Reactive power control method and system for flexible direct current transmission

Abstract

The invention discloses a reactive power control method and system for flexible direct-current power transmission, and belongs to the technical field of flexible direct-current power transmission. The reactive power capability of the flexible direct-current power transmission system is fully utilized, and different reactive power inner loop currents or reactive power instructions are output through judgment of a reactive power control working mode; automatic control of reactive power and voltage of a power grid is realized, and frequent manual reactive power adjustment by operators is avoided; the reactive power quick response capability of the flexible direct-current power transmission system is utilized to quickly adjust alternating-current voltage when the alternating-current voltage is abnormal, meanwhile, information interaction with a power grid reactive power control device is carried out, the power grid reactive power control device inputs corresponding reactive power capacitors and electric reactors according to the interacted information, additional reactive power output by the flexible direct-current power transmission system is replaced, and the reactive power output by the flexible direct-current power transmission system is realized. Therefore, the dual requirements of steady-state reactive power control and fault reactive power control are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible direct current power transmission, and in particular relates to a reactive power control method and system for flexible direct current power transmission. Background Art

[0002] Flexible DC transmission system has the characteristics of flexible control, rapid dynamic response, low harmonic content, etc. It can quickly and independently adjust active power and reactive power, and has broad application prospects. Especially in the field of reactive power control, due to its fast response speed, it can quickly provide reactive power during the AC system fault and recovery stage to support the grid voltage during the fault and accelerate voltage recovery; in the steady-state stage, it can also provide reactive power according to system requirements to achieve steady-state voltage regulation.

[0003] After the flexible DC transmission system is connected to the AC system, the AC voltage changes frequently due to the load changes of the AC system, especially when the AC voltage fails to meet the voltage range requirements of the superior dispatcher, which causes the operating personnel to manually adjust the reactive power frequently. Therefore, the flexible DC transmission system is required to automatically adjust the voltage after the AC voltage exceeds the range to bring the voltage back to the normal range; however, since the reactive power output of the automatic voltage regulation after the AC voltage exceeds the range is too large, the reserve reactive power of the flexible DC system itself is consumed, thereby affecting the effect of reactive power supporting the voltage during a fault. The existing solution cannot meet the dual needs of steady-state reactive power control and fault reactive power control. Summary of the invention

[0004] The technical problem to be solved by the present application is to overcome the defects of the above-mentioned prior art and provide a reactive power control method and system for flexible direct current transmission. By judging the reactive power control working mode, different reactive inner loop currents or reactive power instructions are output to realize automatic control of reactive power and voltage. At the same time, by exchanging information with the reactive power control system of the power grid, the mutual coordination of the flexible direct current reactive power and the reactive reactors and capacitors of the power grid is realized to meet the dual needs of steady-state reactive power control and fault reactive power control.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted in this application is as follows.

[0006] The present application provides a reactive power control method for flexible direct current transmission, comprising the following steps:

[0007] Detect system runtime data;

[0008] Determine the working mode of reactive power control based on the detected data;

[0009] Output reactive power instruction according to the judgment result of working mode and execute the instruction;

[0010] Synchronously transmit the judgment result of the working mode and the reactive power instruction to the reactive power control device of the power grid;

[0011] The reactive power control device of the power grid performs reactive power control in response to the reactive power control instruction issued.

[0012] In some embodiments, the operating modes include an abnormally low voltage operating mode, a normal operating mode, an abnormally high voltage operating mode, a first low voltage ride through operating mode, a second low voltage ride through operating mode, and a high voltage ride through operating mode.

