currents of each line to determine the over-limit lines. The over-limit lines are the lines that fail the thermal stability verification. The thermal stability verification can include steady-state thermal stability verification and transient thermal stability verification. The over-limit lines can be used to determine the linearized thermal stability constraints.

[0082] In order to dynamically adjust the maximum transmission capacity of the line to adapt to the real-time working conditions, when generating the economic dispatch plan, the problem of line dynamic capacity increase needs to be considered. For this purpose, in the embodiments of the present application, a transient thermal balance equation can be used to describe the dynamic change process of the line temperature. If the linearized transient thermal balance equation is directly added to the constraint conditions of the economic dispatch model, a high-dimensional constraint set will be formed, which will slow down the solution speed of the economic dispatch model. Therefore, the embodiments of the present application provide a constraint iteration generation strategy to accelerate the solution of the economic dispatch model.

[0083] Next, the transient thermal balance will be introduced first.

[0084] For the line , a transient thermal balance equation for considering the dynamic change of the line temperature can be constructed according to the parameters of the power system. The expression of the transient thermal balance equation with forward difference is as follows: (22) (23) In formulas (22) and (23), is the line temperature of the line at time is the line mass of the line , is the specific heat capacity of the line , is the difference division step size, is the radiative heat dissipation of the line at time is the Line at a certain moment is the convective heat dissipation of the line, and is the solar heat absorption of the line, and is the line heat generation of the line at a certain moment, and is the line current of the line at a certain moment, and is the line AC resistance of the line, and

[0085] is the upper limit of the line temperature. Equation (22) is the transient heat balance equation in forward difference form, and Equation (23) is the line temperature constraint. The transient heat balance equation has a non - linear term. Therefore, it is necessary to linearize the transient heat balance equation to obtain a linearized transient heat balance equation. Further, the radiative heat dissipation, convective heat dissipation, solar heat absorption, and line heat generation are expanded, and the radiative heat dissipation, convective heat dissipation, and line heat generation are linearized, converting the transient heat balance equation in forward difference form into a first - order linear difference equation.

[0086] 1) Radiative heat dissipation The expression of the radiative heat dissipation is as follows: (24) In Equation (24), is the outer diameter of the conductor of the line , is the radiative heat dissipation coefficient of the conductor surface of the line , and is the line temperature of the line at a certain moment, and is the ambient temperature. Generally speaking, the line models in the power system are the same. Therefore, it can be considered that the outer diameters of the conductors and the radiative heat dissipation coefficients of the conductor surfaces of each line are the same. It should be noted that within the dispatching period

[0087]

[0088] the ambient temperature is a fixed value and can be set according to the actual scenario. In different dispatching periods, the ambient temperature may be the same or different. When the external meteorological factors are given, the radiative heat dissipation is a quartic function of the conductor temperature, and the radiative heat dissipation can be linearly segmented. The external meteorological factors can include ambient temperature, solar radiation intensity, wind speed, and the angle between the wind and the conductor, etc.The linearly segmented expression of the radiative heat dissipation is as follows: (25) In formula (25), is the line temperature of the line at time, is the lower limit of the line temperature of the line taken for piecewise linearization. In the embodiments of the present application, can be set according to the actual situation. Exemplarily, can be set to 0 , is the slope value of the th segment of the function curve, is the value of the temperature increment of the th segment of the function curve, is the 0-1 auxiliary variable introduced for the piecewise linearization of the th segment of the function curve, is the width of the segmentation interval of the th segment of the function curve, is the upper limit of the line temperature of the line taken for piecewise linearization. In the embodiments of the present application, can be set according to the actual situation. Exemplarily, can be set to 90 . is always greater than 0. Therefore, the function curve only takes the part where is greater than 0, the piecewise linearization strategy of the function curve is as shown in Figure 3 . The value of can be set according to the actual situation. Generally speaking, the larger the value of , the better the approximation effect, but the longer the solution time. If the function curve has symmetry, then the value of

[0089] 2) Convective heat dissipation The convective heat dissipation is expressed as follows: (26) (27) (28) In formulas (26), (27) and (28), is the introduced intermediate temperature variable, is the air thermal conductivity, is the wind direction factor, is the wind direction angle,​​​ is the air density, is the altitude of the area where the power system is located, is the dynamic viscosity of air, is the Reynolds number, is the outer diameter of the wire, is the wind speed, For the line the convective heat dissipation in a low wind speed environment, For the line the convective heat dissipation in a high wind speed environment, For the line the convective heat dissipation in a zero wind speed environment, For the line the convective heat dissipation, Take , and the maximum value among them.

