Calculation and optimization method of regional power transmission constraints in areas with UHV DC and new energy access

Abstract

The present invention provides a method for calculating and optimizing power transmission constraints in areas with ultra-high voltage direct current (UHVDC) and new energy access. The calculation method includes: obtaining the operating parameter information of the target power grid, taking the period of the most severe power constraints in the target area as a typical calculation scenario; based on the typical calculation scenario, determining the power generation power of various power sources, the ultra-high voltage direct current (UHVDC) transmission power of the target power grid, and the average power load of the target power grid; determining the power transmission demand of the target power grid under the typical calculation scenario and the theoretical maximum transmission power of the power transmission channel of the target power grid, and determining the power transmission constraint power of the target power grid based on the two. The optimization method includes: taking the maximum scale consumption of new energy in the target power grid as the optimization target, and constructing a power transmission constraint optimization objective function under the constraints of the target power grid. The present invention can improve the new energy consumption capacity and safety and stability of the new power system, and reduce the problems of wind and solar power abandonment.

Description

Technical Field

[0001] The present invention relates to the technical field of new power systems, and in particular to a method for calculating and optimizing power transmission constraints in areas with ultra-high voltage direct current and new energy access. Background Art

[0002] In recent years, under the premise of ensuring energy security, we have vigorously implemented renewable energy substitution, accelerated the construction of a clean, low-carbon, safe and efficient energy system, and the installed capacity of new energy has grown rapidly. However, due to the shortcomings of unstable output of new energy represented by wind and solar energy, the problem of "abandoning wind and solar power" has become increasingly prominent, especially during the flood season when the load demand is not large, but the power grid hydropower and wind power are generated at the same time, and there is a serious problem of "grabbing the channel" for power output. On the other hand, the existing power transmission channel is restricted by the stability of the power grid operation, and the transmission scale is very limited. With the landing of UHV DC in new energy-rich areas, the difficulty of absorbing new energy in the region has been increased to a certain extent. During the flood season, wind and water are generated at the same time, and DC power transmission is superimposed. The power transmission channel will have a risk of heavy overload, which will pose a certain threat to the operation of the power grid.

[0003] Therefore, in order to ensure the effective absorption of regional power output after the introduction of UHV DC and large-scale renewable energy, and reduce the abandonment of wind and solar power, it is necessary to accurately and reliably measure and study the current status and future development of regional renewable energy carrying capacity, find the key factors that restrict the absorption of renewable energy, and propose optimization methods and a series of solutions based on the calculation results.

[0004] In summary, there is an urgent need for a method for calculating and optimizing regional power transmission constraints with UHV DC and new energy access to solve the problems existing in the existing technology. Summary of the invention

[0005] The purpose of the present invention is to provide a method for calculating the power transmission restriction in a region where ultra-high voltage direct current and new energy are connected, aiming to solve the problem that in the prior art, it is impossible to accurately and reliably quantify the current status and future development of regional power supply carrying capacity after large-scale access of ultra-high voltage direct current and new energy, resulting in the inability of power grid planning and operation personnel to accurately capture the key factors that restrict the consumption of new energy, and it is difficult to provide effective solutions to improve the consumption of new energy from the perspectives of "source-grid-load-storage". The specific technical solution is as follows:

[0006] A method for calculating power transmission limitation in a region with ultra-high voltage direct current and new energy access, comprising the following steps:

[0007] S1. Obtain the operating parameter information of the target power grid, and take the most severely restricted power period in the target area as a typical calculation scenario;

[0008] S2. Based on typical calculation scenarios, determine the theoretical minimum power generation of thermal power units in the target power grid, the theoretical power generation of hydropower units, the theoretical power generation of wind power units, the theoretical power generation of photovoltaic units, the UHV DC transmission power of the target power grid, and the average power load of the target power grid;

[0009] S3. Determine the target grid power transmission demand under typical calculation scenarios based on the theoretical minimum power generation of the target grid’s thermal power units, the theoretical power generation of the hydropower units, the theoretical power generation of the wind power units, the theoretical power generation of the photovoltaic units, the UHV DC transmission power of the target grid, and the average power load of the target grid; at the same time, determine the theoretical maximum transmission power of the target grid power transmission channel;

[0010] S4. Determine the power transmission limited power of the target power grid according to the power transmission demand of the target power grid and the theoretical maximum transmission power of the power transmission channel of the target power grid.

[0011] In the above technical solution, the theoretical minimum power generation capacity of the thermal power unit of the target power grid is preferably:

[0012] (1),

[0013] In the formula, Indicates the theoretical minimum power generation capacity of thermal power units in the target power grid; It represents the theoretical minimum startup capacity of thermal power units in the target power grid; Indicates the minimum output coefficient of deep peak regulation of thermal power units.

