CN114006395B - Hybrid multi-feed direct current system, reactive coordination control method thereof and controller - Google Patents

Hybrid multi-feed direct current system, reactive coordination control method thereof and controller Download PDF

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Publication number
CN114006395B
CN114006395B CN202111179600.5A CN202111179600A CN114006395B CN 114006395 B CN114006395 B CN 114006395B CN 202111179600 A CN202111179600 A CN 202111179600A CN 114006395 B CN114006395 B CN 114006395B
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current
direct current
pcc
voltage
reactive
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CN114006395A (en
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姚伟
李佳
严才
夏勇军
张侃君
陈堃
胡兴洋
文劲宇
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Huazhong University of Science and Technology
Electric Power Research Institute of State Grid Hubei Electric Power Co Ltd
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Huazhong University of Science and Technology
Electric Power Research Institute of State Grid Hubei Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The application discloses a mixed multi-feed direct current system, a reactive coordination control method and a controller thereof, wherein the control method comprises the following steps: step S1: obtaining a public bus alternating voltage U PCC Comparing the current alternating voltage U PCC Maximum operating voltage U max And a minimum operating voltage U min : when U is PCC ＞U max When the step is performed, the step S2 is skipped; when U is PCC ＜U min When the step is performed, the step S3 is skipped; when U is min ≤U PCC ≤U max When the step is performed, the step S4 is skipped; step S2: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationSetting the reactive current output quantity of the external loop fixed alternating voltage control to judge whether U is satisfied PCC ≤U rate If yes, jumping to the step S4, otherwise, repeating the step S2; step S3: will reference valuePositive sequence current q-component set to feed into common bus of phase-regulatorJudging whether U is satisfied PCC ≥U rate If yes, jumping to the step S4, otherwise, repeating the step S3; step S4: will reference valueSet to 0. By the method, the reactive response speed can be increased.

Description

Hybrid multi-feed direct current system, reactive coordination control method thereof and controller
Technical Field
The application belongs to the field of power grid control, and in particular relates to a hybrid multi-feed direct current system, a reactive coordination control method and a controller thereof.
Background
With the wide application of high-voltage direct-current transmission, the problem of strong-direct-weak intersection of the power system in China is prominent, and the reactive power supporting capability of the alternating-current side is reduced. In order to ensure safe and stable operation of the direct current system, the national grid company plans to configure a phase regulator at a transmitting and receiving end converter station of a cross-region high-voltage direct current project, and dynamic reactive support is simultaneously provided by the phase regulator and a flexible direct current transmission (Voltage Source Converter based High Voltage Direct Current, VSC-HVDC) converter station in the mixed multi-feed direct current system. The phase modulator can emit a large amount of reactive power at the moment of failure as synchronous rotating equipment, so that the reactive power supporting capacity of the system is improved. The existing research is mainly aimed at providing dynamic reactive support for high-voltage direct current transmission (Line Commutated Converter based High Voltage Direct Current, LCC-HVDC) independently by a plurality of reactive compensation devices of a voltage regulator or VSC-HVDC, however, the reactive response speed of the mode is still to be improved, and therefore, the reactive coordination control of the voltage regulator and the VSC-HVDC in a mixed multi-feed direct current system is further researched to further improve the reactive response speed.
Disclosure of Invention
In order to meet the above defects or improvement demands of the prior art, the application provides a hybrid multi-feed direct current system, a reactive coordination control method and a controller thereof, and aims to accelerate the reactive response speed of reactive compensation equipment.
To achieve the above object, according to a first aspect of the present application, there is provided a reactive power coordination control method of a hybrid multi-feed direct current system including a common bus, and a flexible direct current power transmission converter station and a regulator for feeding reactive power to the common bus, the control method comprising:
step S1: obtaining the current alternating current voltage U of a public bus PCC Comparing the current alternating voltage U of the public bus PCC Maximum operating voltage U max And a minimum operating voltage U min : when U is PCC ＞U max When the step is performed, the step S2 is skipped; when U is PCC ＜U min When the step is performed, the step S3 is skipped; when U is min ≤U PCC ≤U max When the step is performed, the step S4 is skipped;
step S2: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationThe reactive current output quantity controlled by the external ring fixed alternating voltage is set, and the current alternating voltage U of the public bus is judged PCC Whether or not it is smaller than or equal to the rated operating voltage U rate If yes, jumping to the step S4, otherwise, repeating the step S2;
step S3: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationPositive sequence current q-component set to feed a common bus for a dimmer +.>Judging the current alternating current voltage U of a public bus PCC Whether or not it is greater than or equal to the rated operating voltage U rate If yes, jumping to the step S4, otherwise, repeating the step S3;
step S4: to be flexible and straightReference value of positive sequence current q component of positive sequence inner loop decoupling control of current transmission converter stationSet to 0.
