CN114006395A - Hybrid multi-feed-in direct current system and reactive power coordination control method and controller thereof - Google Patents

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

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CN114006395A
CN114006395A CN202111179600.5A CN202111179600A CN114006395A CN 114006395 A CN114006395 A CN 114006395A CN 202111179600 A CN202111179600 A CN 202111179600A CN 114006395 A CN114006395 A CN 114006395A
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current
voltage
pcc
reference value
positive sequence
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CN114006395B (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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  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention discloses a hybrid multi-feed-in direct current system and a reactive power coordination control method and a controller thereof, wherein the control method comprises the following steps: step S1: obtaining AC voltage U of public busPCCComparing the current AC voltage UPCCMaximum operating voltage UmaxAnd a minimum operating voltage Umin: when U is turnedPCC＞UmaxIf yes, jumping to step S2; when U is turnedPCC＜UminIf yes, jumping to step S3; when U is turnedmin≤UPCC≤UmaxIf yes, jumping to step S4; step S2: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure DDA0003295085800000011
Setting the output quantity of reactive current controlled by the outer ring fixed alternating voltage to judge whether the output quantity meets UPCC＜UrateIf yes, jumping to step S4, otherwise, repeating step S2; step S3: reference value
Figure DDA0003295085800000012
Setting as positive sequence current q component of phase modulator feeding common bus
Figure DDA0003295085800000013
Judging whether U is satisfiedPCC＞UrateIf yes, jumping to step S4, otherwise, repeating step S3; step S4: reference value
Figure DDA0003295085800000014
Is set to 0. By the method, the reactive response speed can be increased.

Description

Hybrid multi-feed-in direct current system and reactive power coordination control method and controller thereof
Technical Field
The invention belongs to the field of power grid control, and particularly relates to a hybrid multi-feed-in direct current system, a reactive power coordination control method thereof and a controller.
Background
With the wide application of high-voltage direct-current transmission, the problem of 'strong and weak cross' of a power system in China is prominent, and the reactive power supporting capability of an alternating-current side is reduced. In order to ensure safe and stable operation of a Direct Current system, a national grid company plans to configure a phase modulator at a transmitting-receiving end Converter station of a trans-regional High-Voltage Direct Current project, and a dynamic reactive support is simultaneously provided in a hybrid multi-feed Direct Current system through the phase modulator and a flexible Direct Current (VSC-HVDC) Converter station. As synchronous rotating equipment, the phase modulator can emit a large amount of reactive power in the moment of fault occurrence, and reactive support capability of the system is improved. In the prior art, a plurality of reactive compensation devices for a multi-camera or VSC-HVDC independently provide dynamic reactive support for High Voltage Direct Current (LCC-HVDC) transmission, however, the reactive response speed of the method still needs to be improved, and therefore, further research on reactive coordination control of a phase modulator and VSC-HVDC in a hybrid multi-feed Direct Current system is needed to further improve the reactive response speed.
Disclosure of Invention
In view of the above drawbacks and needs of the prior art, the present invention provides a hybrid multi-feed dc system, a reactive power coordination control method thereof, and a controller thereof, which aim to increase the reactive power response speed of a reactive power compensation device.
To achieve the above object, according to a first aspect of the present invention, there is provided a reactive power coordination control method for a hybrid multi-feed dc system, the hybrid multi-feed dc system including a common bus, and a flexible dc transmission converter station and a phase modulator that feed reactive power into the common bus, the control method including:
step S1: obtaining the current AC voltage U of the public busPCCComparing the current AC voltage U of the public busPCCMaximum operating voltage UmaxAnd a minimum operating voltage Umin: when U is turnedPCC＞UmaxIf yes, jumping to step S2; when U is turnedPCC＜UminIf yes, jumping to step S3; when U is turnedmin≤UPCC≤UmaxIf yes, jumping to step S4;
step S2: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure BDA0003295085780000021
Setting the output quantity of reactive current controlled by the outer ring fixed AC voltage to judgeCurrent ac voltage U of common busPCCWhether it is less than the rated operation voltage UrateIf yes, jumping to step S4, otherwise, repeating step S2;
step S3: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure BDA0003295085780000022
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000023
Judging the current AC voltage U of the public busPCCWhether it is higher than rated operation voltage UrateIf yes, jumping to step S4, otherwise, repeating step S3;
step S4: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure BDA0003295085780000024
Is set to 0.
Preferably, the reactive outer loop control at two ends of the flexible direct current transmission converter station adopts constant alternating current voltage control, the active outer loop control at a transmitting end adopts constant direct current voltage control, and the active outer loop control at a receiving end adopts constant active power control.
Preferably, the reference value is adjusted
Figure BDA0003295085780000025
While limiting the reference value
Figure BDA0003295085780000026
Maximum amplitude i ofqmax＝Qmax/SnLimiting the reference value
Figure BDA0003295085780000027
Minimum amplitude i ofqmin＝-Qmax/SnWherein Q ismaxIs the maximum value of reactive power regulation of the flexible direct current transmission converter station,
Figure BDA0003295085780000028
Snrated full load power, P, of a flexible DC transmission converter stationnIs the running power of the flexible direct current transmission converter station.