[0014] In the above technical solution, the theoretical power generation capacity of the hydroelectric unit is preferably:

[0015] (2),

[0016] In the formula, represents the theoretical power generation of the hydropower unit in the target grid, Indicates that the target power grid does not have the ability to regulate the installed capacity of hydropower units, Indicates the installed capacity of hydropower generators with regulation capability of the target power grid, Indicates the minimum output coefficient of a hydropower unit with regulation capability.

[0017] In the above technical solutions, the theoretical power generation of wind power and photovoltaic units is preferably:

[0018] (3),

[0019] In the formula, represents the theoretical power generation of wind turbines in the target grid, represents the theoretical power generation power of the photovoltaic unit in the target grid, represents the installed capacity of wind turbines in the target grid, represents the installed capacity of the target grid photovoltaic unit, represents the theoretical output synchronization rate of wind turbines in the target grid, Indicates the theoretical output synchronization rate of photovoltaic units in the target power grid.

[0020] In the above technical solutions, the target power grid power transmission demand in the typical measurement scenario is preferably:

[0021] (4),

[0022] In the formula, Indicates the power transmission demand of the target power grid; represents the UHV DC transmission power of the target grid, Indicates the average power load of the target power grid; represents the theoretical power generation of wind turbines in the target power grid; Indicates the theoretical power generation power of the photovoltaic unit of the target power grid; represents the theoretical power generation capacity of the hydropower units in the target power grid; It represents the theoretical minimum power generation capacity of thermal power units in the target power grid.

[0023] The preferred technical solution is to perform flow verification and stability verification on the target power grid power transmission channel, respectively, to obtain the maximum theoretical transmission power of the transmission channel under the flow verification constraint and the maximum theoretical transmission power of the transmission channel under the stability verification constraint, and select the minimum value as the theoretical maximum transmission power of the target power grid power transmission channel. .

[0024] In the above technical solution, preferably, the power transmission limited power of the target power grid in S4 is:

[0025] (5),

[0026] In the formula, represents the power transmission limit of the target power grid, represents the theoretical maximum transmission power of the target power grid power transmission channel, Indicates the power transmission demand of the target power grid.

[0027] The present invention also provides a method for optimizing regional power transmission constraints with UHV DC and new energy access. After confirming that the target power grid has power transmission constraints by using the above-mentioned method for calculating regional power transmission constraints with UHV DC and new energy access, the maximum scale consumption of new energy in the target power grid is taken as the optimization target. Under the constraints of the target power grid, a power transmission constraint optimization objective function is constructed to guide the optimization of the power transmission constraints of the target power grid.

[0028] In the above technical solutions, the target power grid constraint conditions preferably include: power balance constraint, target power grid thermal power output constraint, target power grid hydropower output constraint, target power grid wind power output constraint, target power grid photovoltaic output constraint, target power grid UHV DC transmission power constraint and target power grid power transmission channel transmission power constraint;

[0029] Among them, the power balance constraint of the target power grid is:

[0030] (6),

[0031] In the formula, represents the power generation of the thermal power unit of the target power grid at time t, represents the power generation of the hydropower unit of the target power grid at time t, represents the power generation of the wind turbine in the target grid at time t, represents the power generation of the photovoltaic unit of the target grid at time t, represents the transmission power of UHV DC at time t, represents the transmission power of the target power grid transmission channel at time t, represents the total power load of the target power grid at time t;

[0032] The output constraints of thermal power, hydropower, wind power and photovoltaic power in the target power grid are:

[0033] (7),

[0034] In the formula, represents the installed capacity of thermal power units in the target power grid, represents the theoretical minimum power generation capacity of the thermal power units in the target power grid, represents the installed capacity of hydropower units in the target grid, represents the installed capacity of wind turbines in the target grid, represents the installed capacity of photovoltaic units in the target power grid;

[0035] The UHV DC transmission power constraint of the target power grid is:

[0036] (8),

[0037] In the formula, It represents the theoretical maximum transmission power of UHV DC;

[0038] The transmission power constraint of the target power grid power transmission channel is:

[0039] (9),

[0040] In the formula, It represents the theoretical maximum transmission power of the target power grid’s power transmission channel.

[0041] In the above technical solution, preferably, the objective function constructed based on the optimization goal and the constraint conditions is:

[0042] (10),

[0043] Where T is the total optimization period.