[0013] In some embodiments, when U m Meet U m ≤k L2 U N When the reactive power control is in the second low voltage ride-through working mode;

[0014] When U m Satisfy k L2 U N m ≤k L1 U N When the reactive power control is in the first low voltage ride-through working mode;

[0015] When U m Satisfy k L1 U N m ≤k L U N When , the reactive power control is in the abnormally low voltage working mode;

[0016] When U m Satisfy k L U N m <k H U N When , the reactive power control is in the normal working mode;

[0017] When U m Satisfy k H U N ≤U m <k H1 U N When , the reactive power control is in the abnormally high voltage working mode;

[0018] When U m Satisfy k H1 U N ≤U m When , the reactive power control is in the high voltage ride through working mode;

[0019] Among them, U m ​​​is the amplitude of the positive sequence component of the AC system voltage, U N is the rated value of the positive sequence component of the AC system voltage, k L ,k L1 ,k L2 ,k H ,k H1 All are voltage coefficients and satisfy the relationship: 0 <k L2 <k L1 <k L <1 <k H <k H1 .

[0020] In some embodiments, when the reactive power control is in the second low voltage ride-through working mode, its reactive current inner loop reference instruction i qref =0 or i qref =k LF2 ; where k LF2 is the reactive current reference command setting value in the second low voltage ride-through working mode, satisfying: 0≤k LF2 ≤1p.u.;

[0021] When the reactive power control is in the first low voltage ride-through working mode, its reactive current inner loop reference instruction i qref =k LF1 , where k LF1 =G LF1 (U N -U m ), G LF1 A proportional-integral controller for a first low voltage ride-through operating mode;

[0022] When the reactive power control is in abnormally low voltage working mode, its reactive power control reference instruction Q ref =Q ord +Q L , where Q ord is the reactive power command input to the system, Q L It is the additional reactive power instruction in abnormal low voltage working mode, Q L =G L (k L U N -U m ), G L A proportional-integral controller for abnormally low voltage operation mode;

[0023] When the reactive power control is in normal working mode, its reactive power control reference instruction Q ref =Q ord ;

[0024] When the reactive power control is in abnormally high voltage working mode, its reactive power control reference instruction Q ref =Q ord+Q H , where Q H It is the additional reactive power instruction in abnormally high voltage working mode, Q H =G H (k H U N -U m ), G H Proportional-integral controller for abnormally high voltage operation mode;

[0025] When the reactive power control is in the high voltage ride-through mode, the reactive current inner loop reference command i qref =k HF1 , where k HF1 =G HF1 (U N -U m ), G HF1 It is a proportional-integral controller for high voltage ride-through mode.

[0026] In some embodiments, when the reactive power control is in the first low voltage ride-through mode, 0≤k LF1 =G LF1 (U N -U m )≤I qL1set , I qL1set It is the reactive current reference value set according to the system voltage.

[0027] In some embodiments, the input reactive power command Q ord Satisfaction: Q min ≤Q ord ≤Q max , reactive power control reference instruction Q ref Satisfaction: Q min ≤Q ref ≤Q max , Q min ,Q max are the minimum and maximum reactive power values ​​calculated based on the system.

[0028] In some embodiments, when the reactive power control is in the high voltage ride through mode, I qHset ≤k HF1 =G HF1 (U N -U m )≤0,I qHset It is the reactive current reference value set according to the system voltage.

[0029] The embodiment of the present application further provides a reactive power control system for flexible direct current transmission, which is applied to the reactive power control method for flexible direct current transmission as described in any of the above embodiments, wherein the reactive power control system comprises: a reactive power control device for flexible direct current transmission and a reactive power control device for a power grid which are electrically connected;

[0030] The flexible direct current power transmission reactive power control device comprises:

[0031] The reactive working mode judgment module is used to judge the working mode of the reactive control according to the detected data and obtain the result of the working mode judgment;

[0032] A reactive instruction output module, used for outputting a reactive current inner loop reference instruction or a reactive control reference instruction or an additional reactive instruction for an abnormally low voltage working mode or an additional reactive instruction for an abnormally high voltage working mode according to the result of the reactive working mode judgment module;

[0033] A reactive communication module, used for transmitting the results of the reactive working mode determination module and the reactive instruction output module to the power grid reactive control device, and receiving reactive control instructions issued by the power grid reactive control device;

[0034] A reactive power execution module, used for executing reactive power instructions by taking the result of the reactive power instruction output module as a reference value;

[0035] The grid reactive power control device puts the corresponding reactive reactor or capacitor into operation according to the communication data transmitted by the reactive power communication module: the additional reactive power instruction of the abnormally low voltage working mode or the additional reactive power instruction of the abnormally high voltage working mode.

