A dynamic frequency coordination control method for flexible DC co-frequency control and normal DC double-side FLC

Abstract

The present application discloses a method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC, which belongs to the technical field of power system. The method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC includes: when the system is disturbed, the flexible direct current co-frequency control is preferentially used to stabilize the grid frequency, and the power adjustment amount output by the flexible direct current co-frequency control is used as the start criterion of the normal direct current double-side FLC control; when the power adjustment amount exceeds the preset limit range, and the system frequency deviation exceeds the control dead zone of the normal direct current double-side FLC control, the normal direct current double-side FLC control is used to determine and output the conventional direct current power adjustment amount; based on the conventional direct current power adjustment amount, the flexible direct current additional reactive power control is used to provide additional reactive power to the normal direct current to adjust the voltage stability of the grid. Through the above method, the frequency stability of the grid is improved and the service life of the power equipment is extended.

Description

Technical Field

[0001] The present application relates to the field of power systems, and in particular to a method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC. Background Art

[0002] In the asynchronous interconnection project between Yunnan Power Grid and Southern Power Grid, the two are connected by DC and have no AC communication channel. This fundamentally solves the defect that DC faults cause large-scale power transfer to parallel AC channels during synchronous interconnection.

[0003] However, after the asynchronous interconnection between Yunnan Power Grid and the Southern Power Grid, Yunnan Power Grid has many large-capacity units and DC systems, but the total installed capacity is relatively small and the load level is low, which also reduces the frequency stability of each synchronous power grid. In particular, since the Yunnan power grid is no longer supported by the Southern Power Grid, severe DC blocking faults, large unit tripping or large power plant tripping may cause large changes in the frequency of the Yunnan power grid system, and even cause the frequency to exceed the limit for a long time, which poses a severe challenge to the frequency stability of the Yunnan power grid. In view of this, it is urgent to propose a frequency coordination control method to improve the frequency stability of the Yunnan power grid.

[0004] The above contents are only used to assist in understanding the technical solution of the present application and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The main purpose of this application is to provide a method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC, aiming to propose a frequency coordination control method to improve the frequency stability of Yunnan power grid.

[0006] To achieve the above object, the present application provides a method for dynamic frequency coordination control of flexible direct current co-frequency control and FLC on both sides of a normal direct current, the method comprising:

[0007] When the system is disturbed, the flexible direct current co-frequency control is used to stabilize the grid frequency, and the power adjustment amount output by the flexible direct current co-frequency control is used as the starting criterion of the normal direct current double-side FLC control;

[0008] When the power regulation amount exceeds the preset limit range and the system frequency deviation exceeds the control dead zone of the normally direct double-sided FLC control, the normally direct double-sided FLC control is used to determine and output the conventional DC power regulation amount;

[0009] Based on the conventional DC power regulation amount, the flexible DC additional reactive power control is used to provide additional reactive power to the normal DC to adjust the voltage stability of the power grid.

[0010] In one embodiment, the inputs of the flexible direct current co-frequency control are respectively a first difference between the sending-end power grid frequency and the system frequency reference value, and a second difference between the receiving-end power grid frequency and the system frequency reference value, and the method further includes:

[0011] Determining a flexible DC power adjustment amount based on the preprocessed first difference and the second difference;

[0012] The flexible DC power adjustment amount and the flexible DC original power reference value are superimposed to determine the active power instruction of the flexible DC;

[0013] Based on the active power instruction, the actual operating active power of the flexible direct current is adjusted.

[0014] In one embodiment, the inputs of the normally direct double-sided FLC control are respectively a first difference value corresponding to the frequency of the power grid at the sending end and the system frequency reference value, and a second difference value corresponding to the frequency of the power grid at the receiving end and the system frequency reference value, and the method further includes:

[0015] Determine a conventional DC power adjustment amount of the normally direct double-sided FLC control output based on the first difference and the second difference after preprocessing;

[0016] After performing logical judgment, per-unit processing, and PI control on the conventional DC power adjustment amount based on the judgment logic, the corresponding trigger angle adjustment amount is calculated;

[0017] Based on the trigger angle adjustment amount, the actual operating active power of the conventional direct current is adjusted.

[0018] In one embodiment, the method further comprises:

[0019] The flexible DC power regulation amount is used as an input signal of the judgment logic;

[0020] Converting the input signal into additional reactive energy of flexible DC;

[0021] Superimposing the additional reactive power with the original reactive power instruction of the flexible direct current to generate a new reactive power instruction of the flexible direct current;

[0022] Based on the reactive power instruction, the actual operating reactive power of the flexible direct current is adjusted.