Preferably, the reactive outer ring control at two ends of the flexible direct current transmission converter station adopts fixed alternating voltage control, the active outer ring control at the transmitting end adopts fixed direct current voltage control, and the active outer ring control at the receiving end adopts fixed active power control.
Preferably, in adjusting the reference valueLimiting the reference value->Is greater than the maximum amplitude i of (1) qmax ＝Q max /S n Limiting the reference value->Is the minimum amplitude i of (2) qmin ＝-Q max /S n Wherein Q is max Is the reactive regulation maximum value of the flexible direct current power transmission converter station,/-for>S n Is rated full-load power of flexible direct-current transmission converter station, P n Is the operating power of the flexible direct current transmission converter station.
Preferably, in adjusting the reference valueWhen, limiting the reference value according to the preset parameters>Is a rate of change of (c).
Preferably, the negative sequence current q-component and d-component of the negative sequence inner loop decoupling control of the flexible direct current power transmission converter station are set to 0.
Preferably, the alternating current on the public bus is rectified and inverted through the high-voltage direct-current transmission converter station and then is transmitted to the load center.
According to a second aspect of the present application there is provided a hybrid multi-feed dc system reactive coordination controller for controlling a flexible dc power transmission converter station and a dimmer to feed reactive power to a common bus, the controller comprising:
an acquisition unit for acquiring the current alternating voltage U of the public bus PCC ；
A judging unit for comparing the current AC voltage U of the public bus PCC Maximum operating voltage U max And a minimum operating voltage U min : when U is PCC ＞U max When the current setting unit sends a first instruction to the current setting unit and the common bus is at the current alternating voltage U PCC Less than or equal to rated operating voltage U rate Sending a third instruction; when U is PCC ＜U min When the current setting unit sends a second instruction to the current setting unit and the current alternating voltage U of the public bus is reached during the second instruction PCC Greater than or equal to rated operating voltage U rate Sending a third instruction; when U is min ≤U PCC ≤U max When the current setting unit is started, a third instruction is sent to the current setting unit;
a current setting unit for decoupling the reference value of the positive sequence current q component of the positive sequence inner loop of the flexible direct current transmission converter station when receiving the first instructionSetting the reactive current output quantity of the external loop fixed alternating voltage control and receiving a second instruction to decouple the reference value of the positive sequence current q component of the positive sequence internal loop of the flexible direct current transmission converter stationPositive sequence current q-component set to feed a common bus for a dimmer +.>Upon receiving the third instructionReference value +.f. of positive sequence current q-component for decoupling control of positive sequence inner loop of flexible DC power transmission converter station>Set to 0.
Preferably, the method further comprises:
a current limiting unit for adjusting the reference valueLimiting the reference value->Is greater than the maximum amplitude i of (1) qmax ＝Q max /S n Limiting the reference value->Is the minimum amplitude i of (2) qmin ＝-Q max /S n Wherein Q is max Is the reactive regulation maximum value of the flexible direct current power transmission converter station,/-for>S n Is rated full-load power of flexible direct-current transmission converter station, P n Is the operating power of the flexible direct current transmission converter station.
According to a third aspect of the present application, there is provided a hybrid multi-feed dc system comprising a common bus, a flexible dc power converter station and a rectifier feeding power to the common bus, a high voltage dc power converter station delivering power from the common bus to a load center, and a controller, wherein the controller is a reactive coordination controller of the hybrid multi-feed dc system described above.
In general, compared with the prior art, the application is based on the current alternating voltage U of the public bus PCC And maximum operating voltage U max And a minimum operating voltage U min To adjust the reference value of the positive sequence current q component of the positive sequence inner loop decoupling control of VSC-HVDCWhen the public bus is at the current alternating voltage U PCC At the allowable minimum operating voltage U min And maximum allowable operating voltage U max In between, reference value +.f of positive sequence current q-component of positive sequence inner loop decoupling control of VSC-HVDC>Set to 0, i.e. preferably with a dimmer to adjust reactive power, VSC-HVDC does not participate in the adjustment of reactive power; when the public bus AC voltage U PCC Fluctuation is greater than allowable maximum operating voltage U max When the VSC-HVDC auxiliary regulator is used for reactive power regulation, the reference value of the positive sequence current q component of the positive sequence inner loop decoupling control of the VSC-HVDC is +.>The reactive current output quantity is set to be the reactive current output quantity controlled by external fixed alternating voltage, and the VSC-HVDC is used for assisting in absorbing reactive power; when the public bus AC voltage U PCC Fluctuation is smaller than allowable maximum operating voltage U max When the VSC-HVDC auxiliary regulator is used for reactive power regulation, the reference value of the positive sequence current q component of the positive sequence inner loop decoupling control of the VSC-HVDC is +.>Positive sequence current q-component set to feed a common bus for a dimmer +.>The reactive response of the VSC-HVDC is enabled to follow the reactive response of the rectifier, the reactive response speed of the VSC-HVDC is accelerated, the voltage reduction of the public bus at the moment of fault occurrence and the reactive power overcompensation of the VSC-HVDC after fault removal are restrained.