[0036] In some embodiments, the communication content between the reactive communication module and the grid reactive control device also includes: the operation mode of the flexible direct current transmission system, the reactive limit value, the unlocking state and the reactive control mode.

[0037] In some embodiments, the period during which the grid reactive power control device switches on or off reactive capacitors or reactors is greater than or equal to reactive power execution time of the flexible direct current transmission system.

[0038] In some embodiments, the grid reactive power control device sends a reactive power command value to the flexible DC transmission reactive power control device, and the reactive power command value is used as the reactive power command Q input by the system. ord .

[0039] Compared with the prior art, this application has the following beneficial effects:

[0040] A reactive power control method for flexible direct current transmission of the present application includes the following steps: detecting data during system operation; judging the working mode of reactive control according to the detected data; outputting reactive instructions according to the judgment result of the working mode; transmitting the judgment result of the working mode and the reactive instructions to the reactive control device of the power grid; the reactive control device of the power grid issues reactive control instructions to perform reactive control. The present application makes full use of the reactive power of the flexible direct current transmission system itself, outputs different reactive inner loop currents or reactive instructions through the judgment of the reactive control working mode, realizes automatic control of reactive power and voltage of the power grid, and avoids frequent manual adjustment of reactive power by operators in steady state; utilizes the reactive power fast response capability of the flexible direct current transmission system, quickly adjusts the AC voltage when the AC voltage is abnormal, and at the same time, exchanges information with the reactive control device of the power grid, and the reactive control device of the power grid invests corresponding reactive capacitors and reactors according to the exchanged information, and replaces the additional reactive power output by the flexible direct current transmission system, thereby meeting the dual needs of steady-state reactive control and fault reactive control.

[0041] An embodiment of the present application also provides a reactive power control system for flexible direct current transmission, which is applied to the control method as described above. It can be understood that the reactive power control system can realize the function of the reactive power control method and thus has the same beneficial effects as the reactive power control method, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 It is a flow chart of a reactive power control method of flexible direct current transmission of the present application;

[0044] Figure 2 It is a schematic diagram of the abnormally low voltage working mode, the normal working mode, and the abnormally high voltage working mode of the present application;

[0045] Figure 3 It is a schematic diagram of the first low voltage ride through working mode, the second low voltage ride through working mode, and the high voltage ride through working mode of the present application;

[0046] Figure 4 It is a reactive power instruction block diagram of the flexible direct current transmission reactive power control device of the present application;

[0047] Figure 5 It is a schematic diagram of the device composition of the reactive power control system of the flexible direct current transmission of the present application. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application. In addition, in the description of the present application, the term "including" means "including but not limited to". In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0049] The applicant noted that after the flexible DC transmission system is connected to the AC system, the AC voltage changes frequently due to changes in the load of the AC system, especially when the AC voltage fails to meet the voltage range requirements of the superior dispatcher, which causes the operating personnel to manually adjust the reactive power frequently. Therefore, the flexible DC transmission system is required to automatically adjust the voltage after the AC voltage exceeds the range so that the voltage returns to the normal range; however, since the reactive power output of the automatic voltage regulation after the AC voltage exceeds the range is too large, the reserve reactive power of the flexible DC system itself is consumed, thereby affecting the effect of reactive power supporting the voltage during a fault. The existing solution cannot meet the dual needs of steady-state reactive power control and fault reactive power control.

[0050] In view of this, the present application provides a reactive power control method and system for flexible direct current transmission, which can coordinate reactive voltage and avoid operators from frequently manually adjusting reactive power, while meeting the dual needs of steady-state reactive power control and fault reactive power control.

[0051] It should be noted that the description order of the following embodiments is not intended to limit the preferred order of the embodiments.