[0023] In one embodiment, the judgment logic includes:

[0024] If the flexible DC power regulation amount is greater than the maximum power regulation amount threshold of the flexible DC co-frequency controller, or the power regulation amount is less than the minimum power regulation amount threshold of the flexible DC co-frequency controller, the normal DC double-side FLC control outputs the conventional DC regulation amount;

[0025] If the flexible DC power regulation amount is greater than or equal to the minimum power regulation amount threshold of the flexible DC co-frequency controller, and less than or equal to the maximum power regulation amount threshold of the flexible DC co-frequency controller, the normal DC double-side FLC control output is 0.

[0026] In one embodiment, the active power command of the flexible direct current and the reactive power command of the flexible direct current are subjected to a dynamic limiting link including PI control to generate a target active power command and a target reactive power command required for the flexible direct current inner loop control, and the target active power command and the target reactive power command meet preset dynamic limiting constraints.

[0027] In one embodiment, the maximum power regulation threshold of the flexible direct current frequency controller is calculated as follows:

[0028] Calculate a first product value corresponding to the flexible DC power rating and the flexible DC overload capacity coefficient;

[0029] Calculating a third difference between the product value and the actual power of the flexible DC power, and using the third difference as the maximum power adjustment threshold; and

[0030] The calculation method of the minimum power adjustment threshold of the flexible direct current frequency controller is:

[0031] Calculate a second product value corresponding to the flexible DC power minimum operating level coefficient and the flexible DC power rated value;

[0032] A fourth difference between the actual operating power of the flexible direct current and the second product value is calculated, and the fourth difference is used as the minimum power adjustment amount threshold.

[0033] In one embodiment, the control dead zone of the normally direct double-sided FLC control is ±0.1 Hz to ±0.14 Hz.

[0034] In one embodiment, the additional reactive energy is the additional reactive energy of the flexible direct current, and the calculation method of the additional reactive energy of the flexible direct current is:

[0035] The product of the conventional DC power regulation amount and tanφ is calculated, wherein φ is the power factor of the conventional DC valve side connected to the flexible DC.

[0036] In one embodiment, the power regulation amount of the normally straight double-sided FLC further corresponds to an upper limit of the power regulation amount and a lower limit of the power regulation amount, and the calculation method of the upper limit of the power regulation amount is:

[0037] Calculate the third product value corresponding to the conventional DC power rating and the conventional DC overload capacity coefficient;

[0038] Calculating a fifth difference value corresponding to the third product value and the actual operating power of the conventional DC power, and using the fifth difference value as the upper limit of the power adjustment amount; and,

[0039] The calculation method of the lower limit of the power regulation amount is:

[0040] Calculate a fourth product value corresponding to the conventional DC power minimum operating level coefficient and the conventional DC power rated value;

[0041] A sixth difference value corresponding to the actual operating power of the conventional DC and the fourth product value is calculated, and the sixth difference value is used as the lower limit of the power adjustment amount.

[0042] The embodiment of the present application provides a dynamic frequency coordination control method of flexible direct current co-frequency control and normal direct current double-side FLC, including: flexible direct current co-frequency control, normal direct current double-side FLC control, and power coordination control. First, when a disturbance occurs in the system, the flexible direct current co-frequency control is preferentially used to stabilize the grid frequency, and the power adjustment amount output by the flexible direct current co-frequency control is used as the start criterion for the control of the normal direct current double-side FLC control and the power coordination control. When the power adjustment amount exceeds the preset limit range and the system frequency deviation exceeds the control dead zone of the normal direct current double-side FLC control, the normal direct current double-side FLC control is used to determine and output the conventional DC power adjustment amount. Finally, based on the conventional DC power adjustment amount, the flexible direct current additional reactive power control is used to provide additional reactive power to the normal direct current to adjust the frequency stability of the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of a first embodiment of a method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC in this application;

[0044] Figure 2 This is a schematic diagram of the simulation structure of the Luxi back-to-back model of this application;

[0045] Figure 3 This is a schematic diagram of the power grid frequency simulation results of this application, where: Figure 3 (a) is the simulation result of the power grid frequency with only flexible DC co-frequency control. Figure 3 (b) is the simulation result of the power grid frequency with only the FLC on both sides of the DC power grid put into operation. Figure 3 (c) is a graph showing the simulation results of the power grid frequency when only the coordinated control proposed in this application is put into use;

[0046] Figure 4 This is a schematic diagram of the conventional DC valve side voltage simulation results of this application.

