AC line simulation control method suitable for large capacity systems

Abstract

This invention discloses an AC line simulation control method suitable for large-capacity systems, comprising the following steps: treating the sending end as an infinite system, obtaining the steady-state operating frequency of the receiving end and using it as a reference value for the receiving end frequency, and obtaining the active power of the receiving end MMC during steady-state operation; obtaining the actual value of the receiving end frequency, and calculating the receiving end frequency difference based on the receiving end frequency reference value, and calculating the receiving end phase difference based on the receiving end frequency difference; obtaining the AC bus voltages of the sending and receiving ends, and calculating the virtual impedance of the DC line during simulation control based on the AC bus voltages of the sending and receiving ends; calculating the difference in active power of the controlled receiving end MMC based on the receiving end phase difference and the virtual impedance of the DC line, and calculating the controlled receiving end MMC active power based on the received end MMC active power; inputting the controlled receiving end MMC active power into the receiving end MMC to cover the original received end MMC active power, and completing the AC line simulation control when the receiving end frequency recovers to its steady-state value.

Description

Technical Field

[0001] This invention relates to the field of asynchronous interconnection technology for flexible DC transmission systems, and more particularly to an AC line simulation control method suitable for large-capacity systems. Background Technology

[0002] In the context of new power systems, asynchronous interconnection technology has been widely applied. Multi-terminal DC transmission technology based on Modular Multilevel Converters (MMCs) offers advantages such as low loss, flexible and controllable power output, and the ability to receive power from multiple points over long distances, making it applicable to various engineering scenarios, including asynchronous interconnection. AC line simulation is a key technology employed by MMCs to achieve asynchronous interconnection.

[0003] However, for large-capacity systems, during conventional AC line simulation control, due to the inherent characteristics of the AC power grid, the frequencies of the two asynchronous grids are controlled to be consistent, resulting in simultaneous operation of the two grids. If a fault occurs at this time, it will lead to tight grid coupling, increasing the scope of the fault's impact. Moreover, when the two asynchronous grids are large, it places higher demands on the capacity of the flexible DC interconnection, increasing the difficulty and cost of DC system construction. Furthermore, modern large power grids are typically divided into zones for independent operation and dispatch, and conflicts may arise in management modes after simultaneous operation. Therefore, the conventional AC line simulation control method requires improvement in its control logic.

[0004] Existing research mainly focuses on the simulation control of conventional AC lines and the synchronization of asynchronous power grids. The aim is to achieve frequency synchronization between the two grids, without considering the limitations of large-capacity AC systems. Therefore, a controllable asynchronous synchronization control method is needed. This method should be able to simulate the power regulation characteristics of AC lines in a large-capacity power grid using small-capacity flexible DC transmission equipment, rather than achieving strict physical frequency synchronization between large power grids. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects and shortcomings of existing technologies and provide an AC line simulation control method suitable for large-capacity systems. This control method treats the sending-end power grid as an infinitely large system and controls only the receiving end. It obtains the difference between the receiving-end power grid frequency and its steady-state frequency, uses proportional-integral control to derive the difference between the receiving-end phase and its steady-state phase, and then calculates the difference in active power reference value at the receiving end according to the AC line active power transmission formula, thereby obtaining the receiving-end active power reference value. This invention controls only the receiving end, reconstructs the control objective, and avoids strict frequency synchronization between the two systems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An AC line simulation control method suitable for large-capacity systems includes the following steps:

[0008] S1: Treat the sending-end power grid as an infinite system, obtain the steady-state operating frequency of the receiving-end power grid, and use it as the frequency reference value of the receiving-end power grid. Obtain the active power reference value of the receiving-end MMC when the receiving-end power grid is in steady state.

[0009] S2: Obtain the actual value of the receiving end power grid frequency, combine it with the receiving end power grid frequency reference value, calculate the receiving end power grid frequency difference, and calculate the receiving end power grid phase difference based on the receiving end power grid frequency difference;

[0010] S3: Obtain the AC bus voltage of the sending-end grid and the receiving-end grid, and calculate the virtual impedance of the DC line during AC line simulation control based on the AC bus voltage of the sending-end grid and the receiving-end grid.

