Method for coordinated distribution of output power between stations of a multi-terminal direct current project with frequency control function

Abstract

The application discloses a kind of station intercoordination distribution methods of multi-terminal DC engineering frequency control function output power, steps are as follows: dynamically obtaining the AC system capacity connected by each converter station to be undertaken frequency control function output power;According to AC system capacity, determine the power distribution coefficient of each converter station;According to power distribution coefficient, coordinate the output power of frequency control function undertaken by each converter station;Considering due to AC system safety and stability boundary, power transmission and reception willingness, upper and lower limit of each converter station transmission capacity and other factors, part of converter station actually fails to undertake corresponding power distribution, and power redistribution is needed.The application proposes a kind of station intercoordination distribution methods of frequency control function output power suitable for multi-terminal DC engineering, convenient and feasible, safe and reliable, avoids the system risk possibly caused by converter station due to passive undertaking frequency control function output power from design principle, effectively guarantees AC / DC power grid safe and stable operation.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, and in particular to a method for coordinated allocation of output power of frequency control function in multi-terminal DC projects between stations. Background Technology

[0002] In AC / DC interconnection projects, the Frequency Limit Control (FLC) function in the DC control and protection system serves as an important frequency stability control measure. When AC system units are out of service, line faults, or other reasons cause the system frequency to exceed the limit, it can quickly adjust the power and promptly suppress the rise or fall of the system frequency, playing a vital role in the safe and stable operation of the AC / DC system.

[0003] In a two-terminal DC project, the rectifier station and the inverter station can be configured with FLC function. The output power of the FLC function is superimposed on the power command by the rectifier station (the inverter station transmits the command to the rectifier station through inter-station communication). Since the power output by the rectifier station minus the line loss is equal to the power of the inverter station, there is no problem of FLC power coordination and allocation between the two-terminal DC projects.

[0004] Similar to two-terminal DC systems, in multi-terminal DC projects, each converter station can be configured with FLC (Fluorescent Cell Controller) functionality. However, unlike two-terminal DC systems, multi-terminal DC systems require consideration of the coordination of FLC output power among the various passive FLC converter stations. Current research is based on power coordination allocation methods with a fixed allocation coefficient. When the AC system operating mode changes, it's possible that addressing the frequency issue of the AC system connected to a particular converter station (the active FLC station) can cause frequency or voltage stability problems in the AC systems connected to other passive FLC converter stations. (When a frequency change in the AC system connected to a converter station causes its FLC to adjust its DC power, that converter station is called the active FLC converter station; other converter stations passively handling the FLC output power are called passive FLC converter stations.)

[0005] The method of coordinating and allocating power between FLC passive-end converter stations is very important, as it relates to the safe and stable operation of AC / DC systems. Current research strategies are insufficient, and there is an urgent need to develop a convenient, feasible, safe, and reliable method for coordinating and allocating the functional output power of FLCs that is applicable to multi-terminal DC projects. Summary of the Invention

[0006] The purpose of this invention is to provide a convenient, feasible, safe and reliable method for coordinating the distribution of frequency control function output power between stations, applicable to multi-terminal DC projects.

[0007] The technical solution adopted in this invention is: a method for inter-station coordinated allocation of output power of multi-terminal DC engineering frequency control function, including (the process is as follows) Figure 1As shown):

[0008] Step 1): Dynamically obtain the AC system capacity connected to each converter station that will perform frequency control output power; where the AC system capacity S connected to converter station n is... n The following methods are used to dynamically obtain the information:

[0009]

[0010]

[0011] Where n = 1, 2, ..., N, N is the total number of converter stations to undertake frequency control functions and output power, U n I is the effective value of the phase voltage of the AC system connected to converter station n. n k is the short-circuit current of the AC system connected to converter station n. n This is a correction factor, with a value range of 0.9 to 1.1. Let dQ be the impedance angle of the equivalent circuit of the AC system connected to converter station n. n dU represents the change in reactive power, whether active or passive, of the AC system connected to converter station n within a certain time period. n This represents the change in the effective value of the phase voltage of the AC system connected to converter station n within the corresponding time period.

