Method and device for optimizing short-circuit impedance of a converter transformer

Abstract

This application discloses a method and apparatus for optimizing the short-circuit impedance of converter transformers. The method includes: establishing the relationship between the cost of each transformer and its short-circuit impedance, the relationship between the loss discount of each transformer and its short-circuit impedance, and the relationship between the reactive power consumption of the converter valve and its short-circuit impedance; further determining the relationship between the number of reactive power compensation devices and the short-circuit impedance of the transformers, thereby determining the relationship between the cost of the reactive power compensation devices and the short-circuit impedance of the transformers; integrating these relationships to obtain a comprehensive cost function of the system cost with respect to the transformer short-circuit impedance; and determining the target short-circuit impedance value. It is evident that the comprehensive cost function considers the cost of the transformers, the loss discount, and the reactive power compensation devices. Therefore, in the design process of equipment in a high-voltage direct current transmission system, not only the cost of the transformers, but also the cost of losses and reactive power consumption are considered, and the determined target short-circuit impedance value is the most economical design value.

Description

Technical Field

[0001] This application relates to the field of long-distance power transmission, and more specifically, to a method and apparatus for optimizing the short-circuit impedance of a converter transformer. Background Technology

[0002] With the continuous increase in electricity consumption, the power supply in some areas cannot meet local demand, necessitating long-distance or even inter-regional power transmission, such as offshore power transmission. Because high-voltage direct current (HVDC) transmission systems possess the capability for long-distance, high-capacity power transmission, the design of the HVDC main circuit is a crucial aspect of HVDC design, determining the design parameters of equipment such as converter valves, converter transformers, and reactive power compensation devices. In HVDC transmission systems, the design of various devices is typically done separately, without coordinated optimization. This often results in excessive margins in equipment parameter design, failing to achieve the most economical design.

[0003] For converter transformers in high-voltage direct current transmission systems, the minimum short-circuit impedance is currently calculated using the following formula:

[0004]

[0005] Among them, S n S represents the capacity of any converter transformer. kmax I represents the maximum short-circuit capacity of the AC grid to be converted in a high-voltage direct current transmission system. dn This refers to the rated DC current of the high-voltage direct current transmission system. The maximum short-circuit current that a high-voltage direct current transmission system can withstand is the same for all converter transformers in the system.

[0006] However, in reality, the cost of a high-voltage direct current (HVDC) transmission system is related to the cost, losses, and reactive power consumption of the converter transformer. But the minimum short-circuit impedance of the converter transformer can only give the minimum cost of the converter transformer, not the minimum cost of the HVDC transmission system. Therefore, the most economical design cannot be achieved. Summary of the Invention

[0007] In view of the above problems, this application is made to provide a method and apparatus for optimizing the short-circuit impedance of converter transformers, so as to save the design cost of high voltage direct current transmission systems.

[0008] To achieve the above objectives, the following specific solutions are proposed:

[0009] A method for optimizing the short-circuit impedance of a converter transformer includes:

[0010] The relationship between the cost of each converter transformer in a high-voltage direct current (HVDC) transmission system and the short-circuit impedance of any single converter transformer is used as the first short-circuit impedance variation relationship for the cost of each converter transformer. The HVDC transmission system includes a target AC grid to be converted, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to one converter valve. Of the four converter transformers, two are connected to the target AC grid to be converted, and the other two are connected to the target AC grid. The four converter valves are connected in series via DC lines. The reactive power compensation device is connected to the target AC grid.

[0011] The relationship between the loss discount of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed as the second short-circuit impedance change relationship of the loss discount of each converter transformer.

[0012] The relationship between the reactive power consumption of each converter valve in the high voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve is constructed as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve.

[0013] Based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve, and the preset group capacity of the reactive power compensation device, the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined, and this relationship is used as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device.

[0014] Based on the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device is determined, and its relationship with the short-circuit impedance of any converter transformer is established. This relationship is then used as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device.

[0015] By integrating the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained.

[0016] Determine the target short-circuit impedance value, which is the short-circuit impedance obtained when the comprehensive cost is lowest in the comprehensive cost function.

[0017] Optionally, the relationship between the cost of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer includes:

[0018] The relationship between the cost of each converter transformer in a high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer is used as the relationship between the cost of a single converter transformer and the change in short-circuit impedance.

[0019] Using the number of converter transformers in the high-voltage direct current transmission system as the cost relationship fusion coefficient, and fusing the single-cost short-circuit impedance variation relationship, the relationship between the cost of each converter transformer and the short-circuit impedance of any converter transformer is obtained.

[0020] Optionally, the relationship between the cost of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer includes:

[0021] The following formula can be used to construct the relationship between the cost of each converter transformer in a high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer:

[0022]

[0023] Where, p tra The cost of each converter transformer, X r Let be the short-circuit impedance of any converter transformer, a be the second-order cost coefficient of any converter transformer, b be the first-order cost coefficient of any converter transformer, and c be the cost constant coefficient of any converter transformer.

[0024] Optionally, the relationship between the loss discount of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed, including:

[0025] The relationship between the loss of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed, which serves as the single-loss short-circuit impedance variation relationship of the loss of a single converter transformer.

[0026] Using the number of converter transformers in the high-voltage direct current transmission system and the preset equivalent pricing coefficient as loss relationship fusion coefficients, the relationship between the loss discount of each converter transformer and the short-circuit impedance of any converter transformer is obtained by fusing the single-loss short-circuit impedance change relationship.