[0044] The application of the technical solution of the present invention has the following beneficial effects:

[0045] (1) When UHV DC and high-proportion new energy are connected to the regional power grid on a large scale, in order to ensure the effective absorption of new energy and reduce wind and solar power abandonment, it is necessary to calculate in detail the target power grid's power transmission demand, transmission channel capacity and power transmission restriction in a certain period of time; the calculation method provided by the present invention takes into account the selection of typical calculation scenarios and the theoretical power generation power of various power sources, transmission channel capacity and power transmission restriction, and the calculation results are accurate and reliable. The power transmission restriction calculation value of the target power grid can be used to guide the reasonable layout of future regional new energy installations and the optimization of the cross-sectional structure of the power transmission channel, thereby continuously improving the new energy absorption capacity and safety and stability of the new power system.

[0046] (2) Based on the power constraint estimation method provided by the present invention, the key factors affecting the new energy consumption in the target area are accurately captured. The maximum scale consumption of new energy in the target power grid is taken as the optimization goal. Under the constraint conditions of the target power grid, a power transmission constraint optimization objective function is constructed to guide the power grid planning and operation personnel to take corresponding optimization measures according to different optimization periods to reduce the problem of wind and solar power abandonment.

[0047] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0049] Figure 1 It is a flow chart of the method for calculating the power transmission limitation in the area where UHV DC and new energy are connected;

[0050] Figure 2 It is a flow chart of the method for optimizing power transmission constraints in areas with UHV DC and new energy access;

[0051] Figure 3 is a schematic diagram of a power system in an application case of an embodiment;

[0052] Figure 4 It is a schematic diagram of the simulation analysis of the stability verification calculation of the power transmission channel in the application case of the embodiment. DETAILED DESCRIPTION

[0053] In order to facilitate the understanding of the present invention, the present invention will be described more fully below, and preferred embodiments of the present invention are provided. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0055] Example:

[0056] See also Figure 1 This embodiment provides a method for calculating power transmission limitation in a region with ultra-high voltage direct current and new energy access, which specifically includes the following steps:

[0057] S1. Obtain the operating parameter information of the target power grid, and take the most severely restricted power period in the target area as a typical calculation scenario;

[0058] S2. Based on typical calculation scenarios, determine the theoretical minimum power generation of thermal power units in the target power grid, the theoretical power generation of hydropower units, the theoretical power generation of wind power units, the theoretical power generation of photovoltaic units, the UHV DC transmission power of the target power grid, and the average power load of the target power grid;

[0059] S3. Determine the target grid power transmission demand under typical calculation scenarios based on the theoretical minimum power generation of the target grid’s thermal power units, the theoretical power generation of the hydropower units, the theoretical power generation of the wind power units, the theoretical power generation of the photovoltaic units, the UHV DC transmission power of the target grid, and the average power load of the target grid; at the same time, determine the theoretical maximum transmission power of the target grid power transmission channel;

[0060] S4. Determine the power transmission limited power of the target power grid according to the power transmission demand of the target power grid and the theoretical maximum transmission power of the power transmission channel of the target power grid.

[0061] Preferably, the new energy mentioned in this embodiment refers to wind turbines and photovoltaic units.

[0062] Preferably, in the operation of the power grid, the flood season is usually the period when power transmission is most severely restricted, so the flood season is generally selected as a typical calculation scenario in step S1.

[0063] Preferably, the theoretical minimum power generation capacity of the thermal power units in the target power grid is determined by checking the minimum startup mode, specifically:

[0064] According to the power load of the power grid and the UHV DC transmission power during the flood season, the minimum startup static safety and stability analysis and system stability special verification of the target power grid are carried out to ensure that there is no overload or over-limit in the static safety analysis, and no voltage, power angle, and frequency instability in the system stability special verification, so as to determine the minimum startup and rotation requirements of the thermal power unit and obtain the minimum startup capacity of the thermal power unit. ;

[0065] In order to ensure the maximum consumption of clean energy during the flood season, the startup capacity of thermal power units must meet the minimum startup requirements. In actual operation, thermal power units should also adopt deep peak regulation to reduce the unit output to the minimum under the premise of meeting safety and environmental protection requirements. Therefore, the theoretical minimum power generation capacity of thermal power units in the flood season (i.e., the typical calculation scenario) is:

[0066] (1),

[0067] In the formula, Indicates the theoretical minimum power generation capacity of thermal power units in the target power grid; It represents the theoretical minimum startup capacity of thermal power units in the target power grid, which needs to be determined by conducting minimum startup static safety analysis and system stability and safety verification on the target power grid; It indicates the minimum output coefficient of deep peak regulation of thermal power units. Usually, the minimum output coefficient of deep peak regulation of thermal power units is calculated. =30%.