Drawings
FIG. 1 is a flow chart of a reactive coordination control method of a hybrid multi-feed DC system according to an embodiment of the application;
FIG. 2 is a schematic diagram of a hybrid multi-feed DC system according to an embodiment of the application;
fig. 3 is a basic structural diagram of a camera according to an embodiment of the present application;
FIG. 4 is a schematic illustration of an embodiment of the present application adjusting a phasor diagram of the camera when the camera is over-excited and under-excited;
fig. 5 is a VSC-HVDC equivalent model diagram in an embodiment of the present application;
fig. 6 is a block diagram of VSC-HVDC positive and negative sequence current inner loop control in an embodiment of the present application;
FIG. 7 is a reference value of the positive sequence current q component of the VSC-HVDC positive sequence inner loop decoupling control in an embodiment of the applicationIs selected by a user;
fig. 8 is an analysis diagram of a dimmer and VSC-HVDC fixed ac voltage control in an embodiment of the present application;
FIG. 9 is a graph of simulation results of independent control and coordinated control under a symmetric failure in an embodiment of the present application;
FIG. 10 is a graph of simulation results of independent control and coordinated control under an asymmetric fault in an embodiment of the present application.
Detailed Description
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application. In addition, the technical features of the embodiments of the present application described below may be combined with each other as long as they do not collide with each other.
To facilitate an understanding of the present application, the main components of the hybrid multi-feed dc system of the present application will be described. As shown in fig. 2, the multi-feed direct current system comprises a common bus, VSC-HVDC and a regulator, the VSC-HVDC feeds power to the common bus through a tie, the LCC-HVDC feeds power to a load center, P VSC And Q VSC Representing the active and reactive power, respectively, of a VSC-HVDC feed to a common bus, U PCC Representing a common busIs set, the alternating voltage amplitude of (a) is set. Due to the close electrical distance between the VSC-HVDC receiving end and the LCC-HVDC rectifying side, the VSC-HVDC receiving end may provide dynamic reactive support for the LCC-HVDC rectifying side. In order to further improve the reactive power supporting capability of the grid system at the LCC-HVDC rectifying side, a phase regulator, Q, is also arranged at the LCC-HVDC rectifying side SC Representing the reactive power that the dimmer feeds into the common bus.
The basic structure of the camera system is as shown in fig. 3, and mainly includes a camera body, an excitation system, a starting system, a cooling system, a step-up transformer, and the like. The phase-change machine is actually a synchronous motor operating without mechanical load (no-load), and the active power absorbed from the electric network only supplies the loss of the motor itself, so that the electromagnetic power and the power factor of the motor are approximately zero during operation.
If the total loss of the regulator is ignored, the armature current is all reactive, and the electromotive force equation is:
in the middle ofFor stator voltage, +.>Is electromotive force (E)>For armature current, X S Is equivalent reactance. The phasor diagram of the shunt in the over-excitation and under-excitation is shown in FIG. 4, and the shunt is +.>Advance->Outputting inductive reactive power; in case of lack of excitation->Hysteresis->Absorbing inductive reactive power. So that the property and the magnitude of the reactive power thereof can be flexibly adjusted as long as the exciting current is adjusted.
On the dq coordinate axis, the reactive power provided by the camera to the system is:
Q SC ＝U q i d -U d i q (2)
q in SC Is the reactive power provided by the camera, U d And U q D-axis component and q-axis component, i of voltage of high-voltage bus connected by camera d And i q The d-axis component (active current) and the q-axis component (reactive current) of the current, respectively. Neglecting all losses, with U d Approximately U, where formula (2) can be expressed as:
Q SC ≈-U d i q ≈-Ui q (3)
during system disturbance, the regulator can be equivalent to a voltage source with constant internal potential, and then reactive current can be expressed as:
in E' q Is the internal potential of the camera, U is the voltage of the camera connected to the high-voltage bus, X' d Is the sub-transient reactance of the camera, X T Is the impedance of the step-up transformer.
As can be seen from the formula (4), in the disturbance process of the system, the magnitude of the reactive current fed into the public bus by the regulator is mainly related to the voltage variation amplitude and the secondary transient reactance, and the larger the voltage variation amplitude is, the smaller the secondary transient reactance is, and the larger the reactive current is. The transient reactance of the new generation of cameras widely used at present is smaller, and a large amount of reactive power is immediately emitted at the moment of failure, so that the reactive power supporting capability of a power grid system is effectively improved.
Wherein the method comprises the steps ofThe VSC-HVDC can be regarded as an ac voltage source with adjustable phase and amplitude, the equivalent model of which is shown in fig. 5, wherein the reactance is the equivalent reactance of the bridge arm reactance and the leakage reactance of the converter transformer. Wherein, us < 0 > is the voltage of the converting bus, and the initial phase angle is set to 0; uc is the fundamental voltage amplitude of the outlet of the VSC converter; delta is the phase shift angle; xc is the equivalent reactance; is the line current; p (P) VSC And Q VSC Active power and reactive power output by the VSC-HVDC converter respectively.