[0027] Optionally, the relationship between the losses of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed, including:

[0028] The following formula can be used to construct the relationship between the loss discount of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer:

[0029] L o (Xr )=dX r +e

[0030] Among them, L o The loss of each converter transformer, X r Let d be the short-circuit impedance of any converter transformer, d be the primary loss coefficient of any converter transformer, and e be the loss constant coefficient of any converter transformer.

[0031] Optionally, the relationship between the reactive power consumption of each converter valve in the high-voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve is constructed, including:

[0032] The relationship between the reactive power consumption of each converter valve in the HVDC transmission system and the short-circuit impedance of the converter transformer connected to that converter valve can be constructed using the following formula:

[0033]

[0034] Among them, Q dc Let P be the reactive power consumption of each converter valve, P be the DC power of that converter valve, α be the rectifier firing angle of that converter valve, and X be the reactive power consumption of each converter valve. r I is the short-circuit impedance of the converter transformer connected to this converter valve. d E represents the DC current of the high-voltage direct current transmission system. 11 This is the no-load voltage of the valve-side winding of the converter transformer connected to the converter valve.

[0035] Optionally, determining the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve and the preset group capacity of the reactive power compensation device includes:

[0036] The relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined using the following formula:

[0037] N(X r ) = RoundUp(Q dc (X r ) / Q0)

[0038] Where N is the number of groups of the reactive power compensation device, Q dc (X r ) represents the third short-circuit impedance change relationship of reactive power consumption of any converter valve, Q0 is the preset group capacity of the reactive power compensation device, and RoundUp() is the round-up function.

[0039] Optionally, based on the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device is determined, and its relationship with the short-circuit impedance of any converter transformer is included, including:

[0040] Using the preset cost coefficient of the reactive power compensation device group as the group cost relationship fusion coefficient, and integrating the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device and the short-circuit impedance of any converter transformer are obtained.

[0041] Optionally, by integrating the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained, including:

[0042] By integrating the first, second, and fifth short-circuit impedance change relationships using the following formula, a comprehensive cost function for the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer can be obtained:

[0043] P rice (X r ) = P tra (X r )+P Loss (X r )+P acf (X r )

[0044] Among them, P tra (X r P represents the first short-circuit impedance variation relationship. Loss (X r ) represents the second short-circuit impedance variation relationship, P acf (X r The fifth short-circuit impedance variation relationship is shown below.

[0045] An optimization device for the short-circuit impedance of a converter transformer, comprising:

[0046] The first impedance relationship construction unit is used to construct the relationship between the cost of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, which serves as the first short-circuit impedance change relationship for the cost of each converter transformer. The high voltage direct current transmission system includes a converter AC grid, a target converter AC grid, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to a converter valve. Of the four converter transformers, two are connected to the converter AC grid, and the other two are connected to the target converter AC grid. The four converter valves are connected in series via DC lines. The reactive power compensation device is connected to the converter AC grid.

[0047] The second impedance relationship construction unit is used to construct the relationship between the loss discount of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as the second short-circuit impedance change relationship of the loss discount of each converter transformer.

[0048] The third impedance relationship construction unit is used to construct the relationship between the reactive power consumption of each converter valve in the high voltage DC transmission system and the short-circuit impedance of the converter transformer connected to the converter valve, as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve.

[0049] The fourth impedance relationship determination unit is used to determine the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve and the preset group capacity of the reactive power compensation device, and to use it as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device.

[0050] The fifth impedance relationship determination unit is used to determine the cost of the reactive power compensation device and its relationship with the short-circuit impedance of any converter transformer based on the fourth short-circuit impedance change relationship, and to use the fifth short-circuit impedance change relationship as the cost of the reactive power compensation device.

[0051] The impedance relationship fusion unit is used to fuse the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship to obtain a comprehensive cost function of the high voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer.

[0052] A target short-circuit impedance determination unit is used to determine a target short-circuit impedance value, wherein the target short-circuit impedance value is the short-circuit impedance obtained when the comprehensive cost is the lowest in the comprehensive cost function.

[0053] Optionally, the first impedance relationship construction unit includes:

[0054] The first intermediate relationship construction unit is used to construct the relationship between the cost of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as a single cost short-circuit impedance change relationship of the cost of a single converter transformer.

[0055] The cost coefficient fusion unit is used to fuse the single-cost short-circuit impedance change relationship with the number of converter transformers in the high-voltage direct current transmission system as the cost relationship fusion coefficient, thereby obtaining the relationship between the cost of each converter transformer and the short-circuit impedance of any converter transformer, and using this relationship as the first short-circuit impedance change relationship for the cost of each converter transformer.

[0056] Optionally, the first intermediate relationship construction unit includes:

[0057] The first intermediate relationship construction sub-unit is used to construct the relationship between the cost of each converter transformer in a high-voltage direct current transmission system and the short-circuit impedance of any converter transformer using the following formula:

[0058]

[0059] Where, p tra The cost of each converter transformer, X r Let be the short-circuit impedance of any converter transformer, a be the second-order cost coefficient of any converter transformer, b be the first-order cost coefficient of any converter transformer, and c be the cost constant coefficient of any converter transformer.

[0060] Optionally, the second impedance relationship building unit includes:

[0061] The second intermediate relationship construction unit is used to construct the relationship between the loss of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as the single loss short-circuit impedance change relationship of the loss of a single converter transformer.

[0062] The pricing loss coefficient fusion unit is used to fuse the single-loss short-circuit impedance change relationship with the number of converter transformers in the high-voltage direct current transmission system and the preset equal pricing coefficient as loss relationship fusion coefficients, so as to obtain the relationship between the loss discount of each converter transformer and the short-circuit impedance of any converter transformer.

