New energy maximum access calculation method based on DLR and OTS

Abstract

The invention belongs to the technical field of power system operation optimization, and particularly relates to a new energy maximum access calculation method based on a DLR and an OTS, and the method comprises the steps: constructing a renewable energy access amount maximization model based on a dynamic line limiting current DLR and an optimal line switching OTS; acquiring operation data of the power system and real-time conductor temperature data and current data of the power transmission line; calculating a dynamic maximum allowable current value of the power transmission line; calculating the renewable energy access capacity and the voltage stability margin of the current power system; judging whether the static voltage stability margin meets the threshold requirement at the moment, if not, executing a three-stage method to solve the switched power transmission line meeting the threshold requirement, and if yes, calculating the renewable energy access quantity at the next moment; executing a three-stage method; and outputting the power transmission line switching schemes and the maximum renewable energy access capacity corresponding to each power transmission line switching scheme. According to the invention, the access capacity of renewable energy sources can be improved to the greatest extent.

Description

Technical Field

[0001] The invention belongs to the technical field of power system operation optimization, and in particular relates to a maximum access calculation method for new energy sources based on DLR and OTS. Background Art

[0002] As the demand for clean energy continues to grow, the penetration rate of renewable energy such as wind power and photovoltaics is increasing significantly. However, due to the limited transmission capacity of the power system, the problems of wind and solar power abandonment occur frequently. This phenomenon not only wastes precious energy resources, but also restricts the large-scale promotion and application of renewable energy. At the same time, traditional grid expansion plans often require lengthy planning and construction cycles, and are accompanied by high capital investment, making it difficult to respond quickly to growing energy demand. Therefore, how to improve transmission capacity by optimizing existing grid assets without relying on large-scale new transmission facilities has become one of the key topics in current power system research.

[0003] In addition, the large-scale grid connection of renewable energy has replaced the active power of conventional generators, and the reduction of reactive power sources cannot provide enough reactive power to the grid. Therefore, reactive power output will be transferred to the remaining online units and other reactive power sources. This shift may bring the available reactive power sources close to their operating limits. At the same time, the changes in active power access caused by wind and solar access may change the distribution of power and voltage across the entire network, especially in areas with insufficient reactive power. These reasons may lead to voltage stability problems in the power system or even voltage collapse.

[0004] Dynamic Line Rating (DLR) and Optimal Transmission Switching (OTS) technologies are flexible measures for economic operation and preventive control of power systems, and are widely used to improve the grid's ability to accept renewable energy and its stability. Specifically, the dynamic line rating technology can dynamically adjust the rated value of the transmission line according to the actual temperature and environmental parameters of the conductor by real-time monitoring of the conductor's operating environment, thereby improving the grid's ability to accept renewable energy. Optimal transmission switching technology further improves the ability to access renewable energy through reasonable transmission line topology optimization. Therefore, the combination of DLR and OTS has become a key way to improve the access of renewable energy.

[0005] Traditional grid-side resources are often underutilized, such as static line ratings and fixed transmission topologies. This approach is difficult to cope with the uncertainty of renewable energy and grid load fluctuations across time periods. In complex power systems, it is difficult to deliver more renewable energy power to the load center using a static model alone. Therefore, it is necessary to propose a comprehensive optimization method that takes into account voltage stability constraints and transmission safety requirements, using dynamic line ratings and optimal transmission switching to maximize the access capacity of renewable energy while ensuring system safety.

[0006] In terms of mathematical essence, the mathematical model for maximizing renewable energy access based on dynamic line ratings and optimal transmission switching is a nonlinear and nonconvex optimization model, which is characterized by nonlinear objective functions and constraints. Existing solution methods are usually computationally inefficient and difficult to converge. The difficulty in solving it lies in: (1) Reactive power balance has a direct impact on the static voltage stability of the power system. The DC power flow model ignores the correlation between reactive power and voltage and cannot accurately reflect the voltage change and stability requirements of the system. Therefore, the linearized DC power flow model cannot be simply used in analysis and solution. In addition, in the study of voltage stability, a more complex AC power flow model must be used to fully consider the reactive power, node voltage amplitude and its impact on the overall stability of the system. (2) The model contains a large number of nonlinear and nonconvex constraints, which makes its solution process more complicated. Nonlinear constraints such as AC power flow equations and AC continuous power flow equations involve complex relationships between variables, and nonconvex constraints make it difficult for traditional optimization algorithms to solve them directly. These nonlinear and nonconvex constraints not only increase the computational difficulty of the model, but also put forward higher requirements on the globality of the optimization results. (3) Traditional DLR implementation methods are usually based on the IEEE 738 standard to evaluate the thermal balance state of transmission line conductors under specific environmental conditions. The dynamic transmission capacity of the line is determined by accurately measuring and calculating parameters such as conductor temperature, ambient wind speed, and solar radiation. However, it is well known that the electrical parameters of the line (such as resistance and inductance) will change accordingly with changes in temperature. Summary of the invention

[0007] In view of the above deficiencies in the prior art, the purpose of the present invention is to provide a new energy maximum access calculation method based on DLR and OTS, by dynamically adjusting the line rating by utilizing dynamic line rating technology, and selecting the optimal line switching scheme in combination with optimal transmission switching technology, so as to maximize the access capacity of renewable energy while meeting the voltage stability and transmission safety requirements of the power grid.