[0090] For in Equation (27), and , linearization approximations can be adopted, and the specific expressions are as follows: (29) In Equation (29), is the convective heat dissipation at low wind speed when the line temperature is taken as , is the convective heat dissipation at low wind speed when the line temperature is taken as , is the convective heat dissipation at high wind speed when the line temperature is taken as , is the convective heat dissipation at high wind speed when the line temperature is taken as , is the convective heat dissipation at zero wind speed when the line temperature is taken as , is the convective heat dissipation at zero wind speed when the line temperature is taken as . Further, for the maximum value constraint of Equation (28), the maximum value constraint can be linearized by introducing a 0-1 auxiliary variable, and the linearized expression of the maximum value constraint is as follows: (30) In Equation (30), is the introduced 0-1 auxiliary variable, is a relatively large constant introduced for linearization.

[0091] 3) Heat absorption due to sunlight The expression of the heat absorption due to sunlight is as follows: (31) In formula (31), is the endothermic coefficient, is the sunshine intensity, is the outer diameter of the wire.

[0092] It can be seen from the expression of the heat absorbed by sunshine that the heat absorbed by sunshine has nothing to do with the wire temperature. When the sunshine intensity is given, the heat absorbed by sunshine is a constant.

[0093] 4) Heat generation of the line AC resistance The expression of is as follows: (32) In formula (32), is the skin effect coefficient, is the conductor temperature effect coefficient, is the line at the line temperature at the moment, is the DC resistance of the wire.

[0094] Taking a conservative assumption for the expression of the AC resistance, let , then there is: (33) The line the square term of the current The expression of is as follows: (34) In formula (34), is the conductance of the line , is the susceptance of the line , is the voltage of node at the moment, is the voltage of node at the moment, is at the moment from node to node the phase angle difference, is the phase angle of node at the moment, is the phase angle of node at the moment. Among them, The conversion process of is as follows: (35) Therefore, an expression for the heat generation of the line can be obtained. The heat generation of the line has the following expression: (36) There are square terms of two variables in Equation (36), namely and . In the embodiments of the present application, piecewise linearization processing can be adopted for and . Taking as an example, the specific piecewise linearization strategy is as shown in Figure 4 , where can be converted from a linear combination of the voltage square terms and .

[0095] The piecewise linearization expression of the square term of the voltage squared difference is as follows: (37) In Equation (37), is the voltage of node at time , is the voltage of node at time , is the lower voltage limit of node , is the upper voltage limit of node , is the lower voltage limit of node , is the upper voltage limit of node , is the slope value of the th segment of the function curve, is the value of the voltage squared difference of the th segment of the function curve, is the 0-1 auxiliary variable introduced for the th segment piecewise linearization of the function curve, is the width of the piecewise interval of the th segment of the function curve, is the minimum value of is the maximum value of is the voltage of node , is the voltage of node .

[0096] The square of the phase angle difference The piecewise linearization expression of is as follows: (38) In formula (38), For slave nodes To Node The lower limit of the phase angle difference is For Time from node To Node The phase angle difference, For slave nodes To Node The upper limit of the phase angle difference is for Function curve The slope value of the segment, for Function curve The value of the phase angle difference between the segments, For Function curve The 0-1 auxiliary variable introduced by the piecewise linearization, for Function curve The width of the segment interval. Piecewise linearization strategy of function curves and The function curve is similar, you can refer to Figure 4 To understand.

[0097] Through the above process, the radiation heat dissipation, convection heat dissipation and line heat generation are all transformed into linear forms, and the solar heat absorption is in the form of a constant term. At this point, the transient heat balance equation in the forward difference form is transformed into a linearized difference equation. The embodiment of the present application linearizes the transient heat balance equation in the forward difference form, which can improve the convergence speed when solving the problem to meet the real-time requirements.