[0063] Optionally, the second intermediate relationship construction unit includes:

[0064] The second intermediate relationship construction subunit is used to construct the relationship between the loss discount of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer using the following formula:

[0065] L o (X r )=dX r +e

[0066] Among them, L o The loss of each converter transformer, X r Let d be the short-circuit impedance of any converter transformer, d be the primary loss coefficient of any converter transformer, and e be the loss constant coefficient of any converter transformer.

[0067] Optionally, the third impedance relationship construction unit includes:

[0068] The third impedance relationship construction subunit is used to construct the relationship between the reactive power consumption of each converter valve in the high-voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve using the following formula, and serves as the third short-circuit impedance change relationship for the reactive power consumption of each converter valve:

[0069]

[0070] Among them, Q dc Let P be the reactive power consumption of each converter valve, P be the DC power of that converter valve, α be the rectifier firing angle of that converter valve, and X be the reactive power consumption of each converter valve. r I is the short-circuit impedance of the converter transformer connected to this converter valve. d E represents the DC current of the high-voltage direct current transmission system. 11 This is the no-load voltage of the valve-side winding of the converter transformer connected to the converter valve.

[0071] Optionally, the fourth impedance relationship determination unit includes:

[0072] The fourth impedance relationship construction subunit is used to determine the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve using the following formula, and serves as the fourth short-circuit impedance variation relationship for the number of groups of the reactive power compensation device:

[0073] N(X r ) = RoundUp(Q dc (X r ) / Q0)

[0074] Where N is the number of groups of the reactive power compensation device, Q δc (X r ) represents the third short-circuit impedance change relationship of reactive power consumption of any converter valve, Q0 is the preset group capacity of the reactive power compensation device, and RoundUp() is the round-up function.

[0075] Optionally, the fifth impedance relationship determination unit includes:

[0076] The fifth impedance relationship construction sub-unit is used to integrate the fourth short-circuit impedance change relationship with the preset reactive power compensation device group cost coefficient as the group cost relationship fusion coefficient, thereby obtaining the relationship between the cost of the reactive power compensation device and the short-circuit impedance of any converter transformer, and serving as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device.

[0077] Optionally, the impedance relationship fusion unit includes:

[0078] The impedance relationship fusion subunit is used to fuse the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship using the following formula to obtain a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer:

[0079] P rice (X r ) = P tra (X r )+P Loss (X r )+P acf (X r )

[0080] Among them, P tra (X r P represents the first short-circuit impedance variation relationship. Loss (X r ) represents the second short-circuit impedance variation relationship, P acf (X r The fifth short-circuit impedance variation relationship is shown below.

[0081] By employing the above technical solution, this application establishes a relationship between the cost of each converter transformer in the high-voltage direct current (HVDC) transmission system and the short-circuit impedance of any single converter transformer, serving as the first short-circuit impedance change relationship for the cost of each converter transformer. It also establishes a relationship between the loss discount of each converter transformer in the HVDC transmission system and the short-circuit impedance of any single converter transformer, serving as the second short-circuit impedance change relationship for the loss discount of each converter transformer. Furthermore, it establishes a relationship between the reactive power consumption of each converter valve in the HVDC transmission system and the short-circuit impedance of the converter transformer connected to that converter valve, serving as the third short-circuit impedance change relationship for the reactive power consumption of each converter valve. Based on the third short-circuit impedance change relationship for the reactive power consumption of any single converter valve and the preset group capacity of the reactive power compensation device, it determines... The relationship between the number of reactive power compensation devices in a group and the short-circuit impedance of the converter transformer connected to the converter valve is determined, and this relationship is used as the fourth short-circuit impedance change relationship for the number of reactive power compensation devices in a group. Based on the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device is determined, and its relationship with the short-circuit impedance of any converter transformer is determined, and this relationship is used as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device. By combining the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained. A target short-circuit impedance value is determined, which is the short-circuit impedance obtained when the comprehensive cost is lowest in the comprehensive cost function. Therefore, the comprehensive cost function of the converter transformer's short-circuit impedance in relation to the overall cost of a high-voltage direct current (HVDC) transmission system incorporates the first short-circuit impedance variation relationship of the converter transformer's cost, the second short-circuit impedance variation relationship of the converter transformer's loss discount, and the fifth short-circuit impedance variation relationship of the reactive power compensation device's cost. Thus, in the design process of equipment in a HVDC transmission system, considering not only the cost of the converter transformer but also its loss cost and reactive power consumption cost, the determined target short-circuit impedance value is the most economical design value. Attached Figure Description

[0082] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0083] Figure 1 A schematic flowchart illustrating the optimization of the short-circuit impedance of a converter transformer, provided as an embodiment of this application;

[0084] Figure 2A circuit topology diagram of a high-voltage direct current transmission system provided in this application embodiment;

[0085] Figure 3 A schematic diagram of a device for optimizing the short-circuit impedance of a converter transformer, provided in an embodiment of this application;

[0086] Figure 4 This is a schematic diagram of a device for optimizing the short-circuit impedance of a converter transformer, provided as an embodiment of this application. Detailed Implementation

[0087] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0088] The proposed solution can be implemented based on a terminal with data processing capabilities, such as a computer, server, or cloud platform.

[0089] Next, combined Figure 1 The method for optimizing the short-circuit impedance of the converter transformer in this application may include the following steps:

[0090] Step S110: Construct the relationship between the cost of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, and use this relationship as the first short-circuit impedance change relationship of the cost of each converter transformer.