[0011] S4: Based on the phase difference of the receiving-end power grid and the virtual impedance of the DC line, calculate the difference in the control receiving-end MMC active power reference value, and combine it with the receiving-end MMC active power reference value to calculate the control receiving-end MMC active power reference value.

[0012] S5: Input the active power reference value of the receiving-end MMC into the receiving-end MMC, overwriting the original active power reference value of the receiving-end MMC. When the receiving-end grid frequency returns to a steady-state value, complete the AC line simulation control.

[0013] Before issuing AC line simulation control commands suitable for large-capacity systems, the receiving-end grid operates in a conventional power control mode. When the flexible DC system receives AC line simulation control commands suitable for large-capacity systems, it treats the sending-end grid as an infinitely large system.

[0014] Furthermore, in step S1, the sending-end power grid is regarded as an infinite system, that is, it is assumed that the voltage amplitude and frequency of the sending-end power grid are constant, the internal impedance is zero, and it has infinite inertia and power capacity.

[0015] Furthermore, in step S2, the formula for calculating the frequency difference Δf between the receiving and receiving power grids is as follows:

[0016] ;

[0017] In the formula, f in Indicates the actual value of the receiving-end power grid frequency; f in0 This indicates the reference value for the receiving-end power grid frequency.

[0018] Furthermore, based on the frequency difference of the receiving-end power grid, the phase difference Δδ of the receiving-end power grid is calculated using proportional-integral control, and the calculation formula is as follows:

[0019] ;

[0020] In the formula, kp1 k is the proportional parameter of the PI controller. i1 is the integral parameter of the PI controller; s is the Laplace operator.

[0021] Furthermore, in step S3, the method for obtaining the virtual impedance X of the DC line during AC line simulation control is through line impedance calculation or through steady-state operating value calculation.

[0022] X is calculated using the line impedance, and the formula is as follows:

[0023] ;

[0024] In the formula, f is the power grid frequency; L0 is the inductance per unit length of the original AC line; l is the length of the original AC line; the original AC line refers to the AC line that was replaced by the DC line using AC line simulation control; since the resistance per unit length in an AC line is much smaller than the inductance, the line resistance is ignored in the virtual impedance.

[0025] X is calculated from the steady-state operating value, using the following formula:

[0026] ;

[0027] In the formula, U re U is the AC bus voltage of the sending-end power grid; in The voltage of the AC bus at the receiving end of the power grid; δ re For the sending-end power grid phase; δ in P1 represents the phase of the receiving-end power grid; P2 represents the active power transmitted by the flexible DC system.

[0028] Further, in step S4, the difference between the active power reference values ​​of the control receiver MMC is calculated. The calculation principle is as follows:

[0029] Treating the sending-end power grid as an infinite system, given the frequency and initial phase of the sending-end power grid, the initial phase δ of the sending-end power grid is... re0 Set to 0 degrees, and set the angular frequency w of the sending-end power grid. re It is set to be equal to the steady-state angular frequency w0 of the receiving-end power grid, that is:

[0030] ;

[0031] In the formula, δ in0 This is the initial phase of the receiving-end power grid;

[0032] When a flexible DC system is disturbed, the sending-end grid remains unchanged as an infinite system. Therefore, only the phase change of the receiving-end grid needs to be considered. In power control, the active power increment ΔP of the receiving-end MMC is expressed as:

[0033] ;

[0034] In the formula, w is the actual value of the receiving-end grid angular frequency; Δw is the increment of the receiving-end grid angular frequency; and ΔP is the difference between the receiving-end MMC active power reference value and the AC line simulation control suitable for large-capacity systems.