[0008] To achieve the above objectives, the present invention provides a new energy maximum access calculation method based on DLR and OTS, comprising the following steps: S1. Construct a renewable energy access maximization model based on dynamic line limit current DLR and optimal line switching OTS. The model takes maximizing renewable energy access as the optimization goal and takes AC power flow balance constraint, AC continuous power flow balance constraint, limit margin demand constraint, generator output power constraint, line transmission power constraint, voltage amplitude constraint and line switching quantity constraint as constraints. S2. Obtaining the operation data of the power system, including the topological structure of the power system, the operation status of each transmission line, the power output and load demand of each generator set (including renewable energy generator sets and traditional generator sets); S3, obtaining real-time conductor temperature data of the transmission line through a temperature sensor installed on the transmission line, and obtaining current data of the transmission line through a current transformer installed on the transmission line; S4. Calculate the dynamic maximum allowable current value of the transmission line according to the DLR technology taking into account the line parameter correction (the known DLR technology may also be used to obtain the dynamic maximum allowable current value of the transmission line); S5. Use a continuous power flow algorithm (a known algorithm may be used) to calculate the renewable energy access capacity of the current power system and its voltage stability margin; during the calculation process, gradually increase the access amount of renewable energy and load demand until the voltage stability limit or line transmission limit or voltage amplitude limit is reached; record the maximum access amount of renewable energy at this time, the reasons for limiting the access of renewable energy, and the power system status at the limit point (including the voltage amplitude of each node, the voltage phase angle, and the power of each branch); S6, judging whether the static voltage stability margin meets the threshold requirement at this time, if not, executing a three-stage method to solve the switching transmission line that meets the threshold requirement, the three-stage method includes a pre-screening stage, a sorting stage and a detailed calculation stage; if it meets, calculating the amount of renewable energy access at the next moment; S7. Execute the pre-screening stage: S71. If the reason for limiting the access of renewable energy is the transmission capacity limitation of the transmission line or the voltage amplitude limitation, then at this limit point, a power flow calculation is performed on the power system after each transmission line is disconnected by using a fast decoupling power flow algorithm, and a set of candidate switching transmission lines is pre-screened and sent to S8; S72. If the reason for limiting the access of renewable energy is the static voltage stability limitation, then the load margin change after switching each transmission line is calculated, and the candidate transmission line set is obtained by sorting, and sent to S8; S8, execution sorting stage: applying the look-ahead load margin estimation method (a known estimation method may be used) to estimate the load margin from the operation point of the power system to the thermal limit point, the voltage amplitude limit point and the static voltage stability limit point after each switching transmission line, and sorting the candidate switching transmission lines in descending order according to the estimated load margin, and sending the top-ranked candidate switching transmission lines to S9; S9, executing detailed calculation stage: applying continuous power flow method to calculate renewable energy access capacity of the power system after candidate switching transmission lines are switched one by one, and the candidate switching transmission line corresponding to the maximum access capacity is the optimal switching transmission line; S10. After completing the three-stage method calculation, output the transmission line switching scheme and the maximum renewable energy access capacity corresponding to each transmission line switching scheme.

[0009] As a preferred solution of the present invention, in S1, the objective function of the renewable energy access maximization model is: (1); In the formula, is a set of nodes containing renewable energy units, represents the i-th node with renewable energy units; is the load margin; , They are respectively the active power output and active power change of the renewable energy unit on node i.

[0010] As a preferred solution of the present invention, in S1, the AC power flow balance constraint is: (2); In the formula, is the active power output of the traditional generator set at node i; is the active power of the load on node i; , are the reactive power outputs of the traditional generator set and renewable energy generator set at node i respectively; is the reactive power required by the load at node i; , are the voltage amplitudes of nodes i and j respectively; is the voltage phase angle difference between node i and node j; , are the conductance and susceptance of the transmission line ij respectively; is a 0-1 integer variable, indicating the operating status of the transmission line ij. When ij is disconnected, it means that the transmission line ij is in disconnected state. When ij is in operation, it indicates that the transmission line ij is in operation; is the total number of nodes; The AC continuous power flow balance constraint is: (3); (4); In the formula, is the active power change of the traditional generator set at node i; is the change in active power of the load at node i; is the reactive power change of the traditional generator set at node i; , They are the voltage amplitudes of node i and node j when the power system reaches the limit point of renewable energy access; is the voltage phase angle difference between node i and node j when the renewable energy access limit point is reached; , They are the growth directions of active power and reactive power of the power system; The load margin requirement constraint is: (5); In the formula, , , They are the load margin from the operating point to the thermal limit point, the voltage amplitude limit point and the static voltage stability limit point; is the set load margin requirement; The generator output power constraint is: (6); In the formula, , are the minimum and maximum active power output of the traditional generator set at node i, respectively; , are the minimum and maximum active power output of the renewable energy unit at node i, respectively; , are the minimum and maximum reactive power outputs of the traditional generator set at node i, respectively; , are the minimum and maximum reactive power outputs of renewable energy units at node i, respectively; The line transmission constraints are: (7); In the formula, is the current value of the transmission line ij at the limit operating point; is the maximum allowable current value of the transmission line ij at the tth moment; The voltage amplitude constraint is: (8); (9); In the formula, , are the minimum and maximum values ​​of the voltage amplitude on node i respectively; The line switching quantity constraint is: (10); In the formula, is the number of transmission lines allowed to be switched.

