Evaluation Method for the Maximum Combined Transmission Capacity of Two Large Power Sources with Close Electrical Distance

Abstract

The present invention discloses a method for evaluating the maximum joint transmission capacity of two large power sources with close electrical distances. Based on actual power grid operation mode data, the present invention considers multiple control sections for two large power sources with close electrical distances, and first calculates the transfer coefficient of the large power output power rise and fall changes to each control section; then, two control sections are selected in turn as section combinations, and the corresponding large power output power pre-arranged values when the two control sections are simultaneously operating at their respective stability limits are obtained, and the solution combinations with pre-arranged values less than 0 are eliminated; finally, the combination with the smallest sum of the pre-arranged output powers of the two large power sources is selected to obtain its maximum joint transmission capacity and the corresponding main control section. The present invention can be used for actual power grid operation mode analysis and arrangement, quickly and accurately evaluate the maximum joint transmission capacity of two large power sources with close electrical distances under any power grid operation mode, and improve the simulation analysis efficiency and safe operation level of ultra-high voltage AC and DC large power grids.

Description

Technical Field

[0001] The present invention relates to the fields of power system power access system evaluation and source and network coordinated development adaptability analysis. Specifically, it is a method for evaluating the maximum joint transmission capacity of two large power sources with similar electrical distances in a power grid, taking into account multi-section constraints. The method is suitable for evaluating the power evacuation capacity of large-capacity power plants, generator groups and ultra-high voltage direct current in ultra-high voltage AC / DC hybrid power grids. Background Art

[0002] Power transmission capacity and evacuation and absorption have always been key concerns for power control and operation personnel, impacting power system power balance and operational safety risks. To meet rapidly growing power supply demands in the future, grid planning calls for the intensive commissioning of large-capacity power plants and ultra-high voltage direct current (UHVDC) systems over the next few years. This has led to a lack of coordination between grid and power source development and insufficient grid strength adaptability. Due to the relatively slow growth of the grid and the constraints of local grid sections, large power sources (including large-capacity power plants and UHVDC) in AC / DC hybrid grids are unable to deliver full power, impacting the safe and reliable power supply of the power system.

[0003] Furthermore, with the development of new power systems and the large-scale commissioning of renewable energy, the operational characteristics of power grids are becoming increasingly complex. The uncertainty and volatility of renewable energy output are making it increasingly difficult to control power flows in power transmission sections. Therefore, it is imperative to fully tap and maximize the operational potential and efficiency of traditional power sources within the power grid.

[0004] Reference 1, "Challenges and Countermeasures for the Operation of DC Transmission Systems under AC / DC Hybrid Grids" (Power System Technology, 2022, 46(2): 503-510), points out that in recent years, AC / DC systems have influenced each other, including the mutual influence between UHVDC and AC systems, and DC and new energy power sources, and regional AC / DC hybrid grids have shown complex operating characteristics. Reference 2, "Adaptive Expansion Planning of Transmission Networks Considering Network-Source Collaboration" (Power System Technology, 2019, 43(9): 3360-3369), proposes grid structure and power capacity adaptability indicators that take into account the safety and efficiency of grid operation and the balance of supply and demand, and establishes a planning model that considers network-source collaborative optimization. The above analysis effectively improves the adaptability and flexibility of grid planning schemes, but there is currently a lack of effective and concise methods to quickly evaluate the maximum output capacity of two specific power sources in actual grid modes to directly guide grid operation mode arrangements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned existing technologies. Starting from the adaptability of power supply capacity and grid structure, a method for evaluating the maximum joint transmission capacity of two large power sources with similar electrical distances in the power grid considering multi-section constraints is provided. The method is based on the actual grid operation mode data, and for two large power sources with relatively close electrical distances, the method finds the constraint sections and calculates the pre-arranged values of the output power of the two large power sources considering that each constraint section does not exceed the limit. The method evaluates the maximum joint transmission capacity of the large power sources and the corresponding main constraint sections, which are used to analyze the power transmission capacity in the actual operation mode, guide the actual operation mode arrangement of the power grid, and ensure the safe and efficient operation of the power grid.