The VSC-HVDC adopts a vector control method based on direct current control, and has quick current response characteristic and good current limiting capability. The vector control consists of an outer loop control strategy and an inner loop control strategy, and the voltage outer loop provides a current reference value for the current inner loop.
The outer loop control mainly comprises active power control and reactive power control, and the outer loop control adopts the reactive power control. The reactive power control comprises fixed reactive power control and fixed alternating voltage control, wherein the fixed alternating voltage control is adopted in the application, and the alternating bus voltage is stabilized through the fixed alternating voltage control. The control circuit of the external loop ac control is a conventional circuit, and will not be described in detail herein.
The inner loop control adopts positive sequence current and negative sequence current decomposition to independently control. Fig. 6 shows a positive and negative sequence current inner loop control block diagram of the VSC-HVDC, wherein the positive and negative sequence current inner loop control block diagram is also a conventional circuit and will not be described in detail herein. The main function of the positive sequence current inner loop controller is to regulate the power/voltage of the VSC-HVDC converter station according to the power/voltage command of the outer loop control; the main function of the negative sequence current inner loop controller is to restrain the negative sequence current and to make the reference value of the d component of the negative sequence currentAnd reference value of q component->Set to 0.
In the application, the reference value of the q component of the positive sequence current is controlled mainly by setting the inner loop of the positive sequence currentTo regulate the speed of reactive response of the VSC-HVDC. According to the current AC voltage U of the public bus PCC Reference value +.f. of positive sequence current q-component for positive sequence inner loop decoupling control>Is selected from the group consisting of (a). Specifically, reference value->There are three options. The first option is to add a reference value +.>The reactive current output quantity set to the external fixed AC voltage control, i.e. the output current corresponding to Mode 1 in FIG. 7, will be referenced +.>Access Mode 1 is denoted as switching the Switch to access port 1, i.e., switch=1. The second option is to add a reference value +.>Positive sequence current q-component set to feed a common bus for a dimmer +.>I.e. the output current corresponding to Mode 2 in FIG. 7, will be referenced +.>Access Mode 2 is denoted as switching the Switch to access port 2, i.e., switch=2. The third option is to add the reference value +.>Setting to 0, i.e. the output current corresponding to Mode0 in fig. 7, will reference the value +.>Access Mode0 is denoted as switching the Switch to access port 0, i.e., switch=0.
Referring to fig. 1, fig. 1 is a flowchart of a reactive coordination control method of a hybrid multi-feed dc system according to an embodiment of the application, where the control method includes:
step S1: obtaining the current alternating current voltage U of a public bus PCC Comparing the current alternating voltage U of the public bus PCC Maximum operating voltage U max And a minimum operating voltage U min : when U is PCC ＞U max When the step is performed, the step S2 is skipped; when U is PCC ＜U min When the step is performed, the step S3 is skipped; when U is min ≤U PCC ≤U max If so, the process goes to step S4.
In one embodiment, the current AC voltage U of the common bus can be compared PCC And maximum operating voltage U max Judging whether U is satisfied PCC ＞U max If yes, jumping to step S2, otherwise, further comparing the current alternating current voltage U of the public bus PCC And a minimum operating voltage U min Judging whether U is satisfied PCC ＜U min If yes, go to step S3, if no, go to step S4.
Step S2: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationThe reactive current output quantity controlled by the external ring fixed alternating voltage is set, and the current alternating voltage U of the public bus is judged PCC Whether or not it is smaller than or equal to the rated operating voltage U rate If yes, jumping to the step S4, otherwise, repeating the step S2.
In one embodiment, step S2 includes two sub-steps:
substep S2-1: let switch=1, i.e. the reference valueAnd setting the reactive current output quantity of the external ring fixed alternating voltage control.
Specifically, when U PCC ＞U max The current common bus voltage is too high, and reactive power absorption is needed. The phase-shifting device has stronger overcurrent capability, better delay phase capability (output reactive power) and capability of sending out reactive power with rated capacity more than 2 times in short time, poorer phase-advancing capability (absorption reactive power) and capability of only absorbing reactive power with about half of rated capacity, so that the reactive power of a public bus is absorbed by utilizing the feedback regulation function of the phase-shifting device, VSC-HVDC auxiliary absorption reactive power is added at the same time, and the reference value is used for adjusting the phase-shifting deviceThe reactive current output quantity is set to be the reactive current output quantity controlled by the external fixed alternating voltage, so that the VSC-HVDC can absorb reactive power, and the voltage regulator can absorb bus reactive power in combination with the VSC-HVDC, thereby better inhibiting the rise of the common bus voltage.
Substep S2-2: judging whether the current voltage of the public bus meets U PCC ≤U rate If yes, go to step S4, if no, continue to execute substep S2-1.