[0091] Among them, such as Figure 2 As shown, the high-voltage direct current (HVDC) transmission system includes a target AC grid for switching, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to one converter valve. Of the four converter transformers, two are connected to the target AC grid, and the other two are connected to the target AC grid. The four converter valves are connected in series via DC lines. The reactive power compensation device is connected to the target AC grid. All converter transformers in the HVDC transmission system are identical; when the parameters of one converter transformer change, the parameters of the other converter transformers change synchronously. Similarly, all converter valves in the HVDC transmission system are identical; when the parameters of one converter valve change, the parameters of the other converter valves change synchronously.

[0092] Specifically, the first short-circuit impedance change relationship can represent the relationship between the cost of each converter transformer and the change in the short-circuit impedance of the converter transformer.

[0093] Step S120: Construct the relationship between the loss discount of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as the second short-circuit impedance change relationship of the loss discount of each converter transformer.

[0094] Specifically, the cost of each converter transformer can be expressed as the relationship between the cost of each converter transformer and the change in the short-circuit impedance of the converter transformer.

[0095] Step S130: Construct the relationship between the reactive power consumption of each converter valve in the high voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve, as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve.

[0096] Specifically, the third short-circuit impedance change relationship can represent the relationship between the reactive power consumption of each converter valve and the change in the short-circuit impedance of the converter transformer connected to the converter valve.

[0097] Step S140: Based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve and the preset group capacity of the reactive power compensation device, determine the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve, and use this as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device.

[0098] Specifically, the fourth short-circuit impedance change relationship can represent the relationship between the number of reactive power compensation devices and the change in the short-circuit impedance of the converter transformer.

[0099] Step S150: Based on the fourth short-circuit impedance change relationship, determine the cost of the reactive power compensation device and its relationship with the short-circuit impedance of any converter transformer, and use this as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device.

[0100] Specifically, the fifth short-circuit impedance change relationship can represent the relationship between the cost of the reactive power compensation device and the change in the short-circuit impedance of the converter transformer.

[0101] Step S160: By integrating the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained.

[0102] Specifically, the cost composite function can represent the relationship between the overall cost of a high-voltage direct current transmission system and the change in the short-circuit impedance of the converter transformer.

[0103] Step S170: Determine the target short-circuit impedance value, which is the short-circuit impedance obtained when the comprehensive cost is the lowest in the comprehensive cost function.

[0104] The method for optimizing the short-circuit impedance of converter transformers provided in this embodiment establishes a relationship between the cost of each converter transformer in the HVDC transmission system and the short-circuit impedance of any single converter transformer, serving as a first short-circuit impedance variation relationship for the cost of each converter transformer. It then establishes a relationship between the loss discount of each converter transformer in the HVDC transmission system and the short-circuit impedance of any single converter transformer, serving as a second short-circuit impedance variation relationship for the loss discount of each converter transformer. Finally, it establishes a relationship between the reactive power consumption of each converter valve in the HVDC transmission system and the short-circuit impedance of the converter transformer connected to that valve, serving as a third short-circuit impedance variation relationship for the reactive power consumption of each converter valve. Based on the third short-circuit impedance variation relationship for the reactive power consumption of any single converter valve, and the preset small value of the reactive power compensation device... The group capacity is determined, and the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined. This relationship serves as the fourth short-circuit impedance change relationship for the number of groups of the reactive power compensation device. Based on this fourth short-circuit impedance change relationship, the cost of the reactive power compensation device is determined, and its relationship with the short-circuit impedance of any converter transformer is determined. This relationship serves as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device. By combining the first, second, and fifth short-circuit impedance change relationships, a comprehensive cost function of the HVDC transmission system with respect to the short-circuit impedance of any converter transformer is obtained. A target short-circuit impedance value is then determined, which is the short-circuit impedance obtained when the comprehensive cost is lowest in the comprehensive cost function. Therefore, the comprehensive cost function of the converter transformer's short-circuit impedance in relation to the overall cost of a high-voltage direct current (HVDC) transmission system incorporates the first short-circuit impedance variation relationship of the converter transformer's cost, the second short-circuit impedance variation relationship of the converter transformer's loss discount, and the fifth short-circuit impedance variation relationship of the reactive power compensation device's cost. Thus, in the design process of equipment in a HVDC transmission system, considering not only the cost of the converter transformer but also its loss cost and reactive power consumption cost, the determined target short-circuit impedance value is the most economical design value.

[0105] In some embodiments of this application, the process of relating the cost of each converter transformer in a high-voltage direct current transmission system to the short-circuit impedance of any single converter transformer, as mentioned in the above embodiments, is described. This process may include:

[0106] S1. Construct the relationship between the cost of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as the single-cost short-circuit impedance variation relationship of the cost of a single converter transformer.

[0107] Specifically, the relationship between the cost of each converter transformer in a high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer can be constructed using the following formula:

[0108]

[0109] Where, p tra The cost of each converter transformer, X r Let be the short-circuit impedance of any converter transformer, a be the second-order cost coefficient of any converter transformer, b be the first-order cost coefficient of any converter transformer, and c be the cost constant coefficient of any converter transformer.

[0110] Understandably, the cost quadratic coefficient, cost primary coefficient, and cost constant coefficient of a converter transformer are design parameters of the converter transformer. The cost quadratic coefficient has the greatest impact on the cost of the converter transformer, the cost primary coefficient has a moderate impact on the cost of the converter transformer, and the cost constant coefficient has the least impact on the cost of the converter transformer.