[0011] As a preferred solution of the present invention, in said S4, the process of calculating the dynamic maximum allowable current value of the transmission line is: S41. Express the conductor heat dissipation power function as the conductor temperature (that is, the measured conductor temperature) is an m-order rational polynomial. At this time, the thermal balance equation of the transmission line conductor is expressed as: (11); In the formula, The conductor is The resistance value under is the thermal inertia value of the conductor; are the polynomial coefficients; express zth power; I is the current passing through the transmission line; t is time, indicating the moment; S42, take m=2, the heat balance equation at time t is expressed as: (12); In the formula, , and are the coefficients of the polynomial to be determined; For the tth moment The derivative of is expressed as: (13); In the formula, is the measured temperature of the conductor at the tth moment; For the The measured temperature of the conductor at the time; is the time interval between two adjacent conductor temperature measurements; is between two adjacent moments (i.e., the tth moment and the The average conductor current flowing through the conductor at the time (same below); For conductors Resistance value at temperature; is the average conductor temperature between two adjacent moments, expressed as: (14); S43, using the conductor temperature data measured at the tth moment and the previous M moments, construct a temperature matrix A; using the current values ​​flowing through the conductor measured at the tth moment and the previous M moments, construct a current matrix Y; define a threshold and : S431, if , then A and Y are expressed as: (15); (16); In the formula, That is the time The derivative of , and the other symbols are similar (for example For the Moment and The average conductor temperature between two adjacent moments in time); S432, if ,and , then A and Y are expressed as: (17); (18); S433, if ,and , then the dynamic maximum allowable current of the transmission line at time t is , and go to S5 ( That is the The dynamic maximum allowable current of the transmission line at the moment); S44. Based on the heat balance equation of M+1 m-order rational polynomials, a matrix equation is formed, that is, Y=AX, where X is the coefficient matrix to be determined. If ,but ;if ,and ,but ; S45. Use the least squares method to make the best estimate of X and obtain all the X to be calculated: (19); (T stands for transpose) S46. Correction of the length of the transmission line , the calculation formula is: (20); In the formula, is the linear expansion coefficient of the conductor; is the secondary expansion coefficient of the conductor; It is the maximum temperature allowed for the conductor; is the initial conductor temperature; is Length of transmission line under S47, modify the transmission line Resistance value at temperature If the transmission line is a short-distance transmission line (less than 100 km in length), use formula (21) to calculate If the transmission line is a long-distance transmission line (length greater than or equal to 100 km), use formula (22) to calculate , respectively expressed as: (twenty one); (twenty two); In the formula, The conductor is Resistance value at temperature; is the wave impedance of the conductor; is the propagation coefficient of the conductor; represents the hyperbolic sine function; real represents the real part of the complex number; S48, Solution , expressed as: (twenty three).

[0012] As a preferred embodiment of the present invention, Take 0.2°C / s, Choose 0.1A or 0.5A.

[0013] As a preferred solution of the present invention, in the above S71, the formula for pre-screening the candidate switching transmission line set is: (twenty four); (25); In the formula, is an indicator of candidate switching transmission lines due to thermal rating limitations; is an indicator of candidate switching transmission lines due to voltage amplitude limitations; is the current of transmission line ij after switching transmission line k; , if the transmission line ij is equipped with DLR technology and equipment, then is the dynamic maximum allowable current value of the transmission line ij at time t, otherwise it is the static maximum allowable current value of the transmission line ij; is the voltage amplitude at node i after switching transmission line k; is the current value on transmission line ij before switching transmission line k.

[0014] As a preferred solution of the present invention, in the above S72, the calculation process of the load margin change after switching each transmission line is as follows: S721. The AC continuous power flow equation is expressed in compact form as: (26); Where x is the state variable, including voltage amplitude, voltage phase angle, line power and generator output power; p represents the impedance of the switchable transmission line; is the static voltage stability margin; S722, with increase, or will reach the upper limit, i.e. or , then the AC continuous power flow equation is expressed in compact form as: (27); At the static voltage stability limit point At , there exists a non-zero vector ω that is orthogonal to the Jacobian matrix J, that is, ωJ=0, so: (28); The load margin change caused by switching the transmission line is The calculation formula is: (29); In the formula, , are the derivatives of (26) and (27) with respect to x respectively; , are the derivatives of (26) and (27) with respect to p; , They are respectively: If the transmission line is disconnected, then is the negative value of the impedance parameter of the transmission line; if the transmission line is put into operation, then is the impedance parameter of the transmission line; is an intermediate variable, expressed as: (30); Therefore, the change in load margin due to switching transmission line k is The calculation formula is: (31); In the formula, is the impedance parameter change caused by switching transmission line k. If transmission line k is disconnected, then is the negative value of the impedance parameter of the transmission line k; if the transmission line is put into operation, then is the impedance parameter of the transmission line k; After calculation by formula (31), select transmission line and send it to S8.

[0015] As a preferred solution of the present invention, in S8, the specific calculation steps for executing the sorting stage are: S81, from the candidate switching transmission line k selected by S7, apply the look-ahead load margin estimation method to quickly estimate the load margin of the thermal limit point of the power system after switching the transmission line k , Load margin at voltage amplitude limit point and load margin at the static voltage stability limit point ; S82. Calculate the load margin of the power system after switching transmission line k , the calculation formula is: (32); S83, Judgment Whether the threshold requirement is met, i.e. , if it is satisfied, then the transmission line k is retained, otherwise the transmission line k is eliminated; S84, repeating steps S81-S83 until all candidate switching transmission lines screened in step S7 are calculated, and then executing S85; S85. Sort all the retained switching transmission lines in descending order according to the load margin calculated by S82, and send the candidate switching transmission lines ranked 20% to S9.

[0016] As a preferred embodiment of the present invention, in the above S9, the specific steps of executing the detailed calculation stage are: applying the continuous power flow method to sequentially calculate the thermal limit point margin, voltage amplitude limit point margin, static voltage stability limit point margin of the system after switching and the renewable energy access capacity of the power system after switching the transmission line for the candidate switching transmission lines sorted in S8; outputting the calculated maximum accessible capacity and its corresponding candidate switching transmission line, which is the optimal switching line solution.

[0017] The algorithm involved in the present invention can be executed by an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the above algorithm calculation is implemented by executing the software by the processor.

[0018] The beneficial effects of the present invention are: The present invention combines the dynamic line rating DLR technology and the optimal transmission switching OTS technology. By utilizing the DLR technology to dynamically adjust the line rating and combining the OTS technology to select the optimal line switching solution, the access capacity of renewable energy can be maximized while meeting the voltage stability and transmission safety requirements of the power grid.

[0019] The present invention significantly improves the grid's ability to accept renewable energy (such as wind power and photovoltaic power generation) by combining DLR technology and OTS technology. By introducing static voltage stability constraints, it ensures that the voltage stability of the power system is guaranteed while improving the access to renewable energy.