[0098] During the research process, it was found that steady-state thermal stability verification can be used as a pre-filtering method for transient thermal stability verification. Figure 5 The line temperature curves calculated using the steady-state heat balance equation and the transient heat balance equation are shown in the real-time dispatch time scale of 15 minutes. Figure 5 It can be seen that the line temperature obtained by the steady-state heat balance equation undergoes a step change at each scheduling moment, while the line temperature obtained by the transient heat balance equation can reflect the dynamic change process of the line temperature.

[0099] On the one hand, when the environmental parameters and line current are given, for the process of line temperature rise, the solution of the steady-state heat balance equation will provide an upper bound for the transient heat balance equation. That is, for a time scale of 15 minutes, the temperature calculated by the steady-state heat balance equation is greater than or equal to the temperature calculated by the transient heat balance equation, where the temperature calculated by the transient heat balance equation conforms to the actual situation. On the other hand, the calculation speed of the steady-state heat balance equation is faster than that of the transient heat balance equation. Therefore, using the steady-state thermal stability check as a pre-filtering means for the transient thermal stability check can obtain a more conservative and rapid solution, that is, it can quickly filter out the lines with high line temperature, avoiding performing the transient thermal stability check on all lines, aiming to improve the efficiency of the thermal stability check.

[0100] Therefore, in a possible implementation manner, performing a thermal stability check on each line according to the square term of the current of each line to determine the over-limit lines may include: S141, performing a steady-state thermal stability check on each line according to the square term of the current of each line to obtain the steady-state over-limit lines.

[0101] After obtaining the square term of the current of each line in the embodiment of the present application, a steady-state thermal stability check may be performed on each line to obtain the steady-state over-limit lines. Among them, the steady-state over-limit lines are the lines that fail to pass the steady-state thermal stability check.

[0102] First, analyze the check criterion for the steady-state thermal stability of the line.

[0103] In the steady-state heat balance equation, the values of the radiation heat dissipation, convective heat dissipation, and AC resistance value are taken at a certain time, and the expression of the steady-state heat balance equation is as follows: (39) In Equation (39), is the maximum allowable current that the line can carry under the given external meteorological conditions, is the line temperature of the line , is the upper limit of the line temperature, is when the radiation heat dissipation, is when the convective heat dissipation, is when the AC resistance value, is the solar radiation heat absorption. The external meteorological factors may include environmental temperature, solar radiation intensity, wind speed, and the angle between the wind and the conductor, etc.

[0104] Therefore, the steady-state thermal stability check of the line is as follows: when When the line passes the verification of the steady-state heat balance equation; otherwise, the line does not pass the verification of the steady-state heat balance equation. That is to say, at any moment , the line the flowing current is not greater than the maximum allowable current .

[0105] The above analyzes the verification criterion of the steady-state heat balance equation. Further, during the dynamic process of the unit ramping, the current of the line will change. Therefore, for a real-time scheduling period , the embodiment of the present application uses the following expression as the line steady-state thermal stability verification criterion: (40) Equation (40) means that for each moment in the scheduling period , the square term of the current of the line is calculated, and the maximum value is obtained. This maximum value is compared with the square term of the maximum allowable current of the steady-state heat balance equation. If is not greater than , then the line passes the steady-state thermal stability verification, and at this time the steady-state current of the line does not exceed the limit. If is greater than , then the line does not pass the steady-state thermal stability verification, and at this time the steady-state current of the line exceeds the limit, and the line is a steady-state over-limit line. After obtaining the steady-state over-limit line, the steady-state over-limit line is added to the steady-state over-limit set .

[0106] S142, use the square term of the current of the steady-state over-limit line to perform transient heat balance calculation to obtain the final temperature of the line of the steady-state over-limit line.

[0107] S143, perform transient thermal stability verification on the steady-state over-limit line according to the final temperature of the line of the steady-state over-limit line to obtain the over-limit line.