[0047] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0048] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0049] The present application embodiment provides a method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC, referring to Figure 1 , Figure 1 The present invention is a flowchart of a first embodiment of a method for dynamic frequency coordination control of flexible direct current co-frequency control and normally direct current double-side FLC.

[0050] In this embodiment, the method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC includes:

[0051] Step S10: When a disturbance occurs in the system, the flexible direct current co-frequency control is preferentially used to stabilize the grid frequency, and the power adjustment amount output by the flexible direct current co-frequency control is used as the starting criterion of the normal direct current double-side FLC control.

[0052] Step S20: When the power adjustment amount exceeds the preset limit range and the system frequency deviation exceeds the control dead zone of the normally direct dual-side FLC control, the normally direct dual-side FLC control is used to determine and output a conventional DC power adjustment amount.

[0053] Step S30: Based on the conventional DC power adjustment amount, the flexible DC additional reactive power control is used to provide additional reactive power to the normal DC to adjust the voltage stability of the power grid.

[0054] In this embodiment, three control methods are comprehensively applied, namely, flexible direct current frequency control, DC double-side FLC (Frequency Limit Control), and power coordination control. Among them, the flexible direct current frequency control technology can effectively realize the frequency synchronization operation between partitioned asynchronous power grids and the real-time and automatic sharing of the frequency regulation resources of the whole network. The DC double-side FLC control enhances the ability of the DC transmission system to provide inertia and primary frequency regulation support for the power grids on both sides by introducing additional frequency control on the rectifier side and the inverter side in the DC transmission system. Power coordination control is used to optimize power flow and stability in the power system.

[0055] Furthermore, when the system is disturbed, the flexible direct current co-frequency control method is used to stabilize the grid frequency, and the power regulation amount (hereinafter referred to as ΔP d1 Instead) as the start criterion for the normal direct dual-side FLC control and power coordination control, when ΔP d1When the frequency exceeds the preset limit range and the system frequency deviation exceeds the control dead zone of the FLC on both sides of the DC, the FLC on both sides of the DC starts to output the conventional DC power adjustment amount, and then based on the conventional DC power adjustment amount, the flexible DC additional reactive control is used to provide the DC with the additional reactive amount ΔQ it needs, so as to adjust the voltage stability of the power grid.

[0056] In the power system, the control dead zone of the FLC on both sides of the direct current is used to prevent the power system from adjusting the control input too frequently within a small error range. When the system frequency deviation does not exceed the control dead zone of the FLC control on both sides of the direct current, no adjustment is required at this time. When the system frequency deviation exceeds the control dead zone of the FLC control on both sides of the direct current, the output power adjustment amount is required. Optionally, in a feasible implementation, the dead zone of the FLC on both sides of the direct current is set to ±0.1Hz ~±0.14Hz. The calculation formula for the additional reactive power ΔQ of the flexible direct current is as follows:

[0057] ΔQ = ΔPd2tanφ,

[0058] Where φ is the power factor of the conventional DC valve side connected to the flexible DC.

[0059] In this embodiment, by utilizing flexible direct current co-frequency control, the frequencies of the sending-end power grid and the receiving-end power grid can be guaranteed to be consistent and synchronous within the power regulation range, thereby realizing real-time and automatic sharing of the frequency regulation resources of the sending-end power grid and the receiving-end power grid. By utilizing the FLC on both sides of the direct current, the frequency regulation effect can be increased, taking into account the frequency fluctuations of the sending-end power grid and the receiving-end power grid. By utilizing power coordinated control, reactive power support can be provided for conventional direct current, avoiding frequent operation of the direct current converter transformer and filter during the operation of the FLC on both sides of the direct current, thereby increasing the service life of the direct current equipment. Through the above method, the power stability of the power grid system is improved.

[0060] Furthermore, in another embodiment, the inputs of the flexible direct current frequency control are the sending-end grid frequency f R With the system frequency reference value f ref The corresponding first difference, the receiving end grid frequency f I With the system frequency reference value f ref The calculated frequency deviation will also be pre-processed by filtering, DC isolation, PI control, limiting and other control links. Based on the pre-processed first difference and second difference, the flexible DC power adjustment amount ΔP is output. d1 , the flexible DC power adjustment amount is superimposed on the flexible DC original power reference value P0, so as to obtain a new flexible DC active power instruction P ref , based on the flexible DC active power instruction P ref , the actual operating power of the flexible DC will be automatically adjusted.