[0020] The three-stage optimization solution strategy (pre-screening, sorting, and detailed calculation) proposed in the present invention greatly reduces the computational complexity of problem solving. Compared with the traditional global optimization algorithm, the three-stage method can not only obtain a feasible solution in a shorter time, but also provide multiple options for practical applications. This makes the present invention have stronger real-time application potential and is suitable for the optimization dispatch of large-scale power systems.

[0021] The present invention also proposes a method for calculating a dynamic line rating with a line parameter correction function. The method incorporates the thermal expansion effect caused by conductor temperature changes into the line operating parameters to obtain a more accurate dynamic rating of the transmission line. This improvement can effectively improve the accuracy of DLR calculation, thereby improving the operating efficiency and safety of the transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 It is a comparison diagram of renewable energy access power using SLR and DLR technologies in the IEEE 118 node system during the verification process of the present invention; Figure 3 is a PV curve diagram after switching lines 15–17 and 30–38 in the IEEE 118-node system during the verification process of the present invention; Figure 4 It is a comparison diagram of renewable energy access of IEEE118 node system under heavy load and light load conditions during the verification process of the present invention; Figure 5 It is a comparison chart of the results of DLR calculation by IEEE24-node system and IEEE738 standard during the verification process of the present invention. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are further described below in conjunction with the accompanying drawings: like Figure 1 As shown, the maximum access calculation method of new energy based on DLR and OTS includes the following steps: S1. Construct a renewable energy access maximization model based on dynamic line limit current DLR and optimal line switching OTS. The model takes maximizing renewable energy access as the optimization goal and takes AC power flow balance constraint, AC continuous power flow balance constraint, limit margin demand constraint, generator output power constraint, line transmission power constraint, voltage amplitude constraint and line switching quantity constraint as constraints. S2. Obtaining the operation data of the power system, including the topological structure of the power system, the operation status of each transmission line, the power output and load demand of each generator set; S3, obtaining real-time conductor temperature data of the transmission line through a temperature sensor installed on the transmission line, and obtaining current data of the transmission line through a current transformer installed on the transmission line; S4. Calculate the dynamic maximum allowable current value of the transmission line according to the DLR technology taking into account the line parameter correction; S5. Use the continuous power flow algorithm to calculate the renewable energy access capacity and voltage stability margin of the current power system; during the calculation process, gradually increase the access amount of renewable energy and load demand until the voltage stability limit or line transmission limit or voltage amplitude limit is reached; record the maximum access amount of renewable energy at this time, the reasons for limiting the access of renewable energy, and the power system status at the limit point; S6, judging whether the static voltage stability margin meets the threshold requirement at this time, if not, executing a three-stage method to solve the switching transmission line that meets the threshold requirement, the three-stage method includes a pre-screening stage, a sorting stage and a detailed calculation stage; if it meets, calculating the amount of renewable energy access at the next moment; S7. Execute the pre-screening stage: Due to different restrictions on renewable energy access under different operating conditions of the power system, the maximum access to renewable energy power in the power system may be constrained by voltage amplitude limitations, thermal rating limitations or voltage stability limitations. Therefore, in order to quickly screen out the effective lines of all candidate lines, several indicators are defined to quickly evaluate the performance of OTS in improving the renewable energy acceptability of the power grid; S71. If the reason for limiting the access of renewable energy is the transmission capacity limitation of the transmission line or the voltage amplitude limitation, then at this limit point, a power flow calculation is performed on the power system after each transmission line is disconnected by using a fast decoupling power flow algorithm, and a set of candidate switching transmission lines is pre-screened and sent to S8; S72. If the reason for limiting the access of renewable energy is the static voltage stability limitation, then the load margin change after switching each transmission line is calculated, and the candidate transmission line set is obtained by sorting, and sent to S8; S8, execution sorting stage: apply the look-ahead load margin estimation method to estimate the load margin from the operating point of the power system to the thermal limit point, voltage amplitude limit point and static voltage stability limit point after each switching transmission line, and sort the candidate switching transmission lines in descending order according to the estimated load margin, and send the top-ranked candidate switching transmission lines to S9; through this fast estimation, the transmission lines with the potential to increase the capacity of the power grid can be quickly screened out, sorted according to their contribution to the power system margin, and the top-ranked line solutions are retained for further detailed calculations. The goal of this stage is to ensure the selection of the optimal switching solution through fast calculations and reduce unnecessary waste of computing resources; S9, executing detailed calculation stage: applying continuous power flow method to calculate renewable energy access capacity of the power system after candidate switching transmission lines are switched one by one, and the candidate switching transmission line corresponding to the maximum access capacity is the optimal switching transmission line; S10. After completing the three-stage method calculation, output the transmission line switching scheme and the maximum renewable energy access capacity corresponding to each transmission line switching scheme.

[0024] In S1, the objective function of the renewable energy access maximization model is: (1); In the formula, is a set of nodes containing renewable energy units, represents the i-th node with renewable energy units (i.e., the node of the power system); is the load margin; , They are respectively the active power output and active power change of the renewable energy unit on node i. The objective function consists of two parts, one is the current output of the renewable energy unit, and the other is the active power that the renewable unit can increase.