[0108] For the steady-state over-limit set that does not pass the steady-state thermal stability verification, perform transient thermal stability verification. Substitute the square term of the current of the steady-state over-limit line into the transient heat balance equation, calculate the transient temperature rise process, and obtain the end moment (e.g. 15min) of line temperature and compare it with the upper limit of line temperature. Finally, add the line with temperature exceeding the limit to the transient limit collection .

[0109] line The transient thermal stability verification criteria include equations (22) to (27), (29) to (31) and (36) to (38). The transient thermal balance equations (22), (24) to (27), (29) to (31) and (36) to (38) are forward differentiated to calculate the current flowing through the line at each discretized moment. Temperature ; Then through formula (23), check (e.g. 15min) line temperature Whether it exceeds the limit. (e.g. 15min) line temperature If there is no temperature limit, the circuit Through transient thermal stability verification, if Line temperature at If the temperature exceeds the limit, it means that the circuit There is a transient temperature exceeding the limit, and the transient thermal stability check fails. Add to transient limit set . Transient out-of-limit set The line in is an over-limit line. The line end temperature is (e.g. 15min) line temperature.

[0110] Compared with the transient heat balance equation, the calculation method of the steady-state heat balance equation is simpler and has a faster verification speed. Therefore, the embodiment of the present application first uses the steady-state heat balance equation to constrain all lines in the power system, quickly pre-check, and then pre-check the lines that have not passed the steady-state thermal stability check (i.e., the set ), and further use of transient heat balance equations for rigorous verification can improve line verification efficiency.

[0111] If the collection and / or collection If it is empty, the solution of the economic dispatch model will be used as the economic dispatch plan of the power system.

[0112] If the collection If it is not empty, the collection The linearized line thermal stability constraints corresponding to each line in are added to the constraints of the economic dispatch model, and the set The linearized circuit thermal stability constraints corresponding to each circuit in are the set Substitute the square terms of the currents of each line in the power system into Equations (22) to (27), (29) to (31), and (36) to (38).

[0113] In the embodiment of the present application, by performing thermal stability verification on the lines, the over-limit situation of the lines can be determined. If a line fails the thermal stability verification, the linearized line thermal stability constraint corresponding to this line is added to the economic dispatch model to form an iteration until all lines pass the thermal stability verification. The constraint iteration generation strategy is as Figure 6 shown.

[0114] S15. Perform iterative solution on the power economic dispatch model to obtain the economic dispatch plan of the power system. The power economic dispatch model is obtained by adding the linearized line thermal stability constraint to the economic dispatch model.

[0115] After performing thermal stability verification on each line, if there is a line that fails the thermal stability verification, add the linearized line thermal stability constraint of the line that fails the thermal stability verification to the economic dispatch model to obtain the power economic dispatch model. Solve the power economic dispatch model to obtain the square terms of the currents of each line in the power system. Then, perform thermal stability verification on each line according to the square terms of the currents of each line to determine the over-limit lines. That is, after adding the linearized line thermal stability constraint of the over-limit lines to the economic dispatch model, repeat the execution of S13 to S15 to obtain multiple power economic dispatch models. The linearized line thermal stability constraints of different power economic dispatch models are different until there are no over-limit lines, forming an iterative generation of constraint conditions, and solve the final power economic dispatch model to obtain the economic dispatch plan of the power system. In the embodiment of the present application, the economic dispatch model including the linearized line thermal stability constraint is used as the power economic dispatch model. Among them, the linearized line thermal stability constraint is determined based on the over-limit lines. Calculate the linearized transient thermal balance equation based on the square terms of the currents of the over-limit lines, that is, substitute the square terms of the currents of the over-limit lines into the linearized transient thermal balance equation to obtain the linearized line thermal stability constraint. The linearized transient thermal balance equation may include Equations (22) to (27), (29) to (31), and (36) to (38).

[0116] Obtain the square terms of the currents of each line from the economic dispatch plan of the power system, and execute S114 until the set and / or the set is empty, then the final economic dispatch plan of the power system is obtained.