[0061] Furthermore, the input of the DC double-side FLC control is also the sending-end grid frequency f R With the system frequency reference value f ref The first difference, the terminal grid frequency f I With the system frequency reference value f ref The calculated frequency deviation will be pre-processed through the dead zone, PI control, limiting and other control links. Based on the pre-processed data, the conventional DC power adjustment value ΔP of the normal direct double-side FLC control output can be obtained. d2 , conventional DC power regulation ΔP d2 The corresponding trigger angle adjustment amount Δα is calculated through logic judgment A, standardization processing, PI control and other links. Based on the trigger angle adjustment amount Δα, the actual operating power of conventional DC can be automatically adjusted. The logic judgment A is based on the judgment logic.

[0062] The power coordination control includes: judgment logic A, judgment logic A input signal ΔP d1 , input signal ΔP d1 The additional reactive energy ΔQ after conversion is superimposed on the original flexible DC reactive power instruction Q0 to generate a new flexible DC reactive power instruction Q ref Among them, the judgment logic A includes: if the flexible DC power adjustment amount ΔP d1 >The maximum power regulation threshold ΔP of the flexible DC frequency controller max1 , or, the flexible DC power regulation value ΔP d1 <The minimum power adjustment threshold of the flexible DC frequency controller ΔP min1 , then the DC double-side FLC control outputs the conventional DC regulation value ΔP d2 , if the minimum power regulation threshold ΔP of the flexible DC frequency controller min1 ≤Flexible DC power adjustment value ΔP d1 ≤ΔP of flexible DC frequency controller max1 The maximum power regulation threshold is set, and the FLC control output of both sides is always 0. In addition, the active power command and reactive power command are used to control the active power and reactive power of the power grid. The active power command controls the injection or absorption of actual power for power transmission, while the reactive power command controls the voltage and power factor of the power grid to ensure the voltage stability of the power grid.

[0063] It should be noted that the flexible DC active power instruction P ref With flexible DC reactive power instruction Q ref The target active power command i required for flexible DC inner loop control will be generated through the dynamic limiting link including PI control dref and target reactive power command i qref , active command i dref and reactive power command i qrefThe dynamic clipping constraints are satisfied as follows:

[0064]

[0065] Next, in another embodiment, the maximum power adjustment threshold ΔP of the flexible direct current frequency controller is max1 The calculation method is: calculate the first product value corresponding to the flexible DC power rating and the flexible DC overload capacity coefficient, calculate the third difference between the product value and the flexible DC power actual power, and use the third difference as the maximum power regulation threshold. The specific calculation formula is as follows:

[0066] ΔP max1 =k1P N1 –P1,

[0067] Where P N1 is the rated value of flexible DC power, P1 is the actual operating power of flexible DC, k1 is the overload capacity coefficient of flexible DC. At present, the maximum value of k1 is generally 1.05, but as the capacity of flexible DC converter valve switching devices increases, the maximum value of k1 will continue to increase.

[0068] Minimum power regulation threshold ΔP min1 The calculation method is as follows: calculate the second product value corresponding to the flexible DC power minimum operating level coefficient and the flexible DC power rating, calculate the fourth difference between the flexible DC actual operating power and the second product value, and use the fourth difference as the minimum power regulation threshold. Specifically, the minimum power regulation threshold ΔP of the flexible DC frequency controller is min1 The calculation formula is as follows:

[0069] ΔP min1 = P1 – m1P N1 ,

[0070] Wherein, m1 is the coefficient of the minimum operating level of the flexible DC power. When the flexible DC converter valve adopts a hybrid structure of full-bridge submodule and half-bridge submodule, m1 can be zero. When the value of m1 is less than zero, the flexible DC power flow reverses. The value of m1 is determined by the specific operating conditions.

[0071] In addition, the FLC on both sides of the straight line also corresponds to the upper limit of the power regulation ΔP max2 And the lower limit of power regulation ΔP min2 . Power regulation upper limit ΔP max2 The calculation method is as follows: calculate the third product value corresponding to the conventional DC power rating and the conventional DC overload capacity coefficient, calculate the fifth difference value corresponding to the third product value and the conventional DC actual operating power, and use the fifth difference value as the upper limit of the power adjustment amount. Specifically, the upper limit of the power adjustment amount ΔP max2 The calculation formula is as follows:

[0072] ΔP max2 =k2P N2 – P2,

[0073] Where P N2 is the rated value of conventional DC power, P2 is the actual operating power of conventional DC, k2 is the overload capacity coefficient of conventional DC. In case of long-term overload, the maximum value of k2 is generally 1.1, and in case of short-term overload, the maximum value of k2 is generally 1.2.

