A Day-ahead Economic Dispatch Method for Power Grid Adapting to Three-terminal DC Mode

Abstract

The present invention discloses a method for day-ahead economic dispatch of a power grid adapted to a three-terminal DC mode, which is applicable to a three-terminal DC complex operation mode. The present invention relates to the field of power dispatch operation technology, which includes the following steps: constructing an optimization target for economic dispatch of a regional power grid, wherein the optimization target at least includes the lowest transmission loss of the regional power grid and the least amount of regional new energy loss within the scope of the regional power grid; constructing constraints for economic dispatch of the regional power grid; based on the optimization target and the constraints, constructing and solving an optimization model for economic dispatch of the regional power grid, and constructing and solving a model for economic dispatch of a provincial power grid; making a convergence judgment on the solution result, and if the convergence condition is met, outputting the power transmission plan obtained by the current iteration; otherwise, substituting the solution result into a re-iterative calculation. The present invention solves the problem that the economic dispatch method under the conventional AC / DC hybrid regional power grid is difficult to directly apply to the three-terminal DC system.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power dispatching and operation, and in particular to a day-ahead economic dispatching method for a power grid adapted to a three-terminal direct current mode. Background Art

[0002] Regional power grid interconnection is an important way to improve the power grid's clean energy consumption capacity and achieve a wider range of optimal resource allocation. At present, regional power grid interconnection is mainly achieved through ultra-high voltage / ultra-high voltage AC or DC transmission lines. Although there are significant differences in the operating characteristics of AC and DC systems, they are both essentially two-terminal devices in terms of physical structure, that is, there are clear sending and receiving ends. For the day-ahead economic dispatch problem of regional power grids with only two-terminal devices, there are certain research and practical results.

[0003] With the large-scale access of new energy and the deepening of power market reform, the demand for regional power grid interconnection and transmission has become more urgent. Limited by factors such as inter-regional channel space resources, in order to meet the requirements of regional power grid interconnection, three-terminal direct current has been widely studied and applied as a new way of regional power grid interconnection channel (see the attached three-terminal direct current transmission diagram for details). Figure 1 ). However, compared with the traditional two-terminal AC and DC transmission, the operation mode and operation requirements of three-terminal DC have changed significantly due to the addition of a DC terminal, which is reflected in:

[0004] (i) The operation mode of three-terminal DC is more complicated. From the perspective of transmission direction, there are only 1-2 power transmission modes in traditional AC and DC transmission lines, that is, from end A to end B or from end B to end A. In actual operation, due to requirements such as power transmission protocol and stability control device configuration, generally only one of the power transmission modes can be supported. There are at least 14 power transmission modes for three-terminal DC, and the typical power transmission modes are shown in Table 1. From the perspective of mathematical modeling, if mixed integer variables are used to describe the three-terminal DC power transmission mode, at least 14 mixed integer variables need to be introduced, which will greatly increase the burden of modeling and optimization solution.

[0005] Table 1: Typical three-terminal DC power transmission methods

[0006]

[0007]

[0008] (II) The assessment of three-terminal DC transmission loss is more complicated. The traditional AC and DC transmission line transmission loss assessment methods are relatively mature, but there is currently a lack of assessment methods for three-terminal DC transmission loss.

[0009] Inter-regional power grid interconnection is an important way to improve the clean energy consumption capacity of power grids. The three-terminal DC system has become one of the important ways of interconnecting inter-regional power grids with its advantages such as large transmission capacity and flexible operation mode. However, the operation mode of three-terminal DC is more diverse, which is significantly different from the traditional two-terminal DC. In terms of operation mode and transmission loss assessment, the characteristics of the three-terminal DC system make it difficult to directly apply the economic dispatch method under the conventional AC / DC hybrid regional power grid. Summary of the invention

[0010] In view of the deficiencies in the prior art, the present invention provides a method that adapts to the complex operation mode of three-terminal DC to solve the problem that the economic dispatch method under the conventional AC / DC hybrid regional power grid is difficult to directly apply to the three-terminal DC system.