[0012] Step 2): Determine the frequency control function output power allocation coefficient for each converter station according to the capacity ratio of the AC systems connected to each converter station, wherein the frequency control function output power allocation coefficient Coff for converter station n is... n for:

[0013]

[0014] Where S i S n Dir represents the capacity of the AC systems connected to converter stations i and n, where n = 1 to N, and N is the total number of converter stations that need to perform frequency control functions and output power. n The directional coefficient for converter station n, with a value of 1 or -1, Corr i Corr n The correction coefficients for converter stations i and n are 0.0 to 1.2.

[0015] Step 3): Calculate the frequency control function output power of each converter station by multiplying the frequency control function output power allocation coefficient of each converter station by the sum of the frequency control function output power to be undertaken, where the frequency control function output power ΔP allocated to converter station n is... n for:

[0016] ΔP n=Coff n *Pflc

[0017] Where Pflc represents the total output power of the frequency control function to be performed.

[0018] Step 4): Determine whether the total output power of each converter station is within the safe power range. The criterion is:

[0019] Pmin n ≤P n +ΔP n +ΔP′ n ≤Pmax n

[0020] Where P n ΔP represents the original power output of converter station n when it does not perform frequency control functions. n The output power Pmin for the frequency control function undertaken by converter station n n Pmax is the lower limit of the safe power of converter station n. n ΔP is the upper limit of the safe power of converter station n. n ′ represents the frequency control function output power redistributed to converter station n, with an initial value of 0.

[0021] If the power exceeds the safe power range, proceed to step 5; if the power is within the safe power range, proceed to step 7.

[0022] Step 5): Calculate the output power of the frequency control functions that the converter station has undertaken and the output power of the frequency control functions that it has not undertaken, which are outside the safe power range.

[0023] If P n +ΔP n +ΔP n ′>Pmax n The frequency control output power of converter station n, which is outside the safe power range, is Pmax. n -P n The converter station n failed to perform its frequency control function due to exceeding the safe power range, resulting in an output power Pflc that was not fulfilled. n ′=P n +ΔP n +ΔP n ′-Pmax n ;

[0024] If P n +ΔP n +ΔP n ′ <Pmin n The frequency control function output power of converter station n, which is outside the safe power range, is P. n -Pminn The converter station n failed to perform its frequency control function due to exceeding the safe power range, resulting in an output power Pflc that was not fulfilled. n ′=Pmin n -(P n +ΔP n +ΔP n ′).

[0025] Step 6): Calculate the total output power of the frequency control function that all converter stations outside the safe power range failed to undertake, the redistribution coefficient of the frequency control function output power of each converter station within the safe power range, and calculate the redistributed frequency control function output power by multiplying the redistribution coefficient by the total output power of the frequency control function that failed to undertake.

[0026] The sum of the output power Pflc′ of all converter stations that failed to perform frequency control functions due to exceeding the safe power range is given by the formula:

[0027]

[0028] Where Y represents the total number of converter stations that failed to fully assume the frequency control function's output power due to exceeding the safe power range; Over y The out-of-limit directional coefficient for converter station y that fails to fully assume the frequency control function output power due to exceeding the safe power range is 1 or -1.

[0029] The frequency control function of converter station n output power redistribution coefficient Coff n 'for:

[0030]

[0031] Where S m For the capacity of the AC system connected to converter station m, Corr m Let m be the correction coefficient for converter station m, and M be the total number of converter stations participating in the frequency control function output power redistribution.

[0032] The frequency control function of the converter station n redistribution output power ΔP n 'for:

[0033] ΔP n ′=Coff′ n *Pflc′.

[0034] Step 7): Calculate the total output power of each converter station and the output power of the frequency control function undertaken by each converter station based on the output power of the frequency control function undertaken by each converter station and the redistributed frequency control function output power. Return to Step 4) until the output power of the frequency control function to be undertaken is allocated. The power output by converter station n is P. n +ΔP n +ΔP n The frequency control function it undertakes has an output power of ΔP. n +ΔP n ′.

[0035] In step 1) above, the capacity S of the AC system connected to converter station n is... n The following methods are used to dynamically obtain the information:

[0036]

[0037]

[0038] U n I is the effective value of the phase voltage of the AC system connected to converter station n. n For the short-circuit current of the AC system, k n This is a correction factor, with a value range of 0.9 to 1.1. Impedance angle of the equivalent circuit of an AC system, dQ n dU represents the change in reactive power, whether active or passive, over a certain time period. n This represents the change in the effective value of the phase voltage of the AC system within the corresponding time period.