[0068] Preferably, the theoretical power generation of the hydropower unit is determined according to the different regulation capabilities of the hydropower units in the target power grid, specifically:

[0069] The theoretical power generation of hydropower units during the flood season is related to their regulation capacity. Generally, small hydropower units without regulation capacity should generate full power during the flood season according to the principle of "generating as much as possible". Large hydropower units with regulation capacity should have water storage conditions before the flood season, and reduce their output as much as possible according to their own regulation capacity when water comes. Therefore, the theoretical power generation of hydropower units in the target grid during the flood season (i.e., the typical calculation scenario) is:

[0070] (2),

[0071] In the formula, represents the theoretical power generation of the hydropower unit in the target grid, Indicates that the target power grid does not have the ability to regulate the installed capacity of hydropower units, Indicates the installed capacity of hydropower generators with regulation capability of the target power grid, Indicates the minimum output coefficient of the hydropower unit with regulation capability, It is related to the overall regulation performance of the hydropower units with regulation capabilities in the target power grid.

[0072] Preferably, the historical output data of new energy units in the target power grid are collected to determine the theoretical power generation of wind power and photovoltaic units in a typical measurement scenario:

[0073] (3),

[0074] In the formula, represents the theoretical power generation of wind turbines in the target grid, represents the theoretical power generation power of the photovoltaic unit in the target grid, represents the installed capacity of wind turbines in the target grid, represents the installed capacity of the target grid photovoltaic unit, represents the theoretical output synchronization rate of wind turbines in the target grid, Indicates the theoretical output simultaneity rate of the target grid PV units;

[0075] Specifically, the theoretical output simultaneity of wind power and photovoltaic units requires statistics on the historical output data of wind power and photovoltaic units in the target power grid during the flood season (with a time resolution of 15 minutes), and the output simultaneity of wind power and photovoltaic units at different times of the flood season and the corresponding probability statistics, so as to determine the theoretical output simultaneity of wind power and photovoltaic units. and .

[0076] Preferably, the target power grid power transmission demand of the target power grid in S3 under a typical measurement scenario is:

[0077] (4),

[0078] In the formula, represents the power transmission demand of the target power grid, represents the UHV DC transmission power of the target grid, Indicates the average power load of the target power grid; when the power transmission demand of the target power grid during the flood season When it is greater than 0, it means that the output of UHV DC and various power sources of the target power grid is greater than the load absorption level, and the surplus power needs to be transmitted to other power-consuming areas through power transmission channels.

[0079] Preferably, in S3, flow check and stability check are respectively performed on the target power grid power transmission channel to determine the theoretical maximum transmission power of the target power grid power transmission channel, specifically:

[0080] Power transmission channel flow verification calculation: determine all the transmission line groups included in the target power grid power transmission channel, disconnect each group of lines in turn in an N-1 manner, and ensure that there is no overload on the remaining lines when disconnecting the components of each line group in turn; determine the bottleneck factors that restrict the power transmission of the transmission channel in the process of disconnecting each group of lines in turn in an N-1 manner, and calculate the maximum theoretical transmission power of the transmission channel that just meets the power flow verification constraints after the bottleneck restriction failure occurs ; Where N is the total number of transmission line groups. If there are lines on the same pole in a single transmission line group, all the lines in the group need to be disconnected;

[0081] Power transmission channel stability check calculation: gradually increase the power transmission power in the target area, conduct transient stability check, ensure that the voltage and power angle remain transiently stable when any AC transmission line group or UHV DC fault occurs in the entire network, and calculate the maximum theoretical transmission power of the transmission channel that meets the stability check constraint conditions ;

[0082] Furthermore, if the maximum theoretical transmission power of the stability check is small and the power transmission is restricted, measures to improve the system stability can be considered as the stability check calculation boundary, such as adding phase regulators and reserving rotating reserve capacity for thermal power units. After taking measures to improve the system stability, the maximum theoretical transmission power of the transmission channel under the stability check constraint can be increased to ;

[0083] The theoretical maximum transmission power of the target power grid's power transmission channel should meet the constraints of power flow verification and stability verification at the same time. When the measures to improve system stability are not considered, the theoretical maximum transmission power of the target power grid's power transmission channel is ; When considering measures to improve system stability, the theoretical maximum transmission power of the power transmission channel .

[0084] Preferably, the power transmission limited power of the target power grid in S4 is:

[0085] (5),

[0086] In the formula, represents the power transmission limit of the target power grid, It can be used to guide the rational layout and effective construction of various types of power generation capacity in the target power grid.