[0074] Power regulation lower limit ΔP min2 The calculation method is as follows: calculate the fourth product value corresponding to the conventional DC power minimum operating level coefficient and the conventional DC power rating, calculate the sixth difference value corresponding to the conventional DC actual operating power and the fourth product value, and use the sixth difference value as the power regulation amount lower limit. Specifically, the power regulation amount lower limit ΔP of the FLC on both sides of the DC is min2 The calculation formula is as follows:

[0075] ΔP min2 = P2 – m2P N2 ,

[0076] Where m2 is the coefficient of the minimum operating level of conventional DC power, and the value of m2 is 0.5.

[0077] It can be understood that the words "first", "second", "third", etc. in the various embodiments of the present application are only used to distinguish nouns, and do not limit the order or size of the nouns.

[0078] In order to verify that this application provides a flexible DC co-frequency control and a DC double-side FLC dynamic frequency coordination control technology, a simulation platform is built in the PSCAD / EMTDC (a simulation platform name) as follows Figure 2 The Luxi back-to-back simulation model shown in the figure simulates a single-pole blocking of a back-to-back conventional DC LCC at 5s, with a power loss of 400MW. Figure 3 As shown, the schematic diagram of the power grid frequency simulation result of this application is shown. Figure 3 (a) shows the simulation result of the grid frequency when only flexible DC co-frequency control is put into use. Figure 3 (b) shows the grid frequency simulation result diagram with only the FLC on both sides of the DC power grid put into operation. Figure 3 (c) shows the simulation result of the power grid frequency when only the coordinated control proposed in this application is put into use. It can be seen that after the conventional DC single-pole blocking occurs, the frequency on the Yunnan side is high and the frequency on the main grid side is low. Figure 3 (a) ~ Figure 3(c) By comparison, it can be seen that: when flexible direct current and same frequency control is adopted, the peak frequency of Yunnan power grid is 50.12Hz, and the minimum frequency of the main power grid is 49.78Hz. Because the power regulation amount exceeds the limit, the frequency on both sides cannot be restored to a synchronous state; when normal direct current and double-sided FLC is adopted, the peak frequency of Yunnan power grid is 50.27Hz, and the minimum frequency of the main power grid is 49.58Hz. Because the power regulation amount exceeds the limit, the frequency on both sides cannot enter the control dead zone; when the coordinated control of this application is adopted, the peak frequency of Yunnan power grid is 50.12Hz, and the minimum frequency of the main power grid is 49.78Hz. The frequency on both sides can be restored to a synchronous state. The frequency control effect of the coordinated control proposed in this application is obvious. Figure 4 As shown, the schematic diagram of the conventional DC valve side voltage simulation results of the present application shows that during the operation of the FLC on both sides of the normal direct current, the AC voltage oscillation on the Yunnan side and the main grid side is large. However, after adopting the coordinated control technology proposed in the present application, the flexible direct current provides real-time reactive power support to the normal direct current, and the AC voltage oscillation on the Yunnan side and the main grid side becomes smaller.

[0079] The description of the above specific implementation methods is to facilitate ordinary technicians in this technical field to understand and apply the present application, but the present application is not limited to the described implementation methods. The basic idea of ​​the present application is to provide a dynamic frequency coordination control technology of flexible direct current same-frequency control and normal direct current double-sided FLC, rather than the power grid system to which the coordinated control technology is applied. Any power grid system that uses the coordinated control technology provided by this application and this application falls within the protection scope of this application. Therefore, the present application is not limited to the above embodiments, and improvements and modifications made to the present application by those skilled in the art based on the disclosure of this application should be within the protection scope of this application.

[0080] In addition, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of more restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or system that includes the element.

[0081] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0082] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present application is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes a number of instructions for a terminal device (which can be a mobile phone, computer, server, or network device, etc.) to execute the methods described in each embodiment of the present application.