[0039] Beneficial effects:

[0040] This invention effectively overcomes the shortcomings of existing FLC power station coordination and allocation methods, providing a new coordination and allocation approach. Compared to current methods, the data required by this invention can be readily and completely obtained from existing control and protection systems. The process logic provided by this invention is convenient and feasible to implement. The method considers safe power range criteria, and its design principle avoids potential system risks caused by FLC passive-end converter stations bearing FLC power, effectively ensuring the safe and stable operation of AC / DC power grids. This invention is applicable to multi-terminal DC projects, including multi-terminal LCC DC, multi-terminal VSC DC, and multi-terminal LCC+VSC hybrid DC projects. Attached Figure Description

[0041] Figure 1 This is a flowchart of the inter-station coordinated allocation method for the output power of the multi-terminal DC engineering frequency control function in this invention.

[0042] Figure 2This is a schematic diagram of a three-terminal DC engineering project in a specific embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram of a four-terminal DC engineering project in a specific implementation example of the present invention. Detailed Implementation

[0044] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details.

[0045] Example 1

[0046] This embodiment is a three-terminal hybrid DC FLC power station coordination allocation method. The schematic diagram of the three-terminal hybrid DC is shown in Figure 2: the three stations are converter station 1 (LCC converter station, sending end), converter station 2 (VSC converter station, receiving end), and converter station 3 (VSC converter station, receiving end). The AC systems connected to converter station 1, converter station 2, and converter station 3 are AC system 1, AC system 2, and AC system 3, respectively.

[0047] The AC system capacities of AC system 1, AC system 2, and AC system 3 are S1, S2, and S3, respectively; the effective values ​​of the phase voltages are U1, U2, and U3, respectively; the short-circuit current levels are I1, I2, and I3, respectively; the short-circuit current level correction coefficients are k1 and k2, respectively; and the impedance angles of the equivalent circuits of the AC systems are: The active or passive reactive power changes within a certain time period are dQ1, dQ2, and dQ3, respectively; the corresponding changes in the effective values ​​of the AC system phase voltages within the same time period are dU1, dU2, and dU3, respectively.

[0048] AC system 1 frequency exceeded limit, and the FLC function in converter station 1 activated to adjust the DC power to P. flc This embodiment provides a method for coordinated power distribution of a three-terminal DC power supply (FLC) between converter station 2 and converter station 3, including:

[0049] Step 1): Obtain the AC system capacity connected to each converter station whose FLC power is to be allocated;

[0050] Step 2): Determine the FLC power allocation coefficient for each converter station based on the AC system capacity;

[0051] Step 3): Coordinate the FLC power assigned to each converter station according to the FLC power allocation coefficient;

[0052] Step 4): Determine whether the power of converter station n is within the safe power range. If the power of converter station n is not within the safe power range, proceed to step 5). If the power of converter station n is within the safe power range, proceed to step 7).

[0053] Step 5): Calculate the frequency control function output power undertaken by converter station n that exceeds the safe power range, and calculate the power that converter station n is unable to undertake due to exceeding the safe power range;

[0054] Step 6): Calculate the total power that all converter stations failed to handle due to exceeding the safe power range, and the power redistribution coefficient of converter station n. Calculate the frequency control function output power redistributed by converter station n, and then execute step 4).

[0055] Step 7): Output the power of the frequency control function undertaken by the output converter station n.

[0056] Detailed explanation is as follows:

[0057] Step 1) Obtaining the AC system capacity of each FLC power to be allocated, the AC system capacities S2 and S3 connected to converter station 2 and converter station 3 are obtained in the following way:

[0058]

[0059]

[0060] Step 2) The FLC power allocation coefficients for each converter station, and the FLC power allocation coefficients Coff2 and Coff3 for converter station 2 and converter station 3 are as follows:

[0061]

[0062]

[0063] Step 3) The FLC power undertaken by each converter station, and the FLC power ΔP2 and ΔP3 allocated to converter station 2 and converter station 3 are as follows:

[0064] Pflc = Pflc1

[0065] ΔP2=Coff2*Pflc

[0066] ΔP3=Coff3*Pflc

[0067] Step 4): Determine whether the power of converter station 2 and converter station 3 is within the safe power range. The criterion is:

[0068] Pmin2≤P2+ΔP2+ΔP2′≤Pmax2

[0069] Pmin3≤P3+ΔP3+ΔP3′≤Pmax3

[0070] This example assumes that the power of converter station 2 and converter station 3 are both within the safe power range.