[0035] Furthermore, the active power reference value P of the control receiver MMC is calculated using the following formula:

[0036] ;

[0037] In the formula, P0 is the reference value of the active power of the receiving-end MMC during steady-state operation of the receiving-end power grid.

[0038] Furthermore, in step S5, the active power reference value of the receiving-end MMC is input into the receiving-end MMC to overwrite the original active power reference value of the receiving-end MMC. When the receiving-end grid frequency returns to the steady-state value, the ΔP value will also return to 0, thereby completing the AC line simulation control suitable for large-capacity systems.

[0039] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the AC line analog control method suitable for large-capacity systems as described above.

[0040] A storage medium, a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the AC line analog control method suitable for large-capacity systems as described above.

[0041] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0042] This invention can simulate AC lines in asynchronous interconnection while taking into account the characteristics and limitations of large-capacity power grids. By assuming the sending-end power grid is an infinitely large system, and responding and controlling only for the frequency deviation of the receiving-end power grid, it not only achieves the normal function of AC line simulation, but also avoids the problem in conventional AC line simulation control where the natural characteristics of the AC power grid force both sides of the power grid to operate at the same frequency, thereby expanding the scope of fault impact. It effectively achieves regional isolation of fault impact, improving the security of the interconnected power grid. At the same time, it reduces the capacity configuration requirements of the flexible DC converters connecting the two large-capacity power grids, lowers costs and design complexity, and improves engineering economics.

[0043] This invention offers advantages at the power grid management level. Modern large power grids generally adopt a zoned independent operation and dispatch mode. Using conventional AC lines for simulation would cause the sending-end and receiving-end grids to operate at the same frequency, easily leading to conflicts in operation and management responsibilities. This invention does not pursue strict physical frequency synchronization; it only simulates the power regulation characteristics of AC lines, allowing the sending-end and receiving-end grids to operate independently within their respective recognized frequency ranges. The flexible DC system serves only as a power support channel, perfectly meeting the operation and management requirements of zoned asynchronous interconnection. Attached Figure Description

[0044] Figure 1 A flowchart for an AC line simulation control method suitable for large-capacity systems.

[0045] Figure 2 A control block diagram for an AC line analog control method suitable for large-capacity systems.

[0046] Figure 3 This is a schematic diagram of the flexible DC system used in Application Example 1.

[0047] Figure 4 The waveforms of the sending and receiving end frequencies, DC power, and frequency difference between the sending and receiving ends are shown in Example 1 without control.

[0048] Figure 5 The waveforms of the sending and receiving end frequencies, DC power, and frequency difference between the sending and receiving ends are shown in Example 1 of the application of conventional AC line simulation control.

[0049] Figure 6 The waveforms of the sending and receiving end frequencies, DC power, and frequency difference between the sending and receiving ends are shown in Example 1, which is suitable for AC line simulation control of large-capacity systems.

[0050] Figure 7 The waveforms of the sending and receiving end frequencies, DC power, and frequency difference between the sending and receiving ends are shown in Example 2 without control.

[0051] Figure 8 The waveforms of the sending and receiving end frequencies, DC power, and frequency difference between the sending and receiving ends are shown in Example 2 for the application of conventional AC line simulation control.

[0052] Figure 9 The waveforms of the sending and receiving end frequencies, DC power, and frequency difference between the sending and receiving ends are shown in Example 2 for AC line simulation control suitable for large-capacity systems. Detailed Implementation

[0053] The AC line simulation control method of the present invention, suitable for large-capacity systems, will be further described below with reference to the accompanying drawings and specific embodiments.

[0054] Please see Figure 1This invention discloses an AC line simulation control method suitable for large-capacity systems, comprising the following steps:

[0055] S1: Treat the sending-end power grid as an infinite system, obtain the steady-state operating frequency of the receiving-end power grid, and use it as the frequency reference value of the receiving-end power grid. Obtain the active power reference value of the receiving-end MMC when the receiving-end power grid is in steady state.