[0117] Add the thermal stability constraint of the linearized line of the line that fails the thermal stability check to the economic dispatch model to obtain the power economic dispatch model, and the power economic dispatch model is still a MILP. The solution method for the power economic dispatch model can be set according to the actual scenario. As an example, the embodiments of the present application can use an optimization solver to solve the power economic dispatch model, and the optimization solver can be Cplex, Gurobi, etc.

[0118] In the embodiments of the present application, an objective function with the minimum operating cost of the units in the power system as the goal is established; the constraint conditions of the objective function are determined according to the parameters of the power system, and the constraint conditions include unit constraints, network variable constraints, power adjustment rate constraints, and linearized AC power flow constraints; the economic dispatch model is solved to obtain the square term of the current of each line in the power system, and the economic dispatch model includes the objective function and the constraint conditions; thermal stability checks are performed on each line according to the square term of the current of each line to determine the over-limit lines, and the over-limit lines are the lines that fail the thermal stability check, and the over-limit lines are used to determine the thermal stability constraint of the linearized line; the power economic dispatch model is iteratively solved to obtain the economic dispatch plan of the power system, and the power economic dispatch model is obtained by adding the thermal stability constraint of the linearized line to the economic dispatch model. The embodiments of the present application improve the calculation accuracy of the line temperature rise by determining the power adjustment rate constraint and considering the unit ramp dynamic process in detail. By constructing the power system economic dispatch model into a mixed integer linear programming model and performing thermal stability checks on the solution results of the economic dispatch model, constraint iteration generation can be performed for the high-dimensional constraint set caused by considering the unit ramp dynamic process, which can accelerate the model solution.

[0119] To facilitate further understanding of the advantages of the technical solutions provided by the embodiments of the present application, the power system economic dispatch method provided by the embodiments of the present application is applied to the IEEE 39-bus system as an example for an overall exemplary introduction below. The IEEE 39-bus system is a regional transmission system network in the field of power systems.

[0120] The embodiments of the present application use the IEEE 39-bus as an example, which includes a total of 46 lines, and dynamic capacity increase is performed on all lines. The network topology diagram of the IEEE 39-bus system is as Figure 7 shown.

[0121] The specific settings of the example parameters are as follows: For the real-time economic dispatch scenario, in a set of scheduling discretization time periods the time interval of the scheduling instruction (i.e., the time interval of t) is 15 minutes, and the discretization time interval of the line transient thermal balance equation (i.e., The time interval is taken as 1 min. The basic parameters of each generator, line, and load all adopt the example parameters provided by the MATPOWER 8.0 toolbox. In addition, for each generating unit, and are respectively set to 1% and 3% of the maximum capacity of the unit, with the unit being MW / min.

[0122] The line conductor parameters and environmental parameters are shown in Table 1.

[0123] Table 1 Line Conductor Parameters and Environmental Parameters

[0124]

[0125] First, to verify the necessity of considering the dynamic process of unit ramping, the load rate is suddenly increased to 1.15 times the initial value. Within 15 min, the line temperature rise curves are calculated using the transient thermal balance equation under two conditions: considering the unit ramping process and not considering the unit dynamic ramping process. Taking line L8 (starting node 4, ending node 5) as an example, its temperature change curve is as Figure 8 shown.

[0126] According to Figure 8 , for the two cases of considering the unit ramping process and not considering the unit ramping process, there are significant differences in the line temperature rise curves. The line temperature rise curve considering the ramping process is lower than the temperature rise curve without considering the unit ramping process. In addition, at 15 min, the line temperatures calculated under the two conditions are 36.7 , 34.2 respectively, and the relative error is 7.31%. This is because during the unit ramping adjustment process, the line current changes dynamically, and the line heat generation of the transient thermal balance equation can be calculated more accurately, thus improving the accuracy of the line temperature rise calculation curve.