Claims

1. A method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC, characterized in that: The method for dynamic frequency coordination control of flexible direct current co-frequency control and normal direct current double-side FLC includes: When the system is disturbed, the flexible direct current co-frequency control is used to stabilize the grid frequency, and the power adjustment amount output by the flexible direct current co-frequency control is used as the starting criterion of the normal direct current double-side FLC control; When the power regulation amount exceeds the preset limit range and the system frequency deviation exceeds the control dead zone of the normally direct double-sided FLC control, the normally direct double-sided FLC control is used to determine and output the conventional DC power regulation amount; Based on the conventional DC power regulation amount, the flexible DC additional reactive power control is used to provide additional reactive power to the normal DC to adjust the voltage stability of the power grid; The method further comprises: The flexible DC power regulation amount is used as an input signal of the judgment logic; Converting the input signal into additional reactive energy of flexible DC; Superimposing the additional reactive power with the original reactive power instruction of the flexible direct current to generate a new reactive power instruction of the flexible direct current; Based on the reactive power instruction, adjusting the actual operating reactive power of the flexible direct current; The judgment logic includes: If the flexible DC power regulation amount is greater than the maximum power regulation amount threshold of the flexible DC co-frequency controller, or the power regulation amount is less than the minimum power regulation amount threshold of the flexible DC co-frequency controller, the normal DC double-side FLC control outputs the conventional DC regulation amount; If the flexible DC power regulation amount is greater than or equal to the minimum power regulation amount threshold of the flexible DC co-frequency controller, and less than or equal to the maximum power regulation amount threshold of the flexible DC co-frequency controller, the normal DC double-side FLC control output is 0; The additional reactive power is the additional infinite work of the flexible direct current, and the calculation method of the additional infinite work of the flexible direct current is: The product of the conventional DC power regulation amount and tanφ is calculated, wherein φ is the power factor of the conventional DC valve side connected to the flexible DC.

2. The method according to claim 1, characterized in that The inputs of the flexible direct current frequency control are respectively a first difference between the sending-end power grid frequency and the system frequency reference value, and a second difference between the receiving-end power grid frequency and the system frequency reference value. The method further includes: Determining a flexible DC power adjustment amount based on the preprocessed first difference and the second difference; The flexible DC power adjustment amount and the flexible DC original power reference value are superimposed to determine the active power instruction of the flexible DC; Based on the active power instruction, the actual operating active power of the flexible direct current is adjusted.

3. The method according to claim 1, characterized in that The inputs of the normally direct double-sided FLC control are respectively a first difference value corresponding to the frequency of the power grid at the sending end and the system frequency reference value, and a second difference value corresponding to the frequency of the power grid at the receiving end and the system frequency reference value. The method further includes: Determine a conventional DC power adjustment amount of the normally direct double-sided FLC control output based on the first difference and the second difference after preprocessing; After performing logical judgment, per-unit processing, and PI control on the conventional DC power adjustment amount based on the judgment logic, the corresponding trigger angle adjustment amount is calculated; Based on the trigger angle adjustment amount, the actual operating active power of the conventional direct current is adjusted.

4. The method according to claim 1, characterized in that The active power command and the reactive power command of the flexible direct current are passed through a dynamic limiting link including PI control to generate a target active power command and a target reactive power command required for the flexible direct current inner loop control, and the target active power command and the target reactive power command meet preset dynamic limiting constraints.

5. The method according to claim 1, characterized in that The maximum power regulation threshold of the flexible direct current frequency controller is calculated as follows: Calculate a first product value corresponding to the flexible DC power rating and the flexible DC overload capacity coefficient; Calculating a third difference between the product value and the actual power of the flexible DC power, and using the third difference as the maximum power adjustment threshold; and The calculation method of the minimum power adjustment threshold of the flexible direct current frequency controller is: Calculate a second product value corresponding to the flexible DC power minimum operating level coefficient and the flexible DC power rated value; A fourth difference value corresponding to the actual operating power of the flexible direct current and the second product value is calculated, and the fourth difference value is used as the minimum power adjustment amount threshold.

6. The method according to claim 1, characterized in that The control dead zone of the normally direct double-sided FLC control is ±0.1Hz~±0.14Hz.

7. The method according to claim 1, characterized in that The power regulation amount of the normally straight double-side FLC also corresponds to an upper limit of the power regulation amount and a lower limit of the power regulation amount. The calculation method of the upper limit of the power regulation amount is: Calculate the third product value corresponding to the conventional DC power rating and the conventional DC overload capacity coefficient; Calculating a fifth difference value corresponding to the third product value and the conventional DC actual operating power, and using the fifth difference value as the upper limit of the power adjustment amount; as well as, The calculation method of the lower limit of the power regulation amount is: Calculate a fourth product value corresponding to the conventional DC power minimum operating level coefficient and the conventional DC power rated value; A sixth difference value corresponding to the actual operating power of the conventional DC and the fourth product value is calculated, and the sixth difference value is used as the lower limit of the power adjustment amount.

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