[0056] S2: Obtain the actual value of the receiving end power grid frequency, combine it with the receiving end power grid frequency reference value, calculate the receiving end power grid frequency difference, and calculate the receiving end power grid phase difference based on the receiving end power grid frequency difference;

[0057] S3: Obtain the AC bus voltage of the sending-end grid and the receiving-end grid, and calculate the virtual impedance of the DC line during AC line simulation control based on the AC bus voltage of the sending-end grid and the receiving-end grid.

[0058] S4: Based on the phase difference of the receiving-end power grid and the virtual impedance of the DC line, calculate the difference in the control receiving-end MMC active power reference value, and combine it with the receiving-end MMC active power reference value to calculate the control receiving-end MMC active power reference value.

[0059] S5: Input the active power reference value of the receiving-end MMC into the receiving-end MMC, overwriting the original active power reference value of the receiving-end MMC. When the receiving-end grid frequency returns to a steady-state value, complete the AC line simulation control.

[0060] Before issuing AC line simulation control commands suitable for large-capacity systems, the receiving-end grid operates in a conventional power control mode. When the flexible DC system receives AC line simulation control commands suitable for large-capacity systems, it treats the sending-end grid as an infinitely large system. The sending-end MMC of the flexible DC system is connected to the sending-end grid, and the receiving-end MMC of the flexible DC system is connected to the receiving-end grid.

[0061] Step S1: Treat the sending-end power grid as an infinite system, obtain the steady-state operating frequency of the receiving-end power grid, and use it as the frequency reference value of the receiving-end power grid. Obtain the active power reference value of the receiving-end MMC during the steady-state operation of the receiving-end power grid.

[0062] The sending-end power grid is treated as an infinite system, meaning its voltage amplitude and frequency are constant, its internal impedance is zero, and it possesses infinite inertia and power capacity. The steady-state operating frequency of the receiving-end power grid is obtained and used as a frequency reference value; the MMC active power reference value of the receiving-end power grid during steady-state operation is also obtained.

[0063] Step S2: Obtain the actual value of the receiving-end power grid frequency, combine it with the receiving-end power grid frequency reference value, calculate the receiving-end power grid frequency difference, and calculate the receiving-end power grid phase difference based on the receiving-end power grid frequency difference.

[0064] The frequency difference between the receiving and receiving power grids is calculated based on the actual frequency and the reference frequency. The formula for calculating the frequency difference Δf is as follows:

[0065] ;

[0066] In the formula, f in Indicates the actual value of the receiving-end power grid frequency; f in0 This indicates the reference value for the receiving-end power grid frequency.

[0067] Based on the frequency difference of the receiving-end power grid, the phase difference Δδ of the receiving-end power grid is calculated using proportional-integral control. The calculation formula is as follows:

[0068] ;

[0069] In the formula, k p1 k is the proportional parameter of the PI controller. i1 is the integral parameter of the PI controller; s is the Laplace operator.

[0070] Step S3: Obtain the AC bus voltage of the sending-end grid and the receiving-end grid, and calculate the virtual impedance of the DC line during AC line simulation control based on the AC bus voltage of the sending-end grid and the receiving-end grid.

[0071] The virtual impedance X of a DC line during AC line simulation control can be obtained by calculating the line impedance or by calculating the steady-state operating value. The formula for calculating X using line impedance is as follows:

[0072] ;

[0073] In the formula, f is the power grid frequency; L0 is the inductance per unit length of the original AC line; l is the length of the original AC line; the original AC line refers to the AC line that was replaced by the DC line using AC line simulation control; since the resistance per unit length in an AC line is generally much smaller than the inductance, the line resistance is ignored in the virtual impedance.

[0074] The formula for calculating X from the steady-state operating value is as follows:

[0075] ;

[0076] In the formula, U re U is the AC bus voltage of the sending-end power grid; in The voltage of the AC bus at the receiving end of the power grid; δ re For the sending-end power grid phase; δ in P1 represents the phase of the receiving-end power grid; P2 represents the active power transmitted by the flexible DC system.