[0071] Step 5): The power of the frequency control function undertaken by converter station 2 and converter station 3 is:

[0072] ΔP2=Coff2*Pflc

[0073] ΔP3=Coff3*Pflc

[0074] Example 2

[0075] This embodiment is a four-terminal hybrid DC FLC power station coordination allocation method. The schematic diagram of the three-terminal hybrid DC is shown in Figure 3. The four stations are converter station 1 (LCC converter station, sending end), converter station 2 (LCC converter station, sending end), converter station 3 (VSC converter station, receiving end), and converter station 4 (VSC converter station, receiving end). The AC systems connected to converter stations 1, 2, 3, and 4 are AC system 1, AC system 2, AC system 3, and AC system 4, respectively.

[0076] The AC system capacities of AC systems 1, 2, 3, and 4 are S1, S2, S3, and S4, respectively; the effective phase voltage values ​​are U1, U2, U3, and U4, respectively; the short-circuit current levels are I1, I2, I3, and I4, respectively; the short-circuit current level correction coefficients are k1, k2, k3, and k4, respectively; and the impedance angles of the equivalent circuits of the AC systems are: The active or passive reactive power changes within a certain time period are dQ1, dQ2, dQ3, and dQ4, respectively; the corresponding changes in the effective values ​​of the AC system phase voltages within the same time period are dU1, dU2, dU3, and dU4, respectively.

[0077] AC system 3 frequency exceeded limit, converter station 3's FLC function activated and adjusted DC power to P. flc This embodiment provides a method for coordinated power distribution of a four-terminal DC power supply (FLC) in converter station 1, converter station 2, and converter station 4, including:

[0078] Step 1): Obtain the AC system capacity connected to each converter station whose FLC power is to be allocated;

[0079] Step 2): Determine the FLC power allocation coefficient for each converter station based on the AC system capacity;

[0080] Step 3): Coordinate the FLC power assigned to each converter station according to the FLC power allocation coefficient;

[0081] Step 4): Determine whether the power of converter station n is within the safe power range. If the power of converter station n is not within the safe power range, proceed to step 5). If the power of converter station n is within the safe power range, proceed to step 7).

[0082] Step 5): Calculate the frequency control function output power undertaken by converter station n that exceeds the safe power range, and calculate the power that converter station n is unable to undertake due to exceeding the safe power range;

[0083] Step 6): Calculate the total power that all converter stations failed to handle due to exceeding the safe power range, and the power redistribution coefficient of converter station n. Calculate the frequency control function output power redistributed by converter station n, and then execute step 4).

[0084] Step 7): Output the power of the frequency control function undertaken by the output converter station n.

[0085] Detailed explanation is as follows:

[0086] Step 1) Obtaining the AC system capacity of each FLC power to be allocated, the AC system capacities S1, S2, and S4 connected to converter station 1, converter station 2, and converter station 4 are obtained in the following manner:

[0087]

[0088]

[0089]

[0090] Step 2) The FLC power allocation coefficients for each converter station, and the FLC power allocation coefficients Coff1, Coff2, and Coff4 for converter station 1, converter station 2, and converter station 4 are as follows:

[0091]

[0092]

[0093]

[0094] Step 3) The FLC power undertaken by each converter station, and the FLC power ΔP allocated to converter station n. n for:

[0095] ΔP1=Coff1*P flc

[0096] ΔP2=Coff2*P flc

[0097] ΔP4=Coff4*P flc

[0098] Step 4): Determine whether the power of converter station n is within the safe power range. If the power of converter station n is not within the safe power range, proceed to step 5). If the power of converter station n is within the safe power range, proceed to step 7).