[0011] To achieve the above object, the present invention can adopt the following technical solutions:

[0012] A day-ahead economic dispatching method for a power grid adapted to a three-terminal DC mode is applicable to a three-terminal DC complex operation mode, and includes the following steps:

[0013] Step 1: Constructing the optimization target of regional power grid economic dispatch, wherein the optimization target at least includes minimizing the transmission loss of the regional power grid and minimizing the power loss of regional renewable energy within the regional power grid;

[0014] Step 2: Construct constraints for economic dispatch of regional power grid;

[0015] Step 3: Based on the optimization objective and the constraint conditions, an optimization model for economic dispatch of a regional power grid is constructed and solved, and a model for economic dispatch of a provincial power grid is constructed and solved;

[0016] Step 4: Determine the convergence of the solution result. If the convergence condition is met, output the power transmission plan obtained in this round of iteration; otherwise, substitute the solution result into step 1 and iterate again.

[0017] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0018] The transmission loss of the regional power grid is the sum of the transmission losses of each transmission line, that is:

[0019] The transmission loss of two-terminal mode AC and DC transmission lines can be uniformly expressed as:

[0020]

[0021] In the formula, is the transmission loss of the conventional two-terminal AC and DC transmission line at time t, is the transmission power flow of the transmission line at that moment, a l 、b l、c l are the coefficients of the quadratic, linear and constant terms of transmission loss respectively.

[0022] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0023] The three-terminal DC transmission loss is the sum of the transmission losses of the three-terminal DC transmission line and the supporting AC / DC conversion device, that is:

[0024] The three-terminal DC transmission loss can be expressed as:

[0025]

[0026] In the formula, is the transmission loss of the three-terminal DC at time tl, The three-terminal DC a, b, and c are injected into the power flow at time t. are the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of the transmission loss of the DC transmission line at end a and its supporting AC / DC conversion device, are the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of the transmission loss of the DC transmission line at end B and its supporting AC / DC conversion device, It is the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of transmission loss of the DC transmission line at end C and its supporting AC / DC conversion device.

[0027] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0028] The optimization objective of constructing a three-terminal DC system can be expressed as:

[0029]

[0030] In the formula, F 1 is the optimization target of the regional power grid day-ahead economic dispatch problem, E NLoss is the expected loss of renewable energy electricity caused by wind and solar power abandonment in the regional power grid and the provinces and regions, α 1,1 , α 1,2 is the weight coefficient of the two optimization objectives, N T is the number of optimization periods, and ΔT is the optimization time interval. In the initial stage, the regional power grid new energy loss power E NLoss Set to 0 and update according to the value change during the iteration process.

[0031] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0032] For any conventional AC / DC transmission line, its transmission power does not exceed its transmission capacity. For a three-terminal DC transmission line, the transmission power at any end is required to not exceed the transmission capacity of that end, which can be expressed as:

[0033]

[0034] In the formula, They are the transmission capacity limits of end a, end b and end c in three-terminal DC respectively.

[0035] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0036] The transmission power constraint requires that the inter-provincial transmission power be the same as its exchange power plan. The inter-provincial transmission power and the transmission power at each end should satisfy the following relationship:

[0037]

[0038] In the formula, the three-terminal DC terminals are located in different provinces, and their inter-provincial transmission powers are recorded as in, Indicates that the power grid at the provincial region where end a is located transmits power to the power grid at the provincial region where end b is located through three-terminal direct current. Indicates that the power grid at the provincial region where end a is located transmits power to the power grid at the provincial region where end c is located through three-terminal direct current. It indicates that the power grid in the province where end b is located transmits power to the power grid in the province where end b is located through three-terminal direct current during the period; the value of the transmitted power indicates the size of the transmission power, and its sign indicates the transmission direction. When the value is positive, it indicates positive transmission, otherwise it indicates negative transmission.