[0087] It can be seen from the above-mentioned power restriction calculation method that when the transmission demand of the target power grid at any moment is greater than the transmission power of the transmission channel, power transmission restriction will occur; in order to cope with the situation of power transmission restriction, this embodiment also provides a method for optimizing power transmission restriction in areas with ultra-high voltage direct current and new energy access, specifically: taking the maximum scale consumption of new energy in the target power grid as the optimization goal, constructing a power transmission restriction optimization objective function under the constraint conditions of the target power grid to guide the optimization of power transmission restriction of the target power grid, such as Figure 2 shown.

[0088] Among them, the constraints of the target power grid include: power balance constraints, target power grid thermal power output constraints, target power grid hydropower output constraints, target power grid wind power output constraints, target power grid photovoltaic output constraints, target power grid ultra-high voltage direct current transmission power constraints and target power grid power transmission channel transmission power constraints.

[0089] Preferably, the power balance constraint of the target power grid is used to describe the balance relationship between power generation of various power sources, UHV DC transmission power, power transmission channel transmission power and load consumption of the target power grid at any time, and the specific expression is:

[0090] (6),

[0091] In the formula, represents the power generation of the thermal power unit of the target power grid at time t, represents the power generation of the hydropower unit of the target power grid at time t, represents the power generation of the wind turbine in the target grid at time t, represents the power generation of the photovoltaic unit of the target grid at time t, represents the transmission power of UHV DC at time t, represents the transmission power of the target power grid transmission channel at time t, represents the total power load of the target power grid at time t;

[0092] Preferably, the output constraints of thermal power, hydropower, wind power and photovoltaic power in the target power grid are:

[0093] (7),

[0094] In the formula, represents the installed capacity of thermal power units in the target power grid, represents the theoretical minimum power generation capacity of the thermal power units in the target power grid, represents the installed capacity of hydropower units in the target grid, represents the installed capacity of wind turbines in the target grid, Represents the installed capacity of photovoltaic units in the target grid.

[0095] Preferably, the target power grid UHV DC transmission power constraint is:

[0096] (8),

[0097] In the formula, It represents the theoretical maximum transmission power of UHV DC, which is mainly constrained by DC near-area evacuation, dynamic stability and transient stability.

[0098] Preferably, the transmission power constraint of the target power grid power transmission channel is:

[0099] (9),

[0100] In the formula, It represents the theoretical maximum transmission power of the target power grid’s power transmission channel.

[0101] Preferably, in order to reduce the situation of wind and solar power abandonment, the objective function is constructed based on the optimization goal and constraint conditions as follows:

[0102] (10),

[0103] Where T is the total optimization period.

[0104] Furthermore, based on the different total optimization periods T and the objective function, the optimization strategies for power transmission constraints include:

[0105] (1) If it is necessary to optimize and reduce the power of the transmission channel within the day, it can be achieved by adjusting the output of the units in the province: give priority to reducing the output of thermal power units. If the output of thermal power units has been reduced to the minimum theoretical output of thermal power but is still insufficient to eliminate the power limitation of the section, then reduce the output of hydropower units; if reducing the output of hydropower units still cannot eliminate the power limitation of the section, then reduce the output and allocate it to wind turbines and / or photovoltaic units until the power of the transmission channel meets the safety constraints;

[0106] (2) If it is necessary to optimize and reduce the power of the transmission channel M days in advance and M days is not enough to adjust the theoretical maximum transmission power of the target power grid power transmission channel When the limiting factors are measured, the UHV DC transmission power, thermal power unit output and hydropower unit output are reduced to eliminate the power limitation of the section; if the UHV DC transmission power, thermal power unit output and hydropower unit output still cannot eliminate the power limitation of the section, the output reduction will be allocated to wind turbines and / or photovoltaic units until the power of the transmission channel meets the safety constraint conditions; where M is an integer greater than or equal to 1.

[0107] (3) If the optimized total time period is sufficient to adjust the theoretical maximum transmission power of the target power grid power transmission channel When calculating the constraints, the constraints are adjusted to make the transmission channel power meet the safety constraints; for example, by optimizing the cross-sectional structure, adding devices to improve system stability, and rationally planning the scale of new energy installed capacity and energy storage devices.

[0108] Application examples:

[0109] like Figure 3 In the power system shown, the target power grid is the UHV DC and renewable energy feed-in area (i.e., the target area), which transmits surplus power to other power-consuming areas through the power transmission channel; wherein: the UHV DC and renewable energy feed-in area includes substations P, C, Z, X, and Y, and the other power-consuming areas include substations M, H, and G; the power transmission channel is a transmission section composed of double-circuit AC lines PM, CH, and YG, and all lines are not parallel-mounted lines on the same pole.