[0025] In S1, the AC power flow balance constraint is: (2); In the formula, is the active power output of the traditional generator set at node i; is the active power of the load on node i; , are the reactive power outputs of the traditional generator set and renewable energy generator set at node i respectively; is the reactive power required by the load at node i; , are the voltage amplitudes of nodes i and j respectively; is the voltage phase angle difference between node i and node j; , are the conductance and susceptance of the transmission line ij respectively; is a 0-1 integer variable, indicating the operating status of the transmission line ij. When ij is disconnected, it means that the transmission line ij is in disconnected state. When ij is in operation, it indicates that the transmission line ij is in operation; is the total number of nodes; The AC continuous power flow balance constraint is: (3); (4); In the formula, is the active power change of the traditional generator set at node i; is the change in active power of the load at node i; is the reactive power change of the traditional generator set at node i; , They are the voltage amplitudes of node i and node j when the power system reaches the limit point of renewable energy access; is the voltage phase angle difference between node i and node j when the renewable energy access limit point is reached; , They are the growth directions of active power and reactive power of the power system; The load margin requirement constraint is: (5); In the formula, , , They are the load margin from the operating point to the thermal limit point, the voltage amplitude limit point and the static voltage stability limit point; is the set load margin requirement; The generator output power constraint is: (6); In the formula, , are the minimum and maximum active power output of the traditional generator set at node i, respectively; , are the minimum and maximum active power output of the renewable energy unit at node i, respectively; , are the minimum and maximum reactive power outputs of the traditional generator set at node i, respectively; , are the minimum and maximum reactive power outputs of renewable energy units at node i, respectively; The line transmission constraints are: (7); In the formula, is the current value of the transmission line ij at the limit operating point; is the maximum allowable current value of the transmission line ij at the tth moment; The voltage amplitude constraint is: (8); (9); In the formula, , are the minimum and maximum values ​​of the voltage amplitude on node i respectively; The line switching quantity constraint is: (10); In the formula, is the number of transmission lines that are allowed to be switched. Switching multiple lines may result in connecting more renewable energy to the grid (power system), but this is not economical and is different from the common operation in the actual power system. Therefore, switching a single line is given priority.

[0026] In S4, the process of calculating the dynamic maximum allowable current value of the transmission line is: S41. Express the conductor heat dissipation power function as the conductor temperature The m-th order rational polynomial, the thermal balance equation of the transmission line conductor is expressed as: (11); In the formula, The conductor is The resistance value under is the thermal inertia value of the conductor; are the polynomial coefficients; express zth power; I is the current passing through the transmission line; t is time, indicating the moment; S42, take m=2, the heat balance equation at time t is expressed as: (12); In the formula, , and are the coefficients of the polynomial to be determined; For the tth moment The derivative of is expressed as: (13); In the formula, is the measured temperature of the conductor at the tth moment; For the The measured temperature of the conductor at the time; is the time interval between two adjacent conductor temperature measurements; is the average conductor current flowing between two adjacent moments; For conductors Resistance value at temperature; is the average conductor temperature between two adjacent moments, expressed as: (14); S43, using the conductor temperature data measured at the tth moment and the previous M moments, construct a temperature matrix A; using the current values ​​flowing through the conductor measured at the tth moment and the previous M moments, construct a current matrix Y; define a threshold and : S431, if , then A and Y are expressed as: (15); (16); In the formula, That is the time The derivative of , and the other symbols are the same; S432, if ,and , then A and Y are expressed as: (17); (18); S433, if ,and , then the dynamic maximum allowable current of the transmission line at time t is , and go to S5; S44. Based on the heat balance equation of M+1 m-order rational polynomials, a matrix equation is formed, that is, Y=AX, where X is the coefficient matrix to be determined. If ,but ;if ,and ,but ; S45. Use the least squares method to make the best estimate of X and obtain all the X to be calculated: (19); S46. Correction of the length of the transmission line , the calculation formula is: (20); In the formula, is the linear expansion coefficient of the conductor; is the secondary expansion coefficient of the conductor; It is the maximum temperature allowed for the conductor; is the initial conductor temperature; is Length of transmission line under S47, modify the transmission line Resistance value at temperature , if the transmission line is a short-distance transmission line, use formula (21) to calculate , if the transmission line is a long-distance transmission line, use formula (22) to calculate , respectively expressed as: (twenty one); (twenty two); In the formula, The conductor is Resistance value at temperature; is the wave impedance of the conductor; is the propagation coefficient of the conductor; represents the hyperbolic sine function; real represents the real part of the complex number; S48, Solution , expressed as: (twenty three).

[0027] Take 0.2°C / s, Choose 0.1A or 0.5A.

[0028] In S71, the formula for pre-screening the candidate switching transmission line set is: (twenty four); (25); In the formula, is an indicator of candidate switching transmission lines due to thermal rating limitations; is an indicator of candidate switching transmission lines due to voltage amplitude limitations; is the current of transmission line ij after switching transmission line k; , if the transmission line ij is equipped with DLR technology and equipment, then is the dynamic maximum allowable current value of the transmission line ij at time t, otherwise it is the static maximum allowable current value of the transmission line ij; is the voltage amplitude at node i after switching transmission line k; is the current value on transmission line ij before switching transmission line k.

[0029] Theoretically, in the system after each switching line, the above two indicators after each candidate line output can be obtained through an accurate power flow algorithm. In order to strike a balance between calculation speed and accuracy, this embodiment uses a fast decoupling power flow method. It should be noted that the fast decoupling power flow method is performed at the limit point (i.e., the thermal limit or voltage amplitude limit point) rather than at the operating point.

[0030] In S72, the calculation process of the load margin change after switching each transmission line is as follows: S721. The AC continuous power flow equation is expressed in compact form as: (26); Where x is the state variable, including voltage amplitude, voltage phase angle, line power and generator output power; p represents the impedance of the switchable transmission line; is the static voltage stability margin; S722, with increase, or will reach the upper limit, i.e. or , then the AC continuous power flow equation is expressed in compact form as: (27); At the static voltage stability limit point At , there exists a non-zero vector ω that is orthogonal to the Jacobian matrix J, that is, ωJ=0, so: (28); The load margin change caused by switching the transmission line is The calculation formula is: (29); In the formula, , are the derivatives of (26) and (27) with respect to x respectively; , are the derivatives of (26) and (27) with respect to p; , They are respectively: If the transmission line is disconnected, then is the negative value of the impedance parameter of the transmission line; if the transmission line is put into operation, then is the impedance parameter of the transmission line; is an intermediate variable, expressed as: (30); Therefore, the change in load margin due to switching transmission line k is The calculation formula is: (31); In the formula, is the impedance parameter change caused by switching transmission line k. If transmission line k is disconnected, then is the negative value of the impedance parameter of the transmission line k; if the transmission line is put into operation, then is the impedance parameter of the transmission line k; After calculation by formula (31), select transmission line and send it to S8.