Preferably, the reference value is adjusted
Figure BDA0003295085780000029
While limiting the reference value according to preset parameters
Figure BDA00032950857800000210
The 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 transmission converter station are set to 0.
Preferably, the alternating current on the common bus is rectified and inverted by the high-voltage direct-current transmission converter station and then is transmitted to the load center.
According to a second aspect of the present invention, there is provided a hybrid multi-infeed dc system reactive power coordination controller for controlling a flexible dc transmission converter station and a phase modifier to feed reactive power into a common bus, the controller comprising:
an obtaining unit for obtaining the current AC voltage U of the public busPCC；
A judging unit for comparing the current AC voltage U of the common busPCCMaximum operating voltage UmaxAnd a minimum operating voltage Umin: when U is turnedPCC＞UmaxWhen the current setting unit is started, a first instruction is sent to the current setting unit, and the current AC voltage U of the public bus is obtained during the first instructionPCCLess than nominal operating voltage UrateSending a third instruction; when U is turnedPCC＜UminWhen the current setting unit is started, a second instruction is sent to the current setting unit, and the current AC voltage U of the public bus is obtained during the second instructionPCCGreater than the rated operating voltage UrateSending a third instruction; when U is turnedmin≤UPCC≤UmaxThen, sending a third instruction to the current setting unit;
current setting unit, usingReference value of positive sequence current q component for decoupling control of positive sequence inner loop of flexible direct current transmission converter station upon reception of first instruction
Figure BDA0003295085780000031
Setting the reactive current output quantity controlled by the outer-loop fixed alternating voltage, and decoupling and controlling the positive sequence current q component reference value of the positive sequence inner loop of the flexible direct current transmission converter station when receiving a second instruction
Figure BDA0003295085780000032
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000033
When a third instruction is received, a reference value of a positive sequence current q component of a positive sequence inner ring decoupling control of the flexible direct current transmission converter station is obtained
Figure BDA0003295085780000034
Is set to 0.
Preferably, the method further comprises the following steps:
a current limiting unit for adjusting the reference value
Figure BDA0003295085780000035
While limiting the reference value
Figure BDA0003295085780000036
Maximum amplitude i ofqmax＝Qmax/SnLimiting the reference value
Figure BDA0003295085780000037
Minimum amplitude i ofqmin＝-Qmax/SnWherein Q ismaxIs the maximum value of reactive power regulation of the flexible direct current transmission converter station,
Figure BDA0003295085780000038
Snrated full load power, P, of a flexible DC transmission converter stationnIs a flexible DC transmission converter stationThe operating power of (c).
According to a third aspect of the present invention, there is provided a hybrid multi-infeed dc system comprising a common bus, a flexible dc transmission converter station and a phase modifier feeding power into the common bus, a hvdc transmission converter station transmitting power from the common bus to a load center, and a controller, wherein the controller is the hybrid multi-infeed dc system reactive power coordination controller described above.
In general, compared to the prior art, the present application is based on the current ac voltage U of the common busPCCTo the maximum operating voltage UmaxAnd a minimum operating voltage UminTo adjust a reference value of a positive sequence current q component of a positive sequence inner loop decoupling control of VSC-HVDC
Figure BDA0003295085780000041
When the current AC voltage U of the public busPCCAt the minimum allowable operating voltage UminAnd the maximum allowable operating voltage UmaxIn time, a reference value of a positive sequence current q component for decoupling control of a positive sequence inner ring of VSC-HVDC
Figure BDA0003295085780000042
Setting to 0, namely preferably utilizing a phase modulator to adjust the reactive power, wherein VSC-HVDC does not participate in adjusting the reactive power; when the common bus AC voltage UPCCThe fluctuation being greater than the maximum allowable operating voltage UmaxThen, reactive power regulation is carried out by utilizing a VSC-HVDC auxiliary phase modulator, and a reference value of a positive sequence current q component controlled by decoupling a positive sequence inner ring of the VSC-HVDC is used
Figure BDA0003295085780000043
Setting the reactive current output quantity controlled by the outer ring fixed alternating voltage, and absorbing reactive power by VSC-HVDC (voltage source converter-high voltage direct current) in an auxiliary way; when the common bus AC voltage UPCCFluctuation less than allowable maximum operating voltage UmaxThen, reactive power regulation is carried out by utilizing a VSC-HVDC auxiliary phase modulator, and a reference value of a positive sequence current q component controlled by decoupling a positive sequence inner ring of the VSC-HVDC is used
Figure BDA0003295085780000044
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000045
The reactive response of the VSC-HVDC is made to follow the reactive response of the phase modulator, the reactive response speed of the VSC-HVDC is increased, and instantaneous reduction of the public bus voltage when a fault occurs and reactive power overcompensation of the VSC-HVDC after the fault is removed are suppressed.