[0052] Please refer to Figure 1 , Figure 2 , Figure 3 and Figure 4 , a reactive power control method for flexible direct current transmission provided by an embodiment of the present application comprises the following steps:

[0053] S1: Data when the detection system is running.

[0054] Specifically, it refers to detecting the voltage positive sequence component amplitude U of the AC system m .

[0055] S2: Determine the working mode of reactive power control based on the detected data.

[0056] Specifically, according to the detected AC system voltage positive sequence component amplitude U mThe different working modes of reactive control can be divided into different working modes. The corresponding working modes of reactive control include: abnormal low voltage working mode, normal working mode, abnormal high voltage working mode, first low voltage crossing working mode, second low voltage crossing working mode and high voltage crossing working mode. For the different working modes of these reactive controls, the control method of the present application gives corresponding judgment conditions, which are as follows.

[0057] When U m Meet U m ≤k L2 U N When the reactive power control is in Figure 3 The second low voltage ride through operating mode is shown.

[0058] When U m Satisfy k L2 U N m ≤k L1 U N When the reactive power control is in Figure 3 The first low voltage ride through operating mode is shown.

[0059] When U m Satisfy k L1 U N m ≤k L U N When the reactive power control is in Figure 2 Abnormal low voltage operating mode shown.

[0060] When U m Satisfy k L U N m <k H U N When , reactive power control is in normal working mode.

[0061] When U m Satisfy k H U N ≤U m <k H1 U N When the reactive power control is in abnormally high voltage working mode.

[0062] When U m Satisfy k H1 U N ≤U m When the reactive power control is in Figure 3 The high voltage ride through mode of operation is shown.

[0063] Among them, U m ​​​is the amplitude of the positive sequence component of the AC system voltage, U N is the rated value of the positive sequence component of the AC system voltage, k L ,k L1 ,k L2 ,k H ,k H1 All are voltage coefficients and satisfy the relationship: 0 <k L2 <k L1 <k L <1 <k H <k H1 .

[0064] S3: Output reactive power instruction according to the judgment result of the working mode and execute the instruction.

[0065] According to the judgment result of the above working mode, the reactive inner loop current or reactive command required for reactive power control is output accordingly.

[0066] Specifically, when the reactive power control is in the second low voltage ride-through working mode, its reactive current inner loop reference instruction i qref =0 or i qref =k LF2 ; where k LF2 is the reactive current reference command setting value in the second low voltage ride-through working mode, satisfying: 0≤k LF2 ≤1p.u.

[0067] When the reactive power control is in the first low voltage ride-through working mode, its reactive current inner loop reference instruction i qref =k LF1 , where k LF1 =G LF1 (U N -U m ), G LF1 It is a proportional-integral controller of the first low voltage ride-through working mode.

[0068] Furthermore, when the reactive power control is in the first low voltage ride-through working mode, 0≤k LF1 =G LF1 (U N -U m )≤I qL1set , where I qL1set It is the reactive current reference value set according to the system voltage.

[0069] When the reactive power control is in abnormally low voltage working mode, its reactive power control reference instruction Q ref =Q ord +Q L ,like Figure 4 As shown, where Q ord is the reactive power command input to the system, QL It is the additional reactive power instruction in abnormal low voltage working mode, Q L =G L (k L U N -U m ), G L It is a proportional-integral controller for abnormal low voltage operation mode.

[0070] Further, such as Figure 4 As shown, the input reactive power command Q ord Satisfaction: Q min ≤Q ord ≤Q max , reactive power control reference instruction Q ref Satisfaction: Q min ≤Q ref ≤Q max , where Q min ,Q max are the minimum and maximum reactive power values ​​calculated based on the system.

[0071] When the reactive power control is in normal working mode, its reactive power control reference instruction Q ref =Q ord .

[0072] When the reactive power control is in abnormally high voltage working mode, its reactive power control reference instruction Q ref =Q ord +Q H ,like Figure 4 As shown, Q H It is the additional reactive power instruction in abnormally high voltage working mode, Q H =G H (k H U N -U m ), G H It is a proportional-integral controller for abnormally high voltage operation mode.