[0111] S2. Using the number of converter transformers in the high-voltage direct current transmission system as the cost relationship fusion coefficient, the single-cost short-circuit impedance change relationship is fused to obtain the relationship between the cost of each converter transformer and the short-circuit impedance of any converter transformer.

[0112] It is understandable that a high-voltage direct current transmission system has four converter transformers. Therefore, the relationship between the cost of each converter transformer and the short-circuit impedance of any one converter transformer can be expressed as P. tra (X r ) = 4p tra (X r ).

[0113] In some embodiments of this application, the process of constructing the relationship between the loss discount of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer, as mentioned in the above embodiments, is described. This process may include:

[0114] S1. Construct the relationship between the loss of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as the single-loss short-circuit impedance change relationship of the loss of a single converter transformer.

[0115] Specifically, the relationship between the loss of each converter transformer in the HVDC transmission system and the short-circuit impedance of any single converter transformer can be constructed using the following formula, which represents the single-loss short-circuit impedance variation relationship of a single converter transformer's loss:

[0116] L o (X r )=dX r +e

[0117] Among them, L o The loss of each converter transformer, X r Let d be the short-circuit impedance of any converter transformer, d be the primary loss coefficient of any converter transformer, and e be the loss constant coefficient of any converter transformer.

[0118] It is understandable that the primary loss coefficient and the loss constant coefficient of a converter transformer are design parameters of the converter transformer. The primary loss coefficient has the greatest impact on the loss of the converter transformer, while the loss constant coefficient has the least impact on the loss of the converter transformer.

[0119] S2. Using the number of converter transformers in the high-voltage direct current transmission system and the preset equal pricing coefficient as loss relationship fusion coefficients, the single-loss short-circuit impedance change relationship is fused to obtain the relationship between the loss discount of each converter transformer and the short-circuit impedance of any converter transformer.

[0120] It is understandable that a high-voltage direct current transmission system has four converter transformers. Therefore, the relationship between the loss discount of each converter transformer and the short-circuit impedance of any one converter transformer can be expressed as P. Loss (X r ) = K loss *4*L o (X r ), K loss This is the equivalent pricing factor for converter transformers.

[0121] In some embodiments of this application, the process of constructing the relationship between the reactive power consumption of each converter valve in the high-voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve, as mentioned in the above embodiments, is described. This process may include:

[0122] The relationship between the reactive power consumption of each converter valve in the HVDC transmission system and the short-circuit impedance of the converter transformer connected to that converter valve can be constructed using the following formula:

[0123]

[0124] Among them, Q dcLet P be the reactive power consumption of each converter valve, P be the DC power of that converter valve, α be the rectifier firing angle of that converter valve, and X be the reactive power consumption of each converter valve. r I is the short-circuit impedance of the converter transformer connected to this converter valve. d E represents the DC current of the high-voltage direct current transmission system. 11 U is the open-circuit voltage of the valve-side winding of the converter transformer connected to the converter valve, φ is the power factor angle of the converter valve, μ is the commutation overlap angle of the converter valve, and U is the open-circuit voltage of the converter transformer connected to the converter valve. d U is the extreme DC voltage of the DC current. dio The ideal no-load voltage of the converter transformer connected to this converter valve can be E. 11 of times.

[0125] In some embodiments of this application, the process of determining the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve, as mentioned in the above embodiments, based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve and the preset group capacity of the reactive power compensation device, is described. This process may include:

[0126] The relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined using the following formula:

[0127] N(X r ) = RoundUp(Q dc (X r ) / Q0)

[0128] Where N is the number of groups of the reactive power compensation device, Q dc (X r ) represents the third short-circuit impedance change relationship of reactive power consumption of any converter valve, Q0 is the preset group capacity of the reactive power compensation device, and RoundUp() is the round-up function.

[0129] In some embodiments of this application, the relationship between determining the cost of the reactive power compensation device based on the fourth short-circuit impedance change relationship, as mentioned in the above embodiments, and the short-circuit impedance of any converter transformer is described. This process may include:

[0130] Using the preset cost coefficient of the reactive power compensation device group as the group cost relationship fusion coefficient, and integrating the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device and the short-circuit impedance of any converter transformer are obtained.

[0131] Specifically, the relationship between the cost of the reactive power compensation device and the short-circuit impedance of any converter transformer is P. acf (Xr )=N(X r )*K acf K acf This is the cost coefficient for the reactive power compensation device group.

[0132] In some embodiments of this application, the process of obtaining the comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer by fusing the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship described above in step S160 is introduced. This process may include:

[0133] By integrating the first, second, and fifth short-circuit impedance change relationships using the following formula, a comprehensive cost function for the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer can be obtained:

[0134] P rice (X r ) = P tra (X r )+P Loss (X r )+P acf (X r )

[0135] Among them, P tra (X r P represents the first short-circuit impedance variation relationship. Loss (X r ) represents the second short-circuit impedance variation relationship, P acf (X r The fifth short-circuit impedance variation relationship is shown below.

[0136] The apparatus for optimizing the short-circuit impedance of a converter transformer provided in the embodiments of this application will be described below. The apparatus for optimizing the short-circuit impedance of a converter transformer described below can be referred to in correspondence with the method for optimizing the short-circuit impedance of a converter transformer described above.

[0137] See Figure 3 , Figure 3 This is a schematic diagram of a device structure for optimizing the short-circuit impedance of a converter transformer, as disclosed in an embodiment of this application.