[0039] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0040] Assuming that the three-terminal DC terminal a is located in the provincial A grid and the terminal b is located in the provincial B grid, the power transmitted from the provincial A grid to the provincial B grid is the sum of the transmission power of all conventional AC and DC interconnection lines of the two provincial grids and the three-terminal DC inter-provincial transmission power. The sum can be expressed as:

[0041]

[0042] Where P t A-B is the power transmitted from the power grid of province A to the power grid of province B at time t, P lac,t , P ldc,tare the transmission powers of the conventional AC transmission line lac and the conventional DC transmission line ldc at time t, lac∈LAC-AB and ldc∈LDC-AB respectively indicate that the conventional AC transmission line lac and the conventional DC transmission line ldc belong to the conventional AC transmission line set LAC-AB and the conventional DC transmission line set LDC-AB connecting the power grid of province A and the power grid of province B;

[0043] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0044] The transmission power constraint can be expressed as:

[0045]

[0046] In the formula, E A-B It is a plan for exchanging electricity between the power grid of province A and the power grid of province B.

[0047] The above-mentioned power grid day-ahead economic dispatch method adapted to the three-terminal DC mode further includes:

[0048] The transmission power constraint requires that the transmission power between provincial power grids must be within the scope specified in the contract, and the transmission power between peak and valley periods should meet the peak-valley power ratio allocation requirements, which can be expressed as:

[0049]

[0050] Where P A-B,max , P A-B,min are the maximum and minimum values ​​of inter-provincial exchange power respectively. are the maximum and minimum values ​​of the peak-valley power ratio stipulated in the inter-provincial exchange power, T P , T L They are peak time and trough time respectively.

[0051] As described above, the day-ahead economic dispatch method of the power grid adapted to the three-terminal DC mode, further, selects the energy loss of new energy as the convergence judgment index, then the convergence judgment condition can be expressed as:

[0052]

[0053] In the formula, are the new energy loss electricity obtained in the n+1th round of iteration and the nth round of iteration respectively, and ε is the convergence coefficient.

[0054] Compared with the prior art, the present invention has the following beneficial effects: the present invention proposes a day-ahead economic dispatch method for a power grid that is adapted to a three-terminal DC mode for a three-terminal DC system, thereby solving the problem that the economic dispatch method under a conventional AC / DC hybrid regional power grid is difficult to directly apply to a three-terminal DC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0056] Figure 1 is a schematic structural diagram of a three-terminal direct current transmission system in an embodiment of the present invention;

[0057] Figure 2 The flowchart of the day-ahead economic dispatching method of a power grid adapted to a three-terminal DC mode in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0059] Example:

[0060] It should be noted that the terms "including" and "having" and any variations of the embodiments of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0061] The present invention proposes a method for day-ahead economic dispatch of a power grid that is adaptable to a three-terminal DC complex operation mode. Figure 2 As shown, the implementation steps are as follows:

[0062] 1. Establishing the optimization target of regional power grid economic dispatch

[0063] The purpose of this step is to construct the optimization target of regional power grid economic dispatch.

[0064] The optimization objectives of regional power grid economic dispatch in this patent include two parts: (1) the transmission loss of the regional power grid is the lowest; (2) the regional renewable energy power loss within the regional power grid is the lowest. The transmission loss of the regional power grid represents the economic efficiency of the regional power grid operation. The higher the loss, the lower the economic efficiency. The renewable energy power loss is not only related to the economic efficiency of the power grid operation, but also an important reference indicator for the energy conservation and environmental protection level of the power grid operation.

[0065] The transmission loss of the regional power grid is the sum of the transmission losses of each transmission line. The transmission loss of the traditional two-terminal AC and DC transmission lines can be expressed as a quadratic function of the active power transmitted, which can be uniformly expressed as:

[0066]

[0067] In the formula, is the transmission loss of the conventional two-terminal AC and DC transmission line at time t, is the transmission power flow of the transmission line at that moment, a l 、b l 、c l are the coefficients of the quadratic, linear and constant terms of transmission loss respectively.