[0127] Furthermore, to verify the solution speed and solution accuracy of the power economic dispatch model proposed in the embodiments of the present application, the following three different algorithms are designed for comparison, and the specific settings are shown in Table 2: Table 2 Settings of Three Comparison Algorithms

[0128]

[0129] The solution results and solution times obtained by the three different algorithms are shown in Table 3: Table 3 Comparison of Solution Results and Solution Times of Different Algorithms

[0130]

[0131] As can be seen from Table 3, for Algorithm 1 and Algorithm 2, as the number of iterations increases, the number of lines with violations in the steady-state thermal balance equation and the transient thermal balance equation verification both continuously decrease, and all lines pass the transient thermal balance equation verification at the end of the iteration. For the same number of iterations, the number of lines with violations in the steady-state thermal balance equation verification is greater than or equal to the number of lines with violations in the transient thermal balance equation verification because during the line temperature rise process, the steady-state thermal balance equation verifies the line temperature more conservatively, while the verification result of the transient thermal balance verification is more accurate.

[0132] Comparing the objective function values, when the algorithms converge after iteration, the objective function values obtained by Algorithm 1, Algorithm 2, and Algorithm 3 are the same, indicating that the constraint iteration generation strategy proposed in the embodiments of the present application can identify all temperature-limited lines and obtain the global optimal solution.

[0133] Comparing the solution times, the total solution times of Algorithm 1, Algorithm 2, and Algorithm 3 are 59.2 seconds (s), 67.2 s, and 164.8 s respectively. The solution time of Algorithm 1 is the shortest, which is 88.1% and 35.9% of Algorithm 2 and Algorithm 3 respectively. Comparing Algorithm 1 and Algorithm 3, the constraint iteration generation strategy designed by Algorithm 1 can identify the key bottleneck lines of thermal stability and iteratively add constraint conditions to improve the model solution efficiency. Comparing Algorithm 1 and Algorithm 2, Algorithm 1 first performs a quick pre-verification through the steady-state thermal balance equation with a shorter time, and then uses the transient thermal balance equation with a longer time for strict verification, which can further accelerate the model verification speed and improve the solution efficiency.

[0134] Therefore, in the embodiments of the present application, for short-time scale scenarios, in the economic dispatch model considering the transient thermal balance equation of lines, the calculation accuracy of line temperature rise is improved while ensuring the real-time nature of the solution. Specifically, the calculation accuracy of line temperature rise is improved by considering the detailed ramp process of units, and the model solution speed is improved by the constraint iteration generation strategy, so that the solution speed meets the real-time requirement.

[0135] Next, an economic dispatch device for a power system considering line dynamic capacity increase provided by the embodiments of the present application will be introduced. The economic dispatch device for a power system considering line dynamic capacity increase introduced below can be correspondingly referred to the economic dispatch method for a power system considering line dynamic capacity increase introduced above.

[0136] Please refer to Figure 9 , which shows a schematic structural diagram of an economic dispatch device for a power system provided by the embodiments of the present application. The device includes: A building module 901, configured to build an objective function with the minimum operating cost of the units in the power system as the objective; A determination module 902, configured to determine the constraint conditions of the objective function according to the parameters of the power system, where the constraint conditions include unit constraints, network variable constraints, power adjustment rate constraints, and linearized AC power flow constraints; A model solving module 903, configured to solve the economic dispatch model to obtain the square terms of the currents of each line in the power system, where the economic dispatch model includes the objective function and the constraint conditions; A verification module 904, configured to perform thermal stability verification on each line according to the square terms of the currents of each line to determine the over-limit lines, where the over-limit lines are the lines that fail the thermal stability verification, and the over-limit lines are used to determine the linearized line thermal stability constraints; An iterative solving module 905, configured to iteratively solve the power economic dispatch model to obtain the economic dispatch plan of the power system, where the power economic dispatch model is obtained by adding the linearized line thermal stability constraints to the economic dispatch model.

[0137] In the embodiment of the present application, the verification module 904 includes: A steady-state verification unit, configured to perform steady-state thermal stability verification on each line according to the square terms of the currents of each line to obtain steady-state over-limit lines, where the steady-state over-limit lines are the lines that fail the steady-state thermal stability verification; A transient calculation unit, configured to perform transient thermal balance calculation by using the square terms of the currents of the steady-state over-limit lines to obtain the final temperatures of the lines of the steady-state over-limit lines; A transient verification unit, configured to perform transient thermal stability verification on the steady-state over-limit lines according to the final temperatures of the lines of the steady-state over-limit lines to obtain the over-limit lines.