[0073] When the reactive power control is in the high voltage ride-through mode, the reactive current inner loop reference command i qref =k HF1 , where k HF1 =G HF1 (U N -U m ), G HF1 It is a proportional-integral controller for high voltage ride-through mode.

[0074] Furthermore, when the reactive power control is in the high voltage ride-through mode, I qHset ≤k HF1 =G HF1 (U N-U m )≤0, where I qHset It is the reactive current reference value set according to the system voltage.

[0075] S4: Synchronously transmit the judgment result of the working mode and the reactive power instruction to the reactive power control device of the power grid.

[0076] S5: The grid reactive power control device performs reactive power control in response to the reactive power control instruction.

[0077] This application uses a flexible direct current transmission reactive control device to determine the working mode of reactive control, and outputs reactive instructions according to the working mode. At the same time, the flexible direct current transmission system executes the reactive instruction to output reactive power, and then synchronously transmits the judgment result of the working mode of reactive control and the reactive instruction to the power grid reactive control device. The power grid reactive control device issues the corresponding reactive control instruction, and uses reactive capacitors and reactors to replace the above reactive power, thereby realizing online automatic control of reactive power and voltage. It avoids the operator's frequent manual adjustment of reactive power in steady state, effectively liberates manpower, and at the same time realizes the support of system voltage and rapid recovery of voltage in case of fault.

[0078] It should be noted that the present application detects the amplitude of the positive-sequence component of the AC system voltage and can divide the reactive power control working mode according to the rated value of the positive-sequence component of the AC system voltage and the corresponding voltage coefficient. The measurement data is small and the calculation involved is simple, thus avoiding complicated data measurement and complex calculation.

[0079] The embodiment of the present application further provides a reactive power control system for flexible direct current power transmission, which is applied to the reactive power control method for flexible direct current power transmission as described in any of the above embodiments, wherein the reactive power control system comprises: a reactive power control device for flexible direct current power transmission and a reactive power control device for a power grid which are electrically connected;

[0080] The flexible direct current power transmission reactive power control device comprises:

[0081] The reactive working mode judgment module is used to judge the working mode of the reactive control according to the detected data and obtain the result of the working mode judgment;

[0082] A reactive instruction output module, used for outputting a reactive current inner loop reference instruction or a reactive control reference instruction or an additional reactive instruction for an abnormally low voltage working mode or an additional reactive instruction for an abnormally high voltage working mode according to the result of the reactive working mode judgment module;

[0083] A reactive communication module, used for transmitting the results of the reactive working mode determination module and the reactive instruction output module to the power grid reactive control device, and receiving reactive control instructions issued by the power grid reactive control device;

[0084] A reactive power execution module, used for executing reactive power instructions by taking the result of the reactive power instruction output module as a reference value;

[0085] The grid reactive power control device puts the corresponding reactive reactor or capacitor into operation according to the communication data transmitted by the reactive power communication module: the additional reactive power instruction of the abnormally low voltage working mode or the additional reactive power instruction of the abnormally high voltage working mode.

[0086] In some embodiments, the communication content between the reactive communication module and the grid reactive control device also includes: the operation mode of the flexible direct current transmission system, the reactive limit value, the unlocking state and the reactive control mode.

[0087] The flexible DC transmission system transmits these communication contents to the grid reactive power control device through the reactive power communication module, so that the grid reactive power control device can monitor the working status of the flexible DC transmission system in real time, and then can promptly and reliably control the flexible DC transmission system.

[0088] In some embodiments, the period during which the grid reactive power control device switches on or off reactive capacitors or reactors is greater than or equal to reactive power execution time of the flexible direct current transmission system.