[0077] Step S4: Calculate the difference in active power reference value of the MMC at the receiving end based on the phase difference of the receiving end power grid and the virtual impedance of the DC line. Combine this with the active power reference value of the MMC at the receiving end to calculate the active power reference value of the MMC at the receiving end.

[0078] The difference between the active power reference values ​​of the receiving-end MMC and the active power reference value P of the receiving-end MMC during AC line simulation control is calculated for a large-capacity system. The calculation principle is as follows:

[0079] When simulating control of a conventional AC line, the expression for the power transmission P1 of the flexible DC system is:

[0080] ;

[0081] In the formula, the phase δ of the sending-end power grid re Phase δ of the receiving end power grid in The expression is:

[0082] ;

[0083] In the formula, δ re0 The initial phase of the sending-end power grid; δ in0 The initial phase of the receiving-end power grid; w re The sending-end grid angular frequency; w in Here is the angular frequency of the receiving-end power grid. At this point, the phase of both the sending-end and receiving-end power grids will affect the transmission power.

[0084] Treating the sending-end power grid as an infinite system, given the frequency and initial phase of the sending-end power grid, the initial phase δ of the sending-end power grid is... re0 Set to 0 degrees, and set the angular frequency w of the sending-end power grid. re It is set to be equal to the steady-state angular frequency w0 of the receiving end, that is:

[0085] ;

[0086] In the formula, δ in0 This is the initial phase of the receiving-end power grid;

[0087] When a flexible DC system is disturbed, the sending-end grid remains unchanged as an infinite system; therefore, only the phase change of the receiving-end grid needs to be considered. In power control, the active power increment ΔP of the receiving-end MMC is:

[0088] ;

[0089] In the formula, w is the actual value of the receiving-end grid angular frequency; Δw is the increment of the receiving-end grid angular frequency; and ΔP is the difference between the receiving-end MMC active power reference value and the AC line simulation control suitable for large-capacity systems.

[0090] Therefore, the formula for calculating the reference value P of the active power of the MMC at the control end is as follows:

[0091] ;

[0092] In the formula, P0 is the reference value of the active power of the receiving-end MMC during steady-state operation of the receiving-end power grid.

[0093] Step S5: Input the active power reference value of the receiving-end MMC into the receiving-end MMC, overwriting the original active power reference value of the receiving-end MMC. When the receiving-end grid frequency returns to a steady-state value, the AC line simulation control is completed.

[0094] The calculated active power reference value of the receiving-end MMC is input into the receiving-end MMC to overwrite the original active power reference value of the receiving-end MMC. When the receiving-end grid frequency returns to the steady-state value, the ΔP value will also return to 0, thus completing the AC line simulation control suitable for large-capacity systems.

[0095] Application Example 1

[0096] Based on the AC line simulation control method suitable for large-capacity systems disclosed in this invention, its control block diagram is as follows: Figure 2 As shown, this application embodiment uses an improved two-zone four-machine system, as follows: Figure 3 As shown, AC line simulation is performed using individual MMCs. Each MMC is a 302 level controller. The sending-end MMC uses constant DC voltage control, and the receiving-end MMC uses constant active power control. Each MMC has a rated capacity of 1000MVA, a grid-side rated voltage of 230kV, and a DC-side rated voltage of ±574kV. The MMC issues AC line simulation control commands suitable for large-capacity systems, and then enters this control mode. Under steady-state conditions, the receiving-end grid frequency is 50.01Hz.