[0068] The three-terminal DC transmission loss is the sum of the transmission losses of the three-terminal DC transmission line and the supporting AC-DC conversion device. The loss of each end of the DC transmission line and its supporting AC-DC conversion device can be expressed as a quadratic function with reference to the conventional DC transmission line loss model. The entire three-terminal DC transmission loss can be expressed as:

[0069]

[0070] In the formula, is the transmission loss of the three-terminal DC at time tl, The three-terminal DC a, b, and c are injected into the power flow at time t. are the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of the transmission loss of the DC transmission line at end a and its supporting AC / DC conversion device, are the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of the transmission loss of the DC transmission line at end B and its supporting AC / DC conversion device, It is the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of transmission loss of the DC transmission line at end C and its supporting AC / DC conversion device.

[0071] Preferably, the weighted comprehensive method is used to integrate the two optimization target items to construct the optimization target of the three-terminal DC system, which can be expressed as:

[0072]

[0073] In the formula, F 1 is the optimization target of the regional power grid day-ahead economic dispatch problem, E NLoss is the expected loss of renewable energy electricity caused by wind and solar power abandonment in the regional power grid and the provinces and regions, α 1,1 , α 1,2 is the weight coefficient of the two optimization objectives, N Tis the number of optimization periods, and ΔT is the optimization time interval. In the initial stage, the regional power grid new energy loss power E NLoss Set to 0 and update according to the value change during the iteration process.

[0074] 2. Constructing constraints for regional power grid economic dispatch

[0075] The purpose of this step is to construct the constraints of regional power grid economic dispatch. The constraints of traditional regional power grid economic dispatch mainly include transmission capacity constraints, transmission quantity constraints, and transmission power constraints. However, the traditional economic dispatch method is only applicable to two-terminal AC and DC transmission lines, not three-terminal DC transmission lines. Therefore, the key to this step is to construct the constraints of the regional power grid economic dispatch model that is suitable for three-terminal DC.

[0076] First, the transmission capacity constraint requires that the transmission power of any transmission line does not exceed its transmission capacity. For any conventional AC / DC transmission line, its transmission power does not exceed its transmission capacity. For a three-terminal DC transmission line, the transmission power of any end is required to not exceed the transmission capacity of that end, which can be expressed as:

[0077]

[0078] In the formula, They are the transmission capacity limits of end a, end b and end c in three-terminal DC respectively.

[0079] Secondly, the transmission power constraint requires that the inter-provincial transmission power is the same as its exchange power plan. In order to associate the inter-provincial transmission power with the transmission power of each end of the three-terminal DC, the three-terminal DC transmission power variable is introduced. This modeling method is equivalent to equating the three-terminal DC to three groups of conventional DC. Each end of the three-terminal DC is located in a different province, and its inter-provincial transmission power is recorded as The power transmission value indicates the magnitude of the transmission power, and its sign indicates the transmission direction. When the value is positive, it indicates positive transmission, otherwise it indicates negative transmission. The inter-provincial transmission power and the transmission power at each end should satisfy the following relationship:

[0080]

[0081] Without affecting the main innovation of the present invention, it is stipulated that the three-terminal DC terminal a is located in the provincial A power grid, and the terminal b is located in the provincial B power grid. Then the power transmitted from the provincial A power grid to the provincial B power grid is the power transmitted by all conventional AC and DC interconnection lines of the two provincial power grids and the three-terminal DC inter-provincial transmission power. The sum can be expressed as:

[0082]

[0083] Where P t A-B is the power transmitted from the power grid of province A to the power grid of province B at time t, P lac,t , P ldc,t are the transmission powers of the conventional AC transmission line lac and the conventional DC transmission line ldc at time t, lac∈LAC-AB and ldc∈LDC-AB respectively indicate that the conventional AC transmission line lac and the conventional DC transmission line ldc belong to the conventional AC transmission line set LAC-AB and the conventional DC transmission line set LDC-AB connecting the power grids of province A and province B.