Drawings
Fig. 1 is a flowchart of a reactive power coordination control method of a hybrid multi-feed dc system according to an embodiment of the present invention;
fig. 2 is a system diagram of a hybrid multi-feed dc system according to an embodiment of the invention;
FIG. 3 is a basic block diagram of a phase modulator in one embodiment of the present invention;
FIG. 4 is a phasor diagram of the phase modulator with overdrive and underexcitation according to an embodiment of the present invention;
FIG. 5 is a VSC-HVDC equivalent model diagram in an embodiment of the present invention;
FIG. 6 is a VSC-HVDC positive-negative sequence current inner loop control block diagram in an embodiment of the invention;
FIG. 7 shows reference values of positive sequence current q components for VSC-HVDC positive sequence inner loop decoupling control in an embodiment of the present invention
Figure BDA0003295085780000051
Selecting the switching;
FIG. 8 is an analysis of a phase modulator and VSC-HVDC constant AC voltage control in an embodiment of the invention;
FIG. 9 is a diagram of simulation results of independent control and coordinated control under a symmetric fault in one embodiment of the present invention;
FIG. 10 is a diagram of simulation results of independent control and coordinated control under an asymmetric fault in an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
For the understanding of the present application, the main components of the hybrid multi-feed dc system in the present application will be described first. As shown in FIG. 2, the multi-feed DC system comprises a common bus, VSC-HVDC and a phase modulator, the VSC-HVDC feeds power into the common bus through a connecting line, the LCC-HVDC then sends the power to a load center, PVSCAnd QVSCRespectively representing the active and reactive power, U, of the VSC-HVDC feed to the common busPCCRepresenting the ac voltage amplitude of the common bus. Due to the fact that the electrical distance between the VSC-HVDC receiving end and the LCC-HVDC rectifying side is short, the VSC-HVDC receiving end can provide dynamic reactive power support for the LCC-HVDC rectifying side. In order to further improve the reactive support capability of the power grid system at the LCC-HVDC rectification side, a phase modulator and a phase modulator Q are also arranged at the LCC-HVDC rectification sideSCRepresenting the reactive power fed by the phase modulator to the common bus.
The basic structure of the phase modulator system is shown in fig. 3, and mainly includes a phase modulator body, an excitation system, a starting system, a cooling system, a step-up transformer, and the like. The phase modulator is in fact a synchronous motor operating without mechanical load (no load), the active power it absorbs from the grid being supplied only to the losses of the motor itself, so that both the electromagnetic power and the power factor of the motor are approximately zero during operation.
If the total loss of the phase modulator is neglected, the armature current is all reactive components, and the electromotive force equation is:
Figure BDA0003295085780000061
in the formula
Figure BDA0003295085780000062
Is the voltage of the stator and is,
Figure BDA0003295085780000063
in order to be an electromotive force,
Figure BDA0003295085780000064
is armature current, XSIs an equivalent reactance. The phasor diagram of the phase modulator at over-excitation and under-excitation is shown in fig. 4
Figure BDA0003295085780000065
Advance in
Figure BDA0003295085780000066
Outputting inductive reactive power; under excitation
Figure BDA0003295085780000067
Hysteresis
Figure BDA0003295085780000068
Absorbing inductive reactive power. Therefore, the nature and the magnitude of the reactive power can be flexibly adjusted only by adjusting the exciting current.
On the dq coordinate axis, the reactive power provided by the phase modulator to the system is:
QSC＝Uqid-Udiq (2)
in the formula QSCIs reactive power, U, provided by a phase modulatordAnd UqD-and q-axis components, i, of the voltage of the phase modulator, respectively, connected to the high-voltage busdAnd iqRespectively, a d-axis component (active current) and a q-axis component (reactive current) of the current. Neglecting all losses, there is UdU, when equation (2) can be expressed as:
QSC≈-Udiq≈-Uiq (3)
during a system disturbance, the phase modulator may be equivalent to a voltage source with constant internal potential, and the reactive current may be expressed as:
Figure BDA0003295085780000069
in the formula E ″)qIs the internal potential of the phase modulator, U is the voltage of the phase modulator connected to the high voltage bus, X ″dIs the sub-transient reactance of the phase modulator, XTIs the impedance of the step-up transformer.
It can be seen from equation (4) that, during the system disturbance, the magnitude of the reactive current fed into the common bus by the phase modulator is mainly related to the voltage variation amplitude and the sub-transient reactance, and the larger the voltage variation amplitude is, the smaller the sub-transient reactance is, the larger the reactive current is. At present, a new generation phase modulator widely applied is smaller in transient reactance, a large amount of reactive power is immediately sent out at the moment of fault, and the reactive support capability of a power grid system is powerfully improved.