[0031] In S8, the specific calculation steps for executing the sorting phase are: S81, from the candidate switching transmission line k selected by S7, apply the look-ahead load margin estimation method to quickly estimate the load margin of the thermal limit point of the power system after switching the transmission line k , Load margin at voltage amplitude limit point and load margin at the static voltage stability limit point ; S82. Calculate the load margin of the power system after switching transmission line k , the calculation formula is: (32); S83, Judgment Whether the threshold requirement is met, i.e. , if it is satisfied, then the transmission line k is retained, otherwise the transmission line k is eliminated; S84, repeating steps S81-S83 until all candidate switching transmission lines screened in step S7 are calculated, and then executing S85; S85. Sort all the retained switching transmission lines in descending order according to the load margin calculated by S82, and send the candidate switching transmission lines ranked 20% to S9.

[0032] In S9, the specific steps of executing the detailed calculation stage are: applying the continuous power flow method to calculate the thermal limit point margin, voltage amplitude limit point margin, static voltage stability limit point margin of the system after switching and the renewable energy access capacity of the power system after switching the transmission line for the candidate switching transmission lines sorted in S8 one by one in sequence; outputting the calculated maximum value of the accessible capacity and its corresponding candidate switching transmission line, which is the optimal switching line solution.

[0033] The verification process is: Taking the IEEE 118-node system (a classic power system simulation test system, including 118 nodes and 186 lines) as an example, 7 renewable energy generators are set on different nodes #6, #8, #18, #61, #72, #80, and #103, with a total rated power of 727MW. The lines connecting the renewable energy units to the grid are set to the lines that apply DLR, including transmission lines 17-18, 8-30, 60-61, 68-81 and 103-110. The simulation results show the effect of the system's maximum renewable energy access capacity after applying traditional static line rating and dynamic line rating technologies, as well as the improvement effect after applying the feasible solution of the transmission switching line selected by the three-stage method. During the period from 00:05 to 05:00, when the SLR technology was used, the renewable energy power absorbed by the power system was 58533MW, while through the DLR technology, the renewable energy power absorbed by the power system increased to 68904MW, an increase of 17.72%, such as Figure 2 This shows that DLR technology can significantly increase the power system's ability to accommodate renewable energy by dynamically increasing the transmission capacity of transmission lines.

[0034] At 00:05, after switching transmission line 15-17, the renewable energy power absorbed by the power system increased from 1034MW to 1135.1MW, with an improvement of 10.1%, which was achieved by the combination of DLR and OTS methods. In addition, the three-stage method can provide multiple candidate transmission line switching schemes, as shown in Table 1. Among them, the top-ranked transmission lines (such as lines 15-17, 30-38, etc.) can significantly improve the power system's ability to accept renewable energy. The PV curves of the power system before and after switching transmission lines 15-17 and 30-38 are shown in Figure 1. Figure 3 shown.

[0035] Table 1 Solutions for switching transmission lines at 00:05

[0036] The verification process also tested the performance of the power system under light and heavy load conditions. Under heavy load, the power system absorbed slightly less renewable energy power than under light load. For example, under SLR, the power system absorbed 834.8MW of renewable energy power under heavy load and 979.6MW under light load. Figure 4 This indicates that the load increase makes it easier for the power system to reach the thermal stability limit or voltage limit.

[0037] The test of DLR technology in the IEEE118 node system has significantly improved the acceptance capacity of renewable energy, and by combining the optimal transmission switching technology, the access power of renewable energy has been further improved. Specifically, DLR solves the conservative limitations of traditional static line ratings in actual operation by dynamically adjusting the line ratings in real time. OTS optimizes the topology of the power grid and redistributes the power flow, allowing more renewable energy to be connected to the power system. The simulation results show that the combined application of DLR and OTS can significantly improve the flexibility of the power system and increase the ability of the power system to accept renewable energy. The results prove the effectiveness of the combination of DLR and OTS technology in improving the efficiency of power grid operation, reducing the wind and solar power abandonment rate, and promoting the development of sustainable energy.

[0038] In addition, the DLR technology taking into account line parameter correction proposed by S4 of this embodiment is verified separately: Taking line 21-22 in the IEEE 24-node system (a commonly used example of a power system) as an example, the calculation process of the technology proposed in S4 of this embodiment is described. In this example, there are 10 generators and 17 load nodes. The units at nodes 7 and 12 are set as renewable energy units with a total capacity of 490MW.

[0039] Figure 5 The dynamic rating of the line obtained by the calculation method based on the IEEE738 standard and the DLR technology of this embodiment is shown. In the time period from 2:00 to 18:00, the trends of the two are basically the same. And compared with the static line rating, the current rating of DLR has been significantly improved, which shows that this embodiment can make more full use of the capacity of the transmission line. The line rating gain obtained by using the DLR calculation method proposed in this embodiment is between 45% and 93%. This shows that this method effectively enhances the transmission potential of the line and allows operators to transmit more renewable energy to the load center. In the time period from 10:25 to 10:50, the conductor temperature rises, and the dynamic rating of the line calculated by this embodiment gradually decreases. In the time period from 10:50 to 12:00, the conductor temperature drops, and the dynamic rating of the line calculated by this embodiment gradually increases. These two trends show that the DLR calculation method of this embodiment can dynamically adjust the current rating according to the real-time temperature change to avoid damage caused by overheating of the line, and can effectively develop the transmission potential of the transmission line when the conductor temperature is low.