[0099] The criterion for ensuring that the power of converter station n is within the safe range is:

[0100] Pmin1≤P1+ΔP1+ΔP1′≤Pmax1

[0101] Pmin2≤P2+ΔP2+ΔP2′≤Pmax2

[0102] Pmin4≤P4+ΔP4+ΔP4′≤Pmax4

[0103] Step 5): Output the frequency control function output power of converter station n that exceeds the safe power range, and calculate the power that converter station n failed to bear due to exceeding the safe power range;

[0104] If P1 + ΔP1 + ΔP1′ > Pmax1:

[0105] The output power of converter station 1 is Pmax1, and the output power of its frequency control function is: Pmax1 - P1

[0106] The power that converter station 1 could not handle due to exceeding the safe power range is Pflc1′=P1+ΔP1+ΔP1′-Pmax1;

[0107] If P1+ΔP1+ΔP1′ <Pmin1:

[0108] The output power of converter station 1 is Pmin1, of which the output power for frequency control function is: P1 - Pmin1.

[0109] If converter station 1 is unable to handle the power exceeding the safe power range, then Pflc1′=Pmin1-(P1+ΔP1+ΔP1′).

[0110] If P2 + ΔP2 + ΔP2′ > Pmax2:

[0111] The output power of converter station 2 is Pmax2, of which the output power for frequency control function is: Pmax2 - P2

[0112] The power that converter station 2 could not handle due to exceeding the safe power range is Pflc2′=P2+ΔP2+ΔP2′-Pmax2;

[0113] If P2 + ΔP2 + ΔP2′ <Pmin2:

[0114] The output power of converter station 2 is Pmin2, of which the output power for frequency control function is: P2 - Pmin2

[0115] The power that converter station 2 could not handle due to exceeding the safe power range is Pflc2′=Pmin2-(P2+ΔP2+ΔP2′);

[0116] If P4 + ΔP4 + ΔP4′ > Pmax4:

[0117] The output power of converter station 4 is Pmax4, of which the output power for frequency control function is: Pmax4 - P4

[0118] The power that converter station 4 could not handle due to exceeding the safe power range is Pflc4′=P4+ΔP4+ΔP4′-Pmax4;

[0119] If P4 + ΔP4 + ΔP4′ <Pmin4:

[0120] The output power of converter station 4 is Pmin4, of which the output power for frequency control function is: P4 - Pmin4.

[0121] The power that converter station 4 could not handle due to exceeding the safe power range is Pflc4′=Pmin4-(P4+ΔP4+ΔP4′);

[0122] Step 6): Calculate the total power that all converter stations failed to handle due to exceeding the safe power range, and the power redistribution coefficient of converter station n. Calculate the frequency control function output power redistributed by converter station n, and then execute step 4).

[0123] Considering factors such as the safety and stability boundaries of the AC system, the willingness to send and receive power, and the upper and lower limits of the transmission capacity of each converter station, assuming that converter station 2 exceeds the upper limit, the FLC power P that it cannot handle... flc Redistribute

[0124] Pflc′=Pflc2′

[0125] The FLC power redistribution factors for converter station 1 and converter station 4 are:

[0126]

[0127]

[0128] FLC power ΔP redistributed between converter station 1 and converter station 4 n 'for:

[0129] ΔP1′=Coff1′*Pflc′

[0130] ΔP4′=Coff4′*Pflc′

[0131] Step 7): The power of converter station n is P n +ΔP n+ΔP n The frequency control function of this component has an output power of ΔP. n +ΔP n ′.

[0132] The power of converter station 1 is P1+ΔP1+ΔP1′, of which the output power of the frequency control function is: ΔP1+ΔP1′;

[0133] The power of converter station 2 is Pmax2, and the output power of the frequency control function it undertakes is: Pmax2-P2;

[0134] The power of converter station 4 is P4+ΔP4+ΔP4′, of which the output power of the frequency control function is ΔP4+ΔP4′.