[0110] It is expected that by 2025, the target area will have UHV DC transmission capacity of 8,000MW, the target power grid will have a thermal power installed capacity of 6,980MW, a hydropower installed capacity of 11,200MW (of which 5,500MW is adjustable hydropower installed capacity and 5,700MW is non-adjustable hydropower installed capacity), a wind power installed capacity of 13,000MW, and a photovoltaic installed capacity of 5,000MW. The target power grid will have an annual load level of 6,000MW-16,000MW, with an average load of 10,000MW during the flood season.

[0111] According to the minimum startup requirements of thermal power units under the flood season load level, the minimum startup capacity of thermal power units in the target power grid during the flood season is 3200MW. Considering the minimum output coefficient of deep peak regulation of thermal power units during the flood season is 30%, the theoretical minimum power generation capacity of thermal power units in the target power grid is 960MW according to formula (1).

[0112] During the flood season, hydropower is generated in large quantities. Hydropower units without regulation capabilities are required to generate 5700MW according to the principle of "generating as much as possible". Hydropower units with regulation capabilities are required to generate as little as possible according to the hydropower regulation performance of the target area. The minimum output coefficient is 10%. According to formula (2), the theoretical generating capacity of the hydropower units in the target grid is 6250MW.

[0113] According to the statistical results of wind turbine operation in the target power grid during the flood season in 2022 (see Table 1), the number of days when the wind power concurrency rate exceeds 50% accounts for 10% of the entire flood season, which has a significant impact on the power of the power grid. Therefore, when calculating the output of wind turbines, the wind power concurrency rate is considered to be 50%. The installed capacity of wind power in the target power grid is 13,000 MW. According to formula (3), the theoretical power generation capacity of the wind turbine is 6,500 MW.

[0114]

[0115] According to the operation statistics of photovoltaic units in the target grid during the flood season in 2022, the wind power concurrency rate exceeds 50%, and the corresponding photovoltaic concurrency rate is about 28%; therefore, when calculating the output of photovoltaic units, the photovoltaic concurrency rate is considered to be 28%; the photovoltaic installed capacity of the target grid is 5000MW, and the theoretical power generation capacity of the photovoltaic unit is 1400MW according to formula (3).

[0116] Since the power demand of the target power grid during the flood season is not high, the UHV DC transmission power during the flood season is considered to be 4000MW, and the average power load of the target power grid during the flood season is 10000MW. According to formula (4), the power transmission demand of the target power grid is calculated as:

[0117]

[0118] It can be seen that the power transmission demand of the target power grid during the flood season is greater than 0, which means that the output of UHV DC and various power sources of the target power grid is greater than the load absorption level, and the surplus power needs to be transmitted to other power-consuming areas through power transmission channels.

[0119] The power flow check and stability check are performed on the target power grid power transmission channel to determine the theoretical maximum transmission power of the target power grid power transmission channel, specifically:

[0120] Power flow verification: For all AC line groups (PM, CH double circuit, YG double circuit) of the target power grid power transmission channel, N-1 static safety verification is carried out in sequence. The verification results are shown in Table 2 below:

[0121]

[0122] From the above table, we can see that the factor that restricts the power flow power of the target power grid transmission channel is that the PM line after CH line N-1 is overloaded. The maximum theoretical transmission power of the power flow verification transmission channel is calculated as =6200MW;

[0123] Stability check: determine the system's temporary stability control fault and the load bus that recovers the slowest under the control fault, gradually increase the power transmission power in the target area, and perform transient stability check. When the power of the power transmission channel is 2998MW, the system maintains critical stability; if the target grid phase regulator is added, the system's temporary stability level can be further improved. By adding 1 or 2 phase regulators, the transmission channel capacity can be increased to 3864 or 5137MW; the transient stability check simulation curve of the power transmission channel is as follows Figure 4 As shown;

[0124] According to the results of power flow verification and stability verification, the transmission power of the target power grid's power transmission channel is mainly constrained by transient stability. Considering that the target power grid has 0, 1, and 2 phase-shifting units, the maximum theoretical transmission power of the transmission channel is 2998, 3864, and 5137 MW, respectively.

[0125] Considering that the target grid has 0, 1, and 2 phase regulators, the theoretical power constraints of the target grid are 6112, 5246, and 3973 MW respectively according to formula (5).

[0126] Then, according to the above-mentioned optimization method, taking the maximum-scale consumption of new energy in the target power grid as the optimization goal, a power transmission restricted optimization objective function is constructed under the constraints of the target power grid to guide the optimization of the power transmission restriction of the target power grid.