[0040] Therefore, the transmission line dynamic rating calculation method taking into account line parameter correction proposed in this embodiment can significantly improve the transmission line rating, and does not require high investment costs and long cycles like new transmission lines. The use of DLR technology is one of the current measures with low investment costs, short cycles and high flexibility. The transmission line dynamic rating calculation method taking into account line parameter correction proposed in this embodiment can dynamically adjust the current rating according to real-time temperature changes to avoid damage caused by overheating of the line.

Claims

1. A new energy maximum access calculation method based on DLR and OTS, characterized in that The following steps are involved: S1. Construct a renewable energy access maximization model based on dynamic line limit current DLR and optimal line switching OTS. The model takes maximizing renewable energy access as the optimization goal and takes AC power flow balance constraint, AC continuous power flow balance constraint, limit margin demand constraint, generator output power constraint, line transmission power constraint, voltage amplitude constraint and line switching quantity constraint as constraints. S2. Obtaining the operation data of the power system, including the topological structure of the power system, the operation status of each transmission line, the power output and load demand of each generator set; S3, obtaining real-time conductor temperature data of the transmission line through a temperature sensor installed on the transmission line, and obtaining current data of the transmission line through a current transformer installed on the transmission line; S4. Calculate the dynamic maximum allowable current value of the transmission line according to the DLR technology taking into account the line parameter correction; S5. Calculate the renewable energy access capacity and voltage stability margin of the current power system using the continuous power flow algorithm; During the calculation process, the access amount of renewable energy and the load demand are gradually increased until the voltage stability limit or the line transmission limit or the voltage amplitude limit is reached; the maximum access amount of renewable energy, the reasons for limiting the access of renewable energy, and the state of the power system at the limit point are recorded; S6, judging whether the static voltage stability margin meets the threshold requirement at this time, if not, executing a three-stage method to solve the switching transmission line that meets the threshold requirement, the three-stage method includes a pre-screening stage, a sorting stage and a detailed calculation stage; if it meets, calculating the amount of renewable energy access at the next moment; S7. Execute the pre-screening stage: S71. If the reason for limiting the access of renewable energy is the transmission capacity limitation of the transmission line or the voltage amplitude limitation, then at this limit point, a power flow calculation is performed on the power system after each transmission line is disconnected by using a fast decoupling power flow algorithm, and a set of candidate switching transmission lines is pre-screened and sent to S8; S72. If the reason for limiting the access of renewable energy is the static voltage stability limitation, then the load margin change after switching each transmission line is calculated, and the candidate transmission line set is obtained by sorting, and sent to S8; S8, execution sorting stage: apply the look-ahead load margin estimation method to estimate the load margin from the operation point of the power system to the thermal limit point, the voltage amplitude limit point and the static voltage stability limit point after each switching transmission line, and sort the candidate switching transmission lines in descending order according to the estimated load margin, and send the top-ranked candidate switching transmission lines to S9; S9, executing detailed calculation stage: applying continuous power flow method to calculate renewable energy access capacity of the power system after candidate switching transmission lines are switched one by one, and the candidate switching transmission line corresponding to the maximum access capacity is the optimal switching transmission line; S10. After completing the three-stage method calculation, output the transmission line switching scheme and the maximum renewable energy access capacity corresponding to each transmission line switching scheme.

2. The maximum access calculation method of new energy based on DLR and OTS according to claim 1 is characterized in that: In S1, the objective function of the renewable energy access maximization model is: （1）； In the formula, is a set of nodes containing renewable energy units, represents the i-th node with renewable energy units; is the load margin; , They are respectively the active power output and active power change of the renewable energy unit on node i.

3. The maximum access calculation method of new energy based on DLR and OTS according to claim 2 is characterized in that: In S1, the AC power flow balance constraint is: （2）； In the formula, is the active power output of the traditional generator set at node i; is the active power of the load on node i; , are the reactive power outputs of the traditional generator set and renewable energy generator set at node i respectively; is the reactive power required by the load at node i; , are the voltage amplitudes of nodes i and j respectively; is the voltage phase angle difference between node i and node j; , are the conductance and susceptance of the transmission line ij respectively; is a 0-1 integer variable, indicating the operating status of the transmission line ij. When ij is disconnected, it means that the transmission line ij is in disconnected state. When ij is in operation, it indicates that the transmission line ij is in operation; is the total number of nodes; The AC continuous power flow balance constraint is: （3）； （4）； In the formula, is the active power change of the traditional generator set at node i; is the change in active power of the load at node i; is the reactive power change of the traditional generator set at node i; , They are the voltage amplitudes of node i and node j when the power system reaches the limit point of renewable energy access; is the voltage phase angle difference between node i and node j when the renewable energy access limit point is reached; , They are the growth directions of active power and reactive power of the power system; The load margin requirement constraint is: （5）； In the formula, , , They are the load margin from the operating point to the thermal limit point, the voltage amplitude limit point and the static voltage stability limit point; is the set load margin requirement; The generator output power constraint is: （6）； In the formula, , are the minimum and maximum active power output of the traditional generator set at node i, respectively; , are the minimum and maximum active power output of the renewable energy unit at node i, respectively; , are the minimum and maximum reactive power outputs of the traditional generator set at node i, respectively; , are the minimum and maximum reactive power outputs of renewable energy units at node i, respectively; The line transmission constraints are: （7）； In the formula, is the current value of the transmission line ij at the limit operating point; is the maximum allowable current value of the transmission line ij at time t; The voltage amplitude constraint is: （8）； （9）； In the formula, , are the minimum and maximum values ​​of the voltage amplitude on node i respectively; The line switching quantity constraint is: （10）； In the formula, is the number of transmission lines allowed to be switched.