The VSC-HVDC can be regarded as an ac voltage source with adjustable phase and amplitude, and an equivalent model thereof is shown in fig. 5, where the reactance is an equivalent reactance of a bridge arm reactance and a leakage reactance of a converter transformer. Wherein Us & lt 0 is the commutation bus voltage, and the initial phase angle is set to 0; uc is the fundamental voltage amplitude of the VSC converter outlet; delta is a phase shift angle; xc is the equivalent reactance; is line current; pVSCAnd QVSCAnd respectively outputting active power and reactive power by the VSC-HVDC converter.
VSC-HVDC adopts a vector control method based on direct current control, and has a rapid current response characteristic and good current limiting capacity. The vector control is composed of an outer ring control strategy and an inner ring control strategy, and the voltage outer ring provides a current reference value for the current inner ring.
The outer loop control mainly comprises active power control and reactive power control, and the outer loop control in the application adopts reactive power control. Reactive power control includes deciding reactive power control, deciding alternating voltage control, adopts in this application to decide alternating voltage control, stabilizes the alternating bus voltage through deciding alternating voltage control. The control circuit of the external loop fixed ac control is a conventional circuit, and will not be described in detail here.
The inner loop control adopts the decomposition and independent control of positive sequence current and negative sequence current. FIG. 6 shows a VSC-HVDC positive-negative sequence current inner loop control block diagram, wherein the positive-negative sequence current inner loop control block diagramAlso conventional, 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 instruction controlled by the outer loop; the negative sequence current inner loop controller has the main functions of restraining the negative sequence current and converting the reference value of the d component of the negative sequence current
Figure BDA0003295085780000071
And reference value of q component
Figure BDA0003295085780000072
Is set to 0.
In the present application, the reference value of the positive sequence current q-component, which is controlled mainly by setting the positive sequence current inner loop
Figure BDA0003295085780000073
To regulate the speed of reactive response of the VSC-HVDC. According to the current AC voltage U of the public busPCCReference value of positive sequence current q component for positive sequence inner loop decoupling control
Figure BDA0003295085780000074
And (4) selecting. In particular, reference values
Figure BDA0003295085780000075
There are three options. The first option being to use the reference value
Figure BDA0003295085780000076
Setting the reactive current output quantity of the outer ring constant AC voltage control, namely the output current corresponding to the Mode 1 in FIG. 7, as a reference value
Figure BDA0003295085780000081
Access Mode 1 is indicated as switching Switch to access port 1, i.e. Switch ═ 1. The second option being to use the reference value
Figure BDA0003295085780000082
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000083
That is, the reference value is set to correspond to the output current of Mode 2 in FIG. 7
Figure BDA0003295085780000084
Access Mode 2 is indicated as switching Switch to access port 2, i.e. Switch ═ 2. A third option is to use the reference value
Figure BDA0003295085780000085
Set to 0, i.e., corresponding to the output current of Mode0 in fig. 7, the reference value
Figure BDA0003295085780000086
Access Mode0 is indicated as switching Switch to access port 0, i.e., Switch ═ 0.
Referring to fig. 1, fig. 1 is a flowchart of a reactive power coordination control method for a hybrid multi-feed dc system according to an embodiment of the present application, where the control method includes:
step S1: obtaining the current AC voltage U of the public busPCCComparing the current AC voltage U of the public busPCCMaximum operating voltage UmaxAnd a minimum operating voltage Umin: when U is turnedPCC＞UmaxIf yes, jumping to step S2; when U is turnedPCC＜UminIf yes, jumping to step S3; when U is turnedmin≤UPCC≤UmaxThen, the process proceeds to step S4.
In one embodiment, the present ac voltage U of the common bus may be compared firstPCCAnd a maximum operating voltage UmaxJudging whether U is satisfiedPCC＞UmaxIf yes, jumping to step S2, otherwise, further comparing the current AC voltage U of the public busPCCAnd a minimum operating voltage UminJudging whether U is satisfiedPCC＜UminIf so, the process goes to step S3, and if not, the process goes to step S4.
Step S2: positive sequence current q for decoupling control of positive sequence inner ring of flexible direct current transmission converter stationReference value of a component
Figure BDA0003295085780000087
Setting the output quantity of reactive current controlled by the outer ring fixed alternating voltage, and judging the current alternating voltage U of the public busPCCWhether it is less than the rated operation voltage UrateIf so, go to step S4, otherwise, repeat step S2.
In one embodiment, step S2 includes two substeps:
substep S2-1: let Switch equal to 1, i.e. the reference value
Figure BDA0003295085780000088
And setting the reactive current output quantity controlled by the outer ring fixed alternating voltage.