[0127] The various constraints in the target power grid are as follows:

[0128] The power balance constraint of the target power grid needs to satisfy formula (6);

[0129] The output constraint of thermal power is ;

[0130] The output constraint of hydropower is ;

[0131] The output constraint of wind power is ;

[0132] The photovoltaic output constraint is ;

[0133] The UHV DC transmission power constraint of the target power grid is: ;

[0134] The transmission power constraint of the target power grid power transmission channel is: , where: the target power grid opens 0, 1, or 2 phase regulators, They are 6112, 5246 and 3973MW respectively.

[0135] In order to reduce the situation of wind and solar power curtailment, the objective function is constructed based on the optimization objectives and constraints as shown in formula (10).

[0136] Based on the different optimization time periods T and objective functions, the optimization strategies for power transmission constraints include:

[0137] (1) If it is necessary to optimize and reduce the power of the transmission channel within the day, it can be achieved by adjusting the output of the units in the province: give priority to reducing the output of thermal power units. If the output of thermal power units has been reduced to the minimum theoretical output of thermal power but is still insufficient to eliminate the power limitation of the section, then reduce the output of hydropower units; if reducing the output of hydropower units still cannot eliminate the power limitation of the section, then reduce the output and allocate it to wind turbines and / or photovoltaic units until the power of the transmission channel meets the safety constraints;

[0138] (2) If it is necessary to optimize and reduce the power of the transmission channel M days in advance and M days is not enough to adjust the theoretical maximum transmission power of the target power grid power transmission channel When the constraints are calculated, the UHV DC transmission power, thermal power unit output and hydropower unit output are reduced to eliminate the power limitation of the section; if the reduction of UHV DC transmission power, thermal power unit output and hydropower unit output still cannot eliminate the power limitation of the section, the output reduction will be allocated to wind turbines and / or photovoltaic units until the power of the transmission channel meets the safety constraint conditions; where M is an integer greater than or equal to 1. For example: consider arranging UHV DC to participate in the peak load regulation within the province during the flood season, and coordinate the arrangement of hydropower, new energy output and UHV DC transmission power.

[0139] (3) If the optimized total time period is sufficient to adjust the theoretical maximum transmission power of the target power grid power transmission channel When calculating the constraints, the constraints are adjusted to make the power of the transmission channel meet the safety constraints. Specifically, in the case, the power calculation constraint of the target power grid's power transmission channel is a temporary stability constraint, which can be achieved by optimizing the section structure and adding devices to improve system stability (such as phase-shifting machines, SVG) to increase the section transmission limit, thereby optimizing the level of new energy consumption.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating power transmission constraints in areas with ultra-high voltage direct current and new energy access, characterized in that: The following steps are involved: S1. Obtain the operating parameter information of the target power grid, and take the most severely restricted power period in the target area as a typical calculation scenario; S2. Based on typical calculation scenarios, determine the theoretical minimum power generation of thermal power units in the target power grid, the theoretical power generation of hydropower units, the theoretical power generation of wind power units, the theoretical power generation of photovoltaic units, the UHV DC transmission power of the target power grid, and the average power load of the target power grid; S3. Determine the target grid power transmission demand under typical calculation scenarios based on the theoretical minimum power generation of the target grid’s thermal power units, the theoretical power generation of the hydropower units, the theoretical power generation of the wind power units, the theoretical power generation of the photovoltaic units, the UHV DC transmission power of the target grid, and the average power load of the target grid; at the same time, determine the theoretical maximum transmission power of the target grid power transmission channel; S4. Determine the power transmission restricted power of the target power grid according to the power transmission demand of the target power grid and the theoretical maximum transmission power of the power transmission channel of the target power grid; The power transmission channel of the target power grid is subjected to flow verification and stability verification respectively, and the maximum theoretical transmission power of the transmission channel under the flow verification constraint and the maximum theoretical transmission power of the transmission channel under the stability verification constraint are obtained respectively, and the minimum value is selected as the theoretical maximum transmission power of the power transmission channel of the target power grid. ; Power transmission channel flow verification calculation: determine all the transmission line groups included in the target power grid power transmission channel, disconnect each group of lines in turn in an N-1 manner, and ensure that there is no overload on the remaining lines when disconnecting the components of each line group in turn; determine the bottleneck factors that restrict the power transmission of the transmission channel in the process of disconnecting each group of lines in turn in an N-1 manner, and calculate the maximum theoretical transmission power of the transmission channel that just meets the power flow verification constraints after the bottleneck restriction failure occurs ; Where N is the total number of transmission line groups. If there are lines on the same pole in a single transmission line group, all the lines in the group need to be disconnected; Stability verification calculation of power transmission channel: gradually increase the power transmission power in the target area, conduct transient verification, ensure that the voltage and power angle remain transiently stable when any AC transmission line group or UHV DC fault occurs in the whole network, and calculate the maximum theoretical transmission power of the transmission channel under the stability verification constraint conditions .