4. The maximum access calculation method of new energy based on DLR and OTS according to claim 1 is characterized in that: In the above-mentioned S4, the process of calculating the dynamic maximum allowable current value of the transmission line is: S41. Express the conductor heat dissipation power function as the conductor temperature The m-th order rational polynomial, the thermal balance equation of the transmission line conductor is expressed as: （11）； In the formula, The conductor is The resistance value under is the thermal inertia value of the conductor; are the polynomial coefficients; express zth power; I is the current passing through the transmission line; t is time, indicating the moment; S42, take m=2, the heat balance equation at time t is expressed as: （12）； In the formula, , and are the coefficients of the polynomial to be determined; For the tth moment The derivative of is expressed as: （13）； In the formula, is the measured temperature of the conductor at the tth moment; For the The measured temperature of the conductor at the time; is the time interval between two adjacent conductor temperature measurements; is the average conductor current flowing between two adjacent moments; For conductors Resistance value at temperature; is the average conductor temperature between two adjacent moments, expressed as: （14）； S43, using the conductor temperature data measured at the tth moment and the previous M moments, construct a temperature matrix A; using the current values ​​flowing through the conductor measured at the tth moment and the previous M moments, construct a current matrix Y; define a threshold and : S431, if , then A and Y are expressed as: （15）； （16）； In the formula, That is the time The derivative of , and the other symbols are the same; S432, if ,and , then A and Y are expressed as: （17）； （18）； S433, if ,and , then the dynamic maximum allowable current of the transmission line at time t is , and go to S5; S44. Based on the heat balance equation of M+1 m-order rational polynomials, a matrix equation is formed, that is, Y=AX, where X is the coefficient matrix to be determined. If ,but ;if ,and ,but ; S45. Use the least squares method to make the best estimate of X and obtain all the X to be calculated: （19）； S46. Correction of the length of the transmission line , the calculation formula is: （20）； In the formula, is the linear expansion coefficient of the conductor; is the secondary expansion coefficient of the conductor; It is the maximum temperature allowed for the conductor; is the initial conductor temperature; is Length of transmission line under S47, modify the transmission line Resistance value at temperature , if the transmission line is a short-distance transmission line, use formula (21) to calculate , if the transmission line is a long-distance transmission line, use formula (22) to calculate , respectively expressed as: （21）； （22）； In the formula, The conductor is Resistance value at temperature; is the wave impedance of the conductor; is the propagation coefficient of the conductor; represents the hyperbolic sine function; real represents the real part of the complex number; S48, Solution , expressed as: （23）。 5. The maximum access calculation method of new energy based on DLR and OTS according to claim 4 is characterized in that: Take 0.2°C / s, Choose 0.1A or 0.5A.

6. The maximum access calculation method of new energy based on DLR and OTS according to claim 3 is characterized in that: In the above S71, the formula for pre-screening the candidate switching transmission line set is: （24）； （25）； In the formula, is an indicator of candidate switching transmission lines due to thermal rating limitations; is an indicator of candidate switching transmission lines due to voltage amplitude limitations; is the current of transmission line ij after switching transmission line k; , if the transmission line ij is equipped with DLR technology and equipment, then is the dynamic maximum allowable current value of the transmission line ij at time t, otherwise it is the static maximum allowable current value of the transmission line ij; is the voltage amplitude at node i after switching transmission line k; is the current value on transmission line ij before switching transmission line k.

7. The maximum access calculation method of new energy based on DLR and OTS according to claim 6 is characterized in that: In the above S72, the calculation process of the load margin change after switching each transmission line is as follows: S721. The AC continuous power flow equation is expressed in compact form as: （26）； Where x is the state variable, including voltage amplitude, voltage phase angle, line power and generator output power; p represents the impedance of the switchable transmission line; is the static voltage stability margin; S722, with increase, or will reach the upper limit, i.e. or , then the AC continuous power flow equation is expressed in compact form as: （27）； At the static voltage stability limit point At , there exists a non-zero vector ω that is orthogonal to the Jacobian matrix J, that is, ωJ=0, so: （28）； The load margin change caused by switching the transmission line is The calculation formula is: （29）； In the formula, , are the derivatives of (26) and (27) with respect to x respectively; , are the derivatives of (26) and (27) with respect to p; , They are respectively: If the transmission line is disconnected, then It is the negative value of the impedance parameter of the transmission line; If the transmission line is put into operation, is the impedance parameter of the transmission line; is an intermediate variable, expressed as: （30）； Therefore, the change in load margin due to switching transmission line k is The calculation formula is: （31）； In the formula, is the impedance parameter change caused by switching transmission line k. If transmission line k is disconnected, then is the negative value of the impedance parameter of the transmission line k; If the transmission line is put into operation, is the impedance parameter of the transmission line k; After calculation by formula (31), select transmission line and send it to S8.

8. The maximum access calculation method of new energy based on DLR and OTS according to claim 7 is characterized in that: In the above S8, the specific calculation steps for executing the sorting phase are: S81, from the candidate switching transmission line k selected by S7, apply the look-ahead load margin estimation method to quickly estimate the load margin of the thermal limit point of the power system after switching the transmission line k , Load margin at voltage amplitude limit point and load margin at the static voltage stability limit point ; S82. Calculate the load margin of the power system after switching transmission line k , the calculation formula is: （32）； S83, Judgment Whether the threshold requirement is met, i.e. , if it is satisfied, then the transmission line k is retained, otherwise the transmission line k is eliminated; S84, repeating steps S81-S83 until all candidate switching transmission lines screened in step S7 are calculated, and then executing S85; S85. Sort all the retained switching transmission lines in descending order according to the load margin calculated by S82, and send the candidate switching transmission lines ranked 20% to S9.

9. The maximum access calculation method of new energy based on DLR and OTS according to claim 8, characterized in that: In the above-mentioned S9, the specific steps of executing the detailed calculation stage are: applying the continuous power flow method to sequentially calculate the thermal limit point margin, voltage amplitude limit point margin, static voltage stability limit point margin of the system after switching and the renewable energy access capacity of the power system after switching the transmission line for the candidate switching transmission lines sorted in S8; The calculated maximum accessible capacity and its corresponding candidate switching transmission line are output, and the switching transmission line is the optimal switching line solution.

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