Specifically, when U isPCC＞UmaxAnd the situation that the voltage of the current public bus is too high and reactive power absorption is needed is explained. Although the phase modulator has strong overcurrent capacity and good phase delay capacity (output reactive power), and can send out reactive power more than 2 times of rated capacity in a short time, the phase modulator has poor phase-entering capacity (reactive power absorption) and can only absorb about half of the reactive power of the rated capacity, so that the reactive power of a public bus is absorbed by utilizing the feedback regulation function of the phase modulator, and simultaneously VSC-HVDC auxiliary absorption reactive power is added, and a reference value is obtained by adding a VSC-HVDC auxiliary absorption reactive power
Figure BDA0003295085780000091
The reactive current output quantity controlled by the outer-loop fixed alternating voltage can enable the VSC-HVDC to absorb reactive power, and the phase modulator is combined with the VSC-HVDC to absorb reactive power of the bus together, so that the voltage rise of the common bus can be better inhibited.
Substep S2-2: judging whether the current voltage of the common bus meets UPCC＜UrateIf so, go to step S4, otherwise, go to step S2-1.
Specifically, during the reactive power absorption by the VSC-HVDC converter, the bus voltage gradually decreases, and when the bus voltage reaches the rated value, the system resumes normal operation, at which time, the process may jump to step S4 to exit the VSC-HVDC converter. Namely, the phase modulator is preferentially used for adjusting reactive power under the conditions of normal working condition and small voltage disturbance, the VSC-HVDC does not participate in reactive power adjustment, and the adjustment capacity of the phase modulator is fully utilized.
Step S3: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure BDA0003295085780000092
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000093
Judging the current AC voltage U of the public busPCCWhether it is higher than rated operation voltage UrateIf so, go to step S4, otherwise, repeat step S3.
In one embodiment, step S3 also includes two substeps:
substep S3-1: let Switch equal to 2, i.e. the reference value
Figure BDA0003295085780000094
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000095
Specifically, when U isPCC＜UminAnd the current public bus voltage is too low, and reactive compensation is needed. At the moment, the phase modulator and the VSC-HVDC jointly provide reactive compensation for the common bus.
In the conventional art, it is common that a phase modulator and VSC-HVDC operate independently. However, the reactive response speed of the phase modulator is faster than that of the VSC-HVDC at the moment of fault occurrence and after fault removal. As shown in fig. 8, at the moment of fault occurrence, the voltage of the common bus is rapidly reduced, the reactive power output of the phase modifier reaches the maximum value in about 35ms, and the reactive power output of the VSC-HVDC reaches the maximum value in about 80ms under the control of the constant alternating voltage, so that the response speed of the phase modifier output reactive power is faster than that of the VSC-HVDC at the moment of fault; after the fault is removed, the voltage of the public bus is increased, the reactive power output by the phase modulator is reduced, but the VSC-HVDC cannot reduce the output of the reactive power immediately under the control of the constant alternating voltage, reactive overcompensation occurs, the voltage of the public bus is increased, the current of an LCC-HVDC direct current line is increased, the phase conversion area required by the LCC-HVDC inversion side converter valve is increased, and the risk of phase conversion failure of the LCC-HVDC is increased. In general, the reactive response speed of the phase modulator is faster than that of VSC-HVDC under the control of constant AC voltage at the moment of fault occurrence and after fault removal.
Therefore, the application sets the reactive current reference value of the inner loop control of VSC-HVDC at this stage
Figure BDA0003295085780000101
The reactive current change of the VSC-HVDC is made to follow the change of the reactive current of the phase modulator, namely the change of the reactive power transmitted by the VSC-HVDC is made to follow the change of the reactive power transmitted by the phase modulator, so that the reactive response speed of the VSC-HVDC in the moment of fault occurrence and after fault removal can be increased, the reactive power can be rapidly transmitted to the public bus in the moment of fault occurrence, and the reactive power can be timely reduced to be output after the fault removal.
Substep S3-2: judging whether the current voltage of the common bus meets UPCC＞UrateIf so, go to step S4, otherwise, go to step S3-1.
The VSC-HVDC following phase modulator compensates reactive power for the public bus, the voltage of the public bus is raised, and when a fault is removed, the VSC-HVDC following phase modulator reduces the output of the reactive power until the voltage of the public bus is UPCCIs raised to rated voltage UrateAnd the system recovers normal operation, and at the moment, the method can jump to step S4 to exit VSC-HVDC.
Step S4: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure BDA0003295085780000102
Is set to 0.
Let Switch equal to 0, reference value
Figure BDA0003295085780000103
And (4) setting the voltage to be 0, exiting the VSC-HVDC, namely preferentially utilizing the phase modulator to adjust the reactive power under the conditions of normal working condition and small voltage disturbance, and fully utilizing the adjusting capacity of the phase modulator without participating in reactive power adjustment by the VSC-HVDC.