[0084] The transmission power constraint can be expressed as:

[0085]

[0086] In the formula, E A-B It is a plan for exchanging electricity between the power grid of province A and the power grid of province B.

[0087] Preferably, the transmission power constraint requires that the transmission power between provincial power grids must be within the scope specified in the contract, and the transmission power between peak and valley periods should meet the peak-valley power ratio allocation requirements, which can be expressed as:

[0088]

[0089] Where P A-B,max , P A-B,min are the maximum and minimum values ​​of inter-provincial exchange power respectively. are the maximum and minimum values ​​of the peak-valley power ratio stipulated in the inter-provincial exchange power, T P , T L They are peak time and trough time respectively.

[0090] (III) Constructing and solving the regional power grid economic dispatch optimization model

[0091] The purpose of this step is to construct and solve the regional power grid economic dispatch optimization model.

[0092] Preferably, the regional power grid economic dispatch optimization model uses formula (3) in step 1 as the optimization target and formulas (4), (5), (7) and (8) in step 2 as constraints. This model is a quadratic programming problem and can be solved directly using commercial planning software packages such as Cplex or using the interior point method. The specific solution process will not be described in detail as it does not affect the main innovation of the present invention.

[0093] (IV) Constructing and solving the provincial power grid economic dispatch model

[0094] The purpose of this step is to construct the economic dispatch model for each provincial level in the regional power grid and solve for the expected loss of renewable energy electricity.

[0095] Preferably, the provincial power grid economic dispatch model should take the expected loss of new energy as the minimum as the optimization goal, and consider constraints such as power balance constraints, section transmission capacity constraints, and generator set operating characteristics constraints. This model is also a quadratic nonlinear programming problem, which can be solved directly using commercial planning software packages such as Cplex, or using the interior point method. It does not affect the main innovation of the present invention, and its specific solution process is not repeated.

[0096] (V) Convergence determination

[0097] The purpose of this step is to determine whether the convergence requirements are met based on the changes in the new energy loss power indicators during the iteration process.

[0098] Preferably, the energy loss of new energy is selected as the convergence determination index, and the convergence determination condition can be expressed as:

[0099]

[0100] In the formula, are the new energy loss electricity obtained in the n+1th round of iteration and the nth round of iteration respectively, and ε is the convergence coefficient.

[0101] If the convergence conditions are met, the power transmission plan obtained in this round of iteration is output; otherwise, the latest new energy loss electricity is brought into step one and the iterative calculation is repeated.