[0006] To this end, the present invention adopts the following technical solution: a method for evaluating the maximum combined transmission capacity of two large power sources with similar electrical distances, comprising:

[0007] Step 1: Based on the target provincial power grid operation mode data, select two target large power sources to be evaluated and arrange them to operate at rated power. At the same time, evenly adjust the output of coal-fired units within the province to ensure that the boundary conditions of the province's power supply remain unchanged. Perform power flow calculations to obtain the power flow distribution results of the power grid and determine whether there is at least one cross-limit section where the power flow exceeds the stability limit. If so, proceed to step 2. Otherwise, output the evaluation result that the two large power sources can simultaneously transmit at full power under the target operation mode.

[0008] Step 2: Calculate the transfer coefficient of each cross-limit section in the first step for each single target large power source power change. After the large power source power arrangement value changes, it is also necessary to uniformly adjust the output of coal-fired units in the province to ensure that the boundary conditions of the province's incoming power remain unchanged before and after the change.

[0009] Step 3: Select two sections from the over-limit sections as a combination in turn. Based on the initial operation mode and transfer coefficient, calculate the corresponding large power source pre-arranged power value when the over-limit section combination operates simultaneously at the stability limit. Determine whether the pre-arranged power values of the two large power sources are both greater than or equal to 0. If so, go to step 5; otherwise, go to step 4.

[0010] Step 4: Eliminate the selected cross-section combination and go to step 3;

[0011] Step 5: Calculate the sum of the pre-arranged power values of the two major power sources when the selected cross-limit section combination operates simultaneously within the stability limit;

[0012] Step 6: Determine whether all the combinations of cross-limit sections have been considered. If so, go to step 7; otherwise, go to step 3.

[0013] Step 7: Obtain the minimum value of the sum of the pre-arranged power values of the two major power sources in each out-of-limit section combination after consideration and elimination, and the corresponding out-of-limit section combination.

[0014] Furthermore, in the first step, the large power source object refers to a large-capacity power plant, a group of generators or an ultra-high voltage direct current converter station.

[0015] Furthermore, in the second step, the transfer coefficient refers to the sensitivity of large-source power variations to the cross-limit section. Its value is unaffected by large-source power variations and is solely dependent on the grid structure. Optimizing the grid structure will affect the transfer coefficient and the cross-section stability limit, thereby altering the power delivery capacity of the grid.

[0016] Furthermore, in the second step, the calculation formula of the transfer coefficient is as follows:

[0017]

[0018] Where i is the cross-limit section, j is the large power source x, y to be evaluated, and k ij Refers to the transfer coefficient of the large power source j to be evaluated to the cross-limit section i; P i0 、P j0 is the initial power value, P i1 、P j1 is the power value corresponding to the change.

[0019] Furthermore, the calculation formula involved in the third step is as follows, taking the combination of cross-limit sections a and b as an example:

[0020] P a0 +k ax (P x -P x0 )+k ay (P y -P y0 )≤P a_max

[0021] P b0 +k bx (P x -P x0 )+k by (P y -P y0 )≤P b_max

[0022] Where, P a0 、P b0 They are the initial arrangement power values of the cross section flow in the initial operation mode; P x0 、P y0 are the initial power values of the large power sources x and y in the initial operation mode; P x 、P y are the pre-arranged power values of large power sources x and y corresponding to the cross-limit section combination when operating at the stable limit at the same time; P a_maxis the stability limit of the cross-limit section a, that is, the maximum allowable transmission flow of the cross-limit section a to ensure the safe and stable operation of the power grid; P b_max It is the stability limit of the cross-limit section b, that is, the maximum allowable transmission flow of the cross-limit section b to ensure the safe and stable operation of the power grid.

[0023] Furthermore, in the third step, if the pre-arranged power value of the large power source is less than 0, it means that the two selected sections cannot reach the stability limit at the same time in actual operation, that is, the power of one section reaches the stability limit value, and the power of the other section does not exceed the stability limit value.