Specifically, during the period of absorbing reactive power by the VSC-HVDC, the busbar voltage gradually decreases, and when the busbar voltage reaches the rated value, the system resumes normal operation, at this time, the step S4 can be skipped, and the VSC-HVDC can be exited. The reactive power is regulated by the regulating camera preferentially under the conditions of normal working conditions and small voltage disturbance, the reactive power is not regulated by the VSC-HVDC, and the regulating capacity of the regulating camera is fully utilized.
Step S3: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationPositive sequence current q-component set to feed a common bus for a dimmer +.>Judging the common bus asFront ac voltage U PCC Whether or not it is greater than or equal to the rated operating voltage U rate If yes, jumping to the step S4, otherwise, repeating the step S3.
In one embodiment, step S3 also includes two sub-steps:
substep S3-1: let switch=2, i.e. the reference valuePositive sequence current q-component set to feed a common bus for a dimmer +.>
Specifically, when U PCC ＜U min Indicating that the current common bus voltage is too low and reactive compensation is needed. At this point, the regulator and the VSC-HVDC together provide reactive compensation for the common bus.
In the conventional art, it is common that the camera and the VSC-HVDC operate independently. However, at the moment of failure occurrence and after failure removal, the reactive response speed of the camera is faster than that of VSC-HVDC. As shown in fig. 8, at the moment of failure, the common bus voltage is rapidly reduced, the reactive power output of the voltage regulator reaches a maximum value at about 35ms, and the reactive power output of the VSC-HVDC reaches a maximum value at about 80ms under the control of the fixed ac voltage, so that the response speed of the output reactive power of the voltage regulator at the moment of failure is faster than that of the VSC-HVDC; after the fault is removed, the common bus voltage rises, the reactive power output by the phase-regulating device is reduced along with the rise, but the VSC-HVDC cannot immediately reduce the output of the reactive power under the control of the fixed alternating voltage, reactive overcompensation occurs, the common bus voltage is lifted, the current of an LCC-HVDC direct current line is increased, the required phase-change area of an LCC-HVDC inversion side converter valve is increased, and the risk of phase-change failure of the LCC-HVDC is increased. In general, the reactive response speed of the phase-locked loop is faster than that of the VSC-HVDC under the control of fixed alternating voltage at the moment of fault occurrence and after fault removal.
The present application thus sets the reactive current reference value of the inner loop control of the VSC-HVDC at this stage toThe reactive current change of the VSC-HVDC is enabled to follow the reactive current change of the phase-adjusting device, namely the reactive power change of the VSC-HVDC is enabled to follow the reactive power change of the phase-adjusting device, so that the reactive response speed of the VSC-HVDC at the moment of fault occurrence and after fault removal can be quickened, the reactive power is quickly transmitted to a public bus at the moment of fault occurrence, and the reactive power is timely reduced to be output after the fault removal.
Substep S3-2: judging whether the current voltage of the public bus meets U PCC ≥U rate If yes, go to step S4, if no, continue to execute substep S3-1.
The VSC-HVDC following regulator compensates reactive power for a public bus, the voltage of the public bus is raised, and after a fault is removed, the VSC-HVDC following regulator reduces the output of the reactive power until the voltage of the public bus U PCC Is raised to rated voltage U rate The system resumes normal operation, at which point it may jump to step S4, exiting the VSC-HVDC.
Step S4: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationSet to 0.
Let switch=0, reference valueAnd the voltage regulator is set to be 0, the VSC-HVDC is exited, namely, the reactive power is regulated by the voltage regulator preferentially under the conditions of normal working conditions and small voltage disturbance, the VSC-HVDC does not participate in reactive power regulation, and the regulation capacity of the voltage regulator is fully utilized.
In the above steps, the current AC voltage U of the public bus can be obtained by measurement PCC . Maximum operating voltage U max Minimum operating voltage U min And rated operating voltage U rate Are known parameters. In general, the steady-state voltage operating range of the bus is usually 0.95pu to 1.05pu, and the rated operating voltage U of the common bus is set rate =1.0 pu, allowing maximum operating voltage U max =1.05pu, allowing minimum operating voltage U min ＝0.95pu。
In an embodiment, to ensure normal operation of the VSC-HVDC, the reference value is adjustedWhen limiting the reference valueIs greater than the maximum amplitude i of (1) qmax ＝Q max /S n Limiting the reference value->Is the minimum amplitude i of (2) qmin ＝-Q max /S n Wherein Q is max Is the reactive regulation maximum of VSC-HVDC, < >>S n Is the rated full power of VSC-HVDC, P n Is the operating power of the VSC-HVDC. Specifically, considering that the VSC-HVDC has limited overload bearing capacity, the VSC-HVDC reactive regulation limit is calculated according to the full load power, in this embodiment, the rated full load power of the VSC-HVDC is 1250mw, the active power delivered by the operation of the VSC-HVDC receiving end is 1000MW, and the maximum value of the reactive regulation of the VSC-HVDC is 750Mvar, so that the following is set>Is limited i qmax ＝0.6pu，i qmin ＝-0.6pu。
In one embodiment, the reference value is adjustedIn order to avoid that the current change is too fast to influence the normal operation of the device, a speed limiter is also arranged, and the amplitude limit is set to be +/-50/s.