[0089] It should be noted that the reactive power control device of the power grid in the present application is based on the communication data transmitted by the reactive communication module: the additional reactive power instruction of the abnormally low voltage working mode or the additional reactive power instruction of the abnormally high voltage working mode, and puts into operation the corresponding reactive reactor or capacitor to which it belongs, with the purpose of replacing the additional reactive power output by the flexible DC transmission system, thereby meeting the dual requirements of steady-state reactive power control and fault reactive power control. At this time, it is ensured that the cycle of putting into operation or removing the reactive capacitor or reactor is greater than or equal to the reactive power execution time of the flexible DC transmission system, and that the reactive capacitor or reactor can fully complete the replacement of the additional reactive power output by the flexible DC transmission system, thereby ensuring the steady-state reactive power control and fault reactive power control of the system.

[0090] In some embodiments, the grid reactive power control device may send a reactive power command value to the flexible DC transmission reactive power control device, and the reactive power command value may be used as the reactive power command Q input by the system. ord This configuration eliminates the need to set up a control unit in the flexible DC power transmission reactive power control device or the flexible DC power transmission system to control the system to input reactive power instructions.

[0091] In summary, the reactive power control method and system of a flexible direct current transmission of the present application fully utilize the reactive power of the flexible direct current transmission system itself, output different reactive inner loop currents or reactive commands through the judgment of the reactive control working mode, realize automatic control of the reactive power and voltage of the power grid, and avoid the operator manually and frequently adjusting the reactive power in steady state; utilize the reactive power rapid response capability of the flexible direct current transmission system to rapidly adjust the AC voltage when the AC voltage is abnormal, and at the same time, exchange information with the reactive power control device of the power grid, and the reactive power control device of the power grid invests corresponding reactive capacitors and reactors according to the exchanged information to replace the additional reactive power output by the flexible direct current transmission system, thereby meeting the dual needs of steady-state reactive power control and fault reactive power control.

[0092] The above embodiments are only for illustrating the technical concept of the present application and cannot be used to limit the protection scope of the present application. A person skilled in the art should understand that any modification or equivalent replacement of the specific implementation of the present application without departing from the technical concept and scope proposed by the present application should be included in the scope of the claims of the present application.

Claims

1. A reactive power control method for flexible direct current transmission, characterized in that: The steps include: Detect system runtime data; Determine the working mode of reactive power control based on the detected data; Output reactive power instruction according to the judgment result of working mode and execute the instruction; Synchronously transmit the judgment result of the working mode and the reactive power instruction to the reactive power control device of the power grid; The reactive power control device of the power grid performs reactive power control in response to the reactive power control instruction issued.

2. The reactive power control method for flexible direct current transmission according to claim 1, characterized in that: The operating modes include an abnormally low voltage operating mode, a normal operating mode, an abnormally high voltage operating mode, a first low voltage ride through operating mode, a second low voltage ride through operating mode, and a high voltage ride through operating mode.

3. The reactive power control method for flexible direct current transmission according to claim 2, characterized in that: When U m Meet U m ≤k L2 U N When the reactive power control is in the second low voltage ride-through working mode; When U m Satisfy k L2 U N m ≤k L1 U N When the reactive power control is in the first low voltage ride-through working mode;​ When U m Satisfy k L1 U N m ≤k L U N When , the reactive power control is in the abnormally low voltage working mode;​ When U m Satisfy k L U N m <k H U N When , the reactive power control is in the normal working mode;​ When U m Satisfy k H U N ≤U m <k H1 U N When , the reactive power control is in the abnormally high voltage working mode; When U m Satisfy k H1 U N ≤U m When , the reactive power control is in the high voltage ride through working mode; Among them, U m is the amplitude of the positive sequence component of the AC system voltage, U N is the rated value of the positive sequence component of the AC system voltage, k L ,k L1 ,k L2 ,k H ,k H1 All are voltage coefficients and satisfy the relationship: 0 <k L2 <k L1 <k L <1 <k H <k H1 .