[0097] When the system had been running for 12 seconds, the receiving-end power grid added a three-phase load of 90MW. A comparison was made between uncontrolled, conventional AC line simulation control and a simulation control method suitable for large-capacity AC lines. Figure 4 , Figure 5 and Figure 6 It can be seen that, without any control, the frequency of the sending-end power grid drops by approximately 0.2Hz, while the sending-end power grid frequency remains unchanged. If conventional AC line simulation control is used, the frequencies of the sending-end and receiving-end power grids are controlled to be consistent, and the receiving-end power grid frequency cannot be restored to its original operating state. If AC line simulation control suitable for large capacity is used, the receiving-end power grid frequency can be restored to its original operating state. Since the sending-end power grid is considered an infinitely large system, its frequency change is negligible. This embodiment verifies the feasibility of the method, showing that this method can effectively control the receiving-end power grid frequency while achieving the effect of AC line simulation.

[0098] Application Example 2

[0099] Based on the AC line simulation control method suitable for large-capacity systems disclosed in this invention, its control block diagram is as follows: Figure 2 As shown, this application embodiment uses an improved two-zone four-machine system, as follows: Figure 3 As shown, AC line simulation is performed using individual MMCs. Each MMC is at level 302. The sending-end MMC uses constant DC voltage control, and the receiving-end MMC uses constant active power control. Each MMC has a rated capacity of 1000MVA, a grid-side rated voltage of 230kV, and a DC-side rated voltage of ±574kV. The MMC issues AC line simulation control commands suitable for large-capacity systems, and then enters this control mode. Under steady-state conditions, the receiving-end grid frequency is 50.01Hz.

[0100] When the flexible DC system has been running for 12 seconds, the sending-end grid adds a three-phase load of 30MW. A comparison is made between uncontrolled, conventional AC line simulation control and a simulation control method suitable for large-capacity AC lines. Figure 7 , Figure 8 and Figure 9 It is known that, without any control, the frequency of the sending-end grid drops by approximately 0.06 Hz after a disturbance. If conventional AC line simulation control is used, the DC power decreases simultaneously due to the disturbance in the sending-end grid frequency, causing the sending-end and receiving-end grids to be controlled in unison. This leads to the transmission of faults from the sending-end grid to the receiving-end grid, causing a frequency drop in the receiving-end grid and adversely affecting its operation. However, if an AC line simulation method suitable for large-capacity systems is used, the DC power does not change with the sending-end grid frequency. Therefore, when the sending-end grid is disturbed, the DC power remains constant, and the receiving-end grid frequency also remains constant. This prevents the transmission of faults from the sending-end grid to the receiving-end grid, allows the sending-end and receiving-end grids to maintain a certain frequency asynchrony, and avoids management conflicts between the two grids.

[0101] This invention also discloses an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the AC line simulation control method suitable for large-capacity systems described above. The electronic device of this invention can execute the AC line simulation control method suitable for large-capacity systems of this invention, and can execute any combination of the steps of the method embodiments, possessing the corresponding functions and beneficial effects of the method.

[0102] This invention also discloses a storage medium, a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the AC line simulation control method suitable for large-capacity systems described above. The computer-readable storage medium of this invention can execute the AC line simulation control method suitable for large-capacity systems of this invention, and can execute any combination of the steps of the method embodiments, possessing the corresponding functions and beneficial effects of the method.

[0103] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit disclosed in the present invention should fall within the patent scope covered by the present invention.

Claims

1. An AC line simulation control method suitable for a large capacity system, characterized by, Includes the following steps: S1: Treat the sending-end power grid as an infinite system, obtain the steady-state operating frequency of the receiving-end power grid, and use it as the frequency reference value of the receiving-end power grid. Obtain the active power reference value of the receiving-end MMC when the receiving-end power grid is in steady state. S2: Obtain the actual value of the receiving end power grid frequency, combine it with the receiving end power grid frequency reference value, calculate the receiving end power grid frequency difference, and calculate the receiving end power grid phase difference based on the receiving end power grid frequency difference; S3: Obtain the AC bus voltage of the sending-end grid and the receiving-end grid, and calculate the virtual impedance of the DC line during AC line simulation control based on the AC bus voltage of the sending-end grid and the receiving-end grid. S4: Based on the phase difference of the receiving-end power grid and the virtual impedance of the DC line, calculate the difference in the control receiving-end MMC active power reference value, and combine it with the receiving-end MMC active power reference value to calculate the control receiving-end MMC active power reference value. S5: Input the active power reference value of the receiving-end MMC into the receiving-end MMC, overwriting the original active power reference value of the receiving-end MMC. When the receiving-end grid frequency returns to a steady-state value, complete the AC line simulation control.