In order to verify the effectiveness of the reactive power coordination control method of the hybrid multi-feed direct current system, a hybrid multi-feed direct current system model with a camera access as shown in fig. 2 is built on PSCAD/EMTDC simulation software, main parameters of LCC-HVDC and VSC-HVDC direct current systems in the hybrid multi-feed direct current system are shown in table 1, and main parameters of the camera are shown in table 2. In the case, the grid systems at the two ends of the VSC-HVDC are weaker, so that the reactive outer ring control at the two ends adopts constant alternating voltage control, and in addition, the active outer ring control at the transmitting end of the VSC-HVDC adopts constant direct voltage control, and the active outer ring control at the receiving end of the VSC-HVDC adopts constant active power control.
TABLE 1
TABLE 2
Parameter name Parameter value
Rated capacity/Mvar 300
Boosting rated transformation ratio 20kV/530kV
Direct axis steady state reactance/% 150.5
Direct axis transient reactance/% 14.0
Direct axis subtotal reactance/% 11.3
Open circuit time constant/s of straight axis 8.8
Direct axis short circuit time constant/s 0.72
Forced excitation voltage multiple 3.5
In order to verify the effectiveness of the method, three-phase grounding short-circuit faults are arranged on the LCC-HVDC rectifying side, the fault occurrence time is 3.0s, the fault distance is 0.30H, and the fault duration time is 0.1s; observing the turn-off angle gamma of LCC-HVDC inversion side, and the alternating current voltage U of public bus PCC LCC-HVDC DC line current I d Reactive power Q transmitted to public bus by VSC-HVDC receiving end VSC Reactive power Q delivered to common bus by a dimmer SC The results are shown in FIG. 9. From fig. 9, from the aspect of reactive response, at the moment of occurrence of a fault, the reactive power output of the VSC-HVDC under independent control reaches a maximum value at about 80ms, the reactive power of the VSC-HVDC under coordinated control reaches a maximum value at about 50ms, and the reactive response speed under coordinated control is faster; after the fault is removed, reactive power overcompensation occurs to the VSC-HVDC under independent control, the reactive power output by the VSC-HVDC under coordination control is reduced, and the reactive response speed under coordination control is faster.
From the control effect, the voltage of the public bus is rapidly reduced at the moment of occurrence of faults, the minimum value of the voltage of the public bus under independent control is 443kV, the minimum value of the voltage of the public bus under coordinated control is 451kV, and the transient low-voltage inhibition effect under coordinated control is better; after the fault is removed, the reactive power overcompensation of the VSC-HVDC under independent control causes the commutation failure of the LCC-HVDC, and the VSC-HVDC under coordinated control reduces the output reactive power, thereby reducing the current of the LCC-HVDC direct current line, and the commutation failure of the LCC-HVDC does not occur.
To further illustrate the effectiveness of the method of the present application, the effect of independent control and coordinated control in suppressing LCC-HVDC commutation failure at different times of failure and at different failure distance conditions was observed, and the results are shown in table 3. It can be seen from table 3 that, compared with the independent control of the phase regulator and the VSC-HVDC, the reactive power coordination control method of the phase regulator and the VSC-HVDC can reduce the risk of commutation failure after the power grid fault at the transmitting end of the LCC-HVDC is removed.
TABLE 3 Table 3
To further illustrate the applicability of the method of the application, an asymmetrical fault of a single-phase-to-earth short circuit is arranged on the LCC-HVDC rectifying side, the fault occurrence time is 3.0s, the fault distance is 0.10H, the fault duration time is 0.1s, the turn-off angle gamma of the rectifier and the LCC-HVDC on the inversion side of the LCC-HVDC under independent control and coordinated control is compared, and the alternating voltage U of a public bus is calculated PCC Reactive power Q transmitted to public bus by VSC-HVDC receiving end VSC Reactive power Q delivered to common bus by a dimmer SC The results are shown in FIG. 10. As can be seen from fig. 10, at the moment of occurrence of the fault, compared with the independent control of the voltage regulator and the VSC-HVDC, the reactive response speed of the VSC-HVDC under the coordination control is faster, and the transient low voltage suppression effect is better; after fault removal, the VSC-HVDC under coordinated control reduces reactive power to be output more quickly, and transient high voltage is better restrained.