[0138] like Figure 3 As shown, the device may include:

[0139] The first impedance relationship construction unit 11 is used to construct the relationship between the cost of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, which serves as the first short-circuit impedance change relationship of the cost of each converter transformer. The high voltage direct current transmission system includes a converter AC grid, a target converter AC grid, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to a converter valve. Of the four converter transformers, two are connected to the converter AC grid and the other two are connected to the target converter AC grid. The four converter valves are connected in series through a DC line. The reactive power compensation device is connected to the converter AC grid.

[0140] The second impedance relationship construction unit 12 is used to construct the relationship between the loss discount of each converter transformer in the high voltage DC transmission system and the short-circuit impedance of any converter transformer, as the second short-circuit impedance change relationship of the loss discount of each converter transformer.

[0141] The third impedance relationship construction unit 13 is used to construct the relationship between the reactive power consumption of each converter valve in the high voltage DC transmission system and the short-circuit impedance of the converter transformer connected to the converter valve, as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve.

[0142] The fourth impedance relationship determination unit 14 is used to determine the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve and the preset group capacity of the reactive power compensation device, and to use it as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device.

[0143] The fifth impedance relationship determination unit 15 is used to determine the cost of the reactive power compensation device and the short-circuit impedance of any converter transformer based on the fourth short-circuit impedance change relationship, and use it as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device.

[0144] Impedance relationship fusion unit 16 is used to fuse the first short-circuit impedance change relationship, the second short-circuit impedance change relationship and the fifth short-circuit impedance change relationship to obtain a comprehensive cost function of the high voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer.

[0145] The target short-circuit impedance determination unit 17 is used to determine the target short-circuit impedance value, which is the short-circuit impedance obtained when the comprehensive cost is the lowest in the comprehensive cost function.

[0146] Optionally, the first impedance relationship construction unit includes:

[0147] The first intermediate relationship construction unit is used to construct the relationship between the cost of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as a single cost short-circuit impedance change relationship of the cost of a single converter transformer.

[0148] The cost coefficient fusion unit is used to fuse the single-cost short-circuit impedance change relationship with the number of converter transformers in the high-voltage direct current transmission system as the cost relationship fusion coefficient, thereby obtaining the relationship between the cost of each converter transformer and the short-circuit impedance of any converter transformer, and using this relationship as the first short-circuit impedance change relationship for the cost of each converter transformer.

[0149] Optionally, the first intermediate relationship construction unit includes:

[0150] The first intermediate relationship construction sub-unit is used to construct the relationship between the cost of each converter transformer in a high-voltage direct current transmission system and the short-circuit impedance of any converter transformer using the following formula:

[0151]

[0152] Where, p tra The cost of each converter transformer, X r Let be the short-circuit impedance of any converter transformer, a be the second-order cost coefficient of any converter transformer, b be the first-order cost coefficient of any converter transformer, and c be the cost constant coefficient of any converter transformer.

[0153] Optionally, the second impedance relationship building unit includes:

[0154] The second intermediate relationship construction unit is used to construct the relationship between the loss of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as the single loss short-circuit impedance change relationship of the loss of a single converter transformer.

[0155] The pricing loss coefficient fusion unit is used to fuse the single-loss short-circuit impedance change relationship with the number of converter transformers in the high-voltage direct current transmission system and the preset equal pricing coefficient as loss relationship fusion coefficients, so as to obtain the relationship between the loss discount of each converter transformer and the short-circuit impedance of any converter transformer.

[0156] Optionally, the second intermediate relationship construction unit includes:

[0157] The second intermediate relationship construction subunit is used to construct the relationship between the loss discount of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer using the following formula:

[0158] L o (X r )=dX r +e

[0159] Among them, L o The loss of each converter transformer, X r Let d be the short-circuit impedance of any converter transformer, d be the primary loss coefficient of any converter transformer, and e be the loss constant coefficient of any converter transformer.

[0160] Optionally, the third impedance relationship construction unit includes:

[0161] The third impedance relationship construction subunit is used to construct the relationship between the reactive power consumption of each converter valve in the high-voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve using the following formula, and serves as the third short-circuit impedance change relationship for the reactive power consumption of each converter valve:

[0162]

[0163] Among them, Q dc Let P be the reactive power consumption of each converter valve, P be the DC power of that converter valve, α be the rectifier firing angle of that converter valve, and X be the reactive power consumption of each converter valve. r I is the short-circuit impedance of the converter transformer connected to this converter valve. d E represents the DC current of the high-voltage direct current transmission system. 11 This is the no-load voltage of the valve-side winding of the converter transformer connected to the converter valve.

[0164] Optionally, the fourth impedance relationship determination unit includes:

[0165] The fourth impedance relationship construction subunit is used to determine the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve using the following formula, and serves as the fourth short-circuit impedance variation relationship for the number of groups of the reactive power compensation device:

[0166] N(X r ) = RoundUp(Q dc (X r ) / Q0)

[0167] Where N is the number of groups of the reactive power compensation device, Q δc (X r ) represents the third short-circuit impedance change relationship of reactive power consumption of any converter valve, Q0 is the preset group capacity of the reactive power compensation device, and RoundUp() is the round-up function.

[0168] Optionally, the fifth impedance relationship determination unit includes:

[0169] The fifth impedance relationship construction sub-unit is used to integrate the fourth short-circuit impedance change relationship with the preset reactive power compensation device group cost coefficient as the group cost relationship fusion coefficient, thereby obtaining the relationship between the cost of the reactive power compensation device and the short-circuit impedance of any converter transformer, and serving as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device.