[0138] In the embodiment of the present application, the determination module 902 includes: A ramp dynamic construction unit, configured to construct a power adjustment rate equation for accounting for the ramp dynamic process according to the parameters of the power system; A ramp dynamic linearization unit, configured to perform linearization processing on the power adjustment rate equation to obtain the power adjustment rate constraints.

[0139] In the embodiment of the present application, the iterative solving module 905 includes: A calculation unit, configured to calculate the linearized line thermal stability constraints based on the square terms of the currents of the over-limit lines for a linearized transient thermal balance equation, where the linearized transient thermal balance equation is constructed according to the parameters of the power system.

[0140] In the embodiment of the present application, the device further includes: A transient construction module for constructing a transient thermal balance equation considering the dynamic change of line temperature according to the parameters of the power system; A transient linearization module for linearizing the transient thermal balance equation to obtain a linearized transient thermal balance equation.

[0141] An embodiment of the present application also provides a computer device, including: a memory and a processor; Wherein, the memory is used to store a computer program; The processor is used to execute the computer program in the memory to implement the method described in the above method embodiment.

[0142] An embodiment of the present application also provides a computer-readable storage medium storing instructions, which when running on a computer, cause the computer to execute the method described in the above method embodiment.

[0143] In the embodiment of the present application, a target function with the minimum operating cost of the units in the power system as the target is established by the establishment module; the determination module determines the constraint conditions of the target function according to the parameters of the power system, and the constraint conditions include unit constraints, network variable constraints, power adjustment rate constraints, and linearized AC power flow constraints; the model solution module solves the economic dispatch model to obtain the square term of the current of each line in the power system, and the economic dispatch model includes the target function and the constraint conditions; the verification module performs thermal stability verification on each line according to the square term of the current of each line to determine the over-limit lines, and the over-limit lines are the lines that do not pass the thermal stability verification, and the over-limit lines are used to determine the linearized line thermal stability constraints; the iterative solution module iteratively solves the power economic dispatch model to obtain the economic dispatch plan of the power system, and the power economic dispatch model is obtained by adding the linearized line thermal stability constraints to the economic dispatch model. In the embodiment of the present application, by determining the power adjustment rate constraints and considering the dynamic process of unit ramp-up in detail, the calculation accuracy of line temperature rise is improved. By constructing the power system economic dispatch model into a mixed-integer linear programming model and performing thermal stability verification on the solution result of the economic dispatch model, it is possible to iteratively generate constraints for the high-dimensional constraint set caused by considering the dynamic process of unit ramp-up, which can accelerate the model solution.

[0144] It should be noted that the same or similar parts among the various embodiments can be referred to each other. For the device embodiments and system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiments.

[0145] For the foregoing embodiments, for the sake of simple description, they are all expressed as a series of combinations of actions. However, those skilled in the art should know that this application is not limited by the described order of actions, because according to this application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0146] Finally, it should also be noted that in this text, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such a process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0147] The above description of the disclosed embodiments enables those skilled in the art to implement or use this application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

[0148] The above is only the preferred embodiment of this application. It should be noted that for those of ordinary skill in the art, without departing from the principle of this application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of this application.

Claims

1. A method for economic dispatching of a power system taking into account dynamic capacity increase of lines, characterized in that: The method comprises: Establish an objective function with the goal of minimizing the unit operating cost of the power system; Determining constraints of the objective function according to the parameters of the power system, wherein the constraints include unit constraints, network variable constraints, power adjustment rate constraints and linearized AC power flow constraints; Solving the economic dispatch model to obtain the square term of the current of each line in the power system, the economic dispatch model including the objective function and the constraint condition; Performing a thermal stability check on each of the circuits according to the square term of the current of each of the circuits, and determining an out-of-limit circuit, wherein the out-of-limit circuit is a circuit that fails the thermal stability check, and the out-of-limit circuit is used to determine a thermal stability constraint of a linearized circuit; The electric power economic dispatch model is iteratively solved to obtain an economic dispatch plan for the electric power system, wherein the electric power economic dispatch model is obtained by adding the linearized line thermal stability constraint to the economic dispatch model.