In the above steps, the current ac voltage U of the common bus can be obtained by measurementPCC. Maximum operating voltage UmaxMinimum operating voltage UminAnd rated operating voltage UrateAre all known parameters. Normally, the steady-state voltage operation range of the bus is usually 0.95 pu-1.05 pu, and the rated operation voltage U of the common bus is setrateMaximum operating voltage U is allowed 1.0pumax1.05pu, minimum operating voltage U allowedmin＝0.95pu。
In one embodiment, to ensure proper operation of the VSC-HVDC, the reference value is adjusted
Figure BDA0003295085780000111
While limiting the reference value
Figure BDA0003295085780000112
Maximum amplitude i ofqmax＝Qmax/SnLimiting the reference value
Figure BDA0003295085780000113
Minimum amplitude i ofqmin＝-Qmax/SnWherein Q ismaxIs the maximum value of reactive power regulation of the VSC-HVDC,
Figure BDA0003295085780000114
Snrated full load power, P, of VSC-HVDCnIs the operating power of the VSC-HVDC. Specifically, considering that the overload bearing capacity of the VSC-HVDC is limited, the VSC-HVDC reactive regulation limit value 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 transmitted by the VSC-HVDC receiving end is 1000MW, and the maximum reactive regulation value of the VSC-HVDC obtained through calculation is 750Mvar, so that the setting is performed
Figure BDA0003295085780000115
Is limited byqmax＝0.6pu，iqmin＝-0.6pu。
In one embodiment, the reference value is adjusted
Figure BDA0003295085780000116
In order to avoid the influence of the too fast current change on the normal operation of the device, a rate 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 phase modifier access as shown in fig. 2 is built on PSCAD/EMTDC simulation software, the 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 the main parameters of phase modifiers 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, 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
Figure BDA0003295085780000121
TABLE 2
Parameter name Value of parameter
Rated capacity/Mvar 300
Step-up rated transformation ratio 20kV/530kV
Straight axis steady state reactance/%) 150.5
Direct axis transient reactance/%) 14.0
Direct axis sub-transient reactance/%) 11.3
Open-circuit time constant/s of straight axis 8.8
Time constant/s of direct short circuit 0.72
Multiple of forced excitation voltage 3.5
In order to verify the effectiveness of the method, a three-phase grounding short-circuit fault is arranged on the rectifying side of the LCC-HVDC, the fault occurrence time is 3.0s, the fault distance is 0.30H, and the fault duration is 0.1 s; observing the turn-off angle gamma of the LCC-HVDC inverter side, the AC voltage U of the common busPCCLCC-HVDC direct line current IdReactive power Q transmitted from VSC-HVDC receiving end to public busVSCReactive power Q delivered by phase modulator to common busSCThe results are shown in FIG. 9. As can be seen from fig. 9, from the aspect of reactive response, at the moment of a fault, the reactive power output of the VSC-HVDC under independent control reaches the maximum value in about 80ms, the reactive power of the VSC-HVDC under coordinated control reaches the maximum value in about 50ms, and the reactive response speed under coordinated control is faster; after the fault is removed, reactive overcompensation occurs in VSC-HVDC under independent controlThe reactive power output by the VSC-HVDC under the regulation control is reduced, and the reactive response speed under the coordination control is higher.
From the control effect, at the moment of fault occurrence, the voltage of the common bus is rapidly reduced, the minimum value of the voltage of the common bus under independent control is 443kV, the minimum value of the voltage of the common bus under coordinated control is 451kV, and the transient low voltage suppression effect under coordinated control is better; after the fault is removed, the VSC-HVDC reactive overcompensation under independent control leads to the phase commutation failure of the LCC-HVDC, the VSC-HVDC under coordinated control reduces output reactive power, further reduces the current of the LCC-HVDC direct-current line, and the LCC-HVDC does not have the phase commutation failure.
In order to further illustrate the effectiveness of the method, the effect of inhibiting the LCC-HVDC from generating commutation failure by independent control and coordinated control at different fault occurrence moments and different fault distance working conditions is observed, and the result is shown in Table 3. As can be seen from Table 3, compared with the independent control of the phase modulator and the VSC-HVDC, the reactive power coordination control method of the phase modulator and the VSC-HVDC can reduce the risk of phase commutation failure after the fault of the LCC-HVDC transmission-end power grid is removed.
TABLE 3
Figure BDA0003295085780000131
To further illustrate the adaptability of the method of the invention, an asymmetric fault of a single-phase grounding short circuit is arranged on the rectification side of the LCC-HVDC, the fault occurrence time is 3.0s, the fault distance is 0.10H, the fault duration is 0.1s, the turn-off angle gamma of the phase modifier and the VSC-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 busPCCReactive power Q transmitted from VSC-HVDC receiving end to public busVSCReactive power Q delivered by phase modulator to common busSCThe results are shown in FIG. 10. As can be seen from fig. 10, at the moment of a fault, compared with the phase modulator and VSC-HVDC independent control, the VSC-HVDC under the coordinated control has faster reactive response speed and better transient low voltage suppression effect; VSC-HVDC under coordinated control decreases faster after fault removalThe reactive power is output, and the transient high voltage is better restrained.