[0135] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for coordinated allocation of output power of multi-terminal DC engineering frequency control function between stations, characterized in that, include: Step 1): Dynamically obtain the AC system capacity connected to each converter station that will perform frequency control function output power; Step 2): Determine the frequency control function output power allocation coefficient of each converter station according to the capacity ratio of the AC systems connected to each converter station; Step 3): Calculate the output power of the frequency control function undertaken by each converter station by multiplying the output power allocation coefficient of each converter station by the total output power of the frequency control function to be undertaken; Step 4): Determine whether the total output power of each converter station is within the safe power range. If it exceeds the safe power range, proceed to step 5. If within the safe power range, proceed to step 7); Step 5): Calculate the output power of the frequency control functions that the converter station has undertaken and the output power of the frequency control functions that it has not undertaken, which are outside the safe power range; Step 6): Calculate the total output power of the frequency control function that all converter stations that are outside the safe power range fail to undertake, the redistribution coefficient of the output power of the frequency control function of each converter station within the safe power range, and calculate the redistributed output power of the frequency control function by multiplying the redistribution coefficient of the frequency control function by the total output power of the frequency control function that failed to undertake. Step 7): Calculate the total output power of each converter station and the output power of the frequency control function undertaken by each converter station based on the output power of the frequency control function undertaken by each converter station and the redistributed frequency control function output power. Return to step 4) until the output power of the frequency control function to be undertaken is allocated.

2. The method according to claim 1, characterized in that, In step 1), the capacity S of the AC system connected to converter station n is... n The following methods are used to dynamically obtain the information: Where n = 1, 2, ..., N, N is the total number of converter stations to undertake frequency control functions and output power, U n I is the effective value of the phase voltage of the AC system connected to converter station n. n k is the short-circuit current of the AC system connected to converter station n. n For correction factor, Let dQ be the impedance angle of the equivalent circuit of the AC system connected to converter station n. n dU represents the change in reactive power, whether active or passive, of the AC system connected to converter station n within a certain time period. n This represents the change in the effective value of the phase voltage of the AC system connected to converter station n within the corresponding time period.

3. The method according to claim 1, characterized in that, In step 2), the frequency control function of converter station n outputs the power distribution coefficient Coff. n for: Where S i S n Dir represents the AC system capacity connected to converter stations i and n, where i, n = 1, 2, ..., N, and N is the total number of converter stations to undertake frequency control functions and output power. n For converter station n, the directional coefficient is Corr. i Corr n These are the correction coefficients for converter stations i and n.

4. The method according to claim 1, characterized in that, In step 3), the frequency control function of converter station n outputs power ΔP. n for: ΔP n =Coff n *Pflc Where Pflc represents the total output power of the frequency control function to be performed.

5. The method according to claim 1, characterized in that, The criterion for determining whether the total output power of converter station n in step 4) is within the safe power range is: Pmin n ≤P n +ΔP n +ΔP n ′≤Pmax n Where P n ΔP represents the original power output of converter station n when it does not perform frequency control functions. n The output power Pmin for the frequency control function undertaken by converter station n n Pmax is the lower limit of the safe power of converter station n. n ΔP is the upper limit of the safe power of converter station n. n ′ represents the frequency control function output power redistributed to converter station n, with an initial value of 0.

6. The method according to claim 5, characterized in that, In step 5): If P n +ΔP n +ΔP n ′>Pmax n The frequency control output power of converter station n, which is outside the safe power range, is Pmax. n -P n The converter station n failed to perform its frequency control function due to exceeding the safe power range, resulting in an output power Pflc that was not fulfilled. n ′=P n +ΔP n +ΔP n ′-Pmax n ; If P n +ΔP n +ΔP n ′ <Pmin n The frequency control function output power of converter station n, which is outside the safe power range, is P. n -Pmin n The converter station n failed to perform its frequency control function due to exceeding the safe power range, resulting in an output power Pflc that was not fulfilled. n ′=Pmin n -(P n +ΔP n +ΔP n ′).

7. The method according to claim 1, characterized in that, In step 6), the total output power Pflc′ of all converter stations that failed to perform frequency control functions due to exceeding the safe power range is calculated using the following formula: Where Y represents the total number of converter stations that failed to fully assume the frequency control function's output power due to exceeding the safe power range, Over y The out-of-limit directional coefficient of converter station y for output power that exceeds the safe power range and is unable to fully assume the frequency control function. The frequency control function of converter station n output power redistribution coefficient Coff n 'for: Where S m For the capacity of the AC system connected to converter station m, Corr m is the correction coefficient for converter station m, and M is the total number of converter stations participating in the frequency control function output power redistribution; The frequency control function of the converter station n redistribution output power ΔP n 'for: ΔP n ′=Coff′ n *Pflc′。 8. The method according to claim 1, characterized in that, Step 7) The total output power of converter station n is P n +ΔP n +ΔP n ′, where the power output responsible for frequency control is: ΔP n +ΔP n ′.

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