The application also relates to a hybrid multi-feed direct current system reactive power coordination controller for controlling a flexible direct current power transmission converter station and a phase-change modulator to feed reactive power into a common bus, the controller comprising:
an acquisition unit for acquiring the current alternating voltage U of the public bus PCC 。
A judging unit for comparing the current AC voltage U of the public bus PCC Maximum operating voltage U max And a minimum operating voltage U min ：
When U is PCC ＞U max When the current setting unit sends a first instruction to the current setting unit and the common bus is at the current alternating voltage U PCC Less than or equal to rated operating voltage U rate Sending a third instruction;
when U is PCC ＜U min When the current setting unit sends a second instruction to the current setting unit and the current alternating voltage U of the public bus is reached during the second instruction PCC Greater than or equal to rated operating voltage U rate Sending a third instruction;
when U is min ≤U PCC ≤U max When the current setting unit is started, a third instruction is sent to the current setting unit;
a current setting unit for decoupling the reference value of the positive sequence current q component of the positive sequence inner loop of the flexible direct current transmission converter station when receiving the first instructionSetting the reactive current output quantity of the external loop fixed alternating voltage control and receiving a second instruction to decouple the reference value of the positive sequence current q component of the positive sequence internal loop of the flexible direct current transmission converter stationPositive sequence current q-component set to feed a common bus for a dimmer +.>Reference value +.f. of positive sequence current q-component of positive sequence inner loop decoupling control of flexible DC power transmission converter station upon receipt of third instruction>Set to 0.
In one embodiment, the controller further comprises a current limiting unit for adjusting the reference valueLimiting the reference value->Is greater than the maximum amplitude i of (1) qmax ＝Q max /S n Limiting the reference value->Is the minimum amplitude i of (2) qmin ＝-Q max /S n Wherein Q is max Is the reactive regulation maximum value of the flexible direct current power transmission converter station,/-for>S n Is rated full-load power of flexible direct-current transmission converter station, P n Is the operating power of the flexible direct current transmission converter station.
The specific functions of each unit of the controller are corresponding to each step of the control method, and may be specifically described with reference to the above, and will not be repeated herein.
The application also relates to a hybrid multi-feed direct current system, as shown in fig. 2, comprising a common bus, a flexible direct current transmission converter station and a regulator for feeding power into the common bus, a high voltage direct current transmission converter station for transmitting the power of the common bus to a load center, and a controller, wherein the controller is the reactive coordination controller of the hybrid multi-feed direct current system.
The application is based on the current alternating voltage U of the public bus PCC And maximum operating voltage U max And a minimum operating voltage U min To adjust the reference value of the positive sequence current q component of the positive sequence inner loop decoupling control of VSC-HVDCWhen the public bus is at the current alternating voltage U PCC At the allowable minimum operating voltage U min And maximum allowable operating voltage U max In between, reference value +.f of positive sequence current q-component of positive sequence inner loop decoupling control of VSC-HVDC>Set to 0, i.e. preferably with a dimmer to adjust reactive power, VSC-HVDC does not participate in the adjustment of reactive power; when the public bus AC voltage U PCC Fluctuation is greater than allowable maximum operating voltage U max When the VSC-HVDC auxiliary regulator is used for reactive power regulation, the reference value of the positive sequence current q component of the positive sequence inner loop decoupling control of the VSC-HVDC is +.>The reactive current output quantity is set to be the reactive current output quantity controlled by external fixed alternating voltage, and the VSC-HVDC is used for assisting in absorbing reactive power; when the public bus AC voltage U PCC Fluctuation is smaller than allowable maximum operating voltage U max When the VSC-HVDC auxiliary regulator is used for reactive power regulation, the reference value of the positive sequence current q component of the positive sequence inner loop decoupling control of the VSC-HVDC is +.>Positive sequence current q-component set to feed a common bus for a dimmer +.>The reactive response of the VSC-HVDC is enabled to follow the reactive response of the rectifier, the reactive response speed of the VSC-HVDC is accelerated, the voltage reduction of the public bus at the moment of fault occurrence and the reactive power overcompensation of the VSC-HVDC after fault removal are restrained.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the application and is not intended to limit the application, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the application are intended to be included within the scope of the application.

Claims (9)

1. The reactive power coordination control method of the hybrid multi-feed direct current system is characterized in that the hybrid multi-feed direct current system comprises a public bus, and a flexible direct current power transmission converter station and a camera which feed reactive power into the public bus, and the control method comprises the following steps:
step S1: acquisition pinCommon bus current AC voltage U PCC Comparing the current alternating voltage U of the public bus PCC Maximum operating voltage U max And a minimum operating voltage U min : when U is PCC ＞U max When the step is performed, the step S2 is skipped; when U is PCC ＜U min When the step is performed, the step S3 is skipped; when U is min ≤U PCC ≤U max When the step is performed, the step S4 is skipped;
step S2: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationThe reactive current output quantity controlled by the external ring fixed alternating voltage is set, and the current alternating voltage U of the public bus is judged PCC Whether or not it is smaller than or equal to the rated operating voltage U rate If yes, jumping to the step S4, otherwise, repeating the step S2;
step S3: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationPositive sequence current q-component set to feed a common bus for a dimmer +.>Judging the current alternating current voltage U of a public bus PCC Whether or not it is greater than or equal to the rated operating voltage U rate If yes, jumping to the step S4, otherwise, repeating the step S3;
step S4: reference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter stationSet to 0.