[0024] Furthermore, in the third step, if there is only one out-of-limit section, the rated power operation of the large power source with a small transfer coefficient is considered, and then the pre-arranged power value of the large power source with a large transfer coefficient is calculated when the out-of-limit section operates at the stability limit.

[0025] Furthermore, the calculation formula involved in the fifth step is as follows:

[0026] P xy =P x +P y

[0027] Where, P x 、P y They are respectively the pre-arranged power values of large power sources x and y corresponding to the over-limit section combination when operating at the stability limit at the same time.

[0028] Furthermore, in the seventh step, the minimum value of the sum of the pre-arranged power values of the two major power sources in each over-limit section combination, that is, the maximum joint transmission capacity of the two large power sources to be evaluated to ensure that each section does not exceed the limit, the corresponding over-limit section combination is the main restricting section that restricts the evacuation of the two large power sources to be evaluated.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The process is simple and the calculation is fast. The proposed method for evaluating the maximum combined transmission capacity of large power sources meets the requirements of grid regulation and operation and can be effectively applied to the actual grid operation mode arrangement.

[0031] 2. Based on the actual operation mode, considering the pre-arranged power values of large power sources and the maximum joint transmission capacity obtained after each over-limit section, the actual grid operation mode is guided to maximize the power supply capacity while meeting safety constraints.

[0032] 3. The fast and accurate evaluation method is easy to calculate and highly accurate, which solves the shortcomings of traditional analysis, which is highly dependent on the experience of control operators, multiple adjustments to tide data for trial and error, and slow and gradual approach to results. The process is repetitive, tedious, error-prone, and time-consuming. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 is a flow chart of the evaluation method of the present invention;

[0035] Figure 2 Schematic diagram of a power grid in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0037] Amidst rapidly growing power demand and incomplete coordination between power sources and grid development, large power sources within close electrical proximity in AC / DC hybrid grids are facing constraints from relatively lagging grid development and localized grid sections. Under certain operating modes, these sources may not be able to deliver full power simultaneously, impacting the reliable supply of the power system. Furthermore, the large-scale commissioning of renewable energy sources, coupled with their fluctuating and uncertain output, is making power flow control within grid transmission sections increasingly difficult, necessitating an urgent need to explore and evaluate the potential of traditional power sources in grid operation.

[0038] Based on the above reasons, the present invention provides a method for evaluating the maximum joint transmission capacity of two large power sources with similar electrical distances in a power grid, taking into account multi-section constraints. The overall flow chart is as follows: Figure 1 The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0039] Step 1: According to the target provincial power grid operation mode data, select two target large power sources x and y to be evaluated, and arrange the large power sources x and y to be evaluated to the rated power P x_rated and P y_rated Operation is carried out while uniformly adjusting the output of coal-fired units within the province to ensure that the boundary conditions for the province's power supply remain unchanged. Using BPA simulation software, power flow calculations are performed to obtain the power grid power distribution results. Sections a, b, c, and d where power flows exceed their stability limits are screened out and the process proceeds to the second step. Otherwise, the evaluation results are output, indicating that the large power source under evaluation can simultaneously transmit at full power.

[0040] Step 2: Calculate the transfer coefficient k for each of the over-limit sections a, b, c, and d in Step 1, based on the power change of a single target large power source, x or y. The power change can be 100,000 kilowatts. After the power schedule of the large power source changes, the output of coal-fired units within the province must be uniformly adjusted to ensure that the boundary conditions for the province's power supply remain unchanged before and after the change.

[0041]

[0042] Where i is the cross-limit section a, b, c, d, etc., j is the large power source x, y to be evaluated, and k ij Refers to the transfer coefficient of large power source j to section i. i0 、P j0 is the initial power value, P i1 、P j1 is the power value corresponding to the change.