[0170] Optionally, the impedance relationship fusion unit includes:

[0171] The impedance relationship fusion subunit is used to fuse the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship using the following formula to obtain a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer:

[0172] P rice (X r ) = P tra (X r )+P Loss (X r )+P acf (X r )

[0173] Among them, P tra (X r P represents the first short-circuit impedance variation relationship. Loss (X r ) represents the second short-circuit impedance variation relationship, P acf (X r The fifth short-circuit impedance variation relationship is shown below.

[0174] The apparatus for optimizing the short-circuit impedance of a converter transformer provided in this application embodiment can be applied to devices that optimize the short-circuit impedance of a converter transformer, such as terminals: mobile phones, computers, etc. Optionally, Figure 4 The hardware block diagram of the device for optimizing the short-circuit impedance of the converter transformer is shown. (Refer to...) Figure 4 The hardware structure of the device for optimizing the short-circuit impedance of the converter transformer may include: at least one processor 1, at least one communication interface 2, at least one memory 3, and at least one communication bus 4.

[0175] In this embodiment of the application, the number of processor 1, communication interface 2, memory 3, and communication bus 4 is at least one, and processor 1, communication interface 2, and memory 3 communicate with each other through communication bus 4;

[0176] Processor 1 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present invention.

[0177] Memory 3 may include high-speed RAM, and may also include non-volatile memory, such as at least one disk storage device;

[0178] The memory stores a program, which the processor can call. The program is used for:

[0179] The relationship between the cost of each converter transformer in a high-voltage direct current (HVDC) transmission system and the short-circuit impedance of any single converter transformer is used as the first short-circuit impedance variation relationship for the cost of each converter transformer. The HVDC transmission system includes a target AC grid to be converted, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to one converter valve. Of the four converter transformers, two are connected to the target AC grid to be converted, and the other two are connected to the target AC grid. The four converter valves are connected in series via DC lines. The reactive power compensation device is connected to the target AC grid.

[0180] The relationship between the loss discount of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed as the second short-circuit impedance change relationship of the loss discount of each converter transformer.

[0181] The relationship between the reactive power consumption of each converter valve in the high voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve is constructed as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve.

[0182] Based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve, and the preset group capacity of the reactive power compensation device, the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined, and this relationship is used as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device.

[0183] Based on the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device is determined, and its relationship with the short-circuit impedance of any converter transformer is established. This relationship is then used as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device.

[0184] By integrating the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained.

[0185] Determine the target short-circuit impedance value, which is the short-circuit impedance obtained when the comprehensive cost is lowest in the comprehensive cost function.

[0186] Optionally, the refined and extended functions of the program can be found in the description above.

[0187] This application embodiment also provides a storage medium that can store a program suitable for execution by a processor, the program being used for:

[0188] The relationship between the cost of each converter transformer in a high-voltage direct current (HVDC) transmission system and the short-circuit impedance of any single converter transformer is used as the first short-circuit impedance variation relationship for the cost of each converter transformer. The HVDC transmission system includes a target AC grid to be converted, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to one converter valve. Of the four converter transformers, two are connected to the target AC grid to be converted, and the other two are connected to the target AC grid. The four converter valves are connected in series via DC lines. The reactive power compensation device is connected to the target AC grid.

[0189] The relationship between the loss discount of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed as the second short-circuit impedance change relationship of the loss discount of each converter transformer.

[0190] The relationship between the reactive power consumption of each converter valve in the high voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that converter valve is constructed as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve.

[0191] Based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve, and the preset group capacity of the reactive power compensation device, the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined, and this relationship is used as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device.

[0192] Based on the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device is determined, and its relationship with the short-circuit impedance of any converter transformer is established. This relationship is then used as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device.

[0193] By integrating the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained.

[0194] Determine the target short-circuit impedance value, which is the short-circuit impedance obtained when the comprehensive cost is lowest in the comprehensive cost function.

[0195] Optionally, the refined and extended functions of the program can be found in the description above.

[0196] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0197] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0198] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for optimizing the short-circuit impedance of a converter transformer, characterized in that, include: The relationship between the cost of each converter transformer in a high-voltage direct current (HVDC) transmission system and the short-circuit impedance of any single converter transformer is used as the first short-circuit impedance variation relationship for the cost of each converter transformer. The HVDC transmission system includes a target AC grid to be converted, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to one converter valve. Of the four converter transformers, two are connected to the target AC grid to be converted, and the other two are connected to the target AC grid. The four converter valves are connected in series via DC lines. The reactive power compensation device is connected to the target AC grid. The relationship between the loss discount of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed as the second short-circuit impedance change relationship of the loss discount of each converter transformer. The relationship between the reactive power consumption of each converter valve in the high voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to the converter valve is constructed as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve. Based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve, and the preset group capacity of the reactive power compensation device, the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined, and this relationship is used as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device. Based on the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device is determined, and its relationship with the short-circuit impedance of any converter transformer is established. This relationship is then used as the fifth short-circuit impedance change relationship for the cost of the reactive power compensation device. By integrating the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained. Determine the target short-circuit impedance value, which is the short-circuit impedance obtained when the comprehensive cost is lowest in the comprehensive cost function.

2. The method according to claim 1, characterized in that, The relationship between the cost of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer includes: The relationship between the cost of each converter transformer in a high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer is used as the relationship between the cost of a single converter transformer and the change in short-circuit impedance. Using the number of converter transformers in the high-voltage direct current transmission system as the cost relationship fusion coefficient, and fusing the single-cost short-circuit impedance variation relationship, the relationship between the cost of each converter transformer and the short-circuit impedance of any converter transformer is obtained.