2. The method for calculating power transmission limitation in areas with UHV DC and new energy access according to claim 1 is characterized in that: The theoretical minimum power generation capacity of the thermal power units in the target power grid is: （1）， In the formula, Indicates the theoretical minimum power generation capacity of thermal power units in the target power grid; It represents the theoretical minimum startup capacity of thermal power units in the target power grid; Indicates the minimum output coefficient of deep peak regulation of thermal power units.

3. The method for calculating power transmission limitation in areas with UHV DC and new energy access according to claim 1 is characterized in that: The theoretical power generation capacity of the hydropower unit is: （2）， In the formula, represents the theoretical power generation of the hydropower unit in the target grid, Indicates that the target power grid does not have the ability to regulate the installed capacity of hydropower units, Indicates the installed capacity of hydropower generators with regulation capability of the target power grid, Indicates the minimum output coefficient of a hydropower unit with regulation capability.

4. The method for calculating power transmission limitation in areas with UHV DC and new energy access according to claim 1 is characterized in that: The theoretical power generation of wind power and photovoltaic units is: （3）， In the formula, represents the theoretical power generation of wind turbines in the target grid, represents the theoretical power generation power of the photovoltaic unit in the target grid, represents the installed capacity of wind turbines in the target grid, represents the installed capacity of the target grid photovoltaic unit, represents the theoretical output synchronization rate of wind turbines in the target grid, Indicates the theoretical output synchronization rate of photovoltaic units in the target power grid.

5. The method for calculating power transmission limitation in areas with UHV DC and new energy access according to claim 1 is characterized in that: The target grid power transmission demand in a typical measurement scenario is: （4）， In the formula, Indicates the power transmission demand of the target power grid; represents the UHV DC transmission power of the target grid, Indicates the average power load of the target power grid; represents the theoretical power generation of wind turbines in the target power grid; Indicates the theoretical power generation power of the photovoltaic unit of the target power grid; represents the theoretical power generation capacity of the hydropower units in the target power grid; It represents the theoretical minimum power generation capacity of thermal power units in the target power grid.

6. The method for calculating power transmission limitation in areas with UHV DC and new energy access according to claim 1 is characterized in that: The power transmission limit of the target power grid in S4 is: （5）， In the formula, represents the power transmission limit of the target power grid, represents the theoretical maximum transmission power of the target power grid power transmission channel, Indicates the power transmission demand of the target power grid.

7. A method for optimizing regional power transmission constraints with UHV DC and new energy access, characterized in that: After confirming that the target power grid has power transmission constraints by using the regional power transmission constraint calculation method for UHV DC and new energy access as described in any one of claims 1 to 6, taking the maximum scale consumption of new energy in the target power grid as the optimization goal, a power transmission constraint optimization objective function is constructed under the constraints of the target power grid to guide the optimization of the power transmission constraint of the target power grid.

8. The method for optimizing regional power transmission constraints for UHV DC and new energy access according to claim 7, characterized in that: The constraints of the target power grid include: power balance constraints, thermal power output constraints of the target power grid, hydropower output constraints of the target power grid, wind power output constraints of the target power grid, photovoltaic output constraints of the target power grid, UHV DC transmission power constraints of the target power grid, and transmission power constraints of the power transmission channel of the target power grid; Among them, the power balance constraint of the target power grid is: （6）， In the formula, represents the power generation of the thermal power unit of the target power grid at time t, represents the power generation of the hydropower unit of the target power grid at time t, represents the power generation of the wind turbine in the target grid at time t, represents the power generation of the photovoltaic unit of the target grid at time t, represents the transmission power of UHV DC at time t, represents the transmission power of the target power grid transmission channel at time t, represents the total power load of the target power grid at time t; The output constraints of thermal power, hydropower, wind power and photovoltaic power in the target power grid are: （7）， In the formula, represents the installed capacity of thermal power units in the target power grid, represents the theoretical minimum power generation capacity of the thermal power units in the target power grid, represents the installed capacity of hydropower units in the target grid, represents the installed capacity of wind turbines in the target grid, represents the installed capacity of photovoltaic units in the target power grid; The UHV DC transmission power constraint of the target power grid is: （8）， In the formula, It represents the theoretical maximum transmission power of UHV DC; The transmission power constraint of the target power grid power transmission channel is: （9）， In the formula, It represents the theoretical maximum transmission power of the target power grid’s power transmission channel.

9. The method for optimizing regional power transmission constraints for UHV DC and new energy access according to claim 8, characterized in that: The objective function is constructed based on the optimization goal and constraints: （10）， Where T is the total optimization period.

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