[0043] Step 3: Select two cross-limit sections from the cross-limit sections in turn as a combination, and calculate the corresponding large power supply pre-arranged power value P when the cross-limit section combination operates at the stability limit based on the initial operation mode and transfer coefficient k. x and P y , determine whether the pre-arranged power values of the two large power supplies are both greater than or equal to 0. If so, go to step 5, otherwise go to step 4.

[0044] P a0 +k ax (P x -P x0 )+k ay (P Y -P Y0 )≤P a_max

[0045] P b0 +k bx (P x -P x0 )+k by (P y -P y0 )≤P b_max

[0046] Taking the combination of sections a and b as an example, where P a0 、P b0 、P x0 、P y0 They are the section flow in the initial operation mode and the initial arranged power value of the large power source.

[0047] Step 4: Obtain P x and P yIf a value less than 0 exists, it indicates that the selected section combination cannot operate simultaneously within the stable limit value level in actual operation. That is, the power of one section reaches the stable limit value while the power of the other section does not exceed the limit. Eliminate the selected cross-section combination that exceeds the limit and go to step 3.

[0048] Step 5: Calculate the sum of the pre-arranged power of the two power sources when the selected cross-limit section combination operates at the stable limit. xy .

[0049] P xy =P x +P y

[0050] Step 6: Determine whether all pairwise cross-limit section combinations have been considered. If so, go to step 7; otherwise, go to step 3.

[0051] Step 7: Output the minimum value of the sum of the pre-arranged power values of the two power sources corresponding to all cross-limit section combinations, that is, min(P x +P y The minimum sum of the pre-arranged power values obtained is the maximum joint transmission capacity of the two large power sources to be evaluated to ensure that all sections do not exceed the limit. The cross-limit section combination corresponding to the minimum sum of the pre-arranged power values is the main restricting section that restricts the evacuation of the two large power sources to be evaluated.

[0052] Effect verification: In order to test the effectiveness of the method described in the present invention, the present invention is used to simulate and verify the actual power grid in Zhejiang Province.

[0053] For a typical operation mode of the Zhejiang power grid, large power sources x and y are analyzed and evaluated. There are four over-limit sections a, b, c, and d. The schematic diagram of the power grid structure is shown in Figure 2 The corresponding parameter values and transfer coefficient calculation results are shown in Table 1.

[0054] Table 1 Evaluation and analysis results of a typical method of Zhejiang power grid

[0055]

[0056] According to Table 1, the concatenation formula in step 3 of the present invention can be obtained as follows.

[0057] 398+0.1557(P x -750)+0.1416(P y -690)≤310

[0058] 287+0.1537(P x -750)-0.2116(P y -690)≤300

[0059] 308+0.1017(P x -750)+0.49(P y -690)≤380

[0060] 310+0.3134(P x -750)-0.2116(P y -690)≤300

[0061] According to the above-mentioned joint formula, we select two combinations of cross-limit sections and calculate the corresponding large power supply pre-arranged power values when the combined sections reach the stability limit at the same time. The calculation results are shown in Table 2 below.

[0062] Table 2 Pre-arranged power values of large power sources corresponding to each cross-limit section combination (unit: 10,000 kilowatts)

[0063]

[0064]

[0065] From the results in Table 2, we can see that under this typical method, considering all the constraints of the over-limit sections, the maximum joint transmission capacity of the two large power sources is about 8.5 million kilowatts. The over-limit section combinations a and d corresponding to the minimum value of the joint transmission capacity are the most important restrictive sections that restrict the joint transmission of the two large power sources.

[0066] According to the calculated pre-arranged power value, the typical operation mode data is manually adjusted and compiled in the typical operation mode, and the flow distribution result finally obtained by the flow calculation is consistent with the evaluation and analysis conclusion of the present invention.