The application also relates to a hybrid multi-feed-in DC system reactive power coordination controller for controlling a flexible DC power transmission converter station and a phase modulator to feed reactive power into a common bus, the controller comprising:
an obtaining unit for obtaining the current AC voltage U of the public busPCC。
A judging unit for comparing the current AC voltage U of the common busPCCMaximum operating voltage UmaxAnd a minimum operating voltage Umin：
When U is turnedPCC＞UmaxWhen the current setting unit is started, a first instruction is sent to the current setting unit, and the current AC voltage U of the public bus is obtained during the first instructionPCCLess than nominal operating voltage UrateSending a third instruction;
when U is turnedPCC＜UminWhen the current setting unit is started, a second instruction is sent to the current setting unit, and the current AC voltage U of the public bus is obtained during the second instructionPCCGreater than the rated operating voltage UrateSending a third instruction;
when U is turnedmin≤UPCC≤UmaxThen, sending a third instruction to the current setting unit;
a current setting unit, configured to decouple a reference value of a positive sequence current q component of a positive sequence inner loop of the flexible direct current transmission converter station when receiving the first instruction
Figure BDA0003295085780000141
Setting the reactive current output quantity controlled by the outer-loop fixed alternating voltage, and decoupling and controlling the positive sequence current q component reference value of the positive sequence inner loop of the flexible direct current transmission converter station when receiving a second instruction
Figure BDA0003295085780000142
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000143
Upon receipt of the third instructionReference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure BDA0003295085780000144
Is set to 0.
In an embodiment, the controller further comprises a current clipping unit for clipping the reference value when adjusting the reference value
Figure BDA0003295085780000151
While limiting the reference value
Figure BDA0003295085780000152
Maximum amplitude i ofqmax＝Qmax/SnLimiting the reference value
Figure BDA0003295085780000153
Minimum amplitude i ofqmin＝-Qmax/SnWherein Q ismaxIs the maximum value of reactive power regulation of the flexible direct current transmission converter station,
Figure BDA0003295085780000154
Snrated full load power, P, of a flexible DC transmission converter stationnIs the running power of the flexible direct current transmission converter station.
Each unit of the controller is configured to implement each step of the hybrid multi-feed dc system reactive power coordination control method, and specific functions of each unit correspond to each step of the control method, which may be specifically described with reference to the above description, and are not described herein again.
The present application also relates to a hybrid multi-infeed dc system, as shown in fig. 2, which includes a common bus, a flexible dc transmission converter station and a phase modifier feeding power into the common bus, a hvdc transmission converter station transmitting the power of the common bus to a load center, and a controller, wherein the controller is the above-described hybrid multi-infeed dc system reactive power coordination controller.
The application is based on the current AC voltage U of the public busPCCTo the maximum operating voltage UmaxAnd a minimum operating voltage UminTo adjust a reference value of a positive sequence current q component of a positive sequence inner loop decoupling control of VSC-HVDC
Figure BDA0003295085780000155
When the current AC voltage U of the public busPCCAt the minimum allowable operating voltage UminAnd the maximum allowable operating voltage UmaxIn time, a reference value of a positive sequence current q component for decoupling control of a positive sequence inner ring of VSC-HVDC
Figure BDA0003295085780000156
Setting to 0, namely preferably utilizing a phase modulator to adjust the reactive power, wherein VSC-HVDC does not participate in adjusting the reactive power; when the common bus AC voltage UPCCThe fluctuation being greater than the maximum allowable operating voltage UmaxThen, reactive power regulation is carried out by utilizing a VSC-HVDC auxiliary phase modulator, and a reference value of a positive sequence current q component controlled by decoupling a positive sequence inner ring of the VSC-HVDC is used
Figure BDA0003295085780000157
Setting the reactive current output quantity controlled by the outer ring fixed alternating voltage, and absorbing reactive power by VSC-HVDC (voltage source converter-high voltage direct current) in an auxiliary way; when the common bus AC voltage UPCCFluctuation less than allowable maximum operating voltage UmaxThen, reactive power regulation is carried out by utilizing a VSC-HVDC auxiliary phase modulator, and a reference value of a positive sequence current q component controlled by decoupling a positive sequence inner ring of the VSC-HVDC is used
Figure BDA0003295085780000158
Setting as positive sequence current q component of phase modulator feeding common bus
Figure BDA0003295085780000159
The reactive response of the VSC-HVDC is made to follow the reactive response of the phase modulator, the reactive response speed of the VSC-HVDC is increased, and instantaneous reduction of the public bus voltage when a fault occurs and reactive power overcompensation of the VSC-HVDC after the fault is removed are suppressed.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. A reactive power coordination control method for a hybrid multi-feed dc system, wherein the hybrid multi-feed dc system includes a common bus, and a flexible dc power transmission converter station and a phase modifier that feed reactive power into the common bus, and the control method includes:
step S1: obtaining the current AC voltage U of the public busPCCComparing the current AC voltage U of the public busPCCMaximum operating voltage UmaxAnd a minimum operating voltage Umin: when U is turnedPCC＞UmaxIf yes, jumping to step S2; when U is turnedPCC＜UminIf yes, jumping to step S3; when U is turnedmin≤UPCC≤UmaxIf yes, jumping to step S4;
step S2: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure FDA0003295085770000011
Setting the output quantity of reactive current controlled by the outer ring fixed alternating voltage, and judging the current alternating voltage U of the public busPCCWhether it is less than the rated operation voltage UrateIf yes, jumping to step S4, otherwise, repeating step S2;
step S3: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure FDA0003295085770000012
Setting as positive sequence current q component of phase modulator feeding common bus
Figure FDA0003295085770000013
Judging the current AC voltage U of the public busPCCWhether it is higher than rated operation voltage UrateIf yes, go to step S4, otherwiseThen, step S3 is repeated;
step S4: reference value of positive sequence current q component for decoupling control of positive sequence inner ring of flexible direct current transmission converter station
Figure FDA0003295085770000014
Is set to 0.