2. The reactive coordination control method of a hybrid multi-feed direct current system according to claim 1, wherein reactive outer loop control at two ends of the flexible direct current power transmission converter station adopts constant alternating current voltage control, active outer loop control at a transmitting end adopts constant direct current voltage control, and active outer loop control at a receiving end adopts constant active power control.
3. The reactive power coordination control method of a hybrid multi-feed direct current system according to claim 1, wherein, in adjusting the reference valueLimiting the reference value->Is greater than the maximum amplitude i of (1) qmax ＝Q max /S n Limiting the reference value->Is the minimum amplitude i of (2) qmin ＝-Q max /S n Wherein Q is max Is the reactive regulation maximum value of the flexible direct current power transmission converter station,/-for>S n Is rated full-load power of flexible direct-current transmission converter station, P n Is the operating power of the flexible direct current transmission converter station.
4. The reactive power coordination control method of a hybrid multi-feed direct current system according to claim 1, wherein, in adjusting the reference valueWhen, limiting the reference value according to the preset parameters>Is a rate of change of (c).
5. The reactive power coordination control method of a hybrid multi-feed direct current system according to claim 1, wherein the negative sequence current q component and d component of the negative sequence inner loop decoupling control of the flexible direct current transmission converter station are set to 0.
6. The reactive power coordination control method of the hybrid multi-feed direct current system according to claim 1, wherein alternating current on the common bus is rectified and inverted through a high-voltage direct current power transmission converter station and then is transmitted to a load center.
7. A hybrid multi-feed direct current system reactive coordination controller for controlling a flexible direct current power transmission converter station and a dimmer to feed reactive power into a common bus, the controller comprising:
an acquisition unit for acquiring the current alternating voltage U of the public bus PCC ；
A judging unit for comparing the current AC voltage U of the public bus PCC Maximum operating voltage U max And a minimum operating voltage U min : when U is PCC ＞U max When the current setting unit sends a first instruction to the current setting unit and the common bus is at the current alternating voltage U PCC Less than or equal to rated operating voltage U rate Sending a third instruction; when U is PCC ＜U min When the current setting unit sends a second instruction to the current setting unit and the current alternating voltage U of the public bus is reached during the second instruction PCC Greater than or equal to rated operating voltage U rate Sending a third instruction; when U is min ≤U PCC ≤U max When the current setting unit is started, a third instruction is sent to the current setting unit;
a current setting unit for decoupling the reference value of the positive sequence current q component of the positive sequence inner loop of the flexible direct current transmission converter station when receiving the first instructionSetting the reactive current output quantity of the external loop fixed alternating voltage control and referencing the positive sequence current q component of the positive sequence internal loop decoupling control of the flexible direct current transmission converter station when receiving a second instructionValue->Positive sequence current q-component set to feed a common bus for a dimmer +.>Reference value +.f. of positive sequence current q-component of positive sequence inner loop decoupling control of flexible DC power transmission converter station upon receipt of third instruction>Set to 0.
8. The hybrid multi-feed direct current system reactive coordination controller of claim 7, further comprising:
a current limiting unit for adjusting the reference valueLimiting the reference value->Is greater than the maximum amplitude i of (1) qmax ＝Q max /S n Limiting the reference value->Is the minimum amplitude i of (2) qmin ＝-Q max /S n Wherein Q is max Is the reactive regulation maximum value of the flexible direct current power transmission converter station,/-for>S n Is rated full-load power of flexible direct-current transmission converter station, P n Is the operating power of the flexible direct current transmission converter station.
9. A hybrid multi-feed direct current system, comprising a common bus, a flexible direct current transmission converter station and a regulator for feeding power into the common bus, a high voltage direct current transmission converter station for transmitting the power of the common bus to a load center, and a controller, wherein the controller is the reactive coordination controller of the hybrid multi-feed direct current system according to claim 7 or 8.
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CN103401263A (en) * 2013-07-30 2013-11-20 浙江大学 Mixed type three-pole direct current power transmission system and control method thereof
CN107925249A (en) * 2015-11-10 2018-04-17 西门子公司 The method and system that the network voltage of distributed energy resource is adjusted
CN111106630A (en) * 2019-12-31 2020-05-05 国网江西省电力有限公司电力科学研究院 Control method for improving high voltage ride through capability of doubly-fed wind turbine by participation of phase modulator

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103401263A (en) * 2013-07-30 2013-11-20 浙江大学 Mixed type three-pole direct current power transmission system and control method thereof
CN107925249A (en) * 2015-11-10 2018-04-17 西门子公司 The method and system that the network voltage of distributed energy resource is adjusted
CN111106630A (en) * 2019-12-31 2020-05-05 国网江西省电力有限公司电力科学研究院 Control method for improving high voltage ride through capability of doubly-fed wind turbine by participation of phase modulator

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