[0102] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0103] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A day-ahead economic dispatch method for a power grid adapted to a three-terminal DC mode, suitable for a three-terminal DC complex operation mode, characterized in that: The following steps are involved: Step 1: Constructing the optimization target of regional power grid economic dispatch, wherein the optimization target at least includes minimizing the transmission loss of the regional power grid and minimizing the power loss of regional renewable energy within the regional power grid; Step 2: Construct constraints for economic dispatch of regional power grid; Step 3: Based on the optimization objective and the constraint conditions, an optimization model for economic dispatch of the regional power grid is constructed and solved, and a model for economic dispatch of the provincial power grid is constructed and solved; wherein the optimization model for economic dispatch of the regional power grid is determined according to the following formula: In the formula, F 1 is the optimization target of the regional power grid day-ahead economic dispatch problem, E NLoss is the expected loss of renewable energy electricity caused by wind and solar power abandonment in the regional power grid and the provinces and regions, α 1,1 , α 1,2 is the weight coefficient of the two optimization objectives, N T is the number of optimization periods, ΔT is the optimization time interval, is the transmission loss of the three-terminal DC at time tl; in the initial stage, the new energy loss of the regional power grid is E NLoss Set to 0 and update according to the value changes during the iteration; The constraint condition is determined according to the following formula: For any conventional AC / DC transmission line, its transmission power does not exceed its transmission capacity. For a three-terminal DC transmission line, the transmission power at any end is required to not exceed the transmission capacity of that end, which can be expressed as: In the formula, They are the transmission capacity limits of terminal a, terminal b and terminal c in three-terminal DC respectively; The transmission power constraint requires that the inter-provincial transmission power be the same as its exchange power plan. The inter-provincial transmission power and the transmission power at each end should satisfy the following relationship: In the formula, the three-terminal DC terminals are located in different provinces, and their inter-provincial transmission powers are recorded as in, Indicates that the power grid at the provincial region where end a is located transmits power to the power grid at the provincial region where end b is located through three-terminal direct current. Indicates that the power grid at the provincial region where end a is located transmits power to the power grid at the provincial region where end c is located through three-terminal direct current. Indicates that the power grid of the province where end b is located transmits power to the power grid of the province where end b is located through three-terminal direct current during the period; the value of the transmission power indicates the magnitude of the transmission power, and its sign indicates the transmission direction. When the value is positive, it indicates positive transmission, otherwise it indicates negative transmission; Assuming that the three-terminal DC terminal a is located in the provincial A grid and the terminal b is located in the provincial B grid, the power transmitted from the provincial A grid to the provincial B grid is the sum of the transmission power of all conventional AC and DC interconnection lines of the two provincial grids and the three-terminal DC inter-provincial transmission power. The sum can be expressed as: Where P t A-B is the power transmitted from the power grid of province A to the power grid of province B at time t, P lac,t , P ldc,t are the transmission powers of the conventional AC transmission line lac and the conventional DC transmission line ldc at time t, lac∈LAC-AB and ldc∈LDC-AB respectively indicate that the conventional AC transmission line lac and the conventional DC transmission line ldc belong to the conventional AC transmission line set LAC-AB and the conventional DC transmission line set LDC-AB connecting the power grid of province A and the power grid of province B; The transmission power constraint can be expressed as: In the formula, E A-B A plan for exchanging electricity between the power grid of province A and the power grid of province B; The transmission power constraint requires that the transmission power between provincial power grids must be within the scope specified in the contract, and the transmission power between peak and valley periods should meet the peak-valley power ratio allocation requirements, which can be expressed as: Where P A-B,max , P A-B,min are the maximum and minimum values ​​of inter-provincial exchange power respectively. are the maximum and minimum values ​​of the peak-valley power ratio specified for inter-provincial power exchange, T P , T L They are peak time and trough time respectively; The provincial power grid economic dispatch model takes the minimum expected loss of renewable energy as the optimization goal; Step 4: Convergence judgment is performed on the solution result. If the convergence condition is met, the power transmission plan obtained in this round of iteration is output; otherwise, the solution result is substituted into step 1 for re-iteration calculation; among them, the power loss of new energy is selected as the convergence judgment indicator, and the convergence judgment condition can be expressed as: In the formula, are the new energy loss electricity obtained in the n+1th round of iteration and the nth round of iteration respectively, and ε is the convergence coefficient.

2. The method for day-ahead economic dispatch of a power grid adapted to a three-terminal DC mode according to claim 1, characterized in that: The three-terminal DC transmission loss is the sum of the transmission losses of the three-terminal DC transmission line and the supporting AC / DC conversion device, that is, the three-terminal DC transmission loss can be expressed as: In the formula, is the transmission loss of the three-terminal DC at time tl, The three-terminal DC a, b, and c are injected into the power flow at time t. are the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of the transmission loss of the DC transmission line at end a and its supporting AC / DC conversion device, are the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of the transmission loss of the DC transmission line at end B and its supporting AC / DC conversion device, It is the quadratic term coefficient, linear term coefficient and constant term coefficient of the quadratic function of transmission loss of the DC transmission line at end C and its supporting AC / DC conversion device.

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