2. The hybrid multi-feed dc system reactive power coordination control method according to claim 1, wherein the reactive outer loop control at both ends of the flexible dc transmission converter station adopts constant ac voltage control, the active outer loop control at the transmitting end adopts constant dc voltage control, and the active outer loop control at the receiving end adopts constant active power control.
3. The reactive power coordinated control method for hybrid multi-feed direct current system according to claim 1, wherein the reference value is adjusted
Figure FDA0003295085770000015
While limiting the reference value
Figure FDA0003295085770000016
Maximum amplitude i ofqmax＝Qmax/SnLimiting the reference value
Figure FDA0003295085770000017
Minimum amplitude i ofqmin＝-Qmax/SnWherein Q ismaxIs the maximum value of reactive power regulation of the flexible direct current transmission converter station,
Figure FDA0003295085770000021
Snrated full load power, P, of a flexible DC transmission converter stationnIs the running power of the flexible direct current transmission converter station.
4. The reactive power coordination control method for hybrid multi-feed DC system according to claim 1, characterized in thatCharacterised by adjusting the reference value
Figure FDA0003295085770000022
While limiting the reference value according to preset parameters
Figure FDA0003295085770000023
The rate of change of (c).
5. The hybrid multi-infeed direct current system reactive power coordination control method according to claim 1, characterized in that negative sequence current q-component and d-component of 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 for hybrid multi-feed direct current system according to claim 1, wherein the alternating current on the common bus is rectified and inverted by the HVDC converter station and then is transmitted to the load center.
7. A hybrid multi-infeed dc system reactive coordination controller for controlling a flexible dc transmission converter station and a phase modulator to feed reactive power into a common bus, the controller comprising:
an obtaining unit for obtaining the current AC voltage U of the public busPCC；
A judging unit for comparing the current AC voltage U of the common busPCCMaximum operating voltage UmaxAnd a minimum operating voltage Umin: when U is turnedPCC＞UmaxWhen the current setting unit is started, a first instruction is sent to the current setting unit, and the current AC voltage U of the public bus is obtained during the first instructionPCCLess than nominal operating voltage UrateSending a third instruction; when U is turnedPCC＜UminWhen the current setting unit is started, a second instruction is sent to the current setting unit, and the current AC voltage U of the public bus is obtained during the second instructionPCCGreater than the rated operating voltage UrateSending a third instruction; when U is turnedmin≤UPCC≤UmaxThen, sending a third instruction to the current setting unit;
a current setting unit, configured to decouple a reference value of a positive sequence current q component of a positive sequence inner loop of the flexible direct current transmission converter station when receiving the first instruction
Figure FDA0003295085770000024
Setting the reactive current output quantity controlled by the outer-loop fixed alternating voltage, and decoupling and controlling the positive sequence current q component reference value of the positive sequence inner loop of the flexible direct current transmission converter station when receiving a second instruction
Figure FDA0003295085770000025
Setting as positive sequence current q component of phase modulator feeding common bus
Figure FDA0003295085770000026
When a third instruction is received, a reference value of a positive sequence current q component of a positive sequence inner ring decoupling control of the flexible direct current transmission converter station is obtained
Figure FDA0003295085770000027
Is set to 0.
8. The hybrid multi-feed dc system reactive power coordinated controller of claim 7, further comprising:
a current limiting unit for adjusting the reference value
Figure FDA0003295085770000031
While limiting the reference value
Figure FDA0003295085770000032
Maximum amplitude i ofqmax＝Qmax/SnLimiting the reference value
Figure FDA0003295085770000033
Minimum amplitude i ofqmin＝-Qmax/SnWherein Q ismaxIs flexible DC power transmissionThe maximum value of the reactive power regulation of the converter station,
Figure FDA0003295085770000034
Snrated full load power, P, of a flexible DC transmission converter stationnIs the running power of the flexible direct current transmission converter station.
9. A hybrid multi-infeed dc system comprising a common bus, a flexible dc transmission converter station and a phase modifier feeding power into the common bus, a hvdc transmission converter station transmitting power from the common bus to a load center, and a controller, wherein the controller is the hybrid multi-infeed dc system reactive power coordination controller of claim 7 or 8.
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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

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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