2. The AC line simulation control method for bulk systems according to claim 1, wherein, In step S1, the sending-end power grid is regarded as an infinite system, that is, it is assumed that the voltage amplitude and frequency of the sending-end power grid are constant, the internal impedance is zero, and it has infinite inertia and power capacity.

3. The AC line simulation control method for bulk systems as set forth in claim 2, characterized by, In step S2, the formula for calculating the frequency difference Δf between the receiving and receiving ends of the power grid is as follows: ； In the formula, f in represents the actual value of the receiving end power grid frequency; f in0 represents the reference value of the receiving end power grid frequency.

4. The AC line simulation control method for bulk systems according to claim 3, wherein, The phase difference Δδ of the receiving-end power grid is calculated using proportional-integral control, and the calculation formula is as follows: ； where k p1 is the proportional parameter of the PI controller; k i1 is the integral parameter of the PI controller; s is the Laplace operator.

5. The AC line simulation control method for bulk systems of claim 4, wherein, In step S3, the method for obtaining the virtual impedance X of the DC line during AC line simulation control is through line impedance calculation or through steady-state operating value calculation. X is calculated using the line impedance, and the formula is as follows: ； In the formula, f is the power grid frequency; L0 is the inductance per unit length of the original AC line; and l is the length of the original AC line. The original AC line refers to the AC line that was replaced by the DC line using AC line simulation control; since the resistance per unit length in an AC line is much smaller than the inductance, the line resistance is ignored in the virtual impedance. X is calculated from the steady-state operating value, using the following formula: ； In the formula, U re is the sending end power grid AC bus voltage; U in is the receiving end power grid AC bus voltage; δ re is the sending end power grid phase; δ in is the receiving end power grid phase; P1 is the active power transmitted by the flexible DC system.

6. The AC line simulation control method for bulk systems as set forth in claim 5, wherein, In step S4, the difference between the active power reference values ​​of the control receiver MMC is calculated. The calculation principle is as follows: The sending end power grid is regarded as an infinite system, the sending end power grid frequency and initial phase are given, the initial phase δ re0 is set to 0 degree, the sending end power grid angular frequency w re is set to be equal to the steady-state angular frequency w0 of the receiving end power grid, that is: ； In the formula, δ in0 is the initial phase of the receiving power grid; When a flexible DC system is disturbed, the sending-end grid remains unchanged as an infinite system. Therefore, only the phase change of the receiving-end grid needs to be considered. In power control, the active power increment ΔP of the receiving-end MMC is expressed as: ； In the formula, w is the actual value of the receiving-end grid angular frequency; Δw is the increment of the receiving-end grid angular frequency; and ΔP is the difference between the receiving-end MMC active power reference value and the AC line simulation control suitable for large-capacity systems.

7. The AC line simulation control method for bulk systems as set forth in claim 6, wherein, The active power reference value P of the control receiver MMC is calculated using the following formula: ； In the formula, P0 is the reference value of the active power of the receiving-end MMC during steady-state operation of the receiving-end power grid.

8. The AC line simulation control method suitable for large-capacity systems according to claim 7, characterized in that, In step S5, the active power reference value of the receiving-end MMC is input into the receiving-end MMC, overwriting the original active power reference value of the receiving-end MMC. When the receiving-end grid frequency returns to the steady-state value, the ΔP value will also return to 0, thereby completing the AC line simulation control suitable for large-capacity systems.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the AC line analog control method suitable for large-capacity systems as described in any one of claims 1 to 8.

10. A storage medium, a computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the AC line analog control method suitable for large-capacity systems as described in any one of claims 1 to 8.

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