3. The method according to claim 2, characterized in that, The relationship between the cost of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer includes: The following formula can be used to construct the relationship between the cost of each converter transformer in a high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer: in, The cost of each converter transformer Let be the short-circuit impedance of any converter transformer. Let be the quadratic cost coefficient of any converter transformer, b be the primary cost coefficient of any converter transformer, and c be the constant cost coefficient of any converter transformer.

4. The method according to claim 1, characterized in that, The relationship between the loss discount of each converter transformer in the aforementioned high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer is constructed, including: The relationship between the loss of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer is constructed, which serves as the single-loss short-circuit impedance variation relationship of the loss of a single converter transformer. Using the number of converter transformers in the high-voltage direct current transmission system and the preset equivalent pricing coefficient as loss relationship fusion coefficients, the relationship between the loss discount of each converter transformer and the short-circuit impedance of any converter transformer is obtained by fusing the single-loss short-circuit impedance change relationship.

5. The method according to claim 4, characterized in that, The relationship between the losses of each converter transformer in the aforementioned high-voltage direct current transmission system and the short-circuit impedance of any single converter transformer is constructed, including: The following formula can be used to construct the relationship between the loss discount of each converter transformer in the high-voltage direct current transmission system and the short-circuit impedance of any converter transformer: in, The loss of each converter transformer. Let d be the short-circuit impedance of any converter transformer, d be the primary loss coefficient of any converter transformer, and e be the loss constant coefficient of any converter transformer.

6. The method according to claim 1, characterized in that, The relationship between the reactive power consumption of each converter valve in the aforementioned high-voltage direct current transmission system and the short-circuit impedance of the converter transformer connected to that valve is established, including: The relationship between the reactive power consumption of each converter valve in the HVDC transmission system and the short-circuit impedance of the converter transformer connected to that valve can be constructed using the following formula: in, The reactive power consumption of each converter valve, This refers to the DC-side power of the converter valve. This refers to the rectification firing angle of the converter valve. The short-circuit impedance of the converter transformer connected to the converter valve. The DC current of the high-voltage direct current transmission system is given. This refers to the no-load voltage of the valve-side winding of the converter transformer connected to the converter valve.

7. The method according to claim 1, characterized in that, The step of determining the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve and the preset group capacity of the reactive power compensation device includes: The relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve is determined using the following formula: Where N is the number of groups of the reactive power compensation device. The relationship between the reactive power consumption and the change in the third short-circuit impedance for any converter valve is given. The preset group capacity of the reactive power compensation device. () is the floor function.

8. The method according to claim 1, characterized in that, Based on the aforementioned fourth short-circuit impedance change relationship, determine the cost of the reactive power compensation device and its relationship with the short-circuit impedance of any converter transformer, including: Using the preset cost coefficient of the reactive power compensation device group as the group cost relationship fusion coefficient, and integrating the fourth short-circuit impedance change relationship, the cost of the reactive power compensation device and the short-circuit impedance of any converter transformer are obtained.

9. The method according to any one of claims 1-8, characterized in that, By integrating the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship, a comprehensive cost function of the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer is obtained, including: By integrating the first, second, and fifth short-circuit impedance change relationships using the following formula, a comprehensive cost function for the high-voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer can be obtained: in, The first short-circuit impedance variation relationship is shown below. This is the second short-circuit impedance variation relationship. This refers to the fifth short-circuit impedance variation relationship.

10. A device for optimizing the short-circuit impedance of a converter transformer, characterized in that, include: The first impedance relationship construction unit is used to construct the relationship between the cost of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, which serves as the first short-circuit impedance change relationship of the cost of each converter transformer. The high voltage direct current transmission system includes a converter AC grid, a target converter AC grid, a reactive power compensation device, four converter transformers, and four converter valves. Each converter transformer is connected to a converter valve. Of the four converter transformers, two are connected to the converter AC grid, and the other two are connected to the target converter AC grid. The four converter valves are connected in series through a DC line. The reactive power compensation device is connected to the converter AC grid. The second impedance relationship construction unit is used to construct the relationship between the loss discount of each converter transformer in the high voltage direct current transmission system and the short-circuit impedance of any converter transformer, as the second short-circuit impedance change relationship of the loss discount of each converter transformer. The third impedance relationship construction unit is used to construct the relationship between the reactive power consumption of each converter valve in the high voltage DC transmission system and the short-circuit impedance of the converter transformer connected to the converter valve, as the third short-circuit impedance change relationship of the reactive power consumption of each converter valve. The fourth impedance relationship determination unit is used to determine the relationship between the number of groups of the reactive power compensation device and the short-circuit impedance of the converter transformer connected to the converter valve based on the third short-circuit impedance change relationship of the reactive power consumption of any converter valve and the preset group capacity of the reactive power compensation device, and to use it as the fourth short-circuit impedance change relationship of the number of groups of the reactive power compensation device. The fifth impedance relationship determination unit is used to determine the cost of the reactive power compensation device and its relationship with the short-circuit impedance of any converter transformer based on the fourth short-circuit impedance change relationship, and to use the fifth short-circuit impedance change relationship as the cost of the reactive power compensation device. The impedance relationship fusion unit is used to fuse the first short-circuit impedance change relationship, the second short-circuit impedance change relationship, and the fifth short-circuit impedance change relationship to obtain a comprehensive cost function of the high voltage direct current transmission system with respect to the short-circuit impedance of any converter transformer. A target short-circuit impedance determination unit is used to determine a target short-circuit impedance value, wherein the target short-circuit impedance value is the short-circuit impedance obtained when the comprehensive cost is the lowest in the comprehensive cost function.

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