2. The method according to claim 1, characterized in that The step of performing thermal stability check on each circuit according to the square term of the current of each circuit to determine the circuit that exceeds the limit includes: Performing a steady-state thermal stability check on each of the circuits according to the square term of the current of each of the circuits to obtain a steady-state over-limit circuit, wherein the steady-state over-limit circuit is a circuit that fails the steady-state thermal stability check; Performing transient heat balance calculation using the square term of the current of the steady-state over-limit line to obtain the line terminal temperature of the steady-state over-limit line; A transient thermal stability check is performed on the steady-state over-limit line according to the line terminal temperature of the steady-state over-limit line to obtain the over-limit line.

3. The method according to claim 1, characterized in that Determining the power adjustment rate constraint according to the parameters of the power system includes: Constructing a power regulation rate equation for taking into account the dynamic process of ramping according to the parameters of the power system; The power adjustment rate equation is linearized to obtain the power adjustment rate constraint.

4. The method according to any one of claims 1 to 3, characterized in that: Determining the thermal stability constraints of the linearization circuit includes: A linearized transient heat balance equation is calculated based on the square term of the current of the out-of-limit line to obtain the linearized line thermal stability constraint, and the linearized transient heat balance equation is constructed according to the parameters of the power system.

5. The method according to any one of claims 1 to 3, characterized in that: Before performing thermal stability verification on each of the circuits according to the square term of the current of each of the circuits to determine the out-of-limit circuit, the method further includes: Constructing a transient heat balance equation for taking into account the dynamic change of line temperature according to the parameters of the power system; The transient heat balance equation is linearized to obtain a linearized transient heat balance equation.

6. An economic dispatching device for a power system taking into account dynamic capacity increase of lines, characterized in that: The device comprises: Establishing a module for establishing an objective function with the goal of minimizing the unit operation cost of the power system; A determination module, used for determining the constraint conditions of the objective function according to the parameters of the power system, wherein the constraint conditions include unit constraint, network variable constraint, power adjustment rate constraint and linearized AC power flow constraint; A model solving module, used for solving the economic dispatch model to obtain the square term of the current of each line in the power system, wherein the economic dispatch model includes the objective function and the constraint condition; A verification module, used for performing a thermal stability check on each of the circuits according to the square term of the current of each of the circuits, and determining an out-of-limit circuit, wherein the out-of-limit circuit is a circuit that fails the thermal stability check, and the out-of-limit circuit is used to determine the thermal stability constraint of the linearization circuit; The iterative solution module is used to iteratively solve the power economic dispatch model to obtain the economic dispatch plan of the power system. The power economic dispatch model is obtained by adding the linearized line thermal stability constraint to the economic dispatch model.

7. The device according to claim 6, characterized in that The verification module comprises: A steady-state verification unit, configured to perform a steady-state thermal stability verification on each of the circuits according to the square term of the current of each of the circuits, and obtain a steady-state over-limit circuit, wherein the steady-state over-limit circuit is a circuit that fails the steady-state thermal stability verification; A transient calculation unit, used to perform transient heat balance calculation using the square term of the current of the steady-state over-limit line to obtain the line terminal temperature of the steady-state over-limit line; The transient check unit is used to perform a transient thermal stability check on the steady-state over-limit line according to the line terminal temperature of the steady-state over-limit line to obtain the over-limit line.

8. The device according to claim 6, characterized in that The determining module comprises: A ramp-climbing dynamic construction unit, used to construct a power adjustment rate equation for taking into account the ramp-climbing dynamic process according to the parameters of the power system; The ramp dynamic linearization unit is used to perform linearization processing on the power adjustment rate equation to obtain the power adjustment rate constraint.

9. A computer device, characterized in that: include: Memory and processor; The memory is used to store computer programs; The processor is configured to execute the computer program in the memory to implement the method according to any one of claims 1 to 5.

10. A computer-readable storage medium, characterized in that: The device stores instructions which, when executed on a computer, cause the computer to execute the method according to any one of claims 1 to 5.

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