4. The reactive power control method for flexible direct current transmission according to claim 3 is characterized in that: When the reactive power control is in the second low voltage ride-through working mode, its reactive current inner loop reference instruction i qref =0 or i qref =k LF2 ; where k LF2 is the reactive current reference command setting value in the second low voltage ride-through working mode, satisfying: 0≤k LF2 ≤1p.u.; When the reactive power control is in the first low voltage ride-through working mode, its reactive current inner loop reference instruction i qref =k LF1 , where k LF1 =G LF1 (U N -U m ), G LF1 A proportional-integral controller for a first low voltage ride-through operating mode; When the reactive power control is in abnormally low voltage working mode, its reactive power control reference instruction Q ref =Q ord +Q L , where Q ord is the reactive power command input to the system, Q L It is the additional reactive power instruction in abnormal low voltage working mode, Q L =G L (k L U N -U m ), G L A proportional-integral controller for abnormally low voltage operation mode; When the reactive power control is in normal working mode, its reactive power control reference instruction Q ref =Q ord ; When the reactive power control is in abnormally high voltage working mode, its reactive power control reference instruction Q ref =Q ord +Q H , where Q H It is the additional reactive power instruction in abnormally high voltage working mode, Q H =G H (k H U N -U m ), G H Proportional-integral controller for abnormally high voltage operation mode; When the reactive power control is in the high voltage ride-through mode, the reactive current inner loop reference command i qref =k HF1 , where k HF1 =G HF1 (U N -U m ), G HF1 It is a proportional-integral controller for high voltage ride-through mode.

5. The reactive power control method for flexible direct current transmission according to claim 4 is characterized in that: When the reactive power control is in the first low voltage ride-through mode, 0≤k LF1 =G LF1 (U N -U m )≤I qL1set , I qL1set It is the reactive current reference value set according to the system voltage.

6. The reactive power control method for flexible direct current transmission according to claim 4, characterized in that: Input reactive power command Q ord Satisfaction: Q min ≤Q ord ≤Q max , reactive power control reference instruction Q ref Satisfaction: Q min ≤Q ref ≤Q max , Q min ,Q max are the minimum and maximum reactive power values ​​calculated based on the system.

7. The reactive power control method for flexible direct current transmission according to claim 4, characterized in that: When the reactive power control is in the high voltage ride through mode, I qHset ≤k HF1 =G HF1 (U N -U m )≤0,I qHset It is the reactive current reference value set according to the system voltage.

8. A reactive power control system for flexible direct current transmission, characterized in that: The reactive power control method for flexible direct current transmission applied to any one of claims 1 to 7, wherein the reactive power control system comprises: a flexible direct current transmission reactive power control device and a power grid reactive power control device electrically connected; The flexible direct current power transmission reactive power control device comprises: The reactive working mode judgment module is used to judge the working mode of the reactive control according to the detected data and obtain the result of the working mode judgment; A reactive instruction output module, used for outputting a reactive current inner loop reference instruction or a reactive control reference instruction or an additional reactive instruction for an abnormally low voltage working mode or an additional reactive instruction for an abnormally high voltage working mode according to the result of the reactive working mode judgment module; A reactive communication module, used for transmitting the results of the reactive working mode determination module and the reactive instruction output module to the power grid reactive control device, and receiving reactive control instructions issued by the power grid reactive control device; A reactive power execution module, used for executing reactive power instructions by taking the result of the reactive power instruction output module as a reference value; The grid reactive power control device puts the corresponding reactive reactor or capacitor into operation according to the communication data transmitted by the reactive power communication module: the additional reactive power instruction of the abnormally low voltage working mode or the additional reactive power instruction of the abnormally high voltage working mode.

9. The reactive power control system of flexible direct current transmission according to claim 8, characterized in that: The communication content between the reactive communication module and the reactive power control device of the power grid also includes: the operation mode of the flexible direct current transmission system, the reactive power limit value, the unlocking state and the reactive power control mode.

10. The reactive power control system of flexible direct current transmission according to claim 8, characterized in that: The period in which the reactive power control device of the power grid switches on or off reactive capacitors or reactors is greater than or equal to the reactive power execution time of the flexible direct current transmission system.

11. The reactive power control system of flexible direct current transmission according to claim 8, characterized in that: The grid reactive power control device sends a reactive power command value to the flexible DC power transmission reactive power control device, and the reactive power command value is used as the reactive power command Q input by the system. ord .

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