[0067] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the specific embodiments described above. The specific embodiments and descriptions in the specification are merely intended to further illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances, characterized in that: include: Step 1: Based on the target provincial power grid operation mode data, select two target large power sources to be evaluated and arrange them to operate at rated power. At the same time, evenly adjust the output of coal-fired units within the province to ensure that the boundary conditions of the province's power supply remain unchanged. Perform power flow calculations to obtain the power flow distribution results of the power grid and determine whether there is at least one cross-limit section where the power flow exceeds the stability limit. If so, proceed to step 2. Otherwise, output the evaluation result that the two large power sources can simultaneously transmit at full power under the target operation mode. Step 2: Calculate the transfer coefficient of each cross-limit section in the first step for each change in the power of a single target large power source. The transfer coefficient refers to the sensitivity of the impact of the change in the power of a large power source on the cross-limit section. After the power arrangement value of the large power source changes, it is also necessary to uniformly adjust the output of the coal-fired units in the province to ensure that the boundary conditions of the province's incoming electricity remain unchanged before and after the change. Step 3: Select two sections from the over-limit sections as a combination in turn. Based on the initial operation mode and transfer coefficient, calculate the corresponding large power source pre-arranged power value when the over-limit section combination operates simultaneously at the stability limit. Determine whether the pre-arranged power values of the two large power sources are both greater than or equal to 0. If so, go to step 5; otherwise, go to step 4. The calculation formula involved in the third step is as follows: ， ， Where, P a0 、P b0 They are the cross-limit sections a in the initial operation mode 、 b. Initial arrangement power value of the power flow; P x0 、P y0 They are the initial arranged power values of large power sources x and y in the initial operation mode respectively; P x 、P y They are respectively the cross-limit section a 、 b. The pre-arranged power values of large power sources x and y corresponding to the combination operating at the stability limit; is the stability limit of the cross-limit section a; is the stability limit of the cross-limit section b; Step 4: Eliminate the selected cross-section combination and go to step 3; Step 5: Calculate the sum of the pre-arranged power values of the two major power sources when the selected cross-limit section combination operates simultaneously within the stability limit; Step 6: Determine whether all the combinations of cross-limit sections have been considered. If so, go to step 7; otherwise, go to step 3. Step 7: Obtain the minimum value of the sum of the pre-arranged power values of the two major power sources in each out-of-limit section combination after consideration and elimination, and the corresponding out-of-limit section combination.

2. The method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances according to claim 1 is characterized in that: In the first step, the large power source object refers to a large-capacity power plant, a group of units or an ultra-high voltage direct current converter station.

3. The method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances according to claim 1 is characterized in that: In the second step, the value of the transfer coefficient is not affected by the change of large power source power and is only related to the grid structure.

4. The method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances according to claim 3 is characterized in that: In the second step, the transfer coefficient is calculated as follows: ， Where, i For the cross-limit section, j are the large power sources x and y to be evaluated, k ij Refers to the large power supply to be evaluated j Cross-limit section i The transfer coefficient of P i0 、P j0 is the initial power value, P i1 、P j1 is the power value corresponding to the change.

5. The method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances according to claim 1 is characterized in that: In the third step, if the pre-arranged power value of the large power source is less than 0, it means that the two selected sections cannot reach the stability limit at the same time in actual operation, that is, the power of one section reaches the stability limit value, and the power of the other section does not exceed the stability limit value.

6. The method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances according to claim 1, characterized in that: In the third step, if there is only one out-of-limit section, consider the rated power operation of the large power source with a small transfer coefficient, and then calculate the pre-arranged power value of the large power source with a large transfer coefficient when the out-of-limit section operates at the stability limit.

7. The method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances according to claim 1, characterized in that: The calculation formula involved in the fifth step is as follows: P xy = P x +P y ， Where, P x 、P y They are respectively the pre-arranged power values of large power sources x and y corresponding to the over-limit section combination when operating at the stability limit at the same time.

8. The method for evaluating the maximum combined output capacity of two large power sources with similar electrical distances according to claim 1, characterized in that: In the seventh step, the minimum value of the sum of the pre-arranged power values of the two major power sources in each over-limit section combination, that is, the maximum joint transmission capacity of the two large power sources to be evaluated to ensure that each section does not exceed the limit, the corresponding over-limit section combination is the main restricting section restricting the evacuation of the two large power sources to be evaluated.

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